Abstract
Soluble Klotho (sKl) in the circulation can be generated directly by alterative splicing of the Klotho transcript or the extracellular domain of membrane Klotho can be released from membrane-anchored Klotho on the cell surface. Unlike membrane Klotho which functions as a coreceptor for fibroblast growth factor-23 (FGF23), sKl, acts as hormonal factor and plays important roles in anti-aging, anti-oxidation, modulation of ion transport, and Wnt signaling. Emerging evidence reveals that Klotho deficiency is an early biomarker for chronic kidney diseases as well as a pathogenic factor. Klotho deficiency is associated with progression and chronic complications in chronic kidney disease including vascular calcification, cardiac hypertrophy, and secondary hyperparathyroidism. In multiple experimental models, replacement of sKl, or manipulated up-regulation of endogenous Klotho protect the kidney from renal insults, preserve kidney function, and suppress renal fibrosis, in chronic kidney disease. Klotho is a highly promising candidate on the horizon as an early biomarker, and as a novel therapeutic agent for chronic kidney disease.
INTRODUCTION
As one approach almost one and one-half decade of research since its discovery in 1997, Klotho biology is eventually entering into the public health domain where its dysregulation is implicated in human pathophysiology, and its diagnostic and therapeutic potential are beginning to enter the realm of reality. We will take a preclinical viewpoint of the status of Klotho in this aspect using kidney disease as a vehicle. Klotho is a single transmembrane 130 KDa protein encoded by the Klotho gene. A secreted form of Klotho of 70 kD is a product of alternative splicing4–7 and the extracellular domain of membrane Klotho can be released into blood8,9 thus functioning as a circulating substance to exert multiple systemic biological actions on distant organs.10–13 This cleaved extracellular domain of membrane Klotho is referred as soluble Klotho (sKl) in this chapter. sKl could function as a β-glucuronidase7,14 and sialidase.15,16 Klotho is principally synthesized in kidney and brain although it is expressed in multiple organs.6,17 Klotho-deficient mice (Kl−/−) manifest multi-organ premature aging while over-expression of Klotho through virus-mediated delivery or genetic overexpression can rescue the Klotho-deficient phenotype at baseline6,19,20 and enhance mice’s resistance to oxidant stress and ischemic damage.6,21–23
One important biological function of Klotho is to maintain mineral homeostasis, which is both fibroblast growth factor-23 (FGF23)-dependent and FGF23-independent. From a renal point of view, sKl regulates urinary calcium,16,24 potassium15 and phosphorus excretion.14 In addition, Klotho suppresses 1α-hydroxylase in the kidney to regulate calcium metabolism25,26 and participates in the regulation of PTH synthesis in parathyroid gland by FGF23.27,28
The study of Klotho in human biology has been limited to association studies of clinical features with Klotho polymorphisms with potential but yet to be determined significance.29–36 The association of genetic variations in the KLOTHO gene with high mortality in hemodialysed patients was shown, but this link could be modified by activated vitamin D supplementation.38 This modification of association of nucleotide polymorphisms in the KLOTHO gene may result from epigenetic upregulation of Klotho expression by Vitamin D26 and subsequently affects the outcome of CKD patients. Interestingly, unlike the myriads of phenotypic features described in the rodent models of Klotho deficiency or excess, both Klotho deficiency caused by loss-of-function missense mutation45 and presumed Klotho overexpression due to translocation in human Klotho gene47 display disturbances in mineral metabolism but surprisingly both deficient and excess states have high FGF23 and hyperparathyroidism. These findings support the important role of Klotho in mineral homeostasis and suggest that there is still higher level of complexity that is beyond our comprehension at the moment.
In this book, there are several comprehensive reviews addressing Klotho’s effect on aging, renal ion channels and transporter, and Pi homeostasis. This chapter will be mainly focused on the role of sKl in chronic kidney diseases and potential clinical implications.
KIDNEY: THE MAJOR SITE FOR KLOTHO SYNTHESIS
The association of kidney disease with Klotho can be view as intuitive considering the expression pattern of Klotho. The distribution of Klotho mRNA is restricted to few tissues with the strongest expression in the kidney and weaker ones in the brain, heart, parathyroid gland and testis.6,48 RT-PCR detects Klotho expression in more tissues including aorta, colon, pituitary gland, thyroid gland, pancreas, and gonads but the kidney still has the strongest Klotho expression. From the onset, the findings suggest that the kidney might be a major source of endocrine Klotho. The higher Klotho protein in the suprarenal vein than that in infrarenal vein in rodents (personal observation) and the low circulating plasma levels observed in rodent with renal failure2 strongly suggests that the kidney is a main source for Klotho in the blood circulation (Fig. 1 A).
Figure 1.
Circulating Klotho. A) Klotho is synthesized in few organs but the kidney is main resource of circulating blood Klotho. Whether parathyroid gland and brain contribute significantly to circulating Klotho is not clear. B) Both renal proximal convoluted tubules (PCT) and distal convoluted tubules (DCT) produce Klotho. Klotho is released into the capillaries (C) and systemic circulation. The relative contribution of these two segments to circulating Klotho is unknown. Conversely, Klotho from the blood may enter the urine potentially via transcytosis of the tubular epithelium. Luminal Klotho from the PCT can travel axially down the nephron to the DCT lumen. Klotho from PCT cells and/or DCT cells may also exert paracrine actions on tubular epithelium. C) Membrane form of Klotho transcript arises from Klotho gene. Secreted Klotho be derived from alternative RNA splicing. The internal splice donor site is in exon 3 of Klotho gene. The resultant alternatively spliced transcript contains 50 bp insertion after exon 3 (grey) with an in-frame translation stop codon introduced. The product contains only Kl1 and is released into blood circulation. On the other hand, the Klotho protein encoded by membrane form of Klotho transcript is a plasma membrane-anchored protein in Klotho producing cells. Extracellular domain of membrane Klotho containing Kl1 and Kl2 repeats is shed and cleaved by α and β-secretases, and released into blood stream. Thus in blood circulation, there are two forms of Klotho, one is derived from cleavage of the extracellular domain of membrane Klotho. Another one is secreted membrane derived from an alternatively spliced Klotho transcript.
In mammalian kidney including mouse, rat and human, Klotho is prominently expressed in distal convoluted tubules (DCT),17 but Klotho is also unequivocally found in the proximal convoluted tubule (PCT) although in lower levels compared to DCT.14 The presence of Klotho mRNA is confirmed by RT-PCR in micro dissected rat nephron segments, and in OK cells, a renal proximal tubule-like cell line. The PCT mRNA rules out Klotho protein uptake as an explanation for Klotho antigen in the PCT (Fig. 1B).14
Klotho protein is present in cerebrospinal fluid (CSF),49 blood2,49,50 and urine of mammals.2,14,50 This soluble Klotho protein of 130 kDa by SDS-PAGE49 is different from the secreted Klotho encoded by a spliced transcript of Klotho with a predicted size of 70 kDa.4,5 The extracellular domain of Klotho is shed from full length membrane Klotho protein by cc-secretase, ADAM (a disintegrin and metalloprotease) 10 and 17 and β-secretase, β-APP cleaving enzyme 1, and released into blood circulation (Fig. 1C).9 The cleavage and release of the extracellular domain of Klotho by ADAM 10 and ADAM 17 is stimulated by insulin and inhibited by metalloproteinase inhibitors.8 ADAM 10 is expressed in the DCT and is potentially perfectly poised to cleave Klotho.51 To date, whether other molecules are also able to regulate membrane Klotho shedding is not known. The substrates for ADAM 10/17 are massively broad and what regulates ADAM 10/17-mediated ectodoamin shedding requires much more studies. This is a serious void in the database as the control of release from the parental pre-molecule is a crucial step for any endocrine substance.
sKl plays important roles in a variety of physiological and pathological processes including modulation of Wnt signal transduction,11 anti-oxidation52 and renal ion channels15,16,24 and transporters.14 Another possible role of the cleaved extracellular domain of Klotho may act to modify the signal transduction role played by membrane Klotho as a coreceptor for FGF23 but there is no data to date to support Klotho’s ability to quench soluble FGF23 (as a decoy) or to block the Klotho-FGF receptor complex (as a competitive inhibitor).
In addition to the final urine, Klotho protein is detected in the proximal tubule urine.14 This location of Klotho is absolutely necessary for it to function as a phosphaturic substance.14 Currently, the origin of this proximal luminal Klotho is unclear. It may be directly cleaved from proximal tubular cell or derived from the pertibular blood circulation via transcytosis (Fig. 1B). The only route that cannot be true is glomerular filtration as Klotho is too large for the glomerular basement membrane selectivity filter. Indeed, there is no detectable Klotho antigen in the glomerular Bowman space proto-urine (personal observation).
The kidney is a principal organ in calcium16,24,53 and phosphate14 homeostasis and directly modulates blood 1,25-(OH)2 Vitamin D3 and indirectly PTH, and FGF23 levels.25,27,28,54–56 In addition to being commanded by calciotropic hormones as an operative, the kidney is endowed with the calcium sensing receptor57 which renders it a self-sufficient afferent and efferent organ for calcium homeostasis. Although the identity of the phosphate sensor is elusive, the proximal tubule is clearly responding to ambient phosphate concentrations58 and exerts it effect by regulating Na-phosphate cotransporters directly59 and 1α-hydroxylase expression and activity.60 Although 1α-hydroxylation is present in many organs,60 the proximal tubule activity is the most important and regulated.61 Klotho protein is poised in the central place of this network of mineral metabolism homeostasis where it is in direct apposition with the sensors and effectors. The physical proximity and functional coupling of the glomerulus, proximal, and distal tubule renders this ensemble a perfect locale for a paracrine, autocrine, and endocrine hormone.
When normal rats were subjected to ischemia-reperfusion injury, adenovirus-mediated Klotho gene delivery results in significantly improved serum creatinine, dramatically ameliorated renal histological changes, and remarkably diminished apoptotic cells in the kidneys.23 It is important to note that the gene transfer occurred only in the liver and not in kidney. This experimental finding strongly suggests that Klotho functions as a circulating substance to exert renoprotection.
CHRONIC KIDNEY DISEASE: A STATE OF KLOTHO DEFICIENCY
As a general principle, if the organ of origin of an endocrine substance is diseased, it is logical to suspect that endocrine deficiency of that substance ensues. There are many similar features between the clinical manifestations of CKD with the phenotypes of Kl−/− mice (Table 1), which is the first suggestion that CKD might be a state of Klotho deficiency. Experimental data and clinical findings have thus far supported this view. There is a significant reduction of renal Klotho transcript and protein in CKD with varied etiology including ischemic perfusion injury, subtotal nephrectomy, oxidant stress, and exposure to angiotensin II (Ang II) and calcineurin inhibitors, and also in human CKD including chronic glomerulonephritis, obstructive nephropathy, diabetic nephropathy, and chronic graft rejection (Table 2). Hyperphosphatemia is a prominent abnormality in CKD, and is a major contributor to cardiovascular disease, which accounts for significant mortality in this population. Severe hyperphosphatemia is also found in Klotho-deficient mice.6,14 High FGF23 level in the blood is a feature in patients with CKD,62,63 and could contribute to decline of the 1α-hydroxylase activity, hyperparathyroidism, bone disease and cardiac hypertrophy in CKD.63,64 This can be viewed as a revisited version of the “trade-off hypothesis” in CKD. High plasma FGF23 is also observed in Klotho-deficient mice.65 In patients with CKD, ectopic calcification is frequently encountered.66,67 Interestingly, Kl−/− mice have very severe and wide-spread ectopic calcifications including vascular calcification.2,6
Table 1.
Similar clinical characteristics between Klotho−/− animals and CKD subjects
Klotho−/− | CKD | |
---|---|---|
Blood creatinine | ↑ | ↑↑↑ |
Renal Klotho expression | ↓↓↓ | ↓↓ |
Serum Pi | ↑↑↑ | ↑↑ |
Serum FGF23 | ↑↑↑ | ↑↑↑ |
Ectopic calcification | Present | Present |
Artherosclerosis | Present | Present |
Growth | Severe retardation | Retardation in children |
Anemia | No or mild | Severe |
Life span | ↓↓↓ | ↓↓ |
Table 2.
Endocrine and Renal Klotho deficiency in chronic kidney disease in humans and in rodent models
Category of Kidney Disease |
Cause or Animal Model |
Renal Klotho Protein |
Renal Klotho mRNA |
Blood Klotho |
Urine Klotho |
Human or Rodent | |||||
---|---|---|---|---|---|---|---|---|---|---|---|
IB | IHC | NB | qPCR | Assay | Assay | Mouse | Rat | Human | Citation | ||
CKD | CGN | ✓ | ✓ | ✓ | ✓ | 1 | |||||
CKD | DN | ✓ | ✓ | ✓ | ✓ | 1 | |||||
Graft rejection | CGR | ✓ | ✓ | ✓ | ✓ | 1 | |||||
CKD | Npx+IRI | ✓ | ✓ | ✓ | ✓ | IP + IB | IB | ✓ | ✓ | 2 | |
CKD | 5/6 Npx | ✓ | ✓ | 3 | |||||||
CKD | ICGN | ✓ | 18 | ||||||||
CKD | Npx in apo-E−/− | ✓ | ✓ | ELISA | ✓ | 37 | |||||
Hypertension | SHR | ✓ | ✓ | 3 | |||||||
Hypertension | DOCA | ✓ | ✓ | 3 | |||||||
Hypertension | AngII | ✓ | ✓ | ✓ | ✓ | 21 | |||||
Hypertension | AngII | ✓ | ✓ | ✓ | 39 | ||||||
DM | OLETF | ✓ | ✓ | 3 | |||||||
DM | Streptozotocin | ✓ | ✓ | 40 | |||||||
Nephrotoxicity | CsA | ✓ | ✓ | ✓ | ✓ | 41 | |||||
Nephrotoxicity | FK | ✓ | ✓ | ✓ | ✓ | 41 | |||||
Nephrotoxicity | SRL+CsA or FK | ✓ | ✓ | ✓ | ✓ | 41 | |||||
Nephrotoxicity | CsA | ✓ | ✓ | ✓ | 42 | ||||||
Childrn/adults | Normal | ELISA | ✓ | 43 | |||||||
Age/aged kidney | Normal | ✓ | ✓ | 44 | |||||||
Age/aged kidney | Normal | ✓ | ✓ | 46 |
CGN: Chronic glomerulonephritis; CsA: cyclosporine A; DM: Diabetes mellitus; DN: Diabetic nephropathy; DOCA-salt: Deoxycorticosterone acetate and high salt intake (DOCA-Salt); FK: FK-506, or called Tacrolimus; IB: Immunoblot; ICGN: ICR-derived spontaneous glomerulonephritis; IHC: Immunohistochemistry; IP: immunoprecipitation; NB: Northern blot; Npx: nephrectomy; OLETF: the Otsuka Long-Evans Tokushima Fatty Rat; RT: Reverse transcription; SHR: Spontaneous hypertension; SRL: Sirolimus; qPCR: quantitative or real time PCR.
A hypothesis can be raised that the Klotho deficiency may be one of the factors triggering complications in CKD and correction of Klotho deficiency may be a therapeutic possibility for treatment of kidney diseases.
Renal Klotho Deficiency
Aging Kidney
Aging is a complicated and chronic degenerative biologic process that affects kidney function and morphology. Aging is associated with decline in kidney function68 coincident with a progressive decrease in the number of functioning nephrons and increase in glomerular and tubulointerstitial scarring.69 These changes may cause secondary abnormal systemic hemodynamics, and disturbed mineral and hormonal homeostasis.70
The aged kidney is more prone to ischemic injury and nephrotoxin.71,72 Epidemiological data clearly shows that CKD is common in the elderly and associated with higher morbidity and mortality. More than 40% Canadian residents at 65 years or older has moderate CKD (estimated GFR < 60 ml/min/1.73 m2). Among American CKD patients, about 30% are from age 75 to 84 and 50% of patients of age 85 to 100 have at least moderate CKD.73
Aged mice (29 months) have low renal Klotho protein expression compared to young mice (4 weeks).46 Furthermore, aged rats (male, 27 months) have significantly higher serum creatinine than that of young rats (12-months). Notably, aged rats have significantly decreased renal Klotho protein levels along with increase in oxidative stress, overproduction of proinfiammatory cytokine and activation of endothelin signal transduction.44
In one report using a newly developed human plasma Klotho assay, an inverse relationship was found between the plasma Klotho levels and age.43 One possibility is that the physiologic decrease in renal function with age reduces Klotho expression and shedding into circulation, which consequently promote multi-organ senescence. On the other hand, age-related renal Klotho decline renders the kidneys more susceptible to insults such as hypertension, ischemia, and nephrotoxins. However regardless of how Klotho is down-regulated with aging, Klotho supplementation has potential beneficial impact in renoprotection and slowing of aging.
Rodent CKD from Ablation of Renal Mass
CKD rats with subtotal (5/6) nephrectomy have hypertension, proteinuria, azotemia, anemia, lower urinary concentrating ability74 and vascular calcification.75 5/6th nephrectomized rats have low Klotho mRNA expression in the kidney at 8 weeks after surgery.3 Low renal Klotho protein and mRNA expression is also demonstrated in another rodent model generated by unilateral nephrectomy plus contralateral ischemic reperfusion injury followed by high dietary phosphate intake.2 Renal histology reveals the same changes as those in the 5/6th subtotal ablation model. In addition, animals have high plasma creatinine concentration, hyperphosphatemia, anemia, and ectopic calcification in soft tissues including the kidney, aorta, heart and stomach.
Similar findings are observed in apolipoprotein E-deficient (apo-E−/−) uremic mice induced by nephrectomy plus electrocautery.37 Furthermore, apo-E−/− uremic mice have lower blood Klotho than apo-E−/− non-uremic mice.37
Immune-Mediated Chronic Glomerulonephritis
In addition to CKD model by ablation of renal mass, immune-mediated chronic glomerulonephritis, which is a major cause of CKD in humans, also have reduced renal Klotho mRNA.18 Imprinting Control Region (ICR) strain-derived mice with spontaneous chronic glomerulonephritis due to mutation in Tensin2 have shorter life span, which is reversed by Klotho overexpression. Klotho overexpression improves renal function, and ameliorates renal histology. The improvements are associated with less superoxide anion generation and lipid peroxidation, and with decreased levels markers of cell senescence, mitochondrial DNA fragmentation, and apoptosis. Thus Klotho protein might serve as a renoprotective factor by diminishing oxidative stress, cell senescence and apoptosis.18
Metabolic Syndrome and Diabetes
The association of kidney disease with the metabolic syndrome is known in humans and rodents.76–78 OLETF rat is a rodent model for the metabolic syndrome.79,80 OLETF rats have lower level of Klotho mRNA in the kidneys than age-matched control rats.3,80
The administration of thiazolidinedione to OLETF rats significantly increases renal Klotho mRNA expression, and attenuates abnormal lipid and glucose metabolism and reduces systolic blood pressure.80 The effects of thiazolidinedione on OLETF rats is also observed in OLETF rats overexpressing the Klotho gene, suggesting that the capacity of thiazolidinedione to restore the phenotypes in OLETF rats may results from an increase in renal Klotho expression.80
In rats with streptozotocin-induced diabetes,40 Klotho protein in the kidneys is notably decreased along with kidney destruction.40 Both insulin and phloridzin corrects hyperglycemia, reverses the reduced renal Klotho expression, and improves kidney function and histology of diabetic rats. Klotho protein in Madin-Darby Canine Kidney cell (MDCK) is reduced in vitro by incubation in high glucose medium. Insulin has been shown to participate in the shedding of extracellular domain of Klotho,8 which may increase the blood Klotho concentrations.
Hemodynamic Effect in Animal Models
Emerging data suggest a role ofKlotho in hypertension. In spontaneous hypertensive rats and in rats administered deoxycorticosterone acetate plus high salt intake, which is a volume-dependent type of hypertension, renal Klotho mRNA expression is significantly reduced compared to normotensive control rats.3 Hypotension per se does not seem to affect renal Klotho, because Klotho gene and protein are not decreased in the kidneys of rats with low systolic blood pressure due to myocardial infarction or phlebotomy.3,81 However, decreased renal Klotho expression is observed in rats with hypotension induced by lipopolysaccharide (LPS) injection.81 Thus the upstream regulator is more likely inflammatory mediators including TNF-α and IFN-γ released during LPS injection than hypotension (Table 3).82
Table 3.
Factors that downregulate renal Klotho in CKD setting
Loss of functional kidney mass |
---|
Abnormal cytokine production |
TNF-α ↑ |
IFN-γ ↑ |
Oxidative stress |
H2O2 ↑ |
Lipid peroxidation ↑ |
Over activation of renal RAS |
Ang II ↑ |
Abnormal hormone |
1,25-VD3 ↓ |
Disturbed mineral metabolism |
Pi overload |
Blood Pi ↑ |
Small uremic toxin |
Indoxyl sulphate ↑ |
Calcineurin Inhibitor Related Nephrotoxicity
Calcineurin inhibitors (CNI’s) such as cyclosporine A (CsA) and tacrolimus (also called FK-506, FK) were introduced for immunosuppression in organ transplantation.83,84 CNI’s are also widely used for treatment of immune-mediated nephrotic syndrome and glomerulonephritis.85,86 But CNI-induced nephrotoxicity is frequently a cumbersome limitation for its clinical utilization.87,88 Mice treated with CsA or FK have reduced renal Klotho mRNA, and protein, and increased urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG), an oxidative stress marker, excretion compared with vehicle-treated mice. In addition, there is a strong inverse correlation between Klotho protein levels and urinary 8-OHdG excretion. The CNIs-induced down-regulation of renal Klotho expression is correlated with increased renal angiotensinogen and renin expression, tubulointerstitial fibrosis and urinary 8-OHdG excretion, which are reversed by angiotensin II Type I receptor blocker, Losartan.42 These results suggest that Ang II-induced Klotho down regulation in the kidneys may be involved in CsA nephropathy.
Moreover, combination of CNI’s with sirolimus (SRL), commonly used to enhance immunosuppression for renal transplantation89 accelerates CNI-induced oxidative stress and down-regulates renal Klotho expression in the kidney.41 Those results may alarm the higher nephrotoxicity induced by mTOR and CNI’s combination.
Human CKD
Thus far, measurements of blood Klotho in human CKD have been limited. Renal expression of the Klotho gene is reported to be markedly decreased in patients with CKD (Table 2). The levels of Klotho mRNA and protein are reduced in nephrectomy samples from patients with CKD or end stage renal disease (ESRD), obstructive nephropathy, rejected transplanted kidneys, diabetic nephropathy and chronic glomerulonephritis.1
Klotho transcript and protein expression in kidneys from human and animal is clearly decreased. However, the relationship between the renal Klotho expression and the plasma Klotho levels remains to be studied and the mechanisms underlying the relationship between renal Klotho down-regulation and kidney diseases in humans remain unclear. These are studies of the highest priority at this juncture.
Endocrine Klotho Deficiency in CKD
The apo-E−/− 5/6th nephrectomized mice have decreased plasma Klotho and this decline increases with age. Furthermore, the reduction of plasma Klotho was more dramatic compared to non-uremic apo-E−/− mice.37 In another CKD model of uninephrectomy plus contralateral ischemia reperfusion in mice and rats, plasma Klotho concentration was remarkably decreased in CKD compared to Sham animals. The degree of decreased plasma Klotho is similar in magnitude to that of decreased Klotho protein in the kidneys and in the urine.2 Transgenic mice with Klotho overexpression also have reduction in their renal, blood and urine Klotho levels with CKD but still maintain levels comparable to wild type mice without kidney disease (Fig. 2) and have better kidney function and less vascular calcification.2 Soft tissue calcium content is inversely related to Klotho levels. Klotho overexpressing mice have lower, and haploinsufficient Kl+/− mice have higher calcium contents than WT mice do at baseline and after induction of CKD.2 Thus in rodents, CKD is a state of endocrine Klotho deficiency in addition to renal Klotho deficiency, the systemic Klotho levels efficiently affect the renal function preservation as well as calcification development in CKD animals.2
Figure 2.
Klotho protein in humans and rodents with CKD. A) Representative immunoblot for Klotho protein with serial dilutions of known concentration of recombinant mouse Klotho (rMKI) as standard and concentrated human urine samples of identical amount of creatinine. Lower panel shows summary of urinary Klotho protein concentration (open bars) and of Klotho normalized by creatinine (black bars) of normal subjects and CKD patients. Significant difference when P < 0.05 between groups analyzed by one-way ANOVA followed by Student-Newman-Keuls test. *: P < 0.05, **: P < 0.01 vs. Normal. B) Klotho levels in plasma, urine, and kidney in a murine model of CKD. Representative blots of Klotho protein in plasma, urine and kidney in CKD mice. Co-IP of Klotho in 100 µl of mouse serum was followed by immunoblot. IgG heavy chain = loading control. Urine Klotho was examined by directly immunoblotting ~40 µl of animal fresh urine with identical amount of creatinine. Klotho protein in the kidney was analyzed by immunoblotting 30 µg of the total kidney lysate. Lower panel shows summary of blood, urinary and renal Klotho protein of Sham (open bars) and CKD (black bars) mice. Quantitative data represented as means ± SEM and analyzed by the unpaired t-test. *P < 0.05, **P < 0.01 between Sham and CKD mice.
Equivalent data in human plasma Klotho are yet to be acquired. Urinary Klotho levels of CKD patients are significantly decreased and this decrease starts at very early stage and sustain ably reduced with progression of CKD (Fig. 2).2 Thus far, rodent plasma, kidney and urine Klotho appears to covary rather tightly.2 To date, one ELISA kit for plasma Klotho measurement is available and using this kit, plasma Klotho levels are found to be negatively related to the plasma creatinine concentration in children and adults without kidney disease.43 Further confirmation is required.
ROLE OF KLOTHO DEFICIENCY IN PROGRESSION AND COMPLICATIONS OF CKD
In rodents, endocrine and renal Klotho deficiency is striking in CKD. The most important question is whether this is a mere biomarker of the presence of CKD or whether the Klotho deficiency is a pathogenetic factor for CKD development, progression, and complications.2
Potential Mechanism of Klotho Deficiency
Renal, plasma, and urine Klotho are decreased very acutely upon ischemic-reperfusion injury50 and in CKD, it is one of the earliest abnormality.2 This begs the question as to how Klotho is decreased with kidney injury.
Phosphotoxicity
Klotho is a phosphaturic hormone. Klotho deficiency impairs phosphaturia,14 and consequently accelerates Pi accumulation in CKD. The higher level of serum Pi, the greater the degree of soft tissue calcification, and the greater risk of mortality.90 Control of serum Pi significantly improves survival in CKD and ESRD patients, decreases vascular calcification, and suppresses proliferation of parathyroid glands.90–92 There is little doubt that the prevailing thought is that Pi is one of “uremic toxins” but the concept of phosphotoxicity extends beyond just CKD.93
Phosphate overload suppresses Klotho expression in the kidney. Normal mice fed high Pi diet have dramatically decreased Klotho protein and mRNA in the kidney, while Klotho hypomorph mice fed low Pi diet regain part of their Klotho expression.94 Whether the blood Klotho concentration is regulated by physiologic changes in dietary Pi is yet to be determined.
Vitamin D Deficiency
Low 1,25-(OH)2-vitamin D3 is a major component of disturbance of mineral metabolism, and is conventionally attributed to cause bone disease and secondary hyperparathryoidism in CKD.95 The increase in plasma FGF23 in CKD plays an important role in suppression of 1α-hydroxylase in the kidney and initiates or accelerates vitamin D deficiency.96,97 Importantly, administration of 1,25-(OH)2-vitamin D3 induces klotho expression in the kidney.26 It is plausible that low vitamin D level in CKD further worsens renal Klotho deficiency (Table 3).
Angiotensin II
Long-term infusion of Ang II down-regulates renal Klotho mRNA and protein. Administration of norepinephrine,21,39 or L-NAME, an inhibitor of NO synthesis,81 cause a comparable hypertensive effect as that of Ang II, but does not affect renal Klotho expression. Continuous infusion of low dose of Ang II in rats that does not affect systolic blood pressure, also down-regulates Klotho mRNA in the kidney21,39 suggesting that the Ang II-induced Klotho down-regulation is not dependent on blood pressure. In addition, both losartan, an angiotensin Type 2 receptor antagonist, and hydralazine block the rise in blood pressure by Ang II, but only losartan completely blocks the Ang II-induced decrease in Klotho indicating that the Ang II effect on Klotho is via an Ang II Type 2 receptor.21 This suggests a significant role of Ang II in the regulation of Klotho expression in the kidney and infers important therapeutic possibilities.
Oxidative Stress
Oxidative stress in the kidney originates not only from infiltrating inflammatory cells, but also from damaged kidney cells. Oxidative stress does not only trigger acute kidney injury but also accelerates chronic progression of kidney disease.98,99 H2O2 suppresses Klotho mRNA and protein expression in cultured mIMCD3 cells.22 Adenovirus-mediated overexpression of the klotho gene reduces apoptosis in mIMCD3 cells, suggesting that klotho may be protective against oxidative stress injury and apoptosis at least in this cell line.22
Indoxyl Sulfate Toxicity
Indoxyl sulfate is one of uremic toxins, and significantly increased in the blood of CKD.100,101 It is not only a biomarker for kidney damage,101 but also seems to promote progression of CKD and cardiovascular disease in CKD.101 Indoxyl sulfate reduces renal Klotho expression, and contributes to cell senescence in the kidneys and enhances renal fibrosis of hypertensive rats.102 The mechanism of Klotho down-regulation in the kidney of CKD is complicated and is summarized in Table 3.
Potential Pathogenetic Roles of Klotho Deficiency in Kidney Disease
The fact that Klotho-deficient mice have more severe kidney damage and fibrosis, and Klotho overexpressors have milder kidney dysfunction and fibrosis after CKD induction surgery, strongly supports the notion that Klotho might be a pathogenic intermediate for CKD development.2
Reduced Ability of Regeneration
Klotho deficiency is associated with stem cell dysfunction and depletion, which is part of normal aging.11 The decrease in stem cell number is associated with an increase in progenitor cell senescence. Secreted Klotho binds to various Wnt family members and inhibits their biological activity. Wnt signaling activity is significantly increased in tissues from Kl−/− mice, while suppressed by genetic Klotho overexpression.11 Administration of exogenous Wnt could stimulate Wnt signal transduction, and trigger or accelerate cell senescence both in vitro and in vivo. Thus, Klotho appears to be a secreted Wnt antagonist and antagonizes mammalian aging.
Cell senescence is a complicated process present not only in normal aging but also in several pathophysiological states.18,103,108 Secondary Klotho deficiency in kidney diseases could enhance cell senescence accompanying oxidative stress.18,102,109 Cell culture studies confirm that Klotho deficiency directly promotes senescence of renal epithelial cells.110 Klotho supplementation could block senescence induced by oxidative stress.52,111 Excessive senescence or apoptosis and secondary stem cell deletion might decrease the ability of kidney to defend against renal insults and impair regeneration.
Abnormal Endothelial Function and Angiogenesis
Abnormal endothelial function and impairment of angiogenesis and vasculogenesis can delay kidney regeneration post injury and contribute to progression of CKD and aging of the kidney.112–116 There are two abnormal aspects in the vasculature of the Kl−/− mice. One is abnormal vasodilatation due to abnormal endothelial function;117 another is impaired angiogenesis and vasculogenesis.118 The aortas of Kl+/− mice has exaggerated contractile response to norepinephrine and attenuated responses to acetylcholine and superoxide dismutase. Kl+/− mice have low urinary NO metabolites (NO2−/NO3−) and cGMP concentrations, but normal the prostaglandin.117 Low NO which is as result of low expression of NO synthase117 may be one of causes of hypertension in Kl+/− mice (personal observation).
The defect in angiogenesis and vasculogenesis is well known with aging, but its mechanism is not completely understood. Kl+/− mice have delayed angiogenesis and vasculogenesis and low blood-flow after hind limb ischemia.119 The HMG co-enzyme A reductase inhibitor cerivastatin increases Klotho levels and restores the impaired neovascularization.118 The low vasculogenesis and angiogenesis in Kl+/− mice might be attributable to down-regulation of vascular endothelial growth factor (VEGF) in the aorta.117
Klotho incubation mitigates increased cell senescence and apoptosis in endothelial cells triggered by oxidative stress or by Klotho deficiency.111 In addition, Klotho suppresses TNF-α-induced expression of intracellular adhesion molecule-1 and vascular cell adhesion molecule-1, attenuates NF-kappaB activation, and reverses the inhibition of eNOS phosphorylation by TNF-α. Thus Klotho protein may have another role in protection of vasculature by inhibition of endothelial inflammation.120
Renal Fibrosis
Renal fibrosis is one striking histological characteristic in CKD, and is generally attributed to epithelial-mesenchymal transition (EMT).121,126 TGF-β1, a major fibrotic progression protein, plays a key role in EMT in the kidneys.125,127,129 Kl−/− mice have more appreciable renal tubulointerstitial fibrosis,130 which is associated with up-regulation of TGF-β1 in the kidneys. The renal fibrosis in unilateral ureteral obstruction (UUO) is accompanied by up-regulation o f TGF-β1 and fibronectin, and down-regulation of Klotho mRNA and protein. These alterations are more exaggerated in Kl+/− UUO mice than in WT UUO mice. HK2 cells incubated with TGF-β1 have down-regulation of Klotho expression which is attenuated with TGF-β1 receptor inhibitor (ALK5 inhibitor).130 Secreted Klotho alleviates renal fibrosis induced by UUO and suppresses expression of fibrosis markers and TGF-β1 target genes (Snail, Twist), but does not reduce TGF-β1 expression in UUO kidney.131 Furthermore, Klotho suppresses TGF-β1 induced Smad2 phosphorylation in a rat tubular epithelial cell line (NRK52E), suggesting that Klotho protein suppresses renal fibrosis primarily through inhibiting TGF-β1 signaling.131
Plasminogen activator inhibitor-1 (PAI-1) is a member of the serine protease inhibitor family and regulates fibrinolysis and proteolysis through inhibiting plasminogen activation.132,133 PAI-1 levels are increased in the kidneys of human with glomerulonephritis, hypertensive nephrosclerosis, diabetic nephropathy, and chronic allograft nephropathy, CysA nephrotoxicity134 and lupus nephritis in female MRL Ipr/lpr mice.132,133 PAI-1 mRNA and activity are strikingly elevated in multiple tissues in Kl−/− mice compared with WT mice. This increase in PAI-1 is age-dependent and linked to the development of ectopic calcification, and glomerular fibrin deposition in the kidneys of Kl−/− mice.135 Thus, the lack of Klotho increases PAI-1 mRNA and activity.
Potential Contribution of Klotho Deficiency to Complications of CKD
The emerging view is that Klotho deficiency not only worsens renal disease but also exacerbates extra renal complications in CKD.
Ectopic Calcification
Cardiovascular calcificaion is a heterogeneous disorder with overlapping yet distinct mechanisms of initiation and progression.67,136,137 Vascular calcification is a dynamic process resulting from the imbalance between promoters and inhibitors.136,138 Abnormal FGF23 and Klotho can contribute to ectopic calcification in soft tissue.2,6,65
The fact that Kl−/− mice have extensive ectopic calcification in soft tissue, which is also observed in CKD subjects strongly suggests a pathogenetic association between Klotho deficiency and calcification. CKD animals and human patients have significantly low Klotho protein and mRNA in the kidneys (Table 2) and CKD animals have low plasma and urinary Klotho protein.2 Administration of exogenous Klotho protein (personal observation) or increasing Klotho level via genetically engineered manipulation2 significantly inhibits vascular calcification in CKD animals suggesting that Klotho deficiency is associated with vascular calcification in CKD.
Elevated plasma Pi is associated with vascular calcification in experimental animals and in CKD patients and cellular Pi influx is believed to be mediated by the NaPi-3 group of Na+-coupled transporters (also named Pit1 and Pit2) in vascular smooth muscle cells (VMSC).139 Kl−/− mice have high levels of Pit1 and Pit2 mRNA and higher tissue calcium contents compared to WT litter mates. In addition, Kl+/− CKD mice have higher and Tg-Kl CKD mice have lower Pit1/2 mRNA in the aortas than WT CKD mice. Upregulation of expression and activity of Pit1/2 in the aortas which may result from high ambient Pi and/or unknown uremic toxin (s) could increase intracellular Pi concentration, induce VSMC de-differentiation, and increase or trigger vascular calcification.2
FGF23-deficient mice have ectopic calcification in soft tissues including vasculature, raising the possibility that FGF23 may be protective for the vasculature. However, the high plasma FGF23 in CKD patients challenges this notion. One possible explanation might be that the target organ loses the response to FGF23 in CKD. Klotho and FGFR1/3 expression are down-regulated when human aorta derived-SMCs are incubated with high phosphate and calcium. These cells exhibit concomitant osteo/chondrocytic transformation and loss of contractile phenotype. De-differentiation of SMC and loss of the ability to respond to FGF23 may result from down-regulation of Klotho-FGFRl/3 expression in the arteries.140
Cardiac Hypertrophy
Cardiac hypertrophy in CKD, also referred to as “uremic cardiomyopathy” by some, is another pathological feature of cardiovascular complication. Clinically, it is characterized by cardiac arrest or sudden death, left ventricular hypertrophy, and congestive heart failure, which may be distinct from hypertensive and ischemic cardiomyopathy.141,142 Left ventricular hypertrophy is more frequent in CKD patients than the general population when age and gender are matched, and has a negative impact on cardiovascular prognosis.143 In addition to traditional risk factors such as smoking, hypertension, dyslipidemia, diabetes, anemia, AV fistula, volume overload, hypoalbuminemia, oxidative stress, chronic inflammation, and secondary hyperparathyroidism,144 additional risk factors include inappropriate activation of the RAS (renin-angiotensin-aldosterone system),145,146 vitamin D deficiency,147 high FGF23 in blood,148 and more recently, low Klotho in blood.2 We have observed left ventricular hypertrophy in Klotho-deficient animals without kidney disease (personal observation).
In the heart, Klotho is expressed solely at the sinoatrial node.48 The high rate of sudden death of Kl−/− mice under restraint is likely caused by sinoatrial node dysfunction.48 Intrinsic heart rate after pharmacological blockade of autonomic nerves in Kl−/− mice was significantly lower than that in WT mice. The sinus node recovery time after overdrive pacing is significantly longer in Kl−/− mice than in WT mice; but there is no degenerative structural change in the sinoatrial node, suggesting that normal Klotho gene expression is essential for the sinoatrial node to function as a dependable pacemaker under conditions of stress.48 Whether sKl also functions as regulator of the pacemaker is still unclear. Recently, we have observed cardiac fibrosis in Kl−/− mice, and this change is progressive with aging (personal observation). These findings suggest that Klotho may suppress intrinsic fibro genesis in heart, but whether the mechanism of fibrosis is same between the heart and the kidney is not known. Since there is normally no Klotho expression in the ventricles, the cardiac phenotype in Kl−/− mice is mostly likely due to deficiency in circulating Klotho or other factors. There is no data on Klotho expression in the heart of CKD patients. Thus the direct role of Klotho deficiency on the high cardiovascular mortality and morbidity in CKD patients remains to be confirmed.
Secondary Hyperparathyroidism
Secondary hyperparathyroidism is part of the CKD-Metabolic bone disease (MBD) spectrum.149,150 The role of PTH in CKD-MBD is well known and the role of FGF23 and Klotho in CKD-MBD is attracting attention. CKD subjects have high blood level and over activity of FGF2362 and low Klotho and FGFR(s) in parathyroid gland151,152 although some studies have argued for up-regulation of Klotho protein in uremic parathyroid gland.153 In normal subjects with normal kidney function, FGF23 plays a crucial role, both as a phosphaturic factor12,64,154 and as a suppressor of active vitamin D (1,25D) production in the kidney,97 and of PTH production in the parathyroid gland.28 In contrast, FGF23 fails to inhibit PTH production probably due to down-regulation of Klotho and FGFR(s) in parathyroid gland in the uremic setting.151,152
Bone Disease
Renal bone disease is the skeletal component of CKD-MBD (Mineral and Bone Disorder), and is characterized by either high or low turn-over and either presence or absence of mineralization defect.155,156 Secondary hyperparathyroidism, poor calcium intake, Pi retention, deficiency of 1,25-dihydroxy vitamin D, high FGF23 and low Klotho may all potentially contribute to CKD-MBD.157–159 Kl−/− mice have high blood FGF23, and low turn-over form of osteopenia160,161 associated with reduced number of osteoblast progenitors and low activity of osteoblastic cells in ex vivo bone marrow cultures derived from Kl−/− mice. This suggests independent impairment of both osteoblast and osteoclast differentiation leading to low-turnover osteopenia observed in Kl−/− mice.160,161 The bone disease in Kl−/− mice is not the same as those in CKD patients. The direct effect of Klotho on CKD-MBD remains to be clarified.
MECHANISMS OF HOW SECRETED KLOTHO PRESERVES KIDNEY FUNCTION AND AMELIORATES COMPLICATIONS IN CKD
Induction of Phosphaturia
Hyperphosphatemia results mainly from renal phosphorus retention,14,26 and is a prominent feature in the Kl−/− mice.6,14 The restoration of Klotho levels via genetic manipulation,20 or viral-based delivery162 successfully normalizes blood phosphate level. Kl−/− mice display increased activity of Na-coupled phosphate (NaPi) cotransport and elevation of NaPi-2a and NaPi-2c cotransporter proteins compared with wild-type (WT) mice.163 This suggests that the hyperphosphatemia at least in part is of renal origin. Moreover, NaPi-2b protein and mRNA in gut are higher in Kl−/− mice than in Wt mice163 indicating that increased intestinal phosphorus absorption may exacerbate augmentation of blood Pi concentration in Kl−/− mice. Transgenic Klotho overexpressing mice (Tg-Kl) have lower blood Pi, while renal fractional excretion of phosphorus (FEphos) is increased indicating a renal leak of Pi.14 Injection of sKl significantly increases FEphos and decreases blood Pi in the normal rat.14
Klotho protein inhibits NaPi cotransport activity in renal brush border membrane (BBM) and in OK cells.14 Klotho dramatically reduces NaPi-2a abundance in apical NaPi-2a protein in kidney and OK cells after 4 or more hours in vivo and in vitro respectively, indicating that the more sustained effects of Klotho on NaPi involves the canonical pathway of NaPi-2a internalization.14
The extracellular domain of Klotho contains two tandem repeats with 20%–40% amino acid identity with members of the glycosidase family including β-glucosidase, and has β-glucuronidase-like enzymatic activity.67 NaPi-2a is a glycosylatedprotein.164 The direct and acute inhibition of NaPi transport by Klotho can be mimicked by recombinant β-glucuronidase but not by sialidase. The substrate of this glycuronidase activity in the BBM is not known. While protease inhibitors abolish the proteolysis, they do not reverse the Klotho-induced inhibition of transport, indicating that Klotho-induced deglycosylation is sufficient and that subsequent proteolysis is not required to suppress Na-dependent Pi transport. Klotho modulates NaPi-2a in a biphasic fashion with dual distinct mechanisms. It acutely (<4 hrs) decreases its intrinsic transport activity via removal of glucuronate from some yet to be identified substrate, followed by proteolytie cleavage, and in a second phase (>4 hrs) induces changes in cell surface NaPi-2a.14
Hyperphosphatemia is universally observed in CKD patients, and is a potent predictor of cardiovascular morbidity and mortality.90,165 Controlling blood phosphate by restriction of intake,166 phosphate binder,92 and more efficient dialysis167 all improve clinical outcome in CKD patients. Undoubtedly, lack of the phosphaturic action of Klotho protein is an important pathogenic factor in CKD and means of restoring Klotho is of potential benefit.
Antivascular Calcification: Inhibition of Type III Na-Phosphate Cotransporter
Klotho can decrease soft tissue calcification by lowering plasma phosphate levels through promotion of phosphaturia. In addition, overexpression of Klotho improves kidney function after CKD induction surgery. Both of these actions can reduce the calcium content in soft tissues. The third most important and direct effect of Klotho on inhibition of calcification is the modulation of the NaPi-3’s-Pit1 and Pit2, key modulators for Pi influx into vascular smooth muscle cells (VSMC).2
While there is abundant calcification in the multiple organs of both WT and Kl+/− CKD mice, Tg-Kl-CKD animals have very few or no calcification.2 Calcium content is higher in the aortas and the kidneys of CKD than Sham in both the Wt and Kl+/− mice. This increase is ameliorated by overexpression of Klotho.82 Pit1, Pit2, and Runx2 (a marker of osteoblast-like phenotype) mRNA are increased and SM22 (a marker of contractile smooth muscle cell) is decreased in Kl−/−, while overexpression of Klotho has the opposite effect. Klotho may control the balance between differentiation and de-differentiation of VMSC.2 CKD induces a similar pattern as Klotho deficiency and Klotho overexpression completely blocked the changes induced by CKD. When rat VMSC are grown in vitro, Klotho inhibits Na-dependent Pi influx and minimizes the mineralization induced by high ambient Pi.2 The up-regulation of Runx2, and down-regulation of SM22 by high Pi is reversed by recombinant Klotho protein, suggesting that Klotho directly blocks Pi-induced de-differentiation of rat VMSC.2
Anti-Oxidation
The pathogenic effect of reactive oxygen species in initiation or exacerbation of kidney damage is well-known.22,168–171 Part of the anti-aging effect of Klotho is thought to be mediated by anti-oxidation or increased resistance to oxidant stress.172
Kl−/− mice have high level of oxidative stress and damage, while Tg-Kl mice have lower levels as compared with WT mice.172 Klotho-transfected mIMCD3 cells exposed to H2O2, show fewer apoptotic cells.22 Paraquat-induced increase in lipid peroxidation is suppressed in HeLa cells treated with Klotho protein.172 These results suggest that the Klotho may be involved in prevention of oxidative injury and apoptosis possibly related to activation of FOXO transcription signal and stimulation of MnSOD.172
Anticell Senescence
The permanent and irreversible growth arrest of cell and cell senescence are central paradigms of aging173 and diseases secondary to ischemia, toxin, inflammation, and so on.18,103,104,106,108,109,174 senescent cells may secrete altered levels of growth factors, increase susceptibility to apoptosis, and delay the repair and regeneration in the aging kidney. Thus prevention of cell senescence may provide an important beneficial impact on aging as well as kidney disease.106 Klotho functions as a secreted Wnt antagonist by directly binding to Wnt3/5 proteins klotho and inhibits cell senescence.11
Cell senescence and oxidative stress are closely associated and implicated in acute and chronic kidney disease. Mice with spontaneous chronic glomerular disease carrying a mutation in Tensin2 have low renal Klotho, high level of lipid peroxidation, superoxide anion production, mitochondrial oxidative stress, and severe cell senescence in the kidney.18 Genetic Klotho overexpression ameliorates renal injury associated with a dramatic improvement in mitochondria damage, reduction in senescent cells, decreased oxidant stress, and reduced apoptosis in the kidney.18
Suppression of Angiotensin II Effects
It is known that the angiotensin II (Ang II) activity and production are significantly upregulated in a variety of kidney diseases. Ang II is a proinflammatory mediator and oxidant.175–179 Animal experiments clearly revealed that Ang II decreases Klotho mRNA and protein expression in the kidney which could be blocked by Angiotensin Type I receptor antagonist.21 Moreover, Klotho gene transfer also blocks Ang II-induced kidney damage, suggesting that the Ang II may act upstream of Klotho and produce pathogenic effects by reducing Klotho.21
In addition, Ang II receptor antagonists do not only block the downregulation of Klotho, but also abrogate the induction of TGF-β, p-p38 and p53 expression in cultured NRK cells by Ang II. Therefore, blocking Ang II action causes upregulation of Klotho and exerts a cytoprotective role.180 Similarly HMG-CoA reductase inhibitors effectively blunt Ang II-induced reduction of Klotho expression in mIMCD3 cell line.181 Upregulation of Klotho may be one of therapeutic mechanisms of HMG-CoA reductase inhibitor action.
VALUE OF MEASURING KLOTHO IN CKD
CKD is one of major diseases affecting human life span and quality of life. Early diagnosis is paramount for one to initiate early and effective treatment. Extensive effort has been devoted to search for early biomarker for kidney diseases focusing mostly on acute kidney disease and less on CKD by transcriptomics, proteomics, metabolomics, lipidomics, and gene arrays.182–184 In addition to traditional clinical parameters such as eGFR, proteinuria, albuminuria, N-acetyl-beta-D-glucosaminidase, and cystatin c,185–190 novel proteins as adiponectin,191,192 γ-Glutamyltransferase,193,194 endothelin-1,195,196 uric acid,197–199 and FGF23200 have been proposed as biomarkers but remained to be validated in population studies.
Klotho has two potentials in terms of its role as a biomarker. First is that fall in plasma or urinary Klotho can be one of the earliest abnormality in CKD from a variety of causes. The most promising data thus far is that urinary Klotho is reduced at a very early stage CKD (Stage 1 and 2) and is progressively lowered with declining eGFR (Table 2).2 Hopefully, urinary Klotho protein could be an ideal early biomarker for CKD; as it declines much earlier than other parameters (Fig. 3). Second, in the presence of CKD, Klotho levels may bear prognostic value in predicting progression and complications of CKD. Judging from the rodent model, for the same degree of renal insufficiency and hyperphosphatemia, the lower the Klotho level, the more severe the soft tissue calcification.2 A longitude study is required to reveal the prognostic value of Klotho in CKD patients.
Figure 3.
Proposed model and time profile of changes in Klotho and hormones relevant to mineral metabolism in CKD. Left panel depicts a model where the decline in Klotho is an early event which then leads to other secondary changes. The secondary changes constitute a downhill spiral that exacerbates each other. The decline of Klotho protein in the kidney, urine and blood is an early event, and continues to decrease with CKD progression. Low Klotho consequently induces FGF23 resistance causing compensatory increase in blood FGF23 levels to maintain Pi homeostasis in CKD. The compensatory increase in FGF23 then suppresses vitamin D synthesis. In addition, low vitamin D and high blood Pi increases PTH. The high PTH may contribute to high FGF23 at late stage of CKD. The proposed time profile is shown on the right.
To date, there are limited assays available to determine the blood Klotho in humans. Immunoprecipitation from human plasma have proven to be not readily reproducible.47 Recently, one sandwich ELISA became available to detect soluble Klotho in human blood.43 This first report states that human serum Klotho ranges from 239 to 1266 pg/ml with a mean of 562 ± 146 pg/ml in normal adults. It is inversely related to blood creatinine and age. Normal children (7.1 ± 4.8 years) have significantly higher blood Klotho (952 ± 282 pg/ml). In addition, plasma Kl is correlated negatively with age and serum Ca, and positively with serum Pi.43 To date, there is no publication on plasma Klotho levels in CKD patients.
POTENTIAL STRATEGIES TO INCREASE KLOTHO PROTEIN
The animal data to date is overwhelmingly strong to indicate that Klotho is not merely an early biomarker for CKD, but also a pathogenetic intermediate for accelerating CKD progression and for development of complications. Restoration of endogenous Klotho or administration of exogenous Klotho might provide novel treatment strategies for CKD patients. There are two ways to increase soluble Klotho-administering exogenous Klotho or enhancing endogenous Klotho (Fig. 4).
Figure 4.
Potential strategies to increase Klotho protein. Prevention and retardation of progression of CKD could theoretically block the decline of endogenous Klotho protein in the kidney. Administration of exogenous Klotho protein or Klotho gene could directly provide high levels of Klotho in the blood. This is potentially useful for advanced CKD or ESRD. For early or moderate CKD patients where endogenous Klotho-producing cells are not destroyed completely or simply suppressed, stimulation of endogenous renal Klotho is of potential therapeutic benefit.
Administration of Exogenous Klotho
Ideally, administration of exogenous Klotho to CKD subjects is one simple and effective means to treat an endocrine deficiency similar to replacement of erythropoietin and vitamin D. Klotho can potentially reverse or retard the progression of CKD. Even in advanced stages of CKD, Klotho supplementation can alleviate extra renal complications of CKD.
Delivery of Klotho Gene to CKD Subjects
Gene therapy is broadly defined as the insertion, alteration, or removal of genes within an individual’s to change the phenotype. One form of gene therapy involves the insertion of functional genes into an unspecified genomic location to replace a mutated gene or enhance or silence the target gene. Other forms involve directly correcting the mutation or modifying normal gene via a viral carrier. Although the technology is still rather experimental, it has been used with some success.
Theoretically, gene therapy has distinct potential to treat CKD and complications at the most fundamental level. The present viral vector systems seem to have limitations for clinical use because of uncertainties regarding their toxicity and immunogenicity. But animal experiments have shown encouraging results. Adenovirus-mediated gene transfer has succeeded in gene expression in the kidney. Adeno-associated virus has a potential to be utilized as a vector targeting both kidney and skeletal muscle. Non-viral vectors such as the haemagglutinating virus of Japan (HVJ)-liposome method and cationic liposome are possibilities, but their efficiency needs to be improved. Electric pulse is emerging as a new and less harmful strategy of gene transfer to various tissues, including the kidney.201,202
Klotho gene delivery via adeno-associated virus (AAV) carrying mouse klotho full-length cDNA (AAV.mKl) efficiently attenuates the progression of spontaneous hypertension and renal damage in spontaneous hypertensive rats (SHR). A single dose of AAV. mKl prevents the progression of spontaneous hypertension for at least 12 weeks and reverses reduced Klotho expression in SHR rats. AAV.mKl attenuates renal tubular atrophy and dilation, tubular deposition of protein aceous material, glomerular collapse, and collagen deposition seen in SHRs, indicating that Klotho gene delivery limits renal damage induced by hypertension.203
Administration of Soluble Klotho Protein
Administration of exogenous Klotho protein is more direct, safe, and easier modality to correct endocrine Klotho deficiency in CKD compared with delivery Klotho gene. Following the history of use of Calcitriol and active derivative,204–207 and erythropoiesis-stimulating agents208–210 for CKD patients, Klotho protein may be a viable option in the horizon.
Compared with viral delivery system, fewer studies were reported for Klotho protein delivery. Recombinant Klotho protein of the full length of extracellular domain is able to inhibit IGF signal transduction to prolong animal life span,20 suppress Wnt signal pathway to decrease cell senescence and retain more stem cells,11 modulate renal ion channel or transporter10,14–16 or control FGF23 signal transduction.211 Klotho administration has been proven successful in the setting of acute kidney injury in animals which is a state of acute Klotho deficiency.50 Klotho protein was injected intraperitoneally into rats after ischemia-reperfusion injury. Rats given Klotho had better renal function, less kidney damage, and lower neutrophil gelatinase-associated lipocalin.50 More interestingly, this Klotho preparation inhibits renal fibrosis in UUO model by suppressing expression of fibrosis markers (α-Smooth muscle actin, Vimentin, Collagen-1, Metalloproteases) and TGF-β1 target genes (Snail, Twist) in a dose dependent manner. Klotho does not reduce TGF-β1 production but rather inhibits TGF-β1 signaling suggesting that Klotho prevents renal fibrosis primarily through inhibiting TGF-β1 signaling.131 The authors’ laboratories found that administration of Klotho protein does not only ameliorate kidney functions and histology, but also alleviates vascular calcification in CKD rats (personal observation). Thus, exogenous Klotho protein supplementation is a potentially feasible way of replacement therapy in Klotho deficient states (Fig. 4).
Up-Regulation of Endogenous Klotho Protein
In instances where endogenous Klotho-producing cells are not destroyed but simply suppressed, strategies to increase its production will be of therapeutic benefit, especially to early CKD patients (Fig. 4).
Blockage of Angiotensin II
Ang II is known to be an important mediator for initiation and progression of kidney diseases. Ang II contributes to hypertension, intraglomerular hyper filtration, oxidant stress and lipid peroxidation and tubulointerstitial inflammation and fibrosis in acute or chronic kidney diseases.212–222 Angiotensin converting enzyme inhibitor and angiotensin receptor antagonist are extensively used in the treatment of chronic kidney diseases. Recent studies have demonstrated that Ang II contributes to the pathogenesis of kidney diseases by reducing Klotho expression in the kidney.21 Induction of endogenous Klotho protein expression may have potential as a therapeutic agent in treating Ang II-related kidney disease.21,223 Similar therapeutic effect was observed in Ang II-perfused rats when treated with angiotensin receptor antagonist.
Angiotensin II Type I receptor antagonist, Losartan, doesnot only block the down-regulation of Klotho in the kidney of rats perfused with Ang II, but also in the kidney of rats treated with Cyclosporin A with improvement of kidney function, histology and less oxidative stress,42 suggesting that (1) CsA triggers oxidative stress and downregulates Klotho expression; both amplifying each other to cause nephropathy; (2) angiotensin Type I receptor antagonist interrupts the vicious cycle and attenuates kidney damage induced by CsA.
Free radical scavenger is able to suppress Ang II-induced downregulation of Klotho in the kidneys of rats, to decrease plasma oxidative stress marker, and to block the decline in creatinine clearance, indicating oxidative stress is involved in downregulation of renal Klotho induced by Ang II.39
HMG-CoA Reductase Inhibitor
3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase inhibitors are effective in lowering plasma concentration of LDL-cholesterol and are widely used in patients with hypercholesterolemia. Recently, this group of drugs called statins, have been shown to decrease the incidence of myocardial infarction and other ischemic vascular events independent of their lipid lowering properties.119 An ischemic hind limb model in mice achieved by ligation of femoral and saphenous arteries showed higher percentage of leg loss in Kl+/− mice compared to WT mice suggesting that lower angiogenesis and impairing blood flow recovery and diminishing capillary growth in Kl+/− mice.119 A HMG CoA reductase inhibitor, cerivastatin, enhances angiogenesis and restores the impaired neovascularization in Kl+/− mice after ischemic lind limb illustrated by similar blood perfusion between Kl+/− mice treated with cerivastatin and WT mice.118 The mechanism by which statins accelerate angiogenesis and vasculogenesis in Klotho-deficient mice is at least partly related to maintenance of Klotho,181,224 and secondary to improvement of endothelial function through endothelium-derived NO production.117
An in vitro study reveals that pretreatment with atorvastatin ameliorates the Ang II-induced reduction of Klotho mRNA.181 However, whether this in vitro effect of HMG CoA reductase inhibitors translates to an in vivo effect on the kidneys of whole animals or humans needs to be further defined.
PPAR-γ Agonists
Peroxisome proliferator-activated receptors (PPAR) are a group of nuclear receptors that function as transcription regulators of metabolic pathways. PPAR-gamma (PPAR-γ), also known as the glitazone receptor, is the molecular target of thiazolidinediones (TZDs), and has been used for treatment of Type II diabetes mellitus (DM) in human.225
In addition to therapeutic benefits of improved insulin sensitivity, thiazolidinediones upregulate Klotho expression both in vivo and in vitro. The induction of both Klotho mRNA and protein expression in HEK293 cells by PPAR-γ agonist is blocked by PPAR-γ antagonists or siRNA-mediated gene silencing of PPAR-γ. This induction is mediated by binding of PPAR-γ to 5′-flanking region of Klotho gene. Moreover, thiazolidinediones or adenovirus-mediated overexpression of PPAR-γ increases Klotho expression in mouse kidneys while renal klotho expression was attenuated in mice treated with PPAR-gamma antagonists. These results demonstrate that Klotho is a downstream target gene along PPAR-γ signal transduction.226 This effect may be one of mechanisms of PPAR-γ action on aging, DM and bone disease.227
Oral administration of troglitazone for 10 weeks significantly up-regulates renal Klotho mRNA expression, enhances endothelium-dependent aortic relaxation, and reduces systolic blood pressure, plasma glucose and triglyceride levels in OLETF rats, suggesting that improvement of the vascular endothelium function and dyslipidemia by troglitazone might be accompanied by up-regulation of renal Klotho.80 Pioglitazone not only improves metabolic abnormalities of diabetes and consequent diabetic nephropathy, but also protects against nondiabetic chronic kidney disease in experimental models of aging kidney. It reduces proteinuria, improves GFR, decreases sclerosis, and alleviates cell senescence in the kidneys of aged rats. A similar effect is observed by increased the expression of PPAR-γ in the kidney.108 Proposed underlying mechanisms include increased expression of Klotho, decreased systemic and renal oxidative stress, and decreased mitochondrial injury.108
PPAR-α is another member of the PPAR family and is highly expressed in the kidney. PPAR-α activation is able to protect the kidney from acute injury either by cisplatin or ischemic reperfusion.228,229 But whether PPAR-α modulates renal Klotho as PPAR-γ does has not been studied yet.
Anti-Oxidant and Free Radical Scavenger
Oxidative stress in the kidney plays an important role in the development and progression of kidney disease. Oxidative stress directly suppresses Klotho expression in a kidney epithelial cell line in vitro22 and in the kidney in vivo.22,39,230 Oxidative stress is also implicated in Ang II39 or CsA-induced Klotho downregulation.42 The moderate efficacy of antioxidants used for treatment of acute and chronic kidney disease has been shown most in animal studies and not in CKD patients.39,168,169,231
Animals with genetic or secondary Klotho deficiency have low anti-oxidants or/and over production of free radicals and lipid peroxidation in the kidneys.23,39,40,170,172 In contrast, Klotho-overexpressing mice and animals who received Klotho gene, or treated for up-regulation of endogenous Klotho have exactly the opposite changes.18,42,108,172,232
Thus it appears that Klotho deficiency increases oxidative stress or makes cells more prone to oxidative stress induced injury, and oxidative stress further down-regulates Klotho expression. Anti-oxidants are potentially useful in interrupting the deterioration spiral.
CONCLUSION AND PERSPECTIVES
In animal models, CKD is a sustained state of pan Klotho deficiency in the kidney, plasma, and urine. This fact remains to be established in humans. Klotho plays a pathogenetic role in kidney disease progression, and development of disturbed mineral metabolism such as secondary hyperthyroidism and vascular calcification. As such, it is more than a biomarker. Early administration of exogenous Klotho protein, delivery of Klotho gene, or enhancement of endogenous Klotho could correct Klotho deficiency and improve kidney function in CKD (Fig. 4). The potential utility of Klotho in clinical practice is at least two-fold. First, Klotho could serve as an early and sensitive biomarker of presence of kidney diseases. But its specificity and its prognostic value and differential diagnostic value remain to be studied in humans. Second, Klotho supplementation may provide novel therapy for AKI patients to retard or block its progression to CKD and for CKD by slowing progression as well as preventing and reversing complications.
The therapeutic efficacy of Klotho in kidney disease has been unequivocally demonstrated in several animal models. One needs to validate the efficacy of Klotho in larger variety of kidney diseases and most importantly how Klotho exerts its effects which in variably will be pleiotropic. The mechanism of decline of renal Klotho in kidney diseases is not completely clarified. The upstream regulators of Klotho need to be identified. However, some therapeutic modalities including ACE inhibitor, HMG Co A reductase inhibitor, and anti-oxidants could sustain or increase endogenous Klotho expression to normal levels. The immediate challenge is to test whether human CKD resembles the rodent counterpart and if so, how to more efficiently increase Klotho levels in patients with kidney disease by stimulating endogenous Klotho or giving recombinant Klotho.
REFERENCES
- 1.Koh N, Fujimori T, Nishiguchi S, et al. Severely reduced production of klotho in human chronic renal failure kidney. Biochem Biophys Res Commun. 2001;280(4):1015–1020. doi: 10.1006/bbrc.2000.4226. [DOI] [PubMed] [Google Scholar]
- 2.Hu MC, Shi M, Zhang J, et al. Klotho deficiency causes vascular calcification in chronic kidney disease. J Am Soc Nephrol. 2011;22(1):124–136. doi: 10.1681/ASN.2009121311. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Aizawa H, Saito Y, Nakamura T, et al. Downregulation of the Klotho gene in the kidney under sustained circulatory stress in rats. Biochem Biophys Res Commun. 1998;249(3):865–871. doi: 10.1006/bbrc.1998.9246. [DOI] [PubMed] [Google Scholar]
- 4.Matsumura Y, Aizawa H, Shiraki-Iida T, et al. Identification of the human klotho gene and its two transcripts encoding membrane and secreted klotho protein. Biochem Biophys Res Commun. 1998;242(3):626–630. doi: 10.1006/bbrc.1997.8019. [DOI] [PubMed] [Google Scholar]
- 5.Shiraki-Iida T, Aizawa H, Matsumura Y, et al. Structure of the mouse klotho gene and its two transcripts encoding membrane and secreted protein. FEBS Lett. 1998;424(1–2):6–10. doi: 10.1016/s0014-5793(98)00127-6. [DOI] [PubMed] [Google Scholar]
- 6.Kuro-o M, Matsumura Y, Aizawa H, et al. Mutation of the mouse klotho gene leads to a syndrome resembling ageing. Nature. 1997;390(6655):45–51. doi: 10.1038/36285. [DOI] [PubMed] [Google Scholar]
- 7.Tohyama O, Imuxa A, Iwano A, et al. Klotho is a novel beta-glucuronidase capable of hydrolyzing steroid beta-glucuxonides. J Biol Chem. 2004;279(11):9777–9784. doi: 10.1074/jbc.M312392200. [DOI] [PubMed] [Google Scholar]
- 8.Chen CD, Podvin S, Gillespie E, et al. Insulin stimulates the cleavage and release of the extracellular domain of Klotho by ADAM10 and ADAM17. Proc Natl Acad Sci USA. 2007;104(50):19796–19801. doi: 10.1073/pnas.0709805104. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Bloch L, Sineshchekova O, Reichenbach D, et al. Klotho is a substrate for alpha-, beta- and gamma-secretase. FEBS Lett. 2009;583(19):3221–3224. doi: 10.1016/j.febslet.2009.09.009. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Huang CL. Regulation of ion channels by secreted Klotho: mechanisms and implications. Kidney Int. 2010;77(10):855–860. doi: 10.1038/ki.2010.73. [DOI] [PubMed] [Google Scholar]
- 11.Liu H, Fergusson MM, Castilho RM, et al. Augmented Wnt signaling in a mammalian model of accelerated aging. Science. 2007;317(5839):803–806. doi: 10.1126/science.1143578. [DOI] [PubMed] [Google Scholar]
- 12.Goetz R, Nakada Y, Hu MC, et al. Isolated C-terminal tail of FGF23 alleviates hypophosphatemia by inhibiting FGF23-FGFR-Klotho complex formation. Proc Natl Acad Sci USA. 2010;107(1):407–412. doi: 10.1073/pnas.0902006107. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Carpenter TO, Insogna KL, Zhang JH, et al. Circulating Levels of Soluble Klotho and FGF23 in X-Linked Hypophosphatemia: Circadian Variance, Effects of Treatment and Relationship to Parathyroid Status. J Clin Endocrinol Metab. 2010;95(11):E352–E357. doi: 10.1210/jc.2010-0589. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Hu MC, Shi M, Zhang J, et al. Klotho: a novel phosphaturic substance acting as an autocrine enzyme in the renal proximal tubule. FASEB J. 2010;24(9):3438–3450. doi: 10.1096/fj.10-154765. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Cha SK, Hu MC, Kurosu H, et al. Regulation of renal outer medullary potassium channel and renal K(+) excretion by Klotho. Mol Pharmacol. 2009;76(1):38–46. doi: 10.1124/mol.109.055780. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Cha SK, Ortega B, Kurosu H, et al. Removal of sialic acid involving Klotho causes cell-surface retention of TRPV5 channel via binding to galectin-1. Proc Natl Acad Sci USA. 2008;105(28):9805–9810. doi: 10.1073/pnas.0803223105. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Kato Y, Arakawa E, Kinoshita S, et al. Establishment of the anti-Klotho monoclonal antibodies and detection of Klotho protein in kidneys. Biochem Biophys Res Commun. 2000;267(2):597–602. doi: 10.1006/bbrc.1999.2009. [DOI] [PubMed] [Google Scholar]
- 18.Haruna Y, Kashihara N, Satoh M, et al. Amelioration of progressive renal injury by genetic manipulation of Klotho gene. Proc Natl Acad Sci USA. 2007;104(7):2331–2336. doi: 10.1073/pnas.0611079104. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Saito Y, Nakamura T, Ohyama Y, et al. In vivo klotho gene delivery protects against endothelial dysfunction in multiple risk factor syndrome. Biochem Biophys Res Commun. 2000;276(2):767–772. doi: 10.1006/bbrc.2000.3470. [DOI] [PubMed] [Google Scholar]
- 20.Kurosu H, Yamamoto M, Clark JD, et al. Suppression of aging in mice by the hormone Klotho. Science. 2005;309(5742):1829–1833. doi: 10.1126/science.1112766. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Mitani H, Ishizaka N, Aizawa T, et al. In vivo klotho gene transfer ameliorates angiotensin II-induced renal damage. Hypertension. 2002;39(4):838–843. doi: 10.1161/01.hyp.0000013734.33441.ea. [DOI] [PubMed] [Google Scholar]
- 22.Mitobe M, Yoshida T, Sugiura H, et al. Oxidative stress decreases klotho expression in a mouse kidney cell line. Nephron Exp Nephrol. 2005;101(2):e67–e74. doi: 10.1159/000086500. [DOI] [PubMed] [Google Scholar]
- 23.Sugiura H, Yoshida T, Tsuchiya K, et al. Klotho reduces apoptosis in experimental ischaemic acute renal failure. Nephrol Dial Transplant. 2005;20(12):2636–2645. doi: 10.1093/ndt/gfi165. [DOI] [PubMed] [Google Scholar]
- 24.Chang Q, Hoefs S, van der Kemp AW, et al. The beta-glucuronidase klotho hydrolyzes and activates the TRPV5 channel. Science. 2005;310(5747):490–493. doi: 10.1126/science.1114245. [DOI] [PubMed] [Google Scholar]
- 25.Yoshida T, Fujimori T, Nabeshima Y. Mediation of unusually high concentrations of 1,25-dihydroxy vitamin D in homozygous klotho mutant mice by increased expression of renal lalpha-hydroxylase gene. Endocrinology. 2002;143(2):683–689. doi: 10.1210/endo.143.2.8657. [DOI] [PubMed] [Google Scholar]
- 26.Tsujikawa H, Kurotaki Y, Fujimori T, et al. Klotho, a gene related to a syndrome resembling human premature aging, functions in a negative regulatory circuit of vitamin D endocrine system. Mol Endocrinol. 2003;17(12):2393–2403. doi: 10.1210/me.2003-0048. [DOI] [PubMed] [Google Scholar]
- 27.Silver J, Naveh-Many T. FGF23 and the parathyroid glands. Pediatr Nephrol. 2010;25(11):2241–2245. doi: 10.1007/s00467-010-1565-3. [DOI] [PubMed] [Google Scholar]
- 28.Ben-Dov IZ, Galitzer H, Lavi-Moshayoff V, et al. The parathyroid is a target organ for FGF23 in rats. J Clin Invest. 2007;117(12):4003–4008. doi: 10.1172/JCI32409. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 29.Invidia L, Salvioli S, Altilia S, et al. The frequency of Klotho KL-VS polymorphism in a large Italian population, from young subjects to centenarians, suggests the presence of specific time windows for its effect. Biogerontology. 2010;11(1):67–73. doi: 10.1007/s10522-009-9229-z. [DOI] [PubMed] [Google Scholar]
- 30.Zhang F, Zhai G, Kato BS, et al. Association between KLOTHO gene and hand osteoarthritis in a female Caucasian population. Osteoarthritis Cartilage. 2007 doi: 10.1016/j.joca.2006.12.002. [DOI] [PubMed] [Google Scholar]
- 31.Rhee EJ, Oh KW, Lee WY, et al. The differential effects of age on the association of KLOTHO gene polymorphisms with coronary artery disease. Metabolism. 2006;55(10):1344–1351. doi: 10.1016/j.metabol.2006.05.020. [DOI] [PubMed] [Google Scholar]
- 32.Rhee EJ, Oh KW, Yun EJ, et al. Relationship between polymorphisms G395A in promoter and C1818T in exon 4 of the KLOTHO gene with glucose metabolism and cardiovascular risk factors in Korean women. J Endocrinol Invest. 2006;29(7):613–618. doi: 10.1007/BF03344160. [DOI] [PubMed] [Google Scholar]
- 33.Nolan VG, Adewoye A, Baldwin C, et al. Sickle cell leg ulcers: associations with haemolysis and SNPs in Klotho, TEK and genes of the TGF-beta/BMP pathway. Br J Haematol. 2006;133(5):570–578. doi: 10.1111/j.1365-2141.2006.06074.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34.Arking DE, Becker DM, Yanek LR, et al. KLOTHO allele status and the risk of early-onset occult coronary artery disease. Am J Hum Genet. 2003;72(5):1154–1161. doi: 10.1086/375035. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 35.Arking DE, Kiebsova A, Macek M, Sr, et al. Association of human aging with a functional variant of klotho. Proc Natl Acad Sci USA. 2002;99(2):856–861. doi: 10.1073/pnas.022484299. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 36.Kawano K, Ogata N, Chiano M, et al. Klotho gene polymorphisms associated with bone density of aged postmenopausal women. J Bone Miner Res. 2002;17(10):1744–1751. doi: 10.1359/jbmr.2002.17.10.1744. [DOI] [PubMed] [Google Scholar]
- 37.Yu J, Deng M, Zhao J, et al. Decreased expression of klotho gene in uremic atherosclerosis in apolipoprotein E-deficient mice. Biochem Biophys Res Commun. 2010;391(1):261–266. doi: 10.1016/j.bbrc.2009.11.046. [DOI] [PubMed] [Google Scholar]
- 38.Friedman DJ, Afkarian M, Tamez H, et al. Klotho variants and chronic hemodialysis mortality. J Bone Miner Res. 2009;24(11):1847–1855. doi: 10.1359/JBMR.090516. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 39.Saito K, Ishizaka N, Mitani H, et al. Iron chelation and a free radical scavenger suppress angiotensin II-induced downregulation of klotho, an anti-aging gene, in rat. FEBS Lett. 2003;551(1–3):58–62. doi: 10.1016/s0014-5793(03)00894-9. [DOI] [PubMed] [Google Scholar]
- 40.Cheng MF, Chen LJ, Cheng JT. Decrease of Klotho in the kidney of streptozotocin-induced diabetic rats. J Biomed Biotechnol. 2010;2010:513853. doi: 10.1155/2010/513853. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 41.Han DH, Piao SG, Song JH, et al. Effect of sirolimus on calcineurin inhibitor-induced nephrotoxicity using renal expression of KLOTHO, an antiaging gene. Transplantation. 2010;90(2):135–141. doi: 10.1097/TP.0b013e3181e117b4. [DOI] [PubMed] [Google Scholar]
- 42.Yoon HE, Ghee JY, Piao S, et al. Angiotensin II blockade upregulates the expression of Klotho the anti-ageing gene, in an experimental model of chronic cyclosporine nephropathy. Nephrol Dial Transplant. 2011;26(3):800–813. doi: 10.1093/ndt/gfq537. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 43.Yamazaki Y, Imura A, Urakawa I, et al. Establishment of sandwich ELISA for soluble alpha-Klotho measurement: Age-dependent change of soluble alpha-Klotho levels in healthy subjects. Biochem Biophys Res Commun. 2010;398(3):513–518. doi: 10.1016/j.bbrc.2010.06.110. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 44.Zuo Z, Lei H, Wang X, et al. Aging-related kidney damage is associated with a decrease in klotho expression and an increase in superoxide production. Age (Dordr) 2010 doi: 10.1007/s11357-010-9176-2. Epub ahead of press. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 45.Ichikawa S, Imel EA, Kreiter ML, et al. A homozygous missense mutation in human KLOTHO causes severe tumoral calcinosis. J Clin Invest. 2007;117(9):2684–2691. doi: 10.1172/JCI31330. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 46.Manya H, Akasaka-Manya K, Endo T. Klotho protein deficiency and aging. Geriatr Gerontol Int. 2010;10(Suppl 1):S80–S87. doi: 10.1111/j.1447-0594.2010.00596.x. [DOI] [PubMed] [Google Scholar]
- 47.Brownstein CA, Adler F, Nelson-Williams C, et al. A translocation causing increased alpha-klotho level results in hypophosphatemic rickets and hyperparathyroidism. Proc Natl Acad Sci USA. 2008;105(9):3455–3460. doi: 10.1073/pnas.0712361105. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 48.Takeshita K, Fujimori T, Kurotaki Y, et al. Sinoatrial node dysfunction and early unexpected death of mice with a defect of klotho gene expression. Circulation. 2004;109(14):1776–1782. doi: 10.1161/01.CIR.0000124224.48962.32. [DOI] [PubMed] [Google Scholar]
- 49.Imura A, Iwano A, Tohyama O, et al. Secreted Klotho protein in sera and CSF: implication for posttranslational cleavage in release of Klotho protein from cell membrane. FEBS Lett. 2004;565(1–3):143–147. doi: 10.1016/j.febslet.2004.03.090. [DOI] [PubMed] [Google Scholar]
- 50.Hu MC, Shi M, Zhang J, et al. Klotho deficiency is an early biomarker of renal ischemia-reperfusion injury and its replacement is protective. Kidney Int. 2010;78(12):1240–1251. doi: 10.1038/ki.2010.328. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 51.Schramme A, Abdel-Bakky MS, Gutwein P, et al. Characterization of CXCL16 and ADAM10 in the normal and transplanted kidney. Kidney Int. 2008;74(3):328–338. doi: 10.1038/ki.2008.181. [DOI] [PubMed] [Google Scholar]
- 52.Kuro-o M. Klotho as a regulator of oxidative stress and senescence. Biol Chem. 2008;389(3):233–241. doi: 10.1515/BC.2008.028. [DOI] [PubMed] [Google Scholar]
- 53.Huang BS, Leenen FH. Dietary Na, age and baroreflex control of heart rate and renal sympathetic nerve activity in rats. Am J Physiol. 1992;262(5 Pt 2):H1441–H1448. doi: 10.1152/ajpheart.1992.262.5.H1441. [DOI] [PubMed] [Google Scholar]
- 54.Yamazaki M, Ozono K, Okada T, et al. Both FGF23 and extracellular phosphate activate Raf/MEK/ERK pathway via FGF receptors in HEK293 cells. J Cell Biochem. 2010;111(5):1210–1221. doi: 10.1002/jcb.22842. [DOI] [PubMed] [Google Scholar]
- 55.Mazzaferro S, Pasquali M, Pirro G, et al. The bone and the kidney. Arch Biochem Biophys. 2010;503(1):95–102. doi: 10.1016/j.abb.2010.06.028. [DOI] [PubMed] [Google Scholar]
- 56.Keisala T, Minasyan A, Lou YR, et al. Premature aging in vitamin D receptor mutant mice. J Steroid Biochem Mol Biol. 2009;115(3–5):91–97. doi: 10.1016/j.jsbmb.2009.03.007. [DOI] [PubMed] [Google Scholar]
- 57.Chattopadhyay N, Baum M, Bai M, et al. Ontogeny of the extracellular calcium-sensing receptor in rat kidney. Am J Physiol. 1996;271(3 Pt 2):F736–F743. doi: 10.1152/ajprenal.1996.271.3.F736. [DOI] [PubMed] [Google Scholar]
- 58.Biber J, Hernando N, Forster I, et al. Regulation of phosphate transport in proximal tubules. Pflugers Arch. 2009;458(1):39–52. doi: 10.1007/s00424-008-0580-8. [DOI] [PubMed] [Google Scholar]
- 59.Moe OW. PiT-2 coming out of the pits. Am J Physiol Renal Physiol. 2009;296(4):F689–F690. doi: 10.1152/ajprenal.00007.2009. [DOI] [PubMed] [Google Scholar]
- 60.Panda DK, Al Kawas S, Seldin MF, et al. 25-hydroxy vitamin D 1alpha-hydroxylase: structure of the mouse gene, chromosomal assignment, and developmental expression. J Bone Miner Res. 2001;16(1):46–56. doi: 10.1359/jbmr.2001.16.1.46. [DOI] [PubMed] [Google Scholar]
- 61.Lai WP, Chau TS, Cheung PY, et al. Adaptive responses of 25-hydroxyvitamin D3 1-alpha hydroxylase expression to dietary phosphate restriction in young and adult rats. Biochim Biophys Acta. 2003;1639(1):34–42. doi: 10.1016/s0925-4439(03)00123-6. [DOI] [PubMed] [Google Scholar]
- 62.Shimada T, Urakawa I, Isakova T, et al. Circulating fibroblast growth factor 23 in patients with end-stage renal disease treated by peritoneal dialysis is intact and biologically active. J Clin Endocrinol Metab. 2010;95(2):578–585. doi: 10.1210/jc.2009-1603. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 63.Fukagawa M, Kazama JJ. With or without the kidney: the role of FGF23 in CKD. Nephrol Dial Transplant. 2005;20(7):1295–1298. doi: 10.1093/ndt/gfh827. [DOI] [PubMed] [Google Scholar]
- 64.Weber TJ, Liu S, Indridason OS, et al. Serum FGF23 levels in normal and disordered phosphorus homeostasis. J Bone Miner Res. 2003;18(7):1227–1234. doi: 10.1359/jbmr.2003.18.7.1227. [DOI] [PubMed] [Google Scholar]
- 65.Nakatani T, Sarraj B, Ohnishi M, et al. In vivo genetic evidence for klotho-dependent, fibroblast growth factor 23 (Fgf23)-mediated regulation of systemic phosphate homeostasis. FASEB J. 2009;23(2):433–441. doi: 10.1096/fj.08-114397. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 66.Jono S, Shioi A, Ikari Y, et al. Vascular calcification in chronic kidney disease. J Bone Miner Metab. 2006;24(2):176–181. doi: 10.1007/s00774-005-0668-6. [DOI] [PubMed] [Google Scholar]
- 67.London GM. Cardiovascular calcifications in uremic patients: clinical impact on cardiovascular function. J Am Soc Nephrol. 2003;14(9) Suppl 4:S305–S309. doi: 10.1097/01.asn.0000081664.65772.eb. [DOI] [PubMed] [Google Scholar]
- 68.Weinstein JR, Anderson S. The aging kidney: physiological changes. Adv Chronic Kidney Dis. 2010;17(4):302–307. doi: 10.1053/j.ackd.2010.05.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 69.Martin JE, Sheaff MT. Renal ageing. J Pathol. 2007;211(2):198–205. doi: 10.1002/path.2111. [DOI] [PubMed] [Google Scholar]
- 70.Lerma EV. Anatomic and physiologic changes of the aging kidney. Clin Geriatr Med. 2009;25(3):325–329. doi: 10.1016/j.cger.2009.06.007. [DOI] [PubMed] [Google Scholar]
- 71.Chen G, Bridenbaugh EA, Akintola AD, et al. Increased susceptibility of aging kidney to ischemic injury: identification of candidate genes changed during aging, but corrected by caloric restriction. Am J Physiol Renal Physiol. 2007;293(4):F1272–F1281. doi: 10.1152/ajprenal.00138.2007. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 72.Musso CG, Liakopoulos V, Ioannidis I, et al. Acute renal failure in the elderly: particular characteristics. Int Urol Nephrol. 2006;38(3–4):787–793. doi: 10.1007/s11255-006-0084-4. [DOI] [PubMed] [Google Scholar]
- 73.Campbell KH, O'Hare AM. Kidney disease in the elderly: update on recent literature. Curr Opin Nephrol Hypertens. 2008;17(3):298–303. doi: 10.1097/MNH.0b013e3282f5dd90. [DOI] [PubMed] [Google Scholar]
- 74.Hu MC, Bankir L, Michelet S, et al. Massive reduction of urea transporters in remnant kidney and brain of uremic rats. Kidney Int. 2000;58(3):1202–1210. doi: 10.1046/j.1523-1755.2000.00275.x. [DOI] [PubMed] [Google Scholar]
- 75.Tamura K, Suzuki Y, Matsushita M, et al. Prevention of aortic calcification by etidronate in the renal failure rat model. Eur J Pharmacol. 2007;558(1–3):159–166. doi: 10.1016/j.ejphar.2006.12.006. [DOI] [PubMed] [Google Scholar]
- 76.Peralta CA, Kurella M, Lo JC, et al. The metabolic syndrome and chronic kidney disease. Curr Opin Nephrol Hypertens. 2006;15(4):361–365. doi: 10.1097/01.mnh.0000232875.27846.7e. [DOI] [PubMed] [Google Scholar]
- 77.Nagase M, Yoshida S, Shibata S, et al. Enhanced aldosterone signaling in the early nephropathy of rats with metabolic syndrome: possible contribution of fat-derived factors. J Am Soc Nephrol. 2006;17(12):3438–3446. doi: 10.1681/ASN.2006080944. [DOI] [PubMed] [Google Scholar]
- 78.Locatelli F, Pozzoni P, Del Vecchio L. Renal manifestations in the metabolic syndrome. J Am Soc Nephrol. 2006;17(4) Suppl 2:S81–S85. doi: 10.1681/ASN.2005121332. [DOI] [PubMed] [Google Scholar]
- 79.Kawano K, Hirashima T, Mori S, et al. Spontaneous long-term hyperglycemic rat with diabetic complications. Otsuka Long-Evans Tokushima Fatty (OLETF) strain. Diabetes. 1992;41(11):1422–1428. doi: 10.2337/diab.41.11.1422. [DOI] [PubMed] [Google Scholar]
- 80.Yamagishi T, Saito Y, Nakamura T, et al. Troglitazone improves endothelial function and augments renal klotho mRNA expression in Otsuka Long-Evans Tokushima Fatty (OLETF) rats with multiple atherogenic risk factors. Hypertens Res. 2001;24(6):705–709. doi: 10.1291/hypres.24.705. [DOI] [PubMed] [Google Scholar]
- 81.Ohyama Y, Kurabayashi M, Masuda H, et al. Molecular cloning of rat klotho cDNA: markedly decreased expression of klotho by acute inflammatory stress. Biochem Biophys Res Commun. 1998;251(3):920–925. doi: 10.1006/bbrc.1998.9576. [DOI] [PubMed] [Google Scholar]
- 82.Thurston RD, Larmonier CB, Majewski PM, et al. Tumor necrosis factor and interferon-gamma down-regulate Klotho in mice with colitis. Gastroenterology. 2010;138(4):1384–1394. doi: 10.1053/j.gastro.2009.12.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 83.Webster AC, Woodroffe RC, Taylor RS, et al. Tacrolimus versus ciclosporin as primary immunosuppression for kidney transplant recipients: meta-analysis and meta-regression of randomised trial data. BMJ. 2005;331(7520):810. doi: 10.1136/bmj.38569.471007.AE. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 84.Jiang H, Sakuma S, Fujii Y, et al. Tacrolimus versus cyclosporin A: a comparative study on rat renal allograft survival. Transpl Int. 1999;12(2):92–99. doi: 10.1007/s001470050192. [DOI] [PubMed] [Google Scholar]
- 85.Gulati S, Prasad N, Sharma RK, et al. Tacrolimus: a new therapy for steroid-resistant nephrotic syndrome in children. Nephrol Dial Transplant. 2008;23(3):910–913. doi: 10.1093/ndt/gfm688. [DOI] [PubMed] [Google Scholar]
- 86.Tang S, Tang AW, Tarn MK, et al. Use of tacrolimus in steroid- and cyclophosphamide-resistant minimal change nephrotic syndrome. Am J Kidney Dis. 2003;42(5):E13–E15. doi: 10.1016/j.ajkd.2003.07.011. [DOI] [PubMed] [Google Scholar]
- 87.Ziolkowski J, Paczek L, Senatorski G, et al. Renal function after liver transplantation: calcineurin inhibitor nephrotoxicity. Transplant Proc. 2003;35(6):2307–2309. doi: 10.1016/s0041-1345(03)00786-3. [DOI] [PubMed] [Google Scholar]
- 88.Naesens M, Kuypers DR, Sarwal M. Calcineurin inhibitor nephrotoxicity. Clin J Am Soc Nephrol. 2009;4(2):481–508. doi: 10.2215/CJN.04800908. [DOI] [PubMed] [Google Scholar]
- 89.Formica RN, Jr, Lorber KM, Friedman AL, et al. Sirolimus-based immunosuppression with reduce dose cyclosporine or tacrolimus after renal transplantation. Transplant Proc. 2003;35(3 Suppl):95S–98S. doi: 10.1016/s0041-1345(03)00216-1. [DOI] [PubMed] [Google Scholar]
- 90.Kestenbaum B, Sampson JN, Rudser KD, et al. Serum phosphate levels and mortality risk among people with chronic kidney disease. J Am Soc Nephrol. 2005;16(2):520–528. doi: 10.1681/ASN.2004070602. [DOI] [PubMed] [Google Scholar]
- 91.Cannata-Andia JB, Rodriguez-Garcia M. Hyperphosphataemia as a cardiovascular risk factor — how to manage the problem. Nephrol Dial Transplant. 2002;17(Suppl 11):16–19. doi: 10.1093/ndt/17.suppl_11.16. [DOI] [PubMed] [Google Scholar]
- 92.Isakova T, Gutierrez OM, Chang Y, et al. Phosphorus binders and survival on hemodialysis. J Am Soc Nephrol. 2009;20(2):388–396. doi: 10.1681/ASN.2008060609. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 93.Kuro-o M. A potential link between phosphate and aging—lessons from Klotho-deficient mice. Mech Ageing Dev. 2010;131(4):270–275. doi: 10.1016/j.mad.2010.02.008. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 94.Morishita K, Shirai A, Kubota M, et al. The progression of aging in klotho mutant mice can be modified by dietary phosphorus and zinc. J Nutr. 2001;131(12):3182–3188. doi: 10.1093/jn/131.12.3182. [DOI] [PubMed] [Google Scholar]
- 95.Lips P. Vitamin D deficiency and secondary hyperparathyroidism in the elderly: consequences for bone loss and fractures and therapeutic implications. Endocr Rev. 2001;22(4):477–501. doi: 10.1210/edrv.22.4.0437. [DOI] [PubMed] [Google Scholar]
- 96.Gutierrez OM. Fibroblast growth factor 23 and disordered vitamin D metabolism in chronic kidney disease: updating the “trade-off” hypothesis. Clin J Am Soc Nephrol. 2010;5(9):1710–1716. doi: 10.2215/CJN.02640310. [DOI] [PubMed] [Google Scholar]
- 97.Liu S, Tang W, Zhou J, et al. Fibroblast growth factor 23 is a counter-regulatory phosphaturic hormone for vitamin D. J Am Soc Nephrol. 2006;17(5):1305–1315. doi: 10.1681/ASN.2005111185. [DOI] [PubMed] [Google Scholar]
- 98.Palm F, Nangaku M, Fasching A, et al. Uremia induces abnormal oxygen consumption in tubules and aggravates chronic hypoxia of the kidney via oxidative stress. Am J Physiol Renal Physiol. 2010;299(2):F380–F386. doi: 10.1152/ajprenal.00175.2010. [DOI] [PubMed] [Google Scholar]
- 99.Polichnowski AJ, Jin C, Yang C, et al. Role of renal perfusion pressure versus angiotensin II on renal oxidative stress in angiotensin II-induced hypertensive rats. Hypertension. 2010;55(6):1425–1430. doi: 10.1161/HYPERTENSIONAHA.110.151332. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 100.Yu M, Kim YJ, Kang DH. Indoxyl Sulfate-Induced Endothelial Dysfunction in Patients with Chronic Kidney Disease via an Induction of Oxidative Stress. Clin J Am Soc Nephrol. 2011;6(1):30–39. doi: 10.2215/CJN.05340610. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 101.Barreto FC, Barreto DV, Liabeuf S, et al. Serum indoxyl sulfate is associated with vascular disease and mortality in chronic kidney disease patients. Clin J Am Soc Nephrol. 2009;4(10):1551–1558. doi: 10.2215/CJN.03980609. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 102.Niwa T, Adijiang A, Higuchi Y, et al. Indoxyl Sulfate Reduces Klotho Expression and Promotes Senescence in the Kidney of Hypertensive Rats (Abstract) J Am Soc Nephrol. 2010;21:746A. doi: 10.1053/j.jrn.2010.10.020. [DOI] [PubMed] [Google Scholar]
- 103.Jennings P, Koppelstaetter C, Aydin S, et al. Cyclosporine A induces senescence in renal tubular epithelial cells. Am J Physiol Renal Physiol. 2007;293(3):F831–F838. doi: 10.1152/ajprenal.00005.2007. [DOI] [PubMed] [Google Scholar]
- 104.Kailong L, Du X, Yani H, et al. P53-Rb signaling pathway is involved in tubular cell senescence in renal ischemia/reperfusion injury. Bio cell. 2007;31(2):213–223. [PubMed] [Google Scholar]
- 105.Dmitrieva NI, Burg MB. High NaCl promotes cellular senescence. Cell Cycle. 2007;6(24):3108–3113. doi: 10.4161/cc.6.24.5084. [DOI] [PubMed] [Google Scholar]
- 106.Yang H, Fogo AB. Cell senescence in the aging kidney. J Am Soc Nephrol. 2010;21(9):1436–1439. doi: 10.1681/ASN.2010020205. [DOI] [PubMed] [Google Scholar]
- 107.Nakano-Kurimoto R, Ikeda K, Uraoka M, et al. Replicative senescence of vascular smooth muscle cells enhances the calcification through initiating the osteoblastic transition. Am J Physiol Heart Circ Physiol. 2009;297(5):H1673–H1684. doi: 10.1152/ajpheart.00455.2009. [DOI] [PubMed] [Google Scholar]
- 108.Yang HC, Deleuze S, Zuo Y, et al. The PPARgamma agonist pioglitazone ameliorates aging-related progressive renal injury. J Am Soc Nephrol. 2009;20(11):2380–2388. doi: 10.1681/ASN.2008111138. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 109.Shimizu H, Bolati D, Adijiang A, et al. Senescence and dysfunction of proximal tubular cells are associated with activated p53 expression by indoxyl sulfate. Am J Physiol Cell Physiol. 2010;299(5):C1110–C1117. doi: 10.1152/ajpcell.00217.2010. [DOI] [PubMed] [Google Scholar]
- 110.De Oliveira RM. Klotho RNAi induces premature senescence of human cells via a p53/p21 dependent pathway. FEBS Lett. 2006;580(24):5753–5758. doi: 10.1016/j.febslet.2006.09.036. [DOI] [PubMed] [Google Scholar]
- 111.Ikushima M, Rakugi H, Ishikawa K, et al. Anti-apoptotic and anti-senescence effects of Klotho on vascular endothelial cells. Biochem Biophys Res Commun. 2006;339(3):827–832. doi: 10.1016/j.bbrc.2005.11.094. [DOI] [PubMed] [Google Scholar]
- 112.Taniyama Y, Morishita R. Does therapeutic angiogenesis overcome CKD? Hypertens Res. 2010;33(2):114–115. doi: 10.1038/hr.2009.208. [DOI] [PubMed] [Google Scholar]
- 113.Mu W, Long DA, Ouyang X, et al. Angiostatin over expression is associated with an improvement in chronic kidney injury by an anti-inflammatory mechanism. Am J Physiol Renal Physiol. 2009;296(1):F145–F152. doi: 10.1152/ajprenal.90430.2008. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 114.Westerweel PE, Hoefer IE, Blankestijn PJ, et al. End-stage renal disease causes an imbalance between endothelial and smooth muscle progenitor cells. Am J Physiol Renal Physiol. 2007;292(4):F1132–F1140. doi: 10.1152/ajprenal.00163.2006. [DOI] [PubMed] [Google Scholar]
- 115.Chade AR, Zhu X, Mushin OP, et al. Simvastatin promotes angiogenesis and prevents microvascular remodeling in chronic renal ischemia. FASEB J. 2006;20(10):1706–1708. doi: 10.1096/fj.05-5680fje. [DOI] [PubMed] [Google Scholar]
- 116.Reinders ME, Rabelink TJ, Briscoe DM. Angiogenesis and endothelial cell repair in renal disease and allograft rejection. J Am Soc Nephrol. 2006;17(4):932–942. doi: 10.1681/ASN.2005121250. [DOI] [PubMed] [Google Scholar]
- 117.Nakamura T, Saito Y, Ohyama Y, et al. Production of nitric oxide, but not prostacyclin, is reduced in klotho mice. Jpn J Pharmacol. 2002;89(2):149–156. doi: 10.1254/jjp.89.149. [DOI] [PubMed] [Google Scholar]
- 118.Shimada T, Takeshita Y, Murohara T, et al. Angiogenesis and vasculogenesis are impaired in the precocious-aging klotho mouse. Circulation. 2004;110(9):1148–1155. doi: 10.1161/01.CIR.0000139854.74847.99. [DOI] [PubMed] [Google Scholar]
- 119.Fukino K, Suzuki T, Saito Y, et al. Regulation of angiogenesis by the aging suppressor gene klotho. Biochem Biophys Res Commun. 2002;293(1):332–337. doi: 10.1016/S0006-291X(02)00216-4. [DOI] [PubMed] [Google Scholar]
- 120.Maekawa Y, Ishikawa K, Yasuda O, et al. Klotho suppresses TNF-alpha-induced expression of adhesion molecules in the endothelium and attenuates NF-kappaB activation. Endocrine. 2009;35(3):341–346. doi: 10.1007/s12020-009-9181-3. [DOI] [PubMed] [Google Scholar]
- 121.Zeisberg M, Duffield JS. Resolved: EMT produces fibroblasts in the kidney. J Am Soc Nephrol. 2010;21(8):1247–1253. doi: 10.1681/ASN.2010060616. [DOI] [PubMed] [Google Scholar]
- 122.Liu Y. New insights into epithelial-mesenchymal transition in kidney fibrosis. J Am Soc Nephrol. 2010;21(2):212–222. doi: 10.1681/ASN.2008121226. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 123.Ardura JA, Rayego-Mateos S, Ramila D, et al. Parathyroid hormone-related protein promotes epithelial-mesenchymal transition. J Am Soc Nephrol. 2010;21(2):237–248. doi: 10.1681/ASN.2009050462. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 124.Kalluri R, Neilson EG. Epithelial-mesenchymal transition and its implications for fibrosis. J Clin Invest. 2003;112(12):1776–1784. doi: 10.1172/JCI20530. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 125.Zeisberg M, Hanai J, Sugimoto H, et al. BMP-7 counteracts TGF-beta1-induced epithelial-to-mesenchymal transition and reverses chronic renal injury. Nat Med. 2003;9(7):964–968. doi: 10.1038/nm888. [DOI] [PubMed] [Google Scholar]
- 126.Iwano M, Plieth D, Danoff TM, et al. Evidence that fibroblasts derive from epithelium during tissue fibrosis. J Clin Invest. 2002;110(3):341–350. doi: 10.1172/JCI15518. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 127.Iwano M. EMT and TGF-beta in renal fibrosis. Front Biosci (Schol Ed) 2010;2:229–238. doi: 10.2741/s60. [DOI] [PubMed] [Google Scholar]
- 128.Hills CE, Squires PE. TGF-beta1-induced epithelial-to-mesenchymal transition and therapeutic intervention in diabetic nephropathy. Am J Nephrol. 2010;31(1):68–74. doi: 10.1159/000256659. [DOI] [PubMed] [Google Scholar]
- 129.Sato M, Muragaki Y, Saika S, et al. Targeted disruption of TGF-betal/Smad3 signaling protects against renal tubulointerstitial fibrosis induced by unilateral ureteral obstruction. J Clin Invest. 2003;112(10):1486–1494. doi: 10.1172/JCI19270. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 130.Sugiura H, Yoshida T, Kohei J, et al. TGF-β Was Upregulated in Renal Fibrosis Model of Klotho Defect Mouse and Affected Renal Klotho Expression Level (Abstract) J Am Soc Nephrol. 2010;21:376A. [Google Scholar]
- 131.Doi S, Yorioka N, Kuroo M. Secreted Klotho Protein Counteracts Renal Fibrosis through Inhibiting TGF-b1 Signaling (Abstract) J Am Soc Nephrol. 2010;21:270A. [Google Scholar]
- 132.Yamamoto K, Loskutoff DJ. The kidneys of mice with autoimmune disease acquire a hypofibrinolytic/procoagulant state that correlates with the development of glomerulonephritis and tissue microthrombosis. Am J Pathol. 1997;151(3):725–734. [PMC free article] [PubMed] [Google Scholar]
- 133.Yamamoto K, Loskutoff DJ, Saito H. Renal expression of fibrinolytic genes and tissue factor in a murine model of renal disease as a function of age. Semin Thromb Hemost. 1998;24(3):261–268. doi: 10.1055/s-2007-995852. [DOI] [PubMed] [Google Scholar]
- 134.Eddy AA, Fogo AB. Plasminogen activator inhibitor-1 in chronic kidney disease: evidence and mechanisms of action. J Am Soc Nephrol. 2006;17(11):2999–3012. doi: 10.1681/ASN.2006050503. [DOI] [PubMed] [Google Scholar]
- 135.Takeshita K, Yamamoto K, Ito M, et al. Increased expression of plasminogen activator inhibitor-1 with fibrin deposition in a murine model of aging, "Klotho" mouse. Semin Thromb Hemost. 2002;28(6):545–554. doi: 10.1055/s-2002-36699. [DOI] [PubMed] [Google Scholar]
- 136.Moe SM, Chen NX. Mechanisms of vascular calcification in chronic kidney disease. J Am Soc Nephrol. 2008;19(2):213–216. doi: 10.1681/ASN.2007080854. [DOI] [PubMed] [Google Scholar]
- 137.Cannata-Andia JB, Rodriguez-Garcia M, Carrillo-Lopez N, et al. Vascular calcifications: pathogenesis, management, and impact on clinical outcomes. J Am Soc Nephrol. 2006;17(12) Suppl 3:S267–S273. doi: 10.1681/ASN.2006080925. [DOI] [PubMed] [Google Scholar]
- 138.Mizobuchi M, Towler D, Slatopolsky E. Vascular calcification: the killer of patients with chronic kidney disease. J Am Soc Nephrol. 2009;20(7):1453–1464. doi: 10.1681/ASN.2008070692. [DOI] [PubMed] [Google Scholar]
- 139.Li X, Yang HY, Giachelli CM. Role of the sodium-dependent phosphate cotransporter, Pit-1, in vascular smooth muscle cell calcification. Circ Res. 2006;98(7):905–912. doi: 10.1161/01.RES.0000216409.20863.e7. [DOI] [PubMed] [Google Scholar]
- 140.Lim K, Lu T-S, Zehnder D, et al. Development of Klotho-FGFR1/3 Dependent Resistance to FGF-23 in Human Aortic Smooth Muscle Cells Exposed to Calcifying Stress. J Am Soc Nephrol. 2010;21:140A. [Google Scholar]
- 141.London GM, Marchais SJ, Guerin AP, et al. Contributive factors to cardiovascular hypertrophy in renal failure. Am J Hypertens. 1989;2(11 Pt 2):261S–263S. doi: 10.1093/ajh/2.11.261s. [DOI] [PubMed] [Google Scholar]
- 142.Guerin AP, Pannier B, Marchais SJ, et al. Cardiovascular disease in the dialysis population: prognostic significance of arterial disorders. Curr Opin Nephrol Hypertens. 2006;15(2):105–110. doi: 10.1097/01.mnh.0000203186.11772.21. [DOI] [PubMed] [Google Scholar]
- 143.Cerasola G, Nardi E, Palermo A, et al. Epidemiology and pathophysiology of left ventricular abnormalities in chronic kidney disease: a review. J Nephrol. 2011;24(1):1–10. doi: 10.5301/jn.2010.2030. [DOI] [PubMed] [Google Scholar]
- 144.Rinat C, Becker-Cohen R, Nir A, et al. A comprehensive study of cardiovascular risk factors, cardiac function and vascular disease in children with chronic renal failure. Nephrol Dial Transplant. 2010;25(3):785–793. doi: 10.1093/ndt/gfp570. [DOI] [PubMed] [Google Scholar]
- 145.Edwards NC, Steeds RP, Stewart PM, et al. Effect of spironolactone on left ventricular mass and aortic stiffness in early-stage chronic kidney disease: a randomized controlled trial. J Am Coll Cardiol. 2009;54(6):505–512. doi: 10.1016/j.jacc.2009.03.066. [DOI] [PubMed] [Google Scholar]
- 146.Burrell LM, Johnston CI. Angiotensin II receptor antagonists. Potential in elderly patients with cardiovascular disease. Drugs Aging. 1997;10(6):421–434. doi: 10.2165/00002512-199710060-00003. [DOI] [PubMed] [Google Scholar]
- 147.Achinger SG, Ayus JC. The role of vitamin D in left ventricular hypertrophy and cardiac function. Kidney Int. 2005;95(Suppl):S37–S42. doi: 10.1111/j.1523-1755.2005.09506.x. [DOI] [PubMed] [Google Scholar]
- 148.Mirza MA, Larsson A, Melhus H, et al. Serum intact FGF23 associate with left ventricular mass, hypertrophy and geometry in an elderly population. Atherosclerosis. 2009;207(2):546–551. doi: 10.1016/j.atherosclerosis.2009.05.013. [DOI] [PubMed] [Google Scholar]
- 149.Galitzer H, Ben-Dov IZ, Silver J, et al. Parathyroid cell resistance to fibroblast growth factor 23 in secondary hyperparathyroidism of chronic kidney disease. Kidney Int. 2010;77(3):211–218. doi: 10.1038/ki.2009.464. [DOI] [PubMed] [Google Scholar]
- 150.Khan S. Vitamin D deficiency and secondary hyperparathyroidism among patients with chronic kidney disease. Am J Med Sci. 2007;333(4):201–207. doi: 10.1097/MAJ.0b013e31803bb129. [DOI] [PubMed] [Google Scholar]
- 151.Krajisnik T, Olauson H, Mirza MA, et al. Parathyroid Klotho and FGF-receptor 1 expression decline with renal function in hyperparathyroid patients with chronic kidney disease and kidney transplant recipients. Kidney Int. 2010;78(10):1024–1032. doi: 10.1038/ki.2010.260. [DOI] [PubMed] [Google Scholar]
- 152.Canalejo R, Canalejo A, Martinez-Moreno JM, et al. FGF23 fails to inhibit uremic parathyroid glands. J Am Soc Nephrol. 2010;21(7):1125–1135. doi: 10.1681/ASN.2009040427. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 153.Hofman-Bang J, Martuseviciene G, Santini MA, et al. Increased parathyroid expression of klotho in uremic rats. Kidney Int. 2010;78(11):1119–1127. doi: 10.1038/ki.2010.215. [DOI] [PubMed] [Google Scholar]
- 154.Gattineni J, Baum M. Regulation of phosphate transport by fibroblast growth factor 23 (FGF23): implications for disorders of phosphate metabolism. Pediatr Nephrol. 2010;25(4):591–601. doi: 10.1007/s00467-009-1273-z. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 155.Carter JL, O'Riordan SE, Eaglestone GL, et al. Bone mineral metabolism and its relationship to kidney disease in a residential care home population: a cross-sectional study. Nephrol Dial Transplant. 2008;23(11):3554–3565. doi: 10.1093/ndt/gfn302. [DOI] [PubMed] [Google Scholar]
- 156.Oliveira RB, Cancela AL, Graciolli FG, et al. Early control of PTH and FGF23 in normophosphatemic CKD patients: a new target in CKD-MBD therapy? Clin J Am Soc Nephrol. 2010;5(2):286–291. doi: 10.2215/CJN.05420709. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 157.Fukagawa M, Kazama JJ. FGF23: its role in renal bone disease. Pediatr Nephrol. 2006;21(12):1802–1806. doi: 10.1007/s00467-006-0230-3. [DOI] [PubMed] [Google Scholar]
- 158.Tomida K, Hamano T, Mikami S, et al. Serum 25-hydroxy vitamin D as an independent determinant of 1–84 PTH and bone mineral density in nondiabetic predialysis CKD patients. Bone. 2009;44(4):678–683. doi: 10.1016/j.bone.2008.11.016. [DOI] [PubMed] [Google Scholar]
- 159.Jassal SK, von Muhlen D, Barrett-Connor E. Measures of renal function, BMD, bone loss, and osteoporotic fracture in older adults: the Rancho Bernardo study. J Bone Miner Res. 2007;22(2):203–210. doi: 10.1359/jbmr.061014. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 160.Kawaguchi H, Manabe N, Miyaura C, et al. Independent impairment of osteoblast and osteoclast differentiation in klotho mouse exhibiting low-turnover osteopenia. J Clin Invest. 1999;104(3):229–237. doi: 10.1172/JCI5705. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 161.Kawaguchi H, Manabe N, Chikuda H, et al. Cellular and molecular mechanism of low-turnover osteopenia in the klotho-deficient mouse. Cell Mol Life Sci. 2000;57(5):731–737. doi: 10.1007/s000180050037. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 162.Shiraki-Iida T, Iida A, Nabeshima Y, et al. Improvement of multiple pathophysiological phenotypes of klotho (kl/kl) mice by adenovirus-mediated expression of the klotho gene. J Gene Med. 2000;2(4):233–242. doi: 10.1002/1521-2254(200007/08)2:4<233::AID-JGM110>3.0.CO;2-5. [DOI] [PubMed] [Google Scholar]
- 163.Segawa H, Yamanaka S, Ohno Y, et al. Correlation between hyperphosphatemia and type II Na-Pi cotransporter activity in klotho mice. Am J Physiol Renal Physiol. 2007;292(2):F769–F779. doi: 10.1152/ajprenal.00248.2006. [DOI] [PubMed] [Google Scholar]
- 164.Sorribas V, Markovich D, Hayes G, et al. Cloning of a Na/Pi cotransporter from opossum kidney cells. J Biol Chem. 1994;269(9):6615–6621. [PubMed] [Google Scholar]
- 165.Ramos AM, Albalate M, Vazquez S, et al. Hyperphosphatemia and hyperparathyroidism in incident chronic kidney disease patients. Kidney Int. 2008;111(Suppl):S88–S93. doi: 10.1038/ki.2008.543. [DOI] [PubMed] [Google Scholar]
- 166.Koizumi T, Murakami K, Nakayama H, et al. Role of dietary phosphorus in the progression of renal failure. Biochem Biophys Res Commun. 2002;295(4):917–921. doi: 10.1016/s0006-291x(02)00793-3. [DOI] [PubMed] [Google Scholar]
- 167.Tonelli M, Wang W, Hemmelgarn B, et al. Phosphate removal with several thrice-weekly dialysis methods in overweight hemodialysis patients. Am J Kidney Dis. 2009;54(6):1108–1115. doi: 10.1053/j.ajkd.2009.05.018. [DOI] [PubMed] [Google Scholar]
- 168.Marshall CB, Pippin JW, Krofft RD, et al. Puromycin amino nucleoside induces oxidant-dependent DNA damage in podocytes in vitro and in vivo. Kidney Int. 2006;70(11):1962–1973. doi: 10.1038/sj.ki.5001965. [DOI] [PubMed] [Google Scholar]
- 169.Diamond JR. Reactive oxygen species and progressive glomerular disease. J Lab Clin Med. 1994;124(4):468–469. [PubMed] [Google Scholar]
- 170.Shih PH, Yen GC. Differential expressions of antioxidant status in aging rats: the role of transcriptional factor Nrf2 and MAPK signaling pathway. Biogerontology. 2007;8(2):71–80. doi: 10.1007/s10522-006-9033-y. [DOI] [PubMed] [Google Scholar]
- 171.Kachiwala SJ, Harris SE, Wright AF, et al. Genetic influences on oxidative stress and their association with normal cognitive ageing. Neurosci Lett. 2005;386(2):116–120. doi: 10.1016/j.neulet.2005.05.067. [DOI] [PubMed] [Google Scholar]
- 172.Yamamoto M, Clark JD, Pastor JV, et al. Regulation of oxidative stress by the anti-aging hormone klotho. J Biol Chem. 2005;280(45):38029–38034. doi: 10.1074/jbc.M509039200. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 173.Feng R, He W, Ochi H. A new murine oxidative stress model associated with senescence. Mech Ageing Dev. 2001;122(6):547–559. doi: 10.1016/s0047-6374(01)00232-9. [DOI] [PubMed] [Google Scholar]
- 174.Melk A, Schmidt BM, Braun H, et al. Effects of donor age and cell senescence on kidney allograft survival. Am J Transplant. 2009;9(1):114–123. doi: 10.1111/j.1600-6143.2008.02500.x. [DOI] [PubMed] [Google Scholar]
- 175.Yang F, Huang XR, Chung AC, et al. Essential role for Smad3 in angiotensin II-induced tubular epithelial-mesenchymal transition. J Pathol. 2010;221(4):390–401. doi: 10.1002/path.2721. [DOI] [PubMed] [Google Scholar]
- 176.Liang XB, Ma LJ, Naito T, et al. Angiotensin type 1 receptor blocker restores podocyte potential to promote glomerular endothelial cell growth. J Am Soc Nephrol. 2006;17(7):1886–1895. doi: 10.1681/ASN.2005020205. [DOI] [PubMed] [Google Scholar]
- 177.Park SY, Song CY, Kim BC, et al. Angiotensin II mediates LDL-induced superoxide generation in mesangial cells. Am J Physiol Renal Physiol. 2003;285(5):F909–F915. doi: 10.1152/ajprenal.00160.2003. [DOI] [PubMed] [Google Scholar]
- 178.Stevenson KM, Edgley AJ, Bergstrom G, et al. Angiotensin II infused intrarenally causes preglomerular vascular changes and hypertension. Hypertension. 2000;36(5):839–844. doi: 10.1161/01.hyp.36.5.839. [DOI] [PubMed] [Google Scholar]
- 179.Peters H, Border WA, Noble NA. Angiotensin II blockade and low-protein diet produce additive therapeutic effects in experimental glomerulonephritis. Kidney Int. 2000;57(4):1493–1501. doi: 10.1046/j.1523-1755.2000.00994.x. [DOI] [PubMed] [Google Scholar]
- 180.Zhou Q, Lin S, Tang R, et al. Role of Fosinopril and Valsartan on Klotho Gene Expression Induced by Angiotensin II in Rat Renal Tubular Epithelial Cells. Kidney Blood Press Res. 2010;33(3):186–192. doi: 10.1159/000316703. [DOI] [PubMed] [Google Scholar]
- 181.Narumiya H, Sasaki S, Kuwahara N, et al. HMG-CoA reductase inhibitors up-regulate anti-aging klotho mRNA via RhoA inactivation in IMCD3 cells. Cardiovasc Res. 2004;64(2):331–336. doi: 10.1016/j.cardiores.2004.07.011. [DOI] [PubMed] [Google Scholar]
- 182.Rosner MH. Urinary biomarkers for the detection of renal injury. Adv Clin Chem. 2009;49:73–97. doi: 10.1016/s0065-2423(09)49004-8. [DOI] [PubMed] [Google Scholar]
- 183.Perco P, Wilflingseder J, Bernthaler A, et al. Biomarker candidates for cardiovascular disease and bone metabolism disorders in chronic kidney disease: a systems biology perspective. J Cell Mol Med. 2008;12(4):1177–1187. doi: 10.1111/j.1582-4934.2008.00280.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 184.Kovesdy CP, Kalantar-Zadeh K. Review article: Biomarkers of clinical outcomes in advanced chronic kidney disease. Nephrology (Carlton) 2009;14(4):408–415. doi: 10.1111/j.1440-1797.2009.01119.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 185.Devarajan P. The use of targeted biomarkers for chronic kidney disease. Adv Chronic Kidney Dis. 2010;17(6):469–479. doi: 10.1053/j.ackd.2010.09.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 186.Guh JY. Proteinuria versus albuminuria in chronic kidney disease. Nephrology (Carlton) 2010;15(Suppl 2):53–56. doi: 10.1111/j.1440-1797.2010.01314.x. [DOI] [PubMed] [Google Scholar]
- 187.Bokenkamp A, Domanetzki M, Zinck R, et al. Reference values for cystatin C serum concentrations in children. Pediatr Nephrol. 1998;12(2):125–129. doi: 10.1007/s004670050419. [DOI] [PubMed] [Google Scholar]
- 188.Galteau MM, Guyon M, Gueguen R, et al. Determination of serum cystatin C: biological variation and reference values. Clin Chem Lab Med. 2001;39(9):850–857. doi: 10.1515/CCLM.2001.141. [DOI] [PubMed] [Google Scholar]
- 189.Shlipak MG, Wassel Fyr CL, Chertow GM, et al. Cystatin C and mortality risk in the elderly: the health, aging, and body composition study. J Am Soc Nephrol. 2006;17(1):254–261. doi: 10.1681/ASN.2005050545. [DOI] [PubMed] [Google Scholar]
- 190.Djousse L, Kurth T, Gaziano JM. Cystatin C and risk of heart failure in the Physicians' Health Study (PHS) Am Heart J. 2008;155(1):82–86. doi: 10.1016/j.ahj.2007.08.023. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 191.Drechsler C, Krane V, Winkler K, et al. Changes in adiponectin and the risk of sudden death, stroke, myocardial infarction, and mortality in hemodialysis patients. Kidney Int. 2009;76(5):567–575. doi: 10.1038/ki.2009.200. [DOI] [PubMed] [Google Scholar]
- 192.Saraheimo M, Forsblom C, Thorn L, et al. Serum adiponectin and progression of diabetic nephropathy in patients with type 1 diabetes. Diabetes Care. 2008;31(6):1165–1169. doi: 10.2337/dc07-2306. [DOI] [PubMed] [Google Scholar]
- 193.Baggio B, Gambaro G, Briani G, et al. Urinary excretion of glycosaminoglycans and brush border and lysosomal enzymes as markers of glomerular and tubular involvement in kidney diseases. Contrib Nephrol. 1984;42:107–110. doi: 10.1159/000409968. [DOI] [PubMed] [Google Scholar]
- 194.Ryu S, Chang Y, Kim DI, et al. gamma-Glutamyltransferase as a predictor of chronic kidney disease in nonhypertensive and nondiabetic Korean men. Clin Chem. 2007;53(1):71–77. doi: 10.1373/clinchem.2006.078980. [DOI] [PubMed] [Google Scholar]
- 195.Dhaun N, Lilitkarntakul P, Macintyre IM, et al. Urinary endothelin-1 in chronic kidney disease and as a marker of disease activity in lupus nephritis. Am J Physiol Renal Physiol. 2009;296(6):F1477–F1483. doi: 10.1152/ajprenal.90713.2008. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 196.Cottone S, Mule G, Guarneri M, et al. Endothelin-1 and F2-isoprostane relate to and predict renal dysfunction in hypertensive patients. Nephrol Dial Transplant. 2009;24(2):497–503. doi: 10.1093/ndt/gfn489. [DOI] [PubMed] [Google Scholar]
- 197.Chang HY, Tung CW, Lee PH, et al. Hyperuricemia as an independent risk factor of chronic kidney disease in middle-aged and elderly population. Am J Med Sci. 2010;339(6):509–515. doi: 10.1097/MAJ.0b013e3181db6e16. [DOI] [PubMed] [Google Scholar]
- 198.Feig DI. Uric acid: a novel mediator and marker of risk in chronic kidney disease? Curr Opin Nephrol Hypertens. 2009;18(6):526–530. doi: 10.1097/MNH.0b013e328330d9d0. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 199.Madero M, Sarnak MJ, Wang X, et al. Uric acid and long-term outcomes in CKD. Am J Kidney Dis. 2009;53(5):796–803. doi: 10.1053/j.ajkd.2008.12.021. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 200.Yilmaz MI, Sonmez A, Saglam M, et al. FGF-23 and vascular dysfunction in patients with stage 3 and 4 chronic kidney disease. Kidney Int. 2010;78(7):679–685. doi: 10.1038/ki.2010.194. [DOI] [PubMed] [Google Scholar]
- 201.Appledorn DM, Seregin S, Amalfitano A. Adenovirus vectors for renal-targeted gene delivery. Contrib Nephrol. 2008;159:47–62. doi: 10.1159/000125581. [DOI] [PubMed] [Google Scholar]
- 202.Imai E. Gene therapy approach in renal disease in the 21st century. Nephrol Dial Transplant. 2001;16(Suppl 5):26–34. doi: 10.1093/ndt/16.suppl_5.26. [DOI] [PubMed] [Google Scholar]
- 203.Wang Y, Sun Z. Klotho gene delivery prevents the progression of spontaneous hypertension and renal damage. Hypertension. 2009;54(4):810–817. doi: 10.1161/HYPERTENSIONAHA.109.134320. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 204.Brown AJ, Slatopolsky E. Drug insight: vitamin D analogs in the treatment of secondary hyperparathyroidism in patients with chronic kidney disease. Nat Clin Pract Endocrinol Metab. 2007;3(2):134–144. doi: 10.1038/ncpendmet0394. [DOI] [PubMed] [Google Scholar]
- 205.Gal-Moscovici A, Sprague SM. Role of vitamin D deficiency in chronic kidney disease. J Bone Miner Res. 2007;22(Suppl 2):V91–V94. doi: 10.1359/jbmr.07s203. [DOI] [PubMed] [Google Scholar]
- 206.Gal-Moscovici A, Sprague SM. Use of vitamin D in chronic kidney disease patients. Kidney Int. 2010;78(2):146–151. doi: 10.1038/ki.2010.113. [DOI] [PubMed] [Google Scholar]
- 207.Andress DL. Vitamin D treatment in chronic kidney disease. Semin Dial. 2005;18(4):315–321. doi: 10.1111/j.1525-139X.2005.18408.x. [DOI] [PubMed] [Google Scholar]
- 208.Chen HH, Tarng DC, Lee KF, et al. Epoetin alfa and darbepoetin alfa: effects on ventricular hypertrophy in patients with chronic kidney disease. J Nephrol. 2008;21(4):543–549. [PubMed] [Google Scholar]
- 209.Coles GA, Cavill I. Erythropoiesis in the anaemia of chronic renal failure: the response to CAPD. Nephrol Dial Transplant. 1986;1(3):170–174. [PubMed] [Google Scholar]
- 210.Dharmarajan TS, Widjaja D. Erythropoiesis-stimulating agents in anemia: use and misuse. J Am Med Dir Assoc. 2009;10(9):607–616. doi: 10.1016/j.jamda.2009.05.003. [DOI] [PubMed] [Google Scholar]
- 211.Kurosu H, Ogawa Y, Miyoshi M, et al. Regulation of fibroblast growth factor-23 signaling by klotho. J Biol Chem. 2006;281(10):6120–6123. doi: 10.1074/jbc.C500457200. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 212.Hall RL, Wilke WL, Fettman MJ. Captopril slows the progression of chronic renal disease in partially nephrectomized rats. Toxicol Appl Pharmacol. 1985;80(3):517–526. doi: 10.1016/0041-008x(85)90397-7. [DOI] [PubMed] [Google Scholar]
- 213.Brezis M, Greenfeld Z, Shina A, et al. Angiotensin II augments medullary hypoxia and predisposes to acute renal failure. Eur J Clin Invest. 1990;20(2):199–207. doi: 10.1111/j.1365-2362.1990.tb02269.x. [DOI] [PubMed] [Google Scholar]
- 214.Hall JE. The renin-angiotensin system: renal actions and blood pressure regulation. Compr Ther. 1991;17(5):8–17. [PubMed] [Google Scholar]
- 215.Nabokov A, Amann K, Gassmann P, et al. The renoprotective effect of angiotensin-converting enzyme inhibitors in experimental chronic renal failure is not dependent on enhanced kinin activity. Nephrol Dial Transplant. 1998;13(1):173–176. doi: 10.1093/ndt/13.1.173. [DOI] [PubMed] [Google Scholar]
- 216.Tojo A, Onozato ML, Kobayashi N, et al. Angiotensin II and oxidative stress in Dahl Salt-sensitive rat with heart failure. Hypertension. 2002;40(6):834–839. doi: 10.1161/01.hyp.0000039506.43589.d5. [DOI] [PubMed] [Google Scholar]
- 217.Muller DN, Mullally A, Dechend R, et al. Endothelin-converting enzyme inhibition ameliorates angiotensin II-induced cardiac damage. Hypertension. 2002;40(6):840–846. doi: 10.1161/01.hyp.0000039748.88581.a0. [DOI] [PubMed] [Google Scholar]
- 218.Agarwal R. Proinflammatory effects of oxidative stress in chronic kidney disease: role of additional angiotensin II blockade. Am J Physiol Renal Physiol. 2003;284(4):F863–F869. doi: 10.1152/ajprenal.00385.2002. [DOI] [PubMed] [Google Scholar]
- 219.Remuzzi G, Perico N, Macia M, et al. The role of renin-angiotensin-aldosterone system in the progression of chronic kidney disease. Kidney Int. 2005;99(Suppl):S57–S65. doi: 10.1111/j.1523-1755.2005.09911.x. [DOI] [PubMed] [Google Scholar]
- 220.Wenzel RR. Renal protection in hypertensive patients: selection of antihypertensive therapy. Drugs. 2005;65(Suppl 2):29–39. doi: 10.2165/00003495-200565002-00005. [DOI] [PubMed] [Google Scholar]
- 221.Mizuno M, Sada T, Kato M, et al. The effect of angiotensin II receptor blockade on an end-stage renal failure model of type 2 diabetes. J Cardiovasc Pharmacol. 2006;48(4):135–142. doi: 10.1097/01.fjc.0000245241.79959.d6. [DOI] [PubMed] [Google Scholar]
- 222.Lebel M, Rodrigue ME, Agharazii M, et al. Antihypertensive and renal protective effects of renin-angiotens in system blockade in uremic rats treated with erythropoietin. Am J Hypertens. 2006;19(12):1286–1292. doi: 10.1016/j.amjhyper.2006.06.019. [DOI] [PubMed] [Google Scholar]
- 223.Negri AL. The klotho gene: a gene predominantly expressed in the kidney is a fundamental regulator of aging and calcium/phosphorus metabolism. J Nephrol. 2005;18(6):654–658. [PubMed] [Google Scholar]
- 224.Kuwahara N, Sasaki S, Kobara M, et al. HMG-CoA reductase inhibition improves anti-aging klotho protein expression and arteriosclerosis in rats with chronic inhibition of nitric oxide synthesis. Int J Cardiol. 2008;123(2):84–90. doi: 10.1016/j.ijcard.2007.02.029. [DOI] [PubMed] [Google Scholar]
- 225.Wang X, Liu X, Zhan Y, et al. Pharmacogenomic, physiological, and biochemical investigations on safety and efficacy biomarkers associated with the peroxisome proliferator-activated receptor-gamma activator rosiglitazone in rodents: a translational medicine investigation. J Pharmacol Exp Ther. 2010;334(3):820–829. doi: 10.1124/jpet.110.167635. [DOI] [PubMed] [Google Scholar]
- 226.Zhang H, Li Y, Fan Y, et al. Klotho is a target gene of PPAR-gamma. Kidney Int. 2008;74(6):732–739. doi: 10.1038/ki.2008.244. [DOI] [PubMed] [Google Scholar]
- 227.Zhang R, Zheng F. PPAR-gamma and aging: one link through klotho? Kidney Int. 2008;74(6):702–704. doi: 10.1038/ki.2008.382. [DOI] [PubMed] [Google Scholar]
- 228.Lopez-Hernandez FJ, Lopez-Novoa JM. Potential utility of PPARalpha activation in the prevention of ischemic and drug-induced acute renal damage. Kidney Int. 2009;76(10):1022–1024. doi: 10.1038/ki.2009.229. [DOI] [PubMed] [Google Scholar]
- 229.Li S, Nagothu KK, Desai V, et al. Transgenic expression of proximal tubule peroxisome proliferator-activated receptor-alpha in mice confers protection during acute kidney injury. Kidney Int. 2009;76(10):1049–1062. doi: 10.1038/ki.2009.330. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 230.Rakugi H, Matsukawa N, Ishikawa K, et al. Anti-oxidative effect of Klotho on endothelial cells through cAMP activation. Endocrine. 2007;31(1):82–87. doi: 10.1007/s12020-007-0016-9. [DOI] [PubMed] [Google Scholar]
- 231.Shah SV, Baliga R, Rajapurkar M, et al. Oxidants in chronic kidney disease. J Am Soc Nephrol. 2007;18(1):16–28. doi: 10.1681/ASN.2006050500. [DOI] [PubMed] [Google Scholar]
- 232.Sugiura H, Yoshida T, Mitobe M, et al. Klotho reduces apoptosis in experimental ischaemic acute kidney injury via HSP-70. Nephrol Dial Transplant. 2010;25(1):60–68. doi: 10.1093/ndt/gfp451. [DOI] [PubMed] [Google Scholar]