The interaction between klotho protein and epigenetic alteration in diabetes and treatment options

Abstract

Introduction

Klotho is a membrane protein predominantly expressed in the kidneys, and its discovery was serendipitously made through gene-targeting experiments conducted on mice. Klotho has a favorable role in the regulation of multiple cellular processes, such as aging, oxidative stress, inflammation, and apoptosis. This regulation occurs through the targeting of diverse signaling molecules, cell membrane receptors, and ion channels, achieved by physical contacts or enzymatic activities of Klotho. This review examines the role of Klotho in the epigenetic regulation of molecules associated with diabetes.

Methods

Authors conducted a thorough literature search using the PubMed®, Web of Science™, and Scopus®. Relevant articles up to September 2023, published in the English language were considered. We reviewed research databases searching for studies that included keywords klotho, epigenetic, and diabetes.

Results

14 related papers about epigenetic modification of proteins involved in diabetes pathogenesis were selected to be included in this narrative review. In the studies, the kidney was the most investigated organ regarding this correlation. Also, phosphorylation and methylation were the common epigenetic modifications of proteins by Klotho.

Conclusion

Klotho has a significant role in the maturation of adipocytes and the regulation of systemic glucose metabolism, exhibiting a strong association with the pathogenesis of diabetes. Both epigenetic alterations and the modulation of protein phosphorylation by Klotho play significant roles in the regulation of Klotho expression and the modulation of other molecules implicated in the etiology of diabetes.

Background

Klotho has been demonstrated to possess anti-aging properties, as evidenced by its ability to increase the lifespan of mice by 30% and provide protection against various illnesses, particularly those affecting renal tissue [1]. The predominant form of Klotho protein is referred to as α-Klotho. There exist two distinct categories of soluble α-Klotho protein, namely shed and secreted variants. The activity of membrane proteases, specifically disintegrin and metalloproteinase domain-containing proteins (ADAM)10 and ADAM17, leads to the formation of three different types of shed α-Klotho. The ADAMs enzymes are responsible for the cleavage of Klotho fragments from the extracellular domain of Klotho that is linked to the cell membrane. These cleaved fragments are then released into the bloodstream, urine, and cerebrospinal fluid in humans [2]. Two more genes, encoding β-Klotho and γ-Klotho proteins, have been described based on their sequence similarity to Klotho [3]. Klotho has a notable impact on reducing inflammation by inhibiting the activation of several proinflammatory mediators and receptors. Additionally, it has been observed that Klotho exerts inhibitory effects on tissue fibrosis [1, 4]. Hence, it has the potential to alleviate some pathological alterations associated with hyperglycemia-induced diabetes. In the experimental model of streptozotocin (STZ)-induced type 1 diabetes (T1D) in mice, administration of Klotho exhibited inhibitory effects on cardiac inflammation, mitigated oxidative stress, and averted death of cardiac cells [5]. Epigenetic changes, including DNA methylation, post-translational histone modifications, and miRNAs, play a regulatory role in modulating the expression of Klotho in the context of diabetes. Epigenetics pertains to the capacity to control gene expression without modifying the fundamental nucleotide sequence. In other words, it encompasses the ability to produce phenotypic alterations, such as histone modifications, DNA methylation, and noncoding RNA activity, without modifying the genotype [6–8]. Epigenetic changes are commonly perceived to exhibit stability and heritability throughout the process of cell division [9–11]. Nevertheless, several factors, including oxidative stress, inflammation, cytokines, growth hormones, and age have the potential to influence the reversibility of the aforementioned conditions [12–14]. Epigenetic alterations may be intimately associated with the development and progression of diabetes [15, 16]. In diabetes, aberrant DNA methylation can be attributed not only to hyperglycemia, but also to reactive oxidative stress (ROS), inflammation, and cytokines [12, 17]. According to studies, people with diabetic kidney disease (DKD) have a different amount of DNA methylation than diabetics without kidney disease [18, 19]. There is a combination of epigenetic and non-epigenetic mechanisms involved in the process of regulating the expression of endogenous Klotho. Also, there are various factors involved in diabetes pathogenesis which are regulated using epigenetic mechanisms. In this review, we describe the role that Klotho plays in the epigenetic control of diabetes-related molecules, and spot light on how targeting Klotho could be used as a novel therapeutic approach in the treatment of diabetes.

Materials and methods

A narrative review of the literature was conducted to investigate epigenetic alternation of proteins involved in diabetes pathogenesis by klotho protein. This study was investigated by searching three databases (PubMed®, Web of Science™, and Scopus®) for relevant papers up to September 2023 according to a following keywords: “klotho”, “epigenetic”, “methylation”, “acetylation”, “miRNA”, “phosphorylation”, “histone modification”, and “diabetes”. All type of studies except the Letters, editorial comments, replies from authors, case reports, meeting abstracts, and non-English language articles were included.14 related papers including human and animal studies were selected to be in this review. Two senior authors (S.H., and F.M) selected the most relevant studies for design, and level of evidence, according to their knowledge and experience. Other authors reviewed and approved the study selection.

The biological function of klotho

The formation of a receptor complex consisting of three Klothos and fibroblast growth factor receptors (FGFRs) is a necessary and inherent process. This complex enables FGFRs to exhibit a specific and preferential binding affinity towards endocrine FGFs. The endocrine FGF family consists of three members, namely FGF15 (the mouse counterpart of human FGF19), FGF21, and FGF23. The biological action of classic fibroblast growth factors (FGFs) is elicited through autocrine and/or paracrine mechanisms [20]. β-Klotho plays a crucial role in the control of energy metabolism by serving as an essential co-receptor for FGF15 and FGF21 [21]. The regulation of FGF15/19 expression in the intestinal tract is influenced by bile acid in mice [22, 23]. The intestinal-liver endocrine axis, which is regulated by FGF19 and β-Klotho, plays a crucial role in the maintenance of bile acid homeostasis. This is supported by the observation that mice lacking FGF15, β-Klotho, or FGFR4 demonstrate elevated expression of Cyp7α1 and enhanced synthesis of bile acids in the liver [24]. On the contrary, the liver secretes FGF21 in response to fasting, which subsequently exerts its effects on adipose tissue through stimulating lipolysis [25]. The expression of β-Klotho and FGFRs has been shown in both pancreatic islets and acinar tissue, hence facilitating the signaling of FGF21 in both the exocrine and endocrine components of the pancreas. FGF21 exerts a protective action against apoptosis of pancreatic β-cells, hence facilitating the maintenance of pancreatic β-cell function and viability [26]. In contrast to control mice, the absence of FGF21 in mice results in deformities of the islets and acinus, along with the development of insulin resistance during the intraperitoneal glucose tolerance test (IPGTT) [27, 28]. The specific deletion of β-Klotho in acinar cells leads to the buildup of zymogen granules but impairs the ability to secrete digestive enzymes in response to FGF21 stimulation. This suggests that FGF21 promotes the secretion of digestive enzymes from pancreatic acinar cells through an autocrine/paracrine mechanism, which necessitates signaling via the FGFR/β-Klotho complex [29]. Therefore, β-Klotho assumes a significant role in facilitating the exocrine and endocrine processes of the pancreas (Fig. 1).

Fig. 1.

The processes underlying the regulatory role of the FGF21-β-Klotho axis in glucose metabolism. The FGF21-β-Klotho axis plays a crucial role in maintaining metabolic homeostasis of glucose by exerting its effects on several metabolic organs, such as the brain, liver, pancreas, and adipose tissue. The FGF21-β-Klotho axis inside the brain is responsible for upregulating the expression of CRH and subsequently activating the HPA axis. This activation ultimately leads to the promotion of gluconeogenesis in the liver. The FGF21-β-Klotho axis has been found to stimulate Oxt neurons and glutamatergic neurons, resulting in a decrease in food consumption and a suppression of sugar preference. The hepatic gluconeogenesis is potentially enhanced by the FGF21-β-Klotho axis in the liver, potentially mediated by PGC-1α. The FGF21-β-Klotho axis has been found to play a role in promoting glucose absorption and enhancing WAT browning in both WAT and BAT. In particular, FGF21 enhances the secretion of adiponectin from adipocytes, hence facilitating the overall impact of FGF21 on energy metabolism and insulin sensitivity. The FGF21-β-Klotho axis inside the pancreas facilitates the process of insulin manufacturing by initiating ERK1/2 signaling in pancreatic β cells. Additionally, it hinders the occurrence of β cell death and fosters the survival of β cells through the activation of the Akt signaling pathway. The impact of the FGF21-β-Klotho axis on many metabolic organs plays a significant role in regulating glucose metabolism

Legend: BAT: brown adipose tissue; CRH: corticotropin releasing hormone; HPA: hypothalamic pituitary adrenal; OXT: oxytocin; PGC-1α: peroxisome proliferator-activated receptor-gamma coactivator protein-1α; WAT: white adipose tissue

The γ-Klotho protein has been observed to establish complexes with FGFR1b, FGFR1c, FGFR2c, and FGFR4, hence enhancing the activity of FGF19. The expression of γ-Klotho is notably high and specific in brown adipose tissue and the eye, and it can serve as an extra co-receptor for FGF19 in cultured cells [20]. Nevertheless, the precise biological role of γ-Klotho remains mainly unknown.

The klotho protein in diabetes

The dysregulation of phosphate and calcium metabolism, the induction of oxidative stress, the initiation of inflammatory responses, the progression of fibrotic processes, and the elevation of the rate of β-cell and podocyte loss by apoptosis can lead to pathological conditions that bear resemblance to premature aging. The protein Klotho serves a protective role in mitigating the effects of accelerated aging and cellular damage in individuals with (T1DM) and diabetic nephropathy (DN) [30]. Additionally, it has been observed that there is a decrease in the levels of circulating soluble Klotho in plasma and urine as individuals age. This reduction is particularly evident in cells with short telomeres or those undergoing stress-induced premature senescence. Furthermore, it is associated with various detrimental factors such as widespread tissue injury, inflammation, oxidative stress, and vascular calcification. These factors commonly occur during the progression of chronic kidney disease (CKD). Furthermore, it has been observed that individuals with CKD exhibit decreased levels of calcitriol, which is the active form of vitamin D3. This reduction in calcitriol has been shown to exacerbate the deficit of renal Klotho [31, 32]. It is worth noting that DN stands as the primary cause of CKD in Western nations [33]. It was expected that patients with DN would exhibit reduced levels of both Klotho mRNA and protein. This theory was empirically validated in diabetic mice. The reduction of Klotho was observed to trigger apoptosis of insulin-producing β-cells in two models of T1DM. Nevertheless, the adverse impact was alleviated with the introduction of Klotho overexpression, hence providing protection against apoptosis [34]. In addition, the administration of Klotho demonstrated enhanced β-cell functionality and a protective effect against the progression of T2D [35]. The progression of nephropathy in individuals with T2D was found to be predicted by low levels of Klotho in plasma, but not in urine. Furthermore, these low plasma levels of Klotho were observed to be inversely linked with a decline in the glomerular filtration rate (GFR) [36]. Furthermore, the lack of Klotho was seen to worsen proteinuria caused by diabetes, and increase oxidative stress as demonstrated by higher levels of ROS inside cells. This deficit also led to podocyte damage and apoptosis, which were caused by the activation of protein kinase Cα (PKCα). Conversely, these detrimental effects were somewhat alleviated through the overexpression of Klotho [37]. The levels of soluble Klotho in both plasma and urine were shown to be lower in individuals with intrinsic acute kidney injury (AKI) compared to those with prerenal AKI. In addition, there was an observed rise in the levels of proinflammatory ligands, specifically S100A8/A9 calgranulins, which are known to activate Toll-like receptor 4 (TLR4) [38]. Hence, it has been suggested that measuring plasma or urine levels of the Klotho protein could potentially function as a biomarker for detecting early kidney impairment in individuals with diabetes.

Kidney

The miRNA-199a-5p molecule has a crucial role in regulating the expression of Klotho in DN. According to existing literature, it has been observed in renal cell assays that elevated glucose levels are associated with an upregulation of miRNA-199a-5p expression. This upregulation is followed by a notable decrease in Klotho expression, both at the mRNA and protein levels. The activation of NF-κB signaling and the promotion of fibrotic and inflammatory reactions were observed in response to high glucose levels. These effects were shown to be mitigated by either inhibiting miR-199a-5p or introducing exogenous Klotho [39]. Similarly, the extracellular vesicles (EVs) produced from HK-2 cells were found to stimulate macrophage M1 polarization through the targeting of the Klotho/TLR4 signaling pathway by miRNA-199a-5p. This mechanism was observed to contribute to the accelerated development of DN [40]. In concurrence with these findings, Kang et al.. aimed to assess the impact of atrasentan as an endothelin-A receptor antagonist on the down-regulation of miR-199b-5p expression in DN. In conjunction with increased albuminuria, there was an observed increase in the serum miR-199b-5p level and a decrease in Klotho concentration in patients. The administration of atrasentan resulted in the down-regulation of miR-199b-5p and the up-regulation of Klotho in HK-2 cells that were subjected to high glucose levels (20 mmol/L). One potential method via which atrasentan may protect against renal tubular injury in DN is by modulating the levels of serum Klotho, facilitated by miR-199b-5p [41].

In the case of animal studies, one potential approach for protecting the kidneys could involve the restoration of Klotho expression through the reduction of hypermethylation in the Klotho promoter region [42]. The study conducted by Yang et al.. sought to investigate the potential of epigallocatechin-3-gallate (EGCG) in ameliorating renal damage in diabetic db/db mice and high-glucose-induced injury in HK-2 cells through the modulation of Klotho gene promoter methylation levels. Following treatment with EGCG, the expression of Klotho and DNA methyltransferases (DNMT)3b proteins was shown to be elevated, whereas the expression of DNMT1 and DNMT3a were found to be downregulated. The application of EGCG also resulted in a decrease in the methylation status of the promoter region of the Klotho gene, as well as a reduction in the binding of DNMT3a to the promoter region of the Klotho gene [43]. Baicalin is a compound classified as a flavone glycoside, which exhibits a wide range of pharmacological effects. Zhang et al.. utilized an STZ-induced diabetic mice model to investigate the potential effects of baicalin on the pathological alterations in kidney function and morphology induced by diabetes [44]. They indicated that baicalin exhibited a mitigating effect on these diabetes-induced abnormalities by decreasing both inflammation and oxidative stress. The upregulation of Klotho expression following treatment with baicalin can be attributed to the hypomethylation of the Klotho promoter region, which is a result of abnormal expression of methyltransferase 3 A [44]. Kale et al.. investigated the underlying mechanisms involved in the modulation of Klotho in acute renal damage exacerbated by hyperglycemia. A notable augmentation was observed in the levels of kidney-specific histone deacetylases (HDACs), apoptotic and inflammatory proteins, while a decline was noted in the levels of endogenous Klotho, H3K9Ac, and H3K27Ac proteins in diabetic rats with hyperglycemic bilateral ischemia-reperfusion injury (IRI) and chemical hypoxia-reperfusion injury (HRI). Inhibition of HDACs that are unique to the kidneys has demonstrated reno-protection by recovering the loss of endogenous Klotho [45], (Fig. 2). To investigate the potential effects of atrasentan on renal tubular injury in DN, a murine model was generated through the administration of STZ. The primary objective of this study was to examine if atrasentan could down-regulate the expression of miR-199b-5p, therefore leading to an increase in Klotho levels and subsequent prevention of renal tubular injury in DN. The administration of atrasentan resulted in the down-regulation of miR-199b-5p and up-regulation of Klotho in DN mice that were subjected to high glucose levels. The effects of atrasentan on Klotho expression and death of renal tubular cells were negated by the overexpression of miR-199b-5p [41]. In another study, the renoprotective effects of Klotho in mitigating podocyte injury in the context of DN were evaluated. The researchers conducted an experiment wherein cultured mouse podocytes were exposed to palmitate to produce podocyte injury through lipotoxicity. The level of Klotho was found to be reduced in podocytes of mice podocytes that were treated with palmitate [35]. The inhibition of Forkhead Box O3 (FOXO3) phosphorylation by Klotho, followed by its nuclear translocation and subsequent upregulation of manganese superoxide dismutase (MnSOD) expression, suggests that Klotho may hold promise as a therapeutic intervention for managing podocyte injury in obese individuals with DN [35]. The study revealed that the presence of Klotho deficit in KL(+/-) mutant mice intensified the effects of STZ-induced increases in urine albumin, blood urea nitrogen, enlargement of the mesangial matrix in renal glomeruli, and kidney hypertrophy. Klotho deficiency in early diabetic mice resulted in an elevation in the phosphorylation of mammalian target of rapamycin (mTOR) and downstream molecules of mTOR. The absence of the Klotho gene has been found to worsen the progression of early DN by increasing the activation of both TGF-β1 and mTOR signaling pathways in the kidneys [46]. Zhao et al. investigated the potential influence of Klotho levels on kidney inflammation in diabetic mice. The expression of renal Klotho was found to be considerably reduced in db/db mice. Klotho was found to selectively suppress the phosphorylation of RelA at Ser(536) and its subsequent binding to promoter DNA [47]. RelA binds to a specific DNA sequence as a homodimer or as heterodimers with other members of the nuclear factor kappa B (NF-κB) family regulating transcription of a variety of genes. RelA has a bipartite structure a DNA-binding Rel homology region (RHR) and a C-terminal transcription activation domain [48]. These observations indicate that Klotho functions as an anti-inflammatory regulator by negatively modulating the synthesis of NF-κB-associated inflammatory proteins through a mechanism involving the phosphorylation of Ser(536) within the transactivation domain of RelA [47].

Fig. 2.

The impact of Hyperglycemia on the regulation of Klotho, the exacerbation of AKI, and the underlying mechanisms involved. Hyperglycemia has been found to exacerbate AKI generated by IRI or HRI, as supported by both biochemical and histological evidence. The hyperglycemic IRI/HRI groups exhibit a notable rise in the expression of kidney-specific HDACs, apoptotic and inflammatory proteins. Conversely, there is a decrease in the levels of endogenous Klotho, H3K9Ac, and H3K27Ac proteins

Legend: AKI: acute kidney injury; HRI: hemorrhagic shock and resuscitation injury; IRI: ischemia-reperfusion injury

Heart

The relationship between soluble Klotho and insulin resistance (IR) is highly significant, as IR plays a pivotal role in the advancement of diabetic cardiomyopathy (DCM). The objective of the study conducted by Li et al.. was to examine the influence of soluble Klotho on the regulation of DCM and elucidate the underlying mechanism. A murine model of TDM was established with the administration of a high-fat diet and injection of STZ [49]. The overexpression of soluble Klotho demonstrated a mitigating effect on IR and metabolic disruption. In diabetes, the presence of inflammation, fibrosis, and an elevated ratio of collagen I/III content was dramatically diminished. Moreover, the diminished phosphorylation of Akt was reinstated through the overexpression of the soluble Klotho gene, whereas the heightened phosphorylation of extracellular signal-regulated kinase 1/2 in DCM was decreased [49].

Pancreas

Lin et al.. discovered that a loss in Klotho (KL(+/-)) had a detrimental effect on STZ-induced diabetes included hyperglycemia, glucose intolerance, reduced insulin storage in the islets, and an increase in apoptotic β-cells. On the other hand, the targeted expression of the mouse Klotho gene (mKL) specifically in β-cells in vivo resulted in a reduction in β-cell death and served as a protective measure against diabetes produced by STZ. mKL was found to enhance cellular adherence to collagen IV, induce phosphorylation of FAK and Akt, and suppress caspase 3 cleavage in MIN6 β-cell cultures. The administration of mKL effectively reversed the inhibitory effects of STZ and tumor necrosis factor-alpha (TNF-α) on focal adhesion kinase (FAK) and Akt phosphorylation, caspase 3 cleavage, and β-cell death [50].

Trophoblast cell line

The pathophysiology of gestational diabetes mellitus (GDM) is significantly influenced by IR. The protein Klotho, which is involved in the process of aging, has been demonstrated to have a significant association with IR. The HTR-8/SVneo cell model of GDM was stimulated by elevated glucose levels. The expression of Klotho was found to be up-regulated in cells that were stimulated by high glucose. The upregulation of Klotho resulted in the suppression of insulin-like growth factor 1(IGF-1), IGF-1R/p-IGF-1R, as well as the phosphorylation and activation of the signal transduction molecules phosphoinositide 3-kinases (PI3K)/Akt/mTOR. In contrast, it is plausible that the deletions of Klotho may potentially elicit a reversal of the aforementioned alterations in HTR-8/SVneo cells that have been produced by high glucose conditions [51].

Therapeutic targeting of klotho in diabetes

Several studies have investigated the therapeutic effects of recombinant Klotho and the induction of Klotho overexpression. These studies have utilized various methods such as the administration of calcitriol, peroxisome proliferator-activated receptor γ (PPAR-γ) ligands such as pioglitazone [52], and viral vector-mediated Klotho gene delivery. The findings indicate that these interventions can reduce oxidative stress, mitigate the damage caused by high glucose levels in renal glomerular endothelial cells in a model of DN, suppress diabetes-induced renal hypertrophy, and elicit other immunotherapeutic effects in the context of DN [53, 54]. Also, the therapeutic effects of recombinant Klotho and the induction of Klotho overexpression were examined.

Studies have indicated that entertain-based therapy, such as the administration of glucagon-like peptide-1 receptor agonist (GLP-1RA) and dipeptidyl peptidase-4 (DPP-4) inhibitors, have demonstrated the ability to elevate Klotho levels [55, 56]. Previous studies have demonstrated that Thiazolidinediones (TZDs) can effectively promote the expression of the Klotho gene in renal epithelial cells, with the extent of induction being dependent on both the duration of exposure and the dosage of TZDs. This induction of Klotho gene expression has potential implications for the amelioration of symptoms and pathology associated with DN [57, 58]. A clinical trial filed with the clinical trials registry (NCT03585777) is underway to examine the impact of different oral hypoglycemic medications (glimepiride, metformin, and linagliptin) on blood Klotho levels. In a rat model of STZ-induced diabetes-associated renal fibrosis, the administration of a combination of metformin and a plant extract derived from Abelmoschus manihot (L.) medic, which has a traditional usage for CKD, was found to exert its effects partially through the Klotho/TGF-β1/p38 mitogen-activated protein kinase (MAPK) signaling pathway. This treatment significantly decreased the body weight of rats with DN, and reduced their blood glucose levels, urine protein levels, and the extent of renal tubule damage, apoptosis, glomerulopathy, and renal fibrosis [59].

Sodium-glucose co-transporter 2 (SGLT-2) inhibitors have well-established cardiorenal protective properties. Multiple studies have demonstrated that the utilization of SGLT-2 inhibitors has the potential to effectively enhance Klotho levels, hence leading to improvements in both diabetes and its concomitant cardiorenal problems [60, 61]. mTOR inhibitors, such as rapamycin, are frequently employed as autophagy inducers and have demonstrated efficacy in the treatment of DN as well as immunosuppression following organ transplantation [62]. Mizusaki et al., demonstrated that mTOR inhibitors have the potential to enhance Klotho expression in individuals who have underwent renal transplantation. However, Klotho levels were higher after transplantation even in the absence of mTOR inhibitor than before transplantation indicating that kidneys are the main provider of Klotho [63]. Moreover, it has been demonstrated that mTOR inhibitors are effective drugs for augmenting Klotho levels [64]. Pentoxifylline (PTX) is predominantly employed for the management of ischemic peripheral vascular disease and assumes a pivotal role in the treatment of vascular disease associated with diabetes and degenerative vascular consequences [65]. The administration of PTX has been observed to result in a dose-dependent elevation in the expression of Klotho protein and mRNA. This is accompanied by a concurrent rise in the levels of Klotho identified in both blood and urine. In phase 2 clinical research, it was shown that the injection of PTX resulted in the preservation of Klotho levels and with a concomitant decrease in proteinuria in individuals with DN [66].

The investigation of therapeutic interventions aimed at modulating signaling pathways suppressed by Klotho has exhibited encouraging outcomes in terms of enhancing the well-being of individuals diagnosed with diabetes. The delivery of soluble Klotho protein demonstrated a mitigating effect on renal fibrosis, resulting in the inhibition of profibrotic markers and TGF-β1 target genes, as well as the suppression of the Wnt signaling pathway [67]. Furthermore, Chen et al.. found that KP6, a peptide generated from Klotho, exhibits strong therapeutic properties in mitigating DKD in both T1D induced by STZ and T2D caused by the genetic mutation db/db. The administration of KP6 has been found to effectively reduce glomerular injury, ameliorate podocyte damage, reverse albuminuria, and prevent the development of glomerulosclerosis. In terms of its mechanism of action, KP6 exhibits binding affinity towards Wnt ligands, hence impeding their capacity to engage with LRP6 [68]. The summary of the above-mentioned studies regarding therapeutic targeting of klotho is shown in Table 1.

Table 1.

Therapeutic approaches targeting klotho in diabetes

Component	Class	Outcome	Ref.
GLP-1RA	Entertain-based therapies	Upregulation of Klotho	[55, 56]
DPP-4 inhibitor	Entertain-based therapies	Upregulation of Klotho	[55, 56]
TZD	Agonists of PPAR-γ	Upregulation of Klotho Improving the DN	[57]
Metformin and a plant extract from Abelmoschus manihot (L.) medic	Anti-hyperglycemic agent	Action via Klotho/TGF- β1/p38MAPK signaling pathway Reduces blood glucose and urine protein levels,	[59]
SGLT-2 inhibitor	Glucose transporter	Restore Klotho levels Improve diabetes-associated cardiorenal complications	[60]
Rapamycin	mTOR inhibitor	Upregulation of Klotho Effective in treating DN	[62]
PTX	PDE inhibitor	Upregulation of Klotho in serum and urine	[65]
KP6	Small Klotho-derived peptide,	Ameliorates DKD	[68]

GLP-1RA: glucagon-like peptide-1 receptor agonist; DPP-4: dipeptidyl peptidase-4; SGLT-2: Sodium glucose co-transporter 2; PTX: Pentoxifylline; PPAR-γ: peroxisome proliferator-activated receptor γ; DN: diabetic nephropathy; PDE: phosphodiesterase; DKD: diabetic kidney disease

Conclusion

In recent years, there has been a notable focusing on investigating the physiological function of Klotho and its associated molecular pathways in the context of diabetes. The restoration of Klotho levels to their natural state or their upregulation can be achieved through both epigenetic and non-epigenetic methods. It is obvious that epigenetic modifications are involved in Klotho expression. On the other hand, Klotho per se can modulate the expression of other related molecules in diabetes pathogenesis through epigenetic changes, particularly protein phosphorylation. The therapeutic potential of targeting Klotho in the treatment of diabetes can be explored through multiple paths. Given the increasing relevance of epigenome-directed editing technology, it is anticipated that epigenetic treatments will emerge as viable, safe and effective approach in the treatment of diabetes. There are several gaps in our understanding of the mechanisms underlying the action of Klotho, particularly in the context of human organisms. So far, there have been no documented clinical investigations conducted on the injection of recombinant Klotho in human subjects. Additional data obtained from studies including healthy individuals or those with diabetes is necessary to enhance our comprehension of this matter.

Author contributions

This research was conducted in collaboration with all authors. S.H, and F.M were responsible for idea design, collection data, selection of literature to review. S.D, A.S, and M.L contributed to the final approval and manuscript writing. A.F contributed in figure designing and writing the manuscript. All authors contributed to the article and approved the submitted version.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Data availability

It is not applicable.

Declarations

Ethical approval

It is not applicable.

Informed consent

It is not applicable.

Conflict of interest

None.