Skip to main content
NCBI home page
Cell Stress & Chaperones logoLink to Cell Stress & Chaperones
. 2020 Jan 22;25(2):245–251. doi: 10.1007/s12192-020-01067-3

Erythropoietin promotes functional recovery via anti-apoptotic mechanisms in mouse unilateral ureteral obstruction

Elliya Park 1, Michael Cox 2, Kymora Scotland 1, Ralph Buttyan 2, Dirk Lange 1,✉
PMCID: PMC7058756  PMID: 31970695

Abstract

The purpose of the work was to investigate mechanisms of erythropoietin-induced protection and accelerated recovery of kidneys and ureters from obstructive injury. Unilateral ureteral obstruction was established for 24, 48, and 72 h in C57BL/6 mice using a non-traumatic micro-clip followed by the microscopic quantification of ureteral peristalsis pre- and post-obstruction. Expression of erythropoietin, erythropoietin receptor, β-common receptor, and downstream apoptosis-related markers was assessed by RT-PCR and immunohistochemistry in ureters and kidneys and compared to the respective organs on the contralateral side within each animal. Expression of genes in kidneys and ureters from mice treated with 20 IU of erythropoietin daily for 72 h prior to obstruction was compared to that of untreated mice following obstruction. Apoptosis in ureteral tissues after 72-h obstruction was assessed via TUNEL assay. Ureteral obstruction increased apoptosis in affected ureters, with peristaltic function halted following all periods of obstruction. Erythropoietin treatment suppressed apoptosis in obstructed tissues and increased the percentage of mice retaining ureteral function immediately following obstruction reversal. Erythropoietin, erythropoietin receptor, Bcl-2, and Bcl-xl mRNA expression were down-regulated, while phospho-Nf-ĸb p65 was up-regulated in ureteral epithelia following obstruction. Erythropoietin treatment induced anti-apoptotic signaling via down-regulated Bax mRNA expression and abrogated phospho-Nf-ĸb p65. Erythropoietin-induced protection of ureteral function and accelerated recovery post-obstruction removal is mediated via anti-apoptotic mechanisms. Ureteral function is disrupted even following obstruction removal, negatively affecting renal function due to delayed recovery. Thus, our results represent a potential target for the development of safe therapeutic agents aimed at improving functional recovery from obstructive injury.

Keywords: Erythropoietin, Apoptosis, Obstruction, Stretch-induced stress, Ureteral function, Peristalsis

Introduction

The ureter transports urine from the kidney to the bladder via peristaltic movements consisting of coordinated contractions of ureteral smooth muscle. Ureteral function can be compromised by obstructive diseases that include nephrolithiasis, ureteral tumors, benign prostatic hypertrophy, or traumatic injury (Jay and Nicol 2017). Untreated ureteral obstruction leads to acute hydronephrosis that can cause urosepsis or renal damage leading to urosepsis and/or failure. The onset of ureteral obstruction initially increases ureteral peristaltic activity acutely, followed by the gradual decrease of peristaltic movements as the obstruction persists, eventually resulting in aperistalsis (Lennon et al. 1993). In a mouse model of unilateral ureteral obstruction, impaired ureteral function was not recovered for up to 10 days after obstruction reversal (Janssen et al. 2015), suggesting prolonged negative effects on the kidneys far beyond the resolution of hydronephrosis. Given this, there is a need for the development of interventions to promote peristaltic recovery following obstruction reversal.

Erythropoietin (EPO), a peptide hormone best known for its role in erythropoiesis, has protective effects in nonhematopoietic tissues subjected to a broad range of injuries (Ghezzi and Brines 2004). EPO receptor (EPOR) is expressed in a wide range of tissues, including the ureter, and influences cell proliferation and survival through the activation of Ras/MEK/ERK, PI3-kinase/AKT, and JAK-STAT signaling pathways (Ghezzi and Brines 2004). Furthermore, signaling through a heteroreceptor consisting of EPOR and the β-common receptor (βCR) is believed to result in more potent EPO-induced protective effects (Brines et al. 2004). Previous work from our laboratory showed that prophylactic EPO treatment accelerated the recovery of ureteral peristalsis and resolution of hydronephrosis following acute unilateral ureteral obstruction (UUO) in a mouse model (Janssen et al. 2015). These results parallel similar findings in the intestine where EPO treatment facilitated the functional recovery of intestinal tissue from a hypocontractile state (Nagib et al. 2012; Ozdamar et al. 2006). Given the protective effects of EPO observed in our previous studies, the present work is aimed at understanding downstream effects of EPO involved in accelerating recovery from the obstructive insult. For this, we focused on the effects of EPO on the expression of its receptors and downstream regulators of apoptosis, a process known to be increased in obstructed ureters (Chuang et al. 2002).

Materials and methods

Animals

All procedures were approved by the University of British Columbia Animal Care Committee. A total of 50 female C57BL/6 mice (Jax, Bar Harbor, ME, USA) at age 10–12 weeks were used in the experiments. Mice were randomly assigned to five groups (untreated 24-h UUO, untreated 48-h UUO, untreated 72-h UUO, EPO-treated 24-h UUO, and EPO-treated 72-h UUO) with ten mice per group. The behavior of the mice was carefully examined and recovered normal behavior within 12 h after the surgery.

Transient UUO surgical induction and ureteral function assessment

Under anesthesia with isoflurane, 10-min preoperative administration of 2 mg/kg meloxicam, 0.05 mg/kg bupivacaine, and 6 mg/kg buprenorphine was provided for pain management. Unilateral ureteral obstruction for 24, 48, or 72 h was induced in left distal ureters using non-traumatic RS-6470 vascular clip (Roboz Surgical Instrument Co. Gaithersburg, MD, USA), and ureteral function was quantified during a 2-min interval as described previously (Janssen et al. 2015). Ureteral tissues above the obstructed area were collected for further analysis.

EPO treatment

20 IU of human biosynthetic epoetin alfa (Eprex 2000 IU/0.5 ml, Janssen Inc., Beerse, Belgium) was administered every 24 h intraperitoneally for 4 consecutive days before and on the day of ureteral obstruction. Half-life of human EPO in rodents was shown to be 4.4 h compared to 6 h of that in human while exhibiting comparable effects in rodents, which allows for the use of recombinant human EPO for these experiments (Fares, Havron and Fima 2011).

Immunohistochemistry

After embedding the mouse ureters in paraffin, 4 mm sections were cut and stained with 1:400 anti-Nf-ĸb p65 (phospho S536) antibody (Abcam, Cambridge, UK). All slides were scanned with a scanner (Leica Microsystems), and digital images were analyzed by a blinded pathologist (LF). The number of positive staining cells per area was counted in three random areas and averaged.

TUNEL assay

Detection of apoptotic cells by the TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay was performed using terminal transferase (Roche, Basel, Switzerland), dATP (Sigma-Aldrich, St. Louis, MO, USA), and DIG-11-dUTP (Roche, Basel, Switzerland) according to manufacturer instructions. The number of TUNEL-positive cells was assessed in four random areas and analyzed by a blinded pathologist (LF).

Quantitative real-time PCR

RNA from mouse ureters and kidneys was isolated using TRIzol (Invitrogen, Carlsbad, CA, USA) according to manufacturer instructions. cDNA was synthesized using total RNA isolated via a Transcriptor First Strand cDNA Synthesis Kit (Roche, Basel, Switzerland) with random hexamer primers. qPCR was performed using FastStart Universal SYBR Green Master (Rox) (Roche, Basel, Switzerland). Experimentally validated primers specific to mouse EpoR, Csf2rb1 (βcr), Bcl2l1 (Bcl-xl), Bax, and Actb (β-actin) were purchased from GeneCopoeia (Rockville, MD, USA) and EPO primer from Qiagen (Hilden, Germany). qPCR assays were performed on a Life Technologies ViiA 7 Real-Time PCR System (Thermo Fisher, Waltham, MA, USA). Triplicate CT values were averaged and normalized to β-actin (endogenous control). RNA expression of obstructed ureters and kidneys was compared to that of the contralateral side in each mouse exposed to the procedure.

Hemodynamic analysis

Blood samples were obtained from the renal vena cava of sedated mice. Samples were analyzed using a blood gas/electrolyte analyzer VetScan VS2 (Abaxis, Union City, CA, USA).

Statistical analysis

Statistical analysis was performed with GraphPad Prism 8. Mean was analyzed using either t-test, Fisher’s exact test, or ANOVA test followed by Tukey’s multiple comparison test as appropriate. Data are represented as mean ± SEM. p < 0.05 was considered statistically significant.

Results

Effect of obstruction on ureteral peristaltic function

Our previous work showed ureteral peristalsis to be significantly impaired following UUO. To ensure that this phenotype was observed in the present study, we quantified peristaltic activity of obstructed and unobstructed contralateral ureters microscopically. After 24-h UUO, 70% of obstructed ureters showed no peristalsis (0.16-fold, p < 0.001). By 48 to 72 h post-obstruction, all obstructed ureters were aperistaltic (p < 0.01). Ureteral obstruction induced severe distension of ureters and renal tubules (Fig. 1A). Surprisingly, decreased peristaltic activity of contralateral unobstructed ureters was observed in animals following 48-h UUO, while normal peristaltic function was observed in animals with 72-h UUO.

Fig. 1.

Fig. 1

Open in a new tab

Effect of obstruction on ureteral peristaltic function with or without EPO treatment. (A) Ureteral peristalsis after 24 and 72-h UUO with EPO pre-treatment. Double asterisks indicate p < 0.01. Triple asterisks indicate p < 0.001. Quadruple asterisks indicate p < 0.0001 BL/6, C57BL/6. (B) Representative photo of upper urinary tract dilation after 72-h UUO in one animal (right: obstructed, left: unobstructed). (C) Effect of EPO treatment on peristalsis of normal ureters

Effect of EPO on peristalsis of obstructed ureters

To determine the effect of EPO treatment on ureteral function, we quantified ureteral peristalsis in both ureters of unilaterally obstructed animals. As is shown in Fig. 1D, EPO treatment for 72 h did not change ureteral peristaltic activity in the absence of obstruction. In contrast, EPO pre-treatment prior to 24-h UUO resulted in greater peristaltic activity in obstructed ureters, though this did not rise to the level of significance (2.2-fold, p = 0.0698). Eighty percent of 24-h UUO ureters retained peristaltic function with EPO pre-treatment compared to 30% without treatment. Interestingly, one out of ten 72-h UUO ureters retained peristaltic activity with EPO pre-treatment, compared to none in the untreated group.

Effect of EPO on erythropoiesis

EPO expression is known to be increased in the kidney in response to hypoxic conditions caused by decreased blood flow in obstructed kidneys, triggering erythropoiesis to increase red blood cell production (Hegarty et al. 2001). To determine whether any effect on ureteral peristalsis by EPO could be attributed to erythropoiesis, we studied whether EPO treatment with 20 IU’s was sufficient to change red blood cell levels during the acute period involved in our study. Compared to saline treatment, EPO treatment neither enhanced nor reduced RBC counts (1.03-fold, 9.280 vs 9.008, p = 0.6824, normal range: 7.0–12.0 *1012/L), hematocrit (1.12-fold, 15.920 vs 14.18, p = 0.1616, normal range: 12.2–16.2%), and hemoglobin (1.08-fold, 45.02 vs 41.45, p = 0.2063, normal range: 35.0–45.0 g/dl), respectively, suggesting that EPO treatment did not influence erythropoiesis during the period of our experiment.

Effect of EPO on apoptosis in obstructed ureters

To determine whether EPO treatment prior to UUO had an effect on the level of apoptosis in obstructed ureters, we performed TUNEL immunostaining on tissues from obstructed and unobstructed ureters. Ureters obstructed for 72 h showed more intense staining indicative of increased apoptosis compared to contralateral unobstructed ureters (2.21-fold, p < 0.05). Prophylactic EPO treatment suppressed apoptosis in 72 h obstructed ureters (5.78-fold, p < 0.05) compared to that in untreated animals. There was no difference in the level of apoptosis of untreated and EPO-treated contralateral ureters in obstructed animals (0.50-fold, p = 0.9404). The ratio of TUNEL immunostaining in obstructed ureters compared to its own contralateral ureter in individual mice was decreased after EPO treatment (0.31-fold, p < 0.01).

Effect of EPO on EpoR-βcR signaling after UUO

To validate our previous findings of ureteral EPO expression and to examine the effect of obstruction on EpoR signaling, we analyzed EPO, EpoR-βcR, and its downstream apoptosis-related regulatory genes in UUO ureters and kidneys. Overall, we observed decreased expression of EPO along with that of anti-apoptotic genes in both ureters and kidneys following UUO. EPO and EpoR were down-regulated by UUO, and βcR was up-regulated in obstructed kidneys. The downstream anti-apoptotic gene Bcl-xl was also down-regulated in UUO ureters and kidneys. The downstream pro-apoptotic downstream gene Bax was down-regulated in EPO-treated UUO ureters, whereas no difference was found in obstructed ureters without treatment.

Phospho-Nf-κb p65 immunostaining in ureters from non-treated animals obstructed for 72 h increased in the epithelium (1.19-fold, p < 0.05). EPO treatment suppressed Nf-κb activation compared to contralateral ureters (0.75-fold, p < 0.05), and phospho-Nf-κb staining did not differ in obstructed and contralateral unobstructed ureters after EPO treatment (0.89-fold, p = 0.2035).

Discussion

The overall results from the current study suggest that EPO-induced protection of ureteral function following UUO is via the suppression of apoptosis. Ureteral function was lost in the majority of animals after 24-h obstruction and completely lost after 48-h obstruction. This indicates that the adverse effects of obstruction on ureteral function develop within the first 24 h. Similar results have previously been reported for partial ureteral obstructions as well (Janssen et al. 2017; Ryan et al. 1994). Furthermore, significantly delayed recovery of ureteral peristalsis following obstruction reversal has previously been reported (Janssen et al. 2015). As a result, early intervention to promote recovery of normal ureteral function following obstruction reversal is important to decrease prolonged negative effects on renal function. In the present study, EPO pre-treatment promoted recovery of ureteral function from aperistalsis after 24-h UUO, not only validating previously reported beneficial effects of EPO by our group (Janssen et al. 2015) but confirming that any mechanistic changes identified in the present work contribute directly to promoting ureteral recovery following UUO.

To our knowledge, the present study is the first to study peristaltic function of contralateral ureters following UUO. Interestingly, the peristaltic activity of unobstructed contralateral ureters was found to be decreased after 48-h UUO. While this is not likely a direct response to the obstruction itself, it is possible that contralateral ureters may respond to systemic acute inflammatory cytokines released as a result of the obstruction (Jay and Nicol 2017). The fact that this effect was not observed at 24 h is supportive of this, as cytokines need some time to be triggered and reach sites distant from the original insult and affect contralateral function. Cytokines in the absence of inflammatory insult have been shown to affect intestinal smooth muscle contractility (Akiho et al. 2002). That said, any negative effect on contralateral ureteral function appears to only be transient, as contralateral ureteral function was similar to basal levels in the 72-h obstructed animals.

Given that one of the major functions of EPO is to respond to hypoxic conditions via erythropoiesis, we wanted to determine whether this also played a role in promoting recovery of ureteral function following UUO reversal, as obstruction may cause a hypoxic environment within the ureteral tissues. No significant differences were observed in the hematologic studies, indicating that erythropoiesis was not triggered in the timeframe of our studies, which is consistent with previous reports showing erythropoietic effects following EPO administration to be triggered 2 weeks after the start of treatment in rodents (Srisawat et al. 2008). This suggests that the protective effect of EPO observed in the current study is driven by mechanisms independent of any erythropoietic effects.

Previous studies using non-erythropoietic derivatives of EPO have exhibited protective effects against obstructive nephropathy via activation of an EpoR-βcR heteroreceptor (Kitamura et al. 2008; Srisawat et al. 2008). To better understand a potential role for mechanisms involving the heteroreceptor, we studied the expression of Epo, EpoR, and βcR in both ureters and kidneys of unilaterally obstructed animals. Overall, the pattern of expression observed in this study was consistent with that from our previous study (Janssen et al. 2015). In addition to this, results from the present study showed Epo and its receptor to be down-regulated as a physiological response towards obstruction in both ureters and kidneys with subsequent activation of apoptotic pathways. This is consistent with previous studies showing that injury-induced cellular stress results in decreased EPO-signaling (Dzietko et al. 2004; La Ferla et al. 2002). In this study, supplemental EPO was shown to promote recovery despite decreased EPOR expression, which may be due to EPO supplementation providing ligand for the few receptors that may still be expressed under these injury conditions. While we did find increased βcR expression in obstructed kidneys, this may be reflective of increased inflammatory processes in the injured tissue (including Nfĸb activation) rather than a reflection of increased signaling through the EPOR- βcR heterodimer pathway. More targeted studies are required to determine the role of this pathway in promoting EPO-induced accelerated recovery of ureteral peristalsis following UUO.

One mechanism induced by EPO to protect tissues from injury is decreasing apoptosis, which could also play a role in our model as previous studies have reported UUO-induced apoptosis in ureteral myocytes and renal tubules (Chuang et al. 2001; Miyajima et al. 2000). To determine whether this is a potential mechanism in our model, we studied apoptosis in ureteral tissues from obstructed and unobstructed ureters. We chose to study apoptosis in tissues from animals obstructed for 72 h as we believed the degree of injury to be greatest in this group. Overall, we found increased apoptosis in ureteral tissues following 72-h UUO, which may be a response to overstretching of ureteral epithelial cells due to increased pressure buildup from accumulating urine in the obstructed ureter and development of hydronephrosis (Fig. 1B). Along with increased TUNEL staining, the expression of the anti-apoptotic Bcl-xl, an important BCL-2 family regulator of apoptosis, was significantly decreased in obstructed ureters. It must be pointed out that while we did still observe significant differences in apoptosis between EPO-treated and untreated animals after 72-h UUO, this difference may be an underestimation as a large proportion of apoptotic cells may already have been removed via phagocytes as part of the early inflammatory response, meaning that differences may be greater at earlier timepoints (24 and 48-h) where we also observed accelerated recovery of peristaltic activity Figs 2, 3 and 4.

Fig. 2.

Fig. 2

Open in a new tab

Effect of EPO treatment on erythropoiesis over a 72- h period. Erythropoietic measurement after treatment with EPO or saline (control). RBC, red blood cell count. HGB, hemoglobin. HCT, hematocrit

Fig. 3.

Fig. 3

Open in a new tab

Effect of EPO treatment on apoptosis in 72-h obstructed ureters as determined via a TUNEL assay. (A) Representative photomicrographs of TUNEL straining following 72-h UUO. (B) Quantitative analysis of TUNEL-positive cells in 72-h UUO ureters and unobstructed contralateral ureters with or without EPO pre-treatment. Asterisk indicates p < 0.05. Contra, contralateral

Fig. 4.

Fig. 4

Open in a new tab

Effect of EPO treatment on EPOR signaling in UUO ureter and kidney. (A) RNA expression of Epo, EpoR, βcr, Bax, and Bcl-xl normalized by β-actin in ureters and kidneys after 72-h UUO was analyzed by qRT-PCR. (B) Representative photomicrographs showing immunohistochemical staining for phospho-Nf-ĸb p65 following 72-h UUO. (C) Quantitative analysis of phospho-Nf-ĸb staining in 72-h UUO urothelium. Asterisk indicates p < 0.05. Ctrl, untreated control. Obst, obstruction. Contra, contralateral

Stretch-induced apoptosis of renal tubular epithelial cells has previously been observed (Power et al. 2004), and it is possible that apoptosis of ureteral cells may be the result of overstretching due to development of hydroureter. This is also supported by the fact that apoptosis was increased in dysfunctional ureters associated with congenital obstructive uropathy, a condition leading to severe hydroureter and hydronephrosis (Kajbafzadeh et al. 2006; Kang et al. 2009). Apoptosis of ureteral cells may explain the significant delay in ureteral recovery following UUO reversal observed in our previous study (Janssen et al. 2015), as time is required for cells to regenerate and recover their function following the apoptosis in response to the obstructive insult.

Overall our findings are in line with studies showing the anti-apoptotic effects of EPO treatment in obstructed kidneys (Chang et al. 2009), as apoptosis in ureteral tissues of EPO-treated animals exposed to UUO for 72 h was significantly decreased. This decrease in apoptosis may in part be driven by down-regulation of pro-apoptotic Bax, the expression of which was decreased in obstructed compared to unobstructed contralateral ureters of EPO-treated animals. Several studies have shown that EPO decreased apoptosis by down-regulating Bax in renal ischemic injury (Johnson et al. 2006; Yang et al. 2003). Prolonged UUO was shown to up-regulate Bax and increase apoptosis in ureteral myocytes (Chuang et al. 2002), suggesting the importance of Bax in transmitting apoptotic signaling in obstructive uropathy, which is blocked by EPO treatment. Our studies are the first to show this effect of EPO in the ureter in the context of UUO.

Together with the results from the present study, this indicates that EPO-induced protection of the upper urinary tract in the setting of UUO via an anti-apoptotic mechanism occurs not only directly in the kidney but also via improvement of peristaltic function to accelerate recovery of overall urinary tract function. Given that no difference was found in the level of apoptosis between obstructed and unobstructed contralateral ureters in EPO-treated animals indicates the significant role EPO-induced signaling has on protecting the urinary tract from negative effects of UUO. Our previous and present publications are the first to show a role for EPO in protecting the upper urinary tract via its effect on the ureter.

EPO-induced anti-apoptotic mechanisms have previously been shown to be mediated via suppression of Nf-ĸb p65 in obstructed kidneys, where it plays a role in fibrosis and deformation of smooth muscle (Nakatani et al. 2002; Tashiro et al. 2003; Acikgoz et al. 2014). Results from the present study suggest that a similar mechanism plays a role in the ureter, as EPO treatment was shown to decrease the expression of Nf-ĸb p65 in obstructed ureters, while it was up-regulated in the absence of treatment. Our finding is in line with studies by Chuang et al. where inhibition of Nf-ĸb suppressed apoptosis in obstructed ureteral smooth muscle (Chuang et al. 2009).

It must be pointed out that the anti-apoptotic effect triggered by EPO may involve additional mechanisms not investigated here, including the role of other BCL-2 family regulators of apoptosis such as BAK and BAD as well as their translational and post-translational regulation. Similarly, signaling through EPOR may induce additional downstream pathways not investigated here. The present work is the first to show that the activation of anti-apoptotic mechanisms in the ureter results in accelerated recovery of ureteral peristalsis following UUO reversal. The fact that this accelerated recovery was only observed in the **24-h UUO group may be due to the duration of EPO administration, as 3-day prophylactic treatment may only result in protective functions that are “short-lived.” Future studies in our laboratory are focusing on the effect of varying the time of EPO administration pre-, intra-, and post-UUO to identify which timeline gives the most protection. The present work illustrates that EPO acts by decreasing apoptosis from UUO and lays the foundation for studies to identify additional mechanisms that could be the target for future therapeutic agents, as EPOs use is limited by a serious side-effect profile and significant expense.

Conclusion

EPO treatment protected ureteral function and accelerated its recovery from obstructive injury via an anti-apoptotic mechanism. EPO may be a novel pharmacological intervention to treat ureteral dysfunction and renal damage after removal of ureteral obstruction.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

  1. Acikgoz Y, Can B, Bek K, Acikgoz A, Ozkaya O, Genc G, Sarikaya S. The effect of simvastatin and erythropoietin on renal fibrosis in rats with unilateral ureteral obstruction. Ren Fail. 2014;36(2):252–257. doi: 10.3109/0886022X.2013.836936. [DOI] [PubMed] [Google Scholar]
  2. Akiho H, Blennerhassett P, Deng Y, Collins SM. Role of IL-4, IL-13, and STAT6 in inflammation-induced hypercontractility of murine smooth muscle cells. Am J Physiol Gastrointest Liver Physiol. 2002;282(2):G22–G232. doi: 10.1152/ajpgi.2002.282.2.G226. [DOI] [PubMed] [Google Scholar]
  3. Brines M, Grasso G, Fiordaliso F, Sfacteria A, Ghezzi P, Fratelli M, et al. Erythropoietin mediates tissue protection through an erythropoietin and common β-subunit heteroreceptor. Proc Natl Acad Sci U S A. 2004;101(41):14907–14912. doi: 10.1073/pnas.0406491101. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Chang Y, Choi DE, Na K, Lee S, Suh K, Kim SY, Shin YT, Lee KW. Erythropoietin attenuates renal injury in an experimental model of rat unilateral ureteral obstruction via anti-inflammatory and anti-apoptotic effects. J Urol. 2009;181(3):1434–1443. doi: 10.1016/j.juro.2008.10.105. [DOI] [PubMed] [Google Scholar]
  5. Chuang Y, Chuang W, Huang S, Huang C. Over-expression of apoptosis-related proteins contributes to muscular damage in the obstructed ureter of the rat. BJU Int. 2002;89(1):106–112. doi: 10.1046/j.1464-410X.2002.02554.x. [DOI] [PubMed] [Google Scholar]
  6. Chuang Y, Chuang W, Huang C. Myocyte apoptosis in the pathogenesis of ureteral damage in rats with obstructive uropathy. Urology. 2001;58(3):463–470. doi: 10.1016/S0090-4295(01)01260-2. [DOI] [PubMed] [Google Scholar]
  7. Chuang Y, Chuang W, Huang S, Liu C, Huang C. Inhibition of nuclear factor-kappa B (NF-κB) activation attenuates ureteric damage in obstructive uropathy. Pharmacol Res. 2009;60(4):347–357. doi: 10.1016/j.phrs.2009.05.004. [DOI] [PubMed] [Google Scholar]
  8. Dzietko M, Felderhoff-Mueser U, Sifringer M, Krutz B, Bittigau P, Thor F, Heumann R, Bührer C, Ikonomidou C, Hansen HH. Erythropoietin protects the developing brain against N-methyl-D-aspartate receptor antagonist neurotoxicity. Neurobiol Dis. 2004;15(2):177–187. doi: 10.1016/j.nbd.2003.10.006. [DOI] [PubMed] [Google Scholar]
  9. Fares F, Havron A, Fima E (2011, 2011) Designing a long acting erythropoietin by fusing three carboxyl-terminal peptides of human chorionic gonadotropin subunit to the N-terminal and C-terminal coding sequence. Int J Cell Biol [DOI] [PMC free article] [PubMed]
  10. Ghezzi P, Brines M. Erythropoietin as an antiapoptotic, tissue-protective cytokine. Cell Death Differ. 2004;11:S3–S44. doi: 10.1038/sj.cdd.4401450. [DOI] [PubMed] [Google Scholar]
  11. Hegarty NJ, Young LS, Kirwan CN, O'Neill AJ, Bouchier-Hayes DM, Sweeney P, Watson RW, Fitzpatrick JM. Nitric oxide in unilateral ureteral obstruction: effect on regional renal blood flow. Kidney Int. 2001;59(3):1059–1065. doi: 10.1046/j.1523-1755.2001.0590031059.x. [DOI] [PubMed] [Google Scholar]
  12. Janssen C, Buttyan R, Seow CY, Jäger W, Solomon D, Fazli L, et al. A role for the hedgehog effector Gli1 in mediating stent-induced ureteral smooth muscle dysfunction and aperistalsis. Urology. 2017;104(242):e-242–e-2e8. doi: 10.1016/j.urology.2017.01.029. [DOI] [PubMed] [Google Scholar]
  13. Janssen C, Jger W, Moskalev I, Fazli L, Throff JW, Lange D. Erythropoietin accelerates the regeneration of ureteral function in a murine model of obstructive uropathy. J Urol. 2015;193(2):714–721. doi: 10.1016/j.juro.2014.08.110. [DOI] [PubMed] [Google Scholar]
  14. Jay AP, Nicol DL (2017) Chapter 3: The pathophysiology of upper tract obstruction. In Kulkarni R (ed) Ureteric Stenting, John Wiley & Sons Ltd, p 16–28
  15. Johnson DW, Pat B, Vesey DA, Guan Z, Endre Z, Gobe GC. Delayed administration of darbepoetin or erythropoietin protects against ischemic acute renal injury and failure. Kidney Int. 2006;69(10):1806–1813. doi: 10.1038/sj.ki.5000356. [DOI] [PubMed] [Google Scholar]
  16. Kajbafzadeh A, Payabvash S, Salmasi AH, Monajemzadeh M, Tavangar SM. Smooth muscle cell apoptosis and defective neural development in congenital ureteropelvic junction obstruction. J Urol. 2006;176(2):718–723. doi: 10.1016/j.juro.2006.03.041. [DOI] [PubMed] [Google Scholar]
  17. Kang HJ, Lee HY, Jin MH, Jeong HJ, Han SW. Decreased interstitial cells of Cajal-like cells, possible cause of congenital refluxing megaureters: histopathologic differences in refluxing and obstructive megaureters. Urology. 2009;74(2):318–323. doi: 10.1016/j.urology.2009.02.062. [DOI] [PubMed] [Google Scholar]
  18. Kitamura H, Isaka Y, Takabatake Y, Imamura R, Suzuki C, Takahara S, Imai E. Nonerythropoietic derivative of erythropoietin protects against tubulointerstitial injury in a unilateral ureteral obstruction model. Nephrol Dial Transplant. 2008;23(5):1521–1528. doi: 10.1093/ndt/gfm842. [DOI] [PubMed] [Google Scholar]
  19. La Ferla K, Reimann C, Jelkmann W, Hellwig-Bürgel T. Inhibition of erythropoietin gene expression signaling involves the transcription factors GATA-2 and NF-κB. FASEB J. 2002;16(13):1811–1813. doi: 10.1096/fj.02-0168fje. [DOI] [PubMed] [Google Scholar]
  20. Lennon GM, Ryan PC, Fitzpatrick JM. Recovery of ureteric motility following complete and partial ureteric obstruction. BJU Int. 1993;72(5):702–707. doi: 10.1111/j.1464-410X.1993.tb16251.x. [DOI] [PubMed] [Google Scholar]
  21. Miyajima A, Chen J, Lawrence C, Ledbetter S, Soslow RA, Stern J, et al. Antibody to transforming growth factor-β ameliorates tubular apoptosis in unilateral ureteral obstruction. Kidney Int. 2000;58(6):2301–2313. doi: 10.1046/j.1523-1755.2000.00414.x. [DOI] [PubMed] [Google Scholar]
  22. Nagib EM, El-Sayed MH, Ahmed MA, Youssef MH. Intestinal motility in acute uremia and effects of erythropoietin. Saudi Med J. 2012;33(5):500–507. [PubMed] [Google Scholar]
  23. Nakatani T, Tamada S, Asai T, Iwai Y, Kim T, Tsujino T, et al. Role of renin-angiotensin system and nuclear factor-κB in the obstructed kidney of rats with unilateral ureteral obstruction. Jpn J Pharmacol. 2002;90(4):361–364. doi: 10.1254/jjp.90.361. [DOI] [PubMed] [Google Scholar]
  24. Ozdamar A, Topcu K, Gumustekin M, Gurel D, Gelal A, Ozer E, et al. Erythropoietin restores bowel damage and hypoperistalsis in gastroschisis. J Pediatr Surg. 2006;41(2):352–357. doi: 10.1016/j.jpedsurg.2005.11.012. [DOI] [PubMed] [Google Scholar]
  25. Power RE, Doyle BT, Higgins D, Brady HR, Fitzpatrick JM, Watson RWG. Mechanical deformation induced apoptosis in human proximal renal tubular epithelial cells is caspase dependent. J Urol. 2004;171(1):457–461. doi: 10.1097/01.ju.0000091106.61065.e3. [DOI] [PubMed] [Google Scholar]
  26. Ryan PC, Lennon GM, McLean PA, Fitzpatrick JM. The effects of acute and chronic JJ stent placement on upper urinary tract motility and calculus transit. Br J Urol. 1994;74(4):434–439. doi: 10.1111/j.1464-410X.1994.tb00418.x. [DOI] [PubMed] [Google Scholar]
  27. Srisawat N, Manotham K, Eiam-Ong S, Katavetin P, Praditpornsilpa K, Eiam-Ong S. Erythropoietin and its non-erythropoietic derivative: do they ameliorate renal tubulointerstitial injury in ureteral obstruction? Int J Urol. 2008;15(11):1011–1017. doi: 10.1111/j.1442-2042.2008.02149.x. [DOI] [PubMed] [Google Scholar]
  28. Tashiro K, Tamada S, Kuwabara N, Komiya T, Takekida K, Asai T, et al. Attenuation of renal fibrosis by proteasome inhibition in rat obstructive nephropathy: possible role of nuclear factor κB. Int J Mol Med. 2003;12(4):587–592. [PubMed] [Google Scholar]
  29. Yang CW, Li C, Jung JY, Shin SJ, Choi BS, Lim SW, et al. Preconditioning with erythropoietin protects against subsequent ischemia-reperfusion injury in rat kidney. FASEB J. 2003;17(12):1754–1755. doi: 10.1096/fj.02-1191fje. [DOI] [PubMed] [Google Scholar]

Articles from Cell Stress & Chaperones are provided here courtesy of Elsevier

RESOURCES