Erythropoietin decreases renal fibrosis in mice with ureteral obstruction: role of inhibiting TGF-beta-induced epithelial-to-mesenchymal transition

Lefty A attenuates the TGF-beta1-induced epithelial to mesenchymal transition of human renal proximal epithelial tubular cells

The epithelial to mesenchymal transition (EMT) is a crucial event for renal fibrosis that can be elicited by TGF-beta1/Smads signaling and its downstream mediator connective tissue growth factor (CTGF). As a distinct member of the TGF-beta superfamily, Lefty A has been shown to be significantly downregulated in the kidneys of patients with severe ureteral obstruction, suggesting its role in renal fibrosis induced by obstructive nephropathy. In order to determine whether Lefty A prevents TGF-beta1-induced EMT, human proximal tubule epithelial cells (HK-2) were stably transfected with Lefty A or control vectors and stimulated with 10 ng/ml TGF-beta1 for 48 h. The results show that stimulation with TGF-beta1 led to EMT including cell morphology changes, Smad2/3 signaling pathway activation, increased alpha-SMA, collagen type I, and CTGF expression, and decreased E-cadherin expression in mock-transfected HK-2 cells. Overexpression of Lefty A efficiently blocked p-Smad2/3 activation and attenuated all these EMT changes induced by TGF-beta1. This finding suggests that Lefty A may serve as a potential new therapeutic target to inhibit or even reverse EMT during the process of renal fibrosis.

The effects of low-dose erythropoiesis-stimulating agents on peritoneal fibrosis induced by chemical peritonitis and on peritoneal tissue MMP-2 and TIMP-2 Levels in rats

AIM

The objective of the present study was to investigate the effect of low-dose erytropoesis-stimulating agents (ESA) on the development of peritoneal fibrosis in chlorhexidine gluconate-induced peritoneal sclerosing rats and to assess the peritoneal tissue levels of MMP-2 and TIMP-2, which may be regarded as factors in the development of peritoneal fibrosis.

SUBJECTS AND METHODS

Twenty-four Wistar albino rats were divided into three groups. The control group received 0.9% saline (3 ml/d) intraperitoneally, the CH group received 3 ml daily injections of 0.1% chlorhexidine gluconate (CH) intraperitoneally, and the CH+ESA group received 3 ml daily injections of 0.1% CH intraperitoneally and epoetin beta (3 x 20 IU/kg/week) subcutaneously. On the twenth-first day, rats were sacrificed, and parietal peritoneum samples were obtained from the left anterior abdominal wall. Pathological samples were examined using Hematoxyline & Eosin (HE) stains. The thickness, vascular proliferation, and inflammation were determined by light microscopy. MMP-2 and TIMP-2 were studied immunohistochemically by monoclonal antibody staining.

RESULTS

Inflammation, vascular proliferation, and fibrotic area percentages were not statistically significant between groups. Histopathologically control, CH, CH+ESA groups peritoneal thickness were 8.02 +/- 2.89, 146.74 +/- 26.1, and 48.12 +/- 16.8 micrometers, respectively. The decrease in thickness of parietal peritoneum in CH+ESA group was statistically significant when compared to CH. Immunohistochemically, interferon was shown to decrease MMP-2 expression on parietal peritoneum than group CH, but has no effect on TIMP-2.

DISCUSSION

Low-dose ESA histopatologically reduces peritoneal fibrosis induced by chlorhexidine gluconate. However, from dosage and duration points of view, we need extended clinical and experimental studies.

Erythropoietin attenuates hypertrophy of neonatal rat cardiac myocytes induced by angiotensin-II in vitro

OBJECTIVE

Erythropoietin (EPO) is a haematopoietic hormone that has been confirmed as a novel cardioprotective agent. In this study, we test the hypothesis that EPO inhibits angiotensin-II (Ang-II)-induced hypertrophy in cultured neonatal rat cardiomyocytes.

MATERIAL AND METHODS

Cultured neonatal rat cardiomyocytes were used to evaluate the effects of EPO on Ang-II-induced hypertrophy in vitro. The surface area and mRNA expression of atrial natriuretic (ANF) myocytes were employed to detect cardiac hypertrophy. A phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002 and an endothelial nitric oxide synthase (eNOS) inhibitor L-NAME were also employed to detect the underlying mechanism of EPO. Intracellular signal molecules, such as Akt (PKB), phosphorylated Akt, eNOS and transforming growth factor-beta1 (TGF-beta1) protein expression were determined by Western blot. Nitric oxide (NO) levels in the supernatant of cultured cardiomyocytes were assayed using an NO assay kit.

RESULTS

The results indicate that EPO significantly attenuates Ang-II-induced hypertrophy shown as inhibition of increases in cell surface area and ANF mRNA levels. NO production was also increased proportionally in the EPO-treated group. EPO enhanced Akt activation and eNOS protein expression, whereas LY294002 or L-NAME partially abolished the anti-hypertrophic effect of EPO, accompanied by a decrease in Akt activation, eNOS protein expression and/or a reduction of NO production. EPO also down-regulated the protein expression of TGF-beta1.

CONCLUSION

We conclude that EPO attenuates cardiac hypertrophy via activation of the PI3K-Akt-eNOS-NO pathway and the down-regulation of TGF-beta1.

Age-dependent renal expression of acid-base transporters in neonatal ureter obstruction

Congenital obstructive nephropathy accounts for a major proportion of renal insufficiency in infancy and childhood. In an earlier investigation we demonstrated that bilateral complete ureteral obstruction (BUO) in rats is associated with inadequate urinary acidification [Am J Physiol Renal Physiol. 295(2):F497-506, 2008]. The aim of the study reported here was to determine whether this defect is also associated with unilateral ureteral obstruction (UUO), which is clinically more common than BUO. The time-course of the changes in protein expression levels of major renal acid-base transporters was examined at 7 and 14 weeks in rats with neonatally induced partial unilateral ureteral obstruction (PUUO), which was performed within the first 48 h of life. We observed that protein expression of the renal acid-base transporters NHE3, NBC1, NBCn1, pendrin and Na(+)-K(+)-ATPase was increased in both obstructed and non-obstructed kidneys 7 weeks after the induction of neonatal PUUO. This was confirmed by immunocytochemistry. In contrast, 14 weeks after the induction of PUUO, there was a significant downregulation of the renal acid-base transporters NBC1, NBCn1 and Na(+)-K(+)-ATPase in the obstructed kidneys. These time/age-dependent changes in protein expression were associated with parallel changes in renal function resulting in urine acidification in response to exogenous acid loading. In conclusion, these results show that downregulation of protein expression is a time/age-dependent response to PUUO, which could contribute to the decreased net acid excretion and development of metabolic acidosis in neonatal rats with PUUO.

Mast cells decrease renal fibrosis in unilateral ureteral obstruction

Mast cells regulate both inflammatory responses and tissue repair in human diseases but there are conflicting reports on the role of these cells in the pathogenesis of various kidney diseases. Here we measured mast cell function in unilateral ureteral obstruction, a well-characterized model of renal fibrosis, using Kit(W)/Kit(W-v) mice genetically deficient in mast cells, wild-type mice, and deficient mice reconstituted by adoptive transfer with mast cells from the wild-type animals. Mast cell-deficient mice had higher levels of renal tubular damage, more stromal fibrosis, higher numbers of infiltrating ERHR3-positive macrophages and CD3-positive T cells, and higher tissue levels of profibrotic transforming growth factor-beta1 than wild-type mice or mice reconstituted by adoptive transfer of mast cells 3 weeks after ureteral obstruction. Similarly, while wild-type and adoptively transferred mice had increased alpha-smooth muscle actin and decreased E-cadherin expression, which are indicators of epithelial-mesenchymal transition, the obstructed kidneys of the mast cell-deficient mice had significant attenuation of those indicators. Thus, our study suggests that mast cells protect the kidney against fibrosis by modulation of inflammatory cell infiltration and by transforming growth factor-beta1-driven epithelial-to-mesenchymal transitions.

Erythropoietin attenuates renal injury in an experimental model of rat unilateral ureteral obstruction via anti-inflammatory and anti-apoptotic effects

PURPOSE

Erythropoietin was recently shown to exert important cytoprotective and anti-apoptotic effects in injury models of the brain, heart and kidney. We examined whether erythropoietin also attenuates renal injury in a rat model of unilateral ureteral obstruction via anti-apoptotic and anti-inflammatory actions.

MATERIALS AND METHODS

We divided Sprague-Dawley rats (Korea Research Institute of Bioscience and Biotechnology, Daejeon, Korea) into 4 groups, including 1-vehicle treated with sham operation, 2-vehicle treated with unilateral ureteral obstruction for 3 days, 3-erythropoietin treatment with sham operation and 4-erythropoietin treatment for unilateral ureteral obstruction for 3 days. The erythropoietin treatment dose was 3,000 IU/kg per day intraperitoneally, administered daily. We compared competitive reverse transcriptase-polymerase chain reaction data on transforming growth factor-beta, tumor necrosis factor-alpha, monocyte chemoattractant protein-1, osteopontin, Fas and Bcl-2. Furthermore, we examined Western blots for caspase-3 and light microscopy findings with hematoxylin and eosin staining. We applied immunohistochemistry for transforming growth factor-beta, ED-1 and caspase-3, and TUNEL in each group.

RESULTS

Transforming growth factor-beta, tumor necrosis factor-alpha, monocyte chemoattractant protein-1, osteopontin and Fas mRNA levels in the erythropoietin treated, unilateral ureteral obstruction group were significantly lower than in the obstruction only group. The Bcl-2 mRNA level in the erythropoietin treated obstruction group was significantly higher than in the obstruction only group. Caspase-3 activity in the erythropoietin treated obstruction group was significantly lower than in the obstruction only group. On light microscopy interstitially infiltrated inflammatory cells were significantly decreased in the erythropoietin treated obstruction group compared to the obstruction only group. On immunohistochemistry the erythropoietin treated obstruction group showed significantly fewer reactions for transforming growth factor-beta, ED-1 and caspase-3 compared to the obstruction only group. Erythropoietin treatment in rats with unilateral ureteral obstruction significantly decreased the number of TUNEL positive cells.

CONCLUSIONS

Erythropoietin exerts renoprotective effects in an experimental unilateral ureteral obstruction rat model via anti-apoptotic and anti-inflammatory actions.

Increased E-cadherin expression in the ligated kidney following unilateral ureteric obstruction

E-cadherin expression in the kidney is used as a surrogate marker of epithelial mesenchymal transition for the testing of various antifibrotic strategies. Here we reexamined E-cadherin expression in the kidneys of rats with unilateral ureteric obstruction, which was previously reported to decrease in parallel with the development of tubulointerstitial disease in this widely used experimental model of renal fibrosis and epithelial mesenchymal transition. E-cadherin mRNA expression was consistently increased both acutely (hours) and chronically (days) in the ligated kidney compared to the cognate non-ligated kidney. Increased E-cadherin protein levels were also found in the ligated kidney particularly in dilated tubular segments. Simulation of early pressure changes in the ligated kidney by mechanical stretch of human renal epithelial cells in culture did not alter E-cadherin expression. Porcine LLCPK-1 cells subjected to hypotonic stretch, however, did have increased E-cadherin mRNA and protein levels, responses that were not prevented by transforming growth factor-beta, a cytokine that promotes epithelial mesenchymal transition. Our findings question the utility of E-cadherin as a marker of epithelial mesenchymal transition in this model of renal fibrosis.

Epithelial-to-mesenchymal transition and chronic allograft tubulointerstitial fibrosis

Chronic allograft tubular atrophy/interstitial fibrosis (TA/IF) is a major cause of late allograft loss. A major challenge to the future of kidney transplantation is to dissect the identifiable causes of chronic allograft TA/IF and to develop cause-specific treatment strategies. Emerging evidence suggests that epithelial-to-mesenchymal transition (EMT) is an important event in native and transplant kidney injury, including chronic allograft TA/IF. During EMT, tubular epithelial cells are transformed into myofibroblasts through a stepwise process including loss of cell-cell adhesion and E-cadherin expression, de novo alpha-smooth muscle actin expression, actin reorganization, tubular basement membrane disruption, cell migration, and fibroblast invasion with production of profibrotic molecules such as collagen types I and III and fibronectin. We examined in this review the molecular and cellular pathways of EMT and their involvement in chronic allograft tubulointerstitial fibrosis. We examined the role of alloimmune T cells and oxidative stress in this context and evaluated EMT as a marker of disease progression. Potential therapeutic options are discussed. In conclusion, there is enough evidence demonstrating that EMT is involved in the pathogenesis of chronic allograft tubulointerstitial fibrosis. However, the extent of its contribution to allograft fibrogenesis remains unknown, and only interventional trials will enable us to clarify this question. Furthermore, additional data are required to determine whether EMT may be used as a surrogate marker of disease progression in kidney transplant recipients.

Heme oxygenase-1 deficiency promotes epithelial-mesenchymal transition and renal fibrosis

Induction of heme oxygenase-1 (HO-1) is associated with potential antifibrogenic effects. The effects of HO-1 expression on epithelial-mesenchymal transition (EMT), which plays a critical role in the development of renal fibrosis, are unknown. In this study, HO-1(-/-) mice demonstrated significantly more fibrosis after 7 d of unilateral ureteral obstruction compared with wild-type mice, despite similar degrees of hydronephrosis. The obstructed kidneys of HO-1(-/-) mice also had greater macrophage infiltration and renal tubular TGF-beta1 expression than wild-type mice. In addition, the degree of EMT was more extensive in obstructed HO-1(-/-) kidneys, as assessed by alpha-smooth muscle actin and expression of S100A4 in proximal tubular epithelial cells. In vitro studies using proximal tubular cells isolated from HO-1(-/-) and wild-type kidneys confirmed these observations. In conclusion, HO-1 deficiency is associated with increased fibrosis, tubular TGF-beta1 expression, inflammation, and enhanced EMT in obstructive kidney disease. Modulation of the HO-1 pathway may provide a new therapeutic approach to progressive renal diseases.

Snail1 is involved in the renal epithelial–mesenchymal transition

The pathological significance of the tubular epithelial-mesenchymal transition (EMT) in kidney diseases is becoming increasingly recognized, and the transcription factor Snail1 plays a critical role in EMT. The results of this study show that Snail1 mRNA and protein were upregulated in the tubular epithelial cells of the obstructed kidneys in a rat model of unilateral ureteral obstruction and in human proximal tubule HKC-8 cells treated with TGF-beta1. Glycogen synthase kinase-3beta (GSK-3beta) regulates the Snail1 level by degrading Snail1 protein. The level of the phosphorylated inactive form of GSK-3beta was increased in the tubular epithelial cells of the obstructed kidney. TGF-beta1 increased the phosphorylated form of GSK-3beta in HKC-8 cells, and inhibition of GSK-3beta by the selective inhibitors lithium and TDZD-8 caused Snail1 protein to accumulate. This study demonstrated that Snail1 is involved in renal tubular EMT and that TGF-beta1 regulates Snail1 at the transcription and protein degradation levels.