Bcl-2 and Bax expression on rat ischemic kidney

Berberine prevents the apoptosis of mouse podocytes induced by TRAF5 overexpression by suppressing NF-κB activation

Berberine (BBR) has previously been found to exert beneficial effects on renal injury in experimental rats. However, the mechanisms underlying these effects are not yet fully understood. Tumor necrosis factor (TNF) receptor-associated factor 5 (TRAF5) has been demonstrated to mediate the activation of nuclear factor-κB (NF-κB), which has been implicated in the pathogenesis of chronic kidney disease (CKD). The aim of this study was to investigate the effects of BBR on kidney injury and the activation of the NF-κB signaling pathway in mouse podocytes. TRAF5 was found to be overexpressed in patients with CKD and chronic renal failure (CRF) (data obtained from the dataset GSE48944, as well as from patients at Shuguang Hospital). TRAF5 overexpression significantly inhibited cell viability and induced the apoptosis of mouse podocytes. However, BBR prevented the decrease in cell viability and the apoptosis induced by TRAF5 overexpression. The NF-κB inhibitor, caffeic acid phenethyl ester (CAPE), mimicked the protective effects of BBR, as evidenced by the increased expression of nephrin and podocin, and the decreased the expression of caspase-3 and the ratio of Bax/Bcl-2. Moreover, BBR prevented the decrease in cell viability decrease and the apoptosis induced by TNF-α, interleukin (IL)-6 and lipopolysaccharide (LPS). Taken together, our data indicate that BBR exerts protective effects against CRF partly through the TRAF5-mediated activation of the NF-κB signaling pathway in mouse podocytes.

N-cadherin is depleted from proximal tubules in experimental and human acute kidney injury

Ischemia remains the most common cause of acute kidney injury (AKI). Decreased intercellular adhesion and alterations in adhesion molecules may contribute to the loss of renal function observed in AKI. In the present study, we evaluated the distribution of adhesion molecules in the human kidney and analyzed their expression in human and experimental AKI. Specimens of human kidneys obtained from patients with and without AKI were stained for the cell adhesion molecules E-cadherin, N-cadherin and beta-catenin. Experimental AKI in rats was induced by renal artery clamping. Immunostaining and immunoblotting were carried out for E-cadherin, N-cadherin and beta-catenin. Proximal tubule cells from opossum kidneys (OKs) were used to analyze the effect of chemical hypoxia (ATP depletion) in vitro. In the adult human kidney, N-cadherin was expressed in proximal tubules, while E-cadherin was expressed in other nephron segments. beta-Catenin was expressed in both proximal and distal tubules. In human AKI and in ischemic rat kidneys, N-cadherin immunostaining was depleted from proximal tubules. There was no change in E-cadherin or beta-catenin. In vitro, OK cells expressed N-cadherin only in the presence of collagen, and ATP depletion led to a depletion of N-cadherin. Collagen IV staining was reduced in ischemic rat kidneys compared to controls. The results of the study suggest that N-cadherin may play a significant role in human and experimental AKI.

CREB mediates ERK-induced survival of mouse renal tubular cells after oxidant stress

BACKGROUND

We showed that extracellular signal-regulated protein kinase (ERK) is prosurvival during oxidant stress both in the kidney and in cultured mouse proximal tubule (TKPTS) cells and demonstrated concomitant activation of ERK as well as the cyclic adenosine monophosphate (cAMP)-responsive element binding protein (CREB), during survival in vitro. We now show that CREB is a necessary prosurvival target of ERK.

METHODS

Ischemia/reperfusion (I/R) injury was induced in 129Sv mice. Oxidant stress was induced by hydrogen peroxide (H(2)O(2)) in TKPTS cells. Activation of CREB was determined by immunohistochemistry and Western blotting. Inhibition and activation of CREB was achieved by mutant or activated CREB-containing adenoviruses in vitro. The effects of oxidant stress on cell survival, CREB binding, and CREB-mediated transcription was determined by cell counting, gelshift analysis, and luciferase assay, respectively.

RESULTS

I/R activates CREB in the surviving distal nephron segments of the kidney. Inhibition of ERK and CREB abrogates survival after 0.5 mmol/L H(2)O(2) treatment, while overexpression of CREB ameliorates necrotic death caused by 1 mmol/L H(2)O(2). Inhibition of ERK also inhibited CREB activation. Binding of phosphorylated CREB to a CREB oligonucleotide was significantly increased after 0.5 mmol/L H(2)O(2) but decreased after 1 mmol/L H(2)O(2). Similarly, CREB-mediated transcription was significantly increased after 0.5 mmol/L H(2)O(2) treatment, while 1 mmol/L H(2)O(2) inhibited it. Interestingly, transcription from the CREB-driven bcl-2 promoter was unchanged after 0.5 mmol/L but decreased after 1 mmol/L H(2)O(2) treatment in agreement with Western blot studies.

CONCLUSION

We show that survival during oxidant stress is mediated through CREB and identification of its downstream targets will reveal important survival pathways.

Renal cells apoptosis and Bax, Bcl-2 expression in rats with severe acute pancreatitis

AIM: To explore the roles of renal cell apoptosis and expression of Bax and Bcl-2 in renal injury in rats with severe acute pancreatitis (SAP).

METHODS: Thirty rats were randomized into sham operation (SO, n = 15) and SAP group (n = 15). The model of SAP was established by retrograde injection of 50 g/L sodium taurocholate into the biliopancreatic duct in the rats. Serum creatinine (Cr) and blood urea nitrogen (BUN) were determined 6, 12, and 18 h after injection. The pathological changes were observed by light and electron microscopy. The apoptosis of renal cells was determined by TUNEL method, and the expression of Bax and Bcl-2 was detected by immunohistochemical staining (SABC assay).

RESULTS: As compared with those in SO group at the same phase, serum Cr and BUN in SAP group increased markedly. Significant injuries of renal tissue were observed under light and electron microscope.The apoptotic index of renal glomerular cells increased significantly 6, 12, 18 h after injection (3.2±1.1 vs 0.8±0.1, P <0.05; 3.9±1.8 vs 0.9±0.1, P <0.05; 4.8±1.7 vs 0.8±0.2, P <0.01, respectively). The apoptotic index of renal tubule cells also increased significantly (9.8±1.1 vs 1.3±0.5, P <0.01; 12.6±2.3 vs 1.2±0.3, P <0.01; 15.7±2.6 vs 1.3±0.3, P <0.01, respectively). The expression of Bax in renal glomerulus and tubule increased significantly at 6, 12, 18 h, respectively (glomerulus: 3.05±0.86 vs 1.01±0.04, P <0.05; 3.37±1.13 vs 1.06±0.05, P <0.05; 4.11±1.24 vs 1.09±0.03, P <0.05; tubule: 8.17±2.16 vs 1.53±0.07, P <0.01; 12.92±1.81 vs 1.61±0.05, P <0.01; 13.08±2.53 vs 1.59±0.05, P <0.01), and increased continuously. Bcl-2 was mainly expressed in the regions of renal tubule, and it also increased in SAP group at 6, 12, 18 h, respectively (3.38±1.07 vs 1.58±0.02, P <0.05; 4.26±1.13 vs 1.59±0.06, P <0.05; 7.21±1.04 vs 1.61±0.02, P <0.01). The level of Bcl-2 expression in renal glomerulus was higher in SAP group than that in SO group at 6, 12, 18 h, respectively (2.18±0.65 vs 1.04±0.02; 2.42±0.63 vs 1.03±0.05, P <0.05; 2.69±0.47 vs 1.08±0.04, P <0.05), but decreased with the duration of the injuries.

CONCLUSION: Renal cell apoptosis, which relates to the up-regulated expression of Bax and downed regulated expression of Bcl-2, may be involved in the pathogenesis of renal injury in patients with SAP.

Apoptotic mechanisms in acute renal failure

It has been generally accepted that a catastrophic breakdown of regulated cellular homeostasis, known as necrosis, is the mode of cellular injury in various forms of acute renal failure. One of the major advances in our understanding of cell death has been the recognition that the pathways traditionally associated with apoptosis as described in the landmark study by Kerr, Wyllie, and Currie in 1972 maybe very critical in the form of cell injury associated with necrosis. The pathway that is followed by the cell varies with both nature and severity of insults and may evolve from an apoptotic to a necrotic form of cell death. It is also likely that there are some common pathways that are shared and regulated in the two modes of cell death. In this review, we first describe evidence for the role of apoptotic pathways in ischemic acute renal failure, and then consider the potential mechanisms that may participate in this model of acute renal tubular injury. We then summarize the current information of apoptotic pathways related to other common causes of acute renal failure including endotoxin-induced, toxic acute renal failure and transplant rejection. A better understanding of the mechanisms of apoptosis could lead to safer and more specific therapeutic interventions for acute renal failure.