The Role Of SIRT1 In Podocyte Apoptosis In Diabetic Nephropathy

Background and ObjectiveDiabetic nephropathy is a leading cause of end stage renal disease,accounting for up to 40% of patients undergoing renal replacement therapy.Proteinuria is a common clinical feature of diabetic nephropathy.Podocytes play a critical role in the development of diabetic nephropathy.Dysregulation of RAS and high glucose take part in the loss of podocytes.Blockage of the renin-angiotensin system(RAS)with angiotensin II receptor blockers(ARBs)can prevente albuminuria and progressive renal failure in diabetic nephropathy.SIRT1 is a silencing information modulator with NAD +-dependent histone / non-histone deacetylase.It is implicated in the pathogenesis of various diseases,including diabetic nephropathy.SIRT1 is involved in inflammation,apoptosis and fibrosis in diabetic nephropathy.Previous studies have shown that high glucose and Ang-? can affect the expression and activity of SIRT1 through different signaling pathways.Ang-? induced endothelial cell apoptosis by activated P38 / SIRT1 pathway.High glucose induced podocyte apoptosis through AMPK / SIRT1 pathway.Olmesartan inhibited albuminuria only in diabetic patients with better glycemic control,suggesting that high glucose and Ang-? may induce podocyte apoptosis through different pathways.We therefore hypothesized that high glucose and Ang-? induced podocyte apoptosis by different signaling pathways(AMPK / SIRT1 pathway and P38 / SIRT1 pathway).Olmesartan is a common angiotensin?inhibitor,which inhibits the binding of angiotensin?and angiotensin? receptor.It has been demonstrated that Ang-? leads to podocyte apoptosis in diabetic nephropathy.MAP kinase signaling cascade,specifically ERK1/2 pathway,is one of the main mechanisms involved in Ang-II-induced podocyte apoptosis.But the role of Ang-?/P38/SIRT1 pathway in podocyte apoptosis has not been confirmed.Methods1.In vivo animal experiment: 10 to 12-week old db/db mice was divided into two groups.10 diabetic mice and 10 non-diabetic mice(WT)were fed with placebo(0.5% CMC),and 10 diabetic mice were fed with 20 mg/kg olmesartan.Fasting blood glucose was measured at the 2nd,4th,4th,6th,8th,10 th,12th week;24 hours urine protein was collected.Animals were sacrificed at the 12 th week,and the renal tissues were harvested.The pathways were analyzed by western blot and immunostaining.2.In vitro cell experiments: Conditionally immortalized mouse podocytes was cultured and propagated with RPMI 1640(Gibco)containing10% fetal bovine serum and 1 × 104 U / L interferon-? in 33 ? cell box.To induce differentiation,podocytes were maintained without interferon-? at 37°C for 14 days.Differentiated podocytes were treated with glucose,Ang-?,olmesartan or p38 inhibitor s8307 in different experimental conditions.Cells were harvested,the apoptotic cells were extracted by flow cytometry and the pathways were analyzed by western blot.3.statistical analysis: All data are expressed as means ± SD,Graphpad Prism 5.0 software was used to analyse the data.One way ANOVA was used to analyze the statistical differences.P value <0.05 was considered as statistically significant.Result1.Olmesartan administration reduce urine protein in the db / db mouse,but have no effect on body weight and blood glucose.In kidneys of db/db mice,olmesartan prevented podocyte loss via p38/SIRT1 pathway.While the effect on AMPK was little.2.Olmesartan partly inhibited high glucose induced podocyte apoptosis which was triggered by AMPK/SIRT1 pathway.3.Olmesartan inhibited angiotensin II induced podocyte apoptosis via p38/SIRT1 pathway.ConclusionThis study demonstrated that SIRT1 play an important role in protecting podocyte in diabetic nephropathy.High glucose induced podocyte apoptosis by activting AMPK pathway.Angiotensin II induced podocyte apoptosis via the p38 / SIRT1 pathway,which can be inhibited by olmesartan and p38 inhibitor.