Research On The Protective Roles Of Sitagliptin In Mitochondrial Dysfunction In Diabetic Kidney Disease And Underlying Mechanisms

Background: The pathogenesis of diabetic kidney disease(DKD)still unknown,mitochondrial abnormalities play critical roles in diabetic tubular injury progression.Sitagliptin(Sita),is a valid DPP4 inhibitor,which can prevent the degradation of intestinal insulinotropic hormones and promote the release of insulin to control blood glucose.Recent studies also found their renal beneficial roles in non-diabetic animals,which DPP4 inhibitors play their renal protective effect and oxidative stress other than controlling blood glucose in DKD,however,their underlying mechanism remains unclear.So we propose the hypothesis: Sitagliptin alleviate renal tubular injuries and maintain mitochondrial dynamic homeostasis in managing DKD.Objectives: DBA2 / J mice were injected intraperitoneally with streptozotocin(STZ)to induce type 1 diabetic mice,and Sitagliptin was administered by gavage to observe its beneficial effects against tubular injuries and mitochondrial dysfunction in diabetic mice.In vitro,experiments were performed in conditionally immortalized human renal tubular epithelial cells(HK-2 cells)to investigate the mechanism by which Sitagliptin exerts mitochondrial protection,and to explore the possible pathogenetic mechanism and treatment of diabetic nephropathy.Methods: 1.To clarify the changes of blood glucose,kidney pathological damage and proteinuria in STZ-induced diabetic mice when compared to control mice.2.To clarify the gavage treatment of Sitagliptin in STZ-induced diabetic mice whether plays beneficial effects on diabetic renal injuries and mitochondrial dynamics homoestasis,and to further study the effects of sitagliptin treatment on the SDF-1?/CXCR4 pathway in diabetic mice.3.In vitro culture conditional immortalized human HK-2 cells,to clarify whether sitagliptin treatment alleviate human serum albumin(HSA)induced mitochondrial dysfunction and fragmentation in HK-2 cells,and further study the effects on SDF-1? / CXCR4 pathway and mitochondrial STAT3 in HSA-treated HK-2 cells;4.Transfecting the over-expressed DPP4 plasmid into HK-2 cells,and observe the effects of HSA on the expressions of mitochondrial dynamic proteins,SDF-1? / CXCR4 pathway and mitochondrial STAT3 in HK-2 cells.5.By upregulating and downregulating the expression of STAT3 in HK-2 cells,we observe the effects of mitochondrial dynamic protein expressions in HSA-treated HK-2 cells,and further determine whether Sitagliptin treatent regulates the interaction between STAT3 and mitochondrial protein and the potential mechanisms.Results: 1.In comparison to non-diabetic control mice,STZ-induced diabetic mice had improved blood glucose,urinary albumin/creatinine ratios(ACR),serum creatinine and severe renal pathologic injuries;.2.Treating diabetic mice with Sita notably alleviated urinary ACR,improved tubulointerstitial lesions,renal pathological injuries,and alleviated mitochondrial fragmentation,but faied to play significant roles in maintaining blood glucose;3.Sita-treated diabetic mice significantly inhibited the overexpresed DPP4 enzyme activity,improved SDF-1? / CXCR4 pathway activity,and significantly increased mitochondrial STAT3 protein levels;4.Sitagliptin significantly alleviated mitochondrial dysfunction and mitochondrial fragmentation in HSA-induced HK-2 cells,whereas overexpressed DPP4 significantly accentuated mitochondrial injuries of HK-2 cells induced by HSA;5.Sita inhibited the elevated DPP4 expression of HSA-induced HK-2 cells,and significantly improved the expressions of SDF-1? and mitochondrial STAT3.However,overexpression of DPP4 significantly aggravates SDF-1 inhibition and decreased mitochondrial STAT3 expression in HSA-treated HK-2 cells.6.In vitro,we found that STAT3 regulates the expressions of mitochondrial dynamic proteins and has a direct interaction with mitochondrial fusion protein OPA1.Sita may protect STAT3-OPA1 interaction via SDF-1?/CXCR4 pathway to maintain mitochondrial homeostasis in HSA-treated HK-2 cells.Conclusion: The results suggest that a novel mechanism links the DPP4 enzyme to impaired mitochondrial dynamics homeostasis during tubular injury in DKD and highlight that the SDF-1?/CXCR4/STAT3 signalling pathway could become a potential target for managing DKD.