The Mechanism Of Saxagliptin Protect Islets Function In Diabetic Rats Via Inhibit SDF-1α Degretion

ObjectiveDiabetes mellitus(DM) is a complicated disease characterized by glucose and lipid metabolism disorder and and beta-cell failure represent the core defects. Under regular conditions, the mass of islet beta cells depend on the mass of pancreas progenitor cells and sustain the overall balance among proliferation, necrosis or apoptosis. Currently, the apoptosis process of β cell have been widely researched.The progressive damage of beta cell is inevitable even the glucose levels was well controlled. Therefor, distinguish potential factors that could promote beta cell proliferation is a critical task. Stromal cell-derived factor(SDF)-1/CXCL12 is a small peptide chemokine and now recognized it could induce the downstream wnt signaling pathway and had a role in promote β cell proliferation. But dipeptidyl peptidase 4, an ubiquitous serine proteases, could degradation the SDF-1 that increased in type 2 diabetes patients and eliminate the SDF-1’s beneficial effect on βcell. Therefore, our present study intended to observe the influences of a DPP-4inhibitor, saxagliptin, on the activity of DPP-4, expression of SDF-1 α and islet function of an animal model of type 2 diabetes mellitus induced by HFD+STZ and investigate the underlying mechanism in the same time.MethodsThe male SD rats of 8 weeks old randomly divided into N(n=8), D(n=8) and S(n=8) group. N was the normal control group, feeding with regular diets. After 8weeks, the rats were injected with citrate buffer liquid in tail vein; D and S were the type 2 diabetes model group and the saxagliptin group respectively, feeding with the high-fat diets, 8 weeks later injected the aqueous solution of streptozotocin(STZ) at a dose of 30mg/Kg body weight in tail vein. Begin the end of the ninth week,saxagliptin was administered orally by a gavage needle once daily at the dose of 1mg/kg and vehicle was used as control. The body weight and the blood glucose were measured each week or every two weeks respectively. After twelve weeks,hyperglycemic clamps were performed to evaluate function of pancreatic β cells.Weight the pancreatic tissue of SD rats, and fixed one part of pancreatic tissue by10% formaldehyde. Use haematoxylin and eosin staining to assessed the structure of pancreas. Immunohistochemistry with anti-PCNA was performed to observe the proliferation rate of pancreatic β cells. Immunofluorescence double staining with anti-insulin, anti-glucagon and anti-SDF-1ɑ were performed to observe the expression of insulin, glucagon and SDF-1ɑ in pancreatic tissue. Western blot was performed to test the expression of Akt、p-Akt、βcatenin and free-βcatenin protein and Reverse Transcription Polymerase Chain Reaction(RT-PCR) was performed to test the level of c-myc and cyclin D1 m RNA in pancreatic tissue.Results⑴ Compared with N group, the level of FBG of D and S group increased and body weight reduced, but there were no significant difference in the level of FBG and body weight between D and S group.⑵ At the end of twelfth week, the plasma level of ALT, AST, BUN, TC, TG and LDL were significantly elevated; compared with D groups, saxagliptin interference significantly improved the level of ALT, BUN and TG.⑶ At the end of twelfth week, hyperglycemic clamp shown that STZ attenuated both first and second phase of insulin secretion in STZ- treated rats, but saxagliptin incompletely reversed the attenuation.⑷ At the end of twelfth week, the structure of pancreas of D group arranged disordered, and the cells in islets arranged irregularly and vacuolar degeneration of pancreas of was frequently found. However, the structure of pancreas of the saxagliptin interference group arranged orderly and swelling and necrosis of islets cells was seldom found. Furthermore, the number of β cells of S group observed by immunofluorescence increased.⑸ At the end of twelfth week, PCNA immunostaining shown that the proliferation rate of islets in S group was increased, furthermore, the m RNA that associated with proliferation were increased as well.⑹ At the end of twelfth week, immunofluorescence double staining shown that the expression of SDF-1ɑ in S group was increased; compared with D group, the downstream level of Akt、p-Akt、βcatenin and free-βcatenin protein of pancreas of S group significantly increased as well.ConclusionDPP-4 inhibitor saxagliptin could inhibit the activity of DPP-4 and thenreduce the degradation of SDF-1ɑ. The protein Akt, p-Akt, β catenin, free- βcatenin and m RNA cyclin D1 、 c-Myc that associated with proliferation were also activated. Ultimately, DPP-4 inhibitor saxagliptin induced the proliferation of βcell and significantly improved pancreas function.