| Objective: Diabetic nephropathy (DN) is one of the major microvascular complications of diabetes mellitus. Long-term of hyperglycemia and related metabolic disorder can activate many pathways which cause renal irreversible pathological changes. DN, a principal cause of end-stage renal diseases, is characterized by glomerular sclerosis, thickening of glomerular basement membrane and extracellular matrix deposition. The pathogenesis of DN is not clarified at present. Generous researches indicated that transforming growth factor (TGF)-β1 played an important role in DN. Overexpression of TGFβ1 in diabetic glomeruli is believed to contribute to the glomerular hypertrophy, matrix accumulation, filtration barrier lesion, mediating interstitial fibrosis, promoting apoptosis and accelerating the progression of DN ultimately. Inhibition of TGFβ1 may be the new target of DN treatment. Researches showed that pigment epithlium-derived factor (PEDF) might act as an endogenous inhibitor of TGFβ1 expression and play a protection role in DN. PEDF, glycoprotein widely distributed in a variety of organs, is a potent angiogenic inhibitor and neurotrophy factor. PEDF involves in many metabolic diseases, especially in diabetic retinopathy (DR). The decrease of its level may be one of the causes of DR. The results of cell culture and animal experiments indicated that PEDF could inhibit the overexpression of TGFβ1. Streptozotocin (STZ)-induced diabetic rats with an adenovirus expressing PEDF can significantly alleviated microalbuminuria in early stage of diabetes. These findings indicated that PEDF might be a protective or even therapeutic potential factor in diabetic kidney. In this study, rat model of type 1 diabetes was set up by a high-dose intraperitoneal injection of STZ and overview the changes of renal morphous and function. PEDF and TGFβ1 contents in renal cortex and serum level of PEDF were detected to explore the possible relationship among PEDF, TGFβ1 and pathogenesis of DN.Methods: 25 male SD rats were randomly assigned into normal control group (NC group, 10) and diabetic group (DM group, 15). Rat model was set up by intrapenitoneal injection STZ (55mg/kg) in DM group rats after an overnight fast. NC group rats received an injection of citrate buffer alone. Only the rats with over 16.7mmol/L blood glucose (BG) levels were considered as diabetic model rat after 72 hours of injecting STZ. The experiment lasted 12 weeks. BG was measured at the end of 4, 8 and 12 weeks respectively. After 12 weeks, body weight, 24 hours urinary albumin excretion (UAE), blood urea nitrogen (BUN), serum creatinine(Scr), triglyceride(TG), total cholesterol (TC), low-density lipid-cholesterol (LDL-C), very low-density lipid-cholesterol (VLDL-C), alanine amino- transferase (ALT) and aspartate aminotransferase (AST) were measured. Serum PEDF was detected by ELISA. Kidney specimens were prepared for H.E stain to observe the changes of renal morphous. The protein expression and location of PEDF and TGFβ1 were examined by immunohistochemistry and immunofluorescence. PEDF and TGFβ1 expression in renal cortex were determined by Western- blot.Results1 72 hours after injecting STZ, BG, which exceed 16.7mmol/L, was markedly increased in DM group compared with NC group (P<0.01). It suggested the model of type 1 diabetic mellitus was set up. At the end of 4, 8 and 12 weeks, BG was significantly higher in DM group than those in NC group (P<0.01, P<0.01, P<0.01).2 After 12 weeks, compared with NC group, body weight was markedly decreased in DM group (P<0.01), while kidney mass/body mass were markedly increased in DM group (P<0.01).3 At the end of 12 weeks, UAE was significantly increased in DM group (P<0.01).4 Compared with NC group, BUN, Scr, TG, TC, LDL-C, ALT and AST increased in DM group (P<0.01, P<0.01, P<0.05, P<0.05, P<0.05, P<0.01, P<0.01), while VLDL-C had no significant difference in two groups. 5 In DM group, H.E stain showed that glomerular hypetrophy, mesangial expansion thickening of glomerular basement membrance and vacuolar degeneration in some renal tubules.6 Immunohistochemistry suggested that the expression of PEDF was obviously decreased (P<0.01), while the expression of TGFβ1 was significantly increased (P<0.01) in DM group than those of NC group. Immunofluorescence implicated that compared with NC group the expression of PEDF was lower in DM group, while the expression of TGFβ1 was higher in DM group.7 Compared with NC group, Western-blot showed that protein expression of PEDF was markedly decreased (P<0.01) while the level of TGFβ1 increased (P<0.01) in DM group.8 Compared with NC group, serum level of PEDF was slightly increased in DM group, while the difference was no significance (P=0.152).Conclusions1 Rat model of type 1 diabetic mellitus can be set up by high-dose intrapenitoneal injection of STZ. The model characterized by typical diabetic features analog to human. So this model can satisfy the need of diabetic complication researches.2 As hyperglycemia persistent, irreversible renal pathological changes caused renal dysfunction. Morphology and laboratory examination are both consistent with DN. Therefore, the model can be used for DN related investigation.3 Dysglycemia can cause dyslipidemia and hepatic dysfunction. These disturbances may play an adverse role in organism.4 As an important mesomerism in progression of DN, the expression of TGFβ1 increased in DM group, which according with the damage of kidney. The results indicated that TGFβ1 can effect the progression of DN.5 The protein expression of PEDF was higher in DM group, which decreased when renal dysfunction was present which was opposite to TGFβ1. This result implicates that the interaction of PEDF and TGFβ1 may exist and influence the progression of DN.6 PEDF content in serum did not alter so significantly compared with in renal tissue when diabetes occurs and the renal pathological changes. This result indicated that PEDF in circulation may compensatory maintain its level through other pathways.
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