| Objective: To investigate the effect of ubiquitin proteasome inhibitor MG132 on early stage diabetic nephropathy in STZ-induced rats.Methods:①Establishment of diabetic rat model: All 50 Wistar rats were randomly divided into diabetes group (n=40) and negative control group (N group,n=10). The rats in diabetes group were injected intraperitoneally with streptozotion(STZ) at dosage of 60mg/kg, while the negative control group was injected with same volume of citric acid buffer solution.At 1 week after STZ treatment, we randomly select 30 rats whose FBG were higher than 16.8mmol/L to the following experiment.②Grouping:All 30 diabetic rats were randomly divided into diabetic control group (D group,n=10), MG132 high concentration (0.1mg/kg) group (H group,n=10), MG132 low concentration ( 0.05mg/kg) group ( L group ,n=10). Meanwhile, the N group was administered as negative control group. Half of rats in each group were killed at 6 week and 8 week after treatment.③Detection of blood and urine:The results were evaluated by measurement of fasting blood glucose(FBG),urinary albumin(UAlb)④HE,Masson staining and electron microscopy were used to observe pathologic changes in renal tissue.⑤Western-Bloting to detect the expression of TGF-? and smad7, RT-PCR to detect the expression of FN mRNA.⑥Statistical analysis:Data were expressed as average±standard devidation.SPSS15.0 was used for one-way analysis of variance with several group, and P values less than 0.05 is considered to be statistical significance.Results:①General observation:Compared with rats in N group,rats in D group ingested more food , drinked much water , increased urine volume , lossed the lustre of hair color;Compared with rats in D group, the general situation of rats in H group and L group were lightest.②Body weight (BW) and fasting blood glucose(FBG): At 6 week and 8 week , the BW of rats in model group decreased while FBG increased significantly compared with that in N group(P<0.01); After the rats were treated with MG132, the BW of rats in H group and L group increased significantly compared with that in D group(P<0.05); At 8 week, the BW of rats in D group decreased significantly while in H group and L group increased compared with the BW of rats at 6 week(P<0.05).③kidney weight (KW) and kidney weight/body weight (KW/BW) :At 6 week and 8 week after treated with MG132, the KW and KW/BW of rats in model group increased significantly compared with that in N group (P <0.05), while the KW and KW/BW of rats in H and L group decreased compared with that in D group (P <0.05).④volume of urine (UV),24 hours microalbuminuria (UAlb) and urinary protein/urinary creatinine (Up/UCr): Compared with rats in N group, the UV,UAlb and Up/UCr of rats in model group at 6 and 8 week increased significantly (P <0.01), while in H and L group decreased compared with that in D group (P <0.05).⑤Comparison of blood urea nitrogen (BUN) and serum creatinine (Scr): The BUN of rats in model group increased significantly while the Scr decreased compared with that in N group, (P <0.01); The BUN of rats in D group, was higher but Scr was lower than that in H group,L group (P <0.05).⑥The structural changes of rats kidney: Under light microscope, the renal glomerulus enlarged obviously in model group and it is most remarkable in diabetes control group; Under electron micrographs, the glomerular basement membrane was thickened and endothelial cells were edematous partly with effacement of some visceral epithelial cell foot processes in diabetic group. These changes are the lightest in H group, which in L group are more heavy,while D group are the most heavy.⑦The expression of TGF-βand smad7 protein in kidney: The expression of TGF-βof rats in model group were significantly increased (P <0.01), while smad7 was decreased in D group compared with that in N group(P <0.01); After the rats were treated with MG132, there were statistical differences among D,H and Lgroup(P <0.05), With time ,the differences between 6 week and 8 week became obivous more and more(P <0.05).⑧The expression of FN mRNA in rats kidney: The expression of fibronectin (FN) mRNA of rats in model group at 6 week and 8 week increased significantly (P <0.05) compared with that in N group,while in H and L group decreased compared with that in D group(P <0.05). Conclusion: 1. MG132 may be useful to decrease the microalbuminuria ,alleviate the basement membrane thickening,podocyte injury and endothelial cell edema, block the expresson of TGF-βprotein,FN mRNA,increase the expresson of smad7 protein in early DN rats.2: The increased Ubiquitin-dependent degradation of smad7 may be related to the pathogenesis of diabetic nephropathy.Thus,to effectively inhibit the activity of Ubiquitin proteasome pathway will be a possibility to prevent and control diabetic nephropathy.
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