骨誘導蛋白-7與中藥-當歸對於糖尿病腎病變腎臟對抗高糖誘導的氧化壓力之研究

Renal failure caused by diabetes mellitus, called the diabetic nephropathy (DN), is a serious health problem in the world. Identifying molecular mechanism of the pathogenesis of DN may be helpful in developing new therapeutics. Oxidative stress in mesangial cell caused by hyperglycemia is closely related to the development of DN. Bone morphorgenetic protein-7 (BMP-7) helps to maintain renal functions and structural integrity; the molecule, however, disappears early during diabetic nephropathy progression. This study aims to investigate 1) how to preserve renal BMP-7 expression during DN progression; 2) whether BMP-7 could prevent kidney or renal mesangial cell (RMCs) from DN through reducing hyperglycemia induced oxidative stress; 3) whether DangGui (Angelica polymorpha Maxim. var sinensis Olive; Radix Angelica sinensis), a traditional Chinese medicine, could improve renal function through reserving renal BMP-7 expression or inhibiting hyperglycemia induced oxidative stress in streptozotocin-induced diabetic rats . Rats develop initial stage of DN 9 weeks after type-1 like diabetes is induced by STZ injection, and at 13 weeks the DN is at its established stage. Insulin and phloridzin both attenuated hyperglycemia and renal function of STZ-DN rats. The treatment increased the expressions of BMP-7 and BMP receptor (BMP-RII) but decreased TGF-β and fibronectin expressions in kidney via reducing hyperglycemia at the initial stage but not at the established stage of STZ-DN rats. We also determined the effect of glucose on BMP-7 and BMP-RII expressions in RMCs. BMP-7 and BMP-RII in RMCs were markedly reduced by high glucose (HG). We further investigated the interaction between oxidative stress induced by hyperglycemia and renal BMP-7/BMP-RII expression in STZ-DN rats. The results showed that treatment with antioxidant, tiron, which didn’t changed blood glucose in STZ-DN rats, decreased BUN and creatinine levels and renal fibronectin expression. On the other hand, tiron increased the expressions of BMP-7 and BMP-RII in kidney at the organ level and HG exposed RMCs at the cellular level. Moreover, recombinant human BMP-7 (rhBMP-7) decreased the HG-induced reactive oxygen species (ROS) or TGF-β level in RMCs. The ROS level in RMCs was raised by lowering endogenous BMP-7 either siRNA or anti-BMP-RII treatment. Also, rhBMP-7 increased smad-1, 5, 8 phosphorylation and decreased PKCζ and JNK kinase phosphorylation to lower extracellular matrix synthesis in HG incubated RMCs. We further investigated further effects of DangGui (Radix A. sinensis) on regulating renal functions, BMP-7 expression, and HG induced ROS generation. After 1-week or 4-week treatment, DangGui improved renal functions by up-regulating the expression of BMP-7 protein in kidney tissue of STZ-DN rats. DangGui also reversed BMP-7 expression reduced by HG in RMCs. Because transfection with BMP-7 RNAi with HG in the culture medium cause RMCs to detach from the culture dish, we hence used normal medium to knock down BMP-7 in RMCs with RNAi. DangGui increased BMP-7 expression in those RMCs transfected by BMP-7 RNAi. Direct activation of BMP-7 gene expression by DangGui could be considered. The anti-oxidative ability of DangGui was identified using DPPH assay, DHE stain, and lucigenin assay in HG exposed RMC. DangGui decreased HG-induced ROS in RMCs. In conclusion, we found that control of hyperglycemia may improve renal function and reverse renal BMP-7 and BMP-RII in STZ-DN at initial stage of DN. Endogenous BMP-7 is raised by antioxidant to activate BMP-RII for renal protection against the HG induced oxidative stress. DangGui could improve renal functions in STZ-DN rats through increasing renal BMP-7 expression and decreasing the high glucose-induced oxidative stress.