Increased PKG Activity Prevents the Development of Diabetic Nephropathy

Kidney disease, or nephropathy, is a frequent complication of diabetes. In diabetic nephropathy, kidney cells produce excessive amount of extracellular proteins (ECM), leading to hardening of kidney vessels, and resulting in end-stage renal failure (ESRD). Patients of ESRD require dialysis or a kidney transplant in order to live. Diabetic nephropathy is the leading cause of ESRD. Therefore, determining the mechanisms of diabetic nephropathy and finding therapeutic interventions are very important, which are the purpose of this proposed study. It is known that high level of blood sugar is a main initiating factor in diabetic nephropathy. It up-regulates a growth factor called transforming growth factor-beta (TGF-beta), which stimulates kidney cells to produce more ECM, leading to diabetic nephropathy. We have demonstrated that high glucose concentrations up-regulate TSP1 expression and TSP1 -dependent TGF-fO bioactivity through a reduction in nitric oxide bioavailability and a resultant decrease in cGMP-dependent protein kinase (PKG) activity. Importantly, we demonstrate that PKG activity is decreased in kidney from type 1 diabetic mice as well, which is associated with increased expression of TSP1 and TGF-~] activity. Increasing PKG activity by inducible expression of constitutively active PKG inhibits glucose-mediated up-regulation of TSP1 gene expression, TGF-f] activity and resultant ECM production in mesangial cells. These data suggest that increased PKG activity prevents the development of DN through inhibition of TSP1 -dependent TGF-~J activity. This hypothesis will be tested by using our recently developed PKG transgenic mice. Type 1 diabetes will be induced in wild type and PKG transgenic mice by injection of streptozotocin. The renal structural and functional changes will be determined. Alternatively, a specific phosphodiesterase type 5 (PDE5) inhibitor-sildenafil will be utilized to increase PKG activity in control mice in the presence of type 1 diabetes. The development of diabetic nephropathy in these mice will be evaluated. These in vivo studies will determine the importance of PKG in the development of diabetic nephropathy. Importantly, increasing PKG activity may become a novel avenue in the prevention and treatment of diabetic nephropathy.