Upstream Stimulatory Factor 2 Regulation of Renin in Diabetic Nephropathy

Diabetic nephropathy is the most common cause of end-stage renal failure, and is highly prevalent in both type 1 and type 2 diabetics. Hyperglycemia and the activation of the intrarenal renin-angiotensin system (RAS) in diabetes have been suggested to play a critical role in the pathogenesis of diabetic nephropathy. However, the mechanisms for the effectiveness of inhibitors of the RAS, or for angiotensin II as a mediator of diabetic nephropathy are not well defined. Transforming growth factor –â (TGF-â) is a major effector leading to renal fibrosis in response to hyperglycemia. Preliminary data demonstrate that Upstream Stimulatory Factor (USF2) is an important transcription factor in high glucose-induced TGF-â production in mesangial cells. Importantly, USF2 expression is increased in the kidneys of diabetic mice and correlates with the glomerular mesangial matrix expansion. Furthermore, over-expression of USF2 accelerates the development of diabetic nephropathy in a type 1 diabetic mouse model, supporting the role of this transcription factor in the development of diabetic nephropathy. Our preliminary studies describe a novel effect of USF2 to promote renin gene expression and angiotensin II formation in mesangial cells. This effect of USF2 was linked to glucose-induced regulation of TGF-â production, suggesting that this pathway may contribute to the development of diabetic nephropathy. The working hypothesis of this proposal is that USF2 stimulates the renal RAS to promote production of TGF-â and the development of diabetic nephropathy. The proposed studies will define the role of USF2 in the development of diabetic nephropathy focusing on regulation of mesangial cell renin as the mechanistic target. In aim 1, the mechanisms by which USF2 regulates renin gene expression and angiotensin II production in mesangial cells under normal or high glucose conditions will be determined. In aim 2, the role of USF2-mediated renin expression and angiotensin II production in high glucose induced TGF-â levels and extracellular matrix protein (ECM) expression in mesangial cells will be defined. In aim 3, the role of USF2-mediated up-regulation of the renal RAS in the development of diabetic nephropathy in vivo will be determined. Our approach utilizes both in vitro and in vivo studies to provide new information on the mechanisms of activation of the intrarenal RAS system in diabetes, and will lead to the development of novel therapies to ameliorate this major complication of diabetes.