Renal (pro)renin receptor contributes to development of diabetic kidney disease through transforming growth factor-β1-connective tissue growth factor signalling cascade.

Transforming growth factor β1 (TGFβ1) and connective tissue growth factor (CTGF) are expressed in renal glomeruli and contribute to development of diabetic nephropathy. Recently we demonstrated that (pro)renin receptor (PRR) is upregulated in the kidneys of streptozocin (STZ)-induced diabetes rat model. We hypothesized that in the presence of hyperglycemia, increased renal PRR expression contributes to enhanced TGFβ1-CTGF signaling activity, leading to development of diabetic kidney disease. In vivo and in vitro studies were conducted in Sprague-Dawley rats and rat mesangial cells (RMCs). PRR blockade was achieved in vivo by treating STZ induced diabetes rats with the handle region peptide (HRP) of prorenin and in vitro by HRP or PRR siRNA in RMCs. Angiotensin AT1 receptor blockade was achieved by Valsartan treatment. Results showed that expression of PRR, TGFβ1 and CTGF were upregulated in diabetic kidneys and RMCs exposed to high glucose. Glucose exposure also induced PRR phosphorylation, a process that was inhibited by HRP, Valsartan or PRR siRNA. HRP and Valsartan significantly attenuated renal TGFβ1 and CTGF expression in diabetic animals and high glucose treated RMCs. Similar results were observed in high glucose exposed RMCs in response to PRR siRNA. TGFβ receptor blockade decreased CTGF expression in RMCs. Combined administration of Valsartan and PRR siRNA demonstrated further reduction of TGFβ1 and CTGF expression in RMCs. In conclusion, PRR contributes to kidney disease in diabetes through enhanced TGFβ1-CTGF signaling cascade. Keywords: (pro)renin receptor, Transforming growth factor β1, Connective tissue growth factor, hyperglycemia, kidney, mesangial cells INTRODUCTION Previous studies demonstrated that activation of renin-angiotensin-system (RAS) contributes to increased activity of the transforming growth factor β (TGFβ)- connective tissue growth factor (CTGF) axis in renal diseases (1–12). Similarly, TGFβ and CTGF expressions and their intracellular signals are increased in diabetes (13–19). CTGF gene contains a novel TGFβ response element inits promoter region (20) and is thought to be a downstream mediator of TGFβ effects (21, 22). Thus, TGFβ-CTGF axis activation contributes to development of kidney disease in diabetes. (Pro)renin receptor (PRR), a new member of RAS, is a 350 amino acid protein with a single transmembrane domain that binds and activates prorenin (23, 24). The role of PRR in the development of kidney disease is not established yet. Our previous studies showed that PRR is upregulated in kidneys of diabetic rats and renal mesangial cells (RMCs) exposed to high glucose concentration (25–28). PRR blockade attenuated diabetic proteiuria (27, 29–30) and also inhibited cytokines production (26, 27). In this study, we hypothesized that hyperglycemia induced PRR expression enhances TGFβ1-CTGF signaling pathway leading to the development of kidney disease. The influence of PRR function or expression on TGFβ1-CTGF axis was evaluated in vivo and in vitro by utilization of the PRR blocker, handle region peptide (HRP) of prorenin, the angiotensin AT1 receptor blocker Valsartan and PRR small interference RNA (siRNA) in RMCs exposed to high glucose.