Abstract 1091: Renin and Prorenin Increase GLUT-1 Expression in Human Mesangial Cells Through an Angiotensin II and ERK1/2-Independent Mechanism
High glucose and glomerular hypertension (HTN) promote the development and progression of diabetic nephropathy. GLUT-1 is a high-affinity glucose transporter in glomerular mesangial cells that operates at maximal capacity under physiological glucose concentrations. Overexpression of GLUT-1 in mesangial cells exposed to physiologic glucose concentrations increases glucose transport and induces a “diabetic cellular phenotype” with increased matrix production due to upregulation of TGF-beta. We have shown that glomerular HTN in vivo and mechanical mesangial cell stretching in vitro increase GLUT-1 expression, glucose transport, and TGF-beta synthesis, which in turn maintains upregulation of GLUT-1. Angiotensin (Ang) II plays a critical role in diabetic nephropathy by upregulating GLUT-1 and TGF-beta. Binding of either prorenin or renin to the (pro)renin receptor activates ERK1/2 independently of Ang II and induces mesangial cells to produce TGF-beta, thereby increasing fibronectin synthesis. Here we investigated the regulation of GLUT-1 expression by prorenin and renin in human mesangial cells. Human mesangial cells, quiescent for 48 hours, were incubated for 30 minutes in the presence or absence of the Ang II type 1 receptor blocker (ARB) candesartan (10umol/L), ERK1/2 inhibitors PD98059 (10umol/L) or UO126 (50umol/L), or TGF-beta antibody (5ug/mL) followed by 24 hour treatment with vehicle, Ang II (100nmol/L), prorenin (10nmol/L), or renin (10nmol/L). By western blot, Ang II (2.2±0.38), prorenin (1.6±0.09), and renin (1.7±0.12) increased GLUT-1 protein expression in human mesangial cells (all fold-increase vs. vehicle; P<0.05), accompanied by increased TGF-beta and fibronectin protein expression. The Ang II-induced increase in GLUT-1 was inhibited by ARB (1±0.15), PD98059 (1.1±0.01), UO126 (1.1±0.24), or TGF-beta antibody (0.9±0.12; all P<0.05 vs. Ang II). TGF-beta antibody, but not ARB, PD98059, or UO126, blocked the prorenin (1.1±0.07; P<0.05) and renin (0.85±0.3; P<0.05) induced increase in GLUT-1. These studies are the first demonstration in human mesangial cells of an Ang II and ERK1/2-independent prorenin/renin activation of GLUT-1 that may participate in the initiation and progression of diabetic nephropathy.