Advanced glycation end-products activate the renin-angiotensin system through the RAGE/PI3-K signaling pathway in podocytes

Abstract

The purpose of this study was to investigate the effects of advanced glycation end-products (AGEs) on the components of the renin-angiotensin system (RAS) in podocytes and to understand the mechanism of these effects. Immortalized mouse podocytes were exposed to various concentrations of AGEs for different time intervals. The expression levels of angiotensinogen (AGT), angiotensin II type 1 and 2 receptors (AT1R and AT2R) and renin were examined by real-time PCR and western blot; the receptor for AGEs (RAGE) and both Akt and phosphorylated Akt were examined by western blot; levels of angiotensin II (Ang II) were assayed by ELISA, and the activity of angiotensin-converting enzyme (ACE) was evaluated by measuring the production of hippuric acid in vitro. Treatment with AGEs resulted in significant increases in the expression of AGT (62%, P=0.002) and AT1R (59%, P=0.01). Moreover, Ang II levels increased significantly in both cell lysates (70%, P=0.018) and conditioned media (65%, P=0.01). ACE activity was also significantly higher in cell lysates (68% , P= 0.035) and conditioned media (65%, P=0.023). There were no changes in renin or AT2R expression (P > 0.05). AGEs did increase the expression of RAGE by 50% (P=0.012) and the phosphorylation of Akt by 100% (P=0.001). When podocytes were pretreated with anti-RAGE antibody (50 µg/ml) or the phosphoinositide 3-kinase (PI3-K) inhibitor, LY294002 (10 µM), the AGEs-induced increases in AGT and AT1R expression were reduced. Likewise, Ang II levels and ACE activity decreased significantly. AGEs activate the RAS in podocytes through the RAGE-PI3-K/Akt-dependent pathway and lead to an increase in podocyte apoptosis.