Purpose: 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.
Methods: 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.
Results: 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.
Conclusion: AGEs activate the RAS in podocytes through the RAGE-PI3-K/Akt-dependent pathway and lead to an increase in podocyte apoptosis.