Abstract 233: Angiotensin-(1-7) Abolishes AGE-Induced Chronic ERK Activation and Myofibroblast Transition

Abstract

Advanced glycated end products (AGEs) including glucose and methylglyoxal-modified albumin (MGA) may play a key role in tissue injury arising from various pathologies. Activation of AGE receptor (RAGE) induces myofibroblast transition (MT), hypertrophy and tubulointerstial fibrosis associated with diabetic nephropathy. AGE-RAGE signaling evokes activation of the renal angiotensin system (RAS) and the Ang II-AT1 receptor may facilitate the actions of AGE; however, the role of the Ang-(1-7)-Mas receptor axis in the AGE pathway is unknown. Moreover, there are reports that Ang-(1-7) directly induces renal MT and fibrosis. Therefore, the current study addressed the functional influence of Ang-(1-7) in AGE-induced signaling in the NRK-52E proximal tubule cell line following MGA treatment for 48-72 hours. MGA exposure enhanced cellular hypertrophy 175% (p<0.05 vs. control), increased α-SMA protein 300% (0.4±0.1 vs. 0.1±0.1U; p<0.05), stimulated myofibroblast transition (MT) and markedly increased the cellular release of TGF-β 350% (1.2±0.1 vs. 0.3±0.1 ng/ml; p<0.05). Ang-(1-7) (100 nM) essentially abolished the MGA-induced cell hypertrophy (175±0.1% vs. 85±0.1%), α-SMA expression (0.4±0.1 vs. 0.1±0.1U; p<0.05), and MT, but did not attenuate the increase in TGF-β release (1.2±0.1 vs. 1.3±0.1 ng/ml). Since TGF-β and MAP kinases are integral to the AGE-RAGE signaling cascade, we assessed the effect of TGF-β receptor kinase (SB525334, SB) and ERK1/2 (PD98059, PD) inhibitors. Similar to Ang-(1-7) treatment, SB and PD abolished MGA-induced hypertrophy, α-SMA expression and MT. We further show that both Ang-(1-7) and SB abolished the chronic activation of ERK1/2 at 48 hour MGA exposure. Finally, Ang-(1-7) abolished the TGF-β stimulation of ERK1/2. Pre-treatment of the MGA exposed cells with the AT7/Mas receptor antagonist D-Ala7-Ang-(1-7) reversed the inhibitory actions of Ang-(1-7), but did not potentiate the responses. In summary, we report that Ang-(1-7) abolished AGE activation of TGF-β and ERK1/2 pathways in the NRK-52E cells. We conclude that Ang-(1-7) may provide a potential therapeutic approach in addition to current RAS blockade regimens to prevent the progression of diabetic injury and the decline in renal function.