Abstract 097: EGF Receptor And ER Stress Mediate End-organ Damage But Not Hypertension Induced By Angiotensin II In Mice

Abstract

In cultured vascular smooth muscle cells (VSMC), a metalloprotease ADAM17-dependent EGF receptor (EGFR) activation mediates ERK1/2 activation and subsequent hypertrophy induced by angiotensin II (Ang II). Both ER and oxidative stress are implicated in hypertensive end-organ damage. We hypothesized that pharmacological inhibition of EGFR may prevent end-organ damage but not hypertension in mice infused with Ang II via suppression of ER/oxidative stress. To test this hypothesis, we have evaluated Ang II-induced end-organ damage as well as hypertension in C57Bl/6 mice with or without an EGFR inhibitor erlotinib (20mg/kg/day ip) or ER stress inhibitor 4-phenyl butyric acid (PBA: 1g/kg/day in drinking water). Upon Ang II infusion (1000 ng/kg/min) for 2 weeks, control mice showed phenotypes of cardiac hypertrophy including increased HW/BW ratio (mg/g: 7.9±0.7 vs 5.7±0.6 p<0.01 n=8) and increased LVPWd assessed by cardiac echo (mm: 0.98±0.14 vs 0.69±0.05, p<0.05 n=8) compared with saline infusion. Histological assessments demonstrated medial hypertrophy and perivascular fibrosis of coronary arteries with Ang II infusion. In contrast, cardiac hypertrophy and vascular remodeling were attenuated in mice with Ang II plus erlotinib or PBA; HW/BW ratio (6.8±0.6 or 6.2±0.6 n=8), and cardiac echo (LVPWd: 0.65±0.07 or 0.80±0.07 n=8) compared with saline infusion. Renal fibrosis observed with Ang II infusion was also attenuated in mice with Ang II plus erotinib or PBA. However, Ang II induced similar levels of hypertension in non-treated, erlotinib-treated or PBA-treated mice assessed by telemetry (MAP mmHg: 144±9 vs 149±20 or 139±4). Ang II infusion in mice enhanced ADAM17 and phospho-Tyr EGFR staining in vasculatures of heart and kidney, whereas mice with Ang II plus erlotinib or PBA had diminished phospho-Tyr EGFR staining and no ADAM17 staining in the vasculatures. In addition, IHC analyses revealed less oxidative stress and less ER stress in heart and kidney of Ang II-infused mice with erlotinib or PBA. These data suggest that EGFR activation and subsequent ER stress enhancement are critical for end organ damage via induction of ADAM17 and oxidative stress and is independent from blood pressure regulation.