Abstract 244: Vascular Induction of Adam17 in vitro and in Vivo By Angiotensin Ii: Potential Involvement of a Hypoxia Responsible Element

Abstract

ADAM17 has been shown to play critical roles in angiotensin II (AngII)-dependent as well as independent types of pathophysiological vascular remodeling in vitro and in vivo. Enzymatic activation of ADAM17 by AngII has been described, however, little is known regarding regulation of ADAM17 protein expression in the cardiovascular system. Here we test our hypothesis that AngII induces ADAM17 protein expression to originate a feed forward loop of ADAM17 activation/induction in the vasculature. 8 week old control mice were infused with 1000 ng/kg/min AngII for 2 weeks via osmotic minipump. Serum starved rat VSMCs were stimulated with 100 nM AngII. ADAM17 expression was evaluated by immunohistochemistry and immunoblotting, respectively. In AngII-infused mice, marked ADAM17 induction was seen in vasculatures in heart and kidney, and carotid arteries and aortae. In VSMCs, AngII as well as PDGF-BB (50 ng/mL) time-dependently induced ADAM17 expression up to 24 hours (AngII 24h: 2.34±0.25 fold induction). Both AngII and PDGF-BB also stimulated ADAM17 promoter activity in VSMCs (AngII 24h: 2.90±0.17 fold induction). The ADAM17 promoter contains 6 typical hypoxia responsible elements (HREs). By using deletion and mutation constructs, the PDGF-BB response seems to require HRE4 located between -991 to -410 of the promoter. AngII-induced promoter activation was also lost in the HRE4 mutant. Moreover, both AngII and PDGF-BB stimulated HIF-1alpha protein expression in VSMCs at 4-8 hours. From these data, we conclude that AngII and PDGF induce ADAM17 expression in VSMCs via HIF1alpha/HRE-dependent transcriptional upregulation. The induction of ADAM17 via the HIF1/HRE-dependent mechanism likely promotes a feed-forward loop of ADAM17 activation/induction under a variety of pathophysiological conditions including hypoxia/ischemia leading to end organ damages in the cardiovascular system.