Abstract 5074: The Rho Exchange Factor Arhgef1 in Vascular Smooth Muscle Cells is Essential for Angiotensin II-induced Hypertension
Rho exchange factors (Rho-GEFs) are responsible for Rho protein activation by catalyzing the exchange of GDP for GTP. Although over-activation of RhoA and its effector Rho kinase is recognized as a critical component of the pathogenesis of hypertension in experimental models and in human, the molecular mechanisms and the RhoA-GEF(s) involved in this activation of RhoA signaling in vascular smooth muscle cells (VSMCs) are unknown. Among the Rho-GEFs family, Arhgef1 (p115) constitutes with Arhgef11 (PDZ-Rho GEF) and Arhgef12 (Larg) the subfamily of RGS-containing Rho-GEFs that have been suggested to couple G-protein associated receptors to RhoA activation. To establish the role of Arhgef1 in the regulation of vascular tone and hypertension in vivo, we generated mice lacking Arhgef1 specifically in SMCs (SM-Arhgef1-KO). We used Arhgef1lox/lox mice, which were mated to SMMHC-CreERT2. SM-Arhgef1-KO mice were then obtained by treatment with tamoxifen (1 mg/day, IP, 5 days). In VSMCs from SM-Arhgef1-KO mice, stimulation with angiotensin II (Ang II, 0.1 μM) was unable to induce RhoA/Rho kinase activation whereas that produced by U46619, phenylephrine (PhE), and endothelin-1 (ET1) was similar to that recorded in control mice. Ex vivo analysis of the contractile properties showed that, in aortic segments from SM-Arhgef1-KO mice, KCl-, PhE-, U46619- and ET1-induced contractions were similar to those obtained in control mice. In contrast, Ang II-induced contractions were severely reduced. In vivo, acute pressor responses to U46619 (3–100 μg/kg), ET1 (0.03–1 μg/kg) and PhE (0.1–100 μg/kg) were similar in control and SM-Arhgef1-KO mice, but responses to Ang II (0.1–30 μg/kg) were abolished. Basal blood pressure levels were similar in SM-Arhgef1-KO and control mice. In control mice, chronic infusion of Ang II (1 mg/kg/day) increased blood pressure whereas SM-Arhgef1-KO mice were resistant to the development of Ang II-induced hypertension. We therefore conclude that Arhgef1, as the molecular link between Ang II, RhoA activation and vascular tone regulation, provides an alternative target to reducing elevated vascular tone under hypertensive conditions without affecting normal blood pressure regulation by other vasoactive factors.