Abstract
Sustained overactivation of RhoA is a common component for the pathogenesis of several cardiovascular disorders, including hypertension. Although activity of Rho proteins depends on Rho exchange factors (Rho-GEFs), the identity of Rho-GEFs expressed in vascular smooth muscle cells (VSMC) and participating in the control of Rho protein activity and Rho-dependent functions remains unknown. To address this question, we analyzed by quantitative RT-PCR the expression profile of 28 RhoA-GEFs in arteries of normotensive (saline-treated) and hypertensive (ANG II-treated) rats. Sixteen RhoA-GEFs were downregulated in mesenteric arteries of hypertensive rats, among which nine are also downregulated in cultured VSMC stimulated by ANG II (100 nM, 48 h), suggesting a direct effect of ANG II. Inhibition of type 1 ANG II receptors (losartan, 1 μM) or Rho kinase (fasudil, 10 μM) prevented ANG II-induced RhoA-GEF downregulation. Functionally, ANG II-induced downregulation of RhoA-GEFs is associated with decreased Rho kinase activation in response to endothelin-1, norepinephrine, and U-46619. This work thus identifies a group of RhoA-GEFs that controls RhoA and RhoA-dependent functions in VSMC, and a negative feedback of RhoA/Rho kinase activity on the expression of these RhoA-GEFs that may play an adaptative role to limit RhoA/Rho kinase activation.
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