Abstract 1362: The Rho Guanine Exchange Factor ECT2 is Upregulated in a Stretch-Dependent Manner in Arteries of Hypertensive Rats and Contributes to Cell Proliferation
Rho exchange factors (Rho-GEFs) are signaling molecules responsible for Rho protein activation by catalyzing the exchange of GDP for GTP. Although over-activation of RhoA is recognized as a common component for the pathogenesis of hypertension and vascular proliferative disorders, the molecular mechanisms and the Rho-GEFs regulating Rho protein activity in vascular smooth muscle cells are still unknown. Here, we hypothesized that Rho-GEFs participating in the control of vascular smooth muscle functions could be upregulated in hypertension. We analyzed by quantitative PCR the expression of the 29 rat RhoA-GEFs in the L-NAME (50 mg/kg/day) and angiotensin II (Ang II, 250 ng/kg/min) models of hypertension in rat. The more important changes observed in both models affected ECT2. At 14 days, ECT2 mRNA level was increased to 640±80% and 620±110% in aorta (n=4, p<0.005) and to 330±60% and 340±30% in mesenteric artery (n=4, p<0.01), in L-NAME and Ang II rats, respectively. No change was observed in the pulmonary artery. To assess a potential role of mechanical factors resulting from elevated blood pressure, arteries were maintained in organ culture at normal (80 mmHg) or high (150 mmHg) intraluminal pressure. After 24 hours, high pressure induced a 1.8-fold increase in ECT2 mRNA compared to controls (n=4, p<0.05). All these changes in ECT2 mRNA were confirmed at protein level by western blot analysis. In cultured aortic smooth muscle cells, cyclic stretch (20%, 4Hz, 48 h) stimulated cell proliferation, in association with Rho protein activation and increase in ECT2 mRNA and protein expression. Small interfering RNA-mediated ECT2 silencing inhibited stretch-induced proliferation. Expression of Rho protein mutants (RhoA, Rac1, Cdc42) indicated that the effect of ECT2 on vascular smooth muscle cell proliferation involved the Rho protein Cdc42. We conclude that high blood pressure up-regulates the expression of the Rho-GEF ECT2 in arterial walls through mechanism involving mechanical stretch. This upregulation of ECT2, known as a cell cycle regulator, could participate to RhoA-dependent arterial remodeling associated with hypertension.