Abstract 511: Emilin1 Controls Myogenic Response of Resistance Arteries by Modulation of TRPC6 Through the TGFß/ALK5/ADAM17/EGFR Pathway

Abstract

Emilin1 (E1), a protein of the extracellular matrix expressed in the cardiovascular system, regulates TGFβ bioavailability through proteolysis of the proTGFβ, that releases the growth factor. E1 null mice are hypertensive, with increased TGFβ activation. As E1 is expressed in blood vessels starting from embryonic life to adulthood, is still unknown whether the E1 null phenotype results from a developmental defect or lack of a homeostatic role exerted during the adult life. To dissect this issue, we used a conditional gene targeting approach to inactivate E1 in smooth muscle cells (SMCs) of adult mice, by the use of floxed E1 and CreER T2 [a tamoxifen (TAM) inducible Cre recombinase] under the control of the smooth muscle myosin heavy chain (Smmhc) promoter. TAM induced Cre activity selectively in SMCs, as shown in mice with the Rosa26R mutation. When E1 fl/fl mice carrying the Smmhc-CreER T2 (Smmhc-CreER T2 E1 fl/fl ) were given TAM, E1 protein completely disappeared and blood pressure significantly increased, as compared to E1 fl/fl . While no structural changes of arteries were detected, we found that mesenteric arteries of Smmhc-CreER T2 E1 fl/fl displayed an increased myogenic response to pressure as compared to E1 fl/fl . Since the hypertensive phenotype of Smmhc-CreER T2 E1 fl/fl mice was rescued by a treatment with a TGFβ neutralizing antibody, we investigated the molecular mechanism in SMCs that, downstream to this pathway, could lead to an increased Ca 2+ -mediated contractility. In particular, also the increased myogenic response was rescued by exposure of resistance arteries to a TGFβ neutralizing antibody and, more important, by the inhibition of TGFβ receptor ALK5, obtained by in vivo vessels transfection with an adenovirus carrying a dominant negative ALK5 mutant. Moreover, we found that the increased TGFβ signaling, by phosphorylating the ADAM17/EGFR cascade, converged on overactivation of the Transient receptor potential cation channel C6 (TRPC6), rescued by in vivo vessels transfection with an adenovirus carrying a dominant negative TRPC6 mutant. Our results demonstrate that E1 exerts a homeostatic control of myogenic response by regulating the TRPC6 Ca 2+ channel, through a modulation of the TGFβ/ALK5/ADAM17/EGFR signaling pathway in SMCs.