Abstract 660: Inducible Ablation Of Emilin1 In Smooth Muscle Cells Increases Blood Pressure And Myogenic Tone By Enhancing Tgf-beta/alk5 Signaling.

Abstract

Emilin1 (E1), a protein of the elastic extracellular matrix expressed in the cardiovascular system, regulates TGFβ bioavailability through proteolysis of the proTGFβ, precursor to the LAP/TGFβ complex, that releases the growth factor. E1 null mice are hypertensives, with an increased activation of TGFβ. As E1 is expressed in blood vessels starting from early 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 administration induced Cre activity selectively in SMCs, as shown in mice with the Rosa26R mutation. When E1 flox/flox mice carrying the Smmhc -CreER T2 ( Smmhc -CreER T2 E1 flox/flox ) were given TAM for 7 days, E1 completely disappeared in 10 days from start of treatment. After that, blood pressure significantly increased in Smmhc -CreER T2 E1 flox/flox as compared to E1 flox/flox (124±1 vs 106±1 mmHg, n=10), whereas no structural changes of both large and resistance arteries were detected. Interestingly, a treatment with anti-TGFβ antibodies rescued the hypertensive phenotype of Smmhc -CreER T2 E1 flox/flox mice. Then, we found that isolated resistance arteries of Smmhc -CreER T2 E1 flox/flox displayed and increased myogenic response to perfusion pressure as compared to E1 flox/flox (7±1 vs 16±2 %, n=10). Moreover, we further clarified that the increased myogenic response was rescued by resistance arteries exposure to TGFβ neutralizing antibody. Finally, we found that the inhibition of TGFβ receptor ALK5, obtained transfecting isolated vessels with an adenovirus carrying a dominant negative ALK5mutant, rescued as well the increased myogenic response of Smmhc -CreER T2 E1 flox/flox. . Our results demonstrate that E1 exerts a homeostatic control of blood pressure by regulating myogenic tone of resistance arteries, through TGFβ/ALK5 in SMCs, thus suggesting that this pathway should be carefully investigated in essential hypertension.