The integrin ligand SVEP1 regulates GPCR-mediated vasoconstriction via integrins alpha 9 beta 1 and alpha 4 beta 1

Background and Purpose: Vascular tone is regulated by the relative contractile state of vascular smooth muscle cells (VSMCs). Several integrins directly modulate VSMC contraction by regulating calcium influx through L-type voltage-gated Ca2+ channels (VGCCs). Genetic variants in ITGA9, which encodes the alpha 9 subunit of integrin alpha 9 beta 1, and SVEP1, a ligand for integrin alpha 9 beta 1, associate with elevated blood pressure; however, neither SVEP1 nor integrin alpha 9 beta 1 has reported roles in vasoregulation. We determined whether SVEP1 and integrin alpha 9 beta 1 can regulate VSMC contraction. Experimental Approach: SVEP1 and integrin binding were confirmed by immunoprecipitation and cell binding assays. Human induced pluripotent stem cell-derived VSMCs were used in in vitro [Ca2+](i) studies, and aortas from a Svep1(+/-) knockout mouse model were used in wire myography to measure vessel contraction. Key Results: We confirmed the ligation of SVEP1 to integrin alpha 9 beta 1 and additionally found SVEP1 to directly bind to integrin alpha 4 beta 1. Inhibition of SVEP1, integrin alpha 4 beta 1 or alpha 9 beta 1 significantly enhanced [Ca2+](i) levels in isolated VSMCs to G alpha(q/11)-vasoconstrictors. This response was confirmed in whole vessels where a greater contraction to U46619 was seen in vessels from Svep1(+/-) mice compared to littermate controls or when integrin alpha 4 beta 1 or alpha 9 beta 1 was inhibited. Inhibition studies suggested that this effect was mediated via VGCCs, PKC and Rho A/Rho kinase dependent mechanisms. Conclusions and Implications: Our studies reveal a novel role for SVEP1 and the integrins alpha 4 beta 1 and alpha 9 beta 1 in reducing VSMC contractility. This could provide an explanation for the genetic associations with blood pressure risk at the SVEP1 and ITGA9 loci.