Abstract
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 α9 subunit of integrin α9β1, and
SVEP1, a ligand for integrin α9β1, associate with elevated blood
pressure, however, neither SVEP1 nor integrin α9β1 have reported roles
in vasoregulation. We therefore determined whether SVEP1 and integrin
α9β1 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 α9β1 and
additionally found SVEP1 to directly bind to integrin α4β1. Inhibition
of SVEP1, integrin α4β1 or α9β1 significantly enhanced [Ca2+]i
release in isolated VSMCs to Gαq/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 α4β1 or α9β1 were inhibited. Inhibition studies suggested
that this effect was mediated via VGCCs in a PKC dependent mechanism.
Conclusions and Implications Our studies reveal a novel role for SVEP1
and the integrins α4β1 and α9β1 in reducing vascular
hyper-contractility. This could provide an explanation for the genetic
associations with blood pressure risk at the SVEP1 and ITGA9 loci.