SVEP1 and integrin α4 or α9 deficiency enhances VSMC [Ca2+]i release
SVEP1 siRNA treated isolated iVSMCs showed significant increases in Ca2+ release to a panel of vasoconstrictors that signal via different GPCRs including endothelin (ET)-1 (Fig. 3A,P <0.05), or carbachol (Fig. 3B,P <0.001) compared to non-targeted control (NTC) siRNA transfected cells. This effect was confirmed inSVEP1-/- iVSMCs where maximal calcium release to ET-1 (SF. 8A, P <0.01) and carbachol (SF. 8B,P <0.05), were also significantly enhanced compared to isotype control iVSMCs. Inhibition of either integrin α4β1 or α9β1 using siRNA caused enhanced iVSMC Ca2+ release to ET-1 (Fig. 4A, P <0.01 & P <0.05 respectively), whilst simultaneous inhibition of integrin α4β1 and α9β1 did not cause additional Ca2+ release (Fig. 4A,P <0.001). Similarly, SVEP1 deficiency and blocking either integrin α4β1 (SF. 9A, P <0.05), integrin α9β1 (SF. 9B P <0.001), or integrin α4β1 and α9β1 dual inhibition using siRNA (Fig. 4B, P <0.05) or the dual integrin α4β1/α9β1 inhibitor BOP29 (Fig. 4C,P <0.05) did not cause additional ET-1-mediated Ca2+ release compared to cells treated withSVEP1 siRNA alone. Similar results were seen in iVSMCs stimulated with carbachol (SF. 9E P <0.05) and was confirmed in ET-1-stimulated SVEP1-/- iVSMCs treated with BOP (SF. 9D, P <0.05). These data show that SVEP1 reduces iVSMC Ca2+ release to several Gαq/11 agonists via integrin α4β1 and α9β1.