SVEP1-integrin α4/9 signalling inhibits whole vessel contraction
Perinatal mortality is observed in Svep1 null mice, with mice displaying edema at E18.514.Svep1 +/- mice, which are viable with no gross phenotypic effects14,24 were therefore used forex vivo analysis of vessel contraction.
Aortic vessel contraction was measured in response to several vasoconstrictors, with the thromboxane-A2 agonist U46619 providing the most reliable response (SF.10A-D), which was then used in subsequent experiments. Vessels from Svep1+/-  mice showed a significantly higher contraction to U46619 (Fig. 5A, 1.23 mN/mm2, P <0.001, concentration independent) and PE (SF. 10E, 0.31 mN/mm2,P <0.0001, concentration independent), compared to littermate controls. Incubation of vessels from C57BL/6J mice with an integrin α4 blocking antibody (10 µg/ml MCA1230Ga, Fig. 5B), or an integrin α9 blocking antibody (10 µg/ml 55A2C, Fig. 5C) significantly enhanced contraction to U46619 (ITGA4: 0.72 mN/mm2,P =0.015, concentration independent. ITGA9: 1.45 (25 µg/ml) to 1.7 (100 µg/ml) mN/mm2, P <0.0001, concentration dependent). Simultaneous blocking of integrin α4β1 and α9β1 using blocking antibodies (Fig. 5D) or BOP (3 µM, Fig. 5E) caused significant increase in vessel tension (Blocking antibodies: 1.09 mN/mm2, P <0.0001, concentration independent. BOP: 1.53 (25 µg/ml) to 1.98 (100 µg/ml) mN/mm2, all P <0.0001, concentration dependent), but did not enhance contraction compared to inhibition of individual integrins in isolation. Inhibition of integrin α4β1 and α9β1 using BOP did not enhance contraction inSvep1+/- mice (P =0.85, Fig. 5F).