Activation of the integrins a5b1 and avb3 and focal adhesion kinase (FAK) during arteriogenesis

Abstract Migration and proliferation of smooth muscle cells (SMC) are important events during arteriogenesis, but the underlying mechanism is still only partially understood. The present study investigates the expression of integrins a5b1 and vb3 as well as focal adhesion kinase (FAK) and phosphorylated FAK (pY397), key mediators for cell migration and proliferation, in collateral vessels (CV) in rabbit hind limbs induced by femoral ligation or an arte-riovenous (AV) shunt created between the distal femoral artery stump and the accompanying femoral vein by con-focal immunofluorescence. In addition, the effect of the extracellular matrix components fibronectin (FN), laminin (LN), and Matrigel on expression of these focal adhesion molecules proliferation was studied in cultured SMCs. We found that: (1) in normal vessels (NV), both integrins a5b1 and avb3 were mainly expressed in endothelial cells, very weak in smooth muscle cells (SMC); (2) in CVs, both a5b1 and avb3 were significantly upregulated (P \ 0.05); this was more evident in the shunt-side CVs, 1.5 and 1.3 times higher than that in the ligation side, respectively; (3) FAK and FAK(py397) were expressed in NVs and CVs in a similar profile as was a5b1 and avb3; (4) in vitro SMCs cultured on fibronectin (overexpressed in collaterals) expressed higher levels of FAK, FAK (pY397), a5b1, and avb3 than on laminin, whereas SMCs growing inside Matrigel expressed little of these proteins and showed no proliferation. In conclusion, our data demonstrate for the first time that the integrin-FAK signaling axis is activated in collateral vessels and that altered expression of FN and LN may play a crucial role in mediating the integrin-FAK signaling pathway activation. These findings explain a large part of the positive remodeling that collateral vessels undergo under the influence of high fluid shear stress