Activation of the integrins α5β1 and αvβ3 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 α5β1 and vβ3 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 arteriovenous (AV) shunt created between the distal femoral artery
stump and the accompanying femoral vein by confocal 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 α5β1 and αvβ3 were mainly expressed in
endothelial cells, very weak in smooth muscle cells (SMC); (2) in CVs, both α5β1 and αvβ3 were significantly upregulated (P<0.05); this was more evident in the shunt-side CVs, 1.5 and 1.3times 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 α5β1 and αvβ3; (4) invitro SMCs cultured
on fibronectin (overexpressed in collaterals) expressed higher levels of FAK, FAK (pY397), α5β1, and αvβ3 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.