Integrin profile and in vivo homing of human smooth muscle progenitor cells

Background-Recently, we identified circulating smooth muscle progenitor cells (SPCs) in human peripheral blood. The integrin profile of such progenitors is currently unknown and may affect their in vivo homing characteristics. In this study, we determined the integrin profile of vascular progenitors and SPC adhesion to extracellular matrix (ECM) proteins in vitro and in vivo. Methods and Results-SPCs and endothelial progenitor cells (EPCs) were isolated from peripheral blood of healthy human subjects, and expression of surface integrins and adhesion to several vascular ECM proteins were determined. Homing of SPCs in vivo to specific ECM protein was determined by intracoronary infusion of fluorescent SPCs into porcine coronary arteries containing a fibronectin-coated mesh stent. SPCs had high expression of β₁ integrin, moderate expression of α₁, low levels of α_vβ ₃, and did not express α_vβ₅, β₂, α₂β₁, or α₄β₁ integrins. In contrast, EPCs had high expression of α₂β₁, α_vβ ₃, α_vβ₅, β₁, and α₁ and minimal expression of α₄β ₁. Moreover, SPCs showed increased adherence to fibronectin and collagen type I compared with vitronectin, consistent with their integrin profile, and demonstrated a similar degree of in vivo attachment to fibronectin-coated mesh. Conclusions-These data for the first time show a spectrum of integrin expression on vascular progenitors and suggest the potential importance of integrins in mediating adherence of SPCs to specific ECM both in vitro and in vivo.