Objective: To determine the intracellular mechanisms mediating the angiogenic effects of integrin alpha v beta 5 overexpression in circulating angiogenic cells (CACs).
Methods and results: Integrin alpha v beta 5 is expressed on angiogenic endothelial cells, and integrin alpha v beta 5 activation was shown to improve the reparative functions of endothelial progenitors within the cardiovascular system. CACs were transiently transfected with the full-length cDNA of human integrin beta 5 (CAC-ITGB5) or control-vector (CAC-vector). Integrin beta 5 overexpression was confirmed using flow cytometry, Western blot, and PCR analysis; it enhanced the angiogenic capacities of CACs in vitro (spheroid and Matrigel angiogenesis assay) and stimulated new vessel formation in vivo (murine hind limb ischemia model). Overexpression of ITGB5 resulted in integrin alpha v beta 5 phosphorylation and activation of Src kinase and signal transducer and activator of transcription (STAT) 3. Furthermore, elevated mRNA and protein expression of the CXC chemokine CXCL8 and the CC chemokine CCL2 was detected in CAC-ITGB5, and conditioned medium from CAC-ITGB5 enhanced the sprouting of coincubated human endothelial cells in a STAT3-, CXCL8-, and CCL2-dependent manner.
Conclusions: Src kinase-mediated activation of STAT3 and subsequent angiogenic gene expression mediate the effects of integrin alpha v beta 5 and may be exploited to enhance the paracrine activities of CACs.