The overexpression of integrin ß5 enhances the angiogenetic properties of endothelial progenitor cells

Angiogenesis is a hallmark of diverse physiological and pathological processes, including ischemia, inflammation, wound healing and tumor growth. The angiogenetic process depends on the proliferation, migration and morphogenesis of endothelial cells. In addition to local endothelial cells, endothelial progenitor cells (EPCs), mobilized from the bone marrow into the circulation in response to tissue injury have been shown to contribute to reendothelialization and neovascularisation. The vitronectin receptor integrin avß5 is expressed on endothelial progenitor cells and integrin activation was shown to improve the reparative function of endothelial progenitor cells in the cardiovascular system. But the exact function of integrin avß5 during the angiogenetic process remains incompletely understood. While studies with gene-deleted mice have shown that the angiogenetic process expire nearly undisturbed, data obtained after integrin functional blockade resulted in an reduced neovaskularisation. To determine the exact function of the integrin avß5 during the angiogenetic process and to find out the intracellular mechanism mediating the angiogenetic efferct of integrin avß5, EPCs were transfected with the full-length cDNA of human integrin ß5 (EPC-ITGB5) or control-vector (EPC-vector). The overexpression of integrin ß5 could be confirmed by using PCR analysis, Western blot and flow cytomerty. In two different in vitro angiogenesis assays, the spheroid and the Matrigel angiogenesis assay, we could show, that the integrin ß5 overexpression enhances the angiogenetic capacities of endothelial progenitor cells and stimulate new vessel formation in vivo by using the mouse model of the unilateral hind limb ischemia. The overexpression of integrin ß5 leads to a significant increased phosphorylation of avß5 and the activation and nuclear translocation of signal transducer and activator of transcription (STAT) 3. Furthermore, we could detect an enhanced mRNA and protein expression of the cytokines IL-8 and MCP-1 in ITGB5-transfected EPCs. Also, we could find a higher concentration of IL-8 and MCP-1 in the conditioned medium from EPC-ITGB5, suggests an increased secretion of these chemokines. In functional assays we could show, that the conditioned medium from EPC-ITGB5 enhanced the sprouting activity of coincubated human endothelial cells in a STAT3-, MCP-1- and IL-8-dependent manner. The results of our studies suggests, that the activation of integrin avß5 leads via intracellular signal transduction to an increased activation of STAT3. After nuclear translocation, STAT3 seems to regulate the gene expression of the chemokines IL-8 and MCP-1. The increased secretion of these chemokines may be exploited to enhance the paracrine activities of EPCs.2015-10-2