In vitro model of vasculo-angiogenesis: demonstration that bone marrow derived endothelial progenitor cells form new hybrid capillary blood vessels jointly with gastric endothelial cells.

Regeneration of blood vessels (neovascularization) is critical for tissue injury healing. The contribution of bone marrow-derived endothelial progenitor cells (BMD-EPCs) to neovascularization during tissue injury healing is not fully elucidated and it is not clear whether BMD-EPCs can form new capillary blood vessels independently or jointly with fully differentiated endothelial cells (ECs). The aim of this study was to establish an in vitro model of vasculogenesis/angiogenesis by co-culture of BMD-EPCs and gastric endothelial cells (GECs) on Matrigel, examine direct interactions of these cells; and, identify the mechanisms involved. We isolated BMD-EPCs and GECs from bone marrow and stomach of rats, respectively. In these cells, we examined the expression of CD34, CD133, CD31, VEGF-R2, stromal derived factor 1 (SDF-1) and CXCR4, and, their ability to form capillary-like tubes when cultured separately or when co-cultured (1:5 ratio) on growth factor-reduced Matrigel. Fluorescence-labeled BMD-EPCs seeded alone on Matrigel formed capillary-like tubes reflecting in vitro vasculogenesis, and when co-cultured with GECs on Matrigel, formed 'hybrid' tubes containing BMD-EPCs nested between GECs thus reflecting in vitro angio-vasculogenesis. These 'hybrid' tubes were 1.5-fold wider (P < 0.001) and had more extensive (5.1-fold increase) loops (P < 0.01) at the junctions of BMD-EPCs and GECs versus tubes formed by GECs alone. GECs expressed SDF-1 that likely mediated homing of BMD-EPCs (which expressed the SDF-1 receptor, CXCR4) and their incorporation during neovascularization. BMD-EPCs can independently form capillary-like tubes on Matrigel, and when co-cultured with fully differentiated ECs on Matrigel, form capillary-like 'hybrid' tubes comprised of both cell types. Both BMD-EPCs and GECs express SDF-1 and CXCR4, which indicate direct paracrine interactions between these cells during neovascularization.