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The mechanisms of proangiogenic activity of multipotent stromal cells from human umbilical cord were analyzed in vitro. The absence of secreted forms of proangiogenic growth factor VEGF-A in the culture medium conditioned by umbilical cord-derived multipotent stromal cells was shown by ELISA. However, the possibility of paracrine stimulation of cell proliferation, mobility, and directed migration of endothelial EA.hy926 cells was demonstrated by using MTT test, Transwell system, and monolayer wound modeling. The capacity of multipotent stromal cells to acquire the phenotype of endothelium-like cells was analyzed using differentiation media of three types. It was found that VEGF-A is an essential but not sufficient inductor of differentiation of umbilical cord-derived multipotent stromal cells into CD31+ cells.

Short-term cell culturing on basement membrane matrix is a common and very convenient in vitro model of angiogenesis. We studied the possibility of interaction of multipotent stromal cells from the umbilical cord and Ea.hy926 endothelial cells on this model at the early and late periods of the experiment. Multipotent stromal cells alone and in combination with endothelial cells formed an unstable tubular network. Clusters formed after its disassembling later became the sprouting centers in co-culture of the two cell types, but not in pure culture of multipotent stromal cells. Multipotent stromal cells with CD31+ phenotype constitute the structural basis of newly formed stable 3D capillary-like network. Prolongation of the time of culturing and combination of the two in vitro models of angiogenesis (tubulogenesis and sprouting) allowed more complete assessment of the angiogenic potential of multipotent stromal cells.