Summary
Circulating endothelial progenitor cells have been shown to instigate new vessel formation
via angiogenesis and neovascularisation and to induce ongoing vascular and tissue
repair by domiciliation to sites of vascular or tissue damage. However, the mechanisms
that recruit circulating endothelial progenitor cells towards vascular lesions and
regulate repair mechanisms of ischemic peripheral organs are poorly described. Domiciliation
of endothelial progenitor cells in peripheral tissue is a multi-step cascade including
initial adhesion to subendothelial matrix or endothelium, transmigration and invasion
of the target tissue. Platelets are the first circulating blood cells that interact
with the injured vessel wall. They contain a number of growth factors, chemokines,
cytokines and adhesive proteins that are released or surface-expressed upon platelet
activation including adhesion. Recent studies suggest that platelet interaction with
endothelial progenitor cells influences chemotaxis, adhesion, activation and differentiation
of progenitor cells. Release of the chemokine SDF-1 from platelets enhances neovascularization
through mobilization of progenitor cells. Adherent platelets recruit bone marrow-derived
progenitor cells to arterial thrombi in vitroand in vivoand induce their subsequent differentiation towards an endothelial phenotype. Moreover,
platelet accumulation in a co-culture system with CD34+ progenitor cells results in the differentiation of the latter to macrophages in vitro. Although further studies are needed to elucidate the mechanisms that platelets determine
the fate of endothelial progenitor cells into vascular lesions, platelet interaction
with progenitor cells seems to play a decisive role in vascular and tissue regeneration.
Keywords
Endothelial progenitor cells - platelets - vascular adhesion - endothelial injury