Endothelial progenitor cells in vascular repair and remodeling

Postnatal bone marrow contains a subtype of unique progenitor cells that have the capacity to differentiate into functional endothelial cells. Hence, these cells have been termed endothelial progenitor cells (EPCs). In general, circulating EPCs were characterized by the expression of CD133, CD34 and the vascular endothelial growth factor receptor-2 (VEGFR2). Recent data have additionally described some CD14(+/low) myeloid subsets as functional endothelial precursors. Convincing evidence in vivo has further emerged that the vascular homing of EPCs contributes to endothelial regeneration thereby limiting neointimal hyperplasia after arterial injury. However, in the context of primary atherosclerosis, plaque progression and destabilization, injection of EPCs as well as application of stem-cell mobilizing factors have been shown to correlate with conversion to unstable plaque phenotype. Clinically, the number and function of EPCs have been positively linked with an improved endothelial function or regeneration but frequently inversely correlated with cardiovascular risk (factors). Thus, considering the dual contribution of EPCs in vascular repair and remodeling in primary atherosclerosis versus arterial injury and identifying mechanisms for selective control of their recruitment appears crucial to improve prediction and to directly modulate endogenous vascular homeostasis.