Introduction: Endothelial progenitor cells (EPCs) have an important role in the process of vascular injury repair. Platelets have been shown to mediate EPC recruitment, maturation and differentiation. However, it has also been shown that platelets have the ability to induce differentiation of human CD34+ cells into foam cells, and that platelets derived from patients with cardiovascular risk factor fail to augment EPCs functional properties. Thus, in this study we aim to explore the variable effect platelets exert on EPCs
Methods: Human EPCs were isolated from donated buffy coats and cultured with or without platelets in the presence or absence of bFGF/PDGF receptor inhibitor (PDGFRI) / TGFβ receptor II (TGFβ RII) inhibitor. After 7 days of culture, EPCs ability to form colonies, proliferate and differentiate was examined.
Results: After 7 days of culture, in 60% of experiments EPCs functional properties were enhanced following co-incubation with platelets, while in 40% of the experiments platelets reduced the capacity of EPCs to form colonies and differentiate. In the 60% “positive” experiments EPC function was reduced by PDGFRI and TGFβ RII inhibition, while in the other 40% of experiments FGF and TGFβ RII inhibition improved EPC function. When searching for factors that were associated with the effect platelets exert on EPCs, we found that the initial capacity of EPCs to express endothelial markers largely determines the direction of the platelets’ effect. When the initial functional state of EPCs was attenuated platelets exerted a positive effect on them. As the initial expression of endothelial markers by EPCs increased, the effect of platelets was diminished.
Conclusions: the initial functional state of EPCs and their preliminary ability to express endothelial markers is strongly related to the subsequent effect platelets exert on these cells following co-culture.
