Endothelial progenitor cells express PAF receptor and respond to PAF via Ca-dependent signaling

Endothelial progenitor cell (EPC) therapy is a promising approach to promote angiogenesis and endothelial repair in patients with cardiovascular diseases (CVD). However, their release of proinflammatory mediators may compromise the therapeutic efficacy. Little is known about the role of Platelet-Activating Factor (PAF) in EPC functional response. Here, we investigated the expression of PAF receptor (PAF-R) in early EPC and the release of PAF under stimulation with factors involved in endothelial dysfunction. Results indicated that early EPC express the PAF-R and respond to PAF signaling via a transient increase of cytoplasmic Ca²⁺ concentration. EPC release PAF in a time dependent manner upon stimulation with tumor necrosis factor-α (TNF-α) or high-glucose concentration with a peak at 30 min and 10 min (p < 0.01 vs. control), respectively. PAF, starting at concentration of 50 ng/ml, exerted a detrimental effect on EPC number with a concomitant increase of p38 activity. Furthermore, both the reduction of early EPC number and the enhanced p38 activity induced by PAF were abolished by CV3988, a PAF receptor antagonist. These novel findings, revealing that early EPC respond to PAF signaling, unveil an inflammatory pathway that may play a crucial role in the outcome of cardiovascular cell therapy with EPC.