Inhibition of endothelial progenitor cell differentiation by VEGI

Endothelial progenitor cells (EPCs) play a critical role in postnatal and tumor vasculogenesis. Vascular endothelial growth inhibitor (VEGI; TNFSF15) has been shown to inhibit endothelial cell proliferation by inducing apoptosis. We report here that VEGI inhibits the differentiation of EPCs from mouse bone marrow-derived Sca1(+) mononuclear cells. Analysis of EPC markers indicates a significant decline of the expression of endothelial cell markers, but not stem cell markers, on VEGI-treated cells. Consistently, the VEGI-treated cells exhibit a decreased capability to adhere, migrate, and form capillary-like structures on Matrigel. In addition, VEGI induces apoptosis of differentiated EPCs but not early-stage EPCs. When treated with VEGI, an increase of phospho-Erk and a decrease of phospho-Akt are detected in early-stage EPCs, whereas activation of nuclear factor-kappaB, jun N-terminal kinase, and caspase-3 is seen in differentiated EPCs. Furthermore, VEGI-induced apoptosis of differentiated EPC is, at least partly, mediated by death receptor-3 (DR3), which is detected on differentiated EPC only. VEGI-induced apoptosis signals can be inhibited by neutralizing antibodies against DR3 or recombinant extracellular domain of DR3. These findings indicate that VEGI may participate in the modulation of postnatal vasculogenesis by inhibiting EPC differentiation.