Treprostinil indirectly regulates endothelial colony forming cell angiogenic properties by increasing VEGF-A produced by mesenchymal stem cells

<b>Background:</b> Pulmonary vasodilators have markedly improved the outcome of patients with pulmonary hypertension (PH). Endothelial dysfunction is a key feature of PH, and we previously reported that treprostinil therapy increases number and proliferative potential of endothelial colony forming cells (ECFC) isolated from PH patients. <b>Aims:</b> objectives were to determine how treprostinil contributes to the proangiogenic functions of ECFC. <b>Methods:</b> We examined effect of treprostinil on ECFC in terms of colony numbers, proliferative and clonogenic properties in vitro, as well as in vivo vasculogenic properties. <b>Results:</b> Surprisingly, treprostinil inhibited viability of cultured ECFC but did not modify their clonogenic properties nor their endothelial differentiation potential from cord blood stem cells. Treprostinil treatment significantly increased the vessel-forming ability of ECFC combined with mesenchymal stem cells (MSC) in Matrigel implanted in nude mice. In vitro, ECFC proliferation was stimulated by conditioned media from treprostinil-pretreated MSC, and this effect was inhibited either by VEGF-A blocking antibodies or siRNA VEGF-A in MSC. Silencing VEGF-A gene in MSC also blocked the pro-angiogenic effect of treprostinil in vivo. clinical relevance of these data was confirmed by the high level of VEGF-A detected in plasma from pediatric PH patients treated with treprostinil. <b>Conclusion:</b> In conclusion, increased VEGF-A produced by MSC can account for the increased vessel formation observed during treprostinil treatment. Moreover, our results suggest that VEGF-A level in patients could be a surrogate biomarker of treprostinil efficacy.