Endothelial progenitor cells undergo an endothelial-to-mesenchymal transition-like process mediated by TGFβRI

Endothelial progenitor cells (EPC) have been shown to repair pulmonary endothelium, although they can also migrate into the arterial intima and differentiate into smooth muscle-like (mesenchymal) cells contributing to intimal hyperplasia. The molecular mechanisms by which this process proceeds have not been fully elucidated. Here, we study whether genes involved in the endothelial-to-mesenchymal transition (EnMT) may contribute to the mesenchymal phenotype acquisition of EPC and we evaluate whether transforming growth factor beta 1 (TGF beta 1) is involved in this process. Our results show that co-culture of EPC with smooth muscle cells (SMC) increases the expression of the mesenchymal cell markers alpha-smooth muscle actin, sm22-alpha, and myocardin, and decreases the expression of the endothelial cell marker CD31. In the same conditions, we also observed a concomitant increase in the gene expression of the EnMT-related transcription factors: slug, snail, zeb1, and endothelin-1. This indicates that mesenchymal phenotype acquisition occurred through an EnMT-like process. Inhibition of TGF beta receptor I (TGF beta RI) downregulated snail gene expression, blocked the EnMT, and facilitated the differentiation of EPC to the endothelial cell lineage. Furthermore, TGF beta RI inhibition decreased migration of EPC stimulated by SMC without affecting their functionality and adhesion capacity. These results indicate that EPC may differentiate into SMC-like cells through an EnMT-like process and that TGF beta I plays an important role in the fate of EPC.