Snail is required for TGF-induced endothelial-mesenchymal transition of embryonic stem cell-derived endothelial cells

Epithelial-mesenchymal transition (EMT) plays important roles in various physiological and pathological processes, and is regulated by signaling pathways mediated by cytokines, including transforming growth factor (TGF). Embryonic endothelial cells also undergo differentiation into mesenchymal cells during heart valve formation and aortic maturation. However, the molecular mechanisms that regulate such endothelial-mesenchymal transition (EndMT) remain to be elucidated. Here we show that TGF plays important roles during mural differentiation of mouse embryonic stem cell-derived endothelial cells (MESECs). TGF2 induced the differentiation of MESECs into mural cells, with a decrease in the expression of the endothelial marker claudin 5, and an increase in expression of the mural markers smooth muscle -actin, SM22 and calponin, whereas a TGF type I receptor kinase inhibitor inhibited EndMT. Among the transcription factors involved in EMT, Snail was induced by TGF2 in MESECs. Tetracycline-regulated expression of Snail induced the differentiation of MESECs into mural cells, whereas knockdown of Snail expression abrogated TGF2-induced mural differentiation of MESECs. These results indicate that Snail mediates the actions of endogenous TGF signals that induce EndMT.