FGF2 inhibits endothelial-mesenchymal transition through microRNA-20a-mediated repression of canonical TGF-β signaling

Endothelial-to-mesenchymal transition (EndMT) is characterized by the loss of endothelial cell markers and functions, and coincides with de novo expression of mesenchymal markers. EndMT is induced by TGF beta 1 and changes endothelial microRNA expression. We found that miR-20a is decreased during EndMT, and that ectopic expression of miR-20a inhibits EndMT induction. TGF beta 1 induces cellular hypertrophy in human umbilical vein endothelial cells and abrogates VE-cadherin expression, reduces endothelial sprouting capacity and induces the expression of the mesenchymal marker SM22 alpha (also known as TAGLN). We identified ALK5 (also known as TGFBR1), TGFBR2 and SARA (also known as ZFYVE9) as direct miR-20a targets. Expression of miR-20a mimics abrogate the endothelial responsiveness to TGF beta 1, by decreasing ALK5, TGFBR2 and SARA, and inhibit EndMT, as indicated by the maintenance of VE-cadherin expression, the ability of the cells to sprout and the absence of SM22 alpha expression. FGF2 increases miR-20a expression and inhibits EndMT in TGF beta 1-stimulated endothelial cells. In summary, FGF2 controls endothelial TGF beta 1 signaling by regulating ALK5, TGFBR2 and SARA expression through miR-20a. Loss of FGF2 signaling combined with a TGF beta 1 challenge reduces miR-20a levels and increases endothelial responsiveness to TGF beta 1 through elevated receptor complex levels and activation of Smad2 and Smad3, which culminates in EndMT.