FGF2-induced Ras/Erk MAPK signalling maintains lymphatic endothelial cell identity by up-regulating endothelial cell-specific gene expression and suppressing TGFβ signalling via Smad2

Abstract

The lymphatic endothelial cell (LEC) fate decision program during development has been described. However, the mechanism underlying the maintenance of differentiated LEC identity remains largely unknown. Here, we show that fibroblast growth factor 2 (FGF2) plays a fundamental role in maintaining a differentiated LEC trait. In addition to demonstrating the appearance of LECs expressing a-smooth muscle actin in mouse lymphedematous skin in vivo, we found that mouse immortalised LECs lose their characteristics and undergo endothelial-to-mesenchymal transition (EndMT) when cultured in FGF2-depleted medium. FGF2 depletion acted synergistically with transforming growth factor (TGF) b to induce EndMT. We also found that H-Ras-overexpressing LECs were resistant to EndMT. Activation of H-Ras not only upregulated FGF2-induced activation of the Erk mitogen activated protein kinases (MAPK3 and MAPK1), but also suppressed TGFb-induced activation of Smad2 by modulating Smad2 phosphorylation by MAPKs. These results suggest that FGF2 regulates LEC-specific gene expression and suppresses TGFb signalling in LECs through Smad2 in a Ras-MAPK-dependent manner. Taken together, our findings provide a new insight into the FGF2-Ras-MAPK-dependent mechanism that maintains and modulates the LEC trait.

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

“…Interestingly, the expression of another microRNA that inhibits ALK5 expression, let-7b, is also highly dependent on FGF2 signaling, as the loss of FGFR1 results in the ablation of let-7b levels and an increase TGFβ activity and EndMT (Chen et al, 2012). These data corroborate and extend earlier reports where FGF2 was reported to reduce endothelial sensitivity to TGFβ (Kawai-Kowase et al, 2004;Ichise et al, 2014).…”

“…Interestingly, although we and others describe a protective effect of FGF2 against EndMT induction in mature and progenitor endothelial cells (Moonen et al, 2010;Ichise et al, 2014), others have linked FGF2 signaling to EndMT induction (Ghosh et al, 2010;Lee et al, 2012). Indeed, FGF2 is known to inhibit EndMT in macrovascular endothelial cells, whereas it induces EndMT is some microvascular endothelial cell types (Lee et al, 2004;Lee and Kay, 2006).…”

“…Endothelial mitogens inhibit EndMT (Medici and Kalluri, 2012;Okayama et al, 2012;Ichise et al, 2014;Zhang et al, 2015). We questioned whether this inhibitory effect might be (in part) due to the induction of miR-20a.…”

Fibroblast Growth Factor 2 as an Antifibrotic: Antagonism of Myofibroblast Differentiation and Suppression of Pro-Fibrotic Gene Expression

“…Overexpression of H-Ras rescued the EndMT-suppressing effects of FGF2 depletion via inhibition of TGFβ-mediated SMAD2 activation, implicating FGF2/FGFR/Ras in TGFβ signaling and maintenance of endothelial cellular identity. Knockdown of endogenous Ras reduced endothelial markers, suggesting that baseline Ras activity maintains endothelial and suppresses mesenchymal phenotypes in endothelial cells [103]. Taken together, these data suggest that FGF2 is able to prevent or reverse transdifferentiation to myofibroblasts from precursors such as endothelial and epithelial cells.…”

Receptor Tyrosine Kinases Endocytosis in Endothelium

“…2D) 62 . FGF2 also induces ERK1/2 activation 63 . And FGF2-dependent ERK1/2 signaling plays a key role in the maintenance of VEGFR2 expression 1 .…”