Primary and immortalized mouse epicardial cells undergo differentiation in response to TGFβ

Cells derived from the epicardium are required for coronary vessel development. Transforming growth factor beta (TGF beta) induces loss of epithelial character and smooth muscle differentiation in chick epicardial cells. Here, we show that epicardial explants from embryonic day (E) 11.5 mouse embryos incubated with TGF beta 1 or TGF beta 2 lose epithelial character and undergo smooth muscle differentiation. To further study TGF beta Signaling, we generated immortalized mouse epicardial cells. Cells from E10.5,11.5, and 13.5 formed tightly packed epithelium and expressed the epicardial marker Wilm's tumor 1 (WT1). TGF beta induced the loss of zonula occludens-1 (ZO-1) and the appearance of SM22 alpha and calponin consistent with smooth muscle differentiation. Inhibition of activin receptor-like kinase (ALK) 5 or p160 rho kinase activity prevented the effects of TGF beta while inhibition of p38 mitogen activated protein (MAP) kinase did not. These data demonstrate that TGF beta induces epicardial cell differentiation and that immortalized epicardial cells provide a suitable model for differentiation.