TGFB1 and atrial fibrillation: Accordingly, in AF-MSCs exposed to both bFGF and selenium, selenium might increase TGF-β secretion while the cells intensively secrete paracrine factors, including VEGF and IL-6, through bFGF- and TGF-β-induced signaling (Fig. 2a, b), supported by the relatively high levels of VEGF and IL-6 secreted from CM (−/s) (Fig. 5a, b).