FGF4 and ascorbic acid enhance the maturation of induced cardiomyocytes by activating JAK2-STAT3 signaling.

Direct cardiac reprogramming represents a novel therapeutic strategy to convert non-cardiac cells such as fibroblasts into cardiomyocytes (CMs). This process involves essential transcription factors, such as Mef2c, Gata4, Tbx5 (MGT), MESP1, and MYOCD (MGTMM). However, the small molecules responsible for inducing immature induced CMs (iCMs) and the signaling mechanisms driving their maturation remain elusive. Our study explored the effects of various small molecules on iCM induction and discovered that the combination of FGF4 and ascorbic acid (FA) enhances CM markers, exhibits organized sarcomere and T-tubule structures, and improves cardiac function. Transcriptome analysis emphasized the importance of ECM-integrin-focal adhesions and the upregulation of the JAK2-STAT3 and TGFB signaling pathways in FA-treated iCMs. Notably, JAK2-STAT3 knockdown affected TGFB signaling and the ECM and downregulated mature CM markers in FA-treated iCMs. Our findings underscore the critical role of the JAK2-STAT3 signaling pathway in activating TGFB signaling and ECM synthesis in directly reprogrammed CMs. Schematic showing FA enhances direct cardiac reprogramming and JAK-STAT3 signaling pathways underlying cardiomyocyte maturation.