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 - Mef2c, Gata4 , and Tbx5 (MGT), MESP1 and MYOCD (MGTMM). However, the small molecules responsible for inducing immature induced CM (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 significance of ECM-integrins-focal adhesions and the upregulation of JAK2-STAT3 and TGFB signaling pathways in FA-treated iCMs. Notably, JAK2-STAT3 knockdown affected TGFB signaling, ECMs, and downregulated mature CM markers in FA-treated iCMs. Our findings underscore the critical role of the JAK2-STAT3 signaling pathway in directly reprogrammed CMs by activating TGFB signaling and ECM synthesis.