Translational landscape of direct cardiac reprogramming reveals a role of Ybx1 in repressing cardiac fate acquisition

Abstract

Direct reprogramming of fibroblasts into induced cardiomyocytes (iCMs) holds great promise for heart regeneration. Although considerable progress has been made in understanding the transcriptional and epigenetic mechanisms of iCM reprogramming, its translational regulation remains largely unexplored. Here, we characterized the translational landscape of iCM reprogramming through integrative ribosome and transcriptomic profiling, and found extensive translatome repatterning during this process. Loss-of-function screening for translational regulators uncovered Y-box binding protein 1 (Ybx1) as a critical barrier to iCM induction. In a mouse model of myocardial infarction, removing Ybx1 enhanced in vivo reprogramming, resulting in improved heart function and reduced scar size. Mechanistically, Ybx1 depletion de-repressed the translation of its direct targets Srf and Baf60c, both of which mediated the effect of Ybx1 depletion on iCM generation. Furthermore, removal of Ybx1 allowed single-factor, Tbx5-mediated iCM conversion. In summary, the findings reveal a new layer of regulatory mechanism that controls cardiac reprogramming at the translational level.