Transient BRD4 degradation improves cardiac reprogramming by inhibiting macrophage/Oncostatin M induced JAK/STAT pathway

Reprogramming fibroblasts into induced cardiomyocytes (iCMs) holds great potential for cardiac regeneration. However, low conversion rate both in vitro and in vivo remains a significant challenge. To address this challenge, we focused on potential epigenetic barriers and screened 33 small-molecule inhibitors/degraders targeting histone acetyl post-translational modifications and related epigenetic factors. BET degraders were found to enhance cardiac reprogramming efficiency by degrading BRD4 and repressing genes involved in immune response, particularly those in the JAK/STAT pathway. We further identified that macrophage/oncostatin M activated the JAK/STAT pathway to repress cardiac reprogramming. BRD4 degrader treatment improved iCMs formation by inhibiting macrophage/oncostatin M-induced activation of the JAK/STAT pathway. Moreover, BRD4 degrader treatment enhanced MGT-mediated cardiac regeneration in vivo and improved myocardial performance post-myocardial infarction. These findings provide new insights into BRD4, macrophage/oncostatin M and JAK/STAT pathway in fibroblast to cardiomyocyte-like cell conversion and offer promising targets and small molecules to improve iCM reprogramming for clinical applications. Highlights Screen of histone acetylation modifiers identified BRD4, a histone acetylation reader, as an important regulator in cardiac reprogramming. BRD4 degradation promoted cardiac reprogramming by repressing inflammation and the JAK-STAT pathway. BRD4 degradation inhibited macrophage/oncostatin M-induced activation of the JAK/STAT pathway. BRD4 degradation enhanced MGT-mediated cardiac regeneration in vivo and improved myocardial performance post-myocardial infarction.