Reconstruction of Extracellular Matrix by Grhl3 Modulates Cell Fate Commitment from Fibroblasts to Induced Cardiomyocytes

Direct cardiac reprogramming provides a promising therapeutic strategy for heart regeneration by leveraging the endogenous fibroblast population to restore myocardial structure and function. While cardiac transcription factors such as Mef2c, Gata4 and Tbx5 (MGT) drive the generation of induced cardiomyocyte (iCM), the role of extracellular matrix (ECM) components during this process remain largely unexplored. Here, we investigated ECM dynamics during iCM reprogramming and identified integrin subunit alpha 8 (Itga8) as a critical ECM component that suppresses iCM conversion. A loss-of-function screen revealed grainyhead-like protein 3 homolog (Grhl3) as a transcriptional regulator of ECM, including Itga8. Multi-omics analyses demonstrated that Grhl3 efficiency remodels ECM composition to a cardiomyocyte-like state, enhancing iCM reprogramming efficiency and functional maturation. In a mouse model of myocardial infarction, removing Grhl3 enhanced in vivo cardiac reprogramming, and contributed to reduced scar size and improved heart function. These findings establish ECM remodeling as a critical determinant of cardiac reprogramming and identify Grhl3 as a promising therapeutic target to advance myocardial repair strategies.