Abstract P1116: Histone Deacetylase Complexes Regulate Direct Cardiac Conversion From Human Fibroblasts

Direct cardiac reprogramming is a promising approach to generate functional cardiomyocytes from non-myocytes for regenerative medicine, drug screening, and disease modeling. This method involves the transformation of specialized cells into functional cardiomyocytes using specific transcription factors or molecular signals. Epigenetic modulators, such as histone deacetylase (HDAC) complexes, may play a critical role in chromatin remodeling underlying cardiac reprogramming. To investigate the role of HDAC complexes in direct cardiac conversion, induced cardiomyocyte-like cells (iCMs) were derived from human fibroblasts through ectopic expression of reprogramming factors, and the changes of histone acetylation were evaluated by western blotting. The results showed decreased levels of H3K9ac, H3K14ac, and H3K27ac along with direct cardiac reprogramming, suggesting the significant chromatin remodeling and gene regulation. A loss-of-function screen of all the components associated with HDAC complex was performed to determine the responsible histone acetylation modifiers. The screen results showed that most of the HDAC components are necessary for direct cardiac reprogramming. Further investigation focused on a newly identified HDAC complex, mitotic deacetylase complex (MiDAC), consisting of mitotic deacetylase associated SANT domain protein MiDEAS (ELMSAN1), DNTTIP1, and HDAC1. Knocking down each of the MiDAC components led to similar reprogramming repression and cell death, indicating that MiDAC plays a critical role in cardiac reprogramming. In addition, the expression analysis of DNTTIP1 and HDAC1 showed a gradual decrease throughout the conversion, while ELMSAN1 diminished at the early stage of reprogramming, suggesting that ELMSAN1 is likely required for MiDAC stability. Furthermore, overexpression of ELMSAN1 significantly improved reprogramming efficiency and led to the increase of H3K9ac, H3K14ac, and H3K27ac levels globally, suggesting that ELMSAN1 and MiDAC might be responsible for the regulation of such histone modifications during the process. Overall, our findings provide novel insights into the epigenetic regulation of direct cardiac reprogramming and reveal the potential role of MiDAC in this process.