Abstract 442: Epigenetic Regulation of Ezh2 in Direct Human Cardiac Reprogramming

Abstract

Cardiovascular disease is still the leading cause of death in the United States. Due to the limited regenerative capacity of adult hearts, the damage caused by heart injury could not be reversed and often progressed into heart failure. In need of cardiovascular disease treatment, many therapies aimed at either cell transplantation or cell regeneration have been proposed. Direct reprogramming of somatic cells into induced cardiomyocytes (iCMs) is considered to be a promising strategy for regenerative medicine. The induction of cardiomyocytes from non-myocytes has been achieved efficiently via ectopic expression of reprogramming factors both in vitro and in vivo with mice models. However, as human cells are more resistant to the reprogramming process, the generation of human iCMs (hiCMs) has been restricted by the factor that using more complex cocktails generated only functionally immature cells with lower efficiency and longer conversion time. The inefficiency of hiCMs production called for the identification and elucidation of underlying species-specific regulatory mechanisms in human, and removal of the additional epigenetic barriers which might be damping the hiCMs reprogramming. Here, we identified a human-specific epigenetic barrier, Enhancer of zesta homolog 2 (EZH2), via an unbiased loss-of-function screening. With the knockdown of EZH2, the hiCM reprogramming efficiency was significantly increased, accompanied with profound repression of collagen and extracellular matrix genes, which are related to the formation of fibrosis. Consistently, Inhibition of EZH2 catalytic activity via small molecules promotes hiCM reprogramming, suggesting that EZH2’s inhibitory effect was mediated by epigenetic regulation of histone modifications. Therefore, our study revealed a previously unrecognized regulatory mechanism of human cardiac reprogramming, which allows us to overcome the fibroblast fate barriers and ease the cardiac cell fate conversion.