Abstract 103: TBX20 Activates Cardiac Maturation Gene Programs Promoting Direct Human Cardiac Reprogramming

Abstract

Direct cardiac reprogramming to generate induced cardiomyocyte like cells (iCMs) from fibroblasts has emerged as a promising therapeutic strategy for the treatment of heart failure, which is still the leading cause of mortality and morbidity in developed countries. While much is known regarding iCMs generated from mouse cells, the adaptation of direct cardiac reprogramming to human cells is hurdled with low efficiency and poor quality because of intrinsic differences between species. Recently, our single cell transcriptomic analysis during human direct cardiac reprogramming demonstrated the immature features of human iCMs (hiCMs) compared to endogenous cardiomyocytes (CMs) at the transcriptome level, suggesting that key factors required for CM maturation remain unidentified. We then utilized computational analyses of genomic and epigenomic data to identify the regulators underexpressed in hiCMs comparing to CMs derived from human heart tissue or stem cell differentiation. Among them, the top hit is T-box family transcription factor TBX20, whose role in direct cardiac reprogramming remains to be explored. Supplementing TBX20 in reprogramming cocktails, we found significantly increased sarcomeric protein expression, like αMHC and αActinin in hiCMs and the formation of well-organized myofibrils. TBX20’s effect has also been supported by transcriptomic analysis, where we found TBX20 activates a large number of underexpressed genes associated with sarcomere structure and ion channels, such as MYH7 , MYL2 , MYBPC3, SCN5A and KCNQ1 , suggesting that TBX20 likely enhances maturation and contractility of hiCMs. We also found that TBX20 cannot replace any of the reprogramming factors, suggesting that its potential role is complimentary to and interacting with the current cocktail. Moreover, known TBX20 targets showed inconsistent alteration in TBX20-transduced hiCMs, suggesting its novel regulation in a direct reprogramming setting. These findings assign a novel reprogramming factor TBX20 playing an essential role in generating mature hiCMs by establishing gene programs associated with cardiac muscle contractility.