Stoichiometry of transcription factors is critical for cardiac reprogramming.

Abstract

Direct reprogramming of fibroblasts into cardiomyocytes holds great potential for cardiovascular disease research and treatment. This new technology may be used for patient-specific drug screening, cardiac disease modeling, and regenerative purposes. We reported first that a combination of 3 cardiac-specific transcription factors, Gata4 (G), Mef2c (M), and Tbx5 (T), constituted the minimum requirement to directly reprogram mouse cardiac fibroblasts (CFs) into induced cardiomyocytes (iCMs).1 Subsequently, multiple groups have achieved and improved direct cardiac reprogramming from mouse and human fibroblasts by overexpressing other combinations of cardiac transcription factors and cardiac-enriched miRNAs.2–9 Intriguingly, it was reported that gene delivery of reprogramming factors into mouse infarcted hearts converted endogenous CFs into functional iCMs, reduced scar size, and improved cardiac function after myocardial infarction.4,10,11 Although these recent achievements are promising, the low reprogramming efficiency of fully reprogrammed functional iCMs and the reproducibility of cardiac reprogramming continue to be controversial aspects of this technology. Chen et al12 showed that transduction of pooled lentiviruses expressing G, M, and T was insufficient to reprogram fibroblasts into a cardiac fate. We reported that a polycistronic vector and a mixture of individual vectors expressing G, M, and T could reprogram resident CFs into iCMs in vivo, but the efficiency of cardiac reprogramming in this study was lower than that in other reports.13 These findings suggest that slight technical or biological differences might result in variable reprogramming efficiency.14 Therefore, critical factors for cardiac reprogramming need to be identified, and standardized platforms for efficient and reproducible cardiac induction should be established to advance this field. In …