Chemical Enhancement of In Vitro and In Vivo Direct Cardiac Reprogramming

BACKGROUND: -Reprogramming of cardiac fibroblasts into induced cardiomyocyte-like cells (iCMs) in situ represents a promising strategy for cardiac regeneration. A combination of three cardiac transcription factors, Gata4, Mef2c and Tbx5 (GMT), can convert fibroblasts into iCMs, albeit with low efficiency in vitro METHODS: -We screened 5,500 compounds in primary cardiac fibroblasts to identify the pathways that can be modulated to enhance cardiomyocyte reprogramming.

RESULTS: -We found that a combination of the transforming growth factor (TGF)-β inhibitor SB431542 and the WNT inhibitor XAV939 increased reprogramming efficiency eight-fold when added to GMT-overexpressing cardiac fibroblasts. The small-molecules also enhanced the speed and the quality of cell conversion, as we observed beating cells as early as 1 week after reprogramming compared to 6-8 weeks with GMT alone. In vivo, mice exposed to GMT, SB431542, and XAV939 for 2 weeks after myocardial infarction showed significantly improved reprogramming and cardiac function compared to those exposed to only GMT. Human cardiac reprogramming was similarly enhanced upon TGF-β and WNT inhibition and was achieved most efficiently with GMT plus Myocardin.

CONCLUSIONS: -Thus, TGF-β and WNT inhibitors jointly enhance GMT-induced direct cardiac reprogramming from cardiac fibroblasts in vitro and in vivo and provide a more robust platform for cardiac regeneration.