Inefficient reprogramming of fibroblasts into cardiomyocytes using Gata4, Mef2c, and Tbx5.

RATIONALE Direct reprogramming of fibroblasts into cardiomyocytes is a novel strategy for cardiac regeneration. However, the key determinants involved in this process are unknown. OBJECTIVE To assess the efficiency of direct fibroblast reprogramming via viral overexpression of GATA4, Mef2c, and Tbx5 (GMT). METHODS AND RESULTS We induced GMT overexpression in murine tail tip fibroblasts (TTFs) and cardiac fibroblasts (CFs) from multiple lines of transgenic mice carrying different cardiomyocyte lineage reporters. We found that the induction of GMT overexpression in TTFs and CFs is inefficient at inducing molecular and electrophysiological phenotypes of mature cardiomyocytes. In addition, transplantation of GMT infected CFs into injured mouse hearts resulted in decreased cell survival with minimal induction of cardiomyocyte genes. CONCLUSIONS Significant challenges remain in our ability to convert fibroblasts into cardiomyocyte-like cells and a greater understanding of cardiovascular epigenetics is needed to increase the translational potential of this strategy.