A new approach to transcription factor screening for reprogramming of fibroblasts to cardiomyocyte-like cells.

The simultaneous overexpression of several transcription factors has emerged as a successful strategy to convert fibroblasts into other cell types including pluripotent cells, neurons, and cardiomyocytes. The selection and screening of factors are critical, and have often involved testing a large pool of transcription factors, followed by successive removal of single factors. Here, to identify a cardiac transcription factor combination facilitating mouse fibroblast reprogramming into cardiomyocytes, we directly screened all triplet combinations of 10 candidate factors combined with a Q-PCR assay reporting induction of multiple cardiac-specific genes. Through this screening method the combination of Tbx5, Mef2c, and Myocd was identified to upregulate a broader spectrum of cardiac genes compared to the combination of Tbx5, Mef2c, and Gata4 that was recently shown to induce reprogramming of fibroblasts into cardiomyocytes. Cells cotransduced with Tbx5, Mef2c, Myocd expressed cardiac contractile proteins, had cardiac-like potassium and sodium currents and action potentials could be elicited. In summary the alternative screening approach that is presented here avoided the elimination of transcription factors whose potency is masked in complex transcription factor mixes. Furthermore, our results point to the importance of verifying multiple lineage specific genes when assessing reprogramming.