Conservation of miR combo based direct cardiac reprogramming

There is considerable interest in regenerating the injured heart by reprogramming resident fibroblasts into new functional cardiomyocytes. Cardiac reprogramming has been achieved via transcription factors or miRNAs. Transcription factor combinations appear to be species-specific as evidenced by the fact that combinations of transcription factors which are effective for the reprogramming of mouse fibroblasts are ineffective in pigs and humans. Whether miRNA based cardiac reprogramming suffers from the same limitation is unknown. We have previously demonstrated that mouse cardiac fibroblasts can be directly converted into cardiomyocytes both in vitro and in vivo via a combination of four microRNAs (miR-1, miR-133a, miR-208a and miR-499) termed "miR combo." To assess species-specificity, miR combo was transfected into cardiac fibroblasts isolated from the left ventricle of dogs, pigs and humans. QPCR analysis indicated that miR combo effectively reprogrammed fibroblasts from all of the tested mammalian species. Significant upregulation of cardiac developmental, sarcomere, and cardiac ion channel genes was observed. Through Actn2+ staining, we also found that miR combo transfection induced dog, pig and human cardiac fibroblasts to develop into cardiomyocyte-like cells. In conclusion, we have demonstrated that in contrast to transcription factor based approaches, miR combo effectively reprograms mammalian cardiac fibroblasts into cardiomyocyte-like cells.