MiR‐590 Promotes Transdifferentiation of Porcine and Human Fibroblasts Toward a Cardiomyocyte‐Like Fate by Directly Repressing Specificity Protein 1

Background Reprogramming of cardiac fibroblasts into induced cardiomyocyte‐like cells represents a promising potential new therapy for treating heart disease, inducing significant improvements in postinfarct ventricular function in rodent models. Because reprogramming factors effective in transdifferentiating rodent cells are not sufficient to reprogram human cells, we sought to identify reprogramming factors potentially applicable to human studies. Methods and Results Lentivirus vectors expressing Gata4, Mef2c, and Tbx5 ( GMT ); Hand2 (H), Myocardin (My), or microRNA (miR)‐590 were administered to rat, porcine, and human cardiac fibroblasts in vitro. induced cardiomyocyte‐like cell production was then evaluated by assessing expression of the cardiomyocyte marker, cardiac troponin T ( cTnT ), whereas signaling pathway studies were performed to identify reprogramming factor targets. GMT administration induced cTnT expression in ≈6% of rat fibroblasts, but failed to induce cTnT expression in porcine or human cardiac fibroblasts. Addition of H/My and/or miR‐590 to GMT administration resulted in cTNT expression in ≈5% of porcine and human fibroblasts and also upregulated the expression of the cardiac genes, MYH 6 and TNNT 2. When cocultured with murine cardiomyocytes, cTnT ‐expressing porcine cardiac fibroblasts exhibited spontaneous contractions. Administration of GMT plus either H/My or miR‐590 alone also downregulated fibroblast genes COL 1A1 and COL 3A1. miR‐590 was shown to directly suppress the zinc finger protein, specificity protein 1 (Sp1), which was able to substitute for miR‐590 in inducing cellular reprogramming. Conclusions These data support porcine studies as a surrogate for testing human cardiac reprogramming, and suggest that miR‐590‐mediated repression of Sp1 represents an alternative pathway for enhancing human cardiac cellular reprogramming.