• Kohei Inagawa, Kazutaka Miyamoto, Hiroyuki Yamakawa, Naoto Muraoka, Taketaro Sadahiro, Tomohiko Umei, Rie Wada, Yoshinori Katsumata, Ruri Kaneda, Koji Nakade, Chitose Kurihara, Yuichi Obata, Koichi Miyake, Keiichi Fukuda, and Masaki Ieda.
• Department of Clinical and Molecular Cardiovascular Research, Department of Cardiology, Keio University School of Medicine, Tokyo, Japan.
• Circ. Res. 2012 Oct 12; 111 (9): 1147-56.

RationaleAfter myocardial infarction (MI), massive cell death in the myocardium initiates fibrosis and scar formation, leading to heart failure. We recently found that a combination of 3 cardiac transcription factors, Gata4, Mef2c, and Tbx5 (GMT), reprograms fibroblasts directly into functional cardiomyocytes in vitro.ObjectiveTo investigate whether viral gene transfer of GMT into infarcted hearts induces cardiomyocyte generation.Methods And ResultsCoronary artery ligation was used to generate MI in the mouse. In vitro transduction of GMT retrovirus converted cardiac fibroblasts from the infarct region into cardiomyocyte-like cells with cardiac-specific gene expression and sarcomeric structures. Injection of the green fluorescent protein (GFP) retrovirus into mouse hearts, immediately after MI, infected only proliferating noncardiomyocytes, mainly fibroblasts, in the infarct region. The GFP expression diminished after 2 weeks in immunocompetent mice but remained stable for 3 months in immunosuppressed mice, in which cardiac induction did not occur. In contrast, injection of GMT retrovirus into α-myosin heavy chain (αMHC)-GFP transgenic mouse hearts induced the expression of αMHC-GFP, a marker of cardiomyocytes, in 3% of virus-infected cells after 1 week. A pooled GMT injection into the immunosuppressed mouse hearts induced cardiac marker expression in retrovirus-infected cells within 2 weeks, although few cells showed striated muscle structures. To transduce GMT efficiently in vivo, we generated a polycistronic retrovirus expressing GMT separated by 2A "self-cleaving" peptides (3F2A). The 3F2A-induced cardiomyocyte-like cells in fibrotic tissue expressed sarcomeric α-actinin and cardiac troponin T and had clear cross striations. Quantitative RT-PCR also demonstrated that FACS-sorted 3F2A-transduced cells expressed cardiac-specific genes.ConclusionsGMT gene transfer induced cardiomyocyte-like cells in infarcted hearts.

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