C-MYC-Independent Nuclear Reprogramming Favors Cardiogenic Potential of Induced Pluripotent Stem Cells

Induced pluripotent stem cell (iPS) technology has launched a new platform in regenerative medicine aimed at deriving unlimited replacement tissue from autologous sources through somatic cell reprogramming using stemness factor sets. In this way, authentic cardiomyocytes have been obtained from iPS and recently demonstrated in proof-of-principle studies to repair infarcted heart. Optimizing the cardiogenic potential of iPS progeny would ensure a maximized yield of bioengineered cardiac tissue. Here, we reprogrammed fibroblasts in the presence or absence of c-MYC to determine if the acquired cardiogenicity is sensitive to the method of nuclear reprogramming. Using lentiviral constructs that expressed stemness factors SOX2, OCT4, and KLF4 with or without c-MYC, iPS clones generated through fibroblast reprogramming demonstrated indistinguishable characteristics for 5 days of differentiation with similar cell morphology, growth rates, and chimeric embryo integration. However, four-factor c-MYC-dependent nuclear reprogramming produced iPS progeny that consistently prolonged the expression of pluripotent Oct4 and Fgf4 genes and repressed cardiac differentiation. In contrast, three-factor c-MYC-less iPS clones efficiently upregulated precardiac (CXCR4, Flk1, and Mesp1/2) and cardiac (Nkx2.5, Mef2c, and myocardin) gene expression patterns. In fact, three-factor iPS progeny demonstrated early and robust cardiogenesis during in vitro differentiation with consistent beating activity, sarcomere maturation, and rhythmical intracellular calcium dynamics. Thus, nuclear reprogramming independent of c-MYC enhances production of pluripotent stem cells with innate cardiogenic potential.