Project description:Background: Direct cardiac reprogramming of fibroblasts into cardiomyocytes has emerged as one of the promising strategies to remuscularize the injured myocardium. Yet, it is still insufficient to generate functional induced cardiomyocytes (iCMs) from human fibroblasts using conventional reprogramming cocktails, such as our previously published combination consisting of MEF2C, GATA4, TBX5 and microRNA miR-133 (MGT133). Results: To discover potential missing factors for human direct reprogramming, we performed transcriptomic comparison between human iCMs and functional cardiomyocytes (CMs). We identified T-box transcription factor TBX20 as the top CM gene that is unable to be activated by MGT133. TBX20 is required for normal heart development and cardiac function in adult CMs but its role on cardiac reprogramming remains undefined. Here, we found that transduction of MGT133+TBX20 in human cardiac fibroblasts resulted in enhanced reprogramming featured with significantly activated contractility gene programs and signatures more similar to ventricular CMs. Human iCMs produced with MGT133+TBX20 more frequently demonstrated beating and calcium oscillation in co-culture with pluripotent stem cell derived CMs. More mitochondria and higher mitochondrial respiration were also detected in iCMs after TBX20 overexpression. Mechanistically, comprehensive transcriptomic, chromatin occupancy and epigenomic integration revealed that TBX20 localized to the cis-regulatory enhancers of under-expressed cardiac genes, such as MYBPC3, MYH7 and MYL4, to activate gene expression via strengthening the occupancy and co-occupancy of transcription factors. Furthermore, we identified TBX20-regulated enhancers and confirmed the synergistic effect of MGT and TBX20 on enhancer activation. Conclusions: TBX20 promotes cardiac cell fate conversion via direct activating cardiac enhancers. Human iCMs generated with TBX20 showed enhanced cardiac function in terms of contractility and mitochondrial respiration.

Project description:Recent establishment of induced pluripotent stem (iPS) cells opened new avenues for generating human patient-specific stem cell derivatives that can be used for in vitro modeling of human disease, drug development and cell replacement therapy. In this study we analyzed the molecular and functional properties of cardiomyocytes (CM) differentiated from human iPS cells. Clusters of synchronously beating cells were first observed at day 11 of iPS cell differentiation. Beating clusters that were microdissected at day 18 of differentiation expressed high levels of cardiospecific transcripts NKx2.5, alpha-MHC, MLC2v, alpha-actinin and troponin T. Immunocytochemical stainings for alpha-actinin and troponin T revealed cross-striations typical of CM. Functional assessment of iPS cell-derived CM showed that these cells possess intact calcium transients and respond to beta-adrenergic and muscarinic stimulation. Molecular, structural and electrophysiological properties of iPS cell-derived CMs were highly comparable to their human ES cell-derived counterparts at the same differentiation stage. Comparison of global gene expression profiles of human ES and iPS cells and the corresponding microdissected beating areas further confirmed their similarity. We conclude that human iPS cells can differentiate into functional CM, which are indistinguishable from human ES cell-derived CMs and may fulfill the basic requirement for their use in disease modeling, drug screening and future therapeutic applications. Six different experimental groups were included into analysis: undifferentiated human ES cells (1) and undifferentiated human iPS cells (2), human ES cell-derived cardiomyocytes (3) and human iPS cell-derived cardiomyocytes (4) enriched by microdissection of spontaneously contracting embryoid body outgrowths, and human fetal (5) and adult (6) heart tissue. Total RNA samples were prepared from three independent biological replicates in groups 1-4. In groups 5 and 6, single RNA probes were analyzed as three technical replicates.

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Transient epigenetic changes promote cardiomyocyte differentiation of the subcutaneous adipose stromal vascular fraction

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