Comparative Single Cell Transcriptomics Reveals Distinct Cell Fate Transition Statuses during Human Cardiac Reprogramming

Direct lineage conversion among various somatic cell types revolutionized the field of stem cell and regenerative medicine. In addition, the platform of cellular reprogramming offered a powerful system to gain new knowledge about cell plasticity and cell fate determination and ultimately challenged previous notions of cell identity. Previously, we successfully utilized single cell transcriptomics to reconstruct the molecular routes of how a murine fibroblast adopts cardiomyocyte fate following a continuum of states. In this study, we employed a comparative single cell transcriptomics approach to study human cardiac reprogramming. In comparison with murine fibroblasts and other human cell types, we identified unexpected heterogeneity in human cardiac fibroblasts that was mainly due to variance in cell cycle status. Trajectories inferred by SLICER suggest molecular routes and pathways taken by human fibroblasts when transiting into CM fate. Importantly, by assigning a “cell fate index” to each single cell on the iCM trajectories resolved from both mouse and human fibroblasts, we discovered species differences in fibroblast plasticity and intermediate cell fate statuses when reprogrammed towards a CM fate. Collectively, our comparative single cell transcriptomics study of human cardiac reprogramming revealed previously unrecognized molecular features of human cardiac fibroblasts and regulatory mechanisms in human cardiomyocyte cell fate control.