Molecular Maturation Of Engrafted Human Pluripotent Stem Cell- derived Cardiomyocytes

The transplantation of human pluripotent stem cell derived cardiomyocytes (hPSC-CMs) represents an attractive strategy to regenerate myocardium lost following injury and mitigate the pathological remodeling that ultimately leads to heart failure. However, in vitro hPSC-CMs have an immature phenotype that likely contributes to the transient arrhythmias observed during the initial weeks following hPSC-CM transplantation in large-animal models, hindering safe translation into the clinic. We hypothesized that maturational changes in hPSC-CMs in vivo facilitate the improved electrophysiological behavior of graft tissue observed at later time-points. Because the changing phenotype of hPSC-CM graft tissue remains largely unexplored, we used single nucleus RNA sequencing to evaluate the transcriptional dynamics and cell population heterogeneity of hPSC-CMs prior to transplantation and at 2- and 8-weeks following transplantation in a guinea pig cardiac cryoinjury model (n=3). We used methods based on the sorting of nuclei labeled by a genetically-encoded fluorescent reporter to enrich the proportion of human nuclei sequenced from the graft site and created a comprehensive atlas (> 20,000 cells) of host and graft cells present at the implantation site at both time-points. We identified an upregulation of genes involved in intracellular calcium handling, AMPK, and cAMP signaling pathways, as well as a metabolic shift in engrafted hPSC-CMs that we speculate supports their growth and enhanced electrophysiological function. Our study includes a comprehensive description of the temporal changes in hPSC-CM graft tissue at the single-cell resolution and provides unique insights into how these cells adapt to the injured heart environment and mature in vivo.