SummaryDespite over a decade of intense research, the identity and differentiation potential of human adult cardiac progenitor cells (aCPC) remains controversial. Cardiospheres have been proposed as a means to expand aCPCs in vitro, but the identity of the progenitor cell within these 3D structures is unknown. We show that clones derived from cardiospheres could be subdivided based on expression of thymocyte differentiation antigen 1 (THY-1/CD90) into two distinct populations that exhibit divergent cardiac differentiation potential. One population, which is CD90+, expressed markers consistent with a mesenchymal/myofibroblast cell. The second clone type was CD90− and could form mature, functional myocytes with sarcomeres albeit at a very low rate. These two populations of cardiogenic clones displayed distinct cell surface markers and unique transcriptomes. Our study suggests that a rare aCPC exists in cardiospheres along with a mesenchymal/myofibroblast cell, which demonstrates incomplete cardiac myocyte differentiation.

SummaryResident neural precursor cells (NPCs) have been reported for a number of adult tissues. Understanding their physiological function or, alternatively, their activation after tissue damage or in vitro manipulation remains an unsolved issue. Here, we investigated the source of human dermal NPCs in adult tissue. By following an unbiased, comprehensive approach employing cell-surface marker screening, cell separation, transcriptomic characterization, and in vivo fate analyses, we found that p75NTR+ precursors of human foreskin can be ascribed to the Schwann (CD56+) and perivascular (CD56−) cell lineages. Moreover, neural differentiation potential was restricted to the p75NTR+CD56+ Schwann cells and mediated by SOX2 expression levels. Double-positive NPCs were similarly obtained from human cardiospheres, indicating that this phenomenon might be widespread.

BackgroundCardiovascular progenitor cells (CPCs) have been identified within the developing mouse heart and differentiating pluripotent stem cells by intracellular transcription factors Nkx2.5 and Islet 1 (Isl1). Study of endogenous and induced pluripotent stem cell (iPSC)-derived CPCs has been limited due to the lack of specific cell surface markers to isolate them and conditions for their in vitro expansion that maintain their multipotency.Methodology/Principal FindingsWe sought to identify specific cell surface markers that label endogenous embryonic CPCs and validated these markers in iPSC-derived Isl1+/Nkx2.5+ CPCs. We developed conditions that allow propagation and characterization of endogenous and iPSC-derived Isl1+/Nkx2.5+ CPCs and protocols for their clonal expansion in vitro and transplantation in vivo. Transcriptome analysis of CPCs from differentiating mouse embryonic stem cells identified a panel of surface markers. Comparison of these markers as well as previously described surface markers revealed the combination of Flt1+/Flt4+ best identified and facilitated enrichment for Isl1+/Nkx2.5+ CPCs from embryonic hearts and differentiating iPSCs. Endogenous mouse and iPSC-derived Flt1+/Flt4+ CPCs differentiated into all three cardiovascular lineages in vitro. Flt1+/Flt4+ CPCs transplanted into left ventricles demonstrated robust engraftment and differentiation into mature cardiomyocytes (CMs).Conclusion/SignificanceThe cell surface marker combination of Flt1 and Flt4 specifically identify and enrich for an endogenous and iPSC-derived Isl1+/Nkx2.5+ CPC with trilineage cardiovascular potential in vitro and robust ability for engraftment and differentiation into morphologically and electrophysiologically mature adult CMs in vivo post transplantation into adult hearts.