Transcriptionally and Functionally Distinct Mesenchymal Subpopulations Are Generated from Human Pluripotent Stem Cells.
The clinical potential of pluripotent stem cells (PSC) for use in regenerative medicine will be realized only when the process by which tissues are generated from these cells is significantly more efficient and controlled than is currently the case. The overall goal of our research was to discover if the cell types produced during differentiation of PSC into blood produce the microenvironment needed for hematopoietic (blood) stem cells (HSC) to develop. HSC survive and grow in the bone marrow only if they are physically close to specialized cell types, the so-called HSC "niche". In this work we found that two types of "mesenchymal" niche cells can be produced from PSC, one of which is significantly better than the other at supporting the growth and maintenance of human HSC. We performed gene expression analyses on these different types of mesenchyme to uncover which molecular pathways are important for the support HSC in culture.
Various mesenchymal cell types have been identified as critical components of the hematopoietic stem/progenitor cell (HSPC) niche. Although several groups have described the generation of mesenchyme from human pluripotent stem cells (hPSCs), the capacity of such cells to support hematopoiesis has not been reported. Here, we demonstrate that distinct mesenchymal subpopulations co-emerge from mesoderm during hPSC differentiation. Despite co-expression of common mesenchymal markers (CD73, CD105, CD90, and PDGFRbeta), a subset of cells defined as CD146(hi)CD73(hi) expressed genes associated with the HSPC niche and supported the maintenance of functional HSPCs ex vivo, while CD146(lo)CD73(lo) cells supported differentiation. Stromal support of HSPCs was contact dependent and mediated in part through high JAG1 expression and low WNT signaling. Molecular profiling revealed significant transcriptional similarity between hPSC-derived CD146(++) and primary human CD146(++) perivascular cells. The derivation of functionally diverse types of mesenchyme from hPSCs opens potential avenues to model the HSPC niche and develop PSC-based therapies.