Stress-Induced Changes in Bone Marrow Stromal Cell Populations Revealed through Single-Cell Protein Expression Mapping

Stromal cell populations that maintain hematopoietic stem and progenitor cells (HSPCs) are generally characterized in steady-state conditions. Here, we report a comprehensive atlas of bone marrow stromal cell subpopulations under homeostatic and stress conditions using mass cytometry (CyTOF)based single-cell protein analysis. We identified 28 subsets of non-hematopoietic cells during homeostasis, 14 of which expressed hematopoietic regulatory factors. Irradiation-based conditioning for HSPC transplantation led to the loss of most of these populations, including the LeptinR(+) and Nestin(+) subsets. In contrast, a subset expressing Ecto-5'-nucleotidase (CD73) was retained and a specific CD73(+) NGFR high population expresses high levels of cyto-kines during homeostasis and stress. Genetic ablation of CD73 compromised HSPC transplantation in an acute setting without long-term changes in bone marrow HSPCs. Thus, this protein-based expression mapping reveals distinct sets of stromal cells in the bone marrow and how they change in clinically relevant stress settings to contribute to early stages of hematopoietic regeneration.