Characterization of adult human skeletal cells in different tissues reveals a CD90+CD34+ periosteal stem cell population
Skeletal stem and progenitor cells are critical for bone homeostasis and healing, but their identity and diversity in humans are not well understood. In this study, we compared stromal populations in matched tissues from the femoral head and neck of 21 human participants using spectral flow cytometry of freshly isolated cells. High-level analysis indicated significant differences in marker distribution between periosteum, articular cartilage, endosteum and bone marrow stromal populations, and identified populations that were highly enriched or unique to specific tissues. Periosteum-enriched markers included CD90 and CD34. Articular cartilage, which has very poor regenerative potential, showed enrichment of multiple markers, including the PDPN+CD73+CD164+ population previously reported to represent human skeletal stem cells. We further characterized periosteal populations by combining CD90 with other strongly expressed markers. CD90+CD34+ cells sorted directly from periosteum showed significant colony-forming unit fibroblasts (CFU-F) enrichment, rapid expansion, and consistent multi-lineage differentiation of clonal populations. In situ, CD90+CD34+ cells include a perivascular population in the outer layer of the periosteum and non-perivascular cells closer to the bone surface. In conclusion, our study indicates considerable diversity in the stromal cell populations in different tissue compartments within the adult human skeleton, and suggests that periosteal stem cells reside within the CD90+CD34+ population.