Oral Virtual Presentation (Virtual only) ESA-SRB-ANZBMS 2021

Human skeletal stem cells (SSCs) have been recently isolated from fetal long bones, however, the identity of adult SSCs remains elusive. Tissue-resident stem/progenitor cells support skeletal homeostasis and regeneration throughout life. Periosteum is a major source of cells involved in fracture healing. We hypothesize that progenitor populations are vary in different skeletal tissue compartments, and periosteum is enriched for SSC populations.

 Cell surface marker expression was compared in human skeletal tissues by multi-colour flow cytometry with a 21-colour-panel. In brief, cells were isolated by enzymatic digestion of tissue from femoral heads of adults undergoing hip replacement for osteoarthritis: bone marrow, endosteum (or bone-associated cells) from cleaned trabecular bone, periosteum from the femoral neck, chondrocytes from the damaged and undamaged articular cartilage. Total haematopoietic cells were excluded using CD235a/CD15/CD31/CD45.

Within total non-haematopoietic cells, principal component analysis (PCA, Figure 1) of cell surface marker expression separates periosteum, cartilage and bone marrow/endosteum groups indicating substantial difference in marker expression in different tissues. Specifically, CD90, CD73, CD51, and CD34 were highly expressed in the periosteum. A number of markers were enriched in the cartilage, including CD105, CD106, CD133, CD164, CD271, PDGFRa, and PDPN, while CD24 was unique to the endosteum and bone marrow.

When total non-haematopoietic cells were sorted, surprisingly cartilage formed the most fibroblastic colonies (CFU-F), although they tended to remain smaller than periosteum and endosteum-derived CFU-F. Bone marrow did not form any colonies at the density tested. CD73+ and PDPN+ cells from periosteum, cartilage, and endosteum formed more CFU-F compared with total non-haematopoietic cells, and all these populations were highly osteogenic in vitro.

Using cell surface markers we identified populations of skeletal stem/progenitor cells with osteogenic potential in vitro. Our findings suggest that progenitor populations vary in different skeletal compartments and there may be cell populations unique to certain tissue compartments.