Circulating osteoprogenitors (COP) cells, found within the peripheral blood, express characteristics of mesenchymal stem cells (MSCs) with the capacity to proliferate and differentiate into bone, muscle and fat. While some aspects of their in vitro and in vivo behaviour as mesenchymal progenitors has been established, much remains unknown about their role in age-related musculoskeletal diseases such as osteoporosis and sarcopenia. In this study, our aim was to identify if a relationship exists between COP cells and important muscle and bone parameters.
Thirty-eight healthy older people [mean age 72 (±6yrs), mean BMI 28.4] were recruited from the community. Exclusion criteria included recent history of fracture, or initiation of osteoporosis medication, type 2 diabetes mellitus, haematological, myelodysplastic or myeloproliferative disorders. Participants underwent a series of assessments including a blood sample, anthropometry and body composition analysis via densitometry. Peripheral blood samples were analysed for via flow cytometry, with COP cells defined as peripheral blood mononuclear cells (PBMCs) co-expressing the CD45 and osteocalcin markers. COP cell number is expressed as a percentage of the total PBMC population. Regression analysis was used to identify relationships between variables.
Increased COP cell number was associated with increased femoral (r=0.442, p=0.008,) and total BMD (r=0.376, p=0.025) and tended to correlate with ALM (r=0.314, p=0.06). These results remained consistent after adjustment for age and BMI.
COP cell number is linked to bone and muscle parameters in vivo. This raises the hypothesis that COP cells have a role in the maintenance and cross talk between these tissues. Future studies should evaluate whether COP cells can be used as a novel biomarker for diseases such as osteosarcopenia.