Association between Circulating Osteoprogenitor Cells and Sarcopenia

<b><i>Background:</i></b> Circulating osteoprogenitor (COP) cells are a surrogate of the bone marrow mesenchymal stem cells with high levels observed in osteoporosis and the initial stages of fracture healing. Conversely, a low percentage of COP cells (%COP) is strongly associated with frailty and disability. However, it is unknown whether %COP is associated with sarcopenia, a musculoskeletal disease closely related to frailty. <b><i>Objectives:</i></b> This study sought to determine the associations between %COP and sarcopenia defined using the Sarcopenia Definitions and Outcomes Consortium (SDOC) criteria. <b><i>Methods:</i></b> Data from a random sample of 73 community-dwelling older persons enrolled in the Nepean Osteoporosis and Frailty study (median age 74 years; 60% female) were analyzed. %COP was quantified by flow cytometry using selective gating of CD45/osteocalcin (OCN) + cells. Sarcopenia was defined using handgrip strength and gait speed with cut points as per the SDOC criteria. Linear regression was used for analysis. <b><i>Results:</i></b> Sarcopenia was identified in 19% of participants, all of whom were frail. After adjusting for age, sex, and interleukin 6, sarcopenic participants had 36% lower %COP (95% confidence interval [CI] −56%, −6%, <i>p =</i> 0.024). Both grip strength and gait speed showed associations with %COP (<i>p =</i> 0.065 and 0.002, respectively); however, after adjusting for age and frailty, only gait speed remained associated with %COP (0.1 m/s increase in gait velocity was associated with a 5% increase in %COP cells (95% CI 0%, 10%, <i>p =</i> 0.052). <b><i>Conclusions:</i></b> High levels of %COP are associated with better muscle function. Future longitudinal studies are required to elucidate the clinical utility of %COP as a potential biomarker or disease stratifier for sarcopenia.