Kalco, H.; Pajevic, P. D.; Thompson, L. V.; Connizzo, B. K.

Musculoskeletal disorders, particularly those affecting the shoulder, are a significant health concern, especially in aging populations. Nevertheless, the initiating factors of joint degeneration remain poorly understood. Research has primarily focused on age-related changes in individual musculoskeletal tissues, with limited investigation into the complex interactions between tissues. Recent studies on interorgan communication between musculoskeletal tissues and other organs have gained attention, but local interactions within the shoulder remain underexplored. This study aims to investigate age- and sex-related differences in bone-tendon-muscle (BTM) crosstalk, hypothesizing that these interactions vary by age and sex, with older and female tissues exhibiting a reduced secretory phenotype. Using novel in vitro monoculture and co-cultures of explanted whole tissues, we assessed inflammatory responses across bone, tendon, and muscle from young and aged male and female C57BL/6J mice. Our results demonstrate significant age- and sex-dependent differences in cytokine secretion, with aged males and females showing altered inflammatory profiles. We observed a general increase in pro-inflammatory cytokine secretion in monocultures, with aging amplifying this response. Tissue co-cultures revealed that crosstalk between bone and tendon was primarily mediated through secreted factors, while muscle-tendon communication required physical proximity or contact, suggesting a distinct mode of interaction between these tissues. Sex differences were evident in both the individual tissue responses and in the patterns of inter-tissue communication. Importantly, our findings suggest that tendon plays a crucial role in mediating inter-tissue communication, with aging disrupting this crosstalk. However, these sex differences diminished with aging, indicating that the age-related decline in tissue-specific signaling may override sex-based distinctions.