The Secretome From Mechanically Loaded Myoblasts Enhances Tenocyte-Mediated Wound Healing in a 3D In Vitro Tendon Model.

Exercise is well known to promote tendon healing, an effect traditionally attributed to mechanical loading-induced responses within the tendon itself. However, skeletal muscle also functions as a secretory organ, releasing bioactive factors (secretome) during exercise that influence various tissues. We hypothesized that muscle-derived secretome released during exercise may also contribute to tendon healing. To test this, we applied mechanical loading to cultured muscle cells (myoblasts) using the FlexCell tension system to simulate exercise in vitro. Our previous studies, using 2D-cultured tendon cells (tenocytes), have demonstrated that secretome from statically loaded myoblasts, particularly under 2% loading, enhanced tendon healing-related responses. Building upon these findings, we employed a 3D tendon construct model to more closely mimic in vivo healing conditions. We found that secretome derived from statically loaded myoblasts, especially at 2% loading, promoted tendon healing-related processes as compared with the control group, which received no secretome treatment (no conditioned media). These included increased cell-covered area, expression of the tenocyte marker scleraxis (SCX), and elevated production of Type I and III collagens at an early stage (Day 7). Additionally, a reduction in type III collagen production was found at a later stage (Day 14), suggesting a potentially accelerated healing process. These findings highlight the therapeutic potential of the muscle-derived secretome in promoting tendon healing and may inform future strategies for rehabilitation and regenerative medicine.