Mitigating aging and doxorubicin induced bone loss in mature mice via mechanobiology based treatments.

Aging leads to a reduced anabolic response to mechanical stimuli and a loss of bone mass and structural integrity. Chemotherapy agents such as doxorubicin exacerbate the degeneration of aging skeleton and further subject older cancer patients to a higher fracture risk. To alleviate this clinical problem, we proposed and tested a novel mechanobiology-based therapy. Building upon prior findings that i) Yoda1, the Piezo1 agonist, promoted bone growth in young adult mice and suppressed bone resorption markers in aged mice, and ii) moderate tibial loading protected bone from breast cancer-induced osteolysis, we hypothesized that combined Yoda1 and moderate loading would improve the structural integrity of adult and aged skeletons in vivo and protect bones from deterioration after chemotherapy. We first examined the effects of 4-week Yoda1 (dose 5 mg/kg, 5 times/week) and moderate tibial loading (4.5 N peak load, 4 Hz, 300 cycles for 5 days/week), individually and combined, on mature mice (∼50 weeks of age). Combined Yoda1 and loading was found to mitigate age-associated cortical and trabecular bone loss better than individual interventions. As expected, the non-treated controls experienced an average drop of cortical polar moment of inertia (Ct.pMOI) by -4.3 % over four weeks and the bone deterioration occurred in the majority (64 %) of the samples. Relative to no treatment, loading alone, Yoda1 alone, and combined Yoda1 and loading increased Ct.pMOI by +7.3 %, +9.5 %, +12.0 % and increased the % of samples with positive Ct.pMOI changes by +32 %, +26 %, and +43 %, respectively, suggesting an additive protection of aging-related bone loss for the combined therapy. We further tested if the treatment efficacy was preserved in mature mice following two weeks (six injections) of doxorubicin at the dose of 2.5 or 5 mg/kg. As expected, doxorubicin increased osteocyte apoptosis, altered bone remodeling, and impaired bone structure. However, the effects induced by DOX were too severe to be rescued by Yoda1 and loading, alone or combined, although loading and Yoda1 individually, or combined, increased the number of mice showing positive responsiveness by 0 %, +15 %, and +29 % relative to no intervention after doxorubicin exposure. Overall, this study supported the potentials and challenges of the Yoda1-based strategy in mitigating the detrimental skeletal effects caused by aging and doxorubicin.