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

Different effects of moderate tibial loading and Yoda1 on breast cancer-induced osteolysis in aged mice

Elderly breast cancer patients and survivors are at high risk of bone loss but experience obstacles to harness the known benefits of exercise due to aging, cancer, and cancer treatment. Previously, we and others showed that moderate mechanical loading suppressed breast cancer-induced osteolysis in young adult mice. To overcome the mechano-transduction deficits in aged skeletons, we recently tested a dual therapy combining mechanical and Yoda1 activation of mechanosensitive Piezo1 channels. We found that the dual therapy was more effective in mitigating bone loss due to aging and doxorubicin in mature mice than the individual interventions. In the present study, we further tested the hypothesis that dual therapy combining moderate tibial loading and Yoda1 protects aged skeleton from breast cancer-induced osteolysis better than individual treatments. Aged female C57BL/6 J mice (∼74-week-old) receiving Py8119 breast cancer cells in both tibiae were assigned to the four experimental groups (n = 5-8 per group) to examine 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 per day, 5 days/week), individually or combined on bone structural integrity. At the end of 4 weeks' experiments, the dual therapy group had the lowest incidence of osteolytic perforation (56 %) compared to the non-treated group (80 %), loading only group (70 %), and Yoda1 only group (100 %). The relative drop of cortical polar moment of inertia (Ct.pMOI), calculated as [(Week 4- Week 0)/Week 0, %], were analyzed at the proximal end, mid-diaphysis, and tibial-fibular junction of the tibia. The average values over the three locations were - 12.7 %, -3.2 %, -24.0 %, -4.2 % for the non-treated, loading only, Yoda1 only, and dual therapy groups, respectively. Furthermore, the % of samples with decreased Ct.pMOI (indication of structural deterioration) was suppressed in the dual therapy group (33 %), compared with nontreated (100 %), loading only (80 %), and Yoda1 only (100 %) groups. Each treatment differentially affected the osteoclast activity, tumor proliferation, and apoptosis of osteocytes, marrow cells and tumor cells, revealing the complex interactions of bone, tumor, and mechanical stimulations. In summary, the dual therapy resulted in skeletal benefits comparable to or slightly better than loading only treatment. However, the exacerbated bone loss and cortical perforation associated with Yoda1 call for further investigation on safe and effective treatments of skeletal damages caused by metastatic breast cancers.

Combined Effects of Mechanical Loading and Piezo1 Chemical Activation on 22-Months-Old Female Mouse Bone Adaptation

With age, bones mechanosensitivity is reduced, which limits their ability to adapt to loading. The exact mechanism leading to this loss of mechanosensitvity is still unclear, making developing effective treatment challenging. Current treatments mostly focus on preventing bone mass loss (such as bisphosphonates) or promoting bone formation (such as Sclerostin inhibitors) to limit the decline of bones mass. However, treatments do not target the cause of bone mass loss which may be, in part, due to the bone's inability to initiate a normal bone mechanoadaptation response. In this work, we investigated the effects of 2 weeks of tibia loading, and Piezo1 agonist injection in vivo on 22-month-old mouse bone adaptation response. We used an optimized loading profile, which induced high fluid flow velocity and low strain magnitude in adult mouse tibia. We found that tibia loading and Yoda2 injection have an additive effect on increasing cortical bone parameters in 22-month-old mice. In vivo osteocytes calcium signaling imaging suggests that Yoda2 is able to reach osteocytes and activate Piezo1. This combination of mechanical and chemical stimulation could be a promising treatment strategy to help promote bone formation in patients who have low bone mass due to aging.

Skeletal response to Yoda1 and whole-body vibration in mice varied with animal age, bone compartment, treatment duration, and radiation exposure

In this study, we investigated the skeletal effects of Yoda1, an agonist of the mechanosensitive Piezo1 channels, and whole-body vibration (WBV), alone and combined, in young mice (8-week-old) and in mature (31- to 36-week-old) mice after radiation exposure. Our goal was to determine whether the two mechanobiology-based interventions, known to induce anabolic response individually in young subjects, could promote bone health of older subjects undergoing cancer treatments such as radiotherapy. Our hypothesis was that the combination of Yoda1 and WBV could improve young skeletons and protect mature skeletons after radiotherapy better than Yoda1 or WBV alone. Our in vivo experiments demonstrated (1) that Yoda1 (5 mg/kg body weight) alone or combined with WBV (0.3 g, 13 Hz, 30 min/day, 5 days/week, 4 weeks) enhanced bone growth similarly (∼2 folds relative to nontreated controls) in young mice; (2) that mature mice were unresponsive to individual interventions but exhibited less polar moment of inertia loss (-56 %) in the tibiae receiving the combination of Yoda1 and WBV (15 min/day) but no radiation exposure; and (3) that the contralateral tibiae receiving fractionated radiation (2 × 8 Gy over three days) did not show different treatment responses in Week 4, while they responded to the combination therapy (increased cortical bone formation) in Week 2. Interestingly, pair comparisons of the irradiated and non-irradiated tibiae of the same animals revealed that radiation exposure resulted in decreased trabecular bone loss regardless of the treatments and increased the percentage of tibiae maintaining better cortical polar moment of inertia and cortical area in the groups receiving Yoda1 or the combination therapy. The complex skeletal responses to Yoda1 and/or WBV were compartment specific (cortical or trabecular bone) and dependent on animal age, radiation exposure, and treatment duration. This study partially supported our original hypothesis, while suggesting the need of finetuning the Yoda1 and WBV regimens and elucidating the underlying mechanisms in order to effectively treat age and radiation induced bone loss.