Irisin prevents trabecular bone damage and tumor invasion in a mouse model of multiple myeloma

Bone disease (BD) associated with multiple myeloma (MM) is characterized by osteolytic lesions and pathological fractures, which remain a therapeutic priority despite new drugs improving MM patient survival. Antiresorptive molecules represent the main option for the treatment of MMBD whereas osteoanabolic molecules are under investigation. Among these latter, we here focused on the myokine irisin, able to enhance bone mass in healthy mice, prevent bone loss in osteoporotic mouse models, and accelerate fracture healing in mice. Therefore, we investigated irisin effect on MMBD in a mouse model of MM induced by intratibial injection of myeloma cells followed by weekly administration of 100 μg/Kg of recombinant-irisin for 5 weeks. By micro-Ct analysis, we demonstrated that irisin improves MM-induced trabecular bone damage by partially preventing the reduction of femur Trabecular Bone Volume/Total Volume (p = 0.0028), Trabecular Number (p = 0.0076), and Trabecular Fractal Dimension (p = 0.0044), and increasing Trabecular Separation (p = 0.0003) in MM mice. In cortical bone, irisin downregulates the expression of Sclerostin, the bone formation inhibitor, and RankL, the pro-osteoclastogenic molecule, and in bone marrow (BM) upregulates Opg, the anti-osteoclastogenic cytokine. We found that in the BM tibia of irisin-treated MM mice, the percentage of MM cells displays a reduction trend, while in the femur it decreases significantly. This is in line with the in vitro reduction of myeloma cell viability after 48 hours of irisin stimulation at both 200 and 500 ng/ml and after 72 hours already at 100 ng/ml rec-irisin. These results could be due to irisin ability to downregulate the expression of Notch 3, important for cell-to-cell communication in the tumor niche, and Cyclin D1, regulator of cell cycle progression, supporting an inhibitory effect of irisin in MM cell proliferation. Overall, our findings suggest that irisin could be a new promising strategy to counteract MMBD and tumor burden in one shot.