Irisin ameliorates bone loss in ovariectomized mice

<b>Purpose:</b> This study aimed to evaluate the effects of irisin on bones of ovariectomized (OVX) mice, to explore a possible treatment for postmenopausal osteoporosis. <b>Methods:</b> The OVX mice were treated with intraperitoneal injections of recombinant irisin (r-irisin) or saline twice a week for 5 weeks. The trabecular bone structure of the femur, the bone strength of the tibia, and serum parameters were assessed. <b>Results:</b> Treatment with r-irisin prevented the trabecular bone loss of the OVX mice. The r-irisin-treated OVX mice exhibited a greater bone microarchitecture, with significantly increased bone mineral density, bone volume to tissue volume ratio, connection density, and trabecular number parameters compared to those of the saline-treated OVX mice. The improved bone microarchitecture induced an increased bone stiffness in r-irisin-treated OVX mice. Consistently, the OVX mice treated with r-irisin showed a significantly increased number of osteoblasts on the trabecular surface and a significantly decreased number of osteoclasts. The r-irisin-treated OVX mice also had a higher osteocalcin level and a lower tartrate-resistant acid phosphatase concentration in serum. <b>Conclusion:</b> Irisin increases osteoblasts and decreases the number of osteoclasts, which leads to the maintenance of bone mass and quality in OVX mice. Irisin likely preserves the bone microarchitecture via building a ‘new balance’. Therefore, our study extended the understanding of the role of irisin in bone metabolism and revealed the possibility of therapeutic application of irisin for postmenopausal osteoporosis.