Irisin Ameliorates Bone Loss in Ovariectomized Mice

This study aimed to evaluate the effects of irisin on bones of ovariectomized (OVX) mice, to explore a possible treatment for postmenopausal osteoporosis. 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. 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. 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.