Improvement of Cortical Bone Mineral Density associated with physical exercise is exerted through the myokine Irisin.

It has been recently reported that, after physical activity, the skeletal muscle releases Irisin, the newly identified myokine able of driving transition of white adipocytes into brown. This result supported the role of skeletal muscle as endocrine organ, suggesting that it could target other tissues besides adipose tissue. In our previous work, we demonstrated that conditioned media collected from primary myoblasts of exercised mice were able to increase OB differentiation and this effect was Irisin-mediated. Here we show that Irisin has positive effect on cortical mineral density and geometry in vivo. Young male mice were injected with r-Irisin and cortical bone adaptation was analyzed by micro-CT at tibial midshaft. Our results show that cortical tissue mineral density is significantly increased in Irisin-injected mice compared to vehicle-injected littermates (+8,16%; p<0,02). Furthermore, this higher density of calcium hydroxyapatite at cortical site is accompanied by increase in periosteal circumference (+7,5%; p<0,03) and polar moment of Inertia (pMOI +19,21%; p