Irisin/FNDC5: A Novel Player in Musculoskeletal Health

Osteoporosis is a major health problem that affects mainly aging and postmenopausal women and is characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility. Emerging shreds of evidence suggested that physical exercise has a beneficial effect on bone loss/osteoporosis. Irisin is a novel hormone-like myokine that was reported in 2012 and proposed to be produced in abundance by skeletal muscle as well as bone tissue in response to exercise. The studies have provided shreds of evidence that irisin can promote osteoblast differentiation, mineralization and increases bone mass and mechanical strength, and geometry in mice. We also review the autocrine effects of irisin in skeletal muscle, in which it upregulates expression of several pro-myogenic and exercise response genes in skeletal muscle including the expression of its precursor (FNDC5). In this review, we emphasize the structure and function of irisin and its functional role in skeletal homeostasis as well as skeletal muscle mass and regeneration. Further, the review narrates the future efficacy of irisin restoring the bone and reversing muscle wasting and could be developed as an irisin-based therapy for physically weaken and osteoporosis patients.