Bone and skeletal muscle are the two largest tissues within the musculoskeletal system, which also includes tendons, ligaments, cartilage, vascular, and nervous tissue. As the major function of the musculoskeletal system is locomotion, the mechanical interactions between bone and muscle have been a singular area of research and has been investigated for decades. However, within the past few years, more attention has come to bear on the potential for molecular and biochemical interactions between these tissues, especially bone and muscle.
Independent of their mechanical interactions, it has recently been shown that bone and muscle can interact in an endocrine fashion through the production of secreted proteins and metabolites. This endocrine axis produces and releases factors that can influence other adjacent or distant tissues and organs, such as pancreas, liver, vasculature, and adipose tissue. Muscles release peptides or proteins termed “myokines” that provide a reservoir for communication with other organs in an autocrine, paracrine or endocrine manner. The importance of these myokines for human fitness and their roles in diseases, such as diabetes and obesity are beginning to emerge. Muscle factors include myostatin, leukemia inhibitory factor (LIF), Insulin-like growth factor I (IGF-1), fibroblast growth factor 2 (FGF2), and follistatin-like protein 1, IL-8 that stimulates angiogenesis, brain-derived neutrophic factor (BDNF), irisin, a potent regulator of the conversion of white fat into brown fat, and IL-15, a muscle factor that reduces adiposity. Many of these factors also have an effect on bone.