Apelin/APJ system: A novel therapeutic target for locomotor system diseases.

Apelin is an endogenous ligand of G protein-coupled receptor APJ. Apelin/APJ system is widely expressed in abundant tissues, especially bone, joint and muscle tissue. This review focus on the effects of apelin/APJ system on locomotor system. An increasing number of evidence suggests that apelin/APJ system plays a crucial role in many physiological and pathological processes of locomotor system. Physiologically, apelin/APJ system promotes bone formation, muscle metabolism and skeletal muscle production. Pathologically, apelin/APJ system exacerbates osteoarthritis pathogenesis, whereas it alleviates osteoporosis. Besides, the level of apelin expression is regulated by different training modes, including continuous aerobic exercise, high-intensity interval training and resistance exercises. More importantly, exercise-induced apelin may be a potent pharmacological agent for the treatment of diseases and the regulation of physiological processes. Considering the pleiotropic effects of apelin on locomotor system, apelin/APJ system may be an important therapeutic target for locomotor system diseases.