Abstract
Growing evidence has shown that skeletal muscle secretes several bioactive proteins from the cell into extracellular fluid. The secretion of several proteins, whose levels increase in response to exercise, can regulate the functions of several organs via autocrine, paracrine, and endocrine actions, and mediate exercise-induced benefits such as metabolic improvement, anti-inflammation, and muscle building; this is known as the myokine theory. These secretory proteins may be biomarkers that reflect muscular function and beneficial adaptation achieved by exercise training, and could estimate adequate condition of exercise to obtain its beneficial effects. Recently, we found a novel myokine, secreted protein acidic and rich in cysteine (SPARC), a secreted matricellular glycoprotein. In a colon cancer mouse model, regular exercise reduced the formation of the precursor lesions of colon adenocarcinoma in wild-type mice but not SPARC-null mice. Furthermore, regular exercise enhanced apoptosis in colon mucosal cells and increased the cleaved form of caspase in wild-type mice but not SPARC-null mice. The muscle-secreted protein SPARC can support underlying mechanisms of epidemiological studies that suggest that regular exercise prevents the incidence of colon cancer.
