a novel myokine osteonectin, or sparc (secreted protein acidic and rich in cysteine), plays a vital role in bone mineralization, cell-matrix interactions, and collagen binding. osteonectin inhibits tumorigenesis in mice. osteonectin can be classed as a myokine, as it was found that even a single bout of exercise increased its expression and secretion in skeletal muscle in both mice and humans.