Sclerostin is produced by the osteocyte and has catabolic effects on bone formation. This protein, with a length of 113 residues, has a dssp secondary structure that is 28% beta sheet (6 strands; 32 residues. Sclerostin has an inhibitory effect on the lifetime of the osteoblast. Sclerostin production by osteocytes is inhibited by parathyroid hormone, mechanical loading and cytokines including oncostatin M, cardiotrophin-1 and leukemia inhibitory factor. Sclerostin production is increased by calcitonin. Thus, osteoblast activity is self regulated by a negative feedback system.Sclerostin was recently identified as a component of parathyroid hormone (PTH) signal transduction.