UPDATE ON THE BIOLOGY OF OSTEOCALCIN.

A genetics approach has uncovered that bone has more functions than expected. In particular, bone is an endocrine organ that secretes a growing number of hormones. In that context, the discovery of the osteoblast-derived hormone osteocalcin has significantly broadened the field of bone biology because of the number of physiologic processes regulated by this hormone. At present, osteocalcin has been shown to enhance several aspects of energy metabolism, brain development, and cognition. These discoveries shed light on the cross-talk between multiple organs and provide credence to the search for additional endocrine functions of bone. ABBREVIATIONS: ECM = extracellular matrix; Gprc6a = G protein-coupled receptor family C group 6 member A; IL-6 = interleukin-6; WT = wild-type.