Leptin is a powerful inhibitor of bone formation in vivo. This antiosteogenic function involves
leptin binding to its receptors on ventromedial hypothalamic neurons, the autonomous nervous system and
beta-adrenergic receptors on osteoblasts. However, the mechanisms whereby
leptin controls the function of ventromedial hypothalamic antiosteogenic neurons remain unclear. In this study, we compared the ability of
leptin to regulate
body weight and bone mass and show that
leptin antiosteogenic and anorexigenic functions are affected by similar amounts of
leptin. Using a knock-in of LacZ in the
leptin locus, we failed to detect any
leptin synthesis in the central nervous system. However, increasing serum
leptin level, even dramatically, reduced bone mass. Conversely, reducing serum-free
leptin level by overexpressing a soluble receptor for
leptin increased bone mass. Congruent with these results, the high bone mass of lipodystrophic mice could be corrected by restoring serum
leptin level, suggesting that
leptin is an adipocyte product both necessary and sufficient to control bone mass. Consistent with the high bone
mass phenotype of lipodystrophic mice, we observed an advanced bone age, an indirect reflection of premature bone formation, in lipodystrophic patients. Taken together, these results indicate that adipocyte-derived circulating
leptin is a determinant of bone formation and suggests that
leptin antiosteogenic function is conserved in vertebrates.