Osteocalcin, a protein synthesized in bone, has an extraskeletal role in maintaining calcium homeostasis under normal conditions and during acute "fight or flight" stress. This function will be impaired in the absence of catecholamines, resulting from deletion of the gene in mice for dopamine beta-hydroxylase (DBH-/-). DBH is the enzyme that converts dopamine to norepinephrine (NE), from which epinephrine (E) is formed by action of a second enzyme. DBH-/- mice make it possible to determine more precisely the effects of the catecholamine hormones on osteocalcin in circulation and in bone. It will also be possible to separate effects of NE from those of other sympathetic neural hormones released in response to stressful stimuli. Bone resorption requires NE, therefore will be decreased, leading to a greater quantity of bone in mutant mice compared with heterozygous littermates. Vertebrae and femurs from mutant and heterozygous (normal) littermates will be prepared for extraction of mineral and osteocalcin. Bone calcium, phosphorous, and osteocalcin will be analyzed. Plasma osteocalcin, corticosterone, and prolactin from the same mice will also be analyzed. Subsequently, experiments will be performed to determine the response of these mice to foot-restraint immobilization, an acute stressor that acutely increases NE, E, and corticosterone, and also osteocalcin. Both normal bone metabolism and the acute stress response are expected to be altered in DBH-/- mice.
Data obtained from this POWRE award is expected to provide a sound foundation for submission of a regular research proposal. The work described is an innovative, though as yet untried, approach to bone research. Demonstration of the ability to obtain external funding could have a significant impact on this PI's future career.
