Ovariectomy and genes encoding core circadian regulatory proteins in murine bone

This study investigated the influence of ovarian hormone deficiency on core circadian regulatory protein (CCRP) in the context of bone loss. Our data suggest that ovarian hormone deficiency disrupts diurnal rhythmicity and CCRP expression in bone. Further studies should determine if chronobiology provides a novel therapeutic target for osteoporosis intervention. CCRP synchronize metabolic activities and display an oscillatory expression profile in murine bone. In vitro studies using bone marrow mesenchymal stromal/stem cells have demonstrated that the CCRP is present and can be regulated within osteoblast progenitors. In vivo studies have shown that the CCRP regulates bone mass via leptin/neuroendocrine pathways. The current study used an ovariectomized murine model to test the hypothesis that ovarian hormone deficiency is associated with either an attenuation and/or temporal phase shift of the CCRP oscillatory expression in bone and that these changes are correlated with the onset of osteoporosis. Sham-operated controls and ovariectomized female C57BL/6 mice were euthanized at 4-h intervals 2 weeks post-operatively. Ovariectomy attenuated the oscillatory expression of CCRP mRNAs in the femur and vertebra relative to the controls and reduced the wheel-running activity profile. Ovarian hormone deficiency modulates the expression profile of the CCRP with potential impact on bone marrow mesenchymal stem cell lineage commitment.