title: The Effects of Aging and Sex Steroid Deficiency on the Murine Skeleton Are Independent and Mechanistically Distinct.
abstract: Old age and sex steroid deficiency are the two most critical factors for the development of osteoporosis. It remains unknown, however, whether the molecular culprits of the two conditions are similar or distinct. We show herein that at 19.5 months of age-a time by which the age-dependent decline of cortical and cancellous bone mass and cortical porosity were fully manifested in C57BL/6J mice-these animals remained functionally estrogen sufficient. Transgenic mice with conditional expression of mitochondria-targeted catalase-a potent H2O2inactivating enzyme-in cells of the myeloid lineage (mitoCAT;LysM-Cre mice) were protected from the loss of cortical, but not cancellous, bone caused by gonadectomy in either sex. Consistent with these findings, in vitro studies with ERα-deficient Prx1+ cells and gonadectomized young adult mice showed that in both sexes decreased ERα signaling in Prx1+ cells leads to an increase in SDF1, a.k.a. CXCL12, an osteoclastogenic cytokine whose effects were abrogated in macrophages from mitoCAT;LysM-Cre mice. In contrast to sex steroid deficiency, the adverse effects of aging on either cortical or cancellous bone were unaffected in mitoCAT;LysM-Cre mice. On the other hand, attenuation of H2O2generation in cells of the mesenchymal lineage targeted by Prx1-Cre partially prevented the loss of cortical bone caused by old age. Our results suggest the effects of sex steroid deficiency and aging on the murine skeleton are independent and result from distinct mechanisms. In the former, the prevailing mechanism of the cortical bone loss in both sexes is increased osteoclastogenesis caused by estrogen deficiency; this is likely driven, at least in part, by mesenchymal/stromal cell-derived SDF1. Decreased osteoblastogenesis, owing in part to increased H2O2,combined with increased osteoclastogenesis caused by aging mechanisms independent of estrogen deficiency, are the prevailing mechanisms of the loss of cortical bone with old age. © 2016 American Society for Bone and Mineral Research.
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Serra
authors.initials: S
authors.lastname: Ucer
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Srividhya
authors.initials: S
authors.lastname: Iyer
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Ha-Neui
authors.initials: HN
authors.lastname: Kim
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Han
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Rutlen
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Kelly
authors.initials: K
authors.lastname: Allison
authors.affiliation: Department of Biostatistics, University of Arkansas for Medical Sciences, Little Rock, AR, USA.
authors.forename: Jeff D
authors.initials: JD
authors.lastname: Thostenson
authors.affiliation: Translational Gerontology Branch, National Institute on Aging, Baltimore, MD, USA.
authors.forename: Rafael
authors.initials: R
authors.lastname: de Cabo
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Jilka
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: O'Brien
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Maria
authors.initials: M
authors.lastname: Almeida
authors.affiliation: Division of Endocrinology and Metabolism, Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, and the Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: Stavros C
authors.initials: SC
authors.lastname: Manolagas
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D001862:Bone Resorption / Q000473:pathology / Q000503:physiopathology; D001842:Bone and Bones / Q000502:physiology*; D002113:Calcification, Physiologic; D000071556:Cancellous Bone / Q000502:physiology; D002452:Cell Count; D019070:Cell Lineage; D054377:Chemokine CXCL12 / Q000378:metabolism; D000071538:Cortical Bone / Q000502:physiology; D047628:Estrogen Receptor alpha / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism; D005260:Female; D012739:Gonadal Steroid Hormones / Q000172:deficiency* / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D008297:Male; D059630:Mesenchymal Stem Cells / Q000378:metabolism; D008810:Mice, Inbred C57BL; D022423:Myeloid Cells / Q000378:metabolism; D010010:Osteoclasts / Q000378:metabolism; D010052:Ovariectomy; D016062:Porosity
chemical_list: D054377:Chemokine CXCL12; D047628:Estrogen Receptor alpha; D004967:Estrogens; D012739:Gonadal Steroid Hormones; D006861:Hydrogen Peroxide
keywords: AGING; MOLECULAR PATHWAYS-REMODELING; OSTEOBLASTS; OSTEOCLASTS; SEX STEROIDS