title: Glucocorticoids mediate circadian timing in peripheral osteoclasts resulting in the circadian expression rhythm of osteoclast-related genes.
abstract: Circadian rhythms are prevalent in bone metabolism. However, the molecular mechanisms involved are poorly understood. Recently, we suggested that output signals from the suprachiasmatic nucleus (SCN) are transmitted from the master circadian rhythm to peripheral osteoblasts through β-adrenergic and glucocorticoid signaling. In this study, we examined how the master circadian rhythm is transmitted to peripheral osteoclasts and the role of clock gene in osteoclast. Mice were maintained under 12-hour light/dark periods and sacrificed at Zeitgeber times 0, 4, 8, 12, 16 and 20. mRNA was extracted from femur (cancellous bone) and analyzed for the expression of osteoclast-related genes and clock genes. Osteoclast-related genes such as cathepsin K (CTSK) and nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) showed circadian rhythmicity like clock genes such as period 1 (PER1), PER2 and brain and muscle Arnt-like protein 1 (BMAL1). In an in vitro study, not β-agonist but glucocorticoid treatment remarkably synchronized clock and osteoclast-related genes in cultured osteoclasts. Chromatin immunoprecipitation (ChIP) assay showed the interaction between BMAL1 proteins and promoter region of CTSK and NFATc1. To examine whether endogenous glucocorticoids influence the osteoclast circadian rhythms, mice were adrenalectomized (ADX) and maintained under 12-hour light/dark periods at least two weeks before glucocorticoid injection. A glucocorticoid injection restarted the circadian expression of CTSK and NFATc1 in ADX mice. These results suggest that glucocorticoids mediate circadian timing to peripheral osteoclasts and osteoclast clock contributes to the circadian expression of osteoclast-related genes such as CTSK and NFATc1.
authors.affiliation: Department of Pharmacology, School of Dentistry, Aichi Gakuin University, Japan; Department of Periodontology, School of Dentistry, Aichi Gakuin University, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fujihara
authors.affiliation: Department of Pharmacology, School of Dentistry, Aichi Gakuin University, Japan.
authors.forename: Hisataka
authors.initials: H
authors.lastname: Kondo
authors.affiliation: Department of Periodontology, School of Dentistry, Aichi Gakuin University, Japan.
authors.forename: Toshihide
authors.initials: T
authors.lastname: Noguchi
authors.affiliation: Department of Pharmacology, School of Dentistry, Aichi Gakuin University, Japan. Electronic address: togariaf@dpc.aichi-gakuin.ac.jp.
authors.forename: Akifumi
authors.initials: A
authors.lastname: Togari
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000502:physiology*; D056926:CLOCK Proteins / Q000096:biosynthesis* / Q000235:genetics; D047369:Chromatin Immunoprecipitation; D002940:Circadian Rhythm / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology; D005938:Glucocorticoids / Q000378:metabolism*; D061346:Laser Capture Microdissection; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010010:Osteoclasts / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D059467:Transcriptome
chemical_list: D005938:Glucocorticoids; D056926:CLOCK Proteins
keywords: Circadian rhythm; Clock gene; Glucocorticoid; Osteoclast