Glucocorticoids mediate circadian timing in peripheral osteoclasts resulting in the circadian expression rhythm of osteoclast-related genes

• Published in: Bone (New York, N.Y.) Vol. 61; pp. 1 - 9
• Main Authors: Fujihara, Yuko, Kondo, Hisataka, Noguchi, Toshihide, Togari, Akifumi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.04.2014; Elsevier
• Subjects: Animals; Biological and medical sciences; Bone and Bones - physiology; Chromatin Immunoprecipitation; Circadian rhythm; Circadian Rhythm - physiology; Clock gene; CLOCK Proteins - biosynthesis; CLOCK Proteins - genetics; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation - physiology; Glucocorticoid; Glucocorticoids - metabolism; Laser Capture Microdissection; Male; Mice; Mice, Inbred C57BL; Orthopedics; Osteoclast; Osteoclasts - physiology; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; Transcriptome; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Osteoclast; Circadian rhythm; Clock gene; Glucocorticoid; Timing; Morphology
• ISSN: 8756-3282; 1873-2763
• DOI: 10.1016/j.bone.2013.12.026

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.