Project description:Disruption of circadian rhythms predisposes shift workers to many chronic conditions, including osteoporosis. However, the effects of disrupted circadian rhythms on bone remodeling remain largely unknown. Here, we show that one of the core circadian regulators PER1 inhibits osteoclastogenesis by upregulating genes involved in inflammation. The conditional knockout of Per1 in osteoclasts and related cells resulted in decreased bone mass in the femurs of mice, along with increased osteoclasts and decreased osteoblasts. Osteoclastogenesis was also promoted by Per1 depletion in vitro with 16 downregulated inflammatory genes. Seven of these genes were known to promote or inhibit osteoclastogenesis depending on the stage of osteoclastogenesis and the presence or absence of infection. Knockdown of Nlrp3, Tlr8, or Tlr9 in the group of genes promoted osteoclastogenesis, mirroring the effects of Per1 knockout and offering a mechanistic explanation for the Per1-mediated inhibition of osteoclastogenesis. These results were not observed following the knockout of a paralog Per2. Per1 knockout mice maintain general circadian rhythms, unlike arrhythmic Per1;Per2 double knockout mice. This gives credence to Per1 as a selective target for therapeutic interventions without disrupting the circadian rhythms. This study uncovered a molecular link between a circadian regulator and osteoclastogenesis in the broader context of inflammatory reactions. Our findings may be mechanistically relevant to inflammatory bone diseases influenced by circadian rhythms, such as rheumatoid arthritis and osteoarthritis, as well as other bone diseases predisposed by chronic circadian disruption.
Project description:Disruption of circadian rhythms predisposes shift workers to many chronic conditions, including osteoporosis. However, the effects of disrupted circadian rhythms on bone remodeling remain largely unknown. Here, we show that one of the core circadian regulators PER1 inhibits osteoclastogenesis by upregulating genes involved in inflammation. The conditional knockout of Per1 in osteoclasts and related cells resulted in decreased bone mass in the femurs of mice, along with increased osteoclasts and decreased osteoblasts. Osteoclastogenesis was also promoted by Per1 depletion in vitro with 16 downregulated inflammatory genes. Seven of these genes were known to promote or inhibit osteoclastogenesis depending on the stage of osteoclastogenesis and the presence or absence of infection. Knockdown of Nlrp3, Tlr8, or Tlr9 in the group of genes promoted osteoclastogenesis, mirroring the effects of Per1 knockout and offering a mechanistic explanation for the Per1-mediated inhibition of osteoclastogenesis. These results were not observed following the knockout of a paralog Per2. Per1 knockout mice maintain general circadian rhythms, unlike arrhythmic Per1;Per2 double knockout mice. This gives credence to Per1 as a selective target for therapeutic interventions without disrupting the circadian rhythms. This study uncovered a molecular link between a circadian regulator and osteoclastogenesis in the broader context of inflammatory reactions. Our findings may be mechanistically relevant to inflammatory bone diseases influenced by circadian rhythms, such as rheumatoid arthritis and osteoarthritis, as well as other bone diseases predisposed by chronic circadian disruption.
Project description:Clarification of the mechanisms underlying osteoclast differentiation enable us to understand the physiology of bone metabolism as well as the pathophysiology of bone diseases, such as osteoporosis. Recently, it has been reported that epigenetics can determine the cell fate and regulate cell type specific gene expression. However, little is known about epigenetics during osteoclastogenesis. To reveal a part of epigenetics, especially focused on chromatin dynamics, during early osteoclastogenesis and identify novel transcription factors involved in osteoclastogenesis, we investigated genome-wide analysis of open chromatin during receptor activator of nuclear factor-M-NM-:B ligand (RANKL)-induced osteoclastogenesis using DNase I hypersensitive sites sequencing (DNase-seq). DNase-seq was performed using the extracted nuclei obtained from RAW264 cells treated with or without RANKL for 24 hours, followed by several bioinformatic analyses. DNase I hypersensitive sites (DHSs) during RANKL-induced osteoclastogenesis were dynamically changed and accumulated in promoter regions, although the distributions of DHSs among cis-regulatory DNA regions were identical regardless of RANKL stimulation. Motif discoveries from DHSs successfully identified well-known osteoclastogenic transcription factors such as Jun, CREB1, FOS, ATF2 and ATF4, but also novel transcription factors for osteoclastogenesis such as Zscan10, Atf1 Nrf1 and Srebf2. siRNA knockdown of these identified novel transcription factors impaired osteoclastogenesis. Taken together, DNase-seq can be a useful tool for comprehension of epigenetics, especially chromatin dynamics during osteoclastogenesis and for identification of novel transcription factors involved in osteoclastogenesis. This study may reveal underlying mechanisms that determine cell-type specific differentiation of bone cells and may lead to investigate novel therapeutic targets for osteoporosis. Examination of genome-wide DNase Hypersensitive Sites in differentiated and undifferentiated RAW264 cells.
Project description:To screen for altered gene expression during osteoclastogenesis, BMM cells treated with RANKL or RANKL+LEA were subjected to gene expression profiling.