title: Stimulation of osteoclast formation by RANKL requires interferon regulatory factor-4 and is inhibited by simvastatin in a mouse model of bone loss.
abstract: Diseases of bone loss are a major public health problem. Here, we report the novel therapeutic action of simvastatin in osteoclastogenesis and osteoprotection, demonstrated by the ability of simvastatin to suppress osteoclast formation in vitro and in vivo. We found that in vitro, IRF4 expression is upregulated during osteoclast differentiation induced by RANKL (receptor activator of nuclear factor-κB ligand), while simvastatin blocks RANKL-induced osteoclastogenesis and decreases expression of NFATc1 (nuclear factor of activated T-cells, cytoplasmic, calcineurin-dependent 1), IRF4 and osteoclast markers. We also show that IRF4 acts in cooperation with NFATc2 and NF-κB on the promoter region of NFATc1 to accelerate its initial transcription during the early stage of osteoclastogenesis. Moreover, our study using IRF4 siRNA knockdown directly demonstrates the requirement for IRF4 in NFATc1 mRNA transcription and its necessity in RANKL-induced osteoclast differentiation. Our results suggest that the reduction in osteoclastogenesis is partly due to the inhibition of IRF4 production in RANKL-induced osteoclast differentiation. To investigate the in vivo effects of simvastatin in RANKL-treated mice, we examined the bone mineral density (BMD) of a mouse model of bone loss, and found that simvastatin significantly reduced bone loss by suppressing osteoclast numbers in vivo, even in the presence of high concentrations of RANKL. These results suggest that the depletion of osteoclasts is not due to the reduction in RANKL produced by osteoblasts in vivo. The results are consistent with the hypothesis that simvastatin blocks RANKL-induced IRF4 expression in osteoclastogenesis. We propose that the expression of IRF4 by osteoclasts could be a promising new therapeutic target in bone-loss diseases.
authors.affiliation: Department of Histology and Oral Histology, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Nakashima
authors.forename: Tatsuji
authors.initials: T
authors.lastname: Haneji
mesh_terms: D000818:Animals; D015519:Bone Density / Q000187:drug effects; D050071:Bone Density Conservation Agents / Q000494:pharmacology*; D002454:Cell Differentiation; D002460:Cell Line; D004353:Drug Evaluation, Preclinical; D044127:Epigenesis, Genetic; D005260:Female; D015870:Gene Expression; D006657:Histones / Q000378:metabolism; D006801:Humans; D050835:Interferon Regulatory Factors / Q000235:genetics / Q000378:metabolism*; D008745:Methylation; D051379:Mice; D008810:Mice, Inbred C57BL; D050778:NFATC Transcription Factors / Q000378:metabolism; D010010:Osteoclasts / Q000187:drug effects* / Q000502:physiology; D010024:Osteoporosis / Q000188:drug therapy* / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D053245:RANK Ligand / Q000494:pharmacology / Q000502:physiology*; D015398:Signal Transduction; D019821:Simvastatin / Q000494:pharmacology*; D000099218:Interferon Regulatory Factor-4
chemical_list: D050071:Bone Density Conservation Agents; D006657:Histones; D050835:Interferon Regulatory Factors; D050778:NFATC Transcription Factors; D053245:RANK Ligand; D019821:Simvastatin; D000099218:Interferon Regulatory Factor-4; C494007:Nfatc2 protein, mouse; C505689:Tnfsf11 protein, mouse
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