title: Mechanical loading prevents the stimulating effect of IL-1β on osteocyte-modulated osteoclastogenesis.
abstract: Inflammatory diseases such as rheumatoid arthritis are often accompanied by higher plasma and synovial fluid levels of interleukin-1β (IL-1β), and by increased bone resorption. Since osteocytes are known to regulate bone resorption in response to changes in mechanical stimuli, we investigated whether IL-1β affects osteocyte-modulated osteoclastogenesis in the presence or absence of mechanical loading of osteocytes. MLO-Y4 osteocytes were pre-incubated with IL-1β (0.1-1 ng/ml) for 24h. Cells were either or not subjected to mechanical loading by 1h pulsating fluid flow (PFF; 0.7 ± 0.3 Pa, 5 Hz) in the presence of IL-1β (0.1-1 ng/ml). Conditioned medium was collected after 1h PFF or static cultures. Subsequently mouse bone marrow cells were seeded on top of the IL-1β-treated osteocytes to determine osteoclastogenesis. Conditioned medium from mechanically loaded or static IL-1β-treated osteocytes was added to co-cultures of untreated osteocytes and mouse bone marrow cells. Gene expression of cysteine-rich protein 61 (CYR61/CCN1), receptor activator of nuclear factor kappa-B ligand (RANKL), and osteoprotegerin (OPG) by osteocytes was determined immediately after PFF. Incubation of osteocytes with IL-1β, as well as conditioned medium from static IL-1β-treated osteocytes increased the formation of osteoclasts. However, conditioned medium from mechanically loaded IL-1β-treated osteocytes prevented osteoclast formation. Incubation with IL-1β upregulated RANKL and downregulated OPG gene expression by static osteocytes. PFF upregulated CYR61, RANKL, and OPG gene expression by osteocytes. Our results suggest that IL-1β increases osteocyte-modulated osteoclastogenesis, and that mechanical loading of osteocytes may abolish IL-1β-induced osteoclastogenesis.
authors.affiliation: Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam, University of Amsterdam and VU University Amsterdam, Research Institute MOVE, Amsterdam, The Netherlands.
authors.forename: Rishikesh N
authors.initials: RN
authors.lastname: Kulkarni
authors.forename: Astrid D
authors.initials: AD
authors.lastname: Bakker
authors.forename: Vincent
authors.initials: V
authors.lastname: Everts
authors.forename: Jenneke
authors.initials: J
authors.lastname: Klein-Nulend
mesh_terms: D000818:Animals; D001862:Bone Resorption / Q000503:physiopathology*; D002478:Cells, Cultured; D055515:Cysteine-Rich Protein 61 / Q000096:biosynthesis; D053583:Interleukin-1beta / Q000494:pharmacology*; D051379:Mice; D010010:Osteoclasts / Q000187:drug effects* / Q000502:physiology; D010011:Osteocytes / Q000187:drug effects* / Q000502:physiology; D013314:Stress, Mechanical; D015854:Up-Regulation
chemical_list: C491850:CCN1 protein, mouse; D055515:Cysteine-Rich Protein 61; D053583:Interleukin-1beta