title: Rheumatoid and pyrophosphate arthritis synovial fibroblasts induce osteoclastogenesis independently of RANKL, TNF and IL-6.
abstract: Bone destruction is a common feature of inflammatory arthritis and is mediated by osteoclasts, the only specialized cells to carry out bone resorption. Aberrant expression of receptor activator of nuclear factor kappa β ligand (RANKL), an inducer of osteoclast differentiation has been linked with bone pathology and the synovial fibroblast in rheumatoid arthritis (RA). In this manuscript, we challenge the current concept that an increase in RANKL expression governs osteoclastogenesis and bone destruction in autoimmune arthritis. We isolated human fibroblasts from RA, pyrophosphate arthropathy (PPA) and osteoarthritis (OA) patients and analyzed their RANKL/OPG expression profile and the capacity of their secreted factors to induce osteoclastogenesis. We determined a 10-fold increase of RANKL mRNA and protein in fibroblasts isolated from RA relative to PPA and OA patients. Peripheral blood mononuclear cells (PBMC) from healthy volunteers were cultured in the presence of RA, PPA and OA synovial fibroblast conditioned medium. Osteoclast differentiation was assessed by expression of tartrate-resistant acid phosphatase (TRAP), vitronectin receptor (VNR), F-actin ring formation and bone resorption assays. The formation of TRAP(+), VNR(+) multinucleated cells, capable of F-actin ring formation and lacunar resorption in synovial fibroblast conditioned medium cultures occured in the presence of osteoprotegerin (OPG) a RANKL antagonist. Osteoclasts did not form in these cultures in the absence of macrophage colony stimulating factor (M-CSF). Our data suggest that the conditioned medium of pure synovial fibroblast cultures contain inflammatory mediators that can induce osteoclast formation in human PBMC independently of RANKL. Moreover inhibition of the TNF or IL-6 pathway was not sufficient to abolish osteoclastogenic signals derived from arthritic synovial fibroblasts. Collectively, our data clearly show that alternate osteoclastogenic pathways exist in inflammatory arthritis and place the synovial fibroblast as a key regulatory cell in bone and joint destruction, which is a hallmark of autoimmune arthritis.
authors.affiliation: University of California, Davis, Department of Internal Medicine, Division of Rheumatology, Allergy and Clinical Immunology, Davis, CA, USA.
authors.forename: Tiffany J
authors.initials: TJ
authors.lastname: Dickerson
authors.forename: Erika
authors.initials: E
authors.lastname: Suzuki
authors.forename: Catherine
authors.initials: C
authors.lastname: Stanecki
authors.forename: Hyun-Seock
authors.initials: HS
authors.lastname: Shin
authors.forename: Hong
authors.initials: H
authors.lastname: Qui
authors.forename: Iannis E
authors.initials: IE
authors.lastname: Adamopoulos
mesh_terms: D000135:Acid Phosphatase / Q000235:genetics / Q000276:immunology; D000199:Actins / Q000235:genetics / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D001862:Bone Resorption; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D002805:Chondrocalcinosis / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D017077:Culture Media, Conditioned / Q000494:pharmacology; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000235:genetics / Q000276:immunology; D015850:Interleukin-6 / Q000235:genetics / Q000276:immunology; D007527:Isoenzymes / Q000235:genetics / Q000276:immunology; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D010003:Osteoarthritis / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D053244:Osteoprotegerin / Q000494:pharmacology; D053245:RANK Ligand / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction / Q000187:drug effects; D013582:Synovial Fluid / Q000166:cytology; D000071681:Tartrate-Resistant Acid Phosphatase; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000276:immunology
chemical_list: D000199:Actins; D017077:Culture Media, Conditioned; C508600:IL6 protein, human; D039302:Integrin alphaVbeta3; D015850:Interleukin-6; D007527:Isoenzymes; D053244:Osteoprotegerin; D053245:RANK Ligand; C439524:TNF protein, human; C505688:TNFSF11 protein, human; D014409:Tumor Necrosis Factor-alpha; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase