Involvement of SOCS3 in Regulation of CD11c ⁺ Dendritic Cell-Derived Osteoclastogenesis and Severe Alveolar Bone Loss

Abstract

To investigate the role of suppressor of cytokine signaling (SOCS) molecules in periodontal immunity and RANKL-mediated dendritic cell (DC)-associated osteoclastogenesis, we analyzed SOCS expression profiles in CD4؉ T cells and the effect of SOCS3 expression in CD11c ؉ DCs during periodontal inflammation-induced osteoclastogenesis and bone loss in nonobese diabetic (NOD) versus humanized NOD/SCID mice. Our results of ex vivo and in vitro analyses showed that (i) there is significantly higher SOCS3 expression associated with RANKL ؉ T-cell-mediated bone loss in correlation with increased CD11c ؉ DC-mediated osteoclastogenesis; (ii) the transfection of CD11c ؉ DC using an adenoviral vector carrying a dominant negative SOCS3 gene significantly abrogates TRAP and bone-resorptive activity; and (iii) inflammation-induced TRAP expression, bone resorption, and SOCS3 activity are not associated with any detectable change in the expression levels of TRAF6 and mitogen-activated protein kinase signaling adaptors (i.e., Erk, Jnk, p38, and Akt) in RANKL ؉ T cells. We conclude that SOCS3 plays a critical role in modulating cytokine signaling involved in RANKL-mediated DC-derived osteoclastogenesis during immune interactions with T cells and diabetes-associated severe inflammation-induced alveolar bone loss. Therefore, the development of SOCS3 inhibitors may have therapeutic potential as the target to halt inflammation-induced bone loss under pathological conditions in vivo.Inflammatory bone diseases affect a large portion of the skeletal system, particularly those portions underlying mucosal surfaces, where inflammation-induced bone loss is closely associated with elevated osteoclast (OC) activity (15, 48). Inflammation-induced bone loss is readily manifested in periodontal disease (i.e., periodontitis), resulting in attachments loss, including periodontal connective tissues and supporting alveolar bone, as a consequence of the interplays between the specific subgingival biofilm and the host's immune/inflammatory responses (36, 37). The tumor necrosis factor (TNF) family member receptor activator of NF-B ligand (RANKL), its receptor, RANK, and the natural antagonist, osteoprotegrin (OPG), have been shown to be the key regulators of the differentiation, activation, and survival of OCs and OC. precursors (5,[16][17][18][23][24][25]44,55,58). In addition, it is now clear that the host responses, especially T-cell immunity, play a pivotal role in regulating osteoclastogenesis and homeostasis of the bone tissues (termed osteoimmunology [5]). Activated CD4 ϩ T cells express RANKL, which can directly trigger osteoclastogenesis and bone loss, and they can also negatively regulate RANKL activity via OPG production. For instance, it has been shown that OPG treatment results in significantly reduced bone loss in arthritis, osteoporosis, and cancer-related bone metastasis (16-18, 24, 45, 48, 55, 58). In murine models of periodontitis, OPG injections yield a robust inhibition of alveolar bone loss of up to 80 to 100%, suggesting that the R...

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