Efficient osteoclast differentiation requires local complement activation

Abstract

Previous studies using blocking antibodies suggested that bone marrow (BM)-derived C3 is required for efficient osteoclast (OC) differentiation, and that C3 receptors are involved in this process. However, the detailed underlying mechanism and the possible involvement of other complement receptors remain unclear. In this report, we found that C3 ؊/؊ BM cells exhibited lower RANKL/OPG expression ratios, produced smaller amounts of macrophage colonystimulating factor and interleukin-6 (IL-6), and generated significantly fewer OCs than wild-type (WT) BM cells. During differentiation, in addition to C3, WT BM cells locally produced all other complement components required to activate C3 and to generate C3a/C5a through the alternative pathway, which is required for efficient OC differentiation. Abrogating C3aR/C5aR activity either genetically or pharmaceutically suppressed OC generation, while stimulating WT or C3 ؊/؊ BM cells with exogenous C3a and/or C5a augmented OC differentiation. Furthermore, supplementation with IL-6 rescued OC generation from C3 ؊/؊ BM cells, and neutralizing antibodies to IL-6 abolished the stimulatory effects of C3a/C5a on OC differentiation. These data indicate that during OC differentiation, BM cells locally produce components, which are activated through the alternative pathway to regulate OC differentiation. In addition to C3 receptors, C3aR/C5aR also regulate OC differentiation, at least in part, by modulating local IL-6 production. (Blood. 2010;116(22):4456-4463) IntroductionC3 is the central part of the complement system, which is pivotal in fighting infection and clearing out immune complexes as part of the innate immunity. For C3 to impact any cell, it needs to be activated through 1 of the 3 activating pathways: the classical, the alternative, or the lectin pathway. To form the C3 convertase (C3bBb) that is required in the alternative-pathway complement-activation cascade, C3b is generated from spontaneous C3 hydrolysis and binds to the active form of factor B (Bb), which is produced by the enzymatic activity of factor D. After the enzymatic activities of these C3/C5 convertases, the resultant complement-activation products bind to their receptors, facilitating cell migration, 1 phagocytosis, 2 as well as many other cellular activities. For cell surface-bound complement activation products, such as C3b and its derivatives, there are the C3 receptors, CR1, 3 CR2, 4 CR3, 5 and CR4 6 ; for the released complement-activation products, such as C3a and C5a, 1 there are C3aR 7 and C5aR. 8 C3aR and C5aR are G protein-coupled receptors that are present on a broad spectrum of cells. 9 C3a and C5a (also known as, anaphylatoxins) are small polypeptides, 10 which bind to C3aR and C5aR with high affinity (K d ϭ 1 nM) to modulate many cell activities, including stimulating the production of interleukin (IL)-6 (reviewed in Haas and van Strijp 11 ).In 1993, Dr Suda and his colleagues reported that the activated form of vitamin D, 1,25(OH) 2 vitamin D 3 , induces bone marrow (BM) cells to locally p...

Rapid-onset clinical and mechanistic effects of anti-C5aR treatment in the mouse collagen-induced arthritis model

“…Also, as anti-mC5aR mAb reduced the levels of several chemotactic factors, such as KC, MCP-1 and MCP-5, C5aR blockade may not only directly inhibit influx of inflammatory cells into the affected paws, but also -by reducing the release of other chemotactic factors -indirectly reduce chemotaxis. Finally, it should be mentioned that the impact on bone erosion may be caused by blocking a direct effect of C5a on osteoclastogenesis as described by others [19,20]. The effect of C5aR-blockade on the number of osteoclasts was, however, not investigated in this study.…”

“…Further, an increased proportion of mast cells isolated from synovial tissue from patients with RA were found positive for the C5aR compared to mast cells from patients with OA [18]. C5a may also be involved in osteoclastogenesis, as a C5aR antagonist partially inhibits vitamin D3-induced human bone marrow differentiation to osteoclasts, and furthermore C5a can induce osteoclast differentiation from peripheral blood mononuclear cells (PBMCs) [19,20]. In summary, blockade of C5aR in RA represents another mode of action compared to the current therapies and holds promising potential for beneficial effects in patients who fail current therapy and/or in subgroups of patients with a disease driven by C5a-mediated influx and activation of neutrophils and macrophages.…”

Vancomycin-Modified Implant Surface Inhibits Biofilm Formation and Supports Bone-Healing in an Infected Osteotomy Model in Sheep

“…Localized bacterial infection has been shown to be capable of generating a low pH 48 , which could result in cleavage of the vancomycin-titanium bond. A second factor, which may be due to vancomycin-induced complement activation resulting in upregulated osteoclastogenesis, is the high population of osteoclasts visible under the plate 49,50 . Osteoclastic cleavage of the vancomycin bond could diminish antivancomycin reactivity and generate a low level of staining.…”

The role of complement component 3 (C3) in differentiation of myeloid-derived suppressor cells

“…42,43 We and others have recently demonstrated that ligation of C3aR is also integrally involved in the regulation of the T-cell response 44,45 and osteoclast differentiation. 46 Interestingly, in these circumstances, as well as in the experimental settings used in this study, the effector complement components are locally produced by related cells, not systemic complement components produced by hepatocytes, which is most likely due to the relatively high concentrations of complement in the local environment outside of the vasculature. Local production and activation of complement have been shown to play a role in T-cell activation and generation of Th1 responses.…”