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Atp6v0d2 is an essential component of the osteoclast-specific proton pump that mediates extracellular acidification in bone resorption.

ABSTRACT: Bone resorption relies on the extracellular acidification function of vacuolar (V-) ATPase proton pump(s) present in the plasma membrane of osteoclasts. The exact configuration of osteoclast-specific V-ATPases remains largely unknown. In this study, we found that Atp6v0d2 (d2), an isoform of the d subunit in the V-ATPase, showed 5-fold higher expression than that of Atp6v0d1 (d1) in mature osteoclasts, indicating a potential function in osteoclastic bone resorption. When d2 was depleted at an early stage of RANKL-induced osteoclast differentiation in vitro, formation of multinucleated cells was severely impaired. However, depletion of d2 at a late differentiation stage did not affect osteoclast fusion but did abolish the activity of extracellular acidification and bone resorption of mature osteoclasts. We also showed the association of the two tagged-proteins d2 and a3 when co-expressed in mammalian cells with a co-immunoprecipitation assay. Moreover, glutathione-S-transferase (GST) pull-down assay showed the direct interaction of d2 with the N terminus of Atp6v0a3 (a3), which is the functionally identified osteoclast-specific component of V-ATPase. Therefore, our results show the dual function of d2 as a regulator of cell fusion in osteoclast differentiation and as an essential component of the osteoclast-specific proton pump that mediates extracellular acidification in bone resorption.

SUBMITTER: Wu H

PROVIDER: S-EPMC2672205 | biostudies-literature | 2009 May

REPOSITORIES: biostudies-literature

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Atp6v0d2 is an essential component of the osteoclast-specific proton pump that mediates extracellular acidification in bone resorption.

Wu Haiping H Xu Guoliang G Li Yi-Ping YP

Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research 20090501 5

Bone resorption relies on the extracellular acidification function of vacuolar (V-) ATPase proton pump(s) present in the plasma membrane of osteoclasts. The exact configuration of osteoclast-specific V-ATPases remains largely unknown. In this study, we found that Atp6v0d2 (d2), an isoform of the d subunit in the V-ATPase, showed 5-fold higher expression than that of Atp6v0d1 (d1) in mature osteoclasts, indicating a potential function in osteoclastic bone resorption. When d2 was depleted at an ea ...[more]

PMID: 19113919

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Project description:Endodontic disease is characterized by inflammation and destruction of periapical tissues, leading to severe bone resorption and tooth loss. ATP6AP1 (Ac45) has been implicated in human immune diseases, yet the mechanism underlying how Ac45 regulates immune response and reaction in inflammatory diseases remains unknown. We generated endodontic disease mice through bacterial infection as an inflammatory disease model and used adeno-associated virus (AAV)-mediated Ac45 RNA interference knockdown to study the function of Ac45 in periapical inflammation and bone resorption. We demonstrated that the AAV small hairpin RNA targeting Ac45 (AAV-sh-Ac45) impaired cellular acidification, extracellular acidification, and bone resorption. Our results showed that local delivery of AAV-sh-Ac45 in periapical tissues in bacterium-induced inflammatory lesions largely reduced bone destruction, inhibited inflammation, and dramatically reduced mononuclear immune cells. T-cell, macrophage, and dendritic cell infiltration in the periapical lesion was dramatically reduced, and the periodontal ligament was protected from inflammation-induced destruction. Furthermore, AAV-sh-Ac45 significantly reduced osteoclast formation and the expression of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-10 (IL-10), IL-12, IL-1α, IL-6, and IL-17. Interestingly, AAV-sh-Ac45 impaired mature cathepsin K secretion more significantly than that by AAV-sh-C1 and AAV-sh-CtsK Unbiased genome-wide transcriptome sequencing analysis of Ctsk-/- dendritic cells stimulated with lipopolysaccharide demonstrated that the ablation of Ctsk dramatically reduced dendritic cell-mediated inflammatory signaling. Taken together, our results indicated that AAV-sh-Ac45 simultaneously inhibits osteoclast-mediated bone resorption and attenuates dendritic cell-mediated inflammation through impairing acidification and cathepsin K secretion. Thus, Ac45 may be a novel target for therapeutic approaches to attenuate inflammation and bone erosion in endodontic disease and other inflammation-related osteolytic diseases.

Project description:ObjectiveAutoantibodies are detected in most patients with rheumatoid arthritis (RA) and can be of the IgM, IgG or IgA subclass. Correlations between IgA autoantibodies and more severe disease activity have been previously reported, but the functional role of IgA autoantibodies in the pathogenesis of RA is ill understood. In this study, we explored the effect of IgA immune complexes on osteoclast mediated bone resorption.MethodsAnti-citrullinated peptide antibody (ACPA) and anti-carbamylated protein (anti-CarP) antibody levels of the IgA and IgG isotype and rheumatoid factor (RF) IgA were determined in synovial fluid (SF) of RA patients. Monocytes, neutrophils, and osteoclasts were stimulated with precipitated immune complexes from SF of RA patients or IgA- and IgG-coated beads. Activation was determined by neutrophil extracellular trap (NET) release, cytokine secretion, and bone resorption.ResultsNET formation by neutrophils was enhanced by SF immune complexes compared to immune complexes from healthy or RA serum. Monocytes stimulated with isolated SF immune complexes released IL-6 and IL-8, which correlated with the levels of ACPA IgA levels in SF. Osteoclasts cultured in the presence of supernatant of IgA-activated monocytes resorbed significantly more bone compared to osteoclasts that were cultured in supernatant of IgG-activated monocytes (p=0.0233). Osteoclasts expressed the Fc receptor for IgA (FcαRI; CD89) and Fc gamma receptors. IgA-activated osteoclasts however produced significantly increased levels of IL-6 (p<0.0001) and IL-8 (p=0.0007) compared to IgG-activated osteoclasts. Both IL-6 (p=0.03) and IL-8 (p=0.0054) significantly enhanced bone resorption by osteoclasts.ConclusionIgA autoantibodies induce release of IL-6 and IL-8 by immune cells as well as osteoclasts, which enhances bone resorption by osteoclasts. We anticipate that this will result in more severe disease activity in RA patients. Targeting IgA-FcαRI interactions therefore represents a promising novel therapeutic strategy for RA patients with IgA autoantibodies.

Dataset Information

Atp6v0d2 is an essential component of the osteoclast-specific proton pump that mediates extracellular acidification in bone resorption.

Publications

Atp6v0d2 is an essential component of the osteoclast-specific proton pump that mediates extracellular acidification in bone resorption.

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