TLR2-dependent modulation of osteoclastogenesis by Porphyromonas gingivalis through differential induction of NFATc1 and NF-kappaB.

Department of Pediatric Dentistry, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
Journal of Biological Chemistry (Impact Factor: 4.6). 05/2011; 286(27):24159-69. DOI: 10.1074/jbc.M110.198085
Source: PubMed

ABSTRACT Osteolytic diseases, including rheumatoid arthritis, osteomyelitis, and periodontitis, are usually associated with bacterial infections. However, the precise mechanisms by which bacteria induce bone loss still remain unclear. Evidence exists that Toll-like receptor (TLR) signaling regulates both inflammation and bone metabolism and that the receptor activator of NF-κB ligand (RANKL) and its receptor RANK are the key regulators for bone remodeling and for the activation of osteoclasts. Here, we investigate the direct effects of the periodontal pathogen Porphyromonas gingivalis on osteoclast differentiation and show that P. gingivalis differentially modulates RANKL-induced osteoclast formation contingent on the state of differentiation of osteoclast precursors. In addition, although an optimal induction of cytokines by P. gingivalis is dependent on TLR2 and TLR4, as well as myeloid differentiation factor 88 and Toll/IL-1R domain-containing adaptor-inducing IFN-β, P. gingivalis utilizes TLR2/ myeloid differentiation factor 88 in modulating osteoclast differentiation. P. gingivalis modulates RANKL-induced osteoclast formation by differential induction of NFATc1 and c-Fos. More importantly, RANKL-mediated lineage commitment also has an impact on P. gingivalis-induced cytokine production. RANKL inhibits P. gingivalis-induced cytokine production by down-regulation of TLR/NF-κB and up-regulation of NFATc1. Our findings reveal novel aspects of the interactions between TLR and RANK signaling and provide a new model for understanding the mechanism underlying the pathogenesis of bacteria-mediated bone loss.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Background: Different serotypes of Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis have shown to induce differential dendritic cell (DC) response. This study aimed to investigate whether the cytokine and CC-chemokine receptor (CCR) production by DCs stimulated with the different serotypes of A. actinomycetemcomitans or P. gingivalis was toll-like receptor (TLR)2 and/or TLR4-dependent. Methods: DCs were obtained from healthy individuals and primed at a multiplicity of infection (MOI) of 10(2) with the different A. actinomycetemcomitans or P. gingivalis serotypes in the presence or the absence of anti-TLR2 or anti-TLR4 blocking antibodies. The TLR2 and TLR4 expression, the CCR5 and CCR6 expression as well as the interleukin (IL)-1β, IL-10, IL-12 and IL-23 expression and secretion were quantified by flow cytometry, real-time RT-PCR, and ELISA. Results: When DCs were stimulated with the serotype b of A. actinomycetemcomitans or serotype K1 of P. gingivalis, higher levels of TLR2 or TLR4, respectively, were detected compared with DCs stimulated with the other serotypes. Similarly, higher levels of cytokines and CCRs were detected in serotype b or K1-primed DCs compared with the others, and these increased levels positively correlated with the detected levels of TLR2 or TLR4. When the TLR2 signaling was blocked using a specific anti-TLR2 monoclonal antibody, the serotype b-induced cytokine and CCR mRNA expression was abrogated; whereas, when the TLR4 signaling was blocked, the serotype K1-induced response was abrogated. Conclusion: These results demonstrate that the variability on the secretion of cytokines and expression of CCRs detected in DCs stimulated with the different serotypes of A. actinomycetemcomitans or P. gingivalis is TLR2 or TLR4-dependent, respectively.
    Journal of Periodontology 09/2014; 86(1):1-21. DOI:10.1902/jop.2014.140326 · 2.57 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Toll-like receptors (TLRs) play a key role in the innate immune responses to periodontal pathogens in periodontal disease. The present study is to determine the role of TLR2 and TLR4 signaling in alveolar bone resorption using P. gingivalis-associated ligature-induced periodontitis model in mice. Wild Type (WT), Tlr2(-/-) and TLR4(-/-) mice (8-10 weeks old) of C57/BL6 background were used. Silk ligatures were applied to the maxillary second molars in the presence or absence of live P. gingivalis infection. Ligatures were removed from the second molars on Day 14 and mice were kept for another 2 weeks before sacrifice for final analysis (Day 28). On Day 14, there was no difference in alveolar bone resportion and gingival RANKL expression between mice treated with ligation + P. gingivalis infection and mice treated with ligation alone. Gingival IL-1β and TNF-α expression were increased whereas IL-10 expression was decreased in WT and Tlr2(-/-) mice but not in TLR4(-/-) mice. On Day 28, WT and Tlr4(-/-) mice treated with ligation + P. gingivalis infection showed significantly increased bone loss and gingival RANKL expression compared to those treated with ligation alone, whereas such increase was diminished in Tlr2(-/-) mice. Gingival TNF-α up-regulation and IL-10 down-regulation were only observed in WT and Tlr4(-/-) mice but not in TLR2(-/-) mice. In all mice, bone resorption induced by ligation + P. gingivalis infection was antagonized by local anti-RANKL antibody administration. This study suggests that P. gingivalis exacerbates ligature-induced RANKL-dependent periodontal bone resorption via differential regulation of TLR2 and TLR4 signaling.
    Infection and Immunity 07/2014; 82(10). DOI:10.1128/IAI.02084-14 · 4.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Background: Toll-like receptors (TLRs) play pivotal roles in host immune responses and have been suggested to be involved in the development of many infectious diseases. In this study, the mRNA expression levels of TLR2, TLR4, and TLR9 and their relationship with periodontopathic bacteria in periodontal tissue are examined. Furthermore, the mechanism of TLR induction by Porphyromonas gingivalis is investigated in human gingival fibroblasts (HGFs). Methods: Gingival tissue and subgingival plaque samples were collected from 19 patients with chronic periodontitis (CP) and 16 control individuals without periodontitis. Gene expression levels in the tissues and in HGFs were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). The numbers of periodontopathic bacteria were determined by quantitative real-time PCR. Results: The expression levels of TLR2 and TLR9 were significantly higher in the tissues of patients with CP compared to the tissues of control individuals. The mRNA levels of TLR2 and TLR9, but not TLR4, were positively correlated with the number of P. gingivalis in subgingival plaque. P. gingivalis sonicated extract, P. gingivalis lipopolysaccharide, P. gingivalis DNA, and tumor necrosis factor-alpha (TNF-alpha) could significantly upregulate the mRNA expression of TLR2 in HGFs. Furthermore, P. gingivalis-mediated TLR2 expression was suppressed by TNF-alpha antibody. Conclusions: This study suggests that P. gingivalis infection induces TLR2 and TLR9 upregulation in patients with CP. P. gingivalis-induced TLR2 expression in HGFs is partially dependent on TNF-alpha and may lead to sensitization of HGFs to bacterial components encountered in the periodontal microenvironment.
    Journal of Periodontology 07/2013; 84(7):1010-1018. DOI:10.1902/jop.2012.120362 · 2.57 Impact Factor