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Porphyromonas gingivalis Stimulates Bone Resorption by Enhancing RANKL (Receptor Activator of NF-kappa B Ligand) through Activation of Toll-like Receptor 2 in Osteoblasts
Umeå University, Faculty of Medicine, Department of Odontology.
Umeå University, Faculty of Medicine, Department of Odontology.
Umeå University, Faculty of Medicine, Department of Odontology.
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2015 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 290, no 33, 20147-20158 p.Article in journal (Refereed) Published
Abstract [en]

Periodontitis has been associated with rheumatoid arthritis. In experimental arthritis, concomitant periodontitis caused by oral infection with Porphyromonas gingivalis enhances articular bone loss. The aim of this study was to investigate how lipopolysaccharide (LPS) from P. gingivalis stimulates bone resorption. The effects by LPS P. gingivalis and four other TLR2 ligands on bone resorption, osteoclast formation, and gene expression in wild type and Tlr2-deficient mice were assessed in ex vivo cultures of mouse parietal bones and in an in vivo model in which TLR2 agonists were injected subcutaneously over the skull bones. LPS P. gingivalis stimulated mineral release and matrix degradation in the parietal bone organ cultures by increasing differentiation and formation of mature osteoclasts, a response dependent on increased RANKL (receptor activator of NF-kappa B ligand). LPS P. gingivalis stimulated RANKL in parietal osteoblasts dependent on the presence of TLR2 and through a MyD88 and NF-kappa B-mediated mechanism. Similarly, the TLR2 agonists HKLM, FSL1, Pam2, and Pam3 stimulated RANKL in osteoblasts and parietal bone resorption. LPS P. gingivalis and Pam2 robustly enhanced osteoclast formation in periosteal/endosteal cell cultures by increasing RANKL. LPS P. gingivalis and Pam2 also up-regulated RANKL and osteoclastic genes in vivo, resulting in an increased number of periosteal osteoclasts and immense bone loss in wild type mice but not in Tlr2-deficient mice. These data demonstrate that LPS P. gingivalis stimulates periosteal osteoclast formation and bone resorption by stimulating RANKL in osteoblasts via TLR2. This effect might be important for periodontal bone loss and for the enhanced bone loss seen in rheumatoid arthritis patients with concomitant periodontal disease.

Place, publisher, year, edition, pages
2015. Vol. 290, no 33, 20147-20158 p.
National Category
URN: urn:nbn:se:umu:diva-108135DOI: 10.1074/jbc.M115.655787ISI: 000359608900017PubMedID: 26085099OAI: diva2:855510
Available from: 2015-09-21 Created: 2015-09-04 Last updated: 2015-10-20Bibliographically approved
In thesis
1. Toll-like receptors (TLRs) and inflammatory bone modeling
Open this publication in new window or tab >>Toll-like receptors (TLRs) and inflammatory bone modeling
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Toll-liknande receptorer och inflammatorisk benmodellering
Abstract [en]

Patients with inflammatory or infectious conditions such as periodontitis, peri-implantitis, osteomyelitis, rheumatoid arthritis, septic arthritis and loosened joint prosthesis display varying severity of destruction in the adjacent bone tissue. Bone loss in inflammatory diseases is considered a consequence of cytokine induced RANKL and subsequent enhanced osteoclast formation. Hence, osteotropic cytokines and their receptors have been suggested to be important for the pathogenesis of inflammation-induced osteolysis. It is, here, suggested that bacterial components, so called “pathogen associated molecular patterns=PAMPs”, may also be involved. Varieties of cells express receptors for PAMPs, including Toll-like receptors (TLRs) which are the first line of defence in the innate immune system. LPS (lipopolysaccharide), fimbria and lipoproteins from pathogenic bacteria such as P. gingivalis, S. aureus are ligands for TLR2 and flagellin from pathogenic flagellated bacteria like S. typhimurium is a ligand for TLR5.


Since the susceptibility to, or the severity of inflammation-associated bone diseases are likely related to differences in the tissue response, and the mechanisms by which PAMPs interact with bone cells are not fully understood, we aimed to elucidate the importance of different TLRs for inflammation induced bone loss by conducting in vitro and in vivo investigations.

Activation of TLR2 and TLR5 in organ cultured mouse parietal bones increased bone resorption in a time- and concentration-dependent manner by a process inhibited by OPG and bisphosphonate, showing the crucial role of RANKL-induced osteoclast formation. In addition, the number of osteoclasts, expression of osteoclastic genes and osteoclastogenic transcription factors were increased. In the bones and in osteoblasts isolated from the bones, TLR2 agonists increased the expression of RANKL without affecting OPG, while TLR5 activation resulted in enhanced RANKL and decreased OPG. Activation of both TLR2 and TLR5 stimulated the expression in both bones and osteoblasts of prostaglandins and pro-inflammatory cytokines, known to stimulate RANKL. By blocking the cytokines and prostaglandin, we showed that TLR2 and TLR5 induced bone resorption and RANKL expression are independent of these molecules.

Activation of TLR2, but not TLR5, in mouse bone marrow macrophage cultures inhibited RANKL-induced osteoclast formation, an effect not observed in committed pre-osteoclasts.

Local administration in vivo of TLR2 and TLR5 agonists on the top of mouse skull bones enhanced local and systemic osteoclast formation and bone resorption. Using knockout mice, we showed that the effects by LPS from P. gingivalis (used as TLR2 agonist) and flagellins (used as TLR5 agonists) are explicit for TLR2 and TLR5 ex vivo and in vivo, respectively.

These data show that stimulation of TLR2 and TLR5 results in bone resorption in vitro and in vivo mediated by increased RANKL in osteoblasts and thus may be one mechanism for developing inflammatory bone loss.

Interestingly, histological analyses of skull bones of mice treated locally with TLR2 and TLR5 agonists revealed that the bones not only reacted with locally increased osteoclastogenesis (osteoclast formation), but also with locally increased new bone formation. This was observed on both periosteal and endosteal sides of the bones, as well as in the bone marrow compartment. The formation of new bone was seen close to osteoclasts in some parts, but also in other areas, distant from these cells. The response was associated with active, cuboidal osteoblasts, extensive cell proliferation and increased expression of genes coding for bone matrix proteins and osteoblastic transcription factors.

In conclusion, activation of TLR2 and TLR5 in osteoblasts results in bone loss associated with enhanced osteoclast formation and bone resorption, as well as with increased osteoblast differentiation and new bone formation, indicating that inflammation causes bone modeling. The data provide an explanation why LPS from P. gingivalis and flagellin from flagella-expressing bacteria can stimulate bone loss. Since TLR2 and TLR5 can be activated not only by bacterial components, but also by endogenous ligands produced in inflammatory processes, the data also contribute to the understanding of inflammation induced bone loss in autoimmune diseases. Hopefully, these findings will contribute to the development of treatment strategies for inflammation induced bone loss.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2015. 133 p.
Umeå University odontological dissertations, ISSN 0345-7532 ; 134
Toll-like receptor, osteoclast, osteoblast, bone resorption, bone formation, P. gingivalis, S. aureus, flagellin.
National Category
Cell and Molecular Biology Dentistry
urn:nbn:se:umu:diva-110296 (URN)978-91-7601-370-0 (ISBN)
Public defence
2015-11-11, Hörsal B, Tandläkarhögskolan, plan 9, Norrlands universitetssjukhus§, Umeå, 09:00 (English)
Swedish Research Council
Available from: 2015-10-21 Created: 2015-10-19 Last updated: 2015-10-22Bibliographically approved

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Kassem, AliLundberg, PernillaSouza, Pedro P. C.Lerner, Ulf H.
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