Porphyromonas gingivalis Exacerbates Ligature-Induced, RANKL-Dependent Alveolar Bone Resorption via Differential Regulation of Toll-Like Receptor 2 (TLR2) and TLR4

Abstract

dToll-like receptors (TLRs) play a key role in the innate immune responses to periodontal pathogens in periodontal disease. The present study was performed to determine the roles of TLR2 and TLR4 signaling in alveolar bone resorption, using a Porphyromonas gingivalis-associated ligature-induced periodontitis model in mice. Wild-type (WT), Tlr2 ؊/؊ , and Tlr4 ؊/؊ mice (8 to 10 weeks old) in the 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 were no differences in alveolar bone resorption and gingival RANKL expression between mice treated with ligation plus P. gingivalis infection and mice treated with ligation alone. Gingival interleukin-1␤ (IL-1␤) and tumor necrosis factor alpha (TNF-␣) expression was 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 plus P. gingivalis infection showed significantly increased bone loss and gingival RANKL expression compared to those treated with ligation alone, whereas such an increase was diminished in Tlr2 ؊/؊ mice. Gingival TNF-␣ upregulation and IL-10 downregulation were observed only in WT and Tlr4 ؊/؊ mice, not in Tlr2 ؊/؊ mice. In all mice, bone resorption induced by ligation plus 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.

Porphyromonas gingivalis Stimulates Bone Resorption by Enhancing RANKL (Receptor Activator of NF-κB Ligand) through Activation of Toll-like Receptor 2 in Osteoblasts

“…In agreement with these findings, bone loss and enhanced mRNA expression of Acp5 and Ctsk as well as increased Tnfsf11 mRNA were not observed in skull bones in Tlr2-deficient mice when LPS P. gingivalis or Pam2 were injected subcutaneously. Similarly, decreased alveolar bone volume observed in mice with oral infection of P. gingivalis was not seen in Tlr2-deficient mice (17,19). All together, these findings show that P. gingivalis can stimulate osteoclast formation, bone loss, and RANKL production by activating TLR2, although we cannot exclude that P. gingivalis bacteria can affect bone cells also through other pattern recognition receptors than TLR2.…”

“…LPS preparations from P. gingivalis often are potent agonists of TLR2 due to contamination with a lipoprotein with affinity to TLR2 (16). Oral infection with P. gingivalis in mice causes inflammation-induced alveolar bone loss through activation of TLR2 (17)(18)(19). The mechanism by which P. gingivalis induces bone loss is not fully understood as the role of TLR2 in osteoclastogenesis has been studied less as compared with TLR4.…”

Using Tn-seq To Identify Pigmentation-Related Genes of Porphyromonas gingivalis: Characterization of the Role of a Putative Glycosyltransferase

“…Four different lipid A moieties and at least two distinct repeating oligosaccharides attached to the core oligosaccharide have been identified (6,7). P. gingivalis LPS can be an agonist or antagonist for Toll-like receptor 2 (TLR2) and TLR4, causes alveolar bone resorption, and is an important target for antimicrobial compounds (8,9). Alterations or loss of LPS structure may lead to changes on the outer surface of the bacterial cell, which in turn may result in loss of heme binding.…”

Importance of heterogeneity in Porhyromonas gingivalis lipopolysaccharide lipid A in tissue specific inflammatory signalling

“…In terms of bone loss, in vitro and in vivo experiments have provided conflicting data. For example, when P. gingivalis is co-cultured with bone cells in vitro , the effect on bone resorbing cells appears to be mediated through engagement of both TLR2 and TLR4 [15,19]. However, similar experiments conducted in experimental animals orally infected with P. gingivalis predominantly show bone loss to be mediated by TLR2 [20–22].…”