Different engagement of TLR2 and TLR4 in Porphyromonas gingivalis vs. ligature-induced periodontal bone loss

Abstract

This study was conducted to investigate the roles of different Toll-like receptor (TLR) signaling in Porphyromonas gingivalis (P. gingivalis)-induced and ligature-induced experimental periodontal bone resorption in mice. Wild-type (WT), TLR2 knockout (KO), TLR4KO, and TLR2&4 KO mice with C57/BL6 background were divided into three groups: control, P. gingivalis infection, and ligation. Live P. gingivalis or silk ligatures were placed in the sulcus around maxillary second molars over a 2-week period. Images were captured by digital stereomicroscopy, and the bone resorption area was measured with ImageJ software. The protein expression level of gingival RANKL was measured by ELISA. The gingival mRNA levels of RANKL, IL-1β, TNF-α, and IL-10 were detected by RT-qPCR. The results showed that P. gingivalis induced significant periodontal bone resorption in WT mice and TLR2 KO mice but not in TLR4 KO mice or TLR2&4 KO mice. For all four types of mice, ligation induced signifcant bone loss compared with that in control groups, and this bone loss was signifcantly higher than that in the P. gingivalis infection group. RANKL protein expression was signifcantly increased in the ligation group compared with that in the control group for all four types of mice, and in the P. gingivalis infection group of WT, TLR2 KO, and TLR4 KO mice. Expression patterns of RANKL, IL-1β, TNF-α, and IL-10 mRNA were different in the P. gingivalis infection group and the ligation group in different types of mice. In summary, P. gingivalis-induced periodontal bone resorption is TLR4-dependent, whereas ligation-induced periodontal bone resorption is neither TLR2- nor TLR4-dependent.

TLR4 mediates alveolar bone resorption in experimental peri‐implantitis through regulation of CD45+ cell infiltration, RANKL/OPG ratio, and inflammatory cytokine production

“…5B) observed in WT mice were diminished in TLR4 KO mice. The differences in pathogenesis and disease progression between peri‐implantitis and periodontitis may be a reason why the RANKL/OPG ratio was significantly changed between the control group and the P. gingivalis‐ Lig group in the TLR4 KO mice in experimental periodontitis but not in experimental peri‐implantitis (Fig. 3E).…”

“…Our previously studies indicated that TLR4 could recognize the surface components of P. gingivalis and promote the proinflammatory cytokine responses and osteoclastogenesis in P. gingivalis associated ligature induced periodontitis . Moreover, P. gingivalis ‐induced periodontal bone resorption is TLR4‐dependent . The purpose of this study is to determine the role of TLR4 signaling in peri‐implantitis inflammation and bone loss and its associated cellular and molecular mechanism, using a mouse model of P. gingivalis ‐associated ligature induced experimental peri‐implantitis.…”

RANKL blockade alleviates peri-implant bone loss and is enhanced by anti-inflammatory microRNA-146a through TLR2/4 signaling

“…TRAP-positive cells (red color) with 3 or more nuclei were considered osteoclasts and were shown in the control group, ligation group, ligation with anti-RANKL antibody treatment group, and ligation with anti-RANKL antibody + miR-146a treatment group in WT mice and TLR2/4 KO mice (a) (Im, implant; Av, alveolar bone; scale bar, 100 μm). The quantities of TRAP-positive cells were analyzed in each group of WT mice (b) and TLR2/4 KO mice (c) (mean ± SD, n = 6, **p < 0.01) are essential signaling proteins in progression of inflammation and related bone metabolism in periodontitis [28,29,39,40]. However, little is known about the functions of TLR2 and TLR4 signaling in peri-implantitis.…”

“…Toll-like receptors (TLR) are a family of wellcharacterized pattern recognition receptors (PRRs) and play an important role in the induction of pro-inflammatory cytokines by recognizing the signature molecules of the host innate immunity [25][26][27]. Our previous studies showed that TLR2 are associated with implant bone loss in a mouse model of peri-implantitis [5] and TLR4 is essential for periodontal bone loss [28,29]. In our previous study, we examined the changes of inflammatory cytokines and bone metabolism cytokines in either TLR2 only KO mice or TLR4 only KO mice [5,29].…”

“…Our previous studies showed that TLR2 are associated with implant bone loss in a mouse model of peri-implantitis [5] and TLR4 is essential for periodontal bone loss [28,29]. In our previous study, we examined the changes of inflammatory cytokines and bone metabolism cytokines in either TLR2 only KO mice or TLR4 only KO mice [5,29]. However, since anti-RANKL antibody and miR-146a may interact with both TLR2 and TLR4 pathways, TLR2 and TLR4 double knockout (TLR2/ 4 KO) mice were specially employed in the present study to determine whether the effects of local anti-RANKL antibody administration in the presence or absence of miR-146a on ligature-induced peri-implant bone loss are dependent on both TLR2 and TLR4.…”