Effect of anti-CD14 antibody on experimental periodontitis induced by Porphyromonas gingivalis lipopolysaccharide

Mechanism of alveolar bone destruction in periodontitis - Periodontal bacteria and inflammation

Periodontal disease is an inflammatory disease caused by periodontopathogenic bacteria, which eventually leads to bone tissue (alveolar bone) destruction as inflammation persists. Periodontal tissues have an immune system against the invasion of these bacteria, however, due to the persistent infection by periodontopathogenic bacteria, the host innate and acquired immunity is impaired, and tissue destruction, including bone tissue destruction, occurs. Osteoclasts are essential for bone destruction. Osteoclast progenitor cells derived from hematopoietic stem cells differentiate into osteoclasts. In addition, bone loss occurs when bone resorption by osteoclasts exceeds bone formation by osteoblasts. In inflammatory bone disease, inflammatory cytokines act on osteoblasts and receptor activator of nuclear factor-κB ligand (RANKL)-producing cells, resulting in osteoclast differentiation and activation. In addition to this mechanism, pathogenic factors of periodontal bacteria and mechanical stress activate osteoclasts and destruct alveolar bone in periodontitis. In this review, we focused on the mechanism of osteoclast activation in periodontitis and provide an overview based on the latest findings.

Cytotoxicity and potential anti-inflammatory activity of velutin on RAW 264.7 cell line differentiation: Implications in periodontal bone loss

OBJECTIVES

Hypoxia-inducible factor-1α (HIF-1α) has been implicated in periodontal tissue inflammation and possibly in osteoclast differentiation, while polyphenols are known to be anti-inflammatory natural compounds that are capable of regulating the NF-κB protein complex pathway. The objective of this study was to investigate cytotoxicity and HIF-1α expression through the NF-κB pathway by polyphenol velutin (Euterpe oleracea Mart.), found in the pulp of acai fruit, during inflammatory RAW 264.7 differentiation.

DESIGN

RAW 264.7 mouse monocyte macrophage cells were stimulated with RANKL (30ng/mL) and Porphyromonas gingivalis lipopolysaccharide (1μg/mL). Cells were treated with various concentrations of velutin (0.5-2μM) to check for viability, morphology, osteoclast differentiation, and HIF-1α expression (Western blot).

RESULTS

Alamar blue cell viability assay showed no toxicity to RAW cells with the use of velutin in all concentrations tested (p>0.05). Velutin did not induce cell apoptosis based on caspase 3/7 assay (p>0.05). Fluorescence images stained by DAPI showed no alteration in the morphology of RAW cell nuclei (p>0.05) treated with velutin. TRAP assays demonstrated a dose-dependent reduction in osteoclast formation by velutin when compared with control (p<0.05). Velutin showed a reduction in HIF-1α expression related to IκB phosphorylation when compared with control (p<0.001).

CONCLUSIONS

At the tested concentrations, velutin was not cytotoxic to RAW 264.7 and differentiated cells. Velutin reduced osteoclast differentiation and downregulated HIF-1α through the NF-κB pathway.

Lipopolysaccharide and IL-1β coordinate a synergy on cytokine production by upregulating MyD88 expression in human gingival fibroblasts

Both lipopolysaccharide (LPS) and interleukin (IL)-1β activate the MyD88-dependent signaling pathways to stimulate proinflammatory cytokine expression. However, it remains unknown how LPS and IL-1β interact with each other to coordinate the stimulation. In this study, we sought to investigate the interaction between LPS and IL-1β on MyD88-dependent signaling pathways in human gingival fibroblasts (HGFs). Results showed that LPS derived from Porphyromonas gingivalis (Pg LPS) and IL-1β cooperatively stimulated mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NFκB) signaling pathways, and subsequent expression of proinflammatory cytokine expression. Furthermore, our results showed that Pg LPS and IL-1β exerted a synergy on MyD88 expression and knockdown of MyD88 expression by small interfering RNA diminished the synergistic effect of Pg LPS and IL-1β on IL-6 expression, suggesting that upregulation of MyD88 is involved in the coordinated stimulation by Pg LPS and IL-1β of proinflammatory cytokine expression. Finally, our results showed that pharmacological inhibitors for MAPK and NFκB significantly reduced IL-6 secretion stimulated by Pg LPS and IL-1β, indicating that the MyD88-dependent MAPK and NFκB signaling pathways are essential for the upregulation of proinflammatory cytokine expression by Pg LPS and IL-1β. Taken together, this study showed that LPS and IL-1β coordinate a synergy on cytokine production by upregulating MyD88 expression in HGFs.

Suppressive effect of the antimicrobial peptide LL-37 on expression of IL-6, IL-8 and CXCL10 induced by Porphyromonas gingivalis cells and extracts in human gingival fibroblasts

Porphyromonas gingivalis is a major periodontogenic bacterium and possesses immunostimulatory components, such as lipopolysaccharides (LPS) and fimbriae. The host antimicrobial peptide, LL-37, suppresses proinflammatory responses of immune cells but its effect on human gingival fibroblasts (HGFs) is not known. In this study, we assessed the effect of LL-37 on the proinflammatory responses of HGFs stimulated with P. gingivalis cells and their components. Live P. gingivalis cells did not induce proinflammatory responses of HGFs, and LL-37 did not alter these responses. However, LL-37 was able to suppress the killed P. gingivalis cell-induced secretion of interleukin (IL)-6 and IL-8. LL-37 also suppressed the expression of IL6, IL8, and CXCL10 genes that was induced by P. gingivalis components, including phenol-water extracts, lipid A, and fimbriae, and the induction of phosphorylation of p38 and extracellular signal-regulated kinase (ERK) by P. gingivalis lipopolysaccharide (LPS). CAMP was found to be expressed in oral epithelial cells but not in HGFs, despite stimulation with P. gingivalis components. Therefore, LL-37 can exert a suppressive effect on P. gingivalis-induced proinflammatory responses of HGFs in a paracrine manner, suggesting that excess inflammatory responses to P. gingivalis in the gingival tissue are suppressed by LL-37 in vivo.

Porphyromonas gingivalis lipids inhibit osteoblastic differentiation and function

Porphyromonas gingivalis produces unusual sphingolipids that are known to promote inflammatory reactions in gingival fibroblasts and Toll-like receptor 2 (TLR2)-dependent secretion of interleukin-6 from dendritic cells. The aim of the present study was to examine whether P. gingivalis lipids inhibit osteoblastic function. Total lipids from P. gingivalis and two fractions, phosphoglycerol dihydroceramides and phosphoethanolamine dihydroceramides, were prepared free of lipid A. Primary calvarial osteoblast cultures derived from 5- to 7-day-old CD-1 mice were used to examine the effects of P. gingivalis lipids on mineralized nodule formation, cell viability, apoptosis, cell proliferation, and gene expression. P. gingivalis lipids inhibited osteoblast differentiation and fluorescence expression of pOBCol2.3GFP in a concentration-dependent manner. However, P. gingivalis lipids did not significantly alter osteoblast proliferation, viability, or apoptosis. When administered during specific intervals of osteoblast growth, P. gingivalis total lipids demonstrated inhibitory effects on osteoblast differentiation only after the proliferation stage of culture. Reverse transcription-PCR confirmed the downregulation of osteoblast marker genes, including Runx2, ALP, OC, BSP, OPG, and DMP-1, with concurrent upregulation of RANKL, tumor necrosis factor alpha, and MMP-3 genes. P. gingivalis total lipids and lipid fractions inhibited calvarial osteoblast gene expression and function in vivo, as determined by the loss of expression of another osteoblast differentiation reporter, pOBCol3.6GFPcyan, and reduced uptake of Alizarin complexone stain. Finally, lipid inhibition of mineral nodule formation in vitro was dependent on TLR2 expression. Our results indicate that inhibition of osteoblast function and gene expression by P. gingivalis lipids represents a novel mechanism for altering alveolar bone homeostasis at periodontal disease sites.

Cleavage of protease-activated receptors on an immortalized oral epithelial cell line by Porphyromonas gingivalis gingipains

Porphyromonas gingivalis activates protease-activated receptors (PARs) on oral keratinocytes, resulting in downstream signalling for an innate immune response. Activation depends on P. gingivalis gingipains, but could be confounded by lipopolysaccharide signalling through Toll-like receptors. We therefore hypothesized that P. gingivalis cleaves oral keratinocyte PARs in an Arg- (Rgp) or Lys- (Kgp) gingipain-specific manner to upregulate pro-inflammatory cytokines. Immortalized human oral keratinocytes (TERT-2) were incubated with wild-type P. gingivalis (ATCC 33277) or strains from a panel of isogenic gingipain deletion mutants: Kgp-deficient (KDP 129); Rgp-deficient (KDP 133); or Kgp- and Rgp-deficient (KDP 136). After incubation with P. gingivalis, keratinocytes were probed with specific antibodies against the N-terminus of PAR-1 and PAR-2. Using flow cytometry and immunofluorescence, receptor cleavage was marked by loss of specific antibody binding to the respective PARs. TERT-2 cells constitutively expressed high levels of PAR-1 and PAR-2, and lower levels of PAR-3. P. gingivalis ATCC 33277 cleaved PAR-1 and PAR-2 in a dose-dependent manner, while the receptors were unaffected by the protease-negative double mutant (KDP 136) at all m.o.i. tested. The single Kgp-negative mutant preferentially cleaved PAR-1, whereas the Rgp-negative mutant cleaved PAR-2. Wild-type or Kgp-negative mutant cleavage of PAR-1 upregulated expression of IL-1alpha, IL-1beta, IL-6 and TNF-alpha; the Rgp-negative mutant did not modulate these cytokines. Selective cleavage of PAR-1 on oral epithelial cells by P. gingivalis Rgp therefore upregulates expression of pro-inflammatory cytokines.

Down-regulation of epidermal growth factor receptor-dependent signaling by Porphyromonas gingivalis lipopolysaccharide in life-expanded human gingival fibroblasts

BACKGROUND AND OBJECTIVE

Human gingival fibroblasts exhibit proliferative responses following epidermal growth factor exposure, which are thought to enhance periodontal regeneration in the absence of bacterial products such as lipopolysacharide. However, lipopolysaccharide challenge activates human gingival fibroblasts to release several inflammatory mediators that contribute to the immune response associated with periodontitis and attenuate wound repair. We tested the hypothesis that Porphyromonas gingivalis lipopolysaccharide-activated signaling pathways down-regulate epidermal growth factor receptor-dependent events.

MATERIAL AND METHODS

To study lipopolysaccharide/epidermal growth factor interactions in human gingival fibroblasts, we introduced the catalytic subunit of human telomerase into human gingival fibroblasts, thereby generating a more long-lived cellular model. These cells were characterized and evaluated for lipopolysaccharide/epidermal growth factor responsiveness and regulation of epidermal growth factor-dependent pathways.

RESULTS

Comparison of human telomerase-transduced gingival fibroblasts with human gingival fibroblasts revealed that both cell lines exhibit a spindle-like morphology and express similar levels of epidermal growth factor receptor, CD14 and Toll-like receptors 2 and 4. Importantly, human telomerase-transduced gingival fibroblasts proliferation rates are increased 5-9 fold over human gingival fibroblasts and exhibit a longer life span in culture. In addition, human telomerase-transduced gingival fibroblasts and human gingival fibroblasts exhibit comparable profiles of mitogen-activated protein kinase kinase (extracellular signal-regulated kinase 1/2) activation upon epidermal growth factor or P. gingivalis lipopolysaccharide administration. Interestingly, treatment with P. gingivalis lipopolysaccharide leads to a down-regulation of epidermal growth factor-dependent extracellular signal-regulated kinase 1/2, p38 and cyclic-AMP response element binding protein phosphorylation in both cell types.

CONCLUSION

These studies demonstrate that human telomerase-transduced gingival fibroblasts exhibit an extended life span and recapitulate human gingival fibroblasts biology. Moreover, this system has allowed for the first demonstration of lipopolysaccharide down-regulation of epidermal growth factor activated pathways in human gingival fibroblasts and should facilitate the analysis of signaling events relevant to the pathogenesis and treatment of periodontitis.

Expression of TOLL-like receptors (TLR) by bovine antigen-presenting cells-potential role in pathogen discrimination?

Invading pathogens are controlled by the innate and adaptive arms of the immune system. Adaptive immunity, mediated by B and T lymphocytes, recognises pathogens via high affinity receptors. However, the establishment of a primary adaptive immune response is not rapid enough to eradicate invading microorganisms as it involves cell proliferation, gene activation and protein synthesis. More rapid defence mechanisms are provided by innate immunity, which recognises invading pathogens by germ-line-encoded pattern recognition receptors. Recent evidence shows that this recognition can mainly be attributed to the family of TOLL-like receptors (TLR). Binding of pathogen-associated molecular patterns to TLR induces the production of reactive oxygen and nitrogen intermediates, pro-inflammatory cytokines, and up-regulates expression of co-stimulatory molecules, subsequently initiating the adaptive immunity. In this paper, we will discuss the current knowledge with regards to the TLR, and in particular the bovine family of TLR. In addition, we will show the expression of TLR mRNA in bovine antigen-presenting cell subsets, summarise the discovery and the critical roles of TLR2 in host defence against Mycobacteria, and provide evidence for a mycobacteria species-specific response of bovine macrophages.

Generation of inflammatory stimuli: how bacteria set up inflammatory responses in the gingiva

OBJECTIVES

The primary aetiologic factor of periodontal disease is the bacterial biofilm. Gram-positive and gram-negative bacteria possess a plethora of structural or secreted components that may cause direct destruction to periodontal tissues or stimulate host cells to activate a wide range of inflammatory responses. These responses are intended to eliminate the microbial challenge, but may often cause further tissue damage.

METHODS

This review has been divided into three parts: (a) bacterial virulence factors, which includes basic information on bacterial virulence factors, and the principle inflammatory responses that host cells elicit against these factors, (b) main receptors and signalling pathways, which includes basic information about the main receptors that interact with the bacterial virulence factors, the nature of these interactions, and the activated signalling pathways that lead to inflammatory responses, and (c) initiation of inflammation, which includes a model by which the virulence factors may interact with host cells and lead to inflammatory responses in the gingiva.

FINDINGS AND CONCLUSIONS

Bacterial components/virulence factors may be involved in modulating inflammatory responses and include: lipopolysaccharides (LPS), peptidoglycans, lipotechoic acids, fimbriae, proteases, heat-shock proteins, formyl-methionyl peptides, and toxins. Potential host cell receptors involved in recognizing bacterial components and initiating signalling pathways that lead to inflammatory responses include: Toll-like receptors (TLRs), CD14, nucleotide-binding oligomerization domain proteins (Nod) and G-protein-coupled receptors, including formyl-methionyl peptide receptors and protease-activated receptors. Of the above bacterial and host molecules, evidence from experimental animal studies implicate LPS, fimbriae, proteases, TLRs, and CD14 in periodontal tissue or alveolar bone destruction. However, evidence verifying the involvement of any of the above molecules in periodontal tissue destruction in humans does not exist.

A genetic basis for the “Adonis” phenotype of low adiposity and strong bones

Toll receptors in Drosophila contribute to host defense and establish the body plan. Mammalian homologues of Toll, the Toll-like receptors (TLRs), are thought to function only in host defense. Here, we report that mice harboring mutations in TLR4 or in CD14, a co-receptor for TLR4, have an "ideal" body plan consisting of increased bone mineral content, density, and size as well as decreased body fat. These mutant mice live long lives, have normal activity and fertility, and show no evidence of infection. Unlike many strains of caged wild-type mice, they do not become obese. Although all mice continue to gain body fat, bone content, and overall weight, the difference in bone content and body fat between mutant and wild-type mice increases with age. Thus, defects in TLR4/CD14 complex generate an "Adonis" phenotype, characterized by this ideal body type, and this function could potentially be exploited for the treatment of osteoporosis and obesity.