Epithelial cell pro-inflammatory cytokine response differs across dental plaque bacterial species

Functional biomarkers for chronic periodontitis and insights into the roles of Prevotella nigrescens and Fusobacterium nucleatum; a metatranscriptome analysis

BACKGROUND/OBJECTIVES

Periodontitis is the most prevalent inflammatory disease worldwide and is caused by a dysbiotic subgingival biofilm. Here we used metatranscriptomics to determine the functional shift from health to periodontitis, the response of individual species to dysbiosis and to discover biomarkers.

METHODS

Sixteen individuals were studied, from which six were diagnosed with chronic periodontitis. Illumina sequencing of the total messenger RNA (mRNA) yielded ~42 million reads per sample. A total of 324 human oral taxon phylotypes and 366,055 open reading frames from the HOMD database reference genomes were detected.

RESULTS

The transcriptionally active community shifted from Bacilli and Actinobacteria in health to Bacteroidia, Deltaproteobacteria, Spirochaetes and Synergistetes in periodontitis. Clusters of orthologous groups (COGs) related to carbohydrate transport and catabolism dominated in health, whereas protein degradation and amino acid catabolism dominated in disease. The LEfSe, random forest and support vector machine methods were applied to the 2,000 most highly expressed genes and discovered the three best functional biomarkers, namely haem binding protein HmuY from Porphyromonas gingivalis, flagellar filament core protein FlaB3 from Treponema denticola, and repeat protein of unknown function from Filifactor alocis. They predicted the diagnosis correctly for 14 from 16 individuals, and when applied to an independent study misclassified one out of six subjects only. Prevotella nigrescens shifted from commensalism to virulence by upregulating the expression of metalloproteases and the haem transporter. Expression of genes for the synthesis of the cytotoxic short-chain fatty acid butyrate was observed by Fusobacterium nucleatum under all conditions. Four additional species contributed to butyrate synthesis in periodontitis and they used an additional pathway.

CONCLUSION

Gene biomarkers of periodontitis are highly predictive. The pro-inflammatory role of F. nucelatum is not related to butyrate synthesis.

Chemokine function in periodontal disease and oral cavity cancer

The chemotactic cytokines, or chemokines, comprise a superfamily of polypeptides with a wide range of activities that include recruitment of immune cells to sites of infection and inflammation, as well as stimulation of cell proliferation. As such, they function as antimicrobial molecules and play a central role in host defenses against pathogen challenge. However, their ability to recruit leukocytes and potentiate or prolong the inflammatory response may have profound implications for the progression of oral diseases such as chronic periodontitis, where tissue destruction may be widespread. Moreover, it is increasingly recognized that chronic inflammation is a key component of tumor progression. Interaction between cancer cells and their microenvironment is mediated in large part by secreted factors such as chemokines, and serves to enhance the malignant phenotype in oral and other cancers. In this article, we will outline the biological and biochemical mechanisms of chemokine action in host–microbiome interactions in periodontal disease and in oral cancer, and how these may overlap and contribute to pathogenesis.

TLR2 promoter hypermethylation creates innate immune dysbiosis

Periodontitis is a common chronic inflammatory disease that is initiated by a complex microbial biofilm that poses significant health and financial burdens globally. Porphyromonas gingivalis is a predominant pathogen that maintains chronic inflammatory periodontitis. Toll-like receptors (TLRs) play an important role in periodontitis by recognizing pathogens and maintaining tissue homeostasis. Deficiencies in TLR expression and downstream signaling may reduce the host's innate defenses against pathogens, leading to bacterial persistence and exacerbated inflammation, which are now being better appreciated in disease pathologies. In the case of periodontitis, gingival epithelial cells form the first line of defense against pathogens. Innate immune dysregulation in these cells relates to severe disease pathology. We recently identified a blunted TLR2 expression in certain gingival epithelial cells expressing diminished cytokine signaling upon P. gingivalis stimulation. Upon detailed analysis of the TLR2 promoter CpG Island, we noted higher CpG methylation in this dysregulated cell type. When these cells were treated with DNA methyltransferase inhibitor, TLR2 mRNA and cytokine expression were significantly increased. If TLR2 expression plasmid was ectopically expressed in dysfunctional cells prior to P. gingivalis stimulation, the cytokine expression was increased, confirming the requirement of TLR2 in the P. gingivalis-mediated inflammatory response. We designed a chronic in vitro infection model to test if P. gingivalis can induce DNA methylation in normal gingival epithelial cells that express higher TLR2 upon agonist stimulation. Chronic treatment of normal epithelial cells with P. gingivalis introduced de novo DNA methylation within the cells. In addition, increased DNA methylation was observed in the gingiva of mice infected with P. gingivalis in a periodontitis oral gavage model. Moreover, tissues obtained from periodontitis patients also exhibited differential TLR2 promoter methylation, as revealed by bisulfite DNA sequencing. Taken together, DNA methylation of TLR2 can modulate host innate defense mechanisms that may confer increased disease susceptibility.

Interactions of anaerobic bacteria with dental stem cells: an in vitro study

BACKGROUND

In patients with periodontitis, it is highly likely that local (progenitor) cells encounter pathogenic bacteria. The purpose of this in vitro study was to elucidate how human dental follicle stem cells (hDFSC) react towards a direct challenge with anaerobic periodontal pathogens under their natural oxygen-free atmosphere. HDFSC were compared to human bone marrow mesenchymal stem cells (hBMSC) and differentiated primary human gingival fibroblasts (hGiF), as well as permanent gingival carcinoma cells (Ca9-22).

METHODOLOGY/PRINCIPAL FINDINGS

The different cell types were investigated in a co-culture system with Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum). The viability of the cells and pathogens under anaerobic conditions, as well as interactions in terms of adherence and internalization, were examined. Additionally, the release of pro-inflammatory interleukin-8 (IL-8) and anti-inflammatory interleukin-10 (IL-10) was quantified via enzyme-linked immunosorbent assay. The bacteria adhered less efficiently to hDFSC compared to Ca9-22 (P. gingivalis: 0.18% adherence to hDFSC; 3.1% adherence to Ca9-22). Similar results were observed for host cell internalization (F. nucleatum: 0.002% internalization into hDFSC; 0.09% internalization into Ca9-22). Statistically significantly less IL-8 was secreted from hDFSC after stimulation with F. nucleatum and P. gingivalis in comparison with hGiF (F. nucleatum: 2080.0 pg/ml--hGiF; 19.7 pg/ml--hDFSC). The IL-10 response of the differentiated cells was found to be low in relation to their pro-inflammatory IL-8 response.

CONCLUSIONS/SIGNIFICANCE

The results indicate that dental stem cells are less prone to interactions with pathogenic bacteria than differentiated cells in an anaerobic environment. Moreover, during bacterial challenge, the stem cell immune response seems to be more towards an anti-inflammatory reaction. For a potential future therapeutic use of hDFSC, these findings support the idea of a save application.

Porphyromonas gingivalis stimulates IL-6 and IL-8 secretion in GMSM-K, HSC-3 and H413 oral epithelial cells

Infection of oral epithelial cells with periodontopathogenic bacteria results in the production of pro-inflammatory cytokines involved in the initiation and progression of periodontal disease. The purpose of this study was to examine the release of interleukin (IL)-6 and IL-8 by oral epithelial cells after exposure to Porphyromonas gingivalis. Non-tumor-derived, immortalized human GMSM-K cells, and human oral squamous cell carcinoma, HSC-3 and H413 cells, were co-cultured with live and heat-inactivated P. gingivalis 2561 (ATCC 33277) and W83 (ATCC BAA-308™). IL-6 and IL-8 were quantified in the culture supernatants after 6 and 24 h. The basal levels of both cytokines and the responses to P. gingivalis were strongly dependent on cell type. GMSM-K cells produced less IL-8 than HSC-3 and H413 cells. Live P. gingivalis induced significant IL-6 and IL-8 secretion in GMSM-K and HSC-3 cells, and heat-inactivation of bacteria enhanced greatly IL-6 and IL-8 stimulation in these cells. Uninfected H413 cells produced high levels of IL-6 and IL-8, but were not responsive to live P. gingivalis; heat-inactivated P. gingivalis up-regulated IL-6 and IL-8 secretion in these cells. Since base-line secretion of IL-6 and IL-8, and responses to P. gingivalis depend on the cell type, conclusions on the responses to P. gingivalis should not be based on studies with a single cell type.

Anti-inflammatory and protective effects of 2-methacryloyloxyethyl phosphorylcholine polymer on oral epithelial cells

Periodontitis is a chronic inflammatory disease initiated by a microbial biofilm formed in the periodontal pocket. Gingival epithelium plays important roles as the first physical barrier to bacterial invasion and in orchestrating the innate immune reaction via toll-like receptors (TLRs), which recognize various bacterial products, and maintaining its function. Newly developed oral care products to inhibit bacterial adherence, subsequent inflammatory reaction and protect the gingival epithelium are expected. We previously reported that 2-methacryloyloxyethyl phosphorylcholine (MPC)-polymer coating decreased bacterial adhesion to human oral keratinocytes, RT-7, and mouth-rinsing with MPC-polymer inhibited the increase of oral bacteria. In this study, regarding the possibility of MPC-polymer application for preventing the adherence of periodontal pathogen, subsequent inflammatory reaction and protection of gingival epithelium, we examined the effects of MPC-polymer on the adherence of Porphyromonas gingivalis, major periodontitis-related pathogen, and TLR2 ligand to RT-7 and subsequent interleukin (IL)-8 production. MPC-polymer treatment significantly reduced P. gingivalis adherence by 44% and TLR2-mediated IL-8 production by blocking the binding of its specific-ligand in a concentration-dependent manner. Furthermore, MPC-polymer pretreatment protected RT-7 from injury by chemical irritants, cetylpyridinium chloride. These findings suggest that MPC-polymer is potentially useful for oral care to prevent oral infection and to maintain oral epithelial function.

Breaking bad: manipulation of the host response by Porphyromonas gingivalis

Recent metagenomic and mechanistic studies are consistent with a new model of periodontal pathogenesis. This model proposes that periodontal disease is initiated by a synergistic and dysbiotic microbial community rather than by a select few bacteria traditionally known as "periopathogens." Low-abundance bacteria with community-wide effects that are critical for the development of dysbiosis are now known as keystone pathogens, the best-documented example of which is Porphyromonas gingivalis. Here, we review established mechanisms by which P. gingivalis interferes with host immunity and enables the emergence of dysbiotic communities. We integrate the role of P. gingivalis with that of other bacteria acting upstream and downstream in pathogenesis. Accessory pathogens act upstream to facilitate P. gingivalis colonization and co-ordinate metabolic activities, whereas commensals-turned pathobionts act downstream and contribute to destructive inflammation. The recent concepts of keystone pathogens, along with polymicrobial synergy and dysbiosis, have profound implications for the development of therapeutic options for periodontal disease.

Inflammatory bone loss in experimental periodontitis induced by Aggregatibacter actinomycetemcomitans in interleukin-1 receptor antagonist knockout mice

The interleukin-1 receptor antagonist (IL-1Ra) binds to IL-1 receptors and inhibits IL-1 activity. However, it is not clear whether IL-1Ra plays a protective role in periodontal disease. This study was undertaken to compare experimental periodontitis induced by Aggregatibacter actinomycetemcomitans in IL-1Ra knockout (KO) mice and wild-type (WT) mice. Computed tomography (CT) analysis and hematoxylin-and-eosin (H&E) and tartrate-resistant acid phosphatase (TRAP) staining were performed. In addition, osteoblasts were isolated; the mRNA expression of relevant genes was assessed by real-time quantitative PCR (qPCR); and calcification was detected by Alizarin Red staining. Infected IL-1Ra KO mice exhibited elevated (P, <0.05) levels of antibody against A. actinomycetemcomitans, bone loss in furcation areas, and alveolar fenestrations. Moreover, protein for tumor necrosis factor alpha (TNF-α) and IL-6, mRNA for macrophage colony-stimulating factor (M-CSF), and receptor activator of NF-κB ligand (RANKL) in IL-1Ra KO mouse osteoblasts stimulated with A. actinomycetemcomitans were increased (P, <0.05) compared to in WT mice. Alkaline phosphatase (ALP), bone sialoprotein (BSP), osteocalcin (OCN)/bone gla protein (BGP), and runt-related gene 2 (Runx2) mRNA levels were decreased (P, <0.05). IL-1α mRNA expression was increased, and calcification was not observed, in IL-1 Ra KO mouse osteoblasts. In brief, IL-1Ra deficiency promoted the expression of inflammatory cytokines beyond IL-1 and altered the expression of genes involved in bone resorption in A. actinomycetemcomitans-infected osteoblasts. Alterations consistent with rapid bone loss in infected IL-Ra KO mice were also observed for genes expressed in bone formation and calcification. In short, these data suggest that IL-1Ra may serve as a potential therapeutic drug for periodontal disease.

Anaerobic co-culture of mesenchymal stem cells and anaerobic pathogens - a new in vitro model system

Background

Human mesenchymal stem cells (hMSCs) are multipotent by nature and are originally isolated from bone marrow. In light of a future application of hMSCs in the oral cavity, a body compartment with varying oxygen partial pressures and an omnipresence of different bacterial species i.e. periodontitis pathogens, we performed this study to gain information about the behavior of hMSC in an anaerobic system and the response in interaction with oral bacterial pathogens.

Methodology/Principal Findings

We established a model system with oral pathogenic bacterial species and eukaryotic cells cultured in anaerobic conditions. The facultative anaerobe bacteria Fusobacterium nucleatum, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans were studied. Their effects on hMSCs and primary as well as permanent gingival epithelial cells (Ca9-22, HGPEC) were comparatively analyzed. We show that hMSCs cope with anoxic conditions, since 40% vital cells remain after 72 h of anaerobic culture. The Ca9-22 and HGPEC cells are significantly more sensitive to lack of oxygen. All bacterial species reveal a comparatively low adherence to and internalization into hMSCs (0.2% and 0.01% of the initial inoculum, respectively). In comparison, the Ca9-22 and HGPEC cells present better targets for bacterial adherence and internalization. The production of the pro-inflammatory chemokine IL-8 is higher in both gingival epithelial cell lines compared to hMSCs and Fusobacterium nucleatum induce a time-dependent cytokine secretion in both cell lines. Porphyromonas gingivalis is less effective in stimulating secretion of IL-8 in the co-cultivation experiments.

Conclusions/significance

HMSCs are suitable for use in anoxic regions of the oral cavity. The interaction with local pathogenic bacteria does not result in massive pro-inflammatory cytokine responses. The test system established in this study allowed further investigation of parameters prior to set up of oral hMSC in vivo studies.

Environmental stimuli shape biofilm formation and the virulence of periodontal pathogens

Periodontitis is a common inflammatory disease affecting the tooth-supporting structures. It is initiated by bacteria growing as a biofilm at the gingival margin, and communication of the biofilms differs in health and disease. The bacterial composition of periodontitis-associated biofilms has been well documented and is under continual investigation. However, the roles of several host response and inflammation driven environmental stimuli on biofilm formation is not well understood. This review article addresses the effects of environmental factors such as pH, temperature, cytokines, hormones, and oxidative stress on periodontal biofilm formation and bacterial virulence.

The serine phosphatase SerB of Porphyromonas gingivalis suppresses IL-8 production by dephosphorylation of NF-κB RelA/p65

Porphyromonas gingivalis is a major pathogen in severe and chronic manifestations of periodontal disease, which is one of the most common infections of humans. A central feature of P. gingivalis pathogenicity is dysregulation of innate immunity at the gingival epithelial interface, including suppression of IL-8 production by epithelial cells. NF-κB is a transcriptional regulator that controls important aspects of innate immune responses, and NF-κB RelA/p65 homodimers regulate transcription of IL8. Phosphorylation of the NF-κB p65 subunit protein on the serine 536 residue affects nuclear translocation and transcription of target genes. Here we show that SerB, a haloacid dehalogenase (HAD) family serine phosphatase secreted by P. gingivalis, is produced intracellularly and can specifically dephosphorylate S536 of p65 in gingival epithelial cells. A P. gingivalis mutant lacking SerB was impaired in dephosphorylation of p65 S536, and ectopically expressed SerB bound to p65 and co-localized with p65 in the cytoplasm. Ectopic expression of SerB also resulted in dephosphorylation of p65 with reduced nuclear translocation in TNF-α-stimulated epithelial cells. In contrast, the p105/50 subunit of NF-κB was unaffected by SerB. Co-expression of a constitutively active p65 mutant (S536D) relieved inhibition of nuclear translocation. Both the activity of the IL8 promoter and production of IL-8 were diminished by SerB. Deletion and truncation mutants of SerB lacking the HAD-family enzyme motifs of SerB were unable to dephosphorylate p65, inhibit nuclear translocation or abrogate IL8 transcription. Specific dephosphorylation of NF-κB p65 S536 by SerB, and consequent inhibition of nuclear translocation, provides the molecular basis for a bacterial strategy to manipulate host inflammatory pathways and repress innate immunity at mucosal surfaces.

Periodontal diseases are one of the most common infections of humans, and are characterized by gingival inflammation and destruction of the hard and soft tissues that support the tooth, eventually causing tooth loss. Porphyromonas gingivalis is a major pathogen in periodontal diseases and a key pathogenic attribute of this organism is the ability to disrupt host innate immunity. Infection of gingival epithelial cells by P. gingivalis suppresses production of the neutrophil chemokine IL-8. This inhibitory process is associated with the P. gingivalis serine phosphatase, SerB. In this study we show that SerB has a potent and specific ability to inhibit activation the NF-κB transcription factor which regulates IL-8 production. Mechanistically, SerB binds to and dephosphorylates the p65 subunit of NF-κB which prevents nuclear translocation and subsequent transcription of the IL8 gene. Targeting the NF-κB p65 subunit allows P. gingivalis to dampen IL-8 dependent inflammatory responses, facilitate survival and potentially to establish a favorable niche for the entire periodontal microbial community.

Effect of Porphyromonas gingivalis and Lactobacillus acidophilus on secretion of IL1B, IL6, and IL8 by gingival epithelial cells

Porphyromonas gingivalis alters cytokine expression in gingival epithelial cells, stimulating inflammatory responses that may lead to periodontal disease. This study explored the effect of Lactobacillus acidophilus on the specific expressions of the interleukins (ILs) IL1B, IL6, and IL8 induced by the pathogen. Human gingival epithelial cells were co-cultured with P. gingivalis, L. acidophilus, or L. acidophilus + P. gingivalis; the control group consisted of the cells alone. Protein and gene expression levels of the ILs were detected using ELISA and qRT-PCR, respectively. The supernatant from the P. gingivalis group held significantly higher protein and mRNA levels of IL1B, IL6, and IL8, compared to the control group. In the mixed bacterial group (L. acidophilus + P. gingivalis), the levels of all three ILs decreased with increasing concentrations of L. acidophilus and were significantly different from the P. gingivalis group. This suggests that in gingival cells, L. acidophilus offsets the P. gingivalis-induced secretion of these ILs in a dose-dependent manner.

Oral epithelial cell responses to multispecies microbial biofilms

This report describes the use of a novel model of multispecies biofilms to stimulate profiles of cytokines/chemokines from oral epithelial cells that contribute to local inflammation in the periodontium. Streptococcus gordonii (Sg)/S. oralis (So)/S. sanguinis (Ss) and Sg/Fusobacterium nucleatum (Fn)/Porphyromonas gingivalis (Pg) biofilms elicited significantly elevated levels of IL-1α and showed synergistic stimulatory activity compared with an additive effect of the 3 individual bacteria. Only the Sg/Actinomyces naeslundii (An)/Fn multispecies biofilms elicited IL-6 levels above those of control. IL-8 was a primary response to the Sg/An/Fn biofilms, albeit the level was not enhanced compared with a predicted composite level from the monospecies challenges. These results represent some of the first data documenting alterations in profiles of oral epithelial cell responses to multispecies biofilms.

Virulence mechanism of bacteria in mixed infection: attenuation of cytokine levels and evasion of polymorphonuclear leukocyte phagocytosis

BACKGROUND

The objective of the present study is to evaluate the effect of bacterial viability on the virulence of mixed infection.

METHODS

Expression of pro- and anti-inflammatory cytokines (interleukin [IL]-1β and IL-10, respectively) was tested in vivo, following live versus heat-killed infection (mono or mixed), using the mouse chamber model of infection. Ex vivo, phagocytosis of fluorescently labeled bacteria was tested in primary mouse polymorphonuclear leukocytes by flow cytometry.

RESULTS

In monoinfection, heat-killed Porphyromonas gingivalis led to augmented levels of IL-1β 2 hours postinfection, whereas IL-10 levels remained unaffected. Phagocytosis of heat-killed P. gingivalis was reduced compared with that of the live P. gingivalis, whereas phagocytosis of heat-killed Fusobacterium nucleatum was augmented compared with that of live F. nucleatum. In mixed infection, both IL-1β and IL-10 levels were augmented 24 hours postinfection when the bacteria were heat-killed. Although the phagocytosis pattern of F. nucleatum in the mixed infection remained similar to that upon monoinfection, phagocytosis of P. gingivalis was reduced following mixed infection.

CONCLUSIONS

The inflammatory response to live mixed infection is attenuated with reduced phagocytosis, compared with that of heat-killed mixed infection. The lower response to live mixed infection could stem from a mechanism enabling the bacteria to evade the host response, thereby increasing bacterial survival.

Porphyromonas gingivalis promotes Th17 inducing pathways in chronic periodontitis

In periodontitis, a common chronic inflammatory condition, gram-negative-rich bacterial biofilms trigger, in susceptible individuals, perpetuating inflammation that results in extensive tissue damage of tooth supporting structures. To delineate immune cell-dependent mechanisms whereby bacterial challenge drives persistent destructive inflammation in periodontitis and other inflammatory diseases, we studied involved tissues ex vivo and investigated host cell responses to the periodontal pathogen Porphyromonas gingivalis, in vitro. Diseased lesions were populated by abundant Th17 cells, linked to infection, chronic inflammation/autoimmunity and tissue pathology. In vitro, P. gingivalis, particularly the more virulent strain W83, stimulated myeloid antigen presenting cells (APC) to drive Th17 polarization. Supernatants from myeloid APC exposed to P. gingivalis were capable of enhancing Th17 but not Th1 polarization. P. gingivalis favored the generation of Th17 responses by stimulating the production of Th17 related cytokines IL-1β, IL-6 and IL-23, but not Th1 related IL-12. By inducing NFκB activation, P. gingivalis promoted IL-1β, IL-6 and IL-12p40 production, but not IRF3 phosphorylation, connected to generation of the IL-12p35 chain, ultimately restricting formation of the intact IL-12 molecule. Promotion of Th17 lineage responses was also aided by P. gingivalis proteases, which appeared to differentially degrade pivotal cytokines. In this regard, IL-12 was largely degraded by P. gingivalis, whereas IL-1β was more resistant to proteolysis. Our data unveil multiple pathways by which P. gingivalis may orchestrate chronic inflammation, providing insights into interventional strategies.

Interleukin-1β is internalised by viable Aggregatibacter actinomycetemcomitans biofilm and locates to the outer edges of nucleoids

The opportunistic pathogen Aggregatibacter actinomycetemcomitans causes periodontitis, which is a biofilm infection that destroys tooth-supportive tissues. Interleukin (IL)-1β, a central proinflammatory cytokine of periodontitis, is an essential first line cytokine for local inflammation that modulates the cell proliferation and anti-pathogen response of human gingival keratinocytes. Previously, we demonstrated that A. actinomycetemcomitans biofilms bind IL-1β; however, whether this binding is an active process is not known. In this study, we showed for the first time with immuno-electron microscopy that viable bacterial biofilm cells internalised IL-1β when co-cultured with an organotypic mucosa. Decreased biofilm viability hindered the ability of biofilm to sequester IL-1β and caused IL-1β leakage into the culture medium. In some A. actinomycetemcomitans cells, intracellular IL-1β localized to the outer edges of the nucleoids. We identified the DNA-binding protein HU as an IL-1β interacting protein with mass spectroscopy and showed the interaction of recombinant HU and IL-1βin vitro using enzyme-linked immunosorbent assay (ELISA). Close contact with a viable A. actinomycetemcomitans biofilm decreased the proliferation and apoptosis of human gingival keratinocytes as demonstrated using Ki-67 and the terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) staining, respectively. Our results suggest that viable A. actinomycetemcomitans biofilms may disturb the critical first steps of local inflammation in periodontitis by binding and internalising IL-1β. The interaction of IL-1β with conserved HU provides a potential mechanism for shaping bacterial gene expression.

Role of the junctional epithelium in periodontal innate defense and homeostasis

BACKGROUND AND OBJECTIVE

  The junctional epithelium provides the front-line defense against periodontal bacterial infection. The migration of neutrophils into the junctional epithelium might represent a protective reaction against bacterial infections. However, neutrophils penetrate into the junctional epithelium even under sterile conditions. In this study, we analyzed and compared the number of neutrophils and the cytokine expression related to neutrophil migration in the junctional epithelium in conventional and germ-free mice.

MATERIAL AND METHODS

  Germ-free and conventional ICR mice were used at 12 wk of age. Frozen sections were used for the detection of Gr-1, macrophage inflammatory protein-2 (MIP-2/CXCL2) and proliferating cell nuclear antigen-positive cells in the two groups of mice. Laser capture microdissection and RT-PCR analysis were used to evaluate the expression of keratinocyte-derived chemokine (KC/CXCL1), MIP-2, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) mRNAs in the two groups of mice.

RESULTS

  Morphometric examination indicated an increase in the area of the junctional epithelium upon bacterial infection. Immunohistochemical studies also detected an increased number of neutrophils in the junctional epithelium upon bacterial infection. Higher up-regulation of KC and MIP-2 were detected in the junctional epithelium of conventional mice than in germ-free mice, whereas the expression of Il-1β and Tnfα mRNAs was not affected.

CONCLUSION

  Junctional epithelium cells constitutively expressed several types of chemokines and cytokines and the expression of chemokines was augmented by bacterial infection. Therefore, the constitutive expression of cytokines in junctional epithelium might be related to the morphological and functional homeostasis of the junctional epithelium in addition to the defense against the bacterial infection.

Detection of Fusobacterium nucleatum in chorionic tissues of high-risk pregnant women

AIM

This study was undertaken to investigate the existence of a periodontopathic bacterium, Fusobacterium nucleatum, in chorionic tissues of pregnant women, and the effects of F. nucleatum on human chorion-derived cells.

MATERIALS AND METHODS

Oral and chorionic tissue samples were collected from 24 high-risk pregnant women and 15 normal pregnant women. The presence of F. nucleatum in the samples was detected using polymerase chain reaction. Chorion-derived cells and Toll-like receptor (TLR)-2 or TLR-4 gene-silenced chorion-derived cells were stimulated with F. nucleatum lipopolysaccharide (LPS). Interleukin (IL)-6 and corticotrophin-releasing hormone (CRH) levels in the culture supernatants were measured using ELISA.

RESULTS

F. nucleatum was detected in all oral samples and seven chorionic tissues from the high-risk pregnant women, but was not detected in chorionic tissues from the normal pregnant women. F. nucleatum LPS significantly increased IL-6 and CRH secretion by chorion-derived cells. The F. nucleatum LPS-induced IL-6 and CRH levels were significantly reduced in TLR-2 or TLR-4 gene-silenced chorion-derived cells.

CONCLUSIONS

We suggest that F. nucleatum is detected in chorionic tissues of high-risk pregnant women, but not in chorionic tissues of normal pregnant women, and that F. nucleatum induces IL-6 and CRH production via both TLR-2 and TLR-4 in chorion-derived cells.

Oral microbial biofilm stimulation of epithelial cell responses

Oral bacterial biofilms trigger chronic inflammatory responses in the host that can result in the tissue destructive events of periodontitis. However, the characteristics of the capacity of specific host cell types to respond to these biofilms remain ill-defined. This report describes the use of a novel model of bacterial biofilms to stimulate oral epithelial cells and profile select cytokines and chemokines that contribute to the local inflammatory environment in the periodontium. Monoinfection biofilms were developed with Streptococcus sanguinis, Streptococcus oralis, Streptococcus gordonii, Actinomyces naeslundii, Fusobacterium nucleatum, and Porphyromonas gingivalis on rigid gas-permeable contact lenses. Biofilms, as well as planktonic cultures of these same bacterial species, were incubated under anaerobic conditions with a human oral epithelial cell line, OKF4, for up to 24h. Gro-1α, IL1α, IL-6, IL-8, TGFα, Fractalkine, MIP-1α, and IP-10 were shown to be produced in response to a range of the planktonic or biofilm forms of these species. P. gingivalis biofilms significantly inhibited the production of all of these cytokines and chemokines, except MIP-1α. Generally, the biofilms of all species inhibited Gro-1α, TGFα, and Fractalkine production, while F. nucleatum biofilms stimulated significant increases in IL-1α, IL-6, IL-8, and IP-10. A. naeslundii biofilms induced elevated levels of IL-6, IL-8 and IP-10. The oral streptococcal species in biofilms or planktonic forms were poor stimulants for any of these mediators from the epithelial cells. The results of these studies demonstrate that oral bacteria in biofilms elicit a substantially different profile of responses compared to planktonic bacteria of the same species. Moreover, certain oral species are highly stimulatory when in biofilms and interact with host cell receptors to trigger pathways of responses that appear quite divergent from individual bacteria.

Signaling transduction analysis in gingival epithelial cells after infection with Aggregatibacter actinomycetemcomitans

Periodontal diseases result from the interaction of bacterial pathogens with the host's gingival tissue. Gingival epithelial cells are constantly challenged by microbial cells and respond by altering their transcription profiles, inducing the production of inflammatory mediators. Different transcription profiles are induced by oral bacteria and little is known about how the gingival epithelium responds after interaction with the periodontopathogenic organism Aggregatibacter actinomycetemcomitans. In the present study, we examined the transcription of genes involved in signaling transduction pathways in gingival epithelial cells exposed to viable A. actinomycetemcomitans. Immortalized gingival epithelial cells (OBA-9) were infected with A. actinomycetemcomitans JP2 for 24 h and the transcription profile of genes encoding human signal transduction pathways was determined. Functional analysis of inflammatory mediators positively transcribed was performed by ELISA in culture supernatant and in gingival tissues. Fifteen of 84 genes on the array were over-expressed (P < 0.01) after 24 h of infection with viable A. actinomycetemcomitans. Over-expressed genes included those implicated in tissue remodeling and bone resorption, such as CSF2, genes encoding components of the LDL pathway, nuclear factor-κB-dependent genes and other cytokines. The ELISA data confirmed that granulocyte-macrophage colony-stimulating factor/colony-stimulating factor 2, tumor necrosis factor-α and intercellular adhesion molecule-1 were highly expressed by infected gingival cells when compared with control non-infected cells, and presented higher concentrations in tissues from patients with aggressive and chronic periodontitis than in tissues from healthy controls. The induction in epithelial cells of factors such as the pro-inflammatory cytokine CSF2, which is involved in osteoclastogenesis, may help to explain the outcomes of A. actinomycetemcomitans infection.

Filifactor alocis interactions with gingival epithelial cells

An association between the gram-positive anaerobe Filifactor alocis and periodontal disease has recently emerged; however, possible pathogenic mechanisms have not been investigated. In this study we examined the responses of primary cultures of gingival epithelial cells (GECs) to infection with F. alocis. Secretion of the pro-inflammatory cytokines interleukin-1β, interleukin-6 and tumor necrosis factor-α from GECs was stimulated by F. alocis infection. F. alocis also induced apoptosis in GECs through pathways that involved caspase-3 but not caspase-9. Apoptosis was coincident with inhibition of mitogen-activated protein kinase kinase (MEK) activation. These results show that F. alocis has characteristics in common with established periodontal pathogens and has the potential to contribute to periodontal tissue destruction.

Fusobacterium nucleatum: an emerging gut pathogen?

The Gram-negative, non-sporulating, obligately anaerobic species, Fusobacterium nucleatum, is rapidly gaining notoriety as a pathogen with a surprising number of associated diseases. Recently, we have found that F. nucleatum is a more common resident of the GI tract than originally thought, and thus, through several studies, we have attempted to determine its gut-relevant potential for virulence. We have found that F. nucleatum possesses a number of pathogenic traits with relevance to gut diseases such as inflammatory bowel disease (IBD), however, we have also documented strain-associated differences in virulence. An intriguing picture emerges that paints F. nucleatum as both conferring beneficial as well as detrimental effects on host cells; and we suggest that the ultimate effects of F. nucleatum infection in the gut are a consequence of the microbes with which this species aggregates.

Staphylococcus aureus Biofilm and Planktonic cultures differentially impact gene expression, mapk phosphorylation, and cytokine production in human keratinocytes

Background

Many chronic diseases, such as non-healing wounds are characterized by prolonged inflammation and respond poorly to conventional treatment. Bacterial biofilms are a major impediment to wound healing. Persistent infection of the skin allows the formation of complex bacterial communities termed biofilm. Bacteria living in biofilms are phenotypically distinct from their planktonic counterparts and are orders of magnitude more resistant to antibiotics, host immune response, and environmental stress. Staphylococcus aureus is prevalent in cutaneous infections such as chronic wounds and is an important human pathogen.

Results

The impact of S. aureus soluble products in biofilm-conditioned medium (BCM) or in planktonic-conditioned medium (PCM) on human keratinocytes was investigated. Proteomic analysis of BCM and PCM revealed differential protein compositions with PCM containing several enzymes involved in glycolysis. Global gene expression of keratinocytes exposed to biofilm and planktonic S. aureus was analyzed after four hours of exposure. Gene ontology terms associated with responses to bacteria, inflammation, apoptosis, chemotaxis, and signal transduction were enriched in BCM treated keratinocytes. Several transcripts encoding cytokines were also upregulated by BCM after four hours. ELISA analysis of cytokines confirmed microarray results at four hours and revealed that after 24 hours of exposure, S. aureus biofilm induced sustained low level cytokine production compared to near exponential increases of cytokines in planktonic treated keratinocytes. The reduction in cytokines produced by keratinocytes exposed to biofilm was accompanied by suppressed phosphorylation of MAPKs. Chemical inhibition of MAPKs did not drastically reduce cytokine production in BCM-treated keratinocytes suggesting that the majority of cytokine production is mediated through MAPK-independent mechanisms.

Conclusions

Collectively the results indicate that S. aureus biofilms induce a distinct inflammatory response compared to their planktonic counterparts. The differential gene expression and production of inflammatory cytokines by biofilm and planktonic cultures in keratinocytes could have implications for the formation and persistence of chronic wounds. The formation of a biofilm should be considered in any study investigating host response to bacteria.

Porphyromonas gingivalis induction of microRNA-203 expression controls suppressor of cytokine signaling 3 in gingival epithelial cells

Porphyromonas gingivalis is a pathogen in severe periodontal disease. Able to exploit an intracellular lifestyle within primary gingival epithelial cells (GECs), a reservoir of P. gingivalis can persist within the gingival epithelia. This process is facilitated by manipulation of the host cell signal transduction cascades which can impact cell cycle, cell death, and cytokine responses. Using microarrays, we investigated the ability of P. gingivalis 33277 to regulate microRNA (miRNA) expression in GECs. One of several miRNAs differentially regulated by GECs in the presence of P. gingivalis was miRNA-203 (miR-203), which was upregulated 4-fold compared to uninfected controls. Differential regulation of miR-203 was confirmed by quantitative reverse transcription-PCR (qRT-PCR). Putative targets of miR-203, suppressor of cytokine signaling 3 (SOCS3) and SOCS6, were evaluated by qRT-PCR. SOCS3 and SOCS6 mRNA levels were reduced >5-fold and >2-fold, respectively, in P. gingivalis-infected GECs compared to controls. Silencing of miR-203 using a small interfering RNA construct reversed the inhibition of SOCS3 expression. A dual luciferase assay confirmed binding of miR-203 to the putative target binding site of the SOCS3 3' untranslated region. Western blot analysis demonstrated that activation of signal transducer and activator of transcription 3 (Stat3), a downstream target of SOCS, was diminished following miR-203 silencing. This study shows that induction of miRNAs by P. gingivalis can modulate important host signaling responses.

Interaction of oral bacteria with gingival epithelial cell multilayers

Primary gingival epithelial cells were cultured in multilayers as a model for the study of interactions with oral bacteria associated with health and periodontal disease. Multilayers maintained at an air-liquid interface in low-calcium medium displayed differentiation and cytokeratin properties characteristic of junctional epithelium. Multilayers were infected with fluorescently labeled Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum or Streptococcus gordonii, and bacterial association was determined by confocal microscopy and quantitative image analysis. Porphyromonas gingivalis invaded intracellularly and spread from cell to cell; A. actinomycetemcomitans and F. nucleatum remained extracellular and showed intercellular movement through the multilayer; whereas S. gordonii remained extracellular and predominantly associated with the superficial cell layer. None of the bacterial species disrupted barrier function as measured by transepithelial electrical resistance. P. gingivalis did not elicit secretion of proinflammatory cytokines. However, A. actinomycetemcomitans and S. gordonii induced interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), IL-6 and IL-8 secretion; and F. nucleatum stimulated production of IL-1β and TNF-α. Aggregatibacter actinomycetemcomitans, F. nucleatum and S. gordonii, but not P. gingivalis, increased levels of apoptosis after 24 h infection. The results indicate that the organisms with pathogenic potential were able to traverse the epithelium, whereas the commensal bacteria did not. In addition, distinct host responses characterized the interaction between the junctional epithelium and oral bacteria.

Oxygen tension modulates the cytokine response of oral epithelium to periodontal bacteria

BACKGROUND

There is an inverse relationship between pocket depth and pocket oxygen tension with deep pockets being associated with anaerobic bacteria. However, little is known about how the host tissues respond to bacteria under differing oxygen tensions within the periodontal pocket.

AIM

To investigate the effect of different oxygen tensions upon nuclear factor-kappa B (NF-κB) activation and the inflammatory cytokine response of oral epithelial cells when exposed to nine species of oral bacteria.

MATERIALS AND METHODS

H400 oral epithelial cells were equilibrated at 2%, 10% or 21% oxygen. Cells were stimulated with heat-killed oral bacteria at multiplicity of infection 10:1, Escherichia coli lipopolysaccharide (15 μg/ml) or vehicle control. Interleukin-8 (IL-8) and tumour necrosis factor-alpha (TNF-α) levels were measured by enzyme-linked immunosorbent assay and NF-κB activation was measured by reporter vector or by immunohistochemical analysis.

RESULTS

Tannerella forsythensis, Porphyromonas gingivalis and Prevotella intermedia elicited the greatest epithelial NF-κB activation and cytokine responses. An oxygen-tension-dependent trend in cytokine production was observed with the highest IL-8 and TNF-α production observed at 2% oxygen and lowest at 21% oxygen.

CONCLUSIONS

These data demonstrate a greater pro-inflammatory host response and cell signalling response to bacteria present in more anaerobic conditions, and hypersensitivity of epithelial cells to pro-inflammatory stimuli at 2% oxygen, which may have implications for disease pathogenesis and/or therapy.