Interaction of oral bacteria with gingival epithelial cell multilayers

Interleukin-8 induces DNA synthesis, migration and down-regulation of cleaved caspase-3 in cultured human gingival epithelial cells

BACKGROUND AND OBJECTIVE

Migration of the junctional epithelium occurs in association with the formation of a periodontal pocket. Although the migration of junctional epithelium is known to be related to the proliferation and migration of gingival junctional epithelial cells, the mechanism has not been clarified. In patients with periodontitis, the levels of interleukin-8 (IL-8) in both gingival tissue and gingival crevicular fluid are dramatically increased. IL-8 has broad bioactive functions. In this study, we examined the role of IL-8 in DNA synthesis, migration and protection against apoptosis in cultured human gingival epithelial cells (HGEC).

MATERIAL AND METHODS

DNA synthesis was estimated by measuring the incorporation of bromodeoxyuridine. The migration of gingival epithelial cells was assessed in a wound-healing assay. The expression of integrin beta-1 was analyzed using immunofluorescence confocal microscopy and western blotting. Cleaved caspase-3 was detected using western blotting and a Caspase-Glo assay kit.

RESULTS

IL-8 increased the synthesis of DNA in HGEC, and the maximal effect was seen at 25 or 50 ng/mL of IL-8. In addition, 50 ng/mL of IL-8 induced cell migration, and a neutralizing antibody of integrin beta-1 inhibited the migration. IL-8 also activated expression of integrin beta-1. Furthermore, IL-8 reduced the Aggregatibacter actinomycetemcomitans-induced increase in caspase-3 expression in HGEC.

CONCLUSION

IL-8 may facilitate the migration of gingival junctional epithelium by enhancing DNA synthesis, migration and preventing apoptosis of gingival epithelial cells.

Smad2 is involved in Aggregatibacter actinomycetemcomitans-induced apoptosis

Apoptosis is thought to contribute to the progression of periodontitis. It has been suggested that the apoptosis of epithelial cells may contribute to the loss of epithelial barrier function. Smad2, a downstream signaling molecule of TGF-β receptors (TGF-βRs), is critically involved in apoptosis in several cell types. However, the relationship between smad2 and bacteria-induced apoptosis has not yet been elucidated. It is possible that the regulation of apoptosis induced by periodontopathic bacteria may lead to novel preventive therapies for periodontitis. Therefore, in the present study, we investigated the involvement of smad2 phosphorylation in apoptosis of human gingival epithelial cells induced by Aggregatibacter actinomycetemcomitans (Aa). Aa apparently induced the phosphorylation of smad2 in primary human gingival epithelial cells (HGECs) or the human gingival epithelial cell line, OBA9 cells. In addition, Aa induced phosphorylation of the serine residue of the TGF-β type I receptor (TGF-βRI) in OBA9 cells. SB431542 (a TGF-βRI inhibitor) and siRNA transfection for TGF-βRI, which reduced both TGF-βRI mRNA and protein levels, markedly attenuated the Aa-induced phosphorylation of smad2. Furthermore, the disruption of TGF-βRI signaling cascade by SB431542 and siRNA transfection for TGF-βRI abrogated the activation of cleaved caspase-3 expression and repressed apoptosis in OBA9 cells treated with Aa. Thus, Aa induced apoptosis in gingival epithelial cells by activating the TGF-βRI-smad2-caspase-3 signaling pathway. The results of the present study may suggest that the periodontopathic bacteria, Aa, activates the TGF-βR/smad2 signaling pathway in human gingival epithelial cells and induces apoptosis in epithelial cells, which may lead to new therapeutic strategies that modulate the initiation of periodontitis.

Amphotericin B down-regulates Aggregatibacter actinomycetemcomitans-induced production of IL-8 and IL-6 in human gingival epithelial cells

Gingival epithelium is the primary barrier against microorganism invasion and produces inflammatory cytokines. Amphotericin B, a major antifungal drug, binds to cholesterol in the mammalian cell membrane in addition to fungal ergosterol. Amphotericin B has been shown to regulate inflammatory cytokines in host cells. To investigate the suppressive effect of amphotericin B on the gingival epithelium, we examined the expression of interleukin (IL)-8 and IL-6 and involvement of MAP kinase in human gingival epithelial cells (HGEC) stimulated by Aggregatibacter actinomycetemcomitans. Amphotericin B and the p38 MAP kinase inhibitor down-regulated the A. actinomycetemcomitans-induced increase in the expression of IL-8 and IL-6 at the mRNA. The ERK inhibitor suppressed the A. actinomycetemcomitans-induced IL-8 mRNA expression. Amphotericin B inhibited the A. actinomycetemcomitans-induced phosphorylation of ERK and p38 MAP kinase. Furthermore, amphotericin B inhibited the A. actinomycetemcomitans-induced production of prostaglandin E2. These results suggest that amphotericin B regulate inflammatory responses in HGEC.

Development of an in vitro periodontal biofilm model for assessing antimicrobial and host modulatory effects of bioactive molecules

Background

Inflammation within the oral cavity occurs due to dysregulation between microbial biofilms and the host response. Understanding how different oral hygiene products influence inflammatory properties is important for the development of new products. Therefore, creation of a robust host-pathogen biofilm platform capable of evaluating novel oral healthcare compounds is an attractive option. We therefore devised a multi-species biofilm co-culture model to evaluate the naturally derived polyphenol resveratrol (RSV) and gold standard chlorhexidine (CHX) with respect to anti-biofilm and anti-inflammatory properties.

Methods

An in vitro multi-species biofilm containing S. mitis, F. nucleatum, P. gingivalis and A. actinomycetemcomitans was created to represent a disease-associated biofilm and the oral epithelial cell in OKF6-TERT2. Cytotoxicity studies were performed using RSV and CHX. Multi-species biofilms were either treated with either molecule, or alternatively epithelial cells were treated with these prior to biofilm co-culture. Biofilm composition was evaluated and inflammatory responses quantified at a transcriptional and protein level.

Results

CHX was toxic to epithelial cells and multi-species biofilms at concentrations ranging from 0.01-0.2%. RSV did not effect multi-species biofilm composition, but was toxic to epithelial cells at concentrations greater than 0.01%. In co-culture, CHX-treated biofilms resulted in down regulation of the inflammatory chemokine IL-8 at both mRNA and protein level. RSV-treated epithelial cells in co-culture were down-regulated in the release of IL-8 protein, but not mRNA.

Conclusions

CHX possesses potent bactericidal properties, which may impact downstream inflammatory mediators. RSV does not appear to have bactericidal properties against multi-species biofilms, however it did appear to supress epithelial cells from releasing inflammatory mediators. This study demonstrates the potential to understand the mechanisms by which different oral hygiene products may influence gingival inflammation, thereby validating the use of a biofilm co-culture model.

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.

Breaking the Gingival Epithelial Barrier: Role of the Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin in Oral Infectious Disease

The Gram-negative bacterium Aggregatibacter actinomycetemcomitans is part of the HACEK group that causes infective endocarditis, a constituent of the oral flora that promotes some forms of periodontal disease and a member of the family of species that secrete a cytolethal distending toxin (Cdt). The family of bacteria that express the cdt genes participate in diseases that involve the disruption of a mucosal or epithelial layer. In vitro studies have shown that human gingival epithelial cells (HGEC) are native targets of the Cdt that typically induces DNA damage that signals growth arrest at the G₂/M interphase of the cell cycle. The gingival epithelium is an early line of defense in the oral cavity against microbial assault. When damaged, bacteria collectively gain entry into the underlying connective tissue where microbial products can affect processes and pathways in infiltrating inflammatory cells culminating in the destruction of the attachment apparatus of the tooth. One approach has been the use of an ex vivo gingival explant model to assess the effects of the Cdt on the morphology and integrity of the tissue. The goal of this review is to provide an overview of these studies and to critically examine the potential contribution of the Cdt to the breakdown of the protective gingival barrier.

Inhibitory effects of ameloblastin on epithelial cell proliferation

OBJECTIVE

Ameloblastin is an enamel matrix protein expressed in several tissues. Many potential mechanisms have been identified by which ameloblastin functions as an extracellular matrix protein. However, the biological effects of ameloblastin on gingival epithelial cells remain unclear. In the present study, we established a novel system to purify recombinant human ameloblastin and clarified its biological functions in epithelial cells in vitro.

DESIGN

Recombinant human ameloblastin was isolated from COS-7 cells overexpressing HaloTag-fused human ameloblastin by the HaloTag system and then purified further by reverse-phase high-performance liquid chromatography. SCC-25 cells, derived from human oral squamous cell carcinoma, were treated with recombinant ameloblastin and then cell survival was assessed by a WST-1 assay. Cell cycle analysis was performed by flow cytometry.

RESULTS

The novel purification system allowed effective recovery of the recombinant ameloblastin proteins at a high purity. Recombinant ameloblastin protein was found to suppress the proliferation of SCC-25 cells. Flow cytometric analysis showed that ameloblastin treatment induced cell cycle arrest G1 phase.

CONCLUSIONS

We developed a procedure for production of highly purified recombinant human ameloblastin. Biological analyses suggest that ameloblastin induces cell cycle arrest in epithelial cells and regulates the progression of periodontitis.

Biological responses of human gingival fibroblasts (HGFs) in an innovative co-culture model with Streptococcus mitis to thermosets coated with a silver polysaccharide antimicrobial system

This study sought to evaluate the in vitro biological response of human gingival fibroblasts (HGFs) co-coltured with Streptococcus mitis to bisphenol A glycidylmethacrylate/triethylene glycol dimethacrylate (BisGMA/TEGDMA) thermosets coated with Chitlac-nAg, a nanocomposite system with antimicrobial properties. To avoid bacterial adhesion to dental devices and to reduce cytotoxicity against eukaryotic cells, we coated BisGMA/TEGDMA methacrylic thermosets with a new material, Chitlac-nAg, formed by stabilizing silver nanoparticles, which have well-known antimicrobial properties, with a polyelectrolyte solution containing Chitlac. Cytotoxicity, cell morphology, cell migration and inflammatory interleukine-6 (IL-6) and prostaglandin E2 (PGE2) secretion were evaluated. Our results showed that the cytotoxicity exerted on HGFs by our nanocomposite material was absent in our co-culture model, where fibroblasts are able to adhere and migrate. After 24 h thermosets coated with Chitlac as well as those coated with Chitlac-nAg exerted a minimal cytotoxic effect on HGFs, while after 48 h LDH release rises up 20%. Moreover the presence of S. mitis reduced this release in a greater amount with Chitlac-nAg coated thermosets. The secretion of IL-6 was significant in both Chitlac and Chitlac-nAg coated thermosets, but PGE2 production was minimal, suggesting that the IL-6 production was not related to an inflammatory response. Co-culture and the addiction of saliva did not influence IL-6 and PGE2 secretion. Data obtained in the present work suggest that Chitlac n-Ag coated thermosets could significantly improve the success rates of restorative dentistry, since they limit bacterial adhesion and are not toxic to HGFs.

The function of TLR4 in interferon gamma or interleukin-13 exposed and lipopolysaccharide stimulated gingival epithelial cell cultures

Gingival epithelial cells are part of the first line of host defense against infection. Toll-like receptors (TLRs) serve important immune and nonimmune functions. We investigated how interferon gamma (INF-γ) and interleukin 13 (IL-13) are involved in the TLR4 ligand-induced regulation of interleukin-8 (IL-8) effects on gingival epithelial cells. We used immunohistochemistry to localize TLR4 in ten healthy and ten periodontitis tissue specimens. Gingival epithelial cells then were primed with Th1 cytokine (INF-γ) or Th2 cytokine (IL-13) before stimulation with Escherichia coli-derived lipopolysaccharide (LPS) and enzyme-linked immunosorbent assay (ELISA) was performed to detect the level of IL-8 secretion in cell culture supernatants. Although both healthy and periodontitis gingival tissue samples expressed TLR4, the periodontitis samples showed more intense expression on gingival epithelial cells. Gingival epithelial cell cultures were primed with either INF-γ or IL-13 before stimulation with TLR4 ligand. Supernatants from co-stimulated epithelial cells exhibited IL-8 production in opposite directions, i.e., as one stimulates the release, the other reduces the release. INF-γ significantly increased TLR4 function, whereas IL-13 significantly decreased TLR4 function, i.e., production of IL-8. Pathogen associated molecular pattern-LPS, shared by many different periodonto-pathogenic bacteria, activates the gingival epithelial cells in a TLR-dependent manner. Diminished or increased TLR function in gingival epithelial cells under the influence of different Th cell types may protect or be harmful due to the altered TLR signaling.

Characterisation and optimisation of organotypic oral mucosal models to study Porphyromonas gingivalis invasion

Porphyromonas gingivalis is a Gram-negative, keystone pathogen in periodontitis that leads to tissue destruction and ultimately tooth loss. The organism is able to infect oral epithelial cells and two-dimensional (monolayer) cultures have been used to investigate this process. However, recently there has been interest in the use of three-dimensional, organotypic mucosal models to analyse infection. These models are composed of collagen-embedded fibroblasts overlain with multilayers of oral epithelial cells. In this study we report for the first time significant differences in the response of oral mucosal models to P. gingivalis infection when compared to monolayer cultures of oral epithelial cells. Intracellular survival (3-fold) and bacterial release (4-fold) of P. gingivalis was significantly increased in mucosal models compared with monolayer cultures, which may be due to the multi-layered nature and exfoliation of epithelial cells in these organotypic models. Furthermore, marked differences in the cytokine profile between infected organotypic models and monolayer cultures were observed, particularly for CXCL8 and IL6, which suggested that degradation of cytokines by P. gingivalis may be less pronounced in organotypic compared to monolayer cultures. These data suggest that use of oral mucosal models may provide a greater understanding of the host responses to P. gingivalis invasion than simple monolayer cultures.

Dendritic cells of the oral mucosa

The oral cavity contains distinct mucosal surfaces, each with its own unique distribution of dendritic cell (DC) subsets. In addition to tissue-specific properties, such organization might confer differential immune outcomes guided by tissue-resident DCs, which translate in the lymph node into an overall immune response. This process is further complicated by continual exposure and colonization of the oral cavity with enormous numbers of diverse microbes, some of which might induce destructive immunity. As a central cell type constantly monitoring changes in oral microbiota and orchestrating T-cell function, oral DCs are of major importance in deciding whether to induce immunity or tolerance. In this review, an overview of the phenotype and distribution of DCs in the oral mucosa is provided. In addition, the role of the various oral DC subsets in inducing immunity vs. tolerance, as well as their involvement in several oral pathologies is discussed.

The role of factors associated with apoptosis in assessing periodontal disease status

BACKGROUND

Little is known about the release of apoptotic proteins during periodontal breakdown. This pilot study investigates the presence of factors associated with apoptosis in serum, saliva, and gingival crevicular fluid (GCF) and their association with periodontal disease severity and activity.

METHODS

GCF, whole saliva, and serum were obtained from 47 adult patients with chronic periodontitis (CP) and 10 healthy controls. Clinical measurements, including probing depth (PD), clinical attachment level (CAL), and radiographs, were used to classify patients into healthy, mild, and moderate/severe CP groups. Enzyme-linked immunosorbent assays were used to measure apoptosis or DNA fragmentation in GCF and active caspase-3, soluble Fas (sFas), and sFas ligand (sFasL) in saliva and serum. Western immunoblotting was used to detect Fas, FasL, sFasL, and caspase-3 expression in GCF.

RESULTS

DNA fragmentation was positively correlated with PD and CAL regardless of patient disease status (P <0.001). sFas and sFasL were present in saliva and serum, but there were no differences between groups. In GCF, the greater odds of detecting Fas, sFasL, and caspase-3 increased with increasing PD and CAL (P <0.05). In addition, sites with inflammation and PD ≥5 mm had significantly greater odds of exhibiting Fas, sFasL, and caspase-3 expression compared with sites without inflammation and PD <5 mm (P <0.05). Caspase-3 was not detected in saliva or serum. At the patient level, only FasL and disease status were significantly correlated (P <0.05).

CONCLUSION

Factors associated with apoptosis were detected in GCF in patients with CP.

P. gingivalis modulates keratinocytes through FOXO transcription factors

P. gingivalis is a prominent periodontal pathogen that has potent effects on host cells. In this study we challenged gingival epithelial cells with P. gingivalis with the aim of assessing how mRNA levels of key target genes were modulated by P. gingivalis via the transcription factors FOXO1 and FOXO3. Primary mono- and multi-layer cultures of gingival epithelial cells were challenged and barrier function was examined by fluorescent dextran and apoptosis was measured by cytoplasmic histone associated DNA. Gene expression levels were measured by real-time PCR with and without FOXO1 and FOXO3 siRNA compared to scrambled siRNA. P. gingivalis induced a loss of barrier function and stimulated gingival epithelial cell apoptosis in multilayer cultures that was in part gingipain dependent. P. gingivalis stimulated an increase in FOXO1 and FOXO3 mRNA, enhanced mRNA levels of genes associated with differentiated keratinocyte function (keratin-1, -10, -14, and involucrin), increased mRNA levels of apoptotic genes (BID and TRADD), reduced mRNA levels of genes that regulate inflammation (TLR-2 and -4) and reduced those associated with barrier function (integrin beta-1, -3 and -6). The ability of P. gingivalis to modulate these genes was predominantly FOXO1 and FOXO3 dependent. The results indicate that P. gingivalis has pronounced effects on gingival keratinocytes and modulates mRNA levels of genes that affect host response, differentiation, apoptosis and barrier function. Moreover, this modulation is dependent upon the transcription factors FOXO1 or FOXO3. In addition, a new function for FOXO1 was identified, that of suppressing TLR-2 and TLR-4 and maintaining integrin beta -1, beta -3 and beta -6 basal mRNA levels in keratinocytes.

Bacterial infection increases periodontal bone loss in diabetic rats through enhanced apoptosis

Periodontal disease is the most common osteolytic disease in humans and is significantly increased by diabetes mellitus. We tested the hypothesis that bacterial infection induces bone loss in diabetic animals through a mechanism that involves enhanced apoptosis. Type II diabetic rats were inoculated with Aggregatibacter actinomycetemcomitans and treated with a caspase-3 inhibitor, ZDEVD-FMK, or vehicle alone. Apoptotic cells were measured with TUNEL; osteoblasts and bone area were measured in H&E sections. New bone formation was assessed by labeling with fluorescent dyes and by osteocalcin mRNA levels. Osteoclast number, eroded bone surface, and new bone formation were measured by tartrate-resistant acid phosphatase staining. Immunohistochemistry was performed with an antibody against tumor necrosis factor-α. Bacterial infection doubled the number of tumor necrosis factor-α-expressing cells and increased apoptotic cells adjacent to bone 10-fold (P < 0.05). Treatment with caspase inhibitor blocked apoptosis, increased the number of osteoclasts, and eroded bone surface (P < 0.05); yet, inhibition of apoptosis resulted in significantly greater net bone area because of an increase in new bone formation, osteoblast numbers, and an increase in bone coupling. Thus, bacterial infection in diabetic rats stimulates periodontitis, in part through enhanced apoptosis of osteoblastic cells that reduces osseous coupling through a caspase-3-dependent mechanism.

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.

Polymersome-mediated intracellular delivery of antibiotics to treat Porphyromonas gingivalis-infected oral epithelial cells

The gram-negative anaerobe Porphyromonas gingivalis colonizes the gingival crevice and is etiologically associated with periodontal disease that can lead to alveolar bone damage and resorption, promoting tooth loss. Although susceptible to antibiotics, P. gingivalis can evade antibiotic killing by residing within gingival keratinocytes. This provides a reservoir of organisms that may recolonize the gingival crevice once antibiotic therapy is complete. Polymersomes are nanosized amphiphilic block copolymer vesicles that can encapsulate drugs. Cells internalize polymersomes by endocytosis into early endosomes, where they are disassembled by the low pH, causing intracellular release of their drug load. In this study, polymersomes were used as vehicles to deliver antibiotics in an attempt to kill intracellular P. gingivalis within monolayers of keratinocytes and organotypic oral mucosal models. Polymersome-encapsulated metronidazole or doxycycline, free metronidazole, or doxycycline, or polymersomes alone as controls, were used, and the number of surviving intracellular P. gingivalis was quantified after host cell lysis. Polymersome-encapsulated metronidazole or doxycycline significantly (P<0.05) reduced the number of intracellular P. gingivalis in both monolayer and organotypic cultures compared to free antibiotic or polymersome alone controls. Polymersomes are effective delivery vehicles for antibiotics that do not normally gain entry to host cells. This approach could be used to treat recurrent periodontitis or other diseases caused by intracellular-dwelling organisms.

Cell junction remodeling in gingival tissue exposed to a microbial toxin

The gingival epithelium plays a key role in protecting the supporting structures of the teeth from bacteria and their products. In ex vivo experiments, we recently showed that the cytolethal distending toxin (Cdt) from the periodontal pathogen Aggregatibacter actinomycetemcomitans causes extensive damage to gingival tissue. Morphological changes included detachment of the keratinized outer layer, distention of spinous and basal cells in the oral epithelium, disruption of rete pegs, and apparent dissolution of cell junctions. Adherens junctions (zonula adherens) are essential for maintaining barrier function and integrity of gingival epithelium. Therefore, immunohistochemical and RT-PCR analyses of human gingival explants (HGX) and human gingival epithelial cells (HGEC) were utilized for a closer examination of the effects of the Cdt on E-cadherin, the key membrane component of adherens junctions. Although there was some variability among tissue donors, exposure of gingival tissue or isolated epithelial cells to the toxin generally resulted in a pronounced increase in the expression and cytosolic distribution of E-cadherin, accompanied by an increase in levels of the intracellular scaffolding proteins β-catenin and β-actin. These results indicate that the Cdt induced substantial remodeling of adherens junctions, with a potential impact on the barrier function of gingival epithelium.

ABBREVIATIONS

cytolethal distending toxin (Cdt), 4',6-diamidino-2-phenylindole (DAPI), human gingival epithelial cells (HGEC), human gingival explants (HGX), human gingival fibroblasts (HGF), transepithelial resistance (TER).

Neutrophils alter epithelial response to Porphyromonas gingivalis in a gingival crevice model

A gingival crevice model (epithelial cell-Porphyromonas gingivalis-neutrophil) was established and used to profile gingipain, matrix metalloproteinase (MMP), MMP mediators [neutrophil gelatinase-associated lipocalin (NGAL) and tissue inhibitor of metalloproteinases 1 (TIMP-1)] and cytokine networks. Smoking is the primary environmental risk factor for periodontitis. Therefore, the influence of cigarette smoke extract (CSE) was also monitored in the same model. Porphyromonas gingivalis alone induced low levels of interleukin-1β and interleukin-8 from epithelial cells, but high levels of both cytokines were produced on the addition of neutrophils. Exposure to CSE (100 and 1000 ng ml(-1) nicotine equivalency) significantly compromised P. gingivalis-induced cytokine secretion (both P < 0.05). P. gingivalis induced impressive secretion of NGAL (P < 0.05) that was not influenced by CSE. The influence of CSE on gingipain production was strain-specific. Purified gingipains effectively and rapidly degraded both TIMP-1 and MMP-9. Induction of large amounts of NGAL, degradation of TIMP-1, and increased gingipain activity would each be expected to prolong collagen degradation and promote disease progression. However, gingipains also degrade MMP-9. Hence, P. gingivalis exerts a complex influence on the proteolytic balance of a gingival crevice model. Exposure to CSE reduces the proinflammatory cytokine burden, which may be expected to promote P. gingivalis survival. In addition to novel findings that provide mechanistic insight into periodontal disease progression, these results are in keeping with the recognized clinical dogma of decreased inflammation/increased disease in smokers. This straightforward gingival crevice model is established as a suitable vehicle for the elucidation of mechanisms that contribute to susceptibility to periodontitis.

Establishment and characterization of a telomerase immortalized human gingival epithelial cell line

BACKGROUND AND OBJECTIVE

Gingival keratinocytes are used in model systems to investigate the interaction between periodontal bacteria and the epithelium in the initial stages of the periodontal disease process. Primary gingival epithelial cells (GECs) have a finite lifespan in culture before they enter senescence and cease to replicate, while epithelial cells immortalized with viral proteins can exhibit chromosomal rearrangements. The aim of this study was to generate a telomerase immortalized human gingival epithelial cell line and compare its in vitro behaviour to that of human GECs.

MATERIAL AND METHODS

Human primary GECs were immortalized with a bmi1/hTERT combination to prevent cell cycle triggers of senescence and telomere shortening. The resultant cell-line, telomerase immortalized gingival keratinocytes (TIGKs), were compared to GECs for cell morphology, karyotype, growth and cytokeratin expression, and further characterized for replicative lifespan, expression of toll-like receptors and invasion by P. gingivalis.

RESULTS

TIGKs showed morphologies, karyotype, proliferation rates and expression of characteristic cytokeratin proteins comparable to GECs. TIGKs underwent 36 passages without signs of senescence and expressed transcripts for toll-like receptors 1-6, 8 and 9. A subpopulation of cells underwent stratification after extended time in culture. The cytokeratin profiles of TIGK monolayers were consistent with basal cells. When allowed to stratify, cytokeratin profiles of TIGKs were consistent with suprabasal cells of the junctional epithelium. Further, TIGKs were comparable to GECs in previously reported levels and kinetics of invasion by wild-type P. gingivalis and an invasion defective ΔserB mutant.

CONCLUSION

Results confirm bmi1/hTERT immortalization of primary GECs generated a robust cell line with similar characteristics to the parental cell type. TIGKs represent a valuable model system for the study of oral bacteria interactions with host gingival cells.

Differential interactions of Streptococcus gordonii and Staphylococcus aureus with cultured osteoblasts

The impedance of normal osteoblast function by microorganisms is at least in part responsible for the failure of dental or orthopedic implants. Staphylococcus aureus is a major pathogen of bone, and exhibits high levels of adhesion and invasion of osteoblasts. In this article we show that the commensal oral bacterium Streptococcus gordonii also adheres to and is internalized by osteoblasts. Entry of S. gordonii cells had typical features of phagocytosis, similar to S. aureus, with membrane protrusions characterizing initial uptake, and closure of the osteoblast membrane leading to engulfment. The sensitivities of S. gordonii internalization to inhibitors cytochalasin D, colchicine and monensin indicated uptake through endocytosis, with requirement for actin accumulation. Internalization levels of S. gordonii were enhanced by expression of S. aureus fibronectin-binding protein A (FnBPA) on the S. gordonii cell surface. Lysosomal-associated membrane protein-1 phagosomal membrane marker accumulated with intracellular S. aureus and S. gordonii FnBPA, indicating trafficking of bacteria into the late endosomal/lysosomal compartment. Streptococcus gordonii cells did not survive intracellularly for more than 12 h, unless expressing FnBPA, whereas S. aureus showed extended survival times (>48 h). Both S. aureus and S. gordonii DL-1 elicited a rapid interleukin-8 response by osteoblasts, whereas S. gordonii FnBPA was slower. Only S. aureus elicited an interleukin-6 response. Hence, S. gordonii invades osteoblasts by a mechanism similar to that exhibited by S. aureus, and elicits a proinflammatory response that may promote bone resorption.

Irsogladine maleate regulates the inflammatory related genes in human gingival epithelial cells stimulated by Aggregatibacter actinomycetemcomitans

Periodontitis is an infectious inflammatory disease. Our previous studies have revealed that irsogladine maleate (IM) regulates intercellular junctional function and chemokine secretion in gingival epithelium, resulting in the suppression of the onset of periodontal disease in a rat model. Therefore, it is plausible that IM is a promising preventive remedy for periodontal disease. In this study, to gain a better understanding of IM in gingival epithelial cells, we employed a DNA microarray analysis. More specifically, human gingival epithelial cells (HGEC) were exposed to Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) in the presence or absence of IM. Then, a human genome focus array was used. A. actinomycetemcomitans facilitated the expression of several inflammatory-related genes, including these for matrix metalloproteinase (MMP)-3, interleukin (IL)-6, and intercellular adhesion molecule-1 (ICAM-1) in HGEC, while these mRNA levels were attenuated by IM treatment. Importantly, consistent with mRNA levels, immunoblotting, immunofluorescence staining and ELISA analysis indicated that IM also abrogated the A. actinomycetemcomitans-induced increase in MMP-3, IL-6, and ICAM-1 at the protein level. In addition, inhibition of the ERK or p38 MAP kinase signaling cascade, previously reported to be disturbed by IM treatment in HGEC, clearly blocked A. actinomycetemcomitans-induced MMP-3, IL-6, or ICAM-1 protein expression. Moreover, animal study revealed that IM-pretreatment inhibited the A. actinomycetemcomitans-induced increase of ICAM-1 in gingival junctional epithelium. Taken together, these results suggested that IM can regulate inflammatory responses in HGEC by inhibiting the ERK or p38 MAP kinase signaling cascade, which may result in suppression of inflammation in gingival tissue, thereby contributing to the prevention of periodontitis.

Smad2 is involved in the apoptosis of murine gingival junctional epithelium associated with inhibition of Bcl-2

OBJECTIVE

Gingival junctional epithelium (JE) actively contributes to the homeostasis of the periodontium. Altered activation of TGF-β signalling is implicated in the epithelium from chronic periodontitis. However, little is known about the effects of TGF-β signalling on the JE. In this study, we investigated the relationship between Smad2, which plays an important role in mediating TGF-β signal, and induction of apoptosis in the JE.

METHODS

K14-Smad2 transgenic mice were used to observe the effect of over-expression of Smad2 driven by CK14 promoter in the JE. We performed TUNEL technique to evaluate the epithelial apoptosis. Expression of apoptosis related genes was examined using real-time PCR and immunofluorescence.

RESULTS

K14-Smad2 mice showed an increased number of phospho-Smad2 positive JE cells associated with an increase in TGF-β1 expression. K14-Smad2 mice have a significantly higher percentage of TUNEL positive cells in the JE. Immunofluorescence double labelling revealed that TUNEL positive cells showed immunoreactivity to phospho-Smad2. Real-time PCR analysis of apoptosis related gene expression provided evidence of lower expression of Bcl-2 in the gingival tissue from K14-Smad2 mice. There was a strong positive reaction for Bcl-2 protein in the junctional epithelium of wild type mice, while the gingival tissue of K14-Smad2 transgenic mice had only a faint signal for Bcl-2.

CONCLUSIONS

The present study provided evidence that Smad2 plays a crucial role in the induction of apoptosis in gingival JE through inhibition of Bcl-2.

Oral microbial habitat a dynamic entity

Oral microbial habitat is composed of wide variety of species. These species play a significant role in maintaining the well being of the oral cavity by contributing in various ways. However the proper functioning of these oral microbes can be detrimental for the human oral cavity if the conditions are not suitable such as redox potential (Eh), pH of a site, the activity of the host defenses, and the presence of antimicrobial agents. The oral microbial community represents the best-characterized group associated with the human host. There are strong correlations between the qualitative composition of the oral microbiota and clinically healthy or diseased states. Amongst the bacteria of more than 700 species now identified within the human oral microbiota, it is the streptococci that are numerically predominant. Interactions between mucosal surfaces and microbial microbiota are key to host defense, health, and disease. These surfaces are exposed to high numbers of microbes and must be capable of distinguishing between those that are beneficial or avirulent and those that will invade and cause disease. Our understanding of the mechanisms involved in these discriminatory processes has recently begun to expand as new studies bring to light the importance of epithelial cells and novel immune cell subsets such as T(h)17 T cells in these processes. In this review article we have tried to find out the factors responsible for maintaining oral microbial habitat intact and the reasons which cause changes in its composition.

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.

Host-bacteria crosstalk at the dentogingival junction

The dentogingival junction is of crucial importance in periodontal host defense both structurally and functionally. Oral bacteria exert a constant challenge to the host cells and tissues at the dentogingival junction. The host response is set up to eliminate the pathogens by the innate and adaptive defense mechanisms. In health, the commensal bacteria and the host defense mechanisms are in a dynamic steady state. During periodontal disease progression, the dental bacterial plaque, junctional epithelium (JE), inflammatory cells, connective tissue, and bone all go through a series of changes. The tissue homeostasis is turned into tissue destruction and progression of periodontitis. The classical study of Slots showed that in the bacterial plaque, the most remarkable change is the shift from gram-positive aerobic and facultatively anaerobic flora to a predominantly gram-negative and anaerobic flora. This has been later confirmed by several other studies. Furthermore, not only the shift of the bacterial flora to a more pathogenic one, but also bacterial growth as a biofilm on the tooth surface, allows the bacteria to communicate with each other and exert their virulence aimed at favoring their growth. This paper focuses on host-bacteria crosstalk at the dentogingival junction and the models studying it in vitro.

Aggregatibacter actinomycetemcomitans infection enhances apoptosis in vivo through a caspase-3-dependent mechanism in experimental periodontitis

The purpose of this study was to test the hypothesis that diabetes aggravates periodontal destruction induced by Aggregatibacter actinomycetemcomitans infection. Thirty-eight diabetic and 33 normal rats were inoculated with A. actinomycetemcomitans and euthanized at baseline and at 4, 5, and 6 weeks after inoculation. Bone loss and the infiltration of polymorphonuclear leukocytes (PMNs) in gingival epithelium were measured in hematoxylin-eosin-stained sections. The induction of tumor necrosis factor alpha (TNF-α) was evaluated by immunohistochemistry and of apoptotic cells by a TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) assay. After A. actinomycetemcomitans infection, the bone loss in diabetic rats was 1.7-fold and the PMN infiltration 1.6-fold higher than in normoglycemic rats (P < 0.05). The induction of TNF-α was 1.5-fold higher and of apoptotic cells was up to 3-fold higher in diabetic versus normoglycemic rats (P < 0.05). Treatment with a caspase-3 inhibitor significantly blocked noninflammatory cell apoptosis induced by A. actinomycetemcomitans infection in gingival epithelium and connective tissue (P < 0.05). These results provide new insight into how diabetes aggravates A. actinomycetemcomitans-induced periodontal destruction in rats by significantly increasing the inflammatory response, leading to increased bone loss and enhancing apoptosis of gingival epithelial and connective tissue cells through a caspase-3-dependent mechanism. Antibiotics had a more pronounced effect on many of these parameters in diabetic than in normoglycemic rats, suggesting a deficiency in the capacity of diabetic animals to resist infection.

Synergistic interaction between Candida albicans and commensal oral streptococci in a novel in vitro mucosal model

Candida albicans is a commensal colonizer of the gastrointestinal tract of humans, where it coexists with highly diverse bacterial communities. It is not clear whether this interaction limits or promotes the potential of C. albicans to become an opportunistic pathogen. Here we investigate the interaction between C. albicans and three species of streptococci from the viridans group, which are ubiquitous and abundant oral commensal bacteria. The ability of C. albicans to form biofilms with Streptococcus oralis, Streptococcus sanguinis, or Streptococcus gordonii was investigated using flow cell devices that allow abiotic biofilm formation under salivary flow. In addition, we designed a novel flow cell system that allows mucosal biofilm formation under conditions that mimic the environment in the oral and esophageal mucosae. It was observed that C. albicans and streptococci formed a synergistic partnership where C. albicans promoted the ability of streptococci to form biofilms on abiotic surfaces or on the surface of an oral mucosa analogue. The increased ability of streptococci to form biofilms in the presence of C. albicans could not be explained by a growth-stimulatory effect since the streptococci were unaffected in their growth in planktonic coculture with C. albicans. Conversely, the presence of streptococci increased the ability of C. albicans to invade organotypic models of the oral and esophageal mucosae under conditions of salivary flow. Moreover, characterization of mucosal invasion by the biofilm microorganisms suggested that the esophageal mucosa is more permissive to invasion than the oral mucosa. In summary, C. albicans and commensal oral streptococci display a synergistic interaction with implications for the pathogenic potential of C. albicans in the upper gastrointestinal tract.

Toll-like receptor 9 mediates oral bacteria-induced IL-8 expression in gingival epithelial cells

Previously, we reported that various oral bacteria regulate interleukin (IL)-8 production differently in gingival epithelial cells. The aim of this study was to characterize the pattern recognition receptor(s) that mediate bacteria-induced IL-8 expression. Among ligands that mimic bacterial components, only a Toll-like receptor (TLR) 9 ligand enhanced IL-8 expression as determined by ELISA. Both normal and immortalized human gingival epithelial (HOK-16B) cells expressed TLR9 intracellularly and showed enhanced IL-8 expression in response to CpG-oligonucleotide. The ability of eight strains of four oral bacterial species to induce IL-8 expression in HOK-16B cells, and their invasion capacity were examined in the absence or presence of 2% human serum. The ability of purified bacterial DNA (bDNA) to induce IL-8 was also examined. Six out of eight strains increased IL-8 production in the absence of serum. Usage of an endosomal acidification blocker or a TLR9 antagonist inhibited the IL-8 induction by two potent strains. In the presence of serum, many strains lost the ability to induce IL-8 and presented substantially reduced invasion capacity. The IL-8-inducing ability of bacteria in the absence or presence of serum showed a strong positive correlation with their invasion index. The IL-8-inducing ability of bacteria in the absence of human serum was also correlated with the immunostimulatory activity of its bDNA. The observed immunostimulatory activity of the bDNA could not be linked to its CpG motif content. In conclusion, oral bacteria induce IL-8 in gingival epithelial cells through TLR9 and the IL-8-inducing ability depends on the invasive capacity and immunostimulating DNA.