Intrinsic apoptotic pathways of gingival epithelial cells modulated by Porphyromonas gingivalis

Oral environment and cancer

Cancer is now the leading cause of death in Japan. A rapid increase in cancer mortality is expected as Japan is facing a super-aged society. Many causes of cancer are known to be closely linked to life style factors, such as smoking, drinking, and diet. The oral environment is known to be involved in the pathogenesis and development of various diseases such as bronchitis, pneumonia, diabetes, heart disease, and dementia. Because the oral cavity acts as the bodily entrance for air and food, it is constantly exposed to foreign substances, including bacteria and viruses. A large number of bacteria are endemic to the oral cavity, and indigenous oral flora act to prevent the settlement of foreign bacteria. The oral environment is influenced by local factors, including dental plaque, tartar, teeth alignment, occlusion, an incompatible prosthesis, and bad lifestyle habits, and systemic factors, including smoking, consumption of alcohol, irregular lifestyle and eating habits, obesity, stress, hormones, and heredity. It has recently been revealed that the oral environment is associated with cancer. In particular, commensal bacteria in the oral cavity are involved in the development of cancer. Moreover, Candida, human papilloma virus and Epstein-Barr virus as well as commensal bacteria have been reported to be associated with the pathogenesis of cancer. In this review, we introduce recent findings of the correlation between the oral environment and cancer.

The Periodontal Pathogen Porphyromonas gingivalis Preferentially Interacts with Oral Epithelial Cells in S Phase of the Cell Cycle

Porphyromonas gingivalis, a key periodontal pathogen, is capable of invading a variety of cells, including oral keratinocytes, by exploiting host cell receptors, including alpha-5 beta-1 (α5β1) integrin. Previous studies have shown that P. gingivalis accelerates the cell cycle and prevents apoptosis of host cells, but it is not known whether the cell cycle phases influence bacterium-cell interactions. The cell cycle distribution of oral keratinocytes was characterized by flow cytometry and BrdU (5-bromo-2-deoxyuridine) staining following synchronization of cultures by serum starvation. The effect of cell cycle phases on P. gingivalis invasion was measured by using antibiotic protection assays and flow cytometry, and these results were correlated with gene and surface expression levels of α5 integrin and urokinase plasminogen activator receptor (uPAR). There was a positive correlation (R = 0.98) between the number of cells in S phase and P. gingivalis invasion, the organism was more highly associated with cells in S phase than with cells in G2 and G1 phases, and S-phase cells contained 10 times more bacteria than did cells that were not in S phase. Our findings also show that α5 integrin, but not uPAR, was positively correlated with cells in S phase, which is consistent with previous reports indicating that P. gingivalis invasion of cells is mediated by α5 integrin. This study shows for the first time that P. gingivalis preferentially associates with and invades cells in the S phase of the cell cycle. The mechanism of targeting stable dividing cells may have implications for the treatment of periodontal diseases and may partly explain the persistence of this organism at subgingival sites.

Porphyromonas gingivalis Differentially Modulates Cell Death Profile in Ox-LDL and TNF-α Pre-Treated Endothelial Cells

Objective

Clinical studies demonstrated a potential link between atherosclerosis and periodontitis. Porphyromonas gingivalis (Pg), one of the main periodontal pathogen, has been associated to atheromatous plaque worsening. However, synergism between infection and other endothelial stressors such as oxidized-LDL or TNF-α especially on endothelial cell (EC) death has not been investigated. This study aims to assess the role of Pg on EC death in an inflammatory context and to determine potential molecular pathways involved.

Methods

Human umbilical vein ECs (HUVECs) were infected with Pg (MOI 100) or stimulated by its lipopolysaccharide (Pg-LPS) (1μg/ml) for 24 to 48 hours. Cell viability was measured with AlamarBlue test, type of cell death induced was assessed using Annexin V/propidium iodide staining. mRNA expression regarding caspase-1, -3, -9, Bcl-2, Bax-1 and Apaf-1 has been evaluated with RT-qPCR. Caspases enzymatic activity and concentration of APAF-1 protein were evaluated to confirm mRNA results.

Results

Pg infection and Pg-LPS stimulation induced EC death. A cumulative effect has been observed in Ox-LDL pre-treated ECs infected or stimulated. This effect was not observed in TNF-α pre-treated cells. Pg infection promotes EC necrosis, however, in infected Ox-LDL pre-treated ECs, apoptosis was promoted. This effect was not observed in TNF-α pre-treated cells highlighting specificity of molecular pathways activated. Regarding mRNA expression, Pg increased expression of pro-apoptotic genes including caspases-1,-3,-9, Bax-1 and decreased expression of anti-apoptotic Bcl-2. In Ox-LDL pre-treated ECs, Pg increased significantly the expression of Apaf-1. These results were confirmed at the protein level.

Conclusion

This study contributes to demonstrate that Pg and its Pg-LPS could exacerbate Ox-LDL and TNF-α induced endothelial injury through increase of EC death. Interestingly, molecular pathways are differentially modulated by the infection in function of the pre-stimulation.

Presence of Porphyromonas gingivalis in esophagus and its association with the clinicopathological characteristics and survival in patients with esophageal cancer

Background

Mounting evidence suggests a causal relationship between specific bacterial infections and the development of certain malignancies. However, the possible role of the keystone periodontal pathogen, Porphyromonas gingivalis, in esophageal squamous cell carcinoma (ESCC) remains unknown. Therefore, we examined the presence of P. gingivalis in esophageal mucosa, and the relationship between P. gingivalis infection and the diagnosis and prognosis of ESCC.

Methods

The presence of P. gingivalis in the esophageal tissues from ESCC patients and normal controls was examined by immunohistochemistry using antibodies targeting whole bacteria and its unique secreted protease, the gingipain Kgp. qRT-PCR was used as a confirmatory approach to detect P. gingivalis 16S rDNA. Clinicopathologic characteristics were collected to analyze the relationship between P. gingivalis infection and development of ESCC.

Results

P. gingivalis was detected immunohistochemically in 61 % of cancerous tissues, 12 % of adjacent tissues and was undetected in normal esophageal mucosa. A similar distribution of lysine-specific gingipain, a catalytic endoprotease uniquely secreted by P. gingivalis, and P. gingivalis 16S rDNA was also observed. Moreover, statistic correlations showed P. gingivalis infection was positively associated with multiple clinicopathologic characteristics, including differentiation status, metastasis, and overall survival rate.

Conclusion

These findings demonstrate for the first time that P. gingivalis infects the epithelium of the esophagus of ESCC patients, establish an association between infection with P. gingivalis and the progression of ESCC, and suggest P. gingivalis infection could be a biomarker for this disease. More importantly, these data, if confirmed, indicate that eradication of a common oral pathogen could potentially contribute to a reduction in the overall ESCC burden.

Electronic supplementary material

The online version of this article (doi:10.1186/s13027-016-0049-x) contains supplementary material, which is available to authorized users.

Porphyromonas gingivalis initiates a mesenchymal-like transition through ZEB1 in gingival epithelial cells

The oral anaerobe Porphyromonas gingivalis is associated with the development of cancers including oral squamous cell carcinoma (OSCC). Here, we show that infection of gingival epithelial cells with P. gingivalis induces expression and nuclear localization of the ZEB1 transcription factor, which controls epithelial-mesenchymal transition. P. gingivalis also caused an increase in ZEB1 expression as a dual species community with Fusobacterium nucleatum or Streptococcus gordonii. Increased ZEB1 expression was associated with elevated ZEB1 promoter activity and did not require suppression of the miR-200 family of microRNAs. P. gingivalis strains lacking the FimA fimbrial protein were attenuated in their ability to induce ZEB1 expression. ZEB1 levels correlated with an increase in expression of mesenchymal markers, including vimentin and MMP-9, and with enhanced migration of epithelial cells into matrigel. Knockdown of ZEB1 with siRNA prevented the P. gingivalis-induced increase in mesenchymal markers and epithelial cell migration. Oral infection of mice by P. gingivalis increased ZEB1 levels in gingival tissues, and intracellular P. gingivalis were detected by antibody staining in biopsy samples from OSCC. These findings indicate that FimA-driven ZEB1 expression could provide a mechanistic basis for a P. gingivalis contribution to OSCC.

[Research progress on the relationship between Porphyromonas gingivalis and oral squamous cell carcinoma]

Substantial evidence supports the relationship between chronic inflammation and cancer development. Numerous studies suggest that chronic inflammatory disease, such as periodontitis, contributes to head and neck squamous cell carcinoma development. Oral squamous cell carcinoma (OSCC) is the most common malignant tumor in the oral and maxillofacial regions. Porphyromonas gingivalis, one of the most important pathogens in association with periodontal disease, might have a potential correlation with OSCC. Along with the development of molecular biological techniques, the association between Porphyromonas gingivalis and OSCC has been greatly emphasized in recent years. This review summarizes the association between these variables and the potential mechanisms involved in such relationship.

The Porphyromonas gingivalis O antigen is required for inhibition of apoptosis in gingival epithelial cells following bacterial infection

BACKGROUND AND OBJECTIVE

Porphyromonas gingivalis infection induces apoptosis inhibition in gingival epithelial cells; however, it is not fully understood which bacterial effectors are involved in this process. The aim of this study is to evaluate whether the P. gingivalis lipopolysaccharide (LPS), specifically the O-antigen region, affects adherence, invasion, viability and apoptosis of gingival epithelial cells.

MATERIAL AND METHODS

Gingival epithelial cells (OKF6/TERT2 line) were infected by different freshly prepared P. gingivalis clinical isolates, obtained from subjects with chronic periodontitis (CP3 and CP4) and healthy individuals (H1 and H3). Periodontitis and healthy isolates show differences in O-antigen production, as healthy isolates lack the O-antigen region. In addition, cells were infected by a site-specific mutant lacking the O-antigen portion. After 24 h postinfection, cell proliferation, viability and apoptosis were evaluated by Trypan blue, MTS and annexin V assays, respectively. Bacterial invasion, adhesion and proliferation were measured by gentamicin/metronidazole protection assays. Finally, toll-like receptor (TLR)2 and TLR4 mRNA expression was evaluated by quantitative reverse transcription-polymerase chain reaction. Statistical analysis was performed using ANOVA, Tukey's or Dunnett's tests (p < 0.05).

RESULTS

At 24 h postinfection, strains lacking the O-antigen region (healthy isolates and O-antigen ligase-deficient strain) were unable to increase proliferation and viability, or decrease apoptosis as compared with strains producing intact LPS (periodontitis isolates and reference strain). However, the presence of the O-antigen neither contributed to changes in the ability of the bacteria to adhere to or invade cells, nor to intracellular survival. The presence of O-antigen also increased the expression of TLR4 (nearly sixfold), which correlated with inhibition of apoptosis.

CONCLUSION

The O-antigen region of P. gingivalis LPS is required to increase gingival epithelial cell viability upon infection by bacteria and this increase is attributable to a reduction in apoptosis. Moreover, although bacterial internalization is required, the effects observed are not due to alterations in P. gingivalis adherence, invasion or intracellular survival. Interestingly, inhibition of apoptosis correlates with increased TLR4 expression, suggesting a role for TLR4 in this process.

Reverse-Phase Microarray Analysis Reveals Novel Targets in Lymph Nodes of Bacillus anthracis Spore-Challenged Mice

Anthrax is a frequently fatal infection of many animal species and men. The causative agent Bacillus anthracis propagates through the lymphatic system of the infected host; however, the specific interactions of the host and microbe within the lymphatics are incompletely understood. We report the first description of the phosphoprotein signaling in the lymph nodes of DBA/2 mice using a novel technique combining the reverse-phase microarray with the laser capture microdissesction. Mice were challenged into foot pads with spores of toxinogenic, unencapsulated Sterne strain. The spores quickly migrated to the regional popliteal lymph nodes and spread to the bloodstream as early as 3 h post challenge. All mice died before 72 h post challenge from the systemic disease accompanied by a widespread LN tissue damage by bacteria, including the hemorrhagic necrotizing lymphadenitis, infiltration of CD11b+ and CD3+ cells, and massive proliferation of bacteria in lymph nodes. A macrophage scavenger receptor CD68/macrosialin was upregulated and found in association with vegetative bacteria likely as a marker of their prior interaction with macrophages. The major signaling findings among the 65 tested proteins included the reduced MAPK signaling, upregulation of STAT transcriptional factors, and altered abundance of a number of pro- and anti-apoptotic proteins with signaling properties opposing each other. Downregulation of ERK1/2 was associated with the response of CD11b+ macrophages/dendritic cells, while upregulation of the pro-apoptotic Puma indicated a targeting of CD3+ T-cells. A robust upregulation of the anti-apoptotic survivin was unexpected because generally it is not observed in adult tissues. Taken together with the activation of STATs it may reflect a new pathogenic mechanism aimed to delay the onset of apoptosis. Our data emphasize a notion that the net biological outcome of disease is determined by a cumulative impact of factors representing the microbial insult and the protective capacity of the host.

Noncanonical activation of β-catenin by Porphyromonas gingivalis

Porphyromonas gingivalis is an established pathogen in periodontal disease and an emerging pathogen in serious systemic conditions, including some forms of cancer. We investigated the effect of P. gingivalis on β-catenin signaling, a major pathway in the control of cell proliferation and tumorigenesis. Infection of gingival epithelial cells with P. gingivalis did not influence the phosphorylation status of β-catenin but resulted in proteolytic processing. The use of mutants deficient in gingipain production, along with gingipain-specific inhibitors, revealed that gingipain proteolytic activity was required for β-catenin processing. The β-catenin destruction complex components Axin1, adenomatous polyposis coli (APC), and GSK3β were also proteolytically processed by P. gingivalis gingipains. Cell fractionation and Western blotting demonstrated that β-catenin fragments were translocated to the nucleus. The accumulation of β-catenin in the nucleus following P. gingivalis infection was confirmed by immunofluorescence microscopy. A luciferase reporter assay showed that P. gingivalis increased the activity of the β-catenin-dependent TCF/LEF promoter. P. gingivalis did not increase Wnt3a mRNA levels, a finding consistent with P. gingivalis-induced proteolytic processing causing the increase in TCF/LEF promoter activity. Thus, our data indicate that P. gingivalis can induce the noncanonical activation of β-catenin and disassociation of the β-catenin destruction complex by gingipain-dependent proteolytic processing. β-Catenin activation in epithelial cells by P. gingivalis may contribute to a proliferative phenotype.

FOXO responses to Porphyromonas gingivalis in epithelial cells

Porphyromonas gingivalis is a prominent periodontal, and emerging systemic, pathogen that redirects host cell signalling pathways and modulates innate immune responses. In this study, we show that P. gingivalis infection induces the dephosphorylation and activation of forkhead box-O (FOXO)1, 3 and 4 in gingival epithelial cells. In addition, immunofluorescence showed that FOXO1 accumulated in the nucleus of P. gingivalis-infected cells. Quantitative reverse transcription PCR demonstrated that transcription of genes involved in protection against oxidative stress (Cat, Sod2, Prdx3), inflammatory responses (IL1β) and anti-apoptosis (Bcl-6) was induced by P. gingivalis, while small-interfering RNA (siRNA)-mediated knockdown of FOXO1 suppressed the transcriptional activation of these genes. P. gingivalis-induced secretion of interleukin (IL)-1β and inhibition of apoptosis were also impeded by FOXO1 knockdown. Neutralization of reactive oxygen species (ROS) by N-acetyl-l-cysteine blocked the activation of FOXO1 by P. gingivalis and concomitantly suppressed the activation of oxidative stress responses, anti-apoptosis programmes and IL-β production. Inhibition of c-Jun-N-terminal kinase (JNK) either pharmacologically or by siRNA, reduced FOXO1 activation and downstream FOXO1-dependent gene regulation in response to P. gingivalis. The results indicate that P. gingivalis-induced ROS activate FOXO transcription factors through JNK signalling, and that FOXO1 controls oxidative stress responses, inflammatory cytokine production and cell survival. These data position FOXO as an important signalling node in the epithelial cell-P. gingivalis interaction, with particular relevance to cell fate and dysbiotic host responses.

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.

Secretome of gingival epithelium in response to subgingival biofilms

Periodontitis is the chronic inflammatory destruction of periodontal tissues as a result of bacterial biofilm formation on the tooth surface. Proteins secreted by the gingival epithelium challenged by subgingival biofilms represent an important initial response for periodontal inflammation. The aim of this in vitro study was to characterize the whole secreted proteome of gingival epithelial tissue challenged by subgingival biofilms, and to evaluate the differential effects of the presence of the red-complex species in the biofilm. Multi-layered human gingival epithelial cultures were challenged with a 10-species in vitro biofilm model or its seven-species variant excluding the red complex. Liquid chromatography-tandem mass spectrometry for label-free quantitative proteomics was applied to identify and quantify the secreted epithelial proteins in the culture supernatant. A total of 192 proteins were identified and quantified. The biofilm challenge resulted in more secreted proteins being downregulated than upregulated. Even so, presence of the red complex in the biofilm was responsible for much of this downregulatory effect. Over 24 h, the upregulated biological processes were associated with inflammation and apoptosis, whereas the downregulated processes were associated with the disruption of epithelial tissue integrity and impairment of tissue turnover. Over 48 h, negative regulation of several metabolic processes and degradation of various molecular complexes was further intensified. Again, many of these biological regulations were attributed to the presence of the red complex. In conclusion, the present study provides the secreted proteome profile of gingival epithelial tissue to subgingival biofilms, and identifies a significant role for the red-complex species in the observed effects.

Periodontitis: from microbial immune subversion to systemic inflammation

Periodontitis is a dysbiotic inflammatory disease with an adverse impact on systemic health. Recent studies have provided insights into the emergence and persistence of dysbiotic oral microbial communities that can mediate inflammatory pathology at local as well as distant sites. This Review discusses the mechanisms of microbial immune subversion that tip the balance from homeostasis to disease in oral or extra-oral sites.

P. gingivalis in Periodontal Disease and Atherosclerosis - Scenes of Action for Antimicrobial Peptides and Complement

According to the NHS, it is estimated that over 50% of the adult population are, to some extent, affected by gum disease and approximately 15% of UK population have been diagnosed with severe periodontitis. Periodontitis, a chronic polymicrobial disease of the gums, causes inflammation in its milder form, whereas in its severe form affects the surrounding tissues and can result in tooth loss. During periodontitis, plaque accumulates and sits between the junctional epithelium and the tooth itself, resulting in inflammation and the formation of a periodontal pocket. An interface is formed directly between the subgingival bacteria and the junctional epithelial cells. Bacterial pathogens commonly associated with periodontal disease are, among others, Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola, together known as the "red complex." This review will mostly concentrate on the role of P. gingivalis, a Gram-negative anaerobic bacterium and one of the major and most studied contributors of this disease. Because periodontal disease is associated with the development of atherosclerosis, it is important to understand the local immune response to P. gingivalis. Innate immune players, in particular, complement and antimicrobial peptides and their effects with regard to P. gingivalis during periodontitis and in the development of atherosclerosis will be presented.

Attenuation of the phosphatidylinositol 3-kinase/Akt signaling pathway by Porphyromonas gingivalis gingipains RgpA, RgpB, and Kgp

Porphyromonas gingivalis is a major pathogen of periodontal diseases, including periodontitis. We have investigated the effect of P. gingivalis infection on the PI3K/Akt (protein kinase B) signaling pathway in gingival epithelial cells. Here, we found that live P. gingivalis, but not heat-killed P. gingivalis, reduced Akt phosphorylation at both Thr-308 and Ser-473, which implies a decrease in Akt activity. Actually, PI3K, which is upstream of Akt, was also inactivated by P. gingivalis. Furthermore, glycogen synthase kinase 3α/β, mammalian target of rapamycin, and Bad, which are downstream proteins in the PI3K/Akt cascade, were also dephosphorylated, a phenomenon consistent with Akt inactivation by P. gingivalis. However, these events did not require direct interaction between bacteria and host cells and were independent of P. gingivalis invasion into the cells. The use of gingipain-specific inhibitors and a gingipain-deficient P. gingivalis mutant KDP136 revealed that the gingipains and their protease activities were essential for the inactivation of PI3K and Akt. The associations between the PI3K regulatory subunit p85α and membrane proteins were disrupted by wild-type P. gingivalis. Moreover, PDK1 translocation to the plasma membrane was reduced by wild-type P. gingivalis, but not KDP136, indicating little production of phosphatidylinositol 3,4,5-triphosphate by PI3K. Therefore, it is likely that PI3K failed to transmit homeostatic extracellular stimuli to intracellular signaling pathways by gingipains. Taken together, our findings indicate that P. gingivalis attenuates the PI3K/Akt signaling pathway via the proteolytic effects of gingipains, resulting in the dysregulation of PI3K/Akt-dependent cellular functions and the destruction of epithelial barriers.

Porphyromonas gingivalis fimbriae dampen P2X7-dependent interleukin-1β secretion

Porphyromonas gingivalis is a major contributor to the pathogenesis of periodontitis, an infection-driven inflammatory disease that leads to bone destruction. This pathogen stimulates pro-interleukin (IL)-1β synthesis but not mature IL-1β secretion, unless the P2X7 receptor is activated by extracellular ATP (eATP). Here, we investigated the role of P. gingivalis fimbriae in eATP-induced IL-1β release. Bone marrow-derived macrophages (BMDMs) from wild-type (WT) or P2X7-deficient mice were infected with P. gingivalis (381) or isogenic fimbria-deficient (DPG3) strain with or without subsequent eATP stimulation. DPG3 induced higher IL-1β secretion after eATP stimulation compared to 381 in WT BMDMs, but not in P2X7-deficient cells. This mechanism was dependent on K(+) efflux and Ca(2+)-independent phospholipase A2 activity. Accordingly, non-fimbriated P. gingivalis failed to inhibit apoptosis via the eATP/P2X7 pathway. Furthermore, P. gingivalis-driven stimulation of IL-1β was Toll-like receptor 2 and MyD88 dependent, and not associated with fimbria expression. Fimbria-dependent down-modulation of IL-1β was selective, as levels of other cytokines remained unaffected by P2X7 deficiency. Confocal microscopy demonstrated the presence of discrete P2X7 expression in the absence of P. gingivalis stimulation, which was enhanced by 381-stimulated cells. Notably, DPG3-infected macrophages revealed a distinct pattern of P2X7 receptor expression with a marked focus formation. Collectively, these data demonstrate that eATP-induced IL-1β secretion is impaired by P. gingivalis fimbriae in a P2X7-dependent manner.

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.

Genetic exchange of fimbrial alleles exemplifies the adaptive virulence strategy of Porphyromonas gingivalis

Porphyromonas gingivalis is a gram–negative anaerobic bacterium, a member of the human oral microbiome, and a proposed “keystone” pathogen in the development of chronic periodontitis, an inflammatory disease of the gingiva. P. gingivalis is a genetically diverse species, and is able to exchange chromosomal DNA between strains by natural competence and conjugation. In this study, we investigate the role of horizontal DNA transfer as an adaptive process to modify behavior, using the major fimbriae as our model system, due to their critical role in mediating interactions with the host environment. We show that P. gingivalis is able to exchange fimbrial allele types I and IV into four distinct strain backgrounds via natural competence. In all recombinants, we detected a complete exchange of the entire fimA allele, and the rate of exchange varies between the different strain backgrounds. In addition, gene exchange within other regions of the fimbrial genetic locus was identified. To measure the biological implications of these allele swaps we compared three genotypes of fimA in an isogenic background, strain ATCC 33277. We demonstrate that exchange of fimbrial allele type results in profound phenotypic changes, including the quantity of fimbriae elaborated, membrane blebbing, auto-aggregation and other virulence-associated phenotypes. Replacement of the type I allele with either the type III or IV allele resulted in increased invasion of gingival fibroblast cells relative to the isogenic parent strain. While genetic variability is known to impact host-microbiome interactions, this is the first study to quantitatively assess the adaptive effect of exchanging genes within the pan genome cloud. This is significant as it presents a potential mechanism by which opportunistic pathogens may acquire the traits necessary to modify host-microbial interactions.

The alpha 7 nicotinic receptor agonist PHA-543613 hydrochloride inhibits Porphyromonas gingivalis-induced expression of interleukin-8 by oral keratinocytes

Objective

The alpha 7 nicotinic receptor (α7nAChR) is expressed by oral keratinocytes. α7nAChR activation mediates anti-inflammatory responses. The objective of this study was to determine if α7nAChR activation inhibited pathogen-induced interleukin-8 (IL-8) expression by oral keratinocytes.

Materials and methods

Periodontal tissue expression of α7nAChR was determined by real-time PCR. OKF6/TERT-2 oral keratinocytes were exposed to Porphyromonas gingivalis in the presence and absence of a α7nAChR agonist (PHA-543613 hydrochloride) alone or after pre-exposure to a specific α7nAChR antagonist (α-bungarotoxin). Interleukin-8 (IL-8) expression was measured by ELISA and real-time PCR. Phosphorylation of the NF-κB p65 subunit was determined using an NF-κB p65 profiler assay and STAT-3 activation by STAT-3 in-cell ELISA. The release of ACh from oral keratinocytes in response to P. gingivalis lipopolysaccharide was determined using a GeneBLAzer M3 CHO-K1-bla cell reporter assay.

Results

Expression of α7nAChR mRNA was elevated in diseased periodontal tissue. PHA-543613 hydrochloride inhibited P. gingivalis-induced expression of IL-8 at the transcriptional level. This effect was abolished when cells were pre-exposed to a specific α7nAChR antagonist, α-bungarotoxin. PHA-543613 hydrochloride downregulated NF-κB signalling through reduced phosphorylation of the NF-κB p65-subunit. In addition, PHA-543613 hydrochloride promoted STAT-3 signalling by maintenance of phosphorylation. Furthermore, oral keratinocytes upregulated ACh release in response to P. gingivalis lipopolysaccharide.

Conclusion

These data suggest that α7nAChR plays a role in regulating the innate immune responses of oral keratinocytes.

Looking in the Porphyromonas gingivalis cabinet of curiosities: the microbium, the host and cancer association

The past decades of biomedical research have yielded massive evidence for the contribution of the microbiome in the development of a variety of chronic human diseases. There is emerging evidence that Porphyromonas gingivalis, a well-adapted opportunistic pathogen of the oral mucosa and prominent constituent of oral biofilms, best known for its involvement in periodontitis, may be an important mediator in the development of a number of multifactorial and seemingly unrelated chronic diseases, such as rheumatoid arthritis and orodigestive cancers. Orodigestive cancers represent a large proportion of the total malignancies worldwide, and include cancers of the oral cavity, gastrointestinal tract and pancreas. For prevention and/or enhanced prognosis of these diseases, a good understanding of the pathophysiological mechanisms and the interaction between P. gingivalis and host is much needed. With this review, we introduce the currently accumulated knowledge on P. gingivalis's plausible association with cancer as a risk modifier, and present the putative cancer-promoting cellular and molecular mechanisms that this organism may influence in the oral mucosa.

Porphyromonas gingivalis-induced autophagy suppresses cell proliferation through G1 arrest in oral cancer cells

OBJECTIVES

We investigated the response of oral cancer cells to intracellular invasion of Porphyromonas gingivalis to define changes in the biological characteristics of oral cancer cells evoked by the presence of oral pathogenic bacteria within a tumour microenvironment.

DESIGNS

The proliferative activity, cell cycle, and autophagic response were evaluated in oral cancer cells infected with P. gingivalis 381. ROS generation was detected in these cells by DCFDA assay, and its role in the responses of oral cancer cells to P. gingivalis infection was further investigated.

RESUTLS

P. gingivalis inhibited proliferation of oral cancer cells by inducing G1 cell cycle arrest, but had no effect on apoptosis. Following infection with P. gingivalis, the expression of cyclin D1 and cdk4 was decreased in oral cancer cells, whereas p21, a Cdk inhibitor, was upregulated, in comparison with non-infected controls. Autophagy was prominently enhanced in these infected cells, presumably contributing to the suppressed proliferation. Further experiments revealed that such autophagic response was activated by the formation of reactive oxygen species, as evidenced by the lack of autophagic response and cell proliferation upon removal of reactive oxygen species.

CONCLUSIONS

These findings provide a novel insight into the mechanism by which cancer cells are influenced by tumour microenvironment including oral bacteria.

Genetic diversity in the oral pathogen Porphyromonas gingivalis: molecular mechanisms and biological consequences

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium that colonizes the human oral cavity. It is implicated in the development of periodontitis, a chronic periodontal disease affecting half of the adult population in the USA. To survive in the oral cavity, these bacteria must colonize dental plaque biofilms in competition with other bacterial species. Long-term survival requires P. gingivalis to evade host immune responses, while simultaneously adapting to the changing physiology of the host and to alterations in the plaque biofilm. In reflection of this highly variable niche, P. gingivalis is a genetically diverse species and in this review the authors summarize genetic diversity as it relates to pathogenicity in P. gingivalis. Recent studies revealing a variety of mechanisms by which adaptive changes in genetic content can occur are also reviewed. Understanding the genetic plasticity of P. gingivalis will provide a better framework for understanding the host-microbe interactions associated with periodontal disease.

Porphyromonas gingivalis modulates Pseudomonas aeruginosa-induced apoptosis of respiratory epithelial cells through the STAT3 signaling pathway

Pseudomonas aeruginosa is an important opportunistic bacterial pathogen, causing infections of respiratory and other organ systems in immunocompromised hosts that may invade and proliferate in mucosal epithelial cells to induce apoptosis. Previous studies suggest that oral bacteria, especially gram-negative periodontal pathogens, may enhance P. aeruginosa invasion into respiratory epithelial cells to augment tissue destruction. In this study, we investigated the effect of the periodontopathogen Porphyromonas gingivalis on P. aeruginosa-induced epithelial cell apoptosis. P. gingivalis invasion transiently inhibited P. aeruginosa-induced apoptosis in respiratory epithelial cells via the signal transducer and activator of transcription 3 (STAT3) signaling pathway. The activated STAT3 up-regulated the downstream anti-apoptotic moleculars survivin and B-cell leukemia-2 (bcl-2). This process was accompanied by down-regulation of pro-apoptosis molecular Bcl-2-associated death promoter (bad) and caspase-3 activity inhibition. In addition, the activation of the STAT3 pathway was affected by P. gingivalis in a dose-dependent manner. Finally, co-invasion of P. aeruginosa and P. gingivalis led to greater cell death compared with P. aeruginosa challenge alone. These results suggest that regulation of P. aeruginosa-induced apoptosis by P. gingivalis contributes to the pathogenesis of respiratory disease. Interference with this process may provide a potential therapeutic strategy for the treatment and prevention of respiratory disease.

Periodontal innate immune mechanisms relevant to obesity

Obesity affects over 35% of the adult population of the USA, and obesity-related illnesses have emerged as the leading cause of preventable death worldwide, according to the World Health Organization. Obesity's secondary morbidities include increased risk of cardiovascular disease, type II diabetes, and cancer, in addition to increased occurrence and severity of infections. Sedentary lifestyle and weight gain caused by consumption of a high-fat diet contribute to the development of obesity, with individuals having a body mass index (BMI) score > 30 being considered obese. Genetic models of obesity (ob/ob mice, db/db mice, and fa/fa rats) have been insufficient to study human obesity because of the overall lack of genetic causes for obesity in human populations. To date, the diet-induced obese (DIO) mouse model best serves research studies relevant to human health. Periodontal disease presents with a wide range of clinical variability and severity. Research in the past decade has shed substantial light on both the initiating infectious agents and host immunological responses in periodontal disease. Up to 46% of the general population harbors the microorganism(s) associated with periodontal disease, although many are able to limit the progression of periodontal disease or even clear the organism(s) if infected. In the last decade, several epidemiological studies have found an association between obesity and increased incidence of periodontal disease. This review focuses on exploring the immunological consequences of obesity that exacerbate effects of infection by pathogens, with focus on infection by the periodontal bacterium Porphyromonas gingivalis as a running example.

25-Hydroxyvitamin D3 attenuates experimental periodontitis through downregulation of TLR4 and JAK1/STAT3 signaling in diabetic mice

Vitamin D has been known to be closely associated with diabetes and periodontitis while the underlying mechanism has yet to be clarified. The present study aimed to discover the effect of 25-hydroxyvitamin D3 (25-OHD3) on glycemic control and periodontal health in mice with periodontitis superimposed on experimental diabetes (known as diabetic periodontitis). We showed that 25-OHD3 intraperitoneal injection attenuated diabetic periodontitis by reducing serum fasting blood glucose, glycosylated hemoglobin and TNF-α levels, which led to decreased alveolar bone loss. Immunohistochemical staining and western blot analysis of gingival epithelia revealed that vitamin D receptor (VDR) expression was enhanced upon 25-OHD3 treatment, while toll-like receptor 4 (TLR4) expression was reduced. The expressions of Janus family kinase (JAK) 1 and signal transducer and activator of transcription (STAT) 3 as well as their phosphorylation were inhibited in gingival epithelia of diabetic periodontitis mice, whereas the expression and phosphorylation of STAT1 remained unchanged. These results suggest that 25-OHD3 could improve diabetic periodontitis through downregulation of TLR4 and JAK1/STAT3 signaling in the gingival epithelium. Our study extends the previous findings on the regulation of diabetes with periodontitis, and may also provide a potential therapy for the patients with this disease.

Suppression of T-cell chemokines by Porphyromonas gingivalis

Porphyromonas gingivalis is a major pathogen in periodontal disease and is associated with immune dysbiosis. In this study, we found that P. gingivalis did not induce the expression of the T-cell chemokine IP-10 (CXCL10) from neutrophils, peripheral blood mononuclear cells (PBMCs), or gingival epithelial cells. Furthermore, P. gingivalis suppressed gamma interferon (IFN-γ)-stimulated release of IP-10, ITAC (CXCL11), and Mig (CXCL9) from epithelial cells and inhibited IP-10 secretion in a mixed infection with the otherwise stimulatory Fusobacterium nucleatum. Inhibition of chemokine expression occurred at the level of gene transcription and was associated with downregulation of interferon regulatory factor 1 (IRF-1) and decreased levels of Stat1. Ectopic expression of IRF-1 in epithelial cells relieved P. gingivalis-induced inhibition of IP-10 release. Direct contact between P. gingivalis and epithelial cells was not required for IP-10 inhibition. These results highlight the immune-disruptive potential of P. gingivalis. Suppression of IP-10 and other Th1-biasing chemokines by P. gingivalis may perturb the balance of protective and destructive immunity in the periodontal tissues and facilitate the pathogenicity of oral microbial communities.

The effects of Porphyromonas gingivalis on the cell cycle progression of human gingival epithelial cells

OBJECTIVE

Porphyromonas gingivalis is a major pathogen in the development and progression of periodontal disease. The interactions or cross-talk between bacteria and gingival epithelial cells drive bacteria to manipulate the cell cycle to favor bacterial survival and virulence expression within the host. This study aims to dissect the effects of P. gingivalis on the cell cycle in human gingival epithelial cells.

MATERIALS AND METHODS

We established a model of P. gingivalis invading IHGE cells. The cell cycle distribution of human gingival epithelial cells was analyzed by flow cytometry. Cyclin D and cyclin E mRNA and protein were detected by real-time PCR and Western blot, respectively.

RESULTS

Porphyromonas gingivalis-induced facilitation of cell growth was correlated with the acceleration of G1 phase of cell cycle. Cyclin D1 mRNA levels were significantly upregulated from 6 to 12 h after infection. Cyclin E protein and mRNA levels were elevated at 10 and 12 h after invasion.

CONCLUSIONS

We confirmed that P. gingivalis significantly enhances IHGE cell proliferation by promoting the G1/S transition, involving the up-regulation of cyclin D and cyclin E.

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.

Integrin α5β1-fimbriae binding and actin rearrangement are essential for Porphyromonas gingivalis invasion of osteoblasts and subsequent activation of the JNK pathway

BACKGROUND

Chronic periodontitis is an infectious disease of the periodontium, which includes the gingival epithelium, periodontal ligament and alveolar bone. The signature clinical feature of periodontitis is resorption of alveolar bone and subsequent tooth loss. The Gram-negative oral anaerobe, Porphyromonas gingivalis, is strongly associated with periodontitis, and it has been shown previously that P. gingivalis is capable of invading osteoblasts in a dose- and time-dependent manner resulting in inhibition of osteoblast differentiation and mineralization in vitro. It is not yet clear which receptors and cytoskeletal components mediate the invasive process, nor how the signaling pathways and viability of osteoblasts are affected by bacterial internalization. This study aimed to investigate these issues using an in vitro model system involving the inoculation of P. gingivalis ATCC 33277 into primary osteoblast cultures.

RESULTS

It was found that binding between P. gingivalis fimbriae and integrin α5β1 on osteoblasts, and subsequent peripheral condensation of actin, are essential for entry of P. gingivalis into osteoblasts. The JNK pathway was activated in invaded osteoblasts, and apoptosis was induced by repeated infections.

CONCLUSIONS

These observations indicate that P. gingivalis manipulates osteoblast function to promote its initial intracellular persistence by prolonging the host cell life span prior to its intercellular dissemination via host cell lysis. The identification of molecules critical to the interaction between P. gingivalis and osteoblasts will facilitate the development of new therapeutic strategies for the prevention of periodontal bone loss.

Porphyromonas gingivalis-nucleoside-diphosphate-kinase inhibits ATP-induced reactive-oxygen-species via P2X7 receptor/NADPH-oxidase signalling and contributes to persistence

Ligation of P2X7 receptors with a 'danger signal', extracellular ATP (eATP), has recently been shown to result in production of intracellular reactive-oxygen-species (ROS) in macrophages. We show that primary gingival epithelial cells (GECs) produce sustained, robust cellular ROS upon stimulation by eATP. The induction of ROS was mediated by P2X7 receptor signalling coupled with NADPH-oxidase activation, as determined by pharmacological inhibition and RNA interference. Furthermore, Porphyromonas gingivalis, an oral opportunistic pathogen, upregulated the antioxidant glutathione response, modulated eATP-induced cytosolic and mitochondrial ROS generated through P2X7 /NADPH-oxidase interactome, and subsequently blocked oxidative stress in GECs via temporal secretion of a P. gingivalis effector, nucleoside-diphosphate-kinase (Ndk). An ndk-deficient P. gingivalis mutant lacked the ability to inhibit ROS production and persist intracellularly following eATP stimulation. Treatment with recombinant Ndk significantly diminished eATP-evoked ROS production. P. gingivalis infection elicited a strong, time-dependent increase in anti-oxidativemitochondrial UCP2 levels, whereas ndk-deficient mutant did not cause any change. The results reveal a novel signalling cascade that is tightly coupled with eATP signalling and ROS regulation. Ndk by P. gingivalis counteracts these antimicrobial signalling activities by secreting Ndk, thus contributing to successful persistence of the pathogen.

Insights into the virulence of oral biofilms: discoveries from proteomics

This review covers developments in the study of polymicrobial communities, biofilms and selected areas of host response relevant to dental plaque and related areas of oral biology. The emphasis is on recent studies in which proteomic methods, particularly those using mass spectrometry as a readout, have played a major role in the investigation. The last 5-10 years have seen a transition of such methods from the periphery of oral biology to the mainstream, as in other areas of biomedical science. For reasons of focus and space, the authors do not discuss biomarker studies relevant to improved diagnostics for oral health, as this literature is rather substantial in its own right and deserves a separate treatment. Here, global gene regulation studies of plaque-component organisms, biofilm formation, multispecies interactions and host-microbe interactions are discussed. Several aspects of proteomics methodology that are relevant to the studies of multispecies systems are commented upon.

Proteomic and bioinformatic profile of primary human oral epithelial cells

Wounding of the oral mucosa occurs frequently in a highly septic environment. Remarkably, these wounds heal quickly and the oral cavity, for the most part, remains healthy. Deciphering the normal human oral epithelial cell (NHOEC) proteome is critical for understanding the mechanism(s) of protection elicited when the mucosal barrier is intact, as well as when it is breached. Combining 2D gel electrophoresis with shotgun proteomics resulted in identification of 1662 NHOEC proteins. Proteome annotations were performed based on protein classes, molecular functions, disease association and membership in canonical and metabolic signaling pathways. Comparing the NHOEC proteome with a database of innate immunity-relevant interactions (InnateDB) identified 64 common proteins associated with innate immunity. Comparison with published salivary proteomes revealed that 738/1662 NHOEC proteins were common, suggesting that significant numbers of salivary proteins are of epithelial origin. Gene ontology analysis showed similarities in the distributions of NHOEC and saliva proteomes with regard to biological processes, and molecular functions. We also assessed the interindividual variability of the NHOEC proteome and observed it to be comparable with other primary cells. The baseline proteome described in this study should serve as a resource for proteome studies of the oral mucosa, especially in relation to disease processes.

Beyond the red complex and into more complexity: the polymicrobial synergy and dysbiosis (PSD) model of periodontal disease etiology

Recent advancements in the periodontal research field are consistent with a new model of pathogenesis according to which periodontitis is initiated by a synergistic and dysbiotic microbial community rather than by select 'periopathogens', such as the 'red complex'. In this polymicrobial synergy, different members or specific gene combinations within the community fulfill distinct roles that converge to shape and stabilize a disease-provoking microbiota. One of the core requirements for a potentially pathogenic community to arise involves the capacity of certain species, termed 'keystone pathogens', to modulate the host response in ways that impair immune surveillance and tip the balance from homeostasis to dysbiosis. Keystone pathogens also elevate the virulence of the entire microbial community through interactive communication with accessory pathogens. Other important core functions for pathogenicity require the expression of diverse molecules (e.g. appropriate adhesins, cognate receptors, proteolytic enzymes and proinflammatory surface structures/ligands), which in combination act as community virulence factors to nutritionally sustain a heterotypic, compatible and proinflammatory microbial community that elicits a non-resolving and tissue-destructive host response. On the basis of the fundamental concepts underlying this model of periodontal pathogenesis, that is, polymicrobial synergy and dysbiosis, we term it the PSD model.

Transcriptional profiling of bone marrow stromal cells in response to Porphyromonas gingivalis secreted products

Periodontitis is an infectious inflammatory disease that destroys the tooth-supporting (periodontal) tissues. Porphyromonas gingivalis is an oral pathogen highly implicated in the pathogenesis of this disease. It can exert its effects to a number of cells, including osteogenic bone marrow stromal cells which are important for homeostastic capacity of the tissues. By employing gene microarray technology, this study aimed to describe the overall transcriptional events (>2-fold regulation) elicited by P. gingivalis secreted products in bone marrow stromal cells, and to dissect further the categories of genes involved in bone metabolism, inflammatory and immune responses. After 6 h of challenge with P. gingivalis, 271 genes were up-regulated whereas 209 genes were down-regulated, whereas after 24 h, these numbers were 259 and 109, respectively. The early (6 h) response was characterised by regulation of genes associated with inhibition of cell cycle, induction of apoptosis and loss of structural integrity, whereas the late (24 h) response was characterised by induction of chemokines, cytokines and their associated intracellular pathways (such as NF-κB), mediators of connective tissue and bone destruction, and suppression of regulators of osteogenic differentiation. The most strongly up-regulated genes were lipocalin 2 (LCN2) and serum amyloid A3 (SAA3), both encoding for proteins of the acute phase inflammatory response. Collectively, these transcriptional changes elicited by P. gingivalis denote that the fundamental cellular functions are hindered, and that the cells acquire a phenotype commensurate with propagated innate immune response and inflammatory-mediated tissue destruction. In conclusion, the global transcriptional profile of bone marrow stromal cells in response to P. gingivalis is marked by deregulated homeostatic functions, with implications in the pathogenesis of periodontitis.

Porphyromonas gingivalis mediates inflammasome repression in polymicrobial cultures through a novel mechanism involving reduced endocytosis

The interleukin (IL)-1β-processing inflammasome has recently been identified as a target for pathogenic evasion of the inflammatory response by a number of bacteria and viruses. We postulated that the periodontal pathogen, Porphyromonas gingivalis may suppress the inflammasome as a mechanism for its low immunogenicity and pathogenic synergy with other, more highly immunogenic periodontal bacteria. Our results show that P. gingivalis lacks signaling capability for the activation of the inflammasome in mouse macrophages. Furthermore, P. gingivalis can suppress inflammasome activation by another periodontal bacterium, Fusobacterium nucleatum. This repression affects IL-1β processing, as well as other inflammasome-mediated processes, including IL-18 processing and cell death, in both human and mouse macrophages. F. nucleatum activates IL-1β processing through the Nlrp3 inflammasome; however, P. gingivalis repression is not mediated through reduced levels of inflammasome components. P. gingivalis can repress Nlrp3 inflammasome activation by Escherichia coli, and by danger-associated molecular patterns and pattern-associated molecular patterns that mediate activation through endocytosis. However, P. gingivalis does not suppress Nlrp3 inflammasome activation by ATP or nigericin. This suggests that P. gingivalis may preferentially suppress endocytic pathways toward inflammasome activation. To directly test whether P. gingivalis infection affects endocytosis, we assessed the uptake of fluorescent particles in the presence or absence of P. gingivalis. Our results show that P. gingivalis limits both the number of cells taking up beads and the number of beads taken up for bead-positive cells. These results provide a novel mechanism of pathogen-mediated inflammasome inhibition through the suppression of endocytosis.

Porphyromonas gingivalis influences actin degradation within epithelial cells during invasion and apoptosis

Porphyromonas gingivalis, a Gram-negative oral pathogen, has been shown to induce apoptosis in human gingival epithelial cells, yet the underlining cellular mechanisms controlling this process are poorly understood. We have previously shown that the P. gingivalis proteases arginine and lysine gingipains, are necessary and sufficient to induce host cell apoptosis. In the present study, we demonstrate that 'P. gingivalis-induced apoptosis' is mediated through degradation of actin leading to cytoskeleton collapse. Stimulation of human gingival epithelial cells with P. gingivalis strains 33277 and W50 at moi:100 induced β-actin cleavage as early as 1 h and human serum inhibited this effect. By using gingipain-deficient mutants of P. gingivalis and purified gingipains, we demonstrate that lysine gingipain is involved in actin hydrolysis in a dose and time-dependent manner. Use of Jasplakinolide and cytochalasin D revealed that P. gingivalis internalization is necessary for actin cleavage. Further, we also show that lysine gingipain from P. gingivalis can cleave active caspase 3. Taken together, we have identified actin as a substrate for lysine gingipain and demonstrated a novel mechanism involved in microbial host cell invasion and apoptosis.

Nucleoside-diphosphate-kinase: a pleiotropic effector in microbial colonization under interdisciplinary characterization

Emerging evidence identifies multiple roles for nucleoside-diphosphate-kinase in host-microbe interaction. We provide the first synopsis of utilization of this molecule by various microorganisms during colonization of host tissues. Additionally, we propose novel mechanisms this effector may participate in, which could be crucial for microbial adaptation in chronic host infection.

Porphyromonas gingivalis SerB-mediated dephosphorylation of host cell cofilin modulates invasion efficiency

Porphyromonas gingivalis, a host-adapted opportunistic pathogen, produces a serine phosphatase, SerB, known to affect virulence, invasion and persistence within the host cell. SerB induces actin filament rearrangement in epithelial cells, but the mechanistic basis of this is not fully understood. Here we investigated the effects of SerB on the actin depolymerizing host protein cofilin. P. gingivalis infection resulted in the dephosphorylation of cofilin in gingival epithelial cells. In contrast, a SerB-deficient mutant of P. gingivalis was unable to cause cofilin dephosphorylation. The involvement of cofilin in P. gingivalis invasion was determined by quantitative image analysis of epithelial cells in which cofilin had been knocked down or knocked in with various cofilin constructs. siRNA-silencing of cofilin led to a significant decrease in numbers of intracellular P. gingivalis marked by an absence of actin colocalization. Transfection with wild-type cofilin or constitutively active cofilin both increased numbers of intracellular bacteria, while constitutively inactive cofilin abrogated invasion. Expression of LIM kinase resulted in reduced P. gingivalis invasion, an effect that was reversed by expression of constitutively active cofilin. These results show that P. gingivalis SerB activity induces dephosphorylation of cofilin, and that active cofilin is required for optimal invasion into gingival epithelial cells.

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.

Activation of Akt by the bacterial inositol phosphatase, SopB, is wortmannin insensitive

Salmonella enterica uses effector proteins translocated by a Type III Secretion System to invade epithelial cells. One of the invasion-associated effectors, SopB, is an inositol phosphatase that mediates sustained activation of the pro-survival kinase Akt in infected cells. Canonical activation of Akt involves membrane translocation and phosphorylation and is dependent on phosphatidyl inositide 3 kinase (PI3K). Here we have investigated these two distinct processes in Salmonella infected HeLa cells. Firstly, we found that SopB-dependent membrane translocation and phosphorylation of Akt are insensitive to the PI3K inhibitor wortmannin. Similarly, depletion of the PI3K regulatory subunits p85α and p85ß by RNAi had no inhibitory effect on SopB-dependent Akt phosphorylation. Nevertheless, SopB-dependent phosphorylation does depend on the Akt kinases, PDK1 and rictor-mTOR. Membrane translocation assays revealed a dependence on SopB for Akt recruitment to Salmonella ruffles and suggest that this is mediated by phosphoinositide (3,4) P(2) rather than phosphoinositide (3,4,5) P(3). Altogether these data demonstrate that Salmonella activates Akt via a wortmannin insensitive mechanism that is likely a class I PI3K-independent process that incorporates some essential elements of the canonical pathway.

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.

The role of reactive-oxygen-species in microbial persistence and inflammation

The mechanisms of chronic infections caused by opportunistic pathogens are of keen interest to both researchers and health professionals globally. Typically, chronic infectious disease can be characterized by an elevation in immune response, a process that can often lead to further destruction. Reactive-Oxygen-Species (ROS) have been strongly implicated in the aforementioned detrimental response by host that results in self-damage. Unlike excessive ROS production resulting in robust cellular death typically induced by acute infection or inflammation, lower levels of ROS produced by host cells are increasingly recognized to play a critical physiological role for regulating a variety of homeostatic cellular functions including growth, apoptosis, immune response, and microbial colonization. Sources of cellular ROS stimulation can include “danger-signal-molecules” such as extracellular ATP (eATP) released by stressed, infected, or dying cells. Particularly, eATP-P2X₇ receptor mediated ROS production has been lately found to be a key modulator for controlling chronic infection and inflammation. There is growing evidence that persistent microbes can alter host cell ROS production and modulate eATP-induced ROS for maintaining long-term carriage. Though these processes have yet to be fully understood, exploring potential positive traits of these “injurious” molecules could illuminate how opportunistic pathogens maintain persistence through physiological regulation of ROS signaling.

Human trophoblast responses to Porphyromonas gingivalis infection

Porphyromonas gingivalis is a periodontal pathogen that is also associated with preterm low-birthweight delivery. We investigated the transcriptional responses of human extravillous trophoblasts (HTR-8) to infection with P. gingivalis. Over 2000 genes were differentially regulated in HTR-8 cells by P. gingivalis. In ontology analyses of regulated genes, overpopulated biological pathways included mitogen-activated protein (MAP) kinase signaling and cytokine production. Immunoblots confirmed overexpression of the MAP kinase pathway components MEK3, p38 and Max. Furthermore, P. gingivalis infection induced phosphorylation and activation of MEK3 and p38. Increased production of interleukin (IL)-1beta and IL-8 by HTR-8 cells was demonstrated phenotypically by enzyme-linked immunosorbent assay of HTR-8 cell lysates and culture supernatants. Hence, infection of trophoblasts by P. gingivalis can impact signal transduction pathways and modulate cytokine expression, outcomes that could disrupt the maintenance of pregnancy.