Inactivation of membrane tumor necrosis factor alpha by gingipains from Porphyromonas gingivalis

Arginine-specific gingipains (RgpA/RgpB) knockdown modulates neutrophil machinery

Background

Gingipains are important virulence factors present in Porphyromonas gingivalis. Arginine-specific gingipains (RgpA and RgpB) are critically associated with increased proteolytic activity and immune system dysfunction, including neutrophilic activity. In this study, we assessed the impact of gingipains (RgpA and RgpB) on neutrophil function.

Methods

Peripheral blood samples were obtained; neutrophils were isolated and incubated with P. gingivalis A7436, W50, and the double RgpA/RgpB double knockout mutant E8 at MOI 20 for 2 hours. Neutrophil viability was assessed by Sytox staining. Phagocytic capacity and apoptosis were measured by flow cytometry. Superoxide release was measured by superoxide dismutase and cytochrome c reduction assay. Gene expression of TLR2, p47-phox, p67-phox, and P2 × 7was measured by qPCR. Inflammatory cytokine and chemokine production was measured by IL-1β, IL-8, RANTES, and TNF-α in cell supernatants.

Results

Neutrophil TLR2 gene expression was reduced in the absence of RgpA/RgpB (p < 0.05), while superoxide production was not significantly impacted. RgpA/RgpB-/- significantly impaired neutrophil phagocytic function (p < 0.05) and increased TNF-α production when compared with the wild-type control (p < 0.05). Neutrophil apoptosis was not altered when exposed to RgpA/RgpB-/- E8 (p > 0.05).

Conclusion

These data suggest that arginine-specific gingipains (RgpA/RgpB) can modulate neutrophil responses against P. gingivalis infection.

Local and Systemic Effects of Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a leading etiological agent in periodontitis. This infectious pathogen can induce a dysbiotic, proinflammatory state within the oral cavity by disrupting commensal interactions between the host and oral microbiota. It is advantageous for P. gingivalis to avoid complete host immunosuppression, as inflammation-induced tissue damage provides essential nutrients necessary for robust bacterial proliferation. In this context, P. gingivalis can gain access to the systemic circulation, where it can promote a prothrombotic state. P. gingivalis expresses a number of virulence factors, which aid this pathogen toward infection of a variety of host cells, evasion of detection by the host immune system, subversion of the host immune responses, and activation of several humoral and cellular hemostatic factors.

Express Diagnostics of Proteolytic Activity of Periodontopathogens-Methodological Approach

The species spectrum of the oral microbiome is considered to be the key factor in the development and progression of periodontal inflammatory disorders. The “red complex” including Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola has the highest pathogenic potential. These bacteria have several biochemical mechanisms that allow them to colonize and destroy periodontal tissues. Proteolytic enzymes play a crucial role in this process. Early diagnosis of pathological conditions induced by microbial contamination allows for the timely treatment of periodontitis. Otherwise, the development of the disease may lead to tooth loss. A total of 48 patients aged 18 to 65 years old who required professional oral hygiene were recruited for this clinical study. Microbial content analysis of dental plaque from the interdental space and the back of the tongue was performed using real-time PCR. To determine the proteolytic activity of oral bacteria, the new express diagnostic method was applied (diagnostic sensitivity, 0.875; specificity, 0.928). The results demonstrate a strong and significant correlation between the new method and the PCR analysis (r = 0.785, p < 0.001). These results show that the new express method can be valuable as an early diagnostic method for periodontal inflammatory disorders caused by the “red complex” bacteria.

Do Periodontal Pathogens or Associated Virulence Factors Have a Deleterious Effect on the Blood-Brain Barrier, Contributing to Alzheimer's Disease?

The central nervous system (CNS) is protected by a highly selective barrier, the blood-brain barrier (BBB), that regulates the exchange and homeostasis of bloodborne molecules, excluding xenobiotics. This barrier forms the first line of defense by prohibiting pathogens from crossing to the CNS. Aging and chronic exposure of the BBB to pathogens renders it permeable, and this may give rise to pathology in the CNS such as Alzheimer's disease (AD). Researchers have linked pathogens associated with periodontitis to neuroinflammation and AD-like pathology in vivo and in vitro. Although the presence of periodontitis-associated bacteria has been linked to AD in several clinical studies as DNA and virulence factors were confirmed in brain samples of human AD subjects, the mechanism by which the bacteria traverse to the brain and potentially influences neuropathology is unknown. In this review, we present current knowledge about the association between periodontitis and AD, the mechanism whereby periodontal pathogens might provoke neuroinflammation and how periodontal pathogens could affect the BBB. We suggest future studies, with emphasis on the use of human in vitro models of cells associated with the BBB to unravel the pathway of entry for these bacteria to the CNS and to reveal the molecular and cellular pathways involved in initiating the AD-like pathology. In conclusion, evidence demonstrate that bacteria associated with periodontitis and their virulence factors are capable of inflecting damage to the BBB and have a role in giving rise to pathology similar to that found in AD.

Proteolysis of Gingival Keratinocyte Cell Surface Proteins by Gingipains Secreted From Porphyromonas gingivalis - Proteomic Insights Into Mechanisms Behind Tissue Damage in the Diseased Gingiva

Porphyromonas gingivalis, the main etiologic agent of periodontitis, secretes cysteine proteases named gingipains. HRgpA and RgpB gingipains have Arg-specificity, while Kgp gingipain is Lys-specific. Together they can cleave an array of proteins and importantly contribute to the development of periodontitis. In this study we focused on gingipain-exerted proteolysis at the cell surface of human gingival epithelial cells [telomerase immortalized gingival keratinocytes (TIGK)] in order to better understand the molecular mechanisms behind tissue destruction in periodontitis. Using mass spectrometry, we investigated the whole sheddome/degradome of TIGK cell surface proteins by P. gingivalis strains differing in gingipain expression and by purified gingipains, and performed the first global proteomic analysis of gignpain proteolysis at the membrane. Incubation of TIGK cells with P. gingivalis resulted in massive degradation of proteins already at low multiplicity of infection, whereas incubating cells with purified gingipains resulted in more discrete patterns, indicative of a combination of complete degradation and shedding of membrane proteins. Most of the identified gingipain substrates were molecules involved in adhesion, suggesting that gingipains may cause tissue damage through cleavage of cell contacts, resulting in cell detachment and rounding, and consequently leading to anoikis. However, HRgpA and RgpB gingipains differ in their mechanism of action. While RgpB rapidly degraded the proteins, HRgpA exhibited a much slower proteolysis indicative of ectodomain shedding, as demonstrated for the transferrin receptor protein 1 (TFRC). These results reveal a molecular underpinning to P. gingivalis-induced tissue destruction and enhance our knowledge of the role of P. gingivalis proteases in the pathobiology of periodontitis. Proteomics data are available via ProteomeXchange with identifier PXD015679.

Host cell-surface proteins as substrates of gingipains, the main proteases of Porphyromonas gingivalis

Gingipains are extracellular cysteine proteases of the oral pathogen Porphyromonas gingivalis and are its most potent virulence factors. They can degrade a great variety of host proteins, thereby helping the bacterium to evade the host immune response, deregulate signaling pathways, trigger anoikis and, finally, cause tissue destruction. Host cell-surface proteins targeted by gingipains are the main focus of this review and span three groups of substrates: immune-regulatory proteins, signaling pathways regulators and adhesion molecules. The analysis of published data revealed that gingipains predominantly inactivate their substrates by cleaving them at one or more sites, or through complete degradation. Sometimes, gingipains were even found to initially shed their membrane substrates, but this was mostly just the first step in the degradation of cell-surface proteins.

Manipulation of Neutrophils by Porphyromonas gingivalis in the Development of Periodontitis

The pathogenesis of the chronic periodontal disease is associated with a skewed host inflammatory response to periodontal pathogens, such as Porphyromonas gingivalis, that accounts for the majority of periodontal tissue damage. Neutrophils are the most abundant leukocytes in periodontal pockets and depending on the stage of the disease, also plentiful PMNs are present in the inflamed gingival tissue and the gingival crevice. They are the most efficient phagocytes and eliminate pathogens by a variety of means, which are either oxygen-dependent or -independent. However, these secretory lethal weapons do not strictly discriminate between pathogens and host tissue. Current studies describe conflicting findings about neutrophil involvement in periodontal disease. On one hand literature indicate that hyper-reactive neutrophils are the main immune cell type responsible for this observed tissue damage and disease progression. Deregulation of neutrophil survival and functions, such as chemotaxis, migration, secretion of antimicrobial peptides or enzymes, and production of reactive oxygen species, contribute to observed tissue injury and the clinical signs of periodontal disease. On the other hand neutrophils deficiencies in patients and mice also result in periodontal phenotype. Therefore, P. gingivalis represents a periodontal pathogen that manipulates the immune responses of PMNs, employing several virulence factors, such as gingipains, serine proteases, lipid phosphatases, or fimbriae. This review will sum up studies devoted to understanding different strategies utilized by P. gingivalis to manipulate PMNs survival and functions in order to inhibit killing by a granular content, prolong inflammation, and gain access to nutrient resources.

Contribution of cationic amino acids toward the inhibition of Arg-specific cysteine proteinase (Arg-gingipain) by the antimicrobial dodecapeptide, CL(14-25), from rice protein

CL(14-25), a dodecapeptide, exhibits antimicrobial activity against Porphyromonas gingivalis with the 50% growth-inhibitory concentration (IC50 ) value of 145 µM, and arginine-specific gingipain (Rgp)-inhibitory activity. Kinetic analysis revealed that CL(14-25) is a mixed-type inhibitor, with inhibition constants (Ki and Ki ' values) of 1.4 × 10(-6) M and 4.3 × 10(-6) M, respectively. To elucidate the contributions of four cationic amino acid residues at the N- and C-termini of CL(14-25) toward Rgp-inhibitory activity, we investigated the Rgp-inhibitory activities of truncated and alanine-substituted analogs of CL(14-25). Rgp-inhibitory activities significantly decreased by truncated analogs, CL(15-25) and CL(16-25), whereas those of CL(14-24) and CL(14-23) were almost as high as that of CL(14-25). Rgp-inhibitory activities of alanine-substituted analogs, CL(R14A) and CL(R14A, R15A) also significantly decreased, whereas those of CL(K25A) and CL(R24A, K25A) were higher than that of CL(14-25). These results suggest that the arginine residue at position 15 substantially contributes to the Rgp-inhibitory activity and that the arginine residue at position 14 plays important roles in exerting Rgp-inhibitory activity. In this study, we demonstrated that CL(K25A) was a potent, dual function, peptide inhibitor candidate, exhibiting Rgp-inhibitory activity with Ki and Ki ' of 9.6 × 10(-7) M and 1.9 × 10(-6) M, respectively, and antimicrobial activity against P. gingivalis with an IC50 value of 51 µM.

Gingipains: Critical Factors in the Development of Aspiration Pneumonia Caused by Porphyromonas gingivalis

Aspiration pneumonia is a life-threatening infectious disease often caused by oral anaerobic and periodontal pathogens such as Porphyromonas gingivalis. This organism produces proteolytic enzymes, known as gingipains, which manipulate innate immune responses and promote chronic inflammation. Here, we challenged mice with P. gingivalis W83 and examined the role of gingipains in bronchopneumonia, lung abscess formation, and inflammatory responses. Although gingipains were not required for P. gingivalis colonization and survival in the lungs, they were essential for manifestation of clinical symptoms and infection-related mortality. Pathologies caused by wild-type (WT) P. gingivalis W83, including hemorrhage, necrosis, and neutrophil infiltration, were absent from lungs infected with gingipain-null isogenic strains or WT bacteria preincubated with gingipain-specific inhibitors. Damage to lung tissue correlated with systemic inflammatory responses, as manifested by elevated levels of TNF, IL-6, IL-17, and C-reactive protein. These effects were unequivocally dependent on gingipain activity. Gingipain activity was also implicated in the observed increase in IL-17 in lung tissues. Furthermore, gingipains increased platelet counts in the blood and activated platelets in the lungs. Arginine-specific gingipains made a greater contribution to P. gingivalis-related morbidity and mortality than lysine-specific gingipains. Thus, inhibition of gingipain may be a useful adjunct treatment for P. gingivalis-mediated aspiration pneumonia.

Self-assembled hybrid supraparticles that proteolytically degrade tumor necrosis factor-α

The strategies of pathogens to evade the human immune system are highly sophisticated and modulate a variety of inflammatory pathways. The similarities in the demands for modulation of inflammatory responses during disease treatment and during pathogenic infection provide opportunities to use pathogenic virulence factors to develop a new class of therapeutic materials that control inflammation. In this work, we harness a strategy from Porphyromonas gingivalis by transforming its major virulence factor, an arginine-specific cysteine protease, into self-assembled protease-inorganic hybrid supraparticles. The cysteine protease degrades the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α). It is an irreversible inhibition of TNF-α, which avoids some of the adverse effects of current TNF-α antagonists. We fabricated self-assembled porous supraparticles that specifically incorporate the pathogen-derived protease and showed improved inactivation of TNF-α over soluble enzyme, creating a potential therapeutic for various autoimmune diseases or other sources of inflammation.

Cleavage of host cytokeratin-6 by lysine-specific gingipain induces gingival inflammation in periodontitis patients

BACKGROUND/PURPOSE

Lysine-specific gingipain (Kgp) is a virulence factor secreted from Porphyromonas gingivalis (P. gingivalis), a major etiological bacterium of periodontal disease. Keratin intermediate filaments maintain the structural integrity of gingival epithelial cells, but are targeted by Kgp to produce a novel cytokeratin 6 fragment (K6F). We investigated the release of K6F and its induction of cytokine secretion.

METHODS

K6F present in the gingival crevicular fluid of periodontal disease patients and in gingipain-treated rat gingival epithelial cell culture supernatants was measured by matrix-assisted laser desorption/ionization time-of-flight mass spectrometer-based rapid quantitative peptide analysis using BLOTCHIP. K6F in gingival tissues was immunostained, and cytokeratin 6 protein was analyzed by immunofluorescence staining and flow cytometry. Activation of MAPK in gingival epithelial cells was evaluated by immunoblotting. ELISA was used to measure K6F and the cytokines release induced by K6F. Human gingival fibroblast migration was assessed using a Matrigel invasion chamber assay.

RESULTS

We identified K6F, corresponding to the C-terminus region of human cytokeratin 6 (amino acids 359-378), in the gingival crevicular fluid of periodontal disease patients and in the supernatant from gingival epithelial cells cultured with Kgp. K6F antigen was distributed from the basal to the spinous epithelial layers in gingivae from periodontal disease patients. Cytokeratin 6 on gingival epithelial cells was degraded by Kgp, but not by Arg-gingipain, P. gingivalis lipopolysaccharide or Actinobacillus actinomycetemcomitans lipopolysaccharide. K6F, but not a scrambled K6F peptide, induced human gingival fibroblast migration and secretion of interleukin (IL)-6, IL-8 and monocyte chemoattractant protein-1. These effects of K6F were mediated by activation of p38 MAPK and Jun N-terminal kinase, but not p42/44 MAPK or p-Akt.

CONCLUSION

Kgp degrades gingival epithelial cell cytokeratin 6 to K6F that, on release, induces invasion and cytokine secretion by human gingival fibroblasts. Thus, Kgp may contribute to the development of periodontal disease.

A pathogenic trace of Tannerella forsythia - shedding of soluble fully active tumor necrosis factor α from the macrophage surface by karilysin

Tannerella forsythia is implicated as a pathogen causing chronic and aggressive periodontitis. However, its virulence factors, including numerous putative proteases, are mostly uncharacterized. Karilysin is a newly described matrix metalloprotease-like enzyme of T. forsythia. Since pathogen-derived proteases may affect the host defense system via modulation of the cytokine network, the aim of this study was to determine the influence of karilysin on tumor necrosis factor-α (TNF-α). The results showed that karilysin cleaved the membrane form of TNF-α on the surface of macrophages, and that this led to an increased concentration of soluble TNF-α in the conditioned medium. Importantly, despite partial degradation of soluble TNF-α by karilysin, the released cytokine retained its biological activity, inducing apoptosis and stimulating autocrine pathway of pro-inflammatory gene expression. Notably, the observed effect required proteolytic activity by karilysin, since a catalytically inactive mutant of the enzyme did not affect TNF-α secretion. The shedding was independent of the activity of ADAM17, a major endogenous TNF-α converting enzyme. Karilysin-dependent TNF-α release from the cell surface is likely to occur in vivo because human plasma, the main constituent of gingival crevicular fluid, only slightly affected the sheddase activity of karilysin. Taken together, these results indicate that karilysin modulates the host immune response through regulation of TNF-α secretion, and should therefore be considered as a new virulence factor of T. forsythia.

Porphyromonas gingivalis gingipains selectively reduce CD14 expression, leading to macrophage hyporesponsiveness to bacterial infection

Cysteine proteases (gingipains) from Porphyromonas gingivalis are key virulence factors in chronic periodontitis. Innate immune receptors CD14, Toll-like receptor (TLR) 2 and TLR4 are important in P. gingivalis recognition. We examined the ability of gingipains to cleave CD14, TLR2 and TLR4, and the consequences for the cellular response to bacterial challenge. Macrophages were exposed to Arg (RgpA and RgpB)- and Lys (Kgp)-gingipains, and residual expression of TLR2, TLR4 and CD14 was determined by flow cytometry. The cellular response to live bacteria following exposure to purified gingipains was evaluated by TNFα production and bacterial phagocytosis. RgpA and Kgp decreased CD14 detection in a concentration (p = 0.0000002)- and time (p = 0.03)-dependent manner, whereas RgpB had no significant effect. TLR2 and TLR4 expression were unaffected. Reduction in CD14 expression was more efficient with Lys-gingipain than with Arg-gingipain. A reduced CD14 surface level correlated with decreased TNFα secretion and bacterial phagocytosis following challenge with live P. gingivalis, but the response to heat-killed bacteria was unaffected. Therefore, gingipains reduce CD14 expression without affecting expression of the bacterial-sensing TLRs. Reduced CD14 expression depends on the gingipain hemagglutinin/adhesion site and results in macrophage hyporesponsiveness to bacterial challenge. Further studies are needed to determine if reduced CD14 expression is linked to periodontitis induced by P. gingivalis.

kgp, rgpA, and rgpB DNA vaccines induce antibody responses in experimental peri-implantitis

BACKGROUND

Peri-implantitis is the key factor for implant failure. This study aims to evaluate kgp, rgpA, and rgpB DNA vaccines to induce an immune response and prevent peri-implantitis.

METHODS

The kgp, rgpA, and rgpB genes were amplified by polymerase chain reaction (PCR) from Porphyromonas gingivalis (Pg) ATCC 33277 and cloned into the pVAX1 vector. Titanium implants were placed into the mandibular bone of dogs. Three months later, the animals were divided into four groups, immunized with pVAX1-kgp, pVAX1-rgpA, pVAX1-rgpB, or pVAX1. Cotton ligatures infiltrated with Pg were tied around the neck of the implants. Immunoglobulin (Ig)G and IgA antibodies were detected by enzyme-linked immunosorbent assay before and after immunization.

RESULTS

The kgp, rgpA, and rgpB genes were successfully cloned into the pVAX1 plasmid. Animals immunized with pVAX1-kgp and pVAX1-rgpA showed higher titers of IgG and IgA antibodies compared to those before immunization (P <0.05) and compared to those that were immunized with pVAX1 and pVAX1-rgpB, whereas there were no significant differences in the animals treated with pVAX1 and pVAX1-rgpB. Furthermore, among these, the kgp DNA vaccine was more effective. The bone losses of the groups with pVAX1-kgp and pVAX1-rgpA were significantly attenuated.

CONCLUSION

pVAX1-kgp and pVAX1-rgpA DNA vaccines enhanced immunity responses and significantly retarded bone loss in experimental peri-implantitis animal models, whereas pVAX1-rgpB was ineffective.

Gingipains Inactivate a Cell Surface Ligand onPorphyromonas gingivalisThat Induces TLR2- and TLR4-Independent Signaling

Arginine-specific gingipain and lysine-specific gingipain are two major cysteine proteinases produced by Porphyromonas gingivalis. To clarify the role of gingipains in the interaction between P. gingivalis and the innate immune system, CHO reporter cells expressing TLR2 or TLR4 were stimulated with wildtype or gingipain-deficient P. gingivalis cells and activation of nuclear factor-kappaB in these cells was examined. While CHO/CD14 cells and 7.19 cells, an MD-2-defective mutant derived from CHO/CD14 cells, failed to respond to wild-type P. gingivalis, they responded to gingipain-deficient P. gingivalis. On the other hand, CHO/CD14/TLR2 cells responded to both wild-type and gingipain-deficient P. gingivalis. These results suggested that gingipains have no effects on TLR2-dependent signaling from P. gingivalis but have inhibitory effects on TLR2-and TLR4-independent signaling in CHO cells. Indeed, the activity of gingipain-deficient P. gingivalis to induce the activation of 7.19 cells was diminished after treatment of the bacterial cells with gingipains. We next partially purified bacterial cell components activating 7.19 cells from gingipain-deficient P. gingivalis. The activity of the partially purified components was diminished by treatment with heat or gingipains. It is also noteworthy that anti-CD14 mAb inhibited the activation of 7.19 cells induced by the partially purified components. These results indicated that the components of P. gingivalis that were able to induce TLR2-and TLR4-independent signaling were inactivated by gingipains before being recognized by CD14. The inactivation of the components would be helpful for P. gingivalis to escape from the innate immune system.

The role of RgpA in the pathogenicity of Porphyromonas gingivalis in the murine periodontitis model

AIM

To investigate the in vivo role of gingipains in Porphyromonas gingivalis' virulence, and suggest a possible host mechanisms through which the bacteria cause alveolar bone loss.

MATERIALS AND METHODS

Mice were orally infected with P. gingivalis wild type, or the gingipains mutants (RgpA⁻, Kgp⁻, RgpA⁻/Kgp⁻). Mice were analysed for alveolar bone loss using micro-computed tomography. The molecular effects of the proteases were evaluated using the subcutaneous chamber model. Mice were infected with P. gingivalis wild type or mutants. Exudates were analysed for cytokine and leukocytes levels, in vivo phagocytosis, P. gingivalis survival and serum anti-P. gingivalis IgG titres.

RESULTS

Only RgpA-expressing bacteria induced significantly alveolar bone loss, and suppressed phagocytosis resulting in increased survival of P. gingivalis in the chamber exudates. In addition, RgpA-expressing bacteria induced higher levels of leukocytes and cytokines 2 h post-infection, and reduced levels of serum anti-P. gingivalis IgG titres 7 days post-infection.

CONCLUSIONS

Our findings showed that elimination of RgpA from P. gingivalis diminished inflammation, but augmented phagocytosis and antibody titres, coincidental with reduced alveolar bone loss. These findings support the hypothesis that RgpA is a critical virulence factor in the pathogenesis of experimental periodontitis in mice.

Masters, marionettes and modulators: intersection of pathogen virulence factors and mammalian death receptor signaling

TNF and its receptor, TNFR1, are members of the TNF superfamily and play important roles during infection by orchestrating an inflammatory response. The key role that TNFR1 signaling plays in host defense singles it out as a frequent target of pathogen manipulation. This review describes how the TNFR1 signaling pathway is attacked by pathogen virulence factors and how the different TNFR1 signaling pathways, in particular the death signaling response, have evolved to counteract these pathogen manipulations. We examine recent data showing that other 'Death Receptors' in the TNF superfamily, namely TRAIL-R and Fas, also participate in the immune response to pathogens. Finally we explore how knowledge of the inhibition of these pathways is being translated for clinical applications.

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.

A novel virulence strategy for Pseudomonas aeruginosa mediated by an autotransporter with arginine-specific aminopeptidase activity

The opportunistic human pathogen, Pseudomonas aeruginosa, is a major cause of infections in chronic wounds, burns and the lungs of cystic fibrosis patients. The P. aeruginosa genome encodes at least three proteins exhibiting the characteristic three domain structure of autotransporters, but much remains to be understood about the functions of these three proteins and their role in pathogenicity. Autotransporters are the largest family of secreted proteins in Gram-negative bacteria, and those characterised are virulence factors. Here, we demonstrate that the PA0328 autotransporter is a cell-surface tethered, arginine-specific aminopeptidase, and have defined its active site by site directed mutagenesis. Hence, we have assigned PA0328 with the name AaaA, for arginine-specific autotransporter of P. aeruginosa. We show that AaaA provides a fitness advantage in environments where the sole source of nitrogen is peptides with an aminoterminal arginine, and that this could be important for establishing an infection, as the lack of AaaA led to attenuation in a mouse chronic wound infection which correlated with lower levels of the cytokines TNFα, IL-1α, KC and COX-2. Consequently AaaA is an important virulence factor playing a significant role in the successful establishment of P. aeruginosa infections.

We present a new Pseudomonas aeruginosa virulence factor that promotes chronic skin wound infections. We propose the name AaaA for this cell-surface tethered autotransporter. This arginine-specific aminopeptidase confers a growth advantage upon P. aeruginosa, providing a fitness advantage by creating a supply of arginine in chronic wounds where oxygen availability is limited and biofilm formation is involved. To our knowledge, this is the first mechanistic evidence linking the upregulation of genes involved in arginine metabolism with pathogenicity of P. aeruginosa, and we propose potential underlying mechanisms. The superbug P. aeruginosa is the leading cause of morbidity in cystic fibrosis patients. The ineffective host immune response to bacterial colonization is likely to play a critical role in the demise of these patients, making the possibility that AaaA could interface with the innate immune system, influencing the activity of iNOS and consequently the host's defence against invading pathogens. The surface localisation of AaaA makes it accessible to inhibitors that could reduce growth of P. aeruginosa during colonisation and alter biofilm formation, potentially improving the efficacy of current antimicrobials. Indeed, structurally related aminopeptidases play a central role in several disease states (stroke, diabetes, cancer, HIV and neuropsychiatric disorders), and inhibitors alleviate symptoms.

The K1K2 region of Lys-gingipain of Porphyromonas gingivalis blocks induction of HLA expression by gamma interferon

In the context of periodontal disease, cysteine proteinases or gingipains from Porphyromonas gingivalis have been implicated in the hydrolysis of cytokines, including gamma interferon (IFN-γ). This cytokine plays a crucial role in host defenses, in part, by regulating expression of major histocompatibility complex molecules. Our recent analysis has identified three structurally defined modules, K1, K2, and K3, of the hemagglutinin region of the lysine gingipain Kgp. These three structurally homologous domains have a common β-sandwich topology that is similar to that found in a superfamily of adhesins and carbohydrate binding domains. The three Kgp hemagglutinin modules are distinguished by variation in some of the loops projecting from the β-sandwich core. Recombinant products corresponding to both single and multidomain regions as well as native Kgp bound IFN-γ with similar affinities. Among the adhesin domain constructs, only the K1K2 polypeptide inhibited the upregulation of HLA-1 expression in a human erythroleukemia (K562) line induced by both recombinant and native IFN-γ. The K1K2 polypeptide also inhibited HLA-DR expression induced by IFN-γ in human umbilical vein endothelial cells. These effects were competitively inhibited by coincubation with sodium or potassium chloride solution. The N-terminal residues of IFN-γ were implicated in mediating the effect of K1K2, while antibody binding to loop 1 of K2 blocked the action of K1K2. The findings indicate the potential significance of structurally defined Kgp adhesin modules in the inactivation of IFN-γ but also the potential of K1K2 in locating the target for the catalytic domain of Kgp.

Pathogen-mediated proteolysis of the cell death regulator RIPK1 and the host defense modulator RIPK2 in human aortic endothelial cells

Porphyromonas gingivalis is the primary etiologic agent of periodontal disease that is associated with other human chronic inflammatory diseases, including atherosclerosis. The ability of P. gingivalis to invade and persist within human aortic endothelial cells (HAEC) has been postulated to contribute to a low to moderate chronic state of inflammation, although how this is specifically achieved has not been well defined. In this study, we demonstrate that P. gingivalis infection of HAEC resulted in the rapid cleavage of receptor interacting protein 1 (RIPK1), a mediator of tumor necrosis factor (TNF) receptor-1 (TNF-R1)-induced cell activation or death, and RIPK2, a key mediator of both innate immune signaling and adaptive immunity. The cleavage of RIPK1 or RIPK2 was not observed in cells treated with apoptotic stimuli, or cells stimulated with agonists to TNF-R1, nucleotide oligomerization domain receptor 1(NOD1), NOD2, Toll-like receptor 2 (TLR2) or TLR4. P. gingivalis-induced cleavage of RIPK1 and RIPK2 was inhibited in the presence of a lysine-specific gingipain (Kgp) inhibitor. RIPK1 and RIPK2 cleavage was not observed in HAEC treated with an isogenic mutant deficient in the lysine-specific gingipain, confirming a role for Kgp in the cleavage of RIPK1 and RIPK2. Similar proteolysis of poly (ADP-ribose) polymerase (PARP) was observed. We also demonstrated direct proteolysis of RIPK2 by P. gingivalis in a cell-free system which was abrogated in the presence of a Kgp-specific protease inhibitor. Our studies thus reveal an important role for pathogen-mediated modification of cellular kinases as a potential strategy for bacterial persistence within target host cells, which is associated with low-grade chronic inflammation, a hallmark of pathogen-mediated chronic inflammatory disorders.

Cleavage of IgG1 and IgG3 by gingipain K from Porphyromonas gingivalis may compromise host defense in progressive periodontitis

Degradation of immunoglobulins is an effective strategy of bacteria to evade the immune system. We have tested whether human IgG is a substrate for gingipain K of Porphyromonas gingivalis and found that the enzyme can hydrolyze subclass 1 and 3 of human IgG. The heavy chain of IgG(1) was cleaved at a single site within the hinge region, generating Fab and Fc fragments. IgG(3) was also cleaved within the heavy chain, but at several sites around the CH2 region. Investigation of the enzyme kinetics of IgG proteolysis by gingipain K, using FPLC- and isothermal titration calorimetry-based assays followed by Hill plots, revealed non-Michaelis-Menten kinetics involving a mechanism of positive cooperativity. In ex vivo studies, it was shown that gingipain K retained its IgG hydrolyzing activity in human plasma despite the high content of natural protease inhibitors; that IgG(1) cleavage products were detected in gingival crevicular fluid samples from patients with severe periodontitis; and that gingipain K treatment of serum samples from patients with high antibody titers against P. gingivalis significantly hindered opsonin-dependent phagocytosis of clinical isolates of P. gingivalis by neutrophils. Altogether, these findings underline a biological function of gingipain K as an IgG protease of pathophysiological importance.

Smoking and periodontal disease: discrimination of antibody responses to pathogenic and commensal oral bacteria

Smoking is an independent risk factor for the initiation, extent and severity of periodontal disease. This study examined the ability of the host immune system to discriminate commensal oral bacteria from pathogens at mucosal surfaces, i.e. oral cavity. Serum immunoglobulin (Ig)G antibody reactive with three pathogenic and five commensal oral bacteria in 301 current smokers (age range 21-66 years) were examined by enzyme-linked immunosorbent assay. Clinical features of periodontal health were used as measures of periodontitis. Antibody to the pathogens and salivary cotinine levels were related positively to disease severity; however, the antibody levels were best described by the clinical disease unrelated to the amount of smoking. The data showed a greater immune response to pathogens than commensals that was related specifically to disease extent, and most noted in black males. Significant correlations in individual patient responses to the pathogens and commensals were lost with an increasing extent of periodontitis and serum antibody to the pathogens. Antibody to Porphyromonas gingivalis was particularly distinct with respect to the discriminatory nature of the immune responses in recognizing the pathogens. Antibody responses to selected pathogenic and commensal oral microorganisms differed among racial groups and genders. The antibody response to the pathogens was related to disease severity. The level of antibody to the pathogens, and in particular P. gingivalis, was correlated with disease severity in black and male subsets of patients. The amount of smoking did not appear to impact directly serum antibody levels to these oral bacteria.

Porphyromonas gingivalis-dendritic cell interactions: consequences for coronary artery disease

An estimated 80 million US adults have one or more types of cardiovascular diseases. Atherosclerosis is the single most important contributor to cardiovascular diseases; however, only 50% of atherosclerosis patients have currently identified risk factors. Chronic periodontitis, a common inflammatory disease, is linked to an increased cardiovascular risk. Dendritic cells (DCs) are potent antigen presenting cells that infiltrate arterial walls and may destabilize atherosclerotic plaques in cardiovascular disease. While the source of these DCs in atherosclerotic plaques is presently unclear, we propose that dermal DCs from peripheral inflamed sites such as CP tissues are a potential source. This review will examine the role of the opportunistic oral pathogen Porphyromonas gingivalis in invading DCs and stimulating their mobilization and misdirection through the bloodstream. Based on our published observations, combined with some new data, as well as a focused review of the literature we will propose a model for how P. gingivalis may exploit DCs to gain access to systemic circulation and contribute to coronary artery disease. Our published evidence supports a significant role for P. gingivalis in subverting normal DC function, promoting a semimature, highly migratory, and immunosuppressive DC phenotype that contributes to the inflammatory development of atherosclerosis and, eventually, plaque rupture.

The native 67-kilodalton minor fimbria of Porphyromonas gingivalis is a novel glycoprotein with DC-SIGN-targeting motifs

We recently reported that the oral mucosal pathogen Porphyromonas gingivalis, through its 67-kDa Mfa1 (minor) fimbria, targets the C-type lectin receptor DC-SIGN for invasion and persistence within human monocyte-derived dendritic cells (DCs). The DCs respond by inducing an immunosuppressive and Th2-biased CD4(+) T-cell response. We have now purified the native minor fimbria by ion-exchange chromatography and sequenced the fimbria by tandem mass spectrometry (MS/MS), confirming its identity and revealing two putative N-glycosylation motifs as well as numerous putative O-glycosylation sites. We further show that the minor fimbria is glycosylated by ProQ staining and that glycosylation is partially removed by treatment with beta(1-4)-galactosidase, but not by classic N- and O-linked deglycosidases. Further monosaccharide analysis by gas chromatography-mass spectrometry (GC-MS) confirmed that the minor fimbria contains the DC-SIGN-targeting carbohydrates fucose (1.35 nmol/mg), mannose (2.68 nmol/mg), N-acetylglucosamine (2.27 nmol/mg), and N-acetylgalactosamine (0.652 nmol/mg). Analysis by transmission electron microscopy revealed that the minor fimbria forms fibers approximately 200 nm in length that could be involved in targeting or cross-linking DC-SIGN. These findings shed further light on molecular mechanisms of invasion and immunosuppression by this unique mucosal pathogen.

Degradation of vascular endothelial thrombomodulin by arginine- and lysine-specific cysteine proteases from Porphyromonas gingivalis

BACKGROUND

The endothelial cell surface glycoprotein thrombomodulin (TM) inhibits vascular coagulation and inflammation via regulation of thrombin-mediated activation of protein C. Porphyromonas gingivalis is the major periodontopathic bacterium and has been found in vessel walls and atherosclerotic lesions in humans. P. gingivalis-derived cysteine proteases (gingipains) are known to enhance inflammatory and coagulant responses of vascular endothelial cells. However, it has not been elucidated whether gingipains affect vascular endothelial TM.

METHODS

Purified arginine-specific gingipains (Rgps) and lysine-specific gingipain (Kgp) from P. gingivalis were used to investigate the effects of gingipains on recombinant human TM by immunoblot analyses. Flow cytometry and activated protein C assay were carried out to examine the effects of gingipains on vascular endothelial cell surface TM. Immunohistochemistry was performed to investigate TM expression in microvascular endothelia in gingival tissues taken from patients with periodontitis.

RESULTS

Rgps and Kgp cleaved TM in vitro. Endothelial cell surface TM was also degraded by Rgps. Thrombin-mediated activation of protein C was reduced by Rgps through TM inactivation. Gingival microvascular endothelial TM was reduced in patients with periodontitis.

CONCLUSIONS

P. gingivalis gingipains induced the degradation and inactivation of endothelial TM, which may promote vascular coagulation and inflammation. In addition, in vivo relevance was demonstrated by reduced expression of TM in gingival microvascular endothelia in patients with periodontitis, which may be involved in the pathogenesis of periodontitis.

Identification of a gingipain-sensitive surface ligand of Porphyromonas gingivalis that induces Toll-like receptor 2- and 4-independent NF-kappaB activation in CHO cells

Porphyromonas gingivalis is a major periodontal pathogen that has the pathogenic proteinases Arg-specific gingipain and Lys-specific gingipain. We previously found that a cell surface component on P. gingivalis is able to induce Toll-like receptor 2 (TLR2)- and TLR4-independent signaling in 7.19 cells and that this component can be degraded by gingipains. In this study, we purified this component from the P. gingivalis gingipain-null mutant KDP136 and obtained two candidate proteins. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry analysis showed that the proteins, with molecular masses of 123 and 43 kDa, were encoded by PGN_0748 and PGN_0728 (pgm6), respectively, in the P. gingivalis ATCC 33277 genome sequence. The PGN_0748-encoded protein, which we refer to as gingipain-sensitive ligand A (GslA), reacted with antiserum that could effectively inhibit the activity of KDP136 to induce NF-kappaB activation in 7.19 cells, but Pgm6 did not. To further determine what protein is responsible for the NF-kappaB activation, we constructed gslA, pgm6, and pgm6 pgm7 deletion mutants from KDP136. When 7.19 cells were exposed to those mutants, the gslA deletion mutant did not induce NF-kappaB activation, whereas the pgm6 and pgm6 pgm7 deletion mutants did. Furthermore, NF-kappaB activation in 7.19 cells induced by KDP136 was partially inhibited by antiserum against a recombinant protein expressed from the 5'-terminal third of gslA. These results indicate that GslA is one of the factors that induce NF-kappaB activation in 7.19 cells. Interestingly, the gslA gene was present in four of seven P. gingivalis strains tested. This restricted distribution might be associated with the virulence potential of each strain.

The gingipains: scissors and glue of the periodontal pathogen, Porphyromonas gingivalis

The anaerobic bacterium, Porphyromonas gingivalis, is associated with chronic periodontal disease (periodontitis or gum disease). The disease is not only the leading cause of tooth loss in the developed world, but is associated with a number of systemic diseases, such as cardiovascular disease and diabetes. The most potent virulence factors of this bacterium are the gingipains, three cysteine proteases that bind and cleave a wide range of host proteins. This article summarizes current knowledge of the structure and function of the enzymes, with a particular focus on what remains to be elucidated regarding the structure and function of the nonenzymatic adhesin domains of the high-molecular-weight forms of the proteases.

The host cytokine response to Porphyromonas gingivalis is modified by gingipains

BACKGROUND/AIMS

Clinical studies indicate that primary proinflammatory cytokines, such as interleukin-1beta (IL-1beta) are elevated in the gingival crevice around teeth with periodontitis but the secondary cytokines and chemokines, IL-6 and IL-8, are not. The human gingival epithelial cells (HGECs) lining the gingival sulcus respond to perturbation by microbes of dental plaque by releasing a wide range of cytokines. Porphyromonas gingivalis, a putative periodontal pathogen, possesses numerous virulence factors some of which directly impact on the host response. In the present study, we sought to determine how P. gingivalis influences the inflammatory cytokine responses.

METHODS

HGECs were challenged with P. gingivalis and other putative periodontal pathogens, and the resultant production of IL-1beta, IL-6, and IL-8 was assayed by enzyme-linked immunosorbent assay (ELISA). Culture supernatants and recombinant human cytokines were challenged with live P. gingivalis wild-type and gingipain-deficient strains and the resultant cytokine profile was assessed by ELISA and Western blot.

RESULTS

We show here that primary HGECs challenged with live P. gingivalis result in high levels of IL-1beta but not the related secondary cytokines IL-6 and IL-8. We further demonstrate that cytokine response differences are the result of the action of P. gingivalis proteases, with lysine gingipain being the most effective.

CONCLUSION

We conclude that P. gingivalis, through lysine gingipain, can subvert the protective host proinflammatory response by direct cytokine degradation. Changes in the crevicular cytokine profile have consequences in periodontal disease pathogenesis that should be considered in the development of diagnostic and therapeutic modalities.

Lysine-specific gingipain promotes lipopolysaccharide- and active-vitamin D3-induced osteoclast differentiation by degrading osteoprotegerin

Porphyromonas gingivalis is one of the major pathogens of periodontitis, a condition characterized by excessive alveolar bone resorption by osteoclasts. The bacterium produces cysteine proteases called gingipains, which are classified according to their cleavage-site specificity into Kgps (lysine-specific gingipains) and Rgps (arginine-specific gingipains). In the present study we examined the effects of gingipains on osteoclast differentiation. In co-cultures of mouse bone-marrow cells and osteoblasts, formation of multinucleated osteoclasts induced by 1alpha,25(OH)(2)D(3) (1alpha,25-dihydroxyvitamin D(3)) was augmented by Kgp but not by RgpB. A physiological concentration (0.1 nM) of 1alpha,25(OH)(2)D(3) induced the osteoclast formation in the presence of 100 nM Kgp to an extent comparable with that induced by 10 nM 1alpha,25(OH)(2)D(3). Kgp also enhanced osteoclastogenesis induced by various microbial components, including lipopolysaccharide. Combined use of Kgp and 1alpha,25(OH)(2)D(3) or lipopolysaccharide also increased the number of resorption pits developed on dentin slices, indicating that the osteoclasts formed in the presence of Kgp possess bone-resorbing activity. The enhanced osteoclastogenesis by Kgp was correlated with a depletion of osteoprotegerin in co-culture medium and was proteolytic-activity-dependent, since benzyloxycarbonyl-L-phenylalanyl-L-lysylacycloxyketone, an inhibitor of Kgp, completely abolished osteoclastogenesis induced by Kgp. Kgp digested osteoprotegerin, since its recombinant protein was susceptible to degradation by Kgp in the presence of serum. As a result, Kgp did not augment osteoclastogenesis in co-cultures of osteoprotegerin-deficient osteoblasts and bone-marrow cells. In addition, enhanced osteoclastogenesis by Kgp was abolished by an excess amount of recombinant osteoprotegerin. These findings suggest that degradation of osteoprotegerin is one of the mechanisms underlying promotion of osteoclastogenesis by Kgp.

Degradation of human alpha- and beta-defensins by culture supernatants of Porphyromonas gingivalis strain 381

Porphyromonas gingivalis produces proteases capable of degrading cytokines, host heme proteins and some antimicrobial peptides. In this study, we show that P. gingivalis culture supernatants fully or partially degrade human neutrophil peptide alpha-defensins and human beta-defensins after 30 min. This observation suggests that proteases from P. gingivalis degrade defensins and this activity could abrogate defensin-related innate immune functions.

Gingipain enzymes from Porphyromonas gingivalis preferentially bind immobilized extracellular proteins: a mechanism favouring colonization?

BACKGROUND AND OBJECTIVE

Porphyromonas gingivalis, an anaerobic bacterium associated with adult periodontal disease, employs a number of pathogenic mechanisms, including protease/adhesin complexes (gingipains), fimbriae and hemagglutinins, to maintain attachment within colonized hosts. Here we examined the binding of gingipains and whole, live P. gingivalis cells to immobilized extracellular matrix proteins in the presence of soluble forms of the same proteins, to investigate whether this may constitute a colonization mechanism in the oral environment.

MATERIAL AND METHODS

Binding of purified gingipain molecules and whole bacterial cells to immobilized matrix proteins was examined in the presence and absence of soluble competitors using enzyme-linked immunosorbent assays.

RESULTS

Purified gingipains or whole, live bacteria preferentially bound immobilized forms of matrix proteins, even in the presence of soluble forms of the same proteins. Fimbriae appeared to be redundant for adhesion to immobilized proteins in the presence of the gingipains, indicating that the protease/adhesins and hemagglutinins may be more important for adhesion under these conditions.

CONCLUSION

The data presented here provide evidence for a model of adhesion for P. gingivalis within the fluid environment of the oral cavity, where preferential binding of matrix-located proteins over soluble forms facilitates colonization of the host.

The broad effects of the functional IL-10 promoter-592 polymorphism: modulation of IL-10, TIMP-3, and OPG expression and their association with periodontal disease outcome

Periodontal diseases are infectious diseases, in which periodontopathogens trigger chronic inflammatory and immune responses that lead to tissue destruction. It occurs through the generation of metalloproteinases and the activation of bone resorption mechanisms. Anti-inflammatory cytokines such as IL-10 seem to attenuate periodontal tissue destruction through the induction of tissue inhibitors of metalloproteinases (TIMPs) and the inhibitor of osteoclastogenesis osteoprotegerin (OPG). A high individual variation in levels of IL-10 mRNA is verified in periodontitis patients, which is possibly determined by genetic polymorphisms. In this study, the IL-10 promoter -592C/A single nucleotide polymorphism (SNP), which is associated with a decrease in IL-10 production, was analyzed by RFLP in 116 chronic periodontitis (CP) patients and 173 control (C) subjects, and the IL-10, TIMPs, and OPG mRNA expression levels in diseased gingival tissues were determined by real-time-PCR. The IL-10-592 SNP CA (P=0.0012/OR=2.4/CI:1.4-4.1), AA (P=0.0458/OR=2.3/CI:1.1-4.9), and CA+AA (P=0.0006/OR=2.4/CI:1.4-3.4) genotypes and the allele A (P=0.0036/OR=1.7/CI:1.2-2.4) were found to be significantly more prevalent in the CP group when compared with control subjects. Both CA and AA genotypes were associated with lower levels of IL-10, TIMP-3, and OPG mRNA expression in diseased periodontal tissues and were also associated with disease severity as mean pocket depth. Taken together, the results presented here demonstrate that IL10-592 SNP is functional in CP, being associated with lower levels of IL-10 mRNA expression, which is supposed to consequently decrease the expression of the downstream genes TIMP-3 and OPG, and influence periodontal disease outcome.

Gingipain-dependent interactions with the host are important for survival of Porphyromonas gingivalis

Porphyromonas gingivalis, a major periodontal pathogen, must acquire nutrients from host derived substrates, overcome oxidative stress and subvert the immune system. These activities can be coordinated via the gingipains which represent the most significant virulence factor produced by this organism. In the context of our contribution to this field, we will review the current understanding of gingipain biogenesis, glycosylation, and regulation, as well as discuss their role in oxidative stress resistance and apoptosis. We can postulate a model, in which gingipains may be part of the mechanism for P. gingivalis virulence.

Blockade of protease-activated receptors on T cells correlates with altered proteolysis of CD27 by gingipains of Porphyromonas gingivalis

Cysteine proteinases, termed gingipains, of Porphyromonas gingivalis are able to inactivate a broad range of host proteins involved in cellular responses and have been implicated as key virulence factors in the onset and progression of adult periodontitis. In the present study, the high molecular weight Arg-gingipain, RgpA, produced a time- and concentration-dependent hydrolysis of the tumour necrosis factor (TNF)-alpha receptor family member CD27 on resting T cells. As a consequence of CD27 degradation, a reduction in CD27-ligation dependent co-stimulatory CD40L expression was observed. Concomitantly, RgpA activated the protease-activated receptors (PAR)-1, PAR-2 and PAR-4 and induced CD69 and CD25 expression on T cells, thereby demonstrating T cell activation. The Lys-gingipain Kgp demonstrated a low capacity to degrade CD27 but the ability to affect CD27 expression and biological activity was increased when T cells were pretreated with blocking peptide against PAR-2. CD70, the ligand for CD27 induced on activated B cells, was significantly reduced by RgpA treatment and weakly affected by Kgp. These findings suggest that while RgpA can activate T cells through PARs, the parallel action of direct hydrolysis of membrane CD27 as well as CD70 indicates a potential down-regulatory effect through inhibition of CD27/CD70-mediated cell activation in periodontitis.

Complement and c4 null alleles in severe chronic adult periodontitis

Severe forms of chronic periodontitis affect up to 10% of adults. Tumour necrosis factor and lymphotoxin-alpha genes in the major histocompatibility complex are associated with severe periodontitis. Complement factor C4 is a nearby, polymorphic, functionally relevant gene region. Although associated with chronic mucosal infections, C4 deficiencies have not been assessed in adult periodontitis patients. We tested whether complement levels are systemically altered and C4 deficiencies associated with severe chronic periodontitis. In a case-control study, we analysed levels of plasma C3, and C4, serum classical pathway haemolytic activity, C4 allotypes and C4 gene numbers in 37 patients with severe chronic periodontitis and in 150 voluntary controls. Plasma levels of C3 were higher, and classical pathway haemolytic activity was lower in patients than in controls. Partial C4 gene deficiencies were more frequent in patients than in controls (odds ratio 2.4, 95% confidence interval 1.1-5.5, P = 0.032). Changes in complement levels may reflect chronic, recurring inflammation. C4 gene deficiencies are associated with predisposition to chronic periodontitis.

Interleukin-1? stimulation in monocytes by periodontal bacteria: antagonistic effects of Porphyromonas gingivalis

Periodontal pathogenic bacteria are associated with elevated levels of interleukin-1alpha (IL-1alpha) but it is unclear if all species can induce cytokine production equally. Porphyromonas gingivalis may be able antagonize IL-1alpha induced by other species through the activity of its proteases or lipopolysaccharide (LPS). Monomac-6 cells and primary human monocytes were treated with culture supernatants from Porphyromonas gingivalis, Fusobacterium nucleatum, Campylobacter rectus, Actinobacillus actinomycetemcomitans, Prevotella intermedius, Veillonella atypical and Prevotella nigrescens. IL-1alpha protein levels were measured after 6 h of incubation. In addition, monocytes were co-stimulated with supernatants from P. gingivalis and other bacteria. The role of P. gingivalis proteases was tested using Arg-X and Lys-X mutant strains. The role of LPS was investigated using purified P. gingivalis LPS and polymixin depletion. All species tested induced significant IL-1alpha production, but P. gingivalis was the weakest. Co-stimulation of monocytes with P. gingivalis antagonized the ability of other bacterial species to induce IL-1alpha production. This effect was at its greatest with C. rectus (resulting in a 70% reduction). Gingipain mutant strains and chemical inhibition of protease activity did not reduce antagonistic activity. However, 100 ng/ml of P. gingivalis LPS can reproduce the antagonistic activity of P. gingivalis culture supernatants. Periodontitis-associated bacterial species stimulate IL-1alpha production by monocytes. P. gingivalis can antagonize this effect, and its LPS appears to be the crucial component. This study highlights the importance of mixed infections in the pathogenesis of periodontal disease because reduction of pro-inflammatory cytokine levels may impair the ability of the host to tackle infection.

Arginine-specific gingipains from Porphyromonas gingivalis deprive protective functions of secretory leucocyte protease inhibitor in periodontal tissue

Chronic periodontitis is correlated with Porphyromonas gingivalis infection. In this study, we found that the expression of secretory leucocyte protease inhibitor (SLPI), an endogenous inhibitor for neutrophil-derived proteases, was reduced in gingival tissues with chronic periodontitis associated with P. gingivalis infection. The addition of vesicles of P. gingivalis decreased the amount of SLPI in the media of primary human gingival keratinocytes compared to untreated cultures. We therefore investigated how arginine-specific gingipains (Rgps) affect the functions of SLPI, because Rgps are the major virulence factors in the vesicles and cleave a wide range of in-host proteins. We found that Rgps digest SLPI in vitro, suppressing the release of SLPI. Rgps proteolysis of SLPI disrupted SLPI functions, which normally suppresses neutrophil elastase and neutralizes pro-inflammatory effects of bacterial cell wall compounds in cultured human gingival fibroblasts. The protease inhibitory action of SLPI was not exerted towards Rgps. These results suggest that Rgps reduce the protective effects of SLPI on neutrophil proteases and bacterial proinflammatory compounds, by which disease in gingival tissue may be accelerated at the sites with P. gingivalis infection.

Effects of elastase and cathepsin G on the levels of membrane and soluble TNFα

Neutrophil elastase (NE) and cathepsin G (CG), the proteolytic enzymes localized in azurophil granules of neutrophils (PMN), are involved in PMN responses to various stimuli. When released at sites of inflammation, they participate in the degradation of numerous proteins involved in the regulation of the immune response. In this study, we employed ADAM17(-/-) fibroblasts stably transfected with cDNA of human pro-tumor necrosis factor alpha (proTNFalpha) (ADAM17(-/-)TNF(+)) to investigate the effects of NE and CG on shedding and degradation of TNFalpha. Both NE and CG were found to diminish the level of membrane TNFalpha (mTNFalpha) as measured by flow cytometry. This process was accompanied by the accumulation of biologically active soluble TNFalpha (sTNFalpha) in the culture medium, as determined by an increase in both the cytotoxic activity of TNFalpha and its ability to serve as a co-stimulator in the induction of inducible nitric oxide synthase (iNOS). However, in contrast to CG, NE at high concentrations was able to degrade sTNFalpha released from the cell surface. Using soluble recombinant human TNFalpha, we identified Val(93)-Ala(94) and Val(117)-Glu(118) as the NE cleavage sites within the sTNFalpha molecule. Taken together, the ability of NE and CG to modulate levels of membrane and soluble forms of TNFalpha may contribute to the proinflammatory activity of neutrophils.