Gingipain-Specific IgG in the Sera of Patients With Periodontal Disease Is Necessary for Opsonophagocytosis ofPorphyromonas 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.

A dual functional polypeptide with antibacterial and anti-inflammatory properties for the treatment of periodontitis

Periodontitis has been reported as the sixth most prevalent disease in human beings. This destructive disease is closely related to systemic diseases. Existing local drug delivery systems for periodontitis suffer from poor antibacterial effect and drug resistance. Inspired by the pathogenesis of periodontitis, we implemented a strategy to construct a dual functional polypeptide LL37-C15, which exhibited remarkable antibacterial effect against P. gingivalis and A. actinomycetemcomitans. In addition, LL37-C15 inhibits the release of pro-inflammatory cytokines by controlling the inflammatory pathway and reversing macrophage M1. Furthermore, the anti-inflammatory effect of LL37-C15 was also verified in vivo in a periodontitis rat model through the morphometry and histological observations of alveolar bone, hematoxylin-eosin, and Trap staining in gingival tissue. The results of molecular dynamics simulations showed that LL37-C15 could selectively destroy the bacterial cell membrane and protect the animal cell membrane in a self-destructive manner. The results showed that the polypeptide LL37-C15, as a novel promising therapeutic agent, exhibited a great potential for the periodontitis management. What's more, this dual functional polypeptide provides a promising strategy for building a multifunctional therapeutic platform against the inflammation and other diseases.

Immunization with cell-free-generated vaccine protects from Porphyromonas gingivalis-induced alveolar bone loss

Introduction

Periodontal diseases (PD) are complex oral inflammatory diseases initiated by keystone bacteria such as Porphyromonas gingivalis. A vaccine for PD is desirable as clinical treatment involves protracted maintenance strategies aimed to retain dentition. Although prior immunization approaches targeting P. gingivalis have reported variable success in limiting facets of disease such as oral bone loss, it remains that a vaccine for this disease may be attainable.

Aim

To investigate cell‐free protein synthesis (CFPS) as a platform to produce vaccinable targets suitable for efficacy testing in a P. gingivalis‐induced murine oral bone loss model.

Materials and Methods

Recombinantly generated P. gingivalis minor fimbriae protein (Mfa1), RgpA gingipain hemagglutinin domain 1 (HA1), and RgpA gingipain hemagglutinin domain 2 (HA2) were combined in equivalent doses in adjuvants and injected intramuscularly to immunize mice. Serum levels of protein‐specific antibody were measured by ELISA, and oral bone levels were defined by morphometrics.

Results

Recombinantly generated P. gingivalis proteins possessed high fidelity to predicted size and elicited protein‐specific IgG following immunization. Importantly, immunization with the vaccine cocktail protected from P. gingivalis elicited oral bone loss.

Conclusion

These data verify the utility of the CFPS technology to synthesize proteins that have the capacity to serve as novel vaccines.

Mechanisms by which Porphyromonas gingivalis evades innate immunity

The oral cavity is home to unique resident microbial communities whose interactions with host immunity are less frequently studied than those of the intestinal microbiome. We examined the stimulatory capacity and the interactions of two oral bacteria, Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum), on Dendritic Cell (DC) activation, comparing them to the effects of the well-studied intestinal microbe Escherichia coli (E. coli). Unlike F. nucleatum and E. coli, P. gingivalis failed to activate DCs, and in fact silenced DC responses induced by F. nucleatum or E. coli. We identified a variant strain of P. gingivalis (W50) that lacked this immunomodulatory activity. Using biochemical approaches and whole genome sequencing to compare the two substrains, we found a point mutation in the hagA gene. This protein is though to be involved in the alteration of the PorSS/gingipain pathway, which regulates protein secretion into the extracellular environment. A proteomic comparison of the secreted products of the two substrains revealed enzymatic differences corresponding to this phenotype. We found that P. gingivalis secretes gingipain(s) that inactivate several key proinflammatory mediators made by DCs and/or T cells, but spare Interleukin-1 (IL-1) and GM-CSF, which can cause capillary leaks that serve as a source of the heme that P. gingivalis requires for its survival, and GM-CSF, which can cause epithelial-cell growth. Taken together, our results suggest that P. gingivalis has evolved potent mechanisms to modulate its virulence factors and dampen the innate immune response by selectively inactivating most proinflammatory cytokines.

Vaccination with recombinant RgpA peptide protects against Porphyromonas gingivalis-induced bone loss

OBJECTIVE

Following Porphyromonas gingivalis infection in mice, the efficacy of vaccination by recombinant and native RgpA in modulating the early local anti-inflammatory and immune responses and periodontal bone loss were examined.

MATERIAL AND METHODS

Using the subcutaneous chamber model, exudates were analyzed for cytokines after treatment with native RgpA and adjuvant (test), or adjuvant and saline alone (controls). Mice were also immunized with recombinant RgpA after being orally infected with P. gingivalis. After 6 wk, serum was examined for anti-P. gingivalis IgG1 and IgG2a titers and for alveolar bone resorption.

RESULTS

Immunization with native RgpA shifted the immune response toward an anti-inflammatory response as demonstrated by decreased proinflammatory cytokine IL-1β production and greater anti-inflammatory cytokine IL-4 in chamber exudates. Systemically, immunization with recombinant RgpA peptide prevented alveolar bone loss by 50%, similar to immunization with heat-killed whole bacteria. Furthermore, recombinant RgpA shifted the humoral response toward high IgG1 and low IgG2a titers, representing an in vivo anti-inflammatory response.

CONCLUSIONS

The present study demonstrates the potential of RgpA to shift the early local immune response toward an anti-inflammatory response while vaccination with recRgpA protected against P. gingivalis-induced periodontitis.

Liver X receptors contribute to periodontal pathogen-elicited inflammation and oral bone loss

Periodontal diseases are chronic oral inflammatory diseases that are polymicrobial in nature. The presence of specific bacteria in subgingival plaque such as Porphyromonas gingivalis is associated with microbial dysbiosis and the modulation of host immune response. Bacterially elicited innate immune activation and inflammation are key elements implicated in the destruction of soft and hard tissues supporting the teeth. Liver X receptors (LXRs) are nuclear hormone receptors with important function in lipid homeostasis, inflammation, and host response to infection; however, their contribution to chronic inflammatory diseases such as periodontal disease is not understood. The aim of this study was to define the contribution of LXRs in the development of immune response to P. gingivalis and to assess the roles that LXRs play in infection-elicited oral bone loss. Employing macrophages, we observed that P. gingivalis challenge led to reduced LXRα and LXRβ gene expression compared with that observed with unchallenged wild-type cells. Myeloid differentiation primary response gene 88 (MyD88)-independent, Toll/interleukin-1 receptor-domain-containing adapter-inducing interferon-β (TRIF)-dependent signaling affected P. gingivalis-mediated reduction in LXRα expression, whereas neither pathway influenced the P. gingivalis effect on LXRβ expression. Employing LXR agonist and mice deficient in LXRs, we observed functional effects of LXRs in the development of a P. gingivalis-elicited cytokine response at the level of the macrophage, and participation of LXRs in P. gingivalis-elicited oral bone loss. These findings identify novel importance for LXRs in the pathogenesis of P. gingivalis infection-elicited inflammation and oral bone loss.

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.

Interaction of the core fragments of the LL-37 host defense peptide with actin

Host defense peptides are effector molecules of the innate immunity that possess antimicrobial and health-promoting properties. Due to their potential therapeutic activities, host defense peptides are being explored as alternatives for antibiotics. The human LL-37 and its shorter, cost-effective, bactericidal core peptide derivates have been suggested for their therapeutic potential. Bacteria evade host defense peptides by proteolytic inactivation. Actin released from necrotized cells and abundant in infected sites was shown to bind and protect LL-37 from microbial proteolytic degradation, and to enable the peptide's antimicrobial action despite the presence of the proteases. Here, we characterized the interactions of the 10-13 residues long LL-37 core peptides with actin. We show that the LL-37 core peptides associate with actin with a lower affinity than that of LL-37. Their association with actin, which is very ionic strength sensitive, is mainly based on electrostatic interactions. Likewise, the antimicrobial activity against Escherichia coli of the minimal antimicrobial peptide KR-12 but not FK-13 nor LL-37 is also very sensitive to salts. In addition, the antimicrobial activity of the FK-13 core peptide is protected by actin against the tested bacterial proteases in a similar manner to that of LL-37, supporting its potential for therapeutic use.

Role of Porphyromonas gingivalis gingipains in multi-species biofilm formation

Background

Periodontal diseases are polymicrobial diseases that cause the inflammatory destruction of the tooth-supporting (periodontal) tissues. Their initiation is attributed to the formation of subgingival biofilms that stimulate a cascade of chronic inflammatory reactions by the affected tissue. The Gram-negative anaerobes Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola are commonly found as part of the microbiota of subgingival biofilms, and they are associated with the occurrence and severity of the disease. P. gingivalis expresses several virulence factors that may support its survival, regulate its communication with other species in the biofilm, or modulate the inflammatory response of the colonized host tissue. The most prominent of these virulence factors are the gingipains, which are a set of cysteine proteinases (either Arg-specific or Lys-specific). The role of gingipains in the biofilm-forming capacity of P. gingivalis is barely investigated. Hence, this in vitro study employed a biofilm model consisting of 10 “subgingival” bacterial species, incorporating either a wild-type P. gingivalis strain or its derivative Lys-gingipain and Arg-gingipan isogenic mutants, in order to evaluate quantitative and qualitative changes in biofilm composition.

Results

Following 64 h of biofilm growth, the levels of all 10 species were quantified by fluorescence in situ hybridization or immunofluorescence. The wild-type and the two gingipain-deficient P. gingivalis strains exhibited similar growth in their corresponding biofilms. Among the remaining nine species, only the numbers of T. forsythia were significantly reduced, and only when the Lys-gingipain mutant was present in the biofilm. When evaluating the structure of the biofilm by confocal laser scanning microscopy, the most prominent observation was a shift in the spatial arrangement of T. denticola, in the presence of P. gingivalis Arg-gingipain mutant.

Conclusions

The gingipains of P. gingivalis may qualitatively and quantitatively affect composition of polymicrobial biofilms. The present experimental model reveals interdependency between the gingipains of P. gingivalis and T. forsythia or T. denticola.

Immuno-pathogenesis of Periodontal Disease: Current and Emerging Paradigms

Periodontal disease (PD) is a highly complex disease involving many factors; however, two principal facets central to initiation and progression of the majority of PD are the composition of the microbes in the sub-gingival plaque, and the host immune response to these organisms. Numerous studies point to the complexity of PD, and to the fact that despite innate and adaptive immune activation, and resultant inflammation, our immune response fails to cure disease. Stunning new findings have begun to clarify several complexities of the host-pathogen interaction of PD pointing to key roles for microbial dysboisis and immune imbalance in the pathogenesis of disease. Furthermore, these investigations have identified novel translational opportunities to intercede in PD treatment. In this review we will highlight a select few recent findings in innate and adaptive immunity, and host pathogen interactions of PD at a micro-environmental level that may have profound impact on PD progression.

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.

Destructive and protective roles of cytokines in periodontitis: a re-appraisal from host defense and tissue destruction viewpoints

Periodontal diseases (PD) are chronic infectious inflammatory diseases characterized by the destruction of tooth-supporting structures, being the presence of periodontopathogens required, but not sufficient, for disease development. As a general rule, host inflammatory mediators have been associated with tissue destruction, while anti-inflammatory mediators counteract and attenuate disease progression. With the discovery of several T-cell subsets bearing distinct immunoregulatory properties, this pro- vs. anti-inflammatory scenario became more complex, and a series of studies has hypothesized protective or destructive roles for Th1, Th2, Th17, and Treg subpopulations of polarized lymphocytes. Interestingly, the "protective vs. destructive" archetype is usually considered in a framework related to tissue destruction and disease progression. However, it is important to remember that periodontal diseases are infectious inflammatory conditions, and recent studies have demonstrated that cytokines (TNF-α and IFN-γ) considered harmful in the context of tissue destruction play important roles in the control of periodontal infection. Therefore, in this review, the state-of-the-art knowledge concerning the protective and destructive roles of host inflammatory immune response will be critically evaluated and discussed from the tissue destruction and control-of-infection viewpoints.

Saliva enables the antimicrobial activity of LL-37 in the presence of proteases of Porphyromonas gingivalis

Proteolysis is a common microbial virulence mechanism that enables the destruction of host tissue and evasion from host defense mechanisms. Antimicrobial peptides, also known as host defense peptides, are effector molecules of the innate immunity that demonstrate a broad range of antimicrobial and immunoregulatory activities. Deficiency of the human LL-37 antimicrobial peptide was previously correlated with severe periodontal disease. Porphyromonas gingivalis, the major pathogen associated with periodontitis, is highly proteolytic. In this study, P. gingivalis was found capable of degrading LL-37 by utilizing its arginine-specific gingipains. Saliva collected from volunteers with a healthy periodontium protected LL-37 from proteolysis by P. gingivalis. Salivary protection of LL-37 was heat resistant and specific and enabled LL-37 to inhibit growth of Escherichia coli in the presence of the P. gingivalis proteases. Previously, saliva and other body fluids have been shown to inhibit the antimicrobial activity of LL-37. Here we demonstrate that at a cost of a small reduction in the bactericidal activity of LL-37, saliva enables the antibacterial activity of LL-37 despite the presence of proteases secreted by the main periodontopathogen.

Neutrophils in chronic and aggressive periodontitis in interaction with Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans

BACKGROUND AND OBJECTIVE

This study analyzed the interaction of Porphyromonas gingivalis ATCC 33277 and Aggregatibacter actinomycetemcomitans Y4 with peripheral blood polymorphonuclear neutrophils taken from patients with aggressive periodontitis and chronic periodontitis.

MATERIAL AND METHODS

Peripheral blood polymorphonuclear neutrophils obtained from 12 patients with chronic periodontitis, six patients with aggressive periodontitis and 12 healthy controls were exposed to P. gingivalis and A. actinomycetemcomitans following opsonization of the bacteria using the patient's own serum. Serum immunoglobulin G (IgG) levels against both periodontopathogens were measured. Phagocytosis and killing of the bacteria, as well as the extracellular human neutrophil elastase activity, were quantified. The total amount and the extracellular release of reactive oxygen species were measured using luminol-dependent and isoluminol-dependent chemiluminescence.

RESULTS

Polymorphonuclear neutrophils from patients with chronic (62.16 +/- 19.39%) and aggressive (43.26 +/- 26.63%) periodontitis phagocytosed more P. gingivalis than the healthy controls (24.43 +/- 19.87%) at the 30-min time point after exposure to the bacteria (p < 0.05). High serum IgG levels against P. gingivalis and A. actinomycetemcomitans were detected in subjects with periodontitis. Polymorphonuclear neutrophils from subjects with chronic and aggressive periodontitis released significantly more reactive oxygen species and demonstrated greater human neutrophil elastase activity in the absence of any stimulus than polymorphonuclear neutrophils from healthy controls (p < 0.05). Polymorphonuclear neutrophils in chronic periodontitis released significantly more reactive oxygen species when exposed to P. gingivalis and A. actinomycetemcomitans than polymorphonuclear neutrophils in aggressive periodontitis.

CONCLUSION

High serum IgG levels against P. gingivalis and A. actinomycetemcomitans promote phagocytosis in periodontitis. The extracellular release of reactive oxygen species and neutrophil elastase by polymorphonuclear neutrophils may also contribute to damage of the surrounding periodontal tissues.

Biphasic effect of gingipains from Porphyromonas gingivalis on the human complement system

Periodontitis is an inflammatory disease of the supporting structures of the teeth and is caused by, among other agents, Porphyromonas gingivalis. P. gingivalis is very resistant to killing by human complement, which is present in a gingival fluid at 70% of the serum concentration. We found that the incubation of human serum with purified cysteine proteases of P. gingivalis (gingipains) or P. gingivalis wild-type strains W83 and W50 resulted in a drastic decrease of the bactericidal activity of the serum. In contrast, serum treated with P. gingivalis mutants lacking gingipains (particularly strains without HRgpA) maintained significant bactericidal activity. To understand in detail the mechanism by which gingipains destroy the serum bactericidal activity, we investigated the effects of gingipains on the human complement system. We found that all three proteases degraded multiple complement components, with arginine-specific gingipains (HRgpA and RgpB) being more efficient than lysine-specific gingipain (Kgp). Interestingly, all three proteases at certain concentrations were able to activate the C1 complex in serum, which resulted in the deposition of C1q on inert surfaces and on bacteria themselves. It is therefore plausible that P. gingivalis activates complement when present at low numbers, resulting in a local inflammatory reaction and providing the bacteria with a colonization opportunity and nutrients. At later stages of infection the concentration of proteases is high enough to destroy complement factors and thus render the bacteria resistant to the bactericidal activity of complement.