Gingipains from Porphyromonas gingivalis W83 synergistically disrupt endothelial cell adhesion and can induce caspase-independent apoptosis

Periodontitis and atherosclerotic cardiovascular disease: A critical appraisal

In spite of intensive research efforts driving spectacular advances in terms of prevention and treatments, cardiovascular diseases (CVDs) remain a leading health burden, accounting for 32% of all deaths (World Health Organization. "Cardiovascular Diseases (CVDs)." WHO, February 1, 2017, https://www.who.int/news-room/fact-sheets/detail/cardiovascular-diseases-(cvds)). Cardiovascular diseases are a group of disorders affecting the heart and blood vessels. They encompass a collection of different conditions, among which atherosclerotic cardiovascular disease (ASCVD) is the most prevalent. CVDs caused by atherosclerosis, that is, ASCVD, are particularly fatal: with heart attack and stroke being together the most prevalent cause of death in the world. To reduce the health burden represented by ASCVD, it is urgent to identify the nature of the "residual risk," beyond the established risk factors (e.g., hypertension) and behavioral factors already maximally targeted by drugs and public health campaigns. Remarkably, periodontitis is increasingly recognized as an independent cardiovascular risk factor.

Interleukin-22 Inhibits Apoptosis of Gingival Epithelial Cells Through TGF-β Signaling Pathway During Periodontitis

Periodontitis is a chronic inflammatory disease characterized by the destruction of tooth-supporting tissues. The gingival epithelium is the first barrier of periodontal tissue against oral pathogens and harmful substances. The structure and function of epithelial lining are essential for maintaining the integrity of the epithelial barrier. Abnormal apoptosis can lead to the decrease of functional keratinocytes and break homeostasis in gingival epithelium. Interleukin-22 is a cytokine that plays an important role in epithelial homeostasis in intestinal epithelium, inducing proliferation and inhibiting apoptosis, but its role in gingival epithelium is poorly understood. In this study, we investigated the effect of interleukin-22 on apoptosis of gingival epithelial cells during periodontitis. Interleukin-22 topical injection and Il22 gene knockout were performed in experimental periodontitis mice. Human gingival epithelial cells were co-cultured with Porphyromonas gingivalis with interleukin-22 treatment. We found that interleukin-22 inhibited apoptosis of gingival epithelial cells during periodontitis in vivo and in vitro, decreasing Bax expression and increasing Bcl-xL expression. As for the underlying mechanisms, we found that interleukin-22 reduced the expression of TGF-β receptor type II and inhibited the phosphorylation of Smad2 in gingival epithelial cells during periodontitis. Blockage of TGF-β receptors attenuated apoptosis induced by Porphyromonas gingivalis and increased Bcl-xL expression stimulated by interleukin-22. These results confirmed the inhibitory effect of interleukin-22 on apoptosis of gingival epithelial cells and revealed the involvement of TGF-β signaling pathway in gingival epithelial cell apoptosis during periodontitis.

The Effects of Porphyromonas gingivalis on Atherosclerosis-Related Cells

Atherosclerosis (AS), one of the most common types of cardiovascular disease, has initially been attributed to the accumulation of fats and fibrous materials. However, more and more researchers regarded it as a chronic inflammatory disease nowadays. Infective disease, such as periodontitis, is related to the risk of atherosclerosis. Porphyromonas gingivalis (P. gingivalis), one of the most common bacteria in stomatology, is usually discovered in atherosclerotic plaque in patients. Furthermore, it was reported that P. gingivalis can promote the progression of atherosclerosis. Elucidating the underlying mechanisms of P. gingivalis in atherosclerosis attracted attention, which is thought to be crucial to the therapy of atherosclerosis. Nevertheless, the pathogenesis of atherosclerosis is much complicated, and many kinds of cells participate in it. By summarizing existing studies, we find that P. gingivalis can influence the function of many cells in atherosclerosis. It can induce the dysfunction of endothelium, promote the formation of foam cells as well as the proliferation and calcification of vascular smooth muscle cells, and lead to the imbalance of regulatory T cells (Tregs) and T helper (Th) cells, ultimately promoting the occurrence and development of atherosclerosis. This article summarizes the specific mechanism of atherosclerosis caused by P. gingivalis. It sorts out the interaction between P. gingivalis and AS-related cells, which provides a new perspective for us to prevent or slow down the occurrence and development of AS by inhibiting periodontal pathogens.

Porphyromonas gingivalis Induces Proinflammatory Cytokine Expression Leading to Apoptotic Death through the Oxidative Stress/NF-κB Pathway in Brain Endothelial Cells

Porphyromonas gingivalis, a periodontal pathogen, has been proposed to cause blood vessel injury leading to cerebrovascular diseases such as stroke. Brain endothelial cells compose the blood-brain barrier that protects homeostasis of the central nervous system. However, whether P. gingivalis causes the death of endothelial cells and the underlying mechanisms remain unclear. This study aimed to investigate the impact and regulatory mechanisms of P. gingivalis infection in brain endothelial cells. We used bEnd.3 cells and primary mouse endothelial cells to assess the effects of P. gingivalis on endothelial cells. Our results showed that infection with live P. gingivalis, unlike heat-killed P. gingivalis, triggers brain endothelial cell death by inducing cell apoptosis. Moreover, P. gingivalis infection increased intracellular reactive oxygen species (ROS) production, activated NF-κB, and up-regulated the expression of IL-1β and TNF-α. Furthermore, N-acetyl-L-cysteine (NAC), a most frequently used antioxidant, treatment significantly reduced P. gingivalis-induced cell apoptosis and brain endothelial cell death. The enhancement of ROS production, NF-κB p65 activation, and proinflammatory cytokine expression was also attenuated by NAC treatment. The impact of P. gingivalis on brain endothelial cells was also confirmed using adult primary mouse brain endothelial cells (MBECs). In summary, our results showed that P. gingivalis up-regulates IL-1β and TNF-α protein expression, which consequently causes cell death of brain endothelial cells through the ROS/NF-κB pathway. Our results, together with the results of previous case-control studies and epidemiologic reports, strongly support the hypothesis that periodontal infection increases the risk of developing cerebrovascular disease.

From the Matrix to the Nucleus and Back: Mechanobiology in the Light of Health, Pathologies, and Regeneration of Oral Periodontal Tissues

Among oral tissues, the periodontium is permanently subjected to mechanical forces resulting from chewing, mastication, or orthodontic appliances. Molecularly, these movements induce a series of subsequent signaling processes, which are embedded in the biological concept of cellular mechanotransduction (MT). Cell and tissue structures, ranging from the extracellular matrix (ECM) to the plasma membrane, the cytosol and the nucleus, are involved in MT. Dysregulation of the diverse, fine-tuned interaction of molecular players responsible for transmitting biophysical environmental information into the cell's inner milieu can lead to and promote serious diseases, such as periodontitis or oral squamous cell carcinoma (OSCC). Therefore, periodontal integrity and regeneration is highly dependent on the proper integration and regulation of mechanobiological signals in the context of cell behavior. Recent experimental findings have increased the understanding of classical cellular mechanosensing mechanisms by both integrating exogenic factors such as bacterial gingipain proteases and newly discovered cell-inherent functions of mechanoresponsive co-transcriptional regulators such as the Yes-associated protein 1 (YAP1) or the nuclear cytoskeleton. Regarding periodontal MT research, this review offers insights into the current trends and open aspects. Concerning oral regenerative medicine or weakening of periodontal tissue diseases, perspectives on future applications of mechanobiological principles are discussed.

Porphyromonas gingivalis Outer Membrane Vesicles Increase Vascular Permeability

Periodontitis is increasingly associated with increased risk of cardiovascular and other systemic diseases. The Gram-negative anaerobe, Porphyromonas gingivalis, is a key periodontal pathogen, and several lines of evidence link the presence of this bacterium in the circulation with vascular disease. The outer membrane vesicles (OMVs) produced by P. gingivalis have been shown to play a role in periodontitis, although, to date, little is known about their interaction with the vasculature; therefore, this study assessed the effects of P. gingivalis OMVs on the endothelium. OMVs were isolated from wild-type strain W83 and the gingipain-deficient strain ΔK/R-ab. Immunoblotting along with cryo-EM showed gingipain expression in W83 but not ΔK/R-ab-derived OMVs, where gingipains were localized to the cell wall surface. Confluent endothelial cell monolayers infected with either W83 or W83-derived OMV displayed significantly increased dextran permeability over those infected with ΔK/R-ab or its OMV. Moreover, W83-derived OMVs induced significantly more vascular disease in a zebrafish larvae systemic infection model over 72 h compared to those injected with gingipain-deficient OMVs or controls. In line with these data, human microvascular endothelial cells (HMEC-1) displayed an OMV-associated, gingipain-dependent decrease in cell surface levels of the intercellular adhesion molecule PECAM-1 (CD31) when examined by flow cytometry. These data show, for the first time, that OMVs from P. gingivalis mediate increased vascular permeability, leading to a diseased phenotype both in vitro and in vivo. Moreover, these data strongly implicate gingipains present on the OMV surface in mediating these vascular events, most likely via a mechanism that involves proteolytic cleavage of endothelial cell-cell adhesins such as PECAM-1. These data provide important evidence for the role of bacterial-derived OMVs in mediating systemic disease.

Porphyromonas gingivalis and adverse pregnancy outcomes: a review on its intricate pathogenic mechanisms

Porphyromonas gingivalis (P. gingivalis), a Gram-negative facultative anaerobe of the oral cavity, is associated with the onset of various adverse pregnancy outcomes. P. gingivalis is linked with the development of preeclampsia, preterm labour, spontaneous abortion, gestational diabetes, foetal growth restriction, and misconception. The unique virulence factors, surface adhesions, enzymes of P. gingivalis can directly injure and alter the morphology, microbiome the foetal and maternal tissues. P. gingivalis can even exaggerate the production of cytokines, free radicals and acute-phase proteins in the uterine compartment that increases the risk of myometrial contraction and onset of preterm labour. Although evidence confirms the presence of P. gingivalis in the amniotic fluid and placenta of women with poor pregnancy outcomes, the intricate molecular mechanisms by which P. gingivalis initiates various antenatal and postnatal maternal and foetal complications are not well explained in the literature. Therefore, the present review aims to comprehensively summarise and highlight the recent and unique molecular pathogenic mechanisms of P. gingivalis associated with adverse pregnancy outcomes.

Roles of Porphyromonas gingivalis and its virulence factors in periodontitis

Periodontitis is an infection-driven inflammatory disease, which is characterized by gingival inflammation and bone loss. Periodontitis is associated with various systemic diseases, including cardiovascular, respiratory, musculoskeletal, and reproductive system related abnormalities. Recent theory attributes the pathogenesis of periodontitis to oral microbial dysbiosis, in which Porphyromonas gingivalis acts as a critical agent by disrupting host immune homeostasis. Lipopolysaccharide, proteases, fimbriae, and some other virulence factors are among the strategies exploited by P. gingivalis to promote the bacterial colonization and facilitate the outgrowth of the surrounding microbial community. Virulence factors promote the coaggregation of P. gingivalis with other bacteria and the formation of dental biofilm. These virulence factors also modulate a variety of host immune components and subvert the immune response to evade bacterial clearance or induce an inflammatory environment. In this chapter, our focus is to discuss the virulence factors of periodontal pathogens, especially P. gingivalis, and their roles in regulating immune responses during periodontitis progression.

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.

Effect of Lactobacillus acidophilus and Porphyromonas gingivalis on proliferation and apoptosis of gingival epithelial cells

PURPOSE

This study aimed to evaluate the possible antagonistic effects of Lactobacillus acidophilus on Porphyromonas gingivalis, and detect inhibition of Lactobacillus acidophilus on Porphyromonas gingivalis when they are co-cultured with human gingival epithelial cells.

MATERIALS AND METHODS

Human gingival epithelial cells were co-cultured with Lactobacillus acidophilus and Porphyromonas gingivalis alone or together. The amount of Porphyromonas gingivalis adhering to or invading the epithelial cells were determined by bacterial counts. The cellular proliferation was assayed by the MTT method. Apoptosis was detected by flow cytometry with apoptosis detection kit.

RESULTS

On one hand, Lactobacillus acidophilus reduced the inhibitory effect of Porphyromonas gingivalis on the human gingival epithelial cells proliferation in a dose dependent manner. On the other hand, Porphyromonas gingivalis induced significant apoptosis on human gingival epithelial cells, and Lactobacillus acidophilus inhibited this apoptosis-inducing effect of Porphyromonas gingivalis in a dose dependent manner.

CONCLUSIONS

Porphyromonas gingivalis inhibits the proliferation and induces the apoptosis of human gingival epithelial cells. Lactobacillus acidophilus could attenuate this effect in a dose-dependent manner, and it thus reduces the destruction from pathogens. Lactobacillus acidophilus could be an effective candidate for probiotic therapy in periodontal diseases.

Oral Mucosal Epithelial Cells

Cellular Phenotype and Apoptosis: The function of epithelial tissues is the protection of the organism from chemical, microbial, and physical challenges which is indispensable for viability. To fulfill this task, oral epithelial cells follow a strongly regulated scheme of differentiation that results in the formation of structural proteins that manage the integrity of epithelial tissues and operate as a barrier. Oral epithelial cells are connected by various transmembrane proteins with specialized structures and functions. Keratin filaments adhere to the plasma membrane by desmosomes building a three-dimensional matrix.

Cell-Cell Contacts and Bacterial Influence: It is known that pathogenic oral bacteria are able to affect the expression and configuration of cell-cell junctions. Human keratinocytes up-regulate immune-modulatory receptors upon stimulation with bacterial components. Periodontal pathogens including P. gingivalis are able to inhibit oral epithelial innate immune responses through various mechanisms and to escape from host immune reaction, which supports the persistence of periodontitis and furthermore is able to affect the epithelial barrier function by altering expression and distribution of cell-cell interactions including tight junctions (TJs) and adherens junctions (AJs).

In the pathogenesis of periodontitis a highly organized biofilm community shifts from symbiosis to dysbiosis which results in destructive local inflammatory reactions.

Cellular Receptors: Cell-surface located toll like receptors (TLRs) and cytoplasmatic nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) belong to the pattern recognition receptors (PRRs). PRRs recognize microbial parts that represent pathogen-associated molecular patterns (PAMPs).

A multimeric complex of proteins known as inflammasome, which is a subset of NLRs, assembles after activation and proceeds to pro-inflammatory cytokine release.

Cytokine Production and Release: Cytokines and bacterial products may lead to host cell mediated tissue destruction. Keratinocytes are able to produce diverse pro-inflammatory cytokines and chemokines, including interleukin (IL)-1, IL-6, IL-8 and tumor necrosis factor (TNF)-α. Infection by pathogenic bacteria such as Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) can induce a differentiated production of these cytokines.

Immuno-modulation, Bacterial Infection, and Cancer Cells: There is a known association between bacterial infection and cancer. Bacterial components are able to up-regulate immune-modulatory receptors on cancer cells. Interactions of bacteria with tumor cells could support malignant transformation an environment with deficient immune regulation.

The aim of this review is to present a set of molecular mechanisms of oral epithelial cells and their reactions to a number of toxic influences.

Inhibition of osteoclastogenesis by opsonized Porphyromonas gingivalis

A crucial step in the pathogenesis of periodontal disease (PD) is activation of osteoclasts (OC) by numerous virulence factors produced by Porphyromonas gingivalis (Pg). To understand pathogenesis of PD and the role of specific adaptive immune responses, effects of antibodies on Pg‐induced OC differentiation and function were investigated. Human peripheral blood‐derived monocytes were differentiated to OC in the presence or absence of: (a) Pg; (b) antibodies to Pg; and (c) antibody‐opsonized Pg. Findings suggest significant induction of osteoclastogenesis by Pg when compared to control cultures, whereas opsonization decreased osteoclastogenesis by 45%. Immune receptor gene expression profile in the presence of opsonized Pg showed marked upregulation of TLR1 (three‐fold) and TLR2 (twofold) along with FcγRIIB (two‐fold) and FcγRIII receptors (five‐fold), but not TLR4 and FcRγ receptors. Interestingly, blocking FcγRIIB, but not FcγRIII receptor, reversed the inhibitory effects of opsonized Pg suggesting a critical role played by FcγRIIB in osteoclastogenesis. Furthermore, opsonized Pg transformed OC precursors to a “macrophage phenotype” suggesting a bone protective role of the immune complexes in modulating osteoclastogenesis, probably by competing as an agonist for pattern recognition receptors, and inducing selective activation of FcγRs with simultaneous suppression of FcRγ which regulates bone resorptive process. Further defining effective antibody isotypes, avidity, and antigenic specificity could improve targets for eliciting protective immunity.

Metabolic Remodeling, Inflammasome Activation, and Pyroptosis in Macrophages Stimulated by Porphyromonas gingivalis and Its Outer Membrane Vesicles

Porphyromonas gingivalis is one of the bacterial species most closely associated with periodontitis and can shed large numbers of outer membrane vesicles (OMVs), which are increasingly thought to play a significant role in bacterial virulence and pathogenicity. Macrophages are amongst the first immune cells to respond to bacteria and their products, so we sought to directly compare the response of macrophages to P. gingivalis or its purified OMVs. Macrophages stimulated with OMVs produced large amounts of TNFα, IL-12p70, IL-6, IL-10, IFNβ, and nitric oxide compared to cells infected with P. gingivalis, which produced very low levels of these mediators. Both P. gingivalis and OMVs induced a shift in macrophage metabolism from oxidative phosphorylation (OXPHOS) to glycolysis, which was supported by enhanced lactate release, decreased mitochondrial oxygen consumption with reduced spare respiratory capacity, as well as increased mitochondrial reactive oxygen species (ROS) production. Corresponding to this metabolic shift, gene expression analysis of macrophages infected with P. gingivalis or stimulated with OMVs revealed a broad transcriptional upregulation of genes critical to glycolysis and a downregulation of genes associated with the TCA cycle. Upon examination of inflammasome signaling and pyroptosis it was found that P. gingivalis did not activate the inflammasome in macrophages as the mature forms of caspase-1, IL-1β, and IL-18 were not detected and there was no extracellular release of lactate dehydrogenase (LDH) or 7-AAD staining. In comparison, macrophages stimulated with OMVs potently activated caspase-1, produced large amounts of IL-1β, IL-18, released LDH, and were positive for 7-AAD indicative of pyroptotic cell death. These data directly quantitate the distinct effects of P. gingivalis and its OMVs on macrophage inflammatory phenotype, mitochondrial function, inflammasome activation, and pyroptotic cell death that may have potential implications for their roles in chronic periodontitis.

Oral application of a periodontal pathogen impacts SerpinE1 expression and pancreatic islet architecture in prediabetes

BACKGROUND AND OBJECTIVES

Epidemiological studies suggest a close association between periodontitis and prediabetes/insulin resistance (IR) but whether periodontitis causes prediabetes in humans is not known. Using various animal models, we have recently established that periodontitis can be an initiator of prediabetes, which is characterized by glucose intolerance, hyperinsulinemia and IR. In addition, our in vitro studies indicated that Porphyromonas gingivalis (Pg) induced insulin secretion in MIN6 β cells and this induction was in part SerpinE1 (plasminogen activator inhibitor 1, PAI1) dependent. However, the mechanism(s) by which periodontitis induces prediabetes is not known. As α and β cells in pancreatic islets are the major modulators of glucose levels, we investigated whether experimental periodontitis by oral application of a periodontal pathogen caused molecular and/or cellular alterations in pancreatic islets and whether SerpinE1 was involved in this process.

MATERIAL AND METHODS

We induced periodontitis in C57BL/6 mice by oral application of a periodontal pathogen, Pg, and determined changes that occurred in islets following 22 weeks of Pg application. Pancreatic islet architecture was determined by 2-D and 3-D immunofluorescence microscopy and SerpinE1 and its target, urokinase plasminogen activator (uPA), as well as insulin, glucagon and Pg/gingipain in islets were detected by immunofluorescence. The presence of apoptotic islet cells was determined by both histochemical and immunofluorescence TUNEL assays. To investigate further the direct effect of Pg on apoptosis and the involvement of SerpinE1 in this process, we used SerpinE1 knockdown and scrambled control clones of the MIN6 pancreatic β-cell line.

RESULTS

Pg/gingipain was detected in both the periodontium and pancreas in the experimental group. Islets from animals that were administered Pg orally (experimental group) developed significant changes in islet architecture, upregulation of SerpinE1, and increased β-cell apoptosis compared with the control group. We also observed that exposure of MIN6 cells to Pg in vitro resulted in apoptosis. However, apoptosis was significantly reduced when SerpinE1 expression by MIN6 cells was knocked down.

CONCLUSION

Oral application of the periodontal pathogen Pg to C57BL/6 mice induces periodontitis, translocation of Pg/gingipain to the pancreas and results in complex alterations in pancreatic islet morphology. SerpinE1 appears to be involved in this process.

Adhesion of Porphyromonas gingivalis and Tannerella forsythia to dentin and titanium with sandblasted and acid etched surface coated with serum and serum proteins - An in vitro study

OBJECTIVE

To evaluate the adhesion of selected bacterial strains incl. expression of important virulence factors at dentin and titanium SLA surfaces coated with layers of serum proteins.

METHODS

Dentin- and moderately rough SLA titanium-discs were coated overnight with human serum, or IgG, or human serum albumin (HSA). Thereafter, Porphyromonas gingivalis, Tannerella forsythia, or a six-species mixture were added for 4h and 24h. The number of adhered bacteria (colony forming units; CFU) was determined. Arg-gingipain activity of P. gingivalis and mRNA expressions of P. gingivalis and T. forsythia proteases and T. forsythia protease inhibitor were measured.

RESULTS

Coating specimens never resulted in differences exceeding 1.1 log10 CFU, comparing to controls, irrespective the substrate. Counts of T. forsythia were statistically significantly higher at titanium than dentin, the difference was up to 3.7 log10 CFU after 24h (p=0.002). No statistically significant variation regarding adhesion of the mixed culture was detected between surfaces or among coatings. Arg-gingipain activity of P. gingivalis was associated with log10 CFU but not with the surface or the coating. Titanium negatively influenced mRNA expression of T. forsythia protease inhibitor at 24h (p=0.026 uncoated, p=0.009 with serum).

CONCLUSIONS

The present findings indicate that: a) single bacterial species (T. forsythia) can adhere more readily to titanium SLA than to dentin, b) low expression of T. forsythia protease inhibitor may influence the virulence of the species on titanium SLA surfaces in comparison with teeth, and c) surface properties (e.g. material and/or protein layers) do not appear to significantly influence multi-species adhesion.

Zebrafish as a new model to study effects of periodontal pathogens on cardiovascular diseases

Porphyromonas gingivalis (Pg) is a keystone pathogen in the aetiology of chronic periodontitis. However, recent evidence suggests that the bacterium is also able to enter the bloodstream, interact with host cells and tissues, and ultimately contribute to the pathogenesis of cardiovascular disease (CVD). Here we established a novel zebrafish larvae systemic infection model showing that Pg rapidly adheres to and penetrates the zebrafish vascular endothelium causing a dose- and time-dependent mortality with associated development of pericardial oedemas and cardiac damage. The in vivo model was then used to probe the role of Pg expressed gingipain proteases using systemically delivered gingipain-deficient Pg mutants, which displayed significantly reduced zebrafish morbidity and mortality compared to wild-type bacteria. In addition, we used the zebrafish model to show efficacy of a gingipain inhibitor (KYT) on Pg-mediated systemic disease, suggesting its potential use therapeutically. Our data reveal the first real-time in vivo evidence of intracellular Pg within the endothelium of an infection model and establishes that gingipains are crucially linked to systemic disease and potentially contribute to CVD.

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.

Porphyromonas gingivalis Outer Membrane Vesicles Induce Selective Tumor Necrosis Factor Tolerance in a Toll-Like Receptor 4- and mTOR-Dependent Manner

Porphyromonas gingivalis is an important member of the anaerobic oral flora. Its presence fosters growth of periodontal biofilm and development of periodontitis. In this study, we demonstrated that lipophilic outer membrane vesicles (OMV) shed from P. gingivalis promote monocyte unresponsiveness to live P. gingivalis but retain reactivity to stimulation with bacterial DNA isolated from P. gingivalis or AIM2 ligand poly(dA·dT). OMV-mediated tolerance of P. gingivalis is characterized by selective abrogation of tumor necrosis factor (TNF). Neutralization of interleukin-10 (IL-10) during OMV challenge partially restores monocyte responsiveness toP. gingivalis; full reactivity toP. gingivalis can be restored by inhibition of mTOR signaling, which we previously identified as the major signaling pathway promoting Toll-like receptor 2 and Toll-like receptor 4 (TLR2/4)-mediated tolerance in monocytes. However, despite previous reports emphasizing a central role of TLR2 in innate immune recognition of P. gingivalis, our current findings highlight a selective role of TLR4 in the promotion of OMV-mediated TNF tolerance: only blockade of TLR4-and not of TLR2-restores responsiveness toP. gingivalis Of further note, OMV-mediated tolerance is preserved in the presence of cytochalasin B and chloroquine, indicating that triggering of surface TLR4 is sufficient for this effect. Taking the results together, we propose that P. gingivalis OMV contribute to local immune evasion of P. gingivalis by hampering the host response.

Porphyromonas gingivalis gingipain is involved in the detachment and aggregation of Aggregatibacter actinomycetemcomitans biofilm

Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans are major periodontal pathogens that cause several types of periodontal disease. Our previous study suggested that P. gingivalis gingipains secreted in the subgingival environment are related to the detachment of A.actinomycetemcomitans biofilms. However, it remains unclear whether arginine-specific cysteine proteinase (Rgp) and lysine-specific proteinase (Kgp) play different roles in the detachment of A. actinomycetemcomitans biofilm. The aim of this study was to investigate possible disruptive roles of Kgp and Rgp in the aggregation and attachment of A. actinomycetemcomitans. While P. gingivalis ATCC33277 culture supernatant has an ability to decrease autoaggregation and coaggregation of A. actinomycetemcomitans cells, neither the boiled culture supernatant of ATCC33277 nor the culture supernatant of KDP136 showed this ability. The addition of KYT-1 and KYT-36, specific inhibitors of Rgp and Kgp, respectively, showed no influence on the ability of P. gingivalis culture supernatant. The result of gelatin zymography suggested that other proteases processed by gingipains mediated the decrease of A. actinomycetemcomitans aggregations. We also examined the biofilm-destructive effect of gingipains by assessing the detachment of A. actinomycetemcomitans from polystyrene surfaces. Scanning electron microscope analysis indicated that A. actinomycetemcomitans cells were detached by P. gingivalis Kgp. The quantity of A. actinomycetemcomitans in biofilm was decreased in co-culture with P. gingivalis. However, this was not found after the addition of KYT-36. These findings suggest that Kgp is a critical component for the detachment and decrease of A. actinomycetemcomitans biofilms.

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.

Protective role of the PG1036-PG1037-PG1038 operon in oxidative stress in Porphyromonas gingivalis W83

As an anaerobe, Porphyromonas gingivalis is significantly affected by the harsh inflammatory environment of the periodontal pocket during initial colonization and active periodontal disease. We reported previously that the repair of oxidative stress-induced DNA damage involving 8-oxo-7,8-dihydroguanine (8-oxoG) may occur by an undescribed mechanism in P. gingivalis. DNA affinity fractionation identified PG1037, a conserved hypothetical protein, among other proteins, that were bound to the 8-oxoG lesion. PG1037 is part of the uvrA-PG1037-pcrA operon in P. gingivalis which is known to be upregulated under H2O2 induced stress. A PCR-based linear transformation method was used to inactivate the uvrA and pcrA genes by allelic exchange mutagenesis. Several attempts to inactivate PG1037 were unsuccessful. Similar to the wild-type when plated on Brucella blood agar, the uvrA and pcrA-defective mutants were black-pigmented and beta-hemolytic. These isogenic mutants also had reduced gingipain activities and were more sensitive to H2O2 and UV irradiation compared to the parent strain. Additionally, glycosylase assays revealed that 8-oxoG repair activities were similar in both wild-type and mutant P. gingivalis strains. Several proteins, some of which are known to have oxidoreducatse activity, were shown to interact with PG1037. The purified recombinant PG1037 protein could protect DNA from H2O2-induced damage. Collectively, these findings suggest that the uvrA-PG1037-pcrA operon may play an important role in hydrogen peroxide stress-induced resistance in P. gingivalis.

Propeptide-mediated inhibition of cognate gingipain proteinases

Porphyromonas gingivalis is a major pathogen associated with chronic periodontitis. The organism’s cell-surface cysteine proteinases, the Arg-specific proteinases (RgpA, RgpB) and the Lys-specific proteinase (Kgp), which are known as gingipains have been implicated as major virulence factors. All three gingipain precursors contain a propeptide of around 200 amino acids in length that is removed during maturation. The aim of this study was to characterize the inhibitory potential of the Kgp and RgpB propeptides against the mature cognate enzymes. Mature Kgp was obtained from P. gingivalis mutant ECR368, which produces a recombinant Kgp with an ABM1 motif deleted from the catalytic domain (rKgp) that enables the otherwise membrane bound enzyme to dissociate from adhesins and be released. Mature RgpB was obtained from P. gingivalis HG66. Recombinant propeptides of Kgp and RgpB were produced in Escherichia coli and purified using nickel-affinity chromatography. The Kgp and RgpB propeptides displayed non-competitive inhibition kinetics with K_i values of 2.04 µM and 12 nM, respectively. Both propeptides exhibited selectivity towards their cognate proteinase. The specificity of both propeptides was demonstrated by their inability to inhibit caspase-3, a closely related cysteine protease, and papain that also has a relatively long propeptide. Both propeptides at 100 mg/L caused a 50% reduction of P. gingivalis growth in a protein-based medium. In summary, this study demonstrates that gingipain propeptides are capable of inhibiting their mature cognate proteinases.

Cleavage of extracellular matrix in periodontitis: gingipains differentially affect cell adhesion activities of fibronectin and tenascin-C

Gingipains are cysteine proteases that represent major virulence factors of the periodontopathogenic bacterium Porphyromonas gingivalis. Gingipains are reported to degrade extracellular matrix (ECM) of periodontal tissues, leading to tissue destruction and apoptosis. The exact mechanism is not known, however. Fibronectin and tenascin-C are pericellular ECM glycoproteins present in periodontal tissues. Whereas fibronectin mediates fibroblast adhesion, tenascin-C binds to fibronectin and inhibits its cell-spreading activity. Using purified proteins in vitro, we asked whether fibronectin and tenascin-C are cleaved by gingipains at clinically relevant concentrations, and how fragmentation by the bacterial proteases affects their biological activity in cell adhesion. Fibronectin was cleaved into distinct fragments by all three gingipains; however, only arginine-specific HRgpA and RgpB but not lysine-specific Kgp destroyed its cell-spreading activity. This result was confirmed with recombinant cell-binding domain of fibronectin. Of the two major tenascin-C splice variants, the large but not the small was a substrate for gingipains, indicating that cleavage occurred primarily in the alternatively spliced domain. Surprisingly, cleavage of large tenascin-C variant by all three gingipains generated fragments with increased anti-adhesive activity towards intact fibronectin. Fibronectin and tenascin-C fragments were detected in gingival crevicular fluid of a subset of periodontitis patients. We conclude that cleavage by gingipains directly affects the biological activity of both fibronectin and tenascin-C in a manner that might lead to increased cell detachment and loss during periodontal disease.

Benzamidine derivatives inhibit the virulence of Porphyromonas gingivalis

We have previously shown that benzamidine-type compounds can inhibit the activity of arginine-specific cysteine proteinases (gingipains HRgpA and RgpB); well-known virulence factors of Porphyromonas gingivalis. They also hinder in vitro growth of this important periodontopathogenic bacterium. Apparently growth arrest is not associated with their ability to inhibit these proteases, because pentamidine, which is a 20-fold less efficient inhibitor of gingipain than 2,6-bis-(4-amidinobenzyl)-cyclohexanone (ACH), blocked P. gingivalis growth far more effectively. To identify targets for benzamidine-derived compounds other than Arg-gingipains, and to explain their bacteriostatic effects, P. gingivalis ATCC 33277 and P. gingivalis M5-1-2 (clinical isolate) cell extracts were subjected to affinity chromatography using a benzamidine-Sepharose column to identify proteins interacting with benzamidine. In addition to HRgpA and RgpB the analysis revealed heat-shock protein GroEL as another ligand for benzamidine. To better understand the effect of benzamidine-derived compounds on P. gingivalis, bacteria were exposed to benzamidine, pentamidine, ACH and heat, and the expression of gingipains and GroEL was determined. Exposure to heat and benzamidine-derived compounds caused significant increases in GroEL, at both the mRNA and protein levels. Interestingly, despite the fact that gingipains were shown to be the main virulence factors in a fertilized egg model of infection, mortality rates were strongly reduced, not only by ACH, but also by pentamidine, a relatively weak gingipain inhibitor. This effect may depend not only on gingipain inhibition but also on interaction of benzamidine derivatives with GroEL. Therefore these compounds may find use in supportive periodontitis treatment.

Vitamin D inhibits the expression of interleukin-8 in human periodontal ligament cells stimulated with Porphyromonas gingivalis

OBJECTIVE

Vitamin D has been known to be closely associated with periodontitis while the exact mechanisms remain unclear. The present study aimed to discover the effects of 1a,25-dihydroxyvitamin D3 (1,25D) on the expressions of interleukin (IL)-6 and IL-8 in human periodontal ligament cells (hPDLCs) stimulated with Porphyromonas gingivalis (P. gingivalis) W83.

DESIGN

Primary cultures of hPDLCs from ten donors were established and the cells of passage four were treated with 1,25D or P. gingivalis individually or 1,25D combined with P. gingivalis. The levels of IL-6 and IL-8 protein in hPDLCs were detected with enzyme-linked immunosorbent assay (ELISA) and the mRNA levels were detected with real-time RT-PCR.

RESULTS

P. gingivalis significantly promoted the protein expressions of IL-6 and IL-8. P. gingivalis at the multiplicity of infection (MOI) 100 exerted the strongest promotion effect on the IL-6 protein expression by 5.83-fold compared with the controls (2482.88±26.53pg/ml versus 425.80±77.25pg/ml, P<0.0005) and the IL-8 protein expression by 12.39-fold (4965.81±1072.55pg/ml versus 400.75±2.27pg/ml, P=0.005) in hPDLCs at 24h. At 48h, 10(-8)mol/L 1,25D had the best inhibition on the IL-8 protein expression in hPDLCs by 2.00-fold compared with the controls (100.76±21.11pg/ml versus 201.75±18.15pg/ml, P<0.0005) and the IL-8 mRNA expression by 2.13-fold (P<0.0005). 10(-8)mol/L 1,25D combined with P. gingivalis (MOI 100) exerted the strongest inhibition effect on the IL-8 protein expression by 1.54-fold compared with P. gingivalis treatment alone (3077.33±210.04pg/ml versus 4738.24±1386.17pg/ml, P=0.018) and the IL-8 mRNA expression by 1.78-fold (P=0.012) in hPDLCs at 12h. 1,25D did not influence the expression of IL-6 in hPDLCs with or without P. gingivalis treatment.

CONCLUSION

Vitamin D may potentially inhibit the periodontal inflammation induced by P. gingivalis partly by decreasing the IL-8 expression in hPDLCs.

Oxidative stress resistance in Porphyromonas gingivalis

Porphyromonas gingivalis, a black-pigmented, Gram-negative anaerobe, is an important etiologic agent of periodontal disease. The harsh inflammatory condition of the periodontal pocket implies that this organism has properties that will facilitate its ability to respond and adapt to oxidative stress. Because the stress response in the pathogen is a major determinant of its virulence, a comprehensive understanding of its oxidative stress resistance strategy is vital. We discuss multiple mechanisms and systems that clearly work in synergy to defend and protect P. gingivalis against oxidative damage caused by reactive oxygen species. The involvement of multiple hypothetical proteins and/or proteins of unknown function in this process may imply other unique mechanisms and potential therapeutic targets.

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.

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.

The periodontal pathogen Porphyromonas gingivalis induces the Epstein-Barr virus lytic switch transactivator ZEBRA by histone modification

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus that usually results in latent infection of B cells. The EBV BZLF1 gene product ZEBRA is a master regulator of the transition from latency to the lytic replication cycle. In the latent state, hypoacetylation of histone proteins in the BZLF1 promoter by histone deacetylases (HDACs) is primarily involved in maintaining EBV latency. Although the mechanism that regulates the switch between latency and lytic replication has been a central research focus in EBV infection, the causal link between HDAC inhibition and the disruption of viral latency is not well understood. Periodontal disease is a complex chronic inflammatory disease caused by subgingival infection with oral anaerobic bacteria, typically Porphyromonas gingivalis. Periodontal disease occurs worldwide and is among the most prevalent microbial diseases in humans. In this study, we examined the biological effect of P. gingivalis infection on EBV reactivation and found that P. gingivalis induced expression of ZEBRA. This activity was associated with supernatant from bacterial culture, but not with other bacterial components such as lipopolysaccharide or fimbriae. We demonstrated that culture supernatant from P. gingivalis, which contained high concentrations of butyric acid, inhibited HDACs, thus increasing histone acetylation and the transcriptional activity of the BZLF1 gene. Chromatin immunoprecipitation assays revealed that HDACs were present in the BZLF1 promoter during latent state and that they were dissociated from the promoter concomitantly with the association of acetylated histone H3, upon stimulation by culture supernatant from P. gingivalis. Thus, P. gingivalis induced EBV reactivation via chromatin modification, and butyric acid-a bacterial metabolite-was responsible for this effect. These findings suggest that periodontal disease is a risk factor for EBV reactivation in infected individuals and might therefore contribute to progression of EBV-related diseases.

Evaluating periodontal risk for patients at risk of or suffering from atherosclerosis: recent biological hypotheses and therapeutic consequences

Cardiovascular disease, such as atherosclerosis, is the main cause of mortality in developed countries. Most atherosclerosis risk factors have been identified and are treated, improving patient cardiovascular status and reducing mortality, but some remain unknown. Periodontal disease is generally defined as inflammatory disease initiated by accumulation of dental bacterial plaque, leading to the destruction of tissues that support the teeth. Severe forms have a high prevalence (15% of the population) and are associated with the presence of virulent pathogens such as Porphyromonas gingivalis. Epidemiological studies have shown that severe periodontal disease negatively influences cardiovascular status. The aim of this paper was to present a synthesis of the most recent biological data related to the link between periodontal and cardiovascular disease. The potential biological mechanisms involved in these two inflammatory diseases (bacteriological theory, inflammatory theory, immune theory) were developed. According to the observed positive effects of periodontal treatment on systemic conditions, the benefit of a reinforced collaboration between dentists and cardiologists was discussed, especially for patients at risk for cardiovascular disease.

Involvement of extracytoplasmic function sigma factors in virulence regulation in Porphyromonas gingivalis W83

Extracytoplasmic function (ECF) sigma factors are known to play an important role in the bacterial response to various environmental stresses and can significantly modulate their pathogenic potential. In the genome of Porphyromonas gingivalis W83, six putative ECF sigma factors were identified. To further evaluate their role in this organism, a PCR-based linear transformation method was used to inactivate five ECF sigma factor genes (PG0162, PG0214, PG0985, PG1660, and PG1827) by allelic exchange mutagenesis. All five isogenic mutants formed black-pigmented colonies on blood agar. Mutants defective in PG0985, PG1660, and PG1827 genes were more sensitive to 0.25 mM of hydrogen peroxide compared with the wild-type strain. Isogenic mutants of PG0162 and PG1660 showed a 50% decrease in gingipain activity. Reverse transcription-PCR analysis showed that there was no alteration in the expression of rgpA, rgpB, and kgp gingipain genes in these mutants. Hemolytic and hemagglutination activities were decreased by more than 50% in the PG0162 mutant compared with the wild type. Taken together, these findings suggest that ECF sigma factors can modulate important virulence factors in P. gingivalis. ECF sigma factors encoded by the PG0162 and PG1660 genes might also be involved in the post-transcriptional regulation of the gingipains.

"Gum bug, leave my heart alone!"--epidemiologic and mechanistic evidence linking periodontal infections and atherosclerosis

Evidence from epidemiologic studies suggests that periodontal infections are independently associated with subclinical and clinical atherosclerotic vascular disease. Although the strength of the reported associations is modest, the consistency of the data across diverse populations and a variety of exposure and outcome variables suggests that the findings are not spurious or attributable only to the effects of confounders. Analysis of limited data from interventional studies suggests that periodontal treatment generally results in favorable effects on subclinical markers of atherosclerosis, although such analysis also indicates considerable heterogeneity in responses. Experimental mechanistic in vitro and in vivo studies have established the plausibility of a link between periodontal infections and atherogenesis, and have identified biological pathways by which these effects may be mediated. However, the utilized models are mostly mono-infections of host cells by a limited number of 'model' periodontal pathogens, and therefore may not adequately portray human periodontitis as a polymicrobial, biofilm-mediated disease. Future research must identify in vivo pathways in humans that may (i) lead to periodontitis-induced atherogenesis, or (ii) result in treatment-induced reduction of atherosclerosis risk. Data from these studies will be essential for determining whether periodontal interventions have a role in the primary or secondary prevention of atherosclerosis.

regT can modulate gingipain activity and response to oxidative stress in Porphyromonas gingivalis

Recombinant VimA protein can interact with the gingipains and several other proteins that may play a role in its biogenesis in Porphyromonas gingivalis. In silico analysis of PG2096, a hypothetical protein that was shown to interact with VimA, suggests that it may have environmental stress resistance properties. To further evaluate the role(s) of PG2096, the predicted open reading frame was PCR amplified from P. gingivalis W83 and insertionally inactivated using the ermF-ermAM antibiotic-resistance cassette. One randomly chosen PG2096-defective mutant created by allelic exchange and designated FLL205 was further characterized. Under normal growth conditions at 37 °C, Arg-X and Lys-X gingipain activities in FLL205 were reduced by approximately 35 % and 21 %, respectively, compared to the wild-type strain. However, during prolonged growth at an elevated temperature of 42 °C, Arg-X activity was increased by more than 40 % in FLL205 in comparison to the wild-type strain. In addition, the PG2096-defective mutant was more resistant to oxidative stress when treated with 0.25 mM hydrogen peroxide. Taken together these results suggest that the PG2096 gene, designated regT (regulator of gingipain activity at elevated temperatures), may be involved in regulating gingipain activity at elevated temperatures and be important in oxidative stress resistance in P. gingivalis.

Translocation of Porphyromonas gingivalis gingipain adhesin peptide A44 to host mitochondria prevents apoptosis

Porphyromonas gingivalis, a Gram-negative oral anaerobe, is associated with periodontal diseases that, in some form, affect up to 80% of the U.S. population. The organism is highly proteolytic, and noncatalytic adhesin domains of the major proteases, gingipains, are involved in bacterium-host interactions. Recently, we showed that gingipain adhesin peptide A44 hijacks the host's clathrin-dependent endocytosis system, allowing the peptide and whole bacteria to be internalized by epithelial cells. In the present study, we found by cell fractionation assays and confocal microscopy that peptide A44 translocated to host mitochondria. Cell viability assays and quantitative real-time PCR showed that the peptide interacted with the cell death machinery by triggering upregulation of antiapoptotic factors bcl-2 and bcl-XL and prevented staurosporine-induced apoptosis for up to 12 h. We confirmed these findings with Western blot analyses of caspase-9 activation in time course experiments with staurosporine. Finally, we verified a similar antiapoptotic effect for P. gingivalis, showing for the first time that the organism manipulated mitochondrial functions during the first hours of infection, thus resisting host cell clearance by apoptosis of infected cells. This mechanism may enable the bacteria to persist in the protected cellular environment until the next step in pathogenesis, progression or resolution of infection.

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.

Porphyromonas gingivalis invades human trophoblasts and inhibits proliferation by inducing G1 arrest and apoptosis

Porphyromonas gingivalis is an oral pathogen that is also associated with serious systemic conditions such as preterm delivery. Here we investigated the interaction between P. gingivalis and a cell line of extravillous trophoblasts (HTR-8) derived from the human placenta. P. gingivalis internalized within HTR-8 cells and inhibited proliferation through induction of arrest in the G1 phase of the cell cycle. G1 arrest was associated with decreased expression of cyclin D and of CDKs 2, 4 and 6. In addition, levels of CDK inhibitors p15, p16, p18 and p21 were increased following P. gingivalis infection. The amount of Rb was diminished by P. gingivalis, and transient overexpression of Rb, with concomitant upregulation of phospho-Rb, relieved P. gingivalis-induced G1 arrest. HTR-8 cells halted in the G1 phase became apoptotic, and apoptosis was accompanied by an increase in the ratio of Bax/Bcl-2 and increased activity of caspases 3, 7 and 9. HTR-8 cells infected with P. gingivalis also exhibited a sustained activation of ERK1/2, and knock-down of ERK1/2 activity with siRNA abrogated both G1 arrest and apoptosis. Thus, P. gingivalis can invade placental trophoblasts and induce G1 arrest and apoptosis through pathways involving ERK1/2 and its downstream effectors, properties that provide a mechanistic basis for pathogenicity in complications of pregnancy.

Porphyromonas gingivalis induce apoptosis in human gingival epithelial cells through a gingipain-dependent mechanism

BACKGROUND

The oral pathogen Porphyromonas gingivalis has been shown to modulate apoptosis in different cell types, but its effect on epithelial cells remains unclear.

RESULTS

We demonstrate that primary human gingival epithelial cells (HGECs) challenged with live P. gingivalis for 24 hours exhibit apoptosis, and we characterize this by M30 epitope detection, caspase-3 activity, DNA fragmentation and Annexin-V staining. Live bacteria strongly upregulated intrinsic and extrinsic apoptotic pathways. Pro-apoptotic molecules such as caspase-3, -8, -9, Bid and Bax were upregulated after 24 hours. The anti-apoptotic Bcl-2 was also upregulated, but this was not sufficient to ensure cell survival. The main P. gingivalis proteases arginine and lysine gingipains are necessary and sufficient to induce host cell apoptosis. Thus, live P. gingivalis can invoke gingival epithelial cell apoptosis in a time and dose dependent manner with significant apoptosis occurring between 12 and 24 hours of challenge via a gingipain-dependent mechanism.

CONCLUSION

The present study provides evidence that live, but not heat-killed, P. gingivalis can induce apoptosis after 24 hours of challenge in primary human gingival epithelial cells. Either arginine or lysine gingipains are necessary and sufficient factors in P. gingivalis elicited apoptosis.

DNA repair of 8-oxo-7,8-dihydroguanine lesions in Porphyromonas gingivalis

The persistence of Porphyromonas gingivalis in the inflammatory environment of the periodontal pocket requires an ability to overcome oxidative stress. DNA damage is a major consequence of oxidative stress. Unlike the case for other organisms, our previous report suggests a role for a non-base excision repair mechanism for the removal of 8-oxo-7,8-dihydroguanine (8-oxo-G) in P. gingivalis. Because the uvrB gene is known to be important in nucleotide excision repair, the role of this gene in the repair of oxidative stress-induced DNA damage was investigated. A 3.1-kb fragment containing the uvrB gene was PCR amplified from the chromosomal DNA of P. gingivalis W83. This gene was insertionally inactivated using the ermF-ermAM antibiotic cassette and used to create a uvrB-deficient mutant by allelic exchange. When plated on brucella blood agar, the mutant strain, designated P. gingivalis FLL144, was similar in black pigmentation and beta-hemolysis to the parent strain. In addition, P. gingivalis FLL144 demonstrated no significant difference in growth rate, proteolytic activity, or sensitivity to hydrogen peroxide from that of the parent strain. However, in contrast to the wild type, P. gingivalis FLL144 was significantly sensitive to UV irradiation. The enzymatic removal of 8-oxo-G from duplex DNA was unaffected by the inactivation of the uvrB gene. DNA affinity fractionation identified unique proteins that preferentially bound to the oligonucleotide fragment carrying the 8-oxo-G lesion. Collectively, these results suggest that the repair of oxidative stress-induced DNA damage involving 8-oxo-G may occur by a still undescribed mechanism in P. gingivalis.

Acyl chain specificity of the acyltransferases LpxA and LpxD and substrate availability contribute to lipid A fatty acid heterogeneity in Porphyromonas gingivalis

Porphyromonas gingivalis lipid A is heterogeneous with regard to the number, type, and placement of fatty acids. Analysis of lipid A by matrix-assisted laser desorption ionization-time of flight mass spectrometry reveals clusters of peaks differing by 14 mass units indicative of an altered distribution of the fatty acids generating different lipid A structures. To examine whether the transfer of hydroxy fatty acids with different chain lengths could account for the clustering of lipid A structures, P. gingivalis lpxA (lpxA(Pg)) and lpxD(Pg) were cloned and expressed in Escherichia coli strains in which the homologous gene was mutated. Lipid A from strains expressing either of the P. gingivalis transferases was found to contain 16-carbon hydroxy fatty acids in addition to the normal E. coli 14-carbon hydroxy fatty acids, demonstrating that these acyltransferases display a relaxed acyl chain length specificity. Both LpxA and LpxD, from either E. coli or P. gingivalis, were also able to incorporate odd-chain fatty acids into lipid A when grown in the presence of 1% propionic acid. This indicates that E. coli lipid A acyltransferases do not have an absolute specificity for 14-carbon hydroxy fatty acids but can transfer fatty acids differing by one carbon unit if the fatty acid substrates are available. We conclude that the relaxed specificity of the P. gingivalis lipid A acyltransferases and the substrate availability account for the lipid A structural clusters that differ by 14 mass units observed in P. gingivalis lipopolysaccharide preparations.