Protease-activated receptor 2 mediates human beta-defensin 2 and CC chemokine ligand 20 mRNA expression in response to proteases secreted by Porphyromonas gingivalis

The human oral virome: Shedding light on the dark matter

Mediators of the initiation, development, and recurrence of periodontitis include the oral microbiome embedded in subgingival plaque and the host immune response to a dysbiosis within this dynamic and complex microbial community. Although mediators have been studied extensively, researchers in the field have been unable to fully ascribe certain clinical presentations of periodontitis to their nature. Emergence of high-throughput sequencing technologies has resulted in better characterization of the microbial oral dysbiosis that extends beyond the extensively studied putative bacterial periodontopathogens to a shift in the oral virome composition during disease conditions. Although the biological dark matter inserted by retroviruses was once believed to be nonfunctional, research has revealed that it encodes historical viral-eukaryotic interactions and influences host development. The objective of this review is to evaluate the proposed association of herpesviruses to the etiology and pathogenesis of periodontal disease and survey the highly abundant prokaryotic viruses to delineate their potential roles in biofilm dynamics, as well as their interactions with putative bacterial periodontopathogens and eukaryotic cells. The findings suggest that potential novel periodontal therapies targeting or utilizing the oral virome can alleviate certain clinical presentations of periodontitis. Perhaps it is time to embrace the viral dark matter within the periodontal environment to fully comprehend the pathogenesis and systemic implications of periodontitis.

Activation of calcium signaling in human gingival fibroblasts by recombinant Porphyromonas gingivalis RgpB protein

Arginine-specific cysteine proteinases, such as Arg-gingipain B (RgpB), mediate inflammation by activating protease-activated receptors (PARs). Arg-gingipain B is produced by Porphyromonas gingivalis, and is implicated in the causation of periodontal disease. The purpose of the present study was to observe the influence of recombinant RgpB protein (rRgpB) on PAR activation by monitoring intracellular Ca2+ ion concentration ([Ca2+]i) and inositol-1,4,5-triphosphate (IP3) levels in human gingival fibroblasts (HGFs). Our findings showed that rRgpB could cause a transient increase in [Ca2+]i. This increase in [Ca2+]i was completely suppressed by vorapaxar, a PAR-1 antagonist. Recombinant Arg-gingipain B increased the concentration of IP3, reaching a maximum at 60 s after treatment; this was completely inhibited by vorapaxar. We therefore conclude that rRgpB-induced calcium signaling in HGFs is mainly caused by PAR-1 activation. This suggests that PAR-1 activation plays a significant role in chronic inflammatory periodontal disease induced by P. gingivalis RgpB.

Proteinases and their receptors in inflammatory arthritis: an overview

Proteinases are enzymes with established roles in physiological and pathological processes such as digestion and the homeostasis, destruction and repair of tissues. Over the past few years, the hormone-like properties of circulating proteinases have become increasingly appreciated. Some proteolytic enzymes trigger cell signalling via proteinase-activated receptors, a family of G protein-coupled receptors that have been implicated in inflammation and pain in inflammatory arthritis. Proteinases can also regulate ion flux owing to the cross-sensitization of transient receptor potential cation channel subfamily V members 1 and 4, which are associated with mechanosensing and pain. In this Review, the idea that proteinases have the potential to orchestrate inflammatory signals by interacting with receptors on cells within the synovial microenvironment of an inflamed joint is revisited in three arthritic diseases: osteoarthritis, spondyloarthritis and rheumatoid arthritis. Unanswered questions are highlighted and the therapeutic potential of modulating this proteinase-receptor axis for the management of disease in patients with these types of arthritis is also discussed.

Apple- and Hop-Polyphenols Inhibit Porphyromonas gingivalis-Mediated Precursor of Matrix Metalloproteinase-9 Activation and Invasion of Oral Squamous Cell Carcinoma Cells

BACKGROUND

Recent epidemiologic studies have revealed a significant association between periodontitis and oral squamous cell carcinoma (OSCC). Furthermore, periodontitis is markedly associated with orodigestive cancer mortality, whereas Porphyromonas gingivalis (Pg) infection has been identified as a specific and potentially independent microbial factor related to increased risk of orodigestive cancer death. The authors previously reported that Pg induced the precursor form of matrix metalloproteinase-9 (proMMP-9) production via proteinase-activated receptor (PAR)-related pathways, after which proMMP-9 was activated by gingipains to enhance cellular invasion of SAS cells. In the present study, effects of selected polyphenols as inhibitors of cellular invasion caused by Pg gingipains in SAS cells are examined.

METHODS

OSCC cells were infected with Pg strains including gingipain mutants. To evaluate effects of inhibitors: 1) apple polyphenol (AP); 2) hop bract polyphenol (HBP); 3) high-molecular-weight fractions of HBP (HMW-HBP); 4) low-molecular-weight fractions of HBP (LMW-HBP); 5) epigallocatechin gallate (EGCg); 6) KYT-1 (Arg-gingipain inhibitor); and KYT-36 (Lys-gingipain inhibitor) in combination are used. PAR2 and PAR4 mRNA expressions are examined using real-time reverse transcription polymerase chain reaction, and signaling pathways are evaluated by western blotting analysis.

RESULTS

KYT-1/KYT-36, AP, HBP, and HMW-HBP significantly inhibited PAR2 and PAR4 mRNA expressions, proMMP-9 activation, and cellular invasion. Furthermore, AP, HBP, and HMW-HBP reduced activation of heat shock protein 27 and Ets1 and nuclear translocation of nuclear factor-kappa B, whereas EGCg and LMW-HBP did not.

CONCLUSION

These results suggest that AP, HBP, HMW-HBP are potent inhibitors of proMMP-9 activation and cellular invasion mediated with Pg in OSCC cells.

Porphyromonas gingivalis Gingipain-Dependently Enhances IL-33 Production in Human Gingival Epithelial Cells

The cytokine IL-33 is constitutively expressed in epithelial cells and it augments Th2 cytokine-mediated inflammatory responses by regulating innate immune cells. We aimed to determine the role of the periodontal pathogen, Porphyromonas gingivalis, in the enhanced expression of IL-33 in human gingival epithelial cells. We detected IL-33 in inflamed gingival epithelium from patients with chronic periodontitis, and found that P. gingivalis increased IL-33 expression in the cytoplasm of human gingival epithelial cells in vitro. In contrast, lipopolysaccharide, lipopeptide, and fimbriae derived from P. gingivalis did not increase IL-33 expression. Specific inhibitors of P. gingivalis proteases (gingipains) suppressed IL-33 mRNA induction by P. gingivalis and the P. gingivalis gingipain-null mutant KDP136 did not induce IL-33 expression. A small interfering RNA for protease-activated receptor-2 (PAR-2) as well as inhibitors of phospholipase C, p38 and NF-κB inhibited the expression of IL-33 induced by P. gingivalis. These results indicate that the PAR-2/IL-33 axis is promoted by P. gingivalis infection in human gingival epithelial cells through a gingipain-dependent mechanism.

Fusobacterium nucleatum infection of gingival epithelial cells leads to NLRP3 inflammasome-dependent secretion of IL-1β and the danger signals ASC and HMGB1

Fusobacterium nucleatum is an invasive anaerobic bacterium that is associated with periodontal disease. Previous studies have focused on virulence factors produced by F. nucleatum, but early recognition of the pathogen by the immune system remains poorly understood. Although an inflammasome in gingival epithelial cells (GECs) can be stimulated by danger-associated molecular patterns (DAMPs) (also known as danger signals) such as ATP, inflammasome activation by this periodontal pathogen has yet to be described in these cells. This study therefore examines the effects of F. nucleatum infection on pro-inflammatory cytokine expression and inflammasome activation in GECs. Our results indicate that infection induces translocation of NF-κB into the nucleus, resulting in cytokine gene expression. In addition, infection activates the NLRP3 inflammasome, which in turn activates caspase-1 and stimulates secretion of mature IL-1β. Unlike other pathogens studied until now, F. nucleatum activates the inflammasome in GECs in the absence of exogenous DAMPs such as ATP. Finally, infection promotes release of other DAMPs that mediate inflammation, such as high-mobility group box 1 protein and apoptosis-associated speck-like protein, with a similar time-course as caspase-1 activation. Thus, F. nucleatum expresses the pathogen-associated molecular patterns necessary to activate NF-κB and also provides an endogenous DAMP to stimulate the inflammasome and further amplify inflammation through secretion of secondary DAMPs.

Gingival crevicular fluid levels of protease-activated receptors type 1 and type 2 in diabetic patients with periodontitis

BACKGROUND AND OBJECTIVE

Protease activated receptor type 1 (PAR1 ) seems to play a role in periodontal repair, while PAR2 is associated with periodontal inflammation. As diabetes is a known risk factor for periodontal disease, the aim of this study was to evaluate the influence of type 2 diabetes on PAR1 and PAR2 mRNA expression in the gingival crevicular fluid of patients with chronic periodontitis before and after non-surgical periodontal treatment.

MATERIAL AND METHODS

Gingival crevicular fluid samples and clinical parameters consisting of measuring probing depth, clinical attachment level, bleeding on probing and plaque index were collected from systemically healthy patients and patients with type 2 diabetes and chronic periodontitis, at baseline and after non-surgical periodontal therapy. PAR1 and PAR2 , as well as the presence of the proteases RgpB gingipain and neutrophil proteinase-3 were assessed by quantitative polymerase chain reaction in the gingival crevicular fluid.

RESULTS

The periodontal clinical parameters significantly improved after periodontal therapy (p < 0.01). Diabetes led to increased expression of PAR1 in gingival crevicular fluid, and in the presence of chronic periodontitis, it significantly decreased the expression of PAR1 and PAR2 (p < 0.05). Moreover, non-surgical periodontal treatment in diabetics resulted in increased expression of PAR1 and PAR2 (p < 0.05), and decreased expression of RgpB gingipain and proteinase-3 (p < 0.05).

CONCLUSION

The present data demonstrated that diabetes was associated with an altered expression of PAR1 and PAR2 in the gingival crevicular fluid cells of subjects with chronic periodontitis. Future studies are necessary to elucidate the effects of PAR1 upregulation in periodontally healthy sites and PAR2 downregulation in chronic periodontitis sites on the increased susceptibility and severity of periodontitis in diabetes.

Genotype-specific regulation of oral innate immunity by T2R38 taste receptor

The bitter taste receptor T2R38 has been shown to regulate mucosal innate immune responses in the upper airway epithelium. Furthermore, SNPs in T2R38 influence the sensitivity to 6-n-propylthiouracil (PROP) and are associated with caries risk/protection. However, no study has been reported on the role of T2R38 in the innate immune responses to oral bacteria. We hypothesize that T2R38 regulates oral innate immunity and that this regulation is genotype-specific. Primary gingival epithelial cells carrying three common genotypes, PAV/PAV (PROP super-taster), AVI/PAV (intermediate) and AVI/AVI (non-taster) were stimulated with cariogenic bacteria Streptococcus mutans, periodontal pathogen Porphyromonas gingivalis or non-pathogen Fusobacterium nucleatum. QRT-PCR analyzed T2R38 mRNA, and T2R38-specific siRNA and ELISA were utilized to evaluate induction of hBD-2 (antimicrobial peptide), IL-1α and IL-8 in various donor-lines. Experiments were set up in duplicate and repeated three times. T2R38 mRNA induction in response to S. mutans was highest in PAV/PAV (4.3-fold above the unstimulated controls; p<0.05), while lowest in AVI/AVI (1.2-fold). In PAV/PAV, hBD-2 secretion in response to S. mutans was decreased by 77% when T2R38 was silenced. IL-1α secretion was higher in PAV/PAV compared to AVI/PAV or AVI/AVI with S. mutans stimulation, but it was reduced by half when T2R38 was silenced (p<0.05). In response to P. gingivalis, AVI/AVI showed 4.4-fold increase (p<0.05) in T2R38 expression, whereas the levels in PAV/PAV and AVI/PAV remained close to that of the controls. Secretion levels of IL-1α and IL-8 decreased in AVI/AVI in response to P. gingivalis when T2R38 was silenced (p<0.05), while the changes were not significant in PAV/PAV. Our data suggest that the regulation of gingival innate immunity by T2R38 is genotype-dependent and that the ability to induce a high level of hBD-2 by PAV/PAV carriers may be a reason for protection against caries in this group.

Airborne allergens induce protease activated receptor-2-mediated production of inflammatory cytokines in human gingival epithelium

OBJECTIVE

In reaching the airways inhaled allergens pass through and contact with the oral mucosa. Although they are often responsible for initiating asthmatic attacks, it is unknown whether airborne allergens can also trigger chronic inflammation of gingival epithelial cells leading to chronic periodontitis. In this study, we investigated the inflammatory responses of human gingival epithelial cells (HGECs) to airborne allergens, particularly German cockroach extract (GCE) with a focus on calcium signaling.

DESIGN

HGECs isolated from healthy donors were stimulated with GCE. Intracellular Ca(2+) concentration ([Ca(2+)]i) was measured with Fura-2-acetoxymethyl ester (Fura-2/AM) staining. Expression of inflammatory cytokines interleukin (IL)-8, IL-1β, IL-6, and NOD-like receptor family, pyridine domain-containing (NLRP) 3 was analyzed using reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

GCE promoted increase in the [Ca(2+)]i in a dose-dependent manner. Depletion of endoplasmic reticulum (ER) Ca(2+) by the ER Ca(2+) ATPase inhibitor thapsigargin (Tg) but not the depletion of extracellular Ca(2+) abolished the GCE-induced increase in [Ca(2+)]i. Treatment of phospholipase C (PLC) inhibitor (U73122) or 1,4,5-trisinositolphosphate (IP3) receptor inhibitor (2-APB) also prevented GCE-induced increase in [Ca(2+)]i. Protease activated receptor (PAR)-2 activation mainly mediated the GCE-induced increase in [Ca(2+)]i and enhanced the expression of IL-8, NLRP3, IL-1β, and IL-6 in HGECs.

CONCLUSIONS

GCE activates PAR-2, which can induce PLC/IP3-dependent Ca(2+) signaling pathway, ultimately triggering inflammation via the production of pro-inflammatory cytokines such as IL-1β, IL-6, IL-8, and NLRP 3 in HGECs.

Modulation of protease-activated receptor expression by Porphyromonas gingivalis in human gingival epithelial cells

Background

Protease-activated receptors (PARs) are G-protein-coupled receptors with an active role in mediating inflammation, pain and other functions. The oral pathogen Porphyromonas gingivalis (P. gingivalis) secretes proteases that activate PARs. The aim of this study was to elucidate the role of PARs in the pathogenesis of chronic periodontitis by expression analysis of PARs in human gingival epithelial cells (GECs) before and after P. gingivalis supernatants treatment.

Methods

GECs were isolated from healthy human gingival tissue samples. The expression of PARs in GECs was determined by reverse transcription-polymerase chain reaction (RT-PCR) and flow cytometry. The effect of P. gingivalis proteases was investigated by quantitative real-time reverse transcription polymerase chain reaction (QRT-PCR) and flow cytometry.

Results

PAR-1, PAR-2, and PAR-3 were expressed in GECs. PAR-4 was not found by both RT-PCR and flow cytometry. Analysis of gene expression using QRT-PCR showed an up-regulation of PAR-2 mRNA in comparison to the untreated control cells (P < 0.05). In contrast, the mRNA expressions of PAR-1 and PAR-3 were significantly down-regulated (P > 0.05) in response to P. gingivalis supernatant compared to that in unstimulated control cells. This effect was abrogated by the protease inhibitor TLCK (P < 0.05). The results of flow cytometry indicated PARs protein levels consistent with mRNA levels in the results of QRT-PCR.

Conclusions

Our study shows that PAR-1, PAR-2 and PAR-3 are expressed in GECs. P. gingivalis proteases play a role in the regulation of innate immune responses in GECs. GECs use PARs to recognize P. gingivalis and mediate cell responses involved in innate immunity.

Houttuynia cordata modulates oral innate immune mediators: potential role of herbal plant on oral health

OBJECTIVE

Epithelial cells play an active role in oral innate immunity by producing various immune mediators. Houttuynia cordata Thunb (H. cordata), a herbal plant found in Asia, possesses many activities. However, its impacts on oral innate immunity have never been reported. The aim of this study was to determine the effects of H. cordata extract on the expression of innate immune mediators produced by oral epithelial cells.

MATERIALS AND METHODS

Primary gingival epithelial cells (GECs) were treated with various concentrations of the extract for 18 h. The gene expression of hBD2, SLPI, cytokines, and chemokines was measured using quantitative real-time RT-PCR. The secreted proteins in the culture supernatants were detected by ELISA or Luminex assay. Cytotoxicity of the extract was assessed using CellTiter-Blue Assay.

RESULTS

H. cordata significantly induced the expression of hBD2, SLPI, IL-8, and CCL20 in a dose-dependent manner without cytotoxicity. The secreted hBD2 and SLPI proteins were modulated, and the levels of IL-2, IL-6, IL-8, and IFN-γ were significantly induced by the extract.

CONCLUSIONS

Our data indicated that H. cordata can modulate oral innate immune mediators. These findings may lead to the development of new topical agents from H. cordata for the prevention and treatment of immune-mediated oral diseases.

Protease-activated receptors expression in gingiva in periodontal health and disease

OBJECTIVE

Protease-activated receptors (PARs) are a unique class of receptors which are implicated in mediating inflammation, pain and other functions. The aim of this study was to elucidate the role of PARs in the pathogenesis of chronic periodontitis by differential expression analysis of PARs in the gingival tissues of chronic periodontitis patients compared with those of healthy control individuals.

DESIGN

Gingival tissue specimens were collected from chronic periodontitis patients (n=20) and control individuals (n=20). The expression of PAR-1, -2, -3 and -4 was determined in these tissues by immunohistochemistry and differential expression between the two groups was investigated by quantitative real-time reverse transcription-polymerase chain reaction analysis.

RESULTS

PAR-1, -2, -3 and -4 were expressed in all gingival tissues. A significant overexpression of PAR-3 was detected in chronic periodontitis-affected tissues compared to healthy gingival tissues. However, expression of PAR-2 was decreased in periodontal lesions.

CONCLUSIONS

Our study shows that PAR-1, -2, -3 and -4 are expressed in both healthy and inflamed gingival tissues. Furthermore, PAR-2 and PAR-3 may contribute to the inflammatory responses associated with chronic periodontitis.

Risk factor-dependent dynamics of atopic dermatitis: modelling multi-scale regulation of epithelium homeostasis

Epithelial tissue provides the body with its first layer of protection against harmful environmental stimuli by enacting the regulatory interplay between a physical barrier preventing the influx of external stimuli and an inflammatory response to the infiltrating stimuli. Importantly, this interdependent regulation occurs on different time scales: the tissue-level barrier permeability is regulated over the course of hours, whereas the cellular-level enzymatic reactions leading to inflammation take place within minutes. This multi-scale regulation is key to the epithelium's function and its dysfunction leads to various diseases. This paper presents a mathematical model of regulatory mechanisms in the epidermal epithelium that includes processes on two different time scales at the cellular and tissue levels. We use this model to investigate the essential regulatory interactions between epidermal barrier integrity and skin inflammation and how their dysfunction leads to atopic dermatitis (AD). Our model exhibits a structure of dual (positive and negative) control at both cellular and tissue levels. We also determined how the variation induced by well-known risk factors for AD can break the balance of the dual control. Our model analysis based on time-scale separation suggests that each risk factor leads to qualitatively different dynamic behaviours of different severity for AD, and that the coincidence of multiple risk factors dramatically increases the fragility of the epithelium's function. The proposed mathematical framework should also be applicable to other inflammatory diseases that have similar time-scale separation and control architectures.

EprS, an autotransporter protein of Pseudomonas aeruginosa, possessing serine protease activity induces inflammatory responses through protease-activated receptors

PA3535 (EprS), an autotransporter (AT) protein of Pseudomonas aeruginosa, is predicted to contain a serine protease motif. The eprS encodes a 104.5 kDa protein with a 30-amino-acid-long signal peptide, a 51.2 kDa amino-terminal secreted passenger domain and a 50.1 kDa carboxyl-terminal outer membrane channel formed translocator. Although the majority of AT proteins have been reported to be virulence factors, little is known about the functions of EprS in the pathogenicity of P. aeruginosa. In this study, we performed functional analyses of recombinant EprS secreted by Escherichia coli. The proteolytic activity of EprS was markedly decreased by changing Ser to Ala at position 308 or by serine protease inhibitors. EprS preferred to cleave substrates that terminated with arginine or lysine residues. Thus, these results indicate that EprS, a serine protease, displays the substrate specificity, cleaving after basic residues. We demonstrated that EprS activates NF-κB-driven promoters through protease-activated receptor (PAR)-1, -2 or -4 and induces IL-8 production through PAR-2 in a human bronchiole epithelial cell line. Moreover, EprS cleaved the peptides corresponding to the tethered ligand region of PAR-1, -2 and -4 at a specific site with exposure oftheir tethered ligands. Collectively, these results suggest that EprS activates host inflammatory responses through PARs.

Role of cockroach proteases in allergic disease

Allergic asthma is on the rise in developed countries, and cockroach exposure is a major risk factor for the development of asthma. In recent years, a number of studies have investigated the importance of allergen-associated proteases in modulating allergic airway inflammation. Many of the studies have suggested the importance of allergen-associated proteases as having a direct role on airway epithelial cells and dendritic cells. In most cases, activation of the protease activated receptor (PAR)-2 has been implicated as a mechanism behind the potent allergenicity associated with cockroaches. In this review, we focus on recent evidence linking cockroach proteases to activation of a variety of cells important in allergic airway inflammation and the role of PAR-2 in this process. We will highlight recent data exploring the potential mechanisms involved in the biological effects of the allergen.

Human β-defensin 2 and protease activated receptor-2 expression in patients with chronic periodontitis

OBJECTIVE

Some previous studies have shown that gingipains, trypsin-like proteases produced by Porphyromonas gingivalis, up-regulate human β defensin-2 (HBD-2) mRNA expression through protease-activated receptor-2 (PAR(2)) in gingival epithelial cells. This study aimed at investigating salivary HBD-2 levels and crevicular PAR(2) mRNA expression in human chronic periodontitis and evaluating whether periodontal treatment affected this process.

METHODS

Salivary and gingival crevicular fluid (GCF) samples were collected from periodontally healthy (control) and chronic periodontitis patients at baseline and 50 days after non-surgical periodontal treatment. Salivary HBD-2, and GCF TNF-α levels were analysed by ELISA, and PAR(2) mRNA at the GCF was evaluated by RT-PCR.

RESULTS

P. gingivalis was significantly (p<0.05) more prevalent in patients with chronic periodontitis when compared to controls. This prevalence decreased after periodontal therapy (p<0.0001). The control group showed statistically significant lower levels of HBD-2, TNF-α, and PAR(2) expression when compared to the chronic periodontitis group. In addition, periodontal treatment significantly reduced PAR(2) expression and HBD-2 levels in chronic periodontitis patients (p<0.001).

CONCLUSIONS

Our results suggest that salivary HBD-2 levels and PAR(2) mRNA expression from GCF are higher in subjects with chronic periodontitis than in healthy subjects, and that periodontal treatment decreases both HBD-2 levels and PAR(2) expression.

Protease-activated receptor 2 signaling in inflammation

Protease-activated receptors (PARs) are G protein-coupled receptors that are activated by proteolytical cleavage of the amino-terminus and thereby act as sensors for extracellular proteases. While coagulation proteases activate PARs to regulate hemostasis, thrombosis, and cardiovascular function, PAR2 is also activated in extravascular locations by a broad array of serine proteases, including trypsin, tissue kallikreins, coagulation factors VIIa and Xa, mast cell tryptase, and transmembrane serine proteases. Administration of PAR2-specific agonistic and antagonistic peptides, as well as studies in PAR2 knockout mice, identified critical functions of PAR2 in development, inflammation, immunity, and angiogenesis. Here, we review these roles of PAR2 with an emphasis on the role of coagulation and other extracellular protease pathways that cleave PAR2 in epithelial, immune, and neuronal cells to regulate physiological and pathophysiological processes.

Effects of fruit and vegetable low molecular mass fractions on gene expression in gingival cells challenged with Prevotella intermedia and Actinomyces naeslundii

Low molecular mass (LMM) fractions obtained from extracts of raspberry, red chicory, and Shiitake mushrooms have been shown to be an useful source of specific antibacterial, antiadhesion/coaggregation, and antibiofilm agent(s) that might be used for protection towards caries and gingivitis. In this paper, the effects of such LMM fractions on human gingival KB cells exposed to the periodontal pathogens Prevotella intermedia and Actinomyces naeslundii were evaluated. Expression of cytokeratin 18 (CK18) and β4 integrin (β4INT) genes, that are involved in cell proliferation/differentiation and adhesion, and of the antimicrobial peptide β2 defensin (HβD2) in KB cells was increased upon exposure to either live or heat-killed bacteria. All LMM fractions tested prevented or reduced the induction of gene expression by P. intermedia and A. naeslundii depending on the experimental conditions. Overall, the results suggested that LMM fractions could modulate the effects of bacteria associated with periodontal disease in gingival cells.

Epigenetic regulation of human β-defensin 2 and CC chemokine ligand 20 expression in gingival epithelial cells in response to oral bacteria

Gingival epithelia utilize multiple signaling pathways to regulate innate immune responses to various oral bacteria, but little is understood about how these bacteria alter epithelial epigenetic status. In this study we report that DNA methyltransferase (DNMT1) and histone deacetylase expression were decreased in gingival epithelial cells treated with oral pathogen Porphyromonas gingivalis and nonpathogen Fusobacterium nucleatum. Pretreatment with trichostatin A and sodium butyrate, which increase acetylation of chromatin histones, significantly enhanced the gene expression of antimicrobial proteins human β-defensin 2 (hBD2) and CC chemokine ligand 20 (CCL20) in response to both bacterial challenges. Pretreatment with DNMT inhibitor 5'-azacytidine increased hBD2 and CCL20 expression in response to F. nucleatum, but not to P. gingivalis. Furthermore, we observed a differential pattern of protein levels of H3K4me3, which has been associated with chromatin remodeling and activation of gene transcription, in response to P. gingivalis vs. F. nucleatum. This study provides a new insight into the bacteria-specific innate immune responses via epigenetic regulation.

Antimicrobial peptides and periodontal disease

AIMS

The goal of this review is to identify the antimicrobial proteins in the oral fluids, saliva and gingival crevicular fluid and identify functional families and candidates for antibacterial treatment.

RESULTS

Periodontal biofilms initiate a cascade of inflammatory and immune processes that lead to the destruction of gingival tissues and ultimately alveolar bone loss and tooth loss. Treatment of periodontal disease with conventional antibiotics does not appear to be effective in the absence of mechanical debridement. An alternative treatment may be found in antimicrobial peptides and proteins, which can be bactericidal and anti-inflammatory and block the inflammatory effects of bacterial toxins. The peptides have co-evolved with oral bacteria, which have not developed significant peptide resistance. Over 45 antibacterial proteins are found in human saliva and gingival crevicular fluid. The proteins and peptides belong to several different functional families and offer broad protection from invading microbes. Several antimicrobial peptides and proteins (AMPs) serve as templates for the development of therapeutic peptides and peptide mimetics, although to date none have demonstrated efficacy in human trials.

CONCLUSIONS

Existing and newly identified AMPs may be developed for therapeutic use in periodontal disease or can serve as templates for peptide and peptide mimetics with improved therapeutic indices.

Staphylococcus aureus Biofilm and Planktonic cultures differentially impact gene expression, mapk phosphorylation, and cytokine production in human keratinocytes

Background

Many chronic diseases, such as non-healing wounds are characterized by prolonged inflammation and respond poorly to conventional treatment. Bacterial biofilms are a major impediment to wound healing. Persistent infection of the skin allows the formation of complex bacterial communities termed biofilm. Bacteria living in biofilms are phenotypically distinct from their planktonic counterparts and are orders of magnitude more resistant to antibiotics, host immune response, and environmental stress. Staphylococcus aureus is prevalent in cutaneous infections such as chronic wounds and is an important human pathogen.

Results

The impact of S. aureus soluble products in biofilm-conditioned medium (BCM) or in planktonic-conditioned medium (PCM) on human keratinocytes was investigated. Proteomic analysis of BCM and PCM revealed differential protein compositions with PCM containing several enzymes involved in glycolysis. Global gene expression of keratinocytes exposed to biofilm and planktonic S. aureus was analyzed after four hours of exposure. Gene ontology terms associated with responses to bacteria, inflammation, apoptosis, chemotaxis, and signal transduction were enriched in BCM treated keratinocytes. Several transcripts encoding cytokines were also upregulated by BCM after four hours. ELISA analysis of cytokines confirmed microarray results at four hours and revealed that after 24 hours of exposure, S. aureus biofilm induced sustained low level cytokine production compared to near exponential increases of cytokines in planktonic treated keratinocytes. The reduction in cytokines produced by keratinocytes exposed to biofilm was accompanied by suppressed phosphorylation of MAPKs. Chemical inhibition of MAPKs did not drastically reduce cytokine production in BCM-treated keratinocytes suggesting that the majority of cytokine production is mediated through MAPK-independent mechanisms.

Conclusions

Collectively the results indicate that S. aureus biofilms induce a distinct inflammatory response compared to their planktonic counterparts. The differential gene expression and production of inflammatory cytokines by biofilm and planktonic cultures in keratinocytes could have implications for the formation and persistence of chronic wounds. The formation of a biofilm should be considered in any study investigating host response to bacteria.

Mucosal allergic sensitization to cockroach allergens is dependent on proteinase activity and proteinase-activated receptor-2 activation

We have shown that proteinase-activated receptor-2 (PAR(2)) activation in the airways leads to allergic sensitization to concomitantly inhaled Ags, thus implicating PAR(2) in the pathogenesis of asthma. Many aeroallergens with proteinase activity activate PAR(2). To study the role of PAR(2) in allergic sensitization to aeroallergens, we developed a murine model of mucosal sensitization to cockroach proteins. We hypothesized that PAR(2) activation in the airways by natural allergens with serine proteinase activity plays an important role in allergic sensitization. Cockroach extract (CE) was administered to BALB/c mice intranasally on five consecutive days (sensitization phase) and a week later for four more days (challenge phase). Airway hyperresponsiveness (AHR) and allergic airway inflammation were assessed after the last challenge. To study the role of PAR(2), mice were exposed intranasally to a receptor-blocking anti-PAR(2) Ab before each administration of CE during the sensitization phase. Mucosal exposure to CE induced eosinophilic airway inflammation, AHR, and cockroach-specific IgG1. Heat-inactivated or soybean trypsin inhibitor-treated CE failed to induce these effects, indicating that proteinase activity plays an important role. The use of an anti-PAR(2) blocking Ab during the sensitization phase completely inhibited airway inflammation and also decreased AHR and the production of cockroach-specific IgG1. PAR(2) activation by CE acts as an adjuvant for allergic sensitization even in the absence of functional TLR4. We conclude that CE induces PAR(2)-dependent allergic airway sensitization in a mouse model of allergic airway inflammation. PAR(2) activation may be a general mechanism used by aeroallergens to induce allergic sensitization.

Protease-activated receptor-2 mediates the expression of inflammatory cytokines, antimicrobial peptides, and matrix metalloproteinases in keratinocytes in response to Propionibacterium acnes

Propionibacterium acnes (P. acnes) has been known to produce various exogenous proteases, however, their role in acne pathogenesis remains largely unknown. Proteases elicit cellular responses, at least in part, via proteinase-activated receptor-2 (PAR-2), which is known to mediate inflammation and immune response. In this study, we investigated whether proteases from P. acnes could activate PAR-2 on keratinocytes and induce pro-inflammatory cytokines, antimicrobial peptides (AMPs), and matrix metalloproteinases (MMPs) via PAR-2 signaling. We examined PAR-2 expression and protease activity in acne lesions using immunofluorescence staining and in situ zymography. The effect of the culture supernatant of P. acnes on Ca(2+) signaling in immortalized keratinocytes (HaCaT) was measured using a fluorescence method. HaCaT cells were treated with P. acnes strain ATCC 6919 culture supernatant, with or without pretreatment with serine protease inhibitor or selective PAR-2 antagonist and the gene expression of pro-inflammatory cytokines, AMPs, and MMPs was detected using real-time reverse transcription-polymerase chain reaction. We found that the protease activity and PAR-2 expression were increased in acne lesions. The P. acnes culture supernatant induced calcium signaling in keratinocytes via PAR-2 and stimulated the mRNA expression of interleukin (IL)-1α, -8, tumor necrosis factor (TNF)-α, human beta defensin (hBD)-2, LL-37, MMP-1, -2, -3, -9, and -13 in keratinocytes, which was significantly inhibited by serine protease inhibitor as well as selective PAR-2 specific antagonist. These results indicate that PAR-2 plays an important role in the pathogenesis of acne by inducing inflammatory mediators in response to proteases secreted from P. acnes.

PAR1- and PAR2-induced innate immune markers are negatively regulated by PI3K/Akt signaling pathway in oral keratinocytes

Background

Protease-Activated Receptors (PARs), members of G-protein-coupled receptors, are activated by proteolytic activity of various proteases. Activation of PAR1 and PAR2 triggers innate immune responses in human oral keratinocytes (HOKs), but the signaling pathways downstream of PAR activation in HOKs have not been clearly defined. In this study, we aimed to determine if PAR1- and PAR2-mediated signaling differs in the induction of innate immune markers CXCL3, CXCL5 and CCL20 via ERK, p38 and PI3K/Akt.

Results

Our data show the induction of innate immunity by PAR1 requires both p38 and ERK MAP kinases, while PAR2 prominently signals via p38. However, inhibition of PI3K enhances expression of innate immune markers predominantly via suppressing p38 phosphorylation signaled by PAR activation.

Conclusion

Our data indicate that proteases mediating PAR1 and PAR2 activation differentially signal via MAP kinase cascades. In addition, the production of chemokines induced by PAR1 and PAR2 is suppressed by PI3K/Akt, thus keeping the innate immune responses of HOK in balance. The results of our study provide a novel insight into signaling pathways involved in PAR activation.

Fusobacterium nucleatum-associated beta-defensin inducer (FAD-I): identification, isolation, and functional evaluation

Human β-defensins (hBDs) are small, cationic antimicrobial peptides, secreted by mucosal epithelial cells that regulate adaptive immune functions. We previously reported that Fusobacterium nucleatum, a ubiquitous gram-negative bacterium of the human oral cavity, induces human β-defensin 2 (hBD2) upon contact with primary oral epithelial cells. We now report the isolation and characterization of an F. nucleatum (ATCC 25586)-associated defensin inducer (FAD-I). Biochemical approaches revealed a cell wall fraction containing four proteins that stimulated the production of hBD2 in human oral epithelial cells (HOECs). Cross-referencing of the N-terminal sequences of these proteins with the F. nucleatum genome revealed that the genes encoding the proteins were FadA, FN1527, FN1529, and FN1792. Quantitative PCR of HOEC monolayers challenged with Escherichia coli clones expressing the respective cell wall proteins revealed that FN1527 was most active in the induction of hBD2 and hence was termed FAD-I. We tagged FN1527 with a c-myc epitope on the C-terminal end to identify and purify it from the E. coli clone. Purified FN1527 (FAD-I) induced hBD2 mRNA and protein expression in HOEC monolayers. F. nucleatum cell wall and FAD-I induced hBD2 via TLR2. Porphorymonas gingivalis, an oral pathogen that does not induce hBD2 in HOECs, was able to significantly induce expression of hBD2 in HOECs only when transformed to express FAD-I. FAD-I or its derivates offer a potentially new paradigm in immunoregulatory therapeutics because they may one day be used to bolster the innate defenses of vulnerable mucosae.

Corruption of innate immunity by bacterial proteases

The innate immune system of the human body has developed numerous mechanisms to control endogenous and exogenous bacteria and thus prevent infections by these microorganisms. These mechanisms range from physical barriers such as the skin or mucosal epithelium to a sophisticated array of molecules and cells that function to suppress or prevent bacterial infection. Many bacteria express a variety of proteases, ranging from non-specific and powerful enzymes that degrade many proteins involved in innate immunity to proteases that are extremely precise and specific in their mode of action. Here we have assembled a comprehensive picture of how bacterial proteases affect the host's innate immune system to gain advantage and cause infection. This picture is far from being complete since the numbers of mechanisms utilized are as astonishing as they are diverse, ranging from degradation of molecules vital to innate immune mechanisms to subversion of the mechanisms to allow the bacterium to hide from the system or take advantage of it. It is vital that such mechanisms are elucidated to allow strategies to be developed to aid the innate immune system in controlling bacterial infections.

Interplay of protease-activated receptors and NOD pattern recognition receptors in epithelial innate immune responses to bacteria

Protease-activated receptors (PARs), nucleotide-binding oligomerization domain (NOD) receptors and Toll-like receptors (TLRs) play a role in innate immunity, but little is known about interaction between these receptors. The goal of this study was to investigate how silencing one receptor affects the expression of other receptors and downstream innate immune markers in response to bacteria. Human gingival epithelial cells (GECs) were transfected with siRNA specific for PAR1 or PAR2, then stimulated with periopathogen Porphyromonas gingivalis, bridging organism between pathogens and non-pathogens Fusobacterium nucleatum, or non-pathogen Streptococcus gordonii. PAR1 or PAR2 knock-down resulted in up-regulated NOD1 and NOD2 expression with P. gingivalis or F. nucleatum stimulation (p<0.01), as well as enhanced TLR2 and TLR4 expression when cells were stimulated by bacteria that utilize TLR2 or TLR4, respectively. Involvement of PARs for induction of CC chemokine ligand 20 (CCL20), a cytokine with antimicrobial properties, was observed following stimulation of the three bacterial species. Furthermore, results from multiple cytokine ELISA array showed receptors utilized in the induction of various innate immune markers are tailored to individual bacterium tested. Our data suggest complex interplay of several receptors is required for appropriate innate immune responses to the different types of bacteria present within the oral cavity and that receptor expression itself is altered depending on which organism the cell encounters.

German cockroach frass proteases modulate the innate immune response via activation of protease-activated receptor-2

Allergen exposure can induce an early innate immune response; however, the mechanism by which this occurs has not been addressed. In this report, we demonstrate a role for the active serine proteases in German cockroach (GC) feces (frass) and protease-activated receptor (PAR)-2 in modulating the innate immune response. A single exposure of GC frass induced inflammatory cytokine production and cellular infiltration in the airways of mice. In comparison, exposure to protease-depleted GC frass resulted in diminution of inflammatory cytokine production and airway neutrophilia, but had no effect on macrophage infiltration. Selective activation of PAR-2 confirmed that PAR-2 was sufficient to induce airway inflammation. Exposure of GC frass to PAR-2-deficient mice led to decreased immune responses to GC frass compared to wild-type mice. Using the macrophage as an early marker of the innate immune response, we found that GC frass induced significant release of tumor necrosis factor-alpha from primary alveolar macrophages. This effect was dependent on the intrinsic proteases in GC frass. We confirmed GC frass-induced cytokine expression was mediated by activation of NF-kappaB and ERK in a macrophage cell line. Collectively, these data suggest a central role for GC frass protease-PAR-2 activation in regulating the innate immune response through the activation of alveolar macrophages. Understanding the potential role of protease-PAR-2 activation as a danger signal or adjuvant could yield attractive therapeutic targets.

Novel signaling interactions between proteinase-activated receptor 2 and Toll-like receptors in vitro and in vivo

Toll-like receptors (TLRs) and proteinase-activated receptors (PARs) function as innate immune biosensors in mucosal epithelial cells (ECs). We previously reported the functional and physical interactions between TLR4 and PAR(2). We have extended these findings herein by showing the cooperation between PAR(2) and TLR2, TLR3, or TLR4 for activation of nuclear factor-kappaB-dependent signaling in mucosal EC lines. In contrast, activation of PAR(2) negatively regulated TLR3-dependent antiviral pathway, blunting the expression of TLR3/interferon regulatory factor-3 (IRF-3)-driven genes, as well as activation of IRF-3 and STAT1. Consistent with these in vitro observations, PAR(2)(-/-) and TLR4(-/-) mice, which were refractory to footpad edema induced by PAR(2) agonist peptide, were protected from mouse-adapted H1N1 influenza A virus-induced lethality when compared to wild-type (WT) mice. These data support and extend our recently described, novel model of PAR(2)-TLR4 "receptor cooperativity" and highlight the complexity of signaling integration between heterologous innate immune biosensors.

Phospholipase C, p38/MAPK, and NF-kappaB-mediated induction of MIP-3alpha/CCL20 by Porphyromonas gingivalis

Macrophage inflammatory protein-3alpha/C-C chemokine ligand 20 (MIP-3alpha/CCL20) is an antimicrobial peptide that plays an important role in innate immunity. In addition to direct microbicidal effects, MIP-3alpha/CCL20 also exhibits cytokine-like functions that are critical during dendritic cell activation. The aim of the present study was to investigate further which signaling pathways are involved in the MIP-3alpha/CCL20 mRNA expression in response to whole-cell Porphyromonas gingivalis. Primary gingival epithelial cells (GECs) and the immortalized oral keratinocyte cell-line OKF6/TERT-2 were stimulated with whole-cell P. gingivalis. Prior to stimulation, GECs and OKF6/TERT-2 cells were pretreated with specific inhibitors for nuclear-factor-kappaB (NF-kappaB), mitogen-activated protein kinase (MAPK), phospholipase C (PLC), and phosphatidylinositol-3-kinase (PI3K). In GECs and OKF6/TERT-2 cells, activation of NF-kappaB was examined after exposure to P. gingivalis. The gene expression of MIP-3alpha/CCL20 was significantly induced in response to P. gingivalis (P <or= 0.05) compared to unstimulated control cells. This induction was specifically blocked when cells were pre-incubated with inhibitors for NF-kappaB, MAPK, and PLC (P <or= 0.05), but not for PI3K. These results demonstrate that P. gingivalis induces the MIP-3alpha/CCL20 mRNA in a NF-kappaB-, PLC-, and MAPK-dependent manner.

Modulation of expression of innate immunity markers CXCL5/ENA-78 and CCL20/MIP3alpha by protease-activated receptors (PARs) in human gingival epithelial cells

Protease-activated receptors (PARs) are G-protein-coupled receptors with an active role in host defense. The two most highly expressed members of the PAR family in gingival epithelial cells (GECs) are PAR1 and PAR2. The major virulence factors of periodontal pathogen Porphyromonas gingivalis are its proteases which can activate PAR2. However, little is known about the function of PARs in GECs when they are activated by their endogenous agonist enzymes. The purpose of this study was to characterize how the expression of innate immune markers is modulated when PAR1 and PAR2 are activated by their agonist enzymes, thrombin and trypsin, respectively. Here, we report that activation of PAR1 and PAR2 induces cell proliferation at low concentration. Activation of PAR via proteolytic activity of thrombin and trypsin induces expression of CXCL5/ENA-78 and CCL20/MIP3alpha in a concentration-dependent manner. Induction of CXCL5 via PAR1 was inhibited in the presence of PAR1 cleavage blocking antibodies and by PAR1 siRNA. The induction of CXCL5 and CCL20 via PAR2 was inhibited by PAR2 siRNA. These findings indicate an active role in innate immune responses by PAR1 and PAR2 in GECs. Modulation of innate immunity by PARs may contribute to co-ordinated and balanced immunosurveillance in GECs.

SELDI-TOF-MS of gingival crevicular fluid--a methodological approach

Human neutrophil peptides (HNPs) and the human cathelicidin LL-37 are antimicrobial peptides secreted by neutrophils, which play a crucial role in innate immune responses. The aim of this study was to establish a new method for ProteinChip arrays in combination with surface enhanced laser desorption/ionization (SELDI) technology and time-of-flight mass spectrometry to analyze gingival crevicular fluid (GCF) samples. To optimize experimental conditions, four different ProteinChip arrays (NP20; CM10, pH 4; CM10, pH 7; IMAC) along with corresponding binding buffers were tested. GCF samples were collected from patients showing healthy periodontal sites and sites with early signs of inflammation (gingivitis), but with no pocket depth greater than 4 mm. For GCF analysis, NP20 arrays and CM10 (pH 4) arrays showed specific and reproducible profiles in the range of 2.5-30.0 kDa. Donors that demonstrated significantly higher intensity peaks corresponding to the mass of LL-37 (p=0.01) also tended to show greater intensity peaks corresponding to the masses of HNP-1 and HNP-2 in samples from inflamed compared to healthy periodontal sites. The findings indicate that analysis of GCF samples by SELDI-TOF mass spectrometry is a useful approach to simultaneously analyze multiple markers, such as antimicrobial peptides, which may be beneficial for determination of new periodontal risk factors.

Immunoglobulin A with protease activity secreted in human milk activates PAR-2 receptors, of intestinal epithelial cells HT-29, and promotes beta-defensin-2 expression

Secretory antibodies of the immunoglobulin A (sIgA) class constitute the first line of antigen-specific immune protection against pathogens and other antigens at mucosal surfaces. Although initially perceived as potentially deleterious, catalytic antibodies have been proposed to participate in the removal of metabolic wastes and in protection against infection. Here we show that the presence of sIgA endowed with serine protease-like hydrolytic activity in milk strongly correlates with PAR-2 activation in human intestinal epithelial cells. F(ab')(2) fragments of sIgA activated the epithelial cells in culture to produce beta-defensin-2 (hBD2). Intracellular Ca(2+) mobilization was induced by treatment with (1) sIgA-F(ab')(2) fragments; (2) trypsin, a recognized PAR-2 agonist; or (3) a synthetic PAR-2 agonist peptide (SLIGKV). The co-treatment with a synthetic PAR-2 antagonist peptide (FSLLRY) and sIgA-F(ab')(2) fragments eliminates the latter's effect; nevertheless, cells were not refractory to subsequent stimulation with sIgA-F(ab')(2) fragments. Both the induction of hBD-2 expression in epithelial cells and the increase in intracellular [Ca(2+)] stimulated by sIgA-F(ab')(2) fragments were inhibited by treatment with serine protease inhibitors or pertussis toxin (PTX). These findings suggest that catalytic antibodies can activate intestinal epithelial cells through G-protein-coupled PAR-2, and could actively participate in the immune system of breastfed babies inducing the production of peptides related to innate defense, such as defensins.