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 Receptor Type 1 Activation Enhances Osteogenic Activity in Human Periodontal Ligament Stem Cells

Protease-activated receptor 1 (PAR₁) has been associated to tissue repair and bone healing. The aim of the present study was to evaluate the effect of PAR₁ activation on the osteogenic activity of human periodontal ligament stem cells (PDLSCs). PDLSCs were cultured in the presence of PAR₁-selective agonist peptide (100 nM), thrombin (0.1 U/mL), or PAR₁ antagonist peptide (100 nM). Calcium deposits, calcium concentration (supernatant), alkaline phosphatase activity (ALP), cell proliferation, and gene (qPCR) and protein expression (ELISA assay) of osteogenic factors were assessed at 2, 7, and 14 days. PAR₁ activation led to increased calcium deposits (p < 0.05), calcium concentration (p < 0.05), ALP activity (p < 0.05), and cell proliferation (p < 0.05). Further, PAR₁ activation may increase gene and protein expression of Runx2 (p < 0.05) and OPG (p < 0.05). In conclusion, PAR₁ activation increases osteogenic activity of PDLSCs, providing a possible new strategy for periodontal regenerative therapies.

Expression of protease-activated receptors 1 and 2 in individuals with healthy gingiva and chronic periodontitis

Background

Protease-activated receptors (PAR-1 and PAR-2) are found to be immensely exhibited in the periodontal tissues. These receptors are involved in the inflammatory and repair processes. Activation of PARs is mainly by the bacterial and endogenous enzymes. The aim of the study was to determine the role of PAR-1 and PAR-2 in initiating periodontal inflammation and to immunolocalize these receptors in the gingival tissues of healthy and chronic periodontitis individuals.

Materials and Methods

A total of 50 patients were selected for this study, of which 25 were healthy controls and 25 were chronic periodontitis patients. Gingival tissues were excised from the marginal gingiva and interdental papilla under local anesthesia (xylocaine with 2% adrenaline) during crown lengthening procedure or during periodontal therapy depending on the respective groups. Immunohistochemical analyses of PARs were done by staining the samples with hematoxylin and eosin and with primary and secondary antibody for PAR-1 and PAR-2.

Results

The Hematoxylin and Eosin staining showed more inflammatory changes in the periodontitis group compared to healthy gingiva. In chronic periodontitis, PAR-1-positive cells were seen in the basal layer with a weak expression and were showing negative expression in the superficial layer. In consideration of PAR-2, there was a very strong expression up to the superficial layer of the epithelium, compared to PAR-1. On comparing the intensity of staining in the connective tissue of chronic periodontitis sample, there was an increased expression of PAR-2 compared with PAR-1. A low positive expression of PAR-1 and PAR-2 was observed in the epithelium and connective tissue of the healthy tissues.

Conclusion

The results clearly demonstrated the role of PAR-1 and 2 in periodontal inflammation.

The Role of Proteinase-Activated Receptors 1 and 2 in the Regulation of Periodontal Tissue Metabolism and Disease

Proteinase-activated receptors 1 (PAR1) and 2 (PAR2) are the most highly expressed members of the PAR family in the periodontium. These receptors regulate periodontal inflammatory and repair processes through their activation by endogenous and bacterial enzymes. PAR1 is expressed by the periodontal cells such as human gingival fibroblasts, gingival epithelial cells, periodontal ligament cells, osteoblasts, and monocytic cells and can be activated by thrombin, matrix metalloproteinase 1 (MMP-1), MMP-13, fibrin, and gingipains from Porphyromonas gingivalis. PAR2 is expressed by neutrophils, osteoblasts, oral epithelial cells, and human gingival fibroblasts, and its possible activators in the periodontium are gingipains, neutrophil proteinase 3, and mast cell tryptase. The mechanisms through which PARs can respond to periodontal enzymes and result in appropriate immune responses have until recently been poorly understood. This review discusses recent findings that are beginning to identify a cardinal role for PAR1 and PAR2 on periodontal tissue metabolism.

The role of toll-like and protease-activated receptors and associated intracellular signaling in Porphyromonas gingivalis-infected gingival fibroblasts

Porphyromonas gingivalis, which is considered a keystone agent in periodontitis, has evolved elaborate mechanisms to grow and survive in a hostile milieu. The gingival fibroblast is the major cell type in the gingiva and is considered to be important in the periodontitis-associated inflammation. As a part of the innate immune response, they produce cytokines such as CXCL8 and interleukin (IL)-6 which are believed to contribute to the destruction of the tooth-supporting tissues. This study investigates how the expression of protease-activated receptors (PAR1, PAR2) and toll-like receptors (TLR2, TLR4) changes with P. gingivalis exposure and how silencing of one receptor affects the expression of the other receptors. The importance of protein kinase C (PKC) and p38 in the regulation of CXCL8 and IL-6 was also examined. Receptors were knockdown with small-interfering RNA. PKC or p38 was blocked prior to stimulation with P. gingivalis. Fibroblasts were able to compensate for PAR1 knockdown with increased expression of PAR2. PKC and p38 were involved in the regulation of P. gingivalis-induced CXCL8 and IL-6. Our results indicate that PAR1 and PAR2 could be implicated in periodontitis and that PKC and P38 play a role in the inflammatory response in P. gingivalis-infected gingival fibroblasts.

ADAM10 mediates the house dust mite-induced release of chemokine ligand CCL20 by airway epithelium

BACKGROUND

House dust mite (HDM) acts on the airway epithelium to induce airway inflammation in asthma. We previously showed that the ability of HDM to induce allergic sensitization in mice is related to airway epithelial CCL20 secretion.

OBJECTIVE

As a disintegrin and metalloprotease (ADAM)s have been implicated in chemokine shedding, we sought to determine their involvement in HDM-induced release of chemokines, including CCL20, by airway epithelial cells.

METHODS

We studied the effects of pharmacological ADAM inhibitors as well as ADAM10 and ADAM17 siRNA downregulation on chemokine release using (multiplex) ELISA in supernatants from HDM-exposed human bronchial epithelial 16HBE cells and primary normal human bronchial epithelial cells (NHBE) at 4-24 h.

RESULTS

House dust) mite markedly increased CCL20 levels in both 16HBE and NHBE cells (16-24 h). In 16HBE cells, the HDM-induced increase was observed as early as 4 h upon exposure and the use of specific inhibitors indicated the involvement of ADAM10/17-mediated shedding. siRNA knockdown of ADAM10, but not of ADAM17, significantly reduced the HDM-induced release of CCL20 in both 16HBE and NHBE cells. A similar effect was observed for HDM-induced CCL2, CCL5, and CXCL8 release in NHBE cells. The HDM-induced increase in CCL20 levels was not affected by protein synthesis inhibitor cycloheximide nor protein transport inhibitor monensin, indicating that HDM induces surface shedding of chemokines.

CONCLUSION

Our data show for the first time that ADAM10 activity contributes to HDM-induced shedding of chemokines, including CCL20. The ADAM10/CCL20 axis may be a target for novel therapeutic strategies in asthma.

Expression of protease activated receptor-1 in chronic periodontitis

BACKGROUND

Protease activated receptor-1 (PAR1) activation by thrombin may play a role in repair and homeostasis of periodontal tissues. The main objective of this study is to investigate PAR1 expression in patients with periodontitis, before and after non-surgical periodontal treatment, and to associate its expression with the presence of inflammatory biomarkers and PAR2 expression.

METHODS

Gingival crevicular fluid (GCF) samples and clinical parameters, including probing depth, clinical attachment level, bleeding on probing, and gingival and plaque indices, were collected from periodontally healthy individuals and patients with moderate chronic periodontitis (CP) before and 6 weeks after periodontal non-surgical treatment. PAR1 and PAR2 messenger RNA (mRNA) at the GCF were evaluated by quantitative polymerase chain reaction (qPCR). Flow cytometry analysis identified the GCF PAR1-expressing cells. GCF inflammatory biomarkers were also determined.

RESULTS

Clinical parameters were significantly improved after therapy (P <0.01). The qPCR analysis showed that, before therapy, PAR1 mRNA levels in CP were similar to controls. Periodontal treatment led to increased PAR1 expression in CP (P <0.05). PAR1 expression was inversely correlated to PAR2 expression and with interleukins 6 and 8, tumor necrosis factor-α, interferon-γ, and matrix metalloproteinase-2 levels.

CONCLUSIONS

Periodontal treatment results in PAR1 overexpression in the GCF, and PAR1 expression is associated with decreased expression of inflammatory biomarkers and inversely correlated to PAR2 expression in the GCF. Therefore, the data suggest the importance of PAR1 mediating the known anabolic actions of thrombin in the periodontium.

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.

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.

House dust mite-induced calcium signaling instigates epithelial barrier dysfunction and CCL20 production

BACKGROUND

House dust mite (HDM) affects the immunological and physical barrier function of airway epithelium, leading to allergic sensitization, airway remodeling, and eosinophilic inflammation in mouse models, although the mechanisms are still largely unknown.

OBJECTIVE

Given the implications for adenosine triphosphate (ATP)-dependent Ca(2+) signaling in allergic sensitization in mice, we sought to determine the role of intracellular Ca(2+) concentration ([Ca(2+)](i)) in HDM-induced barrier dysfunction and pro-inflammatory activity of bronchial epithelium.

METHODS

We investigated the effect of HDM on accumulation of [Ca(2+)](i) levels, barrier function, and CCL20 release in human bronchial epithelial 16HBE cells and primary bronchial epithelial cells (PBECs) from healthy subjects and asthma patients. Involvement of ATP-dependent activation of purinergic receptors and downstream Ca(2+) influx was studied, using the ATP hydrolyzing agent apyrase, the purinergic receptor agonist PPADS, the calcium chelator BAPTA-AM, and calpain inhibitors.

RESULTS

Asthma PBECs were more susceptible to HDM-induced barrier dysfunction, CCL20 secretion, and Ca(2+) influx than healthy PBECs. Furthermore, we show that the HDM-induced increase in CCL20 in PBECs and 16HBE cells and the HDM-induced barrier dysfunction in 16HBE cells are dependent on [Ca(2+)](i) accumulation. Additionally, we demonstrate that [Ca(2+)](i) accumulation is initiated partly through the activation of purinergic receptors, which contributes to HDM-induced epithelial barrier dysfunction by disruption of cell-cell contacts, but not CCL20 secretion.

CONCLUSION

Our data show for the first time that Ca(2+) signaling plays a crucial role in barrier dysfunction and the pro-inflammatory response of bronchial epithelium upon HDM exposure and may thus have important implications for the development of allergic asthma.

Toward drugs for protease-activated receptor 2 (PAR2)

PAR2 has a distinctive functional phenotype among an unusual group of GPCRs called protease activated receptors, which self-activate after cleavage of their N-termini by mainly serine proteases. PAR2 is the most highly expressed PAR on certain immune cells, and it is activated by multiple proteases (but not thrombin) in inflammation. PAR2 is expressed on many types of primary human cells and cancer cells. PAR2 knockout mice and PAR2 agonists and antagonists have implicated PAR2 as a promising target in inflammatory conditions; respiratory, gastrointestinal, metabolic, cardiovascular, and neurological dysfunction; and cancers. This article summarizes salient features of PAR2 structure, activation, and function; opportunities for disease intervention via PAR2; pharmacological properties of published or patented PAR2 modulators (small molecule agonists and antagonists, pepducins, antibodies); and some personal perspectives on limitations of assessing their properties and on promising new directions for PAR2 modulation.

Inhibition of the Plasma-Membrane-Associated Serine Protease Cathepsin G by Mycobacterium tuberculosis Rv3364c Suppresses Caspase-1 and Pyroptosis in Macrophages

Tuberculosis is a disease associated with the infection of a great part of the world’s population and is responsible for the death of two to three million people annually. Mycobacterium tuberculosis infects macrophages and subverts its mechanisms of killing. The pathogen suppresses macrophage apoptosis by many different mechanisms. We describe that, upon uptake by macrophages, M. tuberculosis overexpresses an operon Rv3361c-Rv3365c and secretes Rv3364c. The Rv3365c knockout strain is deficient in apoptosis inhibition. The Rv3364c protein binds to the serine protease cathepsin G on the membrane, inhibiting its enzymatic activity and the downstream activation of caspase-1-dependent apoptosis. In summary, M. tuberculosis prevents macrophage pyroptosis by a novel mechanism involving cytoplasmic surveillance proteins.

German cockroach proteases and protease-activated receptor-2 regulate chemokine production and dendritic cell recruitment

We recently showed that serine proteases in German cockroach (GC) feces (frass) decreased experimental asthma through the activation of protease-activated receptor (PAR)-2. Since dendritic cells (DCs) play an important role in the initiation of asthma, we queried the role of GC frass proteases in modulating CCL20 (chemokine C-C motif ligand 20) and granulocyte macrophage colony-stimulating factor (GM-CSF) production, factors that regulate pulmonary DCs. A single exposure to GC frass resulted in a rapid, but transient, increase in GM-CSF and a steady increase in CCL20 in the airways of mice. Instillation of protease-depleted GC frass or instillation of GC frass in PAR-2-deficient mice significantly decreased chemokine release. A specific PAR-2-activating peptide was also sufficient to induce CCL20 production. To directly assess the role of the GC frass protease in chemokine release, we enriched the protease from GC frass and confirmed that the protease was sufficient to induce both GM-CSF and CCL20 production in vivo. Primary airway epithelial cells produced both GM-CSF and CCL20 in a protease- and PAR-2-dependent manner. Finally, we show a decreased percentage of myeloid DCs in the lung following allergen exposure in PAR-2-deficient mice compared to wild-type mice. However, there was no difference in GC frass uptake. Our data indicate that, through the activation of PAR-2, allergen-derived proteases are sufficient to induce CCL20 and GM-CSF production in the airways. This leads to increased recruitment and/or differentiation of myeloid DC populations in the lungs and likely plays an important role in the initiation of allergic airway responses.

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.

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.