Expression patterns of tight junction components induced by CD24 in an oral epithelial cell-culture model correlated to affected periodontal tissues

Anti-Periodontitis Effects of Dendropanax morbiferus H.Lév Leaf Extract on Ligature-Induced Periodontitis in Rats

Periodontitis is caused by pathogens in the oral cavity. It is a chronic infectious disease that causes symptoms including gingival bleeding and tooth loss resulting from the destruction of periodontal tissues coupled with inflammation. Dendropanax morbiferus H.Lév (DM) is a natural product that exhibits various biological activities with few side effects. In this study, the potential of DM leaf hot-water extracts (DMWE) as a treatment for periodontitis was determined and its anti-oxidant and anti-inflammatory effects were evaluated. Compounds in DMWE were identified by high-performance liquid chromatography (HPLC) and nitric oxide (NO) and prostaglandin E₂ (PGE₂) production was measured in RAW 264.7 cells. We measured the gingival index and gingival sulcus depth, and micro-CT was performed in vivo using a ligature-induced periodontitis rat model, which is similar to human periodontitis. The DMWE-treated group exhibited a decrease in cytokine concentration and relieved the gingival index and gingival sulcus depth compared with the periodontitis-induced control group. In addition, micro-CT and histological analysis revealed that DMWE exhibited anti-inflammatory effects and improved alveolar bone loss in periodontitis-induced rats. These findings suggest that DMWE has excellent anti-oxidant and anti-inflammatory effects that protect and prevent periodontal tissue damage and tooth loss caused by the inflammatory response.

Impaired function of epithelial plakophilin-2 is associated with periodontal disease

BACKGROUND AND OBJECTIVES

Plakophilin-2 (PKP2) is an intracellular desmosomal anchoring protein that has been implicated in a genome-wide association study, in which genetic variants of PKP2 are associated with Porphyromonas gingivalis (P.gingivalis) -dominant periodontal dysbiosis. In this study, we compared the ex vivo PKP2 expression in periodontitis gingival biopsies to periodontitis-free subjects and assessed the in vitro role of PKP2 in gingival epithelial barrier function and the mechanism by which P.gingivalis modulates PKP2 expression.

MATERIAL AND METHODS

Using reverse transcription quantitative real-time PCR (RT-qPCR), we determined PKP2 mRNA expression levels in gingival biopsies collected from 11 periodontally healthy, 10 experimental gingivitis, and 10 chronic periodontitis subjects. PKP2 protein expression in gingival biopsies was detected by immunohistochemistry. We then challenged primary gingival epithelial cells with bacteria including P.gingivalis, Campylobacter rectus, and various Toll-like receptor agonists. Western blot and immunofluorescence staining were used to detect protein expression. Inhibitors blocking proteases pathways were tested for P.gingivalis-mediated PKP2 protein degradations. We also knocked down endogenous epithelial PKP2 using lentiviral short-hairpin RNA (shRNA) and evaluated cell proliferation, spreading, and barrier function.

RESULTS

Periodontitis gingival biopsies had approximately twofold less PKP2 mRNA than did healthy controls (p < .05). PKP2 protein was predominantly expressed in gingival epithelium. In primary gingival epithelial cells, P.gingivalis challenge increased PKP2 mRNA levels, while protein expression decreased, which suggests that P.gingivalis has a protein degradation mechanism. Cysteine proteases inhibitors greatly attenuated P.gingivalis-mediated PKP2 protein degradation. Epithelial cells with deficient PKP2 exhibited inhibited cell proliferation and spreading and failed to form monolayers. Finally, P.gingivalis impaired gingival epithelial barrier function.

CONCLUSIONS

PKP2 appears to be critical in maintaining gingival epithelial barrier function and is susceptible to degradation by cysteine proteases produced by P.gingivalis. Our findings have identified a mechanism by which P.gingivalis impairs epithelial barrier function by promoting PKP2 degradation.

Runx2 deficiency in junctional epithelium of mouse molars decreases the expressions of E-cadherin and junctional adhesion molecule 1

Junctional epithelium (JE) attaching to the enamel surface seals gaps around the teeth, functioning as the first line of gingival defense. Runt-related transcription factor 2 (Runx2) plays a role in epithelial cell fate, and the deficiency of Runx2 in JE causes periodontal destruction, while its effect on the barrier function of JE remains largely unexplored. In the present study, hematoxylin-eosin (H&E) staining revealed the morphological differences of JE between wild-type (WT) and Runx2 conditional knockout (cKO) mice. We speculated that these changes were related to the down-regulation of E-cadherin (E-cad), junctional adhesion molecule 1 (JAM1), and integrin β6 (ITGB6) in JE. Moreover, immunohistochemistry (IHC) was conducted to assess the expressions of these proteins. To verify the relationship between Runx2 and the three above-mentioned proteins, human gingival epithelial cells (HGEs) were cultured for in vitro experiment. The expression of Runx2 in HEGs was depleted by lentivirus. Quantitative real-time PCR (qRT-PCR) and Western blotting analysis were adopted to analyze the differences in mRNA and protein expressions. Taken together, Runx2 played a crucial role in maintaining the structure and function integrality of JE via regulating the expressions of E-cad and JAM1.

Porphyromonas gingivalis induces penetration of lipopolysaccharide and peptidoglycan through the gingival epithelium via degradation of junctional adhesion molecule 1

Porphyromonas gingivalis is a major pathogen in severe and chronic manifestations of periodontal disease, which is one of the most common infections of humans. A central feature of P. gingivalis pathogenicity is dysregulation of innate immunity at the gingival epithelial interface; however, the molecular basis underlying P. gingivalis–dependent abrogation of epithelial barrier function remains unknown. Gingival epithelial cells express junctional adhesion molecule (JAM1), a tight junction–associated protein, and JAM1 homodimers regulate epithelial barrier function. Here we show that Arg-specific or Lys-specific cysteine proteases (gingipains) secreted by P. gingivalis can specifically degrade JAM1 at K134 and R234 in gingival epithelial cells, resulting in permeability of the gingival epithelium to 40 kDa dextran, lipopolysaccharide (LPS), and proteoglycan (PGN). A P. gingivalis strain lacking gingipains was impaired in degradation of JAM1. Knockdown of JAM1 in monolayer cells and a three-dimensional multilayered tissue model also increased permeability to LPS, PGN, and gingipains. Inversely, overexpression of JAM1 in epithelial cells prevented penetration by these agents following P. gingivalis infection. Our findings strongly suggest that P. gingivalis gingipains disrupt barrier function of stratified squamous epithelium via degradation of JAM1, allowing bacterial virulence factors to penetrate into subepithelial tissues.

Periodontal diseases, which are among the most common infections of humans, are characterized by gingival inflammation and destruction of the hard and soft tissues that support the tooth, eventually causing tooth loss. Porphyromonas gingivalis is a major pathogen in periodontal diseases. Infection of gingival epithelial cells by P. gingivalis increases epithelial permeability. However, the molecular mechanism and pathological significance of P. gingivalis–dependent barrier dysfunction in human gingival epithelium remain unknown. In this study, we developed a three-dimensional multilayered tissue model of gingival epithelium infected by P. gingivalis and used it to monitor penetration of bacterial products derived from P. gingivalis and other bacteria. We found that P. gingivalis proteases, called gingipains, have a potent and specific ability to degrade JAM1, which regulates epithelial barrier function. Mechanistically, gingipains degrade mature form of JAM1 on the plasma membrane, increasing penetration of 40 kDa dextran, lipopolysaccharide, peptidoglycan, and gingipains. Our study provides new insights into the etiological role of P. gingivalis, leading to periodontal destruction.

What information can be obtained from the tears of a patient with primary open angle glaucoma?

Since tears are a biological fluid, they have a potential diagnostic value for ophthalmic diseases. The aim of this study was to compare tear supernatants and pellets obtained from patients suffering from primary open angle glaucoma (POAG) and healthy persons (HPs) using transmission electron microscopy (TEM) and molecular biological methods. Tear supernatants and pellets were prepared using ultrafiltration and ultracentrifugation and were examined by negative staining and immunogold labelling TEM. DNA of the pellets was isolated, quantified and sequenced using a MiSeq (Illumina, USA) genomic sequencer with the Reagent Kit v3 (600 cycles, Illumina, USA). MicroRNA was isolated and quantified from the pellets; miR-146b, miR-16 and miR-126 were detected using TaqMan MicroRNA Assays (Applied Biosystems, USA). TEM of tear supernatants from both POAG patients and HPs revealed identical constituents: spherical or cup-shaped vesicles, "non-vesicles", cell debris and macromolecular aggregates. Pellets of POAG patients and HPs contained small extracellular vesicles (sEVs) non-labelled vesicles and "non-vesicles"; pellets of sick persons also contained sEVs with "a capsule". POAG-patient tear pellets showed elevated concentrations of genomic ds-DNA and SINE-repeats, and different expressions of miR-146b, miR-16 and miR-126 and a different set of bacterial DNA in comparison with pellets obtained from the tears of HPs. The data obtained indicate that the tears of HPs and POAG patients could serve as an object for TEM studies and as a source of sEV-containing preparations (pellets), which, in turn, could be used for the isolation and study of genomic ds-DNA and RNA. Our data provide the basis for using tears for diagnostic applications.

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.

Bicellular Tight Junctions and Wound Healing

Bicellular tight junctions (TJs) are intercellular junctions comprised of a variety of transmembrane proteins including occludin, claudins, and junctional adhesion molecules (JAMs) as well as intracellular scaffold proteins such as zonula occludens (ZOs). TJs are functional, intercellular structures that form a barrier between adjacent cells, which constantly seals and unseals to control the paracellular passage of molecules. They are primarily present in the epithelial and endothelial cells of all tissues and organs. In addition to their well-recognized roles in maintaining cell polarity and barrier functions, TJs are important regulators of signal transduction, which modulates cell proliferation, migration, and differentiation, as well as some components of the immune response and homeostasis. A vast breadth of research data is available on TJs, but little has been done to decipher their specific roles in wound healing, despite their primary distribution in epithelial and endothelial cells, which are essential contributors to the wound healing process. Some data exists to indicate that a better understanding of the functions and significance of TJs in healing wounds may prove crucial for future improvements in wound healing research and therapy. Specifically, recent studies demonstrate that occludin and claudin-1, which are two TJ component proteins, are present in migrating epithelial cells at the wound edge but are absent in chronic wounds. This indicates that functional TJs may be critical for effective wound healing. A tremendous amount of work is needed to investigate their roles in barrier function, re-epithelialization, angiogenesis, scar formation, and in the interactions between epithelial cells, endothelial cells, and immune cells both in the acute wound healing process and in non-healing wounds. A more thorough understanding of TJs in wound healing may shed new light on potential research targets and reveal novel strategies to enhance tissue regeneration and improve wound repair.

An early report: a modified porphyrin-linked metronidazole targeting intracellular Porphyromonas gingivalis in cultured oral epithelial cells

Porphyromonas gingivalis (P. gingivalis) has a strong association with the pathogenesis of periodontal disease. Recurrence of periodontal disease following therapy is attributed to numerous factors, and of growing interest is the potential problem of intracellular bacteria that are able to persist and multiply within the host cell, thereby facilitating relapse of infection. The effect of antibiotic therapy in controlling P. gingivalis is questionable. Accordingly, while metronidazole is very effective against anaerobic extracellular P. gingivalis by disrupting the DNA of anaerobic microbial cells, this antibiotic does not effectively penetrate into mammalian cells to inhibit intracellular bacteria. Therefore in the present study, a modified porphyrin-linked metronidazole adducts, developed in our laboratory, was used to kill intracellular P. gingivalis. A series of experiments were performed, including cytotoxicity assays and cellular uptake of adducts by flow cytometry coupled with live cell imaging analysis, P. gingivalis invasion and elimination assays, and the analysis of colocalization of P. gingivalis and porphyrin-linked metronidazole by confocal laser scanning microscopy. Findings indicated that P. gingivalis and porphyrin-linked metronidazole were colocalized in the cytoplasm, and this compound was able to kill P. gingivalis intracellular with a sufficient culture time. This is a novel antimicrobial approach in the elimination of P. gingivalis from the oral cavity.

Assessment of the impact of aerosol from a potential modified risk tobacco product compared with cigarette smoke on human organotypic oral epithelial cultures under different exposure regimens

Cigarette smoke (CS) is affecting considerably the oral mucosa. Heating, instead of burning, tobacco reduces consistently the amount of toxic compounds and may exert a lower impact on oral health than combusted cigarettes. The carbon-heated tobacco product 1.2 (CHTP1.2) is a potential modified risk tobacco product (MRTP) based on heat-not-burn technology. Using a systems toxicology assessment framework, we compared the effects of exposure to CHTP1.2 aerosol with those of CS from a reference cigarette (3R4F). Human organotypic cultures derived from buccal and gingival epithelia were exposed acutely (28-min) or repeatedly (28 min/day for 3 days), respectively, to two matching concentrations of CHTP1.2 aerosol or 3R4F CS, and a non-diluted (100%) CHTP1.2 aerosol. The results showed an absence of cytotoxicity, reduction in pathophysiological alterations, toxicological marker proteins, and inflammatory mediators following exposure to CHTP1.2 aerosol compared with 3R4F CS. Changes in mRNA and miRNA expression were linked by an integrative analysis approach, suggesting a regulatory role of miRNAs in several smoke/disease-relevant biological processes induced by 3R4F CS. The identification of mechanisms by which potential MRTPs can reduce the impact of tobacco use on biological systems is of great importance in understanding the molecular basis of the smoking harm reduction paradigm.

Impaired bone healing at tooth extraction sites in CD24-deficient mice: A pilot study

AIM

To use a micro-computed tomography (micro-CT) to quantify bone healing at maxillary first molar extraction sites, and test the hypothesis that bone healing is impaired in CD24-knockout mice as compared with wild-type C57BL/6J mice.

MATERIALS AND METHODS

Under ketamine-xylazine general anaesthesia, mice had either extraction of the right maxillary first molar tooth or sham operation. Mice were sacrificed 1 (n = 12/group), 2 (n = 6/group) or 4 (n = 6/group) weeks postoperatively. The right maxillae was disected. Micro-CT was used to quantify differences in bone microstructural features at extrction sites, between CD24-knockout mice and wild-type mice.

RESULTS

CD24-Knockout mice displayed impaired bone healing at extraction sites that was manifested as decreased trabecular bone density, and decreased number and thickness of trabeculae.

CONCLUSIONS

This pilot study suggests that CD24 plays an important role in extraction socket bone healing and may be used as a novel biomarker of bone quality and potential therapeutic target to improve bone healing and density following alveolar bone injury.

The expression of gingival epithelial junctions in response to subgingival biofilms

Periodontitis is an infectious inflammatory disease that destroys the tooth-supporting tissues. It is caused by the formation of subgingival biofilms on the surface of the tooth. Characteristic bacteria associated with subgingival biofilms are the Gram-negative anaerobes Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola, collectively known as the “red complex” species. Inter-epithelial junctions ensure the barrier integrity of the gingival epithelium. This may however be disrupted by the biofilm challenge. The aim of this in vitro study was to investigate the effect of subgingival biofilms on the expression of inter-epithelial junctions by gingival epithelia, and evaluate the relative role of the red complex. Multi-layered human gingival epithelial cultures were challenged with a 10-species in vitro subgingival biofilm model, or its variant without the red complex, for 3 h and 24 h. A low-density array microfluidic card platform was then used for analyzing the expression of 62 genes encoding for tight junctions, gap junctions, adherens junctions, and desmosomes. Although there was a limited effect of the biofilms on the expression of tight, adherens and gap junctions, the expression of a number of desmosomal components was affected. In particular, Desmoglein-1 displayed a limited and transient up-regulation in response to the biofilm. In contrast, Desmocollin-2, Desmoplakin and Plakoglobin were down-regulated equally by both biofilm variants, after 24 h. In conclusion, this subgingival biofilm model may down-regulate selected desmosomal junctions in the gingival epithelium, irrespective of the presence of the “red complex.” In turn, this could compromise the structural integrity of the gingival tissue, favoring bacterial invasion and chronic infection.

Comparative Study of Extracellular Vesicles from the Urine of Healthy Individuals and Prostate Cancer Patients

Recent studies suggest that extracellular vesicles may be the key to timely diagnosis and monitoring of genito-urological malignancies. In this study we investigated the composition and content of extracellular vesicles found in the urine of healthy donors and prostate cancer patients. Urine of 14 PCa patients and 20 healthy volunteers was clarified by low-speed centrifugation and total extracellular vesicles fraction was obtain by high-speed centrifugation. The exosome-enriched fraction was obtained by filtration of total extracellular vesicles through a 0.1 μm pore filter. Transmission electron microscopy showed that cell-free urine in both groups contained vesicles from 20 to 230 nm. Immunogold staining after ultrafiltration demonstrated that 95% and 90% of extracellular vesicles in healthy individuals and cancer patients, respectively, were exosomes. Protein, DNA and RNA concentrations as well as size distribution of extracellular vesicles in both fractions were analyzed. Only 75% of the total protein content of extracellular vesicles was associated with exosomes which amounted to 90–95% of all vesicles. Median DNA concentrations in total extracellular vesicles and exosome-enriched fractions were 18 pg/ml and 2.6 pg/ml urine, correspondingly. Urine extracellular vesicles carried a population of RNA molecules 25 nt to 200 nt in concentration of no more than 290 pg/ml of urine. Additionally, concentrations of miR-19b, miR-25, miR-125b, and miR-205 were quantified by qRT-PCR. MiRNAs were shown to be differently distributed between different fractions of extracellular vesicles. Detection of miR-19b versus miR-16 in total vesicles and exosome-enriched fractions achieved 100%/93% and 95%/79% specificity/sensitivity in distinguishing cancer patients from healthy individuals, respectively, demonstrating the diagnostic value of urine extracellular vesicles.

Lysophosphatidic acid regulates adhesion molecules and enhances migration of human oral keratinocytes

Oral keratinocytes are connected via cell-to-cell adhesions to protect underlying tissues from physical and bacterial damage. Lysophosphatidic acids (LPAs) are a family of phospholipid mediators that have the ability to regulate gene expression, cytoskeletal rearrangement, and cytokine/chemokine secretion, which mediate proliferation, migration, and differentiation. Several forms of LPA are found in saliva and gingival crevicular fluid, but it is unknown how they affect human oral keratinocytes (HOK). The aim of the present study was therefore to examine how different LPA forms affect the expression of adhesion molecules and the migration and proliferation of HOK. Keratinocytes were isolated from gingival biopsies obtained from healthy donors and challenged with different forms of LPA. Quantitative real-time RT-PCR, immunocytochemistry, and flow cytometry were used to analyze the expression of adhesion molecules. Migration and proliferation assays were performed. Lysophosphatidic acids strongly promoted expression of E-cadherin and occludin mRNAs and translocation of E-cadherin protein from the cytoplasm to the membrane. Occludin and claudin-1 proteins were up-regulated by LPA. Migration of HOK in culture was increased, but proliferation was reduced, by the addition of LPA. This indicates that LPA can have a role in the regulation of the oral epithelial barrier by increasing the expression of adhesion molecules of HOK, by promotion of migration and by inhibition of proliferation.

Mouthguards: does the indigenous microbiome play a role in maintaining oral health?

The existence of symbiotic relationships between bacteria and their hosts in various ecosystems have long been known to science. The human body also hosts vast numbers of bacteria in several habitats. Emerging evidence from the gastro-intestinal tract, genito-urinary tract and respiratory indicates that there are several health benefits to hosting a complex and diverse microbial community. Bacteria colonize the oral cavity within a few minutes after birth and form stable communities. Our knowledge of the oral microbiome has expanded exponentially with development of novel exploratory methods that allow us to examine diversity, structure, function, and topography without the need to cultivate the individual components of the biofilm. The purpose of this perspective, therefore, is to examine the strength of current evidence supporting a role for the oral microbiome in maintaining oral health. While several lines of evidence are emerging to suggest that indigenous oral microbiota may have a role in immune education and preventing pathogen expansion, much more work is needed to definitively establish whether oral bacteria do indeed contribute to sustaining oral health, and if so, the mechanisms underlying this role.

Increased bacterial invasion and differential expression of tight-junction proteins, growth factors, and growth factor receptors in periodontal lesions

BACKGROUND

Many pathogens are known to modulate epithelial physical barriers, particularly tight-junction (TJ) proteins, to enter host cells and/or tissues. Growth factors have been implicated in the regulation of TJ proteins. The aim of this study is to determine differences in the levels of TJ proteins, growth factors, and their receptors in relation to bacterial invasion in diseased gingival tissues obtained from patients with periodontitis.

METHODS

The presence of bacteria and expression of junctional adhesion molecule (JAM)-A, occludin, epidermal growth factor (EGF), keratinocyte growth factor (KGF), insulin-like growth factor-I (IGF-I), EGF receptor, KGF receptor, and IGF-1 receptor (IGF-1R) were evaluated in gingival tissues from healthy (n = 10) and diseased (n = 10) sites in patients with periodontitis by in situ hybridization and immunohistochemistry.

RESULTS

The bacterial invasion of gingival tissue was increased in periodontal lesions compared with healthy sites. Although the levels of JAM-A and occludin were not significantly different between the healthy and diseased sites, aberrant cytoplasmic expression of JAM-A and occluding was often observed in the lesions. In addition, more leukocytes expressing JAM-A or occludin were observed within the disease-associated epithelia. Compared with the healthy sites, the differential expression of KGF, IGF-I, and IGF-1R was observed in the periodontal lesions. The levels of TJ proteins showed positive correlations with those of growth factors.

CONCLUSION

The aberrant expression of growth factors and TJ proteins may contribute to increased bacterial invasion and disease progression in periodontal lesions.