Expression patterns of E-cadherin, involucrin, and connexin gap junction proteins in the lining epithelia of inflamed gingiva

Discrimination of epithelium-like and fibroblast-like phenotypes derived from ethanol-treated immortalised human gingival keratinocytes in epithelial equivalents

Ethanol treatment of immortalised human gingival keratinocytes (IHGK) yields in an epithelium-like (EPI) and fibroblast-like (FIB) phenotype. With respect to the stratified gingival epithelium, putative structural and molecular differences assigning cells to these phenotypes have not, to date, been analysed in a three-dimensional tissue/epithelial context. Therefore, we generated epithelial equivalents (EEs) in organotypic co-cultures of IHGK, EPI and FIB cells for 1 and 2 weeks and conducted protein and gene expression studies on the EEs for epithelial biomarkers including keratin K14, integrin subunits alpha6 and beta1, E-cadherin, and mesenchymal vimentin. As in the EEs of IHGK and EPI, indirect immunofluorescence revealed continuous expression of beta1 integrin in EEs of FIB cells. However, FIB cells exhibited a significant down-regulation in K14 and integrin alpha6 protein and a loss of E-cadherin at week 2, whereas vimentin was increased. FIB EEs were devoid of transcripts for E-cadherin at both time points, although transcription of the other genes remained constant in all phenotypes. Thus, the FIB phenotype exhibited a poor epithelial structure coinciding with disturbances in the expression of epithelial biomarkers and the persistence of mesenchymal vimentin. Transcription analysis revealed post-transcriptional regulation of vimentin in IHGK and EPI and of K14 and alpha6 in FIB cells. Our findings indicate that differences in the epithelial integrity and expression of molecules in EEs allow for the discrimination of EPI and FIB cells. This suggests that FIB cells share features of epithelial-mesenchymal transition and reflect a more progressive stage in epithelial cell transformation.

Regulation of E-cadherin and TGF-β3 expression by CD24 in cultured oral epithelial cells

We previously reported evidence that patients with periodontitis have serum antibodies to oral Gram positive bacteria that are cross-reactive with epithelial antigens, including CD24. High level expression of CD24 was confined to the reactive periodontal epithelium and inflamed gingival attachment. As a model for the reactive epithelium of chronic periodontitis, H413 epithelial cells derived from a human oral squamous cell carcinoma were cloned and lines expressing high levels of CD24 were selected. RNA interference protocols were designed to determine if CD24 could modulate intercellular interactions and regulate the biology of these epithelial cells. Knock-down of CD24 protein was demonstrated by Western blot and flow cytometry. The level of mRNA for CD24 was reduced 90% by RNAi treatment as assayed by real-time, reverse transcriptase (RT)-PCR. Gene products known to be important in epithelial biology, including E-cadherin and TGF-beta3 that were demonstrated to undergo altered expression patterns in the periodontal lesion, were investigated. Down-regulation of CD24 mRNA was associated with reduced e-cadherin expression and up-regulated expression of snail, twist, and tgf-beta3. The cells were treated with monoclonal antibodies to CD24 to mimic the action of auto-reactive antibodies to CD24 detected in affected patients. Relative to isotype control antibody, stimulation by anti-CD24 antibodies induced up-regulated expression of e-cadherin and down-regulation of tgf-beta3 as assessed by real-time RT-PCR. No consistent changes for expression of beta-catenin, connexins, integrins, icam-1, tgf-beta1 or tgf-beta2 were observed. CD24 could play an important role in modulating expression of genes that regulate epithelial differentiation in periodontal disease.

Expression pattern of adhesion molecules in junctional epithelium differs from that in other gingival epithelia

BACKGROUND AND OBJECTIVE

The gingival epithelium is the physiologically important interface between the bacterially colonized gingival sulcus and periodontal soft and mineralized connective tissues, requiring protection from exposure to bacteria and their products. However, of the three epithelia comprising the gingival epithelium, the junctional epithelium has much wider intercellular spaces than the sulcular epithelium and oral gingival epithelium. Hence, the aim of the present study was to characterize the cell adhesion structure in the junctional epithelium compared with the other two epithelia.

MATERIAL AND METHODS

Gingival epithelia excised at therapeutic flap surgery from patients with periodontitis were examined for expression of adhesion molecules by immunofluorescence.

RESULTS

In the oral gingival epithelium and sulcular epithelium, but not in the junctional epithelium, desmoglein 1 and 2 in cell-cell contact sites were more abundant in the upper than the suprabasal layers. E-cadherin, the main transmembranous molecule of adherens junctions, was present in spinous layers of the oral gingival epithelium and sulcular epithelium, but was scarce in the junctional epithelium. In contrast, desmoglein 3 and P-cadherin were present in all layers of the junctional epithelium as well as the oral gingival epithelium and sulcular epithelium. Connexin 43 was clearly localized to spinous layers of the oral gingival epithelium, sulcular epithelium and parts of the junctional epithelium. Claudin-1 and occludin were expressed in the cell membranes of a few superficial layers of the oral gingival epithelium.

CONCLUSION

These findings indicated that the junctional epithelium contains only a few desmosomes, composed of only desmoglein 3; adherens junctions are probably absent because of defective E-cadherin. Thus, the anchoring junctions connecting junctional epithelium cells are lax, causing widened intercellular spaces. In contrast, the oral gingival epithelium, which has a few tight junctions, functions as a barrier.

Identification of epithelial auto-antigens associated with periodontal disease

We previously reported evidence that patients with periodontitis have serum antibodies to oral Gram positive bacteria that are cross-reactive with epithelial antigens. In the present report cross-reactive epithelial antigens including CD24, lactate dehydrogenase A [LDM-A], antioxidant protein 2 [AOP 2] and nuclear factor of activated T cells 5 [NFAT 5], were identified by screening a cDNA expression library with pooled patient sera. Titres of antibodies to CD24 peptide correlated negatively with indices of periodontal disease severity. Strong expression of CD24 in the reactive periodontal epithelium and inflamed gingival attachment contrasted with low to undetectable expression in the external gingival epithelium. In periodontitis, a local action of these auto-reactive antibodies could modulate the regulatory potential associated with expression of CD24 in this epithelium.

The junctional epithelium: from health to disease

The junctional epithelium is located at a strategically important interface between the gingival sulcus, populated with bacteria, and the periodontal soft and mineralized connective tissues that need protection from becoming exposed to bacteria and their products. Its unique structural and functional adaptation enables the junctional epithelium to control the constant microbiological challenge. The antimicrobial defense mechanisms of the junctional epithelium, however, do not preclude the development of gingival and periodontal lesions. The conversion of the junctional to pocket epithelium, which is regarded as a hallmark in disease initiation, has been the focus of intense research in recent years. Research has shown that the junctional epithelial cells may play a much more active role in the innate defense mechanisms than previously assumed. They synthesize a variety of molecules directly involved in the combat against bacteria and their products. In addition, they express molecules that mediate the migration of polymorphonuclear leukocytes toward the bottom of the gingival sulcus. Periodontopathogens-such as Actinobacillus actinomycetemcomitans or, in particular, Porphyromonas gingivalis-have developed sophisticated methods to perturb the structural and functional integrity of the junctional epithelium. Research has focused on the direct effects of gingipains, cysteine proteinases produced by Porphyromonas gingivalis, on junctional epithelial cells. These virulence factors may specifically degrade components of the cell-to-cell contacts. This review will focus on the unique structural organization of the junctional epithelium, on the nature and functions of the various molecules expressed by its cells, and on how gingipains may attenuate the junctional epithelium's structural and functional integrity.

Comparison of differentiation markers between normal and two squamous cell carcinoma cell lines in culture

This study examines differences between cultures of normal human oral epithelial cells and two squamous cell carcinoma cell lines (SCC15 and SCC25) in the expression of structural proteins, adhesion molecules, plasma membrane lipid composition, and intercellular junctions. Based on immunocytochemistry, most normal cell cultures appeared to express more E-cadherin, integrin beta-1, cytokeratin (CK) 14, CK19, and involucrin than SCC cultures. By Western blot analysis, normal cultures expressing high levels of E-cadherin also expressed high levels of involucrin and low levels of CK19. Both SCC cultures demonstrated lower expression of E-cadherin and involucrin, whereas only SCC15 cells showed high levels of CK19. Expression of beta-catenin, an E-cadherin associated protein with potential oncogene function, did not vary among normal and SCC cells. Proportions of saturated fatty acids quantified by thin layer chromatography were higher in the normal cell cultures, than in both SCC cell lines. No morphological differences were evident by transmission electron microscopy (TEM) between normal and SCC cell-cell intercellular junctions. Although no quantitation was attempted, observation suggested that normal cells form more intercellular junctions (TEM observation) and larger intercellular bridges (SEM observation) compared to both SCC cell lines. Of the factors examined, main variations between cultures of normal oral epithelium and the two SCC cell lines examined include the expression of structural and adhesion proteins, lipid composition, and intercellular junctions. The extent of the differences varies according to the stage of terminal differentiation demonstrated by the normal cell cultures.

Syntheses of prostaglandin E2 and E-cadherin and gene expression of beta-defensin-2 by human gingival epithelial cells in response to Actinobacillus actinomycetemcomitans

The interaction between epithelial cells and microorganisms is the most important step in bacterial infections. Actinobacillus actinomycetemcomitans was suggested to play a significant role in the initiation of periodontitis because of its bacteriological characteristics. Prostaglandins (PG) mediate the inflammatory response. Human beta-defensin-2 (hBD-2) is an antimicrobial peptide and contributes to innate immunity. E-cadherin is responsible for an epithelial intercellular junction. In this study, we investigated the syntheses of PGE2 and E-cadherin and the expression of hBD-2 in human gingival epithelial cells (HGEC) following exposure to A. actinomycetemcomitans. The levels of PGE2 and cyclooxygenase-2, which are responsible for an increase in PGE2, were increased depending on bacteria exposure time. hBD-2 mRNA was induced by A. actinomycetemcomitans, while HGEC exposed to A. actinomycetemcomitans showed a decrease in E-cadherin levels. Etodolac, a selective cyclooxygenase-2 inhibitor reinforced the increase in hBD-2 mRNA levels by A. actinomycetemcomitans. Furthermore, the etodolac suppressed the decrease in E-cadherin levels. Thus, endogenous PGE2 is involved in the hBD-2 and E-cadherin responses of HGEC to A. actinomycetemcomitans. These findings suggest that the inflammatory and antimicrobial response of gingival epithelial cells to A. actinomycetemcomitans is involved in the initiation of periodontal inflammation. A. actinomycetemcomitans may destroy the mechanical epithelial barrier by destroying E-cadherin.

Differential expression of transforming growth factors-β1, -β2, -β3 and the type I, II, III receptors in the lining epithelia of inflamed gingiva

AIMS

To investigate the distribution of transforming growth factor-beta isoforms in chronically inflamed periodontal tissues.

METHODS

The present study determined, by immunohistochemistry, the expression patterns of TGF-betas and their receptors in the lining epithelia of inflamed gingiva. Frozen sections were obtained from 22 human gingival biopsies.

RESULTS

TGF-beta 1 was not detected in gingival epithelial cells in examined sections. Detection of TGF-beta 2 indicated a progressive reduction of staining from the external oral epithelium through to gingival sulcus and the gingival attachment or pocket epithelium. TGF-beta 3 showed intense staining in all domains of both minimally inflamed gingiva and advanced periodontitis tissues. TGF-beta RI was visualised as focal staining of the spinous layer in the external oral epithelium of both periodontitis lesions and minimally inflamed tissues. TGF-beta RII was present throughout the strata, but with progressive reduction in intensity from the oral epithelium to gingival attachment or pocket epithelium respectively while, conversely, TGF-beta RIII showed an increase in diffuse staining intensity from external oral epithelium to pocket epithelium.

CONCLUSIONS

A distinct expression profile was observed within different individuals for TGF-betas and the corresponding receptors. These findings provide a basis for evaluation of the role of these growth factors in the pathogenesis of periodontitis.

Streptococci and Actinomyces induce antibodies which cross react with epithelial antigens in periodontitis

Perturbation of epithelial structure is a prominent but poorly understood feature of the immunopathological response to bacterial antigens which characterizes the destructive lesion of periodontitis. Western analysis of sera from 22 patients with periodontitis detected multiple antigens in extracts of epithelial cells whereas sera from 12 periodontally healthy subjects displayed only trace reaction with epithelial antigens. To investigate a possible relationship between the bacterial flora adjacent to diseased sites and the presence of antibodies reactive with epithelium, subgingival plaque samples were taken from deep periodontal pockets and cultured anaerobically. Gram positive bacteria containing antigens cross-reactive with epithelial cells were reproducibly isolated by probing membrane colony-lifts with affinity-isolated (epithelium-specific) antibodies and identified by 16S rDNA sequence homology as streptococci (S. mitis, S. constellatus and two S. intermedius strains) and Actinomyces (A. georgiae, and A. sp. oral clone). Conversely, when serum from patients with periodontitis was absorbed with the captured bacterial species the number of epithelial antigens recognized was specifically reduced. It was concluded that development of cross-reactive antibodies related to these organisms may contribute to perturbation of the epithelial attachment to the tooth and the progression of periodontitis. These autoreactive antibodies could also be a contributing factor in other diseases affecting epithelia.