Candida albicans enhances invasion of human gingival epithelial cells and gingival fibroblasts by Porphyromonas gingivalis

Although Candida albicans has been isolated from periodontal pockets, its relationship to periodontitis is unclear. In this study, we investigated the effect of C. albicans on the adhesion and invasion of Ca9-22, a human gingival epithelial cell line, and human gingival fibroblasts by Porphyromonas gingivalis. Heat-killed C. albicans and water-soluble mannoprotein-β-glucan complex from C. albicans (CAWS) did not enhance P. gingivalis adhesion or upregulate the expression of β1 integrin and ICAM-1, which are required for P. gingivalis invasion; both the epithelial cells and fibroblasts expressed dectin-1, which recognizes components of the C. albicans cell wall. However, pretreatment of Ca9-22 cells and human gingival fibroblasts with heat-killed C. albicans or CAWS significantly enhanced P. gingivalis invasion. These results suggest that C. albicans may exacerbate infectious disease by enhancing the invasion of host cells by anaerobic bacteria.     

Porphyromonas gingivalis induces RANKL in bone marrow stromal cells: involvement of the p38 MAPK

Periodontitis is a bacterially-induced oral inflammatory disease that is characterised by tissue degradation and bone loss. Porphyromonas gingivalis is a gram negative bacterial species highly associated with the pathogenesis of chronic periodontitis. Receptor activator of nuclear factor-kB ligand (RANKL) induces bone resorption whilst osteoprotegerin (OPG) is a decoy receptor that blocks this process. Cyclooxygenase-2 (COX-2) is an enzyme responsible for the production of prostaglandin (PGE)_2, which is a major inflammatory mediator of bone resorption. Mitogen-activated protein kinases (MAPK) are intracellular signalling molecules involved in various cell processes, including inflammation. This study aimed to investigate the effect of P. gingivalis on MAPKs and their involvement in the regulation of RANKL, OPG and COX-2 expression in bone marrow stromal cells. P. gingivalis challenge resulted in the phosphorylation of primarily the p38 MAPK. RANKL and COX-2 mRNA expressions were up-regulated, whereas OPG was down-regulated by P. gingivalis. The p38 synthetic inhibitor SB203580 abolished the P. gingivalis-induced RANKL and COX-2 expression, but did not affect OPG. Collectively, these results suggest that the p38 MAPK pathway is involved in the induction of RANKL and COX-2 by P. gingivalis, providing further insights into the pathogenic mechanisms of periodontitis.     

Differential ability of periodontopathic bacteria to modulate invasion of human gingival epithelial cells by Porphyromonas gingivalis

Periodontitis is a polymicrobial infection caused by selected gram-negative bacteria including Porphyromonas gingivalis. Host cell invasion by P. gingivalis has been proposed as a possible mechanism of pathogenesis in periodontitis. The aim of the present study was to assess the influence of periodontopathogens on P. gingivalis invasion of gingival epithelial cells in polymicrobial infection. P. gingivalis was tested for its ability to invade a human gingival epithelial cell line Ca9-22 in co-infection with periodontopathogens, using an antibiotic protection assay. Among the pathogens tested, only Fusobacterium nucleatum demonstrated the ability to significantly promote P. gingivalis invasion (P < 0.01). This increased invasion was confirmed by confocal scanning laser microscopy utilizing a dual labeling technique. In contrast, co-infection with Aggregatibacter actinomycetemcomitans or Tannerella forsythia attenuated P. gingivalis invasion. The fusobacterial enhancement of host cell invasion was not observed in co-incubation with other periodontopathogens tested. These results suggested that complex synergistic or antagonistic physiologic mechanisms are intimately involved in host cell invasion by P. gingivalis in polymicrobial infection.     

Loss of lipopolysaccharide receptor CD14 from the surface of human macrophage-like cells mediated by Porphyromonas gingivalis outer membrane vesicles

Porphyromonas gingivalis, the major etiologic agent of chronic periodontitis, produces a broad spectrum of virulence factors, including outer membrane vesicles. In this study, we investigated the capacity of P. gingivalis vesicles to promote the shedding or cleavage of the lipopolysaccharide (LPS) receptor CD14 from the surface of human U937 macrophage-like cells. SDS-PAGE/Western immunoblotting analysis of gingival crevicular fluid samples from patients affected by moderate or advanced periodontitis revealed the presence of soluble CD14 and CD14 fragments, thus supporting the hypothesis of an in vivo shedding and cleavage of CD14 receptors. Flow cytometry analysis of macrophage-like cells treated with a vesicle-containing culture supernatant of P. gingivalis showed a significant decrease in the binding of anti-human CD14 to the cell surface. However, no accumulation of soluble CD14 or immunoreactive CD14 fragments in the assay supernatant could be demonstrated by ELISA. Treatment of macrophage-like cells with various concentrations of P. gingivalis vesicles substantially suppressed TNF-alpha production triggered by Escherichia coli LPS. This suppressive effect was much less important using heat-treated vesicles or in the presence of leupeptin, a gingipain inhibitor, during the treatment. Recombinant human CD14 receptors were found to be susceptible to proteolytic degradation by P. gingivalis vesicles. A purified Arg-gingipain preparation produced much more degradation than a Lys-gingipain preparation. This study provides evidence that P. gingivalis outer membrane vesicles contribute to the loss of membrane-bound CD14 receptors and that gingipains degrade this LPS receptor. Such a phenomenon, which results in an hyporesponsiveness of macrophages to LPS stimulation, may contribute to an increased capacity of P. gingivalis, and other periodontopathogens, to evade the host immune system mechanisms.     

Regulation of RANKL and OPG gene expression in human gingival fibroblasts and periodontal ligament cells by Porphyromonas gingivalis: a putative role of the Arg-gingipains

Porphyromonas gingivalis is highly implicated in the pathogenesis of periodontitis, which is characterized by the destruction of periodontal connective tissues and the supporting alveolar bone. Receptor Activator of NF-kappaB Ligand (RANKL) stimulates bone resorption, whereas osteoprotegerin (OPG) blocks its action, and this bi-molecular system is implicated in periodontitis. The aim of this work was (a) to investigate the regulation of RANKL and OPG gene expression in human periodontal ligament (PDL) cells and gingival fibroblasts (GF), in response to P. gingivalis culture supernatants, by quantitative real-time PCR and (b) to attempt to identify putative virulence factors involved in this process. The results indicated that P. gingivalis induced RANKL and reduced OPG mRNA expression by the studied cells, resulting in an increased RANKL/OPG expression ratio. Heat-inactivation of P. gingivalis resulted in significant reduction of RANKL mRNA expression. A Lys-gingipain mutant strain did not affect, whereas an Arg-gingipain mutant strain further enhanced RANKL mRNA expression, compared to their parental wild-type strain. In conclusion, P. gingivalis up-regulates the RANKL/OPG expression ratio in GF and PDL cells, denoting an enhanced osteoclastogenic potential by the cells. The component mainly responsible for RANKL induction appears to be proteinaceous, and it may be regulated by the Arg-gingipains.     

B7-H1 and B7-DC receptors of oral squamous carcinoma cells are upregulated by Porphyromonas gingivalis

The up-regulation of the B7-H1 receptors in host cells might influence the chronicity of inflammatory disorders that frequently precede the development of human cancers. B7-H1 expression has been detected in the majority of human cancers, leading to anergy and apoptosis of activated T cells, and enabling tumor cells to overcome host response. Porphyromonas gingivalis (P. gingivalis), a putative periodontal pathogen, is an etiologic agent of periodontitis and expresses a variety of virulence factors. In this study, the expression of B7-H1 and B7-DC receptors on squamous cell carcinoma cells SCC-25 and BHY and primary human gingival keratinocytes (PHGK) was analyzed after infection with two virulent P. gingivalis strains in vitro. After 48 h, the cells were stained with antibodies for human B7-H1 and B7-DC and further analyzed by flow cytometry. RNA was extracted and gene expression of B7-H1 or B7-DC was quantified by real time PCR. After infection with P. gingivalis, both B7-H1 and B7-DC receptors were up-regulated.The mean fluorescence intensity (MFI) increased from 4.5 to 9.9 (B7-H1) and from 6.9 to 15.0 (B7-DC) (p < 0.05, respectively) in SCC-25 cells. PHGK showed an increase from 4.8 to 12.4 (B7-H1) and from 5.5 to 15.6 (B7-DC) (p < 0.05, respectively). Streptococcus salivarius K12, a commensal bacterium, caused no up-regulation. After 24 h, the expression of B7H1 and B7-DC mRNA in infected cells, normalized to GAPDH and in relation to non-infected cells, was 6.4 fold (B7-H1) and 8.6 fold (B7-DC) higher. In PHGK B7-H1/DC mRNA expression increased 8.2 fold (B7-H1) and 5.9 fold (B7DC) (p < 0.05) respectively. The results of the study demonstrate that in contrast to S. salivarius K12 virulent P. gingivalis strains are able to induce the expression of the B7-H1 and B7-DC receptors in squamous carcinoma cells and human gingival keratinocytes, which might facilitate immune evasion by oral cancers.