Virulence mechanisms of Tannerella forsythia

Characterization and scope of S-layer protein O-glycosylation in Tannerella forsythia

Cell surface glycosylation is an important element in defining the life of pathogenic bacteria. Tannerella forsythia is a Gram-negative, anaerobic periodontal pathogen inhabiting the subgingival plaque biofilms. It is completely covered by a two-dimensional crystalline surface layer (S-layer) composed of two glycoproteins. Although the S-layer has previously been shown to delay the bacterium's recognition by the innate immune system, we characterize here the S-layer protein O-glycosylation as a potential virulence factor. The T. forsythia S-layer glycan was elucidated by a combination of electrospray ionization-tandem mass spectrometry and nuclear magnetic resonance spectroscopy as an oligosaccharide with the structure 4-Me-β-ManpNAcCONH(2)-(1→3)-[Pse5Am7Gc-(2→4)-]-β-ManpNAcA-(1→4)-[4-Me-α-Galp-(1→2)-]-α-Fucp-(1→4)-[-α-Xylp-(1→3)-]-β-GlcpA-(1→3)-[-β-Digp-(1→2)-]-α-Galp, which is O-glycosidically linked to distinct serine and threonine residues within the three-amino acid motif (D)(S/T)(A/I/L/M/T/V) on either S-layer protein. This S-layer glycan obviously impacts the life style of T. forsythia because increased biofilm formation of an UDP-N-acetylmannosaminuronic acid dehydrogenase mutant can be correlated with the presence of truncated S-layer glycans. We found that several other proteins of T. forsythia are modified with that specific oligosaccharide. Proteomics identified two of them as being among previously classified antigenic outer membrane proteins that are up-regulated under biofilm conditions, in addition to two predicted antigenic lipoproteins. Theoretical analysis of the S-layer O-glycosylation of T. forsythia indicates the involvement of a 6.8-kb gene locus that is conserved among different bacteria from the Bacteroidetes phylum. Together, these findings reveal the presence of a protein O-glycosylation system in T. forsythia that is essential for creating a rich glycoproteome pinpointing a possible relevance for the virulence of this bacterium.

TLR2 signaling and Th2 responses drive Tannerella forsythia-induced periodontal bone loss

Periodontal disease (PD) is a chronic inflammation of the tooth-supporting soft tissue and alveolar bone due to infection by a select group of gram-negative microbes, which leads to tooth loss if untreated. Because mice deficient in CD4(+) cells are resistant to infection-induced alveolar bone loss, Th cells have been implicated in bone-destructive processes during PD. However, the extent to which different Th cell subtypes play roles in pathogenesis or host protection remains to be defined and is likely to vary depending on the dominant microorganism involved. By far, Porphyromonas gingivalis is the best-studied periodontal microbe in PD. Although the gram-negative anaerobe Tannerella forsythia is also a vital contributor to periodontal bone loss, almost nothing is known about immune responses to this organism. Previous studies from our laboratory revealed that T. forsythia induces periodontal bone loss in mice and that this bone loss depends on the bacterially expressed BspA protein. In this study, we showed that T. forsythia activates murine APCs primarily through TLR2-dependent signaling via BspA. Furthermore, T. forsythia infection causes a pronounced Th2 bias, evidenced by T cell expression of IL-5, but not IFN-γ or IL-17, in draining lymph nodes. Consistently, deficiencies in TLR2 or STAT6 result in resistance to T. forsythia-induced alveolar bone loss. Thus, TLR2 signaling and Th2 cells play pathogenic roles in T. forsythia-induced alveolar bone destruction.

Tannerella forsythia invasion in oral epithelial cells requires phosphoinositide 3-kinase activation and clathrin-mediated endocytosis

Tannerella forsythia, a Gram-negative anaerobe implicated in periodontitis, has been detected within human buccal epithelial cells and shown to invade oral epithelial cells in vitro. We have previously shown that this bacterium triggers host tyrosine kinase-dependent phosphorylation and actin-dependent cytoskeleton reorganization for invasion. On the bacterial side, the leucine-rich repeat cell-surface BspA protein is important for entry. The present study was undertaken to identify host signalling molecules during T. forsythia entry into human oral and cervical epithelial cells. Specifically, the roles of phosphatidylinositol 3-kinase (PI3K), Rho-family GTPases, cholesterol-rich membrane microdomains and the endocytic protein clathrin were investigated. For this purpose, cell lines were pretreated with chemical inhibitors or small interfering RNAs (siRNAs) that target PI3Ks, Rho GTPases, clathrin and cholesterol (a critical component of 'lipid rafts'), and the resulting effects on T. forsythia uptake were determined. Our studies revealed that T. forsythia entry is dependent on host PI3K signalling, and that purified BspA protein causes activation of this lipid kinase. Bacterial entry also requires the cooperation of host Rac1 GTPase. Finally, our findings indicate an important role for clathrin and cholesterol-rich lipid microdomains in the internalization process.

Levels of serum immunoglobulin G specific to bacterial surface protein A of Tannerella forsythia are related to periodontal status

BACKGROUND

Tannerella forsythia (Tf) is a Gram-negative anaerobe implicated in the development of periodontal disease. Bacterial surface protein A (BspA) is a surface-expressed and -secreted protein that is recognized as an important virulence factor of Tf. This study was undertaken to determine whether Tf BspA induces an antibody response in periodontal disease. We hypothesized that serum immunoglobulin (Ig)G antibody levels against BspA correlate with the disease of patients.

METHODS

Sera were obtained from 100 patients with cardiac disorders and periodontal disease and 73 patients who experienced myocardial infarction but were periodontally healthy. Sera samples were assayed for anti-BspA antibody (total IgG and IgG subtypes) by enzyme-linked immunosorbent assay (ELISA). Antibody levels were measured in ELISA units by using an arbitrary patient as a standard.

RESULTS

A negative correlation was found with BspA-specific total IgG antibody titers and the severity of disease measured as the clinical attachment level (CAL) when healthy and diseased groups were analyzed separately (healthy group: [-0.23, correlation value] Student's t value [73 degrees of freedom] = 1.99; P = 0.05; diseased group: [-0.21] t [100 degrees of freedom] = 2.12; P = 0.03]). However, there was a positive correlation ([0.18 correlation value] Student's t value [173 degrees of freedom] = 2.39; P = 0.017) when healthy and diseased groups were combined. A strong positive correlation ([0.338 correlation value] Student's t value [173 degrees of freedom] = 4.69; P <0.0001) between the BspA-specific IgG titers and periodontal probing depth was observed when healthy and disease groups were combined.

CONCLUSIONS

Data demonstrated that antibodies to Tf BspA were elicited in patients with periodontal disease, and antibody levels were associated with the disease severity. Furthermore, data suggested that anti-BspA IgG might have a protective function in periodontal disease by minimizing the loss of tooth attachment tissue.

Salivary infectious agents and periodontal disease status

BACKGROUND AND OBJECTIVES

The potential of salivary microorganisms to diagnose periodontal disease and to guide periodontal treatment is a research topic of current interest. This study aimed to determine whether the salivary counts of periodontopathic microbes correlated with the periodontal pocket counts of the same infectious agents, and whether the salivary counts of the test infectious agents could distinguish among individuals with periodontal health and various types of periodontal disease.

MATERIAL AND METHODS

The study included 150 systemically healthy adults, of whom 37 were periodontally healthy, 31 had gingivitis, 46 had chronic periodontitis and 36 had aggressive periodontitis. Each study subject contributed microbial samples from the two deepest periodontal pockets of the dentition and from whole saliva. Aggregatibacter actinomycetemcomitans, Campylobacter rectus, Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella intermedia, Tannerella forsythia and Epstein-Barr virus were identified using the TaqMan real-time PCR methodology. Statistical analysis was performed using the Mann-Whitney U-test and the receiver operating characteristic statistics.

RESULTS

C. rectus, F. nucleatum, P. gingivalis, P. intermedia and T. forsythia occurred with significantly higher copy-counts in salivary samples from patients with gingivitis, chronic periodontitis and aggressive periodontitis than from periodontally healthy individuals. A. actinomycetemcomitans only showed higher salivary copy-counts in subjects with aggressive periodontitis compared with subjects with healthy periodontium, and the salivary copy-counts of Epstein-Barr virus did not reveal any significant difference among the four subject groups studied. The diagnostic sensitivity for periodontitis was 89.19 for P. gingivalis and for T. forsythia and 86.49 for P. intermedia, with specificities ranging from 83.78 to 94.59. The optimal copy-counts per mL saliva for identifying periodontitis were 40,000 for P. gingivalis, 700,000 for T. forsythia and 910,000 for P. intermedia.

CONCLUSION

Salivary copy-counts of P. gingivalis, T. forsythia and P. intermedia appear to have the potential to identify the presence of periodontitis, whereas the salivary level of the other test infectious agents may possess little or no diagnostic utility. Longitudinal studies are warranted to determine the ability of salivary copy-counts of major periodontopathic bacteria to predict future periodontal breakdown.

Role of Tannerella forsythia NanH sialidase in epithelial cell attachment

Tannerella forsythia is a Gram-negative oral anaerobe which contributes to the development of periodontitis, an inflammatory disease of the tooth-supporting tissues leading to tooth loss. The mechanisms by which this bacterium colonizes the oral cavity are poorly understood. The bacterium has been shown to express two distinct sialidases, namely, SiaHI and NanH, with the latter being the major sialidase. Bacterial sialidases can play roles in pathogenesis by cleaving sialic acids on host glycoproteins, destroying their integrity, and/or unmasking hidden epitopes on host surfaces for colonization. In the present study, we investigated the roles of the SiaHI and NanH sialidases by generating and characterizing specific deletion mutants. Our results showed that the NanH deficiency resulted in a total loss of sialidase activity associated with the outer-membrane and secreted fractions. On the other hand, the SiaHI deficiency resulted in only a slight reduction in the total sialidase activity, with no significant differences in the levels of sialidase activity in the outer membrane or secreted fractions compared to that in the wild-type strain. The results demonstrated that NanH is both surface localized and secreted. The NanH-deficient mutant but not the SiaHI-deficient mutant was significantly attenuated in epithelial cell binding and invasion abilities compared to the wild-type strain. Moreover, the NanH-deficient mutant alone was impaired in cleaving surface sialic acids on epithelial cells. Thus, our study suggests that NanH sialidase might play roles in bacterial colonization by exposing sialic acid-hidden epitopes on epithelial cells.