Molecular pathogenesis of the cell surface proteins and lipids from Treponema denticola

Comparative Lipidomics of Oral Commensal and Opportunistic Bacteria

The oral cavity contains a vast array of microbes that contribute to the balance between oral health and disease. In addition, oral bacteria can gain access to the circulation and contribute to other diseases and chronic conditions. There are a limited number of publications available regarding the comparative lipidomics of oral bacteria and fungi involved in the construction of oral biofilms, hence our decision to study the lipidomics of representative oral bacteria and a fungus. We performed high-resolution mass spectrometric analyses (<2.0 ppm mass error) of the lipidomes from five Gram-positive commensal bacteria: Streptococcus oralis, Streptococcus intermedius, Streptococcus mitis, Streptococcus sanguinis, and Streptococcus gordonii; five Gram-positive opportunistic bacteria: Streptococcus mutans, Staphylococcus epidermis, Streptococcus acidominimus, Actinomyces viscosus, and Nanosynbacter lyticus; seven Gram-negative opportunistic bacteria: Porphyromonas gingivalis. Prevotella brevis, Proteus vulgaris, Fusobacterium nucleatum, Veillonella parvula, Treponema denticola, and Alkermansia muciniphila; and one fungus: Candida albicans. Our mass spectrometric analytical platform allowed for a detailed evaluation of the many structural modifications made by microbes for the three major lipid scaffolds: glycerol, sphingosine and fatty acyls of hydroxy fatty acids (FAHFAs).

Oral microbiota and oral squamous cell carcinoma: a review of their relation and carcinogenic mechanisms

Oral Squamous Cell Carcinoma (OSCC) is the most common type of head and neck cancer worldwide. Emerging research suggests a strong association between OSCC and the oral microbiota, a diverse community of bacteria, fungi, viruses, and archaea. Pathogenic bacteria, in particular Porphyromonas gingivalis and Fusobacterium nucleatum, have been closely linked to OSCC. Moreover, certain oral fungi, such as Candida albicans, and viruses, like the human papillomavirus, have also been implicated in OSCC. Despite these findings, the precise mechanisms through which the oral microbiota influences OSCC development remain unclear and necessitate further research. This paper provides a comprehensive overview of the oral microbiota and its relationship with OSCC and discusses potential carcinogenic pathways that the oral microbiota may activate or modulate are also discussed.

Neuroinflammation in neurodegeneration via microbial infections

Recent epidemiological studies show a noticeable correlation between chronic microbial infections and neurological disorders. However, the underlying mechanisms are still not clear due to the biological complexity of multicellular and multiorgan interactions upon microbial infections. In this review, we show the infection leading to neurodegeneration mediated by multiorgan interconnections and neuroinflammation. Firstly, we highlight three inter-organ communications as possible routes from infection sites to the brain: nose-brain axis, lung-brain axis, and gut-brain axis. Next, we described the biological crosstalk between microglia and astrocytes upon pathogenic infection. Finally, our study indicates how neuroinflammation is a critical player in pathogen-mediated neurodegeneration. Taken together, we envision that antibiotics targeting neuro-pathogens could be a potential therapeutic strategy for neurodegeneration.

Microbial involvement in Alzheimer disease development and progression

Alzheimer disease (AD) is the most prominent form of dementia and the 5th leading cause of death in individuals over 65. AD is a complex disease stemming from genetic, environmental, and lifestyle factors. It is known that AD patients have increased levels of senile plaques, neurofibrillary tangles, and neuroinflammation; however, the mechanism(s) by which the plaques, tangles, and neuroinflammation manifest remain elusive. A recent hypothesis has emerged that resident bacterial populations contribute to the development and progression of AD by contributing to neuroinflammation, senile plaque formation, and potentially neurofibrillary tangle accumulation (Fig. 1). This review will highlight recent studies involved in elucidating microbial involvement in AD development and progression.

Oral treponeme major surface protein: Sequence diversity and distributions within periodontal niches

Treponema denticola and other species (phylotypes) of oral spirochetes are widely considered to play important etiological roles in periodontitis and other oral infections. The major surface protein (Msp) of T. denticola is directly implicated in several pathological mechanisms. Here, we have analyzed msp sequence diversity across 68 strains of oral phylogroup 1 and 2 treponemes; including reference strains of T. denticola, Treponema putidum, Treponema medium, 'Treponema vincentii', and 'Treponema sinensis'. All encoded Msp proteins contained highly conserved, taxon-specific signal peptides, and shared a predicted 'three-domain' structure. A clone-based strategy employing 'msp-specific' polymerase chain reaction primers was used to analyze msp gene sequence diversity present in subgingival plaque samples collected from a group of individuals with chronic periodontitis (n=10), vs periodontitis-free controls (n=10). We obtained 626 clinical msp gene sequences, which were assigned to 21 distinct 'clinical msp genotypes' (95% sequence identity cut-off). The most frequently detected clinical msp genotype corresponded to T. denticola ATCC 35405^T , but this was not correlated to disease status. UniFrac and libshuff analysis revealed that individuals with periodontitis and periodontitis-free controls harbored significantly different communities of treponeme clinical msp genotypes (P<.001). Patients with periodontitis had higher levels of clinical msp genotype diversity than periodontitis-free controls (Mann-Whitney U-test, P<.05). The relative proportions of 'T. vincentii' clinical msp genotypes were significantly higher in the control group than in the periodontitis group (P=.018). In conclusion, our data clearly show that both healthy and diseased individuals commonly harbor a wide diversity of Treponema clinical msp genotypes within their subgingival niches.

Outer membrane protein 100 of Aggregatibacter actinomycetemcomitans act as a biopharmaceutical target for photodynamic therapy: An in silico analysis

BACKGROUND

Periodontitis is a polymicrobial, chronic, and degenerative disease that can lead to destruction of the teeth-supporting tissues and eventually to loss of teeth. Aggregatibacter actinomycetemcomitans is predominantly associated with periodontal diseases. Outer membrane protein (Omp) 100 is a more important virulence factor of A. actinomycetemcomitans due to the effect of adhesion and invasion into human gingival epithelial cells. Attachment of A. actinomycetemcomitans inhibition is significant in the treatment process.

METHODS

We evaluated the capacity of Omp100 in A. actinomycetemcomitans as a novel target for photodynamic therapy (PDT) using a range of bioinformatic tools. In silico analysis was used to predict molecular modeling, the hierarchical nature of protein structure and backbone, and sub-cellular localization.

RESULTS

The results showed that Omp100 is most similar to thiamine-phosphate pyrophosphorylase [Haemophilus influenzae PittGG], with a 74% similarity. The predicted structure of Omp100 displayed that it is a protein with positive charge (10.4) in pH 7 and alpha helix dominates other secondary structures located outside the cell. Protein-protein interaction network showed that Omp100 interacted with extracellular matrix protein adhesion, glycoside hydrolase, Omp 64, phospholipase D/Transphosphatidylase, Flp pilus assembly protein, and heme acquisition system receptor.

CONCLUSION

According to the results, anionic indocyanine green tends to interact with Omp100 during PDT as a major target.

Residual structure of Streptococcus mutans biofilm following complete disinfection favors secondary bacterial adhesion and biofilm re-development

Chemical disinfection of oral biofilms often leaves biofilm structures intact. This study aimed to examine whether the residual structure promotes secondary bacterial adhesion. Streptococcus mutans biofilms generated on resin-composite disks in a rotating disc reactor were disinfected completely with 70% isopropyl alcohol, and were again cultured in the same reactor after resupplying with the same bacterial solution. Specimens were subjected to fluorescence confocal laser scanning microscopy, viable cell counts and PCR-Invader assay in order to observe and quantify secondarily adhered cells. Fluorescence microscopic analysis, particularly after longitudinal cryosectioning, demonstrated stratified patterns of viable cells on the disinfected biofilm structure. Viable cell counts of test specimens were significantly higher than those of controls, and increased according to the amount of residual structure and culture period. Linear regression analysis exhibited a high correlation between viable and total cell counts. It was concluded that disinfected biofilm structures favored secondary bacterial adhesion.

Characterization of Treponema denticola mutants defective in the major antigenic proteins, Msp and TmpC

Treponema denticola, a gram-negative and anaerobic spirochete, is associated with advancing severity of chronic periodontitis. In this study, we confirmed that two major antigenic proteinswere Msp and TmpC, and examined their physiological and pathological roles using gene-deletion mutants. Msp formed a large complex that localized to the outer membrane, while TmpC existed as a monomer and largely localized to the inner membrane. However, TmpC was also detected in the outer membrane fraction, but its cell-surface exposure was not detected. Msp defects increased cell-surface hydrophobicity and secretion of TNF-α from macrophage-like cells, whereas TmpC defects decreased autoagglutination and chymotrypsin-like protease activities. Both mutants adhered to gingival epithelial cells similarly to the wild-type and showed slightly decreased motility. In addition, in Msp-defective mutants, the TDE1072 protein, which is a major membrane protein, was abolished; therefore, phenotypic changes in the mutant can be, at least in part, attributed to the loss of the TDE1072 protein. Thus, the major antigenic proteins, Msp and TmpC, have significant and diverse impacts on the characteristics of T. denticola, especially cell surface properties.

Major membrane protein TDE2508 regulates adhesive potency in Treponema denticola

The cultivation and genetic manipulation of Treponema denticola, a Gram-negative oral spirochaeta associated with periodontal diseases, is still challenging. In this study, we formulated a simple medium based on a commercially available one, and established a transformation method with high efficiency. We then analyzed proteins in a membrane fraction in T. denticola and identified 16 major membrane-associated proteins, and characterized one of them, TDE2508, whose biological function was not yet known. Although this protein, which exhibited a complex conformation, was presumably localized in the outer membrane, we did not find conclusive evidence that it was exposed on the cell surface. Intriguingly, a TDE2508-deficient mutant exhibited significantly increased biofilm formation and adherent activity on human gingival epithelial cells. However, the protein deficiency did not alter autoaggregation, coaggregation with Porphyromonas gingivalis, hemagglutination, cell surface hydrophobicity, motility, or expression of Msp which was reported to be an adherent molecule in this bacteria. In conclusion, the major membrane protein TDE2508 regulates biofilm formation and the adhesive potency of T. denticola, although the underlying mechanism remains unclear.

The fate of Treponema denticola within human gingival epithelial cells

Treponema denticola is one of the major pathogens associated with chronic periodontitis. Bacterial invasion into gingival tissues is a critical process in the pathogenesis of periodontal disease. We recently reported that T. denticola can invade gingival epithelial cells. The aim of this study is to determine the fate of internalized T. denticola in gingival epithelial cells. Immortalized human gingival epithelial HOK-16B cells were infected with 5- (and 6-) carboxy-fluorescein diacetate succinimidyl ester (CFSE)-labeled live or heat-killed T. denticola for 24 h, and the presence of bacteria inside the cells was confirmed by confocal microscopy. Live T. denticola, but not heat-killed bacteria, invaded HOK-16B cells. Confocal microscopy also revealed that internalized T. denticola rarely colocalized with either endosomes or lysosomes. Transmission electron microscopy of infected cells showed that intracellular T. denticola was localized inside endosome-like structures. Although a culture-based antibiotics protection assay could not detect viable intracellular T. denticola 12 h after infection, a substantial number of bacteria were observed by confocal microscopy and weak expression of bacterial 16S ribosomal RNA was detected 48 h after infection. In addition, flow cytometric analysis of HOK-16B cells infected with CFSE-labeled T. denticola showed no loss of fluorescence over 48 h. Collectively, T. denticola invades gingival epithelial cells and remains within the host cells for many hours by resisting endolysosomal degradation. These findings may provide new insight into the role of T. denticola in the pathogenesis of periodontitis.

Dentipain, a Streptococcus pyogenes IdeS protease homolog, is a novel virulence factor of Treponema denticola

Treponema denticola is a major pathogen of chronic periodontitis. Analysis of the T. denticola genome revealed a gene orthologous with a cysteine protease-encoding gene from Streptococcus pyogenes (IdeS). IdeS interferes with IgG-dependent opsonophagocytosis by specific cleavage of IgG molecules. Analysis of this gene (termed ideT) revealed it to encode a two-domain protein whose N-terminus is composed of tandem immunoglobulin-like domains followed by a C-terminal IdeS-like protease domain. In this study we show that during secretion the IdeT protein is processed into an N-terminal fragment which remains associated with the cell, and a C-terminal part released into the medium. Although the secreted domain of IdeT, termed dentipain, shows only 25% identity to the IdeS protease, the putative catalytic cysteine and histidine residues are strongly conserved. Recombinant dentipain cleaves the insulin β-chain, an activity which is inhibited by E-64, a diagnostic inhibitor of cysteine proteases. Apart from insulin no cleavage of other protein substrates was detected, suggesting that dentipain has oligopeptidase activity. A mutant strain was constructed expressing a modified IdeT variant, the dentipain domain of which was deleted. This strain was found to be significantly reduced in its abscess-forming activity compared with the parental strain in a murine abscess model, suggesting that dentipain contributes to the virulence of T. denticola.

Treponema denticola activates mitogen-activated protein kinase signal pathways through Toll-like receptor 2

Treponema denticola, a spirochete indigenous to the oral cavity, is associated with host inflammatory responses to anaerobic polymicrobial infections of the root canal, periodontium, and alveolar bone. However, the cellular mechanisms responsible for the recognition of T. denticola by the innate immune system and the underlying cell signaling pathways that regulate the inflammatory response to T. denticola are currently unresolved. In this study, we demonstrate that T. denticola induces innate immune responses via the utilization of Toll-like receptor 2 (TLR2) but not TLR4. Assessment of TLR2/1 and TLR2/6 heterodimers revealed that T. denticola predominantly utilizes TLR2/6 for the induction of cellular responses. Analysis of the mitogen-activated protein kinase (MAPK) signaling pathway in T. denticola-stimulated monocytes identified a prolonged up-regulation of the MAPK extracellular signal-related kinase 1/2 (ERK1/2) and p38, while no discernible increase in phospho-c-Jun N-terminal kinase 1/2 (JNK1/2) levels was observed. With the aid of pharmacological inhibitors selectively targeting ERK1/2 via the mitogen-activated protein kinase/extracellular signal-related kinase 1/2 kinase and p38, we further demonstrate that ERK1/2 and p38 play a major role in T. denticola-mediated pro- and anti-inflammatory cytokine production.

The Treponema denticola surface protease dentilisin degrades interleukin-1 beta (IL-1 beta), IL-6, and tumor necrosis factor alpha

Dentilisin is a major surface protease and virulence factor of the bacterium Treponema denticola. In this study, we found that T. denticola reduced inflammatory cytokines, including interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor alpha, in peripheral blood mononuclear cells through degradation by dentilisin.

Outer membrane proteins of pathogenic spirochetes

Pathogenic spirochetes are the causative agents of several important diseases including syphilis, Lyme disease, leptospirosis, swine dysentery, periodontal disease and some forms of relapsing fever. Spirochetal bacteria possess two membranes and the proteins present in the outer membrane are at the site of interaction with host tissue and the immune system. This review describes the current knowledge in the field of spirochetal outer membrane protein (OMP) biology. What is known concerning biogenesis and structure of OMPs, with particular regard to the atypical signal peptide cleavage sites observed amongst the spirochetes, is discussed. We examine the functions that have been determined for several spirochetal OMPs including those that have been demonstrated to function as adhesins, porins or to have roles in complement resistance. A detailed description of the role of spirochetal OMPs in immunity, including those that stimulate protective immunity or that are involved in antigenic variation, is given. A final section is included which covers experimental considerations in spirochetal outer membrane biology. This section covers contentious issues concerning cellular localization of putative OMPs, including determination of surface exposure. A more detailed knowledge of spirochetal OMP biology will hopefully lead to the design of new vaccines and a better understanding of spirochetal pathogenesis.

Multiple functions of the leucine-rich repeat protein LrrA of Treponema denticola

The gene lrrA, encoding a leucine-rich repeat protein, LrrA, that contains eight consensus tandem repeats of 23 amino acid residues, has been identified in Treponema denticola ATCC 35405. A leucine-rich repeat is a generally useful protein-binding motif, and proteins containing this repeat are typically involved in protein-protein interactions. Southern blot analysis demonstrated that T. denticola ATCC 35405 expresses the lrrA gene, but the gene was not identified in T. denticola ATCC 33520. In order to analyze the functions of LrrA in T. denticola, an lrrA-inactivated mutant of strain ATCC 35405 and an lrrA gene expression transformant of strain ATCC 33520 were constructed. Characterization of the mutant and transformant demonstrated that LrrA is associated with the extracytoplasmic fraction of T. denticola and expresses multifunctional properties. It was demonstrated that the attachment of strain ATCC 35405 to HEp-2 cell cultures and coaggregation with Tannerella forsythensis were attenuated by the lrrA mutation. In addition, an in vitro binding assay demonstrated specific binding of LrrA to a portion of the Tannerella forsythensis leucine-rich repeat protein, BspA, which is mediated by the N-terminal region of LrrA. It was also observed that the lrrA mutation caused a reduction of swarming in T. denticola ATCC 35405 and consequently attenuated tissue penetration. These results suggest that the leucine-rich repeat protein LrrA plays a role in the attachment and penetration of human epithelial cells and coaggregation with Tannerella forsythensis. These properties may play important roles in the virulence of T. denticola.

Mixed infections with Porphyromonas gingivalis and Treponema denticola cause excessive inflammatory responses in a mouse pneumonia model compared with monoinfections

Periodontopathic anaerobes such as Porphyromonas gingivalis are frequently found in aspiration pneumonia and lung abscesses. However, defense mechanisms and responses to these bacterial infections in the lung in vivo remain poorly understood. The coexistence of P. gingivalis with Treponema denticola has been found at higher levels and proportions in periodontally diseased sites. We hypothesized that mixed infections with P. gingivalis and T. denticola can cause severe respiratory disease. In the present study, inflammatory responses to mono- and mixed inoculations with P. gingivalis and T. denticola in the bronchoalveolar lavage (BAL) fluid were investigated. Acute pneumonia and lung abscesses in mice with the mixed infection resulted in a 40% mortality rate within 72 h, compared with only 10% mortality for the respective monoinfections. Pulmonary clearance of P. gingivalis was delayed in the mice with mixed infections with P. gingivalis and T. denticola. Tumor necrosis factor alpha (TNFalpha) interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) levels from BAL fluid of mice with mixed infections at 24 h after inoculation were significantly higher than those after P. gingivalis monoinfection (TNFalpha: P < 0.05, Il-1beta: P < 0.001, IL-6: P < 0.05). The chemokine KC level from BAL fluid of mice at 48 h (P < 0.05) and 72 h after mixed infection was also significantly increased when compared with that after P. gingivalis monoinfection (P < 0.001). The present study demonstrates that a mixed infection of P. gingivalis with T. denticola in mouse causes a marked bronchopneumonia and lung abscess in the mouse model.

A 43-kDa protein ofTreponema denticolais essential for dentilisin activity

A protease of Treponema denticola, dentilisin, is thought to be part of a complex with 43- and 38-kDa proteins. A sequence encoding a 43-kDa protein was located in the 3' region of the prcA gene upstream of the dentilisin gene (prtP). The 43-kDa protein was apparently generated from digestion of PrcA. To clarify the function of the protein, we constructed a mutant of the 43-kDa protein following homologous recombination. The mutant lacked detectable dentilisin activity. Immunoblot analysis demonstrated that the dentilisin protein was degraded in the mutant. The results of real-time polymerase chain reaction suggested that prtP mRNA expression in the mutant was somewhat decreased compared with the wild-type strain. These data suggest that the 43-kDa protein is involved in the stabilization of the dentilisin protein.

Bacterial protease inhibitors

Serine-, cysteine-, and metalloproteases are widely spread in many pathogenic bacteria, where they play critical functions related to colonization and evasion of host immune defenses, acquisition of nutrients for growth and proliferation, facilitation of dissemination, or tissue damage during infection. Since all the antibiotics used clinically at the moment share a common mechanism of action, acting as inhibitors of the bacterial cell wall biosynthesis or affecting protein synthesis on ribosomes, resistance to these pharmacological agents represents a serious medical problem, which might be resolved by using new generation of antibiotics, possessing a different mechanism of action. Bacterial protease inhibitors constitute an interesting such possibility, due to the fact that many specific as well as ubiquitous proteases have recently been characterized in some detail in both gram-positive as well as gram-negative pathogens. Few potent, specific inhibitors for such bacterial proteases have been reported at this moment except for some signal peptidase, clostripain, Clostridium histolyticum collagenase, botulinum neurotoxin, and tetanus neurotoxin inhibitors. No inhibitors of the critically important and ubiquitous AAA proteases, degP or sortase have been reported, although such compounds would presumably constitute a new class of highly effective antibiotics. This review presents the state of the art in the design of such enzyme inhibitors with potential therapeutic applications, as well as recent advances in the use of some of these proteases in therapy.

Role of Treponema denticola in periodontal diseases

Among periodontal anaerobic pathogens, the oral spirochetes, and especially Treponema denticola, have been associated with periodontal diseases such as early-onset periodontitis, necrotizing ulcerative gingivitis, and acute pericoronitis. Basic research as well as clinical evidence suggest that the prevalence of T denticola, together with other proteolytic gram-negative bacteria in high numbers in periodontal pockets, may play an important role in the progression of periodontal disease. The accumulation of these bacteria and their products in the pocket may render the surface lining periodontal cells highly susceptible to lysis and damage. T. denticola has been shown to adhere to fibroblasts and epithelial cells, as well as to extracellular matrix components present in periodontal tissues, and to produce several deleterious factors that may contribute to the virulence of the bacteria. These bacterial components include outer-sheath-associated peptidases, chymotrypsin-like and trypsin-like proteinases, hemolytic and hemagglutinating activities, adhesins that bind to matrix proteins and cells, and an outer-sheath protein with pore-forming properties. The effects of T. denticola whole cells and their products on a variety of host mucosal and immunological cells has been studied extensively (Fig. 1). The clinical data regarding the presence of T. denticola in periodontal health and disease, together with the basic research results involving the role of T. denticola factors and products in relation to periodontal diseases, are reviewed and discussed in this article.