Localization of Outer Membrane Proteins in Treponema denticola by Quantitative Proteome Analyses of Outer Membrane Vesicles and Cellular Fractions

Topology and functional characterization of major outer membrane proteins of Treponema maltophilum and Treponema lecithinolyticum

Numerous Treponema species are prevalent in the dysbiotic subgingival microbial community during periodontitis. The major outer sheath protein is a highly expressed virulence factor of the well-characterized species Treponema denticola. Msp forms an oligomeric membrane protein complex with adhesin and porin properties and contributes to host-microbial interaction. Treponema maltophilum and Treponema lecithinolyticum species are also prominent during periodontitis but are relatively understudied. Msp-like membrane surface proteins exist in T. maltophilum (MspA) and T. lecithinolyticum (MspTL), but limited information exists regarding their structural features or functionality. Protein profiling reveals numerous differences between these species, but minimal differences between strains of the same species. Using protein modeling tools, we predict MspA and MspTL monomeric forms to be large β-barrel structures composed of 20 all-next-neighbor antiparallel β strands which most likely adopt a homotrimer formation. Using cell fractionation, Triton X-114 phase partitioning, heat modifiability, and chemical and detergent release assays, we found evidence of amphiphilic integral membrane-associated oligomerization for both native MspA and MspTL in intact spirochetes. Proteinase K accessibility and immunofluorescence assays demonstrate surface exposure of MspA and MspTL. Functionally, purified recombinant MspA or MspTL monomer proteins can impair neutrophil chemotaxis. Expressions of MspA or MspTL with a PelB leader sequence in Escherichia coli also demonstrate surface exposure and can impair neutrophil chemotaxis in an in vivo air pouch model of inflammation. Collectively, our data demonstrate that MspA and MspTL membrane proteins can contribute to pathogenesis of these understudied oral spirochete species.

Bacterial Membrane Vesicles: The Missing Link Between Bacterial Infection and Alzheimer Disease

Periodontitis is a common chronic inflammatory disease, affecting approximately 19% of the global adult population. A relationship between periodontal disease and Alzheimer disease has long been recognized, and recent evidence has been uncovered to link these 2 diseases mechanistically. Periodontitis is caused by dysbiosis in the subgingival plaque microbiome, with a pronounced shift in the oral microbiota from one consisting primarily of Gram-positive aerobic bacteria to one predominated by Gram-negative anaerobes, such as Porphyromonas gingivalis. A common phenomenon shared by all bacteria is the release of membrane vesicles to facilitate biomolecule delivery across long distances. In particular, the vesicles released by P gingivalis and other oral pathogens have been found to transport bacterial components across the blood-brain barrier, initiating the physiologic changes involved in Alzheimer disease. In this review, we summarize recent data that support the relationship between vesicles secreted by periodontal pathogens to Alzheimer disease pathology.

Comprehensive Overview of Treponema pallidum Outer Membrane Proteins

Treponema pallidum, the causative agent of syphilis, is a sexually transmitted microorganism that exhibits remarkable motility capabilities, allowing it to affect various systems. Despite its structural resemblance to gram-negative bacteria due to its dual-membrane, T. pallidum possesses a lower abundance of outer membrane proteins (OMPs), which enables it to effectively conceal itself. This review presents a comprehensive analysis of the clinical diagnostic potential associated with the OMPs of T. pallidum. Furthermore, the known OMPs in T. pallidum that are responsible for mediating host interactions have been progressively elucidated. This review aims to shed light on the pathogenesis of syphilis, encompassing aspects such as vascular inflammation, chancre self-healing, neuroinvasion, and reinfection. Additionally, this review offers a detailed overview of the current state and prospects of development in the field of syphilis vaccines, with the ultimate goal of establishing a foundation for understanding the pathogenesis and implementing effective prevention strategies against syphilis.

Localization and pathogenic role of the cysteine protease dentipain in Treponema denticola

The Msp protein complex and the serine protease dentilisin are the best-characterized virulence factors in Treponema denticola, the major etiological agent of chronic periodontitis. In addition to these outer sheath factors, the cysteine protease dentipain contributes to pathogenicity, but its secretion, processing, cellular localization, and role in T. denticola virulence are not fully understood. In this study, we found that full-sized dentipain (74-kDa) and the 52-kDa truncated form of the enzyme are located, respectively, in the outer sheath derived from T. denticola dentilisin- and the Msp-deficient mutants. Furthermore, dentipain was barely detected in the wild-type strain. These results suggest that dentilisin and Msp, the major outer sheath proteins, are involved in the secretion and maturation of dentipain. Inactivation of the dentipain gene slowed the growth of T. denticola, and the effect was more profound in serum-free medium than in serum-containing medium. Several genes, including those encoding transporters and methyl-accepting chemotaxis proteins, were differentially expressed in the dentipain-deficient mutant. Furthermore, the mutant strain was more hydrophobic than the wild-type strain. Finally, the mutant showed less autoaggregation activity and adhesion to IgG in a serum-free medium than the wild-type strain. These findings suggest that dentipain contributes to the virulence of T. denticola by facilitating adhesion and acquisition of nutrients essential for colonization and proliferation in the gingival crevice under serum-rich conditions.

The role of extracellular vesicles in periodontitis: pathogenesis, diagnosis, and therapy

Periodontitis is a prevalent disease and one of the leading causes of tooth loss. Biofilms are initiating factor of periodontitis, which can destroy periodontal tissue by producing virulence factors. The overactivated host immune response is the primary cause of periodontitis. The clinical examination of periodontal tissues and the patient's medical history are the mainstays of periodontitis diagnosis. However, there is a lack of molecular biomarkers that can be used to identify and predict periodontitis activity precisely. Non-surgical and surgical treatments are currently available for periodontitis, although both have drawbacks. In clinical practice, achieving the ideal therapeutic effect remains a challenge. Studies have revealed that bacteria produce extracellular vesicles (EVs) to export virulence proteins to host cells. Meanwhile, periodontal tissue cells and immune cells produce EVs that have pro- or anti-inflammatory effects. Accordingly, EVs play a critical role in the pathogenesis of periodontitis. Recent studies have also presented that the content and composition of EVs in saliva and gingival crevicular fluid (GCF) can serve as possible periodontitis diagnostic indicators. In addition, studies have indicated that stem cell EVs may encourage periodontal regeneration. In this article, we mainly review the role of EVs in the pathogenesis of periodontitis and discuss their diagnostic and therapeutic potential.

Activation of bone marrow-derived dendritic cells and CD4+ T cell differentiation by outer membrane vesicles of periodontal pathogens

Outer membrane vesicles (OMVs) released from gram-negative bacteria harbor diverse molecules to communicate with host cells. In this study, we evaluated the OMVs of periodontal pathogens for their effects on the activation of dendritic cells and CD4⁺ T cell differentiation. OMVs of Porphyromonas gingivalis ATCC 33277, Treponema denticola ATCC 33521, and Tannerella forsythia ATCC 43037 (‘red complex’ pathogens) were isolated by density gradient ultracentrifugation. Mouse bone marrow-derived dendritic cells (BMDCs) were treated with OMVs, and OMV-primed BMDCs were cocultured with naïve CD4⁺ T cells to analyze the polarization of effector helper T cells. The OMVs upregulated maturation markers, including MHC class II, CD80, CD86, and CD40, on BMDCs. OMVs of P. gingivalis and T. forsythia induced the expression of the proinflammatory cytokines IL-1β, IL-6, IL-23, and IL-12p70 in BMDCs. In T. denticola OMV-primed BMDCs, proinflammatory cytokines were poorly detected, which may be attributed to posttranslational degradation due to the highly proteolytic nature of OMVs. In cocultures of naïve CD4⁺ T cells with OMV-primed BMDCs, OMVs of P. gingivalis and T. denticola induced the differentiation of Th17 cells, whereas T. forsythia OMVs induced Th1 cell differentiation. These results demonstrate that OMVs derived from the ‘red complex’ periodontal pathogens induce maturation of BMDCs and differentiation of naïve CD4⁺ T cells to Th1 or Th17 cells.

The identification of polyvalent protective immunogens and immune abilities from the outer membrane proteins of Aeromonas hydrophila in fish

Among aquaculture vaccines, polyvalent vaccines (for immunoprotection against multiple bacterial species) are more efficient and can better avoid bacterial resistance and antibiotic residues in fish. Here, 15 outer membrane proteins (OMPs) of Aeromonas hydrophila were cloned and purified, and mouse antisera were prepared. Passive immunization to Carassius auratus showed that four OMPs sera (OmpW, OmpAII, P5, and AHA2685) and the entire OMPs serum held effective immunoprotection against A. hydrophila infection. Furthermore, the active immunization of four OMPs to C. auratus showed that OmpW, OmpAII, P5, and AHA2685 held effective immunoprotection against A. hydrophila, and OmpW held active cross-protection against Vibrio alginolyticus. The mechanisms of these four candidate vaccines in triggering immune responses were subsequently explored. They all could activate innate immune responses in active immunization, down-regulate (p < 0.05) the inflammation-related genes expression to reduce the inflammatory reaction induced by A. hydrophila, and down-regulate (p < 0.05) antioxidant-related factors to reduce the antioxidant reaction for bacterial infection. Noteablely, the four OMPs had protective abilities on kidney and spleen tissues of C. auratus after challenged with A. hydrophila and V. alginolyticus by histopathological observation. Collectively, our results identify OmpW as a polyvalent vaccine candidate, and OmpAII, P5, and AHA2685 as vaccine candidates against A. hydrophila infection in fish.

Notes on syphilis vaccine development

The quest for a syphilis vaccine to provide protection from infection or disease began not long after the isolation of the first Treponema pallidum subspecies pallidum (T. pallidum) strain in 1912. Yet, a practical and effective vaccine formulation continues to elude scientists. Over the last few years, however, efforts toward developing a syphilis vaccine have increased thanks to an improved understanding of the repertoire of T. pallidum outer membrane proteins (OMPs), which are the most likely syphilis vaccine candidates. More has been also learned about the molecular mechanisms behind pathogen persistence and immune evasion. Published vaccine formulations based on a subset of the pathogen's OMPs have conferred only partial protection upon challenge of immunized laboratory animals, primarily rabbits. Nonetheless, those experiments have improved our approach to the choice of immunization regimens, adjuvants, and vaccine target selection, although significant knowledge gaps remain. Herein, we provide a brief overview on current technologies and approaches employed in syphilis vaccinology, and possible future directions to develop a vaccine that could be pivotal to future syphilis control and elimination initiatives.

Membrane vesicles from periodontal pathogens and their potential roles in periodontal disease and systemic illnesses

Periodontium is an ordered ecological system where a dynamic equilibrium exists between oral microorganisms and the host defense system, and periodontal disease occurs whenever the balance is broken. Periodontal pathogens mainly include gram-negative anaerobic bacteria and emerging gram-positive microbes, which have a large variety of virulence factors and influence disease initiation and progression. Recently, different types of bacterial membrane vesicles (MVs), formed by bubbling of membrane materials from living cells or in conditions of endolysin-triggered cell death, have gained interests as a novel virulence factor for periodontopathogens. MVs load multiple sorted cargo molecules, such as proteins, lipids, and genetic materials, and actively participate in toxin transport, signal delivery, and periodontal disease pathogenesis. Since periodontitis is recognized as a risk factor for many systemic diseases, periodontal MVs could work as a bridge for periodontal diseases and systemic illnesses. Furthermore, MVs with unique nature and advantages are promising candidates as vaccines and drug delivery vehicles. In this review, we provided an overview of different types and compositions of periodontal MVs, described their involvements in the pathogenesis of periodontitis and several general diseases, and discussed potential applications of periodontal MVs in vaccination and drug delivery.

Investigation of the potential regulator proteins associated with the expression of major surface protein and dentilisin in Treponema denticola

ObjectiveTreponema denticola is involved in ‘chronic’ periodontitis pathogenesis. The mechanism underlying the regulation of the expression of its virulence factors, such as major surface protein (Msp) and prolyl-phenylalanine specific protease (dentilisin) is yet to be clarified. We determined the gene expression profiles of Msp- and dentilisin-deficient mutants of T. denticola to identify the regulation network of gene expression concomitant with the inactivation of these virulence genes.

Methods Gene expression profiles of T. denticola ATCC 35405 (wild type), dentilisin-deficient mutant K1, and msp-deficient mutant DMSP3 were determined using DNA microarray analysis and quantitative real-time reverse transcription PCR (qRT-PCR). Msp and dentilisin protein levels were determined by immunoblotting and proteolytic activity assays.

Results In addition to several differentially expressed genes, dentilisin expression was reduced in DMSP3; msp expression was significantly reduced in K1 (p < 0.05), both at the gene and protein levels. To identify the regulatory system involved, the expression levels of the potential regulators whose expression showed changes in the mutants were evaluated using qRT-PCR. Transcriptional regulators TDE_0127 and TDE_0814 were upregulated in K1, and the potential repressor, TDE_0344, was elevated in DMSP3.

Conclusions Dentilisin and Msp expression were interrelated, and gene expression regulators, such as TDE_0127, may be involved in their regulation.

Oral and intestinal bacterial exotoxins: Potential linked to carcinogenesis

Growing evidence suggests that imbalances in resident microbes (dysbiosis) can promote chronic inflammation, immune-subversion, and production of carcinogenic metabolites, thus leading to neoplasia. Yet, evidence to support a direct link of individual bacteria species to human sporadic cancer is still limited. This chapter focuses on several emerging bacterial toxins that have recently been characterized for their potential oncogenic properties toward human orodigestive cancer and the presence of which in human tissue samples has been documented. These include cytolethal distending toxins produced by various members of gamma and epsilon Proteobacteria, Dentilisin from mammalian oral Treponema, Pasteurella multocida toxin, two Fusobacterial toxins, FadA and Fap2, Bacteroides fragilis toxin, colibactin, cytotoxic necrotizing factors and α-hemolysin from Escherichia coli, and Salmonella enterica AvrA. It was clear that these bacterial toxins have biological activities to induce several hallmarks of cancer. Some toxins directly interact with DNA or chromosomes leading to their breakdowns, causing mutations and genome instability, and others modulate cell proliferation, replication and death and facilitate immune evasion and tumor invasion, prying specific oncogene and tumor suppressor pathways, such as p53 and β-catenin/Wnt. In addition, most bacterial toxins control tumor-promoting inflammation in complex and diverse mechanisms. Despite growing laboratory evidence to support oncogenic potential of selected bacterial toxins, we need more direct evidence from human studies and mechanistic data from physiologically relevant experimental animal models, which can reflect chronic infection in vivo, as well as take bacterial-bacterial interactions among microbiome into consideration.

The Msp Protein of Treponema denticola Interrupts Activity of Phosphoinositide Processing in Neutrophils

Periodontal disease is a significant health burden, causing tooth loss and poor oral and overall systemic health. Dysbiosis of the oral biofilm and a dysfunctional immune response drive chronic inflammation, causing destruction of soft tissue and alveolar bone supporting the teeth. Treponema denticola, a spirochete abundant in the plaque biofilm of patients with severe periodontal disease, perturbs neutrophil function by modulating appropriate phosphoinositide (PIP) signaling. Through a series of immunoblotting and quantitative PCR (qPCR) experiments, we show that Msp does not alter the gene transcription or protein content of key enzymes responsible for PIP3 signaling: 3' phosphatase and tensin homolog (PTEN), phosphatidylinositol 3-kinase (PI3K), or 5' Src homology 2 domain-containing inositol phosphatase 1 (SHIP1). Instead, using immunoblotting and enzyme-linked immunosorbent assays (ELISAs), we found that Msp activates PTEN through dephosphorylation specifically at the S380 site. Msp in intact organisms or outer membrane vesicles also restricts PIP signaling. SHIP1 phosphatase release was assessed using chemical inhibition and immunoprecipitation to show that Msp moderately decreases SHIP1 activity. Msp also prevents secondary activation of the PTEN/PI3K response. We speculate that this result is due to the redirection of the PIP3 substrate away from SHIP1 to PTEN. Immunofluorescence microscopy revealed a redistribution of PTEN from the cytoplasm to the plasma membrane following exposure to Msp, which may contribute to PTEN activation. Mechanisms of how T. denticola modulates and evades the host immune response are still poorly described, and here we provide further mechanistic evidence of how spirochetes modify PIP signaling to dampen neutrophil function. Understanding how oral bacteria evade the immune response to perpetuate the cycle of inflammation and infection is critical for combating periodontal disease to improve overall health outcomes.