Differential Responses of Pattern Recognition Receptors to Outer Membrane Vesicles of Three Periodontal Pathogens

Highly purified outer membrane vesicles (OMVs) of the periodontal pathogens, Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia were produced using tangential flow ultrafiltration, ultracentrifugation and Optiprep density gradient separation. Cryo-TEM and light scattering showed OMVs to be single lipid-bilayers with modal diameters of 75 to 158 nm. Enumeration of OMVs by nanoparticle flow-cytometry at the same stage of late exponential culture indicated that P. gingivalis was the most prolific OMV producer. P. gingivalis OMVs induced strong TLR2 and TLR4-specific responses and moderate responses in TLR7, TLR8, TLR9, NOD1 and NOD2 expressing-HEK-Blue cells. Responses to T. forsythia OMVs were less than those of P. gingivalis and T. denticola OMVs induced only weak responses. Compositional analyses of OMVs from the three pathogens demonstrated differences in protein, fatty acids, lipopolysaccharide, peptidoglycan fragments and nucleic acids. Periodontal pathogen OMVs induced differential pattern recognition receptor responses that have implications for their role in chronic periodontitis.

Treponema denticola major outer sheath protein impairs the cellular phosphoinositide balance that regulates neutrophil chemotaxis

The major outer sheath protein (Msp) of Treponema denticola inhibits neutrophil polarization and directed chemotaxis together with actin dynamics in vitro in response to the chemoattractant N-formyl-methionine-leucine-phenylanine (fMLP). Msp disorients chemotaxis through inhibition of a Rac1-dependent signaling pathway, but the upstream mechanisms are unknown. We challenged murine bone marrow neutrophils with enriched native Msp to determine the role of phospholipid modifying enzymes in chemotaxis and actin assembly downstream of fMLP-stimulation. Msp modulated cellular phosphoinositide levels through inhibition of phosphatidylinositol 3-kinase (PI3-kinase) together with activation of the lipid phosphatase, phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Impaired phosphatidylinositol[(3,4,5)]-triphosphate (PIP3) levels prevented recruitment and activation of the downstream mediator Akt. Release of the actin capping proteins gelsolin and CapZ in response to fMLP was also inhibited by Msp exposure. Chemical inhibition of PTEN restored PIP3 signaling, as measured by Akt activation, Rac1 activation, actin uncapping, neutrophil polarization and chemotaxis in response to fMLP-stimulation, even in the presence of Msp. Transduction with active Rac1 also restored fMLP-mediated actin uncapping, suggesting that Msp acts at the level of PIP3 in the hierarchical feedback loop of PIP3 and Rac1 activation. Taken together, Msp alters the phosphoinositide balance in neutrophils, impairing the cell “compass”, which leads to inhibition of downstream chemotactic events.

Treponema denticola alters cell vitality and induces HO-1 and Hsp70 expression in porcine aortic endothelial cells

Treponema denticola is an oral spirochete that is associated with periodontal disease and detected occasionally in extraoral lesions associated with systemic disorders such as cardiovascular diseases. The effect of specific bacterial products from oral treponemes on endothelium is poorly investigated. This study analyzed the ability of components of the outer membrane of T. denticola (OMT) to induce apoptosis and heat shock proteins (HO-1 and Hsp70) in porcine aortic endothelial cells (pAECs), compared with results obtained with classical pro-inflammatory lipopolysaccharide (LPS) treatment. Cellular apoptosis was detected when pAECs were treated with either OMT or LPS, suggesting that OMT can damage endothelium integrity by reducing endothelial cell vitality. Stimulation with OMT, similarly to LPS response, increased HO-1 and Hsp-70 protein expression in a time-dependent manner, correlating with a rise in HO-1 and Hsp-70 mRNA. Collectively, these results support the hypothesis that T. denticola alters endothelial cell function. Moreover, our in vitro experiments represent a preliminary investigation to further in vivo study using a pig model to elucidate how T. denticola leaves the initial endodontic site and participates in the development of several systemic diseases.

An actin-stabilizing peptide conjugate deduced from the major outer sheath protein of the bacterium Treponema denticola

A synthetic peptide conjugated to bovine serum albumin, P34(BSA), based on a 10-mer in the deduced amino acid sequence of the major outer sheath protein of Treponema denticola, was found to stabilize actin filaments of fibroblasts. Pretreatment of cells with P34(BSA) inhibited the actin disruption induced by cytochalasin D and latrunculin B. P34(BSA) was taken up by the cells and localized among actin filaments. P34(BSA) bound actin from fibroblast lysates, and cell exposure to P34(BSA) led to the activation of RhoA, a key regulator of actin filament assembly in fibroblasts. Exposure of fibroblasts to P34(BSA) retarded their migration on a collagen substratum. P34(BSA) also inhibited chemotaxis of murine neutrophils. Our findings with a novel peptide conjugate imply that bacterial proteins known to perturb the cytoskeleton represent a rich source of molecular models upon which to design synthetic reagents for modulating actin-dependent cellular functions.

Modulation of human neutrophil functions in vitro by Treponema denticola major outer sheath protein

In this study of human polymorphonuclear leukocytes (PMNs), pretreatment with Treponema denticola major outer sheath protein (Msp) inhibited formyl-methionyl-leucyl-phenylalanine (fMLP)-induced chemotaxis, phagocytosis of immunoglobulin G-coated microspheres, fMLP-stimulated calcium transients, and actin assembly. Msp neither altered oxidative responses to phorbol myristate or fMLP nor induced apoptosis. Msp selectively impairs chemotaxis and phagocytosis by impacting the PMN cytoskeleton.

The metabolism of cholesterol and certain hormonal steroids by Treponema denticola

The aim was to investigate whether reference cultures and fresh isolates of Treponema denticola are able to 5alpha-reduce and further metabolise testosterone, 4-androstenedione, progesterone, corticosterone, cortisol or cholesterol. Two reference and five freshly isolated cultures of T. denticola were incubated with either radiolabeled or unlabeled steroid substrates; in the first case products were identified by thin layer chromatography and in the latter by gas chromatography-mass spectroscopy. All the substrates were 5alpha-reduced. Both reference cultures and fresh isolates of T. denticola presented 3beta- and 17beta-hydroxy steroid dehydrogenase activity. It was concluded that T. denticola was capable of steroid metabolism and hypotheses are discussed regarding the in vivo function of this metabolism including, T. denticola utilising host supplied steroids as growth factors and T. denticola steroid metabolism acting as a virulence factor.

Probing the role of Tyr 64 of Treponema denticola cystalysin by site-directed mutagenesis and kinetic studies

Tyr 64, hydrogen-bonded to coenzyme phosphate in Treponema denticola cystalysin, was changed to alanine by site-directed mutagenesis. Spectroscopic and kinetic properties of the Tyr 64 mutant were investigated in an effort to explore the differences in coenzyme structure and kinetic mechanism relative to those of the wild-type enzyme. The wild type displays coenzyme absorbance bands at 418 and 320 nm, previously attributed to ketoenamine and substituted aldamine, respectively. The Tyr 64 mutant exhibits absorption maxima at 412 and 325 nm. However, the fluorescence characteristics of the latter band are consistent with its assignment to the enolimine form of the Schiff base. pK(spec) values of approximately 8.3 and approximately 6.5 were observed in a pH titration of the wild-type and mutant coenzyme absorbances, respectively. Thus, Tyr 64 is probably the residue involved in the nucleophilic attack on C4' of pyridoxal 5'-phosphate (PLP) in the internal aldimine. Although the Tyr 64 mutant exhibits a lower affinity for PLP and lower turnover numbers for alpha,beta-elimination and racemization than the wild type, the pH profiles for their Kd(PLP) and kinetic parameters are very similar. Rapid scanning stopped-flow and chemical quench experiments suggest that, in contrast to the wild type, for which the rate-determining step of alpha,beta-elimination of beta-chloro-L-alanine is the release of pyruvate, the rate-determining step for the mutant in the same reaction is the formation of alpha-aminoacrylate. Altogether, these results provide new insights into the catalytic mechanism of cystalysin and highlight the functional role of Tyr 64.