Mapping of the proinflammatory domains of MspTL of Treponema lecithinolyticum

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.

Inflammasome activators induce fibronectin expression and release in macrophages

Extracellular fibronectin (Fn) can activate pro-inflammatory pathways and serves as an endogenous danger signalling molecule; thus, it has been suggested as a biomarker for several diseases. In the present study, we found that pathogen-derived activators of the inflammasomes induce the expression and secretion of Fn in macrophages through a mechanism involving adenosine triphosphate and caspase-1 activation. We also found that plasma Fn induces caspase-1 activation and cell death in macrophages, epithelial cells, and fibroblasts. Together, these results indicate that Fn plays a critical role in inflammasome-activated cells by amplifying caspase-1 activation and inducing inflammatory cell death.

Novel Pathogens in Periodontal Microbiology

Periodontitis is a polymicrobial disease caused by complex interactions between distinct pathogens in a biofilm resulting in the destruction of periodontal tissues. It seems evident that unknown microorganisms might be involved in onset or progression of periodontitis. For many decades, research in the field of oral microbiology failed to identify certain subgingival microbiota due to technical limitations but, over a period of 12 years using molecular approaches and sequencing techniques, it became feasible to reveal the existence of new periodontal pathogens. Therefore, it is evident that in addition to conventional periodontal pathogens, other microbes might be involved in onset and progression of periodontitis. The novel pathogens enlisted under periodontal phylogeny include Cryptobacterium curtum, Dialister pneumosintes, Filifactor alocis, Mitsuokella dentalis, Slackia exigua, Selenomonas sputigena, Solobacterium moorei, Treponema lecithinolyticum, and Synergistes. The polymicrobial etiology of periodontitis has been elucidated by comprehensive techniques, and studies throwing light on the possible virulence mechanisms possessed by these novel periodontal pathogens are enlisted.

Integrin α5β1 activates the NLRP3 inflammasome by direct interaction with a bacterial surface protein

Integrins are cell-surface heterodimeric glycoproteins composed of alpha and beta subunits that mediate cell-cell, cell-extracellular matrix, and cell-pathogen interactions. In this study, we report a specific role of integrin α5β1 in NLRP3 inflammasome activation in macrophages stimulated by Td92, a surface protein of the periodontopathogen, Treponema denticola. The direct interaction of Td92 with the cell membrane integrin α5β1 resulted in ATP release and K(+) efflux, which are the main events in NLRP3 activation. This interaction was arginine-glycine-aspartate (RGD)-independent, and Td92 internalization was not required for the activity. An integrin α5β1 antibody and oxATP, an ATP receptor antagonist, inhibited NLRP3 expression, caspase-1 activation, interleukin-1β (IL-1β) secretion, and proIL-1β synthesis, all of which were regulated by NF-κB activation. Therefore, our data has identified the integrin α5β1 as a principal cell membrane receptor for both NLRP3 inflammasome activation and IL-1β transcription by a bacterial protein, which could exaggerate inflammation, a characteristic of periodontitis.

The major outer membrane protein of a periodontopathogen induces IFN-beta and IFN-stimulated genes in monocytes via lipid raft and TANK-binding kinase 1/IFN regulatory factor-3

Surface molecules of pathogens play an important role in stimulating host immune responses. Elucidation of the signaling pathways activated by critical surface molecules in host cells provides insight into the molecular pathogenesis resulting from bacteria-host interactions. MspTL is the most abundant outer membrane protein of Treponema lecithinolyticum, which is associated with periodontitis, and induces expression of a variety of proinflammatory factors. Although bacteria and bacterial components like LPS and flagellin are known to induce IFN-beta, induction by bacterial surface proteins has not been reported. In the present study, we investigated MspTL-mediated activation of signaling pathways stimulating up-regulation of IFN-beta and IFN-stimulated genes in a human monocytic cell line, THP-1 cells, and primary cultured human gingival fibroblasts. MspTL treatment of the cells induced IFN-beta and the IFN-stimulated genes IFN-gamma-inducible protein-10 (IP-10) and RANTES. A neutralizing anti-IFN-beta Ab significantly reduced the expression of IP-10 and RANTES, as well as STAT-1 activation, which was also induced by MspTL. Experiments using specific small interfering RNA showed that MspTL activated TANK-binding kinase 1 (TBK1), but not inducible IkappaB kinase (IKKi). MspTL also induced dimerization of IFN regulatory factor-3 (IRF-3) and translocation into the nucleus. The lipid rapid-disrupting agents methyl-beta-cyclodextrin, nystatin, and filipin inhibited the MspTL internalization and cellular responses, demonstrating that lipid raft activation was a prerequisite for MspTL cellular signaling. Our results demonstrate that MspTL, the major outer protein of T. lecithinolyticum, induced IFN-beta expression and subsequent up-regulation of IP-10 and RANTES via TBK1/IRF-3/STAT-1 signaling secondary to lipid raft activation.

Propofol inhibits cyclo-oxygenase activity in human monocytic THP-1 cells

PURPOSE

Monocytes/macrophages are key players in innate and adaptive immunity. Upon stimulation, they secrete prostanoids, which are produced by cyclooxygenase from arachidonic acid. Prostanoids influence inflammation and immune responses. We investigated the effect of propofol on prostaglandin E(2) and thromboxane B(2) production by the human monocytic cell line THP-1.

METHODS

The THP-1 cells were cultured with lipopolysaccharide (1 microg ml(-1)) in the presence of clinically relevant sedative/anesthetic concentrations of propofol (0-30 microM) for 18 h, and the concentration of prostaglandin E(2) and thromboxane B(2) in culture supernatants was measured using an enzyme immunoassay. Intracellular cyclooxygenase protein expression was measured by flow cytometry. Cyclooxygenase activity was assessed by measuring production of prostaglandin E(2) and thromboxane B(2) by THP-1 cells after arachidonic acid (10 microM) substrate provision.

RESULTS

Propofol decreased the production of prostaglandin E(2) (75.4 +/- 6.4 pg ml(-1) at 0 microM vs. 28.5 +/- 11.2 pg ml(-1) at 30 microM; P < 0.001) and thromboxane B(2) (282.4 +/- 79.2 pg ml(-1) at 0 microM vs. 40.4 +/- 21.7 pg ml(-1) at 30 microM; P < 0.001). The inhibition was not due to the decreased cyclooxygenase protein expression because intracellular staining of this enzyme was not affected by propofol. After arachidonic acid provision, prostaglandin E(2) and thromboxane B(2) production from activated THP-1 cells was significantly (P < 0.001) decreased with propofol, indicating direct suppression of cyclooxygenase activity with propofol.

CONCLUSIONS

Propofol may modulate inflammation via the suppression of cyclooxygenase activity. Through the inhibition of prostanoid production, propofol may enhance immune responses.

Highly conserved surface proteins of oral spirochetes as adhesins and potent inducers of proinflammatory and osteoclastogenic factors

Oral spirochetes include enormously heterogeneous Treponema species, and some have been implicated in the etiology of periodontitis. In this study, we characterized highly conserved surface proteins in four representative oral spirochetes (Treponema denticola, T. lecithinolyticum, T. maltophilum, and T. socranskii subsp. socranskii) that are homologs of T. pallidum Tp92, with opsonophagocytic potential and protective capacity against syphilis. Tp92 homologs of oral spirochetes had predicted signal peptides (20 to 31 amino acids) and molecular masses of 88 to 92 kDa for mature proteins. They showed amino acid sequence identities of 37.9 to 49.3% and similarities of 54.5 to 66.9% to Tp92. The sequence identities and similarities of Tp92 homologs of oral treponemes to one another were 41.6 to 71.6% and 59.9 to 85.6%, respectively. The tp92 gene homologs were successfully expressed in Escherichia coli, and the recombinant proteins were capable of binding to KB cells, an epithelial cell line, and inhibited the binding of the whole bacteria to the cells. Antiserum (the immunoglobulin G fraction) raised against a recombinant form of the T. denticola Tp92 homolog cross-reacted with homologs from three other species of treponemes. The Tp92 homologs stimulated various factors involved in inflammation and osteoclastogenesis, like interleukin-1beta (IL-1beta), tumor necrosis factor alpha, IL-6, prostaglandin E(2), and matrix metalloproteinase 9, in host cells like monocytes and fibroblasts. Our results demonstrate that Tp92 homologs of oral spirochetes are highly conserved and may play an important role in cell attachment, inflammation, and tissue destruction. The coexistence of various Treponema species in a single periodontal pocket and, therefore, the accumulation of multiple Tp92 homologs may amplify the pathological effect in periodontitis.