ABSTRACT
Clinical and epidemiological studies have implicated chronic infections in the development of atherosclerosis. It has been proposed that common mechanisms of signaling via TLRs link stimulation by multiple pathogens to atherosclerosis. However, how pathogen-specific stimulation of TLR4 contributes to atherosclerosis progression remains poorly understood. In this study, atherosclerosis-prone apolipoprotein-E null (ApoE(-/-)) and TLR4-deficient (ApoE(-/-)TLR4(-/-)) mice were orally infected with the periodontal pathogen Porphyromonas gingivalis. ApoE(-/-)TLR4(-/-) mice were markedly more susceptible to atherosclerosis after oral infection with P. gingivalis. Using live animal imaging, we demonstrate that enhanced lesion progression occurs progressively and was increasingly evident with advancing age. Immunohistochemical analysis of lesions from ApoE(-/-)TLR4(-/-) mice revealed an increased inflammatory cell infiltrate composed primarily of macrophages and IL-17 effector T cells (Th17), a subset linked with chronic inflammation. Furthermore, enhanced atherosclerosis in TLR4-deficient mice was associated with impaired development of Th1 immunity and regulatory T cell infiltration. In vitro studies suggest that the mechanism of TLR4-mediated protective immunity may be orchestrated by dendritic cell IL-12 and IL-10, which are prototypic Th1 and regulatory T cell polarizing cytokines. We demonstrate an atheroprotective role for TLR4 in response to infection with the oral pathogen P. gingivalis. Our results point to a role for pathogen-specific TLR signaling in chronic inflammation and atherosclerosis.
Subject(s)
Atherosclerosis/immunology , Bacteroidaceae Infections/immunology , Gingivitis/immunology , Inflammation Mediators/physiology , Porphyromonas gingivalis/immunology , Signal Transduction/immunology , Toll-Like Receptor 4/physiology , Animals , Apolipoproteins E/deficiency , Apolipoproteins E/genetics , Atherosclerosis/genetics , Atherosclerosis/pathology , Bacteroidaceae Infections/genetics , Bacteroidaceae Infections/pathology , Disease Progression , Gingivitis/genetics , Gingivitis/pathology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Porphyromonas gingivalis/pathogenicity , Signal Transduction/genetics , Toll-Like Receptor 4/deficiency , Toll-Like Receptor 4/geneticsABSTRACT
Since Neisseria gonorrhoeae and Neisseria meningitidis are obligate human pathogens, a comparison with commensal species of the same genus could reveal differences important in pathogenesis. The recent completion of commensal Neisseria genome draft assemblies allowed us to perform a comparison of the genes involved in the catalysis, assembly and regulation of the denitrification pathway, which has been implicated in the virulence of several bacteria. All species contained a highly conserved nitric oxide reductase (NorB) and a nitrite reductase (AniA or NirK) that was highly conserved in the catalytic but divergent in the N-terminal lipid modification and C-terminal glycosylation domains. Only Neisseria mucosa contained a nitrate reductase (Nar), and only Neisseria lactamica, Neisseria cinerea, Neisseria subflava, Neisseria flavescens and Neisseria sicca contained a nitrous oxide reductase (Nos) complex. The regulators of the denitrification genes, FNR, NarQP and NsrR, were highly conserved, except for the GAF domain of NarQ. Biochemical examination of laboratory strains revealed that all of the neisserial species tested except N. mucosa had a two- to fourfold lower nitrite reductase activity than N. gonorrhoeae, while N. meningitidis and most of the commensal Neisseria species had a two- to fourfold higher nitric oxide (NO) reductase activity. For N. meningitidis and most of the commensal Neisseria, there was a greater than fourfold reduction in the NO steady-state level in the presence of nitrite as compared with N. gonorrhoeae. All of the species tested generated an NO steady-state level in the presence of an NO donor that was similar to that of N. gonorrhoeae. The greatest difference between the Neisseria species was the lack of a functional Nos system in the pathogenic species N. gonorrhoeae and N. meningitidis.
Subject(s)
Neisseria/genetics , Neisseria/metabolism , Nitrites/metabolism , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Genes, Bacterial , Genomics , Humans , Neisseria/growth & development , Neisseria/pathogenicity , Nitrite Reductases/chemistry , Nitrite Reductases/genetics , Nitrite Reductases/metabolism , Oxidoreductases/genetics , Oxidoreductases/metabolism , Protein Structure, Tertiary , Species Specificity , VirulenceABSTRACT
Neisseria gonorrhoeae encodes a number of important genes that aid in survival during times of oxidative stress. The same immune cells capable of oxygen-dependent killing mechanisms also have the capacity to generate reactive nitrogen species (RNS) that may function antimicrobially. F62 and eight additional gonococcal strains displayed a high level of resistance to peroxynitrite, while Neisseria meningitidis and Escherichia coli showed a four- to seven-log and a four-log decrease in viability, respectively. Mutation of gonococcal orthologues that are known or suspected to be involved in RNS defence in other bacteria (ahpC, dnrN and msrA) resulted in no loss of viability, suggesting that N. gonorrhoeae has a novel mechanism of resistance to peroxynitrite. Whole-cell extracts of F62 prevented the oxidation of dihydrorhodamine, and decomposition of peroxynitrite was not dependent on ahpC, dnrN or msrA. F62 grown in co-culture with E. coli strain DH10B was shown to protect E. coli viability 10-fold. Also, peroxynitrite treatment of F62 did not result in accumulation of nitrated proteins, suggesting that an active peroxynitrite reductase is responsible for peroxynitrite decomposition rather than a protein sink for amino acid modification.