In Vitro Pre-Clinical Evaluation of a Gonococcal Trivalent Candidate Vaccine Identified by Transcriptomics

Gonorrhea, a sexually transmitted disease caused by Neisseria gonorrhoeae, poses a significant global public health threat. Infection in women can be asymptomatic and may result in severe reproductive complications. Escalating antibiotic resistance underscores the need for an effective vaccine. Approaches being explored include subunit vaccines and outer membrane vesicles (OMVs), but an ideal candidate remains elusive. Meningococcal OMV-based vaccines have been associated with reduced rates of gonorrhea in retrospective epidemiologic studies, and with accelerated gonococcal clearance in mouse vaginal colonization models. Cross-protection is attributed to shared antigens and possibly cross-reactive, bactericidal antibodies. Using a Candidate Antigen Selection Strategy (CASS) based on the gonococcal transcriptome during human mucosal infection, we identified new potential vaccine targets that, when used to immunize mice, induced the production of antibodies with bactericidal activity against N. gonorrhoeae strains. The current study determined antigen recognition by human sera from N. gonorrhoeae-infected subjects, evaluated their potential as a multi-antigen (combination) vaccine in mice and examined the impact of different adjuvants (Alum or Alum+MPLA) on functional antibody responses to N. gonorrhoeae. Our results indicated that a stronger Th1 immune response component induced by Alum+MPLA led to antibodies with improved bactericidal activity. In conclusion, a combination of CASS-derived antigens may be promising for developing effective gonococcal vaccines.

Increase in Multidrug Resistant Neisseria gonorrhoeae FC428-Like Isolates Harboring the Mosaic penA 60.001 Gene, in Nanjing, China (2017-2020)

Background

Since the first Chinese report of the ceftriaxone-resistant Neisseria gonorrhoeae FC428 clone in 2016, additional FC428-like, penA 60.001 isolates have been identified in China.

Objective

To document the rise in penA 60.001 isolates in Nanjing, China, and characterize their molecular and epidemiological features.

Methods

N. gonorrhoeae minimum inhibitory concentrations (MICs, mg/L) for ceftriaxone, cefixime, penicillin, tetracycline, ciprofloxacin, azithromycin, spectinomycin, gentamicin and zoliflodacin were determined by agar dilution. MICs for ertapenem were measured by E-test. N. gonorrhoeae antimicrobial sequence typing (NG-STAR) of seven loci (penA, mtrR, porB, ponA, gyrA, parC and 23S rRNA) was analyzed together with N. gonorrhoeae multiantigen sequence typing (NG-MAST) and multilocus sequence typing (MLST). Phylogenetic analysis was also performed using whole genomic sequencing (WGS).

Results

Fourteen FC428-related penA 60.001 N. gonorrhoeae infections were identified out of 677 infections from 2017 to 2020, in Nanjing, representing an incremental yearly rise in the percentage of the city's N. gonorrhoeae isolates that were FC428-related. Seven FC428-related N. gonorrhoeae infections were acquired in Nanjing, proper; four others in eastern Chinese cities and three from unknown locations. All FC428-related isolates were resistant to ceftriaxone, cefixime, ciprofloxacin, tetracycline and penicillin but susceptible to spectinomycin, gentamicin, ertapenem and zoliflodacin; three strains were resistant to azithromycin. penA 60.001 isolates displayed closely related MLST types and NG-STAR types but relatively distant NG-MAST types. WGS showed a phylogenetic analysis that intermingled with other international isolates.

Conclusion

penA 60.001 N. gonorrhoeae isolates emerged in Nanjing, China, beginning in 2017, and have continued to rise.

Diet-Induced Non-alcoholic Fatty Liver Disease and Associated Gut Dysbiosis Are Exacerbated by Oral Infection

Increasing evidence indicates that chronic inflammation due to periodontal disease is associated with progression of non-alcoholic fatty liver disease (NAFLD) caused by a Western diet. NAFLD has also been associated with oral infection with the etiological agent of periodontal disease, Porphyromonas gingivalis. P. gingivalis oral infection has been shown to induce cardiometabolic disease features including hepatic lipid accumulation while also leading to dysbiosis of the gut microbiome. However, the impact of P. gingivalis infection on the gut microbiota of mice with diet-induced NAFLD and the potential for those changes to mediate NAFLD progression has yet to be determined. In the current study, we have demonstrated that P. gingivalis infection induced sustained alterations of the gut microbiota composition and predicted functions, which was associated with the promotion of NAFLD in steatotic mice. Reduced abundance of short-chain fatty acid-producing microbiota was observed after both acute and chronic P. gingivalis infection. Collectively, our findings demonstrate that P. gingivalis infection produces a persistent change in the gut microbiota composition and predicted functions that promotes steatosis and metabolic disease.

Pooling for SARS-CoV2 Surveillance: Validation and Strategy for Implementation in K-12 Schools

Repeated testing of a population is critical for limiting the spread of the SARS-CoV-2 virus and for the safe reopening of educational institutions such as kindergarten-grade 12 (K-12) schools and colleges. Many screening efforts utilize the CDC RT-PCR based assay which targets two regions of the novel Coronavirus nucleocapsid gene. The standard approach of testing each person individually, however, poses a financial burden to these institutions and is therefore a barrier to using testing for re-opening. Pooling samples from multiple individuals into a single test is an attractive alternate approach that promises significant cost savings-however the specificity and sensitivity of such approaches needs to be assessed prior to deployment. To this end, we conducted a pilot study to evaluate the feasibility of analyzing samples in pools of eight by the established RT-PCR assay. Participants (1,576) were recruited from amongst the Tufts University community undergoing regular screening. Each volunteer provided two swabs, one analyzed separately and the other in a pool of eight. Because the positivity rate was very low, we spiked approximately half of the pools with laboratory-generated swabs produced from known positive cases outside the Tufts testing program. The results of pooled tests had 100% correspondence with those of their respective individual tests. We conclude that pooling eight samples does not negatively impact the specificity or sensitivity of the RT-PCR assay and suggest that this approach can be utilized by institutions seeking to reduce surveillance costs.

Oral infection with a periodontal pathogen alters oral and gut microbiomes

Periodontal disease, an inflammatory bone disease of the oral cavity, affects more than 50% of the United States population over the age of 30. The Gram-negative, anaerobic bacterium Porphyromonas gingivalis, the etiological agent of periodontal disease, is known to induce dysbiosis of the oral microbiome while promoting inflammatory bone loss. We have recently reported that P. gingivalis can also alter the gut microbiota of mice prone to develop inflammatory atherosclerosis. However, it is still unknown whether P. gingivalis induces similar changes to the gut microbiome as it does to oral microbiome. In this study, we demonstrate that P. gingivalis infection increases the diversity of the oral microbiome, allowing for colonization of potentially opportunistic species in the oral microbiome and overgrowth of commensal species in both the oral and gut microbiomes. Since periodontal disease treatment in humans typically involves antibiotic treatment, we also examined the combined effect of P. gingivalis infection on mice pretreated with oral antibiotics. By correlating the oral and cecal microbiota of P. gingivalis-infected mice fed a normal chow diet, we identified blooms of the Gram-negative genera Barnesiella and Bacteroides and imbalances of mucin-degrading bacteria. These disrupted community structures were predicted to have increased detrimental functional capacities including increased flavonoid degradation and l-histidine fermentation. Though antibiotic pretreatment (without P. gingivlais) had a dominant impact on the cecal microbiome, P. gingivalis infection of mice with or without antibiotic pretreatment increased the abundance of the phylum Firmicutes and the Porphyromonadaceae family in the cecum. Collectively, our study demonstrates that P. gingivalis oral infection disrupted the oral and cecal microbiomes of otherwise unperturbed mice, altering their community membership and functional potential.

Epidemiological and Clinical Observations of Gonococcal Infections in Women and Prevention Strategies

Neisseria gonorrhoeae is rapidly developing antimicrobial resistance. There is an urgent need for an effective gonococcal vaccine. In this study we examined epidemiological and clinical factors associated with gonorrhea in a cohort of women exposed to men with gonococcal urethritis attending the National Center for STD Control clinic in Nanjing, China, to understand the natural history and the risk factors for gonorrhea in this vulnerable population. This analysis will help identify the best target populations for vaccination, which is essential information for the development of vaccine strategies. We observed that 75% of the women in our cohort yielded a N. gonorrhoeae positive culture (infected women) and reported multiple sexual exposures to their infected partner. Infected women were younger than exposed but uninfected women. Contrary to the general belief that gonorrhea is asymptomatic in most women, 68% of the infected women acknowledged symptoms during their STD clinic visit, and overt inflammatory responses were detected upon medical examination in 88% of subjects. Other sexually transmitted infections were detected in 85% of subjects. This study confirmed that N. gonorrhoeae infections are underdiagnosed in women and, consequentially, untreated. Thus, our analysis reinforces the need to establish strategies for gonococcal prevention through the determination of the target population for a gonococcal vaccine.

Susceptibility Trends of Zoliflodacin against Multidrug-Resistant Neisseria gonorrhoeae Clinical Isolates in Nanjing, China, 2014 to 2018

Previously, we reported the potent activity of a novel spiropyrimidinetrione, zoliflodacin, against Neisseria gonorrhoeae isolates collected in 2013 from symptomatic men in Nanjing, China. Here, we investigated trends of susceptibilities to zoliflodacin in 986 isolates collected from men between 2014 and 2018. N. gonorrhoeae isolates were tested for susceptibility to zoliflodacin and seven other antibiotics. Mutations in the gyrA, gyrB, parC, parE, and mtrR genes were determined by PCR and sequencing. The MICs of zoliflodacin ranged from ≤0.002 to 0.25 mg/liter; the overall MIC50 and MIC90 were 0.06 mg/liter and 0.125 mg/liter, respectively, in 2018, increasing 2-fold from 2014. However, the percentage of isolates with lower zoliflodacin MICs declined in each year sequentially, while the percentage with higher MICs increased yearly (P ≤ 0.00001). All isolates were susceptible to spectinomycin but resistant to ciprofloxacin (MIC ≥ 1 mg/liter); 21.2% (209/986) were resistant to azithromycin (≥1 mg/liter), 43.4% (428/986) were penicillinase-producing N. gonorrhoeae (PPNG), 26.9% (265/986) were tetracycline-resistant N. gonorrhoeae (TRNG), and 19.4% (191/986) were multidrug-resistant (MDR) isolates. 202 isolates with the lowest (≤0.002 to 0.015 mg/liter) and highest (0.125 to 0.25 mg/liter) zoliflodacin MICs were quinolone resistant with double or triple mutations in gyrA; 193/202 (95.5%) also had mutations in parC There were no D429N/A and/or K450T mutations in GyrB identified in the 143 isolates with higher zoliflodacin MICs; an S467N mutation in GyrB was identified in one isolate. We report that zoliflodacin continues to have excellent in vitro activity against clinical gonococcal isolates, including those with high-level resistance to ciprofloxacin, azithromycin, and extended-spectrum cephalosporins.

Global Network Analysis of Neisseria gonorrhoeae Identifies Coordination between Pathways, Processes, and Regulators Expressed during Human Infection

Neisseria gonorrhoeae is a Gram-negative diplococcus that is responsible for the sexually transmitted infection gonorrhea, a high-morbidity disease in the United States and worldwide. Over the past several years, N. gonorrhoeae strains resistant to antibiotics used to treat this infection have begun to emerge across the globe. Thus, new treatment strategies are needed to combat this organism. Here, we utilized N. gonorrhoeae transcriptomic data sets, including those obtained from natural infection of the human genital tract, to infer the first global gene coexpression network of this pathogen. Interrogation of this network revealed genes central to the network that are likely critical for gonococcal growth, metabolism, and virulence, including genes encoding hypothetical proteins expressed during mucosal infection. In addition, network analysis revealed overlap in the response of N. gonorrhoeae to incubation with neutrophils and exposure to hydrogen peroxide stress in vitro Network analysis also identified new targets of the gonococcal global regulatory protein Fur, while examination of the network neighborhood of genes allowed us to assign additional putative categories to several proteins. Collectively, the characterization of the first gene coexpression network for N. gonorrhoeae described here has revealed new regulatory pathways and new categories for proteins and has shown how processes important to gonococcal infection in both men and women are linked. This information fills a critical gap in our understanding of virulence strategies of this obligate human pathogen and will aid in the development of new treatment strategies for gonorrhea.IMPORTANCE Neisseria gonorrhoeae is the causative agent of the sexually transmitted infection (STI) gonorrhea, a disease with high morbidity worldwide with an estimated 87 million cases annually. Current therapeutic and pharmacologic approaches to treat gonorrhea have been compromised by increased antibiotic resistance worldwide, including to the most recent FDA-approved antibiotic. New treatment strategies are urgently needed to combat this organism. In this study, we used network analysis to interrogate and define the coordination of pathways and processes in N. gonorrhoeae An analysis of the gonococcal network was also used to assign categories to genes and to expand our understanding of regulatory strategies. Network analysis provides important insights into pathogenic mechanisms of this organism that will guide the design of new strategies for disease treatment.

Strategies for Global RNA Sequencing of the Human Pathogen Neisseria gonorrhoeae

Over the last several years transcriptomic analysis of bacterial pathogens has become easier and less expensive. This technique is used to determine expression levels for all genes of a particular species or collection of species under a given condition, including genes that are not yet known to exist. While transcriptomics can be a powerful tool to better understand bacterial regulatory responses to specific host environments, the experimental approach and data analysis must be performed correctly to ensure robust, accurate, and translational results. Here, we describe experimental protocols related to transcriptomic analysis of the sexually transmitted disease pathogen Neisseria gonorrhoeae. Methods are described for the extraction of high-quality RNA, examination of RNA to ensure quality, the generation of cDNA libraries for sequencing and the downstream analysis of raw sequencing data to determine gene expression levels. Much of this work can be carried out with equipment and reagents that are readily available, and the methods can be performed by a majority of laboratory groups. RNA-seq and transcriptomic analyses are set to become even more common in the coming years. The protocols described here will provide a standardized set of methods for applying this powerful technique to the study of N. gonorrhoeae under a variety of conditions.

Increased virulence of the oral microbiome in oral squamous cell carcinoma revealed by metatranscriptome analyses

Oral squamous cell carcinoma (OSCC) is the most prevalent and most commonly studied oral cancer. However, there is a void regarding the role that the oral microbiome may play in OSCC. Although the relationship between microbial community composition and OSCC has been thoroughly investigated, microbial profiles of the human microbiome in cancer are understudied. Here we performed a small pilot study of community-wide metatranscriptome analysis to profile mRNA expression in the entire oral microbiome in OSCC to reveal molecular functions associated with this disease. Fusobacteria showed a statistically significantly higher number of transcripts at tumour sites and tumour-adjacent sites of cancer patients compared to the healthy controls analysed. Regardless of the community composition, specific metabolic signatures were consistently found in disease. Activities such as iron ion transport, tryptophanase activity, peptidase activities and superoxide dismutase were over-represented in tumour and tumour-adjacent samples when compared to the healthy controls. The expression of putative virulence factors in the oral communities associated with OSCC showed that activities related to capsule biosynthesis, flagellum synthesis and assembly, chemotaxis, iron transport, haemolysins and adhesins were upregulated at tumour sites. Moreover, activities associated with protection against reactive nitrogen intermediates, chemotaxis, flagellar and capsule biosynthesis were also upregulated in non-tumour sites of cancer patients. Although they are preliminary, our results further suggest that Fusobacteria may be the leading phylogenetic group responsible for the increase in expression of virulence factors in the oral microbiome of OSCC patients.

The ironclad truth: how in vivo transcriptomics and in vitro mechanistic studies shape our understanding of Neisseria gonorrhoeae gene regulation during mucosal infection

Neisseria gonorrhoeae is one of the most prevalent sexually transmitted infections worldwide. This obligate human pathogen has been extensively studied in vitro, where bacterial factors that are known to contribute to gonococcal disease and their regulation are relatively well defined. However, these in vitro experimental conditions only loosely replicate the host specific environment encountered by the bacteria in vivo. We recently reported on the complete gonococcal transcriptome expressed during natural human mucosal infection using RNA-seq analysis. Gene transcripts expressed in vivo (in vivo expressed factors) included genes encoding antibiotic resistance determinants, and a large number of hypothetical genes. A comparison of the gonococcal transcriptome expressed in vivo with the corresponding strain grown in vitro identified sets of genes regulated by infection, including those regulated by iron and the transcriptional regulatory protein Fur. We highlight here the role of Fur and gonococcal-specific regulatory processes important for infection and pathogenicity. We have determined that the genes controlled by Fur follow the same expression pattern in vivo as described previously in vitro, confirming Fur's regulatory role during infection. Collectively, these studies provide new insights into how bacterial fitness and pathogenicity are modulated during human mucosal infection.

Role for the Aryl Hydrocarbon Receptor and Diverse Ligands in Oral Squamous Cell Carcinoma Migration and Tumorigenesis

Over 45,000 new cases of oral and pharyngeal cancers are diagnosed and account for over 8,000 deaths a year in the United States. An environmental chemical receptor, the aryl hydrocarbon receptor (AhR), has previously been implicated in oral squamous cell carcinoma (OSCC) initiation as well as in normal tissue-specific stem cell self-renewal. These previous studies inspired the hypothesis that the AhR plays a role in both the acquisition and progression of OSCC, as well as in the formation and maintenance of cancer stem-like cells. To test this hypothesis, AhR activity in two oral squamous cell lines was modulated with AhR prototypic, environmental and bacterial AhR ligands, AhR-specific inhibitors, and phenotypic, genomic and functional characteristics were evaluated. The data demonstrate that: (i) primary OSCC tissue expresses elevated levels of nuclear AhR as compared with normal tissue, (ii) AhR mRNA expression is upregulated in 320 primary OSCCs, (iii) AhR hyperactivation with several ligands, including environmental and bacterial ligands, significantly increases AhR activity, ALDH1 activity, and accelerates cell migration, (iv) AhR inhibition blocks the rapid migration of OSCC cells and reduces cell chemoresistance, (v) AhR knockdown inhibits tumorsphere formation in low adherence conditions, and (vi) AhR knockdown inhibits tumor growth and increases overall survival in vivo These data demonstrate that the AhR plays an important role in development and progression of OSCC, and specifically cancer stem-like cells. Prototypic, environmental, and bacterial AhR ligands may exacerbate OSCC by enhancing expression of these properties.

IMPLICATIONS

This study, for the first time, demonstrates the ability of diverse AhR ligands to regulate AhR activity in oral squamous cell carcinoma cells, as well as regulate several important characteristics of oral cancer stem cells, in vivo and in vitro Mol Cancer Res; 14(8); 696-706. ©2016 AACR.

Immune dysregulation mediated by the oral microbiome: potential link to chronic inflammation and atherosclerosis

Cardiovascular disease is an inflammatory disorder characterized by the progressive formation of plaque in coronary arteries, termed atherosclerosis. It is a multifactorial disease that is one of the leading causes of death worldwide. Although a number of risk factors have been associated with disease progression, the underlying inflammatory mechanisms contributing to atherosclerosis remain to be fully delineated. Within the last decade, the potential role for infection in inflammatory plaque progression has received considerable interest. Microbial pathogens associated with periodontal disease have been of particular interest due to the high levels of bacteremia that are observed after routine dental procedures and every day oral activities, such as tooth brushing. Here, we explore the potential mechanisms that may explain how periodontal pathogens either directly or indirectly elicit immune dysregulation and consequently progressive inflammation manifested as atherosclerosis. Periodontal pathogens have been shown to contribute directly to atherosclerosis by disrupting endothelial cell function, one of the earliest indicators of cardiovascular disease. Oral infection is thought to indirectly induce elevated production of inflammatory mediators in the systemic circulation. Recently, a number of studies have been conducted focusing on how disruption of the gut microbiome influences the systemic production of proinflammatory cytokines and consequently exacerbation of inflammatory diseases such as atherosclerosis. It is clear that the immune mechanisms leading to atherosclerotic plaque progression, by oral infection, are complex. Understanding the immune pathways leading to disease progression is essential for the future development of anti-inflammatory therapies for this chronic disease.

Periodontal disease and risk of all cancers among male never smokers: an updated analysis of the Health Professionals Follow-up Study

BACKGROUND

Periodontal disease has a direct impact on the immune response and has been linked to several chronic diseases, including atherosclerosis and stroke. Few studies have examined the association between periodontal disease and cancer.

PATIENTS AND METHODS

A total of 19 933 men reported being never smokers (of cigarette, pipes or cigars) in the Health Professionals' Follow-up Study. Periodontal disease status and teeth number were self-reported at baseline and during follow-up. All cancers were ascertained during 26 years of follow-up. Cox's proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) adjusting for risk factors.

RESULTS

A 13% increase in total cancer was observed among men reporting periodontitis at baseline, and a 45% increase in risk was observed among men with advanced periodontitis (periodontitis with <17 remaining teeth). Periodontitis was not associated with prostate cancer, colorectal cancer or melanoma, the three most common cancers in this cohort of never smokers, but a 33% increase in risk was observed for smoking-related cancers (lung, bladder, oropharnygeal, esophageal, kidney, stomach and liver cancers; HR = 1.33, 95% CI 1.07-1.65). Men with advanced periodontitis had an HR of 2.57 (95% CI 1.56-4.21; P = 0.0002) for smoking-related cancers, compared with men who did not have periodontitis and had 17 teeth or more. Advanced periodontitis was associated with elevated risks of esophageal and head and neck cancers (HR = 6.29, 95% CI 2.13-18.6; based on five cases with advanced periodontitis) and bladder cancer (HR = 5.06, 95% CI 2.32-11.0; based on nine cases with advanced periodontitis).

CONCLUSIONS

Advanced periodontitis was associated with a 2.5-fold increase in smoking-related cancers among never smokers. Periodontitis may impact cancer risk through system immune dysregulation. Further studies need to examine the immune impact of advanced periodontitis on cancer, especially for cancers known to be caused by smoking.

Porphyromonas gingivalis evasion of autophagy and intracellular killing by human myeloid dendritic cells involves DC-SIGN-TLR2 crosstalk

Signaling via pattern recognition receptors (PRRs) expressed on professional antigen presenting cells, such as dendritic cells (DCs), is crucial to the fate of engulfed microbes. Among the many PRRs expressed by DCs are Toll-like receptors (TLRs) and C-type lectins such as DC-SIGN. DC-SIGN is targeted by several major human pathogens for immune-evasion, although its role in intracellular routing of pathogens to autophagosomes is poorly understood. Here we examined the role of DC-SIGN and TLRs in evasion of autophagy and survival of Porphyromonas gingivalis in human monocyte-derived DCs (MoDCs). We employed a panel of P. gingivalis isogenic fimbriae deficient strains with defined defects in Mfa-1 fimbriae, a DC-SIGN ligand, and FimA fimbriae, a TLR2 agonist. Our results show that DC-SIGN dependent uptake of Mfa1+P. gingivalis strains by MoDCs resulted in lower intracellular killing and higher intracellular content of P. gingivalis. Moreover, Mfa1+P. gingivalis was mostly contained within single membrane vesicles, where it survived intracellularly. Survival was decreased by activation of TLR2 and/or autophagy. Mfa1+P. gingivalis strain did not induce significant levels of Rab5, LC3-II, and LAMP1. In contrast, P. gingivalis uptake through a DC-SIGN independent manner was associated with early endosomal routing through Rab5, increased LC3-II and LAMP-1, as well as the formation of double membrane intracellular phagophores, a characteristic feature of autophagy. These results suggest that selective engagement of DC-SIGN by Mfa-1+P. gingivalis promotes evasion of antibacterial autophagy and lysosome fusion, resulting in intracellular persistence in myeloid DCs; however TLR2 activation can overcome autophagy evasion and pathogen persistence in DCs.

Among the most successful of human microbes are intracellular pathogens. By entering the intracellular milieu, these pathogens are protected from harsh environmental factors in the host, including the humoral and cellular immune responses. Porphyromonas gingivalis is an opportunistic pathogen that colonizes the oral mucosa and accesses the bloodstream and distant sites such as the blood vessel walls, brain, placenta and other organs. Still unclear is how P. gingivalis traverses from oral mucosa to these distant sites. Dendritic cells are highly migratory antigen presenting cells that “patrol” the blood, skin, mucosa and all the major organ systems. Capture of microbes by dendritic cells activates a tightly regulated series of events, including directed migration towards the secondary lymphoid organs, where processed antigens are ostensibly presented to T cells. Autophagy is now recognized as an integral component of microbial clearance, antigen processing and presentation by dendritic cells. We report here that P. gingivalis is able to subvert autophagic destruction within dendritic cells. This occurs through its glycoprotein fimbriae, called Mfa-1, which targets the C-type lectin DC-SIGN on dendritic cells. The other major fimbriae on P. gingivalis, FimA, targets TLR2, which promotes autophagic destruction of P. gingivalis. We conclude that DC-SIGN-TLR2 crosstalk determines the intracellular fate of this pathogen within dendritic cells, and may have profound implications for the treatment of many chronic diseases involving low-grade infections.

Distinct gene signatures in aortic tissue from ApoE-/- mice exposed to pathogens or Western diet

Background

Atherosclerosis is a progressive disease characterized by inflammation and accumulation of lipids in vascular tissue. Porphyromonas gingivalis (Pg) and Chlamydia pneumoniae (Cp) are associated with inflammatory atherosclerosis in humans. Similar to endogenous mediators arising from excessive dietary lipids, these Gram-negative pathogens are pro-atherogenic in animal models, although the specific inflammatory/atherogenic pathways induced by these stimuli are not well defined. In this study, we identified gene expression profiles that characterize P. gingivalis, C. pneumoniae, and Western diet (WD) at acute and chronic time points in aortas of Apolipoprotein E (ApoE^-/-) mice.

Results

At the chronic time point, we observed that P. gingivalis was associated with a high number of unique differentially expressed genes compared to C. pneumoniae or WD. For the top 500 differentially expressed genes unique to each group, we observed a high percentage (76%) that exhibited decreased expression in P. gingivalis-treated mice in contrast to a high percentage (96%) that exhibited increased expression in WD mice. C. pneumoniae treatment resulted in approximately equal numbers of genes that exhibited increased and decreased expression. Gene Set Enrichment Analysis (GSEA) revealed distinct stimuli-associated phenotypes, including decreased expression of mitochondrion, glucose metabolism, and PPAR pathways in response to P. gingivalis but increased expression of mitochondrion, lipid metabolism, carbohydrate and amino acid metabolism, and PPAR pathways in response to C. pneumoniae; WD was associated with increased expression of immune and inflammatory pathways. DAVID analysis of gene clusters identified by two-way ANOVA at acute and chronic time points revealed a set of core genes that exhibited altered expression during the natural progression of atherosclerosis in ApoE^-/- mice; these changes were enhanced in P. gingivalis-treated mice but attenuated in C. pneumoniae-treated mice. Notable differences in the expression of genes associated with unstable plaques were also observed among the three pro-atherogenic stimuli.

Conclusions

Despite the common outcome of P. gingivalis, C. pneumoniae, and WD on the induction of vascular inflammation and atherosclerosis, distinct gene signatures and pathways unique to each pro-atherogenic stimulus were identified. Our results suggest that pathogen exposure results in dysregulated cellular responses that may impact plaque progression and regression pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1176) contains supplementary material, which is available to authorized users.

A mouse model for pathogen-induced chronic inflammation at local and systemic sites

Chronic inflammation is a major driver of pathological tissue damage and a unifying characteristic of many chronic diseases in humans including neoplastic, autoimmune, and chronic inflammatory diseases. Emerging evidence implicates pathogen-induced chronic inflammation in the development and progression of chronic diseases with a wide variety of clinical manifestations. Due to the complex and multifactorial etiology of chronic disease, designing experiments for proof of causality and the establishment of mechanistic links is nearly impossible in humans. An advantage of using animal models is that both genetic and environmental factors that may influence the course of a particular disease can be controlled. Thus, designing relevant animal models of infection represents a key step in identifying host and pathogen specific mechanisms that contribute to chronic inflammation. Here we describe a mouse model of pathogen-induced chronic inflammation at local and systemic sites following infection with the oral pathogen Porphyromonas gingivalis, a bacterium closely associated with human periodontal disease. Oral infection of specific-pathogen free mice induces a local inflammatory response resulting in destruction of tooth supporting alveolar bone, a hallmark of periodontal disease. In an established mouse model of atherosclerosis, infection with P. gingivalis accelerates inflammatory plaque deposition within the aortic sinus and innominate artery, accompanied by activation of the vascular endothelium, an increased immune cell infiltrate, and elevated expression of inflammatory mediators within lesions. We detail methodologies for the assessment of inflammation at local and systemic sites. The use of transgenic mice and defined bacterial mutants makes this model particularly suitable for identifying both host and microbial factors involved in the initiation, progression, and outcome of disease. Additionally, the model can be used to screen for novel therapeutic strategies, including vaccination and pharmacological intervention.

Aging and contribution of MyD88 and TRIF to expression of TLR pathway-associated genes following stimulation with Porphyromonas gingivalis

BACKGROUND AND OBJECTIVE

Periodontal disease is a highly complex chronic inflammatory disease of the oral cavity. Multiple factors influence periodontal disease, including socio-economic status, genetics and age; however, inflammation elicited by the presence of specific bacteria in the subgingival space is thought to drive the majority of soft- and hard-tissue destruction. Porphyromonas gingivalis is closely associated with periodontal disease. Toll-like receptors (TLRs) and their intracellular signaling pathways play roles in the host response to P. gingivalis. The focus of the current study was to use microarray analysis to define the contributions of the TLR adaptor molecules myeloid differentiation factor 88 (MyD88) and Toll/interleukin-1 receptor domain-containing adaptor inducing interferon-beta (TRIF), and aging, on the expression of TLR pathway-associated mRNAs in response to P. gingivalis.

MATERIAL AND METHODS

Bone marrow-derived macrophages (BMØ) from wild-type (Wt), MyD88 knockout (MyD88-KO) and Trif(Lps2) [i.e. containing a point mutation in the lipopolysaccharide 2 (Lps2) gene rendering the Toll/interleukin (IL)-1 receptor domain-containing adaptor inducing interferon-beta (TRIF) protein nonfunctional] mice, at 2-and 12-mo of age, were cultured with P. gingivalis. Expression of genes in BMØ cultured with P. gingivalis was determined in comparison with expression of genes in BMØ cultured in medium only.

RESULTS

Using, as criteria, a twofold increase or decrease in mRNA expression, differential expression of 32 genes was observed when Wt BMØ from 2-mo-old mice were cultured with P. gingivalis compared with the medium-only control. When compared with 2-mo-old Wt mice, 21 and 12 genes were differentially expressed (p < 0.05) as a result of the mutations in MyD88 or TRIF, respectively. The expression of five genes was significantly (p < 0.05) reduced in Wt BMØ from 12-mo-old mice compared with those from 2-mo-old mice following culture with P. gingivalis. Age also influenced the expression of genes in MyD88-KO and Trif(Lps2) mice challenged with P. gingivalis.

CONCLUSIONS

Our results indicate that P. gingivalis induces differential expression of TLR pathway-associated genes, and both MyD88 and TRIF play roles in the expression of these genes. Age also played a role in the expression of TLR-associated genes following stimulation of BMØ with P. gingivalis.

Abstract 272: Targeted Activatable Cell-Penetrating Peptides Identify Atherosclerotic Plaques in Mice with Noninvasive Magnetic Resonance Imaging

Atherosclerotic plaque progression from stable lesions to advanced plaques that can spontaneously disrupt is promoted by numerous enzymes, including thrombin and extracellular matrix metalloproteases (MMPs). Assessing the activity of these enzymes in vivo by noninvasive MRI could be a valuable tool for the risk assessment of plaque disruption and a powerful method for monitoring the effectiveness of therapies. Novel thrombin- and MMP-targeted activatable cell-penetrating peptides (ACPPs) have a mechanism for activation and retention at sites of high enzymatic activity and show great promise for plaque detection due to incorporation of gadolinium (Gd), an MR active agent. In addition to the morphological information that is traditionally provided by MRI, both ACPPs also allow for a functional assessment of plaque. We hypothesized that these new targeted ACPPs would provide enhanced contrast at a smaller dosage and improve the sensitivity and specificity of plaque detection. The aorta of fat fed male ApoE knockout mice were imaged with a T1-weighted spin echo sequence before and after the administration of a substandard dose of non-targeted Gd-DTPA (2.5 μmol/kg, compared to the standard dose of 0.1-0.2 mol/kg). Administration of a comparable dose of thrombin- or MMP-targeted ACPP yielded a great increase in contrast around the aortic plaques (Figure 1). In conclusion, administration of the targeted ACPP achieved superior contrast and, therefore, demonstrates the potential to achieve high detection power of plaques with a much lower and safer dose of Gd.

Interleukin 1 receptor 1 and interleukin 1β regulate megakaryocyte maturation, platelet activation, and transcript profile during inflammation in mice and humans

OBJECTIVE

Interleukin 1 Receptor 1 (IL1R1) and its ligand, IL1β, are upregulated in cardiovascular disease, obesity, and infection. Previously, we reported a higher level of IL1R1 transcripts in platelets from obese individuals of the Framingham Heart Study (FHS), but its functional effect in platelets has never been described. Additionally, IL1β levels are increased in atherosclerotic plaques and in bacterial infections. The aim of this work is to determine whether IL1β, through IL1R1, can activate platelets and megakaryocytes to promote atherothrombosis.

APPROACH AND RESULTS

We found that IL1β-related genes from platelets, as measured in 1819 FHS participants, were associated with increased body mass index, and a direct relationship was shown in wild-type mice fed a high-fat diet. Mechanistically, IL1β activated nuclear factor-κB and mitogen-activated protein kinase signaling pathways in megakaryocytes. IL1β, through IL1R1, increased ploidy of megakaryocytes to 64+ N by 2-fold over control. IL1β increased agonist-induced platelet aggregation by 1.2-fold with thrombin and 4.2-fold with collagen. IL1β increased adhesion to both collagen and fibrinogen, and heterotypic aggregation by 1.9-fold over resting. High fat diet-enhanced platelet adhesion was absent in IL1R1(-/-) mice. Wild-type mice infected with Porphyromonas gingivalis had circulating heterotypic aggregates (1.5-fold more than control at 24 hours and 6.2-fold more at 6 weeks) that were absent in infected IL1R1(-/-) and IL1β(-/-) mice.

CONCLUSIONS

In summary, IL1R1- and IL1β-related transcripts are elevated in the setting of obesity. IL1R1/IL1β augment both megakaryocyte and platelet functions, thereby promoting a prothrombotic environment during infection and obesity; potentially contributing to the development of atherothrombotic disease.

Disruption of immune regulation by microbial pathogens and resulting chronic inflammation

Activation of the immune response is a tightly regulated, coordinated effort that functions to control and eradicate exogenous microorganisms, while also responding to endogenous ligands. Determining the proper balance of inflammation is essential, as chronic inflammation leads to a wide array of host pathologies. Bacterial pathogens can instigate chronic inflammation via an extensive repertoire of evolved evasion strategies that perturb immune regulation. In this review, we discuss two model pathogens, Mycobacterium tuberculosis and Porphyromonas gingivalis, which efficiently escape various aspects of the immune system within professional and non-professional immune cell types to establish chronic inflammation.

Noncanonical dendritic cell differentiation and survival driven by a bacteremic pathogen

Maintenance of blood DC homeostasis is essential to preventing autoimmunity while controlling chronic infection. However, the ability of bacteremic pathogens to directly regulate blood DC homeostasis has not been defined. One such bacteremic pathogen, Porphyromonas gingivalis, is shown by our group to survive within mDCs under aerobic conditions and therein, metastasize from its oral mucosal niche. This is accompanied by expansion of the blood mDC pool in vivo, independently of canonical DC poietins. We presently know little of how this bacteremic pathogen causes blood DC expansion and the pathophysiological significance. This work shows that optimum differentiation of MoDCs from primary human monocytes, with or without GM-CSF/IL-4, is dependent on infection with P. gingivalis strains expressing the DC-SIGN ligand mfa-1. DC differentiation is lost when DC-SIGN is blocked with its ligand HIV gp120 or knocked out by siRNA gene silencing. Thus, we have identified a novel, noncanonical pathway of DC differentiation. We term these PDDCs and show that PDDCs are bona fide DCs, based on phenotype and phagocytic activity when immature and the ability to up-regulate accessory molecules and stimulate allo-CD4(+) T cell proliferation when matured. The latter is dependent on the P. gingivalis strain used to initially "educate" PDDCs. Moreover, we show that P. gingivalis-infected, conventional MoDCs become resistant to apoptosis and inflammatory pyroptosis, as determined by levels of Annexin V and caspase-8, -3/7, and -1. Taken together, we provide new insights into how a relatively asymptomatic bacteremia may influence immune homeostasis and promote chronic inflammation.

Computational analysis of bacterial RNA-Seq data

Recent advances in high-throughput RNA sequencing (RNA-seq) have enabled tremendous leaps forward in our understanding of bacterial transcriptomes. However, computational methods for analysis of bacterial transcriptome data have not kept pace with the large and growing data sets generated by RNA-seq technology. Here, we present new algorithms, specific to bacterial gene structures and transcriptomes, for analysis of RNA-seq data. The algorithms are implemented in an open source software system called Rockhopper that supports various stages of bacterial RNA-seq data analysis, including aligning sequencing reads to a genome, constructing transcriptome maps, quantifying transcript abundance, testing for differential gene expression, determining operon structures and visualizing results. We demonstrate the performance of Rockhopper using 2.1 billion sequenced reads from 75 RNA-seq experiments conducted with Escherichia coli, Neisseria gonorrhoeae, Salmonella enterica, Streptococcus pyogenes and Xenorhabdus nematophila. We find that the transcriptome maps generated by our algorithms are highly accurate when compared with focused experimental data from E. coli and N. gonorrhoeae, and we validate our system’s ability to identify novel small RNAs, operons and transcription start sites. Our results suggest that Rockhopper can be used for efficient and accurate analysis of bacterial RNA-seq data, and that it can aid with elucidation of bacterial transcriptomes.

Macrophage-specific TLR2 signaling mediates pathogen-induced TNF-dependent inflammatory oral bone loss

Porphyromonas gingivalis is a primary etiological agent of chronic periodontal disease, an infection-driven chronic inflammatory disease that leads to the resorption of tooth-supporting alveolar bone. We previously reported that TLR2 is required for P. gingivalis-induced alveolar bone loss in vivo, and our in vitro work implicated TNF as a key downstream mediator. In this study, we show that TNF-deficient (Tnf(-/-)) mice are resistant to alveolar bone loss following oral infection with P. gingivalis, and thus establish a central role for TNF in experimental periodontal disease. Using bone marrow-derived macrophages (BMDM) from wild-type and gene-specific knockout mice, we demonstrate that the initial inflammatory response to P. gingivalis in naive macrophages is MyD88 dependent and requires cooperative signaling of TLR2 and TLR4. The ability of P. gingivalis to activate cells via TLR2 or TLR4 was confirmed in TLR2- or TLR4-transformed human embryonic kidney cells. Additional studies using bacterial mutants demonstrated a role for fimbriae in the modulation of TLR-mediated activation of NF-κB. Whereas both TLR2 and TLR4 contributed to TNF production in naive macrophages, P. gingivalis preferentially exploited TLR2 in endotoxin-tolerant BMDM to trigger excessive TNF production. We found that TNF induced surface TLR2 expression and augmented TLR-induced cytokine production in P. gingivalis-stimulated BMDM, establishing a previously unidentified TNF-dependent feedback loop. Adoptive transfer of TLR2-expressing macrophages to TLR2-deficient mice restored the ability of P. gingivalis to induce alveolar bone loss in vivo. Collectively, our results identify a TLR2- and TNF-dependent macrophage-specific mechanism underlying pathogen-induced inflammatory bone loss in vivo.

Protective role for TLR4 signaling in atherosclerosis progression as revealed by infection with a common oral pathogen

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.

Microbial carriage state of peripheral blood dendritic cells (DCs) in chronic periodontitis influences DC differentiation, atherogenic potential

The low-grade oral infection chronic periodontitis (CP) has been implicated in coronary artery disease risk, but the mechanisms are unclear. In this study, a pathophysiological role for blood dendritic cells (DCs) in systemic dissemination of oral mucosal pathogens to atherosclerotic plaques was investigated in humans. The frequency and microbiome of CD19(-)BDCA-1(+)DC-SIGN(+) blood myeloid DCs (mDCs) were analyzed in CP subjects with or without existing acute coronary syndrome and in healthy controls. FACS analysis revealed a significant increase in blood mDCs in the following order: healthy controls < CP < acute coronary syndrome/CP. Analysis of the blood mDC microbiome by 16S rDNA sequencing showed Porphyromonas gingivalis and other species, including (cultivable) Burkholderia cepacia. The mDC carriage rate with P. gingivalis correlated with oral carriage rate and with serologic exposure to P. gingivalis in CP subjects. Intervention (local debridement) to elicit a bacteremia increased the mDC carriage rate and frequency in vivo. In vitro studies established that P. gingivalis enhanced by 28% the differentiation of monocytes into immature mDCs; moreover, mDCs secreted high levels of matrix metalloproteinase-9 and upregulated C1q, heat shock protein 60, heat shock protein 70, CCR2, and CXCL16 transcripts in response to P. gingivalis in a fimbriae-dependent manner. Moreover, the survival of the anaerobe P. gingivalis under aerobic conditions was enhanced when within mDCs. Immunofluorescence analysis of oral mucosa and atherosclerotic plaques demonstrate infiltration with mDCs, colocalized with P. gingivalis. Our results suggest a role for blood mDCs in harboring and disseminating pathogens from oral mucosa to atherosclerosis plaques, which may provide key signals for mDC differentiation and atherogenic conversion.

Biomolecular detection employing the Interferometric Reflectance Imaging Sensor (IRIS)

The sensitive measurement of biomolecular interactions has use in many fields and industries such as basic biology and microbiology, environmental/agricultural/biodefense monitoring, nanobiotechnology, and more. For diagnostic applications, monitoring (detecting) the presence, absence, or abnormal expression of targeted proteomic or genomic biomarkers found in patient samples can be used to determine treatment approaches or therapy efficacy. In the research arena, information on molecular affinities and specificities are useful for fully characterizing the systems under investigation.

Many of the current systems employed to determine molecular concentrations or affinities rely on the use of labels. Examples of these systems include immunoassays such as the enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR) techniques, gel electrophoresis assays, and mass spectrometry (MS). Generally, these labels are fluorescent, radiological, or colorimetric in nature and are directly or indirectly attached to the molecular target of interest. Though the use of labels is widely accepted and has some benefits, there are drawbacks which are stimulating the development of new label-free methods for measuring these interactions. These drawbacks include practical facets such as increased assay cost, reagent lifespan and usability, storage and safety concerns, wasted time and effort in labelling, and variability among the different reagents due to the labelling processes or labels themselves. On a scientific research basis, the use of these labels can also introduce difficulties such as concerns with effects on protein functionality/structure due to the presence of the attached labels and the inability to directly measure the interactions in real time.

Presented here is the use of a new label-free optical biosensor that is amenable to microarray studies, termed the Interferometric Reflectance Imaging Sensor (IRIS), for detecting proteins, DNA, antigenic material, whole pathogens (virions) and other biological material. The IRIS system has been demonstrated to have high sensitivity, precision, and reproducibility for different biomolecular interactions [1-3]. Benefits include multiplex imaging capacity, real time and endpoint measurement capabilities, and other high-throughput attributes such as reduced reagent consumption and a reduction in assay times. Additionally, the IRIS platform is simple to use, requires inexpensive equipment, and utilizes silicon-based solid phase assay components making it compatible with many contemporary surface chemistry approaches.

Here, we present the use of the IRIS system from preparation of probe arrays to incubation and measurement of target binding to analysis of the results in an endpoint format. The model system will be the capture of target antibodies which are specific for human serum albumin (HSA) on HSA-spotted substrates.

Review: Pathogen-induced inflammation at sites distant from oral infection: bacterial persistence and induction of cell-specific innate immune inflammatory pathways

A hallmark of infection with the gram-negative pathogen Porphyromonas gingivalis is the induction of a chronic inflammatory response. P. gingivalis induces a local chronic inflammatory response that results in oral inflammatory bone destruction, which manifests as periodontal disease. In addition to chronic inflammation at the initial site of infection, mounting evidence has accumulated supporting a role for P. gingivalis-mediated periodontal disease as a risk factor for several systemic diseases including, diabetes, preterm birth, stroke, and atherosclerotic cardiovascular disease. A growing number of in vitro studies have demonstrated that P. gingivalis infection stimulates cell activation commensurate with expected responses paralleling inflammatory atherosclerotic-type responses. Furthermore, various mouse models have been used to examine the ability of P. gingivalis to stimulate chronic inflammatory plaque accumulation and recent studies have pointed to a pivotal role for innate immune signaling via the Toll-like receptors in the chronic inflammation associated with P. gingivalis infection. In this review we discuss the pathogen and host cell specificity of these responses and discuss possible mechanisms by which this oral pathogen can induce and maintain a chronic state of inflammation at sites distant from oral infection.

Porphyromonas gingivalis accelerates inflammatory atherosclerosis in the innominate artery of ApoE deficient mice

OBJECTIVE

Studies in humans support a role for the oral pathogen Porphyromonas gingivalis in the development of inflammatory atherosclerosis. The goal of this study was to determine if P. gingivalis infection accelerates inflammation and atherosclerosis in the innominate artery of mice, an artery which has been reported to exhibit many features of human atherosclerotic disease, including plaque rupture.

METHODS AND RESULTS

Apolipoprotein E-deficient (ApoE-/-) mice were orally infected with P. gingivalis, and magnetic resonance imaging (MRI) was used to monitor the progression of atherosclerosis in live mice. P. gingivalis infected mice exhibited a statistically significant increase in atherosclerotic plaque in the innominate artery as compared to uninfected mice. Polarized light microscopy and immunohistochemistry revealed that the innominate arteries of infected mice had increased lipids, macrophages and T cells as compared to uninfected mice. Increases in plaque, total cholesterol esters and cholesterol monohydrate crystals, macrophages, and T cells were prevented by immunization with heat-killed P. gingivalis prior to pathogen exposure.

CONCLUSIONS

These are the first studies to demonstrate progression of inflammatory plaque accumulation in the innominate arteries by in vivo MRI analysis following pathogen exposure, and to document protection from plaque progression in the innominate artery via immunization.

Porphyromonas gingivalis accelerates inflammatory atherosclerosis in the innominate artery of ApoE deficient mice

OBJECTIVE

Studies in humans support a role for the oral pathogen Porphyromonas gingivalis in the development of inflammatory atherosclerosis. The goal of this study was to determine if P. gingivalis infection accelerates inflammation and atherosclerosis in the innominate artery of mice, an artery which has been reported to exhibit many features of human atherosclerotic disease, including plaque rupture.

METHODS AND RESULTS

Apolipoprotein E-deficient (ApoE-/-) mice were orally infected with P. gingivalis, and magnetic resonance imaging (MRI) was used to monitor the progression of atherosclerosis in live mice. P. gingivalis infected mice exhibited a statistically significant increase in atherosclerotic plaque in the innominate artery as compared to uninfected mice. Polarized light microscopy and immunohistochemistry revealed that the innominate arteries of infected mice had increased lipids, macrophages and T cells as compared to uninfected mice. Increases in plaque, total cholesterol esters and cholesterol monohydrate crystals, macrophages, and T cells were prevented by immunization with heat-killed P. gingivalis prior to pathogen exposure.

CONCLUSIONS

These are the first studies to demonstrate progression of inflammatory plaque accumulation in the innominate arteries by in vivo MRI analysis following pathogen exposure, and to document protection from plaque progression in the innominate artery via immunization.

Pathogen-mediated inflammatory atherosclerosis is mediated in part via Toll-like receptor 2-induced inflammatory responses

Studies in humans have established that polymorphisms in genes encoding the innate immune Toll-like receptors (TLRs) are associated with inflammatory atherosclerosis. In hyperlipidemic mice, TLR2 and TLR4 have been reported to contribute to atherosclerosis progression. Human and mouse studies support a role for the oral pathogen Porphyromonas gingivalis in atherosclerosis, although the mechanisms by which this pathogen stimulates inflammatory atherosclerosis via innate immune system activation is not known. Using a genetically defined apolipoprotein E-deficient (ApoE(-/-)) mouse model we demonstrate that pathogen-mediated inflammatory atherosclerosis occurs via both TLR2-dependent and TLR2-independent mechanisms. P. gingivalis infection in mice possessing functional TLR2 induced the accumulation of macrophages as well as inflammatory mediators including CD40, IFN-gamma and the pro-inflammatory cytokines IL-1 beta, IL-6 and tumor necrosis factor-alpha in atherosclerotic lesions. The expression of these inflammatory mediators was reduced in atherosclerotic lesions from P. gingivalis-infected TLR2-deficient (TLR2(-/-)) mice. These studies provide a mechanistic link between an innate immune receptor and pathogen-accelerated atherosclerosis by a clinically and biologically relevant bacterial pathogen.

Stimulation of Toll-like receptor 2 in human platelets induces a thromboinflammatory response through activation of phosphoinositide 3-kinase

Cells of the innate immune system use Toll-like receptors (TLRs) to initiate the proinflammatory response to microbial infection. Recent studies have shown acute infections are associated with a transient increase in the risk of vascular thrombotic events. Although platelets play a central role in acute thrombosis and accumulating evidence demonstrates their role in inflammation and innate immunity, investigations into the expression and functionality of platelet TLRs have been limited. In the present study, we demonstrate that human platelets express TLR2, TLR1, and TLR6. Incubation of isolated platelets with Pam(3)CSK4, a synthetic TLR2/TLR1 agonist, directly induced platelet aggregation and adhesion to collagen. These functional responses were inhibited in TLR2-deficient mice and, in human platelets, by pretreatment with TLR2-blocking antibody. Stimulation of platelet TLR2 also increased P-selectin surface expression, activation of integrin alpha(IIb)beta(3), generation of reactive oxygen species, and, in human whole blood, formation of platelet-neutrophil heterotypic aggregates. TLR2 stimulation also activated the phosphoinositide 3-kinase (PI3-K)/Akt signaling pathway in platelets, and inhibition of PI3-K significantly reduced Pam(3)CSK4-induced platelet responses. In vivo challenge with live Porphyromonas gingivalis, a Gram-negative pathogenic bacterium that uses TLR2 for innate immune signaling, also induced significant formation of platelet-neutrophil aggregates in wild-type but not TLR2-deficient mice. Together, these data provide the first demonstration that human platelets express functional TLR2 capable of recognizing bacterial components and activating the platelet thrombotic and/or inflammatory pathways. This work substantiates the role of platelets in the immune and inflammatory response and suggests a mechanism by which bacteria could directly activate platelets.

Bacterial fimbriae stimulate proinflammatory activation in the endothelium through distinct TLRs

The major and minor fimbriae proteins produced by the human pathogen Porphyromonas gingivalis are required for invasion of human aortic endothelial cells and for the stimulation of potent inflammatory responses. In this study, we report that native forms of both the major and minor fimbriae proteins bind to and signal through TLR2 for this response. Major and minor fimbriae bound to a human TLR2:Fc chimeric protein with an observed K(d) of 28.9 nM and 61.7 nM, respectively. Direct binding of the major and minor fimbriae to a human chimeric CD14-Fc protein also established specific binding of the major and minor fimbriae to CD14 with classic saturation kinetics. Using a P. gingivalis major and minor fimbriae mutant, we confirmed that TLR2 binding in whole cells is dependent on the expression of the major and minor fimbriae. Although we did not observe binding with the major or minor fimbriae to the TLR4-Fc chimeric protein, signaling through TLR4 for both proteins was demonstrated in human embryonic kidney 293 cells transfected with TLR4 and only in the presence MD-2. Transient transfection of dominant-negative forms of TLR2 or TLR4 reduced IL-8 production by human aortic endothelial cells following stimulation with major or minor fimbriae. The ability of two well-defined microbe-associated molecular patterns to select for innate immune recognition receptors based on accessory proteins may provide a novel way for a pathogen to sense and signal in appropriate host environments.

cis- and trans-acting elements involved in regulation of norB (norZ), the gene encoding nitric oxide reductase in Neisseria gonorrhoeae

The ability of Neisseria gonorrhoeae to reduce nitric oxide (NO) may have important immunomodulatory effects on the host during infection. Therefore, a comprehensive understanding of the regulatory mechanism of the nitric oxide reductase gene (norB) needs to be elucidated. To accomplish this, we analysed the functional regions of the norB upstream region. The promoter contains an extended -10 motif (TGNTACAAT) that is required for high-level expression. Deletion and substitution analysis of the norB upstream region revealed that no sequence upstream of the -10 motif is involved in norB regulation under anaerobic conditions or in the presence of NO. However, replacement of a 29 bp inverted repeat sequence immediately downstream of the extended -10 motif gave high levels of aerobic expression of a norB : : lacZ fusion. Insertional inactivation of gonococcal nsrR, predicted to bind to this inverted repeat sequence, resulted in the loss of norB repression and eliminated NO induction capacity. Single-copy complementation of nsrR in trans restored regulation of both norB transcription and NorB activity by NO. In Escherichia coli, expression of a gonococcal nsrR gene repressed gonococcal norB; induction of norB occurred in the presence of exogenously added NO. NsrR also regulates aniA and dnrN, as well as its own expression. We also determined that Fur regulates norB by a novel indirect activation method, by preventing the binding of a gonococcal ArsR homologue, a second repressor whose putative binding site overlaps the Fur binding site.

Porphyromonas gingivalis mediated periodontal disease and atherosclerosis: disparate diseases with commonalities in pathogenesis through TLRs

Toll-like receptors (TLRs) are a group of pathogen-associated molecular pattern receptors, which play an important role in innate immune signaling in response to microbial infection. It has been demonstrated that TLRs are differentially up regulated in response to microbial infection and chronic inflammatory diseases such as atherosclerosis. Furthermore hyperlipidemic mice deficient in TLR2, TLR4, and MyD88 signaling exhibit diminished inflammatory responses and decreased atherosclerosis. Accumulating evidence has implicated specific infectious agents including the periodontal disease pathogen Porphyromonas gingivalis in the progression of atherosclerosis. Evidence in humans suggesting that periodontal infection predisposes to atherosclerosis is derived from studies demonstrating that the periodontal pathogen P. gingivalis resides in the wall of atherosclerotic vessels and seroepidemiological studies demonstrating an association between pathogen-specific IgG antibodies and atherosclerosis. We have established that the inflammatory signaling pathways that P. gingivalis utilizes is dependent on the cell type and this specificity clearly influences innate immune signaling in the context of local and distant chronic inflammation induced by this pathogen. We have demonstrated that P. gingivalis requires TLR2 to induce oral inflammatory bone lose in mice. Furthermore, we have demonstrated that P. gingivalis infection accelerates atherosclerosis in hyperlipidemic mice with an associated increase in expression of TLR2 and TLR4 in atherosclerotic lesions. Our recent work with P. gingivalis has demonstrated the effectiveness of specific intervention strategies (immunization) in the prevention of pathogen-accelerated atherosclerosis. Improved understanding of the mechanisms driving infection, and chronic inflammation during atherosclerosis may ultimately provide new targets for therapy.

Engagement of specific innate immune signaling pathways during Porphyromonas gingivalis induced chronic inflammation and atherosclerosis

Toll-like receptors (TLRs) are a group of pathogen-associated molecular pattern receptors, which play an important role in innate immune signaling in response to microbial infection. It has been demonstrated that TLRs are differentially up regulated in response to microbial infection and chronic inflammatory diseases such as atherosclerosis. The expression of TLRs are markedly augmented in human atherosclerotic lesions and this occurs preferentially by endothelial cells and macrophages in areas infiltrated with inflammatory cells. Furthermore polymorphisms in the human gene encoding one TLR receptor (TLR4) which attenuates receptor signaling and diminishes the inflammatory response to gram-negative pathogens, is associated with low levels of certain circulating mediators of inflammation and a decreased risk for atherosclerosis in humans. Recent advances have established a fundamental role for inflammation in mediating all stages of atherosclerosis. However, the triggers that initiate and sustain the inflammatory process have not been definitively identified. Although definitive proof of a role of infection contributing to atherogenesis is lacking, multiple investigations have demonstrated that infectious agents evoke cellular and molecular changes supportive of such a role. Evidence in humans suggesting that periodontal infection predisposes to atherosclerosis is derived from studies demonstrating that the periodontal pathogen Porphyromonas gingivalis resides in the wall of atherosclerotic vessels and seroepidemiological studies demonstrating an association between pathogen-specific IgG antibodies and atherosclerosis. Our recent work with P. gingivalis has demonstrated the effectiveness of specific intervention strategies (immunization) in the prevention of pathogen-accelerated atherosclerosis. We have also established that the inflammatory signaling pathways that P. gingivalis utilizes is dependent on the cell type and this specificity clearly influences innate immune signaling in the context of local chronic inflammation versus distant chronic inflammation. We postulate that bacterial infection mediates inflammatory responses that involve specific innate immune pathways in defined host cells. Furthermore, these inflammatory responses can be correlated with atherosclerosis and ultimately thrombotic complications.

Toll-like receptor 2 plays a critical role in the progression of atherosclerosis that is independent of dietary lipids

OBJECTIVE

Toll-like receptors (TLRs), a group of pathogen-associated microbial pattern recognition receptors, play an important role in innate immune signaling and are differentially regulated in chronic inflammatory diseases such as atherosclerosis. However, the involvement of TLRs in the progression of atherosclerosis is still unclear.

METHODS AND RESULTS

TLR2 and apolipoprotein E double knockout (Tlr2(-/-)Apoe(-/-)) mice were generated and the progressive formation of atherosclerotic plaque in the aortas was examined in mice fed a normal chow diet. We demonstrate that inactivation of TLR2 resulted in reduced progression of atherosclerosis in both male and female Apoe(-/-) mice. Likewise, TLR2 deficiency resulted in a reduction in lipid accumulation and decreased macrophage recruitment to the aortic sinus, as well as reduced monocyte chemoattractant protein-1 (MCP-1) levels. Furthermore, macrophages isolated from Tlr2(-/-)Apoe(-/-) mice demonstrated significantly reduced MCP-1 production upon stimulation with a TLR2 ligand. However, no differences in acetylated low-density lipoprotein uptake and foam cell formation were observed in macrophages isolated from Tlr2(-/-)Apoe(-/-) mice as compared to Apoe(-/-) mice.

CONCLUSIONS

TLR2 plays a critical role in the progression of atherosclerosis in Apoe(-/-) mice, which is independent of dietary lipids and macrophage lipid uptake.

A novel fur- and iron-regulated small RNA, NrrF, is required for indirect fur-mediated regulation of the sdhA and sdhC genes in Neisseria meningitidis

Iron is both essential for bacterial growth and toxic at higher concentrations; thus, iron homeostasis is tightly regulated. In Neisseria meningitidis the majority of iron-responsive gene regulation is mediated by the ferric uptake regulator protein (Fur), a protein classically defined as a transcriptional repressor. Recently, however, microarray studies have identified a number of genes in N. meningitidis that are iron and Fur activated, demonstrating a new role for Fur as a transcriptional activator. Since Fur has been shown to indirectly activate gene transcription through the repression of small regulatory RNA molecules in other organisms, we hypothesized that a similar mechanism could account for Fur-dependent, iron-activated gene transcription in N. meningitidis. In this study, we used a bioinformatics approach to screen for the presence of Fur-regulated small RNA molecules in N. meningitidis MC58. This screen identified one small RNA, herein named NrrF (for neisserial regulatory RNA responsive to iron [Fe]), which was demonstrated to be both iron responsive and Fur regulated and which has a well-conserved orthologue in N. gonorrhoeae. In addition, this screen identified a number of other likely, novel small RNA transcripts. Lastly, we utilized a new bioinformatics approach to predict regulatory targets of the NrrF small RNA. This analysis led to the identification of the sdhA and sdhC genes, which were subsequently demonstrated to be under NrrF regulation in an nrrF mutant. This study is the first report of small RNAs in N. meningitidis and the first to use a bioinformatics approach to identify, a priori, regulatory targets of a small RNA.

Expression of the iron-activated nspA and secY genes in Neisseria meningitidis group B by Fur-dependent and -independent mechanisms

Our whole-genome microarray studies of Neisseria meningitidis MC58 previously identified a set of 153 genes whose transcription was activated during growth in iron. In this study, Fur-mediated regulation of the iron-activated nspA gene was confirmed, whereas iron-activated regulation of the secY gene was demonstrated to be Fur independent. Analysis of the Fur binding sequences in the nspA gene and an additional iron-activated and Fur-regulated gene identified a hexameric (G/T)ATAAT unit in the operator regions of these genes similar to that observed in Fur- and iron-repressed genes. These studies indicate that the expression of the iron-activated nspA and secY genes in N. meningitidis occur by Fur-dependent and -independent mechanisms, respectively.

Innate immune signaling and Porphyromonas gingivalis-accelerated atherosclerosis

Periodontal diseases are a group of diseases that lead to erosion of the hard and soft tissues of the periodontium, which, in severe cases, can result in tooth loss. Anecdotal clinical observations have suggested that poor oral health may be associated with poor systemic health; however, only recently have appropriate epidemiological studies been initiated, with defined clinical endpoints of periodontal disease, to address the association of periodontal disease with increased risk for cardiovascular and cerebrovascular disease. Although conflicting reports exist, these epidemiological studies support this connection. Paralleling these epidemiological studies, emerging basic scientific studies also support that infection may represent a risk factor for atherosclerosis. With P. gingivalis as a model pathogen, in vitro studies support that this organism can activate host innate immune responses associated with atherosclerosis, and in vivo studies demonstrate that this organism can accelerate atheroma deposition in animal models. In this review, we focus primarily on the basic scientific studies performed to date which support that infection with bacteria, most notably P. gingivalis, accelerates atherosclerosis. Furthermore, we attempt to bring together these studies to provide an up-to-date framework of emerging theories into the mechanisms underlying periodontal disease and increased risk for atherosclerosis, as well as identify intervention strategies to reduce the incidence of periodontal disease in humans, in an attempt to decrease risk for systemic complications of periodontal disease such as atherosclerotic cardiovascular disease.

Hemin-dependent modulation of the lipid A structure of Porphyromonas gingivalis lipopolysaccharide

Porphyromonas gingivalis is a periopathogen strongly associated with the development of adult-type periodontitis. Both the virulence characteristics of periopathogens and host-related factors are believed to contribute to periodontitis. P. gingivalis lipopolysaccharide (LPS) displays a significant amount of lipid A structural heterogeneity, containing both penta- and tetra-acylated lipid A structures. However, little is known concerning how the lipid A structural content of P. gingivalis is regulated. Alterations in the lipid A content may facilitate the ability of P. gingivalis to modulate the innate host response to this bacterium. In this report, it is shown that the concentration of hemin in the growth medium significantly modulates the lipopolysaccharide lipid A structural content of P. gingivalis. Hemin is a key microenvironmental component of gingival cervicular fluid which is believed to vary depending upon the state of vascular ulceration. At low hemin concentrations, one major penta-acylated lipid A structure was found, whereas at high concentrations of hemin, multiple tetra- and penta-acylated lipid A structures were observed. Hemin concentrations, not iron acquisition, were responsible for the alterations in the lipid A structural content. The modifications of the lipid A structural content were independent of the LPS extraction procedure and occurred in a variety of laboratory strains as well as a freshly obtained clinical isolate. The known hemin binding proteins Kgp and HmuR contributed to the lipid A modulation sensing mechanism. To the best of our knowledge, this is the first report that hemin, a clinically relevant microenvironmental component for P. gingivalis, can modulate the lipid A structure found in a bacterium. Since tetra- and penta-acylated P. gingivalis lipid A structures have opposing effects on Toll-like receptor 4 activation, the alteration of the lipid A structural content may have significant effects on the host response to this bacterium.

Sensitization of human aortic endothelial cells to lipopolysaccharide via regulation of Toll-like receptor 4 by bacterial fimbria-dependent invasion

Toll-like receptors (TLRs) are differentially up-regulated in response to microbial infection and chronic inflammatory diseases such as atherosclerosis. Epidemiological data support the idea that periodontal disease may be a risk factor for acceleration of atherosclerosis. Porphyromonas gingivalis, the etiological agent of periodontal disease, invades endothelium, has been detected in human atheromatous tissue, and accelerates atheroma formation in apolipoprotein E-/- mice with concurrent induction of TLRs in the aorta. As endothelial cells can present antigen via TLRs and play an important role in the development of atherosclerosis, we examined TLR expression in human aortic endothelial cells (HAEC) cultured with wild-type P. gingivalis, a fimbria-deficient mutant, and purified antigens. We observed increased TLR expression in HAEC infected with wild-type P. gingivalis by fluorescence-activated cell sorter, but not with noninvasive, fimbria-deficient mutant or purified P. gingivalis antigens. Following a wild-type P. gingivalis challenge, functional TLR2 and TLR4 activation was assessed by subsequent stimulation with TLR agonists Staphylococcus aureus lipoteichoic acid (SLTA; TLR2 ligand) and Escherichia coli lipopolysaccharide (LPS; TLR4 ligand). Unchallenged HAEC failed to elicit monocyte chemoattractant protein 1 (MCP-1) in response to LPS or SLTA but did so when cultured with wild-type P. gingivalis. P. gingivalis-induced TLR2 and -4 expression on HAEC functionally reacted to SLTA and E. coli LPS as measured by a further increase in MCP-1 production. Furthermore, MCP-1 expression elicited by E. coli LPS was inhibitable with TLR4-specific antibody and polymyxin B. These results indicate that invasive P. gingivalis stimulates TLR expression on the surface of endothelium and these primed cells respond to defined TLR-specific ligands.

Porphyromonas gingivalis fimbria-dependent activation of inflammatory genes in human aortic endothelial cells

Epidemiological and pathological studies have suggested that infection with the oral pathogen Porphyromonas gingivalis can potentiate atherosclerosis and human coronary heart disease. Furthermore, infection with invasive, but not noninvasive P. gingivalis has been demonstrated to accelerate atherosclerosis in apolipoprotein E-deficient (ApoE(-/-)) mice and to accelerate local inflammatory responses in aortic tissue. In the present study, using high-density oligonucleotide microarrays, we have defined the gene expression profile of human aortic endothelial cells (HAEC) after infection with invasive and noninvasive P. gingivalis. After infection of HAEC with invasive P. gingivalis strain 381, we observed the upregulation of 68 genes. Genes coding for the cytokines Gro2 and Gro3; the adhesion molecules intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule (VCAM)-1, and ELAM-1 (E-selectin); the chemokine interleukin-8 (IL-8); and the proinflammatory molecules IL-6 and cyclooxygenase-2 were among the most highly upregulated genes in P. gingivalis 381-infected HAEC compared to uninfected HAEC control. Increased mRNA levels for signaling molecules, transcriptional regulators, and cell surface receptors were also observed. Of note, only 4 of these 68 genes were also upregulated in HAEC infected with the noninvasive P. gingivalis fimA mutant. Reverse transcription-PCR, enzyme-linked immunosorbent assay, and fluorescence-activated cell sorting analysis confirmed the expression of ICAM-1, VCAM-1, E-/P-selectins, IL-6, and IL-8 in HAEC infected with invasive P. gingivalis. We also demonstrated that increased expression of ICAM-1 and VCAM-1 in aortic tissue of ApoE(-/-) mice orally challenged with invasive P. gingivalis but not with the noninvasive P. gingivalis fimA mutant by immunohistochemical analysis. Taken together, these results demonstrate that P. gingivalis fimbria-mediated invasion upregulates inflammatory gene expression in HAEC and in aortic tissue and indicates that invasive P. gingivalis infection accelerates inflammatory responses directly in the aorta.

The gonococcal Fur-regulated tbpA and tbpB genes are expressed during natural mucosal gonococcal infection

Iron is limiting in the human host, and bacterial pathogens respond to this environment by regulating gene expression through the ferric uptake regulator protein (Fur). In vitro studies have demonstrated that Neisseria gonorrhoeae controls the expression of several critical genes through an iron- and Fur-mediated mechanism. While most in vitro experiments are designed to determine the response of N. gonorrhoeae to an exogenous iron concentration of zero, these organisms are unlikely to be exposed to such severe limitations of iron in vivo. To determine if N. gonorrhoeae expresses iron- and Fur-regulated genes in vivo during uncomplicated gonococcal infection, we examined gene expression profiles of specimens obtained from male subjects with urethral infections. RNA was isolated from urethral swab specimens and used as a template to amplify, by reverse transcriptase PCR (RT-PCR), gonococcal genes known to be regulated by iron and Fur (tbpA, tbpB, and fur). The constitutively expressed gonococcal rmp gene was used as a positive control. RT-PCR analysis indicated that gonorrhea-positive specimens where rmp expression was seen were also 93% (51/55) fbpA positive, 87% (48/55) tbpA positive, and 86% (14 of 16 tested) tbpB positive. In addition, we detected a fur transcript in 79% (37 of 47 tested) of positive specimens. We also measured increases in levels of immunoglobulin G antibody against TbpA (91%) and TbpB (73%) antigens in sera from infected male subjects compared to those in uninfected controls. A positive trend between tbpA gene expression and TbpA antibody levels in sera indicated a relationship between levels of gene expression and immune response in male subjects infected with gonorrhea for the first time. These results indicate that gonococcal iron- and Fur-regulated tbpA and tbpB genes are expressed in gonococcal infection and that male subjects with mucosal gonococcal infections exhibit antibodies to these proteins.

The C-terminal domains of the gingipain K polyprotein are necessary for assembly of the active enzyme and expression of associated activities

The Porphyromonas gingivalis lysine-specific cysteine protease (gingipain K, Kgp) is expressed as a large precursor protein consisting of a leader sequence, a pro-fragment, a catalytic domain with a C-terminal IgG-like subdomain (IgSF) and a large haemagglutinin/adhesion (HA) domain. In order to directly study the role of these non-catalytic domains in pro-Kgp processing and maturation in P. gingivalis, the wild-type form of the gene was replaced with deletion variants encoding C-terminally truncated proteins, including KgpDeltaHA3/4 (Delta1292-1732 aa), KgpDeltaHA2-4 (Delta1157-1732 aa), KgpDeltaHA1-4 (Delta738-1732 aa), KgpDeltaC-term/HA (Delta681-1732 aa) and KgpDeltaIg/C-term/HA (602-1732 aa). Northern blot and reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that all truncated variants of the kgp gene were transcribed in P. gingivalis. Despite high levels of kgpDeltaC-term/HA and kgpDeltaIg/C-term/HA transcripts, no Kgp-specific antigen was detected in cultures of these mutants as determined by Western blot analysis with monoclonal antibodies specific for the Kgp catalytic domain. Furthermore, only barely measurable amounts of Kgp-specific activity were detected in these two mutants. The remaining mutants expressed significant Kgp activity, however, at lower levels when compared with the parental strain. The decreased activity most probably resulted from altered folding and/or hindered secretion of the protein. The kgp gene truncation was also demonstrated to alter the distribution of the gingipain protein between membrane-associated and -secreted forms. While both gingipain K activity and the protein were cell membrane-associated in the parental strain, the mutants released significant amounts of both protein and activity into the media. Taken together, these results suggest that the C-terminal HA domains of Kgp are not only essential for full expression of gingipain activity, but also for proper processing of the multiprotein complex assembly on the P. gingivalis outer membrane. Moreover, our results indicate that the immunoglobulin-like subdomain is indispensable for proper folding and expression of the gingipains.

Inducible nitric oxide synthase mediates bone development and P. gingivalis-induced alveolar bone loss

The role of inducible nitric oxide synthase (iNOS) in bone development and bacterially induced periodontal bone loss was examined using mice with targeted mutation of the iNOS gene. Femurs of iNOS KO mice showed 30% and 9% higher bone mineral density compared to wild type (WT) at 4 and 9 weeks of age, respectively. Micro-computed tomography revealed that cortical thickness and cortical bone density is increased in the absence of iNOS, while trabecular bone thickness and bone density remains unchanged. Histochemical analysis using TRAP staining showed that osteoclast numbers are lower by 25% in iNOS KO femurs compared to WT femurs. When bone marrow cells were stimulated with M-CSF and RANKL in vitro, iNOS KO cultures developed 51% fewer TRAP-positive multinuclear cells compared to WT cultures. When similar cultures were grown on dentine discs, resorption pit area was decreased by 54% in iNOS KO cultures. Gene expression studies showed that iNOS expression is induced by M-CSF and RANKL in WT bone marrow cultures, while no iNOS transcript was detected in iNOS KO. No compensatory change was detected in the expression of neuronal or endothelial NOS isoforms. There was no difference in RANK and osteoprotegerin expression between iNOS KO and WT bone marrow cultures after M-CSF and RANKL-treatment, while Traf6 expression was significantly lower in the absence of iNOS. In the alveolar bone of the maxilla, the distance between the cementoenamel junction and the alveolar bone crest was larger in iNOS KO compared to WT mice from 6 to 14 weeks of age, indicating a developmental effect of iNOS in oral tissues. Oral administration of the periodontal pathogen Porphyromonas gingivalis caused alveolar bone loss in the maxilla of WT mice, but failed to do so in iNOS KO mice. Expression of the osteoclast marker cathepsin K was 25% lower in iNOS KO alveolar bone. These data indicate that iNOS promotes bone resorption during bone development as well as after bacterial infection, and that iNOS is an important signal for normal osteoclast differentiation.

Lysine-specific gingipain K and heme/hemoglobin receptor HmuR are involved in heme utilization in Porphyromonas gingivalis

We have previously reported on the identification and characterization of the Porphyromonas gingivalis A7436 strain outer membrane receptor HmuR, which is involved in the acquisition of hemin and hemoglobin. We demonstrated that HmuR interacts with the lysine- (Kgp) and arginine- (HRgpA) specific proteases (gingipains) and that Kgp and HRgpA can bind and degrade hemoglobin. Here, we report on the physiological significance of the HmuR-Kgp complex in heme utilization in P. gingivalis through the construction and characterization of a defined kgp mutant and a hmuR kgp double mutant in P. gingivalis A7436. The P. gingivalis kgp mutant exhibited a decreased ability to bind both hemin and hemoglobin. Growth of this strain with hemoglobin was delayed and its ability to utilize hemin as a sole iron source was diminished as compared to the wild type strain. Inactivation of both the hmuR and kgp genes resulted in further decreased ability of P. gingivalis to bind hemoglobin and hemin, as well as diminished ability to utilize either hemin or hemoglobin as a sole iron source. Collectively, these in vivo results further confirmed that both HmuR and Kgp are involved in the utilization of hemin and hemoglobin in P. gingivalis A7436.

Lysine-specific gingipain K and heme/hemoglobin receptor HmuR are involved in heme utilization in Porphyromonas gingivalis

We have previously reported on the identification and characterization of the Porphyromonas gingivalis A7436 strain outer membrane receptor HmuR, which is involved in the acquisition of hemin and hemoglobin. We demonstrated that HmuR interacts with the lysine- (Kgp) and arginine- (HRgpA) specific proteases (gingipains) and that Kgp and HRgpA can bind and degrade hemoglobin. Here, we report on the physiological significance of the HmuR-Kgp complex in heme utilization in P. gingivalis through the construction and characterization of a defined kgp mutant and a hmuR kgp double mutant in P. gingivalis A7436. The P. gingivalis kgp mutant exhibited a decreased ability to bind both hemin and hemoglobin. Growth of this strain with hemoglobin was delayed and its ability to utilize hemin as a sole iron source was diminished as compared to the wild type strain. Inactivation of both the hmuR and kgp genes resulted in further decreased ability of P. gingivalis to bind hemoglobin and hemin, as well as diminished ability to utilize either hemin or hemoglobin as a sole iron source. Collectively, these in vivo results further confirmed that both HmuR and Kgp are involved in the utilization of hemin and hemoglobin in P. gingivalis A7436.