Loreto Abusleme

The subgingival microbiome in health and periodontitis and its relationship with community biomass and inflammation

The goals of this study were to better understand the ecology of oral subgingival communities in health and periodontitis and elucidate the relationship between inflammation and the subgingival microbiome. Accordingly, we used 454-pyrosequencing of 16S rRNA gene libraries and quantitative PCR to characterize the subgingival microbiome of 22 subjects with chronic periodontitis. Each subject was sampled at two sites with similar periodontal destruction but differing in the presence of bleeding, a clinical indicator of increased inflammation. Communities in periodontitis were also compared with those from 10 healthy individuals. In periodontitis, presence of bleeding was not associated with different α-diversity or with a distinct microbiome, however, bleeding sites showed higher total bacterial load. In contrast, communities in health and periodontitis largely differed, with higher diversity and biomass in periodontitis. Shifts in community structure from health to periodontitis resembled ecological succession, with emergence of newly dominant taxa in periodontitis without replacement of primary health-associated species. That is, periodontitis communities had higher proportions of Spirochetes, Synergistetes, Firmicutes and Chloroflexi, among other taxa, while the proportions of Actinobacteria, particularly Actinomyces, were higher in health. Total Actinomyces load, however, remained constant from health to periodontitis. Moreover, an association existed between biomass and community structure in periodontitis, with the proportion of specific taxa correlating with bacterial load. Our study provides a global-scale framework for the ecological events in subgingival communities that underline the development of periodontitis. The association, in periodontitis, between inflammation, community biomass and community structure and their role in disease progression warrant further investigation.

Defective Neutrophil Recruitment in Leukocyte Adhesion Deficiency Type I Disease Causes Local IL-17–Driven Inflammatory Bone Loss

Inflammatory bone loss from periodontal infections in leukocyte adhesion deficiency disease can be reversed by treatment with antibodies to IL-17 or IL-23. Lessening Bone Loss and Bacterial Burden Nothing dazzles like a beautiful smile, but it’s hard to flash a red carpet–worthy grin when you have leukocyte adhesion deficiency type I (LAD-I). These patients suffer inflammatory degeneration of the bone that cradles the pearly whites (periodontium) as well as other oral pathologies. The periodontal bone loss was thought to result from a lack of neutrophil surveillance of LAD-associated frequent periodontal infections. Now, Moutsopoulos et al. show that cytokine IL-17 secreted by immune T lymphocytes drives periodontal bone loss, thus pinpointing a therapeutic target for LAD-I. Neutrophils are white blood cells that form the first line of defense against microbial infections. These cells carry on their surfaces the LFA-1 β2 integrin (CD11a/CD18), a leukocyte adhesion molecule that is essential for neutrophil movement from the blood to peripheral tissues (extravasation) in response to infection. LAD-I is caused by mutations in the CD18 subunit of β2 integrins and is associated with frequent oral microbial infections and severe periodontal bone loss. The authors showed that defective neutrophil recruitment to the periodontal space in LAD-I patients or in LFA-1–deficient mice (which exhibit the LAD-I periodontal phenotype) was associated with excessive production of the inflammatory cytokine IL-17, mostly from T cells. Local treatment with antibodies to IL-17 in LFA-1–deficient mice blocked inflammatory periodontal bone loss and reduced the total bacterial burden. These findings suggest that IL-17–targeted therapy for periodontitis might be effective in LAD-I patients, which would clearly be a reason to smile. Leukocyte adhesion deficiency type I (LAD-I), a disease syndrome associated with frequent microbial infections, is caused by mutations on the CD18 subunit of β2 integrins. LAD-I is invariably associated with severe periodontal bone loss, which historically has been attributed to the lack of neutrophil surveillance of the periodontal infection. We provide an alternative mechanism by showing that the cytokine interleukin-17 (IL-17) plays a major role in the oral pathology of LAD-I. Defective neutrophil recruitment in LAD-I patients or in LFA-1 (CD11a/CD18)–deficient mice—which exhibit the LAD-I periodontal phenotype—was associated with excessive production of predominantly T cell–derived IL-17 in the periodontal tissue, although innate lymphoid cells also contributed to pathological IL-17 elevation in the LFA-1–deficient mice. Local treatment with antibodies to IL-17 or IL-23 in LFA-1–deficient mice not only blocked inflammatory periodontal bone loss but also caused a reduction in the total bacterial burden, suggesting that the IL-17–driven pathogenesis of LAD-I periodontitis leads to dysbiosis. Therefore, our findings support an IL-17–targeted therapy for periodontitis in LAD-I patients.

Aggregatibacter actinomycetemcomitans–induced hypercitrullination links periodontal infection to autoimmunity in rheumatoid arthritis

Aggregatibacter actinomycetemcomitans generates citrullinated autoantigens involved in rheumatoid arthritis through its pore-forming toxin leukotoxin A. A joint effect of bacteria and genetics Although rheumatoid arthritis is an autoimmune disease, scientists have long suspected that bacterial infections (and in particular, periodontal infections) may play a role in its pathogenesis. Konig et al. now demonstrate that a particular periodontal pathogen called Aggregatibacter actinomycetemcomitans (Aa) induces changes in neutrophil function, including hypercitrullination of host proteins, an abnormality that is also observed in the joints of patients with rheumatoid arthritis. Moreover, the effect of HLA-DRB1, an allele associated with increased risk of rheumatoid arthritis, was only observed in patients exposed to Aa, suggesting the possibility of eventually using these results to identify and possibly even treat high-risk patients. A bacterial etiology of rheumatoid arthritis (RA) has been suspected since the beginnings of modern germ theory. Recent studies implicate mucosal surfaces as sites of disease initiation. The common occurrence of periodontal dysbiosis in RA suggests that oral pathogens may trigger the production of disease-specific autoantibodies and arthritis in susceptible individuals. We used mass spectrometry to define the microbial composition and antigenic repertoire of gingival crevicular fluid in patients with periodontal disease and healthy controls. Periodontitis was characterized by the presence of citrullinated autoantigens that are primary immune targets in RA. The citrullinome in periodontitis mirrored patterns of hypercitrullination observed in the rheumatoid joint, implicating this mucosal site in RA pathogenesis. Proteomic signatures of several microbial species were detected in hypercitrullinated periodontitis samples. Among these, Aggregatibacter actinomycetemcomitans (Aa), but not other candidate pathogens, induced hypercitrullination in host neutrophils. We identified the pore-forming toxin leukotoxin A (LtxA) as the molecular mechanism by which Aa triggers dysregulated activation of citrullinating enzymes in neutrophils, mimicking membranolytic pathways that sustain autoantigen citrullination in the RA joint. Moreover, LtxA induced changes in neutrophil morphology mimicking extracellular trap formation, thereby releasing the hypercitrullinated cargo. Exposure to leukotoxic Aa strains was confirmed in patients with RA and was associated with both anticitrullinated protein antibodies and rheumatoid factor. The effect of human lymphocyte antigen–DRB1 shared epitope alleles on autoantibody positivity was limited to RA patients who were exposed to Aa. These studies identify the periodontal pathogen Aa as a candidate bacterial trigger of autoimmunity in RA.

Using high throughput sequencing to explore the biodiversity in oral bacterial communities

High throughput sequencing of 16S ribosomal RNA gene amplicons is a cost-effective method for characterization of oral bacterial communities. However, before undertaking large-scale studies, it is necessary to understand the technique-associated limitations and intrinsic variability of the oral ecosystem. In this work we evaluated bias in species representation using an in vitro-assembled mock community of oral bacteria. We then characterized the bacterial communities in saliva and buccal mucosa of five healthy subjects to investigate the power of high throughput sequencing in revealing their diversity and biogeography patterns. Mock community analysis showed primer and DNA isolation biases and an overestimation of diversity that was reduced after eliminating singleton operational taxonomic units (OTUs). Sequencing of salivary and mucosal communities found a total of 455 OTUs (0.3% dissimilarity) with only 78 of these present in all subjects. We demonstrate that this variability was partly the result of incomplete richness coverage even at great sequencing depths, and so comparing communities by their structure was more effective than comparisons based solely on membership. With respect to oral biogeography, we found inter-subject variability in community structure was lower than site differences between salivary and mucosal communities within subjects. These differences were evident at very low sequencing depths and were mostly caused by the abundance of Streptococcus mitis and Gemella haemolysans in mucosa. In summary, we present an experimental and data analysis framework that will facilitate design and interpretation of pyrosequencing-based studies. Despite challenges associated with this technique, we demonstrate its power for evaluation of oral diversity and biogeography patterns.

On-going Mechanical Damage from Mastication Drives Homeostatic Th17 Cell Responses at the Oral Barrier.

&NA; Immuno‐surveillance networks operating at barrier sites are tuned by local tissue cues to ensure effective immunity. Site‐specific commensal bacteria provide key signals ensuring host defense in the skin and gut. However, how the oral microbiome and tissue‐specific signals balance immunity and regulation at the gingiva, a key oral barrier, remains minimally explored. In contrast to the skin and gut, we demonstrate that gingiva‐resident T helper 17 (Th17) cells developed via a commensal colonization‐independent mechanism. Accumulation of Th17 cells at the gingiva was driven in response to the physiological barrier damage that occurs during mastication. Physiological mechanical damage, via induction of interleukin 6 (IL‐6) from epithelial cells, tailored effector T cell function, promoting increases in gingival Th17 cell numbers. These data highlight that diverse tissue‐specific mechanisms govern education of Th17 cell responses and demonstrate that mechanical damage helps define the immune tone of this important oral barrier. Graphical Abstract Figure. No caption available. HighlightsDistinct signals shape the Th17 cell network at the oral barrierOral barrier Th17 cells develop independently of commensal microbe colonizationPhysiologic damage through mastication promotes the generation of oral Th17 cellsBarrier damage triggers oral Th17‐cell‐mediated protective immunity and inflammation &NA; The signals regulating immunity at the gingiva, a key oral barrier, remain unclear. Dutzan et al. show that oral barrier Th17 cells are induced in response to mastication rather than commensal colonization, identifying physiologic mechanical damage as a unique tissue‐specific cue conditioning local immunity and inflammation at the oral barrier.

Transplantation-Associated Long-Term Immunosuppression Promotes Oral Colonization by Potentially Opportunistic Pathogens without Impacting Other Members of the Salivary Bacteriome

ABSTRACT Solid-organ transplant recipients rely on pharmacological immunosuppression to prevent allograft rejection. The effect of such chronic immunosuppression on the microflora at mucosal surfaces is not known. We evaluated the salivary bacterial microbiome of 20 transplant recipients and 19 nonimmunosuppressed controls via 454 pyrosequencing of 16S rRNA gene amplicons. Alpha-diversity and global community structure did not differ between transplant and control subjects. However, principal coordinate analysis showed differences in community membership. Taxa more prevalent in transplant subjects included operational taxonomic units (OTUs) of potentially opportunistic Gammaproteobacteria such as Klebsiella pneumoniae, Pseudomonas fluorescens, Acinetobacter species, Vibrio species, Enterobacteriaceae species, and the genera Acinetobacter and Klebsiella. Transplant subjects also had increased proportions of Pseudomonas aeruginosa, Acinetobacter species, Enterobacteriaceae species, and Enterococcus faecalis, among other OTUs, while genera with increased proportions included Klebsiella, Acinetobacter, Staphylococcus, and Enterococcus. Furthermore, in transplant subjects, the dose of the immunosuppressant prednisone positively correlated with bacterial richness, while prednisone and mycophenolate mofetil doses positively correlated with the prevalence and proportions of transplant-associated taxa. Correlation network analysis of OTU relative abundance revealed a cluster containing potentially opportunistic pathogens as transplant associated. This cluster positively correlated with serum levels of C-reactive protein, suggesting a link between the resident flora at mucosal compartments and systemic inflammation. Network connectivity analysis revealed opportunistic pathogens as highly connected to each other and to common oral commensals, pointing to bacterial interactions that may influence colonization. This work demonstrates that immunosuppression aimed at limiting T-cell-mediated responses creates a more permissive oral environment for potentially opportunistic pathogens without affecting other members of the salivary bacteriome.

Subgingival microbial communities in Leukocyte Adhesion Deficiency and their relationship with local immunopathology.

Leukocyte Adhesion Deficiency I (LAD-I) is a primary immunodeficiency caused by single gene mutations in the CD18 subunit of β2 integrins which result in defective transmigration of neutrophils into the tissues. Affected patients suffer from recurrent life threatening infections and severe oral disease (periodontitis). Microbial communities in the local environment (subgingival plaque) are thought to be the triggers for inflammatory periodontitis, yet little is known regarding the microbial communities associated with LAD-I periodontitis. Here we present the first comprehensive characterization of the subgingival communities in LAD-I, using a 16S rRNA gene-based microarray, and investigate the relationship of this tooth adherent microbiome to the local immunopathology of periodontitis. We show that the LAD subgingival microbiome is distinct from that of health and Localized Aggressive Periodontitits. Select periodontitis-associated species in the LAD microbiome included Parvimonas micra, Porphyromonas endodontalis, Eubacterium brachy and Treponema species. Pseudomonas aeruginosa, a bacterium not typically found in subgingival plaque is detected in LAD-I. We suggest that microbial products from LAD-associated communities may have a role in stimulating the local inflammatory response. We demonstrate that bacterial LPS translocates into the lesions of LAD-periodontitis potentially triggering immunopathology. We also show in in vitro assays with human macrophages and in vivo in animal models that microbial products from LAD-associated subgingival plaque trigger IL-23-related immune responses, which have been shown to dominate in patient lesions. In conclusion, our current study characterizes the subgingival microbial communities in LAD-periodontitis and supports their role as triggers of disease pathogenesis.

Influence of DNA extraction on oral microbial profiles obtained via 16S rRNA gene sequencing

Background and objective The advent of next-generation sequencing has significantly facilitated characterization of the oral microbiome. Despite great efforts in streamlining the processes of sequencing and data curation, upstream steps required for amplicon library generation could still influence 16S rRNA gene-based microbial profiles. Among upstream processes, DNA extraction is a critical step that could represent a great source of bias. Accounting for bias introduced by extraction procedures is important when comparing studies that use different methods. Identifying the method that best portrays communities is also desirable. Accordingly, the aim of this study was to evaluate bias introduced by different DNA extraction procedures on oral microbiome profiles. Design Four DNA extraction methods were tested on mock communities consisting of seven representative oral bacteria. Additionally, supragingival plaque samples were collected from seven individuals and divided equally to test two commonly used DNA extraction procedures. Amplicon libraries of the 16S rRNA gene were generated and sequenced via 454-pyrosequencing. Results Evaluation of mock communities revealed that DNA yield and bacterial species representation varied with DNA extraction methods. Despite producing the lowest yield of DNA, a method that included bead beating was the only protocol capable of detecting all seven species in the mock community. Comparison of the performance of two commonly used methods (crude lysis and a chemical/enzymatic lysis+column-based DNA isolation) on plaque samples showed no effect of extraction protocols on taxa prevalence but global community structure and relative abundance of individual taxa were affected. At the phylum level, the latter method improved the recovery of Actinobacteria, Bacteroidetes, and Spirochaetes over crude lysis. Conclusion DNA extraction distorts microbial profiles in simulated and clinical oral samples, reinforcing the importance of careful selection of a DNA extraction protocol to improve species recovery and facilitate data comparison across oral microbiology studies.

Matriptase promotes inflammatory cell accumulation and progression of established epidermal tumors

Deregulation of matriptase is a consistent feature of human epithelial cancers and correlates with poor disease outcome. We have previously shown that matriptase promotes multi-stage squamous cell carcinogenesis in transgenic mice through dual activation of pro-hepatocyte growth factor–cMet–Akt–mTor proliferation/survival signaling and PAR-2–Gαi–NFκB inflammatory signaling. Matriptase was congenitally and constitutively deregulated in our prior studies, and therefore it was unclear if aberrant matriptase signaling supports only initiation of tumor formation or if it is also critical for the progression of established tumors. To determine this, we here have generated triple-transgenic mice with constitutive deregulation of matriptase and simultaneous inducible expression of the cognate matriptase inhibitor, hepatocyte growth factor inhibitor (HAI)-2. As expected, constitutive expression of HAI-2 suppressed the formation of matriptase-dependent tumors in 7,12-Dimethylbenz(a)anthracene-treated mouse skin. Interestingly, however, the induction of HAI-2 expression in already established tumors markedly impaired malignant progression and caused regression of individual tumors. Tumor regression correlated with reduced accumulation of tumor-associated inflammatory cells, likely caused by diminished expression of pro-tumorigenic inflammatory cytokines. The data suggest that matriptase-dependent signaling may be a therapeutic target for both squamous cell carcinoma chemoprevention and for the treatment of established tumors.

Isolation, Characterization and Functional Examination of the Gingival Immune Cell Network.

Immune cell networks in tissues play a vital role in mediating local immunity and maintaining tissue homeostasis, yet little is known of the resident immune cell populations in the oral mucosa and gingiva. We have established a technique for the isolation and study of immune cells from murine gingival tissues, an area of constant microbial exposure and a vulnerable site to a common inflammatory disease, periodontitis. Our protocol allows for a detailed phenotypic characterization of the immune cell populations resident in the gingiva, even at steady state. Our procedure also yields sufficient cells with high viability for use in functional studies, such as the assessment of cytokine secretion ex vivo. This combination of phenotypic and functional characterization of the gingival immune cell network should aid towards investigating the mechanisms involved in oral immunity and periodontal homeostasis, but will also advance our understanding of the mechanisms involved in local immunopathology.