The Novel ASIC2 Locus is Associated with Severe Gingival Inflammation

Potential risk factors and genetic variants associated with dental caries incidence in Appalachia using genome-wide survival analysis

OBJECTIVE

The aim of this study was to identify the potential risk factors and genetic variants associated with dental caries incidence using survival analysis.

METHODS

The Center for Oral Health Research in Appalachia recruited and prospectively followed pregnant women and their children. A total of 909 children followed from birth for up to 7 years were included in this study. Annual intra-oral examinations were performed to assess dental caries experience including the approximate time to first caries incidence in the primary dentition. Cox proportional hazards models were used to assess the associations of time to first caries incidence with self-reported risk factors and 4.9 million genetic variants ascertained using a genome-wide genotyping array.

RESULTS

A total of 196 of 909 children (21.56%) had their first primary tooth caries event during follow-up. Household income, home water source, and mother's educational attainment were significantly associated with time to first caries incidence in the stepwise Cox model. The heritability (i.e., proportion of variance explained by genetics) of time to first caries was 0.54. Though no specific genetic variants were associated at the genome-wide significance level (P < 5E-8), we identified 14 loci at the suggestive significance level (5E-8 < P < 1E-5), some of which were located within or near genes with plausible biological functions in dental caries.

CONCLUSION

Our findings indicate that household income, home water source, and mother's educational attainment are independent risk factors for dental caries incidence. We nominate several suggestive loci for further investigation.

An updated review on the link between oral infections and atherosclerotic cardiovascular disease with focus on phenomics

Atherosclerotic cardiovascular diseases (ACVD) and oral infections such as periodontal disease, dental caries, and apical periodontitis are diseases that affect a great portion of the worldwide population. Both are complex in nature and several studies show that they share etiological factors but a causal relationship between them has not been yet established due to the lack of well-designed clinical trials. Many studies in the recent years show convincing evidence of different mechanisms that might be involved in this association including chronic inflammation and immune response. However, some of these mechanisms are controversial because of confounding factors. It has been suggested that maladaptive inflammatory reactivity, determined in part by single nucleotide polymorphisms (SNPs) in pathway genes, could influence the association between oral infections, and cardiovascular diseases as pleiotropic genes. That is, these conditions could be outcomes of similar inflammatory pathways. Phenomics, the study of the changes in phenotypes or traits considering environmental variables and genetics is efficient in assessing and determining pleiotropic genes. Future research should focus on analyzing a combination of oral inflammatory conditions instead of focusing on one inflammatory phenotype alone and consider pleiotropy as a mechanistic contributor for these associations. Further, prospective observational studies seeking to follow the development of oral disease and subclinical ACVD will foster the understanding of the impact of oral health on general systemic health. Lastly, to demonstrate that oral infections would increase risk for subclinical ACVD development, clinical trials proposing to treat those infections considering genetic background and all other confounders are needed.

Mechanisms of Action of the Peptide Toxins Targeting Human and Rodent Acid-Sensing Ion Channels and Relevance to Their In Vivo Analgesic Effects

Acid-sensing ion channels (ASICs) are voltage-independent H⁺-gated cation channels largely expressed in the nervous system of rodents and humans. At least six isoforms (ASIC1a, 1b, 2a, 2b, 3 and 4) associate into homotrimers or heterotrimers to form functional channels with highly pH-dependent gating properties. This review provides an update on the pharmacological profiles of animal peptide toxins targeting ASICs, including PcTx1 from tarantula and related spider toxins, APETx2 and APETx-like peptides from sea anemone, and mambalgin from snake, as well as the dimeric protein snake toxin MitTx that have all been instrumental to understanding the structure and the pH-dependent gating of rodent and human cloned ASICs and to study the physiological and pathological roles of native ASICs in vitro and in vivo. ASICs are expressed all along the pain pathways and the pharmacological data clearly support a role for these channels in pain. ASIC-targeting peptide toxins interfere with ASIC gating by complex and pH-dependent mechanisms sometimes leading to opposite effects. However, these dual pH-dependent effects of ASIC-inhibiting toxins (PcTx1, mambalgin and APETx2) are fully compatible with, and even support, their analgesic effects in vivo, both in the central and the peripheral nervous system, as well as potential effects in humans.

Interferon activated gene 204 protects against bone loss in experimental periodontitis

BACKGROUND

Periodontal destruction can be the result of different known and yet-to-be-discovered biological pathways. Recent human genetic association studies have implicated interferon-gamma inducible protein 16 (IFI16) and absent in melanoma 2 (AIM2) with high periodontal interleukin (IL)-1β levels and more destructive disease, but mechanistic evidence is lacking. Here, we sought to experimentally validate these observational associations and better understand IFI16 and AIM2's roles in periodontitis.

METHODS

Periodontitis was induced in Ifi204-/- (IFI16 murine homolog) and Aim2-/- mice using the ligature model. Chimeric mice were created to identify the main source cells of Ifi204 in the periodontium. IFI16-silenced human endothelial cells were treated with periodontal pathogens in vitro. Periodontal tissues from Ifi204-/- mice were evaluated for alveolar bone (micro-CT), cell inflammatory infiltration (MPO+ staining), Il1b (qRT-PCR), and osteoclast numbers (cathepsin K+ staining).

RESULTS

Ifi204-deficient mice> exhibited >20% higher alveolar bone loss than wild-type (WT) (P < 0.05), while no significant difference was found in Aim2-/- mice. Ifi204's effect on bone loss was primarily mediated by a nonbone marrow source and was independent of Aim2. Ifi204-deficient mice had greater neutrophil/macrophage trafficking into gingival tissues regardless of periodontitis development compared to WT. In human endothelial cells, IFI16 decreased the chemokine response to periodontal pathogens. In murine periodontitis, Ifi204 depletion elevated gingival Il1b and increased osteoclast numbers at diseased sites (P < 0.05).

CONCLUSIONS

These findings support IFI16's role as a novel regulator of inflammatory cell trafficking to the periodontium that protects against bone loss and offers potential targets for the development of new periodontal disease biomarkers and therapeutics.

Association of the CD14 -260C/T polymorphism with plaque-induced gingivitis depends on the presence of Porphyromonas gingivalis

BACKGROUND

Plaque-induced gingivitis is the most prevalent periodontal disease associated with pathogenic biofilms. The host immune system responds to pathogens through pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs) and their co-receptor cluster of differentiation 14 (CD14).

AIM

This study investigated the association between the functional polymorphism in the CD14 gene and the dental plaque microbiota in children with gingivitis.

DESIGN

A total of 590 unrelated children (307 with plaque-induced gingivitis and 283 controls, aged 13-15 years) were enrolled in this case-control study. Dental plaque was processed using a ParoCheck^® 20 detection kit. The CD14 -260C/T (rs2569190) polymorphism was determined with the PCR-RFLP method.

RESULTS

Gingivitis was detected in 64.2% of boys and 35.8% of girls (P < .001). Children with gingivitis had a significantly higher occurrence of dental caries (P < .001). No significant differences in the CD14 -260C/T allele and genotype distribution among individuals with or without gingivitis in the whole cohort were found. Children with gingivitis and P gingivalis, however, were significantly more frequent carriers of the CT and TT genotypes than children with gingivitis without P gingivalis or healthy controls (P < .05).

CONCLUSIONS

The CD14 -260C/T polymorphism acts in cooperation with P gingivalis to trigger plaque-induced gingivitis in Czech children.

Impaired function of epithelial plakophilin-2 is associated with periodontal disease

BACKGROUND AND OBJECTIVES

Plakophilin-2 (PKP2) is an intracellular desmosomal anchoring protein that has been implicated in a genome-wide association study, in which genetic variants of PKP2 are associated with Porphyromonas gingivalis (P.gingivalis) -dominant periodontal dysbiosis. In this study, we compared the ex vivo PKP2 expression in periodontitis gingival biopsies to periodontitis-free subjects and assessed the in vitro role of PKP2 in gingival epithelial barrier function and the mechanism by which P.gingivalis modulates PKP2 expression.

MATERIAL AND METHODS

Using reverse transcription quantitative real-time PCR (RT-qPCR), we determined PKP2 mRNA expression levels in gingival biopsies collected from 11 periodontally healthy, 10 experimental gingivitis, and 10 chronic periodontitis subjects. PKP2 protein expression in gingival biopsies was detected by immunohistochemistry. We then challenged primary gingival epithelial cells with bacteria including P.gingivalis, Campylobacter rectus, and various Toll-like receptor agonists. Western blot and immunofluorescence staining were used to detect protein expression. Inhibitors blocking proteases pathways were tested for P.gingivalis-mediated PKP2 protein degradations. We also knocked down endogenous epithelial PKP2 using lentiviral short-hairpin RNA (shRNA) and evaluated cell proliferation, spreading, and barrier function.

RESULTS

Periodontitis gingival biopsies had approximately twofold less PKP2 mRNA than did healthy controls (p < .05). PKP2 protein was predominantly expressed in gingival epithelium. In primary gingival epithelial cells, P.gingivalis challenge increased PKP2 mRNA levels, while protein expression decreased, which suggests that P.gingivalis has a protein degradation mechanism. Cysteine proteases inhibitors greatly attenuated P.gingivalis-mediated PKP2 protein degradation. Epithelial cells with deficient PKP2 exhibited inhibited cell proliferation and spreading and failed to form monolayers. Finally, P.gingivalis impaired gingival epithelial barrier function.

CONCLUSIONS

PKP2 appears to be critical in maintaining gingival epithelial barrier function and is susceptible to degradation by cysteine proteases produced by P.gingivalis. Our findings have identified a mechanism by which P.gingivalis impairs epithelial barrier function by promoting PKP2 degradation.

Identification of Gingivitis-Related Genes Across Human Tissues Based on the Summary Mendelian Randomization

Periodontal diseases are among the most frequent inflammatory diseases affecting children and adolescents, which affect the supporting structures of the teeth and lead to tooth loss and contribute to systemic inflammation. Gingivitis is the most common periodontal infection. Gingivitis, which is mainly caused by a substance produced by microbial plaque, systemic disorders, and genetic abnormalities in the host. Identifying gingivitis-related genes across human tissues is not only significant for understanding disease mechanisms but also disease development and clinical diagnosis. The Genome-wide association study (GWAS) a commonly used method to mine disease-related genetic variants. However, due to some factors such as linkage disequilibrium, it is difficult for GWAS to identify genes directly related to the disease. Hence, we constructed a data integration method that uses the Summary Mendelian randomization (SMR) to combine the GWAS with expression quantitative trait locus (eQTL) data to identify gingivitis-related genes. Five eQTL studies from different human tissues and one GWAS studies were referenced in this paper. This study identified several candidates SNPs and genes relate to gingivitis in tissue-specific or cross-tissue. Further, we also analyzed and explained the functions of these genes. The R program for the SMR method has been uploaded to GitHub(https://github.com/hxdde/SMR).

An Evidence-Based Update on the Molecular Mechanisms Underlying Periodontal Diseases

Several investigators have reported about the intricate molecular mechanism underlying periodontal diseases (PD). Nevertheless, the role of specific genes, cells, or cellular mechanisms involved in the pathogenesis of periodontitis are still unclear. Although periodontitis is one of the most prevalent oral diseases globally, there are no pre-diagnostic markers or therapeutic targets available for such inflammatory lesions. A pivotal role is played by pro- and anti-inflammatory markers in modulating pathophysiological and physiological processes in repairing damaged tissues. In addition, effects on osteoimmunology is ever evolving due to the ongoing research in understanding the molecular mechanism lying beneath periodontal diseases. The aim of the current review is to deliver an evidence-based update on the molecular mechanism of periodontitis with a particular focus on recent developments. Reports regarding the molecular mechanism of these diseases have revealed unforeseen results indicative of the fact that significant advances have been made to the periodontal medicine over the past decade. There is integrated hypothesis-driven research going on. Although a wide picture of association of periodontal diseases with immune response has been further clarified with present ongoing research, small parts of the puzzle remain a mystery and require further investigations.

Periodontal inflammation: Integrating genes and dysbiosis

Biofilm bacteria co‐evolve and reach a symbiosis with the host on the gingival surface. The disruption of the homeostatic relationship between plaque bacteria and the host can initiate and promote periodontal disease progression. Recent advances in sequencing technologies allow researchers to profile disease‐associated microbial communities and quantify microbial metabolic activities and host transcriptional responses. In addition to confirming the findings from previous studies, new putative pathogens and novel genes that have not previously been associated with periodontitis, emerge. For example, multiple studies have reported that Synergistetes bacteria are associated with periodontitis. Genes involved in epithelial barrier defense were downregulated in periodontitis, while excessive expression of interleukin‐17 was associated with a hyperinflammatory response in periodontitis and with a unique microbial community. Bioinformatics‐enabled gene ontology pathway analyses provide a panoramic view of the bacterial and host activities as they shift from periodontal health to disease. Additionally, host innate factors, such as genetic variants identified by either a candidate‐gene approach or genome‐wide association analyses, have an impact on subgingival bacterial colonization. Transgenic mice carrying candidate genetic variants, or with the deletion of candidate genes mimicking the deleterious loss‐of‐function variant effect, provide experimental evidence validating the biologic relevance of the novel markers associated with the microbial phenotype identified through a statistical approach. Further refinement in bioinformatics, data management approaches, or statistical tools, are required to gain insight into host‐microbe interactions by harmonizing the multidimensional “big” data at the genomic, transcriptional, and proteomic levels.

Genomics of periodontal disease and tooth morbidity

In this review we critically summarize the evidence base and the progress to date regarding the genomic basis of periodontal disease and tooth morbidity (ie, dental caries and tooth loss), and discuss future applications and research directions in the context of precision oral health and care. Evidence for these oral/dental traits from genome-wide association studies first emerged less than a decade ago. Basic and translational research activities in this domain are now under way by multiple groups around the world. Key departure points in the oral health genomics discourse are: (a) some heritable variation exists for periodontal and dental diseases; (b) the environmental component (eg, social determinants of health and behavioral risk factors) has a major influence on the population distribution but probably interacts with factors of innate susceptibility at the person-level; (c) sizeable, multi-ethnic, well-characterized samples or cohorts with high-quality measures on oral health outcomes and genomics information are required to make decisive discoveries; (d) challenges remain in the measurement of oral health and disease, with current periodontitis and dental caries traits capturing only a part of the health-disease continuum, and are little or not informed by the underlying biology; (e) the substantial individual heterogeneity that exists in the clinical presentation and lifetime trajectory of oral disease can be identified and leveraged in a precision medicine framework or, if unappreciated, can hamper translational efforts. In this review we discuss how composite or biologically informed traits may offer improvements over clinically defined ones for the genomic interrogation of oral diseases. We demonstrate the utility of the results of genome-wide association studies for the development and testing of a genetic risk score for severe periodontitis. We conclude that exciting opportunities lie ahead for improvements in the oral health of individual patients and populations via advances in our understanding of the genomic basis of oral health and disease. The pace of new discoveries and their equitable translation to practice will largely depend on investments in the education and training of the oral health care workforce, basic and population research, and sustained collaborative efforts..

Plaque-induced gingivitis: Case definition and diagnostic considerations

OBJECTIVE

Clinical gingival inflammation is a well-defined site-specific condition for which several measurement systems have been proposed and validated, and epidemiological studies consistently indicate its high prevalence globally. However, it is clear that defining and grading a gingival inflammatory condition at a site level (i.e. a "gingivitis site") is completely different from defining and grading a "gingivitis case" (GC) (i.e. a patient affected by gingivitis), and that a "gingivitis site" does not necessarily mean a "GC". The purpose of the present review is to summarize the evidence on clinical, biochemical, microbiologic, genetic markers as well as symptoms associated with plaque-induced gingivitis and to propose a set of criteria to define GC.

IMPORTANCE

A universally accepted case definition for gingivitis would provide the necessary information to enable oral health professionals to assess the effectiveness of their prevention strategies and treatment regimens; help set priorities for therapeutic actions/programs by health care providers; and undertake surveillance.

FINDINGS

Based on available methods to assess gingival inflammation, GC could be simply, objectively and accurately identified and graded using bleeding on probing score (BOP%) CONCLUSIONS: A patient with intact periodontium would be diagnosed as a GC according to a BOP score ≥ 10%, further classified as localized (BOP score ≥ 10% and ≤30%) or generalized (BOP score > 30%). The proposed classification may also apply to patients with a reduced periodontium, where a GC would characterize a patient with attachment loss and BOP score ≥ 10%, but without BOP in any site probing ≥4 mm in depth.

Biologically Defined or Biologically Informed Traits Are More Heritable Than Clinically Defined Ones: The Case of Oral and Dental Phenotypes

The genetic basis of oral health has long been theorized, but little information exists on the heritable variance in common oral and dental disease traits explained by the human genome. We sought to add to the evidence base of heritability of oral and dental traits using high-density genotype data in a well-characterized community-based cohort of middle-age adults. We used genome-wide association (GWAS) data combined with clinical and biomarker information in the Dental Atherosclerosis Risk In Communities (ARIC) cohort. Genotypes comprised SNPs directly typed on the Affymetrix Genome-Wide Human SNP Array 6.0 chip with minor allele frequency of >5% (n = 656,292) or were imputed using HapMap II-CEU (n = 2,104,905). We investigated 30 traits including "global" [e.g., number of natural teeth (NT) and incident tooth loss], clinically defined (e.g., dental caries via the DMFS index, periodontitis via the CDC/AAP and WW17 classifications), and biologically informed (e.g., subgingival pathogen colonization and "complex" traits). Heritability (i.e., variance explained; h²) was calculated using Visscher's Genome-wide Complex Trait Analysis (GCTA), using a random-effects mixed linear model and restricted maximum likelihood (REML) regression adjusting for ancestry (10 principal components), age, and sex. Heritability estimates were modest for clinical traits-NT = 0.11 (se = 0.07), severe chronic periodontitis (CDC/AAP) = 0.22 (se = 0.19), WW17 Stage 4 vs. 1/2 = 0.15 (se = 0.11). "High gingival index" and "high red complex colonization" had h² > 0.50, while a periodontal complex trait defined by high IL-1β GCF expression and Aggregatibacter actinomycetemcomitans subgingival colonization had the highest h² = 0.72 (se = 0.32). Our results indicate that all GWAS SNPs explain modest levels of the observed variance in clinical oral and dental measures. Subgingival bacterial colonization and complex phenotypes encompassing both bacterial colonization and local inflammatory response had the highest heritability, suggesting that these biologically informed traits capture aspects of the disease process and are promising targets for genomics investigations, according to the notion of precision oral health.

Protocols, Methods, and Tools for Genome-Wide Association Studies (GWAS) of Dental Traits

Oral health and disease are known to be influenced by complex interactions between environmental (e.g., social and behavioral) factors and innate susceptibility. Although the exact contribution of genomics and other layers of "omics" to oral health is an area of active research, it is well established that the susceptibility to dental caries, periodontal disease, and other oral and craniofacial traits is substantially influenced by the human genome. A comprehensive understanding of these genomic factors is necessary for the realization of precision medicine in the oral health domain. To aid in this direction, the advent and increasing affordability of high-throughput genotyping has enabled the simultaneous interrogation of millions of genetic polymorphisms for association with oral and craniofacial traits. Specifically, genome-wide association studies (GWAS) of dental caries and periodontal disease have provided initial insights into novel loci and biological processes plausibly implicated in these two common, complex, biofilm-mediated diseases. This paper presents a summary of protocols, methods, tools, and pipelines for the conduct of GWAS of dental caries, periodontal disease, and related traits. The protocol begins with the consideration of different traits for both diseases and outlines procedures for genotyping, quality control, adjustment for population stratification, heritability and association analyses, annotation, reporting, and interpretation. Methods and tools available for GWAS are being constantly updated and improved; with this in mind, the presented approaches have been successfully applied in numerous GWAS and meta-analyses among tens of thousands of individuals, including dental traits such as dental caries and periodontal disease. As such, they can serve as a guide or template for future genomic investigations of these and other traits.