Streptococcus gordonii programs epithelial cells to resist ZEB2 induction by Porphyromonas gingivalis

Promising dawn in tumor microenvironment therapy: engineering oral bacteria

Despite decades of research, cancer continues to be a major global health concern. The human mouth appears to be a multiplicity of local environments communicating with other organs and causing diseases via microbes. Nowadays, the role of oral microbes in the development and progression of cancer has received increasing scrutiny. At the same time, bioengineering technology and nanotechnology is growing rapidly, in which the physiological activities of natural bacteria are modified to improve the therapeutic efficiency of cancers. These engineered bacteria were transformed to achieve directed genetic reprogramming, selective functional reorganization and precise control. In contrast to endotoxins produced by typical genetically modified bacteria, oral flora exhibits favorable biosafety characteristics. To outline the current cognitions upon oral microbes, engineered microbes and human cancers, related literatures were searched and reviewed based on the PubMed database. We focused on a number of oral microbes and related mechanisms associated with the tumor microenvironment, which involve in cancer occurrence and development. Whether engineering oral bacteria can be a possible application of cancer therapy is worth consideration. A deeper understanding of the relationship between engineered oral bacteria and cancer therapy may enhance our knowledge of tumor pathogenesis thus providing new insights and strategies for cancer prevention and treatment.

Oral microbiota and oral squamous cell carcinoma: a review of their relation and carcinogenic mechanisms

Oral Squamous Cell Carcinoma (OSCC) is the most common type of head and neck cancer worldwide. Emerging research suggests a strong association between OSCC and the oral microbiota, a diverse community of bacteria, fungi, viruses, and archaea. Pathogenic bacteria, in particular Porphyromonas gingivalis and Fusobacterium nucleatum, have been closely linked to OSCC. Moreover, certain oral fungi, such as Candida albicans, and viruses, like the human papillomavirus, have also been implicated in OSCC. Despite these findings, the precise mechanisms through which the oral microbiota influences OSCC development remain unclear and necessitate further research. This paper provides a comprehensive overview of the oral microbiota and its relationship with OSCC and discusses potential carcinogenic pathways that the oral microbiota may activate or modulate are also discussed.

Identification of a glutathione transporter in A. actinomycetemcomitans

IMPORTANCE

Microbes produce a large array of extracellular molecules, which serve as signals and cues to promote polymicrobial interactions and alter the function of microbial communities. This has been particularly well studied in the human oral microbiome, where key metabolites have been shown to impact both health and disease. Here, we used an untargeted mass spectrometry approach to comprehensively assess the extracellular metabolome of the pathogen Aggregatibacter actinomycetemcomitans and the commensal Streptococcus gordonii during mono- and co-culture. We generated and made publicly available a metabolomic data set that includes hundreds of potential metabolites and leveraged this data set to identify an operon important for glutathione secretion in A. actinomycetemcomitans.

Potential role of epithelial-mesenchymal transition induced by periodontal pathogens in oral cancer

With the increasing incidence of oral cancer in the world, it has become a hotspot to explore the pathogenesis and prevention of oral cancer. It has been proved there is a strong link between periodontal pathogens and oral cancer. However, the specific molecular and cellular pathogenic mechanisms remain to be further elucidated. Emerging evidence suggests that periodontal pathogens-induced epithelial-mesenchymal transition (EMT) is closely related to the progression of oral cancer. Cells undergoing EMT showed increased motility, aggressiveness and stemness, which provide a pro-tumour environment and promote malignant metastasis of oral cancer. Plenty of studies proposed periodontal pathogens promote carcinogenesis via EMT. In the current review, we discussed the association between the development of oral cancer and periodontal pathogens, and summarized various mechanisms of EMT caused by periodontal pathogens, which are supposed to play an important role in oral cancer, to provide targets for future research in the fight against oral cancer.

Periodontitis and risk of cancer: Mechanistic evidence

This review aims to critically analyze the pathways of interaction and the pathogenic mechanisms linking periodontitis and oral bacteria with the initiation/progression of cancer at different body compartments. A higher risk of head and neck cancer has been consistently associated with periodontitis. This relationship has been explained by the local promotion of dysbiosis, chronic inflammation, immune evasion, and direct (epi)genetic damage to epithelial cells by periodontal pathobionts and their toxins. Epidemiological reports have also studied a possible link between periodontitis and the incidence of other malignancies at distant sites, such as lung, breast, prostate, and digestive tract cancers. Mechanistically, different pathways have been involved, including the induction of a chronic systemic inflammatory state and the spreading of oral pathobionts with carcinogenic potential. Indeed, periodontitis may promote low-grade systemic inflammation and phenotypic changes in the mononuclear cells, leading to the release of free radicals and cytokines, as well as extracellular matrix degradation, which are all mechanisms involved in carcinogenic and metastatic processes. Moreover, the transient hematogenous spill out or micro-aspiration/swallowing of periodontal bacteria and their virulence factors (i.e., lipopolysaccharides, fimbriae), may lead to non-indigenous bacterial colonization of multiple microenvironments. These events may in turn replenish the tumor-associated microbiome and thus influence the molecular hallmarks of cancer. Particularly, specific strains of oral pathobionts (e.g., Porphyromonas gingivalis and Fusobacterium nucleatum) may translocate through the hematogenous and enteral routes, being implicated in esophageal, gastric, pancreatic, and colorectal tumorigenesis through the modulation of the gastrointestinal antitumor immune system (i.e., tumor-infiltrating T cells) and the increased expression of pro-inflammatory/oncogenic genes. Ultimately, the potential influence of common risk factors, relevant comorbidities, and upstream drivers, such as gerovulnerability to multiple diseases, in explaining the relationship cannot be disregarded. The evidence analyzed here emphasizes the possible relevance of periodontitis in cancer initiation/progression and stimulates future research endeavors.

Molecular commensalism-how to investigate underappreciated health-associated polymicrobial communities

The study of human commensal bacteria began with the first observation of prokaryotes >340 years ago. Since then, the study of human-associated microbes has been justifiably biased toward the study of infectious pathogens. However, the role of commensal microbes has in recent years begun to be understood with some appreciation of them as potential protectors of host health rather than bystanders. As our understanding of these valuable microbes grows, it highlights how much more remains to be learned about them and their roles in maintaining health. We note here that a thorough framework for the study of commensals, both in vivo and in vitro is overall lacking compared to well-developed methodologies for pathogens. The modification and application of methods for the study of pathogens can work well for the study of commensals but is not alone sufficient to properly characterize their relationships. This is because commensals live in homeostasis with the host and within complex communities. One difficulty is determining which commensals have a quantifiable impact on community structure and stability as well as host health, vs benign microbes that may indeed serve only as bystanders. Human microbiomes are composed of bacteria, archaea, fungi, and viruses. This review focuses particularly on oral bacteria, yet many of the principles of commensal impacts on host health observed in the mouth can translate well to other host sites. Here, we discuss the value of commensals, the shortcomings involved in model systems for their study, and some of the more notable impacts they have upon not only each other but host health.

Social networking at the microbiome-host interface

Microbial species colonizing host ecosystems in health or disease rarely do so alone. Organisms conglomerate into dynamic heterotypic communities or biofilms in which interspecies and interkingdom interactions drive functional specialization of constituent species and shape community properties, including nososymbiocity or pathogenic potential. Cell-to-cell binding, exchange of signaling molecules, and nutritional codependencies can all contribute to the emergent properties of these communities. Spatial constraints defined by community architecture also determine overall community function. Multilayered interactions thus occur between individual pairs of organisms, and the relative impact can be determined by contextual cues. Host responses to heterotypic communities and impact on host surfaces are also driven by the collective action of the community. Additionally, the range of interspecies interactions can be extended by bacteria utilizing host cells or host diet to indirectly or directly influence the properties of other organisms and the community microenvironment. In contexts where communities transition to a dysbiotic state, their quasi-organismal nature imparts adaptability to nutritional availability and facilitates resistance to immune effectors and, moreover, exploits inflammatory and acidic microenvironments for their persistence.

Epigenome-wide association study using peripheral blood leukocytes identifies genomic regions associated with periodontal disease and edentulism in the Atherosclerosis Risk in Communities study

AIM

To investigate individual susceptibility to periodontitis by conducting an epigenome-wide association study using peripheral blood.

MATERIALS AND METHODS

We included 1077 African American and 457 European American participants of the Atherosclerosis Risk in Communities (ARIC) study who had completed a dental examination or reported being edentulous at Visit 4 and had available data on DNA methylation from Visit 2 or 3. DNA methylation levels were compared by periodontal disease severity and edentulism through discovery analyses and subsequent testing of individual CpGs.

RESULTS

Our discovery analysis replicated findings from a previous study reporting a region in gene ZFP57 (6p22.1) that was significantly hypomethylated in severe periodontal disease compared with no/mild periodontal disease in European American participants. Higher methylation levels in a separate region in an unknown gene (located in Chr10: 743,992-744,958) was associated with significantly higher odds of edentulism compared with no/mild periodontal disease in African American participants. In subsequent CpG testing, four CpGs in a region previously associated with periodontitis located within HOXA4 were significantly hypermethylated in severe periodontal disease compared with no/mild periodontal disease in African American participants (odds ratio per 1 SD increase in methylation level: cg11015251: 1.28 (1.02, 1.61); cg14359292: 1.24 (1.01, 1.54); cg07317062: 1.30 (1.05, 1.61); cg08657492: 1.25 (1.01, 1.55)).

CONCLUSIONS

Our study highlights epigenetic variations in ZPF57 and HOXA4 that are significantly and reproducibly associated with periodontitis. Future studies should evaluate gene regulatory mechanisms in the candidate regions of these loci.

Illuminating the oral microbiome: cellular microbiology

Epithelial cells line mucosal surfaces such as in the gingival crevice and provide a barrier to the ingress of colonizing microorganisms. However, epithelial cells are more than a passive barrier to microbial intrusion, and rather constitute an interactive interface with colonizing organisms which senses the composition of the microbiome and communicates this information to the underlying cells of the innate immune system. Microorganisms, for their part, have devised means to manipulate host cell signal transduction pathways to favor their colonization and survival. Study of this field, which has become known as cellular microbiology, has revealed much about epithelial cell physiology, bacterial colonization and pathogenic strategies, and innate host responses.

Spent culture supernatant of Streptococcus gordonii mitigates inflammation of human periodontal cells and inhibits proliferation of pathogenic oral microbes

BACKGROUND

The oral commensal bacterial species Streptococcus gordonii has been reported to regulate the inflammation of oral epithelial cells stimulated by the periodontal pathogen Porphyromonas gingivalis. This study investigated the activities of S. gordonii metabolites in S. gordonii spent culture supernatants (Sg-SCS) on periodontal-related bacterial growth and periodontitis-associated inflammatory cytokines.

METHODS

Sg-SCS was collected from S. gordonii cultures grown in Dulbecco Modified Eagle Medium and added to the growth media of representative health- and disease-related oral species: S. gordonii, Streptococcus sanguinis, Streptococcus mitis, Streptococcus oralis, P. gingivalis, Tannerella forsythia, and Treponema denticola. The Sg-SCS was also tested for its ability to regulate the expression of proinflammatory cytokines by human macrophages, epithelial cells, and gingival fibroblasts upon stimulation with P. gingivalis-derived lipopolysaccharide (Pg-LPS).

RESULTS

Sg-SCS significantly reduced transcript and protein levels of interleukin (IL)-1β, 6, and 8 induced by Pg-LPS stimulation in multiple types of periodontal cells. mRNA sequencing and bioinformatics analyses indicated that Sg-SCS significantly affects 10 inflammatory pathways. Additionally, Sg-SCS exhibited suppression of the growth of periodontal disease-related bacteria, including T. denticola and P. gingivalis, along with the primary plaque-colonizing species S. oralis. At a low concentration, Sg-SCS also inhibits P. gingivalis adhesion.

CONCLUSIONS

These results strongly suggest that S. gordonii-derived SCS contains metabolites that have anti-inflammatory properties and an ability to inhibit periodontitis-associated pathogenic bacteria. Further investigation will be needed to identify the individual metabolites within the Sg-SCS to develop a novel metabolite-based approach to treating and preventing periodontitis.

P. gingivalis Infection Upregulates PD-L1 Expression on Dendritic Cells, Suppresses CD8+ T-cell Responses, and Aggravates Oral Cancer

Accumulating evidence shows that PD-L1 expression on dendritic cells (DC) is critical for cancer immunotherapy and that Porphyromonas gingivalis (Pg) colonization aggravates the progression of upper gastrointestinal cancers. However, the effects of Pg infection on PD-L1 expression on DCs and related immune consequences in the infection milieu of oral cancer remain unexplored. Here, we found that Pg infection robustly enhanced PD-L1 expression on DCs in a gingipain-dependent manner in cultured cell and systemic infection assays. Pg infection suppressed antigen-specific CD8+ T cells through upregulation of PD-L1 expression on ovalbumin (OVA)-pulsed DCs. This suppression was manifested by decreased IFNγ, perforin, granzyme B, and CD107a. Further analysis showed that Pg drastically reduced CD8+ T cells' ability to lyse OVA-pulsed target cells. Additionally, Pg infection increased the phosphorylation of Akt and STAT3, leading to a significant increase in PD-L1 expression. This was substantiated by using siRNA, overexpression plasmids, and pharmacologic inhibitors. Consistent with the in vitro observations, in a syngeneic mouse oral cancer model, Pg infection significantly enhanced PD-L1 expression on DCs from intratumoral tissues and cervical lymph nodes and exacerbated oral cancer progression, whereas a Pg lysine-specific, gingipain-defective mutant failed to do so. These influences of Pg were largely diminished when tumor cells were pretreated with antibiotics or a STAT3 inhibitor. Therefore, we demonstrated that Pg infection upregulates PD-L1 expression on DCs through Akt-STAT3 signaling, suppresses CD8+ T-cell cytotoxicity, and aggravates oral cancer growth, suggesting targeting Pg, and/or its mediated signaling, could be a therapeutic strategy to improve the efficacy of checkpoint blockade immunotherapy.

Role of oral microbiome in oral oncogenesis, tumor progression, and metastasis

Squamous cell carcinoma is the most common malignant tumor of the oral cavity and its adjacent sites, which endangers the physical and mental health of patients and has a complex etiology. Chronic infection is considered to be a risk factor in cancer development. Evidence suggests that periodontal pathogens, such as Porphyromonas gingivalis, Fusobacterium nucleatum, and Treponema denticola, are associated with oral squamous cell carcinoma (OSCC). They can stimulate tumorigenesis by promoting epithelial cells proliferation while inhibiting apoptosis and regulating the inflammatory microenvironment. Candida albicans promotes OSCC progression and metastasis through multiple mechanisms. Moreover, oral human papillomavirus (HPV) can induce oropharyngeal squamous cell carcinoma (OPSCC). There is evidence that HPV16 can integrate with host cells' DNA and activate oncogenes. Additionally, oral dysbiosis and synergistic effects in the oral microbial communities can promote cancer development. In this review, we will discuss the biological characteristics of oral microbiome associated with OSCC and OPSCC and then highlight the mechanisms by which oral microbiome is involved in oral oncogenesis, tumor progression, and metastasis. These findings may have positive implications for early diagnosis and treatment of oral cancer.

Microbial dysbiosis in oral squamous cell carcinoma: A systematic review and meta-analysis

Objective

The aim of this study was to summarize previously published data and assess the alterations in the composition of the oral microbiome in OSCC using a systematic review and meta-analysis.

Design

Electronic databases were systematically searched for studies on the oral microbiome in OSCC published before December 2021. Qualitative assessments of compositional variations at the phylum level were performed. The meta-analysis on abundance changes of bacteria genera was performed via a random-effects model.

Results

A total of 18 studies involving 1056 participants were included. They consisted of two categories of studies: 1) case-control studies (n = 9); 2) nine studies that compared the oral microbiome between cancerous tissues and paired paracancerous tissues. At the phylum level, enrichment of Fusobacteria but depletion in Actinobacteria and Firmicutes in the oral microbiome was demonstrated in both categories of studies. At the genus level, Fusobacterium showed an increased abundance in OSCC patients (SMD = 0.65, 95% CI: 0.43-0.87, Z = 5.809, P = 0.000) and in cancerous tissues (SMD = 0.54, 95% CI: 0.36-0.72, Z = 5.785, P = 0.000). The abundance of Streptococcus was decreased in OSCC (SMD = -0.46, 95% CI: -0.88-0.04, Z = -2.146, P = 0.032) and in cancerous tissues (SMD = -0.45, 95% CI: -0.78-0.13, Z = -2.726, P = 0.006).

Conclusions

Disturbances in the interactions between enriched Fusobacterium and depleted Streptococcus may participate in or prompt the occurrence and development of OSCC and could be potential biomarkers for detection of OSCC.

Antimicrobial potential of known and novel probiotics on in vitro periodontitis biofilms

Several oral diseases are characterized by a shift within the oral microbiome towards a pathogenic, dysbiotic composition. Broad-spectrum antimicrobials are often part of patient care. However, because of the rising antibiotic resistance, alternatives are increasingly desirable. Alternatively, supplying beneficial species through probiotics is increasingly showing favorable results. Unfortunately, these probiotics are rarely evaluated comparatively. In this study, the in vitro effects of three known and three novel Lactobacillus strains, together with four novel Streptococcus salivarius strains were comparatively evaluated for antagonistic effects on proximal agar growth, antimicrobial properties of probiotic supernatant and the probiotic's effects on in vitro periodontal biofilms. Strain-specific effects were observed as differences in efficacy between genera and differences within genera. While some of the Lactobacillus candidates were able to reduce the periodontal pathobiont A. actinomycetemcomitans, the S. salivarius strains were not. However, the S. salivarius strains were more effective against periodontal pathobionts P. intermedia, P. gingivalis, and F. nucleatum. Vexingly, most of the Lactobacillus strains also negatively affected the prevalence of commensal species within the biofilms, while this was lower for S. salivarius strains. Both within lactobacilli and streptococci, some strains showed significantly more inhibition of the pathobionts, indicating the importance of proper strain selection. Additionally, some species showed reductions in non-target species, which can result in unexpected and unexplored effects on the whole microbiome.

Decoding the coupled decision-making of the epithelial-mesenchymal transition and metabolic reprogramming in cancer

Cancer metastasis relies on an orchestration of traits driven by different interacting functional modules, including metabolism and epithelial-mesenchymal transition (EMT). During metastasis, cancer cells can acquire a hybrid metabolic phenotype (W/O) by increasing oxidative phosphorylation without compromising glycolysis and they can acquire a hybrid epithelial/mesenchymal (E/M) phenotype by engaging EMT. Both the W/O and E/M states are associated with high metastatic potentials, and many regulatory links coupling metabolism and EMT have been identified. Here, we investigate the coupled decision-making networks of metabolism and EMT. Their crosstalk can exhibit synergistic or antagonistic effects on the acquisition and stability of different coupled metabolism-EMT states. Strikingly, the aggressive E/M-W/O state can be enabled and stabilized by the crosstalk irrespective of these hybrid states' availability in individual metabolism or EMT modules. Our work emphasizes the mutual activation between metabolism and EMT, providing an important step toward understanding the multifaceted nature of cancer metastasis.

Oral Commensal Streptococci: Gatekeepers of the Oral Cavity

Oral commensal streptococci are primary colonizers of the oral cavity. These streptococci produce many adhesins, metabolites, and antimicrobials that modulate microbial succession and diversity within the oral cavity. Often, oral commensal streptococci antagonize cariogenic and periodontal pathogens such as Streptococcus mutans and Porphyromonas gingivalis, respectively. Mechanisms of antagonism are varied and range from the generation of hydrogen peroxide, competitive metabolite scavenging, the generation of reactive nitrogen intermediates, and bacteriocin production. Furthermore, several oral commensal streptococci have been shown to alter the host immune response at steady state and in response to oral pathogens. Collectively, these features highlight the remarkable ability of oral commensal streptococci to regulate the structure and function of the oral microbiome. In this review, we discuss mechanisms used by oral commensal streptococci to interact with diverse oral pathogens, both physically and through the production of antimicrobials. Finally, we conclude by exploring the critical roles of oral commensal streptococci in modulating the host immune response and maintaining health and homeostasis.

Chitosan and its application in dental implantology

OBJECTIVE

The aim of this review was to evaluate the properties of chitosan for an application in dental implantology.

METHODS

Electronic Databases: PubMed, Google Scholar, Scopus, were used to recherche the articles published from 2010 to 2021. The keywords used were: chitosan, biocompatible, antibacterial, osseointegration, implant, bioactive. After a carefully selection according to the above keywords 46 articles met the condition to be studied RESULTS: Chitosan is a biopolymer, that can be easy produced. Its antibacterial, anti-inflammatory, anti-fugal, hemostatic, analgesic, mucoadhesive, osseointegrative properties and its excellent film-forming ability make chitosan a material with a future in dental implantology and in other areas of dental applications. Titan implants coated with chitosan showed better bioactive properties than uncoated implants. The treatment of the implant surface played an important role on the stability of implants. The activity of osteoblasts increased when the surface was laser-treated followed by coating with chitosan. The subsequent coating with apatite improved the bioactivity of chitosan.

CONCLUSION

Chitosan is a promising biocompatible and bioactive material in dental implantology. Its antibacterial properties can be enhanced by modification of its structure. Its bioactive properties can be improved when mixing with hydroxy apatite.

Type-2 epithelial-mesenchymal transition in oral mucosal nonneoplastic diseases

The oral mucosa is a membranous structure comprising epithelial and connective tissue that covers the oral cavity. The oral mucosa is the first immune barrier to protect the body against pathogens for systemic protection. It is frequently exposed to mechanical abrasion, chemical erosion, and pathogenic invasion, resulting in oral mucosal lesions, particularly inflammatory diseases. Epithelial-mesenchymal transition (EMT) is a crucial biological process in the pathogenesis of oral mucosal disorders, which are classified into three types (types 1, 2, and 3) based on their physiological consequences. Among these, type-2 EMT is crucial in wound repair, organ fibrosis, and tissue regeneration. It causes infectious and dis-infectious immunological diseases, such as oral lichen planus (OLP), oral leukoplakia, oral submucosal fibrosis, and other precancerous lesions. However, the mechanism and cognition between type-2 EMT and oral mucosal inflammatory disorders remain unknown. This review first provides a comprehensive evaluation of type-2 EMT in chronically inflammatory oral mucosal disorders. The aim is to lay a foundation for future research and suggest potential treatments.

Oral Microbiome in Orthodontic Acrylic Retainer

The oral microbiome can be shifted if the patients wear the acrylic retainers for a lengthy period. It is essential to understand the components of the plaque in order to forestall the development of dental caries and gingivitis. The aim of this study is to report the bacterial communities that adhere to the acrylic retainers by full-length nanopore 16S sequencing. Six healthy participants were allocated into 2 groups (chemical tablet and brushing groups). Plaque samples were collected from the acrylic retainer surfaces before and after cleaning. The bacterial communities were reported using full-length nanopore 16S sequencing. The results showed that 7 distinct phyla were identified by sequencing. The most prevalent of these was the Firmicutes. We found a total of 72 genera. The most common microorganism across all samples was Streptococcus, followed by Neisseria, Rothia, and Gemella. The beta diversity showed a significant difference between before and after cleaning (p < 0.05). This study revealed the novel finding that a combination of chemical and mechanical cleaning methods was the most effective method of eliminating retainer biofilms. Moreover, retainer cleaning tablets did not alter the homeostatic balance of the bacterial communities adhering to the acrylic retainers.

A Review of the Role of Oral Microbiome in the Development, Detection, and Management of Head and Neck Squamous Cell Cancers

The role of the microbiome in the development and propagation of head and neck squamous cell cancer (HNSCC) is largely unknown and the surrounding knowledge lags behind what has been discovered related to the microbiome and other malignancies. In this review, the authors performed a structured analysis of the available literature from several databases. The authors discuss the merits and detriments of several studies discussing the microbiome of the structures of the aerodigestive system throughout the development of HNSCC, the role of the microbiome in the development of malignancies (generally and in HNSCC) and clinical applications of the microbiome in HNSCC. Further studies will be needed to adequately describe the relationship between HNSCC and the microbiome, and to push this relationship into a space where it is clinically relevant outside of a research environment.

Periodontal Pathogens: A Crucial Link Between Periodontal Diseases and Oral Cancer

Emerging evidence shows a striking link between periodontal diseases and various human cancers including oral cancer. And periodontal pathogens, leading to periodontal diseases development, may serve a crucial role in oral cancer. This review elucidated the molecular mechanisms of periodontal pathogens in oral cancer. The pathogens directly engage in their own unique molecular dialogue with the host epithelium to acquire cancer phenotypes, and indirectly induce a proinflammatory environment and carcinogenic substance in favor of cancer development. And functional, rather than compositional, properties of oral microbial community correlated with cancer development are discussed. The effect of periodontal pathogens on periodontal diseases and oral cancer will further detail the pathogenesis of oral cancer and intensify the need of maintaining oral hygiene for the prevention of oral diseases including oral cancer.

Oral Microbiota-Driven Cell Migration in Carcinogenesis and Metastasis

The oral cavity harbors approximately 1,000 microbial species, and both pathogenic and commensal strains are involved in the development of carcinogenesis by stimulating chronic inflammation, affecting cell proliferation, and inhibiting cell apoptosis. Moreover, some substances produced by oral bacteria can also act in a carcinogenic manner. The link between oral microbiota and chronic inflammation as well as cell proliferation has been well established. Recently, increasing evidence has indicated the association of the oral microbiota with cell migration, which is crucial in regulating devastating diseases such as cancer. For instance, increased cell migration induced the spread of highly malignant cancer cells. Due to advanced technologies, the mechanistic understanding of cell migration in carcinogenesis and cancer metastasis is undergoing rapid progress. Thus, this review addressed the complexities of cell migration in carcinogenesis and cancer metastasis. We also integrate recent findings on the molecular mechanisms by which the oral microbiota regulates cell migration, with emphasis on the effect of the oral microbiota on adhesion, polarization, and guidance. Finally, we also highlight critical techniques, such as intravital microscopy and superresolution microscopy, for studies in this field.

The Role of Zinc Finger Proteins in Various Oral Conditions

The zinc finger proteins (ZNFs) are essential transcription factors, and the genes encoding them constitute about 3% of the entire human genome. They are involved in the development of several tissues, and any alterations in their structure may promote chronic conditions like diabetes and tumorigenesis. Lately, their role in the development, progression, and metastasis of Oral Squamous Cell Carcinoma (OSCC), Epithelial Dysplasia, Oral Lichen Planus, and Periodontitis has been found. The present review aims to describe their role in various oral conditions. Electronic databases like Medline (PubMed) and Scopus were searched for original studies related to the role of ZNFs in various oral conditions. It yielded 48 studies included in the review. It was found that the ZNFs influenced chronic conditions like Oral Cancer and Periodontitis. They act both as tumor suppressors and oncogenes and have an anti-inflammatory effect. The knowledge from the present review may be utilized in designing drugs that prevent unusual expression of specific ZNFs. Besides, they may be applied as prognostic markers due to their high expression specificity in some tumors.

Role of Porphyromonas gingivalis in oral and orodigestive squamous cell carcinoma

Oral and esophageal squamous cell carcinomas harbor a diverse microbiome that differs compositionally from precancerous and healthy tissues. Though causality is yet to be definitively established, emerging trends implicate periodontal pathogens such as Porphyromonas gingivalis as associated with the cancerous state. Moreover, infection with P. gingivalis correlates with a poor prognosis, and P. gingivalis is oncopathogenic in animal models. Mechanistically, properties of P. gingivalis that have been established in vitro and could promote tumor development include induction of a dysbiotic inflammatory microenvironment, inhibition of apoptosis, increased cell proliferation, enhanced angiogenesis, activation of epithelial-to-mesenchymal transition, and production of carcinogenic metabolites. The microbial community context is also relevant to oncopathogenicity, and consortia of P. gingivalis and Fusobacterium nucleatum are synergistically pathogenic in oral cancer models in vivo. In contrast, oral streptococci, such as Streptococcus gordonii, can antagonize protumorigenic epithelial cell phenotypes induced by P. gingivalis, indicating functionally specialized roles for bacteria in oncogenic communities. Consistent with the notion of the bacterial community constituting the etiologic unit, metatranscriptomic data indicate that functional, rather than compositional, properties of the tumor-associated communities have more relevance to cancer development. A consistent association of P. gingivalis with oral and orodigestive carcinoma could have diagnostic potential for early detection of these conditions that have a high incidence and low survival rates.

Streptococcus gordonii-induced miRNAs regulate CCL20 responses in human oral epithelial cells

The mechanisms through which oral commensal bacteria mitigates uncontrolled inflammatory responses of the oral mucosa remain unknown. Here, we show that representative oral bacterial species normally associated with oral health [S. gordonii (Sg), V. parvula (Vp); A. naeslundii (An); C. sputigena (Cs), and N. mucosa (Nm)] enhanced differential chemokine responses in oral epithelial cells (OECs), with some bacteria (An, Vp, and Nm) inducing higher chemokine levels (CXCL1, CXCL8) than others (Sg, Cs). Although all bacterial species (except Cs) increased CCL20 mRNA levels consistent with protein elevations in cell lysates, only An, Vp and Nm induced higher CCL20 secretion, similar to the effect of the oral pathogen F. nucleatum (Fn). In contrast, most CCL20 remained associated with OECs exposed to Sg and negligible amounts released into the cell supernatants. Consistently, Sg attenuated An-induced CCL20. MiR-4516 and miR-663a were identified as Sg-specifically induced miRNAs modulating validated targets of chemokine-associated pathways. Cell transfection with miR-4516 and miR-663a decreased An- and Fn-induced CCL20. MiRNAs up-regulation and attenuation of An-induced CCL20 by Sg were reversed by catalase. Up-regulation of both miRNAs was specifically enhanced by oral streptococci H₂O₂-producers. These findings suggest that CCL20 levels produced by OECs in response to bacterial challenge are regulated by Sg-induced miR-4516 and miR-663a in a mechanism that involves hydrogen peroxide. This type of molecular mechanism could partly explain the central role of specific oral streptococcal species in balancing inflammatory and antimicrobial responses given the critical role of CCL20 in innate (antimicrobial) and adaptive immunity (modulates Th17 responses).

Porphyromonas gingivalis upregulates calbindin 1 and thus promotes the proliferation of gingival epithelial cells

OBJECTIVES

This study aims to investigate the effect of calbindin 1 on the proliferation and apoptosis of gingival epithelial cells affected by Porphyromonas gingivalis (P. gingivalis)invitro.

METHODS

A model of P. gingivalis infecting CA9-22 was established in vitro. At 24 h after infection, the expression of calbindin 1 (CALB1) was detected by real-time fluorescent quantitative polymerase chain reaction, Western blot, and immunofluorescence analyses. The expression of CALB1 was further inhibited by RNA interference. Cell proliferation was detected by BrdU analysis, and cell apoptosis was detected by caspase 3 activity. The expression of MDM2 and p53 was detected by Western blot analysis.

RESULTS

P. gingivalis infection upregulated the expression of CALB1 in CA9-22 cells with multiplicity-dependent manner. CALB1 promoted the proliferation of CA9-22 cells, increased the expression of MDM2, and inhibited the expression of p53. Inhibiting CALB1 expression did not affect the inhibitory effect of P. gingivalis infection on CA9-22 apoptosis.

CONCLUSIONS

P. gingivalis infection can promote the proliferation of CA9-22 cells by increasing CALB1 expression. The related mechanism may be associated with MDM2-p53.

Porphyromonas gingivalis in oral squamous cell carcinoma: A review

Oral cancer contributes significantly to the global cancer burden. Oral bacteria play an important role in the spread of oral cancer, according to mounting evidence. The most proven instance is the carcinogenic implications of Porphyromonas gingivalis, a key pathogen in chronic periodontitis. It is imperative to understand the pathogenesis of P. gingivalis in OSCC. This review aims to gather and assess scientific shreds of evidence on the involvement of Porphyromonas gingivalis in the molecular mechanism of oral squamous cell carcinoma.

Outer membrane vesicles of Porphyromonas gingivalis: Novel communication tool and strategy

Extracellular vesicles (EVs) have been recognized as a universal method of cellular communications and are reportedly produced in bacteria, archaea, and eukaryotes. Bacterial EVs are often called “Outer Membrane Vesicles” (OMVs) as they were the result of a controlled blebbing of the outer membrane of gram-negative bacteria such as Porphyromonas gingivalis (P. gingivalis). Bacterial EVs are natural messengers, implicated in intra- and inter-species cell-to-cell communication among microorganism populations present in microbiota. Bacteria can incorporate their pathogens into OMVs; the content of OMVs differs, depending on the type of bacteria. The production of distinct types of OMVs can be mediated by different factors and routes. A recent study highlighted OMVs ability to carry crucial molecules implicated in immune modulation, and, nowadays, they are considered as a way to communicate and transfer messages from the bacteria to the host and vice versa. This review article focuses on the current understanding of OMVs produced from major oral bacteria, P. gingivalis: generation, characteristics, and contents as well as the involvement in signal transduction of host cells and systemic diseases. Our recent study regarding the action of P. gingivalis OMVs in the living body is also summarized.

Regulation of olfactomedin 4 by Porphyromonas gingivalis in a community context

At mucosal barriers, the virulence of microbial communities reflects the outcome of both dysbiotic and eubiotic interactions with the host, with commensal species mitigating or potentiating the action of pathogens. We examined epithelial responses to the oral pathogen Porphyromonas gingivalis as a monoinfection and in association with a community partner, Streptococcus gordonii. RNA-Seq of oral epithelial cells showed that the Notch signaling pathway, including the downstream effector olfactomedin 4 (OLFM4), was differentially regulated by P. gingivalis alone; however, regulation was overridden by S. gordonii. OLFM4 was required for epithelial cell migratory, proliferative and inflammatory responses to P. gingivalis. Activation of Notch signaling was induced through increased expression of the Notch1 receptor and the Jagged1 (Jag1) agonist. In addition, Jag1 was released in response to P. gingivalis, leading to paracrine activation. Following Jag1-Notch1 engagement, the Notch1 extracellular domain was cleaved by P. gingivalis gingipain proteases. Antagonism by S. gordonii involved inhibition of gingipain activity by secreted hydrogen peroxide. The results establish a novel mechanism by which P. gingivalis modulates epithelial cell function which is dependent on community context. These interrelationships have relevance for innate inflammatory responses and epithelial cell fate decisions in oral health and disease.

Porphyromonas gingivalis infection exacerbates oesophageal cancer and promotes resistance to neoadjuvant chemotherapy

BACKGROUND

The effect of Porphyromonas gingivalis (Pg) infection on oesophageal squamous cell carcinoma (ESCC) prognosis, chemotherapeutic efficacy, and oesophageal cancer cell apoptosis resistance and proliferation remain poorly understood.

METHODS

Clinicopathological data from 312 ESCC oesophagectomy patients, along with the computed tomography imaging results and longitudinal cancerous tissue samples from a patient subset (n = 85) who received neoadjuvant chemotherapy (NACT), were analysed. Comparison of overall survival and response rate to NACT between Pg-infected and Pg-uninfected patients was made by multivariate Cox analysis and Response Evaluation Criteria in Solid Tumours v.1.1 criteria. The influence of Pg on cell proliferation and drug-induced apoptosis was examined in ESCC patients and validated in vitro and in vivo.

RESULTS

The 5-year overall survival was lower in Pg-positive patients, and infection was associated with multiple clinicopathological factors and pathologic tumour, node, metastasis stage. Of the 85 patients who received NACT, Pg infection was associated with a lower response rate and 5-year overall survival. Infection with Pg resulted in apoptosis resistance in ESCC and promoted ESCC cell viability, which was confirmed in longitudinal cancerous tissue samples. Pg-induced apoptosis resistance was dependent on fimbriae and STAT3.

CONCLUSIONS

Pg infection is associated with a worse ESCC prognosis, reduced chemotherapy efficacy, and can potentiate the aggressive behaviour of ESCC cells.

Differential Response of Oral Mucosal and Gingival Cells to Corynebacterium durum, Streptococcus sanguinis, and Porphyromonas gingivalis Multispecies Biofilms

Polymicrobial interactions with oral mucosal surfaces determine the health status of the host. While a homeostatic balance provides protection from oral disease, a dysbiotic polymicrobial community promotes tissue destruction and chronic oral diseases. How polymicrobial communities transition from a homeostatic to a dysbiotic state is an understudied process. Thus, we were interested to investigate this ecological transition by focusing on biofilm communities containing high abundance commensal species and low abundance pathobionts to characterize the host-microbiome interactions occurring during oral health. To this end, a multispecies biofilm model was examined using the commensal species Corynebacterium durum and Streptococcus sanguinis and the pathobiont Porphyromonas gingivalis. We compared how both single and multispecies biofilms interact with different oral mucosal and gingival cell types, including the well-studied oral keratinocyte cell lines OKF4/TERT-1and hTERT TIGKs as well as human primary periodontal ligament cells. While single species biofilms of C. durum, S. sanguinis, and P. gingivalis are all characterized by unique cytokine responses for each species, multispecies biofilms elicited a response resembling S. sanguinis single species biofilms. One notable exception is the influence of P. gingivalis upon TNF-α and Gro-α production in hTERT TIGKs cells, which was not affected by the presence of other species. This study is also the first to examine the host response to C. durum. Interestingly, C. durum yielded no notable inflammatory responses from any of the tested host cells, suggesting it functions as a true commensal species. Conversely, S. sanguinis was able to induce expression and secretion of the proinflammatory cytokines IL-6 and IL-8, demonstrating a much greater inflammatory potential, despite being health associated. Our study also demonstrates the variability of host cell responses between different cell lines, highlighting the importance of developing relevant in vitro models to study oral microbiome-host interactions.

A bacterial tyrosine phosphatase modulates cell proliferation through targeting RGCC

Tyrosine phosphatases are often weaponized by bacteria colonizing mucosal barriers to manipulate host cell signal transduction pathways. Porphyromonas gingivalis is a periodontal pathogen and emerging oncopathogen which interferes with gingival epithelial cell proliferation and migration, and induces a partial epithelial mesenchymal transition. P. gingivalis produces two tyrosine phosphatases, and we show here that the low molecular weight tyrosine phosphatase, Ltp1, is secreted within gingival epithelial cells and translocates to the nucleus. An ltp1 mutant of P. gingivalis showed a diminished ability to induce epithelial cell migration and proliferation. Ltp1 was also required for the transcriptional upregulation of Regulator of Growth and Cell Cycle (RGCC), one of the most differentially expressed genes in epithelial cells resulting from P. gingivalis infection. A phosphoarray and siRNA showed that P. gingivalis controlled RGCC expression through Akt, which was activated by phosphorylation on S473. Akt activation is opposed by PTEN, and P. gingivalis decreased the amount of PTEN in epithelial cells. Ectopically expressed Ltp1 bound to PTEN, and reduced phosphorylation of PTEN at Y336 which controls proteasomal degradation. Ltp-1 induced loss of PTEN stability was prevented by chemical inhibition of the proteasome. Knockdown of RGCC suppressed upregulation of Zeb2 and mesenchymal markers by P. gingivalis. RGCC inhibition was also accompanied by a reduction in production of the proinflammatory cytokine IL-6 in response to P. gingivalis. Elevated IL-6 levels can contribute to periodontal destruction, and the ltp1 mutant of P. gingivalis incited less bone loss compared to the parental strain in a murine model of periodontal disease. These results show that P. gingivalis can deliver Ltp1 within gingival epithelial cells, and establish PTEN as the target for Ltp1 phosphatase activity. Disruption of the Akt1/RGCC signaling axis by Ltp1 facilitates P. gingivalis-induced increases in epithelial cell migration, proliferation, EMT and inflammatory cytokine production.

Bacteria colonizing the oral cavity can induce inflammatory destruction of the periodontal tissues, and are increasingly associated with oral squamous cell carcinoma. P. gingivalis, a major periodontal pathogen, can subvert epithelial pathways that control important physiological processes relating to innate immunity and cell fate; however, little is known about the effector molecules. Here we show that P. gingivalis can deliver a tyrosine phosphatase, Ltp1, within epithelial cells, and Ltp1 phosphatase activity destabilizes PTEN, a negative regulator of Akt1 signaling. The production of RGCC is thus increased and this leads to increased epithelial cell migration, proliferation, a partial mesenchymal phenotype and inflammatory cytokine production. Ltp1 phosphatase activity thus provides a mechanistic basis for a number of P. gingivalis properties that contribute to disease. Indeed, an Ltp1-deficient mutant was less pathogenic in a murine model of periodontitis. These results contribute to deciphering the pathophysiological events that underlie oral bacterial diseases that initiate at mucosal barriers.

Forkhead Box Protein O1: Functional Diversity and Post-Translational Modification, a New Therapeutic Target?

Forkhead box protein O1 (FoXO1) is a transcription factor involved in the regulation of a wide variety of physiological process including glucose metabolism, lipogenesis, bone mass, apoptosis, and autophagy. FoXO1 dysfunction is involved in the pathophysiology of various diseases including metabolic diseases, atherosclerosis, and tumors. FoXO1 activity is regulated in response to different physiological or pathogenic conditions by changes in protein expression and post-translational modifications. Various modifications cooperate to regulate FoXO1 activity and FoXO1 target gene transcription. In this review, we summarize how different post-translational modifications regulate FoXO1 physiological function, which may provide new insights for drug design and development.

The Roles of FOXO1 in Periodontal Homeostasis and Disease

Periodontitis is an oral chronic inflammatory disease that is initiated by periodontal microbial communities and requires disruption of the homeostatic responses. The prevalence of periodontal disease increases with age; more than 70% of adults 65 years and older have periodontal disease. A pathogenic microbial community is required for initiating periodontal disease. Dysbiotic immune-inflammatory response and bone remodeling are characteristics of periodontitis. The transcription factor forkhead box protein O1 (FOXO1) is a key regulator of a number of cellular processes, including cell survival and differentiation, immune status, reactive oxygen species (ROS) scavenging, and apoptosis. Although accumulating evidence indicates that FOXO1 activity can be induced by periodontal pathogens, the roles of FOXO1 in periodontal homeostasis and disease have not been well documented. The present review summarizes how the FOXO1 signaling axis can regulate periodontal bacteria-epithelial interactions, immune-inflammatory response, bone remodeling, and wound healing.

Porphyromonas gingivalis and Its Systemic Impact: Current Status

The relationship between periodontitis and systemic diseases, notably including atherosclerosis and diabetes, has been studied for several years. Porphyromonas gingivalis, a prominent component of oral microorganism communities, is the main pathogen that causes periodontitis. As a result of the extensive analysis of this organism, the evidence of its connection to systemic diseases has become more apparent over the last decade. A significant amount of research has explored the role of Porphyromonas gingivalis in atherosclerosis, Alzheimer's disease, rheumatoid arthritis, diabetes, and adverse pregnancy outcomes, while relatively few studies have examined its contribution to respiratory diseases, nonalcoholic fatty liver disease, and depression. Here, we provide an overview of the current state of knowledge about Porphyromonas gingivalis and its systemic impact in an aim to inform readers of the existing epidemiological evidence and the most recent preclinical studies. Additionally, the possible mechanisms by which Porphyromonas gingivalis is involved in the onset or exacerbation of diseases, together with its effects on systemic health, are covered. Although a few results remain controversial, it is now evident that Porphyromonas gingivalis should be regarded as a modifiable factor for several diseases.

The Role of the Microbiome in Oral Squamous Cell Carcinoma with Insight into the Microbiome-Treatment Axis

Oral squamous cell carcinoma (OSCC) is one of the leading presentations of head and neck cancer (HNC). The first part of this review will describe the highlights of the oral microbiome in health and normal development while demonstrating how both the oral and gut microbiome can map OSCC development, progression, treatment and the potential side effects associated with its management. We then scope the dynamics of the various microorganisms of the oral cavity, including bacteria, mycoplasma, fungi, archaea and viruses, and describe the characteristic roles they may play in OSCC development. We also highlight how the human immunodeficiency viruses (HIV) may impinge on the host microbiome and increase the burden of oral premalignant lesions and OSCC in patients with HIV. Finally, we summarise current insights into the microbiome–treatment axis pertaining to OSCC, and show how the microbiome is affected by radiotherapy, chemotherapy, immunotherapy and also how these therapies are affected by the state of the microbiome, potentially determining the success or failure of some of these treatments.

Oral commensal bacteria differentially modulate epithelial cell death

OBJECTIVE

Epithelial cell death is an important innate mechanism at mucosal surfaces, which enables the elimination of pathogens and modulates immunoinflammatory responses. Based on the antimicrobial and anti-inflammatory properties of cell death, we hypothesized that oral epithelial cell (OECs) death is differentially modulated by oral bacteria.

MATERIAL AND METHODS

We evaluated the effect of oral commensals Streptococcus gordonii (Sg), Streptococcus sanguinis (Ss), and Veillonella parvula (Vp), and pathogens Porphyromonas gingivalis (Pg), Tannerella forsythia (Tf), and Fusobacterium nucleatum (Fn) on OEC death. Apoptosis and necrosis were evaluated by flow cytometry using FITC Annexin-V and Propidium Iodide staining. Caspase-3/7 and caspase-1 activities were determined as markers of apoptosis and pyroptosis, respectively. IL-1β and IL-8 protein levels were determined in supernatants by ELISA.

RESULTS

Significant increases in apoptosis and necrosis were induced by Sg and Ss. Pg also induced apoptosis, although at a substantially lower level than the commensals. Vp, Tf, and Fn showed negligible effects on cell viability. These results were consistent with Sg, Ss, and Pg activating caspase-3/7. Only Ss significantly increased the levels of activated caspase-1, which correlated to IL-1β over-expression.

CONCLUSIONS

OEC death processes were differentially induced by oral commensal and pathogenic bacteria, with Sg and Ss being more pro-apoptotic and pro-pyroptotic than pathogenic bacteria. Oral commensal-induced cell death may be a physiological mechanism to manage the extent of bacterial colonization of the outer layers of mucosal epithelial surfaces. Dysbiosis-related reduction or elimination of pro-apoptotic oral bacterial species could contribute to the risk for persistent inflammation and tissue destruction.

Screening of Health-Associated Oral Bacteria for Anticancer Properties in vitro

While extensive literature exists about the role of oral bacterial pathogens like Porphyromonas gingivalis and Fusobacterium nucleatum in oral squamous cell carcinoma (OSCC), the role of health-associated species has been largely unexplored. In this study, we assessed the effect of Streptococcus mitis, Rothia mucilaginosa, Neisseria flavescens, Haemophilus parainfluenzae, Lautropia mirabilis, and Veillonella parvula on proliferation and expression of marker genes (IL-6, TNF-α, MMP3, CD36, CCD1, and NANOG) in OSCC cell lines CAL27, SCC25, and SCC4. Porphyromonas gingivalis was included as a pathogenic control. Both bacterial lysates (3 concentrations) and live cells (3 MOIs) were tested. S. mitis, H. parainfluenzae, and N. flavescens resulted in substantial, dose-dependent reduction of proliferation, which was found to be mediated by H₂O₂ for the former and intracellular infection in the latter two species. However, only H. parainfluenzae showed differential antiproliferative effect against the cancer cell lines vs. the normal control (TIGKs). In the gene expression assays, the health-associated species mostly downregulated CD36, a gene that plays an important role in tumor growth and metastasis, while P. gingivalis upregulated it. IL6 and TNF expression, on the other hand, was upregulated by almost all species, particularly the Gram-negatives including P. gingivalis. The effect on other genes was less evident and varied significantly by cell line. This exploratory study is the first insight into how health-associated bacteria may interact with OSCC. Further studies to explore whether the observed effects may have implications for the prevention or treatment of oral cancer are warranted.

Association or Causation? Exploring the Oral Microbiome and Cancer Links

Several epidemiological investigations have found associations between poor oral health and different types of cancer, including colorectal, lung, pancreatic, and oral malignancies. The oral health parameters underlying these relationships include deficient oral hygiene, gingival bleeding, and bone and tooth loss. These parameters are related to periodontal diseases, which are directly and indirectly mediated by oral bacteria. Given the increased accessibility of microbial sequencing platforms, many recent studies have investigated the link between the oral microbiome and these cancers. Overall, it seems that oral dysbiotic states can contribute to tumorigenesis in the oral cavity as well as in distant body sites. Further, it appears that certain oral bacterial species can contribute to carcinogenesis, in particular, Fusobacterium nucleatum and Porphyromonas gingivalis, based on results from epidemiological as well as mechanistic studies. Yet, the strength of the findings from these investigations is hampered by the heterogeneity of the methods used to measure oral diseases, the treatment of confounding factors, the study design, the platforms employed for microbial analysis, and types of samples analyzed. Despite these limitations, there is an overall indication that the presence of oral dysbiosis that leads to oral diseases may directly and/or indirectly contribute to carcinogenesis. Proper methodological standardized approaches should be implemented in future epidemiological studies as well as in the mechanistic investigations carried out to explore these results.

Porphyromonas gingivalis adopts intricate and unique molecular mechanisms to survive and persist within the host: a critical update

is an obligate, asaccharolytic, gram-negative bacteria commonly associated with increased periodontal and systemic inflammation. P. gingivalis is known to survive and persist within the host tissues as it modulates the entire ecosystem by either engineering its environment or modifying the host's immune response. It interacts with various host receptors and alters signaling pathways of inflammation, complement system, cell cycle, and apoptosis. P. gingivalis is even known to induce suicidal cell death of the host and other microbes in its vicinity with the emergence of pathobiont species. Recently, new molecular and immunological mechanisms and virulence factors of P. gingivalis that increase its chance of survival and immune evasion within the host have been discovered. Thus, the present paper aims to provide a consolidated update on the new intricate and unique molecular mechanisms and virulence factors of P. gingivalis associated with its survival, persistence, and immune evasion within the host.

In Vitro Effects of Streptococcus oralis Biofilm on Peri-Implant Soft Tissue Cells

Human gingival epithelial cells (HGEps) and fibroblasts (HGFs) are the main cell types in peri-implant soft tissue. HGEps are constantly exposed to bacteria, but HGFs are protected by connective tissue as long as the mucosa-implant seal is intact. Streptococcus oralis is one of the commensal bacteria, is highly abundant at healthy implant sites, and might modulate soft tissue cells-as has been described for other streptococci. We have therefore investigated the effects of the S. oralis biofilm on HGEps and HGFs. HGEps or HGFs were grown separately on titanium disks and responded to challenge with S. oralis biofilm. HGFs were severely damaged after 4 h, exhibiting transcriptional inflammatory and stress responses. In contrast, challenge with S. oralis only induced a mild transcriptional inflammatory response in HGEps, without cellular damage. HGFs were more susceptible to the S. oralis biofilm than HGEps. The pro-inflammatory interleukin 6 (IL-6) was attenuated in HGFs, as was interleukin 8 (CXCL8) in HGEps. This indicates that S. oralis can actively protect tissue. In conclusion, commensal biofilms can promote homeostatic tissue protection, but only if the implant-mucosa interface is intact and HGFs are not directly exposed.

A20 Restricts Inflammatory Response and Desensitizes Gingival Keratinocytes to Apoptosis

The pathophysiology of periodontal disease involves a perturbed immune system to a dysbiotic microflora leading to unrestrained inflammation, collateral tissue damage, and various systemic complications. Gingival epithelial cells function as an important part of immunity to restrict microbial invasion and orchestrate the subsequent innate responses. A20 (TNFAIP3), an ubiquitin-editing enzyme, is one of the key regulators of inflammation and cell death in numerous tissues including gastrointestinal tract, skin, and lungs. Emerging evidence indicates A20 as an essential molecule in the oral mucosa as well. In this study, we characterized the role of A20 in human telomerase immortalized gingival keratinocytes (TIGKs) through loss and gain of function assays in preclinical models of periodontitis. Depletion of A20 through gene editing in TIGKs significantly increased IL-6 and IL-8 secretion in response to Porphyromonas gingivalis infection while A20 over-expression dampened the cytokine production compared to A20 competent cells through modulating NF-κB signaling pathway. In the subsequent experiments which assessed apoptosis, A20 depleted TIGKs displayed increased levels of cleaved caspase 3 and DNA fragmentation following P. gingivalis infection and TNF/CHX challenge compared to A20 competent cells. Consistently, there was reduced apoptosis in the cells overexpressing A20 compared to the control cells expressing GFP further substantiating the role of A20 in regulating gingival epithelial cell fate in response to exogenous insult. Collectively, our findings reveal first systematic evidence and demonstrate that A20 acts as a regulator of inflammatory response in gingival keratinocytes through its effect on NF-κB signaling and desensitizes cells to bacteria and cytokine induced apoptosis in the oral mucosa. As altered A20 levels can have profound effect on different cellular responses, future studies will determine whether A20-targeted therapies can be exploited to restrain periodontal inflammation and maintain oral mucosa tissue homeostasis.

From Beyond the Pale to the Pale Riders: The Emerging Association of Bacteria with Oral Cancer

Oral cancer, predominantly oral squamous cell carcinoma (OSCC), is the eighth-most common cancer worldwide, with a 5-y survival rate <50%. There are numerous risk factors for oral cancer, among which periodontal disease is gaining increasing recognition. The creation of a sustained dysbiotic proinflammatory environment by periodontal bacteria may serve to functionally link periodontal disease and oral cancer. Moreover, traditional periodontal pathogens, such as Porphyromonas gingivalis, Fusobacterium nucleatum, and Treponema denticola, are among the species most frequently identified as being enriched in OSCC, and they possess a number of oncogenic properties. These organisms share the ability to attach and invade oral epithelial cells, and from there each undergoes its own unique molecular dialogue with the host epithelium, which ultimately converges on acquired phenotypes associated with cancer, including inhibition of apoptosis, increased proliferation, and activation of epithelial-to-mesenchymal transition leading to increased migration of epithelial cells. Additionally, emerging properties of structured bacterial communities may increase oncogenic potential, and consortia of P. gingivalis and F. nucleatum are synergistically pathogenic within in vivo oral cancer models. Interestingly, however, some species of oral streptococci can antagonize the phenotypes induced by P. gingivalis, indicating functionally specialized roles for bacteria in oncogenic communities. Transcriptomic data support the concept that functional, rather than compositional, properties of oral bacterial communities have more relevance to cancer development. Collectively, the evidence is consistent with a modified polymicrobial synergy and dysbiosis model for bacterial involvement in OSCC, with driver mutations generating a conducive microenvironment on the epithelial boundary, which becomes further dysbiotic by the synergistic action of bacterial communities.