B cells promote obesity-associated periodontitis and oral pathogen-associated inflammation

Periodontitis and Diabetes Differentially Affect Inflammation in Obesity

Periodontitis (PD) potentiates systemic inflammatory diseases and fuels a feed-forward loop of pathogenic inflammation in obesity and type 2 diabetes (T2D). Published work in this area often conflates obesity with obesity-associated T2D; thus, it remains unclear whether PD similarly affects the inflammatory profiles of these 2 distinct systemic diseases. We collected peripheral blood mononuclear cells (PBMCs) from cross-sectionally recruited subjects to estimate the ability of PD to affect cytokine production in human obesity and/or T2D. We analyzed 2 major sources of systemic inflammation: T cells and myeloid cells. Bioplex quantitated cytokines secreted by PBMCs stimulated with T cell- or myeloid-targeting activators, and we combinatorially analyzed outcomes using partial least squares discriminant analysis. Our data show that PD significantly shifts peripheral T cell- and myeloid-generated inflammation in obesity. PD also changed myeloid- but not T cell-generated inflammation in T2D. T2D changed inflammation in samples from subjects with PD, and PD changed inflammation in samples from subjects with T2D, consistent with the bidirectional relationship of inflammation between these 2 conditions. PBMCs from T2D subjects with stage IV PD produced lower amounts of T cell and myeloid cytokines compared with PBMCs from T2D subjects with stage II to III PD. We conclude that PD and T2D affect systemic inflammation through overlapping but nonidentical mechanisms in obesity, indicating that characterizing both oral and metabolic status (beyond obesity) is critical for identifying mechanisms linking PD to systemic diseases such as obesity and T2D. The finding that stage IV PD cells generate fewer cytokines in T2D provides an explanation for the paradoxical findings that the immune system can appear activated or suppressed in PD, given that many studies do not report PD stage. Finally, our data indicate that a focus on multiple cellular sources of cytokines will be imperative to clinically address the systemic effects of PD in people with obesity.

Obesity-associated Airway Hyperresponsiveness: Mechanisms Underlying Inflammatory Markers and Possible Pharmacological Interventions

Obesity is rapidly becoming a global health problem affecting about 13% of the world's population affecting women and children the most. Recent studies have stated that obese asthmatic subjects suffer from an increased risk of asthma, encounter severe symptoms, respond poorly to anti-asthmatic drugs, and ultimately their quality-of-life decreases. Although, the association between airway hyperresponsiveness (AHR) and obesity is a growing concern among the public due to lifestyle and environmental etiologies, however, the precise mechanism underlying this association is yet to establish. Apart from aiming at the conventional antiasthmatic targets, treatment should be directed towards ameliorating obesity pathogenesis too. Understanding the pathogenesis underlying the association between obesity and AHR is limited, however, a plethora of obesity pathologies have been reported viz., increased pro-inflammatory and decreased anti-inflammatory adipokines, depletion of ROS controller Nrf2/HO-1 axis, NLRP3 associated macrophage polarization, hypertrophy of WAT, and down-regulation of UCP1 in BAT following down-regulated AMPKα and melanocortin pathway that may be correlated with AHR. Increased waist circumference (WC) or central obesity was thought to be related to severe AHR, however, some recent reports suggest body mass index (BMI), not WC tends to exaggerate airway closure in AHR due to some unknown mechanisms. This review aims to co-relate the above-mentioned mechanisms that may explain the copious relation underlying obesity and AHR with the help of published reports. A proper understanding of these mechanisms discussed in this review will ensure an appropriate treatment plan for patients through advanced pharmacological interventions.

Influence of type 2 diabetes on immunohistochemical detection of TRAF6, cFos and NFATC1 in the gingiva in cases of chronic periodontitis

Type 2 diabetes (T2D) and chronic periodontitis (CP) are common diseases worldwide. Although T2D increases the severity of CP and alveolar bone loss, the mechanism of this is not well understood. We investigated using immunohistochemistry the expression of three osteoclast proteins, TRAF6, cFos and NFATc1, in gingival tissues. Gingival tissues were obtained from three groups: HC group, healthy controls; CP group, patients with CP; T2D + CP group, patients with both T2D and CP. Strong immunostaining for TRAF6, cFos and NFATc1 was observed in the gingival epithelium as well as in inflammatory cells in the CP and T2D + CP groups. Immunostaining was most intense in the T2D + CP group. We found strong up-regulation of TRAF6, cFos and NFATC1 in gingiva tissue of subjects with both T2D and CP, which corroborates our hypothesis that T2D potentiates osteoclastogenesis in CP.

Immunomodulatory nanotherapeutic approaches for periodontal tissue regeneration

Periodontitis is an infection-induced inflammatory disease characterized by progressive destruction of tooth supporting tissues, which, if left untreated, can result in tooth loss. The destruction of periodontal tissues is primarily caused by an imbalance between the host immune protection and immune destruction mechanisms. The ultimate goal of periodontal therapy is to eliminate inflammation and promote the repair and regeneration of both hard and soft tissues, so as to restore the physiological structure and function of periodontium. Advancement in nanotechnologies has enabled the development of nanomaterials with immunomodulatory properties for regenerative dentistry. This review discusses the immune mechanisms of the major effector cells in the innate and adaptive immune systems, the physicochemical and biological properties of nanomaterials, and the research advancements in immunomodulatory nanotherapeutic approaches for the management of periodontitis and the regeneration of periodontal tissues. The current challenges, and prospects for future applications of nanomaterials are then discussed so that researchers at the intersections of osteoimmunology, regenerative dentistry and materiobiology will continue to advance the development of nanomaterials for improved periodontal tissue regeneration.

Comparative Analysis of Gene Expression Patterns for Oral Epithelial Cell Functions in Periodontitis

The structure and function of epithelial cells are critical for the construction and maintenance of intact epithelial surfaces throughout the body. Beyond the mechanical barrier functions, epithelial cells have been identified as active participants in providing warning signals to the host immune and inflammatory cells and in communicating various detailed information on the noxious challenge to help drive specificity in the characteristics of the host response related to health or pathologic inflammation. Rhesus monkeys were used in these studies to evaluate the gingival transcriptome for naturally occurring disease samples (GeneChip® Rhesus Macaque Genome Array) or for ligature-induced disease (GeneChip® Rhesus Gene 1.0 ST Array) to explore up to 452 annotated genes related to epithelial cell structure and functions. Animals were distributed by age into four groups: ≤ 3 years (young), 3–7 years (adolescent), 12–16 years (adult), and 18–23 years (aged). For naturally occurring disease, adult and aged periodontitis animals were used, which comprised 34 animals (14 females and 20 males). Groups of nine animals in similar age groups were included in a ligature-induced periodontitis experiment. A buccal gingival sample from either healthy or periodontitis-affected tissues were collected, and microarray analysis performed. The overall results of this investigation suggested a substantial alteration in epithelial cell functions that occurs rapidly with disease initiation. Many of these changes were prolonged throughout disease progression and generally reflect a disruption of normal cellular functions that would presage the resulting tissue destruction and clinical disease measures. Finally, clinical resolution may not signify biological resolution and represent a continued risk for disease that may require considerations for additional biologically specific interventions to best manage further disease.

Adaptive immune cells shape obesity-associated type 2 diabetes mellitus and less prominent comorbidities

Obesity and type 2 diabetes mellitus (T2DM) are increasing in prevalence owing to decreases in physical activity levels and a shift to diets that include addictive and/or high-calorie foods. These changes are associated with the adoption of modern lifestyles and the presence of an obesogenic environment, which have resulted in alterations to metabolism, adaptive immunity and endocrine regulation. The size and quality of adipose tissue depots in obesity, including the adipose tissue immune compartment, are critical determinants of overall health. In obesity, chronic low-grade inflammation can occur in adipose tissue that can progress to systemic inflammation; this inflammation contributes to the development of insulin resistance, T2DM and other comorbidities. An improved understanding of adaptive immune cell dysregulation that occurs during obesity and its associated metabolic comorbidities, with an appreciation of sex differences, will be critical for repurposing or developing immunomodulatory therapies to treat obesity and/or T2DM-associated inflammation. This Review critically discusses how activation and metabolic reprogramming of lymphocytes, that is, T cells and B cells, triggers the onset, development and progression of obesity and T2DM. We also consider the role of immunity in under-appreciated comorbidities of obesity and/or T2DM, such as oral cavity inflammation, neuroinflammation in Alzheimer disease and gut microbiome dysbiosis. Finally, we discuss previous clinical trials of anti-inflammatory medications in T2DM and consider the path forward.

Influence of anti-rheumatic agents on the periodontal condition of patients with rheumatoid arthritis and periodontitis: A systematic review and meta-analysis

OBJECTIVE

To evaluate the influence of diverse anti-rheumatic agents on the periodontal condition and to provide clinical medication guidance for patients with rheumatoid arthritis (RA) and periodontitis.

BACKGROUND

In recent years, the correlation between RA and periodontitis has become a hot research topic, but no medication recommendations for patients with RA and periodontitis are available at present.

METHODS

The protocol of this review was registered in advance with PROSPERO (CRD42021248827). Electronic search and manual searches up to March 20, 2021 were conducted. The inclusion criteria for the studies were as follows: included patients diagnosed with periodontitis and RA submitted to anti-rheumatic agent therapy; with a control group receiving no anti-rheumatic agent therapy; with outcomes including at least one periodontal parameter. Probing depth (PD) and clinical attachment loss (CAL) were pooled using weighted mean difference (WMD) and 95% confidence intervals (CI) while gingival index (GI)/modified gingival index (MGI) was analyzed by standardized mean difference (SMD) and 95% CI.

RESULTS

One thousand four hundred and seventy-eight studies potentially related to the aim of this review were screened, but only 463 patients from 14 studies were included in the qualitative analysis, and 146 patients from 4 studies were included in the meta-analysis. Statistically significant reductions were observed among the subjects who received anti-rheumatic agents for PD [WMD = -0.20; 95% CI (-0.33, -0.07); effect p = .003; I²  = 50%; p = .11], CAL [WMD = -0.4; 95% CI (-0.66, -0.15); effect p = .002; I²  = 57%; p = .07] and GI/MGI [SMD = -0.61;95% CI (-0.94, -0.27; effect p = .0004; I²  = 26%; p = .25]. Consistent with the above results, this systematic review produced promising results that PD, CAL, GI/MGI, and bleeding on probing (BOP) decreased when patients with RA and periodontitis were treated with conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs), anti-B lymphocyte agents, anti-IL-6R agents, or JAK inhibitors. PD and CAL declined after the administration of anti-TNF-α agents; most studies reported decreased GI/MGI and BOP, while 2 studies reported increased GI/MGI and BOP.

CONCLUSIONS

These results revealed that csDMARDs, anti-B lymphocyte agents, anti-IL-6R agents, anti-TNF-α agents, and JAK inhibitors had potential positive effects in improving the periodontal condition of patients with RA and periodontitis. However, future research is needed to elucidate whether anti-TNF-α agents have a side effect of increased gingival inflammation.

Biocompatibility Evolves: Phenomenology to Toxicology to Regeneration

The word "biocompatibility," is inconsistent with the observations of healing for so-called biocompatible biomaterials. The vast majority of the millions of medical implants in humans today, presumably "biocompatible," are walled off by a dense, avascular, crosslinked collagen capsule, hardly suggestive of life or compatibility. In contrast, one is now seeing examples of implant biomaterials that lead to a vascularized reconstruction of localized tissue, a biological reaction different from traditional biocompatible materials that generate a foreign body capsule. Both the encapsulated biomaterials and the reconstructive biomaterials qualify as "biocompatible" by present day measurements of biocompatibility. Yet, this new generation of materials would seem to heal "compatibly" with the living organism, where older biomaterials are isolated from the living organism by the dense capsule. This review/perspective article will explore this biocompatibility etymological conundrum by reviewing the history of the concepts around biocompatibility, today's standard methods for assessing biocompatibility, a contemporary view of the foreign body reaction and finally, a compendium of new biomaterials that heal without the foreign body capsule. A new definition of biocompatibility is offered here to address advances in biomaterials design leading to biomaterials that heal into the body in a facile manner.

Porphyromonas gingivalis induces periodontitis, causes immune imbalance, and promotes rheumatoid arthritis

Periodontitis induced by bacteria especially Porphyromonas gingivalis (P. gingivalis) is the most prevalent microbial disease worldwide and is a significant risk factor for systemic diseases such as rheumatoid arthritis (RA). RA and periodontitis share similar clinical and pathologic features. Moreover, the prevalence of RA is much higher in patients with periodontitis than in those without periodontitis. To explore the immunologic mechanism of periodontitis involved in RA, we established a mouse model of periodontitis and then induced RA. According to the results of paw thickness, arthritis clinical score, arthritis incidence, microscopic lesion using H&E staining, and micro-CT analysis, periodontitis induced by P. gingivalis promoted the occurrence and development of collagen-induced arthritis (CIA) in mice. Furthermore, periodontitis enhanced the frequency of CD19⁺ B cells, Th17, Treg, gMDSCs, and mMDSCs, whereas down-regulated IL-10 producing regulatory B cells (B10) in CIA mice preinduced for periodontitis with P. gingivalis. In vitro stimulation with splenic cells revealed that P. gingivalis directly enhanced differentiation of Th17, Treg, and mMDSCs but inhibited the process of B cell differentiation into B10 cells. Considering that adoptive transfer of B10 cells prevent RA development, our study, although preliminary, suggests that down-regulation of B10 cells may be the key mechanism that periodontitis promotes RA as the other main immune suppressive cells such as Treg and MDSCs are up-regulated other than down-regulated in group of P. gingivalis plus CIA.

Role of Tonsillar Chronic Inflammation and Commensal Bacteria in the Pathogenesis of Pediatric OSA

Immune responses at the boundary between the host and the world beyond are complex and mucosal tissue homeostasis relies on them. Obstructive sleep apnea (OSA) is a syndrome suffered by children with hypertrophied tonsils. We have previously demonstrated that these tonsils present a defective regulatory B cell (Breg) compartment. Here, we extend those findings by uncovering the crucial role of resident pro-inflammatory B and T cells in sustaining tonsillar hypertrophy and hyperplasia by producing TNFα and IL17, respectively, in ex vivo cultures. Additionally, we detected prominent levels of expression of CD1d by tonsillar stratified as well as reticular epithelium, which have not previously been reported. Furthermore, we evidenced the hypertrophy of germinal centers (GC) and the general hyperplasia of B lymphocytes within the tissue and the lumen of the crypts. Of note, such B cells resulted mainly (IgG/IgM)⁺ cells, with some IgA⁺ cells located marginally in the follicles. Finally, by combining bacterial culture from the tonsillar core and subsequent identification of the respective isolates, we determined the most prevalent species within the cohort of OSA patients. Although the isolated species are considered normal oropharyngeal commensals in children, we confirmed their capacity to breach the epithelial barrier. Our work sheds light on the pathological mechanism underlying OSA, highlighting the relevance taken by the host immune system when defining infection versus colonization, and opening alternatives of treatment.

Phenotypes, roles, and modulation of regulatory lymphocytes in periodontitis and its associated systemic diseases

Periodontitis is a common chronic inflammatory disease that can result in tooth loss and poses a risk to systemic health. Lymphocytes play important roles in periodontitis through multiple mechanisms. Regulatory lymphocytes including regulatory B cells (Bregs) and T cells (Tregs) are the main immunosuppressive cells that maintain immune homeostasis, and are critical to our understanding of the pathogenesis of periodontitis and the development of effective treatments. In this review, we discuss the phenotypes, roles, and modulating strategies of regulatory lymphocytes including Bregs and Tregs in periodontitis and frequently cooccurring inflammatory diseases such as rheumatoid arthritis, Alzheimer disease, diabetes mellitus, and stroke. The current evidence suggests that restoring immune balance through therapeutic targeting of regulatory lymphocytes is a promising strategy for the treatment of periodontitis and other systemic inflammatory diseases.

Polymicrobial communities in periodontal disease: Their quasi-organismal nature and dialogue with the host

In health, indigenous polymicrobial communities at mucosal surfaces maintain an ecological balance via both inter-microbial and host-microbial interactions that promote their own and the host's fitness, while preventing invasion by exogenous pathogens. However, genetic and acquired destabilizing factors (including immune deficiencies, immunoregulatory defects, smoking, diet, obesity, diabetes and other systemic diseases, and aging) may disrupt this homeostatic balance, leading to selective outgrowth of species with the potential for destructive inflammation. This process, known as dysbiosis, underlies the development of periodontitis in susceptible hosts. The pathogenic process is not linear but involves a positive-feedback loop between dysbiosis and the host inflammatory response. The dysbiotic community is essentially a quasi-organismal entity, where constituent organisms communicate via sophisticated physical and chemical signals and display functional specialization (eg, accessory pathogens, keystone pathogens, pathobionts), which enables polymicrobial synergy and dictates the community's pathogenic potential or nososymbiocity. In this review, we discuss early and recent studies in support of the polymicrobial synergy and dysbiosis model of periodontal disease pathogenesis. According to this concept, disease is not caused by individual "causative pathogens" but rather by reciprocally reinforced interactions between physically and metabolically integrated polymicrobial communities and a dysregulated host inflammatory response.

Single-Cell Analysis of the Periodontal Immune Niche in Type 2 Diabetes

Periodontitis (PD) is a common source of uncontrolled inflammation in obesity-associated type 2 diabetes (T2D). PD apparently fuels the inflammation of T2D and associates with poor glycemic control and increased T2D morbidity. New therapeutics are critically needed to counter the sources of periodontal infection and inflammation that are accelerated in people with T2D. The precise mechanisms underlying the relationship between PD and T2D remain poorly understood. Every major immune cell subset has been implicated in the unresolved inflammation of PD, regardless of host metabolic health. However, analyses of inflammatory cells in PD with human periodontal tissue have generally focused on mRNA quantification and immunohistochemical analyses, both of which provide limited information on immune cell function. We used a combination of flow cytometry for cell surface markers and enzyme-linked immunospot methods to assess the subset distribution and function of immune cells isolated from gingiva of people who had PD and were systemically healthy, had PD and T2D (PD/T2D), or, for flow cytometry, were systemically and orally healthy. T-cell subsets dominated the cellular immune compartment in gingiva from all groups, and B cells were relatively rare. Although immune cell frequencies were similar among groups, a higher proportion of CD11b⁺ or CD4⁺ cells secreted IFNγ/IL-10 or IL-8, respectively, in cells from PD/T2D samples as compared with PD-alone samples. Our data indicate that fundamental differences in gingival immune cell function between PD and T2D-potentiated PD may account for the increased risk and severity of PD in subjects with T2D. Such differences may suggest unexpected therapeutic targets for alleviating periodontal inflammation in people with T2D.

Osteoimmunology: Inflammatory osteolysis and regeneration of the alveolar bone

AIM

Osteoimmunology covers the cellular and molecular mechanisms responsible for inflammatory osteolysis that culminates in the degradation of alveolar bone. Osteoimmunology also focuses on the interplay of immune cells with bone cells during bone remodelling and regeneration. The aim of this review was to provide insights into how osteoimmunology affects alveolar bone health and disease.

METHOD

This review is based on a narrative approach to assemble mouse models that provide insights into the cellular and molecular mechanisms causing inflammatory osteolysis and on the impact of immune cells on alveolar bone regeneration.

RESULTS

Mouse models have revealed the molecular pathways by which microbial and other factors activate immune cells that initiate an inflammatory response. The inflammation-induced alveolar bone loss occurs with the concomitant suppression of bone formation. Mouse models also showed that immune cells contribute to the resolution of inflammation and bone regeneration, even though studies with a focus on alveolar socket healing are rare.

CONCLUSIONS

Considering that osteoimmunology is evolutionarily conserved, osteolysis removes the cause of inflammation by provoking tooth loss. The impact of immune cells on bone regeneration is presumably a way to reinitiate the developmental mechanisms of intramembranous and endochondral bone formation.

Aberrant Periodontal and Systemic Immune Response of Overweight Rodents to Periodontal Infection

This study aimed to explore periodontal and systemic immune response of overweight hosts to periodontitis. Forty C57 BL/6J male mice were divided into high (HF) or low fat (LF) diet groups and fed with the two diets, respectively, for 8 weeks. Each diet group was then divided into periodontitis (P) or control (C) groups (n = 10 per group) for 10-day ligation or sham-ligation. Overweight-related parameters including body weight were measured. Alveolar bone loss (ABL) was morphometrically analyzed and periodontal osteoclasts were stained. Periodontal immune response including leukocyte and macrophage number and inflammatory cytokines were analyzed by histology and quantitative PCR. Serum cytokine and lipid levels were quantified using electrochemiluminescence immunoassays, enzyme-linked immunosorbent assays, and biochemistry. It was found that HF group had 14.4% body weight gain compared with LF group (P < 0.01). ABL and periodontal osteoclast, leukocyte, and macrophage number were higher in P group than C group regardless of diet (P < 0.05). ABL and periodontal osteoclast number were not affected by diet regardless of ligation or sham-ligation. Leukocyte and macrophage number and protein level of tumor necrosis factor α (TNF-α) in periodontium and serum interleukin-6 level were downregulated by HF diet in periodontitis mice (P < 0.05). Periodontal protein level of TNF-α was highly correlated with serum interleukin-6 and low-density lipoprotein cholesterol levels (P < 0.01). These findings indicated that impaired immune response occurs both periodontally and systemically in preobesity overweight individuals. Given a well-reported exacerbating effect of obesity on periodontitis, overweight, if let uncontrolled, might place the individuals at potential risk for future periodontal tissue damage.

[Impacts of periodontitis on visceral organ weight and weight percentage in obese mice]

OBJECTIVE

This study aimed to explore the impacts of periodontitis on the visceral weight and weight percentage of obese animal models.

METHODS

A total of 64 C57BL/6J mice were divided into the following diet groups: high-fat diet (HFD) group (n=36), which was fed with high-fat diet to induce obesity, and low-fat diet (LFD) group (n=28), which was fed with low-fat diet as the control. After 16 weeks on diet, each diet group was divided into periodontitis (P) and control (C) groups. The P groups were induced for periodontitis by ligation with Porphyromonas gingivalis-adhered silk for 5 or 10 days, and the C groups were sham-ligated as the control. Visceral organs were resected and weighed. The organ weight percentage was calculated.

RESULTS

Compared with the LFD group, the HFD group significantly upregulated the weight and weight percentage of visceral adipose tissue and spleen (P<0.05), upregulated the weight of liver and kidney (P<0.05), and downregulated the weight percentage of liver and kidney (P<0.01). In the HFD group, the weight and weight percentage of spleen were downregulated in the P group (P<0.05), but were upregulated in the 10-day group compared with the 5-day group (P<0.05).

CONCLUSIONS

Periodontitis can affect the general morphology of the viscera (especially spleen) in obese animal models. Pathological indications in terms of immunometabolism might be present in the correlation between obesity and periodontitis.

Revisiting the Page & Schroeder model: the good, the bad and the unknowns in the periodontal host response 40 years later

In their classic 1976 paper, Page & Schroeder described the histopathologic events and the types of myeloid cells and lymphocytes involved in the initiation and progression of inflammatory periodontal disease. The staging of periodontal disease pathogenesis as 'initial', 'early', 'established' and 'advanced' lesions productively guided subsequent research in the field and remains fundamentally valid. However, major advances regarding the cellular and molecular mechanisms underlying the induction, regulation and effector functions of immune and inflammatory responses necessitate a reassessment of their work and its integration with emerging new concepts. We now know that each type of leukocyte is actually represented by functionally distinct subsets with different, or even conflicting, roles in immunity and inflammation. Unexpectedly, neutrophils, traditionally regarded as merely antimicrobial effectors in acute conditions and protagonists of the 'initial' lesion, are currently appreciated for their functional versatility and critical roles in chronic inflammation. Moreover, an entirely new field of study, osteoimmunology, has emerged and sheds light on the impact of immunoinflammatory events on the skeletal system. These developments and the molecular dissection of crosstalk interactions between innate and adaptive leukocytes, as well as between the immune system and local homeostatic mechanisms, offer a more nuanced understanding of the host response in periodontitis, with profound implications for treatment. At the same time, deeper insights have generated new questions, many of which remain unanswered. In this review, 40 years after Page & Schroeder proposed their model, we summarize enduring and emerging advances in periodontal disease pathogenesis.

Adaptive Immunity and Metabolic Health: Harmony Becomes Dissonant in Obesity and Aging

Adipose tissue (AT) is the primary energy reservoir organ, and thereby plays a critical role in energy homeostasis and regulation of metabolism. AT expands in response to chronic overnutrition or aging and becomes a major source of inflammation that has marked influence on systemic metabolism. The chronic, sterile inflammation that occurs in the AT during the development of obesity or in aging contributes to onset of devastating diseases such as insulin resistance, diabetes, and cardiovascular pathologies. Numerous studies have shown that inflammation in the visceral AT of humans and animals is a critical trigger for the development of metabolic syndrome. This work underscores the well-supported conclusion that the inflammatory immune response and metabolic pathways in the AT are tightly interwoven by multiple layers of relatively conserved mechanisms. During the development of diet-induced obesity or age-associated adiposity, cells of the innate and the adaptive immune systems infiltrate and proliferate in the AT. Macrophages, which dominate AT-associated immune cells in mouse models of obesity, but are less dominant in obese people, have been studied extensively. However, cells of the adaptive immune system, including T cells and B cells, contribute significantly to AT inflammation, perhaps more in humans than in mice. Lymphocytes regulate recruitment of innate immune cells into AT, and produce cytokines that influence the helpful-to-harmful inflammatory balance that, in turn, regulates organismal metabolism. This review describes inflammation, or more precisely, metabolic inflammation (metaflammation) with an eye toward the AT and the roles lymphocytes play in regulation of systemic metabolism during obesity and aging. © 2017 American Physiological Society. Compr Physiol 7:1307-1337, 2017.

Quantifying deleterious effects of regulatory variants

The majority of genome-wide association study (GWAS) risk variants reside in non-coding DNA sequences. Understanding how these sequence modifications lead to transcriptional alterations and cell-to-cell variability can help unraveling genotype-phenotype relationships. Here, we describe a computational method, dubbed CAPE, which calculates the likelihood of a genetic variant deactivating enhancers by disrupting the binding of transcription factors (TFs) in a given cellular context. CAPE learns sequence signatures associated with putative enhancers originating from large-scale sequencing experiments (such as ChIP-seq or DNase-seq) and models the change in enhancer signature upon a single nucleotide substitution. CAPE accurately identifies causative cis-regulatory variation including expression quantitative trait loci (eQTLs) and DNase I sensitivity quantitative trait loci (dsQTLs) in a tissue-specific manner with precision superior to several currently available methods. The presented method can be trained on any tissue-specific dataset of enhancers and known functional variants and applied to prioritize disease-associated variants in the corresponding tissue.

Macrophage functions in lean and obese adipose tissue

Interactions between macrophages and adipocytes influence both metabolism and inflammation. Obesity-induced changes to macrophages and adipocytes lead to chronic inflammation and insulin resistance. This paper reviews the various functions of macrophages in lean and obese adipose tissue and how obesity alters adipose tissue macrophage phenotypes. Metabolic disease and insulin resistance shift the balance between numerous pro- and anti-inflammatory regulators of macrophages and create a feed-forward loop of increasing inflammatory macrophage activation and worsening adipocyte dysfunction. This ultimately leads to adipose tissue fibrosis and diabetes. The molecular mechanisms underlying these processes have therapeutic implications for obesity, metabolic syndrome, and diabetes.

Periodontitis induced by Porphyromonas gingivalis drives periodontal microbiota dysbiosis and insulin resistance via an impaired adaptive immune response

OBJECTIVE

To identify a causal mechanism responsible for the enhancement of insulin resistance and hyperglycaemia following periodontitis in mice fed a fat-enriched diet.

DESIGN

We set-up a unique animal model of periodontitis in C57Bl/6 female mice by infecting the periodontal tissue with specific and alive pathogens like Porphyromonas gingivalis (Pg), Fusobacterium nucleatum and Prevotella intermedia. The mice were then fed with a diabetogenic/non-obesogenic fat-enriched diet for up to 3 months. Alveolar bone loss, periodontal microbiota dysbiosis and features of glucose metabolism were quantified. Eventually, adoptive transfer of cervical (regional) and systemic immune cells was performed to demonstrate the causal role of the cervical immune system.

RESULTS

Periodontitis induced a periodontal microbiota dysbiosis without mainly affecting gut microbiota. The disease concomitantly impacted on the regional and systemic immune response impairing glucose metabolism. The transfer of cervical lymph-node cells from infected mice to naive recipients guarded against periodontitis-aggravated metabolic disease. A treatment with inactivated Pg prior to the periodontal infection induced specific antibodies against Pg and protected the mouse from periodontitis-induced dysmetabolism. Finally, a 1-month subcutaneous chronic infusion of low rates of lipopolysaccharides from Pg mimicked the impact of periodontitis on immune and metabolic parameters.

CONCLUSIONS

We identified that insulin resistance in the high-fat fed mouse is enhanced by pathogen-induced periodontitis. This is caused by an adaptive immune response specifically directed against pathogens and associated with a periodontal dysbiosis.

The emerging roles of B cells as partners and targets in periodontitis

Initial studies of periodontal disease suggested that T cell-mediated immunity against oral Gram-negative microorganisms is a key player in the pathogenesis of this inflammatory disease. Recent investigations, however, revealed that B cells are also engaged. Given their chief role in innate-like and adaptive immune responses, B cells could exert protective functions in periodontitis. However, the periodontal bacteria-specific antibody response is generally unable to halt disease progression in affected subjects, suggesting that the antibodies produced could exhibit low anti-bacterial blocking functions or opsonophagocytic potential, and/or unfavorable effects. Moreover, although microbial antigens are involved in the induction of the inflammatory responses in human adult periodontitis, endogenous antigens also may contribute to the chronicity of this common disease. Not only antibodies to self-antigens, such as collagen, are locally produced, but the autoreactivities observed in aggressive periodontitis are more severe and diverse than those observed in chronic periodontitis, suggesting that autoimmune reactivity could play a role in the tissue destruction of periodontal disease. Further support for a pathological role of B cells in periodontitis comes from the finding that B cell-deficient mice are protected from bacterial infection-induced alveolar bone loss. Studies in patients indicate that B cells and plasma cells, together with osteoclastogenic factors (RANKL and osteoprotegerin) and specific cytokines involved in their growth and differentiation (BAFF and APRIL) participate in the induction of the pathological bone loss in periodontitis. This novel insight suggests that selective targeting of B cells could represent a future therapeutic avenue for severe periodontal disease.

Variants of Porphyromonas gingivalis lipopolysaccharide alter lipidation of autophagic protein, microtubule-associated protein 1 light chain 3, LC3

Porphyromonas gingivalis often subverts host cell autophagic processes for its own survival. Our previous studies document the association of the cargo sorting protein, melanoregulin (MREG), with its binding partner, the autophagic protein, microtubule-associated protein 1 light chain 3 (LC3) in macrophages incubated with P. gingivalis (strain 33277). Differences in the lipid A moiety of lipopolysaccharide (LPS) affect the virulence of P. gingivalis; penta-acylated LPS₁₆₉₀ is a weak Toll-like receptor 4 agonist compared with Escherichia coli LPS, whereas tetra-acylated LPS_1435/1449 acts as an LPS₁₆₉₀ antagonist. To determine how P. gingivalis LPS₁₆₉₀ affects autophagy we assessed LC3-dependent and MREG-dependent processes in green fluorescent protein (GFP)-LC3-expressing Saos-2 cells. LPS₁₆₉₀ stimulated the formation of very large LC3-positive vacuoles and MREG puncta. This LPS₁₆₉₀ -mediated LC3 lipidation decreased in the presence of LPS_1435/1449 . When Saos-2 cells were incubated with P. gingivalis the bacteria internalized but did not traffic to GFP-LC3-positive structures. Nevertheless, increases in LC3 lipidation and MREG puncta were observed. Collectively, these results suggest that P. gingivalis internalization is not necessary for LC3 lipidation. Primary human gingival epithelial cells isolated from patients with periodontitis showed both LC3II and MREG puncta whereas cells from disease-free individuals exhibited little co-localization of these two proteins. These results suggest that the prevalence of a particular LPS moiety may modulate the degradative capacity of host cells, so influencing bacterial survival.

Activation and resolution of periodontal inflammation and its systemic impact

Inflammation is a highly organized event impacting upon organs, tissues and biological systems. Periodontal diseases are characterized by dysregulation or dysfunction of resolution pathways of inflammation that results in failure to heal and in a dominant chronic, progressive, destructive and predominantly unresolved inflammation. The biological consequences of inflammatory processes may be independent of the etiological agents, such as trauma, microbial organisms and stress. The impact of the inflammatory pathological process depends upon the tissues or organ system affected. Whilst mediators are similar, there is tissue specificity for the inflammatory events. It is plausible that inflammatory processes in one organ could directly lead to pathologies in another organ or tissue. Communication between distant parts of the body and their inflammatory status is also mediated by common signaling mechanisms mediated via cells and soluble mediators. This review focuses on periodontal inflammation, its systemic associations and advances in therapeutic approaches based on mediators acting through orchestration of natural pathways to resolution of inflammation. We also discuss a new treatment concept in which natural pathways of resolution of periodontal inflammation can be used to limit systemic inflammation and promote healing and regeneration.

The B Cell-Stimulatory Cytokines BLyS and APRIL Are Elevated in Human Periodontitis and Are Required for B Cell-Dependent Bone Loss in Experimental Murine Periodontitis

B-lineage cells (B lymphocytes and plasma cells) predominate in the inflammatory infiltrate of human chronic periodontitis. However, their role in disease pathogenesis and the factors responsible for their persistence in chronic lesions are poorly understood. In this regard, two cytokines of the TNF ligand superfamily, a proliferation-inducing ligand (APRIL) and B-lymphocyte stimulator (BLyS), are important for the survival, proliferation, and maturation of B cells. Thus, we hypothesized that APRIL and/or BLyS are upregulated in periodontitis and contribute to induction of periodontal bone loss. This hypothesis was addressed in both human and mouse experimental systems. We show that, relative to healthy controls, the expression of APRIL and BLyS mRNA and protein was upregulated in natural and experimental periodontitis in humans and mice, respectively. The elevated expression of these cytokines correlated with increased numbers of B cells/plasma cells in both species. Moreover, APRIL and BLyS partially colocalized with κ L chain-expressing B-lineage cells at the epithelial-connective tissue interface. Ligature-induced periodontitis resulted in significantly less bone loss in B cell-deficient mice compared with wild-type controls. Ab-mediated neutralization of APRIL or BLyS diminished the number of B cells in the gingival tissue and inhibited bone loss in wild-type, but not in B cell-deficient, mice. In conclusion, B cells and specific cytokines involved in their growth and differentiation contribute to periodontal bone loss. Moreover, APRIL and BLyS have been identified as potential therapeutic targets in periodontitis.

A Dual Role for P2X7 Receptor during Porphyromonas gingivalis Infection

Emerging evidence suggests a role for purinergic signaling in the activation of multiprotein intracellular complexes called inflammasomes, which control the release of potent inflammatory cytokines, such as interleukin (IL) -1β and -18. Porphyromonas gingivalis is intimately associated with periodontitis and is currently considered one of the pathogens that can subvert the immune system by limiting the activation of the NLRP3 inflammasome. We recently showed that P. gingivalis can dampen eATP-induced IL-1β secretion by means of its fimbriae in a purinergic P2X7 receptor-dependent manner. Here, we further explore the role of this purinergic receptor during eATP-induced IL-1β processing and secretion by P. gingivalis-infected macrophages. We found that NLRP3 was necessary for eATP-induced IL-1β secretion as well as for caspase 1 activation irrespective of P. gingivalis fimbriae. Additionally, although the secretion of IL-1β from P. gingivalis-infected macrophages was dependent on NLRP3, its adaptor protein ASC, or caspase 1, the cleavage of intracellular pro-IL-1β to the mature form was found to occur independently of NLRP3, its adaptor protein ASC, or caspase 1. Our in vitro findings revealed that P2X7 receptor has a dual role, being critical not only for eATP-induced IL-1β secretion but also for intracellular pro-IL-1β processing. These results were relevant in vivo since P2X7 receptor expression was upregulated in a P. gingivalis oral infection model, and reduced IFN-γ and IL-17 were detected in draining lymph node cells from P2rx7(-/-) mice. Furthermore, we demonstrated that P2X7 receptor and NLRP3 transcription were modulated in human chronic periodontitis. Overall, we conclude that the P2X7 receptor has a role in periodontal immunopathogenesis and suggest that targeting of the P2X7/NLRP3 pathway should be considered in future therapeutic interventions in periodontitis.

Oral Infections, Metabolic Inflammation, Genetics, and Cardiometabolic Diseases

Although several epidemiologic studies reported plausible and potentially causal associations between oral infections and cardiometabolic diseases (CMDs), controversy still lingers. This might be due to unrecognized confounding from metabolic inflammation and genetics, both of which alter the immune responses of the host. Low-grade inflammation termed metainflammation is the hallmark of obesity, insulin resistance, type 2 diabetes, and CMDs. According to the common soil theory, the continuum of obesity to CMDs is the same pathology at different time points, and early metainflammations, such as hyperglycemia and obesity, display many adverse cardiometabolic characteristics. Consequently, adipose tissue is now considered a dynamic endocrine organ that expresses many proinflammatory cytokines such as TNF-α, IL-6, plasminogen activator inhibitor 1, and IL-1β. In metainflammation, IL-1β and reactive oxygen species are generated, and IL-1β is a pivotal molecule in the pathogenesis of CMDs. Note that the same cytokines expressed in metainflammation are also reported in oral infections. In metabolic inflammation and oral infections, the innate immune system is activated through pattern recognition receptors-which include transmembrane receptors such as toll-like receptors (TLRs), cytosolic receptors such as nucleotide-binding oligomerization domain-like receptors, and multiprotein complexes called inflammasome. In general, TLR-2s are presumed to recognize lipoteichoic acid of Gram-positive microbes-and TLR-4s, lipopolysaccharide of Gram-negative microbes-while nucleotide-binding oligomerization domain-like receptors detect both Gram-positive and Gram-negative peptidoglycans on the bacterial cell walls. However, a high-fat diet activates TLR-2s, and obesity activates TLR-4s and induces spontaneous increases in serum lipopolysaccharide levels (metabolic endotoxemia). Moreover, genetics controls lipid-related transcriptome and the differentiation of monocyte and macrophages. Additionally, genetics influences CMDs, and this creates a confounding relationship among oral infections, metainflammation, and genetics. Therefore, future studies must elucidate whether oral infections can increase the risk of CMDs independent of the aforementioned confounding factors.

The effects of diet-induced obesity on B cell function

B-1 and B-2 B cell subsets carry out a diverse array of functions that range broadly from responding to innate stimuli, antigen presentation, cytokine secretion and antibody production. In this review, we first cover the functional roles of the major murine B cell subsets. We then highlight emerging evidence, primarily in preclinical rodent studies, to show that select B cell subsets are a therapeutic target in obesity and its associated co-morbidities. High fat diets promote accumulation of select murine B cell phenotypes in visceral adipose tissue. As a consequence, B cells exacerbate inflammation and thereby insulin sensitivity through the production of autoantibodies and via cross-talk with select adipose resident macrophages, CD4(+) and CD8(+) T cells. In contrast, interleukin (IL)-10-secreting regulatory B cells counteract the proinflammatory profile and improve glucose sensitivity. We subsequently review data from rodent studies that show pharmacological supplementation of obesogenic diets with long chain n-3 polyunsaturated fatty acids or specialized pro-resolving lipid mediators synthesized from endogenous n-3 polyunsaturated fatty acids boost B cell activation and antibody production. This may have potential benefits for improving inflammation in addition to combating the increased risk of viral infection that is an associated complication of obesity and type II diabetes. Finally, we propose potential underlying mechanisms throughout the review by which B cell activity could be differentially regulated in response to high fat diets.

What is passing through toll gate 4: lipids or infection?

In this issue of the journal, Zhou and colleagues reported that hyperlipidemia might play a role in the expression of pro-inflammatory cytokines such as TNF-α and IL-1β which are associated with type 2 diabetes (T2D) and periodontitis. Not only hyperlipidemia but many obesity-related conditions such as hyperglycemia, insulin resistance, and metabolic syndrome are perceived as "threats" or as a "danger" by the innate immune system and express these cytokines. T2D is one of these conditions that elicit metabolic inflammation (meta-inflammation) and the hallmark of meta-inflammation is low grade inflammation. In addition, T2D and periodontitis are strongly correlated to each other and to innate immunity. This creates a confounding relationship. The dental research community is now required to acknowledge the concept that infection is not the only trigger for innate immune activation. The review by Zhou et al. may be the first step in the right direction to establish the orthogonal contribution of oral infection independent of meta-inflammation.

Immune regulators of inflammation in obesity-associated type 2 diabetes and coronary artery disease

PURPOSE OF REVIEW

To summarize current work identifying inflammatory components that underlie associations between obesity-associated type 2 diabetes and coronary artery disease.

RECENT FINDINGS

Recent studies implicate immune cells as drivers of pathogenic inflammation in human type 2 diabetes. Inflammatory lymphocytes characterize unhealthy adipose tissue, but regional adipose volume, primarily visceral and pericardial fat, also predict severity and risk for obesity-associated coronary artery disease. Having a greater understanding of shared characteristics between inflammatory cells from different adipose tissue depots and a more accessible tissue, such as blood, will facilitate progress toward clinical translation of our appreciation of obesity as an inflammatory disease.

SUMMARY

Obesity predisposes inflammation and metabolic dysfunction through multiple mechanisms, but these mechanisms remain understudied in humans. Studies of obese patients have identified disproportionate impacts of specific T cell subsets in metabolic diseases like type 2 diabetes. On the basis of demonstration that adipose tissue inflammation is depot-specific, analysis of adiposity by waist-to-hip ratio or MRI will increase interpretive value of lymphocyte-focused studies and aid clinicians in determining which obese individuals are at highest risk for coronary artery disease. New tools to combat obesity-associated coronary artery disease and other comorbidities will stem from identification of immune cell-mediated inflammatory networks that are amenable to pharmacological interventions.

Histopathologic Responses of the Dental Pulp to Calcium-Enriched Mixture (CEM) and Mineral Trioxide Aggregate (MTA) in Diabetic and Non-Diabetic Rats

Diabetes mellitus is a chronic disease which affects the healing ability of the pulp and periodontium. The aim of the present study was to assess the histopathologic response of dental pulp to pulp capping using MTA or CEM cement in diabetic rats. Thirty two Wistar male rats aged between 8 and 10 weeks (weight: 200-250g) were divided into two groups of diabetic (n=16) and healthy (n=16) animals and then subdivided into MTA and CEM subgroups. In each group, 10 MTA treated, 10 CEM treated and 12 intact (without any intervention) teeth were analyzed. Intact teeth were considered as a baseline inflammation control. Then, class I cavity was made in the maxillary first molars teeth with pinpoint pulpal exposure. Either MTA or CEM cement was then placed over exposed pulp as pulp capping agent and the cavities were restored using resin- modified glass ionomer cement. Both teeth of rats in subgroups remained intact without any intervention. After four weeks, the rats were sacrificed and the teeth were subjected to histological evaluation in terms of inflammation intensity, dentin bridge formation and dentin bridge continuity. The CEM cement treated diabetic rats exhibited a significant higher inflammatory response when compared to healthy control group (P=0.004) whereas, MTA treated diabetic rats did not exhibit a significant higher inflammatory response in comparison to healthy controls. There was no significant difference between MTA and CEM cement in the induction of dentin bridge formation in diabetic and healthy controls. This preliminary study suggests that MTA is a superior dental material than CEM cement for pulp therapy in subjects with diabetes.