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

Supplementation with Citrus Low-Methoxy Pectin Reduces Levels of Inflammation and Anxiety in Healthy Volunteers: A Pilot Controlled Dietary Intervention Study

Background/Objective: Although low-methoxy (LM) pectin (polysaccharides extracted from citrus peels) can reduce inflammation by binding to and inhibiting the TLR-2 pathway in animal models and in vitro studies, the anti-inflammatory effects of LM pectin in humans and mood have not been explored to date. The purpose of this study is to assess the role of dietary supplementation with LM pectin in healthy volunteers on inflammatory markers and on mood, specifically anxiety and depression. Methods: We carried out a 4-week dietary intervention with LM citrus pectin on healthy volunteers (N = 14, age 40 ± 16 y, BMI 24.7 ± 3.0 kg/m2, sex F 57%) comparing the effects of daily supplementation with 20 g of LM citrus pectin versus 10 g of maltodextrin as the control (N = 15 age 43.2 ± 11 y, BMI 25.18 ± 2.0 kg/m2, sex F 66%). The effects on mood and inflammation were also tested with LM pectin at 5 g, 10 g and 15 g (2 weeks each) in an independent cohort of n = 15 healthy volunteers (age 36 ± 21 y, BMI 23.5 ± 2.4 kg/m2, sex F 80%). We assessed serum levels of TNF-alpha (downstream from TLR-2 activation), IL-1 beta, IL-6, IL-10, INF-gamma, CRP, zonulin and TLR-2 concentration which were measured using ELISA in blood samples collected at both the baseline and follow-up visits. Validated measures of anxiety and depression were collected at baseline and follow-up. Results: Supplementation with 20 g of LM pectin resulted in decreases in the pro-inflammatory markers TNF-alpha, IL-1 beta, IL-6 and INF-gamma (all p < 0.05) and an increase in anti-inflammatory marker IL-10 (p = 0.01) at the end of the 4 weeks. No such effects were observed in the control group. In addition, a significant drop in anxiety scores (from 8.38 to 4.46, p < 0.006) was found with the 20 g/day intervention but not in the control arm. In the dose-response study, anti-inflammatory effects were seen only at 15 g for TNFα (p < 0.003) and a suggestive increase in IL-10 (p = 0.08), alongside a drop in TLR-2 (p < 0.027). No significant anti-inflammatory effects were observed at 5 g and 10 g doses of LM pectin supplementation. Significant dose-dependent drops in both anxiety and depression scores were found with 10 g (p < 0.001) and 15 g per day (p < 0.0002). Conclusions: The current study identifies anxiety-reducing and anti-inflammatory effects of supplementation with 15 g/day LM pectin in healthy humans. Further research is needed to elucidate the precise mechanism and to validate the efficient dose and minimum duration of supplementation.

Exosomal GDNF from Bone Marrow Mesenchymal Stem Cells Moderates Neuropathic Pain in a Rat Model of Chronic Constriction Injury

Both of exosomes derived from mesenchymal stem cells (MSCs) and glial cell line-derived neurotrophic factor (GDNF) show potential for the treatment of neuropathic pain. Here, the analgesic effects of exosomes derived from bone marrow MSCs (BMSCs) were investigated. BMSCs-derived exosomes were isolated and characterized. Chronic constriction injury (CCI) was constructed to induce neuropathic pain in rats, which were then treated with exosomes. Pain behaviors were evaluated by measuring paw withdrawal thresholds and latency. The changes of key proteins, including cytokines, were explored using Western blot and ELISA. Administration of BMSCs-derived exosomes alleviated neuropathic pain, as demonstrated by the decrease of thermal hyperalgesia and mechanical allodynia, as well as the reduced secretion of pro-inflammatory cytokines in CCI rats. These effects were comparable to the treatment of GDNF alone. Mechanically, the exosomes suppressed the CCI-induced activation of TLR2/MyD88/NF-κB signaling pathway, while GDNF knockdown impaired their analgesic effects on CCI rat. BMSCs-derived exosomes may alleviate CCI-induced neuropathic pain and inflammation in rats by transporting GDNF.

A new direction in periodontitis treatment: biomaterial-mediated macrophage immunotherapy

Periodontitis is a chronic inflammation caused by a bacterial infection and is intimately associated with an overactive immune response. Biomaterials are being utilized more frequently in periodontal therapy due to their designability and unique drug delivery system. However, local and systemic immune response reactions driven by the implantation of biomaterials could result in inflammation, tissue damage, and fibrosis, which could end up with the failure of the implantation. Therefore, immunological adjustment of biomaterials through precise design can reduce the host reaction while eliminating the periodontal tissue's long-term chronic inflammation response. It is important to note that macrophages are an active immune system component that can participate in the progression of periodontal disease through intricate polarization mechanisms. And modulating macrophage polarization by designing biomaterials has emerged as a new periodontal therapy technique. In this review, we discuss the role of macrophages in periodontitis and typical strategies for polarizing macrophages with biomaterials. Subsequently, we discuss the challenges and potential opportunities of using biomaterials to manipulate periodontal macrophages to facilitate periodontal regeneration.

Neutrophils in Inflammatory Bone Diseases

PURPOSE OF REVIEW

In this review, we summarize the current evidence that suggests that neutrophils play a key role in facilitating damage to local bone structures.

RECENT FINDINGS

Neutrophil infiltration is a hallmark of inflammatory bone diseases such as rheumatoid arthritis (RA) and periodontitis disease (PD). Both of these human diseases are marked by an imbalance in bone homeostasis, favoring the degradation of local bone which ultimately leads to erosions. Osteoclasts, a multinucleated resident bone cell, are responsible for facilitating the turnover of bone and the bone damage observed in these diseases. The involvement of neutrophils and neutrophil extracellular trap formation have recently been implicated in exacerbating osteoclast function through direct and indirect mechanisms. We highlight a recent finding that NET proteins such as histones and elastase can generate non-canonical, inflammatory osteoclasts, and this process is mediated by post-translational modifications such as citrullination and carbamylation, both of which act as autoantigens in RA. It appears that NETs, autoantibodies, modified proteins, cytokines, and osteoclasts all ultimately contribute to local and permanent bone damage in RA and PD. However, more studies are needed to fully understand the role of neutrophils in inflammatory bone diseases.

P. gingivalis-Induced TLR2 Interactome Analysis Reveals Association with PARP9

Porphyromonas gingivalis is a Gram-negative anaerobic bacterium strongly associated with periodontal disease. Toll-like receptor 2 (TLR2) is indispensable for the host response to P. gingivalis, but P. gingivalis escapes from immune clearance via TLR2-dependent activation of phosphoinositide-3-kinase (PI3K). To probe the TLR2-dependent escape pathway of P. gingivalis, we analyzed the TLR2 interactome induced following P. gingivalis infection or activation by a synthetic lipopeptide TLR2/1 agonist on human macrophages overexpressing TLR2. Interacting proteins were stabilized by cross-linking and then immunoprecipitated and analyzed by mass spectrometry. In total, 792 proteins were recovered and network analysis enabled mapping of the TLR2 interactome at baseline and in response to infection. The P. gingivalis infection-induced TLR2 interactome included the poly (ADP-ribose) polymerase family member mono-ADP-ribosyltransferase protein 9 (PARP9) and additional members of the PARP9 complex (DTX3L and NMI). PARP9 and its complex members are highly upregulated in macrophages exposed to P. gingivalis or to the synthetic TLR2/1 ligand Pam3Cys-Ser-(Lys)4 (PAM). Consistent with its known role in virally induced interferon production, PARP9 knockdown blocked type I interferon (IFN-I) production in response to P. gingivalis and reduced inflammatory cytokine production. We found that P. gingivalis drives signal transducer and activation of transcription (STAT) 1 (S727) phosphorylation through TLR2-PARP9, explaining PARP9's role in the induction of IFN-I downstream of TLR2. Furthermore, PARP9 knockdown reduced PI3K activation by P. gingivalis, leading to improved macrophage bactericidal activity. In summary, PARP9 is a novel TLR2 interacting partner that enables IFN-I induction and P. gingivalis immune escape in macrophages downstream of TLR2 sensing.

Osteoprotective effect by interleukin-4 (IL-4) on lipoprotein-induced periodontitis

Lipoproteins are immunostimulatory bacterial components suggested to participate in inflammation-induced bone loss in periodontal disease through stimulation of osteoclast differentiation. Toll-like receptor 2 activation by Pam2CSK4 (PAM2), known to mimic bacterial lipoproteins, was previously shown to enhance periodontal bone resorption in mice. The anti-inflammatory cytokine interleukin-4 (IL-4) is a known inhibitor of RANKL-induced bone resorption in vitro. Here, we have investigated whether IL-4 could decrease PAM2-induced periodontal bone loss and osteoclastogenesis in vivo. In a model of periodontitis induced by gingival injections of PAM2 in mice, concomitant injections of IL-4 reduced bone loss. Histologically, IL-4 reduced the recruitment of inflammatory cells and the formation of TRAP+ osteoclasts stimulated by PAM2. Mouse bone marrow macrophages (BMMs) and neonatal calvarial osteoblasts were used to assess the effect of IL-4 on PAM2-induced osteoclastogenesis in vitro. In RANKL-primed BMMs stimulated by PAM2 Nfatc1, Ctsk, and Acp5 gene expression was up-regulated and resulted in robust formation of TRAP+ multinucleated osteoclasts, effects which were impaired by IL-4. These effects were mediated by impairment in PAM2-induced c-fos expression. In primary calvarial osteoblast cultures, IL-4 decreased PAM2-induced Tnfsf11 (encoding RANKL) mRNA and enhanced Tnfrsf11b (encoding OPG) expression. Our data demonstrate that the osteoprotective effect by IL-4 on lipoprotein-induced periodontal disease occurs through the inhibition of osteoclastogenesis by three mechanisms, one by acting directly on osteoclast progenitors, another by acting indirectly through decreasing the expression of osteoclast-regulating cytokines in osteoblasts and a third by decreasing inflammation.

Macrophage-related gingival transcriptomic patterns and microbiome alterations in experimental periodontitis in nonhuman primates

OBJECTIVE

This study examined the microbiome features specifically related to host macrophage polarization in health, initiation and progression of periodontitis, and in resolution samples using a nonhuman primate model of ligature-induced periodontitis.

BACKGROUND

The oral microbiome is a complex of bacterial phyla, genera, and species acquired early in life into the individual autochthonous oral ecology. The microbiome changes overtime in response to both intrinsic and extrinsic stressors, and transitions to a dysbiotic ecology at sites of periodontal lesions.

METHODS

Comparisons were made between the microbial and host features in young (≤7 years) and adult (≥12 years) cohorts of animals. Footprints of macrophage-related genes in the gingival tissues were evaluated using expression profiles including M0, M1, and M2 related genes.

RESULTS

Within the gingival tissues, similar macrophage-related gene patterns were observed with significant increases with disease initiation and continued elevation throughout disease in both age groups. Approximately, 70% of the taxa were similar in relative abundance between the two groups; however, the adults showed a large number of OTUs that were significantly altered compared with the younger animals. Developing a correlation map identified three major node levels of interactions that comprised approximately ⅓ of the Operational Taxonomic Units (OTUs) that dominated the microbiomes across the samples. Also noted was a much greater frequency of significant correlations of individual OTUs with the macrophage phenotype markers, compared with disease and resolution samples in both age groups, with a greater frequency in the younger group. Moreover, these correlations were assigned to differentially expressed genes representing M0, M1, and M2-related phenotypes. A cluster analyses across the macrophage-related transcriptome and the OTUs demonstrated multiple somewhat distinct bacterial consortia, incorporating both commensal and putative pathogens, linked to the gene responses that differed in health, disease, and resolution samples. Finally, there were minimal alterations in the OTUs in individual clusters with specific macrophage-related responses in the younger group, while in the adult samples substantial variations were noted with genes from all macrophage phenotypes.

CONCLUSIONS

The results confirmed important features that could reflect macrophage polarization in periodontal lesions, and provided some initial data supporting specific members of the oral microbiome feature prominently related to specific gene response patterns consistent with macrophages in the gingival tissues.

TLR2 mediates renal apoptosis in neonatal mice subjected experimentally to obstructive nephropathy

Urinary tract obstruction during renal development leads to inflammation, tubular apoptosis, and interstitial fibrosis. Toll like receptors (TLRs) expressed on leukocytes, myofibroblasts and renal cells play a central role in acute inflammation. TLR2 is activated by endogenous danger signals in the kidney; its contribution to renal injury in early life is still a controversial topic. We analyzed TLR2 for a potential role in the neonatal mouse model of congenital obstructive nephropathy. Inborn obstructive nephropathies are a leading cause of end-stage kidney disease in children. Thus, newborn Tlr2-/- and wild type (WT) C57BL/6 mice were subjected to complete unilateral ureteral obstruction (UUO) or sham-operation on the 2nd day of life. The neonatal kidneys were harvested and analyzed at days 7 and 14 of life. Relative expression levels of TLR2, caspase-8, Bcl-2, Bax, GSDMD, GSDME, HMGB1, TNF, galectin-3, α-SMA, MMP-2, and TGF-β proteins were quantified semi-quantitatively by immunoblot analyses. Tubular apoptosis, proliferation, macrophage- and T-cell infiltration, tubular atrophy, and interstitial fibrosis were analyzed immunohistochemically. Neonatal Tlr2-/- mice kidneys exhibited less tubular and interstitial apoptosis as compared to those of WT C57BL/6 mice after UUO. UUO induced neonatally did trigger pyroptosis in kidneys, however to similar degrees in Tlr2-/- and WT mice. Also, tubular atrophy, interstitial fibrosis, tubular proliferation, as well as macrophage and T-cell infiltration were unremarkable. We conclude that while TLR2 mediates apoptosis in the kidneys of neonatal mice subjected to UUO, leukocyte recruitment, interstitial fibrosis, and consequent neonatal obstructive nephropathy might lack a TLR2 involvement.

Relationship between TLR-2 level and clinical or radiological severity on patients with tuberculosis spondylitis in Dr. Wahidin Sudirohusodo hospital Makassar

Spinal tuberculosis or TB spondylitis is one of the most common types of extra pulmonary tuberculosis, which is about 15% of all cases. It causes severe morbidity, neurological deficits, and severe deformities in the patients. The growth of Mycobacterium tuberculosis in culture specimens obtained from infected tissue is the single gold standard diagnostic test for spinal TB. Toll-like receptor (TLR) is one of the important receptors in the first-line defence system against microbes. TLR-2 and TLR-4 are known to be associated with tuberculosis infection. Based on this background, the researchers were interested in examining the relationship between TLR-2 levels and the clinical and radiological severity of TB spondylitis patients. A cross-sectional study was conducted with patients diagnosed with tuberculosis spondylitis at Dr Wahidin Sudirohusodo Makassar. Patients diagnosed with TB spondylitis confirmed by blood tests, GeneExpert, and magnetic resonance imaging without prior treatment were included. Data analysis were conducted by using descriptive analysis and one-way ANOVA for bivariate analysis. The mean value of TLR2 levels in TB spondylitis patients was 9.1 g/dL. TLR2 levels in paraesthesia were significantly higher than normal (P < .05). Similar trend were analyzed on the motor neurologic status with TLR2 levels in paraparesis were significantly higher than those in normal (P < .05). There is a significant relationship between the TLR2 levels in TB spondylitis and their impaired motor and sensory function. Spinal destruction has been shown to provide significant relationship with TLR2 value in spondylitis TB.

Dysbiosis and Alzheimer's disease: role of probiotics, prebiotics and synbiotics

Alzheimer's disease (AD) is a neurodegenerative disease characterized by dementia and the accumulation of amyloid beta in the brain. Recently, microbial dysbiosis has been identified as one of the major factors involved in the onset and progression of AD. Imbalance in gut microbiota is known to affect central nervous system (CNS) functions through the gut-brain axis and involves inflammatory, immune, neuroendocrine and metabolic pathways. An altered gut microbiome is known to affect the gut and BBB permeability, resulting in imbalance in levels of neurotransmitters and neuroactive peptides/factors. Restoration of levels of beneficial microorganisms in the gut has demonstrated promising effects in AD in pre-clinical and clinical studies. The current review enlists the important beneficial microbial species present in the gut, the effect of their metabolites on CNS, mechanisms involved in dysbiosis related to AD and the beneficial effects of probiotics on AD. It also highlights challenges involved in large-scale manufacturing and quality control of probiotic formulations.

Wnt signaling in periodontitis

OBJECTIVE

This study aimed to evaluate the Wnt/β-catenin signaling pathway activity in gingival samples obtained from patients with periodontitis.

MATERIALS AND METHODS

Fifteen patients with stage III grade B (SIIIGB) and eleven with stage III grade C (SIIIGC) periodontitis were included and compared to 15 control subjects. β-Catenin, Wnt 3a, Wnt 5a, and Wnt 10b expressions were evaluated by Q-PCR. Topographic localization of tissue β-catenin, Wnt 5a, and Wnt 10b was measured by immunohistochemical analysis. TNF-α was used to assess the inflammatory state of the tissues, while Runx2 was used as a mediator of active destruction.

RESULTS

Wnt 3a, Wnt 5a, and Wnt 10b were significantly higher in gingival tissues in both grades of stage 3 periodontitis compared to the control group (p < 0.05). β-Catenin showed intranuclear staining in connective tissue in periodontitis, while it was confined to intracytoplasmic staining in epithelial tissue and the cell walls in the control group. Wnt5a protein expression was elevated in periodontitis, with the most intense staining observed in the connective tissue of SIIIGC samples. Wnt10b showed the highest density in the connective tissue of patients with periodontitis.

CONCLUSIONS

Our findings suggested that periodontal inflammation disrupts the Wnt/β-catenin signaling pathway.

CLINICAL RELEVANCE

Periodontitis disrupts Wnt signaling in periodontal tissues in parallel with tissue inflammation and changes in morphology. This change in Wnt-related signaling pathways that regulate tissue homeostasis in the immunoinflammatory response may shed light on host-induced tissue destruction in the pathogenesis of the periodontal disease.

The role of HMGB1 in digestive cancer

High mobility group box protein B1 (HMGB1) belongs to the HMG family, is widely expressed in the nucleus of digestive mucosal epithelial cells, mesenchymal cells and immune cells, and binds to DNA to participate in genomic structural stability, mismatch repair and transcriptional regulation to maintain normal cellular activities. In the context of digestive inflammation and tumors, HMGB1 readily migrates into the extracellular matrix and binds to immune cell receptors to affect their function and differentiation, further promoting digestive tract tissue injury and tumor development. Notably, HMGB1 can also promote the antitumor immune response. Therefore, these seemingly opposing effects in tumors make targeted HMGB1 therapies important in digestive cancer. This review focuses on the role of HMGB1 in tumors and its effects on key pathways of digestive cancer and aims to provide new possibilities for targeted tumor therapy.

Osteocyte RANKL Drives Bone Resorption in Mouse Ligature-Induced Periodontitis

Mouse ligature-induced periodontitis (LIP) has been used to study bone loss in periodontitis. However, the role of osteocytes in LIP remains unclear. Furthermore, there is no consensus on the choice of alveolar bone parameters and time points to evaluate LIP. Here, we investigated the dynamics of changes in osteoclastogenesis and bone volume (BV) loss in LIP over 14 days. Time-course analysis revealed that osteoclast induction peaked on days 3 and 5, followed by the peak of BV loss on day 7. Notably, BV was restored by day 14. The bone formation phase after the bone resorption phase was suggested to be responsible for the recovery of bone loss. Electron microscopy identified bacteria in the osteocyte lacunar space beyond the periodontal ligament (PDL) tissue. We investigated how osteocytes affect bone resorption of LIP and found that mice lacking receptor activator of NF-κB ligand (RANKL), predominantly in osteocytes, protected against bone loss in LIP, whereas recombination activating 1 (RAG1)-deficient mice failed to resist it. These results indicate that T/B cells are dispensable for osteoclast induction in LIP and that RANKL from osteocytes and mature osteoblasts regulates bone resorption by LIP. Remarkably, mice lacking the myeloid differentiation primary response gene 88 (MYD88) did not show protection against LIP-induced bone loss. Instead, osteocytic cells expressed nucleotide-binding oligomerization domain containing 1 (NOD1), and primary osteocytes induced significantly higher Rankl than primary osteoblasts when stimulated with a NOD1 agonist. Taken together, LIP induced both bone resorption and bone formation in a stage-dependent manner, suggesting that the selection of time points is critical for quantifying bone loss in mouse LIP. Pathogenetically, the current study suggests that bacterial activation of osteocytes via NOD1 is involved in the mechanism of osteoclastogenesis in LIP. The NOD1-RANKL axis in osteocytes may be a therapeutic target for bone resorption in periodontitis. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Inflammatory macrophages exploited by oral streptococcus increase IL-1B release via NLRP6 inflammasome

Chronic inflammatory periodontal disease develops in part from the infiltration of a large number of classically activated inflammatory macrophages that release inflammatory cytokines important for disease progression, including inflammasome-dependent interleukin (IL)-1β. Streptococcus gordonii is a normally commensal oral microorganism; while not causative, recent evidence indicates that commensal oral microbes are required for the full development of periodontal disease. We have recently reported that inflammatory macrophages counterintuitively allow for the increased survival of phagocytosed S. gordonii over nonactivated or alternatively activated macrophages. This survival is dependent on increased reactive oxygen species production within the phagosome of the inflammatory macrophages, and resistance by the bacterium and can result in S. gordonii damaging the phagolysosomes. Here, we show that activated macrophages infected with live S. gordonii release more IL-1β than non-activated macrophages infected with either live or dead S. gordonii, and that the survival of oral Streptococci are more dependent on macrophage activation than other Gram positive microbes, both classical pathogens and commensals. We also find that S. gordonii-dependent inflammatory macrophage inflammasome activation requires the cytoplasmic NLRP6. Overall, our results suggest S. gordonii is capable of evading immune destruction, increasing inflammatory mediators, and increasing inflammatory macrophage response, and that this ability is increased under conditions of inflammation. This work reveals additional mechanisms by which normally commensal oral streptococci-macrophage interactions can change, resulting in increased release of mature IL-1β, potentially contributing to an environment that perpetuates inflammation.

Gingival transcriptomic patterns of macrophage polarization during initiation, progression, and resolution of periodontitis

Phenotypic and functional heterogeneity of macrophages is clearly a critical component of their effective functions in innate and adaptive immunity. This investigation hypothesized that altered profiles of gene expression in gingival tissues in health, disease, and resolution would reflect changes in macrophage phenotypes occurring in these tissues. The study used a nonhuman primate model to evaluate gene expression profiles as footprints of macrophage variation using a longitudinal experimental model of ligature-induced periodontitis in animals from 3 to 23 years of age to identify aging effects on the gingival environment. Significant differences were observed in distribution of expressed gene levels for M0, M1, and M2 macrophages in healthy tissues with the younger animals showing the least expression. M0 gene expression increased with disease in all but the aged group, while M1 was increased in adult and young animals, and M2 in all age groups, as early as disease initiation (within 0.5 months). Numerous histocompatibility genes were increased with disease, except in the aged samples. An array of cytokines/chemokines representing both M1 and M2 cells were increased with disease showing substantial increases with disease initiation (e.g. IL1A, CXCL8, CCL19, CCL2, CCL18), although the aged tissues showed a more limited magnitude of change across these macrophage genes. The analytics of macrophage genes at sites of gingival health, disease, and resolution demonstrated distinct profiles of host response interactions that may help model the disease mechanisms occurring with the formation of a periodontal lesion.

Metformin, Empagliflozin, and Their Combination Modulate Ex-Vivo Macrophage Inflammatory Gene Expression

Type-2 Diabetes Mellitus is a complex, chronic illness characterized by persistent high blood glucose levels. Patients can be prescribed anti-diabetes drugs as single agents or in combination depending on the severity of their condition. Metformin and empagliflozin are two commonly prescribed anti-diabetes drugs which reduce hyperglycemia, however their direct effects on macrophage inflammatory responses alone or in combination are unreported. Here, we show that metformin and empagliflozin elicit proinflammatory responses on mouse bone-marrow-derived macrophages with single agent challenge, which are modulated when added in combination. In silico docking experiments suggested that empagliflozin can interact with both TLR2 and DECTIN1 receptors, and we observed that both empagliflozin and metformin increase expression of Tlr2 and Clec7a. Thus, findings from this study suggest that metformin and empagliflozin as single agents or in combination can directly modulate inflammatory gene expression in macrophages and upregulate the expression of their receptors.

Osteocytes directly regulate osteolysis via MYD88 signaling in bacterial bone infection

The impact of bone cell activation on bacterially-induced osteolysis remains elusive. Here, we show that matrix-embedded osteocytes stimulated with bacterial pathogen-associated molecular patterns (PAMPs) directly drive bone resorption through an MYD88-regulated signaling pathway. Mice lacking MYD88, primarily in osteocytes, protect against osteolysis caused by calvarial injections of bacterial PAMPs and resist alveolar bone resorption induced by oral Porphyromonas gingivalis (Pg) infection. In contrast, mice with targeted MYD88 restoration in osteocytes exhibit osteolysis with inflammatory cell infiltration. In vitro, bacterial PAMPs induce significantly higher expression of the cytokine RANKL in osteocytes than osteoblasts. Mechanistically, activation of the osteocyte MYD88 pathway up-regulates RANKL by increasing binding of the transcription factors CREB and STAT3 to Rankl enhancers and by suppressing K48-ubiquitination of CREB/CREB binding protein and STAT3. Systemic administration of an MYD88 inhibitor prevents jawbone loss in Pg-driven periodontitis. These findings reveal that osteocytes directly regulate inflammatory osteolysis in bone infection, suggesting that MYD88 and downstream RANKL regulators in osteocytes are therapeutic targets for osteolysis in periodontitis and osteomyelitis.

Porphyromonas gingivalis Virulence Factors and Clinical Significance in Periodontal Disease and Coronary Artery Diseases

Porphyromonas gingivalis is a gram-negative, anaerobic bacterium that lives in the oral cavity. It is an integral part of the oral microbiome, which includes more than 500 types of bacteria. Under certain circumstances, as a consequence of virulence factors, it can become very destructive and proliferate to many cells in periodontal lesions. It is one of the causative agents present extremely often in dental plaque and is the main etiological factor in the development of periodontal disease. During various therapeutic procedures, P. gingivalis can enter the blood and disseminate through it to distant organs. This primarily refers to the influence of periodontal agents on the development of subacute endocarditis and can facilitate the development of coronary heart disease, atherosclerosis, and ischemic infarction. The action of P. gingivalis is facilitated by numerous factors of virulence and pathogenicity such as fimbriae, hemolysin, hemagglutinin, capsules, outer membrane vesicles, lipopolysaccharides, and gingipains. A special problem is the possibility of biofilm formation. P. gingivalis in a biofilm is 500 to 1000 times less sensitive to antimicrobial drugs than planktonic cells, which represents a significant problem in the treatment of infections caused by this pathogen.

HDAC5-Mediated Acetylation of p100 Suppresses Its Processing

INTRODUCTION

Periodontitis is a condition involving chronic inflammation in the gums, periodontal ligaments, cementum, and alveolar bone. Nuclear factor-κB (NF-κB) activation is the prominent mediator of inflammation and osteoclast differentiation. The role of histone deacetylase 5 (HDAC5) in periodontitis development and NF-κB regulation is not fully understood.

METHODS

We used primary mouse bone marrow-derived osteoclast cultures in vitro and a mouse model of chronic periodontists (CPD) treated with the HDAC4/5 inhibitor LMK-235. Real-time polymerase chain reaction, micro computed tomography, flow cytometry, western blot, and immunoprecipitation were used to study proinflammatory cytokines, NF-κB activation, HDAC5 activity, and the interaction of HDAC5 with NF-κB p100.

RESULTS

LMK-235, a selective inhibitor of HDAC4 and HDAC5, reduced osteoclast marker gene expression (Cstk, Acp5, and Calcr) and tartrate-resistant acid phosphatase activity in primary osteoclast cultures. LMK-235 reduced the increase in cementoenamel junction-alveolar bone crest distance, inflammatory cell infiltration of gingival tissues, and expression levels of interleukin (IL)-1β, tumor necrosis factor alpha, IL-6, and IL-23a, indicating an ameliorative effect on CPD. Immunoprecipitation experiments have further confirmed p100-HDAC5 interaction, acetylation levels of p100, and NF-κB activation.

CONCLUSIONS

These results indicate that HDAC5 binds and deacetylates p100, leading to its activation, increased proinflammatory cytokine production, gingival infiltration, and osteoclast differentiation, thus promoting alveolar bone resorption. HDAC5 inhibition is therefore a potentially promising therapeutic strategy for the treatment of periodontitis.

Insight into the Relationship between Oral Microbiota and the Inflammatory Bowel Disease

Inflammatory bowel disease has been a growing concern of lots of people globally, including both adults and children. As a chronic inflammatory disease of the intestine, even though the etiology of inflammatory bowel disease is still unclear, the available evidence from clinic observations has suggested a close association with microorganisms. The oral microbiota possesses the characteristics of a large number and abundant species, second only to the intestinal microbiota in the human body; as a result, it successfully attracts the attention of researchers. The highly diverse commensal oral microbiota is not only a normal part of the oral cavity but also has a pronounced impact on the pathophysiology of general health. Numerous studies have shown the potential associations between the oral microbiota and inflammatory bowel disease. Inflammatory bowel disease can affect the composition of the oral microbiota and lead to a range of oral pathologies. In turn, there are a variety of oral microorganisms involved in the development and progression of inflammatory bowel disease, including Streptococcus spp., Fusobacterium nucleatum, Porphyromonas gingivalis, Campylobacter concisus, Klebsiella pneumoniae, Saccharibacteria (TM7), and Candida albicans. Based on the above analysis, the purpose of this review is to summarize this relationship of mutual influence and give further insight into the detection of flora as a target for the diagnosis and treatment of inflammatory bowel disease to open up a novel approach in future clinical practice.

Lipopolysaccharide from Porphyromonas gingivalis, but Not from Porphyromonas endodontalis, Induces Macrophage M1 Profile

Apical Lesions of Endodontic Origin (ALEO) are initiated by polymicrobial endodontic canal infection. Porphyromonas gingivalis (Pg) and Porphyromonas endodontalis (Pe) lipopolysaccharides (LPS) can induce a pro-inflammatory macrophage response through their recognition by TLR2 and TLR4. However, polarization responses induced by Pg and/or Pe LPS in macrophages are not fully understood. We aimed to characterize the polarization profiles of macrophages differentiated from THP-1 cells following Pg and/or Pe LPS stimulation from reference strain and clinical isolates. A modified LPS purification protocol was implemented and the electrophoretic LPS profiles were characterized. THP-1 human monocytes differentiated to macrophages were stimulated with Pg and Pe LPS. Polarization profiles were characterized through cell surface markers and secreted cytokines levels after 24 h of stimulation. TLR2 and TLR4 cell surfaces and transcriptional levels were determined after 24 or 2 h of LPS stimulation, respectively. LPS from Pg induced a predominant M1 profile in macrophages evidenced by changes in the expression of the surface marker CD64 and pro-inflammatory cytokine profiles, TNF-α, IL-1β, IL-6, and IL-12. Pe LPS was unable to induce a significant response. TLR2 and TLR4 expressions were neither modified by Pg or Pe LPS. Pg LPS, but not Pe LPS, induced a macrophage M1 Profile.

Effects of extracellular vesicles derived from oral bacteria on osteoclast differentiation and activation

Dysbiosis of the oral microbiota plays an important role in the progression of periodontitis, which is characterized by chronic inflammation and alveolar bone loss, and associated with systemic diseases. Bacterial extracellular vesicles (EVs) contain various bioactive molecules and show diverse effects on host environments depending on the bacterial species. Recently, we reported that EVs derived from Filifactor alocis, a Gram-positive periodontal pathogen, had osteoclastogenic activity. In the present study, we analysed the osteoclastogenic potency and immunostimulatory activity of EVs derived from the Gram-negative periodontal pathogens Porphyromonas gingivalis and Tannerella forsythia, the oral commensal bacterium Streptococcus oralis, and the gut probiotic strain Lactobacillus reuteri. Bacterial EVs were purified by density gradient ultracentrifugation using OptiPrep (iodixanol) reagent. EVs from P. gingivalis, T. forsythia, and S. oralis increased osteoclast differentiation and osteoclstogenic cytokine expression in osteoclast precursors, whereas EVs from L. reuteri did not. EVs from P. gingivalis, T. forsythia, and S. oralis preferentially activated Toll-like receptor 2 (TLR2) rather than TLR4 or TLR9, and induced osteoclastogenesis mainly through TLR2. The osteoclastogenic effects of EVs from P. gingivalis and T. forsythia were reduced by both lipoprotein lipase and polymyxin B, an inhibitor of lipopolysaccharide (LPS), while the osteoclastogenic effects of EVs from S. oralis were reduced by lipoprotein lipase alone. These results demonstrate that EVs from periodontal pathogens and oral commensal have osteoclastogenic activity through TLR2 activation by lipoproteins and/or LPS.

Blocking of Caspases Exerts Anti-Inflammatory Effects on Periodontal Cells

Periodontitis is an inflammatory process that is associated with caspase activity. Caspases could thus become molecular targets for the modulation of the inflammatory response to harmful factors, such as lipopolysaccharides (LPS) and TNFα. Here, the impact of the pan-caspase inhibitor Z-VAD-FMK (carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoro-methyl ketone) on the modulation of the LPS-induced inflammatory response of murine RAW 264.7 cells and primary macrophages was examined. Moreover, the inflammatory responses of human gingival fibroblasts, HSC2 oral squamous carcinoma cells and murine ST2 mesenchymal fibroblasts when exposed to TNFα were studied. Data showed that Z-VAD-FMK significantly lowered the inflammatory response of RAW 264.7 cells and primary macrophages, as indicated by the expression of IL1 and IL6. In murine ST2 mesenchymal fibroblasts, the TNFα-induced expression of CCL2 and CCL5 was significantly reduced. In human gingival fibroblasts and HSC2 cells, Z-VAD-FMK considerably reduced the TNFα-induced expression of CXCL8 and CXCL10. These findings suggest that pharmacological blocking of caspases in an inflammatory environment lowers the expression of cytokines and chemokines in periodontal cells.

Interleukin-34 Permits Porphyromonas gingivalis Survival and NF-κB p65 Inhibition in Macrophages

Interleukin-34 (IL-34) is a cytokine that supports the viability and differentiation of macrophages. An important cytokine for the development of epidermal immunity, IL-34 is present and plays a role in the immunity of the oral environment. IL-34 has been linked to inflammatory periodontal diseases, which involve innate phagocytes, including macrophages. Whether IL-34 can alter the ability of macrophages to effectively interact with oral microbes is currently unclear. Using macrophages derived from human blood monocytes with either the canonical cytokine colony-stimulating factor (CSF)1 or IL-34, we compared the ability of the macrophages to phagocytose, kill, and respond through the production of cytokines to the periodontal keystone pathogen Porphyromonas gingivalis. While macrophages derived from both cytokines were able to engulf the bacterium equally, IL-34 derived macrophages were much less capable of killing internalized P. gingivalis. Of the macrophage cell surface receptors known to interact with P. gingivalis, DC-SIGN was found to have the largest variation between IL-34 and CSF1-derived macrophages. We also found that upon interaction with P. gingivalis, IL-34 derived macrophages produced significantly less of the neutrophil chemotactic factor IL-8 than macrophages derived in the presence of CSF1. Mechanistically, we identified that levels of IL-8 corresponded with P. gingivalis survival and dephosphorylation of the major transcription factor NF-κB p65. Overall, we found that macrophages differentiated in the presence of IL-34, a dominant cytokine in the oral gingiva, have a reduced ability to kill the keystone pathogen P. gingivalis and may be susceptible to specific bacteria-mediated cytokine modification. This article is protected by copyright. All rights reserved.

Sex Variations in the Oral Microbiomes of Youths with Severe Periodontitis

Objective

Periodontitis is an inflammatory disease of microbial etiology caused primarily by dysbiosis of the oral microbiota. Our aim was to compare variations in the composition of the oral microbiomes of youths with severe periodontitis according to gender.

Methods

Subgingival plaque samples collected from 17 patients with severe periodontitis (11 males and 6 females) were split for 16S rRNA gene sequencing. The composition, α-diversity, and β-diversity of the patients' oral microbiomes were compared between the males and the females. Linear discriminant analysis effect size (LEfSe) was used to analyze the specific taxa enriched in the two groups. Functional profiles (KEGG pathways) were obtained using PICRUSt based on 16S rRNA gene sequencing data.

Results

The Chao1 index and phylogenetic diversity whole tree were significantly higher in males than in females. The Simpson and Shannon indices were not significantly different between the two groups. β-Diversity suggested that the samples were reasonably divided into groups. The Kruskal-Wallis test based on the relative abundance of species, combined with the LEfSe analysis showed that the dominant bacteria in males were Pseudomonas and Papillibacter, whereas the dominant bacteria in women were Fusobacteriales and Tannerella. KEGG analysis predicted that the variation in the oral microbiome may be related to the immune system in women, whereas immune system diseases were the dominant pathway in men.

Conclusion

We found sex-specific differences in the oral microbiome in a sample of youths with severe periodontitis. The differences may be related to changes in immune homeostasis and lead to a better understanding of periodontitis.

Beyond Immunity: Underappreciated Functions of Intestinal Macrophages

The gastrointestinal tract hosts the largest compartment of macrophages in the body, where they serve as mediators of host defense and immunity. Seeded in the complex tissue-environment of the gut, an array of both hematopoietic and non-hematopoietic cells forms their immediate neighborhood. Emerging data demonstrate that the functional diversity of intestinal macrophages reaches beyond classical immunity and includes underappreciated non-immune functions. In this review, we discuss recent advances in research on intestinal macrophage heterogeneity, with a particular focus on how non-immune functions of macrophages impact tissue homeostasis and function. We delve into the strategic localization of distinct gut macrophage populations, describe the potential factors that regulate their identity and functional heterogeneity within these locations, and provide open questions that we hope will inspire research dedicated to elucidating a holistic view on macrophage-tissue cell interactions in the body's largest mucosal organ.

Porphyromonas gingivalis outside the oral cavity

Porphyromonas gingivalis, a Gram-negative anaerobic bacillus present in periodontal disease, is considered one of the major pathogens in periodontitis. A literature search for English original studies, case series and review articles published up to December 2019 was performed using the MEDLINE, PubMed and GoogleScholar databases, with the search terms "Porphyromonas gingivalis" AND the potentially associated condition or systemic disease Abstracts and full text articles were used to make a review of published research literature on P. gingivalis outside the oral cavity. The main points of interest of this narrative review were: (i) a potential direct action of the bacterium and not the systemic effects of the inflammatory acute-phase response induced by the periodontitis, (ii) the presence of the bacterium (viable or not) in the organ, or (iii) the presence of its virulence factors. Virulence factors (gingipains, capsule, fimbriae, hemagglutinins, lipopolysaccharide, hemolysin, iron uptake transporters, toxic outer membrane blebs/vesicles, and DNA) associated with P. gingivalis can deregulate certain functions in humans, particularly host immune systems, and cause various local and systemic pathologies. The most recent studies linking P. gingivalis to systemic diseases were discussed, remembering particularly the molecular mechanisms involved in different infections, including cerebral, cardiovascular, pulmonary, bone, digestive and peri-natal infections. Recent involvement of P. gingivalis in neurological diseases has been demonstrated. P. gingivalis modulates cellular homeostasis and increases markers of inflammation. It is also a factor in the oxidative stress involved in beta-amyloid production.

Pathological and Therapeutic Approach to Endotoxin-Secreting Bacteria Involved in Periodontal Disease

It is widely recognized that periodontal disease is an inflammatory entity of infectious origin, in which the immune activation of the host leads to the destruction of the supporting tissues of the tooth. Periodontal pathogenic bacteria like Porphyromonas gingivalis, that belongs to the complex net of oral microflora, exhibits a toxicogenic potential by releasing endotoxins, which are the lipopolysaccharide component (LPS) available in the outer cell wall of Gram-negative bacteria. Endotoxins are released into the tissues causing damage after the cell is lysed. There are three well-defined regions in the LPS: one of them, the lipid A, has a lipidic nature, and the other two, the Core and the O-antigen, have a glycosidic nature, all of them with independent and synergistic functions. Lipid A is the "bioactive center" of LPS, responsible for its toxicity, and shows great variability along bacteria. In general, endotoxins have specific receptors at the cells, causing a wide immunoinflammatory response by inducing the release of pro-inflammatory cytokines and the production of matrix metalloproteinases. This response is not coordinated, favoring the dissemination of LPS through blood vessels, as well as binding mainly to Toll-like receptor 4 (TLR4) expressed in the host cells, leading to the destruction of the tissues and the detrimental effect in some systemic pathologies. Lipid A can also act as a TLRs antagonist eliciting immune deregulation. Although bacterial endotoxins have been extensively studied clinically and in a laboratory, their effects on the oral cavity and particularly on periodontium deserve special attention since they affect the connective tissue that supports the tooth, and can be linked to advanced medical conditions. This review addresses the distribution of endotoxins associated with periodontal pathogenic bacteria and its relationship with systemic diseases, as well as the effect of some therapeutic alternatives.

Sphingolipid-Containing Outer Membrane Vesicles Serve as a Delivery Vehicle To Limit Macrophage Immune Response to Porphyromonas gingivalis

Sphingolipids (SLs) are essential structural components of mammalian cell membranes. Our group recently determined that the oral anaerobe Porphyromonas gingivalis delivers its SLs to host cells and that the ability of P. gingivalis to synthesize SLs limits the elicited host inflammatory response during cellular infection.

Sphingolipids (SLs) are essential structural components of mammalian cell membranes. Our group recently determined that the oral anaerobe Porphyromonas gingivalis delivers its SLs to host cells and that the ability of P. gingivalis to synthesize SLs limits the elicited host inflammatory response during cellular infection. As P. gingivalis robustly produces outer membrane vesicles (OMVs), we hypothesized that OMVs serve as a delivery vehicle for SLs, that the SL status of the OMVs may impact cargo loading to OMVs, and that SL-containing OMVs limit elicited host inflammation similar to that observed by direct bacterial challenge. Transwell cell culture experiments determined that in comparison to the parent strain W83, the SL-null mutant elicited a hyperinflammatory immune response from THP-1 macrophage-like cells with elevated tumor necrosis factor alpha (TNF-α), interleukin 1β (IL-1β), and IL-6. Targeted assessment of Toll-like receptors (TLRs) identified elevated expression of TLR2, unchanged TLR4, and elevated expression of the adaptor molecules MyD88 and TRIF (Toll/IL-1 receptor domain-containing adaptor-inducing beta interferon) by SL-null P. gingivalis. No significant differences in gingipain activity were observed in our infection models, and both strains produced OMVs of similar sizes. Using comparative two-dimensional gel electrophoresis, we identified differences in the protein cargo of the OMVs between parent and SL-null strain. Importantly, use of purified OMVs recapitulated the cellular inflammatory response observed in the transwell system with whole bacteria. These findings provide new insights into the role of SLs in P. gingivalis OMV cargo assembly and expand our understanding of SL-OMVs as bacterial structures that modulate the host inflammatory response.

Microbial Lipid A Remodeling Controls Cross-Presentation Efficiency and CD8 T Cell Priming by Modulating Dendritic Cell Function

The majority of Gram-negative bacteria elicit a potent immune response via recognition of lipid A expressed on the outer bacterial membrane by the host immune receptor Toll-like receptor 4 (TLR4). However, some Gram-negative bacteria evade detection by TLR4 or alter the outcome of TLR4 signaling by modification of lipid A species. Although the role of lipid A modifications on host innate immunity has been examined in some detail, it is currently unclear how lipid A remodeling influences host adaptive immunity. One prototypic Gram-negative bacterium that modifies its lipid A structure is Porphyromonas gingivalis, an anaerobic pathobiont that colonizes the human periodontium and induces chronic low-grade inflammation that is associated with periodontal disease as well as a number of systemic inflammatory disorders. P. gingivalis produces dephosphorylated and deacylated lipid A structures displaying altered activities at TLR4. Here, we explored the functional role of P. gingivalis lipid A modifications on TLR4-dependent innate and adaptive immune responses in mouse bone marrow-derived dendritic cells (BMDCs). We discovered that lipid A 4'-phosphate removal is required for P. gingivalis to evade BMDC-dependent proinflammatory cytokine responses and markedly limits the bacterium's capacity to induce beta interferon (IFN-β) production. In addition, lipid A 4'-phosphatase activity prevents canonical bacterium-induced delay in antigen degradation, which leads to inefficient antigen cross-presentation and a failure to cross-prime CD8 T cells specific for a P. gingivalis-associated antigen. We propose that lipid A modifications produced by this bacterium alter host TLR4-dependent adaptive immunity to establish chronic infections associated with a number of systemic inflammatory disorders.

TLR2 and TLR4 Differentially Regulate the Osteogenic Capacity of Human Periodontal Ligament Fibroblasts

AIMS

To test that the osteogenic capacity of periodontal ligament (PDL) fibroblasts can be mediated by TLR2 and TLR4 activation.

MATERIALS AND METHODS

Human PDL fibroblasts were cultured in osteogenic medium and treated with TLR2 and TLR4 agonists (Pam3CSK4 and monophosphoryl Lipid A (MPLA), respectively). Cell proliferation was measured by MTT and BrdU incorporation. Osteogenic differentiation was measured by alkaline phosphatase (ALP) activity. Nodule formation was measured for osteoblast function. The expression of markers of potential signaling pathways (RUNX2, OCN, BSP and Osterix) was evaluated by quantitative PCR.

RESULTS

PDL fibroblasts grew at the same rate during the first 5 days in response to both Pam3CSK5 and MPLA. On day 7, cells cultured in the presence of Pam3CSK4 had a significantly higher rate of DNA replication, while cells in MPLA group had a significantly lower DNA replication rate (one-third) compared to the control (p less than 0.05). Pam3CSK4 induced significantly higher ALP activity and larger calcified nodules. TLR4 activation significantly reduced the expression of RUNX2 and osterix and enhanced OCN. Neither TLR2 nor TLR4 affected BSP expression.

CONCLUSIONS

These data suggest that the activation of TLR2 and TLR4 differentially and perhaps antagonistically modulate osteogenesis by human PDL fibroblasts and have a direct role of TLR-mediated PDL function during periodontal regeneration as a potential target for therapeutics.

Receptor for advanced glycation end products up-regulation in cerebral endothelial cells mediates cerebrovascular-related amyloid β accumulation after Porphyromonas gingivalis infection

Cerebrovascular‐related amyloidogenesis is found in over 80% of Alzheimer's disease (AD) cases, and amyloid β (Aβ) generation is increased in the peripheral macrophages during infection of Porphyromonas gingivalis (P. gingivalis), a causal bacterium for periodontitis. In this study, we focused on receptor for advanced glycation end products (RAGE), the key molecule involves in Aβ influx after P. gingivalis infection to test our hypothesis that Aβ transportation from periphery into the brain, known as “Aβ influx,” is enhanced by P. gingivalis infection. Using cultured hCMEC/D3 cell line, in comparison to uninfected cells, directly infection with P. gingivalis (multiplicity of infection, MOI = 5) significantly increased a time‐dependent RAGE expression resulting in a dramatic increase in Aβ influx in the hCMEC/D3 cells; the P. gingivalis‐up‐regulated RAGE expression was significantly decreased by NF‐κB and Cathepsin B (CatB)‐specific inhibitors, and the P.gingivalis‐increased IκBα degradation was significantly decreased by CatB‐specific inhibitor. Furthermore, the P. gingivalis‐increased Aβ influx was significantly reduced by RAGE‐specific inhibitor. Using 15‐month‐old mice (C57BL/6JJmsSlc, female), in comparison to non‐infection mice, systemic P. gingivalis infection for three consecutive weeks (1 × 10⁸ CFU/mouse, every 3 days, intraperitoneally) significantly increased the RAGE expression in the CD31‐positive endothelial cells and the Aβ loads around the CD31‐positive cells in the mice's brains. The RAGE expression in the CD31‐positive cells was positively correlated with the Aβ loads. These observations demonstrate that the up‐regulated RAGE expression in cerebral endothelial cells mediates the Aβ influx after P. gingivalis infection, and CatB plays a critical role in regulating the NF‐κB/RAGE expression.

Infectious Triggers in Periodontitis and the Gut in Rheumatoid Arthritis (RA): A Complex Story About Association and Causality

Rheumatoid arthritis (RA) is a systemic immune mediated inflammatory disease of unknown origin, which is predominantly affecting the joints. Antibodies against citrullinated peptides are a rather specific immunological hallmark of this heterogeneous entity. Furthermore, certain sequences of the third hypervariable region of human leukocyte antigen (HLA)-DR class II major histocompatibility (MHC) molecules, the so called "shared epitope" sequences, appear to promote autoantibody positive types of RA. However, MHC-II molecule and other genetic associations with RA could not be linked to immune responses against specific citrullinated peptides, nor do genetic factors fully explain the origin of RA. Consequently, non-genetic factors must play an important role in the complex interaction of endogenous and exogenous disease factors. Tobacco smoking was the first environmental factor that was associated with onset and severity of RA. Notably, smoking is also an established risk factor for oral diseases. Furthermore, smoking is associated with extra-articular RA manifestations such as interstitial lung disease in anatomical proximity to the airway mucosa, but also with subcutaneous rheumatoid nodules. In the mouth, Porphyromonas gingivalis is a periodontal pathogen with unique citrullinating capacity of foreign microbial antigens as well as candidate RA autoantigens. Although the original hypothesis that this single pathogen is causative for RA remained unproven, epidemiological as well as experimental evidence linking periodontitis (PD) with RA is rapidly accumulating. Other periopathogens such as Aggregatibacter actinomycetemcomitans and Prevotella intermedia were also proposed to play a specific immunodominant role in context of RA. However, demonstration of T cell reactivity against citrullinated, MHC-II presented autoantigens from RA synovium coinciding with immunity against Prevotella copri (Pc.), a gut microbe attracted attention to another mucosal site, the intestine. Pc. was accumulated in the feces of clinically healthy subjects with citrulline directed immune responses and was correlated with RA onset. In conclusion, we retrieved more than one line of evidence for mucosal sites and different microbial taxa to be potentially involved in the development of RA. This review gives an overview of infectious agents and mucosal pathologies, and discusses the current evidence for causality between different exogenous or mucosal factors and systemic inflammation in RA.

Receptor for advanced glycation end products up-regulation in cerebral endothelial cells mediates cerebrovascular-related amyloid β accumulation after Porphyromonas gingivalis infection

Cerebrovascular-related amyloidogenesis is found in over 80% of Alzheimer's disease (AD) cases, and amyloid β (Aβ) generation is increased in the peripheral macrophages during infection of Porphyromonas gingivalis (P. gingivalis), a causal bacterium for periodontitis. In this study, we focused on receptor for advanced glycation end products (RAGE), the key molecule involves in Aβ influx after P. gingivalis infection to test our hypothesis that Aβ transportation from periphery into the brain, known as "Aβ influx," is enhanced by P. gingivalis infection. Using cultured hCMEC/D3 cell line, in comparison to uninfected cells, directly infection with P. gingivalis (multiplicity of infection, MOI = 5) significantly increased a time-dependent RAGE expression resulting in a dramatic increase in Aβ influx in the hCMEC/D3 cells; the P. gingivalis-up-regulated RAGE expression was significantly decreased by NF-κB and Cathepsin B (CatB)-specific inhibitors, and the P.gingivalis-increased IκBα degradation was significantly decreased by CatB-specific inhibitor. Furthermore, the P. gingivalis-increased Aβ influx was significantly reduced by RAGE-specific inhibitor. Using 15-month-old mice (C57BL/6JJmsSlc, female), in comparison to non-infection mice, systemic P. gingivalis infection for three consecutive weeks (1 × 10⁸  CFU/mouse, every 3 days, intraperitoneally) significantly increased the RAGE expression in the CD31-positive endothelial cells and the Aβ loads around the CD31-positive cells in the mice's brains. The RAGE expression in the CD31-positive cells was positively correlated with the Aβ loads. These observations demonstrate that the up-regulated RAGE expression in cerebral endothelial cells mediates the Aβ influx after P. gingivalis infection, and CatB plays a critical role in regulating the NF-κB/RAGE expression. Cover Image for this issue: https://doi.org/10.1111/jnc.15073.

Glycine Lipids of Porphyromonas gingivalis Are Agonists for Toll-Like Receptor 2

The serine-glycine dipeptide lipid classes, including lipid 430 and lipid 654, are produced by the periodontal pathogen Porphyromonas gingivalis and can be detected in lipid extracts of diseased periodontal tissues and teeth of humans. Both serine-glycine lipid classes were previously shown to engage human and mouse Toll-like receptor 2 (TLR2) and to inhibit mouse osteoblast differentiation and function through engagement of TLR2. It is not clear if other lipids related to serine-glycine lipids are also produced by P. gingivalis The goal of this investigation was to determine whether P. gingivalis produces additional lipid classes similar to the serine-glycine lipids that possess biological properties. P. gingivalis (ATCC 33277) was grown in broth culture, and lipids were extracted and fractionated by high-performance liquid chromatography (HPLC). Lipids were separated using semipreparative HPLC, and specific lipid classes were identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and liquid chromatography-multiple reaction monitoring (LC-MRM) mass spectrometric approaches. Two glycine lipid classes were identified, termed lipid 567 and lipid 342, and these lipid classes are structurally related to the serine-glycine dipeptide lipids. Both glycine lipid classes were shown to promote TLR2-dependent tumor necrosis factor alpha (TNF-α) release from bone marrow macrophages, and both were shown to activate human embryonic kidney (HEK) cells through TLR2 and TLR6 but not TLR1. These results demonstrate that P. gingivalis synthesizes glycine lipids and that these lipids engage TLR2 similarly to the previously reported serine-glycine dipeptide lipids.

Roles of Porphyromonas gingivalis and its virulence factors in periodontitis

Periodontitis is an infection-driven inflammatory disease, which is characterized by gingival inflammation and bone loss. Periodontitis is associated with various systemic diseases, including cardiovascular, respiratory, musculoskeletal, and reproductive system related abnormalities. Recent theory attributes the pathogenesis of periodontitis to oral microbial dysbiosis, in which Porphyromonas gingivalis acts as a critical agent by disrupting host immune homeostasis. Lipopolysaccharide, proteases, fimbriae, and some other virulence factors are among the strategies exploited by P. gingivalis to promote the bacterial colonization and facilitate the outgrowth of the surrounding microbial community. Virulence factors promote the coaggregation of P. gingivalis with other bacteria and the formation of dental biofilm. These virulence factors also modulate a variety of host immune components and subvert the immune response to evade bacterial clearance or induce an inflammatory environment. In this chapter, our focus is to discuss the virulence factors of periodontal pathogens, especially P. gingivalis, and their roles in regulating immune responses during periodontitis progression.

IL-36γ is a pivotal inflammatory player in periodontitis-associated bone loss

Periodontitis is a prevalent chronic inflammatory disease due to the host response (IL-1β, IL-6, TNF-α and IL-17A) to oral bacteria such as Porphyromonas gingivalis. The newer members of the IL-1 family, IL-36s (IL-36α/IL-36β/IL-36γ/IL-36Ra/IL-38) are known to be involved in host defense against P. gingivalis in oral epithelial cells (OECs) and are considered as key inflammatory mediators in chronic diseases. The aim of this study was to investigate the potential role of IL-36s in periodontitis. We showed here that IL-36γ mRNA gingival expression is higher in periodontitis patients, whereas IL-36β and IL-36Ra mRNA expression are lower compared to healthy controls. Interestingly, the elevated IL-36γ expression in patients is positively correlated with the RANKL/OPG ratio, an index of bone resorption. In vitro, IL-36γ expression was induced through TLR2 activation in primary OECs infected with P. gingivalis but not in gingival fibroblasts, the most widespread cell type in gingival connective tissue. In OECs, recombinant IL-36γ enhanced the expression of inflammatory cytokines (IL-1β, IL-6, TNF-α and IL-36γ), of TLR2 and importantly, the RANKL/OPG ratio. These findings suggest that IL-36γ could be a pivotal inflammatory player in periodontitis by perpetuating gingival inflammation and its associated alveolar bone resorption and could be a relevant therapeutic target.

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.

IL-15 and GM-CSF stimulated macrophages enhances phagocytic activity in ENU induced leukemic mice

Murine splenic macrophage plays a decisive role in host immunity through phagocytosis against pathogens. It was reported that, macrophages also involves in phagocytosis of some tumour cells upon its activation initiated by certain cytokines produced by other immune cell or by indigenously treated. In this study, we have investigated the killing of leukemic blast cells by macrophages upon stimulated with IL-15 and GM-CSF alone or in combination in ENU challenged leukemic murine model. Along with, the release of TNF-α, IL-12 and IFN-γ by macrophages were assayed by ELISA. NO production by macrophages was also investigated. The molecular expressions like GM-CSF and TLRs were investigated for better understand of macrophage-leukemic cell interaction. Result shows that in disease condition macrophages have poor phagocytic activities which may be due to less release of TNF-α, IL-12 and IFN-γ by macrophages. This impaired phagocytic activity in leukemic mice was increase upon stimulation with IL-15 and GM-CSF.

Transcription modulation by CDK9 regulates inflammatory genes and RIPK3-MLKL-mediated necroptosis in periodontitis progression

Cyclin-dependent kinase 9 (CDK9), one crucial molecule in promoting the transition from transcription pausing to elongation, is a critical modulator of cell survival and death. However, the pathological function of CDK9 in bacterial inflammatory diseases has never been explored. CDK9 inhibition or knock-down attenuated Porphyromonas gingivalis-triggered inflammatory gene expression. Gene-expression microarray analysis of monocytes revealed that knock-down of CDK9 not only affected inflammatory responses, but also impacted cell death network, especially the receptor-interacting protein kinase 3 (RIPK3)-mixed lineage kinase domain-like (MLKL)-mediated necroptosis after P. gingivalis infection. Inhibition of CDK9 significantly decreased necroptosis with downregulation of both MLKL and phosphorylated MLKL. By regulating caspase-8 and cellular FLICE inhibitory protein (cFLIP), key molecules in regulating cell survival and death, CDK9 affected not only the classic RIPK1-RIPK3-mediated necroptosis, but also the alternate TIR-domain-containing adapter-inducing interferon-β-RIPK3-mediated necroptosis. CDK9 inhibition dampened pro-inflammatory gene production in the acute infection process in the subcutaneous chamber model in vivo. Moreover, CDK9 inhibition contributed to the decreased periodontal bone loss and inflammatory response induced by P. gingivalis in the periodontal micro-environment. In conclusion, by modulating the RIPK3-MLKL-mediated necroptosis, CDK9 inhibition provided a novel mechanism to impact the progress of bacterial infection in the periodontal milieu.

The Distinct Immune-Stimulatory Capacities of Porphyromonas gingivalis Strains 381 and ATCC 33277 Are Determined by the fimB Allele and Gingipain Activity

The Porphyromonas gingivalis strain ATCC 33277 (33277) and 381 genomes are nearly identical. However, strain 33277 displays a significantly diminished capacity to stimulate host cell Toll-like receptor 2 (TLR2)-dependent signaling and interleukin-1β (IL-1β) production relative to 381, suggesting that there are strain-specific differences in one or more bacterial immune-modulatory factors. Genomic sequencing identified a single nucleotide polymorphism in the 33277 fimB allele (A→T), creating a premature stop codon in the 33277 fimB open reading frame relative to the 381 fimB allele. Gene exchange experiments established that the 33277 fimB allele reduces the immune-stimulatory capacity of this strain. Transcriptome comparisons revealed that multiple genes related to carboxy-terminal domain (CTD) family proteins, including the gingipains, were upregulated in 33277 relative to 381. A gingipain substrate degradation assay demonstrated that cell surface gingipain activity is higher in 33277, and an isogenic mutant strain deficient for the gingipains exhibited an increased ability to induce TLR2 signaling and IL-1β production. Furthermore, 33277 and 381 mutant strains lacking CTD cell surface proteins were more immune-stimulatory than the parental wild-type strains, consistent with an immune-suppressive role for the gingipains. Our data show that the combination of an intact fimB allele and limited cell surface gingipain activity in P. gingivalis 381 renders this strain more immune-stimulatory. Conversely, a defective fimB allele and high-level cell surface gingipain activity reduce the capacity of P. gingivalis 33277 to stimulate host cell innate immune responses. In summary, genomic and transcriptomic comparisons identified key virulence characteristics that confer divergent host cell innate immune responses to these highly related P. gingivalis strains.

Pathogenesis of Important Virulence Factors of Porphyromonas gingivalis via Toll-Like Receptors

Periodontitis is a common intraoral infection and is inextricably linked to systemic diseases. Recently, the regulation between host immunologic response and periodontal pathogens has become a hotspot to explain the mechanism of periodontitis and related systemic diseases. Since Porphyromonas gingivalis (P. gingivalis) was proved as critical periodontal pathogen above all, researches focusing on the mechanism of its virulence factors have received extensive attention. Studies have shown that in the development of periodontitis, in addition to the direct release of virulent factors by periodontal pathogens to destroy periodontal tissues, over-low or over-high intrinsic immune and inflammatory response mediated by Toll-like receptors (TLRs) can lead to more lasting destruction of periodontal tissues. It is very necessary to sort out how various cytopathic factors of P. gingivalis mediate inflammation and immune responses between the host through TLRs so as to help precisely prevent, diagnose, and treat periodontitis in clinic. This review summarizes the role of three most widely studied pathogenic factors produced by P. gingivalis (lipopolysaccharide, gingipains, pili) and their interactions with TLRs at the cellular and molecular level in the progress of periodontitis.

Immunological Pathways Triggered by Porphyromonas gingivalis and Fusobacterium nucleatum: Therapeutic Possibilities?

Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) are Gram-negative anaerobic bacteria possessing several virulence factors that make them potential pathogens associated with periodontal disease. Periodontal diseases are chronic inflammatory diseases of the oral cavity, including gingivitis and periodontitis. Periodontitis can lead to tooth loss and is considered one of the most prevalent diseases worldwide. P. gingivalis and F. nucleatum possess virulence factors that allow them to survive in hostile environments by selectively modulating the host's immune-inflammatory response, thereby creating major challenges to host cell survival. Studies have demonstrated that bacterial infection and the host immune responses are involved in the induction of periodontitis. The NLRP3 inflammasome and its effector molecules (IL-1β and caspase-1) play roles in the development of periodontitis. We and others have reported that the purinergic P2X7 receptor plays a role in the modulation of periodontal disease and intracellular pathogen control. Caspase-4/5 (in humans) and caspase-11 (in mice) are important effectors for combating bacterial pathogens via mediation of cell death and IL-1β release. The exact molecular events of the host's response to these bacteria are not fully understood. Here, we review innate and adaptive immune responses induced by P. gingivalis and F. nucleatum infections and discuss the possibility of manipulations of the immune response as therapeutic strategies. Given the global burden of periodontitis, it is important to develop therapeutic targets for the prophylaxis of periodontopathogen infections.

Macrophage immunomodulation in chronic osteolytic diseases-the case of periodontitis

Periodontitis (PD) is a chronic osteolytic disease that shares pathogenic inflammatory features with other conditions associated with nonresolving inflammation. A hallmark of PD is inflammation-mediated alveolar bone loss. Myeloid cells, in particular polymorphonuclear neutrophils (PMN) and macrophages (Mac), are essential players in PD by control of gingival biofilm pathogenicity, activation of adaptive immunity, as well as nonresolving inflammation and collateral tissue damage. Despite mounting evidence of significant innate immune implications to PD progression and healing after therapy, myeloid cell markers and targets for immune modulation have not been validated for clinical use. The remarkable plasticity of monocytes/Mac in response to local activation factors enables these cells to play central roles in inflammation and restoration of tissue homeostasis and provides opportunities for biomarker and therapeutic target discovery for management of chronic inflammatory conditions, including osteolytic diseases such as PD and arthritis. Along a wide spectrum of activation states ranging from proinflammatory to pro-resolving, Macs respond to environmental changes in a site-specific manner in virtually all tissues. This review summarizes the existing evidence on Mac immunomodulation therapies for osteolytic diseases in the broader context of conditions associated with nonresolving inflammation, and discusses osteoimmune implications of Macs in PD.

Activation of Toll-like receptor 2 induces B1 and B2 kinin receptors in human gingival fibroblasts and in mouse gingiva

The regulation of the kallikrein-kinin system is an important mechanism controlling vasodilation and promoting inflammation. We aimed to investigate the role of Toll-like receptor 2 (TLR2) in regulating kinin B₁ and B₂ receptor expression in human gingival fibroblasts and in mouse gingiva. Both P. gingivalis LPS and the synthetic TLR2 agonist Pam₂CSK₄ increased kinin receptor transcripts. Silencing of TLR2, but not of TLR4, inhibited the induction of kinin receptor transcripts by both P. gingivalis LPS and Pam₂CSK₄. Human gingival fibroblasts (HGF) exposed to Pam₂CSK₄ increased binding sites for bradykinin (BK, B₂ receptor agonist) and des-Arg¹⁰-Lys-bradykinin (DALBK, B₁ receptor agonist). Pre-treatment of HGF for 24 h with Pam₂CSK₄ resulted in increased PGE₂ release in response to BK and DALBK. The increase of B1 and B2 receptor transcripts by P. gingivalis LPS was not blocked by IL-1β neutralizing antibody; TNF-α blocking antibody did not affect B₁ receptor up-regulation, but partially blocked increase of B₂ receptor mRNA. Injection of P. gingivalis LPS in mouse gingiva induced an increase of B₁ and B₂ receptor mRNA. These data show that activation of TLR2 in human gingival fibroblasts as well as in mouse gingival tissue leads to increase of B₁ and B₂ receptor mRNA and protein.

The activity of bacterial peptidylarginine deiminase is important during formation of dual-species biofilm by periodontal pathogen Porphyromonas gingivalis and opportunistic fungus Candida albicans

Porphyromonas gingivalis, an anaerobic Gram-negative bacterium critically involved in the development of human periodontitis, belongs to the late colonizers of the oral cavity. The success of this pathogen in the host colonization and infection results from the presence of several virulence factors, including extracellular peptidylarginine deiminase (PPAD), an enzyme that converts protein arginine residues to citrullines. A common opportunistic fungal pathogen of humans, Candida albicans, is also frequently identified among microorganisms that reside at subgingival sites. The aim of the current work was to verify if protein citrullination can influence the formation of mixed biofilms by both microorganisms under hypoxic and normoxic conditions. Quantitative estimations of the bacterial adhesion to fungal cells demonstrated the importance of PPAD activity in this process, since the level of binding of P. gingivalis mutant strain deprived of PPAD was significantly lower than that observed for the wild-type strain. These results were consistent with mass spectrometric detection of the citrullination of selected surface-exposed C. albicans proteins. Furthermore, a viability of P. gingivalis cells under normoxia increased in the presence of fungal biofilm compared with the bacteria that formed single-species biofilm. These findings suggest a possible protection of these strict anaerobes under unfavorable aerobic conditions by C. albicans during mixed biofilm formation.

Inhibition of the histone demethylase KDM4B leads to activation of KDM1A, attenuates bacterial-induced pro-inflammatory cytokine release, and reduces osteoclastogenesis

Periodontal disease (PD) afflicts 46% of Americans with no effective adjunctive therapies available. While most pharmacotherapy for PD targets bacteria, the host immune response is responsible for driving tissue damage and bone loss in severe disease. Herein, we establish that the histone demethylase KDM4B is a potential drug target for the treatment of PD. Immunohistochemical staining of diseased periodontal epithelium revealed an increased abundance of KDM4B that correlates with inflammation. In murine calvarial sections exposed to Aggregatibacter actinomycetemcomitans lipopolysaccharide (Aa-LPS), immunohistochemical staining revealed a significant increase in KDM4B protein expression. The 8-hydroxyquinoline ML324 is known to inhibit the related demethylase KDM4E in vitro, but has not been evaluated against any other targets. Our studies indicate that ML324 also inhibits KDM4B (IC50: 4.9 μM), and decreases the pro-inflammatory cytokine response to an Aa-LPS challenge in vitro. Our results suggest that KDM4B inhibition-induced immunosuppression works indirectly, requiring new protein synthesis. In addition, fluorescence-stained macrophages exhibited a significant decrease in global monomethyl histone 3 lysine 4 (H3K4me) levels following an Aa-LPS challenge that was prevented by KDM4B inhibition, suggesting this effect is produced through KDM1A-mediated demethylation of H3K4. Finally, ML324 inhibition of KDM4B in osteoclast progenitors produced a significant reduction in Aa-LPS-induced osteoclastogenesis. These data link histone methylation with host immune response to bacterial pathogens in PD, and suggest a previously unreported, alternative mechanism for epigenetic control of the host inflammatory environment. As such, KDM4B represents a new therapeutic target for treating hyper-inflammatory diseases that result in bone destruction.