The C5a receptor impairs IL-12-dependent clearance of Porphyromonas gingivalis and is required for induction of periodontal bone loss

Immunosenescence and inflammaging: Conspiracies against alveolar bone turnover

OBJECTIVE

Inflammaging and immunosenescence are characteristics of senescent immune system alterations. This review provides insights into inflammaging and immunosenescence in periodontitis and focuses on the innerlink of inflammaging and immunosenescence in alveolar bone turnover from a perspective of cell-cell interaction.

METHODS

This review is conducted by a narrative approach to discuss the effect of inflammaging and immunosenescence in aging-related alveolar bone loss. A comprehensive literature research in PubMed and Google was applied to identify reports in English.

RESULTS

Inflammaging is concerned with abnormal M1 polarization and increasing circulating inflammatory cytokines, while immunosenescence involves reduced infection and vaccine responses, depressed antimicrobial function, and infiltration of aged B cells and memory T cells. TLR-mediated inflammaging and altered adaptive immunity significantly affect alveolar bone turnover and aggravate aging-related alveolar bone loss. Besides, energy consumption also plays a vital role in aged immune and skeletal system of periodontitis.

CONCLUSIONS

Senescent immune system exerts a significant function in aging-related alveolar bone loss. Inflammaging and immunosenescence interact functionally and mechanistically, which affects alveolar bone turnover. Therefore, further clinical treatment strategies targeting alveolar bone loss could be based on the specific molecular mechanism connecting inflammaging, immunosenescence, and alveolar bone turnover.

Periodontitis increases the risk of gastrointestinal dysfunction: an update on the plausible pathogenic molecular mechanisms

Periodontitis is an immuno-inflammatory disease of the soft tissues surrounding the teeth. Periodontitis is linked to many communicable and non-communicable diseases such as diabetes, cardiovascular disease, rheumatoid arthritis, and cancers. The oral-systemic link between periodontal disease and systemic diseases is attributed to the spread of inflammation, microbial products and microbes to distant organ systems. Oral bacteria reach the gut via swallowed saliva, whereby they induce gut dysbiosis and gastrointestinal dysfunctions. Some periodontal pathogens like Porphyromonas. gingivalis, Klebsiella, Helicobacter. Pylori, Streptococcus, Veillonella, Parvimonas micra, Fusobacterium nucleatum, Peptostreptococcus, Haemophilus, Aggregatibacter actinomycetomcommitans and Streptococcus mutans can withstand the unfavorable acidic, survive in the gut and result in gut dysbiosis. Gut dysbiosis increases gut inflammation, and induce dysplastic changes that lead to gut dysfunction. Various studies have linked oral bacteria, and oral-gut axis to various GIT disorders like inflammatory bowel disease, liver diseases, hepatocellular and pancreatic ductal carcinoma, ulcerative colitis, and Crohn's disease. Although the correlation between periodontitis and GIT disorders is well established, the intricate molecular mechanisms by which oral microflora induce these changes have not been discussed extensively. This review comprehensively discusses the intricate and unique molecular and immunological mechanisms by which periodontal pathogens can induce gut dysbiosis and dysfunction.

The complement system as a key modulator of the oral microbiome in health and disease

In this review, we address the interplay between the complement system and host microbiomes in health and disease, focussing on oral bacteria known to contribute to homeostasis or to promote dysbiosis associated with dental caries and periodontal diseases. Host proteins modulating complement activities in the oral environment and expression profiles of complement proteins in oral tissues were described. In addition, we highlight a sub-set of bacterial proteins involved in complement evasion and/or dysregulation previously characterized in pathogenic species (or strains), but further conserved among prototypical commensal species of the oral microbiome. Potential roles of these proteins in host-microbiome homeostasis and in the emergence of commensal strain lineages with increased virulence were also addressed. Finally, we provide examples of how commensal bacteria might exploit the complement system in competitive or cooperative interactions within the complex microbial communities of oral biofilms. These issues highlight the need for studies investigating the effects of the complement system on bacterial behaviour and competitiveness during their complex interactions within oral and extra-oral host sites.

A guide to complement biology, pathology and therapeutic opportunity

Complement has long been considered a key innate immune effector system that mediates host defence and tissue homeostasis. Yet, growing evidence has illuminated a broader involvement of complement in fundamental biological processes extending far beyond its traditional realm in innate immunity. Complement engages in intricate crosstalk with multiple pattern-recognition and signalling pathways both in the extracellular and intracellular space. Besides modulating host-pathogen interactions, this crosstalk guides early developmental processes and distinct cell trajectories, shaping tissue immunometabolic and regenerative programmes in different physiological systems. This Review provides a guide to the system-wide functions of complement. It highlights illustrative paradigm shifts that have reshaped our understanding of complement pathobiology, drawing examples from evolution, development of the central nervous system, tissue regeneration and cancer immunity. Despite its tight spatiotemporal regulation, complement activation can be derailed, fuelling inflammatory tissue pathology. The pervasive contribution of complement to disease pathophysiology has inspired a resurgence of complement therapeutics with major clinical developments, some of which have challenged long-held dogmas. We thus highlight major therapeutic concepts and milestones in clinical complement intervention.

Biomaterials Functionalized with Inflammasome Inhibitors-Premises and Perspectives

This review aimed at searching literature for data regarding the inflammasomes' involvement in the pathogenesis of oral diseases (mainly periodontitis) and general pathologies, including approaches to control inflammasome-related pathogenic mechanisms. The inflammasomes are part of the innate immune response that activates inflammatory caspases by canonical and noncanonical pathways, to control the activity of Gasdermin D. Once an inflammasome is activated, pro-inflammatory cytokines, such as interleukins, are released. Thus, inflammasomes are involved in inflammatory, autoimmune and autoinflammatory diseases. The review also investigated novel therapies based on the use of phytochemicals and pharmaceutical substances for inhibiting inflammasome activity. Pharmaceutical substances can control the inflammasomes by three mechanisms: inhibiting the intracellular signaling pathways (Allopurinol and SS-31), blocking inflammasome components (VX-765, Emricasan and VX-740), and inhibiting cytokines mediated by the inflammasomes (Canakinumab, Anakinra and Rilonacept). Moreover, phytochemicals inhibit the inflammasomes by neutralizing reactive oxygen species. Biomaterials functionalized by the adsorption of therapeutic agents onto different nanomaterials could represent future research directions to facilitate multimodal and sequential treatment in oral pathologies.

Social networking at the microbiome-host interface

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

C3a-C3aR signaling is a novel modulator of skeletal homeostasis

Osteoimmune studies have identified complement signaling as an important regulator of the skeleton. Specifically, complement anaphylatoxin receptors (i.e., C3aR, C5aR) are expressed on osteoblasts and osteoclasts, implying that C3a and/or C5a may be candidate mediators of skeletal homeostasis. The study aimed to determine how complement signaling influences bone modeling/remodeling in the young skeleton. Female C57BL/6J C3aR-/-C5aR-/- vs. wildtype and C3aR-/- vs. wildtype mice were examined at age 10 weeks. Trabecular and cortical bone parameters were analyzed by micro-CT. In situ osteoblast and osteoclast outcomes were determined by histomorphometry. Osteoblast and osteoclast precursors were assessed in vitro. C3aR-/-C5aR-/- mice displayed an increased trabecular bone phenotype at age 10 weeks. In vitro studies revealed C3aR-/-C5aR-/- vs. wildtype cultures had less bone-resorbing osteoclasts and increased bone-forming osteoblasts, which were validated in vivo. To determine whether C3aR alone was critical for the enhanced skeletal outcomes, wildtype vs. C3aR-/- mice were evaluated for osseous tissue outcomes. Paralleling skeletal findings in C3aR-/-C5aR-/- mice, C3aR-/- vs. wildtype mice had an enhanced trabecular bone volume fraction, which was attributed to increased trabecular number. There was elevated osteoblast activity and suppressed osteoclastic cells in C3aR-/- vs. wildtype mice. Furthermore, primary osteoblasts derived from wildtype mice were stimulated with exogenous C3a, which more profoundly upregulated C3ar1 and the pro-osteoclastic chemokine Cxcl1. This study introduces the C3a/C3aR signaling axis as a novel regulator of the young skeleton.

Effects of periodontitis on cancer outcomes in the era of immunotherapy

Periodontitis results from dysbiosis of the oral microbiome and affects up to 70% of US adults aged 65 years and older. More than 50 systemic inflammatory disorders and comorbidities are associated with periodontitis, many of which overlap with immunotherapy-associated toxicities. Despite the increasing use of immunotherapy for the treatment of cancer, uncertainty remains as to whether the microbial shift associated with periodontal disease can influence response rates and tolerance to cancer immunotherapy. We herein review the pathophysiology of periodontitis and the local and systemic inflammatory conditions related to oral dysbiosis, and discuss the overlapping adverse profiles of periodontitis and immunotherapy. The effects of the presence of Porphyromonas gingivalis, a key pathogen in periodontitis, highlight how the oral microbiome can affect the hosts' systemic immune responses, and further research into the local and systemic influence of other microorganisms causing periodontal disease is necessary. Addressing periodontitis in an ageing population of people with cancer could have potential implications for the clinical response to (and tolerability of) immunotherapy and warrants further investigation.

Porphyromonas gingivalis regulates atherosclerosis through an immune pathway

Atherosclerosis (AS) is a chronic inflammatory disease, involving a pathological process of endothelial dysfunction, lipid deposition, plaque rupture, and arterial occlusion, and is one of the leading causes of death in the world population. The progression of AS is closely associated with several inflammatory diseases, among which periodontitis has been shown to increase the risk of AS. Porphyromonas gingivalis (P. gingivalis), presenting in large numbers in subgingival plaque biofilms, is the “dominant flora” in periodontitis, and its multiple virulence factors are important in stimulating host immunity. Therefore, it is significant to elucidate the potential mechanism and association between P. gingivalis and AS to prevent and treat AS. By summarizing the existing studies, we found that P. gingivalis promotes the progression of AS through multiple immune pathways. P. gingivalis can escape host immune clearance and, in various forms, circulate with blood and lymph and colonize arterial vessel walls, directly inducing local inflammation in blood vessels. It also induces the production of systemic inflammatory mediators and autoimmune antibodies, disrupts the serum lipid profile, and thus promotes the progression of AS. In this paper, we summarize the recent evidence (including clinical studies and animal studies) on the correlation between P. gingivalis and AS, and describe the specific immune mechanisms by which P. gingivalis promotes AS progression from three aspects (immune escape, blood circulation, and lymphatic circulation), providing new insights into the prevention and treatment of AS by suppressing periodontal pathogenic bacteria.

Neutrophils in the periodontium: Interactions with pathogens and roles in tissue homeostasis and inflammation

Neutrophils are of key importance in periodontal health and disease. In their absence or when they are functionally defective, as occurs in certain congenital disorders, affected individuals develop severe forms of periodontitis in early age. These observations imply that the presence of immune-competent neutrophils is essential to homeostasis. However, the presence of supernumerary or hyper-responsive neutrophils, either because of systemic priming or innate immune training, leads to imbalanced host-microbe interactions in the periodontium that culminate in dysbiosis and inflammatory tissue breakdown. These disease-provoking imbalanced interactions are further exacerbated by periodontal pathogens capable of subverting neutrophil responses to their microbial community's benefit and the host's detriment. This review attempts a synthesis of these findings for an integrated view of the neutrophils' ambivalent role in periodontal disease and, moreover, discusses how some of these concepts underpin the development of novel therapeutic approaches to treat periodontal disease.

Stiffness-tuned and ROS-sensitive hydrogel incorporating complement C5a receptor antagonist modulates antibacterial activity of macrophages for periodontitis treatment

Periodontitis is admittedly a microbe-driven intractable infectious disease, in which Porphyromonas gingivalis (Pg) plays a keystone role. Pg can selectively impair the antimicrobial responses of periodontal resident macrophages including their phagocytic and bactericidal activity without interfering their proinflammatory activity, which leads to microflora disturbance, destructive periodontal inflammation and alveolar bone loss eventually. Here, an injectable ROS-sensitive hydrogel is developed for releasing active bone marrow-derived macrophages (named ex-situ macrophages hereafter) and a complement C5a receptor antagonist (C5A) to the gingival crevice. Through appropriately tuning the hydrogel stiffness, the phagocytic activity of these macrophages is greatly enhanced, reaching an optimal performance at the elastic modulus of 106 kPa. Meanwhile, C5A avoids undesired C5a receptor activation by Pg to ensure the bacterial killing activity of both the ex-situ and in-situ macrophages. Besides, the ROS-sensitive hydrogels show another distinct feature of decreasing the ROS level in periodontal niche, which contributes to the alleviated periodontal inflammation and attenuated bone loss as well. This study highlights the potential of utilizing hydrogels with tailored biomechanical properties to remodel the functions of therapeutic cells, which is expected to find wide applications even beyond periodontitis treatment.

Local and Systemic Effects of Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a leading etiological agent in periodontitis. This infectious pathogen can induce a dysbiotic, proinflammatory state within the oral cavity by disrupting commensal interactions between the host and oral microbiota. It is advantageous for P. gingivalis to avoid complete host immunosuppression, as inflammation-induced tissue damage provides essential nutrients necessary for robust bacterial proliferation. In this context, P. gingivalis can gain access to the systemic circulation, where it can promote a prothrombotic state. P. gingivalis expresses a number of virulence factors, which aid this pathogen toward infection of a variety of host cells, evasion of detection by the host immune system, subversion of the host immune responses, and activation of several humoral and cellular hemostatic factors.

DNA methylation changes underlie the long-term association between periodontitis and atherosclerotic cardiovascular disease

Periodontitis, the leading cause of adult tooth loss, has been identified as an independent risk factor for cardiovascular disease (CVD). Studies suggest that periodontitis, like other CVD risk factors, shows the persistence of increased CVD risk even after mitigation. We hypothesized that periodontitis induces epigenetic changes in hematopoietic stem cells in the bone marrow (BM), and such changes persist after the clinical elimination of the disease and underlie the increased CVD risk. We used a BM transplant approach to simulate the clinical elimination of periodontitis and the persistence of the hypothesized epigenetic reprogramming. Using the low-density lipoprotein receptor knockout (LDLR^o ) atherosclerosis mouse model, BM donor mice were fed a high-fat diet to induce atherosclerosis and orally inoculated with Porphyromonas gingivalis (Pg), a keystone periodontal pathogen; the second group was sham-inoculated. Naïve LDLR ^o mice were irradiated and transplanted with BM from one of the two donor groups. Recipients of BM from Pg-inoculated donors developed significantly more atherosclerosis, accompanied by cytokine/chemokines that suggested BM progenitor cell mobilization and were associated with atherosclerosis and/or PD. Using whole-genome bisulfite sequencing, 375 differentially methylated regions (DMRs) and global hypomethylation in recipients of BM from Pg-inoculated donors were observed. Some DMRs pointed to the involvement of enzymes with major roles in DNA methylation and demethylation. In validation assays, we found a significant increase in the activity of ten-eleven translocase-2 and a decrease in the activity of DNA methyltransferases. Plasma S-adenosylhomocysteine levels were significantly higher, and the S-adenosylmethionine to S-adenosylhomocysteine ratio was decreased, both of which have been associated with CVD. These changes may be related to increased oxidative stress as a result of Pg infection. These data suggest a novel and paradigm-shifting mechanism in the long-term association between periodontitis and atherosclerotic CVD.

Periodontal Treatment and Usual Care for Nonalcoholic Fatty Liver Disease: A Multicenter, Randomized Controlled Trial

INTRODUCTION

Periodontal disease is associated with nonalcoholic fatty liver disease (NAFLD). We evaluated periodontal treatment efficacy in patients with NAFLD and periodontal disease.

METHODS

This multicenter, 2-arm, randomized study recruited adult patients with NAFLD and periodontitis, alanine aminotransferase levels ≥40 U/L, and equivalent steatosis grade ≥1. Forty eligible patients (18 men and 22 women) were randomly assigned to 2 groups (scaling and root planning [SRP; n = 20] and tooth brushing [n = 20] groups) stratified by age and sex. The primary and secondary endpoints were changes in alanine aminotransferase levels and serum Porphyromonas gingivalis IgG antibody titers from baseline to 12 weeks, respectively. Efficacy analysis was performed using an intention-to-treat approach ( t test). This trial was registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN000022079).

RESULTS

We observed a significantly higher decrease in absolute alanine aminotransferase levels and P. gingivalis IgG antibody titers in the SRP group than in the tooth brushing group (-12 vs 1 U/L; mean difference [δ], -12; 95% confidence interval [CI], -20 to -5; P = 0.002). The decrease in P. gingivalis IgG antibody titer was significantly higher in the SRP group than in the tooth brushing group (FDC381, -1.6 [2.5]; δ, -1.6; 95% CI, -2.7 to -0.4; P = 0.0092; SU63, -1.7 [2.0]; δ, -1.7; 95% CI, -2.7 to -0.7). No life-threatening events or treatment-related deaths occurred.

DISCUSSION

Periodontal treatment induced significant short-term and mid-term reductions in liver enzyme levels and antibody titers. Further research is warranted to clearly define SRP efficacy and tolerability in patients with NAFLD and periodontitis.

SAP deficiency aggravates periodontitis possibly via C5a-C5aR signaling-mediated defective macrophage phagocytosis of Porphyromonas gingivalis

INTRODUCTION

Serum amyloid P component (SAP) regulates the innate immune system and microbial diseases. Periodontitis is an inflammatory oral disease developed by the host immune system's interaction with the dysbiotic oral microbiome, thereby SAP could play a role in periodontitis pathogenicity.

OBJECTIVES

To investigate the role of SAP in oral microbiome modulation and peridontitis pathogenicity.

METHODS

In this study, wildtype and SAP-knockout (KO) mice were used. Ligature-based periodontitis was developed in mice. Oral microbiome diversity was analyzed by 16 s rRNA sequencing. Macrophages and Porphyromonas gingivalis (P. gingivalis) co-culture system analyzed the effect of SAP in macrophage phagocytosis of P. gingivalis.

RESULTS

The level of SAP was upregulated in the periodontitis-affected periodontium of humans and mice but not in the liver and blood circulation. Periodontal macrophages were the key source of upregulated SAP in periodontitis. SAP-KO aggravated periodontal inflammation, periodontitis, and a higher number of M1-type inflammatory macrophage infiltration in the periodontium. The oral microbiome of SAP-KO periodontitis mice was altered with a higher abundance of Porphyromonas at the genus level. SAP-KO macrophages showed compromised phagocytosis of P. gingivalis in the co-culture system. Co-culture of SAP-KO macrophages and P. gingivalis induced the C5a expression and exogenous SAP treatment nullified this effect. Exogenous recombinant SAP treatment did not affect P. gingivalis growth and opsonization. PMX205, an antagonist of C5a, treatment robustly enhanced P. gingivalis phagocytosis by SAP-KO macrophages, indicating the involvement of the C5a-C5aR signaling in the compromised P. gingivalis phagocytosis by SAP-KO macrophages.

CONCLUSION

SAP deficiency aggravates periodontitis possibly via C5a-C5aR signaling-mediated defective macrophage phagocytosis of P. gingivalis. A higher abundance of P. gingivalis during SAP deficiency could promote M1 macrophage polarization and periodontitis. This finding suggests the possible protecting role of elevated levels of periodontal SAP against periodontitis progression.

Transcriptome Analysis of Monocytes and Fibroblasts Provides Insights Into the Molecular Features of Periodontal Ehlers-Danlos Syndrome

Periodontal Ehlers–Danlos syndrome (pEDS) is a rare hereditary disorder characterized by severe early-onset periodontitis with premature tooth loss, pretibial hyperpigmentation, and skin fragility. It is caused by mutant variants in the C1R and C1S genes that result in C4 cleavage and local complement cascade activation, as well as other possible consequences. However, the exact functional consequences of this activation remain unclear. To shed light on molecular mechanisms underlying pEDS and to identify novel molecular targets that may expand treatment strategies, we performed transcriptome profiling by RNA sequencing of monocytes and gingival fibroblasts from two patients with pEDS. Compared to normal controls, differential expression of genes was found only in monocytes but not gingival fibroblasts. Most of the significant genes were enriched in biological processes such as neutrophil-mediated immunity, response to bacterium, TNF-α and IL-17 pathway which are related to inflammation response and immune response. In disease ontology enrichment analysis, genes related to periodontal host defense, inflammatory response, skin disease, and vascular development, including MMP9, VEGFA, IL10, IL1A, IL1B, IL2RA, and IL6, were significantly enriched and also validated by qPCR and ELISA. Overall, the present study provides the transcriptomic data of pEDS for the first time and the distinct molecular features in monocytes of pEDS might serve as a tool to better understand the disease.

Osteoimmunology in Periodontitis: Local Proteins and Compounds to Alleviate Periodontitis

Periodontitis is one of the most common oral diseases resulting in gingival inflammation and tooth loss. Growing evidence indicates that it results from dysbiosis of the oral microbiome, which interferes with the host immune system, leading to bone destruction. Immune cells activate periodontal ligament cells to express the receptor activator of nuclear factor kappa-B (NF-κB) ligand (RANKL) and promote osteoclast activity. Osteocytes have active roles in periodontitis progression in the bone matrix. Local proteins are involved in bone regeneration through functional immunological plasticity. Here, we discuss the current knowledge of cellular and molecular mechanisms in periodontitis, the roles of local proteins, and promising synthetic compounds generating a periodontal regeneration effect. It is anticipated that this may lead to a better perception of periodontitis pathophysiology.

Modulating the Immune Response in Periodontitis

Periodontitis is a chronic inflammatory condition initiated by the accumulation of bacterial biofilm. It is highly prevalent and when left untreated can lead to tooth loss. The presence of bacterial biofilm is essential for the initiation of the inflammatory response but is not the sole initiator. Currently it is unknown which mechanisms drive the dysbiosis of the bacterial biofilm leading to the dysregulation of the inflammatory response. Other players in this equation include environmental, systemic, and genetic factors which can play a role in exacerbating the inflammatory response. Treatment of periodontal disease consists of removal of the bacterial biofilm with the goal of resolving the inflammatory response; however, this does not occur in every case. Understanding the way the inflammatory response does not return to a state of homeostasis has led investigators to consider both systemic and local pharmacological interventions. Nonetheless, a better understanding of the impact that genetics and environmental factors may have on the inflammatory response could be key to helping identify how inflammation can be modulated therefore stopping the destruction of the periodontium. In this article, we will explore the current evidence associating the microbial dysbiosis and the dysregulation of the immune response, potential mechanisms or pathways that may be targeted for the modulation of the inflammatory response, and discuss the advantages and drawbacks associated with local and systemic inflammatory modulation in the management of periodontal disease. This information will be valuable for those interested in understanding potential adjunct methods for managing periodontal diseases, but not limited to, dental professionals, clinical researchers and the public at large.

Role of PG0192 and PG0193 in the modulation of pro-inflammatory cytokines in macrophages in response to Porphyromonas gingivalis

Porphyromonas gingivalis is the main pathogen of chronic periodontitis. However, the specific mechanisms through which P. gingivalis induces immune and inflammatory responses in periodontitis have not been completely elucidated. In this study, we investigated the effects of the P. gingivalis outer membrane protein OmpH (encoded by PG0192 and PG0193) on interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) expression in macrophages to assess the pro-inflammatory cytokine responses. A PG0192-PG0193 deletion mutant strain and a com△PG0192-0193 strain were constructed. Furthermore, rOmpH-1 and rOmpH-2 encoded by PG0192 and PG0193, respectively, were cloned, expressed, and purified for subsequent experiments. Notably, the expression of IL-6 and TNF-α at mRNA and protein levels was downregulated upon treatment of macrophages with the PG0192-PG0193 deletion mutant strain, whereas treatment of macrophages with P. gingivalis W83 co-incubated with rOmpH-1 or rOmpH-2 upregulated IL-6 and TNF-α mRNA levels. The addition of C5aR antagonist blocked this induction. Overall, our findings provided important insights into the roles of PG0192 and PG0193 for promoting IL-6 and TNF-α expression in macrophages exposed to P. gingivalis and revealed the involvement of C5aR in the pro-inflammatory response.

Complement receptor C5aR1 on osteoblasts regulates osteoclastogenesis in experimental postmenopausal osteoporosis

In recent years, evidence has accumulated that the complement system, an integral part of innate immunity, may be involved in the regulation of bone homeostasis as well as inflammatory bone loss, for example, in rheumatoid arthritis and periodontitis. Complement may also contribute to osteoporosis development, but investigation of the mechanism is limited. Using mice with a conditional deletion of the complement anaphylatoxin receptor C5aR1, we here demonstrated that C5aR1 in osteoblasts (C5aR1 ^Runx2-Cre mice) or osteoclasts (C5aR1 ^LysM-Cre mice) did not affect physiological bone turnover or age-related bone loss in either sex, as confirmed by micro-computed tomography, histomorphometry, and biomechanical analyses of the bone and by the measurement of bone turnover markers in the blood serum. When female mice were subjected to ovariectomy (OVX), a common model for postmenopausal osteoporosis, significant bone loss was induced in C5aR1 ^fl/fl and C5aR1 ^LysM-Cre mice, as demonstrated by a significantly reduced bone volume fraction, trabecular number and thickness as well as an increased trabecular separation in the trabecular bone compartment. Confirming this, the osteoclast number and the receptor activator of nuclear factor k-B (RANK) ligand (RANKL) serum level were significantly elevated in these mouse lines. By contrast, C5aR1 ^Runx2-Cre mice were protected from bone loss after OVX and the serum RANKL concentration was not increased after OVX. These data suggested that bone cell-specific C5aR1 may be redundant in bone homeostasis regulation under physiological conditions. However, C5aR1 on osteoblasts was crucial for the induction of bone resorption under osteoporotic conditions by stimulating RANKL release, whereas C5aR1 on osteoclasts did not regulate OVX-induced bone loss. Therefore, our results implicate C5aR1 on osteoblasts as a potential target for treating postmenopausal osteoporosis.

The effect of local application of thymoquinone, Nigella sativa’s bioactive component, on bone healing in experimental bone defects infected with Porphyromonas gingivalis

Purpose

This study was performed to evaluate the influence of local application of thymoquinone (TQ) on bone healing in experimental bone defects infected with Porphyromonas gingivalis (PG).

Methods

Forty-two female rats were randomly divided into 6 groups. A bone defect was created on the right tibia of all animals. The PG, PG/collagen membrane (COL) and PG/TQ/COL groups were infected with PG. In the COL and PG/COL groups, the defects were covered with a COL; in the TQ/COL and PG/TQ/COL groups, the defects were covered with a TQ-containing COL. After 28 days, all animals were sacrificed. Quantitative measurements of new bone formation and osteoblast lining, as well as semiquantitative measurements of capillary density and tissue response, were analyzed. Furthermore, the presence of bacterial infections in defect areas was evaluated.

Results

The new bone formation, osteoblast number, and capillary density were significantly higher in the TQ groups than in the control groups (P<0.001, P<0.001, and P<0.01, respectively). In a comparison between the TQ/COL group, with a TQ-containing COL (TQ/COL), and the PG–infected TQ-containing COL (PG/TQ/COL) group, the newly formed bone and capillary density were higher in the TQ/COL group (P<0.01). When the control group was compared to the PG, PG/COL, and PG/TQ/COL groups in terms of tissue response, the differences were statistically significant (P<0.001, P=0.02, and P=0.041, respectively). The intensity of the inflammatory cell reaction was higher in the PG, PG/COL, and PG/TQ/COL groups (P<0.05).

Conclusions

Within the limitations of this study, the local application of a TQ-containing COL positively affected bone healing even if the bone defects were infected. The results suggest that TQ increased angiogenesis and showed promise for accelerating bone defect healing. Further research is warranted to support these findings and reach more definitive conclusions.

The Th17/Treg cell balance: crosstalk among the immune system, bone and microbes in periodontitis

Periodontopathic bacteria constantly stimulate the host, which causes an immune response, leading to host-induced periodontal tissue damage. The complex interaction and imbalance between Th17 and Treg cells may be critical in the pathogenesis of periodontitis. Furthermore, the RANKL/RANK/OPG system plays a significant role in periodontitis bone metabolism, and its relationship with the Th17/Treg cell imbalance may be a bridge between periodontal bone metabolism and the immune system. This article reviews the literature related to the Th17/Treg cell imbalance mediated by pathogenic periodontal microbes, and its mechanism involving RANKL/RANK/OPG in periodontitis bone metabolism, in an effort to provide new ideas for the study of the immunopathological mechanism of periodontitis.

Polarized Macrophages in Periodontitis: Characteristics, Function, and Molecular Signaling

Periodontitis (PD) is a common chronic infectious disease. The local inflammatory response in the host may cause the destruction of supporting periodontal tissue. Macrophages play a variety of roles in PD, including regulatory and phagocytosis. Moreover, under the induction of different factors, macrophages polarize and form different functional phenotypes. Among them, M1-type macrophages with proinflammatory functions and M2-type macrophages with anti-inflammatory functions are the most representative, and both of them can regulate the tendency of the immune system to exert proinflammatory or anti-inflammatory functions. M1 and M2 macrophages are involved in the destructive and reparative stages of PD. Due to the complex microenvironment of PD, the dynamic development of PD, and various local mediators, increasing attention has been given to the study of macrophage polarization in PD. This review summarizes the role of macrophage polarization in the development of PD and its research progress.

Impact of tooth loss due to periodontal disease on the prognosis of rehabilitation

When periodontal disease is diagnosed, it is difficult to predict the clinical response of treatment of a tooth over time because the result of treatment is affected by several factors and will depend on the maintenance and support of periodontal treatment. Rehabilitation with removable dental prostheses, fixed prostheses, and dental implants makes it possible to restore the function and esthetics of patients with tooth loss due to periodontal disease. The predictive factors of tooth loss in periodontitis patients should be assessed by dentists to inform their clinical decision-making during dental treatment planning. This will provide detailed individualized information and level of risk of patients considered suitable for dental rehabilitation. Therefore, the aim of this article was to review the subject of "Impact of tooth loss due to periodontal disease on the prognosis of rehabilitation" and the effect of fixed, removable, and implant-supported prostheses in periodontal patients.

Oral microbiota in the oral-genitourinary axis: identifying periodontitis as a potential risk of genitourinary cancers

Periodontitis has been proposed as a novel risk factor of genitourinary cancers: although periodontitis and genitourinary cancers are two totally distinct types of disorders, epidemiological and clinical studies, have established associations between them. Dysbiosis of oral microbiota has already been established as a major factor contributing to periodontitis. Recent emerging epidemiological evidence and the detection of oral microbiota in genitourinary organs indicate the presence of an oral-genitourinary axis and oral microbiota may be involved in the pathogenesis of genitourinary cancers. Therefore, oral microbiota provides the bridge between periodontitis and genitourinary cancers. We have carried out this narrative review which summarizes epidemiological studies exploring the association between periodontitis and genitourinary cancers. We have also highlighted the current evidence demonstrating the capacity of oral microbiota to regulate almost all hallmarks of cancer, and proposed the potential mechanisms of oral microbiota in the development of genitourinary cancers.

Microbiota-Host Immunity Communication in Neurodegenerative Disorders: Bioengineering Challenges for In Vitro Modeling

Human microbiota communicates with its host by secreting signaling metabolites, enzymes, or structural components. Its homeostasis strongly influences the modulation of human tissue barriers and immune system. Dysbiosis-induced peripheral immunity response can propagate bacterial and pro-inflammatory signals to the whole body, including the brain. This immune-mediated communication may contribute to several neurodegenerative disorders, as Alzheimer's disease. In fact, neurodegeneration is associated with dysbiosis and neuroinflammation. The interplay between the microbial communities and the brain is complex and bidirectional, and a great deal of interest is emerging to define the exact mechanisms. This review focuses on microbiota-immunity-central nervous system (CNS) communication and shows how gut and oral microbiota populations trigger immune cells, propagating inflammation from the periphery to the cerebral parenchyma, thus contributing to the onset and progression of neurodegeneration. Moreover, an overview of the technological challenges with in vitro modeling of the microbiota-immunity-CNS axis, offering interesting technological hints about the most advanced solutions and current technologies is provided.

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.

Current understanding of periodontal disease pathogenesis and targets for host-modulation therapy

Recent advances indicate that periodontitis is driven by reciprocally reinforced interactions between a dysbiotic microbiome and dysregulated inflammation. Inflammation is not only a consequence of dysbiosis but, via mediating tissue dysfunction and damage, fuels further growth of selectively dysbiotic communities of bacteria (inflammophiles), thereby generating a self-sustained feed-forward loop that perpetuates the disease. These considerations provide a strong rationale for developing adjunctive host-modulation therapies for the treatment of periodontitis. Such host-modulation approaches aim to inhibit harmful inflammation and promote its resolution or to interfere directly with downstream effectors of connective tissue and bone destruction. This paper reviews diverse strategies targeted to modulate the host periodontal response and discusses their mechanisms of action, perceived safety, and potential for clinical application.

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

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

Using next-generation sequencing to detect oral microbiome change following periodontal interventions: A systematic review

Objectives

This systematic review was to evaluate the change of oral microbiome based on next‐generation sequencing (NGS)‐metagenomic analysis following periodontal interventions among systematically healthy subjects.

Materials and Methods

A structured search strategy consisting of “metagenomics” and “oral diseases” was applied to PubMed, EMBASE, and Web of Science to identify effective papers. The included studies were original studies published in English, using metagenomic approach to analyze the effectiveness of periodontal intervention on oral microbiome among systematically healthy human subjects with periodontitis.

Results

A total of 12 papers were included in this review. Due to the heterogeneity of selected study, quantitative analysis was not performed. The findings as to how alpha diversity changed after interventions were not consistent across studies. Six studies illustrated clear separation of microbial composition between dental plaque samples collected before and after intervention using principal coordinates/component analysis. The most commonly detected genera before intervention were Porphyromonas, Treponema, Tannerella, and Prevotella, while Streptococcus and Actinomyces usually increased and became the dominant genera after intervention. Correlation network analysis revealed that after intervention, the topology of network was different compared to the corresponding pre‐interventional samples.

Conclusion

Existing evidence of metagenomic studies depicts a complex change in oral microbiome after periodontal intervention.

Efficacy and safety of PERIOdontal treatment versus usual care for Nonalcoholic liver disease: protocol of the PERION multicenter, two-arm, open-label, randomized trial

Background

We report the first protocol for a multicenter, randomized comparison study to compare the efficacies of periodontal scaling and root-planing treatment against that of tooth-brushing treatment for nonalcoholic fatty liver disease (NAFLD) (PERION: PERIOdontal treatment for NAFLD). Nonalcoholic steatohepatitis (NASH) is an advanced form of NAFLD, which can progress to cirrhosis and hepatocellular carcinoma. Increased endotoxemia is associated with the progression of NAFLD. Periodontal bacteria possess endotoxins; Porphyromonas gingivalis is well-known as a major pathogenic bacterium in periodontitis, and serum antibody levels for P. gingivalis are high in patients with periodontitis. Several reports have indicated that P. gingivalis is related to NAFLD. This study aims to investigate the effect of periodontal treatment for liver damage, P. gingivalis infection, and endotoxemia on patients with NAFLD.

Methods

We will include adult patients (20–85 years old) with NAFLD, alanine aminotransferase (ALT) ≥ 40 IU/L, and equivalent steatosis grade ≥ 1 (target sample size, n = 40 patients; planned number of patients with outcome data, n = 32). Participants will be randomly assigned to one of two groups: a scaling and root-planing group or tooth-brushing as the usual group. The primary outcome will be the change in ALT levels from baseline to 12 weeks; the key secondary outcome will be the change in the serum immunoglobulin G (IgG) antibody titer for P. gingivalis at 12 weeks.

Discussion

This study should determine whether periodontal treatment decreases liver damage, P. gingivalis infection, and endotoxemia in patients with NAFLD.

Trial registration

University Hospital Medical Information Network (UMIN) Clinical Trials Registry, ID: UMIN000022079.

Porphyromonas gingivalis: Immune subversion activities and role in periodontal dysbiosis

Purpose of review

This review summarizes mechanisms by which Porphyromonas gingivalis interacts with community members and the host so that it can persist in the periodontium under inflammatory conditions that drive periodontal disease.

Recent findings

Recent advances indicate that, in great part, the pathogenicity of P. gingivalis is dependent upon its ability to establish residence in the subgingival environment and to subvert innate immunity in a manner that uncouples the nutritionally favorable (for the bacteria) inflammatory response from antimicrobial pathways. While the initial establishment of P. gingivalis is dependent upon interactions with early colonizing bacteria, the immune subversion strategies of P. gingivalis in turn benefit co-habiting species.

Summary

Specific interspecies interactions and subversion of the host response contribute to the emergence and persistence of dysbiotic communities and are thus targets of therapeutic approaches for the treatment of periodontitis.

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.

Inhibition of osteoclast activity by complement regulation with DF3016A, a novel small-molecular-weight C5aR inhibitor

Recent insights have indicated an active role of the complex complement system not only in immunity, but also in bone remodeling. Evidence from knockout mice and observations from skeletal diseases have drawn attention to the C5a/C5aR axis of the complement cascade in the modulation of osteoclast functions and as potential therapeutic targets for treatment of bone pathologies. With the aim to identify novel C5aR regulators, a medicinal chemistry program was initiated, driven by structural information on a minor pocket of C5aR that has been proposed to be a key motif for C5aR intracellular activation. The impact of the peptidomimetic orthosteric C5aR antagonist (PMX-53), of two newly synthesized allosteric C5aR antagonists (DF2593A, DF3016A), and of C5aR down-regulation by specific siRNAs, were examined for regulation of osteoclastogenesis, using a well-validated in-vitro model starting from RAW264.7 precursor cells. Both pharmacological and molecular approaches reduced osteoclast maturation of RAW264.7 cells induced by receptor-activator of nuclear factor kappa-B ligand (RANKL), which limited the transcription of several differentiation markers evaluated by real-time PCR, including nuclear factor of activated T-cell 1, matrix metalloproteinase-9, cathepsin-K, and tartrate-resistant acid phosphatase. These treatments were ineffective on the subsequent step of osteoclast syncytium formation, apparently as a consequence of reduction of C5aR mRNA levels in the course of osteoclastogenesis, as monitored by real-time PCR. Among the C5aR antagonists analyzed, DF3016A inhibited osteoclast degradation activity through inhibition of C5aR signal transduction and transcription. These data confirm the preclinical relevance of this novel therapeutic candidate.

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.

Osteoimmunology of Oral and Maxillofacial Diseases: Translational Applications Based on Biological Mechanisms

The maxillofacial skeleton is highly dynamic and requires a constant equilibrium between the bone resorption and bone formation. The field of osteoimmunology explores the interactions between bone metabolism and the immune response, providing a context to study the complex cellular and molecular networks involved in oro-maxillofacial osteolytic diseases. In this review, we present a framework for understanding the potential mechanisms underlying the immuno-pathobiology in etiologically-diverse diseases that affect the oral and maxillofacial region and share bone destruction as their common clinical outcome. These otherwise different pathologies share similar inflammatory pathways mediated by central cellular players, such as macrophages, T and B cells, that promote the differentiation and activation of osteoclasts, ineffective or insufficient bone apposition by osteoblasts, and the continuous production of osteoclastogenic signals by immune and local stromal cells. We also present the potential translational applications of this knowledge based on the biological mechanisms involved in the inflammation-induced bone destruction. Such applications can be the development of immune-based therapies that promote bone healing/regeneration, the identification of host-derived inflammatory/collagenolytic biomarkers as diagnostics tools, the assessment of links between oral and systemic diseases; and the characterization of genetic polymorphisms in immune or bone-related genes that will help diagnosis of susceptible individuals.

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.

Differential effects of anaphylatoxin C5a on antigen presenting cells, roles for C5aR1 and C5aR2

The anaphylatoxin C5a is well-known for its role as chemoattractant and contributes to immune cell recruitment into inflamed tissue and local inflammation. C5a has recently been implicated in modulation of antigen presenting cell function, such as macrophages and dendritic cells, which are pivotal for T cell activation and final T cell effector function. The published data on the effect of C5a on APC function and subsequent adaptive immune responses are in part conflicting, as both pro and anti-inflammatory effects have been described. In this review the opposing effects of C5a on APC function in mice and human are summarized and discussed in relation to origin of the involved APC subset, being either of the monocyte-derived lineage or dendritic cell lineage. In addition, the current knowledge on the expression of C5aR1 and C5aR2 on the different APC subsets is summarized. Based on the combined data, we propose that the differential effects of C5a on APC function may be attributed to absence or presence of co-expression of C5aR2 and C5aR1 on the specific APC.

Complement-Dependent Mechanisms and Interventions in Periodontal Disease

Periodontitis is a prevalent inflammatory disease that leads to the destruction of the tooth-supporting tissues. Current therapies are not effective for all patients and this oral disease continues to be a significant public health and economic burden. Central to periodontal disease pathogenesis is a reciprocally reinforced interplay between microbial dysbiosis and destructive inflammation, suggesting the potential relevance of host-modulation therapies. This review summarizes and discusses clinical observations and pre-clinical intervention studies that collectively suggest that complement is hyperactivated in periodontitis and that its inhibition provides a therapeutic benefit. Specifically, interception of the complement cascade at its central component, C3, using a locally administered small peptidic compound (Cp40/AMY-101) protected non-human primates from induced or naturally occurring periodontitis. These studies indicate that C3-targeted intervention merits investigation as an adjunctive treatment of periodontal disease in humans.

The oral microbiota: dynamic communities and host interactions

The dynamic and polymicrobial oral microbiome is a direct precursor of diseases such as dental caries and periodontitis, two of the most prevalent microbially induced disorders worldwide. Distinct microenvironments at oral barriers harbour unique microbial communities, which are regulated through sophisticated signalling systems and by host and environmental factors. The collective function of microbial communities is a major driver of homeostasis or dysbiosis and ultimately health or disease. Despite different aetiologies, periodontitis and caries are each driven by a feedforward loop between the microbiota and host factors (inflammation and dietary sugars, respectively) that favours the emergence and persistence of dysbiosis. In this Review, we discuss current knowledge and emerging mechanisms governing oral polymicrobial synergy and dysbiosis that have both enhanced our understanding of pathogenic mechanisms and aided the design of innovative therapeutic approaches for oral diseases.

The involvement of C5a in the progression of experimental arthritis with Porphyromonas gingivalis infection in SKG mice

Background

Epidemiological evidence to suggest that periodontal disease (PD) is involved in the progression of rheumatoid arthritis (RA) is increasing. The complement system plays a critical role in immune responses. C5a has been implicated in chronic inflammatory diseases, including PD and RA. Porphyromonas gingivalis is the major causative bacteria of PD and can produce C5a. Therefore, it is hypothesized that P. gingivalis infection is involved in the progression of RA by elevating C5a levels. In the present study, P. gingivalis–infected RA model mice were established to investigate the involvement of C5a.

Methods

SKG mice orally infected with P. gingivalis were immunized with intraperitoneal injection of laminarin (LA) to induce arthritis. Arthritis development was assessed by arthritis score (AS), bone destruction on the talus, histology, and serum markers of RA. In order to investigate the effects of serum C5a on bone destruction, osteoclast differentiation of bone marrow mononuclear cells was examined by using serum samples from each group of mice. The relationship between C5a levels and antibody titers to periodontal pathogens in patients with RA was investigated by enzyme-linked immunosorbent assay.

Results

P. gingivalis oral infection increased AS, infiltration of inflammatory cells, bone destruction on the talus, and serum markers of RA in mice immunized with LA. The addition of serum from LA-injected mice with the P. gingivalis oral infection promoted osteoclast differentiation, and the addition of a neutralization antibody against C5a suppressed osteoclast differentiation. C5a levels of serum in RA patients with positive P. gingivalis antibody were elevated compared with those in RA patients with negative P. gingivalis antibody.

Conclusions

These results suggest that P. gingivalis infection enhances the progression of RA via C5a.

Egg yolk immunoglobulins' impact on experimental periodontitis caused by Porphyromonas gingivalis

BACKGROUND

Periodontitis is a chronic inflammatory disease caused by Porphyromonas gingivalis that leads to a series of periodontal tissue injuries. Egg yolk immunoglobulins (IgY) is procuded in egg yolk and inhibits P. gingivalis.

OBJECTIVE

The aim was to evaluate the effect of IgY on experimental periodontitis caused by P. gingivalis.

METHODS

The second molars of rats were ligatured using medical 5-0 silk and smeared with P. gingivalis to induce experimental periodontitis. Then, the rats were smeared with 2 mL IgY solutions or 0.9% NaCl in the oral cavity for up to 4 wk. The scores for gingival index, plaque index and probe on bleeding, the levels of IL-6 and TNF-α, X-ray radiography and histology were used to determine the efficacy of the IgY on experimental periodontitis.

RESULTS

The clinical indices improved; the levels of IL-6 and TNF-α were significantly (p< 0.05) decreased; the X-rays and histomorphological observations suggested that the periodontal inflammation and periodontitis were alleviated compared to the control.

CONCLUSIONS

IgY showed significant effects on anti-inflammatory, anti-coaggregation activity, and protected against alveolar bone loss. Therefore, it had a beneficial effect on preventing experimental periodontitis caused by P. gingivalis.

C5aR1 interacts with TLR2 in osteoblasts and stimulates the osteoclast-inducing chemokine CXCL10

The anaphylatoxin C5a is generated upon activation of the complement system, a crucial arm of innate immunity. C5a mediates proinflammatory actions via the C5a receptor C5aR1 and thereby promotes host defence, but also modulates tissue homeostasis. There is evidence that the C5a/C5aR1 axis is critically involved both in physiological bone turnover and in inflammatory conditions affecting bone, including osteoarthritis, periodontitis, and bone fractures. C5a induces the migration and secretion of proinflammatory cytokines of osteoblasts. However, the underlying mechanisms remain elusive. Therefore, in this study we aimed to determine C5a‐mediated downstream signalling in osteoblasts. Using a whole‐genome microarray approach, we demonstrate that C5a activates mitogen‐activated protein kinases (MAPKs) and regulates the expression of genes involved in pathways related to insulin, transforming growth factor‐β and the activator protein‐1 transcription factor. Interestingly, using coimmunoprecipitation, we found an interaction between C5aR1 and Toll‐like receptor 2 (TLR2) in osteoblasts. The C5aR1‐ and TLR2‐signalling pathways converge on the activation of p38 MAPK and the generation of C‐X‐C motif chemokine 10, which functions, among others, as an osteoclastogenic factor. In conclusion, C5a‐stimulated osteoblasts might modulate osteoclast activity and contribute to immunomodulation in inflammatory bone disorders.

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.

The Role of Skin and Orogenital Microbiota in Protective Immunity and Chronic Immune-Mediated Inflammatory Disease

The skin and orogenital mucosae, which constitute complex protective barriers against infection and injuries, are not only the first to come into contact with pathogens but are also colonized by a set of microorganisms that are essential to maintain a healthy physiological environment. Using 16S ribosomal RNA metagenomic sequencing, scientists recognized that the microorganism colonization has greater diversity and variability than previously assumed. These microorganisms, such as commensal bacteria, affect the host’s immune response against pathogens and modulate chronic inflammatory responses. Previously, a single pathogen was thought to cause a single disease, but current evidence suggests that dysbiosis of the tissue microbiota may underlie the disease status. Dysbiosis results in aberrant immune responses at the surface and furthermore, affects the systemic immune response. Hence, understanding the initial interaction between the barrier surface immune system and local microorganisms is important for understanding the overall systemic effects of the immune response. In this review, we describe current evidence for the basis of the interactions between pathogens, microbiota, and immune cells on surface barriers and offer explanations for how these interactions may lead to chronic inflammatory disorders.

Complement receptors C5aR1 and C5aR2 act differentially during the early immune response after bone fracture but are similarly involved in bone repair

Severely injured patients frequently suffer compromised fracture healing because of systemic post-traumatic inflammation. An important trigger of the posttraumatic immune response is the complement anaphylatoxin C5a, which acts via two receptors, C5aR1 and C5aR2, expressed on immune and bone cells. The blockade of C5a-mediated inflammation during the early inflammatory phase was demonstrated to improve fracture healing after severe injury. However, the distinct roles of the two complement receptors C5aR1 and C5aR2 in bone has to date not been studied. Here, we investigated bone turnover and regeneration in mice lacking either C5aR1 or C5aR2 in a model of isolated fracture and after severe injury, combining the fracture with an additional thoracic trauma. Both C5aR1^−/− and C5aR2^−/− mice displayed an increased bone mass compared to wild-type controls due to reduced osteoclast formation and increased osteoblast numbers, respectively. Following fracture, the inflammatory response was differently affected in these strains: It was decreased in C5aR1^−/− mice but enhanced in C5aR2^−/− mice. Both strains exhibited impaired fracture healing, disturbed osteoclastogenesis and delayed cartilage-to-bone transformation. Thus, our data suggest that C5aR1 and C5aR2 differentially regulate the immune response after fracture and are required for effective cartilage-to-bone transformation in the fracture callus and for undisturbed bone healing.

Monitoring C5aR2 Expression Using a Floxed tdTomato-C5aR2 Knock-In Mouse

The biological significance of C5a receptor [(C5aR)2/C5L2], a seven-transmembrane receptor binding C5a and C5adesArg, remains ill-defined. Specific ligation of C5aR2 inhibits C5a-induced ERK1/2 activation, strengthening the view that C5aR2 regulates C5aR1-mediated effector functions. Although C5aR2 and C5aR1 are often coexpressed, a detailed picture of C5aR2 expression in murine cells and tissues is still lacking. To close this gap, we generated a floxed tandem dye (td)Tomato-C5aR2 knock-in mouse that we used to track C5aR2 expression in tissue-residing and circulating immune cells. We found the strongest C5aR2 expression in the brain, bone marrow, and airways. All myeloid-derived cells expressed C5aR2, although with different intensities. C5aR2 expression in blood and tissue neutrophils was strong and homogeneous. Specific ligation of C5aR2 in neutrophils from tdTomato-C5aR2 mice blocked C5a-driven ERK1/2 phosphorylation, demonstrating functionality of C5aR2 in the reporter mice. In contrast to neutrophils, we found tissue-specific differences in C5aR2 expression in eosinophils, macrophages, and dendritic cell subsets. Naive and activated T cells stained negative for C5aR2, whereas B cells from different tissues homogeneously expressed C5aR2. Also, NK cell subsets in blood and spleen strongly expressed C5aR2. Activation of C5aR2 in NK cells suppressed IL-12/IL-18-induced IFN-γ production. Intratracheal IL-33 challenge resulted in decreased C5aR2 expression in pulmonary eosinophils and monocyte-derived dendritic cells. In summary, we provide a detailed map of murine C5aR2 immune cell expression in different tissues under steady-state conditions and upon pulmonary inflammation. The C5aR2 knock-in mouse will help to reliably track and conditionally delete C5aR2 expression in experimental models of inflammation.

More than complementing Tolls: complement-Toll-like receptor synergy and crosstalk in innate immunity and inflammation

Complement and Toll-like receptors (TLRs) play key roles in the host immune response and are swiftly activated by infection or other types of immunological stress. This review focuses on the capacity of complement and TLRs to engage in signaling crosstalk, ostensibly to coordinate immune and inflammatory responses through synergistic or antagonistic (regulatory) interactions. However, overactivation or dysregulation of either system may lead-often synergistically-to exaggerated inflammation and host tissue injury. Intriguingly, moreover, certain pathogens can manipulate complement-TLR crosstalk pathways in ways that undermine host immunity and favor their persistence. In the setting of polymicrobial inflammatory disease, subversion of complement-TLR crosstalk by keystone pathogens can promote dysbiosis. Knowledge of the molecular mechanisms underlying complement-TLR crosstalk pathways can, therefore, be used productively for tailored therapeutic approaches, such as, to enhance host immunity, mitigate destructive inflammation, or counteract microbial subversion of the host response.