Caspase-11 mediated inflammasome activation in macrophages by systemic infection of A. actinomycetemcomitans exacerbates arthritis.

Clinical studies have shown that Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) is associated with aggressive periodontitis and can potentially trigger or exacerbate rheumatoid arthritis (RA). However, the mechanism is poorly understood. Here, we show that systemic infection with A. actinomycetemcomitans triggers the progression of arthritis in mice anti-collagen antibody-induced arthritis (CAIA) model following IL-1ß secretion and cell infiltration in paws in a manner that is dependent on caspase-11-mediated inflammasome activation in macrophages. The administration of polymyxin B (PMB), chloroquine, and anti-CD11b antibody suppressed inflammasome activation in macrophages and arthritis in mice, suggesting that the recognition of lipopolysaccharide (LPS) in the cytosol after bacterial degradation by lysosomes and invasion via CD11b are needed to trigger arthritis following inflammasome activation in macrophages. These data reveal that the inhibition of caspase-11-mediated inflammasome activation potentiates aggravation of RA induced by infection with A. actinomycetemcomitans. This work highlights how RA can be progressed by inflammasome activation as a result of periodontitis-associated bacterial infection and discusses the mechanism of inflammasome activation in response to infection with A. actinomycetemcomitans.

High fat diet increases the severity of collagen-induced arthritis in mice by altering the gut microbial community.

OBJECTIVES: Research has demonstrated that obesity may be associated with rheumatoid arthritis (RA). In addition, gut microbiota and its metabolites contribute to the occurrence and development of RA and obesity. However, the mechanism by which obesity affects RA remains unclear. In this study, we aimed to investigate whether gut microbiota and their metabolites alter the effects of high fat diet (HFD) on the severity of collagen-induced arthritis (CIA) in mice. METHODS: Briefly, mice were divided into normal group (N), CIA model group (C), HFD group (T), and HFD CIA group (CT). Hematoxylin and Eosin staining(HE) and Safranin O-fast green staining were conducted, and levels of blood lipid and inflammatory cytokines were measured. 16S rDNA sequencing technique and liquid chromatography-mass spectrometry (LC-MS)-based metabolomics were performed to explore changes in the microbiota structure to further reveal the pathomechanism of HFD on CIA. RESULTS: HFD aggravated the severity of CIA in mice. The CT group had the highest proportion of microbial abundance of Blautia, Oscillibacter, Ruminiclostridium-9, and Lachnospiraceae UCG 006 at the genus level, but had a lower proportion of Alistipes. Additionally, the fecal metabolic phenotype of the combined CT group shows significant changes, with differential metabolites enriched in 9 metabolic pathways, including primary bile acid biosynthesis, arginine biosynthesis, sphingolipid metabolism, purine metabolism, linoleic acid metabolism, oxytocin signaling pathway, aminoacyl-tRNA biosynthesis, the pentose phosphate pathway, and sphingolipid signaling pathway. Correlation analysis revealed that some of the altered gut microbiota genera were strongly correlated with changes in fecal metabolites, total cholesterol (TC), triglyceride (TG), and inflammatory cytokine levels. CONCLUSIONS: This study shows that HFD may aggravate inflammatory reaction in CIA mice by altering the gut microbiota and metabolic pathways.

Host-microbiota interactions in collagen-induced arthritis rats treated with human umbilical cord mesenchymal stem cell exosome and ginsenoside Rh2.

Mesenchymal stem cell exosome (MSCs-exo) is a class of products secreted by mesenchymal stem cells (MSCs) that contain various biologically active substances. MSCs-exo is a promising alternative to MSCs due to their lower immunogenicity and lack of ethical constraints. Ginsenoside Rh2 (Rh2) is a hydrolyzed component of the primary active substance of ginsenosides. Rh2 has a variety of pharmacological functions, including anti-inflammatory, anti-tumor, and antioxidant. Studies have demonstrated that gut microbiota and metabolites are critical in developing rheumatoid arthritis (RA). In this study, we constructed a collagen-induced arthritis (CIA) model in rats. We used MSCs-exo combined with Rh2 to treat CIA rats. To observe the effect of MSCs-exo combined with Rh2 on joint inflammation, rat feces were collected for 16 rRNA amplicon sequencing and untargeted metabolomics analysis. The results showed that the arthritis index score and joint swelling of CIA rats treated with MSCs-exo in combination with Rh2 were significantly lower than those of the model and MSCs-exo alone groups. MSCs-exo and Rh2 significantly ameliorated the disturbed gut microbiota in CIA rats. The regulation of Candidatus_Saccharibacteria and Clostridium_XlVb regulation may be the most critical. Rh2 enhanced the therapeutic effect of MSCs-exo compared with the MSCs-exo -alone group. Furthermore, significant changes in gut metabolites were observed in the CIA rat group, and these differentially altered metabolites may act as messengers for host-microbiota interactions. These differential metabolites were enriched into relevant critical metabolic pathways, revealing possible pathways for host-microbiota interactions.

Vitamin C alleviates rheumatoid arthritis by modulating gut microbiota balance.

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic and symmetric in-flammation. Our previous research revealed an imbalance in the gut flora of RA patients and showed that certain gut microbiota can accelerate RA progression by enhancing vitamin C degradation. However, it is unclear whether vitamin C supplementation could improve the gut microbiota to prevent the development of arthritis by interfering with the gut-joint axis. In this work, we aimed to evaluate the effects of vitamin C in regulating the gut microbiota and to elucidate its potential role in the onset and progression of RA in a mouse model, thus providing a basis for the development of new intervention strategies and treatments for RA. In this study, collagen-induced arthritis (CIA) mouse models, biochemical, histological and 16S rRNA microbiological methods were used to investigate the role and possible mechanism of vitamin C in rheumatoid arthritis. The results showed that treatment of CIA mice with vitamin C effectively rescued the gut mi-crobiota imbalance and suppressed the inflammatory response associated with RA, and effectively alleviated arthritis symptoms in mice in which levels of the pro-inflammatory cytokines IL-6 and TNF-α were specifi-cally reduced. In conclusion, our results demonstrate the potential of vitamin C as a potential therapeutic choice for RA.

Immunomodulatory effects of berberine on Staphylococcus aureus-induced septic arthritis through down-regulation of Th17 and Treg signaling pathways.

OBJECTIVES: The preseaant study was aimed to investigate the immunomodulatory effects of berberine on Staphylococcus aureus-induced septic arthritis through the downstream signaling mechanism of Th17 and Treg, in the control and prevention of disease progression of Staphylococcus aureus induced septic arthritis of blood, spleen and synovial joints. METHODS: The study was conducted in mice induced with septic arthritis by S. aureus for 15 days. The infected mice were treated with berberine (50 or 100 or 200 mg/Kg) to evaluate the effects on the isolated cells of Th17 and Treg from synovial joints, blood and spleen against the septic arthritic induced mice followed by JNK, RANKL and NF-κB expressions in the lysates of Th17 and Tregs isolated cells. The evaluation of serum IL-21 and TGF-ß levels was also conducted after 15 days post-infection in Th17 and Treg population. RESULTS: Our findings showed that berberine exerted excellent inhibitory effects on the S. aureus (AS-789) strain for inducing sepsis-induced arthritis. The results from the S. aureus testing revealed that at concentrations below 640 µg/mL, the strain was more resistant to berberine, as it had an increased rate of growth. The assessment of S. aureus induced septic arthritis (joint swelling and arthritis index) substantial reduction in the joint swelling and arthritis index (p<0.01) in the berberine-treated groups. The percentage of Th17 cells with CD4 and RORγt; Treg cells with CD4, CD25 and FOXp3 in the synovial joints, blood and spleen was substantially declined in the drug-treated groups (p<0.01) as compared to the S. aureus infected mice. The TGF-ß and IL-21 serum levels determinations in S. aureus induced septic arthritis revealed a substantial decrease in serum TGF-ß levels (p<0.01) in drug-treated groups compared to the infected animals. The post hoc test revealed a substantial decrease in JNK, NF-κB and RANKL expressions in the lysates of Th17 and Treg isolated cells in the drug-treated animals (p<0.01) when compared to the S. aureus-infected cluster. CONCLUSION: Our findings demonstrated that a possible strategy for combating disease severity with berberine treatment in Staphylococcus aureus induced septic arthritis in mice, which targets the Th17 and Treg cells have driven the NF-κB/JNK-RANKL axis.

Active rheumatoid arthritis in a mouse model is not an independent risk factor for periprosthetic joint infection.

INTRODUCTION: Periprosthetic joint infection (PJI) represents a devastating complication of total joint arthroplasty associated with significant morbidity and mortality. Literature suggests a possible higher incidence of periprosthetic joint infection (PJI) in patients with rheumatoid arthritis (RA). There is, however, no consensus on this purported risk nor a well-defined mechanism. This study investigates how collagen-induced arthritis (CIA), a validated animal model of RA, impacts infectious burden in a well-established model of PJI. METHODS: Control mice were compared against CIA mice. Whole blood samples were collected to quantify systemic IgG levels via ELISA. Ex vivo respiratory burst function was measured via dihydrorhodamine assay. Ex vivo Staphylococcus aureus Xen36 burden was measured directly via colony forming unit (CFU) counts and crystal violet assay to assess biofilm formation. In vivo, surgical placement of a titanium implant through the knee joint and inoculation with S. aureus Xen36 was performed. Bacterial burden was then quantified by longitudinal bioluminescent imaging. RESULTS: Mice with CIA demonstrated significantly higher levels of systemic IgG compared with control mice (p = 0.003). Ex vivo, there was no significant difference in respiratory burst function (p = 0.89) or S. aureus bacterial burden as measured by CFU counts (p = 0.91) and crystal violet assay (p = 0.96). In vivo, no significant difference in bacterial bioluminescence between groups was found at all postoperative time points. CFU counts of both the implant and the peri-implant tissue were not significantly different between groups (p = 0.82 and 0.80, respectively). CONCLUSION: This study demonstrated no significant difference in S. aureus infectious burden between mice with CIA and control mice. These results suggest that untreated, active RA may not represent a significant intrinsic risk factor for PJI, however further mechanistic translational and clinical studies are warranted.

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

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

Polysaccharides and glycosides from Aralia echinocaulis protect rats from arthritis by modulating the gut microbiota composition.

ETHNOPHARMACOLOGICAL RELEVANCE: Aralia echinocaulis has been used in traditional medicines in China and exhibits good effects on rheumatoid arthritis (RA). AIM OF THE STUDY: Aralia echinocaulis is rich in polysaccharides and glycosides. This study aims to explore the effect of total polysaccharide and glycoside (TPG) from A. echinocaulis on an RA rat model and the role of alterations in gut microbes mediated by TPG. MATERIALS AND METHODS: In this study, a collagen-induced arthritis (CIA) rat model was constructed and used to evaluate the effects of TPG in vivo. 16S rRNA sequencing was used to detect the changes in the gut microbiota. A cooccurrence analysis was conducted by calculating Spearman's rank correlations. Microbial functions were predicted using PICRUSt with the KEGG and COG databases. RESULTS: The results showed that TPG from A. echinocaulis could inhibit arthritis, reduce serum IL-1ß and TNF-α levels, and improve synovial pathology in the RA rat model but failed to produce the same results in a pseudoaseptic RA rat model. 16S rRNA sequencing verified that TPG could modulate the gut microbiota community structure of RA rats. The cooccurrence analysis found 19 out of the 50 most abundant genera in a cooccurrence network, of which 16 showed a positive correlation and 3 showed a negative correlation. KEGG pathway and COG function analyses found that TPG-induced alterations in the gut microbiota might be correlated with the circulatory system, excretory system, metabolic diseases, signaling molecules and interactions, coenzyme transport and metabolism, and nucleotide transport and metabolism. CONCLUSIONS: TPG from A. echinocaulis had significant effects on the RA rat model, which are related to the modulation of the gut microbiota. These results are useful to better understanding the mechanisms of TPG in RA.

Role of different Th17 and Treg downstream signalling pathways in the pathogenesis of Staphylococcus aureus infection induced septic arthritis in mice.

Septic arthritis is a condition of bone disorder caused predominantly by Staphylococcus aureus. Following the bacterial entry activated immune cells specially macrophages and dendritic cells release pro-inflammatory mediators such as IL-6, TNF-α, IL-1ß etc., which not only create an inflammatory microenvironment but also play crucial roles in the proliferation of different CD+ T cell subsets. Among them, Th17 and Tregs are of major concern in recent times because of their potential roles in regulating the ongoing inflammation in many diseases including experimental arthritis. But the downstream signalling mechanism of these cells in regulating the severity of inflammation in case of septic arthritis is not known yet. So, here we have established a murine model of S. aureus induced septic arthritis and kept the animal upto 15 days post-infection. To examine the signalling mechanism, Th17 and Treg cells were isolated from blood, spleen and synovial joints of control and infected mice and observed the expression of JNK, NFκB and RANKL in the lysate of isolated Th17 and Tregs. We have also estimated the levels of serum IL-21 and TGF-ß. NFκB, JNK and RANKL expression was found to be higher at 3 and 15 days post-infection along with serum IL-21 levels. On the other hand, maximum TGF-ß level was observed at 9 days post-infection along with increased Treg population. In conclusion it was hypothesized that bone resorption is related with downstream signalling pathways of Th17 cells, which stimulate osteoclast generation via NFκB/JNK-RANKL axis and helps in the persistence of the disease.

Exopolysaccharide from Lactobacillus rhamnosus KL37 Inhibits T Cell-dependent Immune Response in Mice.

Exopolysaccharides (EPSs), major components of the bacterial biofilm, display strong strain-specific immunomodulatory properties. Previously, we have shown that crude EPS derived from Lactobacillus rhamnosus KL37 depresses the production of arthritogenic anti-collagen IgG and ameliorates collagen-induced arthritis (CIA) in DBA/1 mice, when lipopolysaccharide (LPS) was used as adjuvant. In this study, we used highly purified EPS from L. rhamnosus KL37 (EPS-37) to verify its anti-inflammatory properties and the ability to suppress T cell-dependent humoral response. We have employed the model of active CIA, in which mice immunized with type II collagen (CII) along with LPS were treated with pure EPS-37. Intravenous administration of purified EPS-37 markedly ameliorated arthritis and reduced CII-specific antibody production. EPS-37 injected subcutaneously reduced the clinical symptoms of CIA but without the reduction of arthritogenic antibodies. In addition, the effect of EPS-37 on T-cell functions was tested ex vivo and in vitro. EPS-37 inhibited the in vitro proliferation of T cells activated both in vivo (CII immunization) and in vitro (antigen/mitogen), and markedly reduced the production of interferon (IFN)-γ. These results together with other reports suggest that anti-inflammatory potential of EPS-37 depends on its ability to inhibit either one or the other or both possible inflammatory signaling pathways. Namely, Th1 → IFN-γ → M1 inflammatory macrophages → arthritis and/or Th1 → IFN-γ → B cells → arthritogenic antibodies → arthritis. We suggest that L. rhamnosus KL37 EPS might be utilized to control T cell-dependent immune responses in various inflammatory diseases. However, the most effective route of EPS-37 administration needs to be tailored for a given disorder.

Targeting zonulin and intestinal epithelial barrier function to prevent onset of arthritis.

Gut microbial dysbiosis is associated with the development of autoimmune disease, but the mechanisms by which microbial dysbiosis affects the transition from asymptomatic autoimmunity to inflammatory disease are incompletely characterized. Here, we identify intestinal barrier integrity as an important checkpoint in translating autoimmunity to inflammation. Zonulin family peptide (zonulin), a potent regulator for intestinal tight junctions, is highly expressed in autoimmune mice and humans and can be used to predict transition from autoimmunity to inflammatory arthritis. Increased serum zonulin levels are accompanied by a leaky intestinal barrier, dysbiosis and inflammation. Restoration of the intestinal barrier in the pre-phase of arthritis using butyrate or a cannabinoid type 1 receptor agonist inhibits the development of arthritis. Moreover, treatment with the zonulin antagonist larazotide acetate, which specifically increases intestinal barrier integrity, effectively reduces arthritis onset. These data identify a preventive approach for the onset of autoimmune disease by specifically targeting impaired intestinal barrier function.

Alteration of the gut microbiota in tumor necrosis factor-α antagonist-treated collagen-induced arthritis mice.

AIM: Gut microbiota play an important role in rheumatoid arthritis (RA). Biological therapies targeting tumor necrosis factor-α (TNF-α) have been used for treatment in RA patients. However, whether TNF-α antagonist has some influence on gut microbiota is still unknown. This study aims to investigate the distribution of gut microbiota in collagen-induced arthritis (CIA) mice treated with the TNF-α antagonist etanercept. METHODS: Collagen-induced arthritis mice were induced by type II collagen. Cytokine expression was detected by real-time polymerase chain reaction. 16S ribosomal RNA sequencing was performed to characterize the gut microbiota in CIA mice treated with vehicle or etanercept. Sequencing reads were processed by Microbial Ecology software program. RESULTS: Compared with vehicle-treated mice, we showed that CIA mice treated with etanercept led to attenuation of inflammation and reduced expression of TNF-α, interferon (IFN)-γ, interleukin (IL)-6 and IL-21. Meanwhile, results showed operational taxonomic units, richness estimators and the diversity indices of gut microbiota in etanercept-treated mice were lower than that in vehicle-treated mice. Moreover, bacterial abundance analyses showed that genus Escherichia/Shigella was more abundant in etanercept-treated mice, and Lactobacillus, Clostridium XlVa, Tannerella were less abundant. The altered bacterial genus was correlated with TNF-α, IFN-γ, IL-6, IL-21 and IL-10. CONCLUSION: Our results revealed that TNF-α antagonist treatment can reduce the abundance and diversity of gut microbiota in CIA mice. Targeted gut microbiota may be a new therapeutic strategy for the treatment of RA.

Potential anti-arthritic and anti-inflammatory effects of TNF-α processing inhibitor-1 (TAPI-1): A new approach to the treatment of S. aureus arthritis.

Treatment of septic arthritis has become more challenging due to the rise of multidrug resistant strains of Staphylococcus aureus (S. aureus) in recent years. Failure of antibiotic therapies has compelled to initiate the search for new alternatives. This study aimed to unveil the potential anti-arthritic effects of TAPI-1 (TNF-α processing inhibitor-1), an inhibitor that inhibits TACE (TNF-α converting enzyme) mediated release of soluble TNF-α and its receptors along with attenuation of other inflammatory and joint destructive factors responsible for the progression of arthritis. Male Swiss albino mice were inoculated with live S. aureus (5 × 106 cells/mouse) for the development of septic arthritis. TAPI-1 was administered intraperitoneally (10 mg/kg body weight) post S. aureus infection at regular intervals. Throughout the experiment, the severity of arthritis was obtained to be significantly low after TAPI-1 administration. Arthritis index and histopathology confirmed effectiveness of TAPI-1 in mitigating inflammation induced paw swelling and less bone-cartilage destruction in the arthritic knee joints. Lower levels of soluble tumor necrosis factor alpha (sTNF-α) and soluble tumor necrosis factor alpha receptor-1 (sTNFR-1) were detected in the TAPI-1 treated group suggesting TAPI-1 mediated blocking of TACE with subsequent inhibition of TNF-α signalling. Treatment with TAPI-1 lowered the levels of reactive species; matrix metalloproteinase-2 (MMP-2), receptor activator of nuclear factor kappa-B ligand (RANKL) and osteopontin (OPN) denoting less matrix degradation and less osteoclastic bone resorption. Together, this experimental work authenticates TAPI-1 as an alternative therapeutic intervention for the treatment of S. aureus arthritis.

Changes in Radixin Expression and Interaction with Efflux Transporters in the Liver of Adjuvant-Induced Arthritic Rats.

Scaffold proteins such as radixin help to modulate the plasma membrane localization and transport activity of the multidrug resistance-associated protein 2 (MRP2/ABCC2) and P-glycoprotein (P-gp/ABCB1) efflux transporters in the liver. We examined changes in radixin expression and interaction with efflux transporters in adjuvant-induced arthritic (AA) rats, an animal model of rheumatoid arthritis, as well as in human liver cancer (HepG2) cells because inflammation affects drug pharmacokinetics via the efflux transporters. The expression levels of radixin and phosphorylated radixin (p-radixin) were measured 24 h after treatment with inflammatory cytokines comprising tumor necrosis factor (TNF)-α, interleukin (IL)-1ß, IL-6 or sodium nitroprusside (SNP; a nitric oxide donor). The protein levels of radixin, MRP2, and P-gp in the rat liver were next examined. We also investigated whether inflammation affected the formation of complexes between radixin and MRP2 or P-gp. The mRNA and protein levels of radixin in HepG2 cells were significantly decreased by TNF-α treatment, while minimal changes were observed after treatment with IL-1ß, IL-6 or SNP. TNF-α also significantly decreased the protein levels of p-radixin, suggesting that TNF-α inhibited the activation of radixin and thereby reduced the activity of the efflux transporters. Complex formation of radixin with MRP2 and P-gp was significantly decreased in AA rats but this was reversed by prednisolone and dexamethasone treatment, indicating that decreased interactions of radixin with MRP2 and P-gp likely occur during liver inflammation. These data suggest that liver inflammation reduces radixin function by decreasing its interactions with MRP2 and P-gp.

Saponins from Clematis mandshurica Rupr. regulates gut microbiota and its metabolites during alleviation of collagen-induced arthritis in rats.

Gut microbiota and their metabolites (short-chain fatty acids, SCFAs) are associated with the pathogenesis of rheumatoid arthritis (RA). Total Clematis triterpenoid saponins (CTSs) prepared from Clematis mandshurica Rupr. possess therapeutic benefits for arthritic diseases. However, the poor pharmacokinetic properties of CTSs have obstructed the translation of these natural agents to drugs. Here, we examined the effects of CTSs on arthritis symptoms, gut microbiota and SCFAs in rats with collagen-induced arthritis (CIA). Our results showed that the arthritis index scores of CIA rats treated with CTSs were significantly lower than those of the model group. Most importantly, CTSs moderated gut microbial dysbiosis and significantly downregulated the total SCFA concentration in CIA rats. Compared to the control group, CTSs treatment have no significant side effects on the gut microbiota and SCFA metabolism in normal rats. Two differential analyses (LEfSe and DESeq2) were combined to study the details of the changes in gut microbiome, and twenty-four marker taxa at the genus level were identified via a comparison among control, model and CIA rats treated with high doses of CTSs. In particular, the mostly significantly increased gram-negative (G-) and decreased gram-positive (G+) genera in CIA rats were well restored by CTSs. The observed SCFA concentrations demonstrated that CTSs tend to maintain the balance of the gut microbiota. The data presented herein suggest that CTSs could ameliorate arthritis-associated gut microbial dysbiosis and may be potential adjuvant drugs that could provide relief from the gastrointestinal damage caused as a side effect of commonly used drugs.

Inflammatory arthritis disrupts gut resolution mechanisms, promoting barrier breakdown by Porphyromonas gingivalis.

Rheumatoid arthritis is linked with altered host immune responses and severe joint destruction. Recent evidence suggests that loss of gut homeostasis and barrier breach by pathobionts, including Porphyromonas gingivalis, may influence disease severity. The mechanism(s) leading to altered gut homeostasis and barrier breakdown in inflammatory arthritis are poorly understood. In the present study, we found a significant reduction in intestinal concentrations of several proresolving mediators during inflammatory arthritis, including downregulation of the gut-protective mediator resolvin D5n-3 DPA (RvD5n-3 DPA). This was linked with increased metabolism of RvD5n-3 DPA to its inactive 17-oxo metabolite. We also found downregulation of IL-10 expression in the gut of arthritic mice that was coupled with a reduction in IL-10 and IL-10 receptor (IL-10R) in lamina propria macrophages. These changes were linked with a decrease in the number of mucus-producing goblet cells and tight junction molecule expression in the intestinal epithelium of arthritic mice when compared with naive mice. P. gingivalis inoculation further downregulated intestinal RvD5n-3 DPA and Il-10 levels and the expression of gut tight junction proteins. RvD5n-3 DPA, but not its metabolite 17-oxo-RvD5n-3 DPA, increased the expression of both IL-10 and IL-10R in macrophages via the upregulation of the aryl hydrocarbon receptor agonist l-kynurenine. Administration of RvD5n-3 DPA to arthritic P. gingivalis-inoculated mice increased intestinal Il-10 expression, restored gut barrier function, and reduced joint inflammation. Together, these findings uncover mechanisms in the pathogenesis of rheumatoid arthritis, where disruption of the gut RvD5n-3 DPA-IL-10 axis weakens the gut barrier, which becomes permissive to the pathogenic actions of the pathobiont P. gingivalis.

Novel Inter-omic Analysis Reveals Relationships Between Diverse Gut Microbiota and Host Immune Dysregulation in HLA-B27-Induced Experimental Spondyloarthritis.

OBJECTIVE: To define inflammation-related host-microbe interactions in experimental spondyloarthritis (SpA) using novel inter-omic approaches. METHODS: The relative frequency of gut microbes was determined by 16S ribosomal RNA (rRNA) gene sequencing, and gene expression using RNA-Seq of host tissue. HLA-B27/human ß2 -microglobulin-transgenic (HLA-B27-transgenic) and wild-type rats from dark agouti, Lewis, and Fischer backgrounds were used. Inter-omic analyses using Cytoscape were employed to identify relevant relationships. PICRUSt was used to predict microbial functions based on known metagenomic profiles. RESULTS: Inter-omic analysis revealed several gut microbes that were strongly associated with dysregulated cytokines driving inflammatory response pathways, such as interleukin-17 (IL-17), IL-23, IL-17, IL-1, interferon-γ (IFNγ), and tumor necrosis factor (TNF). Many microbes were uniquely associated with inflammation in Lewis or Fischer rats, and one was relevant on both backgrounds. Several microbes that were strongly correlated with immune dysregulation were not differentially abundant in HLA-B27-transgenic compared to wild-type controls. A multi-omic network analysis revealed non-overlapping clusters of microbes in Lewis and Fischer rats that were strongly linked to overlapping dysregulated immune/inflammatory genes. Prevotella, Clostridiales, and Blautia were important in Lewis rats, while Akkermansia muciniphila and members of the Lachnospiraceae family dominated in Fischer rats. Inflammation-associated metabolic pathway perturbation (e.g., butanoate, propanoate, lipopolysaccharide, and steroid biosynthesis) was also predicted from both backgrounds. CONCLUSION: Inter-omic and network analysis of gut microbes and the host immune response in experimental SpA provides an unprecedented view of organisms strongly linked to dysregulated IL-23, IL-17, IL-1, IFNγ, and TNF. Functional similarities between these organisms may explain why animals of different genetic backgrounds exhibit common patterns of immune dysregulation, possibly through perturbation of similar metabolic pathways. These results highlight the power of linking analyses of gut microbiota with the host immune response to gain insights into the role of dysbiotic microbes in SpA beyond taxonomic profiling.

Periodontal treatment prevents arthritis in mice and methotrexate ameliorates periodontal bone loss.

Recent studies indicate a causal relationship between the periodontal pathogen P. gingivalis and rheumatoid arthritis involving the production of autoantibodies against citrullinated peptides. We therefore postulated that therapeutic eradication P. gingivalis may ameliorate rheumatoid arthritis development and here turned to a mouse model in order to challenge our hypothesis. F1 (DBA/1 x B10.Q) mice were orally inoculated with P. gingivalis before collagen-induced arthritis was provoked. Chlorhexidine or metronidazole were orally administered either before or during the induction phase of arthritis and their effects on arthritis progression and alveolar bone loss were compared to intraperitoneally injected methotrexate. Arthritis incidence and severity were macroscopically scored and alveolar bone loss was evaluated via microcomputed tomography. Serum antibody titres against P. gingivalis were quantified by ELISA and microbial dysbiosis following oral inoculation was monitored in stool samples via microbiome analyses. Both, oral chlorhexidine and metronidazole reduced the incidence and ameliorated the severity of collagen-induced arthritis comparable to methotrexate. Likewise, all three therapies attenuated alveolar bone loss. Relative abundance of Porphyromonadaceae was increased after oral inoculation with P. gingivalis and decreased after treatment. This is the first study to describe beneficial effects of non-surgical periodontal treatment on collagen-induced arthritis in mice and suggests that mouthwash with chlorhexidine or metronidazole may also be beneficial for patients with rheumatoid arthritis and a coexisting periodontitis. Methotrexate ameliorated periodontitis in mice, further raising the possibility that methotrexate may also positively impact on the tooth supporting tissues of patients with rheumatoid arthritis.

Host-Microbiome Synergistic Control on Sphingolipid Metabolism by Mechanotransduction in Model Arthritis.

Chronic inflammatory autoimmune disorders are systemic diseases with increasing incidence and still lack a cure. More recently, attention has been placed in understanding gastrointestinal (GI) dysbiosis and, although important progress has been made in this area, it is currently unclear to what extent microbiome manipulation can be used in the treatment of autoimmune disorders. Via the use of appropriate models, rheumatoid arthritis (RA), a well-known exemplar of such pathologies, can be exploited to shed light on the currently overlooked effects of existing therapies on the GI microbiome. In this direction, we here explore the crosstalk between the GI microbiome and the host immunity in model arthritis (collagen induced arthritis, CIA). By exploiting omics from samples of limited invasiveness (blood and stools), we assess the host-microbiome responses to standard therapy (methotrexate, MTX) combined with mechanical subcutaneous stimulation (MS) and to mechanical stimulation alone. When MS is involved, results reveal the sphingolipid metabolism as the trait d'union among known hallmarks of (model) RA, namely: Imbalance in the S1P-S1PR1 axis, expansion of Prevotellasp., and invariant Natural Killer T (iNKT)-penia, thus offering the base of a rationale to mechanically modulate this pathway as a therapeutic target in RA.

Porphyromonas gingivalis experimentally induces periodontis and an anti-CCP2-associated arthritis in the rat.

OBJECTIVES: Association between periodontal disease (PD) and rheumatoid arthritis (RA) has been extensively described, but direct evidence of causal involvement of PD in RA is missing. We investigated the priming role of oral Porphyromonas gingivalis (P. gingivalis) in PD and subsequent RA and we assessed biomarkers of bone resorption and arthritis development in rats. METHODS: Lewis rats were orally exposed to either P. gingivalis, Prevotella intermedia or control gel for 1 month and then followed for 8 months. The onset and development of PD was assessed by serology, gingivitis severity and micro-CT (µCT). We investigated arthritis development using circulating proinflammatory markers, anticyclic citrullinated peptide (CCP), anticitrullinated protein antibody (ACPA), ankle histology and µCT. RESULTS: PD was only observed in the P. gingivalis treated rats, as early as 1 month postexposure. Joint and systemic inflammation were detected only in the P. gingivalis group after 4 and 8 months. At 8 months, inflammatory cell infiltrate was observed in ankle joints and paralleled cortical erosions and overall cortical bone reduction. Furthermore, anti-CCP2 correlated with local and systemic bone loss. CONCLUSIONS: In our long-term study, PD induced by oral exposure to P. gingivalis triggered seropositive arthritis, with systemic inflammation and bone erosions. This is the first in vivo demonstration of arthritis induced by oral priming with P. gingivalis.