TLR5, a novel and unidentified inflammatory mediator in rheumatoid arthritis that correlates with disease activity score and joint TNF-α levels

Monocyte-derived transcriptomes explain the ineffectiveness of abatacept in rheumatoid arthritis

BACKGROUND

The biological mechanisms underlying the differential response to abatacept in patients with rheumatoid arthritis (RA) are unknown. Here, we aimed to identify cellular, transcriptomic, and proteomic features that predict resistance to abatacept in patients with RA.

METHODS

Blood samples were collected from 22 RA patients treated with abatacept at baseline and after 3 months of treatment. Response to treatment was defined by the European League Against Rheumatism (EULAR) response criteria at 3 months, and seven patients were classified as responders and the others as non-responders. We quantified gene expression levels by RNA sequencing, 67 plasma protein levels, and the expression of surface molecules (CD3, 19, and 56) by flow cytometry. In addition, three gene expression data sets, comprising a total of 27 responders and 50 non-responders, were used to replicate the results.

RESULTS

Among the clinical characteristics, the number of monocytes was significantly higher in the non-responders before treatment. Cell type enrichment analysis showed that differentially expressed genes (DEGs) between responders and non-responders were enriched in monocytes. Gene set enrichment analysis, together with single-cell analysis and deconvolution analysis, identified that Toll-like receptor 5 (TLR5) and interleukin-17 receptor A (IL17RA) pathway in monocytes was upregulated in non-responders. Hepatocyte growth factor (HGF) correlated with this signature showed higher concentrations in non-responders before treatment. The DEGs in the replication set were also enriched for the genes expressed in monocytes, not for the TLR5 and IL17RA pathway but for the oxidative phosphorylation (OXPHOS) pathway.

CONCLUSIONS

Monocyte-derived transcriptomic features before treatment underlie the differences in abatacept efficacy in patients with RA. The pathway activated in monocytes was the TLR5 and IL17RA-HGF signature in the current study, while it was the OXPHOS pathway in the replication set. Elevated levels of HGF before treatment may serve as a potential biomarker for predicting poor responses to abatacept. These findings provide insights into the biological mechanisms of abatacept resistance, contributing valuable evidence for stratifying patients with RA.

Metabolic reprogramming by Syntenin-1 directs RA FLS and endothelial cell-mediated inflammation and angiogenesis

A novel rheumatoid arthritis (RA) synovial fluid protein, Syntenin-1, and its receptor, Syndecan-1 (SDC-1), are colocalized on RA synovial tissue endothelial cells and fibroblast-like synoviocytes (FLS). Syntenin-1 exacerbates the inflammatory landscape of endothelial cells and RA FLS by upregulating transcription of IRF1/5/7/9, IL-1β, IL-6, and CCL2 through SDC-1 ligation and HIF1α, or mTOR activation. Mechanistically, Syntenin-1 orchestrates RA FLS and endothelial cell invasion via SDC-1 and/or mTOR signaling. In Syntenin-1 reprogrammed endothelial cells, the dynamic expression of metabolic intermediates coincides with escalated glycolysis along with unchanged oxidative factors, AMPK, PGC-1α, citrate, and inactive oxidative phosphorylation. Conversely, RA FLS rewired by Syntenin-1 displayed a modest glycolytic-ATP accompanied by a robust mitochondrial-ATP capacity. The enriched mitochondrial-ATP detected in Syntenin-1 reprogrammed RA FLS was coupled with mitochondrial fusion and fission recapitulated by escalated Mitofusin-2 and DRP1 expression. We found that VEGFR1/2 and Notch1 networks are responsible for the crosstalk between Syntenin-1 rewired endothelial cells and RA FLS, which are also represented in RA explants. Similar to RA explants, morphological and transcriptome studies authenticated the importance of VEGFR1/2, Notch1, RAPTOR, and HIF1α pathways in Syntenin-1 arthritic mice and their obstruction in SDC-1 deficient animals. Consistently, dysregulation of SDC-1, mTOR, and HIF1α negated Syntenin-1 inflammatory phenotype in RA explants, while inhibition of HIF1α impaired synovial angiogenic imprint amplified by Syntenin-1. In conclusion, since the current therapies are ineffective on Syntenin-1 and SDC-1 expression in RA synovial tissue and blood, targeting this pathway and its interconnected metabolic intermediates may provide a novel therapeutic strategy.

Underpinning Endogeneous Damp EDA-Fibronectin in the Activation of Molecular Targets of Rheumatoid Arthritis and Identifcation of its Effective Inhibitors by Computational Methods

Rheumatoid arthritis (RA) is one of the most severe inflammatory diseases that cause swelling, stiffness and pain in the joints, which pose a significant threat worldwide. Damage-associated molecular patterns (DAMPs) are danger molecules of endogenous origin, released during cell injury or cell death, interacts with various Pattern recognition receptors (PRRs) and activates various inflammatory diseases. One of the DAMP molecules, so-called EDA-fibronectin (Fn) is also responsible for causing RA. EDA-Fn triggers RA through its interaction with TLR4. Apart from TLR4, it is divulged that certain other PRR's are also responsible for RA, but the identity and mechanism of those PRRs remain unknown until now. Hence, for the first time, we tried to reveal those PRR's interaction with EDA-Fn in RA through computational methods. Protein-protein interaction (PPI) was checked using ClusPro between EDA-Fn and certain Pattern recognition receptors (PRRs) to explore the binding affinities of the potential PRRs. Protein-protein docking unveiled that TLR5, TLR2 and RAGE has good interaction with EDA-Fn than the well-reported TLR4. Macromolecular simulation was performed for TLR5, TLR2 and RAGE complexes along with the control group TLR4 for 50 ns to further investigate the stability, leading to the identification of TLR2, TLR5 and RAGE as the stable complexes. Hence, TLR2, TLR5 and RAGE on interaction with EDA-Fn may lead to the progression of RA that may need additional validations through in vitro and in vivo animal models. Molecular docking was used to analyse the binding force of the top 33 active anti-arthritic compounds with the target protein EDA-Fn. Molecular docking study showed that withaferin A has a good binding activity with EDA-fibronectin target. Hence, it is emphasized that guggulsterone and berberine could modulate the EDA-Fn-mediated TLR5/TLR2/RAGE pathways, thereby it could inhibit the deteriorating effects of RA which needs further in vitro and in vivo experimental validations.

HMGB1 and Toll-like receptors: potential therapeutic targets in autoimmune diseases

HMGB1, a nucleoprotein, is expressed in almost all eukaryotic cells. During cell activation and cell death, HMGB1 can function as an alarm protein (alarmin) or damage-associated molecular pattern (DAMP) and mediate early inflammatory and immune response when it is translocated to the extracellular space. The binding of extracellular HMGB1 to Toll-like receptors (TLRs), such as TLR2 and TLR4 transforms HMGB1 into a pro-inflammatory cytokine, contributing to the occurrence and development of autoimmune diseases. TLRs, which are members of a family of pattern recognition receptors, can bind to endogenous DAMPs and activate the innate immune response. Additionally, TLRs are key signaling molecules mediating the immune response and play a critical role in the host defense against pathogens and the maintenance of immune balance. HMGB1 and TLRs are reported to be upregulated in several autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and autoimmune thyroid disease. The expression levels of HMGB1 and some TLRs are upregulated in tissues of patients with autoimmune diseases and animal models of autoimmune diseases. The suppression of HMGB1 and TLRs inhibits the progression of inflammation in animal models. Thus, HMGB1 and TLRs are indispensable biomarkers and important therapeutic targets for autoimmune diseases. This review provides comprehensive strategies for treating or preventing autoimmune diseases discovered in recent years.

B-cell capacity for expansion and differentiation into plasma cells are altered in osteoarthritis

OBJECTIVE

Autoantibody (autoAbs) production in osteoarthritis (OA), coupled with evidence of disturbed B-cell homoeostasis, suggest a potential role for B-cells in OA. B-cells can differentiate with T-cell help (T-dep) or using alternative Toll like recptor (TLR) co-stimulation (TLR-dep). We analysed the capacity for differentiation of B-cells in OA versus age-matched healthy controls (HCs) and compared the capacity of OA synovitis-derived stromal cells to provide support for plasma cell (PC) maturation.

METHODS

B-cells were isolated from OA and HC. Standardised in vitro models of B-cell differentiation were used comparing T-dep (CD40 (cluster of differentiation-40/BCR (B-cell receptor)-ligation) versus TLR-dep (TLR7/BCR-activation). Differentiation marker expression was analysed by flow-cytometry; antibody secretion (immunnoglobulins IgM/IgA/IgG) by ELISA (enzyme-linked immunosorbent assay), gene expression by qPCR (quantitative polymerase chain reaction).

RESULTS

Compared to HC, circulating OA B-cells showed an overall more mature phenotype. The gene expression profile of synovial OA B-cells resembled that of PCs. Circulating B-cells differentiated under both TLR-dep and T-dep, however OA B-cells executed differentiation faster in terms of change in surface marker and secreted more antibody at Day 6, while resulting in similar PC numbers at Day 13, with an altered phenotype at Day 13 in OA. The main difference was reduced early B-cells expansion in OA (notably in TLR-dep) and reduced cell death. Stromal cells support from OA-synovitis allowed better PC survival compared to bone marrow, with an additional population of cells and higher Ig-secretion.

CONCLUSION

Our findings suggest that OA B-cells present an altered capacity for proliferation and differentiation while remaining able to produce antibodies, notably in synovium. These findings may partly contribute to autoAbs development as recently observed in OA synovial fluids.

Arginine vasopressin hormone receptor antagonists in experimental autoimmune encephalomyelitis rodent models: A new approach for human multiple sclerosis treatment

Multiple sclerosis (MS) is a chronic demyelinating and neurodegenerative disease that affects the central nervous system. MS is a heterogeneous disorder of multiple factors that are mainly associated with the immune system including the breakdown of the blood-brain and spinal cord barriers induced by T cells, B cells, antigen presenting cells, and immune components such as chemokines and pro-inflammatory cytokines. The incidence of MS has been increasing worldwide recently, and most therapies related to its treatment are associated with the development of several secondary effects, such as headaches, hepatotoxicity, leukopenia, and some types of cancer; therefore, the search for an effective treatment is ongoing. The use of animal models of MS continues to be an important option for extrapolating new treatments. Experimental autoimmune encephalomyelitis (EAE) replicates the several pathophysiological features of MS development and clinical signs, to obtain a potential treatment for MS in humans and improve the disease prognosis. Currently, the exploration of neuro-immune-endocrine interactions represents a highlight of interest in the treatment of immune disorders. The arginine vasopressin hormone (AVP) is involved in the increase in blood−brain barrier permeability, inducing the development and aggressiveness of the disease in the EAE model, whereas its deficiency improves the clinical signs of the disease. Therefore, this present review discussed on the use of conivaptan a blocker of AVP receptors type 1a and type 2 (V1a and V2 AVP) in the modulation of immune response without completely depleting its activity, minimizing the adverse effects associated with the conventional therapies becoming a potential therapeutic target in the treatment of patients with multiple sclerosis.

Nutritional immunomodulation of Atlantic salmon response to Renibacterium salmoninarum bacterin

We investigated the immunomodulatory effect of varying levels of dietary ω6/ω3 fatty acids (FA) on Atlantic salmon (Salmo salar) antibacterial response. Two groups were fed either high-18:3ω3 or high-18:2ω6 FA diets for 8 weeks, and a third group was fed for 4 weeks on the high-18:2ω6 diet followed by 4 weeks on the high-18:3ω3 diet and termed “switched-diet”. Following the second 4 weeks of feeding (i.e., at 8 weeks), head kidney tissues from all groups were sampled for FA analysis. Fish were then intraperitoneally injected with either a formalin-killed Renibacterium salmoninarum bacterin (5 × 10⁷ cells mL⁻¹) or phosphate-buffered saline (PBS control), and head kidney tissues for gene expression analysis were sampled at 24 h post-injection. FA analysis showed that the head kidney profile reflected the dietary FA, especially for C₁₈ FAs. The qPCR analyses of twenty-three genes showed that both the high-ω6 and high-ω3 groups had significant bacterin-dependent induction of some transcripts involved in lipid metabolism (ch25ha and lipe), pathogen recognition (clec12b and tlr5), and immune effectors (znrf1 and cish). In contrast, these transcripts did not significantly respond to the bacterin in the “switched-diet” group. Concurrently, biomarkers encoding proteins with putative roles in biotic inflammatory response (tnfrsf6b) and dendritic cell maturation (ccl13) were upregulated, and a chemokine receptor (cxcr1) was downregulated with the bacterin injection regardless of the experimental diets. On the other hand, an inflammatory regulator biomarker, bcl3, was only significantly upregulated in the high-ω3 fed group, and a C-type lectin family member (clec3a) was only significantly downregulated in the switched-diet group with the bacterin injection (compared with diet-matched PBS-injected controls). Transcript fold-change (FC: bacterin/PBS) showed that tlr5 was significantly over 2-fold higher in the high-18:2ω6 diet group compared with other diet groups. FC and FA associations highlighted the role of DGLA (20:3ω6; anti-inflammatory) and/or EPA (20:5ω3; anti-inflammatory) vs. ARA (20:4ω6; pro-inflammatory) as representative of the anti-inflammatory/pro-inflammatory balance between eicosanoid precursors. Also, the correlations revealed associations of FA proportions (% total FA) and FA ratios with several eicosanoid and immune receptor biomarkers (e.g., DGLA/ARA significant positive correlation with pgds, 5loxa, 5loxb, tlr5, and cxcr1). In summary, dietary FA profiles and/or regimens modulated the expression of some immune-relevant genes in Atlantic salmon injected with R. salmoninarum bacterin. The modulation of Atlantic salmon responses to bacterial pathogens and their associated antigens using high-ω6/high-ω3 diets warrants further investigation.

Shoc2 recognizes bacterial flagellin and mediates antibacterial Erk/Stat signaling in an invertebrate

Flagellin is a key bacterial virulence factor that can stimulate molecular immune signaling in both animals and plants. The detailed mechanisms of recognizing flagellin and mounting an efficient immune response have been uncovered in vertebrates; however, whether invertebrates can discriminate flagellin remains largely unknown. In the present study, the homolog of human SHOC2 leucine rich repeat scaffold protein in kuruma shrimp (Marsupenaeus japonicus), designated MjShoc2, was found to interact with Vibrio anguillarum flagellin A (FlaA) using yeast two-hybrid and pull-down assays. MjShoc2 plays a role in antibacterial response by mediating the FlaA-induced expression of certain antibacterial effectors, including lectin and antimicrobial peptide. FlaA challenge, via MjShoc2, led to phosphorylation of extracellular regulated kinase (Erk), and the subsequent activation of signal transducer and activator of transcription (Stat), ultimately inducing the expression of effectors. Therefore, by establishing the FlaA/MjShoc2/Erk/Stat signaling axis, this study revealed a new antibacterial strategy in shrimp, and provides insights into the flagellin sensing mechanism in invertebrates.

Flagellin sensing has been proven as a general antibacterial strategy. Recognition of bacterial flagellin by the transmembrane receptor toll like receptor 5 (TLR5) leads to the activation of nuclear factor kappa B (NF-κB) pathway and induction of proinflammatory cytokines, while recognition by the intracellular nucleotide-binding leucine-rich (NLR) receptor leads to caspase-activation and cytokines-expression. Although flagellin is an effective immune stimulator that induces antimicrobial peptides in Drosophila and in crustaceans, how an invertebrate host senses flagellin and mounts an immune response is poorly understood. Here, we used the flagellin (FlaA) from Vibrio anguillarum, a pathogen of shrimp, as a bait protein to screen a yeast two-hybrid library derived from kuruma shrimp (Marsupenaeus japonicus). We found a scaffold protein, MjShoc2, able to interact with FlaA. We also found that FlaA could effectively induce the expression of certain recognized antibacterial effectors in shrimp depending on MjShoc2. We revealed that extracellular regulated kinase (Erk) phosphorylation occurred downstream of FlaA/MjShoc2, and led to signal transducer and activator of transcription (Stat) activation, resulting in transcription of certain effectors. Therefore our study provides new insights into the FlaA-induced molecular immunity in invertebrates.

The Expression of Inflammasomes NLRP1 and NLRP3, Toll-Like Receptors, and Vitamin D Receptor in Synovial Fibroblasts From Patients With Different Types of Knee Arthritis

Activated rheumatoid arthritis (RA) synovial fibroblasts (SFs) are among the most important cells promoting RA pathogenesis. They are considered active contributors to the initiation, progression, and perpetuation of the disease; therefore, early detection of RASF activation could advance contemporary diagnosis and adequate treatment of undifferentiated early inflammatory arthritis (EA). In this study, we investigated the expression of nucleotide-binding, oligomerization domain (NOD)-like receptor family, pyrin domain containing (NLRP)1, NLRP3 inflammasomes, Toll-like receptor (TLR)1, TLR2, TLR4, vitamin D receptor (VDR), and secretion of matrix metalloproteinases (MMPs) in SFs isolated from patients with RA, osteoarthritis (OA), EA, and control individuals (CN) after knee surgical intervention. C-reactive protein, general blood test, anticyclic citrullinated peptide (anti-CCP), rheumatoid factor (RF), and vitamin D (vitD) in patients’ sera were performed. Cells were stimulated or not with 100 ng/ml tumor necrosis factor alpha (TNF-α) or/and 1 nM or/and 0.01 nM vitamin D3 for 72 h. The expression levels of NLRP1, NLRP3, TLR1, TLR2, TLR4, and VDR in all examined SFs were analyzed by quantitative real-time PCR (RT-qPCR). Additionally, the secretion of IL-1β by SFs and MMPs were determined by ELISA and Luminex technology. The expression of NLRP3 was correlated with the levels of CRP, RF, and anti-CCP, suggesting its implication in SF inflammatory activation. In the TNF-α-stimulated SFs, a significantly lower expression of NLRP3 and TLR4 was observed in the RA group, compared with the other tested forms of arthritis. Moreover, upregulation of NLRP3 expression by TNF-α alone or in combination with vitD3 was observed, further indicating involvement of NLRP3 in the inflammatory responses of SFs. Secretion of IL-1β was not detected in any sample, while TNF-α upregulated the levels of secreted MMP-1, MMP-7, MMP-8, MMP-12, and MMP-13 in all patient groups. Attenuating effects of vitD on the expression of NLRP3, TLR1, and TLR4 suggest potential protective effects of vitD on the inflammatory responses in SFs. However, longer studies may be needed to confirm or fully rule out the potential implication of vitD in SF activation in inflammatory arthritis. Both VDR and NLRP3 in the TNF-α-stimulated SFs negatively correlated with the age of patients, suggesting potential age-related changes in the local inflammatory responses.

IRAK4 inhibitor mitigates joint inflammation by rebalancing metabolism malfunction in RA macrophages and fibroblasts

Recent studies show a connection between glycolysis and inflammatory response in rheumatoid arthritis (RA) macrophages (MΦs) and fibroblasts (FLS). Yet, it is unclear which pathways could be targeted to rebalance RA MΦs and FLS metabolic reprogramming. To identify novel targets that could normalize RA metabolic reprogramming, TLR7-mediated immunometabolism was characterized in RA MΦs, FLS and experimental arthritis. We uncovered that GLUT1, HIF1α, cMYC, LDHA and lactate were responsible for the TLR7-potentiated metabolic rewiring in RA MΦs and FLS, which was negated by IRAK4i. While in RA FLS, HK2 was uniquely expanded by TLR7 and negated by IRAK4i. Conversely, TLR7-driven hypermetabolism, non-oxidative PPP (CARKL) and oxidative phosphorylation (PPARγ) were narrowly dysregulated in TLR7-activated RA MΦs and FLS and was reversed by IRAK4i. Consistently, IRAK4i therapy disrupted arthritis mediated by miR-Let7b/TLR7 along with impairing a broad-range of glycolytic intermediates, GLUT1, HIF1α, cMYC, HK2, PFKFB3, PKM2, PDK1 and RAPTOR. Notably, inhibition of the mutually upregulated glycolytic metabolites, HIF1α and cMYC, was capable of mitigating TLR7-induced inflammatory imprint in RA MΦs and FLS. In keeping with IRAK4i, treatment with HIF1i and cMYCi intercepted TLR7-enhanced IRF5 and IRF7 in RA MΦs, distinct from RA FLS. Interestingly, in RA MΦs and FLS, IRAK4i counteracted TLR7-induced CARKL reduction in line with HIF1i. Whereas, cMYCi in concordance with IRAK4i, overturned oxidative phosphorylation via PPARγ in TLR7-activated RA MΦs and FLS. The blockade of IRAK4 and its interconnected intermediates can rebalance the metabolic malfunction by obstructing glycolytic and inflammatory phenotypes in RA MΦs and FLS.

Methylated (-)-epigallocatechin 3-O-gallate potentiates the effect of split vaccine accompanied with upregulation of Toll-like receptor 5

Split-virus vaccine serves as a major countermeasure against influenza virus, but its effectiveness and protective action are not complete. We previously demonstrated the effect of Benifuuki, a green tea cultivar in Japan, on enhancing the split-virus vaccine-elicited immune response. However, little is known about the detail mechanisms. Here, we show that EGCG3"Me intake significantly potentiated the vaccine-elicited hemagglutination inhibition titer increase. Flow cytometry analysis revealed the increased Toll-like receptor 5 (TLR5) expression after EGCG3"Me treatment in lamina propria dendritic cells (LPDCs) and macrophages, which play crucial roles in the humoral immune system. TLR5 expression correlated with the level of interleukin-6 (IL-6)/C-C chemokine type receptor 5, which are important mediators of the humoral immunity. Taken together, In vivo and ex vivo studies showed that EGCG3"Me potentiated the split-virus vaccine-elicited immune response accompanied with the upregulation of TLR5 in intestine and splenocyte macrophages.

CYT387 Inhibits the Hyperproliferative Potential of Fibroblast-like Synoviocytes via Modulation of IL-6/JAK1/STAT3 Signaling in Rheumatoid Arthritis

Fibroblast-like synoviocytes (FLS) are the critical effector cells primarily involved in rheumatoid arthritis (RA) disease pathogenesis. Interleukin (IL)-6, a proinflammatory cytokine most abundantly expressed in the rheumatoid synovium, promotes Janus kinase (JAK)/signal transducer and transcriptional activator (STAT) signaling cascade activation in RA-FLS, thus leading to its aggressive phenotype, invasiveness, and joint destruction. Momelotinib (CYT387) is a selective small-molecule inhibitor of JAK1/2 and is clinically approved to treat myelofibrosis. However, the therapeutic efficacy of CYT387 in FLS mediated RA pathogenesis is less known. In the present study, we investigated the modulatory effect of CYT387 on IL6/JAK/STAT signaling cascade in FLS induced RA pathogenesis. CYT387 treatment inhibited IL-6 induced high proliferative and migratory potential of FLS cells isolated from adjuvant-induced arthritic (AA) rats. CYT387 reduced the expression of PRMT5, survivin, and HIF-1α mediated by IL-6/sIL-6R in AA-FLS in a dose-dependent manner. The IL-6/sIL-6R induced expression of angiogenic factors such as VEGF and PIGF in AA-FLS cells was found downregulated by CYT387 treatment. Importantly, CYT387 significantly reduced IL-6/sIL-6R dependent activation of JAK1 and STAT3 and increased SOCS3 expression in AA-FLS cells. Next, the S3I-201 mediated blockade of STAT3 activation supported the inhibitory effect of CYT387 on IL-6/JAK1/STAT3 signaling cascade in AA-FLS. Overall, this study proves that CYT387 inhibits proliferation, migration, and pathogenic disease potential of FLS isolated from adjuvant-induced arthritic (AA) rats via targeting IL-6/JAK1/STAT3 signaling cascade.

Upregulating miR-27a-3p inhibits cell proliferation and inflammation of rheumatoid arthritis synovial fibroblasts through targeting toll-like receptor 5

Rheumatoid arthritis (RA) is a serious chronic inflammatory disease and synovial fibroblasts (SFs) serve a vital role in the pathogenesis and progression of RA. Current studies have demonstrated that dysregulation of microRNAs is involved in RA etiopathogenesis. The present study aimed to investigate the role of microRNA (miR)-27a-3p in RASFs, as well as its molecular mechanism. RASFs were isolated from synovial tissues from patients with RA. Expression of miR-27a-3p and toll-like receptor 5 (TLR5) was detected using reverse transcription-quantitative polymerase chain reaction and western blotting. Cell proliferation, apoptosis and inflammatory response were measured with MTT assay, flow cytometry and ELISA kits, respectively. The target binding between miR-27a-3p and TLR5 was predicted on DIANA TOOLS software, and confirmed by dual-luciferase reporter assay and Biotin-coupled miRNA pull-down assay. Expression of miR-27a-3p was downregulated and TLR5 was upregulated in synovial tissues and RASFs isolated from patients with RA. Functionally, upregulating miR-27a-3p may promote the apoptosis rate of RASFs and suppress cell proliferation and secretions of interleukin (IL)-1β, IL-6 and tumor necrosis factor-α. TLR5 was validated as a downstream target for miR-27a-3p in RASFs, and its expression was negatively regulated by miR-27a-3p. Silencing TLR5 in RASFs may exert similar effects to miR-27a-3p-overexpression; whereas, restoring TLR5 counteracted the suppression of miR-27a-3p-overexpression on RASF proliferation and inflammation, as well as the promotion on apoptosis. miR-27a-3p upregulation may suppress RA progression by inhibiting RASFs proliferation and inflammation through targeting TLR5.

IRAK4 inhibition: a promising strategy for treating RA joint inflammation and bone erosion

Flares of joint inflammation and resistance to currently available biologic therapeutics in rheumatoid arthritis (RA) patients could reflect activation of innate immune mechanisms. Herein, we show that a TLR7 GU-rich endogenous ligand, miR-Let7b, potentiates synovitis by amplifying RA monocyte and fibroblast (FLS) trafficking. miR-Let7b ligation to TLR7 in macrophages (MΦs) and FLSs expanded the synovial inflammatory response. Moreover, secretion of M1 monokines triggered by miR-Let7b enhanced Th1/Th17 cell differentiation. We showed that IRAK4 inhibitor (i) therapy attenuated RA disease activity by blocking TLR7-induced M1 MΦ or FLS activation, as well as monokine-modulated Th1/Th17 cell polarization. IRAK4i therapy also disrupted RA osteoclastogenesis, which was amplified by miR-Let7b ligation to joint myeloid TLR7. Hence, the effectiveness of IRAK4i was compared with that of a TNF inhibitor (i) or anti-IL-6R treatment in collagen-induced arthritis (CIA) and miR-Let7b-mediated arthritis. We found that TNF or IL-6R blocking therapies mitigated CIA by reducing the infiltration of joint F480+iNOS+ MΦs, the expression of certain monokines, and Th1 cell differentiation. Unexpectedly, these biologic therapies were unable to alleviate miR-Let7b-induced arthritis. The superior efficacy of IRAK4i over anti-TNF or anti-IL-6R therapy in miR-Let7b-induced arthritis or CIA was due to the ability of IRAK4i therapy to restrain the migration of joint F480+iNOS+ MΦs, vimentin+ fibroblasts, and CD3+ T cells, in addition to negating the expression of a wide range of monokines, including IL-12, MIP2, and IRF5 and Th1/Th17 lymphokines. In conclusion, IRAK4i therapy may provide a promising strategy for RA therapy by disconnecting critical links between inflammatory joint cells.

Tofacitinib therapy intercepts macrophage metabolic reprogramming instigated by SARS-CoV-2 Spike protein

The molecular mechanism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike protein was characterized to identify novel therapies. The impact of tofacitinib, IL-6R Ab, or TNFi therapy was determined on Spike protein or LPS/IFN-γ-induced signaling, inflammation, and metabolic reprogramming in MΦs and/or rheumatoid arthritis (RA) fibroblast-like synoviocyte (FLS). ACE2 frequency was markedly expanded in MΦs compared to T cells and RA FLS. Tofacitinib suppresses Spike protein potentiated STAT1 signaling, whereas this function was unchanged by TNFi. Tofacitinib impairs IL-6/IFN/LPS-induced STAT1 and STAT3 phosphorylation in RA MΦs and FLS. Interestingly, tofacitinib had a broader inhibitory effect on the monokines, glycolytic regulators, or oxidative metabolites compared to IL-6R Ab and TNFi in Spike-protein-activated MΦs. In contrast, all three therapies disrupted IFN-α and IFN-β secretion in response to Spike protein; nonetheless, the IFN-γ was only curtailed by tofacitinib or IL-6R Ab. While tofacitinib counteracted MΦ metabolic rewiring instigated by Spike protein, it was inconsequential on the glycolysis expansion mediated via HK2 and/or LDHA in the activated RA MΦ and FLS. Nevertheless, the potentiated inflammatory response and the diminished oxidative phosphorylation modulated by Spike protein and/or LPS/IFN-γ stimulation in MΦs or RA FLS were reversed by tofacitinib. In conclusion, tofacitinib suppresses MΦ inflammation and immunometabolism triggered by Spike protein and may provide a promising strategy for COVID-19 patients.

TLR5 Supports Development of Placental Labyrinthine Zone in Mice

Toll plays an important role in innate immunity and embryonic development in lower-ranked animals, but in mammals, the homolog toll-like receptors (TLR) are reported to facilitate postnatal development of immunity only. Here, we discovered a role of TLR5 in placental development. Tlr5 was highly transcribed during the placenta-forming and functional phases. TLR5 deletion led to a smaller placental labyrinthine zone and lower embryo weight, and the smaller size of embryo was overcorrected, resulting in a higher postnatal body weight. Examination of TLR5-deficient conceptus revealed a decrease in nuclear cAMP-response element-binding protein (CREB), mechanistic target of rapamycin (mTOR) and insulin growth factor-1 receptor (IGF1R) abundances in the placenta-forming phase. Non-flagellin-based TLR5 ligands were detected in serum of female mice and the overexpression of TLR5 alone was sufficient to induce CREB nuclear translocation and mTOR transcriptional activation in trophoblasts. Taken together, we uncovered the participation of TLR5 in the early placental formation in mice, unveiling a role of TLR in embryonic development in higher-ranked animals.

Contribution of Toll-Like Receptors and the NLRP3 Inflammasome in Rheumatoid Arthritis Pathophysiology

Rheumatoid arthritis (RA) is a progressive autoimmune disease that is characterized by inflammation of the synovial joints leading to cartilage and bone damage. The pathogenesis is sustained by the production of pro-inflammatory cytokines including tumor necrosis factor (TNF), interleukin (IL)-1 and IL-6, which can be targeted therapeutically to alleviate disease severity. Several innate immune receptors are suggested to contribute to the chronic inflammation in RA, through the production of pro-inflammatory factors in response to endogenous danger signals. Much research has focused on toll-like receptors and more recently the nucleotide-binding domain and leucine-rich repeat pyrin containing protein-3 (NLRP3) inflammasome, which is required for the processing and release of IL-1β. This review summarizes the current understanding of the potential involvement of these receptors in the initiation and maintenance of inflammation and tissue damage in RA and experimental arthritis models.

CCL25 and CCR9 is a unique pathway that potentiates pannus formation by remodeling RA macrophages into mature osteoclasts

This study elucidates the mechanism of CCL25 and CCR9 in rheumatoid arthritis (RA). RA synovial fluid (SF) expresses elevated levels of CCL25 compared to OA SF and plasma from RA and normal. CCL25 was released into RA SF by fibroblasts (FLS) and macrophages (MΦs) stimulated with IL-1β and IL-6. CCR9 is also presented on IL-1β and IL-6 activated RA FLS and differentiated MΦs. Conversely, in RA PBMCs neither CCL25 nor CCR9 are impacted by 3-month longitudinal TNF inhibitor therapy. CCL25 amplifies RA FLS and monocyte infiltration via p38 and ERK phosphorylation. CCL25-stimulated RA FLS secrete potentiated levels of IL-8 which is disrupted by p38 and ERK inhibitors. CCL25 polarizes RA monocytes into nontraditional M1 MΦs that produce IL-8 and CCL2. Activation of p38 and ERK cascades are also responsible for the CCL25-induced M1 MΦ development. Unexpectedly, CCL25 was unable to polarize RA PBMCs into effector Th1/Th17 cells. Consistently, lymphokine like RANKL was uninvolved in CCL25-induced osteoclastogenesis; however, this manifestation was regulated by osteoclastic factors such as RANK, cathepsin K (CTSK), and TNF-α. In short, we reveal that CCL25/CCR9 manipulates RA FLS and MΦ migration and inflammatory phenotype in addition to osteoclast formation via p38 and ERK activation.

TLR1/2 and 5 induce elevated cytokine levels from rheumatoid arthritis monocytes independent of ACPA or RF autoantibody status

OBJECTIVE

RA is an autoimmune inflammatory joint disease. Both RF and ACPA are associated with more progressive disease and higher levels of systemic inflammation. Monocyte activation of toll-like receptors (TLRs) by endogenous ligands is a potential source of increased production of systemic cytokines. RA monocytes have elevated TLRs, some of which are associated with the disease activity score using 28 joints (DAS28). The aim of this study was to measure TLR-induced cytokine production from monocytes, stratified by autoantibody status, to assess if their capacity to induce cytokines is related to autoantibody status or DAS28.

METHODS

Peripheral blood monocytes isolated from RA patients and healthy controls were stimulated with TLR1/2, TLR2/6, TLR4, TLR5, TLR7, TLR8 and TLR9 ligands for 18 h before measuring IL-6, TNFα and IL-10. Serum was used to confirm the autoantibody status. Cytokine levels were compared with RF, ACPA and DAS28.

RESULTS

RA monocytes demonstrated significantly increased IL-6 and TNFα upon TLR1/2 stimulation and IL-6 and IL-10 upon TLR5 activation. TLR7 and TLR9 activation did not induce cytokines and no significant differences were observed between RA and healthy control monocytes upon TLR2/6, TLR4 or TLR8 activation. When stratified by ACPA or RF status there were no correlations between autoantibody status and elevated cytokine levels. However, TLR1/2-induced IL-6 did correlate with DAS28.

CONCLUSIONS

Elevated TLR-induced cytokines in RA monocytes were not related to ACPA or RF status. However, TLR1/2-induced IL-6 was associated with disease activity.

TLR expression profiles are a function of disease status in rheumatoid arthritis and experimental arthritis

The role of the innate immune system has been established in the initiation and perpetuation of inflammatory disease, but less attention has been paid to its role in the resolution of inflammation and return to homeostasis. Toll-like receptor (TLR) expression profiles were analysed in tissues with differing disease status in rheumatoid arthritis (RA), ankylosing spondylitis (AS), and in experimental arthritis. TLR gene expression was measured in whole blood and monocytes, before and after TNF blockade. In RA and osteoarthritis synovia, the expression of TLRs was quantified by standard curve qPCR. In addition, four distinct stages of disease were defined and validated in collagen-induced arthritis (CIA), the gold standard animal model for RA - pre-onset, early disease, late disease and immunised mice that were resistant to the development of disease. TLR expression was measured in spleens, lymph nodes, blood cells, liver and the paws (inflamed and unaffected). In RA whole blood, the expression of TLR1, 4 and 6 was significantly reduced by TNF blockade but the differences in TLR expression profiles between responders and non-responders were less pronounced than the differences between RA and AS patients. In RA non-responders, monocytes had greater TLR2 expression prior to therapy compared to responders. The expression of TLR1, 2, 4 and 8 was higher in RA synovium compared to control OA synovium. Circulating cytokine levels in CIA resistant mice were similar to naïve mice, but anti-collagen antibodies were similar to arthritic mice. Distinct profiles of inflammatory gene expression were mapped in paws and organs with differing disease status. TLR expression in arthritic paws tended to be similar in early and late disease, with TLR1 and 2 moderately higher in late disease. TLR expression in unaffected paws varied according to gene and disease status but was generally lower in resistant paws. Disease status-specific profiles of TLR expression were observed in spleens, lymph nodes, blood cells and the liver. Notably, TLR2 expression rose then fell in the transition from naïve to pre-onset to early arthritis. TLR gene expression profiles are strongly associated with disease status. In particular, increased expression in the blood precedes clinical manifestation.

Comparative analysis on the anti-inflammatory/immune effect of mesenchymal stem cell therapy for the treatment of pulmonary arterial hypertension

Despite the advancement of targeted therapy for pulmonary arterial hypertension (PAH), poor prognosis remains a reality. Mesenchymal stem cells (MSCs) are one of the most clinically feasible alternative treatment options. We compared the treatment effects of adipose tissue (AD)-, bone marrow (BD)-, and umbilical cord blood (UCB)-derived MSCs in the rat monocrotaline-induced pulmonary hypertension (PH) model. The greatest improvement in the right ventricular function was observed in the UCB-MSCs treated group. The UCB-MSCs treated group also exhibited the greatest improvement in terms of the largest decrease in the medial wall thickness, perivascular fibrosis, and vascular cell proliferation, as well as the lowest levels of recruitment of innate and adaptive immune cells and associated inflammatory cytokines. Gene expression profiling of lung tissue confirmed that the UCB-MSCs treated group had the most notably attenuated immune and inflammatory profiles. Network analysis further revealed that the UCB-MSCs group had the greatest therapeutic effect in terms of the normalization of all three classical PAH pathways. The intravenous injection of the UCB-MSCs, compared with those of other MSCs, showed superior therapeutic effects in the PH model for the (1) right ventricular function, (2) vascular remodeling, (3) immune/inflammatory profiles, and (4) classical PAH pathways.

LPS-Induced Inflammation Prior to Injury Exacerbates the Development of Post-Traumatic Osteoarthritis in Mice

Osteoarthritis (OA) is a debilitating and painful disease characterized by the progressive loss of articular cartilage. Post-traumatic osteoarthritis (PTOA) is an injury-induced type of OA that persists in an asymptomatic phase for years before it becomes diagnosed in ~50% of injured individuals. Although PTOA is not classified as an inflammatory disease, it has been suggested that inflammation could be a major driver of PTOA development. Here we examined whether a state of systemic inflammation induced by lipopolysaccharide (LPS) administration 5-days before injury would modulate PTOA outcomes. RNA-seq analysis at 1-day post-injury followed by micro-computed tomography (μCT) and histology characterization at 6 weeks post-injury revealed that LPS administration causes more severe PTOA phenotypes. These phenotypes included significantly higher loss of cartilage and subchondral bone volume. Gene expression analysis showed that LPS alone induced a large cohort of inflammatory genes previously shown to be elevated in synovial M1 macrophages of rheumatoid arthritis (RA) patients, suggesting that systemic LPS produces synovitis. This synovitis was sufficient to promote PTOA in MRL/MpJ mice, a strain previously shown to be resistant to PTOA. The synovium of LPS-treated injured joints displayed an increase in cellularity, and immunohistological examination confirmed that this increase was in part attributable to an elevation in type 1 macrophages. LPS induced the expression of Tlr7 and Tlr8 in both injured and uninjured joints, genes known to be elevated in RA. We conclude that inflammation before injury is an important risk factor for the development of PTOA and that correlating patient serum endotoxin levels or their state of systemic inflammation with PTOA progression may help develop new, effective treatments to lower the rate of PTOA in injured individuals. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Antibiotic Treatment Prior to Injury Improves Post-Traumatic Osteoarthritis Outcomes in Mice

Osteoarthritis (OA) is a painful and debilitating disease characterized by the chronic and progressive degradation of articular cartilage. Post-traumatic OA (PTOA) is a secondary form of OA that develops in ~50% of cases of severe articular injury. Inflammation and re-occurring injury have been implicated as contributing to the progression of PTOA after the initial injury. However, there is very little known about external factors prior to injury that could affect the risk of PTOA development. To examine how the gut microbiome affects PTOA development we used a chronic antibiotic treatment regimen starting at weaning for six weeks prior to ACL rupture, in mice. A six-weeks post-injury histological examination showed more robust cartilage staining on the antibiotic (AB)-treated mice than the untreated controls (VEH), suggesting slower disease progression in AB cohorts. Injured joints also showed an increase in the presence of anti-inflammatory M2 macrophages in the AB group. Molecularly, the phenotype correlated with a significantly lower expression of inflammatory genes Tlr5, Ccl8, Cxcl13, and Foxo6 in the injured joints of AB-treated animals. Our results indicate that a reduced state of inflammation at the time of injury and a lower expression of Wnt signaling modulatory protein, Rspo1, caused by AB treatment can slow down or improve PTOA outcomes.

TLR-4, TLR-5 and IRF4 are diagnostic markers of knee osteoarthritis in the middle-aged and elderly patients and related to disease activity and inflammatory factors

Expression and diagnostic value of serum toll-like receptor-4 (TLR-4), Toll-like receptor-5 (TLR-5) and interferon regulatory factor 4 (IRF4) in middle-aged and elderly patients with knee osteoarthritis (KOA) and their correlation with Interleukin 1β (IL-1β), interleukin-6 (IL-6), matrix metalloproteinase-1 and tumor necrosis factor-α (TNF-α) were investigated. Sixty-eight middle-aged and elderly patients with KOA in Puyang Hospital of Traditional Chinese Medicine were selected as the study group and 49 healthy people receiving physical examination were the control group. Levels of serum TLR-4, TLR-5, IRF4, IL-1β, IL-6, MMP-1 and TNF-α were measured by enzyme linked immunosorbent assay (ELISA). Correlation between the expression levels of serum TLR-4, TLR-5, IRF4 and K-L grades was determined by Spearman correlation analysis. The diagnostic efficacy of serum TLR-4, TLR-5 and IRF4 for KOA was analyzed by the receiver operator characteristics analysis (ROC). Expression of serum TLR-4, TLR-5 and IRF4 in the study group was significantly higher than those in the control group. The sensitivity and specificity of TLR-4 in the diagnosis of KOA were, respectively, 76.47 and 93.88%, those of TLR-5 were 73.29 and 87.76%, those of IRF4 were 72.06 and 95.92%, and those of TLR-4, TLR-5 and IRF4 were 94.12 and 97.96%. Expression of serum TLR-4, TLR-5 and IRF4 was significantly higher in the severe group than in the moderate group, and significantly higher in the moderate group than those the in mild group, and significantly higher in the mild group than those in the suspected mild group. Expression of TLR-4, TLR-5 and IRF4 in serum was positively correlated with the concentration of IL-1β, IL-6, MMP-1 and TNF-α, respectively (P<0.001). The combined detection of TLR-4, TLR-5 and IRF4 can be used for early diagnosis of KOA, and they are positively correlated with IL-1β and IL-6, MMP-1 and TNF-α.

Innate immunity drives pathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease affecting ∼1% of the general population. This disease is characterized by persistent articular inflammation and joint damage driven by the proliferating synovial tissue fibroblasts as well as neutrophil, monocyte and lymphocyte trafficking into the synovium. The factors leading to RA pathogenesis remain poorly elucidated although genetic and environmental factors have been proposed to be the main contributors to RA. The majority of the early studies focused on the role of lymphocytes and adaptive immune responses in RA. However, in the past two decades, emerging studies showed that the innate immune system plays a critical role in the onset and progression of RA pathogenesis. Various innate immune cells including monocytes, macrophages and dendritic cells are involved in inflammatory responses seen in RA patients as well as in driving the activation of the adaptive immune system, which plays a major role in the later stages of the disease. Here we focus the discussion on the role of different innate immune cells and components in initiation and progression of RA. New therapeutic approaches targeting different inflammatory pathways and innate immune cells will be highlighted here. Recent emergence and the significant roles of innate lymphoid cells and inflammasomes will be also discussed.

CCL21/CCR7 signaling in macrophages promotes joint inflammation and Th17-mediated osteoclast formation in rheumatoid arthritis

In rheumatoid arthritis (RA), synovial tissue abundantly expresses CCL21, a chemokine strongly associated with RA susceptibility. In this study, we aimed to characterize the functional significance of CCL21/CCR7 signaling in different phases of RA pathogenesis. We determined that CCR7 is a hallmark of RA M1 synovial fluid (SF) macrophages, and its expression in RA monocytes and in vitro differentiated macrophages is closely associated with disease activity score (DAS28). In early stages of RA, monocytes infiltrate the synovial tissue. However, blockade of SF CCL21 or CCR7 prevents RA SF-mediated monocyte migration. CCR7 expression in the newly migrated macrophages can be accentuated by LPS and IFNγ and suppressed by IL-4 treatment. We also uncovered that CCL21 stimulation increases the number of M1-polarized macrophages (CD14+CD86+), resulting in elevated transcription of IL-6 and IL-23. These CCL21-induced M1 cytokines differentiate naïve T cells to Th17 cells, without affecting Th1 cell polarization. In the erosive stages of disease, CCL21 potentiates RA osteoclastogenesis through M1-driven Th17 polarization. Disruption of this intricate crosstalk, by blocking IL-6, IL-23, or IL-17 function, impairs the osteoclastogenic capacity of CCL21. Consistent with our in vitro findings, we establish that arthritis mediated by CCL21 expands the joint inflammation to bone erosion by connecting the differentiation of M1 macrophages with Th17 cells. Disease progression is further exacerbated by CCL21-induced neovascularization. We conclude that CCL21 is an attractive novel target for RA therapy, as blockade of its function may abrogate erosive arthritis modulated by M1 macrophages and Th17 cell crosstalk.

Eklund K. Osteoarthritis and Toll-Like Receptors: When Innate Immunity Meets Chondrocyte Apoptosis

Osteoarthritis (OA) has long been viewed as a degenerative disease of cartilage, but accumulating evidence indicates that inflammation has a critical role in its pathogenesis. In particular, chondrocyte-mediated inflammatory responses triggered by the activation of innate immune receptors by alarmins (also known as danger signals) are thought to be involved. Thus, toll-like receptors (TLRs) and their signaling pathways are of particular interest. Recent reports suggest that among the TLR-induced innate immune responses, apoptosis is one of the critical events. Apoptosis is of particular importance, given that chondrocyte death is a dominant feature in OA. This review focuses on the role of TLR signaling in chondrocytes and the role of TLR activation in chondrocyte apoptosis. The functional relevance of TLR and TLR-triggered apoptosis in OA are discussed as well as their relevance as candidates for novel disease-modifying OA drugs (DMOADs).

Toll-like receptors in mediating pathogenesis in systemic sclerosis

Toll-like receptors (TLRs) are evolutionarily conserved receptors essential for the host defence against pathogens. Both immune and non-immune cells can express TLRs, although at different levels. Systemic sclerosis (SSc) is a chronic disease in which autoimmunity, dysregulated profibrotic mediator release and activation of fibroblasts lead to dysregulated collagen deposition and fibrosis. There is now increasing knowledge that the innate immune system and, in particular, TLRs take a part in SSc pathogenesis. The list of endogenous ligands that can stimulate TLRs in SSc is growing: these ligands represent specific danger-associated molecular patterns (DAMPs), involved either in the initiation or the perpetuation of inflammation, and in the release of factors that sustain the fibrotic process or directly stimulate the cells that produce collagen and the endothelial cells. This review reports evidences concerning TLR signalling involvement in SSc. We report the new DAMPs, as well as the TLR-linked pathways involved in disease, with emphasis on type I interferon signature in SSc, the role of plasmacytoid dendritic cells (pDCs) and platelets. The dissection of the contribution of all these pathways to disease, and their correlation with the disease status, as well as their values as prognostic tools, can help to plan timely intervention and design new drugs for more appropriate therapeutic strategies.

Receptor targeting drug delivery strategies and prospects in the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA), a chronic inflammatory disease, is characterized by cartilage damage, bone tissue destruction, morphological changes in synovial fluids, and synovial joint inflammation. The inflamed synovial tissue has potential for passive and active targeting because of enhanced permeability and retention effect and the existence of RA synovial macrophages and fibroblasts that selectively express surface receptors such as folate receptor β, CD44 and integrin αVβ. Although there are numerous interventions in RA treatment, they are not safe and effective. Therefore, it is important to develop new drug or drug delivery systems that specifically targets inflamed/swollen joints but attenuates other possible damages to healthy tissues. Recently some receptors such as toll-like receptors (TLRs), the nucleotide-binding oligomerization domain-like receptors, and Fc-γ receptor have been identified in synovial tissue and immune cells that are involved in induction or suppression of arthritis. Analysis of the TLR pathway has moreover suggested new insights into the pathogenesis of RA. In the present paper, we have reviewed drug delivery strategies based on receptor targeting with novel ligand-anchored carriers exploiting CD44, folate and integrin αVβ as well as TLRs expressed on synovial monocytes and macrophages and antigen presenting cells, for possible active targeting in RA. TLRs could not only open a new horizon for developing new drugs but also their antagonists or humanized monoclonal antibodies that block TLRS specially TLR4 and TLR9 signaling could be used as targeting agents to antigen presenting cells and dendritic cells. As a conclusion, common conventional receptors and multifunctional ligands that arte involved in targeting receptors or developing nanocarriers with appropriate ligands for TLRs can provide profoundly targeting drug delivery systems for the effective treatment of RA.

Pattern recognition receptors as potential drug targets in inflammatory disorders

Pattern recognition receptors (PRRs) are a key part of the innate immune system, the body's first line of defense against infection and tissue damage. This superfamily of receptors including Toll-like receptors (TLRs), NOD-like receptors (NLRs), C-type lectin-like receptors (CLRs) and RIG-like receptors (RLRs) are responsible for initiation of the inflammatory response by their recognition of molecular patterns present in invading microorganisms (such as bacteria, viruses or fungi) during infection or in molecules released following tissue damage during acute or chronic disease states (such as sepsis or arthritis). These receptors are widely expressed and located on the cell surface, in intracellular compartments or in the cytoplasm can detect a single or subset of molecules including lipoproteins, carbohydrates or nucleic acids. In response, they initiate an intracellular signaling cascade that culminates in the synthesis and release of cytokines, chemokines and vasoactive molecules. These steps are necessary to maintain tissue homeostasis and remove potentially dangerous pathogens. However, during extreme or acute responses or during chronic disease, this can be damaging and even lead to death. Therefore, it is thought that targeting such receptors may offer a therapeutic approach in chronic inflammatory diseases or in cases of acute infection leading to sepsis. Herein, the current knowledge on the molecular biology of PRRs is reviewed along with their association with inflammatory and infectious diseases. Finally, the testing of therapeutic compounds and their future merit as targets is discussed.

Role of TLR5 in inflammation and tissue damage after intestinal ischemia-reperfusion injury

BACKGROUND

Intestinal ischemia/reperfusion (I/R) injury is a life-threatening complication that leads to inflammation and remote organ damage. However, the underlying mechanism is not yet fully understood. Toll-like receptor 5 (TLR5) is highly expressed in mucosa and recognizes flagellin, the main component of the bacterial flagella. Here, we investigated the role of TLR5 in inflammation and tissue damage after intestinal I/R injury using TLR5-deficient mice.

METHODS AND RESULTS

Intestinal levels of TLR5 mRNA and flagellin protein were elevated in wild-type mice subjected to intestinal I/R. Although TLR5 deficiency had no effect on intestinal flagellin levels, it significantly attenuated intestinal injury and inflammatory responses after intestinal I/R. TLR5 deficiency also markedly improved survival in mice after intestinal I/R injury. In wild-type mice, intestinal I/R injury induced remote organ damage, particularly in the lung, which was attenuated by TLR5 deficiency. Furthermore, TLR5 deficiency prevented lung inflammatory responses and vascular permeability after intestinal I/R injury.

CONCLUSION

These findings demonstrate a novel role of TLR5 and provide new insights into the mechanism underlying inflammation and tissue damage after intestinal I/R injury.

Cross-Disease Innate Gene Signature: Emerging Diversity and Abundance in RA Comparing to SLE and SSc

Overactivation of the innate immune system together with the impaired downstream pathway of type I interferon-responding genes is a hallmark of rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and systemic sclerosis (SSc). To date, limited data on the cross-disease innate gene signature exists among those diseases. We compared therefore an innate gene signature of Toll-like receptors (TLRs), seven key members of the interleukin (IL)1/IL1R family, and CXCL8/IL8 in peripheral blood mononuclear cells from well-defined patients with active stages of RA (n = 36, DAS28 ≥ 3.2), SLE (n = 28, SLEDAI > 6), and SSc (n = 22, revised EUSTAR index > 2.25). Emerging diversity and abundance of the innate signature in RA patients were detected: RA was characterized by the upregulation of TLR3, TLR5, IL1RAP/IL1R3, IL18R1, and SIGIRR/IL1R8 when compared to SSc (P corr < 0.02) and of TLR2, TLR5, and SIGIRR/IL1R8 when compared to SLE (P corr < 0.02). Applying the association rule analysis, six rules (combinations and expression of genes describing disease) were identified for RA (most frequently included high TLR3 and/or IL1RAP/IL1R3) and three rules for SLE (low IL1RN and IL18R1) and SSc (low TLR5 and IL18R1). This first cross-disease study identified emerging heterogeneity in the innate signature of RA patients with many upregulated innate genes compared to that of SLE and SSc.

The effects of metabolic syndrome, obesity, and the gut microbiome on load-induced osteoarthritis

OBJECTIVE

Metabolic syndrome is characterized by obesity, hyperglycemia, hypertension, insulin resistance, and dyslipidemia. Metabolic syndrome is associated with osteoarthritis (OA), but it is unclear if the association is attributable to increased mechanical loading on joints caused by obesity or other aspects of metabolic syndrome. Here we examined the effects of altered metabolism, obesity, and the gut microbiome on load-induced OA.

DESIGN

Cartilage damage was induced through cyclic compressive loading in four groups of adult male mice: Toll-like receptor-5 deficient (TLR5KO) mice that develop metabolic syndrome due to alterations in the gut microbiome, TLR5KO mice submitted to chronic antibiotics to prevent metabolic syndrome (TLR5KOΔMicrobiota), C57BL/6J mice fed a high fat diet to cause obesity (HFD), and untreated C57BL/6J mice (WT). Loading was applied for 2 weeks (n = 10-11/group) or 6 weeks (n = 10-11/group).

RESULTS

After 2 weeks of loading, cartilage damage (OARSI score) was not different among groups. After 6 weeks of loading, HFD mice had increased load-induced cartilage damage, while TLR5KO mice had cartilage damage comparable to WT mice. TLR5KOΔMicrobiota mice had less cartilage damage than other groups. HFD mice had elevated serum inflammatory markers. Each group had a distinct gut microbiome composition.

CONCLUSIONS

Severe obesity increased load-induced cartilage damage, while milder changes in adiposity/metabolic syndrome seen in TLR5KO mice did not. Furthermore, the effects of systemic inflammation/obesity on cartilage damage depend on the duration of mechanical loading. Lastly, reduced cartilage damage in the TLR5KOΔMicrobiota mice suggests that the gut microbiome may influence cartilage pathology.

MiR-3926 inhibits synovial fibroblasts proliferation and inflammatory cytokines secretion through targeting toll like receptor 5

Rheumatoid arthritis synovial fibroblasts (RASFs) play a key role in the pathogenesis of rheumatoid arthritis (RA). This study was aimed to investigate the effects of miR-3926 on the biological activities of RASFs. The results showed that miR-3926 was significantly down-regulated in RASFs and RA synovial tissue. Overexpression of miR-3926 significantly inhibited RASFs proliferation and decreased the secretion of inflammatory cytokines including TNF-α, IL-1β and IL-6 in RASFs. TLR5 was identified to be a direct target of miR-3926. TLR5 showed an opposite expression trends with miR-3926 in RASFs and RA synovial tissue. Overexpression of miR-3926 led to a reduction of endogenous TLR5 in RASFs, whereas down-regulation of miR-3926 increased TLR5 expression. Knocking down of TLR5 significantly inhibited RASFs proliferation and inflammatory cytokines secretion. Rescue experiments with a miR-3926-resistant variant of TLR5 showed that overexpression of TLR5 restored RASFs proliferation and inflammatory cytokines secretion in miR-3926-overexpressing RASFs. In conclusion, miR-3926 is downregulated in RA synovial tissues and its overexpression caused the inhibitory effects on RASF proliferation and inflammatory cytokines secretion by targeting TLR5. The miR-3926/TLR5 pathway may represent a novel target for prevention and treatment of RA.

Bone erosions in rheumatoid arthritis: recent developments in pathogenesis and therapeutic implications

Bone erosions develop early in the course of rheumatoid arthritis (RA) and deteriorate progressively, causing joint damage and resulting in impaired functional capacity of patients. During the last years, considerable number of studies has increased our understanding of the pathogenetic mechanisms mediating the development of bone erosions in RA. Increased production of RANKL and other cytokines, dysregulation of innate immune mechanisms, autoantibodies specific to RA and alterations of microRNA expression stimulate differentiation and function of osteoclasts, which are responsible for the development of bone erosions. Besides, increased levels of cytokines, overproduction of antagonists of the canonical Wnt signaling pathway and deficient production of bone morphogenetic proteins result in impaired osteoblast differentiation and function, undermining the capacity of bone erosions to repair. Disease-modifying antirheumatic drugs, synthetic or biological, currently used in the treatment of RA, can halt the progression of bone erosions and may even lead to partial repair, although complete repair is unattainable. Targeting pathogenetic mechanisms participating in the erosive process may add to the therapeutic effect of DMARDs and help in the prevention or repair of bone erosions. However, more studies are still needed to confirm whether such therapeutic strategies are effective.

The Anti-Inflammatory Mediator, Vasoactive Intestinal Peptide, Modulates the Differentiation and Function of Th Subsets in Rheumatoid Arthritis

Genetic background, epigenetic modifications, and environmental factors trigger autoimmune response in rheumatoid arthritis (RA). Several pathogenic infections have been related to the onset of RA and may cause an inadequate immunological tolerance towards critical self-antigens leading to chronic joint inflammation and an imbalance between different T helper (Th) subsets. Vasoactive intestinal peptide (VIP) is a mediator that modulates all the stages comprised between the arrival of pathogens and Th cell differentiation in RA through its known anti-inflammatory and immunomodulatory actions. This “neuroimmunopeptide” modulates the pathogenic activity of diverse cell subpopulations involved in RA as lymphocytes, fibroblast-like synoviocytes (FLS), or macrophages. In addition, VIP decreases the expression of pattern recognition receptor (PRR) such as toll-like receptors (TLRs) in FLS from RA patients. These receptors act as sensors of pathogen-associated molecular pattern (PAMP) and damage-associated molecular pattern (DAMP) connecting the innate and adaptive immune system. Moreover, VIP modulates the imbalance between Th subsets in RA, decreasing pathogenic Th1 and Th17 subsets and favoring Th2 or Treg profile during the differentiation/polarization of naïve or memory Th cells. Finally, VIP regulates the plasticity between theses subsets. In this review, we provide an overview of VIP effects on the aforementioned features of RA pathology.

Bone Loss in Rheumatoid Arthritis: Basic Mechanisms and Clinical Implications

Patients with rheumatoid arthritis (RA) have historically developed progressive damage of articular bone and cartilage, which correlates with disability over time. In addition, these patients are prone to periarticular and systemic bone loss, carrying additional morbidity. In contrast to what is seen in many other rheumatic diseases, the impact of inflammation on bone in RA is uniquely destructive. Loss of articular bone (erosions) and periarticular bone (demineralization) is a result of excessive bone resorption and markedly limited bone formation. There has been tremendous progress in preventing net bone loss in RA with the advent of disease-modifying agents, including biologic agents and small molecules, that both limit inflammation and may have a direct impact on the prevention of cytokine- and antibody-driven osteoclastogenesis. However, repair of existing bone erosions, although feasible, is observed infrequently. Lack of repair is a consequence of suppression of osteoblast function and bone formation by some of the same mechanisms that promote osteoclastogenesis and bone resorption. As new agents are introduced to control inflammation in RA, and novel mechanisms to target synovitis are identified, it may be possible in the future to fully repair damaged bone.

IL-11 facilitates a novel connection between RA joint fibroblasts and endothelial cells

IL-11 has been detected in inflamed joints; however, its role in the pathogenesis of arthritis is not yet clear. Studies were conducted to characterize the expression and functional significance of IL-11 and IL-11Rα in rheumatoid arthritis (RA). IL-11 levels were elevated in RA synovial fluid (SF) compared to osteoarthritis (OA) SF and plasma from RA, OA and normal individuals (NLs). Morphologic studies established that IL-11 was detected in lining fibroblasts and macrophages in addition to sublining endothelial cells and macrophages at higher levels in RA compared to NL synovial tissues. Since IL-11Rα was exclusively expressed in RA fibroblasts and endothelial cells, macrophages were not involved in IL-11 effector function. Ligation of IL-11 to IL-11Rα strongly provoked fibroblast infiltration into RA joint, while cell proliferation was unaffected by this process. Secretion of IL-8 and VEGF from IL-11 activated RA fibroblasts was responsible for the indirect effect of IL-11 on endothelial cell transmigration and tube formation. Moreover, IL-11 blockade impaired RA SF capacity to elicit endothelial cell transmigration and tube formation. We conclude that IL-11 binding to endothelial IL-11Rα can directly induce RA angiogenesis. In addition, secretion of proangiogenic factors from migrating fibroblasts potentiated by IL-11 can indirectly contribute to RA neovascularization.

VLR Recognition of TLR5 Expands the Molecular Characterization of Protein Antigen Binding by Non-Ig-based Antibodies

Variable lymphocyte receptors (VLRs) are unconventional adaptive immune receptors relatively recently discovered in the phylogenetically ancient jawless vertebrates, lamprey and hagfish. VLRs bind antigens using a leucine-rich repeat fold and are the only known adaptive immune receptors that do not utilize an immunoglobulin fold for antigen recognition. While immunoglobulin antibodies have been studied extensively, there are comparatively few studies on antigen recognition by VLRs, particularly for protein antigens. Here we report isolation, functional and structural characterization of three VLRs that bind the protein toll-like receptor 5 (TLR5) from zebrafish. Two of the VLRs block binding of TLR5 to its cognate ligand flagellin in functional assays using reporter cells. Co-crystal structures revealed that these VLRs bind to two different epitopes on TLR5, both of which include regions involved in flagellin binding. Our work here demonstrates that the lamprey adaptive immune system can be used to generate high-affinity VLR clones that recognize different epitopes and differentially impact natural ligand binding to a protein antigen.

HMGB1 Activates Proinflammatory Signaling via TLR5 Leading to Allodynia

Infectious and sterile inflammatory diseases are correlated with increased levels of high mobility group box 1 (HMGB1) in tissues and serum. Extracellular HMGB1 is known to activate Toll-like receptors (TLRs) 2 and 4 and RAGE (receptor for advanced glycation endproducts) in inflammatory conditions. Here, we find that TLR5 is also an HMGB1 receptor that was previously overlooked due to lack of functional expression in the cell lines usually used for studying TLR signaling. HMGB1 binding to TLR5 initiates the activation of NF-κB signaling pathway in a MyD88-dependent manner, resulting in proinflammatory cytokine production and pain enhancement in vivo. Biophysical and in vitro results highlight an essential role for the C-terminal tail region of HMGB1 in facilitating interactions with TLR5. These results suggest that HMGB1-modulated TLR5 signaling is responsible for pain hypersensitivity.

Second-generation Flagellin-rPAc Fusion Protein, KFD2-rPAc, Shows High Protective Efficacy against Dental Caries with Low Potential Side Effects

Dental caries is one of the most common global chronic diseases affecting all ages of the population; thus a vaccine against caries is urgently needed. Our previous studies demonstrated that a fusion protein, KF-rPAc, in which rPAc of S. mutans is directly fused to the C-terminal of E. coli-derived flagellin (KF), could confer high prophylactic and therapeutic efficiency against caries. However, possible side effects, including the high antigenicity of flagellin and possible inflammatory injury induced by flagellin, may restrict its clinical usage. Here, we produced a second-generation flagellin-rPAc fusion protein, KFD2-rPAc, by replacing the main antigenicity region domains D2 and D3 of KF with rPAc. Compared with KF-rPAc, KFD2-rPAc has lower TLR5 agonist efficacy and induces fewer systemic inflammatory responses in mice. After intranasal immunization, KFD2-rPAc induces significantly lower flagellin-specific antibody responses but a comparable level of rPAc-specific antibody responses in mice. More importantly, in rat challenge models, KFD2-rPAc induces a robust rPAc-specific IgA response, and confers efficient prophylactic and therapeutic efficiency against caries as does KF-rPAc, while the flagellin-specific antibody responses are highly reduced. In conclusion, low side effects and high protective efficiency against caries makes the second-generation flagellin-rPAc fusion protein, KFD2-rPAc, a promising vaccine candidate against caries.

A nonsense mutation in TLR5 is associated with survival and reduced IL-10 and TNF-α levels in human melioidosis

BACKGROUND

Melioidosis, caused by the flagellated bacterium Burkholderia pseudomallei, is a life-threatening and increasingly recognized emerging disease. Toll-like receptor (TLR) 5 is a germline-encoded pattern recognition receptor to bacterial flagellin. We evaluated the association of a nonsense TLR5 genetic variant that truncates the receptor with clinical outcomes and with immune responses in melioidosis.

METHODOLOGY/PRINCIPAL FINDINGS

We genotyped TLR5 c.1174C>T in 194 acute melioidosis patients in Thailand. Twenty-six (13%) were genotype CT or TT. In univariable analysis, carriage of the c.1174C>T variant was associated with lower 28-day mortality (odds ratio (OR) 0.21, 95% confidence interval (CI) 0.05-0.94, P = 0.04) and with lower 90-day mortality (OR 0.25, 95% CI 0.07-086, P = 0.03). In multivariable analysis adjusting for age, sex, diabetes and renal disease, the adjusted OR for 28-day mortality in carriers of the variant was 0.24 (95% CI 0.05-1.08, P = 0.06); and the adjusted OR for 90-day mortality was 0.27 (95% CI 0.08-0.97, P = 0.04). c.1174C>T was associated with a lower rate of bacteremia (P = 0.04) and reduced plasma levels of IL-10 (P = 0.049) and TNF-α (P < 0.0001). We did not find an association between c.1174C>T and IFN-γ ELISPOT (T-cell) responses (P = 0.49), indirect haemagglutination titers or IgG antibodies to bacterial flagellin during acute melioidosis (P = 0.30 and 0.1, respectively).

CONCLUSIONS/SIGNIFICANCE

This study independently confirms the association of TLR5 c.1174C>T with protection against death in melioidosis, identifies lower bacteremia, IL-10 and TNF-α production in carriers of the variant with melioidosis, but does not demonstrate an association of the variant with acute T-cell IFN-γ response, indirect haemagglutination antibody titer, or anti-flagellin IgG antibodies.

Differential impact of obesity on the pathogenesis of RA or preclinical models is contingent on the disease status

OBJECTIVE

Studies were performed to uncover the significance of obesity in rheumatoid arthritis (RA) and preclinical models.

METHODS

Preclinical arthritis models were used to examine the impact of obesity on disease onset and remission. Conditioned media from RA adipose tissues were used to investigate the mechanism contributing to joint neutrophil influx and M1 macrophage differentiation observed in early and remission phases of arthritis.

RESULTS

We report that mice fed with high fat diet (HFD) have an earlier onset of collagen-induced arthritis (CIA) compared with mice on regular diet. However, the differences in CIA joint swelling between the two diet groups are lost once disease is established. We found that early arthritis triggered by obesity is due to elevated joint MIP2/interleukin-8 levels detected in CIA as well as in the RA and mouse adipose tissues and the effect of this chemokine on neutrophil recruitment. Although active disease progression is similarly affected in both diet groups, arthritis resolution is accelerated in lean mice while joint inflammation is sustained in obese mice. We document that HFD can prolong toll-like receptor (TLR)4-induced arthritis by increasing joint monocyte migration and further remodelling the recruited cells into M1 macrophages. Consistently, we show that adipose condition media can transform RA and wild-type naïve myeloid cells into M1 macrophages; however, this function is impaired by TLR4 blockade or deficiency.

CONCLUSIONS

We conclude that despite established disease being unaffected by obesity, the early and the resolution phases of RA are impacted by obesity through different mechanisms.

An inflammatory gene signature distinguishes neurofibroma Schwann cells and macrophages from cells in the normal peripheral nervous system

Neurofibromas are benign peripheral nerve tumors driven by NF1 loss in Schwann cells (SCs). Macrophages are abundant in neurofibromas, and macrophage targeted interventions may have therapeutic potential in these tumors. We generated gene expression data from fluorescence-activated cell sorted (FACS) SCs and macrophages from wild-type and mutant nerve and neurofibroma to identify candidate pathways involved in SC-macrophage cross-talk. While in 1-month-old Nf1 mutant nerve neither SCs nor macrophages significantly differed from their normal counterparts, both macrophages and SCs showed significantly altered cytokine gene expression in neurofibromas. Computationally reconstructed SC-macrophage molecular networks were enriched for inflammation-associated pathways. We verified that neurofibroma SC conditioned medium contains macrophage chemo-attractants including colony stimulation factor 1 (CSF1). Network analysis confirmed previously implicated pathways and predict novel paracrine and autocrine loops involving cytokines, chemokines, and growth factors. Network analysis also predicted a central role for decreased type-I interferon signaling. We validated type-I interferon expression in neurofibroma by protein profiling, and show that treatment of neurofibroma-bearing mice with polyethylene glycolyated (PEGylated) type-I interferon-α2b reduces the expression of many cytokines overexpressed in neurofibroma. These studies reveal numerous potential targetable interactions between Nf1 mutant SCs and macrophages for further analyses.

TLRs, future potential therapeutic targets for RA

Toll like receptors (TLR)s have a central role in regulating innate immunity and in the last decade studies have begun to reveal their significance in potentiating autoimmune diseases such as rheumatoid arthritis (RA). Earlier investigations have highlighted the importance of TLR2 and TLR4 function in RA pathogenesis. In this review, we discuss the newer data that indicate roles for TLR5 and TLR7 in RA and its preclinical models. We evaluate the pathogenicity of TLRs in RA myeloid cells, synovial tissue fibroblasts, T cells, osteoclast progenitor cells and endothelial cells. These observations establish that ligation of TLRs can transform RA myeloid cells into M1 macrophages and that the inflammatory factors secreted from M1 and RA synovial tissue fibroblasts participate in TH-17 cell development. From the investigations conducted in RA preclinical models, we conclude that TLR-mediated inflammation can result in osteoclastic bone erosion by interconnecting the myeloid and TH-17 cell response to joint vascularization. In light of emerging unique aspects of TLR function, we summarize the novel approaches that are being tested to impair TLR activation in RA patients.

Links Between the Microbiome and Bone

The human microbiome has been shown to influence a number of chronic conditions associated with impaired bone mass and bone quality, including obesity, diabetes, and inflammatory bowel disease. The connection between the microbiome and bone health, however, has not been well studied. The few studies available demonstrate that the microbiome can have a large effect on bone remodeling and bone mass. The gut microbiome is the largest reservoir of microbial organisms in the body and consists of more than a thousand different species interacting with one another in a stable, dynamic equilibrium. How the microbiome can affect organs distant from the gut is not well understood but is believed to occur through regulation of nutrition, regulation of the immune system, and/or translocation of bacterial products across the gut endothelial barrier. Here we review each of these mechanisms and discuss their potential effect on bone remodeling and bone mass. We discuss how preclinical studies of bone-microbiome interactions are challenging because the microbiome is sensitive to genetic background, housing environment, and vendor source. Additionally, although the microbiome exhibits a robust response to external stimuli, it rapidly returns to its original steady state after a disturbance, making it difficult to sustain controlled changes in the microbiome over time periods required to detect alterations in bone remodeling, mass, or structure. Despite these challenges, an understanding of the mechanisms by which the gut microbiome affects bone has the potential to provide insights into the dissociation between fracture risk and bone mineral density in patients including those with obesity, diabetes, or inflammatory bowel disease. In addition, alteration of the gut microbiome has the potential to serve as a biomarker of bone metabolic activity as well as a target for therapies to improve bone structure and quality using pharmaceutical agents or pre- or probiotics. © 2016 American Society for Bone and Mineral Research.

Toll-like receptors in the pathogenesis of autoimmune diseases: recent and emerging translational developments

Autoinflammatory diseases are defined as the loss of self-tolerance in which an inflammatory response to self-antigens occurs, which are a significant global burden. Toll-like receptors are key pattern recognition receptors, which integrate signals leading to the activation of transcription factors and ultimately proinflammatory cytokines. Recently, it has become apparent that these are at the nexus of autoinflammatory diseases making them viable and attractive drug targets. The aim of this review was to evaluate the role of innate immunity in autoinflammatory conditions alongside the role of negative regulation while suggesting possible therapeutic targets.