KIF1C and new Huntingtin-interacting protein 1 binding proteins regulate rheumatoid arthritis fibroblast-like synoviocytes' phenotypes.

Background: Huntingtin-interacting protein-1 (HIP1) is a new arthritis severity gene implicated in the regulation of the invasive properties of rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS). These invasive properties of FLS strongly correlate with radiographic and histology damage in patients with RA and rodent models of arthritis. While HIP1 has several intracellular functions, little is known about its binding proteins, and identifying them has the potential to expand our understanding of its role in cell invasion and other disease-contributing phenotypes, and potentially identify new targets for therapy. Methods: FLS cell lines from arthritic DA (highly invasive) and from arthritis-protected congenic rats R6 (minimally invasive), which differ in an amino-acid changing HIP1 SNP, were cultured and lysed, and proteins were immunoprecipitated with an anti-HIP1 antibody. Immunoprecipitates were analyzed by mass spectrometry. Differentially detected (bound) proteins were selected for functional experiments using siRNA knockdown in human RA FLS to examine their effect in cell invasiveness, adhesion, cell migration and proliferation, and immunofluorescence microscopy. Results: Proteins detected included a few known HIP1-binding proteins and several new ones. Forty-five proteins differed in levels detected in the DA versus R6 congenic mass spectrometry analyses. Thirty-two of these proteins were knocked down and studied in vitro, with 10 inducing significant changes in RA FLS phenotypes. Specifically, knockdown of five HIP1-binding protein genes (CHMP4BL1, COPE, KIF1C, YWHAG, and YWHAH) significantly decreased FLS invasiveness. Knockdown of KIF1C also reduced RA FLS migration. The binding of four selected proteins to human HIP1 was confirmed. KIF1C colocalized with lamellipodia, and its knockdown prevented RA FLS from developing an elongated morphology with thick linearized actin fibers or forming polarized lamellipodia, all required for cell mobility and invasion. Unlike HIP1, KIF1C knockdown did not affect Rac1 signaling. Conclusion: We have identified new HIP1-binding proteins and demonstrate that 10 of them regulate key FLS phenotypes. These HIP1-binding proteins have the potential to become new therapeutic targets and help better understand the RA FLS pathogenic behavior. KIF1C knockdown recapitulated the morphologic changes previously seen in the absence of HIP1, but did not affect the same cell signaling pathway, suggesting involvement in the regulation of different processes.

Cell-Specific Gene Networks and Drivers in Rheumatoid Arthritis Synovial Tissues.

Rheumatoid arthritis (RA) is a common autoimmune and inflammatory disease characterized by inflammation and hyperplasia of the synovial tissues. RA pathogenesis involves multiple cell types, genes, transcription factors (TFs) and networks. Yet, little is known about the TFs, and key drivers and networks regulating cell function and disease at the synovial tissue level, which is the site of disease. In the present study, we used available RNA-seq databases generated from synovial tissues and developed a novel approach to elucidate cell type-specific regulatory networks on synovial tissue genes in RA. We leverage established computational methodologies to infer sample-specific gene regulatory networks and applied statistical methods to compare network properties across phenotypic groups (RA versus osteoarthritis). We developed computational approaches to rank TFs based on their contribution to the observed phenotypic differences between RA and controls across different cell types. We identified 18,16,19,11 key regulators of fibroblast-like synoviocyte (FLS), T cells, B cells, and monocyte signatures and networks, respectively, in RA synovial tissues. Interestingly, FLS and B cells were driven by multiple independent co-regulatory TF clusters that included MITF, HLX, BACH1 (FLS) and KLF13, FOSB, FOSL1 (synovial B cells). However, monocytes were collectively governed by a single cluster of TF drivers, responsible for the main phenotypic differences between RA and controls, which included RFX5, IRF9, CREB5. Among several cell subset and pathway changes, we also detected reduced presence of NKT cell and eosinophils in RA synovial tissues. Overall, our novel approach identified new and previously unsuspected KDG, TF and networks and should help better understanding individual cell regulation and co-regulatory networks in RA pathogenesis, as well as potentially generate new targets for treatment.

Gene Network Analyses Identify Co-regulated Transcription Factors and BACH1 as a Key Driver in Rheumatoid Arthritis Fibroblast-like Synoviocytes.

RNA-sequencing and differential gene expression studies have significantly advanced our understanding of pathogenic pathways underlying Rheumatoid Arthritis (RA). Yet, little is known about cell-specific regulatory networks and their contributions to disease. In this study, we focused on fibroblast-like synoviocytes (FLS), a cell type central to disease pathogenesis and joint damage in RA. We used a strategy that computed sample-specific gene regulatory networks (GRNs) to compare network properties between RA and osteoarthritis FLS. We identified 28 transcription factors (TFs) as key regulators central to the signatures of RA FLS. Six of these TFs are new and have not been previously implicated in RA, and included BACH1, HLX, and TGIF1. Several of these TFs were found to be co-regulated, and BACH1 emerged as the most significant TF and regulator. The main BACH1 targets included those implicated in fatty acid metabolism and ferroptosis. The discovery of BACH1 was validated in experiments with RA FLS. Knockdown of BACH1 in RA FLS significantly affected the gene expression signatures, reduced cell adhesion and mobility, interfered with the formation of thick actin fibers, and prevented the polarized formation of lamellipodia, all required for the RA destructive behavior of FLS. This is the first time that BACH1 is shown to have a central role in the regulation of FLS phenotypes, and gene expression signatures, as well as in ferroptosis and fatty acid metabolism. These new discoveries have the potential to become new targets for treatments aimed at selectively targeting the RA FLS.

Role of mitochondria-bound HK2 in rheumatoid arthritis fibroblast-like synoviocytes.

Background: Glucose metabolism, specifically, hexokinase 2 (HK2), has a critical role in rheumatoid arthritis (RA) fibroblast-like synoviocyte (FLS) phenotype. HK2 localizes not only in the cytosol but also in the mitochondria, where it protects mitochondria against stress. We hypothesize that mitochondria-bound HK2 is a key regulator of RA FLS phenotype. Methods: HK2 localization was evaluated by confocal microscopy after FLS stimulation. RA FLSs were infected with Green fluorescent protein (GFP), full-length (FL)-HK2, or HK2 lacking its mitochondrial binding motif (HK2ΔN) expressing adenovirus (Ad). RA FLS was also incubated with methyl jasmonate (MJ; 2.5 mM), tofacitinib (1 µM), or methotrexate (1 µM). RA FLS was tested for migration and invasion and gene expression. Gene associations with HK2 expression were identified by examining single-cell RNA sequencing (scRNA-seq) data from murine models of arthritis. Mice were injected with K/BxN serum and given MJ. Ad-FLHK2 or Ad-HK2ΔN was injected into the knee of wild-type mice. Results: Cobalt chloride (CoCl2) and platelet-derived growth factor (PDGF) stimulation induced HK2 mitochondrial translocation. Overexpression of the HK2 mutant and MJ incubation reversed the invasive and migrative phenotype induced by FL-HK2 after PDGF stimulation, and MJ also decreased the expression of C-X-C Motif Chemokine Ligand 1 (CXCL1) and Collagen Type I Alpha 1 Chain (COL1A1). Of interest, tofacitinib but not methotrexate had an effect on HK2 dissociation from the mitochondria. In murine models, MJ treatment significantly decreased arthritis severity, whereas HK2FL was able to induce synovial hypertrophy as opposed to HK2ΔN. Conclusion: Our results suggest that mitochondrial HK2 regulates the aggressive phenotype of RA FLS. New therapeutic approaches to dissociate HK2 from mitochondria offer a safer approach than global glycolysis inhibition.

Magnesium increases numbers of Foxp3+ Treg cells and reduces arthritis severity and joint damage in an IL-10-dependent manner mediated by the intestinal microbiome.

BACKGROUND: Rheumatoid arthritis (RA) is a common autoimmune disease with emerging environmental and microbiome risk factors. The western diet is typically deficient in magnesium (Mg), and there is some evidence suggesting that Mg may have anti-inflammatory properties. But the actual role of Mg supplementation in arthritis or in T cell subsets has not been explored. METHODS: We investigated the role of a high Mg diet in two different mouse models of RA induced with the KRN serum, and collagen-induced arthritis. We also characterized the phenotypes of splenocytes, gene expression, and an extensive intestinal microbiome analyses including fecal material transplantation (FMT). FINDINGS: The high Mg diet group was significantly protected with reduced arthritis severity and joint damage, and reduced expression of IL-1ß, IL-6, and TNFα. The high Mg group also had increased numbers of Foxp3+ Treg cells and IL-10-producing T cells. The high Mg protective effect disappeared in IL-10 knockout mice. FMT from the high Mg diet mice recreated the phenotypes seen in the diet-treated mice, with reduced arthritis severity, increased Foxp3+ Treg, and increased IL-10-producing T cells. Intestinal microbiome analyses using 16S rDNA sequencing revealed diet-specific changes, including reduced levels of RA-associated Prevotella in the high Mg group, while increasing levels of Bacteroides and other bacteria associated with increased production of short-chain fatty acids. Metagenomic analyses implicated additional pathways including L-tryptophan biosynthesis and arginine deiminase. INTERPRETATION: We describe a new role for Mg in suppressing arthritis, in expanding Foxp3+ T reg cells and in the production of IL-10, and show that these effects are mediated by the intestinal microbiome. Our discoveries suggest a novel strategy for modifying the intestinal microbiome to treat RA and other autoimmune and inflammatory diseases. FUNDING: None.

Combination therapy of a TRPV2 agonist with a TNF inhibitor achieves sustained suppression of disease severity and reduced joint damage.

We aimed to compare a transient receptor potential vanilloid 2 (TRPV2) agonist with a TNF inhibitor, and to test the potential of their combination in collagen-induced arthritis (CIA) as a potential future strategy for rheumatoid arthritis (RA). Following the onset of CIA DBA1/j mice were started on treatment with either vehicle, etanercept (8 mg/kg three times a week), the TRPV2 agonist O1821 (20-30 mg/kg/day), or a combination of both. Mice were scored over a 61-day period. Synovial tissues were obtained for RNA sequencing. Mice on monotherapy with either O1821 or etanercept developed milder clinical disease. The O1821 protection was observed at an earlier time-point than in the etanercept group. The combination therapy group achieved a more robust and sustained reduction in disease severity than either monotherapy group. All treatment groups had reduced scores for synovial inflammation, synovial hyperplasia, and erosive changes, compared with controls, with the combination group achieving the most significant protection. RNA sequencing and pathway analyses of synovial tissues identified pathways and processes regulated by the TRPV2 agonist, such as chemotaxis and cytokine receptor signaling, including IL6R. The combination therapy affected additional pathways not seen in the monotherapy groups. In conclusion, the TRPV2 agonist achieved an overall similar reduction in arthritis severity and histology scores as etanercept, but the combination therapy achieved a more sustained disease control and more pronounced reduction in joint damage, suggesting a potential future option for improving disease control in RA. RNA sequencing analyses identified new pathways regulated by TRPV2, and also by the combination treatment.

Antioxidant Carbon Nanoparticles Inhibit Fibroblast-Like Synoviocyte Invasiveness and Reduce Disease Severity in a Rat Model of Rheumatoid Arthritis.

Reactive oxygen species have been involved in the pathogenesis of rheumatoid arthritis (RA). Our goal was to determine the effects of selectively scavenging superoxide (O2•-) and hydroxyl radicals with antioxidant nanoparticles, called poly(ethylene glycol)-functionalized hydrophilic carbon clusters (PEG-HCCs), on the pathogenic functions of fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and on the progression of an animal model of RA. We used human FLS from patients with RA to determine PEG-HCC internalization and effects on FLS cytotoxicity, invasiveness, proliferation, and production of proteases. We used the pristane-induced arthritis (PIA) rat model of RA to assess the benefits of PEG-HCCs on reducing disease severity. PEG-HCCs were internalized by RA-FLS, reduced their intracellular O2•-, and reduced multiple measures of their pathogenicity in vitro, including proliferation and invasion. In PIA, PEG-HCCs caused a 65% reduction in disease severity, as measured by a standardized scoring system of paw inflammation and caused a significant reduction in bone and tissue damage, and circulating rheumatoid factor. PEG-HCCs did not induce lymphopenia during PIA. Our study demonstrated a role for O2•- and hydroxyl radicals in the pathogenesis of a rat model of RA and showed efficacy of PEG-HCCs in treating a rat model of RA.

RTD-1 therapeutically normalizes synovial gene signatures in rat autoimmune arthritis and suppresses proinflammatory mediators in RA synovial fibroblasts.

Rhesus theta defensin-1 (RTD-1), a macrocyclic immunomodulatory host defense peptide from Old World monkeys, is therapeutic in pristane-induced arthritis (PIA) in rats, a model of rheumatoid arthritis (RA). RNA-sequence (RNA-Seq) analysis was used to interrogate the changes in gene expression in PIA rats, which identified 617 differentially expressed genes (DEGs) in PIA synovial tissue of diseased rats. Upstream regulator analysis showed upregulation of gene expression pathways regulated by TNF, IL1B, IL6, proinflammatory cytokines, and matrix metalloproteases (MMPs) involved in RA. In contrast, ligand-dependent nuclear receptors like the liver X-receptors NR1H2 and NR1H3 and peroxisome proliferator-activated receptor gamma (PPARG) were downregulated in arthritic synovia. Daily RTD-1 treatment of PIA rats for 1-5 days following disease presentation modulated 340 of the 617 disease genes, and synovial gene expression in PIA rats treated 5 days with RTD-1 closely resembled the gene signature of naive synovium. Systemic RTD-1 inhibited proinflammatory upstream regulators such as TNF, IL1, and IL6 and activated antiarthritic ligand-dependent nuclear receptor pathways, including PPARG, NR1H2, and NR1H3, that were suppressed in untreated PIA rats. RTD-1 also inhibited proinflammatory responses in IL-1ß-stimulated human RA fibroblast-like synoviocytes (FLS) in vitro and diminished expression of human orthologs of disease genes that are induced in rat PIA synovium. Thus, the antiarthritic mechanisms of systemic RTD-1 include homeostatic regulation of arthritogenic gene networks in a manner that correlates temporally with clinical resolution of rat PIA.

TRPV2 suppresses Rac1 and RhoA activation and invasion in rheumatoid arthritis fibroblast-like synoviocytes.

The TRPV2 cation channel has been recently implicated in the regulation of arthritis severity, joint damage, and in the invasive behavior of the fibroblast-like synoviocyte (FLS). However, its mechanism of action was unknown. In this study we characterize the cell signaling events mediating the TRPV2 suppressive activity in FLS invasiveness. Studies with FLS cell lines derived from patients with RA revealed that TRPV2-specific stimulation significantly reduced FLS adhesion to different extracellular matrices that shared binding to αν, ß1 and ß3 integrins. Localization of these integrins to the plasma membrane and numbers of thick and organized actin filaments were diminished by TRPV2 specific stimulation, and cells developed a round and non-polarized morphology. TRPV2 stimulation significantly reduced levels of activated RhoA, Rac1 and cofilin. RhoA activators were able to overcome the TRPV2-induced suppression on both RhoA activation and invasion. These new discoveries suggest that TRPV2 regulates key intracellular processes implicated in cell invasion in arthritis and other processes such as cancer, and has the potential to become a useful target for drug development.

KCa1.1 and Kv1.3 channels regulate the interactions between fibroblast-like synoviocytes and T lymphocytes during rheumatoid arthritis.

BACKGROUND: Fibroblast-like synoviocytes (FLS) and CCR7- effector memory T (TEM) cells are two of the major cell types implicated in the progression of rheumatoid arthritis (RA). In particular, FLS become highly invasive, whereas TEM cells proliferate and secrete proinflammatory cytokines, during RA. FLS and T cells may also interact and influence each other's phenotypes. Inhibition of the pathogenic phenotypes of both FLS and TEM cells can be accomplished by selectively blocking the predominant potassium channels that they upregulate during RA: KCa1.1 (BK, Slo1, MaxiK, KCNMA1) upregulated by FLS and Kv1.3 (KCNA3) upregulated by activated TEM cells. In this study, we investigated the roles of KCa1.1 and Kv1.3 in regulating the interactions between FLS and TEM cells and determined if combination therapies of KCa1.1- and Kv1.3-selective blockers are more efficacious than monotherapies in ameliorating disease in rat models of RA. METHODS: We used in vitro functional assays to assess the effects of selective KCa1.1 and Kv1.3 channel inhibitors on the interactions of FLS isolated from rats with collagen-induced arthritis (CIA) with syngeneic TEM cells. We also used flow cytometric analyses to determine the effects of KCa1.1 blockers on the expression of proteins used for antigen presentation on CIA-FLS. Finally, we used the CIA and pristane-induced arthritis models to determine the efficacy of combinatorial therapies of KCa1.1 and Kv1.3 blockers in reducing disease severity compared with monotherapies. RESULTS: We show that the interactions of FLS from rats with CIA and of rat TEM cells are regulated by KCa1.1 and Kv1.3. Inhibiting KCa1.1 on FLS reduces the ability of FLS to stimulate TEM cell proliferation and migration, and inhibiting Kv1.3 on TEM cells reduces TEM cells' ability to enhance FLS expression of KCa1.1 and major histocompatibility complex class II protein, as well as stimulates their invasion. Furthermore, we show that combination therapies of selective KCa1.1 and Kv1.3 blockers are more efficacious than monotherapies at reducing signs of disease in two rat models of RA. CONCLUSIONS: Our results demonstrate the importance of KCa1.1 and Kv1.3 in regulating FLS and TEM cells during RA, as well as the value of combined therapies targeting both of these cell types to treat RA.

Huntingtin-interacting protein 1 (HIP1) regulates arthritis severity and synovial fibroblast invasiveness by altering PDGFR and Rac1 signalling.

OBJECTIVES: While new treatments for rheumatoid arthritis (RA) have markedly improved disease control by targeting immune/inflammatory pathways, current treatments rarely induce remission, underscoring the need for therapies that target other aspects of the disease. Little is known about the regulation of disease severity and joint damage, which are major predictors of disease outcome, and might be better or complementary targets for therapy. In this study, we aimed to discover and characterise a new arthritis severity gene. METHODS: An unbiased and phenotype-driven strategy including studies of unique congenic rat strains was used to identify new arthritis severity and joint damage genes. Fibroblast-like synoviocytes (FLS) from rats and patients with RA expressing or not Huntingtin-interacting protein 1 (HIP1) were studied for invasiveness, morphology and cell signalling. HIP1 knockout mice were used in in vivo confirmatory studies. Paired t-test was used. RESULTS: DNA sequencing and subcongenic strains studied in pristane-induced arthritis identified a new amino acid changing functional variant in HIP1. HIP1 was required for the increased invasiveness of FLS from arthritic rats and from patients with RA. Knocking down HIP1 expression reduced receptor tyrosine kinase-mediated responses in RA FLS, including RAC1 activation, affecting actin cytoskeleton and cell morphology and interfering with the formation of lamellipodia, consistent with reduced invasiveness. HIP1 knockout mice were protected in KRN serum-induced arthritis and developed milder disease. CONCLUSION: HIP1 is a new arthritis severity gene and a potential novel prognostic biomarker and target for therapy in RA.

Comprehensive epigenetic landscape of rheumatoid arthritis fibroblast-like synoviocytes.

Epigenetics contributes to the pathogenesis of immune-mediated diseases like rheumatoid arthritis (RA). Here we show the first comprehensive epigenomic characterization of RA fibroblast-like synoviocytes (FLS), including histone modifications (H3K27ac, H3K4me1, H3K4me3, H3K36me3, H3K27me3, and H3K9me3), open chromatin, RNA expression and whole-genome DNA methylation. To address complex multidimensional relationship and reveal epigenetic regulation of RA, we perform integrative analyses using a novel unbiased method to identify genomic regions with similar profiles. Epigenomically similar regions exist in RA cells and are associated with active enhancers and promoters and specific transcription factor binding motifs. Differentially marked genes are enriched for immunological and unexpected pathways, with "Huntington's Disease Signaling" identified as particularly prominent. We validate the relevance of this pathway to RA by showing that Huntingtin-interacting protein-1 regulates FLS invasion into matrix. This work establishes a high-resolution epigenomic landscape of RA and demonstrates the potential for integrative analyses to identify unanticipated therapeutic targets.

Targeting KCa1.1 Channels with a Scorpion Venom Peptide for the Therapy of Rat Models of Rheumatoid Arthritis.

Fibroblast-like synoviocytes (FLSs) are a key cell type involved in rheumatoid arthritis (RA) progression. We previously identified the KCa1.1 potassium channel (Maxi-K, BK, Slo 1, KCNMA1) as a regulator of FLSs and found that KCa1.1 inhibition reduces disease severity in RA animal models. However, systemic KCa1.1 block causes multiple side effects. In this study, we aimed to determine whether the KCa1.1 ß1-3-specific venom peptide blocker iberiotoxin (IbTX) reduces disease severity in animal models of RA without inducing major side effects. We used immunohistochemistry to identify IbTX-sensitive KCa1.1 subunits in joints of rats with a model of RA. Patch-clamp and functional assays were used to determine whether IbTX can regulate FLSs through targeting KCa1.1. We then tested the efficacy of IbTX in ameliorating disease in two rat models of RA. Finally, we determined whether IbTX causes side effects including incontinence or tremors in rats, compared with those treated with the small-molecule KCa1.1 blocker paxilline. IbTX-sensitive subunits of KCa1.1 were expressed by FLSs in joints of rats with experimental arthritis. IbTX inhibited KCa1.1 channels expressed by FLSs from patients with RA and by FLSs from rat models of RA and reduced FLS invasiveness. IbTX significantly reduced disease severity in two rat models of RA. Unlike paxilline, IbTX did not induce tremors or incontinence in rats. Overall, IbTX inhibited KCa1.1 channels on FLSs and treated rat models of RA without inducing side effects associated with nonspecific KCa1.1 blockade and could become the basis for the development of a new treatment of RA.

Suppression and resolution of autoimmune arthritis by rhesus θ-defensin-1, an immunomodulatory macrocyclic peptide.

θ-defensins constitute a family of macrocyclic peptides expressed exclusively in Old World monkeys. The peptides are pleiotropic effectors of innate immunity, possessing broad spectrum antimicrobial activities and immunoregulatory properties. Here we report that rhesus θ-defensin 1 (RTD-1) is highly effective in arresting and reversing joint disease in a rodent model of rheumatoid arthritis (RA). Parenteral RTD-1 treatment of DA/OlaHsd rats with established pristane-induced arthritis (PIA) rapidly suppressed joint disease progression, restored limb mobility, and preserved normal joint architecture. RTD-1 significantly reduced joint IL-1ß levels compared with controls. RTD-1 dose-dependently inhibited fibroblast-like synoviocyte (FLS) invasiveness and FLS IL-6 production. Consistent with the inhibition of FLS invasiveness, RTD-1 was a potent inhibitor of arthritogenic proteases including ADAMs 17 and 10 which activate TNFα, and inhibited matrix metalloproteases, and cathepsin K. RTD-1 was non-toxic, non-immunogenic, and effective when administered as infrequently as once every five days. Thus θ-defensins, which are absent in humans, have potential as retroevolutionary biologics for the treatment of RA.

KCa1.1 channels regulate ß1-integrin function and cell adhesion in rheumatoid arthritis fibroblast-like synoviocytes.

Large-conductance calcium-activated potassium channel (KCa1.1; BK, Slo1, MaxiK, KCNMA1) is the predominant potassium channel expressed at the plasma membrane of rheumatoid arthritis fibroblast-like synoviocytes (RA-FLSs) isolated from the synovium of patients with RA. It is a critical regulator of RA-FLS migration and invasion and therefore represents an attractive target for the therapy of RA. However, the molecular mechanisms by which KCa1.1 regulates RA-FLS invasiveness have remained largely unknown. Here, we demonstrate that KCa1.1 regulates RA-FLS adhesion through controlling the plasma membrane expression and activation of ß1 integrins, but not α4, α5, or α6 integrins. Blocking KCa1.1 disturbs calcium homeostasis, leading to the sustained phosphorylation of Akt and the recruitment of talin to ß1 integrins. Interestingly, the pore-forming α subunit of KCa1.1 coimmunoprecipitates with ß1 integrins, suggesting that this physical association underlies the functional interaction between these molecules. Together, these data outline a new signaling mechanism by which KCa1.1 regulates ß1-integrin function and therefore invasiveness of RA-FLSs.-Tanner, M. R., Pennington, M. W., Laragione, T., Gulko, P. S., Beeton, C. KCa1.1 channels regulate ß1-integrin function and cell adhesion in rheumatoid arthritis fibroblast-like synoviocytes.

Short-term low-magnesium diet reduces autoimmune arthritis severity and synovial tissue gene expression.

Magnesium has been suggested to have anti-inflammatory properties in short-term, mostly in vitro studies. To examine the effect of dietary magnesium modifications in arthritis severity and joint damage DA rats were placed on one of three diet regimens before the induction of autoimmune pristane-induced arthritis (PIA): a 4 wk low-magnesium diet, normal diet, and a magnesium-supplemented diet. The diets were switched to a normal diet 14 days after the induction of PIA (typical time of disease onset). Arthritis severity was scored for 38 days, and joints were examined by histology and quantitative PCR for proinflammatory genes. Rats on the low-magnesium diet were significantly and reproducibly protected and had 70% lower median arthritis severity score, with preservation of normal joint histology without erosive changes. Rats on the normal or magnesium-supplemented diets were not protected and developed equally severe and erosive disease. While the dietary modifications were at disease onset (day 14 postinduction), the protective effect of the short-term low-magnesium diet persisted, suggesting a lasting effect on a critical pathogenic pathway. Rats on the low-magnesium diet had significant reduction in synovial tissue expression of IL-6, RORA, and RORC, which are genes required for the development of Th17 T cells. This study revealed a novel role for dietary magnesium in the regulation of autoimmune arthritis and opens new possibilities for the treatment of autoimmune diseases such as rheumatoid arthritis and psoriatic arthritis with short courses of dietary or drug-induced modulations of magnesium levels.

Brief treatment with a highly selective immunoproteasome inhibitor promotes long-term cardiac allograft acceptance in mice.

Constitutive proteasomes (c-20S) are ubiquitously expressed cellular proteases that degrade polyubiquitinated proteins and regulate cell functions. An isoform of proteasome, the immunoproteasome (i-20S), is highly expressed in human T cells, dendritic cells (DCs), and B cells, suggesting that it could be a potential target for inflammatory diseases, including those involving autoimmunity and alloimmunity. Here, we describe DPLG3, a rationally designed, noncovalent inhibitor of the immunoproteasome chymotryptic subunit ß5i that has thousands-fold selectivity over constitutive ß5c. DPLG3 suppressed cytokine release from blood mononuclear cells and the activation of DCs and T cells, diminished accumulation of effector T cells, promoted expression of exhaustion and coinhibitory markers on T cells, and synergized with CTLA4-Ig to promote long-term acceptance of cardiac allografts across a major histocompatibility barrier. These findings demonstrate the potential value of using brief posttransplant immunoproteasome inhibition to entrain a long-term response favorable to allograft survival as part of an immunomodulatory regimen that is neither broadly immunosuppressive nor toxic.

Different expression of ß subunits of the KCa1.1 channel by invasive and non-invasive human fibroblast-like synoviocytes.

BACKGROUND: Fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA-FLS) contribute to joint inflammation and damage characteristic of the disease. RA-FLS express KCa1.1 (BK, Slo1, MaxiK, KCNMA1) as their major plasma membrane potassium channel. Blocking KCa1.1 reduces the invasive phenotype of RA-FLS and attenuates disease severity in animal models of RA. This channel has therefore emerged as a promising therapeutic target in RA. However, the pore-forming α subunit of KCa1.1 is widely distributed in the body, and blocking it induces severe side effects, thus limiting its value as a therapeutic target. On the other hand, KCa1.1 channels can also contain different accessory subunits with restricted tissue distribution that regulate channel kinetics and pharmacology. Identification of the regulatory subunits of KCa1.1 expressed by RA-FLS may therefore provide the opportunity for generating a selective target for RA treatment. METHODS: Highly invasive RA-FLS were isolated from patients with RA, and FLS from patients with osteoarthritis (OA) were used as minimally invasive controls. The ß subunit expression by FLS was assessed by quantitative reverse transcription polymerase chain reactions, Western blotting, and patch-clamp electrophysiology combined with pharmacological agents. FLS were sorted by flow cytometry on the basis of their CD44 expression level for comparison of their invasiveness and with their expression of KCa1.1 α and ß subunits. ß1 and ß3 subunit expression was reduced with small interfering RNA (siRNA) to assess their specific role in KCa1.1α expression and function and in FLS invasiveness. RESULTS: We identified functional ß1 and ß3b regulatory subunits in RA-FLS. KCa1.1 ß3b subunits were expressed by 70 % of the cells and were associated with highly invasive CD44(high) RA-FLS, whereas minimally invasive CD44(low) RA-FLS and OA-FLS expressed either ß1 subunit. Furthermore, we found that silencing the ß3 but not the ß1 subunit with siRNA reduced KCa1.1 channel density at the plasma membrane of RA-FLS and inhibited RA-FLS invasiveness. CONCLUSIONS: Our findings suggest the KCa1.1 channel composed of α and ß3b subunits as an attractive target for the therapy of RA.

The cation channel Trpv2 is a new suppressor of arthritis severity, joint damage, and synovial fibroblast invasion.

Little is known about the regulation of arthritis severity and joint damage in rheumatoid arthritis (RA). Fibroblast-like synoviocytes (FLS) have a central role in joint damage and express increased levels of the cation channel Trpv2. We aimed at determining the role of Trpv2 in arthritis. Treatment with Trpv2-specific agonists decreased the in vitro invasiveness of FLS from RA patients and arthritic rats and mice. Trpv2 stimulation suppressed IL-1ß-induced expression of MMP-2 and MMP-3. Trpv2 agonists, including the new and more potent LER13, significantly reduced disease severity in KRN serum- and collagen-induced arthritis, and reduced histologic joint damage, synovial inflammation, and synovial blood vessel numbers suggesting anti-angiogenic activity. In this first in vivo use of Trpv2 agonists we discovered a new central role for Trpv2 in arthritis. These new compounds have the potential to become new therapies for RA and other diseases associated with inflammation, invasion, and angiogenesis.