Cellular metabolic adaptations in rheumatoid arthritis and their therapeutic implications

Inflammatory stimulus-responsive polymersomes reprogramming glucose metabolism mitigates rheumatoid arthritis

Inflammation-resident cells within arthritic sites undergo a metabolic shift towards glycolysis, which greatly aggravates rheumatoid arthritis (RA). Reprogramming glucose metabolism can suppress abnormal proliferation and activation of inflammation-related cells without affecting normal cells, holding potential for RA therapy. Single 2-deoxy-d-glucose (2-DG, glycolysis inhibitor) treatment often cause elevated ROS, which is detrimental to RA remission. The rational combination of glycolysis inhibition with anti-inflammatory intervention might cooperatively achieve favorable RA therapy. To improve drug bioavailability and exert synergetic effect, stable co-encapsulation of drugs in long circulation and timely drug release in inflamed milieu is highly desirable. Herein, we designed a stimulus-responsive hyaluronic acid-triglycerol monostearate polymersomes (HTDD) co-delivering 2-DG and dexamethasone (Dex) to arthritic sites. After intravenous injection, HTDD polymersomes facilitated prolonged circulation and preferential distribution in inflamed sites, where overexpressed matrix metalloproteinases and acidic pH triggered drug release. Results indicated 2-DG can inhibit the excessive cell proliferation and activation, and improve Dex bioavailability by reducing Dex efflux. Dex can suppress inflammatory signaling and prevent 2-DG-induced oxidative stress. Thus, the combinational strategy ultimately mitigated RA by inhibiting glycolysis and hindering inflammatory signaling. Our study demonstrated the great potential in RA therapy by reprogramming glucose metabolism in arthritic sites.

Hyaluronic acid-coated polypeptide nanogel enhances specific distribution and therapy of tacrolimus in rheumatoid arthritis

Rheumatoid arthritis (RA) involves chronic inflammation, oxidative stress, and complex immune cell interactions, leading to joint destruction. Traditional treatments are often limited by off-target effects and systemic toxicity. This study introduces a novel therapeutic approach using hyaluronic acid (HA)-conjugated, redox-responsive polyamino acid nanogels (HA-NG) to deliver tacrolimus (TAC) specifically to inflamed joints. The nanogels' disulfide bonds enable controlled TAC release in response to high intracellular glutathione (GSH) levels in activated macrophages, prevalent in RA-affected tissues. In vitro results demonstrated that HA-NG/TAC significantly reduced TAC toxicity to normal macrophages and showed high biocompatibility. In vivo, HA-NG/TAC accumulated more in inflamed joints compared to non-targeted NG/TAC, enhancing therapeutic efficacy and minimizing side effects. Therapeutic evaluation in collagen-induced arthritis (CIA) mice revealed HA-NG/TAC substantially reduced paw swelling, arthritis scores, synovial inflammation, and bone erosion while suppressing pro-inflammatory cytokine levels. These findings suggest that HA-NG/TAC represents a promising targeted drug delivery system for RA, offering potential for more effective and safer clinical applications.

Endogenous Melanin and Hydrogen-Based Specific Activated Theranostics Nanoagents: A Novel Multi-Treatment Paradigm for Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disorder characterized by excessive proliferation of rheumatoid arthritis synovial fibroblasts (RASFs) and accumulation of inflammatory cytokines. Exploring the suppression of RASFs and modulation of the RA microenvironment is considered a comprehensive strategy for RA. In this work, specifically activated nanoagents (MAHI NGs) based on the hypoxic and weakly acidic RA microenvironment are developed to achieve a second near-infrared fluorescence (NIR-II FL)/photoacoustic (PA) dual-model imaging-guided multi-treatment. Due to optimal size, the MAHI NGs passively accumulate in the diseased joint region and undergo rapid responsive degradation, precisely releasing functionalized components: endogenous melanin-nanoparticles (MNPs), hydrogen gas (H2), and indocyanine green (ICG). The released MNPs play a crucial role in ablating RASFs within the RA microenvironment through photothermal therapy (PTT) guided by accurate PA imaging. However, the regional hyperthermia generated by PTT may exacerbate reactive oxygen species (ROS) production and inflammatory response following cell lysis. Remarkably, under the acidic microenvironment, the controlled release of H2 exhibits precise synergistic antioxidant and anti-inflammatory effects with MNPs. Moreover, the ICG, the second near-infrared dye currently approved for clinical use, possesses excellent NIR-II FL imaging properties that facilitate the diagnosis of deep tissue diseases and provide the right time-point for PTT.

Itaconate reduces proliferation and migration of fibroblast-like synoviocytes and ameliorates arthritis models

Fibroblast-like synoviocytes (FLS) play critical roles in rheumatoid arthritis (RA). Itaconate (ITA), an endogenous metabolite derived from the tricarboxylic acid (TCA) cycle, has attracted attention because of its anti-inflammatory, antiviral, and antimicrobial effects. This study evaluated the effect of ITA on FLS and its potential to treat RA. ITA significantly decreased FLS proliferation and migration in vitro, as well as mitochondrial oxidative phosphorylation and glycolysis measured by an extracellular flux analyzer. ITA accumulates metabolites including succinate and citrate in the TCA cycle. In rats with type II collagen-induced arthritis (CIA), intra-articular injection of ITA reduced arthritis and bone erosion. Irg1-deficient mice lacking the ability to produce ITA had more severe arthritis than control mice in the collagen antibody-induced arthritis. ITA ameliorated CIA by inhibiting FLS proliferation and migration. Thus, ITA may be a novel therapeutic agent for RA.

Hyaluronic-Acid-Nanomedicine Hydrogel for Enhanced Treatment of Rheumatoid Arthritis by Mediating Macrophage-Synovial Fibroblast Cross-Talk

The occurrence of rheumatoid arthritis (RA) is highly correlated with progressive and irreversible damage of articular cartilage and continuous inflammatory response. Here, inspired by the unique structure of synovial lipid-hyaluronic acid (HA) complex, we developed supramolecular HA-nanomedicine hydrogels for RA treatment by mediating macrophage-synovial fibroblast cross-talk through locally sustained release of celastrol (CEL). Molecular dynamics simulation confirmed that HA conjugated with hydrophobic segments could interspersed into the CEL-loaded [poly(ε-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-undecanone)-poly(ethylene glycol)-poly(ε-caprolaone-co-1,4,8-trioxa[4.6]spiro-9-undecanone] (PECT) nanoparticles to form the supramolecular nanomedicine hydrogel HA-poly(ε-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-un-decanone)/PECT@CEL (HP@CEL), enabling fast hydrogel formation after injection and providing a 3-dimensional environment similar with synovial region. More importantly, the controlled release of CEL from HP@CEL inhibited the macrophage polarization toward the proinflammatory M1 phenotype and further suppressed the proliferation of synovial fibroblasts by regulating the Toll-like receptor pathway. In collagen-induced arthritis model in mice, HP@CEL hydrogel treatment substantial attenuated clinical symptoms and bone erosion and improved the extracellular matrix deposition and bone regeneration in ankle joint. Altogether, such a bioinspired injectable polymer-nanomedicine hydrogel represents an effective and promising strategy for suppressing RA progression through augmenting the cross-talk of macrophages and synovial fibroblast for regulation of chronic inflammation.

Neutrophil-Mimetic, ROS Responsive, and Oxygen Generating Nanovesicles for Targeted Interventions of Refractory Rheumatoid Arthritis

Rheumatoid arthritis (RA) is the most prevalent inflammatory joint disease worldwide, leading to irreversible disability and even mortality. Unfortunately, current treatment regimens fail to cure RA due to low therapeutic responses and off-target side effects. Herein, a neutrophil membrane-cloaked, natural anti-arthritic agent leonurine (Leo), and catalase (CAT) co-loaded nanoliposomal system (Leo@CAT@NM-Lipo) is constructed to remodel the hostile microenvironment for RA remission. Due to the inflammation tropism inherited from neutrophils, Leo@CAT@NM-Lipo can target and accumulate in the inflamed joint cavity where high-level ROS can be catalyzed into oxygen by CAT to simultaneously accelerate the drug release and alleviate hypoxia at the lesion site. Besides, the neutrophil membrane camouflaging also enhances the anti-inflammatory potentials of Leo@CAT@NM-Lipo by robustly absorbing pro-arthritogenic cytokines and chemokines. Consequently, Leo@CAT@NM-Lipo successfully alleviated paw swelling, reduced arthritis score, mitigated bone and cartilage damage, and reversed multiple organ dysfunctions in adjuvant-induced arthritis rats (AIA) rats by synergistic effects of macrophage polarization, inflammation resolution, ROS scavenging, and hypoxia relief. Furthermore, Leo@CAT@NM-Lipo manifested excellent biocompatibility both at the cellular and animal levels. Taken together, the study provided a neutrophil-mimetic and ROS responsive nanoplatform for targeted RA therapy and represented a promising paradigm for the treatment of a variety of inflammation-dominated diseases.

Effect of the antirheumatic medication methotrexate (MTX) on biomechanical compressed human periodontal ligament fibroblasts (hPDLFs)

BACKGROUND

The aim of this study was to investigate the in vitro effect of the antirheumatic drug methotrexate (MTX) on biomechanically compressed human periodontal ligament fibroblasts (hPDLFs), focusing on the expression of interleukin 6 (IL-6), as its upregulation is relevant to orthodontic tooth movement.

METHODS

Human PDLFs were subjected to pressure and simultaneously treated with MTX. Cell proliferation, viability and morphology were studied, as was the gene and protein expression of IL-6.

RESULTS

Compared with that in untreated fibroblasts, IL-6 mRNA expression in mechanically compressed ligament fibroblasts was increased (two to sixfold; ****p < 0.0001). Under compression, hPDLFs exhibited a significantly more expanded shape with an increase of cell extensions. MTX with and without pressure did not affect IL-6 mRNA expression or the morphology of hPDLFs.

CONCLUSION

MTX has no effect on IL-6 expression in compressed ligament fibroblasts.

Mechanistic role of quercetin as inhibitor for adenosine deaminase enzyme in rheumatoid arthritis: systematic review

Rheumatoid arthritis (RA) is an autoimmune disease involving T and B lymphocytes. Autoantibodies contribute to joint deterioration and worsening symptoms. Adenosine deaminase (ADA), an enzyme in purine metabolism, influences adenosine levels and joint inflammation. Inhibiting ADA could impact RA progression. Intracellular ATP breakdown generates adenosine, which increases in hypoxic and inflammatory conditions. Lymphocytes with ADA play a role in RA. Inhibiting lymphocytic ADA activity has an immune-regulatory effect. Synovial fluid levels of ADA are closely associated with the disease's systemic activity, making it a useful parameter for evaluating joint inflammation. Flavonoids, such as quercetin (QUE), are natural substances that can inhibit ADA activity. QUE demonstrates immune-regulatory effects and restores T-cell homeostasis, making it a promising candidate for RA therapy. In this review, we will explore the impact of QUE in suppressing ADA and reducing produced the inflammation in RA, including preclinical investigations and clinical trials.

CXCL9 and its Receptor CXCR3, an Important Link Between Inflammation and Cardiovascular Risks in RA Patients

Cardiovascular disease (CVD) is the most common cause of mortality in rheumatoid arthritis (RA), and Inflammation has a decisive role in its pathogenesis. CXCL9 contributes to multi aspects of inflammatory reactions associated with the pathogenesis of CVD. In the current study, we evaluated the association of plasma CXCL9 and CXCR3 gene expression with Cardiovascular risk factors in RA patients for the first time. Thirty newly diagnosed, 30 on-treatment RA patients, and 30 healthy subjects were recruited in this study. The plasma concentration of CXCL9 and CXCR3 gene expression were measured using ELISA and Real-Time PCR, respectively. The CVD risk was evaluated using Framingham Risk Score (FRS) and Systematic Coronary Risk Evaluation (SCORE). The plasma levels of CXCL9 were significantly higher in the newly diagnosed and on-treatment RA patients compared to the control group (P < 0.0001 and P < 0.001, respectively). Also, The CXCR3 gene expression was strongly elevated in newly diagnosed and on-treatment patients (P < 0.001 and P < 0.01, respectively). The CXCL9 and CXCR3 were significantly associated with RA disease activity (P = 0.0005, r = 0.436; P = 0.0002, r = 0.463, respectively). The FRS was remarkably higher in newly diagnosed and on-treatment patients (P = 0.014 and P = 0.035, respectively). The CXCR3 gene expression significantly correlated with age, systolic blood pressure, FRS, and SCORE (P = 0.020, r = 0.298; P = 0.006, r = 0.346; P = 0.006, r = 0.349; P = 0.007, r = 0.341, respectively). The CXCL9 plasma concentration had a significant negative correlation with plasma HDL and LDL levels (P = 0.033, r = -0.275; P = 0.021, r = -0.296, respectively). CXCL9 and CXCR3 correlates with different variables of CVD in RA.

Precise Lipidomics Decipher Circulating Ceramide and Sphingomyelin Cycle Associated with the Progression of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a long-term autoimmune condition that causes joint and surrounding tissue inflammation. Lipid mediators are involved in inflammation and deterioration of the joints. Despite attempts to discover effective drug targets to intervene with lipid metabolism in the disease, progress has been limited. In this study, precise lipidomic technology was employed to quantify a broad range of serum ceramides and sphingomyelin (SM) in a large cohort, revealing an association between the accumulation of circulating ceramides and disturbed ceramide/SM cycles during the progression of RA. In our investigation, we discovered that eight ceramides exhibited a positive correlation with the activity of RA, thereby enhancing the accuracy of RA diagnosis, particularly in patients with serum antibody-negative RA. Furthermore, the enzyme SM phosphodiesterase 3 (SMPD3) was found to disrupt the circulating SM cycle and accelerate the progression of RA. The activity of SMPD3 can be inhibited by methotrexate, resulting in decreased metabolic conversion of SM to ceramide. These findings suggest that targeting the SM cycle may provide a new therapeutic option for RA.

A pH-Responsive DNA Tetrahedron/Methotrexate Drug Delivery System Used for Rheumatoid Arthritis Treatment

Rheumatoid arthritis (RA) is a chronic autoimmune disorder that leads to progressive and aggressive joint inflammation. The disease process is characterized by the activation of macrophages, which then release tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), accelerating tissue damage. Tackling tissue damage is a crucial target in the treatment of RA. In this study, a macrophage-targeted and pH-response DNA tetrahedron/methotrexate drug delivery system was constructed by loading methotrexate (MTX) onto a DNA duplex. MTX was used as a drug model, and a pH-response DNA tetrahedron (TET) was used as the drug carrier, which was modified with hyaluronic acid (HA) to target macrophages. The aim of this study was to evaluate the potential of TET as an effective drug carrier for the treatment of RA. On this basis, we successfully prepared TETs loaded with MTX, and in vitro assays showed that the MTX-TET treatment could successfully target macrophages and induce macrophages to polarize to M1 phenotype. At the same time, we also injected MTX-TET intravenously into collagen-induced arthritis (CIA) model mice, and the redness and swelling of the paws of mice were significantly alleviated, proving that the MTX-TET could successfully target inflamed joints and release MTX to treat joint swelling. In addition, the histochemical results showed that the MTX-TET could reduce synovitis and joint swelling in CIA mice, reduce the level of inflammatory factors in vivo, and improve the disease status while maintaining a good biosafety profile. This study showed that the MTX-TET treatment has beneficial therapeutic effects on RA, providing a new strategy for the clinical treatment of RA.

Rosmarinic acid nanomedicine for rheumatoid arthritis therapy: Targeted RONS scavenging and macrophage repolarization

The infiltration of inflammatory cells, especially macrophages, integrated with the production of reactive oxygen and nitrogen species (RONS) and the release of inflammatory cytokines play a crucial role in the pathogenesis of rheumatoid arthritis (RA). Synergistic combination of RONS scavenging and macrophage repolarization from pro-inflammatory M1 phenotype towards anti-inflammatory M2 phenotype, provides a promising strategy for efficient RA treatment. Herein, this study reported a unique self-assembly strategy to construct distinct rosmarinic acid nanoparticles (RNPs) for efficient RA treatment using the naturally occurring polyphenol-based compound, rosmarinic acid (RosA). The designed RNPs exhibited favorable capability in scavenging RONS and pro-inflammatory cytokines produced by macrophages. Attributing to the widened vascular endothelial-cell gap at inflammation sites, RNPs could target and accumulate at the inflammatory joints of collagen-induced arthritis (CIA) rats for guaranteeing therapeutic effect. In vivo investigation demonstrated that RNPs alleviated the symptoms of RA, including joint swelling, synovial hyperplasia, cartilage degradation, and bone erosion in CIA rats. Additionally, the designed RNPs promoted macrophage polarization from M1 phenotype towards M2 phenotype, resulting in the suppressed progression of RA. Therefore, this research represents the representative paradigm for RA therapy using antioxidative nanomedicine deriving from the natural polyphenol-based compound.

Tyro3 receptor tyrosine kinase contributes to pathogenic phenotypes of fibroblast-like synoviocytes in rheumatoid arthritis and disturbs immune cell balance in experimental arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disorder characterized by synovitis and joint damage, the underlying causes of which remain unclear. Our prior investigations revealed a notable correlation between the expression of Tyro3 Protein Tyrosine Kinase (Tyro3TK) and the progression of RA. To further elucidate the pathogenic role of Tyro3TK in RA, we analyzed the influence of Tyro3TK on pathogenic phenotypes of RA fibroblast like synoviocyte (FLS) in vitro and compared disease severity, joint damages and immunological parameters of K/BxN serum transfer arthritis (STA) in Tyro3TK-/- deficient mice and wild type controls. Our findings underscored the remarkable effectiveness of Tyro3TK blockade, as evidenced by diminished secretion of inflammatory cytokines and matrix metalloproteinases (MMPs), curtailed migration and invasiveness of RAFLS, and attenuated differentiation of pathogenic helper T cell subsets mediated by RAFLS. Correspondingly, our in vivo investigations illuminated the more favorable outcomes in Tyro3TK-deficient mice, characterized by reduced joint pathology, tempered synovial inflammation, and restored immune cell equilibrium. These data suggested that Tyro3TK might contribute to aggravated autoimmune arthritis and immunological pathology and act as a potential therapeutic target for RA.

Ferrihydrite Nanoparticles Alleviate Rheumatoid Arthritis by Nanocatalytic Antioxidation and Oxygenation

Oxidative stress and hypoxia are two key biochemical factors in the development of rheumatoid arthritis (RA). As both reactive oxygen species (ROS) and oxygen gas (O2) are oxygen-related chemicals, we suggest that a redox reaction converting ROS into O2 can mitigate oxidative stress and hypoxia concurrently, synergistically modulating the inflammatory microenvironment. In this work, ferrihydrite, a typical iron oxyhydroxide, is prepared in nanodimensions in which tetrahedrally coordinated Fe can form a composite catalytic center by coupling with an adjacent hydroxyl group, cooperatively facilitating H2O2 decomposition and O2 generation, presenting a high catalase-like activity. In the RA region, the nanomaterial catalyzes the conversion of excess H2O2 into O2, achieving both antioxidation and oxygenation favoring the alleviation of inflammation. Both cellular and in vivo experiments demonstrate the desirable efficacy of ferrihydrite nanoparticles for RA treatment. This work provides a methodology for the catalytic therapy of inflammatory diseases featuring both oxidative stress and hypoxia.

The development and function of human monocyte-derived dendritic cells regulated by metabolic reprogramming

Human monocyte-derived dendritic cells (moDCs) that develop from monocytes play a key role in innate inflammatory responses as well as T cell priming. Steady-state moDCs regulate immunogenicity and tolerogenicity by changing metabolic patterns to participate in the body's immune response. Increased glycolytic metabolism after danger signal induction may strengthen moDC immunogenicity, whereas high levels of mitochondrial oxidative phosphorylation were associated with the immaturity and tolerogenicity of moDCs. In this review, we discuss what is currently known about differential metabolic reprogramming of human moDC development and distinct functional properties.

Enhanced Anti-Rheumatoid Arthritis Activity of Total Alkaloids from Picrasma Quassioides in Collagen-Induced Arthritis Rats by a Targeted Drug Delivery System

New drug delivery systems have rarely been used in the formulation of traditional Chinese medicine, especially those that are crude active Chinese medicinal ingredients. In the present study, hyaluronic acid decorated lipid-polymer hybrid nanoparticles were used to prepare a targeted drug delivery system (TDDS) for total alkaloid extract from Picrasma quassioides (TAPQ) to improve its targeting property and anti-inflammatory activity. Picrasma quassioides, a common-used traditional Chinese medicine (TCM), containing a series of hydrophobic total alkaloids including β-carboline and canthin-6-one alkaloids show great anti-inflammatory activity. However, its high toxicity (IC50= 8.088±0.903 μg/ml), poor water solubility (need to dissolve with 0.8% Tween-80) and poor targeting property severely limits its clinical application. Herein, hyaluronic acid (HA) decorated lipid-polymer hybrid nanoparticles loaded with TAPQ (TAPQ-NPs) were designed to overcome above mentioned deficiencies. TAPQ-NPs have good water solubility, strong anti-inflammatory activity and great joint targeting property. The in vitro anti-inflammatory activity assay showed that the efficacy of TAPQ-NPs was significantly higher than TAPQ(P<0.001). Animal experiments showed that the nanoparticles had good joint targeting property and had strong inhibitory activity against collagen-induced arthritis (CIA). These results indicate that the application of this novel targeted drug delivery system in the formulation of traditional Chinese medicine is feasible.

Glucose metabolic reprogramming in autoimmune diseases

Autoimmune diseases are conditions in which the immune system mistakenly targets and damages healthy tissue in the body. In recent decades, the incidence of autoimmune diseases has increased, resulting in a significant disease burden. The current autoimmune therapies focus on targeting inflammation or inducing immunosuppression rather than addressing the underlying cause of the diseases. The activity of metabolic pathways is elevated in autoimmune diseases, and metabolic changes are increasingly recognized as important pathogenic processes underlying these. Therefore, metabolically targeted therapies may represent an important strategy for treating autoimmune diseases. This review provides a comprehensive overview of the evidence surrounding glucose metabolic reprogramming and its potential applications in drug discovery and development for autoimmune diseases, such as type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, and systemic sclerosis.

Rheumatoid arthritis macrophages are primed for inflammation and display bioenergetic and functional alterations

OBJECTIVES

Myeloid cells with a monocyte/macrophage phenotype are present in large numbers in the RA joint, significantly contributing to disease; however, distinct macrophage functions have yet to be elucidated. This study investigates the metabolic activity of infiltrating polarized macrophages and their impact on pro-inflammatory responses in RA.

METHODS

CD14+ monocytes from RA and healthy control (HC) bloods were isolated and examined ex vivo or following differentiation into 'M1/M2' macrophages. Inflammatory responses and metabolic analysis ± specific inhibitors were quantified by RT-PCR, western blot, Seahorse XFe technology, phagocytosis assays and transmission electron microscopy along with RNA-sequencing (RNA-seq) transcriptomic analysis.

RESULTS

Circulating RA monocytes are hyper-inflammatory upon stimulation, with significantly higher expression of key cytokines compared with HC (P < 0.05) a phenotype which is maintained upon differentiation into mature ex vivo polarized macrophages. This induction in pro-inflammatory mechanisms is paralleled by cellular bioenergetic changes. RA macrophages are highly metabolic, with a robust boost in both oxidative phosphorylation and glycolysis in RA along with altered mitochondrial morphology compared with HC. RNA-seq analysis revealed divergent transcriptional variance between pro- and anti-inflammatory RA macrophages, revealing a role for STAT3 and NAMPT in driving macrophage activation states. STAT3 and NAMPT inhibition results in significant decrease in pro-inflammatory gene expression observed in RA macrophages. Interestingly, NAMPT inhibition specifically restores macrophage phagocytic function and results in reciprocal STAT3 inhibition, linking these two signalling pathways.

CONCLUSION

This study demonstrates a unique inflammatory and metabolic phenotype of RA monocyte-derived macrophages and identifies a key role for NAMPT and STAT3 signalling in regulating this phenotype.

Unraveling the mechanisms behind joint damage

A subtype of myeloid monocyte mediates the transition from autoimmunity to joint destruction in rheumatoid arthritis.

Mitochondria as disease-relevant organelles in rheumatoid arthritis

Mitochondria are the controllers of cell metabolism and are recognized as decision makers in cell death pathways, organizers of cytoplasmic signaling networks, managers of cellular stress responses, and regulators of nuclear gene expression. Cells of the immune system are particularly dependent on mitochondrial resources, as they must swiftly respond to danger signals with activation, trafficking, migration, and generation of daughter cells. Analogously, faulty immune responses that lead to autoimmunity and tissue inflammation rely on mitochondria to supply energy, cell building blocks and metabolic intermediates. Emerging data endorse the concept that mitochondrial fitness, and the lack of it, is of particular relevance in the autoimmune disease rheumatoid arthritis (RA) where deviations of bioenergetic and biosynthetic flux affect T cells during early and late stages of disease. During early stages of RA, mitochondrial deficiency allows naïve RA T cells to lose self-tolerance, biasing fundamental choices of the immune system toward immune-mediated tissue damage and away from host protection. During late stages of RA, mitochondrial abnormalities shape the response patterns of RA effector T cells engaged in the inflammatory lesions, enabling chronicity of tissue damage and tissue remodeling. In the inflamed joint, autoreactive T cells partner with metabolically reprogrammed tissue macrophages that specialize in antigen-presentation and survive by adapting to the glucose-deplete tissue microenvironment. Here, we summarize recent data on dysfunctional mitochondria and mitochondria-derived signals relevant in the RA disease process that offer novel opportunities to deter autoimmune tissue inflammation by metabolic interference.

Complete Freund's Adjuvant Induces a Fibroblast-like Synoviocytes (FLS) Metabolic and Migratory Phenotype in Resident Fibroblasts of the Inoculated Footpad at the Earliest Stage of Adjuvant-Induced Arthritis

The fibroblast-like synoviocytes (FLS) have a crucial role in the pathogenesis of Rheumatoid Arthritis (RA); however, its precise mechanisms remain partially unknown. The involvement of the fibroblast in activating adjuvant-induced arthritis (AA) has not been previously reported. The objective was to describe the participation of footpads' fibroblasts in the critical initial process that drives the AA onset. Wistar rats were injected with Complete Freund's Adjuvant (CFA) or saline solution in the hind paws' footpads and euthanized at 24 or 48 h for genetic and histological analyses. Microarrays revealed the differentially expressed genes between the groups. The CFA dysregulated RA-linked biological processes at both times. Genes of MAPK, Jak-STAT, HIF, PI3K-Akt, TLR, TNF, and NF-κB signaling pathways were altered 24 h before the arrival of immune cells (CD4, CD8, and CD68). Key markers TNF-α, IL-1β, IL-6, NFκB, MEK-1, JAK3, Enolase, and VEGF were immunodetected in fibroblast in CFA-injected footpads at 24 h but not in the control group. Moreover, fibroblasts in the CFA inoculation site overexpressed cadherin-11, which is linked to the migration and invasion ability of RA-FLS. Our study shows that CFA induced a pathological phenotype in the fibroblast of the inoculation site at very early AA stages from 24 h, suggesting a prominent role in arthritis activation processes.

TRPM7 channel inhibition attenuates rheumatoid arthritis articular chondrocyte ferroptosis by suppression of the PKCα-NOX4 axis

A role for ferroptosis in articular cartilage destruction associated with rheumatoid arthritis (RA) has not been identified. We previously reported transient receptor potential melastatin 7 (TRPM7) expression was correlated with RA cartilage destruction. Herein, we further characterized a role for TRPM7 in chondrocyte ferroptosis. The expression of TRPM7 was found to be elevated in articular chondrocytes derived from adjuvant arthritis (AA) rats, human RA patients, and cultured chondrocytes treated with the ferroptosis inducer, erastin. TRPM7 knockdown or pharmacological inhibition protected primary rat articular chondrocytes and human chondrocytes (C28/I2 cells) from ferroptosis. Moreover, TRPM7 channel activity was demonstrated to contribute to chondrocyte ferroptosis by elevation of intracellular Ca2+. Mechanistically, the PKCα-NOX4 axis was found to respond to stimulation with erastin, which resulted in TRPM7-mediated chondrocyte ferroptosis. Meanwhile, PKCα was shown to directly bind to NOX4, which could be reduced by TRPM7 channel inhibition. Adeno-associated virus 9-mediated TRPM7 silencing or TRPM7 blockade with 2-APB alleviated articular cartilage destruction in AA rats and inhibited chondrocyte ferroptosis. Collectively, both genetic and pharmacological inhibitions of TRPM7 attenuated articular cartilage damage and chondrocyte ferroptosis via the PKCα-NOX4 axis, suggesting that TRPM7-mediated chondrocyte ferroptosis is a promising target for the prevention and treatment of RA.