Critical Role of Synovial Tissue-Resident Macrophage and Fibroblast Subsets in the Persistence of Joint Inflammation

Black holes in hand anatomy: exploring research areas in hand surgery

The term 'black holes' has been applied to anatomical areas needing further study. The historical account On Growth and Form (D'AW Thompson, Cambridge University Press, 1917) applies mathematical principles to explain how physical forces influence the morphology of bone, tendon, ligament and fascia. The trabecular structure of bone is maintained by force loading, providing a map of strain concentrations to better understand fracture fixation and bone healing. The flexor tendon is classified in zones of sheath pathology, but the site of tendon injury depends on the posture at the moment of injury. Ligaments are multistranded structures and in maintaining joint stability throughout motion different fibrous strands must share load by ligament buckling. The fascial description of Guimberteau visualizes the human body as consisting of microvacuoles, quantifiable from the physical Laws of Plateau. Human morphology can be understood through mathematics. These 'black holes' offer possible research avenues to manage some of the unsolved problems in hand surgery or to optimize outcomes.

Synovium-on-a-Chip Reveals Fibroblast-Macrophage Crosstalk Underpinning Joint Homeostasis and Evaluation of Gout Therapies

The synovium maintains joint homeostasis and regulates immune responses through fibroblast-like synoviocytes (FLS) and macrophage-like synoviocytes (MLS). However, investigation of the intricate FLS-MLS interactions is limited by the lack of physiologically relevant in vitro models. Here, this work presents a synovium-on-a-chip model that faithfully mimics the structural and functional properties of the human synovial lining, established with collagen/alginate hybrid hydrogel (CAHG). The functional phenotype of FLS observed in vivo is replicated on chip when cultured with CAHG. Moreover, co-culture with M2c macrophages derived from CD14+ monocytes enables the reconstruction of key immune functions of the synovial lining, including expression of junction proteins (ZO-1 and CLD5) and immunoregulatory markers (TREM2 and VSIG4). CD44 blockade, disrupting FLS-MLS interactions, significantly suppresses inflammasome-related pathways, underscoring the regulatory role of FLS in synovial immune responses. Our model is further validated by modeling gout, where treatment with monosodium urate crystals trigger NLRP3 inflammasome activation, macrophage polarization, and neutrophil extravasation. Pharmacological interventions with MCC950 and entrectinib effectively inhibit the inflammasome activation, demonstrating the platform's utility for preclinical drug evaluation. This synovium-on-a-chip provides a reliable in vitro model for studying synovial inflammation and serves as a valuable tool for the therapeutic discovery of inflammatory joint diseases.

Panaxynol from dietary sources modulates ferroptosis through ceRNA networks in synovium: a novel strategy for alleviating rheumatoid arthritis through functional food intervention

Panaxynol (PAL), a bioactive polyacetylene abundant in dietary plants such as carrots and ginseng, has shown potential in mitigating immune-related diseases, including rheumatoid arthritis (RA). This study investigates the anti-RA effects of PAL through ferroptosis induction and anti-inflammatory mechanisms. In vitro experiments revealed that PAL significantly reduced the viability of collagen-induced arthritis fibroblast-like synoviocytes (CIA-FLS) by triggering ferroptosis, as evidenced by decreased glutathione (GSH) levels, increased lipid peroxidation (LPO) and iron accumulation, and downregulation of key ferroptosis regulators (SLC7A11, GPX4). Furthermore, PAL inhibited the NF-κB pathway, leading to reduced secretion of pro-inflammatory cytokines (TNF-α, IL-1β). In vivo studies using a CIA rat model demonstrated that PAL alleviated joint swelling, reduced the arthritis index, and improved trabecular bone density, highlighting its therapeutic potential. Transcriptomic analysis revealed that PAL modulated ferroptosis and NF-κB signaling through ceRNA networks, with experimental validation confirming the involvement of TFR1 and NIK axes. Notably, inflammatory factors were found to attenuate the sensitivity of CIA-FLS to PAL-induced ferroptosis, suggesting a complex interplay between inflammation and cell death regulation. These findings not only elucidate the mechanism of PAL in RA mitigation but also underscore its potential as a dietary intervention for chronic inflammatory diseases. By integrating traditional dietary knowledge with modern functional food science, this study provides a theoretical basis for the development of functional foods rich in PAL to support joint health.

Urolithin a attenuates rheumatoid arthritis by inhibiting inflammation and pyroptosis in fibroblasts via the AMPK/ NF-κB signaling pathway

Urolithin A (UA), a metabolite of natural polyphenols produced by the gut microbiota, alleviates the symptoms of rheumatoid arthritis (RA) by inhibiting the inflammatory response. UA alleviates the clinical symptoms of RA by inhibiting the occurrence of an inflammatory response, but the specific regulatory mechanism remains unclear. In this study, we established a CIA model in 8-week-old DBA mice and chose LPS-stimulated NIH/3 T3 cells to explore the effects of UA and attempted to elucidate its potential mechanisms. Our results showed UA significantly reduced arthritis scores, and inhibited inflammation, pannus formation, and cartilage and bone destruction of inflamed joints in CIA mice. In vitro, UA inhibited LPS-induced migration and proliferation, and alleviated NLRP3-mediated pyroptosis, significantly inhibiting the protein expression levels of NLRP3, N-terminal gasdermin D, interleukin-1β, caspase-1, and ASC in NIH/3T3 cells. A mechanistic investigation revealed that LPS enhanced phosphorylation of NF-κB and downregulated that of AMPK, which were categorically counteracted by UA treatment. Therefore, UA represents a new class of promising RA treatments targeting fibroblasts, widening the therapeutic options for RA.

Causal relationship between immunophenotypes and rheumatoid arthritis: A 2-sample Mendelian randomization study

As previous studies have demonstrated an association between immune inflammation and rheumatoid arthritis (RA), our study aimed to lend novel insight by exploring the potential causal association between RA and different immunophenotypes. Data were obtained from the genome-wide association study (GWAS) from Finn Gen. The dataset of GWAS contains a cohort of 6236 RA cases and 147,221 controls in European population. Data on immune cell traits are publicly available from the GWAS catalog. A total of 731 immunophenotypes were included in this study including absolute cell counts (ACs), median fluorescence intensity, morphological parameters, and relative cell counts. Mendelian randomization analysis was performed by several methods, and sensitivity analysis and visualization of the results were also carried out. After being adjusted by false discovery rate (FDR), 6 immune phenotypes were significantly and causally associated with the development of RA: CD16 on CD14+ CD16+ monocytes (adjusted odds ratio [OR]: 0.950, 95% confidence interval [CI]: 0.924-0.977, P = 4.04 × 10-4), CD62L-CD86+ myeloid DC %DC (adjusted OR: 1.048, 95% CI: 1.021-1.076, P = 4.29 × 10-4), CD62L-CD86+ myeloid DC AC (adjusted OR: 1.050, 95% CI: 1.024-1.076, P = 1.11 × 10-4), CD62L- myeloid DC AC (adjusted OR: 1.067, 95% CI: 1.033-1.101, P = 8.35 × 10-5), DC AC (adjusted OR: 1.105, 95% CI: 1.062-1.149, P = 7.73 × 10-7), myeloid DC AC (adjusted OR: 1.060, 95% CI: 1.029-1.091, P = 9.96 × 10-5). In addition, we found that CD62L- Dendritic cell % increases with the onset of RA (OR: 1.136, 95% CI: 1.064-1.213, P = 1.36 × 10-4, PFDR = 0.099). This study explored the association between different immunophenotypes and RA, which may lend some novel insights into RA pathogenesis and facilitate the development of new treatments.

Hyaluronic acid-modified PtPdCo-CQ nanocatalyst with triple enzyme-like activities regulates macrophage polarization and autophagy levels for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation and imbalanced macrophage polarization. Pro-inflammatory M1 macrophages exacerbate joint damage through excessive production of reactive oxygen species (ROS), while anti-inflammatory M2 macrophages are prone to ferroptosis, limiting the long-term efficacy of existing nanozyme therapies. This study aimed to develop a novel nanocatalyst combining efficient ROS scavenging and M2 macrophage protection to synergistically regulate macrophage polarization and autophagy levels for sustained RA remission. We designed a hyaluronic acid-modified PtPdCo-CQ nanocatalyst (HPPCQ) with triple enzyme-like activities-superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). In vitro experiments demonstrated that HPPCQ activated the Nrf2/HO-1 antioxidant pathway by scavenging ROS, promoted M1-to-M2 phenotypic repolarization, and protected M2 macrophages from autophagy-dependent ferroptosis via controlled release of chloroquine (CQ). In a collagen-induced arthritis (CIA) mouse model, HPPCQ targeted inflamed joints, significantly reducing clinical scores, synovial hyperplasia, and pro-inflammatory cytokine levels (TNF-α, IL-1β). Histological analysis revealed markedly alleviated cartilage destruction and inflammatory infiltration in HPPCQ-treated mice. By integrating ROS scavenging, macrophage reprogramming, and ferroptosis inhibition, this work provides a novel therapeutic strategy with enhanced efficacy and durability for RA treatment.

Interdisciplinary integration strategy reveals the anti-inflammatory efficacy and potential mechanism of Jianpi Qingre Tongluo prescription in rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic synovitis and associated with high rates of disability and systemic damage. Jianpi Qingre Tongluo prescription (Huangqin Qingre Chubi Capsule, HQC), an herbal formula with abundant clinical applications, has played a definite role in both clinical and experimental studies of RA. However, the specific mechanisms by which HQC relieves inflammation in RA have not been fully elucidated.

OBJECTIVE

This study aimed to elucidate the anti-inflammatory efficacy and potential molecular mechanisms of HQC in RA and provide new targets and strategies for its clinical treatment.

METHODS

An adjuvant-induced arthritis with damp-heat pattern rat model was established to observe the in vivo effects of HQC. Hematoxylin-eosin and toluidine blue staining, and enzyme-linked immunosorbent assay were used to assess potential efficacy. Bioinformatics methods and molecular docking were used to predict potential targets and intervention pathways in which HQC might act on RA. Clinical samples, overexpressed / silenced genes, and pathway agonists were selected to investigate the clinical relevance and regulatory relationships of the pathways. The regulatory mechanism of HQC was confirmed in an in vitro co-culture of neutrophils and fibroblast-like synoviocytes (FLSs) and an in vivo model.

RESULTS

HQC dose-dependently reversed synovial pathological injury and systemic inflammatory responses in rats in vivo. Integrated bioinformatics and molecular docking identified the p38 mitogen-activated protein kinase (MAPK) signaling pathway and neutrophil extracellular trap (NET) formation as the key mechanisms by which HQC exerts anti-inflammatory effects on RA. Subsequently, a high correlation between circ0005732, p38 MAPK, and clinical features of RA was confirmed in clinical samples. In vitro experiments demonstrated that HQC alleviated the proliferation and inflammatory response of FLSs by regulating circ0005732 expression to inhibit NET formation driven by the p38 MAPK signaling pathway. Finally, RT-qPCR and western blotting confirmed that HQC modulated circ0005732, p38 MAPK pathway, and NET formation to alleviate RA in vivo.

CONCLUSION

HQC exerts therapeutic effects against RA by modulating circ0005732 to inhibit p38 MAPK signaling pathway-mediated NET generation and inflammation progression.

Advances in nanodelivery systems based on apoptosis strategies for enhanced rheumatoid arthritis therapy

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disorder primarily characterized by persistent synovial inflammation and progressive bone erosion. The pathogenesis of RA involves a complex cascade of cellular and molecular events, including sustained hyperactivation of macrophages, excessive recruitment and activation of neutrophils, pathological proliferation and invasion of fibroblast-like synoviocytes (FLS), and dysregulated differentiation and function of osteoclasts (OCs). The inflammatory factors secreted by these dysregulated cells significantly disrupt the joint microenvironment through multiple pathological mechanisms, primarily by promoting synovial inflammation, cartilage matrix degradation, osteoclast-mediated bone erosion, and pathological angiogenesis. Therapeutic strategies targeting the induction of apoptosis in these malignant cells have demonstrated considerable potential in preclinical studies, offering a promising approach to enhance treatment outcomes by simultaneously reducing inflammatory cytokine production and inhibiting pathogenic cell proliferation. However, conventional therapeutic drugs are limited in clinical applications because of their high toxicity and side effects. Inflammation induces morphological and functional changes in cells within the rheumatoid arthritis microenvironment (RAM), particularly the overexpression of specific receptors on cell membranes. This phenomenon has driven the development of ligand-modified targeted nanodelivery systems (NDSs), which can specifically target and induce apoptosis in specific cell types, thereby enhancing therapeutic efficacy. This paper comprehensively reviews the research progress of targeted NDSs based on apoptosis strategies for RA therapy, with a detailed discussion of their advantages in inducing apoptosis in various disease-associated cells. Furthermore, the potential of combining apoptosis of multiple cell types for RA treatment is explored. This review is expected to improve insights into the apoptosis of malignant cells to enhance RA therapy. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in nanodelivery systems (NDSs) based on apoptotic strategies for enhanced rheumatoid arthritis (RA) therapy. Unlike conventional NDSs, these optimized systems specifically induce apoptosis in malignant cells within the RA microenvironment by integrating multiple therapeutic strategies. By summarizing the latest research, our work demonstrates the potential of these NDSs to suppress inflammatory responses and prevent bone destruction through targeted elimination of malignant cells, offering a novel direction for RA treatment. This review is significant as it provides a comprehensive overview for researchers and clinicians, facilitating the development of more effective therapeutic approaches for RA and other chronic inflammatory diseases.

Methyltransferase-like 3-mediated RNA N6-methyladenosine contributes to immune dysregulation: diagnostic biomarker and therapeutic target

Methyltransferase-like 3 (METTL3) plays a crucial role in post-transcriptional gene regulation. Substantial evidence links METTL3 to various immune dysfunctions, such as the suppression of antiviral immunity during viral infections and the disruption of immune tolerance in conditions like autoimmune diseases, myeloid leukemia, skin cancers, and anticancer immunotherapy. However, a thorough review and analysis of this evidence is currently missing, which limits the understanding of METTL3's mechanisms and significance in immune dysfunctions. This review aims to elucidate the roles and mechanisms of METTL3 in these immune issues, highlighting its connections and proposing new insights into its modulation of immune responses. Analysis results in this review suggest that METTL3 hampers antiviral immunity, worsens viral replication and infection, and disrupts immune tolerance; conversely, regulating METTL3 enhances antiviral immunity and facilitates viral clearance. Moreover, clinical data corroborates these findings, showing that METTL3 overexpression is associated with increased susceptibility to viral infections and autoimmune conditions. This review establishes a theoretical basis for considering METTL3 as a novel regulator, an important diagnostic biomarker, and a potential target for treating immune dysfunctions.

Advances in Extracellular Matrix-Associated Diagnostics and Therapeutics

The extracellular matrix (ECM) is the common denominator of more than 50 chronic diseases. Some of these chronic pathologies lead to enhanced tissue formation and deposition, whereas others are associated with increased tissue degradation, and some exhibit a combination of both, leading to severe tissue alterations. To develop effective therapies for diseases affecting the lung, liver, kidney, skin, intestine, musculoskeletal system, heart, and solid tumors, we need to modulate the ECM's composition to restore its organization and function. Across diverse organ diseases, there are common denominators and distinguishing factors in this fibroinflammatory axis, which may be used to foster new insights into drug development across disease indications. The 2nd Extracellular Matrix Pharmacology Congress took place in Copenhagen, Denmark, from 17 to 19 June 2024 and was hosted by the International Society of Extracellular Matrix Pharmacology. The event was attended by 450 participants from 35 countries, among whom were prominent scientists who brought together state-of-the-art research on organ diseases and asked important questions to facilitate drug development. We highlight key aspects of the ECM in the liver, kidney, skin, intestine, musculoskeletal system, lungs, and solid tumors to advance our understanding of the ECM and its central targets in drug development. We also highlight key advances in the tools and technology that enable this drug development, thereby supporting the ECM.

Adipose-derived stem cells attenuate rheumatoid arthritis by restoring CX3CR1+ synovial lining macrophage barrier

BACKGROUND

Rheumatoid arthritis (RA) is a chronic autoimmune disease and the integrity of CX3CR1+ synovial macrophage barrier significantly impacts its progression. However, the mechanisms driving the dynamic changes of this macrophage barrier remain unclear. Traditional drug therapies for RA have substantial limitations. Mesenchymal stem cells (MSCs)-based cell therapy, especially adipose-derived stem cells (ADSCs), hold therapeutic promise. Nevertheless, the underlying therapeutic mechanism of ADSCs, especially their interactions with CX3CR1+ macrophages, require further investigation.

METHODS

To explore the interaction between ADSCs and CX3CR1+ synovial macrophages during barrier reconstruction, underlying the therapeutic mechanism of ADSCs and the mechanisms on the dynamic changes of the macrophage barrier, scRNA-seq analysis was conducted 4 days after ADSCs injection in serum transfer-induced arthritis model mice. The roles of mitochondria transfer and ADSCs transplantation were also explored. Bulk RNA-seq analysis was performed after the co-culture of ADSCs and CX3CR1+ synovial macrophages. To study the in vivo fate of ADSCs, bulk RNA-seq was performed on ADSCs retrieved at 0, 2, 4, and 7 days post-injection.

RESULTS

Intra-articular injection of ADSCs effectively attenuated the pathological progression of mice with serum transfer-induced arthritis. ADSCs gradually adhered to CX3CR1+ macrophages, facilitating the restore of the macrophage barrier, while the absence of this barrier greatly weakened the therapeutic effect of ADSCs. scRNA-seq analysis revealed an Atf3high Ccl3high subset of CX3CR1+ macrophages with impaired oxidative phosphorylation that increased during RA progression. ADSCs-mediated reduction of this subset appeared to be linked to mitochondrial transfer, and transplantation of isolated ADSCs-derived mitochondria also proved effective in treating RA. Both bulk RNA-seq and scRNA-seq analyses revealed multiple interaction mechanisms between ADSCs and CX3CR1+ macrophages, including Cd74/Mif axis and GAS6/MERTK axis, which contribute to barrier restoration and therapeutic effects. Furthermore, bulk RNA-seq analysis showed that ADSCs primarily contribute to tissue repair and immune regulation subsequently.

CONCLUSIONS

Our results suggest that ADSCs ameliorated the energy metabolism signature of CX3CR1+ lining macrophages and may promote barrier restoration through mitochondria transfer. In addition, we elucidated the fate of ADSCs and the therapeutic potential of mitochondria in RA treatment.

Exploring the Role of Macrophages and Their Associated Structures in Rheumatoid Arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic, invasive autoimmune disease characterized by symmetrical polyarthritis involving synovial inflammation. Epidemiological studies indicate that the incidence of RA continues to rise, yet the pathogenesis of this disease remains not fully understood. A significant infiltration of macrophages is observed in the synovium of RA patients. It can be inferred that macrophages likely play a crucial role in the onset and progression of RA.

SUMMARY

This review aims to summarize the research progress on the mechanisms by which macrophages and their associated structures contribute to RA, as well as potential therapeutic approaches, aiming to provide new insights into the study of RA pathogenesis and its clinical treatment.

KEY MESSAGES

During the course of RA, besides the inherent roles of macrophages, these cells respond to microenvironmental changes such as pathogen invasion or tissue damage by undergoing polarization, pyroptosis, or forming macrophage extracellular traps (METs), all of which influence inflammatory responses and immune homeostasis, thereby mediating the occurrence and development of RA. Additionally, macrophages secrete exosomes, which participate in intercellular communication and signal transduction processes, thus contributing to the progression of RA. Therefore, it is critical to elucidate how macrophages and their related structures function in RA.

BACKGROUND

Rheumatoid arthritis (RA) is a chronic, invasive autoimmune disease characterized by symmetrical polyarthritis involving synovial inflammation. Epidemiological studies indicate that the incidence of RA continues to rise, yet the pathogenesis of this disease remains not fully understood. A significant infiltration of macrophages is observed in the synovium of RA patients. It can be inferred that macrophages likely play a crucial role in the onset and progression of RA.

SUMMARY

This review aims to summarize the research progress on the mechanisms by which macrophages and their associated structures contribute to RA, as well as potential therapeutic approaches, aiming to provide new insights into the study of RA pathogenesis and its clinical treatment.

KEY MESSAGES

During the course of RA, besides the inherent roles of macrophages, these cells respond to microenvironmental changes such as pathogen invasion or tissue damage by undergoing polarization, pyroptosis, or forming macrophage extracellular traps (METs), all of which influence inflammatory responses and immune homeostasis, thereby mediating the occurrence and development of RA. Additionally, macrophages secrete exosomes, which participate in intercellular communication and signal transduction processes, thus contributing to the progression of RA. Therefore, it is critical to elucidate how macrophages and their related structures function in RA.

Resident synovial macrophages in synovial fluid: Implications for immunoregulation

Resident synovial macrophages (RSMs) are anti-inflammatory, self-renewing macrophages that provide physical immune sequestration of the joint space from the peripheral immune system. Increased permeability of this structure is associated with peripheral immune cells in the synovial fluid (SF). Direct measures of synovial barrier integrity are possible with tissue histology, but after barrier breakdown, if these cells perpetuate or initiate chronic inflammation in SF remains unknown. We sought to identify RSM in human SF as an indirect measure of synovial barrier integrity. To validate findings, we created a novel ex vivo explant model using human synovium. scRNA-seq revealed these SF RSMs upregulated pro-fibrotic and pro-osteoclastic pathways in inflammatory arthritis, but not septic arthritis. Increased frequencies of RSMs in SF was associated with increased sRANKL regardless of underlying pathology. These findings suggest the frequency of RSMs in SF may correlate with synovial barrier damage and in turn, potential damage to joint structures.

Tissue-resident immune cells: from defining characteristics to roles in diseases

Tissue-resident immune cells (TRICs) are a highly heterogeneous and plastic subpopulation of immune cells that reside in lymphoid or peripheral tissues without recirculation. These cells are endowed with notably distinct capabilities, setting them apart from their circulating leukocyte counterparts. Many studies demonstrate their complex roles in both health and disease, involving the regulation of homeostasis, protection, and destruction. The advancement of tissue-resolution technologies, such as single-cell sequencing and spatiotemporal omics, provides deeper insights into the cell morphology, characteristic markers, and dynamic transcriptional profiles of TRICs. Currently, the reported TRIC population includes tissue-resident T cells, tissue-resident memory B (BRM) cells, tissue-resident innate lymphocytes, tissue-resident macrophages, tissue-resident neutrophils (TRNs), and tissue-resident mast cells, but unignorably the existence of TRNs is controversial. Previous studies focus on one of them in specific tissues or diseases, however, the origins, developmental trajectories, and intercellular cross-talks of every TRIC type are not fully summarized. In addition, a systemic overview of TRICs in disease progression and the development of parallel therapeutic strategies is lacking. Here, we describe the development and function characteristics of all TRIC types and their major roles in health and diseases. We shed light on how to harness TRICs to offer new therapeutic targets and present burning questions in this field.

L-selectin Promotes Migration, Invasion and Inflammatory Response of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis via NF-kB Signaling Pathway

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease characterized by chronic inflammation of the synovium and progressive joint damage. Fibroblast-like synoviocytes (FLSs) exhibit excessive proliferative and aggressive phenotypes and play a major role in the pathophysiology of RA. Previous studies have confirmed the pathologic role of L-selectin in cell adhesion and migration. In rheumatoid arthritis models, L-selectin regulates leukocyte homing, which leads to joint inflammation. Moreover, in L-selectin knockout mice, there is a reduction in joint inflammation. However, the associations of L-selectin with FLSs in RA remain unclear. This study aims to reveal the effect of L-selectin on RA-FLSs and to investigate the molecular mechanism of L-selectin in RA. Our findings indicated that L-selectin was significantly expressed in RA synovial tissues and RA-FLSs. L-selectin silencing reduced RA-FLSs migration and invasion and attenuated the secretion of pro-inflammatory cytokines TNF-α, IL-1β and IL-6 in vitro. Moreover, investigations into mechanisms revealed that L-selectin activated the nuclear factor kappa-B (NF-κB) signaling pathway while blocking this signaling pathway could compromise the effects of L-selectin. Finally, in vivo experiments with a collagen-induced arthritis rat model revealed that silencing L-selectin alleviated inflammatory infiltration of the synovium and cartilage destruction, and validated the NF-κB signaling pathways findings observed in vitro. In summary, we show that L-selectin enhances the migration and invasion of RA-FLSs through the activation of NF-κB signaling pathways, ultimately worsening the progression of RA.

Meeting report: Hidden links in autoimmunity

A NIAID-sponsored workshop was held in September 2024, where challenges to understanding common mechanisms in autoimmune disease were discussed as opportunities to advance research.

The role of macrophage polarization in rheumatoid arthritis and osteoarthritis: Pathogenesis and therapeutic strategies

Rheumatoid arthritis (RA) and osteoarthritis (OA) are common and debilitating joint disorders affecting millions of individuals worldwide. Despite their distinct pathological features, both conditions share a crucial role of macrophages in disease progression. Macrophages exhibit remarkable plasticity, polarizing into pro-inflammatory M1 or anti-inflammatory M2 phenotypes in response to environmental cues. An imbalance in macrophage polarization, particularly a shift towards the M1 phenotype, contributes to chronic inflammation and joint damage in RA and OA. This review explores the complex interplay between macrophages and various cell types, including T cells, B cells, synovial fibroblasts, osteoclasts, chondrocytes, and adipocytes, in the pathogenesis of these diseases. We discuss the current understanding of macrophage polarization in RA and OA, highlighting the molecular mechanisms involved. Furthermore, we provide an overview of potential therapeutic strategies targeting macrophage polarization, such as disease-modifying anti-rheumatic drugs, traditional Chinese medicine, nanomedicines, proteins, chemical compounds, and physical therapies. By elucidating the precise mechanisms governing macrophage polarization and its interactions with other cells in the joint microenvironment, researchers can identify novel therapeutic targets and develop targeted interventions to alleviate disease progression and improve patient outcomes in RA and OA.

Macrophage depletion in inflamed rat knees prevents the activation of synovial mesenchymal stem cells by weakening Nampt and Spp1 signaling

BACKGROUND

Macrophages and mesenchymal stem cells (MSCs) engage in crucial interplay during inflammation and have significant roles in tissue regeneration. Synovial MSCs, as key players in joint regeneration, are known to proliferate together with macrophages in synovitis. However, the crosstalk between synovial MSCs and macrophages remains unclear. In this study, we investigated changes in the activation of synovial MSCs in inflamed rat knees following selective depletion of macrophages with clodronate liposomes.

METHODS

Acute inflammation was induced in rat knee joints by injection of carrageenan (day 0). Clodronate liposomes were administered intra-articularly on days 1 and 4 to deplete macrophages, with empty liposomes as a control. Knee joints were collected on day 7 for evaluation by histology, flow cytometry, and colony-forming assays. Concurrently, synovial MSCs were cultured and subjected to proliferation assays, flow cytometry, and chondrogenesis assessments. We also analyzed their crosstalk using single-cell RNA sequencing (scRNA-seq).

RESULTS

Clodronate liposome treatment significantly reduced CD68-positive macrophage numbers and suppressed synovitis. Immunohistochemistry and flow cytometry showed decreased expression of CD68 (a macrophage marker) and CD44 and CD271 (MSC markers) in the clodronate group, while CD73 expression remained unchanged. The number of colony-forming cells per 1000 nucleated cells and per gram of synovium was significantly lower in the clodronate group than in the control group. Cultured synovial MSCs from both groups showed comparable proliferation, surface antigen expression, and chondrogenic capacity. scRNA-seq identified seven distinct synovial fibroblast (SF) subsets, with a notable decrease in the Mki67+ SF subset, corresponding to synovial MSCs, in the clodronate group. Clodronate treatment downregulated genes related to extracellular matrix organization and anabolic pathways in Mki67+ SF. Cell-cell communication analysis revealed diminished Nampt and Spp1 signaling interaction between macrophages and Mki67+ SF and diminished Ccl7, Spp1, and Csf1 signaling interaction between Mki67+ SF and macrophages in the clodronate group. Spp1 and Nampt promoted the proliferation and/or chondrogenesis of synovial MSCs.

CONCLUSIONS

Macrophage depletion with clodronate liposomes suppressed synovitis and reduced the number and activity of synovial MSCs, highlighting the significance of macrophage-derived Nampt and Spp1 signals in synovial MSC activation. These findings offer potential therapeutic strategies to promote joint tissue regeneration by enhancing beneficial signals between macrophages and synovial MSCs.

Engineered self-regulating macrophages for targeted anti-inflammatory drug delivery

BACKGROUND

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by increased levels of inflammation that primarily manifests in the joints. Macrophages act as key drivers for the progression of RA, contributing to the perpetuation of chronic inflammation and dysregulation of pro-inflammatory cytokines such as interleukin 1 (IL-1). The goal of this study was to develop a macrophage-based cell therapy for biologic drug delivery in an autoregulated manner.

METHODS

For proof-of-concept, we developed "smart" macrophages to mitigate the effects of IL-1 by delivering its inhibitor, IL-1 receptor antagonist (IL-1Ra). Bone marrow-derived macrophages were lentivirally transduced with a synthetic gene circuit that uses an NF-κB inducible promoter upstream of either the Il1rn or firefly luciferase transgenes. Two types of joint like cells were utilized to examine therapeutic protection in vitro, miPSCs derived cartilage and isolated primary mouse synovial fibroblasts while the K/BxN mouse model of RA was utilized to examine in vivo therapeutic protection.

RESULTS

These engineered macrophages were able to repeatably produce therapeutic levels of IL-1Ra that could successfully mitigate inflammatory activation in co-culture with both tissue-engineered cartilage constructs and synovial fibroblasts. Following injection in vivo, macrophages homed to sites of inflammation and mitigated disease severity in the K/BxN mouse model of RA.

CONCLUSION

These findings demonstrate the successful development of engineered macrophages that possess the ability for controlled, autoregulated production of IL-1 based on inflammatory signaling such as via the NF-κB pathway to mitigate the effects of this cytokine for applications in RA or other inflammatory diseases. This system provides proof of concept for applications in other immune cell types as self-regulating delivery systems for therapeutic applications in a range of diseases.

Unveiling the macrophage dynamics in osteoarthritic joints: From inflammation to therapeutic strategies

Osteoarthritis (OA) is an incurable, painful, and debilitating joint disease affecting over 500 million people worldwide. The OA joint tissues are infiltrated by various immune cells, particularly macrophages, which are able to induce or perpetuate inflammation. Notably, synovitis and its macrophage component represent a target of interest for developing treatments. In this review, we describe the latest advances in understanding the heterogeneity of macrophage origins, phenotypes, and functions in the OA joint and the effect of current symptomatic therapies on these cells. We then highlight the therapeutic potential of anticytokines/chemokines, nano- and microdrug delivery, and future strategies to modulate macrophage functions in OA.

Trained immunity of synovial macrophages is associated with exacerbated joint inflammation and damage after Staphylococcus aureus infection

OBJECTIVES

Investigate whether and which synoviocytes would acquire trained immunity characteristics that could exacerbate joint inflammation following a secondary Staphylococcus aureus infection.

METHODS

Lipopolysaccharide (LPS) and S. aureus were separately or double injected (21 days of interval) into the tibiofemoral joint cavity of male C57BL/6 mice. At different time points after these stimulations, mechanical nociception was analyzed followed by the analysis of signs of inflammation and damage in the affected joints. The trained immunity markers, including the glycolytic and mTOR pathway, were analyzed in whole tissue or isolated synoviocytes. A group of mice was treated with Rapamycin, an mTOR inhibitor before LPS or S. aureus stimulation.

RESULTS

The double LPS - S. aureus hit promoted intense joint inflammation and damage compared to single joint stimulation, including markers in synoviocyte activation, production of proinflammatory cytokines, persistent nociception, and bone damage, despite not reducing the bacterial clearance. The double LPS - S. aureus hit joints increased the synovial macrophage population expressing CX3CR1 alongside triggering established epigenetic modifications associated with trained immunity events in these cells, such as the upregulation of the mTOR signaling pathway (p-mTOR and HIF1α) and the trimethylation of histone H3. Mice treated with Rapamycin presented reduced CX3CR1+ macrophage activation, joint inflammation, and bone damage.

CONCLUSIONS

There is a trained immunity phenotype in CX3CR1+ synovial macrophages that contributes to the exacerbation of joint inflammation and damage during septic arthritis caused by S. aureus.

Characterization of the single cell landscape in normal and osteoarthritic equine joints

Background

Osteoarthritis (OA) is a major source of pain and disability worldwide. Understanding of disease progression is evolving, but OA is increasingly thought to be a multifactorial disease in which the innate immune system plays a role in regulating and perpetuating low-grade inflammation. The aim of this study was to enhance our understanding of OA immunopathogenesis through characterization of the transcriptomic responses in OA joints, with the goal to facilitate the development of targeted therapies.

Methods

Single-cell RNA sequencing (scRNA-seq) was completed on cells isolated from the synovial fluid of three normal and three OA equine joints. In addition to synovial fluid, scRNA-seq was also performed on synovium from one normal joint and one OA joint.

Results

Characterization of 28,639 cells isolated from normal and OA-affected equine synovial fluid revealed the composition to be entirely immune cells (CD45+) with 8 major populations and 26 subpopulations identified. In synovial fluid, we found myeloid cells (macrophage and dendritic cells) to be overrepresented and T cells (CD4 and CD8) to be underrepresented in OA relative to normal joints. Through subcluster and differential abundance analysis of T cells we further identified a relative overrepresentation of IL23R+ gamma-delta (γδ) T cells in OA-affected joints (a cell type we report to be enriched in gene signatures associated with T helper 17 mediated immunity). Analysis of an additional 17,690 cells (11 distinct cell type clusters) obtained from synovium of one horse led to the identification of an OA-associated reduction in the relative abundance of synovial macrophages, which contrasts with the increased relative abundance of macrophages in synovial fluid. Completion of cell-cell interaction analysis implicated myeloid cells in disease progression, suggesting that the myeloid-myeloid interactions were increased in OA-affected joints.

Conclusions

Overall, this work provides key insights into the composition of equine synovial fluid and synovium in health and OA. The data generated in this study provides equine-specific cell type gene signatures which can be applied to future investigations. Furthermore, our analysis highlights the potential role of macrophages and IL23R+ γδ T cells in OA immunopathogenesis.

Cell-based therapy in the treatment of musculoskeletal diseases

A limited number of tissues can spontaneously regenerate following injury, and even fewer can regenerate to a state comparable to mature, healthy adult tissue. Mesenchymal stem cells (MSCs) were first described in the 1960s-1970s by Friedenstein et al as a small population of bone marrow cells with osteogenic potential and abilities to differentiate into chondrocytes. In 1991, Arnold Caplan coined the term "mesenchymal cells" after identifying these cells as a theoretical precursor to bone, cartilage, tendon, ligament, marrow stroma, adipocyte, dermis, muscle, and connective tissues. MSCs are derived from periosteum, fat, and muscle. Another attractive property of MSCs is their immunoregulatory and regenerative properties, which result from crosstalk with their microenvironment and components of the innate immune system. Collectively, these properties make MSCs potentially attractive for various therapeutic purposes. MSCs offer potential in sports medicine, aiding in muscle recovery, meniscal tears, and tendon and ligament injuries. In joint disease, MSCs have the potential for chondrogenesis and reversing the effects of osteoarthritis. MSCs have also demonstrated potential application to the treatment of degenerative disc disease of the cervical, thoracic, and lumbar spine.

Enhancing Endogenous Hyaluronic Acid in Osteoarthritic Joints with an Anti-Inflammatory Supramolecular Nanofiber Hydrogel Delivering HAS2 Lentivirus

Osteoarthritis (OA) management remains challenging because of its intricate pathogenesis. Intra-articular injections of drugs, such as glucocorticoids and hyaluronic acid (HA), have certain limitations, including the risk of joint infection, pain, and swelling. Hydrogel-based therapeutic strategies have attracted considerable attention because of their enormous therapeutic potential. Herein, a supramolecular nanofiber hydrogel is developed using dexamethasone sodium phosphate (DexP) as a vector to deliver lentivirus-encoding hyaluronan synthase 2 (HAS2) (HAS2@DexP-Gel). During hydrogel degradation, HAS2 lentivirus and DexP molecules are slowly released. Intra-articular injection of HAS2@DexP-Gel promotes endogenous HA production and suppresses synovial inflammation. Additionally, HAS2@DexP-Gel reduces subchondral bone resorption in the anterior cruciate ligament transection-induced OA mice, attenuates cartilage degeneration, and delays OA progression. HAS2@DexP-Gel exhibited good biocompatibility both in vitro and in vivo. The therapeutic mechanisms of the HAS2@DexP-Gel are investigated using single-cell RNA sequencing. HAS2@DexP-Gel optimizes the microenvironment of the synovial tissue by modulating the proportion of synovial cell subpopulations and regulating the interactions between synovial fibroblasts and macrophages. The innovative nanofiber hydrogel, HAS2@DexP-Gel, effectively enhances endogenous HA production while reducing synovial inflammation. This comprehensive approach holds promise for improving joint function, alleviating pain, and slowing OA progression, thereby providing significant benefits to patients.

Inflammatory tissue priming: novel insights and therapeutic opportunities for inflammatory rheumatic diseases

Due to optimised treatment strategies and the availability of new therapies during the last decades, formerly devastating chronic inflammatory diseases such as rheumatoid arthritis or systemic sclerosis (SSc) have become less menacing. However, in many patients, even state-of-the-art treatment cannot induce remission. Moreover, the risk for flares strongly increases once anti-inflammatory therapy is tapered or withdrawn, suggesting that underlying pathological processes remain active even in the absence of overt inflammation. It has become evident that tissues have the ability to remember past encounters with pathogens, wounds and other irritants, and to react more strongly and/or persistently to the next occurrence. This priming of the tissue bears a paramount role in defence from microbes, but on the other hand drives inflammatory pathologies (the Dr Jekyll and Mr Hyde aspect of tissue adaptation). Emerging evidence suggests that long-lived tissue-resident cells, such as fibroblasts, macrophages, long-lived plasma cells and tissue-resident memory T cells, determine inflammatory tissue priming in an interplay with infiltrating immune cells of lymphoid and myeloid origin, and with systemically acting factors such as cytokines, extracellular vesicles and antibodies. Here, we review the current state of science on inflammatory tissue priming, focusing on tissue-resident and tissue-occupying cells in arthritis and SSc, and reflect on the most promising treatment options targeting the maladapted tissue response during these diseases.

NAT10 promotes synovial aggression by increasing the stability and translation of N4-acetylated PTX3 mRNA in rheumatoid arthritis

OBJECTIVE

Recent studies indicate that N-acetyltransferase 10 (NAT10)-mediated ac4C modification plays unique roles in tumour metastasis and immune infiltration. This study aimed to uncover the role of NAT10-mediated ac4C in fibroblast-like synoviocytes (FLSs) functions and synovial immune cell infiltration in rheumatoid arthritis (RA).

METHODS

FLSs were obtained from active established patients with RA. Protein expression was determined by western blotting or immunohistochemistry or multiplexed immunohistochemistry. Cell migration was measured using a Boyden chamber. ac4C-RIP-seq combined with RNA-seq was performed to identify potential targets of NAT10. RNA immunoprecipitation was used to validate the interaction between protein and mRNA. NAT10 haploinsufficiency, inhibitor remodelin or intra-articular Adv-NAT10 was used to suppress arthritis in mice with delayed-type hypersensitivity arthritis (DYHA) and collagen II-induced arthritis (CIA) and rats with CIA.

RESULTS

We found elevated levels of NAT10 and ac4C in FLSs and synovium from patients with RA. NAT10 knockdown or specific inhibitor treatment reduced the migration and invasion of RA FLSs. Increased NAT10 level in the synovium was positively correlated with synovial infiltration of multiple types of immune cells. NAT10 inhibition in vivo attenuated the severity of arthritis in mice with CIA and DTHA, and rats with CIA. Mechanistically, we explored that NAT10 regulated RA FLS functions by promoting stability and translation efficiency of N4-acetylated PTX3 mRNA. PTX3 also regulated RA FLS aggression and is associated with synovial immune cell infiltration.

CONCLUSION

Our findings uncover the important roles of NAT10-mediated ac4C modification in promoting rheumatoid synovial aggression and inflammation, indicating that NAT10 may be a potential target for the treatment of RA, even other dysregulated FLSs-associated disorders.

Exploring the molecular mechanisms and shared potential drugs between rheumatoid arthritis and arthrofibrosis based on large language model and synovial microenvironment analysis

Rheumatoid arthritis (RA) and arthrofibrosis (AF) are both chronic synovial hyperplasia diseases that result in joint stiffness and contractures. They shared similar symptoms and many common features in pathogenesis. Our study aims to perform a comprehensive analysis between RA and AF and identify novel drugs for clinical use. Based on the text mining approaches, we performed a correlation analysis of 12 common joint diseases including arthrofibrosis, gouty arthritis, infectious arthritis, juvenile idiopathic arthritis, osteoarthritis, post infectious arthropathies, post traumatic osteoarthritis, psoriatic arthritis, reactive arthritis, rheumatoid arthritis, septic arthritis, and transient arthritis. 5 bulk sequencing datasets and 4 single-cell sequencing datasets of RA and AF were integrated and analyzed. A novel drug repositioning method was found for drug screening, and text mining approaches were used to verify the identified drugs. RA and AF performed the highest gene similarity (0.77) and functional ontology similarity (0.84) among all 12 joint diseases. We figured out that they share the same key pathogenic cell including CD34 + sublining fibroblasts (CD34-SLF) and DKK3 + sublining fibroblasts (DKK3-SLF). Potential therapeutic target database (PTTD) was established with the differential expressed genes (DEGs) of these key pathogenic cells. Based on the PTTD, 15 potential drugs for AF and 16 potential drugs for RA were identified. This work provides a new perspective on AF and RA study which enhances our understanding of their pathogenesis. It also shed light on their underlying mechanism and open new avenues for drug repositioning studies.

Inflammation dynamically regulates steroid hormone metabolism and action within macrophages in rheumatoid arthritis

RATIONALE

In inflammatory diseases such as rheumatoid arthritis (RA), steroid metabolism is a central component mediating the actions of immuno-modulatory glucocorticoids and sex steroids. However, the regulation and function of cellular steroid metabolism within key leukocyte populations such as macrophages remain poorly defined. In this study, the inflammatory regulation of global steroid metabolism was assessed in RA macrophages.

METHODS

Bulk RNA-seq data from RA synovial macrophages was used to assess transcripts encoding key enzymes in steroid metabolism and signalling. Changes in metabolism were assessed in synovial fluids, correlated to measures of disease activity and functionally validated in primary macrophage cultures.

RESULTS

RNA-seq revealed a unique pattern of differentially expressed genes, including changes in genes encoding the enzymes 11β-HSD1, SRD5A1, AKR1C2 and AKR1C3. These correlated with disease activity, favouring increased glucocorticoid and androgen levels. Synovial fluid 11β-HSD1 activity correlated with local inflammatory mediators (TNFα, IL-6, IL-17), whilst 11β-HSD1, SRD5A1 and AKR1C3 activity correlated with systemic measures of disease and patient pain (ESR, DAS28 ESR, global disease activity). Changes in enzyme activity were evident in inflammatory activated macrophages in vitro and revealed a novel androgen activating role for 11β-HSD1. Together, increased glucocorticoids and androgens were able to suppress inflammation in macrophages and fibroblast-like-synoviocytes.

CONCLUSIONS

This study underscores the significant increase in androgen and glucocorticoid activation within inflammatory polarized macrophages of the synovium, contributing to local suppression of inflammation. The diminished profile of inactive steroid precursors in postmenopausal women may contribute to disturbances in this process, leading to increased disease incidence and severity.

Fibrotic pathways and fibroblast-like synoviocyte phenotypes in osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis, characterized by osteophyte formation, cartilage degradation, and structural and cellular alterations of the synovial membrane. Activated fibroblast-like synoviocytes (FLS) of the synovial membrane have been identified as key drivers, secreting humoral mediators that maintain inflammatory processes, proteases that cause cartilage and bone destruction, and factors that drive fibrotic processes. In normal tissue repair, fibrotic processes are terminated after the damage has been repaired. In fibrosis, tissue remodeling and wound healing are exaggerated and prolonged. Various stressors, including aging, joint instability, and inflammation, lead to structural damage of the joint and micro lesions within the synovial tissue. One result is the reduced production of synovial fluid (lubricants), which reduces the lubricity of the cartilage areas, leading to cartilage damage. In the synovial tissue, a wound-healing cascade is initiated by activating macrophages, Th2 cells, and FLS. The latter can be divided into two major populations. The destructive thymocyte differentiation antigen (THY)1─ phenotype is restricted to the synovial lining layer. In contrast, the THY1+ phenotype of the sublining layer is classified as an invasive one with immune effector function driving synovitis. The exact mechanisms involved in the transition of fibroblasts into a myofibroblast-like phenotype that drives fibrosis remain unclear. The review provides an overview of the phenotypes and spatial distribution of FLS in the synovial membrane of OA, describes the mechanisms of fibroblast into myofibroblast activation, and the metabolic alterations of myofibroblast-like cells.

Microneedle-assisted dual delivery of PUMA gene and celastrol for synergistic therapy of rheumatoid arthritis through restoring synovial homeostasis

Abnormal proliferation of aggressive fibroblast-like synoviocytes (FLS) and perpetuate synovial inflammation can inevitably accelerate the progression of rheumatoid arthritis (RA). Herein, a strategy of simultaneously promoting FLS apoptosis and inhibiting inflammation as mediated by macrophages is proposed to restore synovial homeostasis for effective RA therapy. A hyaluronic acid-based dissolvable microneedle (MN) is fabricated for transdermal delivery of dual human serum albumin (HSA)-contained biomimetic nanocomplexes to regulate RA FLS and macrophages. Upon skin insertion, dual nanocomplexes are released rapidly from the MN and accumulate in RA joint microenvironment through both passive and active targeting as mediated by HSA. Thioketal-crosslinked fluorinated polyethyleneimine 1.8 K (TKPF) was constructed to bind the plasmid encoding pro-apoptotic gene PUMA with HSA coating layer (TKPF/pPUMA@HSA, TPH). TPH nanocomplexes can upregulate PUMA through RA FLS transfection to trigger efficient apoptosis. Also, HSA nanocomplexes encapsulating the classic anti-inflammatory natural product celastrol (Cel@HSA, CH) can inhibit inflammation of macrophages through blocking NF-κB pathway activation. TPH/CH MN can deplete RA FLS and inhibit M1 macrophage activation, suppress synovial hyperplasia as well as reduce bone and cartilage erosion in a collagen-induced arthritis (CIA) mouse model, demonstrating a promising strategy for efficient RA treatment.

FGF23 facilitates IL-1β synthesis in rheumatoid arthritis through activating PI3K, Akt, and NF-κB pathways

Rheumatoid arthritis (RA) is a well-known autoimmune disorder related with joint pain, joint swelling, cartilage and bone degradation as well as deformity. Fibroblast growth factor 23 (FGF23) is an endocrine factor of the FGF family primarily produced by osteocytes and osteoblasts, involves an essential effect in pathogenesis of RA. IL-1β is a vital proinflammatory factor in the development of RA. However, the role of FGF23 on IL-1β synthesis in RA has not been fully explored. Our analysis of database revealed higher levels of FGF23 and IL-1β in RA samples compared with healthy controls. High-throughput screening demonstrated that IL-1β is a potential candidate factor after FGF23 treatment in RA synovial fibroblasts (RASFs). FGF23 concentration dependently promotes IL-1β synthesis in RASFs. FGF23 enhances IL-1β expression by activating the PI3K, Akt, and NF-κB pathways. Our findings support the notion that FGF23 is a promising target in the remedy of RA.

Tissue fibroblasts are versatile immune regulators: An evaluation of their impact on the aging process

Fibroblasts are abundant stromal cells which not only control the integrity of extracellular matrix (ECM) but also act as immune regulators. It is known that the structural cells within tissues can establish an organ-specific immunity expressing many immune-related genes and closely interact with immune cells. In fact, fibroblasts can modify their immune properties to display both pro-inflammatory and immunosuppressive activities in a context-dependent manner. After acute insults, fibroblasts promote tissue inflammation although they concurrently recruit immunosuppressive cells to enhance the resolution of inflammation. In chronic pathological states, tissue fibroblasts, especially senescent fibroblasts, can display many pro-inflammatory and immunosuppressive properties and stimulate the activities of different immunosuppressive cells. In return, immunosuppressive cells, such as M2 macrophages and myeloid-derived suppressor cells (MDSC), evoke an excessive conversion of fibroblasts into myofibroblasts, thus aggravating the severity of tissue fibrosis. Single-cell transcriptome studies on fibroblasts isolated from aged tissues have confirmed that tissue fibroblasts express many genes coding for cytokines, chemokines, and complement factors, whereas they lose some fibrogenic properties. The versatile immune properties of fibroblasts and their close cooperation with immune cells indicate that tissue fibroblasts have a crucial role in the aging process and age-related diseases.

Engineered Self-Regulating Macrophages for Targeted Anti-inflammatory Drug Delivery

Background

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by increased levels of inflammation that primarily manifests in the joints. Macrophages act as key drivers for the progression of RA, contributing to the perpetuation of chronic inflammation and dysregulation of pro-inflammatory cytokines such as interleukin 1 (IL-1). The goal of this study was to develop a macrophage-based cell therapy for biologic drug delivery in an autoregulated manner.

Methods

For proof-of-concept, we developed "smart" macrophages to mitigate the effects of IL-1 by delivering its inhibitor, IL-1 receptor antagonist (IL-1Ra). Bone marrow-derived macrophages were lentivirally transduced with a synthetic gene circuit that uses an NF-κB inducible promoter upstream of either the Il1rn or firefly luciferase transgenes. Two types of joint like cells were utilized to examine therapeutic protection in vitro, miPSCs derived cartilage and isolated primary mouse synovial fibroblasts while the K/BxN mouse model of RA was utilized to examine in vivo therapeutic protection.

Results

These engineered macrophages were able to repeatably produce therapeutic levels of IL-1Ra that could successfully mitigate inflammatory activation in co-culture with both tissue engineered cartilage constructs and synovial fibroblasts. Following injection in vivo, macrophages homed to sites of inflammation and mitigated disease severity in the K/BxN mouse model of RA.

Conclusion

These findings demonstrate the successful development of engineered macrophages that possess the ability for controlled, autoregulated production of IL-1 based on inflammatory signaling such as the NF-κB pathway to mitigate the effects of this cytokine for applications in RA or other inflammatory diseases. This system provides proof of concept for applications in other immune cell types as self-regulating delivery systems for therapeutic applications in a range of diseases.

Ficolin-A induces macrophage polarization to a novel pro-inflammatory phenotype distinct from classical M1

BACKGROUND

Macrophages are key inflammatory immune cells that orchestrate the initiation and progression of autoimmune diseases. The characters of macrophage in diseases are determined by its phenotype in response to the local microenvironment. Ficolins have been confirmed as crucial contributors to autoimmune diseases, with Ficolin-2 being particularly elevated in patients with autoimmune diseases. However, whether Ficolin-A stimulates macrophage polarization is still poorly understood.

METHODS

We investigated the transcriptomic expression profile of murine bone marrow-derived macrophages (BMDMs) stimulated with Ficolin-A using RNA-sequencing. To further confirm a distinct phenotype activated by Ficolin-A, quantitative RT-PCR and Luminex assay were performed in this study. Additionally, we assessed the activation of underlying cell signaling pathways triggered by Ficolin-A. Finally, the impact of Ficolin-A on macrophages were investigated in vivo through building Collagen-induced arthritis (CIA) and Dextran Sulfate Sodium Salt (DSS)-induced colitis mouse models with Fcna-/- mice.

RESULTS

Ficolin-A activated macrophages into a pro-inflammatory phenotype distinct to LPS-, IFN-γ- and IFN-γ + LPS-induced phenotypes. The transcriptomic profile induced by Ficolin-A was primarily characterized by upregulation of interleukins, chemokines, iNOS, and Arginase 1, along with downregulation of CD86 and CD206, setting it apart from the M1 and M2 phenotypes. The activation effect of Ficolin-A on macrophages deteriorated the symptoms of CIA and DSS mouse models, and the deletion of Fcna significantly alleviated the severity of diseases in mice.

CONCLUSION

Our work used transcriptomic analysis by RNA-Seq to investigate the impact of Ficolin-A on macrophage polarization. Our findings demonstrate that Ficolin-A induces a novel pro-inflammatory phenotype distinct to the phenotypes activated by LPS, IFN-γ and IFN-γ + LPS on macrophages.

Sodium chloride promotes macrophage pyroptosis and aggravates rheumatoid arthritis by activating SGK1 through GABA receptors Slc6a12

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by synovial inflammation and the production of autoantibodies. Previous studies have indicated an association between high-salt diets (HSD) and an increased risk of RA, yet the underlying mechanisms remain unclear. Macrophage pyroptosis, a pro-inflammatory form of cell death, plays a pivotal role in RA. In this study, we demonstrate that HSD exacerbates the severity of arthritis in collagen-induced arthritis (CIA) mice, correlating with macrophage infiltration and inflammatory lesions. Given the significant alterations observed in macrophages from CIA mice subjected to HSD, we specifically investigate the impact of HSD on macrophage responses in the inflammatory milieu of RA. In our in vitro experiments, pretreatment with NaCl enhances LPS-induced pyroptosis in RAW.264.7 and THP-1 cells through the p38 MAPK/NF-κB signaling pathway. Subsequent experiments reveal that Slc6a12 inhibitors and SGK1 silencing inhibit sodium-induced activation of macrophage pyroptosis and the p38 MAPK/NF-κB signaling pathway, whereas overexpression of the SGK1 gene counteracts the effect of sodium on macrophages. In conclusion, our findings verified that high salt intake promotes the progression of RA and provided a detailed elucidation of the activation of macrophage pyroptosis induced by sodium transportation through the Slc6a12 channel.

Identification of PPARG as key gene to link coronary atherosclerosis disease and rheumatoid arthritis via microarray data analysis

BACKGROUND

Inflammation is the common pathogenesis of coronary atherosclerosis disease (CAD) and rheumatoid arthritis (RA). Although it is established that RA increases the risk of CAD, the underlining mechanism remained indefinite. This study seeks to explore the molecular mechanisms of RA linked CAD and identify potential target gene for early prediction of CAD in RA patients.

MATERIALS AND METHODS

The study utilized five raw datasets: GSE55235, GSE55457, GSE12021 for RA patients, and GSE42148 and GSE20680 for CAD patients. Gene Set Enrichment Analysis (GSEA) was used to investigate common signaling pathways associated with RA and CAD. Then, weighted gene co-expression network analysis (WGCNA) was performed on RA and CAD training datasets to identify gene modules related to single-sample GSEA (ssGSEA) scores. Overlapping module genes and differentially expressed genes (DEGs) were considered as co-susceptible genes for both diseases. Three hub genes were screened using a protein-protein interaction (PPI) network analysis via Cytoscape plug-ins. The signaling pathways, immune infiltration, and transcription factors associated with these hub genes were analyzed to explore the underlying mechanism connecting both diseases. Immunohistochemistry and qRT-PCR were conducted to validate the expression of the key candidate gene, PPARG, in macrophages of synovial tissue and arterial walls from RA and CAD patients.

RESULTS

The study found that Fc-gamma receptor-mediated endocytosis is a common signaling pathway for both RA and CAD. A total of 25 genes were screened by WGCNA and DEGs, which are involved in inflammation-related ligand-receptor interactions, cytoskeleton, and endocytosis signaling pathways. The principal component analysis(PCA) and support vector machine (SVM) and receiver-operator characteristic (ROC) analysis demonstrate that 25 DEGs can effectively distinguish RA and CAD groups from normal groups. Three hub genes TUBB2A, FKBP5, and PPARG were further identified by the Cytoscape software. Both FKBP5 and PPARG were downregulated in synovial tissue of RA and upregulated in the peripheral blood of CAD patients and differential mRNAexpreesion between normal and disease groups in both diseases were validated by qRT-PCR.Association of PPARG with monocyte was demonstrated across both training and validation datasets in CAD. PPARG expression is observed in control synovial epithelial cells and foamy macrophages of arterial walls, but was decreased in synovial epithelium of RA patients. Its expression in foamy macrophages of atherosclerotic vascular walls exhibits a positive correlation (r = 0.6276, p = 0.0002) with CD68.

CONCLUSION

Our findings suggest that PPARG may serve as a potentially predictive marker for CAD in RA patients, which provides new insights into the molecular mechanism underling RA linked CAD.

Synovial Tissue Insights into Heterogeneity of Rheumatoid Arthritis

PURPOSE OF REVIEW

Rheumatoid arthritis is one of the most common rheumatic and autoimmune diseases. While it can affect many different organ systems, RA primarily involves inflammation in the synovium, the tissue that lines joints. Patients with RA exhibit significant clinical heterogeneity in terms of presence or absence of autoantibodies, degree of permanent deformities, and most importantly, treatment response. These clinical characteristics point to heterogeneity in the cellular and molecular pathogenesis of RA, an area that several recent studies have begun to address.

RECENT FINDINGS

Single-cell RNA-sequencing initiatives and deeper focused studies have revealed several RA-associated cell populations in synovial tissues, including peripheral helper T cells, autoimmunity-associated B cells (ABCs), and NOTCH3+ sublining fibroblasts. Recent large transcriptional studies and translational clinical trials present frameworks to capture cellular and molecular heterogeneity in RA synovium. Technological developments, such as spatial transcriptomics and machine learning, promise to further elucidate the different types of RA synovitis and the biological mechanisms that characterize them, key elements of precision medicine to optimize patient care and outcomes in RA. This review recaps the findings of those recent studies and puts our current knowledge and future challenges into scientific and clinical perspective.

Zerumbone reduces TLR2 stimulation-induced M1 macrophage polarization pattern via upregulation of Nrf-2 expression in murine macrophages

Hyperuricemia contributes significantly to gout arthritis pathogenesis, which promotes urate crystal deposition in the joints and activates joint-resident macrophages and circulating monocytes to initiate a state of inflammatory arthritis. In the joint, macrophages have an immune defense role where the presence of urate crystals results in the inflammatory mediators secretion, inflammatory cells recruitment to the joint, and shift macrophage population toward M1 pro-inflammatory phenotypes. Current treatment modalities of gout arthritis have side effects that limit their use in the elderly. A novel treatment that targets macrophage polarization to re-establish homeostasis may initiate a drug discovery program of novel disease-modifying agents for gout. Zerumbone (Zer) is a sesquiterpenoid bioactive compound found in the rhizome of Zingiberaceae family and possesses anti-inflammatory, antioxidant, and anti-proliferative activity. Our study hypothesized that soluble uric acid (sUA) and Pam3CSK4 (TLR2 agonist) reduce the anti-inflammatory function of murine M2 bone marrow-derived macrophages and change the expression of M2 genetic markers toward M1 phenotypes. We observed that priming of M2 macrophages with sUA and Pam3CSK4 significantly decreased M2 specific markers expression, e.g., Arg-1, Ym-1, and Fizz-1, enhanced mRNA expression of IL-1β, TNF-α, CXCL2, and iNOS and increased oxidative stress in M2 macrophages, as exhibited by a reduction in Nrf2 expression. We also aimed to study the impact of Zer on reducing the pro-inflammatory effect of sUA in TLR2-stimulated M2 macrophages. We noticed that Zer treatment significantly reduced L-1β and TNF-α production following Pam3CSK4 + sUA treatment on M2 macrophages. Furthermore, Zer reduced the caspase-1 activity without altering cytosolic NLRP3 content in challenged M2 BMDMs. We also observed that Zer significantly enhanced M2-associated marker's expression, e.g., Arg-1, Ym-1, and Fizz-1, and augmented Nrf-2 and other antioxidant proteins, including HMOX1 and srxn1expression following Pam3CSK4 + sUA treatment. We draw the conclusion that Zer is a potentially effective anti-inflammatory treatment for gout arthritis linked to hyperuricemia.

CXCL13 promotes TNF-α synthesis in rheumatoid arthritis through activating ERK/p38 pathway and inhibiting miR-330-3p generation

Rheumatoid arthritis (RA) is a well-known autoimmune disorder associated with joint pain, joint swelling, cartilage and bone degradation as well as deformity. The chemokine (C-X-C motif) ligand 13 (CXCL13) plays a crucial role in multiple cellular pathogenesis processes, including RA. TNF-α is a vital proinflammatory factor in the progression of RA. However, the role of CXCL13 in TNF-α production in RA has not been fully explored. Our analysis of both database and clinical samples revealed higher levels of CXCL13 and TNF-α in RA samples compared to healthy controls. CXCL13 concentration-dependently induces TNF-α synthesis in RA synovial fibroblasts. CXCL13 enhances TNF-α expression by interacting with the CXCR5 receptor, activating the ERK/p38 pathways, and inhibiting miR-330-3p generation. Importantly, treatment with CXCL13 shRNA counteracted the upregulation of TNF-α production induced by collagen-induced arthritis. Our findings support the notion that CXCL13 is a promising target in the treatment of RA.

Inflammation in Development and Aging: Insights from the Zebrafish Model

Zebrafish are an emergent animal model to study human diseases due to their significant genetic similarity to humans, swift development, and genetic manipulability. Their utility extends to the exploration of the involvement of inflammation in host defense, immune responses, and tissue regeneration. Additionally, the zebrafish model system facilitates prompt screening of chemical compounds that affect inflammation. This study explored the diverse roles of inflammatory pathways in zebrafish development and aging. Serving as a crucial model, zebrafish provides insights into the intricate interplay of inflammation in both developmental and aging contexts. The evidence presented suggests that the same inflammatory signaling pathways often play instructive or beneficial roles during embryogenesis and are associated with malignancies in adults.

Development and preclinical assessment of nanoemulgel loaded with phytoconstituents for the management of rheumatoid arthritis

In recent years, natural ingredients have gained importance for therapeutic treatment due to their minimal toxicity. However, the delivery of these phytoconstituents poses a challenge to provide better efficacy. Current research reports the development of nanoemulgel (NEG) loaded with ginger oleoresin (GOR) and lipid guggul extract (LGE) for the management of rheumatoid arthritis (RA). The nanoemulsion (NE) was developed using the spontaneous emulsification technique by the pseudo-ternary method. The optimized nanoemulsion exhibited globule size of 16.08 ± 2.55 nm, PDI of 0.187 ± 0.06, and zeta potential of - 22.4 ± 0.31 mV. The cumulative release from in vitro diffusion studies at pH 7.4 was about 99.72 ± 3.47%, 57.98 ± 2.11%, and 86.42 ± 5.13% of 6-gingerol, E-guggulsterone, and Z-guggulsterone respectively at the end of 24 h. The ex vivo studies on porcine ear skin showed sustained release with 92.8 ± 3.21% for 6-gingerol, 55.61 ± 0.91% for E-guggulsterone, and 84.2 ± 4.22% for Z-guggulsterone released at the end of 24 h. The cell culture studies on RAW 264.7 cells indicated a robust inhibition of LPS-induced IL-6 and TNF-α production indicating its efficacy in the management of RA. The preclinical studies on male Wistar rats suggest that the developed NEG exhibited a comparable decrease in paw edema inflammation as compared to the marketed diclofenac sodium gel. These encouraging results demonstrate the potential of the developed nanoemulgel containing combination of GOR and LGE for the management of RA.

Targeting YAP1-regulated Glycolysis in Fibroblast-Like Synoviocytes Impairs Macrophage Infiltration to Ameliorate Diabetic Osteoarthritis Progression

The interplay between immune cells/macrophages and fibroblast-like synoviocytes (FLSs) plays a pivotal role in initiating synovitis; however, their involvement in metabolic disorders, including diabetic osteoarthritis (DOA), is largely unknown. In this study, single-cell RNA sequencing (scRNA-seq) is employed to investigate the synovial cell composition of DOA. A significant enrichment of activated macrophages within eight distinct synovial cell clusters is found in DOA synovium. Moreover, it is demonstrated that increased glycolysis in FLSs is a key driver for DOA patients' synovial macrophage infiltration and polarization. In addition, the yes-associated protein 1 (YAP1)/thioredoxin-interacting protein (TXNIP) signaling axis is demonstrated to play a crucial role in regulating glucose transporter 1 (GLUT1)-dependent glycolysis in FLSs, thereby controlling the expression of a series of adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) which may subsequently fine-tune the infiltration of M1-polarized synovial macrophages in DOA patients and db/db diabetic OA mice. For treatment, M1 macrophage membrane-camouflaged Verteporfin (Vt)-loaded PLGA nanoparticles (MVPs) are developed to ameliorate DOA progression by regulating the YAP1/TXNIP signaling axis, thus suppressing the synovial glycolysis and the infiltration of M1-polarized macrophages. The results provide several novel insights into the pathogenesis of DOA and offer a promising treatment approach for DOA.

Exploring the mechanism of Celastrol in the treatment of rheumatoid arthritis based on systems pharmacology and multi-omics

To explore the molecular network mechanism of Celastrol in the treatment of rheumatoid arthritis (RA) based on a novel strategy (integrated systems pharmacology, proteomics, transcriptomics and single-cell transcriptomics). Firstly, the potential targets of Celastrol and RA genes were predicted through the database, and the Celastrol-RA targets were obtained by taking the intersection. Then, transcriptomic data and proteomic data of Celastrol treatment of RA were collected. Subsequently, Celastrol-RA targets, differentially expressed genes, and differentially expressed proteins were imported into Metascape for enrichment analysis, and related networks were constructed. Finally, the core targets of Celastrol-RA targets, differentially expressed genes, and differentially expressed proteins were mapped to synoviocytes of RA mice to find potential cell populations for Celastrol therapy. A total of 195 Celastrol-RA targets, 2068 differential genes, 294 differential proteins were obtained. The results of enrichment analysis showed that these targets, genes and proteins were mainly related to extracellular matrix organization, TGF-β signaling pathway, etc. The results of single cell sequencing showed that the main clusters of these targets, genes, and proteins could be mapped to RA synovial cells. For example, Mmp9 was mainly distributed in Hematopoietic cells, especially in Ptprn+fibroblast. The results of molecular docking also suggested that Celastrol could stably combine with molecules predicted by network pharmacology. In conclusion, this study used systems pharmacology, transcriptomics, proteomics, single-cell transcriptomics to reveal that Celastrol may regulate the PI3K/AKT signaling pathway by regulating key targets such as TNF and IL6, and then play an immune regulatory role.

Current situation and trend of non-coding RNA in rheumatoid arthritis: a review and bibliometric analysis

Background

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease that affects multiple joints and has adverse effects on various organs throughout the body, often leading to a poor prognosis. Recent studies have shown significant progress in the research of non-coding RNAs (ncRNAs) in RA. Therefore, this study aims to comprehensively assess the current status and research trends of ncRNAs in RA through a bibliometric analysis.

Methods

This study retrieved articles relevant to ncRNAs and RA from the Science Citation Index Expanded Database of the Web of Science Core Collection between January 1st, 2003, and July 31st, 2023. The relevant articles were screened based on the inclusion criteria. VOSviewer and CiteSpace are utilized for bibliometric and visual analysis.

Results

A total of 1697 publications were included in this study, and there was a noticeable increase in annual publications from January 1st, 2003, to July 31st, 2023. China, the United States, and the United Kingdom were the most productive countries in this field, contributing to 43.81%, 13.09%, and 3.87% of the publications. Anhui Medical University and Lu Qianjin were identified as the most influential institution and author. Frontiers In Immunology stood out as the most prolific journal, while Arthritis & Rheumatology was the most co-cited journal. Additionally, the research related to "circular RNA", "oxidative stress", "proliferation", and "migration" have emerged as new hotspots in the field.

Conclusion

In this study, we have summarized the publication characteristics related to ncRNA and RA and identified the most productive countries, institutions, authors, journals, hot topics, and trends.

Identification of sulfur metabolism-related gene signature in osteoarthritis and TM9SF2's sustenance effect on M2 macrophages' phagocytic activity

BACKGROUND

Osteoarthritis (OA) is a chronic and low-grade inflammatory disease associated with metabolism disorder and multiple cell death types in the synovial tissues. Sulfur metabolism has not been studied in OA.

METHODS

First, we calculated the single sample gene set enrichment analysis score of sulfur metabolism-associated annotations (i.e., cysteine metabolism process, regulation of sulfur metabolism process, and disulfidptosis) between healthy and synovial samples from patients with OA. Sulfur metabolism-related differentially expressed genes (DEGs) were analyzed in OA. Least absolute shrinkage and selection operator COX regression were used to identify the sulfur metabolism-associated gene signature for diagnosing OA. Correlation and immune cell deconvolution analyses were used to explore the correlated functions and cell specificity of the signature gene, TM9SF2. TM9SF2's effect on the phagocytosis of macrophages M2 was analyzed by coculturing macrophages with IgG-coated beads or apoptotic Jurkat cells.

RESULTS

A diagnostic six gene signature (i.e., MTHFD1, PDK4, TM9SF2, POU4F1, HOXA2, NCKAP1) was identified based on the ten DEGs, validated using GSE12021 and GSE1919 datasets. TM9SF2 was upregulated in the synovial tissues of OA at both mRNA and protein levels. The relationship between TM9SF2 and several functional annotations, such as antigen processing and presentation, lysosome, phagosome, Fcγ-mediated phagocytosis, and tyrosine metabolism, was identified. TM9SF2 and macrophages M2 were significantly correlated. After silencing TM9SF2 in THP-1-derived macrophages M2, a significantly reduced phagocytosis and attenuated activation of PLC-γ1 were observed.

CONCLUSION

A sulfur metabolism-associated six-gene signature for OA diagnosis was constructed and upregulation of the phagocytosis-associated gene, TM9SF2, was identified. The findings are expected to deepen our understanding of the molecular mechanism underlying OA development and be used as potential therapeutic targets.

Genetically engineered macrophages derived from iPSCs for self-regulating delivery of anti-inflammatory biologic drugs

In rheumatoid arthritis, dysregulated cytokine signaling has been implicated as a primary factor in chronic inflammation. Many antirheumatic and biological therapies are used to suppress joint inflammation, but despite these advances, effectiveness is not universal, and delivery is often at high doses, which can predispose patients to significant off-target effects. During chronic inflammation, the inappropriate regulation of signaling factors by macrophages accelerates progression of disease by driving an imbalance of inflammatory cytokines, making macrophages an ideal cellular target. To develop a macrophage-based therapy to treat chronic inflammation, we engineered a novel induced pluripotent stem cell (iPSC)-derived macrophage capable of delivering soluble TNF receptor 1 (TNFR1), an anti-inflammatory biologic inhibitor of tumor necrosis factor alpha (TNF-α), in an auto-regulated manner in response to TNF-α. Murine iPSCs were differentiated into macrophages (iMACs) over a 17-day optimized protocol with continued successful differentiation confirmed at key timepoints. Varying inflammatory and immunomodulatory stimuli demonstrated traditional macrophage function and phenotypes. In response to TNF-α, therapeutic iMACs produced high levels of sTNFR1 in an autoregulated manner, which inhibited inflammatory signaling. This self-regulating iMAC system demonstrated the potential for macrophage-based drug delivery as a novel therapeutic approach for a variety of chronic inflammatory diseases.

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.

Crosstalk between synovial macrophages and fibroblasts in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease associated with chronic inflammation of joints. Abnormally activated cells such as synovial macrophages and synovial fibroblasts induce RA pathogenesis and ultimately joint destruction. Since macrophages can change their own characteristics depending on the microenvironmental condition, it has been suggested that activation and remission of RA are regulated by crosstalk between synovial macrophages and other cells. Moreover, recent findings of heterogeneity of synovial macrophages and fibroblasts support the idea that complex interactions regulate RA from its onset to remission. Importantly, an understanding of the intercellular crosstalk in RA is far from complete. Here, we summarize the molecular mechanisms underlying the pathological development of RA with particular reference to the crosstalk between synovial macrophages and fibroblasts.

Intra-articular bone marrow mononuclear cell therapy improves lameness from naturally occurring equine osteoarthritis

Osteoarthritis (OA) can be debilitating and is related to impaired resolution of synovial inflammation. Current treatments offer temporary relief of clinical signs, but have potentially deleterious side effects. Bone marrow mononuclear cells (BMNC) are a rich source of macrophage progenitors that have the ability to reduce OA symptoms in people and inflammation in experimentally-induced synovitis in horses. The objective of this study was to evaluate the ability of intra-articular BMNC therapy to improve clinical signs of naturally occurring equine OA. Horses presenting with clinical and radiographic evidence of moderate OA in a single joint were randomly assigned to 1 of 3 treatment groups: saline (negative control), triamcinolone (positive control), or BMNC (treatment group). Lameness was evaluated subjectively and objectively, joint circumference measured, and synovial fluid collected for cytology and growth factor/cytokine quantification at 0, 7, and 21 days post-injection. Data were analyzed using General Estimating Equations with significance set at p < 0.05. There were no adverse effects noted in any treatment group. There was a significant increase in synovial fluid total nucleated cell count in the BMNC-treated group on day 7 (median 440; range 20-1920 cells/uL) compared to day 0. Mononuclear cells were the predominant cell type across treatments at all time points. Joint circumference decreased significantly in the BMNC-treated group from days 7 to 21 and was significantly lower at day 21 in the BMNC-treated group compared to the saline-treated group. Median objective lameness improved significantly in the BMNC group between days 7 and 21. GM-CSF, IL-1ra, IGF-1, and TNF-α were below detectable limits and IL-6, IL-1β, FGF-2 were detectable in a limited number of synovial fluid samples. Inconsistent and limited differences were detected over time and between treatment groups for synovial fluid PGE2, SDF-1, MCP-1 and IL-10. Decreased lameness and joint circumference, coupled with a lack of adverse effects following BMNC treatment, support a larger clinical trial using BMNC therapy to treat OA in horses.

Nrf2 activation improves experimental rheumatoid arthritis

Rheumatoid arthritis is a systemic autoimmune disease with pain and functional disorder of joints. Multiple strategies toward treatment of the rheumatoid arthritis are operating, while there are concerns of serious adverse effects of the therapeutic drugs. Here, we show that activation of Nrf2 (Nuclear factor erythroid 2-related factor 2) efficiently improves arthritis of SKG mice, which develop T cell-mediated autoimmune arthritis by zymosan A injection. We found that genetic Nrf2 activation by knockdown of Keap1 (Kelch-like ECH-associated protein 1), a negative regulator of Nrf2, repressed arthritis by inhibiting the expression of pro-inflammatory cytokines and inducing the expression of antioxidant enzymes in SKG mice. In addition, oral administration of CDDO-Im, a representative chemical inducer of Nrf2, had effects of both prevention and treatment toward arthritis of SKG mice in an Nrf2-dependent manner. We also found that Nrf2 activation through myeloid-cell lineage-specific Keap1 disruption did not achieve significant improvement in the arthritis of SKG mice. In contrast, expressions of pro-inflammatory cytokine genes were decreased, and those of antioxidant enzyme genes were increased in fibroblast-like synoviocytes (FLS) isolated from SKG mouse. Our results thus demonstrate that Nrf2 activation exerts marked anti-arthritis effects in the SKG experimental rheumatoid arthritis model mice, supporting the contention that the Nrf2 activation is a new therapeutic strategy for the rheumatoid arthritis.