Macrophage heterogeneity in the context of rheumatoid arthritis

Role of CCL2/CCR2 axis in the immunopathogenesis of rheumatoid arthritis: Latest evidence and therapeutic approaches

Evidence suggests that uncontrolled immune system responses and their components play a significant role in developing rheumatoid arthritis (RA), which is considered an autoimmune disease (AD). Among immune system mediators, cytokines and chemokines are involved in numerous physiological and pathological processes. CCL2 or monocyte chemoattractant protein-1 (MCP-1) is known as a CC chemokine that can induce the locomotion and recruitment of monocytes and macrophages to the site of injury. When CCL2 binds to its receptors, the most important of which is CCR2, various signaling pathways are triggered, eventually leading to various immunological events such as inflammation. This chemokine also participates in several events involved in RA pathogenesis, such as osteoclastogenesis, migration of effector T cells to the RA synovium tissue, and angiogenesis. In this review article, the role of the CCL2/CCR2 axis in RA pathogenesis and the immunotherapy opportunities based on CCL2/CCR2 axis targeting has been discussed based on existing investigations.

The immunology of rheumatoid arthritis

The immunopathogenesis of rheumatoid arthritis (RA) spans decades, beginning with the production of autoantibodies against post-translationally modified proteins (checkpoint 1). After years of asymptomatic autoimmunity and progressive immune system remodeling, tissue tolerance erodes and joint inflammation ensues as tissue-invasive effector T cells emerge and protective joint-resident macrophages fail (checkpoint 2). The transition of synovial stromal cells into autoaggressive effector cells converts synovitis from acute to chronic destructive (checkpoint 3). The loss of T cell tolerance derives from defective DNA repair, causing abnormal cell cycle dynamics, telomere fragility and instability of mitochondrial DNA. Mitochondrial and lysosomal anomalies culminate in the generation of short-lived tissue-invasive effector T cells. This differentiation defect builds on a metabolic platform that shunts glucose away from energy generation toward the cell building and motility programs. The next frontier in RA is the development of curative interventions, for example, reprogramming T cell defects during the period of asymptomatic autoimmunity.

Hydrogen Sulfide: a Novel Immunoinflammatory Regulator in Rheumatoid Arthritis

Hydrogen sulfide (H₂S), an endogenous, gaseous, signaling transmitter, has been shown to have vasodilative, anti-oxidative, anti-inflammatory, and cytoprotective activities. Increasing evidence also indicates that H₂S can suppress the production of inflammatory mediators by immune cells, for example, T cells and macrophages. Inflammation is closely related to an immune response in several diseases such as rheumatoid arthritis (RA), multiple sclerosis (MS), systemic lupus erythematosus (SLE), and cancer. Considering these biological effects of H₂S, a potential role in the treatment of immune-related RA is being exploited. In the present review, we will provide an overview of the therapeutic potential of H₂S in RA treatment.

Targeted silver nanoparticles for rheumatoid arthritis therapy via macrophage apoptosis and Re-polarization

Infiltration of inflammatory cells, especially the M1 macrophages that secrete various types of inflammation cytokines, play crucial roles in the pathogenesis of rheumatoid arthritis (RA). To relief synovial inflammation, M1 macrophages must be eliminated or switched to anti-inflammatory M2 phenotype. We herein developed folic acid modified silver nanoparticles (FA-AgNPs) that can actively deliver into M1 macrophages to synergistically induce M1 macrophages reduction and M2 macrophages polarization for effective RA treatment. The AgNPs was facilely prepared, PEGylated and modified with FA to realize M1 macrophages targeting delivery via folate receptor overexpressed on M1 macrophages surface. After entering cells, FA-AgNPs dissolved and released Ag+ in response to intracellular glutathione (GSH), which is the key element to exert a series of anti-inflammatory functions, such as M1 macrophages apoptosis and reactive oxygen species (ROS) scavenging to facilitate M2 macrophages polarization, both of which contributed to RA treatment. This nano-system could passively accumulate into inflamed joints, permit potent anti-inflammatory activity, and impose strong therapeutic efficacy in mice RA models with high biosafety. After treatment, FA-AgNPs could be gradually cleared from the body mainly via feces without tissue accumulation, and did not show any appreciable long-term toxicity. This work declares the first example of using bio-active nanoparticles for RA treatment without loading any drugs, and highlights the potential of FA-AgNPs for targeted RA therapy via simultaneous M1 macrophage apoptosis and M1-to-M2 macrophages re-polarization.

A Novel Hypothesis: A Role for Follicle Stimulating Hormone in Abdominal Aortic Aneurysm Development in Postmenopausal Women

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal aorta, which can potentially be fatal due to exsanguination following rupture. Although AAA is less prevalent in women, women with AAA have a more severe AAA progression compared to men as reflected by enhanced aneurysm growth rates and a higher rupture risk. Women are diagnosed with AAA at an older age than men, and in line with increased osteoporosis and cardiovascular events, the delayed AAA onset has been attributed to the reduction of the protective effect of oestrogens during the menopausal transition. However, new insights have shown that a high follicle stimulating hormone (FSH) level during menopause may also play a key role in those diseases. In this report we hypothesize that FSH may aggravate AAA development and progression in postmenopausal women via a direct and/or indirect role, promoting aorta pathology. Since FSH receptors (FSHR) are reported on many other cell types than granulosa cells in the ovaries, it is feasible that FSH stimulation of FSHR-bearing cells such as aortic endothelial cells or inflammatory cells, could promote AAA formation directly. Indirectly, AAA progression may be influenced by an FSH-mediated increase in osteoporosis, which is associated with aortic calcification. Also, an FSH-mediated decrease in cholesterol uptake by the liver and an increase in cholesterol biosynthesis will increase the cholesterol level in the circulation, and subsequently promote aortic atherosclerosis and inflammation. Lastly, FSH-induced adipogenesis may lead to obesity-mediated dysfunction of the microvasculature of the aorta and/or modulation of the periaortic adipose tissue. Thus the long term increased plasma FSH levels during the menopausal transition may contribute to enhanced AAA disease in menopausal women and could be a potential novel target for treatment to lower AAA-related events in women.

Influence of β-D-mannuronic Acid, as a New Member of Non-steroidal Anti- Inflammatory Drugs Family, on the Expression Pattern of Chemokines and their Receptors in Rheumatoid Arthritis

BACKGROUND

Based on the encouraging results of phase III clinical trial of β-Dmannuronic acid (M2000) (as a new anti-inflammatory drug) in patients with RA, in this study, we aimed to evaluate the effects of this drug on the expression of chemokines and their receptors in PBMCs of RA patients.

METHODS

PBMCs of RA patients and healthy controls were separated and the patients' cells were treated with low, moderate and high doses (5, 25 and 50 μg/mL) of M2000 and optimum dose (1 μg/mL) of diclofenac, as a control in RPMI-1640 medium. Real-time PCR was used for evaluating the mRNA expression of CXCR3, CXCR4, CCR2, CCR5 and CCL2/MCP-1. Cell surface expression of CCR2 was investigated using flow cytometry.

RESULTS

CCR5 mRNA expression reduced significantly, after treatment of the patients' cells with all three doses of M2000 and optimum dose of diclofenac. CXCR3 mRNA expression was downregulated significantly followed by the treatment of these cells with moderate and high doses of M2000 and optimum dose of diclofenac. CXCR4 mRNA expression declined significantly after the treatment of these cells with moderate and high doses of M2000. CCL2 mRNA expression significantly reduced only followed by the treatment of these cells with a high dose of M2000, whereas, mRNA and cell surface expressions of CCR2 diminished significantly followed by the treatment of these cells with a high dose of M2000 and optimum dose of diclofenac.

CONCLUSION

According to our results, M2000 through the down-regulation of chemokines and their receptors may restrict the infiltration of immune cells into the synovium.

Preclinical Evaluation of a Novel 99mTc-Labeled CB86 for Rheumatoid Arthritis Imaging

Early diagnosis and therapy are crucial to control disease progression optimally and achieve a good prognosis in rheumatoid arthritis (RA). Previous study showed that a technetium-99m (^99mTc)-labeled TSPO ligand (^99mTc-CB256 [2-(8-(2-(bis(pyridin-2-yl)methyl)amino)acetamido)-2-(4-chlorophenyl)H-imidazo[1,2-a]pyridin-3-yl)-N,N-dipropylacetamide] composed of a translocator protein (TSPO) ligand CB86 [[2-(4-chlorophenyl)-8-amino-imidazo[1,2-a]-pyridin-3-yl]-N,N-di-n-propylacetamide] and di-(2-picolyl)amine, a bifunctional chelate agent, was used to image a TSPO-rich cancer cell in vitro; however, few ^99mTc-CB256 in vivo evaluation has been reported so far probably due to the cytotoxicity of CB256 (ca. 75 times more than analogous CB86). Herein, we describe a novel TSPO targeting radiopharmaceutical consisting of CB86 and diethylenetriaminepentaacetic acid (DTPA), a conventional bifunctional chelating ligand in clinical trials used to prepare ^99mTc-labeled CB86, and its evaluation as a ^99mTc-single-photon emission computed tomography (SPECT) probe. The radiosynthesis and characterization of ^99mTc-DPTA-CB86 including hydrophilicity and stability tests were determined. Additionally, the binding affinity and specificity of ^99mTc-DTPA-CB86 to TSPO were evaluated using RAW264.7 macrophage cells. Biodistribution and ^99mTc-SPECT studies were conducted on rheumatoid arthritis (RA) rat models after the injection of ^99mTc-DTPA-CB86 with or without co-injection of unlabeled DTPA-CB86. The radiosynthesis of ^99mTc-DTPA-CB86 was completed successfully with the labeling yields and radiochemical purity of 95.86 ± 2.45 and 97.45 ± 0.69%, respectively. The probe displayed good stability in vitro and binding specificity to RAW264.7 macrophage cells. In the biodistribution studies, ^99mTc-DTPA-CB86 exhibited rapid inflammatory ankle accumulation. At 180 min after administration, ^99mTc-DTPA-CB86 uptakes of the left inflammatory ankle were 2.35 ± 0.10 percentage of the injected radioactivity per gram of tissue (% ID/g), significantly higher than those of the normal tissues. ^99mTc-SPECT imaging studies revealed that ^99mTc-DTPA-CB86 could clearly identify the left inflammatory ankle with good contrast at 30-180 min after injection. Therefore, ^99mTc-DTPA-CB86 may be a promising probe for arthritis ^99mTc-SPECT imaging.

Rational design of metal-organic frameworks to deliver methotrexate for targeted rheumatoid arthritis therapy

Methotrexate (MTX) has been used as an anchor drug for the treatment of rheumatoid arthritis (RA), while the patients with chronic MTX administration suffer from severe side-effects. To this end, targeted delivery of MTX by nanomedicine has attracted great interest. In this work, we aimed to employ metal-organic frameworks (MOFs) as nanocarrier to deliver MTX by virtue of its facile and green preparation and exceptionally high drug loading. While MTX could be easily and effectively loaded via different MOF construction strategies, such as direct coordination, physical encapsulation, and covalent conjugation, we found that most of the MTX loading MOFs showed premature and burst drug release, attributable to the unstable coordination between MTX and metals. To address this issue, we rationally designed the MOFs by conjugating MTX with tannic acid (TA) at 2:1 M ratio and then coordinating with ferric ion (Fe³⁺), followed by surface modification of hyaluronic acid (HA). The resulting MOFs achieved ultra-high drug loading (45%) and sustained drug release, and could selectively recognize the diseased cells for anti-inflammatory effect. The in vivo therapeutic evaluation suggested that the MOFs could enhance the anti-rheumatic activity of MTX while minimizing its toxic effects by targeted drug delivery, resulting in improved therapeutic index. This work provides a biocompatible nano-platform to deliver MTX for RA treatment, and importantly, calls for special attention to the gap between MOFs design and their biological applications, and the gap needs to be filled by careful evaluation of in vivo stability and burst drug release.

The Role of Chronic Inflammatory Bone and Joint Disorders in the Pathogenesis and Progression of Alzheimer's Disease

Late-onset Alzheimer's Disease (LOAD) is a devastating neurodegenerative disorder that causes significant cognitive debilitation in tens of millions of patients worldwide. Throughout disease progression, abnormal secretase activity results in the aberrant cleavage and subsequent aggregation of neurotoxic Aβ plaques in the cerebral extracellular space and hyperphosphorylation and destabilization of structural tau proteins surrounding neuronal microtubules. Both pathologies ultimately incite the propagation of a disease-associated subset of microglia-the principle immune cells of the brain-characterized by preferentially pro-inflammatory cytokine secretion and inhibited AD substrate uptake capacity, which further contribute to neuronal degeneration. For decades, chronic neuroinflammation has been identified as one of the cardinal pathophysiological driving features of AD; however, despite a number of works postulating the underlying mechanisms of inflammation-mediated neurodegeneration, its pathogenesis and relation to the inception of cognitive impairment remain obscure. Moreover, the limited clinical success of treatments targeting specific pathological features in the central nervous system (CNS) illustrates the need to investigate alternative, more holistic approaches for ameliorating AD outcomes. Accumulating evidence suggests significant interplay between peripheral immune activity and blood-brain barrier permeability, microglial activation and proliferation, and AD-related cognitive decline. In this work, we review a narrow but significant subset of chronic peripheral inflammatory conditions, describe how these pathologies are associated with the preponderance of neuroinflammation, and posit that we may exploit peripheral immune processes to design interventional, preventative therapies for LOAD. We then provide a comprehensive overview of notable treatment paradigms that have demonstrated considerable merit toward treating these disorders.

BAD inactivation exacerbates rheumatoid arthritis pathology by promoting survival of sublining macrophages

The resistance of synovial sublining macrophages to apoptosis has a crucial role in joint inflammation and destruction in rheumatoid arthritis (RA). However, the underlying mechanism is incompletely understood. Here we report that inactivation of the pro-apoptotic BCL-2 family protein BAD is essential for survival of synovial sublining macrophage in RA. Genetic disruption of Bad leads to more severe joint inflammation and cartilage and bone damage with reduced apoptosis of synovial sublining macrophages in collagen-induced arthritis (CIA) and TNFα transgenic (TNF-Tg) mouse models. Conversely, Bad3SA/3SA mice, in which BAD can no longer be inactivated by phosphorylation, are protected from collagen-induced arthritis. Mechanistically, phosphorylation-mediated inactivation of BAD specifically protects synovial sublining macrophages from apoptosis in highly inflammatory environment of arthritic joints in CIA and TNF-Tg mice, and in patients with RA, thereby contributing to RA pathology. Our findings put forward a model in which inactivation of BAD confers the apoptosis resistance on synovial sublining macrophages, thereby contributing to the development of arthritis, suggesting that BAD may be a potential therapeutic target for RA.

Senescent cells and macrophages: key players for regeneration?

Over the last decade, our understanding of the physiological role of senescent cells has drastically evolved, from merely indicators of cellular stress and ageing to having a central role in regeneration and repair. Increasingly, studies have identified senescent cells and the senescence-associated secretory phenotype (SASP) as being critical in the regenerative process following injury; however, the timing and context at which the senescence programme is activated can lead to distinct outcomes. For example, a transient induction of senescent cells followed by rapid clearance at the early stages following injury promotes repair, while the long-term accumulation of senescent cells impairs tissue function and can lead to organ failure. A key role of the SASP is the recruitment of immune cells to the site of injury and the subsequent elimination of senescent cells. Among these cell types are macrophages, which have well-documented regulatory roles in all stages of regeneration and repair. However, while the role of senescent cells and macrophages in this process is starting to be explored, the specific interactions between these cell types and how these are important in the different stages of injury/reparative response still require further investigation. In this review, we consider the current literature regarding the interaction of these cell types, how their cooperation is important for regeneration and repair, and what questions remain to be answered to advance the field.

Effects of Biological Therapies on Molecular Features of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune and chronic inflammatory disease primarily affecting the joints, and closely related to specific autoantibodies that mostly target modified self-epitopes. Relevant findings in the field of RA pathogenesis have been described. In particular, new insights come from studies on synovial fibroblasts and cells belonging to the innate and adaptive immune system, which documented the aberrant production of inflammatory mediators, oxidative stress and NETosis, along with relevant alterations of the genome and on the regulatory epigenetic mechanisms. In recent years, the advances in the understanding of RA pathogenesis by identifying key cells and cytokines allowed the development of new targeted disease-modifying antirheumatic drugs (DMARDs). These drugs considerably improved treatment outcomes for the majority of patients. Moreover, numerous studies demonstrated that the pharmacological therapy with biologic DMARDs (bDMARDs) promotes, in parallel to their clinical efficacy, significant improvement in all these altered molecular mechanisms. Thus, continuous updating of the knowledge of molecular processes associated with the pathogenesis of RA, and on the specific effects of bDMARDs in the correction of their dysregulation, are essential in the early and correct approach to the treatment of this complex autoimmune disorder. The present review details basic mechanisms related to the physiopathology of RA, along with the core mechanisms of response to bDMARDs.

The Application of Single-Cell RNA Sequencing in Studies of Autoimmune Diseases: a Comprehensive Review

Complex composition is one of the most important features of the immune system, involving many types of organs, tissues, cells, and molecules that perform immune functions. The normal function of each component of the immune system is the guarantee for maintaining the relatively stable immune function of the body. When the self-immune tolerance mechanism of the body is unregulated or destroyed, the immune system reacts to autoantigens, resulting in damage to self-tissues and organs or an immunopathological state with abnormal functions. Autoimmune diseases are diverse, and their pathogenesis is complicated. Various immune cells and their interactions play significant roles in the occurrence and development of diseases. The solution to heterogeneity of immune cells is the basic science and translational understanding of how genes and the environment interact to induce disease so that we can develop personalized medicine, a goal that has to this point eluded scientists. Single-cell RNA sequencing (scRNA-Seq) refers to a new technique allowing high-throughput sequencing analysis of the whole transcriptome to reveal the gene expression status of individual cells. It has emerged as an indispensable tool in the field of life science research, and can help identify the complex mechanism of cell heterogeneity, discover new cell subsets, and help uncover the molecular mechanisms of pathogenesis, the evolution of disorders, and drug resistance. This information can provide us with new strategies for diagnosis and prognostic evaluation, as well as monitoring treatment responses. In this review, we summarize the crucial experimental procedures used for single-cell RNA sequencing, and the current applications of this technique to study autoimmune diseases are described in detail. This technique will be widely used in more in-depth studies of autoimmune diseases and will contribute to the diagnosis and therapies of these disorders.

Prediction of Targets of Curculigoside A in Osteoporosis and Rheumatoid Arthritis Using Network Pharmacology and Experimental Verification

Purpose

Network pharmacology is considered to be the next-generation drug development model that uses bioinformatics to predict and identify multiple drug targets and interactions in diseases. Here, network pharmacology was used to investigate the mechanism by which Curculigoside A (CA) acts in rheumatoid arthritis (RA) and osteoporosis.

Methods

First, TCMSP and SwissADME were applied to predict the druggability of CA. Then, potential targets were identified from overlapping data in SwissTarget and TargetNet, and targets were analyzed using Genemania and DAVID6.8 to obtain information about the GO and KEGG pathways. Ultimately, the drug-target-pathway network was identified after using Cytoscape 3.0 for visualization. Besides, qPCR was used to validate the predicted five major genes targets (EGFR, MAP2K1, MMP2, FGFR1, and MCL1).

Results

The results of TCMSP and SwissADME demonstrated that CA exhibits good druggability; 26 potential protein targets were classified by SwissTarget and TargetNet. The results of Genemania and DAVID6.8 indicated that CA probably caused anti-osteoporosis and anti-RA effects by regulating some biological pathways, especially nitrogen metabolism, estrogen signaling pathway, Rap1 signaling pathway, and PI3K/Akt signaling pathway. Besides, the result of Cytoscape 3.0 showed that the 26 targets participate in osteoporosis and RA-related pathways, metabolism, and other physiological processes. In vitro induced inflammation cell model experiments, the qPCR results showed that CA pretreatment significantly decreased the expression of EGFR, MAP2K1, MMP2, FGFR1, and MCL1 genes.

Conclusion

These results suggested that network pharmacology may provide possible mechanism of how CA exerts therapeutic effects in osteoporosis and RA.

Pristane promotes anaerobic glycolysis to facilitate proinflammatory activation of macrophages and development of arthritis

Pristane-induced arthritis (PIA) could be adoptively transferred by splenic T cells in rats, and innate immunity should play critical roles in T cell activation. However, in pre-clinical stage, the activation mechanism of innate cells like macrophages remains unclear. Here we found that PIA was dependent on macrophages since cell depletion alleviated disease severity. Splenic macrophages of PIA rats showed M1 phenotypic shifting. The quantitative proteomics analysis suggested that macrophages initiated metabolic reprogramming with the conversion of aerobic oxidation to glycolysis in response to pristane in vivo. Notably, macrophages treated with pristane showed mitochondrial dysregulation and increased glycolysis flux and enzyme activity. Additionally, TNFα production, strongly associating with the glycolysis enzyme Ldha/Ldhb, could be reduced as glycolysis was inhibited or be enhanced as citrate cycle was blocked. This work provides detailed insights into the molecular mechanisms of pristane-mediated metabolic reprogramming in macrophages and suggests a new therapeutic strategy for arthritic disorders.

HtrA2 is required for inflammatory responses in BMDMs via controlling TRAF2 stability in collagen-induced arthritis

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by the destruction of cartilage and bone. The present study aims to investigate the role of HtrA serine peptidase 2 (HtrA2) in the collagen-induced arthritis. The expressions of HtrA2 were determined in the database BioGPS and bone marrow-derived macrophages (BMDMs). The populations of myeloid and lymphoid cells were determined in wild type and HtrA2 knockout (HtrA2^MKO) mice using flow cytometry. In addition, the expressions of pro-inflammatory cytokines (Il6, Tnf, and Il1β) were determined in the activated BMDMs from wild type (WT) and HtrA2^MKO mice. STRING database was used to predict the interactive proteins of HtrA2 and Co-Immunoprecipitation was used to confirm these interactions. A collagen-induced arthritis model was established to investigate the effects of HtrA2 on the arthritis symptoms. It was found that HtrA2 reduction was associated with the activation of myeloid cells. Interestingly, HtrA2 deficiency did not affect the development of myeloid and lymphoid cells. Further studies demonstrated that HtrA2 deficiency suppressed the production of pro-inflammatory cytokines in BMDMs induced by lipopolysaccharide or CpG. Co-Immunoprecipitation results demonstrated that HtrA2 enhanced the stability of TNF receptor-associated factor 2 (TRAF2). HtrA2 participated in the activation of the inflammatory response in a collagen-induced arthritis model. In summary, HtrA2 modulates inflammatory responses in BMDMs by controlling TRAF2 stability in a collagen-induced arthritis mouse model.

An Emerging Target in the Battle against Osteoarthritis: Macrophage Polarization

Osteoarthritis (OA) is one of the most prevalent chronic joint diseases worldwide, which causes a series of problems, such as joint pain, muscle atrophy, and joint deformities. Benefiting from some advances in the clinical treatment of OA, the quality of life of OA patients has been improved. However, the clinical need for more effective treatments for OA is still very urgent. Increasing findings show that macrophages are a critical breakthrough in OA therapy. Stimulated by different factors, macrophages are differentiated into two phenotypes: the pro-inflammatory M1 type and anti-inflammatory M2 type. In this study, various therapeutic reagents for macrophage-dependent OA treatment are summarized, including physical stimuli, chemical compounds, and biological molecules. Subsequently, the mechanisms of action of various approaches to modulating macrophages are discussed, and the signaling pathways underlying these treatments are interpreted. The NF-κB signaling pathway plays a vital role in the occurrence and development of macrophage-mediated OA, as NF-κB signaling pathway agonists promote the occurrence of OA, whereas NF-κB inhibitors ameliorate OA. Besides, several signaling pathways are also involved in the process of OA, including the JNK, Akt, MAPK, STAT6, Wnt/β-catenin, and mTOR pathways. In summary, macrophage polarization is a critical node in regulating the inflammatory response of OA. Reagents targeting the polarization of macrophages can effectively inhibit inflammation in the joints, which finally relieves OA symptoms. Our work lays the foundation for the development of macrophage-targeted therapeutic molecules and helps to elucidate the role of macrophages in OA.

Spatial considerations in the resolution of inflammation: Elucidating leukocyte interactions via an experimentally-calibrated agent-based model

Many common medical conditions (such as cancer, arthritis, chronic obstructive pulmonary disease (COPD), and others) are associated with inflammation, and even more so when combined with the effects of ageing and multimorbidity. While the inflammatory response varies in different tissue types, under disease and in response to therapeutic interventions, it has common interactions that occur between immune cells and inflammatory mediators. Understanding these underlying inflammatory mechanisms is key in progressing treatments and therapies for numerous inflammatory conditions. It is now considered that constituent mechanisms of the inflammatory response can be actively manipulated in order to drive resolution of inflammatory damage; particularly, those mechanisms related to the pro-inflammatory role of neutrophils and the anti-inflammatory role of macrophages. In this article, we describe the assembly of a hybrid mathematical model in which the spatial spread of inflammatory mediators is described through partial differential equations, and immune cells (neutrophils and macrophages) are described individually via an agent-based modelling approach. We pay close attention to how immune cells chemotax toward pro-inflammatory mediators, presenting a model for cell chemotaxis that is calibrated against experimentally observed cell trajectories in healthy and COPD-affected scenarios. We illustrate how variations in key model parameters can drive the switch from resolution of inflammation to chronic outcomes, and show that aberrant neutrophil chemotaxis can move an otherwise healthy outcome to one of chronicity. Finally, we reflect on our results in the context of the on-going hunt for new therapeutic interventions.

Inflammation is the body’s primary defence to harmful stimuli such as infections, toxins and tissue strain but also underlies a much broader range of conditions, including asthma, arthritis and cancer. The inflammatory response is key in resolving injury to facilitate recovery, and involves a range of interactions between immune cells (leukocytes, neutrophils and macrophages in particular) and inflammatory mediators. Immune cells are recruited from the blood stream in response to injury. Once in tissue, neutrophils release toxins to kill invading agents and resolve damage; however, if not carefully managed by other immune cells (mainly macrophages), their responses can increase inflammation instead of helping to resolve it. We model these interactions in response to damage using a spatial model, examining how a healthy response can prevent localised inflammation from spreading. We pay close attention to how cells migrate toward the damaged area, as many inflammatory conditions are associated with impairment of this process. We calibrate our model against experimentally-observed cell trajectories from healthy patients and patients with chronic obstructive pulmonary disease. We illustrate that a healthy outcome depends strongly upon efficient cell migration and a delicate balance between the pro- and anti-inflammatory effects of neutrophils and macrophages.

New insights into macrophage heterogeneity in rheumatoid arthritis

Rheumatoid arthritis (RA) is a prototypic autoimmune disease that primarily affects joints. Clinical studies and animal models evidenced that mononuclear phagocytes including monocytes and macrophages are crucial to RA pathogenesis, contributing to inflammation and destruction of cartilage and bone. The last decade of research has tremendously changed our view on the origin of tissue-resident macrophages. In light of the recent publications that reveal important phenotypic and functional heterogeneity among macrophages, it is of paramount importance to identify the synovial macrophage subsets that might amplify the inflammatory response or promote the restoration of tissue homeostasis. In this review, we highlight latest studies applying single-cell RNA sequencing that provide deeper insights in macrophage subsets and their putative functions within both human and mouse synovial joint tissue.

Ceria-based nanotheranostic agent for rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease that affects 1-2% of the human population worldwide, and effective therapies with targeted delivery for local immune suppression have not been described. We address this problem by developing a novel theranostic nanoparticle for RA and assessed its therapeutic and targeting effects under image-guidance. Methods: Albumin-cerium oxide nanoparticles were synthesized by the biomineralization process and further conjugated with near-infrared, indocyanine green (ICG) dye. Enzymatic-like properties and reactive oxygen species (ROS) scavenging activities, as well as the ability to reprogram macrophages, were determined on a monocyte cell line in culture. The therapeutic effect and systemic targeting potential were evaluated in collagen-induced arthritis (CIA) mouse model using optical/optoacoustic tomographic imaging. Results: Small nanotheranostics with narrow size distribution and high colloidal stability were fabricated and displayed high ROS scavenging and enzymatic-like activity, as well as advanced efficacy in a converting pro-inflammatory macrophage phenotype into anti-inflammatory phenotype. When administrated into affected animals, these nanoparticles accumulated in inflamed joints and revealed a therapeutic effect similar to the gold-standard therapy for RA, methotrexate. Conclusions: The inflammation-targeting, inherent contrast and therapeutic activity of this new albumin-cerium oxide nanoparticle may make it a relevant agent for assessing severity in RA, and other inflammatory diseases, and controlling inflammation with image-guidance. The design of these nanotheranostics will enable potential clinical translation as systemic therapy for RA.

Disease-Specific Autoantibodies Induce Trained Immunity in RA Synovial Tissues and Its Gene Signature Correlates with the Response to Clinical Therapy

Much evidence suggests that trained immunity is inappropriately activated in the synovial tissue in rheumatoid arthritis (RA), but the underlying mechanism remains unclear. Here, we describe how RA-specific autoantibody deposits can train human monocytes to exert the hyperactive inflammatory response, particularly via the exacerbated release of tumor necrosis factor α (TNFα). Comparative transcriptomic analysis by plate-bound human IgG (cIgG) or β-glucan indicated that metabolic shift towards glycolysis is a crucial mechanism for trained immunity. Moreover, the cIgG-trained gene signatures were enriched in synovial tissues from patients with ACPA- (anticitrullinated protein antibody-) positive arthralgia and undifferentiated arthritis, and early RA and established RA bore a great resemblance to the myeloid pathotype, suggesting a historical priming event in vivo. Additionally, the expression of the cIgG-trained signatures is higher in the female, older, and ACPA-positive populations, with a predictive role in the clinical response to infliximab. We conclude that RA-specific autoantibodies can train monocytes in the inflamed lesion as early as the asymptomatic stage, which may not merely improve understanding of disease progression but may also suggest therapeutic and/or preventive strategies for autoimmune diseases.

Inflammation-Targeted Celastrol Nanodrug Attenuates Collagen-Induced Arthritis through NF-κB and Notch1 Pathways

Rheumatoid arthritis (RA) is a systemic inflammatory disorder which can cause bone and cartilage damage leading to disability, yet the treatment remains unsatisfactory nowadays. Celastrol (Cel) has shown antirheumatic activity against RA. However, the frequent parenteral delivery and poor water solubility of Cel restrict its further therapeutic applications. Here, aiming at effectively overcoming the poor water solubility and short half-life of Cel to boost its beneficial effects for treating RA, we developed a polymeric micelle for Cel delivery based on a reactive oxygen species (ROS) sensitive polymer. Our results demonstrated that Cel may inhibit the repolarization of macrophages toward the pro-inflammatory M1 pheno-type via regulating the NF-κB and Notch1 pathways, which resulted in significantly decreased secretion of multiple pro-inflammatory cytokines to suppress the RA progression. Consequently, the Cel-loaded micelle effectively alleviated the major RA-associated symptoms including articular scores, ankle thickness, synovial inflammation, bone erosion, and cartilage degradation.

CircRNA_09505 aggravates inflammation and joint damage in collagen-induced arthritis mice via miR-6089/AKT1/NF-κB axis

A number of circular RNAs (circRNAs) have been implicated in rheumatoid arthritis (RA) pathogenesis; however, little is known about their function and hidden molecular mechanism in immune and inflammation regulation. We investigated the role and the underlying mechanism of circRNA_09505 in RA in this study. Real-time PCR and fluorescence in situ hybridization (FISH) are adopted to estimate the quantitative expression and localization of circRNA_09505 in macrophages. The altering effect of circRNA_09505 on inflammation is investigated in vitro and in vivo by use of macrophage cell models and collagen-induced arthritis (CIA) mice. Luciferase reporter assay and RNA-binding protein immunoprecipitation (RIP) are used to confirm the circRNA_09505/miR-6089 ceRNA network predicted by bioinformatics analysis. Compared with controls, the expression of circRNA_09505 is upregulated in peripheral blood mononuclear cells (PBMCs) from patients with RA. The proliferation and cell cycle are significantly promoted when circRNA_09505 is upregulated in macrophages, whereas knockdown of circRNA_09505 inhibits macrophage proliferation and cell- cycle progression. Besides, circRNA_09505 can act as a miRNA sponge for miR-6089 in macrophages, and promote the production of TNF-α, IL-6, and IL-12 through ceRNA mechanism. Moreover, AKT1 is a direct target of miR-6089. CircRNA_09505 can promote AKT1 expression by acting as a miR-6089 sponge via IκBα/NF-κB signaling pathway in macrophages. Most interestingly, knockdown of circRNA_09505 significantly alleviates arthritis and inflammation in vivo in CIA mice. These data support the hypothesis that circRNA_09505 can function as a miR-6089 sponge and regulate inflammation via miR-6089/AKT1/NF-κB axis in CIA mice.

Neutrophil-mediated carbamylation promotes articular damage in rheumatoid arthritis

Formation of autoantibodies to carbamylated proteins (anti-CarP) is considered detrimental in the prognosis of erosive rheumatoid arthritis (RA). The source of carbamylated antigens and the mechanisms by which anti-CarP antibodies promote bone erosion in RA remain unknown. Here, we find that neutrophil extracellular traps (NETs) externalize carbamylated proteins and that RA subjects develop autoantibodies against carbamylated NET (cNET) antigens that, in turn, correlate with levels of anti-CarP. Transgenic mice expressing the human RA shared epitope (HLADRB1* 04:01) immunized with cNETs develop antibodies to citrullinated and carbamylated proteins. Furthermore, anti-carbamylated histone antibodies correlate with radiographic bone erosion in RA subjects. Moreover, anti-carbamylated histone-immunoglobulin G immune complexes promote osteoclast differentiation and potentiate osteoclast-mediated matrix resorption. These results demonstrate that carbamylated proteins present in NETs enhance pathogenic immune responses and bone destruction, which may explain the association between anti-CarP and erosive arthritis in RA.

The Natural Compound Notopterol Binds and Targets JAK2/3 to Ameliorate Inflammation and Arthritis

The traditional Chinese medicinal herb Notopterygium incisum Ting ex H.T. Chang has anti-rheumatism activity, and a mass spectrometry assay of patients' serum after administration of the herb revealed that notopterol is the most abundant component enriched. However, the functions of notopterol and its molecular target in rheumatoid arthritis (RA) treatment remain unknown. Here, we show in different RA mouse strains that both oral and intraperitoneal administration of notopterol result in significant therapeutic effects. Mechanistically, notopterol directly binds Janus kinase (JAK)2 and JAK3 kinase domains to inhibit JAK/signal transducers and activators of transcription (JAK-STAT) activation, leading to reduced production of inflammatory cytokines and chemokines. Critically, combination therapy using both notopterol and tumor necrosis factor (TNF) blocker results in enhanced therapeutic effects compared to using TNF blocker alone. We demonstrate that notopterol ameliorates RA pathology by targeting JAK-STAT signaling, raising the possibility that notopterol could be effective in treating other diseases characterized by aberrant JAK-STAT signaling pathway.

NOTCH3 signaling is essential for NF-κB activation in TLR-activated macrophages

Macrophage activation by Toll receptors is an essential event in the development of the response against pathogens. NOTCH signaling pathway is involved in the control of macrophage activation and the inflammatory processes. In this work, we have characterized NOTCH signaling in macrophages activated by Toll-like receptor (TLR) triggering and determined that DLL1 and DLL4 are the main ligands responsible for NOTCH signaling. We have identified ADAM10 as the main protease implicated in NOTCH processing and activation. We have also observed that furin, which processes NOTCH receptors, is induced by TLR signaling in a NOTCH-dependent manner. NOTCH3 is the only NOTCH receptor expressed in resting macrophages. Its expression increased rapidly in the first hours after TLR4 activation, followed by a gradual decrease, which was coincident with an elevation of the expression of the other NOTCH receptors. All NOTCH1, 2 and 3 contribute to the increased NOTCH signaling detected in activated macrophages. We also observed a crosstalk between NOTCH3 and NOTCH1 during macrophage activation. Finally, our results highlight the relevance of NOTCH3 in the activation of NF-κB, increasing p65 phosphorylation by p38 MAP kinase. Our data identify, for the first time, NOTCH3 as a relevant player in the control of inflammation.

Hsp70 and NF-kB Mediated Control of Innate Inflammatory Responses in a Canine Macrophage Cell Line

The pathogenesis of many inflammatory diseases is associated with the uncontrolled activation of nuclear factor kappa B (NF-κB) in macrophages. Previous studies have shown that in various cell types, heat shock protein 70 (Hsp70) plays a crucial role in controlling NF-κB activity. So far, little is known about the role of Hsp70 in canine inflammatory processes. In this study we investigated the potential anti-inflammatory effects of Hsp70 in canine macrophages as well as the mechanisms underlying these effects. To this end, a canine macrophage cell line was stressed with arsenite, a chemical stressor, which upregulated Hsp70 expression as detected by flow cytometry and qPCR. A gene-edited version of this macrophage cell line lacking inducible Hsp70 was generated using CRISPR-Cas9 technology. To determine the effects of Hsp70 on macrophage inflammatory properties, arsenite-stressed wild-type and Hsp70 knockout macrophages were exposed to lipopolysaccharide (LPS), and the expression of the inflammatory cytokines IL-6, IL-1β and tumor necrosis factor-α (TNF-α) and levels of phosphorylated NF-κB were determined by qPCR and Western Blotting, respectively. Our results show that non-toxic concentrations of arsenite induced Hsp70 expression in canine macrophages; Hsp70 upregulation significantly inhibited the LPS-induced expression of the pro-inflammatory mediators TNF-α and IL-6, as well as NF-κB activation in canine macrophages. Furthermore, the gene editing of inducible Hsp70 by CRISPR-Cas9-mediated gene editing neutralized this inhibitory effect of cell stress on NF-κB activation and pro-inflammatory cytokine expression. Collectively, our study reveals that Hsp70 may regulate inflammatory responses through NF-κB activation and cytokine expression in canine macrophages.

Triamcinolone-Gold Nanoparticles Repolarize Synoviocytes and Macrophages in an Inflamed Synovium

Understanding the crosstalk between synoviocytes and macrophages is very important for the development of strategies to regulate inflammatory responses in an inflamed synovium. Simultaneous regulation of the pro- and anti-inflammatory responses of synoviocytes and macrophages (repolarization) is critical for the treatment of arthritis. Thus, the immune regulatory functions of an ideal nanodrug should not only decrease the pro-inflammatory response but also effectively increase the anti-inflammatory response. In this study, crosstalk between synoviocytes and macrophages was found to be significantly involved in the activation and deactivation of inflammatory responses in the synovium. Interestingly, a developed triamcinolone-gold nanoparticle (Triam-AuNP) complex both decreased the pro-inflammatory responses and increased the anti-inflammatory responses of fibroblast-like synoviocytes (FLSs) and macrophages via repolarization of macrophages from the M1 to the M2 phenotype. In contrast, triamcinolone alone only decreased the pro-inflammatory responses of FLSs and macrophages without upregulating their anti-inflammatory responses. In vitro (human), ex vivo (human), and in vivo (mouse) analyses clearly indicated that Triam-AuNPs effectively regulated the expression of both pro- and anti-inflammatory cytokines in FLSs and effectively repolarized activity of macrophages in the inflamed synovium. Furthermore, Triam-AuNPs significantly promoted cartilage regeneration, whereas triamcinolone alone did not induce either FLS anti-inflammatory activity or macrophage repolarization.

The structure of myeloid cell-specific TNF inhibitors affects their biological properties

Spatial organization and conformational changes of antibodies may significantly affect their biological functions. We assessed the effect of mutual organization of the two V_H H domains within bispecific antibodies recognizing human TNF and the surface molecules of murine myeloid cells (F4/80 or CD11b) on TNF retention and inhibition. TNF-neutralizing properties in vitro and in vivo of MYSTI-2 and MYSTI-3 antibodies were compared with new variants with interchanged V_H H domains and different linker sequences. The most effective structure of MYSTI-2 and MYSTI-3 proteins required the Ser/Gly-containing 'superflexible' linker. The orientation of the modules was crucial for the activity of the proteins, but not for MYSTI-3 with the Pro/Gln-containing 'semi-rigid' linker. Our results may contribute toward the development of more effective drug prototypes.

Dextran sulfate-modified pH-sensitive layered double hydroxide nanocomposites for treatment of rheumatoid arthritis

To reduce the side effects of methotrexate and increase its anti-inflammatory effect, we developed a drug delivery system, dextran sulfate-modified methotrexate-loaded layered double hydroxide nanocomposites (LDH-MTX-DS), with both targeting and pH-sensitivity for the treatment of rheumatoid arthritis. The nanocomposites had a mean particle size of 303.1 ± 8.07 nm, zeta potential of - 12.4 ± 0.7 mV, encapsulation efficiency of 49.64%, and loading efficiency of 16.81%. In vitro release experiments demonstrated that the drug was released faster in PBS at pH 5.5 than at pH 7.4, which reflected the pH-sensitivity of this system. Cellular uptake assays displayed higher cellular uptake rate of the dextran sulfate-modified targeting carrier compared with that of a non-targeting carrier (P < 0.01), which indicated that the LDH-MTX-DS could actively target scavenger receptors on the surface of activated RAW 264.7 cells. In vivo pharmacodynamic experiments showed that, after the second (P < 0.001) and third (P < 0.05) administrations, the preparation group exhibited significantly improved therapeutic efficacy in adjuvant-induced arthritis (AIA) rats when compared with free MTX alone. These results indicated that this drug delivery system was promising in the treatment of rheumatoid arthritis. Graphical abstract.

The Urokinase Plasminogen Activation System in Rheumatoid Arthritis: Pathophysiological Roles and Prospective Therapeutic Targets

Rheumatoid Arthritis (RA) is a chronic and progressive inflammatory disease characterized in its early stages by synovial hyperplasia and inflammatory cell infiltration and later by irreversible joint tissue destruction. The Plasminogen Activation System (PAS) is associated with a wide range of physiological and pathophysiological states involving fibrinolysis, inflammation and tissue remodeling. Various components of the PAS are implicated in the pathophysiology of RA. Urokinase Plasminogen Activator (uPA) in particular is a pro-inflammatory mediator that appears to play an important role in the bone and cartilage destruction associated with RA. Clinical studies have shown that uPA and its receptor uPAR are overexpressed in synovia of patients with rheumatoid arthritis. Further, genetic knockdown and antibody-mediated neutralization of uPA have been shown to be protective against induction or progression of arthritis in animal models. The pro-arthritic role of uPA is differentiated from its haemodynamic counterpart, tissue plasminogen activator (tPA), which appears to play a protective role in RA animal models. This review summarises available evidence supporting the PAS as a critical determinant of RA pathogenesis and highlights opportunities for the development of novel uPAS-targeting therapeutics.

Peripheral mechanisms of arthritic pain: A proposal to leverage large animals for in vitro studies

Pain arising from musculoskeletal disorders such as arthritis is one of the leading causes of disability. Whereas the past 20-years has seen an increase in targeted therapies for rheumatoid arthritis (RA), other arthritis conditions, especially osteoarthritis, remain poorly treated. Although modulation of central pain pathways occurs in chronic arthritis, multiple lines of evidence indicate that peripherally driven pain is important in arthritic pain. To understand the peripheral mechanisms of arthritic pain, various in vitro and in vivo models have been developed, largely in rodents. Although rodent models provide numerous advantages for studying arthritis pathogenesis and treatment, the anatomy and biomechanics of rodent joints differ considerably to those of humans. By contrast, the anatomy and biomechanics of joints in larger animals, such as dogs, show greater similarity to human joints and thus studying them can provide novel insight for arthritis research. The purpose of this article is firstly to review models of arthritis and behavioral outcomes commonly used in large animals. Secondly, we review the existing in vitro models and assays used to study arthritic pain, primarily in rodents, and discuss the potential for adopting these strategies, as well as likely limitations, in large animals. We believe that exploring peripheral mechanisms of arthritic pain in vitro in large animals has the potential to reduce the veterinary burden of arthritis in commonly afflicted species like dogs, as well as to improve translatability of pain research into the clinic.

Protective effect of bergapten in acetic acid-induced colitis in rats

Bergapten (5-methoxysporalen) is a furanocoumarin extracted from several species of citrus and bergamot oil. Bergamot essential oil is used traditionally in the management of inflammatory conditions. Previous studies on bergapten have explored mainly its in vitro anti-inflammatory activities which include suppression of the expression and release of pro-inflammatory cytokines such as TNF-α and interleukins as well as prostaglandins. Bergapten enhances the clearance of neutrophils and macrophages from the site of inflammation and reduces oxidative stress by inhibition of reactive oxygen species (ROS). Bergapten was assessed for its anti-inflammatory properties in acetic acid-induced colitis. Animals were obtained and randomly placed in six (6) groups (n = 5) after acclimatization. Colitis was induced by rectal administration using 4% v/v acetic acid in Sprague Dawley rats after pre-treatment for 5 days. Bergapten was administered at doses of 3, 10, and 30 mg kg-1 p.o. while the control group received saline 5 mL kg-1 p.o. and the standard drug employed was sulphasalazine at a dose of 500 mg kg-1. Assessments made for colon-weight-to-length ratio, colonic injury, and mucosal mast cell degranulation. There were reduced colon-weight-to-length ratios in animals treated with bergapten which was significant (p < 0.5) for doses 10 and 30 mg kg-1 compared to the disease control group Both macroscopic and microscopic damage were reduced as well, with a lesser percentage of degranulated mast cells. Macroscopic damage was reduced for bergapten at doses 10 and 30 mg kg-1 significantly at p < 0.5 and p < 0.001, respectively. Similarly, microscopic damage was reduced at p < 0.01 and p < 0.001 respectively for bergapten 10 and 30 mg kg-1. The reduction of degranulation by bergapten was significant at p < 0.001. There was generally reduced damage at inflammatory sites as well as decreased infiltration of inflammatory cells. Overall, bergapten reduces inflammation in acetic acid-induced colitis.

Distinct synovial tissue macrophage subsets regulate inflammation and remission in rheumatoid arthritis

Immune-regulatory mechanisms of drug-free remission in rheumatoid arthritis (RA) are unknown. We hypothesized that synovial tissue macrophages (STM), which persist in remission, contribute to joint homeostasis. We used single-cell transcriptomics to profile 32,000 STMs and identified phenotypic changes in patients with early/active RA, treatment-refractory/active RA and RA in sustained remission. Each clinical state was characterized by different frequencies of nine discrete phenotypic clusters within four distinct STM subpopulations with diverse homeostatic, regulatory and inflammatory functions. This cellular atlas, combined with deep-phenotypic, spatial and functional analyses of synovial biopsy fluorescent activated cell sorted STMs, revealed two STM subpopulations (MerTKposTREM2high and MerTKposLYVE1pos) with unique remission transcriptomic signatures enriched in negative regulators of inflammation. These STMs were potent producers of inflammation-resolving lipid mediators and induced the repair response of synovial fibroblasts in vitro. A low proportion of MerTKpos STMs in remission was associated with increased risk of disease flare after treatment cessation. Therapeutic modulation of MerTKpos STM subpopulations could therefore be a potential treatment strategy for RA.

Mouse CD163 deficiency strongly enhances experimental collagen-induced arthritis

The scavenger receptor CD163 is highly expressed in macrophages in sites of chronic inflammation where it has a not yet defined role. Here we have investigated development of collagen-induced arthritis (CIA) and collagen antibody-induced arthritis (CAIA) in CD163-deficient C57BL/6 mice. Compared to wild-type mice, the CIA in CD163-deficient mice had a several-fold higher arthritis score with early onset, prolonged disease and strongly enhanced progression. Further, the serum anti-collagen antibody isotypes as well as the cytokine profiles and T cell markers in the inflamed joints revealed that CD163-deficient mice after 52 days had a predominant Th2 response in opposition to a predominant Th1 response in CD163+/+ mice. Less difference in disease severity between the CD163+/+ and CD163-/- mice was seen in the CAIA model that to a large extent induces arthritis independently of T-cell response and endogenous Th1/Th2 balance. In conclusion, the present set of data points on a novel strong anti-inflammatory role of CD163.

Origin and Differentiation of Nerve-Associated Macrophages

The mature peripheral nervous system is a steady network structure yet shows remarkable regenerative properties. The interaction of peripheral nerves with myeloid cells has largely been investigated in the context of damage, following trauma or infection. Recently, specific macrophages dedicated to homeostatic peripheral nerves have come into focus. These macrophages are defined by tissue and nerve type, are seeded in part prenatally, and self-maintain via proliferation. Thus, they are markedly distinct from monocyte-derived macrophages invading after local disturbance of nerve integrity. The phenotypic and transcriptional adaptation of macrophages to the discrete nervous niche may exert axon guidance and nerve regeneration and thus contribute to the stability of the peripheral nervous network. Deciphering these conserved macrophage-nerve interactions offers new translational perspectives for chronic diseases of the peripheral nervous system, such as diabetic neuropathy and pain.

Innate immunity drives pathogenesis of rheumatoid arthritis

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

Macrophages are the primary effector cells in IL-7-induced arthritis

Synovial macrophages are crucial in the development of joint inflammation and bone damage; however, the pathways that control macrophage remodeling in inflammatory M1 cells or bone-eroding osteoclasts are not fully understood. We determined that elevated IL-7R/CD127 expression is the hallmark of rheumatoid arthritis (RA) M1 macrophages and that these cells are highly responsive to interleukin-7 (IL-7)-driven osteoclastogenesis. We established that lipopolysaccharide (LPS), interferon-γ (IFNγ), and tumor necrosis factor-α (TNFα), the classic M1 macrophage mediators, enhance IL-7R expression in RA and murine macrophages. The local expression of IL-7 provokes arthritis, predominantly through escalating the number of F480+iNOS+ cells rather than CD3+ T cells. Ectopic LPS injection stabilizes IL-7-induced arthritis by increasing myeloid IL-7R expression, in part via IFNγ induction. Hence, in RAG-/- mice, IL-7-mediated arthritis is suppressed because of the reduction in myeloid IL-7R expression due to the lack of IFNγ. Moreover, the amelioration of IL-7-induced arthritis by anti-TNF therapy is due to a decrease in the number of cells in the unique F480+iNOS+IL-7R+CCL5+ subset, with no impact on the F480+Arginase+ cell or CD3+ T cell frequency. Consistent with the preclinical findings, the findings of a phase 4 study performed with RA patients following 6 months of anti-TNF therapy revealed that IL-7R expression was reduced without affecting the levels of IL-7. This study shifts the paradigm by discovering that IL-7-induced arthritis is dependent on F480+iNOS+IL-7R+CCL5+ cell function, which activates TH-1 cells to amplify myeloid IL-7R expression and disease severity.

ER-localized Hrd1 ubiquitinates and inactivates Usp15 to promote TLR4-induced inflammation during bacterial infection

The special organelle-located MAVS, STING and TLR3 are important for clearing viral infections. Although TLR4 triggers NF-κB activation to produce pro-inflammatory cytokines for bacterial clearance, effectors with special organelle localization have not been identified. Here, we screened more than 280 E3 ubiquitin ligases and discovered that the endoplasmic reticulum-located Hrd1 regulates TLR4-induced inflammation during bacterial infection. Hrd1 interacts directly with the deubiquitinating enzyme Usp15. Unlike the classical function of Hrd1 in endoplasmic reticulum-associated degradation, Usp15 is not degraded but loses its deubiquitinating activity for IκBα deubiquitination, resulting in excessive NF-κB activation. Importantly, Hrd1 deficiency in macrophages protects mice against lipopolysaccharide-induced septic shock, and knockdown of Usp15 in Hrd1-knockout macrophages restores the reduced IL-6 production. This study proposes that there is crosstalk between Hrd1 and TLR4, thereby linking the endoplasmic reticulum-plasma membrane function during bacterial infection.

Classic and new mediators for in vitro modelling of human macrophages

Macrophages are key immune cells in the activation and regulation of immune responses. These cells are present in all tissues under homeostatic conditions and in many disease settings. Macrophages can exhibit a wide range of phenotypes depending on local and systemic cues that drive the differentiation and activation process. Macrophage heterogeneity is also defined by their ontogeny. Tissue macrophages can either derive from circulating blood monocytes or are seeded as tissue-resident macrophages during embryonic development. In humans, the study of in vivo-generated macrophages is often difficult with laborious and cell-changing isolation procedures. Therefore, translatable, reproducible, and robust in vitro models for human macrophages in health and disease are necessary. Most of the methods for studying monocyte-derived macrophages are based on the use of limited factors to differentiate the monocytes into macrophages. Current knowledge shows that the in vivo situation is more complex, and a wide range of molecules in the tissue microenvironment promote and impact on monocyte to macrophage differentiation as well as activation. In this review, macrophage heterogeneity is discussed and the human in vitro models that can be applied for research, especially for monocyte-derived macrophages. We also focus on new molecules (IL-34, platelet factor 4, etc.) used to generate macrophages expressing different phenotypes.

Emerging role of targeting macrophages in rheumatoid arthritis: Focus on polarization, metabolism and apoptosis

Macrophages maintain a dynamic balance in physiology. Various known or unknown microenvironmental signals influence the polarization, activation and death of macrophages, which creates an imbalance that leads to disease. Rheumatoid arthritis (RA) is characterized by the massive infiltration of a variety of chronic inflammatory cells in synovia. Abundant activated macrophages found in RA synovia are an early hallmark of RA, and the number of these macrophages can be decreased after effective treatment. In RA, the proportion of M1 (pro‐inflammatory macrophages) is higher than that of M2 (anti‐inflammatory macrophages). The increased pro‐inflammatory ability of macrophages is related to their excessive activation and proliferation as well as an enhanced anti‐apoptosis ability. At present, there are no clinical therapies specific to macrophages in RA. Understanding the mechanisms and functional consequences of the heterogeneity of macrophages will aid in confirming their potential role in inflammation development. This review will outline RA‐related macrophage properties (focus on polarization, metabolism and apoptosis) as well as the origin of macrophages. The molecular mechanisms that drive macrophage properties also be elucidated to identify novel therapeutic targets for RA and other autoimmune disease.

Folate Receptor β (FRβ) Expression in Tissue-Resident and Tumor-Associated Macrophages Associates with and Depends on the Expression of PU.1

As macrophages exhibit a huge functional plasticity under homeostasis and pathological conditions, they have become a therapeutic target for chronic inflammatory diseases. Hence, the identification of macrophage subset-specific markers is a requisite for the development of macrophage-directed therapeutic interventions. In this regard, the macrophage-specific Folate Receptor β (FRβ, encoded by the FOLR2 gene) has been already validated as a target for molecular delivery in cancer as well as in macrophage-targeting therapeutic strategies for chronic inflammatory pathologies. We now show that the transcriptome of human macrophages from healthy and inflamed tissues (tumor; rheumatoid arthritis, RA) share a significant over-representation of the “anti-inflammatory gene set”, which defines the gene profile of M-CSF-dependent IL-10-producing human macrophages (M-MØ). More specifically, FOLR2 expression has been found to strongly correlate with the expression of M-MØ-specific genes in tissue-resident macrophages, tumor-associated macrophages (TAM) and macrophages from inflamed synovium, and also correlates with the presence of the PU.1 transcription factor. In fact, PU.1-binding elements are found upstream of the first exon of FOLR2 and most M-MØ-specific- and TAM-specific genes. The functional relevance of PU.1 binding was demonstrated through analysis of the proximal regulatory region of the FOLR2 gene, whose activity was dependent on a cluster of PU.1-binding sequences. Further, siRNA-mediated knockdown established the importance of PU.1 for FOLR2 gene expression in myeloid cells. Therefore, we provide evidence that FRβ marks tissue-resident macrophages as well as macrophages within inflamed tissues, and its expression is dependent on PU.1.

New insights into IFN-γ in rheumatoid arthritis: role in the era of JAK inhibitors

The treatment of rheumatoid arthritis (RA) is now entering a new era, the era of Janus kinase (JAK) inhibitors. JAK inhibitors target multiple cytokines including IL-6 and exhibit a beneficial treatment effect in patients with RA and inadequate response to conventional synthetic or biologic disease-modifying anti-rheumatic drugs. Since the treatment effect of JAK inhibitors is promising even for patients refractory to anti-IL-6 therapy, it needs to be considered how multiple cytokines play roles in the pathogenesis of RA. It is also worth noting that an increased risk of herpes zoster is specifically related to the use of JAK inhibitors. Among cytokines targeted by JAK inhibitors, the current review focuses on IFN-γ, particularly on its role in synovial biology, autoimmunity, bone metabolism, pain, and varicella zoster virus infection. Recent studies provided new insights into IFN-γ in the pathogenesis of RA, which may account for the efficacy of JAK inhibitors.

Exosomes: Effectual players in rheumatoid arthritis

Rheumatoid arthritis is a well-known chronic inflammatory joint disorder. It encompasses systemic inflammation, autoimmunity and development of several joint abnormalities leading to the lifelong disability and increased mortality. Exosomes are nano-sized (30-100 nm) mammalian extracellular particles with essential properties to regulate biological processes and cellular signaling by transferring protein and genetic materials. Understanding the diversity in the exosomal contents and their corresponding targets may contribute to better recognition of the processes that are implicated in the development and progression of diseases such as autoimmune disorders. Exosomes may act as a potential biomarker for the diagnosis of autoimmune disorders. In the present review, we aimed to bring together the relevant evidence on the biology of exosomes in rheumatoid arthritis, and also discuss the recent findings regarding the diagnostic, prognostic and therapeutic promise of these nanoparticles.

Anti-Inflammatory Activity of Miodesin™: Modulation of Inflammatory Markers and Epigenetic Evidence

PURPOSE

To investigate the effects of a combined herbal medicine Miodesin™ on the inflammatory response of key cells involved in the acute and chronic inflammatory processes as well as the possible epigenetic involvement.

METHODS

After the establishment of the IC50 dose, the chondrocyte, keratinocyte, and macrophage cell lines were pretreated for 2 hours with Miodesin™ (200 μg/mL) and stimulated with LPS (1 μg/mL) for 24 hours. The supernatant was used to measure the levels of cytokines (IL-1β, IL-6, IL-8, and TNF-α) and chemokines (CCL2, CCL3, and CCL5), and the cells were used to extract the mRNA for the transcription factor (NF-κβ), inflammatory enzymes (COX-1, COX-2, PLA2, and iNOS), and chemokines (CCL2, CCL3, and CCL5).

RESULTS

Miodesin™ inhibited the release of LPS-induced cytokines (IL-1β, IL-6, IL-8, and TNF-α; p < 0.01) and chemokines (CCL2, CCL3, and CCL5; p < 0.01) and the expression of the transcription factor (NF-κβ; p < 0.01), inflammatory enzymes (COX-1, COX-2, PLA2, iNOS; p < 0.01), and chemokines (CCL2, CCL3, and CCL5; p < 0.01). In addition, the evaluation of epigenetic mechanism revealed that Miodesin™ did not induce changes in DNA methylation, assuring the genetic safeness of the compound in terms of the inflammatory response.

CONCLUSIONS

Miodesin™ presents anti-inflammatory properties, inhibiting hyperactivation of chondrocytes, keratinocytes, and macrophages, involving epigenetics in such effects.

From GWAS to Function: Using Functional Genomics to Identify the Mechanisms Underlying Complex Diseases

Genome-wide association studies (GWAS) have successfully mapped thousands of loci associated with complex traits. These associations could reveal the molecular mechanisms altered in common complex diseases and result in the identification of novel drug targets. However, GWAS have also left a number of outstanding questions. In particular, the majority of disease-associated loci lie in non-coding regions of the genome and, even though they are thought to play a role in gene expression regulation, it is unclear which genes they regulate and in which cell types or physiological contexts this regulation occurs. This has hindered the translation of GWAS findings into clinical interventions. In this review we summarize how these challenges have been addressed over the last decade, with a particular focus on the integration of GWAS results with functional genomics datasets. Firstly, we investigate how the tissues and cell types involved in diseases can be identified using methods that test for enrichment of GWAS variants in genomic annotations. Secondly, we explore how to find the genes regulated by GWAS loci using methods that test for colocalization of GWAS signals with molecular phenotypes such as quantitative trait loci (QTLs). Finally, we highlight potential future research avenues such as integrating GWAS results with single-cell sequencing read-outs, designing functionally informed polygenic risk scores (PRS), and validating disease associated genes using genetic engineering. These tools will be crucial to identify new drug targets for common complex diseases.

Dextran sulfate-triamcinolone acetonide conjugate nanoparticles for targeted treatment of osteoarthritis

Osteoarthritis (OA) is a synovial inflammatory condition characterized by cartilage destruction and osteophyte formation. Macrophages play a central role in OA pathogenesis by producing proinflammatory cytokines. Intra-articular corticosteroid administration can relieve refractory pain and inflamed effusion of knee joints. However, limitations, such as rapid clearance from the joint space, potential damage to articular cartilage, and accelerated joint degeneration, may hamper the clinical application of corticosteroids. In this study, we reported the design and preparation of dextran sulfate-triamcinolone acetonide conjugate (DS-TA) nanoparticles (NPs) for treating OA by specifically targeting scavenger receptor class A (SR-A) on activated macrophages. We verified the excellent targeting specificity of DS-TA NPs to SR-A by flow cytometry and confocal laser scanning microscopy. DS-TA NPs were found to effectively reduce the viability of activated macrophages (RAW 264.7 cells) and the expression of proinflammatory cytokines. Intra-articular injection of DS-TA NPs effectively alleviated the structural damages to the joint cartilage, as confirmed in histopathological analysis. Additionally, DS-TA NPs decreased the expression of proinflammatory cytokines, including IL-1β, IL-6, and TNF-α, in the cartilage tissue. Thus, DS-TA NPs are a potential therapeutic nanomedicine for the targeted treatment of OA.

Anti-inflammatory effects of naproxen sodium on human osteoarthritis synovial fluid immune cells

OBJECTIVE

To evaluate the anti-inflammatory effects of clinically relevant naproxen sodium (Nx) concentrations on human monocyte-derived macrophages in a controlled in vitro system and human primary synovial fluid (SF) cells.

DESIGN

Using phorbol 12-myristate 13-acetate, THP-1 human monocytic cells were differentiated into mature monocyte-derived macrophages in vitro then treated with Nx pre- or post-activating an inflammatory response with lipopolysaccharide (LPS) and hyaluronan (HA) fragments (n = 8/group). Cell culture supernatants were assessed for NF-κB activity and prostaglandin E₂ (PGE₂), indicating cyclooxygenase enzyme activity. Under Duke IRB approval, primary human SF cells were collected at the time of knee joint replacement (n = 19 individuals) for osteoarthritis (OA), and cultured with LPS, HA and Nx; SF cells were characterized by polychromatic flow cytometry for cell surface markers and intracellular cytokines.

RESULT

Compared to placebo treatment of THP-1 cells, low dose Nx (corresponding 27.5-440 mg/L orally) added both pre- and post-activation with LPS/HA, significantly reduced NF-κB activity and PGE2: mean reduction to 73%, 61%, 17% and 10% of placebo, respectively. LPS/HA treatment of primary OA SF cells significantly increased the number of IL-1β producing primary monocytes and macrophages, and by 24 h the overall production of secreted cytokines (IL-1β, IL-6, IL8, and TNF-α). Low dose Nx reduced the percentage of IL-1β producing primary monocytes and macrophages.

CONCLUSION

LPS/HA induced inflammation of THP-1 monocytic and primary human SF cells. Low dose Nx both prevented and reduced inflammatory responses of a human monocytic cell line and reduced IL-1β production by primary human SF monocytes and macrophages.