Mast cells in rheumatoid arthritis

Activity-dependent FosB gene expression negatively regulates mast cell functions

Mast cells are innate immune cells that play a crucial role in numerous physiological processes across tissues by releasing pre-stored and newly synthesized mediators in response to stimuli, an activity largely driven by changes in gene expression. Given their widespread influence, dysfunction in mast cells can contribute to a variety of pathologies including allergies, long COVID, and autoimmune and neuroinflammatory disorders. Despite this, the specific transcriptional mechanisms that control mast cell mediator release remain poorly understood, significantly hindering the development of effective therapeutic strategies. We found that the two proteins encoded by the transcription factor FosB, FOSB and the highly stable variant ΔFOSB, are robustly expressed upon stimulation in both murine and human mast cell progenitors. Motivated by these findings, we generated a novel mouse model with targeted ablation of FosB gene expression specifically in mast cells (MC FosB- ) by crossing a mast cell-specific Cre reporter line (Mcpt5-Cre) with a Cre-dependent floxed FosB mouse lines. We found that mast cell progenitors derived from MC FosB- mice, compared to wild types (WT), exhibit baseline increased histamine content and vesicle numbers. Additionally, they show enhanced calcium mobilization, degranulation, and histamine release following allergy-related IgE-mediated stimulation, along with heightened IL-6 release in response to infection-like LPS stimulation. In vivo experiments with IgE- mediated and LPS challenges revealed that MC FosB- mice experience greater drops in body temperature, heightened activation of tissue-resident mast cells, and increased release of pro-inflammatory mediators compared to their WT counterparts. These findings suggest that FosB products play a crucial regulatory role in moderating stimulus-induced mast cell activation in response to both IgE and LPS stimuli. Lastly, by integrating CUT&RUN and RNAseq data, we identified several genes targeted by ΔFOSB that could mediate these observed effects, including Mir155hg, CLCF1, DUSP4, and Trib1. Together, this study provides the first evidence that FOSB/ΔFOSB modulate mast cell functions and provides a new possible target for therapeutic interventions aimed at ameliorating mast cell-related diseases.

Patient-reported allergies are associated with increased rate of postoperative stiffness after arthroscopic rotator cuff repair

BACKGROUND

Several risk factors have been identified for the development of postoperative shoulder stiffness, and there has been increasing interest in orthopedic literature regarding patient-reported allergy (PRA) as an identifiable risk factor for adverse outcomes. The purpose of this study is to determine whether PRAs are associated with subsequent rates of diagnosis of adhesive capsulitis (AC) or return to the operating room for postoperative shoulder stiffness within 2 years after arthroscopic rotator cuff repair (ARCR).

METHODS

Current Procedural Terminology surgical billing codes were used to retrospectively identify patients who underwent ARCR at a single urban academic institution from January 2012 to December 2020 with minimum 2-year follow-up. Lysis of adhesions (LOA), manipulation under anesthesia (MUA), and AC of the shoulder were further queried within 2 years postoperatively for the ipsilateral shoulder. Patients were excluded if they had undergone ipsilateral MUA/LOA or received a diagnosis of AC before the index procedure. Demographic characteristics and medical comorbidities (hypertension, diabetes, hyperlipidemia, and hypothyroidism) were extracted from electronic medical records. Baseline characteristics were compared between patients with and without PRAs. Multivariate logistic regression analyses were performed to determine the association of the presence of PRAs overall, as well as the presence of 1, 2, or 3 or more PRAs, with subsequent MUA/LOA or diagnosis of AC within 2 years postoperatively.

RESULTS

Of 7057 patients identified in the study period, 6583 were eligible for the final analysis. The mean age was 56.6 ± 11.7 years, and the mean body mass index was 29.1 ± 5.6. Overall, 19.3% of patients (n = 1271) reported at least 1 allergy, and 7.1% (n = 469) had >1 PRA. A total of 44 patients (0.7%) underwent subsequent ipsilateral MUA/LOA within 2 years postoperatively, whereas 93 patients (1.4%) received a diagnosis of ipsilateral AC in the same time frame. PRAs were significantly associated with subsequent diagnosis of AC (odds ratio [OR]: 2.39; 95% confidence interval [CI]: 1.45-3.92; P < .001), but not MUA/LOA (OR: 1.97, 95% CI: 1.26-3.61; P = .133). Patients with 2 PRAs had greater odds of being diagnosed with AC than patients with 1 PRA (OR: 2.74; 95% CI: 1.14-5.99; P = .012). Although this association was nonsignificant for MUA/LOA, patients with 2 PRAs (OR: 2.67; 95% CI: 0.96-8.80; P = .059) demonstrated a similar statistical trend.

CONCLUSION

PRAs are associated with increased odds of receiving a diagnosis of AC within 2 years after ARCR but were not found to be associated with return to the operating room for postoperative stiffness.

Molecular and Cellular Heterogeneity in Rheumatoid Arthritis: Mechanisms and Clinical Implications

Rheumatoid arthritis is an autoimmune disease that exhibits significant clinical heterogeneity. There are various treatments for rheumatoid arthritis, including disease-modifying anti-rheumatic drugs (DMARDs), glucocorticoids, non-steroidal anti-inflammatory drugs (NSAIDs), and inflammatory cytokine inhibitors (ICI), typically associated with differentiated clinical effects and characteristics. Personalized responsiveness is observed to the standard treatment due to the pathophysiological heterogeneity in rheumatoid arthritis, resulting in an overall poor prognosis. Understanding the role of individual variation in cellular and molecular mechanisms related to rheumatoid arthritis will considerably improve clinical care and patient outcomes. In this review, we discuss the source of pathophysiological heterogeneity derived from genetic, molecular, and cellular heterogeneity and their possible impact on precision medicine and personalized treatment of rheumatoid arthritis. We provide emphasized description of the heterogeneity derived from mast cells, monocyte cell, macrophage fibroblast-like synoviocytes and, interactions within immune cells and with inflammatory cytokines, as well as the potential as a new therapeutic target to develop a novel treatment approach. Finally, we summarize the latest clinical trials of treatment options for rheumatoid arthritis and provide a suggestive framework for implementing preclinical and clinical experimental results into clinical practice.

Mast Cells as Important Regulators in Autoimmunity and Cancer Development

Mast cells are an essential part of the immune system and are best known as important modulators of allergic and anaphylactic immune responses. Upon activation, mast cells release a multitude of inflammatory mediators with various effector functions that can be both protective and damage-inducing. Mast cells can have an anti-inflammatory or pro-inflammatory immunological effect and play important roles in regulating autoimmune diseases including rheumatoid arthritis, type 1 diabetes, and multiple sclerosis. Importantly, chronic inflammation and autoimmunity are linked to the development of specific cancers including pancreatic cancer, prostate cancer, colorectal cancer, and gastric cancer. Inflammatory mediators released from activated mast cells regulate immune responses and promote vascular permeability and the recruitment of immune cells to the site of inflammation. Mast cells are present in increased numbers in tissues affected by autoimmune diseases as well as in tumor microenvironments where they co-localize with T regulatory cells and T effector cells. Mast cells can regulate immune responses by expressing immune checkpoint molecules on their surface, releasing anti-inflammatory cytokines, and promoting vascularization of solid tumor sites. As a result of these immune modulating activities, mast cells have disease-modifying roles in specific autoimmune diseases and cancers. Therefore, determining how to regulate the activities of mast cells in different inflammatory and tumor microenvironments may be critical to discovering potential therapeutic targets to treat autoimmune diseases and cancer.

Regulation of osteoclastogenesis by mast cell in rheumatoid arthritis

Background

In the pathogenesis of rheumatoid arthritis (RA), the role of mast cells has not been revealed clearly. We aimed to define the inflammatory and tissue-destructive roles of mast cells in rheumatoid arthritis (RA).

Methods

Serum and synovial fluid (SF) concentration levels of tryptase, chymase, and histamine were quantified using ELISA. After activating mast cells using IL-33, the production of TNF-α, IL-1β, IL-6, IL-17, RANKL, and MMPs was determined using real-time PCR and ELISA. Osteoclastogenesis was assessed in CD14+ monocytes from peripheral blood and SF, which were cultured with IL-33-activated mast cells, by counting TRAP-positive multinucleated cells.

Results

The concentration levels of serum tryptase, chymase, and histamine and SF histamine were higher in patients with RA than in controls. FcεR1 and c-kit-positive mast cells were higher in RA synovium than in osteoarthritic (OA) synovium. Stimulation of mast cells by IL-33 increased the number of trypatse+chymase− and tryptase+chymase+ mast cells. IL-33 stimulation also increased the gene expression levels of TNF-α, IL-1β, IL-6, IL-17, RANKL, and MMP-9 in mast cells. Furthermore, IL-33 stimulated human CD14+ monocytes to differentiate into TRAP+ multinucleated osteoclasts. When CD14+ monocytes were co-cultured with mast cells, osteoclast differentiation was increased. Additionally, IL-33-activated mast cells stimulated osteoclast differentiation. The inhibition of intercellular contact between mast cells and monocytes using inserts reduced osteoclast differentiation.

Conclusions

IL-33 increased inflammatory and tissue-destructive cytokines by activation of mast cells. Mast cells stimulated osteoclast differentiation in monocytes. Mast cells could stimulate osteoclastogenesis indirectly through production of tissue-destructive cytokines and directly through stimulation of osteoclast precursors.

Chemerin 156F, generated by chymase cleavage of prochemerin, is elevated in joint fluids of arthritis patients

BACKGROUND

Chemerin is a chemoattractant involved in immunity that also functions as an adipokine. Chemerin is secreted as an inactive precursor (chem163S), and its activation requires proteolytic cleavages at its C-terminus, involving proteases in coagulation, fibrinolysis, and inflammation. Previously, we found chem158K was the dominant chemerin form in synovial fluids from patients with arthritis. In this study, we aimed to characterize a distinct cleaved chemerin form, chem156F, in osteoarthritis (OA) and rheumatoid arthritis (RA).

METHODS

Purified chem156F was produced in transfected CHO cells. To quantify chem156F in OA and RA samples, we developed a specific ELISA for chem156F using antibody raised against a peptide representing the C-terminus of chem156F.

RESULTS

Ca²⁺ mobilization assays showed that the EC₅₀ values for chem163S, chem156F, and chem157S were 252 ± 141 nM, 133 ± 41.5 nM, and 5.83 ± 2.48 nM, respectively. chem156F was more active than its precursor, chem163S, but very much less potent than chem157S, the most active chemerin form. Chymase was shown to be capable of cleaving chem163S at a relevant rate. Using the chem156F ELISA we found a substantial amount of chem156F present in synovial fluids from patients with OA and RA, 24.06 ± 5.51 ng/ml and 20.35 ± 5.19 ng/ml (mean ± SEM, n = 25) respectively, representing 20% of total chemerin in OA and 76.7% of chemerin in RA synovial fluids.

CONCLUSIONS

Our data show that chymase cleavage of chem163S to partially active chem156F can be found in synovial fluids where it can play a role in modulation of the inflammation in joints.

Angiogenic Factors produced by Hypoxic Cells are a leading driver of Anastomoses in Sprouting Angiogenesis-a computational study

Angiogenesis - the growth of new blood vessels from a pre-existing vasculature - is key in both physiological processes and on several pathological scenarios such as cancer progression or diabetic retinopathy. For the new vascular networks to be functional, it is required that the growing sprouts merge either with an existing functional mature vessel or with another growing sprout. This process is called anastomosis. We present a systematic 2D and 3D computational study of vessel growth in a tissue to address the capability of angiogenic factor gradients to drive anastomosis formation. We consider that these growth factors are produced only by tissue cells in hypoxia, i.e. until nearby vessels merge and become capable of carrying blood and irrigating their vicinity. We demonstrate that this increased production of angiogenic factors by hypoxic cells is able to promote vessel anastomoses events in both 2D and 3D. The simulations also verify that the morphology of these networks has an increased resilience toward variations in the endothelial cell's proliferation and chemotactic response. The distribution of tissue cells and the concentration of the growth factors they produce are the major factors in determining the final morphology of the network.

Mast Cell-Intervertebral disc cell interactions regulate inflammation, catabolism and angiogenesis in Discogenic Back Pain

Low back pain (LBP) is a widespread debilitating disorder of significant socio-economic importance and intervertebral disc (IVD) degeneration has been implicated in its pathogenesis. Despite its high prevalence the underlying causes of LBP and IVD degeneration are not well understood. Recent work in musculoskeletal degenerative diseases such as osteoarthritis have revealed a critical role for immune cells, specifically mast cells in their pathophysiology, eluding to a potential role for these cells in the pathogenesis of IVD degeneration. This study sought to characterize the presence and role of mast cells within the IVD, specifically, mast cell-IVD cell interactions using immunohistochemistry and 3D in-vitro cell culture methods. Mast cells were upregulated in painful human IVD tissue and induced an inflammatory, catabolic and pro-angiogenic phenotype in bovine nucleus pulposus and cartilage endplate cells at the gene level. Healthy bovine annulus fibrosus cells, however, demonstrated a protective role against key inflammatory (IL-1β and TNFα) and pro-angiogenic (VEGFA) genes expressed by mast cells, and mitigated neo-angiogenesis formation in vitro. In conclusion, mast cells can infiltrate and elicit a degenerate phenotype in IVD cells, enhancing key disease processes that characterize the degenerate IVD, making them a potential therapeutic target for LBP.

Yohimbine hydrochloride ameliorates collagen type-II-induced arthritis targeting oxidative stress and inflammatory cytokines in Wistar rats

Rheumatoid arthritis (RA) is the most common type of chronic inflammatory disease which is triggered by dysfunction in the immune system which in turn affects synovial joints. Current treatment of RA with NSAIDs and DMRDs is limited by their side effect. As a result, the interest in alternative, well tolerated anti-inflammatory remedies has re-emerged. Our aim was to evaluate the antioxidant and anti-inflammatory activities underlying the anti-RA effect of Yohimbine hydrochloride (YCL) in collagen induced arthritis (CIA) in Wistar rats. The YCL was administered at doses of 5 and 10 mg kg^-1 body weight once daily for 28 days. The effects of treatment in the rats were assessed by biochemical parameter (articular elastase, LPO, GSH, catalase, SOD), hematological parameter (ESR, WBC, C-reactive protein (CRP), immunohistochemical expression (COX2, TNF-α, and NF-κB), and histological changes in joints. YCL showed anti-RA efficacy as it significantly reduced articular elastase, LPO and catalase level and ameliorates histological changes. This is in addition to its antioxidant efficacy as YCL shown a significant increase in GSH and SOD level. Also, YCL showed effective anti-inflammatory activity as it significantly decreased the expression of COX-2, TNF-α, and NF-ĸB. The therapeutic effect of YCL against RA was also evident from lower arthritis scoring and reduced hematological parameter (ESR, WBC, and C-reactive protein level). The abilities to inhibit proinflammatory cytokines and modulation of antioxidant states that the protective effect of YCL on arthritis rats might be mediated via the modulation of the immune system. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 619-629, 2017.

Prostaglandin D2 metabolites as a biomarker of in vivo mast cell activation in systemic mastocytosis and rheumatoid arthritis

Mast cells (MCs) participate in diseases such as systemic mastocytosis (SM) and allergic conditions. Less well understood is the role of MCs in non‐allergic inflammatory disorders like rheumatoid arthritis (RA). Studying definitive roles for MCs in human diseases has been hampered by the lack of a well‐accepted biomarker for monitoring in vivo MC activation. This study aimed to investigate the utility of urinary tetranor PGDM (T‐PGDM) as a biomarker of in vivo MC activation in patients with SM, and apply this biomarker to assess MC involvement in relation to RA disease activity. A prospective, cross‐sectional cohort study was conducted to measure a major urinary metabolite of prostaglandin D₂, T‐PGDM. Urine samples were collected from patients with RA (n = 60), SM (n = 17) and healthy normal controls (n = 16) and T‐PGDM excretion was determined by enzyme immunoassay as nanograms per milligram of urinary creatinine (ng/mg Cr). Mean urinary T‐PGDM excretion was significantly higher (p < 0.01) in patients with SM compared to controls (37.2 vs. 11.5 ng/mg Cr) with 65% of SM patients showing elevated levels. One third of patients with RA had elevated T‐PGDM excretion, and the mean level in the RA group (20.0 ng/mg Cr) was significantly higher than controls (p < 0.01). Medications inhibiting cyclooxygenase reduced T‐PGDM excretion. Urinary T‐PGDM excretion appears promising as a biomarker of in vivo MC activity and elevated levels in 33% of patients with RA provides evidence of MC activation in this disease.

DNA methylation: roles in rheumatoid arthritis

Rheumatoid arthritis (RA) is an immune-mediated disease of unknown cause that primarily affects the joints and ultimately leads to joint destruction. In recent years, the potential role of DNA methylation in the development of RA is raising great expectations among clinicians and researchers. DNA methylation influences diverse aspects of the disease and regulates epigenetic silencing of genes and behavior of several cell types, especially fibroblast-like synoviocytes (FLS), the most resident cells in joints. The activation of FLS is generally regarded as a key process in the development of RA that actively results in the promotion of ongoing inflammation and joint damage. It has also been shown that aberrant DNA methylation occurs in the pathogenesis of RA and contributes to the development of the disease. Recently, there has been an impressive increase in studies involving DNA methylation in RA. In this paper, we consider the role of DNA methylation in the development of RA.

Orchestration of angiogenesis by immune cells

It is widely accepted that the tumor microenvironment (TUMIC) plays a major role in cancer and is indispensable for tumor progression. The TUMIC involves many "players" going well beyond the malignant-transformed cells, including stromal, immune, and endothelial cells (ECs). The non-malignant cells can acquire tumor-promoting functions during carcinogenesis. In particular, these cells can "orchestrate" the "symphony" of the angiogenic switch, permitting the creation of new blood vessels that allows rapid expansion and progression toward malignancy. Considerable attention within the context of tumor angiogenesis should focus not only on the ECs, representing a fundamental unit, but also on immune cells and on the inflammatory tumor infiltrate. Immune cells infiltrating tumors typically show a tumor-induced polarization associated with attenuation of anti-tumor functions and generation of pro-tumor activities, among these angiogenesis. Here, we propose a scenario suggesting that the angiogenic switch is an immune switch arising from the pro-angiogenic polarization of immune cells. This view links immunity, inflammation, and angiogenesis to tumor progression. Here, we review the data in the literature and seek to identify the "conductors" of this "orchestra." We also suggest that interrupting the immune → inflammation → angiogenesis → tumor progression process can delay or prevent tumor insurgence and malignant disease.

Identification of microRNAs regulating the developmental pathways of bone marrow derived mast cells

Background

MicroRNAs (miRNAs) play important roles in leukocyte differentiation, although those utilised for specific programs and key functions remain incompletely characterised. As a global approach to gain insights into the potential regulatory role of miRNA in mast cell differentiation we characterised expression in BM cultures from the initiation of differentiation. In cultures enriched in differentiating mast cells we characterised miRNA expression and identified miRNA targeting the mRNA of putative factors involved in differentiation pathways and cellular identity. Detailed pathway analysis identified a unique miRNA network that is intimately linked to the mast cell differentiation program.

Methodology/Principal Findings

We identified 86 unique miRNAs with expression patterns that were up- or down- regulated at 5-fold or more during bone marrow derived mast cells (BMMC) development. By employing TargetScan and MeSH databases, we identified 524 transcripts involved in 30 canonical pathways as potentially regulated by these specific 86 miRNAs. Furthermore, by applying miRanda and IPA analyses, we predict that 7 specific miRNAs of this group are directly associated with the expression of c-Kit and FcεRIα and likewise, that 18 miRNAs promote expression of Mitf, GATA1 and c/EBPα three core transcription factors that direct mast cell differentiation. Furthermore, we have identified 11 miRNAs that may regulate the expression of STATs-3, -5a/b, GATA2 and GATA3 during differentiation, along with 13 miRNAs that target transcripts encoding Ndst2, mMCP4 and mMCP6 and thus may regulate biosynthesis of mast cell secretory mediators.

Conclusions/Significance

This investigation characterises changes in miRNA expression in whole BM cultures during the differentiation of mast cells and predicts functional links between miRNAs and their target mRNAs for the regulation of development. This information provides an important resource for further investigations of the contributions of miRNAs to mast cell differentiation and function.

Tryptase inhibitor APC 366 prevents hepatic fibrosis by inhibiting collagen synthesis induced by tryptase/protease-activated receptor 2 interactions in hepatic stellate cells

Protease-activated receptor (PAR) 2 is a G-protein-coupled receptor that is activated by mast cell tryptase. PAR-2 activation augments profibrotic pathways through the induction of extracellular matrix proteins. PAR-2 is widely expressed in hepatic stellate cells (HSCs), but the role of tryptase/PAR-2 interaction in liver fibrosis is unclear. We studied the development of bile duct ligation (BDL)-induced hepatic fibrosis in rats treated with mast cell tryptase inhibitor APC 366, and showed that APC 366 reduced hepatic fibrosis scores, collagen content and serum biochemical parameters. Reduced fibrosis was associated with decreased expression of PAR-2 and α-smooth muscle actin (α-SMA). Our findings demonstrate that mast cell tryptase induces PAR-2 activation to augment HSC proliferation and promote hepatic fibrosis in rats. Treatment with tryptase antagonists may be a novel therapeutic approach to prevent fibrosis in patients with chronic liver disease.

A focus on mast cells and pain

Mast cells (MCs) are immunocytes with secretory functions that act locally in peripheral tissues to modulate local hemodynamics, nociceptor activation and pain. They are also able to infiltrate the central nervous system (CNS), especially the spinal cord and the thalamus, but their cerebral function remains an enigma. A role in regulating the opening of the blood-brain barrier has been proposed. Paracrine-like action of MCs on synaptic transmission might also signal a modulation of the nervous system by the immune system. In this review, we examine the link between MCs and nociceptive process, at the periphery as well as in the CNS.

The role of leukotrienes in immunopathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder of joints for which there is no strict cure. However, conventional medications can reduce inflammation, relieve pain, and slow joint damage. Leukotrienes are a family of paracrine agents derived from oxidative metabolism of arachidonic acid. Synthesis of lipid mediators and subsequent induction of receptor activity are tightly regulated under normal physiological conditions, so that enzyme and/or receptor dysfunction can lead to a variety of clinical signs and symptoms of disease, such as local pain and tissue edema. In these tissues, immunocompetent cells accumulate at the site of injury, contributing to tissue damage and perpetuation of the disease process. Leukotrienes (often leukotriene B4) as potent chemotactic agents can provoke most signs and symptoms in rheumatoid arthritis by initiating, coordinating, sustaining, and amplifying the inflammatory response, through recruitment of leukocytes. A number of studies have reported that pharmacological modulation in this field can significantly attenuate clinical manifestations associated with different inflammatory pathologies.

Mast cells: an expanding pathophysiological role from allergy to other disorders

The mast cells are multi-effector cells with wide distribution in the different body parts and traditionally their role has been well-defined in the development of IgE-mediated hypersensitivity reactions including bronchial asthma. Due to the availability of genetically modified mast cell-deficient mice, the broadened pathophysiological role of mast cells in diverse diseases has been revealed. Mast cells exert different physiological and pathophysiological roles by secreting their granular contents, including vasoactive amines, cytokines and chemokines, and various proteases, including tryptase and chymase. Furthermore, mast cells also synthesize plasma membrane-derived lipid mediators, including prostaglandins and leukotrienes, to produce diverse biological actions. The present review discusses the pathophysiological role of mast cells in different diseases, including atherosclerosis, pulmonary hypertension, ischemia-reperfusion injury, male infertility, autoimmune disorders such as rheumatoid arthritis and multiple sclerosis, bladder pain syndrome (interstitial cystitis), anxiety, Alzheimer's disease, nociception, obesity and diabetes mellitus.

Chemerin activates fibroblast-like synoviocytes in patients with rheumatoid arthritis

Introduction

Chemerin is a chemotactic agonist identified as a ligand for ChemR23 that is expressed on macrophages and dendritic cells (DCs). In this study, we analyzed the expression of chemerin and ChemR23 in the synovium of rheumatoid arthritis (RA) patients and the stimulatory effects of chemerin on fibroblast-like synoviocytes (FLSs) from RA patients.

Methods

Chemerin and ChemR23 expression in the RA synovium was ascertained by immunohistochemistry and Western blot analysis. Chemerin expression on cultured FLSs was analyzed by ELISA. ChemR23 expression on FLSs was determined by immunocytochemistry and Western blot analysis. Cytokine production from FLSs was measured by ELISA. FLS cell motility was evaluated by utilizing a scrape motility assay. We also examined the stimulating effect of chemerin on the phosphorylation of mitogen-activated protein kinase (MAPK), p44/42 mitogen-activated protein kinase (ERK1/2), p38MAPK, c-Jun N-terminal kinase (JNK)1/2 and Akt, as well as on the degradation of regulator of NF-κB (IκBα) in FLSs, by Western blot analysis.

Results

Chemerin was expressed on endothelial cells and synovial lining and sublining cells. ChemR23 was expressed on macrophages, immature DCs and FLSs and a few mature DCs in the RA synovium. Chemerin and ChemR23 were highly expressed in the RA synovium compared with osteoarthritis. Chemerin and ChemR23 were expressed on unstimulated FLSs. TNF-α and IFN-γ upregulated chemerin production. Chemerin enhanced the production of IL-6, chemokine (C-C motif) ligand 2 and matrix metalloproteinase 3 by FLSs, as well as increasing FLS motility. The stimulatory effects of chemerin on FLSs were mediated by activation of ERK1/2, p38MAPK and Akt, but not by JNK1/2. Degradation of IκB in FLSs was not promoted by chemerin stimulation. Inhibition of the ERK1/2, p38MAPK and Akt signaling pathways significantly suppressed chemerin-induced IL-6 production. Moreover, blockade of the p38MAPK and Akt pathways, but not the ERK1/2 pathway, inhibited chemerin-enhanced cell motility.

Conclusions

The interaction of chemerin and ChemR23 may play an important role in the pathogenesis of RA through the activation of FLSs.

Hybrid 18F-FDG PET-MRI of the hand in rheumatoid arthritis: initial results

18F-fluorodeoxyglucose PET (18F-FDG PET) is highly sensitive to inflammatory changes within the synovial tissue in rheumatoid arthritis (RA). However, the highest spatial resolution for soft tissue can be achieved with MRI. Here, we report on the first true hybrid PET-MRI examination of the hand in early RA exploiting the advantages of both modalities. PET-MRI was performed with a prototype of an APD-based magneto-insensitive BrainPET detector (Siemens Healthcare, Erlangen, Germany) operated within a standard 3T MR scanner (MAGNETOM Trio, Siemens). PET images were normalized, random, attenuation and scatter-corrected, iteratively reconstructed and calibrated to yield standardized uptake values (SUV) of 18F-FDG uptake. T1-weighted TSE in coronal as well as sagittal orientation prior to and following Gadolinium administration were acquired. Increased 18F-FDG uptake was present in synovitis and tenovaginitis as identified on contrast-enhanced MRI. The tracer distribution was surrounding the metacarpophalangeal joints II and III. Maximum SUV of 3.1 was noted. In RA, true hybrid 18F-FDG PET-MRI of the hand is technically feasible and bears the potential to directly visualize inflammation.

Pathogenesis, classification and treatment of mastocytosis: state of the art in 2010 and future perspectives

Mastocytosis is a myeloid neoplasm characterized by abnormal accumulation and frequent activation of mast cells (MCs) in various organs. Organ systems typically involved are the bone marrow, skin, liver and gastrointestinal tract. In most adult patients, the systemic form of mastocytosis (SM) is diagnosed, which includes an indolent subvariant, an aggressive subvariant and a leukemic subvariant, also termed MC leukemia. Whereas in pediatric mastocytosis, which is usually confined to the skin, a number of different KIT mutations and other defects may be detected, the KIT mutation D816V is detectable in most (adult) patients with SM. In a subset of these patients, additional oncogenic factors may lead to enhanced survival and growth of MCs and, thus, to advanced SM. Other factors may lead to MC activation, with consecutive anaphylactic reactions that can be severe or even fatal. Treatment of SM usually focuses on symptom relief by histamine receptor antagonists and other supportive therapy. However, in aggressive and leukemic variants, cytoreductive and targeted drugs must be applied. Unfortunately, the prognosis in these patients remains poor, even when treated with novel KIT-targeting agents, polychemotherapy or stem cell transplantation. This article provides a summary of our knowledge on the pathogenesis and on treatment options in SM.

Mast cell proteases: multifaceted regulators of inflammatory disease

Mast cells (MCs) are currently receiving increased attention among the scientific community, largely because of the recent identification of crucial functions for MCs in a variety of disorders. However, it is in many cases not clear exactly how MCs contribute in the respective settings. MCs express extraordinarily high levels of a number of proteases of chymase, tryptase, and carboxypeptidase A type, and these are stored in high amounts as active enzymes in the MC secretory granules. Hence, MC degranulation leads to the massive release of fully active MC proteases, which probably have a major impact on any condition in which MC degranulation occurs. Indeed, the recent generation and evaluation of mouse strains lacking individual MC proteases have indicated crucial contributions of these to a number of different disorders. MC proteases may thus account for many of the effects ascribed to MCs and are currently emerging as promising candidates for treatment of MC-driven disease. In this review, we discuss these findings.

Butrin, isobutrin, and butein from medicinal plant Butea monosperma selectively inhibit nuclear factor-kappaB in activated human mast cells: suppression of tumor necrosis factor-alpha, interleukin (IL)-6, and IL-8

Activation of mast cells in rheumatoid synovial tissue has often been associated with tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-8 production and disease pathogenesis by adjacent cell types. Butea monosperma (BM) is a well known medicinal plant in India and the tropics. The aim of this study was to examine whether a standardized extract of BM flower (BME) could inhibit inflammatory reactions in human mast cells (HMC) using activated HMC-1 cells as a model. Four previously characterized polyphenols--butrin, isobutrin, isocoreopsin, and butein--were isolated from BME by preparative thin layer chromatography, and their purity and molecular weights were determined by liquid chromatography/mass spectrometry analysis. Our results showed that butrin, isobutrin, and butein significantly reduced the phorbol 12-myristate 13-acetate and calcium ionophore A23187-induced inflammatory gene expression and production of TNF-alpha, IL-6, and IL-8 in HMC-1 cells by inhibiting the activation of NF-kappaB. In addition, isobutrin was most potent in suppressing the NF-kappaB p65 activation by inhibiting IkappaBalpha degradation, whereas butrin and butein were relatively less effective. In vitro kinase activity assay revealed that isobutrin was a potent inhibitor of IkappaB kinase complex activity. This is the first report identifying the molecular basis of the reported anti-inflammatory effects of BME and its constituents butrin, isobutrin, and butein. The novel pharmacological actions of these polyphenolic compounds indicate potential therapeutic value for the treatment of inflammatory and other diseases in which activated mast cells play a role.

Mast cells: novel clinical perspectives from recent insights

Mast cells are still generally viewed as mediators of type I allergic or pseudoallergic reactions. Research over the past 10 years revealed that our view was too small and that mast cells are of key importance in innate immunity and also types II, III and IV adaptive immune reactions. Understanding their role in modulating and amplifying of inflammatory responses provides important insights into the pathogenesis of skin diseases such as psoriasis, atopic dermatitis, bullous pemphigoid or the control of infections. This helps us to understand the course of these diseases, their trigger mechanisms, and, the new role of agents, which can modulate the function of mast cells. These insights will help to develop new therapeutic approaches.

Involvement of CD44 in mast cell proliferation during terminal differentiation

By using the recently established culture system that reproduces the terminal differentiation process of connective tissue-type mast cells, we found significant transcriptional induction of CD44. As CD44 is a primary receptor for hyaluronan (HA), which is one of the major extracellular matrix components, we investigated the role of CD44 in cutaneous mast cells. When co-cultured with fibroblasts, mouse bone marrow-derived cultured mast cells (BMMCs) were found to form clusters in an HA-dependent manner. As compared with BMMCs derived from the wild-type mice, those from the CD44(-/-) mice exhibited impaired growth during the co-cultured period. Furthermore, in the peritoneal cavities and ear tissues, mature mast cells were fewer in number in the CD44(-/-) mice than in the wild-type mice. We investigated roles of CD44 in mast cell proliferation by reconstituting BMMCs into the tissues of mast cell-deficient, Kit(W)/Kit(W-v) mice, and found that the number of metachromatic cells upon acidic toluidine blue staining in the tissues transplanted with CD44(-/-) BMMCs was not significantly changed for 10 weeks, whereas that in the tissues transplanted with the CD44(+/+) BMMCs was significantly increased. These results suggest that CD44 plays a crucial role in the regulation of the cutaneous mast cell number.

Polyphenol-rich pomegranate fruit extract (POMx) suppresses PMACI-induced expression of pro-inflammatory cytokines by inhibiting the activation of MAP Kinases and NF-kappaB in human KU812 cells

BACKGROUND

Mast cells and basophils are multifunctional effector cells and contain plentiful secretary granules in their cytoplasm. These cell types are involved in several inflammatory and immune events and are known to produce an array of mediators including a broad spectrum of cytokines. Pomegranate fruit is rich in anthocyanins and hydrolysable tannins; a group of polyphenolic compounds shown to be potent antioxidant with anti-inflammatory activity. However, no studies have been undertaken to investigate whether a polyphenol-rich pomegranate fruit extract (POMx) inhibits the inflammatory activity of activated human mast cells and basophils. The aim of this study was to examine whether POMx modulates inflammatory reactions using human basophilic cell line KU812.

METHODS

KU812 cells were stimulated with phorbol-12-myristate 13-acetate plus calcium inophore A23187 (PMACI). The inhibitory effect of POMx on pro-inflammatory cytokine gene expression and production by stimulated KU812 cells was measured by quantitative RT-PCR, and cytokine-specific ELISA assays, respectively. Western blotting was used to analyze the effect of POMx on the activation of mitogen-activated protein kinases (MAPKs), and the nuclear factor (NF)-kappaB in PMACI stimulated KU812 cells. Effect on the activity of NF-kappaB was determined using Luciferase reporter assay. Significance of differences from control values were analyzed by means of standard statistical methods.

RESULTS

POMx significantly decreased PMACI stimulated inflammatory gene expression and production of interleukin (IL)-6 and IL-8 in KU812 cells. The inhibitory effect of POMx on the pro-inflammatory cytokines was MAPK subgroups c-jun N-terminal kinase (JNK)- and extracellular-regulated kinase (ERK) dependent. In addition, POMx suppressed the NF-kappaB activation induced by PMACI by inhibiting IkappaB-degradation in human basophil cells. POMx also suppressed the powerful induction of NF-kappaB promoter-mediated luciferase activity in transiently transfected KU812 cells.

CONCLUSION

These novel pharmacological actions of POMx provide new suggestion that POMx or POMx-derived compounds may be of therapeutic use for the treatment of inflammatory diseases by suppressing mast cells/basophils activation.

Mast cell chymase contributes to the antibody response and the severity of autoimmune arthritis

Mast cells are implicated in rheumatoid arthritis, but the mechanism by which they contribute to disease progression is not clarified. Here we investigated whether mouse mast cell protease-4 (mMCP-4), a chymase present in the mast cell secretory granule, contributes to experimental arthritis. Two models of arthritis were investigated in mMCP-4(+/+) and mMCP-4(-/-) DBA/1 mice: collagen-induced arthritis (CIA) was induced by immunization with collagen II (CII) in Freund's complete adjuvant, and a passive model of arthritis was induced by administration of anti-CII antibodies. The clinical scores were significantly reduced in the mMCP-4(-/-) animals as compared to mMCP-4(+/+) controls in both arthritis models. In CIA, the number of affected paws was lower in the CII-immunized mMCP-4(-/-) mice, with less cartilage destruction, pannus formation, and mononuclear cell and mast cell influx in the mMCP-4(-/-) joints. Interestingly, the lower clinical scores in the CII-immunized mMCP-4(-/-) mice coincided with lower serum levels of immunoglobulin G anti-CII antibodies. Our findings identify a pathogenic role of mMCP-4 in autoimmune arthritis.

Dramatic regulation of heparanase activity and angiogenesis gene expression in synovium from patients with rheumatoid arthritis

OBJECTIVE

Although heparanase is recognized as a proangiogenic factor, the involvement of heparanase in rheumatoid arthritis (RA) is unclear. In this study, we assessed heparanase activity in synovial fluid (SF) and synovial tissue (ST) from patients with RA or osteoarthritis (OA), and analyzed the expression of angiogenic pathway-focused genes in ST from RA and OA patients.

METHODS

SF and ST were obtained from the knees of patients with either RA or OA and from asymptomatic donors with no documented history of degenerative or inflammatory joint diseases. Heparanase activity was determined by an enzymatic assay using a radiolabeled substrate, and the presence of heparanase in ST was demonstrated by Western blotting. The expression of angiogenesis genes, including heparanase, in ST was analyzed by real-time quantitative polymerase chain reaction.

RESULTS

Heparanase activity was dramatically higher (>100-fold) in SF and ST from RA patients than in SF and ST from OA patients and asymptomatic donors. Active heparanase enzyme was detected and heparanase messenger RNA was up-regulated in ST from RA patients. We also found that angiogenesis gene expression was significantly regulated in RA synovium, and was correlated with heparanase activity.

CONCLUSION

These findings are novel and contribute to our understanding of joint destruction in RA, suggesting that heparanase may be a reliable prognostic factor for RA progression and an attractive target for the treatment of RA.

JunB is required for IgE-mediated degranulation and cytokine release of mast cells

Mast cells are effector cells of IgE-mediated immune responses frequently found at the vicinity of blood vessels, the margins of diverse tumors and at sites of potential infection and inflammation. Upon IgE-mediated stimulation, mast cells produce and secrete a broad spectrum of cytokines and other inflammatory mediators. Recent work identified JunB, a member of the AP-1 transcription factor family, as critical regulator of basal and induced expression of inflammatory mediators in fibroblasts and T cells. To study the impact of JunB on mast cell biology, we analyzed JunB-deficient mast cells. Mast cells lacking JunB display a normal in vivo maturation, and JunB-deficient bone marrow cells in vitro differentiated to mast cells show no alterations in proliferation or apoptosis. But these cells exhibit impaired IgE-mediated degranulation most likely due to diminished expression of SWAP-70, Synaptotagmin-1, and VAMP-8, and due to impaired influx of extracellular calcium. Moreover, JunB-deficient bone marrow mast cells display an altered cytokine expression profile in response to IgE stimulation. In line with these findings, the contribution of JunB-deficient mast cells to angiogenesis, as analyzed in an in vitro tube formation assay on matrigel, is severely impaired due to limiting amounts of synthesized and secreted vascular endothelial growth factor. Thus, JunB is a critical regulator of intrinsic mast cell functions including cross-talk with endothelial cells.

Angiogenesis and chronic inflammation: cause or consequence?

Evidence has been gathered regarding the association between angiogenesis and inflammation in pathological situations. These two phenomena have long been coupled together in many chronic inflammatory disorders with distinct etiopathogenic origin, including psoriasis, rheumatoid arthritis, Crohn's disease, diabetes, and cancer. Lately, this concept has further been substantiated by the finding that several previously established non-inflammatory disorders, such as osteoarthritis and obesity, display both inflammation and angiogenesis in an exacerbated manner. In addition, the interplay between inflammatory cells, endothelial cells and fibroblasts in chronic inflammation sites, together with the fact that inflammation and angiogenesis can actually be triggered by the same molecular events, further strengthen this association. Therefore, elucidating the underlying cellular and molecular mechanisms that gather together the two processes is mandatory in order to understand their synergistic effect, and to develop new therapeutic approaches for the management of these disorders that cause a great deal of discomfort, disability, and in some cases death.