Mast cells at sites of cartilage erosion in the rheumatoid joint

Distinct mast cell subpopulations within and around lymphatic vessels regulate lymph flow and progression of inflammatory-erosive arthritis in TNF-transgenic mice

Objective

Inflammatory-erosive arthritis is exacerbated by dysfunction of joint-draining popliteal lymphatic vessels (PLVs). Synovial mast cells are known to be pro-inflammatory in rheumatoid arthritis (RA). In other settings they have anti-inflammatory and tissue reparative effects. Herein, we elucidate the role of mast cells on PLV function and inflammatory-erosive arthritis in tumor necrosis factor transgenic (TNF-tg) mice that exhibit defects in PLVs commensurate with disease progression.

Methods

Whole mount immunofluorescent microscopy, toluidine blue stained histology, scanning electron microscopy, and in silico bioinformatics were performed to phenotype and quantify PLV mast cells. Ankle bone volumes were assessed by μCT, while corresponding histology quantified synovitis and osteoclasts. Near-infrared indocyanine green imaging measured lymphatic clearance as an outcome of PLV draining function. Effects of genetic MC depletion were assessed via comparison of 4.5-month-old WT, TNF-tg, MC deficient KitW-sh/W-sh (cKit-/-), and TNF-tg x cKit-/- mice. Pharmacological inhibition of mast cells was assessed by treating TNF-tg mice with placebo or cromolyn sodium (3.15mg/kg/day) for 3-weeks.

Results

PLVs are surrounded by MCT+/MCPT1+/MCPT4+ mast cells whose numbers are increased 2.8-fold in TNF-tg mice. The percentage of peri-vascular degranulating mast cells was inversely correlated with ICG clearance. A population of MCT+/MCPT1-/MCPT4- mast cells were embedded within the PLV structure. In silico single-cell RNA-seq (scRNAseq) analyses identified a population of PLV-associated mast cells (marker genes: Mcpt4, Cma1, Cpa3, Tpsb2, Kit, Fcer1a & Gata2) with enhanced TGFβ-related signaling that are phenotypically distinct from known MC subsets in the Mouse Cell Atlas. cKit-/- mice have greater lymphatic defects than TNF-tg mice with exacerbation of lymphatic dysfunction and inflammatory-erosive arthritis in TNF-tg x cKit-/- vs. TNF-Tg mice. Cromolyn sodium therapy stabilized PLV mast cells, increased TNF-induced bone loss, synovitis, and osteoclasts, and decreased ICG clearance.

Conclusions

Mast cells are required for normal lymphatic function. Genetic ablation and pharmacological inhibition of mast cells exacerbates TNF-induced inflammatory-erosive arthritis with decreased lymphatic clearance. Together, these findings support an inflammatory role of activated/degranulated peri-PLV mast cells during arthritic progression, and a homeostatic role of intra-PLV mast cells, in which loss of the latter dominantly exacerbates arthritis secondary to defects in joint-draining lymphatics, warranting investigation into specific cellular mechanisms.

Scientific validation of anti-arthritic effect of Kashayams - A polyherbal formulation in collagen induced arthritic rats

BACKGROUND

Toll-like receptor-4 (TLR-4) mediates activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) resulting in induction of proinflammatory genes such as that encoding tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) which played a significant role in cartilage destruction of rheumatoid arthritis (RA). Low risk and better efficacy made herbal drugs more reliable than nonsteroid anti-inflammatory drugs (NSAIDS) in RA treatment. Gugguluthiktam Kashayam (GuK), Punarnavadi Kashayam (PuK) and Balaguluchiadi Kashayam (BgK) are ayurvedic polyherbal formulations prescribed in classical ayurvedic texts Sahasrayogam and Ashtangahridayam as medicines for the treatment of RA.

OBJECTIVE

The objective of the present study was to elucidate the molecular mechanism of anti-arthritic effect of these Kashayams on TLR-4 signal transduction pathway in collagen induced arthritic rats.

MATERIAL AND METHODS

The wistar rats grouped into group I - Normal, group II- Collagen induced arthritis (CIA), group III- CIA + BgK, group IV- CIA + PuK, group V- CIA + GuK, group VI - CIA + Indomethacin (3 mg/kg b.wt.). Treatment with Kashayam (2 ml/kg b.wt) started after 14 days of primary immunization with type II collagen and continued for a period of 45 days.

RESULTS

Arthritis index, C-reactive protein (CRP), rheumatoid factor (RF) and myeloperoxidase (MPO) in serum and protein level of TLR-4, myeloid differentiation factor 88 (MYD88), NF-κB, TNF-α, IL-1β, inducible nitric oxide synthase (iNOS), cyclooxygenase-2 COX-2) and prostaglandin E-2 (PGE-2) in cartilage were significantly elevated in CIA rats. Further, treatment with Kashayams downregulated all these inflammatory mediators hitherto TLR-4-NF-kB signal transduction pathway except IL-10, an anti-inflammatory cytokine which showed a reverse effect.

CONCLUSION

This molecular mechanism of the investigation confirmed the clinical efficacy of Kashayams in preventing the progression of RA and gave an intuition of the scientific validation of Kashayams, an Ayurvedic classical medicine.

Emerging Roles for MAS-Related G Protein-Coupled Receptor-X2 in Host Defense Peptide, Opioid, and Neuropeptide-Mediated Inflammatory Reactions

Mast cells (MCs) are tissue-resident immune cells that contribute to host defense but are best known for their roles in allergic and inflammatory diseases. In humans, MCs are divided into two subtypes based on the protease content of their secretory granules. Thus, human lung MCs contain only tryptase and are known as MC_T, whereas skin MCs contain both tryptase and chymase and are known as MC_TC. Patients with severe asthma display elevated MCs in the lung, which undergo phenotypic change from MC_T to MC_TC. Although the human genome contains four Mas related G protein coupled receptor X (MRGPRX) genes, an important feature of MC_TC is that they selectively express MRGPRX2. It is activated by antimicrobial host defense peptides such as human β-defensins and the cathelicidin LL-37 and likely contributes to host defense. MRGPRX2 is also a receptor for the neuropeptide substance P, major basic protein, eosinophil peroxidase, opioids, and many FDA-approved cationic drugs. Increased expression of MRGPRX2 or enhanced downstream signaling likely contributes to chronic inflammatory diseases such as rosacea, atopic dermatitis, chronic urticaria, and severe asthma. In this chapter, I will discuss the expression profile and function of MRGPRX1-4 and review the emerging roles of MRGPRX2 on host defense, chronic inflammatory diseases, and drug-induced pseudoallergic reactions. I will also examine the novel aspects of MRGPRX2 signaling in MCs as it related to degranulation and review the mechanisms of its regulation.

Systematic Evaluation of the Cellular Innate Immune Response During the Process of Human Atherosclerosis

Background

The concept of innate immunity is well recognized within the spectrum of atherosclerosis, which is primarily dictated by macrophages. Although current insights to this process are largely based on murine models, there are fundamental differences in the atherosclerotic microenvironment and associated inflammatory response relative to humans. In this light, we characterized the cellular aspects of innate immune response in normal, nonprogressive, and progressive human atherosclerotic plaques.

Methods and Results

A systematic analysis of innate immune response was performed on 110 well‐characterized human perirenal aortic plaques with immunostaining for specific macrophage subtypes (M1 and M2 lineage) and their activation markers, neopterin and human leukocyte antigen–antigen D related (HLA‐DR), together with dendritic cells (DCs), natural killer (NK) cells, mast cells, neutrophils, and eosinophils. Normal aortae were devoid of low‐density lipoprotein, macrophages, DCs, NK cells, mast cells, eosinophils, and neutrophils. Early, atherosclerotic lesions exhibited heterogeneous populations of (CD68⁺) macrophages, whereby 25% were double positive “M1” (CD68⁺/ inducible nitric oxide synthase [iNOS]⁺/CD163⁻), 13% “M2” double positive (CD68⁺/iNOS⁻/CD163⁺), and 17% triple positive for (M1) iNOS (M2)/CD163 and CD68, with the remaining (≈40%) only stained for CD68. Progressive fibroatheromatous lesions, including vulnerable plaques, showed increasing numbers of NK cells and fascin‐positive cells mainly localized to the media and adventitia whereas the M1/M2 ratio and level of macrophage activation (HLA‐DR and neopterin) remained unchanged. On the contrary, stabilized (fibrotic) plaques showed a marked reduction in macrophages and cell activation with a concomitant decrease in NK cells, DCs, and neutrophils.

Conclusions

Macrophage “M1” and “M2” subsets, together with fascin‐positive DCs, are strongly associated with progressive and vulnerable atherosclerotic disease of human aorta. The observations here support a more complex theory of macrophage heterogeneity than the existing paradigm predicated on murine data and further indicate the involvement of (poorly defined) macrophage subtypes or greater dynamic range of macrophage plasticity than previously considered.

Activated mast cells promote differentiation of B cells into effector cells

Based on the known accumulation of mast cells (MCs) in B cell-dependent inflammatory diseases, including rheumatoid arthritis, we hypothesized that MCs directly modulate B cells. We show here that degranulated, and to a lesser extent naïve or IgE-sensitized, MCs activate both naïve and B cell receptor-activated B cells. This was shown by increased proliferation, blast formation, and expression of CD19, MHC class II and CD86 in the B cells. Further, MCs stimulated the secretion of IgM and IgG in IgM⁺ B cells, indicating that MCs can induce class-switch recombination in B cells. We also show that coculture of MCs with B cells promotes surface expression of L-selectin, a homing receptor, on the B cells. The effects of MCs on B cells were partly dependent on cell-cell contact and both follicular and marginal zone B cells could be activated by MCs. Our findings suggest that degranulated MCs support optimal activation of B cells, a finding that is in line with in vivo studies showing that MCs frequently degranulate in the context of B-cell driven pathologies such as arthritis. Together, our findings show that MCs have the capacity to differentiate B cells to effector cells.

Mast cell promotion of T cell-driven antigen-induced arthritis despite being dispensable for antibody-induced arthritis in which T cells are bypassed

OBJECTIVE

The function of mast cells (MCs) in autoimmune disorders has been a subject of controversy recently. MC-deficient Kit(W/W-v) mice were found to be resistant to K/BxN serum-transfer arthritis, whereas Kit(W-sh/W-sh) mice and a genetic model of MC deficiency independent of the Kit mutation were found to be fully susceptible. This debate might lead to the assumption that MCs are dispensable in autoimmunity in general. Thus, the purpose of this study was to examine the relevance of MCs to arthritis using a genetic model of inducible MC deficiency without compromised Kit signaling.

METHODS

We compared MC functions in K/BxN serum-induced arthritis and in collagen-induced arthritis (CIA) in a mouse model of inducible MC deficiency by analyzing joint inflammation, parameters of cartilage degradation and bone erosion, and the autoreactive adaptive immune response.

RESULTS

We observed a redundant role of MCs in K/BxN serum-induced arthritis, where joint inflammation is triggered by cartilage-bound immune complexes independently of T cells. In contrast, we found MCs to be critically relevant in CIA, which is provoked by two arms of autoimmune attack: autoreactive antibodies and effector T cells. In addition to diminished joint inflammation in the absence of MCs, we found a dramatic loss of T cell expansion upon immunization, accompanied by reduced T cell cytokine responses.

CONCLUSION

In this analysis of an arthritis model in which the cellular arm of adaptive immunity was not bypassed, we identified MCs as important promoters of T cell-conditioned autoimmune disorders and, consequently, as potential therapeutic targets in rheumatoid arthritis.

Neuroinflammatory Mechanisms of Connective Tissue Fibrosis: Targeting Neurogenic and Mast Cell Contributions

Significance: The pathogenesis of fibrogenic wound and connective tissue healing is complex and incompletely understood. Common observations across a vast array of human and animal models of fibroproliferative conditions suggest neuroinflammatory mechanisms are important upstream fibrogenic events. Recent Advances: As detailed in this review, mast cell hyperplasia is a common observation in fibrotic tissue. Recent investigations in human and preclinical models of hypertrophic wound healing and post-traumatic joint fibrosis provides evidence that fibrogenesis is governed by a maladaptive neuropeptide-mast cell-myofibroblast signaling pathway. Critical Issues: The blockade and manipulation of these factors is providing promising evidence that if timed correctly, the fibrogenic process can be appropriately regulated. Clinically, abnormal fibrogenic healing responses are not ubiquitous to all patients and the identification of those at-risk remains an area of priority. Future Directions: Ultimately, an integrated appreciation of the common pathobiology shared by many fibrogenic connective tissue conditions may provide a scientific framework to facilitate the development of novel antifibrotic prevention and treatment strategies.

Fc receptor beta chain deficiency exacerbates murine arthritis in the anti-type II collagen antibody-induced experimental model

OBJECTIVE

Fc receptor β chain (FcRβ) acts as a signaling component of FcγRIII in immune cells such as mast cells (MCs) or basophils. Recent studies reported that FcγRIII contributes to the development of arthritic inflammation. These findings suggest that FcRβ may play a pivotal role in the pathogenesis of arthritic inflammation. To address this possibility, we examined the function of FcRβ in arthritic inflammation employing a mouse model.

METHODS

For the induction of arthritis, we injected 2 mg of a cocktail of anti-type II collagen (CII) monoclonal antibodies (mAbs) into C57BL/6J mice (FcRβ(+/+)) and FcRβ(-/-) mice intravenously. Three days later, 100 μg lipopolysaccharide (LPS; Escherichia coli 055:B5) was intraperitoneally injected. Joint swelling was evaluated by inspection. Histopathology of joint tissues was examined by hematoxylin and eosin (H&E) or tartrate-resistant acid phosphatase staining.

RESULTS

Here, we demonstrate in a well-established experimental arthritis model induced by LPS and anti-CII mAbs that FcRβ(-/-) mice exhibit exacerbated arthritic inflammation manifested in paw swelling, leukocyte infiltration into the knee joint, and bone erosion and tissue cytokine expression.

CONCLUSION

Our findings clearly indicate that FcRβ negatively regulates arthritic inflammation in an experimental arthritis model.

Phagocytosis of mast cell granules results in decreased macrophage superoxide production

The mechanism by which phagocytosed mast cell granules (MCGs) inhibit macrophage superoxide production has not been defined. In this study, rat peritoneal macrophages were co-incubated with either isolated intact MCGs or MCG-sonicate, and their respiratory burst capacity and morphology were studied. Co-incubation of macrophages with either intact MCGs or MCG-sonicate resulted in a dose-dependent inhibition of superoxide- mediated cytochrome c reduction. This inhibitory effect was evident within 5 min of incubation and with MCG-sonicate was completely reversed when macrophages were washed prior to activation with PMA. In the case of intact MCGs, the inhibitory effect was only partially reversed by washing after a prolonged co-incubation time. Electron microscopic analyses revealed that MCGs were rapidly phagocytosed by macrophages and were subsequently disintegrated within the phagolysosomes. Assay of MCGs for superoxide dismutase (SOD) revealed the presence of significant activity of this enzyme. A comparison of normal macrophages and those containing phagocytosed MCGs did not reveal a significant difference in total SOD activity. It is speculated that, although there was no significant increase in total SOD activity in macrophages containing phagocytosed MCGs, the phagocytosed MCGs might cause a transient increase in SOD activity within the phagolysosomes. This transient rise in SOD results in scavenging of the newly generated superoxide. Alternatively, MCG inhibition of NADPH oxidase would explain the reported observations.

A 4-trifluoromethyl analogue of celecoxib inhibits arthritis by suppressing innate immune cell activation

Introduction

Celecoxib, a highly specific cyclooxygenase-2 (COX-2) inhibitor has been reported to have COX-2-independent immunomodulatory effects. However, celecoxib itself has only mild suppressive effects on arthritis. Recently, we reported that a 4-trifluoromethyl analogue of celecoxib (TFM-C) with 205-fold lower COX-2-inhibitory activity inhibits secretion of IL-12 family cytokines through a COX-2-independent mechanism that involves Ca²⁺-mediated intracellular retention of the IL-12 polypeptide chains. In this study, we explored the capacity of TFM-C as a new therapeutic agent for arthritis.

Methods

To induce collagen-induced arthritis (CIA), DBA1/J mice were immunized with bovine type II collagen (CII) in Freund's adjuvant. Collagen antibody-induced arthritis (CAIA) was induced in C57BL/6 mice by injecting anti-CII antibodies. Mice received 10 μg/g of TFM-C or celecoxib every other day. The effects of TFM-C on clinical and histopathological severities were assessed. The serum levels of CII-specific antibodies were measured by ELISA. The effects of TFM-C on mast cell activation, cytokine producing capacity by macophages, and neutrophil recruitment were also evaluated.

Results

TFM-C inhibited the severity of CIA and CAIA more strongly than celecoxib. TFM-C treatments had little effect on CII-specific antibody levels in serum. TFM-C suppressed the activation of mast cells in arthritic joints. TFM-C also suppressed the production of inflammatory cytokines by macrophages and leukocyte influx in thioglycollate-induced peritonitis.

Conclusion

These results indicate that TFM-C may serve as an effective new disease-modifying drug for treatment of arthritis, such as rheumatoid arthritis.

Heparin-like heparan sulfate from rabbit cartilage

Glycosaminoglycans were extracted from both young rabbit growth plate (GRP) and articular (ART) cartilage tissues and enzymatically treated to selectively eliminate chondroitin sulfates and hyaluronic acid. The procedure avoided any fractionation step that could enrich the extract with over- or under-sulfated species. Isolated heparan sulfate (HS) was characterized by mono- and bidimensional nuclear magnetic resonance (NMR) spectroscopy to quantify their specific structural features and/or by mass spectrometry to establish the disaccharide composition. Both GRP and ART HSs, despite differing in their yield (GRP at least 100 times greater than ART), exhibited a surprisingly high degree of sulfation. Quantitative two-dimensional heteronuclear single-quantum coherence-NMR analysis of GRP HS revealed unusually high N-sulfated glucosamine and 2-O-sulfated iduronic acid contents, similar to heparin. The unique pentasaccharide sequence of the binding site for antithrombin was also detected in a significant amount. High-performance liquid chromatography mass spectrometry analysis of the enzymatic digests with a cocktail of heparin lyases of both cartilaginous HSs confirmed the NMR results. As well as the discovery of an unusual HS structure in the two different types of rabbit cartilage, the feasibility of the analytical method adopted here has been demonstrated within this study. Such a method can be used to isolate and analyze HS from both normal and pathologic tissues. Characterization of healthy and pathological HS structures will contribute to improve the understanding of diseases related to malfunctions of HS biosynthesis and/or metabolism.

IL-33 exacerbates autoantibody-induced arthritis

Rheumatoid arthritis pathogenesis comprises dysregulation in both innate and adaptive immunity. There is therefore intense interest in the factors that integrate these immunologic pathways in rheumatoid arthritis. In this paper, we report that IL-33, a novel member of the IL-1 family, can exacerbate anti-glucose-6-phosphate isomerase autoantibody-induced arthritis (AIA). Mice lacking ST2 (ST2(-/-)), the IL-33 receptor alpha-chain, developed attenuated AIA and reduced expression of articular proinflammatory cytokines. Conversely, treatment of wild-type mice with rIL-33 significantly exacerbated AIA and markedly enhanced proinflammatory cytokine production. However, IL-33 failed to increase the severity of the disease in mast cell-deficient or ST2(-/-) mice. Furthermore, mast cells from wild-type, but not ST2(-/-), mice restored the ability of ST2(-/-) recipients to mount an IL-33-mediated exacerbation of AIA. IL-33 also enhanced autoantibody-mediated mast cell degranulation in vitro and in synovial tissue in vivo. Together these results demonstrate that IL-33 can enhance autoantibody-mediated articular inflammation via promoting mast cell degranulation and proinflammatory cytokine production. Because IL-33 is derived predominantly from synovial fibroblasts, this finding provides a novel mechanism whereby a host tissue-derived cytokine can regulate effector adaptive immune response via enhancing innate cellular activation in inflammatory arthritis.

The anti-allergic compound tranilast attenuates inflammation and inhibits bone destruction in collagen-induced arthritis in mice

BACKGROUND AND PURPOSE

Recent findings suggest the importance of mast cells in the pathogenesis of rheumatoid arthritis and their potential as a therapeutic target. Tranilast is an anti-allergic compound with a potent membrane-stabilizing effect on mast cells and a wide range of anti-inflammatory effects, thus may be advantageous in the treatment of arthritis. Here, we have evaluated the effects of tranilast on the progression of collagen-induced arthritis in mice.

EXPERIMENTAL APPROACH

Tranilast (400 mg.kg(-1).day(-1)) was orally administered for 8 weeks to mice with established collagen-induced arthritis. Arthritis was assessed by clinical signs and X-ray scores. In paw tissue, the numbers of mast cells and osteoclasts were measured by histological analysis, and several inflammatory factors were assessed by RT-PCR and Western blot analysis.*

KEY RESULTS

TNF-alpha-positive mast cells were present extensively throughout the inflamed synovium of vehicle-treated arthritic mice, with some mast cells in close proximity to osteoclasts in areas of marked bone and cartilage destruction. Tranilast significantly reduced clinical and X-ray scores of arthritis and decreased numbers of TNF-alpha-positive mast cells and mRNA levels of TNF-alpha, chymase (mouse mast cell protease 4), tryptase (mouse mast cell protease 6), stem cell factor, interleukin-6, cathepsin-K, receptor activator of nuclear factor-kappaB, and of receptor activator of nuclear factor-kappaB-ligand, but increased interleukin-10 mRNA level in paws of arthritic mice. Osteoclast numbers were decreased by treatment with tranilast.

CONCLUSIONS AND IMPLICATIONS

Tranilast possesses significant anti-rheumatic efficacy and, probably, this therapeutic effect is partly mediated by inhibition of mast cell activation and osteoclastogenesis.

The mouse mast cell-restricted tetramer-forming tryptases mouse mast cell protease 6 and mouse mast cell protease 7 are critical mediators in inflammatory arthritis

OBJECTIVE

Increased numbers of mast cells (MCs) that express beta tryptases bound to heparin have been detected in the synovium of patients with rheumatoid arthritis (RA). The corresponding tryptases in mice are mouse MC protease 6 (mMCP-6) and mMCP-7. Although MCs have been implicated in RA and some animal models of arthritis, no direct evidence for a MC-restricted tryptase in the pathogenesis of inflammatory arthritis has been shown. We created transgenic mice that lack heparin and different combinations of mMCP-6 and mMCP-7, to evaluate the roles of MC-restricted tryptase-heparin complexes in an experimental model of arthritis.

METHODS

The methylated bovine serum albumin/interleukin-1beta (mBSA/IL-1beta) experimental protocol was used to induce inflammatory monarthritis in different mouse strains. Mice were killed at the time of peak disease on day 7, and histochemical methods were used to assess joint pathology.

RESULTS

Arthritis was induced in the knee joints of mBSA/IL-1beta-treated mMCP-6(+)/mMCP-7(-) and mMCP-6(-)/mMCP-7(+) C57BL/6 mice, and numerous activated MCs that had exocytosed the contents of their secretory granules were observed in the diseased mice. In contrast, arthritis was markedly reduced in heparin-deficient mice and in mMCP-6(-)/mMCP-7(-) C57BL/6 mice.

CONCLUSION

MC-derived tryptase-heparin complexes play important roles in mBSA/IL-1beta-induced arthritis. Because mMCP-6 and mMCP-7 can compensate for each other in this disease model, the elimination of both tryptases is necessary to reveal the prominent roles of these serine proteases in joint inflammation and destruction. Our data suggest that the inhibition of MC-restricted tryptases could have therapeutic potential in the treatment of RA.

IL-33 exacerbates antigen-induced arthritis by activating mast cells

IL-33, a cytokine of the IL-1 family, is closely associated with type II T cell responses. Here, we report an unexpected proinflammatory role of IL-33 in inflammatory arthritis. IL-33 was expressed in synovial fibroblasts from patients with rheumatoid arthritis (RA). Expression was markedly elevated in vitro by inflammatory cytokines. Mice lacking ST2, the IL-33 receptor alpha-chain, developed attenuated collagen-induced arthritis (CIA) and reduced ex vivo collagen-specific induction of proinflammatory cytokines (IL-17, TNFalpha, and IFNgamma), and antibody production. Conversely, treatment of wild-type (WT) but not ST2(-/-) mice with IL-33 exacerbated CIA and elevated production of both proinflammatory cytokines and anti-collagen antibodies. Mast cells expressed high levels of ST2 and responded directly to IL-33 to produce a spectrum of inflammatory cytokines and chemokines in vitro. In vivo, IL-33 treatment exacerbated CIA in ST2(-/-) mice engrafted with mast cells from WT but not from ST2(-/-) mice. Disease exacerbation was accompanied by elevated expression levels of proinflammatory cytokines. Our results demonstrate that IL-33 is a critical proinflammatory cytokine for inflammatory joint disease that integrates fibroblast activation with downstream immune activation mainly via an IL-33-driven, mast-cell-dependent pathway. Thus, this IL-1 superfamily member represents a therapeutic target for RA.

Mast cells and cancer--no longer just basic science

The incorporation of new anti-cancer kinase inhibitors within cancer management is rapidly increasing. Mast cells are sensitive to several of these new anti-cancer agents most notably to c-Kit inhibitors. As a result, studies investigating the role of mast cells in tumors may have direct clinical relevance and consequently, important clinical implications. Here we review some of the basic attributes of mast cells, especially those related to the new "targeted" drugs. Mast cell roles such as modulators of regulatory T-cells, inducers of angiogenesis and promoters of clot formation are discussed. We also review recent mouse tumor models and human pathological data which implicate mast cells as having both pro- and anti-tumor growth properties. These studies expose a complex, emerging picture of mast cell involvement in tumor biology. It seems that mast cell modulator drugs may improve the efficacy of anti-tumor therapy under certain circumstances, whilst under others, may negatively affect drug efficacy.

Synovial mast cells: role in acute and chronic arthritis

Mast cells reside in the normal synovium and increase strikingly in number in rheumatoid arthritis and other joint diseases. Given the broad spectrum of activity of this lineage, it has for decades been considered probable that mast cells are involved in the pathophysiology of synovitis. Recent work in murine arthritis has substantiated this suspicion, showing that mast cells can contribute importantly to the initiation of inflammatory arthritis. However, the role of the greatly expanded population of synovial mast cells in established arthritis remains unknown. Here we review the current understanding of mast cell function in acute arthritis and consider the potentially important influence of this cell on key processes within the chronically inflamed synovium, including leukocyte recruitment and activation, fibroblast proliferation, angiogenesis, matrix remodeling, and injury to collagen and bone. We also consider recent evidence supporting an immunomodulatory or anti-inflammatory role for mast cells as well as pharmacologic approaches to the mast cell as a therapeutic target in inflammatory arthritis.

Selective tyrosine kinase inhibition by imatinib mesylate for the treatment of autoimmune arthritis

Tyrosine kinases play a central role in the activation of signal transduction pathways and cellular responses that mediate the pathogenesis of rheumatoid arthritis. Imatinib mesylate (imatinib) is a tyrosine kinase inhibitor developed to treat Bcr/Abl-expressing leukemias and subsequently found to treat c-Kit-expressing gastrointestinal stromal tumors. We demonstrate that imatinib potently prevents and treats murine collagen-induced arthritis (CIA). We further show that micromolar concentrations of imatinib abrogate multiple signal transduction pathways implicated in RA pathogenesis, including mast cell c-Kit signaling and TNF-alpha release, macrophage c-Fms activation and cytokine production, and fibroblast PDGFR signaling and proliferation. In our studies, imatinib attenuated PDGFR signaling in fibroblast-like synoviocytes (FLSs) and TNF-alpha production in synovial fluid mononuclear cells (SFMCs) derived from human RA patients. Imatinib-mediated inhibition of a spectrum of signal transduction pathways and the downstream pathogenic cellular responses may provide a powerful approach to treat RA and other inflammatory diseases.

Pathophysiological role of mast cells in collagen-induced arthritis: study with a cysteinyl leukotriene receptor antagonist, montelukast

Our previous study showed that the number of mast cells was increased in the inflamed paws of collagen-induced arthritis in mice, and treatment with a mast cell-stabilizing compound effectively suppressed the development of collagen-induced arthritis. A recent in vitro study showed that mast cells express cysteinyl leukotriene type 1 receptor, and that a cysteinyl leukotriene type 1 receptor antagonist inhibits the production of TNF-alpha by mast cells. To further investigate the role of mast cells in vivo, we evaluated the therapeutic effects of a cysteinyl leukotriene type 1 receptor antagonist, montelukast, on the development of collagen-induced arthritis in mice. Montelukast (10 mg/kg/day) or vehicle was orally administered to mice for 12 weeks, starting 6 weeks after immunization with bovine type II collagen. Treatment with montelukast significantly reduced clinical scores and X-ray scores of collagen-induced arthritis, and decreased the number of mast cells in the inflamed paws of collagen-induced arthritic mice. Immunohistochemical analysis revealed that mast cells in the inflamed synovium were one of the major cells producing TNF-alpha and that the number of TNF-alpha positive mast cells was significantly reduced by treatment with montelukast. Furthermore, TNF-alpha and SCF mRNA levels in the paws of collagen-induced arthritic mice were markedly decreased by montelukast treatment. Montelukast may lead to a beneficial therapeutic effect by inhibiting TNF-alpha production by mast cells.

Inhibitory effect of inflammatory cytokines production from activated mast cells by Gamisopoonghwanghyul-tang

Rheumatoid arthritis (RA) is a chronic inflammatory disease and its exact cause and pathophysiological process remain unclear. Because the mast cell contains potent mediators, including multifunctional cytokines, its potential contributions to the processes of inflammation and matrix degradation have recently become evident. Gamisopoonghwanghyul-tang (GSPHHT) has been used as a traditional Korean medicine for the treatment of RA. In this study, we investigated the effect of Gamisopoonghwanghyul-tang (GSPHHT) on the production of inflammatory cytokines by activated human mast cell line HMC-1 cells. When GSPHHT (1 mg/ mL) was added, the production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, IL-10 was inhibited by 36.3%, 36.3%, 30.8%, 48.7% respectively in phorbol 12-myristate 13-acetate plus calcium ionophore A23187-stimulated HMC-1 cells. However, the production of IL-4 was significantly increased at 0.01 mg/mL. GSPHHT had no effect on TNF-alpha mRNA expression. These results suggest that GSPHHT regulates production of inflammatory cytokines from activated mast cells.

Mast cells in inflammatory arthritis

Mast cells are present in limited numbers in normal human synovium, but in rheumatoid arthritis and other inflammatory joint diseases this population can expand to constitute 5% or more of all synovial cells. Recent investigations in a murine model have demonstrated that mast cells can have a critical role in the generation of inflammation within the joint. This finding highlights the results of more than 20 years of research indicating that mast cells are frequent participants in non-allergic immune responses as well as in allergy. Equipped with a diversity of surface receptors and effector capabilities, mast cells are sentinels of the immune system, detecting and delivering a first response to invading bacteria and other insults. Accumulating within inflamed tissues, mast cells produce cytokines and other mediators that may contribute vitally to ongoing inflammation. Here we review some of the non-allergic functions of mast cells and focus on the potential role of these cells in murine and human inflammatory arthritis.

The role of FcgammaR signaling in the K/B x N serum transfer model of arthritis

Spontaneous arthritis in the KRN transgenic mouse (K/BxN) model is due to the autoreactivity of the transgenic TCR and subsequent induction of autoantibodies directed against glucose-6-phosphate isomerase. These autoantibodies transfer clinically apparent arthritis into most recipient mouse strains and systemic catabolism of the transferred Abs attenuates paw swelling. Although mice deficient in the common gamma-chain of the FcgammaR did not show clinical synovitis after receiving K/BxN sera, erosive lesions in the bone still developed. Further analysis demonstrated that FcgammaRII(-/-) mice manifested accelerated arthritis whereas the FcgammaRIII(-/-) mice had a more slowly progressing arthritis. Paw swelling required FcgammaR expression by bone marrow-derived cells and mast cells substantially contributed to the acute phase of paw swelling. In the K/BxN serum transfer model of arthritis, there is a clinically apparent acute phase, which is modulated by FcgammaRII and FcgammaRIII, and a subacute component, which results in bone erosion, even in the absence of FcgammaR signaling.

Analysis of the cell infiltrate and expression of matrix metalloproteinases and granzyme B in paired synovial biopsy specimens from the cartilage-pannus junction in patients with RA

OBJECTIVES

Examination of synovial tissue (ST) obtained at surgery because of end stage destructive rheumatoid arthritis (RA) showed that macrophages and fibroblasts are the major cell types at the cartilage-pannus junction (CPJ). This study aimed at defining the cell infiltrate and mediators of joint destruction in ST selected at arthroscopy from the CPJ in patients with RA who did not require joint surgery.

METHODS

Paired synovial biopsy specimens were obtained at arthroscopy from ST adjacent to the CPJ and the suprapatellar pouch from the knee joints of 17 patients with RA. Immunohistological analysis was performed using monoclonal antibodies to detect T cells, B cells, plasma cells, macrophages, fibroblast-like synoviocytes, mast cells, and granzyme B+ cytotoxic cells as well as the expression of metalloproteinase (MMP)-1, MMP-3, and MMP-13. The sections were evaluated by computer assisted image analysis and semiquantitative analysis.

RESULTS

The cell infiltrate comprised mainly T cells, macrophages, and plasma cells. The ST was also infiltrated by the other cell types, but at lower numbers. Expression of MMPs was abundant, especially MMP-3. The features of ST at the CPJ were generally similar to those at the suprapatellar pouch.

CONCLUSIONS

The synovium at the CPJ in patients with RA who did not require joint surgery exhibits, in general, the same type of cell infiltrate and expression of MMPs and granzymes as ST from the suprapatellar pouch. The pathological changes that have been described at the CPJ in patients with RA with end stage, destructive disease may well reflect the transition to a process in which macrophages, fibroblast-like synoviocytes, and other cell types become increasingly important.

Functional reconstitution of an active recombinant human chymase from Pichia pastoris cell lysate

We have previously reported efficient production of mature human chymase (h-chymase) using an original system of expression in Pichia pastoris (Nakakubo et al., 2000), whereby recombinant h-chymase (rh-chymase) was secreted as a mature form with the correct N-terminal amino acid sequence and was easily purified. In the course of investigation of secretory rh-chymase, we also found large amounts of chymase to be present in insoluble form in the transformant cell. Although the cellular rh-chymase had no proteolytic activity, its chymotryptic activity was restored in a reconstitution process utilizing guanidine and glutathione. As with secretory rh-chymase, efficient purification was possible by heparin affinity chromatography. The purified cellular rh-chymase showed the same mobility as secretory rh-chymase in sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) before and after deglycosylation. N-terminal amino acid sequence analysis revealed that the signal peptide had been correctly removed. K(m) value (5.93 mM), as well as pH profile and inhibition profile toward protease inhibitors of reconstituted cellular rh-chymase, indicated that the rh-chymase enzymatically closely resembles native h-chymase. Furthermore, it showed a greatly restricted proteolytic activity towards Ang I, and formed Ang II without the further cleavage which is a feature of h-chymase. It was thus found that the insoluble rh-chymase stored in the cells could be solubilized and reconstituted to give the same structure as h-chymase, not only in terms of enzyme active site but also of substrate recognition site.

Secretory production of recombinant human chymase as an active form in Pichia pastoris

We succeeded in expressing in a Pichia pastoris (P. pastoris) host a cDNA encoding a mature human chymase (h-chymase) which was secreted directly into the culture medium. Recombinant human heart chymase (rh-chymase) was purified from the culture medium via a single one-step heparin-agarose column chromatography tracing, using succinyl-Ala-Ala-Pro-Phe-para-nitroanilide (Suc-AAPF-pNA) hydrolysing activity. On SDS-polyacrylamide gel electrophoresis (SDS-PAGE), the rh-chymase showed a diffused protein band with molecular weight of 32-37 kDa. After deglycosylation, however, rh-chymase changed to a sharp protein band with molecular weight 28 kDa, which is equal in size to deglycosylated h-chymase. The rh-chymase had an activity to convert one of the natural substrates, angiotensin I, to angiotensin II. Double reciprocal plot analysis revealed that the K(m) value ofrh-chymase against Suc-AAPF-pNA was approximately 5.1 mM, which is close to that of purified h-chymase.

Mast cell activation and its relation to proinflammatory cytokine production in the rheumatoid lesion

INTRODUCTION

Increased numbers of mast cells (MCs) are found in the synovial tissues and fluids of patients with rheumatoid arthritis (RA), and at sites of cartilage erosion. MC activation has been reported for a significant proportion of rheumatoid specimens. Because the MC contains potent mediators, including histamine, heparin, proteinases, leukotrienes and multifunctional cytokines, its potential contributions to the processes of inflammation and matrix degradation have recently become evident. Proinflammatory cytokines are important mediators of inflammation, immunity, proteolysis, cell recruitment and proliferation. Tumour necrosis factor (TNF) reportedly plays a pivotal role in the pathogenesis o RA, especially its ability to regulate interleukin (IL)-1beta expression, this being important for the induction of prostanoid and matrix metalloproteinase production by synovial fibroblasts and chondrocytes. IL-15 has been assigned numerous biological effects and has been assigned numerous biological effects and has been implicated as an important factor in TNF-alpha expression by monocyte/macrophages. Some in vitro studies have placed IL-15 upstream from TNF-alpha in the cytokine cascade, suggesting an interdependence between TNF, IL-1 and IL-15 for the promotion of proinflammatory cytokine expression in the rheumatoid joint.

AIMS

To examine the in situ relationships of TNF-alpha, IL-1beta and IL-15 in relation to MC activation in rheumatoid tissues by use of immunolocalization techniques; and to compare quantitatively the proinflammatory cytokine production by specific cell cultures and rheumatoid synovial explants with and without exposure to a MC secretagogue.

MATERIALS AND METHODS

Samples of rheumatoid synovial tissue and cartilage-pannus junction were obtained from patients (n=15) with classic late-stage RA. Tissue sections were immunostained for MC (tryptase) and the proinflammatory cytokines IL-1, TNF-alpha and IL-15. Rheumatoid synovial tissue explants were cultured in Dulbecco's modified Eagles medium (DMEM) containing either the MC secretagogue rabbit antihuman immunoglobulin (Ig)E, or control rabbit IgG. Primary rheumatoid synovial cell cultures, human articular chondrocytes, synovial fibroblasts and synovial macrophages were prepared as described in the full article. Conditioned culture media from these cultures were collected and assayed for IL-1beta, TNF-alpha and IL-15 using enzyme-linked immunosorbent assay methodology.

RESULTS

Immunohistological studies of rheumatoid synovial tissues have demonstrated local concentrations of MCs in most specimens of the rheumatoid lesion. Sites of MC activation were associated with localized oedema, and TNF-alpha, IL-1alpha and IL-1beta production by a proportion of mononuclear inflammatory cells. By contrast, no evidence was found for IL-15 production in tissue sites containing either intact or activated MCs, and IL-15 expression, when observed, bore no relation to tissue sites where TNF-alpha and IL-1beta were evident. The immunodetection of IL-15 was restricted to microfocal sites and was not typical of most junctional specimens, but was associated with a proportion of articular chondrocytes in a minority of junctional specimens. MC activation within synovial explant cultures was induced by the addition of polyclonal antibody to human IgE. MC activation significantly reduced the levels of TNF-alpha and IL-1beta released into the medium, this representing approximately 33% of control values. By contrast, MC activation had little effect of the levels of IL-15 released into the culture medium, the average value being very low in relation to the release of TNF-alpha and IL-1beta. Thus, induced MC activation brings about changes in the amounts of released tryptase, TNF-alpha and IL-1beta, but not of IL-15. Four preparations of primary rheumatoid synovial cell cultures produced more IL-1beta than TNF-alpha, with only modest values for IL-15 production, indicating that all three cytokines are produced and released as free ligands by these cultures. Of specific cell types that produced IL-15 in vitro, macrophages produced more than fibroblasts, which in turn produced more than chondrocytes. This demonstrates that all three cell types have the potential to produce IL-15 in situ.

DISCUSSION

The biological consequences of MC activation in vivo are extremely complex, and in all probability relate to the release of various combinations of soluble and granular factors, as well as to the expression of appropriate receptors by neighbouring cells. The subsequent synthesis and release of cytokines such as TNF-alpha and IL-1 may well follow at specific stages after activation, or may be an induced cytokine response by adjacent macrophagic or fibroblastic cells. However, because no IL-15 was detectable either in or around activated or intact MCs, and the induced MC activation explant study showed no change in IL-15 production, it seems unlikely that the expression of this cytokine is regulated by MCs. The immunohistochemistry (IHC) demonstration of IL-15 at sites of cartilage erosion, and especially by some chondrocytes of articular cartilage, showed no spatial relationship with either T cells or neutrophils, and suggests other functional properties in these locations. The lack of evidence for an in situ association of IL-15 with TNF and IL-1 does not support a role for IL-15 in a proinflammatory cytokine 'cascade', as proposed by other in vitro experiments. We believe that sufficient evidence is available, however, to suggest that MC activation makes a significant contribution to the pathophysiological processes of the rheumatoid lesion.

Human mast cells produce matrix metalloproteinase 9

Extracellular matrix-destructive enzymes, like matrix metalloproteinases (MMP), have been recognized in the process of inflammation and tissue remodeling and repair. The affected tissues often contain markedly increased numbers of mast cells. Although mast cells are capable of activating latent collagenase and proMMP, it has so far been unknown whether human mast cells themselves produce and secrete MMP9. In this study, MMP9 production by cord blood-derived cultured human mast cells and HMC-1 human mast cells was examined by reverse-transcriptase PCR, gelatin zymography and Western blot analysis using an antibody against MMP9. Cultured mast cells and HMC-1 cells treated with phorbol 12-myristate 13-acetate were shown to express MMP9 mRNA, and the cultured conditioned media from these cells showed gelatinolytic activity, identical with MMP9. Immunohistochemical examination was performed to detect MMP9 in tissue mast cells; mast cells localized in the skin, lung and synovial tissue showed strongly positive reactions for MMP9. Thus, these findings indicate that human mast cells can produce MMP9, which might contribute to extracellular matrix degradation and absorption in the process of allergic and nonallergic responses.

Stereological quantification of mast cells in human synovium

Mast cells participate in both the acute allergic reaction as well as in chronic inflammatory diseases. Earlier studies have revealed divergent results regarding the quantification of mast cells in the human synovium. The aim of the present study was therefore to quantify these cells in the human synovium, using stereological techniques. Different methods of staining and quantification have previously been used for mast cell quantification in human synovium. Stereological techniques provide precise and unbiased information on the number of cell profiles in two-dimensional tissue sections of, in this case, human synovium. In 10 patients suffering from osteoarthritis a median of 3.6 mast cells/mm2 synovial membrane was found. The total number of cells (synoviocytes, fibroblasts, lymphocytes, leukocytes) present was 395.9 cells/mm2 (median). The mast cells constituted 0.8% of all the cell profiles present in the synovium. A significantly positive correlation was demonstrated between the number of mast cells and the total number of cells. Thus, the present study reports stereological quantification of the mast cells and the total number of cells in synovium from patients with osteoarthritis. A possible link between the mast cell and osteoarthritis is discussed upon obtaining a precise estimate of cell profiles in human synovium.

The 2.2 A crystal structure of human chymase in complex with succinyl-Ala-Ala-Pro-Phe-chloromethylketone: structural explanation for its dipeptidyl carboxypeptidase specificity

Human chymase (HC) is a chymotrypsin-like serine proteinase expressed by mast cells. The 2.2 A crystal structure of HC complexed to the peptidyl inhibitor, succinyl-Ala-Ala-Pro-Phe-chloromethylketone (CMK), was solved and refined to a crystallographic R-factor of 18.4 %. The HC structure exhibits the typical folding pattern of a chymotrypsin-like serine proteinase, and shows particularly similarity to rat chymase 2 (rat mast cell proteinase II) and human cathepsin G. The peptidyl-CMK inhibitor is covalently bound to the active-site residues Ser195 and His57; the peptidyl moiety juxtaposes the S1 entrance frame segment 214-217 by forming a short antiparallel beta-sheet. HC is a highly efficient angiotensin-converting enzyme. Modeling of the chymase-angiotensin I interaction guided by the geometry of the bound chloromethylketone inhibitor indicates that the extended substrate binding site contains features that may generate the dipeptidyl carboxypeptidase-like activity needed for efficient cleavage and activation of the hormone. The C-terminal carboxylate group of angiotensin I docked into the active-site cleft, with the last two residues extending beyond the active site, is perfectly localized to make a favorable hydrogen bond and salt bridge with the amide nitrogen of the Lys40-Phe41 peptide bond and with the epsilon-ammonium group of the Lys40 side-chain. This amide positioning is unique to the chymase-related proteinases, and only chymases from primates possess a Lys residue at position 40. Thus, the structure conveniently explains the preferred conversion of angiotensin I to angiotensin II by human chymase.

Expression of the C5a receptor (CD88) on synovial mast cells in patients with rheumatoid arthritis

OBJECTIVE

To analyze the immunophenotype and functional properties of synovial mast cells (SyMC) in patients with rheumatoid arthritis (RA) and osteoarthritis (OA).

METHODS

Synovial tissue was obtained from 25 patients with RA and 17 patients with OA. Tissue was dispersed by enzymatic digestion using collagenase. Surface receptor expression on SyMC was analyzed by monoclonal antibodies (MAb) and indirect immunofluorescence staining. Histamine release experiments were performed using the MC agonist recombinant human (rHu) stem cell factor (SCF), the anaphylatoxin rHuC5a, and an anti-IgE antibody.

RESULTS

In both groups of patients (RA and OA), SyMC were found to react with MAb to IgE, SCF receptor (c-kit, CD117), as well as CD antigens likewise expressed in lung MC (CD9, CD29, CD33, CD43, CD44, CD45). However, a significantly increased proportion of SyMC from RA patients reacted with MAb against C5a receptor (C5aR; CD88), compared with SyMC from OA (mean +/- SD percentage of SyMC reacting with CD88 MAb S5/1 in RA 27.5 +/- 8.6% versus 0.0% in OA, and with CD88 MAb W17/1 in RA 58.3 +/- 15.2% versus 12.5 +/- 15.0% in OA; P < 0.05). Furthermore, in RA, significant histamine release from SyMC above control was induced by rHuC5a, anti-IgE, and rHuSCF, whereas SyMC in OA released histamine after stimulation with anti-IgE and rHuSCF, but not rHuC5a.

CONCLUSION

SyMC exhibit phenotypic and functional properties similar to MC in other tissues. In patients with RA, but not OA, SyMC express significant amounts of C5aR (CD88) and release histamine in response to rHuC5a. These results indicate a role for SyMC and C5a/C5aR in the pathogenesis of RA.

Effects of induced mast cell activation on prostaglandin E and metalloproteinase production by rheumatoid synovial tissue in vitro

OBJECTIVE

To determine whether induced mast cell activation/degranulation in rheumatoid synovial explants modulates the production of prostaglandin E (PGE2), and the matrix metalloproteinases (MMPs) collagenase 1, gelatinase A, and stromelysin 1.

METHODS

Synovial explant cultures were treated either with rabbit IgG anti-human IgE as a mast cell (MC) secretagogue or with non-immune rabbit IgG as controls. After 20 hours conditioned medium was assayed for the release of MC tryptase, PGE2, collagenase 1, gelatinase A, and stromelysin 1 using radioimmunoassay, enzyme linked immunosorbent assay, western blot, and zymogram techniques; tissue explants were examined immunohistologically for the relative distributions of MC tryptase, collagenase 1, and stromelysin 1.

RESULTS

Over a 20 hour incubation period the MC secretagogue treated explants showed a significant increase in the quantities of released tryptase and PGE2 compared with controls. By contrast, the three MMPs showed variable values between experiments in response to MC activation; no reproducible trend of either an increased or decreased production of each MMP over control values was evident. Each MMP initially appeared as an inactive precursor form; collagenase 1 and stromelysin 1 were more effectively processed to active forms in the MC activated cultures. Immunolocalisation studies of MC activated explants showed that areas of extracellular tryptase were commonly associated with the local production of both collagenase 1 and stromelysin 1.

CONCLUSION

MC degranulation induced artificially in rheumatoid synovial explant cultures consistently resulted in an increased production of PGE2 but had variable effects on the quantification of released collagenase 1, gelatinase A, and stromelysin 1. Such observations support the concept that activated synovial MCs within their native environment stimulate the production of non-MC derived PGE2 and may contribute to the regulation and processing of specific MMPs; both aspects represent important components of the inflammatory and degradative processes of the rheumatoid lesion.

Crystal structure of phenylmethanesulfonyl fluoride-treated human chymase at 1.9 A

The X-ray crystal structure of human chymase has been determined to 1.9 A resolution using molecular replacement methods. This first structure of human chymase is present as the Ser 195 ester of alpha-toluenesulfonic acid. The refined structure (Rcryst = 0.183) shows that the inhibitor phenyl moiety lies at the top of the major specificity pocket, S1, while the sulfur is covalently linked to Ser 195-O gamma. The sulfonyl oxygens interact with the oxyanion hole and with His 57-N delta 1. The presence of the inhibitor disturbs the usual gauche position of His 57 and forces it to the trans conformer. Though the primary binding pockets are similarly specific in chymase and chymotrypsin, examination of the extended substrate binding sites reveals the structural basis for chymase's greater discrimination in choosing substrates. The larger 30s loop and its proximity to the active site indicates that it contacts substrate residues C-terminal to the scissile bond. Modeling of substrate at the chymase active site suggests that binding energy may be gained by three main-chain hydrogen bonds provided by substrate residues P2' and P4' and that discriminating interactions with substrate side chains are also likely. The presence of Lys 40 in S1' of human chymase explains its preference for Asp/Glu at P1'. Moreover, the cationic nature of S1' provides a structural basis for human chymase's poor catalytic efficiency when angiotensin II is the substrate.

Lactoferrin regulates the activity of heparin proteoglycan-bound mast cell chymase: characterization of the binding of heparin to lactoferrin

Rat mast cell protease 1 (RMCP-1) is a secretory granule serine protease (chymase) that is recovered in vivo in a macromolecular complex with heparin proteoglycan (PG). We have previously shown that heparin activates RMCP-1 and that RMCP-1, when bound to heparin PG, is largely resistant to inhibition by a variety of macromolecular protease inhibitors. In the search for alternative mechanisms in the regulation of RMCP-1 activity, we hypothesized that heparin antagonists, by interfering with the RMCP-1/heparin PG interaction, might influence the activity of heparin-bound mast cell chymase. In the present study, lactoferrin (LF), a heparin-binding protein, was assessed for RMCP-1 inhibiting activity. LF proved to decrease the activity of heparin PG-associated RMCP-1, although a portion of the enzyme activity was resistant to regulation. The mechanism of regulation was shown to involve the displacement of RMCP-1 from heparin PG, and LF caused an approx. 6-fold increase in the apparent Km of the RMCP-1-heparin PG complex for the chromogenic substrate S-2586. The interaction of LF with heparin was characterized. Pig mucosal heparin and endogenous heparin PG were equally effective in binding LF, whereas heparan sulphate bound with lower affinity. None of dermatan sulphate, chondroitin sulphate or hyaluronan were effective in binding LF. Further, the 6-O-, 2-O- and N-sulphate groups in heparin were of approximately equal importance for binding. Octasaccharides were the smallest heparin oligosaccharides showing significant binding to LF.

Percutaneous needle biopsy and synovial histology

Percutaneous needle biopsies of synovium are successfully used for diagnosis and investigation of joint disease by an increasing number of groups around the world. This procedure can be done in the office with little morbidity; a large number of samples can minimize the potential limitation of sampling error. Clinical indications for 'imaging the joint' by looking at morphological and other features of the actual tissue include undiagnosed acute or chronic mono- or oligoarthritis, haemarthrosis, suspected deposition diseases, new developments in previous stable disease and less often unexplained polyarthritis. Research into any joint disease can be helped by study of synovium especially using newer immunohistochemical, EM and molecular techniques. This report has reviewed other methods used for obtaining synovium, described the different percutaneous biopsy needles, detailed the methods used for biopsy with the Parker-Pearson needle and described how our group handles tissue so as to obtain maximal impact. The very few side effects of needle biopsy include haemarthrosis and, rarely, needle breakage. Finally, we have provided a brief overview of normal synovium and some aspects of synovium in a variety of joint diseases.

Topical tretinoin increases dermal mast cells, induces epidermal mast cell growth factor (c-kit ligand) and modulates its distribution in hairless mice

In previous studies we have noted that mast cells are increased in tretinoin-treated photoaged hairless mouse skin. Because UV radiation is known to increase mast cell numbers, we were interested in whether tretinoin alone would modulate the mast cell population in unirradiated mice. Animals were treated topically with 0.05% tretinoin, 5 days a week, for 2, 4, 6, 8 and 10 weeks. Untreated and vehicle controls were included. Biopsies were processed for light microscopy and stained with toluidine blue. Mast cells in the upper and lower dermis were scored separately under high magnification. After 2 weeks of tretinoin, mast cells in the upper dermis were significantly increased, as indicated by the appearance of small, moderately metachromatically granulated cells near the dermal-epidermal junction. Mast cells in the lower dermis, the site of a granulomatous reaction, were large, densely granular and significantly increased after 6 weeks of treatment. Immunohistochemical evaluation for mast cell growth factor (MGF) revealed a marked increase in keratinocyte cytoplasmic staining by week 2. After 4-6 weeks, membrane-associated or intercellular staining was evident. Cells in the upper dermis also showed membrane reactivity for MGF. By 8-10 weeks, epidermal MGF reactivity had dissipated in the more basal keratinocytes. These findings show that topical tretinoin can induce epidermal MGF along with an associated mast cell hyperplasia. It is suggested that the two populations of dermal mast cells may have different functions.

Mast cell activation in human synovium explants by calcium ionophore A23187, compound 48/80, and rabbit IgG anti-human IgE, but not morphine sulfate

To investigate human synovial mast cell physiology, we developed a model in which mast cells in human synovial explant cultures were activated by immunologic or non-immunologic mechanisms. Small (3 mm) cubes of synovial membrane were incubated with or without secretagogue for 30, 45 or 60 min, and supernatant histamine concentrations were quantified. We measured significant histamine release with compound 48/80 at concentrations > or = 1 mg/ml, and with calcium ionophore A23187 at > or = 5 micrograms/ml. Rabbit IgG anti-human IgE induced significant histamine release at all concentrations tested, maximum at 78 micrograms/ml. Morphine sulfate produced no histamine release from synovial explants, in contrast to its significant stimulation of histamine release from neonatal foreskin explants in our explant system. We confirmed synovial mast cell degranulation by electron microscopy, and showed that it corresponded with measurable histamine release. Furthermore, histamine release was not due to secretagogue-induced cytotoxicity, as assessed by supernatant lactate dehydrogenase levels and by ultrastructural analysis. Since morphine sulfate induces mast cell degranulation and histamine release in adult and neonatal human skin, our data show that although synovial and dermal mast cells have a similar granule enzyme profile and electron microscopic morphology, they differ in functional responses. These observations support recent data that among similar human mast cell subtypes there are physiologic differences. Finally, our explant model will be useful in studies of mast cell involvement in arthritis.

Histamine-stimulated production of matrix metalloproteinase 1 by human rheumatoid synovial fibroblasts is mediated by histamine H1-receptors

The purpose of this study was to investigate the role of histamine in human rheumatoid synovial fibroblasts in the production of factors responsible for tissue remodelling and cartilage breakdown in rheumatoid arthritis. We examined the effects of histamine of tritiated thymidine incorporation, production of matrix metalloproteinase-1 (MMP-1), histamine H1-receptor expression, phosphoinositide metabolism and intracellular calcium ion concentration ([Ca2+]i) in human rheumatoid synovial fibroblasts. Tritiated thymidine incorporation studies demonstrated that histamine markedly stimulated the proliferation of rheumatoid synovial fibroblasts. Immunofluorescence and Northern blot analyses revealed that proMMP-1 production was also stimulated by histamine. The levels of inositol phosphates and [Ca2+]i in the cells were elevated in response to histamine, indicating that the cells expressed histamine H1-receptors; and Northern blot analysis indicated that these H1-receptors were up-regulated by histamine. In in situ hybridization, large amounts of histamine H1-receptor mRNA were also detected in rheumatoid synovial tissue. These results suggest that the interaction between H1-receptor expression in rheumatoid synovial fibroblasts and histamine secretion by mast cells and macrophages in the affected sites is an important event responsible for tissue remodelling and joint destruction in rheumatoid arthritis.

Mast cells, cytokines, and metalloproteinases at the rheumatoid lesion: dual immunolocalisation studies

OBJECTIVES

To examine the distribution and activation of mast cells (MCs) in the rheumatoid lesion (cartilage-pannus junctions demonstrating cartilage erosion), and to determine whether or not their tissue distribution is related to that for tumour necrosis factor alpha (TNF alpha), interleukin-1 (IL-1), stromelysin-1, and collagenase.

METHODS

Immunolocalisation of MC-tryptase was used to identify MCs and their states of degranulation in 35 specimens of cartilage-pannus junctions. Dual immunolocalisation techniques using alkaline phosphatase and peroxidase conjugated antibodies were used to compare the distributions of MCs with the proinflammatory cytokines TNF alpha and IL-1, and the cartilage or matrix degrading enzymes stromelysin-1 and collagenase.

RESULTS

Stromelysin-1, TNF alpha, and IL-1 beta were especially prominent at the cartilage-pannus junctions, albeit with patchy distributions. Extracellular MC tryptase, indicative of MC activation/degranulation, was commonly observed at sites of cartilage erosion, and was often associated with the microenvironmental expression of TNF alpha, IL-1 beta, stromelysin-1, and collagenase. Such observations were often associated with localised sites of tissue oedema and stromal disruption.

CONCLUSION

MC activation was frequently associated with proinflammatory cytokine and metalloproteinase expression by neighbouring cells, thereby suggesting an important contributory role for the MC in mediating matrix degradation and oedematous changes within microfoci of the rheumatoid lesion.

Regulation of rat mast cell protease 1 activity. Protease inhibition is prevented by heparin proteoglycan

Rat mast cell protease 1 (RMCP-1) is a chymotrypsin-like serine protease (chymase) that is specifically expressed by connective-tissue-type mast cells. It is stored in the secretory granules of the cells in a complex with heparin proteoglycan, and the chymase/heparin proteoglycan complexes are released following mast cell activation. The present study was undertaken to examine if the association with heparin proteoglycan influenced the regulation of RMCP-1 by various macromolecular protease inhibitors. Endogenous mast cell heparin proteoglycan was shown to significantly block the inhibition of RMCP-1 by the serpins alpha 1-protease inhibitor and alpha 1-antichymotrypsin, as well as the inhibition by alpha 2-macroglobulin, soybean trypsin inhibitor and plasma. The blocking of protease inhibition showed an optimum at a RMCP-1/proteoglycan ratio of 5:1 (by mass), corresponding to approximately 80 RMCP-1 molecules bound/proteoglycan molecule. Chymase activity present on intact peritoneal mast cells, i.e. present in its native complex with heparin proteoglycan, was also shown to be largely resistant to inhibition by alpha 1-antichymotrypsin and alpha 1-protease inhibitor. Heparin 10-saccharides and 20-saccharides were inefficient in preventing the interaction of RMCP-1 with alpha 1-antichymotrypsin, whereas pig mucosal heparin (approximately 50 monosaccharide units) blocked protease inhibition. We have previously shown that heparin potentiates the catalytic activity of RMCP-1 and, in the present study, we show that the mechanism for chymase activation involves a sixfold reduction of the Km,app value of RMCP-1 for the chromogenic substrate S-2586. Thus, the association of mast cell chymase with heparin proteoglycan may serve both to potentiate the catalytic activity of the enzyme and to increase the life-span of the chymases by preventing their inhibition after exocytosis.

Infiltrates of activated mast cells at the site of coronary atheromatous erosion or rupture in myocardial infarction

BACKGROUND

Erosion and rupture of coronary atheromas are the events preceding the vast majority of acute coronary syndromes. The shoulder regions of atheromas, the sites at which erosion or rupture is most likely to occur, are the sites at which mast cells accumulate. These cells are filled with neutral proteases capable of triggering extracellular matrix degradation via activation of matrix metalloproteinases. To obtain more direct evidence for the participation of mast cells in the acute coronary syndromes, we quantified the numbers of mast cells at eroded or ruptured sites of coronary atheromas in patients who died of myocardial infarction.

METHODS AND RESULTS

In specimens of coronary arteries from 20 patients who had died of acute myocardial infarction, the site of atheromatous erosion or rupture was identified. The specimens were stained with monoclonal antibodies against the two major proteases of mast cells, tryptase and chymase, and against macrophages, T lymphocytes, and smooth muscle cells. At the immediate site of erosion or rupture, mast cells amounted to 6% of all nucleated cells, in the adjacent atheromatous area to 1%, and in the unaffected intimal area to 0.1%. The proportions of these mast cells that were activated, ie, had been stimulated to degranulate and release some of their tryptase and chymase contents, were 86% at the site of erosion or rupture, 63% in the adjacent atheromatous area, and 27% in the unaffected intima. At the site of erosion or rupture, the numbers of macrophages and T lymphocytes were also increased, but the number of smooth muscle cells was decreased.

CONCLUSIONS

The accumulation of activated mast cells (200-fold more than in the unaffected coronary intima) at the site of atheromatous erosion or rupture suggests that in thrombotic coronary occlusion the role played by mast cells is significant.

Human mast cell chymase and leukocyte elastase release latent transforming growth factor-beta 1 from the extracellular matrix of cultured human epithelial and endothelial cells

Monolayer cultures of human epithelial and endothelial cells were used to study the association of latent transforming growth factor-beta 1 (TGF-beta 1) to extracellular matrices and its release and activation during matrix degradation. Human umbilical vein endothelial cells and embryonic lung fibroblasts produced relatively high levels of TGF-beta 1, its propeptide (beta 1-latency-associated protein), and latent TGF-beta-binding protein and incorporated latent TGF-beta 1 into their matrices as shown by immunoblotting. Amnion epithelial cells produced lower levels of these proteins. Confluent cultures of epithelial cells were exposed to matrix-degrading proteases and glycosidases. Mast cell chymase, leukocyte elastase, and plasmin efficiently released matrix-bound latent TGF-beta 1 complexes, while chondroitinase ABC and heparitinases were ineffective. The ability of the proteases to activate recombinant latent TGF-beta 1 was tested using growth inhibition assays and a novel sodium deoxycholate-polyacrylamide gel electrophoresis followed by immunoblotting. Sodium deoxycholate solubilized M(r) 25,000 TGF-beta 1 but did not dissociate high M(r) latent TGF-beta 1 complexes, allowing separation of these forms by polyacrylamide gel electrophoresis. Mast cell chymase and leukocyte elastase did not activate latent TGF-beta 1, suggesting that its release from matrix and activation are controlled by different mechanisms. The release of TGF-beta from the matrix by leukocyte and mast cell enzymes may contribute to the accumulation of connective tissue in inflammation.

Activation of precursors for matrix metalloproteinases 1 (interstitial collagenase) and 3 (stromelysin) by rat mast-cell proteinases I and II

Histological studies have previously demonstrated an association between mast-cell activation/degranulation and areas of connective-tissue lysis in vivo; in addition, mast-cell extracts have been shown to activate latent forms of collagenase and stromelysin. In the present study we have examined the potential roles of rat mast-cell proteinase (RMCP) I and RMCP II as activators of the precursors of matrix metalloproteinase (MMP)-1 (interstitial collagenase), MMP-2 (gelatinase A) and MMP-3 (stromelysin 1). Both RMCPs I and II activated proMMP-3 by converting the 57 kDa precursor into a 45 kDa polypeptide. The N-terminal amino acid of 45 kDa MMP-3 activated by RMCP II was identified as Phe83. By contrast, only RMCP II activated the 52 kDa proMMP-1 by converting it into a 41 kDa protein and generating the new N-termini, namely Gln80 and Val82. The collagenolytic activity which resulted from this cleavage was only 35% of the full activity, but this could not be augmented by subsequent treatment with MMP-3, the latter being a crucial enzyme for the generation of the fully active MMP-1 with Phe81 at the N-terminus, in conjunction with other serine proteinases. Thus RMCP II activates proMMP-1 via a mechanism different from that reported for the stepwise processing by combinations of other trypsin-like enzymes and MMP-3. ProMMP-2 (pro-gelatinase A) was not activated by either RMCP I or RMCP II, despite processing to smaller products.

Captopril reduces collagen and mast cell and eosinophil accumulation in pig serum-induced rat liver fibrosis

The effect of captopril on the development of hepatic septal fibrosis in a specific experimental model produced by repeated injections of whole pig serum into the peritoneal cavity of rats was studied. The results afforded four basic conclusions. First, the experimental model used seems to be a pure form of septal fibrosis, which depends on active tissue fibroplasia, without hepatocyte necrosis. The fibrotic septa, located between limiting plates of adjacent classic hepatic lobules, and delimiting the classic liver lobule, consisted of collagen fibers infiltrated by eosinophils, mast cells, fat-storing cells (Ito cells), transitional cells and interstitial fibroblasts. Second, the angiotensin-converting enzyme inhibitor captopril attenuated the hepatic fibrosis induced by pig serum administration, as proven by a decrease in hepatic hydroxyproline concentration and histological examination of the liver. Third, this attenuation of hepatic fibrosis might be related, at least in part, to diminished mast cell and eosinophil accumulation in the hepatic tissue. Finally, these data may indicate a novel action of angiotensin-converting enzyme inhibitor in general, and for captopril in particular, as drugs potentially capable of reducing eosinophils in fibrotic processes.