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1.  Joint Tissues Amplify Inflammation and Alter Their Invasive Behavior via Leukotriene B4 in Experimental Inflammatory Arthritis 
Mechanisms by which mesenchymal-derived tissue lineages participate in amplifying and perpetuating synovial inflammation in arthritis have been relatively underinvestigated and are therefore poorly understood. Elucidating these processes is likely to provide new insights into the pathogenesis of multiple diseases. Leukotriene B4 (LTB4) is a potent proinflammatory lipid mediator that initiates and amplifies synovial inflammation in the K/BxN model of arthritis. We sought to elucidate mechanisms by which mesenchymal-derived fibroblast-like synoviocytes (FLSs) perpetuate synovial inflammation. We focused on the abilities of FLSs to contribute to LTB4 synthesis and to respond to LTB4 within the joint. Using a series of bone marrow chimeras generated from 5-lipoxygenase–/– and leukotriene A4 (LTA4) hydrolase–/– mice, we demonstrate that FLSs generate sufficient levels of LTB4 production through transcellular metabolism in K/BxN serum-induced arthritis to drive inflammatory arthritis. FLSs—which comprise the predominant lineage populating the synovial lining—are competent to metabolize exogenous LTA4 into LTB4 ex vivo. Stimulation of FLSs with TNF increased their capacity to generate LTB4 3-fold without inducing the expression of LTA4 hydrolase protein. Moreover, LTB4 (acting via LTB4 receptor 1) was found to modulate the migratory and invasive activity of FLSs in vitro and also promote joint erosion by pannus tissue in vivo. Our results identify novel roles for FLSs and LTB4 in joints, placing LTB4 regulation of FLS biology at the center of a previously unrecognized amplification loop for synovial inflammation and tissue pathology.
PMCID: PMC3690310  PMID: 20876351
2.  Characterization of a novel human mast cell line that responds to stem cell factor and expresses functional FcεRI 
Studies of human mast cells are constrained by the paucity of functional cell lines, the expense of maintaining mast cells in culture, and technical complexities.
We derived and characterized a human mast cell line that arose spontaneously from a culture of non-transformed hematopoietic progenitor cells.
CD34+-enriched mononuclear cells derived from a donor with aspirin exacerbated respiratory disease were cultured for 8 weeks with stem cell factor and interleukin-6 and with interleukin-3 for the first week only. The cells (termed LUVA cells) survived and proliferated without further addition of any growth factors and have been maintained in culture for ~2 years.
LUVA cells possess metachromatic cytoplasmic granules that are immunoreactive for tryptase, cathepsin G, and carboxypeptidase A3. They express transcripts encoding genes for FcεRI, c-kit, chymase, tryptase, histidine decarboxylase, carboxypeptidase A3, and the type 1 receptor for cysteinyl leukotrienes. Flow cytometry confirmed uniform expression of FcεRI, c-kit and FcγRII. FcεRI cross-linkage induced the release of β-hexosaminidase, prostaglandin D2, thromboxane A2, and macrophage inflammatory protein-1β. Immortalization was not associated with either a known genomic mutation of c-kit in the donor or a somatic mutation of c-kit within the cells, and it was not associated with c-kit autophosphorylation.
LUVA cells are an immortalized human mast cell line that can be maintained without stem cell factor and display high levels of normally signaling c-kit and FcεRI. These cells will prove valuable for functional human mast cell studies.
PMCID: PMC3052637  PMID: 21281958
Mast cell; SCF; FcεRI; c-Kit; Tryptase; CPA3
3.  The Catalytic Architecture of Leukotriene C4 Synthase with Two Arginine Residues* 
The Journal of Biological Chemistry  2011;286(18):16392-16401.
Leukotriene (LT) C4 and its metabolites, LTD4 and LTE4, are involved in the pathobiology of bronchial asthma. LTC4 synthase is the nuclear membrane-embedded enzyme responsible for LTC4 biosynthesis, catalyzing the conjugation of two substrates that have considerably different water solubility; that amphipathic LTA4 as a derivative of arachidonic acid and a water-soluble glutathione (GSH). A previous crystal structure revealed important details of GSH binding and implied a GSH activating function for Arg-104. In addition, Arg-31 was also proposed to participate in the catalysis based on the putative LTA4 binding model. In this study enzymatic assay with mutant enzymes demonstrates that Arg-104 is required for the binding and activation of GSH and that Arg-31 is needed for catalysis probably by activating the epoxide group of LTA4.
PMCID: PMC3091245  PMID: 21454538
Crystal Structure; Eicosanoid-specific Enzymes; Enzyme Mechanisms; Enzyme Structure; Membrane Proteins; LTC4S; Leukotriene C4 Synthase
4.  Role of group V phospholipase A2 in zymosan-induced eicosanoid generation and vascular permeability revealed by targeted gene disruption* 
The Journal of biological chemistry  2004;279(16):16488-16494.
Conclusions regarding the contribution of low molecular weight secretory phospholipase A2 (sPLA2) enzymes in eicosanoid generation have relied on data obtained from transfected cells or the use of inhibitors that fail to discriminate between individual members of the large family of mammalian sPLA2 enzymes. To elucidate the role of group V sPLA2, we used targeted gene disruption to generate mice lacking this enzyme. Zymosan-induced generation of leukotriene C4 and prostaglandin E2 was attenuated ~50% in peritoneal macrophages from group V sPLA2-null mice compared to macrophages from wild-type littermates. Furthermore, the early phase of plasma exudation in response to intraperitoneal injection of zymosan and the accompanying in vivo generation of cysteinyl leukotrienes were markedly attenuated in group V sPLA2-null mice compared to wild-type controls. These data provide clear evidence of a role for group V sPLA2 in regulating eicosanoid generation in response to an acute innate stimulus of the immune response both in vitro and in vivo, suggesting a role for this enzyme in innate immunity.
PMCID: PMC1201398  PMID: 14761945
5.  Neutrophil-derived leukotriene B4 is required for inflammatory arthritis 
Neutrophils serve as a vanguard of the acute innate immune response to invading pathogens. Neutrophils are also abundant at sites of autoimmune inflammation, such as the rheumatoid joint, although their pathophysiologic role is incompletely defined and relevant effector functions remain obscure. Using genetic and pharmacologic approaches in the K/BxN serum transfer model of arthritis, we find that autoantibody-driven erosive synovitis is critically reliant on the generation of leukotrienes, and more specifically on leukotriene B4 (LTB4), for disease induction as well as perpetuation. Pursuing the cellular source for this mediator, we find via reconstitution experiments that mast cells are a dispensable source of leukotrienes, whereas arthritis susceptibility can be restored to leukotriene-deficient mice by intravenous administration of wild-type neutrophils. These experiments demonstrate a nonredundant role for LTB4 in inflammatory arthritis and define a neutrophil mediator involved in orchestrating the synovial eruption.
PMCID: PMC2118292  PMID: 16567388
6.  T Helper Cell Type 2 Cytokines Coordinately Regulate Immunoglobulin E–Dependent Cysteinyl Leukotriene Production by Human Cord Blood–Derived Mast Cells 
Human mast cells (hMCs) derived in vitro from cord blood mononuclear cells exhibit stem cell factor (SCF)-dependent comitogenic responses to T helper cell type 2 (Th2) cytokines. As cysteinyl leukotriene (cys-LT) biosynthesis is a characteristic of immunoglobulin (Ig)E-activated mucosal hMCs, we speculated that Th2 cytokines might regulate eicosanoid generation by hMCs. After passive sensitization for 5 d with IgE in the presence of SCF, anti-IgE–stimulated hMCs elaborated minimal cys-LT (0.1 ± 0.1 ng/106 hMCs) and abundant prostaglandin (PG)D2 (16.2 ± 10.3 ng/106 hMCs). Priming of hMCs by interleukin (IL)-4 with SCF during passive sensitization enhanced their anti-IgE–dependent histamine exocytosis and increased their generation of both cys-LT (by 27-fold) and PGD2 (by 2.5-fold). Although priming with IL-3 or IL-5 alone for 5 d with SCF minimally enhanced anti-IgE–mediated cys-LT generation, these cytokines induced further six- and fourfold increases, respectively, in IgE-dependent cys-LT generation when provided with IL-4 and SCF; this occurred without changes in PGD2 generation or histamine exocytosis relative to hMCs primed with IL-4 alone. None of these cytokines, either alone or in combination, substantially altered the levels of cytosolic phospholipase A2 (cPLA2), 5-lipoxygenase (5-LO), or 5-LO activating protein (FLAP) protein expression by hMCs. In contrast, IL-4 priming dramatically induced the steady-state expression of leukotriene C4 synthase (LTC4S) mRNA within 6 h, and increased the expression of LTC4S protein and functional activity in a dose- and time-dependent manner, with plateaus at 10 ng/ml and 5 d, respectively. Priming by either IL-3 or IL-5, with or without IL-4, supported the localization of 5-LO to the nucleus of hMCs. Thus, different Th2-derived cytokines target distinct steps in the 5-LO/LTC4S biosynthetic pathway (induction of LTC4S expression and nuclear import of 5-LO, respectively), each of which is necessary for a full integrated functional response to IgE-dependent activation, thus modulating the effector phenotype of mature hMCs.
PMCID: PMC2195887  PMID: 11136826
eicosanoids; asthma; allergy; prostaglandin D2; FcεRI

Results 1-6 (6)