Receptors and signaling mechanisms required for prostaglandin E2-mediated regulation of mast cell degranulation and IL-6 production

Carnosic acid inhibits secretion of allergic inflammatory mediators in IgE-activated mast cells via direct regulation of Syk activation

Mast cells are essential regulators of inflammation most recognized for their central role in allergic inflammatory disorders. Signaling via the high-affinity immunoglobulin E (IgE) receptor, FcεRI, leads to rapid degranulation of preformed granules and the sustained release of newly-synthesized pro-inflammatory mediators. Our group recently established rosemary extract (RE) as a potent regulator of mast cell functions, attenuating MAPK and NF-κB signaling. Carnosic acid (CA)-a major polyphenolic constituent of RE-has been shown to exhibit anti-inflammatory effects in other immune cell models, but its role as a potential modulator of mast cell activation is undefined. Therefore, we sought here to determine the modulatory effects of CA in a mast cell model of allergic inflammation. We sensitized bone marrow-derived mast cells (BMMCs) with anti-trinitrophenyl (TNP) IgE and activated with allergen (TNP-BSA) under stem cell factor (SCF) potentiation, in addition to treatment with CA. Our results indicate that CA significantly inhibits allergen-induced early phase responses including Ca²⁺ mobilization, ROS production, and subsequent degranulation. We also show CA treatment reduced late phase responses, including the release of all cytokines and chemokines examined following IgE stimulation, and corresponding gene expression excepting that of CCL2. Importantly, we determined that CA mediates its inhibitory effects through modulation of tyrosine kinase Syk and downstream effectors TAK1 (Ser412) and Akt (Ser473) as well as NF-κB signaling, while phosphorylation of FcεRI (γ chain) and MAPK proteins remained unaltered. These novel findings establish CA as a potent modulator of mast cell activation, warranting further investigation as a putative anti-allergy therapeutic.

The ingenious mast cell: Contemporary insights into mast cell behavior and function

Mast cells are (in)famous for their role in allergic diseases, but the physiological and pathophysiological roles of this ingenious cell are still not fully understood. Mast cells are important for homeostasis and surveillance of the human system, recognizing both endogenous and exogenous agents, which induce release of a variety of mediators acting on both immune and non-immune cells, including nerve cells, fibroblasts, endothelial cells, smooth muscle cells, and epithelial cells. During recent years, clinical and experimental studies on human mast cells, as well as experiments using animal models, have resulted in many discoveries that help decipher the function of mast cells in health and disease. In this review, we focus particularly on new insights into mast cell biology, with a focus on mast cell development, recruitment, heterogeneity, and reactivity. We also highlight the development in our understanding of mast cell-driven diseases and discuss the development of novel strategies to treat such conditions.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

TAK1 signaling activity links the mast cell cytokine response and degranulation in allergic inflammation

Mast cells drive the inappropriate immune response characteristic of allergic inflammatory disorders via release of pro-inflammatory mediators in response to environmental cues detected by the IgE-FcεRI complex. The role of TGF-β-activated kinase 1 (TAK1), a participant in related signaling in other contexts, remains unknown in allergy. We detect novel activation of TAK1 at Ser412 in response to IgE-mediated activation under SCF-c-kit potentiation in a mast cell-driven response characteristic of allergic inflammation, which is potently blocked by TAK1 inhibitor 5Z-7-oxozeaenol (OZ). We, therefore, interrogated the role of TAK1 in a series of mast cell-mediated responses using IgE-sensitized murine bone marrow-derived mast cells, stimulated with allergen under several TAK1 inhibition strategies. TAK1 inhibition by OZ resulted in significant impairment in the phosphorylation of MAPKs p38, ERK, and JNK; and mediation of the NF-κB pathway via IκBα. Impaired gene expression and near abrogation in release of pro-inflammatory cytokines TNF, IL-6, IL-13, and chemokines CCL1, and CCL2 was detected. Finally, a significant inhibition of mast cell degranulation, accompanied by an impairment in calcium mobilization, was observed in TAK1-inhibited cells. These results suggest that TAK1 acts as a signaling node, not only linking the MAPK and NF-κB pathways in driving the late-phase response, but also initiation of the degranulation mechanism of the mast cell early-phase response following allergen recognition and may warrant consideration in future therapeutic development.

Mammalian diaphanous-related formin 1 (mDia1) coordinates mast cell migration and secretion through its actin-nucleating activity

BACKGROUND

Actin remodeling is a key regulator of mast cell (MC) migration and secretion. However, the precise mechanism underlying the coordination of these processes has remained obscure.

OBJECTIVE

We sought to characterize the actin rearrangements that occur during MC secretion or chemotactic migration and identify the underlying mechanism of their coordination.

METHODS

Using high-resolution microscopy, we analyzed the dynamics of actin rearrangements in MCs triggered to migration by IL-8 or prostaglandin E2 or to FcεRI-stimulated secretion.

RESULTS

We show that a major feature of the actin skeleton in MCs stimulated to migration is the buildup of pericentral actin clusters that prevent cell flattening and converge the secretory granules (SGs) in the cell center. This migratory phenotype is replaced on encounter of an IgE cross-linking antigen that stimulates secretion through a secretory phenotype characterized by cell flattening, reduction of actin mesh density, ruffling of cortical actin, and mobilization of SGs. Furthermore, we show that knockdown of mammalian diaphanous-related formin 1 (mDia1) inhibits chemotactic migration and its typical actin rearrangements, whereas expression of an active mDia1 mutant recapitulates the migratory actin phenotype and enhances cell migration while inhibiting FcεRI-triggered secretion. However, mice deficient in mDia1 appear to have normal numbers of MCs in various organs at baseline.

CONCLUSION

Our results demonstrate a unique role of actin rearrangements in clustering the SGs and inhibiting their secretion during MC migration. We identify mDia1 as a novel regulator of MC response that coordinates MC chemotaxis and secretion through its actin-nucleating activity.

Changing the threshold-Signals and mechanisms of mast cell priming

Mast cells play a key role in allergy and other inflammatory diseases involving engagement of multivalent antigen with IgE bound to high-affinity IgE receptors (FcεRIs). Aggregation of FcεRIs on mast cells initiates a cascade of signaling events that eventually lead to degranulation, secretion of leukotrienes and prostaglandins, and cytokine and chemokine production contributing to the inflammatory response. Exposure to pro-inflammatory cytokines, chemokines, bacterial and viral products, as well as some other biological products and drugs, induces mast cell transition from the basal state into a primed one, which leads to enhanced response to IgE-antigen complexes. Mast cell priming changes the threshold for antigen-mediated activation by various mechanisms, depending on the priming agent used, which alone usually do not induce mast cell degranulation. In this review, we describe the priming processes induced in mast cells by various cytokines (stem cell factor, interleukins-4, -6 and -33), chemokines, other agents acting through G protein-coupled receptors (adenosine, prostaglandin E₂ , sphingosine-1-phosphate, and β-2-adrenergic receptor agonists), toll-like receptors, and various drugs affecting the cytoskeleton. We will review the current knowledge about the molecular mechanisms behind priming of mast cells leading to degranulation and cytokine production and discuss the biological effects of mast cell priming induced by several cytokines.

Meloxicam Improves Cognitive Impairment of Diabetic Rats through COX2-PGE2-EPs-cAMP/pPKA Pathway

Diabetics often face greater risk of cognitive impairment than nondiabetics. However, how to prevent this disease is still unconfirmed. In this study, we investigated the potential protection and mechanism of meloxicam on cognitive impairment in diabetic rats. The diabetic rat model was established with a high-fat diet and a small dose of streptozotocin (40 mg/kg). The changes of spatial learning and memory, histopathology, and the protein expressions of amyloid protein precursor (APP) and β-amyloid (Aβ) indicated that diabetic rats had neuronal injury and cognitive impairment. Tumor necrosis factor α (TNFα), interleukin 6 (IL-6), C reactive protein (CRP) and prostaglandin E2 (PGE2) levels, and microglial cell number were significantly increased in the diabetic rat brain. Meanwhile, the protein expressions of APP, Aβ, cyclooxygenases2 (COX2), E-type prostanoid recptors 1 (EP1) and EP2, and the level of cyclic adenosine monophosphate (cAMP) were significantly increased, while the protein expressions of EP3 and phosphorylated protein kinase A (pPKA) were significantly decreased in the diabetic rat hippocampus and cortex. However, the EP4 protein expression had no significant changes. Meloxicam significantly improved neuronal injury and cognitive impairment, and significantly decreased inflammatory cytokines levels. Meloxicam also significantly decreased the protein expressions of APP, Aβ, COX2, EP1 and EP2, and the level of cAMP and significantly increased the EP3 and pPKA protein expressions in rat hippocampus and cortex. However, meloxicam did not significantly influence the levels of blood glucose, lipids, and insulin of rats. Our results suggest that meloxicam could significantly protect diabetic rats from cognitive impairment via a mechanism that may be associated with rebalancing the COX2-PGE2-EPs-cAMP/PKA pathway.

Genomic and transcriptomic comparison of allergen and silver nanoparticle-induced mast cell degranulation reveals novel non-immunoglobulin E mediated mechanisms

Mast cells represent a crucial cell type in host defense; however, maladaptive responses are contributing factors in the pathogenesis of allergic diseases. Previous work in our laboratory has shown that exposure to silver nanoparticles (AgNPs) results in mast cell degranulation via a non-immunoglobulin E (IgE) mechanism. In this study, we utilized a systems biology approach to identify novel genetic factors playing a role in AgNP-induced mast cell degranulation compared to the classical activation by antigen-mediated FcεRI crosslinking. Mast cell degranulation was assessed in bone marrow-derived mast cells isolated from 23 strains of mice following exposure to AgNPs or FcεRI crosslinking with dinitrophenyl (DNP). Utilizing strain-dependent mast cell degranulation, an association mapping study identified 3 chromosomal regions that were significantly associated with mast cell degranulation by AgNP and one non-overlapping region associated with DNP-mediated degranulation. Two of the AgNP-associated regions correspond to genes previously reported to be associated with allergic disorders (Trac2 on chromosome 1 and Traf6 on chromosome 2) and an uncharacterized gene identified on chromosome 1 (Fam126b). In conjunction, RNA-sequencing performed on mast cells from the high and low responder strains revealed 3754 and 34 differentially expressed genes that were unique to DNP and AgNP exposures, respectively. Select candidate genes include Ptger4, a gene encoding a G-protein coupled receptor in addition to a multifunctional adaptor protein, Txnip, that may be driving mast cell degranulation by AgNP. Taken together, we identified novel genes that have not been previously shown to play a role in nanoparticle-mediated mast cell activation. With further functional evaluation in the future, these genes may be potential therapeutic targets in the treatment of non-IgE mediated mast cell-linked disorders.

Frontline Science: Corticotropin-releasing factor receptor subtype 1 is a critical modulator of mast cell degranulation and stress-induced pathophysiology

Life stress is a major risk factor in the onset and exacerbation of mast cell-associated diseases, including allergy/anaphylaxis, asthma, and irritable bowel syndrome. Although it is known that mast cells are highly activated upon stressful events, the mechanisms by which stress modulates mast cell function and disease pathophysiology remains poorly understood. Here, we investigated the role of corticotropin-releasing factor receptor subtype 1 (CRF₁) in mast cell degranulation and associated disease pathophysiology. In a mast cell-dependent model of IgE-mediated passive systemic anaphylaxis (PSA), prophylactic administration of the CRF₁-antagonist antalarmin attenuated mast cell degranulation and hypothermia. Mast cell-deficient Kit^W-sh/W-sh mice engrafted with CRF₁^-/- bone marrow-derived mast cells (BMMCs) exhibited attenuated PSA-induced serum histamine, hypothermia, and clinical scores compared with wild-type BMMC-engrafted Kit^W-sh/W-sh mice. Kit^W-sh/W-sh mice engrafted with CRF₁^-/- BMMCs also exhibited suppressed in vivo mast cell degranulation and intestinal permeability in response to acute restraint stress. Genetic and pharmacologic experiments with murine BMMCs, rat RBL-2H3, and human LAD2 mast cells demonstrated that although CRF₁ activation did not directly induce MC degranulation, CRF₁ signaling potentiated the degranulation responses triggered by diverse mast cell stimuli and was associated with enhanced release of Ca²⁺ from intracellular stores. Taken together, our results revealed a prominent role for CRF₁ signaling in mast cells as a positive modulator of stimuli-induced degranulation and in vivo pathophysiologic responses to immunologic and psychologic stress.

TNFα Increases RANKL Expression via PGE₂-Induced Activation of NFATc1

Tumor necrosis factor α (TNFα) is known to upregulate the expression of receptor activator of NF-κB ligand (RANKL). We investigated the role of the calcineurin/nuclear factor of activated T-cells (NFAT) signaling pathway in TNFα-induced RANKL expression in C2C12 and primary cultured mouse calvarial cells. TNFα-induced RANKL expression was blocked by the calcineurin/NFAT pathway inhibitors. TNFα increased NFAT transcriptional activity and subsequent RANKL promoter binding. Mutations in the NFAT-binding element (MT(N)) suppressed TNFα-induced RANKL promoter activity. TNFα increased prostaglandin E2 (PGE₂) production, which in turn enhanced NFAT transcriptional activity and binding to the RANKL promoter. MT(N) suppressed PGE₂-induced RANKL promoter activity. TNFα and PGE₂ increased the expression of RANKL, NFAT cytoplasmic-1 (NFATc1), cAMP response element-binding protein (CREB), and cyclooxygenase 2 (COX2); which increment was suppressed by indomethacin, a COX inhibitor. Mutations in the CRE-like element blocked PGE₂-induced RANKL promoter activity. PGE₂ induced the binding of CREB to the RANKL promoter, whereas TNFα increased the binding of both CREB and NFATc1 to this promoter through a process blocked by indomethacin. The PGE₂ receptor antagonists AH6809 and AH23848 blocked TNFα-induced expression of RANKL, NFATc1, and CREB; transcriptional activity of NFAT; and binding of NFATc1 or CREB to the RANKL promoter. These results suggest that TNFα-induced RANKL expression depends on PGE₂ production and subsequent transcriptional activation/enhanced binding of NFATc1 and CREB to the RANKL promoter.

Human Mesenchymal Stem Cell-Derived Microvesicles Prevent the Rupture of Intracranial Aneurysm in Part by Suppression of Mast Cell Activation via a PGE2-Dependent Mechanism

Activation of mast cells participates in the chronic inflammation associated with cerebral arteries in intracranial aneurysm formation and rupture. Several studies have shown that the anti-inflammatory effect of mesenchymal stem cells (MSCs) is beneficial for the treatment of aneurysms. However, some long-term safety concerns exist regarding stem cell-based therapy for clinical use. We investigated the therapeutic potential of microvesicles (MVs) derived from human MSCs, anuclear membrane bound fragments with reparative properties, in preventing the rupture of intracranial aneurysm in mice, particularly in the effect of MVs on mast cell activation. Intracranial aneurysm was induced in C57BL/6 mice by the combination of systemic hypertension and intrathecal elastase injection. Intravenous administration of MSC-derived MVs on day 6 and day 9 after aneurysm induction significantly reduced the aneurysmal rupture rate, which was associated with reduced number of activated mast cells in the brain. A23187-induced activation of both primary cultures of murine mast cells and a human mast cell line, LAD2, was suppressed by MVs treatment, leading to a decrease in cytokine release and tryptase and chymase activities. Upregulation of prostaglandin E2 (PGE2) production and E-prostanoid 4 (EP4) receptor expression were also observed on mast cells with MVs treatment. Administration of an EP4 antagonist with the MVs eliminated the protective effect of MVs against the aneurysmal rupture in vivo. Human MSC-derived MVs prevented the rupture of intracranial aneurysm, in part due to their anti-inflammatory effect on mast cells, which was mediated by PGE2 production and EP4 activation. Stem Cells 2016;34:2943-2955.

IFNγ-Dependent Interactions between ICAM-1 and LFA-1 Counteract Prostaglandin E2-Mediated Inhibition of Antitumor CTL Responses

Tumor-expressed ICAM-1 interaction with LFA-1 on naïve tumor-specific CD8(+) T cells not only stabilizes adhesion, but, in the absence of classical B7-mediated costimulation, is also able to provide potent alternative costimulatory signaling resulting in the production of antitumor cytotoxic T lymphocyte (CTL) responses. This study shows that overproduction of prostaglandin (PG) E2 by metastatic murine renal carcinoma (Renca) cells inhibited direct priming of tumor-specific CTL responses in vivo by preventing the IFNγ-dependent upregulation of ICAM-1 that is vital during the initial priming of naïve CD8(+) T cells. The addition of exogenous IFNγ during naïve CD8(+) T-cell priming abrogated PGE2-mediated suppression, and overexpression of ICAM-1 by tumor cells restored IFNγ production and proliferation among PGE2-treated tumor-specific CD8(+) T cells; preventing tumor growth in vivo These findings suggest that novel anticancer immunotherapies, which increase expression of ICAM-1 on tumor cells, could help alleviate PGE2-mediated immunosuppression of antitumor CTL responses. Cancer Immunol Res; 4(5); 400-11. ©2016 AACR.

Dynamic model of eicosanoid production with special reference to non-steroidal anti-inflammatory drug-triggered hypersensitivity

The authors developed a mathematical model of arachidonic acid (AA) degradation to prostaglandins (PGs) and leukotrienes (LTs), which are implicated in the processes of inflammation and hypersensitivity to non-steroidal anti-inflammatory drugs (NSAIDs). The model focuses on two PGs (PGE2 and PGD2) and one LT (LTC4), their % increases and their ratios. Results are compared with experimental studies obtained from non-asthmatics (NAs), and asthmatics tolerant (ATA) or intolerant (AIA) to aspirin. Simulations are carried out for predefined model populations NA, ATA and three AIA, based on the differences of two enzymes, PG E synthase and/or LTC4-synthase in two states, that is, no-inflammation and inflammation. Their model reveals that the model population with concomitant malfunctions in both enzymes is the most sensitive to NSAIDs, since the duration and the capacity for bronchoconstriction risk are highest after simulated oral dosing of indomethacin. Furthermore, inflammation prolongs the duration of the bronchoconstriction risk in all AIA model populations, and the sensitivity analysis reveals multiple possible scenarios leading to hypersensitivity, especially if inflammatory processes affect the expression of multiple enzymes of the AA metabolic pathway. Their model estimates the expected fold-changes in enzyme activities and gives valuable information for further targeted transcriptomic/proteomic and metabolomic studies.

Mast Cell: A Multi-Functional Master Cell

Mast cells are immune cells of the myeloid lineage and are present in connective tissues throughout the body. The activation and degranulation of mast cells significantly modulates many aspects of physiological and pathological conditions in various settings. With respect to normal physiological functions, mast cells are known to regulate vasodilation, vascular homeostasis, innate and adaptive immune responses, angiogenesis, and venom detoxification. On the other hand, mast cells have also been implicated in the pathophysiology of many diseases, including allergy, asthma, anaphylaxis, gastrointestinal disorders, many types of malignancies, and cardiovascular diseases. This review summarizes the current understanding of the role of mast cells in many pathophysiological conditions.

Leukotriene D4 and prostaglandin E2 signals synergize and potentiate vascular inflammation in a mast cell-dependent manner through cysteinyl leukotriene receptor 1 and E-prostanoid receptor 3

BACKGROUND

Although arachidonic acid metabolites, cysteinyl leukotrienes (cys-LTs; leukotriene [LT] C4, LTD4, and LTE4), and prostaglandin (PG) E2 are generated at the site of inflammation, it is not known whether crosstalk exists between these 2 classes of inflammatory mediators.

OBJECTIVE

We sought to determine the role of LTD4-PGE2 crosstalk in inducing vascular inflammation in vivo, identify effector cells, and ascertain specific receptors and pathways involved in vitro.

METHODS

Vascular (ear) inflammation was assessed by injecting agonists into mouse ears, followed by measuring ear thickness and histology, calcium influx with Fura-2, phosphorylation and expression of signaling molecules by means of immunoblotting, PGD2 and macrophage inflammatory protein 1β generation by using ELISA, and expression of transcripts by using RT-PCR. Candidate receptors and signaling molecules were identified by using antagonists and inhibitors and confirmed by using small interfering RNA.

RESULTS

LTD4 plus PGE2 potentiated vascular permeability and edema, gearing the system toward proinflammation in wild-type mice but not in Kit(W-sh) mice. Furthermore, LTD4 plus PGE2, through cysteinyl leukotriene receptor 1 (CysLT1R) and E-prostanoid receptor (EP) 3, enhanced extracellular signal-regulated kinase (Erk) and c-fos phosphorylation, inflammatory gene expression, macrophage inflammatory protein 1β secretion, COX-2 upregulation, and PGD2 generation in mast cells. Additionally, we uncovered that this synergism is mediated through Gi, protein kinase G, and Erk signaling. LTD4 plus PGE2-potentiated effects are partially sensitive to CysLT1R or EP3 antagonists but completely abolished by simultaneous treatment both in vitro and in vivo.

CONCLUSIONS

Our results unravel a unique LTD4-PGE2 interaction affecting mast cells through CysLT1R and EP3 involving Gi, protein kinase G, and Erk and contributing to vascular inflammation in vivo. Furthermore, current results also suggest an advantage of targeting both CysLT1R and EP3 in attenuating inflammation.

The role of macrophage migration inhibitory factor in mast cell-stimulated fibroblast proliferation and collagen production

Current clinical and translational studies have shown that mast cell plays a pivotal role in multiple fibrotic diseases including scleroderma. However, the lack of mature human mast cell culture model exhibits a major obstacle for further dissection of cytokines and signaling molecules required for mast cell mediated fibrosis in various diseases. Macrophage Migration Inhibitory Factor is a mast cell released pro-inflammatory cytokine which is deregulated in scleroderma patients and is also involved in non-scleroderma related fibrosis. In the current study, we successfully generated a practical and reliable human mast cell culture system with bone marrow CD34+ hematopietic precursors. The derivative mast cell is normal in terms of both morphology and function as manifested by normal degranulation. More importantly, we were able to show mast cell conditioned medium as well as MIF supplementation augments fibroblast proliferation and collagen synthesis. This positive regulatory effect of mast cell conditioned medium can be dampened by MIF antibody. In addition, MIF-knockdown significantly inhibits pro-fibrotic activities of CD34+ hematopietic precursor derived mast cells. These data strongly suggest that mast cell released MIF is required for mast cell mediated fibrogenic activities. The current manuscript seems to be the first mechanistic report showing the significance of MIF in mast cell mediated fibrosis, which may pave the way for the development of potential MIF-targeted therapy for fibrotic diseases to a further extent. Moreover, we strongly believe mast cell culture and differentiation model as well as corresponding genetic manipulation methodology will be helpful in characterizing novel mast cell based therapeutic targets.

New insights on the signaling and function of the high-affinity receptor for IgE

Clustering of the high-affinity receptor for immunoglobulin E (FcεRI) through the interaction of receptor-bound immunoglobulin E (IgE) antibodies with their cognate antigen is required to couple IgE antibody production to cellular responses and physiological consequences. IgE-induced responses through FcεRI are well known to defend the host against certain infectious agents and to lead to unwanted allergic responses to normally innocuous substances. However, the cellular and/or physiological response of individuals that produce IgE antibodies may be markedly different and such antibodies (even to the same antigenic epitope) can differ in their antigen-binding affinity. How affinity variation in the interaction of FcεRI-bound IgE antibodies with antigen is interpreted into cellular responses and how the local environment may influence these responses is of interest. In this chapter, we focus on recent advances that begin to unravel how FcεRI distinguishes differences in the affinity of IgE-antigen interactions and how such discrimination along with surrounding environmental stimuli can shape the (patho) physiological response.

Role of the prostaglandin E2/E-prostanoid 2 receptor signalling pathway in TGFβ-induced mice mesangial cell damage

The prostaglandin E2 receptor, EP2 (E-prostanoid 2), plays an important role in mice glomerular MCs (mesangial cells) damage induced by TGFβ1 (transforming growth factor-β1); however, the molecular mechanisms for this remain unknown. The present study examined the role of the EP2 signalling pathway in TGFβ1-induced MCs proliferation, ECM (extracellular matrix) accumulation and expression of PGES (prostaglandin E₂ synthase). We generated primary mice MCs. Results showed MCs proliferation promoted by TGFβ1 were increased; however, the production of cAMP and PGE₂ (prostaglandin E₂) was decreased. EP2 deficiency in these MCs augmented FN (fibronectin), Col I (collagen type I), COX2 (cyclooxygenase-2), mPGES-1 (membrane-associated prostaglandin E1), CTGF (connective tissue growth factor) and CyclinD1 expression stimulated by TGFβ1. Silencing of EP2 also strengthened TGFβ1-induced p38MAPK (mitogen-activated protein kinase), ERK1/2 (extracellular-signal-regulated kinase 1/2) and CREB1 (cAMP responsive element-binding protein 1) phosphorylation. In contrast, Adenovirus-mediated EP2 overexpression reversed the effects of EP2-siRNA (small interfering RNA). Collectively, the investigation indicates that EP2 may block p38MAPK, ERK1/2 and CREB1 phosphorylation via activation of cAMP production and stimulation of PGE₂ through EP2 receptors which prevent TGFβ1-induced MCs damage. Our findings also suggest that pharmacological targeting of EP2 receptors may provide new inroads to antagonize the damage induced by TGFβ1.

A maladaptive role for EP4 receptors in mouse mesangial cells

Roles of the prostaglandin E2 E-prostanoid 4 receptor (EP4) on extracellular matrix (ECM) accumulation induced by TGF-β1 in mouse glomerular mesangial cells (GMCs) remain unknown. Previously, we have identified that TGF-β1 stimulates the expression of FN and Col I in mouse GMCs. Here we asked whether stimulation of EP4 receptors would exacerbate renal fibrosis associated with enhanced glomerular ECM accumulation. We generated EP4^Flox/Flox and EP4^+/− mice, cultured primary WT, EP4^Flox/Flox and EP4^+/− GMCs, AD-EP4 transfected WT GMCs (EP4 overexpression) and AD-Cre transfected EP4^Flox/Flox GMCs (EP4 deleted). We found that TGF-β1-induced cAMP and PGE2 synthesis decreased in EP4 deleted GMCs and increased in EP4 overexpressed GMCs. Elevated EP4 expression in GMCs augmented the coupling of TGF-β1 to FN, Col I expression and COX2/PGE2 signaling, while TGF-β1 induced FN, Col I expression and COX2/PGE2 signaling were down-regulated in EP4 deficiency GMCs. 8 weeks after 5/6 nephrectomy (Nx), WT and EP4^+/− mice exhibited markedly increased accumulation of ECM compared with sham-operated controls. Albuminuria, blood urea nitrogen and creatinine (BUN and Cr) concentrations were significantly increased in WT mice as compared to those of EP4^+/− mice. Urine osmotic pressure was dramatically decreased after 5/6 Nx surgery in WT mice as compared to EP4^+/− mice. The pathological changes in kidney of EP4^+/− mice was markedly alleviated compared with WT mice. Immunohistochemical analysis showed significant reductions of Col I and FN in the kidney of EP4^+/− mice compared with WT mice. Collectively, this investigation established EP4 as a potent mediator of the pro-TGF-β1 activities elicited by COX2/PGE2 in mice GMCs. Our findings suggested that prostaglandin E2, acting via EP4 receptors contributed to accumulation of ECM in GMCs and promoted renal fibrosis.

The role of mast cells in ischemia and reperfusion injury

INTRODUCTION

Ischemia and reperfusion (IR) injury is a challenging clinical problem that is triggered by ischemia in an organ followed by subsequent restoration of the blood supply. The effects of mast cell (MC) in IR injury are not totally clear.

MATERIALS AND METHODS

We review the body of literature on the role of MCs in IR injury based on an unrestricted Pubmed search for the descriptors "mast cell", "ischemia" and "reperfusion injury", as well as discuss implications for treatment and future directions.

RESULTS

Shortly after IR, chemicals released by MC can trigger vasoactive substance formation, tissue leakage, upregulation of adhesive molecules followed by leukocyte recruitment and infiltration, and pronecrotic pathway activation, among other physiologic changes. In the long term, MCs may influence tissue remodeling and repair as well as blood restoration after IR. Consistent with these findings, methods and drugs that target MCs have been shown to attenuate IR injury.

CONCLUSION

It has been demonstrated that MCs play a role in IR injury, but the mechanisms are complex and need to be further studied.

COX-2 inhibitors arrest prostate cancer cell cycle progression by down-regulation of kinetochore/centromere proteins

BACKGROUND

Previous studies have shown that COX-2 inhibitors inhibit cancer cell proliferation. However, the molecular mechanism remains elusive.

METHODS

Prostate cancer LNCaP, 22Rv1, and PC3 cells were cultured and treated with the COX-2 inhibitors celecoxib and CAY10404. Knockdown of COX-2 in LNCaP cells was carried out using lentiviral vector-loaded COX-2 shRNA. Cell cycle progression and cell proliferation were analyzed by flow cytometry, microscopy, cell counting, and the MTT assay. The antagonists of EP1, EP2, EP3, and EP4 were used to examine the effects of the PGE2 signaling. The effect of COX-2 inhibitors and COX-2 knockdown on expression of the kinetochore/centromere genes and proteins was determined by RT-PCR and immunoblotting.

RESULTS

Treatment with the COX-2 inhibitors celecoxib and CAY10404 or knockdown of COX-2 significantly inhibited prostate cancer cell proliferation. Flow-cytometric analysis and immunofluorescent staining confirmed the cell cycle arrested at the G2/M phase. Biochemical analysis showed that inhibition of COX-2 or suppression of COX-2 expression induced a dramatic down-regulation of key proteins in the kinetochore/centromere assembly, such as ZWINT, Cdc20, Ndc80, CENP-A, Bub1, and Plk1. Furthermore, the EP1 receptor antagonist SC51322, but not the EP2, EP3, and EP4 receptor antagonists, produced similar effects to the COX-2 inhibitors on cell proliferation and down-regulation of kinetochore/centromere proteins, suggesting that the effect of the COX-2 inhibition is through inactivation of the EP1 receptor signaling.

CONCLUSIONS

Our studies indicate that inhibition of COX-2 can arrest prostate cancer cell cycle progression through inactivation of the EP1 receptor signaling and down-regulation of kinetochore/centromere proteins.

The PGE2-EP2-mast cell axis: an antiasthma mechanism

Despite the fact that cyclooxygenase and its products, prostaglandins, have been traditionally associated with the development of inflammation, PGE2 was implicated early on as potentially beneficial in asthma. During the 1970s and 1980s, several studies reported the bronchodilator effect of PGE2 in asthma patients. In parallel, it was being shown to exert an inhibitory effect on mast cells in vitro. In spite of this, data supporting the beneficial role for PGE2 in asthma were scarce and sometimes controversial. Many years later, in vitro and in vivo studies suggested a range of biological activities attributable to PGE2, others than the ability to relax smooth muscle, that potentially explained some of the observed positive effects in asthma. The identification and cloning of the four PGE2 receptors made available new tools with which to fine-tune investigation of the anti-inflammatory, pro-inflammatory, immunoregulatory, and bronchodilation mechanisms of PGE2. Among these, several suggested involvement of mast cells, a cell population known to play a fundamental role in acute and chronic asthma. Indeed, it has been shown that PGE2 prevents human and murine MC activity in vitro through activation of the EP2 receptor, and also that both exogenously administered and endogenous PGE2 inhibit airway MC activity in vivo in mouse models of asthma (likely through an EP2-mediated mechanism as well). In the last few years, we have furthered into the functional connection between PGE2-induced mast cells inhibition and attenuated damage, in asthma and allergy models. The validity of the findings supporting a beneficial effect of PGE2 in different asthma phases, the direct effect of PGE2 on mast cells populations, and the functional implications of the PGE2-MC interaction on airway function are some of the topics addressed in this review, under the assumption that increased understanding of the PGE2-EP2-mast cell axis will likely lead to the discovery of novel antiasthma targets.

IgE receptor-mediated mast-cell renin release

Renin is a newly discovered constituent of mast cells. Given that mast cells play a major role in IgE-mediated allergic hypersensitivity, we investigated whether activation of the high-affinity IgE receptor FcεRI elicits release of mast-cell renin. Cross-linking of FcεRI on the surface of mature bone marrow-derived mast cells elicited release of enzymatically active renin protein. The angiotensin I-forming activity of the renin protein was completely blocked by the selective renin inhibitor BILA 2157, which excludes formation of angiotensin I by proteases other than renin. FcεRI-mediated mast-cell renin release was inhibited by dexamethasone and potentiated by the proinflammatory mediator PGE2. Furthermore, cross-linking of mast-cell FcεRI in ex vivo murine hearts passively sensitized with monoclonal anti-DNP IgE also resulted in mast-cell degranulation and overflow of renin. Our findings indicate that IgE-mediated allergic hypersensitivity provokes release of renin from both cultured and resident cardiac mast cells, a process likely to be exacerbated in a chronic inflammatory background. Given the widespread distribution of mast cells, and the presence of angiotensinogen and angiotensin-converting enzyme in many tissues, renin release in immediate hypersensitivity reactions could result in local angiotensin II generation and multiorgan dysfunctions.

Locally administered prostaglandin E2 prevents aeroallergen-induced airway sensitization in mice through immunomodulatory mechanisms

Prostaglandin E2 attenuates airway pathology in asthmatic patients and exerts a protective effect in antigen-sensitized mice when administered systemically. We aimed to establish the consequences of intranasal PGE2 administration on airway reactivity to aeroallergens in mice and reveal the underlying immunoinflammatory mechanisms. PGE2 was administered either daily during a 10-day exposure to house dust mite (HDM) extracts or for limited intervals. Airway hyperreactivity was measured by whole-body and invasive plethysmography. The phenotypes of lung immune cells and cytokine production were analysed by flow cytometry and ELISA, respectively. Airway hyperreactivity was sustainably reduced only when PGE2 administration was restricted to the initial 5 days of exposure to HDM. Lung inflammation, IL-4 production, and airway mast cell activity were also prevented under this early short-term treatment with PGE2. Interestingly, a Th2 response was already committed on day 5 of exposure to HDM. This was paralleled by GM-CSF and osteopontin upregulation and a decreased number of plasmacytoid dendritic and T regulatory cells, as well as a trend towards reduced IL-10 expression. Local PGE2 administration prevented the increase of airway IL-13 and osteopontin and kept lung plasmacytoid dendritic cell counts close to baseline. GM-CSF and Tregs were unaffected by the treatment. These findings suggest that the protection provided by PGE2 is a result of the modulation of early lung immunomodulatory mechanisms, and possibly a shift in the balance of dendritic cells towards a tolerogenic profile.

E-prostanoid 2 receptors dampen mast cell degranulation via cAMP/PKA-mediated suppression of IgE-dependent signaling

The experimental administration of PGE(2) for the treatment of asthma dampens clinical symptoms, and similar efficacy has been found in dust mite-induced hypersensitivity reactions in animal models. Here, we investigate the mechanism by which PGE(2) mediates suppression of MC degranulation. We find that the effect of PGE(2) on FcεRI-dependent MC degranulation varies from activating to suppressing, depending on the relative ratio of EP(2) to EP(3) expression on these cells with suppression evident only in cells having increased EP(2) to EP(3) expression. Consistent with a role for EP(2) in suppressing MC responses in vitro, we found that a selective EP(2) agonist, Butaprost, inhibited MC-mediated FcεRI-induced immediate hypersensitivity in a model of PCA. EP(2) engagement on MCs increased cAMP production and inhibited FcεRI-mediated calcium influx. In addition, it also decreased the extent of FcεRI-induced Fyn kinase activity, leading to decreased phosphorylation of key signaling molecules such as Gab2 and Akt. Treatment with an antagonist of cAMP or shRNA down-regulation of PKA (the principal intracellular target of cAMP) reversed the EP(2)-mediated inhibitory effect on MC degranulation and restored calcium influx and phosphorylation of Akt. Collectively, the findings demonstrate that EP(2) suppresses the Fyn-mediated signals that are central to FcεRI-dependent MC degranulation, suggesting that engagement of the EP(2) on MCs may be beneficial in dampening allergic responses.

Gs-coupled adenosine receptors differentially limit antigen-induced mast cell activation

Mast cell activation results in the immediate release of proinflammatory mediators prestored in cytoplasmic granules, as well as initiation of lipid mediator production and cytokine synthesis by these resident tissue leukocytes. Allergen-induced mast cell activation is central to the pathogenesis of asthma and other allergic diseases. Presently, most pharmacological agents for the treatment of allergic disease target receptors for inflammatory mediators. Many of these mediators, such as histamine, are released by mast cells. Targeting pathways that limit antigen-induced mast cell activation may have greater therapeutic efficacy by inhibiting the synthesis and release of many proinflammatory mediators produced in the mast cell. In vitro studies using cultured human and mouse mast cells, and studies of mice lacking A(2B) receptors, suggest that adenosine receptors, specifically the G(s)-coupled A(2A) and A(2B) receptors, might provide such a target. Here, using a panel of mice lacking various combinations of adenosine receptors, and mast cells derived from these animals, we show that adenosine receptor agonists provide an effective means of inhibition of mast cell degranulation and induction of cytokine production both in vitro and in vivo. We identify A(2B) as the primary receptor limiting mast cell degranulation, whereas the combined activity of A(2A) and A(2B) is required for the inhibition of cytokine synthesis.

Tumor-associated stromal cells expressing E-prostanoid 2 or 3 receptors in prostate cancer: correlation with tumor aggressiveness and outcome by angiogenesis and lymphangiogenesis

OBJECTIVE

To clarify the detailed pathologic roles of prostaglandin E(2) in prostate cancer tissues, the present study investigated the clinical significance and prognostic roles of the density of tumor-associated stromal cells expressing specific receptors for prostaglandin E2, termed "E-prostanoid (EP)1-4 receptors (EP1R-4Rs)."

METHODS

The expression of each receptor was immunohistochemically examined in 114 formalin-fixed biopsy specimens. Correlations with clinicopathologic features were investigated in these specimens. Angiogenesis and lymphangiogenesis were measured by the percentage of CD34-stained vessels (microvessel density) and D2-40-stained vessels (lymph vessel density). The relationships between the density of each EPR-stained cells and the microvessel density or lymph vessel density were evaluated in 62 prostate cancer tissues obtained by radical surgery for more detailed analysis in a wider area of prostate cancer tissue.

RESULTS

The density of tumor-associated cells with EP2R expression was positively associated with the N (P<.001) and M (P=.002) stages. Similarly, EP3R-positive stromal cell density was significantly associated with the N (P=.033) and M (P=.026) stages. The density of EP2R- and EP3R-stained cells correlated with the microvessel density (r=0.42, P<.001) and lymph vessel density (r=0.36, P=.012), respectively. A greater density of EP2R-stained cells was recognized as an independent predictor of progression (hazard ratio 7.26, P=.002) on multivariate analysis.

CONCLUSION

EP2R- and EP3R-stained cells might play important roles in tumor progression, angiogenesis, and lymphangiogenesis in prostate cancer. The density of EP2R-stained stromal cells could offer a useful predictor of biochemical recurrence after radical surgery.

Role of PGE2 in asthma and nonasthmatic eosinophilic bronchitis

Eosinophilic bronchitis is a common cause of chronic cough, which like asthma is characterized by sputum eosinophilia, but unlike asthma there is no variable airflow obstruction or airway hyperresponsiveness. Several studies suggest that prostaglandins may play an important role in orchestrating interactions between different cells in several inflammatory diseases such as asthma. PGE₂ is important because of the multiplicity of its effects on immune response in respiratory diseases; however, respiratory system appears to be unique in that PGE₂ has beneficial effects. We described that the difference in airway function observed in patients with eosinophilic bronchitis and asthma could be due to differences in PGE₂ production. PGE₂ present in induced sputum supernatant from NAEB patients decreases BSMC proliferation, probably due to simultaneous stimulation of EP2 and EP4 receptors with inhibitory activity. This protective effect of PGE₂ may not only be the result of a direct action exerted on airway smooth-muscle proliferation but may also be attributable to the other anti-inflammatory actions.

Prostaglandin E(2) produced by the lung augments the effector phase of allergic inflammation

Elevated PGE(2) is a hallmark of most inflammatory lesions. This lipid mediator can induce the cardinal signs of inflammation, and the beneficial actions of nonsteroidal anti-inflammatory drugs are attributed to inhibition of cyclooxygenase (COX)-1 and COX-2, enzymes essential in the biosynthesis of PGE(2) from arachidonic acid. However, both clinical studies and rodent models suggest that, in the asthmatic lung, PGE(2) acts to restrain the immune response and limit physiological change secondary to inflammation. To directly address the role of PGE(2) in the lung, we examined the development of disease in mice lacking microsomal PGE(2) synthase-1 (mPGES1), which converts COX-1/COX-2-derived PGH(2) to PGE(2). We show that mPGES1 determines PGE(2) levels in the naive lung and is required for increases in PGE(2) after OVA-induced allergy. Although loss of either COX-1 or COX-2 increases the disease severity, surprisingly, mPGES1(-/-) mice show reduced inflammation. However, an increase in serum IgE is still observed in the mPGES1(-/-) mice, suggesting that loss of PGE(2) does not impair induction of a Th2 response. Furthermore, mPGES1(-/-) mice expressing a transgenic OVA-specific TCR are also protected, indicating that PGE(2) acts primarily after challenge with inhaled Ag. PGE(2) produced by the lung plays the critical role in this response, as loss of lung mPGES1 is sufficient to protect against disease. Together, this supports a model in which mPGES1-dependent PGE(2) produced by populations of cells native to the lung contributes to the effector phase of some allergic responses.

IL-4 amplifies the pro-inflammatory effect of adenosine in human mast cells by changing expression levels of adenosine receptors

Adenosine inhalation produces immediate bronchoconstriction in asthmatics but not in normal subjects. The bronchospastic effect of adenosine is largely mediated through adenosine-induced mast cell activation, the mechanism of which is poorly understood due to limitations in culturing human primary mast cells. Here, we show that human umbilical cord blood -derived mast cells incubated with the Th2 cytokine IL-4 develop increased sensitivity to adenosine. Potentiation of anti-IgE- induced and calcium ionophore/PMA-induced degranulation was augmented in mast cells cultured with IL-4, and this effect was reduced or abolished by pre-treatment with A_2BsiRNA and selective A_2B receptor antagonists, respectively. IL-4 incubation resulted in the increased expression of A_2B and reduced expression of A_2A adenosine receptors on human mast cells. These results suggest that Th2 cytokines in the asthmatic lung may alter adenosine receptor expression on airway mast cells to promote increased responsiveness to adenosine.

Analysis of two major intracellular phospholipases A(2) (PLA(2)) in mast cells reveals crucial contribution of cytosolic PLA(2)α, not Ca(2+)-independent PLA(2)β, to lipid mobilization in proximal mast cells and distal fibroblasts

Mast cells release a variety of mediators, including arachidonic acid (AA) metabolites, to regulate allergy, inflammation, and host defense, and their differentiation and maturation within extravascular microenvironments depend on the stromal cytokine stem cell factor. Mouse mast cells express two major intracellular phospholipases A(2) (PLA(2)s), namely group IVA cytosolic PLA(2) (cPLA(2)α) and group VIA Ca(2+)-independent PLA(2) (iPLA(2)β), and the role of cPLA(2)α in eicosanoid synthesis by mast cells has been well documented. Lipidomic analyses of mouse bone marrow-derived mast cells (BMMCs) lacking cPLA(2)α (Pla2g4a(-/-)) or iPLA(2)β (Pla2g6(-/-)) revealed that phospholipids with AA were selectively hydrolyzed by cPLA(2)α, not by iPLA(2)β, during FcεRI-mediated activation and even during fibroblast-dependent maturation. Neither FcεRI-dependent effector functions nor maturation-driven phospholipid remodeling was impaired in Pla2g6(-/-) BMMCs. Although BMMCs did not produce prostaglandin E(2) (PGE(2)), the AA released by cPLA(2)α from BMMCs during maturation was converted to PGE(2) by microsomal PGE synthase-1 (mPGES-1) in cocultured fibroblasts, and accordingly, Pla2g4a(-/-) BMMCs promoted microenvironmental PGE(2) synthesis less efficiently than wild-type BMMCs both in vitro and in vivo. Mice deficient in mPGES-1 (Ptges(-/-)) had an augmented local anaphylactic response. These results suggest that cPLA(2)α in mast cells is functionally coupled, through the AA transfer mechanism, with stromal mPGES-1 to provide anti-anaphylactic PGE(2). Although iPLA(2)β is partially responsible for PGE(2) production by macrophages and dendritic cells, it is dispensable for mast cell maturation and function.

Regulators of Ca(2+) signaling in mast cells: potential targets for treatment of mast cell-related diseases?

A calcium signal is essential for degranulation, generation of eicosanoids and optimal production of cytokines in mast cells in response to antigen and other stimulants. The signal is initiated by phospholipase C-mediated production of inositol1,4,5-trisphosphate resulting in release of stored Ca(2+) from the endoplasmic reticulum (ER) and Golgi. Depletion of these stores activates influx of extracellular Ca(2+), usually referred to as store-operated calcium entry (SOCE), through the interaction of the Ca(2+)-sensor, stromal interacting molecule-1 (STIM1 ), in ER with Orai1(CRACM1) and transient receptor potential canonical (TRPC) channel proteins in the plasma membrane (PM). This interaction is enabled by microtubular-directed reorganization of ER to form ER/PM contact points or "punctae" in which STIM1 and channel proteins colocalize. The ensuing influx of Ca(2+) replenishes Ca(2+) stores and sustains elevated levels of cytosolic Ca(2+) ions-the obligatory signal for mast-cell activation. In addition, the signal can acquire spatial and dynamic characteristics (e.g., calcium puffs, waves, oscillations) that encode signals for specific functional outputs. This is achieved by coordinated regulation of Ca(2+) fluxes through ATP-dependent Ca(2+)-pumps and ion exchangers in mitochondria, ER and PM. As discussed in this chapter, studies in mast cells revealed much about the mechanisms described above but little about allergic and autoimmune diseases although studies in other types of cells have exposed genetic defects that lead to aberrant calcium signaling in immune diseases. Pharmacologic agents that inhibit or activate the regulatory components of calcium signaling in mast cells are also discussed along with the prospects for development of novel SOCE inhibitors that may prove beneficial in the treatment inflammatory mast-cell related diseases.

Distinct PGE2-responder and non-responder phenotypes in human mast cell populations: "all or nothing" enhancement of antigen-dependent mediator release

Reports indicate that prostaglandin (PG)E(2) markedly enhances antigen-mediated degranulation in mouse bone marrow-derived mast cells (BMMCs) but not in human mast cells (HuMCs). We have examined the underlying mechanism(s) for this disparity in HuMCs derived from the peripheral blood of multiple donors in addition to mouse BMMCs. HuMCs from half of these donors failed to respond to PGE(2) and the PGE(2) EP3 receptor agonist, sulprostone. However, HuMCs from the remaining donors and the LAD2 human MC line responded to PGE(2) and sulprostone with marked enhancement of antigen-mediated degranulation and IL-8 production in a similar manner to that observed in mouse BMMCs. The EP2 agonist, butaprost, failed to modulate antigen-mediated responses in any type of MCs. These distinct phenotypes could not be explained by differences in EP2 or EP3 expression nor by differences in the ability of PGE(2) to elevate levels of cAMP, a signal recognized to down-regulate mast cell activation. Moreover, both responder and non-responder HuMC populations exhibited similar activation of phosphatidylinositol 3-kinase, and MAP kinases. However, translocation of PLCγ(1) to the cell membrane and the associated calcium signal were enhanced only in the responder HuMC population indicating that the link between EP3 and PLCγ is impaired in the non-responder HuMCs.

CONCLUSIONS

These data provide a cautionary note for the translating of observations in the mouse to human mast cell-dependent disorders, but may also provide a basis for examining the effects of co-activating receptors in patients susceptible to allergic conditions.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Bone marrow stromal cells inhibit mast cell function via a COX2-dependent mechanism

BACKGROUND

Mast cells (MCs) have a central role in the induction of allergic inflammation, such as seen in asthma, and contribute to the severity of certain autoimmune diseases, such as rheumatoid arthritis. The MC thus represents an important inflammatory cell, and one which has resisted therapeutic attempts to alter its role in disease.

OBJECTIVE

Because bone marrow-derived stromal cells (BMSC, also known as mesenchymal stem cells or MSCs) have been reported to alter allergic inflammation in vivo, we chose to study the interaction between mouse BMSC and mouse bone marrow-derived MCs.

METHODS

MC degranulation, cytokine production and chemotaxis were evaluated in vitro following co-culture with BMSCs either in cell contact or a transwell. In addition, MC degranulation was assessed in vivo following administration of BMSCs in a model of passive cutaneous anaphylaxis and a peritoneal degranulation assay. Mechanisms of MC suppression by BMSCs were determined through use of inhibitors or antibodies to COX1, COX2, nitric oxide, indoleamine 2, 3-dioxygenase, EP1-4 receptors, TGF-β and IL-10. Lastly, we utilized either BMSCs or MCs deficient in COX1, COX2 or EP1-4 receptors to confirm the mechanisms of inhibition of MC function by BMSCs.

RESULTS

We discovered that BMSCs will effectively suppress specific MC functions in vitro as well as in vivo. When MCs are cocultured with BMSCs to allow cell-to-cell contact, BMSCs suppressed MC degranulation, pro-inflammatory cytokine production, chemokinesis and chemotaxis. Similarly, MC degranulation within mouse skin or the peritoneal cavity was suppressed following in vivo administration of BMSCs. Further, we found that these inhibitory effects were dependent on up-regulation of COX2 in BMSCs; and were facilitated through the activation of EP4 receptors on MCs.

CONCLUSION AND CLINICAL RELEVANCE

These observations support the concept that BMSCs have the ability to suppress MC activation and therefore could be the basis for a novel cell based therapeutic approach in the treatment of MC driven inflammatory diseases.

Bone marrow stromal cells inhibit mast cell function via a COX2-dependent mechanism

BACKGROUND

Mast cells (MCs) have a central role in the induction of allergic inflammation, such as seen in asthma, and contribute to the severity of certain autoimmune diseases, such as rheumatoid arthritis. The MC thus represents an important inflammatory cell, and one which has resisted therapeutic attempts to alter its role in disease.

OBJECTIVE

Because bone marrow-derived stromal cells (BMSC, also known as mesenchymal stem cells or MSCs) have been reported to alter allergic inflammation in vivo, we chose to study the interaction between mouse BMSC and mouse bone marrow-derived MCs.

METHODS

MC degranulation, cytokine production and chemotaxis were evaluated in vitro following co-culture with BMSCs either in cell contact or a transwell. In addition, MC degranulation was assessed in vivo following administration of BMSCs in a model of passive cutaneous anaphylaxis and a peritoneal degranulation assay. Mechanisms of MC suppression by BMSCs were determined through use of inhibitors or antibodies to COX1, COX2, nitric oxide, indoleamine 2, 3-dioxygenase, EP1-4 receptors, TGF-β and IL-10. Lastly, we utilized either BMSCs or MCs deficient in COX1, COX2 or EP1-4 receptors to confirm the mechanisms of inhibition of MC function by BMSCs.

RESULTS

We discovered that BMSCs will effectively suppress specific MC functions in vitro as well as in vivo. When MCs are cocultured with BMSCs to allow cell-to-cell contact, BMSCs suppressed MC degranulation, pro-inflammatory cytokine production, chemokinesis and chemotaxis. Similarly, MC degranulation within mouse skin or the peritoneal cavity was suppressed following in vivo administration of BMSCs. Further, we found that these inhibitory effects were dependent on up-regulation of COX2 in BMSCs; and were facilitated through the activation of EP4 receptors on MCs.

CONCLUSION AND CLINICAL RELEVANCE

These observations support the concept that BMSCs have the ability to suppress MC activation and therefore could be the basis for a novel cell based therapeutic approach in the treatment of MC driven inflammatory diseases.

Regulation of mast cell responses in health and disease

Mast cells are multifunctional cells that initiate not only IgE-dependent allergic diseases but also play a fundamental role in innate and adaptive immune responses to microbial infection. They are also thought to play a role in angiogenesis, tissue remodeling, wound healing, and tumor repression or growth. The broad scope of these physiologic and pathologic roles illustrates the flexible nature of mast cells, which is enabled in part by their phenotypic adaptability to different tissue microenvironments and their ability to generate and release a diverse array of bioactive mediators in response to multiple types of cell-surface and cytosolic receptors. There is increasing evidence from studies in cell cultures that release of these mediators can be selectively modulated depending on the types or groups of receptors activated. The intent of this review is to foster interest in the interplay among mast cell receptors to help understand the underlying mechanisms for each of the immunological and non-immunological functions attributed to mast cells. The second intent of this review is to assess the pathophysiologic roles of mast cells and their products in health and disease. Although mast cells have a sufficient repertoire of bioactive mediators to mount effective innate and adaptive defense mechanisms against invading microorganisms, these same mediators can adversely affect surrounding tissues in the host, resulting in autoimmune disease as well as allergic disorders.

Prostaglandin E2 activates and utilizes mTORC2 as a central signaling locus for the regulation of mast cell chemotaxis and mediator release

Prostaglandin (PG) E(2), a potent mediator produced in inflamed tissues, can substantially influence mast cell responses including adhesion to basement membrane proteins, chemotaxis, and chemokine production. However, the signaling pathways by which PGE(2) induces mast cell chemotaxis and chemokine production remains undefined. In this study, we identified the downstream target of phosphatidylinositol 3-kinase, mammalian target of rapamycin (mTOR), as a key regulator of these responses. In mouse bone marrow-derived mast cells, PGE(2) was found to induce activation of mTORC1 (mTOR complexed to raptor) as indicated by increased p70S6K and 4E-BP1 phosphorylation, and activation of mTORC2 (mTOR complexed to rictor), as indicated by increased phosphorylation of AKT at position Ser(473). Selective inhibition of the mTORC1 cascade by rapamycin or by the use of raptor-targeted shRNA failed to decrease PGE(2)-mediated chemotaxis or chemokine generation. However, inhibition of the mTORC2 cascade through the dual mTORC1/mTORC2 inhibitor Torin, or through rictor-targeted shRNA, resulted in a significant attenuation in PGE(2)-mediated chemotaxis, which was associated with a comparable decrease in actin polymerization. Furthermore, mTORC2 down-regulation decreased PGE(2)-induced production of the chemokine monocyte chemoattractant protein-1 (CCL2), which was linked to a significant reduction in ROS production. These findings are consistent with the conclusion that activation of mTORC2, downstream of PI3K, represents a critical signaling locus for chemotaxis and chemokine release from PGE(2)-activated mast cells.

Discrepancy between strong cephalic arterial dilatation and mild headache caused by prostaglandin D2 (PGD2)

Introduction: Prostaglandins (PGs) are involved in nociception and mast cell degranulation. Prostaglandin D2 (PGD2) is a vasodilatator released during mast cell degranulation. The headache-eliciting effect of PGD2 has not been studied in man.

Subjects and methods: Twelve healthy volunteers were randomly allocated to receive intravenous infusion of 384 ng/kg/min PGD2 over 25 min in a placebo-controlled, double-blind cross-over study. We recorded headache intensity and associated symptoms, velocity in the middle cerebral artery (VMCA) and diameter of the superficial temporal artery (STA) and radial artery (RA) using ultrasonography.

Results: In the period 0–14 h, 11 subjects reported headache on PGD2 compared to one subject on placebo ( P = 0.002). During the in-hospital phase (0–120 min), the area under the headache curve was larger on PGD2 compared to placebo ( P < 0.05). Median peak headache, 1 (0–1), occurred 10 min after start of PGD2 infusion. There was no difference in incidence of headache in the post-hospital phase between PGD2 ( n = 3) and placebo ( n = 1). There was a decrease in VMCA ( P < 0.001), increase in STA ( P < 0.001) and RA ( P < 0.006) diameter during PGD2 infusion compared to placebo. Peak decrease in VMCA was 28.3% after 10 min and peak increase in STA was 55.7% after 20 min on the PGD2 day. Conclusions: The present study shows that PGD2 is a very strong vasodilator of MCA, STA and RA, but causes only mild headache.

Human embryonic stem cells: a source of mast cells for the study of allergic and inflammatory diseases

Human mast cells are tissue resident cells with a principal role in allergic disorders. Cross-linking of the high-affinity receptor for immunoglobulin E (FcepsilonRI) results in release of inflammatory mediators initiating the clinical symptoms of allergy and anaphylaxis. Much of our knowledge regarding the mechanisms of mast cell activation comes from studies of mouse bone marrow-derived mast cells. However, clear differences have been identified between human and mouse mast cells. Studies of human mast cells are hampered by the limited sources available for their isolation, the resistance of these cells to genetic manipulation, and differences between cultures established from different persons. To address this limitation, we developed a simple coculture-free method for obtaining mast cells from human embryonic stem cells (hES). These hES-derived mast cells respond to antigen by releasing mast cell mediators. Moreover, the cells can be generated in numbers sufficient for studies of the pathways involved in their effector functions. Genetically modified mast cells, such as GFP-expressing cells, can be obtained by introduction and selection for modification in hES cells before differentiation. This direct coculture-free differentiation of hES cells represents a new and unique model to analyze the function and development of human mast cells.

PGE2 signaling through the EP4 receptor on fibroblasts upregulates RANKL and stimulates osteolysis

Periprosthetic osteolysis is the most common cause of aseptic loosening in total joint arthroplasty. The role of inflammatory mediators such as prostaglandin E2 (PGE2) and osteoclast promoting factors including RANKL in the pathogenesis of osteolysis has been well characterized. However, the PGE2 receptor (EP1, EP2, or EP4), and cell type in which it is expressed, which is responsible for PGE2 induction of RANKL during wear debris-induced osteolysis, has yet to be elucidated. To address this, we used mice genetically deficient in these EP receptors to assess PGE2 and wear debris responses in vitro and in vivo. Wear debris-induced osteolysis and RANKL expression were observed at similar levels in WT, EP1(-/-), and EP2(-/-) mice, indicating that these receptors do not mediate PGE2 signals in this process. A conditional knockout approach was used to eliminate EP4 expression in FSP1(+) fibroblasts that are the predominant source of RANKL. In the absence of EP4, fibroblasts do not express RANKL after stimulation with particles or PGE2, nor do they exhibit high levels of osteoclasts and osteolysis. These results show that periprosthetic fibroblasts are important mediators of osteolysis through the expression of RANKL, which is induced after PGE2 signaling through the EP4 receptor.

Prostaglandin E2 receptor EP2, EP3, and EP4 agonists inhibit antigen-induced mucus hypersecretion in the nasal epithelium of sensitized rats

OBJECTIVES

Prostaglandin (PG) E2 is a potential anti-inflammatory mediator that attenuates airway inflammation. To elucidate the functions of the PGE2 receptors (EP1, EP2, EP3, and EP4) in allergic inflammation, we examined the in vivo effects of EP agonists on mucus hypersecretion and eosinophil infiltration in rat nasal epithelium.

METHODS

We induced hypertrophic and metaplastic changes in goblet cells in nasal epithelium of ovalbumin-sensitized rats by intranasal challenge with ovalbumin. The effects of subcutaneous injections of EP agonists on mucus production and eosinophil infiltration were examined.

RESULTS

The EP4 agonist (1 to 100 microg/kg) dose-dependently inhibited ovalbumin-induced mucus production. The EP2 and EP3 agonists (100 microg/kg) also significantly inhibited mucus production. The EP3 agonist inhibited antigen-induced eosinophil infiltration, whereas the EP1 agonist showed no effect. This suppression of mucus production by the EP4 agonist was only effective when the EP4 agonist was given in the effector phase; administration in the induction phase resulted in no effect.

CONCLUSIONS

These results indicate that PGE2 acts as an anti-inflammatory mediator via the EP receptors of airways in allergic inflammation. Selective EP agonists may provide a new therapeutic strategy for airway mucus hypersecretion.

Prostaglandin E(2)-EP(3) signaling suppresses skin inflammation in murine contact hypersensitivity

BACKGROUND

Prostaglandin (PG) E(2) exerts a variety of actions through 4 G protein-coupled receptors designated as EP(1), EP(2), EP(3), and EP(4). We have reported that PGE(2) acts on EP(3) in airway epithelial cells and exerts anti-inflammatory actions in ovalbumin-induced murine allergic asthma. Although EP(3) is also expressed in skin and PGE(2) is produced abundantly during skin allergic inflammation, the role of PGE(2)-EP(3) signaling in skin allergic inflammation remains unknown.

OBJECTIVE

We sought to investigate whether PGE(2)-EP(3) signaling exerts anti-inflammatory actions in skin allergic inflammation.

METHODS

We used a murine contact hypersensitivity (CHS) model and examined the role of EP(3) by using an EP(3)-selective agonist, ONO-AE-248 (AE248), and EP(3)-deficient mice. The inflammation was evaluated by the thickness and histology of the hapten-challenged ear. Inflammation-associated changes in gene expression and effects of AE248 were examined by means of microarray analysis of the skin. Localization of EP(3) was examined by staining for beta-galactosidase knocked in at the EP(3) locus in EP(3)-deficient mice. EP(3) action was also examined in cultured keratinocytes.

RESULTS

Administration of AE248 during the elicitation phase significantly suppressed CHS compared with that seen in vehicle-treated mice. Microarray analysis revealed that administration of AE248 inhibited the gene expression of neutrophil-recruiting chemokines, including CXCL1, at the elicitation site. X-gal staining in EP(3)-deficient mice revealed EP(3) expression in keratinocytes, which was further confirmed by anti-EP(3) antibody in wild-type mice. In cultured keratinocytes AE248 suppressed CXCL1 production induced by TNF-alpha.

CONCLUSION

PGE(2)-EP(3) signaling inhibits keratinocytes activation and exerts anti-inflammatory actions in murine CHS.

Engagement of the EP2 prostanoid receptor closes the K+ channel KCa3.1 in human lung mast cells and attenuates their migration

Human lung mast cells (HLMC) express the Ca(2+)-activated K(+) channel K(Ca)3.1, which plays a crucial role in their migration to a variety of diverse chemotactic stimuli. K(Ca)3.1 activation is attenuated by the beta(2)-adrenoceptor and the adenosine A(2A) receptor through a G(s)-coupled mechanism independent of cyclic AMP. Prostaglandin E(2) promotes degranulation and migration of mouse bone marrow-derived mast cells through the G(i)-coupled EP(3) prostanoid receptor, and induces LTC(4) and cytokine secretion from human cord blood-derived mast cells. However, PGE(2) binding to the G(s)-coupled EP(2) receptor on HLMC inhibits their degranulation. We show that EP(2) receptor engagement closes K(Ca)3.1 in HLMC. The EP(2) receptor-specific agonist butaprost was more potent than PGE(2) in this respect, and the effects of both agonists were reversed by the EP(2) receptor antagonist AH6809. Butaprost markedly inhibited HLMC migration induced by chemokine-rich airway smooth muscle-conditioned media. Interestingly, PGE(2) alone was chemotactic for HLMC at high concentrations (1 microM), but was a more potent chemoattractant for HLMC following EP(2) receptor blockade. Therefore, the G(s)-coupled EP(2) receptor closes K(Ca)3.1 in HLMC and attenuates both chemokine- and PGE(2)-dependent HLMC migration. EP(2) receptor agonists with K(Ca)3.1 modulating function may be useful for the treatment of mast cell-mediated disease.

Essential role of EP3 subtype in prostaglandin E2-induced adhesion of mouse cultured and peritoneal mast cells to the Arg-Gly-Asp-enriched matrix

Accumulating evidence has indicated that mast cells can modulate a wide variety of immune responses. Migration and adhesion play a critical role in regulation of tissue mast cell function, in particular, under inflammatory conditions. We previously demonstrated that prostaglandin (PG) E2 stimulates adhesion of a mouse mastocytoma cell line, P-815, to the Arg-Gly-Asp (RGD)-enriched matrix through cooperation between two PGE2 receptor subtypes: EP3 and EP4 (Hatae N, Kita A, Tanaka S, Sugimoto Y, Ichikawa A. J Biol Chem 278: 17977–17981, 2003). We here investigated PGE2-induced adhesion of IL-3-dependent bone marrow-derived cultured mast cells (BMMCs). In contrast to the elevated cAMP-dependent adhesion of P-815 cells, EP3-mediated Ca2+ mobilization plays a pivotal role in PGE2-induced adhesion of BMMCs. Adhesion and Ca2+ mobilization induced by PGE2 were abolished in the Ptger3−/− BMMCs and were significantly suppressed by treatment with pertussis toxin, a phospholipase C inhibitor, U-73122, and a store-operated Ca2+ channel inhibitor, SKF 36965, indicating the involvement of Gi-mediated Ca2+ influx. We then investigated PGE2-induced adhesion of peritoneal mast cells to the RGD-enriched matrix. EP3 subtype was found to be the dominant PGE receptor that expresses in mouse peritoneal mast cells. PGE2 induced adhesion of the peritoneal mast cells of the Ptger3+/+ mice, but not that of the Ptger3−/− mice. In rat peritoneal mast cells, PGE2 or an EP3 agonist stimulated both Ca2+ mobilization and adhesion to the RGD-enriched matrix. These results suggested that the EP3 subtype plays a pivotal role in PGE2-induced adhesion of murine mast cells to the RGD-enriched matrix through Ca2+ mobilization.