Regulation of prostaglandin endoperoxide synthase-2 and IL-6 expression in mouse bone marrow-derived mast cells by exogenous but not endogenous prostanoids

New Pathways for the Skin's Stress Response: The Cholinergic Neuropeptide SLURP-1 Can Activate Mast Cells and Alter Cytokine Production in Mice

Background: The alpha7 nicotinic acetylcholine receptor (Chrna7) plays an essential anti-inflammatory role in immune homeostasis and was recently found on mast cells (MC). Psychosocial stress can trigger MC hyperactivation and increases pro-inflammatory cytokines in target tissues such as the skin. If the cholinergic system (CS) and Chrna7 ligands play a role in these cascades is largely unknown.

Objective: To elucidate the role of the CS in the response to psychosocial stress using a mouse-model for stress-triggered cutaneous inflammatory circuits.

Methods: Key CS markers (ACh, Ch, SLURP-1, SLURP-2, Lynx1, Chrm3, Chrna7, Chrna9, ChAT, VAChT, Oct3, AChE, and BChE) in skin and its MC (sMC), MC activation, immune parameters (TNFα, IL1β, IL10, TGFβ, HIF1α, and STAT3) and oxidative stress were analyzed in skin from 24 h noise-stressed mice and in cultured MC (cMC) from C57BL/6 or Chrna7-Knockout mice.

Results: First, Chrna7 and SLURP-1 mRNA were exclusively upregulated in stressed skin. Second, histomorphometry located Chrna7 and SLURP-1 in nerves and sMC and demonstrated upregulated contacts and increased Chrna7+ sMC in stressed skin, while 5 ng/mL SLURP-1 degranulated cMC. Third, IL1β+ sMC were high in stressed skin, and while SLURP-1 alone had no significant effect on cMC cytokines, it upregulated IL1β in cMC from Chrna7-KO and in IL1β-treated wildtype cMC. In addition, HIF1α+ sMC were high in stressed skin and Chrna7-agonist AR-R 17779 induced ROS in cMC while SLURP-1 upregulated TNFα and IL1β in cMC when HIF1α was blocked.

Conclusions: These data infer that the CS plays a role in the regulation of stress-sensitive inflammatory responses but may have a surprising pro-inflammatory effect in healthy skin, driving IL1β expression if SLURP-1 is involved.

Leptin Elicits In Vivo Eosinophil Migration and Activation: Key Role of Mast Cell-Derived PGD2

Eosinophils are key regulators of adipose tissue homeostasis, thus characterization of adipose tissue-related molecular factors capable of regulating eosinophil activity is of great interest. Leptin is known to directly activate eosinophils in vitro, but leptin ability of inducing in vivo eosinophilic inflammatory response remains elusive. Here, we show that leptin elicits eosinophil influx as well as its activation, characterized by increased lipid body biogenesis and LTC₄ synthesis. Such leptin-triggered eosinophilic inflammatory response was shown to be dependent on activation of the mTOR signaling pathway, since it was (i) inhibited by rapamycin pre-treatment and (ii) reduced in PI3K-deficient mice. Local infiltration of activated eosinophils within leptin-driven inflammatory site was preceded by increased levels of classical mast cell-derived molecules, including TNFα, CCL5 (RANTES), and PGD₂. Thus, mice were pre-treated with a mast cell degranulating agent compound 48/80 which was capable to impair leptin-induced PGD₂ release, as well as eosinophil recruitment and activation. In agreement with an indirect mast cell-driven phenomenon, eosinophil accumulation induced by leptin was abolished in TNFR-1 deficient and also in HQL-79-pretreated mice, but not in mice pretreated with neutralizing antibodies against CCL5, indicating that both typical mast cell-driven signals TNFα and PGD₂, but not CCL5, contribute to leptin-induced eosinophil influx. Distinctly, leptin-induced eosinophil lipid body (lipid droplet) assembly and LTC₄ synthesis appears to depend on both PGD₂ and CCL5, since both HQL-79 and anti-CCL5 treatments were able to inhibit these eosinophil activation markers. Altogether, our data show that leptin triggers eosinophilic inflammation in vivo via an indirect mechanism dependent on activation of resident mast cell secretory activity and mediation by TNFα, CCL5, and specially PGD₂.

Prostaglandin E2 prevents hyperosmolar-induced human mast cell activation through prostanoid receptors EP2 and EP4

Background

Mast cells play a critical role in allergic and inflammatory diseases, including exercise-induced bronchoconstriction (EIB) in asthma. The mechanism underlying EIB is probably related to increased airway fluid osmolarity that activates mast cells to the release inflammatory mediators. These mediators then act on bronchial smooth muscle to cause bronchoconstriction. In parallel, protective substances such as prostaglandin E₂ (PGE₂) are probably also released and could explain the refractory period observed in patients with EIB.

Objective

This study aimed to evaluate the protective effect of PGE₂ on osmotically activated mast cells, as a model of exercise-induced bronchoconstriction.

Methods

We used LAD2, HMC-1, CD34-positive, and human lung mast cell lines. Cells underwent a mannitol challenge, and the effects of PGE₂ and prostanoid receptor (EP) antagonists for EP_1–4 were assayed on the activated mast cells. Beta-hexosaminidase release, protein phosphorylation, and calcium mobilization were assessed.

Results

Mannitol both induced mast cell degranulation and activated phosphatidyl inositide 3-kinase and mitogen-activated protein kinase (MAPK) pathways, thereby causing de novo eicosanoid and cytokine synthesis. The addition of PGE₂ significantly reduced mannitol-induced degranulation through EP₂ and EP₄ receptors, as measured by beta-hexosaminidase release, and consequently calcium influx. Extracellular-signal-regulated kinase 1/2, c-Jun N-terminal kinase, and p38 phosphorylation were diminished when compared with mannitol activation alone.

Conclusions

Our data show a protective role for the PGE₂ receptors EP₂ and EP₄ following osmotic changes, through the reduction of human mast cell activity caused by calcium influx impairment and MAP kinase inhibition.

Role of prostaglandin E2 in the synthesis of the pro-inflammatory cytokine interleukin-6 in primary sensory neurons: an in vivo and in vitro study

Following various types of nerve injury, cyclooxygenase 2 and prostaglandin E2 (PGE2) are universally and chronically up-regulated in injured nerves and contribute to the genesis of neuropathic pain. Persistent high levels of PGE2 likely exert chronic effects on nociceptive dorsal root ganglion (DRG) neurons. In the present study, we tested the hypothesis that injured nerve-derived PGE2 contributes to the up-regulation of the pro-inflammatory cytokine interleukin-6 (IL-6) in DRG neurons following partial sciatic nerve ligation. In naive adult rats, IL-6 was expressed in only a few small size DRG neurons which all co-expressed EP4 receptors. Partial sciatic nerve ligation increased and shifted IL-6 expression from small to medium and large size damaged DRG neurons. Perineural injection of a selective cyclooxygenase 2 inhibitor or a selective EP4 receptor antagonist significantly suppressed the up-regulation of IL-6 in DRG, suggesting that injured nerve derived PGE2 contributes to the de novo synthesis of IL-6 in DRG neurons through EP4 receptors. In cultured sensory ganglion explants, a stabilized PGE2 analog increased IL-6 mRNA and protein levels through the activation of EP4, protein kinase A, protein kinase C, extracellular regulated protein kinase/MAPK, cAMP response element binding protein and NFκB signalling pathways. Taken together, these data indicate that facilitating the de novo synthesis of pain-related cytokines in injured medium and large size DRG neurons is a novel mechanism underlying the role of injured nerve derived PGE2 in the genesis of neuropathic pain.

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.

Mast cells function as an alternative modulator of adipogenesis through 15-deoxy-delta-12, 14-prostaglandin J2

Mast cells are one of the major producers of prostaglandins (PGs). The final metabolite of PGs 15-deoxy-delta-12,14-PGJ(2) (15-deoxy-delta PGJ(2)) is the endogenous ligand of the peroxisome proliferator-activated receptor (PPAR) γ. PPARγ modulates adipocyte differentiation; therefore, we attempted to investigate whether PGs derived from mast cells influenced on adipogenesis. We found the increase of mast cell numbers in fat tissue of obese mice fed with a high-fat diet allowed us to speculate contributions of mast cells to adipogenesis. Mast cell-mediated induction of adipogenesis was evaluated by using 3T3 L1 cells. Supernatants obtained from mast cells stimulated with calcium ionophore or the high-glucose condition contained 15-deoxy-delta PGJ(2) and induced adipogenesis of 3T3 L1 cells. Agonistic activity of PGJ(2) from the supernatants on PPARγ was confirmed by a reporter gene assay. Culture medium collected from calcium ionophore-stimulated bone marrow-derived cultured mast cells (BMCMC) activated PPAR-responsive element in NIH3T3 fibroblasts, and the specific inhibitor of PPARγ canceled the activation. Contribution of mast cells to obesity was evaluated by using mast cell-deficient mice fed with a Western diet. Weight gain of mast cell-deficient mice during high-fat feeding was impaired compared with their littermate wild-type mice; on the other hand, transplantation of bone marrow-derived cultured mast cells to mast cell-deficient mice restored the weight gain by intake of a high-fat diet. In this study, we clearly demonstrated that mast cells produced PGs in response to the high-glucose condition and induced adipocyte differentiation and possibly obesity. This is the first study that provides evidence for a novel role of mast cells in adipogenesis via PPARγ activation.

Characterization and modulation of canine mast cell derived eicosanoids

Mast cells play an important role in both innate and acquired immunity as well as several pathological conditions including allergy, arthritis and neoplasia. They influence these processes by producing a variety of mediators including cytokines, chemokines and eicosanoids. Very little is currently known about the spectrum of inflammatory mediators, particularly eicosanoids (prostaglandins and leukotrienes), produced by canine mast cells. This is important since modulating mast cell derived eicosanoids may help in the treatment of autoimmune and inflammatory disorders. The purpose of this study was to investigate the spectrum of eicosanoids produced by normal canine mast cells and to evaluate the effects of cytokines and non-steroidal anti-inflammatory mediators (NSAIDS) on eicosanoid production and release. Canine bone marrow derived cultured mast cells (cBMCMCs) expressed COX-1, COX-2, and 5-LOX and synthesized and released PGD2, PGE2, LTB4, and LTC4 following activation by a variety of stimuli. The selective COX-2 NSAIDs carprofen (Rimadyl) and deracoxib (Deramaxx) inhibited PGD2 and PGE2 production but only slightly inhibited LTB4 and LTC4. The mixed COX-1/COX-2 inhibitor piroxicam blocked PGD2 and PGE2 production, but upregulated LTC4 following treatment while tepoxilan (Zubrin), a pan COX/LOX inhibitor, markedly reduced the production of all eicosanoids. The LOX inhibitor nordihydroguaiaretic acid (NDGA) prevented LTB4/LTC4 release and BMBMC degranulation. Pre-incubation of cBMCMCs with IL-4 and SCF sensitized these cells to degranulation in response to substance P. In conclusion, canine BMCMCs produce an array of eicosanoids similar to those produced by mast cells from other species. Tepoxilan appeared to be the most effective NSAID for blocking eicosanoid production and thus may be useful for modulating mast cell mediated responses in dogs.

PPARalpha/gamma-Independent Effects of PPARalpha/gamma Ligands on Cysteinyl Leukotriene Production in Mast Cells

Peroxisome proliferator-activated receptor (PPAR) α ligands (Wy-14,643, and fenofibrate) and PPARγ ligands (troglitazone and ciglitazone) inhibit antigen-induced cysteinyl leukotriene production in immunoglobulin E-treated mast cells. The inhibitory effect of these ligands on cysteinyl leukotriene production is quite strong and is almost equivalent to that of the anti-asthma compound zileuton. To develop new aspects for anti-asthma drugs the pharmacological target of these compounds should be clarified. Experiments with bone-marrow-derived mast cells from PPARα knockout mice and pharmacological inhibitors of PPARγ suggest that the inhibitory effects of these ligands are independent of PPARs α and γ. The mechanisms of the PPAR-independent inhibition by these agents on cysteinyl leukotriene production are discussed in this review.

Mast cell IL-6 improves survival from Klebsiella pneumonia and sepsis by enhancing neutrophil killing

The pleiotropic cytokine IL-6 has favorable and harmful effects on survival from bacterial infections. Although many innate immune cells produce IL-6, little is known about relevant sources in vivo and the nature of its contributions to host responses to severe bacterial infections. To examine these roles, we subjected mast cell-specific IL-6-deficient mice to the cecal ligation and puncture model of septic peritonitis, finding that survival in these mice is markedly worse than in controls. Following intranasal or i.p. inoculation with Klebsiella pneumoniae, IL-6 (-/-) mice are less likely to survive than wild-type controls and at the time of death have higher numbers of bacteria but not inflammatory cells in lungs and peritoneum. Similarly, mast cell-specific IL-6-deficient mice have diminished survival and higher numbers of K. pneumoniae following i.p. infection. Neutrophils lacking IL-6 have greater numbers of live intracellular K. pneumonia, suggesting impaired intracellular killing contributes to reduced clearance in IL-6(-/-) mice. These results establish that mast cell IL-6 is a critical mediator of survival following K. pneumoniae infection and sepsis and suggest that IL-6 protects from death by augmenting neutrophil killing of bacteria.

Exogenous nitric oxide regulates cyclooxygenase-2 expression and prostaglandin D(2) generation through p38 MAPK in mouse bone marrow-derived mast cells

Nitric oxide (NO) is an important signaling molecule that regulates MC function. However, the involvement of NO in an important lipid mediator, prostaglandin (PG) D(2) production by MC, is unclear. The role of NO in cyclooxygenase (COX)-2 expression and PGD(2) generation as well as IL-6 production in mouse bone marrow-derived MC (BMMC) was investigated using NO donors. Exogenous NO augmented COX-2 protein expression and increased COX-2-dependent PGD(2) generation in response to SCF, IL-10, and IL-1beta, or antigen activation in combination with IL-10 and IL-1beta after sensitization with IgE. The increased expression of COX-2 by NO donors was inhibited by hemoglobin. Moreover it was not affected by soluble guanylyl cyclase inhibitor, but reduced by the p38 MAPK inhibitor, SB202190. Downstream of p38 MAPK, NO donors augmented not only COX-2 mRNA transcription but also its stability. Exogenous NO also augmented IL-6 production by SCF, IL-10, and IL-1beta. These results show that exogenous NO can increase COX-2-dependent PGD(2) and IL-6 production by MC in inflammatory environments through the p38 MAPK pathway. Therefore, our novel observations suggest that the effect of NO on MC is not limited to the suppression of their activation as has been the emphasis previously, but can also augment certain MC responses.

Sphingosine 1-Phosphate-Mediated Trafficking of Pathogenic Th2 and Mast Cells for the Control of Food Allergy

Sphingosine 1-phosphate (S1P) has been proposed as a regulator of lymphocyte trafficking, but its role in mucosa-associated diseases, such as in food allergies, remains to be elucidated. To examine the role of S1P in allergic diseases in the intestine, we used a Th2 cell-mediated Ag-specific allergic diarrhea model and demonstrated that type 1 S1P receptor (S1P(1)) expression was preferentially associated with pathogenic CD4(+) T cells for the development of allergic reactions. Consistent with this demonstration, treatment with FTY720, a modulator of the S1P(1), prevented allergic diarrhea by inhibiting the migration of systemically primed pathogenic CD4(+) T cells induced by oral challenge with allergen into the large intestine. In addition, FTY720 hampered mast cell infiltration into the large intestine, whereas eosinophil infiltration into the large intestine and total and allergen-specific serum IgE production were comparable between mock- and FTY720-treated groups. These results suggest that modulation of the S1P-mediated pathway to inhibit the migration of pathogenic CD4(+) T cells and mast cells into the large intestine could be a novel strategy for preventing allergic diarrhea.

Simultaneous quantification of seven prostanoids using liquid chromatography/tandem mass spectrometry: the effects of arachidonic acid on prostanoid production in mouse bone marrow-derived mast cells

We have developed a method for the simultaneous estimation of the levels of the prostanoids 6-keto prostaglandin (PG) Flalpha, PGB2, PGD2, PGE2, PGF2(alpha), PGJ2, and thromboxane (TX) B2 in blood- or serum-containing medium using liquid chromatography-tandem mass spectrometry. These prostanoids and their deuterium derivatives, which were used as internal standards, were subjected to solid-phase extraction using Empore C18 HD disk cartridges and analyzed in the selected reaction-monitoring mode. A linear response curve starting at 10 pg of prostanoid/tube was observed for each prostanoid. The accuracy of the method was demonstrated with samples containing known amounts of the prostanoids. Furthermore, we used this method to analyze the prostanoids produced in mouse bone marrow-derived mast cells stimulated with arachidonic acid, which resulted in the production of PGD2, PGE2, PGF2alpha, and TXB2. The results suggest that this simultaneous quantification method is useful for the analysis of the production of biomedically important prostanoids.

Comparison of the influence of NSAIDs with different COX-selectivity on histamine release from mast cells isolated from naïve and sensitized rats

Mast cell stimulation leads to an early response with histamine release and prostaglandin (PGD(2)) production but attempts to link these two events have been contradictory. In IgE-mediated mast cell activation, a late-phase PGD(2)-production is caused by increased cyclooxygenase-2 (COX-2) expression whereas a COX-2 involvement in the early response is uncertain. The present study compares the influence of four COX-inhibitors (NSAIDs) on the histamine release of mast cells from naïve and actively sensitized rats. NSAIDs of different COX-1 vs. COX-2 selectivity were used, i.e. acetylsalicylic acid (ASA), piroxicam, meloxicam, and NS-398, a selective COX-2-inhibitor. All could inhibit antigen-induced histamine release, with 64%, 34%, 27% and 85% inhibition by ASA (5 mM), piroxicam (100 microM), meloxicam (100 microM) and NS-398 (100 microM), respectively. Similar inhibition was found with compound 48/80 without calcium added to the medium whereas compound 48/80 with calcium was affected less by ASA and NS-398 and unaffected by the oxicams. Only small differences between the two kinds of mast cells were found, except with NS-398 which was a significantly more effective inhibitor of naïve than sensitized cells when exposed to compound 48/80 with calcium present. The results do not show any consistent relationship between the influence of the NSAIDs and their COX-2-selectivity. The high NSAID-concentrations required for inhibition cast doubt about an involvement of COX-inhibition and indicate additional or other targets. The results seem to exclude toxic effects on mast cell energy production but are consistent with an interference with the calcium disposition.

Mast cell mediators in allergic inflammation and mastocytosis

Mast cells possess an array of potent inflammatory mediators capable of inducing acute symptoms after cell activation, including urticaria, angioedema, bronchoconstriction, diarrhea, vomiting, hypotension, cardiovascular collapse, and death in few minutes. In contrast, mast cells can provide an array of beneficial mediators in the setting of acute infections, cardiovascular diseases, and cancer. The balance between the detrimental and beneficial roles of mast cells is not completely understood. Although the symptoms of acute mast cell mediator release can be reversed with epinephrine, adrenergic agonists, and mediator blockers, the continued release of histamine, proteases, prostaglandins, leukotrienes, cytokines, and chemokines leads to chronic and debilitating disease, such as mastocytosis. Identification of the molecular factors and mechanisms that control the synthesis and release of mast cell mediators should benefit all patients with mast cell activation syndromes and mastocytosis.

A functional comparison of canine and murine bone marrow derived cultured mast cells

Disorders involving mast cells are extremely common in dogs, ranging from allergic diseases to neoplastic transformation resulting in malignant mast cell tumors. Relatively little is known regarding the basic biologic properties of normal canine mast cells, largely due to the difficulty in reliably purifying large numbers from canine skin. In vitro generated bone marrow derived cultured mast cells (BMCMCs) are routinely used in both human and murine studies as a ready source of material for in vitro and in vivo studies. We previously developed a technique to generate canine BMCMCs from bone marrow derived CD34+ cells and demonstrated that these cells exhibit the phenotypic properties characteristic of mast cells and release histamine in response to IgE cross-linking. The purpose of the following study was to characterize the functional properties of these canine BMCMCs and contrast these with the functional properties of murine BMCMCs. Our work demonstrates that both IL-4 and IL-10 promote canine BMCMC proliferation, possibly through upregulation of Kit expression, while TGFbeta inhibits proliferation. The canine BMCMCs produce a variety of cytokines and chemokines in response to IgE cross-linking and chemical stimulation including IL-3, IL-4, IL-13, GM-CSF, RANTES, and MIP1alpha. Interestingly, the canine BMCMCs released significantly larger amounts of MCP-1 and tryptase and significantly smaller amounts of IL-6 following chemical stimulation and IgE cross-linking when compared to murine BMCMCs. Lastly, the canine BMCMCs produced larger amounts of active MMP9 than their murine counterparts. In summary, canine BMCMCs exhibit unique functional properties that distinguish them from murine BMCMCs and provide insight into the contribution of these cells to mast cell disorders in the dog.

Group V secretory phospholipase A2 amplifies the induction of cyclooxygenase 2 and delayed prostaglandin D2 generation in mouse bone marrow culture-derived mast cells in a strain-dependent manner

Activation of mouse bone marrow-derived mast cells (BMMC) with stem cell factor (SCF) or IgE and antigen elicits exocytosis and an immediate phase of prostaglandin (PG) D(2) and leukotriene (LT) C(4) generation. Activation of BMMC by SCF, IL-1beta and IL-10 elicits a delayed phase of PGD(2) generation dependent on cyclooxygenase (COX) 2 induction. Cytosolic phospholipase A(2) alpha provides arachidonic acid in both phases and amplifies COX-2 induction. Pharmacological experiments implicate an amplifying role for secretory (s) PLA(2). We used mice lacking the gene encoding group V sPLA(2) (Pla2g5-/-) to definitively test its role in eicosanoid generation by BMMC. Pla2g5-/- BMMC on a C57BL/6 genetic background showed a modest reduction in exocytosis and immediate PGD(2) generation after activation with SCF or with IgE and antigen, while LTC(4) generation was not modified. Delayed-phase PGD(2) generation and COX-2 induction were reduced approximately 35% in C57BL/6 Pla2g5-/- BMMC and were restored by exogenous PGE(2). There was no deficit in either phase of eicosanoid generation by Pla2g5-/- BMMC on a BALB/c background. Thus, group V sPLA(2) amplifies COX-2 expression and delayed phase PGD(2) generation in a strain-dependent manner; it has at best a limited role in immediate eicosanoid generation by BMMC.

The mast cell mediator PGD2 suppresses IL-12 release by dendritic cells leading to Th2 polarized immune responses in vivo

Dendritic cells (DC) and mast cells (MC) are colocalized in superficial organs such as the skin. Both cell types recognize and respond to pathogens. DC capture and transport antigens to the draining lymph node for CD4+ T cell priming and T helper 1 (Th1) or Th2 polarization. As MC are mainly associated with Th2 responses, DC-MC interactions may favor Th2 priming by DC. Here, we show the role of different MC mediators on IL-12 and IL-10 production by DC. While histamine, leukotriene C4, heparin and chondroitin sulfate A had little and unspecific effects on the cytokine production, prostaglandin D2 (PGD2) downregulated IL-10, IL-12p70 and p40. After subcutaneous (s.c.) injection of ovalbumin (OVA)-loaded, lipopolysaccharide (LPS)-matured DC into Th1-prone C57BL/6 mice, the levels of IFN-gamma produced by Th1 cells were decreased while IL-4 production remained low. When TNF-matured DC were pretreated with PGD2, loaded with the endotoxin-free antigen KLH and injected s.c. into Th2-prone BALB/c mice, we found a dose- and time-dependent upregulation of IL-4 and downregulation of IFN-gamma by T cells. Together, MC-derived PGD2 instructs DC to polarize CD4+ T cells towards Th2 responses. As a consequence, such a DC-MC cooperation may contribute to the maintenance of Th2 responses in allergic patients.

Human mast cells express multiple EP receptors for prostaglandin E2 that differentially modulate activation responses

Prostaglandin E2 (PGE2) blocks mast-cell (MC)-dependent allergic responses in humans but activates MCs in vitro. We assessed the functions of the EP receptors for PGE2 on cultured human MCs (hMCs). hMCs expressed the EP3, EP2, and EP4 receptors. PGE2 stimulated the accumulation of cyclic adenosine monophosphate (cAMP), and suppressed both Fc epsilonRI-mediated eicosanoid production and tumor necrosis factor-alpha (TNF-alpha) generation. PGE2 also caused phosphorylation of extracellular signal-regulated kinase (ERK), exocytosis, and production of prostaglandin D2 (PGD2), as well as leukotriene C4 (LTC4) when protein kinase A (PKA) was inhibited. An EP3 receptor-selective agonist, AE-248, mimicked PGE2-mediated ERK phosphorylation, exocytosis, and eicosanoid formation. Selective agonists of both EP2 and EP4 receptors (AE1-259-01 and AE-329, respectively) stimulated cAMP accumulation. No selective agonist, alone or in combination, was as effective as PGE2. AE-248, AE1-259-01, and AE-329 all inhibited Fc epsilonRI-mediated TNF-alpha generation, while AE1-259-01 blocked eicosanoid production. PGE2 caused the expression of inducible cAMP early repressor (ICER) by a pathway involving PKA and ERK. Thus, while PGE2 activates MCs through EP3 receptors, it also counteracts Fc epsilonRI-mediated eicosanoid production through EP2 receptors and PKA, and blocks cytokine transcription. These functions explain the potency of PGE2 as a suppressor of early- and late-phase allergic responses.

Prostaglandin E2 induces cyclooxygenase-2 expression in human non-pigmented ciliary epithelial cells through activation of p38 and p42/44 mitogen-activated protein kinases

Prostaglandins (PGs) have been implicated in lowering intraocular pressure (IOP). A possible role of cyclooxygenase-2 (COX-2) in this process was emphasized by findings showing impaired COX-2 expression in the non-pigmented ciliary epithelium (NPE) of patients with primary open-angle glaucoma. The present study investigates the effect of the major COX-2 product, PGE(2), on the expression of its synthesizing enzyme in human NPE cells (ODM-2). PGE(2) led to an increase of COX-2 mRNA and protein expression, whereas the expression of COX-1 remained unchanged. Upregulation of COX-2 expression by PGE(2) was accompanied by time-dependent phosphorylations of p38 mitogen-activated protein kinase (MAPK) and p42/44 MAPK, and was abrogated by inhibitors of both pathways. Moreover, PGE(2)-induced COX-2 expression was suppressed by the intracellular calcium chelator, BAPTA/AM, and the protein kinase C inhibitor bisindolylmaleimide II, whereas the protein kinase A inhibitor H-89 was inactive in this respect. Induction of COX-2 expression was also elicited by butaprost (EP(2) receptor agonist) and 11-deoxy PGE(1) (EP(2)/EP(4) receptor agonist), but not by EP(1)/EP(3) receptor agonists (17-phenyl-omega-trinor PGE(2), sulprostone). Consistent with these findings, the EP(1)/EP(2) receptor antagonist, AH-6809, and the selective EP(4) receptor antagonist, ONO-AE3-208, significantly reduced PGE(2)-induced COX-2 expression. Collectively, our results demonstrate that PGE(2) at physiologically relevant concentrations induces COX-2 expression in human NPE cells via activation of EP(2)- and EP(4) receptors and phosphorylation of p38 and p42/44 MAPKs. Positive feedback regulation of COX-2 may contribute to the production of outflow-facilitating PGs and consequently to regulation of IOP.

Evaluation of selective prostaglandin E2 (PGE2) receptor agonists as therapeutic agents for the treatment of asthma

Prostaglandin E2 (PGE2) released in asthmatic airways has bronchodilator properties and inhibits allergen-induced bronchoconstriction and release of inflammatory mediators. Although considered as a potential treatment for asthma, PGE2 also has some proinflammatory properties. PGE2 acts through four different receptor subtypes (EP1, EP2, EP3, and EP4) that may explain some of PGE2's diverse effects. In a mouse model of allergic inflammation in which the four receptors were individually deleted, only EP3(-/-) mice showed an enhancement of inflammation, whereas an EP3 agonist was inhibitory, with PGE2 being inactive. Thus, EP3 agonists may lead to a new approach for the treatment of asthma. However, other PGE2 receptor subtypes may also have beneficial effects, and a greater understanding of the signaling pathways of these receptor subtypes will help to clarify the role of these receptors in asthma.

Ciglitazone inhibits the antigen-induced leukotrienes production independently of PPARgamma in RBL-2H3 mast cells

Peroxisome prolifelator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor, through which PPARgamma agonists have been demonstrated to down-regulate inflammatory cell functions. Recently, the agonists are reported to exert, in some conditions, their inhibitory actions independently of PPARgamma. Previously, we showed that a PPARgamma agonist, troglitazone, inhibited cysteinyl (Cys)-leukotrienes production in RBL-2H3 cells after IgE receptor triggering. Here we examined whether the inhibition of cycteinyl-leukotrienes production in the cells was dependent on the activation of PPARgamma. A PPARgamma agonist, ciglitazone, significantly inhibited Cys-leukotrienes, but not prostaglandin D2, production. The inhibition was not attenuated by the pretreatment with a PPARgamma antagonist. Ciglitazone did not alter the mRNA expression of acyl-coenzyme A binding protein, the gene expression of which is up-regulated by PPARgamma, nor induce the nucleus translocation of PPARgamma. These results suggest that the inhibition by PPARgamma agonists of Cys-leukotrienes production in RBL-2H3 cells after IgE receptor triggering is not through the activation of PPARgamma.

Up‐regulation of interleukin‐6 induced by prostaglandin E 2 from invading macrophages following nerve injury: an in vivo and in vitro study

The mechanisms underlying neuropathic pain caused by nerve injury are not well understood. Inflammatory responses in injured nerves are likely to be key contributing factors in the generation and maintenance of neuropathic pain. The pro-inflammatory cytokine interleukin-6 (IL-6) is up-regulated in invading macrophages and has been implicated in the development of neuropathic pain. We previously demonstrated that invading macrophages up-regulate cyclooxygenase 2 (COX2) and prostaglandin E2 (PGE2) receptors EP1 and EP4, suggesting that PGE2 may affect macrophage function via autocrine or paracrine mechanisms. This study was undertaken to determine whether PGE2 is involved in the up-regulation of IL-6 in invading macrophages. Two weeks following partial sciatic nerve ligation, numerous IL-6 immunoreactive (IR) cell profiles were present in injured nerves. Colocalization of IL-6 with the invading macrophage marker ED1 or with COX2 was frequently observed. IL-6-IR, COX2-IR and ED1-IR cells were present only in cultures derived from injured nerve segments. PGE2 and IL-6 release from cultured cells derived from injured nerves was increased significantly compared with uninjured nerves. Non-selective and selective COX2 inhibitors suppressed PGE2 and IL-6 release. Treatment with PGE2 further enhanced IL-6 release in a concentration- and time-dependent manner. A selective EP4 receptor antagonist L-161982 was able to suppress IL-6 release, whereas an EP1 receptor antagonist, SC19220, was ineffective. Moreover, a protein kinase C inhibitor, calphostin C, dramatically suppressed IL-6 release, whereas a protein kinase A inhibitor H-89 and a Ca2+ chelator EGTA failed. Taken together, our data suggest that PGE2 is involved in mediating the up-regulation of IL-6 occurring in invading macrophages. This action is mediated through an EP4 receptor and the protein kinase C signaling pathway.

Bcl6 regulates Th2 type cytokine productions by mast cells activated by FcepsilonRI/IgE cross-linking

Bcl6-deficient (Bcl6-/-) mice displayed Th2 type inflammation, which caused by abnormality of non-lymphoid cells. However, initiators for the Th2 type inflammation were not clear. In order to elucidate the initiators, we investigated property and function of mast cells derived from Bcl6-/- mice. Mast cells were developed from bone marrow cells cultured with IL-3 (BMMCs). Although the development of BMMCs from Bcl6-/- mice was similar to that from wild-type mice, proliferation of Bcl6-/- BMMCs stimulated with IL-3 was slightly lower than that of wild-type BMMCs. When these BMMCs were stimulated by FcepsilonRI/IgE cross-linking, Bcl6-/- BMMCs produced Th2 cytokines more than wild-type BMMCs did. Thus, Bcl6-/- mast cells are one of the initiators for Th2 type inflammation in Bcl6-/- mice, and Bcl6 may be a molecular target for Th2 type allergic diseases.

Peroxisome Proliferator-Activated Receptor-γ Suppresses Cyclooxygenase-2 Expression in Human Prostate Cells

Recent studies have found that cyclooxygenase-2 (COX-2) protein expression was low and inducible with cytokines in prostate cancer cells (in the absence of serum) and that, in contrast, COX-2 expression was high in normal prostate epithelial cells (EC). Peroxisome proliferator-activated receptor-γ (PPAR-γ) was expressed at high levels in the prostate cancer cell line PC-3 but not in ECs. In contrast to previous findings by others, PPAR-γ ligands did not induce PPAR-γ expression in EC or PC-3. The present study examined the relationship between PPAR-γ and COX-2 expression patterns in EC and PC-3 in the presence and absence of serum and/or the PPAR-γ agonist 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2). We also evaluated the effects that the forced expression of PPAR-γ1 and PPAR-γ2 had on COX-2 in ECs. We found that expression of PPAR-γ and COX-2 protein was inversely correlated in ECs and PC-3. Low COX-2 expression in PC-3 was up-regulated by serum, and 15d-PGJ2 blocked serum-induced COX-2 expression and activity in a dose-dependent manner. 15d-PGJ2 had no effect on COX-2 expression in ECs or PPAR-γ expression in either cell type. However, forced expression of PPAR-γ1 or PPAR-γ2 in ECs suppressed the high level of endogenous COX-2. This effect was not isoform specific and was augmented by 15d-PGJ2. The present study showed that PPAR-γ activation can be an important regulator of COX-2 in prostate cells and may be an important target for prostate cancer chemoprevention.

MITF is necessary for generation of prostaglandin D2 in mouse mast cells

Mast cells generate eicosanoids that are linked to asthma and other inflammatory diseases. A basic-helix-loop-helix leucine zipper transcription factor termed MITF is essential for the development of mast cells. Although other substances also linked to inflammatory reactions (such as various proteases and serotonin) require MITF for their expression, the role of MITF in eicosanoid generation has not been studied. We examined eicosanoid generation in bone marrow-derived mast cells (BMMCs) of tg/tg mice that lack MITF. Most eicosanoids generated by BMMCs are either prostaglandin (PG) D2 or leukotriene C4. The former is synthesized via the cyclooxygenase pathway, whereas the latter is synthesized via the 5-lipoxygenase pathway. In response to stimulation with IgE and antigens, BMMCs of tg/tg mice synthesized leukotriene C4 normally. However, neither immediate nor delayed PGD2 production was detected in these BMMCs. This indicates that MITF is a transcription factor that specifically activates the cyclooxygenase pathway, but not the 5-lipoxygenase pathway. Significant decreases in expression of hematopoietic PGD2 synthase (hPGDS, a terminal synthase for PGD2) were observed at both mRNA and protein levels in tg/tg BMMCs. MITF transactivated the hPGDS gene via a CACCTG motif located in the promoter region. MITF appeared to be essential for generation of PGD2 by enhancing expression of the hPGDS gene in BMMCs.

Bone marrow norepinephrine mediates development of functionally different macrophages after thermal injury and sepsis

OBJECTIVE

We sought to determine the influence of thermal (burn) injury with sepsis and norepinephrine on the clonogenic potential and functional cytokine response to lipopolysaccharide (LPS) stimulation in nonmyeloid committed (CD117) and myeloid committed (ER-MP12) bone marrow progenitor cells.

SUMMARY AND BACKGROUND DATA

We have previously demonstrated that norepinephrine stimulated myelopoiesis after burn injury and sepsis, but the site of this stimulation in monocyte development is unknown. In the present study the influence of norepinephrine on the developmental hierarchy of bone marrow cells after thermal injury and sepsis was determined by assessing the clonogenic potential and LPS-stimulated cytokine responses of mature macrophages derived from CD117 and ER-MP12 bone marrow progenitor cells.

METHODS

Tissue and bone marrow norepinephrine content was ablated by chemical sympathectomy with 6-hydroxydopamine treatment. CD117 and ER-MP12 bone marrow cells were isolated using antibody-linked magnetic microbeads. Clonogenic potential in response to colony-stimulating factors was determined. Both progenitor cell types were differentiated to mature macrophages in vitro and tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 cytokine responses to LPS provocation were determined.

RESULTS

The macrophage- and granulocyte-macrophage colony-stimulating factor responsive clonogenic potential was increased with burn sepsis, suggesting an expansion of both progenitor populations. Such increases were greatly reduced with prior depletion of norepinephrine. TNF-alpha and IL-6 cytokine responses to LPS were markedly influenced by the specific progenitor cells involved as well as the injury conditions and the status of norepinephrine prior to injury. In burn sepsis the depletion of norepinephrine resulted in a dramatic decrease in both IL-6 and TNF-alpha production by both progenitor-derived macrophages.

CONCLUSIONS

Depletion of norepinephrine attenuated burn and burn sepsis-induced bone marrow progenitor clonal growth in response to macrophage- and granulocyte-macrophage colony-stimulating factor. Functional phenotypes of bone marrow progenitor-derived macrophages are greatly influenced by norepinephrine and the milieu created by thermal injury and sepsis.

The biphasic effects of cyclopentenone prostaglandins, prostaglandin J2 and 15-deoxy-Δ12,14-prostaglandin J2 on proliferation and apoptosis in rat basophilic leukemia (RBL-2H3) cells

Mast cells produce chemical mediators, including histamine and arachidonate metabolites such as prostaglandin D(2) (PGD(2)) after antigen stimulation. Cyclopentenone prostaglandins of the J series, prostaglandin J(2) (PGJ(2)) and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), are thought to be derivatives of PGD(2). In this study, the biphasic effects of the PGJ(2) and 15d-PGJ(2) on proliferation and apoptosis in rat basophilic leukemia cells (RBL-2H3), a tumor analog of mast cells, were examined. At low concentrations, 1 or 3 microM PGJ(2) and 15d-PGJ(2) induced cell proliferation, respectively. At high concentrations (10-30 microM) both the inhibition of viability and decrease in histamine content in RBL-2H3 cells were dose dependent. These effects were independent of the nuclear hormone receptor, peroxisome proliferator-activated receptor gamma (PPARgamma), since troglitazone, an agonist of PPARgamma did not cause any effects in RBL-2H3 cells. Cell death induced by PGJ(2) and 15d-PGJ(2) was the result of apoptotic processes, since RBL-2H3 cells treated with 30 microM of the prostaglandins had condensed nuclei, DNA fragmentation and increase in activities of caspase-3 and -9. Moreover, PGJ(2) or 15d-PGJ(2)-induced apoptotic effects were prevented by the caspase inhibitor, z-VAD-fmk. In conclusion, the PGJ(2) or 15d-PGJ(2)-induced apoptosis in RBL-2H3 cells occurs mainly via mitochondrial pathways instead of by PPARgamma-dependent mechanisms.

Signal transduction for inhibition of inducible nitric oxide synthase and cyclooxygenase-2 induction by capsaicin and related analogs in macrophages

1. Although capsaicin analogs might be a potential strategy to manipulate inflammation, the mechanism is still unclear. In this study, the effects and action mechanisms of vanilloid analogs on iNOS and COX-2 expression were investigated in RAW264.7 macrophages. 2. Capsaicin and resiniferatoxin (RTX) can inhibit LPS- and IFN-gamma-mediated NO production, and iNOS protein and mRNA expression with similar IC50 values of around 10 microm. 3. Capsaicin also transcriptionally inhibited LPS- and PMA-induced COX-2 expression and PGE2 production. However, this effect exhibited a higher potency (IC50: 0.2 microm), and RTX failed to elicit such responses at 10 microm. 4. Interestingly, we found that capsazepine, a competitive TRPV1 antagonist, did not prevent the inhibition elicited by capsaicin or RTX. Nevertheless, it mimicked vanilloids in inhibiting iNOS/NO and COX-2/PGE2 induction with an IC50 value of 3 microm. RT-PCR and immunoblotting analysis excluded the expression of TRPV1 in RAW264.7 macrophages. 5. The DNA binding assay demonstrated the abilities of vanilloids to inhibit LPS-elicited NF-kappaB and AP-1 activation and IFN-gamma-elicited STAT1 activation. The reporter assay of AP-1 activity also supported this action. 6. The kinase assay indicated that ERK, JNK, and IKK activation by LPS were inhibited by vanilloids. 7. In conclusion, vanilloids can modulate the expression of inflammatory iNOS and COX-2 genes in macrophages through interference with upstream signalling events of LPS and IFN-gamma. These findings provide new insights into the potential benefits of the active ingredient in hot chilli peppers in inflammatory conditions.

[Role of PPARgamma in inflammatory response related to mast cells]

The peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and ligand-activated transcription factors. The activation of PPARgamma regulates lipid and glucose homeostasis and its agonists have been developed as novel antidiabetic drugs. Recently, it has been reported that PPARgamma plays roles in inflammatory and immunological responses. Especially in monocyte/macrophage system, the expression of PPARgamma and the negative regulation of cytokine production has been reported. Mast cells are derived from stem cells in bone marrow, and their proliferation and differentiation are regulated by stimulation of stem cell factor from fibroblasts and/or IL-3 from T lymphocytes. Recently, it was reported that PPARgamma is expressed in mast cells, but its roles remain uncertain. After antigen stimulation, mast cells produce and release prostaglandin D(2) which is metabolized to 15-deoxy Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)). Because 15d-PGJ(2) acts potently as an endogenous PPARgamma agonist, mast cells might play roles in inflammation and immunological responses via the PPARgamma pathway. In this paper we will discuss PPARgamma function in mast cells using cultured bone marrow derived mast cells obtained from heterozygous PPARgamma-deficient mice.

Phospholipase A(2)

Considerable progress has been made in characterizing the individual participant enzymes and their relative contributions in the generation of eicosanoids, lipid mediators derived from arachidonic acid, such as prostaglandins and leukotrienes. However, the role of individual phospholipase (PL) A(2) enzymes in providing arachidonic acid to the downstream enzymes for eicosanoid generation in biologic processes has not been fully elucidated. In this review, we will provide an overview of the classification of the families of PLA(2) enzymes, their putative mechanisms of action, and their role(s) in eicosanoid generation and inflammation.

Roles of keratinocyte inflammation in oral cancer: regulating the prostaglandin E2, interleukin-6 and TNF-alpha production of oral epithelial cells by areca nut extract and arecoline

Betel quid (BQ) chewing is an etiologic factor of oral cancer and submucus fibrosis (OSF). Keratinocyte inflammation is crucial for the pathogenesis of cancer and tissue fibrosis. We found that areca nut (AN) extract (100-400 micro g/ml) induced PGE2 production by KB cells by 2.34- to 23.1-fold and also TNF-alpha production by gingival keratinocytes (GK). Arecoline (0.2-1.2 mM) elevated PGE2 production by KB cells by 2.5- to 6.1-fold. AN extract (200-400 micro g/ml) also induced IL-6 production by GK (7.5- to 8.4-fold) and KB cells. In contrast, arecoline (0.1-1.2 mM) suppressed IL-6 production by GK and KB cells, with 42-81 and 41-63% inhibition, respectively. A 48 h exposure of GK to 800-1200 micro g/ml AN extract led to 37-69% cell death. Arecoline cytotoxicity to GK was noted at concentrations of 0.8-1.2 mM, which led to 28-38% cell death. AN extract (400-800 micro g/ml) induced Cox-2 and IL-6 mRNA expression and also COX-2 protein production by KB cells. IL-6 (5-100 ng/ml) suppressed GK growth by 20-33%, but enhanced oral fibroblast (OMF) and KB cell growth. PGE2 (0.05-5 micro g/ml) and anti-IL-6 antibody (ab) (50-1000 ng/ml) showed little effect on GK and KB cell growth. Incubation of GK and KB cells with aspirin, anti-IL-6 ab and anti-TNF-alpha ab showed little effect on arecoline- and AN-induced cytotoxicity, cell cycle arrest and apoptosis. Exposure to anti-TNF-alpha ab slightly affected arecoline- and AN-modulated PGE2 and IL-6 production by GK and KB cells. Arecoline- and AN-conditioned medium decreased phytohemagglutinin-mediated CD4+ and CD8+ T cell activation. These results indicate that BQ chewing contributes to the pathogenesis of cancer and OSF by impairing T cell activation and by induction of PGE2, TNF-alpha and IL-6 production, which affect oral mucosal inflammation and growth of OMF and oral epithelial cells.

In vitro effects of eicosanoids derived from different 20-carbon Fatty acids on production of monocyte-derived cytokines in human whole blood cultures

INTRODUCTION

Prostaglandins (PG) and leukotrienes (LT) are usually formed from arachidonic acid (e.g. PGE(2), LTB(4), LTC(4)). The anti-inflammatory effects of fish oil may be mediated through the production of alternative PG and/or LT formed from eicosapentaenoic acid (e.g. PGE(3), LTC(5)). This study examines the effects of PG and LT derived from different fatty acid precursors on lipopolysaccharide-induced cytokine production by cultured human whole blood. Methods Human whole blood was diluted 1:5 and incubated for 48h with lipopolysaccharide. PGE and LT were added and the concentrations of inflammatory cytokines in the cell culture supernatants determined.

RESULTS

Tumour necrosis factor (TNF)-alpha concentrations were significantly decreased by the addition of PGE. At the maximum concentration used (10(-6)M) TNF-alpha concentration was reduced to 100%, 90% and 70% by PGE(1), PGE(2) and PGE(3) respectively. Likewise, interleukin (IL)-1beta concentration was decreased to 60%, 30% and 40% by 10(-6)M PGE(1), PGE(2) and PGE(3), respectively. IL-6 and IL-10 concentrations were not altered by PG. LTB(4), LTC(4) or LTC(5) did not significantly affect cytokine concentrations.

CONCLUSIONS

PGE inhibit lipopolysaccharide-stimulated TNF-alpha and IL-1beta production in human whole blood cultures. PGE(1), PGE(2) and PGE(3) show a similar pattern and magnitude of effect. This suggests that the anti-inflammatory effects of dietary fish oil may not be mediated through a simple substitution of one family of eicosanoids for another.