Shunting of prostanoid biosynthesis in microsomal prostaglandin E synthase-1 null embryo fibroblasts: regulatory effects on inducible nitric oxide synthase expression and nitrite synthesis

Facilitation of colonic T cell immune responses is associated with an exacerbation of dextran sodium sulfate-induced colitis in mice lacking microsomal prostaglandin E synthase-1

Background

Microsomal prostaglandin E synthase-1 (mPGES-1) is a key enzyme that acts downstream of cyclooxygenase and plays a major role in inflammation by converting prostaglandin (PG) H₂ to PGE₂. The present study investigated the effect of genetic deletion of mPGES-1 on the development of immunologic responses to experimental colitis induced by dextran sodium sulfate (DSS), a well-established model of inflammatory bowel disease (IBD).

Methods

Colitis was induced in mice lacking mPGES-1 (mPGES-1^−/− mice) and wild-type (WT) mice by administering DSS for 7 days. Colitis was assessed by body weight loss, diarrhea, fecal bleeding, and histological features. The colonic expression of mPGES-1 was determined by real-time PCR, western blotting, and immunohistochemistry. The impact of mPGES-1 deficiency on T cell immunity was determined by flow cytometry and T cell depletion in vivo.

Results

After administration of DSS, mPGES-1^−/− mice exhibited more severe weight loss, diarrhea, and fecal bleeding than WT mice. Histological analysis further showed significant exacerbation of colonic inflammation in mPGES-1^−/− mice. In WT mice, the colonic expression of mPGES-1 was highly induced on both mRNA and protein levels and colonic PGE₂ increased significantly after DSS administration. Additionally, mPGES-1 protein was localized in the colonic mucosal epithelium and infiltrated inflammatory cells in underlying connective tissues and the lamina propria. The abnormalities consistent with colitis in mPGES-1^−/− mice were associated with higher expression of colonic T-helper (Th)17 and Th1 cytokines, including interleukin 17A and interferon-γ. Furthermore, lack of mPGES-1 increased the numbers of Th17 and Th1 cells in the lamina propria mononuclear cells within the colon, even though the number of suppressive regulatory T cells also increased. CD4⁺ T cell depletion effectively reduced symptoms of colitis as well as colonic expression of Th17 and Th1 cytokines in mPGES-1^−/− mice, suggesting the requirement of CD4⁺ T cells in the exacerbation of DSS-induced colitis under mPGES-1 deficiency.

Conclusions

These results demonstrate that mPGES-1 is the main enzyme responsible for colonic PGE₂ production and deficiency of mPGES-1 facilitates the development of colitis by affecting the development of colonic T cell–mediated immunity. mPGES-1 might therefore impact both the intestinal inflammation and T cell–mediated immunity associated with IBD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41232-021-00188-1.

Inhibition of mPGES-1 or COX-2 Results in Different Proteomic and Lipidomic Profiles in A549 Lung Cancer Cells

Pharmacological inhibition of microsomal prostaglandin E synthase (mPGES)-1 for selective reduction in prostaglandin E₂ (PGE₂) biosynthesis is protective in experimental models of cancer and inflammation. Targeting mPGES-1 is envisioned as a safer alternative to traditional non-steroidal anti-inflammatory drugs (NSAIDs). Herein, we compared the effects of mPGES-1 inhibitor Compound III (CIII) with the cyclooxygenase (COX)-2 inhibitor NS-398 on protein and lipid profiles in interleukin (IL)-1β-induced A549 lung cancer cells using mass spectrometry. Inhibition of mPGES-1 decreased PGE₂ production and increased PGF_2α and thromboxane B₂ (TXB₂) formation, while inhibition of COX-2 decreased the production of all three prostanoids. Our proteomics results revealed that CIII downregulated multiple canonical pathways including eIF2, eIF4/P70S6K, and mTOR signaling, compared to NS-398 that activated these pathways. Moreover, pathway analysis predicted that CIII increased cell death of cancer cells (Z = 3.8, p = 5.1E-41) while NS-398 decreased the same function (Z = -5.0, p = 6.5E-35). In our lipidomics analyses, we found alterations in nine phospholipids between the two inhibitors, with a stronger alteration in the lysophospholipid (LPC) profile with NS-398 compared to CIII. Inhibition of mPGES-1 increased the concentration of sphinganine and dihydroceramide (C_16:0DhCer), while inhibition of COX-2 caused a general decrease in most ceramides, again suggesting different effects on cell death between the two inhibitors. We showed that CIII decreased proliferation and potentiated the cytotoxic effect of the cytostatic drugs cisplatin, etoposide, and vincristine when investigated in a live cell imaging system. Our results demonstrate differences in protein and lipid profiles after inhibition of mPGES-1 or COX-2 with important implications on the therapeutic potential of mPGES-1 inhibitors as adjuvant treatment in cancer. We encourage further investigations to illuminate the clinical benefit of mPGES-1 inhibitors in cancer.

Divergent roles of prostacyclin and PGE2 in human tendinopathy

BACKGROUND

Tendon disease is a significant global healthcare burden whereby patients experience pain and disability; however, the mechanisms that underlie inflammation and pain are poorly understood. Herein, we investigated the role of prostaglandins as important mediators of inflammation and pain in tissues and cells derived from patients with tendinopathy.

METHODS

We studied supraspinatus and Achilles tendon biopsies from symptomatic patients with tendinopathy or rupture. Tendon-derived stromal cells (CD45negCD34neg) isolated from tendons were cultured and treated with interleukin-1β (IL-1β) to investigate prostaglandin production.

RESULTS

Diseased tendon tissues showed increased expression of prostacyclin receptor (IP) and enzymes catalyzing the biosynthesis of prostaglandins, including cyclooxygenase-1 (COX-1), COX-2, prostacyclin synthase (PGIS), and microsomal prostaglandin E synthase-1 (mPGES-1). PGIS co-localized with cells expressing Podoplanin, a marker of stromal fibroblast activation, and the nociceptive neuromodulator NMDAR-1. Treatment with IL-1β induced release of the prostacyclin metabolite 6-keto PGF1α in tendon cells isolated from diseased supraspinatus and Achilles tendons but not in cells from healthy comparator tendons. The same treatment induced profound prostaglandin E2 (PGE2) release in tendon cells derived from patients with supraspinatus tendon tears. Incubation of IL-1β treated diseased tendon cells with selective mPGES-1 inhibitor Compound III, reduced PGE2, and simultaneously increased 6-keto PGF1α production. Conversely, COX blockade with naproxen or NS-398 inhibited both PGE2 and 6-keto PGF1α production. Tendon biopsies from patients in whom symptoms had resolved showed increased PTGIS compared to biopsies from patients with persistent tendinopathy.

CONCLUSIONS

Our results suggest that PGE2 sustains inflammation and pain while prostacyclin may have a protective role in human tendon disease.

Group X Secreted Phospholipase A2 Releases ω3 Polyunsaturated Fatty Acids, Suppresses Colitis, and Promotes Sperm Fertility

Within the secreted phospholipase A2(sPLA2) family, group X sPLA2(sPLA2-X) has the highest capacity to hydrolyze cellular membranes and has long been thought to promote inflammation by releasing arachidonic acid, a precursor of pro-inflammatory eicosanoids. Unexpectedly, we found that transgenic mice globally overexpressing human sPLA2-X (PLA2G10-Tg) displayed striking immunosuppressive and lean phenotypes with lymphopenia and increased M2-like macrophages, accompanied by marked elevation of free ω3 polyunsaturated fatty acids (PUFAs) and their metabolites. Studies usingPla2g10-deficient mice revealed that endogenous sPLA2-X, which is highly expressed in the colon epithelium and spermatozoa, mobilized ω3 PUFAs or their metabolites to protect against dextran sulfate-induced colitis and to promote fertilization, respectively. In colitis, sPLA2-X deficiency increased colorectal expression of Th17 cytokines, and ω3 PUFAs attenuated their production by lamina propria cells partly through the fatty acid receptor GPR120. In comparison, cytosolic phospholipase A2(cPLA2α) protects from colitis by mobilizing ω6 arachidonic acid metabolites, including prostaglandin E2 Thus, our results underscore a previously unrecognized role of sPLA2-X as an ω3 PUFA mobilizerin vivo, segregated mobilization of ω3 and ω6 PUFA metabolites by sPLA2-X and cPLA2α, respectively, in protection against colitis, and the novel role of a particular sPLA2-X-driven PUFA in fertilization.

Prostaglandin E2 Production and T Cell Function in Mouse Adenovirus Type 1 Infection following Allogeneic Bone Marrow Transplantation

Adenovirus infections are important complications of bone marrow transplantation (BMT). We demonstrate delayed clearance of mouse adenovirus type 1 (MAV-1) from lungs of mice following allogeneic BMT. Virus-induced prostaglandin E₂ (PGE₂) production was greater in BMT mice than in untransplanted controls, but BMT using PGE₂-deficient donors or recipients failed to improve viral clearance, and treatment of untransplanted mice with the PGE₂ analog misoprostol did not affect virus clearance. Lymphocyte recruitment to the lungs was not significantly affected by BMT. Intracellular cytokine staining of lung lymphocytes demonstrated impaired production of INF-γ and granzyme B by cells from BMT mice, and production of IFN-γ, IL-2, IL-4, and IL-17 following ex vivo stimulation was impaired in lymphocytes obtained from lungs of BMT mice. Viral clearance was not delayed in untransplanted INF-γ-deficient mice, suggesting that delayed viral clearance in BMT mice was not a direct consequence of impaired IFN-γ production. However, lung viral loads were higher in untransplanted CD8-deficient mice than in controls, suggesting that delayed MAV-1 clearance in BMT mice is due to defective CD8 T cell function. We did not detect significant induction of IFN-β expression in lungs of BMT mice or untransplanted controls, and viral clearance was not delayed in untransplanted type I IFN-unresponsive mice. We conclude that PGE₂ overproduction in BMT mice is not directly responsible for delayed viral clearance. PGE₂-independent effects on CD8 T cell function likely contribute to the inability of BMT mice to clear MAV-1 from the lungs.

Prostaglandin E2 induction during mouse adenovirus type 1 respiratory infection regulates inflammatory mediator generation but does not affect viral pathogenesis

Respiratory viruses cause substantial disease and are a significant healthcare burden. Virus-induced inflammation can be detrimental to the host, causing symptoms during acute infection and leading to damage that contributes to long-term residual lung disease. Prostaglandin E₂ (PGE₂) is a lipid mediator that is increased in response to many viral infections, and inhibition of PGE₂ production during respiratory viral infection often leads to a decreased inflammatory response. We tested the hypothesis that PGE₂ promotes inflammatory responses to mouse adenovirus type 1 (MAV-1) respiratory infection. Acute MAV-1 infection increased COX-2 expression and PGE₂ production in wild type mice. Deficiency of the E prostanoid 2 receptor had no apparent effect on MAV-1 pathogenesis. Virus-induced induction of PGE₂, IFN-γ, CXCL1, and CCL5 was reduced in mice deficient in microsomal PGE synthase-1 (mPGES-1^-/- mice). However, there were no differences between mPGES-1^+/+ and mPGES-1^-/- mice in viral replication, recruitment of leukocytes to airways or lung inflammation. Infection of both mPGES‑1^+/+ and mPGES-1^-/- mice led to protection against reinfection. Thus, while PGE₂ promotes the expression of a variety of cytokines in response to acute MAV-1 infection, PGE₂ synthesis does not appear to be essential for generating pulmonary immunity.

Reduced T cell-dependent humoral immune response in microsomal prostaglandin E synthase-1 null mice is mediated by nonhematopoietic cells

Microsomal PGE synthase-1 (mPGES-1) is an inducible enzyme that specifically catalyzes the conversion of PGH2 to PGE2. We showed that mPGES-1 null mice had a significantly reduced incidence and severity of collagen-induced arthritis compared with wild-type (WT) mice associated with a marked reduction in Abs to type II collagen. In this study, we further elucidated the role of mPGES-1 in the humoral immune response. Basal levels of serum IgM and IgG were significantly reduced in mPGES-1 null mice. Compared with WT mice, mPGES-1 null mice exhibited a significant reduction of hapten-specific serum Abs in response to immunization with the T cell-dependent (TD) Ag DNP-keyhole limpet hemocyanin. Immunization with the T cell-independent type 1 Ag trinitrophenyl-LPS or the T cell-independent type 2 Ag DNP-Ficoll revealed minimal differences between strains. Germinal center formation in the spleen of mPGES-1 null and WT mice were similar after immunization with DNP-keyhole limpet hemocyanin. To determine whether the effect of mPGES-1 and PGE2 was localized to hematopoietic or nonhematopoietic cells, we generated bone marrow chimeras. We demonstrated that mPGES-1 deficiency in nonhematopoietic cells was the critical factor for reduced TD Ab production. We conclude that mPGES-1 and PGE2-dependent phenotypic changes of nonhematopoietic/mesenchymal stromal cells play a key role in TD humoral immune responses in vivo. These findings may have relevance to the pathogenesis of rheumatoid arthritis and other autoimmune inflammatory diseases associated with autoantibody formation.

A highly efficient, high-throughput lipidomics platform for the quantitative detection of eicosanoids in human whole blood

We have developed an ultra-performance liquid chromatography-multiple reaction monitoring/mass spectrometry (UPLC-MRM/MS)-based, high-content, high-throughput platform that enables simultaneous profiling of multiple lipids produced ex vivo in human whole blood (HWB) on treatment with calcium ionophore and its modulation with pharmacological agents. HWB samples were processed in a 96-well plate format compatible with high-throughput sample processing instrumentation. We employed a scheduled MRM (sMRM) method, with a triple-quadrupole mass spectrometer coupled to a UPLC system, to measure absolute amounts of 122 distinct eicosanoids using deuterated internal standards. In a 6.5-min run, we resolved and detected with high sensitivity (lower limit of quantification in the range of 0.4-460 pg) all targeted analytes from a very small HWB sample (2.5 μl). Approximately 90% of the analytes exhibited a dynamic range exceeding 1000. We also developed a tailored software package that dramatically sped up the overall data quantification and analysis process with superior consistency and accuracy. Matrix effects from HWB and precision of the calibration curve were evaluated using this newly developed automation tool. This platform was successfully applied to the global quantification of changes on all 122 eicosanoids in HWB samples from healthy donors in response to calcium ionophore stimulation.

Microsomal Prostaglandin E2 Synthase-1

The prostanoids and leukotrienes (LTs) formed from arachidonic acid (AA) via the cyclooxygenase (COX)-1/2 and 5-lipoxygenase (5-LO) pathway, respectively, mediate inflammatory responses, chronic tissue remodelling, cancer, asthma and autoimmune disorders, but also possess homeostatic functions in the gastrointestinal tract, uterus, brain, kidney, vasculature and host defence. Based on the manifold functions of these eicosanoids, the clinical use of non-steroidal anti-inflammatory drugs (NSAIDs), a class of drugs that block formation of all prostanoids, is hampered by severe side-effects including gastrointestinal injury, renal irritations and cardiovascular risks. Therefore, anti-inflammatory agents interfering with eicosanoid biosynthesis require a well-balanced pharmacological profile to minimize these on-target side-effects. Current anti-inflammatory research aims at identifying compounds that can suppress the massive formation of pro-inflammatory prostaglandin (PG)E2 without affecting homeostatic PGE2 and PGI2 synthesis. The inducible microsomal prostaglandin E2 synthase-1 (mPGES-1) is one promising target enzyme. We will give an overview about the structure, regulation and function of mPGES-1 and then present novel inhibitors of mPGES-1 that may possess a promising pharmacological profile.

Regulation of human microsomal prostaglandin E synthase-1 by IL-1β requires a distal enhancer element with a unique role for C/EBPβ

The studies of PGE2 (prostaglandin E2) biosynthesis have focused primarily on the role of cyclo-oxygenases. Efforts have shifted towards the specific PGE2 terminal synthases, particularly mPGES-1 (microsomal PGE synthase 1), which has emerged as the crucial inducible synthase with roles in pain, cancer and inflammation. mPGES-1 is induced by pro-inflammatory cytokines with studies focusing on the proximal promoter, mediated specifically through Egr-1 (early growth-response factor 1). Numerous studies demonstrate that the mPGES-1 promoter (PTGES) alone cannot account for the level of IL-1β (interleukin 1β) induction. We identified two DNase I-hypersensitive sites within the proximal promoter near the Egr-1 element and a novel distal site near −8.6 kb. Functional analysis of the distal site revealed two elements that co-operate with basal promoter expression and a stimulus-dependent enhancer. A specific binding site for C/EBPβ (CCAAT/enhancer-binding protein β) in the enhancer was directly responsible for inducible enhancer activity. ChIP (chromatin immunoprecipitation) analysis demonstrated constitutive Egr-1 binding to the promoter and induced RNA polymerase II and C/EBPβ binding to the promoter and enhancer respectively. Knockout/knockdown studies established a functional role for C/EBPβ in mPGES-1 gene regulation and the documented interaction between Egr-1 and C/EBPβ highlights the proximal promoter co-operation with a novel distal enhancer element in regulating inducible mPGES-1 expression.

Genetic deletion of mPGES-1 abolishes PGE2 production in murine dendritic cells and alters the cytokine profile, but does not affect maturation or migration

We undertook this study to determine the role of Microsomal PGE Synthase-1 (mPGES-1), and mPGES-1-generated Prostaglandin (PG) E2 on Dendritic Cell (DC) phenotype and function. Using mPGES-1 KnockOut (KO) mice, we generated bone marrow derived DCs and determined their eicosanoid production profile, cell surface marker expression, and cytokine production. We also assessed DC migratory and functional capacity in vivo. Compared to wild-type, mPGES-1 deficient DCs exhibited a markedly attenuated increase in PGE2 production upon LPS stimulation, and displayed preferential shunting towards PGD2 production. mPGES-1 KO DCs did not display deficiencies in maturation, migration or ability to sensitize T cells. However, mPGES-1 deficient DCs generated reduced amounts of the Th1 cytokine IL-12, which may in part be due to increased PGD2 rather than decreased PGE2. These findings provide useful information on the effects of inducible PGE2 on the innate immune system, and have important implications regarding potential consequences of pharmacologic mPGES-1 inhibition.

5-Lipoxygenase-deficient mice infected with Borrelia burgdorferi develop persistent arthritis

The enzyme 5-lipoxygenase (5-LO) catalyzes the conversion of arachidonic acid into the leukotrienes, which are critical regulators of inflammation and inflammatory diseases, such as asthma and arthritis. Although leukotrienes are present in the synovial fluid of Lyme disease patients, their role in the development of Lyme arthritis has not been determined. In the current study, we used a murine model of Lyme arthritis to investigate the role 5-LO products might have in the development of this inflammatory disease. After infection of Lyme arthritis-susceptible C3H/HeJ mice with Borrelia burgdorferi, mRNA expression of 5-LO and 5-LO-activating protein was induced in the joints, and the 5-LO product leukotriene B(4) was produced. Using C3H 5-LO-deficient mice, we demonstrated that 5-LO activity was not necessary for the induction of Lyme arthritis, but that its deficiency resulted in earlier joint swelling and an inability to resolve arthritis as demonstrated by sustained arthritis pathology through day 60 postinfection. Although production of anti-Borrelia IgG was decreased in 5-LO-deficient mice, bacterial clearance from the joints was unaffected. Phagocytosis of B. burgdorferi and efferocytosis of apoptotic neutrophils was defective in macrophages from 5-LO-deficient mice, and uptake of opsonized spirochetes by neutrophils was reduced. These results demonstrate that products of the 5-LO metabolic pathway are not required for the development of disease in all models of arthritis and that caution should be used when targeting 5-LO as therapy for inflammatory diseases.

mPGES-1 null mice are resistant to bleomycin-induced skin fibrosis

Introduction

Microsomal prostaglandin E2 synthase-1 (mPGES-1) is an inducible enzyme that acts downstream of cyclooxygenase (COX) to specifically catalyze the conversion of prostaglandin (PG) H₂ to PGE₂. mPGES-1 plays a key role in inflammation, pain and arthritis; however, the role of mPGES-1 in fibrogenesis is largely unknown. Herein, we examine the role of mPGES-1 in a mouse model of skin scleroderma using mice deficient in mPGES-1.

Methods

Wild type (WT) and mPGES-1 null mice were subjected to the bleomycin model of cutaneous skin scleroderma. mPGES-1 expressions in scleroderma fibroblasts and in fibroblasts derived from bleomycin-exposed mice were assessed by Western blot analysis. Degree of fibrosis, dermal thickness, inflammation, collagen content and the number of α-smooth muscle actin (α-SMA)-positive cells were determined by histological analyses. The quantity of the collagen-specific amino acid hydroxyproline was also measured.

Results

Compared to normal skin fibroblasts, mPGES-1 protein expression was elevated in systemic sclerosis (SSc) fibroblasts and in bleomycin-exposed mice. Compared to WT mice, mPGES-1-null mice were resistant to bleomycin-induced inflammation, cutaneous thickening, collagen production and myofibroblast formation.

Conclusions

mPGES-1 expression is required for bleomycin-induced skin fibrogenesis. Inhibition of mPGES-1 may be a viable method to alleviate the development of cutaneous sclerosis and is a potential therapeutic target to control the onset of fibrogenesis.

Therapeutic effects of TACI-Ig on collagen-induced arthritis by regulating T and B lymphocytes function in DBA/1 mice

To investigate the abnormal function of T and B lymphocytes involved in collagen-induced arthritis in DBA/1 mice and the regulation role of TACI-Ig on T and B lymphocytes, collagen-induced arthritis models were established in DBA/1 mice. Mice were divided randomly into eight groups, including normal, collagen-induced arthritis model, TACI-Ig (0.350, 1.105, 3.333, 10, and 30 mg/kg) and IgG-Fc (10mg/kg) treated groups. The effect of TACI-Ig on collagen-induced arthritis was evaluated by arthritis scores, joints and spleens histopathology, paws radiology, and indices of thymus and spleen. T and B lymphocyte proliferations were assayed by [(3)H]-TdR method. B lymphocyte stimulator and prostaglandin E(2) in serum were assayed by enzyme linked immunosorbent assay. The subsets of T and B lymphocytes were assayed by flow cytometry. Results showed that the onset of paw-swelling was on day 31 after immunization. The peak of inflammation appeared on day 42 and then declined after day 63. Compared with normal mice, collagen-induced arthritis mice have increased arthritis scores, spleen and thymus indices, radiograph scores of joints, and pathology scores of joints and spleens. TACI-Ig could ameliorate these changes and reduce the increased serum level of B lymphocyte stimulator and prostaglandin E(2). Further studies showed that TACI-Ig inhibited T and B lymphocyte proliferation response, and inhibited differentiation and activity of T and B lymphocytes in collagen-induced arthritis mice. In conclusion, TACI-Ig has a good therapeutic action on collagen-induced arthritis mice, which might be related to the regulation of TACI-Ig on inflammation mediators and abnormal function of T and B lymphocytes.

Potential roles of microsomal prostaglandin E synthase-1 in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease which primarily affects the synovial joints leading to inflammation, pain and joint deformities. Nonsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids, both of which inhibit cyclooxygenase (COX), have been extensively used for treating RA patients. Prostaglandin E synthase (PGES) is a specific biosynthetic enzyme that acts downstream of COX and converts prostaglandin (PG) H(2) to PGE(2). Among PGES isozymes, microsomal PGES-1 (mPGES-1) has been shown to be induced in a variety of cells and tissues under inflammatory conditions. The induction of mPGES-1 in the synovial tissue of RA patients is closely associated with the activation of the tissue by proinflammatory cytokines. Although selective mPGES-1 inhibitors have not yet been widely available, mice lacking mPGES-1 (mPGES-1(-/-) mice) have been generated to evaluate the physiological and pathological roles of mPGES-1 in vivo. Recent studies utilizing mPGES-1(-/-) mice have demonstrated the significance of mPGES-1 in the process of chronic inflammation and evocation of humoral immune response in autoimmune arthritis models. These recent findings highlight mPGES-1 as a novel therapeutic target for the treatment of autoimmune inflammatory diseases, including RA. Currently, both natural and synthetic chemicals are being tested for inhibition of mPGES-1 activity to produce PGE(2). The present review focuses on the recent advances in understanding the role of mPGES-1 in the pathophysiology of RA.

Myrtucommulone, a natural acylphloroglucinol, inhibits microsomal prostaglandin E(2) synthase-1

BACKGROUND AND PURPOSE

The selective inhibition of prostaglandin (PG)E(2) formation via interference with microsomal PGE(2) synthase (mPGES)-1 could have advantages in the treatment of PGE(2)-associated diseases, such as inflammation, fever and pain, compared with a general suppression of all PG biosynthesis, provided by inhibition of cyclooxygenase (COX)-1 and 2. Here, we addressed whether the naturally occurring acylphloroglucinol myrtucommulone (MC) from Myrtus communis L. (myrtle) affected mPGES-1.

EXPERIMENTAL APPROACH

The effect of MC on PGE(2) formation was investigated in a cell-free assay by using microsomal preparations of interleukin-1beta-stimulated A549 cells as the source of mPGES-1, in intact A549 cells, and in lipopolysaccharide-stimulated human whole blood. Inhibition of COX-1 and COX-2 activity in cellular and cell-free assays was assessed by measuring 12(S)-hydroxy-5-cis-8,10-trans-heptadecatrienoic acid and 6-oxo PGF(1alpha) formation.

KEY RESULTS

MC concentration-dependently inhibited cell-free mPGES-1-mediated conversion of PGH(2) to PGE(2) (IC(50) = 1 micromol x L(-1)). PGE(2) formation was also diminished in intact A549 cells as well as in human whole blood at low micromolar concentrations. Neither COX-2 activity in A549 cells nor isolated human recombinant COX-2 was significantly affected by MC up to 30 micromol x L(-1), and only moderate inhibition of cellular or cell-free COX-1 was evident (IC(50) > 15 micromol x L(-1)).

CONCLUSIONS AND IMPLICATIONS

MC is the first natural product to inhibit mPGES-1 that efficiently suppresses PGE(2) formation without significant inhibition of the COX enzymes. This provides an interesting pharmacological profile suitable for interventions in inflammatory disorders, without the typical side effects of coxibs and non-steroidal anti-inflammatory drugs.

Prostaglandin E2 activates Rap1 via EP2/EP4 receptors and cAMP-signaling in rheumatoid synovial fibroblasts: involvement of Epac1 and PKA

The small GTPase Rap1 is implicated in a variety of cellar functions. In this study, we investigated the effect of prostaglandin E(2) (PGE(2)) on Rap1 activation in rheumatoid synovial fibroblasts (RSF). Rap1 was expressed in RSF, and GTP-bound active Rap1 (GTP-Rap1) was rapidly increased by PGE(2). The effect of PGE(2) was mimicked by an EP2 receptor agonist, an EP4 agonist and a cAMP-elevating agent forskolin with association to the increase of cAMP, but not by an EP1 or an EP3 agonist. RSF expressed the downstream signaling partners of cAMP, exchange protein directly activated by cAMP (Epac1) and protein kinase A (PKA). Both 8-pCPT-2-O-Me-cAMP (an Epac-specific cAMP analog) and 6-Bnz-cAMP (a PKA-specific cAMP analog) activated Rap1 in RSF. Activation of Rap1 by PGE(2) via cAMP-signaling may play an important role in the articular pathology of rheumatoid arthritis (RA).

Prostaglandins and sickness behavior: old story, new insights

Previous evidence has shown that prostaglandins play a key role in the development of sickness behavior observed during inflammatory states. In particular, prostaglandin E2 (PGE2) is produced in the brain by a variety of inflammatory signals such as endotoxins or cytokines. Its injection has been also shown to induce symptoms of sickness behavior. The role of cyclooxygenase enzymes (COX), the rate-limiting enzymes converting arachidonic acid into prostaglandins, in sickness behavior has been extensively studied, and it has been demonstrated that strategies aiming at inhibiting these enzymes limit anorexia, body weight loss and fever in animals with inflammatory diseases. However, inhibiting COX activity may lead to negative gastric or cardiovascular effects, since COX enzymes play a role in the synthesis of others prostanoids with various and sometimes contrasting properties. Recently, prostaglandin E synthases (PGES), which specifically catalyze the final step of PGE2 biosynthesis, were characterized. Among these enzymes, the microsomal prostaglandin E synthase-1 (mPGES-1) was of a particular interest since it was shown to be up-regulated by inflammatory signals in a variety of cell types. Moreover, mPGES-1 was shown to be crucial for correct immune-to-brain communication and induction of fever and anorexia by pro-inflammatory agents. This review takes stock of previous knowledge and recent advances in understanding the role of prostaglandins and of their specific synthesizing enzymes in the molecular mechanisms underlying sickness behavior. The review concludes with a short summary of key questions that remain to be addressed and points out therapeutic developments in this research field.

Up-regulation of microsomal prostaglandin E synthase-1 in COX-1 and COX-2 knock-out mouse fibroblast cell lines

In this paper we investigated the possible involvement of prostaglandin E synthases (PGESs) in compensatory mechanism. Our findings showed that microsomal (m)PGES-1 expression was significantly up-regulated in COX knock-out (K/O) cells whereas the expression of cytosolic PGES was not changed indicating that the induction of mPGES-1 may, at least in part, contribute to the substantial increase of PGE(2) production in COX K/O cell lines. The selective up-regulation of mPGES-1 in COX-2 K/O cells suggests that mPGES-1 may be metabolically coupled with COX-1 for PGE(2) formation. Addition of arachidonic acid caused significant induction of mPGES-1 and COX-2 in WT cells, whereas COX-1 and cPGES were not affected. Our earlier and the current studies demonstrate the coregulation of cPLA(2), COX, and mPGES-1, in PGE(2) synthesis pathway, and that these enzymes contribute to the elevation of PGE(2) level when one COX isoform is absent.

Consequences of altered eicosanoid patterns for nociceptive processing in mPGES-1-deficient mice

Cyclooxygenase-2 (COX-2)-dependent prostaglandin (PG) E₂ synthesis in the spinal cord plays a major role in the development of inflammatory hyperalgesia and allodynia. Microsomal PGE₂ synthase-1 (mPGES-1) isomerizes COX-2-derived PGH₂ to PGE₂. Here, we evaluated the effect of mPGES-1-deficiency on the noci-ceptive behavior in various models of nociception that depend on PGE₂ synthesis. Surprisingly, in the COX-2-dependent zymosan-evoked hyperalgesia model, the nociceptive behavior was not reduced in mPGES-1-deficient mice despite a marked decrease of the spinal PGE₂ synthesis. Similarly, the nociceptive behavior was unaltered in mPGES-1-deficient mice in the formalin test. Importantly, spinal cords and primary spinal cord cells derived from mPGES-1-deficient mice showed a redirection of the PGE₂ synthesis to PGD₂, PGF_2α and 6-keto-PGF_1α (stable metabolite of PGI₂). Since the latter prostaglandins serve also as mediators of noci-ception they may compensate the loss of PGE₂ synthesis in mPGES-1-deficient mice.

Defective generation of a humoral immune response is associated with a reduced incidence and severity of collagen-induced arthritis in microsomal prostaglandin E synthase-1 null mice

Microsomal PGE synthase-1 (mPGES-1) is an inducible enzyme that acts downstream of cyclooxygenase and specifically catalyzes the conversion of PGH(2) to PGE(2). The present study demonstrates the effect of genetic deletion of mPGES-1 on the developing immunologic responses and its impact on the clinical model of bovine collagen-induced arthritis. mPGES-1 null and heterozygous mice exhibited decreased incidence and severity of arthritis compared with wild-type mice in a gene dose-dependent manner. Histopathological examination revealed significant reduction in lining hyperplasia and tissue destruction in mPGES-1 null mice compared with their wild-type littermates. mPGES-1 deficient mice also exhibited attenuation of mechanical nociception in a gene dose-dependent manner. In addition, mPGES-1 null and heterozygous mice showed a marked reduction of serum IgG against type II collagen, including subclasses IgG1, IgG2a, IgG2b, IgG2c, and IgG3, compared with wild-type mice, which correlated with the reduction in observed inflammatory features. These results demonstrate for the first time that deficiency of mPGES-1 inhibits the development of collagen-induced arthritis, at least in part, by blocking the development of a humoral immune response against type II collagen. Pharmacologic inhibition of mPGES-1 may therefore impact both the inflammation and the autoimmunity associated with human diseases such as rheumatoid arthritis.

Genetic deletion of mPGES-1 suppresses intestinal tumorigenesis

Elevated levels of prostaglandin E(2) (PGE(2)) are often found in colorectal cancers. Thus, nonsteroidal anti-inflammatory drugs, including selective cyclooxygenase-2 (COX-2) inhibitors, are among the most promising chemopreventive agents for colorectal cancer. However, their long-term use is restricted by the occurrence of adverse events believed to be associated with a global reduction in prostaglandin production. In the present study, we evaluated the chemopreventive efficacy of targeting the terminal synthase microsomal PGE(2) synthase 1 (mPGES-1), which is responsible for generating PGE(2), in two murine models of intestinal cancer. We report for the first time that genetic deletion of mPGES-1 in Apc-mutant mice results in marked and persistent suppression of intestinal cancer growth by 66%, whereas suppression of large adenomas (>3 mm) was almost 95%. This effect occurred despite loss of Apc heterozygosity and beta-catenin activation. However, we found that mPGES-1 deficiency was associated with a disorganized vascular pattern within primary adenomas as determined by CD31 immunostaining. We also examined the effect of mPGES-1 deletion on carcinogen-induced colon cancer. The absence of mPGES-1 reduced the size and number of preneoplastic aberrant crypt foci (ACF). Importantly, mPGES-1 deletion also blocked the nuclear accumulation of beta-catenin in ACF, confirming that beta-catenin is a critical target of PGE(2) procarcinogenic signaling in the colon. Our data show the feasibility of targeting mPGES-1 for cancer chemoprevention with the potential for improved tolerability over traditional nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors.

Sequential induction of pro- and anti-inflammatory prostaglandins and peroxisome proliferators-activated receptor-gamma during normal wound healing: a time course study

Lipid mediators generated from metabolism of arachidonic acid play a crucial role in the initiating and resolution of acute inflammation by shifting from pro-inflammatory prostaglandin (PG) E2 to anti-inflammatory PGD2 and its metabolites. The changes in PG levels over time during the normal wound-repair process have not, however, been reported. We determined the temporal expression of PG and their biosynthetic enzymes using the full thickness incisional model of normal wound healing in mice. We demonstrate that during normal wound repair, there is a shift in the metabolism of arachidonate from PGE2 during the acute inflammatory phase to PGD2 during the repair phase. This shift is mediated by temporal changes in the expression of cyclooxygenases (COX) and microsomal PGES (mPGES)-1. Inducible COX (COX-2) expression is sustained throughout the initiation and repair process, but mPGES-1 is increased only during the acute inflammatory phase and its disappearance coincides with increased PGD2. PGD2 and its degradation products are known to mediate their anti-inflammatory effects by binding to peroxisome proliferators-activated receptor gamma (PPARgamma). In this study, we show that PPARgamma is upregulated during the resolution phase of wound repair concomitant with the shift to PGD2, and may be responsible for initiating endogenous mechanism resulting in healing/resolution.

Microsomal prostaglandin E synthase-1 deficiency is associated with elevated peroxisome proliferator-activated receptor gamma: regulation by prostaglandin E2 via the phosphatidylinositol 3-kinase and Akt pathway

mPGES-1 (microsomal PGE synthase-1) is an inducible enzyme that acts downstream of cyclooxygenase (COX) and specifically catalyzes the conversion of prostaglandin (PG) H(2) to PGE(2) under basal as well as inflammatory conditions. In this study, using mouse embryo fibroblasts (MEFs) isolated from mice genetically deficient for the mPges-1 gene, we show basal elevation of peroxisome proliferator-activated receptor gamma (PPARgamma) expression (protein and mRNA) and transcriptional activity associated with reduced basal PGE(2). We further show that basal mPGES-1-derived PGE(2) suppresses the expression of PPARgamma through a cAMP-independent pathway involving phosphatidylinositol 3-kinase and Akt signaling. Using specific PPARgamma agonist (rosiglitazone), PPARgamma ligand (15-deoxy-Delta12,14-PGJ(2)), and PPARgamma inhibitor (GW9662), we confirm that activation of PPARgamma blocks interleukin-1beta-induced up-regulation of COX-2, mPGES-1, and their derived PGE(2). Furthermore, we demonstrate that up-regulation of PPARgamma upon genetic deletion of mPGES-1 is responsible for reduced COX-2 expression under basal as well as interleukin-1beta-stimulated conditions. This study provides evidence for the first time that mPGES-1 deletion not only decreases proinflammatory PGE(2) but also up-regulates anti-inflammatory PPARgamma, which has the ability to suppress COX-2 and mPGES-1 expression and PGE(2) production. Thus, mPGES-1 inhibition may limit inflammation by multiple mechanisms and is a potential therapeutic target.