Reduced pain hypersensitivity and inflammation in mice lacking microsomal prostaglandin e synthase-1

Cardiovascular Consequences of Prostanoid I Receptor Deletion in Microsomal Prostaglandin E Synthase-1-Deficient Hyperlipidemic Mice

BACKGROUND

Inhibitors of cyclooxygenase-2 alleviate pain and reduce fever and inflammation by suppressing the biosynthesis of prostacyclin (PGI2) and prostaglandin E2. However, suppression of these prostaglandins, particularly PGI2, by cyclooxygenase-2 inhibition or deletion of its I prostanoid receptor also predisposes to accelerated atherogenesis and thrombosis in mice. By contrast, deletion of microsomal prostaglandin E synthase 1 (mPGES-1) confers analgesia, attenuates atherogenesis, and fails to accelerate thrombogenesis, while suppressing prostaglandin E2, but increasing biosynthesis of PGI2.

METHODS

To address the cardioprotective contribution of PGI2, we generated mice lacking the I prostanoid receptor together with mPges-1 on a hyperlipidemic background (low-density lipoprotein receptor knockouts).

RESULTS

mPges-1 depletion modestly increased thrombogenesis, but this response was markedly further augmented by coincident deletion of the I prostanoid receptor (n=10-18). By contrast, deletion of the I prostanoid receptor had no effect on the attenuation of atherogenesis by mPGES-1 deletion in the low-density lipoprotein receptor knockout mice (n=17-21).

CONCLUSIONS

Although suppression of prostaglandin E2 accounts for the protective effect of mPGES-1 deletion in atherosclerosis, augmentation of PGI2 is the dominant contributor to its favorable thrombogenic profile. The divergent effects on these prostaglandins suggest that inhibitors of mPGES-1 may be less likely to cause cardiovascular adverse effects than nonsteroidal anti-inflammatory drugs specific for inhibition of cyclooxygenase-2.

Unraveling the Molecular Details Involved in the Intimate Link between the Immune and Neuroendocrine Systems

During systemic infections, the immune system can signal the brain and act on different neuronal circuits via soluble molecules, such as proinflammatory cytokines, that act on the cells forming the blood-brain barrier and the circumventricular organs. These activated cells release prostaglandin of the E2 type (PGE2), which is the endogenous ligand that triggers the pathways involved in the control of autonomic functions necessary to restore homeostasis and provide inhibitory feedback to innate immunity. Among these neurophysiological functions, activation of the circuits that control the plasma release of glucocorticoids is probably the most critical to the survival of the host in the presence of pathogens. This review revisits this issue and describes in depth the molecular details (including the emerging role of Toll-like receptors during inflammation) underlying the influence of circulating inflammatory molecules on the cerebral tissue, focusing on their contribution in the synthesis and action PGE2 in the brain. We also provide an innovative view supporting the concept of “fast and delayed response” involving the same ligands but different groups of cells, signal transduction pathways, and target genes.

Deletion of mPGES-1 affects platelet functions in mice

Microsomal prostaglandin E2 synthase-1 (mPGES-1) constitutes an essential player in inflammation and is involved in the pathogenesis of rheumatoid arthritis. Platelets participate in the regulation of inflammatory processes by the release of proinflammatory mediators and platelet-derived microparticles (PMPs). However, the role of the inducible mPGES-1/PGE2 pathway in platelet functions has not been investigated. In the present study we report a significant impact of mPGES-1 on platelet functions during inflammation. Wild-type (WT) and mPGES-1−/− knockout (KO) mice were stimulated with lipopolysaccharide (LPS) for 24 h. Platelet counts and activation were assessed by flow cytometry analysing CD62P–CD154 expression, PMP numbers, platelet–leukocyte aggregates and platelet aggregation. The accumulation of platelets and fibrinogen in the liver was analysed by immunofluorescent staining. In native platelets from WT and mPGES-1 KO mice, there were no differences among the investigated functions. After LPS treatment, the number of platelets was significantly decreased in WT, but not in KO mice. Platelet activation, platelet–leukocyte aggregates and PMP numbers were all significantly lower in KO mice compared with WT mice after LPS treatment. In addition, KO mice displayed a significant reduction in platelet aggregation ex vivo. In the liver of LPS-stimulated WT and KO mice, there were no differences in platelet accumulation, although the percentage of total vessel area in the KO liver was significantly lower compared with the WT one. Our results demonstrate that systemic inhibition of mPGES-1 prevents platelet activation, which should have important implications with regard to the cardiovascular safety of mPGES-1 inhibitors.

Cyclooxygenase-2: A Role in Cancer Stem Cell Survival and Repopulation of Cancer Cells during Therapy

Cyclooxygenase-2 (COX-2) is an inducible form of the enzyme that catalyses the synthesis of prostanoids, including prostaglandin E2 (PGE₂), a major mediator of inflammation and angiogenesis. COX-2 is overexpressed in cancer cells and is associated with progressive tumour growth, as well as resistance of cancer cells to conventional chemotherapy and radiotherapy. These therapies are often delivered in multiple doses, which are spaced out to allow the recovery of normal tissues between treatments. However, surviving cancer cells also proliferate during treatment intervals, leading to repopulation of the tumour and limiting the effectiveness of the treatment. Tumour cell repopulation is a major cause of treatment failure. The central dogma is that conventional chemotherapy and radiotherapy selects resistant cancer cells that are able to reinitiate tumour growth. However, there is compelling evidence of an active proliferative response, driven by increased COX-2 expression and downstream PGE₂ release, which contribute to the repopulation of tumours and poor patient outcome. In this review, we will examine the evidence for a role of COX-2 in cancer stem cell biology and as a mediator of tumour repopulation that can be molecularly targeted to overcome resistance to therapy.

Simultaneous Inhibition of PGE2 and PGI2 Signals Is Necessary to Suppress Hyperalgesia in Rat Inflammatory Pain Models

Prostaglandin E2 (PGE2) is well known as a mediator of inflammatory symptoms such as fever, arthritis, and inflammatory pain. In the present study, we evaluated the analgesic effect of our selective PGE2 synthesis inhibitor, compound I, 2-methyl-2-[cis-4-([1-(6-methyl-3-phenylquinolin-2-yl)piperidin-4-yl]carbonyl amino)cyclohexyl] propanoic acid, in rat yeast-induced acute and adjuvant-induced chronic inflammatory pain models. Although this compound suppressed the synthesis of PGE2 selectively, no analgesic effect was shown in both inflammatory pain models. Prostacyclin (PGI2) also plays crucial roles in inflammatory pain, so we evaluated the involvement of PGI2 signaling in rat inflammatory pain models using prostacyclin receptor (IP) antagonist, RO3244019. RO3244019 showed no analgesic effect in inflammatory pain models, but concomitant administration of compound I and RO3244019 showed analgesic effects comparable to celecoxib, a specific cyclooxygenase- (COX-) 2 inhibitor. Furthermore, coadministration of PGE2 receptor 4 (EP4) antagonist, CJ-023423, and RO3244019 also showed an analgesic effect. These findings suggest that both PGE2 signaling, especially through the EP4 receptor, and PGI2 signaling play critical roles in inflammatory pain and concurrent inhibition of both signals is important for suppression of inflammatory hyperalgesia.

Role of COX-2-derived PGE2 on vascular stiffness and function in hypertension

BACKGROUND AND PURPOSE

Prostanoids derived from COX-2 and EP receptors are involved in vascular remodelling in different cardiovascular pathologies. This study evaluates the contribution of COX-2 and EP1 receptors to vascular remodelling and function in hypertension.

EXPERIMENTAL APPROACH

Spontaneously hypertensive rats (SHR) and angiotensin II (AngII)-infused (1.44 mg · kg(-1) · day(-1), 2 weeks) mice were treated with the COX-2 inhibitor celecoxib (25 mg · kg(-1) · day(-1) i.p) or with the EP1 receptor antagonist SC19220 (10 mg · kg(-1) · day(-1) i.p.). COX-2(-/-) mice with or without AngII infusion were also used.

KEY RESULTS

Celecoxib and SC19220 treatment did not modify the altered lumen diameter and wall : lumen ratio in mesenteric resistance arteries from SHR-infused and/or AngII-infused animals. However, both treatments and COX-2 deficiency decreased the augmented vascular stiffness in vessels from hypertensive animals. This was accompanied by diminished vascular collagen deposition, normalization of altered elastin structure and decreased connective tissue growth factor and plasminogen activator inhibitor-1 gene expression. COX-2 deficiency and SC19220 treatment diminished the increased vasoconstrictor responses and endothelial dysfunction induced by AngII infusion. Hypertensive animals showed increased mPGES-1 expression and PGE2 production in vascular tissue, normalized by celecoxib. Celecoxib treatment also decreased AngII-induced macrophage infiltration and TNF-α expression. Macrophage conditioned media (MCM) increased COX-2 and collagen type I expression in vascular smooth muscle cells; the latter was reduced by celecoxib treatment.

CONCLUSIONS AND IMPLICATIONS

COX-2 and EP1 receptors participate in the increased extracellular matrix deposition and vascular stiffness, the impaired vascular function and inflammation in hypertension. Targeting PGE2 receptors might have benefits in hypertension-associated vascular damage.

A novel selective prostaglandin E2 synthesis inhibitor relieves pyrexia and arthritis in Guinea pigs inflammatory models

Prostaglandin E2 (PGE2), one of the terminal products in the cyclooxygenase pathway, plays an important role in various inflammatory responses. To determine whether selective inhibition of PGE2 may relieve these inflammatory symptoms, we synthesized a selective PGE2 synthesis inhibitor, compound A [1-(6-fluoro-5,7-dimethyl-1,3-benzothiazol-2-yl)-N-[(1S,2R)-2-(hydroxymethyl)cyclohexyl]piperidine-4-carboxamide], then investigated the effects on pyrexia, arthritis and inflammatory pain in guinea pigs. In LPS-stimulated guinea pig macrophages, compound A selectively inhibited inducible PGE2 biosynthesis in a dose-dependent manner whereas enhanced the formation of thromboxane B2 (TXB2). Compound A suppressed yeast-evoked PGE2 production selectively and enhanced the production of TXB2 and 6-keto PGF1αin vivo. In addition, compound A relieved yeast-induced pyrexia and also suppressed paw swelling in an adjuvant-induced arthritis model. The effect on gastrointestinal (GI) ulcer formation was also evaluated and compound A showed a lower GI adverse effect than indomethacin. However, compound A failed to relieve yeast-induced thermal hyperalgesia. These results suggest that selective inhibition of PGE2 synthesis may have anti-pyretic and anti-inflammatory properties without GI side effect, but lack the analgesic efficacy.

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.

Dose-dependent effects of prostaglandin E2 in macrophage adhesion and migration

Macrophage migration to the focus of infection is a hallmark of the innate immune response. Macrophage spreading, adhesion, and migration through the extracellular matrix require dynamic remodeling of the actin cytoskeleton associated to integrin clustering in podosomes and focal adhesions. Here, we show that prostaglandin E2 (PGE2 ), the main prostaglandin produced by macrophages during inflammation, promote the distinctive dose-dependent formation of podosomes or focal adhesions in macrophages. Low concentrations of PGE2 increased p110γ PI3K expression, phosphorylation of actin-related protein 2, and formation of podosomes, which enhanced macrophage migration in response to chemokines. However, high doses of PGE2 increased phosphorylation of paxillin and focal adhesion kinase, the expression of serine/threonine protein kinase 1, and promoted focal adhesion formation and macrophage adhesion, reducing macrophage chemotaxis. In summary, we describe the dual role of PGE2 as a promoter of macrophage chemotaxis and adhesion, proposing a new model of macrophage migration to the inflammatory focus in the presence of a gradient of PGE2 .

Genetic-deletion of Cyclooxygenase-2 Downstream Prostacyclin Synthase Suppresses Inflammatory Reactions but Facilitates Carcinogenesis, unlike Deletion of Microsomal Prostaglandin E Synthase-1

Prostacyclin synthase (PGIS) and microsomal prostaglandin E synthase-1 (mPGES-1) are prostaglandin (PG) terminal synthases that function downstream of inducible cyclooxygenase (COX)-2 in the PGI₂ and PGE₂ biosynthetic pathways, respectively. mPGES-1 has been shown to be involved in various COX-2-related diseases such as inflammatory diseases and cancers, but it is not yet known how PGIS is involved in these COX-2-related diseases. Here, to clarify the pathophysiological role of PGIS, we investigated the phenotypes of PGIS and mPGES-1 individual knockout (KO) or double KO (DKO) mice. The results indicate that a thioglycollate-induced exudation of leukocytes into the peritoneal cavity was suppressed by the genetic-deletion of PGIS. In the PGIS KO mice, lipopolysaccharide-primed pain nociception (as assessed by the acetic acid-induced writhing reaction) was also reduced. Both of these reactions were suppressed more effectively in the PGIS/mPGES-1 DKO mice than in the PGIS KO mice. On the other hand, unlike mPGES-1 deficiency (which suppressed azoxymethane-induced colon carcinogenesis), PGIS deficiency up-regulated both aberrant crypt foci formation at the early stage of carcinogenesis and polyp formation at the late stage. These results indicate that PGIS and mPGES-1 cooperatively exacerbate inflammatory reactions but have opposing effects on carcinogenesis, and that PGIS-derived PGI₂ has anti-carcinogenic effects.

Physiology and pathophysiology of cyclooxygenase-2 and prostaglandin E2 in the kidney

The cyclooxygenase (COX) enzyme system is the major pathway catalyzing the conversion of arachidonic acid into prostaglandins (PGs). PGs are lipid mediators implicated in a variety of physiological and pathophysiological processes in the kidney, including renal hemodynamics, body water and sodium balance, and the inflammatory injury characteristic in multiple renal diseases. Since the beginning of 1990s, it has been confirmed that COX exists in 2 isoforms, referred to as COX-1 and COX-2. Even though the 2 enzymes are similar in size and structure, COX-1 and COX-2 are regulated by different systems and have different functional roles. This review summarizes the current data on renal expression of the 2 COX isoforms and highlights mainly the role of COX-2 and PGE2 in several physiological and pathophysiological processes in the kidney.

Bromoenol Lactone, an Inhibitor of Calcium-Independent Phospholipase A2, Suppresses Carrageenan-Induced Prostaglandin Production and Hyperalgesia in Rat Hind Paw

Prostaglandin (PG) E₂ and PGI₂ are essential to hyperalgesia in inflammatory tissues. These prostaglandins are produced from arachidonic acid, which is cleaved from membrane phospholipids by the action of phospholipase A₂ (PLA₂). Which isozyme of PLA₂ is responsible for the cleavage of arachidonic acid and the production of prostaglandins essential to inflammation-induced hyperalgesia is not clear. In this study, we examined the effects of two PLA₂ isozyme-specific inhibitors on carrageenan-induced production of PGE₂ and PGI₂ in rat hind paw and behavioral nociceptive response to radiant heat. Local administration of bromoenol lactone (BEL), an inhibitor of calcium-independent PLA₂ (iPLA₂), significantly reduced carrageenan-induced elevation of prostaglandins in the inflamed foot pad 3 h after injection. It also ameliorated the hyperalgesic response between 1 h and 3 h after carrageenan injection. On the other hand, AACOCF₃, an inhibitor of cytosolic PLA₂, suppressed neither prostaglandin production nor the hyperalgesic response. BEL did not suppress the mRNA levels of iPLA₂β, iPLA₂γ, cyclooxygenase-2, microsomal prostaglandin E synthase, prostaglandin I synthase, or proinflammatory cytokines in the inflamed foot pad, indicating that BEL did not suppress inflammation itself. These results suggest that iPLA₂ is involved in the production of prostaglandins and hyperalgesia at the inflammatory loci.

Structural Insights for the Optimization of Dihydropyrimidin-2(1H)-one Based mPGES-1 Inhibitors

The recently crystallized structure of microsomal prostaglandin E2 synthase 1 (mPGES-1) in complex with the inhibitor LVJ (PDB code: 4BPM) offered new structural information for the optimization of the previously identified lead compound 1 (IC50 = 4.16 ± 0.47 μM), which contains the privileged dihydropyrimidin-2-one chemical core. Systematic optimization of 1, through accurate structure-based design, provided compound 4 with a 10-fold improved mPGES-1 inhibitory activity (IC50 = 0.41 ± 0.02 μM). Here we highlight the optimal scaffold decoration pattern of 4 and propose a three-dimensional model for the interaction with this complex trimeric membrane protein. The reported computational insights, together with the accessible one-pot synthetic procedure, stimulate for the generation of further potent dihydropyrimidine-based mPGES-1 inhibitors.

Synergistic effects of NOD1 or NOD2 and TLR4 activation on mouse sickness behavior in relation to immune and brain activity markers

Toll-like receptors (TLRs) and nuclear-binding domain (NOD)-like receptors (NLRs) are sensors of bacterial cell wall components to trigger an immune response. The TLR4 agonist lipopolysaccharide (LPS) is a strong immune activator leading to sickness and depressed mood. NOD agonists are less active but can prime immune cells to augment LPS-induced cytokine production. Since the impact of NOD and TLR co-activation in vivo has been little studied, the effects of the NOD1 agonist FK565 and the NOD2 agonist muramyl dipeptide (MDP), alone and in combination with LPS, on immune activation, brain function and sickness behavior were investigated in male C57BL/6N mice. Intraperitoneal injection of FK565 (0.001 or 0.003mg/kg) or MDP (1 or 3mg/kg) 4h before LPS (0.1 or 0.83mg/kg) significantly aggravated and prolonged the LPS-evoked sickness behavior as deduced from a decrease in locomotion, exploration, food intake and temperature. When given alone, FK565 and MDP had only minor effects. The exacerbation of sickness behavior induced by FK565 or MDP in combination with LPS was paralleled by enhanced plasma protein and cerebral mRNA levels of proinflammatory cytokines (IFN-γ, IL-1β, IL-6, TNF-α) as well as enhanced plasma levels of kynurenine. Immunohistochemical visualization of c-Fos in the brain revealed that NOD2 synergism with TLR4 resulted in increased activation of cerebral nuclei relevant to sickness. These data show that NOD1 or NOD2 synergizes with TLR4 in exacerbating the immune, sickness and brain responses to peripheral immune stimulation. Our findings demonstrate that the known interactions of NLRs and TLRs at the immune cell level extend to interactions affecting brain function and behavior.

Targeting microsomal prostaglandin E2synthase-1 (mPGES-1): the development of inhibitors as an alternative to non-steroidal anti-inflammatory drugs (NSAIDs)

AA cascade and several key residues in the 3D structure of mPGES-1.

The chemistry and biological activity of heterocycle-fused quinolinone derivatives: A review

Among all heterocycles, the heterocycle-fused quinolinone scaffold is one of the privileged structures in drug discovery as heterocycle-fused quinolinone derivatives exhibit various biological activities allowing them to act as anti-inflammatory, anticancer, antidiabetic, and antipsychotic agents. This wide spectrum of biological activity has attracted a great deal of attention in the field of medicinal chemistry. In this review, we provide a comprehensive description of the biological and pharmacological properties of various heterocycle-fused quinolinone scaffolds and discuss the synthetic methods of some of their derivatives.

Il-1β and prostaglandin E2 attenuate the hypercapnic as well as the hypoxic respiratory response via prostaglandin E receptor type 3 in neonatal mice

Prostaglandin E2 (PGE2) serves as a critical mediator of hypoxia, infection, and apnea in term and preterm babies. We hypothesized that the prostaglandin E receptor type 3 (EP3R) is the receptor responsible for PGE2-induced apneas. Plethysmographic recordings revealed that IL-1β (ip) attenuated the hypercapnic response in C57BL/6J wild-type (WT) but not in neonatal (P9) EP3R−/− mice ( P < 0.05). The hypercapnic responses in brain stem spinal cord en bloc preparations also differed depending on EP3R expression whereby the response was attenuated in EP3R−/− preparations ( P < 0.05). After severe hypoxic exposure in vivo, IL-1β prolonged time to autoresuscitation in WT but not in EP3R−/− mice. Moreover, during severe hypoxic stress EP3R−/− mice had an increased gasping duration ( P < 0.01) as well as number of gasps ( P < 0.01), irrespective of intraperitoneal treatment, compared with WT mice. Furthermore, EP3R−/− mice exhibited longer hyperpneic breathing efforts when exposed to severe hypoxia ( P < 0.01). This was then followed by a longer period of secondary apnea before autoresuscitation occurred in EP3R−/− mice ( P < 0.05). In vitro, EP3R−/− brain stem spinal cord preparations had a prolonged respiratory burst activity during severe hypoxia accompanied by a prolonged neuronal arrest during recovery in oxygenated medium ( P < 0.05). In conclusion, PGE2 exerts its effects on respiration via EP3R activation that attenuates the respiratory response to hypercapnia as well as severe hypoxia. Modulation of the EP3R may serve as a potential therapeutic target for treatment of inflammatory and hypoxic-induced detrimental apneas and respiratory disorders in neonates.

Downregulation of the proangiogenic prostaglandin E receptor EP3 and reduced angiogenesis in a mouse model of diabetes mellitus

Vascular complications such as foot ulcers are a hallmark of diabetes mellitus (DM), although the molecular mechanisms that underlie vascular dysfunction remain unclear. Herein, we show that angiogenesis, which is indispensable to the healing of ulcers, is suppressed in polyurethane sponge implants in mice with DM and reduced proangiogenic signaling. DM was induced in male C57BL/6 mice by intraperitoneal injection of streptozotocin (100mg/kg). Polyurethane sponge disks were implanted into subcutaneous tissues on the backs of mice, and angiogenesis and expression of related factors were analyzed in sponge granulation tissues. Densities of platelet endothelial cell adhesion molecule-1 (PECAM-1)-positive vascular structures and PECAM-1 expression in sponge granulation tissues were increased over time in control mice and reduced in diabetic mice. The reductions in diabetic mice were accompanied by reduced expression of inducible cyclo-oxygenase-2 and microsomal prostaglandin E synthase-1. The prostaglandin E receptor subtype EP3 was downregulated in sponge granulation tissues in diabetic mice, whereas EP1, EP2, and EP4 were not. The expression of the proangiogenic growth factor vascular endothelial growth factor (VEGF)-A and the chemokine stromal cell-derived factor-1 (SDF-1) were both reduced in diabetic mice. Treatment of diabetic mice with a selective agonist of EP3, ONO-AE 248 (30 nmol/site/day, topical injection), reversed suppression of angiogenesis in diabetic mice. These results indicate that proangiogenic EP3 signaling is suppressed in diabetic mice with reduced expression of VEGF and SDF-1. Stimulation of EP3 signaling restored angiogenesis in a sponge implant model in mice with DM. This suggests that topical application of an EP3 agonist could be a novel strategy to treat foot ulcers in patients with DM.

Anti-inflammatory effects of 7-hydroxyl-1-methylindole-3-acetonitrile, a synthetic arvelexin derivative, on the macrophages through destabilizing mPGES-1 mRNA and suppressing NF-κB activation

We previously demonstrated that 7-hydroxyl-1-methylindole-3-acetonitrile (7-HMIA), a synthesized analog of arvelexin, showed the strong inhibitory effects on LPS-induced NO and PGE2 production in macrophages. In this study, we focused on elucidating the anti-inflammatory properties of 7-HMIA and the mechanisms involved using in vitro and in vivo experimental models. In LPS-induced RAW 264.7 macrophages, 7-HMIA significantly inhibited the release of proinflammatory mediators such as prostaglandin E2 (PGE2), nitric oxide (NO), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6). We also found that 7-HMIA suppressed PGE2 production not by inhibiting cyclooxygenase-2 (COX-2) expression or activity, but rather by suppressing the mRNA stability of microsomal prostaglandin E synthase (mPGES-1). Furthermore, 7-HMIA mediated attenuation of inducible NO synthase (iNOS), TNF-α, and IL-6 was closely associated with suppression of transcriptional activities of nuclear factor-kappa B (NF-κB), by decreasing p65 nuclear translocation and Akt phosphorylation. Animal studies revealed that 7-HMIA potently suppressed the carrageenan-induced paw edema and myeloperoxidase (MPO) activity in paw tissues. Taken together, our data indicated that the molecular basis for the anti-inflammatory properties of 7-HMIA involved the inhibition of mRNA stability of mPGES-1 and PI3K/Akt-mediated NF-κB pathways.

Endothelial dysfunction and oxidative stress in polycystic kidney disease

Cardiovascular disease (CVD) is the leading cause of premature mortality in ADPKD patients. The aim was to identify potential serum biomarkers associated with the severity of ADPKD. Serum samples from a homogenous group of 61 HALT study A ADPKD patients [early disease group with estimated glomerular filtration rate (eGFR) >60 ml·min(-1)·1.73 m(-2)] were compared with samples from 49 patients from the HALT study B group with moderately advanced disease (eGFR 25-60 ml·min(-1)·1.73 m(-2)). Targeted tandem-mass spectrometry analysis of markers of endothelial dysfunction and oxidative stress was performed and correlated with eGFR and total kidney volume normalized to the body surface area (TKV/BSA). ADPKD patients with eGFR >60 ml·min(-1)·1.73 m(-2) showed higher levels of CVD risk markers asymmetric and symmetric dimethylarginine (ADMA and SDMA), homocysteine, and S-adenosylhomocysteine (SAH) compared with the healthy controls. Upon adjustments for age, sex, systolic blood pressure, and creatinine, SDMA, homocysteine, and SAH remained negatively correlated with eGFR. Resulting cellular methylation power [S-adenosylmethionine (SAM)/SAH ratio] correlated with the reduction of renal function and increase in TKV. Concentrations of prostaglandins (PGs), including oxidative stress marker 8-isoprostane, as well as PGF2α, PGD₂, and PGE₂, were markedly elevated in patients with ADPKD compared with healthy controls. Upon adjustments for age, sex, systolic blood pressure, and creatinine, increased PGD₂ and PGF₂α were associated with reduced eGFR, whereas 8-isoprostane and again PGF₂α were associated with an increase in TKV/BSA. Endothelial dysfunction and oxidative stress are evident early in ADPKD patients, even in those with preserved kidney function. The identified pathways may provide potential therapeutic targets for slowing down the disease progression.

Targeting inflammation: multiple innovative ways to reduce prostaglandin E₂

The PGE2 pathway is important in inflammation-driven diseases and specific targeting of the inducible mPGES-1 is warranted due to the cardiovascular problems associated with the long-term use of COX-2 inhibitors. This review focuses on patents issued on methods of measuring mPGES-1 activity, on drugs targeting mPGES-1 and on other modulators of free extracellular PGE2 concentration. Perspectives and conclusions regarding the status of these drugs are also presented. Importantly, no selective inhibitors targeting mPGES-1 have been identified and, despite the high number of published patents, none of these drugs have yet made it to clinical trials.

Lysine-specific demethylase 1-mediated demethylation of histone H3 lysine 9 contributes to interleukin 1β-induced microsomal prostaglandin E synthase 1 expression in human osteoarthritic chondrocytes

Introduction

Microsomal prostaglandin E synthase 1 (mPGES-1) catalyzes the terminal step in the biosynthesis of PGE₂, a critical mediator in the pathophysiology of osteoarthritis (OA). Histone methylation plays an important role in epigenetic gene regulation. In this study, we investigated the roles of histone H3 lysine 9 (H3K9) methylation in interleukin 1β (IL-1β)-induced mPGES-1 expression in human chondrocytes.

Methods

Chondrocytes were stimulated with IL-1β, and the expression of mPGES-1 mRNA was evaluated using real-time RT-PCR. H3K9 methylation and the recruitment of the histone demethylase lysine-specific demethylase 1 (LSD1) to the mPGES-1 promoter were evaluated using chromatin immunoprecipitation assays. The role of LSD1 was further evaluated using the pharmacological inhibitors tranylcypromine and pargyline and small interfering RNA (siRNA)-mediated gene silencing. The LSD1 level in cartilage was determined by RT-PCR and immunohistochemistry.

Results

The induction of mPGES-1 expression by IL-1β correlated with decreased levels of mono- and dimethylated H3K9 at the mPGES-1 promoter. These changes were concomitant with the recruitment of the histone demethylase LSD1. Treatment with tranylcypromine and pargyline, which are potent inhibitors of LSD1, prevented IL-1β-induced H3K9 demethylation at the mPGES-1 promoter and expression of mPGES-1. Consistently, LSD1 gene silencing with siRNA prevented IL-1β-induced H3K9 demethylation and mPGES-1 expression, suggesting that LSD1 mediates IL-1β-induced mPGES-1 expression via H3K9 demethylation. We show that the level of LSD1 was elevated in OA compared to normal cartilage.

Conclusion

These results indicate that H3K9 demethylation by LSD1 contributes to IL-1β-induced mPGES-1 expression and suggest that this pathway could be a potential target for pharmacological intervention in the treatment of OA and possibly other arthritic conditions.

Myeloid cell microsomal prostaglandin E synthase-1 fosters atherogenesis in mice

Microsomal prostaglandin E synthase-1 (mPGES-1) in myeloid and vascular cells differentially regulates the response to vascular injury, reflecting distinct effects of mPGES-1-derived PGE2 in these cell types on discrete cellular components of the vasculature. The cell selective roles of mPGES-1 in atherogenesis are unknown. Mice lacking mPGES-1 conditionally in myeloid cells (Mac-mPGES-1-KOs), vascular smooth muscle cells (VSMC-mPGES-1-KOs), or endothelial cells (EC-mPGES-1-KOs) were crossed into hyperlipidemic low-density lipoprotein receptor-deficient animals. En face aortic lesion analysis revealed markedly reduced atherogenesis in Mac-mPGES-1-KOs, which was concomitant with a reduction in oxidative stress, reflective of reduced macrophage infiltration, less lesional expression of inducible nitric oxide synthase (iNOS), and lower aortic expression of NADPH oxidases and proinflammatory cytokines. Reduced oxidative stress was reflected systemically by a decline in urinary 8,12-iso-iPF2α-VI. In contrast to exaggeration of the response to vascular injury, deletion of mPGES-1 in VSMCs, ECs, or both had no detectable phenotypic impact on atherogenesis. Macrophage foam cell formation and cholesterol efflux, together with plasma cholesterol and triglycerides, were unchanged as a function of genotype. In conclusion, myeloid cell mPGES-1 promotes atherogenesis in hyperlipidemic mice, coincident with iNOS-mediated oxidative stress. By contrast, mPGES-1 in vascular cells does not detectably influence atherogenesis in mice. This strengthens the therapeutic rationale for targeting macrophage mPGES-1 in inflammatory cardiovascular diseases.

Microsomal prostaglandin E synthase-1 deficiency exacerbates pulmonary fibrosis induced by bleomycin in mice

Microsomal prostaglandin E2 synthase-1 (mPGES-1), an inducible enzyme that converts prostaglandin H2 (PGH₂) to prostaglandin E2 (PGE₂), plays an important role in a variety of diseases. So far, the role of mPGES-1 in idiopathic pulmonary fibrosis (IPF) remained unknown. The current study aimed to investigate the role of mPGES-1 in pulmonary fibrosis induced by bleomycin in mice. We found that mPGES-1 deficient (mPGES-1^−/−) mice exhibited more severe fibrotic lesions with a decrease in PGE₂ content in lungs after bleomycin treatment when compared with wild type (mPGES-1^+/+) mice. The mPGES-1 expression levels and PGE₂ content were also decreased in bleomycin-treated mPGES-1^+/+ mice compared to saline-treated mPGES-1^+/+ mice. Moreover, in both mPGES-1^−/− and mPGES-1^+/+ mice, bleomycin treatment reduced the expression levels of E prostanoid receptor 2 (EP2) and EP4 receptor in lungs, whereas had little effect on EP1 and EP3. In cultured human lung fibroblast cells (MRC-5), siRNA-mediated knockdown of mPGES-1 augmented transforming growth factor-β1 (TGF-β1)-induced α-smooth muscle actin (α-SMA) protein expression, and the increase was reversed by treatment of PGE₂, selective EP2 agonist and focal adhesion kinase (FAK) inhibitor. In conclusion, these findings revealed mPGES-1 exerts an essential effect against pulmonary fibrogenesis via EP2-mediated signaling transduction, and activation of mPGES-1-PGE₂-EP2-FAK signaling pathway may represent a new therapeutic strategy for treatment of IPF patients.

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.

Anti-inflammatory properties of prostaglandin E2: deletion of microsomal prostaglandin E synthase-1 exacerbates non-immune inflammatory arthritis in mice

Prostanoids and PGE2 in particular have been long viewed as one of the major mediators of inflammation in arthritis. However, experimental data indicate that PGE2 can serve both pro- and anti-inflammatory functions. We have previously shown (Kojima et al., J. Immunol. 180 (2008) 8361-8368) that microsomal prostaglandin E synthase-1 (mPGES-1) deletion, which regulates PGE2 production, resulted in the suppression of collagen-induced arthritis (CIA) in mice. This suppression was attributable, at least in part, to the impaired generation of type II collagen autoantibodies. In order to examine the function of mPGES-1 and PGE2 in a non-autoimmune form of arthritis, we used the collagen antibody-induced arthritis (CAIA) model in mice deficient in mPGES-1, thereby bypassing the engagement of the adaptive immune response in arthritis development. Here we report that mPGES-1 deletion significantly increased CAIA disease severity. The latter was associated with a significant (~3.6) upregulation of neutrophil, but not macrophage, recruitment to the inflamed joints. The lipidomic analysis of the arthritic mouse paws by quantitative liquid chromatography/tandem mass-spectrometry (LC/MS/MS) revealed a dramatic (~59-fold) reduction of PGE2 at the peak of arthritis. Altogether, this study highlights mPGES-1 and its product PGE2 as important negative regulators of neutrophil-mediated inflammation and suggests that specific mPGES-1 inhibitors may have differential effects on different types of inflammation. Furthermore, neutrophil-mediated diseases could be exacerbated by inhibition of mPGES-1.

Cyclooxygenase-2 deficiency in macrophages leads to defective p110γ PI3K signaling and impairs cell adhesion and migration

Cyclooxygenase (Cox)-2 dependent PGs modulate several functions in many pathophysiological processes, including migration of immune cells. In this study, we addressed the role of Cox-2 in macrophage migration by using in vivo and in vitro models. Upon thioglycolate challenge, CD11b(+) F4/80(+) macrophages showed a diminished ability to migrate to the peritoneal cavity in cox-2(-/-) mice. In vivo migration of cox-2(-/-) macrophages from the peritoneal cavity to lymph nodes, as well as cell adhesion to the mesothelium, was reduced in response to LPS. In vitro migration of cox-2(-/-) macrophages toward MCP-1, RANTES, MIP-1α, or MIP-1β, as well as cell adhesion to ICAM-1 or fibronectin, was impaired. Defects in cell migration were not due to changes in chemokine receptor expression. Remarkably, cox-2(-/-) macrophages showed a deficiency in focal adhesion formation, with reduced phosphorylation of paxillin (Tyr(188)). Interestingly, expression of the p110γ catalytic subunit of PI3K was severely reduced in the absence of Cox-2, leading to defective Akt phosphorylation, as well as cdc42 and Rac-1 activation. Our results indicate that the paxillin/p110γ-PI3K/Cdc42/Rac1 axis is defective in cox-2(-/-) macrophages, which results in impaired cell adhesion and migration.

Phospholipases of mineralization competent cells and matrix vesicles: roles in physiological and pathological mineralizations

The present review aims to systematically and critically analyze the current knowledge on phospholipases and their role in physiological and pathological mineralization undertaken by mineralization competent cells. Cellular lipid metabolism plays an important role in biological mineralization. The physiological mechanisms of mineralization are likely to take place in tissues other than in bones and teeth under specific pathological conditions. For instance, vascular calcification in arteries of patients with renal failure, diabetes mellitus or atherosclerosis recapitulates the mechanisms of bone formation. Osteoporosis—a bone resorbing disease—and rheumatoid arthritis originating from the inflammation in the synovium are also affected by cellular lipid metabolism. The focus is on the lipid metabolism due to the effects of dietary lipids on bone health. These and other phenomena indicate that phospholipases may participate in bone remodelling as evidenced by their expression in smooth muscle cells, in bone forming osteoblasts, chondrocytes and in bone resorbing osteoclasts. Among various enzymes involved, phospholipases A₁ or A₂, phospholipase C, phospholipase D, autotaxin and sphingomyelinase are engaged in membrane lipid remodelling during early stages of mineralization and cell maturation in mineralization-competent cells. Numerous experimental evidences suggested that phospholipases exert their action at various stages of mineralization by affecting intracellular signaling and cell differentiation. The lipid metabolites—such as arachidonic acid, lysophospholipids, and sphingosine-1-phosphate are involved in cell signaling and inflammation reactions. Phospholipases are also important members of the cellular machinery engaged in matrix vesicle (MV) biogenesis and exocytosis. They may favour mineral formation inside MVs, may catalyse MV membrane breakdown necessary for the release of mineral deposits into extracellular matrix (ECM), or participate in hydrolysis of ECM. The biological functions of phospholipases are discussed from the perspective of animal and cellular knockout models, as well as disease implications, development of potent inhibitors and therapeutic interventions.

Microsomal prostaglandin E synthase-1 aggravates inflammation and demyelination in a mouse model of multiple sclerosis

Microsomal prostaglandin synthetase-1 (mPGES-1) is an inducible terminal enzyme required for prostaglandin E(2) (PGE(2)) biosynthesis. In this study, we examined the role of mPGES-1 in the inflammation and demyelination observed in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). We induced EAE with myelin oligodendrocyte glycoprotein(35-55) peptide in mPGES-1-deficient (mPGES-1(-/-)) and wild-type (WT) mice. First, we examined the histopathology in the early and late phases of EAE progression. Next, we measured the concentration of PGE(2) in the spinal cord and investigated the expression of mPGES-1 using immunohistochemistry. In addition, we examined the progression of the severity of EAE using an EAE score to investigate a correlation between pathological features and paralysis. In this paper, we demonstrate that WT mice showed extensive inflammation and demyelination, whereas mPGES-1(-/-) mice exhibited significantly smaller and more localized changes in the perivascular area. The mPGES-1 protein was induced in vascular endothelial cells and microglia around inflammatory foci, and PGE(2) production was increased in WT mice but not mPGES-1(-/-) mice. Furthermore, mPGES-1(-/-) mice showed a significant reduction in the maximum EAE score and improved locomotor activity. These results suggest that central PGE(2) derived from non-neuronal mPGES-1 aggravates the disruption of the vessel structure, leading to the spread of inflammation and local demyelination in the spinal cord, which corresponds to the symptoms of EAE. The inhibition of mPGES-1 may be useful for the treatment of human MS.