Selective impairment of P2Y signaling by prostaglandin E2 in macrophages: implications for Ca2+-dependent responses

Crosstalk between P2Y receptors and cyclooxygenase activity in inflammation and tissue repair

The role of extracellular nucleotides as modulators of inflammation and cell stress is well established. One of the main actions of these molecules is mediated by the activation of purinergic receptors (P2) of the plasma membrane. P2 receptors can be classified according to two different structural families: P2X ionotropic ion channel receptors, and P2Y metabotropic G protein-coupled receptors. During inflammation, damaged cells release nucleotides and purinergic signaling occurs along the temporal pattern of the synthesis of pro-inflammatory and pro-resolving mediators by myeloid and lymphoid cells. In macrophages under pro-inflammatory conditions, the expression and activity of cyclooxygenase 2 significantly increases and enhances the circulating levels of prostaglandin E2 (PGE2), which exerts its effects both through specific plasma membrane receptors (EP1-EP4) and by activation of intracellular targets. Here we review the mechanisms involved in the crosstalk between PGE2 and P2Y receptors on macrophages, which is dependent on several isoforms of protein kinase C and protein kinase D1. Due to this crosstalk, a P2Y-dependent increase in calcium is blunted by PGE2 whereas, under these conditions, macrophages exhibit reduced migratory capacity along with enhanced phagocytosis, which contributes to the modulation of the inflammatory response and tissue repair.

DUSP1/MKP-1 represents another piece in the P2X7R intracellular signaling puzzle in cerebellar cells: our last journey with Mª Teresa along the purinergic pathways of Eden

The P2X7 receptor (P2X7R) stands out within the purinergic family as it has exclusive pharmacological and regulatory features, and it fulfills distinct roles depending on the type of stimulation and cellular environment. Tonic activation of P2X7R promotes cell proliferation, whereas sustained activation is associated with cell death. Yet strikingly, prolonged P2X7R activation in rat cerebellar granule neurons and astrocytes does not affect cell survival. The intracellular pathways activated by P2X7Rs involve proteins like MAPKs, ERK1/2 and p38, and interactions with growth factor receptors could explain their behavior in populations of rat cerebellar cells. In this study, we set out to characterize the intracellular mechanisms through which P2X7Rs and Trk receptors, EGFR (epidermal growth factor receptor) and BDNFR (brain-derived neurotrophic factor receptor), regulate the dual-specificity phosphatase DUSP1. In cerebellar astrocytes, the regulation of DUSP1 expression by P2X7R depends on ERK and p38 activation. EGFR stimulation can also induce DUSP1 expression, albeit less strongly than P2X7R. Conversely, EGF was virtually ineffective in regulating DUSP1 in granule neurons, a cell type in which BDNF is the main regulator of DUSP1 expression and P2X7R only induces a mild response. Indeed, the regulation of DUSP1 elicited by BDNF reflects the balance between both transcriptional and post-transcriptional mechanisms. Importantly, when the regulation of DUSP1 expression is compromised, the viability of both astrocytes and neurons is impaired, suggesting this phosphatase is essential to maintain proper cell cytoarchitecture and functioning.

Human Amniotic Membrane Mesenchymal Stem Cell-Synthesized PGE2 Exerts an Immunomodulatory Effect on Neutrophil Extracellular Trap in a PAD-4-Dependent Pathway through EP2 and EP4

Human amniotic membrane mesenchymal stem cells (hAM-MSC) secrete a myriad of components with immunosuppressive activities. In the present research, we aimed to describe the effect of prostaglandin E₂ (PGE₂) secreted by hAM-MSCs on neutrophil extracellular trap (NET) release and to characterize the role of its receptors (EP2/EP4) in PAD-4 and NFκB activity in neutrophils. Human peripheral blood neutrophils were ionomycin-stimulated in the presence of hAM-MSC conditioned medium (CM) treated or not with the selective PGE₂ inhibitor MF-63, PGE₂, EP2/EP4 agonists, and the selective PAD-4 inhibitor GSK-484. NET release, PAD-4, and NFκB activation were analyzed. Ionomycin induced NET release, which was inhibited in the presence of hAM-MSC-CM, while CM from hAM-MSCs treated with MF-63 prevented NET release inhibition. PGE₂ and EP2/EP4 agonists, and GSK-484 inhibited NET release. EP2/EP4 agonists and GSK-484 inhibited H3-citrullination but did not affect PAD-4 protein expression. Finally, PGE₂ and EP2/EP4 agonists and GSK-484 increased NFκB phosphorylation. Taken together, these results suggest that hAM-MSC exert their immunomodulatory activities through PGE_2, inhibiting NET release in a PAD-4-dependent pathway. This research proposes a new mechanism by which hAM-MSC exert their activities when modulating the innate immune response and inhibiting NET release.

Graphene Particles Interfere with Pro-Inflammatory Polarization of Human Macrophages: Functional and Electrophysiological Evidence

The interaction of two types of fragmented graphene particles (30-160 nm) with human macrophages is studied. Since macrophages have significant phagocytic activity, the incorporation of graphene particles into cells has an effect on the response to functional polarization stimuli, favoring an anti-inflammatory profile. Incubation of macrophages with graphene foam particles, prepared by chemical vapor deposition, and commercially available graphene nanoplatelet particles does not affect cell viability when added at concentrations up to 100 µg mL^-1 ; macrophages exhibit differential quantitative responses to each type of graphene particles. Although both materials elicit similar increases in the release of reactive oxygen species, the impact on the transcriptional regulation associated with the polarization profile is different; graphene nanoplatelets significantly modify this transcriptomic profile. Moreover, these graphene particles differentially affect the motility and phagocytosis of macrophages. After the incorporation of both graphene types into the macrophages, they exhibit specific responses in terms of the mitochondrial oxygen consumption and electrophysiological potassium currents at the cell plasma membrane. These data support the view that the physical structure of the graphene particles has an impact on human macrophage responses, paving the way for the development of new mechanisms to modulate the activity of the immune system.

Nucleotides-Induced Changes in the Mechanical Properties of Living Endothelial Cells and Astrocytes, Analyzed by Atomic Force Microscopy

Endothelial cells and astrocytes preferentially express metabotropic P2Y nucleotide receptors, which are involved in the maintenance of vascular and neural function. Among these, P2Y₁ and P2Y₂ receptors appear as main actors, since their stimulation induces intracellular calcium mobilization and activates signaling cascades linked to cytoskeletal reorganization. In the present work, we have analyzed, by means of atomic force microscopy (AFM) in force spectroscopy mode, the mechanical response of human umbilical vein endothelial cells (HUVEC) and astrocytes upon 2MeSADP and UTP stimulation. This approach allows for simultaneous measurement of variations in factors such as Young’s modulus, maximum adhesion force and rupture event formation, which reflect the potential changes in both the stiffness and adhesiveness of the plasma membrane. The largest effect was observed in both endothelial cells and astrocytes after P2Y₂ receptor stimulation with UTP. Such exposure to UTP doubled the Young’s modulus and reduced both the adhesion force and the number of rupture events. In astrocytes, 2MeSADP stimulation also had a remarkable effect on AFM parameters. Additional studies performed with the selective P2Y₁ and P2Y₁₃ receptor antagonists revealed that the 2MeSADP-induced mechanical changes were mediated by the P2Y₁₃ receptor, although they were negatively modulated by P2Y₁ receptor stimulation. Hence, our results demonstrate that AFM can be a very useful tool to evaluate functional native nucleotide receptors in living cells.

Specific Effects of Trabectedin and Lurbinectedin on Human Macrophage Function and Fate-Novel Insights

BACKGROUND

Tumor-associated macrophages (TAMs) play a crucial role in suppressing the immunosurveillance function of the immune system that prevents tumor growth. Indeed, macrophages can also be targeted by different chemotherapeutic agents improving the action over immune checkpoints to fight cancer. Here we describe the effect of trabectedin and lurbinectedin on human macrophage cell viability and function.

METHODS

Blood monocytes from healthy donors were differentiated into macrophages and exposed to different stimuli promoting functional polarization and differentiation into tumor-associated macrophages. Cells were challenged with the chemotherapeutic drugs and the effects on cell viability and function were analyzed.

RESULTS

Human macrophages exhibit at least two different profiles in response to these drugs. One-fourth of the blood donors assayed (164 individuals) were extremely sensitive to trabectedin and lurbinectedin, which promoted apoptotic cell death. Macrophages from other individuals retained viability but responded to the drugs increasing reactive oxygen production and showing a rapid intracellular calcium rise and a loss of mitochondrial oxygen consumption. Cell-membrane exposure of programmed-death ligand 1 (PD-L1) significantly decreased after treatment with therapeutic doses of these drugs, including changes in the gene expression profile of hypoxia-inducible factor 1 alpha (HIF-1α)-dependent genes, among other.

CONCLUSIONS

The results provide evidence of additional onco-therapeutic actions for these drugs.

Intracellular Calcium Recording After Purinoceptor Activation Using a Video-Microscopy Equipment

Calcium is one of the most important intracellular messengers, triggering a wide range of cellular responses. Changes in intracellular free calcium concentration can be measured using calcium sensitive fluorescent dyes, which are either EGTA- or BAPTA-based organic molecules that change their spectral properties in response to Ca²⁺ binding. One of the most common calcium indicators is the ratiometric dye Fura-2. The main advantage of using ratiometric dyes is that the ratio signal is independent of the illumination intensity, dye concentration, photobleaching, and focus changes among others, allowing for the concentration of intracellular calcium to be determined independently of these artifacts. In this protocol, we describe the use of Fura-2 to measure intracellular calcium elevations in single cultured cells after purinoceptor activation using a video-microscopy equipment. This method, usually known as calcium imaging, allows for real-time quantification of intracellular calcium dynamics and can be adapted to measure agonist mediated intracellular calcium responses due to the activation of different purinergic receptors in several cellular models using the appropriate growth conditions.

Prostaglandin E2 and an EP4 receptor agonist inhibit LPS-Induced monocyte chemotactic protein 5 production and secretion in mouse cardiac fibroblasts via Akt and NF-κB signaling

BACKGROUND

Prostaglandin E2 (PGE₂) signals through 4 separate G-protein coupled receptor sub-types to elicit a variety of physiologic and pathophysiological effects. We have previously reported that mice lacking the EP4 receptor in the cardiomyocytes develop heart failure with a phenotype of dilated cardiomyopathy. Also, these mice have increased levels of chemokines, like MCP-5, in their left ventricles. We have recently reported that overexpression of the EP4 receptor could improve cardiac function in the myocardial infarction model. Furthermore, we showed that overexpression of EP4 had an anti-inflammatory effect in the whole left ventricle. It has also been shown that PGE₂ can antagonize lipopolysaccharide-induced secretion of chemokines/cytokines in various cell types. We therefore hypothesized that PGE₂ inhibits lipopolysaccharide (LPS)-induced MCP-5 secretion in adult mouse cardiac fibroblasts via its EP4 receptor.

METHODS AND RESULTS

Our hypothesis was tested using isolated mouse adult ventricular fibroblasts (AVF) treated with LPS. Pre-treatment of the cells with PGE₂ and the EP4 agonist CAY10598 resulted in reductions of the pro-inflammatory response induced by LPS. Specifically, we observed reductions in MCP-5 secretion. Western blot analysis showed reductions in phosphorylated Akt and IκBα indicating reduced NF-κB activation. The anti-inflammatory effects of PGE₂ and EP4 agonist signaling appeared to be independent of cAMP, p-44/42, or p38 pathways.

CONCLUSION

Exogenous treatment of PGE₂ and the EP4 receptor agonist blocked the pro-inflammatory actions of LPS. Mechanistically, this was mediated via reduced Akt phosphorylation and inhibition of NF-κB.

Purinergic receptors and the inflammatory response mediated by lipids

The inflammatory response is regulated by the production of different extracellular mediators, including lipids and extracellular nucleotides. In the extracellular environment, intermediate lipids activate specific G-protein-coupled receptors (GPCRs) in target cells and promote cell recruitment and activation. Extracellular nucleotides activate two types of receptors, the ionotropic purinergic P2X and the metabotropic purinergic P2Y receptors, inducing the release of cytokines and promoting cell recruitment. Several P2X receptors are associated with an increase in the production of immunoactive lipids mediators, which in turn are able to interfere with the activation of different P2Y receptors, establishing a tight signalling link between purinergic receptors and lipid mediators. In this review, we summarise recent studies indicating signalling crosstalk between purinergic P2X and P2Y receptor activation and lipid mediators with a focus on inflammatory diseases. Novel concepts arising from this crosstalk would result in the development of combinatorial therapies targeting lipid synthesis together with individual P2 receptors for the management of inflammatory diseases.

Neuroinflammation is induced by tongue-instilled ZnO nanoparticles via the Ca2+-dependent NF-κB and MAPK pathways

Background

The extensive biological applications of zinc oxide nanoparticles (ZnO NPs) in stomatology have created serious concerns about their biotoxicity. In our previous study, ZnO NPs were confirmed to transfer to the central nervous system (CNS) via the taste nerve pathway and cause neurodegeneration after 30 days of tongue instillation. However, the potential adverse effects on the brain caused by tongue-instilled ZnO NPs are not fully known.

Methods

In this study, the biodistribution of Zn, cerebral histopathology and inflammatory responses were analysed after 30 days of ZnO NPs tongue instillation. Moreover, the molecular mechanisms underlying neuroinflammation in vivo were further elucidated by treating BV2 and PC12 cells with ZnO NPs in vitro.

Results

This analysis indicated that ZnO NPs can transfer into the CNS, activate glial cells and cause neuroinflammation after tongue instillation. Furthermore, exposure to ZnO NPs led to a reduction in cell viability and induction of inflammatory response and calcium influx in BV2 and PC12 cells. The mechanism underlying how ZnO NPs induce neuroinflammation via the Ca²⁺-dependent NF-κB, ERK and p38 activation pathways was verified at the cytological level.

Conclusion

This study provided a new way how NPs, such as ZnO NPs, induce neuroinflammation via the taste nerve translocation pathway, a new mechanism for ZnO NPs-induced neuroinflammation and a new direction for nanomaterial toxicity analysis.

Electronic supplementary material

The online version of this article (10.1186/s12989-018-0274-0) contains supplementary material, which is available to authorized users.

Prostaglandin E2 Impairs P2Y2/P2Y4 Receptor Signaling in Cerebellar Astrocytes via EP3 Receptors

Prostaglandin E₂ (PGE₂) is an important bioactive lipid that accumulates after tissue damage or inflammation due to the rapid expression of cyclooxygenase 2. PGE₂ activates specific G-protein coupled EP receptors and it mediates pro- or anti-inflammatory actions depending on the cell-context. Nucleotides can also be released in these situations and they even contribute to PGE₂ production. We previously described the selective impairment of P2Y nucleotide signaling by PGE₂ in macrophages and fibroblasts, an effect independent of prostaglandin receptors but that involved protein kinase C (PKC) and protein kinase D (PKD) activation. Considering that macrophages and fibroblasts influence inflammatory responses and tissue remodeling, a similar mechanism involving P2Y signaling could occur in astrocytes in response to neuroinflammation and brain repair. We analyzed here the modulation of cellular responses involving P2Y₂/P2Y₄ receptors by PGE₂ in rat cerebellar astrocytes. We demonstrate that PGE₂ inhibits intracellular calcium responses elicited by UTP in individual cells and that inhibiting this P2Y signaling impairs the astrocyte migration elicited by this nucleotide. Activation of EP3 receptors by PGE₂ not only impairs the calcium responses but also, the extracellular regulated kinases (ERK) and Akt phosphorylation induced by UTP. However, PGE₂ requires epidermal growth factor receptor (EGFR) transactivation in order to dampen P2Y signaling. In addition, these effects of PGE₂ also occur in a pro-inflammatory context, as evident in astrocytes stimulated with bacterial lipopolysaccharide (LPS). While we continue to investigate the intracellular mechanisms responsible for the inhibition of UTP responses, the involvement of novel PKC and PKD in cerebellar astrocytes cannot be excluded, kinases that could promote the internalization of P2Y receptors in fibroblasts.

Prostaglandin E2-mediated adenosinergic effects on CD14+ cells: Self-amplifying immunosuppression in cancer

CD39 and CD73 are surface-expressed ectonucleotidases that hydrolyze ATP in a highly regulated, serial manner into ADP, AMP and adenosine. The end product, adenosine, has both tumor-promoting and immunosuppressive effects. The aim of this study was to determine CD73 expression on immune cells in pleural effusion (PE) in order to have a better understanding of the immune environment in mesothelioma. PE- or blood-derived CD14⁺ cells of mesothelioma patients and healthy donors were analyzed by flow cytometry for the expression of CD39 and CD73. CD73-induction was studied by exposure of CD14⁺ cells to the soluble fraction of PE (sPE), while the signaling mechanism, responsible for CD73 induction, by phosphoflow cytometry and receptor-inhibition studies. We observed CD73 expression on CD14⁺ cells in PE but not peripheral blood of mesothelioma patients or healthy donors. CD73 expression was inducible on CD14⁺ cells with sPE, cyclic-AMP (cAMP)-inducers (forskolin and prostaglandin-E₂ (PGE₂)) and adenosine. Inhibition of PGE₂ receptors or adenosine A₂ receptors blocked CD73-induction by sPE. sPE treatment triggered protein kinase A and p38 activation. However, signal-transducer and activator of transcription 3 (STAT3)-blocking led to enhanced CD73 expression, demonstrating a hitherto unknown negative control of purinergic signaling by STAT3 in CD14⁺ cells. TNFα production by CD73⁺ CD14⁺ cells was significantly impaired in the presence of AMP, confirming immunosuppressive function. Taken together, CD73 expression can be induced by PGE₂, cAMP or adenosine on human CD14⁺ cells. We suggest that targeting this autocrine loop is a valid therapeutic approach in mesothelioma that may also enhance immunotherapy.

Phospholipid Ozonation Products Activate the 5-Lipoxygenase Pathway in Macrophages

Ozone is a highly reactive environmental toxicant that can react with the double bonds of lipids in pulmonary surfactant. This study was undertaken to investigate the proinflammatory properties of the major lipid-ozone product in pulmonary surfactant, 1-palmitoyl-2-(9'-oxo-nonanoyl)-glycerophosphocholine (16:0/9al-PC), with respect to eicosanoid production. A dose-dependent increase in the formation of 5-lipoxygenase (5-LO) products was observed in murine resident peritoneal macrophages (RPM) and alveolar macrophages (AM) upon treatment with 16:0/9al-PC. In contrast, the production of cyclooxygenase (COX) derived eicosanoids did not change from basal levels in the presence of 16:0/9al-PC. When 16:0/9al-PC and the TLR2 ligand, zymosan, were added to RPM or AM, an enhancement of 5-LO product formation along with a concomitant decrease in COX product formation was observed. Neither intracellular calcium levels nor arachidonic acid release was influenced by the addition of 16:0/9al-PC to RPM. Results from mitogen-activated protein kinase (MAPK) inhibitor studies and direct measurement of phosphorylation of MAPKs revealed that 16:0/9al-PC activates the p38 MAPK pathway in RPM, which results in the activation of 5-LO. Our results indicate that 16:0/9al-PC has a profound effect on the eicosanoid pathway, which may have implications in inflammatory pulmonary disease states where eicosanoids have been shown to play a role.

NMAAP1 Expressed in BCG-Activated Macrophage Promotes M1 Macrophage Polarization

Macrophages are divided into two subpopulations: classically activated macrophages (M1) and alternatively activated macrophages (M2). BCG (Bacilli Calmette-GuC)rin) activates disabled naC/ve macrophages to M1 macrophages, which act as inflammatory, microbicidal and tumoricidal cells through cell-cell contact and/or the release of soluble factors. Various transcription factors and signaling pathways are involved in the regulation of macrophage activation and polarization. We discovered that BCG-activated macrophages (BAM) expressed a new molecule, and we named it Novel Macrophage Activated Associated Protein 1 (NMAAP1). The current study found that the overexpression of NMAAP1 in macrophages results in M1 polarization with increased expression levels of M1 genes, such as inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNF-N1), Interleukin 6 (IL-6), Interleukin 12 (IL-12), Monocyte chemoattractant protein-1 (MCP-1) and Interleukin-1 beta (IL-1N2), and decreased expression of some M2 genes, such as Kruppel-like factor 4 (KLF4) and suppressor of cytokine signaling 1 (SOCS1), but not other M2 genes, including arginase-1 (Arg-1), Interleukin (IL-10), transforming growth factor beta (TGF-N2) and found in inflammatory zone 1 (Fizz1). Moreover, NMAAP1 overexpression in the RAW264.7 cell line increased cytotoxicity against MCA207 tumor cells, which depends on increased inflammatory cytokines rather than cell-cell contact. NMAAP1 also substantially enhanced the phagocytic ability of macrophages, which implies that NMAAP1 promoted macrophage adhesive and clearance activities. Our results indicate that NMAAP1 is an essential molecule that modulates macrophages phenotype and plays an important role in macrophage tumoricidal functions.

Inhibition of P2Y6 receptor-mediated phospholipase C activation and Ca(2+) signalling by prostaglandin E2 in J774 murine macrophages

Extracellular nucleotides act as inflammatory mediators through activation of multiple purinoceptors. Under inflammatory conditions, the purinergic signalling is affected by various inflammatory mediators. We previously showed that prostaglandin (PG) E2 suppressed the elevation of intracellular Ca(2+) concentration ([Ca(2+)]i) stimulated by P2X4, P2Y2, and P2Y6 receptors in J774 murine macrophages. In this study, we examined the mechanism of PGE2 inhibitory effects on P2Y6 receptor-mediated function in J774 cells. The P2Y6 receptor agonist UDP induced a sustained elevation of [Ca(2+)]i by stimulating the phospholipase C (PLC) signalling pathway. PGE2 inhibited [Ca(2+)]i elevation and phosphatidylinositol (PI) hydrolysis in a concentration-dependent manner. J774 cells highly expressed the E-type prostanoid 2 (EP2) receptor subtype, a Gs-coupled receptor. PGE2 and a selective EP2 receptor agonist caused cyclic AMP (cAMP) accumulation in J774 cells. The inhibitory effects of PGE2 on P2Y6 receptor-mediated responses were mimicked by the selective EP2 receptor agonist. Although EP2 receptor is linked to adenylyl cyclase activation, PGE2-induced inhibition of Ca(2+) response and PI hydrolysis could not be mimicked by a lipophilic cAMP derivative, dibutyryl cAMP, or an adenylyl cyclase activator, forskolin. The inhibition of UDP-induced PLC activation by PGE2 was not affected by down-regulation of protein kinase C by phorbol-12-myristate-13-acetate treatment. PGE2 inhibited PLC activation induced by aluminium fluoride, but not by the Ca(2+)-ionophore, ionomycin. Finally, the inhibition of UDP-induced PLC activation by PGE2 was impaired by Gs knockdown using siRNA. These results suggest that EP2 receptor activation in macrophages negatively controls the Gq/11-PLC signalling through a Gs-mediated, but cAMP-independent signalling mechanism.

Inhibitors of the 5-lipoxygenase pathway activate pannexin1 channels in macrophages via the thromboxane receptor

A multitude of environmental signaling molecules influence monocyte and macrophage innate and adaptive immune responses, including ATP and prostanoids. Interestingly, purinergic (P2) and eicosanoid receptor signaling interact such that the activation of P2 receptors leads to prostanoid production, which can then interfere with P2Y-mediated macrophage migration. Recent studies suggest that blockade of 5-lipoxygenase (5-LOX) in macrophages can activate a permeation pathway involved in the influx of dye and the release of ATP. Here, we provide evidence that pannexin1 (Panx1) is a component of this pathway and present the intracellular signaling molecules linking the thromboxane (TP) receptor to Panx1-mediated dye influx and ATP release. Using pharmacological tools and transgenic mice deficient in Panx1, we show that two 5-LOX pathway inhibitors induce ATP release and influx of dye in a Panx1-dependent manner. Electrophysiological recordings performed in wild-type and Panx1-deficient macrophages confirmed that these 5-LOX pathway inhibitors activate currents characteristic of Panx1 channels. We found that the mechanism by which Panx1 channels are activated under this condition involves activation of the TP receptor that is mediated by the cAMP/PKA pathway. This is to our knowledge the first evidence for the involvement of Panx1 in the TP receptor signaling pathway. Future studies aimed to clarify the contribution of this TP-Panx1 signaling network to macrophage immune responses are likely to be important for targeting inflammatory and autoimmune diseases.

Sustained release of prostaglandin E₂ in fibroblasts expressing ectopically cyclooxygenase 2 impairs P2Y-dependent Ca²⁺-mobilization

The nucleotide uridine trisphosphate (UTP) released to the extracellular milieu acts as a signaling molecule via activation of specific pyrimidine receptors (P2Y). P2Y receptors are G protein-coupled receptors expressed in many cell types. These receptors mediate several cell responses and they are involved in intracellular calcium mobilization. We investigated the role of the prostanoid PGE2 in P2Y signaling in mouse embryonic fibroblasts (MEFs), since these cells are involved in different ontogenic and physiopathological processes, among them is tissue repair following proinflammatory activation. Interestingly, Ca(2+)-mobilization induced by UTP-dependent P2Y activation was reduced by PGE2 when this prostanoid was produced by MEFs transfected with COX-2 or when PGE2 was added exogenously to the culture medium. This Ca(2+)-mobilization was important for the activation of different metabolic pathways in fibroblasts. Moreover, inhibition of COX-2 with selective coxibs prevented UTP-dependent P2Y activation in these cells. The inhibition of P2Y responses by PGE2 involves the activation of PKCs and PKD, a response that can be suppressed after pharmacological inhibition of these protein kinases. In addition to this, PGE2 reduces the fibroblast migration induced by P2Y-agonists such as UTP. Taken together, these data demonstrate that PGE2 is involved in the regulation of P2Y signaling in these cells.

Modulation of voltage-dependent and inward rectifier potassium channels by 15-epi-lipoxin-A4 in activated murine macrophages: implications in innate immunity

Potassium channels modulate macrophage physiology. Blockade of voltage-dependent potassium channels (Kv) by specific antagonists decreases macrophage cytokine production and inhibits proliferation. In the presence of aspirin, acetylated cyclooxygenase-2 loses the activity required to synthesize PGs but maintains the oxygenase activity to produce 15R-HETE from arachidonate. This intermediate product is transformed via 5-LOX into epimeric lipoxins, termed 15-epi-lipoxins (15-epi-lipoxin A4 [e-LXA4]). Kv have been proposed as anti-inflammatory targets. Therefore, we studied the effects of e-LXA4 on signaling and on Kv and inward rectifier potassium channels (Kir) in mice bone marrow-derived macrophages (BMDM). Electrophysiological recordings were performed in these cells by the whole-cell patch-clamp technique. Treatment of BMDM with e-LXA4 inhibited LPS-dependent activation of NF-κB and IκB kinase β activity, protected against LPS activation-dependent apoptosis, and enhanced the accumulation of the Nrf-2 transcription factor. Moreover, treatment of LPS-stimulated BMDM with e-LXA4 resulted in a rapid decrease of Kv currents, compatible with attenuation of the inflammatory response. Long-term treatment of LPS-stimulated BMDM with e-LXA4 significantly reverted LPS effects on Kv and Kir currents. Under these conditions, e-LXA4 decreased the calcium influx versus that observed in LPS-stimulated BMDM. These effects were partially mediated via the lipoxin receptor (ALX), because they were significantly reverted by a selective ALX receptor antagonist. We provide evidence for a new mechanism by which e-LXA4 contributes to inflammation resolution, consisting of the reversion of LPS effects on Kv and Kir currents in macrophages.