Roles of prostaglandin E receptors in stress responses

Thromboxane A2 Modulates de novo Synthesis of Adrenal Corticosterone in Mice via p38/14-3-3γ/StAR Signaling

Prostanoids are endogenous lipid bioactive mediators that play essential roles in physiological processes such as glucocorticoid secretion. Here, it is found that the thromboxane (Tx)A2 receptor (TP) is highly expressed in the adrenal cortex of mice. Both global and adrenocortical-specific deletion of the TP receptor lead to increased adiposity in mice by elevating corticosterone synthesis. Mechanistically, the TP receptor deletion increases the phosphorylation of steroidogenic acute regulatory protein (StAR) and corticosterone synthesis in adrenal cortical cells by suppressing p-p38-mediated phosphorylation of 14-3-3γ adapter protein at S71. The activation of the p38 in the adrenal cortical cells by forced expression of the MKK6EE gene attenuates hypercortisolism in TP-deficient mice. These observations suggest that the TxA2/TP signaling regulates adrenal corticosterone homeostasis independent of the hypothalamic-pituitary-adrenal axis and the TP receptor may serve as a promising therapeutic target for hypercortisolism.

Unique brain endothelial profiles activated by social stress promote cell adhesion, prostaglandin E2 signaling, hypothalamic-pituitary-adrenal axis modulation, and anxiety

Chronic stress may precipitate psychiatric disorders including anxiety. We reported that Repeated Social Defeat (RSD) in mice increased accumulation of inflammatory monocytes within the brain vasculature, which corresponded with increased interleukin (IL)-1 Receptor 1-mediated activation of endothelia, and augmented anxiety-like behavior. One unknown, however, is the role of immune-activated endothelia in regulating the physiological and behavioral responses to social stress. Thus, we sought to determine the RNA profile of activated endothelia and delineate the pathways by which these endothelia communicate within the brain to influence key responses to social stress. First, endothelial-specific RiboTag mice were exposed to RSD and brain endothelial mRNA profiles from the whole brain and prefrontal cortex were determined using RNAseq. RSD increased expression of cell adhesion molecules (Icam1), inflammatory genes (Lrg1, Lcn2, Ackr1, Il1r1), and cyclooxygenase-2 (Ptgs2/COX-2). In studies with IL-1R1KO mice, there was clear dependence on IL-1R1 on endothelia-associated transcripts including Lrg1, Icam1, Lcn2. Moreover, prostaglandin (PG)E2 was increased in the brain after RSD and Ptgs2 was localized to endothelia, especially within the hypothalamus. Next, a selective COX-2 inhibitor, Celecoxib (CCB), was used with social stress. RSD increased PGE2 in the brain and this was abrogated by CCB. Moreover, CCB reduced RSD-induced Hypothalamic-Pituitary-Adrenal (HPA) axis activation with attenuation of hypothalamic paraventricular neuron activation, hypothalamic Crh expression, and corticosterone in circulation. Production, release, and accumulation of inflammatory monocytes after RSD was COX-2 independent. Nonetheless, CCB blocked anxiety-like behavior in response to RSD. Collectively, social stress stimulated specific endothelia RNA profiles associated with increased cell adhesion, IL-1 and prostaglandin signaling, HPA axis activation, and anxiety.

The EP3 and EP4 Receptor Subtypes both Mediate the Fever-producing Effects of Prostaglandin E2 in the Rostral Ventromedial Preoptic Area of the Hypothalamus in Rats

This study aimed to re-examine the receptor subtype that mediates the fever-producing effects of prostaglandin E₂ (PGE₂) in the rostral ventromedial preoptic area (rvmPOA) of the hypothalamus. Among the four subtypes of PGE₂ receptors (EP₁, EP₂, EP₃, and EP₄), EP₃ receptor is crucially involved in the febrile effects of PGE₂. However, it is possible for other subtypes of PGE₂ receptor to contribute in the central mechanism of fever generation. Accordingly, effects of microinjection of PGE₂ receptor subtype-specific agonists or antagonists were examined at the locus where a microinjection of a small amount (420 fmol) of PGE₂ elicited prompt increases in the O₂ consumption rate (VO₂), heart rate, and colonic temperature (T_c) in the rvmPOA of urethane-chloralose-anesthetized rats. The EP₃ agonist sulprostone mimicked, whereas its antagonist L-798,106 reduced, the febrile effects of PGE₂ microinjected into the same site. Similarly, the EP₄ agonist rivenprost mimicked, whereas its antagonist ONO-AE3-208 reduced, the effects of PGE₂ microinjected into the same site. In contrast, microinjection of the EP₁ agonist iloprost induced a very small increase in VO₂ but did not have significant influences on the heart rate and T_c, whereas its antagonist, AH6809, did not affect the PGE₂-induced responses. Microinjection of the EP₂ agonist butaprost had no effects on the VO₂, heart rate, and T_c. The results suggest that the EP₃ and EP₄ receptor subtypes are both involved in the fever generated by PGE₂ in the rvmPOA.

The PGE2 receptor EP3 plays a positive role in the activation of hypothalamic-pituitary-adrenal axis and neuronal activity in the hypothalamus under immobilization stress

BACKGROUND

Prostaglandin E2 (PGE2) binds to four receptor subtypes (EP1, EP2, EP3 and EP4) and plays an important role in response to stress. However, the identity of the receptor(s) responsible for PGE2 regulation of neuronal activity and signaling through activation of the hypothalamic-pituitary-adrenal (HPA) axis under immobilization stress is unknown.

PURPOSE

The present study aimed to investigate the role of the hypothalamic PGE2 receptors in the activation of the HPA axis and neuronal activity in a rat model of stress.

METHODS

Stress was induced by immobilization of the animals, after which the stress-induced profile of PGE2 receptor signaling in the rat hypothalamus was determined by real-time polymerase chain reaction and immunohistochemistry. The effect of a selective EP3 receptor antagonist on corticosterone concentrations and c-Fos immunoreactivity was measured.

RESULTS

Expression of EP2 and EP3 receptor genes, but not EP1 and EP4, was increased following immobilization stress. The EP3 receptor was localized to the paraventricular nucleus (PVN) of the hypothalamus, and the integrated density of the EP3 receptor was increased after immobilization stress. Rats given L-798,106, a selective antagonist of the EP3 receptor, showed significant attenuation of stress-increased serum corticosterone levels. EP3 antagonist also significantly suppressed the increase in the gene expression of c-Fos and the number of c-Fos-immunoreactive cells in the PVN of the hypothalamus following immobilization stress.

CONCLUSIONS

These results suggest that immobilization stress may result in increased activation of the HPA axis and neuronal activity through regulating the function of the EP3 receptor.

Febrile temperature change modulates CD4 T cell differentiation via a TRPV channel-regulated Notch-dependent pathway

Fever is a conserved and prominent response to infection. Yet, the issue of how CD4 T cell responses are modulated if they occur at fever temperatures remains poorly addressed. We have examined the priming of naive CD4 T cells in vitro at fever temperatures, and we report notable fever-mediated modulation of their cytokine commitment. When naive CD4 T cells were primed by plate-bound anti-CD3 and anti-CD28 monoclonal antibodies at moderate fever temperature (39 °C), they enhanced commitment to IL4/5/13 (Th2) and away from IFNg (Th1). This was accompanied by up-regulation of the Th2-relevant transcription factor GATA3 and reduction in the Th1-relevant transcription factor Tbet. Fever sensing by CD4 T cells involved transient receptor potential vanilloid cation channels (TRPVs) since TRPV1/TRPV4 antagonism blocked the febrile Th2 switch, while TRPV1 agonists mediated a Th2 switch at 37 °C. The febrile Th2 switch was IL4 independent, but a γ-secretase inhibitor abrogated it, and it was not found in Notch1-null CD4 T cells, identifying the Notch pathway as a major mediator. However, when naive CD4 T cells were primed via antigen and dendritic cells (DCs) at fever temperatures, the Th2 switch was abrogated via increased production of IL12 from DCs at fever temperatures. Thus, immune cells directly sense fever temperatures with likely complex physiological consequences.

Thrombospondin-1 interactions regulate eicosanoid metabolism and signaling in cancer-related inflammation

The metabolism of arachidonic acid and other polyunsaturated fatty acids produces eicosanoids, a family of biologically active lipids that are implicated in homeostasis and in several pathologies that involve inflammation. Inflammatory processes mediated by eicosanoids promote carcinogenesis by exerting direct effects on cancer cells and by affecting the tumor microenvironment. Therefore, understanding how eicosanoids mediate cancer progression may lead to better approaches and chemopreventive strategies for the treatment of cancer. The matricellular protein thrombospondin-1 is involved in processes that profoundly regulate inflammatory pathways that contribute to carcinogenesis and metastatic spread. This review focuses on interactions of thrombospondin-1 and eicosanoids in the microenvironment that promote carcinogenesis and how the microenvironment can be targeted for cancer prevention to increase curative responses of cancer patients.

Resolution of inflammation and mood disorders

Relationship between mood disorders and inflammation is now well-documented, although molecular mechanisms are not understood. Previously mostly pro-inflammatory cytokines of immune system (IL-6, TNF, etc.) were taken into account. However, recent understanding of resolution of inflammation as an active process drew attention to mediators of resolution, which include both proteins and ω-3 and ω-6 polyunsaturated fatty acids derivatives (resolvins, cyclopentenone prostaglandins, etc.). This review takes into account new data on resolution of inflammation and action of mediators of resolution in models of depression. New facts and ideas about mechanisms of chronic inflammation onset are considered in relation to mood disorders. Basic control mechanisms of inflammation at the cellular level and the role of resolution substances in regulation of depression and other mood disorders are discussed. Signaling systems of innate immunity located in non-immune cells and their ability to generate substances that affect an onset of depression are reviewed. A novel hypothesis of depression as a type of abnormal resolution is proposed.

Cytokines, prostaglandins and nitric oxide in the regulation of stress-response systems

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is accepted as one of the fundamental biological mechanisms that underlie major depression. This hyperactivity is caused by diminished feedback inhibition of glucocorticoid (GC)-induced reduction of HPA axis signaling and increased corticotrophin-releasing hormone (CRH) secretion from the hypothalamic paraventricular nucleus (PVN) and extra-hypothalamic neurons. During chronic stress-induced inhibition of systemic feedback, cytosolic glucocorticoid receptor (GR) levels were significantly changed in the prefrontal cortex (PFC) and hippocampus, both structures known to be deeply involved in the pathogenesis of depression. Cytokines secreted by both immune and non-immune cells can markedly affect neurotransmission within regulatory brain circuits related to the expression of emotions; cytokines may also induce hormonal changes similar to those observed following exposure to stress. Proinflammatory cytokines, including interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) are implicated in the etiologies of clinical depression and anxiety disorders. Prolonged stress responses and cytokines impair neuronal plasticity and stimulation of neurotransmission. Exposure to acute stress and IL-1β markedly increased IL-1β levels in the PFC, hippocampus and hypothalamus, as well as overall HPA axis activity. Repeated stress sensitized the HPA axis response to IL-1β. Inflammatory responses in the brain contribute to cellular damage associated with neuropsychiatric diseases related to stress. Physical, psychological or combined-stress conditions evoke a proinflammatory response in the brain and other systems, characterized by a complex release of several inflammatory mediators including cytokines, prostanoids, nitric oxide (NO) and transcription factors. Induced CRH release involves IL-1, IL-6 and TNF-α, for stimulation adrenocorticotropic hormone (ACTH) release from the anterior pituitary. NO also participates in signal transduction pathways that result in the release of corticosterone from the adrenal gland. NO participates in multiple interactions between neuroendocrine and neuroimmune systems in physiological and pathological processes. Neuronal NO synthase (nNOS) modulates learning and memory and is involved in development of neuropsychiatric diseases, including depression. Nitric oxide generated in response to stress exposure is associated with depression-like and anxiety-like behaviors. In the central nervous system (CNS), prostaglandins (PG) generated by the cyclooxygenase (COX) enzyme are involved in the regulation of HPA axis activity. Prior exposure to chronic stress alters constitutive (COX-1) and inducible (COX-2) cyclooxygenase responses to homotypic stress differently in the PFC, hippocampus and hypothalamus. Both PG and NO generated within the PVN participate in this modulation. Acute stress affects the functionality of COX/PG and NOS/NO systems in brain structures. The complex responses of central and peripheral pathways to acute and chronic stress involve cytokines, NO and PG systems that regulate and turn off responses that would be potentially harmful for cellular homeostasis and overall health.

Insights into the inhibition and mechanism of compounds against LPS-induced PGE2 production: a pathway network-based approach and molecular dynamics simulations

In comparison to the current target-based screening approach, it is increasingly evident that active lead compounds based on disease-related phenotypes are more likely to be translated to clinical trials during drug development. That is, because human diseases are in essence the outcome of the abnormal function of multiple genes, especially in complex diseases. Therefore, as a conventional technology in the early phase of active lead compound discovery, computational methods that can connect molecular interactions and disease-related phenotypes to evaluate the efficacy of compounds are in urgently required. In this work, a computational approach that integrates molecular docking and pathway network analysis (network efficiency and network flux) was developed to evaluate the efficacy of a compound against LPS-induced Prostaglandin E2(PGE2) production. The predicted results were then validated in vitro, and a correlation with the experimental results was analyzed using linear regression. In addition, molecular dynamics (MD) simulations were performed to explore the molecular mechanism of the most potent compounds. There were 12 hits out of 28 predicted ingredients separated from Reduning injection (RDN). The predicted results have a good agreement with the experimental inhibitory potency (IC50) (correlation coefficient = 0.80). The most potent compounds could target several proteins to regulate the pathway network. This might partly interpret the molecular mechanism of RDN on fever. Meanwhile, the good correlation of the computational model with the wet experimental results might bridge the gap between molecule-target interactions and phenotypic response, especially for multi-target compounds. Therefore, it would be helpful for active lead compound discovery, the understanding of the multiple targets and synergic essence of traditional Chinese medicine (TCM).

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.

Sacchathridine A, a prostaglandin release inhibitor from Saccharothrix sp

Sacchathridine A (1) was isolated from the fermentation broth of strain Saccharothrix sp. MI559-46F5. The structure was determined as a new naphthoquinone derivative with an acetylhydrazino moiety by a combination of NMR, MS spectral analyses, and chemical degradation. Compound 1 showed inhibitory activity of prostaglandin E2 release in a concentration-dependent manner from human synovial sarcoma cells, SW982, with an IC50 value of 1.0 μM, but had no effect on cell growth up to 30 μM.

At the extreme end of the psychoneuroimmunological spectrum: delirium as a maladaptive sickness behaviour response

Delirium is a common and severe neuropsychiatric syndrome characterised by acute deterioration and fluctuations in mental status. It is precipitated mainly by acute illness, trauma, surgery, or drugs. Delirium affects around one in eight hospital inpatients and is associated with multiple adverse consequences, including new institutionalisation, worsening of existing dementia, and death. Patients with delirium show attentional and other cognitive deficits, altered alertness (mostly reduced, but some patients develop agitation and hyperactivity), altered sleep-wake cycle and psychoses. The pathways from the various aetiologies to the heterogeneous clinical presentations are hardly studied and are poorly understood. One of the key questions, which research is only now beginning to address, is how the factors determining susceptibility interact with the stimuli that trigger delirium. Inflammatory signals arising during systemic infection evoke sickness behaviour, a coordinated set of adaptive changes initiated by the host to respond to, and to counteract, infection. It is now clear that the same systemic inflammatory signals can have severe deleterious effects on brain function when occuring in old age or in the presence of neurodegenerative disease. Multiple animal studies now show that even mild acute systemic inflammation can induce exaggerated sickness behaviour responses and cognitive dysfunction in aged animals or those with prior degenerative pathology when compared to young and/or healthy controls. These findings appear highly promising in understanding aspects of delirium. In this review our aim is to describe and assess the parallels between exaggerated sickness behaviour in vulnerable animals and delirium in older humans. We discuss inflammatory and stress-related triggers of delirium in the context of new animal models that allow us to dissect some aspects of the mechanisms underpinning these episodes. We discuss some differences between the sickness behaviour syndrome model and delirium in the context of the complexity in the latter due to other factors such as prior pathology, psychological stress and drug effects. We conclude that, with appropriate caveats, the study of sickness behaviour in the vulnerable brain offers a promising route to uncover the mechanisms of this common and serious unmet medical need.

Eicosanoids and adipokines in breast cancer: from molecular mechanisms to clinical considerations

Chronic inflammation is one of the foremost risk factors for different types of malignancies, including breast cancer. Additional risk factors of this pathology in postmenopausal women are weight gain, obesity, estrogen secretion, and an imbalance in the production of adipokines, such as leptin and adiponectin. Various signaling products of transcription factor, nuclear factor-kappaB, in particular inflammatory eicosanoids, reactive oxygen species (ROS), and cytokines, are thought to be involved in chronic inflammation-induced cancer. Together, these key components have an influence on inflammatory reactions in malignant tissue damage when their levels are deregulated endogenously. Prostaglandins (PGs) are well recognized in inflammation and cancer, and they are solely biosynthesized through cyclooxygenases (COXs) from arachidonic acid. Concurrently, ROS give rise to bioactive isoprostanes from arachidonic acid precursors that are also involved in acute and chronic inflammation, but their specific characteristics in breast cancer are less demonstrated. Higher aromatase activity, a cytochrome P-450 enzyme, is intimately connected to tumor growth in the breast through estrogen synthesis, and is interrelated to COXs that catalyze the formation of both inflammatory and anti-inflammatory PGs such as PGE(2), PGF(2α), PGD(2), and PGJ(2) synchronously under the influence of specific mediators and downstream enzymes. Some of the latter compounds upsurge the intracellular cyclic adenosine monophosphate concentration and appear to be associated with estrogen synthesis. This review discusses the role of COX- and ROS-catalyzed eicosanoids and adipokines in breast cancer, and therefore ranges from their molecular mechanisms to clinical aspects to understand the impact of inflammation.

Exposure of Wistar rats to 24-h psycho-social stress alters gene expression in the inferior colliculus

Recently, we have demonstrated that the exposure of Wistar rats to psycho-social stress results in a transient auditory hypersensitivity. Here, to learn more about modifications occurring in auditory brainstem, we have analyzed gene expression pattern in inferior colliculus using quantitative RT-PCR. As targets, we have chosen genes associated with: neural activity (FBJ osteosarcoma viral oncogene, cFos), hypoxia (nitric oxide synthase inducible, iNos; superoxide dismutase 2, Sod2), neuroprotection (nerve growth factor beta, Ngfb; heat shock factor 1, Hsf1; heat shock protein 70, Hsp70) and inflammation (tumor necrosis factor alpha, Tnfa; tumor necrosis factor alpha receptor, Tnfar; substance P, Sp; cyclooxygenase 2, Cox2). We found that the expression of all genes was modified following stress, as compared to the controls. Immediately after stress, the number of transcripts encoding iNos, Sod2, Hsf1, Ngfb, Tnfa, Tnfar and Sp was significantly increased, suggesting possible modulation during exposure to stressor. Interestingly, we found that expression of Hsf1 and Ngfb at this particular time was left-right asymmetrical: there were more transcripts of both genes found in the left colliculi, as compared to the right colliculi. Three hours post-stress, iNos, Hsf1, Tnfa and Tnfar were still upregulated, Sod2, Ngfb and Sp went back to baseline and Cox2 was upregulated. Six hours post-stress, cFos mRNA became downregulated. The number of Hsp70 mRNA increased 24h post-stress. Except for the reduced number of cFos transcripts, expression of all other genes tested reached the baseline seven days post-stress. Presented results corroborate the concept of auditory system responding to the psycho-social stress. Post-stress changes in the IC gene expression could likely indicate shift from allostasis to homeostasis in the auditory brainstem.

Prostanoids as regulators of innate and adaptive immunity

Potent, oxygenated lipid molecules called prostanoids regulate a wide variety of physiological responses and pathological processes. Prostanoids are produced by various cell types and act on target cells through specific G protein-coupled receptors. Although prostanoids have historically been considered acute inflammation mediators, studies using specific receptor knockout mice indicate that prostanoids, in fact, regulate various aspects of both innate and adaptive immunity. Each prostanoid, depending on which receptor it acts on, exerts specific effects on immune cells such as macrophages, dendritic cells, and T and B lymphocytes, often in concert with microbial ligands and cytokines, to affect the strength, quality, and duration of immune responses. Prostanoids are also relevant to immunopathology, from inflammation to autoimmunity and cancer. Here, we review the role of prostanoids in regulating immunity, their involvement in immunopathology, and areas of insight that may lead to new therapeutic opportunities.

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

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

Association study of EP1 gene polymorphisms with suicide completers in the Japanese population

BACKGROUND

Both environmental and genetic factors have been reported to be involved in suicidal behaviors. Considerable evidence indicates that impulsive aggression is one of the important risk factors that contribute to suicide. A recent study has shown that prostaglandin E2 type 1 receptor (EP1) signaling regulates impulsive-aggressive behaviors in mice under both social and environmental stresses. To test the possible involvement of the EP1 gene in suicide, we carried out an association study of EP1 gene polymorphisms with suicide completers in the Japanese population.

METHODS

We studied 5 SNPs including one SNP in exon 2 (rs3745459) and four SNPs in the potential promoter region of the EP1 gene (rs3810255, rs3810254, rs3810253 and rs10416814) in 374 healthy control and 287 completed suicide victims using standard Taqman probe genotyping assays.

RESULTS

No significant differences of the genotypic distribution, allelic frequency or haplotype distribution between controls and suicide completers were found. Gender based analysis revealed that genotypic, allelic and haplotypic distributions of rs3810255, rs3810254, rs3810253 and rs10416814 SNPs were significantly different between the female control and female suicide groups, although the differences did not withstand correction for multiple comparisons.

CONCLUSION

We could not find an association of EP1 gene with suicide in the Japanese population. Because several SNPs in the promoter region of the EP1 gene were nominally significantly associated with suicide in the female, further studies with a larger sample size and different population are needed to confirm this result.

CD36 protein is involved in store-operated calcium flux, phospholipase A2 activation, and production of prostaglandin E2

The scavenger receptor FAT/CD36 contributes to the inflammation associated with diabetes, atherosclerosis, thrombosis, and Alzheimer disease. Underlying mechanisms include CD36 promotion of oxidative stress and its signaling to stress kinases. Here we document an additional mechanism for the role of CD36 in inflammation. CD36 regulates membrane calcium influx in response to endoplasmic reticulum (ER) stress, release of arachidonic acid (AA) from cellular membranes by cytoplasmic phospholipase A(2)α (cPLA(2)α) and contributes to the generation of proinflammatory eicosanoids. CHO cells stably expressing human CD36 released severalfold more AA and prostaglandin E(2) (PGE(2)), a major product of AA metabolism by cyclooxygenases, in response to thapsigargin-induced ER stress as compared with control cells. Calcium influx after ER calcium release resulted in phosphorylation of cPLA(2) and its translocation to membranes in a CD36-dependent manner. Peritoneal macrophages from CD36(-/-) mice exhibited diminished calcium transients and reduced AA release after thapsigargin or UTP treatment with decreased ERK1/2 and cPLA(2) phosphorylation. However, PGE(2) production was unexpectedly enhanced in CD36(-/-) macrophages, which probably resulted from a large induction of cyclooxygenase 2 mRNA and protein. The data demonstrate participation of CD36 in membrane calcium influx in response to ER stress or purinergic receptor stimulation resulting in AA liberation for PGE(2) formation. Collectively, these results identify a mechanism contributing to the pleiotropic proinflammatory effects of CD36 and suggest that its targeted inhibition may reduce the acute inflammatory response.

Stress responses: the contribution of prostaglandin E(2) and its receptors

Stress is a state of physiological or psychological strain caused by adverse stimuli; responses to stress include activation of the sympathetic nervous system, glucocorticoid secretion and emotional behaviors. Prostaglandin E(2) (PGE(2)), acting through its four receptor subtypes (EP1, EP2, EP3 and EP4), is involved in these stress responses. Studies of EP-selective drugs and mice lacking specific EPs have identified the neuronal pathways regulated by PGE(2). In animals with febrile illnesses, PGE(2) acts on neurons expressing EP3 in the preoptic hypothalamus. In illness-induced activation of the hypothalamic-pituitary-adrenal axis, EP1 and EP3 regulate distinct neuronal pathways that converge at the paraventricular hypothalamus. During psychological stress, EP1 suppresses impulsive behaviors via the midbrain dopaminergic systems. PGE(2) promotes illness-induced memory impairment, yet also supports hippocampus-dependent memory formation and synaptic plasticity via EP2 in physiological conditions. In response to illness, PGE(2) is synthesized by enzymes induced in various cell types inside and outside the brain, whereas constitutively expressed enzymes in neurons and/or microglia synthesize PGE(2) in response to psychological stress. Dependent on the type of stress stimuli, PGE(2) released from different cell types activates distinct EP receptors, which mobilize multiple neuronal pathways, resulting in stress responses.

The neurobiology of lipid metabolism in autism spectrum disorders

Autism is a neurodevelopmental disorder characterized by impairments in communication and reciprocal social interaction, coupled with repetitive behavior, which typically manifests by 3 years of age. Multiple genes and early exposure to environmental factors are the etiological determinants of the disorder that contribute to variable expression of autism-related traits. Increasing evidence indicates that altered fatty acid metabolic pathways may affect proper function of the nervous system and contribute to autism spectrum disorders. This review provides an overview of the reported abnormalities associated with the synthesis of membrane fatty acids in individuals with autism as a result of insufficient dietary supplementation or genetic defects. Moreover, we discuss deficits associated with the release of arachidonic acid from the membrane phospholipids and its subsequent metabolism to bioactive prostaglandins via phospholipase A(2)-cyclooxygenase biosynthetic pathway in autism spectrum disorders. The existing evidence for the involvement of lipid neurobiology in the pathology of neurodevelopmental disorders such as autism is compelling and opens up an interesting possibility for further investigation of this metabolic pathway.

Polyunsaturated fatty acids modulate prostaglandin synthesis by ovine amnion cells in vitro

Diets or supplements high in n-3 and n-6 polyunsaturated fatty acids (PUFAs) have been shown to influence the timing of parturition. PUFAs are substrates for prostaglandin (PG) synthesis, and PGs play central roles in parturition. Hence, the effects of altering PUFA composition may be mediated through alterations in the type and relative quantities of PGs synthesised. Therefore, we have investigated the effects of a range of n-3 and n-6 PUFAs in vitro on PG synthesis by amnion cells of late gestation ewes. The n-6 PUFA, arachidonic acid (20:4, n-6), increased synthesis of two-series PGs. Degree of stimulation induced by the n-6 PUFAs was dependent on the position of the PUFA in the PG synthetic pathway, i.e. PG production of the two-series (principally prostaglandin E(2):PGE(2)) increased progressively with longer chain PUFAs. Effects of n-3 PUFAs on output of PGE(2) were more modest and variable. The two shorter chain n-3 PUFAs, α-linolenic acid (18:3, n-3) and stearidonic acid (18:4, n-3), induced a small but significant increase in PGE(2) output, while the longest chain n-3 PUFA docosahexaenoic acid (22:6, n-3) inhibited PGE(2) synthesis. Dihomo-γ-linolenic acid (20:3, n-6), the PUFA substrate for synthesis of one-series PGs, induced an increase in PGE(1) generation and a decrease in PGE(2) and PGE(3) outputs. Hence, we have demonstrated that PUFA supplementation of ovine amnion cells in vitro affects the type and quantity of PGs synthesised.

Endotoxin exposure during late pregnancy alters ovine offspring febrile and hypothalamic-pituitary-adrenal axis responsiveness later in life

A growing number of studies indicate that maternal infection during pregnancy is associated with adverse fetal development and neonatal health. In this study, late gestating sheep (day 135) were challenged systemically with saline (0.9%) or Escherichia coli lipopolysaccharide endotoxin (400 ng/kg x 3 consecutive days, or 1.2 microg/kg x 1 day) in order to assess the impact of maternal endotoxemia on the developing fetal neuroendocrine-immune system. During adulthood, cortisol secretion and febrile responses of female offspring and the cortisol response of the male offspring to endotoxin (400 ng/kg), as well as the female cortisol response to adrenocorticotropic hormone (ACTH) challenge, were measured to assess neuroendocrine-immune function. These studies revealed that maternal endotoxin treatment during late gestation altered the female febrile and male and female cortisol response to endotoxin exposure later in life; however, the response was dependent on the endotoxin treatment regime that the pregnant sheep received. The follow-up ACTH challenge suggests that programing of the adrenal gland may be altered in the female fetus during maternal endotoxemia. The long-term health implications of these changes warrant further investigation.