The roles of NADPH oxidase and phospholipases A2 in oxidative and inflammatory responses in neurodegenerative diseases

Reactive oxygen species (ROS) are produced in mammalian cells through enzymic and non-enzymic mechanisms. Although some ROS production pathways are needed for specific physiological functions, excessive production is detrimental and is regarded as the basis of numerous neurodegenerative diseases. Among enzymes producing superoxide anions, NADPH oxidase is widespread in mammalian cells and is an important source of ROS in mediating physiological and pathological processes in the cardiovascular and the CNS. ROS production is linked to the alteration of intracellular calcium homeostasis, activation of Ca(2+)-dependent enzymes, alteration of cytoskeletal proteins, and degradation of membrane glycerophospholipids. There is evolving evidence that ROS produced by NADPH oxidase regulate neuronal functions and degrade membrane phospholipids through activation of phospholipases A(2) (PLA(2)). This review is intended to cover recent studies describing ROS generation from NADPH oxidase in the CNS and its downstream activation of PLA(2), namely, the group IV cytosolic cPLA(2) and the group II secretory sPLA(2). A major focus is to elaborate the dual role of NADPH oxidase and PLA(2) in mediating the oxidative and inflammatory responses in neurodegenerative diseases, including cerebral ischemia and Alzheimer's disease. Elucidation of the signaling pathways linking NADPH oxidase with the multiple forms of PLA(2) will be important in understanding the oxidative and degradative mechanisms that underline neuronal damage and glial activation and will facilitate development of therapeutic intervention for prevention and treatment of these and other neurodegenerative diseases.

Phospholipases A2 mediate amyloid-beta peptide-induced mitochondrial dysfunction

Mitochondrial dysfunction has been implicated in the pathophysiology of Alzheimer's disease (AD) brains. To unravel the mechanism(s) underlying this dysfunction, we demonstrate that phospholipases A2 (PLA2s), namely the cytosolic and the calcium-independent PLA2s (cPLA2 and iPLA2), are key enzymes mediating oligomeric amyloid-beta peptide (Abeta(1-42))-induced loss of mitochondrial membrane potential and increase in production of reactive oxygen species from mitochondria in astrocytes. Whereas the action of iPLA2 is immediate, the action of cPLA2 requires a lag time of approximately 12-15 min, probably the time needed for initiating signaling pathways for the phosphorylation and translocation of cPLA2 to mitochondria. Western blot analysis indicated the ability of oligomeric Abeta(1-42) to increase phosphorylation of cPLA2 in astrocytes through the NADPH oxidase and mitogen-activated protein kinase pathways. The involvement of PLA2 in Abeta(1-42)-mediated perturbations of mitochondrial function provides new insights to the decline in mitochondrial function, leading to impairment in ATP production and increase in oxidative stress in AD brains.

Secretory PLA2-IIA: a new inflammatory factor for Alzheimer's disease

Secretory phospholipase A₂-IIA (sPLA₂-IIA) is an inflammatory protein known to play a role in the pathogenesis of many inflammatory diseases. Although this enzyme has also been implicated in the pathogenesis of neurodegenerative diseases, there has not been a direct demonstration of its expression in diseased human brain. In this study, we show that sPLA₂-IIA mRNA is up-regulated in Alzheimer's disease (AD) brains as compared to non-demented elderly brains (ND). We also report a higher percentage of sPLA₂-IIA-immunoreactive astrocytes present in AD hippocampus and inferior temporal gyrus (ITG). In ITG, the majority of sPLA₂-IIA-positive astrocytes were associated with amyloid β (Aβ)-containing plaques. Studies with human astrocytes in culture demonstrated the ability of oligomeric Aβ_1–42 and interleukin-1β (IL-1β) to induce sPLA₂-IIA mRNA expression, indicating that this gene is among those induced by inflammatory cytokines. Since exogenous sPLA₂-IIA has been shown to cause neuronal injury, understanding the mechanism(s) and physiological consequences of sPLA₂-IIA upregulation in AD brain may facilitate the development of novel therapeutic strategies to inhibit the inflammatory responses and to retard the progression of the disease.

Short-term lifestyle modification alters circulating biomarkers of endothelial health in sedentary, overweight adults

Obesity and inactivity are associated with endothelial dysfunction that may contribute to the development of atherosclerosis. We examined the effects of a short-term lifestyle intervention on circulating biomarkers of endothelial health. Nineteen overweight or obese (mean body mass index (BMI): 28.9 ± 0.7 kg/m2) men and women underwent 6 weeks of body mass reduction induced by moderate energy restriction (~750 kcal/d; 1 kcal = 4.184 kJ) and aerobic training (~400 kcal/d). Fasting serum samples were collected at baseline and after reduction in body mass (week 6) to assess concentrations of nitrotyrosine (NT), secretory phospholipase A2 (sPLA2), and soluble intracellular adhesion molecule-1 (sICAM-1). Body mass was significantly reduced from 81.3 ± 2.8 to 77.3 ± 2.6 kg (p < 0.05). Circulating concentrations of NT and sICAM-1 were significantly reduced with treatment (~25% and ~10%, respectively), whereas sPLA2 levels were significantly elevated (~45%). Elevations in sPLA2 were negatively correlated with changes in NT (r = –0.58, p = 0.047); reductions in NT did not correlate significantly with reductions in sICAM-1. It appears that circulating markers of endothelial health are susceptible to short-term exercise interventions with modest reduction in body mass, and such a lifestyle modification may improve endothelial health by reducing protein nitration products and cellular adhesion.

Amyloid beta-protein1-42 increases cAMP and apolipoprotein E levels which are inhibited by beta1 and beta2-adrenergic receptor antagonists in mouse primary astrocytes

Amyloid beta-protein (Abeta) increases apolipoprotein E (apoE) levels in astrocytes which could alter lipid trafficking. The mechanism for the Abeta-induced increase in apoE levels is not well understood. It is well established that stimulation of beta-adrenergic receptors (betaARs) increases cAMP levels. Elevation of cAMP levels increases apoE abundance. The current study determined if Abeta(1-42) stimulation of cAMP and apoE levels could be inhibited by betaAR antagonists in astrocytes. We demonstrate that Abeta(1-42) but not the reverse protein Abeta(42-1) or Abeta(1-40) stimulated cAMP formation and this stimulation was inhibited by selective betaAR antagonists in mouse primary cortical astrocytes. Abeta(1-42) significantly increased apoE levels which were significantly inhibited by the betaAR selective antagonists with the greatest inhibition observed with the beta(2) antagonist. Separate lines of evidence have suggested that agonist-induced stimulation of betaARs and increases in apoE abundance may serve a neuroprotective role in astrocytes. Our results indicate a potential interaction between betaARs and apoE which may contribute to reducing Abeta(1-42) neurotoxicity.

Ischemia-induced increase in RGS7 mRNA expression in gerbil hippocampus

The present study investigated the changes in the expression of regulators of G-protein-coupled signaling proteins RGS2, 7 and 8 in gerbil hippocampus to better understand alterations of G-protein-coupled receptors signaling after cerebral ischemia. In situ hybridization revealed a transient, robust early increase in RGS7 mRNA levels in the dentate gyrus after ischemia. RGS8 mRNA expression started to increase at a later time point in the CA3 region but no changes were found for RGS2. Our results show a subtype-, time-, and subregion-specific regulation in mRNA expression of RGS proteins after cerebral ischemia in gerbil hippocampus.

Apocynin protects against global cerebral ischemia-reperfusion-induced oxidative stress and injury in the gerbil hippocampus

Increased production of reactive oxygen species (ROS) following cerebral ischemia-reperfusion (I/R) is an important underlying cause for neuronal injury leading to delayed neuronal death (DND). In this study, apocynin, a specific inhibitor for NADPH oxidase, was used to test whether suppression of ROS by the NADPH oxidase inhibitor can protect against ischemia-induced ROS generation and decrease DND. Global cerebral ischemia was induced in gerbils by a 5-min occlusion of bilateral common carotid arteries (CCA). Using measurement of 4-hydroxy-2-nonenal (HNE) as a marker for lipid peroxidation, apocynin (5 mg/kg body weight) injected i.p. 30 min prior to ischemia significantly attenuated the early increase in HNE in hippocampus measured at 3 h after I/R. Apocynin also protected against I/R-induced neuronal degeneration and DND, oxidative DNA damage, and glial cell activation. Taken together, the neuroprotective effects of apocynin against ROS production during early phase of I/R and subsequent I/R-induced neuronal damage provide strong evidence that inhibition of NADPH oxidase could be a promising therapeutic mechanism to protect against stroke damage in the brain.

Neuroprotective mechanisms of curcumin against cerebral ischemia-induced neuronal apoptosis and behavioral deficits

Increased oxidative stress has been regarded as an important underlying cause for neuronal damage induced by cerebral ischemia/reperfusion (I/R) injury. In recent years, there has been increasing interest in investigating polyphenols from botanical source for possible neuroprotective effects against neurodegenerative diseases. In this study, we investigated the mechanisms underlying the neuroprotective effects of curcumin, a potent polyphenol antioxidant enriched in tumeric. Global cerebral ischemia was induced in Mongolian gerbils by transient occlusion of the common carotid arteries. Histochemical analysis indicated extensive neuronal death together with increased reactive astrocytes and microglial cells in the hippocampal CA1 area at 4 days after I/R. These ischemic changes were preceded by a rapid increase in lipid peroxidation and followed by decrease in mitochondrial membrane potential, increased cytochrome c release, and subsequently caspase-3 activation and apoptosis. Administration of curcumin by i.p. injections (30 mg/kg body wt) or by supplementation to the AIN76 diet (2.0 g/kg diet) for 2 months significantly attenuated ischemia-induced neuronal death as well as glial activation. Curcumin administration also decreased lipid peroxidation, mitochondrial dysfunction, and the apoptotic indices. The biochemical changes resulting from curcumin also correlated well with its ability to ameliorate the changes in locomotor activity induced by I/R. Bioavailability study indicated a rapid increase in curcumin in plasma and brain within 1 hr after treatment. Together, these findings attribute the neuroprotective effect of curcumin against I/R-induced neuronal damage to its antioxidant capacity in reducing oxidative stress and the signaling cascade leading to apoptotic cell death.

Molecular determinants of P2Y2 nucleotide receptor function: implications for proliferative and inflammatory pathways in astrocytes

In the mammalian nervous system, P2 nucleotide receptors mediate neurotransmission, release of proinflammatory cytokines, and reactive astrogliosis. Extracellular nucleotides activate multiple P2 receptors in neurons and glial cells, including G protein-coupled P2Y receptors and P2X receptors, which are ligand-gated ion channels. In glial cells, the P2Y2 receptor subtype, distinguished by its ability to be equipotently activated by ATP and UTP, is coupled to pro-inflammatory signaling pathways. In situ hybridization studies with rodent brain slices indicate that P2Y2 receptors are expressed primarily in the hippocampus and cerebellum. Astrocytes express several P2 receptor subtypes, including P2Y2 receptors whose activation stimulates cell proliferation and migration. P2Y2 receptors, via an RGD (Arg-Gly-Asp) motif in their first extracellular loop, bind to alphavbeta3/beta5 integrins, whereupon P2Y2 receptor activation stimulates integrin signaling pathways that regulate cytoskeletal reorganization and cell motility. The C-terminus of the P2Y2 receptor contains two Src-homology-3 (SH3)-binding domains that upon receptor activation, promote association with Src and transactivation of growth factor receptors. Together, our results indicate that P2Y2 receptors complex with both integrins and growth factor receptors to activate multiple signaling pathways. Thus, P2Y2 receptors present novel targets to control reactive astrogliosis in neurodegenerative diseases.

Mechanisms for inhibition of P2 receptors signaling in neural cells

Trophic factors are required to ensure neuronal viability and regeneration after neural injury. Although abundant information is available on the factors that cause the activation of astrocytes, little is known about the molecular mechanisms underlying the regulation of this process. Nucleotides released into the extracellular space from injured or dying neural cells can activate astrocytes via P2 nucleotide receptors. After a brief historical review and update of novel P2 receptor antagonists, this article focuses on recent advancements toward understanding molecular mechanisms that regulate G protein-coupled P2Y receptor signaling. Among P2Y receptor subtypes, the heptahelical P2Y2 nucleotide receptor interacts with vitronectin receptors via an RGD sequence in the first extracellular loop, and this interaction is required for effective signal transduction to activate mitogen-activated protein kinases ERK1/2, to mobilize intracellular calcium stores via activation of phospholipase C, protein kinase C isoforms, and to activate focal adhesion kinase and other signaling events. Ligation of vitronectin receptors with specific antibodies caused an inhibition of P2Y2 receptor-induced ERK1/2 and p38 phosphorylation and P2Y2 receptor-induced cytoskeleton rearrangement and DNA synthesis. Structure-function studies have identified agonist-induced phosphorylation of the C-terminus of the P2Y2 receptor, an important mechanism for receptor desensitization. Understanding selective mechanisms for regulating P2Y2 receptor signaling could provide novel targets for therapeutic strategies in the management of brain injury, synaptogenesis, and neurological disorders.

Kainic acid-mediated excitotoxicity as a model for neurodegeneration

Neuronal excitation involving the excitatory glutamate receptors is recognized as an important underlying mechanism in neurodegenerative disorders. Excitation resulting from stimulation of the ionotropic glutamate receptors is known to cause the increase in intracellular calcium and trigger calcium-dependent pathways that lead to neuronal apoptosis. Kainic acid (KA) is an agonist for a subtype of ionotropic glutamate receptor, and administration of KA has been shown to increase production of reactive oxygen species, mitochondrial dysfunction, and apoptosis in neurons in many regions of the brain, particularly in the hippocampal subregions of CA1 and CA3, and in the hilus of dentate gyrus (DG). Systemic injection of KA to rats also results in activation of glial cells and inflammatory responses typically found in neurodegenerative diseases. KA-induced selective vulnerability in the hippocampal neurons is related to the distribution and selective susceptibility of the AMPA/kainate receptors in the brain. Recent studies have demonstrated ability of KA to alter a number of intracellular activities, including accumulation of lipofuscin-like substances, induction of complement proteins, processing of amyloid precursor protein, and alteration of tau protein expression. These studies suggest that KA-induced excitotoxicity can be used as a model for elucidating mechanisms underlying oxidative stress and inflammation in neurodegenerative diseases. The focus of this review is to summarize studies demonstrating KA-induced excitotoxicity in the central nervous system and possible intervention by anti-oxidants.

P2X(7) nucleotide receptors mediate caspase-8/9/3-dependent apoptosis in rat primary cortical neurons

Apoptosis is a major cause of cell death in the nervous system. It plays a role in embryonic and early postnatal brain development and contributes to the pathology of neurodegenerative diseases. Here, we report that activation of the P2X₇ nucleotide receptor (P2X₇R) in rat primary cortical neurons (rPCNs) causes biochemical (i.e., caspase activation) and morphological (i.e., nuclear condensation and DNA fragmentation) changes characteristic of apoptotic cell death. Caspase-3 activation and DNA fragmentation in rPCNs induced by the P2X₇R agonist BzATP were inhibited by the P2X₇R antagonist oxidized ATP (oATP) or by pre-treatment of cells with P2X₇R antisense oligonucleotide indicating a direct involvement of the P2X₇R in nucleotide-induced neuronal cell death. Moreover, Z-DEVD-FMK, a specific and irreversible cell permeable inhibitor of caspase-3, prevented BzATP-induced apoptosis in rPCNs. In addition, a specific caspase-8 inhibitor, Ac-IETD-CHO, significantly attenuated BzATP-induced caspase-9 and caspase-3 activation, suggesting that P2X₇R-mediated apoptosis in rPCNs occurs primarily through an intrinsic caspase-8/9/3 activation pathway. BzATP also induced the activation of C-jun N-terminal kinase 1 (JNK1) and extracellular signal-regulated kinases (ERK1/2) in rPCNs, and pharmacological inhibition of either JNK1 or ERK1/2 significantly reduced caspase activation by BzATP. Taken together, these data indicate that extracellular nucleotides mediate neuronal apoptosis through activation of P2X₇Rs and their downstream signaling pathways involving JNK1, ERK and caspases 8/9/3.

Distinct signaling pathways for induction of type II NOS by IFNγ and LPS in BV-2 microglial cells

Nitric oxide (NO) release upon microglial cell activation has been implicated in the tissue injury and cell death in many neurodegenerative diseases. Recent studies have indicated the ability of interferon-gamma (IFNgamma) and lipopolysaccharides (LPS) to independently induce type II nitric oxide synthase (iNOS) expression and NO production in BV-2 microglial cells. However, a detailed comparison between the signaling pathways activating iNOS by these two agents has not been accomplished. Analysis of PKC isoforms revealed mainly the presence of PKCdelta, iota and lambda in BV-2 cells. Although both IFNgamma and LPS could specifically enhance the tyrosine phosphorylation of PKCdelta, treatment with IFNgamma induced a steady increase of phospho-PKCdelta for up to 1h, whereas treatment with LPS elevated phospho-PKCdelta levels only transiently, with peak activity at 5 min. Rottlerin, a specific inhibitor for PKCdelta, dose-dependently inhibited IFNgamma- and LPS-induced NO production. Despite the common involvement of PKCdelta, IFNgamma- but not LPS-induced NO production involved extracellular signal-regulated kinases (ERK1/2) cascade and IFNgamma-induced phosphorylation of ERK1/2 was mediated through PKC. On the other hand, LPS- but not IFNgamma-induced NO production was through stimulation of NF-kappaB activation and nuclear translocation to interact with DNA. These results demonstrated distinct signaling pathways for induction of iNOS by IFNgamma and LPS in BV-2 microglial cells.

Hydrogen peroxide alters membrane and cytoskeleton properties and increases intercellular connections in astrocytes

Excess hydrogen peroxide (H2O2) is produced in the pathogenesis of brain injuries and neurodegenerative diseases. H2O2 may damage cells through direct oxidation of lipids, proteins and DNA or it can act as a signaling molecule to trigger intracellular pathways leading to cell death. In this study, H2O2 caused plasma membranes of primary astrocytes to become more gel-like, while artificial membranes of vesicles composed of rat brain lipid extract became more liquid crystalline-like. Besides the effects on membrane phase properties, H2O2 promoted actin polymerization, induced the formation of cell-to-cell tunneling nanotube (TNT)-like connections among astrocytes and increased the colocalization of myosin Va with F-actin. Myosin Va was also observed in the H2O2-induced F-actin-enriched TNT-like connections. Western blot analysis suggests that H2O2 triggered the phosphorylation of the p38 mitogen-activated protein kinase (MAPK), and that SB203580, a specific inhibitor of p38 MAPK, suppressed the changes in membrane phase properties and cytoskeleton resulting from H2O2 treatment. These results suggest that H2O2 alters astrocyte membranes and the cytoskeleton through activation of the p38 MAPK pathway.

Expression of groups I and II metabotropic glutamate receptors in the rat brain during aging

Age-dependent changes in the expression of group I and II metabotropic glutamate (mGlu) receptors were studied by in situ hybridization, Western blot analysis and immunohistochemistry. Male Fisher 344 rats of three ages (3, 12 and 25 months) were tested. Age-related increases in mGlu1 receptor mRNA levels were found in several areas (thalamic nuclei, hippocampal CA3) with parallel increases in mGlu1a receptor protein expression. However, a slight decrease in mGlu1a receptor mRNA expression in individual Purkinje neurons and a decline in cerebellar mGlu1a receptor protein levels were detected in aged animals. In contrast, mGlu1b receptor mRNA levels increased in the cerebellar granule cell layer. Although mGlu5 receptor mRNA expression decreased in many regions, its protein expression remained unchanged during aging. Compared to the small changes in mGlu2 receptor mRNA levels, mGlu3 receptor mRNA levels showed substantial age differences. An increased mGlu2/3 receptor protein expression was found in the frontal cortex, thalamus, hippocampus and corpus callosum in aged animals. These results demonstrate region- and subtype-specific, including splice variant specific changes in the expression of mGlu receptors in the brain with increasing age.

Identification of a novel HLA-DRB1 allele (HLA-DRB1*111902*)

In this paper, we report a new HLA-DRB1 allele identified in a male acute myeloid leukaemia Chinese patient. This sample was initially typed as DRB1*11XX using commercial polymerase chain reaction-sequence-specific primers kit. When it was typed using a chip-based sequence-specific oligonucleotide technique, a novel hybridization pattern that does not match any known alleles was observed. Through sequencing, we have identified this allele as a new HLA-DRB1 allele, which was later named HLA-DRB1*111902 by the WHO Nomenclature Committee. The sequence of this new allele differs from DRB1*111901 by one nucleotide (from G to C) at 203nt of exon 2 but does not cause any amino acid substitution.

Dietary grape supplement ameliorates cerebral ischemia-induced neuronal death in gerbils

Oxidative damage has been implicated as one of the leading causes for neuronal cell death in a number of neurodegenerative diseases including stroke. Many vegetables and fruits are enriched in polyphenolic compounds known to exhibit antioxidant properties. This study is to investigate whether dietary supplement with grape powder (GP) may offer protection against neuronal damage due to global cerebral ischemia induced to Mongolian gerbils by occlusion of the common carotid arteries, a model known to cause delayed neuronal death (DND) in the hippocampal CA1 area. Gerbils were fed either a control diet (AIN76a) or a control diet supplemented with low (5.0 g/kg diet) or high (50 g/kg diet) levels of GP for two months. Four days after ischemia/reperfusion (I/R), the extent of DND, glial cell activation, nuclear DNA oxidation, and apoptotic terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) reaction in hippocampal CA1 region were assessed. Ischemia-induced extensive DND in the CA1 region was accompanied by oxidative and fragmented DNA damage and a marked increase in reactive astrocytes and microglial cells. Dietary GP supplementation significantly protected neurons against I/R-induced DND, DNA damage, and apoptosis as well as attenuated glial cell activation. These results demonstrate that due to the antioxidant properties of polyphenols in GP, nutritional diets supplemented with grape can protect the brain against ischemic damage. The neuroprotective effects of GP supplement may have wide implication in the future for prevention/protection against other neurodegenerative damage.

Resveratrol protects against neurotoxicity induced by kainic acid

Increased oxidative stress has been implicated in the mechanisms of excitotoxicity in hippocampus induced by kainic acid (KA), an excitatory glutamate receptor agonist. Resveratrol, a polyphenolic antioxidant compound enriched in grape, is regarded as an important ingredient in red wine to offer cardiovascular and neural protective effects. This study was designed to investigate whether resveratrol treatment may ameliorate neuronal death after KA administration. Adult Sprague Dawley male rats were treated with KA (8 mg/kg) daily for 5 days and another group was treated similarly with KA plus resveratrol (30 mg/kg/day). Three hr after the last treatment protocol, animals were sacrificed, and brain sections were obtained for histochemical and immunohistochemical identification of neurons, astrocytes and microglial cells. After KA administration, significant neuronal death and activation of astrocytes and microglial cells were observed in the hippocampal CA1, CA3 and polymorphic layer (hilar) of the dentate gyrus (DG) (P < 0.001). The KA-induced hippocampal neuronal damage was significantly attenuated by treatment with resveratrol (P < 0.001). Resveratrol also suppressed KA-induced activation of astrocytes and microglial cells. Since increased oxidative stress is a key factor for KA-induced neurotoxicity, this study demonstrated the ability of resveratrol to act as free radical scavenger to protect against neuronal damage caused by excitotoxic insults.

Polyphenols in Cerebral Ischemia: Novel Targets for Neuroprotection

Plant polyphenols are dietary components that exert a variety of biochemical and pharmacological effects. Recently, considerable interest has been focused on polyphenols because of their antioxidant, anti-inflammatory, and antiproliferative activities. Oxidative stress is thought to be a key event in the pathogenesis of cerebral ischemia. Overproduction of reactive oxygen species during ischemia/reperfusion could cause an imbalance between oxidative and antioxidative processes. Reactive oxygen species can damage lipids, proteins, and nucleic acids, thereby inducing apoptosis or necrosis. There is increasing evidence supporting the hypothesis that plant polyphenols can provide protection against neurodegenerative changes associated with cerebral ischemia. This article reviews the neuroprotective effects of plant extracts and their constituents that have been used in animal models of cerebral ischemia. The use of polyphenols as therapeutic agents in stroke has been suggested.

Phospholipase A2 in Astrocytes: Responses to Oxidative Stress, Inflammation, and G Protein-Coupled Receptor Agonists

Astrocytes comprise the major cell type in the central nervous system (CNS) and they are essential for support of neuronal functions by providing nutrients and regulating cell-to-cell communication. Astrocytes also are immune-like cells that become reactive in response to neuronal injury. Phospholipases A2 (PLA2) are a family of ubiquitous enzymes that degrade membrane phospholipids and produce lipid mediators for regulating cellular functions. Three major classes of PLA2 are expressed in astrocytes: group IV calcium-dependent cytosolic PLA2 (cPLA2), group VI calcium-independent PLA2 (iPLA2), and group II secretory PLA2(sPLA2). Upregulation of PLA2 in reactive astrocytes has been shown to occur in a number of neurodegenerative diseases, including stroke and Alzheimer's disease. This review focuses on describing the effects of oxidative stress, inflammation, and activation of G protein-coupled receptors on PLA2 activation, arachidonic acid (AA) release, and production of prostanoids in astrocytes.

Exercise plus n-3 fatty acids: additive effect on postprandial lipemia

The purpose of this study was to examine changes in postprandial lipemia (PPL) in recreationally active males following aerobic exercise, omega-3 fatty acids (n-3FA) supplementation, and the combination of the two. PPL following a high-fat meal was measured in 10 recreationally active males (25 +/-1.5 years) under each of the following conditions: no exercise and no n-3 FA supplementation (control); exercise and no n-3FA supplementation (exercise); n-3FA supplementation and no exercise (n-3FA); and exercise and n-3 FA supplementation (combined). Blood was collected before the high-fat meal and at 2, 4, 6, and 8 hours after the meal to assess the PPL response. Supplementation consisted of 4.0 g of n-3FA per day for 5 weeks. Triglyceride (TG) peak response, the total area under the TG curve (TG-AUCT), and the incremental area under the TG curve (TG-AUCI) were used to define the PPL response. TG peak response was significantly reduced 38% by n-3FA supplementation and 50% by the combination of exercise and n-3FA supplementation. N-3FAs significantly reduced the TG-AUCT by 27% and by 42% when combined with exercise. When compared with the exercise trial, the TG-AUCT during the combined trial was significantly lower. Exercise, n-3FAs, and the combination significantly reduced the TG-AUCI by 40%, 42%, and 58%, respectively. These results suggest that the combination of exercise and n-3FA supplementation reduce PPL to a greater degree in recreationally active males when compared with the individual treatments.

P2Y2 receptors activate neuroprotective mechanisms in astrocytic cells

Mechanical or ischemic trauma to the CNS causes the release of nucleotides and other neurotransmitters into the extracellular space. Nucleotides can activate nucleotide receptors that modulate the expression of genes implicated in cellular adaptive responses. In this investigation, we used human 1321N1 astrocytoma cells expressing a recombinant P2Y2 receptor to assess the role of this receptor in the regulation of anti-apoptotic (bcl-2 and bcl-xl) and pro-apoptotic (bax) gene expression. Acute treatment with the P2Y2 receptor agonist UTP up-regulated bcl-2 and bcl-xl, and down-regulated bax, gene expression. Activation of P2Y2 receptors was also coupled to the phosphorylation of cyclic AMP responsive element binding protein that positively regulates bcl-2 and bcl-xl gene expression. Cyclic AMP responsive element decoy oligonucleotides markedly attenuated the UTP-induced increase in bcl-2 and bcl-xl mRNA levels. Activation of P2Y2 receptors induced the phosphorylation of the pro-apoptotic factor Bad and caused a reduction in bax/bcl-2 mRNA expression ratio. All these signaling pathways are known to be involved in cell survival mechanisms. Using cDNA microarray analysis and RT-PCR, P2Y2 receptors were found to up-regulate the expression of genes for neurotrophins, neuropeptides and growth factors including nerve growth factor 2; neurotrophin 3; glia-derived neurite-promoting factor, as well as extracellular matrix proteins CD44 and fibronectin precursor--genes known to regulate neuroprotection. Consistent with this observation, conditioned media from UTP-treated 1321N1 cells expressing P2Y2 receptors stimulated the outgrowth of neurites in PC-12 cells. Taken together, our results suggest an important novel role for the P2Y2 receptor in survival and neuroprotective mechanisms under pathological conditions.

Induction of secretory phospholipase A2 in reactive astrocytes in response to transient focal cerebral ischemia in the rat brain

Although mRNA expression of group IIA secretory phospholipase A2 (sPLA2-IIA) has been implicated in responses to injury in the CNS, information on protein expression remains unclear. In this study, we investigated temporal and spatial expression of sPLA2-IIA mRNA and immunoreactivity in transient focal cerebral ischemia induced in rats by occlusion of the middle cerebral artery. Northern blot analysis showed a biphasic increase in sPLA2-IIA mRNA expression following 60-min of ischemia-reperfusion: an early phase at 30 min and a second increase at a late phase ranging from 12 h to 14 days. In situ hybridization localized the early-phase increase in sPLA2-IIA mRNA to the affected ischemic cortex and the late-phase increase to the penumbral area. Besides sPLA2-IIA mRNA, glial fibrillary acidic protein (GFAP) and cyclo-oxygenase-2 mRNAs, but not cytosolic PLA2, also showed an increase in the penumbral area at 3 days after ischemia-reperfusion. Immunohistochemistry of sPLA2-IIA indicated positive cells in the penumbral area similar to the GFAP-positive astrocytes but different from the isolectin B4-positive microglial cells. Confocal microscopy further confirmed immunoreactivity of sPLA2-IIA in reactive astrocytes but not in microglial cells. Taken together, these results demonstrate for the first time an up-regulation of the inflammatory sPLA2-IIA in reactive astrocytes in response to cerebral ischemia-reperfusion.

Chronic Ethanol-Induced Subtype- and Subregion-Specific Decrease in the mRNA Expression of Metabotropic Glutamate Receptors in Rat Hippocampus

BACKGROUND

Chronic ethanol consumption is known to induce adaptive changes in the hippocampal glutamatergic transmission and alter NMDA receptor binding and subunit expression. Metabotropic glutamate (mGlu) receptors have been shown to function as modulators of neuronal excitability and can fine tune glutamatergic transmission. This study was aimed to determine whether chronic ethanol treatment could change the messenger RNA (mRNA) expression of mGlu receptors in the hippocampus.

METHODS

Male Sprague Dawley rats were fed a Lieber-DeCarli liquid diet with 5% (w/v) ethanol or isocaloric amount of maltose for 2 months. Quantitative in situ hybridization was carried out using coronal brain sections through the hippocampus.

RESULTS

The results revealed decreases in mRNA expression of several mGlu receptors in different subregions of the hippocampus. In the dentate gyrus, mGlu3 and mGlu5 receptor mRNA levels were significantly lower in the ethanol-treated rats than in the control rats. In the CA3 region, the mRNA expression of mGlu1, mGlu5, and mGlu7 receptors showed substantial decreases after ethanol exposure. The mGlu7 receptor mRNA levels were also declined in the CA1 region and the polymorph layer of the dentate gyrus. No changes were found in mRNA expression of mGlu2, mGlu4, and mGlu8 receptors.

CONCLUSIONS

Considering the involvement of hippocampal mGlu receptors in learning and memory processes as well as in neurotoxicity and seizure production, the reduced expression of these receptors might contribute to ethanol withdrawal-induced seizures and also may play a role in cognitive deficits and brain damage caused by long-term ethanol consumption.

Effect of exercise on postprandial lipemia following a higher calorie meal in Yucatan miniature swine

Exercise has been shown to attenuate the postprandial lipemic (PPL) response to a modest kcal high-fat meal in numerous human studies, but has not been fully examined in swine. In addition, the effects of exercise on a high-fat meal of larger magnitude have not been examined in humans or in swine. Thus, the purpose of this study was to examine the PPL response to a single, high-fat/cholesterol (HFC) meal (approximately 3,000 kcal, 1,300 kcal from fat) and determine if exercise attenuates the PPL response. Sedentary, female Yucatan miniature swine (n = 10) completed 3 PPL trials: (1) pre diet (PRE); (2) post HFC diet (POST); and (3) post HFC diet plus exercise (EX, 45 minutes at 75% heart rate maximum). Blood samples were collected before (0 hour) and at 2, 4, 6, and 8 hours after the single HFC meal for PPL analysis. Postheparin lipoprotein lipase (LPL) activity was assessed at 8 hours. While fasting LPL activity was significantly increased with the HFC diet, the PPL response to the HFC meal did not differ depending on diet. Furthermore, the PPL response was not significantly altered with a single session of exercise, perhaps because of the severity of the HFC meal, the sedentary nature of the swine, or because LPL activity was not elevated after exercise. These findings suggest that administration of a HFC meal of this magnitude (approximately 3,000 kcal, 1,300 kcal from fat) will promote significant elevations in postprandial triglyceride (TG) concentrations, overwhelm the adaptive response to a HFC diet (elevated LPL activity), and attenuate the beneficial effects of a single exercise session on this system.