Reactive glia express cytosolic phospholipase A2 after transient global forebrain ischemia in the rat

Revisiting the role of phospholipases in alzheimer's: crosstalk with processed food

Phospholipases such as phospholipase-A, phospholipase-B, phospholipase-C and phospholipase-D are important functional enzymes of the cell membrane responsible for a variety of functions such as signal transduction, production of lipid mediators, metabolite digestion and playing a pathological role in central nervous system diseases. Phospholipases have shown an association with Alzheimer's disease and these enzymes have found a correlation with several metabolic pathways that can lead to the activation of inflammatory signals via astrocytes and microglial cells. We also highlighted unhealthy practices like smoking and consuming processed foods, rich in nitroso compounds and phosphatidic acid, which contribute to neuronal damage in AD through phospholipases. A few therapeutic approaches such as the use of inhibitors of phospholipase-D,phospholipase A2 as well as autophagy-mediated inhibition have been discussed to control the onset of AD. This paper serves as a crosstalk between phospholipases and their role in neurodegenerative pathways as well as their influence on other biomolecules of lipid membranes, which are acquired through unhealthy diets and possible methods to treat these anomalies occurring due to their metabolic disorder involving phospholipases acting as major signaling molecules.

Role of alarmins in poststroke inflammation and neuronal repair

Severe loss of cerebral blood flow causes hypoxia and glucose deprivation in the brain tissue, resulting in necrotic cell death in the ischemic brain. Several endogenous molecules, called alarmins or damage-associated molecular patterns (DAMPs), are extracellularly released from the dead cells to activate pattern recognition receptors (PRRs) in immune cells that infiltrate into ischemic brain tissue following the disruption of the blood-brain barrier (BBB) after stroke onset. The activated immune cells produce various inflammatory cytokines and chemokines, triggering sterile cerebral inflammation in the ischemic brain that causes further neuronal cell death. Poststroke inflammation is resolved within several days after stroke onset, and neurological functions are restored to some extent as neural repair occurs around peri-infarct neurons. Clearance of DAMPs from the injured brain is necessary for the resolution of poststroke inflammation. Neurons and glial cells also express PRRs and receive DAMP signaling. Although the role of PRRs in neural cells in the ischemic brain has not yet been clarified, the signaling pathway is likely to be contribute to stroke pathology and neural repair after ischemic stroke. This review describes the molecular dynamics, signaling pathways, and functions of DAMPs in poststroke inflammation and its resolution.

Membrane lipid raft homeostasis is directly linked to neurodegeneration

Age-associated neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD) and Alzheimer's disease (AD) are an unmet health need, with significant economic and societal implications, and an ever-increasing prevalence. Membrane lipid rafts (MLRs) are specialised plasma membrane microdomains that provide a platform for intracellular trafficking and signal transduction, particularly within neurons. Dysregulation of MLRs leads to disruption of neurotrophic signalling and excessive apoptosis which mirrors the final common pathway for neuronal death in ALS, PD and AD. Sphingomyelinase (SMase) and phospholipase (PL) enzymes process components of MLRs and therefore play central roles in MLR homeostasis and in neurotrophic signalling. We review the literature linking SMase and PL enzymes to ALS, AD and PD with particular attention to attractive therapeutic targets, where functional manipulation has been successful in preclinical studies. We propose that dysfunction of these enzymes is upstream in the pathogenesis of neurodegenerative diseases and to support this we provide new evidence that ALS risk genes are enriched with genes involved in ceramide metabolism (P=0.019, OR = 2.54, Fisher exact test). Ceramide is a product of SMase action upon sphingomyelin within MLRs, and it also has a role as a second messenger in intracellular signalling pathways important for neuronal survival. Genetic risk is necessarily upstream in a late age of onset disease such as ALS. We propose that manipulation of MLR structure and function should be a focus of future translational research seeking to ameliorate neurodegenerative disorders.

Early upregulation of cytosolic phospholipase A2α in motor neurons is induced by misfolded SOD1 in a mouse model of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal multifactorial neurodegenerative disease characterized by the selective death of motor neurons. Cytosolic phospholipase A₂ alpha (cPLA₂α) upregulation and activation in the spinal cord of ALS patients has been reported. We have previously shown that cPLA₂α upregulation in the spinal cord of mutant SOD1 transgenic mice (SOD1^G93A) was detected long before the development of the disease, and inhibition of cPLA₂α upregulation delayed the disease's onset. The aim of the present study was to determine the mechanism for cPLA₂α upregulation.

METHODS

Immunofluorescence analysis and western blot analysis of misfolded SOD1, cPLA₂α and inflammatory markers were performed in the spinal cord sections of SOD1^G93A transgenic mice and in primary motor neurons. Over expression of mutant SOD1 was performed by induction or transfection in primary motor neurons and in differentiated NSC34 motor neuron like cells.

RESULTS

Misfolded SOD1 was detected in the spinal cord of 3 weeks old mutant SOD1^G93A mice before cPLA₂α upregulation. Elevated expression of both misfolded SOD1 and cPLA₂α was specifically detected in the motor neurons at 6 weeks with a high correlation between them. Elevated TNFα levels were detected in the spinal cord lysates of 6 weeks old mutant SOD1^G93A mice. Elevated TNFα was specifically detected in the motor neurons and its expression was highly correlated with cPLA₂α expression at 6 weeks. Induction of mutant SOD1 in primary motor neurons induced cPLA₂α and TNFα upregulation. Over expression of mutant SOD1 in NSC34 cells caused cPLA₂α upregulation which was prevented by antibodies against TNFα. The addition of TNFα to NSC34 cells caused cPLA₂α upregulation in a dose dependent manner.

CONCLUSIONS

Motor neurons expressing elevated cPLA₂α and TNFα are in an inflammatory state as early as at 6 weeks old mutant SOD1^G93A mice long before the development of the disease. Accumulated misfolded SOD1 in the motor neurons induced cPLA₂α upregulation via induction of TNFα.

Deletion of Chitinase-3-like 1 accelerates stroke development through enhancement of Neuroinflammation by STAT6-dependent M2 microglial inactivation in Chitinase-3-like 1 knockout mice

Chitinase 3-like 1 (Chi3L1) plays a major role in the pathogenesis of inflammatory diseases. We investigated the effect of Chi3L1 knockout on stroke development. Ischemia/reperfusion was induced by middle cerebral artery occlusion (MCAO) in Chi3L1 knockout and wildtype mice. Significantly increased infarct volume and decreased neurological deficit scores at 24 h after ischemia/reperfusion were found in Chi3L1 knockout mice compared to wildtype mice. Moreover, ischemic neuronal cell death was increased in Chi3L1 knockout mice through increased oxidative stress and release of IL-6 and IL-1β but IL-10 and IL-4 were reduced. Furthermore, expression of inflammation-related proteins (iNOS, COX-2, Iba-1, and GFAP) was significantly increased in Chi3L1 knockout mice compared to wildtype. In microglia isolated from MCAO-injured Chi3L1 knockout mice, expression of M1 markers (iNOS, CD86, IL-1β, and IL-6) was increased and M2 markers (Arg1, Mrc1, IL-10, and IL-4Ra) was decreased. In BV-2 cells, knockdown of Chi3L1 increased TNF-α- and INF-γ-induced expression of iNOS, COX-2, and Iba-1, but decreased the expression of Arg1, MRC1, and IL-4 receptor-alpha (IL-4Rα). Expression of IL-4Rα, an important factor of M2 polarization, and its downstream signals p-JAK1, p-JAK3, and p-STAT6, was much reduced in the knockout mice. Additionally, in BV-2 cells, knockdown of Chi3L1 by siRNA Chi3L1 decreased rhTNF-α- and INF-γ-induced expression of IL-4Rα, p-JAK1, p-JAK3, and p-STAT6. Furthermore, treatment with AS1517499 abolished Chi3L1 knockdown-induced reduced IL-4Rα and Arg1 but not CD86 expression. Our results indicate that deletion of Chi3L1 accelerates stroke development through enhancement of neuroinflammation by markedly decreasing STAT6-dependent M2 macrophage polarization.

Multiple mechanisms underlying neuroprotection by secretory phospholipase A2 preconditioning in a surgically induced brain injury rat model

BACKGROUND

Intra-operative bleeding, post-operative brain edema and neuroinflammation are major complications in patients with surgical brain injury (SBI). Phospholipase A2 (PLA2) is the upstream enzyme which initiates the PLA2, 5-lipoxygenase (5-LOX) and leukotriene B4 (LTB4) inflammatory pathway. We hypothesized PLA2preconditioning (PPC) prior to SBI can activate endogenous anti-inflammatory responses to protect against SBI. This study evaluated if PPC can ameliorate neurosurgical complications and elucidated PPC-mediated possible protective mechanisms in a rat SBI model.

METHODS

Total 105 adult male Sprague Dawley rats were used for this study. SBI was induced by partial resection of the right frontal lobe. PLA2 or 0.9% NaCl was injected via rats' tail vein for 3 consecutive days prior to SBI. For mechanism study, a selective PLA2 inhibitor, Manoalide and 5-LOX inhibitor, Zileuton were injected intravenously with PPC to elucidate the role of PLA2 and 5-LOX in PPC-mediated anti-inflammatory effects. Brain water content (BWC) and lung water content, neurological tests, ELISA, western blot, immunohistochemistry, white blood cells (WBC) count, and spectrophotometric assay for intra-operative hemorrhage volume were evaluated.

RESULTS

First, PPC reduced brain water content, intra-operative bleeding, and improved neurological function after SBI. Second, PPC decreased 5-LOX expression and brain leukocyte infiltration, while increasing glial fibrillary acidic protein (GFAP) expression in the peri-resection brain tissue after SBI. Third, PPC induced peripheral inflammation represented by mild pulmonary inflammation and increased peripheral blood WBC count and LTB4 level. Lastly, PPC increased blood glucose concentration and glucocorticoid levels after SBI. In addition, PPC mediated above-mentioned changes were partially reversed by administration of PLA2 inhibitor, Manoalide and 5-LOX inhibitor, Zileuton.

CONCLUSIONS

PPC conferred neuroprotection against SBI via multi-target involvement induced anti-inflammatory mechanisms.

Agonists for G-protein-coupled receptor 84 (GPR84) alter cellular morphology and motility but do not induce pro-inflammatory responses in microglia

Background

Several G-protein-coupled receptors (GPCRs) have been shown to be important signaling mediators between neurons and glia. In our previous screening for identification of nerve injury-associated GPCRs, G-protein-coupled receptor 84 (GPR84) mRNA showed the highest up-regulation by microglia after nerve injury. GPR84 is a pro-inflammatory receptor of macrophages in a neuropathic pain mouse model, yet its function in resident microglia in the central nervous system is poorly understood.

Methods

We used endogenous, natural, and surrogate agonists for GPR84 (capric acid, embelin, and 6-OAU, respectively) and examined their effect on mouse primary cultured microglia in vitro.

Results

6-n-Octylaminouracil (6-OAU), embelin, and capric acid rapidly induced membrane ruffling and motility in cultured microglia obtained from C57BL/6 mice, although these agonists failed to promote microglial pro-inflammatory cytokine expression. Concomitantly, 6-OAU suppressed forskolin-induced increase of cAMP in cultured microglia. Pertussis toxin, an inhibitor of Gi-coupled signaling, completely suppressed 6-OAU-induced microglial membrane ruffling and motility. In contrast, no 6-OAU-induced microglial membrane ruffling and motility was observed in microglia from DBA/2 mice, a mouse strain that does not express functional GPR84 protein due to endogenous nonsense mutation of the GPR84 gene.

Conclusions

GPR84 mediated signaling causes microglial motility and membrane ruffling but does not promote pro-inflammatory responses. As GPR84 is a known receptor for medium-chain fatty acids, those released from damaged brain cells may be involved in the enhancement of microglial motility through GPR84 after neuronal injury.

Naja sputatrix Venom Preconditioning Attenuates Neuroinflammation in a Rat Model of Surgical Brain Injury via PLA2/5-LOX/LTB4 Cascade Activation

Inflammatory preconditioning is a mechanism in which exposure to small doses of inflammatory stimuli prepares the body against future massive insult by activating endogenous protective responses. Phospholipase A2/5-lipoxygenase/leukotriene-B4 (PLA2/5-LOX/LTB4) axis is an important inflammatory signaling pathway. Naja sputatrix (Malayan spitting cobra) venom contains 15% secretory PLA2 of its dry weight. We investigated if Naja sputatrix venom preconditioning (VPC) reduces surgical brain injury (SBI)-induced neuroinflammation via activating PLA2/5-LOX/LTB4 cascade using a partial frontal lobe resection SBI rat model. Naja sputatrix venom sublethal dose was injected subcutaneously for 3 consecutive days prior to SBI. We observed that VPC reduced brain edema and improved neurological function 24 h and 72 h after SBI. The expression of pro-inflammatory mediators in peri-resection brain tissue was reduced with VPC. Administration of Manoalide, a PLA2 inhibitor or Zileuton, a 5-LOX inhibitor with VPC reversed the protective effects of VPC against neuroinflammation. The current VPC regime induced local skin inflammatory reaction limited to subcutaneous injection site and elicited no other toxic effects. Our findings suggest that VPC reduces neuroinflammation and improves outcomes after SBI by activating PLA2/5-LOX/LTB4 cascade. VPC may be beneficial to reduce post-operative neuroinflammatory complications after brain surgeries.

Regulatory role of cytosolic phospholipase A2 alpha in the induction of CD40 in microglia

Background

The aberrant expression of CD40, a co-stimulatory receptor found on the antigen-presenting cells, is involved in the pathogenesis of various degenerative diseases. Our previous study demonstrated that the reduction of cytosolic phospholipase A₂ alpha (cPLA₂α) protein overexpression and activation in the spinal cord of a mouse model of ALS, hmSOD1 G93A, inhibited CD40 upregulation in microglia. The present study was designed to determine whether cPLA₂α has a direct, participatory role in the molecular events leading to CD40 induction.

Methods

Cultures of primary mouse microglia or BV-2 microglia cell line exposed to lipopolysaccharide (LPS) or interferon gamma (IFNγ) for different periods of time, in order to study the role of cPLA₂α in the events leading to CD40 protein induction.

Results

Addition of LPS or IFNγ caused a significant upregulation of cPLA₂α and of CD40, while prevention of cPLA₂α upregulation by a specific oligonucleotide antisense (AS) prevented the induction of CD40, suggesting a role of cPLA₂α in the induction of CD40. Addition of LPS to microglia caused an immediate activation of cPLA₂α detected by its phosphorylated form, while addition of IFNγ induced cPLA₂α activation at a later time scale (4 h). The activation of cPLA₂α is mediated by ERK activity. Suppression of cPLA₂α activity inhibited superoxide production by NOX2-NADPH oxidase and activation of NF-κB detected by the phosphorylation of p65 on serine 536 at 15 min by LPS and at 4 h by IFNγ. Inhibition of NOX2 prevented NF-κB activation and CD40 induction but did not affect cPLA₂α activation, suggesting cPLA₂α is located upstream to NOX2 and NF-κB. The activation of cPLA₂ by LPS was mediated by both adaptor proteins downstream to LPS receptor; TRIF and MyD88, while the activation of cPLA₂α by IFNγ was mediated by the secreted TNF-α at 4 h. The early activation of STAT1α (detected by phospho-serine727 and phoshpo-tyrosine701) by IFNγ and the late activation of STAT1α by LPS were not affected in the presence of cPLA₂α inhibitors, indicating that STAT1α is not under cPLA₂α regulation.

Conclusions

Our results show for the first time that cPLA₂ upregulates CD40 protein expression induced by either LPS or IFNγ, and this regulatory effect is mediated via the activation of NOX2-NADPH oxidase and NF-κB. Cumulatively, our results indicate that cPLA₂α may serve as a pivotal amplifier of the inflammatory response in the CNS.

Relative quantification of neuronal polar lipids by UPLC-MS reveals the brain protection mechanism of Danhong injection

Promising results from clinical trials have fueled a growing acceptance of Danhong injection (DHI) as a Chinese Materia Medica standardized product for the treatment of ischemic stroke.

Brain Cytosolic Phospholipase A2: Localization, Role, and Involvement in Neurological Diseases

Cytosolic phospholipase A2 (cPLA2) hydrolyzes the arachidonoyl group from the sn-2 position of glycerophospholipids generating arachidonic acid and lysophospholipids. The products of the cPLA2-catalyzed reaction act as second messengers themselves or further metabolize to eicosanoids, platelet activating factor, and lysophosphatidic acid. cPLA2 has not been purified from brain tissue. Immunocytochemical studies have indicated that cPLA2 is expressed in neurons and astrocytes. The hindbrain and spinal cord contain dense immunoreactivity for cPLA2. Activity and immunoreactivity of cPLA2 are markedly increased in ischemia, Alzheimer’s disease, and kainic acid neurotoxicity. This increase in cPLA2 activity and immunoreactivity is accompanied by marked alterations in neural membrane phospholipid composition and the accumulation of lipid peroxides and eicosanoids. At present, it is not known whether the increased activity and immunoreactivity of cPLA2 in neural trauma (e.g., in ischemia) and neurodegenerative disease (Alzheimer’s disease) is the cause or effect of neurodegeneration. Recent studies on the role of this enzyme in brain tissue suggest that cPLA2 may be involved in synaptic plasticity, generation of second messengers, axon regeneration, and neurodegeneration.

Reduction of cytosolic phospholipase A2α upregulation delays the onset of symptoms in SOD1G93A mouse model of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal multifactorial neurodegenerative disease characterized by selective death of motor neurons in the cortex, brainstem, and spinal cord. Cytosolic phospholipase A2 alpha (cPLA2α) upregulation and activation in the spinal cord of patients with sporadic ALS and in the spinal cord of human mutant SOD1G93A (hmSOD1) transgenic mice were recently reported.

METHODS

cPLA2α upregulation in the brainstem and spinal cord was reduced by brain infusion of a specific antisense oligonucleotide against cPLA2α (AS), and the effect was evaluated on disease progression and brain cell activation.

RESULTS

We found that the elevation of cPLA2α protein expression in the spinal cord was first detected at 6-week-old hmSOD1 mice and remained elevated during their whole life span. Reduction of the elevated expression of cPLA2α in the spinal cord of hmSOD1 mice by brain infusion of an AS at week 15 (shortly before the appearance of the disease symptoms), for a duration of 6 weeks, delayed the loss of motor neuron function in comparison with hmSOD1 mice and with sense brain-infused hmSOD1 mice. To characterize the effect of cPLA2α upregulation on different processes taking place at the appearance of the disease symptoms, mice were brain infused with AS or with sense at week 15 for 3-4 weeks. The AS treatment that reduced cPLA2α upregulation in the spinal cord of AS-treated hmSOD1 mice (as analyzed at week 18-19) prevented the reduction in the number of the neurons (detected by NeuN) and inhibited astrocyte activation (detected by GFAP) and microglia activation (detected by Iba-1 and by CD40). In addition, AS treatment blunted the upregulation of the proinflammatory enzyme-inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) detected in hmSOD1 mice.

CONCLUSIONS

Since specific reduction of cPLA2α in the brainstem and spinal cord significantly attenuated the development of the disease, cPLA2α may offer an efficient target for treatment of ALS.

The role of cytosolic phospholipase A2 α in amyloid precursor protein induction by amyloid beta1-42 : implication for neurodegeneration

Amyloid-β peptides generated by proteolysis of the β-amyloid precursor protein (APP) play an important role in the pathogenesis of Alzheimer's disease. The present study aimed to determine whether cytosolic phospholipase A2 α (cPLA2 α) plays a role in elevated APP protein expression induced by aggregated amyloid-β1-42 (Aβ) in cortical neurons and to elucidate its specific role in signal events leading to APP induction. Elevated cPLA2 α and its activity determined by phosphorylation on serine 505 as well as elevated APP protein expression, were detected in primary rat cortical neuronal cultures exposed to Aβ for 24 h and in cortical neuron of human amyloid-β1-42 brain infused mice. Prevention of cPLA2 α up-regulation and its activity by oligonucleotide antisense against cPLA2 α (AS) prevented the elevation of APP protein in cortical neuronal cultures and in mouse neuronal cortex. To determine the role of cPLA2 α in the signals leading to APP induction, increased cPLA2 α expression and activity induced by Aβ was prevented by means of AS in neuronal cortical cultures. Under these conditions, the elevated cyclooxygenase-2 and the production of prostaglandin E2 (PGE2 ) were prevented. Addition of PGE2 or cyclic AMP analogue (dbcAMP) to neuronal cultures significantly increased the expression of APP protein, while the presence protein kinase A inhibitor (H-89) attenuated the elevation of APP induced by Aβ. Inhibition of elevated cPLA2 α by AS prevented the activation of cAMP response element binding protein (CREB) as detected by its phosphorylated form, its translocation to the nucleus and its DNA binding induced by Aβ which coincided with cPLA2 α dependent activation of CREB in the cortex of Aβ brain infused mice. Our results show that accumulation of Aβ induced elevation of APP protein expression mediated by cPLA2 α, PGE2 release, and CREB activation via protein kinase A pathway.

NADPH oxidase-2: linking glucose, acidosis, and excitotoxicity in stroke

SIGNIFICANCE

Neuronal superoxide production contributes to cell death in both glutamate excitotoxicity and brain ischemia (stroke). NADPH oxidase-2 (NOX2) is the major source of neuronal superoxide production in these settings, and regulation of NOX2 activity can thereby influence outcome in stroke.

RECENT ADVANCES

Reduced NOX2 activity can rescue cells from oxidative stress and cell death that otherwise occur in excitotoxicity and ischemia. NOX2 activity is regulated by several factors previously shown to affect outcome in stroke, including glucose availability, intracellular pH, protein kinase ζ/δ, casein kinase 2, phosphoinositide-3-kinase, Rac1/2, and phospholipase A2. The newly identified functions of these factors as regulators of NOX2 activity suggest alternative mechanisms for their effects on ischemic brain injury.

CRITICAL ISSUES

Key aspects of these regulatory influences remain unresolved, including the mechanisms by which rac1 and phospholipase activities are coupled to N-methyl-D-aspartate (NMDA) receptors, and whether superoxide production by NOX2 triggers subsequent superoxide production by mitochondria.

FUTURE DIRECTIONS

It will be important to establish whether interventions targeting the signaling pathways linking NMDA receptors to NOX2 in brain ischemia can provide a greater neuroprotective efficacy or a longer time window to treatment than provided by NMDA receptor blockade alone. It will likewise be important to determine whether dissociating superoxide production from the other signaling events initiated by NMDA receptors can mitigate the deleterious effects of NMDA receptor blockade.

Post-ischemic inflammation regulates neural damage and protection

Post-ischemic inflammation is important in ischemic stroke pathology. However, details of the inflammation process, its resolution after stroke and its effect on pathology and neural damage have not been clarified. Brain swelling, which is often fatal in ischemic stroke patients, occurs at an early stage of stroke due to endothelial cell injury and severe inflammation by infiltrated mononuclear cells including macrophages, neutrophils, and lymphocytes. At early stage of inflammation, macrophages are activated by molecules released from necrotic cells [danger-associated molecular patterns (DAMPs)], and inflammatory cytokines and mediators that increase ischemic brain damage by disruption of the blood–brain barrier are released. After post-ischemic inflammation, macrophages function as scavengers of necrotic cell and brain tissue debris. Such macrophages are also involved in tissue repair and neural cell regeneration by producing tropic factors. The mechanisms of inflammation resolution and conversion of inflammation to neuroprotection are largely unknown. In this review, we summarize information accumulated recently about DAMP-induced inflammation and the neuroprotective effects of inflammatory cells, and discuss next generation strategies to treat ischemic stroke.

The TIR-domain-containing adapter inducing interferon-β-dependent signaling cascade plays a crucial role in ischemia-reperfusion-induced retinal injury, whereas the contribution of the myeloid differentiation primary response 88-dependent signaling cascade is not as pivotal

Toll-like receptor 4 (Tlr4) plays an important role in ischemia–reperfusion (IR)-induced retinal inflammation and damage. However, the role of two Tlr4-dependent signaling cascades, myeloid differentiation primary response 88 (Myd88) and TIR-domain-containing adapter inducing interferon-β (Trif), in retinal IR injury is poorly understood. In this study, we investigated the contribution of the Myd88-dependent and Trif-dependent signaling cascades in retinal damage and inflammation triggered by IR, by using Myd88 knockout (Myd88KO) and Trif knockout (TrifKO) mice. Retinal IR injury was induced by unilateral elevation of intraocular pressure for 45 min by direct corneal cannulation. To study IR-induced retinal ganglion cell (RGC) death in vitro, we used an oxygen and glucose deprivation (OGD) model. Our data suggested that Myd88 was present in many retinal layers of sham-operated and ischemic mice, whereas Trif was mainly present in the ganglion cell layer (GCL). The level of Myd88 was increased in the retina after IR. We found that retinas of TrifKO mice had a significantly reduced neurotoxic pro-inflammatory response and significantly increased survival of the GCL neurons after IR. Although Myd88KO mice had relatively low levels of inflammation in ischemic retinas, their levels of IR-induced retinal damage were notably higher than those of TrifKO mice. We also found that Trif-deficient RGCs were more resistant to death induced by OGD than were RGCs isolated from Myd88KO mice. These data suggested that, as compared with the Myd88-dependent signaling cascade, Trif signaling contributes significantly to retinal damage after IR.

Cytosolic phospholipase A2α upregulation mediates apoptotic neuronal death induced by aggregated amyloid-β peptide1-42

Increased cytosolic phospholipase A2α (cPLA2α) immunoreactivity and transcript were observed in Alzheimer's disease (AD) brain associated with amyloid deposits. Thus, the present study examined whether cPLA2α upregulation participate in cortical neuron damage induced by aggregated Aβ1-42 and determined its role in the signaling events leading to damage, using an antisense technology. Exposure of primary cortical neurons to 1μM aggregated Aβ1-42 for 24h induced up-regulation and activation of cPLA2α and apoptotic cell death of about 30% as detected by: cell count, MTT reduction, caspases-3 and -8 activation, DAPI and TUNEL staining, that were prevented by inhibition of cPLA2α up-regulation and activity in the presence of antisense against cPLA2α (AS). cPLA2α was rapidly activated upon addition of aggregated Aβ1-42, as determined by its phosphorylated form on serine 505, and this activity was dependent on NADPH oxidase activity. NOX2- and NOX4-NADPH oxidase upregulation at 24h of aggregated Aβ1-42 exposure was not affected by the presence of AS, but superoxide production was reduced, probably due to NOX2 inhibition. cPLA2α upregulation led to activation of neutral sphingomyelinase (N-SMase) as its activity was inhibited in the presence of AS, and could be restored by addition of arachidonic acid. Addition of ceramide analog induced caspase-8 activation leading to caspase-3 activation and apoptotic neuronal death. In conclusion, our results suggest that cPLA2α activity plays a crucial role in the signaling cascade leading to apoptotic neuronal death by aggregated Aβ1-42 probably via activation of N-SMase, ceramide production and caspases-3 and -8.

12/15-lipoxygenase expression is increased in oligodendrocytes and microglia of periventricular leukomalacia

Oxidative stress involving premyelinating oligodendrocytes (OLs) is a major factor in the pathogenesis of preterm white matter injury. In animal and cell culture studies, activation of the lipid-oxidizing enzyme 12/15-lipoxygenase (12/15-LOX) plays a central role as an inflammatory mediator in the pathology of oxidative stress and OL cell death, as well as ischemia and neuronal death. The role of 12/15-LOX, however, is unclear in the developing human brain. The mechanism of 12/15-LOX involves the production of reactive oxygen species through the metabolism of arachidonic acid, as well as direct detrimental effects on organelle membranes. Here we tested the hypothesis that the density of 12/15-LOX-expressing cells is increased in periventricular leukomalacia (PVL). Using immunocytochemistry (ICC) in human paraffin-embedded tissue, 12/15-LOX expression was seen in macrophages of the focally necrotic lesions in the periventricular white matter, as well as in glial cells throughout the surrounding white matter with reactive gliosis. Interestingly, no significant 12/15-LOX expression was detected in neurons in the cerebral cortex overlying the damaged white matter. Using a scoring system from 0 to 3, we assessed the density of 12/15-LOX-expressing cells in diffusely gliotic white matter from 20 to 43 postconceptional (PC) weeks in 19 PVL cases (median = 36 PC weeks) and 10 control (non-PVL) cases (median = 34 PC weeks). The density of 12/15-LOX-positive cells was significantly increased in the diffuse component of PVL (score = 1.17 ± 0.15) compared to controls (score = 0.48 ± 0.21; p = 0.014). Using double-label ICC, 12/15-LOX was observed in PVL in OLs of the O4 and O1 premyelinating stages, as well as in mature OLs as determined with the mature OL marker adenomatous polyposis coli (APC). In addition, 12/15-LOX expression was present in a population of CD68-positive activated microglia. There was no 12/15-LOX expression in reactive astrocytes. Finally we observed terminal deoxynucleotide transferase dUTP nick end-labeling-positive cells within the white matter of PVL that expressed 12/15-LOX and/or within close proximity of 12/15-LOX-positive cells. Our data support a role for 12/15-LOX activation as an inflammatory mediator of injury in PVL, with a contribution of 12/15-LOX to PVL-induced damage to or cell death of OLs, including those at the O1 and O4 stages.

The increased activity of TRPV4 channel in the astrocytes of the adult rat hippocampus after cerebral hypoxia/ischemia

The polymodal transient receptor potential vanilloid 4 (TRPV4) channel, a member of the TRP channel family, is a calcium-permeable cationic channel that is gated by various stimuli such as cell swelling, low pH and high temperature. Therefore, TRPV4-mediated calcium entry may be involved in neuronal and glia pathophysiology associated with various disorders of the central nervous system, such as ischemia. The TRPV4 channel has been recently found in adult rat cortical and hippocampal astrocytes; however, its role in astrocyte pathophysiology is still not defined. In the present study, we examined the impact of cerebral hypoxia/ischemia (H/I) on the functional expression of astrocytic TRPV4 channels in the adult rat hippocampal CA1 region employing immunohistochemical analyses, the patch-clamp technique and microfluorimetric intracellular calcium imaging on astrocytes in slices as well as on those isolated from sham-operated or ischemic hippocampi. Hypoxia/ischemia was induced by a bilateral 15-minute occlusion of the common carotids combined with hypoxic conditions. Our immunohistochemical analyses revealed that 7 days after H/I, the expression of TRPV4 is markedly enhanced in hippocampal astrocytes of the CA1 region and that the increasing TRPV4 expression coincides with the development of astrogliosis. Additionally, adult hippocampal astrocytes in slices or cultured hippocampal astrocytes respond to the TRPV4 activator 4-alpha-phorbol-12,-13-didecanoate (4αPDD) by an increase in intracellular calcium and the activation of a cationic current, both of which are abolished by the removal of extracellular calcium or exposure to TRP antagonists, such as Ruthenium Red or RN1734. Following hypoxic/ischemic injury, the responses of astrocytes to 4αPDD are significantly augmented. Collectively, we show that TRPV4 channels are involved in ischemia-induced calcium entry in reactive astrocytes and thus, might participate in the pathogenic mechanisms of astroglial reactivity following ischemic insult.

Cytosolic phospholipase A2α blockade abrogates disease during the tissue-damage effector phase of experimental autoimmune encephalomyelitis by its action on APCs

Cytosolic phospholipase A(2)α (cPLA(2)α) is the rate-limiting enzyme for release of arachidonic acid, which is converted primarily to PGs via the cyclooxygenase 1 and 2 pathways and to leukotrienes via the 5-lipoxygenase pathway. We used adoptive transfer and relapsing-remitting forms of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, in two different strains of mice (SJL or C57BL/6) to demonstrate that blockade of cPLA(2)α with a highly specific small-molecule inhibitor during the tissue-damage effector phase abrogates the clinical manifestation of disease. Using the adoptive transfer model in SJL mice, we demonstrated that the blockade of cPLA(2)α during the effector phase of disease was more efficacious in ameliorating the disease pathogenesis than the blockade of each of the downstream enzymes, cyclooxygenase-1/2 and 5-lipooxygenase. Similarly, blockade of cPLA(2)α was highly efficacious in ameliorating disease pathogenesis during the effector phase of EAE in the adoptive transfer model of EAE in C57BL/6 mice. Investigation of the mechanism of action indicates that cPLA(2)α inhibitors act on APCs to diminish their ability to induce Ag-specific effector T cell proliferation and proinflammatory cytokine production. Furthermore, cPLA(2)α inhibitors may prevent activation of CNS-resident microglia and may increase oligodendrocyte survival. Finally, in a relapsing-remitting model of EAE in SJL mice, therapeutic administration of a cPLA(2)α inhibitor, starting from the peak of disease or during remission, completely protected the mice from subsequent relapses.

Significance of brain tissue oxygenation and the arachidonic acid cascade in stroke

The significance of the hypoxia component of stroke injury is highlighted by hypermetabolic brain tissue enriched with arachidonic acid (AA), a 22:6n-3 polyunsaturated fatty acid. In an ischemic stroke environment in which cerebral blood flow is arrested, oxygen-starved brain tissue initiates the rapid cleavage of AA from the membrane phospholipid bilayer. Once free, AA undergoes both enzyme-independent and enzyme-mediated oxidative metabolism, resulting in the formation of number of biologically active metabolites which themselves contribute to pathological stroke outcomes. This review is intended to examine two divergent roles of molecular dioxygen in brain tissue as (1) a substrate for life-sustaining homeostatic metabolism of glucose and (2) a substrate for pathogenic metabolism of AA under conditions of stroke. Recent developments in research concerning supplemental oxygen therapy as an intervention to correct the hypoxic component of stroke injury are discussed.

Phospholipase A2 and arachidonic acid in Alzheimer's disease

Essential fatty acids (EFA) play a critical role in the brain and regulate many of the processes altered in Alzheimer's disease (AD). Technical advances are allowing for the dissection of complex lipid pathways in normal and diseased states. Arachidonic acid (AA) and specific isoforms of phospholipase A(2) (PLA(2)) appear to be critical mediators in amyloid-beta (Abeta)-induced pathogenesis, leading to learning, memory, and behavioral impairments in mouse models of AD. These findings and ongoing research into lipid biology in AD and related disorders promise to reveal new pharmacological targets that may lead to better treatments for these devastating conditions.

Cytosolic phospholipase A2 alpha amplifies early cyclooxygenase-2 expression, oxidative stress and MAP kinase phosphorylation after cerebral ischemia in mice

Background

The enzyme cytosolic phospholipase A₂ alpha (cPLA₂α) has been implicated in the progression of cerebral injury following ischemia and reperfusion. Previous studies in rodents suggest that cPLA₂α enhances delayed injury extension and disruption of the blood brain barrier many hours after reperfusion. In this study we investigated the role of cPLA₂α in early ischemic cerebral injury.

Methods

Middle cerebral artery occlusion (MCAO) was performed on cPLA₂α^+/+ and cPLA₂α^-/- mice for 2 hours followed by 0, 2, or 6 hours of reperfusion. The levels of cPLA₂α, cyclooxygenase-2, neuronal morphology and reactive oxygen species in the ischemic and contralateral hemispheres were evaluated by light and fluorescent microscopy. PGE₂ content was compared between genotypes and hemispheres after MCAO and MCAO and 6 hours reperfusion. Regional cerebral blood flow was measured during MCAO and phosphorylation of relevant MAPKs in brain protein homogenates was measured by Western analysis after 6 hours of reperfusion.

Results

Neuronal cPLA₂α protein increased by 2-fold immediately after MCAO and returned to pre-MCAO levels after 2 hours reperfusion. Neuronal cyclooxygenase-2 induction and PGE₂ concentration were greater in cPLA₂α^+/+ compared to cPLA₂α^-/- ischemic cortex. Neuronal swelling in ischemic regions was significantly greater in the cPLA₂α^+/+ than in cPLA₂α^-/- brains (+/+: 2.2 ± 0.3 fold vs. -/-: 1.7 ± 0.4 fold increase; P < 0.01). The increase in reactive oxygen species following 2 hours of ischemia was also significantly greater in the cPLA₂α^+/+ ischemic core than in cPLA₂α^-/- (+/+: 7.12 ± 1.2 fold vs. -/-: 3.1 ± 1.4 fold; P < 0.01). After 6 hours of reperfusion ischemic cortex of cPLA₂α^+/+, but not cPLA₂α^-/-, had disruption of neuron morphology and decreased PGE₂ content. Phosphorylation of the MAPKs-p38, ERK 1/2, and MEK 1/2-was significantly greater in cPLA₂a^+/+ than in cPLA₂α^-/- ischemic cortex 6 hours after reperfusion.

Conclusions

These results indicate that cPLA₂α modulates the earliest molecular and injury responses after cerebral ischemia and have implications for the potential clinical use of cPLA₂α inhibitors.

Cerebral arachidonate cascade in dementia: Alzheimer's disease and vascular dementia

Phospholipase A(2) (PLA(2)), cyclooxygenase (COX) and prostaglandin (PG) synthase are enzymes involved in arachidonate cascade. PLA(2) liberates arachidonic acid (AA) from cell membrane lipids. COX oxidizes AA to PGG(2) followed by an endoperoxidase reaction that converts PGG(2) into PGH(2). PGs are generated from astrocytes, microglial cells and neurons in the central nervous system, and are altered in the brain of demented patients. Dementia is principally diagnosed into Alzheimer's disease (AD) and vascular dementia (VaD). In older patients, the brain lesions associated with each pathological process often occur together. Regional brain microvascular abnormalities appear before cognitive decline and neurodegeneration. The coexistence of AD and VaD pathology is often termed mixed dementia. AD and VaD brain lesions interact in important ways to decline cognition, suggesting common pathways of the two neurological diseases. Arachidonate cascade is one of the converged intracellular signal transductions between AD and VaD. PLA(2) from mammalian sources are classified as secreted (sPLA(2)), Ca(2+)-dependent, cytosolic (cPLA(2)) and Ca(2+)-independent cytosolic PLA(2) (iPLA(2)). PLA(2) activity can be regulated by calcium, by phosphorylation, and by agonists binding to G-protein-coupled receptors. cPLA(2) is upregulalted in AD, but iPLA(2) is downregulated. On the other hand, sPLA(2) is increased in animal models for VaD. COX-2 is induced and PGD(2) are elevated in both AD and VaD. This review presents evidences for central roles of PLA(2)s, COXs and PGs in the dementia.

Palm oil-derived natural vitamin E alpha-tocotrienol in brain health and disease

A growing body of research supports that members of the vitamin E family are not redundant with respect to their biological function. Palm oil derived from Elaeis guineensis represents the richest source of the lesser characterized vitamin E, alpha-tocotrienol. One of 8 naturally occurring and chemically distinct vitamin E analogs, alpha-tocotrienol possesses unique biological activity that is independent of its potent antioxidant capacity. Current developments in alpha-tocotrienol research demonstrate neuroprotective properties for the lipid-soluble vitamin in brain tissue rich in polyunsaturated fatty acids (PUFAs). Arachidonic acid (AA), one of the most abundant PUFAs of the central nervous system, is highly susceptible to oxidative metabolism under pathologic conditions. Cleaved from the membrane phospholipid bilayer by cytosolic phospholipase A(2), AA is metabolized by both enzymatic and nonenzymatic pathways. A number of neurodegenerative conditions in the human brain are associated with disturbed PUFA metabolism of AA, including acute ischemic stroke. Palm oil-derived alpha-tocotrienol at nanomolar concentrations has been shown to attenuate both enzymatic and nonenzymatic mediators of AA metabolism and neurodegeneration. On a concentration basis, this represents the most potent of all biological functions exhibited by any natural vitamin E molecule. Despite such therapeutic potential, the scientific literature on tocotrienols accounts for roughly 1% of the total literature on vitamin E, thus warranting further investment and investigation.

Imaging mass spectrometry revealed the production of lyso-phosphatidylcholine in the injured ischemic rat brain

To develop an effective neuroprotective strategy against ischemic injury, it is important to identify the key molecules involved in the progression of injury. Direct molecular analysis of tissue using mass spectrometry (MS) is a subject of much interest in the field of metabolomics. Most notably, imaging mass spectrometry (IMS) allows visualization of molecular distributions on the tissue surface. To understand lipid dynamics during ischemic injury, we performed IMS analysis on rat brain tissue sections with focal cerebral ischemia. Sprague-Dawley rats were sacrificed at 24 h after middle cerebral artery occlusion, and brain sections were prepared. IMS analyses were conducted using matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOF MS) in positive ion mode. To determine the molecular structures, the detected ions were subjected to tandem MS. The intensity counts of the ion signals of m/z 798.5 and m/z 760.5 that are revealed to be a phosphatidylcholine, PC (16:0/18:1) are reduced in the area of focal cerebral ischemia as compared to the normal cerebral area. In contrast, the signal of m/z 496.3, identified as a lyso-phosphatidylcholine, LPC (16:0), was clearly increased in the area of focal cerebral ischemia. In IMS analyses, changes of PC (16:0/18:1) and LPC (16:0) are observed beyond the border of the injured area. Together with previous reports--that PCs are hydrolyzed by phospholipase A(2) (PLA(2)) and produce LPCs,--our present results suggest that LPC (16:0) is generated during the injury process after cerebral ischemia, presumably via PLA(2) activation, and that PC (16:0/18:1) is one of its precursor molecules.

Regulatory role of cytosolic phospholipase A2alpha in NADPH oxidase activity and in inducible nitric oxide synthase induction by aggregated Abeta1-42 in microglia

In Alzheimer's disease, extracellular deposits of amyloid beta(1-42) (Abeta(1-42)) may induce activation of microglial cells by releasing proinflammatory factors that contribute to the neurodegeneration process. Since the activation of cytosolic phospholipase A(2)alpha (cPLA(2)alpha) has been reported in inflammatory conditions, its role in primary rat microglial cell activated by aggregated Abeta(1-42) was elucidated. The results of the present study show that activation of microglia by 5 microM aggregated Abeta(1-42) (as evident by the amoeboid morphology and increased CD68 immunofluorescence reactivity) caused an immediate activation of cPLA(2)alpha, measured by its phosphorylated form and its specific activity, followed by a gradual elevation of its expression and activity during 24 h. Inhibition of cPLA(2)alpha expression and activity by the presence of 1 microM specific antisense resulted in a significant decrease in NADPH oxidase activity that releases superoxides, PGE(2) formation, iNOS expression, and NO production, indicating a major role for cPLA(2)alpha in the regulation of these inflammatory processes. NADPH oxidase activity, which is under cPLA(2)alpha regulation, was found to upregulate cPLA(2)alpha and COX-2 protein expression through the redox-sensitive NFkappaB activation as evident by its phosphorylation on Ser-536, resulting in increased PGE(2) formation. The secreted PGE(2) induced the synthesis of iNOS and the production of NO through the PKA-CREB pathway. Taken together, our results suggest that the response of cPLA(2)alpha to aggregated Abeta(1-42) is probably a key player in the oxidative stress present in AD, regulating potent oxidative agents: the production of superoxides by NADPH oxidase and NO formation by iNOS.

Anxiety after cardiac arrest/cardiopulmonary resuscitation: exacerbated by stress and prevented by minocycline

BACKGROUND AND PURPOSE

Stress is an important risk factor for cardiovascular disease; however, most of the research on this topic has focused on incidence rather than outcome. The goal of this study was to determine the effects of prior exposure to chronic stress on ischemia-induced neuronal death, microglial activation, and anxiety-like behavior.

METHODS

In Experiment 1, mice were exposed to 3 weeks of daily restraint (3 hours) and then subjected to either 8 minutes of cardiac arrest/cardiopulmonary resuscitation (CA/CPR) or sham surgery. Anxiety-like behavior, microglial activation, and neuronal damage were assessed on postischemic Day 4. In Experiment 2, mice were infused intracerebroventricularly with minocycline (10 microg/day) to determine the effect of inhibiting post-CA/CPR microglial activation on the development of anxiety-like behavior and neuronal death.

RESULTS

CA/CPR precipitated anxiety-like behavior and increased microglial activation and neuronal damage within the hippocampus relative to sham surgery. Prior exposure to stress exacerbated these measures among CA/CPR mice, but had no significant effect on sham-operated mice. Treatment with minocycline reduced both neuronal damage and anxiety-like behavior among CA/CPR animals. Anxiety-like behavior was significantly correlated with measures of microglial activation but not neuronal damage.

CONCLUSIONS

A history of stress exposure increases the pathophysiological response to ischemia and anxiety-like behavior, whereas inhibiting microglial activation reduces neuronal damage and mitigates the development of anxiety-like behavior after CA/CPR. Thus, modulating inflammatory signaling after cerebral ischemia may be beneficial in protecting the brain and preventing the development of affective disorders.

The development of stroke therapeutics: promising mechanisms and translational challenges

Ischemic stroke is the second most common cause of death worldwide and a major cause of disability. Intravenous thrombolysis with rt-PA remains the only available acute therapy in patients who present within 3h of stroke onset other than the recently approved mechanical MERCI device, substantiating the high unmet need in available stroke therapeutics. The development of successful therapeutic strategies remains challenging, as evidenced by the continued failures of new therapies in clinical trials. However, significant lessons have been learned and this knowledge is currently being incorporated into improved pre-clinical and clinical design. Furthermore, advancements in imaging technologies and continued progress in understanding biological pathways have established a prolonged presence of salvageable penumbral brain tissue and have begun to elucidate the natural repair response initiated by ischemic insult. We review important past and current approaches to drug development with an emphasis on implementing principles of translational research to achieve a rigorous conversion of knowledge from bench to bedside. We highlight current strategies to protect and repair brain tissue with the promise to provide longer therapeutic windows, preservation of multiple tissue compartments and improved clinical success.

Role of the p38 mitogen-activated protein kinase/cytosolic phospholipase A2 signaling pathway in blood-brain barrier disruption after focal cerebral ischemia and reperfusion

Cytosolic phospholipase A(2) (cPLA(2)) is a key enzyme that mediates arachidonic acid metabolism, which causes cerebral ischemia-induced oxidative injury, blood-brain barrier (BBB) dysfunction, and edema. Recent reports have shown that p38 mitogen-activated protein kinase (MAPK) is related to phosphorylation and activation of cPLA(2) and release of arachidonic acid. However, involvement of the p38 MAPK pathway in cPLA(2) activation and of reactive oxygen species in expression of p38 MAPK/cPLA(2) after ischemia-reperfusion injury in the brain remains unclear. To address these issues, we used a model of transient focal cerebral ischemia (tFCI) in rats. Western blot analysis showed a significant increase in expression of phospho-p38 MAPK and phospho-cPLA(2) in rat brain cortex after tFCI. Activity assays showed that both p38 MAPK and cPLA(2) activation markedly increased 1 day after reperfusion. Intraventricular administration of SB203580 significantly suppressed activation and phosphorylation of cPLA(2) and attenuated BBB extravasation and subsequent edema. Moreover, overexpression of copper/zinc-superoxide dismutase remarkably diminished activation and phosphorylation of both p38 MAPK and cPLA(2) after reperfusion. These findings suggest that the p38 MAPK/cPLA(2) pathway may promote BBB disruption with secondary vasogenic edema and that superoxide anions can stimulate this pathway after ischemia-reperfusion injury.

Cytosolic phospholipase A2 alpha inhibition prevents neuronal NMDA receptor-stimulated arachidonic acid mobilization and prostaglandin production but not subsequent cell death

Phospholipase A(2) (PLA(2)) enzymes encompass a superfamily of at least 13 extracellular and intracellular esterases that hydrolyze the sn-2 fatty acyl bonds of phospholipids to yield fatty acids and lysophospholipids. The purpose of this study was to characterize which phospholipase paralog regulates NMDA receptor-mediated arachidonic acid (AA) release. Using mixed cortical cell cultures containing both neurons and astrocytes, we found that [(3)H]-AA released into the extracellular medium following NMDA receptor stimulation (100 microM) increased with time and was completely prevented by the addition of the NMDA receptor antagonist MK-801 (10 microM) or by removal of extracellular Ca(2+). Neither diacylglycerol lipase inhibition (RHC-80267; 10 microM) nor selective inhibition of Ca(2+)-independent PLA(2) [bromoenol lactone (BEL); 10 microM] alone had an effect on NMDA receptor-stimulated release of [(3)H]-AA. Release was prevented by methyl arachidonyl fluorophosphonate (MAFP) (5 microM) and AACOCF(3) (1 microM), inhibitors of both cytosolic PLA(2) (cPLA(2)) and Ca(2+)-independent PLA(2) isozymes. This inhibition effectively translated to block of NMDA-induced prostaglandin (PG) production. An inhibitor of p38MAPK, SB 203580 (7.5 microM), also significantly reduced NMDA-induced PG production providing suggestive evidence for the role of cPLA(2)alpha. Its involvement in release was confirmed using cultures derived from mice deficient in cPLA(2)alpha, which failed to produce PGs in response to NMDA receptor stimulation. Interestingly, neither MAFP, AACOCF(3) nor cultures derived from cPLA(2)alpha null mutant animals showed any protection against NMDA-mediated neurotoxicity, indicating that inhibition of this enzyme may not be a viable protective strategy in disorders of the cortex involving over-activation of the NMDA receptor.

Ceramide elevates 12-hydroxyeicosatetraenoic acid levels and upregulates 12-lipoxygenase in rat primary hippocampal cell cultures containing predominantly astrocytes

We report, exogenous addition of ceramide significantly increases 12-hydroxyeicosatetraenoic acid [12-(S)-HETE] levels, in a dose-dependent manner. 12-(S)-HETE levels, in 20, 30 and 40microM ceramide exposed rat primary hippocampal cell cultures containing predominantly astrocytes and few neurons and other glial cells (the cultured hippocampal cells were predominantly astrocytes amounting to over 99% of total cells with few neurons and other glial cells) amounted to 207, 260 and 408% of the controls, respectively. However, dihydroceramide, an inactive analog of ceramide did not alter the levels of 12-(S)-HETE. Ceramide also increased the mRNA and protein expression, and activity of 12-lipoxygease (12-LOX) needed for the synthesis of 12(S)-HETE. These results indicate a possible link between ceramide and 12-LOX pathway. However, ceramide did not alter expression of 5-lipoxygenase (5-LOX), another member of the lipoxygenase family. However, ceramide upregulated expression of cytosolic phospholipase-A(2) (cPLA(2)) and cyclooxygenase-2 (COX-2). Further, ceramide caused a significant increase in the levels of reactive oxygen species (ROS). Ceramide-mediated generation of ROS was inhibited by baicalien but not by indomethacin. In addition, ceramide treated cells exhibited increased mRNA expression of DNA damage induced transcript3 (Ddit3). This report which demonstrate induction of pro-carcinogenic 12-LOX pathway by an anticancer ceramide, may be relevant to cancer biologists studying drug resistant tumors and devising potent anticancer therapeutic strategies to treat drug resistant tumors. These results indicate possibility of 12-LOX involvement in ceramide-mediated generation of ROS and cellular oxidative stress. Induction of 12-LOX pathway by ceramide may have implications in understanding pathophysiology of neurodegenerative diseases involving ROS generation and inflammation.

Inhibition of spinal cytosolic phospholipase A(2) expression by an antisense oligonucleotide attenuates tissue injury-induced hyperalgesia

Activation of the spinal phospholipase A(2) (PLA(2)) -cyclooxygenase (COX) -prostaglandin signaling pathway is widely implicated in nociceptive processing. Although the role of spinal COX isoforms in pain signal transmission has been extensively characterized, our knowledge of PLA(2) enzymes in this cascade is limited. Among all PLA(2) groups, cytosolic calcium-dependent PLA(2) group IVA (cPLA(2)IVA) appears to be the predominant PLA(2) enzyme in the spinal cord. In the present study we sought to (i) characterize anatomical and cellular distribution and localization of cPLA(2)IVA in dorsal horn of rat spinal cord, (ii) verify efficacy and selectivity of intrathecal (IT) delivery of an antisense oligonucleotide (AS) targeting rat cPLA(2)IVA mRNA on spinal expression of this enzyme, and (iii) examine the effect of down-regulation of spinal cPLA(2)IVA on peripheral tissue injury-induced pain behavior. Here we demonstrate that cPLA(2)IVA is constitutively expressed in rat spinal cord, predominantly in dorsal horn neurons and oligodendrocytes but not in astrocytes or microglia. Intrathecal injection of AS significantly down-regulated both protein and gene expression of cPLA(2)IVA in rat spinal cord, while control missense oligonucleotide (MS) had no effect. Immunocytochemistry confirmed that the reduction occurred in neurons and oligodendrocytes. cPLA(2)IVA AS did not alter expression of several other PLA(2) isoforms, such as secretory PLA(2) (groups IIA and V) and calcium-independent PLA(2) (group VI), indicating that the AS was specific for cPLA(2)IVA. This selective knockdown of spinal cPLA(2)IVA did not change acute nociception (i.e. paw withdrawal thresholds to acute thermal stimuli and intradermal formalin-induced first phase flinching), however, it significantly attenuated formalin-induced hyperalgesia (i.e. second phase flinching behavior), which reflects spinal sensitization. Thus the present findings suggest that cPLA(2)IVA may specifically participate in spinal nociceptive processing.

Modulation of inflammation in brain: a matter of fat

Neuroinflammation is a host defense mechanism associated with neutralization of an insult and restoration of normal structure and function of brain. Neuroinflammation is a hallmark of all major CNS diseases. The main mediators of neuroinflammation are microglial cells. These cells are activated during a CNS injury. Microglial cells initiate a rapid response that involves cell migration, proliferation, release of cytokines/chemokines and trophic and/or toxic effects. Cytokines/chemokines stimulate phospholipases A2 and cyclooxygenases. This results in breakdown of membrane glycerophospholipids with the release of arachidonic acid (AA) and docosahexaenoic acid (DHA). Oxidation of AA produces pro-inflammatory prostaglandins, leukotrienes, and thromboxanes. One of the lyso-glycerophospholipids, the other products of reactions catalyzed by phospholipase A2, is used for the synthesis of pro-inflammatory platelet-activating factor. These pro-inflammatory mediators intensify neuroinflammation. Lipoxin, an oxidized product of AA through 5-lipoxygenase, is involved in the resolution of inflammation and is anti-inflammatory. Docosahexaenoic acid is metabolized to resolvins and neuroprotectins. These lipid mediators inhibit the generation of prostaglandins, leukotrienes, and thromboxanes. Levels of prostaglandins, leukotrienes, and thromboxanes are markedly increased in acute neural trauma and neurodegenerative diseases. Docosahexaenoic acid and its lipid mediators prevent neuroinflammation by inhibiting transcription factor NFkappaB, preventing cytokine secretion, blocking the synthesis of prostaglandins, leukotrienes, and thromboxanes, and modulating leukocyte trafficking. Depending on its timing and magnitude in brain tissue, inflammation serves multiple purposes. It is involved in the protection of uninjured neurons and removal of degenerating neuronal debris and also in assisting repair and recovery processes. The dietary ratio of AA to DHA may affect neurodegeneration associated with acute neural trauma and neurodegenerative diseases. The dietary intake of docosahexaenoic acid offers the possibility of counter-balancing the harmful effects of high levels of AA-derived pro-inflammatory lipid mediators.

Involvement of Ca2+-independent phospholipase A2 isoforms in oxidant-induced neural cell death

This study determined the roles of Ca2+-independent PLA2 (iPLA2) in phospholipid chemistry and oxidant-induced cell death in human astrocytes. A172 cells expressed both cytosolic Group VIA (iPLA2beta) and microsomal Group VIB (iPLA2gamma) PLA2 as determined by activity assays and immunoblot analysis. Inhibition of total iPLA2 activity using racemic bromoenol lactone (BEL, 2.5 microM) decreased the expression of 14:0-16:0 phosphatidylcholine (PtdCho) 15% and increased 18:0-18:1-PtdCho expression 15%. Treatment of cells with the iPLA2gamma specific inhibitor R-BEL decreased 14:0-16:0-PtdCho 35%, 16:0-16:0-PtdCho 15% and induced a 35% increase in 18:0-18:1-PtdCho. In contrast, treatment of cells with the iPLA2beta inhibitor S-BEL did not alter any phospholipid studied. To determine the roles of iPLA2 in oxidant-induced cell death, A172 cells were exposed to hydrogen peroxide (H2O2) or tert-butylhydroperoxide (TBHP); both induced time- and concentration-dependent increases in cell death as assessed by annexin V and propidium iodide staining. Treatment of cells with racemic-BEL alone did not induce cell death. However, pretreatment with BEL prior to H2O2 (500 microM) or TBHP (200 microM) significantly increased necrosis as determined by increases in propidium iodide staining. Treatment with BEL prior to exposure to oxidants accelerated the loss of ATP levels, but not the formation of reactive oxygen species. These data support the hypothesis that iPLA2 mediates oxidant-induced neural cell death and demonstrates differential roles of iPLA2 isoforms in physiological and pathological events.

Inhibitors of brain phospholipase A2 activity: their neuropharmacological effects and therapeutic importance for the treatment of neurologic disorders

The phospholipase A(2) family includes secretory phospholipase A(2), cytosolic phospholipase A(2), plasmalogen-selective phospholipase A(2), and calcium-independent phospholipase A(2). It is generally thought that the release of arachidonic acid by cytosolic phospholipase A(2) is the rate-limiting step in the generation of eicosanoids and platelet activating factor. These lipid mediators play critical roles in the initiation and modulation of inflammation and oxidative stress. Neurological disorders, such as ischemia, spinal cord injury, Alzheimer's disease, multiple sclerosis, prion diseases, and epilepsy are characterized by inflammatory reactions, oxidative stress, altered phospholipid metabolism, accumulation of lipid peroxides, and increased phospholipase A(2) activity. Increased activities of phospholipases A(2) and generation of lipid mediators may be involved in oxidative stress and neuroinflammation associated with the above neurological disorders. Several phospholipase A(2) inhibitors have been recently discovered and used for the treatment of ischemia and other neurological diseases in cell culture and animal models. At this time very little is known about in vivo neurochemical effects, mechanism of action, or toxicity of phospholipase A(2) inhibitors in human or animal models of neurological disorders. In kainic acid-mediated neurotoxicity, the activities of phospholipase A(2) isoforms and their immunoreactivities are markedly increased and phospholipase A(2) inhibitors, quinacrine and chloroquine, arachidonyl trifluoromethyl ketone, bromoenol lactone, cytidine 5-diphosphoamines, and vitamin E, not only inhibit phospholipase A(2) activity and immunoreactivity but also prevent neurodegeneration, suggesting that phospholipase A(2) is involved in the neurodegenerative process. This also suggests that phospholipase A(2) inhibitors can be used as neuroprotectants and anti-inflammatory agents against neurodegenerative processes in neurodegenerative diseases.

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: Their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.

The role of phospholipases A2 in schizophrenia

A range of neurotransmitter systems have been implicated in the pathogenesis of schizophrenia based on the antidopaminergic activities of antipsychotic medications, and chemicals that can induce psychotic-like symptoms, such as ketamine or PCP. Such neurotransmitter systems often mediate their cellular response via G-protein-coupled release of arachidonic acid (AA) via the activation of phospholipases A2 (PLA2s). The interaction of three PLA2s are important for the regulation of the release of AA--phospholipase A2 Group 2 A, phospholipase A2 Group 4A and phospholipase A2 Group 6A. Gene variations of these three key enzymes have been associated with schizophrenia with conflicting results. Preclinical data suggest that the activity of these three enzymes are associated with monoaminergic neurotransmission, and may contribute to the differential efficacy of antipsychotic medications, as well as other biological changes thought to underlie schizophrenia, such as altered neurodevelopment and synaptic remodelling. We review the evidence and discuss the potential roles of these three key enzymes for schizophrenia with particular emphasis on published association studies.

A novel role of phospholipase A2in mediating spinal cord secondary injury

OBJECTIVE

To investigate whether phospholipase A2 (PLA2) plays a role in the pathogenesis of spinal cord injury (SCI).

METHODS

Biochemical, Western blot, histological, immunohistochemical, electron microscopic, electrophysiological, and behavior assessments were performed to investigate (1) SCI-induced PLA2 activity, expression, and cellular localization after a contusive SCI; and (2) the effects of exogenous PLA2 on spinal cord neuronal death in vitro and tissue damage, inflammation, and function in vivo.

RESULTS

After SCI, both PLA2 activity and cytosolic PLA2 expression increased significantly, with cytosolic PLA2 expression being localized mainly in neurons and oligodendrocytes. Both PLA2 and melittin, an activator of endogenous PLA2, induced spinal neuronal death in vitro, which was substantially reversed by mepacrine, a PLA2 inhibitor. When PLA2 or melittin was microinjected into the normal spinal cord, the former induced confined demyelination and latter diffuse tissue necrosis. Both injections induced inflammation, oxidation, and tissue damage, resulting in corresponding electrophysiological and behavioral impairments. Importantly, the PLA2-induced demyelination was significantly reversed by mepacrine.

INTERPRETATION

PLA2, increased significantly after SCI, may play a key role in mediating neuronal death and oligodendrocyte demyelination following SCI. Blocking PLA2 action may represent a novel repair strategy to reduce tissue damage and increase function after SCI.

CDP-choline significantly restores phosphatidylcholine levels by differentially affecting phospholipase A2 and CTP: phosphocholine cytidylyltransferase after stroke

Phosphatidylcholine (PtdCho) is a major membrane phospholipid, and its loss is sufficient in itself to induce cell death. PtdCho homeostasis is regulated by the balance between hydrolysis and synthesis. PtdCho is hydrolyzed by phospholipase A2 (PLA2), PtdChospecific phospholipase C (PtdCho-PLC), and phospholipase D (PLD). PtdCho synthesis is rate-limited by CTP:phosphocholine cytidylyltransferase (CCT), which makes CDP-choline. The final step of PtdCho synthesis is catalyzed by CDP-choline:1,2-diacylglycerol cholinephosphotransferase. PtdCho synthesis in the brain is predominantly through the CDP-choline pathway. Transient middle cerebral artery occlusion (tMCAO) significantly increased PLA2 activity, secretory PLA2 (sPLA2)-IIA mRNA and protein levels, PtdCho-PLC activity, and PLD2 protein expression following reperfusion. CDP-choline treatment significantly attenuated PLA2 activity, sPLA2-IIA mRNA and protein levels, and PtdCho-PLC activity, but did not affect PLD2 protein expression. tMCAO also resulted in loss of CCT activity and CCTalpha protein, which were partially restored by CDP-choline. No changes were observed in cytosolic PLA2 or calcium-independent PLA2 tMCAO. protein levels after Up-regulation of PLA2, PtdCho-PLC, and PLD and regulation of CCT collectively down-resulted in loss of PtdCho, which was significantly restored by CDP-choline treatment. CDP-choline treatment significantly attenuated the infarction volume by 55 +/- 5% after 1 h of tMCAO and 1 day of reperfusion. Taken together, these results suggest that CDP-choline significantly restores Ptd-Cho levels by differentially affecting sPLA2-IIA, PtdCho-PLC, and CCTalpha after transient focal cerebral ischemia. A hypothetical scheme is proposed integrating results from this study and from other reports in the literature.

Phospholipase A2, reactive oxygen species, and lipid peroxidation in cerebral ischemia

Ischemic stroke is caused by obstruction of blood flow to the brain, resulting in energy failure that initiates a complex series of metabolic events, ultimately causing neuronal death. One such critical metabolic event is the activation of phospholipase A2 (PLA2), resulting in hydrolysis of membrane phospholipids and release of free fatty acids including arachidonic acid, a metabolic precursor for important cell-signaling eicosanoids. PLA2 enzymes have been classified as calcium-dependent cytosolic (cPLA2) and secretory (sPLA2) and calcium-independent (iPLA2) forms. Cardiolipin hydrolysis by mitochondrial sPLA2 disrupts the mitochondrial respiratory chain and increases production of reactive oxygen species (ROS). Oxidative metabolism of arachidonic acid also generates ROS. These two processes contribute to formation of lipid peroxides, which degrade to reactive aldehyde products (malondialdehyde, 4-hydroxynonenal, and acrolein) that covalently bind to proteins/nucleic acids, altering their function and causing cellular damage. Activation of PLA2 in cerebral ischemia has been shown while other studies have separately demonstrated increased lipid peroxidation. To the best of our knowledge no study has directly shown the role of PLA2 in lipid peroxidation in cerebral ischemia. To date, there are very limited data on PLA2 protein by Western blotting after cerebral ischemia, though some immunohistochemical studies (for cPLA2 and sPLA2) have been reported. Dissecting the contribution of PLA2 to lipid peroxidation in cerebral ischemia is challenging due to multiple forms of PLA2, cardiolipin hydrolysis, diverse sources of ROS arising from arachidonic acid metabolism, catecholamine autoxidation, xanthine oxidase activity, mitochondrial dysfunction, activated neutrophils coupled with NADPH oxidase activity, and lack of specific inhibitors. Although increased activity and expression of various PLA2 isoforms have been demonstrated in stroke, more studies are needed to clarify the cellular origin and localization of these isoforms in the brain, their responses in cerebral ischemic injury, and their role in oxidative stress.

Neuroprotection and peptide toxins

Neurodegeneration induced by excitatory neurotransmitter glutamate is considered to be of particular relevance in several types of acute and chronic neurological impairments ranging from cerebral ischaemia to neuropathological conditions such as motor neuron disease, Alzheimer's, Parkinson's disease and epilepsy. The hyperexcitation of glutamate receptors coupled with calcium overload can be prevented or modulated by using well-established competitive and non-competitive antagonists targeting ion/receptor channels. The exponentially increasing body of pharmacological evidence over the years indicates potential applications of peptide toxins, due to their exquisite subtype selectivity on ion channels and receptors, as lead structures for the development of drugs for the treatment of wide variety of neurological disorders. This review comprehensively highlights the overview of the diversity in the molecular as well as neurobiological mechanisms of different peptide toxins derived from venomous animals with particular reference to neuroprotection. In addition, the potential applications of peptide toxins in the diagnosis and treatment of neurological disorders such as neuromuscular disorders, epilepsy, Alzheimer's and Parkinson's diseases, gliomas and ischaemic stroke and their future prospects in the diagnosis as well as in the therapy are addressed.

Mice deficient in cytosolic phospholipase A2 are less susceptible to cerebral ischemia/reperfusion injury

To determine the role of cytosolic phospholipase A2 (cPLA2) in infarct development, wild-type and cPLA2 knock-out mice were subjected to focal cerebral ischemia for 75 min by occluding the middle cerebral artery using nylon filament and subsequent reperfusion by withdrawing the filament. The neurological deficit severity was evaluated by a modified 4-point scale. After the reperfusion period (72 h), mice were killed, and the brains were cut into four 2 mm coronal sections using a rodent brain matrix. Sections were stained with 2% 2,3,5-triphenyltetrazolium chloride (TTC). The infarct volume was 87.19 +/- 27.54 mm3 (mean +/- SD, n = 11) in the wild-type mice and 48.20 +/- 31.32 mm3 (n = 10; P < 0.01 vs. wild-type) in the knock-out mice. Less severe functional neurological deficits were observed in knock-out mice at 72 h after ischemia when compared with wild-type. Thus, disruption of cPLA2 resulted in significant reduction of infarct area and neurological deficit severity in the MCA occlusion model. These data indicate a critical role for cPLA2 in the pathogenesis of cerebral ischemia/ reperfusion injury.

A potentially critical role of phospholipases in central nervous system ischemic, traumatic, and neurodegenerative disorders

Phospholipases are a diverse group of enzymes whose activation may be responsible for the development of injury following insult to the brain. Amongst the numerous isoforms of phospholipase proteins expressed in mammals are 19 different phospholipase A2's (PLA2s), classified functionally as either secretory, calcium dependent, or calcium independent, 11 isozymes belonging to three structural groups of PLC, and 3 PLD gene products. Many of these phospholipases have been identified in selected brain regions. Under normal conditions, these enzymes regulate the turnover of free fatty acids (FFAs) in membrane phospholipids affecting membrane stability, fluidity, and transport processes. The measurement of free fatty acids thus provides a convenient method to follow phospholipase activity and their regulation. Phospholipase activity is also responsible for the generation of an extensive list of intracellular messengers including arachidonic acid metabolites. Phospholipases are regulated by many factors including selective phosphorylation, intracellular calcium and pH. However, under abnormal conditions, excessive phospholipase activation, along with a decreased ability to resynthesize membrane phospholipids, can lead to the generation of free radicals, excitotoxicity, mitochondrial dysfunction, and apoptosis/necrosis. This review evaluates the critical contribution of the various phospholipases to brain injury following ischemia and trauma and in neurodegenerative diseases.

Prostaglandin E2 production in astrocytes: regulation by cytokines, extracellular ATP, and oxidative agents

Upregulation and activation of phospholipases A2 (PLA2) and cyclooxygenases (COX) leading to prostaglandin E2(PGE2) production have been implicated in a number of neurodegenerative diseases. In this study, we investigated PGE2 production in primary rat astrocytes in response to agents that activate PLA2 including pro-inflammatory cytokines (IL-1beta, TNFalpha and IFNgamma), the P2 nucleotide receptor agonist ATP, and oxidants (H2O2 and menadione). Exposure of astrocytes to cytokines resulted in a time-dependent increase in PGE2 production that was marked by increased expression of secretory sPLA2 and COX-2, but not COX-1 and cytosolic cPLA2. Although astrocytes responded to ATP or phorbol ester (PMA) with increased cPLA2 phosphorylation and arachidonic acid release, ATP or PMA only caused a small increase in levels of PGE2. However, when astrocytes were first treated with cytokines, further exposure to ATP or PMA, but not H2O2 or menadione, markedly increased PGE2 production. These results suggest that ATP release during neuronal excitation or injury can enhance the inflammatory effects of cytokines on PGE2 production and may contribute to chronic inflammation seen in Alzheimer's disease.