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

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Abstract

Background

The enzyme cytosolic phospholipase A ₂alpha (cPLA ₂α) has been implicated in the progression of cerebral injury following ischemia and reperfusion. Previous studies in rodents suggest that cPLA ₂α enhances delayed injury extension and disruption of the blood brain barrier many hours after reperfusion. In this study we investigated the role of cPLA ₂α in early ischemic cerebral injury.

Methods

Middle cerebral artery occlusion (MCAO) was performed on cPLA ₂α ^+/+and cPLA ₂α ^-/-mice for 2 hours followed by 0, 2, or 6 hours of reperfusion. The levels of cPLA ₂α, cyclooxygenase-2, neuronal morphology and reactive oxygen species in the ischemic and contralateral hemispheres were evaluated by light and fluorescent microscopy. PGE ₂content 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 cPLA ₂α protein increased by 2-fold immediately after MCAO and returned to pre-MCAO levels after 2 hours reperfusion. Neuronal cyclooxygenase-2 induction and PGE ₂concentration were greater in cPLA ₂α ^+/+compared to cPLA ₂α ^-/-ischemic cortex. Neuronal swelling in ischemic regions was significantly greater in the cPLA ₂α ^+/+than in cPLA ₂α ^-/-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 cPLA ₂α ^+/+ischemic core than in cPLA ₂α ^-/-(+/+: 7.12 ± 1.2 fold vs. -/-: 3.1 ± 1.4 fold; P < 0.01). After 6 hours of reperfusion ischemic cortex of cPLA ₂α ^+/+, but not cPLA ₂α ^-/-, had disruption of neuron morphology and decreased PGE ₂content. Phosphorylation of the MAPKs-p38, ERK 1/2, and MEK 1/2-was significantly greater in cPLA ₂a ^+/+than in cPLA ₂α ^-/-ischemic cortex 6 hours after reperfusion.

Conclusions

These results indicate that cPLA ₂α modulates the earliest molecular and injury responses after cerebral ischemia and have implications for the potential clinical use of cPLA ₂α inhibitors.

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Victor L. Marcheselli, Song Hong, Walter Lukiw … (2003)

Ischemic stroke triggers lipid peroxidation and neuronal injury. Docosahexaenoic acid released from membrane phospholipids during brain ischemia is a major source of lipid peroxides. Leukocyte infiltration and pro-inflammatory gene expression also contribute to stroke damage. In this study using lipidomic analysis, we have identified stereospecific messengers from docosahexaenoate-oxygenation pathways in a mouse stroke model. Aspirin, widely used to prevent cerebrovascular disease, activates an additional pathway, which includes the 17R-resolvins. The newly discovered brain messenger 10,17S-docosatriene potently inhibited leukocyte infiltration, NFkappaB, and cyclooxygenase-2 induction in experimental stroke and elicited neuroprotection. In addition, in neural cells in culture, this lipid messenger also inhibited both interleukin 1-beta-induced NFkappaB activation and cyclooxygenase-2 expression. Thus, the specific novel bioactive docosanoids generated in vivo counteract leukocyte-mediated injury as well as pro-inflammatory gene induction. These results challenge the view that docosahexaenoate only participates in brain damage and demonstrate that this fatty acid is also the endogenous precursor to a neuroprotective signaling response to ischemia-reperfusion.

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Phospholipase A2 reduction ameliorates cognitive deficits in a mouse model of Alzheimer's disease

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Neuronal expression of familial Alzheimer's disease (AD)-mutant human amyloid precursor protein (hAPP) and hAPP-derived amyloid-β (Aβ) peptides causes synaptic dysfunction, inflammation, and abnormal cerebrovascular tone in transgenic mice. Fatty acids may be involved in these processes, but their contribution to AD pathogenesis is uncertain. A lipidomics approach to broadly profile fatty acids in brain tissues of hAPP mice revealed an increase in arachidonic acid and its metabolites, suggesting increased activity of the group IV isoform of phospholipase A2 (GIVA-PLA2). Levels of activated GIVA-PLA2 in the hippocampus were increased in AD patients and hAPP mice. Aβ caused a dose-dependent increase in GIVA-PLA2 phosphorylation in neuronal cultures. Inhibition of GIVA-PLA2 diminished Aβ-induced neurotoxicity. Genetic ablation or reduction of GIVA-PLA2 protected hAPP mice against Aβ-dependent deficits in learning and memory, behavioral alterations, and premature mortality. Inhibition of GIVA-PLA2 may be of benefit in the treatment and prevention of AD.

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Reduced fertility and postischaemic brain injury in mice deficient in cytosolic phospholipase A2.

M. Moskowitz, Michael O’Leary, Z. Huang … (1997)

Phospholipase A2 (PLA2) enzymes are critical regulators of prostaglandin and leukotriene synthesis and can directly modify the composition of cellular membranes. PLA2 enzymes release fatty acids and lysophospholipids, including the precursor of platelet-activating factor, PAF, from phospholipids. Free fatty acids, eicosanoids, lysophospholipids and PAF are potent regulators of inflammation, reproduction and neurotoxicity. The physiological roles of the various forms of PLA2 are not well defined. The cytosolic form, cPLA2, preferentially releases arachidonic acid from phospholipids and is regulated by changes in intracellular calcium concentration. We have now created 'knockout' (cPLA2-/-) mice that lack this enzyme, in order to evaluate its physiological importance. We find that cPLA2-/- mice develop normally, but that the females produce only small litters in which the pups are usually dead. Stimulated peritoneal macrophages from cPLA2-/- animals did not produce prostaglandin E2 or leukotriene B4 or C4. After transient middle cerebral artery occlusion, cPLA2-/- mice had smaller infarcts and developed less brain oedema and fewer neurological deficits. Thus cPLA2 is important for macrophage production of inflammatory mediators, fertility, and in the pathophysiology of neuronal death after transient focal cerebral ischaemia.

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Author and article information

Journal

Journal ID (nlm-ta): J Neuroinflammation

Title: Journal of Neuroinflammation

Publisher: BioMed Central

ISSN (Electronic): 1742-2094

Publication date Collection: 2010

Publication date (Electronic): 30 July 2010

Volume: 7

Page: 42

Affiliations

[1 ]The Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA

Article

Publisher ID: 1742-2094-7-42

DOI: 10.1186/1742-2094-7-42

PMC ID: 2923122

PubMed ID: 20673332

SO-VID: 807ef102-a624-4d35-976e-b113dbefe2d1

License:

This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.