Reactive Glia Express Cytosolic Phospholipase A2 After Transient Global Forebrain Ischemia in the Rat

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Abstract
Background and Purpose Phospholipid breakdown has been reported to be an early event in the brain after global cerebral ischemia. Our earlier observations showing the localization of cytosolic phospholipase A 2 (cPLA 2 ) to astrocytes in aged human brains and the intense glial activation observed after global forebrain ischemia prompted us to investigate the cellular localization of cPLA 2 in the rat brain subjected to global ischemia. Methods Immunohistochemistry was performed in sections through the dorsal hippocampus in rats subjected to 30 minutes of four-vessel occlusion. PLA 2 was localized with the use of a highly selective antiserum. Double immunofluorescent localization was performed to colocalize cPLA 2 with various glial cell types. cPLA 2 levels were also measured by enzymatic assay and Western blot analysis. Results A marked induction of cPLA 2 was observed in activated microglia and astrocytes in the CA1 hippocampal region at 72 hours after ischemia. Only a subset of astrocytes and microglia were immunoreactive for cPLA 2 . Twenty-four hours after ischemia, numerous cPLA 2 immunoreactive astrocytes were observed. Western blot analysis of hippocampal homogenates at 72 hours after ischemia showed induction of a 100-kD band that comigrated with purified human cPLA 2 , and a threefold induction in cPLA 2 activity was demonstrated by enzymatic assay. Conclusions These results indicate that both reactive astrocytes and microglia contain elevated levels of cPLA 2 . Induction of cPLA 2 was confined to areas of neurodegeneration and likely precedes its onset. The results suggest that reactive glia may play a role in the pathophysiology of delayed neuronal death after transient global forebrain ischemia.