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

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.