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Keywords:

  • phospholipase A2;
  • inflammation;
  • Alzheimer's disease;
  • PDAPP;
  • ischemia;
  • axotomy;
  • astrocytes;
  • microglia

Abstract

Many recent studies have emphasized the deleterious role of inflammation in CNS injury. Increases in free fatty acids, eicosanoids, and products of lipid peroxidation are known to occur in various conditions of acute and chronic CNS injury, including cerebral ischemia, traumatic brain injury, and Alzheimer's disease. Although an inflammatory response can be induced by many different means, phospholipases, such as cytosolic phospholipase A2 (cPLA2), may play an important role in the production of inflammatory mediators and in the production of other potential second messengers. cPLA2 hydrolyzes membrane phospholipids and its activity liberates free fatty acids leading directly to the production of eicosanoids. We investigated the cellular localization of cytosolic phospholipase A2 in the CNS following: (1) focal and global cerebral ischemia, (2) facial nerve axotomy, (3) human cases of Alzheimer's disease, (4) transgenic mice overexpressing mutant superoxide dismutase, a mouse model of amyotrophic lateral sclerosis, and (5) transgenic mice overexpressing mutant amyloid precursor protein, which exhibits age-related amyloid deposition characteristic of Alzheimer's disease. We show that in every condition evaluated, cytosolic phospholipase A2 is present in reactive glial cells within the precise region of neuron loss. In conditions where neurons did not degenerate or are protected from death, cytosolic phospholipase A2 is not observed. Both astrocytes and microglial cells are immunoreactive for cytosolic phospholipase A2 following injury, with astrocytes being the most consistent cell type expressing cytosolic phospholipase A2. The presence of cytosolic phospholipase A2 does not merely overlap with reactive astroglia, as reactive astrocytes were observed that did not exhibit cytosolic phospholipase A2 immunoreactivity. In most conditions evaluated, inflammatory processes have been postulated to play a pivotal role and may even participate in neuronal cell death. These results suggest that cytosolic phospholipase A2 may prove an attractive therapeutic target for neurodegeneration. GLIA 27:110–128, 1999. © 1999 Wiley-Liss, Inc.