P4‐146: New aspects of membrane breakdown in Alzheimer's disease brain

Recently, the critical role of the cytosolic calcium dependent phospholipase PLA2 (GIVA-PLA2) in memory deficits of an Alzheimer's disease (AD) mouse model was demonstrated, whereas the mechanisms of neuronal injuries in human brain are partly unknown. Combined neurochemical, immunohistochemical and mRNAPCR (cPLA2) studies were performed on pm brain tissue of AD patients and age-matched non-demented controls. Neuropathologic assessment of AD was performed using CERAD, Braak scores and NIA-Reagan -Institute criteria. ALZAS gene was indentified using a procedure called “disease gene discovery by positional searching”. ALZAS protein contains the sequence of Amyloid beta (Aβ), the APP transmembrane helix and a c-terminal unique sequence which is encoded by intron 17 sequences in the APP gene. Lipid extraction was performed according to the method of Folch and the TLC/FID system, which performs quantitative analysis by detection of zones separated by a CHROMAROD thin layer using a GC-type hydrogen flame ionisation detector. Immunohistochemical Staining: In pm AD brain ALZAS was located intracellularly in neurons and in the inner membrane of cerebral vessels. The intraneuronal and capillary immunostaining of ALZAS was significantly correlated with Braak stages and NIA-Reagan classification. Nine cases (30%) were ALZAS negative, neuronal+/capillary- staining was found in one individual (3.3%), neuronal+/capillary+ALZAS staining in 20 (66.7%) cases. The p38 MAPK immunostaining also correlated with Braak stages and activated cPLA2. Phospholipids: AD frontal cortex (gray matter) showed significant decrease in protein content (-33%) compared to controls and depletion of major phospholipids. Total loss of sphingolipids was about 40% wet weight. There was a significant decrease in phosphatidylethanolamine (42%), phosphatidylinositol (61.9%), in phosphatidylserine (42.7%), in phosphatidylcholine (43%), and of sphingomyelin (44%), whereas galactocerebrosides were reduced to a lesser degree. Cholesterol, when expressed per mg/protein, was unchanged in AD frontal cortex. Therefore catabolic products of phospholipids hydrolyzed by phospholipases and lysophospholipases, increased by 100% in human AD brain, may reflect accelerated breakdown of brain cell membranes. We report the novel observation that ALZAS expression may contribute to the activation of the p38MAPK/cPLA2 pathway resulting in membrane hydrolysis and massive neuronal loss in AD.