A quantitative assessment of glycolipid and protein associated with paired helical filament preparations from Alzheimer's diseased brain

Abstract

Protease resistant paired helical filaments (prcPHF) can be isolated from the brains of Alzheimer's diseased patients. A second type of PHF, A68 PHF, may be extracted in soluble form from brain homogenate and induced to form filaments in vitro. Here we use a variety of analytical techniques to assess the protein, carbohydrate and fatty acid composition of prcPHF and A68 PHF. High-field ¹H NMR of both PHF preparations display similar fatty acid and carbohydrate proton resonances, consistent with the presence of a structurally similar glycolipid. Carbohydrate analysis showed that both preparations contained greater than 82% less than 12% C16:1 was significantly lower in A68 PHF than in prcPHF, both preparations contained otherwise similar fatty acid profiles with the most abundant lipid component being oleic acid (C18:1, 29.3 ± 9.0%) followed by palmitic (C16:0, 28.5 ± 5.6%) 17.6 ± 7.5%) preparations revealed a profile reasonably consistent with that previously determined for PHF-tau but significantly higher in glycine and lower in lysine than would be predicted from the cDNA sequence. On a weight per cent basis, protein accounted for about 51% A68 PHF samples but only about 10% Carbohydrate and fatty acid accounted for about 39% A68 PHF samples but 74% preparations showed strong correlations between the total amount of tau protein and fatty acid. These results suggest that a glycolipid component forms an integral part of the PHF structure.