AB and ApoE in animal models of Alzheimer's disease

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Alzheimer disease (AD) is a dementia affecting over 20 million people worldwide. In the USA, AD represents the fourth greatest cause of death in the elderly. Genetic, chemical and morphological studies strongly suggest a seminal role for amyloid-beta (Abeta) peptides in the pathogenesis of AD. The successful creation of beta-amyloid precursor protein (betaAPP), presenilin 1 (PS1), apolipoprotein E (ApoE) and transforming growth factor-beta1 (TGF-beta1) transgenic (tg) mice has provided an opportunity to investigate the pathophysiology of Abeta amyloidogenesis. Tg mice are of paramount importance in the testing of AD therapeutic agents such as anti-Abeta aggregating compounds, secretase inhibitors and anti-Abeta vaccination. Despite the wide adoption of tg mice models in the search for effective AD treatments, a rigorous chemical characterization and quantification study of the Abeta produced by the genetically and phenotypically diverse tg mice strains has not been attempted. It is hypothesized that: 1) due to differences in lifespan, phylogenetic distance, functional organization and distress conditions of the brain significant quantitative and qualitative differences will be found in Abeta structure and metabolism between humans and mice; 2) failure in the clearance of Abeta from the brain to the blood in tg mice causes the progressive accumulation of both soluble and insoluble Abeta in the brain; 3) the partial loss of some of amino acid domains of ApoE, in an environment rich in proteolytic enzymes such as the AD brain, results in structural changes which would affect the affinity of ApoE for Abeta and the clearance of the complexes. The research plan will characterize the chemical structure and quantify Abeta peptides in the tg mice: APP23, 2576, PDAPP, PS1, TGF-beta1 and the double tg PS1/betaAPP and TGF-beta1/betaAPP. The ApoE associated to Abeta will be quantified and characterized in the tg mice brains. In addition, the effects of Abeta vaccination in the doubly PS1/betaAPP tg mice will be evaluated in terms of the soluble and insoluble Abeta40 and Abeta42 load. To achieve these goals the water-soluble and water-insoluble Abeta and ApoE peptides will be isolated from the tg mice by fast- and high- performance liquid column chromatographies from either brain homogenates or plasma. All purified molecules and derived enzymatic peptides will be chemically characterized by mass spectrometry, amino acid analysis and amino acid sequencing. Quantification of peptides will be performed by Western blot or by sensitive europium immunoassay. These significant characterizations and comparisons will provide important insights in evolutionary, physiological and pathological terms that will be useful for understanding AD and for the interpretation of mitigating treatments in tg mouse models.