Enrichment of cholesterol in microdissected Alzheimer’s disease senile plaques as assessed by mass spectrometry

Laboratoire de Neuropathologie Escourolle, Hôpital de la Salpêtrière, AP-HP Paris, France.
The Journal of Lipid Research (Impact Factor: 4.42). 09/2009; 51(3):598-605. DOI: 10.1194/jlr.M001859
Source: PubMed


Extensive knowledge of the protein components of the senile plaques, one of the hallmark lesions of Alzheimer's disease, has been acquired over the years, but their lipid composition remains poorly known. Evidence suggests that cholesterol contributes to the pathogenesis of Alzheimer's disease. However, its presence within senile plaques has never been ascertained with analytic methods. Senile plaques were microdissected from sections of the isocortex in three Braak VI Alzheimer's disease cases and compared with a similar number of samples from the adjoining neuropil, free of amyloid-beta peptide (A beta) deposit. Two cases were apo epsilon 4/apo epsilon 3, and one case was apo epsilon 3/apoepsilon3. A known quantity of (13)C-labeled cholesterol was added to the samples as a standard. After hexane extraction, cholesterol content was analyzed by liquid chromatography coupled with electrospray ionization mass spectrometry. The mean concentration of free cholesterol was 4.25 +/- 0.1 attomoles/microm(3) in the senile plaques and 2.2 +/- 0.49 attomoles/microm(3) in the neuropil (t = 4.41, P < 0.0009). The quantity of free cholesterol per senile plaque (67 +/- 16 femtomol) is similar to the published quantity of A beta peptide. The highly significant increase in the cholesterol concentration, associated with the increased risk of Alzheimer's disease linked to the apo epsilon 4 allele, suggests new pathogenetic mechanisms.

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    • "Niemann– Pick disease type C results from an inherited defect in proteins involved in neuronal cholesterol homeostasis and extrusion (Lange et al., 2000; S evin et al., 2007). Alzheimer's disease, which affects neurons of the parahippocampal region and neocortex, has been associated with excessive levels of cholesterol (Simons et al., 1998; Puglielli et al., 2003; Panchal et al., 2010; Di Paolo & Kim, 2011). "
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    ABSTRACT: Elevations in neuronal cholesterol have been associated with several degenerative diseases. An enhanced excitability and synchronous firing in surviving neurons are among the sequels of neuronal death in these diseases and also in some epileptic syndromes. Here, we attempted to increase neuronal cholesterol levels, using a short hairpin RNA (shRNA) to suppress expression of the enzyme CYP46A1. This protein hydroxylates cholesterol and so facilitates trans-membrane extrusion. A sh-RNA CYP46A1construction coupled to an adeno-associated virus (AAV5) was injected focally and unilaterally into mouse hippocampus. It was selectively expressed first in neurons of the CA3a region. Cytoplasmic and membrane cholesterol increased, neuronal soma volume increased and then decreased before pyramidal cells died. As CA3a pyramidal cells died, inter-ictal EEG events occurred during exploration and non-REM sleep. With time, neuronal death spread to involve pyramidal cells and interneurons of the CA1 region. CA1 neuronal death was correlated with a delayed local expression of phosphorylated tau. Astrocytes were activated throughout the hippocampus and microglial activation was specific to regions of neuronal death. CA1 neuronal death was correlated with distinct aberrant EEG activity. During exploratory behaviour and rapid eye movement sleep, EEG oscillations at 7-10 Hz (theta) could accelerate to 14-21 Hz (beta) waves. They were accompanied by low amplitude, high-frequency oscillations of peak power at ~300Hz and a range of 250-350 Hz. While episodes of EEG acceleration were not correlated with changes in exploratory behaviour, they were followed in some animals by structured seizure-like discharges. These data strengthen links between increased cholesterol, neuronal sclerosis and epileptic behavior. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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    • "Laser microdissection provides a valuable link between these two approaches. It gives new insights into cellular mechanisms, genetic disorders , tumor biomarker identification patienttailored therapy [13], and even extensive knowledge of the lipid composition which contributes to the pathogenesis of Alzheimer's disease [14] (Figure 6). "
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    • "Age-related changes in membrane composition and/or physical properties may facilitate an increased cellular susceptibility to Ab cytotoxicity. For example, both enhanced cellular cholesterol content (Wood et al., 2002; Cutler et al., 2004; Panchal et al., 2010) and oxidative damage (Chen and Yu, 1994; Choe et al., 1995) are associated with aging, decreased fluidity of membranes, and AD. Oxidative damage of polyunsaturated fatty acids, in general, increase lipid bilayer rigidity as a result of increased steric hindrance restricting the movement of lipid acyl chains (Choe et al., 1995; Choi and Yu, 1995). "
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    ABSTRACT: There are a vast number of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), associated with the rearrangement of specific proteins to non-native conformations that promotes aggregation and deposition within tissues and/or cellular compartments. These diseases are commonly classified as protein-misfolding or amyloid diseases. The interaction of these proteins with liquid/surface interfaces is a fundamental phenomenon with potential implications for protein-misfolding diseases. Kinetic and thermodynamic studies indicate that significant conformational changes can be induced in proteins encountering surfaces, which can play a critical role in nucleating aggregate formation or stabilizing specific aggregation states. Surfaces of particular interest in neurodegenerative diseases are cellular and subcellular membranes that are predominately comprised of lipid components. The two-dimensional liquid environments provided by lipid bilayers can profoundly alter protein structure and dynamics by both specific and non-specific interactions. Importantly for misfolding diseases, these bilayer properties can not only modulate protein conformation, but also exert influence on aggregation state. A detailed understanding of the influence of (sub)cellular surfaces in driving protein aggregation and/or stabilizing specific aggregate forms could provide new insights into toxic mechanisms associated with these diseases. Here, we review the influence of surfaces in driving and stabilizing protein aggregation with a specific emphasis on lipid membranes.
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