Cellular Membrane Composition Defines Aβ-Lipid Interactions

Abstract

Alzheimer's disease pathology has demonstrated amyloid plaque formation associated with plasma membranes and the presence of intracellular amyloid-␤ (A␤) accumulation in specific vesicular compartments. This suggests that lipid composition in different compartments may play a role in A␤ aggregation. To test this hypothesis, we have isolated cellular membranes from human brain to evaluate A␤40/42-lipid interactions. Plasma, endosomal, lysosomal, and Golgi membranes were isolated using sucrose gradients. Electron microscopy demonstrated that A␤ fibrillogenesis is accelerated in the presence of plasma and endosomal and lysosomal membranes with plasma membranes inducing an enhanced surface organization. Alternatively, interaction of A␤ with Golgi membranes fails to progress to fibril formation, suggesting that A␤-Golgi head group interaction stabilizes A␤. Fluorescence spectroscopy using the environment-sensitive probes 1,6-diphenyl-1,3,5-hexatriene, laurdan, N-⑀-dansyl-L-lysine, and merocyanine 540 demonstrated variations in the inherent lipid properties at the level of the fatty acyl chains, glycerol backbone, and head groups, respectively. Addition of A␤40/42 to the plasma and endosomal and lysosomal membranes decreases the fluidity not only of the fatty acyl chains but also the head group space, consistent with A␤ insertion into the bilayer. In contrast, the Golgi bilayer fluidity is increased by A␤40/42 binding which appears to result from lipid head group interactions and the production of interfacial packing defects.Alzheimer's disease is an age-related disorder that is characterized by progressive cognitive decline and neurodegeneration (1, 2). Pathological examinations have demonstrated that one of the key features is the presence of amyloid plaques associated with neuritic degeneration. Senile plaques are composed predominantly of a 40 -42-residue peptide, amyloid-␤ (A␤40/42). The development of Alzheimer's disease pathology has been proposed to be the result of A␤ 1 deposition in association with membrane structures. Recent studies have demonstrated that plaque formation may be initiated in a plasma membrane form (3, 4) and that A␤ deposition in aged dogs is associated with the extracellular leaflet of the plasma membrane (5). Furthermore, the intracellular accumulation of A␤ in lysosomal or late endosomal vesicles in vitro suggest that these compartments may be involved in neurotoxicity (6 -9). A␤ is generated from the proteolytic cleavage of the amyloid precursor protein in the endoplasmic reticulum to generate A␤42 and the trans-Golgi network to generate A␤40 (10 -14). It has also been suggested that A␤40/42 may also be generated at the plasma membrane surface. The presence of A␤ in distinct compartments and the proposal that lipid association is important for both neurotoxicity and fibrillogenesis suggest that the lipid composition and characteristics of these compartments may play vital roles in the disease process. Previous studies (15,16) have demonstrated accumulation of A␤42 in lysosomal compartm...

Promotion of Oxidative Lipid Membrane Damage by Amyloid β Proteins

“…Lyophilized Aβ40 and Aβ42 of greater than 95% purity were obtained from American Peptide (Sunnyvale, CA) or rPeptide (Athens, GA). H13A and H14A variants of Aβ42 were obtained from rPeptide, while Aβ 1-28 , Aβ [22][23][24][25][26][27][28][29][30][31][32][33][34][35] , α-MSH, and neurotensin were obtained from American Peptide. The Aβ42 mutant M35V (21) as well as Aβ42 with an oxidized methionine (M35 OX ) (20) were kindly provided by Dr. Kevin Barnham.…”

“…When DA was used as the oxidizable substrate instead of SAPC, it was also oxidized extensively by Cu(II) and H 2 O 2 over 120 min ( Figure 4C). Aβ42, Aβ 1-28 , and Aβ [22][23][24][25][26][27][28][29][30][31][32][33][34][35] inhibited DA oxidation but not the control peptides α-MSH and neurotensin. We conclude that Aβ peptides specifically inhibit oxidation of substrates such as SAPC and DA under these conditions.…”

“…by Aβ proteins mediates neurotoxicity (20)(21)(22), that merely altering membrane lipid composition protects PC12 cells from Aβ-mediated toxicity (23), and that plasma membranes from human brain are particularly effective at accelerating Aβ fibrillogenesis (24). Thus, it is important to understand the nature of the interaction between Aβ proteins and lipid membranes, particularly membranes subject to oxidative damage.…”

Cholesterol is required for Leishmania donovani infection: implications in leishmaniasis

“…This suggests that the assay is specific for cholesterol in this system and rules out any possible artifact. Moreover, this assay has been previously used for detection of cellular cholesterol by a number of investigators [22][23][24][25]. Acute cholesterol depletion of macrophages resulted in an ∼40% reduction of total cellular cholesterol when 10 mM M␤CD was used for 30 min (Fig.…”

Small molecule inhibitors of Aβ‐aggregation and neurotoxicity

“…In contrast, acidic phospholipids induce b-structured aggregates and fibers [McLaurin and Chakrabartty, 1996;Terzi et al, 1995;Waschuk et al, 2001]. PEGylated phospholipid nanomicelles interact with Ab thereby mitigating b-structural transitions, aggregation, and subsequent neurotoxicity [Pai et al, 2006].…”