Metal Ions, pH, and Cholesterol Regulate the Interactions of Alzheimer's Disease Amyloid-β Peptide with Membrane Lipid

Abstract

The interaction of A␤ peptides with the lipid matrix of neuronal cell membranes plays an important role in the pathogenesis of Alzheimer's disease. By using EPR and CD spectroscopy, we found that in the presence of Cu 2؉ or Zn 2؉ , pH, cholesterol, and the length of the peptide chain influenced the interaction of these peptides with lipid bilayers. In the presence of Zn 2؉ , A␤40 and A␤42 both inserted into the bilayer over the pH range 5.5-7.5, as did A␤42 in the presence of Cu 2؉ . However, A␤40 only penetrated the lipid bilayer in the presence of Cu 2؉ at pH 5.5-6.5; at higher pH there was a change in the Cu 2؉ coordination sphere that inhibited membrane insertion. In the absence of the metals, insertion of both peptides only occurred at pH < 5.5. Raising cholesterol to 0.2 mol fraction of the total lipid inhibited insertion of both peptides under all conditions investigated. Membrane insertion was accompanied by the formation of ␣-helical structures. The nature of these structures was the same irrespective of the conditions used, indicating a single low energy structure for A␤ in membranes. Peptides that did not insert into the membrane formed ␤-sheet structures on the surface of the lipid. Alzheimer's disease (AD)1 is a neurodegenerative disorder affecting the memory and cognitive functions of the brain. A characteristic central nervous system histologic marker in patients with AD is accumulation of the 39 -43-residue amyloid ␤-peptide (A␤) in morphologically heterogeneous neuritic plaques and cerebrovascular deposits (1). A␤ is derived from a proteolytic cleavage of the ␤-amyloid precursor protein (APP). This is a highly conserved and widely expressed integral membrane protein with a single membrane-spanning domain. Possible mechanisms of A␤ toxicity include formation of plasma membrane channels (2) and generation of H 2 O 2 through Cu 2ϩ reduction by the peptide, which make cells more responsive to oxidative stress (3). The mechanisms may be related because reactive oxygen species may cause lipid peroxidation that leads to alterations in the order and fluidity of the bilayer lipids (4) and may also lead to an increase of membrane permeability. The common change observed in cell membrane permeability is an increased intracellular calcium level (5, 6) that could occur either indirectly through A␤ modulating an existing Ca 2ϩ channel or directly through cation-selective channels formed by A␤.The supramolecular structure of membrane-associated A␤, either as an ion channel or a fusogen, is unknown, although Durell et al. (7) have developed theoretical models for the structure of ion channels formed by the membrane-bound A␤40. Recently, Bhatia et al. (8) and Lin et al. (9) used atomic force microscopy, laser confocal microscopy, and fluorescent calcium imaging to examine in real time the acute effects of fresh and globular A␤40, A␤42, and A␤25-35 on cultured endothelial cells. A␤ peptides caused morphological changes within minutes after treatment and led to eventual cellular degeneration. Cellular morphol...

Promotion of Oxidative Lipid Membrane Damage by Amyloid β Proteins

“…Technical difficulties currently preclude verifying this identity by collecting an infrared spectrum of these intermediates or soluble oligomers. It should be noted that prior studies describing metal ion dependencies for Aβ protein association with membranes were performed with lipids that are relatively resistant to oxidative damage (51).…”

Using model membranes for the study of amyloid beta:lipid interactions and neurotoxicity

“…Ab-40 only penetrated the membrane in the presence of Cu II at a narrower pH range of 5.5-6.5. As before, membrane insertion was accompanied with an a-helix peptide conformation, un-inserted peptides formed b-sheet structures (Curtain et al, 2003).…”

“…Model membrane research has advanced our understanding of the role of lipids in the etiopathogenesis of AD (Curtain et al, 2003;Kalvodova et al, 2005;Rojo et al, 2006). In this review, we consider mainly amyloidogenic membrane-associated proteins, that is, membrane-associated proteins implicated directly in the amyloidogenic pathway.…”

“…An increase in cholesterol concentration inhibited peptide insertion into the membrane and the peptides that did not insert, produced b-sheet structures (Curtain et al, 2003). Bokvist et al (2004) presented a model for Ab-40 interactions with model membranes prepared as multilamellar vesicles from two lipids.…”

“…More recently, changes in cholesterol concentration and homeostasis have been linked to AD (Koudinova et al, 2003;Lesdema and Dotti, 2006;Shobab et al, 2005), although the biochemical mechanisms underlying its impact on the onset and progress of the pathology remain largely unknown. The use of model cell membrane systems have greatly increased our understanding of some of the biochemical processes underlining the development and progress of AD (Curtain et al, 2003;Kalvodova et al, 2005;Kojro et al, 2001). In this review, we discuss the current and possible future applications of model membranes for understanding amyloid beta-induced neurotoxicity and degeneration, focusing on the modulating effect of membrane lipid composition.…”