Amyloid beta protein (A beta P) forms senile plaques in the cerebrocortical blood vessels and brain parenchyma of patients with Alzheimer’s disease (AD). The nonfamilial or sporadic AD (SAD), the most prevalent form of AD, has been correlated with an increased level of 40-residue A beta P (A beta P1-40).
However, very little is known about the role of A beta P1-40 in AD pathophysiology. We have examined the activity of A beta P1-40 reconstituted in phospholipid vesicles. A combined light fluorescence and atomic force microscope (AFM) was used to image the structure of reconstituted vesicles and 45Ca2+ uptake was used as an assay for calcium permeability across the vesicular membrane. Vesicles reconstituted with fresh and globular A beta P1-40 contain a significant amount of A0 beta P and exhibit strong immunofluorescence labeling with an antibody raised against the N-terminal domain of A beta P, suggesting the incorporation of A beta P1-40 peptide in the vesicular membrane. Vesicles reconstituted with A beta P1-40 exhibited a significant level of 45Ca2+ uptake.
The vesicular calcium level saturated over time, showing an important ion channel characteristic. The 45Ca2+ uptake was inhibited by (i) a monoclonal antibody raised against the N-terminal region of A beta P and (ii) Zn2+. However, a reducing agent (DTT) did not inhibit the 45Ca2+ uptake, indicating that the oxidation of A beta P or its surrounding lipid molecules is not directly involved in A beta P-mediated Ca2+ uptake.
These findings provide biochemical and structural evidence that fresh and globular A beta P1-40 forms calcium-permeable channels and thus may induce cellular toxicity by regulating the calcium homeostasis in nonfamilial or sporadic Alzheimer’s disease.
Source: Biochemistry 1999 Aug 24;38(34):11189-96
PMID: 10460176, UI: 99389583
(Neuroscience Research Institute, University of California at Santa Barbara 93106, USA. firstname.lastname@example.org)