Abstract
Amyloid accumulation in the brain of Alzheimer’s patients results from altered processing of the 39- to 43-amino acid amyloid β protein (Aβ). The mechanisms for the elevated amyloid (Aβ1–42) are considered to be over-expression of the amyloid precursor protein (APP), enhanced cleavage of APP to Aβ, and decreased clearance of Aβ from the central nervous system (CNS). We report herein studies of Aβ stimulated effects on endothelial cells. We observe an interesting and as yet unprecedented feedback effect involving Aβ1–42 fibril-induced synthesis of APP by Western blot analysis in the endothelial cell line Hep-1. We further observe an increase in the expression of Aβ1–40 by flow cytometry and fluorescence microscopy. This phenomenon is reproducible for cultures grown both in the presence and absence of serum. In the former case, flow cytometry reveals that Aβ1–40 accumulation is less pronounced than under serum-free conditions. Immunofluorescence staining further corroborates these observations. Cellular responses to fibrillar Aβ1–42 treatment involving eNOS upregulation and increased autophagy are also reported.
Highlights
Alzheimer’s disease (AD) is characterized by neuronal degeneration and accumulation of senile plaques, which are composed of amyloid-b (Ab) peptides predominantly consisting of 40 and 42 amino acids [1,2]
amyloid precursor protein (APP) Upregulation by Fibrillar Ab1–42 Ab1–42 fibrils were prepared from synthetic Ab1–42 peptides and morphologically characterized by TEM (Fig. 1A)
It was possible to discriminate between newly synthesized amyloids and the Ab1–42 used to treat Hep-1 cells by using antibodies that are specific for Ab1–40, which only detects low molecular weight Ab1–40, but not fibrils
Summary
Alzheimer’s disease (AD) is characterized by neuronal degeneration and accumulation of senile plaques, which are composed of amyloid-b (Ab) peptides predominantly consisting of 40 and 42 amino acids [1,2]. Postmortem analyses of AD subjects reveal that amyloid plaques in the brain suffuse vascular cells in addition to the parenchymal. The implications of this vascular infiltration for AD has been less well studied than the parenchymal Ab, but has generated considerable interest with studies that b-amyloid fibrils accumulate in small arteries, arterioles and capillaries of the brain [6,7,8]. Cerebrovascular amyloid toxicity generally manifests itself in the breach of the blood-brain-barrier and enhanced inflammation in the cerebrovasculature [9,10]. Two mechanisms that have been proposed involve: (1) The production of excess superoxide by amyloid-b induced oxidative stress [12,13] and (2) the formation of amyloid aggregates whose resistance to protease degradation turns them into cellular ‘‘tombstones’’ that impair blood flow and cellular function [14,15]
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