How amyloid precursor protein protects itself from cleavage

Ginsenoside Rb1 improves learning and memory ability through its anti-inflammatory effect in Aβ1-40 induced Alzheimer's disease of rats

This study measured amyloid-beta (Aβ), interleukin-1 beta (IL-1β), and glial fibrillary acidic protein (GFAP) expression in the hippocampus of Alzheimer's disease (AD) rat models to elucidate the mechanism of anti-inflammatory effect of ginsenoside Rb1 in AD. Eighty-four male Wistar rats were randomly divided into seven groups, learning and memory impairment was induced by Ap1-40 to establish AD rat model. Learning and memory abilities were assessed by a Morris water maze experiment. Immunohistochemistry, RT-PCR and Western blotting were used to measure IL-1β, Aβ and GFAP expression. Nissl staining and methenamine silver staining were performed to observe the morphology of neurons and Nissl Body, and to detect amyloid protein particle deposition. ELISA and LC-MS/MS were applied to detect Aβ1-42 and byproducts of S/MS were applied to IAT, VIV, ITL, VVIA, TVI, and VIT). Ginsenoside Rb1 administration could relieve cognitive deficit, and decrease expressions of IL-1β, Aβ, and GFAP. Neurons and Nissl Body were improved and plaques deposition was decreased obviously after treatment of ginsenoside Rb1, especially in medium dose of ginsenoside Rb1. Ginsenoside Rb1 can increase productions of Aβ1-42 and byproducts of β- and γ-secretase. Collected evidence supported that ginsenoside Rb1 improves learning and memory in AD rat by altering the amyloidogenic process of APP into non-amyloidogenic process, to exert its anti-inflammatory function.

Mutations of beta-amyloid precursor protein alter the consequence of Alzheimer's disease pathogenesis

Alzheimer’s disease is pathologically defined by accumulation of extracellular amyloid-β (Aβ). Approximately 25 mutations in β-amyloid precursor protein (APP) are pathogenic and cause autosomal dominant Alzheimer’s disease. To date, the mechanism underlying the effect of APP mutation on Aβ generation is unclear. Therefore, investigating the mechanism of APP mutation on Alzheimer’s disease may help understanding of disease pathogenesis. Thus, APP mutations (A673T, A673V, E682K, E693G, and E693Q) were transiently co-transfected into human embryonic kidney cells. Western blot assay was used to detect expression levels of APP, beta-secretase 1, and presenilin 1 in cells. Enzyme-linked immunosorbent assay was performed to determine Aβ_1–40 and Aβ_1–42 levels. Liquid chromatography-tandem mass chromatography was used to examine VVIAT, FLF, ITL, VIV, IAT, VIT, TVI, and VVIA peptide levels. Immunofluorescence staining was performed to measure APP and early endosome antigen 1 immunoreactivity. Our results show that the protective A673T mutation decreases Aβ₄₂/Aβ₄₀ rate by downregulating IAT and upregulating VVIA levels. Pathogenic A673V, E682K, and E693Q mutations promote Aβ₄₂/Aβ₄₀ rate by increasing levels of CTF99, Aβ₄₂, Aβ₄₀, and IAT, and decreasing VVIA levels. Pathogenic E693G mutation shows no significant change in Aβ₄₂/Aβ₄₀ ratio because of inhibition of γ-secretase activity. APP mutations can change location from the cell surface to early endosomes. Our findings confirm that certain APP mutations accelerate Aβ generation by affecting the long Aβ cleavage pathway and increasing Aβ_42/40 rate, thereby resulting in Alzheimer’s disease.