Abstract
An early event in Alzheimer’s disease (AD) pathogenesis is the formation of extracellular aggregates of amyloid-β peptide (Aβ), thought to be initiated by a prion-like seeding mechanism. However, the molecular nature and location of the Aβ seeds remain rather elusive. Active Aβ seeds are found in crude homogenates of amyloid-laden brains and in the soluble fraction thereof. To analyze the seeding activity of the pellet fraction, we have either separated or directly immunoisolated membranes from such homogenates. Here, we found considerable Aβ seeding activity associated with membranes in the absence of detectable amyloid fibrils. We also found that Aβ seeds on mitochondrial or associated membranes efficiently induced Aβ aggregation in vitro and seed β-amyloidosis in vivo. Aβ seeds at intracellular membranes may contribute to the spreading of Aβ aggregation along neuronal pathways and to the induction of intracellular pathologies downstream of Aβ.
Highlights
An early event in Alzheimer’s disease (AD) pathogenesis is the formation of extracellular aggregates of amyloid-β peptide (Aβ), thought to be initiated by a prion-like seeding mechanism
We used subcellular fractionation to isolate membrane fractions from Aβplaque bearing amyloid precursor protein (APP) transgenic brain extracts. From both in vitro and in vivo assays our results demonstrate highly potent Aβseeds associated with intracellular membranes including mitochondrial and associated membrane structures
To assess the Aβseeding activity at intracellular membranes we performed first subcellular fractionation and intracellular organelle purification based on established protocols (Supplementary Fig. 1) from aggregated Aβ-laden brain of aged APP23 mice[2,19]
Summary
An early event in Alzheimer’s disease (AD) pathogenesis is the formation of extracellular aggregates of amyloid-β peptide (Aβ), thought to be initiated by a prion-like seeding mechanism. Active Aβ seeds are found in crude homogenates of amyloid-laden brains and in the soluble fraction thereof. Intensively studied, the mechanisms underlying the induction and spreading of the Aβpathology in brain remain unclear, but are thought to include a prion-like seeding process[1]. In vivo experiments have demonstrated that β-amyloidosis can be induced in brains of young β-amyloid precursor protein (APP) transgenic mice by intracerebral injection of crude homogenates of aggregated Aβ-laden brains[2,3]. Follow-up studies revealed Aβseeding activities in both the 100,000 ×g PBS-soluble fraction and the pellet fraction which includes amyloid fibrils and membrane vesicles[3]. We used subcellular fractionation to isolate membrane fractions from Aβplaque bearing APP transgenic brain extracts From both in vitro and in vivo assays our results demonstrate highly potent Aβseeds associated with intracellular membranes including mitochondrial and associated membrane structures.
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