Isotope-labeled amyloid-β does not transmit to the brain in a prion-like manner after peripheral administration
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ABSTRACT:
SUBMITTER: Dr. Mirjam Brackhan
PROVIDER: S-SCDT-EMBOR-2021-54405V1 | biostudies-other |
REPOSITORIES: biostudies-other
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Project description:Findings of early cerebral amyloid-β deposition in mice after peripheral injection of amyloid-β-containing brain extracts, and in humans following cadaveric human growth hormone treatment raised concerns that amyloid-β aggregates and possibly Alzheimer's disease may be transmissible between individuals. Yet, proof that Aβ actually reaches the brain from the peripheral injection site is lacking. Here, we use a proteomic approach combining stable isotope labeling of mammals and targeted mass spectrometry. Specifically, we generate 13 C-isotope-labeled brain extracts from mice expressing human amyloid-β and track 13 C-lysine-labeled amyloid-β after intraperitoneal administration into young amyloid precursor protein-transgenic mice. We detect injected amyloid-β in the liver and lymphoid tissues for up to 100 days. In contrast, injected 13 C-lysine-labeled amyloid-β is not detectable in the brain whereas the mice incorporate 13 C-lysine from the donor brain extracts into endogenous amyloid-β. Using a highly sensitive and specific proteomic approach, we demonstrate that amyloid-β does not reach the brain from the periphery. Our study argues against potential transmissibility of Alzheimer's disease while opening new avenues to uncover mechanisms of pathophysiological protein deposition.
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Project description:Abundant evidence suggests a central role for the amyloid-beta (A?) peptide in Alzheimer's disease (AD) pathogenesis. Production and clearance of different A? isoforms have been established as targets of proposed disease-modifying therapeutic treatments of AD. However, previous studies used multiple sequential purification steps to isolate the isoforms individually and quantitate them based on a common mid-domain peptide. We created a method to simultaneously purify A? isoforms and quantitate them by the specific C-terminal peptides in order to investigate A? isoform physiology in the central nervous system. By using standards generated from in vitro metabolic labeling, the relative quantitation of four peptides representing total amount of A? (A?-Total), A?38, A?40, and A?42 were achieved both in cell culture and in human cerebrospinal fluid (CSF). Standard curves for each isoform demonstrated good sensitivity with very low limits of detection and high accuracy. Because the assay does not require antibody development for each A? isoform peptide, significant improvements in the throughput and accuracy of isoform quantitation were achieved.
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Project description:BackgroundApoJ/clusterin is a multifunctional protein highly expressed in the brain. The implication of ApoJ in β-amyloid (Aβ) fibrillization and clearance in the context of Alzheimer's disease has been widely studied, although the source and concentration of ApoJ that promotes or inhibits Aβ cerebral accumulation is not clear yet. ApoJ is abundant in plasma and approximately 20% can appear bound to HDL-particles. In this regard, the impact of plasmatic ApoJ and its lipidation status on cerebral β-amyloidosis is still not known. Hence, our main objective was to study the effect of a peripheral increase of free ApoJ or reconstituted HDL particles containing ApoJ in an experimental model of cerebral β-amyloidosis.MethodsFourteen-month-old APP23 transgenic mice were subjected to subchronic intravenous treatment with rHDL-rApoJ nanodiscs or free rApoJ for 1 month. Aβ concentration and distribution in the brain, as well as Aβ levels in plasma and CSF, were determined after treatments. Other features associated to AD pathology, such as neuronal loss and neuroinflammation, were also evaluated.ResultsBoth ApoJ-based treatments prevented the Aβ accumulation in cerebral arteries and induced a decrease in total brain insoluble Aβ42 levels. The peripheral treatment with rApoJ also induced an increase in the Aβ40 levels in CSF, whereas the concentration remained unaltered in plasma. At all the endpoints studied, the lipidation of rApoJ did not enhance the protective properties of free rApoJ. The effects obtained after subchronic treatment with free rApoJ were accompanied by a reduction in hippocampal neuronal loss and an enhancement of the expression of a phagocytic marker in microglial cells surrounding Aβ deposits. Finally, despite the activation of this phagocytic phenotype, treatments did not induce a global neuroinflammatory status. In fact, free rApoJ treatment was able to reduce the levels of interleukin-17 (IL17) and keratinocyte chemoattractant (KC) chemokine in the brain.ConclusionsOur results demonstrate that an increase in circulating human rApoJ induces a reduction of insoluble Aβ and CAA load in the brain of APP23 mice. Thus, our study suggests that peripheral interventions, based on treatments with multifunctional physiological chaperones, offer therapeutic opportunities to regulate the cerebral Aβ load.
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Project description:BackgroundThe Blood-brain barrier (BBB) controls brain supply with oxygen and nutrients, and protects the brain from toxic metabolites, such as beta-amyloid (A?) peptides. The neurovascular unit (NVU) couples vascular and neuronal functions by controlling BBB parameters based on brain needs. As such, NVU/BBB dysfunction, associated to irregularities in cerebral blood flow (CBF), has been proposed to contribute in the pathogenesis of Alzheimer's disease (AD), mainly by impairing cerebral A? clearance. However, the spatiotemporal contribution of the NVU/BBB in the neurodegenerative cascades remains elusive.ResultsBy using C57BL/6J mice subjected to right common carotid artery (rCCA) permanent ligation in order to induce mild chronic cerebral hypoperfusion, we show here that cerebral hypoperfusion induced NVU dysfunction by reducing ABCB1 protein expression in brain capillaries. ABCB1 reduction was mainly triggered by an enhanced Glycogen Synthase Kinase 3 (GSK3?) activation, which decreased ?-catenin nuclear abundance. Moreover, cerebral hypoperfusion triggered early vascular deposition of peripherally applied human A?1-42 peptides, which has shifted from highly vascular to the parenchyma 6 weeks later, forming small stable A? deposits. Hypoperfusion induced a deregulation in glucose metabolism, as brain reperfusion, or the administration of a high dose of glucose, diminished GSK3? activation, recuperated ?-catenin nuclear abundance, reestablished ABCB1 protein expression, and prevented A? vascular early deposition. These results demonstrate that mild chronic cerebral hypoperfusion creates a metabolically deregulated microenvironment, thus triggering the brain entry and aggregation of peripherally applied human A?1-42 peptides.ConclusionOur study offers new insights on the initiation of the neurodegenerative cascades observed in AD, which could be valuable in developing adequate treatment strategies.
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