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The amyloid-? degradation intermediate A?34 is pericyte-associated and reduced in brain capillaries of patients with Alzheimer's disease.

ABSTRACT: An impairment of amyloid ?-peptide (A?) clearance is suggested to play a key role in the pathogenesis of sporadic Alzheimer's disease (AD). Amyloid degradation is mediated by various mechanisms including fragmentation by enzymes like neprilysin, matrix metalloproteinases (MMPs) and a recently identified amyloidolytic activity of ?-site amyloid precursor protein cleaving enzyme 1 (BACE1). BACE1 cleavage of A?40 and A?42 results in the formation of a common A?34 intermediate which was found elevated in cerebrospinal fluid levels of patients at the earliest disease stages. To further investigate the role of A?34 as a marker for amyloid clearance in AD, we performed a systematic and comprehensive analysis of A?34 immunoreactivity in hippocampal and cortical post-mortem brain tissue from AD patients and non-demented elderly individuals. In early Braak stages, A?34 was predominantly detectable in a subset of brain capillaries associated with pericytes, while in later disease stages, in clinically diagnosed AD, this pericyte-associated A?34 immunoreactivity was largely lost. A?34 was also detected in isolated human cortical microvessels associated with brain pericytes and its levels correlated with A?40, but not with A?42 levels. Moreover, a significantly decreased A?34/A?40 ratio was observed in microvessels from AD patients in comparison to non-demented controls suggesting a reduced proteolytic degradation of A?40 to A?34 in AD. In line with the hypothesis that pericytes at the neurovascular unit are major producers of A?34, biochemical studies in cultured human primary pericytes revealed a time and dose dependent increase of A?34 levels upon treatment with recombinant A?40 peptides while A?34 production was impaired when A?40 uptake was reduced or BACE1 activity was inhibited. Collectively, our findings indicate that A?34 is generated by a novel BACE1-mediated A? clearance pathway in pericytes of brain capillaries. As amyloid clearance is significantly reduced in AD, impairment of this pathway might be a major driver of the pathogenesis in sporadic AD.

SUBMITTER: Kirabali T

PROVIDER: S-EPMC6892233 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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The amyloid-β degradation intermediate Aβ34 is pericyte-associated and reduced in brain capillaries of patients with Alzheimer's disease.

Kirabali Tunahan T Rigotti Serena S Siccoli Alessandro A Liebsch Filip F Shobo Adeola A Hock Christoph C Nitsch Roger M RM Multhaup Gerhard G Kulic Luka L

Acta neuropathologica communications 20191203 1

An impairment of amyloid β-peptide (Aβ) clearance is suggested to play a key role in the pathogenesis of sporadic Alzheimer's disease (AD). Amyloid degradation is mediated by various mechanisms including fragmentation by enzymes like neprilysin, matrix metalloproteinases (MMPs) and a recently identified amyloidolytic activity of β-site amyloid precursor protein cleaving enzyme 1 (BACE1). BACE1 cleavage of Aβ40 and Aβ42 results in the formation of a common Aβ34 intermediate which was found elevat ...[more]

PMID: 31796114

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Project description:BackgroundParenchymal accumulation of beta-amyloid (Aβ) characterizes Alzheimer's disease (AD). Aβ homeostasis is maintained by two ATP-binding cassette (ABC) transporters (ABCC1 and ABCB1) mediating efflux, and the receptor for advanced glycation end products (RAGE) mediating influx across the blood-brain barrier (BBB). Altered transporter levels and disruption of tight junctions (TJ) were linked to AD. However, Aβ transport and the activity of ABCC1, ABCB1 and RAGE as well as the functionality of TJ in AD are unclear.MethodsISMICAP, a BBB model involving microperfusion of capillaries, was used to assess BBB properties in acute cortical brain slices from Tg2576 mice compared to wild-type (WT) controls using two-photon microscopy. TJ integrity was tested by vascularly perfusing biocytin-tetramethylrhodamine (TMR) and quantifying its extravascular diffusion as well as the diffusion of FM1-43 from luminal to abluminal membranes of endothelial cells (ECs). To assess ABCC1 and ABCB1 activity, calcein-AM was perfused, which is converted to fluorescent calcein in ECs and gets actively extruded by both transporters. To probe which transporter is involved, probenecid or Elacridar were applied, individually or combined, to block ABCC1 and ABCB1, respectively. To assess RAGE activity, the binding of 5-FAM-tagged Aβ by ECs was quantified with or without applying FPS-ZM1, a RAGE antagonist.ResultsIn Tg2576 mouse brain, extravascular TMR was 1.8-fold that in WT mice, indicating increased paracellular leakage. FM1-43 staining of abluminal membranes in Tg2576 capillaries was 1.7-fold that in WT mice, indicating reduced TJ integrity in AD. While calcein was undetectable in WT mice, its accumulation was significant in Tg2576 mice, suggesting lower calcein extrusion in AD. Incubation with probenecid or Elacridar in WT mice resulted in a marked calcein accumulation, yet probenecid alone had no effect in Tg2576 mice, implying the absence of probenecid-sensitive ABC transporters. In WT mice, Aβ accumulated along the luminal membranes, which was undetectable after applying FPS-ZM1. In contrast, marginal Aβ fluorescence was observed in Tg2576 vessels, and FPS-ZM1 was without effect, suggesting reduced RAGE binding activity.ConclusionsDisrupted TJ integrity, reduced ABCC1 functionality and decreased RAGE binding were identified as BBB alterations in Tg2576 mice, with the latter finding challenging the current concepts. Our results suggest to manage AD by including modulation of TJ proteins and Aβ-RAGE binding.

Dataset Information

The amyloid-? degradation intermediate A?34 is pericyte-associated and reduced in brain capillaries of patients with Alzheimer's disease.

Publications

The amyloid-β degradation intermediate Aβ34 is pericyte-associated and reduced in brain capillaries of patients with Alzheimer's disease.

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