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APOE4 cell-specific mechanisms underlying cerebrovascular disorder precede neuronal and synaptic dysfunction and cognitive deficits in mice

ABSTRACT: Apolipoprotein E4 (APOE4), the main susceptibly gene for Alzheimer’s disease1–5, exerts cerebrovascular toxicity6 leading to blood-brain barrier (BBB) breakdown in humans7–9 and APOE4 transgenic mice10–13. Moreover, an early BBB dysfunction predicts cognitive decline in humans7. However, the comprehensive large-scale analysis of cell-specific mechanisms underlying APOE4 cerebrovascular disorder and how it relates to neuronal disorder is lacking. Using single-nucleus RNA-sequencing, phosphoproteome and proteome analysis14–17 here we show that APOE4 compared to APOE3 leads to early disruption of the BBB transcriptome in 2-3-month old APOE4 knock-in mice18 followed by dysregulation in protein signaling networks. This includes proteins regulating cell junctions, cytoskeleton, clathrin-mediated transport, and translation in brain endothelium, and transcription and RNA-splicing suggestive of DNA damage in pericytes. Changes in the BBB signaling mechanisms paralleled an early, progressive BBB breakdown and loss of pericytes starting at 2-3 months of age. The BBB breakdown preceded loss of neurites, post-synaptic interactome dysregulation, and behavioral deficits that developed 2-5 months later, and was associated with astrocyte and microglia response protecting BBB integrity. Thus, disruption of the BBB cell-specific signaling mechanisms could be an initial central contributor to APOE4-mediated neuronal disorder, and possibly a major target to correct APOE4-related cognitive deficits.

INSTRUMENT(S): Orbitrap Eclipse, Q Exactive HF

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Blood-brain Barrier

SUBMITTER: marcelo coba

LAB HEAD: Marcelo P. Coba

PROVIDER: PXD029230 | Pride | 2022-08-23

REPOSITORIES: Pride

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Project description:The blood-brain barrier (BBB) consists of specific physical barriers, enzymes and transporters, which together maintain the necessary extracellular environment of the central nervous system (CNS). The main physical barrier is found in the CNS endothelial cell, and depends on continuous complexes of tight junctions combined with reduced vesicular transport. Other possible constituents of the BBB include extracellular matrix, astrocytes and pericytes, but the relative contribution of these different components to the BBB remains largely unknown. Here we demonstrate a direct role of pericytes at the BBB in vivo. Using a set of adult viable pericyte-deficient mouse mutants we show that pericyte deficiency increases the permeability of the BBB to water and a range of low-molecular-mass and high-molecular-mass tracers. The increased permeability occurs by endothelial transcytosis, a process that is rapidly arrested by the drug imatinib. Furthermore, we show that pericytes function at the BBB in at least two ways: by regulating BBB-specific gene expression patterns in endothelial cells, and by inducing polarization of astrocyte end-feet surrounding CNS blood vessels. Our results indicate a novel and critical role for pericytes in the integration of endothelial and astrocyte functions at the neurovascular unit, and in the regulation of the BBB. The brain microvascular fragments were isolated from mice with different genotypes, each represented by 3-4 biological replicates. Genotypes 1-2: Platelet derived growth factor-B (PDGF-B) retention-motif knockout (pdgfbret/ret) represent the pericyte-deficient situation, and the heterozygous mice (pdgfbret/+) are used as controls. Genotypes 3-4: Hypomorphic PDGF-B mutants that rescue pdgfb-/- null mice, in which a one copy of a conditionally silent human PDGF-B transgene targeted to the Rosa 26 locus (R26P) is turned on by endothelial-specific expression of Cre recombinase. In this data set these mice are named as Tie2Cre, R26P+/0, pdgfb-/- (representing the pericyte-deficient situation). Mice wt for pdgfb (pdgfb+/+) and carrying one silent copy of R26P (R26P+/0), are used as controls. Genotype 5: Adult Notch3+/+ wildtype (WT).

Project description:Cerebrovascular dysfunction is a hallmark feature of Alzheimer's disease (AD). One of the greatest risk factor for AD is the apolipoprotein E4 (E4) allele. APOE4 genotype has been shown to negatively impact on perivascular amyloid clearance, however, its direct influence along with the other APOE variants (APOE2 and APOE3) on the molecular integrity of the cerebrovasculature has not been largely explored. To address this, we employed a 10-plex tandem isobaric mass tag approach in combination with an ultra-high pressure liquid chromatography MS/MS (Q-Exactive) method, to interrogate unbiased proteomic changes in cerebrovessels from AD and healthy control brains on different APOE genotype backgrounds. We first interrogated changes between healthy control homozygote E2/E2, E3/E3 and E4/E4 cases to identify underlying genotype specific effects on cerebrovessels. EIF2 signaling, regulation of eIF4 and 70S6K signaling and mTOR signaling were the top significantly altered pathways in E4/E4 compared to E3/E3 cases. EIF2, nitric oxide and sirtuin signaling pathways were the top significantly altered pathways in E4/E4 compared to E2/E2 cases. We used a Two-way ANOVA analysis to identify AD-dependent changes and their interactions with APOE genotype. The highest number of significantly regulated proteins from this interaction was observed in E3/E4 (192) and E4/E4 (189) cases. As above, EIF2, mTOR signaling and eIF4 and 70S6K signaling were the top three significantly altered pathways in E4 allele carriers (i.e. E3/E4 and E4/E4 genotypes). Of all the cerebrovascular cell specific markers identified in our proteomic analyses, endothelial cell, astrocyte, and smooth muscle cell specific protein markers were significantly altered in E4/E4 cases, while endothelial cells and astrocyte specific protein markers were altered in E3/E4 cases. These proteomic changes provide novel insights to explain the longstanding link between APOE4 and cerebrovascular dysfunction. The early and converging APOE4 dependent changes we identified could provide novel targets in the cerebrovasculature for developing disease modifying strategies to mitigate the effects of APOE4 genotype on increasing the risk for, and the path towards AD pathogenesis.

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APOE4 cell-specific mechanisms underlying cerebrovascular disorder precede neuronal and synaptic dysfunction and cognitive deficits in mice

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