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Isoform-dependent lysosomal degradation and internalization of Apolipoprotein E requires autophagy proteins

ABSTRACT: Alzheimer’s disease (AD), and lysosomal dysfunction has been implicated in AD pathogenesis. We found, by examining cells stably expressing each APOE isoform, that APOE4 increases lysosomal trafficking, accumulates in enlarged lysosomes and late endosomes, alters autophagic flux and the abundance of autophagy proteins and lipid droplets, and alters the proteomic contents of lysosomes following internalization. We investigated APOE-related lysosomal trafficking further in cell culture, and found that APOE from the post-Golgi compartment is degraded through autophagy. We found that this autophagic process requires the lysosomal membrane protein LAMP2 in immortalized neuron-like and hepatic cells, and in mouse brain tissue. Several macroautophagy-associated proteins were also required for autophagic degradation and internalization of APOE in hepatic cells. The dysregulated autophagic flux and lysosomal trafficking of APOE4 that we observed suggest a possible novel mechanism that might contribute to AD pathogenesis.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

SUBMITTER: Joan Steffan

LAB HEAD: Joan Steffan

PROVIDER: PXD031016 | Pride | 2022-01-18

REPOSITORIES: Pride

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ApoE4-dependent lysosomal cholesterol accumulation impairs mitochondrial homeostasis and oxidative phosphorylation in human astrocytes

Project description:Recent developments in genome sequencing have expanded the knowledge of genetic factors associated with late-onset Alzheimer’s disease (AD). Among them, genetic variant e4 of the APOE gene (ApoE4) confers the greatest disease risk. Dysregulated glucose metabolism is an early pathological feature of AD. Using isogenic ApoE3 and ApoE4 astrocytes derived from human-induced pluripotent stem cells, we find that ApoE4 increases glycolytic activity but impairs mitochondrial respiration in astrocytes. Ultrastructural and autophagic flux analyses show that ApoE4-induced cholesterol accumulation impairs lysosome-dependent removal of damaged mitochondria. Acute treatment with cholesterol-depleting agents restores autophagic activity, mitochondrial dynamics, and associated proteomes, and extended treatment rescues mitochondrial respiration in ApoE4 astrocytes. Taken together, our study provides a direct link between ApoE4-induced lysosomal cholesterol accumulation and abnormal oxidative phosphorylation.

2023-09-12 | PXD045298 | Pride

β2-adrenergic agonists rescue lysosome acidification and function in PSEN1 deficiency by reversing defective ER to lysosome delivery of ClC-7

Project description:Lysosomal dysfunction is considered pathogenic in Alzheimer Disease (AD). Loss of Presenilin-1(PSEN1) function causing early onset AD impedes acidification via defective vATPase V0a1 subunit delivery to lysosomes. We report that isoproterenol and related β2-adrenergic agonists re-acidify lysosomes in PSEN1 KO cells and fibroblasts from PSEN1 familial AD(FAD) patients, restores lysosomal calcium homeostasis and proteolysis, and reverses impaired autophagy flux. We identify a novel rescue mechanism involving PKA-mediated facilitated delivery of ClC-7 to lysosomes, which stimulates chloride influx and reverses markedly lowered Cl- content of PSEN1 KO lysosomes. Notably, PSEN1 loss-of-function impedes ER-to-lysosome delivery of ClC-7, thus accounting for lysosomal Cl- deficits that compound pH deficits due to deficient vATPase function. Transcriptomics of PSEN1-deficient cells reveal strongly down-regulated ER-to-lysosome transport pathways and reversibility by isoproterenol. Our findings uncover a broadened PSEN1 role in lysosomal ion homeostasis and novel pH modulation of lysosomes through β-adrenergic regulation of ClC-7, which can be therapeutically modulated.

2020-02-29 | GSE136894 | GEO

A SAGE approach to discovery of apolipoprotein E4 allele-specific genes involved in increased risk in Alzheimer disease

Project description:APOE4 allele is a major risk factor for late-onset Alzheimer disease (AD). The mechanism of action of APOE in AD remains unclear. To study the effects of APOE alleles on gene expression in AD, we have analyzed the gene transcription patterns of human hippocampus from APOE3/3, APOE3/4, APOE4/4 AD patients and normal control using Serial Analysis of Gene Expression (SAGE). Using SAGE, we found gene expression patterns in hippocampus of APOE3/4 and APOE4/4 AD patients differ substantially from those of APOE3/3 AD patients. APOE3/4 and APOE4/4 allele expression may activate similar genes or gene pools with associated functions. APOE4 AD alleles activate multiple tumor suppressors, tumor inducers and negative regulator of cell growth or repressors that may lead to increased cell arrest, senescent and apoptosis. In contrast, there is decreased expression of large clusters of genes associated with synaptic plasticity, synaptic vesicle trafficking (metabolism) and axonal/neuronal outgrowth. In addition, reduction of neurotransmitter receptors and Ca++ homeostasis, disruption of multiple signal transduction pathways, and loss of cell protection and notably mitochondrial oxidative phosphorylation/energy metabolism are associated with APOE3/4 and APOE4/4 AD alleles. These findings help define the mechanisms that APOE4 contribute increased risk for AD and identify new candidate genes conferring susceptibility to AD. Keywords: Serial Analysis of Gene Expression (SAGE); Apolipoprotein E (APOE3/3, APOE3/4, APOE4/4); Alzheimer disease; Hippocampus; apoptosis; signal pathways

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Peripherally-expressed apoE4 impairs brain functions and exacerbates amyloid pathogenesis by compromising cerebrovascular functions

Project description:The apolipoprotein E4 (APOE4) gene is the strongest genetic risk factor for late-onset Alzheimer’s disease (AD). ApoE is a lipid carrier abundantly expressed in both brain and periphery. As peripheral apoE is separated from brain apoE by the blood-brain barrier, it remains unclear whether peripheral apoE impacts brain functions and AD pathogenesis. To investigate this, we developed novel mouse models that conditionally express human APOE3 or APOE4 only in the liver with no detectable apoE in the brain. We found that liver-expressed apoE4 compromised synaptic plasticity and cognitive behaviors likely by impairing cerebrovascular functions. Remarkably, liver-expressed apoE4 exacerbated brain amyloid pathology, whereas apoE3 reduced it. Our findings demonstrate a pathogenic effect of peripheral apoE4, providing strong rationale for targeting peripheral apoE to treat AD.

2022-06-15 | GSE125501 | GEO

Microglia Depletion Reduces Human Neuronal APOE4-Driven Pathologies in a Chimeric Alzheimer’s Disease Model

Project description:Despite strong evidence supporting the involvement of both apolipoprotein E4 (APOE4) and microglia in Alzheimer’s Disease (AD) pathogenesis, the effects of microglia on neuronal APOE4-driven AD pathogenesis remain elusive. Here, we examined such effects utilizing microglial depletion in a chimeric model with human neurons in mouse hippocampus. Specifically, we transplanted homozygous APOE4, isogenic APOE3, and APOE-knockout (APOE-KO) induced pluripotent stem cell (iPSC)-derived human neurons into the hippocampus of human APOE3 or APOE4 knock-in mice, and depleted microglia in half the chimeric mice. We found that both neuronal APOE and microglial presence were important for the formation of Aβ and tau pathologies in an APOE isoform-dependent manner (APOE4 > APOE3). Single-cell RNA-sequencing analysis identified two pro-inflammatory microglial subtypes with high MHC-II gene expression that are enriched in chimeric mice with human APOE4 neuron transplants. These findings highlight the concerted roles of neuronal APOE, especially APOE4, and microglia in AD pathogenesis.

2024-10-25 | GSE248020 | GEO

Cholesterol and matrisome pathways dysregulated in APOE ε4 human microglia and astrocytes [populationAPOE]

Project description:The impact of Apolipoprotein E4 (APOE4), the strongest genetic risk factor for Alzheimer's disease (AD), on human brain cellular function remains unclear. Here we investigated the effects of APOE4 on brain cell types derived from population and isogenic human induced pluripotent stem cell models, post-mortem brain and APOE targeted replacement mice. Population and isogenic models uncover that APOE4 local haplotype rather than a single risk allele alone contributes to the risk. Global transcriptomic analyses reveal human specific, APOE4-driven lipid metabolic dysregulation in astrocytes and microglia. APOE4 leads to elevated de novo cholesterol synthesis despite the intracellular cholesterol accumulation due to lysosomal sequestration of cholesterol in astrocytes. Transcriptome analyses uncovered Matrisome dysregulation associated with upregulated chemotaxis, glial activation and lipid biosynthesis in astrocytes, co-cultured with neurons that recapitulates altered astrocyte matrisome signaling in human brain. Thus, APOE4 initiates glia-specific cell and non-cell autonomous dysregulation that may contribute to increased AD risk.

2022-06-23 | GSE190187 | GEO

Cholesterol and matrisome pathways dysregulated in APOE ε4 human microglia and astrocytes [mouseApoe]

2022-06-23 | GSE190186 | GEO

Cholesterol and matrisome pathways dysregulated in APOE ε4 human microglia and astrocytes [isogenicAPOE]

2022-06-23 | GSE190185 | GEO

Lysosomal dysfunction in Down syndrome is APP-dependent and mediated by APP-βCTF (C99)

Project description:Lysosomal failure underlies pathogenesis of numerous congenital neurodegenerative disorders and is an early and progressive feature of Alzheimer’s disease (AD) pathogenesis. Here, we report that lysosomal dysfunction in Down Syndrome (Trisomy 21) requires the extra gene copy of amyloid precursor protein (APP) and is mediated by the beta cleaved carboxy terminal fragment of APP (APP-βCTF, C99). In primary fibroblasts from individuals with Down Syndrome (DS), lysosomal degradation of autophagic and endocytic substrates is selectively impaired causing them to accumulate in enlarged autolysosomes/lysosomes. Direct measurements of lysosomal pH uncovered a significant elevation (0.6 units) associated with slowed LC3 turnover and the inactivation of cathepsin D (CTSD) and other lysosomal hydrolases known to be unstable or less active when lysosomal pH is persistently elevated. RNA sequencing analysis excluded a transcriptional contribution to hydrolase declines. Normalizing lysosome pH by delivering acidic nanoparticles to lysosomes ameliorated lysosomal deficits, implicating pH elevation as their primary basis. Cortical neurons cultured from the Ts2 mouse model of DS exhibited lysosomal deficits similar to those in DS cells. Lowering APP expression with siRNA or BACE1 inhibition reversed cathepsin deficits in both fibroblasts and neurons. Deleting one BACE1 allele from adult Ts2 mice had similar rescue effects in vivo. The modest elevation of endogenous APP-βCTF needed to disrupt lysosomal function in DS is relevant to sporadic AD where APP-βCTF, but not APP, is also elevated. Our results extend evidence that impaired lysosomal acidification drives progressive lysosomal failure in multiple forms of AD.

2019-05-30 | GSE127880 | GEO

Amelioration of Tau and ApoE4-linked glial lipid accumulation and neurodegeneration with an LXR agonist

Project description:Apolipoprotein E (APOE) is a strong genetic risk factor for late-onset Alzheimer’s disease (AD) with APOE4 increasing and APOE2 decreasing risk relative to APOE3. In the P301S mouse model of tauopathy, ApoE4 increases tau pathology and neurodegeneration when compared to ApoE3 or the absence of ApoE. However, the role of ApoE isoforms in regulating lipid metabolism in the setting of tauopathy is unknown. Here, by using targeted lipidomics coupled with histological analysis, we demonstrate that in P301S tau mice, ApoE4 strongly promotes glial lipid accumulation along with significant perturbations in cholesterol metabolism and lysosomal function. Increasing lipid efflux in glia via administration of the LXR agonist GW3965 reduces lipid droplet accumulation in primary E4 microglia in vitro and GW3965 or Abca1 overexpression strongly attenuates tau pathology, neurodegeneration, and synapse loss in P301S/ApoE4 mice. By immunostaining, bulk and snRNA sequencing, we demonstrate reductions in reactive astrocytes and microglia as well as significant changes in cholesterol biosynthesis and metabolism in glia of tauopathy mice in response to LXR activation. These data suggest that promoting efflux of glial lipids via Abca1 could serve as a therapeutic approach to ameliorate tau and ApoE4-linked neurodegeneration.

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