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APOE-Ɛ4 astrocytes exhibit deficits in endocytic uptake that contribute to the delayed maturation of neuronal network activity and alter neuronal tau uptake in co-cultures of human iPSC-derived brain cells

ABSTRACT: To explore the mechanistic basis of ApoE Ɛ4 vs ApoE Ɛ3 protein expression on endocytic pathways responsible for tau uptake in neurons and astrocytes and the maturation of neuronal networks, we have developed genotype matched co-cultures of iPSC derived astrocytes and neurons derived from isogenic triads of iPSC lines generated by the ADAPTED consortium (Schmid et al., 2019, 2020) . We show that isogenic iPSC derived APOE-E4 expressing astrocytes take up less extracellular tau than APOE-E3 or APOE null astrocytes, while isogenic neurons in monoculture take up equivalent amounts of tau primarily through macropinocytosis. Co-culture of neurons with genotype matched astrocytes increases the general uptake capacity of neurons by increasing the dependence of neuronal endocytosis on dynamin mediated pathways. Co-culture also enhances the emergence of spontaneous neuronal activity; however, the emergence of synchronous network activity is impaired by the expression of APOE-E4 genotype. We performed RNA-Seq on the astrocytes, neurons and co-cultures to understand the molecular pathway changes associated with different ApoE genotypes.

ORGANISM(S): Homo sapiens

PROVIDER: GSE171700 | GEO | 2024/04/08

REPOSITORIES: GEO

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Project description:The APOE gene is diversified by three alleles e2, e3, and e4 encoding corresponding apolipoprotein (apo) E isoforms. The e4 allele promotes age-related cognitive decline, risk of Alzheimer’s disease (AD), and the rate of AD dementia progression. ApoE is produced by astrocytes as high-density lipoprotein-like particles and these are internalized by neurons upon binding to neuron-expressed apoE receptors. ApoE isoforms differentially engage neuronal plasticity through poorly understood mechanisms. We examined here the effects of native apoE lipoproteins produced by immortalized astrocytes homozygous for e2, e3, and e4 alleles on the maturation and the transcriptomic profile of primary hippocampal neurons. Control neurons were grown in the presence of conditioned media from Apoe-/- astrocytes. ApoE2 and apoE3 significantly increase the dendritic arbor branching, the combined neurite length, and the total arbor surface of the hippocampal neurons, while apoE4 fails to produce similar effects and even significantly reduces the combined neurite length compared to the control. ApoE lipoproteins show no systemic effect on dendritic spine density, yet apoE2 and apoE3 increase the mature spines fraction, while apoE4 increases the immature spine fraction. This is associated with opposing effects of apoE2 or apoE3 and apoE4 on the expression of NR1 NMDA receptor subunit and PSD95. There are 1,062 genes differentially expressed across neurons cultured in the presence of apoE lipoproteins compared to the control. KEGG enrichment and gene ontology analyses show common for apoE2 and apoE3 activation of genes involved in neurite branching, and synaptic signaling. In contrast, apoE4 cultured neurons show upregulation of genes related to the glycolipid metabolism, which are involved in dendritic spine turnover and those which are usually silent in neurons and are related to cell cycle and DNA repair. In conclusion our work reveals that lipoprotein particles comprised of various apoE isoforms differentially regulate neuronal development through interaction with neuronal transcriptome. ApoE4 produces a functionally distinct transcriptomic profile, which is associated with attenuated neuronal development. Differential regulation of neuronal transcriptome by apoE isoforms is a newly identified biological mechanism, which has both implication in the development and aging of the CNS.

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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APOE-Ɛ4 astrocytes exhibit deficits in endocytic uptake that contribute to the delayed maturation of neuronal network activity and alter neuronal tau uptake in co-cultures of human iPSC-derived brain cells

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