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Astrocyte transcriptomic changes along the spatiotemporal progression of Alzheimer’s disease

ABSTRACT: Astrocytes are crucial to brain homeostasis, yet their changes along the spatiotemporal progression of Alzheimer’s disease (AD) neuropathology remain largely unexplored. Here, we performed single- nucleus RNA-sequencing of 628,943 astrocytes from five brain regions representing the stereotypical progression of AD pathology, across 32 donors spanning the entire normal aging-to-severe AD continuum. We discovered astrocyte gene expression trajectories that are differentially activated or suppressed at various regions and disease stages. We mapped out several unique astrocyte subclusters that exhibited varying responses to neuropathology across the AD-vulnerable neural network (spatial axis) or AD pathology stage (temporal axis). The proportion of homeostatic, intermediate, and reactive astrocytes changed solely along the spatial axis, whereas two other unique subclusters changed along the temporal axis. One of these, a trophic factor-rich subcluster, declined along pathology stage, whereas the other, defined by proteostasis and metabolic genes, increased in late-stage but unexpectedly returned to baseline levels in end-stage, suggesting exhaustion of response with chronic exposure to neuropathology. Our study underscores the complex and dynamic nature of astrocytic responses in AD and our findings are available at https://ad-progression-atlas.partners.org

ORGANISM(S): Homo sapiens

PROVIDER: GSE268599 | GEO | 2024/07/22

REPOSITORIES: GEO

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Project description:Astrocytes, one of the most resilient cells in the brain, transform into reactive astrocytes in response to toxic proteins such as amyloid beta (Aβ) in Alzheimer’s disease (AD). However, reactive astrocyte-mediated non-cell autonomous neuropathological mechanism is not fully understood yet. We aimed our study to find out whether Aβ-induced proteotoxic stress affects the expression of autophagy genes and the modulation of autophagic flux in astrocytes, and if yes, how Aβ-induced autophagy-associated genes are involved Aβ clearance in astrocytes of animal model of AD. Whole RNA sequencing (RNA-seq) was performed to detect gene expression patterns in Aβ-treated human astrocytes in a time-dependent manner. To verify the role of astrocytic autophagy in an AD mouse model, we developed AAVs expressing shRNAs for MAP1LC3B/LC3B (LC3B) and Sequestosome1 (SQSTM1) based on AAV-R-CREon vector, which is a Cre recombinase-dependent gene-silencing system. Also, the effect of astrocyte-specific overexpression of LC3B on the neuropathology in AD (APP/PS1) mice was determined. Neuropathological alterations of AD mice with astrocytic autophagy dysfunction were observed by confocal microscopy and transmission electron microscope (TEM). Behavioral changes of mice were examined through novel object recognition test (NOR) and novel object place recognition test (NOPR). Here, we show that astrocytes, unlike neurons, undergo plastic changes in autophagic processes to remove Aβ. Aβ transiently induces expression of LC3B gene and turns on a prolonged transcription of SQSTM1 gene. The Aβ-induced astrocytic autophagy accelerates urea cycle and putrescine degradation pathway. Pharmacological inhibition of autophagy exacerbates mitochondrial dysfunction and oxidative stress in astrocytes. Astrocyte-specific knockdown of LC3B and SQSTM1 significantly increases Aβ plaque formation and hypertrophic reactive astrocytes in APP/PS1 mice, along with a significant reduction of neuronal marker and cognitive function. In contrast, astrocyte-specific overexpression of LC3B reduced Ab aggregates in the brain of APP/PS1 mice An increase of LC3B and SQSTM1 protein is found in astrocytes of the hippocampus in AD patients. Taken together, our data indicates that Aβ-induced astrocytic autophagic plasticity is an important cellular event to modulate Aβ clearance and maintain cognitive function in AD mice.

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Astrocyte transcriptomic changes along the spatiotemporal progression of Alzheimer’s disease

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