Astrocytic accumulation of tau fibrils isolated from Alzheimer’s disease brains induces inflammation, cell-to-cell propagation and neuronal impairment

Abstract

Accumulating evidence highlights the involvement of astrocytes in Alzheimer’s disease (AD) progression. We have previously demonstrated that human iPSC-derived astrocytes ingest and modify synthetic tau fibrils in a way that enhances their seeding efficiency. However, synthetic tau fibrils differ significantly from in vivo formed fibrils. To mimic the situation in the brain, we here analyzed astrocytes’ processing of human brain-derived tau fibrils and its consequences for cellular physiology. Tau fibrils were extracted from both AD and control brains, aiming to examine any potential differences in astrocyte response depending on the origin of fibrils. Our results show that human astrocytes internalize, but fail to degrade, both AD and control tau fibrils. Instead, pathogenic, seeding capable tau proteoforms are spread to surrounding cells via tunneling nanotubes and exocytosis. Notably, accumulation of AD tau fibrils induces a stronger reactive state in astrocytes, compared to control fibrils, evident by the augmented expression of vimentin and GFAP, as well as by an increased secretion of the pro-inflammatory cytokines IL-8 and MCP-1. Moreover, conditioned media from astrocytes with AD tau fibril deposits induce synapse and metabolic impairment in human iPSC-derived neurons. Taken together, our data suggest that the accumulation of brain-derived AD tau fibrils induces a more robust inflammatory and neurotoxic phenotype in human astrocytes, accentuating the nature of tau fibrils as an important contributing factor to inflammation and neurodegeneration in AD.

Clathrin mediated endocytosis in Alzheimer’s disease: cell type specific involvement in amyloid beta pathology

“…When treated with chlorpromazine, a pharmacological inhibitor of CME, astrocytes exhibit significantly decreased uptake of Aβ 1-42 and a partial rescue of Aβ 1-42 induced cell death ( Domínguez-Prieto et al, 2018 ). Additionally, astrocytes can take up and accumulate monomeric and oligomeric Tau ( Martini-Stoica et al, 2018 ; Brezovakova et al, 2022 ; Eltom et al, 2024 ; Giusti et al, 2024 ), though to the best of our knowledge the specific endocytic mechanisms involved have not been thoroughly examined and there is no strong link to CME specifically in astrocytes.…”