Lysosomal stress induces amyloid-β aggregate release and reactive transformation in human astrocytes

Astrocytes are essential for brain homeostasis and are involved in amyloid-β (Aβ) clearance, but whether they can produce and release Aβ aggregates remains unclear. Using human iPSC-derived astrocytes, we show that astrocytes cell autonomously generate small, diffusible Aβ aggregates under baseline conditions. By combining ultrasensitive single-molecule imaging (DNA-PAINT) and immunoassays, we detect intracellular aggregates and their release into the media. Notably, lysosomal membrane damage induced by L-leucyl-L-leucine methyl ester (LLOMe) significantly increases Aβ aggregate secretion without altering their size or morphology. Transcriptomic analysis and cytokine profiling reveal that lysosomal stress triggers a reactive astrocyte phenotype marked by upregulation of inflammatory genes and secreted cytokines. These findings suggest that astrocytes are not merely passive Aβ scavengers but can actively contribute to extracellular Aβ accumulation under lysosomal stress. Our study highlights astrocytes as active players in Alzheimer’s disease pathology.