Lysosomal stress induces amyloid-β aggregate release and reactive transformation in human astrocytes
Astrocytes are essential for brain homeostasis and are involved in amyloid-{beta} (A{beta}) clearance, but whether they can produce and release A{beta} aggregates remains unclear. Using human iPSC-derived astrocytes, we show that astrocytes cell autonomously generate small, diffusible A{beta} 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 A{beta} 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 A{beta} scavengers but can actively contribute to extracellular A{beta} accumulation under lysosomal stress. Our study highlights astrocytes as active players in Alzheimer's disease pathology.