Katarzyna M. Grochowska

The disruption of astrocytic catabolic processes contributes to the impairment of amyloid‐β (Aβ) clearance, neuroinflammatory signaling, and the loss of synaptic contacts in late‐onset Alzheimer's disease (AD). While it is known that the posttranslational modifications of Aβ have significant implications on biophysical properties of the peptides, their consequences for clearance impairment are not well understood. It was previously shown that N ‐terminally pyroglutamylated Aβ3(pE)‐42, a significant constituent of amyloid plaques, is efficiently taken up by astrocytes, leading to the release of pro‐inflammatory cytokine tumor necrosis factor α and synapse loss. Here we report that Aβ3(pE)‐42, but not Aβ1‐42, gradually accumulates within the astrocytic endolysosomal system, disrupting this catabolic pathway and inducing the formation of heteromorphous vacuoles. This accumulation alters lysosomal kinetics, lysosome‐dependent calcium signaling, and upregulates the lysosomal stress response. These changes correlate with the upregulation of glial fibrillary acidic protein (GFAP) and increased activity of nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB). Treatment with a lysosomal protease inhibitor, E‐64, rescues GFAP upregulation, NF‐κB activation, and synapse loss, indicating that abnormal lysosomal protease activity is upstream of pro‐inflammatory signaling and related synapse loss. Collectively, our data suggest that Aβ3(pE)‐42‐induced disruption of the astrocytic endolysosomal system leads to cytoplasmic leakage of lysosomal proteases, promoting pro‐inflammatory signaling and synapse loss, hallmarks of AD‐pathology.