Astrocytic uptake of posttranslationally modified amyloid-β leads to endolysosomal system disruption and induction of pro-inflammatory signaling

Abstract

The disruption of astrocytic catabolic processes contributes to the impairment of amyloid-{beta} (A{beta}) clearance, neuroinflammatory signaling, and the loss of synaptic contacts in late-onset Alzheimers disease (AD). While it is known that the posttranslational modifications of A{beta} 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 A{beta}3(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 (TNF) and synapse loss. Here we report that A{beta}3(pE)-42, but not A{beta}1-42, gradually accumulates within the astrocytic endolysosomal system, disrupting this catabolic pathway and inducing formation of heteromorphous vacuoles. This accumulation alters lysosomal kinetics and lysosome-dependent calcium signaling, and upregulates 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 (NFB). Treatment with a lysosomal protease inhibitor, E64, rescues GFAP upregulation, NFB 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 A{beta}3(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.