Local translation controls early reactive changes in perisynaptic astrocyte processes at pre-symptomatic stages of Alzheimer's disease

Early synaptic dysfunction is a hallmark of Alzheimer's disease (AD), yet the astrocytic mechanisms underlying these alterations remain poorly defined. Here, we identify astrocyte perisynaptic processes (PAPs) as subcellular hotspots of early translational dysregulation in AD. Soluble Aβ₁-₄₂ rapidly enhanced global and local protein synthesis in primary astrocytes. In 5.5-month-old APP/PS1-dE9 (APP) mice, translating ribosome affinity purification (TRAP) revealed widespread remodeling of the PAP translatome, while whole-astrocyte translation remained largely unchanged. Dysregulated mRNAs were linked to neuroinflammation, synaptic remodeling, and endoplasmic reticulum stress, and alterations emerged prior to amyloid plaque deposition. Among them, Serpina3n encoding α1-antichymotrypsin exhibited increased mRNA abundance in PAPs, uncovering spatially restricted translational control. Mechanistically, early Serpina3n upregulation was partially driven by JAK-STAT3 signaling, with preferential effects in astrocyte processes. These findings provide a conceptual advance by demonstrating that local translation in astrocyte PAPs is an early and compartment-specific mechanism that may contribute to synaptic dysfunction and disease initiation in AD.