Female‐biased astrocytic priming shapes early locus coeruleus vulnerability in an Aβ oligomer milieu

INTRODUCTION: The locus coeruleus (LC) is an early site of Alzheimer's disease (AD) pathology, yet the role of brainstem astrocytes in early, sex-dependent vulnerability remains unclear. METHODS: In 2- to 3-month-old APP/PS1 mice, we combined in vivo proton magnetic resonance spectroscopy (MRS) of the brainstem with region-resolved molecular analyses, including quantitative real-time polymerase chain reaction, amyloid beta 42 (Aβ42) oligomers enzyme-linked immunosorbent assay, lactate assay, immunohistochemistry, immunoblotting, astrocyte isolation, and 3D structural assessment. Environmental enrichment (EE) served as a non-pharmacologic intervention. RESULTS: Females exhibited higher brainstem Aβ42 oligomers and an astrocyte-weighted MRS profile. Pontine glial fibrillary acidic protein (GFAP), complement component 3, and nuclear factor kappa-light-chain-enhancer of activated B cells were selectively upregulated without pan-reactive astrocytic and microglial markers. LC-restricted GFAP elevation occurred without changes in astrocyte counts or morphology, indicating a "primed" state. Females also showed higher lactate levels, increased monocarboxylate transporter 2 expression, and elevations in selected oxidative phosphorylation-associated transcripts, and reduced astrocytic alpha 2A-adrenergic receptor expression. EE normalized noradrenergic and pontine astrocytic changes. DISCUSSION: Female-biased, LC-centric astrocytic priming emerges early in this amyloid-driven model and is modifiable.