Sex and life experience shape locus coeruleus pretangle tau pathology.

INTRODUCTION: Alzheimer's disease features early a pathology in the locus coeruleus (LC), yet how sex and life experience shape LC vulnerability remains poorly understood. METHODS: We expressed pseudophosphorylated human tau (htauE14) in LC neurons of TH-Cre rats and exposed both sexes to early- or late-life enrichment or stress. Behavioral, histological, protein, and hippocampal single-nucleus RNA sequencing (snRNA-seq) analyses were performed. RESULTS: LC-targeted htauE14 impaired learning and increased anxiety-like behavior. Early enrichment reduced htauE14 spread and LC microglia activation, elevated hippocampal brain-derived neurotrophic factor (BDNF), and improved olfactory learning in males. Late enrichment alleviated anxiety and enhanced spatial memory, whereas late stress exacerbated LC degeneration. Hippocampal snRNA-seq revealed sex- and cell type-specific transcriptional responses, with htauE14 preferentially engaging metabolic and synaptic pathways in females, effects amplified by early stress but stabilized by early enrichment. Late-life experiences primarily recruited homeostatic regulatory programs. DISCUSSION: Sex and developmental history critically shape early LC tau-related vulnerability.