Aspirin alleviates long-term high-fat diet-induced depressive-like behavior in male mice via suppressing arachidonic acid-mediated microglial activation and neuroinflammation.

While Western dietary patterns are increasingly linked to neuropsychiatric disorders, the causal mechanisms by which chronic high-fat diet (HFD) contributes to depression remain elusive. Here, we demonstrate that prolonged ( ≥ 10 weeks) HFD exposure in mice robustly induces depressive-like behaviors, phenocopying chronic stress models. Integrating multi-omics and targeted lipidomics, we reveal that HFD-induced behavioral deficits are underpinned by gut microbiota dysbiosis and a profound disruption of polyunsaturated fatty acid (PUFA) homeostasis. This disruption is characterized by a surge in pro-inflammatory ω-6 metabolites, particularly arachidonic acid (AA), alongside a concomitant reduction in anti-inflammatory ω-3 metabolites. These lipid perturbations strongly correlate with marked microglial activation and elevated pro-inflammatory cytokine levels (IL-6, TNF-α, CCL2) in the prefrontal cortex and hippocampus. Functionally, AA supplementation alone was sufficient to recapitulate depressive-like behaviors in vivo and, through neuron-microglia co-culture assays, directly induce pro-inflammatory microglial activation, NF-κB pathway upregulation, and subsequent synaptic impairment in vitro. Critically, therapeutic intervention with aspirin, a dual COX-1/COX-2 inhibitor, effectively reversed HFD-induced behavioral deficits. This protection was mediated by a dual mechanism: directly inhibiting microglial hyperactivation and normalizing the neuroinflammatory milieu by suppressing the biosynthesis of pro-inflammatory ω-6-derived prostanoids, including AA and 12-HETE. Collectively, our findings identify AA as a critical etiological link between HFD and neuroinflammation, establishing a mechanistic framework for "metabolic depression." The profound therapeutic efficacy of aspirin validates the AA metabolic pathway, specifically COX-1/COX-2, as a promising and targetable node for intervention, offering translational insights for the burgeoning field of nutritional psychiatry.