Isoflurane and surgery aggravate APOE4-dependent lipid dysregulation and neural dysfunction, leading to neurological impairment in male mice

PurposePerioperative exposure to the volatile anesthetic isoflurane (ISO) has been associated with cognitive and olfactory deficits and may increase the risk of Alzheimers disease (AD). Apolipoprotein E4 (APOE4), the strongest genetic risk factor for AD, contributes to disease pathogenesis through disrupted lipid homeostasis. However, whether and how isoflurane interacts with APOE genotype to influence neurological vulnerability remains unclear. MethodsYoung adult, presymptomatic humanized APOE4 and APOE3 knock-in mice underwent laparotomy under 2 h of isoflurane anesthesia. Microglia and astrocytes were isolated from the olfactory bulb (OB) and hippocampus (HI) by magnetic-activated cell sorting. Lipid composition, transcriptional responses, and functional outcomes were assessed using lipidomic, bulk RNA-seq, and longitudinal behavioral testing. In vivo and ex vivo electrophysiological recordings evaluated neuronal excitability and synaptic transmission in both regions. ResultsBy day 7 post-anesthesia, cell type-specific lipidomic profiling of both OB and HI revealed more pronounced lipid perturbations in microglia and astrocytes from APOE4/ISO mice than from APOE3 mice, characterized by elevated free fatty acids, increased lipid peroxidation, triglyceride depletion, and reduced hippocampal hexosylceramides and cardiolipins. Electrophysiological recordings showed greater olfactory circuit dysfunction in APOE4/ISO mice, accompanied by persistent odor memory deficits, transient olfactory sensitivity loss, early motor coordination impairments, and delayed cognitive deficits. RNA sequencing of the OB identified downregulated lipid metabolism and atherosclerosis-related pathways. ConclusionThese findings establish a mechanistic link between APOE4-dependent glial lipid dysregulation, olfactory circuit dysfunction, and delayed cognitive impairment following isoflurane anesthesia and surgery, highlighting lipid homeostasis as a potential therapeutic target.