Subchronic benzo[a]pyrene exposure disrupts APOE4-regulated lipid metabolism to induce Tau hyperphosphorylation and cognitive deficits.

BACKGROUND

Benzo[a]pyrene (B[a]P) is both a carcinogen and a potent neurotoxic pollutant. Despite growing evidence linking B[a]P to neurological dysfunction, the responsible mechanisms have not been elucidated.

METHODS

Here, we employed human apolipoprotein E4 (hAPOE4) transgenic mice and APOE knockout (APOE-KO) mice to evaluate the influence of APOE on B[a]P-mediated neurotoxicity. hAPOE4 mice overexpress the human APOE4 isoform, whereas APOE-KO mice lack APOE expression; wild-type C57BL/6 J mice served as controls. Animals received intraperitoneal injections of B[a]P at 0, 2.5, or 6.25 mg/kg on alternate days for 3 months. Spatial memory and learning were examined via Morris Water Maze (MWM). Neuronal morphology, including dendritic branching and spine density in the CA1 region of the hippocampus and dentate gyrus (DG), was assessed using Golgi-Cox staining. Neurofibrillary tangles were detected by silver glycine staining. Tau, phosphorylated Tau (Ser199 and Ser396), and LRP1 were evaluated using Western blot and immunohistochemical analyses. Chromatin immunoprecipitation PCR (ChIP-PCR) was undertaken to examine the regulation of APOE4 expression by the aryl hydrocarbon receptor (AHR). In addition, both untargeted metabolomics and lipidomics analyses were conducted following B[a]P exposure.

RESULTS

B[a]P led to pronounced impairments in mouse spatial memory and learning, shown by greater escape latency, less time in the target quadrant, and a decreased number of platform crossings in MWM tests. Structural analyses revealed a significant reduction in dendritic branching within the hippocampal CA1 and DG regions. These neurobehavioral and morphological deficits were most severe in hAPOE4 mice, which displayed greater cognitive impairment and more extensive dendritic loss than B[a]P-treated wild-type mice, indicating that APOE4 amplifies B[a]P-induced neurotoxicity. ChIP assays demonstrated that B[a]P modulates APOE4 transcription through AHR-dependent mechanisms. Additionally, metabolomics and lipidomics analyses revealed widespread B[a]P-induced metabolic remodeling, suggesting that disrupted lipid metabolism and altered neuronal membrane integrity may contribute to the observed neurotoxicity and cognitive dysfunction.

CONCLUSION

Collectively, the results indicate that B[a]P-mediated neurotoxicity may be facilitated, at least in part, by APOE4-dependent dysregulation of lipid metabolic pathways.