Disruption of cerebral cholesterol homeostasis by PS-NPs: astrocytic endoplasmic reticulum stress

Cholesterol plays a crucial role in regulating synaptic membrane fluidity and ion channels. Due to the blood-brain barrier, cholesterol in the brain is primarily self-synthesized by astrocytes. However, limited research has been conducted on the effects of polystyrene nanoplastic (PS-NPs) on intracranial cholesterol metabolic pathways. In this study, we exposed whole-brain organoids (WBOs) to PS-NPs and identified significant changes in endoplasmic reticulum stress and cholesterol biosynthesis pathways through whole-transcriptome sequencing. To investigate potential mechanisms of altered cholesterol pathways, we constructed a Transwell neuronal-astrocyte co-culture model. Results demonstrated that PS-NPs induced significant endoplasmic reticulum stress in astrocytes, specifically manifested by elevated levels of ATF4 and CHOP, along with increased autophagy indicated by the elevated LC3-II/I ratio. PS-NPs significantly inhibited the AKT/ACLY pathway of cholesterol biosynthesis, leading to marked reductions in acetyl-CoA and cholesterol within astrocytes (P < 0.05). In addition, PS-NPs led to a significant reduction of apolipoprotein APOE, which hindered cholesterol transport and ultimately inhibited synaptin (SYN) formation. In summary, PS-NPs induce endoplasmic reticulum stress and autophagy in astrocytes, impair cholesterol de novo synthesis and apolipoprotein-mediated transport, ultimately inhibiting neuronal synaptogenesis. Furthermore, specific inhibition of ERs restored cholesterol synthesis in astrocytes and neuronal synapses. This study demonstrates that PS-NPs produce neurotoxic effects by affecting cholesterol homeostasis in the brain.