Adverse outcome pathway of Alzheimer's disease-like changes resulting from autophagy flux blockade after MC-LR exposure

Abstract

Microcystins (MCs) pollution is a worldwide environmental issue concerning about human health. Microcystin-leucine-arginine (MC-LR), the most common type of MCs produced by cyanobacteria, could enter the brain and bring about damage to the nervous system. Up to date, it is not clear about the mechanism of MC-LR-induced neurotoxicity. Amyloid-β (Aβ) deposits are hallmark of Alzheimer's disease (AD). In this study, we revealed that MC-LR exposure at environment-related doses (1, 7.5, 15 μg/L) could promote Aβ accumulation in mouse brain. Mechanically, we firstly found that Aβ accumulation is closely associated with abnormal Aβ degradation due to autophagy flux blockade and lysosome dysfunctions in neurons after MC-LR exposure. Moreover, an adverse outcome pathway (AOP) framework oriented to neurotoxicity of MC-LR was conducted in this study. MC-LR inhibited the activity of protein phosphatase 2A (PP2A) in neurons, which is regarded as a molecular initiating event (MIE). In addition, the abnormalities in autophagy were observed after MC-LR exposure. The hindered autophagosome-lysosome fusion and disrupted lysosomal function were key events (KEs) after MC-LR exposure, which contributed to proteostasis dysregulation, ultimately leading to Aβ abnormal degradation and learning deficits as adverse outcomes (AO) of neurotoxicity. This study provided novel information about MC-LR neurotoxicity and new insights into understanding the mechanisms underlying the environmental chemicals-induced neurodegeneration diseases, which has deep implications for public health.