Pretreatment with metformin prevents microcystin-LR-induced tau hyperphosphorylation via mTOR-dependent PP2A and GSK-3 beta activation

Microcystin-leucine-arginine (MC-LR) is a toxin secreted by freshwater cyanobacteria that is considered a potential environmental risk factor for Alzheimer's disease (AD). A previous study indicated that tau protein hyperphosphorylation via protein phosphatase 2A (PP2A) and GSK-3 beta inhibition was the mechanism by which MC-LR induces neurotoxicity; however, how MC-LR-induced neurotoxicity can be effectively prevented remains unclear. In this study, the reversal effect of metformin on MC-LR-induced neurotoxicity was investigated. The results showed that metformin effectively prevented tau hyperphosphorylation at Ser202 caused by MC-LR through PP2A and GSK-3b activity. The effect of metformin on PP2A activity was dependent on the inhibition of mTOR in MC-LR-treated SH-SY5Y cells. Metformin prevented spatial memory deficits in rats caused by intrahippocampal MC-LR administration. In sum, the results suggested that metformin can ameliorate the MC-LR-induced AD-like phenotype by preventing tau phosphorylation at Ser202, which was mainly mediated by mTOR-dependent PP2A and GSK-3 beta activation.