ABSTRACT
Aim To observe the effects of rapamycin (Rapa) and starvation-induced autophagy on the morphology of neuronal cells, tau protein aggregation and expression of phosphorylated tau protein, to explore the possible mechanism of cytoprotective effect of these two classical autophagy inducers on phosphorylated tau expressing cells.Methods N2a cells were transfected with GFP-tau plasmid, and equal amount of empty vector was used as control.Then cells were incubated with or without okadaic acid(OA) for 12 h, followed by treatment with autophagy inducers rapamycin(Rapa) and EBSS, autophagy inhibitor Bafilomycin A1(Baf A1) for 6 h.DAB was used to observe tau expression and cell morphology.Confocal microscopy was used to observe the intracellular tau aggregation.TUNEL assay and cleaved caspase-3 level were used to detect cell apoptosis.Immunoblot was used to detect the expression of phosphorylated tau and autophagy-related proteins.Results Our study showed that the N2a cells treated with OA exhibited small cell body, retracted processes and increased tau aggregation, compared with only tau-expressing cells.Rapa and EBSS treatment significantly improved cell morphology, decreased tau aggregation and reduced cell apoptosis.On the contrary, Baf A1 treatment induced aberrant cell shape and increased tau aggregation and cell apoptosis.In addition, Rapa significantly decreased the high molecular weight, phosphorylated tau whereas EBSS especially decreased the low molecular weight phosphorylated tau.Conclusions Rapa and EBSS is alleviate hyperphosphorylated tau-induced cytotoxicity through different mechanism.Rapamycin mainly decreases phosphorylated tau oligomers, while EBSS liable to decrease the soluble phosphorylated tau.