CDK5-mediated Tau Accumulation Triggers Methamphetamine-Induced Neuronal Apoptosis Via Endoplasmic Reticulum

ObjectiveThis study aims to investigate the mechanism of apoptosis induced by methamphetamine through endoplasmic reticulum stress-related pathway.MethodsMethamphetamine exposure models of human neuroblastoma cell lines SH-SY5Y and SD rats were constructed.In the two models,the expression of two phosphorylated Tau protein(serine 396 and threonine 231)in methamphetamine exposure was detected in vitro and in vivo by Western Blotting.The expression and distribution of phosphorylated tau protein in two methamphetamine exposed models were observed by immunohistochemical staining and immunofluorescence staining.An upstream regulatory factor of phosphorylated tau protein CDK5 was knocked down by siRNA and virus infection and the expression of phosphorylated tau protein and ubiquitin protein were observed as well as the expression of CD3-?,a substrate of proteasome degradation pathway.Expression of endoplasmic reticulum stress signal molecule phosphorylated PERK and endoplasmic reticulum stress-specific apoptotic signal molecule caspase-12 and the changes of the expression of the two proteins in two exposed models after knockout CDK5 were tested.Results1.Exposure to methamphetamine in vivo and in vitro significantly up-regulates the expression of phosphorylated tau protein(P<0.05).2.Knock down CDK5 inhibites the up-regulation of phosphorylated tau expression induced by methamphetamine exposure(P<0.05).3.Methamphetamine exposure effects on ER associated degradation:Compared with the control group,methamphetamine exposure significantly elevated the expression of protein ubiquitination and CD3-?.(P<0.05).Upon CDK5 knocked down,the overexpression of ubiquitin and CD3-? caused by methamphetamine exposure was significantly inhibited(p<0.05)4.Methamphetamine exposure induces endoplasmic reticulum stress-related neuronal apoptosis:Compared with the control group,methamphetamine exposure resulted in a significant increase in the expression of phosphorylated PERK and caspase-12(p<0.05).After knocking down CDK5,the trend of the increase was significantly inhibited(P<0.05).In the methamphetamine exposure model of SH-SY5Y cells,there was no significant difference of apoptotic rate between the control group and the CDK5 knockdown group(total apoptotic rate:3.60 ± 1.05%vs.3.73 ±0.55g,p>0.05),While knocking down CDK5 and methamphetamine exposure resulted apoptosis rate decreased significantly,compared with the exposure to methamphetamine alone(the total apoptosis rate was 18.70 + 3.91%vs.9.96 + 1.20%,P<0.01).ConclusionMethamphetamine exposure elevates the level of phosphorylated Tau protein.The increase and accumulation of abnormal tau protein impairs the endoplasmic reticulum-associated degradation and block the ubiquitin-depended proteasome degradation pathway.In turn,it triggers unfolded protein response and activates endoplasmic reticulum stress,which induces neuron apoptosis.However,knockdown of CDK5 inhibits over expression of phosphorylated tau,restore damaged endoplasmic reticulum related degradation pathways,and then alleviate endoplasmic reticulum stress-induced apoptosis,and protect neurons.These results suggest that neuronal apoptosis induced by methamphetamine is closely related to excessive phosphorylation of tau protein.However,neurotoxic effects of methamphetamine can be reversed by knocking out CDK5.Based on the above findings,we provide a new theoretical basis and research train of thought for the molecular mechanism of methamphetamine neurotoxicity by inhibiting the abnormal expression of phosphorylated tau protein and decreasing the apoptosis promoting effect of methamphetamine based on CDK5.