The Role Of Delayed Rectifier Potassium Channel Subtype Kv2.1 On Methamphetamine-induced Hippocampal Neuronal Damage

Part one:The delayed rectifier potassium channel Kv2.1 was involved in Methamphetamine-induced hippocampal neuronal apoptosis Mehtamphetamine(Meth)is an illicit psychostimulant that is widely abused in the world.Several lines of evidence suggest that chronic Meth abuse leads to neurodegenerative changes in the human brain,including the loss of neurons possibly elicited by neural apoptosis.Accumulating evidence indicates that voltage-gated potassium(Kv)channels especially the outward delayed-rectifier K+(IDR)channels play imperative roles in cortical neuronal death.Therefore,in the present study,the associations between the outward delayed-rectifier K+ currents(Ik)channel and the hippocampal neuronal death were explored.Our previous work showed that Meth significantly increased the outward potassium currents.We found that Meth markedly up-regulated Kv2.1 protein levels,and pharmacological blockade of Kv2.1 by Guangxitoxin-1E(GxTX-1E)markedly attenuated Meth-induced cell damage.Furthermore,with the assay of overexpression of Kv2.1 by lentivirus transfection to hippocampal neurons,we observed the transfection groups deteriorated Meth-stimulated neural apoptosis.Part two:the role of MAPK pathways in hippocampal neuronal apoptosis induced by MethamphetamineSince MAPKs play critical roles in cellular activation,differentiation,proliferation,survival,death,production of cytokines,it is credible to explore the function of MAPKs in Meth-induced hippocampal neuronal death.The western-blot results showed that the levels of phosphorylated ERK1/2,JNK and p38 MAPK were significantly increased by Meth treatment.However,p38 MAPK rather than ERK1/2 pathway was demonstrated to be participated in Meth-induced hippocampal neural damage,since p38 MAPK antagonist(SB203580)partially abrogated Meth-induced Kv2.1 up-regulation and neural apoptosis.Moreover,JNK pathway was also participated in the regulation of Kv2.1,and SP600125,the JNK antagonist,insignificantly decreased the cleaved-caspase 3 expression.These results,taken together,indicate that Meth induces hippocampal neuronal apoptosis possibly through elevating Kv2.1 expression which was regulated by p38 MAPK pathway.Part three:the role of sigma-1 receptor in hippocampal neuronal apoptosis induced by MethamphetamineSigma-1 receptors comprise a unique family of proteins that have been implicated in the pathophysiology for many central nervous system disorders.As specific binding proteins of psychiatric drugs,sigma-1 receptors have medium affinity to Meth.Noteworthy,the sigma-1 receptor ligands at the cellular level are able to modulate the function of several ion channels(potassium channel,NMDA receptors,IP3 receptors).Based on the fact that sigma-1 receptors inhibited the IDR channel,which is regarded as a potential target of cell apoptosis,we hypothesized that sigma-1 receptor might have an impact on Kv2.1 regulation.Therefore,western blot and cell membrane extraction were performed to explore the role of sigma-1 receptors in Kv2.1 expression and cellular distribution,and the corresponding signal pathways were studied as well.Our results showed that Meth increased the expression of sigma-1 receptor in a dose-dependent manner.While PRE-084(sigma-1 receptor agonist),rather than BD-1063(sigma-1 receptor antagonist),partially counteracted Meth-induced apoptosis.Meanwhile,PRE-084 down-regulated the Kv2.1 expression,prevented against Kv2.1 trafficking to membrane and p38 MAPK phosphoration reduction,which might be involved in neuroprotective effect of sigma-1 receptors.