Effects Of Electromagnetic Irradiation On Tau Phosphorylation In Primary Cultured Rat Cortical Neurons And Its Underlying Mechanism

Objectives: With the development of science and information technology, people noware more easily to be exposed to electromagnetic fields (EMF), and the exposure intensityhas increased too. Therefore, the bio-effects, mechanism and protective measures ofelectromagnetic fields, have become the focus of attention. The previous studies onbio-effects of electromagnetic fields demonstrated that central nervous system (CNS) is oneof the most sensitive targets of electromagnetic exposure. Electromagnetic fields exposurecan cause learning and memory impairment which may result from neuron injury. Tauprotein is a group of microtubule-associated protein mainly present in the neurons. Thebiological function of the tau protein is to regulate microtubule dynamic, axonal transportand neurite outgrowth. In pathological conditions, the hyperphosphorylated tau proteinaffinity for microtubule reduces, which leads to microtubule instability and decrease inaxoplasmic transport. This could give rise to neurodegenerative pathological changes,which eventually lead to learning and memory dysfunction. CDK5(cyclin dependent kinase5) and GSK-3β (glycogen synthase kinase-3β) are the two most important protein kinasewhich regulate tau protein phosphorylation. The purpose of this study was to examine theinfluence of electromagnetic fields exposure on tau protein phosphorylation in the neurons,which may have important implications for treatment and protection of the neuron injuryinduced by electromagnetic fields exposure.Methods:(1) After cultured for8days, the rat primary cortical neurons were exposedto90mW/cm2electromagnetic field for10min.(2) CCK-8Kit was used to evaluate theeffects of electromagnetic fields exposure on cellular viability of neurons.(3) Alterations ofthe axon length after electromagnetic exposure were studied by ICC.(4) Thephosphorylation levels of the tau protein phosphorylation sites ser199/202、ser396andser404were studied by Western-blot.(5) Neurons were pretreated alone or in combinationwith Cdk5inhibitor Roscovitine、GSK-3β inhibitor Licl and calpain inhibitor PD150606,then the phosphorylation levels of the tau protein were studied by Western-blot, and alterations of the axon length after electromagnetic fields exposure were studied by ICC.Results:(1) The cellular viability of neurons decreased significantly at6h,12h afterelectromagnetic fields exposure.(2) The axon length shortened significantly at1h and3hafter electromagnetic fields exposure.(3) Electromagnetic fields exposure did not inducesignificant change in the phosphorylation levels of the tau protein phosphorylation sitesser199/202and ser396, but the phosphorylation levels of ser404significantly increased at1h and3h after electromagnetic fields exposure.(4) Cdk5inhibitor Roscovitine, GSK-3βinhibitor Licl and calpain inhibitor PD150606alone or in combination pretreatmenteffectively antagonize the hyperphosphorylation of the tau protein phosphorylation siteser404induced by electromagnetic fields exposure.(5) Cdk5inhibitor Roscovitine,GSK-3β inhibitor Licl and calpain inhibitor PD150606alone or in combinationpretreatment significantly reversed the shortening of the axon length induced byelectromagnetic fields exposure.Conclusions: Electromagnetic radiation can decrease the cellular viability and causehyperphosphorylation of the tau protein phosphorylation site ser404. The results suggestthat Cdk5, GSK-3β and calpain may play an important role in this process. These data shedsome new insight in understanding the mechanisms of neuron injury induced byelectromagnetic exposure and in developing clinical therapeutical approaches forelectromagnetic exposure induced neuron injury.