Cadmium Activates MTOR Pathway Leading To Apoptosis Of Neuronal Cells And Protective Effect Of NAC

To investigate the mechanisms of mammalian target of rapamycin (mTOR) pathway in cadmium-induced neuronal cell apoptosis and protective effect of N-acetyl-L-cysteine (NAC), PC12cells and primary cerebral cortical neurons of foetal Sprague-Dawley rats at18-19days of gestation were used. The primary cerebral cortical neurons and PC12cells were exposed to10μmol/L cadmium acetate for different times (0,1,2,4,8,12,24h), cadmium at different concentrations (0,5,10and20μmol/L) or10μmol/L cadmium in the absence or the presence of mTOR inhibitor, rapamycin (200nmol/L) or an antioxidant, NAC(primary cerebral cortical neurons,100μmol/L; PC12cells,1mmol/L) for24h. Then the apoptosis rate was analyzed by flow cytometry (FCM), the morphology of the nuclei was observed by hoechst33258staining and the expression of the proteins related with mTOR pathway were observed by western blotting.The results were as follows:①In comparison with the control group, the results showed that the phosphorylation of PTEN and PDK1was significantly down-regulated (P<0.05or P<0.01), but the phosphorylation of Akt, mTOR, p70S6K1,4E-BP1was significantly up-regulated in the primary cerebral cortical neurons and PC12cells that were exposed to10-20μmol/L for24h or10μmol/L after8h (P<0.05orP<0.01), and the above-mentioned caused by cadmium were dose-dependent;②Rapamycin, a mTOR inhibitor, significantly attenuated Cd-induced downregulation of PTEN phosphorylation and upregulation of Akt, mTOR, p70S6K1,4E-BP1phosphorylation (P<0.05orP<0.01);③The neuronal cells exposed to cadmium showed typical morphological changes of apoptosis with nucleus crimpled and chromatin condensedation, even nucleus disintegratation, and the apoptosis rate was increased. Rapamycin decreased the apoptosis rate and morphological changes of nucleus in neuronal cells caused by cadmium;④NAC significantly attenuates cadmium-induced downregulation of PTEN phosphorylation and upregulation of Akt, mTOR, p70S6K1,4E-BP1phosphorylation (P<0.05or P<0.01), as well as apoptosis rate and the morphological changes of nucleus in neuronal cells. Conclusion:The results indicate that cadmium induce neuronal cell apoptosis, in part by down-regulating the expression of phosphorylation of PTEN and PDK1, up-regulating the expression of phosphorylation of Akt, mTOR, p70S6K1, and4E-BP1, activating the mTOR pathway, which was abrogated by NAC.