Role Of Autophagy In Excessive Iodine Induced Neurotoxic Effect On SH-SY5Y Cells

As one of 14 kinds of trace elements, iodine plays an important role in body metabolism. But iodine has a "U" shaped effect on the human body. More and more investigations reveal that excessive iodide has neurotoxic effect, including learning and cognition impairment, but its mechanisim is still unclear. Basal autophagy in non-stressed cells might be essential for neurons due to its protective mechanism. But when stimulation was strong enough to lead a balance destruction between generation and degradation, autophagy could be excessively induced and autophagic death process which was also known as type ?programmol/Led cell death(?-PCD) might be activated. A series of research of excessive iodine neurotoxicity results also show that excessive iodine can make animal brain tissue to produce free radicals, reduce the activity of antioxidant enzymes and cause DNA damage, and these changes induce autophagy occurs, but the role of autophagy in excessive iodine neurotoxicity has not been reported. Here, we exposed human dopaminergic neuroblastoma cell line(SH-SY5Y) to excessive iodine with or without autophagy interference factor, and detected autophagy related indicators to explore this hypothesis. Experiments below were taken to explore the effects of excessive iodine on SH-SY5 Y cells and its mechanism.Part 1: Effects on neurotoxicity of excessive iodine in SH-SY5 Y cellsObjective: study the effects on neurotoxicity of excessive iodine in SH-SY5 Y cellsMethods: Cells were then divided into four groups and treated with triple-distilled water as a control, various concentrations of KI(10, 20, 30 mmol/L). After treated for 24 h, the cells were observed for cellular ultrastructure under a transmission electron microscope. CCK-8 and MDC-staining western blot assays were used to detect the cell viability, autophagy vesicle fluorescence intensity and expression of autophagy related molecules LC3, Beclin1 and p62.Results: The results suggested that the cell viabilities for the treatment groups 20 mmol/L KI and 30 mmol/L KI were significantly lower than the control group(P < 0.05); ultrastructure of SH-SY5 Y cells were obviously changed by forming typical autophagosomes with double membrane, along with dilation and degeneration of mitochondria in the 20 mmol/L KI and 30 mmol/L KI treated groups, especially in the 30 mmol/L KI treated group, as compared to the control group; after MDC-staining, autophagy vesicle fluorescence intensity of 20 and 30 mmol/L KI-treated group were significantly higher than the control group(P < 0.05). Meanwhile, expression ofautophagy related molecules LC3, Beclin1 and p62 of 20 and 30 mmol/L KI-treated groups were significantly higher than the control group(P < 0.05).Conclusion: Excessive iodine could cause neurotoxicity and increase the level of autophagy in SH-SY5 Y cells in a dose-dependent manner.Part2: The role of autophagy in excessive iodine neurotoxicityObjective: Explore the role of autophagy in excessive iodine neurotoxicityMethods: Detect the expression of LC3, Beclin1 and p62 after the cells were treated by excessive iodine(30 mmol/L KI) with or without 3-MA or NAC for 24 h. Meanwhile, treat the cells in different concentration of iodine(0, 10, 20, 30 mmol/L) for 24 h, and detect the cell viability in each group.Results: A significant reduction was detected in m RNA and protein expression levels of LC3, p62 and Beclin1 in the 30 mmol/L KI and 3-MA combined treatment group compared with the 30 mmol/L KI-treated group(P < 0.05, respectively). In CCK-8 assay, the cell viability of 20, 30 mmol/L KI intoxicated group was conspicuously decreased compared with the control group(P < 0.05, respectively), while the treatment group of 10 mmol/L KI showed no difference with the control group(P > 0.05). What's more, cell viability of the intervening group(20 mmol/L KI+3-MA, 30 mmol/L KI+3-MA) was significantly higher than the 20, 30 mmol/L KI treatment group respectively(P < 0.05).Conclusion: Autophagy may be a kind of cell death in the process of SH-SY5 Y cell death induced by KI, and this process is likely to be related with oxidative stress and PI3K/Akt/m TOR pathway.