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Fluoride-Induced Neuron Apoptosis and Expressions of Inflammatory Factors by Activating Microglia in Rat Brain

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Abstract

Excessive exposure to fluoride results in structural and functional damages to the central nervous system (CNS), and neurotoxicity of fluoride may be associated with neurodegenerative changes. Chronic microglial activation appears to cause neuronal damage through producing proinflammatory cytokines and is involved in many neurodegenerative disorders. It is not known about effects on microglia of fluoride. In the present study, healthy adult Wistar rats were exposed to 60 and 120 ppm fluoride in drinking water for 10 weeks, and control rats received deionized water. After 10 weeks, rats were sacrificed under anesthesia then apoptosis in neuron and inflammatory factors secreted by microglia were determined. We found that apoptosis of neurons in fluoride-treated rat brain increased and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive immunofluorescence increased with increasing fluoride concentrations. Bax protein expression increased and Bcl-2 protein expression decreased in fluoride-treated rat brain compared with that of the control rat brain. The microglia in the hippocampus and cortex of fluoride-treated rats were activated by immunostaining with OX-42, a marker of activated microglia, and OX-42-positive microglia cells were more abundant in the hippocampus than in the cortex. The levels of IL-1β and IL-6 protein expression in OX-42-labeled microglial cells were significantly increased in the cortex and hippocampus of rats exposed to fluoride, and TNF-α immunoreactivity in microglial cells of the hippocampus was significantly higher in the 120 ppm fluoride-treated group than that in the control group. Our results indicate that fluoride induced neuron apoptosis and expressions of inflammatory factors by activating microglia in rat brain.

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Acknowledgments

This work was supported by the Research Fund for the Doctoral Program of Higher Education of China (No. 20112104110021).

Conflict of Interest

The authors declare that they have no competing interests.

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Authors and Affiliations

  1. Department of Occupational and Environmental Health, School of Public Health, China Medical University, No. 77 Puhe Road, Shengyang North New Area, Shenyang, Liaoning Provence, 110122, People’s Republic of China

    Nan Yan, Shengnan Liu, Siqi Cao, Fei Wang & Shuhua Xi

  2. Shenyang Medical College, No146 Huanghe North Street, Shenyang, 110034, People’s Republic of China

    Nan Yan, Yan Liu & Zhengdong Wang

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  1. Nan Yan
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  2. Yan Liu
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Correspondence to Shuhua Xi.

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Yan, N., Liu, Y., Liu, S. et al. Fluoride-Induced Neuron Apoptosis and Expressions of Inflammatory Factors by Activating Microglia in Rat Brain. Mol Neurobiol 53, 4449–4460 (2016). https://doi.org/10.1007/s12035-015-9380-2

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