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Hippocampal Neurons Exposed to the Environmental Contaminants Methylmercury and Polychlorinated Biphenyls Undergo Cell Death via Parallel Activation of Calpains and Lysosomal Proteases

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Abstract

Methylmercury (MeHg) and polychlorinated biphenyls (PCBs) are widespread environmental pollutants commonly found as contaminants in the same food sources. Even though their neurotoxic effects are established, the mechanisms of action are not fully understood. In the present study, we have used the mouse hippocampal neuronal cell line HT22 to investigate the mechanisms of neuronal death induced by MeHg, PCB 153, and PCB 126, alone or in combination. All chemicals induced cell death with morphological changes compatible with either apoptosis or necrosis. Mitochondrial functions were impaired as shown by the significant decrease in mitochondrial Ca2+ uptake capacity and ATP levels. MeHg, but not the PCBs, induced loss of mitochondrial membrane potential and release of cytochrome c into the cytosol. Also, pre-treatment with the antioxidant MnTBAP was protective only against cell death induced by MeHg. While caspase activation was absent, the Ca2+-dependent proteases calpains were activated after exposure to MeHg or the selected PCBs. Furthermore, lysosomal disruption was observed in the exposed cells. Accordingly, pre-treatment with the calpain specific inhibitor PD150606 and/or the cathepsin D inhibitor Pepstatin protected against the cytotoxicity of MeHg and PCBs, and the protection was significantly enhanced when the two inhibitors were combined. Simultaneous exposures to lower doses of MeHg and PCBs suggested mostly antagonistic interactions. Taken together, these data indicate that MeHg and PCBs induce caspase-independent cell death via parallel activation of calpains and lysosomal proteases, and that in this model oxidative stress does not play a major role in PCB toxicity.

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Acknowledgments

We thank Dr. Maria Vittoria Vettori and Dr Anna Castoldi for valuable discussions. This work was supported by grants from the European Commission (DEVNERTOX, ATHON) and the Swedish Research Council FORMAS.

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Authors and Affiliations

  1. Department of Neuroscience, Karolinska Institutet, 17177, Stockholm, Sweden

    Roshan Tofighi, Wan Norhamidah Wan Ibrahim & Sandra Ceccatelli

  2. Department of Oncology–Pathology, Karolinska Institutet, Karolinska University Hospital Solna, 17176, Stockholm, Sweden

    Carolina Johansson

  3. Laboratory of Industrial Toxicology, Department of Clinical Medicine, Nephrology and Health Sciences, University of Parma, 43100, Parma, Italy

    Matteo Goldoni & Antonio Mutti

  4. Institute of Environmental Medicine, Karolinska Institutet, 17177, Stockholm, Sweden

    Vladimir Gogvadze

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  1. Roshan Tofighi
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  2. Carolina Johansson
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  3. Matteo Goldoni
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  4. Wan Norhamidah Wan Ibrahim
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  5. Vladimir Gogvadze
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Correspondence to Roshan Tofighi.

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Tofighi, R., Johansson, C., Goldoni, M. et al. Hippocampal Neurons Exposed to the Environmental Contaminants Methylmercury and Polychlorinated Biphenyls Undergo Cell Death via Parallel Activation of Calpains and Lysosomal Proteases. Neurotox Res 19, 183–194 (2011). https://doi.org/10.1007/s12640-010-9159-1

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