Abstract
Mitochondrial calcium ([Ca2+]m) overload and changes in mitochondrial metabolism are key players in neuronal death. Small conductance calcium-activated potassium (SK) channels provide protection in different paradigms of neuronal cell death. Recently, SK channels were identified at the inner mitochondrial membrane, however, their particular role in the observed neuroprotection remains unclear. Here, we show a potential neuroprotective mechanism that involves attenuation of [Ca2+]m uptake upon SK channel activation as detected by time lapse mitochondrial Ca2+ measurements with the Ca2+-binding mitochondria-targeted aequorin and FRET-based [Ca2+]m probes. High-resolution respirometry revealed a reduction in mitochondrial respiration and complex I activity upon pharmacological activation and overexpression of mitochondrial SK2 channels resulting in reduced mitochondrial ROS formation. Overexpression of mitochondria-targeted SK2 channels enhanced mitochondrial resilience against neuronal death, and this effect was inhibited by overexpression of a mitochondria-targeted dominant-negative SK2 channel. These findings suggest that SK channels provide neuroprotection by reducing [Ca2+]m uptake and mitochondrial respiration in conditions, where sustained mitochondrial damage determines progressive neuronal death.
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Acknowledgements
We thank Katharina Elsässer for her excellent technical support and advice, and Emma Jane Esser for careful reading and correction of the manuscript. Further, we thank Prof Bernd Fakler for providing the SK2 channel plasmids, Susanne Michels for performing the MTT assays with MK801 and Maren Richter for providing fluorescence images of Rho2 distribution in HT22 cells. The work of FP was supported by the German Research Foundation (DFG) under the Emmy Noether Programme [PE 2053/1-1] and the Bavarian Ministry of Sciences, Research and the Arts in the framework of the Bavarian Molecular Biosystems Research Network [D2–F5121.2–10c/4822]. This work was supported by a grant from the Deutsche Forschungsgemeinschaft, DFG (DO 1525/3-1) and, in parts, by the von-Behring-Röntgen Stiftung. AMD is the recipient of a Rosalind Franklin Fellowship co-funded by European Union and University of Groningen.
Author contributions
BH, LeM and TM carried out the experiments and performed data analysis. AMD, CC and BH participated in the design of the study and wrote the manuscript. LiM and ND designed, performed and analyzed patch clamp experiments. GKG, AG, BMB, CK and MB provided insightful discussions and contributed to data analysis. HZ, FP, AG and SS provided methods, cells and plasmids. All authors read and approved the final manuscript.
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Honrath, B., Matschke, L., Meyer, T. et al. SK2 channels regulate mitochondrial respiration and mitochondrial Ca2+ uptake. Cell Death Differ 24, 761–773 (2017). https://doi.org/10.1038/cdd.2017.2
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DOI: https://doi.org/10.1038/cdd.2017.2
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