SK channel activation is neuroprotective in conditions of enhanced ER\u2013mitochondrial coupling

Birgit Honrath,Carsten Culmsee,Amalia M Dolga,Nadia Bendridi,Jennifer Rieusset,Inge E Krabbendam,Valentina Pegoretti,Carmen Ijsebaart,Martina Schmidt

doi:10.1038/s41419-018-0590-1

Abstract

Alterations in the strength and interface area of contact sites between the endoplasmic reticulum (ER) and mitochondria contribute to calcium (Ca2+) dysregulation and neuronal cell death, and have been implicated in the pathology of several neurodegenerative diseases. Weakening this physical linkage may reduce Ca2+ uptake into mitochondria, while fortifying these organelle contact sites may promote mitochondrial Ca2+ overload and cell death. Small conductance Ca2+-activated K+ (SK) channels regulate mitochondrial respiration, and their activation attenuates mitochondrial damage in paradigms of oxidative stress. In the present study, we enhanced ER–mitochondrial coupling and investigated the impact of SK channels on survival of neuronal HT22 cells in conditions of oxidative stress. Using genetically encoded linkers, we show that mitochondrial respiration and the vulnerability of neuronal cells to oxidative stress was inversely linked to the strength of ER–mitochondrial contact points and the increase in mitochondrial Ca2+ uptake. Pharmacological activation of SK channels provided protection against glutamate-induced cell death and also in conditions of increased ER–mitochondrial coupling. Together, this study revealed that SK channel activation provided persistent neuroprotection in the paradigm of glutamate-induced oxytosis even in conditions where an increase in ER–mitochondrial coupling potentiated mitochondrial Ca2+ influx and impaired mitochondrial bioenergetics.

Highlights

Multiple lines of evidence indicate that the etiologies of neurodegenerative disorders, such as Alzheimer’s disease (AD) or Parkinson’s disease (PD) are strongly associated with common features of neuronal damage such as dysregulation of calcium (Ca2+) homeostasis and oxidative stress[1,2,3,4,5]
This study revealed that small conductance Ca2+-activated K+ (SK) channel activation provided persistent neuroprotection in the paradigm of glutamate-induced oxytosis even in conditions where an increase in endoplasmic reticulum (ER)–mitochondrial coupling potentiated mitochondrial Ca2+ influx and impaired mitochondrial bioenergetics
A GFP-tagged ER-Flipper control plasmid (FL), co-transfected with OMM-FKBP12-mRFP, failed to co-localize with RFPtagged mitochondria following rapamycin treatment (Fig. 1b), which confirmed the specificity of the hereafter called ER–mitochondrial linkers (EML)

Summary

Introduction

Multiple lines of evidence indicate that the etiologies of neurodegenerative disorders, such as Alzheimer’s disease (AD) or Parkinson’s disease (PD) are strongly associated with common features of neuronal damage such as dysregulation of calcium (Ca2+) homeostasis and oxidative stress[1,2,3,4,5]. Close spatial interactions between the endoplasmic reticulum (ER) and mitochondria are essential for rapid and sustained [Ca2+]m uptake. These close contacts are established at the so called mitochondria-associated ER membranes (MAM), thereby facilitating Ca2+ transfer between ER and mitochondria through mitochondrial voltage-dependent anion channels (VDAC) and ER-. Mutations in MAM-associated proteins have been identified to either enhance or reduce ER–mitochondrial coupling (EMC), thereby leading to dysregulation of MAM interfaces and progressive neuronal degeneration as shown in models of AD and amyotrophic lateral sclerosis[13,14,15]. Activation of small conductance Ca2+-activated K+ (SK) channels regulated Ca2+ uptake and retention in the ER16, and controlled mitochondrial Ca2+ homeostasis and respiration[17]. We aimed to investigate the ability of SK channels to confer protection following oxidative stress in conditions where EMC was increased

Objectives

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Conclusion