Nrf2 signaling links ER oxidative protein folding and calcium homeostasis in health and disease.

Veronica Granatiero,Hibiki Kawamata,Csaba Konrad,Giovanni Manfredi,Kirsten Bredvik

doi:10.26508/lsa.201900563

Veronica Granatiero, Hibiki Kawamata + Show 3 more

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https://doi.org/10.26508/lsa.201900563

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Abstract

We report a signaling pathway linking two fundamental functions of the ER, oxidative protein folding, and intracellular calcium regulation. Cells sense ER oxidative protein folding through H2O2, which induces Nrf2 nuclear translocation. Nrf2 regulates the expression of GPx8, an ER glutathione peroxidase that modulates ER calcium levels. Because ER protein folding is dependent on calcium, this pathway functions as rheostat of ER calcium levels. Protein misfolding and calcium dysregulation contribute to the pathophysiology of many diseases, including amyotrophic lateral sclerosis, in which astrocytic calcium dysregulation participates in causing motor neuron death. In human-derived astrocytes harboring mutant SOD1 causative of familial amyotrophic lateral sclerosis, we show that impaired ER redox signaling decreases Nrf2 nuclear translocation, resulting in ER calcium overload and increased calcium-dependent cell secretion, leading to motor neuron death. Nrf2 activation in SOD1 mutant astrocytes with dimethyl fumarate restores calcium homeostasis and ameliorates motor neuron death. These results highlight a regulatory mechanism of intracellular calcium homeostasis by ER redox signaling and suggest that this mechanism could be a therapeutic target in SOD1 mutant astrocytes.

Highlights

The ER is the major intracellular calcium store, involved in a number of fundamental calcium signaling pathways
We show that H2O2 produced by ER oxidative protein folding regulates nuclear factor E2-related factor 2 (Nrf2) signaling, which in turn modulates the expression of glutathione peroxidase 8 (GPx8), a protein involved in ER calcium regulation through the sarco/endoplasmic reticulum calcium ATPase (SERCA) (Yoboue et al, 2017)
To test the hypothesis that ER oxidative protein folding is functionally linked to ER calcium homeostasis through reactive oxygen species (ROS), we treated HeLa cells with a selective Ero1 inhibitor (EN460), which was shown to block ER protein folding in cultured cells at 50 μM (Blais et al, 2010)

Summary

Introduction

The ER is the major intracellular calcium store, involved in a number of fundamental calcium signaling pathways. The redox state of the ER depends on oxidative protein folding mechanisms, whereby nascent proteins imported into the ER for secretion are folded into disulfide bondcontaining secondary structures by the transfer of electrons from their thiol groups to ER oxidoreductases. The ER redox state is known to directly modulate ER calcium protein activity through cysteine modifications (Li & Camacho, 2004; Higo et al, 2005; Marino et al, 2015; Ushioda et al, 2016), the signaling role of ROS produced by oxidative protein folding and diffused outside of the ER (Appenzeller-Herzog et al, 2016) in regulating ER calcium stores remains to be elucidated

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