The glutathione system maintains the thiol redox balance in the mitochondria of fission yeast
Laura de Cubas, Susanna Boronat, Montserrat Rojo de la Vega, Alba Domènech, Ferran Gómez-Armengol, А. V. Artemov, O. G. Lyublinskaya, José Ayté, Elena Hidalgo
Abstract
The thioredoxin and glutathione (GSH)-glutaredoxin electron donor pathways provide a reducing environment to the cell and maintain homeostasis of numerous redox reactions. The abundant tripeptide GSH has multiple roles, including redox buffering, detoxification, peroxide scavenging and iron-sulfur cluster assembly. Glutathione reductase, Pgr1 in fission yeast, maintains glutathione reduced, and it is essential in most organisms. Cells lacking Pgr1 exhibit severe pleiotropic defects. We used multiple approaches to unravel the compartment-specific roles of Pgr1. Our findings confirmed that Pgr1 had dual cytosolic and mitochondrial localization. Mitochondrial homeostasis was severely impaired in Δ pgr1 cells and most of these defects were restored by expression of an exclusively mitochondrial Pgr1 isoform. As expected, the cytosol of Δ pgr1 cells showed low ratio of reduced-to-oxidized glutathione. However, this did not significantly affect peroxiredoxin-dependent hydrogen peroxide scavenging, suggesting a minimal role, if any, of GSH in cytosolic thiol reduction. The transcriptome of Δ pgr1 cells revealed signatures of oxidative stress and iron deprivation, suggesting that the GSH-containing sensor of iron starvation, the glutaredoxin Grx4, is also a sensor of GSH oxidation. In the mitochondria, Pgr1 not only provided the GSH electron donor for the glutaredoxin-based pathway but also recycled mitochondrial Trx2, thereby contributing to thiol redox homeostasis in the matrix. In conclusion, glutathione reductase is essential for maintaining a balanced redox environment in the mitochondria by recycling Trx2, Grx2 and the GSH-containing Grx5, and therefore contributes to the processes of iron-sulfur cluster assembly and respiration, while controlling Grx4 dynamics in the cytosol. • Fission yeast glutathione reductase Pgr1 localizes to the cytosol and mitochondria. • A mitochondrial-only Pgr1 isoform suppresses the phenotypes of cells lacking Pgr1. • Pgr1 maintains mitochondrial redox balance, aiding iron-sulfur cluster assembly and respiration. • Cytosolic peroxiredoxin-dependent peroxide scavenging is not affected in cells lacking Pgr1. • Grx4 senses iron starvation and GSH oxidation, linking glutathione redox state to iron homeostasis.