Consequences of iron exposure and glutathione depletion on redox balance, lipidome, and neurotransmission in C. elegans

Abstract

Although the redox active essential trace element iron (Fe) is involved in many important biological processes, an overexposure can lead to the excessive formation of reactive oxygen and nitrogen species (RONS). Thus, total Fe accumulation, as for example observed in neurodegenerative diseases or diseases as hemochromatosis, can lead to adverse consequences, especially if the antioxidant system is weakened. This system, and especially the most abundant antioxidant in organisms, glutathione (GSH), can be impaired by excess RONS levels, which is relevant during aging and in the context of neurodegenerative diseases. In this study, we demonstrate the consequences of Fe overdosing or/and GSH depletion in Caenorhabditis elegans (C. elegans) on Fe homeostasis, mitochondrial mass, phospho- and sphingolipidome, and on the neurotransmitter levels of acetylcholine, serotonin, dopamine, and γ-aminobutyric acid. In order to investigate this, we treated L4 nematodes with Fe(III) ammonium citrate (FAC) for 24 h or/and diethyl maleate (DEM) for 2 h or 24 h. While FAC treatment alone did not affect mitochondrial mass and cardiolipin content, it increased the amount of several lipid classes and the neurotransmitter acetylcholine. Treatment with DEM alone resulted in GSH depletion by 70 % and was associated with decreased mitochondrial mass and increased Fe(II), lipid, acetylcholine, and serotonin levels. Genes involved in GSH biosynthesis, Fe homeostasis, mitochondrial stress response, lipid biosynthesis, and neurotransmitter regulation are differentially expressed after DEM treatment. In addition, we were able to determine the GSH-DEM product in the nematode using HPLC-MS/MS. Although FAC treatment increased total Fe content in the nematode fivefold, the combined treatment with DEM showed no further effects compared to treatment with FAC or DEM alone. Together, these findings highlight the consequences of an impaired intracellular redox system on mitochondria, lipidome, and neurological endpoints, and identify several pathways, metabolites, and potential compensatory as well as long lasting effects.

Keywords: C. elegans; Glutathione; Iron; Lipids; Mitochondria; Neurotransmitters.