Proctective role of glutathione reductase in Caenorhabditis elegans models of polyQ diseases

Abstract

Protein aggregation is a major hallmark of many neurodegenerative disorders such as Alzheimer, Parkinson and Huntington Diseases. However, the signaling events and molecular pathways governing this aggregation process are not completely understood. Huntington Disease and other polyQ diseases are characterized by an abnormal CAG codon expansion (that encodes the amino acid glutamine) inspecific genes. When these CAG expansions increase above a threshold of 35 to 40 glutamine residues, the resulting protein shows toxic gain-of-function features, associated to protein misfolding and aggregation. Using Caenorhabditis elegans models of polyQ diseases we have identified a novel protective role of glutathione reductase (GSR-1) against polyQ aggregation and toxicity. First, we found that gsr-1 RNAi downregulation inworms expressing the fusion protein Q40::YFP caused a strong developmental arrest while Q35::YFP animals developed normally. This phenotype was phenocopied by treatment with buthionine sulphoximine (an inhibitor of glutathione synthesis) and diethyl maleate (a glutathione depletory), confirming that 40 glutamine residues set the pathological threshold of polyQ proteins alsoinworms. Consistently, Q40::YFP animals carrying a gsr-1 loss of function mutation showed a remarkable increase of polyQ aggregation in muscle cells. Interestingly, embryos from Q40::YFP worms lacking gsr-1 display a striking phenotype consisting incell membrane blebbing and explosion, a phenotype that is much milder inQ35::YFP; gsr-1 embryos. Finally, our results demonstrate that, inC. elegans, the gsr-1 gene encodes two isoforms that localize to cytoplasm and mitochondria, respectively. Importantly, the cytoplasmic variant is shown to be essential for C. elegans viability while animals devoid of the mitochondrial isoform have no phenotype. Our future plans will focus on validating the results obtained with C. elegans in mammalian cell culture and mice models of Huntington s Disease and other polyQ Diseases. In addition, we will explore the role of glutaredoxins and other glutathione-dependent enzymes in worm models of polyQ and other aggregation-dependent neurodegenerative diseases.