Cytotoxicity of a mutant huntingtin fragment in yeast involves early alterations in mitochondrial OXPHOS complexes II and III

Abstract

Mitochondrial dysfunction may play an important role in the pathogenic mechanism of Huntington's disease (HD). However, the exact mechanism by which mutated huntingtin could cause bioenergetic dysfunction is still unknown. We have constructed a stable inducible yeast model of HD by expressing a human huntingtin fragment containing a mutant polyglutamine tract of 103Q fused to green fluorescent protein (GFP), and a control expressing a wild-type 25Q domain fused to GFP in a wild-type strain. We showed that in yeast cells expressing 103Q, cell respiration was progressively reduced after 4-6 h of induction with galactose, down to 50% of the control after 10 h of induction. The cell respiration defect results from an alteration in the function and amount of mitochondrial respiratory chain complex II+III, in congruency to data obtained from postmortem brain of HD patients and from toxin models. In our model, the production of reactive oxygen species (ROS) is significantly enhanced in cells expressing 103Q. Quenching of ROS with resveratrol partially prevents the cell respiration defect. Mitochondrial morphology and distribution were also altered in cells expressing 103Q, probably resulting from the interaction of aggregates with portions of the mitochondrial web and from a progressive disruption of the actin cytoskeleton. We propose a mechanism for mitochondrial dysfunction in our yeast model of HD in which the interactions of misfolded/aggregated polyglutamine domains with the mitochondrial and actin networks lead to disturbances in mitochondrial distribution and function and to increase in ROS production. Oxidative damage could preferentially affect the stability and function of enzymes containing iron-sulfur clusters such as complexes II and III. Our yeast model represents a very useful paradigm to study mitochondrial physiology alterations in the pathogenic mechanism of HD.

Dysregulation of Mitochondrial Calcium Signaling and Superoxide Flashes Cause Mitochondrial Genomic DNA Damage in Huntington Disease

“…Postmortem studies of symptomatic HD patients revealed a drastic deficiency of complexes II and III and a lesser deficiency of complex IV in the caudate or putamen, with relatively normal levels in the frontal cortex or cerebellum (31,32). Studies with HD cell models expressing Htt exon-1 containing elongated CAG repeats showed decreased complex II enzymatic activity and deficiency of complex III (33,80,81). These observations suggest that impairment of mitochondrial function is important in the progression of the disease.…”

Aberrant Rab11-Dependent Trafficking of the Neuronal Glutamate Transporter EAAC1 Causes Oxidative Stress and Cell Death in Huntington's Disease

“…Neurons were studied in one set of cultures from embryos of WT and HD pregnant mice with each genotype in three culture dishes. chondria dysfunctions, which are major ROS generators (Benchoua et al, 2006;Solans et al, 2006;Fukui and Moraes, 2007;Oliveira et al, 2007;Starkov, 2008). They suggest that the depletion of GSH is a downstream effect of excess ROS.…”

Modeling ALS and FTLD proteinopathies in yeast: An efficient approach for studying protein aggregation and toxicity

“…[30][31][32][33] When polyQ-expanded Huntingtin fragments are overexpressed in yeast, they form toxic cytoplasmic aggregates in a length-dependent fashion that are disruptive to ER-associated degradation, endocytosis and mitochondrial function. [34][35][36] Expression of human Tau in yeast enabled detection of hyperphosphorylated, sarkosyl-insoluble Tau fractions, similar to those found in patients with Alzheimer disease. 37 After isolation from yeast, this fraction efficiently seeded recombinant Tau fibrilization in vitro; moreover, deletion of yeast kinases Mds1 and Pho85 (orthologs of human GSK-3b and cdk5) modulated Tau phosphorylation and aggregation, mimicking processes that occur in diseased tissue.…”