Bioenergetic dysfunction in Huntington's disease human cybrids

Abstract

In this work we studied the mitochondrial-associated metabolic pathways in Huntington's disease (HD) versus control (CTR) cybrids, a cell model in which the contribution of mitochondrial defects from patients is isolated. HD cybrids exhibited an interesting increase in ATP levels, when compared to CTR cybrids. Concomitantly, we observed increased glycolytic rate in HD cybrids, as revealed by increased lactate/pyruvate ratio, which was reverted after inhibition of glycolysis. A decrease in glucose-6-phosphate dehydrogenase activity in HD cybrids further indicated decreased rate of the pentose-phosphate pathway. ATP levels of HD cybrids were significantly decreased under glycolysis inhibition, which was accompanied by a decrease in phosphocreatine. Nevertheless, pyruvate supplementation could not recover HD cybrids' ATP or phosphocreatine levels, suggesting a dysfunction in mitochondrial use of that substrate. Oligomycin also caused a decrease in ATP levels, suggesting a partial support of ATP generation by the mitochondria. Nevertheless, mitochondrial NADH/NAD t levels were decreased in HD cybrids, which was correlated with a decrease in pyruvate dehydrogenase activity and protein expression, suggesting decreased tricarboxylic acid cycle (TCA) input from glycolysis. Interestingly, the activity of alpha-ketoglutarate dehydrogenase, a critical enzyme complex that links the TCA to amino acid synthesis and degradation, was increased in HD cybrids. In accordance, mitochondrial levels of glutamate were increased and alanine was decreased, whereas aspartate and glutamine levels were unchanged in HD cybrids. Conversely, malate dehydrogenase activity from total cell extracts was unchanged in HD cybrids. Our results suggest that inherent dysfunction of mitochondria from HD patients affects cellular bioenergetics in an otherwise functional nuclear background.

An impaired metabolism of nucleotides underpins a novel mechanism of cardiac remodeling leading to Huntington's disease related cardiomyopathy

“…We demonstrated a reduced NADH level and NADH/NAD+ ratio in the mouse models. This may be an indication of redox imbalance, and could suggest an inherent dysfunction of mitochondria, or be indicative of alterations in a mitochondrial function upstream of oxidative phosphorylation [50]. In particular, this could indicate a disrupted efficiency of the Krebs cycle.…”

Potential of protease inhibitor in 3-nitropropionic acid induced Huntington's disease like symptoms: Mitochondrial dysfunction and neurodegeneration

“…It is also accepted that mutant Htt not only impairs mitochondrial function, but also compromises cytosolic and mitochondrial calcium homeostasis. This ultimately contributes to neuronal dysfunction and death in HD (Ferreira et al, 2011). Mitochondria are the main cellular source of ROS and key regulators of cell death.…”

“…The mutant Htt causes cell death by a variety of mechanisms. It causes mitochondrial dysfunction by interacting with the organelle and producing defects in the dynamics of the mitochondria which, in turn, may result in bio-energetic failure (Ferreira et al, 2011). Studies have demonstrated reduced activity of the complex II enzyme succinate dehydrogenase (SDH), a 55-60% decrease in complex II-III activity in the basal ganglia of patients with Huntington's disease decrease along with a decrease in complex IV activity in HD striatum (Leegwater-Kim and Cha, 2004).…”

Mitochondrial disorders: aetiologies, models systems, and candidate therapies

“…Recapitulation of mitochondrial disorders in cell culture has largely relied on cytoplasmic hybrid cells or cybrids, in which the mitochondrial content of a host cell has been manipulated such that endogenous mtDNA has been depleted and repopulated with donor mtDNA from platelets or enucleated cells [37,38]. Cybrids have been used to characterise the disturbances in cellular bioenergetics LHON is caused by mutations in genes encoding components of the mitochondrial respiratory NADH-ubiquinone oxidoreductase complex (complex I).…”