Mitochondrial dysfunction in preclinical genetic prion disease: A target for preventive treatment?

Mitochondrial malfunction is a common feature in advanced stages of neurodegenerative conditions, as is the case for the accumulation of aberrantly folded proteins, such as PrP in prion diseases. In this work, we investigated mitochondrial activity and expression of related factors vis a vis PrP accumulation at the subclinical stages of TgMHu2ME199K mice, modeling for genetic prion diseases. While these mice remain healthy until 5-6 months of age, they succumb to fatal disease at 12-14 months. We found that mitochondrial respiratory chain enzymatic activates and ATP/ROS production, were abnormally elevated in asymptomatic mice, concomitant with initial accumulation of disease related PrP. In parallel, the expression of Cytochrome c oxidase (COX) subunit IV isoform 1(Cox IV-1) was reduced and replaced by the activity of Cox IV isoform 2, which operates in oxidative neuronal conditions. At all stages of disease, Cox IV-1 was absent from cells accumulating disease related PrP, suggesting that PrP aggregates may directly compromise normal mitochondrial function. Administration of Nano-PSO, a brain targeted antioxidant, to TgMHu2ME199K mice, reversed functional and biochemical mitochondrial functions to normal conditions regardless of the presence of misfolded PrP. Our results therefore indicate that in genetic prion disease, oxidative damage initiates long before clinical manifestations. These manifest only when aggregated PrP levels are too high for the compensatory mechanisms to sustain mitochondrial activity.