Friedreich's ataxia: the vicious circle hypothesis revisited

Therapies in inborn errors of oxidative metabolism

Mitochondrial diseases encompass a wide range of presentations and mechanisms, dictating a need to consider both broad-based and disease-specific therapies. The manifestations of mitochondrial dysfunction and the response to therapy vary between individuals. This probably reflects the genetic complexity of mitochondrial biology, which requires an excess of 2000 genes for proper function, with numerous interfering epigenetic and environmental factors. Accordingly, we are increasingly aware of the complexity of these diseases which involve far more than merely decreased ATP supply. Indeed, recent therapeutic progress has addressed only specific disease entities. In this review present and prospective therapeutic approaches will be discussed on the basis of targets and mechanism of action, but with a broad outlook on their potential applications.

Oxidative stress induces mitochondrial fragmentation in frataxin-deficient cells

Friedreich ataxia (FA) is the most common recessive neurodegenerative disease. It is caused by deficiency in mitochondrial frataxin, which participates in iron-sulfur cluster assembly. Yeast cells lacking frataxin (Δyfh1 mutant) showed an increased proportion of fragmented mitochondria compared to wild-type. In addition, oxidative stress induced complete fragmentation of mitochondria in Δyfh1 cells. Genetically controlled inhibition of mitochondrial fission in these cells led to increased resistance to oxidative stress. Here we present evidence that in yeast frataxin-deficiency interferes with mitochondrial dynamics, which might therefore be relevant for the pathophysiology of FA.

The yeast metacaspase is implicated in oxidative stress response in frataxin-deficient cells

Friedreich ataxia is the most common recessive neurodegenerative disease and is caused by reduced expression of mitochondrial frataxin. Frataxin depletion causes impairment in iron-sulfur cluster and heme biosynthesis, disruption of iron homeostasis and hypersensitivity to oxidants. Currently no pharmacological treatment blocks disease progression, although antioxidant therapies proved to benefit patients. We show that sensitivity of yeast frataxin-deficient cells to hydrogen peroxide is partially mediated by the metacaspase. Metacaspase deletion in frataxin-deficient cells results in recovery of antioxidant capacity and heme synthesis. In addition, our results suggest that metacaspase is associated with mitochondrial respiration, intracellular redox control and genomic stability.