Friedreich's ataxia (FRDA) is a trinucleotide repeat expansion neurodegenerative disorder, in which GAA repeats in the first intron of FXN gene, abolish the expression of frataxin. Although congenital, this defect triggers the onset of the pathology predominantly in the second decade of life. One of the main events landmarking the pathologic onset of the disease is the death of dorsal root ganglia (DRG) neurons. However, cognitive defects in FRDA patients point to neurodevelopmental, pre-symptomatic impairments that occur largely before the overt manifestation of symptoms. At cellular level, frataxin deficiency impairs heme- and iron-sulphur cluster-containing protein biosynthesis, causing dysfunction in the respiratory electron transport chain and mitochondrial iron accumulation. This leads to an increase of the oxidative stress and membrane lipid peroxidation, and impairs the antioxidant response, by altering the proper localization and expression of the NF-E2 p45-related factor 2 (NRF2), the master regulator of antioxidant defence. These defects are markers of a recently described type of cell death, known as ferroptosis. We hypothesize that the progressive accumulation of oxidative stress-induced damage in early life triggers this cellular pathway, unleashing the pathologic onset. To investigate this possibility, we propose: (i) to characterize the defects that take place during the cortical development in the Frataxin Knockin/Knockout (KIKO) mouse; (ii) to unveil the molecular determinants that trigger these defects, through a high-throughput approach and to evaluate if re-establishing the cellular antioxidant defence we are able to rescue these defects; (iii) to determine how and when the accumulation of frataxin depletion-induced impairments causes the uprising of ferroptotic markers in the DRG of YG8R mice and if these markers can be traced in the blood of FRDA patients, to be exploited as reliable biomarkers and new therapeutic targets of the pathology.
Up to now there is no cure nor approved therapy for FRDA. Although DRG and cerebellar neurodegeneration along with cardiomyopathy are key steps of the pathology, the mechanisms that underlie these defects are still elusive. Furthermore, it is increasingly coming to light that although FRDA patients exhibit the typical phenotypic defects of the disease starting from the second decade of life, given that they are exposed to the frataxin deficiency since birth, a pre-symptomatic stage of the disease is highly reasonable. In line with this, we and others have demonstrated that the developmental window of neurogenesis is critical, thus making crucial to understand if neurogenesis routes are altered in FRDA, as it is increasingly emerging in other neurodegenerative conditions such as Parkinson¿s, Alzheimer¿s and Huntington¿s diseases (34-36). In line with this, various studies demonstrated that high level of lipid peroxidation are detected in the blood of Parkinson¿s, Huntington¿s and Alzheimer¿s disease patients and ferroptosis markers have been studied in Amyotrophic Lateral sclerosis (ALS) patients, pointing at this recently discovered pathway of cell death as a common thread in neurodegeneration. On the other hand, it is important to note that currently in use therapeutic protocol for FRDA has a 12 months duration before the efficacy is evaluated by measuring specific clinical endpoints, whereas the identification of early biomarkers that would allow the monitoring of the efficacy of a given treatment is increasingly urgent. In this respect, a great opportunity is provided by the fact that impairments in the main pathologic targets, with particular reference to oxidative stress-induced defects, are reflected in cellular districts, which do not represent the primary pathologic sites of FRDA (e. g. blood).
It is therefore expected that results produced within this project will contribute to the identification of reliable and sensitive biomarkers, suitable for the evaluation of effective therapeutic approaches and for monitoring their effect on disease progression. In fact, recent evidence clearly demonstrates that markers of ferroptosis are reliably detectable in the blood of patients, thus paving the way for their introduction in the clinical practice and to be used for the evaluation of interventions aimed at delaying or reverting pathologic symptomatology. For this reason, our approach, by providing a thorough characterization of molecular defects of FRDA pathology, using mouse models and NSCs at stages preceding the overt manifestation of pathological signs, and, then, by identifying reliable blood markers associated to these defects in FRDA patients, will fill medical needs that are still unmeet, although urgent. Besides, contributing to the knowledge of the cellular pathways that are affected by frataxin deficiency, the identification of new biomarkers for the rapid diagnosis and evaluation of disease progression will contribute to novel therapeutical interventions, aimed at ameliorating current treatments and at rewiring the pathologic defects.