A novel cell and gene therapy approach for Friedreich's ataxia

Abstract

Friedreich’s ataxia (FA) is an autosomal-recessive, neurodegenerative incapacitating disease that mainly affects the nervous system and heart, and has a significant effect on the life of affected individuals. FA is closely correlated with the frequency of large normal FXN alleles (>12 GAA motifs) in the population. It is characterised clinically by early onset (usually in childhood or adolescence) spinocerebellar ataxia, dysarthria, proximal weakness, sensory loss, and cardiomyopathy, and leads to dependence on a wheelchair and reduced life expectancy to usually between 40-50 years. It is caused by GAA expansions repeated in the first intron of the frataxin gene on chromosome 9. Trinucleotide expansions repeat in the gene and consequently cause an abnormal conformation in the DNA which leads to decreased transcription of the frataxin gene and therefore to reduced expression of the frataxin protein. Frataxin is a mitochondrial protein required for iron haemostasis and iron-sulphur cluster (Fe-S) formation and it plays an essential role in the protection of cells from oxidative damage. Decreased levels result in reduced iron-sulphur group creation, mitochondrial iron build-up, cytosolic iron diminution, oxidative stress and mitochondrial dysfunction. Several studies have shown that replacement of the frataxin can restore mitochondrial function. The main hypothesis of this research project is that a tissue-penetrating version of frataxin could be delivered to diseased tissues by genetically modified patient-derived haematopoietic stem cells. Therapeutic stem cells should be able to survive in the bone marrow for many years and migrate from their niche to differentiate into different cell lineages within various tissues, so the resultant delivery of frataxin would be continuous and long-term. To validate this strategy, we have generated frataxin fused to tissue penetrating peptides encoded by lentiviral vectors that we have used to infect human cell lines. We confirmed that the different frataxin peptides were secreted by HEK 293T cells and differentiated primary human haematopoietic stem cells. Importantly, supernatants containing the therapeutic peptides rescued the apoptotic phenotype and the aconitase activity deficit of fibroblasts isolated from Friedreich’s patients cells. We have therefore validated a new cell and gene therapy approach that has the potential to provide a permanent cure for the disease.