Understanding Friedreich's ataxia via a disease-specific cell model

Abstract

Friedreich’s ataxia (FA) is a hereditary, neurodegenerative disorder with significant disability and morbidity. The disease is characterised by deficiency of a nuclear encoded small mitochondrial protein frataxin (FXN). The deficiency leads to classic neurological manifestations including ataxia and gait instability owing to the loss of neurons in the dorsal root ganglia (DRG), dentate nucleus of cerebellum, posterior column, and corticospinal tracts of the spinal cord. To date, the underlying neuropathology of Friedreich’s ataxia remains unknown and no existing treatments have been proven effective. Studies of neuropathogenesis and development of effective therapeutics are greatly hindered by the lack of appropriate human in vitro neural models.

In this study, to overcome the limitations of non-human cell models, disease-specific neural crest stem cells (NCSCs) were differentiated via dual SMAD inhibition from induced pluripotent stem cells (iPSCs) reprogrammed from patient’s skin fibroblasts. Further physiological responses under iron overloading challenge of the FA-NCSCs were studied by various assays. Moreover, the effectiveness of common therapeutics, idebenone, deferiprone and ouabain were investigated at a cellular level by determining whether they alleviated iron-induced cytotoxicity using the established FA-NCSCs.

FA-NCSCs derived from the patient-specific iPSCs via a modified dual SMAD inhibition differentiation protocol showed a high percentage yield and recapitulated the hallmark phenotype of FXN deficiency. The FXN-deficient FA-NCSC displayed increased vulnerability to iron overloading in comparison to healthy wild-type control. Iron-challenged FA-NCSCs were noted to have morphological changes, a reduction of mitochondrial membrane potential and viability, increased reactive oxygen species (ROS) production and apoptosis, as well as an increased expression of apoptotic markers. Among the selected therapeutic agents, the antioxidant idebenone failed to rescue the iron-challenged FA-NCSCs whilst the iron chelator deferiprone and the cardiac glycoside ouabain showed significant reduction of apoptosis and increased cell viability.