| Friedreich's ataxia (FRDA) is a genetic disorder characterized by a GAA•TTC triplet repeat expansion in the first intron of the gene frataxin. In unaffected populations, there are less than 40 repeats while diseased patients harbor from 60 repeats up to 1700 repeats. Patients typically exhibit neurodegenerative symptoms such motor incoordination, slurred speech, etc., with late-stage patients commonly succumbing via cardiomyopathy. The repeat expansion causes heterochromatin-mediated compaction of the repeat region, leading to repression of the frataxin gene. Previous studies in FRDA used patient lymphocytes or fibroblasts, which are not relevant to neurodegeneration. Similarly, cell line models may have artifacts due to cell immortalization or artificial frataxin silencing. To address this, we derived induced pluripotent stem cells (iPSCs) from FRDA patient fibroblasts and fully characterized these cells in terms of morphology, gene expression, and functionality. Further, we show that the derivation and propagation of FRDA iPSCs is associated with repeat instability observed in patients, providing a model in which to study this phenomenon. We also demonstrate that this repeat instability is dependent on the DNA mismatch repair enzyme MSH2, providing evidence towards the underlying mechanism that causes repeat instability in patients.;From these studies, we propose that FRDA iPSCs can be used as an in vitro model system to dissect mechanisms of repeat instability. Further, we suggest that the presence of FRDA phenotypes in differentiated neurons as well as the scalable nature of these neurons allows the study of various mechanisms of cellular pathology or drug development.;Additionally, we differentiate FRDA iPSCs to early Tuj1+/MAP2 + neurons and verified this process by morphological characterization and neuronal gene expression analysis. Subsequently, we confirmed the recapitulation of hallmark phenotypes such as heterochromatin-mediated repression of frataxin and loss of frataxin protein. Further, we demonstrate a decreased mitochondrial membrane potential (MMP) in FRDA neurons as compared to unaffected neurons while no differences in the levels of aconitase activity and reactive oxygen species were observed. Treatment with the histone deacetylase inhibitor 109 resulted in a change in the local chromatin structure along the frataxin locus as well as recovery of MMP to wild-type levels. |
