Lentivirus-meditated frataxin gene delivery reverses genome instability in Friedreich ataxia patient and mouse model fibroblasts.

H Khonsari,Y G Chianea,S Al-Mahdawi,M A Pook,M Themis,C Parris,M Schneider

doi:10.1038/gt.2016.61

Abstract

Friedreich ataxia (FRDA) is a progressive neurodegenerative disease caused by deficiency of frataxin protein, with the primary sites of pathology being the large sensory neurons of the dorsal root ganglia and the cerebellum. FRDA is also often accompanied by severe cardiomyopathy and diabetes mellitus. Frataxin is important in mitochondrial iron–sulfur cluster (ISC) biogenesis and low-frataxin expression is due to a GAA repeat expansion in intron 1 of the FXN gene. FRDA cells are genomically unstable, with increased levels of reactive oxygen species and sensitivity to oxidative stress. Here we report the identification of elevated levels of DNA double strand breaks (DSBs) in FRDA patient and YG8sR FRDA mouse model fibroblasts compared to normal fibroblasts. Using lentivirus FXN gene delivery to FRDA patient and YG8sR cells, we obtained long-term overexpression of FXN mRNA and frataxin protein levels with reduced DSB levels towards normal. Furthermore, γ-irradiation of FRDA patient and YG8sR cells revealed impaired DSB repair that was recovered on FXN gene transfer. This suggests that frataxin may be involved in DSB repair, either directly by an unknown mechanism, or indirectly via ISC biogenesis for DNA repair enzymes, which may be essential for the prevention of neurodegeneration.

Highlights

Friedreich ataxia (FRDA) is an autosomal recessive inherited neurodegenerative disorder for which there is no known effective treatment or cure
FRDA pathology is thought to result from defective frataxin expression, which is primarily caused by GAA repeat expansion within the first intron of the FXN gene leading to its epigenetic silencing
FRDA is amenable to lentivirus vectors (LVs) gene therapy, a strategy that offers permanent FXN gene delivery and integration into the host genome

Summary

Introduction

Friedreich ataxia (FRDA) is an autosomal recessive inherited neurodegenerative disorder for which there is no known effective treatment or cure. Neurodegeneration is accompanied by cardiac hypertrophy and heart failure, which is the main cause of mortality usually at ~ 40 years of age.[1] It is the most common hereditary ataxia with a prevalence of 1 in 29 000 in the Caucasian population and a carrier frequency of 1 in 85.2 Neurological symptoms include gait ataxia, dysarthria, fixation instability, loss of joint and vibratory senses, loss of tendon reflexes, abnormal Babinski sign and muscle weakness. Patients lose the ability to stand and walk within 10–15 years of onset and soon become wheelchair bound.[3]. Neurodegenerative pathology occurs primarily in the large sensory neurons of the dorsal root ganglia and cerebellum.[4] In

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Conclusion