Stress-induced Mouse Model of the Cardiac Manifestations of Friedreich's Ataxia Corrected by AAV-mediated Gene Therapy.

Friedreich's ataxia (FA), an autosomal recessive disorder caused by a deficiency in the expression of frataxin (FXN), is characterized by progressive ataxia and hypertrophic cardiomyopathy. Although cardiac dysfunction is the most common cause of mortality in FA, the cardiac disease remains subclinical for most of the clinical course because the neurologic disease limits muscle oxygen demands. PreviousFXNknockout mouse models exhibit fatal cardiomyopathy similar to human FA, but in contrast to the human condition, untreated mice become moribund by 2 months of age, unlike humans where the cardiac disease often does not manifest until the third decade. The study was designed to create a mouse model for early FA disease relevant to the time for which a gene therapy would likely be most effective. To generate a cardiac-specific mouse model of FA cardiomyopathy similar to the human disease, we used a cardiac promoter (alpha Myhc) driving CRE recombinase cardiac-specific excision ofFXNexon 4 to generate a mild, cardiac-specific FA model that is normal at rest, but exhibits the cardiac phenotype with stress. The hearts of alpha Myhc mice had decreased levels of FXN and activity of the mitochondrial complex II/complex IV respiratory chain. At rest, alpha Myhc mice exhibited normal cardiac function as assessed by echocardiographic assessment of ejection fraction and fractional shortening, but when the heart was stressed chemically with dobutamine, alpha Myhc mice compared with littermate control mice had a 62% reduction in the stress ejection fraction (p < 2 x 10(-4)) and 71% reduction in stress-related fractional shortening (p < 10(-5)). When assessing functional cardiac performance using running on an inclined treadmill, alpha Myhc mice stayed above the midline threefold less than littermate controls (p < 0.02). A one-time intravenous administration of 10(11)genome copies of AAVrh.10hFXN, an adeno-associated virus (AAV) serotype rh10 gene transfer vector expressing humanFXN, corrected the stress-induced ejection fraction and fractional shortening phenotypes. Treated alpha Myhc mice exhibited exercise performance on a treadmill indistinguishable from littermate controls (p > 0.07). These alpha Myhc mice provide an ideal model to study long-term cardiac complications due to FA and AAV-mediated gene therapy correction of stress-induced cardiac phenotypes typical of human FA.