Although cardiac dysfunction is the most common cause of mortality in Friedreich's ataxia (FA), the cardiac disease remains subclinical for most of the clinical course because the neurologic disease limits muscle oxygen demands. Previous FXN knockout 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 3rd 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 (αMyhc) driving Cre-recombinase cardiac-specific excision of FXN exon 4 to generate a mild cardiac-specific FA model that is normal at rest but exhibits the cardiac phenotype with stress. The hearts of αMyhc mice had decreased levels of FXN and activity of mitochondrial complex II/complex IV respiratory chain. At rest, the αMyhc 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, αMyhc mice compared to littermate control mice had a 62% reduction in stress ejection fraction (p0.07). These αMyhc 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.
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