Skeletal Muscle Involvement in Friedreich Ataxia and Potential Effects of Recombinant Human Erythropoietin Administration on Muscle Regeneration and Neovascularization

Friedreich ataxia (FRDA) is caused by reduced expression of the mitochondrial protein frataxin. Cardiac muscle involvement has been attributed to mitochondrial dysfunction, but involvement of skeletal muscle has not been fully investigated. Improved motor skills in FRDA patients after administration of recombinant human erythropoietin (rhuEPO) have been reported. To elucidate the characteristics of skeletal muscle in FRDA and assess the potential effects of rhuEPO on skeletal muscle neovascularization and regeneration, 7 genetically confirmed FRDA patients underwent biopsy of the gastrocnemius muscle before and after administration of 3,000 international units of rhuEPO 3 times per week for 2 months. Muscle tissue was investigated using standard histologic methods, immunohistochemistry, and biochemical assays of mitochondrial enzymes. In pretreatment FRDA samples, there were neurogenic and myopathic changes and reduced capillary density versus that in healthy control biopsies (n = 4). Satellite cells were increased, but markers of satellite cell activation and differentiation did not differ from controls. Respiratory chain complex and citrate synthase activities were reduced in FRDA and remained unchanged after treatment. Administration of rhuEPO resulted in increases in muscle capillary densities and in endothelial progenitor cells in peripheral blood. These data indicate that there are morphological and biochemical abnormalities of skeletal muscle in FRDA. The rhuEPO-induced changes were subtle, but increased capillary density might result in improved oxygen supply and myofiber function.