Cyclosporin A delays the terminal disease stage inTfamKO mice without improving mitochondrial energy production

Mitochondrial myopathies are rare genetic disorders characterized by muscle weakness and exercise intolerance. Currently, no effective treatment exists for these myopathies. Interestingly, the pharmacological cyclophilin inhibitor cyclosporine A (CsA) extended lifespan and prevented loss of force and mitochondrial Ca2+overload in muscle fibers in the skeletal muscle-specificTfamknockout mouse model of lethal mitochondrial myopathy (TfamKO). The unaffected expression of proteins involved in mitochondrial energy metabolism suggests that these improvements occurred without improvement in metabolism. In this study, we aimed at investigating the effects of four weeks of CsA administration onin vivocontractile function and mitochondrial energy production inTfamKO mice. The treatment started before the terminal phase with severe muscle weakness and weight loss. Our results show that CsA treatment delayed progression into the terminal disease phase. This occurred without any obvious positive effects on mitochondrial energy production at rest or during fatigue induced by repeated contractions. In conclusion, cyclophilin inhibitors may have the potential of counteracting devastating muscle weakness in patients with mitochondrial myopathies most probably by preventing deleterious effects triggered by excessive mitochondrial Ca2+uptake rather than by improving mitochondrial energy production.