Disrupted cardiac bioenergetics linked to oxidized mitochondrial creatine kinase are rescued by the mitochondrial-targeting peptide SBT-20 in the D2.mdx model of Duchenne muscular dystrophy

Mitochondrial creatine kinase (mtCK) regulates the fast export of phosphocreatine to support cytoplasmic phosphorylation of ADP to ATP which is more rapid than direct ATP export. Such creatine-dependent phosphate shuttling is attenuated in several muscles, including the heart, of the D2.mdx mouse model of Duchenne muscular dystrophy at only 4 weeks of age. Here, we determined whether such attenuations occur in later stages in D2.mdx (12 months of age) in relation to mtCK thiol redox state, and whether this pathway could be preserved through administration of the mitochondrial-targeting, ROS-lowering tetrapeptide, SBT-20, in the D2.mdx mouse. In permeabilized muscle fibres prepared from cardiac left ventricles, we found that aged male D2.mdx mice have reduced creatine-dependent pyruvate oxidation and elevated complex I-supported H2O2 emission (mH2O2). Surprisingly, creatine-independent ADP-stimulated respiration was increased and mH2O2 was lowered suggesting that impairments in the faster mtCK-mediated phosphocreatine export system resulted in compensation of the alternative slower pathway of ATP export. The apparent impairments in mtCK-dependent bioenergetics occurred independent of mtCK protein content but were related to greater thiol oxidation of mtCK and a more oxidized cellular environment (lower GSH:GSSG). We then found that 12 weeks of daily treatment with SBT-20 (from day 4 to ~12 weeks of age) increased respiration and lowered mH2O2 only in the presence of creatine in D2.mdx mice without affecting calcium-induced mitochondrial permeability transition pore activity. In summary, creatine-dependent mitochondrial bioenergetics are attenuated in older D2.mdx mice in relation to mtCK thiol oxidation, which can be preserved with a ROS-lowering mitochondrial-targeting peptide. These results demonstrate a specific relationships between redox stress and metabolic reprogramming during dystrophin deficiency that can be targeted with small peptide therapeutics. ### Competing Interest Statement Stealth Biotherapeutics provided SBT-20 through a material transfer agreement but did not provide funding for this study.