P.11.5 PMO-mediated dystrophin exon 23 skipping restores mitochondrial function in the mdx mouse heart

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Approximately 20% of boys with Duchenne Muscular Dystrophy will die of dilated cardiomyopathy. The cardiomyopathy is characterised by disrupted structure and function of cardiac muscle cells and reduced energy production. However, the mechanisms responsible for the altered energy metabolism have been poorly understood. We have previously sought to identify the mechanisms for metabolic inhibition in mdx mouse cardiomyopathy. Calcium influx through the L-type Ca2+ channel (also known as the dihydropyridine receptor) in cardiac myocytes is essential for contraction. Calcium is also important for the regulation of mitochondrial function and production of ATP that is required to meet the energy demands of the heart. We have shown that the L-type Ca2+ channel can regulate mitochondrial function and metabolic activity in cardiac myocytes. In mdx heart, the communication between the L-type Ca2+ channel and the mitochondria is altered as a result of disruption of the cytoskeletal architecture. This contributes to metabolic inhibition in the mdx heart. We demonstrate that treatment of mdx mice with a phosphorodiamidate morpholino oligomer, designed to induce skipping of dystrophin exon 23, “restored” the increase in mitochondrial membrane potential in mdx cardiomyocytes after activation of the L-type Ca2+ channel with the dihydropyridine receptor agonist BayK (−). These results confirm that metabolic inhibition occurs as a result of the absence of dystrophin, and oligomer therapy may be able to normalise metabolic activity and restore contractility in mdx mouse heart.