Morpholino Oligomer Peptide Therapy Improves Mitochondrial Function in mdx Cardiomyopathy

Abstract

Duchenne Muscular Dystrophy (DMD) is a fatal muscle wasting disorder. It is commonly associated with cardiomyopathy that is characterised by disrupted cytoskeletal architecture and mitochondrial dysfunction. Activation of the L-type Ca2+ channel (LTCC) provides the Ca2+ influx required for contraction, but also causes an increase in mitochondrial membrane potential (Ψm) in a calcium-independent manner. This involves the movement of cytoskeletal proteins and regulation of mitochondrial VDAC. The increase in Ψm (JC-1 fluorescence) after activation of LTCC is absent in cardiomyocytes isolated from hearts of mdx mice, a murine model of DMD (1.5±1.0%, n=4 vs. 12.1±1.4%, n=10 in C57BL/10ScSnArc controls) but can be restored using antisense morpholino oligomers to induce exon skipping of dystrophin exon 23 (M23D). Here we investigate the effects of M23D peptides on changes in Ψm and mitochondrial oxygen consumption (flavoprotein autofluorescence) induced by LTCC activation. Male (M) and female (F) neonatal mdx mice were injected (i.p.) for 3 weeks and divided into two treatment groups: (i) 120mg/kg once per week; (ii) 30mg/kg four times per week. Activation of LTCC with the dihydropyridine agonist BayK(-) induced an increase in Ψm in cardiomyocytes from animals treated with a single weekly dose (M: 17±2%, n=5; F: 16±3%, n=12) and with multiple weekly doses (M: 16±2%, n=6; F: 13±2%, n=15). BayK(-) increased flavoprotein oxidation in mdx cardiomyocytes from animals treated with a single weekly dose (M:13±3%, n=13; F: 10±3%, n=9) and with multiple doses per week (M: 17±2%, n=16; F: 14±2, n=24). These data indicate that either single or multiple i.p. injections per week of morpholino oligo peptides are effective at restoring cardiac mitochondrial function in both male and female mdx mice.