Prevention of Dystrophin-Deficient Cardiomyopathy in Twenty-One-Month-Old Carrier Mice by Mosaic Dystrophin Expression or Complementary Dystrophin/Utrophin Expression

Abstract

Abstract-A cure for dystrophin-deficient muscular dystrophy requires treating both skeletal muscle and the heart. Whereas mosaic dystrophin expression has been shown to protect skeletal muscle, controversy exists over whether mosaic expression is protective in the heart. We have shown recently that mosaic dystrophin expression prevents stress-induced heart damage in young carrier mice. Although an interesting finding, the clinical relevance remains to be established because young dystrophin-null mdx mice do not have heart disease. On the other hand, heart failure has been reported in human carriers. To resolve this mouse/human discrepancy, we evaluated the cardiac phenotype in 21-month-old mdx, carrier, and normal mice. We found dilated cardiomyopathy in old mdx mice but not in age-matched carrier mice. All anatomical parameters and physiological assay results (ECG and closed-chest Millar catheter) were within the normal range in old carrier mice. Focal myocardial inflammation was found in a small fraction of old carrier mice, but it had no major impact on heart function. Dobutamine stress revealed a near normal hemodynamic profile except for a marginal reduction in systolic pressure in old carrier mice. Immunostaining and Western blot showed dystrophin expression in 50% cardiomyocytes in old carrier mice. Interestingly, utrophin was upregulated in dystrophin-negative heart cells in carrier mice. In summary, we have provided the first clear-cut evidence that dilated cardiomyopathy in old mdx mice was prevented by mosaic dystrophin expression or complementary dystrophin/utrophin expression. Our results raise the hope for ameliorating dystrophic cardiomyopathy through partial gene and/or cell therapy. Key Words: cardiomyopathy Ⅲ gene therapy Ⅲ myocardium Ⅲ genetics Ⅲ heart disease H eart disease profoundly affects the life quality of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) patients. 1,2 DMD and BMD are caused by mutations in the dystrophin gene. Dystrophin is a long rodshaped cytoskeletal protein located at the cytosolic surface of the sarcolemma. It glues the cytoskeleton, sarcolemma, and extracellular matrix together to prevent cell membrane damage during muscle contraction. Absence of dystrophin or abnormal dystrophin expression weakens the physical link between the extracellular matrix and the cytoskeleton. As a consequence, the affected muscle cells undergo degeneration and necrosis. Eventually, muscle tissue is replaced by fibrous, bony and/or fatty tissue and loses function.Pathology in the heart and the diaphragm determines the life span in DMD/BMD patients. Until recently, approximately 80% to 90% of DMD patients died from respiratory failure because of a weak diaphragm. With improved respiratory care, heart-related death has become more frequent, even approaching 40% in some studies. 3 Currently, symptomatic management is the only treatment option. The advent of gene and cell therapies brings the hope of a cure for DMD/BMD. 2 In gene therapy, the mutated gene is replaced and...

Effective rescue of dystrophin improves cardiac function in dystrophin-deficient mice by a modified morpholino oligomer

“…S5c). However, heart dysfunction of mdx mice can be demonstrated by hemodynamic analysis under dobutamine stress (21)(22)(23)(24)(25). We therefore examined 4-month-old male mdx mice 3 weeks after two PPMOE23 treatments (30 mg/kg at biweekly intervals) along with age-and sex-matched untreated mdx and healthy C57BL control mice.…”

“…Both potency and cardiac delivery represent major limitations to antisense therapy as an effective treatment for DMD patients. Because DMD patients live longer owing to improved multidisciplinary patient care, rescuing dystrophin expression in cardiac muscle becomes more critical for their longevity and quality of life (16)(17)(18)(19)(20)(21)(22). More importantly, restoration of dystrophin only in skeletal muscles may exacerbate the failure of heart function if dystrophin expression cannot be effectively restored in cardiac muscle (18).…”

Dystrophin deficiency in Drosophila reduces lifespan and causes a dilated cardiomyopathy phenotype

“…We also observed an increased heart rate with age in dys mutant flies, which is mainly because of shorter diastolic phases, and is accompanied by a more regular heart rhythm and less asystolic episodes. Interestingly, a recent report shows that mdx mice have increased heart rate apparently because of a shortened PR interval (Bostick et al, 2008). Moreover, the inactivation of the C. elegans dys-1 gene does not show muscle degeneration, perhaps because of their short lifespan, but these animals display body wall muscle hypercontraction and are hyperactive (Bessou et al, 1998;Carre-Pierrat et al, 2006).…”

Dose-dependent restoration of dystrophin expression in cardiac muscle of dystrophic mice by systemically delivered morpholino

“…As DMD patients live longer because of improved multidisciplinary patient care, rescuing dystrophin expression in cardiac muscle becomes more critical for their longevity and quality of life. [14][15][16][17][18][19][20] More importantly, a recent study suggests that restoration of dystrophin in skeletal muscles only may exacerbate the failure of heart function if dystrophin expression cannot be effectively restored in cardiac muscle. 16 However, both unmodified 2 0 O methyl phosphorothioate AONs and morpholino oligomers have been unable to induce effective exon skipping and dystrophin expression in cardiac muscle.…”