247. Expressing Full-Length Dystrophin in 50% Cardiomyocytes Corrects Cardiomyopathy in the Mdx Mouse Model for Duchenne Muscular Dystrophy

Cardiomyopathy is a major determinant of the clinical outcome in Duchenne and Becker muscular dystrophy (DMD, BMD). Nearly every DMD and BMD patient suffers from some degree of cardiomyopathy. More then one tenth of DMD patients eventually die of heart failure. Clinical success of DMD gene therapy will depend upon functional improvement in both skeletal and cardiac muscle. Substantial progress has been made in DMD skeletal muscle disease gene therapy. However, few studies have been done in DMD cardiomyopathy gene therapy. We recently reported that micro-dystrophin was equally efficient in restoring the dystrophin-glycoprotein complex and maintaining sarcolemma integrity in the mdx heart (Yue et al Circulation 108:1626,2003). The minimal number of dystrophin expressing cells needed for cardiomyopathy therapy has not been determined however. In this study, we used female heterozygous mice (F1 from BL10 and mdx crossing) as an experimental model to evaluate whether dystrophin expression in half of the cardiomyocytes was enough to improve heart function in mdx mice. Consistent with the random X-chromosome inactivation theory, we found that 51.22% and 55.40% of the heart cells were expression dystrophin in maternal and paternal heterozygous mice respectively. The mdx mouse hearts were heavier than the BL10 hearts. Interestingly, weights of the heterozygous mice hearts were similar to those of the BL10. In contrast to previous reports of the benign histology in the mdx hearts, we detected fibrosis in 85.71% of the mdx hearts (N=42). More than half of the fibrosis was in the range of medium-to-large size. Only 43.59% of the heterozygous mice had hearts that contained fibrous regions, and the majority of the fibrosis was localized to small areas. To determine whether full-length dystrophin expression in half of the cardiomyocytes can protect the heart from mechanical-stress induced injury, we challenged the hearts with the inotrope b-isoproterenol. After administrating a vital dye, Evans blue (EBD), we found that 11.26 3.40% of the heart area was EBD positive in mdx mice. In the heterozygous mouse hearts, the EBD positive area was reduced to 2.37 0.70%. This result suggests that a significant improvement in cardiomyocyte sarcolemma integrity has been achieved in the heterozygous mouse hearts. In summary, our results suggest that a 50% correction in the mdx heart is sufficient to ameliorate cardiomyopathy in mdx mice.