Improvement of cardiac fibrosis in dystrophic mice by rAAV9-mediated microdystrophin transduction

Abstract

Duchenne muscular dystrophy (DMD) is the most common form of the progressive muscular dystrophies characterized by defects of the dystrophin gene. Although primarily characterized by degeneration of the limb muscles, cardiomyopathy is a major cause of death. Therefore, the development of curative modalities such as gene therapy is imperative. We evaluated the cardiomyopathic features of mdx mice to observe improvements in response to intravenous administration of recombinant adeno-associated virus (AAV) type 9 encoding microdystrophin. The myocardium was extensively transduced with microdystrophin to significantly prevent the development of fibrosis, and expression persisted for the duration of the study. Intraventricular conduction patterns, such as the QRS complex duration and S/R ratio in electrocardiography, were also corrected, indicating that the transduced microdystrophin has a protective effect on the dystrophin-deficient myocardium. Furthermore, BNP and ANP levels were reduced to normal, suggesting the absence of cardiac dysfunction. In aged mice, prevention of ectopic beats as well as echocardiographic amelioration was also demonstrated with improved exercise performance. These findings indicate that AAV-mediated cardiac transduction with microdystrophin might be a promising therapeutic strategy for the treatment of dystrophin-deficient cardiomyopathy.

Long-Term Preservation of Cardiac Structure and Function After Adeno-Associated Virus Serotype 9-Mediated Microdystrophin Gene Transfer inmdxMice

“…The limitation of a systemic AAV9-based approach with a CMV promoter for lDys expression in skeletal muscle was also confirmed by a study that reported only an unexpectedly low level of skeletal muscle transduction after intravenous injections in juvenile mice with three times higher vector doses than in our study (Shin et al, 2011). The lDys construct used in this study has been tested only in skeletal muscle, not in cardiac muscle ( Jorgensen et al, 2009).…”

Effect of Nuclear Factor κB Inhibition on Serotype 9 Adeno-Associated Viral (AAV9) Minidystrophin Gene Transfer to the mdx Mouse

“…The disease pathology of the mdx mouse diaphragm muscle is chronically progressive, similar to that observed in DMD patient muscle (27). Previous mouse gene transfer studies using AAV9 have shown reporter transgene expression in hindlimb, diaphragm and cardiac muscles of C57BL/10 mice (9), whereas studies using AAV9 vector in the mdx mouse disease model have largely focused on myocardium (28)(29)(30).…”

“…High-level gene transfer to the myocardium was observed, which normalized multiple parameters related to cardiomyopathy, such as heart rate, PR interval and QT interval (28). Similarly, another group performed AAV9-mediated treatment of 4-wk-old mdx and analyzed mice 24 and 72 wks after injection, again revealing improvement in cardiac muscle function in response to vector administration (29). In our study, we observed similarly high levels of minidystrophin expression and would expect to see improvement in cardiac performance in vector-treated animals.…”

“…Many previous studies have documented significantly reduced cardiac contractile performance by electrocardiogram in as early as 8-wk-old mdx mice (29), in trabeculae isolated from 8-wk-old mdx mice (31), in right ventricular trabeculae from 10-wk-old mdx mice (32) and in atria from 12-and 14-wk-old mdx mice (33). We did not perform cardiac muscle function in this current study, but can infer the potential effects of the high-level minidystrophin expression we observed in the myocardium on the basis of previous AAV-mediated mini-and microdystrophin gene delivery studies.…”

Prospect for Pharmacological Therapies to Treat Skeletal Muscle Dysfunction

“…Further, even successful expression of a truncated version of dystrophin in the heart may not adequately address the cardiomyopathy in DMD. Novel therapeutic approaches that are currently being examined to specifically address cardiac symptoms in dystrophinopathy include gene therapy [54,55], exonskipping [56], and a number of experimental drug treatments, including TGF-b inhibition [57].…”