MDA Researchers Improve Health, Survival
Of Mice With Severe Congenital MD

TUCSON, Ariz., Aug. 17, 2005 -- Scientists at the University of Pittsburgh have improved the health and extended the life of mice with a form of congenital muscular dystrophy (CMD) via systemic gene therapy, the Muscular Dystrophy Association (MDA) announced today.

MDA grantees Chunping Qiao and Xiao Xiao were on the Xiao-led team that announced the findings online Aug. 15 in Proceedings of the National Academy of Sciences.

“This work demonstrates that gene therapy should be considered an important strategy in the fight against muscular dystrophy and lends further support for planned human clinical trials,” said Sharon Hesterlee, MDA’s director of Research Development.

Qiao gave mice with a deficiency of a muscle protein called laminin alpha-2, which causes a severe form of congenital muscular dystrophy in both sexes, a miniaturized version of the gene for agrin, a muscle protein that they hoped would help compensate for the missing laminin.

The laminin gene is too large to be inserted into the gene delivery vehicles used in this study, said Xiao, an associate professor and senior author of the paper. In addition, he noted, giving the mice the gene for the laminin protein that they lack would likely have provoked the protein’s rejection by the immune system.

The agrin, or miniagrin, gene that the investigators used is normal in the laminin-deficient mice, prompting the researchers to believe that the immune system would tolerate additional agrin protein.

Like the laminin alpha-2 protein, the agrin protein plays a role in maintaining a supportive sheath around muscle fibers known as the basal lamina. The basal lamina protects muscle fibers from damage and holds proteins around the edge of the fiber in their proper positions.

“We are excited about the outcome of our study, because it shows that somatic (after birth) gene therapy approaches can be used to treat this very severe form of muscular dystrophy and also prolong the lifespan of the dystrophy-affected mice,” Xiao said. “If this outcome could be translated to human patients in the future, there would be a potential treatment for CMD, which has no effective treatment currently available.”

The Pittsburgh researchers performed several experiments, delivering the miniagrin gene by two different methods, each of which utilized a slightly different viral transporter.

In one set of experiments, they delivered miniagrin genes, each inserted into the shell of a virus known as AAV2 (adeno-associated virus 2), directly into the leg muscles of mice with laminin-deficient CMD. Two months after the injections, the treated leg muscles showed more agrin, less scarring and general signs of improvement in muscle health compared to the same muscles in untreated mice.

In another set, they delivered the same genes, this time inserted into AAV1 (adeno-associated virus 1) shells, injected into the abdominal cavity of the mice as a form of systemic therapy.

The systemic delivery resulted in far-reaching therapeutic effects. About four months after treatment, the mice showed increased agrin levels and improvement in the appearance of several skeletal muscles groups, including the respiratory diaphragm and other breathing muscles, and the heart.

The treated muscle fibers were larger and didn’t show the scarring that reflects dystrophy-related muscle damage. The hearts of the treated mice were nearly indistinguishable from those of normal mice, the investigators say.

Only 50 percent of untreated mice with laminin-deficient congenital muscular dystrophy were alive at the age of 4 weeks, while 50 percent of those systemically treated with the miniagrin genes were alive at more than 17 weeks.

MDA is a voluntary health agency working to defeat more than 40 neuromuscular diseases through programs of worldwide research, comprehensive services, and far-reaching professional and public health education.

The University of Pittsburgh is one of three muscular dystrophy centers of excellence co-funded by MDA and the National Institutes of Health. Qiao, who has MDA funding for this project, is the recipient of a development grant for new investigators. Xiao has received MDA funding as a senior investigator to develop AAV gene transport vehicles.