University of Florida researchers have used a common gel to successfully deliver gene therapy to the diaphragm muscle of mice with inherited respiratory weaknesses, enabling them to breathe easier.
The technique, described in the current issue of Molecular Therapy, could eventually lead to a method to correct genetic conditions in humans that cause diaphragm weakness and respiratory failure -- a leading cause of death in tens of thousands of patients with forms of muscular dystrophy, including Pompe’s disease. Thousands of Americans with muscle-weakening diseases are placed on ventilators each year, according to the Muscular Dystrophy Association.
“The heart and diaphragm are two critical muscles for sustaining life,” said study researcher Dr. Barry Byrne, director of the UF Powell Gene Therapy Center and associate chairman of UF’s department of Pediatrics. “This approach essentially makes the genetic background of the muscle normal again and could significantly improve the quality of life for people on ventilators and those who care for them.”
People with muscular dystrophy inherit a mutated gene unable to produce a critical enzyme, which causes their muscles to become increasingly weak as the disease progresses. In Pompe’s disease, the weakness leads to respiratory failure and is fatal.
Cathryn Mah, the study’s principal investigator and a UF research assistant professor of pediatrics, collaborated on the research with several UF scientists, including Byrne, a professor of pediatrics and of molecular genetics and microbiology, and Tom Fraites, a former doctoral student. The study was funded by grants from the National Institutes of Health, and the Florida and Puerto Rico affiliate of the American Heart Association.
In the current study, UF researchers applied a glycerin-based polymer gel they modified to contain corrective copies of the gene to the diaphragms of mice sick with a disorder that mimics Pompe’s disease, thereby strengthening the muscle. This approach was the first time transferring a corrective gene to mouse diaphragm muscle cells was efficient and had a sustained effect, said Byrne, a member of the UF Genetics Institute.
Until now, scientists have been stymied by the mouse diaphragm’s extreme thinness, which prevents direct injection of genes into the muscle. Infusing or injecting genes into veins or arteries also was problematic. In the two-part study, UF researchers first compared the gel-delivery method with a saline rinse used to deliver copies of a gene that stained the cells blue when the cell accepted them.
Next, they tested the gel’s ability to deliver the gene therapy to the weakened muscle cells using the apparently harmless recombinant adeno-associated virus, or rAAV.
Byrne said the polymer gel was crucial to the study’s success because it clung to muscle cells longer than the saline. The gel acted as a time-release mechanism, increasing the muscle’s exposure to the rAAV, which was modified to deliver copies of the gene that produces the missing enzyme, acid alpha-glucosidase. The enzyme also is known as GAA, or acid maltase.
Scientists elsewhere have studied the effectiveness of a water-based gel in certain tissues but found it interfered with the stability of the virus commonly used to carry copies of therapeutic genes into cells. Other gels dissipate too quickly, before enough corrective genes can be transferred to yield beneficial results, researchers said.
“We tested this gel for ease of handling and for its ability to retain its consistency at certain temperatures,” Mah said. “It had the right properties to make it useful for this study.”