|Skeletal muscles without dystrophin (column A) and after dystrophin has been restored (column B), using the CRISPR/Cas9 platform developed by UCLA scientists.
Image: UCLA Broad Stem Cell Research Center
The approach uses a technology called CRISPR/Cas9, or clustered regularly interspaced short palindromic repeats, to correct genetic mutations that cause the disease. The researchers designed the approach to be useful in a clinical setting, and “the method is likely 10 years away from being tested in people,” says Melissa Spencer, PhD, co-director of the UCLA Center for Duchenne Muscular Dystrophy and member of the UCLA Broad Stem Cell Research Center.
Duchenne typically occurs through one mutation in a gene called dystrophin, which produces a protein with the same name. There are hundreds of mutations in the dystrophin gene that can lead to the disease, but in 60 percent of people with Duchenne, their mutation will occur within a specific hot spot of the gene. Duchenne mutations cause abnormally low production of the dystrophin protein, which in turn causes muscles to degenerate and become progressively weaker. Symptoms usually begin in early childhood; patients gradually lose mobility and often die from heart or respiratory failure around age 20. There currently is no cure.
The platform developed by the UCLA researchers focuses on the hot spot of the dystrophin gene. They obtained skin cells from consenting patients who had mutations within the dystrophin gene hot spot. The scientists reprogrammed the cells to create induced pluripotent stem (iPS) cells. After they had produced iPS cells that were free from Duchenne mutations, they differentiated the iPS cells into cardiac-muscle and skeletal-muscle cells. Later, they transplanted the skeletal-muscle cells into mice that had a genetic mutation in the dystrophin gene.
The result was the largest deletion ever observed in the dystrophin gene using CRISPR/Cas9, and the study was the first to create corrected human iPS cells that could directly restore functional muscle tissue affected by Duchenne. The UCLA researchers plan to develop strategies to test the Duchenne-specific CRISPR/Cas9 platform to treat the disease in animals as the next step toward perfecting a method that can be used in humans.
“A Single CRISPR-Cas9 Deletion Strategy that Targets the Majority of DMD Patients Restores Dystrophin Function in hiPSC-Derived Muscle Cells,” Cell Stem Cell, April 7, 2016