Using a powerful gene-editing technique, medical researchers have reported success in treatment of muscle wasting disease Duchenne muscular dystrophy. The serious condition makes it difficult for young boys to even stand as the progressive muscle-wasting disease eventually leads to death due to heart failure or difficulty in breathing. Using Crispr-Cas9 technique, the research teams from Duke University, the University of Texas Southwestern Medical Center and Harvard University, have reported encouraging results for Duchenne muscular dystrophy.
The research teams worked independently and achieved successful results during experiment on mice using Crispr-Cas9 technique. Each group using Crispr-Cas9 technique onto a virus which was used to infect muscle cells in mice. The idea was to use correct gene into damaged cells. Using the technique, research teams were able to cut the DNA of chromosomes at selected sites to remove or insert segments.
The Duke University research team used a non-pathogenic carrier called adeno-associated virus, or AAV, to deliver the gene-editing system.
The research project was supported by Muscular Dystrophy Association, The Hartwell Foundation, the March of Dimes Foundation, the National Institutes of Health, the Duke-Coulter Translational Partnership.
The research was led by Charles A. Gersbach of Duke University, Eric N. Olson of the University of Texas Southwestern Medical Center and Amy J. Wagers of Harvard University. The detailed research paper has been published in the latest issue of journal Science.
The dystrophin protein plays a structural role, anchoring each muscle fiber to the membrane that encloses the muscle-fiber bundle. The dystrophin gene, which guides the protein’s production in the cell, sprawls across about 1 percent of the X chromosome and is the largest in the human genome. Dr. Olson’s team reported that it had been able to edit out the damaged exon, enabling muscle cells to generate a functional protein in year 2014.
A NY Times report said, “Treating a patient’s muscle stem cells could produce a more permanent result than changing ordinary muscle cells, which turn over at a brisk rate in muscular dystrophy patients, though not in healthy people.”
The research paper further informed..
Duchenne muscular dystrophy is caused by problems with the body's ability to produce dystrophin, a long protein chain that binds the interior of a muscle fiber to its surrounding support structure. Dystrophin is coded by a gene containing 79 protein-coding regions, called exons. If any one exon gets a debilitating mutation, the chain does not get built.
Duchenne affects one in 5,000 newborn males. Most patients are wheelchair-bound by age 10 and don't live beyond their 20s or early 30s. The mutation is on the X chromosome so female children with two X chromosomes should have at least one functioning copy of the gene.
While Gersbach has had success in cultured patient cells by using a jolt of electricity to punch holes in their membranes to deliver the CRISPR system, this strategy was not practical in a patient's muscle tissues.
"A major hurdle for gene editing is delivery. We know what genes need to be fixed for certain diseases, but getting the gene editing tools where they need to go is a huge challenge," said Chris Nelson, the fellow in Gersbach's laboratory who led the work.
Nelson and Gersbach began working on packaging gene editing tools into AAV--the most popular virus for delivering genes today. They were assisted through collaborations with AAV experts Aravind Asokan, associate professor at the University of North Carolina -- Chapel Hill School of Medicine, and Dongsheng Duan at the University of Missouri School of Medicine.
"AAV is a really small virus and CRISPR is relatively large," said Gersbach. "It simply doesn't fit well, so we still had a packaging problem."
The solution came from Feng Zhang, an investigator at the Broad Institute of the Massachusetts Institute of Technology and Harvard. Earlier this year, Zhang described a CRISPR system from a different bacterium than the one commonly used.
Besides being much easier and more efficient than replacing the dysfunctional exon with a working copy, simply snipping out the weak link is a strategy that would be effective in a larger swath of the patient population.
Gersbach and his team first delivered the therapy directly to a leg muscle in an adult mouse, resulting in the restoration of functional dystrophin and an increase in muscle strength. They then injected the CRISPR/AAV combination into a mouse's bloodstream to reach every muscle. The results showed some correction of muscles throughout the body, including in the heart -- a major victory because heart failure is often the cause of death for Duchenne patients.