CRISPR, one of the recent and modernized gene editing techniques used to treat inherited diseases still has to deal with the long term chronic health issues. The researchers have overcome a serious underlying issue in the technique which may now pave a path for sustained treatments.
The research team was led by Dongsheng Duan, Ph.D., at the University Of Missouri School Of Medicine. Researchers took an initial step towards this gene-editing technique by getting inspired from the natural defensive ability of the body to fight back viruses.
The study “AAV CRISPR Editing Rescues Cardiac and Muscle Function for 18 Months in Dystrophic Mice,” is published online by JCI insight. The study was funded by National Institutes of Health, the Intramural Research Program of the NIH National Center for Advancing Translational Sciences, the Department of Defense, Hope for Javier, the Jackson Freel DMD Research Fund, the Muscular Dystrophy Association and the Duke Coulter Translational Partnership.
This modern technology has the ability to alter the nucleotides sequence of the DNA by cutting out and replacing the mutated part of the gene which carries a potential threat to disease. Dongsheng Duan and his team members at MU, the National Center for Advancing Translational Sciences at the National Institutes of Health and Duke University, are currently researching on how to take help by CRISPR to cure Duchenne muscular dystrophy (DMD).
Children who are suffering from Duchenne muscular dystrophy (DMD) encounters a gene mutation due to which there is irregular production of the protein known as dystrophin. Dystrophin is one of those necessary proteins needed by the muscles to work efficiently, without it, they become weaker and eventually lose the ability to perform its function.
According to a number of cases reported, there are many children who lose their capability to move as well as the functioning of those muscles which are necessary for breathing and proper functioning of the heart.
“CRISPR essentially cuts out the mutation and stitches the gene back together,” said Duan. Duan works as a Margaret Proctor Mulligan Professor in the field medical research of the Department of Molecular Microbiology and Immunology at the MU School of Medicine.
“In order to do this, the ‘molecular scissors’ in CRISPR, known as Cas9, must know where to cut. The location to cut is flagged by a molecule called gRNA. We were surprised to find that by increasing the number of flags, we could extend the effectiveness of the therapy from three months to 18 months in our mouse model.”
The researchers started their research on 6 months old mice that were going through DMD. After treating the mice with the new CRISPR’s technique, they kept them under observation for 18 months. Like other researchers, Duan’s team also went for using the most widely used strategy.
They administered equal amounts of Cas9 and gRNA in mice. Though the outcomes were amazing when it was directly injected into the muscles but it also resulted poorly when the team hoped to achieve long-term results for all the muscles in the body. A little success was only found in the heart muscles but there was almost no dystrophin restoration in the skeletal muscles.
During the analysis of the results, the researchers found there was an unequal proportion of gRNA and cas9 that is gRNA was in an insufficient amount. There were not enough in number to direct the cas9 where to act. After this observation, the researchers repeated the experiment with an increased amount of gRNA flags. This reformed experiment increased the percentage of dystrophin restoration in both skeletal and heart muscles by the time of 18 months. Furthermore, the functioning of both the muscles was improved to a great extent.
“Our results suggest that gRNA loss is a unique barrier for long-term systemic CRISPR therapy,” Duan said. “We believe this barrier can be overcome by increasing and optimizing gRNA doses. While this has exciting possibilities for improvements to DMD therapies, we believe this principle may also be applied to other CRISPR therapies for a range of other diseases and conditions.”
Before carrying out the clinical trials, the researchers will further work and try to refine this approach more. Researchers hope that with this new approach will be the future milestone for many new treatments using CRISPR gene editing.