Researchers at the Experimental and Clinical Research Center (ECRC), a joint institution of the Max Delbrück Center and Charité -- Universitätsmedizin Berlin, have developed a promising gene-editing approach intended to restore the function of a protein essential for muscle repair in patients with muscular dystrophy diseases. Findings are published in the journal Nature Communications.
The dysferlin protein is primarily responsible for repairing cell membranes. Individuals with certain mutations in the gene coding for dysferlin develop muscular dystrophy, a group of muscle-wasting diseases affecting thousands globally.
Professor Simone Spuler and her team, led by Dr. Helena Escobar in the Myology Lab at ECRC, successfully removed muscle stem cells from two patients with limb-girdle muscular dystrophy, corrected the genetic error, and restored functioning dysferlin proteins in cell culture. In new mouse models of the disease, they collected cells, edited them, and transplanted the corrected cells back into mice, resulting in restored protein function and muscle regrowth.
The preclinical findings give the team confidence to advance to human clinical trials, which would involve taking muscle cells from patients, editing them in the lab, and transplanting the patient's own cells back into targeted muscles. Researchers note this therapy is not a complete cure and would be limited to one or two muscles.
"We have over 600 muscles in our body, and it is not easy to target all of them," says Spuler. "We are starting very humbly with targeting one or two muscles. But if this therapy works, it will heal the muscle."
For nearly 20 years, Spuler and her collaborators have been studying dysferlin, its role in muscular dystrophy, and potential cures for these inherited diseases. Muscle deterioration in limb-girdle muscular dystrophy is progressive, causing young adults to lose the ability to walk and use their arms and hands normally.
"You go from being a good athlete in your teens to being in a wheelchair by 40," Spuler states, reflecting on her patients at an outpatient clinic at ECRC.
Escobar, the first author and a molecular biologist in Spuler's Lab, has been developing methods to collect muscle stem cells from patients and utilize gene-editing tools to correct mutations. "We started with a more common mutation so that we can help as many patients as possible," Escobar explains.
To correct the dysferlin mutation, Escobar employs CRISPR-Cas9, often described as "gene-editing scissors," which earned a Nobel Prize in 2020. This technology targets a specific location on a DNA molecule, cutting it and prompting the cell to repair the DNA.
The goal is to correct the mutation during the repair process, resulting in a properly functioning gene. Researchers tested their editing system in several cellular models, achieving a high success rate with minimal unintended consequences.
Despite the editing not resulting in an exact match to the desired genetic sequence, the generated dysferlin protein exhibited four changes. The team collaborated with Professor Oliver Daumke from the Max Delbrück Center for a thorough analysis of these changes.
"Even with these four changes, the generated protein is very similar in function to the wild type, which is the version seen in healthy individuals. It localized along damaged cell membranes, and muscle was regenerated," Escobar states.
As part of this project, researchers created a new mouse model in collaboration with Dr. Ralf Kühn from the Max Delbrück Center. This model closely mimics the specific dysferlin mutation and the resulting disease, allowing the evaluation of the complete therapy process.
"We didn't see an immune response against the transplanted cells or generated proteins, which is promising for taking this into a clinical trial," Spuler notes.
The team is now seeking funds to initiate the first human clinical trial. If successful, it may still take years before the therapy is widely accessible.
Simone Spuler and Helena Escobar are co-inventors on a pending patent application regarding gene editing of human muscle stem cells. Spuler is also a co-founder of MyoPax GmbH and MyoPax Denmark ApS.