SickKids-led study first to reverse progression of muscular dystrophy in mice using a modified version of CRISPR

TORONTO – In muscular dystrophies, it has long been hypothesized that tissue changes such as scarring and fat replacement of skeletal muscle associated with the disease present an irreversible state that would be resistant to any kind of therapeutic intervention.

In a new study led by researchers at The Hospital for Sick Children (SickKids), an international team of scientists challenged this common consensus by using a modified version of the CRISPR gene-editing tool in a way that may eventually open up entirely new treatment avenues for patients with Congenital Muscular Dystrophy type 1A (MDC1A) and other inherited diseases. The findings are published in the July 24 edition of Nature.

“An important question for many disorders is whether it’s possible to halt the progression of a disease,” says the study’s principal investigator, Dr. Ronald Cohn, President and CEO, Senior Scientist, Paediatrician and Geneticist at SickKids. “Due to the diversity and complexity of neuromuscular disorders, there is an urgent need to develop a strategy that provides a mutation-independent treatment approach for patients with MDC1A and other genetic diseases.”

This new research is the first to conceptualize and test a new CRISPR approach – called CRISPR transcriptional activation (or CRISPR-a) – using a potentially clinically relevant treatment strategy in a mouse model of the disease. In this study, the tool is used to change how genes are expressed without having to break genetic sequences. It also establishes a first-of-its-kind framework for the use of CRISPR-a to rescue disease symptoms.

Data from this study showed successful prevention of symptom progression in a mouse model of MDC1A in vivo right after birth and reversal of the disease phenotype at three weeks of age, when paralysis was already apparent. At the end of the treatment regimen, there was evident absence of paralysis and marked functional improvements in movement in the mice. These findings could hold promise for CRISPR-a as a possible strategy that could one day help treat patients with MDC1A.

“The ability to modify gene expression in animal models using the CRISPR-a approach means that we can now begin to investigate the development of therapeutics and clinical trials in MDC1A, and potentially reverse some of the symptoms caused by muscle fibrosis and nerve abnormalities,” says Cohn, who is also a Professor of Paediatrics and Molecular Genetics at the University of Toronto. “We believe the approach of altering the expression of a disease-modifying gene has broad applicability and could serve as a powerful therapeutic strategy for many inherited diseases.”

Neuromuscular disorders such as MDC1A are often caused by a diverse range of genetic mutations. For this reason, developing a mutation-specific therapy for MDC1A is challenging. To improve disease prognosis, targeting compensatory modifier genes – or genes that can beneficially alter the effect of disease-causing genes – is one plausible therapeutic method that the research team set out to explore.

“One of the strongest reported disease modifiers for MDC1A is the Laminin alpha 1 protein, encoded by the LAMA1 gene. By targeting this gene using CRISPR-a, we were able to prevent muscle fibrosis and paralysis in mice without any disease symptoms, and reverse these outcomes in mice with already existing hind limb paralysis and significant muscle fibrosis,” says Cohn. “These are truly remarkable findings in that even if symptoms of disease are already showing, we can dramatically improve the disease’s progression.”

The researchers are optimistic about what these findings could mean for children with MDC1A and other inherited diseases: “We are currently evaluating the long-term effect of this approach in mice and translating the therapy into patient-derived cells,” says co-first author Dr. Dwi Kemaladewi, a former Research Associate at SickKids and currently an Assistant Professor of Pediatrics at the University of Pittsburgh School of Medicine. “We are also excited about exploring the potential for CRISPR activation technology in treating other incurable inherited and acquired genetic diseases.”

MDC1A is a rare neuromuscular disease affecting one in 150,000 worldwide. It is caused by a mutation in a gene called LAMA2 and is characterized at birth by muscle weakness and low muscle tone, as well as mild brain abnormalities. Children born with this condition usually become wheelchair bound and have a life-limiting disease trajectory.

This research was also supervised by Dr. Evgueni Ivakine, Senior Research Associate at SickKids and co-principal investigator of the study. First authors of the paper are Dr. Kemaladewi; and Prabhpreet S. Bassi, former Graduate Student at the University of Toronto and currently MD candidate at the Wayne State University School of Medicine.

This research was supported by AFM-Telethon, Cure CMD, Muscular Dystrophy Association, Rare Disease Foundation Microgrant, SickKids Restracomp, CIHR Summer Studentship, Natural Sciences and Engineering Research Council of Canada, Canadian Institutes of Health Research (CIHR), R.S. McLaughlin Foundation Chair in Pediatrics, and SickKids Foundation. It is an example of how SickKids is contributing to making Ontario Healthier, Wealthier and Smarter.