Duchenne muscular dystrophy (DMD) is a severe degenerative muscle disease caused by mutations in the gene that encodes dystrophin, an essential muscle-building, shock absorbing and signaling protein. Onset of DMD, which affects about one in 3,500 male births, occurs in early childhood and leads steadily to lost mobility and life-threatening heart and diaphragm malfunctions. While people with DMD can live into middle-age, the best therapies only alleviate symptoms and slow progression of the disease.
Now, a collaboration between researchers from UW Medicine and Seattle Children’s Research Institute (SCRI) will use a five-year, $2.7 million grant from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) to test the use of small molecules to treat DMD in the earliest stages of development. David Mack, an Associate Professor of Rehabilitation Medicine and a faculty member in the Institute for Stem Cell and Regenerative Medicine (ISCRM) will co-lead the effort with Lisa Maves, an Assistant Professor of Pediatrics and an investigator in the Center for Developmental Biology and Regenerative Medicine at SCRI.
For many years, scientists have sought a gene therapy to correct the underlying problem. Researchers at the Senator Paul D. Wellstone Muscular Dystrophy Specialized Research Center (MDSRC), led by ISCRM faculty member Dr. Jeff Chamberlain, are developing a way to deliver functional versions of dystrophin to degenerating muscle in boys with DMD. The efficacy and safety of that treatment is now being evaluated in several clinical trials. However, scientists do not know the extent to which gene therapy can halt the disease and restore lost function – or whether a comprehensive cure might require a combination of interventions.
One newly identified contributor to the underlying malfunction that causes DMD is epigenetic dysregulation. Epigenetics encompasses the changes that occur that affect how an organism’s genetic makeup is expressed during its development and throughout its life. In the case of DMD, loss of the dystrophin gene leads to downstream epigenetic changes in embryonic muscle that may exacerbate disease severity. Mack and Maves believe that close study of the earliest stages of the disease will yield game-changing clues about the most effective ways to prevent and even repair the damage it causes.
“There is broadening appreciation that DMD, like many muscular diseases, has a developmental origin,” says Mack. “Even though the boys don’t show symptoms until they are several years old, their muscle is sick from the time the dystrophin gene fails. We want to track the cascading events that cause the actual clinical symptoms, because the more we understand about how this disease develops, the more we’ll know about when and how to intervene.”
“Gene therapy approaches for correcting the problem are very promising, but extremely challenging,” says Maves. “We think it’s going to be a combination of therapies that is ultimately going to be most effective.”
To gather the insights that may someday point toward new therapies for human patients, Mack and Maves will turn their focus to a combination of research models that they hope will collectively paint a clear picture of the pathway that leads from the initial dystrophin mutation to the stage when symptoms become apparent to caregivers and clinicians. Those models, which will be used in parallel, are human induced pluripotent stem cell-derived skeletal and cardiac muscle, zebrafish, and rats.
“The real power of our investigation is in the combination of these models,” says Mack. “Fish are good for understanding development and for fast and inexpensive drug screens. Stem cells are highly manipulatable. And the rat is the ultimate preclinical model. Our contention is that if a potential drug works in all three, it’s likely to be effective and safe in humans.”
Maves, who works mainly with zebrafish, is excited about the prospect of accessing models that can validate observations her team makes in fish are biologically relevant for human disease. “DMD has historically been thought of as a progressive disease so a lot of treatments have targeted late-stage progression. The stem cell lines grown in the Mack Lab, and the ability to do detailed single-cell RNA sequencing, have given us the best look yet at how the disease begins and develops.”
Mack and Maves began their collaboration with a pilot grant from the Brotman Baty Institute for Precision Medicine (BBI), a partnership between the UW, Seattle Children’s, and Fred Hutchinson Cancer Research Center. “The support from the BBI was instrumental in allowing us to begin applying cutting-edge sequencing technologies to our DMD models,” says Maves.
Going forward, much of the genetic analysis for the NIH award will take place in the ISCRM Genomics Core, a recently opened facility supported in part by the John H. Tietze Foundation Trust. The core is set up to perform rapid, accurate genome-wide sequencing using the latest technology, thereby allowing researchers to watch events unfold at a single-cell level. “The Genomics Core will serve an indispensable function in the course of this investigation,” says Mack.
The UW Medicine Center for Translational Muscle Research (CTMR), another ISCRM-affiliated facility, will also play an import role in the grant, adds Mack. “Part of what we will do is only possible because of the critical mass of muscle biologists and capabilities available at the CTMR. The Muscle Mechanics and Metabolomics cores will help us gather vital data and the connection to Wellstone Center could give us a conduit to test promising drugs that turn up in our modeling.”
What does success look like for the grant?
Maves offers three points. “If we can illustrate the early developmental defects in DMD, that could change how the field views the disease. We also think that revealing how small molecules can be used to manipulate and study DMD can demonstrate the viability of combination therapies. And, we hope that by identifying therapies that work in all three of our models, we can reduce expensive, late-stage failures that are plaguing clinical trials because studies in mice don’t always translate into humans.”
And how might the findings from the grant work in conjunction with progress from Jeff Chamberlain’s DMD research underway in the Wellstone Center?
“The Chamberlain lab is approaching the problem brilliantly from a clinical standpoint,” says Mack. “We are looking at the problem from a developmental angle – what are the underlying mechanisms that cause muscle to go awry. New knowledge about the early stages of DMD could inform how and when we use small molecules in combination with gene therapy. The timing is important because we are talking about treating young children and even newborns.”
Funding and technology will be essential drivers of the investigation. At the same time, Mack stresses the the vital role of another element – collaboration. “There is simply no way Lisa and I would even be this far with the support and partnership of the Brotman Baty Institute, the Tietze Family, the Center for Translational Muscle Research, or the Wellstone Center. It just show the collective will to improve the health of boys suffering from DMD.”