Package delivery to boost repair of muscular dystrophy muscle

Our knowledge of human anatomy hasn’t changed much in a hundred years. What has changed is our understanding about how our bodies build that anatomy and maintain it throughout life. As our tissues and organs develop and heal, every gene that gets activated, every protein that signals a cell to multiply, change shape or move is an opportunity for medicine to make regeneration more efficient for those with disease. As a basic scientist, OIRM researcher Dr. Michael Rudnicki’s career was initially driven by “the joy of discovery and understanding how things work.” His quest to sort out the steps in muscle formation and repair has put him on a path to finding treatments for muscular dystrophy.
Over the years, Rudnicki’s contributions to the well of scientific understanding have been remarkable, from determining which master genes tell cells to become muscle to the identification of bona fide muscle stem cells to the genes and proteins that regulate how those muscle stem cells behave. Rudnicki’s scientific understanding tells us that Wnt7a protein has therapeutic potential for Duchenne Muscular Dystrophy (DMD) because it acts as a messenger to stimulate muscle repair. Now he is testing the feasibilities of whether it can be delivered to muscle in sufficient quantity to have an effect.
In DMD, a protein known as dystrophin, a major structural component of muscle, is missing. This causes muscles to be easily injured by normal use, and muscle regeneration cannot keep up with muscle loss. In addition to the structural role for dystrophin in muscle, Rudnicki’s lab discovered a secondary role for dystrophin in muscle stem cells, which makes DMD muscle stem cells less able to repair damage. Since the root problem is a mutation in the dystrophin gene, researchers have been working on ways to introduce the correct form of dystrophin or force the cellular machinery to skip over the mutation and make a partially functional dystrophin protein. Gene correction could also be achieved by cell therapy, by introducing cells from a healthy donor with the correct form of dystrophin.
While investigating why Wnt7a was particularly active during muscle injury, Rudnicki’s team discovered that muscle stem cells, muscle progenitors and muscle all have receptors that respond to Wnt7a. Muscle stem cells respond by multiplying, increasing the overall number of cells entering the pathway to regenerate muscle. Muscle fibres responded to Wnt7a signals by growing larger and stronger. Rudnicki reasoned that excess amounts of Wnt7a should enhance regeneration in muscular dystrophy. When the team injected Wnt7a into muscles of mice that model DMD it indeed stimulated muscle repair and improved muscle strength.
Unfortunately, using Wnt7a muscle injections for the human body is not practical as it would require far too many injections. The circulation system, which integrates with all muscles in the body became an obvious second choice for transporting Wnt7a. The problem is, blood doesn’t transport insoluble proteins like Wnt7a very well and it has trouble moving across into the muscle. With funding from an OIRM New Ideas grant, Rudnicki is testing a way to wrap up Wnt7a in a package that will allow it to stay in the blood transportation system longer and be delivered to the muscles more effectively. The idea comes from an understanding of the normal biology of Wnt7a within the body: to help this signalling protein reach other cells, Wnt7a is transported in tiny lipid-bound bubbles called exosomes.
At the Sprott Centre for Stem Cell Research at the Ottawa Hospital Research Institute, Rudnicki’s team is extracting exosomes from the fluid cells are cultured in by centrifuging them at extremely high speeds. They will load these exosomes with Wnt7a and test whether exosome packaged Wnt7a has the same activity as free Wnt7a and whether it can be delivered to all the muscle groups in their mouse model. “That requires us to solve problems like manufacturing sufficient amounts of exosomes and identifying the right cell source. We’re making good progress and I think we will be able to answer those questions and really develop a proof of concept that this is an approach that we should pursue,” explains Rudnicki.
In the meantime, Rudnicki’s large group of researchers are split into teams and projects pursuing various lines of research. In another line of research, a shortened version of Wnt7a is being investigated for its ability to be delivered and improve muscle regeneration. Beyond Wnt7a, the ongoing pursuit of basic answers about muscle stem cells and muscle regeneration are adding to the well of knowledge from which they or others may draw future disease-fighting applications.

