Injected Wnt Protein Helps With Muscular Dystrophy


Duchenne muscular dystrophy is a genetic disease that affects one of every 3,500 newborn males. Because the DMD gene is located on the X chromosome, loss-of-function mutations that cause Duchenne muscular dystrophy (DMD) tend to occur in males.

Muscular dystrophy or MS affects skeletal muscles and causes muscle weakness and muscle loss, and unfortunately, the disease often progresses to a state were the muscles are so weak and damaged that even the diaphragm, which is a voluntary muscle, becomes nonfunctional, and the patients dies from an inability to breath.

Recently, Michael Rudnicki, a MS researcher from the Ottawa Hospital Research Institute in Canada, has led a research team that discovered that injections of a protein called “WNT7a” into muscles can increase the size and strength of muscles in MS mice.

Rudnicki is the director of the Regenerative Medicine Program at Ottawa Hospital Research Institute (OHRI), Canada. The results of this work were published on the Nov. 26, 2012, in the Proceedings of the National Academy of Sciences (PNAS).

For these experiments, Rudnicki collaborated with a San Diego-based biotechnology firm known as Fate Therapeutics. Fate Therapeutics specializes in developing pharmaceuticals that are based on stem cell biology, and Rudnicki is one of the founders of this company. Rudnicki hopes to begin a clinical trial of WNT7a for DMD in the near future.

In 2009, Rudnicki and co-workers showed that WNT7a protein is able to stimulate muscle repair by increasing the available supply of a population of muscle stem cells known as “muscle satellite cells.” Muscle satellite cells are located near muscle fibers but they are dormant until they are needed for muscle repair or muscle fiber regeneration. When the muscle is stressed or damaged, the satellite cells increase in number (proliferate) and mature (differentiate).

Muscle Satellite Cells

These newly published findings build on these earlier results. Once injected into the muscles of mice afflicted with DMD, the WNT7a-injected muscles showed significant increases in fiber strength and size. However, Rudnicki and others also found that WNT7a stimulated a two-fold increase in the number of satellite cells in the injected mouse muscles.

Rudnicki was worried that WNT7a was pushing satellite cells to differentiate prematurely, which was disconcerting because such premature differentiation would deplete the muscle satellite population. However, no evidence of premature differentiation was observed. Additionally, WNT7a-injected mouse muscles showed far less contraction-related injury, suggesting that WNT7a has a kind of protective effect on the muscle.

Even though these experiments were done in a mouse model of DMD, would WNT7a also work in a similar fashion in human muscles? To answer this questions, Rudnicki and his colleagues analyzed human muscle tissue from healthy male donors that had been treated with WNT7a. The results showed that the effects of this protein in skeletal muscle are the same in humans as in mice.

To summarize from their own paper: “Our experiments provide compelling evidence that WNT7a treatment counteracts the significant hallmarks of DMD, including muscle weakness, making WNT7a a promising candidate for development as an ameliorative treatment for DMD.”

The remarkable conclusion is that increasing muscle strength by injecting WNT7a into specific, vital muscle groups, such as those involved in breathing, should be considered as a therapeutic approach for this debilitating disease.

Muscle Cells Made from Induced Pluripotent Stem Cells Successfully Treat Mice With Muscular Dystrophy


Work by researchers at the Lillehei Heart Institute at the University of Minnesota have demonstrated the ability of induced pluripotent stem cells (iPSCs) to make muscle-forming cells, and that these cells can be used to treat muscular dystrophy.

Muscular dystrophy refers to a group of inherited diseases that causes muscle fibers to be structurally weak and highly susceptible to damage. The progressive muscle damage causes the muscles to become gradually weaker and weaker until the patient will eventually require a wheelchair.

There are several different types of muscular dystrophy. Most of the varieties of muscular dystrophy causes symptoms appear during childhood, but others cause symptoms to arise during adulthood. The most common form of muscular dystrophy is Duchenne muscular dystrophy (DMD). The symptoms begin early in life (once the child learns to walk), and include frequent falls, difficulty getting up from a lying or sitting position, trouble running and jumping, waddling gait, large calf muscles, and learning disabilities. A less severe and slower progressing form of muscular dystrophy is Becker muscular dystrophy (BMD). Symptoms usually being in the teenage years, but might also not occur until the mid-20s or later. Other types of muscular dystrophy include myotonic (inability to relax muscles at will, most often begins in early adulthood, muscles of the face are usually the first to be affected), Limb-girdle (hip and shoulder muscles are first affected), congenital (apparent at birth or becomes evident before age 2 and varies in severity), fascioscapulohumeral (shoulder blades stick out like wings when the person raises his or her arms, onset occurs in teens or young adults), and oculopharyngeal (drooping of the eyelids and weakness of the muscles of the eye, face and throat, symptoms first appear in a person’s 40s or 50s).

In order to treat muscular dystrophy (MD), many researchers have tried to use gene therapy to place normal versions of the muscular dystrophy gene (which encodes a protein called Dystrophin) into the muscles of MD patients (Romero NB, et al., Hum Gene Ther. 2004;15(11):1065-76 & Mendell JR, et al., Ann Neurol. 2009;66(3):290-7. These types of experiments have met with limited success, since the immune system of muscular dystrophy patients tends to attack the muscles that express dystrophin (Mendell JR, et al., New England Journal of Medicine 2010 7;363(15):1429-37).

In light of the failure of gene therapy trials, researchers have tried stem cell treatments in MD mice. Scientists in the laboratory of Rita Perlingeiro have used muscle precursor cells made from mouse embryonic stem cells to treat MD mice (Radbod Darabi, et al., Exp Neurol. 2009; 220(1): 212–216). Given this early success, Perlingeiro and her co-workers have used mouse iPSCs to make muscle-forming cells that have been used to treat muscular dystrophy in MD mice. In this experiment, suppression of the immune system was not necessary, since the muscle cells were made from cells that came from the patients.

Perlingeiro said of the experiment, “One of the biggest barriers to the development of cell-based therapies for neuromuscular disorders like muscular dystrophy has been obtaining sufficient muscle progenitor cells to produce a therapeutically effective response. Up until now, deriving engraftable skeletal muscle stem cells from human pluripotent stem cells hasn’t been possible. Our results demonstrate that it is indeed possible and sets the stage for the development of a clinically meaningful treatment approach.”

Once transplanted, the muscle-forming cells (myogenic progenitor cells to be exact) moved into the damaged muscles and integrated into them. They formed skeletal muscle and provided extensive and long-term muscle regeneration that resulted in improved muscle function. To make the iPSC cell lines, Perlingeiro and her laboratory workers genetically modified to human iPSC lines with a gene called PAX7. PAX7 encodes a transcription factor that is essential for muscle formation and muscle regeneration. PAX7, with PAX3, designates cells as myogenic progenitor cells. Therefore, inserting the PAX7 gene into iPSCs would drive them to become myogenic progenitor cells.

Once Perlingeiro’s lab perfected the protocol for making myogenic progenitor cells from iPSCs, they found that they could make buckets and buckets of them. The iPSC-derived muscle forming cells were much more efficient at integrating into the muscles and regenerating them than other cell types. Muscle-forming stem cells from human muscle biopsies, for example, failed to persist in the muscle.

Perlingeiro concluded, “Seeing long-term maintenance of these cells without major side effects is exciting. Our research proves that these differentiated stem cells have real staying power in the fight against muscular dystrophy.”