Tuesday, 15 January 2013

Stem cells show promise for treating Duchenne muscular dystrophy

In a study published in December 27, 2012 researchers from the University of Illinois showed that  aorta-derived mesoangioblasts (stem cells derived from heart blood vessels) may be a viable option for treating the Duchenne muscular dystrophy (DMD) condition. The study was carried out on dystrophin-deficient mice.

DMD is a genetic condition, caused by a mutation in the gene responsible for coding the dystrophin protein. Dystrophin is a protein that helps muscle cells to stay in place while they contract. Lack of the protein causes muscle fibre injury and cell death.

computer generated image of dystrophin
Computer-generated image of Dystrophin


During the study the researchers, led by Suzanne Berry-Miller, injected  aorta-derived mesoangioblasts (with a functional dystrophin gene) directly into the hearts of the mice. According to the study, the stem cell treatment prevented or greatly delayed the onset of heart symptoms in all the mice that were asymptomatic prior to the injection. The researchers aren't sure why exactly this happened but they attribute it to one (or a combination) of the following:
  • A small number of the transplanted stem cells differentiated into myocardiocytes (heart muscle cells) which in return produced dystrophin.
  • The treatment induced a small number of the existing heart stem cells to replicate and differentiate into myocardiocytes.
  • The injections induced the formation of new heart vessels.


Picture of a Myocardiocyte
A myocardiocyte
Unfortunately positive results weren't reported on the mice that were symptomatic prior to the treatment. Some of them actually got worse!

One of the main characteristics of DMD is that muscle tissue is replaced with connective tissue (a process called fibrosis). Miller believes that a potential reason that the treatment failed in these mice, is that the injected stem cells landed on a pocket of fibrosis instead in muscle tissue. As a result instead of differentiating into heart stem cells they differentiated into fibroblasts, thus worsening the condition. But as she says, this is just a theory and more research is needed on the matter

Despite the partial failure, Miller is very happy with the results they god. After all, this is the first study in which stem cells show some benefit in a DMD model. She hopes their findings will pave the way for more animal, and perhaps one day,  human clinical trials.

Duchenne muscular dystrophy  is a form of muscular dystrophy.  As mentioned earlier, the condition is caused by a mutation in the dystrophin-producing gene, which is found in the X chromosome. The gene is recessive and this is why occurrences in girls are extremely rare. DMD affects about  1 in every 3.600 boys. Symptoms usually appear before the age of 5, sometimes even during early infance. Some of them include:
  • Enlarged calves and/or deltoid muscles
  • Low endurance
  • Difficulty to stand unaided 
  • Inability to ascend staircases
As of the moment, there is no cure for the condition. Current "treatments" only treat the symptoms and not the true causes, however there are some promising clinical trials running. The mean life expectancy of a DMD patient is 25 years.

A small presentation about DMD



Reference
Chun JL, O'Brien R, Song MH, Wondrasch BF, & Berry SE (2013). Injection of vessel-derived stem cells prevents dilated cardiomyopathy and promotes angiogenesis and endogenous cardiac stem cell proliferation in mdx/utrn-/- but not aged mdx mouse models for duchenne muscular dystrophy. Stem cells translational medicine, 2 (1), 68-80 PMID: 23283493

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