Researchers at the University of Minnesota have developed an  animal research model for facioscapulohumeral muscular dystrophy  (FSHD) to be used for muscle regeneration research as well as  studies of the effectiveness of potential therapies for FSHD.
    The research is published in the current edition of the journal    Cell Reports.  
    There is no treatment for FSHD, which is thought by many to be    the most common type of muscular dystrophy. FSHD is an unusual    genetic disorder because, unlike most genetic diseases, it is    not caused by the loss of a functional gene, but rather by the    modification of an existing gene, through a genetic mutation.    This mutation makes the gene more active so patients with FSHD    express a protein, named DUX4, which interferes in an unknown    way with muscle maintenance.  
    "We felt that an animal model would advance progress towards a    cure for FSHD for two reasons," said Michael Kyba, Ph.D., lead    researcher and associate professor in the Medical School at the    University of Minnesota. "First, it would allow us to    understand what DUX4 does in muscle to cause muscle loss, and    second, it would provide a system in which efficacy of    potential therapies could be evaluated before they are tested    in humans."  
    The mouse model designed by Kyba and his team allows the    disease-associated DUX4 protein to be produced when mice are    treated with doxycycline. The amount of DUX4 can be controlled    by varying the dose of doxycycline. Researchers expected the    mice to be normal until they were treated with doxycycline,    however even when DUX4 was in the "off" state, mice showed    profound disease effects, some related to FSHD as well as    additional effects not seen in FSHD patients.  
    "Nothing is black and white in biology," says Kyba. "No gene is    truly off, and the off state in this case resulted in enough    leaky DUX4 expression to kill the mice."  
    The team solved this problem by moving the gene to the X    chromosome. Because females have two X chromosomes, only one of    which is actively used in each cell, the female mice were    healthy enough to enable the DUX4 mice to reproduce even though    all of their male progeny with the DUX4 gene died. The fact    that multiple levels of turning off the DUX4 gene were    necessary to allow mice to survive showed that DUX4 is more    toxic than researchers expected.  
    "We learned a lot with this animal model, but perhaps the most    important finding was what we observed when we transplanted    skeletal muscle stem cells," said Kyba.  
    The team could isolate muscle stem cells from the male mice    before they died and when they transplanted them into    muscle-damaged recipient mice, they found that the stem cells    were able to regenerate new muscle. But when even low doses of    doxycycline were given to the recipients to turn on DUX4 in the    skeletal muscle stem cells, muscle regeneration was severely    impaired. This suggested that a defect in skeletal muscle    regeneration may contribute to muscle loss in FSHD. The finding    also provides a very sensitive quantitative readout of DUX4    activity.  
    "This assay, in which we count new muscle fibers produced by    transplanted DUX4-expressing muscle stem cells, will be very    useful in testing therapeutics," says Kyba. "Drugs that target    DUX4 should allow these transplanted DUX4-expressing muscle    stem cells to make more new muscle fibers."  
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Researchers find animal model for understudied type of muscular dystrophy