Increasing MuSK activity delays denervation and improves motor function in ALS mice.

Amyotrophic lateral sclerosis (ALS) is a devastating disease that progresses from detachment of motor nerve terminals to complete muscle paralysis and lethal respiratory failure within 5 years of diagnosis. Genetic studies have linked mutations in several genes to ALS, and mice bearing mutations in SOD1 recapitulate hallmark features of the disease. We investigated whether disease symptoms can be ameliorated by co-opting the retrograde signaling pathway that promotes attachment of nerve terminals to muscle. We crossed SOD1G93A mice with transgenic mice that express MuSK, a receptor tyrosine kinase that is required for retrograde signaling, and we used histological and behavioral assays to assess motor innervation and behavior. A 3-fold increase in MuSK expression delayed the onset and reduced the extent of muscle denervation, improving motor function for more than a month without altering survival. These findings suggest that increasing MuSK activity by pharmacological means has the potential to improve motor function in ALS.