Two known zebrafish dystrophin mutants, sapje and sapje-like (sap c/100 ), represent excellent small-animal models of human muscular dystrophy. Using these dystrophin-null zebrafish, we have screened the Prestwick chemical library for small molecules that modulate the muscle phenotype in these fish. With a quick and easy birefringence assay, we have identified seven small molecules that influence muscle pathology in dystrophin-null zebrafish without restoration of dystrophin expression. Three of seven candidate chemicals restored normal birefringence and increased survival of dystrophin-null fish. One chemical, aminophylline, which is known to be a nonselective phosphodiesterase (PDE) inhibitor, had the greatest ability to restore normal muscle structure and up-regulate the cAMP-dependent PKA pathway in treated dystrophin-deficient fish. Moreover, other PDE inhibitors also reduced the percentage of affected sapje fish. The identification of compounds, especially PDE inhibitors, that moderate the muscle phenotype in these dystrophin-null zebrafish validates the screening protocol described here and may lead to candidate molecules to be used as therapeutic interventions in human muscular dystrophy.phosphodiesterase inhibitor | chemical treatment M uscular dystrophy is a disease in which the muscle forms normally at first but then degenerates faster than it can be repaired. The most common form of muscular dystrophy is Duchenne muscular dystrophy (DMD), representing more than 90% of the diagnosed cases. Mutations in the dystrophin gene were found to be the cause of both DMD and Becker muscular dystrophy (1, 2). Currently, prednisone is the only treatment option available for muscular dystrophy patients in the United States, although there are currently other options through approved clinical trials. Other treatments currently being tested or considered for treating muscular dystrophy include the small molecule PTC124, which promotes read-through of nonsense mutations (3), encouraging muscle development by myostatin down-regulation (4, 5), and the use of oligonucleotides to promote exon skipping to restore dystrophin expression (6).Recently, a number of chemical and drug screens have been published using zebrafish embryos (7-11). It is possible to quickly produce large numbers of mutant offspring that can then be assayed in multiwell plates and treated with different chemicals to determine if disease progression is modulated. Many of these screens have been highly successful in disease modeling (7) and drug screening (8-10), making the zebrafish ideal for highthroughput whole-organism screening of candidate compounds. Chemical compounds of relatively small molecular weight can bind to specific proteins and alter their function, resulting in nonheritable phenotype changes.In addition to their suitability for chemical screens, zebrafish also represent a good model to investigate genes involved in muscle development and degeneration, including human muscular dystrophy (12-18). The orthologs of many dystrophin-glycoprot...

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