Differential expression of dystrophin, utrophin, and dystrophin-associated proteins in human muscle culture

The dystrophin-associated protein complex (DAP) plays an important role in sarcolemmal function. Mutations of DAP elements lead to diverse forms of muscular dystrophies, among them Duchenne muscular dystrophy, one of the most severe neuromuscular diseases. Strategies in gene therapy are being assessed to restore DAP stability. However, the relationship between DAP elements and time-course of the DAP formation are still not known in detail. In order to better understand the relationship among DAP proteins, we therefore studied their expression during development in human muscle culture in comparison with developmentally regulated muscle proteins. Desmin immunoreactivity (IR) was detected by 3 days in vitro (DIV3), IR for developmental heavy-chain myosin, vimentin, utrophin, and β-dystroglycan, as well as α-, β-, and γ-sarcoglycan, a day later. δ-Sarcoglycan was found by DIV7; dystrophin could be detected only by DIV11. In general, DAP proteins were first located in the perinuclear region, later diffusely in the cytoplasm, and finally exclusively at the membrane. This sequence of events during muscle development gives further support to our suggestion that utrophin could be a precursor of dystrophin during development and regeneration. These data also suggest that utrophin alone is sufficient to anchor the complex, which is important when utrophin replacement strategies are being investigated for the treatment of dystrophinopathies. In this study we demonstrated the establishment of a culture technique that should allow the close study of DAP expression in diseased muscle, including its use after gene modulatory strategies.