Disturbed trafficking of dystrophin and associated proteins in targetoid phenomena after chronic muscle denervation

Dystrophin and associated proteins form a complex with an important role at the sarcolemma. Expression of this protein complex is highly regulated during development and regeneration. In order to better understand assembling patterns of these proteins, we have studied their expression in targetoid-like phenomena found in human muscle after chronic denervation, a situation known to give rise to abnormal protein trafficking. In eight biopsies of patients with chronic denervation, mainly resulting from amyotrophic lateral sclerosis, we found a number of targetoid phenomena. Selective accumulation of a number of sarcolemmal and sarcoplasmatic proteins occurred in targetoid phenomena. The larger majority of them contained gamma-sarcoglycan (gammaSG), but none contained the developmental heavy chain myosin isoform. In a series of 166 targetoid phenomena which could be studied with 17 different antibodies recognizing sarcolemmal and cytoplasmatic proteins, a high level of colocalization of gammaSG with desmin and alpha-actinin was found. Colocalization rate was much lower with other proteins, including other members of the dystrophin-associated protein complex. These data show that selective changes in expression of otherwise closely related proteins occur during disturbed trafficking leading to target formation. Because members of the dystrophin-associated protein complex do not accumulate in a similar fashion within targets, we suggest that a complex molecular control of gene expression and trafficking of this complex is involved after chronic muscle denervation.