Altered distribution of plectin/HD1 in dystrophinopathies

Plectin/HD1 is a high molecular weight protein (approximately 500 kDa) that has been proposed to act as an important and versatile cytoskeletal cross-linker molecule. Mutations of the human plectin gene have recently been associated with the autosomal recessive disorder epidermolysis bullosa simplex with muscular dystrophy. We studied the expression of plectin/HD1 in various neuromuscular disorders by indirect immunofluorescence. In cross sections of normal human muscle, plectin/HD1 showed a checkerboard-like distribution with moderate to intense cytoplasmic and sarcolemmal staining in type 1 fibers and a faint staining of the sarcolemma in type 2 fibers. In longitudinal sections of plectin/HD1-positive fibers a cross-striation staining pattern was noted. This fiber type-related expression was significantly altered in the group of dystrophinopathies, whereas it was maintained in all other myopathies and denervating disorders. In seven dystrophinopathies studied, a markedly increased plectin/HD1 immunoreactivity at the sarcolemmal level of type 2 fibers was observed. Confocal laser microscopy of normal skeletal muscle revealed a colocalization of desmin and plectin/HD1 at the level of the sarcolemma. This suggests that plectin/HD1- in analogy to its demonstrated involvement in cytokeratin-hemidesmosome linkage in epidermis-may mediate the anchorage of desmin to the sarcolemma (i.e. to costameres).