Increased lysosome-related proteins in the skeletal muscles of distal myopathy with rimmed vacuoles
Investigators have speculated that the degenerative process in distal myopathy with rimmed vacuoles (DMRV) mainly involves the lysosomal system. To investigate possible protein abnormalities related to intracellular lysosomal proteolytic pathways in DMRV-affected muscles, we performed immunohistochemical analyses of certain proteins in muscle biopsy specimens obtained from patients with various neuromuscular diseases, including DMRV, muscular dystrophy, polymyositis, and amyotrophic lateral sclerosis, and in normal human muscles specimens. Immunohistochemically, most muscle fibers in normal control specimens showed little or no reaction for clathrin and alpha- and gamma-subunits of adaptin-constituted adaptin proteins (AP)-1 and AP-2, respectively. Abnormal increases in these proteins were demonstrated mainly in the cytoplasm of atrophic fibers or in necrotic fibers in all diseased specimens. Particularly in DMRV-affected muscles, alpha- and gamma-adaptins were often observed inside or on the rims of vacuoles and in the cytoplasm of vacuolated fibers. Abnormal increases in Golgi-zone protein were also demonstrated in DMRV muscles. The rims of rimmed vacuoles were negative for kinectin, an endoplasmic reticulum-binding protein. Positive staining for both proteins, however, was sometimes seen inside the vacuoles in DMRV-affected fibers. These results suggest increased endocytosis at the plasma membrane as well as secretion involving transport from the trans-Golgi network of the Golgi apparatus in DMRV. Accumulation of various lysosome-related proteins within the rimmed vacuoles indicates at least some of these vacuoles may be autolysosomes.