Fast muscle fibers are preferentially affected in Duchenne muscular dystrophy

Cell fractionation studies indicate that dystrophin is a protein of surface membranes of skeletal muscle

We studied the subcellular localization of dystrophin in rabbit skeletal muscle. In Western-blot analysis of membrane preparations, dystrophin was associated with the sarcolemmal fraction, as indicated by cholesterol content and co-purification with ouabain-binding activity and beta-adrenergic receptor. Dystrophin was also found with junctional T-tubules, but not with 'free' T-tubules, longitudinal portions or terminal cisternae of the sarcoplasmic reticulum. Dystrophin was not solubilized by high salt solutions, but it was solubilized by low concentrations of detergents (Triton X-100 and deoxycholate), suggesting that it is a peripheral membrane protein.

Dystrophin and the integrity of the sarcolemma in Duchenne muscular dystrophy

It is suggested that in Duchenne muscular dystrophy the absence of dystrophin, which is probably a cytoskeletal protein underlying the sarcolemma, causes changes in stretch-activated cation channels rather than direct mechanical tearing of the surface membrane.

Localization of muscle gene products in nuclear domains

The localization of gene products is central to the development of cell polarity and pattern specification during embryogenesis. To monitor the distribution of gene products encoded by different nuclei in the same cell in tissue culture, we fused cells of different species to form multinucleated non-dividing heterokaryons. In previous fusion studies, cell-surface antigens and organelles contributed by disparate cell types intermixed within minutes. Using heterokaryons produced with differentiated muscle cells, we demonstrate here that a muscle membrane component, the Golgi apparatus mediating its transport, and a sarcomeric myosin heavy chain are localized in the vicinity of the nuclei responsible for their synthesis. These results provide direct evidence that products (organelle, membrane and structural proteins) derived from individual nuclei can remain localized in myotubes, a finding with implications both for neuromuscular synapse formation and for the carrier state of Duchenne muscular dystrophy.

Mosaic expression of dystrophin in symptomatic carriers of Duchenne's muscular dystrophy

A deficiency of the protein dystrophin is known to be the cause of Duchenne's muscular dystrophy. To examine the expression of dystrophin in symptomatic female carriers of this X-linked recessive disorder, we performed immunohistochemical studies on muscle-biopsy specimens from three such carriers, using an antiserum raised against a synthetic peptide fragment of dystrophin. In all three carriers, most individual muscle fibers reacted either strongly or not at all to the antiserum for dystrophin; only 2 to 8 percent of fibers showed partial immunostaining. This mosaic staining pattern was present on both cross-sectional and longitudinal muscle specimens. Although the mosaic pattern was seen in all fiber types, more than 80 percent of type 2B and 2C fibers from two of the carriers did not react with the antiserum. Similar studies in nine normal subjects showed consistently strong staining of all muscle fibers. No muscle fibers from 31 patients with Duchenne's muscular dystrophy reacted with the antiserum. We conclude that symptomatic carriers of Duchenne's muscular dystrophy can be identified by a distinct mosaic pattern in the immunohistochemical staining of the surface membrane of skeletal-muscle specimens. This finding may have practical implications for genetic counseling, although it remains to be shown whether the same staining pattern will be found in muscle specimens from asymptomatic carriers of Duchenne's muscular dystrophy.

Lymphocyte antigen Leu-19 as a molecular marker of regeneration in human skeletal muscle

Antigen Leu-19 (Leu19-Ag), a 200- to 220-kDa surface glycoprotein, was originally identified on a subset of human peripheral lymphocytes exhibiting non-major histocompatibility complex-restricted cytotoxicity. Here we report that monoclonal antibody Leu-19 (mAb-Leu19) labels structures in human skeletal muscle: (i) satellite cells, which form the stem cell pool of muscle fiber regeneration, both in normal and diseased muscle; (ii) myotubes and myotube projections in regions of muscle fiber repair; (iii) periodically organized fibrillar structures in areas of regeneration; (iv) the surface of myoblasts and developing myotubes in culture. mAb-Leu19 precipitated a protein of approximately 200 kDa from cultured muscle cells. Our data show that Leu19-Ag is expressed on muscle-specific components of myosegments in repair and thus represents a molecular marker of muscle regeneration. On the basis of this molecular marker and using laser scan microscopy, it is possible to visualize at the light microscopic level hitherto undetectable details of muscle regeneration in routine cryostat sections.

Micromethods in single muscle fibers. 2. Determination of glutathione reductase and glutathione peroxidase

This paper extends the previous study for systems which control intracellular oxidative events in muscle and describes procedures suitable to assay glutathione peroxidase (GSHPx), glutathione reductase (GR), and total glutathione (GSH + GSSG) after fiber typing of individual muscle fibers. In human skeletal muscle, both GR and GSHPx activities were relatively low when compared to those of other tissue. No difference was found among fiber types (I, IIA, and IIB) with regard to GR activity, but in contrast GSHPx activity was significantly lower in type IIB fibers than in the other types. These results suggest that type IIB fibers may have a reduced ability to cope with hydroperoxides generated during oxidative stress, which, in turn, could lead to increased damage to membrane structures by lipid peroxidation or oxidation of sensitive intracellular thiol (-SH) enzymes by hydrogen peroxide. The Km of skeletal muscle GR for GSSG was 27 microM and for NADPH was 22 microM. If one assumes approximately 95% of total glutathione is present in the reduced state, then GSSG concentration would be of the order of 0.3 mmol/kg and under these conditions skeletal muscle GR would be efficient in all muscle fiber types.

Diversity of fast myosin heavy chain expression during development of gastrocnemius, bicep brachii, and posterior latissimus dorsi muscles in normal and dystrophic chickens

The expression of fast myosin heavy chain (MHC) isoforms was examined in developing bicep brachii, lateral gastrocnemius, and posterior latissimus dorsi (PLD) muscles of inbred normal White Leghorn chickens (Line 03) and genetically related inbred dystrophic White Leghorn chickens (Line 433). Utilizing a highly characterized monoclonal antibody library we employed ELISA, Western blot, immunocytochemical, and MHC epitope mapping techniques to determine which MHCs were present in the fibers of these muscles at different stages of development. The developmental pattern of MHC expression in the normal bicep brachii was uniform with all fibers initially accumulating embryonic MHC similar to that of the pectoralis muscle. At hatching the neonatal isoform was expressed in all fibers; however, unlike in the pectoralis muscle the embryonic MHC isoform did not disappear. With increasing age the neonatal MHC was repressed leaving the embryonic MHC as the only detectable isoform present in the adult bicep brachii muscle. While initially expressing embryonic MHC in ovo, the post-hatch normal gastrocnemius expressed both embryonic and neonatal MHCs. However, unlike the bicep brachii muscle, this pattern of expression continued in the adult muscle. The adult normal gastrocnemius stained heterogeneously with anti-embryonic and anti-neonatal antibodies indicating that mature fibers could contain either isoform or both. Neither the bicep brachii muscle nor the lateral gastrocnemius muscle reacted with the adult specific antibody at any stage of development. In the developing posterior latissimus dorsi muscle (PLD), embryonic, neonatal, and adult isoforms sequentially appeared; however, expression of the embryonic isoform continued throughout development. In the adult PLD, both embryonic and adult MHCs were expressed, with most fibers expressing both isoforms. In dystrophic neonates and adults virtually all fibers of the bicep brachii, gastrocnemius, and PLD muscles were identical and contained embryonic and neonatal MHCs. These results corroborate previous observations that there are alternative programs of fast MHC expression to that found in the pectoralis muscle of the chicken (M.T. Crow and F.E. Stockdale, 1986, Dev. Biol. 118, 333-342), and that diversification into fibers containing specific MHCs fails to occur in the fast muscle fibers of the dystrophic chicken. These results are consistent with the hypothesis that avian muscular dystrophy is a developmental disorder that is associated with alterations in isoform switching during muscle maturation.

Cell and fiber-type distribution of dystrophin

Duchenne muscular dystrophy is the result of dystrophin deficiency. We have determined the cell types likely to express the pathogenic effects of this neuromuscular disease by determining the pattern of dystrophin expression in normal cells. We find that all physiological types of muscle cells express dystrophin at similar levels, and that the dystrophin content of various tissues correlates with the myogenic cell population of each tissue. The dystrophin content of brain and spinal cord, however, is found not to correlate with any type of muscle cell, and it is suggested that neurons express dystrophin. The potential involvement of striated muscle fibers, the vasculature, and the nervous system in the etiology of Duchenne muscular dystrophy makes it likely that the disease is a complex disorder of combined pathogenesis. We also find that the dystrophic chicken does not represent an animal model for dystrophin deficiency.

Molecular genetics in muscular dystrophy research: revolutionary progress

The contribution of "reverse genetic" strategies to neuromuscular disease research is evident in the progression of breakthroughs that have recently culminated in the cloning of the Duchenne muscular dystrophy (DMD) cDNA. The resultant improvements in our understanding of the genetic basis of Becker muscular dystrophy (BMD) and DMD serve as models for similar investigation of other heritable disorders. These genetic advances have outpaced concurrent work on the molecular pathogenesis of the dystrophic process, with the curious result that inferences about the DMD protein's amino acid sequence have preceded any information about its function or intracellular localization. In recognition that this foundation sets the stage for the rapid elucidation of the disease's pathogenesis, we review the experimental basis of such advances, with reference to relevant progress in basic myology, pathology, and molecular biology. We conclude with a view towards the ultimate clinical implications of these experimental breakthroughs.