Protein synthesis in chicken muscular dystrophy

Ribosomal protein synthesis in cultured skin fibroblast cells obtained from patients with Duchenne muscular dystrophy

Ribosomes and ribosomal subunits were extracted from cultured skin fibroblasts from patients with Duchenne muscular dystrophy (DMD). A poly(U)-directed polyphenylalanine synthesis system was used to test 80S ribosomes from DMD cells and normal controls as well as hybrid 80S couples of subunits from DMD cells and control cells. The activity of ribosomes extracted from the patients was 38-62% lower than that of normal controls. Of the 80S hybrid ribosomes, only those consisting of 40S subunits from DMD cells and 60S subunits from the control cells, showed a similar decrease in activity. That means that the defect is exclusively based on an alteration in the small ribosomal subunit.

Content and synthesis of glycolytic enzymes and creatine kinase in skeletal muscles and normal and dystrophic chickens

A number of workers have reported that avian muscular dystrophy causes alterations in the levels of certain enzyme activities in "fast-twitch" muscle fibers but has little effect on enzyme activities in "slow-twitch" muscle fibers. In the present work, the effects of this disease on the content and relative rates of synthesis of a number of glycolytic enzymes and the skeletal muscle-specific MM isoenzyme of creatine kinase in chicken muscles was investigated. It was shown that (i) the approximate 50% reductions in steady-state concentrations of three glycolytic enzymes (aldolase, enolase, and glyceraldehyde-3-P dehydrogenase) in dystrophic breast (fast-twitch) muscle result predominantly from decreases in relative rates of synthesis, rather than accelerations in relative rates of degradation, of these proteins in the diseased tissue; (ii) in contrast to the situation with the glycolytic enzymes, muscular dystrophy has only minor effects (25% or less) on the content and relative rate of synthesis of MM creatine kinase in breast muscle fibers; (iii) the muscular dystrophy-associated alterations in content and synthesis of the glycolytic enzymes in breast muscle fibers become apparent only during postembryonic maturation of this tissue; and (iv) as expected, muscular dystrophy has no significant effect on the content or relative rates of synthesis of glycolytic enzymes in slow-twitch lateral adductor muscles of the chicken. These results are discussed in terms of the apparent similarities between the effects of muscular dystrophy and surgical denervation on the protein synthetic programs expressed by mature fast-twitch muscle fibers.

Increase in the amount of elongation factor 2 in chicken muscular dystrophy

The amount of elongation factor 2 (EF2) in the cytoplasm and ribosome of breast muscle cell from normal and dystrophic strains of chicken was measured. Concentration in the cytoplasm of 20-day-old embryonic dystrophic muscle was higher than that in normal muscle, but no difference in content was found in muscles of 15-day-old embryos. The amount of EF2 bound to ribosomes was identical in normal and dystrophic muscles during all stages of development. Peptide mapping patterns of partial proteolytic fragments of EF2 from normal and dystrophic chicken breast muscles were similar. The increase in cytoplasmic protein synthetic activity of dystrophic breast muscles reported previously seems to be due to the corresponding increase in the number of EF2 molecules rather than to their modification in dystrophic muscle.

Development and growth of extensor carpi radialis longus muscle in normal and dystrophic chickens

The development and growth of the skeletal muscles in normal and dystrophic chickens were studied to obtain a clue to the mechanism of dystrophic pathogenesis. A relatively small and isolated muscle--the extensor carpi radialis longus (ECRL) muscle--was utilized to analyze quantitatively the histologic and physiologic parameters. Both normal and dystrophic chickens attained qualitatively the same parameters, but there were some quantitative differences. The first disorder to appear in the dystrophic muscle was a substantial retardation of muscle cell proliferation in the early postnatal development, and the fiber loss was fully compensated by hypertrophy of the remaining cells. The succeeding abnormalities in the dystrophic muscle, e.g., reduction of efficiency in the tension output per unit area, were interpreted as compensating reactions. Therefore, it is likely that the dystrophic lesions in avian muscular dystrophy are caused by retardation of muscle cell proliferation in the early postnatal period. Possible mechanisms for the retardation are discussed in terms of the nerve--muscle trophic interactions which could be greatly intensified in the early postnatal period.

Content and synthesis of several abundant glycolytic enzymes in skeletal muscles of normal and dystrophic mice

In both 2- and 3-month-old 129 ReJ mice, the catalytic activity levels of three enzymes involved in glycogen breakdown (phosphorylase, enolase, and aldolase) were found to be 35-50% lower in hind limb muscles of dystrophic mice as compared with normal mice. The reduced activities of these enzymes in the diseased tissue was directly due to corresponding reductions in the number of enzyme molecules rather than being due to inactivation of the enzymes in the dystrophic muscle. Results of short term double isotope incorporation experiments conducted with muscle explants in vitro suggested that the rates of synthesis of these enzymes, and of most other abundant cytosolic proteins, relative to each other, were similar in hind limb muscles of normal and dystrophic mice. The present work on murine muscular dystrophy is discussed in terms of our previous studies into the influence of avian muscular dystrophy on the content and synthesis of abundant glycolytic enzymes in chicken skeletal muscles.

The 60S ribosomal subunit is altered in the skeletal muscle of dystrophic hamsters

Polysomes from the skeletal muscle of normal and dystrophic hamsters were dissociated into ribosomal subunits by treatment with puromycin and the subunits from both strains were reassociated in all possible combinations. When their protein synthesis activity was assayed in a poly(U)-directed cell-free system at a low magnesium concentration, the reassociated ribosomes from dystrophic hamsters were less active than the ribosomes from control animals. The ribosomal defect is a property of the 60S subunit and is due to a ribosomal component rather than to abnormal binding of a non-ribosomal protein.

Decrease in the rate of protein synthesis by polysomes from cultured fibroblasts of patients and carriers with Duchenne muscular dystrophy

Polysomes extracted from cultured fibroblast cells isolated from patients with Duchenne muscular dystrophy (DMD), carriers of the disease, and normal controls were used for in vitro measurement of protein synthesis in a wheat germ extract system. It was observed that polysomes from patients and carriers (seven of each aged 17 years or older) exhibited a 3-fold and a 1.5-fold decrease in the rate of protein synthesis, respectively, as compared with controls. These results are discussed with a view to developing a sensitive and easily available assay for the detection of DMD carriers.

Age-related changes in protein turnover and ribonucleic acid of the diaphragm muscle of normal and dystrophic hamsters

Diaphragm muscles of dystrophic hamsters were found to be larger than those of control animals at two of three ages studied. The additional growth of these afflicted muscles correlated with large increases in protein synthesis and concentrations of RNA. Protein breakdown was also increased in the dystrophic muscles, but to a smaller extent than synthesis.

Protein synthesis in dystrophic muscle. Activity of the pH 5 supernatant fraction of muscle in dystrophic mice

The pH 5 supernatant fractions prepared from homogenates of tissues of normal and dystrophic mice were used to study the incorporation of [14C]phenylalanyl-tRNA into peptide. The incorpoation was markedly reduced using the muscle pH 5 supernatant fraction from dystrophic animals but no reduction was seen with brain, liver or heart preparations from dystrophic mice. The lower incorporation with dystrophic muscle pH 5 supernatant was not due to altered activity of ribonuclease, elongation factors, proteolytic enzymes, GTP or sulfhydryl reagents, but was attributable to the presence of activity that was inhibitory to protein synthesis.

Myosin in developing normal and dystrophic chicken pectoralis. I. Synthesis and degradation

The synthesis and degradation of pectoralis myosin have been investigated in chickens 15-23 days after hatching. An essentially nonreutilizable tracer amino acid was used to demonstrate differences in the rates of synthesis and degradation of myosin isolated from normal and hypertrophied, cystrophic breast tissue. The analyses have shown that the dystrophic system synthesizes myosin faster than the normal system and that only myosin in dystrophic pectoralis is degraded during the experimental period. Double label experiments have indicated that the heavy chains of dystrophic myosin are destroyed at a rate greater than that characteristic of the light chains.