Enzyme studies in muscular dystrophy. III. In hereditary muscular dystrophy in mice

Decreased parvalbumin contents in skeletal muscles of C57BL/6J(dy2J/dy2J) dystrophic mice

Parvalbumin content is decreased by 40% in hindlimb muscles of adult (3.5 months) dystrophic mice when compared to normal mice of the same age. The concentration of parvalbumin in the dystrophic muscles resembles that of immature muscles of 4-week-old normal mice. The reduction may contribute to an elevation of sarcoplasmic free CA2+, which could stimulate various Ca2+-dependent processes related to the disease.

Abnormal collagen metabolism in cultured skin fibroblasts from patients with Duchenne muscular dystrophy

Total collagen synthesis is decreased by about 29% (P less than 0.01) in skin fibroblasts established in vitro from male patients with Duchenne muscular dystrophy (DMD) as compared with that in normal male skin fibroblasts in vitro. The reduction in collagen synthesis is associated with an approximately 2-fold increase in collagen degradation in DMD fibroblasts. Correlated to these alterations in the metabolism of collagen, DMD fibroblasts express a significantly higher hydroxyproline/proline ratio (DMD: 1.36-1.45; P less than 0.01) than do normal fibroblasts (controls: 0.86-0.89). The increased hydroxylation of proline residues of collagen (composed of type I and type III) could be the cause for the enhanced degradation of collagen in DMD fibroblasts.

Successful treatment of murine muscular dystrophy with the proteinase inhibitor leupeptin

Mice with genetic muscular dystrophy were treated with intraperitoneal injections of the proteinase inhibitor leupeptin, beginning before the onset of weakness. A significant number of the treated animals failed to develop histological evidence of dystrophy, compared with controls. Leupeptin treatment prevented (or delayed) the onset of muscular dystrophy in this experiment.

Dynamic aspects of structural proteins in vertebrate skeletal muscle

In this review, our current knowledge on the structural proteins of vertebrate skeletal muscle is briefly outlined. Structural proteins include the contractile proteins (actin and myosin), the major regulatory proteins (troponin and tropomyosin), the minor regulatory proteins (M-protein, C-protein, F-protein, I-protein, and actinins), and the scaffold proteins (connectin, desmin, and Z-protein). In addition, the relative turnover rates of the muscle proteins (M-protein greater than or equal to troponin greater than soluble protein as a whole greater than tropomyosin not equal to alpha-actinin greater than myosin greater than 10S-actinin greater than actin) are discussed. The changes in the turnover of muscle proteins are compared in denervated and dystrophic muscles. The properties of the various proteases in muscle, including alkaline protease, calcium-activated neutral protease (CANP), and acidic protease (cathepsins), and the structural alterations of myofibrils by these proteases are also described. Finally, the role of proteases and their inhibitors in diseased muscle is summarized, with focus on CANP and its inhibitors, leupeptin and E-64.

Protein degradation in skin fibroblasts from patients with Duchenne muscular dystrophy

The rates of degradation of [3H]leucine-labelled proteins have been measured in cultures of skin fibroblasts obtained from normal controls (five subjects) and patients with Duchenne muscular dystrophy (six subjects). Cultures were incubated with [3H]leucine (10 microCi/ml) for 60 min to label "short-lived" proteins, and with [3H]leucine (5 microCi/ml) for 60 h to label "long-lived" proteins. Optimal wash procedures were devised for removal of [3H]leucine from the extracellular space and from cell pools before beginning degradation measurements. Re-utilization of [3H]leucine released from degraded labelled proteins was prevented by supplementing the medium with 4mM-leucine. Rates of degradation did not depend on the growth state of the cells or on cell age over the range used (passages eight-20). Degradation of long-lived proteins was approximately linear over a 24h period, at a rate of 1.0% per h. 30% of short-lived protein was degraded within 6h. No differences were observed between protein degradation in normal fibroblasts and in those from patients with Duchenne muscular dystrophy.

Muscle breakdown and lysosomal activation (biochemistry)

Muscle tissue levels of lysosomal catheptic enzymes, such as cathepsins D, A, B1, C, and dipeptidyl peptidase II, were measured in control subjects and patients with muscular dystrophies, polymyositis, and certain denervating diseases. The results show that, in general, the activities of these enzymes are increased in muscles of patients with muscular dystrophies and other diseases. The increases in cathepsin D and autolytic activities are not significant until the late stage of the disease process. Cathepsins A, B1, and C are, however, significantly elevated in mildly affected dystrophic and other diseased muscles. Of these catheptic enzymes, cathepsin B1 displays the highest rise at an early stage, suggesting that it may be one of the rate-controlling enzymes of proteolysis. Dipeptidyl peptidase II is increased slightly in dystrophic and other myopathic muscles but is unchanged in denervated muscle. These data clearly implicate the lysosomal group of proteinases as largely responsible for mediating muscle breakdown in the muscular dystrophies and certain other muscle and neuromuscular diseases in man.

Muscular dystrophy: inhibition of degeneration in vivo with protease inhibitors

The protease inhibitors leupeptin and pepstatin were used in vivo in genetically dystrophic chickens to determine their effects on the histological and biochemical changes observed in this disease. These compounds appear to delay the degeneration of muscle tissue which is characteristic of this disorder and thus may have potential therapeutic value in the treatment of muscular dystrophy.

Proteolysis in dystrophic hamster diaphragm and abdominal muscle

Proteolysis, as measured by tyrosine release, was estimated in abdominal and diaphragm muscle of hamsters. There did not appear to be a difference between dystrophic and control hamsters.

Inability of selenium to affect creatine metabolism in rat muscle

1. Two groups of adult rats were placed in a metal-free environment and pair-fed with selenium-supplemented and Se-deficient diets. 2. After 5 months the animals were killed and skeletal muscle concentrations of creatine, creating phosphate, ATP, protein and Se were determined. 3. Se deficiency was indicated by the low Se content of the skeletal muscle from the deficient animals, but no changes were found in the amounts of the other components. 4. These results suggest that Se may not be involved in creatine metabolism and that Se deficiency may not be concerned independently in the development of nutritional dystrophy, where changes are found in the levels of protein, creatine, creatine phosphate and ATP.

Neurogenic control of muscle ribosomal protein synthesis

In vitro protein synthesis of ribosomes extracted from leg muscles of 20 Sprague-Dawley rats denervated 3 and 14 days (high sciatic transections) and 10 control rats was studied. The concentration/mg protein of total ribosomes extracted from the 14-day denervated muscle showed a significant increase. Distribution of muscle polyribosomes on sucrose density gradients was normal in all cases. Noncollagen protein synthesis of the heavy polyribosomes from both early and late denervated muscles showed a significant decrease. SDS polyacrylamide gels suggested that this decrease affected the synthesis of heavy chains of myosin, while the light chains of myosin, actin and tropomyosin had normal structure and amounts. Collagen synthesis of heavy polyribosomes showed slight to moderate increase in only 50 per cent of the cases. Supplementation of ribosomes extracted from denervated muscles with normal muscle soluble enzymes increased their noncollagen synthesis by 66 per cent. This suggests that the neurogenic control of ribosomal protein synthesis is accomplished by hormonal trophic substances contained in the muscle soluble enzymes.

Metabolic effects of human growth hormone and of estrogens in boys with Duchenne muscular dystrophy

Metabolic balance studies were conducted in seven boys with Duchenne-type muscular dystrophy, and in six normal boys of similar age, during a 12 day control period and during a 12 day period of treatment with human growth hormone (HGH) at the following doses: 0.0168, 0.0532, and 0.168 U/kg body weight (BW)((3/4)) per day (doses A, B, and C, respectively). In five of the six normals, dose C caused positive balances in N, P, Na, and K; doses B and A had anabolic effects in two and one normal subjects, respectively. In six of the seven Duchenne cases, dose C caused negative balances of N and K, and sometimes of P. Negative balances were produced in three of the Duchenne subjects by dose B, and in one by dose A. None of the dystrophy cases exhibited an anabolic response to any dosage of HGH tested. The release of endogenous HGH in response to insulin, after 2 days' pretreatment with diethylstilbestrol, was similar in both groups of subjects. In the course of these tests, a marked anabolic effect of diethylstilbestrol in the Duchenne patients was apparent. Therefore metabolic balance studies were repeated, in both Duchenne and normal cases, during a 12 day control period and during 12 days of treatment with diethylstilbestrol (0.106 mg/kg BW((3/4)) per day). In three of the normal children, diethylstilbestrol had no effect on the elemental balances; in two cases, a retention of Na was observed. In all seven Duchenne cases, diethylstilbestrol caused positive balances in N, P, Na, and K. Ethinyl estradiol (0.0106 mg/kg BW((3/4)) per day) produced positive N, P, Na, and K balances in all three Duchenne cases tested with this agent. The data show that exogenous HGH causes a catabolic effect in boys with Duchenne dystrophy. These patients are hyperresponsive to the anabolic effect of diethylstilbestrol. The latter phenomenon may reflect the inhibitory effect of estrogen upon the peripheral actions of these boys' endogenous HGH.

Proteolytic enzymes in normal and dystrophic mouse muscle

Proteolytic enzymes extracted from normal and dystrophic mouse muscle were studied, and optimum conditions for their activities were established. It was found that these enzymes were active at two pH values, 7.5 and 9. In normal and dystrophic mice, the enzymatic activity increased with age. When the activities of dystrophic muscle enzymes were compared with those of normal muscle enzymes, the increase was most significant in animals 60–90 days of age. The results obtained when the enzymes extracted from normal or dystrophic muscle were incubated with substrates from normal or dystrophic muscle indicate that the defect in the muscle is due to an increase in the activities of the proteolytic enzymes rather than to a chemical change in the muscle proteins.

ALDOLASE ACTIVITY IN NORMAL AND DYSTROPHIC MOUSE MUSCLE

Aldolase activity and nitrogen content of the muscle were determined in hereditary muscular dystrophic mice and their normal litter mates at various ages. Aldolase activity was found to decrease in dystrophic muscle when expressed per mg of wet tissue but showed an increase at later stages of the disease when expressed per mg of total nitrogen in muscle. Total nitrogen content of dystrophic muscle decreased considerably during the evolution of the disease. In normal mice, the muscle aldolase activity increases with age.

CREATINE KINASE IN MUSCLE OF NORMAL AND DYSTROPHIC MICE OF STRAIN 129

Hind leg muscle of normal and dystrophic mice of strain 129 was taken for individual analyses of creatine phosphokinase, total nitrogen, and collagen nitrogen. Young mice (18 to 25 days old) from one colony and adult mice (6 weeks to 3 months old) from another colony were used. The enzyme was assayed by measuring the formation of creatine from added creatine phosphate and adenosine diphosphate. Sulphydryl compounds were found to cause a large increase in activity. The enzyme activity was based on non-collagen nitrogen. The values in dystrophic mice were lower than in unaffected littermates, whether young or old, but the difference was significant only in young mice. The total nitrogen content was significantly lower than normal in all dystrophic mice, but there was no difference between dystrophics and normals in collagen nitrogen.

CREATINE KINASE IN NORMAL AND DYSTROPHIC MOUSE MUSCLE

The hind leg muscle of normal mice and mice with hereditary muscular dystrophy was taken for individual analyses of the creatine-phosphorylating enzyme, creatine kinase. Creatine kinase activity was always found to be higher in the muscle of normal mice than in that of dystrophic mice, and the values in each group decreased with increasing age of the mice. The difference was greatest in mice of 2 weeks of age, and in the light of these findings some suggestions are made about the pathogenesis of muscular dystrophy.