Selenoproteins protect against avian nutritional muscular dystrophy by metabolizing peroxides and regulating redox/apoptotic signaling

Nutritional muscular dystrophy (NMD) of chicks is induced by dietary selenium (Se)/vitamin E (Vit. E) deficiencies and may be associated with oxidative cell damage. To reveal the underlying mechanisms related to the presumed oxidative cell damage, we fed four groups of 1-day-old broiler chicks (n = 40/group) with a basal diet (BD; 10 μg Se/kg; no Vit. E added, -Se -Vit. E) or the BD plus all-rac-α-tocopheryl acetate at 50mg/kg (-Se +Vit. E), Se (as sodium selenite) at 0.3mg/kg (+Se -Vit. E), or both of these nutrients (+Se +Vit. E) for 6 weeks. High incidences of NMD (93%) and mortality (36%) of the chicks were induced by the BD, starting at week 3. Dietary Se deficiency alone also induced muscle fiber rupture and coagulation necrosis in the pectoral muscle of chicks at week 3 and thereafter, with increased (P < 0.05) malondialdehyde, decreased (P < 0.05) total antioxidant capacity, and diminished (P < 0.05) glutathione peroxidase activities in the muscle. To link these oxidative damages of the muscle cells to the Se-deficiency-induced NMD, we first determined gene expression of the potential 26 selenoproteins in the muscle of the chicks at week 2 before the onset of symptoms. Compared with the +Se chicks, the -Se chicks had lower (P < 0.05) muscle mRNA levels of Gpx1, Gpx3, Gpx4, Sepp1, Selo, Selk, Selu, Selh, Selm, Sepw1, and Sep15. The -Se chicks also had decreased (P < 0.05) production of 6 selenoproteins (long-form selenoprotein P (SelP-L), GPx1, GPx4, Sep15, SelW, and SelN), but increased levels (P < 0.05) of the short-form selenoprotein P in muscle at weeks 2 and 4. Dietary Se deficiency elevated (P < 0.05) muscle p53, cleaved caspase 3, cleaved caspase 9, cyclooxygenase 2 (COX2), focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3K), phospho-Akt, nuclear factor-κB (NF-κB), p38 mitogen-activated protein kinase (p38 MAPK), phospho-p38 MAPK, phospho-JNK, and phospho-ERK and decreased (P < 0.05) muscle procaspase 3, procaspase 9, and NF-κB inhibitor α. In conclusion, the downregulation of SelP-L, GPx1, GPx4, Sep15, SelW, and SelN by dietary Se deficiency might account for induced oxidative stress and the subsequent peroxidative damage of chick muscle cells via the activation of the p53/caspase 9/caspase 3, COX2/FAK/PI3K/Akt/NF-κB, and p38 MAPK/JNK/ERK signaling pathways. Metabolism of peroxides and redox regulation are likely to be the mechanisms whereby these selenoproteins prevented the onset of NMD in chicks.

[Impact of 3-month simulation of the microgravity effects on the neuromuscular junction structure in rat's m. soleus]

The neuromuscular junctions were investigated in m. soleus of rats subjected to a 3-month tail suspension simulating the microgravity effects. Electron microscopy analysis revealed some ultrastructural signs of atrophy, degeneration and adipose dystrophy of muscle fibers. The aggregate of these findings points to progressive atrophy in m. soleus, while ultrastructural changes in the neuromuscular synapses testify a reduced functional activity of the synapses and partial denervation of the muscle fibers which, probably, underlay the atrophic process in the muscle. Increases in the number of axon terminals found in some neuromuscular synapses as well as of synaptic vesicles in individual axon terminals are likely to reflect formation of a particularly active pool of spinal motoneurons at L5, possibly associated with the growth in the number of fast fibers resulted from transformation.

Overexpression of Myostatin2 in zebrafish reduces the expression of dystrophin associated protein complex (DAPC) which leads to muscle dystrophy

Myostatin, a member of the TGF-beta superfamily, is a potent negative regulator of skeletal muscle and growth. Previously, we reported Mstn1 from zebrafish and studied its influence on muscle development. In this study, we identified another form of Myostatin protein which is referred to as Mstn2. The size of Mstn2 cDNA is 1342 bp with 109 and 132 bp of 5' and 3'-untranslated regions (UTRs), respectively. The coding region is 1101 bp encoding 367 amino acids. The identity between zebrafish Mstn1 and 2 is 66%. The phylogenetic tree revealed that the Mstn2 is an ancestral form of Mstn1. To study the functional aspects, we overexpressed mstn2 and noticed that embryos became less active and the juveniles with bent and curved phenotypes when compared to the control. The RT-PCR and in situ hybridization showed concurrent reduction of dystrophin associated protein complex (DAPC). In cryosection and in situ hybridization, we observed the disintegration of somites, lack of transverse myoseptum and loss of muscle integrity due to the failure of muscle attachment in mstn2 overexpressed embryos. Immunohistochemistry and western blot showed that there was a reduction of dystrophin, dystroglycan and sarcoglycan at translational level in overexpressed embryos. Taken together, these results indicate the suitability of zebrafish as an excellent animal model and our data provide the first in vivo evidence of muscle attachment failure by the overexpression of mstn2 and it leads to muscle loss which results in muscle dystrophy that may contribute to Duchenne syndrome and other muscle related diseases.

Primary role of functional ischemia, quantitative evidence for the two-hit mechanism, and phosphodiesterase-5 inhibitor therapy in mouse muscular dystrophy

BACKGROUND

Duchenne Muscular Dystrophy (DMD) is characterized by increased muscle damage and an abnormal blood flow after muscle contraction: the state of functional ischemia. Until now, however, the cause-effect relationship between the pathogenesis of DMD and functional ischemia was unclear. We examined (i) whether functional ischemia is necessary to cause contraction-induced myofiber damage and (ii) whether functional ischemia alone is sufficient to induce the damage.

METHODOLOGY/PRINCIPAL FINDINGS

In vivo microscopy was used to document assays developed to measure intramuscular red blood cell flux, to quantify the amount of vasodilatory molecules produced from myofibers, and to determine the extent of myofiber damage. Reversal of functional ischemia via pharmacological manipulation prevented contraction-induced myofiber damage in mdx mice, the murine equivalent of DMD. This result indicates that functional ischemia is required for, and thus an essential cause of, muscle damage in mdx mice. Next, to determine whether functional ischemia alone is enough to explain the disease, the extent of ischemia and the amount of myofiber damage were compared both in control and mdx mice. In control mice, functional ischemia alone was found insufficient to cause a similar degree of myofiber damage observed in mdx mice. Additional mechanisms are likely contributing to cause more severe myofiber damage in mdx mice, suggestive of the existence of a "two-hit" mechanism in the pathogenesis of this disease.

CONCLUSIONS/SIGNIFICANCE

Evidence was provided supporting the essential role of functional ischemia in contraction-induced myofiber damage in mdx mice. Furthermore, the first quantitative evidence for the "two-hit" mechanism in this disease was documented. Significantly, the vasoactive drug tadalafil, a phosphodiesterase 5 inhibitor, administered to mdx mice ameliorated muscle damage.

Dissecting muscle and neuronal disorders in a Drosophila model of muscular dystrophy

Perturbation in the Dystroglycan (Dg)-Dystrophin (Dys) complex results in muscular dystrophies and brain abnormalities in human. Here we report that Drosophila is an excellent genetically tractable model to study muscular dystrophies and neuronal abnormalities caused by defects in this complex. Using a fluorescence polarization assay, we show a high conservation in Dg-Dys interaction between human and Drosophila. Genetic and RNAi-induced perturbations of Dg and Dys in Drosophila cause cell polarity and muscular dystrophy phenotypes: decreased mobility, age-dependent muscle degeneration and defective photoreceptor path-finding. Dg and Dys are required in targeting glial cells and neurons for correct neuronal migration. Importantly, we now report that Dg interacts with insulin receptor and Nck/Dock SH2/SH3-adaptor molecule in photoreceptor path-finding. This is the first demonstration of a genetic interaction between Dg and InR.

Sparks, signals and shock absorbers: how dystrophin loss causes muscular dystrophy

The dystrophin-glycoprotein complex (DGC) can be considered as a specialized adhesion complex, linking the extracellular matrix to the actin cytoskeleton, primarily in muscle cells. Mutations in several components of the DGC lead to its partial or total loss, resulting in various forms of muscular dystrophy. These typically manifest as progressive wasting diseases with loss of muscle integrity. Debate is ongoing about the precise function of the DGC: initially a strictly mechanical role was proposed but it has been suggested that there is aberrant calcium handling in muscular dystrophy and, more recently, changes in MAP kinase and GTPase signalling have been implicated in the aetiology of the disease. Here, we discuss new and interesting developments in these aspects of DGC function and attempt to rationalize the mechanical, calcium and signalling hypotheses to provide a unifying hypothesis of the underlying process of muscular dystrophy.

Expression and regulation of CC class chemokines in the dystrophic (mdx) diaphragm

In the murine (mdx) model of Duchenne muscular dystrophy, dystrophic changes are much more severe in the diaphragm than in limb muscles, and the diaphragm more closely resembles the human disease phenotype. Chemokines could play a central role in governing such phenotypic differences, as inflammation is an important disease modifier. Here we report that CC chemokine receptors (CCRs 1, 2, 3, 5) and ligands (macrophage inflammatory protein-1alpha, RANTES) are expressed at higher levels in dystrophic than in wild-type muscles across age groups (6, 12, and 24 wk). Moreover, chemokine ligand expression and muscle inflammation are significantly higher in dystrophic diaphragms than in limb muscles of the same animals. In vitro, CCR1 is constitutively expressed by cultured primary diaphragmatic myotubes. Stimulation of myotubes by proinflammatory cytokines (tumor necrosis factor-alpha, interleukin-1alpha, interferon-gamma) found within the in vivo dystrophic muscle environment, upregulates CCR1 in mdx and wild-type cultures, and also increases expression of its ligand RANTES to a significantly greater degree in the mdx group. Taken together, our results suggest that CC chemokines may play an important role in sustaining inflammation within the mdx diaphragm, which could help account for its more severe phenotype and also offer a target for therapeutic intervention in Duchenne patients.

Sorting of a nonmuscle tropomyosin to a novel cytoskeletal compartment in skeletal muscle results in muscular dystrophy

Tropomyosin (Tm) is a key component of the actin cytoskeleton and >40 isoforms have been described in mammals. In addition to the isoforms in the sarcomere, we now report the existence of two nonsarcomeric (NS) isoforms in skeletal muscle. These isoforms are excluded from the thin filament of the sarcomere and are localized to a novel Z-line adjacent structure. Immunostained cross sections indicate that one Tm defines a Z-line adjacent structure common to all myofibers, whereas the second Tm defines a spatially distinct structure unique to muscles that undergo chronic or repetitive contractions. When a Tm (Tm3) that is normally absent from muscle was expressed in mice it became associated with the Z-line adjacent structure. These mice display a muscular dystrophy and ragged-red fiber phenotype, suggestive of disruption of the membrane-associated cytoskeletal network. Our findings raise the possibility that mutations in these tropomyosin and these structures may underpin these types of myopathies.

Drastic reduction of sarcalumenin in Dp427 (dystrophin of 427 kDa)-deficient fibres indicates that abnormal calcium handling plays a key role in muscular dystrophy

Although the primary abnormality in dystrophin is the underlying cause for mdx (X-chromosome-linked muscular dystrophy), abnormal Ca2+ handling after sarcolemmal microrupturing appears to be the pathophysiological mechanism leading to muscle weakness. To develop novel pharmacological strategies for eliminating Ca2+-dependent proteolysis, it is crucial to determine the fate of Ca2+-handling proteins in dystrophin-deficient fibres. In the present study, we show that a key luminal Ca2+-binding protein SAR (sarcalumenin) is affected in mdx skeletal-muscle fibres. One- and two-dimensional immunoblot analyses revealed the relative expression of the 160 kDa SR (sarcoplasmic reticulum) protein to be approx. 70% lower in mdx fibres when compared with normal skeletal muscles. This drastic reduction in SAR was confirmed by immunofluorescence microscopy. Patchy internal labelling of SAR in dystrophic fibres suggests an abnormal formation of SAR domains. Differential co-immunoprecipitation experiments and chemical cross-linking demonstrated a tight linkage between SAR and the SERCA1 (sarcoplasmic/endoplasmic-reticulum Ca2+-ATPase 1) isoform of the SR Ca2+-ATPase. However, the relative expression of the fast Ca2+ pump was not decreased in dystrophic membrane preparations. This implies that the reduction in SAR and calsequestrin-like proteins plays a central role in the previously reported impairment of Ca2+ buffering in the dystrophic SR [Culligan, Banville, Dowling and Ohlendieck (2002) J. Appl. Physiol. 92, 435-445]. Impaired Ca2+ shuttling between the Ca2+-uptake SERCA units and calsequestrin clusters via SAR, as well as an overall decreased luminal ion-binding capacity, might indirectly amplify the Ca2+-leak-channel-induced increase in cytosolic Ca2+ levels. This confirms the idea that abnormal Ca2+ cycling is involved in Ca2+-induced myonecrosis. Hence, manipulating disturbed Ca2+ handling might represent new modes of abolishing proteolytic degradation in muscular dystrophy.

Duchenne's muscular dystrophy: animal models used to investigate pathogenesis and develop therapeutic strategies

Duchenne's muscular dystrophy (DMD) is a lethal childhood disease caused by mutations of the dystrophin gene, the protein product of which, dystrophin, has a vital role in maintaining muscle structure and function. Homologues of DMD have been identified in several animals including dogs, cats, mice, fish and invertebrates. The most notable of these are the extensively studied mdx mouse, a genetic and biochemical model of the human disease, and the muscular dystrophic Golden Retriever dog, which is the nearest pathological counterpart of DMD. These models have been used to explore potential therapeutic approaches along a number of avenues including gene replacement and cell transplantation strategies. High-throughput screening of pharmacological and genetic therapies could potentially be carried out in recently available smaller models such as zebrafish and Caenorhabditis elegans. It is possible that a successful treatment will eventually be identified through the integration of studies in multiple species differentially suited to addressing particular questions.

Removal of dystroglycan causes severe muscular dystrophy in zebrafish embryos

Muscular dystrophy is frequently caused by disruption of the dystrophin-glycoprotein complex (DGC), which links muscle cells to the extracellular matrix. Dystroglycan, a central component of the DGC, serves as a laminin receptor via its extracellular α subunit, and interacts with dystrophin (and thus the actin cytoskeleton) through its integral membrane β subunit. We have removed the function of dystroglycan in zebrafish embryos. In contrast to mouse, where dystroglycan mutations lead to peri-implantation lethality, dystroglycan is dispensable for basement membrane formation during early zebrafish development. At later stages, however, loss of dystroglycan leads to a disruption of the DGC, concurrent with loss of muscle integrity and necrosis. In addition, we find that loss of the DGC leads to loss of sarcomere and sarcoplasmic reticulum organisation. The DGC is required for long-term survival of muscle cells in zebrafish, but is dispensable for muscle formation. Dystroglycan or the DGC is also required for normal sarcomere and sarcoplasmic reticulum organisation. Because zebrafish embryos lacking dystroglycan share several characteristics with human muscular dystrophy, they should serve as a useful model for the disease. In addition, knowing the dystroglycan null phenotype in zebrafish will facilitate the isolation of other molecules involved in muscular dystrophy pathogenesis.

Mode of inheritance of the low score normal condition in chickens

The abnormal muscle condition termed low score normal (LSN) was first detected in an outcross of chickens with hereditary muscular dystrophy (MD) to a commercial White Leghorn stock. At 2 to 3 mo of age, normal birds can right themselves between 15 and 20 times (exhaustion score) when placed on their back on a flat surface, whereas birds with MD cannot right themselves under similar conditions. Birds classified as LSN are intermediate to these extremes. The inheritance of the LSN abnormality has not been established. In order to determine if the LSN condition was controlled by a single gene, the LSN line was reciprocally crossed with a White Leghorn line to produce two F1 populations. Two F2 populations were produced by randomly mating individuals within each F1 population. Each F1 population was backcrossed to the White Leghorn line. When birds with an exhaustion score of 6 or less were considered LSN, ratios obtained in the F1 population were 3 normal and 134 LSN individuals for the cross of the LSN line males and White Leghorn line females, and 8 normal and 118 LSN for the reciprocal cross, suggesting that the LSN condition was influenced by a dominant gene with incomplete penetrance. The frequencies did not differ between sexes in either F1 cross, suggesting autosomal inheritance. In general, ratios of normal to LSN individuals in the two F2 populations and in the two backcross populations supported the hypothesis that the LSN trait was controlled by a dominant autosomal gene. However, there was an excess of normal females relative to that expected in the cross of the White Leghorn line males and LSN line females. Heritability (h2) of the LSN trait was estimated by regression of F2 offspring on F1 parents. The h2 estimates based on regressions were higher (range = 0.520 to 1.107) in the LSN line male x White Leghorn line female cross than in the reciprocal cross (range = 0.161 to 0.621). The h2 estimates based on regression of offspring on dams were higher for male offspring than for female offspring, suggesting the presence of sex-linked effects. It was concluded that the LSN trait was influenced primarily by an autosomal dominant gene but was also influenced by other genes, some of which were on the sex chromosome.

Structural abnormalities underlying alveolar hypoventilation and fluid imbalance in the dystrophic hamster lung

Bio 14.6 dystrophic hamsters exhibit alveolar hypoventilation and increased lung hydration. This study evaluated whether age- and genotype-related morphometric differences in lungs exist and correlate with the development of lung pathophysiology. Morphometry was used to characterize lungs of young (Y) and mature (M) control (C) and dystrophic (D) hamsters. With age, both C and D had increased barrier surface area [S(a-b,p)] and morphometric diffusing capacity index [mdci], and decreased harmonic thickness. In C but not D, mean capillary diameter [d(c)] and parenchymal volume density [V(v)(p,L)] increased with age, whereas barrier arithmetic thickness decreased. Chord length increased with age, whereas the ratio of parenchymal surface area to airspace volume [S/V] and the intersection density of the air-blood interface [I(v)(a-b,s)] decreased in D but not C. At both ages, lung volume relative to body mass was greater in D than C. With that exception, no genotype differences were found in young hamsters. Mature D displayed lower V(v)(p,L), S/V, d(c), I(v)(a-b,s), S(a-b,p), and mdci than mature C. Independent of age, chord length was greater but arithmetic thickness, airspace surface density, frequency of type II cells, and lamellar body area and volume density were lower in D than C. We conclude: 1) lung volume relative to body growth was greater in dystrophics than controls; 2) parenchymal remodeling was delayed or abnormal in dystrophics; 3) lower diffusing capacity in mature dystrophics may effect alveolar hypoventilation; 4) lower tissue volume, surface area, and the type II cell abnormalities in dystrophics could reduce sodium and water transport leading to greater lung hydration.

Role for alpha-dystrobrevin in the pathogenesis of dystrophin-dependent muscular dystrophies

A dystrophin-containing glycoprotein complex (DGC) links the basal lamina surrounding each muscle fibre to the fibre's cytoskeleton, providing both structural support and a scaffold for signalling molecules. Mutations in genes encoding several DGC components disrupt the complex and lead to muscular dystrophy. Here we show that mice deficient in alpha-dystrobrevin, a cytoplasmic protein of the DGC, exhibit skeletal and cardiac myopathies. Analysis of double and triple mutants indicates that alpha-dystrobrevin acts largely through the DGC. Structural components of the DGC are retained in the absence of alpha-dystrobrevin, but a DGC-associated signalling protein, nitric oxide synthase, is displaced from the membrane and nitric-oxide-mediated signalling is impaired. These results indicate that both signalling and structural functions of the DGC are required for muscle stability, and implicate alpha-dystrobrevin in the former.

Mechanisms of resistance to pathogenesis in muscular dystrophies

A mechanistic definition of the dystrophic process is proposed, and the effects of growth factors vs. down-regulation of growth are critically analyzed. A conceptual scheme is presented to illustrate the steps leading to pathology, and various compensatory systems which ameliorate the pathology are examined, particularly in regards to the mdv mouse which is resistant to the deficiency of dystrophin, the main protein product of the Duchenne and Becker muscular dystrophy (DMD/BMD) gene. These compensatory systems are analyzed in terms of the differential resistance of fiber types to pathogenesis. The generation of a stable population of maturationally arrested centronucleated fibers which express the mature adult myosin isoforms is proposed to be the main strategy of mdx muscle to minimize apoptosis. Physiological properties of these fibers, such as utrophin expression, and high mitochondrial and endoplasmic reticulum content, together with probable increased glycerophosphorylcholine concentrations and facile access to the vascular system, are hypothesized to be instrumental in their resistance to pathogenesis. It is proposed that the major element that determines the susceptibility of most human muscles to the dystrophic process is their inability to arrest the maturation of regenerated fibers at the centronucleated stage with a concomitant expression of the adult myosins.

Dystrophic phenotype induced in vitro by antibody blockade of muscle alpha-dystroglycan-laminin interaction

alpha-dystroglycan is a glycoprotein expressed on the surface of skeletal muscle fibres and other cell types. In muscle, alpha-dystroglycan provides a link between the myofibre cytoskeleton through its indirect binding to dystrophin, and the basal lamina through its binding to laminin-2, a protein of the extracellular matrix. The disruption of this linkage between the myofibre cytoskeleton and the extracellular matrix is a common feature of Duchenne and other muscular dystrophies, though the pathogenic mechanisms leading to muscle wasting remain unknown. By treating primary mouse muscle cultures with a monoclonal antibody which blocks alpha-dystroglycan binding to laminin, we show here the induction of a dystrophic phenotype in vitro. The phenotype is inducible in differentiated cultures only, is characterised by reduced myotube size, myofibril disorganisation, loss of contractile activity, reduced spontaneous clustering of acetylcholine receptors and is reversed by addition of excess exogenous laminin-2. Thus, alpha-dystroglycan may be part of a signalling pathway for the maturation and maintenance of skeletal myofibres. Detailed knowledge of this signalling pathway may provide insights into the molecular pathology of the various inherited muscular dystrophies, and identify valuable pharmacological targets and new therapeutic strategies.

Progressive muscular dystrophy in alpha-sarcoglycan-deficient mice

Limb-girdle muscular dystrophy type 2D (LGMD 2D) is an autosomal recessive disorder caused by mutations in the alpha-sarcoglycan gene. To determine how alpha-sarcoglycan deficiency leads to muscle fiber degeneration, we generated and analyzed alpha-sarcoglycan- deficient mice. Sgca-null mice developed progressive muscular dystrophy and, in contrast to other animal models for muscular dystrophy, showed ongoing muscle necrosis with age, a hallmark of the human disease. Sgca-null mice also revealed loss of sarcolemmal integrity, elevated serum levels of muscle enzymes, increased muscle masses, and changes in the generation of absolute force. Molecular analysis of Sgca-null mice demonstrated that the absence of alpha-sarcoglycan resulted in the complete loss of the sarcoglycan complex, sarcospan, and a disruption of alpha-dystroglycan association with membranes. In contrast, no change in the expression of epsilon-sarcoglycan (alpha-sarcoglycan homologue) was observed. Recombinant alpha-sarcoglycan adenovirus injection into Sgca-deficient muscles restored the sarcoglycan complex and sarcospan to the membrane. We propose that the sarcoglycan-sarcospan complex is requisite for stable association of alpha-dystroglycan with the sarcolemma. The Sgca-deficient mice will be a valuable model for elucidating the pathogenesis of sarcoglycan deficient limb-girdle muscular dystrophies and for the development of therapeutic strategies for this disease.

Effect of propylthiouracil-induced hypothyroidism on the onset of skeletal muscle necrosis in dystrophin-deficient mdx mice

1. Duchenne and Becker muscular dystrophies are X-linked disorders caused by defects in muscle dystrophin. The mdx mouse is an animal model for Duchenne muscular dystrophy which has a point mutation in the dystrophin gene, resulting in little (<3%) or no expression of dystrophin in muscle. Mdx mice show a characteristic pattern of muscle necrosis and regeneration. Muscles are normal until the third postnatal week when widespread necrosis commences. This is followed by muscle regeneration, with the persistence of centrally nucleated fibres. 2. This work has examined the hypothesis that the onset of this muscle necrosis is associated with postnatal maturation of the thyroid endocrine system and that pharmacological inhibition of thyroid hormone synthesis delays the onset of muscle necrosis. 3. Serum T4 and T3 concentrations of mice were found to rise immediately before the onset of muscle necrosis in the mdx mouse, and induction of hypothyroidism by treatment of animals with propylthiouracil was found to delay the onset of muscle necrosis. 4. The results provide the first demonstration of experimental delay of muscle necrosis by manipulation of the endocrine system in muscle lacking dystrophin, and provide a novel insight into the way in which a lack of dystrophin interacts with postnatal development to precipitate muscle necrosis in the mdx mouse.

[A morphological study of skeletal muscles of rats flown aboard the space laboratory SLS-2]

M. soleus and m. gastrocnemius in rats flown aboard SLS-2 during 14 days have been studied histologically and electron-microscopically. It is found that the stay in a weightless environment causes muscular atrophy which is more pronounced in m. soleus. In rats killed on Day 13 of the flight and in five hours post-flight the morphological picture of the muscles was similar although in rats killed postflight the number of dystrophic changed fibers was greater. The availability of the active satellite cells, myoblasts and muscular tubes was indicative of a preserved regenerative capacity of the muscles. After a lapse of 14 days of readaptation to terrestrial gravity the size of muscular fibers in the rats of flight group has reached the level of control animals although the contractile apparatus of m. soleus did not restore completely. In the rats of this group m. soleus had the foci of small newly forming muscular fibers evidently appeared at the sites of fiber destruction as a result of hemodynamic disorders accompanying the transition from microgravity to terrestrial gravitation. Total number and number of functioning capillaries in the rats of flight groups did not change.

The biological activity of natural source tocopherols in chickens fed fresh or oxidized fat rich in linoleic acid

Three experiments were carried out with male broiler chickens reared from day- old to 6 weeks of age on semi-purified diets containing 10% fresh (Expt. 1 and 3) or oxidized (Expt. 2) re-esterified triglycerides with a fatty acid composition similar to that of soya bean oil containing increasing concentrations of either a mixture of d-alpha-, gamma-, delta-tocopherylacetate (d-tocopherols) of natural source or dl-alpha- tocopheryl acetate (dl-tocopherol). In Expt. 1 and 2 the mixture of d-tocopherols consisted of 35.7% d-alpha-, 45.3% d-gamma- and 19.0% d-delta-, while in Expt. 3 the distribution was 25.3% d-alpha-, 28.1% d-gamma- and 10.8% d-gamma- in 35.8% re-esterified triglycerides. The relative biopotency of d-alpha-: gamma-: delta-tocopherol was anticipated to be 100:25:1, whereas that of dl-alpha-tocopherol was 74% relative to d-alpha-tocopherol. The experiments demonstrate that the results obtained for the biological activity depend on the response parameters chosen. With respect to gain in weight, feed conversion, relative organ weight, packed cell volume (PCV), ELP (erythrocyte lipid peroxidation), plasma activities of glutamate-oxaloacetate-transaminase (GOT), creatine kinase (CK) and glutathione peroxidase (GSH-Px) and plasma Na+ concentration, the mixture of natural source tocopherols was identical to that of dl-alpha-tocopheryl acetate, although the concentration of alpha-tocopherol was only about one third of that of dl-alpha-tocopherol. Differences between natural source and synthetic tocopherols were expectedly observed with respect to plasma concentrations of alpha-, gamma-, delta-tocopherol. Differences between the two forms as to muscular dystrophy, in vitro haemolysis and potassium concentration in plasma were ambiguous. It is suggested that the function of d-alpha-, gamma-, delta-tocopherol in erythrocyte fragility and skeletal muscle structure should be compared to that of dl-alpha-tocopherol in future investigations.

Effect of vitamin E-deficiency on the activity of some lysosomal and non-lysosomal proteases in rabbit muscles

The activity of different cathepsins and neutral proteinases was measured in normal and vitamin E-deficient rabbit muscles using specific substrates. Among the changes of enzyme activities in dystrophy caused by vitamin E-deficiency the increase in the activity of cathepsin B is the most striking. The activity of cathepsin H, both in the fast and slow muscles and that of MMP-ase in the slow muscle remains practically unchanged. Activities of other proteases significantly increase. The change in the activity of proteolytic enzymes in striated muscle of vitamin E-deficient rabbits seems to be selective. As a rule the increase in the activity is higher in fast than in slow muscles.

An injury model myopathy mimicking dystrophy: implications regarding the function of dystrophin

The pathogenesis of dystrophin deficient myopathies remains unknown. Rat and human muscles subjected to severe injury following repeated eccentric muscle actions demonstrate histopathological alterations which mimic a dystrophic process. Immunofluorescent histochemical examination of these injured muscles demonstrates a separation of proteoglycans of the basal lamina from the muscle plasma membrane, the identical histopathological alteration observed in Duchenne muscular dystrophy. These findings are consistent with the hypothesis that dystrophin is essential for maintenance of the structural integrity of the sarcolemma.

[Characteristics of myohistogenesis during experimental mono- and bilocal distraction osteosynthesis]

Regularities of the skeletal muscle tissue histogenesis have been studied in the canine shin at its elongation by 50% of its initial length by means of the mono- and bilocal distractive osteosynthesis after Ilizarov. Using light and electron microscopy, it has been stated that under conditions of monolocal distractive osteosynthesis, when the strain effort acts in the area of the muscle belly, together with elongation dystrophic and necrotic changes, proliferation of the intermuscular connective tissue and atrophy of myons increase. In a half of a year, after cessation of distraction there is no complete restoration of the skeletal muscle tissue structure. Under conditions of bilocal distractive osteosynthesis, when the conditions of the muscle distortion are comparable to those existing during the period of the extremity growth, cellular type of regeneration in the skeletal muscle tissue predominates. Therefore growth of the muscle fibers is longitudinal, like that of their growth in the process of ontogenesis and the structure of the muscle tissue of the extremity elongated is preserved. The results of the experiment performed demonstrate certain prospectiveness of application of the bilocal distractive osteosynthesis method in practical orthopedics.

Oxidative stress and muscular dystrophy

Oxidative stress may be the fundamental basis of many of the structural, functional and biochemical changes characteristic of the inherited muscular dystrophies in animals and humans. The presence of by-products of oxidative damage, and the compensatory increases in cellular antioxidants, both indicate oxidative stress may be occurring in dystrophic muscle. Changes in the proportions and metabolism of cellular lipids, abnormal functions of cellular membranes, altered activity of membrane-bound enzymes such as the SR Ca2+-ATPase, disturbances in cellular protein turnover and energy production and a variety of other changes all indicate that these inherited muscular dystrophies appear more like the results of oxidative stress to muscle than any other type of underlying muscle disturbance. Particular details of these altered characteristics of dystrophic muscle, in combination with current knowledge on the processes of oxidative damage to cells, may provide some insight into the underlying biochemical defect responsible for the disease, as well as direct research towards the ultimate goal of an effective treatment.

Induction of eosinophilic enteritis and eosinophilia in rats by vitamin E and selenium deficiency

Eosinophilic enteritis and eosinophilia, in addition to muscular dystrophy and occasionally liver necrosis, were experimentally induced in male Sprague-Dawley rats with a vitamin E- and selenium-deficient diet (basal diet) for 9 weeks. Cecum and ileum were affected more frequently and severely than other segments of the gastrointestinal tract. Eosinophils were multifocally or diffusely distributed in the intestinal wall but were most severe in the muscular layer and in the submucosa. Eosinophils were also present in stomach, liver with massive hepatocellular necrosis, and skeletal muscle with marked myonecrosis. Eosinophilic enteritis and eosinophilia were not observed in rats fed the basal diet supplemented with either vitamin E (100 or 200 ppm) or selenium (0.1 or 1.0 ppm). Eosinophilic enteritis, eosinophilia, and muscular dystrophy regressed when vitamin E- and selenium-deficient rats were subsequently fed either the vitamin E- or selenium-supplemented diet for 4-5 weeks. These findings suggest that vitamin E and selenium deficiency may play a role in the development of a diffuse type of eosinophilic enteritis and eosinophilia.

[Clinical and biochemical response in the prevention of nutritional myodystrophy in heifers]

Clinical and biochemical responses were studied after taking the measures to prevent nutrition muscular dystrophy in young cattle in the given ecological conditions. Analyzing the biological material (blood, hair, feed, soil), we found the sufficiently high saturation of heifer organisms with the microelement selenium and on the contrary, vitamin E deficiency. Sensitive indicators of the break-down of muscular tissue were the enzymes aspartate aminotransferase (AST), alanine aminotransferase (ALT), and mainly creatinine kinase (CPK): the activities of these enzymes increased significantly after the heifers had been driven to pasture. The stay of animals in the run to get them used to the physical load before going to the pasture was not found to be a sufficient measure to prevent muscular nutrition myodystrophy if the animals had not been administered vitamin E and selenium supplements. Of the one hundred heifers we examined, seven animals began to show the signs of nutrition muscular dystrophy; none of these animals had been administered vitamin E and selenium supplements.

Effects of vitamin E deficiency on the distribution of cholesterol in plasma lipoproteins and the activity of cholesterol 7 alpha-hydroxylase in rabbit liver

Vitamin E-deficient rabbits with signs of muscular dystrophy showed accumulation of cholesterol in muscle as well as elevation of plasma cholesterol. The increase in plasma cholesterol was detected in low density lipoprotein (LDL) and very low density lipoprotein (VLDL) but not in high density lipoprotein (HDL) fractions of plasma lipoproteins. In liver, the activity of cholesterol 7 alpha-hydroxylase, the key enzyme involved in degradation of cholesterol, was approximately one-fifth that of control rabbits. Cytochrome P-450 level of liver microsomes was also reduced significantly. These results suggested that accumulation of cholesterol observed in dystrophic muscle of vitamin E-deficient rabbits may be due to an increase in LDL and VLDL cholesterol, the plasma lipoproteins carrying cholesterol to peripheral tissue, and to a decrease in cholesterol 7 alpha-hydroxylase activity, whose activity may have been affected by the reduced level of cytochrome P-450.

Characterization of lymphocyte interferons with different species specificities from normal and genetically dystrophic chickens

Lymphocytes from thymus and spleen of normal (Line 412) and genetically dystrophic (Line 413) chickens produce two types of interferons (IFNs) with different host cell specificities. The first type, referred to as ChIFN-alpha, demonstrates antiviral activity on primary normal chicken embryo (CE) cells. This activity is stable at 60 degrees C for 1 h and, in this respect, ChIFN-alpha is similar to the standard ChIFN-beta. In contrast, the second type, referred to as ChIFN-alpha 1, demonstrates antiviral activity in human and simian cells but not in primary CE cells. This activity is labile at 60 degrees C for 1 h. The amount of these two types of IFNs produced in lymphocytes from the spleen of dystrophic chickens was fourfold greater than that produced from normal chickens under similar experimental conditions. In contrast to the lymphocytes from thymus and spleen, the lymphocytes from the bursa of both the normal and dystrophic chickens produced only one type of IFN, namely ChIFN-alpha 1. The development of antiviral state in human cells by ChIFN-alpha 1 requires host RNA synthesis. Although ChIFN-alpha 1 has antiviral properties similar to HuIFN-alpha in human cells, the two IFNs are not antigenically related.

[Studies on pathogenesis of muscular dystrophy: levels of thiobarbituric acid-reactive products in avian muscular dystrophy]

Lipid peroxidation and other free radical reactions are known to disrupt and damage cellular structures and function, and it has been postulated as possible mechanisms of cellular damage of muscular dystrophy because increased levels of thiobarbituric acid (TBA)-reactive products and increased activities of superoxide dismutase and glutathione peroxidase were reported in avian muscular dystrophy. We reported that activities of superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase were significantly increased in avian muscular dystrophy from the early developmental stage. Since these enzymes protect cellular structures from free radicals and peroxides, increased activities of these enzymes would indicate increased formation of radicals. Then it seems to be important to assay TBA-reactive products which indicate tissue malondialdehyde content, a by-product of lipid peroxidation. We used dystrophic chickens of New Hampshire series line 413 and their controls line 412 for assay of TBA-reactive products. Four or five birds from respective lines were killed by decapitation two weeks, four weeks and four months after hatching. The superficial pectoral muscle was immediately weighed and levels of TBA-reactive products in the muscle homogenate was assayed by fluorophotometry according to the modified method of Ohkawa and Tanizawa. Levels of TBA-reactive products were significantly higher in dystrophic chickens at all stages of development studied than those of the control group. At two weeks of age morphological changes are minimum if present and increased levels of TBA-reactive products cannot be considered as a secondary change of morphological alterations. Therefore, the results indicate involvement of lipid peroxidation damage in pathogenesis of this avian muscular dystrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle fiber types in the dystrophic puboischiofemoralis of commercial broilers

Muscle fiber types, their diameters, lipid content, and nuclei distributions were studied in normal and necrotic puboischiofemoral muscles from commercial broiler chickens of the Hubbard strain. Three categories of puboischiofemoral fiber morphology (alpha R, beta R, and alpha W) occur in the cranial and caudal portions of the pars lateralis and in the cranial, medial, and caudal portions of the pars medialis. The greatest amount of necrosis occurred in the caudal portion of the pars medialis of the puboischiofemoralis. A fiber type characterized by a greatly enlarged and rounded or oval cross-section, decreased fat content, and internalized and clustered nuclei was present in necrotic muscle but not in normal muscle.

[Nutritional muscular dystrophy in a clutch of ostrich chicks]

Six 1 1/2-month old ostrich chickens in the Upington district of the Cape Province developed lameness. Two died and pathological examination of one of them revealed lesions identical to those of white muscle disease in the larger muscle groups. Vitamin E-selenium therapy cured the other 4. The diet of the animals consisted mainly of lucerne (alfalfa).

[Structural-functional alterations in contractile proteins in athyreotic dystrophy of the myocardium]

In athyreotic dystrophy of the heart muscle properties both actin- and myosin-containing fibers protein components are shown to change. Changes in actin-containing filaments become apparent in a decrease in superprecipitation value of hybrid actomyosin consisting of athyreotic actin and myosin from normal myocardium. Disturbances in myosin structure result in a decrease of both, the value and rate of hybrid actomyosin superprecipitation consisting of athyreotic myosin and normal actin. The value of Mg2+-ATPase activity of hybrid actomyosins does not practically differ from that of normal actomyosin. Native athyreotic tropomyosin loses its ability to activate Mg2+-ATPase of purified actomyosin but its Ca2+ sensitivity, as well as its ability to increase the superprecipitation rate of normal actomyosin do not change. The obtained data suggest that a decrease in a tension value developed by bundles of glycerinated muscle fibers of athyreotic myocardium results from changes in the properties of both actin and myosin, while a reduction in the rate of fiber contraction is caused by disturbances of myosin properties and may be of native tropomyosin as well.

Ultrastructural and lysosomal enzyme studies of skeletal muscle and myocardium in rats with long-term vitamin E deficiency

Muscular dystrophy and cardiomyopathy were produced in weanling rats by feeding a vitamin E-deficient diet for 12 mth. Deficient and control rats were killed, and skeletal muscle and myocardium were used for subcellular studies and biochemical assay of selected lysosomal enzymes. Ultrastructurally, the skeletal muscle showed various degrees of pathological changes. In the severely damaged muscle fibres, prominent increase of secondary lysosomes, autophagic vacuoles, residual bodies, disappearance of myofilaments, rupture of sarcolemma and shrinkage of muscle fibres were noted. The damaged muscle fibres finally became dense residual bodies and dispersed in the interstitial spaces, where the macrophages and fibroblasts were found. In the myocardium, some muscle fibres were intact with mild fatty infiltration and marked proliferation of mitochondria. However, in the severely damaged myocardial fibres, the whole fibre was always filled with amorphous dense bodies, and the sarcolemma was ruptured. This resulted in dispersion of many cellular organelles in the surrounding interstitial space. A significant increase of cathepsin and beta-glucuronidase activity in the cytosol of both organs suggests that lysosomal enzymes may play a major role in the destruction of muscle and cardiac fibres in the long-term vitamin E-deficient animals.

Effect of vitamin E deficiency on rabbit intramuscular collagen

The effect of a vitamin E-deficient diet on muscular collagen was studied in young rabbits. Intramuscular collagen content was found to increase in vitamin E-deficient rabbits, both in absolute and relative values, while no changes in urinary hydroxyproline excretion were observed. The overall solubility of intramuscular collagen was higher and the collagen soluble in guanidine hydrochloride was richer in alpha-chains. Such findings would suggest that avitaminosis E induces the production of new intramuscular collagen.

[Possibility of preventing muscular dystrophy in E avitaminosis with alpha-tocopheronolactone and diludin]

The efficacy of pharmacopeial alpha-tocopheryl acetate, alpha-tocopheronolactone and the antioxidant diludin was studied as to the possibilities of preventing E-hypovitaminosis muscle dystrophy in rabbits. alpha-Tocopheronolactone action was similar to that of pharmacopeial alpha-tocopheryl acetate as regards E-vitamin activity that was manifested by an increase in the body mass, decrease in the urine creatine index and maintenance of normal ubiquinone content, as well as of succinate-ubiquinone-reductase, NADH-ubiquinone-reductase and NADH-cytochrome c-reductase activity of rabbit skeletal muscle and heart mitochondria. On the contrary , as a result of the antioxidant administration, no direct correlation was found between ubiquinone content and activity of ubiquinone-dependent enzymatic systems of mitochondria. The data obtained attest to high E-vitamin activity of alpha-tocopheronolactone. The action of the latter was disclosed to be different from that produced by the antioxidant.

[Effectiveness of different alpha-tocopherol derivatives in preventing experimental muscular dystrophy in chickens]

Activity of vitamin E and its derivatives--alpha-tocopheryl quinone, its short chain analogue and alpha-tocopheryl acetate also containing short chain molecule were studied during chicken experimental muscular dystrophy. alpha-Tocopheryl quinone containing short chain molecule proved to be the most active substance; similarly to vitamin E the preparation increased the erythrocyte resistance to osmotic haemolysis, distinctly increased the content of ubiquinone and decreased concentration of ubichromenol in the chicken liver tissue as compared with E-deficient animals. At the same time, the content of ubiquinone was unaltered in skeletal muscles. The data obtained suggest that vitamin E could be effectively substituted by its derivatives for prevention an treatment of muscular dystrophy.

[Efficiency of ubiquinone and p-oxybenzoic acid in prevention of E-hypovitaminosis-induced development of muscular dystrophy]

It is shown that E-hypovitaminosis-induced muscular dystrophy in rabbits is accompanied by a sharp decrease in the body mass, an increase in the urine creatine-index, a decrease in the vitamin E and ubiquinone contents in the liver and skeletal muscle tissues. In the myocardium mitochondria a decrease in the vitamin E content and an increase in the ubiquinone content are observed. The activity of NADH-cytochrome c-, NADH-ubiquinone- and succinate-ubiquinone-reductase also varies in mitochondria of the studied tissues. In myocardium organellas a direct dependence is found between the content of ubiquinone, NADH- and succinate-ubiquinone-reductase activity and an inverse one-between its content and the activity of the NADH-cytochrome c-reductase system. It is established that p-oxybenzoic acid as well as vitamin E prevents development of muscular dystrophy and causes changes analogous in direction in the activity of the ubiquinone-dependent enzymic systems of mitochondria. Ubiquinone-9 is less efficient in preventing the development of muscular dystrophy.

A biochemical and ultrastructural study of skeletal muscle from rats fed a magnesium-deficient diet

In order to study changes in skeletal muscle during a magnesium deficiency, serum and muscle tissues were collected from male Sprague-Dawley rats fed either a control or magnesium-deficient diet. The rats were killed on days 7, 10, 14, 17, 19, 21 and 26 of the experiment. Ion concentrations in serum and muscle were determined by atomic absorption spectrophotometry, taurine concentrations of serum and muscle were determined by the Pentz method, and ultrastructural changes in skeletal muscle were detected with the use of the transmission electron microscope. The results indicated an increase in serum taurine which preceded an increase in muscle taurine concentration in rats fed a magnesium-deficient diet. The electron micrographs showed a swelling of mitochondria on day 14 of the deficiency and a total disorganization of the sarcoplasmic reticulum by day 26. In conclusion, in skeletal muscle from rats fed a magnesium-deficient diet, major ultrastructural changes apparently occur after the serum magnesium concentration is reduced and about the same time as muscle taurine concentration becomes elevated. The changes may be initiated by alterations in membrane permeability which may be influenced by taurine, since taurine has been shown to influence ion movement across membranes or membrane stability.

Ultrastructural studies of the myotendonous junction of selenium-deficient ducklings

An ultrastructural study was made of the changes occurring within the gastrocnemius insertion of normal and selenium-deficient ducklings from 1 to 12 days of age. The cytologic characteristics of the fibroblasts, vessels, collagen, and muscle cells are described. Those exposed to the selenium deficiency showed major alterations of all components. The fibroblasts showed changes ranging from collapsed cisternae and degenerating mitochondria to rupture. The capillary endothelium was abnormal, as was the smooth muscle of arteriolar walls. The collagen sizes were altered, and the muscle cell termini showed major pathologic changes. The above alterations occurred within 4 days of exposure of the deficiency. The muscle cells of the body portion of the gastrocnemius showed no alterations until Day 8. The observations present evidence that indicates that connective-tissue-vascular abnormalities precede myopathic changes in nutritionally induced dystrophy. The significance of these findings is discussed with respect to the etiology of nutritionally induced dystrophy.

[Organ zinc content in an experimental animal disease model: dystrophy-dependent changes in the liver and skeletal muscles and effects of a mineral substitute during the recovery phase]

The zinc content of the liver and the thigh muscle of the rat were measured by means of atomic absorption spectrophotometry under different conditions: standard diet, carbohydrate diet, an experimental dystrophy model and its recovery period. The influence of a parental mineral substitution on the whole body and the organ weight was studied. Carbohydrate diet caused a lower rise of the whole body weight, a decrease of the zinc content of the liver and an increase of the zinc content of the thigh muscle. In dystrophy model, the liver weight decreased to one fifth of the controls. The zinc concentration of the liver increased markedly, the zinc content of the whole liver is equal to that of control animals. The thigh muscle showed an increase of the zinc content, too. The parenteral mineral application had no effect upon the whole body weight and the organ weights. Little influences on the zinc content of the skeletal muscle were seen. The zinc content of parenchymatous organs varies markedly, and it is influenced by diets and disease. In the dystrophy model, zinc is concentrated in atrophic organs in order to protect the organism against zinc deficiency.

[Characteristic of sorption properties of skeletal muscle nuclei in the normal state and with E-avitaminotic muscular dystrophy]

Sorption properties of skeletal muscles nuclei in rabbits in normal state and with E-avitaminosis were studied using organic dyes: neutral red (cationic) and turquoise direct light-fast "K" (anionic) and the influence of calcium-modified membrane of nuclei on their sorption. The nuclear surface is established to have both positive and negative charged groups sorbing turquioise direct and neutral red, respectively. The maximum volume of the dyes binding and the dissociation constants of the membrane-dye complex are estimated. It is shown that with muscular dystrophy the number of charged groups of both signs on the nuclear surface decreases. Calcium ions decrease the cationic dye sorption both in the normal state and with dystrophy and insignificantly decrease the anionic dye with dystrophy.