Visualization of dystrophic muscle fibers in mdx mouse by vital staining with Evans blue: evidence of apoptosis in dystrophin-deficient muscle

Functional improvement of dystrophic muscle by myostatin blockade

Mice and cattle with mutations in the myostatin (GDF8) gene show a marked increase in body weight and muscle mass, indicating that this new member of the TGF-beta superfamily is a negative regulator of skeletal muscle growth. Inhibition of the myostatin gene product is predicted to increase muscle mass and improve the disease phenotype in a variety of primary and secondary myopathies. We tested the ability of inhibition of myostatin in vivo to ameliorate the dystrophic phenotype in the mdx mouse model of Duchenne muscular dystrophy (DMD). Blockade of endogenous myostatin by using intraperitoneal injections of blocking antibodies for three months resulted in an increase in body weight, muscle mass, muscle size and absolute muscle strength in mdx mouse muscle along with a significant decrease in muscle degeneration and concentrations of serum creatine kinase. The functional improvement of dystrophic muscle by myostatin blockade provides a novel, pharmacological strategy for treatment of diseases associated with muscle wasting such as DMD, and circumvents the major problems associated with conventional gene therapy in these disorders.

ADAM12 alleviates the skeletal muscle pathology in mdx dystrophic mice

Muscular dystrophy is characterized by muscle degeneration and insufficient regeneration and replacement of muscle fibers by connective tissue. New therapeutic strategies directed toward various forms of muscular dystrophy are needed to preserve muscle mass and promote regeneration. In this study we examined the role of the transmembrane ADAM12, a disintegrin and metalloprotease, which is normally associated with development and regeneration of skeletal muscle. We demonstrate that ADAM12 overexpression in the dystrophin-deficient mdx mice alleviated the muscle pathology in these animals, as evidenced by less muscle cell necrosis and inflammation, lower levels of serum creatine kinase, and less uptake of Evans Blue dye into muscle fibers. These studies demonstrate that ADAM12 directly or indirectly contributes to muscle cell regeneration, stability, and survival.

Gene transfer studies in animals: what do they really tell us about the prospects for gene therapy in DMD?

There is a pressing need to develop new therapeutic approaches to Duchenne muscular dystrophy, an X-linked fatal disease primarily affecting skeletal and cardiac muscle. Gene therapy is an approach that has attracted much interest since the description of the Duchenne muscular dystrophy gene and its mutations in 1987. Since 1990 numerous reporter and dystrophin gene transfer studies have been conducted on muscles of animals but mostly in mice. Experimental protocols have ranged from germ-line gene transfer (via the production of transgenics) to somatic gene transfer studies using viral or non-viral vectors. But what have we actually learned from such studies that can be applied to patients with Duchenne muscular dystrophy? Various dystrophin, utrophin and integrin recombinant cDNAs have been shown to prevent the development of muscular dystrophy in transgenic dystrophic (mdx) mice. Somatic gene transfer prior to the onset of pathology have been shown to prevent the development of the muscular dystrophy in the mdx mouse but the data is less convincing for the beneficial effects of somatic gene transfer following the establishment of pathology. The time of onset and the course of the disease differ substantially between mouse and man and raise concerns about the applicability of gene therapy in man where the disease manifests in utero and the progression is more severe. The other major concern relates to uncertainty over the efficiency of the different vectors in man, particularly as many patients are likely to have encountered the infectious forms of the viruses that are proposed as vectors.

Interactions between muscle and the immune system during modified musculoskeletal loading

Interactions between the immune system and skeletal muscle may play a significant role in modulating the course of muscle injury and repair after modified musculoskeletal loading. Current evidence indicates that activation of the complement system is an early event during modified loading, which then leads to inflammatory cell invasion. However, the functions of those inflammatory cells are complex and they seem to be capable of promoting additional injury and repair. Recent findings implicate an early invading neutrophil population in increasing muscle damage that is detected by the presence of muscle membrane lesions. Macrophages that invade subsequently serve to remove cellular debris, and seem to promote repair. However, macrophages also have the ability to increase damage in muscle in which there is an impaired capacity to generate nitric oxide. In vivo and in vitro evidence indicates that muscle-derived nitric oxide can serve an important role in protecting muscle from membrane damage by invading inflammatory cells. Collectively, these findings indicate that the dynamic balance between inflammatory cells, the complement system, and muscle-derived free radicals can play important roles in the secondary damage of muscle during modified musculoskeletal loading.

Controlled release of hepatocyte growth factor from gelatin hydrogels based on hydrogel degradation

This paper investigates the controlled release of hepatocyte growth factor (HGF) by biodegradable gelatin hydrogels and their HGF-induced angiogenic effect. Hydrogels of different degradabilities were prepared through chemical crosslinking gelatin with varied amounts of glutaraldehyde. When the gelatin hydrogels were radioiodinated and subcutaneously implanted into the back of mice, the remaining radioactivity of the hydrogels decreased with time. However, the remaining period became longer when the concentration of glutaraldehyde used for hydrogel preparation increased. Following implantation of gelatin hydrogels incorporating 125I-labeled HGF, the HGF radioactivity retained in the mouse subcutis for longer time periods as the glutaraldehyde concentration becomes higher. The time profile of HGF remaining in every gelatin hydrogel was in good accordance with that of hydrogel degradation, indicating HGF release as a result of hydrogel biodegradation. The gelatin hydrogel incorporating HGF histologically induced angiogenic change around the implanted hydrogel. Gelatin hydrogels incorporating 5 and 10 microg HGF significantly enhanced the number of capillaries newly formed around the implanted site. This was in marked contrast to free HGF of same dose form and HGF-free, empty gelatin hydrogel. The gelatin hydrogel incorporating HGF induced VEGF around the implanted site. In vitro bioassay revealed that HGF molecules interacting with gelatin, still exhibited the biological activity. The interacted HGF would be released from gelatin hydrogels only when they were degraded to generate water-soluble gelatin fragments. It is possible that the HGF associating gelatin fragments of bioactivating, results in induced angiogenic effect.

Cardiomyopathy is independent of skeletal muscle disease in muscular dystrophy

Dystrophin and its associated proteins, the sarcoglycans, are normally expressed in heart and skeletal muscle. Mutations that alter the expression of these membrane-associated proteins lead to muscular dystrophy (MD) and cardiomyopathy in humans. Because of the timing and nature of the accompanying cardiomyopathy, it has been suggested that cardiomyopathy develops as a secondary consequence of skeletal muscle dysfunction in the muscular dystrophies. To determine whether skeletal muscle dystrophy contributes to the development of sarcoglycan-mediated cardiomyopathy, we used mice lacking gamma-sarcoglycan and inserted a transgene that "rescued" gamma-sarcoglycan expression only in skeletal muscle. Gamma-sarcoglycan was expressed in skeletal muscle under the control of the skeletal muscle-specific myosin light chain 1/3 promoter. Gamma-sarcoglycan-null mice expressing this transgene fully restore gamma-sarcoglycan expression. Furthermore, the transgene-rescued mice lack the focal necrosis and membrane permeability defects that are a hallmark of MD. Despite correction of the skeletal muscle disease, focal degeneration and membrane permeability abnormalities persisted in cardiac muscle, and notably persisted in the right ventricle. Therefore, heart and skeletal muscle defects are independent processes in sarcoglycan-mediated muscular dystrophies and, as such, therapy should target both skeletal and cardiac muscle correction to prevent sudden death due to cardiomyopathy in the muscular dystrophies.

Tibialis anterior muscles in mdx mice are highly susceptible to contraction-induced injury

Skeletal muscles of patients with Duchenne muscular dystrophy (DMD) and mdx mice lack dystrophin and are more susceptible to contraction-induced injury than control muscles. Our purpose was to develop an assay based on the high susceptibility to injury of limb muscles in mdx mice for use in evaluating therapeutic interventions. The assay involved two stretches of maximally activated tibialis anterior (TA) muscles in situ. Stretches of 40% strain relative to muscle fiber length were initiated from the plateau of isometric contractions. The magnitude of damage was assessed one minute later by the deficit in isometric force. At all ages (2-19 months), force deficits were four- to seven-fold higher for muscles in mdx compared with control mice. For control muscles, force deficits were unrelated to age, whereas force deficits increased dramatically for muscles in mdx mice after 8 months of age. The increase in susceptibility to injury of muscles from older mdx mice did not parallel similar adverse effects on muscle mass or force production. The in situ stretch protocol of TA muscles provides a valuable assay for investigations of the mechanisms of injury in dystrophic muscle and to test therapeutic interventions for reversing DMD.

Progression of dystrophic features and activation of mitogen-activated protein kinases and calcineurin by physical exercise, in hearts of mdx mice

We have previously demonstrated that calcineurin and p38 mitogen-activated protein kinase (MAPK) are up-regulated in the hearts of mdx mice. However, the degree of up-regulation observed was variable, which may reflect variable levels of daily physical activities among the mice. To investigate whether or not exercise affects dystrophic features and activates intracellular signaling molecules in mdx hearts, we subjected mdx and C57BL/10 mice to treadmill exercise and examined intracellular signaling molecules in cardiac muscles, at the protein level. The heart to body weight ratio was significantly increased in exercised mdx mice. Histopathology in exercised mdx hearts showed extensive infiltration of inflammatory cells, together with increases in interstitial fibrosis and adipose tissues, all of which were not observed either in exercised C57BL/10 or non-exercised mdx hearts. Phosphorylated p38 MAPK, phosphorylated extracellular signal-regulated kinase 1/2 and calcineurin, but not phosphorylated c-Jun N-terminal kinase 1, were up-regulated in exercised mdx hearts compared to exercised C57BL/10 or non-exercised mdx hearts. These data suggest that physical exercise accelerates the dystrophic process through activation of intracellular signaling molecules in dystrophin-deficient hearts.

Function and genetics of dystrophin and dystrophin-related proteins in muscle

The X-linked muscle-wasting disease Duchenne muscular dystrophy is caused by mutations in the gene encoding dystrophin. There is currently no effective treatment for the disease; however, the complex molecular pathology of this disorder is now being unravelled. Dystrophin is located at the muscle sarcolemma in a membrane-spanning protein complex that connects the cytoskeleton to the basal lamina. Mutations in many components of the dystrophin protein complex cause other forms of autosomally inherited muscular dystrophy, indicating the importance of this complex in normal muscle function. Although the precise function of dystrophin is unknown, the lack of protein causes membrane destabilization and the activation of multiple pathophysiological processes, many of which converge on alterations in intracellular calcium handling. Dystrophin is also the prototype of a family of dystrophin-related proteins, many of which are found in muscle. This family includes utrophin and alpha-dystrobrevin, which are involved in the maintenance of the neuromuscular junction architecture and in muscle homeostasis. New insights into the pathophysiology of dystrophic muscle, the identification of compensating proteins, and the discovery of new binding partners are paving the way for novel therapeutic strategies to treat this fatal muscle disease. This review discusses the role of the dystrophin complex and protein family in muscle and describes the physiological processes that are affected in Duchenne muscular dystrophy.

A syringe electrode device for simultaneous injection of DNA and electrotransfer

Electroporation for gene delivery has attracted considerable attention recently, because of both the site-specific nature of the delivery and the high efficiency of the method. Electrotransfer of genes involves the application of an electric field to cells to enhance their permeability, facilitating exogenous polynucleotide transit across the cytoplasmic membrane. However, the relatively high electric field strength required for electroporation induces tissue damage, thus limiting its widespread application. We describe here a syringe electrode of our design, with which the same transfection efficiency can be achieved by using much lower electric field strength than that of conventional electrodes, such that the tissue damage is minimized.

Comparative evolution of muscular dystrophy in diaphragm, gastrocnemius and masseter muscles from old male mdx mice

X chromosome-linked muscular dystrophic mdx mouse lacks the sarcolemmal protein dystrophin and represents a genetic homologue of human Duchenne muscular dystrophy (DMD). The present study analysed some aspects of pathological processes such as fibrosis, frequency of centralized nuclei, presence of degenerative or regenerative fibres, expression of utrophin and associated protein complexes, and myosin heavy chain isoforms in three muscles [diaphragm (DIA), gastrocnemius (GTC) and masseter (MAS)] from old male mdx mice. All parameters investigated comparatively in these pathological muscles provided evidence that the MAS mdx muscle presents a slight deterioration pattern in comparison to that of DIA and GTC muscles. Utrophin and associated proteins are present in many cell clusters with continuous membrane labelling in MAS muscle. Respective proportions of myosin heavy chain isoforms, measured by electrophoresis/densitometry, showed only slight change in GTC muscle, significant evolution in DIA muscle but drastic isoform conversions in MAS muscle. These results highlighted the difference in deterioration susceptibility of various muscles to muscular dystrophy. The reason why this occurs in MAS muscles is still obscure and discussed in terms of the comparative developmental origins of these muscles.

Evans Blue Dye as an in vivo marker of myofibre damage: optimising parameters for detecting initial myofibre membrane permeability

Evans Blue Dye (EBD) is widely used to study cellular membrane permeability and has recently been utilised in mdx mice to identify permeable skeletal myofibres that have become damaged as a result of muscular dystrophy. EBD has the potential to be a useful vital stain of myofibre permeability in other models of skeletal muscle injury and membrane-associated fragility. The parameters for its use for such purposes were optimised in the present study, of particular interest is the use of EBD to identify the onset of muscle damage. This study compared intravenous vs. intraperitoneal injection; tissue fixation; volume of EBD; time of availability in tissue; and persistence after injection in mdx mice (with endogenous muscle damage) and control mice. Satisfactory labelling of permeable myofibres was seen in frozen sections viewed with fluorescence microscopy when intraperitoneal injection of a 1% EBD solution injected at 1% volume relative to body mass was administered between 16 and 24 h prior to tissue sampling. EBD labelling was then assessed in three mouse models of experimental injury and repair-cut injury, whole muscle grafts, and exercise-induced muscle damage. These experiments demonstrated that (i) following a cut injury across myofibres, EBD penetrated up to 150 microm from the injury site over a 20-h period; (ii) EBD was present throughout myofibres of avascular whole muscle graft by one day after transplantation; and (iii) damaged myofibres were detected within 20 min after controlled lengthening-contraction exercise. This simple and inexpensive technique has sensitivity for the detection of increased myofibre permeability and/or sublethal damage that has advantages over other traditional histological techniques at the light microscopy level.

Role of apoptosis in Duchenne's muscular dystrophy

We investigated the presence of apoptosis in muscle tissues from 24 patients (average age 5.44 +/- 1.81 years) with Duchenne's muscular dystrophy by in situ tailing of nuclear fragmentation. Muscle tissue from 4 children without histologic evidence of myopathy served as normal controls. Muscle fibers positive for nuclear DNA fragmentation were determined quantitatively by counting an area of at least 400 muscle fibers. Eleven of 24 specimens showed no nuclei with DNA fragmentation. On the other hand, 0.37 +/- 0.48% of fibers in patients with Duchenne's muscular dystrophy and none in controls had DNA fragmentation (P > .05). In this study, the percentage of apoptotic nuclei was higher in Duchenne's muscular dystrophy muscle than in normal controls. However, the difference did not reach a statistically significant level, and further studies with larger control groups are warranted.

Immune evasion by muscle-specific gene expression in dystrophic muscle

Muscle tissue from Duchenne muscular dystrophy patients and the Dmd(mdx/mdx) (hereafter referred to as mdx) mouse is characterized by an abundance of necrotic myofibers and infiltrating macrophages. Both features may provide additional stimulus to the immune response directed against novel antigens, such as those delivered by gene therapy vectors. It has previously been shown that the immune evasion achieved by adeno-associated virus in healthy muscle fails in one model of muscular dystrophy. Here, we examined the immune response to adenoviral vectors and their transgenes in normal and mdx mice. We found that mdx mouse muscles contain 20 times more macrophages and 7 times more dendritic cells than healthy muscles. This higher professional antigen-presenting cell content results in a stronger immune response to antigens that can be directly presented by those cells, including viral antigens and constitutively expressed transgene products. However, we did not detect a significant immune response to beta-galactosidase expressed specifically in muscle, even at high expression levels. This result suggests that cross-presentation is not more effective in mdx mouse muscle, and that targeted vectors and tissue-specific promoters may be useful tools for evasion of the immune response in dystrophic muscle.

A nitric oxide synthase transgene ameliorates muscular dystrophy in mdx mice

Dystrophin-deficient muscles experience large reductions in expression of nitric oxide synthase (NOS), which suggests that NO deficiency may influence the dystrophic pathology. Because NO can function as an antiinflammatory and cytoprotective molecule, we propose that the loss of NOS from dystrophic muscle exacerbates muscle inflammation and fiber damage by inflammatory cells. Analysis of transgenic mdx mice that were null mutants for dystrophin, but expressed normal levels of NO in muscle, showed that the normalization of NO production caused large reductions in macrophage concentrations in the mdx muscle. Expression of the NOS transgene in mdx muscle also prevented the majority of muscle membrane injury that is detectable in vivo, and resulted in large decreases in serum creatine kinase concentrations. Furthermore, our data show that mdx muscle macrophages are cytolytic at concentrations that occur in dystrophic, NOS-deficient muscle, but are not cytolytic at concentrations that occur in dystrophic mice that express the NOS transgene in muscle. Finally, our data show that antibody depletions of macrophages from mdx mice cause significant reductions in muscle membrane injury. Together, these findings indicate that macrophages promote injury of dystrophin-deficient muscle, and the loss of normal levels of NO production by dystrophic muscle exacerbates inflammation and membrane injury in muscular dystrophy.

Myogenic satellite cells: physiology to molecular biology

Adult skeletal muscle has a remarkable ability to regenerate following myotrauma. Because adult myofibers are terminally differentiated, the regeneration of skeletal muscle is largely dependent on a small population of resident cells termed satellite cells. Although this population of cells was identified 40 years ago, little is known regarding the molecular phenotype or regulation of the satellite cell. The use of cell culture techniques and transgenic animal models has improved our understanding of this unique cell population; however, the capacity and potential of these cells remain ill-defined. This review will highlight the origin and unique markers of the satellite cell population, the regulation by growth factors, and the response to physiological and pathological stimuli. We conclude by highlighting the potential therapeutic uses of satellite cells and identifying future research goals for the study of satellite cell biology.

Massive muscle cell degeneration in the early stage of merosin-deficient congenital muscular dystrophy

Primary merosin-deficient congenital muscular dystrophy (CMD) is a severe form of congenital muscular disorder which is caused by mutations in the laminin alpha2 chain gene (LAMA2). The disease is characterized by marked dystrophic changes in skeletal muscles during early infancy, while little is known about the pathological process of the muscle fiber degeneration. Here, we report the immunohistochemical analysis of skeletal muscle in ten patients with primary merosin-deficient CMD using a panel of molecular markers for skeletal muscle proteins, cellular necrosis, and apoptosis. In the youngest patient (a 52 day old baby), prominent massive muscle cell degeneration occurred in association with the deposition of the C5-9 complement membrane attack complex (MAC). Most of the MAC-positive muscle fibers showed a severely deranged immunoreaction to dystrophin, dystroglycans, and other sarcolemmal proteins. In addition, we found scattered positive signals for apoptosis. Similar but milder changes were also observed in six other patients younger than 1 year. In the patients older than 3 years, muscle fibers positive for MAC and apoptotic signals were barely detectable. These findings imply that massive muscle fiber degeneration occurs in the very early stage of merosin-deficient CMD and may contribute to the severe dystrophic changes in muscle from early infancy.

Overexpression of gamma-sarcoglycan induces severe muscular dystrophy. Implications for the regulation of Sarcoglycan assembly

The sarcoglycan complex is found normally at the plasma membrane of muscle. Disruption of the sarcoglycan complex, through primary gene mutations in dystrophin or sarcoglycan subunits, produces membrane instability and muscular dystrophy. Restoration of the sarcoglycan complex at the plasma membrane requires reintroduction of the mutant sarcoglycan subunit in a manner that will permit normal assembly of the entire sarcoglycan complex. To study sarcoglycan gene replacement, we introduced transgenes expressing murine gamma-sarcoglycan into muscle of normal mice. Mice expressing high levels of gamma-sarcoglycan, under the control of the muscle-specific creatine kinase promoter, developed a severe muscular dystrophy with greatly reduced muscle mass and early lethality. Marked gamma-sarcoglycan overexpression produced cytoplasmic aggregates that interfered with normal membrane targeting of gamma-sarcoglycan. Overexpression of gamma-sarcoglycan lead to the up-regulation of alpha- and beta-sarcoglycan. These data suggest that increased gamma-sarcoglycan and/or mislocalization of gamma-sarcoglycan to the cytoplasm is sufficient to induce muscle damage and provides a new model of muscular dystrophy that highlights the importance of this protein in the assembly, function, and downstream signaling of the sarcoglycan complex. Most importantly, gene dosage and promoter strength should be given serious consideration in replacement gene therapy to ensure safety in human clinical trials.

Hepatocyte growth factor ameliorates acute graft-versus-host disease and promotes hematopoietic function

Acute graft-versus-host disease (GVHD) is a major complication of bone marrow transplantation (BMT) and is characterized by hematopoietic dysfunction, immunosuppression, and tissue injury in the skin, liver, and intestinal mucosa. Hepatocyte growth factor (HGF), originally identified and cloned as a potent mitogen for hepatocytes, induces mitogenic and antiapoptotic activity in various epithelial cells and promotes hematopoiesis. Working in a murine model of acute GVHD, we performed repeated transfection of the human HGF cDNA into skeletal muscle and showed that this treatment inhibited apoptosis of intestinal epithelial cells and donor T-cell infiltration into the liver, thereby ameliorating the enteropathy and liver injury caused by acute GVHD. HGF also markedly suppressed IFN-gamma and TNF-alpha expression in the intestine and liver and decreased the serum IL-12. Furthermore, extramedullary hematopoiesis by donor cells was increased, and the survival rate was improved. These results suggest that HGF may be useful for controlling acute GVHD after allogeneic BMT.

Sarcolemmopathy: muscular dystrophies with cell membrane defects

In this article, we review the molecular pathology of muscular dystrophies caused by defects of proteins located within or near cell membranes. These disorders include Bethlem myopathy, merosinopathy, dystrophinopathy, sarcoglycanopathies, integrinopathy, dysferlinopathy and caveolinopathy. We refer to these diseases collectively as sarcolemmopathy. Here, we describe the biological functions of these proteins in the context of muscular contractions and their roles in the infrastructure of muscle; defects of muscle infrastructures cause those diseases. As an example, in dystrophinopathy, cell membranes have mechanical defects due to the absence of dystrophin. Cracks of the cell membrane induced by muscle contraction may allow the influx and efflux of substances that trigger muscle cell degeneration. However, such cracks may be resealed on relaxation. In addition, dystrophinopathy causes secondary defects of various dystrophin-associated proteins suggesting that defects in cell signaling participate in the pathologic process. With regard to other sarcolemmopathies, we discuss pathological mechanisms based on available data.

Myofiber injury and regeneration in a canine homologue of Duchenne muscular dystrophy

OBJECTIVE

To test the hypothesis that differential skeletal muscle involvement, previously observed in dogs with a homologue of Duchenne muscular dystrophy, correlates with the histochemical markers of myofiber injury and regeneration.

DESIGN

Evidence of injury (cellular penetration by Evans blue dye, immunoglobulin G expression, hematoxylin and eosin staining of necrotic figures), myofiber regeneration (fetal myosin heavy chain isoform expression), and morphologic indices in the cranial sartorius (CS), long digital extensor, and vastus lateralis muscles were examined in five dogs with dystrophy and five normal dogs.

RESULTS

Only the CS muscle, at 1 mo, demonstrated significant differences in injury when compared with age-matched controls. By 6 mo, the long digital extensor and vastus lateralis also suffered greater than normal injury. Only the dystrophic CS tissue expressed a notable increase in mean myofiber diameter when compared with other muscles at 6 mo. Normal CS muscles revealed a distinct population of small myofibers at this age.

CONCLUSION

The CS seems unique in its selective pathologic involvement. These differences may contribute to the marked regenerative response of this muscle in the dystrophic state. An improved understanding of mechanisms by which some dystrophin-deficient canine muscles remain spared from injury may provide clues to investigate and prevent the degenerative processes in humans.

Extraocular muscle is spared despite the absence of an intact sarcoglycan complex in gamma- or delta-sarcoglycan-deficient mice

Models of the dystrophin-glycoprotein complex do not reconcile the novel sparing of extraocular muscle in muscular dystrophy. Extraocular muscle sparing in Duchenne muscular dystrophy implies the existence of adaptive properties in these muscles that may extend protection to other neuromuscular diseases. We studied the extraocular muscle morphology and dystrophin-glycoprotein complex organization in murine targeted deletion of the gamma-sarcoglycan (gsg(-/-)) and delta-sarcoglycan (dsg(-/-)) genes, two models of autosomal recessive limb girdle muscular dystrophy. In contrast to limb and diaphragm, the principal extraocular muscles were intact in gsg(-/-) and dsg(-/-) mice. However, central nucleated, presumptive regenerative, fibers were seen in the accessory extraocular muscles (retractor bulbi, levator palpebrae superioris) of both strains. Skeletal muscles of gsg(-/-) mice exhibited in vivo Evans Blue dye permeability, while the principal extraocular muscles did not. Disruption of gamma-sarcoglycan produced secondary displacement of alpha- and beta-sarcoglycans in the extraocular muscles. The intensity of immunofluorescence for dystrophin and alpha- and beta-dystroglycan also appeared to be slightly reduced. Utrophin localization was unchanged. The finding that sarcoglycan disruption was insufficient to elicit alterations in extraocular muscle suggests that loss of mechanical stability and increased sarcolemmal permeability are not inevitable consequences of mutations that disrupt the dystrophin-glycoprotein complex organization and must be accounted for in models of muscular dystrophy.

Increased c-met expression during ductal beta cell neogenesis in experimental autoimmune diabetes

C-met immunoreactivity and its co-expression with duct-associated insulin were evaluated in pancreata of non-obese diabetic (NOD) and low-dose streptozotocin (Id-STZ) mice. Diabetic NOD and non-diabetic NOD at the age of 4-8, 15-22 and 30-41 weeks and Balb/c mice at the same age intervals were studied. Ld-STZ mice were studied at day 12 and 24 after STZ administration. A stronger ductal c-met immunoreactivity and a significantly higher number of c-met positive ducts were found in diabetic NOD vs both non-diabetic NOD and Balb/c mice of comparable age. In non-diabetic NOD, the ductal c-met immunoreactivity progressively increased with age and was significantly higher than controls. In 1d-STZ mice a significantly increased ductal c-met immunoreactivity was detected both at day 12 and 24 vs untreated mice. C-met positive ductal cells were also positive for insulin although insulin positive c-met negative ducts were present. This study showed an increased c-met expression and the co-expression of c-met and duct-associated insulin, in both NOD and 1d-STZ mice.

Pro- and anti-apoptotic members of the Bcl-2 family in skeletal muscle: a distinct role for Bcl-2 in later stages of myogenesis

Apoptotic myonuclei appear during myogenesis and in diseased muscles. To investigate cell death regulation in skeletal muscle, we examined how members of the Bcl-2 family of apoptosis regulators are expressed and function in the C2C12 muscle cell line and in primary muscle cells at different stages of development. Both anti-apoptotic (Bcl-W, Bcl-X(L)) and pro-apoptotic (Bad, Bak, Bax) members of the Bcl-2 family were expressed in developing skeletal muscle in vivo. Each was also expressed in embryonic (E11-12), fetal (E15-16), and neonatal muscle stem cells, myoblasts, and myotubes in vitro. In contrast, Bcl-2 expression was limited to a small group of mononucleate, desmin-positive, myogenin-negative muscle cells that were seen in fetal and neonatal, but not embryonic, muscle cell cultures. The cell surface protein Sca-1, which is associated with muscle and blood stem cells, was found on approximately 1/2 of these Bcl-2-positive cells. Loss of Bcl-2 did not affect expression of other family members, because neonatal muscles of wild-type and Bcl-2-null mice had similar amounts of Bcl-X(L), Bcl-W, Bad, Bak, and Bax mRNAs. Loss of Bcl-2 did have functional consequences; however, because neonatal muscles of Bcl-2-null mice had only approximately 2/3 as many fast muscle fibers as muscles in wild-type mice. Thus, Bcl-2 function is required for particular stages of fetal and postnatal myogenesis.

Loss of calpain 3 proteolytic activity leads to muscular dystrophy and to apoptosis-associated IkappaBalpha/nuclear factor kappaB pathway perturbation in mice

Calpain 3 is known as the skeletal muscle-specific member of the calpains, a family of intracellular nonlysosomal cysteine proteases. It was previously shown that defects in the human calpain 3 gene are responsible for limb girdle muscular dystrophy type 2A (LGMD2A), an inherited disease affecting predominantly the proximal limb muscles. To better understand the function of calpain 3 and the pathophysiological mechanisms of LGMD2A and also to develop an adequate model for therapy research, we generated capn3-deficient mice by gene targeting. capn3-deficient mice are fully fertile and viable. Allele transmission in intercross progeny demonstrated a statistically significant departure from Mendel's law. capn3-deficient mice show a mild progressive muscular dystrophy that affects a specific group of muscles. The age of appearance of myopathic features varies with the genetic background, suggesting the involvement of modifier genes. Affected muscles manifest a similar apoptosis-associated perturbation of the IkappaBalpha/nuclear factor kappaB pathway as seen in LGMD2A patients. In addition, Evans blue staining of muscle fibers reveals that the pathological process due to calpain 3 deficiency is associated with membrane alterations.

Adeno-associated virus vector carrying human minidystrophin genes effectively ameliorates muscular dystrophy in mdx mouse model

Duchenne muscular dystrophy (DMD) is the most common and lethal genetic muscle disorder, caused by recessive mutations in the dystrophin gene. One of every 3,500 males suffers from DMD, yet no treatment is currently available. Genetic therapeutic approaches, using primarily myoblast transplantation and adenovirus-mediated gene transfer, have met with limited success. Adeno-associated virus (AAV) vectors, although proven superior for muscle gene transfer, are too small (5 kb) to package the 14-kb dystrophin cDNA. Here we have created a series of minidystrophin genes (<4.2 kb) under the control of a muscle-specific promoter that readily package into AAV vectors. When injected into the muscle of mdx mice (a DMD model), two of the minigenes resulted in efficient and stable expression in a majority of the myofibers, restoring the missing dystrophin and dystrophin-associated protein complexes onto the plasma membrane. More importantly, this AAV treatment ameliorated dystrophic pathology in mdx muscle and led to normal myofiber morphology, histology, and cell membrane integrity. Thus, we have defined minimal functional dystrophin units and demonstrated the effectiveness of using AAV to deliver the minigenes in vivo, offering a promising avenue for DMD gene therapy.

IGF-II ameliorates the dystrophic phenotype and coordinately down-regulates programmed cell death

Duchenne muscular dystrophy (DMD) is a fatal and crippling disease of skeletal muscle which displays increased fibre turnover and elevated levels of programmed cell death (PCD) in muscle stem cells. Previously we showed that this cell death is inhibited by the growth factor IGF-II. To determine the functional significance of PCD to the dystrophic phenotype, we used a transgene to over-express IGF-II in the mdx mouse. We found that ectopic expression of IGF-II inhibited the elevated PCD observed in skeletal muscles in the absence of functional dystrophin and significantly ameliorates the early gross histopathological changes in skeletal muscles characteristic of the dystrophic phenotype. Replacement of the dystrophin gene abolished abnormal skeletal muscle cell PCD levels in vivo in a dose-dependent manner and in dystrophic SMS cell lines cultured in vitro. Thus elevation of stem cell PCD in dystrophic skeletal muscle is a direct consequence of the loss of functional dystrophin. Together these data demonstrate that elevated skeletal muscle cell PCD is a critical component of dystrophic pathology and is inversely correlated with both dystrophin gene dosage and with muscle fibre pathology. Targeting PCD in dystrophic muscles reduces both PCD and the classical features of dystrophic pathology in the mdx mouse suggesting that IGF-II is a strong candidate for therapeutic intervention in the dystrophinopathies.

Assembly of the dystrophin-associated protein complex does not require the dystrophin COOH-terminal domain

Dystrophin is a multidomain protein that links the actin cytoskeleton to laminin in the extracellular matrix through the dystrophin associated protein (DAP) complex. The COOH-terminal domain of dystrophin binds to two components of the DAP complex, syntrophin and dystrobrevin. To understand the role of syntrophin and dystrobrevin, we previously generated a series of transgenic mouse lines expressing dystrophins with deletions throughout the COOH-terminal domain. Each of these mice had normal muscle function and displayed normal localization of syntrophin and dystrobrevin. Since syntrophin and dystrobrevin bind to each other as well as to dystrophin, we have now generated a transgenic mouse deleted for the entire dystrophin COOH-terminal domain. Unexpectedly, this truncated dystrophin supported normal muscle function and assembly of the DAP complex. These results demonstrate that syntrophin and dystrobrevin functionally associate with the DAP complex in the absence of a direct link to dystrophin. We also observed that the DAP complexes in these different transgenic mouse strains were not identical. Instead, the DAP complexes contained varying ratios of syntrophin and dystrobrevin isoforms. These results suggest that alternative splicing of the dystrophin gene, which naturally generates COOH-terminal deletions in dystrophin, may function to regulate the isoform composition of the DAP complex.

Differential requirement for individual sarcoglycans and dystrophin in the assembly and function of the dystrophin-glycoprotein complex

Sarcoglycan is a multimeric, integral membrane glycoprotein complex that associates with dystrophin. Mutations in individual sarcoglycan subunits have been identified in inherited forms of muscular dystrophy. To evaluate the contributions of sarcoglycan and dystrophin to muscle membrane stability and muscular dystrophy, we compared muscle lacking specific sarcoglycans or dystrophin. Here we report that mice lacking (delta)-sarcoglycan developed muscular dystrophy and cardiomyopathy similar to mice lacking (gamma)-sarcoglycan. However, unlike muscle lacking (gamma)-sarcoglycan, (delta)-sarcoglycan-deficient muscle was sensitive to eccentric contraction-induced disruption of the plasma membrane. In the absence of (delta)-sarcoglycan, (alpha)-, (beta)- and (gamma)-sarcoglycan were undetectable, while dystrophin was expressed at normal levels. In contrast, without (gamma)-sarcoglycan, reduced levels of (alpha)-, (beta)- and (delta)-sarcoglycan were expressed, glycosylated and formed a complex with each other. Thus, the elimination of (gamma)- and (delta)-sarcoglycan had different molecular consequences for the assembly and function of the dystrophin-glycoprotein complex. Furthermore, these molecular differences were associated with different mechanical consequences for the muscle plasma membrane. Through this in vivo analysis, a model for sarcoglycan assembly is proposed.

Calcium ion in skeletal muscle: its crucial role for muscle function, plasticity, and disease

Mammalian skeletal muscle shows an enormous variability in its functional features such as rate of force production, resistance to fatigue, and energy metabolism, with a wide spectrum from slow aerobic to fast anaerobic physiology. In addition, skeletal muscle exhibits high plasticity that is based on the potential of the muscle fibers to undergo changes of their cytoarchitecture and composition of specific muscle protein isoforms. Adaptive changes of the muscle fibers occur in response to a variety of stimuli such as, e.g., growth and differentition factors, hormones, nerve signals, or exercise. Additionally, the muscle fibers are arranged in compartments that often function as largely independent muscular subunits. All muscle fibers use Ca(2+) as their main regulatory and signaling molecule. Therefore, contractile properties of muscle fibers are dependent on the variable expression of proteins involved in Ca(2+) signaling and handling. Molecular diversity of the main proteins in the Ca(2+) signaling apparatus (the calcium cycle) largely determines the contraction and relaxation properties of a muscle fiber. The Ca(2+) signaling apparatus includes 1) the ryanodine receptor that is the sarcoplasmic reticulum Ca(2+) release channel, 2) the troponin protein complex that mediates the Ca(2+) effect to the myofibrillar structures leading to contraction, 3) the Ca(2+) pump responsible for Ca(2+) reuptake into the sarcoplasmic reticulum, and 4) calsequestrin, the Ca(2+) storage protein in the sarcoplasmic reticulum. In addition, a multitude of Ca(2+)-binding proteins is present in muscle tissue including parvalbumin, calmodulin, S100 proteins, annexins, sorcin, myosin light chains, beta-actinin, calcineurin, and calpain. These Ca(2+)-binding proteins may either exert an important role in Ca(2+)-triggered muscle contraction under certain conditions or modulate other muscle activities such as protein metabolism, differentiation, and growth. Recently, several Ca(2+) signaling and handling molecules have been shown to be altered in muscle diseases. Functional alterations of Ca(2+) handling seem to be responsible for the pathophysiological conditions seen in dystrophinopathies, Brody's disease, and malignant hyperthermia. These also underline the importance of the affected molecules for correct muscle performance.

Myogenic stem cell function is impaired in mice lacking the forkhead/winged helix protein MNF

Myocyte nuclear factor (MNF) is a winged helix transcription factor that is expressed selectively in myogenic stem cells (satellite cells) of adult animals. Using a gene knockout strategy to generate a functional null allele at the Mnf locus, we observed that mice lacking MNF are viable, but severely runted. Skeletal muscles of Mnf-/- animals are atrophic, and satellite cell function is impaired. Muscle regeneration after injury is delayed and incomplete, and the normal timing of expression of cell cycle regulators and myogenic determination genes is dysregulated. Mnf mutant mice were intercrossed with mdx mice that lack dystrophin and exhibit only a subtle myopathic phenotype. In contrast, mdx mice that also lack MNF die in the first few weeks of life with a severe myopathy. Haploinsufficiency at the Mnf locus (Mnf+/-) also exacerbates the mdx phenotype to more closely resemble Duchenne's muscular dystrophy in humans. We conclude that MNF acts to regulate genes that coordinate the proliferation and differentiation of myogenic stem cells after muscle injury. Animals deficient in MNF may prove useful for evaluation of potential therapeutic interventions to promote muscle regeneration for patients having Duchenne's muscular dystrophy.

Altered membrane proteins and permeability correlate with cardiac dysfunction in cardiomyopathic hamsters

A mutation in the delta-sarcoglycan (SG) gene with absence of delta-SG protein in the heart has been identified in the BIO14.6 cardiomyopathic (CM) hamster, but how the defective gene leads to myocardial degeneration and dysfunction is unknown. We correlated left ventricular (LV) function with increased sarcolemmal membrane permeability and investigated the LV distribution of the dystrophin-dystroglycan complex in BIO14.6 CM hamsters. On echocardiography at 5 wk of age, the CM hamsters showed a mildly enlarged diastolic dimension (LVDD) with decreased LV percent fractional shortening (%FS), and at 9 wk further enlargement of LVDD with reduction of %FS was observed. The percent area of myocardium exhibiting increased membrane permeability or membrane rupture, assessed by Evans blue dye (EBD) staining and wheat germ agglutinin, was greater at 9 than at 5 wk. In areas not stained by EBD, immunostaining of dystrophin was detected in CM hamsters at sarcolemma and T tubules, as expected, but it was also abnormally expressed at the intercalated discs; in addition, the expression of beta-dystroglycan was significantly reduced compared with control hearts. As previously described, alpha-SG was completely deficient in CM hearts compared with control hearts. In myocardial areas showing increased sarcolemmal permeability, neither dystrophin nor beta-dystroglycan could be identified by immunolabeling. Thus, together with the known loss of delta-SG and other SGs, abnormal distribution of dystrophin and reduction of beta-dystroglycan are associated with increased sarcolemmal permeability followed by cell rupture, which correlates with early progressive cardiac dysfunction in the BIO14.6 CM hamster.

Calcium influx through calcium leak channels is responsible for the elevated levels of calcium-dependent proteolysis in dystrophic myotubes

To estimate calpain proteolysis, we measured the hydrolysis rate of a fluorogenic calpain substrate in individual resting normal and dystrophic mdx mouse myotubes in culture. Hydrolysis rates were high during myoblast and myotube alignment and fusion. After alignment and fusion ceased, hydrolysis rates declined. For normal myotubes, hydrolysis remained low after the development of contractile activity. In contrast, after the development of contractile activity, dystrophic mdx myotubes had abnormally high levels of hydrolysis that were dependent on external calcium and that could be abolished by calpeptin, an inhibitor of calpain. We eliminated the direct effects of contraction during measurements of hydrolysis by the addition of tetrodotoxin. Substrate hydrolysis by lysosomes or proteosomes was controlled for using NH(4)Cl and clasto-lactacystin beta-lactone, respectively. Increased activity of the calcium-activated protease in mature mdx myotubes was linked to the abnormal activity of calcium-specific leak channels because an antagonist of these channels reduced the higher levels of hydrolysis in dystrophic myotubes to nearly normal levels. The abnormal activity of these channels is linked to an increased frequency of transient sarcolemmal disruptions in the more fragile mdx myotubes (, ). Treatment of mdx myotubes with a pro-drug of methylprednisolone also reduced calpain substrate hydrolysis to nearly normal levels. However, this inhibition only required 2.5 h of pretreatment, which was not long enough to act by the known effects of prednisolone on calcium homeostasis.

Immune response to adenovirus-delivered antigens upregulates utrophin and results in mitigation of muscle pathology in mdx mice

The upregulation of endogenous utrophin in skeletal muscle may lead to a new approach to the treatment of Duchenne muscular dystrophy (DMD). We found that injection of an E1, E3-deleted adenovirus vector expressing beta-galactosidase (beta-Gal) or green fluorescent protein (GFP) into the skeletal muscle of neonatal dystrophin-deficient mdx mice alleviated dystrophic pathology. In the adenovirus-infected muscles, an evaluation of sarcolemma stability showed low permeability and immunohistochemistry revealed utrophin upregulation at the extrasynaptic sarcolemma of mature muscle fibers. This utrophin upregulation was concomitant with endomysial cellular infiltration from a host immune reaction. There was no evidence of active muscle regeneration. In normal C57BL/10 mice, utrophin was also upregulated in adenovirus-injected skeletal muscles, where upregulated utrophin often coexisted with dystrophin. FK506 and anti-CD4 antibody administration decreased utrophin expression in adenovirus-injected mdx muscles and prevented the dystrophic phenotype from being mitigated, suggesting that an immune reaction is involved in utrophin upregulation. This is the first report demonstrating the improvement of the dystrophic phenotype as a result of the acquired overexpression of endogenous utrophin. Our findings provide an important clue to understanding the mechanism of utrophin expression and the development of an effective treatment for DMD.

Sarcospan-deficient mice maintain normal muscle function

Sarcospan is an integral membrane component of the dystrophin-glycoprotein complex (DGC) found at the sarcolemma of striated and smooth muscle. The DGC plays important roles in muscle function and viability as evidenced by defects in components of the DGC, which cause muscular dystrophy. Sarcospan is unique among the components of the complex in that it contains four transmembrane domains with intracellular N- and C-terminal domains and is a member of the tetraspan superfamily of proteins. Sarcospan is tightly linked to the sarcoglycans, and together these proteins form a subcomplex within the DGC. Stable expression of sarcospan at the sarcolemma is dependent upon expression of the sarcoglycans. Here we describe the generation and analysis of mice carrying a null mutation in the Sspn gene. Surprisingly, the Sspn-deficient muscle maintains expression of other components of the DGC at the sarcolemma, and no gross histological abnormalities of muscle from the mice are observed. The Sspn-deficient muscle maintains sarcolemmal integrity as determined by serum creatine kinase and Evans blue uptake assays, and the Sspn-deficient muscle maintains normal force and power generation capabilities. These data suggest either that sarcospan is not required for normal DGC function or that the Sspn-deficient muscle is compensating for the absence of sarcospan, perhaps by utilizing another protein to carry out its function.

Detection of DNA fragmentation of myonuclei in myotonic dystrophy by double staining with anti-emerin antibody and by nick end-labeling

To clarify the occurrence of apoptosis in skeletal muscle in pathological conditions, we studied 44 muscle biopsy specimens by immunohistochemical staining with monoclonal antibody against emerin, which is localized in muscle nuclear membrane, and by ApopTag Plus to detect DNA fragmentation. Five of six patients with myotonic dystrophy (DM) showed three to 35 myonuclei stained with anti-emerin antibody and ApopTag Plus in 1500 muscle fibers. Four of the 18 patients with polymyositis, one of those with thyroid myopathy and one with neurogenic atrophy showed a few myonuclei stained positively by these methods. Our study revealed that DNA fragmentation in myonuclei occurred in skeletal muscle fibers regardless of the type of disease, although the frequency was rather low in all of these diseases except DM. The DNA fragmentation detected in most of the patients with DM suggested a significant role of apoptosis in the pathomechanism of this disease.

Sarcoglycans in muscular dystrophy

Muscular dystrophy is a heterogeneous genetic disease that affects skeletal and cardiac muscle. The genetic defects associated with muscular dystrophy include mutations in dystrophin and its associated glycoproteins, the sarcoglycans. Furthermore, defects in dystrophin have been shown to cause a disruption of the normal expression and localization of the sarcoglycan complex. Thus, abnormalities of sarcoglycan are a common molecular feature in a number of dystrophies. By combining biochemistry, molecular cell biology, and human and mouse genetics, a growing understanding of the sarcoglycan complex is emerging. Sarcoglycan appears to be an important, independent mediator of dystrophic pathology in both skeletal muscle and heart. The absence of sarcoglycan leads to alterations of membrane permeability and apoptosis, two shared features of a number of dystrophies. beta-sarcoglycan and delta-sarcoglycan may form the core of the sarcoglycan subcomplex with alpha- and gamma-sarcoglycan less tightly associated to this core. The relationship of epsilon-sarcoglycan to the dystrophin-glycoprotein complex remains unclear. Animals lacking alpha-, gamma- and delta-sarcoglycan have been described and provide excellent opportunities for further investigation of the function of sarcoglycan. Dystrophin with dystroglycan and laminin may be a mechanical link between the actin cytoskeleton and the extracellular matrix. By positioning itself in close proximity to dystrophin and dystroglycan, sarcoglycan may function to couple mechanical and chemical signals in striated muscle. Sarcoglycan may be an independent signaling or regulatory module whose position in the membrane is determined by dystrophin but whose function is carried out independent of the dystrophin-dystroglycan-laminin axis.

Neural regulation of alpha-dystroglycan biosynthesis and glycosylation in skeletal muscle

Alpha-dystroglycan (alpha-DG) is part of a complex of cell surface proteins linked to dystrophin or utrophin, which is distributed over the myofiber surface and is concentrated at neuromuscular junctions. In laminin overlays of muscle extracts from developing chick hindlimb muscle, alpha-DG first appears at embryonic day (E) 10 with an apparent molecular mass of 120 kDa. By E15 it is replaced by smaller (approximately 100 kDa) and larger (approximately 150 kDa) isoforms. The larger form increases in amount and in molecular mass (>200 kDa) as the muscle is innervated and the postsynaptic membrane differentiates (E10-E20), and then decreases dramatically in amount after hatching. In myoblasts differentiating in culture the molecular mass of alpha-DG is not significantly increased by their replication, fusion, or differentiation into myotubes. Monoclonal antibody IIH6, which recognizes a carbohydrate epitope on alpha-DG, preferentially binds to the larger forms, suggesting that the core protein is differentially glycosylated beginning at E16. Consistent with prior observations implicating the IIH6 epitope in laminin binding, the smaller forms of alpha-DG bind more weakly to laminin affinity columns than the larger ones. In blots of adult rat skeletal muscle probed with radiolabeled laminin or monoclonal antibody IIH6, alpha-DG appears as a >200-kDa band that decreases in molecular mass but increases in intensity following denervation. Northern blots reveal a single mRNA transcript, indicating that the reduction in molecular mass of alpha-DG after denervation is not obviously a result of alternative splicing but is likely due to posttranslational modification of newly synthesized molecules. The regulation of alpha-DG by the nerve and its increased affinity for laminin suggest that glycosylation of this protein may be important in myofiber-basement membrane interactions during development and after denervation.

Disruption of the beta-sarcoglycan gene reveals pathogenetic complexity of limb-girdle muscular dystrophy type 2E

Limb-girdle muscular dystrophy type 2E (LGMD 2E) is caused by mutations in the beta-sarcoglycan gene, which is expressed in skeletal, cardiac, and smooth muscle. beta-sarcoglycan-deficient (Sgcb-null) mice developed severe muscular dystrophy and cardiomyopathy with focal areas of necrosis. The sarcoglycan-sarcospan and dystroglycan complexes were disrupted in skeletal, cardiac, and smooth muscle membranes. epsilon-sarcoglycan was also reduced in membrane preparations of striated and smooth muscle. Loss of the sarcoglycan-sarcospan complex in vascular smooth muscle resulted in vascular irregularities in heart, diaphragm, and kidneys. Further biochemical characterization suggested the presence of a distinct epsilon-sarcoglycan complex in skeletal muscle that was disrupted in Sgcb-null mice. Thus, perturbation of vascular function together with disruption of the epsilon-sarcoglycan-containing complex represents a novel mechanism in the pathogenesis of LGMD 2E.

Sarcoglycan isoforms in skeletal muscle

The heterotetrameric sarcoglycan complex, composed of alpha-, beta-, gamma-, and delta-sarcoglycans, is an important component of the dystrophin-associated glycoprotein assembly in striated muscle. Mutations in any of the four genes encoding sarcoglycans cause a deficiency in all sarcoglycans in the sarcolemma and produce one of four types of limb-girdle muscular dystrophy. A fifth widely expressed sarcoglycan, epsilon-sarcoglycan, has been recently described. epsilon-Sarcoglycan is homologous to alpha-sarcoglycan, but whether it associates with the other sarcoglycans in muscle is not known. In this study, we use wild type and alpha-sarcoglycan-deficient mice to analyze the localization and association of sarcoglycans in skeletal muscle in vivo. The amounts of beta-, gamma-, and delta-sarcoglycans are reduced in alpha-sarcoglycan mutants, whereas the amount of epsilon-sarcoglycan is unchanged. We show here that epsilon-sarcoglycan is complexed with beta-, gamma-, and delta-sarcoglycans in both wild type and alpha-sarcoglycan mutant mice. We also use C2C12 myocytes to study the temporal expression and organization of sarcoglycan complexes during muscle cell differentiation in vitro. In C2C12 cells, alpha- and epsilon-sarcoglycans form separate complexes with beta-, gamma-, and delta-sarcoglycans. Both types of complexes are expressed at the cell surface and presumed to be functional. These results suggest that epsilon-sarcoglycan serves a function similar to that of alpha-sarcoglycan and that residual beta-, gamma-, and delta-sarcoglycan seen in mutant mice and alpha-sarcoglycan-deficient patients is due to its association with epsilon-sarcoglycan.

Centrally nucleated fibers (CNFs) compensate the fragility of myofibers in mdx mouse

Centrally nucleated fibers (CNFs) are the myofibers which have nuclei in the center of cytoplasm, and are generally recognized as regenerated myofibers. They are commonly observed in the histopathology of the patients with several types of muscular dystrophies and their animal models. In the mdx mouse, an animal model of Duchenne muscular dystrophy, CNFs are more resistant than non-CNFs to mechanical stresses, as evidenced by the Evans blue infiltration. In relation to the population among muscles, CNFs are supposed to compensate the fragility of muscular tissue in muscular dystrophies and their animal models.

Interferon-gamma upregulates the c-Met/hepatocyte growth factor receptor expression in alveolar epithelial cells

In the repair process after lung injury, the regeneration of alveolar epithelial cells plays an important role by covering the damaged alveolar wall and preventing the activated fibroblasts from invading the intra- alveolar spaces. Hepatocyte growth factor (HGF) is a potent mitogen for alveolar epithelial cells and has been reported to be capable of repressing the fibrosing process by connecting to the c-Met/HGF receptor on alveolar epithelial cells. However, it has been reported that the c-Met expression was downregulated in an acute phase of lung injury, which may limit the effect of HGF for therapeutic use. In the present study we observed that interferon (IFN)-gamma upregulates the c-Met messenger RNA (mRNA) and protein expression in A549 alveolar epithelial cells. We analyzed the mechanism of this upregulation and found that IFN-gamma enhances the transcription of the c-met proto-oncogene, and that it does not prolong the stability of the c-Met mRNA. HGF is known to act as a motogen as well as a mitogen for epithelial cells. We also found that the migratory activity of A549 cells induced by HGF is strongly enhanced by preincubation with IFN-gamma. Finally, we administered recombinant IFN-gamma to C57BL/6 mice and confirmed that this upregulation is also observed in vivo. These results suggest that the combination of HGF and IFN-gamma could be a new therapeutic approach for fibrosing pulmonary diseases.

Myonuclear domains in muscle adaptation and disease

Adult skeletal muscle fibers are among the few cell types that are truly multinucleated. Recently, evidence has accumulated supporting a role for the modulation of myonuclear number during muscle remodeling in response to injury, adaptation, and disease. These studies have demonstrated that muscle hypertrophy is associated with, and is dependent on, the addition of newly formed myonuclei via the fusion of myogenic cells to the adult myofiber, whereas muscle atrophy and disease appear to be associated with the loss of myonuclei, possibly through apoptotic-like mechanisms. Moreover, these studies also have demonstrated that myonuclear domain size, i. e., the amount of cytoplasm per myonucleus, is unchanged following the acute phase of hypertrophy but is reduced following atrophy. Together these data demonstrate that modulation of myonuclear number or myonuclear domain size (or both) is a mechanism contributing to the remodeling of adult skeletal muscle in response to alterations in the level of normal neuromuscular activity.

Loss of the sarcoglycan complex and sarcospan leads to muscular dystrophy in beta-sarcoglycan-deficient mice

beta-Sarcoglycan, one of the subunits of the sarcoglycan complex, is a transmembranous glycoprotein which associates with dystrophin and is the molecule responsible for beta-sarcoglycanopathy, a Duchenne-like autosomal recessive muscular dystrophy. To develop an animal model of beta-sarcoglycanopathy and to clarify the role of beta-sarcoglycan in the pathogenesis of the muscle degeneration in vivo, we developed beta-sarcoglycan-deficient mice using a gene targeting technique. beta-Sarcoglycan-deficient mice (BSG(-)(/-)mice) exhibited progressive muscular dystrophy with extensive degeneration and regeneration. The BSG(-)(/-)mice also exhibited muscular hypertrophy characteristic of beta-sarcoglycanopathy. Immunohistochemical and immunoblot analyses of BSG(-)(/-)mice demonstrated that deficiency of beta-sarcoglycan also caused loss of all of the other sarcoglycans as well as of sarcospan in the sarcolemma. On the other hand, laminin-alpha2, alpha- and beta-dystroglycan and dystrophin were still present in the sarcolemma. However, the dystrophin-dystroglycan complex in BSG(-)(/-)mice was unstable compared with that in the wild-type mice. Our data suggest that loss of the sarcoglycan complex and sarcospan alone is sufficient to cause muscular dystrophy, that beta-sarcoglycan is an important protein for formation of the sarcoglycan complex associated with sarcospan and that the role of the sarcoglycan complex and sarcospan may be to strengthen the dystrophin axis connecting the basement membrane with the cytoskeleton.

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.

Activation of caspase-3 apoptotic pathways in skeletal muscle fibers in laminin alpha2-deficient mice

dy/dy mice, which carry an unidentified mutation in the Lama2 gene, show dystrophic pathologies similar to those of human congenital muscular dystrophy. Laminin alpha2 deficiency induces apoptosis with DNA fragmentation. Caspases, which are involved in various types of cell death, are sequentially activated through a processing by other members of caspases. By using a cleavage site-directed antibody against caspase-3 that specifically reacts with the active form of caspase-3, we immunochemically demonstrated that caspase-3 is activated in the skeletal muscle fiber of dy/dy mice and that some of the activated caspase-3 muscle fibers are TUNEL-positive. Thus the lack of laminin alpha2 signals activates caspase-3, resulting in the apoptosis of muscle fibers.

alpha-Dystroglycan is a laminin receptor involved in extracellular matrix assembly on myotubes and muscle cell viability

alpha-Dystroglycan (alpha-DG) is a laminin-binding protein and member of a glycoprotein complex associated with dystrophin that has been implicated in the etiology of several muscular dystrophies. To study the function of DG, C2 myoblasts were transfected stably with an antisense DG expression construct. Myotubes from two resulting clones (11F and 11E) had at least a 40-50% and 80-90% reduction, respectively, in alpha-DG but normal or near normal levels of alpha-sarcoglycan, integrin beta1 subunit, acetylcholine receptors (AChRs), and muscle-specific kinase (MuSK) when compared with parental C2 cells or three clones (11A, 9B, and 10C) which went through the same transfection and selection procedures but expressed normal levels of alpha-DG. Antisense DG-expressing myoblasts proliferate at the same rate as parental C2 cells and differentiate into myotubes, however, a gradual loss of cells was observed in these cultures. This loss correlates with increased apoptosis as indicated by greater numbers of nuclei with condensed chromatin and more nuclei labeled by the TUNEL method. Moreover, there was no sign of increased membrane permeability to Trypan blue as would be expected with necrosis. Unlike parental C2 myotubes, 11F and 11E myotubes had very little laminin (LN) on their surfaces; LN instead tended to accumulate on the substratum between myotubes. Exogenous LN bound to C2 myotubes and was redistributed into plaques along with alpha-DG on their surfaces but far fewer LN/alpha-DG plaques were seen after LN addition to 11F or 11E myotubes. These results suggest that alpha-DG is a functional LN receptor in situ which is required for deposition of LN on the cell and, further, implicate alpha-DG in the maintenance of myotube viability.

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.

Caspase inhibitors in prevention of apoptosis

Apoptosis, a morphological distinct form of programmed cell death, is a crucial process during development, the maintenance of cell homeostasis and the regulation of the immune system. A variety of diseases have been found to correlate with physiological apoptosis including cancer, autoimmune disease, viral infection and degenerative disorders. Although very different signals initiate apoptosis, the phenotype of apoptosis is surprisingly similar even in different cell types suggesting that the final stages of apoptotic death are highly conserved. The execution of the death program is coordinated by a recently identified class of cysteine proteases termed caspases. The finding that caspases are mainly involved in regulation of this conserved part of the death program has boosted the search for caspase inhibitors which might offer a therapeutic approach to treat apoptotic disorders. Synthetic peptide inhibitors have been developed which exhibit some selectivity for the different caspases. In the last years several natural inhibitors have been discovered which either prevent caspase activation or caspase activity. This review will present the recent advances and discuss the potential of caspase inhibitors as future therapeutics.