Immunohistochemical study of calpain and its endogenous inhibitor in the skeletal muscle of muscular dystrophy

Therapeutic strategies to address neuronal nitric oxide synthase deficiency and the loss of nitric oxide bioavailability in Duchenne Muscular Dystrophy

Duchenne Muscular Dystrophy is a rare and fatal neuromuscular disease in which the absence of dystrophin from the muscle membrane induces a secondary loss of neuronal nitric oxide synthase and the muscles capacity for endogenous nitric oxide synthesis. Since nitric oxide is a potent regulator of skeletal muscle metabolism, mass, function and regeneration, the loss of nitric oxide bioavailability is likely a key contributor to the chronic pathological wasting evident in Duchenne Muscular Dystrophy. As such, various therapeutic interventions to re-establish either the neuronal nitric oxide synthase protein deficit or the consequential loss of nitric oxide synthesis and bioavailability have been investigated in both animal models of Duchenne Muscular Dystrophy and in human clinical trials. Notably, the efficacy of these interventions are varied and not always translatable from animal model to human patients, highlighting a complex interplay of factors which determine the downstream modulatory effects of nitric oxide. We review these studies herein.

Effect of nutrient restriction and re-feeding on calpain family genes in skeletal muscle of channel catfish (Ictalurus punctatus)

BACKGROUND

Calpains, a superfamily of intracellular calcium-dependent cysteine proteases, are involved in the cytoskeletal remodeling and wasting of skeletal muscle. Calpains are generated as inactive proenzymes which are activated by N-terminal autolysis induced by calcium-ions.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we characterized the full-length cDNA sequences of three calpain genes, clpn1, clpn2, and clpn3 in channel catfish, and assessed the effect of nutrient restriction and subsequent re-feeding on the expression of these genes in skeletal muscle. The clpn1 cDNA sequence encodes a protein of 704 amino acids, Clpn2 of 696 amino acids, and Clpn3 of 741 amino acids. Phylogenetic analysis of deduced amino acid sequences indicate that catfish Clpn1 and Clpn2 share a sequence similarity of 61%; catfish Clpn1 and Clpn3 of 48%, and Clpn2 and Clpn3 of only 45%. The domain structure architectures of all three calpain genes in channel catfish are similar to those of other vertebrates, further supported by strong bootstrap values during phylogenetic analyses. Starvation of channel catfish (average weight, 15-20 g) for 35 days influenced the expression of clpn1 (2.3-fold decrease, P<0.05), clpn2 (1.3-fold increase, P<0.05), and clpn3 (13.0-fold decrease, P<0.05), whereas the subsequent refeeding did not change the expression of these genes as measured by quantitative real-time PCR analysis. Calpain catalytic activity in channel catfish skeletal muscle showed significant differences only during the starvation period, with a 1.2- and 1.4- fold increase (P<0.01) after 17 and 35 days of starvation, respectively.

CONCLUSION/SIGNIFICANCE

We have assessed that fasting and refeeding may provide a suitable experimental model to provide us insight into the role of calpains during fish muscle atrophy and how they respond to changes in nutrient supply.

Peptidyl alpha-ketoamides with nucleobases, methylpiperazine, and dimethylaminoalkyl substituents as calpain inhibitors

A series of peptidyl alpha-ketoamides with the general structure Cbz-L-Leu-D,L-AA-CONH-R were synthesized and evaluated as inhibitors for the cysteine proteases calpain I, calpain II, and cathepsin B. Nucleobases, methylpiperazine, and dimethylaminoalkyl groups were incorporated into the primed region of the inhibitors to generate compounds that potentially cross the blood-brain barrier. Two of these compounds (Cbz-Leu-D,L-Abu-CONH-(CH(2))(3)-adenin-9-yl and Cbz-Leu-D,L-Abu-CONH-(CH(2))(3)-(4-methylpiperazin-1-yl) have been shown to have useful concentrations in the brain in animals. The best inhibitor for calpain I was Cbz-Leu-D,L-Abu-CONH-(CH(2))(3)-2-methoxyadenin-9-yl (K(i) = 23 nM), and the best inhibitor for calpain II was Cbz-Leu-D,L-Phe-CONH-(CH(2))(3)-adenin-9-yl (K(i) = 68 nM). On the basis of the crystal structure obtained with heterocyclic peptidyl alpha-ketoamides, we have improved inhibitor potency by introducing a small hydrophobic group on the adenine ring. These inhibitors have good potential to be used in the treatment of neurodegenerative diseases.

Childhood dermatomyositis associated with intracranial tumor and liver cysts

We present a girl with dermatomyositis, liver cysts and choroid plexus papilloma who was treated and followed for 7 years. Muscle histology revealed an inflammatory muscle disease and similar changes were detected in a brain tumor that was surgically removed at onset. Western blot analysis of the muscle revealed severely reduced calpain-3 protein. She was treated with pulse methylprednisolone treatment (800 mg i.v. for 4 days) followed by oral prednisone treatment (16 mg on alternate day) for 14 months, which improved muscle strength. Moreover, the cystic liver formations disappeared during steroid treatment. This is an unusual association of muscular disorder, steroid-responsive liver cysts, intracranial tumor and secondary calpain-3 deficiency. We speculate that this association is not coincidental, but mediated by an autoimmune attack against an antigen that is shared among the target tissues.

Transforming growth factor betas are upregulated in the rat masseter muscle hypertrophied by clenbuterol, a beta2 adrenergic agonist

1. The regulatory mechanism for the hypertrophy of skeletal muscles induced by clenbuterol is unclear. The purpose of the present study was to determine the extent to which transforming growth factor betas (TGFbetas), fibroblast growth factors (FGFs), hepatocyte growth factor (HGF), and platelet-derived growth factors (PDGFs) are involved in the hypertrophy of rat masseter muscle induced by clenbuterol. 2. We measured the mRNA expression levels for TGFbetas, FGFs, HGF, and PDGFs in rat masseter muscle hypertrophied by oral administration of clenbuterol for 3 weeks and determined correlations between the weight of masseter muscle and mRNA expression levels by regression analysis. We determined immunolocalizations of TGFbetas and their receptors (TGFbetaRs). 3. The mRNA expression levels for TGFbeta1, 2, and 3, and for PDGF-B demonstrated clenbuterol-induced elevations and positive correlations with the weight of masseter muscle. In particular, TGFbeta1, 2, and 3 showed strong positive correlations (correlation coefficients >0.6). The mRNA expression levels for PDGF-A, FGF-1 and 2, and HGF showed no significant differences between the control and clenbuterol groups, and no significant correlations. TGFbeta1, 2, and 3 were principally localized in the connective tissues interspaced among myofibers, and TGFbetaRI and II were localized in the periphery and sarcoplasm of the myofibers. 4. These results suggest that paracrine actions of TGFbeta1, 2, and 3 via TGFbetaRI and II could be involved in the hypertrophy of rat masseter muscle induced by clenbuterol. This is the first study to document the involvement of TGFbetas in the hypertrophy of skeletal muscles induced by clenbuterol.

Mitochondrial localization of mu-calpain

Calcium-dependent cysteine proteases, calpains, have physiological roles in cell motility and differentiation but also play a pathological role following insult or disease. The ubiquitous calpains are widely considered to be cytosolic enzymes, although there has been speculation of a mitochondrial calpain. Within a highly enriched fraction of mitochondria obtained from rat cortex and SH-SY5Y human neuroblastoma cells, immunoblotting demonstrated enrichment of the 80kDa mu-calpain large subunit and 28kDa small subunit. In rat cortex, antibodies against domains II and III of the large mu-calpain subunit also detected a 40kDa fragment, similar to the autolytic fragment generated following incubation of human erythrocyte mu-calpain with Ca(2+). Mitochondrial proteins including apoptosis inducing factor and mitochondrial Bax are calpain substrates, but the mechanism by which calpains gain access to these proteins is uncertain. Mitochondrial localization of mu-calpain places the enzyme in proximity to its mitochondrial substrates and to Ca(2+) released from mitochondrial stores.

Calpains in muscle wasting

Calpains are intracellular nonlysosomal Ca(2+)-regulated cysteine proteases. They mediate regulatory cleavages of specific substrates in a large number of processes during the differentiation, life and death of the cell. The purpose of this review is to synthesize our current understanding of the participation of calpains in muscle atrophy. Muscle tissue expresses mainly three different calpains: the ubiquitous calpains and calpain 3. The participation of the ubiquitous calpains in the initial degradation of myofibrillar proteins occurring in muscle atrophy as well as in the necrosis process accompanying muscular dystrophies has been well characterized. Inactivating mutations in the calpain 3 gene are responsible for limb-girdle muscular dystrophy type 2A and calpain 3 has been found to be downregulated in different atrophic situations, suggesting that it has to be absent for the atrophy to occur. The fact that similar regulations of calpain activities occur during exercise as well as in atrophy led us to propose that the calpains control cytoskeletal modifications needed for muscle plasticity.

Identification and molecular characterization of the rainbow trout calpains (Capn1 and Capn2): their expression in muscle wasting during starvation

Calpains are calcium regulated proteases involved in cellular functions that include muscle proteolysis both ante- and postmortem. Here, we describe the molecular characterization of the rainbow trout catalytic subunits of the mu- and m-calpains, respectively. The cDNA sequence for Capn1 encodes a protein of 704 amino acids with a calculated molecular mass of 79.9 kDa. The amino acid sequence shows 66% and 86% identity with the mouse and zebrafish Capn1, respectively. The Capn2 cDNA codes for a protein consisting of 701 amino acid residues with a calculated molecular mass of 78.2 kDa. The protein shows 65% amino acid sequence identity with the mouse and chicken Capn2. The two isozymes of rainbow trout have the characteristic domains: I (propeptide), II (cysteine catalytic site), III (electrostatic switch), and IV (contains five EF-hands). Because starvation induces muscle wasting, the hypothesis of this study was that starvation could affect regulation of the calpain system in muscle. Starvation of rainbow trout fingerlings (15-20 g) for 35 days stimulated the expression of Capn1 (2.2-fold increase, P < 0.01), Capn2 (6.0-fold increase, P < 0.01), and calpastatins (1.6-fold increase, P < 0.05) as measured by quantitative real-time RT-PCR. The mRNA changes led to a 1.23-fold increase in the calpain catalytic activity. The results suggest a potential role of calpains in protein mobilization as a source of energy under fasting condition.

Calpain-dependent α-fodrin cleavage at the sarcolemma in muscle diseases

To clarify the involvement of calpains in sarcolemmal remodeling, we examined the expression of calpains and their substrate, alpha-fodrin, in various disorders of muscle. Although immunohistological reactions for alpha-fodrin and calpains were weak in normal control muscles, intense immunoreactivity for alpha-fodrin at the sarcolemma and for calpains throughout the cytoplasm were detected in small muscle fibers from patients with inflammatory myositis (IM), rhabdomyolysis (Rhab), and Duchenne muscular dystrophy (DMD). Most of the calpain-alpha-fodrin double-positive muscle fibers in IM and Rhab also expressed the developmental form of myosin heavy chain. The sarcolemma of these small muscle fibers reacted with an antibody that specifically recognizes the 150-kDa fragments of alpha-fodrin (SBDP 150s) cleaved by calpain, but not caspase 3. Western blot analysis confirmed these results. These observations indicate that calpain is activated and reacts with alpha-fodrin as a substrate at the sarcolemma, and plays a key role in modulating sarcolemmal proteins to adapt to the specific conditions in each myopathy.

The calpain system

The calpain system originally comprised three molecules: two Ca2+-dependent proteases, mu-calpain and m-calpain, and a third polypeptide, calpastatin, whose only known function is to inhibit the two calpains. Both mu- and m-calpain are heterodimers containing an identical 28-kDa subunit and an 80-kDa subunit that shares 55-65% sequence homology between the two proteases. The crystallographic structure of m-calpain reveals six "domains" in the 80-kDa subunit: 1). a 19-amino acid NH2-terminal sequence; 2). and 3). two domains that constitute the active site, IIa and IIb; 4). domain III; 5). an 18-amino acid extended sequence linking domain III to domain IV; and 6). domain IV, which resembles the penta EF-hand family of polypeptides. The single calpastatin gene can produce eight or more calpastatin polypeptides ranging from 17 to 85 kDa by use of different promoters and alternative splicing events. The physiological significance of these different calpastatins is unclear, although all bind to three different places on the calpain molecule; binding to at least two of the sites is Ca2+ dependent. Since 1989, cDNA cloning has identified 12 additional mRNAs in mammals that encode polypeptides homologous to domains IIa and IIb of the 80-kDa subunit of mu- and m-calpain, and calpain-like mRNAs have been identified in other organisms. The molecules encoded by these mRNAs have not been isolated, so little is known about their properties. How calpain activity is regulated in cells is still unclear, but the calpains ostensibly participate in a variety of cellular processes including remodeling of cytoskeletal/membrane attachments, different signal transduction pathways, and apoptosis. Deregulated calpain activity following loss of Ca2+ homeostasis results in tissue damage in response to events such as myocardial infarcts, stroke, and brain trauma.

Adverse and beneficial functions of proteolytic enzymes in skeletal muscle. An overview

Proteolytic enzymes (proteases) comprise a family of enzymes which hydrolyse protein or peptide substrates in the generalised process of intracellular protein degradation, a process essential for the normal functioning of all cells. Proteases may also have a wide range of additional functions, including metabolic control of physiologically active oligopeptides or precursor protein forms, antigen presentation/recognition by the major histocompatibility complex in the cellular immune response, as well as in digestion, blood clotting, complement activation, etc. In this article, the nomenclature and classification of proteolytic enzymes in skeletal muscle, and their role in normal muscle physiological processes have been reviewed, including exercise, muscle development and ageing. Although proteases play an important role in normal muscle functioning, in pathological situations the enzymes may themselves be regarded as 'toxic agents' in terms of their damaging effects on muscle tissue. Muscle damage resulting from inappropriate activity of proteolytic enzymes in muscle wasting associated with muscular dystrophies, denervation atrophy, inflammatory myopathies, cancer, sepsis, diabetes and alcoholism have been reviewed. In addition, evidence that the adverse effects of drugs known to induce muscle wasting, such as corticosteroids, (or beneficial effects of growth promoting drugs) may be mediated via proteolytic enzymes is also reviewed.

Molecular adaptations of neuromuscular disease-associated proteins in response to eccentric exercise in human skeletal muscle

The molecular events by which eccentric muscle contractions induce muscle damage and remodelling remain largely unknown. We assessed whether eccentric exercise modulates the expression of proteinases (calpains 1, 2 and 3, proteasome, cathepsin B+L), muscle structural proteins (alpha-sarcoglycan and desmin), and the expression of the heat shock proteins Hsp27 and alphaB-crystallin. Vastus lateralis muscle biopsies from twelve healthy male volunteers were obtained before, immediately after, and 1 and 14 days after a 30 min downhill treadmill running exercise. Eccentric exercise induced muscle damage as evidenced by the analysis of muscle pain and weakness, creatine kinase serum activity, myoglobinaemia and ultrastructural analysis of muscle biopsies. The calpain 3 mRNA level was decreased immediately after exercise whereas calpain 2 mRNA level was increased at day 1. Both mRNA levels returned to control values by day 14. By contrast, cathepsin B+L and proteasome enzyme activities were increased at day 14. The alpha-sarcoglycan protein level was decreased immediately after exercise and at day 1, whereas the desmin level peaked at day 14. alphaB-crystallin and Hsp27 protein levels were increased at days 1 and 14. Our results suggest that the differential expression of calpain 2 and 3 mRNA levels may be important in the process of exercise-induced muscle damage, whereas expression of alpha-sarcoglycan, desmin, alphaB-crystallin and Hsp27 may be essentially involved in the subsequent remodelling of myofibrillar structure. This remodelling response may limit the extent of muscle damage upon a subsequent mechanical stress.

Poly A RNA status and expression of milli (m) and micro (μ) calpains in skeletal muscle of duchenne muscular dystrophy patients

Poly A RNA status and itsin vitro translation in a rabbit reticulolysate cell free system, were assessed in the skeletal muscle of young boys with Duchenne muscular dystrophy. Compared to normals there is a significant 48% increase in poly A RNA content of dystrophic muscle and its translatability was increased by 56% based on(35)S methionine incorporation into total protein systhesised. Immunoprecipitation of the translated products with monospecific antibodies showed that there is a 2.6 fold and a 2 fold increase in m and μ calpains respectively. This underlines the importance of both synthetic and degenerative activities in the early pathology in DMD muscle.

The calpain system in human placenta

The calpain system is involved in a number of human pathologies ranging from the muscular dystrophies to Alzheimer's disease. It is important, therefore, to be able to obtain and to characterize both mu-calpain and m-calpain from human tissue. Although human mu-calpain can be conveniently obtained from either erythrocytes or platelets, no readily available source of human m-calpain has been described. Human placenta extracts contain both mu-calpain and m-calpain in nearly equal proportions and in significant quantities (3-4 mg mu-calpain and 4-5 mg m-calpain/1000 g placenta tissue). Placenta also contains calpastatin that elutes off ion-exchange columns over a wide range of KCl concentrations completely masking the mu-calpain activity eluting off these columns and even partly overlapping m-calpain elution. Placenta mu-calpain requires 50-70 microM Ca2+ and placenta m-calpain requires 450-460 microM Ca2+ for half-maximal proteolytic activity. Western analysis of washed placenta tissue shows that placenta contains both mu- and m-calpain, although some of the mu-calpain in whole placenta extracts likely originates from the erythrocytes that are abundant in the highly vascularized placenta. Placenta calpastatin could not be purified with conventional methods. The most prominent form of calpastatin in Western analyses of placenta obtained as soon as possible after birth was approximately 48-51 kDa; partly purified preparations of placenta calpastatin also contained 48-51 and 70 kDa polypeptides. Human placenta extracts likely contain two different calpastatin isoforms, a 48-51 kDa "placenta calpastatin" and a 70 kDa erythrocyte calpastatin.

Heparan sulfate mimetics modulate calpain activity during rat Soleus muscle regeneration

Skeletal muscle regenerates after injury. Tissue remodelling, which takes place during muscle regeneration, is a complex process involving proteolytic enzymes. It is inferred that micro and milli calpains are involved in the protein turnover and structural adaptation associated with muscle myolysis and reconstruction. Using a whole-crush injured skeletal muscle, we previously have shown that in vivo muscle treatment with synthetic heparan sulfate mimetics, called RGTAs (for ReGeneraTing Agents), greatly accelerates and improves muscle regeneration after crushing. This effect was particularly striking in the case of the slow muscle Soleus that otherwise would be atrophied. Therefore, we used this regeneration model to study milli and micro calpain expressions in the regenerating Soleus muscle and to address the question of a possible effect of RGTAs treatment on calpain levels. Micro and milli calpain contents increased by about five times to culminate at days 7 and 14 after crushing respectively, thus during the phases of fibre reconstruction and reinnervation. After 64 days of regeneration, muscles still displayed higher levels of both calpains than an intact uninjured muscle. Milli calpain detected by immunocytochemistry was shown in the cytoplasm whereas micro calpain was in both nuclei and cytoplasm in small myofibres but appeared almost exclusively in nuclei of more mature fibres. Interestingly, the treatment of muscles with RGTA highly reduced the increase of both milli and micro calpain contents in Soleus regenerating muscles. These results suggest that the improvement of muscle regeneration induced by RGTA may be partly mediated by minimising the consequences of calpain activity.

The pathogenic activation of calpain: a marker and mediator of cellular toxicity and disease states

Over-activation of calpain, a ubiquitous calcium-sensitive protease, has been linked to a variety of degenerative conditions in the brain and several other tissues. Dozens of substrates for calpain have been identified and several of these have been used to measure activation of the protease in the context of experimentally induced and naturally occurring pathologies. Calpain-mediated cleavage of the cytoskeletal protein spectrin, in particular, results in a set of large breakdown products (BDPs) that are unique in that they are unusually stable. Over the last 15 years, measurements of BDPs in experimental models of stroke-type excitotoxicity, hypoxia/ischemia, vasospasm, epilepsy, toxin exposure, brain injury, kidney malfunction, and genetic defects, have established that calpain activation is an early and causal event in the degeneration that ensues from acute, definable insults. The BDPs also have been found to increase with normal ageing and in patients with Alzheimer's disease, and the calpain activity may be involved in related apoptotic processes in conjunction with the caspase family of proteases. Thus, it has become increasingly clear that regardless of the mode of disturbance in calcium homeostasis or the cell type involved, calpain is critical to the development of pathology and therefore a distinct and powerful therapeutic target. The recent development of antibodies that recognize the site at which spectrin is cleaved has greatly facilitated the temporal and spatial resolution of calpain activation in situ. Accordingly, sensitive spectrin breakdown assays now are utilized to identify potential toxic side-effects of compounds and to develop calpain inhibitors for a wide range of indications including stroke, cerebral vasospasm, and kidney failure.

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.

Morphological changes in traumatized skeletal muscle: the appearance of 'opaque fibers' of cervical muscles as evidence of compression of the neck

Cervical muscles of 15 cases of compression of the neck and the other traumatized skeletal muscles from 54 autopsy cases were examined histologically and immunohistochemically. Round and thick fibers, that is, opaque fibers were observed in the muscles beneath the compression marks on the neck, whereas in areas where no force had been applied, such fibers did not exist. Furthermore, opaque changes appeared around cavities, which formed within severely compressed injured muscle tissue. The pattern of appearance of opaque fibers in the cases of compression of the neck were mainly divided into two types, 'diffuse' pattern and 'focal' pattern. In both blunt and sharp force injuries, the production of opaque fibers were common in the area directly where damage had been inflicted. In stab wounds especially, the appearance of opaque fibers and wavelike fibers, which fanned out and showed a different color from the other areas, was limited to the marginal zone. These results suggest that there is a close relationship between opaque changes and force. Opaque fibers are probably produced by damage to muscles due to extremely applied force. The high incidence of opaque fibers beneath compression marks on the neck should be regarded as a useful indication of strangulation and/or hanging. Furthermore, the distribution and direction of force to the neck might be presumed by the pattern of opaque fibers in cervical muscles, to a certain extent.

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.

Chick skeletal muscle proteolysis in vitro increased by corticosterone

Six-day-old chick skeletal muscle (extensor digitorum longus) was incubated in the presence of corticosterone (CTC; 0, 3, 30, and 300 ng/ml) for 2 h at 37 degrees C. Tyrosine and N (tau)-methylhistidine releases, as indices of total muscle and myofibrillar proteolysis, were increased by CTC but with different dose responses, indicating an independent regulation of myofibrillar and non-myofibrillar protein degradation.

Expression of three calpain isoform genes in human skeletal muscles

Calpain is thought to be involved in muscular degradation in progressive muscular dystrophy (PMD), especially Duchenne and Becker muscular dystrophies. To assess the expression of calpain genes in skeletal muscles of patients with myopathies, we examined mRNA levels of three calpain isoforms by the quantitative reverse transcriptase-polymerase chain reaction method in biopsied muscles from control, PMD and amyotrophic lateral sclerosis (ALS) patients. There was a statistically significant increase in calpain 1 and calpain 2 mRNA levels in PMD and ALS patients as compared to controls. In contrast, there was a decrease in expression of calpain 3 mRNA in PMD, but it was not statistically significant. Expression of calpain 1 and calpain 2 positively correlated with each other, but not with calpain 3. These results indicate that expression of calpain 1 and calpain 2, but not calpain 3, are upregulated in diseased human muscles, likely playing a regulatory role in the process of myofibrillar degradation at the transcriptional as well as posttranslational level.