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

Identification of muscle necrosis in the mdx mouse model of Duchenne muscular dystrophy using three-dimensional optical coherence tomography

Three-dimensional optical coherence tomography (3D-OCT) was used to image the structure and pathology of skeletal muscle tissue from the treadmill-exercised mdx mouse model of human Duchenne muscular dystrophy. Optical coherence tomography (OCT) images of excised muscle samples were compared with co-registered hematoxylin and eosin-stained and Evans blue dye fluorescence histology. We show, for the first time, structural 3D-OCT images of skeletal muscle dystropathology well correlated with co-located histology. OCT could identify morphological features of interest and necrotic lesions within the muscle tissue samples based on intrinsic optical contrast. These findings demonstrate the utility of 3D-OCT for the evaluation of small-animal skeletal muscle morphology and pathology, particularly for studies of mouse models of muscular dystrophy.

Internal deletion compromises the stability of dystrophin

Duchenne muscular dystrophy (DMD) is a deadly and common childhood disease caused by mutations that disrupt dystrophin protein expression. Several miniaturized dystrophin/utrophin constructs are utilized for gene therapy, and while these constructs have shown promise in mouse models, the functional integrity of these proteins is not well described. Here, we compare the biophysical properties of full-length dystrophin and utrophin with therapeutically relevant miniaturized constructs using an insect cell expression system. Full-length utrophin, like dystrophin, displayed a highly cooperative melting transition well above 37°C. Utrophin constructs involving N-terminal, C-terminal or internal deletions were remarkably stable, showing cooperative melting transitions identical to full-length utrophin. In contrast, large dystrophin deletions from either the N- or C-terminus exhibited variable stability, as evidenced by melting transitions that differed by 20°C. Most importantly, deletions in the large central rod domain of dystrophin resulted in a loss of cooperative unfolding with increased propensity for aggregation. Our results suggest that the functionality of dystrophin therapeutics based on mini- or micro-constructs may be compromised by the presence of non-native protein junctions that result in protein misfolding, instability and aggregation.

Mechanical, biochemical and morphometric alterations in the femur of mdx mice

The bone tissue abnormalities observed in patients with Duchenne muscular dystrophy are frequently attributed to muscle weakness. In this condition, bones receive fewer mechanical stimuli, compromising the process of bone modeling. In the present study we hypothesize that other factors inherent to the disease might be associated with bone tissue impairment, irrespective of the presence of muscle impairment. Mdx mice lack dystrophin and present cycles of muscle degeneration/regeneration that become more intense in the third week of life. As observed in humans with muscular dystrophy, bone tissue abnormalities were found in mdx mice during more intense muscle degeneration due to age. Under these circumstances, muscle deficit is probably one of the factors promoting these changes. To test our hypothesis, we investigated the changes that occur in the femur of mdx mice at 21 days of age when muscle damage is still not significant. The mechanical (structural and material) and biochemical properties and morphometric characteristics of the femur of mdx and control animals were evaluated. The results demonstrated a lower strength, stiffness and energy absorption capacity in mdx femurs. Higher values for structural (load and stiffness) and material (stress, elastic modulus and toughness) properties were observed in the control group. Mdx femurs were shorter and were characterized by a smaller cortical area and thickness and a smaller area of epiphyseal trabecular bone. The hydroxyproline content was similar in the two groups, but there was a significant difference in the Ca/P ratios. Thermogravimetry showed a higher mineral matrix content in cortical bone of control animals. In conclusion, femurs of mdx mice presented impaired mechanical and biochemical properties as well as changes in collagen organization in the extracellular matrix. Thus, mdx mice developed femoral osteopenia even in the absence of significant muscle fiber degeneration. This weakness of the mdx femur is probably due to genetic factors that are directly or indirectly related to dystrophin deficiency.

Nitric oxide donors improve prednisone effects on muscular dystrophy in the mdx mouse diaphragm

In Duchenne muscular dystrophy (DMD), palliative glucocorticoid therapy can produce myopathy or calcification. Since increased nitric oxide synthase activity in dystrophic mice promotes regeneration, the outcome of two nitric oxide (NO) donor drugs, MyoNovin (M) and isosorbide dinitrate (I), on the effectiveness of the anti-inflammatory drug prednisone (P) in alleviating progression of dystrophy was tested. Dystrophic mdx mice were treated (18 days) as controls or with an NO donor ± P. Fiber permeability and DNA synthesis were labeled by Evans blue dye (EBD) and bromodeoxyuridine uptake, respectively. P decreased body weight gain, M increased quadriceps mass, and I increased heart mass. P increased fiber permeability (%EBD+ fibers) and calcification in diaphragm. Treatment with NO donors + P (M+P, I+P) reduced %EBD+ fibers and calcification vs. P alone. %EBD+ fibers in M+P diaphragm did not differ from control. NO donor treatment reduced proliferation and the population of c-met+ cells and accelerated fiber regeneration. Concurrent with P, NO donor treatment suppressed two important detrimental effects of P in mice, possibly by accelerating regeneration, rebalancing satellite cell quiescence and activation in dystrophy, and/or increasing perfusion. Results suggest that NO donors could improve current therapy for DMD.

Therapeutic potential of bone-marrow-derived mesenchymal stem cells differentiated with growth-factor-free coculture method in liver-injured rats

Mesenchymal stem cell (MSC) differentiation by growth factors may be improper due to possibility of clinical risk. We have previously developed a growth-factor-free coculture method and observed rat MSCs differentiated into hepatic progenitor cells. This study was aimed to validate hepatic differentiation potential in vivo. MSCs from bone marrow of green fluorescent protein-transgenic Sprague-Dawley rats were cocultured with hepatocytes from normal Sprague-Dawley rats, sharing growth-factor-free media. After 14 days, cells were implanted into the spleen of carbon tetrachloride (CCl4)-injured rats and kept for 4 weeks. Fibrosis remarkably decreased in CCl4/cocultured MSC at weeks 1, 3, and 4. Immunohistochemistry revealed that albumin, alpha-fetoprotein, and cytokeratin 19 (CK19) expression was high in CCl4/cocultured MSC only at week 1. Reverse transcription-polymerase chain reaction and Western blot revealed that CCl4/cocultured MSC had reduced alpha-fetoprotein expression at week 4, whereas CK18 and CK19 exhibited stronger expression. Albumin in CCl4/cocultured MSC increased at week 4 only in protein level. We assume that cocultured MSCs had stayed at hepatic progenitor stage until week 3, and differentiated into hepatocytes or bile-ductal epithelial cells afterward. Hepatic progenitor cells from MSC differentiation in the growth-factor-free coculture system may contribute to the therapeutic effect for liver disease in vivo.

Prevention of muscle fibrosis and myonecrosis in mdx mice by suramin, a TGF-β1 blocker

Fibrosis is a pathological feature observed in patients with Duchenne muscular dystrophy (DMD) and in mdx mice, the experimental model of DMD. We evaluated the effect of suramin, a transforming growth factor-beta 1 (TGF-β1) blocker, on fibrosis in mdx mice. mdx mice (6 months old) received suramin for 7 weeks. Suramin- and saline-treated (control) mdx mice performed exercise on a treadmill to worsen disease progression. Immunoblotting showed an increase of TGF-β1 in mdx diaphragm, limb, and cardiac muscles. Suramin decreased creatine kinase in mdx mice and attenuated fibrosis in all muscles studied, except for cardiac muscle. Suramin protected limb muscles against damage and reduced the exercise-induced loss of strength over time. These findings support a role for TGF-β1 in fibrinogenesis and myonecrosis during the later stages of disease in mdx mice. Suramin might be a useful therapeutic alternative for the treatment of dystrophinopathies.

Doxorubicin causes diaphragm weakness in murine models of cancer chemotherapy

Doxorubicin is a chemotherapeutic agent prescribed for a variety of tumors. While undergoing treatment, patients exhibit frequent symptoms that suggest respiratory muscle weakness. Cancer patients can receive doxorubicin chemotherapy through either intravenous (IV) or intraperitoneal (IP) injections. We hypothesized that respiratory muscle function would be depressed in a murine model of chemotherapy. We tested this hypothesis by treating C57BL/6 mice with a clinical dose of doxorubicin (20 mg/kg) via IV or IP injection. Three days later we measured contractile properties of muscle fiber bundles isolated from the diaphragm. Doxorubicin consistently depressed diaphragm force with both methods of administration (P < 0.01). Doxorubicin IP exaggerated the depression in diaphragm force and stimulated tissue inflammation and muscle fiber injury. These results suggest that clinically relevant doses of doxorubicin cause respiratory muscle weakness and that the loss of function depends, in part, on the route of administration.

One-year treatment of morpholino antisense oligomer improves skeletal and cardiac muscle functions in dystrophic mdx mice

Antisense therapy has been successful to skip targeted dystrophin exon with correction of frameshift and nonsense mutations of Duchenne muscular dystrophy (DMD). Systemic production of truncated but functional dystrophin proteins has been achieved in animal models. Furthermore, phase I/II clinical trials in United Kingdom and the Netherlands have demonstrated dystrophin induction by local and systemic administrations of antisense oligomers. However, long-term efficacy and potential toxicity remain to be determined. The present study examined 1-year systemic effect of phosphorodiamidate morpholino oligomers (PMO) treatment targeting mutated dystrophin exon 23 in mdx mice. PMO induced dystrophin expression dose-dependently and significantly improved skeletal muscle pathology and function with reduced creatine kinase (CK) levels by a regimen of 60 mg/kg biweekly administration. This regimen induced <2% dystrophin expression in the heart, but improved cardiac functions demonstrated by hemodynamics analysis. The results suggest that low levels of dystrophin induction may be able to provide detectable benefit to cardiac muscle with limited myopathy. Body weight, serum enzyme tests, and histology analysis showed no sign of toxicity in the mice treated with up to 1.5 g/kg PMO for 6 months. These results indicate that PMO could be used safely as effective drugs for long-term systemic treatment of DMD.

SMAD signaling drives heart and muscle dysfunction in a Drosophila model of muscular dystrophy

Loss-of-function mutations in the genes encoding dystrophin and the associated membrane proteins, the sarcoglycans, produce muscular dystrophy and cardiomyopathy. The dystrophin complex provides stability to the plasma membrane of striated muscle during muscle contraction. Increased SMAD signaling due to activation of the transforming growth factor-β (TGFβ) pathway has been described in muscular dystrophy; however, it is not known whether this canonical TGFβ signaling is pathogenic in the muscle itself. Drosophila deleted for the γ/δ-sarcoglycan gene (Sgcd) develop progressive muscle and heart dysfunction and serve as a model for the human disorder. We used dad-lacZ flies to demonstrate the signature of TGFβ activation in response to exercise-induced injury in Sgcd null flies, finding that those muscle nuclei immediately adjacent to muscle injury demonstrate high-level TGFβ signaling. To determine the pathogenic nature of this signaling, we found that partial reduction of the co-SMAD Medea, homologous to SMAD4, or the r-SMAD, Smox, corrected both heart and muscle dysfunction in Sgcd mutants. Reduction in the r-SMAD, MAD, restored muscle function but interestingly not heart function in Sgcd mutants, consistent with a role for activin but not bone morphogenic protein signaling in cardiac dysfunction. Mammalian sarcoglycan null muscle was also found to exhibit exercise-induced SMAD signaling. These data demonstrate that hyperactivation of SMAD signaling occurs in response to repetitive injury in muscle and heart. Reduction of this pathway is sufficient to restore cardiac and muscle function and is therefore a target for therapeutic reduction.

Eicosapentaenoic acid decreases TNF-α and protects dystrophic muscles of mdx mice from degeneration

In dystrophin-deficient fibers of mdx mice and in Duchenne muscular dystrophy, inflammation and increased production of tumor necrosis factor alpha (TNF-α) contribute to myonecrosis. We examined the effects of eicosapentaenoic acid (EPA) on dystrophic muscle degeneration. Mdx mice (14 days old) received EPA for 16 days. The sternomastoid, diaphragm and biceps brachii muscles were removed. Control mdx mice received vehicle. EPA decreased creatine kinase and myonecrosis and reduced the levels of TNF-α. These results suggest that EPA plays a protective role in dystrophic muscle degeneration, possibly by reducing TNF-α, and support further investigations of EPA as a potential therapy for dystrophinopathies.

A human-specific deletion in mouse Cmah increases disease severity in the mdx model of Duchenne muscular dystrophy

During the evolution of humans, an inactivating deletion was introduced in the CMAH (cytidine monophosphate-sialic acid hydroxylase) gene, which eliminated biosynthesis of the common mammalian sialic acid N-glycolylneuraminic acid from all human cells. We found that this human-specific change in sialylation capacity contributes to the marked discrepancy in phenotype between the mdx mouse model for Duchenne muscular dystrophy (DMD) and the human disease. When compared to human patients with DMD, mdx mice show reduced severity or slower development of clinically relevant disease phenotypes, despite lacking dystrophin protein in almost all muscle cells. This is especially true for the loss of ambulation, cardiac and respiratory muscle weakness, and decreased life span, all of which are major phenotypes contributing to DMD morbidity and mortality. These phenotypes occur at an earlier age or to a greater degree in mdx mice that also carry a human-like mutation in the mouse Cmah gene, possibly as a result of reduced strength and expression of the dystrophin-associated glycoprotein complex and increased activation of complement. Cmah-deficient mdx mice are a small-animal model for DMD that better approximates the human glycome and its contributions to muscular dystrophy.

Flt-1 haploinsufficiency ameliorates muscular dystrophy phenotype by developmentally increased vasculature in mdx mice

Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disease caused by mutations in the gene coding for the protein dystrophin. Recent work demonstrates that dystrophin is also found in the vasculature and its absence results in vascular deficiency and abnormal blood flow. This induces a state of ischemia further aggravating the muscular dystrophy pathogenesis. For an effective form of therapy of DMD, both the muscle and the vasculature need to be addressed. To reveal the developmental relationship between muscular dystrophy and vasculature, mdx mice, an animal model for DMD, were crossed with Flt-1 gene knockout mice to create a model with increased vasculature. Flt-1 is a decoy receptor for vascular endothelial growth factor, and therefore both homozygous (Flt-1(-/-)) and heterozygous (Flt-1(+/-)) Flt-1 gene knockout mice display increased endothelial cell proliferation and vascular density during embryogenesis. Here, we show that Flt-1(+/-) and mdx:Flt-1(+/-) adult mice also display a developmentally increased vascular density in skeletal muscle compared with the wild-type and mdx mice, respectively. The mdx:Flt-1(+/-) mice show improved muscle histology compared with the mdx mice with decreased fibrosis, calcification and membrane permeability. Functionally, the mdx:Flt-1(+/-) mice have an increase in muscle blood flow and force production, compared with the mdx mice. Consequently, the mdx:utrophin(-/-):Flt-1(+/-) mice display improved muscle histology and significantly higher survival rates compared with the mdx:utrophin(-/-) mice, which show more severe muscle phenotypes than the mdx mice. These data suggest that increasing the vasculature in DMD may ameliorate the histological and functional phenotypes associated with this disease.

Dynamic distribution of muscle-specific calpain in mice has a key role in physical-stress adaptation and is impaired in muscular dystrophy

Limb-girdle muscular dystrophy type 2A (LGMD2A) is a genetic disease that is caused by mutations in the calpain 3 gene (CAPN3), which encodes the skeletal muscle-specific calpain, calpain 3 (also known as p94). However, the precise mechanism by which p94 functions in the pathogenesis of this disease remains unclear. Here, using p94 knockin mice (termed herein p94KI mice) in which endogenous p94 was replaced with a proteolytically inactive but structurally intact p94:C129S mutant protein, we have demonstrated that stretch-dependent p94 distribution in sarcomeres plays a crucial role in the pathogenesis of LGMD2A. The p94KI mice developed a progressive muscular dystrophy, which was exacerbated by exercise. The exercise-induced muscle degeneration in p94KI mice was associated with an inefficient redistribution of p94:C129S in stretched sarcomeres. Furthermore, the p94KI mice showed impaired adaptation to physical stress, which was accompanied by compromised upregulation of muscle ankyrin-repeat protein-2 and hsp upon exercise. These findings indicate that the stretch-induced dynamic redistribution of p94 is dependent on its protease activity and essential to protect muscle from degeneration, particularly under conditions of physical stress. Furthermore, our data provide direct evidence that loss of p94 protease activity can result in LGMD2A and molecular insight into how this could occur.

Myoferlin regulation by NFAT in muscle injury, regeneration and repair

Ferlin proteins mediate membrane-fusion events in response to Ca(2+). Myoferlin, a member of the ferlin family, is required for normal muscle development, during which it mediates myoblast fusion. We isolated both damaged and intact myofibers from a mouse model of muscular dystrophy using laser-capture microdissection and found that the levels of myoferlin mRNA and protein were increased in damaged myofibers. To better define the components of the muscle-injury response, we identified a discreet 1543-bp fragment of the myoferlin promoter, containing multiple NFAT-binding sites, and found that this was sufficient to drive high-level myoferlin expression in cells and in vivo. This promoter recapitulated normal myoferlin expression in that it was downregulated in healthy myofibers and was upregulated in response to myofiber damage. Transgenic mice expressing GFP under the control of the myoferlin promoter were generated and GFP expression in this model was used to track muscle damage in vivo after muscle injury and in muscle disease. Myoferlin modulates the response to muscle injury through its activity in both myoblasts and mature myofibers.

Dysferlin overexpression in skeletal muscle produces a progressive myopathy

OBJECTIVE

The dose-response effects of dysferlin transgenesis were analyzed to determine if the dysferlin-deficient myopathies are good candidates for gene replacement therapy.

METHODS

We have generated 3 lines of transgenic mice, expressing low, mid, and high levels of full-length human dysferlin from a muscle-specific promoter. Transgenic skeletal muscle was analyzed and scored for morphological and functional deficits.

RESULTS

Overexpression of dysferlin in mice resulted in a striking phenotype of kyphosis, irregular gait, and reduced muscle mass and strength. Moreover, protein dosage correlated with phenotype severity. In contrast to dysferlin-null skeletal muscle, no evidence of sarcolemmal impairment was revealed. Rather, increased levels of Ca(2+)-regulated, dysferlin-binding proteins and endoplasmic reticulum stress chaperone proteins were observed in muscle lysates from transgenic mice as compared with controls.

INTERPRETATION

Expression levels of dysferlin are important for appropriate function without deleterious or cytotoxic effects. As a corollary, we propose that future endeavors in gene replacement for correction of dysferlinopathy should be tailored to take account of this.

Effect of dystrophin deficiency on selected intrinsic laryngeal muscles of the mdx mouse

BACKGROUND

Intrinsic laryngeal muscles (ILM) show biological differences from the broader class of skeletal muscles. Yet most research regarding ILM specialization has been completed on a few muscles, most notably the thyroarytenoid and posterior cricoarytenoid. Little information exists regarding the biology of other ILM. Early evidence suggests that the interarytenoid (IA) and cricothyroid (CT) may be more similar to classic skeletal muscle than their associated laryngeal muscles. Knowledge of the IA and CT's similarity or dissimilarity to typical skeletal muscle may hold implications for the treatment of dysphonia.

PURPOSE

The purpose of this study was to further define IA and CT biology by examining their response to the biological challenge of dystrophin deficiency.

METHOD

Control and dystrophin-deficient superior cricoarytenoid (SCA; mouse counterpart of IA) and CT muscles were examined for fiber morphology, sarcolemmal integrity, and immunohistochemical detection of dystrophin.

RESULTS

Despite the absence of dystrophin, experimental muscles did not show disease markers.

CONCLUSIONS

The SCA and the CT appear spared in dystrophin-deficient mouse models. These laryngeal muscles possess specializations that separate them from typical skeletal muscle. Considered in light of previous research, the CT and IA may represent transitional form of muscle, evidencing properties of typical and specialized skeletal muscle.

Disease-causing missense mutations in actin binding domain 1 of dystrophin induce thermodynamic instability and protein aggregation

Mutations in the dystrophin gene cause Duchenne muscular dystrophy (DMD) most commonly through loss of protein expression. In a small subpopulation of patients, missense mutations can cause DMD, Becker muscular dystrophy, or X-linked cardiomyopathy. Nearly one-half of disease-causing missense mutations are located in actin-binding domain 1 (ABD1) of dystrophin. To test the hypothesis that ABD1 missense mutations cause disease by impairing actin-binding activity, we engineered the K18N, L54R, D165V, A168D, L172H, and Y231N mutations into the full-length dystrophin cDNA and characterized the biochemical properties of each mutant protein. The K18N and L54R mutations are associated with the most severe diseases in humans and each caused a small but significant 4-fold decrease in actin-binding affinity, while the affinities of the other four mutant proteins were not significantly different from WT dystrophin. More interestingly, WT dystrophin was observed to unfold in a single-step, highly cooperative manner. In contrast, all six mutant proteins were significantly more prone to thermal denaturation and aggregation. Our results suggest that missense mutations in ABD1 may all cause loss of dystrophin function via protein instability and aggregation rather than through loss of ligand binding function. However, more severe disease progressions may be due to the combinatorial effects of some mutations on both protein aggregation and impaired actin-binding activity.

Use of Evans blue dye to compare limb muscles in exercised young and old mdx mice

Evans blue dye (EBD) is used to mark damaged and permeable muscle fibers in mouse models of muscular dystrophy and as an endpoint in therapeutic trials. We counted EBD-positive muscle fibers and extracted EBD from muscles sampled throughout the hindlimbs in young adult and old mdx mice to determine if the natural variability in morphology would allow measurement of a functional improvement in one limb compared to the contralateral limb. Following one bout of rotarod or treadmill exercise that greatly increased serum creatine kinase levels, the number of EBD(+) muscle fibers in 12-19-month-old mdx mice increased 3-fold, EBD in the muscles increased, and, importantly, contralateral pairs of muscles contained similar amounts of EBD. In contrast, the intra- and interlimb amounts of EBD in 2-7-month-old mdx mice were much too variable. A therapeutic effect can more readily be measured in old mdx mice. These results will be useful in the design of therapy protocols using the mdx mouse.

Genetic background affects properties of satellite cells and mdx phenotypes

Duchenne muscular dystrophy (DMD) is the most common lethal genetic disorder of children. The mdx (C57BL/10 background, C57BL/10-mdx) mouse is a widely used model of DMD, but the histopathological hallmarks of DMD, such as the smaller number of myofibers, accumulation of fat and fibrosis, and insufficient regeneration of myofibers, are not observed in adult C57BL/10-mdx except for in the diaphragm. In this study, we showed that DBA/2 mice exhibited decreased muscle weight, as well as lower myofiber numbers after repeated degeneration-regeneration cycles. Furthermore, the self-renewal efficiency of satellite cells of DBA/2 is lower than that of C57BL/6. Therefore, we produced a DBA/2-mdx strain by crossing DBA/2 and C57BL/10-mdx. The hind limb muscles of DBA/2-mdx mice exhibited lower muscle weight, fewer myofibers, and increased fat and fibrosis, in comparison with C57BL/10-mdx. Moreover, remarkable muscle weakness was observed in DBA/2-mdx. These results indicate that the DBA/2-mdx mouse is a more suitable model for DMD studies, and the efficient satellite cell self-renewal ability of C57BL/10-mdx might explain the difference in pathologies between humans and mice.

Latent TGF-beta-binding protein 4 modifies muscular dystrophy in mice

Most single-gene diseases, including muscular dystrophy, display a nonuniform phenotype. Phenotypic variability arises, in part, due to the presence of genetic modifiers that enhance or suppress the disease process. We employed an unbiased mapping approach to search for genes that modify muscular dystrophy in mice. In a genome-wide scan, we identified a single strong locus on chromosome 7 that influenced two pathological features of muscular dystrophy, muscle membrane permeability and muscle fibrosis. Within this genomic interval, an insertion/deletion polymorphism of 36 bp in the coding region of the latent TGF-beta-binding protein 4 gene (Ltbp4) was found. Ltbp4 encodes a latent TGF-beta-binding protein that sequesters TGF-beta and regulates its availability for binding to the TGF-beta receptor. Insertion of 12 amino acids into the proline-rich region of LTBP4 reduced proteolytic cleavage and was associated with reduced TGF-beta signaling, decreased fibrosis, and improved muscle pathology in a mouse model of muscular dystrophy. In contrast, a 12-amino-acid deletion in LTBP4 was associated with increased proteolysis, SMAD signaling, and fibrosis. These data identify Ltbp4 as a target gene to regulate TGF-beta signaling and modify outcomes in muscular dystrophy.

Involvement of hepatic stimulator substance in experimentally induced fibrosis and cirrhosis in the rat

Liver fibrosis results from sustained wound healing response to chronic liver injury. Liver cirrhosis, the end stage of the fibrotic process, is characterized by disruption of the entire liver architecture and reduced hepatocyte regenerative ability. Hepatic stimulator substance (HSS) is a liver-specific growth factor triggering hepatocyte proliferation in vitro and in vivo. Previous studies have indicated the involvement of HSS in animal models of acute liver injury. The aim of the present study was to investigate the involvement of HSS in the process of fibrosis and cirrhosis induction. Liver fibrosis and cirrhosis were induced in rats by thioacetamide (TAA) administration (300 mg/l) in the drinking water for 3 months, and animals were killed at 0, 1, 2, and 3 months of treatment. TAA administration resulted in progressively increasing liver fibrosis, leading to the onset of cirrhosis at the end of the experimental time. HSS was continuously produced during the course of fibrosis and cirrhosis induction, peaking at the 2nd month of TAA treatment, coinciding with markers of hepatic proliferative capacity, as thymidine kinase activity and DNA biosynthesis. Significantly reduced HSS activity was noted in cirrhotic liver (3rd month). In this case, the exogenous HSS administration during the 3rd month of TAA treatment suppressed the onset of liver cirrhosis, stimulating the hepatic regenerative capacity. Our data indicate the active participation of HSS in the process of fibrosis and cirrhosis induction post-TAA treatment in rats, suggesting also the beneficial effect of HSS treatment against cirrhosis induction with future possible clinical implications.

Dose-dependent restoration of dystrophin expression in cardiac muscle of dystrophic mice by systemically delivered morpholino

We have earlier shown that antisense morpholino oligomers are able to restore dystrophin expression by systemic delivery in body-wide skeletal muscles of dystrophic mdx mice. However, the levels of dystrophin expression vary considerably and, more importantly, no dystrophin expression has been achieved in cardiac muscle. In this study, we investigate the efficiency of morpholino-induced exon skipping in cardiomyoblasts and myocytes in vitro, and in cardiac muscle in vivo by dose escalation. We showed that morpholino induces targeted exon skipping equally effectively in both skeletal muscle myoblasts and cardiomyoblasts. Effective exon skipping was achieved in cardiomyocytes in culture. In the mdx mice, morpholino rescues dystrophin expression dose dependently in both skeletal and cardiac muscles. Therapeutic levels of dystrophin were achieved in cardiac muscle albeit at higher doses than in skeletal muscles. Up to 50 and 30% normal levels of dystrophin were induced by single systemic delivery of 3 g kg(-1) of morpholino in skeletal and cardiac muscles, respectively. High doses of morpholino treatment reduced the serum levels of creatine kinase without clear toxicity. These findings suggest that effective rescue of dystrophin in cardiac muscles can be achieved by morpholino for the treatment of Duchenne muscular dystrophy.

Ectopic calcification is caused by elevated levels of serum inorganic phosphate in mdx mice

Ectopic calcification occurs in the skeletal muscle of mdx mice, a dystrophin-deficient animal model of Duchenne muscular dystrophy. The purpose of this study was to clarify the mechanism of the calcification. The calcified deposits were identified as hydroxyapatite, a crystallized form of calcium phosphate, and the serum inorganic phosphate (Pi) level in the mdx mice was approximately 1.4 times higher than that in the normal B10 mice, suggesting that Pi plays a critical role in the ectopic calcification. When C2C12 mouse myoblasts were cultured under high-Pi conditions, myogenic differentiation was retarded while the expression of osteogenic markers such as osteocalcin and Runx2 were upregulated. This was followed by the generation of calcium deposition. Moreover, ectopic calcification reduced to an undetectable level in most of the mdx mice fed a Pi-reduced diet. We therefore conclude that the Pi-induced osteogenesis of muscle cells is responsible for ectopic calcification in the skeletal muscle of mdx mice.

Low-level laser therapy attenuates creatine kinase levels and apoptosis during forced swimming in rats

Studies suggest that high-intensity physical exercise can cause damage to skeletal muscles, resulting in muscle soreness, fatigue, inflammatory processes and cell apoptosis. The aim of this study was to investigate the effects of low-level laser therapy (LLLT) on a decrease in creatine kinase (CK) levels and cell apoptosis. Twenty male Wistar rats were randomly divided into two equal groups: group 1 (control), resistance swimming; group 2 (LLLT), resistance swimming with LLLT. They were subjected to a single application of indium gallium aluminum phosphide (InGaAlP) laser immediately following the exercise for 40 s at an output power of 100 mW, wavelength 660 nm and 133.3 J/cm(2). The groups were subdivided according to sample collection time: 24 h and 48 h. CK was measured before and both 24 h and 48 h after the test. Samples of the gastrocnemius muscle were processed to determine the presence of apoptosis using terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end labeling. (There was a significant difference in CK levels between groups (P < 0.0001) as well as between the 24 h and 48 h levels in the control group, whereas there was no significant intra-group difference in the LLLT group at the same evaluation times. In the LLLT group there were 66.3 +/- 13.2 apoptotic cells after 24 h and 39.0 +/- 6.8 apoptotic cells after 48 h. The results suggest that LLLT influences the metabolic profile of animals subjected to fatigue by lowering serum levels of CK. This demonstrates that LLLT can act as a preventive tool against cell apoptosis experienced during high-intensity physical exercise.

Inhibition of prostaglandin D synthase suppresses muscular necrosis

Duchenne muscular dystrophy is a fatal muscle wasting disease that is characterized by a deficiency in the protein dystrophin. Previously, we reported that the expression of hematopoietic prostaglandin D synthase (HPGDS) appeared in necrotic muscle fibers from patients with either Duchenne muscular dystrophy or polymyositis. HPGDS is responsible for the production of the inflammatory mediator, prostaglandin D(2). In this paper, we validated the hypothesis that HPGDS has a role in the etiology of muscular necrosis. We investigated the expression of HPGDS/ prostaglandin D(2) signaling using two different mouse models of muscle necrosis, that is, bupivacaine-induced muscle necrosis and the mdx mouse, which has a genetic muscular dystrophy. We treated each mouse model with the HPGDS-specific inhibitor, HQL-79, and measured both necrotic muscle volume and selected cytokine mRNA levels. We confirmed that HPGDS expression was induced in necrotic muscle fibers in both bupivacaine-injected muscle and mdx mice. After administration of HQL-79, necrotic muscle volume was significantly decreased in both mouse models. Additionally, mRNA levels of both CD11b and transforming growth factor beta1 were significantly lower in HQL-79-treated mdx mice than in vehicle-treated animals. We also demonstrated that HQL-79 suppressed prostaglandin D(2) production and improved muscle strength in the mdx mouse. Our results show that HPGDS augments inflammation, which is followed by muscle injury. Furthermore, the inhibition of HPGDS ameliorates muscle necrosis even in cases of genetic muscular dystrophy.

The value of mammalian models for duchenne muscular dystrophy in developing therapeutic strategies

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy. There is no effective treatment and patients typically die in approximately the third decade. DMD is an X-linked recessive disease caused by mutations in the dystrophin gene. There are three mammalian models of DMD that have been used to understand better the pathogenesis of disease and develop therapeutic strategies. The mdx mouse is the most widely used model of DMD that displays some features of muscle degeneration, but the pathogenesis of disease is comparatively mild. The severity of disease in mice lacking both dystrophin and utrophin is similar to DMD, but one has to account for the discrete functions of utrophin. Canine X-linked muscular dystrophy (cxmd) is the best representation of DMD, but the phenotype of the most widely used golden retriever (GRMD) model is variable, making functional endpoints difficult to ascertain. Although each mammalian model has its limitations, together they have been essential for the development of several treatment strategies for DMD that target dystrophin replacement, disease progression, and muscle regeneration.

Specific knockdown of delta-sarcoglycan gene in C2C12 in vitro causes post-translational loss of other sarcoglycans without mechanical stress

The precise role of delta-sarcoglycan (SG) that is constitutively expressed in skeletal muscle cells and may serve for maintaining the sarcolemmal integrity has not been identified. The delta-SG protein is at first among SG complex. To specifically identify the role in C(2)C(12) cells during the myogenesis, we screened several RNA interference (RNAi) candidates at first, and knocked down both levels of the mRNA and protein, employing adenovirus-mediated RNAi. We found no morphological alteration at both myoblast and myotube stages by suppression of delta-SG. The specific knockdown of delta-SG accompanied a concomitant decrease of alpha-, beta-, and gamma-SGs preserving normal levels of each transcript. As for the localization, alpha-, beta-, and gamma-SGs were weakly stained on the cell membrane in delta-SG knockdown cells, whereas each SG in control cell was localized both on the cell membrane and myoplasm abundantly. This enhanced post-translational loss would represent similitude of the progression of cardiomuscular diseases in vitro. Different from cardiac muscle cells, skeletal muscle cell culture without muscle contraction may imply that mechanical stress per se is not primarily involved in the progression of limb-girdle muscular dystrophy. Furthermore, we have observed translocation of calpain-2 to cell membrane in delta-SG knockdown cells, suggesting that Ca(2+)-sensitive proteases, calpains closely take part in post-translational proteolysis.

Treatment with inhibitors of the NF-kappaB pathway improves whole body tension development in the mdx mouse

The whole body tension (WBT) method was used to evaluate the hypothesis that long term treatment with NF-kappaB inhibitors improves the total forward pulling tension exerted by the limb musculature of the mdx mouse. Mdx mice exhibited significantly reduced WBT values and more profound weakening during the course of generating multiple forward pulling movements than age-matched nondystrophic mice. Long term treatment with the NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC) did not significantly reduce nuclear p65 activation in the costal diaphragm, but increased WBT by 12% in mature (12 month) mice. Daily treatment (30 days) of 1 month old mdx mice with the inhibitor ursodeoxycholic acid (UDCA) reduced costal diaphragm nuclear p65 activation by 40% and increased WBT by 21%. These results indicate that treatment with NF-kappaB inhibitors improves WBT in the mdx mouse and further establishes the utility of the WBT procedure in assessing therapeutic efficacy.

Residual laminin-binding activity and enhanced dystroglycan glycosylation by LARGE in novel model mice to dystroglycanopathy

Hypoglycosylation and reduced laminin-binding activity of α-dystroglycan are common characteristics of dystroglycanopathy, which is a group of congenital and limb-girdle muscular dystrophies. Fukuyama-type congenital muscular dystrophy (FCMD), caused by a mutation in the fukutin gene, is a severe form of dystroglycanopathy. A retrotransposal insertion in fukutin is seen in almost all cases of FCMD. To better understand the molecular pathogenesis of dystroglycanopathies and to explore therapeutic strategies, we generated knock-in mice carrying the retrotransposal insertion in the mouse fukutin ortholog. Knock-in mice exhibited hypoglycosylated α-dystroglycan; however, no signs of muscular dystrophy were observed. More sensitive methods detected minor levels of intact α-dystroglycan, and solid-phase assays determined laminin binding levels to be ∼50% of normal. In contrast, intact α-dystroglycan is undetectable in the dystrophic Large^myd mouse, and laminin-binding activity is markedly reduced. These data indicate that a small amount of intact α-dystroglycan is sufficient to maintain muscle cell integrity in knock-in mice, suggesting that the treatment of dystroglycanopathies might not require the full recovery of glycosylation. To examine whether glycosylation defects can be restored in vivo, we performed mouse gene transfer experiments. Transfer of fukutin into knock-in mice restored glycosylation of α-dystroglycan. In addition, transfer of LARGE produced laminin-binding forms of α-dystroglycan in both knock-in mice and the POMGnT1 mutant mouse, which is another model of dystroglycanopathy. Overall, these data suggest that even partial restoration of α-dystroglycan glycosylation and laminin-binding activity by replacing or augmenting glycosylation-related genes might effectively deter dystroglycanopathy progression and thus provide therapeutic benefits.

Effective rescue of dystrophin improves cardiac function in dystrophin-deficient mice by a modified morpholino oligomer

Antisense oligonucleotide-mediated exon skipping is able to correct out-of-frame mutations in Duchenne muscular dystrophy and restore truncated yet functional dystrophins. However, its application is limited by low potency and inefficiency in systemic delivery, especially failure to restore dystrophin in heart. Here, we conjugate a phosphorodiamidate morpholino oligomer with a designed cell-penetrating peptide (PPMO) targeting a mutated dystrophin exon. Systemic delivery of the novel PPMO restores dystrophin to almost normal levels in the cardiac and skeletal muscles in dystrophic mdx mouse. This leads to increase in muscle strength and prevents cardiac pump failure induced by dobutamine stress in vivo. Muscle pathology and function continue to improve during the 12-week course of biweekly treatment, with significant reduction in levels of serum creatine kinase. The high degree of potency of the oligomer in targeting all muscles and the lack of detectable toxicity and immune response support the feasibility of testing the novel oligomer in treating Duchenne muscular dystrophy patients.

Molecular and cellular adaptations to chronic myotendinous strain injury in mdx mice expressing a truncated dystrophin

Myotendinous strain injury is the most common injury of human skeletal muscles because the majority of muscle forces are transmitted through this region. Although the immediate response to strain injury is well characterized, the chronic response to myotendinous strain injury is less clear. Here we examined the molecular and cellular adaptations to chronic myotendinous strain injury in mdx mice expressing a microdystrophin transgene (microdystrophin(DeltaR4-R23)). We found that muscles with myotendinous strain injury had an increased expression of utrophin and alpha7-integrin together with the dramatic restructuring of peripheral myofibrils into concentric rings. The sarcolemma of the microdystrophin(DeltaR4-R23)/mdx gastrocnemius muscles was highly protected from experimental lengthening contractions, better than wild-type muscles. We also found a positive correlation between myotendinous strain injury and ringed fibers in the HSA(LR) (human skeletal actin, long repeat) mouse model of myotonic dystrophy. We suggest that changes in protein expression and the formation of rings are adaptations to myotendinous strain injury that help to prevent muscle necrosis and retain the function of necessary muscles during injury, ageing and disease.

Muscle diseases: the muscular dystrophies

Dystrophic muscle disease can occur at any age. Early- or childhood-onset muscular dystrophies may be associated with profound loss of muscle function, affecting ambulation, posture, and cardiac and respiratory function. Late-onset muscular dystrophies or myopathies may be mild and associated with slight weakness and an inability to increase muscle mass. The phenotype of muscular dystrophy is an endpoint that arises from a diverse set of genetic pathways. Genes associated with muscular dystrophies encode proteins of the plasma membrane and extracellular matrix, and the sarcomere and Z band, as well as nuclear membrane components. Because muscle has such distinctive structural and regenerative properties, many of the genes implicated in these disorders target pathways unique to muscle or more highly expressed in muscle. This chapter reviews the basic structural properties of muscle and genetic mechanisms that lead to myopathy and muscular dystrophies that affect all age groups.

Long-term survival of transplanted stem cells in immunocompetent mice with muscular dystrophy

Satellite cells refer to resident stem cells in muscle that are activated in response to damage or disease for the regeneration and repair of muscle fibers. The use of stem cell transplantation to treat muscular diseases has been limited by impaired donor cell survival attributed to rejection and an unavailable stem cell niche. We isolated a population of adult muscle mononuclear cells (AMMCs) from normal, strain-matched muscle and transplanted these cells into delta-sarcoglycan-null dystrophic mice. Distinct from other transplant studies, the recipient mice were immunocompetent with an intact endogenous satellite cell pool. We found that AMMCs were 35 times more efficient at restoring sarcoglycan compared with cultured myoblasts. Unlike cultured myoblasts, AMMC-derived muscle fibers expressed sarcoglycan protein throughout their entire length, consistent with enhanced migratory ability. We examined the capacity of single injections of AMMCs to provide long-term benefit for muscular dystrophy and found persistent regeneration after 6 months, consistent with augmentation of the endogenous stem cell pool. Interestingly, AMMCs were more effectively engrafted into aged dystrophic mice for the regeneration of large clusters of sarcoglycan-positive muscle fibers, which were protected from damage, suggesting that the stem cell niche in older muscle remains permissive.

Investigation of Debio 025, a cyclophilin inhibitor, in the dystrophic mdx mouse, a model for Duchenne muscular dystrophy

BACKGROUND AND PURPOSE

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder caused by the absence of the cytoskeletal protein dystrophin. This leads to muscle cell death accompanied by chronic inflammation. Cyclosporin A (CsA) is a powerful immunosuppressive drug, which has been proposed for DMD treatment. CsA also directly regulates the mitochondrial permeability transition pore (mPTP), which participates in cell death pathways through the inhibition of cyclophilin D. Here, we evaluated whether Debio 025, a cyclophilin inhibitor with no immunosuppressive activity, improves the dystrophic condition in a mouse model of DMD, through regulation of mPTP.

EXPERIMENTAL APPROACH

The potency of Debio 025 to protect mouse dystrophic cells against mitochondria-mediated death was assessed by caspase-3 activity and calcium retention capacity assays. Mdx(5Cv) mice (3-week-old) were treated daily by gavage for 2 weeks with Debio 025 (10, 30 or 100 mg kg(-1)), CsA (10 mg kg(-1)) or placebo. The effects on muscle necrosis and function were measured.

KEY RESULTS

In vitro investigations showed protective effect of low concentrations of Debio 025 against cell death. Histology demonstrated that Debio 025 partially protected the diaphragm and soleus muscles against necrosis (10 and 100 mg kg(-1), respectively). Hindlimb muscles from mice receiving Debio 025 at 10 mg kg(-1) relaxed faster, showed alteration in the stimulation frequency-dependent recruitment of muscle fibres and displayed a higher resistance to mechanical stress.

CONCLUSIONS AND IMPLICATIONS

Debio 025 partially improved the structure and the function of the dystrophic mouse muscle, suggesting that therapies targeting the mPTP may be helpful to DMD patients.

Measurement of muscle disease by quantitative second-harmonic generation imaging

Determining the health of muscle cells by in vivo imaging could impact the diagnosis and monitoring of a large number of congenital and acquired muscular or cardiac disorders. However, currently used technologies are hampered by insufficient resolution, lack of specificity, or invasiveness. We have combined intrinsic optical second-harmonic generation from sarcomeric myosin with a novel mathematical treatment of striation pattern analysis, to obtain measures of muscle contractile integrity that correlate strongly with the neuromuscular health of mice suffering from genetic, acquired, and age-related decline in skeletal muscle function. Analysis of biopsies from a pilot group of human volunteers suggests a similar power in quantifying sarcopenic changes in muscle integrity. These results provide the first strong evidence that quantitative image analysis of sarcomere pattern can be correlated with physiological function, and they invite the application of SHG imaging in clinical practice, either in biopsy samples or via microendoscopy.

Laryngeal muscles are spared in the dystrophin deficient mdx mouse

PURPOSE

Duchenne muscular dystrophy (DMD) is caused by the loss of the cytoskeletal protein, dystrophin. The disease leads to severe and progressive skeletal muscle wasting. Interestingly, the disease spares some muscles. The purpose of the study was to determine the effects of dystrophin deficiency on 2 intrinsic laryngeal muscles, the posterior cricoarytenoid and the thyroarytenoid, in the mouse model.

METHOD

Larynges from dystrophin-deficient mdx and normal mice were examined histologically.

RESULTS

Results demonstrate that despite the absence of dystrophin in the mdx laryngeal muscles, membrane damage, inflammation, necrosis, and regeneration were not detected in the assays performed.

CONCLUSIONS

The authors concluded that these muscles are 1 of only a few muscle groups spared in this model of dystrophin deficiency. The muscles may count on intrinsic and adaptive protective mechanisms to cope with the absence of dystrophin. Identifying these protective mechanisms may improve DMD management. The study also highlights the unique aspects of the selected laryngeal skeletal muscles and their dissimilarity to limb skeletal muscle.

Towards developing standard operating procedures for pre-clinical testing in the mdx mouse model of Duchenne muscular dystrophy

This review discusses various issues to consider when developing standard operating procedures for pre-clinical studies in the mdx mouse model of Duchenne muscular dystrophy (DMD). The review describes and evaluates a wide range of techniques used to measure parameters of muscle pathology in mdx mice and identifies some basic techniques that might comprise standardised approaches for evaluation. While the central aim is to provide a basis for the development of standardised procedures to evaluate efficacy of a drug or a therapeutic strategy, a further aim is to gain insight into pathophysiological mechanisms in order to identify other therapeutic targets. The desired outcome is to enable easier and more rigorous comparison of pre-clinical data from different laboratories around the world, in order to accelerate identification of the best pre-clinical therapies in the mdx mouse that will fast-track translation into effective clinical treatments for DMD.

Disodium cromoglycate protects dystrophin-deficient muscle fibers from leakiness

In dystrophin-deficient fibers of mdx mice and in Duchenne dystrophy, the lack of dystrophin leads to sarcolemma breakdown and muscle degeneration. We verified that cromolyn, a mast-cell stabilizer agent, stabilized dystrophic muscle fibers using Evans blue dye as a marker of sarcolemma leakiness. Mdx mice (n=8; 14 days of age) received daily intraperitoneal injections of cromolyn (50 mg/kg body weight) for 15 days. Untreated mdx mice (n=8) were injected with saline. Cryostat cross-sections of the sternomastoid, tibialis anterior, and diaphragm muscles were stained with hematoxylin and eosin. Cromolyn dramatically reduced Evans blue dye-positive fibers in all muscles (P<0.05; Student's t-test) and led to a significant increase in the percentage of fibers with peripheral nuclei. This study supports the protective effects of cromolyn in dystrophic muscles and further indicates its action against muscle fiber leakiness in muscles that are differently affected by the lack of dystrophin.

Transplantation of bone marrow-derived hepatocyte stem cells transduced with adenovirus-mediated IL-10 gene reverses liver fibrosis in rats

Bone marrow stem cells (BMSCs) transplantation alone may not be sufficient for treatment of liver fibrosis because of complicated histopathologic changes in the liver. Interleukin-10 (IL-10) is an anti-fibrosis cytokine. IL-10 gene transfer of beta2m(-)/Thy-1+ bone marrow-derived hepatocyte stem cells (BDHSCs) may be useful for treating liver fibrosis. To determine the effect of liver fibrosis in rats by transplanting BDHSCs transduced with adenovirus-mediated IL-10 gene (AdIL-10), rat BDHSCs were isolated by magnetic bead cell sorting, characterized for liver-associated phenotypes, transduced with AdIL-10, and transplanted into liver-fibrotic rats. We show that BDHSCs secreted high-level IL-10 and retained their albumin expression after AdIL-10 transfer in vitro. Intra-portal-infused BDHSCs were implanted into the liver 2 weeks after transplantation. Transplanting AdIL-10-transduced BDHSCs into liver-fibrotic rats downregulated inflammatory response, promoted liver regeneration, suppressed activation of hepatic stellate cells and improved liver histopathology and liver function. These findings demonstrated the potential utility of this novel combined strategy of IL-10 gene and BDHSCs for the treatment of liver fibrosis.

A common disease-associated missense mutation in alpha-sarcoglycan fails to cause muscular dystrophy in mice

Limb-girdle muscular dystrophy type 2D (LGMD2D) is caused by autosomal recessive mutations in the alpha-sarcoglycan gene. An R77C substitution is the most prevalent cause of the disease, leading to disruption of the sarcoglycan-sarcospan complex. To model this common mutation, we generated knock-in mice with an H77C substitution in alpha-sarcoglycan. The floxed neomycin (Neo)-cassette retained at the targeted H77C alpha-sarcoglycan locus caused a loss of alpha-sarcoglycan expression, resulting in muscular dystrophy in homozygotes, whereas Cre-mediated deletion of the floxed Neo-cassette led to recovered H77C alpha-sarcoglycan expression. Contrary to expectations, mice homozygous for the H77C-encoding allele expressed both this mutant alpha-sarcoglycan and the other components of the sarcoglycan-sarcospan complex in striated muscle, and did not develop muscular dystrophy. Accordingly, conditional rescued expression of the H77C protein in striated muscle of the alpha-sarcoglycan-deficient mice prevented the disease. Adding to the case that the behavior of mutant alpha-sarcoglycan is different between humans and mice, mutant human R77C alpha-sarcoglycan restored the expression of the sarcoglycan-sarcospan complex when introduced by adenoviral vector into the skeletal muscle of previously created alpha-sarcoglycan null mice. These findings indicate that the alpha-sarcoglycan with the most frequent missense mutation in LGMD2D is correctly processed, is transported to the sarcolemma, and is fully functional in mouse muscle. Our study presents an unexpected difference in the behavior of a missense-mutated protein in mice versus human patients, and emphasizes the need to understand species-specific protein quality control systems.

Mechano-Growth Factor Reduces Loss of Cardiac Function in Acute Myocardial Infarction

BACKGROUND

Mechano-growth factor (MGF) is a splice-variant of IGF-I sharing an identical mature region, but with a different E domain. Our objective was to determine if MGF would reduce the area of 'at-risk' myocardium and improve cardiac function in the post-infarct heart.

METHODS

Infarcts were induced by injection of microspheres. In experiment 1, sheep were treated with vehicle, 200 nM each of mature IGF-I, MGF E domain, or full-length MGF. In experiment 2, sheep were treated with vehicle or 200 nM of MGF E domain alone. Cardiac function was assessed using echocardiography and sheep were killed eight days post-MI. Evans Blue dye was injected before death to stain the compromised myocardium. Immunohistochemistry was used to assess the abundance of pAkt(T308) and cleaved caspase 3.

RESULTS

In experiment 1, cardiac function improved in sheep treated with the MGF E domain, while in experiment 2, MGF E domain preserved cardiac function and there was 35% less compromised cardiac muscle than controls. Furthermore, immunostaining of cleaved caspase 3 was absent in MGF E domain-treated hearts, suggesting that MGF E domain reduced infarct expansion.

CONCLUSIONS

We conclude that the E domain of MGF protects the myocardium against ischaemia, thus improving cardiac function post-MI.

Biology of the striated muscle dystrophin-glycoprotein complex

Since its first description in 1990, the dystrophin-glycoprotein complex has emerged as a critical nexus for human muscular dystrophies arising from defects in a variety of distinct genes. Studies in mammals widely support a primary role for the dystrophin-glycoprotein complex in mechanical stabilization of the plasma membrane in striated muscle and provide hints for secondary functions in organizing molecules involved in cellular signaling. Studies in model organisms confirm the importance of the dystrophin-glycoprotein complex for muscle cell viability and have provided new leads toward a full understanding of its secondary roles in muscle biology.

Evans blue staining of cardiomyocytes induced by myocardial contrast echocardiography in rats: evidence for necrosis instead of apoptosis

High mechanical index (MI) echocardiography with contrast agent has been shown to induce Evans blue staining of cardiomyocytes, seen 1 d after exposure, in addition to contraction band necrosis, seen immediately after exposure. This research examined the roles of necrosis vs. apoptosis in these bioeffects. Myocardial contrast echocardiography at high MI with 1:4 electrocardiogram triggering was performed in anesthetized rats at 1.5 MHz. Histologically observable cell injury was accumulated by infusing a high dose of 50 microL/kg ultrasound contrast media via tail vein for 5 min at the start of 10 min of scanning. Evans blue dye or propidium iodide was injected as an indicator of cardiomyocyte plasma membrane integrity. Histologic sections were stained using the terminal dUTP nick-end labeling (TUNEL) method for labeling nuclei with DNA degradation (e.g., apoptosis). Evans blue fluorescent cells were counted on frozen sections or on hematoxylin-stained and TUNEL-labeled paraffin sections. In addition, transmission electron microscopy was used to assess potential apoptotic nuclei. Hypercontraction and propidium iodide staining were observed immediately after imaging exposure. Although TUNEL-positive cells were evident after 4 h, these also had indications of contraction band necrosis, and features of apoptosis were not confirmed by electron microscopy. Inflammatory cell infiltration was evident after 24 h. A second, more subtle injury was recognized by Evans blue staining, with minimal inflammatory cell infiltration at the morphologically intact stained cells after 24 h. Apoptosis was not detected by the TUNEL method in the cardiomyocytes stained with Evans blue at 24 h. However, Evans blue-stained cell numbers declined after 48 h, with continued inflammatory cell infiltration. The initial insult for Evans blue-stained cardiomyocytes apparently induced partial permeability of the plasma membrane, which led to gradual degeneration (but not apoptosis) and necrosis after 24 to 48 h.

Increasing alpha 7 beta 1-integrin promotes muscle cell proliferation, adhesion, and resistance to apoptosis without changing gene expression

The dystrophin-glycoprotein complex maintains the integrity of skeletal muscle by associating laminin in the extracellular matrix with the actin cytoskeleton. Several human muscular dystrophies arise from defects in the components of this complex. The alpha(7)beta(1)-integrin also binds laminin and links the extracellular matrix with the cytoskeleton. Enhancement of alpha(7)-integrin levels alleviates pathology in mdx/utrn(-/-) mice, a model of Duchenne muscular dystrophy, and thus the integrin may functionally compensate for the absence of dystrophin. To test whether increasing alpha(7)-integrin levels affects transcription and cellular functions, we generated alpha(7)-integrin-inducible C2C12 cells and transgenic mice that overexpress the integrin in skeletal muscle. C2C12 myoblasts with elevated levels of integrin exhibited increased adhesion to laminin, faster proliferation when serum was limited, resistance to staurosporine-induced apoptosis, and normal differentiation. Transgenic expression of eightfold more integrin in skeletal muscle did not result in notable toxic effects in vivo. Moreover, high levels of alpha(7)-integrin in both myoblasts and in skeletal muscle did not disrupt global gene expression profiles. Thus increasing integrin levels can compensate for defects in the extracellular matrix and cytoskeleton linkage caused by compromises in the dystrophin-glycoprotein complex without triggering apparent overt negative side effects. These results support the use of integrin enhancement as a therapy for muscular dystrophy.

Growth factors temporally associate with airway responsiveness and inflammation in allergen-exposed mice

BACKGROUND

To clarify whether growth factors play critical roles in the development of airway hyperresponsiveness (AHR) and airway inflammation in the early stages of asthma, the relationship between growth factors and AHR and airway inflammation were analyzed in a mouse model of asthma.

METHODS

Following ovalbumin (OVA) sensitization and challenge, airway function, inflammation, cytokine and growth factor levels were monitored.

RESULTS

AHR to inhaled methacholine increased at 6 h, peaked at 48 h, and remained elevated for 14 days. IL-4 and IL-5 levels in bronchoalveolar lavage (BAL) fluid were increased at 6 h, peaked at 24 h, but returned to baseline quickly. IL-13 levels increased up to 14 days, peaking at 48 h. Increases in BAL fluid transforming growth factor-beta(1) and platelet-derived growth factor were observed at 12 h, and remained elevated at 14 days. Nerve growth factor levels were increased at 24-28 days. BAL fluid hepatocyte growth factor (HGF) was detected at 12 h, peaked at 24 h, and returned to baseline by 72 h. c-Met/HGF receptor was detected in the airways at 6 h, before HGF in the BAL, and continued to be observed 96 h after the last OVA challenge.

CONCLUSIONS

These data identify a temporal association between growth factor production and Th2 cytokine production and the kinetics of AHR. Growth factors may play important roles in the development of allergic airway inflammation and AHR even in the early stages of asthma, before remodeling is initiated.

Hepatocyte growth factor: a regenerative drug for acute hepatitis and liver cirrhosis

Liver cirrhosis is a major cause of morbidity worldwide and is characterized by the loss of hepatocytes with interstitial fibrosis. In this review, we discuss the potential uses of hepatocyte growth factor for treating hepatic diseases, focusing on the molecular mechanisms whereby hepatocyte growth factor reverses liver cirrhosis. Hepatic myofibroblasts play a central role in the development of liver cirrhosis, while myofibroblasts acquire c-Met. Using a rat model of liver cirrhosis, we recently delineated the direct effect of hepatocyte growth factor toward myofibroblasts: the induction of apoptotic cell death associated with matrix degradation, the inhibition of overproliferation and the suppression of transforming growth factor-beta1 production in myofibroblasts. Hepatocyte growth factor elicits mitogenic, anti-apoptotic and anti-inflammatory functions in hepatocytes, therefore contributing to reversing liver dysfunction. Considering the insufficient production of hepatocyte growth factor is responsible for the manifestation of chronic hepatitis, supplementation with or reinduction of hepatocyte growth factor represents a new strategy for attenuating intractable liver diseases.