Effect of genetic background on the dystrophic phenotype in mdx mice

Genetic background significantly affects phenotype in multiple mouse models of human diseases, including muscular dystrophy. This phenotypic variability is partly attributed to genetic modifiers that regulate the disease process. Studies have demonstrated that introduction of the γ-sarcoglycan-null allele onto the DBA/2J background confers a more severe muscular dystrophy phenotype than the original strain, demonstrating the presence of genetic modifier loci in the DBA/2J background. To characterize the phenotype of dystrophin deficiency on the DBA/2J background, we created and phenotyped DBA/2J-congenic Dmdmdx mice (D2-mdx) and compared them with the original, C57BL/10ScSn-Dmdmdx (B10-mdx) model. These strains were compared with their respective control strains at multiple time points between 6 and 52 weeks of age. Skeletal and cardiac muscle function, inflammation, regeneration, histology and biochemistry were characterized. We found that D2-mdx mice showed significantly reduced skeletal muscle function as early as 7 weeks and reduced cardiac function by 28 weeks, suggesting that the disease phenotype is more severe than in B10-mdx mice. In addition, D2-mdx mice showed fewer central myonuclei and increased calcifications in the skeletal muscle, heart and diaphragm at 7 weeks, suggesting that their pathology is different from the B10-mdx mice. The new D2-mdx model with an earlier onset and more pronounced dystrophy phenotype may be useful for evaluating therapies that target cardiac and skeletal muscle function in dystrophin-deficient mice. Our data align the D2-mdx with Duchenne muscular dystrophy patients with the LTBP4 genetic modifier, making it one of the few instances of cross-species genetic modifiers of monogenic traits.

Preclinical drug trials in the mdx mouse: assessment of reliable and sensitive outcome measures

The availability of animal models for Duchenne muscular dystrophy has led to extensive preclinical research on potential therapeutics. Few studies have focused on reliability and sensitivity of endpoints for mdx mouse drug trials. Therefore, we sought to compare a wide variety of reported and novel endpoint measures in exercised mdx and normal control mice at 10, 20, and 40 weeks of age. Statistical analysis as well as power calculations for expected effect sizes in mdx preclinical drug trials across different ages showed that body weight, normalized grip strength, horizontal activity, rest time, cardiac function measurements, blood pressure, total central/peripheral nuclei per fiber, and serum creatine kinase are the most effective measurements for detecting drug-induced changes. These data provide an experimental basis upon which standardization of preclinical drug testing can be developed. Muscle Nerve, 2008.

Metabolic remodeling agents show beneficial effects in the dystrophin-deficient mdx mouse model

Background

Duchenne muscular dystrophy is a genetic disease involving a severe muscle wasting that is characterized by cycles of muscle degeneration/regeneration and culminates in early death in affected boys. Mitochondria are presumed to be involved in the regulation of myoblast proliferation/differentiation; enhancing mitochondrial activity with exercise mimetics (AMPK and PPAR-delta agonists) increases muscle function and inhibits muscle wasting in healthy mice. We therefore asked whether metabolic remodeling agents that increase mitochondrial activity would improve muscle function in mdx mice.

Methods

Twelve-week-old mdx mice were treated with two different metabolic remodeling agents (GW501516 and AICAR), separately or in combination, for 4 weeks. Extensive systematic behavioral, functional, histological, biochemical, and molecular tests were conducted to assess the drug(s)' effects.

Results

We found a gain in body and muscle weight in all treated mice. Histologic examination showed a decrease in muscle inflammation and in the number of fibers with central nuclei and an increase in fibers with peripheral nuclei, with significantly fewer activated satellite cells and regenerating fibers. Together with an inhibition of FoXO1 signaling, these results indicated that the treatments reduced ongoing muscle damage.

Conclusions

The three treatments produced significant improvements in disease phenotype, including an increase in overall behavioral activity and significant gains in forelimb and hind limb strength. Our findings suggest that triggering mitochondrial activity with exercise mimetics improves muscle function in dystrophin-deficient mdx mice.

Long-term treatment with naproxcinod significantly improves skeletal and cardiac disease phenotype in the mdx mouse model of dystrophy

In Duchenne muscular dystrophy (DMD) patients and the mouse model of DMD, mdx, dystrophin deficiency causes a decrease and mislocalization of muscle-specific neuronal nitric oxide synthase (nNOSμ), leading to functional impairments. Previous studies have shown that nitric oxide (NO) donation associated with anti-inflammatory action has beneficial effects in dystrophic mouse models. In this study, we have systematically investigated the effects of naproxcinod, an NO-donating naproxen derivative, on the skeletal and cardiac disease phenotype in mdx mice. Four-week-old mdx and C57BL/10 mice were treated with four different concentrations (0, 10, 21 and 41 mg/kg) of naproxcinod and 0.9 mg/kg of prednisolone in their food for 9 months. All mice were subjected to twice-weekly treadmill sessions, and functional and behavioral parameters were measured at 3, 6 and 9 months of treatment. In addition, we evaluated in vitro force contraction, optical imaging of inflammation, echocardiography and blood pressure (BP) at the 9-month endpoint prior to sacrifice. We found that naproxcinod treatment at 21 mg/kg resulted in significant improvement in hindlimb grip strength and a 30% decrease in inflammation in the fore- and hindlimbs of mdx mice. Furthermore, we found significant improvement in heart function, as evidenced by improved fraction shortening, ejection fraction and systolic BP. In addition, the long-term detrimental effects of prednisolone typically seen in mdx skeletal and heart function were not observed at the effective dose of naproxcinod. In conclusion, our results indicate that naproxcinod has significant potential as a safe therapeutic option for the treatment of muscular dystrophies.

Selective modulation through the glucocorticoid receptor ameliorates muscle pathology in mdx mice

The over-expression of NF-κB signalling in both muscle and immune cells contribute to the pathology in dystrophic muscle. The anti-inflammatory properties of glucocorticoids, mediated predominantly through monomeric glucocorticoid receptor inhibition of transcription factors such as NF-κB (transrepression), are postulated to be an important mechanism for their beneficial effects in Duchenne muscular dystrophy. Chronic glucocorticoid therapy is associated with adverse effects on metabolism, growth, bone mineral density and the maintenance of muscle mass. These detrimental effects result from direct glucocorticoid receptor homodimer interactions with glucocorticoid response elements of the relevant genes. Compound A, a non-steroidal selective glucocorticoid receptor modulator, is capable of transrepression without transactivation. We confirm the in vitro NF-κB inhibitory activity of compound A in H-2K(b) -tsA58 mdx myoblasts and myotubes, and demonstrate improvements in disease phenotype of dystrophin deficient mdx mice. Compound A treatment in mdx mice from 18 days of post-natal age to 8 weeks of age increased the absolute and normalized forelimb and hindlimb grip strength, attenuated cathepsin-B enzyme activity (a surrogate marker for inflammation) in forelimb and hindlimb muscles, decreased serum creatine kinase levels and reduced IL-6, CCL2, IFNγ, TNF and IL-12p70 cytokine levels in gastrocnemius (GA) muscles. Compared with compound A, treatment with prednisolone, a classical glucocorticoid, in both wild-type and mdx mice was associated with reduced body weight, reduced GA, tibialis anterior and extensor digitorum longus muscle mass and shorter tibial lengths. Prednisolone increased osteopontin (Spp1) gene expression and osteopontin protein levels in the GA muscles of mdx mice and had less favourable effects on the expression of Foxo1, Foxo3, Fbxo32, Trim63, Mstn and Igf1 in GA muscles, as well as hepatic Igf1 in wild-type mice. In conclusion, selective glucocorticoid receptor modulation by compound A represents a potential therapeutic strategy to improve dystrophic pathology.

Quality of life before and during antihypertensive treatment: a comparative study of celiprolol and atenolol

Hypertensive patients may be adversely affected by complications and other concomitant processes such as anxiety, sedation, and drug side effects. It has been suggested that some recently developed antihypertensive agents do not affect quality of life by causing adverse effects. We compared the effects of two antihypertensive drugs on quality of life: atenolol, a standard cardioselective beta-blocker, and celiprolol, one of a new class of selective beta-blockers with vasodilatory properties. One hundred thirty-two patients with mild-to-moderate hypertension were eligible to enter a 28-week, double-blind, parallel-group study. The study protocol consisted of a 4-week period on placebo and a 24-week period of dosage-adjusted treatment with either atenolol or celiprolol. We assessed both systolic and diastolic blood pressure and quality of life perception by a selected test battery that included the Bulpitt and Fletcher Quality of Life Questionnaire. Supine blood pressure fell from 167/101 (range 120/95 to 200/116) to 150/92 mm Hg (p < 0. 0001) during celiprolol treatment. This antihypertensive effect was at least as good with celiprolol as with atenolol. Quality of life perception was comparable for the two drugs although adverse effects were seen more frequently with atenolol than with celiprolol, particularly after prolonged treatment. Patient compliance was better for celiprolol than for atenolol. Our results show that the selective beta-blocker with vasodilatory property celiprolol is at least as effective as atenolol and that it is more advantageous in terms of some quality of life variables.

Eps homology domain endosomal transport proteins differentially localize to the neuromuscular junction

Background

Recycling of endosomes is important for trafficking and maintenance of proteins at the neuromuscular junction (NMJ). We have previously shown high expression of the endocytic recycling regulator Eps15 homology domain-containing (EHD)1 proteinin the Torpedo californica electric organ, a model tissue for investigating a cholinergic synapse. In this study, we investigated the localization of EHD1 and its paralogs EHD2, EHD3, and EHD4 in mouse skeletal muscle, and assessed the morphological changes in EHD1^−/− NMJs.

Methods

Localization of the candidate NMJ protein EHD1 was assessed by confocal microscopy analysis of whole-mount mouse skeletal muscle fibers after direct gene transfer and immunolabeling. The potential function of EHD1 was assessed by specific force measurement and α-bungarotoxin-based endplate morphology mapping in EHD1^−/− mouse skeletal muscle.

Results

Endogenous EHD1 localized to primary synaptic clefts of murine NMJ, and this localization was confirmed by expression of recombinant green fluorescent protein labeled-EHD1 in murine skeletal muscle in vivo. EHD1^−/− mouse skeletal muscle had normal histology and NMJ morphology, and normal specific force generation during muscle contraction. The EHD 1–4 proteins showed differential localization in skeletal muscle: EHD2 to muscle vasculature, EHD3 to perisynaptic regions, and EHD4 to perinuclear regions and to primary synaptic clefts, but at lower levels than EHD1. Additionally, specific antibodies raised against mammalian EHD1-4 recognized proteins of the expected mass in the T. californica electric organ. Finally, we found that EHD4 expression was more abundant in EHD1^−/− mouse skeletal muscle than in wild-type skeletal muscle.

Conclusion

EHD1 and EHD4 localize to the primary synaptic clefts of the NMJ. Lack of obvious defects in NMJ structure and muscle function in EHD1^−/− muscle may be due to functional compensation by other EHD paralogs.

Mitochondrial dysfunction and consequences in calpain-3-deficient muscle

BACKGROUND

Nonsense or loss-of-function mutations in the non-lysosomal cysteine protease calpain-3 result in limb-girdle muscular dystrophy type 2A (LGMD2A). While calpain-3 is implicated in muscle cell differentiation, sarcomere formation, and muscle cytoskeletal remodeling, the physiological basis for LGMD2A has remained elusive.

METHODS

Cell growth, gene expression profiling, and mitochondrial content and function were analyzed using muscle and muscle cell cultures established from healthy and calpain-3-deficient mice. Calpain-3-deficient mice were also treated with PPAR-delta agonist (GW501516) to assess mitochondrial function and membrane repair. The unpaired t test was used to assess the significance of the differences observed between the two groups or treatments. ANOVAs were used to assess significance over time.

RESULTS

We find that calpain-3 deficiency causes mitochondrial dysfunction in the muscles and myoblasts. Calpain-3-deficient myoblasts showed increased proliferation, and their gene expression profile showed aberrant mitochondrial biogenesis. Myotube gene expression analysis further revealed altered lipid metabolism in calpain-3-deficient muscle. Mitochondrial defects were validated in vitro and in vivo. We used GW501516 to improve mitochondrial biogenesis in vivo in 7-month-old calpain-3-deficient mice. This treatment improved satellite cell activity as indicated by increased MyoD and Pax7 mRNA expression. It also decreased muscle fatigability and reduced serum creatine kinase levels. The decreased mitochondrial function also impaired sarcolemmal repair in the calpain-3-deficient skeletal muscle. Improving mitochondrial activity by acute pyruvate treatment improved sarcolemmal repair.

CONCLUSION

Our results provide evidence that calpain-3 deficiency in the skeletal muscle is associated with poor mitochondrial biogenesis and function resulting in poor sarcolemmal repair. Addressing this deficit by drugs that improve mitochondrial activity offers new therapeutic avenues for LGMD2A.