Nerve terminal contributes to acetylcholine receptor organization at the dystrophic neuromuscular junction of <i>mdx</i> mice

Marques, Maria Júlia; Taniguti, Ana Paula Tiemi; Minatel, Elaine; Neto, Humberto Santo

doi:10.1002/ar.20421

Cited by 24 publications

(28 citation statements)

References 32 publications

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“…These changes may be explained by a different contribution of sodium and potassium channels in mdx and C57BL/10 animals that could result from a subtle disorganization of the myelin sheath of the peripheral nerve, leading to modifications of the distribution and density of ion channels in mdx mice, which may also influence CMAP amplitude. The fragmentation of the neuromuscular junction, the excessive nerve sprouting (21), and the decrease in the number and depth of synaptic folds that promote the decrease in the density of voltage-gated sodium channels to the synapse (22), described in mdx mice, support our explanation. Moreover, the increased latency of CMAP in saline-treated mdx mice may reflect the morphologic alterations at the neuromuscular junction that influence action potential propagation.…”

Section: Discussionsupporting

confidence: 81%

Low doses of arginine butyrate derivatives improve dystrophic phenotype and restore membrane integrity in DMD models

et al. 2014

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A new approach to treating Duchenne muscular dystrophy was investigated by using the ester or amide covalent association of arginine [nitric oxide (NO) pathway] and butyrate [histone deacetylase (HDAC) inhibition] in mdx mice and patient myotubes. Two prodrugs were synthesized, and the beneficial effects on dystrophic phenotype were studied. Nerve excitability abnormalities detected in saline-treated mice were almost totally rescued in animals treated at low doses (50-100 mg/kg/d). Force and fatigue resistance were improved ≈60% and 3.5-fold, respectively, and the percentage of necrosis in heart sections was reduced ≈90% in the treated mice. A decrease of >50% in serum creatine kinase indicated an overall improvement in the muscles. Restoration of membrane integrity was studied directly by measuring the reduction (≈74%) of Evans blue incorporation in the limb muscles of the treated animals, the increase in utrophin level, and the normalization of lipid composition of the heart. In cultures of human myotubes (primary cells and cell line), both prodrugs and HDAC inhibitors increased by 2- to 4-fold the utrophin level, which was correctly localized at the membrane. β-Dystroglycan and embryonic myosin protein levels were also increased. Finally, a 50% reduction in the number of spontaneous Ca(2+) spikes was observed after treatment with NO synthase substrate and HDAC inhibitors. Overall, the beneficial effects were obtained with doses 10 (in vivo) and 5 (in vitro) times lower than those of the salt formulation. Altogether, these data constitute proof of principle of the beneficial effects of low doses of arginine butyrate derivatives on muscular dystrophy, enhancing the NO pathway and inhibiting HDAC.

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Section: Discussionsupporting

confidence: 81%

Low doses of arginine butyrate derivatives improve dystrophic phenotype and restore membrane integrity in DMD models

et al. 2014

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“…WT NMJs show a typical continuous aggregate of AChRs and after injury, no significant change in morphology. Based on a discontinuity index and number of clusters per NMJ, AChRs in mdx mice are more discontinuous and punctate than in WT mice, consistent with findings of Marques et al (2007) (Fig. 3C and Table 1).…”

Section: Figure 3 Representative Images Of Injured and Non-injured Nsupporting

confidence: 84%

“…Dystrophin is not required for NMJ formation, but is required for end‐plate maintenance (Kong & Anderson, 1999) and likely for end‐plate remodelling in regenerating fibres. Mdx mice show NMJ fragmentation in adult muscle fibres and excessive nerve sprouting compared to wild‐type (WT) mice (Marques et al 2007). Electron microscopy studies indicate a loss in the number and depth of synaptic folds of the motor end‐plate in mdx muscles (Lyons & Slater, 1991; Banks et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Effects of in vivo injury on the neuromuscular junction in healthy and dystrophic muscles

Pratt¹,

Shah

Ward

et al. 2012

The Journal of Physiology

135

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Key points• Strength loss induced by lengthening contractions is typically attributed to damaged force-bearing structures within skeletal muscle. Muscle lacking the structural protein dystrophin, as in Duchenne muscular dystrophy, is particularly susceptible to contractioninduced injury.• We tested the hypothesis that changes in neuromuscular junctions (NMJs) contribute to strength loss following lengthening contractions in wild-type and in dystrophic skeletal muscle.• NMJs in dystrophic (mdx) mice, the murine model of Duchenne muscular dystrophy, show discontinuous and dispersed motor end-plate morphology. Following lengthening contractions, mdx quadriceps muscles show a greater loss in force, increased neuromuscular transmission failure and decreased electromyographic measures compared to wild-type.• Consistent with NMJ disruption as a mechanism contributing to this force loss, only mdx showed increased motor end-plate discontinuity and dispersion of acetylcholine receptor aggregates.• Our results indicate that the NMJ in mdx muscle is particularly susceptible to damage, and might play a role in the exacerbated response to injury in dystrophic muscles. AbstractThe most common and severe form of muscular dystrophy is Duchenne muscular dystrophy (DMD), a disorder caused by the absence of dystrophin, a structural protein found on the cytoplasmic surface of the sarcolemma of striated muscle fibres. Considerable attention has been dedicated to studying myofibre damage and muscle plasticity, but there is little information to determine if damage from contraction-induced injury occurs at or near the nerve terminal axon. We used α-bungarotoxin to compare neuromuscular junction (NMJ) morphology in healthy (wild-type, WT) and dystrophic (mdx) mouse quadriceps muscles and evaluated transcript levels of the post-synaptic muscle-specific kinase signalling complex. Our focus was to study changes in NMJs after injury induced with an established in vivo animal injury model. Neuromuscular transmission, electromyography (EMG), and NMJ morphology were assessed 24 h after injury. In non-injured muscle, muscle-specific kinase expression was significantly decreased in mdx compared to WT. Injury resulted in a significant loss of maximal torque in WT (39 ± 6%) and mdx (76 ± 8%) quadriceps, but significant changes in NMJ morphology, neuromuscular transmission and EMG data were found only in mdx following injury. increased and the EMG measures decreased after injury in mdx mice only. The data show that eccentric contraction-induced injury causes morphological and functional changes to the NMJs in mdx skeletal muscle, which may play a role in excitation-contraction coupling failure and progression of the dystrophic process.

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“…Dystrophin is present in a subset of GABAergic synapses in the CNS allowing the possibility that altered motoneuron function or motor neuropathy could contribute to the fragmentation of the neuromuscular synapses in mdx mice (Graciotti et al, 2008; Knuesel et al, 1999; Kueh et al, 2008; Marques et al, 2007b). Here we show using a muscle-specific human α-skeletal actin promoter that minidysGFP expression selectively in skeletal muscle prevents the fragmentation of the neuromuscular synapse in mdx mice.…”

Section: Discussionmentioning

confidence: 99%

Truncated dystrophins can influence neuromuscular synapse structure

Banks

Chamberlain

Froehner

2009

Molecular and Cellular Neuroscience

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Duchenne muscular dystrophy (DMD) is characterized by muscle degeneration and structural defects in the neuromuscular synapse that are caused by mutations in dystrophin. Whether aberrant neuromuscular synapse structure is an indirect consequence of muscle degeneration or a direct result of loss of dystrophin function is not known. Rational design of truncated dystrophins has enabled the design of expression cassettes highly effective at preventing muscle degeneration in mouse models of DMD using gene therapy. Here we examined the functional capacity of a minidystrophin (minidysGFP) and a microdystrophin (microdystrophin ΔR4-R23 ) transgene on the maturation and maintenance of neuromuscular junctions (NMJ) in mdx mice. We found that minidysGFP prevents fragmentation and the loss of postsynaptic folds at the NMJ. In contrast, microdystrophin ΔR4-R23 was unable to prevent synapse fragmentation in the limb muscles despite preventing muscle degeneration, although fragmentation was observed to temporally correlate with the formation of ringed fibers. Surprisingly, microdystrophin ΔR4-R23 increased the length of synaptic folds in the diaphragm muscles of mdx mice independent of muscle degeneration or the formation of ringed fibers. We also demonstrate that the number and depth of synaptic folds influences the density of voltage-gated sodium channels at the neuromuscular synapse in mdx, microdystrophin ΔR4-R23 / mdx and mdx:utrophin double knockout mice. Together, these data suggest that maintenance of the neuromuscular synapse is governed through its lateral association with the muscle cytoskeleton, and that dystrophin has a direct role in promoting the maturation of synaptic folds to allow more sodium channels into the junction.

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Nerve terminal contributes to acetylcholine receptor organization at the dystrophic neuromuscular junction of mdx mice

Cited by 24 publications

References 32 publications

Low doses of arginine butyrate derivatives improve dystrophic phenotype and restore membrane integrity in DMD models

Low doses of arginine butyrate derivatives improve dystrophic phenotype and restore membrane integrity in DMD models

Effects of in vivo injury on the neuromuscular junction in healthy and dystrophic muscles

Truncated dystrophins can influence neuromuscular synapse structure

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