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Characterization of neuromuscular synapse function abnormalities in multiple Duchenne muscular dystrophy mouse models
Author(s) -
Pijl Elizabeth M.,
Putten Maaike,
Niks Erik H.,
Verschuuren Jan J. G. M.,
AartsmaRus Annemieke,
Plomp Jaap J.
Publication year - 2016
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/ejn.13249
Subject(s) - utrophin , neuromuscular junction , duchenne muscular dystrophy , neuromuscular transmission , dystrophin , acetylcholine receptor , mdx mouse , synaptogenesis , endocrinology , acetylcholine , medicine , postsynaptic potential , agrin , biology , neurotransmission , synapse , neuroscience , receptor
Duchenne muscular dystrophy ( DMD ) is an X‐linked myopathy caused by dystrophin deficiency. Dystrophin is present intracellularly at the sarcolemma, connecting actin to the dystrophin‐associated glycoprotein complex. Interestingly, it is enriched postsynaptically at the neuromuscular junction ( NMJ ), but its synaptic function is largely unknown. Utrophin, a dystrophin homologue, is also concentrated at the NMJ , and upregulated in DMD . It is possible that the absence of dystrophin at NMJ s in DMD causes neuromuscular transmission defects that aggravate muscle weakness. We studied NMJ function in mdx mice (lacking dystrophin) and wild type mice. In addition, mdx/utrn +/− and mdx/utrn −/− mice (lacking utrophin) were used to investigate influences of utrophin levels. The three Duchenne mouse models showed muscle weakness when comparatively tested in vivo , with mdx/utrn −/− mice being weakest. Ex vivo muscle contraction and electrophysiological studies showed a reduced safety factor of neuromuscular transmission in all models. NMJ s had ~ 40% smaller miniature endplate potential amplitudes compared with wild type, indicating postsynaptic sensitivity loss for the neurotransmitter acetylcholine. However, nerve stimulation‐evoked endplate potential amplitudes were unchanged. Consequently, quantal content (i.e. the number of acetylcholine quanta released per nerve impulse) was considerably increased. Such a homeostatic compensatory increase in neurotransmitter release is also found at NMJ s in myasthenia gravis, where autoantibodies reduce acetylcholine receptors. However, high‐rate nerve stimulation induced exaggerated endplate potential rundown. Study of NMJ morphology showed that fragmentation of acetylcholine receptor clusters occurred in all models, being most severe in mdx/utrn −/− mice. Overall, we showed mild ‘myasthenia‐like’ neuromuscular synaptic dysfunction in several Duchenne mouse models, which possibly affects muscle weakness and degeneration.