Characterization of neuromuscular synapse function abnormalities in multiple Duchenne muscular dystrophy mouse models

Area of Science:

• Neuromuscular Biology
• Muscle Physiology
• Synaptic Transmission

Background:

• Duchenne muscular dystrophy (DMD) results from dystrophin deficiency, impacting muscle sarcolemma integrity.
• Dystrophin's role at the neuromuscular junction (NMJ) is unclear, though it's enriched postsynaptically.
• Utrophin, a dystrophin homolog, is also at the NMJ and upregulated in DMD.

Purpose of the Study:

• To investigate neuromuscular junction (NMJ) function in Duchenne muscular dystrophy (DMD) mouse models.
• To assess the impact of dystrophin and utrophin deficiency on neuromuscular transmission.
• To explore potential 'myasthenia-like' synaptic dysfunction in DMD.

Main Methods:

• Electrophysiological recordings of NMJ function in mdx mice (dystrophin-deficient) and mdx/utrophin-deficient mice.
• Ex vivo muscle contraction assays to measure muscle weakness.
• Morphological analysis of NMJ structure and acetylcholine receptor clusters.

Main Results:

• All DMD models exhibited reduced neuromuscular transmission safety factors and smaller miniature endplate potentials.
• Quantal content was significantly increased, indicating compensatory neurotransmitter release.
• Acetylcholine receptor clusters fragmented, most severely in mdx/utrn(-/-) mice, suggesting postsynaptic dysfunction.

Conclusions:

• DMD mouse models display 'myasthenia-like' neuromuscular synaptic dysfunction.
• This synaptic impairment, characterized by altered acetylcholine signaling and receptor fragmentation, likely exacerbates muscle weakness and degeneration in DMD.
• Utrophin deficiency worsens NMJ dysfunction in dystrophin-deficient mice.