Pre- and postsynaptic changes in the neuromuscular junction in dystrophic mice

Area of Science:

• Neuromuscular Biology
• Muscle Physiology
• Disease Pathology

Background:

• Duchenne muscular dystrophy (DMD) is characterized by muscle weakness and impaired repair.
• Research has primarily focused on muscle fibers, neglecting the neuromuscular junction (NMJ).
• Previous studies in mdx mice revealed NMJ alterations and transmission failure post-injury.

Purpose of the Study:

• To investigate pre- vs. postsynaptic morphology and subsynaptic nuclei at the NMJ in healthy (WT) vs. mdx mice.
• To quantify age- and mdx-dependent changes in NMJ structure.
• To understand the NMJ's role in DMD progression.

Main Methods:

• Quantification of terminal nerve discontinuity and branching in adult mice.
• Calculation of NMJ occupancy (presynaptic vesicle footprint vs. motor endplate).
• Analysis of subsynaptic nuclei number and density.

Main Results:

• Mdx mice exhibited increased nerve discontinuity and branching compared to WT mice, with age-dependent changes.
• NMJ occupancy was altered in mdx mice, indicating a dissociation between pre- and postsynaptic structures, independent of age.
• A nearly two-fold increase in subsynaptic nuclei number and density was observed in mdx mice.

Conclusions:

• The neuromuscular junction undergoes substantial remodeling during Duchenne muscular dystrophy progression.
• This remodeling involves plasticity in both presynaptic and postsynaptic components of the NMJ.
• NMJ structural changes may contribute to impaired neuromuscular transmission and muscle function in DMD.