Ultrastructural Changes in Diaphragm Neuromuscular Junctions in a Severe Mouse Model for Spinal Muscular Atrophy and Their Prevention by Bifunctional U7 snRNA Correcting SMN2 Splicing

Neuromuscul Disord. 2010 Nov;20(11):744-52. doi: 10.1016/j.nmd.2010.06.010. Epub 2010 Sep 15.

Abstract

In Spinal Muscular Atrophy (SMA), the SMN1 gene is deleted or inactivated. Because of a splicing problem, the second copy gene, SMN2, generates insufficient amounts of functional SMN protein, leading to the death of spinal cord motoneurons. For a "severe" mouse SMA model (Smn -/-, hSMN2 +/+; with affected pups dying at 5-7 days), which most closely mimicks the genetic set-up in human SMA patients, we characterise SMA-related ultrastructural changes in neuromuscular junctions (NMJs) of two striated muscles with discrete functions. In the diaphragm, but not the soleus muscle of 4-days old SMA mice, mitochondria on both sides of the NMJs degenerate, and perisynaptic Schwann cells as well as endoneurial fibroblasts show striking changes in morphology. Importantly, NMJs of SMA mice in which a modified U7 snRNA corrects SMN2 splicing and delays or prevents SMA symptoms are normal. This ultrastructural study reveals novel features of NMJ alterations - in particular the involvement of perisynaptic Schwann cells - that may be relevant for human SMA pathogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Diaphragm / pathology
  • Diaphragm / ultrastructure*
  • Disease Models, Animal
  • Mice
  • Mice, Transgenic
  • Microscopy, Electron, Transmission
  • Mitochondria / diagnostic imaging
  • Mitochondria / pathology
  • Motor Neurons / pathology
  • Motor Neurons / ultrastructure
  • Muscle, Skeletal / diagnostic imaging
  • Muscle, Skeletal / pathology
  • Muscular Atrophy, Spinal / genetics
  • Muscular Atrophy, Spinal / pathology*
  • Neuromuscular Junction / genetics
  • Neuromuscular Junction / pathology
  • Neuromuscular Junction / ultrastructure*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Survival of Motor Neuron 2 Protein / genetics
  • Ultrasonography

Substances

  • Survival of Motor Neuron 2 Protein