Neuromuscular Junction Changes in a Mouse Model of Charcot-Marie-Tooth Disease Type 4C.

Silvia Cipriani,Andreas Roos,Jean-Jacques Médard,Hanns Lochmüller,Roman Chrast,Vietxuan Phan,Rita Horvath,Sally Spendiff

doi:10.3390/ijms19124072

Abstract

The neuromuscular junction (NMJ) appears to be a site of pathology in a number of peripheral nerve diseases. Charcot-Marie-Tooth (CMT) 4C is an autosomal recessive, early onset, demyelinating neuropathy. Numerous mutations in the SH3TC2 gene have been shown to underlie the condition often associated with scoliosis, foot deformities, and reduced nerve conduction velocities. Mice with exon 1 of the Sh3tc2 gene knocked out demonstrate many of the features seen in patients. To determine if NMJ pathology is contributory to the pathomechanisms of CMT4C we examined NMJs in the gastrocnemius muscle of SH3TC2-deficient mice. In addition, we performed proteomic assessment of the sciatic nerve to identify protein factors contributing to the NMJ alterations and the survival of demyelinated axons. Morphological and gene expression analysis of NMJs revealed a lack of continuity between the pre- and post-synaptic apparatus, increases in post-synaptic fragmentation and dispersal, and an increase in expression of the gamma subunit of the acetylcholine receptor. There were no changes in axonal width or the number of axonal inputs to the NMJ. Proteome investigations of the sciatic nerve revealed altered expression of extracellular matrix proteins important for NMJ integrity. Together these observations suggest that CMT4C pathology includes a compromised NMJ even in the absence of changes to the innervating axon.

Highlights

Charcot-Marie Tooth (CMT) disease was first reported over a hundred years ago [1]
While amyotrophic lateral sclerosis (ALS) is predominantly characterised by the loss of upper and lower motor neurons, the SOD1G93A mouse has demonstrated integrity of the neuromuscular junction (NMJ) is important in the pathomechanisms of the condition with NMJ alterations appearing early in the disease course [19]
Our phenomenological analysis demonstrating an increase in endplate fragmentation and dispersal, increased pre-synaptic branching, and a reduction in the degree of overlap of pre- and post-synaptic apparatus, suggest CMT subtype 4C (CMT4C) should be added to the list of neuropathies that are accompanied by NMJ alterations

Summary

Introduction

Charcot-Marie Tooth (CMT) disease was first reported over a hundred years ago [1]. Research in a well-defined Norwegian population demonstrated a prevalence of 1/2500 [2] suggesting it is one of the most frequent forms of inherited neurological disorders [3]. Several genetic defects have been linked to the demyelinating forms of the disease [3,4,5,6,7], which can be dominant (CMT1) or recessive (CMT4). CMT subtype 4C (CMT4C) is an autosomal recessive form of demyelinating neuropathy usually with an early onset [3,7,8]. Expression of SH3TC2 has recently been described in in cultured Schwann cells [11]. It is a well conserved 144 kDa protein containing Scr homology 3 (SH3) and tetratricopeptide repeat (TRP) domains, suggesting a role as scaffold protein [6,12]. Its role in myelination is supported by its localisation to the plasma membrane and to the perinuclear endocytic recycling compartment [8,12,13,14]

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Conclusion