Mutations in the neurofilament light gene linked to Charcot‐Marie‐Tooth disease cause defects in transport

Abstract

Neurofilament light gene mutations have been linked to a subset of patients with Charcot-Marie-Tooth disease, the most common inherited motor and sensory neuropathy. We have previously shown that Charcot-Marie-Tooth-linked mutant neurofilament light assembles abnormally in non-neuronal cells. In this study, we have characterized the effects of expression of mutant neurofilament light proteins on axonal transport in a neuronal cell culture model. We demonstrated that the Charcot-Marie-Tooth-linked neurofilament light mutations: (i) affect the axonal transport of mutant neurofilaments; (ii) have a dominant-negative effect on the transport of wild-type neurofilaments; (iii) affect the transport of mitochondria and the anterograde axonal transport marker human amyloid precursor protein; (iv) result in alterations of retrograde axonal transport and (v) cause fragmentation of the Golgi apparatus. Increased neuritic degeneration was observed in neuronal cells overexpressing neurofilament light mutants. Our results suggest that these generalized axonal transport defects could be responsible for the neuropathy in Charcot-Marie-Tooth disease.

NEFL Pro22Arg mutation in Charcot-Marie-Tooth disease type 1

“…In previous studies, Pro22Ser and Pro22Thr mutants showed defects in filamentous network formation irregular aggregation in the SW13-cell, and the mutations abolish the Thr-Pro PDPK phosphorylation site in the NEFL head domain, which regulates filament assembly via phosphorylation (Pérez-Ollé et al 2005;Sasaki et al 2006). In our study, patients with the Pro22Arg mutation had the same demyelinating neuropathies as did patients with the Pro22Thr mutation; therefore, it seems that the Pro22Arg mutation also may abolish the Thr-Pro phosphorylation site of the head domain by PDPKs.…”

“…Neurofilament light chain polypeptide (NEFL), which consists of an N-terminal head, a central road, and a C-terminal tail domain, is one of the most abundant cytoskeletal components in the neuron (Brownlees et al 2002). Several missense mutations in the NEFL gene have been reported, and a number of these have been predicted to produce alterations in the formation of the intermediate filament network in neurons (Pérez-Ollé et al 2005;Sasaki et al 2006). Mutations in the NEFL gene were originally reported to be associated with CMT2E (De Jonghe et al 2001;Fabrizi et al 2004).…”

Neurofilament light chain polypeptide gene mutations in Charcot–Marie–Tooth disease: nonsense mutation probably causes a recessive phenotype

“…13 Functional studies have shown that missense mutant NEFL proteins disrupt the assembly with wild-type NEFL and with the NEFM and NEFH, and cause aggregation, resulting in the disruption of axonal neurofilament translocation and anterograde or retrograde axonal transport including mitochondria. [14][15][16] In this study, we found a homozygous nonsense mutation, Glu140-Stop, in one patient (case 2) in addition to four heterozygous missense mutations in five other patients. The parents of case 2 were first cousins, but they never complained of muscle weakness.…”

Intermediate Filaments in Neurodegenerative Diseases

“…The first two CMTassociated NEFL mutations, NFL P8R and NFL Q333P , were identified in respectively a Belgian and a Russian family. In addition to disturb the assembly of NFs, these mutations affect the axonal transport of wild-type and mutant NFs, but also the transport of mitochondria and human amyloid β protein precursor, resulting in alterations of retrograde axonal transport, fragmentation of the Golgi apparatus and increased neuritic degeneration [79,80]. The effect of these mutant proteins on filament assembly was dominant, since wild-type NFL could not rescue the assembly defect.…”

“…These mutations are located throughout the three functional domains of this protein (head, rod and tail) and consist of substitutions, deletions and frame-shift mutations. Co-expression of most NFL mutants with wild-type NFM or NFH subunits disrupted the NF cytoskeleton in vitro, resulting in the formation of aggregates within the cell body [79,80]. The first two CMTassociated NEFL mutations, NFL P8R and NFL Q333P , were identified in respectively a Belgian and a Russian family.…”