Effects of Charcot-Marie-Tooth-linked mutations of the neurofilament light subunit on intermediate filament formation

Abstract

Neurofilaments (NFs) are the major intermediate filaments (IFs) of mature neurons. They play important roles in the structure and function of axons. Recently, two mutations in the neurofilament light (NFL) subunit have been identified in families affected by Charcot-Marie-Tooth (CMT) neuropathy type 2. We have characterized the effects of these NFL mutations on the formation of IF networks using a transient transfection system. Both mutations disrupted the self-assembly of human NFL. The Q333P mutant in the rod domain of NFL also disrupted the formation of rat and human NFL/NFM heteropolymers. The phenotypes produced by the P8R mutation in the head domain of NFL were less severe. The P8R mutant NFL co-polymerized with NFM to form bundled filaments and, less often, aggregates. Our results suggest that alterations in the formation of a normal IF network in neurons elicited by these NFL mutations may contribute to the development of Charcot-Marie-Tooth neuropathy.

Mutant small heat-shock protein 27 causes axonal Charcot-Marie-Tooth disease and distal hereditary motor neuropathy

“…network caused by mutations in NEFL may contribute to the development of neuropathy 22 . We therefore studied whether mutant HSP27 affects neurofilament assembly.…”

“…We therefore studied whether mutant HSP27 affects neurofilament assembly. Human neurofilament light protein (NF-L) can self-assemble into homopolymeric filaments when expressed in SW13.cl.2Vim -cells, an adrenal carcinoma cell line that does not contain an endogenous intermediate filament network 22 . We cotransfected human NEFL and wild-type HSPB1 in these cells and found that NF-L formed a thin filamentous network and, occasionally, thick filament bundles in the presence of overexpressed HSPB1.…”

The cytoskeleton in neurodegenerative diseases

“…For example, both the Q333P mutation in the rod domain and to a lesser degree the P8R mutation in the head domain of NF-L disrupt the self-assembly of NF-L and the formation of NF-L/NF-M heteropolymers in a transient transfection system [64]. Codon deletions and insertions in the phosphorylation domain (KSP) of the tail region of NF-H have been reported in sporadic cases of ALS, and mutations in the NF-L gene located on chromosome 8 have been reported in several cases of CMT with neuroaxonal degeneration [7][8][9][10][11][12][13][14][15][16][17].…”

The Schwann Cell-Axon Link in Normal Condition or Neuro-Degenerative Diseases: An Immunocytochemical Approach

“…This chronic progressive illness has two possible origins: axonal, CMT-II (neurofilament, KIF 1B or Rab7 protein mutations, among others), or Schwann cell, CMT-I (PMP-22, Conexin 32, P0 protein mutations, among others, Mersiyanova et al, 2000, Pérez-Ollé et al, 2002, Verhoeven et al, 2003, Zhao et al, 2001. Regardless the initial alteration, all CMT end in a functional axonopathy, which emphasize the importance of Schwann cell-axon relationship in the context of the gene expression of both cells.…”