Cryptic amyloidogenic elements in mutant NEFH causing Charcot-Marie-Tooth 2 trigger aggresome formation and neuronal death

Abstract

Neurofilament heavy chain (NEFH) gene was recently identified to cause autosomal dominant axonal Charcot-Marie-Tooth disease (CMT2cc). However, the clinical spectrum of this condition and the physio-pathological pathway remain to be delineated. We report 12 patients from two French families with axonal dominantly inherited form of CMT caused by two new mutations in the NEFH gene. A remarkable feature was the early involvement of proximal muscles of the lower limbs associated with pyramidal signs in some patients. Nerve conduction velocity studies indicated a predominantly motor axonal neuropathy. Unique deletions of two nucleotides causing frameshifts near the end of the NEFH coding sequence were identified: in family 1, c.3008_3009del (p.Lys1003Argfs*59), and in family 2 c.3043_3044del (p.Lys1015Glyfs*47). Both frameshifts lead to 40 additional amino acids translation encoding a cryptic amyloidogenic element. Consistently, we show that these mutations cause protein aggregation which are recognised by the autophagic pathway in motoneurons and triggered caspase 3 activation leading to apoptosis in neuroblastoma cells. Using electroporation of chick embryo spinal cord, we confirm that NEFH mutants form aggregates in vivo and trigger apoptosis of spinal cord neurons. Thus, our results provide a physiological explanation for the overlap between CMT and amyotrophic lateral sclerosis (ALS) clinical features in affected patients.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-017-0457-1) contains supplementary material, which is available to authorized users.

Whole-Genome Linkage Analysis with Whole-Exome Sequencing Identifies a Novel Frameshift Variant in <b><i>NEFH</i></b> in a Chinese Family with Charcot-Marie-Tooth 2: A Novel Variant in <b><i>NEFH</i></b> for Charcot-Marie-Tooth 2

“…In addition, the deep tendon reflex was absent in both upper and lower limbs. The phenotype was consistent with that shown in a previous study in which patients who carried another mutation of NEFH had muscle weakness in the proximal muscle of the lower and distal muscle of the upper limbs in the late stage of CMT2CC [10]. The data revealed that the phenotype of CMT2CC in a Chinese population appeared identical to that in a western population.…”

“…2). Thus, the expression of mutant NEFH led to aggregation of NEFH protein as in a previous report of mutant NF proteins leading to similar aberrant aggregation [10-12]. …”

“…Furthermore, 2 new mutations in NEFH were verified in 2 French families with dominant CMT2: c.3008_3009del: p.Lys1003Argfs*59 and c.3043_3044del: p.Lys1015Glyfs*47 [10]. The novel mutations both contained CAE domains.…”

A nonstop variant in REEP1 causes peripheral neuropathy by unmasking a 3′UTR-encoded, aggregation-inducing motif

“…Our study, therefore, is also the first to confirm the general concept of CAE, and to corroborate its pathogenic relevance. Strikingly, the disease associated with the unmasking of CAEs in both genes is CMT2 (Hoyer et al., ; Jacquier et al., ; Rebelo et al., ; present study). This suggests that susceptibility to CAE‐mediated aggregation is particularly high in peripheral axons.…”

“…A somewhat related phenomenon, however, has been reported very recently. Two studies investigated distinct frameshift variants in the NEFH gene (Jacquier et al., ; Rebelo et al., ). These variants all localized to the terminal exon and are thus immune to NMD.…”