Charcot-Marie-Tooth disease (CMT) is a length-dependent peripheral neuropathy. The aminoacyl-tRNA synthetases constitute the largest protein family implicated in CMT. Aminoacyl-tRNA synthetases are predominantly cytoplasmic, but are also present in the nucleus. Here we show that a nuclear function of tyrosyl-tRNA synthetase (TyrRS) is implicated in a Drosophila model of CMT. CMT-causing mutations in TyrRS induce unique conformational changes, which confer capacity for aberrant interactions with transcriptional regulators in the nucleus, leading to transcription factor E2F1 hyperactivation. Using neuronal tissues, we reveal a broad transcriptional regulation network associated with wild-type TyrRS expression, which is disturbed when a CMT-mutant is expressed. Pharmacological inhibition of TyrRS nuclear entry with embelin reduces, whereas genetic nuclear exclusion of mutant TyrRS prevents hallmark phenotypes of CMT in the Drosophila model. These data highlight that this translation factor may contribute to transcriptional regulation in neurons, and suggest a therapeutic strategy for CMT.

Dominant mutations in tyrosyl-tRNA synthetase (YARS1) and six other tRNA ligases cause Charcot-Marie-Tooth peripheral neuropathy (CMT). Loss of aminoacylation is not required for their pathogenicity, suggesting a gain-of-function disease mechanism. By an unbiased genetic screen inDrosophila, we link YARS1 dysfunction to actin cytoskeleton organization. Biochemical studies uncover yet unknown actin-bundling property of YARS1 to be enhanced by a CMT mutation, leading to actin disorganization in theDrosophilanervous system, human SH-SY5Y neuroblastoma cells, and patient-derived fibroblasts. Genetic modulation of F-actin organization improves hallmark electrophysiological and morphological features in neurons of flies expressing CMT-causing YARS1 mutations. Similar beneficial effects are observed in flies expressing a neuropathy-causing glycyl-tRNA synthetase. Hence, in this work, we show that YARS1 is an evolutionary-conserved F-actin organizer which links the actin cytoskeleton to tRNA-synthetase-induced neurodegeneration.

Background: Autosomal recessive axonal neuropathy with neuromyotonia has been linked to loss of functional HINT1. The disease is particularly prevalent in Central and South-East Europe, Turkey and Russia due to the high carrier frequency of the c.110G > C (p.Arg37Pro) founder variant. Results: In a cohort of 748 Norwegian patients with suspected peripheral neuropathy, we identified two seemingly unrelated individuals, compound heterozygous for a new variant (c.284G > A, p.Arg95Gln) and the most common pathogenic founder variant (c.110G > C, p.Arg37Pro) in the HINT1 gene. Probands presented with motor greater than sensory neuropathy of various onset, accompanied by muscle stiffness and cramps in the limbs. Furthermore, they displayed non-classical symptoms, including pain in the extremities and signs of central nervous system involvement. Haplotype analysis in both patients revealed a common chromosomal background for p.Arg95Gln; moreover, the variant was identified in Swedish carriers. Functional characterization in HINT1-knockout and patient-derived cellular models, and in HNT1-knockout yeast, suggested that the new variant is deleterious for the function of HINT1 and provided mechanistic insights allowing patient stratification for future treatment strategies. Conclusion: Our findings broaden the genetic epidemiology of HINT1-neuropathy and have implications for molecular diagnostics of inherited peripheral neuropathies in Scandinavia.

Charcot-Marie-Tooth (CMT) disease is the most common inherited neuromuscular disorder characterized by wide clinical, genetic and pathomechanistic heterogeneity. Recently, the gene encoding peripheral myelin protein 2 (PMP2) was identified as a novel cause for CMT neuropathy with three mutations that structurally cluster together (p.Ile43Asn, p.Thr51Pro, p.Ile52Thr) reported in five families. Using whole exome sequencing and cohort screening we identified two novel missense substitutions in PMP2 in Bulgarian (p.Met114Thr, c.341C > T) and German (p.Val115Ala, c.344 T > C) families. The mutations affect adjacent and highly conserved amino acid residues outside of the known mutation-rich region in the protein. Crystal structure analysis positions the affected residues within a cluster of highly conserved fatty acid coordinating residues implying their functional significance. The clinical, electrophysiological and imaging features in both families were consistent with a childhood onset polyneuropathy with variable patterns of demyelination, slow to very slow progression, and most severe involvement of the peroneal muscles. We expand the genetic and phenotypic spectrum of PMP2-related peripheral neuropathy. Our findings reveal a second mutational cluster in the protein.

In the past decade, mutations in LRSAM1 were identified as the genetic cause of both dominant and recessive forms of axonal CMT type 2P (CMT2P). Despite demonstrating different inheritance patterns, dominant CMT2P is usually characterized by relatively mild, slowly progressive axonal neuropathy, mainly involving lower limbs, with age of onset between the second and fifth decades of life. Asymptomatic individuals were identified in several pedigrees exemplifying the strong phenotypic variability of these patients requiring serial clinical evaluation to establish correct diagnosis; in this respect, magnetic resonance imaging of lower-limb musculature showing fatty atrophy might be helpful in detecting subclinical gene mutation carriers. LRSAM1 is a universally expressed RING-type E3 ubiquitin protein ligase catalysing the final step in the ubiquitination cascade. Strikingly, TSG101 remains the only known ubiquitination target hampering our mechanistic understanding of the role of LRSAM1 in the cell. The recessive CMT mutations lead to complete loss of LRSAM1, contrary to the heterozygous dominant variants. These tightly cluster in the C-terminal RING domain highlighting its importance in governing the CMT disease. The domain is crucial for the ubiquitination function of LRSAM1 and CMT mutations disrupt its function, however it remains unknown how this leads to the peripheral neuropathy. Additionally, recent studies have linked LRSAM1 with other neurodegenerative diseases of peripheral and central nervous systems. In this review we share our experience with the challenging clinical diagnosis of CMT2P and summarize the mechanistic insights about the LRSAM1 dysfunction that might be helpful for the neurodegenerative field at large.