CMT2D neuropathy is linked to the neomorphic binding activity of glycyl-tRNA synthetase

Abstract

Summary Selective neuronal loss is a hallmark of neurodegenerative diseases, which counter-intuitively are often caused by mutations in widely-expressed genes1. Charcot-Marie-Tooth (CMT) diseases are the most common hereditary peripheral neuropathies, for which there are no effective therapies2,3. A subtype of the diseases—CMT2D—is caused by dominant mutations in GARS, encoding the ubiquitously expressed enzyme glycyl-tRNA synthetase (GlyRS). Despite the broad requirement of GlyRS for protein biosynthesis in all cells, mutations in this gene cause a selective degeneration of peripheral axons leading to deficits in distal motor function4. How mutations in GlyRS (GlyRSCMT2D) are linked to motor neuron vulnerability has remained elusive. Here we report that GlyRSCMT2D acquires a neomorphic binding activity that directly antagonizes an essential signaling pathway for motor neuron survival. We find that CMT2D mutations alter the conformation of GlyRS, enabling GlyRSCMT2D to bind the Neuropilin 1 (Nrp1) receptor. This aberrant interaction competitively interferes with the binding of the cognate ligand vascular endothelial growth factor (VEGF) to Nrp1. Genetic reduction of Nrp1 in mice worsens CMT2D symptoms, whereas enhanced expression of VEGF improves motor function. These findings link the selective pathology of CMT2D to the neomorphic binding activity of GlyRSCMT2D that antagonizes the VEGF/Nrp1 interaction, and indicate the VEGF/Nrp1 signaling axis is an actionable target for treating CMT2D.

Trk receptor signaling and sensory neuron fate are perturbed in human neuropathy caused by Gars mutations

“…Although we do not directly show that sensory identity is perturbed during embryonic development, we do observe defective sensory nerve branching in the mutant hind paw at E13.5 ( Fig. 5F), similar to the previously reported embryonic impairment in facial motor neuron migration (18) and suggestive of developmental onset. However, the subtype identity defect appears to be sensory specific, as mutant Gars mice do not show a difference in the proportion of α-and γ-motor neurons (SI Appendix, Fig.…”

“…CMT2D-associated mutant GlyRS was recently shown to aberrantly bind to the neuronal receptor protein NRP1 and antagonize its activity (18). Although NRP1 was the focus of that study, mutant GlyRS was shown to interact with a number of other proteins found on the neuronal surface, albeit to a lesser degree (18).…”

“…CMT2D-linked mutations in GARS have previously been shown to confer neomorphic binding activity on mutant GlyRS, causing it to interact with an extracellular domain of Nrp1 and block VEGF signaling (18). As tropomyosin receptor kinase (Trk) receptors play a key role in sensory neuron development and differentiation (54), and sensory neuron fate is perturbed in CMT2D mice, we hypothesized that mutant GlyRS may also spuriously interact with one or more of the Trk receptors.…”

“…CMT therefore manifests through malfunctioning of the complex interplay between developmental, maturation, and survival programs, which has important implications for therapeutic timing. neuropilin 1 (NRP1), which antagonizes VEGF signaling (18). This aberrant binding and noncell autonomous toxicity is contingent upon GlyRS secretion, which occurs from a number of different cell types in culture and is unaffected by neuropathyassociated mutations (17)(18)(19).…”

Acetylation promotes TyrRS nuclear translocation to prevent oxidative damage

“…Collectively, these results suggested that regulation occurred due to negative feedback among TyrRS, PARP1, and SIRT1 under oxidative stress. In addition to their aminoacylation functions in protein synthesis, many aminoacyl-tRNA synthetases, including TyrRS, have been shown to take on multiple roles (41)(42)(43). Specifically, TyrRS was found to act as a sensor for oxidative stress after translocating to the nucleus, where it activates DNA damage repair genes that are downstream of E2F1 (7).…”