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

Selective neuronal loss is a hallmark of neurodegenerative diseases, which counter-intuitively are often caused by mutations in widely-expressed genes(1). Charcot-Marie-Tooth (CMT) diseases are the most common hereditary peripheral neuropathies, for which there are no effective therapies(2,3). 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 function(4). How mutations in GlyRS (GlyRS(CMT2D)) are linked to motor neuron vulnerability has remained elusive. Here we report that GlyRS(CMT2D) 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 GlyRS(CMT2D) 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 GlyRS(CMT2D) that antagonizes the VEGF/Nrp1 interaction, and indicate the VEGF/Nrp1 signaling axis is an actionable target for treating CMT2D.