Neuropilin 1 sequestration by neuropathogenic mutant glycyl-tRNA synthetase is permissive to vascular homeostasis

James N. Sleigh,Na Wei,Adriana Gómez-Martín,Giampietro Schiavo,Ge Bai,Xiang-Lei Yang

doi:10.1038/s41598-017-10005-w

Abstract

The mechanism by which dominantly inherited mutations in the housekeeping gene GARS, which encodes glycyl-tRNA synthetase (GlyRS), mediate selective peripheral nerve toxicity resulting in Charcot-Marie-Tooth disease type 2D (CMT2D) is still largely unresolved. The transmembrane receptor protein neuropilin 1 (Nrp1) was recently identified as an aberrant extracellular binding partner of mutant GlyRS. Formation of the Nrp1/mutant GlyRS complex antagonises Nrp1 interaction with one of its main natural ligands, vascular endothelial growth factor-A (VEGF-A), contributing to neurodegeneration. However, reduced extracellular binding of VEGF-A to Nrp1 is known to disrupt post-natal blood vessel development and growth. We therefore analysed the vascular system at early and late symptomatic time points in CMT2D mouse muscles, retina, and sciatic nerve, as well as in embryonic hindbrain. Mutant tissues show no difference in blood vessel diameter, density/growth, and branching from embryonic development to three months, spanning the duration over which numerous sensory and neuromuscular phenotypes manifest. Our findings indicate that mutant GlyRS-mediated disruption of Nrp1/VEGF-A signalling is permissive to maturation and maintenance of the vasculature in CMT2D mice.

Highlights

GARS is a widely and constitutively expressed gene that encodes glycyl-tRNA synthase (GlyRS), which serves to covalently attach glycine to its transfer RNA, priming it for protein translation[1]
Given that 1) mutant glycyl-tRNA synthetase (GlyRS) competes with vascular endothelial growth factor-A (VEGF-A) for Nrp[1] binding10, 2) GlyRS is secreted[7, 10, 25] and found circulating in serum of humans and mice[25], and 3) vascular impairment can contribute to neurodegeneration[26], we decided to assess the effect of mutant GlyRS on the vascular system of the GarsC201R/+ murine model of Charcot-Marie-Tooth disease type 2D (CMT2D)
Neomorphic Nrp[1] binding and disturbance of neuropilin 1 (Nrp1)/VEGF-A signalling has been confirmed for a number of GlyRS mutants, including P234KY10

Summary

Introduction

GARS is a widely and constitutively expressed gene that encodes glycyl-tRNA synthase (GlyRS), which serves to covalently attach glycine to its transfer RNA (tRNA), priming it for protein translation[1]. Published work suggests that these neomorphic regions cause mutant GlyRS to aberrantly bind to the transmembrane receptor neuropilin 1 (Nrp1)[10], amongst other proteins[8]. VEGF-A functions in diverse neuronal processes[14, 15], and a mild reduction in VEGF-A causes progressive motor neuron degeneration in mice[16], partially explaining why antagonisation of Nrp1/VEGF-A signalling could be contributing to the neuronal pathology in CMT2D10. Mutating the VEGF-A-binding site of Nrp[1] does not phenocopy the severity of full Nrp[1] knockout mice, it causes a post-natal impairment in angiogenesis and arteriogenesis[21, 22], resembling the milder phenotype of mice expressing VEGF-A isoforms lacking the Nrp1-binding site[23]. Given that 1) mutant GlyRS competes with VEGF-A for Nrp[1] binding10, 2) GlyRS is secreted[7, 10, 25] and found circulating in serum of humans and mice[25], and 3) vascular impairment can contribute to neurodegeneration[26], we decided to assess the effect of mutant GlyRS on the vascular system of the GarsC201R/+ murine model of CMT2D

Methods

Results

Conclusion