RESUMO
Selective neuronal loss is a hallmark of neurodegenerative diseases, which, counterintuitively, are often caused by mutations in widely expressed genes. Charcot-Marie-Tooth (CMT) diseases are the most common hereditary peripheral neuropathies, for which there are no effective therapies. A subtype of these diseases--CMT type 2D (CMT2D)--is caused by dominant mutations in GARS, encoding the ubiquitously expressed enzyme glycyl-transfer RNA (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. 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 signalling 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 that the VEGF-Nrp1 signalling axis is an actionable target for treating CMT2D.
Assuntos
Ligação Competitiva , Doença de Charcot-Marie-Tooth/metabolismo , Glicina-tRNA Ligase/metabolismo , Animais , Axônios/enzimologia , Axônios/metabolismo , Axônios/patologia , Linhagem Celular , Sobrevivência Celular , Doença de Charcot-Marie-Tooth/tratamento farmacológico , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/patologia , Feminino , Glicina-tRNA Ligase/química , Glicina-tRNA Ligase/genética , Ligantes , Masculino , Camundongos , Modelos Moleculares , Neurônios Motores/enzimologia , Neurônios Motores/metabolismo , Neurônios Motores/patologia , Destreza Motora/efeitos dos fármacos , Mutação/genética , Neuropilina-1/deficiência , Neuropilina-1/genética , Neuropilina-1/metabolismo , Ligação Proteica , Multimerização Proteica , Transdução de Sinais , Fator A de Crescimento do Endotélio Vascular/metabolismo , Fator A de Crescimento do Endotélio Vascular/farmacologia , Fator A de Crescimento do Endotélio Vascular/uso terapêuticoRESUMO
Proteins can self-organize into spatial patterns via non-linear dynamic interactions on cellular membranes. Modelling and simulations have shown that small GTPases can generate patterns by coupling guanine nucleotide exchange factors (GEF) to effectors, generating a positive feedback of GTPase activation and membrane recruitment. Here, we reconstituted the patterning of the small GTPase Rab5 and its GEF/effector complex Rabex5/Rabaptin5 on supported lipid bilayers. We demonstrate a 'handover' of Rab5 from Rabex5 to Rabaptin5 upon nucleotide exchange. A minimal system consisting of Rab5, RabGDI and a complex of full length Rabex5/Rabaptin5 was necessary to pattern Rab5 into membrane domains. Rab5 patterning required a lipid membrane composition mimicking that of early endosomes, with PI(3)P enhancing membrane recruitment of Rab5 and acyl chain packing being critical for domain formation. The prevalence of GEF/effector coupling in nature suggests a possible universal system for small GTPase patterning involving both protein and lipid interactions.