RESUMO
Mislocalization of the predominantly nuclear RNA/DNA binding protein, TDP-43, occurs in motor neurons of ~95% of amyotrophic lateral sclerosis (ALS) patients, but the contribution of axonal TDP-43 to this neurodegenerative disease is unclear. Here, we show TDP-43 accumulation in intra-muscular nerves from ALS patients and in axons of human iPSC-derived motor neurons of ALS patient, as well as in motor neurons and neuromuscular junctions (NMJs) of a TDP-43 mislocalization mouse model. In axons, TDP-43 is hyper-phosphorylated and promotes G3BP1-positive ribonucleoprotein (RNP) condensate assembly, consequently inhibiting local protein synthesis in distal axons and NMJs. Specifically, the axonal and synaptic levels of nuclear-encoded mitochondrial proteins are reduced. Clearance of axonal TDP-43 or dissociation of G3BP1 condensates restored local translation and resolved TDP-43-derived toxicity in both axons and NMJs. These findings support an axonal gain of function of TDP-43 in ALS, which can be targeted for therapeutic development.
Assuntos
Axônios/metabolismo , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/metabolismo , Inibição Psicológica , Proteínas Mitocondriais/metabolismo , Junção Neuromuscular/metabolismo , Esclerose Lateral Amiotrófica/tratamento farmacológico , Animais , Proteína C9orf72/genética , DNA Helicases , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/farmacologia , Modelos Animais de Doenças , Feminino , Humanos , Células-Tronco Pluripotentes Induzidas , Camundongos , Camundongos Endogâmicos C57BL , Mitocôndrias/efeitos dos fármacos , Proteínas Mitocondriais/química , Proteínas Mitocondriais/genética , Neurônios Motores , Doenças Neurodegenerativas/tratamento farmacológico , Junção Neuromuscular/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Neurônios Eferentes , Fosforilação , Proteínas de Ligação a Poli-ADP-Ribose , RNA Helicases , Proteínas com Motivo de Reconhecimento de RNARESUMO
Amyotrophic lateral sclerosis (ALS) is a fatal non-cell-autonomous neurodegenerative disease characterized by the loss of motor neurons (MNs). Mutations in CRMP4 are associated with ALS in patients, and elevated levels of CRMP4 are suggested to affect MN health in the SOD1G93A -ALS mouse model. However, the mechanism by which CRMP4 mediates toxicity in ALS MNs is poorly understood. Here, by using tissue from human patients with sporadic ALS, MNs derived from C9orf72-mutant patients, and the SOD1G93A -ALS mouse model, we demonstrate that subcellular changes in CRMP4 levels promote MN loss in ALS. First, we show that while expression of CRMP4 protein is increased in cell bodies of ALS-affected MN, CRMP4 levels are decreased in the distal axons. Cellular mislocalization of CRMP4 is caused by increased interaction with the retrograde motor protein, dynein, which mediates CRMP4 transport from distal axons to the soma and thereby promotes MN loss. Blocking the CRMP4-dynein interaction reduces MN loss in human-derived MNs (C9orf72) and in ALS model mice. Thus, we demonstrate a novel CRMP4-dependent retrograde death signal that underlies MN loss in ALS.