GDF5 as a Multimodal Protector of the Motor Unit in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis is characterized by the progressive dismantling of the motor unit. While “dying back” hypothesis suggests that peripheral neuromuscular dysfunction precedes motor neuron loss, the molecular mechanisms limiting endogenous compensatory responses remain poorly understood. We longitudinally examined neuromuscular decline and GDF5-SMAD1/5/8 signaling in SOD1 ^G93A mice. Our findings revealed a translational checkpoint linked to the lncRNA Myoparr that suppresses GDF5 production at symptom onset. To overcome this deficit, we delivered AAV9-GDF5 at the symptomatic stage. GDF5 supplementation restored SMAD signaling balance, shifting the motor unit from a pro-atrophic TGF-β-SMAD2/3 toward a pro-myogenic SMAD1/5 profile. Treatment preserved muscle mass, reduced mitochondrial reactive oxygen species, and maintained neuromuscular junction integrity, including peri-synaptic glial support. GDF5 also promoted molecular recovery of spinal MNs by enhancing homeostatic marker expression. Together, these findings identify GDF5 as a multimodal stabilizer of the motor unit and highlight its potential as therapeutic target in combinatorial strategies aimed at coupling motor unit stabilization with central neuroprotective interventions.