Muscle-derived miR-126 regulates TDP-43 axonal local synthesis and NMJ integrity in ALS models

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Amyotrophic lateral sclerosis (ALS) is characterized by neuromuscular junction (NMJ) disruption and neurodegeneration. Recent findings highlight a pivotal role for TAR DNA-binding protein 43 (TDP-43) in forming axonal pathological condensates and facilitating NMJ disruption through inhibition of local protein synthesis. However, the mechanisms that drive local TDP-43 accumulation remain unknown. Here we identify that the TDP-43 axonal accumulation in peripheral nerves of SOD1 patients and mice stems from its aberrant local synthesis. This is a non-cell-autonomous process driven by muscle-derived miR-126a-5p extracellular vesicles (EVs). Inhibiting muscle secretion of miR-126a-5p prompts presynaptic TDP-43 synthesis and accumulation, which disrupts axonal translation and causes NMJ degeneration. Introducing miR-126 to SOD1G93A mice, primary co-cultures and human induced pluripotent stem cell (iPSC)-derived co-cultures with ALS mutations exhibits neuroprotective effects and delays motor decline. These findings identify a transcellular communication axis between muscles and motor neurons that regulates axonal local synthesis and NMJ maintenance, offering insights into ALS onset and progression. Ionescu, Ankol et al. show that, in ALS mouse and iPSC models, TDP-43 aggregation at NMJs stems from aberrant axonal translation, normally repressed by muscle EV-derived miR126. Loss of miR126 in ALS increases TDP-43 buildup, impairs local synthesis and triggers degeneration.

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