Spinal Motoneuron TMEM16F Acts at C-boutons to Modulate Motor Resistance and Contributes to ALS Pathogenesis

Neuronal Ca²⁺ entry elicited by electrical activity contributes to information coding via activation of K⁺ and Cl^- channels. While Ca²⁺-dependent K⁺ channels have been extensively studied, the molecular identity and role of Ca²⁺-activated Cl^- channels (CaCCs) remain unclear. Here, we demonstrate that TMEM16F governs a Ca²⁺-activated Cl^- conductance in spinal motoneurons. We show that TMEM16F is expressed in synaptic clusters facing pre-synaptic cholinergic C-boutons in α-motoneurons of the spinal cord. Mice with targeted exon deletion in Tmem16f display decreased motor performance under high-demanding tasks attributable to an increase in the recruitment threshold of fast α-motoneurons. Remarkably, loss of TMEM16F function in a mouse model of amyotrophic lateral sclerosis (ALS) significantly reduces expression of an activity-dependent early stress marker and muscle denervation, delays disease onset, and preserves muscular strength only in male ALS mice. Thus, TMEM16F controls motoneuron excitability and impacts motor resistance as well as motor deterioration in ALS.