Postsynaptic remodeling and F-actin dysregulation in the Dctn1 Δ2–4 mouse model of motor neuron disease

Abstract The microtubule motor dynein and its co-adaptor dynactin govern organelle positioning within highly polarized neurons. The dynactin subunit p150 Glued , encoded by DCTN1 , is associated with motor neuron disease. The p150 Glued G59S mutation disrupts the microtubule-binding domain and drives selective motor neuron degeneration in patients and animal models. The p150 Glued microtubule-binding domain mediates the initiation of retrograde transport at axonal terminals and stabilizes presynaptic sites at neuromuscular junctions. Nevertheless, the key functions of p150 Glued and its microtubule-binding domain within postsynaptic compartments remain poorly defined. Using Dctn1 Δ2–4 mice, in which exons 2–4 of Dctn1 encoding the microtubule-binding domain are deleted, we performed morphological, biochemical, and cellular physiological analyses, together with genetic manipulation and pharmacological intervention, to investigate how loss of p150 Glued microtubule-binding function affects excitatory postsynaptic organization and neuronal vulnerability. We found that excitatory postsynaptic remodeling occurred before overt dendritic degeneration and motor neuron loss in Dctn1 Δ2–4 mice. We further demonstrated that p150 Glued microtubule-binding domain dysfunction induced early remodeling of excitatory postsynaptic densities, leading to increased postsynaptic accumulation of N-methyl- D-aspartate receptors, dysregulated Ca 2+ homeostasis, and heightened susceptibility to glutamate-induced excitotoxicity. Mechanistically, p150 Glued microtubule-binding domain dysfunction promoted the postsynaptic accumulation of endosomes and the Wiskott–Aldrich syndrome protein and SCAR homolog complex, resulting in excessive F-actin assembly and pathological enhancement of postsynaptic density architecture. Furthermore, these postsynaptic abnormalities were rescued by re-expression of wild-type p150 Glued , but not the disease-associated G59S mutant. Pharmacological inhibition of N-methyl-D-aspartate receptors, in turn, attenuated excitotoxic injury and neurodegeneration. Our findings identify a previously unrecognized postsynaptic pathogenic mechanism in DCTN1 -associated motor neuron disease. We propose that loss of p150 Glued microtubule-binding function disrupts postsynaptic endosome positioning, leading to aberrant Wiskott–Aldrich syndrome protein and SCAR homolog-mediated F-actin remodeling, pathological enhancement of excitatory postsynaptic densities, excessive N-methyl-D-aspartate receptor targeting, and increased vulnerability to excitotoxicity.