Stathmin-2 regulates microtubule dynamics and axonal resilience in human motor neurons

Amyotrophic lateral sclerosis (ALS) is characterized by the selective degeneration of motor neurons, yet the mechanisms that either induce neurodegeneration or confer neuronal resilience remain poorly understood. Loss of the microtubule-associated protein Stathmin-2 (STMN2) is a downstream consequence of TDP-43 pathology present in nearly all cases of ALS and has emerged as a central feature of disease. However, the mechanisms by which STMN2 maintains homeostasis in motor neurons remain incompletely defined. Here, we investigated the role of STMN2 in regulating cytoskeletal organization and axonal function. Using TIRF microscopy, we quantified STMN2-dependent changes in microtubule growth and catastrophe at single-microtubule resolution. In human induced pluripotent stem cell-derived motor neurons, STMN2 depletion increased baseline rates of microtubule polymerization. However, STMN2 depletion impaired recovery of axonal microtubules following transient nocodazole-induced depolymerization, indicating that STMN2 is required for efficient cytoskeletal remodeling after stress. Consistent with these findings, STMN2-depleted neurons exhibited impaired microtubule recovery following acute depolymerization and reduced axonal recoil after optically induced local microtubule severing. Finally, STMN2 depletion disrupted the formation of neuromuscular junction-like contacts in human motor neuron-myocyte co-cultures, linking impaired cytoskeletal homeostasis to loss of distal neuronal connectivity. Together, these findings identify STMN2 as a key regulator of cytoskeletal resilience that coordinates microtubule remodeling, mitochondrial transport, and maintenance of neuromuscular junctions. We propose that impaired resilience of the axonal cytoskeleton represents a critical point of vulnerability in motor neurons in patients with ALS, establishing cytoskeletal resilience as a potential therapeutic target downstream of TDP-43 pathology.