The discovery that TDP-43 mutations cause familial ALS and that many patients display pathological TDP-43 mislocalization has nominated altered RNA metabolism as a potential disease mechanism. Despite its importance, the identity of RNAs regulated by TDP-43 in motor neurons remains poorly understood. Here, we report transcripts whose abundances in human motor neurons are sensitive to TDP-43 depletion. Notably, we found STMN2, which encodes a microtubule regulator, declined after TDP-43 knockdown, in patient-specific motor neurons, following TDP-43 mislocalization, and in the postmortem patient spinal cords. Loss of STMN2 upon reduced TDP-43 function was due to the emergence of a cryptic exon, which is of substantial functional importance, as we further demonstrate that STMN2 is necessary for both axonal outgrowth and repair. Importantly, post-translational stabilization of STMN2 could rescue neurite outgrowth and axon regeneration deficits induced by TDP-43 depletion. We propose restoring STMN2 expression warrants future examination as an ALS therapeutic strategy.
