Mapping the Secondary Response to Traumatic Brain Injury Using Spatial Transcriptomics Shows Acute 4-aminopyridine Treatment Mitigates Axonal and Molecular Pathology
Damage to long myelinated axons of white matter tracts is a hallmark pathology resulting from traumatic brain injury (TBI) forces and secondary injury processes. 4-aminopyridine (4-AP) is an FDA-approved Kv1 potassium channel inhibitor designed to mitigate axon dysfunction.  We examined repurposing 4-AP as an acute TBI treatment using clinically-oriented neuropathology of axon damage combined with unbiased genome-wide spatial transcriptomics for comprehensive analysis of secondary injury processes.  Adult male and female mice received a non-penetrating impact TBI with 4-AP (i.p., b.i.d) on days 1-7 post-injury. Along corpus callosum (CC) axons, TBI disrupted node of Ranvier domains, exposing the putative 4-AP target of mislocalized Kv1 channels (p < 0.005). Clinically reasonable 4-AP dosing (0.5 mg/kg) reduced nodal Nav1.6 channel loss (p < 0.05) and Caspr heminode formation (p < 0.005) after injury. Quantification of ß-amyloid precursor protein immunolabeling showed significantly reduced CC axon damage at 4-AP doses of 0.5 mg/kg and 5 mg/kg (each p < 0.005). 4-AP safety, based on potential seizure risk after TBI, was unaltered with vehicle or 0.5 mg/kg 4-AP, while the 5 mg/kg dose induced seizure behavior in sham and TBI groups (p < 0.0001). Spatial transcriptomics mapped molecular signatures to tissue pathology. TBI increased axonal injury response genes in the CC and in motor and somatosensory cortex sites of CC projection neurons. TBI induced disease-associated glial phenotypes that mapped predominantly within the CC. TBI increased pathway expression for immune and vascular functions, neuron and glial cell signaling, and cellular dyshomeostasis, while reducing expression in myelination-related pathways. Gene expression analysis of 4-AP treatment (0.5 mg/kg) indicated potassium channel target engagement and increased neuroaxonal activity, along with dampened secondary injury responses. Collectively, these findings reveal underlying molecular pathology of the secondary injury response and advance 4-AP translation to reduce axon damage and stimulate activity-dependent repair after acute TBI. Overall design: At 8 weeks of age, 24 male C57BL/6J mice received TBI (non-penetrating closed-skull impact, centered at bregma) or sham procedures, followed by 4-AP (0.5 mg/kg) or saline vehicle injections (i.p., b.i.d.) until analyses at 7 days post-injury. To identify comprehensive molecular changes resulting from acute 4-AP treatment in relation to TBI-induced pathology, genome-wide spatial transcriptomic (Visium CytAssist) and complementary adjacent immunohistochemical analyses of 7 µm thick FFPE coronal brain tissue sections were conducted under the impact site in cortical gray and corpus callosum white matter regions of interest.