LAUSR

ABSTRACT Primary Objective: Eph/Ephrin signaling is inhibitory for developing axons and blocking Eph pathways enhances regeneration after spinal cord injury. It was hypothesized that inhibition of Eph signaling promotes cellular and behavioral recovery after traumatic brain injury (TBI). Research design: Lateral fluid percussion (LFP) injury was performed on wildtype (WT) and EphA6 knockout (KO) mice. EphA6-Fc, Ephrin-A5-Fc fusion proteins, and sodium orthovanadate were used to alter the signaling pathway. Immunohistochemistry and tissue explants revealed cellular changes. Rotarod tests demonstrated vestibulomotor function. Outcomes: The EphA6 receptor expression is upregulated following LFP. Uninjured EphA6 KO mice exhibit greater neurite density and clustered Ephrin-A5-Fc causes growth cone collapse in vitro. After LFP, EphA6 KO mice demonstrate longer neurites and decreased neuronal cell death and astrocytosis compared to WT mice. Blocking EphA signaling by soluble EphA6-Fc fusion protein reduces cell death and improves motor function following LFP whereas clustered Ephrin-A5-Fc exacerbates cell death and neurodegeneration. Sodium orthovanadate rescues growth cone collapse in vitro as well as cell death and neurodegeneration in vivo. Conclusions: Eph/Ephrin signaling plays an inhibitory role following TBI. Targeting the Eph signaling pathway with Fc fusion proteins and pharmacological agents can be a novel strategy to counter the damaging effects of TBI. Abbreviations: LFP: lateral fluid percussion; TBI: traumatic brain injury; KO: knockout; WT: wildtype; PTP2: protein phosphotyrosine phosphatase 2; Tg: transgenic; YFP: yellow fluorescent protein; ATM: atmospheres; RT-qPCR: Real-time-quantitative PCR; dpi: days post injury; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; DAPI: 4′,6-diamidino-2-phenylindole; PBS: phosphate buffered saline; GFAP: glial fibrillary acidic protein; FLJC: fluorojade C; CA: cornu ammonis; SEM: standard error of the mean; ANOVA: analysis of variance; PLSD: posthoc least significant difference