MiR-93 Targeting EphA4 Promotes Neurite Outgrowth from Spinal Cord Neurons

The failure of neurite outgrowth in the adult mammalian spinal cord injury is thought to be attributed to the intrinsic growth ability of mature neurons. Ephrin/Eph system is a major growth regulator of many axonal guidance processes. EphA4 is expressed specifically in traumatic central nervous system (CNS) and dynamically regulate target gene expression, suggesting that it may be associated with neural regeneration. Here, we found an alteration in temporal expression of miR-93 following a contusive spinal cord injury (SCI) in adult rats. The messenger RNA (mRNA) expression level of miR-93 was upregulated and the protein expression levels of EphA4, p-Ephexin, and active RhoA were all decreased in traumatic spinal cord relative to those with an intact spinal cord. Infection of cultured spinal cord neurons (SCNs) with miR-93 mimic led to neuronal growth promotion and decreased levels of EphA4, p-Ephexin, and active RhoA protein expression. Dual-luciferase reporter assay confirmed that miR-93 bound to the three prime untranslated region (3' UTR) of EphA4 and inhibited the expression of EphA4 mRNA. These findings provide evidence that miR-93 inhibits EphA4 expression, decreased EphA4 expression could promote neurite outgrowth in SCNs due to reduced levels of p-Ephexin and active RhoA.