Abstract
Activation of the inflammatory response following spinal cord injury (SCI) is thought to exacerbate cellular damage; however, the mechanisms initiating this process are poorly understood. Microglia and astrocytes, resident cells of the central nervous system (CNS), are recruited as part of the innate immune response following traumatic insult. Once triggered, these cells can initiate an inflammatory response by secreting proinflammatory cytokines and chemokines. Here, we examined the role of EphB3/A4 receptors in the immune response following SCI. We show that EphB3 and EphA4 are present on microglia and astrocytes in the adult spinal cord and that these receptors are phosphorylated at 15 minutes post-SCI. Additionally, stimulation of astrocytes and microglia with ephrinB3 ligand mediates the release of several pro-inflammatory cytokines. Cytokine and chemokine protein release, as measured by ELISA, is also increased in both wild type (WT) astrocytes and microglia following stimulation. Eph receptor stimulation in astrocytes also increases mRNA transcript levels of multiple cytokines known to play a role in the immune response, which is significantly attenuated in the absence of EphB3 and EphA4. To test whether inflammatory cytokine production following SCI is mediated by EphB3/A4, tissue was collected from sham or SCI WT and EphB3/A4-/- mice at 4 and 24 hours and analyzed using cytometric bead array. We show that the expression of interleukin-6 (IL-6) and chemokine ligand 2 (CCL-2) are significantly increased at 4 and 24 hour post-SCI in WT mice, which is significantly attenuated in the EphB3/A4-/- mice. Furthermore, using EphB3-/- mice we observed a similar pattern to that seen in vivo in the EphB3/A4-/- mice at 24 hours after SCI. These data suggest that most likely EphB3 but also possibly EphA4, plays a novel role in initiating the acute pro-inflammatory response following SCI.