Involvement Of EphB1/ephrinB1 Signaling In Bone Cancer Pain

Objective:Eph receptors are the largest family of tyrosine kinase receptors. The interaction of Ephs and ephrins has been largely circumscribed to the development of the nervous system. However, both receptors and ligands are expressed in the mature mammalian brain, spinal cord and dorsal root ganglia. Eph/ephrin system was demonstrated to be involved in the modulation of inflammatory and neuropathic pain. The aim of the present study was to investigate whether EphBl/ephrinBl signaling contributed to bone cancer pain and the possible downstream mechanism.Method:Bone cancer pain was induced by intra-tibial inoculation of Walker 256 mammary gland carcinoma cells and evaluated by detecting the body weight, bone destruction, mechanical allodynia. Mechanical allodynia was measured as the hind paw withdrawal response to von Frey hair stimulation in rats. Expressions of EphBl/ephrinBl in spinal cord and dorsal root ganglia were examined in bone cancer pain model of rat by immunohistochemistry, Western blot and RT-PCR. At 16 days post inoculation of Walker 256, the pain relieving effect and the mRNA levels of inflammatory cytokines were detected after intrathecal administration of EphBl-Fc (blocker of EphBl receptor,10μg) by RT-PCR.Result:Tumor-bearing rats displayed a profound decrease in PWT, reaching a lowest level at 16th day post inoculation. The EphBl/ephrinBl protein expression was significantly increased in spinal cord, but ephrinBl was decreased in dorsal root ganglia and EphBl had no change after Walker 256 inoculation. The immunohistochemistry staining result showed that in tumor-bearing rats, the number of EphBl positive cells was strongly increased and ephrinBl was significantly increased in not only superficial layer but also deep layer. The mRNA level of EphBl/ephrinBl had no change in spinal cord and dorsal root ganglia. The mechanical allodynia induced by bone cancer was significantly alleviated by intrathecal administration of EphBl-Fc. Furthermore, the RT-PCR analysis showed that the mRNA levels of IL-1β, IL-6 and TNF-αwere significantly increased at 16 days post Walker 256 inoculation and were significantly suppressed by intrathecal administration of EphBl-Fc in spinal cord.Conclusion:EphBl/ephrinBl might be involved in maintenance of mechanical allodynia, via modulating the expression of spinal inflammatory cytokines, in the present rat model of bone cancer pain. This study suggested that EphBl/ephrinBl signaling would be a new potential target for bone cancer pain relief.