Targeting EphB1 Receptor in Cellular Models: Analysis of Signaling Pathways and Cross-Talk with Opioid Receptors

The activation of EphB1 receptors by their membrane bound ligands ephrins in nociceptive neurons have been implicated in the onset and maintenance of different types of pain and in side effects produced as consequence of prolonged Mor activation. The use of EphB1 blocking reagents rescue opioid-induced analgesia suggesting that antagonists targeting EphB1 receptor could represent a novel class of analgesics. A potential inverse relation between EphB1 and Mor receptors was displayed in a previous investigation by Lombardo Sara where showed that the co-administration of Mor and EphB1 agonists resulted in an occlusion of morphine-mediated p42/44 MAPK phosphorylation. Therefore, the aim of the research was elucidated the signaling pathway and mechanism responsible for the functional crosstalk triggered by the co-administration of both ligands and at the same time developed and tested different EphB1 antagonist peptidomimetics. As results: *ephrinB1/EphB1 activation through PI3K signaling pathways blunted p42/44 activation morphine-mediated and PKC-dependent in SHSY5Y native cells where in addition EphB1 signaling activation seems to be the responsible for blocking the capacity of the morphine to modulate adenylyl cyclase activity. *SHSY5Y cells induced to PMA differentiation produced up regulation of Mor expression and down regulation of EphB1 receptors allowing that morphine significantly activate p42/p44 MAPK even when ephrinB1 was co-administered. *Conversely, in PMA-differentiated SHSY5Y cells exposed to TNF-α, EphB1 expression was significantly up regulated and the morphine failed to increase p42/44 MAPK phosphorylation. * Moreover, were found two novel antagonist peptides capable to counteract ephrinB1-Fc-mediated activation of p42/p44 MAPK phosphorylation. Concluding that when EphB1 is activated morphine no longer triggers PKC-dependent signaling events downstream of Mor activation, explaining the reasons why opioid analgesics are less effective in the treatment of different pain states. At this regards, novel EphB1 receptor antagonists may represent a novel strategy to reduce the negative impact of ephrin system.