Maintenance of neuropathic pain caused by peripheral nerve injury crucially depends on the phosphorylation of GluN2B, a subunit of the NMDA receptor, at its Tyr1472 (Y1472) and subsequent formation of a postsynaptic density (PSD) complex of superficial spinal dorsal horn neurons. Here we took advantage of comparative proteomic analysis based on isobaric stable isotope tags (iTRAQ) between wild-type and knockin mice with a mutation of Y1472 to Phe of GluN2B (Y1472F-KI) to search for PSD proteins in the spinal dorsal horn that mediate the signaling downstream of phosphorylated Y1472 GluN2B. Among several candidate proteins, we focused on brain-enriched guanylate kinase-associated protein (BEGAIN), which was specifically up-regulated in wild-type mice after spared nerve injury (SNI). Immunohistochemical analysis using generated antibody demonstrated that BEGAIN was highly localized at the synapse of inner lamina II in the spinal dorsal horn and that its expression was up-regulated after SNI in wild-type, but not in Y1472F-KI, mice. In addition, alteration of the kinetics of evoked EPSCs for NMDA but not those for AMPA receptors in spinal lamina II was demonstrated by BEGAIN deletion. We demonstrated that mechanical allodynia, a condition of abnormal pain induced by innocuous stimuli, in the SNI model was significantly attenuated in BEGAIN-deficient mice. However, there was no significant difference between naive wild-type and BEGAIN-knockout mice in terms of physiological threshold for mechanical stimuli. These results suggest that BEGAIN was involved in pathological pain transmission through NMDA receptor activation by the phosphorylation of GluN2B at its Y1472 in spinal inner lamina II.
Significance Statement We for the first time revealed that brain-enriched guanylate kinase-associated protein (BEGAIN) plays a crucial role in pathological but not physiological pain. We previously demonstrated that neuropathic pain was attenuated in knockin mice with Y1472F of GluN2B (Y1472F-KI). Here, by proteomic analysis of spinal dorsal horn, we found that the level of BEGAIN protein was increased in wild-type, but not in Y1472F-KI, mice after peripheral nerve injury. BEGAIN was localized at synapses in lamina IIi of the spinal dorsal horn. Moreover, neuropathic pain was significantly attenuated in the knockout mice of BEGAIN after peripheral nerve injury, demonstrating that BEGAIN was involved in pathological pain transmission through NMDAR activation following the phosphorylation of GluN2B at its Y1472 in spinal lamina II.
Authors report no conflict of interest.