N-methyl-d-aspartate (NMDA) glutamate receptors (NMDARs) containing GluN2B subunits are prevalent early after birth in most brain regions in rodents. Upon synapse maturation, GluN2B is progressively removed from synapses, which affects NMDAR function and synaptic plasticity. Aberrant recruitment of GluN2B into mature synapses has been implicated in several neuropathologies that afflict adults. We found that the E3 ubiquitin ligase Cbl-b was enriched in the spinal cord dorsal horn neurons of mice and rats and suppressed GluN2B abundance during development and inflammatory pain. Cbl-b abundance increased from postnatal day 1 (P1) to P14, a critical time period for synapse maturation. Through its N-terminal tyrosine kinase binding domain, Cbl-b interacted with GluN2B. Ubiquitination of GluN2B by Cbl-b decreased the synaptic transmission mediated by GluN2B-containing NMDARs. Knocking down Cbl-b in vivo during P1 to P14 led to sustained retention of GluN2B at dorsal horn synapses, suggesting that Cbl-b limits the synaptic abundance of GluN2B in adult mice. However, peripheral inflammation induced by intraplantar injection of complete Freund’s adjuvant resulted in the dephosphorylation of Cbl-b at Tyr³⁶³, which impaired its binding to and ubiquitylation of GluN2B, enabling the reappearance of GluN2B-containing NMDARs at synapses. Expression of a phosphomimic Cbl-b mutant in the dorsal horn suppressed both GluN2B-mediated synaptic currents and manifestations of pain induced by inflammation. The findings indicate a ubiquitin-mediated developmental switch in NMDAR subunit composition that is dysregulated by inflammation, which can enhance nociception.

N-甲基-d-天冬氨酸 (NMDA) 谷氨酸受体 (NMDAR) 包含 GluN2B 亚基，在啮齿动物的大多数大脑区域出生后早期就普遍存在。突触成熟后，GluN2B 会逐渐从突触中去除，这会影响 NMDAR 功能和突触可塑性。GluN2B 异常募集到成熟突触中与影响成人的几种神经病理学有关。我们发现 E3 泛素连接酶 Cbl-b 在小鼠和大鼠的脊髓背角神经元中富集，并在发育和炎症性​​疼痛期间抑制 GluN2B 丰度。Cbl-b 丰度从出生后第 1 天 (P1) 增加到 P14，这是突触成熟的关键时期。通过其 N 端酪氨酸激酶结合域，Cbl-b 与 GluN2B 相互作用。Cbl-b 对 GluN2B 的泛素化降低了由含有 GluN2B 的 NMDAR 介导的突触传递。在 P1 至 P14 期间体内敲除 Cbl-b 导致 GluN2B 持续保留在背角突触，这表明 Cbl-b 限制了成年小鼠中 GluN2B 的突触丰度。然而，足底内注射完全弗氏佐剂引起的外周炎症导致Tyr的Cbl-b去磷酸化³⁶³，它削弱了它与 GluN2B 的结合和泛素化，使含有 GluN2B 的 NMDAR 在突触处重新出现。背角中磷模拟 Cbl-b 突变体的表达抑制了 GluN2B 介导的突触电流和炎症引起的疼痛表现。研究结果表明，泛素介导的 NMDAR 亚基组成中的发育转换因炎症而失调，可增强伤害感受。