Spinal Fbxo3-dependent Fbxl2 ubiquitination of active zone protein RIM1α mediates neuropathic allodynia through CaV2.2 activation

Abstract

Spinal plasticity, a key process mediating neuropathic pain development, requires ubiquitination-dependent protein turnover. Presynaptic active zone proteins have a crucial role in regulating vesicle exocytosis, which is essential for synaptic plasticity. Nevertheless, the mechanism for ubiquitination-regulated turnover of presynaptic active zone proteins in the progression of spinal plasticity-associated neuropathic pain remains unclear. Here, after research involving Sprague Dawley rats, we reported that spinal nerve ligation (SNL), in addition to causing allodynia, enhances the Rab3-interactive molecule-1α (RIM1α), a major active zone protein presumed to regulate neural plasticity, specifically in the synaptic plasma membranes (SPMs) of the ipsilateral dorsal horn. Spinal RIM1α-associated allodynia was mediated by Fbxo3, which abates Fbxl2-dependent RIM1α ubiquitination. Subsequently, following deubiquitination, enhanced RIM1α directly binds to CaV2.2, resulting in increased CaV2.2 expression in the SPMs of the dorsal horn. While exhibiting no effect on Fbxo3/Fbxl2 signaling, the focal knockdown of spinal RIM1α expression reversed the SNL-induced allodynia and increased spontaneous EPSC (sEPSC) frequency by suppressing RIM1α-facilitated CaV2.2 expression in the dorsal horn. Intrathecal applications of BC-1215 (a Fbxo3 activity inhibitor), Fbxl2 mRNA-targeting small-interfering RNA, and ω-conotoxin GVIA (a CaV2.2 blocker) attenuated RIM1α upregulation, enhanced RIM1α expression, and exhibited no effect on RIM1α expression, respectively. These results confirm the prediction that spinal presynaptic Fbxo3-dependent Fbxl2 ubiquitination promotes the subsequent RIM1α/CaV2.2 cascade in SNL-induced neuropathic pain. Our findings identify a role of the presynaptic active zone protein in pain-associated plasticity. That is, RIM1α-facilitated CaV2.2 expression plays a role in the downstream signaling of Fbxo3-dependent Fbxl2 ubiquitination/degradation to promote spinal plasticity underlying the progression of nociceptive hypersensitivity following neuropathic injury.