circDym prevents chronic neuropathic pain by competitive inhibition of Nlgn2 mRNA transport in neurites

Abstract

Aims: Neuropathic pain (NP) is a chronic syndrome that is refractory to current analgesics through unknown mechanisms. Epigenetic regulation in spinal dorsal horn neurons is reported to contribute to the initiation and maintenance of NP. Circular RNAs (circRNAs) are involved in various biological processes in neurons, but molecular mechanism of how the involvement in NP are lacking. Methods: To study NP, we used a sciatic chronic constriction injury (CCI) model in C57 mice, with the level of mechanical allodynia determined using von Frey monofilaments. The injured ipsilateral spinal dorsal horns in lumbar segments (L3–L5) were collected and total RNA and protein extracted. Transcriptome sequencing, qRT-PCR, western blot analysis, and immunoprecipitation were performed. Bioinformatic analysis was conducted using R packages. The patient cohort was analysed using logistic regression analysis. Results: circDym was identified as one of the NP-related circRNA candidates and qRT-PCR showed that its expression was significantly lower in both the CCI mouse models and in the peripheral blood of patients with NP. Overexpression of circDym significantly attenuated injury induced by NP. Further examination indicated that circDym functions by inhibiting synaptic localization of Nlgn2 mRNA by competitively binding with the RNA-binding protein, Fmrp, resulting in decreased expression of GABAAR, thus leading to the inhibition of chronic pain. Single-cell sequencing results showed that Prodynorphin-positive and Cholecystokinin-positive neurons were likely responsible for this process. Conclusions: We identified circDym, which works through a coupling mechanism, as a novel biomarker and therapeutic target for NP.