N6-Methyladenosine methylase METTL3 contributes to neuropathic pain by epigenetic silencing of mu opioid receptor

We aimed at exploring the role and mechanism of METTL3-mediated m6A modification in neuropathic pain. Male Sprague-Dawley rats were randomly divided into four groups: Sham operation group (Sham group), chronic constriction injury (CCI) of the sciatic nerve model group (NPP group), intrathecal injection of virus down-regulated METTL3 + CCI model group (M3 + NPP group) and intrathecal injection of negative control virus + CCI model group (Scr + NPP group). The M3 + NPP group and the Scr + NPP group were intrathecally injected with virus nineteen days before operation. The paw withdrawal mechanical thresholds and paw withdrawal latency were respectively recorded one day before operation, three days, five days and seven days after oper-ation. The rats were sacrificed on the seventh day after operation, and their spinal cord tissues were taken. The frozen sections of rats were performed to observe the expression of green fluorescent protein of the virus. The methylation level of RNA, the protein expression of m6A-related enzyme (METTL3) and mu opioid receptor (MOR) in spinal cord tissues of the four groups were measured. Downregulation of METTL3 had no effect on the overall methylation level of the spinal cord, but it could regulate the methylation level of the OPRM1 gene RNA encoding MOR, partially restore the expression of MOR, and relieve pain in rats. In the process of NPP, METTL3 may inhibit the expression of MOR by regulating the methylation level of OPRM1 gene RNA encoding MOR, and ultimately promote the occurrence and development of NPP.