Our i-Fect siRNA, miRNA and shRNA Trasfection Kit was recently used to study the impact of G9a-specific siRNA (AGUAACGGGCAUCAAUGC) on Mu Opioid Receptors: Yuhao Zhang, Shao-Rui Chen, Geoffroy Laumet, Hong Chen and Hui-Lin Pan. Nerve Injury Diminishes Opioid Analgesia through Lysine Methyltransferase-Mediated Transcriptional Repression of µ-Opioid Receptors in Primary Sensory Neurons. First Published on February 25, 2016, doi: 10.1074/jbc.M115.711812... In some SNL rats, G9a-specific siRNA (4 µg) or the negative control siRNA was administered intrathecally. G9a-specific siRNA(AGUAACGGGCAUCAAUGC) or universal negative control siRNA (#SIC001, Sigma-Aldrich) was mixed with i-Fect (Neuromics, Edina, MN) to a final concentration of 400 mg/L for the intrathecal injections...
Figures: G9a knockdown with siRNA reverses the MOR expression in the DRG and the morphine analgesic effect diminished by nerve injury. (A,B) Quantitative PCR (A) and Western blotting (B) analyses show the mRNA and protein levels of MORs in the DRGs of sham and SNL rats treated with control or G9a-specific siRNA (n = 10 rats in each group). The ipsilateral L5 and L6 DRG tissues were removed 24 h after the last siRNA injection. The amount of MOR mRNA and protein was normalized to GAPDH in the same samples, and the mean value of MOR levels in sham control rats was considered to be 1. (C) Time course of the intrathecal morphine effects on the tactile and pressure withdrawal thresholds in sham and SNL rats treated with G9a-specific siRNA or negative control siRNA (n = 9 rats in each group). The withdrawal thresholds after the last siRNA injection were plotted as the baseline control (BL).
Summary: The findings provide new insight into the epigenetic mechanism regulating MOR expression in primary sensory neurons in neuropathic pain. This multidisciplinary approach provides conclusive evidence for G9a as a key chromatin regulator responsible for MOR downregulation in the DRG and the analgesic efficacy of opioids reduced by nerve injury. A better understanding of the epigenetic mechanisms underlying nerve injury-induced downregulation of MORs in primary sensory neurons could help improve the analgesic efficacy of opioids for treating chronic neuropathic pain. G9a inhibitors could be used to enhance the opioid analgesic effect and reduce opioid consumption in patients with chronic neuropathic pain.
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