Epigenetics and Pain Research

i-Fect Used to Study Impacts

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.

β-arrestin siRNA Delivery in vivo and Increased Analgesia

I have reported use of our i-FectTM siRNA delivery kit for gene expression analysis studies of Cav1.2, DOR, hTERT, The β3 subunit of the Na+,K+-ATPase, rSNSR1, NTS1. NAV1.8, , TRPV1, Survivin, Flaviviruses and more.

I would like to congratulate Dr. C.R. Lin and his team at National Taiwan University College of Medicine for silencing β-arrestin expression in vivo and the impact on opioid based analgesia. The results could be good news for improving opioid based pain therapies: C.-H.Yang, H.-W. Huang, K.-H.Chen, Y.-S.Chen, S.-M.Sheen-Chen and C.-R.Lin. Antinociceptive potentiation and attenuation of tolerance by intrathecal β-arrestin 2 small interfering RNA in rats. Br. J. Anaesth. (2011) doi: 10.1093/bja/aer291.

Background: Tolerance to the analgesic effect of opioids complicates the management of persistent pain states. We tested whether the intrathecal infusion of small interfering RNA (siRNA) against β-arrestin 2 would reduce tolerance to chronic morphine use and the severity of precipitated morphine withdrawal.

Methods: Intrathecal β-arrestin 2 (2 μg siRNA per 10 μl per rat) was injected once daily for 3 days. Rats then received a continuous intrathecal infusion of morphine (2 nmol h−1) or saline for 7 days. Daily tail-flick (TF) and intrathecal morphine challenge tests were performed to assess the effect of intrathecal β-arrestin 2 siRNA on antinociception and tolerance to morphine. Naloxone withdrawal (2 mg kg−1) was performed to assess morphine dependence.
Results: In the daily TF test, the antinociception of intrathecal morphine was increased and maintained in rats receiving β-arrestin 2 siRNA compared with the control group (morphine alone). In the probe response test, rats receiving morphine infusion with β-arrestin 2 siRNA treatment showed a significant left shift in their dose–response curve, as measured by per cent maximal possible effect (MPE), such that the AD50 was significantly decreased by a factor of 5.6 when compared with that of morphine-infused rats. In the naloxone-induced withdrawal tests, rats receiving β-arrestin 2 siRNA injection with morphine infusion showed a significant reduction in four of the six signs of withdrawal.
Conclusions: We show here that intrathecal β-arrestin 2 siRNA in rats enhances analgesia and attenuates naloxone-induced withdrawal symptoms. This may warrant further investigation in the context of long-term use of intrathecal opioids for controlling chronic pain.

Raf-1- selective siRNA and Response to Pain

I've reported Researchers' success in knocking down in vivo DOR, hTERT, The β3 subunit of the Na+,K+-ATPase, rSNSR1, NTS1. NAV1.8 and more using Neuromics' i-Fect^TM siRNA transfection reagent .

I am pleased to add Raf-1 to this growing list. Here's a recent publication by Dr. EV Varga, University of Arizona:

S Tumati, WR Roeske, T Largent-Milnes, R Wang, TW Vanderah and EV Varga. Sustained morphine-mediated pain sensitization and antinociceptive tolerance are blocked by intrathecal treatment with Raf-1- selective siRNA. This is an Accepted Article that has been peer-reviewed and approved for publication in the British Journal of Pharmacology, but has yet to undergo copy-editing and proof correction. Please cite this article as an "Accepted Article"; doi: 10.1111/j.1476-5381.2010.00869.x.

Background and purpose: Long-term morphine treatment enhances pain neurotransmitter (such as calcitonin gene-related peptide (CGRP)) levels in the spinal cord. It has been suggested previously that increased spinal CGRP may contribute to sustained morphine-mediated paradoxical pain sensitization and antinociceptive tolerance. Previous in vitro studies from our group indicated that Raf-1 kinase-mediated adenylyl cyclase superactivation played a crucial role in sustained morphine-mediated augmentation of basal and evoked CGRP release from cultured primary sensory neurons. The present study was aimed to evaluate the physiological significance of this molecular mechanism in vivo, in rats.

Experimental approach: Rats were intrathecally (i.th) injected with a Raf-1- selective small interfering RNA (siRNA) mixture for 3 days, and were subsequently infused with saline or morphine, s.c. for seven days. Thermal and mechanical sensory thresholds of the animals were assessed by daily behavioural tests. After final behavioural testing (day 6), spinal cords were isolated from each animal group and spinal CGRP and Raf-1 protein levels were measured using ELISA and immunohistochemistry.

Key results: Selective knockdown of spinal Raf-1 protein levels by i.th Raf-1- selective siRNA pre-treatment significantly attenuated sustained morphine-mediated upregulation of CGRP immunoreactivity in the spinal cord of rats and prevented the development of thermal hyperalgesia, mechanical allodynia and antinociceptive tolerance.

Conclusions and implications: Raf-1 played a significant role in sustained morphine-mediated paradoxical pain sensitization and antinociceptive tolerance in vivo. These findings suggest novel pharmacological approaches to improve the long-term utility of opioids in the treatment of chronic pain.