Morphine promotes microglial activation by upregulating the EGFR/ERK signaling pathway.

Yaqiong Yang,Ziheng Wang,Rong Hu,Yu Sun,Jia Yan,Wenlong Li,Hong Jiang,Michael Bader

doi:10.1371/journal.pone.0256870

Yaqiong Yang, Ziheng Wang + Show 6 more

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https://doi.org/10.1371/journal.pone.0256870

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Abstract

Although they represent the cornerstone of analgesic therapy, opioids, such as morphine, are limited in efficacy by drug tolerance, hyperalgesia and other side effects. Activation of microglia and the consequent production of proinflammatory cytokines play a key pathogenic role in morphine tolerance, but the exact mechanisms are not well understood. This study aimed to investigate the regulatory mechanism of epidermal growth factor receptor (EGFR) on microglial activation induced by morphine in mouse microglial BV-2 cells. In this research, BV-2 cells were stimulated with morphine or pretreated with AG1478 (an inhibitor of EGFR). Expression levels of cluster of differentiation molecule 11b (CD11b), EGFR, and phospho-EGFR were detected by immunofluorescence staining. Cell signaling was assayed by Western blot. The migration ability of BV-2 cells was tested by Transwell assay. The production of interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) in the cell supernatant was determined by ELISA. We observed that the expression of CD11b induced by morphine was increased in a dose- and time- dependent manner in BV-2 cells. Phosphorylation levels of EGFR and ERK1/2, migration of BV-2 cells, and production of IL-1β and TNFα were markedly enhanced by morphine treatment. The activation, migration, and production of proinflammatory cytokines in BV-2 cells were inhibited by blocking the EGFR signaling pathway with AG1478. The present study demonstrated that the EGFR/ERK signaling pathway may represent a novel pharmacological strategy to suppress morphine tolerance through attenuation of microglial activation.

Highlights

Opioids, such as morphine, continue to be powerful analgesic drugs for managing chronic pain with a high rate of abuse potential [1]
Activated microglia undergo a dramatic morphological changes from quiescent to a macrophage-like accompanied by increased expression of cell surface markers, such as cluster of differentiation molecule 11b (CD11b), cluster of differentiation (CD14), major histocompatibility complex (MHC) molecules, chemokine receptors, and several other markers, producing large numbers of proinflammatory cytokines, including interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and IL6, which could enhance the reactivity of dorsal horn neurons, induce central sensitization, and reduce the antinociceptive effect of morphine [5, 6]
To further explore whether morphine- and LPS- mediated microglial activation is accompanied by an inflammatory response in BV-2 cells, we investigated the secretion of the key proinflammatory cytokines, IL-1β and TNF-α by Enzyme-linked immunosorbent assay (ELISA) analysis in cellular supernatants

Summary

Introduction

Opioids, such as morphine, continue to be powerful analgesic drugs for managing chronic pain with a high rate of abuse potential [1]. Their analgesic efficacy is limited by drug tolerance, hyperalgesia and other side effects, which hinder the prolonged clinical use of opioid drugs [2]. The inhibition of microglial activation may represent a potential therapeutic strategy for improving the analgesic effect of morphine [7], the specific regulation mechanism is still unclear

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