Morphine creates a neuroinflammatory response and enhances release of the proinflammatory cytokines like interleukin-1β (IL-1β), which compromises morphine analgesia as well as induces morphine tolerance. In this study, we attempted to investigate the mechanisms of morphine induced IL-1β synthesis and release. Microglial cells were treated with morphine (100 μM) once daily for 3 days. Control groups underwent the same procedure but received sterile saline injection instead of morphine. Toll-like receptor 4 (TLR4) and P2X4 receptor (P2X4R) signaling were analyzed using Western blot; immunofluorescence was used to detect the signaling of CD68; real-time RT-PCR and ELISA kit was used to measure the messenger RNA and protein synthesis and release level of IL-1β. Morphine enhanced IL-1β synthesis and P2X4R protein expression. TLR4 were responsible for morphine-induced IL-1β synthesis, while morphine-induced IL-1β release was via P2X4R. Morphine-induced IL-1β release is mediated by endocytosis of TLR4. These results indicated that TLR4 and P2X4R pathways mediated IL-1β synthesis and release in microglia followed chronic morphine. TLR4 internalization is the main mechanism of morphine-induced microglia activation and IL-1β release.
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The authors’ work is supported by grants from the Affiliated Hospital of Qingdao University. We are grateful to Zejun Niu and Zhiqiang Qu for their technical assistance.
Conflict of interest
The authors declare that they have no competing interests. The authors alone are responsible for the content and writing of this paper. This study was partially supported by the Qingdao University.
The experimental protocols were approved by the Animal Care and Protection Committee of Qingdao University. Our use of animals conformed to our Institution’s and Country’s animal welfare laws and our studies were approved.
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Liang, Y., Chu, H., Jiang, Y. et al. Morphine enhances IL-1β release through toll-like receptor 4-mediated endocytic pathway in microglia. Purinergic Signalling 12, 637–645 (2016). https://doi.org/10.1007/s11302-016-9525-4
- Toll-like receptor 4
- P2X4 receptors