Electroacupuncture treatment alleviated peripheral nerve injury-induced mechanical pain hypersensitivity.

PMID: Eur J Pain. 2022 May; 26 (5): 991-1005. Epub 2022 Feb 17. PMID: 35138669 Abstract Title: Electroacupuncture relieves neuropathic pain by inhibiting degradation of the ecto-nucleotidase PAP in the dorsal root ganglions of CCI mice. Abstract: BACKGROUND: Although electroacupuncture is widely used in chronic pain management, it is quite controversial due to its unclear mechanism. We hypothesized that EA alleviates pain by inhibiting degradation of the ecto-nucleotidase prostatic acid phosphatase (PAP) and facilitating ATP dephosphorylation in dorsal root ganglions (DRGs) .METHODS: We applied EA in male C57 mice subjected to chronic constriction injury (CCI) and assessed extracellular ATP and 5′-nucleotidease expression in DRGs. Specifically, we used a luminescence assay, quantitative reverse transcriptase-polymerase chain reaction, Western blotting, immunohistochemistry and nociceptive-related behavioral changes to gather data, and we tested for effects after PAP expression was inhibited with an adeno-associated virus (AAV). Moreover, membrane PAP degradation was investigated in cultured DRG neurons and the inhibitory effects of EA on this degradation were assessed using immunoprecipitation.RESULTS: EA treatment alleviated CCI surgery-induced mechanical pain hypersensitivity. Furthermore, extracellular ATP decreased significantly in both the DRGs and dorsal horn of EA-treated mice. PAP protein but not mRNA increased in L4-L5 DRGs, and inhibition of PAP expression via AAV microinjection reversed the analgesic effect of EA. Membrane PAP degradation occurred through a clathrin-mediated endocytosis pathway in cultured DRG neurons; EA treatment inhibited the phosphorylation of adaptor protein complex 2, which subsequently reduced the endocytosis of membrane PAP.CONCLUSIONS: EA treatment alleviated peripheral nerve injury-induced mechanical pain hypersensitivity in mice by inhibiting membrane PAP degradation via reduced endocytosis and subsequently promote ATP dephospho .SIGNIFICANCE: In a mouse model of chronic pain, electroacupuncture treatment increased levels of prostatic acid phosphatase (PAP: an ecto-nucleotidase known to relieve pain hypersensitivity) by inhibiting PAP degradation in dorsal root ganglions. This promoted extracellular ATP dephosphorylation, inhibited glia activation and eventually alleviated peripheral nerve injury-induced mechanical pain hypersensitivity in mice. Our findings represent an important step forward in clarifying the mechanisms of pain relief afforded by acupuncture treatment.

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