Melatonin Alleviates Microglia-Mediated Neuroinflammation By Suppressing NLRP3 Inflammasome-Mediated Pyroptosis Via ROS/mtDNA/STING Pathway After Spinal Cord Injury

Background: Microglia pyroptosis-induced neuroinflammation has been one of the potential treatment targets for spinal cord injury (SCI). And melatonin is reported to have anti-neuroinflammation effect on SCI, but the underlying mechanism is largely unexplored. In addition, the potential regulatory role of stimulator of interferon genes (STING) mediated innate immune response in the SCI-induced neuroinflammation also remains unknown. The aim of this study is to identify the potential molecular mechanism of the anti-neuroinflammation effect of melatonin in SCI mice and to explore whether STING-mediated signal pathway is involved in this pharmacological process. Methods: In vivo, the C57BL/6 female mice underwent SCI injury or Sham surgery (laminectomy alone). Melatonin and selective STING antagonist C-176 were administered intraperitoneally after injury in the SCI group once a day for 3 or 28 consecutive days for different experiments. The BMS score system was adopted to assess the motor function of mice. In vitro, the Lipopolysaccharide (LPS)/ATP was combinedly used to induce cell pyroptosis in BV2 microglia and the adenovirus was used to overexpress STING. A series of molecular experiments including Western blot (WB), quantitative real-time polymerase chain reaction (RT-qPCR), enzyme linked immunosorbent assay (ELISA) and immunofluorescence (IF) were performed in vivo and in vitro. Results: Our results showed that melatonin effectively suppressed NLRP3 inflammasome-induced pyroptosis and STING-mediated pathway after SCI. In addition, C-176 also alleviated the NLRP3 inflammasome-mediated pyroptosis and promoted functional recovery in vivo. In vitro, we also found that melatonin abrogated NLRP3 inflammasome activation in LPS/ATP-induced BV2 cells, while overexpression of STING reversed the anti-pyroptotic role of melatonin. Subsequent results together indicated that the role of melatonin on STING-dependent NLRP3 inflammasome activation may be mediated by decreasing ROS production and cytosolic mtDNA release. Conclusion: This study preliminarily demonstrated that melatonin exerts its anti-neuroinflammation role on SCI by alleviating the NLRP3 inflammasome-mediated pyroptosis, which was mediated by blocking the ROS/mtDNA/STING pathway. It provides us a better understanding of the pathological mechanism after SCI and offer experiment evidence to promote the use of melatonin for SCI.