NOD2-RIP2 signaling alleviates microglial ROS damage and pyroptosis via ULK1-mediated autophagy during Streptococcus pneumonia infection

Meningitis occurs when S. pneumonia invade the blood-brain barrier, provoking inflammatory host response and neurological injury. Nucleotide-binding oligomerization domain 2 (NOD2) has been identified to promote microglial activation and Autophagy during pneumococcal meningitis, but the mechanism remains unclear. In the present study, we investigated the passway of NOD2-mediated Autophagy activation and the role of Autophagy in inflammatory damage of murine microglia and mouse meningitis model. We demonstrated that Autophagy was activated during S. pneumonia Infection, and NOD2-RIP2 signaling was involved in the process. Treatment of microglia with GSK583, the RIP2 kinase inhibitor resulted in reduced autophagy-related protein and p-ULK1, indicating that RIP2 regulated Autophagy in a kinase-dependent manner by phosphorylating ULK1. In addition, microglia with ULK1 knockdown exhibited enhanced production of ROS, leading to IL-1β and IL-18 release and cellular Pyroptosis. Similar to the in vitro results, NOD2-RIP2 signaling induced Autophagy in the brain in a mouse meningitis model. Moreover, ULK1 or RIP2 silencing significantly increased Pyroptosis of brain and induced more inflammatory damage of pneumococcal meningitis mice. Taken together, our study demonstrate that NOD2-RIP2 signaling is involved in the activation of Autophagy by promoting ULK1 phosphorylation, which alleviates microglial ROS damage and Pyroptosis during S. pneumonia Infection.