Cold-inducible RNA-binding protein through TLR4 signaling induces mitochondrial DNA fragmentation and regulates macrophage cell death after trauma

Trauma is a major cause of systemic inflammatory response syndrome and multiple organ dysfunction syndrome. Macrophages (Mφ) direct trauma-induced inflammation, and Mφ death critically influences the progression of the inflammatory response. In the current study, we explored an important role of trauma in inducing mitochondrial DNA (mtDNA) damage in Mφ and the subsequent regulation of Mφ death. Using an animal pseudo-fracture trauma model, we demonstrated that tissue damage induced NADPH oxidase activation and increased the release of reactive oxygen species via cold-inducible RNA-binding protein (CIRP)-TLR4-MyD88 signaling. This in turn, activates endonuclease G, which serves as an executor for the fragmentation of mtDNA in Mφ. We further showed that fragmented mtDNA triggered both p62-related autophagy and necroptosis in Mφ. However, autophagy activation also suppressed Mφ necroptosis and pro-inflammatory responses. This study demonstrates a previously unidentified intracellular regulation of Mφ homeostasis in response to trauma.