PROJECT SUMMARY Trauma claims for 8% of deaths and 16% of disabilities worldwide. Despite significant improvement in the trauma clinical care, overall mortality remains high largely due to trauma-associated organ injury and secondary infection. Hence, understanding the molecular and cellular mechanism responsible for trauma-associated organ injury and developing novel therapeutic strategies to preserve organ functions will advance the field of trauma care. Traumatic injury leads to a massive activation of the innate immunity likely driven by danger-associated molecular patterns (DAMPs), such as extracellular (ex) nucleic acids, that are released from necrotic or injured cells. DAMP-induced innate immune activation may lead to tissue inflammation and organ injury. Our preliminary data demonstrate that 1) circulating exRNAs are significantly increased in both trauma patients and mice, and capable of activating macrophages (M) with robust cytokine/chemokine productions in trauma; 2) small RNA- seq profiling reveals that miRNAs constitute 80% of plasma exRNAs and their expressions are markedly altered following non-hemorrhagic blunt trauma in humans and mice; 3) genetic deficiency of TLR7, the single-stranded RNA sensor, significantly attenuates trauma plasma exRNA-induced cytokine productions in M and circulating/tissue inflammation after trauma. Based on literature and the preliminary data, we hypothesize that exRNAs function as a molecular driver that activates the innate immunity by regulating M functions and is partially responsible for trauma-induced inflammation and organ injury. To test the hypothesis, this renewed R35 research program will address the following specific questions: 1) What is the precise role and mechanism of exRNAs in innate immune inflammation and remote organ injury after trauma and 2) Could we target exRNA- TLR7 signaling to mitigate trauma-induced organ injury? We will employ multiple complementary approaches – genetically modified animals, adoptive cell transfer and chimeric models, synthetic oligo nucleic acids, pharmacological inhibitors and receptor antagonist, locked nucleic acids-modified anti-miRNA inhibitors – to provide novel insight into how exRNAs regulate host innate immunity and contributes to organ injury after trauma. Successful completion of this research program will lay the foundation for future ex-miRNA-based intervention in trauma care.