Project Summary Severe hemorrhage from extremity injuries is a significant cause of battlefield deaths and preventable trauma fatalities in civilian medicine. Tourniquet use is the most effective means of arresting life-threatening limb hemorrhage in the pre-hospital setting and creating bloodless surgical fields in orthopedic and vascular surgeries; however, tourniquet-related ischemia and subsequent reperfusion (IR) can cause serious IR injuries. These IR injuries have led to the limitations of tourniquet use. Exploring the mechanisms and finding effective therapies can resolve the limitations of tourniquet use and improve outcomes and quality of life in post- traumatic patients. The neuromuscular junction is structured to transmit electrical signals from motor nerve terminals to nicotinic acetylcholine receptors (nAChRs) for affecting muscle function. Our pilot data demonstrated that some nAChR clusters are fragmented in mice with 6 weeks of tourniquet-induced IR. Therefore, in Aim 1, we will determine the relationship between the fragmentation of nAChR clusters and muscle contractile dysfunction in long-term tourniquet-induced IR. Additionally, our preliminary studies have targeted a specific signaling pathway that links fragmentation of nAChR clusters in the injured muscle, namely the inflammatory cytokine-cyclin-dependent kinase 5 (Cdk5-catenin-rapsyn signaling pathway. In Aim 2, we will test if the inflammatory cytokine-Cdk5-catenin-rapsyn signaling pathway mediates fragmentation of nAChR clusters in long-term tourniquet-induced IR. In Aim 3, we will investigate the therapeutic effect of a novel anti- inflammatory drug on long-term functional and structural recovery of the neuromuscular junction via inhibition of pro-inflammatory cytokines in mouse models of tourniquet/IR injury. We will design in vitro and in vivo studies to address our overarching hypothesis that anti-inflammation will promote repair of the neuromuscular junction. Overall, proposed studies will unveil cellular and molecular mechanisms responsible for long-term neuromuscular junction disorder in tourniquet-induced IR. These studies will provide further information that the neuromuscular junction could be a potential therapeutic target in tourniquet/IR injuries, especially through the application of a novel anti-inflammatory drug in this proposal. This approach has significant potential to resolve the limitations of clinical tourniquet use, thereby improving outcomes and quality of life in post- traumatic patients.

Project Narrative Tourniquet-induced traumatic injuries limit its clinical use for effectively stopping life-threatening bleeding in prehospital settings and creating bloodless operating fields in surgeries. This proposal will explore the potential mechanisms about tourniquet-induced traumatic injuries and test whether a new anti-inflammatory drug promotes long-term recovery of the neuromuscular junction from traumatic injuries. The significance of this project is to resolve the limitations of tourniquet use in the clinic and to provide potential therapeutic targets and strategies for improving outcomes and quality of life in post-traumatic patients.