Mechanisms of Complement Activation in Traumatic Injury

Project Summary The leading cause of death from ages 1-44 years in the United States is traumatic injury, responsible for millions of hospital encounters at a cost of over $4 trillion annually. Unfortunately, outcomes in trauma patients who survive the initial injury have not seen the marked improvements observed in other fields of medicine recently, so more research is critical. It is known that a key driver of delayed mortality after injury is organ failure, where a marked inflammatory response and dynamic coagulopathy are both implicated. Approximately 1 in 4 patients who suffer from major trauma have a detectable coagulopathy on clinical coagulation testing, and even more have a perturbation in fibrinolysis, a process mediated by the protease plasmin. A major inflammatory signaling pathway in the blood circulation is called complement, a protease cascade that shares a number of cleavage specificities with the coagulation system with increasing recognition the two processes heavily influence one another. It logically follows that acute traumatic coagulopathy and inflammatory organ failure may therefore be related processes, with complement-mediated inflammation being a key link. In support of this, the extant literature has shown the degree of complement activation correlates with both organ failure and mortality, but the primary mechanism of complement activation after trauma remains unknown. Our preliminary results and prior work suggest that the observed complement activation may occur as a direct result of plasmin cleavage of complement proteins, where plasmin is known to be generated in large amounts in trauma patients with severe shock. In addition, we also know that after trauma the vascular endothelium sheds its glycocalyx into the circulation, which may serve to activate complement via the lectin pathway, which is a complement activation pathway that binds to specific glycans and causes robust complement activation. To further elucidate the mechanism of complement activation after trauma, we are now proposing 3 Aims. In Aim 1, we propose a focused protein and glycan biomarker investigation of plasma from human trauma patients to test whether plasmin generation or circulating endothelial glycocalyx molecules correlate with degree of complement activation. In Aim 2, we will use a human endothelial cell culture model designed to mimic traumatic shock to elucidate whether plasmin, endothelial glycocalyx molecules and the lectin pathway, or both are capable of generating robust complement activation in the absence of other complement pathways to delineate relative contributions and mechanism of activation. Finally, in Aim 3, we will directly investigate the role of complement in generating organ failure in trauma using a mouse model of trauma comparing mice deficient in complement proteins C3 and C5 with wild-type mice. The results of this Aim would highlight the potential role of anti-complement therapies for future clinical study considerations. Taken together, this research program will improve our understanding of the mechanisms of complement activation and inflammatory organ injury after trauma in this leading cause of death in the United States.