Trauma is the leading cause of death in this country in people under the age of 54 years. Except for major head injury, hemorrhage/tissue trauma and its consequences are the most important causes of morbidity and mortality in these often young, otherwise healthy individuals. This Center Grant proposal seeks to advance our understanding of the molecular mechanisms leading to organ injury and dysfunction following trauma and hemorrhage. Our focus is on the events leading to the activation and propagation of inflammatory response with the view that the magnitude of the inflammatory response is the primary determinant of both early organ damage/dysfunction and delayed immune dysfunction following injury. Thus, understanding the inciting events could lead to effective approaches to limit not only the early organ damage but also the susceptibility to late sepsis and multiple organ failure (MOF). We propose that one of the keys to understanding organ injury resulting from hemorrhagic shock is to characterize the earliest molecular events leading to the initiation and propagation of inflammatory changes following the traumatic event. From previous funding cycles, we know that the initiation of inflammatory and stress signaling occurs quickly after the induction of shock and that the amplification of these responses involves a series of overlapping events. Our most recent efforts to identify the proximal steps have provided compelling evidence that pattern recognition receptors (PRR) of the innate immune system (Toll-like receptors) are engaged early following injury and both initiate and drive the inflammatory response. TLR4 and TLR9 are required for the activation of inflammatory signaling, while TLR2 and TLR4 are markedly unregulated and can induce an exaggerated inflammatory response if triggered by microbial ligands. Data from our PI's indicate tissue-specific expression and function patterns for TLR2 and TLR9. Endogenous activators of TLR signaling known as Damage-Associated Molecular Pattern (DAMP) molecules appear to drive the initial activation of TLR4 and TLR9. The nuclear protein high mobility group box-1 (HMGB1) is clearly involved in this process, and serves as an example of a prototypic DAMP in our trauma models. Thus, the danger signaling exemplified by the DAMP-PRR interaction represents a paradigm for the activation of the immune system post-injury. Much of the downstream signaling and organ response follows downstream from these initiating events. Our mechanism-driven approach has proven useful to identify some of the key pathways and mediators. However, as the quantity of information has expanded, we have recognized the need to integrate this information via a series of mathematical models that predict the relationship among key events. Constant refinement of these models will come from the incorporation of new experimental data and validation of experimental data in the clinical setting. Ultimately, these models guide the generation of new hypotheses. Just as the early molecular signaling events in trauma and shock are highly integrated, so is our research approach. Each of the five projects pursues a defined aspect of the host response to trauma and shock. All of the projects are integrated through well-established collaborative channels and co-reliance on three well-organized cores. Project I (Billiar) pursues the mechanisms involved in the activation of the systemic and hepatic inflammatory response emphasizing the roles of TLR4, TLR9, and HMGB1. Project II (Hackam) explores the roles of TLR4 and TLR9 in the dysfunction and damage to the Gl mucosa. Project III (Bauer) studies the mediators leading to gut motor function failure. This project explores the consequences of TLR2 upregulation on intestinal motility changes. Project IV (Fan) examines the pathways leading to the activation of the inflammasome post-injury, with a particular emphasis on TLR4 and HMGB1 in this process. Project V (Vodovotz/Ochoa) integrates the experimental findings into mathematical models of the injury response. Project V also links projects l-VI with the clinical side by gathering clinical data on trauma patients for incorporation into our most translational mathematical model, used for simulated clinical trials of promising therapies as well as for patient-specific outcome prediction. These collaborations and the overall goal of the center will be promoted significantly by the common use of three well-organized cores. The Animal Models Core (Core B) will provide a source of tissues from animals (primarily mice) subjected to standardized protocols of hemorrhagic shock and hemorrhage with tissue trauma under the supervision of technically experienced core personnel. This approach maintains consistency of the models between the projects and permits a detailed comparison of results. The Structural Imaging Core (Core C) will provide extraordinary expertise in state-of-the-art tissue imaging, including immunohistochemistry, confocal microscopy, electron microscopy, quantitative morphology, and in situ hybridization. Since each of the projects tests an individual hypothesis that seeks to identify the molecular events in tissues in hemorrhagic or traumatic shock, efficient and accurate structural imaging to localize these changes is essential to each investigator. The Administrative Core (Core A) will provide the critical organization needed to assure productive collaboration and communication. Based on our progress thus far, we are fully confident that our approach will continue to lead to productive collaboration and effective testing of a novel and important hypotheses.
Showing the most recent 10 out of 302 publications
