PROJECT SUMMARY Our long-term goal is to specify how patient-specific blood cell activities become altered in transcatheter aortic valve replacement (TAVR) in order to optimize the management of patients with aortic valve diseases. The objective of this application is to determine how patient-specific hematological, physiological and procedural factors promote platelet-driven procoagulant and inflammatory complications in TAVR. Our central hypothesis is that patient-specific biochemical and blood flow features in TAVR support the activation of platelet signaling responses, which promote procoagulant platelet generation and responses underlying transcatheter heart valve (THV) complications and degeneration. This hypothesis is rooted in our preliminary data that: 1) activated platelets adhere to THVs in vivo in a manner related to subclinical leaflet thrombosis (SLT); 2) GPVI-mediated platelet procoagulant signaling responses and fibrin formation are upregulated in TAVR patients; 3) patient- specific shear and stasis features of THV expansion and placement promote procoagulant platelet generation ex vivo; and, 4) THV materials upregulate procoagulant platelet generation in vivo in non-human primates. Our team of scientists, engineers and physicians has pioneered experimental approaches well-suited to define how patient-specific biochemical and anatomic factors support procoagulant platelet generation and other blood cell activities underlying complications in TAVR. We propose a set of hypothesis-driven studies to define how patient- specific biochemical and anatomic factors support blood cell activities underlying thrombosis-related complications in TAVR using blood samples from patients undergoing TAVR, as well as blood from in vitro and ex vivo TAVR models, including: 1) quantitative proteomics methods to define platelet phenotypes at unprecedented molecular depth and resolution; 2) in vitro flow loop systems to specify effects of individualized THV configuration and blood biochemistry on THV failure; 3) ex vivo non-human primate models with translational relevance to THV biocompatibility; and, 4) PET imaging methods to follow platelet:THV interactions in TAVR patients in vivo. Building on these innovative experimental approaches, we will determine how patient- specific platelet features contribute to SLT in TAVR (Aim 1); how patient-specific features of aorta anatomy, THV placement and hemodynamics increase procoagulant platelet generation to drive leaflet thrombosis, leaflet thickening and THV degeneration in TAVR (Aim 2); and how to target procoagulant platelet mechanisms in THV thrombogenesis to prevent SLT (Aim 3). Successful completion of these Aims will elucidate patient-specific mechanisms of THV failure and will have a significant positive impact on human health by advancing efforts to manage a rapidly growing population of aortic stenosis and TAVR patients at risk of short- and long-term blood cell-driven complications and mortality.