Genetic architecture of tissue factor expression - Project Summary/Abstract Tissue factor (TF) is the primary initiator of blood coagulation. The expression of TF from the F3 locus must be intricately regulated in a cell type-specific manner to ensure hemostasis following injury but prevent pathologic thrombosis. Indeed, aberrant intravascular TF expression contributes to myocardial infarction, venous thromboembolism (VTE), and stroke, while studies across species demonstrate that reduced TF dosage may predispose to bleeding or protect against thrombosis. Nevertheless, the genetic architecture regulating F3 expression across diverse human tissues and disease states is largely undefined. Our central hypothesis is that rare human genetic variation in the F3 promoter (Aim 1), coding region (Aim 2), and 3’ untranslated region (UTR, Aim 3) disrupts the tight regulation of TF expression and its procoagulant activity to influence human bleeding and thrombotic risk. Our preliminary studies integrate genetic and biochemical approaches to identify new activators and the first repressors of F3 transcription, microRNAs negatively regulating F3 mRNA through its 3’ UTR, and rare human genetic variation in the sequence elements that enable these interactions. We also characterize the first human missense mutations in TF that impact its interaction with factor VII and/or factor X activation. Because routine clinical assays of blood coagulation do not reliably capture the role of endogenous TF, these individuals go undetected in human populations. In Aim 1, we will evaluate new transcriptional activators and repressors of the F3 promoter. We will map the multiple but finite ways a cell can turn on F3 across human tissues, and define rare human genetic variation perturbing this stringent regulation. In Aim 2, we will evaluate an expanded cohort of individuals with F3 null mutations and damaging missense mutations to determine their impact on blood coagulation, factor VII activation, and human disease. In Aim 3, we will characterize the role of microRNAs that negatively regulate F3 expression. Among these, we have identified a microRNA whose action is suppressed by a SNP that is overrepresented in young patients with penetrant thrombosis, suggesting a potential mechanism of thrombophilia attributable to unrestricted TF expression. By systematically evaluating human genetic variation in the F3 promoter, coding region, and 3’ UTR, our findings will establish the first F3 genotype-phenotype relationships in humans and provide a new lens through which to interpret increasingly common human genetic testing that incorporates F3. The findings suggest new mechanisms of human bleeding and thrombotic risk, as well as new therapeutic avenues to specifically target pathologic TF expression.
