PROJECT 4 (ESI) Von Willebrand factor (VWF) is an essential hemostatic protein and alterations of VWF levels are associated with bleeding and thrombosis. VWF levels < 50 IU/dL represent a risk factor for bleeding while VWF levels < 30 IU/dL define Willebrand disease (VWD) and are often associated with mutations in the VWF gene. Alternatively, high levels of VWF are associated with thrombotic conditions such as myocardial infarction and stroke. The wide distribution of VWF levels in the general population indicates that there are multiple factors that regulate VWF levels. To date, major modifiers such as the ABO blood group and specific variants in genes implicated in VWF release (STXBP1, GNA12) or clearance (LRP1, AVPR2, ACE) account for only 30-40% of the known variation. The objective of this proposal is to identify alternative mechanisms that regulate VWF levels. Our central hypothesis is that specific transcriptional and epigenetic mechanisms in endothelial cells are critical determinants of VWF levels. The hypothesis is based on recent reports and our preliminary data that microRNAs levels (miRs), transcription factors, and epigenetic mechanisms can all modify VWF levels. We are uniquely positioned to test this hypothesis using our primary patient-derived blood outgrowth endothelial cells (BOECs) that replicate accurately the disease phenotype. We will test our hypothesis via the following three aims, (1) Determination of transcriptional mechanisms that affect VWF expression in BOECs, (2) Determination of the contribution of methylation and histone-acetylation status of VWF on VWF expression from BOECs and (3) Determination of the role of transcriptional and epigenetic mechanisms on VWF levels in aging. Our preliminary data and our expertise in BOEC models positions us well to carry out these proposed research aims. Successful completion of these aims will (1) confirm novel transcriptional regulators of VWF in low VWF BOECs, such as miR-24 and TCF4, (2) confirm the regulatory role of epigenetic modifiers, such as VWF promoter methylation and histone acetylation, in determining VWF levels, and (3) demonstrate novel transcriptional and epigenetic regulation that may explain the effects of aging on VWF levels. In addition, our un-biased RNA sequencing, methylation arrays, and microRNA arrays may also identify additional targets for VWF regulation. Globally, by evaluating the role of transcriptional and epigenetic regulators on VWF levels it is anticipated that we will identify novel mechanisms of VWF expression and function. Such results are significant as they are expected to advance the understanding of how modifiers outside of the VWF coding region can influence VWF levels and represent novel pathways of VWF regulation that have previously not been well examined.