The vascular endothelium has a key role in the maintenance of cardiovascular homeostasis. It can respond to environmental changes and produces a variety of active substances to maintain a non-thrombotic luminal surface, control vascular smooth muscle tone and regulate inflammatory processes. Endothelial cells (EC) are involved in all major hemostatic pathways, with a pivotal role in maintaining a balance between pro- and anti-inflammatory and coagulation mechanisms. The structural integrity of the endothelium is crucial for normal function, and injury or inappropriate activation, termed ‘endothelial dysfunction’, precedes the development of both arterial and venous cardiovascular disease (CVD). Endothelial dysfunction is an established response to CVD risk factors, but the current knowledge of the underlying pathophysiology remains relatively limited. Importantly, in clinical practice, we lack any clinical tools to measure EC dysfunction, which fulfil the ideal criteria of being safe, non-invasive, standardised and cheap. Such tools would have potential for application into routine screening of risk populations to identify those at risk of CVD development, or those who have asymptomatic disease. Key proteins critical for EC specialised function tend to have EC specific expression profiles (i.e., are expressed only in, or at higher levels in EC). In previous work from the group, a bioinformatic-based method was used to analyse RNAseq data from 32 different human organs, to identify a panel of genes with highly specific endothelial expression across tissues, and subsequently this method was refined to allow the identification of tissue-specific EC enriched genes. This description of the endothelial (EC)-enriched transcriptome forms the cornerstone of this project, based on two main (but overlapping) areas: (A) Biomarker discovery: existing biomarkers that have been successfully implemented into clinical routines tend to have expression specificity to the site of injury or dysfunction, thus, we envisaged that our EC proteins could have applicability as biomarkers for the assessment of vascular status. In recent work from the lab, EC-derived proteins in plasma were analysed in the Swedish CArdioPulmonary bioImage Study (SCAPIS) pilot (see Figure 2 for concept overview). Here, a panel of EC-derived proteins were associated with exposure to one or more CVD risk factor(s). Furthermore, many of these proteins were associated with the Framingham risk scores (FRS) for each individual, a relationship that was strengthened when multiple EC-derived proteins were incorporated into a risk prediction model. The follow up to this study, using the larger SCAPIS cohort, is a key focus of this PhD project. The biomarker discovery part combining with the extraction of data from GWAS will identify protein candidates that will be the subject of mechanistic investigations to determine the functional role of these EC-enriched candidate proteins associated with CVD risk.