A Role of GAS6/Axl Signaling in the Development of Essential Hypertension

PROJECT SUMMARY Hypertension is the leading cause of morbidity and mortality from stroke, myocardial infarction, heart failure, and chronic kidney disease amongst the United States Veterans. Despite the importance of blood pressure control, the pathogenesis of essential hypertension remains poorly understood.

Recently, a new observation has shed light onto potential dendritic cells (DCs) that may be involved in human hypertension. Using single-cell ribonucleic acid (RNA) sequencing, a new subset of DCs has been described with surface expression of Axl and Siglec-6 in normal health subjects. They showed that Axl+ Siglec-6+ DCs (AS DCs) can potently drive T cell proliferation and produce large amounts of

pro-inflammatory cytokines. Based on previously published studies and preliminary data, I propose that hypertension leads to the release of endothelial-derived growth arrest specific 6 (GAS6) that activates Axl on DCs leading to inflammation and its associated end organ damage. In Aim 1, I will test the

hypothesis that hypertensive stimuli lead to GAS6/Axl-dependent inflammasome activation mediated by reactive oxygen species (ROS) in AS DCs. In this aim, I will expose human CD14+ monocytes to GAS6 or hypertensive endothelial cell stretch and assess inflammasome activation, ROS production, and the formation of the highly reactive Isolevuglandin (isoLG)-adducts by flow cytometry. I will also

examine the role of isoLGs on inflammasome activation by scavenging isoLGs using 2- hydroxybenzilamine (2-HOBA) during exposure of human monocytes to hypertensive stimuli and assess cytokine production by flow cytometry. Lastly, I will examine the response of AS DCs from normotensive and hypertensive human subjects in an unbiased fashion by cellular indexing of

transcriptomes and epitopes by sequencing (CITE-seq). I predict that scavenging ROS and/or isoLGs during exposure of GAS6 or endothelial cell stretch will prevent inflammasome activation and pro- inflammatory cytokine release by AS DCs. In Aim 2, I will test the hypothesis that Axl-dependent signaling in DCs promotes hypertension and its associated end-organ damage. I will use mice in which

I have deleted Axl specifically in DCs (Axlfl/fl and AxlCD11cCre). I will examine the in vivo role of Axl in DCs during hypertension by radiotelemetry and flow cytometry. Next, I will investigate the deletion of Axl in DCs on inflammasome activation and T cell proliferation in vitro by flow cytometry. I predict that genetic

deletion of Axl will prevent hypertension, DC activation, and its associated inflammation. In Aim 3, I will test the hypothesis that GAS6 promotes DC activation, hypertension, and its associated inflammation I will use mice that have genetic deletion for GAS6 (GAS6WT/WT and GAS6-/-). I will examine the in vivo

role of GAS6 by performing bone marrow transplantation studies and assess DC activation and development of hypertension by flow cytometry and radiotelemetry. I will genetically delete GAS6 from human endothelial cells and assess DC activation status and cytokine production by flow cytometry. I predict that genetic deletion of GAS6 will prevent hypertension and activation of immune cells. These

studies will advance our understanding of the role DCs play in the development of human hypertension and will provide new therapeutic directions for the treatment of human cardiovascular disease for United States Veterans.