Growth Arrest Specific 6 And Axl Signaling Coordinate Endothelial Cell And Immune Cell Activation To Promote Inflammation And Hypertension

Endothelial cells (ECs) activated by hypertensive (10%) cyclical stretch releases factors including IL-6 and hydrogen peroxide that stimulate the conversion of human monocytes to an intermediate inflammatory phenotype. A novel subset of DCs in humans has been identified that express Axl and Sigelc-6 + (AS DCs) which drive T cells proliferation and produce inflammatory cytokines. The interplay between ECs and AS DCs in hypertension is unkown. We assessed AS DCs by flow cytometry in normotensive (n=23) and hypertensive (n=11) subjects and found a significant increase in AS DCs in hypertensive compared to normotensive subjects (297 ± 73 vs. 108 ± 26/ml; p =0.0304). When moncoytes were exposed to human aortic endothelial cells (HAECs) undergoing 10% stretch, the formation of AS DCs was markedly enhanced compared to 5%. The ligand for Axl is growth arrest specific 6 (GAS6), and we found that 10% HAEC stretch caused a 50% increase in the release of GAS6 by ECs comapred to 5%. We knocked down either EC GAS6 or Axl using siRNA and either of these abrogated the ability of ECs to promote AS DC formation. Using flow cytometry to analyze venous ECs that had been harvested from 23 volunteers to quantify EC activation and GAS6 secretion in vivo, we found a positive association between GAS6 and ICAM-1 (R 2 =0.39, p =0.0012). We found a positive association between pulse pressure and plasma GAS6 (R 2 =0.25, p =0.0079) ands systolic blood pressure and GAS6 (R 2 =0.19, p=0.0025) in volunteers. We found that plasma GAS6 is increased in Ang II hypertension and that either genetic deletion or pharmacological inhibition of Axl lowered blood pressure in reposne to Ang II and reduced renal inflammation. To investigate the role of immunological vs. stromal Axl in vivo, we perfomed bone marrow transplant studies and found that both Axl WT/WT ->Axl -/- and Axl -/- ->Axl W/WT had a significant reduction in blood pressure by 20 mmHg compared to the Axl WT/WT -> Axl WT/WT control. These data show that both immunological and stromal Axl contribute to hypertension and inflammation and GAS6/Axl signlaing may be a novel therapeutic target in this disease.