A window into endothelial injury mechanisms revealed by S1PR1 GPCR reporter mice

[Speaker] Timothy Hla:1
1:Harvard Medical School, Boston Children's Hospital, Boston, MA, USA

Injury of the aortic endothelium occurs frequently due to disturbed flow-induced abnormal shear stress, metabolic abnormalities and hypertension. However, chronic endothelial injury contributes to atherosclerosis and aneurysm. Hemodynamic shear stress response of the endothelium is one the key stimuli. Pulsatile laminar shear forces promote normal homeostasis whereas disturbed shear forces which are common in geometrically challenged areas of the vasculature (branch points, lesser curvature) lead to endothelial injury and dysfunction. We recently showed that sphingosine 1-phosphate (S1P) receptor-1 GFP signaling mice shows marked activation of β-arrestin-coupled GPCR signaling (Galvani et al. (2015) Science Signaling) at sites of endothelial injury. Given the fact that S1pr1 is an inhibitor of vascular injury and atherosclerosis as shown in the aforementioned study, we sorted GFP+ aortic endothelial cells (injured aortic endothelial cells; IAEC) and compared with GFP- aortic endothelial cells (healthy aortic endothelial cells; HAEC). IAEC and HAEC from normal S1pr1 GFP signaling mice (N=4-5; age ~ 8-10 weeks) were used for systems level chromatin profiling (ATACseq) and RNA expression (RNAseq). From this dataset, we found enrichment of signal transduction pathways influencing immune cell infiltration, inflammation, endothelial mesenchymal transition (EndMT), lipid uptake and cell proliferation. Expression of unique transcription factors were modulated and their binding sites were enriched in the open chromatin of IAEC and HAEC. Open chromatin sites were associated with genes that regulate immune cell infiltration, inflammation, EndMT, lipid uptake and cell proliferation. These data suggest that either S1pr1 β-arrestin coupling which is associated with GPCR endocytosis and biased signaling regulates transcriptional events involved in endothelial injury. Alternatively only some of these genes are regulated by S1pr1 signaling whereas the others are regulated directly by disturbed flow-induced biomechanical signaling. We will present our recent data in this area of investigation. These studies are expected to further increase our understanding of endothelial injury at the molecular level and may ultimately lead to the development of novel approaches to treat endothelial injury which occurs in many diseases including chronic inflammatory, autoimmune, cardiovascular, neurological and metabolic conditions.
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