Multi-site analyses of endothelial phenotypes at locations of varying susceptibilities to atherogenesis in normal and hypercholesterolemic swine

Endothelial cells, which line all blood vessels, play a key role in the initiation of atherosclerotic lesions in arteries. This study investigates endothelial phenotype heterogeneity in adult swine at 13 arterial sites that are either susceptible to atherosclerosis or are protected from the disease. The hypothesis is that the regional endothelial transcript profile is indicative of protective or susceptibility endothelial mechanisms at each arterial site.Nucleic acids were isolated from small numbers of endothelial cells harvested from the coronary and non-coronary arteries of normal adult swine, linearly amplified and hybridized to porcine oligo microarrays. Endothelial transcript profiles were analyzed for differential expression between vascular beds and within each bed for protected vs susceptible sites. Gene and protein expression assays were conducted for selected pathways. Functional consequences of the most significant putative pathways were measured in situ. Phenotype differences between endothelium of the coronary and non-coronary circulations were highly significant, necessitating regional comparisons within each circulatory category.Within non-coronary arteries, in athero-susceptible sites, functional categorization of differentially expressed genes identified increased protein biosynthesis. A highly interconnected network of these genes suggested the presence of low grade chronic endoplasmic reticulum (ER) stress. Gene and protein expression measurements determined induction of the unfolded protein response (UPR) pathway in response to ER stress. Consequently, endothelial reactive oxygen species (ROS) was increased 16-fold in freshly harvested aortic arch compared to descending aorta.Within coronary arteries in athero-susceptible regions, functional categories of differentially expressed endothelial genes were similar to non-coronary arteries with the exception of a strong anti-oxidative profile. Therefore, in contrast to non-coronary arteries, endothelial ROS was not significantly different in susceptible vs protected regions. A balance in coronary artery susceptible sites appears tipped towards better protection from oxidative stress whereas UPR appears to be the dominant protective response at non-coronary sites.Two weeks hypercholesterolemia did not induce significant endothelial response except for upregulation of the cholesterol efflux transporter ATP binding cassette A1 in both susceptible and protected regions.This study suggests that ER stress predisposes the endothelium to atherogenesis in susceptible regions but unfolded protein response and anti-oxidative pathways may prevent disease initiation.