UC Davis

Atherosclerosis is a chronic inflammatory disease of arteries that leads to heart attack and stroke in over 3 million people per year in the US. The main risk factors for atherosclerotic cardiovascular disease (ASCVD) include dyslipidemia and disorders of metabolism. Moreover, there is a strong association between arterial flow characteristics and the local regulation of the inflammation that promotes ASCVD. Triglyceride rich lipoproteins (TGRL) are elevated in the circulation of individuals at risk for ASCVD and were shown to act synergistically with low magnitude shear stress (SS) to promote an inflammatory response by cultured human aortic endothelial cells (HAECs). This response was characterized by maximal vascular cell adhesion molecule (VCAM)-1 expression and was dependent upon an endoplasmic reticulum (ER) stress response. The magnitude of this response correlated strongly with enrichment in certain polyunsaturated fatty acid (PUFA) metabolites within the circulating lipoproteins that may be further metabolized by several enzymatic pathways in endothelial cells to produce an array of inflammatory mediators. We hypothesized that shifting endothelial cyclooxygenase (COX)-2-dependent PUFA metabolism alters the ER stress-mediated VCAM 1 upregulation in response to TGRLs.

TGRLs isolated from postprandial human plasma following a high fat test meal were characterized via flow cytometry as pro- or anti-inflammatory based on their impact on up- or down-regulation of VCAM-1 expression by HAEC relative to stimulation with tumor necrosis factor (TNF)α. TNFα stimulated HAEC monolayers were exposed to a SS gradient via artery-on-a-chip (AOC) microfluidics in the presence of TGRL and/or pharmacological intervention to induce or inhibit COX-2. ER stress markers that promote maximal VCAM-1 expression by TGRL in inflamed HAEC were analyzed by western blot. Despite a strong inverse correlation between COX-2 and VCAM-1 expression observed in the SS gradient, the results did not strongly support a direct effect of COX-2 in mediating ER stress-induced VCAM-1 expression but implicated cross talk with other metabolic pathways. COX-2 expression was suppressed by low magnitude (atherosusceptible) SS and enhanced by high magnitude (atheroprotective) SS in the AOC device, registering a 37% increase from static control at 12 dynes/cm2. COX-2 induction with phorbal-12,13-dibutyrate attenuated VCAM-1 across the SS gradient, reducing peak expression at 2 dynes/cm2 by 62%. COX-2 upregulation by pharmacological induction or high magnitude SS suppressed ER stress-mediated VCAM-1 elicited by TNFα and TGRLs. These results are consistent with a protective role for COX- 2 in reducing endothelial inflammation that promotes atherosclerosis and reveal the potential for endothelial PUFA metabolism to modulate an inflammatory response to TGRL. Furthermore, a potent effect of low SS to enhance VCAM-1 expression while suppressing COX-2 expression was observed, consistent with its ability to promote an atherosusceptible phenotype, and demonstrating its importance when studying the inflammation promoting atherosclerosis.