Evolving understanding of the heterogeneous natural history of individual coronary artery plaques and the role of local endothelial shear stress

False Utopia of One Unifying Description of the Vulnerable Atherosclerotic Plaque: A Call for Recalibration That Appreciates the Diversity of Mechanisms Leading to Atherosclerotic Disease

Atherosclerosis is a complex disease characterized by the formation of arterial plaques with a broad diversity of morphological phenotypic presentations. Researchers often apply one description of the vulnerable plaque as a gold standard in preclinical and clinical research that could be applied as a surrogate measure of a successful therapeutic intervention, despite the variability in lesion characteristics that may underly a thrombotic occlusion. The complex mechanistic interplay underlying progression of atherosclerotic disease is a consequence of the broad range of determinants such as sex, risk factors, hemodynamics, medications, and the genetic landscape. Currently, we are facing an overwhelming amount of data based on genetic, transcriptomic, proteomic, and metabolomic studies that all point to heterogeneous molecular profiles of atherosclerotic lesions that lead to a myocardial infarction or stroke. The observed molecular diversity implies that one unifying model cannot fully recapitulate the natural history of atherosclerosis. Despite emerging data obtained from -omics studies, a description of a natural history of atherosclerotic disease in which cell-specific expression of proteins or genes are included is still lacking. This also applies to the insights provided by genome-wide association studies. This review will critically discuss the dogma that the progression of atherosclerotic disease can be captured in one unifying natural history model of atherosclerosis.

Identification of the haemodynamic environment permissive for plaque erosion

Endothelial erosion of atherosclerotic plaques is the underlying cause of approximately 30% of acute coronary syndromes (ACS). As the vascular endothelium is profoundly affected by the haemodynamic environment to which it is exposed, we employed computational fluid dynamic (CFD) analysis of the luminal geometry from 17 patients with optical coherence tomography (OCT)-defined plaque erosion, to determine the flow environment permissive for plaque erosion. Our results demonstrate that 15 of the 17 cases analysed occurred on stenotic plaques with median 31% diameter stenosis (interquartile range 28–52%), where all but one of the adherent thrombi located proximal to, or within the region of maximum stenosis. Consequently, all flow metrics related to elevated flow were significantly increased (time averaged wall shear stress, maximum wall shear stress, time averaged wall shear stress gradient) with a reduction in relative residence time, compared to a non-diseased reference segment. We also identified two cases that did not exhibit an elevation of flow, but occurred in a region exposed to elevated oscillatory flow. Our study demonstrates that the majority of OCT-defined erosions occur where the endothelium is exposed to elevated flow, a haemodynamic environment known to evoke a distinctive phenotypic response in endothelial cells.

Low shear stress damages endothelial function through STAT1 in endothelial cells (ECs)

Low shear stress (LSS) occurs in areas where atherosclerosis is prevalent. Many studies have revealed that signal transducer and activator of transcription 1 (STAT1) plays a significant role in cardiovascular disease. Nonetheless, the mechanism underlying the connection between STAT1 and LSS is not fully understood. The purpose of this study was to investigate the link between LSS and STAT1 in endothelial cells (ECs). Monolayer endothelial cells were stimulated or not stimulated by LSS. Protein expression and phosphorylation levels were determined by western blotting. Immunofluorescence was used to compare the protein expression differences in bifurcated and non-bifurcated human coronary arteries. Endothelial function was assessed by using a dihydroethidium assay, real-time PCR, western blotting and nitric oxide (NO)-sensitive fluorophore. Results showed that STAT1 played a key role in LSS-induced endothelium damage. Firstly, LSS activated STAT1, as evidenced by LSS-induced STAT1 (Tyr701) phosphorylation in ECs in vitro and the increased intimal STAT1 expression at bifurcation of human coronary arteries. Secondly, LSS-induced STAT1 phosphorylation was positively regulated by inhibitor of nuclear factor kappa-B kinase ε (IKKε). Additionally, LSS-promoted inflammatory factor expression was markedly reversed by silencing STAT1 (siSTAT1). LSS also increased reactive oxygen species (ROS) level and decreased endogenous NO release: however, siSTAT1 reversed these adverse effects through upregulating the antioxidant gene heme oxygenase-1(HO-1) and downregulating endothelial nitric oxide synthase (eNOS) Thr495 phosphorylation. According to our results, LSS-mediated EC injury may be associated with the activation of STAT1. Strategies designed to reduce STAT1 expression or inhibit STAT1 activation may be effective approaches for reducing the incidence of atherosclerosis.