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Rationale: In atherosclerotic lesions, synthetic smooth muscle cells (sSMCs) induce aberrant microRNA (miR) profiles in endothelial cells (ECs) under flow stagnation. Increase in shear stress induces favorable miR modulation to mitigate sSMC-induced inflammation. Objective: To address the role of miRs in sSMC-induced EC inflammation and its inhibition by shear stress. Methods and Results: Coculturing ECs with sSMCs under static condition causes initial increases of 4 anti-inflammatory miRs (146a/708/451/98) in ECs followed by decreases below basal levels at 7 days; the increases for miR-146a/708 peaked at 24 hours and those for miR-451/98 lasted for only 6 to 12 hours. Shear stress (12 dynes/cm 2 ) to cocultured ECs for 24 hours augments these 4 miR expressions. In vivo, these 4 miRs are highly expressed in neointimal ECs in injured arteries under physiological levels of flow, but not expressed under flow stagnation. MiR-146a, miR-708, miR-451, and miR-98 target interleukin-1 receptor–associated kinase, inhibitor of nuclear factor–κB kinase subunit-γ, interleukin-6 receptor, and conserved helix-loop-helix ubiquitous kinase, respectively, to inhibit nuclear factor–κB signaling, which exerts negative feedback control on the biogenesis of these miRs. Nuclear factor-E2–related factor (Nrf)-2 is critical for shear-induction of miR-146a in cocultured ECs. Silencing either Nrf-2 or miR-146a led to increased neointima formation of injured rat carotid artery under physiological levels of flow. Overexpressing miR-146a inhibits neointima formation of rat or mouse carotid artery induced by injury or flow cessation. Conclusions: Nrf-2–mediated miR-146a expression is augmented by atheroprotective shear stress in ECs adjacent to sSMCs to inhibit neointima formation of injured arteries.

Objective—Vascular endothelial cells (ECs) are subjected to shear stress and cytokine stimulation. We studied the interplay between shear stress and cytokine in modulating the expression of adhesion molecule genes in ECs.Methods and Results—Shear stress (20 dynes/cm2) was applied to ECs prior to and/or following the addition of tumor necrosis factor (TNF)-α. Shear stress increased the TNF-α–induced expression of intercellular adhesion molecule-1 (ICAM-1) at both mRNA and surface protein levels, but decreased the TNF-α–induced expression of vascular adhesion molecule-1 (VCAM-1) and E-selectin. Transfection studies using promoter reporter gene constructs of ICAM-1, VCAM-1, and E-selectin demonstrated that these shear stress modulations of gene expression occur at the transcriptional levels. After 24-hour preshearing followed by 1 hour of static incubation, the effect of preshearing on TNF-α–induced ICAM-1 mRNA expression vanished. The recovery of the TNF-α–induced VCAM-1 and E-selectin mRNA expressions following preshearing, however, required a static incubation time of >6 hours (complete recovery at 24 hours). Pre- and postshearing caused a reduction in the nuclear factor-κB-DNA binding activity induced by TNF-α in the EC nucleus.Conclusions—Our findings suggest that shear stress plays differential roles in modulating the TNF-α–induced expressions of ICAM-1 versus VCAM-1 and E-selectin genes in ECs.

Vascular endothelial cells (ECs), which exist in close proximity to vascular smooth muscle cells (SMCs), are constantly subjected to blood flow–induced shear stress. Although the effect of shear stress on endothelial biology has been extensively studied, the influence of SMCs on endothelial response to shear stress remains largely unexplored. We examined the potential role of SMCs in regulating the shear stress–induced gene expression in ECs, using a parallel-plate coculture flow system in which these 2 types of cells were separated by a porous membrane. In this coculture system, SMCs tended to orient perpendicularly to the flow direction, whereas the ECs were elongated and aligned with the flow direction. Under static conditions, coculture with SMCs induced EC gene expression of intercellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), and E-selectin, while attenuating EC gene expression of endothelial nitric oxide synthase (eNOS). Shear stress significantly inhibited SMC-induced adhesion molecule gene expression. These EC responses under static and shear conditions were not observed in the absence of close communication between ECs and SMCs, and they were also not observed when ECs were cocultured with fibroblasts instead of SMCs. Our findings indicate that under static conditions, coculture with SMCs induces ICAM-1, VCAM-1, and E-selectin gene expression in ECs. These coculture effects are inhibited by shear stress and require specific interaction between ECs and SMCs in close contact.

In atherosclerotic lesions, synthetic smooth muscle cells (sSMCs) induce aberrant microRNA (miR) profiles in endothelial cells (ECs) under flow stagnation. Increase in shear stress results in favorable miR modulation to mitigate sSMC-induced inflammation. The objective of this study was to address the role of miRs in sSMC-induced EC inflammation and its inhibition by shear stress. Co-culturing ECs with sSMCs under static condition caused initial increases of four anti-inflammatory miRs (146a/708/451/98) in ECs followed by decreases below the basal levels at 7 days; the increases for miR-146a/708 peaked at 24 h and those for miR-451/98 lasted for only 6-12 h. Shear stress (12 dynes/cm2) to ECs co-cultured with sSMCs for 24 h augments the expression of these four miRs. In vivo, these four miRs are not expressed in neointimal ECs in injured arteries under flow stagnation, but become highly expressed under physiological levels of flow. MiR-146a, -708, -451, and -98 target interleukin (IL)-1 receptor-associate...

Vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) are constantly exposed to haemodynamic forces, including blood flow-induced fluid shear stress and cyclic stretch from blood pressure. These forces modulate vascular cell gene expression and function and, therefore, influence vascular physiology and pathophysiology in health and disease. Epigenetics, including DNA methylation, histone modification/chromatin remodelling and RNA-based machinery, refers to the study of heritable changes in gene expression that occur without changes in the DNA sequence. The role of haemodynamic force-induced epigenetic modifications in the regulation of vascular gene expression and function has recently been elucidated. This review provides an introduction to the epigenetic concepts that relate to vascular physiology and pathophysiology. Through the studies of gene expression, cell proliferation, angiogenesis, migration and pathophysiological states, we present a conceptual framework for understanding how mechanical force-induced epigenetic modifications work to control vascular gene expression and function and, hence, the development of vascular disorders. This research contributes to our knowledge of how the mechanical environment impacts the chromatin state of ECs and VSMCs and the consequent cellular behaviours.

Vascular endothelial cells (ECs) are constantly subjected to blood flow-induced shear stress and the influences of neighboring smooth muscle cells (SMCs). In the present study, a coculture flow system was developed to study the effect of shear stress on EC-SMC interactions. ECs and SMCs were separated by a porous membrane with only the EC side subjected to the flow condition. When ECs were exposed to a shear stress of 12 dynes/cm2 for 24 h, the cocultured SMCs tended to orient perpendicularly to the flow direction. This perpendicular orientation of the cocultured SMCs to flow direction was not observed when ECs were exposed to a shear stress of 2 dynes/cm2. Under the static condition, long and parallel actin bundles were observed in the central regions of the cocultured SMCs, whereas the actin filaments localized mainly at the periphery of the cocultured ECs. After 24 h of flow application, the cocultured ECs displayed very long, well-organized, parallel actin stress fibers aligned with the flow direction in the central regions of the cells. Immunostaining of platelet endothelial cell adhesion molecule-1 confirmed the elongation and alignment of the cocultured ECs with the flow direction. Coculture with SMCs under static condition induced EC gene expressions of growth-related oncogene-alpha and monocyte chemotactic protein-1, and shear stress was found to abolish these SMC-induced gene expressions. Our results suggest that shear stress may serve as a down-regulator for the pathophysiologically relevant gene expression in ECs cocultured with SMCs.