Atherosclerotic plaque preferentially develops in arterial curvatures and branching regions, where endothelial cells constantly experience disturbed blood flow. By contrast, the straight arteries are generally protected from plaque formation due to exposure of endothelial cells to vaso-protective laminar blood flow. However, the role of flow patterns on endothelial barrier function remains largely unclear. This study aimed to investigate new mechanisms underlying the blood flow pattern-regulated endothelial integrity. Exposure of human endothelial cells to pulsatile shear (PS, mimicking the laminar flow) compared to oscillatory shear (OS, mimicking the disturbed flow) increased the expressions of long non-coding RNA MALAT1 and tight junction proteins ZO1 and Occludin. This increase was abolished by knocking down MALAT1 or Nesprin1 and 2. PS promoted the association between Nesprin1 and SUN2 at the nuclear envelopes, and induced a nuclear translocation of β-catenin, likely through enhancing the interaction between β-catenin and Nesprin1. In the in vivo study, mice were treated via intraperitoneal injection with β-catenin agonist SKL2001 or its inhibitor XAV939, and they were then subjected to Evans blue injection to assess aortic endothelial permeability. The aortas exhibited a reduced wall permeability to Evans blue in SKL2001-treated mice whereas an enhanced permeability in XAV939-treated mice. We concluded that laminar flow promotes nuclear localization of Nesprins, which facilitates the nuclear access of β-catenin to stimulate MALAT1 transcription, resulting in increased expressions of ZO1 and Occludin to protect endothelial barrier function.
Vascular endothelial cells are exposed to shear stresses with disturbed vs. laminar flow patterns, which lead to proinflammatory vs. antiinflammatory phenotypes, respectively. Effective treatment against endothelial inflammation and the consequent atherogenesis requires the identification of new therapeutic molecules and the development of drugs targeting these molecules. Using Connectivity Map, we have identified vitexin, a natural flavonoid, as a compound that evokes the gene-expression changes caused by pulsatile shear, which mimics laminar flow with a clear direction, vs. oscillatory shear (OS), which mimics disturbed flow without a clear direction. Treatment with vitexin suppressed the endothelial inflammation induced by OS or tumor necrosis factor-α. Administration of vitexin to mice subjected to carotid partial ligation blocked the disturbed flow-induced endothelial inflammation and neointimal formation. In hyperlipidemic mice, treatment with vitexin ameliorated atherosclerosis. Using SuperPred, we predicted that apurinic/apyrimidinic endonuclease1 (APEX1) may directly interact with vitexin, and we experimentally verified their physical interactions. OS induced APEX1 nuclear translocation, which was inhibited by vitexin. OS promoted the binding of acetyltransferase p300 to APEX1, leading to its acetylation and nuclear translocation. Functionally, knocking down APEX1 with siRNA reversed the OS-induced proinflammatory phenotype, suggesting that APEX1 promotes inflammation by orchestrating the NF-κB pathway. Animal experiments with the partial ligation model indicated that overexpression of APEX1 negated the action of vitexin against endothelial inflammation, and that endothelial-specific deletion of APEX1 ameliorated atherogenesis. We thus propose targeting APEX1 with vitexin as a potential therapeutic strategy to alleviate atherosclerosis.
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