Disturbed Shear Stress Induces Inflammation and Atherosclerosis-Role of BMP4 as a Mechanosensitive and Inflammatory Cytokine

Jo, Hanjoong; Song, Hannah

Abstract

Atherosclerosis is an inflammatory disease occurring preferentially in arterial regions exposed to disturbed flow conditions including oscillatory shear stress(OS). In contrast, the arterial regions exposed to laminar shear(LS) are relatively lesion-free. The opposite effects of LS(atheroprotective) and OS(atherogenic) are likely to be determined by differential expression of genes and proteins. Therefore, numerous investigators including us carried out transcript profiling studies to identify mechanosensitive genes that are turned on or off in response to different shear conditions. Through this and subsequent verification approaches using both cultured endothelial cells and human coronary arteries containing atherosclerotic lesions, we discovered that BMP4 expression is a highly regulated by different shear conditions. More importantly, we discovered a novel role of BMP4 as a mechanosensitive pro-inflammatory cytokine. Exposing endothelial cells to OS increased BMP4 protein expression while LS decreased it. Also, we found BMP4 expression only in the selective patches of endothelial cells overlying foam cell lesions in human coronary arteries. Chronic exposure of endothelial cells to OS stimulates inflammatory responses in endothelial cells such as production of intercellular adhesion molecule 1(ICAM-1) leading to monocyte adhesion to endothelium. A series of studies have revealed that exposure to OS induces inflammatory responses by producing BMP4 in endothelial cells. BMP4 then stimulates ICAM-1 expression and monocyte adhesion by the reactive oxygen species(ROS) and NF kappa B-dependent mechanisms. ROS produced in response to OS and BMP4 are derived from NADPH oxidase involving nox1 and p47phox components. These findings strongly suggest that BMP4 is a mechanosensitive, inflammatory factor playing a critical role in early steps of atherogenesis in atheroprone areas. This review is written to summarize this emerging field of shear stress, inflammation and atherosclerosis.