1179 in a PKA-dependent, but Aktindependent manner, whereas the NO ⅐ production is regulated by the mechanisms dependent on both PKA and Akt. A coordinated interaction between Akt and PKA may be an important mechanism by which eNOS activity is regulated in response to physiological stimuli such as shear stress.

Atherosclerosis is now viewed as an inflammatory disease occurring preferentially in arterial regions exposed to disturbed flow conditions, including oscillatory shear stress (OS), in branched arteries. In contrast, the arterial regions exposed to laminar shear (LS) are relatively lesion-free. The mechanisms underlying the opposite effects of OS and LS on the inflammatory and atherogenic processes are not clearly understood. Here, through DNA microarrays, protein expression, and functional studies, we identify bone morphogenic protein 4 (BMP4) as a mechanosensitive and pro-inflammatory gene product. Exposing endothelial cells to OS increased BMP4 protein expression, whereas LS decreased it. In addition, we found BMP4 expression only in the selective patches of endothelial cells overlying foam cell lesions in human coronary arteries. The same endothelial patches also expressed higher levels of intercellular cell adhesion molecule-1 (ICAM-1) protein compared with those of non-diseased areas. Functionally, we show that OS and BMP4 induced ICAM-1 expression and monocyte adhesion by a NF B-dependent mechanism. We suggest that BMP4 is a mechanosensitive, inflammatory factor playing a critical role in early steps of atherogenesis in the lesion-prone areas.Endothelial cells are constantly exposed to shear stress (a dragging force generated by blood flow), which controls cellular structure and function such as regulation of vascular tone and diameter, vessel wall remodeling, hemostasis, and inflammatory responses (1). The importance of various types of shear stress is highlighted by the focal development of atherosclerosis (2). Atherosclerosis preferentially occurs in the arterial regions exposed to unstable shear stress conditions in branched or curved arteries, whereas straight arteries exposed to unidirectional laminar shear (LS) 1 are relatively lesion-free (1-3). Atherosclerosis is now known as an inflammatory disease caused by endothelial dysfunction (3, 4). One of the first visible markers of endothelial dysfunction in the lesion-prone areas is upregulation of inflammatory adhesion molecules such as E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and ICAM-1 (3-6). These endothelial adhesion molecules play essential roles in adhesion and recruitment of monocytes to the subendothelial layer (3, 4).How do unstable shear conditions such as low and oscillating shear stress (OS) cause inflammation in those lesion-prone areas, whereas LS exerts athero-protective effects? The opposite effects of LS and OS may be determined by differential expression of genes and proteins, ultimately inducing anti-and pro-inflammatory and atherogenic responses. Recently, several studies (7-10) have begun to address the initial question to determine the expression profiles of mechanosensitive genes. However, the functional importance of those genes has not been clearly established.Here, we report identification of a mechanosensitive gene, BMP4, by DNA microarray analyses and subsequent verification by a variety of additional approac...

Vascular endothelial cells are directly and continuously exposed to fluid shear stress generated by blood flow. Shear stress regulates endothelial structure and function by controlling expression of mechanosensitive genes and production of vasoactive factors such as nitric oxide (NO). Though it is well known that shear stress stimulates NO production from endothelial nitric oxide synthase (eNOS), the underlying molecular mechanisms remain unclear and controversial. Shear-induced production of NO involves Ca2+/calmodulin-independent mechanisms, including phosphorylation of eNOS at several sites and its interaction with other proteins, including caveolin and heat shock protein-90. There have been conflicting results as to which protein kinases-protein kinase A, protein kinase B (Akt), other Ser/Thr protein kinases, or tyrosine kinases-are responsible for shear-dependent eNOS regulation. The functional significance of each phosphorylation site is still unclear. We have attempted to summarize the current status of understanding in shear-dependent eNOS regulation.

Arterial regions exposed to oscillatory shear (OS) in branched arteries are lesion-prone sites of atherosclerosis, whereas those of laminar shear (LS) are relatively well protected. Here, we examined the hypothesis that OS and LS differentially regulate production of O 2 ؊ from the endothelial NAD(P)H oxidase, which, in turn, is responsible for their opposite effects on a critical atherogenic event, monocyte adhesion. We used aortic endothelial cells obtained from C57BL/6 (MAE-C57) and p47 phox؊/؊ (MAE-p47 ؊/؊ ) mice, which lack a component of NAD(P)H oxidase. O 2 ؊ production was determined by dihydroethidium staining and an electron spin resonance using an electron spin trap methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine. Chronic exposure (18 h) to an arterial level of OS (؎ 5 dynes/cm 2 ) increased O 2 ؊ (2-fold) and monocyte adhesion (3-fold) in MAE-C57 cells, whereas chronic LS (15 dynes/cm 2 , 18 h) significantly decreased both monocyte adhesion and O 2 ؊ compared with static conditions. In contrast, neither LS nor OS were able to induce O 2 ؊ production and monocyte adhesion to MAE-p47 ؊/؊ . Treating MAE-C57 with a cellpermeable superoxide dismutase compound, polyethylene glycol-superoxide dismutase, also inhibited OS-induced monocyte adhesion. In addition, over-expressing p47 phox in MAE-p47 ؊/؊ restored OS-induced O 2 ؊ production and monocyte adhesion. These results suggest that chronic exposure of endothelial cells to OS stimulates O 2 ؊ and/or its derivatives produced from p47 phox -dependent NAD(P)H oxidase, which, in turn, leads to monocyte adhesion, an early and critical atherogenic event.Fluid shear stress, the frictional force generated by blood flow over the vascular endothelium, is a major factor in atherogenesis. The importance of shear stress in vascular biology and pathophysiology has been highlighted by the focal development patterns of atherosclerosis in hemodynamically defined regions. For example, regions of branched and curved arteries experience disturbed blood flow patterns, including oscillatory shear stress (OS), 1 typically ranging Ϯ 5 dynes/cm 2 (Ϯ indicates changes in flow directions) (1, 2). These disturbed shear regions correspond to "lesion-prone" areas that develop early forms of atherosclerotic lesions (1-3). In contrast, relatively straight arteries, which are exposed to steady uni-directional laminar shear stress (typically ranging from 5-25 dynes/cm 2 ), are usually protected from early atherosclerotic plaque development (1, 2). The mechanisms by which laminar shear (LS) acts as atheroprotective force whereas OS initiates or contributes to atherogenesis have been the subject of intense investigation by many researchers.The vascular endothelium is in direct contact with blood flow and acts as a mechanotransducer by sensing and transducing the changes in local mechanical forces into cellular signals. Endothelial function, shape, physiology, and pathophysiology are greatly regulated by the types (uni-directional laminar or disturbed flow conditions) and magnitudes (high or...