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      Differential Global Gene Expression Response Patterns of Human Endothelium Exposed to Shear Stress and Intraluminal Pressure


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          We investigated the global gene expression response of endothelium exposed to shear stress and intraluminal pressure and tested the hypothesis that the two biomechanical forces induce a differential gene expression response pattern. Intact living human conduit vessels (umbilical veins) were exposed to normal or high intraluminal pressure, or to low or high shear stress in combination with a physiological level of the other force in a unique vascular ex vivo perfusion system. Gene expression profiling was performed by the Affymetrix microarray technology on endothelial cells isolated from stimulated vessels. Biomechanical forces were found to regulate a very large number of genes in the vascular endothelium. In this study, 1,825 genes were responsive to mechanical forces, which corresponds to 17% of the expressed genes. Among pressure-responsive genes, 647 genes were upregulated and 519 genes were downregulated, and of shear stress-responsive genes, 133 genes were upregulated and 771 downregulated. The fraction of genes that responded to both pressure and shear stimulation was surprisingly low, only 13% of the regulated genes. Our results indicate that the two different stimuli induce distinct gene expression response patterns, which can also be observed when studying functional groups. Considering the low number of overlapping genes, we suggest that the endothelial cells can distinguish between shear stress and pressure stimulation.

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          Most cited references 17

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          Prolonged fluid shear stress induces a distinct set of endothelial cell genes, most specifically lung Krüppel-like factor (KLF2).

          The endothelium expresses a large repertoire of genes under apparent transcriptional control of biomechanical forces, many of which are neither cell-type nor flow specific. We set out to identify genes that are uniquely flow responsive in human vascular endothelial cells. Transcriptional profiling using commercial DNA microarrays identified 12 of 18 000 genes that were modulated at least 5-fold after 24 hours of steady laminar flow (25 dyne/cm(2)). After a 7-day exposure to unidirectional pulsatile flow (19 +/- 12 dyne/cm(2)), only 3 of 12 remained elevated at least 5-fold. A custom microarray of ~300 vascular cell-related gene fragments was constructed, and expression analysis revealed that many flow-induced genes are also induced by at least one of the following agents: tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), transforming growth factor-beta, vascular endothelial growth factor, or thrombin, indicating a more general role in adaptive or stress responses. Most flow-induced genes were also induced by TNF-alpha but not IL-1beta, suggesting the involvement of reactive oxygen species. A limited panel of genes that are unique for flow-exposed cultures was identified, including lung Krüppel-like factor (LKLF/KLF2) and cytochrome P450 1B1 (CYP1B1). In marked contrast, both these genes were substantially repressed by TNF-alpha. LKLF but not CYP1B1 mRNA was detected exclusively in the vascular endothelium of healthy human aorta by in situ hybridization and appeared to be flow regulated. To date LKLF is the first endothelial transcription factor that is uniquely induced by flow and might therefore be at the molecular basis of the physiological healthy, flow-exposed state of the endothelial cell.
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            Biomechanical activation of vascular endothelium as a determinant of its functional phenotype.

            One of the striking features of vascular endothelium, the single-cell-thick lining of the cardiovascular system, is its phenotypic plasticity. Various pathophysiologic factors, such as cytokines, growth factors, hormones, and metabolic products, can modulate its functional phenotype in health and disease. In addition to these humoral stimuli, endothelial cells respond to their biomechanical environment, although the functional implications of this biomechanical paradigm of activation have not been fully explored. Here we describe a high-throughput genomic analysis of modulation of gene expression observed in cultured human endothelial cells exposed to two well defined biomechanical stimuli-a steady laminar shear stress and a turbulent shear stress of equivalent spatial and temporal average intensity. Comparison of the transcriptional activity of 11,397 unique genes revealed distinctive patterns of up- and down-regulation associated with each type of stimulus. Cluster analyses of transcriptional profiling data were coupled with other molecular and cell biological techniques to examine whether these global patterns of biomechanical activation are translated into distinct functional phenotypes. Confocal immunofluorescence microscopy of structural and contractile proteins revealed the formation of a complex apical cytoskeleton in response to laminar shear stress. Cell cycle analysis documented different effects of laminar and turbulent shear stresses on cell proliferation. Thus, endothelial cells have the capacity to discriminate among specific biomechanical forces and to translate these input stimuli into distinctive phenotypes. The demonstration that hemodynamically derived stimuli can be strong modulators of endothelial gene expression has important implications for our understanding of the mechanisms of vascular homeostasis and atherogenesis.
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              Identification of vascular endothelial genes differentially responsive to fluid mechanical stimuli: cyclooxygenase-2, manganese superoxide dismutase, and endothelial cell nitric oxide synthase are selectively up-regulated by steady laminar shear stress.


                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                October 2005
                28 September 2005
                : 42
                : 5
                : 441-452
                aClinical Experimental Research Laboratory, Cardiovascular Institute Sahlgrenska University Hospital/Östra, and bResearch Centre of Endocrinology and Metabolism, Department of Internal Medicine, Sahlgrenska University Hospital, Göteborg University, Göteborg, Sweden
                87983 J Vasc Res 2005;42:441–452
                © 2005 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 5, References: 29, Pages: 12
                Research Paper


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