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Shear stress effects on endothelial cells: cell surface dynamics
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Friday 14 October 1994: Workshop Abstracts W23 Genetic variation, hypertension and atherosclerosis
laminar high shear stress, but hardly expressed in stagnation areas. Lengths and numbers of membranous particle ridges of the junction, observed by a freeze fracture method, were increased in areas with laminar high shear stress (30-60 dyn/cm*) but not in areas with flow stagnation. Heparan sulfate and chondroitin/dermatan sulfate were increased in the cell surface and medium respective1 when cells were exposed to laminar shear stress of 40 dyn/cms for 24 h, proven by a metabolic labelling assay with 35S and enzymatic digestion. In conclusion, unidirectional laminar shear stress is beneficial for the development of tight junctions and glycocalyx on the endothelial cells, enhancing antiatherogenic properties of the vessel wall. Shear stress effects on endothelial cells: cell surface dynamics Davies, Barbee RA, Lal R, Robotewskyj A, Griem ML, Dept. of Pathol., Pritzker Sch. of Med., Univ. of Chicago, Chicago, IL 60637, USA
There am many diverse responses of endothelial cells to hemodynamically related mechanical stresses, ranging from ion-channel activation to gene regulatory events. The processes of force transmission from the blood to the cell, and force transduction within the endothelium to electrophysiological, biochemical, and gene regulatory responses, are poorly understood. This pmsentation reviews the principal mechanisms currently thought to be involved in flow signalling at the endothelium. Response mechanisms can be divided into two broad groups: those resulting from direct physical perturbation of the cell, and those arising indirectly from a change in the local concentrations of chemicals that influence endothelial biology. Flow-induced alterations of cell tension am manifested as cytoskeletal force transmission and possibly force transduction. Endothelial surface dynamics were observed in real time by atomic force microscopy. The topography of the luminal surface was altered by flow, msulting in differential shear stress gradients on the scale of a single cell. At the abluminal cell surface, focal adhesions appear to be realigned by shear stress applied to the luminal cell surface, the force being transmitted throughout the cell by cytoskeletal elements. An understanding of the interplay between force transmission and mechanotransduction is essential to determine the location(s) of putative flow sensors in endothelium. Endothelial gene regulation by biomechanical forces w, Sumpio BE*, Gimbrone Jr MA, Vascular Res. Div., Dept. of Pathol., Brigham and Women’s Hosp., Boston 021 15, MA: *Vascular Surgery Div., Yale Univ., New Haven, CT, USA
Hemodynamic forces, which include wall shear stress and cyclic strain, have been shown both in vitro and in vivo to modulate the morphology and function of the endothelium. Recently, several groups have demonstrated that, in well-defined in vitro systems, both shear stress and cyclic strain can modulate endothelial gene expression. In particular, our group has demonstrated that PDGFB chain gene transcription is induced by physiologic levels (10 dyn/cm*) of laminar shear stress. We have defined a region
within the PDGF-B chain promoter that is responsible for the induction of the gene by shear stress, and called this the ‘Shear Stress Responsive Element’ (SSRE). This promoter element binds shear-stress inducible nuclear proteins from endothelial cells. A core sequence within the SSRE (GAGACC) is found in the promoters of several other endothelial genes that are responsive to shear stress. This core sequence was found to be the binding site within the SSRE by using mutated SSRE probes in gel retardation assays. Moreover, hybrid promoters containing the SSRE sequence (as taken from the PDGF-B chain promoter) were inducible by shear stress in bovine aortic endothelial cells, thus verifying the fact that the SSRE is both necessary and sufficient for gene induction by laminar shear stress. The presence of SSREbinding proteins in nuclear extracts made from endothelial cells exposed to cyclic strain was also tested. We have found that the SSRE does bind to nuclear proteins from endothelial cells, but not smooth muscle cells exposed to cyclic strain (24% strain, 60 cycles/min), and that this binding peaks at 30 min. These results suggest that biomechanical forces act on the endothelium through a common-cell-type-specific mechanism to activate gene transcription. Arterial responses to alterations in blood flow w, Toronto Hosp. Res. Centre, 200 Elizabeth St., Toronto, M5G 2C4, Canada
Long-term changes in blood flow rates through arteries elicit adaptive adjustments in vessel diameter that are mediated by a direct sensitivity of endothelial cells to flow-derived shear stress. This sensitivity to shear stress provides a potent mechanism for modulating vascular structure according to tissue perfusion mquirements. Flow-induced vessel remodeling has been implicat d in physiological vascular remodeling, such as arterial remodeli g associated with reproductive cycles and pregnancy. In additio , sensitivity of vascular structure to shear stress is an import i t mechanism linking vascular growth to developmental changes in blood flow. Flow-induced arterial remodeling also has important implications for the progression of vascular disease. Acceleration of flow through stenoses at atherosclerotic lesion sites elicits adaptive medial remodeling that apparently limits narrowing of the artery early in the disease process. Conversely, compromised flow in late stage disease can induce narrowing of arteries to exacerbate the disease state. In addition, abnormal vascular geometries, such as severe stenoses and sites of vascular graft implantation, impose unique hemodynamic loads on arterial tissue that can elicit striking vessel remodeling, including poststenotic dilatation and occlusive intimal proliferation at graft sites. The local mechanisms that control flow-induced remodeling are poorly understood despite their importance in normal vascular physiology and in the progression of vascular disease. The mechanisms by which arteries remodel include cell proliferation, cell death, synthesis and degradation of matrix and remodeling of matrix without a net change in content.
W23 GENETIC VARIATION, HYPERTENSION AND ATHEROSCLEROSIS Intermediate phenotypes in early primary hypertension: the Dutch Hypertension and Offspring Study &obbee DE, Dept. of Epidemiology and Biostatistics, Erasmus Univ. Med. Sch., PO Box 1738, 3000 DR Rotterdam, The Netherlands
The roots of primary hypertension are to be found early in life. The development of hypertension is characterized by a gradual deviation of blood pressure levels from normality, as a result of
genetic susceptibility modified by environmental factors. During its development, the pathophysiologic characteristics of hypertension may be obscured by changes in hemodynamics and neurohumoral regulation secondary to sustained elevations in pressure. As a consequence it may be difficult, if not impossible, to disentangle causes from consequences when studying the etiology of high blood pressure in adult hypertensive subjects, Moreover, there is not one etiologic factor in hypertension but different mechanisms may interact and dominate in different hypertensive
Atherosclerosis X, Montreal, October 1994
Friday 14 October 1994: Workshop Abstracts W23 Genetic variation, hypertension and atherosclerosis
laminar high shear stress, but hardly expressed in stagnation areas. Lengths and numbers of membranous particle ridges of the junction, observed by a freeze fracture method, were increased in areas with laminar high shear stress (30-60 dyn/cm*) but not in areas with flow stagnation. Heparan sulfate and chondroitin/dermatan sulfate were increased in the cell surface and medium respective1 when cells were exposed to laminar shear stress of 40 dyn/cms for 24 h, proven by a metabolic labelling assay with 35S and enzymatic digestion. In conclusion, unidirectional laminar shear stress is beneficial for the development of tight junctions and glycocalyx on the endothelial cells, enhancing antiatherogenic properties of the vessel wall. Shear stress effects on endothelial cells: cell surface dynamics Davies, Barbee RA, Lal R, Robotewskyj A, Griem ML, Dept. of Pathol., Pritzker Sch. of Med., Univ. of Chicago, Chicago, IL 60637, USA
There am many diverse responses of endothelial cells to hemodynamically related mechanical stresses, ranging from ion-channel activation to gene regulatory events. The processes of force transmission from the blood to the cell, and force transduction within the endothelium to electrophysiological, biochemical, and gene regulatory responses, are poorly understood. This pmsentation reviews the principal mechanisms currently thought to be involved in flow signalling at the endothelium. Response mechanisms can be divided into two broad groups: those resulting from direct physical perturbation of the cell, and those arising indirectly from a change in the local concentrations of chemicals that influence endothelial biology. Flow-induced alterations of cell tension am manifested as cytoskeletal force transmission and possibly force transduction. Endothelial surface dynamics were observed in real time by atomic force microscopy. The topography of the luminal surface was altered by flow, msulting in differential shear stress gradients on the scale of a single cell. At the abluminal cell surface, focal adhesions appear to be realigned by shear stress applied to the luminal cell surface, the force being transmitted throughout the cell by cytoskeletal elements. An understanding of the interplay between force transmission and mechanotransduction is essential to determine the location(s) of putative flow sensors in endothelium. Endothelial gene regulation by biomechanical forces w, Sumpio BE*, Gimbrone Jr MA, Vascular Res. Div., Dept. of Pathol., Brigham and Women’s Hosp., Boston 021 15, MA: *Vascular Surgery Div., Yale Univ., New Haven, CT, USA
Hemodynamic forces, which include wall shear stress and cyclic strain, have been shown both in vitro and in vivo to modulate the morphology and function of the endothelium. Recently, several groups have demonstrated that, in well-defined in vitro systems, both shear stress and cyclic strain can modulate endothelial gene expression. In particular, our group has demonstrated that PDGFB chain gene transcription is induced by physiologic levels (10 dyn/cm*) of laminar shear stress. We have defined a region
within the PDGF-B chain promoter that is responsible for the induction of the gene by shear stress, and called this the ‘Shear Stress Responsive Element’ (SSRE). This promoter element binds shear-stress inducible nuclear proteins from endothelial cells. A core sequence within the SSRE (GAGACC) is found in the promoters of several other endothelial genes that are responsive to shear stress. This core sequence was found to be the binding site within the SSRE by using mutated SSRE probes in gel retardation assays. Moreover, hybrid promoters containing the SSRE sequence (as taken from the PDGF-B chain promoter) were inducible by shear stress in bovine aortic endothelial cells, thus verifying the fact that the SSRE is both necessary and sufficient for gene induction by laminar shear stress. The presence of SSREbinding proteins in nuclear extracts made from endothelial cells exposed to cyclic strain was also tested. We have found that the SSRE does bind to nuclear proteins from endothelial cells, but not smooth muscle cells exposed to cyclic strain (24% strain, 60 cycles/min), and that this binding peaks at 30 min. These results suggest that biomechanical forces act on the endothelium through a common-cell-type-specific mechanism to activate gene transcription. Arterial responses to alterations in blood flow w, Toronto Hosp. Res. Centre, 200 Elizabeth St., Toronto, M5G 2C4, Canada
Long-term changes in blood flow rates through arteries elicit adaptive adjustments in vessel diameter that are mediated by a direct sensitivity of endothelial cells to flow-derived shear stress. This sensitivity to shear stress provides a potent mechanism for modulating vascular structure according to tissue perfusion mquirements. Flow-induced vessel remodeling has been implicat d in physiological vascular remodeling, such as arterial remodeli g associated with reproductive cycles and pregnancy. In additio , sensitivity of vascular structure to shear stress is an import i t mechanism linking vascular growth to developmental changes in blood flow. Flow-induced arterial remodeling also has important implications for the progression of vascular disease. Acceleration of flow through stenoses at atherosclerotic lesion sites elicits adaptive medial remodeling that apparently limits narrowing of the artery early in the disease process. Conversely, compromised flow in late stage disease can induce narrowing of arteries to exacerbate the disease state. In addition, abnormal vascular geometries, such as severe stenoses and sites of vascular graft implantation, impose unique hemodynamic loads on arterial tissue that can elicit striking vessel remodeling, including poststenotic dilatation and occlusive intimal proliferation at graft sites. The local mechanisms that control flow-induced remodeling are poorly understood despite their importance in normal vascular physiology and in the progression of vascular disease. The mechanisms by which arteries remodel include cell proliferation, cell death, synthesis and degradation of matrix and remodeling of matrix without a net change in content.
W23 GENETIC VARIATION, HYPERTENSION AND ATHEROSCLEROSIS Intermediate phenotypes in early primary hypertension: the Dutch Hypertension and Offspring Study &obbee DE, Dept. of Epidemiology and Biostatistics, Erasmus Univ. Med. Sch., PO Box 1738, 3000 DR Rotterdam, The Netherlands
The roots of primary hypertension are to be found early in life. The development of hypertension is characterized by a gradual deviation of blood pressure levels from normality, as a result of
genetic susceptibility modified by environmental factors. During its development, the pathophysiologic characteristics of hypertension may be obscured by changes in hemodynamics and neurohumoral regulation secondary to sustained elevations in pressure. As a consequence it may be difficult, if not impossible, to disentangle causes from consequences when studying the etiology of high blood pressure in adult hypertensive subjects, Moreover, there is not one etiologic factor in hypertension but different mechanisms may interact and dominate in different hypertensive
Atherosclerosis X, Montreal, October 1994