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- Bergh, Niklas, 1979, et al.
(författare)
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A new biomechanical perfusion system for ex vivo study of small biological intact vessels
- 2005
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Ingår i: Ann Biomed Eng. - : Springer Science and Business Media LLC. - 0090-6964. ; 33:12, s. 1808-18
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Tidskriftsartikel (refereegranskat)abstract
- The vascular endothelium transduces physical stimuli within the circulation into physiological responses, which influence vascular remodelling and tissue homeostasis. Therefore, a new computerized biomechanical ex vivo perfusion system was developed, in which small intact vessels can be perfused under well-defined biomechanical forces. The system enables monitoring and regulation of vessel lumen diameter, shear stress, mean pressure, variable pulsatile pressure and flow profile, and diastolic reversal flow. Vessel lumen measuring technique is based on detection of the amount of flourescein over a vessel segment. A combination of flow resistances, on/off switches, and capacitances creates a wide range of pulsatile pressures and flow profiles. Accuracy of the diameter measurement was evaluated. The diameters of umbilical arteries were measured and compared with direct ultrasonographic measurement of the vessel diameter. As part of the validation the pulsatile pressure waveform was altered, e.g., in terms of pulse pressure, frequency, diastolic shape, and diastolic reversal flow. In a series of simulation experiments, the hemodynamic homeostasis functions of the system were successfully challenged by generating a wide range of vascular diameters in artificial and intact human vessels. We conclude that the system presented may serve as a methodological and technical platform when performing advanced hemodynamic stimulation protocols.
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| 2. |
- Bergh, Niklas, 1979
(författare)
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Development of a New Biomechanical ex vivo Perfusion System - Studies on effects of biomechanical and inflammatory stress on hemostatic genes in human vascular endothelium
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The vascular endothelium is a multifunctional interface constantly exposed to biomechanical forces such as shear and tensile stress. Biomechanical stress is involved in the pathophysiological process of the vessel wall and thus affects vascular remodeling, atherosclerosis and thrombogenesis. Many different systems have been designed to subject endothelial cells to mechanical stress. However, previous systems have had large limitations in creating physiologically relevant biomechanical stress protocols. Therefore, there is a need for more refined biological perfusion systems that as accurately as possible mimics the in vivo conditions. In the present work, a new biomechanical ex vivo perfusion system for integrative physiological and molecular biology studies of intact vessels of different sizes as well as artificial vessels was developed. This model was constructed for advanced perfusion protocols under strictly controlled biomechanical (shear stress, tensile stress) as well as metabolic (temperature, pH, oxygen tension) conditions. The system enables monitoring and regulation of vessel lumen diameter, shear stress, mean pressure, variable pulsatile pressure and flow profiles, and diastolic reversed flow. The vessel lumen measuring technique is based on detection of the amount of flourescein over a vessel segment. A combination of flow resistances, on/off switches and capacitances creates a wide range of possible combinations of pulsatile pressures and flow profiles. The perfusion platform was extensively evaluated technically as well as biologically by perfusion of high precision made glass capillaries, human umbilical arteries as well as endothelialized artificial vessels. Artificial vessels with a confluent human umbilical vein endothelial cell layer were exposed to different levels of shear stress or different levels of static or pulsatile pressure. Shear stress was a more powerful stimulus than static or pulsatile tensile stress. While shear stress affected mRNA expression of all six studied genes (t-PA, PAI-1, u-PA, thrombomodulin, eNOS and VCAM-1), neither gene was found to be regulated by tensile stress. Shear stress suppressed t-PA and VCAM-1 in a dose response dependent way. The expression of thrombomodulin was also reduced by shear stress. u-PA, eNOS and PAI-1 were induced by shear stress, but showed no obvious dose response effect for these genes. Further, the unexpected suppression of t-PA by shear stress was studied by using mechanistic experiments with pharmacologic inhibitors. Our data indicate that the suppressive effect of shear stress on t-PA was mediated by suppression of JNK and not by p38 MAPK and ERK1/2. The interplay between inflammatory stress and different combination of tensile as well as shear stress was studied on six key anti- and pro-thrombotic genes in HUVEC. The endothelial cell response to TNF-α was not modulated by tensile stress. Again, shear stress was a more potent stimulus. Shear stress counteracted the cytokine-induced expression of VCAM-1, and the cytokine-suppressed expression of thrombomodulin and eNOS. Shear stress and TNF-α additively induced PAI-1, whereas shear stress blocked the cytokine effect on t-PA and u-PA. In conclusion, these findings illustrate that biomechanical forces, particularly shear stress, have important regulatory effects on endothelial gene function. A possible pathophysiological scenario is that an unfavourable hemodynamic milieu leads to a lower threshold for the induction of genes related to endothelial dysfunction in lesion-prone areas upon negative stress, such as inflammation.
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| 3. |
- Bergh, Niklas, 1979, et al.
(författare)
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Effects of two complex hemodynamic stimulation profiles on hemostatic genes in a vessel-like environment
- 2008
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Ingår i: Endothelium. - : Informa UK Limited. - 1029-2373 .- 1062-3329. ; 15:5-6, s. 231-8
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Tidskriftsartikel (refereegranskat)abstract
- Endothelial cells are the main sensors of changes in the biomechanical flow environment and play a pivotal role in vascular homeostasis. An in vitro perfusion model was developed to study the regulatory effect on gene expression by different flow and pressure profiles. Human umbilical vein endothelial cells were grown to confluence inside capillary microslides or silicone tubes. Thereafter, they were exposed to different levels of shear stress or different levels of static or pulsatile pressure. Genes representing various hemostasis functions of the endothelial cells were analyzed. Shear stress was a more effortful stimulus than static or pulsatile tensile stress. Although shear stress affected mRNA expression of all six studied genes (tissue-type plasminogen activator [t-PA], plasminogen activator inhibitor [PAI]-1, Thrombomodulin [TM], urokinase-type plasminogen activator [u-PA], vascular cell adhesion molecule [VCAM-1], and endothelial nitric oxide synthase [eNOS]), none of the genes was found regulated by pressure. Shear stress down-regulated t-PA and VCAM-1 in a dose response-dependent way, and up-regulated TM. u-PA, eNOS, and PAI-1 were up-regulated by shear stress, but there was no obvious dose-response effect for these genes. These findings suggest that shear stress has a more powerful gene regulatory effect on endothelial gene expression than tensile stress. Low shear stress induced a more proatherogenic endothelial surface but preserved t-PA gene expression levels compared to high shear stress.
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| 4. |
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| 5. |
- Ulfhammer, Erik, 1974, et al.
(författare)
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Suppression of endothelial t-PA expression by prolonged high laminar shear stress
- 2009
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Ingår i: Biochemical and Biophysical Research Communications. - 1090-2104. ; 379:2, s. 532-536
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Tidskriftsartikel (refereegranskat)abstract
- Primary hypertension is associated with an impaired capacity for acute release of endothelial tissue-type plasminogen activator (t-PA), which is an important local protective response to prevent thrombus extension. As hypertensive vascular remodeling potentially results in increased vascular wall shear stress, we investigated the impact of shear on regulation of t-PA. Cultured human endothelial cells were exposed to low (1.5dyn/cm(2)) or high (25dyn/cm(2)) laminar shear stress for up to 48h in two different experimental models. Using real-time RT-PCR and ELISA, shear stress was observed to time and magnitude-dependently suppress t-PA transcript and protein secretion to approximately 30% of basal levels. Mechanistic experiments revealed reduced nuclear protein binding to the t-PA specific CRE element (EMSA) and an almost completely abrogated shear response with pharmacologic JNK inhibition. We conclude that prolonged high laminar shear stress suppresses endothelial t-PA expression and may therefore contribute to the enhanced risk of arterial thrombosis in hypertensive disease.
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