No description available.

No description available.

No description available.

No description available.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23860号 / 工博第4947号 / 新制||工||1773(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 岸田 潔, 教授 三村 衛, 教授 木村 亮 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 新制・課程博士 / 博士(農学) / 甲第23528号 / 農博第2475号 / 新制||農||1087(附属図書館) / 学位論文||R3||N5359(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 藤原 正幸, 教授 中村 公人, 准教授 藤澤 和謙 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Altered fluid flow, which is found in branches and curvatures of arteries, results in abnormal forces on the endothelial cells (EC). These forces have been shown to alter EC gene expression and phenotype and to activate several cellular structures including G-proteins, ion channels, adhesion molecules, and caveolae. Recently, PECAM-1 has been implicated as the primary sensor of hemodynamic forces in EC. Shear stress rapidly induces tyrosine phosphorylation of PECAM-1 and the recruitment of SHP-2. These events appear to contribute to shear-activation of ERK1/2. Additionally, PECAM-1 has been shown to form a mechanosensory signaling complex with VE-cadherin, VEGFR2, and βcatenin which plays a role in adhesion molecule expression and regulation of NF-κB. Past work has shown that caveolae membrane domains also serve as mechanotransduction sites that regulate many of these same second messengers. Based on these novel observations, we hypothesize that the PECAM-1 mediated mechanotransduction requires caveolar membrane domains to effectively propagate mechano-signals. In this study, we intended to specifically test this hypothesis by 1) evaluating the role of caveolae in shear stress-induced PECAM-1 tyrosine phosphorylation, recruitment of SHP-2, and formation of a signaling complex with VE-cadherin, VEGFR2, and βcatenin and 2) determining the functional significance of PECAM-1 compartmentalization within caveolae with regard to changes in endothelial cell phenotype induced by atherogenic patterns of flow. Here, we have identified a pool of PECAM-1 which localizes within lipid rafts and caveolar membranes. This pool of PECAM-1 was shown to be activated by tyrosine phosphorylation and recruitment of mechanosignaling complex members in response to shear stress. We were also able to demonstrate complex formation in an in vivo model of disturbed blood flow. The significance of PECAM-1 compartmentalization to these membrane microdomains was demonstrated in endothelial cells treated with raft/caveolae disrupting compounds where shear stress-induced PECAM-1 tyrosine phosphorylation was markedly attenuated. Finally, we attempted to generate an adenovirus expressing a mutant form of PECAM-1 which was unable to target to lipid rafts in order to determine the importance of PECAM-1 localization in lipid rafts and caveolae on its downstream signaling in response to shear stress. Results from these studies provide new knowledge as to how endothelial cells respond to changing hemodynamic parameters, which could provide greater insight into how flow influences vascular homeostasis. / Physiology

Purpose/hypothesis: Regular practice of exercise is the most effective non-pharmacological intervention that improves vascular health, which is thought to be mediated by a repeated exposure of vessel walls to increased hemodynamic shear stress (SS). Mitochondria have been shown to be essential cellular structures responsible for a wide variety of vascular functions, and its impairment is often associated with cardiovascular disease. However, researches on vascular mitochondrial adaptations to SS are in a very early stage and many questions remain unresolved. The objective of this study is to investigate the effect of exercise preconditioning on endothelial mitochondria in an angiotensin (Ang) II-induced hypertension model. It was hypothesized that exercise preconditioning prevents Ang II induced-hypertensive phenotypes by improving mitochondrial homeostasis in the endothelium. Methods: High-magnitude laminar SS (LSS) (20 dyne/cm2) was applied to human aortic endothelial cells (HAECs) using a cone-and-plate shear apparatus for 48 hours. Either LSS-preconditioned or static flow-situated HAECs were incubated with Ang II. In in vivo experiments, C57BL/6J mice were singly housed with or without a voluntary running wheel for 7 weeks. Ang II or saline was infused in a constant rate using an implantable osmotic pump for the last 2 weeks of the experimental period. Mitochondrial membrane potential (ÄØm) and mitoROS production were measured using fluorochrome molecular probe-based microscopic techniques, and mtDNA damage was assessed by a long amplicon quantitative PCR (LA-QPCR) method. Results: In HAECs, LSS preconditioning attenuated Ang II-induced mitochondrial dysfunction, which was evidenced by decreased mitoROS generation, increased ÄØm, and reduced mtDNA damage. Likewise, in aortic tissues, Ang II-induced mitochondrial phenotypic changes (i.e. mitoROS production, mtDNA damage and ÄØm reduction) were significantly reduced in exercise-preconditioned mice compared to sedentary controls. Moreover, Ang II-induced blood pressure elevation was completely blocked in exercise preconditioned animals. Conclusion: Taken together, high-magnitude LSS improves endothelial function by enhancing mtDNA integrity and mitochondrial function. These findings further support the idea that aerobic exercise is a prominent life-style modification strategy to prevent hypertension by targeting dysfunctional mitochondria in the vessel wall. / Kinesiology

Endothelial function is influenced by a variety of factors, including shear stress direction and magnitude. Whereas improvements in endothelial function have mostly been attributed to increased anterograde flow, the results of many interventional models in humans suggest that enhancing blood flow in both anterograde and retrograde directions to create a high shear stress oscillatory stimulus may be optimal for improving endothelial function. Well-controlled studies are necessary to further this theory. The purposes of this study were to determine the brachial artery acute shear stress and endothelial function responses to (1) passive heat stress (HEAT), (2) ECG-gated cuff compressions (CUFF), and (3) ECG-gated rhythmic handgrip exercise (HGEX); and (4) to determine if there is a relationship between the degree of shear stress oscillation and endothelial function, regardless of the stimulus applied. We hypothesized that (1) HEAT would increase anterograde shear stress and decrease retrograde shear stress, leading to an unpredictable change in endothelial function; (2) CUFF would increase both anterograde and retrograde shear stress, leading to an increase in endothelial function; (3) HGEX would increase anterograde and retrograde shear stress and exercise metabolites, leading to an increase in endothelial function; and (4) the change in oscillatory shear index would be positively associated with the change in flow-mediated dilation, such that an increment increase in the degree of shear stress oscillation would be accompanied by a proportional improvement in endothelial function. In separate visits, 10 young healthy males (22±3 years) underwent 10 minutes of unilateral HEAT, CUFF, or HGEX on the left arm (EXP), while the right arm served as a within-subject time control (CON). Non-invasive finger plethysmography was used to measure heart rate (HR) and blood pressure (BP) throughout the testing sessions. Ultrasonography was used to obtain measures of blood velocity and arterial diameter from the brachial artery of both limbs throughout the interventions. Anterograde and retrograde shear stress (SS) and oscillatory shear index (OSI) were calculated at baseline and during each intervention to assess the blood flow pattern changes. Endothelial function was assessed before and after each intervention, in both limbs simultaneously using a flow-mediated dilation (FMD) test. HEAT increased HR during the intervention (P < 0.05), mean BP and diastolic BP after the intervention (P < 0.05), anterograde SS in EXP (rest: 15.2 ± 2.9 vs. HEAT: 29.8 ± 8.5 dynes/cm2, P < 0.05), and FMD% in both limbs (P = 0.000). CUFF did not change HR or BP, increased anterograde (rest: 17.9 ± 4.1 vs. CUFF: 43.0 ± 12.4 dynes/cm2, P < 0.05) and retrograde (rest: -3.1 ± 2.5 vs. CUFF: -22.7 ± 6.0 dynes/cm2, P < 0.05) SS in EXP, but did not change FMD% in either limb (P = 0.248). HGEX increased HR during the intervention (P < 0.05), mean BP during and after the intervention (P < 0.05), anterograde SS in EXP (rest: 18.7 ± 5.9 vs. HGEX: 56.4 ± 11.5 dynes/cm2, P < 0.05), and FMD% in both limbs (P = 0.001). These findings suggest that an anterograde-dominant shear stress stimulus may be effective at improving endothelial function, but the confounding effect of sympathetic nervous system activation may play a more dominant role in the acute control response for shorter duration interventions such as the ones explored in this study. / Thesis / Master of Science (MSc) / It has been well established that the pattern of blood flow can impact arterial function, but the nuances of this relationship remain unclear. Through the use of heating, cuff compression, and exercise, this study sought to determine the optimal shear stress pattern to see beneficial changes in arterial function in the arm of young healthy males. Our results show many real life interventions alter not only the shear stress pattern in the artery, but also involve other systems like the brain and muscle that are crucial to maintaining the body’s physiological balance. It is clear that arterial function is regulated through a variety of different mechanisms, and that the changes we observe will depend on the parameters (e.g. duration, intensity, timing of assessment) of the applied stimulus. More specifically, isolating study designs should be constructed to determine the individual contributions of different human body systems to the arterial regulatory response.

The bluehead chub (Nocomis leptocephalus) is a keystone species, an ecosystem engi- neer that constructs mounded gravel nests for spawning. Chubs provide benefits for other spawning fishes, predators, and benthic organisms through their nest construction. This study seeks to apply sediment transport models to find incipient motion criteria and erosion susceptibility of chubs nests. Field water flow velocities were measured with an acoustic Doppler velocimeter (ADV) in Tom's Creek, Blacksburg, Virginia, USA. ADVs are often used to collect in-situ turbulent velocity data. In almost all applications of ADVs, erroneous spikes are recorded during collection, which can significantly distort turbulence statistics de- rived from velocity fluctuations. In this study, a bivariate kernel density estimation despiking algorithm is compared to a novel univariate simplification developed as part of this work. Despiking methods are evaluated using field ADV and direct numerical simulation (DNS) data of a turbulent boundary layer. Visual assessment of despiked velocity time series and power spectra and corresponding changes in statistical moments, as well as response to arti- ficial spiking of DNS data, yield valid performance of the univariate method. After despiking chub nest data, multiple methods of finding bed shear stress from velocity vertical profiles are evaluated. Bed shear stress is found over the profile of 26 field nests. The ambient to peak flow stress amplification due to a nest's bed protrusion is found to be a proportion of τ = 1.66τ to determine a critical ambient Shields parameter of approximately τ∗ = 0.03 pa c,a for nests. / Master of Science / The bluehead chub is a keystone species, an ecosystem engineer that constructs mounded gravel nests for spawning. These nests benefit numerous other species within their habitat. The possibility of nest erosion is characterized in this study using existing sediment transport principles. Nest flow characteristics are measured using an acoustic Doppler velocimeter (ADV). ADVs are often the instrument of choice in measuring water velocity. The high resolution of these devices can capture turbulent flows well, however data collection often results in inclusion of erroneous spikes in velocity. These spikes represent points deemed impossible due to their sudden change in velocity magnitude. Spikes do not have a large effect on average velocities of ADV data, but can influence turbulence statistics that describe the turbulent fluctuations in flow velocities. To remove spikes, multiple methods incorporate different outlier detection principles. This study evaluates a popular method that employs a two-dimensional kernel density estimation (KDE) algorithm. A recent study suggested the possible simplification of this method to use a one-dimensional kernel density estimation instead. Both the 1D and 2D methods are evaluated in this study in how they filter ADV data and whether it results in a clean, improved velocity time series that would be expected in turbulent flows. A novel 1D KDE method was also developed as part of this study. The new method is found to produce the most reliable filtering. Despiked ADV data is used to characterize the hydraulics over bluehead chub nests sampled in Tom's Creek, Blacksburg, Virginia, USA. Hydraulics are evaluated to see if ambient flow upstream of a nest can characterize the flow characteristics over the peak of the nest. Shear stress amplification over the nest is used to find a critical threshold for nest erosion based on ambient flows. Stress amplification in the ambient flow to the peak over the nest is found to be a simple proportion, and amplification factor of 1.66. This means we expect shear stress over the peak of a chub nest to be 1.66 times greater than the ambient bed shear stress upstream of the nest. This amplification factor can be used with existing methods to calculate critical non- dimensional shear stress values, also known as the critical Shields stress. After accounting for the amplification factor of 1.66, a critical Shields of approximately 0.03 is found.