Browsing by Subject "Shear stress"

Now showing 1 - 5 of 5
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    Building a Tensegrity-Based Computational Model to Understand Endothelial Alignment Under Flow
    (2021-12) Al-Muhtaseb, Tamara; Ji, Julie; Na, Sungsoo; Tovar, Andres
    Endothelial cells form the lining of the walls of blood vessels and are continuously subjected to mechanical stimuli from the blood flow. Microtubule-organizing center (MTOC), also known as centrosome is a structure found in eukaryotic cells close to the nucleus. MTOC relocates relative to the nucleus when endothelial cells are exposed to shear stress which determines their polarization, thus it plays a critical role in cell migration and wound healing. The nuclear lamina, a mesh-like network that lies underneath the nuclear membrane, is composed of lamins, type V intermediate filament proteins. Mutations in LMNA gene that encodes A-type lamins cause the production of a mutant form of lamin A called progerin and leads to a rare premature aging disease known as Hutchinson-Gilford Progeria Syndrome (HGPS). The goal of this study is to investigate how fluid flow affects the cytoskeleton of endothelial cells. This thesis consists of two main sections; computational mechanical modeling and laboratory experimental work. The mechanical model was implemented using Ansys Workbench software as a tensegrity-based cellular model in order to simulate the state of an endothelial cell under the effects of induced shear stress from the blood fluid flow. This tensegrity-based cellular model - composed of a plasma membrane, cytoplasm, nucleus, microtubules, and actin filaments - aims to understand the effects of the fluid flow on the mechanics of the cytoskeleton. In addition, the laboratory experiments conducted in this study examined the MTOC-nuclear orientation of endothelial cells under shear stress with the presence of wound healing. Wild-type lamin A and progerin-expressing BAECs were studied under static and sheared conditions. Moreover, a custom MATLAB code was utilized to measure the MTOC-nuclear orientation angle and classification. Results demonstrate that shear stress leads to different responses of the MTOC orientation between the wild-type and progerin-expressing cells around the vertical wound edge. Future directions for this study involve additional experimental work together with the improved simulation results to confirm the MTOC orientation relative to the nucleus under shear stress.
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    GPR68 Senses Flow and Is Essential for Vascular Physiology
    (Elsevier, 2018-04-19) Xu, Jie; Mathur, Jayanti; Vessières, Emilie; Hammack, Scott; Nonomura, Keiko; Favre, Julie; Grimaud, Linda; Petrus, Matt; Francisco, Allain; Li, Jingyuan; Lee, Van; Xiang, Fu-Li; Mainquist, James K.; Cahalan, Stuart M.; Orth, Anthony P.; Walker, John R.; Ma, Shang; Lukacs, Viktor; Bordone, Laura; Bandell, Michael; Laffitte, Bryan; Xu, Yan; Chien, Shu; Henrion, Daniel; Patapoutian, Ardem; Obstetrics and Gynecology, School of Medicine
    Mechanotransduction plays a crucial role in vascular biology. One example of this is the local regulation of vascular resistance via flow-mediated dilation (FMD). Impairment of this process is a hallmark of endothelial dysfunction and a precursor to a wide array of vascular diseases, such as hypertension and atherosclerosis. Yet the molecules responsible for sensing flow (shear stress) within endothelial cells remain largely unknown. We designed a 384-well screening system that applies shear stress on cultured cells. We identified a mechanosensitive cell line that exhibits shear stress-activated calcium transients, screened a focused RNAi library, and identified GPR68 as necessary and sufficient for shear stress responses. GPR68 is expressed in endothelial cells of small-diameter (resistance) arteries. Importantly, Gpr68-deficient mice display markedly impaired acute FMD and chronic flow-mediated outward remodeling in mesenteric arterioles. Therefore, GPR68 is an essential flow sensor in arteriolar endothelium and is a critical signaling component in cardiovascular pathophysiology.
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    Passage dependent changes in nuclear and cytoskeleton structures of endothelial cells under laminar shear stress or cyclic stretch
    (Medip Academy, 2021) Jiang, Yizhi; Witt, Nathaniel; Ji, Julie Y.; Biomedical Engineering, Purdue School of Engineering and Technology
    Background: The ability of vascular endothelium to sense and respond to the mechanical stimuli generated by blood flow is pivotal in maintaining arterial homeostasis. A steady laminar flow tends to provide athero-protective effect via regulating endothelial functions, vascular tone, and further remodeling process. As arterial aging appeared to be an independent risk factor of cardiovascular diseases, it is critical to understand the effects of cell senescence on endothelial dysfunction under dynamic mechanical stimuli. Methods: In this study, we investigated the morphological responses of aortic endothelial cells toward laminar flow or cyclic stretch. Automated image recognition methods were applied to analyze image data to avoid bias. Differential patterns of morphological adaptations toward distinct mechanical stimuli were observed, and the shear-induced changes were found to be more associated with cell passages than that of cyclic strain. Results: Our results demonstrated that the cytoskeleton and nuclear structural adaptations in endothelial cells toward laminar flow were altered over prolonged culture, suggesting that the failure of senescent endothelial cells to adapt to the applied shear stress morphologically could be one of the contributors to endothelial dysfunctions during vascular aging. Conclusions: Results indicated that cells were able to adjust their cytoskeleton and nuclear alignment and nuclear shapes in response to the applied mechanical stimuli, and that the shear-induced changes were more dependent on PD levels, where cells with higher PDL were more responsive to external forces.
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    Progerin-Induced Impairment in Wound Healing and Proliferation in Vascular Endothelial Cells
    (Frontiers Media, 2022-03-14) Jiang, Yizhi; Ji, Julie Y.; Biomedical Engineering, Purdue School of Engineering and Technology
    Progerin as a mutated isoform of lamin A protein was first known to induce premature atherosclerosis progression in patients with Hutchinson-Gilford progeria syndrome (HGPS), and its role in provoking an inflammatory response in vascular cells and accelerating cell senescence has been investigated recently. However, how progerin triggers endothelial dysfunction that often occurs at the early stage of atherosclerosis in a mechanical environment has not been studied intensively. Here, we generated a stable endothelial cell line that expressed progerin and examined its effects on endothelial wound repair under laminar flow. We found decreased wound healing rate in progerin-expressing ECs under higher shear stress compared with those under low shear. Furthermore, the decreased wound recovery could be due to reduced number of cells at late mitosis, suggesting potential interference by progerin with endothelial proliferation. These findings provided insights into how progerin affects endothelial mechanotransduction and may contribute to the disruption of endothelial integrity in HGPS vasculature, as we continue to examine the mechanistic effect of progerin in shear-induced endothelial functions.
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    Shear stress attenuates apoptosis due to TNFα, oxidative stress, and serum depletion via death-associated protein kinase (DAPK) expression
    (BioMed Central, 2015-03-18) Rennier, Keith; Ji, Julie Y.; Department of Biomedical Engineering, School of Engineering and Technology
    BACKGROUND: Misdirected apoptosis in endothelial cells participates in the development of pathological conditions such as atherosclerosis. Tight regulation of apoptosis is necessary to ensure normal cell function. The rate of cell turnover is increased at sites prone to lesion development. Laminar shear stress is protective against atherosclerosis, and helps suppress apoptosis induced by cytokines, oxidative stress, and serum depletion. Current Studies have shown that the pro-apoptotic DAPK expression and function to be regulated in part by shear stress, and that shearing cells already treated with cytokine tumor necrosis factor (TNF) α significantly reduced apoptosis. We investigate further the suppression of endothelial apoptosis by shear stress with other apoptotic triggers, and the involvement of DAPK and caspase 3/7. RESULTS: We have shown that exposure to shear stress (12 dynes/cm(2) for 6 hrs) suppressed endothelial apoptosis triggered by cytokine (TNFα), oxidative stress (H2O2), and serum depletion, either before or after a long term (18 hr) induction. This is correlated with a parallel decrease of DAPK expression and caspase activity compared to non-sheared cells. We found similar modulation of DAPK and apoptosis by shear stress with other pro-apoptotic signals. Changes in DAPK and caspase 3/7 are directly correlated to changes in apoptosis. Interestingly, shear stress applied to cells prior to induction with apoptosis agents resulted in a higher suppression of apoptosis and DAPK and caspase activity, compared to applying shear stress post induction. This is correlated with a higher expression and activation of DAPK in cells sheared at the end of 24-hr experiment. Also, shear stress alone also induced higher apoptosis and DAPK expression, and the effect is sustained even after 18 hrs incubation in static condition, compared to non-sheared cells. CONCLUSIONS: Overall, we show that laminar shear stress inhibits various apoptosis pathways by modulating DAPK activity, as well as caspase activation, in a time-dependent manner. Shear stress could target DAPK as a converging point to exert its effects of suppressing endothelial apoptosis. The temporal shear stress stimulation of DAPK and its role in different apoptosis pathways may help identify key mechanisms of the endothelial mechanotransduction pathway.