Project description:Biomechanical forces such as wall shear stress induced by flowing blood influence the behavior of vascular cells and have been shown to be crucial in the onset of vascular disease. Primary cilia are increasingly recognized as important biological sensors of low WSS. The goal of the study was to investigate gene expression profile of endothelial cell under low flow (2 dynes/cm2) as compared to physiological flow (30 dynes/cm2) in presence or absence of primary cilia.
Project description:The luminal surface of the endothelium is exposed to dynamic blood flow patterns that are known to affect endothelial cell phenotype. In this study, human aortic endothelial cells (HAECs) were exposed to unidirectional laminar flow (20 dynes/cm2) or disturbed flow (±4 dynes/cm2, 2 Hz) for 48 hrs and then subjected to RNA sequencing. The sequencing data was used to analyze changes in endothelial cell gene expression and pathways associated with lipid metabolism.
Project description:RNA-seq technology was used to reveal the transcriptome changes of tubular epithelia in response to fluid flow and determine the role of primary cilia in this process. Many fluid flow-sensitive genes were identified, among which are those regulated by primary cilia sensing of fluid flow. These genes were further validated by RT-qPCR.
Project description:Biomechanical forces influence vascular function, but the molecular mechanisms regulating many of these mechano-activated cellular events remain largely uncharacterized. In particular, the vascular endothelium can sense alterations in hemodynamic shear stress which, in the context of adaptive remodeling or arteriogenesis, has been shown to lead to the generation of endothelial-derived signals critical for controlling blood vessel structure and function. Here, we sought to define the arteriogenic responses evoked in endothelial cells exposed to flow using transciptional profiling. Analysis of these transcriptional programs identified several genes previously shown to be important for endothelial-smooth muscle interactions and vascular remodeling, including the transcription factor kruppel-like factor 2 (KLF2).
Project description:Blood flow within the vasculature is a critical determinant of endothelial cell (EC) identity and functionality, yet the intricate interplay of various hemodynamic forces and their collective impact on endothelial and vascular responses are not fully understood. Specifically, the role of hydrostatic pressure in the context of flow response is understudied, despite its known significance in vascular development and disease. To address this gap, we developed in vitro models to investigate how pressure influences EC responses to flow. Our study demonstrates that elevated pressure conditions significantly modify shear-induced flow alignment and increase endothelial cell density, a phenomenon often observed in vascular diseases. Utilizing both bulk and single-cell RNA sequencing, we found that while flow is the primary driver of transcriptional changes from static conditions, pressure distinctly modulates this flow response by upregulating gene sets linked to arterial cell phenotypes. Conserved pressure-responsive transcriptional signatures identified in human ECs were upregulated during the onset of circulation in early mouse embryonic vascular development, where pressure was notably associated with transcriptional programs essential to arterial and hemogenic EC fates. Our findings emphasize the necessity of an integrative approach to endothelial cell mechanotransduction, one that encompasses the effects induced by pressure alongside other hemodynamic forces.
Project description:Objective The vessel wall is continuously exposed to hemodynamic forces generated by blood flow. Endothelial mechanosensors perceive and translate mechanical signals via cellular signaling pathways into biological processes that control endothelial development, phenotype and function. Here, we aim to unravel the molecular mechanisms underlying endothelial mechanosensing. Approach and results We applied a quantitative mass spectrometry approach combined with cell surface chemical footprinting to assess the hemodynamic effects on the endothelium on a system-wide level. These studies revealed that of the >5000 quantified proteins 104 were altered, which were highly enriched for extracellular matrix proteins and proteins involved in cell-matrix adhesion. Cell surface proteomics furthermore indicated that LAMA4 was proteolytically processed upon flow-exposure, which corresponded to the decreased LAMA4 mass observed on immunoblot. Immunofluorescence microscopy studies highlighted that the endothelial basement membrane was drastically remodeled upon flow exposure. We observed a network-like pattern of LAMA4 and LAMA5, which corresponded to the localization of laminin-adhesion molecules ITGA6 and ITGB4. Furthermore, the adaptation to flow-exposure did not affect the inflammatory response to tumor necrosis factor α, indicating that inflammation and flow trigger fundamentally distinct endothelial signaling pathways with limited reciprocity and synergy. Conclusions Taken together, this study uncovers the blood flow-induced remodeling of the basement membrane and stresses the importance of the subendothelial basement membrane in vascular homeostasis.
Project description:The arterial endothelium’s response to its flow environment is critical to vascular homeostasis. The endothelial glycocalyx has been shown to play a major role in mechanotransduction, but the extent to which the components of the glycocalyx affect the overall function of the endothelium remains unclear. The objective of this study was to further elucidate the role of heparan sulfate as a mechanosensor on the surface of the arterial endothelium, by (1) expanding the variety of shear waveforms investigated, (2) continuously suppressing heparan sulfate expression rather than using a pre-flow batch treatment, and (3) performing microarray analysis on post-flow samples. Porcine aortic endothelial cells were exposed to non-reversing, reversing, and oscillatory shear waveforms for 24 hours with or without continuous heparan sulfate suppression with heparinase. All shear waveforms significantly increased the amount of heparan sulfate on the surface of the endothelium. Suppression of heparan sulfate to less than 25% of control levels did not inhibit shear-induced cell alignment or nitric oxide production, or alter gene expression, for any of the shear waveforms investigated. We infer that heparan sulfate on the surface of porcine aortic endothelial cells is not the primary mechanosensor for many shear-responsive endothelial cell functions in this species. Porcine aortic endothelial cells were exposed to 3 different shear waveforms for 24 hours with or without the addition of 300 mU/ml heparinase III to the flow media. The shear waveforms inculded Non-reversing (15 ± 15 dyne/cm2, 1 Hz), Steady (15 dyne/cm2), or Oscillatory (0 ± 15 dyne/cm2, 1 Hz) shear. Four replicates of each condition were performed for a total of 24 experiments. Each experimental sample was hybridized to an oligonucleotide array along with a standard reference sample (static cells).
Project description:Objective - When endothelium is cultured in wells swirled on an orbital shaker, cells at the well centre experience putatively proatherogenic flow whereas those near the edge experience putatively atheroprotective flow. Transcellular transport is decreased equally in both regions, consistent with it being reduced by a mediator released from cells in one part of the well and mixed in the swirling medium. Here we identify the mediator and the flow characteristics that stimulate its release. Approach and Results - Medium conditioned by cells swirled at the edge, but not by cells swirled at the centre or cultured under static conditions, significantly reduced transendothelial transport of a low density lipoprotein (LDL)-sized tracer. Mass spectrometry identified follistatin-like 1 (FSTL1) as a candidate mediator. Cells from the swirled edge produced more FSTL1 than cells from the swirled centre or from static wells. Exogenous FSTL1 reduced transendothelial transport of the LDL-sized tracer and of LDL itself. An inhibitor of transcytosis similarly inhibited tracer transport. Exogenous FSTL1 and medium conditioned by cells swirled at the well edge also inhibited TNF-α-induced VCAM-1 and ICAM-1 expression, phosphorylation of IκBα, nuclear translocation of NF-κB, and monocyte adhesion. Conclusions - Putatively atheroprotective flow stimulates production of FSTL1 from cultured endothelial cells. FSTL1 reduces transcellular transport of LDL-sized particles and of LDL itself, and inhibits endothelial activation. If this also occurs in vivo, it may account for the atheroprotective nature of such flow. The identification of a mediator linking flow to LDL transport suggests novel therapeutic strategies.
Project description:In order to simulate the effects of shear stress in regions of the vasculature prone to developing atherosclerosis, we subjected human umbilical vein endothelial cells to reversing shear stress, in order to mimic hemodynamic conditions at the wall of the carotid sinus, a site of complex, reversing blood flow and commonly observed atherosclerosis. We compared the effects of reversing shear stress (time-average 1 dyne/cm2, maximum +11 dynes/cm2, minimum -11 dynes/cm2, 1 Hz), arterial steady shear stress (15 dynes/cm2), and low steady shear stress (1 dyne/cm2) in terms of gene expression, cell proliferation, and monocyte adhesiveness. Microarray analysis revealed most differentially expressed genes were similarly regulated by all three shear stress regimens when compared to static culture. Comparisons of the three shear stress regimens to each other allowed identification of 138 genes regulated by low average shear stress and 22 by fluid reversal. Functional assays indicated that low average shear stress induces increased cell proliferation as compared to high shear stress. Reversing shear stress was the only condition that induced monocyte adhesion. Monocyte adhesion was partially inhibited by incubation of the endothelial cells with ICAM-1 blocking antibody. Increased surface heparin sulfate proteoglycan expression was observed in cells exposed to reversing shear stress. When these cells were treated with heparinase III monocyte adhesion was significantly reduced. Our results suggest that low steady shear stress is the major impetus for differential gene expression and cell proliferation, while reversing flow regulates monocyte adhesion.