Flow dependent gene expression in the rat aorta under physiological conditions
ABSTRACT: Objective: Shear forces play a key role in the maintenance of vessel wall integrity. Current understanding regarding shear-dependent gene expression is mainly based on in vitro or in vivo observations with experimentally deranged shear, hence reflecting acute molecular events in relation to flow. Our objective was to combine computational fluid dynamic (CFD) simulations with global microarray analysis to study flow-dependent vessel wall biology in portions of the entire aorta under physiological conditions. Methods and Results: Animal-specific WSS magnitude and vector direction were estimated using CFD based on aortic geometry and flow information acquired by MRI. Two distinct flow pattern regions were identified in the normal rat aorta; the distal part of the inner curvature being exposed to low WSS and a non-uniform vector direction, and a region along the outer curvature being subjected to markedly higher levels of WSS and a uniform vector direction. Microarray analysis identified numerous novel mechanosensitive genes, including Hand2, trpc4 and slain2, and confirmed well-known ones, such as klf2 and BMP4. Three genes were further validated for protein , including Hand2, which showed higher expression in the endothelium in regions exposed to disturbed flow. Gene ontology analysis revealed an over-representation of genes involved in transcriptional regulation. Microarray analysis of two distinct flow pattern regions were identified in the normal rat aorta. Tissue pieces from groups of five animals were pooled for each region giving total of 28 pools; 14 paired sample pools of high and low wall shear stress.
Project description:Blood flow promotes emergence of definitive hematopoietic stem cells (HSCs) in the developing embryo, yet the signals generated by hemodynamic forces that influence hematopoietic potential remain poorly defined. In transplantation assays of hematopoietic reconstitution, we find that fluid shear stress endows long-term multilineage engraftment potential upon early hematopoietic tissues at E9.5 not previously described to harbor HSCs. Effects on hematopoiesis appear to be mediated in part by prostaglandin E2 (PGE2) and the cyclic AMP-protein kinase A (cAMP-PKA) signaling axis. Studies of Ncx1 cardiac mutants corroborate that blood flow is required for sufficient COX2 levels and phosphorylation of CREB. Further implicating PGE2 in mediating the effects of shear stress, we find that E10.5 and E11.5 AGM treated transiently with the synthetic analog dmPGE2 engraft more robustly and contribute to greater lymphoid reconstitution. These data provide a mechanism by which biomechanical forces induced by blood flow modulate hematopoietic potential. - AGM from C57BL/6J embryos at 10.5 days gestation (E10.5) were isolated by microdissection from uteri of pregnant dams, following by gentle dissociation by Accutase with agitation at room temperature for 20 minutes. Single cell suspension was seeded on microfluidic IBIDI VI^0.4 6-channel slides (0.8 to 1x10^7 cells per channel) and permitted to attach for 8 hours. Fluid movement was then applied to each channel using a Harvard Apparatus PHD ULTRA programmable syringe pump for manangement of M5300 Myelocult medium. Cells were exposed either to static/low flow (0.0001 dyne/cm^2) or wall shear stress (WSS) of 5 dyne/cm^2 for 6 hours or 36 hours. In addition, some cells were treated with 10 uM indomethacin (indo) to inhibit COX2 activity and PGE2 synthesis. Upon collection of cells with RLT lysis buffer (QIAGEN RNeasy kit), six channels of identical treatment were pooled to comprise a single sample. 24 samples total are included in this study. 12 samples were collected after 6 hours and 12 after 36 hours. In detail, samples included at 6 hours: 3 static, 3 static with indo, 3 WSS, 3 WSS with indo; and at 36 hours: 3 static, 3 static with indo, 3 WSS, 3 WSS with indo. Sample labels begin with the timepoint collected and end with the replicate number, i.e., 06WSS1 for the 6 hour collection of the first replicate of the WSS sample.
Project description:Intracranial aneurysms tend to form at bifurcation apices, where flow impingement causes high frictional force (or wall shear stress, WSS) and flow acceleration and deceleration that create positive and negative streamwise gradients in WSS (WSSG), respectively. In vivo, intracranial aneurysms initiate under high WSS and positive WSSG. Little is known about the responses of endothelial cells (ECs) to either positive or negative WSSG under high WSS conditions. We used cDNA microarrays to profile EC gene expression exposed to positive WSSG vs. negative WSSG for 24 hours in a flow chamber with converging and diverging channels, respectively. WSS varied between 3.5 and 28.4 Pa in each gradient channel. GO and biological pathway analysis indicated that positive WSSG favored proliferation, apoptosis, and extracellular matrix processing while decreasing expression of pro-inflammatory genes. A subset of characteristic genes was validated using qPCR: Genes for ADAMTS1, CKAP2 and NCEH1 had higher expression under positive WSSG compared to negative WSSG while TAGLN, THBS1, VCAM1, CCL2, and CSF2 had lower expression. To determine if these patterns of expression are also exhibited in vivo, we tested whether the extracellular matrix related protein ADAMTS1 and proliferation were modulated by positive WSSG during intracranial aneurysm initiation. An aneurysm was induced at the basiliar terminus in rabbits by bilateral carotid ligation. WSSG at the bifurcation was determined by computational fluid dynamic simulations from 3D angiography and mapped on immunofluorescence staining for ADAMTS1 and the proliferation marker, Ki-67. Endothelial ADAMTS1 protein and Ki-67 were significantly higher in regions with positive WSSG compared to adjacent sites where WSSG was negative. Our results indicate that WSSG can elicit distinct gene expression profiles in ECs. Increased matrix processing and high levels of proliferation under positive WSSG could contribute to intracranial aneurysm initiation by causing transient gaps in the endothelium or disrupting EC signals to smooth muscle cells. Time-matched bovine aortic endothelial cells were exposed to positive wall shear stress gradient, negative wall shear stress gradient, and two no gradient samples: uniform WSS of 3.5 Pa and high WSS of 28.4 Pa for 24 hrs in an in vitro flow loop system. RNA was extracted and hybridized on Affymetrix microarrays. There were 12 samples in total, four flow conditions with three replicates each.
Project description:Chronic high flow can induce arterial remodeling, and this effect is mediated by endothelial cells (ECs) responding to wall shear stress (WSS). To assess how WSS above physiological normal levels affects ECs, we used DNA microarrays to profile EC gene expression under various flow conditions. Cultured bovine aortic ECs were exposed to no flow (0 Pa), normal WSS (2 Pa) and very high WSS (10 Pa) for 24 hrs. Very high WSS induced a distinct expression profile when compared to both no flow and normal WSS. Gene ontology and biological pathway analysis revealed that high WSS modulated gene expression in ways that promote an anti-coagulant, anti-inflammatory, proliferative and pro-matrix remodeling phenotype. A subset of characteristic genes was validated using quantitative polymerase chain reaction (qPCR): Very high WSS upregulated ADAMTS1, PLAU (uPA), PLAT (tPA) and TIMP3, all of which are involved in extracellular matrix processing, with PLAT and PLAU also contributing to fibrinolysis. Downregulated genes included chemokines CXCL5 and IL-8 and the adhesive glycoprotein THBS1 (TSP1). Expressions of ADAMTS1 and uPA proteins were assessed by immunhistochemistry in rabbit basilar arteries experiencing increased flow after bilaterial carotid artery ligation. Both proteins were significantly increased when WSS was elevated compared to sham control animals. Our results indicate that very high WSS elicits a unique transcriptional profile in ECs that favors particular cell functions and pathways that are important in vessel homeostasis under increased flow. In addition, we identify specific molecular targets that are likely to contribute to adaptive remodeling under elevated flow conditions. Overall design: Time-matched Bovine Aortic Endothelial Cells were exposed to three flow conditions, high WSS (10 Pa), normal WSS (2 Pa) and no flow (0 Pa) static controls for 24 hrs in an in vitro flow loop system. RNA was extracted and hybridized on Affymetrix microarrays. There were 9 samples in total, three flow conditions with three replicates each.
Project description:Biophysical features of the microenvironment such as stiffness of extracellular matrix (ECM), nanotopography, and biomechanical force are critical regulators of cellular potential and behavior, yet the effects of extrinsic mechanical cues on tumor cells remain poorly understood. Here we demonstrate that frictional force, or wall shear stress (WSS), caused by fluid flow supports invasive behavior in cancer cells through activation of negative effectors of the Hippo tumor suppressor pathway, YAP and TAZ. In biomimetic models of lymphatic vasculature, WSS stimulated motility. These effects were accompanied by YAP dephosphorylation at ser-127, YAP and TAZ nuclear localization, and transactivation of YAP/TAZ downstream targets, including CTGF, AMOTL2, and ANKRD1. YAP, but not TAZ, was strictly required for WSS-enhanced motility, as knockdown of YAP or blockade of YAP-TEAD interactions by a small molecule inhibitor, verteporfin, reduced cellular velocity to levels observed in static controls. YAP-mediated effects on motility were dependent upon Rho-associated kinase (ROCK) and LIM-domain kinase (LIMK), as pharmacological inhibition of their activity led to activation of the actin-severing protein cofilin and blocked YAP dephosphorylation by WSS, thereby impairing migration. These data provide a signaling mechanism whereby biomechanical forces may influence cancer cell metastasis and implicate YAP as a core component of mechanosensitive machinery that modulates cancer progression. Overall design: The human prostate cancer cell line PC3 was tested for response to fluid wall shear stress (WSS). One day after seeding in a 6 well plate, cells of siRNA groups were transfected with control siRNA or YAP1 siRNA at 25nM using DharmaFect reagent. 24 hours after transfection, both tranfected cells and normal PC3 cells (10^5 cells per channel; surface area of each channel equaled 248 cm^2) were transferred into each polydimethylsiloxane (PDMS) channel (2.2 MPa surface stiffness) and permitted to attach for 24 hours. Fluid flow was then applied to each channel using a Harvard Apparatus PHD ULTRA programmable syringe pump. Cells were exposed either to static or WSS (0.05 dyne/cm^2) for 3 hours. Upon collection of cells with RLT lysis buffer (QIAGEN RNeasy kit), three channels of identical treatment were pooled to comprise a single sample. 12 samples total are included in this study. In detail, samples included at 3 hours: 3 static, 3 WSS, 3 WSS with siCTL and 3 WSS with siYAP. Sample labels end with the replicate number, i.e., WSS3 for the third replicate of the WSS sample.
Project description:Atherosclerosis preferentially develops in arterial regions where hemodynamic disturbed flow and oxidative stress are present. Epigenomic regulation, especially DNA methylation, plays an essential role in regulating gene expression in response to environmental factors. We investigated the DNA methylation of endothelial cells isolated from distinctly different hemodynamic and oxidative stress environments in normal adult domestic swine: an athero-susceptible site located at the inner curvature of the aortic arch (AA) and an athero-protected region in the descending thoracic aorta (DT). Genome-wide DNA methylation landscapes as well as differential methylation regions (DMRs) were generated by methylated DNA immunoprecipitation sequencing (MeDIP-seq).
Project description:Shear stress is known to regulate endothelial cell orientation along the direction of flow. We asked wither cellular patterning along, in the absence of shear could have similar biological effects as shear. We used DNA microarrays to examine the effect of cellular patterning on their transcriptome. Human microvascular endothelial cells were cultured in parallel micropatterned channels (30um wide channels, 30um apart) composed of polydimethylsiloxane, followed DNA Microarray analysis (Affymetrix 1.0 ST array)
Project description:Arterial stiffness is a prevalent, independent cardiovascular risk factor, but the underlying mechanisms are not well understood. Wall shear stress and shear-sensitive genes may promote arterial stiffening through clinically important signaling pathways. Our goal was to identify how disturbed blood flow leads to arterial stiffness using the mouse partial carotid ligation model. Here we used our in vivo partial carotid ligation model to induce d-flow in the LCA while the contralateral RCA continues to experience stable laminar flow using the C57BL/6x129SvEv mice, TSP-1 knockout (KO), and C57Bl/6J mice. We compared these to aged (80 week) mice which had increased arterial stiffness due to aging. Changes in gene expression were identified using microarrays that were performed on the endothelial-enriched RNA isolated from the carotids exposed to stable flow (RCA) and compared to disturbed flow (LCA). Arterial stiffness was determined ex vivo by biaxial mechanical testing and in vivo by ultrasound techniques. Myointimal hyperplasia and immunohistochemistry were performed in sectioned carotid arteries. In vitro testing of signaling pathways utilized oscillatory and laminar wall shear stress. Human arteries were tested ex vivo to validate critical results found in the animal model. Overall design: Endothelial-enriched RNA was isolated from WT carotids exposed to stable flow or disturbed flow. Three replicates each.
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. Overall design: Gene expression in endothelial cells was measured after 24 hours of exposure to 15 dyne/cm2 steady shear stress, 1 dyne/cm2 steady shear stress, reversing flow, or static culture. Three independent experiments were performed using different lots of endothelial cells each time.
Project description:This study characterizes the response of primary human endothelial cells (human umbilical vein endothelial cells, HUVECs) to the relative shear stress changes that occur during the initiation of arteriogenesis at the entrance regions to a collateral artery network. HUVECs were preconditioned to a baseline level of unidirectional shear of 15 dynes/cm2 for 24 hours. After 24 hours preconditioning, HUVECs were subjected to an arteriogenic stimulus that mimics the shear stress changes observed in the opposing entrance regions into a collateral artery network. The arteriogenic stimulus consisted of a 100% step wise increase in shear stress magnitude to a unidirectional 30 dynes/cm2 in either the same or opposite direction of the preconditioned shear stress. This simulates either the feeding entrance to the collateral artery circuit or the region that drains into the vasculature downstream of an obstruction in a major artery, respectively. In vivo analysis of collateral growth in the mouse hindlimb showed enhanced outward remodeling in the re-entrant (direction reversing) region that reconnects to the downstream arterial tree, suggesting reversal of shear stress direction as a key enhancer of arteriogenesis. Transcriptional profiling using microarray techniques identified that the reversal of shear stress direction, but not an increase in shear stress alone, yielded a broad-based enhancement of the mechanotransduction pathways necessary for the induction of arteriogenesis. Human umbilical vein endothelial cells (HUVECs) were preconditioned to a unidirectional clockwise shear stress of 15 dynes/cm2 for 24 hours. An acute increase in shear stress magnitude to 30 dynes/cm2 in either a clockwise (non-reversed) or counter-clockwise (reversed) direction was applied for 6 hours. An additional preconditioned control culture was maintained under a unidirectional clockwise shear stress of 15 dynes/cm2 and harvested at the same time point, 6 hours post-conditioning. Each condition of reversed, non-reversed, and control was performed in tandem from the same starting cell culture as one replicate. The total experiment consisted of four replicates. Gene transcription was then assessed using microarray expression analysis.
Project description:d9 and d12 Mks were either cultured statically or subjected to shear flow for 30 min; at d9, half the Mks were placed back in culture for 30 min (60 min time point) Megakaryocytes (Mks) are exposed to shear flow as they migrate from the bone marrow hematopoietic compartment into circulation thus releasing platelets and pro/preplatelets directly into the blood stream. Shear forces have been now established as promoting Mk maturation and platelet biogenesis. In order to understand the underlying mechanisms that modulate the response of Mks to shear forces, we carried out transcriptional analysis on immature and mature stem cell-derived Mks that were exposed to physiologically-relevant shear (2.5 dyn/cm2). In immature (d9) Mks, shear exposure upregulated genes related to growth and Mk maturation, while in mature (d12) Mks, it upregulated genes involved in apoptosis and intracellular transport. Following shear-flow exposure, 6 AP-1 transcripts (ATF4, JUNB, JUN, FOSB, FOS, and JUND) were upregulated at d9 and two AP-1 proteins (JunD and c-Fos) were upregulated both at d9 and d12. Our data show that MAPK signaling is linked to both the shear-stress response and AP-1 upregulation. JNK phosphorylation increased significantly following shear stimulation, while JNK inhibition reduced shear-induced JunD protein expression. Although p38 phosphorylation did not increase following shear flow, its inhibition reduced shear-induced JunD and c-Fos protein expression. JNK inhibition reduced fibrinogen binding of d9 and d12 platelet-like particle s (PLPs) and P-selectin expression at d12 PLPs, while p38 inhibition reduced fibrinogen binding of d12 PLPs. Here we show that mechanotransduction of shear forces in Mks results in JNK activation, AP-1 upregulation, and downstream transcriptional changes that promote maturation of immature Mks and platelet biogenesis in mature Mks. Two- and Three-condition experiment (flow vs. static culture condition, d9 vs. d12, and 30 min vs. 60 min at d9); Biological replicates: 3; Technical replicates: 1 (dye-swap)