Shear stress regulates gene expression in vascular endothelial cells in response to tumor necrosis factor-alpha: a study of the transcription profile with complementary DNA microarray

Shear-Induced ITGB4 Promotes Endothelial Cell Inflammation and Atherosclerosis

The local heterogeneity in the distribution of atherosclerotic lesions is caused by local flow patterns. The integrin family plays crucial regulatory roles in diverse biological processes, but knowledge of integrin β4 (ITGB4) in shear stress-induced atherosclerosis is limited. This study clarified that low shear stress (LSS) regulates the generation of ITGB4 in endothelial cells with atheroprone phenotype to identify ITGB4's role in atherosclerosis. We found that LSS led to an increase in ITGB4 protein expression both in vitro and in vivo. ITGB4 knockdown attenuated inflammation and ROS generation in human umbilical vein endothelial cells (HUVECs) and reduced atherosclerotic lesion areas in ApoE^−/− mice fed with HFD, largely independent of effects on the lipid profile. Mechanistically, ITGB4 knockdown altered the phosphorylation levels of SRC, FAK, and NFκB in HUVECs under LSS conditions. In addition, the knockdown of NFκB inhibited the production of ITGB4 and SRC phosphorylation, and the knockdown of SRC downregulated ITGB4 protein expression and NFκB activation. These data demonstrate a critical role of ITGB4 in atherosclerosis via modulation of endothelial cell inflammation, and ITGB4/SRC/NFκB might form a positive feedback loop in the regulation of endothelial cell inflammation.

Vascular Endothelial Cells: Heterogeneity and Targeting Approaches

Forming the inner layer of the vascular system, endothelial cells (ECs) facilitate a multitude of crucial physiological processes throughout the body. Vascular ECs enable the vessel wall passage of nutrients and diffusion of oxygen from the blood into adjacent cellular structures. ECs regulate vascular tone and blood coagulation as well as adhesion and transmigration of circulating cells. The multitude of EC functions is reflected by tremendous cellular diversity. Vascular ECs can form extremely tight barriers, thereby restricting the passage of xenobiotics or immune cell invasion, whereas, in other organ systems, the endothelial layer is fenestrated (e.g., glomeruli in the kidney), or discontinuous (e.g., liver sinusoids) and less dense to allow for rapid molecular exchange. ECs not only differ between organs or vascular systems, they also change along the vascular tree and specialized subpopulations of ECs can be found within the capillaries of a single organ. Molecular tools that enable selective vascular targeting are helpful to experimentally dissect the role of distinct EC populations, to improve molecular imaging and pave the way for novel treatment options for vascular diseases. This review provides an overview of endothelial diversity and highlights the most successful methods for selective targeting of distinct EC subpopulations.

Cigarette smoke extract profoundly suppresses TNFα-mediated proinflammatory gene expression through upregulation of ATF3 in human coronary artery endothelial cells

Endothelial dysfunction caused by the combined action of disturbed flow, inflammatory mediators and oxidants derived from cigarette smoke is known to promote coronary atherosclerosis and increase the likelihood of myocardial infarctions and strokes. Conversely, laminar flow protects against endothelial dysfunction, at least in the initial phases of atherogenesis. We studied the effects of TNFα and cigarette smoke extract on human coronary artery endothelial cells under oscillatory, normal laminar and elevated laminar shear stress for a period of 72 hours. We found, firstly, that laminar flow fails to overcome the inflammatory effects of TNFα under these conditions but that cigarette smoke induces an anti-oxidant response that appears to reduce endothelial inflammation. Elevated laminar flow, TNFα and cigarette smoke extract synergise to induce expression of the transcriptional regulator activating transcription factor 3 (ATF3), which we show by adenovirus driven overexpression, decreases inflammatory gene expression independently of activation of nuclear factor-κB. Our results illustrate the importance of studying endothelial dysfunction in vitro over prolonged periods. They also identify ATF3 as an important protective factor against endothelial dysfunction. Modulation of ATF3 expression may represent a novel approach to modulate proinflammatory gene expression and open new therapeutic avenues to treat proinflammatory diseases.

Shear stress regulated gene expression and angiogenesis in vascular endothelium

The behavior of vascular EC is greatly altered in sites of pathological angiogenesis, such as a developing tumor or atherosclerotic plaque. Until recently it was thought that this was largely due to abnormal chemical signaling, i.e., endothelial cell chemo transduction, at these sites. However, we now demonstrate that the shear stress intensity encountered by EC can have a profound impact on their gene expression and behavior. We review the growing body of evidence suggesting that mechanotransduction, too, is a major regulator of pathological angiogenesis. This fits with the evolving story of physiological angiogenesis, where a combination of metabolic and mechanical signaling is emerging as the probable mechanism by which tight feedback regulation of angiogenesis is achieved in vivo.

Transmission of Anaplasma phagocytophilum from endothelial cells to peripheral granulocytes in vitro under shear flow conditions

Anaplasma phagocytophilum (Ap) is a tick-borne pathogen, which can cause granulocytic anaplasmosis in humans and animals. In vivo this obligate intracellular pathogen is primarily located in circulating mature granulocytes, but it also infects endothelial cells. In order to study the interaction between Ap-infected endothelial cells and human granulocytes under conditions similar to those found naturally in the infected host, an in vitro model that mimics physiological flow conditions in the microvasculature was established. Cell-to-cell interactions were then visualized by microscopy, which showed that granulocytes adhered strongly to Ap-infected endothelial cells at a shear stress of 0.5 dyne/cm(2). In addition, Ap-transmission assays under flow conditions showed that the bacteria transferred from infected endothelial cells to circulating granulocytes and were able to establish infection in constantly moving granulocytes. Cell surface analysis showed that Ap induced up-regulation of the cell adhesion molecules ICAM-1 and VCAM-1 on infected endothelial cells in a dose-dependent manner. Furthermore, IL-8 secretion by endothelial cells indicated that the presence of Ap induced a pro-inflammatory response. In summary, the results of this study suggest that endothelial cells of the microvasculature (1) provide an excellent site for Ap dissemination to peripheral blood granulocytes under flow conditions and therefore may play a crucial role in the development of persistent infection, and (2) are stimulated by Ap to express surface molecules and cytokines that may lead to inflammatory responses at the site of the infection.

The role of Hath6, a newly identified shear-stress-responsive transcription factor, in endothelial cell differentiation and function

The key regulators of endothelial differentiation that is induced by shear stress are mostly unclear. Human atonal homolog 6 (Hath6 or ATOH8) is an endothelial-selective and shear-stress-responsive transcription factor. In this study, we sought to elucidate the role of Hath6 in the endothelial specification of embryonic stem cells. In a stepwise human embryonic stem cell to endothelial cell (hESC-EC) induction system, Hath6 mRNA was upregulated synchronously with endothelial determination. Subsequently, gain-of-function and loss-of-function studies of Hath6 were performed using the hESC-EC induction model and endothelial cell lines. The overexpression of Hath6, which mimics shear stress treatment, resulted in an increased CD45(-)CD31(+)KDR(+) population, a higher tubular-structure-formation capacity and increased endothelial-specific gene expression. By contrast, the knockdown of Hath6 mRNA markedly decreased endothelial differentiation. Hath6 also facilitated the maturation of endothelial cells in terms of endothelial gene expression, tubular-structure formation and cell migration. We further demonstrated that the gene encoding eNOS is a direct target of Hath6 through a reporter system assay and western blot analysis, and that the inhibition of eNOS diminishes hESC-EC differentiation. These results suggest that eNOS plays a key role in linking Hath6 to the endothelial phenotype. Further in situ hybridization studies in zebrafish and mouse embryos indicated that homologs of Hath6 are involved in vasculogenesis and angiogenesis. This study provides the first confirmation of the positive impact of Hath6 on human embryonic endothelial differentiation and function. Moreover, we present a potential signaling pathway through which shear stress stimulates endothelial differentiation.

Early growth response protein 1 promotes restenosis by upregulating intercellular adhesion molecule-1 in vein graft

OBJECTIVES

To verify the relationship between Egr-1 and vein graft restenosis and investigate the related mechanisms.

METHODS

Mouse vein graft models were established in Egr-1 knockout (KO) and wild-type (WT) mice. The vein grafts in the mice were taken for pathological examination and immunohistochemical analysis. The endothelial cells (ECs) were stimulated by using a computer-controlled cyclic stress unit. BrdU staining and PCR were used to detect ECs proliferation activity and Egr-1 and ICAM-1 mRNA expression, respectively. Western-blot analysis was also used to detect expression of Egr-1 and intercellular adhesion molecule-1 (ICAM-1) proteins.

RESULTS

The lumens of vein grafts in Egr-1 KO mice were wider than in WT mice. ECs proliferation after mechanical stretch stimulation was suppressed by Egr-1 knockout (P < 0.05). Both in vein grafts and ECs from WT mice after mechanical stretch stimulation, mRNA expression and protein of Egr-1 and ICAM-1 showed increases (P < 0.05). However, ICAM-1 expression was significantly suppressed in ECs from Egr-1 knockout mice (P < 0.05).

CONCLUSIONS

Egr-1 may promote ECs proliferation and result in vein graft restenosis by upregulating the expression of ICAM-1. As a key factor of vein graft restenosis, it could be a target for the prevention of restenosis after CABG surgery.

Flow-dependent endothelial function and kidney dysfunction

The vascular endothelium constantly integrates biomechanical and humoral signals and responds by secreting or metabolizing multiple factors that act in an autocrine or paracrine manner on the vasculature and adjacent tissues. Several studies have documented the effects of blood flow on renal endothelial cells and its effects on the pathophysiology of the kidney. In contrast, less is known about the effects of acute flow cessation on renal endothelium and kidney function. Here we review our current knowledge on flow cessation, endothelial function, and kidney dysfunction in the context of two clinically relevant settings, namely, the no-reflow phenomenon, observed during periods of renal warm ischemia, and the cold storage of kidney transplants.

Shear stress responses of adult blood outgrowth endothelial cells seeded on bioartificial tissue

Human blood outgrowth endothelial cells (HBOECs) are expanded from circulating endothelial progenitor cells in peripheral blood and thus could provide a source of autologous endothelial cells for tissue-engineered vascular grafts. To examine the suitability of adult HBOECs for use in vascular tissue engineering, the shear stress responsiveness of these cells was examined on bioartificial tissue formed from dermal fibroblasts entrapped in tubular fibrin gels. HBOECs adhered to this surface, deposited collagen IV and laminin, and remained adherent when exposed to 15 dyn/cm(2) shear stress for 24 h. The shear stress responses of HBOECs were compared to human umbilical vein endothelial cells (HUVECs). As with HUVECs, HBOECs upregulated vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 when exposed to tumor necrosis factor (TNF)-α and shear stress decreased the expression of these adhesion molecules on TNF-α-activated monolayers. Nitric oxide production was elevated by shear stress, but did not vary between cell types. Both cell types decreased platelet adhesion to the bioartificial tissue, whereas pre-exposing the cells to flow decreased platelet adhesion further. These results illustrate the potential utility for HBOECs in vascular tissue engineering, as not only do the cells adhere to bioartificial tissue and remain adherent under physiological shear stress, they are also responsive to shear stress signaling.

Modeling of shear stress experienced by endothelial cells cultured on microstructured polymer substrates in a parallel plate flow chamber

The application of physical stimuli to cell populations in tissue engineering and regenerative medicine may facilitate significant scientific and clinical advances. However, for the most part, these stimuli are evaluated in isolation, rather than in combination. This study was designed to combine two physical stimuli. The first being a microstructured tissue culture polystyrene substrate, known to produce changes in cell shape and orientation, and the second being laminar shear stress in a parallel plate flow chamber. The combined effects of these stimuli on endothelial cell monolayers cells were evaluated in a parallel plate flow chamber and using a computational fluid dynamics (CFD) model. The topography of the cell monolayers cultured on different microstructured surfaces was determined using confocal laser scanning microscopy (CLSM), and this topographic information was used to construct the CFD model. This research found that while the specific underlying structures were effectively planarized by the cell monolayer, significant differences in cell shape and orientation were observed on the different microstructured surfaces. Cells cultured on grooved substrates aligned in the direction of the grooves and showed higher retention after 1-h LSS conditioning than those cultured on pillars. The modeled shear stress distributions also showed differences. While minor differences in the magnitude of shear stress were noted, aligned cell monolayers experienced significantly lower spatial gradients of shear stress when compared with cells that were not pre-aligned by surface features. The results presented here provide an analysis of how one form of physical stimulus can be moderated by another and also provide a methodology by which the understanding of cell responses to topographic and mechanical stimuli can be further advanced.

Activation of NF-kappaB by fluid shear stress, but not TNF-alpha, requires focal adhesion kinase in osteoblasts

When bone is mechanically loaded fluid shear stress (FSS) is generated as a result of the movement of interstitial fluid across the membranes of osteoblasts and osteocytes. This external mechanical loading stimulates changes in the activity of cytoplasmic signaling molecules and alters gene expression in bone cells. This process, referred to as mechanotransduction, is vital for maintaining bone health in vivo by regulating the balance between bone formation and bone resorption. This current study focuses on the role of focal adhesions, sites of integrin-mediated cellular attachment to the extracellular matrix, and their proposed function as mechanosensors in bone cells. We examined the role of a key component of focal adhesions and of mechanotransduction, focal adhesion kinase (FAK) in regulation of FSS- and tumor necrosis factor-alpha (TNF-alpha)-induced activation of nuclear factor-kappa B (NF-kappaB) signaling in osteoblasts. Immortalized FAK(+/+) and FAK(-)(/)(-) osteoblasts were exposed to periods of oscillatory fluid shear stress (OFF) and NF-kappaB activation was analyzed. We determined that FAK is required for OFF-induced nuclear translocation and activation of NF-kappaB in osteoblasts. In addition we found that OFF-induced phosphorylation of the IkappaB kinases (IKKalpha/beta) in both FAK(+/+) and FAK(-/-) osteoblasts, but only FAK(+/+) osteoblasts demonstrated the resulting degradation of NF-kappaB inhibitors IkappaBalpha and IkappaBbeta. OFF did not induce the degradation of IkappaBepsilon or the processing of p105 in either FAK(+/+) and FAK(-/-) osteoblasts. To compare the role of FAK in mediating OFF-induced mechanotransduction to the well characterized activation of NF-kappaB by inflammatory cytokines, we exposed FAK(+/+) and FAK(-/-) osteoblasts to TNF-alpha. Interestingly, FAK was not required for TNF-alpha induced NF-kappaB activation in osteoblasts. In addition we determined that TNF-alpha treatment did not induce the degradation of IkappaBbeta as did OFF. These data indicate a novel relationship between FAK and NF-kappaB activation in osteoblast mechanotransduction and demonstrates that the mechanism of FSS-induced NF-kappaB activation in osteoblasts differs from the well characterized TNF-alpha-induced activation.

Engineering RNA for targeted siRNA delivery and medical application

RNA engineering for nanotechnology and medical applications is an exciting emerging research field. RNA has intrinsically defined features on the nanometre scale and is a particularly interesting candidate for such applications due to its amazing diversity, flexibility and versatility in structure and function. Specifically, the current use of siRNA to silence target genes involved in disease has generated much excitement in the scientific community. The intrinsic ability to sequence-specifically downregulate gene expression in a temporally- and spatially controlled fashion has led to heightened interest and rapid development of siRNA-based therapeutics. Although methods for gene silencing have been achieved with high efficacy and specificity in vitro, the effective delivery of nucleic acids to specific cells in vivo has been a hurdle for RNA therapeutics. This article covers different RNA-based approaches for diagnosis, prevention and treatment of human disease, with a focus on the latest developments of non-viral carriers of siRNA for delivery in vivo. The applications and challenges of siRNA therapy, as well as potential solutions to these problems, the approaches for using phi29 pRNA-based vectors as polyvalent vehicles for specific delivery of siRNA, ribozymes, drugs or other therapeutic agents to specific cells for therapy will also be addressed.

Microarray profiling reveals CXCR4a is downregulated by blood flow in vivo and mediates collateral formation in zebrafish embryos

The response to hemodynamic force is implicated in a number of pathologies including collateral vessel development. However, the transcriptional effect of hemodynamic force is extremely challenging to examine in vivo in mammals without also detecting confounding processes such as hypoxia and ischemia. We therefore serially examined the transcriptional effect of preventing cardiac contraction in zebrafish embryos which can be deprived of circulation without experiencing hypoxia since they obtain sufficient oxygenation by diffusion. Morpholino antisense knock-down of cardiac troponin T2 (tnnt2) prevented cardiac contraction without affecting vascular development. Gene expression in whole embryo RNA from tnnt2 or control morphants at 36, 48, and 60 h postfertilization (hpf) was assessed using Affymetrix GeneChip Zebrafish Genome Arrays (>14,900 transcripts). We identified 308 differentially expressed genes between tnnt2 and control morphants. One such (CXCR4a) was significantly more highly expressed in tnnt2 morphants at 48 and 60 hpf than controls. In situ hybridization localized CXCR4a upregulation to endothelium of both tnnt2 morphants and gridlock mutants (which have an occluded aorta preventing distal blood flow). This upregulation appears to be of functional significance as either CXCR4a knock-down or pharmacologic inhibition impaired the ability of gridlock mutants to recover blood flow via collateral vessels. We conclude absence of hemodynamic force induces endothelial CXCR4a upregulation that promotes recovery of blood flow.

Influence of TNF-alpha and biomechanical stress on endothelial anti- and prothrombotic genes

Biomechanical stress modulates vascular tone, vascular remodelling and the spatial localisation of atherosclerotic plaques. Inflammatory cytokines, such as TNF-alpha, regulate expression of genes that impair the function of endothelial cells. This study investigates the combinatory effect of different biomechanical stresses and TNF-alpha on the expression of endothelial anti- and prothrombotic genes. Human umbilical vein endothelial cells were exposed to TNF-alpha and different levels of static/pulsatile tensile stress or shear stress. The response in endothelial cells to TNF-alpha was not modulated by tensile stress. However, 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-alpha additively induced PAI-1, whereas shear stress blocked the cytokine effect on t-PA and u-PA. A flow profile characterized by high laminar shear stress seems to render the endothelial cell more resistant to inflammatory stress.

The addition of tumor necrosis factor plus beta interferon induces a novel synergistic antiviral state against poxviruses in primary human fibroblasts

Tumor necrosis factor (TNF) and members of the interferon (IFN) family have been shown to independently inhibit the replication of a variety of viruses. In addition, previous reports have shown that treatment with various combinations of these antiviral cytokines induces a synergistic antiviral state that can be significantly more potent than addition of any of these cytokines alone. The mechanism of this cytokine synergy and its effects on global gene expression, however, are not well characterized. Here, we use DNA microarray analysis to demonstrate that treatment of uninfected primary human fibroblasts with TNF plus IFN-beta induces a distinct synergistic state characterized by significant perturbations of several hundred genes which are coinduced by the individual cytokines alone, as well as the induction of more than 850 novel host cell genes. This synergy is mediated directly by the two ligands, not by intermediate secreted factors, and is necessary and sufficient to completely block the productive replication and spread of myxoma virus in human fibroblasts. In contrast, the replication of two other poxviruses, vaccinia virus and tanapox virus, are only partially inhibited in these cells by the synergistic antiviral state, whereas the spread of both of these viruses to neighboring cells was efficiently blocked. Taken together, our data indicate that the combination of TNF and IFN-beta induces a novel synergistic antiviral state that is highly distinct from that induced by either cytokine alone.

Divergent and convergent effects on gene expression and function in acute versus chronic endothelial activation

Activation of the vascular endothelium with cytokines such as TNF is widely used to study the role of the vasculature in proinflammatory disease. To gain insight into mechanisms of prolonged vascular endothelial activation we compared changes in gene expression induced by continuous activation in stable tmTNF-expressing cells with changes due to acute TNF challenge in vitro. Affymetrix Genechip analysis was performed on RNA from control, acute and continuous TNF-activated endothelial cells. Only 36% of the significant changes in gene expression were convergent between the acute and continuously activated endothelial cells compared with the control. From the divergently regulated genes, for example the cytokine ENA-78 was specifically induced in chronically activated cells, while E-selectin, a cell adhesion molecule, was upregulated only in acutely activated endothelial cells. Antioxidant SOD gene induction was noted in acute activation, while a regulatory NADPH oxidase subunit was selectively upregulated in continuously activated endothelium in accordance with significant reactive oxygen species induction occurred only in these cells. Accordingly, p38 and ERK1/2, two MAP kinases downstream of reactive oxygen species, were activated in stable transmembrane-spanning precursor (tm) TNF-expressing cells and were refractory to activation with soluble TNF or VEGF. In consequence, the increased p38 MAP kinase activity contributed to increased endothelial cell migration in tmTNF-expressing cells. These data suggest that continuous activation of endothelial cells leads to specific expression and functional changes, consistent with alterations observed in dysfunctional endothelium exposed to or involved in chronic inflammation.

Stability of 2-D colloidal particle aggregates held against flow stress in an ultrasound trap

The formation of a two-dimensional aggregate of 25 microm latex particles in a 1.5 MHz ultrasound standing wave (USW) field and its disintegration in a flow were studied. The aggregate was held in the pressure node plane, which allowed continuous microscope observation and video recording of the processes. The trajectories and velocities of the particles approaching the formation site were analyzed by particle image velocimetry (PIV). Since the direct radiation force on the particles dominated the drag due to acoustic streaming, the acoustic pressure profile in the vicinity of the aggregate was quantifiable. The drag coefficients D(coef) for 2- to 485-particle aggregates were estimated from the balance of the drag force FD and the buoyancy-corrected gravitational force during sedimentation on termination of the ultrasound when the long axis of the aggregate was in the vertical plane. D(coef) were calculated from FD as proportional to the aggregate velocity. Experiments on particle detachment by flow (in-plane velocity measured by PIV) from horizontal aggregates suspended in deionized water and CaCl2 solution of different concentrations showed that the mechanical strength of the aggregates depended on the acoustic pressure amplitude P0 and ionic strength of the solution. In deionized water the flow velocity required to detach the first single particle from an aggregate increased from 1 mm s-1 at P0 = 0.6 MPa to 4.2 mm s-1 at P0 = 1.4 MPa. The balance of forces acting on particles in a USW trap is discussed. The magnitude of the shear stress employed ( approximately 0.05 Pa) and separation forces suggests that this technique can be applied to studying the mechanical responses of cell aggregates to hydrodynamic flow, where cell-cell interaction can be separated from the effects of solid substrata.

Prolonged shear stress and KLF2 suppress constitutive proinflammatory transcription through inhibition of ATF2

Absence of shear stress due to disturbed blood flow at arterial bifurcations and curvatures leads to endothelial dysfunction and proinflammatory gene expression, ultimately resulting in atherogenesis. KLF2 has recently been implicated as a transcription factor involved in mediating the anti-inflammatory effects of flow. We investigated the effect of shear on basal and TNF-alpha-induced genomewide expression profiles of human umbilical vein endothelial cells (HUVECs). Cluster analysis confirmed that shear stress induces expression of protective genes including KLF2, eNOS, and thrombomodulin, whereas basal expression of TNF-alpha-responsive genes was moderately decreased. Promoter analysis of these genes showed enrichment of binding sites for ATF transcription factors, whereas TNF-alpha-induced gene expression was mostly NF-kappaB dependent. Furthermore, human endothelial cells overlying atherosclerotic plaques had increased amounts of phosphorylated nuclear ATF2 compared with endothelium at unaffected sites. In HUVECs, a dramatic reduction of nuclear binding activity of ATF2 was observed under shear and appeared to be KLF2 dependent. Reduction of ATF2 with siRNA potently suppressed basal proinflammatory gene expression under no-flow conditions. In conclusion, we demonstrate that shear stress and KLF2 inhibit nuclear activity of ATF2, providing a potential mechanism by which endothelial cells exposed to laminar flow are protected from basal proinflammatory, atherogenic gene expression.

Functional TRPM7 channels accumulate at the plasma membrane in response to fluid flow

Many cells are constantly exposed to fluid mechanical forces generated by flowing blood, and wall shear stresses modulate aspects of their structure and function. However, the mechanisms for mechanotransduction of flow are not well understood. Here we report that TRPM7, which is both an ion channel and a functional kinase, is translocated within cells in response to laminar flow. After exposure of cells to physiological values of laminar fluid flow, the number of TRPM7 molecules localized at or near the plasma membrane increased up to 2-fold, in less than 100 seconds. This increase in membrane-localized GFP-TRPM7, as seen by total internal reflection fluorescence microscopy, closely correlated with increases in TRPM7 current. Both endogenous and heterologously expressed TRPM7 was found in tubulovesicular structures that were translocated to the region of the plasma membrane on induction of shear stress. In vascular smooth muscle cells, but not in several types of endothelial cells, fluid flow increased endogenous native TRPM7 current amplitude. We hypothesize that TRPM7 plays a role in pathological response to vessel wall injury.