Mechanotransduction by endothelial cells is locally generated, direction-dependent, and ligand-specific.

Vascular endothelial cells display a wide panel of responses to changes in the shear stress that is exerted on them by blood flow. How sensory mechanisms convey information about flow conditions and how this information is integrated remains poorly understood. The issue is confounded by: (1) a large number of potential force sensors, (2) difficulties in differentiating these sensors from downstream sites of signal integration, and (3) the complexities inherent in understanding how forces are transmitted from the apical surface of the cell via the cytoskeleton to intracellular sites.

A system for high-speed microinjection of adherent cells.

This paper reports on a semi-automated microrobotic system for adherent cell injection. Different from embryos/oocytes that have a spherical shape and regular morphology, adherent cells are flat with a thickness of a few micrometers and are highly irregular in morphology. Based on computer vision microscopy and motion control, the system coordinately controls a three-degrees-of-freedom microrobot and a precision XY stage, demonstrating an injection speed of 25 endothelial cells per minute with a survival rate of 95.

Homotypic and endothelial cell adhesions via N-cadherin determine polarity and regulate migration of vascular smooth muscle cells.

Migration of smooth muscle cells from the arterial media to the intima is central to several vascular pathologies including restenosis. This study demonstrates that, like directional migration of other cells, smooth muscle migration is accompanied by a dramatic, polarized reorganization of the cell cytoskeleton that is accompanied by activation of the Rho GTPase Cdc42 and inactivation of glycogen synthase kinase-3beta. We also show, for the first time, that signals generated at the posterior-lateral aspects of wound edge cells by the cell-cell adhesion molecule N-cadherin are required for polarization and rapid migration of vascular smooth muscle.

Integrin-linked kinase in the vascular smooth muscle cell response to injury.

Integrin-mediated interactions between smooth muscle cells (SMCs) and the extracellular matrix regulate cell migration and proliferation during neointimal hyperplasia. Integrin-linked kinase (ILK) is a serine-threonine kinase and scaffolding molecule that acts downstream of integrin receptors to modulate cell adhesion; therefore, we examined ILK function in SMCs during wound repair. Silencing of ILK expression with siRNA in vitro decreased cell adhesion to fibronectin and accelerated both cell proliferation and wound closure in the cell monolayer; it also resulted in the rearrangement of focal adhesions and diminished central actin stress fibers.

The expression of transforming growth factor beta in pregnant rat myometrium is hormone and stretch dependent.

From a quiescent state in early pregnancy to a highly contractile state in labor, the myometrium displays tremendous growth and remodeling. We hypothesize that the transforming growth factor beta (TGFbeta) system is involved in the differentiation of pregnant myometrium throughout gestation and labor. Furthermore, we propose that during pregnancy the mechanical and hormonal stimuli play a role in regulating myometrial TGFbetas.

Arterial adaptations to chronic changes in haemodynamic function: coupling vasomotor tone to structural remodelling.

Healthy mature arteries are usually extremely quiescent tissues with cell proliferation rates much below 1%/day and with extracellular matrix constituents exhibiting half-lives of years to decades. However, chronic physiological or pathological changes in haemodynamic function elicit arterial remodelling processes that may involve substantial tissue synthesis, degradation or turnover. Although these remodelling processes accommodate changing demands placed upon the cardiovascular system by physiological adaptations, they can compromise further perfusion in the context of arterial occlusive disease and they entrench hypertension and may exacerbate its progression.

Force-induced polarized mitosis of endothelial and smooth muscle cells in arterial remodeling.

Arteries display highly directional growth and remodeling that are specific to increases in the mechanical loads imposed on them by blood pressure, blood flow, and lengthwise tensile forces that are transmitted from the tissues to which they are attached. This study examined the effect of mechanical forces on the direction in which mitosis delivers daughter cells, as a mechanism for directional growth. Lateral forces were imposed on surface integrins of cultured endothelial cells by seeding the cells with arginine-glycine-aspartate peptide-coated magnetic microspheres and applying a magnetic field.

Insulin-like growth factors and their binding proteins define specific phases of myometrial differentiation during pregnancy in the rat.

While the insulin-like growth factor (IGF) system is known to regulate uterine function during the estrous cycle, there are limited data on its role in myometrial growth and development during pregnancy. To address this issue, we defined the expression of the Igf hormones (1 and 2), their binding proteins (Igfbp 1-6), and Igf1r receptor genes in pregnant, laboring, and postpartum rat myometrium by real-time PCR. IGF family genes were differentially expressed throughout gestation.

Endothelium-independent flow-induced dilation in the mouse carotid artery.

Background: We investigated the locus of flow regulation of vascular tone in carotid arteries of C57 Bl/6 and eNOS(-/-) mice.

Methods: Arterial segments (2-3 mm) were mounted in a perfusion myograph and preconstricted with 1 muM phenylephrine before monitoring flow-induced changes in lumen diameter.

Results: Both control and eNOS(-/-) mice demonstrated flow-dependent relaxation.

Shear stress regulates forward and reverse planar cell polarity of vascular endothelium in vivo and in vitro.

Cultured vascular endothelium displays profound morphological adaptations to shear stress that include planar cell polarity (PCP) that is directed downstream. Endothelial cells in blood vessels are also polarized; however, the direction of polarity is vessel specific, and shear-independent mechanisms have been inferred. The regulation of endothelial PCP is therefore controversial.

Partial off-loading of longitudinal tension induces arterial tortuosity.

Objectives: Arterial tortuosity is a frequent manifestation of vascular disease and collateral vessel growth, but its causes are poorly understood. This study was designed to assess the relationship between the development of tortuosity and the mechanical forces that are imposed on arterial tissue.

Methods And Results: Axial strain in rabbit carotid arteries was reduced from 62+/-2% to 33+/-2% by implanting an interposition graft, prepared from the contralateral carotid, at the downstream end of the artery.

Shear-induced reorganization of endothelial cell cytoskeleton and adhesion complexes.

Endothelial cells undergo profound morphologic changes in response to alterations in shear stresses that are imposed on them by blood flow, and these responses have important implications for physiologic and pathophysiologic function of blood vessels. Shear-induced changes in cell morphology represent a unique mode of cell motility: elongation of the cells in the direction of shear stress is achieved by a reorientation and assembly of F-actin stress fibers at the basal cell surface that ultimately protrudes the upstream and downstream limits of the plasma membrane. Shape change is also accommodated by dramatic reorganization of cell-substrate and cell-cell junctional complexes.

Mechanical stretch and progesterone differentially regulate activator protein-1 transcription factors in primary rat myometrial smooth muscle cells.

During pregnancy, stretch of the uterus, imposed by the growing fetus, is an important signal for the induction of genes involved in the onset of labor. In this study, the expression of activator protein-1 (AP-1) family mRNAs in response to in vitro stretch was investigated in myometrial cells. Rat primary myometrial smooth muscle cells were plated onto collagen I-coated Flex I culture plates and subjected to 25% static stretch on day 4 of culture.

Assembly and reorientation of stress fibers drives morphological changes to endothelial cells exposed to shear stress.

Fluid shear stress greatly influences the biology of vascular endothelial cells and the pathogenesis of atherosclerosis. Endothelial cells undergo profound shape change and reorientation in response to physiological levels of fluid shear stress. These morphological changes influence cell function; however, the processes that produce them are poorly understood.

Progesterone and gravidity differentially regulate expression of extracellular matrix components in the pregnant rat myometrium.

Myometrial growth and remodeling during pregnancy depends on increased synthesis of interstitial matrix proteins. We hypothesize that the presence of mechanical tension in a specific hormonal environment regulates the expression of extracellular matrix (ECM) components in the uterus. Myometrial tissue was collected from pregnant rats on Gestational Days 0, 12, 15, 17, 19, 21, 22, 23 (labor), and 1 day postpartum and ECM expression was analyzed by Northern blotting.

N-cadherin upregulation and function in response of smooth muscle cells to arterial injury.

Objective: Smooth muscle cell migration is critical to neointimal formation after arterial injury. The purpose of this study was to elucidate the regulation and functional significance of cell-cell adhesion via adherens junctions during this process.

Methods And Results: Using balloon catheter injury of rat carotid artery, we showed that neointimal formation is accompanied by dramatic but transient upregulation of intimal N-cadherin and associated catenins, proteins that mediate adhesion at adherens junctions.

Mitogen-activated protein kinases mediate stretch-induced c-fos mRNA expression in myometrial smooth muscle cells.

Evidence indicates that stretch of the uterus imposed by the growing fetus contributes to the onset of labor. Previously we have shown that mechanically stretching rat myometrial smooth muscle cells (SMCs) induces c-fos expression. To investigate this stretch-induced signaling, we examined the involvement of the mitogen-activated protein kinase (MAPK) family.

Regulation of c-fos expression by static stretch in rat myometrial smooth muscle cells.

Objective: We investigated whether mechanical stretch stimulates expression of the immediate early gene c-fos messenger RNA in rat myometrial smooth muscle cells.

Study Design: Freshly isolated myometrial smooth muscle cells (from virgin rats) were plated on flexible culture plates that were coated with either collagen I, laminin, elastin, or pronectin and were subjected to a static stretch with a computerized strain unit. Immunocytochemistry was used to define smooth muscle cell phenotype, and c-fos expression levels were assessed by Northern blotting.

Wall tissue remodeling regulates longitudinal tension in arteries.

Changes in blood pressure or flow induce arterial remodeling that normalizes mechanical loads that are imposed on arterial tissue. Arteries are also under substantial longitudinal stretch (axial strain) that may be altered by growth or atrophy of tissues to which they are attached. We therefore tested whether axial strain is also regulated in a negative feedback manner through arterial remodeling.

Epidermolysis bullosa and embryonic lethality in mice lacking the multi-PDZ domain protein GRIP1.

Glutamate receptor-interacting protein 1 (GRIP1) is an adaptor protein composed of seven PDZ (postsynaptic density-95/Discs large/zona occludens-1) domains, capable of mediating diverse protein-protein interactions. GRIP1 has been implicated in the regulation of neuronal synaptic function, but its physiologic roles have not been defined in vivo. We find that elimination of murine GRIP1 results in embryonic lethality.

Experimental angiogenesis of arterial vasa vasorum.

Vasa vasorum are important sources of oxygen and nutrients to vascular tissues and their proliferation influences the pathogenesis of arterial disease; however, the regulation of their growth is poorly understood partly because of a lack of appropriate experimental models. We cuffed common carotid arteries of rabbits with segments of the contralateral carotid artery, a procedure that resulted in rapid and extensive elaboration of adventitial vasa vasorum and connective tissue. Endothelium-lined microvessels were observed at 1 week but vessels as large as 300 microm with an organizing media were common by 3 weeks.

Maternal cardiovascular changes during pregnancy and postpartum in mice.

Genetically altered mice may provide useful models for exploring cardiovascular regulation during pregnancy and postpartum if changes in mice mimic humans. We found in awake ICR (CD-1) mice at 17.5 days gestation that hematocrit was reduced 18%, and the pressor response to intravenous angiotensin II was reduced ~33%.