Insights into pathways of arteriogenesis

The compensatory growth of blood vessels after major arterial occlusions has been termed arteriogenesis. Although having some characteristics in common with angiogenesis, marked differences between both forms of vascular growth exist relating to triggers, underlying mechanisms and physiologic effects. Arteriogenesis describes the remodelling of small interconnecting arterial anastomoses with almost no net blood flow to large functional arteries. It has been shown that growth of these collateral arteries is triggered by physical forces, but does not require hypoxia as a stimulus. In this review we describe an animal model which we used to characterize the role of fluid shear stress for arteriogenesis. Fluid shear stress initiates the activation of endothelial cells and modulates processes which control attraction of circulating cells to the collateral wall. Monocytes were shown to have a pivotal role during arteriogenesis. After entering the vascular wall they function as micro-bioreactors producing cytokines and thereby controlling cell proliferation and remodelling. Furthermore, cell proliferation coincides with the transient dismantling of extracellular structures such as the elastic lamina which is required to provide space for the increasing number of wall cells. After the re-arrangement of wall structures collaterals with large calibres represent functional arteries with the ability to compensate blood flow deficits caused by arterial occlusions. It is therefore questionable, whether there is also a form of de novo collateral artery growth with physiologic relevance.

Non-genomic effects of 17beta-estradiol in activation of the ERK1/ERK2 pathway induces cell proliferation through upregulation of cyclin D1 expression in bovine artery endothelial cells

OBJECTIVE

Growing evidence indicates that estrogen's non-genomic effects play important roles in cellular functions and backs up the hypothesis of the existence of a membrane estrogen receptor (mER) in a number of cell types, but little is known about the complementary effects between traditional genomic and novel non-genomic effects of estrogen. The aim of the present study was to explore the non-genomic activation of ERK1/2 mitogen-activated protein kinase (MAPK) by 17beta-estradiol (E(2)) through mER and its role in cell proliferation.

METHODS

On cultured bovine artery endothelial cells (BAECs) we used the [(3)H]thymidine incorporation assay to evaluate the influence of E(2) on cell proliferation and fluorescence microscopy to show the presence of mER on the cell membrane. Scatchard analysis was performed to identify and characterize the mER on a purified membrane fraction of BAECs.

RESULTS

E(2) upregulated cyclin D1 protein expression and enhanced cell proliferation. Inhibition of the MAPK cascade with PD98059 or of G protein with pertussis toxin (PTX) completely abolished the above effects, while the estrogen receptor antagonist tamoxifen attenuated E(2)-dependent upregulation of cyclin D1 and cell proliferation. Accordingly, E(2) rapidly led to ERK1/ERK2 activation, which was prevented by tamoxifen or PTX and was entirely reproduced by membrane-impermeable estradiol-bovine serum albumin conjugate (E(2)coBSA). Immunofluorescent staining with E(2)coBSA-fluorescein isothiocyanate resulted in a punctuate staining pattern of the plasma membrane and Scatchard analysis of the E(2)-binding protein in a purified membrane fraction of BAECs showed that E(2) binds to the membrane fraction with a dissociation constant of 0.2394 nmol/l.

CONCLUSION

Our findings showed that E(2) induces cell proliferation through upregulation of cyclin D1 via non-genomic activation of the ERK1/ERK2 pathway mediated by mER and G protein.

Improved arterial wall model by coculturing vascular endothelial and smooth muscle cells

We have constructed an in vitro arterial wall model by coculturing bovine arterial endothelial cells (ECs) and smooth muscle cells (SMCs). When ECs were seeded directly over SMCs and cocultured in an ordinary culture medium, ECs grew sparsely and did not form a confluent monolayer. Addition of ascorbic acid to the culture medium at concentrations greater than 50 mug/ml increased the production of type IV collagen by the SMCs, and ECs formed a confluent monolayer covering the entire surface of SMCs. Histological studies showed that the thickness of the cell layer composed of ECs and SMCs increased with increasing duration of coculture. This arterial wall model, prepared by our method, may serve as a simple and good in vitro model to study the effects of factors such as biological chemicals and shear stress on cell proliferation and other physiological functions of arterial walls.

Influence of oxidized low density lipoprotein on the proliferation of human artery smooth muscle cells in vitro

The effects of oxidized low density lipoprotein (ox-LDL) on the proliferation of cultured human vascular smooth muscle cells (vSMC) were investigated in vitro. By using NaBr density gradient centrifugation, LDL was isolated and purified from human plasma. Ox-LDL was produced from LDL by being incubated with CuSO(4). ox-LDL was then added to the culture medium at different concentrations (35, 60, 85, 110, 135 and 160 microg/mL) for 7 days. The influence of ox-LDL on vSMC proliferation was observed in growth curve, mitosis index, and in situ determination of apoptosis. The data were analyzed with SPSS 10.0 software. The results showed that the ox-LDL produced in vitro had a good purity and optimal oxidative degree, which was similar to the intrinsic ox-LDL in atherosclerotic plaque. ox-LDL at a concentration of 35 microg/mL demonstrated the strongest proliferation inducement, and at a concentration of 135 microg/mL, ox-LDL could inhibit the growth of vSMC. ox-LDL at concentrations of 35 and 50 microg/mL presented powerful mitotic trigger, and with the increase of ox-LDL concentration, the mitotic index of vSMC was decreased gradually. ox-LDL at higher concentrations promoted more apoptotic vSMCs. ox-LDL at lower concentrations triggered proliferation of vSMCs, and at higher concentrations induced apoptosis in vSMCs. ox-LDL played a promotional role in the pathogenesis and development of atherosclerosis by affecting vSMC proliferation and apoptosis.

Notch signalling limits angiogenic cell behaviour in developing zebrafish arteries

Recent evidence indicates that growing blood-vessel sprouts consist of endothelial cells with distinct cell fates and behaviours; however, it is not clear what signals determine these sprout cell characteristics. Here we show that Notch signalling is necessary to restrict angiogenic cell behaviour to tip cells in developing segmental arteries in the zebrafish embryo. In the absence of the Notch signalling component Rbpsuh (recombining binding protein suppressor of hairless) we observed excessive sprouting of segmental arteries, whereas Notch activation suppresses angiogenesis. Through mosaic analysis we find that cells lacking Rbpsuh preferentially localize to the terminal position in developing sprouts. In contrast, cells in which Notch signalling has been activated are excluded from the tip-cell position. In vivo time-lapse analysis reveals that endothelial tip cells undergo a stereotypical pattern of proliferation and migration during sprouting. In the absence of Notch, nearly all sprouting endothelial cells exhibit tip-cell behaviour, leading to excessive numbers of cells within segmental arteries. Furthermore, we find that flt4 (fms-related tyrosine kinase 4, also called vegfr3) is expressed in segmental artery tip cells and becomes ectopically expressed throughout the sprout in the absence of Notch. Loss of flt4 can partially restore normal endothelial cell number in Rbpsuh-deficient segmental arteries. Finally, loss of the Notch ligand dll4 (delta-like 4) also leads to an increased number of endothelial cells within segmental arteries. Together, these studies indicate that proper specification of cell identity, position and behaviour in a developing blood-vessel sprout is required for normal angiogenesis, and implicate the Notch signalling pathway in this process.

Notch ligand Delta-like 1 is essential for postnatal arteriogenesis

Growth of functional arteries is essential for the restoration of blood flow to ischemic organs. Notch signaling regulates arterial differentiation upstream of ephrin-B2 during embryonic development, but its role during postnatal arteriogenesis is unknown. Here, we identify the Notch ligand Delta-like 1 (Dll1) as an essential regulator of postnatal arteriogenesis. Dll1 expression was specifically detected in arterial endothelial cells, but not in venous endothelial cells or capillaries. During ischemia-induced arteriogenesis endothelial Dll1 expression was strongly induced, Notch signaling activated and ephrin-B2 upregulated, whereas perivascular cells expressed proangiogenic vascular endothelial growth factor, and the ephrin-B2 activator EphB4. In heterozygous Dll1 mutant mice endothelial Notch activation and ephrin-B2 induction after hindlimb ischemia were absent, arterial collateral growth was abrogated and recovery of blood flow was severely impaired, but perivascular vascular endothelial growth factor and EphB4 expression was unaltered. In vitro, angiogenic growth factors synergistically activated Notch signaling by induction of Dll1, which was necessary and sufficient to regulate ephrin-B2 expression and to induce ephrin-B2 and EphB4-dependent branching morphogenesis in human arterial EC. Thus, Dll1-mediated Notch activation regulates ephrin-B2 expression and postnatal arteriogenesis.

Interleukin-1β selectively decreases the synthesis of versican by arterial smooth muscle cells

Proteoglycans accumulate in lesions of atherosclerosis but little is known as to which factors regulate the synthesis of these molecules. Interleukin-1beta (IL-1beta) is a cytokine involved in vascular lesion development but it is not clear whether it has specific effects on proteoglycan synthesis by arterial smooth muscle cells (ASMC). Monkey ASMC were treated with IL-1beta and proteoglycan synthesis assessed using [(35)S]-sulfate and [(35)S]-Trans amino acid labeling. Four prominent size populations of proteoglycans, as determined by SDS-PAGE gradient gel electrophoresis, were observed in the culture medium and identified as versican, biglycan, decorin, and an unknown population that migrated to the gel interface. IL-1beta treatment decreased significantly the synthesis of versican, while increasing the synthesis of decorin, but having no effect on biglycan synthesis. Northern blot analyses confirmed this selective effect on versican and decorin mRNA transcripts. Nuclear run-on and RNA inhibition studies showed that decreased mRNA for versican was due to increased mRNA degradation and not to changes in transcription. In addition, IL-1beta increased the synthesis of the population of proteoglycans that separated at the SDS-PAGE gel interface. Chondroitinase ABC lyase digestion of this population revealed a complex of proteins composed of versican (350 kDa), an unidentified protein (215 kDa), and a 23 kDa protein identified by sequence analyses as serglycin. These data demonstrate that IL-1beta selectively downregulates versican synthesis by ASMC, while positively regulating the synthesis of other proteoglycans.

Culture and Leukocyte Adhesion Assay of Human Arterial Endothelial Cells in a Glass Microchip

Cells are frequently exploited as processing components for integrated chemical systems, such as biochemical reactors and bioassay systems. By culturing vascular endothelial cells (ECs) in integrated chemical devices, vascular models have also been fabricated. Here, we utilized a thermally fused-glass microchip which is chemically and physically stable and favorable for optical detections, and cultured human arterial ECs (HAECs) in it. HAECs reached confluence within 4 days. Survival and tolerance for high shear stress (25 dyn/cm2) of the HAECs were confirmed. Furthermore, HAECs responded to inflammatory cytokine, tumor necrosis facor-alpha (TNF-alpha) and attached to more leukocyte cell line, HL-60 cells than unstimulated HAECs. Our developed device can be applied as a human arterial model, and we propose it as a new method for vascular studies.

Correlation between arterial mechanical properties, vascular biomaterial and tissue engineering

This review presents some of the recent technological developments in biomaterials used for the construction of synthetic cardiovascular vessels that are capable of simulating specific biological responses. However, with respect to the problems of stiffness, a major hypertensive risk factor, it is necessary to underline the important role of mechanical properties, such as vessel strength and composition, in vascular reconstructive surgery. Biomaterials occupy a central place in many cardiovascular disease treatments and they depend on the chemical nature of the polymers, on the biotechnology used, and also on cellular and gene therapy. Several methodologies using animal or human cells have emerged for constructing blood vessel replacements. Tissue-engineered blood vessel (TEBV) substitutes begin to motivate much work and have contributed to the restoration, maintenance, and/or improvement in tissue and organ function. Each methodology has it benefits, its promises, and holds many challenges in future biological, biomaterial and clinical research.

Invasive trophoblasts stimulate vascular smooth muscle cell apoptosis by a fas ligand-dependent mechanism

During pregnancy, trophoblasts migrate from the placenta into uterine spiral arteries, transforming them into wide channels that lack vasoconstrictive properties. In pathological pregnancies, this process is incomplete. To define the fundamental events involved in spiral artery remodeling, we have studied the effect of trophoblasts on vascular smooth muscle cells (SMCs). Here we demonstrate for the first time that apoptosis of SMCs can be initiated by invading trophoblasts. When trophoblasts isolated from normal placenta (primary trophoblasts) or conditioned medium was perfused into spiral or umbilical artery segments, apoptosis of SMCs resulted. Culture of human aortic SMCs (HASMCs) with primary trophoblasts, primary trophoblast-conditioned medium, or a trophoblast-derived cell line (SGHPL-4) also significantly increased SMC apoptosis. Fas is expressed by spiral artery SMCs, and a Fas-activating antibody triggered HASMC apoptosis. Furthermore, a Fas ligand (FasL)-blocking antibody significantly inhibited HASMC apoptosis induced by primary trophoblasts, SGHPL-4, or trophoblast-conditioned medium. Depleting primary trophoblast-conditioned medium of FasL also abrogated SMC apoptosis in vessels in situ. These results suggest that apoptosis triggered by the release of soluble FasL from invading trophoblasts contributes to the loss of smooth muscle from the walls of spiral arteries during pregnancy.

(+/-)-Naringenin as large conductance Ca(2+)-activated K+ (BKCa) channel opener in vascular smooth muscle cells

BACKGROUND AND PURPOSE. The aim of this study was to investigate, in vascular smooth muscle cells, the mechanical and electrophysiological effects of (+/-)-naringenin.

EXPERIMENTAL APPROACH

Aorta ring preparations and single tail artery myocytes were employed for functional and patch-clamp experiments, respectively.

KEY RESULTS

(+/-)-Naringenin induced concentration-dependent relaxation in endothelium-denuded rat aortic rings pre-contracted with either 20 mM KCl or noradrenaline (pIC(50) values of 4.74 and 4.68, respectively). Tetraethylammonium, iberiotoxin, 4-aminopyridine and 60 mM KCl antagonised (+/-)-naringenin-induced vasorelaxation, while glibenclamide did not produce any significant antagonism. Naringin [(+/-)-naringenin 7-beta-neohesperidoside] caused a concentration-dependent relaxation of rings pre-contracted with 20 mM KCl, although its potency and efficacy were significantly lower than those of (+/-)-naringenin. In rat tail artery myocytes, (+/-)-naringenin increased large conductance Ca(2+)-activated K(+) (BK(Ca)) currents in a concentration-dependent manner; this stimulation was iberiotoxin-sensitive and fully reversible upon drug wash-out. (+/-)-Naringenin accelerated the activation kinetics of BK(Ca) current, shifted, by 22 mV, the voltage dependence of the activation curve to more negative potentials, and decreased the slope of activation. (+/-)-Naringenin-induced stimulation of BK(Ca) current was insensitive either to changes in the intracellular Ca(2+) concentration or to the presence, in the pipette solution, of the fast Ca(2+) chelator BAPTA. However, such stimulation was diminished when the K(+) gradient across the membrane was reduced.

CONCLUSIONS AND IMPLICATIONS

The vasorelaxant effect of the naturally-occurring flavonoid (+/-)-naringenin on endothelium-denuded vessels was due to the activation of BK(Ca) channels in myocytes.

Atherogenic properties of LDL particles modified by human group X secreted phospholipase A2 on human endothelial cell function

Increasing evidence suggests that secreted phospholipases A2 (sPLA2s) play an important role in the pathophysiology of atherosclerosis. Among sPLA2s, the human group X (hGX) enzyme has the highest catalytic activity toward phosphatidylcholine, one of the major phospholipid species of cell membranes and low-density lipoprotein (LDL). Our study examined the presence of hGX sPLA2 in human atherosclerotic lesions and investigated the ability of hGX modified LDL to alter human endothelial cell (HUVEC) function. Our results show that hGX sPLA2 is present in human atherosclerotic lesions and that the hydrolysis of LDL by hGX sPLA2 results in a modified particle that induces lipid accumulation in human monocyte-derived macrophages. Acting on endothelial cells, hGX-modified LDL activates the MAP kinase pathway, which leads to increased arachidonic acid release, increased expression of adhesion molecules on the surface of HUVEC, and increased adhesion of monocytes to HUVEC monolayers. Together, our data suggest that LDL modified by hGX, rather than hGX itself may have strong proinflammatory and proatherogenic properties, which could play an important role in the propagation of atherosclerosis.

Cellular mechanism through which parathyroid hormone-related protein induces proliferation in arterial smooth muscle cells: definition of an arterial smooth muscle PTHrP/p27kip1 pathway

Parathyroid hormone-related protein (PTHrP) is present in vascular smooth muscle (VSM), is markedly upregulated in response to arterial injury, is essential for normal VSM proliferation, and also markedly accentuates neointima formation following rat carotid angioplasty. PTHrP contains a nuclear localization signal (NLS) through which it enters the nucleus and leads to marked increases in retinoblastoma protein (pRb) phosphorylation and cell cycle progression. Our goal was to define key cell cycle molecules upstream of pRb that mediate cell cycle acceleration induced by PTHrP. The cyclin D/cdk-4,-6 system and its upstream regulators, the inhibitory kinases (INKs), are not appreciably influenced by PTHrP. In striking contrast, cyclin E/cdk-2 kinase activity is markedly increased by PTHrP, and this is a result of a specific, marked, PTHrP-induced proteasomal degradation of p27(kip1). Adenoviral restoration of p27(kip1) fully reverses PTHrP-induced cell cycle progression, indicating that PTHrP mediates its cell cycle acceleration in VSM via p27(kip1). In confirmation, adenoviral delivery of PTHrP to murine primary vascular smooth muscle cells (VSMCs) significantly decreases p27(kip1) expression and accelerates cell cycle progression. p27(kip1) is well known to be a central cell cycle regulatory molecule involved in both normal and pathological VSM proliferation and is a target of widely used drug-eluting stents. The current observations define a novel "PTHrP/p27(kip1) pathway" in the arterial wall and suggest that this pathway is important in normal arterial biology and a potential target for therapeutic manipulation of the arterial response to injury.

Establishment of a functional ovine fetoplacental artery endothelial cell line with a prolonged life span

To study mechanisms governing fetoplacental vascular function, we have established a primary ovine fetoplacental artery endothelial (OFPAE) cell line. These OFPAE cells produce nitric oxide (NO), proliferate, and migrate in response to fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor (VEGF). To overcome the senescence crisis that this primary OFPAE cell line will eventually enter, we attempted to establish a functional OFPAE cell line with a prolonged life span by transfecting cells with plasmids containing a neomycin resistance gene and a simian virus 40 gene (SV40) expressing large T (T) and small t (t) antigens. The OFPAE cells at passage 8 were transfected. After neomycin selection, the surviving OFPAE (designated SV40 OFPAE) cells were expanded up to passage 80. Up to passage 30, these SV40 OFPAE cells maintained a morphology similar to untransfected OFPAE cells. Expression of T and t antigens in SV40 OFPAE cells was confirmed by immunocytochemistry. These SV40 OFPAE cells exhibited positive uptake of acetylated low-density lipoprotein (Ac-LDL) and positive staining for NO synthase 3 (NOS3) and formed capillary-like tube structures on Matrigel. Up to passages 20-23, these SV40 OFPAE cells proliferated (P < 0.05) and produced (P < 0.05) NO in response to both FGF2 and VEGF. Moreover, this cell proliferation stimulated by FGF2 and VEGF was dose-dependently inhibited (P < 0.05) by PD98059 (a selective mitogen-activated protein kinase 1 and 2 [MAP2K1/2, also termed MEK1/2] inhibitor) or by LY294002 (a selective phosphoinositide 3-kinase [PI3K] inhibitor). These data indicate that SV40 OFPAE cells, at least at passage 23, retain endothelial phenotypes and functions similar to their parental, untransfected OFPAE cells. Thus, a functional OFPAE cell line with an extended life span has been successfully established, potentially providing a valuable cell model for studying fetoplacental endothelial function.

Cytotrophoblast induction of arterial apoptosis and lymphangiogenesis in an in vivo model of human placentation

We studied the vascular effects of invasive human cytotrophoblasts in vivo by transplanting placental villi to the fifth mammary fat pads or beneath the kidney capsules of Scid mice. Over 3 weeks, robust cytotrophoblast invasion was observed in both locations. The architecture of the mammary fat pad allowed for detailed analysis of the cells' interactions with resident murine blood vessels, which revealed specific induction of apoptosis in the endothelial cells and smooth muscle walls of the arterioles. This finding, and confirmation of the results in an in vitro coculture model, suggests that a parallel process is important for enabling cytotrophoblast endovascular invasion during human pregnancy. Cytotrophoblast invasion of the kidney parenchyma was accompanied by a robust lymphangiogenic response, while in vitro, the cells stimulated lymphatic endothelial cell migration via the actions of VEGF family members, FGF, and TNF-alpha. Immunolocalization analyses revealed that human pregnancy is associated with lymphangiogenesis in the decidua since lymphatic vessels were not a prominent feature of the nonpregnant endometrium. Thus, the placenta triggers the development of a decidual lymphatic circulation, which we theorize plays an important role in maintaining fluid balance during pregnancy, with possible implications for maternal-fetal immune cell trafficking.

Hypoxia-mediated activation of Dll4-Notch-Hey2 signaling in endothelial progenitor cells and adoption of arterial cell fate

Adequate response to low oxygen levels (hypoxia) by hypoxia inducible factor (HIF) is essential for normal development and physiology, but this pathway may also contribute to pathological processes like tumor angiogenesis. Here we show that hypoxia is an inducer of Notch signaling. Hypoxic conditions lead to induction of the Notch ligand Dll4 and the Notch target genes Hey1 and Hey2 in various cell lines. Promoter analysis revealed that Hey1, Hey2 and Dll4 are induced by HIF-1alpha and Notch activation. Hypoxia-induced Notch signaling may also determine endothelial identity. Endothelial progenitor cells (EPCs) contain high amounts of COUP-TFII, a regulator of vein identity, while levels of the arterial regulators Dll4 and Hey2 are low. Hypoxia-mediated upregulation of Dll4 and Hey2 leads to repression of COUP-TFII in eEPCs. Finally, we show that Hey factors are capable of repressing HIF-1alpha-induced gene expression, suggesting a negative feedback loop to prevent excessive hypoxic gene induction. Thus, reduced oxygen levels lead to activation of the Dll4-Notch-Hey2 signaling cascade and subsequent repression of COUP-TFII in endothelial progenitor cells. We propose that this is an important step in the developmental regulation of arterial cell fate decision.

Artery/vein specification is governed by opposing phosphatidylinositol-3 kinase and MAP kinase/ERK signaling

Angioblasts are multipotent progenitor cells that give rise to arteries or veins . Genetic disruption of the gridlock gene perturbs the artery/vein balance, resulting in generation of insufficient numbers of arterial cells . However, within angioblasts the precise biochemical signals that determine the artery/vein cell-fate decision are poorly understood. We have identified by chemical screening two classes of compounds that compensate for a mutation in the gridlock gene . Both target the VEGF signaling pathway and reveal two downstream branches emanating from the VEGF receptor with opposing effects on arterial specification. We show that activation of ERK (p42/44 MAP kinase) is a specific marker of early arterial progenitors and is among the earliest known determinants of arterial specification. In embryos, cells fated to contribute to arteries express high levels of activated ERK, whereas cells fated to contribute to veins do not. Inhibiting the phosphatidylinositol-3 kinase (PI3K) branch with GS4898 or known PI3K inhibitors, or by expression of a dominant-negative form of AKT promotes arterial specification. Conversely, inhibition of the ERK branch blocks arterial specification, and expression of constitutively active AKT promotes venous specification. In summary, chemical genetic analysis has uncovered unanticipated opposing roles of PI3K and ERK in artery/vein specification.

Inward rectifying potassium channels facilitate cell-to-cell communication in hamster retractor muscle feed arteries

This study examined whether inward rectifying K+(KIR) channels facilitate cell-to-cell communication along skeletal muscle resistance arteries. With the use of feed arteries from the hamster retractor muscle, experiments examined whether KIRchannels were functionally expressed and whether channel blockade attenuated the conduction of acetylcholine-induced vasodilation, an index of cell-to-cell communication. Consistent with KIRchannel expression, this study observed the following: 1) a sustained Ba2+-sensitive, K+-induced dilation in preconstricted arteries; 2) a Ba2+-sensitive inwardly rectifying K+current in arterial smooth muscle cells; and 3) KIR2.1 and KIR2.2 expression in the smooth muscle layer of these arteries. It was subsequently shown that the discrete application of acetylcholine elicits a vasodilation that conducts with limited decay along the feed artery wall. In the presence of 100 μM Ba2+, the local and conducted response to acetylcholine was attenuated, a finding consistent with a role for KIRin facilitating cell-to-cell communication. A computational model of vascular communication accurately predicted these observations. Control experiments revealed that in contrast to Ba2+, ATP-sensitive- and large-conductance Ca2+activated-K+channel inhibitors had no effect on the local or conducted vasodilatory response to acetylcholine. We conclude that smooth muscle KIRchannels play a key role in facilitating cell-to-cell communication along skeletal muscle resistance arteries. We attribute this facilitation to the intrinsic property of negative slope conductance, a biophysical feature common to KIR2.1- and 2.2-containing channels, which enables them to increase their activity as a cell hyperpolarizes.

Differentiation of arterial and venous endothelial cells and vascular morphogenesis

The vascular system is comprised of an organized hierarchical structure of arteries, veins, and capillaries. Recent studies in zebrafish, chick, and mouse reveal that the identity of artery and vein is governed by genetic factors as well as blood flow. The ephrin/Eph system establishes arterial and venous endothelial cell identity, and is important for structural segregation between arteries and veins. Analyses using loss- or gain-of-function mutations in zebrafish and mice show that Su(H)/RBP-J-dependent Delta/Notch signaling is a key mediator of arterial endothelial cell fate decision and vascular patterning. Vascular endothelial growth factor has also been shown to work upstream of Notch and is a key player in arteriogenesis. On the other hand, an orphan nuclear receptor, COUP-TFII, induces venous endothelial cell differentiation by suppressing the Notch signaling. Arteriovenous malformations are frequently induced by a loss of arterial and venous cell specification. These insights indicate that the balance of these genetic factors and modification by epigenetic factors such as hemodynamics and oxygen tension are important for proper endothelial cell identities in vascular morphogenesis.

Semiautomated computer-assisted image analysis to quantify 3,3'-diaminobenzidine tetrahydrochloride-immunostained small tissues

This work aimed to develop a technique to measure stained areas in images from sample tissue sections, namely when the structure of interest does not fill the entire image field of the microscope. We propose a semiautomated computer-assisted image analysis (SACAIA) method in which brightfield color images of 3,3'-diaminobenzidene tetrahydrochloride (DAB)-stained antigens are converted to their blue component and boundaries are delineated to extract the object of interest. The number of pixels of a defined color (elicited by DAB) is counted and used to measure the stained area relative to the total area of the tissue under study. The percentages of area stained with adenosine A(1) receptor were 40.76+/-2.08 and 42.44+/-2.26% for manual analysis and SACAIA, respectively (P=0.582). A strong linear correlation of A(1) receptor quantification was found (r=0.98, P<0.001, and 95% CI=0.97 to 0.99 for manual method; r=0.99, P<0.001, and 95% CI=0.98 to 0.99 for SACAIA method). The extent to which misclassification affected staining quantification was evaluated by Bland-Altman analysis, indicating that this method can be applied accurately to quantify the immunohistochemical staining area (occupied by a specific antigen) in small sample tissues that do not fill the entire image field of the microscope.

Selective regulation of arterial branching morphogenesis by synectin

Branching morphogenesis is a key process in the formation of vascular networks. To date, little is known regarding the molecular events regulating this process. We investigated the involvement of synectin in this process. In zebrafish embryos, synectin knockdown resulted in a hypoplastic dorsal aorta and hypobranched, stunted, and thin intersomitic vessels due to impaired migration and proliferation of angioblasts and arterial endothelial cells while not affecting venous development. Synectin(-/-) mice demonstrated decreased body and organ size, reduced numbers of arteries, and an altered pattern of arterial branching in multiple vascular beds while the venous system remained normal. Murine synectin(-/-) primary arterial, but not venous, endothelial cells showed decreased in vitro tube formation, migration, and proliferation and impaired polarization due to abnormal localization of activated Rac1. We conclude that synectin is involved in selective regulation of arterial, but not venous, growth and branching morphogenesis and that Rac1 plays an important role in this process.