Asymmetric Subcellular Distribution of Glucose Transporters in the Endothelium of Small Contractile Arteries

The authors have recently reported the presence and asymmetric distribution of the glucose transporters GLUT-1 to -5 and SGLT-1 in the endothelium of rat coronary artery (Gaudreault et al. 2004, Diabetologica, 47, 2081-2092). In the present study the authors investigate and compare the presence and subcellular distribution of the classic glucose transporter isoforms in endothelial cells of cerebral, renal, and mesenteric arteries. The GLUTs and SGLT-1 were examined with immunohistochemistry and wide-field fluorescence microscopy coupled to deconvolution in en face preparation of intact artery. We identified GLUT-1 to -5 and SGLT-1 in the endothelial cells of all three vascular beds. The relative level of expression for each isoform was found comparable amongst arteries. Clusters of the glucose transporter isoforms were found at a high density in proximity to the cell-to-cell junctions. In addition, a consistent asymmetric distribution of GLUT-1 to -5 was found, predominantly located on the abluminal side of the endothelium in all three vascular beds examined (ranging from 68% to 91%, p<.05). The authors conclude that the expression and subcellular distribution of glucose transporters are similar in endothelial cells from vascular beds of comparable diameter and suggest that their subcellular organization may facilitate transendothelial transport of glucose in small contractile arteries.

Effects of Pulsatile Shear Stress on Signaling Mechanisms Controlling Nitric Oxide Production, Endothelial Nitric Oxide Synthase Phosphorylation, and Expression in Ovine Fetoplacental Artery Endothelial Cells

During gestation, placental blood flow, endothelial nitric oxide (NO) production, and endothelial cell nitric oxide synthase (eNOS) expression are elevated dramatically. Shear stress can induce flow-mediated vasodilation, endothelial NO production, and eNOS expression. Both the activity and expression of eNOS are closely regulated because it is the rate-limiting enzyme essential for NO synthesis. The authors adapted CELLMAX artificial capillary modules to study the effects of pulsatile flow/shear stress on ovine fetoplacental artery endothelial (OFPAE) cell NO production, eNOS expression, and eNOS phosphorylation. This model allows for the adaptation of endothelial cells to low physiological flow environments and thus prolonged shear stresses. The cells were grown to confluence at 3 dynes/cm2, then were exposed to 10, 15, or 25 dynes/cm2 for up to 24 h and NO production, eNOS mRNA, and eNOS protein expression were elevated by shear stress in a graded fashion (p < .05). Production of NO by OFPAE cells exposed to pulsatile shear stress was de novo; i.e., inhibited by L-NMMA (N(G)-monomethyl-L-arginine) and reversed by excess NOS substrate L-arginine. Rises in NO production at 25 dynes/cm2 (8-fold) exceeded (p < .05) that seen for eNOS protein (3.6-fold) or eNOS mRNA (1.5-fold). Acute rises in NO production with shear stress occurred by eNOS activation, whereas prolonged NO rises were via elevations in both eNOS expression and enzyme activation. The authors therefore used Western analysis to investigate the signaling mechanisms underlying pulsatile shear stress-induced increases in eNOS phosphorylation and protein expression by "flow-adapted" OFPAE cells. Increasing shear stress from 3 to 15 dynes/cm2 very rapidly increased eNOS Ser1177, ERK1/2 (extracellular signal-regulated kinase 1 and 2) and Akt, but not p38 MAPK (p38 mitogen-activated protein kinase) phosphorylation by Western analysis. Phosphorylation of eNOS Ser1177 under shear stress was elevated by 20 min, a response that was blocked by PI-3K (phosphatidylinositol 3-kinase) inhibitors wortmannin and LY294002, but not the MEK (MAPK kinase) inhibitor UO126. Basic fibroblast growth factor (bFGF) enhanced eNOS protein levels in static culture via a MEK-mediated mechanism, but it could not further augment the elevated eNOS protein levels induced by 15 dynes/cm2 shear stress. Blocking of either signaling pathways or p38 MAPK did not change the shear stress-induced increase in eNOS protein levels. Therefore, shear stress induced rapid eNOS phosphorylation on Ser1177 in OFPAE cells through a PI-3K-dependent pathway. The bFGF-induced rise in eNOS protein levels in static culture was much less than those observed under flow and was blocked by inhibiting MEK. Prolonged shear stress-stimulated increases in eNOS protein levels were not affected by inhibition of MEK- or PI-3K-mediated pathways. In conclusion, pulsatile shear stress greatly induces NO production by OFPAE cells through the mechanisms of both PI-3K-mediated eNOS activation and elevations in eNOS protein levels; bFGF does not further stimulate eNOS expression under flow condition.

Hyperthermia attenuates TNF-alpha-induced up regulation of endothelial cell adhesion molecules in human arterial endothelial cells

BACKGROUND AND AIM

The activation of NF-kappaB induces production of inflammatory cytokines and up regulation of endothelial cell adhesion molecules (ECAM). ECAM (e.g., E-selectin, VCAM-1 and ICAM-1) associates to the recruitment of leukocytes into tissue exposed to inflammatory situation. In this study, we investigated the effects of hyperthermia on the activation of NF-kappaB and the up regulation of E-selectin and VCAM-1 in human endothelial cells stimulated by TNF-alpha.

METHODS

Human arterial endothelial cells (HAEC) were pretreated with hyperthermia for 60 min at 42 degrees C, followed by incubation at 37 degrees C in a passively cooled incubator, before TNF-alpha stimulation. To assess the effects of hyperthermia on TNF-alpha-induced up regulation of ECAM and TNF-alpha-induced activation of NF-kappaB, we measured ECAM by ELISA, and evaluated the activation of NF-kappaB by Western blotting after TNF-alpha stimulation. The accumulation of HO-1, Hsp70 and IkappaBalpha in hyperthermia-treated HAEC was also assessed by Western blotting. To investigate the role of Hsp70, we treated HAEC with geranylgeranylacetone (GGA, Hsp70 inducer) 2 h before hyperthermia, and then measured ECAM in TNF-alpha-stimulated HAEC by ELISA.

RESULTS

Pretreatment of hyperthermia reduced TNF-alpha-induced up regulation of E-selectin and VCAM-1. In addition, accumulation of Hsp70, HO-1 and IkappaBalpha protein were up-regulated after hyperthermia. Furthermore, Western blotting analysis revealed that pretreatment of hyperthermia attenuated TNF-alpha-induced translocation of p65 into the nuclei of HAEC. Moreover, GGA enhanced Hsp70 accumulation induced by hyperthermia. Hyperthermia pretreatment combined with GGA induced further inhibition of TNF-alpha-induced up regulation of ECAM when compared with hyperthermia alone.

CONCLUSION

Pretreatment of hyperthermia blocks TNF-alpha-induced NF-kappaB activation, resulting in the inhibition of ECAM up regulation in HAEC.

Passive cigarette smoking induces inflammatory injury in human arterial walls

BACKGROUND

Epidemiological studies have shown that both active and passive cigarette smoking increase the risk of atherosclerosis. But very little is known about the biological processes induced by passive cigarette smoking that contribute to atherosclerosis. We observe the expression of a few of biological and inflammatory markers in human arterial walls in vitro which were treated with the second-hand smoke solution (sidestream whole, SSW), and discuss the possible mechanism of inflammatory injury induced by second-hand smoke.

METHODS

The biological markers (platelet endothelial cell adhesion molecule-1, PECAM-1; alpha-smooth muscle actin, alpha-SMA; collagen IV, Col IV) and inflammatory markers (vascular cell adhesion molecule-1, VCAM-1; monocyte chemoattractant protein-1, MCP-1; interleukin-8, IL-8) of human aortal wall were tested by immunofluorescence staining. The levels of MCP-1 and IL-8 mRNA expression were detected by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

No distinct difference was observed between SSW and the control group on the expression of biological markers as assessed by the light microscope. But the inflammatory markers VCAM-1, MCP-1 and IL-8 on the subendothelial layer and smooth muscle cell layers, which are near the endothelium of arterial wall, were strongly stained in the SSW group compared with the control group. Their fluorescence intensities in the 1:40 SSW group (VCAM-1: 0.35 +/- 0.04, MCP-1: 0.34 +/- 0.05, IL-8: 0.37 +/- 0.05) and the 1:20 SSW group (VCAM-1: 0.40 +/- 0.04, MCP-1: 0.52 +/- 0.09, IL-8: 0.51 +/- 0.07) were significantly stronger than the control group (VCAM-1: 0.12 +/- 0.04, MCP-1: 0.06 +/- 0.02, IL-8: 0.24 +/- 0.03) by semi-quantitative analysis of immunofluorescence (P < 0.001 vs control). MCP-1 mRNA expression in the 1:40 SSW (0.15 +/- 0.04) and the 1:20 SSW (0.19 +/- 0.06) group was significantly higher than in the control group (0.09 +/- 0.03) (P < 0.05, P < 0.01 vs control); IL-8 mRNA expression in the 1:40 SSW (0.64 +/- 0.12) and 1:20 SSW (0.72 +/- 0.13) groups was also significantly higher than that in the control group (0.49 +/- 0.13) (P < 0.05, P < 0.01 vs control) by RT-PCR.

CONCLUSIONS

It is implied that a second-hand smoke solution induces the inflammatory reaction of the arterial wall by release of inflammatory factors even though there is no distinct structural change on the arterial walls under light microscope, indicating that passive cigarette smoking is related to inflammatory injury in human arterial wall and could be closely related to the early inflammatory stage of atherosclerosis.

Molecular differentiation and specialization of vascular beds

Transport in the large and complex bodies of vertebrate organisms is mediated by extensive and highly branched tubular networks that are formed by endothelial cells. Blood vessels are responsible for systemic circulation, while the lymphatic vasculature drains extravasated plasma, proteins, particles, and cells from the interstitium. Endothelial cells of blood vessels and lymphatic vessels can be distinguished by the expression of certain molecular markers, which accompany or even contribute to functional and morphological differences. Even within the blood vessel network, some molecules and pathways selectively mark the endothelium of arteries, veins and capillaries and are thought to contribute to the differentiation of these vessels. Moreover, microvessels can acquire organ-specific specialization in response to local tissue-derived signals. This review summarizes molecular markers and pathways that are specifically expressed in the endothelium of certain vascular beds and vessel types. Special attention will be given to known functional roles in the morphogenesis of these vessels.

In vivo imaging of the effect of LPS on arterial endothelial cells: molecular imaging of heat shock protein 60 expression

Bacterial endotoxins are known as stress factors for endothelial cells. In 20 normocholesterolemic New Zealand White (NZW) rabbits, endothelial stress was induced by intravenous (i.v.) injection of lipopolysaccharide (LPS), while eight NZW rabbits were sham-treated or served as untreated controls. In vivo molecular imaging was performed using co-registered computer tomography and positron emission tomography 24 h after i.v. injection of (124)I-labeled monoclonal anti-HSP60 or (124)I-radiolabelled isotype control antibodies. Compared to control animals, in vivo images of rabbit aortae revealed significantly increased endothelial binding of (124)I-labeled anti-HSP60 antibodies upon LPS, especially at sites of aortal branching. This was confirmed by immunohistochemistry and autoradiography data. Our results showed, as proof-of-principle, that HSP60-expression in normocholesterolemic rabbits is significantly increased after induction of endothelial stress and that non-invasive in vivo molecular imaging of early aortal HSP60-expression using (124)I-labeled anti-HSP60 monoclonal antibodies is possible.

Expression and biological activity of parathyroid hormone-related peptide in pregnant rat uterine artery: any role for 8-iso-prostaglandin F2alpha?

PTHrP is produced in vessels and acts as a local modulator of tone. We recently reported that PTHrP(1-34) is able to induce vasorelaxation in rat uterine arteries, but in pregnancy, this response is blunted and becomes strictly endothelium dependent. The present study aimed to get insights into the mechanisms involved in these changes because the adaptation of uterine blood flow is essential for fetal development. On d 20 of gestation, RT-PCR analysis of uterine arteries showed that PTH/PTHrP receptor (PTH1R) mRNA expression was decreased, whereas that of PTHrP mRNA was increased. This was associated with a redistribution of the PTHrP/PTH1R system, with both PTH1R protein and PTHrP peptide becoming concentrated in the intimal layer of arteries from pregnant rats. On the other hand, the blunted vasorelaxation induced by PTHrP(1-34) in uterine arteries from pregnant rats was specifically restored by indomethacin and a specific cyclooxygenase-2 inhibitor, NS 398. This was associated with an increase in cyclooxygenase-2 expression and in 8-iso-prostaglandin F(2alpha) release when uterine arteries from pregnant rats were exposed to high levels of PTHrP(1-34). Most interestingly, 8-iso-prostaglandin F(2alpha) itself was able to increase PTHrP expression and reduce PTH1R expression in cultured rat aortic smooth muscle cells. These results suggest a local regulation of uterine artery functions by PTHrP during pregnancy resulting from PTH1R redistribution. Moreover, they shed light on a potential role of 8-iso-prostaglandin F(2alpha).

Addressing thrombogenicity in vascular graft construction

Thrombosis is a major cause of poor patency in synthetic vascular grafts for small diameter vessel (< 6 mm) bypass. Arteries have a host of structural mechanisms by which they prevent triggering of platelet activation and the clotting cascade. Many of these are present in vascular endothelial cells. These mechanisms act together with perpetual feedback at different levels, providing a constantly fine-tuned non-thrombogenic environment. The arterial wall anatomy also serves to promote thrombosis as a healing mechanism when it has been severely injured. Surface modification of synthetic graft surfaces to attenuate the coagulation cascade has reduced thrombosis levels and improved patency in vitro and in animal models. Success in this endeavor is critically dependent on the methods used to modify the surface. Platelets adhere to positively charged surfaces due to their own negative charge. They also preferentially attach to hydrophobic surfaces. Therefore synthetic graft development is concerned with hydrophilic materials with negative surface charge. However, fibrinogen has both hydrophilic and hydrophobic binding sites-amphiphilic materials reduce its adhesion and subsequent platelet activation. The self-endothelializing synthetic graft is an attractive proposition as a confluent endothelial layer incorporates many of the anti-thrombogenic properties of arteries. Surface modification to promote this has shown good results in animal models. The difficulties experienced in achieving spontaneous endothelialisation in humans have lead to the investigation of pre-implantation in vitro endothelial cell seeding. These approaches ultimately aim to result in novel synthetic grafts which are anti-thrombogenic and hence suitable for coronary and distal infrainguinal bypass.

[Rational utilization of a silicone tube flow chamber system]

The silicone tube flow chamber system has been used to study the effects of wall shear stress and circumferential stress on the cultured vascular endothelial cells (ECs). In solviong the problem of how to precisely simulate the wall shear stress and circumferential stress to which ECs are subjected under physiological conditions, it is very essential to select not only the appropriate geometrical and mechanical characteristic but also the proper preload and after-load of the silicone tube flow chamber. Firstly, a method to obtain the geometrical and mechanical characteristic of the chamber was given. Secondly, the procedure to simulate the two main mechanical stimuli under the physiological environment was proposed. Finally, the factors controlling the wall shear stress and circumferential stress were summarized.

Expression of VEGF-A, Flt-1, and Flk-1 in the arterial endothelial cells of the uterine broad ligament throughout the estrous cycle

The aim of the present study was to determine the immunoreactivity of vascular endothelial growth factor (VEGF-A) and its two receptors, viz., Flt-1 (fms-like tyrosine kinase) and Flk-1 (fetal liver kinase), on the surface of endothelial cells of the uterine artery and its branches and of the arcuate arteries in the area of the uterine broad ligament during various phases of the estrous cycle in the pig. We also investigated their expression to determine whether this was phase-related. The highest immunoreactivity for VEGF-A was observed in the uterine artery and arcuate arteries at the early luteal phase and in the branches of the uterine artery during the follicular phase of the estrous cycle. The strongest immunostaining intensity of Flt-1 was found in the uterine artery and its branches at the follicular phase and in arcuate arteries at the mid-luteal phase, whereas Flk-1 immunostaining was at its highest in the uterine artery at the mid-luteal phase and in the branches of the uterine artery and arcuate arteries at the follicular phase. Additionally, VEGF-A expression was assessed by semi-quantitative Western blot analysis, which revealed significantly higher levels of VEGF-A protein during the early luteal and the follicular phase of the estrous cycle (P < 0.001). The phase-related differences in the immunoreactivity and expression of VEGF-A and VEGF receptors suggest that these factors are hormone-dependent during the estrous cycle in the pig.

Enhancement of receptor-operated cation current and TRPC6 expression in arterial smooth muscle cells of deoxycorticosterone acetate-salt hypertensive rats

OBJECTIVES

In deoxycorticosterone acetate (DOCA)-salt hypertensive rats, altered reactivity of blood vessels to vasoactive agonists is frequently associated with an elevation in blood pressure. Canonical transient receptor potential (TRPC) channels are believed to encode receptor-operated cation channels (ROC), the activation of which is involved in smooth muscle depolarization and vasoconstriction. The aims of the present study were to investigate whether the ROC current is increased in DOCA-hypertensive rats and determine whether aldosterone directly enhances the expression of TRPC.

METHODS

The nystatin-perforated patch-clamp technique was used for the recording of receptor-stimulated ion currents in mesenteric arterial smooth muscle cells, which were enzymatically dispersed from sham-operated and DOCA-salt hypertensive rats. Expressions of TRPCs were evaluated by reverse transcriptase-polymerase chain reaction (RT-PCR) and by Western blot analysis.

RESULTS

Receptor-stimulated currents activated by 5-hydroxytryptamine (serotonin) and norepinephrine were increased significantly in the mesenteric arterial smooth muscle cells of DOCA-salt hypertensive rats compared to sham-operated rats. Ion-substitution experiments revealed that the enhanced currents were cation currents (ROC currents). Enhanced expression of TRPC6 in mesenteric arteries from DOCA-salt hypertensive rats was demonstrated by real-time RT-PCR. Up-regulation of TRPC6 by aldosterone treatment in vitro was also observed in A7r5 cells by RT-PCR and in western blots.

CONCLUSION

These results suggest that aldosterone enhances TRPC6 expression and ROC currents in vascular smooth muscle cells, and that this may in turn contribute to altered vascular reactivity and to hypertension.

Blockade of gap junction coupling by glycyrrhetinic acids in guinea pig cochlear artery: a whole-cell voltage- and current-clamp study

BACKGROUND AND PURPOSE

Glycyrrhetinic acids (GAs) are widely used as gap junction blockers, but their efficacy and side effects have not been well determined.

EXPERIMENTAL APPROACH

Whole-cell electrical recordings were made from vascular smooth muscle cells (VSMCs) embedded in or dissociated from, guinea pig cochlear artery segments.

KEY RESULTS

18beta- & 18alpha-GA concentration-dependently increased membrane input resistance (R(in)) of in situ VSMCs, with a maximal input conductance (G(in)=1/R(in)) reduction of 92% & 77% and IC(50) of 2.0 & 4.4 microm, respectively. 18betaGA (30 microM) resulted in a R(in) of 2.2 GOmega and C(in) of 12 pF, comparable to those of freshly dissociated VSMCs (3.1 GOmega & 6.1 pF). The GAs (> or =30 microM) caused a depolarization in VSMCs in situ. In dispersed VSMCs, they both inhibited delayed rectifiers; 18betaGA also activated a non-selective cation conductance while 18alphaGA inactivated a voltage-independent K+-conductance. ACh induced an outward current in VSMCs in situ at -40 mV, with a positive slope I/V relation and a reversal potential near E(K). The ACh-induced current was attenuated by 18beta- & 18alphaGA with an IC(50) of 4.3 & 7.8 microM, respectively.

CONCLUSIONS AND IMPLICATIONS

18betaGA blocked the vascular gap junctions, achieving a complete electrical isolation of the recorded VSMC at > or =30 microM while causing a mild depolarization by a complex conductance alteration. 18betaGA suppressed the ACh-induced current in VSMC by blocking the myoendothelial gap junction and by a non-junctional action. 18alphaGA at 30-100 microM failed to fully block the gap junctions while exerting side actions.

Decorin synthesized by arterial smooth muscle cells is retained in fibrin gels and modulates fibrin contraction

Fibrin serves as a provisional extracellular matrix (ECM) for arterial smooth muscle cells (ASMC) after vascular injury, yet little is known about the effect of fibrin on ECM remodeling by these cells. To address this question, monkey ASMC were grown on fibrin gels and tissue culture (TC) plastic, and proteoglycan synthesis and accumulation were assessed by radiolabeling. Initial rates of (35)S-sulfate incorporation into proteoglycans were identical for both groups, but increased proteoglycan accumulation was observed in cultures grown for 48 h on fibrin. This increased accumulation on fibrin was due to reduced proteoglycan turnover and retention within the fibrin gel. Decorin and biglycan constituted 40 and 14% of the total proteoglycan in the fibrin gels, whereas their combined contribution was only 12% in control matrices. To explore whether the retention of decorin in fibrin had any influence on the properties of the fibrin gel, ASMC-mediated fibrin contraction assays were performed. Both de novo synthesis of decorin as well as decorin added during polymerization inhibited the ability of the cells to contract fibrin. In contrast, decorin added exogenously to mature fibrin matrices had no effect on fibrin gel contraction. This study illustrates that decorin derived from ASMC selectively accumulates in fibrin and modifies fibrin architecture and mechanical properties. Such an accumulation may influence wound healing and the thrombotic properties of this provisional pro-atherosclerotic ECM.

Notch signaling in vascular development and physiology

Notch signaling is an ancient intercellular signaling mechanism that plays myriad roles during vascular development and physiology in vertebrates. These roles include regulation of artery/vein differentiation in endothelial and vascular smooth muscle cells, regulation of blood vessel sprouting and branching during both normal development and tumor angiogenesis, and the differentiation and physiological responses of vascular smooth muscle cells. Defects in Notch signaling also cause inherited vascular and cardiovascular diseases. In this review, I summarize recent findings and discuss the growing relevance of Notch pathway modulation for therapeutic applications in disease.

Imaging collagen in intact viable healthy and atherosclerotic arteries using fluorescently labeled CNA35 and two-photon laser scanning microscopy

We evaluated CNA35 as a collagen marker in healthy and atherosclerotic arteries of mice after both ex vivo and in vivo administration and as a molecular imaging agent for the detection of atherosclerosis. CNA35 conjugated with fluorescent Oregon Green 488 (CNA35/OG488) was administered ex vivo to mounted viable muscular (uterine), elastic (carotid), and atherosclerotic (carotid) arteries and fresh arterial rings. Two-photon microscopy was used for imaging. CNA35/OG488 labeling in healthy elastic arteries was compared with collagen type I, III, and IV antibody labeling in histologic sections. For in vivo labeling experiments, CNA35/OG488 was injected intravenously in C57BL6/J and apolipoprotein E(-/-) mice. Ex vivo CNA35/OG488 strongly labeled collagen in the tunica adventitia, media, and intima of muscular arteries. In healthy elastic arteries, tunica adventitia was strongly labeled, but labeling in tunica media and intima was prevented by endothelium and elastic laminae. Histology confirmed the affinity of CNA35 for type I, III, and IV collagen in arteries. Strong CNA35/OG488 labeling was found in atherosclerotic plaques. In vivo applied CNA35/OG488 minimally labeled the tunica intima of healthy carotid arteries. Atherosclerotic plaques in apolipoprotein E(-/-) mice exhibited large uptake. CNA35/OG488 imaging in organs revealed endothelium as a limiting barrier for in vivo uptake. CNA35/OG488 is a good molecular imaging agent for atherosclerosis.

Yin Yang-1 inhibits vascular smooth muscle cell growth and intimal thickening by repressing p21WAF1/Cip1 transcription and p21WAF1/Cip1-Cdk4-cyclin D1 assembly

Vascular injury initiates a cascade of phenotype-altering molecular events. Transcription factor function in this process, particularly that of negative regulators, is poorly understood. We demonstrate here that the forced expression of the injury-inducible GLI-Krüppel zinc finger protein Yin Yang-1 (YY1) inhibits neointima formation in human, rabbit and rat blood vessels. YY1 inhibits p21(WAF1/Cip1) transcription, prevents assembly of a p21(WAF1/Cip1)-cdk4-cyclin D1 complex, and blocks downstream pRb(Ser249/Thr252) phosphorylation and expression of PCNA and TK-1. Conversely, suppression of endogenous YY1 elevates levels of p21(WAF1/Cip1), PCNA, pRb(Ser249/Thr252) and TK-1, and increases intimal thickening. YY1 binds Sp1 and prevents its occupancy of a distinct element in the p21(WAF1/Cip1) promoter without YY1 itself binding the promoter. Additionally, YY1 induces ubiquitination and proteasome-dependent degradation of p53, decreasing p53 immunoreactivity in the artery wall. These findings define a new role for YY1 as both an inducer of p53 instability in smooth muscle cells, and an indirect repressor of p21(WAF1/Cip1) transcription, p21(WAF1/Cip1)-cdk4-cyclin D1 assembly and intimal thickening.

Transport in rat vessel walls. II. Macromolecular leakage and focal spot size growth in rat arteries and veins

Transendothelial lipid transport into and spread in the subendothelial intima of large arteries, and subsequent lipid accumulation, appear to start plaque formation. We experimentally examine transendothelial horseradish peroxidase (HRP) transport in vessels that are usually, e.g., pulmonary artery (PA), or almost always, e.g., inferior vena cava (IVC), atherosclerosis resistant vs. disease prone, e.g., aorta, vessels. In these vessels, HRP traverses the endothelium at isolated, focal spots, rather than uniformly, for short circulation times. For femoral vein HRP introduction, PA spots have 30-s radii [∼53.2 μm (SD10.4); compare aorta: 54.6 μm (SD8.75)] and grow quickly from 30 s to 1 min (40%, P < 0.05) and more slowly afterward ( P > 0.05). This trend resembles the aorta, suggesting the PA has a similarly sparse intima. With carotid artery (CA) HRP introduction, the 30-s spot (132.86 ± 37.32 μm) is far larger than the PAs, grows little (∼28%, P < 0.05) from 30 to 60 s, and is much flatter than the artery curves. Transverse electron microscopic sections after ∼10 min HRP circulation show thin, intense staining immediately beneath both vessels’ endothelia with an almost step change to diffuse staining beyond. This indicates the existence of a sparse, subendothelial intima, even when there is no internal elastic lamina (IVC). This motivates a simple model that translates growth rates into lower bounds for the flow through focal leaks. The model results and our earlier wall and medial hydraulic conductivity data explain these spot growth curves and point to differences in transport patterns that might be relevant in understanding the immunity of IVC to disease initiation.

PDGF-stimulated cell proliferation and migration of human arterial smooth muscle cells. Colocalization of PDGF isoforms with glycosaminoglycans

Platelet-derived growth factor (PDGF) has been implicated in vascular smooth muscle cell proliferation and migration, a key process in vascular disease. PDGF is a family of dimeric isoforms of structurally related A-, B-, C- and D-chains that bind to PDGF receptors. PDGF A- and B-chains occur with and without basic C-terminal amino acid extensions as long (A(L) and B(L)) and short (A(S) and B(S)) isoforms. This basic sequence has been implicated as a cell retention signal through binding to glycosaminoglycans, especially to heparan sulfate. The aim of this study was to evaluate the biological relevance of PDGF interaction with glycosaminoglycans on the PDGF function in human arterial smooth muscle cells (hASMC). Here, we show that long PDGF isoforms showed greater affinity for hASMC cell surface and that they also presented more colocalization with heparan and chondroitin sulfates present on hASMC cell membrane than did short isoforms. Furthermore, all PDGF isoforms colocalized more with heparan sulfate than with chondroitin sulfate and there was little colocalization between heparan and chondroitin sulfate. PDGF-stimulated hASMC activation of DNA synthesis and directed migration (chemotaxis) was also examined. The isoform PDGF-BB(S) induced maximal proliferation and migration of hASMC. Collagen-I coating significantly increased hASMC motility towards PDGF isoforms, and particularly toward PDGF-BB(S). These results strongly support the notion that cell surface glycosaminoglycans are not essential for receptor-mediated activity of PDGF and may contribute basically to the retention and accumulation of long PDGF isoforms.

Hyaluronan and CD44 antagonize mitogen-dependent cyclin D1 expression in mesenchymal cells

High molecular weight (HMW) hyaluronan (HA) is widely distributed in the extracellular matrix, but its biological activities remain incompletely understood. We previously reported that HMW-HA binding to CD44 antagonizes mitogen-induced S-phase entry in vascular smooth muscle cells (SMCs; Cuff, C.A., D. Kothapalli, I. Azonobi, S. Chun, Y. Zhang, R. Belkin, C. Yeh, A. Secreto, R.K. Assoian, D.J. Rader, and E. Puré. 2001. J. Clin. Invest. 108:1031–1040); we now characterize the underlying molecular mechanism and document its relevance in vivo. HMW-HA inhibits the mitogen-dependent induction of cyclin D1 and down-regulation of p27^kip1 in vascular SMCs. p27^kip1 messenger RNA levels were unaffected by HMW-HA, but the expression of Skp2, the rate-limiting component of the SCF complex that degrades p27^kip1, was reduced. Rescue experiments identified cyclin D1 as the primary target of HMW-HA. Similar results were observed in fibroblasts, and these antimitogenic effects were not detected in CD44-null cells. Analysis of arteries from wild-type and CD44-null mice showed that the effects of HMW-HA/CD44 on cyclin D1 and Skp2 gene expression are detected in vivo and are associated with altered SMC proliferation after vascular injury.

Effects of methyl beta-cyclodextrin on EDHF responses in pig and rat arteries; association between SK(Ca) channels and caveolin-rich domains

BACKGROUND AND PURPOSE

The small and intermediate conductance, Ca2+-sensitive K+ channels (SK(Ca) and IK(Ca), respectively) which are pivotal in the EDHF pathway may be differentially activated. The importance of caveolae in the functioning of IK(Ca) and SK(Ca) channels was investigated.

EXPERIMENTAL APPROACH

The effect of the caveolae-disrupting agent methyl-beta-cyclodextrin (MbetaCD) on IK(Ca) and SK(Ca) localization and function was determined.

KEY RESULTS

EDHF-mediated, SK(Ca)-dependent myocyte hyperpolarizations evoked by acetylcholine in rat mesenteric arteries (following blockade of IK(Ca) with TRAM-34) were inhibited by MbetaCD. Hyperpolarizations evoked by direct SK(Ca) channel activation (using NS309 in the presence of TRAM-34) were also inhibited by MbetaCD, an effect reversed by cholesterol. In contrast, IK(Ca)-dependent hyperpolarizations (in the presence of apamin) were unaffected by MbetaCD. Similarly, in porcine coronary arteries, EDHF-mediated, SK(Ca)-dependent (but not IK(Ca)-dependent) endothelial cell hyperpolarizations evoked by substance P were inhibited by MbetaCD. In mesenteric artery homogenates subjected to sucrose-density centrifugation, caveolin-1 and SK3 (SK(Ca)) proteins but not IK1 (IK(Ca)) protein migrated to the buoyant, caveolin-rich fraction. MbetaCD pretreatment redistributed caveolin-1 and SK3 proteins into more dense fractions. In immunofluorescence images of porcine coronary artery endothelium, SK3 (but not IK1) and caveolin-1 were co-localized. Furthermore, caveolin-1 immunoprecipitates prepared from native porcine coronary artery endothelium contained SK3 but not IK1 protein.

CONCLUSIONS AND IMPLICATIONS

These data provide strong evidence that endothelial cell SK(Ca) channels are located in caveolae while the IK(Ca) channels reside in a different membrane compartment. These studies reveal cellular organisation as a further complexity in the EDHF pathway signalling cascade.

Limits on estimating the width of thin tubular structures in 3D images

This work studies limits on estimating the width of thin tubular structures in 3D images. Based on nonlinear estimation theory we analyze the minimal stochastic error of estimating the width. Given a 3D analytic model of the image intensities of tubular structures, we derive a closed-form expression for the Cramér-Rao bound of the width estimate under image noise. We use the derived lower bound as a benchmark and compare it with three previously proposed accuracy limits for vessel width estimation. Moreover, by experimental investigations we demonstrate that the derived lower bound can be achieved by fitting a 3D parametric intensity model directly to the image data.