Objective

C-type natriuretic peptide (CNP) has recently been suggested to represent an endothelium-derived hyperpolarizing factor (EDHF) in the mammalian resistance vasculature, important in the regulation of local blood flow and systemic blood pressure. Additionally, this peptide has been shown to protect against ischaemia-reperfusion injury and inhibits leukocyte and platelet activation. Herein, we use a novel, selective natriuretic peptide receptor-C (NPR-C) antagonist (M372049) to highlight the pivotal contribution of CNP/NPR-C signalling in the EDHF-dependent regulation of vascular tone and investigate the mechanism(s) underlying the release and biological activity of CNP and EDHF.

Methods

In vitro pharmacological investigation was conducted in rat (Sprague-Dawley) aorta and mesenteric resistance arteries. Relaxant responses to CNP, atrial natriuretic peptide (ANP), the nitric oxide donor spermine-NONOate (SPER-NO) and the endothelium-dependent vasodilator, acetylcholine (ACh) were examined in the absence and presence of M372049 or inhibitor cocktails shown previously to block endothelium-dependent dilatation in the resistance vasculature. RT-PCR was employed to characterize the expression of NPR subtypes in the vessels studied.

Results

M372049 produced concentration-dependent inhibition of the vasorelaxant activity of CNP in rat isolated mesenteric resistance arteries but not aorta; in contrast, M372049 did not affect relaxations to ANP or SPER-NO in either vessel. M372049 or ouabain alone produced small, significant inhibition of EDHF-dependent relaxations in mesenteric arteries and in combination acted synergistically to abolish such responses. A combination of M372049 with established inhibitors of EDHF-dependent relaxation revealed that multiple, distinct pathways coordinate the bioactivity of EDHF in the resistance vasculature, and that CNP/NPR-C signalling represents a major component.

Conclusions

These data substantiate CNP/NPR-C signalling as a fundamental pathway underlying EDHF-dependent regulation of vascular tone in the rat mesenteric resistance vasculature. An increased understanding of the physiological roles of CNP/NPR-C signalling in the vasculature (now facilitated by the identification of a selective NPR-C antagonist) should aid determination of the (patho)physiological importance of EDHF and might provide the rationale for the design of novel therapeutics.

The art and science of the use of deposition markers for the estimation of blood flow distributions throughout the body and within organs is reviewed. Development of diffusible tracer techniques started 50 years ago. Twenty years later, radioactive 15 micron microspheres became the standard marker. Early studies on small animals, fetal sheep in 1967 and rats in 1976, provoked much of the technical development. Needs for avoiding the use of radioactivity, for having long lasting labels, and for providing higher spatial resolution, are driving the continuing exploration of newer techniques using colored and fluorescent microspheres and molecular deposition markers. Strengths and weaknesses of the various methods are compared.

Traditional concepts of vascular inflammation are considered “inside-out” responses centered on the monocyte adhesion and lipid oxidation hypotheses. These mechanisms likely operate in concert, holding the central tenet that the inflammatory response is initiated at the luminal surface. However, growing evidence supports a new paradigm of an “outside-in” hypothesis, in which vascular inflammation is initiated in the adventitia and progresses inward toward the intima. Hallmarks of the outside-in hypothesis include population of the adventitia with exogenous cell types, including monocytes, macrophages, and lymphocytes, the phenotypic switch of adventitial fibroblasts into migratory myofibroblasts, and increased vasa vasorum neovascularization. The resident and migrating cells deposit collagen and matrix components, respond to and upregulate inflammatory chemokines and/or antigens, and regulate the local redox state of the adventitia. B cells and T cells generate local humoral immune responses against local antigen presentation by foam cells and antigen presenting cells. These events result in increased local expression of cytokines and growth factors, evoking an inflammatory response that propagates inward toward the intima. Ultimately, it appears that the basic mechanisms of cellular activation and migration in vascular inflammation are highly conserved across a variety of cardiovascular disease states and that major inflammatory events begin in the adventitia.

Objective

Connexin40 (Cx40) is a gap junction protein expressed specifically in developing and mature atrial myocytes and cells of the conduction system. In this report, we identify cis-acting elements within the mouse Cx40 promoter and unravel part of the complex pathways involved in the cardiac expression of this gene.

Methods

To identify the factors involved in the cardiac expression of Cx40, we used transient transfections in mammalian cells coupled with electrophoretic mobility shift assays (EMSA) and RT-PCR.

Results

Within the promoter region, we identified the minimal elements required for transcriptional activity within 150 base pairs (bp) upstream of the transcriptional start site. Several putative regulatory sites for transcription factors were predicted within this region by computer analysis, and we demonstrated that the nuclear factors Sp1, Nkx2-5, GATA4 and Tbx5 could interact specifically with elements present in the minimal promoter region of the Cx40. Furthermore, co-transfection experiments showed the ability of Nkx2-5 and GATA4 to transactivate the minimal Cx40 promoter while Tbx5 repressed Nkx2-5/GATA4-mediated activation. Mutagenesis of the Nkx2-5 core site in the Cx40 promoter led to significantly decreased activity in rat smooth muscle cell line A7r5. Consistent with this, mouse embryos lacking Nkx2-5 showed a marked decrease in Cx40 expression.

Conclusion

In this work, we cloned the promoter region of the Cx40 and demonstrated that the core promoter was modulated by cardiac transcriptional factors Nkx2-5, Tbx5 and GATA4 acting together with ubiquitous Sp1.

More than 10 years after its discovery, the function of cyclooxygenase-2 (COX-2) in the cardiovascular system remains largely an enigma. Many scholars have assumed that the allegedly detrimental effects of COX-2 in other systems (e.g. proinflammatory actions and tumorigenesis) signify a detrimental role of this protein in cardiovascular homeostasis as well. This view, however, is ill-founded. Recent studies have demonstrated that ischemic preconditioning (PC) upregulates the expression and activity of COX-2 in the heart, and that this increase in COX-2 activity mediates the protective effects of the late phase of PC against both myocardial stunning and myocardial infarction. An obligatory role of COX-2 has been observed in the setting of late PC induced not only by ischemia but also by δ-opioid agonists and physical exercise, supporting the view that the recruitment of this protein is a central mechanism whereby the heart protects itself from ischemia. The beneficial actions of COX-2 appear to be mediated by the synthesis of PGE2 and/ or PGI2. Since inhibition of iNOS in preconditioned myocardium blocks COX-2 activity whereas inhibition of COX-2 does not affect iNOS activity, COX-2 appears to be downstream of iNOS in the protective pathway of late PC. The results of these studies challenge the widely accepted paradigm that views COX-2 activity as detrimental. The discovery that COX-2 plays an indispensable role in the anti-stunning and anti-infarct effects of late PC demonstrates that the recruitment of this protein is a fundamental mechanism whereby the heart adapts to stress, thereby revealing a novel, hitherto unappreciated cardioprotective function of COX-2. From a practical standpoint, the recognition that COX-2 is an obligatory co-mediator (together with iNOS) of the protection afforded by late PC has implications for the clinical use of COX-2 selective inhibitors as well as nonselective COX inhibitors. For example, the possibility that inhibition of COX-2 activity may augment myocardial cell death by obliterating the innate defensive response of the heart against ischemia/reperfusion injury needs to be considered and is the object of much current debate. Furthermore, the concept that the COX-2 byproducts, PGE2 and/ or PGI2, play a necessary role in late PC provides a basis for novel therapeutic strategies designed to enhance the biosynthesis of these cytoprotective prostanoids in the ischemic myocardium. From a conceptual standpoint, the COX-2 hypothesis of late PC expands our understanding of the function of this enzyme in the cardiovascular system and impels a critical reassessment of current thinking regarding the biologic significance of COX-2.

Aims

In cardiomyocytes, protein kinase D1 (PKD1) plays a central role in the response to stress signals. From a yeast two-hybrid assay, we have identified Enigma Homolog 1 (ENH1) as a new binding partner of PKD1. Since in neurons, ENH1, associated with protein kinase Cε, was shown to modulate the activity of N-type calcium channels, and the pore-forming subunit of the cardiac L-type voltage-gated calcium channel, α1C, possesses a potential phosphorylation site for PKD1, we studied here a possible role of ENH1 and PKD1 in the regulation of the cardiac L-type voltage-gated calcium channel.

Methods and results

PKD1-interacting proteins were searched by yeast two-hybrid screening. In vivo protein interactions in cardiomyocytes isolated from heart ventricles of newborn rats were tested by co-immunoprecipitation. Small interfering RNA and a dominant negative mutant of PKD1 were delivered into cardiomyocytes by use of an adenovirus. Calcium currents were measured by the patch-clamp technique. Both ENH1 and PKD1 interact with α1C in cardiomyocytes. This interaction is increased upon stimulation. Silencing of ENH1 prevented the binding of PKD1 to α1C. Moreover, a dominant negative mutant of PKD1 or the silencing of ENH1 inhibited the α-adrenergic-induced increase of L-type calcium currents.

Conclusion

We found a new binding partner, ENH1, and a new target, α1C, for PKD1 in neonatal rat cardiomyocytes. We propose a model where ENH1 scaffolds PKD1 to α1C in order to form a signalling complex that regulates the activity of cardiac L-type voltage-gated Ca2+ channels.

Reducing the heart's temperature by 2–5°C is a potent cardioprotective treatment in animal models of coronary artery occlusion. The anti-infarct benefit depends upon the target temperature and the time at which cooling is instituted. Protection primarily results from cooling during the ischaemic period, whereas cooling during reperfusion or beyond offers little protection. In animal studies, protection is proportional to both the depth and duration of cooling. An optimal cooling protocol must appreciably shorten the normothermic ischaemic time to effectively salvage myocardium. Patients presenting with acute myocardial infarction could be candidates for mild hypothermia since the current door-to-balloon time is typically 90 min. But they would have to be cooled quickly shortly after their arrival. Several strategies have been proposed for ultra-fast cooling, but most like liquid ventilation and pericardial perfusion are too invasive. More feasible strategies might include cutaneous cooling, peritoneal lavage with cold solutions, and endovascular cooling with intravenous thermodes. This last option has been investigated clinically, but the results have been disappointing possibly because the devices lacked capacity to cool the patient quickly or cooling was not implemented soon enough. The mechanism of hypothermia's protection has been assumed to be energy conservation. However, whereas deep hypothermia clearly preserves ATP, mild hypothermia has only a modest effect on ATP depletion during ischaemia. Some evidence suggests that intracellular signalling pathways might be responsible for the protection. It is unknown how cooling could trigger these pathways, but, if true, then it might be possible to duplicate cooling's protection pharmacologically.

Objective

Knockout of the neural and cardiac expressed transcription factor HF-1b causes electrophysiological abnormalities including fatal ventricular arrhythmias that occur with increasing frequency around the 4th week of postnatal life. This study addresses factors that may contribute to conduction disturbance in the ventricle of the HF-1b knockout mouse. Disruptions to gap junctional connexin40 (Cx40) have been reported in distal (i.e., apically located), but not proximal His–Purkinje conduction tissues of the HF-1b knockout mouse. This abnormality in myocardial Cx40 led us to address whether 4-week-old HF-1b knockout postnates display other disruptions to ventricular structure and function.

Methods

Western blotting and immunoconfocal quantification of Cx43 and coronary arteriole density and function were undertaken in the ventricle. Electrical activation was described by optical mapping.

Results

Western blotting and immunoconfocal microscopy indicated that overall levels of Cx43 (p <0.001) and percent of Cx43 localized in intercalated disks (p <0.001) were significantly decreased in the ventricular myocardium of knockouts relative to wildtype littermate controls. Analysis of the reduction in Cx43 level by basal and apical territories revealed that the decrease was most pronounced in the lower, apical half of the ventricle of knockouts relative to controls (p <0.001). Myocyte size also showed a significant decrease in the knockout, that was more marked within the apical half of the ventricle (p <0.05). Optical recordings of ventricular activation indicated apically localized sectors of slowed conduction in knockout ventricles not occurring in controls that could be correlated directly to tissues showing reduced Cx43. These discrete sectors of abnormal conduction in the knockout heart were resolved following point stimulation of the ventricular epicardium and thus were not explained by dysfunction of the His–Purkinje system. To further probe base-to-apex abnormalities in the HF-1b knockout ventricle, we analyzed coronary arterial structure and function. These analyses indicated that relative to controls, the apical ventricular territory of the HF-1b knockout had reductions in the density of small resistance vessels (p <0.01) and deficits in arterial function as assayed by bead perfusion (p <0.01).

Conclusion

The HF-1b knockout ventricle displays abnormalities in Cx43 level, myocyte size, activation spread and coronary arterial structure and function. These abnormalities tend to be more pronounced in the apical territory of the ventricle and seem likely to be factors contributing to the pathological disturbance of cardiac conduction that characterizes the heart of the HF-1b knockout mouse.

Aims

Thrombopoietin (Tpo) is known for its ability to stimulate platelet production. However, it is currently unknown whether Tpo plays a physiological function in the heart.

Methods and results

We assessed the potential protective role of Tpo in vitro and in vivo in two rat models of myocardial ischaemia/reperfusion. Tpo receptor (c-mpl) message was detected in the heart using RT-PCR, and the Tpo receptor protein was detected using western blotting and immunohistochemistry. Tpo treatment immediately before ischaemia reduced myocardial necrosis, apoptosis, and decline in ventricular function following ischaemia/reperfusion in the rat in a concentration- and dose-dependent manner with an optimal concentration of 1.0 ng/mL in vitro and an optimal dose of 0.05 μg/kg iv in vivo. Tpo also reduced infarct size when given after the onset of ischaemia or at reperfusion. Tpo activated JAK-2 (Janus kinase-2) and p44 MAPK (mitogen-activated protein kinase) during reperfusion but not prior to ischaemia. Inhibition of JAK-2 (AG-490), p42/44 MAPK (PD98059), mitochondrial KATP channels (5-HD), and sarcolemmal KATP channels (HMR 1098) abolished Tpo-induced resistance to injury from myocardial ischaemia/reperfusion. AG-490, PD98059, 5-HD, and HMR1098 alone had no effect on cardioprotection. Treatment with a single dose of Tpo (0.05 or 1.0 μg/kg iv) did not result in the elevation of platelet count or haematocrit over a 16-day period.

Conclusion

A single treatment of Tpo confers cardioprotection through JAK-2, p42/44 MAPK, and KATP channels, suggesting a potential therapeutic role of Tpo in the treatment of injury resulting from myocardial ischaemia and reperfusion.

Aims

We investigated whether rapid cooling instituted by total liquid ventilation (TLV) improves cardiac and mitochondrial function in rabbits submitted to ischaemia-reperfusion.

Methods and results

Rabbits were chronically instrumented with a coronary artery occluder and myocardial ultrasonic crystals for assessment of segment length-shortening. Two weeks later they were re-anaesthetized and underwent either a normothermic 30-min coronary artery occlusion (CAO) (Control group, n = 7) or a comparable CAO with cooling initiated by a 10-min hypothermic TLV and maintained by a cold blanket placed on the skin. Cooling was initiated after 5 or 15 min of CAO (Hypo-TLV and Hypo-TLV15′ groups, n = 6 and 5, respectively). A last group underwent normothermic TLV during CAO (Normo-TLV group, n = 6). Wall motion was measured in the conscious state over three days of reperfusion before infarct size evaluation and histology. Additional experiments were done for myocardial sampling in anaesthetized rabbits for mitochondrial studies. The Hypo-TLV procedure induced a rapid decrease in myocardial temperature to 32–34°C. Throughout reperfusion, segment length-shortening was significantly increased in Hypo-TLV and Hypo-TLV15′ vs. Control and Normo-TLV (15.1 ± 3.3%, 16.4 ± 2.3%, 1.8 ± 0.6%, and 1.1 ± 0.8% at 72 h, respectively). Infarct sizes were also considerably attenuated in Hypo-TLV and Hypo-TLV15′ vs. Control and Normo-TLV (4 ± 1%, 11 ± 5%, 39 ± 2%, and 42 ± 5% infarction of risk zones, respectively). Mitochondrial function in myocardial samples obtained at the end of ischaemia or after 10 min of reperfusion was improved by Hypo-TLV with respect to ADP-stimulated respiration and calcium-induced opening of mitochondrial permeability transition pores (mPTP). Calcium concentration opening mPTP was, e.g., increased at the end of ischaemia in the risk zone in Hypo-TLV vs. Control (157 ± 12 vs. 86 ± 12 µM). Histology and electron microscopy also revealed better preservation of lungs and of cardiomyocyte ultrastructure in Hypo-TLV when compared with Control.

Conclusion

Institution of rapid cooling by TLV during ischaemia reduces infarct size as well as other sequelae of ischaemia, such as post-ischaemic contractile and mitochondrial dysfunction.

VEGFs (VEGFs) are key regulators of permeability. The principal evidence behind how they increase vascular permeability in vivo and in vitro, and the consequences of that increase, are here addressed. Detailed analysis of the published literature showed that in vivo and in vitro data on VEGF mediated permeability differed in its time course, but had common involvement of many specific signalling pathways, in particular VEGF-Receptor-2 activation, calcium influx through transient receptor potential channels, activation of phospholipase C gamma and downstream activation of nitric oxide synthase. Downstream of endothelial-nitric oxide synthase appears to involve the guanylyl cyclase mediated activation of the rho-rac pathway and subsequent involvement of junctional signalling proteins such as vascular endothelial-cadherin and the tight junctional proteins zona occludens and occludin linked to the actin cytoskeleton. The signalling appears to be co-ordinated through spatial organisation of the cascade into a signalplex, and arguments for why this may be important are considered. Many proteins have been identified to be involved in the regulation of vascular permeability by VEGF, but still the mechanisms through which these are thought to interact to control permeability are dependent on the experimental system, and a synthesis of existing data reveals that in intact vessels the co-ordination of the pathways is still not understood.

Aims

Vascular smooth muscle cell (VSMC) apoptosis can lead to thinning of the fibrous cap and plaque instability. We previously showed that cell–cell contacts mediated by N-cadherin reduce VSMC apoptosis. This study aimed to determine whether matrix-degrading metalloproteinase (MMP)-dependent N-cadherin cleavage causes VSMC apoptosis.

Methods and results

Induction of human VSMC apoptosis using different approaches, including 200 ng/mL Fas ligand (Fas-L) and culture in suspension, caused N-cadherin cleavage and resulted in the appearance of a C-terminal fragment of N-cadherin (~35 kDa). Appearance of this fragment during apoptosis was inhibited by 47% with the broad-spectrum MMP inhibitor BB-94. We observed retarded cleavage of N-cadherin after treatment with Fas-L in aortic mouse VSMCs lacking MMP-7. Furthermore, VSMC apoptosis, measured by quantification of cleaved caspase-3, was 43% lower in MMP-7 knockout mouse VSMCs compared with wild-type VSMCs following treatment with Fas-L. Addition of recombinant active MMP-7 increased the amount of N-cadherin fragment by 82% and augmented apoptosis by 53%. The involvement of MMP-7 was corroborated using human cells, where a MMP-7 selective inhibitor reduced the amount of fragment formed by 51%. Importantly, we observed that treatment with Fas-L increased levels of active MMP-7 by 80%. Finally, we observed significantly increased cleavage of N-cadherin, MMP-7 activity, and apoptosis in human atherosclerotic plaques compared with control arteries, and a significant reduction in apoptosis in atherosclerotic plaques from MMP-7 knockout mice.

Conclusion

This study demonstrates that MMP-7 is involved in the cleavage of N-cadherin and modulates VSMC apoptosis, and may therefore contribute to plaque development and rupture.

Vascular endothelial growth factors (VEGFs) are key regulators of permeability. The principal evidence behind how they increase vascular permeability in vivo and in vitro and the consequences of that increase are addressed here. Detailed analysis of the published literature has shown that in vivo and in vitro VEGF-mediated permeability differs in its time course, but has common involvement of many specific signalling pathways, in particular VEGF receptor-2 activation, calcium influx through transient receptor potential channels, activation of phospholipase C gamma and downstream activation of nitric oxide synthase. Pathways downstream of endothelial nitric oxide synthase appear to involve the guanylyl cyclase-mediated activation of the Rho–Rac pathway and subsequent involvement of junctional signalling proteins such as vascular endothelial cadherin and the tight junctional proteins zona occludens and occludin linked to the actin cytoskeleton. The signalling appears to be co-ordinated through spatial organization of the cascade into a signalplex, and arguments for why this may be important are considered. Many proteins have been identified to be involved in the regulation of vascular permeability by VEGF, but still the mechanisms through which these are thought to interact to control permeability are dependent on the experimental system, and a synthesis of existing data reveals that in intact vessels the co-ordination of the pathways is still not understood.

Sphingomyelinases (SMases) hydrolyse sphingomyelin, releasing ceramide, and creating a cascade of bioactive lipids. These lipids include sphingosine and sphingosine-1-phosphate, all of which have a specific signalling capacity. SMase activation occurs in different cardiovascular system cell types, namely cardiac myocytes, endothelial and vascular smooth muscle cells, mediating cell proliferation, cell death and contraction of cardiac and vascular myocytes. Three main types of SMases contribute to cardiovascular physiology: the lysosomal and secreted acidic SMases (L- and S-ASMases, respectively) and the membrane neutral SMase (NSMase). These three enzymes have common activators, including ischaemia/reperfusion stress and proinflammatory cytokines, but they differ in their enzymatic properties and subcellular locations which determine the final effect of enzyme activation. This review focuses on the recent advances in the understanding of ASMase and NSMase pathways, and their specific contribution to cardiovascular pathophysiology. Current knowledge indicates that the inhibitors of the different SMase types are potential tools for the treatment of cardiovascular diseases. ASMase inhibitors could be tools against post-ischaemia reperfusion injury, and in the treatment of atherosclerosis. NSMase inhibitors could be tools for the treatment of atherosclerosis, heart failure and age-related decline in vasomotion. However, the design of bioavailable and more specific SMase-type inhibitors remains a challenge.

There is growing recognition that the O-linked attachment of N-acetyl-glucosamine (O-GlcNAc) on serine and threonine residues of nuclear and cytoplasmic proteins is a highly dynamic post-translational modification that plays a key role in signal transduction pathways. Numerous proteins have been identified as targets of O-GlcNAc modifications including kinases, phosphatases, transcription factors, metabolic enzymes, chaperons and cytoskeletal proteins. Modulation of O-GlcNAc levels has been shown to modify DNA binding, enzyme activity, protein-protein interactions, half-life of proteins and subcellular localization. The level of O-GlcNAc is regulated in part by the metabolism of glucose via the hexosamine biosynthesis pathway (HBP) and the metabolic abnormalities associated with insulin resistance and diabetes, such as hyperglycemia, hyperlipidemia and hyperinsulinemia are all associated with increased flux through the HBP and elevated O-GlcNAc levels. Increased HBP flux and O-GlcNAc levels have been implicated in relaxation of isolated cardiomyocytes; blunted response to angiotensin II and phenylephrine; hyperglycemia-induced cardiomyocyte apoptosis and endothelial and vascular cell dysfunction. In contrast to these adverse effects, recent studies have also shown that O-GlcNAc levels increase in response to an acute stress and that this is associated with increased cell survival. Thus, while the relationship between O-GlcNAc levels and cellular function is complex and is not well understood, it is clear that these pathways play a critical role in the regulation of cell function and survival in the cardiovascular system and may be implicated in the adverse effects of metabolic disease on the heart.

Aim

Mechanical forces are important regulators of cell and tissue phenotype. We hypothesized that mechanical loading and boundary conditions would influence neovessel activity during angiogenesis.

Methods

Using an in vitro model of angiogenesis sprouting and a mechanical loading system, we evaluated the effects of boundary conditions and applied loading. The model consisted of rat microvessel fragments cultured in a 3D collagen gel, previously shown to recapitulate angiogenic sprouting observed in vivo. We examined changes in neovascular growth in response to four different mechanical conditions. Neovessel density, diameter, length and orientation were measured from volumetric confocal images of cultures exposed to no external load (free-floating shape control), intrinsic loads (fixed ends, no stretch), static external load (static stretch) or cyclic external load (cyclic stretch).

Results

Neovessels sprouted and grew by the 3rd day of culture and continued to do so during the next 3 days of loading. The numbers of neovessels and branch points were significantly increased in the static stretch group when compared to the free-floating shape control, no stretch or cyclic stretch groups. In all mechanically loaded cultures, neovessel diameter and length distributions were heterogeneous, while they were homogeneous in shape control cultures. Neovessels were significantly more oriented along the direction of mechanical loading than those in the shape controls. Interestingly, collagen fibrils were organized parallel and adjacent to growing neovessels.

Conclusion

Externally applied boundary conditions regulate neovessel sprouting and elongation during angiogenesis, affecting both neovessel growth characteristics and network morphometry. Furthermore, neovessels align parallel to the direction of stress/strain or internally generated traction, and this may be due to collagen fibril alignment induced by the growing neovessels themselves.

Aims

Transient outward potassium current (Ito) is thought to be central to the pathogenesis of the Brugada syndrome (BrS). However, an Ito activator has not been available with which to validate this hypothesis. Here, we provide a direct test of the hypothesis using a novel Ito activator, NS5806.

Methods and results

Isolated canine ventricular myocytes and coronary-perfused wedge preparations were used. Whole-cell patch-clamp studies showed that NS5806 (10 µM) increased peak Ito at +40 mV by 79 ± 4% (24.5 ± 2.2 to 43.6 ± 3.4 pA/pF, n = 7) and slowed the time constant of inactivation from 12.6 ± 3.2 to 20.3 ± 2.9 ms (n = 7). The total charge carried by Ito increased by 186% (from 363.9 ± 40.0 to 1042.0 ± 103.5 pA·ms/pF, n = 7). In ventricular wedge preparations, NS5806 increased phase 1 and notch amplitude of the action potential in the epicardium, but not in the endocardium, and accentuated the ECG J-wave, leading to the development of phase 2 re-entry and polymorphic ventricular tachycardia (n = 9). Although sodium and calcium channel blockers are capable of inducing BrS only in right ventricular (RV) wedge preparations, the Ito activator was able to induce the phenotype in wedges from both ventricles. NS5806 induced BrS in 4/6 right and 2/10 left ventricular wedge preparations.

Conclusion

The Ito activator NS5806 recapitulates the electrographic and arrhythmic manifestation of BrS, providing evidence in support of its pivotal role in the genesis of the disease. Our findings also suggest that a genetic defect leading to a gain of function of Ito could explain variants of BrS, in which ST-segment elevation or J-waves are evident in both right and left ECG leads.

Aim

Transient outward potassium current (Ito) is thought to be central to the activator has not been pathogenesis of the Brugada syndrome (BrS). However, an Ito available with which to validate this hypothesis. Here we provide a direct test of the hypothesis using a novel Ito activator, NS5806.

Methods

Isolated canine ventricular myocytes and coronary-perfused wedge preparations were used.

Results

Whole-cell patch-clamp studies showed that NS5806 (10 μM) increased peak Ito at +40 mV by 79±4% (24.5±2.2 to 43.6±3.4 pA/pF, n=7) and slowed the time-constant increased of inactivation from 12.6±3.2 to 20.3±2.9 ms, n=7. Total charge carried by Ito by 186% (from 363.9 ± 40.0 to 1042.0 ± 103.5 pA ms/pF, n=7). In ventricular wedge preparations, NS5806 increased phase 1 and notch amplitude of the action potential (AP) in epicardium, but not endocardium, and accentuated the ECG J-wave, leading to the development of phase 2 reentry and polymorphic ventricular tachycardia (n=9). While sodium and calcium channel blockers are capable of inducing BrS only in right ventricular wedge preparations, the Ito activator was able to induce the phenotype in wedges from both ventricles. NS5806 induced BrS in 4/6 right and 2/10 left ventricular wedge preparations.

Conclusions

The Ito activator NS5806 recapitulates the electrographic and arrhythmic manifestation of BrS, providing evidence in support of its pivotal role in the genesis of the disease. Our findings also suggest that a genetic defect leading to a gain of function of Ito could explain variants of BrS in which ST-segment elevation or J-waves are evident in both right and left ECG leads.

Over the past two decades, extensive research has focused on arterial remodelling in both physiological and pathological ageing. The concept now describes the growth as well as the rearrangement of cellular components and extracellular matrix, resulting in either reduction or increase in vessel lumen. In diabetes, remodelling extends to capillaries, microvascular beds, and arteries of different calibre. This process is paralleled by accelerated atherosclerosis and accounts for an increased incidence of ischaemic complications. The incapacity of pre-existing and de novo formed collaterals to bypass atherosclerotic occlusions, combined with a decline in tissue capillary density, is responsible for the delayed recovery from ischaemia and ultimately leads to organ failure. The mechanisms of vascular remodelling are incompletely understood, but metabolic and mechanical factors seem to play an important role. Hyperglycaemia represents the main factor responsible for the fast progression of atherosclerosis as well as microangiopathy. However, intensive blood glucose control alone is insufficient to reduce the risk of macrovascular complications. Pharmacological control of oxidative stress and stimulation of nitric oxide release have proved to exert beneficial effects on vascular remodelling in experimental diabetic models. New approaches of regenerative medicine using vascular progenitor cells for the treatment of ischaemic disease have been shown to be safe and are now being tested for efficacy in preclinical and clinical trials.

Aims

Vascular smooth muscle cell (VSMC) apoptosis can lead to thinning of the fibrous cap and plaque instability. We previously showed that cell–cell contacts mediated by N-cadherin reduce VSMC apoptosis. This study aimed to determine whether matrix-degrading metalloproteinase (MMP)-dependent N-cadherin cleavage causes VSMC apoptosis.

Methods and results

Induction of human VSMC apoptosis using different approaches, including 200 ng/mL Fas ligand (Fas-L) and culture in suspension, caused N-cadherin cleavage and resulted in the appearance of a C-terminal fragment of N-cadherin (∼35 kDa). Appearance of this fragment during apoptosis was inhibited by 47% with the broad-spectrum MMP inhibitor BB-94. We observed retarded cleavage of N-cadherin after treatment with Fas-L in aortic mouse VSMCs lacking MMP-7. Furthermore, VSMC apoptosis, measured by quantification of cleaved caspase-3, was 43% lower in MMP-7 knockout mouse VSMCs compared with wild-type VSMCs following treatment with Fas-L. Addition of recombinant active MMP-7 increased the amount of N-cadherin fragment by 82% and augmented apoptosis by 53%. The involvement of MMP-7 was corroborated using human cells, where a MMP-7 selective inhibitor reduced the amount of fragment formed by 51%. Importantly, we observed that treatment with Fas-L increased levels of active MMP-7 by 80%. Finally, we observed significantly increased cleavage of N-cadherin, MMP-7 activity, and apoptosis in human atherosclerotic plaques compared with control arteries, and a significant reduction in apoptosis in atherosclerotic plaques from MMP-7 knockout mice.

Conclusion

This study demonstrates that MMP-7 is involved in the cleavage of N-cadherin and modulates VSMC apoptosis, and may therefore contribute to plaque development and rupture.

Aims

We investigated whether cooling instituted by total liquid ventilation (TLV) improves cardiac and mitochondrial functions in rabbits submitted to lethal myocardial ischemia.

Methods

Rabbits were instrumented with a coronary artery occluder and myocardial ultrasonic crystals for assessment of segment length shortening. Two weeks later they were reanesthetized and underwent either a normothermic 30-min coronary artery occlusion (CAO) (Control group, n=7) or a comparable CAO with cooling initiated after 5-min of occlusion. Cooling was initiated by a 10-min hypothermic TLV episode and then maintained by ice-filled cold blanket put over the skin (Hypo-TLV group, n=6). A last group underwent normothermic TLV during CAO (Normo-TLV group, n=6). Wall motion was measured in the conscious state over 3 days of reperfusion before infarct size evaluation and histology. Additional experiments were done in anesthetized rabbits for myocardial sampling at the end of the ischemic period (electron microscopy and mitochondrial studies).

Results

The cooling procedure induced a rapid decrease in heart temperature to a target 32–34°C. Post-ischemic contractile dysfunction and infarct sizes were significantly decreased in Hypo-TLV vs Control and Normo-TLV (e.g., 4±1, 39±2 and 42±5% of region at risk for infarct sizes, respectively). Mitochondrial function was improved by Hypo-TLV regarding ADP-stimulated respiration and calcium-induced opening of mitochondrial permeability transition pore (mPTP). Histology and electron microscopy revealed also better preservation of lung and cardiomyocyte ultrastructure in Hypo-TLV as compared to Control, respectively.

Conclusion

Institution of hypothermia by TLV during ischemia not only reduces infarct size but also abolishes most consequences of ischemia such as post-ischemic contractile dysfunction and calcium-induced opening of mPTP.

Aims

The role of scavenger receptors in atherogenesis is controversial as a result of conflicting reports and a recent hypothesis suggesting that scavenger receptor absence would enhance the pro-inflammatory, pro-atherogenic milieu. This study addresses the effect of combined absence of scavenger receptors CD36 and SRA I/II on atherosclerosis lesion development in the apolipoprotein E knock-out (apoE°) model.

Methods

We created background-related strains of apoE°, scavenger receptor A I/II knock-out (SRA°)/apoE°, CD36 knock-out (CD36°)/apoE°, and CD36°/SRA°/apoE° mice that were >99% C57Bl/6. Four-week-old mice were fed a Western diet for 12 weeks and were assessed for lesion burden/morphology, risk factors for atherosclerosis, inflammatory mediators, and macrophage function.

Results

There was a 61 and 74% decrease in total aortic lesion area in CD36°/apoE° males and females, respectively, compared with apoE° controls. The absence of SRA was protective (32% decrease in lesion) in female mice. The combined absence of CD36 and SRA provided no further protection in either gender. Macrophages from mice lacking CD36 had decreased pro-inflammatory characteristics and less migration to a pro-inflammatory stimulus. Plasma levels of cytokines/chemokines showed that CD36°/apoE° and CD36°/SRA°/apoE° mice had a less pro-inflammatory phenotype compared with apoE° and SRA°/apoE° mice. Oblivious mice in the apoE° background ruled out potential ‘passenger gene’ effects in the case of CD36.

Conclusion

These results provide new insights into the pro-atherogenic mechanisms of CD36 by implicating processes other than modified lipoprotein uptake.

Objective

Laminar shear stress plays critical roles in vascular homeostasis and exerts various metabolic effects on endothelial cells (ECs). Stearoyl-CoA desaturase-1 (SCD1), which catalyzes the biosynthesis of monounsaturated fatty acids, affects the lipid composition and fluidity of the cell membrane. Thus, we examined the effect of laminar flow on SCD1 expression in ECs.

Methods

A flow chamber was used to impose a laminar shear stress on a confluent monolayer of human vascular ECs. The expression of SCD1 was examined using real-time RT-PCR and Northern and Western blotting. Immunohistochemical staining was used to assess the expression of SCD1 in Sprague–Dawley rat arteries, including the sites of arterial bifurcation.

Results

Laminar shear stress (12 dyn/cm2, 12 h) markedly increased the gene expression of SCD1 in ECs. The flow-induced SCD1 expression was attenuated by peroxisome proliferator-activated receptor (PPAR)-γ antagonists both in vitro and in vivo. Troglitazone and rosiglitazone significantly increased the gene expression of SCD1. Furthermore, overexpression of a constitutively active PPARγ induced the expression of SCD1 in ECs. Immunohistochemical study of cross-sections from rat celiac arteries revealed that endothelial expression of SCD1 was substantially higher on the medial division apex, where the shear stress is high and more laminar, than the lateral aspect, where the shear stress is low and unsteady.

Conclusion

These in vitro and in vivo results demonstrate that laminar flow increased the expression of SCD1 in endothelium through a PPARγ-specific mechanism, which may contribute to the shear stress-mediated protective roles in ECs.

Aims:

To determine the effect of alcohol (EtOH) on endothelial angiogenic activity and to delineate the cell signaling mechanisms involved.

Methods and Results:

Treatment of human umbilical vein endothelial cells (HUVEC) with EtOH (1-100 mM, 24 h) dose-dependently increased their network formation on matrigel (an index of angiogenesis) with a maximum response (2.5 - 3 fold increase) at 25 mM. Ethanol also stimulated the proliferation (by cell counts and PCNA expression) and migration (by scratch wound assay) of HUVEC. In parallel cultures, EtOH stimulated Notch receptor (1 and 4) and Notch target gene (hrt-1, 2, 3) mRNA and protein expression and enhanced CBF-1/RBP-Jk promoter activity. EtOH also stimulated, at a mRNA and protein level, the expression of Angiopoietin 1 (Ang1) and its Tie2 receptor in these cells. Knockdown of Notch 1 or 4 by siRNA, or inhibition of Notch-mediated CBF-1/RBP-Jk regulated gene expression by RPMS-1, inhibited both ethanol-induced Ang1/Tie2 expression in HUVEC and their network formation on matrigel. Moreover, knockdown of Ang1 or Tie2 by siRNA inhibited ethanol-induced endothelial network formation.

Conclusions:

These data demonstrate that ethanol, at levels consistent with moderate consumption, enhances endothelial angiogenic activity in vitro by stimulating a novel Notch/CBF-1/RBP-JK - Ang1/Tie2- dependent pathway. These actions of ethanol may be relevant to the cardiovascular effects of alcohol consumption purported by epidemiological studies.