Wall tension is a potent negative regulator of in vivo thrombomodulin expression

Cell-surface HSP70 associates with thrombomodulin in endothelial cells

Heat shock protein-70 (HSP70) is crucial for proteostasis and displays cell-protective effects. Meanwhile, enhanced levels of cell-surface (cs) and secreted HSP70 paradoxically associate with pathologic cardiovascular conditions. However, mechanisms regulating csHSP70 pool are unknown. We hypothesized that total and csHSP70 expressions are modulated by hemodynamic forces, major contributors to endothelial pathophysiology. We also investigated whether thrombomodulin, a crucial thromboresistance cell-surface protein, is a csHSP70 target. We used proteomic/western analysis, confocal microscopy, and cs-biotinylation to analyze the pattern and specific characteristics of intracellular and csHSP70. HSP70 interaction with thrombomodulin was investigated by confocal colocalization, en face immunofluorescence, proximity assay, and immunoprecipitation. Thrombomodulin activity was assessed by measured protein C activation two-step assay. Our results show that csHSP70 pool in endothelial cells (EC) exhibits a peculiar cluster-like pattern and undergoes enhanced expression by physiological arterial-level laminar shear stress. Conversely, total and csHSP70 expressions were diminished under low shear stress, a known proatherogenic hemodynamic pattern. Furthermore, total HSP70 levels were decreased in aortic arch (associated with proatherogenic turbulent flow) compared with thoracic aorta (associated with atheroprotective laminar flow). Importantly, csHSP70 co-localized with thrombomodulin in cultured EC and aorta endothelium; proximity ligation assays and immunoprecipitation confirmed their physical interaction in EC. Remarkably, immunoneutralization of csHSP70 enhanced thrombomodulin activity in EC and aorta ex vivo. Overall, proatherogenic hemodynamic forces promote reduced total HSP70 expression, which might implicate in disturbed proteostasis; meanwhile, the associated decrease in cs-HSP70 pool associates with thromboresistance signaling. Cell-surface HSP70 (csHSP70) expression regulation and csHSP70 targets in vascular cells are unknown. We showed that HSP70 levels are shear stress-modulated and decreased under proatherogenic conditions. Remarkably, csHSP70 binds thrombomodulin and inhibits its activity in endothelial cells. This mechanism can potentially explain some deleterious effects previously associated with high extracellular HSP70 levels, as csHSP70 potentially could restrict thromboresistance and support thrombosis/inflammation in stress situations.

Atrial endocardial expression of von Willebrand factor and thrombomodulin is associated with recurrence after minimally invasive surgical atrial fibrillation ablation

OBJECTIVES

We retrospectively analysed data from non-valvular atrial fibrillation (AF) patients who underwent minimally invasive surgical AF ablation at our centre. Our purpose was to explore the atrial endocardial expression of von Willebrand factor (vWF) and thrombomodulin (TM) and their association with rhythm results after the procedure.

METHODS

From January 2014 to May 2015, 60 patients underwent minimally invasive surgical AF ablation at our centre. Left atrial appendage samples were obtained during the procedure and immunohistochemistry for endocardial markers including vWF and TM was performed and semi-quantitatively graded. All patients underwent postoperative rhythm documentation at 3, 6, 12 and 24 months.

RESULTS

At the 2-year interval, 49 (82%) patients maintained sinus rhythm, and all patients were asymptomatic. Univariate analysis shows that patients with AF recurrence have higher vWF score 2/3 and longer AF duration (P < 0.05). In the multivariate analysis, AF duration, vWF score, TM score, left atrial diameter (LAD) and non-paroxysmal AF are included. The result suggests that higher vWF score 2/3, lower TM score 0/1 and non-paroxysmal AF are statistically significant (P < 0.05). In addition, higher vWF score 2/3 is associated with larger LAD (45.2 ± 5.6 mm vs 41.2 ± 7.6 mm, P = 0.032), while higher TM score 2/3, on the other hand, is associated with smaller LAD (44.6 ± 6.1 mm vs 39.9 ± 7.8 mm, P = 0.032). The Kaplan-Meier analysis shows that higher vWF score 2/3 and lower TM score 0/1 appear to be accompanied with higher recurrence rate (vWF: P = 0.021; TM: P = 0.036).

CONCLUSIONS

Atrial endocardial expression of vWF and TM might be associated with recurrence after minimally invasive surgical AF ablation. Patients with AF recurrence seem to have elevated vWF expression and decreased TM expression.

Endocardial Changes in Nonvalvular Atrial Fibrillation Without Atrial Thrombus-Thrombomodulin and Tissue Factor Pathway Inhibitor

Atrial fibrillation (AF) is a well-known cause for thromboembolism. Although blood stasis in the left atrium and hypercoagulable state of the blood have been emphasized as important mechanisms, limited attention has been paid to the endocardial changes in maintaining the balance of local coagulation, which may also contribute to the thrombus formation in AF. In the present study, left atrial appendage samples were obtained at heart surgery from nonvalvular AF and non-AF patients without atrial thrombus. Immunohistochemistry for endocardial markers including thrombomodulin (TM) and tissue factor pathway inhibitor (TFPI) was performed and semiquantitatively graded. In immunohistochemistry analysis, decreased expression of TM was found in patients with nonvalvular AF compared with those without AF ( P < .001). There was no difference in TFPI expression between the 2 groups ( P = .213). Patients with TM score of 0 or 1 seemed to have larger left atrial diameter (LAD) than those with TM score of 2 or 3 (44.0 (7.9) vs 40.6 (3.9); P = .009), while no relationship between LAD and TFPI expression was found (43.4 (7.0) vs 42.9 (7.8); P = .485). In conclusion, TM expression in the atrial endocardium is decreased in nonvalvular AF without atrial thrombus, while TFPI expression is not. Downregulated TM expression might be associated with enlarged LAD.

OCT imaging of aorto-coronary vein graft pathology modified by external stenting: 1-year post-surgery

AIMS

The Venous External Support Trial (VEST) evaluated whether a novel external stent attenuated saphenous vein graft (SVG) disease assessed with intravascular ultrasound 1 year following coronary artery bypass graft (CABG) surgery. This sub-study assessed SVGs with and without external stenting using optical coherence tomography (OCT). The aim of this study was to accurately compare quantitative and qualitative features of SVGs with and without a novel external stent using OCT.

METHODS AND RESULTS

Twenty-four of 30 patients (65 ± 8 years) enrolled in VEST underwent coronary angiography with OCT imaging using a non-occlusive technique. Quantitative analysis of lumen area was performed in one frame every 10 mm along the length of the graft, from distal to proximal anastomosis, and pathological features within the lumen were noted. Mean cross-sectional area was greater in unstented vs. stented grafts (8.4 ± 3 vs. 7.6 ± 2.7 mm; P = 0.005). The lumen of the stented grafts was more homogeneous (difference between maximum and minimum lumen diameter was significantly smaller in stented compared with unstented grafts, 0.28 ± 0.19 vs. 0.33 ± 0.23 mm, respectively, P = 0.006), and more circular (mean eccentricity index 0.08 ± 0.06 vs. 0.10 ± 0.06, stented vs. unstented; P = 0.019). Adherent thrombus was identified in three grafts (all unstented).

CONCLUSION

Our findings highlight the early changes occurring in SVGs after implantation of aorto-coronary bypass conduits, changes that may accelerate vein graft failure. External stenting resulted in a more homogeneous and less eccentric lumen with no thrombus formation.

Regulation of thrombomodulin expression and release in human aortic endothelial cells by cyclic strain

Background and Objectives

Thrombomodulin (TM), an integral membrane glycoprotein expressed on the lumenal surface of vascular endothelial cells, promotes anti-coagulant and anti-inflammatory properties. Release of functional TM from the endothelium surface into plasma has also been reported. Much is still unknown however about how endothelial TM is regulated by physiologic hemodynamic forces (and particularly cyclic strain) intrinsic to endothelial-mediated vascular homeostasis.

Methods

This study employed human aortic endothelial cells (HAECs) to investigate the effects of equibiaxial cyclic strain (7.5%, 60 cycles/min, 24 hrs), and to a lesser extent, laminar shear stress (10 dynes/cm², 24 hrs), on TM expression and release. Time-, dose- and frequency-dependency studies were performed.

Results

Our initial studies demonstrated that cyclic strain strongly downregulated TM expression in a p38- and receptor tyrosine kinase-dependent manner. This was in contrast to the upregulatory effect of shear stress. Moreover, both forces significantly upregulated TM release over a 48 hr period. With continuing focus on the cyclic strain-induced TM release, we noted both dose (0–7.5%) and frequency (0.5–2.0 Hz) dependency, with no attenuation of strain-induced TM release observed following inhibition of MAP kinases (p38, ERK-1/2), receptor tyrosine kinase, or eNOS. The concerted impact of cyclic strain and inflammatory mediators on TM release from HAECs was also investigated. In this respect, both TNFα (100 ng/ml) and ox-LDL (10–50 µg/ml) appeared to potentiate strain-induced TM release. Finally, inhibition of neither MMPs (GM6001) nor rhomboids (3,4-dichloroisocoumarin) had any effect on strain-induced TM release. However, significantly elevated levels (2.1 fold) of TM were observed in isolated microparticle fractions following 7.5% strain for 24 hrs.

Conclusions

A preliminary in vitro investigation into the effects of cyclic strain on TM in HAECs is presented. Physiologic cyclic strain was observed to downregulate TM expression, whilst upregulating in a time-, dose- and frequency-dependent manner the release of TM.

Flow reversal promotes intimal thickening in vein grafts

OBJECTIVE

After vascular interventions, unidentified mechanisms disrupt the homeostasis of a focal narrowing to initiate an intimal thickening response. We hypothesize that perturbations in the hemodynamic microenvironment are the initiating event for this disruption of homeostasis and intimal thickening in vein bypass grafts. The objective of this study was to investigate the relation between local flow perturbations and its influence on the vein graft architecture.

METHODS

An external ligature was used to create an 80% focal midgraft stenosis in bilateral rabbit carotid vein grafts. A unilateral distal ligation created a ninefold difference in flow rate between high-flow and low-flow grafts. Ten vein grafts were harvested at 28 days and serially sectioned for morphologic evaluation and vein graft reconstruction. Computational fluid dynamics analyses were performed to examine the hemodynamic environment within these complex flow regions.

RESULTS

The largest intimal thickening occurred exclusively within the region immediately distal to the maximum stenosis in high-flow grafts, which was characterized by persistent flow separation and reversal for the entire cardiac cycle. In regions of low to moderate shear stress (<5 Pa), the typical inverse correlation between intimal thickness and wall shear was observed.

CONCLUSIONS

Regions of vein bypass grafts exposed to persistent flow reversal are most at risk for intimal thickening and loss of lumen.

Thrombomodulin and the vascular endothelium: insights into functional, regulatory, and therapeutic aspects

Thrombomodulin (TM) is a 557-amino acid protein with a broad cell and tissue distribution consistent with its wide-ranging physiological roles. When expressed on the lumenal surface of vascular endothelial cells in both large vessels and capillaries, its primary function is to mediate endothelial thromboresistance. The complete integral membrane-bound protein form displays five distinct functional domains, although shorter soluble (functional) variants comprising the extracellular domains have also been reported in fluids such as serum and urine. TM-mediated binding of thrombin is known to enhance the specificity of the latter serine protease toward both protein C and thrombin activatable fibrinolysis inhibitor (TAFI), increasing their proteolytic activation rate by almost three orders of magnitude with concomitant anticoagulant, antifibrinolytic, and anti-inflammatory benefits to the vascular wall. Recent years have seen an abundance of research into the cellular mechanisms governing endothelial TM production, processing, and regulation (including flow-mediated mechanoregulation)--from transcriptional and posttranscriptional (miRNA) regulation of TM gene expression, to posttranslational processing and release of the expressed protein--facilitating greater exploitation of its therapeutic potential. The goal of the present paper is to comprehensively review the endothelial/TM system from these regulatory perspectives and draw some fresh conclusions. This paper will conclude with a timely examination of the current status of TM's growing therapeutic appeal, from novel strategies to improve the clinical efficacy of recombinant TM analogs for resolution of vascular disorders such as disseminated intravascular coagulation (DIC), to an examination of the complex pleiotropic relationship between statin treatment and TM expression.

Free fatty acids inhibit TM-EPCR expression through JNK pathway: an implication for the development of the prothrombotic state in metabolic syndrome

Metabolic syndrome is associated with significant hypercoagulable prothrombotic tendency; however, the mechanism for the prothrombotic state is not completely understood. We hypothesize that higher circulating plasma free fatty acids (FFAs) in metabolic syndrome inhibit the endothelial thrombomodulin (TM)-endothelial protein C receptor (EPCR) pathway, thereby promoting thrombus formation. Human umbilical vein endothelial cells were cultured in media supplemented with various doses of palmitic acid (PA), in the presence or absence of JNK inhibitor, and the expression of TM and EPCR was measured by western blot. The thrombotic state of high fat fed C57BL/6J mice was examined by tail bleeding time and deep venous thrombosis (DVT) model. As a result, PA inhibited the expression of TM and EPCR in endothelial cells, and this effect was blunted by inhibiting JNK signaling. High fat diet fed mice had higher level of circulating FFAs and exhibited prothrombotic state, evidenced by increased tail bleeding time and enlarged thrombotic size in DVT model, compared to the control diet fed mice. Hence, FFAs inhibit TM-EPCR-Protein C system in endothelial cells through activating JNK signaling, which may be a mechanism for the prothrombotic state in metabolic syndrome.

Anti-PF4/heparin antibodies and venous graft occlusion in postcoronary artery bypass surgery patients randomized to postoperative unfractionated heparin or fondaparinux thromboprophylaxis

BACKGROUND

Anti-PF4/heparin antibodies are frequently generated after coronary artery bypass grafting (CABG) surgery, with platelet-activating IgG implicated in heparin-induced thrombocytopenia (HIT). It is controversial whether non-platelet-activating antibodies are associated with thrombosis.

OBJECTIVES

To determine in post-CABG patients whether thromboprophylaxis using fondaparinux vs. unfractionated heparin (UFH) reduces the frequency of anti-PF4/heparin antibodies, and whether anti-PF4/heparin antibodies are associated with early graft occlusion.

METHODS/PATIENTS

In a pre-planned secondary analysis of a randomized control trial (RCT) comparing fondaparinux vs. UFH thromboprophylaxis post-CABG, we determined the frequency of anti-PF4/heparin antibody formation by solid-phase enzyme-immunoassay (EIA) and of platelet-activating antibodies by serotonin-release assay (SRA); the SRA and fluid-phase EIA were used to assess fondaparinux cross-reactivity. We also examined whether anti-PF4/heparin antibodies were associated with early arterial or venous graft occlusion (6-week CT angiography).

RESULTS

We found no significant difference in the frequency of antibody formation between patients who received fondaparinux vs. UFH (65.3% vs. 46.0%; P = 0.069), and no significant fondaparinux cross-reactivity. Venous graft occlusion(s) occurred in 6/26 patients who formed 'strong' IgG antibodies (≥ 1.0 optical density [OD] units and ≥ 2× baseline) vs. 3/66 who did not (P = 0.0139). In both unadjusted and adjusted analyses, strong postoperative (but not pre-operative) anti-PF4/heparin IgG responses were associated with a markedly increased risk of early venous (but not arterial) graft occlusion (adjusted OR, 9.25 [95% CI, 1.73, 49.43]; P = 0.0093); notably, none of the three SRA-positive patients developed a venous graft occlusion.

CONCLUSIONS

Fondaparinux vs. UFH thromboprophylaxis postCABG does not reduce anti-PF4/heparin antibody formation. Non-platelet-activating anti-PF4/heparin IgG antibodies generated post operatively are associated with early venous graft occlusion.

Thrombomodulin as a regulator of the anticoagulant pathway: implication in the development of thrombosis

Thrombomodulin is a cell surface-expressed glycoprotein that serves as a cofactor for thrombin-mediated activation of protein C (PC), an event further amplified by the endothelial cell PC receptor. The PC pathway is a major anticoagulant mechanism that downregulates thrombin formation and hedges thrombus formation. The objectives of this review were to review recent findings regarding thrombomodulin structure, its involvement in the regulation of hemostasis and further discuss the implication, if any, of the genetic polymorphisms in the thrombomodulin gene in the risk of development of thrombosis. We performed a literature search by using electronic bibliographic databases. Although the direct evaluation of risk situations associated with thrombomodulin mutations/polymorphisms could be of clinical significance, it appears that mutations that affect the function of thrombomodulin are rarely associated with venous thromboembolism. However, several polymorphisms are reported to be associated with increased risk for arterial thrombosis. Additionally studies on knock out mice as well studies on humans bearing rare mutations suggest that thrombomodulin dysfunction may be implicated in the pathogenesis of myocardial infraction.

Inhibition of transforming growth factor-β restores endothelial thromboresistance in vein grafts

BACKGROUND

Thrombosis is a major cause of the early failure of vein grafts (VGs) implanted during peripheral and coronary arterial bypass surgeries. Endothelial expression of thrombomodulin (TM), a key constituent of the protein C anticoagulant pathway, is markedly suppressed in VGs after implantation and contributes to local thrombus formation. While stretch-induced paracrine release of transforming growth factor-β (TGF-β) is known to negatively regulate TM expression in heart tissue, its role in regulating TM expression in VGs remains unknown.

METHODS

Changes in relative mRNA expression of major TGF-β isoforms were measured by quantitative polymerase chain reaction (qPCR) in cultured human saphenous vein smooth muscle cells (HSVSMCs) subjected to cyclic stretch. To determine the effects of paracrine release of TGF-β on endothelial TM mRNA expression, human saphenous vein endothelial cells (HSVECs) were co-cultured with stretched HSVSMCs in the presence of 1D11, a pan-neutralizing TGF-β antibody, or 13C4, an isotype-control antibody. Groups of rabbits were then administered 1D11 or 13C4 and underwent interpositional grafting of jugular vein segments into the carotid circulation. The effect of TGF-β inhibition on TM gene expression was measured by qPCR; protein C activating capacity and local thrombus formation were measured by in situ chromogenic substrate assays; and VG remodeling was assessed by digital morphometry.

RESULTS

Cyclic stretch induced TGF-β(1) expression in HSVSMCs by 1.9 ± 0.2-fold (P < .001) without significant change in the expressions of TGF-β(2) and TGF-β(3). Paracrine release of TGF-β(1) by stretched HSVSMCs inhibited TM expression in stationary HSVECs placed in co-culture by 57 ± 12% (P = .03), an effect that was abolished in the presence of 1D11. Similarly, TGF-β(1) was the predominant isoform induced in rabbit VGs 7 days after implantation (3.5 ± 0.4-fold induction; P < .001). TGF-β(1) protein expression localized predominantly to the developing neointima and coincided with marked suppression of endothelial TM expression (16% ± 2% of vein controls; P < .03), a reduction in situ activated protein C (APC)-generating capacity (53% ± 9% of vein controls; P = .001) and increased local thrombus formation (3.7 ± 0.8-fold increase over vein controls; P < .01). External stenting of VGs to limit vessel distension significantly reduced TGF-β(1) induction and TM downregulation. Systemic administration of 1D11 also effectively prevented TM downregulation, preserved APC-generating capacity, and reduced local thrombus in rabbit VGs without observable effect on neointima formation and other morphometric parameters 6 weeks after implantation.

CONCLUSION

TM downregulation in VGs is mediated by paracrine release of TGF-β(1) caused by pressure-induced vessel stretch. Systemic administration of an anti-TGF-β antibody effectively prevented TM downregulation and preserved local thromboresistance without negative effect on VG remodeling.

Thrombomodulin is silenced in malignant mesothelioma by a poly(ADP-ribose) polymerase-1-mediated epigenetic mechanism

Malignant mesothelioma (MM) is often complicated by thromboembolic episodes, with thrombomodulin (TM) playing a critical role in the anticoagulant process. Heterogeneous expression of TM has been observed in cancer, and low or no TM expression in cancer cells is associated with poor prognosis. In this study, we analyzed TM expression in biopsies of MM patients and compared them with normal mesothelial tissue. The role of DNA methylation-associated gene silencing in TM expression was investigated. To evaluate poly(ADP-ribose) polymerase-1 (PARP1) as responsible for gene promoter epigenetic modifications, nonmalignant mesothelial cells (Met-5A) and MM cells (H28) were silenced for PARP1 and the DNA methylation/acetylation-associated TM expression evaluated. A correlation between low TM expression and high level of TM promoter methylation was found in MM biopsies. Low expression of TM was restored in MM cells by their treatment with 5-aza-2'-deoxycytidine and, to a lesser extent, with trichostatin, whereas the epigenetic agents did not affect TM expression in Met-5A cells. Silencing of PARP1 resulted in a strong down-regulation of TM expression in Met-5A cells, while restoring TM expression in H28 cells. PARP1 silencing induced TM promoter methylation in Met-5A cells and demethylation in MM cells, and this was paralleled by corresponding changes in the DNA methyltransferase activity. We propose that methylation of the TM promoter is responsible for silencing of TM expression in MM tissue, a process that is regulated by PARP1.

Mapping cardiac pacemaker circuits: methodological puzzles of the sinoatrial node optical mapping

Historically, milestones in science are usually associated with methodological breakthroughs. Likewise, the advent of electrocardiography, microelectrode recordings and more recently optical mapping have ushered in new periods of significance of advancement in elucidating basic mechanisms in cardiac electrophysiology. As with any novel technique, however, data interpretation is challenging and should be approached with caution, as it cannot be simply extrapolated from previously used methodologies and with experience and time eventually becomes validated. A good example of this is the use of optical mapping in the sinoatrial node (SAN): when microelectrode and optical recordings are obtained from the same site in myocardium, significantly different results may be noted with respect to signal morphology and as a result have to be interpreted by a different set of principles. Given the rapid spread of the use of optical mapping, careful evaluation must be made in terms of methodology with respect to interpretation of data gathered by optical sensors from fluorescent potential-sensitive dyes. Different interpretations of experimental data may lead to different mechanistic conclusions. This review attempts to address the origin and interpretation of the "double component" morphology in the optical action potentials obtained from the SAN region. One view is that these 2 components represent distinctive signals from the SAN and atrial cells and can be fully separated with signal processing. A second view is that the first component preceding the phase 0 activation represents the membrane currents and intracellular calcium transients induced diastolic depolarization from the SAN. Although the consensus from both groups is that ionic mechanisms, namely the joint action of the membrane and calcium automaticity, are important in the SAN function, it is unresolved whether the double-component originates from the recording methodology or represents the underlying physiology. This overview aims to advance a common understanding of the basic principles of optical mapping in complex 3D anatomic structures.

A coupled SYSTEM of intracellular Ca2+ clocks and surface membrane voltage clocks controls the timekeeping mechanism of the heart's pacemaker

Ion channels on the surface membrane of sinoatrial nodal pacemaker cells (SANCs) are the proximal cause of an action potential. Each individual channel type has been thoroughly characterized under voltage clamp, and the ensemble of the ion channel currents reconstructed in silico generates rhythmic action potentials. Thus, this ensemble can be envisioned as a surface "membrane clock" (M clock). Localized subsarcolemmal Ca(2+) releases are generated by the sarcoplasmic reticulum via ryanodine receptors during late diastolic depolarization and are referred to as an intracellular "Ca(2+) clock," because their spontaneous occurrence is periodic during voltage clamp or in detergent-permeabilized SANCs, and in silico as well. In spontaneously firing SANCs, the M and Ca(2+) clocks do not operate in isolation but work together via numerous interactions modulated by membrane voltage, subsarcolemmal Ca(2+), and protein kinase A and CaMKII-dependent protein phosphorylation. Through these interactions, the 2 subsystem clocks become mutually entrained to form a robust, stable, coupled-clock system that drives normal cardiac pacemaker cell automaticity. G protein-coupled receptors signaling creates pacemaker flexibility, ie, effects changes in the rhythmic action potential firing rate, by impacting on these very same factors that regulate robust basal coupled-clock system function. This review examines evidence that forms the basis of this coupled-clock system concept in cardiac SANCs.

JNK-ATF-2 inhibits thrombomodulin (TM) expression by recruiting histone deacetylase4 (HDAC4) and forming a transcriptional repression complex in the TM promoter

Thrombomodulin (TM) is an important vascular protective molecule that has anticoagulant, anti-inflammatory and anti-apoptotic properties. TM is downregulated in many thrombotic and vascular diseases. However, the mechanisms responsible for TM suppression are not completely understood. In this study, we investigated the mechanism involved in fatty acid-induced suppression of TM expression in human aortic endothelial cells. We found that palmitic acid inhibited TM expression through the JNK and p38 pathways. ATF-2, a JNK and p38 target transcription factor, was involved in the suppression. ATF-2 can bind to the TM promoter, recruit HDAC4 and form a transcriptional repression complex in the promoter, which may lead to chromatin condensation and transcriptional arrest. This study provides novel insight into TM down-regulation by stress signaling pathways.

Cholinergic receptor signaling modulates spontaneous firing of sinoatrial nodal cells via integrated effects on PKA-dependent Ca(2+) cycling and I(KACh)

Prior studies indicate that cholinergic receptor (ChR) activation is linked to beating rate reduction (BRR) in sinoatrial nodal cells (SANC) via 1) a G(i)-coupled reduction in adenylyl cyclase (AC) activity, leading to a reduction of cAMP or protein kinase A (PKA) modulation of hyperpolarization-activated current (I(f)) or L-type Ca(2+) currents (I(Ca,L)), respectively; and 2) direct G(i)-coupled activation of ACh-activated potassium current (I(KACh)). More recent studies, however, have indicated that Ca(2+) cycling by the sarcoplasmic reticulum within SANC (referred to as a Ca(2+) clock) generates rhythmic, spontaneous local Ca(2+) releases (LCR) that are AC-PKA dependent. LCRs activate Na(+)-Ca(2+) exchange (NCX) current, which ignites the surface membrane ion channels to effect an AP. The purpose of the present study was to determine how ChR signaling initiated by a cholinergic agonist, carbachol (CCh), affects AC, cAMP, and PKA or sarcolemmal ion channels and LCRs and how these effects become integrated to generate the net response to a given intensity of ChR stimulation in single, isolated rabbit SANC. The threshold CCh concentration ([CCh]) for BRR was approximately 10 nM, half maximal inhibition (IC(50)) was achieved at 100 nM, and 1,000 nM stopped spontaneous beating. G(i) inhibition by pertussis toxin blocked all CCh effects on BRR. Using specific ion channel blockers, we established that I(f) blockade did not affect BRR at any [CCh] and that I(KACh) activation, evidenced by hyperpolarization, first became apparent at [CCh] > 30 nM. At IC(50), CCh reduced cAMP and reduced PKA-dependent phospholamban (PLB) phosphorylation by approximately 50%. The dose response of BRR to CCh in the presence of I(KACh) blockade by a specific inhibitor, tertiapin Q, mirrored that of CCh to reduced PLB phosphorylation. At IC(50), CCh caused a time-dependent reduction in the number and size of LCRs and a time dependent increase in LCR period that paralleled coincident BRR. The phosphatase inhibitor calyculin A reversed the effect of IC(50) CCh on SANC LCRs and BRR. Numerical model simulations demonstrated that Ca(2+) cycling is integrated into the cholinergic modulation of BRR via LCR-induced activation of NCX current, providing theoretical support for the experimental findings. Thus ChR stimulation-induced BRR is entirely dependent on G(i) activation and the extent of G(i) coupling to Ca(2+) cycling via PKA signaling or to I(KACh): at low [CCh], I(KACh) activation is not evident and BRR is attributable to a suppression of cAMP-mediated, PKA-dependent Ca(2+) signaling; as [CCh] increases beyond 30 nM, a tight coupling between suppression of PKA-dependent Ca(2+) signaling and I(KACh) activation underlies a more pronounced BRR.

Synergism of coupled subsarcolemmal Ca2+ clocks and sarcolemmal voltage clocks confers robust and flexible pacemaker function in a novel pacemaker cell model

Recent experimental studies have demonstrated that sinoatrial node cells (SANC) generate spontaneous, rhythmic, local subsarcolemmal Ca(2+) releases (Ca(2+) clock), which occur during late diastolic depolarization (DD) and interact with the classic sarcolemmal voltage oscillator (membrane clock) by activating Na(+)-Ca(2+) exchanger current (I(NCX)). This and other interactions between clocks, however, are not captured by existing essentially membrane-delimited cardiac pacemaker cell numerical models. Using wide-scale parametric analysis of classic formulations of membrane clock and Ca(2+) cycling, we have constructed and initially explored a prototype rabbit SANC model featuring both clocks. Our coupled oscillator system exhibits greater robustness and flexibility than membrane clock operating alone. Rhythmic spontaneous Ca(2+) releases of sarcoplasmic reticulum (SR)-based Ca(2+) clock ignite rhythmic action potentials via late DD I(NCX) over much broader ranges of membrane clock parameters [e.g., L-type Ca(2+) current (I(CaL)) and/or hyperpolarization-activated ("funny") current (I(f)) conductances]. The system Ca(2+) clock includes SR and sarcolemmal Ca(2+) fluxes, which optimize cell Ca(2+) balance to increase amplitudes of both SR Ca(2+) release and late DD I(NCX) as SR Ca(2+) pumping rate increases, resulting in a broad pacemaker rate modulation (1.8-4.6 Hz). In contrast, the rate modulation range via membrane clock parameters is substantially smaller when Ca(2+) clock is unchanged or lacking. When Ca(2+) clock is disabled, the system parametric space for fail-safe SANC operation considerably shrinks: without rhythmic late DD I(NCX) ignition signals membrane clock substantially slows, becomes dysrhythmic, or halts. In conclusion, the Ca(2+) clock is a new critical dimension in SANC function. A synergism of the coupled function of Ca(2+) and membrane clocks confers fail-safe SANC operation at greatly varying rates.

Brothers and sisters: molecular insights into arterial-venous heterogeneity

The molecular differences between arteries and veins are genetically predetermined and are evident even before the first embryonic heart beat. Although ephrinB2 and EphB4 are expressed in cells that will ultimately differentiate into arteries and veins, respectively, many other genes have been shown to play a significant role in cell fate determination. The expression patterns of ephrinB2 and EphB4 are restricted to arterial-venous boundaries, and Eph/ephrin signaling provides repulsive cues at arterial-venous boundaries that are thought to prevent intermixing of arterial- and venous-fated cells. However, the maintenance of arterial-venous fate is susceptible to some degree of plasticity. Thus, in response to signals from the ambient microenvironment and shear stress, there is flow-mediated intercalation of the arteries and veins that ultimately leads to the formation of a functional, closed-loop circulation. In addition, cells in the blood vessels of each organ undergo epigenetic, morphological, and functional adaptive changes that are specific to the proximate function of their cognate organ(s). These adaptive changes result in an interorgan and intraorgan vessel heterogeneity that manifest clinically in a disparate response of different organs to identical risk factors and injury in the same animal. In this review, we focus on the molecular and physiological factors influencing arterial-venous heterogeneity between and within different organ(s). We explore arterial-venous differences in selected organs, as well as their respective endothelial cell architectural organization that results in their inter- and intraorgan heterogeneity.

Thrombin downregulates thrombomodulin expression and activity in primary human endothelial cells

Thrombomodulin (TM) is a cell surface anticoagulant glycoprotein that plays a key role in the protein C pathway. TM expression in endothelial cells may be modulated by a variety of extracellular signals. Most notably, TM has been shown to be downregulated by inflammatory mediators, such as tumor necrosis factor-alpha and lipopolysaccharide. The objective of this study was to determine the effect of thrombin on TM expression and activity. Thrombin resulted in reduced TM in primary cultures of human endothelial cells by approximately 40% at the level of mRNA, protein, and activity. These effects were blocked by the thrombin inhibitor hirudin. These results suggest that activation of the coagulation cascade may result in a positive-feedback loop consisting of thrombin-mediated repression of TM-dependent protein C activation.

Endothelial cell recovery between comparator polymer-based drug-eluting stents

OBJECTIVES

The purpose of this study was to assess trends in endothelial coverage and recovery among leading polymer-based drug-eluting stents (DES).

BACKGROUND

Autopsy studies of human U.S. Food and Drug Administration (FDA)-approved DES implanted coronary arteries suggest that complications of late stent thrombosis are associated with incomplete endothelial coverage of struts.

METHODS

Rabbits received sirolimus-eluting stents (SES), paclitaxel-eluting stents (PES), zotarolimus-eluting stents (ZES), and everolimus-eluting stents (EES) for 14 or 28 days along with MULTI-LINK (ML) Vision control stents. Endothelial coverage above and between struts was measured by morphometric analysis of images acquired through en face scanning electron microscopy. Dual fluorescent immunolabeling was performed for platelet-endothelial cell adhesion molecule (PECAM)-1 and thrombomodulin (TM), factors involved in cell-to-cell contact and thrombogenicity, respectively. In a separate analysis, the endothelial mitogen, vascular endothelial growth factor (VEGF), was also assessed.

RESULTS

Varying rates of endothelialization among comparator DES were most notable at 14 days, where coverage above struts remained poor in SES, PES, and ZES (<or=30%) relative to EES and ML Vision controls (>or=70%), whereas no significant differences were observed at 28 days. Select DES with poor endothelialization showed a further reduced expression of PECAM-1. All DES showed an absence or weak expression of the antithrombotic cofactor TM. Incomplete endothelialization in select DES was further associated with increased VEGF secretion and messenger ribonucleic acid levels at 14 days, providing evidence of a transitional healing surface.

CONCLUSIONS

The present study marks the first comparator analysis of endothelial coverage in leading polymeric DES, supporting disparities in arterial healing based on endothelial regrowth and recovery, favoring newer designs over the current generation of FDA-approved stents.

Thrombomodulin: from haemostasis to inflammation and tumourigenesis

Thrombomodulin (TM), a transmembrane endothelial receptor, participates in coagulation, in inflammation, in cancer and plays a role during embryogenesis. The nucleotide sequence of the TM cDNA allows the structure of this protein to be visualized. The protein starts with a signal peptide, followed by the N-terminal globular domain, six repeats of epidermal growth factor-like sequence, a serine/threonine-rich region, a transmembrane domain and a cytoplasmic domain. High-resolution nuclear magnetic resonance (NMR) spectroscopy was employed to define the exact thrombin-binding region. Residues Y(413)ILDD(417) and D(423)IDE(426) are crucial for binding to thrombin; the two critical amino acids for thrombin binding, Ile(414) and Ile(424), are brought into spatial proximity by beta-sheet structure. There also exist some residues for co-factor activity, namely Asp(349), Glu(357), Tyr(358), Phe(376) and Met(388). The complex transcriptional and post-transcriptional control of TM underline its importance in a wide variety of biological systems and pathophysiological processes.

Circulating levels of adhesion molecules and markers of endothelial activation in acute inflammation induced by prolonged brisk exercise

OBJECTIVES

To investigate circulating levels of adhesion molecules and markers of endothelial activation in acute inflammation induced by prolonged brisk exercise.

DESIGN AND METHODS

The circulating levels of adhesion molecules E-, L- and P-selectins, intercellular and vascular adhesion molecule-1 (ICAM-1 and VCAM-1), along with those of thrombomodulin (TM), N-terminal pro-brain natriuretic peptide (NT-pro-BNP) and cardiac troponin T, were measured before, at the end of and at 48 h post-race, in athletes participating in this extreme physical stress paradigm.

RESULTS

Levels of L- and P-selectins remained the same before and at the end of the "Spartathlon" race, presenting a similar decline at 48 h post-race. E-Selectin, ICAM-1 and TM reached a maximum value at the end of the race and returned to normal 48 h after the race. A similar profile was observed for VCAM-1 and NT-pro-BNP, with a tendency for a decrease at 48 h post-race, while troponin T was not detected.

CONCLUSIONS

The indices of endothelial activation are strongly affected during "Spartathlon" race, suggesting that, although prolonged brisk exercise activates the endothelium, it rapidly recovers.

Calcium and arrhythmogenesis

Triggered activity in cardiac muscle and intracellular Ca2+ have been linked in the past. However, today not only are there a number of cellular proteins that show clear Ca2+ dependence but also there are a number of arrhythmias whose mechanism appears to be linked to Ca2+-dependent processes. Thus we present a systematic review of the mechanisms of Ca2+ transport (forward excitation-contraction coupling) in the ventricular cell as well as what is known for other cardiac cell types. Second, we review the molecular nature of the proteins that are involved in this process as well as the functional consequences of both normal and abnormal Ca2+ cycling (e.g., Ca2+ waves). Finally, we review what we understand to be the role of Ca2+ cycling in various forms of arrhythmias, that is, those associated with inherited mutations and those that are acquired and resulting from reentrant excitation and/or abnormal impulse generation (e.g., triggered activity). Further solving the nature of these intricate and dynamic interactions promises to be an important area of research for a better recognition and understanding of the nature of Ca2+ and arrhythmias. Our solutions will provide a more complete understanding of the molecular basis for the targeted control of cellular calcium in the treatment and prevention of such.

Phenotypic heterogeneity of the endothelium: II. Representative vascular beds

Endothelial cells, which form the inner cellular lining of blood vessels and lymphatics, display remarkable heterogeneity in structure and function. This is the second of a 2-part review on the phenotypic heterogeneity of blood vessel endothelial cells. The first part discusses the scope, the underlying mechanisms, and the diagnostic and therapeutic implications of phenotypic heterogeneity. Here, these principles are applied to an understanding of organ-specific phenotypes in representative vascular beds including arteries and veins, heart, lung, liver, and kidney. The goal is to underscore the importance of site-specific properties of the endothelium in mediating homeostasis and focal vascular pathology, while at the same time emphasizing the value of approaching the endothelium as an integrated system.

TGF-beta- and CTGF-mediated fibroblast recruitment influences early outward vein graft remodeling

Luminal shearing forces have been shown to impact both geometric remodeling and the development of intimal hyperplasia. Less well studied is the influence of intramural wall stresses on vessel growth and adaptation. Using a vein graft-fistula configuration to isolate the impact of circumferential wall stress, we identify the reorganization of adventitial myofibroblasts as the dominant histological event that limits early outward remodeling of vein grafts in response to elevated wall stress. We hypothesize that increased production of transforming growth factor-beta (TGF-beta) and connective tissue growth factor (CTGF) induces recruitment of myofibroblasts, promotes adventitial reorganization, and limits early outward remodeling in response to increased intramural wall stress. Vein grafts with a distal arteriovenous fistula in the neck of rabbits were constructed, resulting in a fourfold differential in circumferential wall stress. Using this model, we demonstrate 1) elevated wall stress augments the production of TGF-beta and CTGF, 2) increased TGF-beta expression and CTGF expression are correlated with the enhanced differentiation from fibroblasts to myofibroblasts, as evidenced by the significant increase in the alpha-actin-positive cells in adventitia, and 3) the levels of TGF-beta, CTGF, and alpha-actin are inversely correlated with the magnitude of outward remodeling of the graft wall. Increased wall stress after vein graft implantation appears to induce a TGF-beta- and CTGF-mediated recruitment of adventitial fibroblasts and a conversion to a myofibroblast phenotype. Although important in the maintenance of wall stability in the face of an increased mechanical load, this adventitial adaptation limits early outward remodeling of the vein conduit and may prove deleterious in maintaining long-term vein graft patency.

Hemodynamic Modulation of Endocardial Thromboresistance

Background— Patients with heart failure are at increased risk for thromboembolic events, including stroke. Historically attributed to blood stasis, little is known about the adverse effects of elevated chamber filling pressure on endocardial function, which could predispose to intracardiac thrombus formation.

Methods and Results— We investigated changes in the expression of thrombomodulin, a key component of the anticoagulant protein C pathway, in rats subjected to acute atrial pressure overload caused by aortic banding. Acute elevation of left atrial filling pressure, without an associated decline in ventricular systolic function, caused a 70% inhibition of atrial endocardial thrombomodulin expression and resulted in increased local thrombin generation. Targeted restoration of atrial thrombomodulin expression with adenovirus-mediated gene transfer successfully reduced thrombin generation to baseline levels. In vitro co-culture studies revealed that thrombomodulin downregulation is caused by the paracrine release of transforming growth factor-β from cardiac connective tissue in response to mechanical stretch. This was confirmed in vivo by administration of a neutralizing transforming growth factor-β antibody, which effectively prevented thrombomodulin downregulation during acute pressure overload.

Conclusions— These findings suggest that increased hemodynamic load adversely affects endocardial function and is a potentially important contributor to thromboembolus formation in heart failure.

From the nutcracker-phenomenon of the left renal vein to the midline congestion syndrome as a cause of migraine, headache, back and abdominal pain and functional disorders of pelvic organs

This paper presents the hypothesis, that pain and functional disturbances of organs which lie on the midline of the body might be caused by a venous congestion of these organs. Cause of their congestion is the participation of these organs (vertebral column, skull, brain, spinal medullary, uterus, prostate, left ovary/testis, urinary bladder rectum, vagina, urethra) in the collateral circulation of the left renal vein. In many patients with complaints of the above mentioned organs the left renal vein is compressed inside the fork formed by the superior mesenteric artery and the aorta. This so called nutcracker phenomenon is incompletely understood today. It can lead to a marked reduction of left renal perfusion and forces the left renal blood to bypass the venous compression site via abundant collaterals. These collaterals are often not sufficient. Their walls become stretched and distorted - varices with inflamed walls are formed. These dilated veins are painful, interfere with the normal organ's function and demand more space than usual. This way pain in the midline organs and functional derangement of the midline organs can occur. The term "midline congestion syndrome" seems appropriate to reflect the comprehensive nature of this frequent disorder. The rationale for this hypothesis is based on the novel PixelFlux-technique (www.chameleon-software.de) of renal tissue perfusion measurement. With this method a relevant decline of left renal cortical perfusion was measured in 16 affected patients before therapy (left/right ratio: 0.79). After a treatment with acetylsalicylic acid in doses from 15 to 200mg/d within 14-200 days a complete relief of so far long lasting therapy-resistant midline organ symptoms was achieved. Simultaneously the left/right renal perfusion ratio increased significantly to 1.24 (p=0.021). This improvement of left renal perfusion can be explained by a better drainage of collateral veins, diminution of their wall distension, thereby decline of their intramural inflammation, reduction of their mass effects (especially by the replaced spinal fluid inside the spinal canal and the skull), and altogether a reduction of pain and functional derangement in the affected midline organs. The proposed theory might influence the current understanding of such frequent and difficult to treat diseases as chronic back pain, headaches, frequent cystitis, enuresis, abdominal pain, flank pain and might spur new theories of arterial hypertension, placental insufficiency, prostate diseases and myelopathies.

Improved outcomes in peripartum cardiomyopathy with contemporary

BACKGROUND

Prior studies have shown both high morbidity and mortality for patients with peripartum cardiomyopathy (PPCM). These studies were small and predated current advances in heart failure treatment. We sought to determine the outcomes of women with PPCM in the contemporary era and to determine predictors of poor outcome.

METHODS

Patients with PPCM from 1990 to 2003 were identified retrospectively through screening of heart failure clinics and echocardiography records. Their records were reviewed, and current clinical status was determined.

RESULTS

Fifty-five patients were identified with an average follow-up of 43 months. Their mean initial ejection fraction (EF) was 20%. Compared with their initial EF, 62% of patients improved, 25% were unchanged, and 4% declined. No patients died, and 10% eventually required transplant. At 2 months after diagnosis, 75% of those who eventually recovered had an EF >45%. Factors associated with lack of recovery at initial assessment were a left ventricular (LV) end-diastolic dimension >5.6 cm, the presence of LV thrombus, and African-American race. Recovery of LV function was not predicted by the initial EF. Among patients who recovered, the withdrawal of heart failure medications was not associated with decompensation over a follow-up of 29 months.

CONCLUSIONS

The morbidity related to PPCM is less than previously reported. Initial LV end-diastolic dimension and EF at 2 months predict long-term outcomes. The discontinuation of heart failure medications after recovery did not lead to decompensation.

Bradycardia and Slowing of the Atrioventricular Conduction in Mice Lacking Ca V 3.1/α 1G T-Type Calcium Channels

The generation of the mammalian heartbeat is a complex and vital function requiring multiple and coordinated ionic channel activities. The functional role of low-voltage activated (LVA) T-type calcium channels in the pacemaker activity of the sinoatrial node (SAN) is, to date, unresolved. Here we show that disruption of the gene coding for CaV3.1/alpha1G T-type calcium channels (cacna1g) abolishes T-type calcium current (I(Ca,T)) in isolated cells from the SAN and the atrioventricular node without affecting the L-type Ca2+ current (I(Ca,L)). By using telemetric electrocardiograms on unrestrained mice and intracardiac recordings, we find that cacna1g inactivation causes bradycardia and delays atrioventricular conduction without affecting the excitability of the right atrium. Consistently, no I(Ca,T) was detected in right atrium myocytes in both wild-type and CaV3.1(-/-) mice. Furthermore, inactivation of cacna1g significantly slowed the intrinsic in vivo heart rate, prolonged the SAN recovery time, and slowed pacemaker activity of individual SAN cells through a reduction of the slope of the diastolic depolarization. Our results demonstrate that CaV3.1/T-type Ca2+ channels contribute to SAN pacemaker activity and atrioventricular conduction.

Relationship between soluble thrombomodulin in patients with intermittent claudication and critical ischemia

INTRODUCTION

Thrombomodulin (TM) has been described as a marker of endothelial injury in atherosclerosis. The role of TM as a predictor of PAD severity is to be proven. The goal of the present study is to compare the level of plasmatic (TMp) in patients with intermittent claudication with patients with critical ischemia in the lower limbs.

MATERIALS AND METHODS

TMp was measured using ELISA in the plasma of 41 patients with intermittent claudication degree 1 and in 40 patients presenting critical ischemia in the lower limbs degrees 2 and 3, according to TASC. The hypotheses of normality and homogeneity of the variance had been proven via Shapiro-Wilk and Levene tests, respectively. The comparison of the TMp between the groups was done using the t-Student test.

RESULTS

No statistically significant difference was observed. The average levels of TMp for intermittent claudication were 5.2 ng/ml (0.78-13.61 ng/ml) and TMp for critical ischemia in the lower limbs were 6.34 (0.82-18.22 ng/ml) where p=0.265.

CONCLUSION

TMp does not seem to be an appropriate marker for PAD severity.

Endothelial activation, dysfunction, and damage in congestive heart failure and the relation to brain natriuretic peptide and outcomes

Congestive heart failure (CHF) is associated with marked endothelial dysfunction. We hypothesized that acute and chronic CHF may manifest different degrees of endothelial damage/dysfunction and activation, as reflected by different plasma endothelial markers, such as von Willebrand factor (vWF) and soluble thrombomodulin (both are indexes of endothelial damage/dysfunction) and soluble E-selectin (an index of endothelial activation). Second, we hypothesized a relation between endothelial markers and B-type natriuretic peptide (BNP, an index of cardiac function) in acute and chronic CHF that could be linked to prognosis. To test this hypothesis, we studied 35 patients with acute CHF, 40 patients with chronic CHF, and 32 healthy controls. The patients with CHF were followed up for the combined outcomes of cardiovascular death, nonfatal myocardial infarction, stroke, thromboembolism, and recurrent admissions to the hospital. vWF (p = 0.001), soluble thrombomodulin, E-selectin, and BNP (all p <0.0001) were higher in patients with acute and chronic CHF compared with controls. When the 2 CHF groups were compared, no significant differences were found in vWF or E-selectin (p = NS), but soluble thrombomodulin was significantly elevated in acute CHF (Tukey's post hoc test, p <0.05). Only high vWF was associated with a poorer outcome (log-rank test, p = 0.0188). None of the endothelial indexes correlated with plasma BNP. After a median follow-up of 18 months, only high (median or higher) vWF levels were predictive of adverse outcomes in the patients with CHF (log-rank statistic = 5.52, degree of freedom 1, p = 0.0188). In conclusion, despite similar ejection fractions, patients with acute and chronic CHF have different degrees of endothelial damage/dysfunction and activation, which may be related to differences in pathophysiology. High levels of vWF were associated with a worse short-term outcome. These endothelial markers were unrelated to plasma BNP levels and may imply a different release mechanism.

Molecular physiology of cardiac repolarization

The heart is a rhythmic electromechanical pump, the functioning of which depends on action potential generation and propagation, followed by relaxation and a period of refractoriness until the next impulse is generated. Myocardial action potentials reflect the sequential activation and inactivation of inward (Na(+) and Ca(2+)) and outward (K(+)) current carrying ion channels. In different regions of the heart, action potential waveforms are distinct, owing to differences in Na(+), Ca(2+), and K(+) channel expression, and these differences contribute to the normal, unidirectional propagation of activity and to the generation of normal cardiac rhythms. Changes in channel functioning, resulting from inherited or acquired disease, affect action potential repolarization and can lead to the generation of life-threatening arrhythmias. There is, therefore, considerable interest in understanding the mechanisms that control cardiac repolarization and rhythm generation. Electrophysiological studies have detailed the properties of the Na(+), Ca(2+), and K(+) currents that generate cardiac action potentials, and molecular cloning has revealed a large number of pore forming (alpha) and accessory (beta, delta, and gamma) subunits thought to contribute to the formation of these channels. Considerable progress has been made in defining the functional roles of the various channels and in identifying the alpha-subunits encoding these channels. Much less is known, however, about the functioning of channel accessory subunits and/or posttranslational processing of the channel proteins. It has also become clear that cardiac ion channels function as components of macromolecular complexes, comprising the alpha-subunits, one or more accessory subunit, and a variety of other regulatory proteins. In addition, these macromolecular channel protein complexes appear to interact with the actin cytoskeleton and/or the extracellular matrix, suggesting important functional links between channel complexes, as well as between cardiac structure and electrical functioning. Important areas of future research will be the identification of (all of) the molecular components of functional cardiac ion channels and delineation of the molecular mechanisms involved in regulating the expression and the functioning of these channels in the normal and the diseased myocardium.

Rapamycin attenuates vascular wall inflammation and progenitor cell promoters after angioplasty

Rapamycin combines antiproliferative and antiinflammatory properties and reduces neointima formation after angioplasty in patients. Its effect on transcriptional programs governing neointima formation has not yet been investigated. Here, we systematically analyzed the effect of rapamycin on gene expression during neointima formation in a human organ culture model. After angioplasty, renal artery segments were cultured for 21 or 56 days in absence or presence of 100 ng/ml rapamycin. Gene expression analysis of 2312 genes revealed 264 regulated genes with a peak alteration after 21 days. Many of those were associated with recruitment of blood cells and inflammatory reactions of the vessel wall. Likewise, chemokines and cytokines such as M-CSF, IL-1beta, IL-8, beta-thromboglobulin, and EMAP-II were found up-regulated in response to vessel injury. Markers indicative for a facilitated recruitment and stimulation of hematopoetic progenitor cells (HPC), including BST-1 and SDF-1, were also induced. In this setting, rapamycin suppressed the coordinated proadhesive and proinflammatory gene expression pattern next to down-regulation of genes related to metabolism, proliferation, and apoptosis. Our study shows that mechanical injury leads to induction of a proinflammatory, proadhesive gene expression pattern in the vessel wall even in absence of leukocytes. These molecular events could provide a basis for the recruitment of leukocytes and HPC. By inhibiting the expression of such genes, rapamycin may lead to a reduced recruitment of leukocytes and HPC after vascular injury, an effect that may play a decisive role for its effectiveness in reducing restenosis.

Impact of IL-1β on flow-induced outward arterial remodeling

BACKGROUND

Flow reduction upregulates arterial wall interleukin 1beta (IL-1beta), and IL-1beta independently modulates intimal hyperplasia under low flow conditions. We hypothesized that IL-1beta expression is also augmented under high flow, and outward remodeling occurs by way of IL-1beta-dependent mechanisms.

METHODS

Carotid artery (CA) flow was surgically augmented in rabbits (n = 20). CAs were harvested at 1, 3, 7, and 14 days, and assayed via quantitative reverse transcriptase-polymerase chain reaction. IL-1 receptor I null mice (KO) and wild-type controls underwent unilateral CA ligation and harvest 4 weeks later to assess the impact of increased flow on the contralateral CA (n = 82).

RESULTS

The rabbit model led to an immediate 36% increase in contralateral flow (P = .01) with an 80% increase at 14 days (P = .016) with subsequent positive remodeling. High flow induced IL-1beta messenger RNA expression (114-fold at 1 day, P < .05), with levels remaining elevated through 14 days (61-fold, P < .05). In murine experiments, CA ligation resulted in a 44% increase in contralateral flow. Wild-type and KO animals responded with equivalent 83% and 78% increases in luminal area (P = .87).

CONCLUSIONS

Positive and negative perturbations of arterial blood flow induce IL-1beta in a time-dependent fashion. However, as opposed to intimal hyperplasia after flow reduction, positive arterial remodeling in response to increased flow occurs via IL-1beta independent mechanisms.

Thrombomodulin-protein C-EPCR system: integrated to regulate coagulation and inflammation

Late in the 18th century, William Hewson recognized that the formation of a clot is characteristic of many febrile, inflammatory diseases (Owen C. A History of Blood Coagulation. Rochester, Minnesota: Mayo Foundation; 2001). Since that time, there has been steady progress in our understanding of coagulation and inflammation, but it is only in the past few decades that the molecular mechanisms linking these 2 biologic systems have started to be delineated. Most of these can be traced to the vasculature, where the systems most intimately interact. Thrombomodulin (TM), a cell surface-expressed glycoprotein, predominantly synthesized by vascular endothelial cells, is a critical cofactor for thrombin-mediated activation of protein C (PC), an event further amplified by the endothelial cell protein C receptor (EPCR). Activated PC (APC), in turn, is best known for its natural anticoagulant properties. Recent evidence has revealed that TM, APC, and EPCR have activities that impact not only on coagulation but also on inflammation, fibrinolysis, and cell proliferation. This review highlights recent insights into the diverse functions of this complex multimolecular system and how its components are integrated to maintain homeostasis under hypercoagulable and/or proinflammatory stress conditions. Overall, the described advances underscore the usefulness of elucidating the relevant molecular pathways that link both systems for the development of novel therapeutic and diagnostic targets for a wide range of inflammatory diseases.

Murine Model of Neointimal Formation and Stenosis in Vein Grafts

OBJECTIVE

Previous studies have suggested that neointimal formation, a central cause of vein graft stenosis, has several potential cell sources. It was hypothesized that neointimal cells arise primarily from the cells of the vein graft.

METHODS AND RESULTS

This study investigated vein graft neointimal cell origins using a model of vein-to-artery cross-transplantation between transgenic Rosa26 mice (constitutive expression of bacterial beta-galactosidase marker gene) and wild-type mice. Vein-originating cells survived and make a major contribution to neointimal formation within the vein graft, mostly adjacent to the lumen/endothelium, suggesting an intimate association with endothelial cells. Cross-transplantation of veins from thrombomodulin promoter-driven beta-galactosidase reporter transgenic mice to wild-type arteries demonstrated survival of vein graft endothelial cells. Neointimal thickening was greater at the proximal and, to a lesser extent, distal ends, in comparison to the middle of the graft. By contrast, arterial grafts had almost no neointimal formation throughout the graft. The relative neointimal wall thickness is much greater in this model compared with other murine and larger-species vein graft models, even showing near-occlusive stenosis of the perianastomotic region.

CONCLUSIONS

Vein graft neointimal cells arise predominantly from vein-derived cells, suggesting clinical relevance of stenosis-inhibiting therapies directed at the vein graft.

Nonchannel drug targets in atrial fibrillation

Atrial fibrillation (AF) is the most common clinical arrhythmia and one of the most important factors for ischemic stroke. In general, AF is treated with "channel-blocking drugs" to restore sinus rhythm and warfarin is recommended in the majority of patients to prevent atrial thrombus formation and thromboembolic events. In the recent years, a tremendous amount has been learned about the pathophysiology and molecular biology of AF. Thus, pharmacologic interference with specific signal transduction pathways with "non-channel-blocking drugs" appears promising as a novel antiarrhythmic approach to maintain sinus rhythm and to prevent atrial clot formation. Therefore, this review will highlight some novel "nonchannel drug targets" for AF therapy.

Cyclic variation of intracellular calcium: a critical factor for cardiac pacemaker cell dominance

While a diversity of cell types and distribution within the sinoatrial node and cell-cell interactions add complexity to a complete elucidation of the heart's pacemaker function, it has become clear that cyclic variation of submembrane [Ca2+] and activation of the Na+-Ca2+ exchanger during diastolic depolarization (DD) act in concert with ion channels to confer on sinoatrial node cells (SANCs) their status of dominance with respect to pacemaker function. Studies using confocal microscopy indicate that subsarcolemmal Ca2+ release via ryanodine receptors occurs not only in response to the action potential (AP) upstroke, but also during the DD, and this is augmented by beta-adrenergic receptor (beta-AR) stimulation. Spontaneous APs simulated by mathematical SANC models beat at a faster rate when this subsarcolemmal Ca2+ waveform measured under beta-AR stimulation is introduced into the modeling scheme. Thus, in future investigation of pacemaker functioning in health, disease, and disease therapies the "bar ought to be raised" to embrace the impact of cyclic variation in submembrane [Ca2+] on pacemaker function. The full text of this article is available at http://www.circresaha.org.