Blood coagulation and beyond: Position paper from the Fourth Maastricht Consensus Conference on Thrombosis

The 4th Maastricht Consensus Conference on Thrombosis (MCCT), included the following themes: Theme 1: The "coagulome" as a critical driver of cardiovascular disease Blood coagulation proteins also play divergent roles in biology and pathophysiology, related to specific organs, including brain, heart, bone marrow and kidney. Four investigators shared their views on these organ-specific topics. Theme 2: Novel mechanisms of thrombosis Mechanisms linking factor XII to fibrin, including their structural and physical properties, contribute to thrombosis, which is also affected by variation in microbiome status. Virus infections associated-coagulopathies perturb the hemostatic balance resulting in thrombosis and/or bleeding. Theme 3: How to limit bleeding risks: insights from translational studies This theme included state of the art methodology for exploring the contribution of genetic determinants of a bleeding diathesis; determination of polymorphisms in genes that control the rate of metabolism by the liver of P2Y12 inhibitors, to improve safety of antithrombotic therapy. Novel reversal agents for direct oral anticoagulants are discussed. Theme 4: Hemostasis in extracorporeal systems: how to utilize ex vivo models? Perfusion flow chamber and nanotechnology developments are developed for studying bleeding and thrombosis tendencies. Vascularised organoids are utilized for disease modeling and drug development studies. Strategies for tackling extracorporeal membrane oxygenation (ECMO) associated coagulopathy are discussed. Theme 5: Clinical dilemmas in thrombosis and antithrombotic management Plenary presentations addressed controversial areas, ie thrombophilia testing, thrombosis risk assessment in hemophilia, novel antiplatelet strategies and clinically tested factor XI(a) inhibitors,both possibly with reduced bleeding risk. Finally, Covid-19 associated coagulopathy is revisited.

von Willebrand Factor: A Central Regulator of Arteriovenous Fistula Maturation Through Smooth Muscle Cell Proliferation and Outward Remodeling

Background Arteriovenous fistula (AVF) maturation failure is a main limitation of vascular access. Maturation is determined by the intricate balance between outward remodeling and intimal hyperplasia, whereby endothelial cell dysfunction, platelet aggregation, and vascular smooth muscle cell (VSMC) proliferation play a crucial role. von Willebrand Factor (vWF) is an endothelial cell-derived protein involved in platelet aggregation and VSMC proliferation. We investigated AVF vascular remodeling in vWF-deficient mice and vWF expression in failed and matured human AVFs. Methods and Results Jugular-carotid AVFs were created in wild-type and vWF^-/- mice. AVF flow was determined longitudinally using ultrasonography, whereupon AVFs were harvested 14 days after surgery. VSMCs were isolated from vena cavae to study the effect of vWF on VSMC proliferation. Patient-matched samples of the basilic vein were obtained before brachio-basilic AVF construction and during superficialization or salvage procedure 6 weeks after AVF creation. vWF deficiency reduced VSMC proliferation and macrophage infiltration in the intimal hyperplasia. vWF^-/- mice showed reduced outward remodeling (1.5-fold, P=0.002) and intimal hyperplasia (10.2-fold, P<0.0001). AVF flow in wild-type mice was incremental over 2 weeks, whereas flow in vWF^-/- mice did not increase, resulting in a two-fold lower flow at 14 days compared with wild-type mice (P=0.016). Outward remodeling in matured patient AVFs coincided with increased local vWF expression in the media of the venous outflow tract. Absence of vWF in the intimal layer correlated with an increase in the intima-media ratio. Conclusions vWF enhances AVF maturation because its positive effect on outward remodeling outweighs its stimulating effect on intimal hyperplasia.

Thrombin in complex with dabigatran can still interact with PAR-1 via exosite-I and instigate loss of vascular integrity

BACKGROUND

Atrial fibrillation (AF) can lead to the loss of microvascular integrity thereby enhancing AF progression. Mechanistically, the pro-coagulant state that drives the risk of stroke in patients with AF may also play a causal role in microvascular loss. Direct oral anticoagulants (DOACs), the preferred anticoagulants for AF, can target factors upstream (factor Xa [FXa]) or downstream (thrombin) in the coagulation cascade and mediate differential vascular effects through interaction with protease-activated receptors (PARs).

OBJECTIVE

To investigate the potential effect of different DOACs on vascular integrity.

METHODS

To model the impact of DOACs on vascular integrity, we utilized platelet-free plasma in thrombin generation assays and endothelial barrier assays under identical experimental conditions. These multifactorial systems provide all coagulation factors and their respective natural inhibitors in physiological ratios in combination with the pro-coagulant endothelial surface on which coagulation is initiated. Furthermore, the system provides pro- and anti-barrier factors and monitoring both assays simultaneously permits coupling of thrombin kinetics to endothelial barrier dynamics.

RESULTS

We provide evidence that the anti-FXa DOAC rivaroxaban and the anti-thrombin DOAC dabigatran are efficient in blocking their target proteases. However, while rivaroxaban could preserve endothelial barrier function, dabigatran failed to protect endothelial integrity over time, which could be prevented in the presence of a custom-made peptide that blocks thrombin's exosite-I.

CONCLUSIONS

Proteolytically inactive thrombin in complex with dabigatran evokes loss of barrier function that can be prevented by a protease-activated receptor-1 mimicking peptide blocking thrombin's exosite-I.

Prediction Power on Cardiovascular Disease of Neuroimmune Guidance Cues Expression by Peripheral Blood Monocytes Determined by Machine-Learning Methods

Atherosclerosis is the underlying pathology in a major part of cardiovascular disease, the leading cause of mortality in developed countries. The infiltration of monocytes into the vessel walls of large arteries is a key denominator of atherogenesis, making monocytes accountable for the development of atherosclerosis. With the development of high-throughput transcriptome profiling platforms and cytometric methods for circulating cells, it is now feasible to study in-depth the predicted functional change of circulating monocytes reflected by changes of gene expression in certain pathways and correlate the changes to disease outcome. Neuroimmune guidance cues comprise a group of circulating- and cell membrane-associated signaling proteins that are progressively involved in monocyte functions. Here, we employed the CIRCULATING CELLS study cohort to classify cardiovascular disease patients and healthy individuals in relation to their expression of neuroimmune guidance cues in circulating monocytes. To cope with the complexity of human datasets featured by noisy data, nonlinearity and multidimensionality, we assessed various machine-learning methods. Of these, the linear discriminant analysis, Naïve Bayesian model and stochastic gradient boost model yielded perfect or near-perfect sensibility and specificity and revealed that expression levels of the neuroimmune guidance cues SEMA6B, SEMA6D and EPHA2 in circulating monocytes were of predictive values for cardiovascular disease outcome.

SLC44A2 deficient mice have a reduced response in stenosis but not in hypercoagulability driven venous thrombosis

BACKGROUND

Genome wide association studies (GWAS) identified SLC44A2 as a novel susceptibility gene for venous thrombosis (VT) and previous work established that SLC44A2 contributed to clot formation upon vascular injury.

OBJECTIVE

To further investigate the role of SLC44A2 in VT by utilizing SLC44A2 deficient mice (Slc44a2-/- ) in two representative disease models.

METHODS

Mice were included in a hypercoagulability model driven by siRNA-mediated hepatic gene silencing of anticoagulants Serpinc1 (antithrombin) and Proc (protein C) and a flow restriction (stenosis) model induced by partial ligation of the inferior vena cava.

RESULTS

In the hypercoagulability model, no effect in onset was observed in Slc44a2-/- animals; however, a drop in plasma fibrinogen and von Willebrand factor coinciding with an increase in blood neutrophils was recorded. In the neutrophil dependent stenosis model after 48 hours, Slc44a2-/- mice had significantly smaller thrombi both in length and weight with less platelet accumulation as a percentage of the total thrombus area. During the initiation of thrombosis at 6 hours post-stenosis, Slc44a2-/- mice also had smaller thrombi both in length and weight, with circulating platelets remaining elevated in Slc44a2-/- animals. Platelet activation and aggregation under both static- and venous and arterial shear conditions were normal for blood from Slc44a2-/- mice.

CONCLUSIONS

These studies corroborate the original GWAS findings and establish a contributing role for SLC44A2 during the initiation of VT, with indications that this may be related to platelet-neutrophil interaction. The precise mechanism however remains elusive and warrants further investigation.

Loss of Endothelial Glycocalyx Hyaluronan Impairs Endothelial Stability and Adaptive Vascular Remodeling After Arterial Ischemia

We recently reported that loss of hyaluronan (HA) from the endothelial glycocalyx leads to loss of vessel stability in specific microcirculatory vascular beds. Here we hypothesized that such derangements in the glycocalyx may also impair the adaptive response to vascular ischemia. Endothelial specific conditional hyaluronan synthase 2-KO (Has2-cKO) mice revealed reduced endothelial HA expression and lower hindlimb perfusion at baseline compared to control mice. After a single ligation of the common femoral artery in these mice, we observed dysregulated angiogenesis in the gastrocnemius muscle which did not restore capillary perfusion. Mechanistically, decreased endothelial binding of the pericyte-derived molecule angiopoietin1 (Ang1) could be observed in the Has2-cKO mouse. In vitro angiogenesis assays with an endothelial cell-pericyte coculture confirmed such disturbed Ang1-TIE2 signaling resulting in excessive angiogenesis upon loss of HA. These data could be of relevance to diabetes patients, where we confirm loss of endothelial HA in the microcirculation of muscle tissue, indicating that this may contribute to the known disturbed adaptation to ischemia in these patients. In summary, loss of endothelial HA results in impaired microvascular perfusion and endothelial stability in ischemic gastrocnemius muscle. Endothelial HA is a potential target to improve angiogenic therapy in diabetic patients with critical limb ischemia.

Targeting the RNA-Binding Protein QKI in Myeloid Cells Ameliorates Macrophage-Induced Renal Interstitial Fibrosis

In the pathophysiologic setting of acute and chronic kidney injury, the excessive activation and recruitment of blood-borne monocytes prompts their differentiation into inflammatory macrophages, a process that leads to progressive glomerulosclerosis and interstitial fibrosis. Importantly, this differentiation of monocytes into macrophages requires the meticulous coordination of gene expression at both the transcriptional and post-transcriptional level. The transcriptomes of these cells are ultimately determined by RNA-binding proteins such as QUAKING (QKI), that define their pre-mRNA splicing and mRNA transcript patterns. Using two mouse models, namely (1) quaking viable mice (qk^v) and (2) the conditional deletion in the myeloid cell lineage using the lysozyme 2-Cre (QKI^{FL/FL;LysM-Cre} mice), we demonstrate that the abrogation of QKI expression in the myeloid cell lineage reduces macrophage infiltration following kidney injury induced by unilateral urethral obstruction (UUO). The qk^v and QKI^{FL/FL;LysM-Cre} mice both showed significant diminished interstitial collagen deposition and fibrosis in the UUO-damaged kidney, as compared to wild-type littermates. We show that macrophages isolated from QKI^{FL/FL;LysM-Cre} mice are associated with defects in pre-mRNA splicing. Our findings demonstrate that reduced expression of the alternative splice regulator QKI in the cells of myeloid lineage attenuates renal interstitial fibrosis, suggesting that inhibition of this splice regulator may be of therapeutic value for certain kidney diseases.

Development of Macrocycle Kinase Inhibitors for ALK2 Using Fibrodysplasia Ossificans Progressiva-Derived Endothelial Cells

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare congenital form of heterotopic ossification (HO), caused by heterozygous mutations in the activin A type I receptor (ACVR1), that encodes the bone morphogenetic protein (BMP) type I receptor ALK2. These mutations enable ALK2 to induce downstream signaling in response to activins, thereby turning them into bone-inducing agents. To date, there is no cure for FOP. The further development of FOP patient-derived models may contribute to the discovery of novel biomarkers and therapeutic approaches. Nevertheless, this has traditionally been a challenge, as biopsy sampling often triggers HO. We have characterized peripheral blood-derived endothelial colony-forming cells (ECFCs) from three independent FOP donors as a new model for FOP. FOP ECFCs are prone to undergo endothelial-to-mesenchymal transition and exhibit increased ALK2 downstream signaling and subsequent osteogenic differentiation upon stimulation with activin A. Moreover, we have identified a new class of small molecule macrocycles with potential activity against ALK2 kinase. Finally, using FOP ECFCs, we have selected OD36 and OD52 as potent inhibitors with excellent kinase selectivity profiles that potently antagonize mutant ALK2 signaling and osteogenic differentiation. We expect that these results will contribute to the development of novel ALK2 clinical candidates for the treatment of FOP. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Decreased Expression of Vascular Endothelial Growth Factor Receptor 1 Contributes to the Pathogenesis of Hereditary Hemorrhagic Telangiectasia Type 2

BACKGROUND

Hereditary Hemorrhagic Telangiectasia type 2 (HHT2) is an inherited genetic disorder characterized by vascular malformations and hemorrhage. HHT2 results from ACVRL1 haploinsufficiency, the remaining wild-type allele being unable to contribute sufficient protein to sustain endothelial cell function. Blood vessels function normally but are prone to respond to angiogenic stimuli, leading to the development of telangiectasic lesions that can bleed. How ACVRL1 haploinsufficiency leads to pathological angiogenesis is unknown.

METHODS

We took advantage of Acvrl1^+/- mutant mice that exhibit HHT2 vascular lesions and focused on the neonatal retina and the airway system after Mycoplasma pulmonis infection, as physiological and pathological models of angiogenesis, respectively. We elucidated underlying disease mechanisms in vitro by generating Acvrl1^+/- mouse embryonic stem cell lines that underwent sprouting angiogenesis and performed genetic complementation experiments. Finally, HHT2 plasma samples and skin biopsies were analyzed to determine whether the mechanisms evident in mice are conserved in humans.

RESULTS

Acvrl1^+/- retinas at postnatal day 7 showed excessive angiogenesis and numerous endothelial "tip cells" at the vascular front that displayed migratory defects. Vascular endothelial growth factor receptor 1 (VEGFR1; Flt-1) levels were reduced in Acvrl1^+/- mice and HHT2 patients, suggesting similar mechanisms in humans. In sprouting angiogenesis, VEGFR1 is expressed in stalk cells to inhibit VEGFR2 (Flk-1, KDR) signaling and thus limit tip cell formation. Soluble VEGFR1 (sVEGFR1) is also secreted, creating a VEGF gradient that promotes orientated sprout migration. Acvrl1^+/- embryonic stem cell lines recapitulated the vascular anomalies in Acvrl1^+/- (HHT2) mice. Genetic insertion of either the membrane or soluble form of VEGFR1 into the ROSA26 locus of Acvrl1^+/- embryonic stem cell lines prevented the vascular anomalies, suggesting that high VEGFR2 activity in Acvrl1^+/- endothelial cells induces HHT2 vascular anomalies. To confirm our hypothesis, Acvrl1^+/- mice were infected by Mycoplasma pulmonis to induce sustained airway inflammation. Infected Acvrl1^+/- tracheas showed excessive angiogenesis with the formation of multiple telangiectases, vascular defects that were prevented by VEGFR2 blocking antibodies.

CONCLUSIONS

Our findings demonstrate a key role of VEGFR1 in HHT2 pathogenesis and provide mechanisms explaining why HHT2 blood vessels respond abnormally to angiogenic signals. This supports the case for using anti-VEGF therapy in HHT2.

Hypercholesterolemia affects cardiac function, infarct size and inflammation in APOE*3-Leiden mice following myocardial ischemia-reperfusion injury

Background

Hypercholesterolemia is a major risk factor for ischemic heart disease including acute myocardial infarction. However, long-term effects of hypercholesterolemia in a rodent myocardial ischemia-reperfusion injury model are unknown. Therefore, the effects of diet-induced hypercholesterolemia on cardiac function and remodeling were investigated up to eight weeks after myocardial ischemia-reperfusion (MI-R) injury which was induced in either normocholesterolemic (NC-MI) or hypercholesterolemic (HC-MI) APOE*3-Leiden mice.

Methods

Left ventricular (LV) dimensions were serially assessed using parasternal long-axis echocardiography followed by LV pressure-volume measurements. Subsequently, infarct size and the inflammatory response were analyzed by histology and fluorescence-activated cell sorting (FACS) analysis.

Results

Intrinsic LV function eight weeks after MI-R was significantly impaired in HC-MI compared to NC-MI mice as assessed by end-systolic pressure, dP/dt_MAX, and -dP/dt_MIN. Paradoxically, infarct size was significantly decreased in HC-MI compared to NC-MI mice, accompanied by an increased wall thickness. Hypercholesterolemia caused a pre-ischemic peripheral monocytosis, in particular of Ly-6C^hi monocytes whereas accumulation of macrophages in the ischemic-reperfused myocardium of HC-MI mice was decreased.

Conclusion

Diet-induced hypercholesterolemia caused impaired LV function eight weeks after MI-R injury despite a reduced post-ischemic infarct size. This was preceded by a pre-ischemic peripheral monocytosis, while there was a suppressed accumulation of inflammatory cells in the ischemic-reperfused myocardium after eight weeks. This experimental model using hypercholesterolemic APOE*3-Leiden mice exposed to MI-R seems suitable to study novel cardioprotective therapies in a more clinically relevant animal model.

Platelet Adhesion to Collagen in Subtypes of Type I von Willebrand’s Disease Is Dependent on Platelet von Willebrand Factor

Von Willebrand’s disease type I, characterized by low levels of factor VIII coagulant activity (VTII :C), von Willebrand factor antigen (vWF:Ag) and ristocetin cofactor activity (RiCof) (1), can be subdivided on the basis of platelet von Willebrand factor into subtype platelet normal, platelet discordant, and platelet low (2). We have investigated the contribution of platelet von Willebrand factor in these various subtypes to platelet adhesion using the rectangular perfusion chamber of Sakariassen et al. (3) with fibrillar collagen or a fibroblast matrix as adhesive surfaces. Platelet adhesion to fibrillar collagen was decreased in all subtypes of von Willebrand’s disease, but not as low as in severe von Willebrand’s disease. A close correlation was observed between platelet adhesion to collagen and plasma vWF:Ag in severe von Willebrand’s disease, subtype platelet low, subtype platelet discordant, and normal controls. The platelet adhesion in subtype platelet normal was higher than expected from the plasma vWF: Ag level. Perfusions in which washed platelets were added to a human albumin solution together with red blood cells gave similar adhesion values in subtype platelet normal and normal controls; adhesion was decreased in subtype platelet discordant, and the lowest values were found in subtype platelet low and in severe von Willebrand’s disease. These data indicate that platelet von Willebrand factor may contribute to platelet adhesion, when plasma von Willebrand factor is low. Perfusion studies over a fibroblast matrix gave similar low adhesion values for subtype platelet low and platelet normal, indicating that the contribution of platelet von Willebrand factor can only be observed on a strongly activating surface such as fibrillar collagen.

Acute and chronic effects of treatment with mesenchymal stromal cells on LPS-induced pulmonary inflammation, emphysema and atherosclerosis development

BACKGROUND

COPD is a pulmonary disorder often accompanied by cardiovascular disease (CVD), and current treatment of this comorbidity is suboptimal. Systemic inflammation in COPD triggered by smoke and microbial exposure is suggested to link COPD and CVD. Mesenchymal stromal cells (MSC) possess anti-inflammatory capacities and MSC treatment is considered an attractive treatment option for various chronic inflammatory diseases. Therefore, we investigated the immunomodulatory properties of MSC in an acute and chronic model of lipopolysaccharide (LPS)-induced inflammation, emphysema and atherosclerosis development in APOE*3-Leiden (E3L) mice.

METHODS

Hyperlipidemic E3L mice were intranasally instilled with 10 μg LPS or vehicle twice in an acute 4-day study, or twice weekly during 20 weeks Western-type diet feeding in a chronic study. Mice received 0.5x106 MSC or vehicle intravenously twice after the first LPS instillation (acute study) or in week 14, 16, 18 and 20 (chronic study). Inflammatory parameters were measured in bronchoalveolar lavage (BAL) and lung tissue. Emphysema, pulmonary inflammation and atherosclerosis were assessed in the chronic study.

RESULTS

In the acute study, intranasal LPS administration induced a marked systemic IL-6 response on day 3, which was inhibited after MSC treatment. Furthermore, MSC treatment reduced LPS-induced total cell count in BAL due to reduced neutrophil numbers. In the chronic study, LPS increased emphysema but did not aggravate atherosclerosis. Emphysema and atherosclerosis development were unaffected after MSC treatment.

CONCLUSION

These data show that MSC inhibit LPS-induced pulmonary and systemic inflammation in the acute study, whereas MSC treatment had no effect on inflammation, emphysema and atherosclerosis development in the chronic study.

Systemic Monocyte Chemotactic Protein-1 Inhibition Modifies Renal Macrophages and Restores Glomerular Endothelial Glycocalyx and Barrier Function in Diabetic Nephropathy

Inhibition of monocyte chemotactic protein-1 (MCP-1) with the Spiegelmer emapticap pegol (NOX-E36) shows long-lasting albuminuria-reducing effects in diabetic nephropathy. MCP-1 regulates inflammatory cell recruitment and differentiation of macrophages. Because the endothelial glycocalyx is also reduced in diabetic nephropathy, we hypothesized that MCP-1 inhibition restores glomerular barrier function through influencing macrophage cathepsin L secretion, thus reducing activation of the glycocalyx-degrading enzyme heparanase. Four weeks of treatment of diabetic Apoe knockout mice with the mouse-specific NOX-E36 attenuated albuminuria without any change in systemic hemodynamics, despite persistent loss of podocyte function. MCP-1 inhibition, however, increased glomerular endothelial glycocalyx coverage, with preservation of heparan sulfate. Mechanistically, both glomerular cathepsin L and heparanase expression were reduced. MCP-1 inhibition resulted in reduced CCR2-expressing Ly6C^hi monocytes in the peripheral blood, without affecting overall number of kidney macrophages at the tissue level. However, the CD206⁺/Mac3⁺ cell ratio, as an index of presence of anti-inflammatory macrophages, increased in diabetic mice after treatment. Functional analysis of isolated renal macrophages showed increased release of IL-10, whereas tumor necrosis factor and cathepsin L release was reduced, further confirming polarization of tissue macrophages toward an anti-inflammatory phenotype during mouse-specific NOX-E36 treatment. We show that MCP-1 inhibition restores glomerular endothelial glycocalyx and barrier function and reduces tissue inflammation in the presence of ongoing diabetic injury, suggesting a therapeutic potential for NOX-E36 in diabetic nephropathy.

Clinical-Grade Isolated Human Kidney Perivascular Stromal Cells as an Organotypic Cell Source for Kidney Regenerative Medicine

Mesenchymal stromal cells (MSCs) are immunomodulatory and tissue homeostatic cells that have shown beneficial effects in kidney diseases and transplantation. Perivascular stromal cells (PSCs) identified within several different organs share characteristics of bone marrow‐derived MSCs (BM‐MSCs). These PSCs may also possess tissue‐specific properties and play a role in local tissue homeostasis. We hypothesized that human kidney‐derived PSCs (hkPSCs) would elicit improved kidney repair in comparison with BM‐MSCs. Here we introduce a novel, clinical‐grade isolation method of hkPSCs from cadaveric kidneys by enriching for the perivascular marker, NG2. hkPSCs show strong transcriptional similarities to BM‐MSCs but also show organotypic expression signatures, including the HoxD10 and HoxD11 nephrogenic transcription factors. Comparable to BM‐MSCs, hkPSCs showed immunosuppressive potential and, when cocultured with endothelial cells, vascular plexus formation was supported, which was specifically in the hkPSCs accompanied by an increased NG2 expression. hkPSCs did not undergo myofibroblast transformation after exposure to transforming growth factor‐β, further corroborating their potential regulatory role in tissue homeostasis. This was further supported by the observation that hkPSCs induced accelerated repair in a tubular epithelial wound scratch assay, which was mediated through hepatocyte growth factor release. In vivo, in a neonatal kidney injection model, hkPSCs reintegrated and survived in the interstitial compartment, whereas BM‐MSCs did not show this potential. Moreover, hkPSCs gave protection against the development of acute kidney injury in vivo in a model of rhabdomyolysis‐mediated nephrotoxicity. Overall, this suggests a superior therapeutic potential for the use of hkPSCs and their secretome in the treatment of kidney diseases. Stem Cells Translational Medicine2017;6:405–418

Abstract 47: Quaking Post-Transcriptionally Promotes Differentiation of Monocytes Into Pro-Atherogenic Macrophages by Controling Pre-mRNA Splicing and Gene Expression

Aim: Atherosclerosis is accelerated by excessive monocyte recruitment, influx and differentiation into pro-inflammatory macrophages. While the genome-wide mRNA expression profiles of human monocytes and pro-inflammatory macrophages are well-established, their transcriptomes are ultimately defined by factors, such as RNA-binding proteins, that modulate pre-mRNA splicing patterns and mRNA transcript abundance. This prompted us to investigate the role of the RNA-binding protein Quaking in regulating global changes in pre-mRNA splicing and mature mRNA expression as human monocytes acquire the pro-inflammatory macrophage identity.

Methods: We employed RNA-sequencing and splicing-sensitive microarrays to determine genome-wide changes in pre-mRNA splicing and mRNA expression upon conversion of human monocytes into pro-inflammatory macrophages, including those derived from a unique Quaking haploinsufficient patient.

Results: Using laser-capture micro-dissection and immunohistochemistry, we discovered that expression levels of Quaking mRNA and protein are low in monocytes of early human atherosclerotic lesions, but abundant in macrophages of advanced plaques. Depletion of Quaking protein using both siRNA and GapmeR technology significantly impaired monocyte adhesion and migration; delayed differentiation into pro-inflammatory macrophages while maintaining the capacity to adopt the anti-inflammatory phenotype; and diminished foam cell formation in vitro and in vivo. RNA-sequencing and microarray analysis of human monocyte and macrophage transcriptomes revealed striking changes in Quaking-dependent pre-mRNA splicing and mRNA transcript levels, with gene ontology analyses identifying an enrichment in transcripts involved in cellular migration and lipid metabolism. Furthermore, these studies uncovered common as well as novel alternatively spliced transcripts with unknown biological functions in monocytes and macrophages.

Conclusions: Our studies illustrate a central role for Quaking in post-transcriptionally guiding pro-inflammatory macrophage identity and function.

The Role of microRNA-126 in Vascular Homeostasis

MicroRNAs are negative regulators of gene expression that have been shown to be essential elements in the coordination of complex regulatory pathways. One of these short non-coding RNAs, microRNA-126, is highly enriched in the vascular endothelium and was shown to play distinct roles in angiogenesis, vasculogenesis and endothelial inflammation. Abrogation of this microRNA leads to severe complications in the response in vascular development as well as vital repair mechanisms carried out by endothelial cells. Interestingly, recent data suggest that the homeostatic role of microRNA-126 may reach far beyond its endothelial functions as this microRNA was also found to be present in cells of the hematopoietic system and in microvesicles or 'free-form' in the periphery. MicroRNA-126 is controlling the fate and/or function of a variety of cells differentiating from the hematopoietic lineage, including megakaryocytes and erythrocytes. Recent studies identified circulating microRNA-126 as a biomarker for myocardial injury and vascular damage in diabetes. Furthermore, reports have suggested a protective role of circulating microRNA-126 in murine models of organ ischemia. Here, we review current insights in the role of microRNA-126 in vascular homeostasis and conclude that this microRNA may serve to integrate and facilitate both local as well as systemic functions in vascular maintenance and repair.

The RNA-binding protein quaking maintains endothelial barrier function and affects VE-cadherin and β-catenin protein expression

Proper regulation of endothelial cell-cell contacts is essential for physiological functioning of the endothelium. Interendothelial junctions are actively involved in the control of vascular leakage, leukocyte diapedesis, and the initiation and progression of angiogenesis. We found that the RNA-binding protein quaking is highly expressed by endothelial cells, and that its expression was augmented by prolonged culture under laminar flow and the transcription factor KLF2 binding to the promoter. Moreover, we demonstrated that quaking directly binds to the mRNA of VE-cadherin and β-catenin and can induce mRNA translation mediated by the 3′UTR of these genes. Reduced quaking levels attenuated VE-cadherin and β-catenin expression and endothelial barrier function in vitro and resulted in increased bradykinin-induced vascular leakage in vivo. Taken together, we report that quaking is essential in maintaining endothelial barrier function. Our results provide novel insight into the importance of post-transcriptional regulation in controlling vascular integrity.

Abstract 8: RNA-binding Protein Quaking Maintains Endothelial Barrier Function Through β-catenin and VE-cadherin

Endothelial barrier function plays a major role in the onset of atherosclerosis. This barrier is determined largely by adherens junctions. Remarkably little is known about their regulation at the post[[Unable to Display Character: &#8208;]]transcriptional level. We find that the RNA-binding protein Quaking (QKI), known for its function in embryonic blood vessel formation, is highly expressed in quiescent adult endothelial cells (EC) in vivo. In vitro, EC displayed increased levels of QKI when cultured under laminar atheroprotective flow. Using KLF2 overexpression and a human QKI promoter reporter gene, we found that KLF2 mediates this increase in QKI expression.

Subsequently we aimed to investigate the role of QKI in EC vascular integrity. Silencing of QKI markedly impaired (0.65 fold ±0.13; p<0.05) the capacity to form a high resistance endothelial monolayer, as measured using Electric cell-substrate impedance sensing. To confirm a role for QKI in maintaining EC barrier function in vivo, we measured Bradykinin-induced vascular leakage in QKI viable mice (QKIv), which express decreased levels of the QKI protein. Indeed, QKIv mice displayed a 20% (p<0.05) increase in extravascular accumulation of Evans blue-labeled albumin compared to wild type littermates. Interestingly, the mRNA of both β-catenin and VE-cadherin, the prime adhesion proteins in EC adherens junctions, contain conserved QKI-binding sites. Moreover the targeted reduction of QKI resulted in a reduction of β-catenin and VE-cadherin protein expression. Importantly, we identified a direct role for QKI in regulating mRNA biology of β-catenin and VE-cadherin, as RNA immunoprecipitation and luciferase-reporter assays revealed that QKI can directly bind to the mRNA and induces transcript translation, respectively. This effects was perturbed upon reduced QKI expression.

In conclusion, we show that QKI functions as a critical regulator of β-catenin and VE-cadherin in endothelial cells, and the modulation of QKI expression affects endothelial monolayer integrity, in vitro and in vivo. These studies provide novel insight into the importance of post-transcriptional regulation of components of the endothelial adherens junction, and may have wide ranging implications for the preservation of vascular integrity in disease.

Abstract 217: Quaking Post-Transcriptionally Guides Monocyte Adhesion and Differentiation into the Pro-Inflammatory Macrophage

A hallmark of inflammatory diseases is the excessive recruitment and influx of monocytes to sites of tissue damage and their ensuing differentiation into macrophages. Numerous stimuli are known to induce new transcription necessary for macrophage identity, but post-transcriptional control of human macrophage differentiation is less well understood. Here, we detail our discovery that levels of the RNA-binding protein Quaking (QKI) are low in monocytes of early atherosclerotic lesions, but abundant in macrophages of advanced plaques. Specific depletion of QKI protein impaired monocyte adhesion, migration and differentiation into macrophages, and lesion formation. RNA-seq and microarray analysis of human monocyte and macrophage transcriptomes, including those of a unique QKI haploinsufficient patient, reveal developmental changes in RNA levels and alternative splicing of RNA transcripts enriched in QKI-bound sequence elements. The importance of these transcripts and requirement for QKI during differentiation illustrates a central role for QKI in post-transcriptionally guiding macrophage identity and function. These studies implicate QKI as a novel target for therapeutic intervention in inflammatory diseases.

TLR4 accessory molecule RP105 (CD180) regulates monocyte-driven arteriogenesis in a murine hind limb ischemia model

AIMS

We investigated the role of the TLR4-accessory molecule RP105 (CD180) in post-ischemic neovascularization, i.e. arteriogenesis and angiogenesis. TLR4-mediated activation of pro-inflammatory Ly6Chi monocytes is crucial for effective neovascularization. Immunohistochemical analyses revealed that RP105+ monocytes are present in the perivascular space of remodeling collateral arterioles. As RP105 inhibits TLR4 signaling, we hypothesized that RP105 deficiency would lead to an unrestrained TLR4-mediated inflammatory response and hence to enhanced blood flow recovery after ischemia.

METHODS AND RESULTS

RP105-/- and wild type (WT) mice were subjected to hind limb ischemia and blood flow recovery was followed by Laser Doppler Perfusion Imaging. Surprisingly, we found that blood flow recovery was severely impaired in RP105-/- mice. Immunohistochemistry showed that arteriogenesis was reduced in these mice compared to the WT. However, both in vivo and ex vivo analyses showed that circulatory pro-arteriogenic Ly6Chi monocytes were more readily activated in RP105-/- mice. FACS analyses showed that Ly6Chi monocytes became activated and migrated to the affected muscle tissues in WT mice following induction of hind limb ischemia. Although Ly6Chi monocytes were readily activated in RP105-/- mice, migration into the ischemic tissues was hampered and instead, Ly6Chi monocytes accumulated in their storage compartments, bone marrow and spleen, in RP105-/- mice.

CONCLUSIONS

RP105 deficiency results in an unrestrained inflammatory response and monocyte over-activation, most likely due to the lack of TLR4 regulation. Inappropriate, premature systemic activation of pro-inflammatory Ly6Chi monocytes results in reduced infiltration of Ly6Chi monocytes in ischemic tissues and in impaired blood flow recovery.

Abstract 168: Splice Variants of Tissue Factor Determine the Coagulant State of Endothelial Cells and Modulate Vascular Stabilization/Regression

Introduction: Recruitment of pericytes (PC), critical to microvascular maturation, requires deposition of basement membrane proteins such as von Willebrand factor (vWF). Loss of PCs ultimately leads to vessel regression and rarefaction.

Hypothesis: Splice variants of tissue factor (TF) stabilize the vasculature by supporting EC-PC interactions.

Results: We determined that alternatively spliced TF (asTF) resides in Weibel Palade bodies (WPB) of ECs. Overexpression of KLF-2 enhanced asTF protein levels in WPBs. In confluent EC monolayers, asTF was deposited into the extracellular matrix (ECM). In assays employing vascular plexus remodelling on 3D-basement membrane and purified recombinant asTF or full-length TF (flTF), only asTF improved EC-PC interactions. At sites of low KLF-2 expression (low or turbulent flow), total TF mRNA was diminished, leading to low asTF expression. However, upon EC activation by TNFα, total TF mRNA levels rapidly increased and TF protein expression shifted from the ECM-deposited asTF to luminally expressed flTF. Interestingly, flTF-driven EC conversion to a procoagulant state was associated with the release of vWF and asTF from WPBs, depleting the intracellular depots from these proteins. Immunohistochemical staining of kidney specimens of human living donors confirmed that asTF was present at high levels in WPBs of microvascular endothelium. Moreover, after 45 minutes of reperfusion of the transplanted kidney, asTF- and vWF-staining was markedly reduced, consistent with their release from WPB following an inflammatory insult.

Conclusion: We show for the first time that quiescent, KLF-2 expressing ECs predominantly generate non-coagulant asTF, which is stored in WPBs and serves to stabilize the microvasculature by supporting EC-PC interactions. In contrast, in low-flow zones or sites with disturbed flow (e.g. at bifurcations), KLF-2 is downregulated, leading to decreased production of asTF and impaired stabilization of the vasculature. During inflammation, acute perturbation of ECs (e.g. exposure to TNFα) is associated with downregulation of KLF-2 and a post-transcriptionally regulated increase in the production of flTF, resulting in a pro-coagulant phenotype and loss of EC-PC interactions.

Abstract 513: Endothelial Barrier Function is Maintained by the RNA-Binding Protein Quaking

Endothelial barrier function plays a major role in the onset of atherosclerosis. This barrier is maintained largely by adherens junctions. Remarkably, little is known about their regulation at the post–transcriptional level. We found that the RNA-binding protein Quaking (QKI), known for its function in embryonic blood vessel formation, is highly expressed in quiescent endothelial cells (EC) in vivo. In vitro, EC displayed increased levels of QKI when cultured under laminar, atheroprotective flow. Using KLF2 overexpression and a human QKI promoter reporter gene, we found that KLF2 mediates this increase in QKI expression.

Subsequently, we aimed to investigate the role of QKI in EC vascular integrity. Interestingly, the mRNA of VE-cadherin, the prime adhesion protein in EC adherens junctions, contains a conserved QKI-binding site. We identified that the targeted reduction of QKI results in a reduction of VE-cadherin expression and organization at the cell periphery. These studies revealed a direct role for QKI in regulating VE-cadherin mRNA biology, as RNA-immunoprecipitation and luciferase-reporter assays revealed that QKI can directly bind to the VE-cadherin mRNA and induce transcript translation (4 fold ± 0.4; p<0.01), respectively. This effect was perturbed when the QKI-binding site was mutated. These results suggest that QKI acts to enhance barrier function. Overexpression of QKI markedly increased the capacity to form a high resistance endothelial monolayer (1.3 fold ± 0.96), while silencing of QKI markedly impaired EC barrier function (0.65 fold ± 0.13; p<0.05). To validate in vivo, we measured Bradykinin-induced vascular leakage in QKI viable mice (QKIv), which express decreased levels of the QKI protein. Indeed, QKIv mice displayed a 20% (p<0.05) increase in extravascular accumulation of Evans blue-labeled albumin compared to WT littermates.

In conclusion, we show that QKI functions as a critical regulator of VE-cadherin, and the modulation of QKI expression affects endothelial monolayer integrity. These studies provide novel insight into the importance of post-transcriptional regulation on endothelial barrier function, and may have wide ranging implications for the preservation of vascular integrity in disease.

Hematopoietic microRNA-126 protects against renal ischemia/reperfusion injury by promoting vascular integrity

Ischemia/reperfusion injury (IRI) is a central phenomenon in kidney transplantation and AKI. Integrity of the renal peritubular capillary network is an important limiting factor in the recovery from IRI. MicroRNA-126 (miR-126) facilitates vascular regeneration by functioning as an angiomiR and by modulating mobilization of hematopoietic stem/progenitor cells. We hypothesized that overexpression of miR-126 in the hematopoietic compartment could protect the kidney against IRI via preservation of microvascular integrity. Here, we demonstrate that hematopoietic overexpression of miR-126 increases neovascularization of subcutaneously implanted Matrigel plugs in mice. After renal IRI, mice overexpressing miR-126 displayed a marked decrease in urea levels, weight loss, fibrotic markers, and injury markers (such as kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin). This protective effect was associated with a higher density of the peritubular capillary network in the corticomedullary junction and increased numbers of bone marrow-derived endothelial cells. Hematopoietic overexpression of miR-126 increased the number of circulating Lin(-)/Sca-1(+)/cKit(+) hematopoietic stem and progenitor cells. Additionally, miR-126 overexpression attenuated expression of the chemokine receptor CXCR4 on Lin(-)/Sca-1(+)/cKit(+) cells in the bone marrow and increased renal expression of its ligand stromal cell-derived factor 1, thus favoring mobilization of Lin(-)/Sca-1(+)/cKit(+) cells toward the kidney. Taken together, these results suggest overexpression of miR-126 in the hematopoietic compartment is associated with stromal cell-derived factor 1/CXCR4-dependent vasculogenic progenitor cell mobilization and promotes vascular integrity and supports recovery of the kidney after IRI.

Silencing of miRNA-126 in kidney ischemia reperfusion is associated with elevated SDF-1 levels and mobilization of Sca-1+/Lin- progenitor cells

Integrity of the capillary network in the kidney is essential in the recovery from ischemia/ reperfusion injury (IRI), a phenomenon central to kidney transplantation and acute kidney injury. MicroRNA- 126 (miR-126) is known to be important in maintaining vascular homeostasis by facilitating vascular regeneration and modulating the mobilization of vascular progenitor cells. Stromal cell-derived factor 1 (SDF-1), important in the mobilization of vascular progenitor cells, is a direct target of miR-126 and modulation of miR-126 was previously shown to affect the number of circulating Sca-1(+)/Lin(-) vascular progenitor cells in a mouse model for hind limb ischemia. Here, we assessed the in vivo contribution of miR-126 to progenitor cell mobilization and kidney function following IRI in mice. A three day follow up of blood urea levels following kidney IRI demonstrated that systemic antagomir silencing of miR-126 did not impact the loss or subsequent restoration of kidney function. However, whole kidney lysates displayed elevated gene expression levels of Sdf-1, Vegf-A and eNOS after IRI as a result of systemic silencing of miR-126. Furthermore, FACS-analysis on whole blood three days after surgery revealed a marked up regulation of the number of circulating Sca-1(+)/Lin(-) progenitor cells in the antagomir-126 treated mice, in an ischemia dependent manner. Our data indicate that silencing of miR-126 can enhance renal expression of Sdf-1 after IRI, leading to the mobilization of vascular progenitor cells into the circulation.

Quaking, an RNA-binding protein, is a critical regulator of vascular smooth muscle cell phenotype

RATIONALE

RNA-binding proteins are critical post-transcriptional regulators of RNA and can influence pre-mRNA splicing, RNA localization, and stability. The RNA-binding protein Quaking (QKI) is essential for embryonic blood vessel development. However, the role of QKI in the adult vasculature, and in particular in vascular smooth muscle cells (VSMCs), is currently unknown.

OBJECTIVE

We sought to determine the role of QKI in regulating adult VSMC function and plasticity.

METHODS AND RESULTS

We identified that QKI is highly expressed by neointimal VSMCs of human coronary restenotic lesions, but not in healthy vessels. In a mouse model of vascular injury, we observed reduced neointima hyperplasia in Quaking viable mice, which have decreased QKI expression. Concordantly, abrogation of QKI attenuated fibroproliferative properties of VSMCs, while potently inducing contractile apparatus protein expression, rendering noncontractile VSMCs with the capacity to contract. We identified that QKI localizes to the spliceosome, where it interacts with the myocardin pre-mRNA and regulates the splicing of alternative exon 2a. This post-transcriptional event impacts the Myocd_v3/Myocd_v1 mRNA balance and can be modulated by mutating the quaking response element in exon 2a of myocardin. Furthermore, we identified that arterial damage triggers myocardin alternative splicing and is tightly coupled with changes in the expression levels of distinct QKI isoforms.

CONCLUSIONS

We propose that QKI is a central regulator of VSMC phenotypic plasticity and that intervention in QKI activity can ameliorate pathogenic, fibroproliferative responses to vascular injury.

Renal ischemia-reperfusion induces a dysbalance of angiopoietins, accompanied by proliferation of pericytes and fibrosis

Endothelial cells (ECs) are highly susceptible to hypoxia and easily affected upon ischemia-reperfusion (I/R) during renal transplantation. Pericytes and angiopoeitins play important role in modulating EC function. In the present study, we investigate the effect of renal I/R on the dynamics of angiopoietin expression and its association with pericytes and fibrosis development. Male Lewis rats were subjected to unilateral renal ischemia for 45 min followed by removal of the contralateral kidney. Rats were killed at different time points after reperfusion. Endothelial integrity (RECA-1), pericytes [platelet-derived growth factor receptor-β (PDGFR-β)], angiopoietin-2 (Ang-2)/angiopoietin-1 (Ang-1) expression, and interstitial collagen deposition (Sirius red and α-smooth muscle actin) were assessed using immunohistochemistry and RT-PCR. Our study shows an increase in protein expression of Ang-2 starting at 5 h and remaining elevated up to 72 h, with a consequently higher Ang-2/Ang-1 ratio after renal I/R (P < 0.05 at 48 h). This was accompanied by an increase in protein expression of the pericytic marker PDGFR-β and a loss of ECs (both at 72 h after I/R, P < 0.05). Nine weeks after I/R, when renal function was restored, we observed normalization of the Ang-2/Ang-1 ratio and PDGFR-β expression and increase in cortical ECs, which was accompanied by fibrosis. Renal I/R induces a dysbalance of Ang-2/Ang-1 accompanied by proliferation of pericytes, EC loss, and development of fibrosis. The Ang-2/Ang-1 balance was reversed to baseline at 9 wk after renal I/R, which coincided with restoration of cortical ECs and pericytes. Our findings suggest that angiopoietins and pericytes play an important role in renal microvascular remodeling and development of fibrosis.

Lysine acetyltransferase PCAF is a key regulator of arteriogenesis

OBJECTIVE

Therapeutic arteriogenesis, that is, expansive remodeling of preexisting collaterals, using single-action factor therapies has not been as successful as anticipated. Modulation of factors that act as a master switch for relevant gene programs may prove more effective. Transcriptional coactivator p300-CBP-associated factor (PCAF) has histone acetylating activity and promotes transcription of multiple inflammatory genes. Because arteriogenesis is an inflammation-driven process, we hypothesized that PCAF acts as multifactorial regulator of arteriogenesis.

APPROACH AND RESULTS

After induction of hindlimb ischemia, blood flow recovery was impaired in both PCAF(-/-) mice and healthy wild-type mice treated with the pharmacological PCAF inhibitor Garcinol, demonstrating an important role for PCAF in arteriogenesis. PCAF deficiency reduced the in vitro inflammatory response in leukocytes and vascular cells involved in arteriogenesis. In vivo gene expression profiling revealed that PCAF deficiency results in differential expression of 3505 genes during arteriogenesis and, more specifically, in impaired induction of multiple proinflammatory genes. Additionally, recruitment from the bone marrow of inflammatory cells, in particular proinflammatory Ly6C(hi) monocytes, was severely impaired in PCAF(-/-) mice.

CONCLUSIONS

These findings indicate that PCAF acts as master switch in the inflammatory processes required for effective arteriogenesis.

Abstract 487: Aspirin Treatment Hampers the Use of Plasma MicroRNA-126 as Biomarker for the Progression of Vascular Disease

Rationale

MicroRNA-126 (miR-126) facilitates angiogenesis and regulates endothelial cell function. Recent data suggest that miR-126 can serve as a biomarker for cardiovascular disease. Although endothelial cells are enriched for miR-126, platelets also comprise a major pool of miR-126. We investigated the contribution of platelets to the level of miR-126 circulating in the plasma from patients with type 2 diabetes and how this level is affected by aspirin.

Methods & Results

In vitro platelet activation resulted in the transfer of miR-126 from the platelet- to the plasma-compartment, which was prevented by aspirin. In vivo platelet activation was studied in patients with type 2 diabetes, who exhibit disease-mediated platelet activation and are prone to develop cardiovascular disease. Platelet activation was monitored by measuring soluble P-selectin in plasma and correlated significantly with circulating levels of miR-126. Administration of aspirin to the patients in a randomized, placebo-controlled cross-over design, resulted in platelet inhibition and concomitantly reduced circulating levels of platelet-derived microRNAs including miR-126.

Conclusion

The profile of circulating miRs constitutes a fingerprint of activated platelets rather then activated endothelial cells. In particular miR-126 can be derived from activated platelets and the circulating levels of this miRNA can be markedly reduced when aspirin is used in patho-physiological conditions associated with platelet activation such as diabetes type 2. Therefore, the use of platelet inhibitors should be taken into account when using plasma-levels of miR-126 as a biomarker.

Abstract 532: The RNA-binding Protein Quaking Critically Regulates Vascular Smooth Muscle Cell Phenotype

In response to vascular injury, smooth muscle cells (VSMC) adopt a proliferative, synthetic hypocontractile phenotype. This phenotype switch is deemed instrumental in vascular remodeling in both health and disease. Here, we detail a decisive role for the RNA-binding protein Quaking (QKI) in regulating VSMC plasticity. We identified that the RNA-binding protein Quaking (QKI) is highly expressed by neointimal VSMCs of human coronary restenotic lesions, but not in healthy vessels. In a mouse model of vascular injury, we observed reduced neointima hyperplasia in Qk v mice, which have decreased QKI expression. Concordantly, abrogation of QKI attenuated fibroproliferative properties of VSMCs, while potently inducing contractile apparatus protein expression, rendering non-contractile VSMCs with the capacity to contract. We identified that QKI localizes to the spliceosome in proliferative VSMCs, where it interacts with and impacts myocardin (pre)-mRNA metabolism by mediating myocardin exon 2a exclusion. As such, in vitro and in vivo experiments indicate that the modulation of QKI expression directly influences the myocardin_v3 / myocardin_v1 mRNA balance, which could play a role in shifting the Myocardin-induced transcriptional coactivation profile following arterial damage. We propose that QKI is a central regulator of VSMC phenotypic plasticity and that intervention in QKI activity can ameliorate pathogenic, fibroproliferative responses to vascular injury.

Protease-activated receptor (PAR)2, but not PAR1, is involved in collateral formation and anti-inflammatory monocyte polarization in a mouse hind limb ischemia model

AIMS

In collateral development (i.e. arteriogenesis), mononuclear cells are important and exist as a heterogeneous population consisting of pro-inflammatory and anti-inflammatory/repair-associated cells. Protease-activated receptor (PAR)1 and PAR2 are G-protein-coupled receptors that are both expressed by mononuclear cells and are involved in pro-inflammatory reactions, while PAR2 also plays a role in repair-associated responses. Here, we investigated the physiological role of PAR1 and PAR2 in arteriogenesis in a murine hind limb ischemia model.

METHODS AND RESULTS

PAR1-deficient (PAR1-/-), PAR2-deficient (PAR2-/-) and wild-type (WT) mice underwent femoral artery ligation. Laser Doppler measurements revealed reduced post-ischemic blood flow recovery in PAR2-/- hind limbs when compared to WT, while PAR1-/- mice were not affected. Upon ischemia, reduced numbers of smooth muscle actin (SMA)-positive collaterals and CD31-positive capillaries were found in PAR2-/- mice when compared to WT mice, whereas these parameters in PAR1-/- mice did not differ from WT mice. The pool of circulating repair-associated (Ly6C-low) monocytes and the number of repair-associated (CD206-positive) macrophages surrounding collaterals in the hind limbs were increased in WT and PAR1-/- mice, but unaffected in PAR2-/- mice. The number of repair-associated macrophages in PAR2-/- hind limbs correlated with CD11b- and CD115-expression on the circulating monocytes in these animals, suggesting that monocyte extravasation and M-CSF-dependent differentiation into repair-associated cells are hampered.

CONCLUSION

PAR2, but not PAR1, is involved in arteriogenesis and promotes the repair-associated response in ischemic tissues. Therefore, PAR2 potentially forms a new pro-arteriogenic target in coronary artery disease (CAD) patients.

Aspirin treatment hampers the use of plasma microRNA-126 as a biomarker for the progression of vascular disease

AIMS

MicroRNA-126 (miR-126) facilitates angiogenesis and regulates endothelial cell function. Recent data suggest that miR-126 can serve as a biomarker for vascular disease. Although endothelial cells are enriched for miR-126, platelets also contain miR-126. In this paper, we investigated the contribution of platelets to the pool of miR-126 in plasma of patients with type 2 diabetes (DM2) and how this is affected by aspirin.

METHODS AND RESULTS

In vitro platelet activation resulted in the transfer of miR-126 from the platelet to the plasma compartment, which was prevented by aspirin. In vivo platelet activation, monitored in patients with DM2 by measuring soluble P-selectin, correlated directly with circulating levels of miR-126. The administration of aspirin resulted both in platelet inhibition and concomitantly reduced circulating levels of platelet-derived microRNAs including miR-126.

CONCLUSION

Platelets are a major source of circulating miR-126. Consequently, in patho-physiological conditions associated with platelet activation, such as diabetes type 2, the administration of aspirin may lead to reduced levels of circulating miR-126. Thus, the use of platelet inhibitors should be taken into account when using plasma levels of miR-126 as a biomarker.

Blocking toll-like receptors 7 and 9 reduces postinterventional remodeling via reduced macrophage activation, foam cell formation, and migration

OBJECTIVE

The role of toll-like receptors (TLRs) in vascular remodeling is well established. However, the involvement of the endosomal TLRs is unknown. Here, we study the effect of combined blocking of TLR7 and TLR9 on postinterventional remodeling and accelerated atherosclerosis.

METHODS AND RESULTS

In hypercholesterolemic apolipoprotein E*3-Leiden mice, femoral artery cuff placement led to strong increase of TLR7 and TLR9 presence demonstrated by immunohistochemistry. Blocking TLR7/9 with a dual antagonist in vivo reduced neointimal thickening and foam cell accumulation 14 days after surgery by 65.6% (P=0.0079). Intima/media ratio was reduced by 64.5% and luminal stenosis by 62.8%. The TLR7/9 antagonist reduced the arterial wall inflammation, with reduced macrophage infiltration, decreased cytoplasmic high-mobility group box 1 expression, and altered serum interleukin-10 levels. Stimulation of cultured macrophages with TLR7 and TLR9 ligands enhanced tumor necrosis factor-α expression, which is decreased by TLR7/9 antagonist coadministration. Additionally, the antagonist abolished the TLR7/9-enhanced low-density lipoprotein uptake. The antagonist also reduced oxidized low-density lipoprotein-induced foam cell formation, most likely not via decreased influx but via increased efflux, because CD36 expression was unchanged whereas interleukin-10 levels were higher (36.1 ± 22.3 pg/mL versus 128.9 ± 6.6 pg/mL; P=0.008).

CONCLUSIONS

Blocking TLR7 and TLR9 reduced postinterventional vascular remodeling and foam cell accumulation indicating TLR7 and TLR9 as novel therapeutic targets.

MicroRNA-126 modulates endothelial SDF-1 expression and mobilization of Sca-1(+)/Lin(-) progenitor cells in ischaemia

AIMS

MicroRNA-126 (miR-126), which is enriched in endothelial cells, plays a role in angiogenesis. Based on the seed sequence, miR-126 can also be predicted to regulate vasculogenesis by modulating the endothelial expression of stromal cell-derived factor-1 (SDF-1).

METHODS AND RESULTS

Using miR-reporter constructs, we first validated that miR-126 inhibits SDF-1 expression in endothelial cells in vitro. Next, we investigated the potential relevance of this observation with respect to the mobilization of progenitor cells. For this, we studied the migration of human CD34+ progenitor cells towards chemotactic factors present in endothelial cell-conditioned medium. Antagomir-induced silencing of miR-126 elevated SDF-1 expression by human umbilical vein endothelial cells and enhanced migration of the CD34+ cells. In a murine model of hind limb ischaemia, a striking increase in the number of circulating Sca-1(+)/Lin(-) progenitor cells in antagomir-126-treated mice was observed when compared with scramblemir-treated controls. Immunohistochemical staining of capillaries in the post-ischaemic gastrocnemius muscle of miR-126-silenced mice revealed elevated SDF-1 expressing CD31-positive capillaries, whereas a mobilizing effect of miR-126 inhibition was not detected in healthy control animals.

CONCLUSION

miR-126 can regulate the expression of SDF-1 in endothelial cells. In the context of an ischaemic event, systemic silencing of miR-126 leads to the mobilization of Sca-1(+)/Lin(-) progenitor cells into the peripheral circulation, potentially in response to elevated SDF-1 expression by endothelial cells present in the ischaemic tissue.

Hepatocyte-specific IKKβ expression aggravates atherosclerosis development in APOE*3-Leiden mice

OBJECTIVE

The liver is the key organ involved in systemic inflammation, but the relation between hepatic inflammation and atherogenesis is poorly understood. Since nuclear factor-κB (NF-κB) is a central regulator of inflammatory processes, we hypothesized that chronically enhanced hepatic NF-κB activation, through hepatocyte-specific expression of IκB kinase-β (IKKβ) (LIKK), will aggravate atherosclerosis development in APOE*3-Leiden (E3L) mice.

METHODS AND RESULTS

E3L.LIKK and E3L control littermates were fed a Western-type diet for 24 weeks. E3L.LIKK mice showed a 2.3-fold increased atherosclerotic lesion area and more advanced atherosclerosis in the aortic root with less segments without atherosclerotic lesions (11% vs. 42%), and more segments with mild (63% vs. 44%) and severe (26% vs. 14%) lesions. Expression of LIKK did not affect basal levels of inflammatory parameters, but plasma cytokine levels tended to be higher in E3L.LIKK mice after lipopolysaccharide (LPS) administration. E3L.LIKK mice showed transiently increased plasma cholesterol levels, confined to (V)LDL. This transient character resulted in a mild (+17%) increased cumulative plasma cholesterol exposure.

CONCLUSION

We conclude that selective activation of NF-κB in hepatocytes considerably promotes atherosclerosis development which is (at least partly) explained by an increased sensitivity to proinflammatory triggers and transiently increased plasma cholesterol levels.

Intracellular storage and regulated secretion of von Willebrand factor in quantitative von Willebrand disease

Several missense mutations in the von Willebrand Factor (VWF) gene of von Willebrand disease (VWD) patients have been shown to cause impaired constitutive secretion and intracellular retention of VWF. However, the effects of those mutations on the intracellular storage in Weibel-Palade bodies (WPBs) of endothelial cells and regulated secretion of VWF remain unknown. We demonstrate, by expression of quantitative VWF mutants in HEK293 cells, that four missense mutations in the D3 and CK-domain of VWF diminished the storage in pseudo-WPBs, and led to retention of VWF within the endoplasmic reticulum (ER). Immunofluorescence and electron microscopy data showed that the pseudo-WPBs formed by missense mutant C1060Y are indistinguishable from those formed by normal VWF. C1149R, C2739Y, and C2754W formed relatively few pseudo-WPBs, which were often short and sometimes round rather than cigar-shaped. The regulated secretion of VWF was impaired slightly for C1060Y but severely for C1149R, C2739Y, and C2754W. Upon co-transfection with wild-type VWF, both intracellular storage and regulated secretion of all mutants were (partly) corrected. In conclusion, defects in the intracellular storage and regulated secretion of VWF following ER retention may be a common mechanism underlying VWD with a quantitative deficiency of VWF.

Annexin A5 therapy attenuates vascular inflammation and remodeling and improves endothelial function in mice

OBJECTIVE

Annexin A5 (AnxA5) has antithrombotic, antiapoptotic, and antiinflammatory properties; we investigated its effectiveness against vascular inflammation, remodeling, and dysfunction in accelerated atherosclerosis.

METHODS AND RESULTS

AnxA5 (1 mg/kg per day or vehicle) was investigated in vascular injury models in hypercholesterolemic apolipoprotein E (ApoE)3*Leiden mice. AnxA5 treatment reduced adhesion and infiltration of leukocytes by 71% to 69% (P=0.015, P=0.031) and macrophages by 51% to 87% (P=0.014, P=0.018), as well as monocyte chemotactic protein-1 and tumor necrosis factor-α expression in a femoral artery inflammation model (perivascular cuff for 3 days), indicating reduced vascular inflammation. In a vein graft model, 28 days of AnxA5 treatment reduced vein graft thickening (48%; P=0.006) and leukocyte infiltration (46%; P=0.003). In these mice, reduced plasma concentrations of IFN-γ (-72%; P=0.040), granulocyte colony-stimulating factor (-41%; P=0.010), and macrophage inflammatory protein-1β (MIP-1β) (-66%; P=0.020) were measured, indicating reduced systemic inflammation. An in vitro endothelial cell model shows the importance of AnxA5's anticoagulant properties in reducing vascular inflammation. Endothelium-mediated dilatation in hypercholesterolemic ApoE((-/-)) mice was improved by 3 days of AnxA5 treatment, shown by improved systolic and diastolic blood pressure reductions in response to metacholine, which could be abolished by l-Nitro-Arginine-Methyl Ester (l-NAME), indicating nitric oxide involvement.

CONCLUSIONS

AnxA5 reduced local vascular and systemic inflammation and vascular remodeling and improved vascular function, indicating that it has a therapeutic potential against atherosclerotic cardiovascular diseases.

A novel urokinase receptor-targeted inhibitor for plasmin and matrix metalloproteinases suppresses vein graft disease

AIMS

Matrix metalloproteinases (MMP) and plasminogen activator (PA)/plasmin-mediated proteolysis, especially at the cell surface, play important roles in matrix degeneration and smooth muscle cell migration, which largely contributes to vein graft failure. In this study, a novel hybrid protein was designed to inhibit both protease systems simultaneously. MMP and plasmin activity were inhibited at the cell surface by this hybrid protein, consisting of the receptor-binding amino-terminal fragment (ATF) of urokinase-type PA, linked to both the tissue inhibitor of metalloproteinases (TIMP-1) and bovine pancreas trypsin inhibitor (BPTI), a potent protease inhibitor. The effect of overexpression of this protein on vein graft disease was studied.

METHODS AND RESULTS

A non-viral expression vector encoding the hybrid protein TIMP-1.ATF.BPTI was constructed and validated. Next, cultured segments of human veins were transfected with this vector. Expressing TIMP-1.ATF.BPTI in vein segments resulted in a mean 36 ± 14% reduction in neointima formation after 4 weeks. In vivo inhibition of vein graft disease by TIMP-1.ATF.BPTI is demonstrated in venous interpositions placed into carotid arteries of hypercholesterolaemic APOE*3Leiden mice. After 4 weeks, vein graft thickening was significantly inhibited in mice treated with the domains TIMP-1, ATF, or BPTI (36-49% reduction). In the TIMP-1.ATF.BPTI-treated mice, vein graft thickening was reduced by 67±4%, which was also significantly stronger when compared with the individual components.

CONCLUSION

These data provide evidence that cell surface-bound inhibition of the PA and MMP system by the hybrid protein TIMP-1.ATF.BPTI, overexpressed in distant tissues after electroporation-mediated non-viral gene transfer, is a powerful approach to prevent vein graft disease.

Antagomir-mediated silencing of endothelial cell specific microRNA-126 impairs ischemia-induced angiogenesis

MicroRNAs are negative regulators of gene expression that play a key role in cell-type specific differentiation and modulation of cell function and have been proposed to be involved in neovascularization. Previously, using an extensive cloning and sequencing approach, we identified miR-126 to be specifically and highly expressed in human endothelial cells (EC). Here, we demonstrate EC-specific expression of miR-126 in capillaries and the larger vessels in vivo. We therefore explored the potential role of miR-126 in arteriogenesis and angiogenesis. Using miR-reporter constructs, we show that miR-126 is functionally active in EC in vitro and that it could be specifically repressed using antagomirs specifically targeting miR-126. To study the consequences of miR-126 silencing on vascular regeneration, mice were injected with a single dose of antagomir-126 or a control 'scramblemir' and exposed to ischemia of the left hindlimb by ligation of the femoral artery. Although miR-126 was effectively silenced in mice treated with a single, high dose (HD) of antagomir-126, laser Doppler perfusion imaging did not show effects on blood flow recovery. In contrast, quantification of the capillary density in the gastrocnemius muscle revealed that mice treated with a HD of antagomir-126 had a markedly reduced angiogenic response. Aortic explant cultures of the mice confirmed the role of miR-126 in angiogenesis. Our data demonstrate a facilitary function for miR-126 in ischemia-induced angiogenesis and show the efficacy and specificity of antagomir-induced silencing of EC-specific microRNAs in vivo.

Elevated endothelial progenitor cells during painful sickle cell crisis

OBJECTIVE

Circulating endothelial progenitor cells (EPCs) counts were determined in patients with sickle cell disease (SCD) to elucidate their role in SCD-related ischemia-induced angiogenesis and reendothelialization.

MATERIALS AND METHODS

Circulating EPC counts (KDR(+)/CD34(+)/Cd45(dim) cells) and their relation to serum levels of EPC mobilizing growth factors erythropoietin, vascular endothelial growth factor, and interleukin-8 were investigated in SCD patients during asymptomatic state (n=66) and painful crisis (n=36) and compared to healthy controls (n=13).

RESULTS

EPC counts were comparable between controls (0; range, 0-1.1 cells/mL) and patients (0; range, 0-0 cells/mL) in asymptomatic state, but were significantly higher during painful crisis (41.7; range, 0-186 cells/mL; p<0.05). Also in a paired analysis of 12 patients who were included both during asymptomatic state and painful crisis, EPC counts increased significantly during painful crisis (from 0 [range, 0-0] to 26 [range, 0-149 cell/mL; p<0.05). EPC counts were not related to any of the measured growth factors.

CONCLUSION

The higher EPC counts during painful crisis might indicate a role for EPC mobilization in reendothelialization. As a relationship of EPCs with the established mobilizing growth factors, measured in this study was not observed, the mechanism of EPC mobilization in SCD remains to be elucidated.

Differentiation of bone marrow-derived endothelial progenitor cells is shifted into a proinflammatory phenotype by hyperglycemia

Bone marrow (BM)-derived endothelial progenitor cells (EPC) contribute to vascular maintenance by participating in angiogenesis, re-endothelialization, and remodeling. Myeloid progenitor cells in the BM are functionally and quantitatively an important precursor pool for cells that contribute to these processes. However, these precursor pools in the BM also give rise to important effector cells of the innate immune system, such as macrophages and dendritic cells. We hypothesized that the disturbed repair responses that are being observed in diabetes mellitus are also related to an effect on functional and differentiation characteristics at the level of this bone marrow precursor pool. Indeed, we observed that bone marrow differentiation cultures for EPC, macrophages (Mph), or dendritic cells (DC) from hyperglycemic BM yielded 40% fewer EPC and 50% more Mph compared with control BM. These changes were directly related to the hemoglobin A(1C) levels of the donor mice. BM-derived DC numbers were not affected by hyperglycemia. The composition of the BM was not altered; in particular, the numbers of CD31+/Ly6C+ cells, which serve as common progenitors for EPC, Mph, and DC, were unaffected. In addition, BM-derived EPC from hyperglycemic mice were less angiogenic and more proinflammatory in regards to endocytosis, T-cell activation, and interleukin 12 production. HMG-CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase inhibition by statin supplementation of the culture medium counteracted these hyperglycemia-induced changes. Our study results show that hyperglycemia alters the differentiation fate of BM precursor cells, reducing the potential to generate vascular regenerative cells and favoring the development of proinflammatory cells.

Recombinant human GH replacement increases CD34+ cells and improves endothelial function in adults with GH deficiency

OBJECTIVE

Adult patients with GH deficiency (GHD) are at increased risk for cardiovascular morbidity and mortality. Endothelial function, vascular stiffness, and loss of circulating CD34+ cells are considered biomarkers for cardiovascular disease. The aim of this study was to assess vascular structure and function in relation to circulating CD34+ cells in adults with GHD before and during 1 year of recombinant human GH (rhGH) replacement.

DESIGN

One-year intervention with rhGH.

PATIENTS AND METHODS

Vascular function (flow-mediated dilatation (FMD)) and structure (pulse wave velocity (PWV) and analysis) were assessed in 14 adult patients (nine men) with GHD (mean age 57 years, range 27-71 years). In addition, the number of CD34+ cells was evaluated using flow cytometric analysis. Study parameters were analyzed at baseline, and after 6 months and 1 year of rhGH replacement.

RESULTS

rhGH replacement increased IGF-I levels from 10.4+/-4.5 mmol/l at baseline to 18.4+/-10.1 mmol/l, and 20.5+/-8.0 mmol/l, at 6 months, and 1 year respectively (P=0.001). FMD increased from 3.5+/-1.8% to 6.0+/-2.5% and 5.1+/-2.5% during 1 year of rhGH replacement (P=0.008). There was no beneficial effect on PWV, central pulse pressure, central systolic pressure, and augmentation index. The number of CD34+ cells increased from 794.9+/-798.8 to 1270.7+/-580.1 cells/ml and to 1356.9+/-759.0 cells/ml (P=0.010).

CONCLUSION

One year of rhGH replacement in adults with GHD improves endothelial function and increases the number of circulating CD34+ cells.

Properdin binds to late apoptotic and necrotic cells independently of C3b and regulates alternative pathway complement activation

Cells that undergo apoptosis or necrosis are promptly removed by phagocytes. Soluble opsonins such as complement can opsonize dying cells, thereby promoting their removal by phagocytes and modulating the immune response. The pivotal role of the complement system in the handling of dying cells has been demonstrated for the classical pathway (via C1q) and lectin pathway (via mannose-binding lectin and ficolin). Herein we report that the only known naturally occurring positive regulator of complement, properdin, binds predominantly to late apoptotic and necrotic cells, but not to early apoptotic cells. This binding occurs independently of C3b, which is additional to the standard model wherein properdin binds to preexisting clusters of C3b on targets and stabilizes the convertase C3bBb. By binding to late apoptotic or necrotic cells, properdin serves as a focal point for local amplification of alternative pathway complement activation. Furthermore, properdin exhibits a strong interaction with DNA that is exposed on the late stage of dying cells. Our data indicate that direct recognition of dying cells by properdin is essential to drive alternative pathway complement activation.

Met-RANTES reduces endothelial progenitor cell homing to activated (glomerular) endothelium in vitro and in vivo

The chemokine RANTES (regulated upon activation normal T-cell expressed and secreted) is involved in the formation of an inflammatory infiltrate during glomerulonephritis. However, RANTES receptor inhibition, although reducing glomerular leukocyte infiltration, can also increase damage. We hypothesized that RANTES does not only promote the influx and activation of inflammatory leukocytes but also mediates glomerular microvascular repair by stimulating the homing of bone marrow (BM)-derived endothelial progenitor cells. To investigate the role of RANTES in the participation of BM-derived cells in glomerular vascular repair, we used a rat BM transplantation model in combination with reversible anti-Thy-1.1 glomerulonephritis. Twenty-four hours after the induction of glomerulonephritis, BM-transplanted rats were treated for 7 days with either the RANTES receptor antagonist Met-RANTES or saline. The participation of BM-derived endothelial cells in glomerular repair, glomerular monocyte infiltration, and proteinuria was evaluated at days 7 and 28. Furthermore, we used an in vitro perfusion chamber assay to study the role of RANTES receptors in shear-resistant adhesion of the CD34+ stem cells to activated endothelium under flow. In our reversible glomerulonephritis model, RANTES receptor inhibition specifically reduced the participation of BM-derived cells in glomerular vascular repair by more than 40% at day 7 without impairing monocyte influx. However, no obvious change in recovery from proteinuria or morphological damage was observed. Blockade of RANTES receptors on CD34+ cells in vitro partially inhibited platelet-enhanced, shear-resistant firm adhesion of the CD34+ cells to activated endothelium. In conclusion, our data suggest that RANTES is involved in the homing and participation of BM-derived endothelial cells in glomerular repair.

Shear stress-induced changes in atherosclerotic plaque composition are modulated by chemokines

We previously found that low shear stress (LSS) induces atherosclerotic plaques in mice with increased lipid and matrix metalloproteinase content and decreased vascular smooth muscle and collagen content. Here, we evaluated the role of chemokines in this process, using an extravascular device inducing regions of LSS, high shear stress, and oscillatory shear stress (OSS) in the carotid artery. One week of shear stress alterations induced expression of IFN-gamma-inducible protein-10 (IP-10) exclusively in the LSS region, whereas monocyte chemoattractant protein-1 (MCP-1) and the mouse homolog of growth-regulated oncogene alpha (GRO-alpha) were equally upregulated in both LSS and OSS regions. After 3 weeks, GRO-alpha and IP-10 were specifically upregulated in LSS regions. After 9 weeks, lesions with thinner fibrous caps and larger necrotic cores were found in the LSS region compared with the OSS region. Equal levels of MCP-1 expression were observed in both regions, while expression of fractalkine was found in the LSS region only. Blockage of fractalkine inhibited plaque growth and resulted in striking differences in plaque composition in the LSS region. We conclude that LSS or OSS triggers expression of chemokines involved in atherogenesis. Fractalkine upregulation is critically important for the composition of LSS-induced atherosclerotic lesions.

Haematopoietic stem cells and endothelial progenitor cells in healthy men: effect of aging and training

The number of hematopoietic stem cells (HSC) and endothelial progenitor cells (EPC) is thought to be a marker for neovascularization and vascular repair. Because physical inactivity and aging are risk factors for cardiovascular diseases, these factors may influence the numbers of HSCs and EPCs. Therefore, we examined baseline and exercise-induced levels of HSCs and EPCs in sedentary and trained young and older men. To study the role of aging in eight sedentary young (19-28 years) and eight sedentary older men (67-76 years), baseline and acute exercise-induced numbers of HSCs (CD34+-cells) and EPCs (CD34+/VEGFR-2+-cells) were quantified by fluorescence-activated cell sorter (FACS) analysis. To examine the effect of chronic training, eight age-matched trained young men (18-28 years) were compared with sedentary young men, whereas older men performed an 8-week endurance training. Older men showed significantly lower baseline and exercise-induced levels of HSCs/EPCs than the young men (P < 0.05). In young and older men, acute exercise significantly increased HSCs (P < 0.01), but not EPCs. The absolute increase in numbers of HSCs was attenuated in older men (P = 0.03). Apart from the lower baseline numbers of EPCs after chronic training in older men, training status did not alter baseline or exercise-induced levels of HSCs/EPCs in young and older men. We concluded that advancing age results in lower circulating numbers of HSCs and EPCs and attenuates the acute exercise-induced increase in HSCs. Interestingly, in young as well as in older men chronic endurance training does not affect baseline and exercise-induced numbers of HSCs and EPCs.

A single bolus of a long-acting erythropoietin analogue darbepoetin alfa in patients with acute myocardial infarction: a randomized feasibility and safety study

AIMS

Besides stimulating hematopoiesis, erythropoietin (EPO) protects against experimental ischemic injury in the heart. The present study evaluated the safety and tolerability of EPO treatment in non-anemic patients with acute myocardial infarction (MI).

METHODS AND RESULTS

In this single-center, investigator-initiated, prospective study, patients with a first acute MI were randomized to one bolus of 300 microg darbepoetin alfa or no additional medication before primary coronary intervention. Twenty-two patients (mean age 59 +/- 2 years) were included. In the darbepoetin group, serum EPO-levels increased to 130-270 times that of controls, within the first 24 h. After darbepoetin administration, only small and non-significant changes in hematocrit levels were observed, while endothelial progenitor cells (EPCs, CD34+/CD45-) were increased at 72 h (2.8 vs. 1.0 cells/microl in control group, p < 0.01). No adverse events were recorded during the 30-day follow-up. After 4 months, left ventricular ejection fraction was similar in the two groups (52 +/- 3% in darbepoetin vs. 48 +/- 5% in control group, p = NS).

CONCLUSIONS

Intravenous single high-dose darbepoetin alfa in acute MI is both safe and well tolerated. Darbepoetin treatment after MI stimulates EPCs mobilization. The results of this first pilot study support a larger scale clinical trial to establish efficacy of EPO administration in patients after acute MI.

Activated vitronectin as a target for anticancer therapy with human antibodies

The formation of a provisional extracellular matrix represents an important step during tumor growth and angiogenesis. Proteins that participate in this process become activated and undergo conformational changes that expose biologically active cryptic sites. Activated matrix proteins express epitopes not found on their native counterparts. We hypothesized that these epitopes may have a restricted tissue distribution, rendering them suitable targets for therapeutic human monoclonal antibodies (huMabs). In this study, we exploited phage antibody display technology and subtractive phage selection to generate human monoclonal antibody fragments that discriminate between the activated and native conformation of the extracellular matrix protein vitronectin. One of the selected antibody fragments, scFv VN18, was used to construct a fully human IgG/kappa monoclonal antibody with an affinity of 9.3 nM. In immunohistochemical analysis, scFv and huMab VN18 recognized activated vitronectin in tumor tissues, whereas hardly any activated vitronectin was detectable in normal tissues. Iodine 123-radiolabeled huMabVN18 was shown to target to Rous sarcoma virus-induced tumors in chickens, an animal model in which the epitope for huMab VN18 is exposed during tumor development. Our results establish activated vitronectin as a potential target for tumor therapy in humans.

Endothelial Progenitor Cells: More Than an Inflammatory Response?

The formation of new capillaries (angiogenesis) may be of clinical importance in facilitating reperfusion and regeneration of hibernating cardiac tissue after myocardial infarction and in microvascular ischemia. Evidence is accumulating that as part of the response to hypoxia, bone marrow-derived circulating endothelial progenitor cells (CEPs) are mobilized and subsequently differentiate into proper endothelial cells. There are also indications that such CEPs can facilitate endothelial repair and angiogenesis in vivo. It is not clear yet, however, whether these CEPs are essential for these adaptive processes or what the relative contribution of CEP is compared with that of other mononuclear inflammatory cells that are mobilized to areas of ischemia. Moreover, there are still many uncertainties about how cardiovascular risk factors alter CEP function. Particularly when therapeutically mobilizing CEPs, a further understanding of this issue is essential to assess the risk of potentially harmful side effects of altered CEP function.