Dietlind Zohlnhöfer

A Crucial Role of Glycoprotein VI for Platelet Recruitment to the Injured Arterial Wall In Vivo

Platelet adhesion and aggregation at sites of vascular injury is crucial for hemostasis but may lead to arterial occlusion in the setting of atherosclerosis and precipitate diseases such as myocardial infarction. A current hypothesis suggests that platelet glycoprotein (GP) Ib interaction with von Willebrand factor recruits flowing platelets to the injured vessel wall, where subendothelial fibrillar collagens support their firm adhesion and activation. However, so far this hypothesis has not been tested in vivo. Here, we demonstrate by intravital fluorescence microscopy of the mouse carotid artery that inhibition or absence of the major platelet collagen receptor, GPVI, abolishes platelet–vessel wall interactions after endothelial denudation. Unexpectedly, inhibition of GPVI by the monoclonal antibody JAQ1 reduced platelet tethering to the subendothelium by ∼89%. In addition, stable arrest and aggregation of platelets was virtually abolished under these conditions. Using different models of arterial injury, the strict requirement for GPVI in these processes was confirmed in GPVI-deficient mice, where platelets also failed to adhere and aggregate on the damaged vessel wall. These findings reveal an unexpected role of GPVI in the initiation of platelet attachment at sites of vascular injury and unequivocally identify platelet–collagen interactions (via GPVI) as the major determinant of arterial thrombus formation.

Effect of glycoprotein IIb/IIIa receptor blockade on platelet-leukocyte interaction and surface expression of the leukocyte integrin Mac-1 in acute myocardial infarction

OBJECTIVES This prospective randomized study investigated platelet-induced upregulation of Mac-1 on monocytes and its inhibition by glycoprotein (GP) IIb/IIIa blockage in patients with acute myocardial infarction (AMI). BACKGROUND In experimental AMI, Mac-1 on leukocytes is the pivotal adhesion molecule for detrimental inflammatory responses. In vitro, platelet adhesion to monocytes upregulates Mac-1. METHODS Patients undergoing stenting in AMI within 48 h after onset of symptoms were randomly assigned to receive either standard-dose heparin (n = 50) or abciximab plus low-dose heparin (n = 50). In serial blood samples, we assessed platelet-monocyte interaction and Mac-1 surface expression by triple color immunofluorescence flow cytometry. RESULTS Compared with platelet-negative monocytes, Mac-1 surface expression on monocytes with attached platelets was upregulated (median fluorescence intensity [interquartile range]: 259 [179 to 367] vs. 135 [78 to 195] arbitrary units, p < 0.001). As an indicator of platelet-monocyte interaction, mean fluorescence of the platelet marker GP Ib alpha in the monocytes population decreased after abciximab, although it remained unaffected by heparin alone. Abciximab achieved this effect by a reduction in platelet mass attached to monocytes (GP Ib alpha fluorescence intensity of heterotypic aggregates at 24 h [arbitrary units]: 187 [143 to 236] after abciximab vs. 228 [156 to 332] after heparin, p = 0.02), whereas it did not affect the percentage of monocytes with adherent platelets. Reduction of platelet-monocyte interaction resulted in decreased Mac-1 surface expression (fluorescence intensity at 24 h [arbitrary units]: 116 [68 to 153] after abciximab vs. 162 [117 to 239] after heparin, p = 0.001). CONCLUSIONS In patients with AMI, platelet-leukocyte interactions modulate Mac-1 expression on monocytes. Glycoprotein IIb/IIIa blockade is a therapeutic option to interfere with this mechanism.

Randomized, Double-Blind, Placebo-Controlled Trial of Oral Sirolimus for Restenosis Prevention in Patients With In-Stent Restenosis The Oral Sirolimus to Inhibit Recurrent In-stent Stenosis (OSIRIS) Trial

Background—Despite recent advances in interventional cardiology, including the introduction of drug-eluting stents for de novo coronary lesions, the treatment of in-stent restenosis (ISR) remains a challenging clinical issue. Given the efficacy of systemic sirolimus administration to prevent neointimal hyperplasia in animal models and to halt and even reverse the progression of allograft vasculopathy, the aim of the present double-blind, placebo-controlled study was to evaluate the efficacy of a 10-day oral sirolimus treatment with 2 different loading regimens for the prevention of recurrent restenosis in patients with ISR. Methods and Results—Three hundred symptomatic patients with ISR were randomly assigned to 1 of 3 treatment arms: placebo or usual-dose or high-dose sirolimus. Patients received a cumulative loading dose of 0, 8, or 24 mg of sirolimus 2 days before and the day of repeat intervention followed by maintenance therapy of 2 mg/d for 7 days. Angiographic restenosis at 6-month angiography was the primary end point of the study. Restenosis was significantly reduced from 42.2% to 38.6% and to 22.1% in the placebo, usual-dose, and high-dose sirolimus groups, respectively (P=0.005). Similarly, the need for target vessel revascularization was reduced from 25.5% to 24.2% and to 15.2% in the placebo, usual-dose, and high-dose groups, respectively (P=0.08). The sirolimus blood concentration on the day of the procedure correlated significantly with the late lumen loss at follow-up (P<0.001). Conclusions—In patients with ISR, an oral adjunctive sirolimus treatment with an intensified loading regimen before coronary intervention resulted in a significant improvement in the angiographic parameters of restenosis.

Gene Expression Profiling of Human Stent-Induced Neointima by cDNA Array Analysis of Microscopic Specimens Retrieved by Helix Cutter Atherectomy Detection of FK506-Binding Protein 12 Upregulation

Background —Restenosis due to neointima formation is the major limitation of stent-supported balloon angioplasty. Despite abundant animal data, molecular mechanisms of neointima formation have been investigated on only a limited basis in patients. This study sought to establish a method for profiling gene expression in human in-stent neointima and to identify differentially expressed genes that may serve as novel therapeutic targets. Methods and Results —We retrieved tissue specimens from patients with symptomatic in-stent restenosis using a novel helix cutter atherectomy device. cDNA samples prepared from neointima (n=10) and, as a control, from the media of normal arteries (n=14) were amplified using a novel polymerase chain reaction protocol and hybridized to cDNA arrays. Immunohistochemistry characterized the atherectomy material as neointima. cDNA arrays readily identified differentially expressed genes. Some of the differentially expressed genes complied with expected gene expression patterns of neointima, including downregulation of desmin and upregulation of thrombospondin-1, cyclooxygenase-1, and the 70-kDa heat shock protein B. Additionally, we discovered previously unknown gene expression patterns, such as downregulation of mammary-derived growth inhibitor and upregulation of FK506-binding protein 12 (FKBP12). Upregulation of FKBP12 was confirmed at the protein level in neointimal smooth muscle cells. Conclusions —Gene expression patterns of human neointima retrieved by helix-cutter atherectomy can be reliably analyzed by cDNA array technology. This technique can identify therapeutic targets in patients, as exemplified by the findings regarding FKBP12. FKBP12 is the receptor for Rapamycin (sirolimus), which in animal models reduced neointima formation. Our study thus yields a rationale for the use of Rapamycin to prevent restenosis in patients.

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‐1β, IL‐8, β‐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.

Stem cell mobilization by granulocyte-colony-stimulating factor in acute myocardial infarction: lessons from the REVIVAL-2 trial

Experimental studies and early-phase clinical trials suggest that mobilization of bone marrow stem cells by granulocyte-colony-stimulating factor (G-CSF) can be used to improve cardiac regeneration after acute myocardial infarction (AMI). In order to more fully evaluate this intervention in patients with AMI, we conducted the Regenerate Vital Myocardium by Vigorous Activation of Bone Marrow Stem Cells (REVIVAL-2) clinical trial. Following successful reperfusion by percutaneous coronary intervention for AMI, patients were randomly assigned to receive a subcutaneous daily dose of 10 µg/kg G-CSF or placebo for 5 days. Treatment with G-CSF produced a significant mobilization of stem cells. After 4–6 months the reduction in infarct size from baseline, as determined by technetium-99-labeled single-photon-emission CT, did not differ significantly between the G-CSF group and the placebo group. Furthermore, the improvement in left ventricular ejection fraction, as assessed by late-enhancement MRI, did not differ significantly between the two groups. G-CSF treatment did not increase the risk of adverse clinical events and did not promote restenosis. Our trial demonstrates that stem cell mobilization by G-CSF does not improve infarct size, left ventricular function, or coronary restenosis in patients with AMI who have had successful mechanical reperfusion.

Novel Role of the CXC Chemokine Receptor 3 in Inflammatory Response to Arterial Injury Involvement of mTORC1

Atherosclerosis, restenosis, and posttransplant graft atherosclerosis are characterized by endothelial damage, infiltration of inflammatory cells, and proliferation of smooth muscle cells. The CXCR3-activating chemokines interferon-γ inducible protein 10 (IP10) and MIG (monokine induced by interferon-γ) have been implicated in vascular repair and remodeling. The underlying molecular mechanisms, however, remain elusive. Here, we show that wire-mediated arterial injury induced local and systemic expression of IP10 and MIG, resulting in enhanced recruitment of CXCR3+ leukocytes and hematopoietic progenitor cells. This was accompanied by profound activation of mammalian target of rapamycin complex (mTORC)1, increased reactive oxygen species production, apoptosis, and intimal hyperplasia. Genetic and pharmacological inactivation of CXCR3 signaling not only suppressed recruitment of inflammatory cells but also abolished mTORC1 activation, reduced reactive oxygen species generation, and blocked apoptosis of vascular cells, resulting in significant reduction of intimal hyperplasia in vivo. In vitro, stimulation of T cells with IP10 directly activated mTORC1 and induced generation of reactive oxygen species and apoptosis in an mTORC1-dependent manner. These results strongly indicate that CXCR3-dependent activation of mTORC1 directly links stimulation of the Th1 immune system with the proliferative response of intimal cells in vascular remodeling.

Vascular Remodeling in Mice Lacking the Cytoplasmic Domain of Tissue Factor

Tissue factor (TF), the cell surface receptor for the serine protease FVIIa supports cell migration by interaction with the cytoskeleton. Intracellular signaling pathways dependent on the cytoplasmic domain of TF modify cell migration and may alter vascular remodeling. Vascular remodeling was analyzed in a femoral artery injury and a blood flow cessation model in mice with a targeted deletion of the 18 carboxy-terminal intracellular amino acids of TF (TF&Dgr;ct/&Dgr;ct) and compared with TF wild-type mice (TFwt/wt). Morphometric analysis revealed a decrease in the intima/media ratio after vascular injury in arteries from TF&Dgr;ct/&Dgr;ct compared with TFwt/wt mice (femoral artery injury: 2.4±0.3 TFwt/wt versus 0.6±0.3 TF&Dgr;ct/&Dgr;ct, n=9 to 10, P=0.002; carotis ligation: 0.45+0.11 TFwt/wt versus 0.22+0.03 TF&Dgr;ct/&Dgr;ct, n=12 to 14, P=0.09). This was caused by an increase in the media by 54% (P=0.04) in the femoral artery model and by 32% (P=0.03) after carotis ligation and was associated with an increased number of proliferating cells. Isolated aortic smooth muscle cells (SMCs) of TFwt/wt mice showed an increased migratory response toward the TF ligand active site-inhibited FVIIa that was abolished in TF&Dgr;ct/&Dgr;ct SMC. In contrast, the unstimulated proliferation rate was increased in TF&Dgr;ct/&Dgr;ct SMC compared with TFwt/wt SMCs. Thus, retention of SMCs attributable to a migratory defect and increased proliferation results in thickening of the media and in decrease in neointima formation after arterial injury. TF cytoplasmic domain signaling alters vascular remodeling and, thereby, may play a role in the development of restenosis, atherosclerotic disease, and neovascularization.

Role of Bone Marrow–Derived Cells in the Genetic Control of Restenosis

Objective—Angiographic indexes of restenosis after coronary stent placement in patients show a bimodal pattern suggesting the existence of two populations with different risk of restenosis. This is reflected in the arterial remodeling response of inbred mouse strains arguing for a genetic control of the mechanisms leading to lumen narrowing. As bone marrow–derived cells (BMCs) contribute to vascular healing after arterial injury, we investigated the role of BMCs in the genetic control of restenosis. Methods and Results—129X1/SvJ mice developed significantly more neointima and late lumen loss compared to C57BL/6 mice. Gene expression analysis of intimal tissue revealed major differences in the expression of inflammatory and hematopoietic stem and progenitor cell–associated genes in response to arterial injury. In 129X1/SvJ mice stronger mobilization of lin−sca-1+CXCR4+ cells was observed after vascular injury. Bone marrow transplantation identified the extent of neointima formation as clearly dependent on the genetic background of BMCs (ie, mice with 129X1/SvJ BMCs developed more intimal hyperplasia). The inflammatory response and the recruitment of BMCs to the site of arterial injury were significantly increased in mice with 129X1/SvJ BMCs. Conclusions—The genetically controlled mechanisms leading to lumen narrowing in vascular remodeling are dependent on mobilization and recruitment capacities of particular BMCs.

Expression of CXCR4, VLA-1, LFA-3 and transducer of ERB in G-CSF-mobilised progenitor cells in acute myocardial infarction

G-CSF induced mobilisation of progenitor cells is a multistep processes involving chemokines, growth factors, matrix-degrading enzymes, and cell adhesive interactions mediated by specific receptors on haematopoietic cells. This studys aim was to investigate progenitor cells mobilised during myocardial infarction after treatment with granulocyte-stimulating factor (G-CSF). In the randomised, double-blind, placebo-controlled REVIVAL-2 study, 114 patients with acute myocardial infarction were included. Five days after successful percutaneous coronary intervention patients received either 10 microg/kg G-CSF (n=56) or placebo (n=58) subcutaneously for five days. Venous blood samples were analysed on day(s) 1, 3, 5 and 7 after therapy, and progenitor cell mobilisation and surface expression of VLA-4, LFA-1 and CXCR-4 was measured on circulating progenitor cells using flow cytometry. G-CSF induced a significant increase in circulating progenitor cells (72 +/- 20 cells/microl vs. 4.5 +/- 0.8 cells/microl, p<0.05). Surface expression of LFA-1, VLA-4 and CXCR4 on progenitor cells was decreased by 44%, 49% and 60% after G-CSF as compared to placebo (p<0.05). In accordance, mRNA expression of CXCR4 was reduced. Moreover, anti-proliferative transducer of ERB (TOB) mRNA was decreased, suggesting an increased proliferative potential of the mobilised progenitor cells. Decreased expression of adhesion and chemokine receptors on G-CSF mobilised progenitor cells in acute myocardial infarction may alter the homing capacity of circulating cells to the myocardium.