Uwe Schubert

Loss of RAGE in pulmonary fibrosis: molecular relations to functional changes in pulmonary cell types.

The receptor for advanced glycation end products (RAGE) is a transmembrane receptor of the Ig superfamily. While vascular RAGE expression is associated with kidney and liver fibrosis, high expression levels of RAGE are found under physiological conditions in the lung. In this study, RAGE expression in idiopathic pulmonary fibrosis was assessed, and the relationship of the receptor to functional changes of epithelial cells and pulmonary fibroblasts in the pathogenesis of the disease was investigated. Significant down-regulation of RAGE was observed in lung homogenate and alveolar epithelial type II cells from patients with idiopathic pulmonary fibrosis, as well as in bleomycin-treated mice, demonstrated by RT-PCR, Western blotting, and immunohistochemistry. In vitro, RAGE down-regulation was provoked by stimulation of primary human lung fibroblasts and A549 epithelial cells with the proinflammatory cytokines, transforming growth factor-beta1 or TNF-alpha. Blockade of RAGE resulted in impaired cell adhesion, and small interfering RNA-induced knockdown of RAGE increased cell proliferation and migration of A549 cells and human primary fibroblast in vitro. These results indicate that RAGE serves a protective role in the lung, and that loss of the receptor is related to functional changes of pulmonary cell types, with the consequences of fibrotic disease.

The functional role of blood platelet components in angiogenesis

The process of neovascularization greatly depends on the induction of the angiogenic phenotype of endothelial cells that is strictly controlled by humoral factors as well as by cellular communications in the vascular system. Although blood platelets contain several secretable pro- and antiangiogenic components, their overall role in angiogenesis remains poorly understood. In a mouse model of hypoxia-induced retinal angiogenesis, the situation of thrombocytopenia as well as inhibition of platelet aggregation by a highly specific alphaIIbbeta3-integrin antagonist or acetyl salicylic acid (Aspirin) administration, respectively, resulted in about 35-50% reduction of retinal neovascularization, compatible with a significant contribution of blood platelets in angiogenesis. Platelet remnants and microvesicles were found at sites of angiogenic sprouts. In vitro isolated platelets incorporated in a fibrin gel induced capillary sprouting of microvascular endothelial cells. Similarly, platelet releasate elevated the permeability of confluent endothelial cell monolayers to the same extent as hypoxia did. Platelet-derived VEGF as well as butanol-extractable lipid mediators were identified as predominant activators of angiogenesis, particularly of microvascular endothelial cell proliferation and migration. In addition, a synergistic effect between platelet-derived VEGF and bFGF in capillary sprouting and endothelial cell proliferation was found. Based on this proangiogenic role of platelets in neovascularization, anti-platelet substances can be considered as potent inhibitors of angiogenesis.

Extracellular RNA is a natural cofactor for the (auto-)activation of Factor VII-activating protease (FSAP)

FSAP (Factor VII-activating protease) is a new plasma-derived serine protease with putative dual functions in haemostasis, including activation of coagulation Factor VII and generation of urinary-type plasminogen activator (urokinase). The (auto-)activation of FSAP is facilitated by polyanionic glycosaminoglycans, such as heparin or dextran sulphate, whereas calcium ions stabilize the active form of FSAP. In the present study, extracellular RNA was identified and characterized as a novel FSAP cofactor. The conditioned medium derived from various cell types such as smooth muscle cells, endothelial cells, osteosarcoma cells or CHO (Chinese-hamster ovary) cells contained an acidic factor that initiated (auto-)activation of FSAP. RNase A, but not other hydrolytic enzymes (proteases, glycanases and DNase), abolished the FSAP cofactor activity, which was subsequently isolated by anion-exchange chromatography and unequivocally identified as RNA. In purified systems, as well as in plasma, different forms of natural RNA (rRNA, tRNA, viral RNA and artificial RNA) were able to (auto-)activate FSAP into the two-chain enzyme form. The specific binding of FSAP to RNA (but not to DNA) was shown by mobility-shift assays and UV crosslinking, thereby identifying FSAP as a new extracellular RNA-binding protein, the K(D) estimated to be 170-350 nM. Activation of FSAP occurred through an RNA-dependent template mechanism involving a nucleic acid size of at least 100 nt. In a purified system, natural RNA augmented the FSAP-dependent Factor VII activation several-fold (as shown by subsequent Factor Xa generation), as well as the FSAP-mediated generation of urokinase. Our results provide evidence for the first time that extracellular RNA, present at sites of cell damage or vascular injury, can serve an important as yet unrecognized cofactor function in haemostasis by inducing (auto-)activation of FSAP through a novel surface-dependent mechanism.

Defective Angiogenesis Delays Thrombus Resolution A Potential Pathogenetic Mechanism Underlying Chronic Thromboembolic Pulmonary Hypertension

Objective— Restoration of patency is a natural target of vascular remodeling after venous thrombosis that involves vascular endothelial cells and smooth muscle cells, as well as leukocytes. Acute pulmonary emboli usually resolve <6 months. However, in some instances, thrombi transform into fibrous vascular obstructions, resulting in occlusion of the deep veins, or in chronic thromboembolic pulmonary hypertension (CTEPH). We proposed that dysregulated thrombus angiogenesis may contribute to thrombus persistence. Approach and Results— Mice with an endothelial cell–specific conditional deletion of vascular endothelial growth factor receptor 2/kinase insert domain protein receptor were used in a model of stagnant flow venous thrombosis closely resembling human deep vein thrombosis. Biochemical and functional analyses were performed on pulmonary endarterectomy specimens from patients with CTEPH, a human model of nonresolving venous thromboembolism. Endothelial cell–specific deletion of kinase insert domain protein receptor and subsequent ablation of thrombus vascularization delayed thrombus resolution. In accordance with these findings, organized human CTEPH thrombi were largely devoid of vascular structures. Several vessel-specific genes, such as kinase insert domain protein receptor, vascular endothelial cadherin, and podoplanin, were expressed at lower levels in white CTEPH thrombi than in organizing deep vein thrombi and organizing thrombi from aortic aneurysms. In addition, red CTEPH thrombi attenuated the angiogenic response induced by vascular endothelial growth factor. Conclusions— In the present work, we propose a mechanism of thrombus nonresolution demonstrating that endothelial cell–specific deletion of kinase insert domain protein receptor abates thrombus vessel formation, misguiding thrombus resolution. Medical conditions associated with the development of CTEPH may be compromising early thrombus angiogenesis. # Significance {#article-title-44}Objective—Restoration of patency is a natural target of vascular remodeling after venous thrombosis that involves vascular endothelial cells and smooth muscle cells, as well as leukocytes. Acute pulmonary emboli usually resolve <6 months. However, in some instances, thrombi transform into fibrous vascular obstructions, resulting in occlusion of the deep veins, or in chronic thromboembolic pulmonary hypertension (CTEPH). We proposed that dysregulated thrombus angiogenesis may contribute to thrombus persistence. Approach and Results—Mice with an endothelial cell–specific conditional deletion of vascular endothelial growth factor receptor 2/kinase insert domain protein receptor were used in a model of stagnant flow venous thrombosis closely resembling human deep vein thrombosis. Biochemical and functional analyses were performed on pulmonary endarterectomy specimens from patients with CTEPH, a human model of nonresolving venous thromboembolism. Endothelial cell–specific deletion of kinase insert domain protein receptor and subsequent ablation of thrombus vascularization delayed thrombus resolution. In accordance with these findings, organized human CTEPH thrombi were largely devoid of vascular structures. Several vessel-specific genes, such as kinase insert domain protein receptor, vascular endothelial cadherin, and podoplanin, were expressed at lower levels in white CTEPH thrombi than in organizing deep vein thrombi and organizing thrombi from aortic aneurysms. In addition, red CTEPH thrombi attenuated the angiogenic response induced by vascular endothelial growth factor. Conclusions—In the present work, we propose a mechanism of thrombus nonresolution demonstrating that endothelial cell–specific deletion of kinase insert domain protein receptor abates thrombus vessel formation, misguiding thrombus resolution. Medical conditions associated with the development of CTEPH may be compromising early thrombus angiogenesis.

The extracellular adherence protein from Staphylococcus aureus abrogates angiogenic responses of endothelial cells by blocking Ras activation

The extracellular adherence protein (Eap), a broad‐spectrum adhesin secreted by Staphylococcus aureus, was previously shown to curb acute inflammatory responses, presumably through its binding to endothelial cell (EC) ICAM‐1. Examining the effect of Eap on endothelial function in more detail, we here show that, in addition, Eap functions as a potent angiostatic agent. Concomitant treatment of EC with purified Eap resulted in the complete blockage of the mitogenic and sprouting responses elicited by vascular endothelial growth factor (VEGF)165 or basic fibroblast growth factor (bFGF). Moreover, the induction of tissue factor and decay‐accelerating factor were repressed by Eap, as determined by qRT‐polymerase chain reaction (qRT‐PCR), with a corresponding reduction in Egr‐1 protein up‐regulation seen. This angiostatic activity was accompanied by a corresponding inhibition in ERK1/2 phosphorylation, while activation of p38 was not affected. Inhibition occurred downstream of tyrosine kinase receptor activation, as comparable effects were seen on TPA‐induced ERK1/2 phosphorylation. Similar to previously described angiostatic agents like angiopoietin‐1 or the 16‐kDa prolactin fragment, Eap blockage of the Ras/Raf/MEK/ERK cascade was localized by pull‐down assay at the level of Ras activation. Eaps combined anti‐inflammmatory and antiangiogenic properties render this bacterial protein not only an important virulence factor during S. aureus infection but open new perspectives for therapeutic applications in pathological neovascularization.—Sobke, A. C. S., Selimovic, D., Orlova, V., Hassan, M., Chavakis, T., Athanasopoulos, A. N., Schubert, U., Hussain, M., Thiel, G., Preissner, K. T., Herrmann, M. The extracellular adherence protein from Staphylococcus aureus abrogates angiogenic responses of endothelial cells by blocking Ras activation. FASEB J. 20, E2156–E2165 (2006)

Tenilsetam prevents early diabetic retinopathy without correcting pericyte loss

Hyperglycemia-induced mitochondrial overproduction of reactive oxygen species leads to the activation of different biochemical pathways involved in endothelial damage of the diabetic retina. Tenilsetam [(+/-)-3-(2-thienyl)-2-piperazinone] is a dicarbonyl scavenger in the millimolar range and a transition metal ion chelator in the micromolar range. We tested its effect on experimental diabetic retinopathy, and on endothelial cell characteristics in vitro. Streptozotocin diabetic male Wistar rats (60 mg/kg BW) received 50 mg/kg BW tenilsetam (D-T) for 36 weeks, or no treatment (D). The impact of tenilsetam (0-30 mM) on endothelial proliferation, apoptosis, sprouting, cytokine-induced leucocyte-endothelial interaction, and VEGF expression was tested in vitro. Tenilsetam did not affect glycemic control or body weight in diabetic animals. The 3.7 fold increase in acellular capillaries in diabetic rats [p < 0.001 vs. non-diabetic controls (N)] was reduced by 70% (p < 0.001) through treatment, but pericyte loss (D vs. N -33%; p < 0.001) remained unaffected. In vitro, tenilsetam inhibited endothelial proliferation at lower doses, while inducing apoptosis at high doses. Leucocyte adhesion was only inhibited at high doses. Sprouting angiogenesis of bovine retinal endothelial cells was promoted at lower doses (< or = 10 mM). At micromolar concentrations, endothelial VEGF expression was upregulated by 100%. Long-term treatment with the AGE-inhibitor and iron-chelating compound tenilsetam inhibits the formation of acellular capillaries without correcting pericyte loss. The compound has dose-dependent effects on endothelial cell function. These data suggest that, independent of known properties, tenilsetam shows important rescue functions on endothelial cells which could be useful for the treatment of early diabetic retinopathy.

Angiogenesis and parasitic helminth-associated neovascularization

Successful metazoan parasitism, among many other factors, requires a supply of nutrients and the removal of waste products. There is a prerequisite for a parasite-defined vasculature. The angiogenic mechanism(s) involved presumably depend on the characteristics of the tissue- and vascular system-dwelling, parasitic helminths. Simplistically, 2 possibilities or a combination of both have been considered in this review. The multifactorial induction of parasitic helminth-associated neovascularization could arise through, either a host-, a parasite- or a host-/parasite-dependent, angiogenic switch. Most studies appear to support the first and third hypotheses, but evidence exists for the intrahepatic cestode Echinococcus multilocularis, the free-living nematode Caenorhabditis elegans and the intravascular trematode Schistosoma mansoni for the second inference. In contrast, the nematode anti-coagulant protein NAPc2 from adult Ancylostoma caninum is also an anti-angiogenic factor.

Antibody response to the extracellular adherence protein (Eap) of Staphylococcus aureus in healthy and infected individuals.

The extracellular adherence protein (Eap) from Staphylococcus aureus has been suggested as a vaccine candidate and for therapeutic use due to its immunomodulating and antiangiogenic properties; however, little is known about anti-Eap antibodies in humans. We determined anti-Eap antibody titers by enzyme-linked immunosorbent assay and Western blot and measured serum samples from 92 patients with proven S. aureus infections and 93 healthy controls. The functionality of antibodies was assessed by a phagocytosis assay using Eap-coated fluorescent microspheres. Antibodies were detected in all human samples, but not in mice. Patients showed significantly higher titers than controls [immunoglobulin M (IgM), P=0.007; IgG, P<0.0001]. Patients with deep or severe infections showed higher titers than those with superficial or mild disease. Eap alone was sufficient to promote phagocytosis by peripheral blood mononuclear cell and granulocytes that was moderately enhanced in the presence of human serum, but no correlation was found with the levels of anti-Eap antibodies. Anti-Eap antibodies are prevalent in all tested humans and correlate with the severity of S. aureus infection; however, they do not seem to provide protection against invasive infections. Before considering Eap for therapy or as a vaccine candidate, further studies are warranted to assess the impact of the interference between Eap and its specific antibodies.

Artificial and Natural Sialic Acid Precursors Influence the Angiogenic Capacity of Human Umbilical Vein Endothelial Cells

N-acetylneuraminic acid (Neu5Ac) represents the most common terminal carbohydrate residue in many mammalian glycoconjugates and is directly involved in a number of different physiological as well as pathological cellular processes. Endogenous sialic acids derive from the biosynthetic precursor molecule N-acetyl-D-mannosamine (ManNAc). Interestingly, N-acyl-analogues of D-mannosamine (ManN) can also be incorporated and converted into corresponding artificial sialic acids by eukaryotic cells. Within this study, we optimized a protocol for the chemical synthesis of various peracetylated ManN derivatives resulting in yields of approximately 100%. Correct molecular structures of the obtained products ManNAc, N-propanoyl-ManN (ManNProp) and N-butyl-ManN (ManNBut) were verified by GC-, ESI-MS- and NMR-analyses. By applying these substances to human umbilical vein endothelial cells (HUVECs), we could show that each derivative was metabolized to the corresponding N-acylneuraminic acid variant and subsequently incorporated into nascent glycoproteins. To investigate whether natural and/or artificial sialic acid precursors are able to modulate the angiogenic capacity of HUVECs, a spheroid assay was performed. By this means, an increase in total capillary length has been observed when cells incorporated N-butylneuraminic acid (Neu5But) into their glycoconjugates. In contrast, the natural precursor ManNAc inhibited the growth of capillaries. Thus, sialic acid precursors may represent useful agents to modulate blood vessel formation.

Defective Angiogenesis Delays Thrombus ResolutionSignificance

Objective— Restoration of patency is a natural target of vascular remodeling after venous thrombosis that involves vascular endothelial cells and smooth muscle cells, as well as leukocytes. Acute pulmonary emboli usually resolve <6 months. However, in some instances, thrombi transform into fibrous vascular obstructions, resulting in occlusion of the deep veins, or in chronic thromboembolic pulmonary hypertension (CTEPH). We proposed that dysregulated thrombus angiogenesis may contribute to thrombus persistence. Approach and Results— Mice with an endothelial cell–specific conditional deletion of vascular endothelial growth factor receptor 2/kinase insert domain protein receptor were used in a model of stagnant flow venous thrombosis closely resembling human deep vein thrombosis. Biochemical and functional analyses were performed on pulmonary endarterectomy specimens from patients with CTEPH, a human model of nonresolving venous thromboembolism. Endothelial cell–specific deletion of kinase insert domain protein receptor and subsequent ablation of thrombus vascularization delayed thrombus resolution. In accordance with these findings, organized human CTEPH thrombi were largely devoid of vascular structures. Several vessel-specific genes, such as kinase insert domain protein receptor, vascular endothelial cadherin, and podoplanin, were expressed at lower levels in white CTEPH thrombi than in organizing deep vein thrombi and organizing thrombi from aortic aneurysms. In addition, red CTEPH thrombi attenuated the angiogenic response induced by vascular endothelial growth factor. Conclusions— In the present work, we propose a mechanism of thrombus nonresolution demonstrating that endothelial cell–specific deletion of kinase insert domain protein receptor abates thrombus vessel formation, misguiding thrombus resolution. Medical conditions associated with the development of CTEPH may be compromising early thrombus angiogenesis. # Significance {#article-title-44}Objective—Restoration of patency is a natural target of vascular remodeling after venous thrombosis that involves vascular endothelial cells and smooth muscle cells, as well as leukocytes. Acute pulmonary emboli usually resolve <6 months. However, in some instances, thrombi transform into fibrous vascular obstructions, resulting in occlusion of the deep veins, or in chronic thromboembolic pulmonary hypertension (CTEPH). We proposed that dysregulated thrombus angiogenesis may contribute to thrombus persistence. Approach and Results—Mice with an endothelial cell–specific conditional deletion of vascular endothelial growth factor receptor 2/kinase insert domain protein receptor were used in a model of stagnant flow venous thrombosis closely resembling human deep vein thrombosis. Biochemical and functional analyses were performed on pulmonary endarterectomy specimens from patients with CTEPH, a human model of nonresolving venous thromboembolism. Endothelial cell–specific deletion of kinase insert domain protein receptor and subsequent ablation of thrombus vascularization delayed thrombus resolution. In accordance with these findings, organized human CTEPH thrombi were largely devoid of vascular structures. Several vessel-specific genes, such as kinase insert domain protein receptor, vascular endothelial cadherin, and podoplanin, were expressed at lower levels in white CTEPH thrombi than in organizing deep vein thrombi and organizing thrombi from aortic aneurysms. In addition, red CTEPH thrombi attenuated the angiogenic response induced by vascular endothelial growth factor. Conclusions—In the present work, we propose a mechanism of thrombus nonresolution demonstrating that endothelial cell–specific deletion of kinase insert domain protein receptor abates thrombus vessel formation, misguiding thrombus resolution. Medical conditions associated with the development of CTEPH may be compromising early thrombus angiogenesis.