Acidic and basic fibroblast growth factors suppress transcriptional activation of tissue factor and other inflammatory genes in endothelial cells

FGF1 attenuates sepsis-induced coagulation dysfunction and hepatic injury via IL6/STAT3 pathway inhibition

BACKGROUND & AIMS

Sepsis, a globally prevalent and highly lethal condition, remains a critical medical challenge. This investigation aims to assess the relevance of FGF1 as a potential therapeutic target for sepsis.

METHODS

Sepsis was induced in C57BL/6 mice through LPS administration to establish an in vivo animal model. Various in vitro assays were conducted using human umbilical vein endothelial cells to elucidate the role of FGF1 in the disruption of the coagulation system and liver injury associated with sepsis, as well as to explore its underlying molecular mechanisms.

RESULTS

In in vivo experiments, FGF1 ameliorated coagulation system disruption in septic mice by reducing the levels of pro-inflammatory and coagulation-related factors in the bloodstream. FGF1 also enhanced liver function in septic mice, mitigating liver inflammation and cell apoptosis, fostering liver vascular regeneration, increasing liver blood perfusion, and improving mouse survival. In vitro experiments demonstrated that FGF1 could inhibit LPS-induced inflammatory responses and apoptosis in endothelial cells, fortify endothelial cell barrier function, decrease endothelial cell permeability, promote endothelial cell proliferation, and restore endothelial cell tube-forming ability. Both in vivo and in vitro experiments substantiated that FGF1 improved sepsis by inhibiting the IL-6/STAT3 signaling pathway.

CONCLUSION

In summary, our study indicates that FGF1 mitigates excessive inflammatory responses in sepsis by suppressing the IL-6/STAT3 signaling pathway, thereby improving systemic blood circulation and ameliorating liver damage in septic organisms. Consequently, this research identifies FGF1 as a potential clinical target for the treatment of human sepsis.

Alterations to Sphingomyelin Metabolism Affect Hemostasis and Thrombosis

BACKGROUND

Our recent studies suggest that sphingomyelin levels in the plasma membrane influence TF (tissue factor) procoagulant activity. The current study was performed to investigate how alterations to sphingomyelin metabolic pathway would affect TF procoagulant activity and thereby affect hemostatic and thrombotic processes.

METHODS

Macrophages and endothelial cells were transfected with specific siRNAs or infected with adenoviral vectors to alter sphingomyelin levels in the membrane. TF activity was measured in factor X activation assay. Saphenous vein incision-induced bleeding and the inferior vena cava ligation-induced flow restriction mouse models were used to evaluate hemostasis and thrombosis, respectively.

RESULTS

Overexpression of SMS (sphingomyelin synthase) 1 or SMS2 in human monocyte-derived macrophages suppresses ATP-stimulated TF procoagulant activity, whereas silencing SMS1 or SMS2 increases the basal cell surface TF activity to the same level as of ATP-decrypted TF activity. Consistent with the concept that sphingomyelin metabolism influences TF procoagulant activity, silencing of acid sphingomyelinase or neutral sphingomyelinase 2 or 3 attenuates ATP-induced enhanced TF procoagulant activity in macrophages and endothelial cells. Niemann-Pick disease fibroblasts with a higher concentration of sphingomyelin exhibited lower TF activity compared with wild-type fibroblasts. In vivo studies revealed that LPS+ATP-induced TF activity and thrombin generation were attenuated in ASMase^-/- mice, while their levels were increased in SMS2^-/- mice. Further studies revealed that acid sphingomyelinase deficiency leads to impaired hemostasis, whereas SMS2 deficiency increases thrombotic risk.

CONCLUSIONS

Overall, our data indicate that alterations in sphingomyelin metabolism would influence TF procoagulant activity and affect hemostatic and thrombotic processes.

Factor VIIa induces extracellular vesicles from the endothelium: a potential mechanism for its hemostatic effect

Recombinant factor FVIIa (rFVIIa) is used as a hemostatic agent to treat bleeding disorders in hemophilia patients with inhibitors and other groups of patients. Our recent studies showed that FVIIa binds endothelial cell protein C receptor (EPCR) and induces protease-activated receptor 1 (PAR1)-mediated biased signaling. The importance of FVIIa-EPCR-PAR1-mediated signaling in hemostasis is unknown. In the present study, we show that FVIIa induces the release of extracellular vesicles (EVs) from endothelial cells both in vitro and in vivo. Silencing of EPCR or PAR1 in endothelial cells blocked the FVIIa-induced generation of EVs. Consistent with these data, FVIIa treatment enhanced the release of EVs from murine brain endothelial cells isolated from wild-type (WT), EPCR-overexpressing, and PAR1-R46Q-mutant mice, but not EPCR-deficient or PAR1-R41Q-mutant mice. In vivo studies revealed that administration of FVIIa to WT, EPCR-overexpressing, and PAR1-R46Q-mutant mice, but not EPCR-deficient or PAR1-R41Q-mutant mice, increased the number of circulating EVs. EVs released in response to FVIIa treatment exhibit enhanced procoagulant activity. Infusion of FVIIa-generated EVs and not control EVs to platelet-depleted mice increased thrombin generation at the site of injury and reduced blood loss. Administration of FVIIa-generated EVs or generation of EVs endogenously by administering FVIIa augmented the hemostatic effect of FVIIa. Overall, our data reveal that FVIIa treatment, through FVIIa-EPCR-PAR1 signaling, releases EVs from the endothelium into the circulation, and these EVs contribute to the hemostatic effect of FVIIa.

The lipid peroxidation product 4-hydroxy-2-nonenal induces tissue factor decryption via ROS generation and the thioredoxin system

Many pathophysiologic agents transform cryptic tissue factor (TF) on cells to prothrombotic TF, and one such stimulus is 4-hydroxy-2-nonenal (HNE), the most abundant aldehyde produced by the oxidation of ω-6 polyunsaturated fatty acids. HNE was shown to induce reactive oxygen species (ROS) generation and p38 MAPK activation, but the link between them and their role in TF decryption are unclear. The present study was carried out to elucidate potential mechanisms involved in HNE-induced TF decryption in monocytic cells. The data presented herein show that mitochondria are the primary source for HNE-induced ROS generation. The inhibition of mitochondrial electron transport chain complex III and V blocked HNE-induced ROS generation, but not p38 MAPK activation. These inhibitors reduced phosphatidylserine (PS) externalization and TF decryption significantly, but not completely. HNE treatment inhibited the activities of thioredoxin reductase (TrxR) and thioredoxin (Trx), independent of ROS. Inhibition of the TrxR/Trx system by HNE or pharmacological inhibitors induced p38 MAPK activation, PS externalization, and TF decryption. Additional studies revealed that the inhibition of TrxR/Trx led to activation of apoptosis signal-regulating kinase (ASK-1) and mitogen-activated protein kinase kinase 3/6. Inhibition of ASK-1 expression by small interfering RNA or its activity by pharmacological inhibitors diminished HNE-induced TF decryption. Overall, our data suggest that HNE induces TF decryption by 2 distinctive pathways. One is ROS dependent but independent of p38 MAPK activation, and the other is via TrxR/Trx and is p38 MAPK activation dependent. However, both mechanisms result in the enhancement of PS at the outer leaflet that is responsible for TF decryption.

Sphingomyelin encrypts tissue factor: ATP-induced activation of A-SMase leads to tissue factor decryption and microvesicle shedding

A majority of tissue factor (TF) on cell surfaces exists in an encrypted state with minimal to no procoagulant activity. At present, it is unclear whether limited availability of phosphatidylserine (PS) and/or a specific membrane lipid in the outer leaflet of the plasma membrane contributes to TF encryption. Sphingomyelin (SM) is a major phospholipid in the outer leaflet, and SM metabolism is shown to be altered in many disease settings that cause thrombotic disorders. The present study is carried out to investigate the effect of SM metabolism on TF activity and TF+ microvesicles (MVs) release. In vitro studies using TF reconstituted into liposomes containing varying molar ratios of SM showed that a high molar ratio of SM in the proteoliposomes inhibits TF coagulant activity. Treatment of macrophages with sphingomyelinase (SMase) that hydrolyzes SM in the outer leaflet results in increased TF activity at the cell surface and TF+ MVs release without increasing PS externalization. Adenosine triphosphate (ATP) stimulation of macrophages that activates TF and induces MV shedding also leads to translocation of acid-sphingomyelinase (A-SMase) to the plasma membrane. ATP stimulation increases the hydrolysis of SM in the outer leaflet. Inhibition of A-SMase expression or activity not only attenuates ATP-induced SM hydrolysis, but also inhibits ATP-induced TF decryption and TF+ MVs release. Overall, our novel findings show that SM plays a role in maintaining TF in an encrypted state in resting cells and hydrolysis of SM following cell injury removes the inhibitory effect of SM on TF activity, thus leading to TF decryption.

Abnormal Expression of Genes Associated with Development and Inflammation in the Heart of Mouse Maternal Phenylketonuria Offspring

This study descibes gene expression in the fetus hearts obtained from mouse model for Phenylketonuria. These hearts have cardiovascular disease (CVD). Therefore genes involved in CVD were examined. Several genes associated with heart development and inflammation were found to be altered. In order to investigate whether the abnormal gene expression alters transcription and translation, the levels of troponin mRNA and protein were determined. One step real time RT-PCR showed a reduction in cardiac troponin I, troponin T2 and ryanodine receptor 2. Determination of troponin I and T protein levels showed reduced levels of these proteins. Our results suggest that altered gene expression affects protein production. These changes are likely involved in the cardiovascular defects seen in the mouse.

A basic fibroblast growth factor analog for protection and mitigation against acute radiation syndromes

The effects of fibroblast growth factors and their potential as broad-spectrum agents to treat and mitigate radiation injury have been studied extensively over the past two decades. This report shows that a peptide mimetic of basic fibroblast growth factor (FGF-P) protects and mitigates against acute radiation syndromes. FGF-P attenuates both sepsis and bleeding in a radiation-induced bone marrow syndrome model and reduces the severity of gastrointestinal and cutaneous syndromes; it should also mitigate combined injuries. FGF-2 and FGF-P induce little or no deleterious inflammation or vascular leakage, which distinguishes them from most other growth factors, angiogenic factors, and cytokines. Although recombinant FGFs have proven safe in several ongoing clinical trials, they are expensive to synthesize, can only be produced in limited quantity, and have limited shelf life. FGF-P mimics the advantageous features of FGF-2 without these disadvantages. This paper shows that FGF-P not only has the potential to be a potent yet safe broad-spectrum medical countermeasure that mitigates acute radiotoxicity but also holds promise for thermal burns, ischemic wound healing, tissue engineering, and stem-cell regeneration.

Multi-targeted mechanisms underlying the endothelial protective effects of the diabetic-safe sweetener erythritol

Diabetes is characterized by hyperglycemia and development of vascular pathology. Endothelial cell dysfunction is a starting point for pathogenesis of vascular complications in diabetes. We previously showed the polyol erythritol to be a hydroxyl radical scavenger preventing endothelial cell dysfunction onset in diabetic rats. To unravel mechanisms, other than scavenging of radicals, by which erythritol mediates this protective effect, we evaluated effects of erythritol in endothelial cells exposed to normal (7 mM) and high glucose (30 mM) or diabetic stressors (e.g. SIN-1) using targeted and transcriptomic approaches. This study demonstrates that erythritol (i.e. under non-diabetic conditions) has minimal effects on endothelial cells. However, under hyperglycemic conditions erythritol protected endothelial cells against cell death induced by diabetic stressors (i.e. high glucose and peroxynitrite). Also a number of harmful effects caused by high glucose, e.g. increased nitric oxide release, are reversed. Additionally, total transcriptome analysis indicated that biological processes which are differentially regulated due to high glucose are corrected by erythritol. We conclude that erythritol protects endothelial cells during high glucose conditions via effects on multiple targets. Overall, these data indicate a therapeutically important endothelial protective effect of erythritol under hyperglycemic conditions.

Endothelial cell protein C receptor opposes mesothelioma growth driven by tissue factor

The procoagulant protein tissue factor (F3) is a powerful growth promoter in many tumors, but its mechanism of action is not well understood. More generally, it is unknown whether hemostatic factors expressed on tumor cells influence tissue factor-mediated effects on cancer progression. In this study, we investigated the influence of tissue factor, endothelial cell protein C receptor (EPCR, PROCR), and protease activated receptor-1 (PAR1, F2R) on the growth of malignant pleural mesothelioma (MPM), using human MPM cells that lack or express tissue factor, EPCR or PAR1, and an orthotopic nude mouse model of MPM. Intrapleural administration of MPM cells expressing tissue factor and PAR1 but lacking EPCR and PAR2 (F2RL1) generated large tumors in the pleural cavity. Suppression of tissue factor or PAR1 expression in these cells markedly reduced tumor growth. In contrast, tissue factor overexpression in nonaggressive MPM cells that expressed EPCR and PAR1 with minimal levels of tissue factor did not increase their limited tumorigenicity. More importantly, ectopic expression of EPCR in aggressive MPM cells attenuated their growth potential, whereas EPCR silencing in nonaggressive MPM cells engineered to overexpress tissue factor increased their tumorigenicity. Immunohistochemical analyses revealed that EPCR expression in tumor cells reduced tumor cell proliferation and enhanced apoptosis. Overall, our results enlighten the mechanism by which tissue factor promotes tumor growth through PAR1, and they show how EPCR can attenuate the growth of tissue factor-expressing tumor cells.

Mycobacterium tuberculosis infection and tissue factor expression in macrophages

A number of earlier studies reported the occurrence of thrombotic complications, particularly disseminated intravascular coagulation and deep vein thrombosis, in tuberculosis (TB) patients. The aberrant expression of tissue factor (TF), the primary activator of coagulation cascade, is known to be responsible for thrombotic disorders in many diseases including bacterial infections. Further, expression of TF by cells of the monocyte/macrophage lineage is also shown to contribute to the development and progression of local and systemic inflammatory reactions. In the present study, we have investigated whether Mycobacterium tuberculosis (Mtb) infection induces TF expression in macrophages, and various host and pathogenic factors responsible for TF expression. We have tested the effect of live virulent Mtb H37Rv, gamma-irradiated Mtb H37Rv (γ-Mtb) and various components derived from Mtb H37Rv on TF expression in macrophages. The data presented in the manuscript show that both live virulent Mtb and γ-Mtb treatments markedly increased TF activity in macrophages, predominantly in the CD14⁺ macrophages. Detailed studies using γ-Mtb showed that the increased TF activity in macrophages following Mtb treatment is the result of TF transcriptional activation. The signaling pathways of TF induction by Mtb appears to be distinct from that of LPS-induced TF expression. Mtb-mediated TF expression is dependent on cooperation of CD14/TLR2/TLR4 and probably yet another unknown receptor/cofactor. Mtb cell wall core components, mycolyl arabinogalactan peptidoglycan (mAGP), phosphatidylinositol mannoside-6 (PIM6) and lipomannan (LM) were identified as factors responsible for induction of TF in the order of mAGP>PIM6>LM. A direct contact between bacteria and macrophage and not Mtb-released soluble factors is critical for TF induction by Mtb. In summary, our data show that Mtb induces TF expression in macrophages and Mtb signaling pathways that elicit TF induction require cooperation of multiple receptors, co-receptors/co-factors including Toll-like receptors. The importance of TF in granuloma formation and containment of Mtb is discussed.

Plasminogen activator inhibitor-1 inhibits factor VIIa bound to tissue factor

BACKGROUND AND OBJECTIVE

A growing body of experimental evidence supports broad inhibitory and regulatory activity of plasminogen activator inhibitor 1 (PAI-1). The present study was designed to investigate whether PAI-1 inhibits factor (F) VIIa complexed with tissue factor (TF), a well-known procoagulant risk factor.

METHODS AND RESULTS

The ability of PAI-1 to inhibit FVIIa-TF activity was evaluated in both clotting and factor X (FX) activation assays. PAI-1 and its complex with vitronectin inhibit: (i) clotting activity of FVIIa-TF (PAI-1(IC50) , 817 and 125 nm, respectively); (ii) FVIIa-TF-mediated FX activation (PAI-1(IC50) , 260 and 50 nm, respectively); and (iii) FVIIa bound to TF expressed on the surface of stimulated endothelial cells (PAI-1(IC50) , 260 and 120 nm, respectively). The association rate constant (k(a)) for PAI-1 inhibition of FVIIa-TF was determined using a chromogenic assay. K(a) for PAI-1 inhibition of FVIIa bound to relipidated TF is 3.3-fold higher than that for FVIIa bound to soluble TF (k(a) = 0.09 ± 0.01 and 0.027 ± 0.03 μm(-1) min(-1), respectively). Vitronectin increases k(a) for both soluble and relipidated TF by 3.5- and 30-fold, respectively (to 0.094 ± 0.020 and 2.7 ± 0.2 μm(-1) min(-1)). However, only a 3.5- to 5.0-fold increase in the acylated FVIIa was observed on SDS PAGE in the presence of vitronectin for both relipidated and soluble TF, indicating fast formation of PAI-1/vitronectin/FVIIa/relipidated TF non-covalent complex.

CONCLUSIONS

Our results demonstrate potential anticoagulant activity of PAI-1 in the presence of vitronectin, which could contribute to regulation of hemostasis under pathological conditions such as severe sepsis, acute lung injury and pleural injury, where PAI-1 and TF are overexpressed.

Plasmin enhances cell surface tissue factor activity in mesothelial and endothelial cells

BACKGROUND

Mesothelial cells that line the thoracic cavity play an important role in maintaining the local balance between procoagulant and fibrinolytic activity, a role akin to the endothelial cells in blood vessels. The mechanism(s) responsible for increased tissue factor (TF) expression in mesothelial cells in response to injury are at present unclear.

OBJECTIVE

To investigate whether plasmin or thrombin, two major proteases that may be generated on the pleural surface upon injury, induce TF expression in human pleural mesothelial cells (HMC) and elucidate the underlying mechanism(s).

METHODS

Confluent monolayers of HMC and human umbilical vein endothelial cells (HUVEC) were exposed to plasmin or thrombin for varying time periods and TF expression was analyzed by measuring its activity in a factor Xa generation assay, TF antigen levels by immunoblot analysis and TF mRNA by Northern blot analysis.

RESULTS

Both plasmin and thrombin treatments increased cell surface TF activity in HMC by 3- to 4-fold. In contrast to thrombin, plasmin-induced TF activity is not dependent on the de novo synthesis of TF. In HUVEC, plasmin had a minimal effect on unperturbed HUVEC whereas it markedly increased TF activity of activated HUVEC. Plasmin treatment neither affected anionic phospholipid levels at the cell surface nor released protein disulfide isomerase, an oxidoreductase protein that was newly described to play a role in TF activation. Plasmin cleaved cell-associated TFPI.

CONCLUSION

Thrombin up-regulates TF activity in HMC through the transcriptional activation of TF whereas plasmin increases TF activity by inactivating the cell-associated TFPI by a limited proteolysis.

Impact of neutrophil apoptosis on haemostatic activation in chronic liver disease patients

Recent studies suggest the impact of apoptosis on the mechanisms leading to hypercoagulability. We aimed to clarify the potential role of neutrophil apoptosis in neutropenia and hypercoagulable state encountered in chronic liver disease patients. This study was conducted on 15 normal controls and 45 patients with chronic liver disease classified according to modified Child Pugh classification into, Child A, B and C groups (15 cases each). Haemostatic parameters studied include, prothrombin time, partial thromboplastin time, tissue factor, protein C antigen, protein S antigen, and markers of haemostatic activation [prothrombin fragment 1+2 (F1+2), thrombus precursor protein (TpP) and D-dimer]. Flowcytometric study was done for quantitative assay of neutrophil apoptotic subpopulations to detect the percentage of early and late apoptotic, and necrotic neutrophils using Annexin V-FITC/propidium iodide dye. Semiquantitative assay of apoptotic neutrophils showing DNA fragmentation was performed on neutrophil culture using terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labelling test. In addition to enzyme-linked immunosorbent assay for soluble Fas (APO-1/CD95) in culture supernatant. The results revealed a rise in the neutrophil apoptotic and necrotic markers with progression of the disease, and they were inversely correlated with the absolute neutrophil count. The apoptotic neutrophil cells showed a significant positive correlation with several haemostatic parameters (tissue factor, prothrombin fragment 1+2, thrombus precursor protein and D-dimer). Regression analysis proved that apoptotic parameters are independent determinants of prothrombotic markers, which further incriminate the apoptotic mechanisms in the hypercoagulable state encountered in this clinical setting.

Tissue factor activation: is disulfide bond switching a regulatory mechanism?

A majority of tissue factor (TF) on cell surfaces exists in a cryptic form (ie, coagulation function inactive) but retains its functionality in cell signaling. Recent studies have suggested that cryptic TF contains unpaired cysteine thiols and that activation involves the formation of the disulfide bond Cys186-Cys 209 and that protein disulfide isomerase (PDI) regulates TF coagulant and signaling activities by targeting this disulfide bond. This study was carried out to investigate the validity of this novel concept. Although treatment of MDA 231 tumor cells, fibroblasts, and stimulated endothelial cells with the oxidizing agent HgCl(2) markedly increased the cell-surface TF coagulant activity, the increase is associated with increased anionic phospholipids at the cell surface. Annexin V, which binds to anionic phospholipids, attenuated the increased TF coagulant activity. It is noteworthy that treatment of cells with reducing agents also increased the cell surface TF activity. No evidence was found for either detectable expression of PDI at the cell surface or association of TF with PDI. Furthermore, reduction of PDI with the gene silencing had no effect on either TF coagulant or cell signaling functions. Overall, the present data undermine the recently proposed hypothesis that PDI-mediated disulfide exchange plays a role in regulating TF procoagulant and cell signaling functions.

Tissue factor trafficking in fibroblasts: involvement of protease-activated receptor-mediated cell signaling

Tissue factor (TF) is the cellular receptor for clotting factor VIIa (FVIIa), and the formation of TF-FVIIa complexes on cell surfaces triggers the activation of the coagulation cascade and the cell signaling. Our recent studies have shown that a majority of TF resides in various intracellular compartments, predominantly in the Golgi, and that FVIIa binding to cell surface TF induces TF endocytosis and mobilizes the Golgi TF pool to translocate it to the cell surface. This present study is aimed to elucidate the mechanisms involved in TF endocytosis and its mobilization from the Golgi. Activation of protease-activated receptor 1 (PAR1) and PAR2 by specific peptide agonists and proteases, independent of FVIIa, mobilized TF from the Golgi store and increased the cell surface expression of TF. Blocking PAR2 activation, but not PAR1, with neutralizing antibodies fully attenuated the FVIIa-induced TF mobilization. Consistent with these data, silencing the PAR2 receptor, and not PAR1, abrogated the FVIIa-mediated TF mobilization. In contrast to their effect on TF mobilization, PAR1 and PAR2 activation, in the absence of FVIIa, had no effect on TF endocytosis. However, PAR2 activation is found to be critical for the FVIIa-induced TF endocytosis. Overall the data herein provide novel insights into the role of PARs in regulating cell surface TF expression.

Cellular localization and trafficking of tissue factor

Tissue factor (TF) is the cellular receptor for clotting factor VIIa (FVIIa). The formation of TF-FVIIa complexes on cell surfaces triggers the activation of coagulation cascade and cell signaling. In the present study, we characterized the subcellular distribution of TF and its transport in fibroblasts by dual immunofluorescence confocal microscopy and biochemical methods. Our data show that a majority of TF resides in various intracellular compartments, predominantly in the Golgi. Tissue factor at the cell surface is localized in cholesterol-rich lipid rafts and extensively colocalized with caveolin-1. FVIIa binding to TF induces the internalization of TF. Of interest, we found that TF-FVIIa complex formation at the cell surface leads to TF mobilization from the Golgi with a resultant increase in TF expression at the cell surface. This process is dependent on FVIIa protease activity. Overall, the present data suggest a novel mechanism for TF expression at the cell surface by FVIIa. This mechanism could play an important role in hemostasis in response to vascular injury by increasing TF activity where and when it is needed.

Discovery of genetic difference between asthmatic children with high IgE level and normal IgE level by whole genome linkage disequilibrium mapping using 763 autosomal STR markers

The genome-wide linkage disequilibrium screen for loci associated with genetic difference between allergic and nonallergic asthma was conducted with 763 autosomal STR markers and included 190 asthmatic children. Evidence for association with differences between the two forms of asthma was observed for 36 STR markers. Marker-to-marker synergetic effect and by simulation resampling tests revealed D5S2011, D6S305, and D9S286 were important loci in allergic asthma while D6S1574, D8S1769, and D19S226 were important in nonallergic asthma. Our results show strong genetic evidence that these markers play an important role in defining allergic and nonallergic asthma and provides important candidates of susceptible genes in these two categories of asthma. This study further shows that asthma is, indeed, a heterogeneous group of underlying diseases and, although with similar clinical phenotypes, may have different clinical severities, outcomes, and need more tailor-made management.

Fibroblast growth factor/fibroblast growth factor receptor system in angiogenesis

Fibroblast growth factors (FGFs) are a family of heparin-binding growth factors. FGFs exert their pro-angiogenic activity by interacting with various endothelial cell surface receptors, including tyrosine kinase receptors, heparan-sulfate proteoglycans, and integrins. Their activity is modulated by a variety of free and extracellular matrix-associated molecules. Also, the cross-talk among FGFs, vascular endothelial growth factors (VEGFs), and inflammatory cytokines/chemokines may play a role in the modulation of blood vessel growth in different pathological conditions, including cancer. Indeed, several experimental evidences point to a role for FGFs in tumor growth and angiogenesis. This review will focus on the relevance of the FGF/FGF receptor system in adult angiogenesis and its contribution to tumor vascularization.

Acute cholesterol depletion impairs functional expression of tissue factor in fibroblasts: modulation of tissue factor activity by membrane cholesterol

Cholesterol, in addition to providing rigidity to the fluid membrane, plays a critical role in receptor function, endocytosis, recycling, and signal transduction. In the present study, we examined the effect of membrane cholesterol on functional expression of tissue factor (TF), a cellular receptor for clotting factor VIIa. Depletion of cholesterol in human fibroblasts (WI-38) with methyl-beta-cyclodextrin-reduced TF activity at the cell surface. Binding studies with radiolabeled VIIa and TF monoclonal antibody (mAB) revealed that reduced TF activity in cholesterol-depleted cells stems from the impairment of VIIa interaction with TF rather than the loss of TF receptors at the cell surface. Repletion of cholesterol-depleted cells with cholesterol restored TF function. Loss of caveolar structure on cholesterol removal is not responsible for reduced TF activity. Solubilization of cellular TF in different detergents indicated that a substantial portion of TF in fibroblasts is associated with noncaveolar lipid rafts. Cholesterol depletion studies showed that the TF association with these rafts is cholesterol dependent. Overall, the data presented herein suggest that membrane cholesterol functions as a positive regulator of TF function by maintaining TF receptors, probably in noncaveolar lipid rafts, in a high-affinity state for VIIa binding.

Vascular endothelial growth factor–stimulated endothelial cells promote adhesion and activation of platelets

Coagulation abnormalities, including an increased platelet turnover, are frequently found in patients with cancer. Because platelets secrete angiogenic factors on activation, this study tested the hypothesis that platelets contribute to angiogenesis. Stimulation with vascular endothelial growth factor (VEGF, 25 ng/mL) of human umbilical vein endothelial cells (HUVECs) promoted adhesion of nonactivated platelets 2.5-fold. In contrast, stimulation of HUVECs with basic fibroblast growth factor (bFGF) did not promote platelet adhesion. By blocking tissue factor (TF) activity, platelet adhesion was prevented and antibodies against fibrin(ogen) and the platelet-specific integrin, αIIbβ3, inhibited platelet adhesion for 70% to 90%. These results indicate that VEGF-induced platelet adhesion to endothelial cells is dependent on activation of TF. The involvement of fibrin(ogen) and the αIIbβ3 integrin, which exposes a high-affinity binding site for fibrin(ogen) on platelet activation, indicates that these adhering platelets are activated. This was supported by the finding that the activity of thrombin, a product of TF-activated coagulation and a potent platelet activator, was required for platelet adhesion. Finally, platelets at physiologic concentrations stimulated proliferation of HUVECs, indicative of proangiogenic activity in vivo. These results support the hypothesis that platelets contribute to tumor-induced angiogenesis. In addition, they may explain the clinical observation of an increased platelet turnover in cancer patients. Platelets may also play an important role in other angiogenesis-dependent diseases in which VEGF is involved, such as diabetes and autoimmune diseases.

Vascular endothelial growth factor–stimulated endothelial cells promote adhesion and activation of platelets

Coagulation abnormalities, including an increased platelet turnover, are frequently found in patients with cancer. Because platelets secrete angiogenic factors on activation, this study tested the hypothesis that platelets contribute to angiogenesis. Stimulation with vascular endothelial growth factor (VEGF, 25 ng/mL) of human umbilical vein endothelial cells (HUVECs) promoted adhesion of nonactivated platelets 2.5-fold. In contrast, stimulation of HUVECs with basic fibroblast growth factor (bFGF) did not promote platelet adhesion. By blocking tissue factor (TF) activity, platelet adhesion was prevented and antibodies against fibrin(ogen) and the platelet-specific integrin, αIIbβ3, inhibited platelet adhesion for 70% to 90%. These results indicate that VEGF-induced platelet adhesion to endothelial cells is dependent on activation of TF. The involvement of fibrin(ogen) and the αIIbβ3 integrin, which exposes a high-affinity binding site for fibrin(ogen) on platelet activation, indicates that these adhering platelets are activated. This was supported by the finding that the activity of thrombin, a product of TF-activated coagulation and a potent platelet activator, was required for platelet adhesion. Finally, platelets at physiologic concentrations stimulated proliferation of HUVECs, indicative of proangiogenic activity in vivo. These results support the hypothesis that platelets contribute to tumor-induced angiogenesis. In addition, they may explain the clinical observation of an increased platelet turnover in cancer patients. Platelets may also play an important role in other angiogenesis-dependent diseases in which VEGF is involved, such as diabetes and autoimmune diseases.

Regulation of Tissue Factor Pathway Inhibitor Expression in Smooth Muscle Cells

Tissue factor pathway inhibitor (TFPI) is the primary physiological inhibitor that regulates tissue factor-induced blood coagulation. TFPI is thought to be synthesized, in vivo, primarily by microvascular endothelial cells. Little is known about how TFPI is regulated under pathophysiological conditions. In this study, we determined mechanisms by which TFPI expression is regulated by human pulmonary artery smooth muscle cells (PASMC), because these cells contribute to remodeling of the pulmonary vasculature in disease. PASMC in culture constitutively synthesize and secrete TFPI. Exposure of PASMC to phorbol myristate acetate, lipopolysaccharide, tumor necrosis factor , thrombin, interleukin-1, and transforming growth factor-β had no significant effect on expression of TFPI by PASMC. By contrast, treatment of PASMC with serum and basic fibroblast growth factor (bFGF)/heparin markedly upregulated the expression of TFPI activity and antigen. On Western blot analysis, a protein consistent with full-length TFPI (42 kD) was identified in the conditioned media of PASMC, and the levels of the protein were much higher in the conditioned media of serum and bFGF/heparin-treated cells. Northern blot analysis showed that PASMC constitutively express TFPI mRNA, and treatment of cells with serum and bFGF/heparin had a minimal effect on the steady-state levels of TFPI mRNA. Nuclear run-on analysis did not show a significant increase in the transcriptional rate of TFPI gene in PASMC treated with serum or bFGF/heparin. Cycloheximide, but not actinomycin-D, treatment inhibited the serum and bFGF/heparin-induced increase in TFPI activity in PASMC. In conclusion, our data demonstrate that PASMC constitutively synthesize and secrete TFPI and serum or bFGF upregulate its expression, suggesting that growth factors that can stimulate the vessel wall in vivo might locally regulate TFPI expression. Our study also suggests that control of TFPI expression by serum or bFGF occurs via translational rather than transcriptional regulation.

Regulation of Tissue Factor Pathway Inhibitor Expression in Smooth Muscle Cells

Tissue factor pathway inhibitor (TFPI) is the primary physiological inhibitor that regulates tissue factor-induced blood coagulation. TFPI is thought to be synthesized, in vivo, primarily by microvascular endothelial cells. Little is known about how TFPI is regulated under pathophysiological conditions. In this study, we determined mechanisms by which TFPI expression is regulated by human pulmonary artery smooth muscle cells (PASMC), because these cells contribute to remodeling of the pulmonary vasculature in disease. PASMC in culture constitutively synthesize and secrete TFPI. Exposure of PASMC to phorbol myristate acetate, lipopolysaccharide, tumor necrosis factor , thrombin, interleukin-1, and transforming growth factor-β had no significant effect on expression of TFPI by PASMC. By contrast, treatment of PASMC with serum and basic fibroblast growth factor (bFGF)/heparin markedly upregulated the expression of TFPI activity and antigen. On Western blot analysis, a protein consistent with full-length TFPI (42 kD) was identified in the conditioned media of PASMC, and the levels of the protein were much higher in the conditioned media of serum and bFGF/heparin-treated cells. Northern blot analysis showed that PASMC constitutively express TFPI mRNA, and treatment of cells with serum and bFGF/heparin had a minimal effect on the steady-state levels of TFPI mRNA. Nuclear run-on analysis did not show a significant increase in the transcriptional rate of TFPI gene in PASMC treated with serum or bFGF/heparin. Cycloheximide, but not actinomycin-D, treatment inhibited the serum and bFGF/heparin-induced increase in TFPI activity in PASMC. In conclusion, our data demonstrate that PASMC constitutively synthesize and secrete TFPI and serum or bFGF upregulate its expression, suggesting that growth factors that can stimulate the vessel wall in vivo might locally regulate TFPI expression. Our study also suggests that control of TFPI expression by serum or bFGF occurs via translational rather than transcriptional regulation.

Tissue factor in atherosclerosis

Thrombosis is a key feature of the initiation and progression of atherosclerosis and its clinical sequelae. Acute thrombosis can lead to arterial occlusion and consequently provoke myocardial infarction, unstable angina, stroke and sudden death. Acute thrombosis can also be a complication of arterial bypass surgery, balloon angioplasty, atherectomy, or coronary artery stenting. The thrombotic response is influenced by several factors, among them the thrombogenicity of the vessel wall and of certain blood components as well as their interaction with the lipid pool. Tissue factor (TF) is considered to be the primary cofactor of cellular origin that is involved in activation of the coagulation pathway. The active form of TF has been shown to be present in specimens of human coronary artery in association both with acellular lipid areas and with macrophages and smooth muscle cells, which suggests that TF plays a major role in determining plaque thrombogenicity. We discuss here what is currently known about the role of tissue factor in atherogenesis, and focus attention on pharmacological approaches in this area.

Changes in anion permeability following hypotonic challenge in rat brain endothelial cells: different responses in primary cultures and in immortalised RBE4 cells

Hypotonicity-induced anion permeability changes were investigated but not detected in immortalised (RBE4) rat brain endothelial cells using iodide efflux measurements. Large, rapid increases were however observed in primary cultured cells. Both cell types were reinvestigated following culture in a common growth factor-depleted medium. Responses were still undetectable in the immortalised RBE4 cells. Reduced responses were observed in the primary cultured cells that also showed altered morphology and decreased activity of another transporter, P-glycoprotein. Thus both immortalisation and different culture conditions may alter functional expression in these cells of transporters involved in hypotonicity-induced anion permeability changes.