Reversal of angiogenesis in vitro, induction of apoptosis, and inhibition of AKT phosphorylation in endothelial cells by thromboxane A(2)

Recent Advances in the Treatment of Pulmonary Arterial Hypertension Associated with Connective Tissue Diseases

Pulmonary hypertension (PH) is a severe vascular complication of connective tissue diseases (CTD). Patients with CTD may develop PH belonging to diverse groups: (1) pulmonary arterial hypertension (PAH), (2) PH due to left heart disease, (3) secondary PH due to lung disease and/or hypoxia and (4) chronic thromboembolic pulmonary hypertension (CTEPH). PAH most often develops in systemic scleroderma (SSc), mostly in its limited variant. PAH-CTD is a progressive disease characterized by poor prognosis. Therefore, early diagnosis should be established. A specific treatment for PAH-CTD is currently available and recommended: prostacyclin derivative (treprostinil, epoprostenol, iloprost, selexipag), nitric oxide and natriuretic pathway: stimulators of soluble guanylate cyclase (sGC: riociguat) and phosphodiesterase-five inhibitors (PDE5i: sildenafil, tadalafil), endothelin receptor antagonists (ERA: bosentan, macitentan, ambrisentan). Moreover, novel drugs, e.g., sotatercept, have been intensively investigated in clinical trials. We aim to review the literature on recent advances in the treatment strategy and prognosis of patients with PAH-CTD. In this manuscript, we discuss the mechanism of action of PAH-specific drugs and new agents and the latest research conducted on PAH-CTD patients.

Preparing to strike: Acute events in signaling by the serpentine receptor for thromboxane A2

Over the last two decades, awareness of the (patho)physiological roles of thromboxane A₂ signaling has been greatly extended. From humble beginnings as a short-lived stimulus that activates platelets and causes vasoconstriction to a dichotomous receptor system involving multiple endogenous ligands capable of modifying tissue homeostasis and disease generation in almost every tissue of the body. Thromboxane A₂ receptor (TP) signal transduction is associated with the pathogenesis of cancer, atherosclerosis, heart disease, asthma, and host response to parasitic infection amongst others. The two receptors mediating these cellular responses (TPα and TPβ) are derived from a single gene (TBXA2R) through alternative splicing. Recently, knowledge about the mechanism(s) of signal propagation by the two receptors has undergone a revolution in understanding. Not only have the structural relationships associated with G-protein coupling been established but the modulation of that signaling by post-translational modification to the receptor has come sharply into focus. Moreover, the signaling of the receptor unrelated to G-protein coupling has become a burgeoning field of endeavor with over 70 interacting proteins currently identified. These data are reshaping the concept of TP signaling from a mere guanine nucleotide exchange factors for Gα activation to a nexus for the convergence of diverse and poorly characterized signaling pathways. This review summarizes the advances in understanding in TP signaling, and the potential for new growth in a field that after almost 50 years is finally coming of age.

Pathogenic Mechanisms of Pulmonary Arterial Hypertension: Homeostasis Imbalance of Endothelium-Derived Relaxing and Contracting Factors

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease. Sustained pulmonary vasoconstriction and concentric pulmonary vascular remodeling contribute to the elevated pulmonary vascular resistance and pulmonary artery pressure in PAH. Endothelial cells regulate vascular tension by producing endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs). Homeostasis of EDRF and EDCF production has been identified as a marker of the endothelium integrity. Impaired synthesis or release of EDRFs induces persistent vascular contraction and pulmonary artery remodeling, which subsequently leads to the development and progression of PAH. In this review, the authors summarize how EDRFs and EDCFs affect pulmonary vascular homeostasis, with special attention to the recently published novel mechanisms related to endothelial dysfunction in PAH and drugs associated with EDRFs and EDCFs.

The Role and Regulation of Thromboxane A2 Signaling in Cancer-Trojan Horses and Misdirection

Over the last two decades, there has been an increasing awareness of the role of eicosanoids in the development and progression of several types of cancer, including breast, prostate, lung, and colorectal cancers. Several processes involved in cancer development, such as cell growth, migration, and angiogenesis, are regulated by the arachidonic acid derivative thromboxane A₂ (TXA₂). Higher levels of circulating TXA₂ are observed in patients with multiple cancers, and this is accompanied by overexpression of TXA₂ synthase (TBXAS1, TXA₂S) and/or TXA₂ receptors (TBXA2R, TP). Overexpression of TXA₂S or TP in tumor cells is generally associated with poor prognosis, reduced survival, and metastatic disease. However, the role of TXA₂ signaling in the stroma during oncogenesis has been underappreciated. TXA₂ signaling regulates the tumor microenvironment by modulating angiogenic potential, tumor ECM stiffness, and host immune response. Moreover, the by-products of TXA₂S are highly mutagenic and oncogenic, adding to the overall phenotype where TXA₂ synthesis promotes tumor formation at various levels. The stability of synthetic enzymes and receptors in this pathway in most cancers (with few mutations reported) suggests that TXA₂ signaling is a viable target for adjunct therapy in various tumors to reduce immune evasion, primary tumor growth, and metastasis.

The F2-isoprostane 8-iso-PGF2α attenuates atherosclerotic lesion formation in Ldlr-deficient mice - Potential role of vascular thromboxane A2 receptors

The F2-isoprostane 8-iso-PGF_2α (also known as 15-F_2t-isoprostane, iPF_2α-III, 8-epi PGF_2α, 15(S)-8-iso-PGF_2α, or 8-Isoprostane), a thromboxane A₂ receptor (TP) agonist, stable biomarker of oxidative stress, and risk marker of cardiovascular disease, has been proposed to aggravate atherogenesis in genetic mouse models of atherosclerotic vascular disease. Moreover, the TP plays an eminent role in the pathophysiology of endothelial dysfunction, atherogenesis, and cardiovascular disease. Yet it is unknown, how the TP expressed by vascular cells affects atherogenesis or 8-iso-PGF_2α-related effects in mouse models of atherosclerosis. We studied Ldlr-deficient vascular endothelial-specific (EC) and vascular smooth muscle cell (VSMC)-specific TP knockout mice (TP^ECKO/Ldlr KO; TP^VSMCKO/Ldlr KO) and corresponding wild-type littermates (TP^WT/Ldlr KO). The mice were fed a Western-type diet for eight weeks and received either 8-iso-PGF_2α or vehicle infusions via osmotic pumps. Subsequently, arterial blood pressure, atherosclerotic lesion formation, and lipid profiles were analyzed. We found that VSMC-, but not EC-specific TP deletion, attenuated atherogenesis without affecting blood pressure or plasma lipid profiles of the mice. In contrast to a previous report, 8-iso-PGF_2α tended to reduce atherogenesis in TP^WT/Ldlr KO and TP^{EC KO}/Ldlr KO mice, again without significantly affecting blood pressure or lipid profiles of these mice. However, no further reduction in atherogenesis was observed in 8-iso-PGF_2α-treated TP^{VSMC KO}/Ldlr KO mice. Our work suggests that the TP expressed in VSMC but not the TP expressed in EC is involved in atherosclerotic lesion formation in Ldlr-deficient mice. Furthermore, we report an inhibitory effect of 8-iso-PGF_2α on atherogenesis in this experimental atherosclerosis model, which paradoxically appears to be related to the presence of the TP in VSMC.

Thromboxane A2 receptor activation via Gα13-RhoA/C-ROCK-LIMK2-dependent signal transduction inhibits angiogenic sprouting of human endothelial cells

We could previously show that thromboxane A₂ receptor (TP) activation inhibits the angiogenic capacity of human endothelial cells, but the underlying mechanisms remained unclear. Therefore, the aim of this study was to elucidate TP signal transduction pathways relevant to angiogenic sprouting of human endothelial cells. To clarify this matter, we used RNAi-mediated gene silencing as well as pharmacological inhibition of potential TP downstream targets in human umbilical vein endothelial cells (HUVEC) and VEGF-induced angiogenic sprouting of HUVEC spheroids in vitro as a functional read-out. In this experimental set-up, the TP agonist U-46619 completely blocked VEGF-induced angiogenic sprouting of HUVEC spheroids. Moreover, in live-cell analyses TP activation induced endothelial cell contraction, sprout retraction as well as endothelial cell tension and focal adhesion dysregulation of HUVEC. These effects were reversed by pharmacological TP inhibition or TP knockdown. Moreover, we identified a TP-G_α13-RhoA/C-ROCK-LIMK2-dependent signal transduction pathway to be relevant for U-46619-induced inhibition of VEGF-mediated HUVEC sprouting. In line with these results, U-46619-mediated TP activation potently induced RhoA and RhoC activity in live HUVEC as measured by FRET biosensors. Interestingly, pharmacological inhibition of ROCK and LIMK2 also normalized U-46619-induced endothelial cell tension and focal adhesion dysregulation of HUVEC. In summary, our work reveals mechanisms by which the TP may disturb angiogenic endothelial function in disease states associated with sustained endothelial TP activation.

A Thromboxane A2 Receptor-Driven COX-2-Dependent Feedback Loop That Affects Endothelial Homeostasis and Angiogenesis

BACKGROUND

TP (thromboxane A₂ receptor) plays an eminent role in the pathophysiology of endothelial dysfunction and cardiovascular disease. Moreover, its expression is reported to increase in the intimal layer of blood vessels of cardiovascular high-risk individuals. Yet it is unknown, whether TP upregulation per se has the potential to affect the homeostasis of the vascular endothelium.

METHODS

We combined global transcriptome analysis, lipid mediator profiling, functional cell analyses, and in vivo angiogenesis assays to study the effects of endothelial TP overexpression or knockdown/knockout on the angiogenic capacity of endothelial cells in vitro and in vivo.

RESULTS

Here we report that endothelial TP expression induces COX-2 (cyclooxygenase-2) in a G_i/o- and G_q/11-dependent manner, thereby promoting its own activation via the auto/paracrine release of TP agonists, such as PGH₂ (prostaglandin H₂) or prostaglandin F₂ but not TxA₂ (thromboxane A₂). TP overexpression induces endothelial cell tension and aberrant cell morphology, affects focal adhesion dynamics, and inhibits the angiogenic capacity of human endothelial cells in vitro and in vivo, whereas TP knockdown or endothelial-specific TP knockout exerts opposing effects. Consequently, this TP-dependent feedback loop is disrupted by pharmacological TP or COX-2 inhibition and by genetic reconstitution of PGH₂-metabolizing prostacyclin synthase even in the absence of functional prostacyclin receptor expression.

CONCLUSIONS

Our work uncovers a TP-driven COX-2-dependent feedback loop and important effector mechanisms that directly link TP upregulation to angiostatic TP signaling in endothelial cells. By these previously unrecognized mechanisms, pathological endothelial upregulation of the TP could directly foster endothelial dysfunction, microvascular rarefaction, and systemic hypertension even in the absence of exogenous sources of TP agonists.

Antiplatelet Agents Affecting GPCR Signaling Implicated in Tumor Metastasis

Metastasis requires that cancer cells survive in the circulation, colonize distant organs, and grow. Despite platelets being central contributors to hemostasis, leukocyte trafficking during inflammation, and vessel stability maintenance, there is significant evidence to support their essential role in supporting metastasis through different mechanisms. In addition to their direct interaction with cancer cells, thus forming heteroaggregates such as leukocytes, platelets release molecules that are necessary to promote a disseminating phenotype in cancer cells via the induction of an epithelial-mesenchymal-like transition. Therefore, agents that affect platelet activation can potentially restrain these prometastatic mechanisms. Although the primary adhesion of platelets to cancer cells is mainly independent of G protein-mediated signaling, soluble mediators released from platelets, such as ADP, thromboxane (TX) A2, and prostaglandin (PG) E2, act through G protein-coupled receptors (GPCRs) to cause the activation of more additional platelets and drive metastatic signaling pathways in cancer cells. In this review, we examine the contribution of the GPCRs of platelets and cancer cells in the development of cancer metastasis. Finally, the possible use of agents affecting GPCR signaling pathways as antimetastatic agents is discussed.

The calcimimetic R-568 attenuates subarachnoid hemorrhage-induced vasospasm through PI3K/Akt/eNOS signaling pathway in the rat model

Cerebral vasospasm (CVS) causes mortality and morbidity in patients after subarachnoid hemorrhage (SAH). The mechanism and adequate treatment of CVS are still elusive. R-568 is a calcimimetic agent known to exert a vasodilating effect. However, there is no report on its vasodilator effect against SAH-induced vasospasm. In the present study, we investigated the therapeutic effect of R-568 on the SAH-induced CVS model in rats. Seventy-two adult male Sprague-Dawley rats were divided into 8 groups: sham surgery; SAH only; SAH + Vehicle, SAH + R-568; SAH + R-568 + Wortmannin (the PI3K inhibitor); SAH + Wortmannin; SAH + R-568 + Calhex-231 (a calcilytic agent); SAH + Calhex-231. SAH was induced by blood (0.3 mL) given by intracisternal injection. R-568 (20 µM) was administered intracisternal immediately prior to experimental SAH. Basilar arteries (BAs) were obtained to evaluate PI3K/Akt/eNOS pathway (immunoblotting) and morphological changes 48 h after SAH. Perimeters of BAs were decreased by 24.1% in the SAH group compared to the control group and the wall thickness was increased by 75.3%. With R-568 treatment, those percentages were 9.6% and 29.6%, respectively, indicating that vasospasm was considerably improved when compared with the SAH group (P < 0.001 in both). While p-PI3K/PI3K and p-Akt/Akt ratio and eNOS protein expression were markedly decreased in the SAH rats, treatment with R-568 resulted in a significant increase in these levels. The beneficial effects of R-568 were partially blocked in the presence of Calhex-231 and completely blocked in the presence of Wortmannin. Herein, we found that treatment with R-568 would attenuate SAH-induced CVS through the PI3K/Akt/eNOS pathway and demonstrate therapeutic promise in CVS treatment following SAH.

Blockade of AT1 receptor restore the migration of vascular smooth muscle cells in high sodium medium

The present study aimed to test the hypothesis that increased sodium concentration affects the migratory phenotype of vascular smooth muscle cells (VSMCs) independently of the haemodynamic factors. Cell migration was evaluated by wound-healing assay under the following conditions: high sodium (HS, 160 mM) and control (CT, 140 mM). Cell viability was assessed by annexin V and propidium iodide labeling. Cyclooxygenase-2 (COX-2) gene expression was analysed by reverse transcription polymerase chain reaction. ERK1/2 phosphorylation was assessed by western blot. Exposure of VSMCs to HS reduced migration, and AT1R blockade prevented this response. HS increased COX-2 gene expression, and COX-2 blockade prevented the reduction in VSMC migration induced by HS. HS also increased ERK1/2 phosphorylation, and ERK1/2 inhibition recovered VSMC migration as well as blocked COX-2 gene expression. The TXA₂ receptor blocker, but not the prostacyclin receptor blocker, prevented the HS-induced VSMCs migration decrease. HS reduces the migration of VSMCs by increasing COX-2 gene expression via AT1R-ERK1/2 phosphorylation. In addition, increased COX-2 by HS seems to modulate the reduction of VSMCs migration by the TXA₂ receptor.

A current view of G protein-coupled receptor - mediated signaling in pulmonary hypertension: finding opportunities for therapeutic intervention

Pathological vascular remodeling is observed in various cardiovascular diseases including pulmonary hypertension (PH), a disease of unknown etiology that has been characterized by pulmonary artery vasoconstriction, right ventricular hypertrophy, vascular inflammation, and abnormal angiogenesis in pulmonary circulation. G protein-coupled receptors (GPCRs) are the largest family in the genome and widely expressed in cardiovascular system. They regulate all aspects of PH pathophysiology and represent therapeutic targets. We overview GPCRs function in vasoconstriction, vasodilation, vascular inflammation-driven remodeling and describe signaling cross talk between GPCR, inflammatory cytokines, and growth factors. Overall, the goal of this review is to emphasize the importance of GPCRs as critical signal transducers and targets for drug development in PH.

Hyperglycemia via activation of thromboxane A2 receptor impairs the integrity and function of blood-brain barrier in microvascular endothelial cells

Diabetes is one of high risk factors for cardio- and cerebra-vascular diseases, including stroke, atherosclerosis and hypertension. This study was conducted to elucidate whether and how thromboxane receptor (TPr) activation contributes to blood-brain barrier (BBB) dysfunction in diabetes. Human brain microvascular endothelial cells (HBMECs) were cultured. The levels of phosphorylated endothelial nitric oxide synthase (eNOS) at Ser¹¹⁷⁷ (p-eNOS) and Akt at Ser⁴⁷³ (p-Akt) were assayed by western blot. Exposure of HBMECs to either high glucose (HG) or thromboxane A₂ (TxA₂) mimetic U46619, significantly reduced p-eNOS and p-Akt. These effects were abolished by pharmacological or genetic inhibitors of TPr. HG/U46619-induced suppressions of eNOS and Akt phosphorylation were accompanied by upregulation of PTEN and Ser³⁸⁰/Thr^382/383 PTEN phosphorylation. PTEN-specific siRNA restored Akt-eNOS signaling in the face of TPr activation or HG. The small GTPase, Rho, was also activated by HG stimulation, and pretreatment of HBMECs with Y27632, a Rho-associated kinase (ROCK) inhibitor, rescued HG-impaired Akt-eNOS signaling. In STZ-injected rats, we found that hyperglycemia dramatically increased the levels of PTEN and PTEN-Ser³⁸⁰/Thr^382/383 phosphorylation, reduced both levels of p-eNOS and p-Akt, and disrupted BBB function assayed by Evans blue staining, which were abolished by SQ29548 treatment. We conclude that hyperglycemia activates thromboxane A2 receptor to impair the integrity and function of blood-brain barrier via the ROCK-PTEN-Akt-eNOS pathway.

Activation of thromboxane A2 receptors mediates endothelial dysfunction in diabetic mice

BACKGROUND

Diabetes is one of high-risk factors for cardiovascular disease. Improvement of endothelial dysfunction in diabetes reduces vascular complications. However, the underlying mechanism needs to be uncovered. This study was conducted to elucidate whether and how thromboxane A2 receptor (TPr) activation contributes to endothelial dysfunction in diabetes.

METHODS AND RESULTS

Exposure of human umbilical vein endothelial cells (HUVECs) to either TPr agonists, two structurally related thromboxane A₂ (TxA₂) mimetics, significantly reduced phosphorylations of endothelial nitric oxide synthase (eNOS) at Ser¹¹⁷⁷ and Akt at Ser⁴⁷³. These effects were abolished by pharmacological or genetic inhibitors of TPr. TPr-induced suppression of eNOS and Akt phosphorylation was accompanied by upregulation of PTEN (phosphatase and tension homolog deleted on chromosome 10) and Ser³⁸⁰/Thr^382/383 PTEN phosphorylation. PTEN-specific siRNA restored Akt-eNOS signaling in the face of TPr activation. The small GTPase, Rho, was also activated by TPr stimulation, and pretreatment of HUVECs with Y27632, a Rho-associated kinase (ROCK) inhibitor, rescued TPr-impaired Akt-eNOS signaling. In mice, streptozotocin-induced diabetes was associated with aortic PTEN upregulation, PTEN-Ser³⁸⁰/Thr^382/383 phosphorylation, and dephosphorylation of Akt (at Ser⁴⁷³) and eNOS (at Ser¹¹⁷⁷). Importantly, administration of TPr antagonist blocked these changes.

CONCLUSION

We conclude that TPr activation impairs endothelial function by selectively inactivating the ROCK-PTEN-Akt-eNOS pathway in diabetic mice.

Activation of the Thromboxane A2 Receptor by 8-Isoprostane Inhibits the Pro-Angiogenic Effect of Vascular Endothelial Growth Factor in Scleroderma

The pathogenesis of scleroderma (SSc) includes components of autoimmunity, vascular dysfunction, and accumulation of extracellular matrix. 8-isoprostane, an oxidized lipid created by oxidative stress, activates the thromboxane A2 receptor (TXAR) and ROCK pathway. In this study we determined whether the TXAR was activated by 8-isoprostane in SSc endothelial cells (ECs), and whether this pathway inhibited VEGF-induced angiogenesis. Elevated 8-isoprostane was observed in plasma and conditioned media from SSc patients. SSc conditioned media inhibited EC tube formation, while addition of vitamin E, by reducing 8-isoprostane, increased tube formation. VEGF did not induce angiogenesis in SSc ECs, but vitamin E or TXAR inhibition restored its effect. The expression of TXAR, RhoA, and ROCK1/2 were elevated in SSc ECs. ROCK activity and 8-isoprostane-induced ROCK activation were significantly higher in SSc ECs while VEGF had no effect. The hyper-activation of the TXAR leads to inhibition of VEGF-induced angiogenesis, as inhibition of the TXAR pathway results in blockade of 8-isoprostane induced ROCK activation and restoration of VEGF activity. These results suggest that the TXAR pathway plays a crucial role in angiogenesis and that 8-isoprostane is not just a by-product of oxidative stress, but also plays a significant role in the impaired angiogenesis that characterizes SSc.

Nanostructure formation-induced fluorescence turn-on for selectively detecting protein thiols in solutions, bacteria and live cells

We report the design and synthesis of a light-up probe of DBT-2(EEGK-maleimide), which can serve as a unique probe for selectively detecting protein thiols in various environments, including aqueous solutions, bacteria and live cells.

Cardiac thromboxane A2 receptor activation does not directly induce cardiomyocyte hypertrophy but does cause cell death that is prevented with gentamicin and 2-APB

Background

We have previously shown that the thromboxane (TXA2) receptor agonist, U46619, can directly induce ventricular arrhythmias that were associated with increases in intracellular calcium in cardiomyocytes. Since TXA2 is an inflammatory mediator and induces direct calcium changes in cardiomyocytes, we hypothesized that TXA2 released during ischemia or inflammation could also cause cardiac remodeling.

Methods

U46619 (0.1-10 μM) was applied to isolated adult mouse ventricular primary cardiomyocytes, mouse ventricular cardiac muscle strips, and cultured HL-1 cardiomyocytes and markers of hypertrophy and cell death were measured.

Results

We found that TXA2 receptors were expressed in ventricular cardiomyocytes and were functional via calcium imaging. U46619 treatment for 24 h did not increase expression of pathological hypertrophy genes (atrial natriuretic peptide, β-myosin heavy chain, skeletal muscle α-actin) and it did not increase protein synthesis. There was also no increase in cardiomyocyte size after 48 h treatment with U46619 as measured by flow cytometry. However, U46619 (0.1-10 μM) caused a concentration-dependent increase in cardiomyocyte death (trypan blue, MTT assays, visual cell counts and TUNEL stain) after 24 h. Treatment of cells with the TXA2 receptor antagonist SQ29548 and inhibitors of the IP3 pathway, gentamicin and 2-APB, eliminated the increase in cell death induced by U46619.

Conclusions

Our data suggests that TXA2 does not induce cardiac hypertrophy, but does induce cell death that is mediated in part by IP3 signaling pathways. These findings may provide important therapeutic targets for inflammatory-induced cardiac apoptosis that can lead to heart failure.

Liver kinase B1 is required for thromboxane receptor-dependent nuclear factor-κB activation and inflammatory responses

OBJECTIVE

Thromboxane A2 receptor (TPr) has been reported to trigger vascular inflammation. Nuclear factor κ B (NF-κB) is a known transcription factor. The aims of the present study were to determine the contributions of NF-κB activation to TPr-triggered vascular inflammation and elucidate the mechanism(s) underlying TPr activation of NF-κB.

APPROACH AND RESULTS

The effects of TPr activators, [1S-[1 alpha,2 alpha(Z),3beta(1E,3S*), 4 alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (I-BOP) and U46619, on NF-κB activation, phosphorylation of rhoA/rho-associated kinases and liver kinase B1, cell adhesion and migration, proliferation, and endothelium-dependent vasorelaxation were assayed in cultured human umbilical vein endothelial cells, human monocytes, or isolated mouse aortas. Exposure of human umbilical vein endothelial cells to TPr agonists I-BOP and U46619 induced dose-dependent and time-dependent phosphorylation of inhibitor of κB α in parallel with aberrant expression of inflammatory markers cyclooxygenase-2, inducible nitric oxide synthase, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1. Inhibition of NF-κB by pharmacological or genetic means abolished TPr-triggered expression of inflammatory markers. Consistently, exposure of human umbilical vein endothelial cells to either I-BOP or U46619 significantly increased phosphorylation of inhibitor of κB α, I kappaB kinase, rhoA, rho-associated kinases, and liver kinase B1. Pretreatment of human umbilical vein endothelial cells with the TPr antagonist SQ29548 or rho-associated kinases inhibitor Y27632 or silencing of the LKB1 blocked TPr-enhanced phosphorylation of inhibitor of κB α and its upstream kinase, I kappaB kinase. Finally, exposure of isolated mouse aortas to either U46619 or I-BOP enhanced NF-κB activation and vascular inflammation in parallel with reduced endothelium-dependent relaxation in intact vessels.

CONCLUSIONS

TPr stimulation instigates aberrant inflammation and endothelial dysfunction via rho-associated kinases/liver kinase B1/I kappaB kinase-dependent NF-κB activation in vascular endothelial cells.

Current concepts on the role of nitric oxide in portal hypertension

Portal hypertension (PHT) is defined as a pathological increase in portal venous pressure and frequently accompanies cirrhosis. Portal pressure can be increased by a rise in portal blood flow, an increase in vascular resistance, or the combination. In cirrhosis, the primary factor leading to PHT is an increase in intra-hepatic resistance to blood flow. Although much of this increase is a mechanical consequence of architectural disturbances, there is a dynamic and reversible component that represents up to a third of the increased vascular resistance in cirrhosis. Many vasoactive substances contribute to the development of PHT. Among these, nitric oxide (NO) is the key mediator that paradoxically regulates the sinusoidal (intra-hepatic) and systemic/splanchnic circulations. NO deficiency in the liver leads to increased intra-hepatic resistance while increased NO in the circulation contributes to the hyperdynamic systemic/splanchnic circulation. NO mediated-angiogenesis also plays a role in splanchnic vasodilation and collateral circulation formation. NO donors reduce PHT in animals models but the key clinical challenge is the development of an NO donor or drug delivery system that selectively targets the liver.

Early brain injury: a common mechanism in subarachnoid hemorrhage and global cerebral ischemia

Early brain injury (EBI) has become an area of extreme interest in the recent years and seems to be a common denominator in the pathophysiology of global transient ischemia and subarachnoid hemorrhage (SAH). In this paper, we highlight the importance of cerebral hypoperfusion and other mechanisms that occur in tandem in both pathologies and underline their possible roles in triggering brain injury after hemorrhagic or ischemic strokes.

Non-steroid anti-inflammatory drugs, prostaglandins, and cancer

Fatty acids are involved in multiple pathways and play a pivotal role in health. Eicosanoids, derived from arachidonic acid, have received extensive attention in the field of cancer research. Following release from the phospholipid membrane, arachidonic acid can be metabolized into different classes of eicosanoids through cyclooxygenases, lipoxygenases, or p450 epoxygenase pathways. Non-steroid anti-inflammatory drugs (NSAIDs) are widely consumed as analgesics to relieve minor aches and pains, as antipyretics to reduce fever, and as anti-inflammatory medications. Most NSAIDs are nonselective inhibitors of cyclooxygenases, the rate limiting enzymes in the formation of prostaglandins. Long term use of some NSAIDs has been linked with reduced incidence and mortality in many cancers. In this review, we appraise the biological activities of prostanoids and their cognate receptors in the context of cancer biology. The existing literature supports that these lipid mediators are involved to a great extent in the occurrence and progression of cancer.

The thromboxane synthase and receptor signaling pathway in cancer: an emerging paradigm in cancer progression and metastasis

Thromboxane A(2) (TXA(2)) is a biologically active metabolite of arachidonic acid formed by the action of the terminal synthase, thromboxane A(2) synthase (TXA(2)S), on prostaglandin endoperoxide (PGH(2)). TXA(2) is responsible for multiple biological processes through its cell surface receptor, the T-prostanoid (TP) receptor. Thromboxane A(2) synthase and TP are the two necessary components for the functioning of this potent bioactive lipid. Thromboxane A(2) is widely implicated in a range of cardiovascular diseases, owing to its acute and chronic effects in promoting platelet aggregation, vasoconstriction, and proliferation. In recent years, additional functional roles for both TXA(2)S and TP in cancer progression have been indicated. Increased cyclooxygenase (COX)-2 expression has been described in a variety of human cancers, which has focused attention on TXA(2) as a downstream metabolite of the COX-2-derived PGH(2). Several studies suggest potential involvement of TXA(2)S and TP in tumor progression, especially tumor cell proliferation, migration, and invasion that are key steps in cancer progression. In addition, the regulation of neovascularization by TP has been identified as a potent source of control during oncogenesis. There have been several recent reviews of TXA(2)S and TP but thus far none have discussed its role in cancer progression and metastasis in depth. This review will focus on some of the more recent findings and advances with a significant emphasis on understanding the functional role of TXA(2)S and TP in cancer progression and metastasis.

Microarray analysis of the mammalian thromboxane receptor-Trypanosoma cruzi interaction

Trypanosoma cruzi, the etiological agent of Chagas disease, causes vasculopathy and cardiomyopathy in humans and is associated with elevated levels of several vasoactive molecules such as nitric oxide, endothelin-1 and thromboxane A 2 (TXA 2). Parasite derived TXA 2 modulates vasculopathy and other pathophysiological features of Chagasic cardiomyopathy. Previously, we demonstrated that in response to infection with T. cruzi, TXA 2 receptor (TP) null mice displayed increased parasitemia; mortality and cardiac pathology compared with wild type (WT) and TXA 2 synthase null mice. In order to further study the role of TXA 2-TP signaling in the development of Chagas disease, GeneChip microarrays were used to detect transcriptome changes in rat fat pad endothelial cells (RFP-ECs) which is incapable of TXA 2 signaling (TP null) to that of control (wild type) and RFP-EC with reconstituted TP expression. Genes that were significantly regulated due to infection were identified using a time course of 2, 18 and 48 hrs post infection. We identified several key genes such as suppressor of cytokine signaling (SOCS-5), several cytokines (CSF-1, CXCF ligands), and MAP kinases (MAPK-1, Janus kinase) that were upregulated in the absence of TP signaling. These data underscore the importance of the interaction of the parasite with mammalian TP and may explain the increased mortality and cardiovascular pathology observed in infected TP null mice.

Chinese medicine Tongxinluo modulates vascular endothelial function by inducing eNOS expression via the PI-3K/Akt/HIF-dependent signaling pathway

AIM OF THE STUDY

To investigate the molecular mechanisms whereby the Chinese medicinal compound Tongxinluo improves vascular endothelial function through studying the induction of endothelial nitric oxide synthase (eNOS) and its upstream signaling pathway.

MATERIALS AND METHODS

Hyperhomocysteinemia was induced in Wistar rats by a methionine-rich diet followed by Tongxinluo treatment. The aorta ring was isolated for measuring vascular dilation of aorta and eNOS expression. Human umbilical vein endothelial cells (HUVECs) were transfected with AP-1, NF-κB, HRE or eNOS reporter plasmid followed by Tongxinluo exposure. Expression of the reporter genes was measured by luciferase assay. The level of eNOS was studied by western blot and the nitric oxide content was measured using the nitrate reductase method. HUVECs were also transiently transfected with the dominant negative mutant of HIF-1, PI-3K or Akt to explore the role of HIF and PI-3K/Akt pathway in eNOS induction by Tongxinluo.

RESULTS

Tongxinluo could significantly up-regulate the expression of eNOS in the aortic tissue and improve the endothelium-dependent vasodilation of the aorta ring. Additionally, Tongxinluo at various doses could significantly enhance the expression of HRE and eNOS reporter gene as well as up-regulate the protein level of eNOS. Meanwhile, Tongxinluo caused a dose-dependent increase in the NO content in the supernatant of HUVECs. Suppression of HIF-1 activation by DN-HIF or inhibition of PI-3K/Akt pathway by ΔP85 or DN-Akt both attenuated HRE reporter gene activation and eNOS induction by Tongxinluo.

CONCLUSION

Tongxinluo, a compound Chinese traditional medicine, up-regulates the expression of eNOS via the PI-3K/Akt/HIF-dependent signaling pathway, thus improving the endothelium-dependent vasodilation.

Thromboxane and the thromboxane receptor in cardiovascular disease

Thromboxane A(2) (TXA(2)), the primary product of COX-1-dependent metabolism of arachidonic acid, mediates its biological actions through the TXA(2) receptor, termed the TP. Irreversible inhibition of platelet COX-1-derived TXA(2) with low-dose aspirin affords protection against primary and secondary vascular thrombotic events, underscoring the central role of TXA(2) as a platelet agonist in cardiovascular disease. The limitations associated with aspirin use include significant gastrointestinal toxicity, bleeding complications, potential interindividual response variability and poor efficacy in some disease states. This, together with the broad role of TXA(2) in cardiovascular disease beyond the platelet, has refocused interest towards additional TXA(2)-associated drug targets, in particular TXA(2) synthase and the TP. The superiority of these agents over low-dose aspirin, in terms of clinical efficacy, tolerability and commercial viability, remain open questions that are the focus of ongoing research.

Effect of pharmaceutical interventions targeting thromboxane receptors and thromboxane synthase in cardiovascular and renal diseases

The present review focuses on the roles of thromboxane A2 (TxA2) in arterial thrombosis, atherogenesis, vascular stent-related ischemic events and renal proteinuria. Particular emphasis is laid on therapeutic interventions targeting the TxA2 (TP) receptors and TxA2 synthase (TS), including dual TP-receptor antagonists and TS inhibitors. Their significant inhibitory efficacies on arterial thrombogenesis, atherogenesis, restenosis after stent placement, vasoconstriction and proteinuria indicate novel and improved treatments for cardiovascular and selected renal diseases. New therapeutic interventions of the TxA2 pathway may also be beneficial for patients with poor biological antiplatelet drug response, for example, to aspirin and/or clopidogrel. These new TP/TS agents offer novel improved treatments to efficiently and simultaneously interfere with thrombogenesis and atherogenesis, and to enlarge the existing panel of platelet inhibitors for efficient prophylaxis and treatment of arterial thrombosis and renal proteinuria.

Transglutaminases and disease: lessons from genetically engineered mouse models and inherited disorders

The human transglutaminase (TG) family consists of a structural protein, protein 4.2, that lacks catalytic activity, and eight zymogens/enzymes, designated factor XIII-A (FXIII-A) and TG1-7, that catalyze three types of posttranslational modification reactions: transamidation, esterification, and hydrolysis. These reactions are essential for biological processes such as blood coagulation, skin barrier formation, and extracellular matrix assembly but can also contribute to the pathophysiology of various inflammatory, autoimmune, and degenerative conditions. Some members of the TG family, for example, TG2, can participate in biological processes through actions unrelated to transamidase catalytic activity. We present here a comprehensive review of recent insights into the physiology and pathophysiology of TG family members that have come from studies of genetically engineered mouse models and/or inherited disorders. The review focuses on FXIII-A, TG1, TG2, TG5, and protein 4.2, as mice deficient in TG3, TG4, TG6, or TG7 have not yet been reported, nor have mutations in these proteins been linked to human disease.

Thromboxane A2 receptor activates a Rho-associated kinase/LKB1/PTEN pathway to attenuate endothelium insulin signaling

This study was conducted to elucidate the molecular mechanisms of thromboxane A2 receptor (TP)-induced insulin resistance in endothelial cells. Exposure of human umbilical vein endothelial cells (HUVECs) or mouse aortic endothelial cells to either IBOP or U46619, two structurally related thromboxane A(2) mimetics, significantly reduced insulin-stimulated phosphorylation of endothelial nitric-oxide synthase (eNOS) at Ser(1177) and Akt at Ser(473). These effects were abolished by pharmacological or genetic inhibitors of TP. TP-induced suppression of both eNOS and Akt phosphorylation was accompanied by up-regulation of PTEN (phosphatase and tension homolog deleted on chromosome 10), Ser(380)/Thr(382/383) PTEN phosphorylation, and PTEN lipid phosphatase activity. PTEN-specific small interference RNA restored insulin signaling in the face of TP activation. The small GTPase, Rho, was also activated by TP stimulation, and pretreatment of HUVECs with Y27632, a Rho-associated kinase inhibitor, rescued TP-impaired insulin signaling. Consistent with this result, pertussis toxin abrogated IBOP-induced dephosphorylation of both Akt and eNOS, implicating the G(i) family of G proteins in the suppressive effects of TP. In mice, high fat diet-induced diabetes was associated with aortic PTEN up-regulation, PTEN-Ser(380)/Thr(382/383) phosphorylation, and dephosphorylation of both Akt (at Ser(473)) and eNOS (at Ser(1177)). Importantly, administration of TP antagonist blocked these changes. We conclude that TP stimulation impairs insulin signaling in vascular endothelial cells by selectively activating the Rho/Rho-associated kinase/LKB1/PTEN pathway.

Characterization of endothelial thromboxane receptors in rabbit aorta

An increased synthesis of thromboxane (TX) A(2) is associated with a number of cardiovascular diseases including atherosclerosis, unstable angina and hypertension. We previously identified a subgroup of NZW rabbits in which isolated arteries failed to contract to the TX agonists, U46619 or I-BOP. In vascular smooth muscle membranes, there was a significant decrease in TX receptors, termed TP. These rabbits are referred to as vTP- and those with the TP receptor are called vTP+. Because TP receptors are expressed in some types of endothelial cells, the present study was designed to determine whether functional TP receptors are present in endothelial cells cultured from aortas of vTP+ and vTP- rabbits. Radioligand binding studies were performed with (125)I-BOP. Aortic endothelial cells from vTP+ rabbits exhibited specific and saturable binding. In contrast, in endothelial preparations from vTP- rabbit aortas, no measurable binding to (125)I-BOP was detected. Using an anti-TP receptor antibody, we compared the amount of receptor expressed in endothelial cell lysates obtained from vTP+ and vTP- rabbits. Consistent with the results observed radioligand binding assays, the expression of TP receptor protein was decreased in vTP- compared to vTP+ endothelial cells. An in vitro wound healing assay was used on confluent monolayers of endothelial cells. In the untreated vTP+ cells, the area of the scratch was completely closed by 30 h. In the vTP+ cells treated with U46619 (3 microM), the rate of closure of the scratch area was reduced with approximately 12% of the scratch area remaining at 30 h. Pretreatment with the TP receptor antagonist, SQ 29548 (10 microM) prevented the inhibitory effect of U46619. The rate of closure of the scratch in the vTP- was not altered by U46619. In a separate study, U46619 (3 microM) increased the release of 6-keto PGF(1alpha), the stable metabolite of prostacyclin, in vTP+ but not vTP- endothelial cells. Pretreatment with SQ29548 (10 microM) or the cyclooxygenase inhibitor, indomethacin (10 microM) blocked the increase in vTP+ endothelial cells. In vascular reactivity studies in aortas from vTP+ rabbits, removal of the endothelium enhanced the vasoconstrictor response to U46619 indicating that activation of endothelial TP receptors may modulate vascular tone via the release of the vasodilator, prostacyclin. The results of this study suggest an important role for endothelial TP receptors in modulating vascular function.

A novel nuclear signaling pathway for thromboxane A2 receptors in oligodendrocytes: evidence for signaling compartmentalization during differentiation

The present study investigated G protein expression, localization, and functional coupling to thromboxane A(2) receptors (TPRs) during oligodendrocyte (OLG) development. It was found that as OLGs mature, the expression levels of G(q) increase while those of G(13) decrease. In contrast, the expression levels of G(s), G(o), and G(i) do not change significantly. Localization studies revealed that G(q), G(13), and G(i) are present only in the extranuclear compartment, whereas G(s) and G(o) are found in both the extranuclear and the nuclear compartments. Purification of TPR-G protein complexes demonstrated that TPRs couple to both G(q) and G(13) in the extranuclear compartment but only to G(s) in the nuclear compartment. Furthermore, functional analysis revealed that stimulation of nuclear TPR in OLGs stimulates CREB phosphorylation and myelin basic protein transcription and increases survival. Collectively, these results demonstrate that (i) OLGs selectively modulate the expression of certain G proteins during development, (ii) G proteins are differentially localized in OLGs leading to subcellular compartmentalization, (iii) TPRs couple to G(q) and G(13) in the extranuclear compartment and to G(s) only in the nucleus, (iv) mature OLGs have a functional nuclear TPR-G(s) signaling pathway, and (v) nuclear TPR signaling can stimulate CREB phosphorylation and myelin gene transcription and increase cell survival. These findings represent a novel paradigm for selective modulation of G protein-coupled receptor-G protein signaling during cell development.

Sympathy for the devil: the role of thromboxane in the regulation of vascular tone and blood pressure

Historically, the vasodilatory prostanoids, especially prostacyclin and prostaglandin E(2), are believed to contribute significantly to the regulation of normal vascular tone and blood pressure (BP), primarily by counteracting the prevailing effects of the systemic vasoconstrictor systems, including angiotensin II, the catecholamines, and vasopressin. In contrast, the primary vasoconstrictor prostanoid thromboxane A(2) (TxA(2)) is produced in far smaller quantities in the normal state. While TxA(2) is believed to play a significant role in a variety of cardiovascular diseases, such as myocardial infarction, cerebral vasospasm, hypertension, preeclampsia, and various thrombotic disorders, its role in the regulation of vascular tone and BP in the normal physiological state is, at best, uncertain. Numerous studies have firmly established the dogma that TxA(2), while important in pathophysiological states in males, plays little or no role in the regulation of vascular tone or BP in females, except in the pulmonary vasculature. However, this concept is largely based on the predominant and preferential use of males in animal and human studies. Recent studies from our laboratory and others challenge this dogma and reveal that the TxA(2) pathway in the systemic vascular wall is an estrogen-dependent mechanism that appears to play an important role in the regulation of vascular tone and BP in females, in both normal and pathophysiological states. It is proposed that the potent vasoconstrictor action of TxA(2) is beneficial in the female in the normal state by acting as a local counterregulatory mechanism to increase vascular tone and BP and defend against hypotension that could result from the multiple estrogen-sensitive local vasodilator mechanisms present in the female vascular wall. Validation of this proposal must await further studies at the systemic, tissue, and molecular levels.

Chylomicron remnants: mediators of endothelial dysfunction?

Vascular disease is initiated by activation of the endothelium characterized by the predominance of pro-inflammatory and pro-coagulant changes in endothelial cells (ECs) referred to collectively as 'endothelial dysfunction'. There is increasing evidence that lipoproteins of dietary origin modulate EC function and the use of artificial chylomicron remnant-like particles (CRLPs) in vitro is now beginning to shed light on the molecular mechanisms through which these particles influence cell behaviour. CRLPs enriched in n-6 PUFAs (polyunsaturated fatty acids) influence the production of vasoactive mediators by ECs in a pro-inflammatory manner. Thus CRLPs reduce the synthesis and release of nitric oxide and alter the balance of release of vasodilator versus vasoconstrictor eicosanoids. These changes are accompanied by induction of cyclo-oxygenase-2 expression and activity as well as increased expression of adhesion molecules and the antioxidant defence enzyme haem oxygenase-1. CRLPs also activate a number of intracellular signalling pathways, including NF-kappaB (nuclear factor kappaB) and MAPKs (mitogen-activated protein kinases), which may be involved in mediating their effects on gene expression. The effects of CRLPs on EC behaviour can also be modulated by the type of fat/oxidation status of the particles. These findings support the hypothesis that lipoproteins of dietary origin directly regulate molecular events in the vascular wall.

Nitroflurbiprofen, a nitric oxide-releasing cyclooxygenase inhibitor, improves cirrhotic portal hypertension in rats

BACKGROUND & AIMS

We studied whether administration of nitroflurbiprofen (HCT-1026), a cyclooxygenase inhibitor with nitric oxide (NO)-donating properties, modulates the increased intrahepatic vascular tone in portal hypertensive cirrhotic rats.

METHODS

In vivo hemodynamic measurements (n = 8/condition) and evaluation of the increased intrahepatic resistance by in situ perfusion (n = 5/condition) were performed in rats with thioacetamide-induced cirrhosis that received either nitroflurbiprofen (45 mg/kg), flurbiprofen (30 mg/kg, equimolar concentration to nitroflurbiprofen), or vehicle by intraperitoneal injection 24 hours and 1 hour prior to the measurements. Additionally, we evaluated the effect of acute administration of both drugs (250 micromol/L) on the intrahepatic vascular tone in the in situ perfused cirrhotic rat liver (endothelial dysfunction and hyperresponsiveness to methoxamine) and on hepatic stellate cell contraction in vitro. Typical systemic adverse effects of nonsteroidal anti-inflammatory drugs, such as gastrointestinal ulceration, renal insufficiency, and hepatotoxicity, were actively explored.

RESULTS

In vivo, nitroflurbiprofen and flurbiprofen equally decreased portal pressure (8 +/- 0.8 and 8.4 +/- 0.1 mm Hg, respectively, vs 11.8 +/- 0.6 mm Hg) and reduced the total intrahepatic vascular resistance. Systemic hypotension was not aggravated in the different treatment groups (P = .291). In the perfused cirrhotic liver, both drugs improved endothelial dysfunction and hyperresponsiveness. This was associated with a decreased hepatic thromboxane A(2)-production and an increased intrahepatic nitrate/nitrite level. In vitro, nitroflurbiprofen, more than flurbiprofen, decreased hepatic stellate cells contraction. Flurbiprofen-treated rats showed severe gastrointestinal ulcerations (bleeding in 3/8 rats) and nefrotoxicity, which was not observed in nitroflurbiprofen-treated cirrhotic rats.

CONCLUSIONS

Treatment with nitroflurbiprofen, an NO-releasing cyclooxygenase inhibitor, improves portal hypertension without major adverse effects in thioacetamide-induced cirrhotic rats by attenuating intrahepatic vascular resistance, endothelial dysfunction, and hepatic hyperreactivity to vasoconstrictors.

Molecular mechanisms of early brain injury after subarachnoid hemorrhage

OBJECTIVES

Increasing body of experimental and clinical data indicates that early brain injury after initial bleeding largely contributes to unfavorable outcome after subarachnoid hemorrhage (SAH). This review presents molecular mechanisms underlying brain injury at its early stages after SAH.

METHODS

PubMed was searched using term 'subarachnoid hemorrhage' and key words referring to molecular and cellular pathomechanisms of SAH-induced early brain injury.

RESULTS

The authors reviewed intracranial phenomena and molecular agents that contribute to the early development of pathological sequelae of SAH in cerebral and vascular tissues, including cerebral ischemia and its interactions with injurious blood components, blood-brain barrier disruption, brain edema and apoptosis.

DISCUSSION

It is believed that detailed knowledge of molecular signaling pathways after SAH will serve to improve therapeutic interventions. The most promising approach is the protection of neurovascular unit including anti-apoptosis therapy.

Terutroban et récepteurs TP endothéliaux dans l’athérogenèse

Treatment of thrombotic diseases implicates the use of anti-platelet agents, anti-coagulants and pro-fibrinolytic substances. Amongst the anti-platelet drugs, aspirin occupies a unique position. As soon as it became evident that the major action of aspirin is indirect blockade, through inhibition of cyclooxygenase (COX), of the production of thromboxane A2 (TXA2), a powerful vasoconstrictor and platelet activator, research for new anti-thrombotics that interact more specifically with the production and/or the action of TXA2 was started. Terutroban (S 18886) is a selective antagonist of TP receptors, the receptors for TXA2, that are present on platelets and on vascular smooth muscle cells, but also on endothelial cells. The role played by the platelet and smooth muscle cell TP receptors in thrombotic disease is well known, and preclinical and clinical studies with terutroban have illustrated the powerful antithrombotic effects of this agent. The implication of endothelial TP receptors in the development of atherosclerotic disease has only been examined during the past five years and studies with terutroban have been crucial for understanding the role of these endothelial receptors in cardiovascular physiopathology. The goal of the present review is to discuss the arguments in favour of the hypothesis suggesting that activation of endothelial TP receptors, by causing expression of adhesion molecules, favours adhesion and infiltration of monocytes/macrophages in the arterial wall, thereby stimulating the development of atherosclerosis. The review will also highlight the important contribution of the studies performed with terutroban in this research area. The triple activity (anti-thrombotic, anti-vasoconstrictor, anti-atherosclerotic) observed with terutroban in preclinical studies, stressed by the first results in clinical development, places terutroban as an innovative drug with a unique potential for treatment of cardiovascular disorders.

TGF-β1 Released from Activated Platelets Can Induce TNF-Stimulated Human Brain Endothelium Apoptosis: A New Mechanism for Microvascular Lesion during Cerebral Malaria

Platelets have recently been shown to accumulate in brain microvessels of patients with cerebral malaria and to modulate the binding of Plasmodium falciparum-infected red cells to human brain endothelium in vitro. In the present study we used a platelet-endothelial cell coculture model to investigate the mechanisms by which platelets modify the function of human brain microvascular endothelial cells (HBEC). Platelets were found to have a proapoptotic effect on TNF-activated HBEC, and this was contact-dependent, as inhibiting platelet binding prevented endothelial cell killing. We also showed that the supernatants of thrombin-activated platelets killed TNF-stimulated HBEC and that TGF-beta1 was the main molecule involved in endothelial cell death, because its inhibition completely abrogated the activated-platelet supernatant effect. Our data illustrate another aspect of the duality of TGF-beta1 in malaria and may provide new insights into the pathogenesis of cerebral malaria.

PI3-kinase activation by GM-CSF in endothelium is upstream of Jak/Stat pathway: Role of αGMR

GM-CSF has been identified as a growth factor for endothelial cells. In this study, we investigated the role of PI3-kinase pathway in mediating GM-CSF induced angiogenesis. GM-CSF induced tube formation in human umbilical vein endothelial cells, as examined using Matrigel assay, was inhibited by specific inhibitors of PI3-kinase, wortmannin, and LY294002. The regulatory subunit of PI3-kinase (p85) interacted with alphaGMR via its C-SH2 domain in a GM-CSF-dependent fashion with concomitant phosphorylation of p85 and activation of PI3-kinase pathway. p85 binding site on the alphaGMR was essential to induce GM-CSF receptor-dependent Stat activation. Furthermore, inhibition of PI3-kinase activity also abrogated GM-CSF induced Stat activation. These studies underscore the significance of the GM-CSF mediated PI3-kinase activation and its role in angiogenesis.

Dominant Role for Calpain in Thromboxane-Induced Neuromicrovascular Endothelial Cytotoxicity

Thromboxane A(2) (TXA(2)) is an important lipid mediator generated during oxidative stress and implicated in ischemic neural injury. This autacoid was recently shown to partake in this injury process by directly inducing endothelial cytotoxicity. We explored the mechanisms for this TXA(2)-evoked neural microvascular endothelial cell death. Stable TXA(2) mimetics 5-heptenoic acid, 7-[6-(3-hydroxy-1-octenyl)-2-oxabicyclo[2.2.1]hept-5-yl]-[1R-[1alpha,4alpha,5beta(Z),6alpha,(1E,3S)]]-9,11-dedioxy-9alpha,11alpha-methanolpoxy (U-46619) [as well as [1S-[1alpha,2alpha(Z),3beta(1E,3S(*)),4alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.1.1]-hept-2-yl]-5-heptenoic acid; I-BOP] induced a retinal microvascular degeneration in rat pups in vivo and in porcine retinal explants ex vivo and death of porcine brain endothelial cells (in culture). TXA(2) dependence of these effects was corroborated by antagonism using the selective TXA(2) receptor blocker (-)-6,8-difluoro-9-p-methyl-sulfonyl-benzyl-1,2,3,4-tetrahydrocarbazol-1-yl-acetic acid (L670596). In all cases, neurovascular endothelial cell death was prevented by pan-calpain and specific m-calpain inhibitors but not by caspase-3 or pan-caspase inhibitors. Correspondingly, TXA(2) (mimetics) augmented generation of known active m-calpain (but not mu-calpain) form and increased the activity of m-calpain (cleavage of fluorogenic substrate N-succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin; and of alpha-spectrin into specific fragments) but not of pan-caspase or specific caspase-3 (respectively, using sulforhodamine-Val-Arg-Asp-fluoromethyl ketone and detecting its active 17- and 12-kDa fragments). Interestingly, these effects were phospholipase C (PLC)-dependent [associated with increase in inositol triphosphate and inhibited by PLC blocker 1-[6-[[17beta-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122)] and required calcium but were not associated with increased intracellular calcium. U-46619-induced calpain activation resulted in translocation of Bax to the mitochondria, loss of polarization of the latter (using potentiometric probe 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide; JC-1) and in turn release of cytochrome c into the cytosol and depletion of cellular ATP; these effects were all blocked by calpain inhibitors. Overall, this work identifies (specifically) m-calpain as a dominant protease in TXA(2)-induced neurovascular endothelial cell death.

The Lsc RhoGEF mediates signaling from thromboxane A2 to actin polymerization and apoptosis in thymocytes

The Lsc RhoGEF (also known as p115-RhoGEF) is a GTP exchange factor (GEF), an activator of GTPases of the Rho family. Lsc has a RhoGEF domain specific for Rho GTPase and a regulator of G protein signaling (RGS) domain specific for Galpha(12/13) subunits. One G protein receptor that can couple to Galpha(12/13) subunits is the receptor for thromboxane A(2 )(TXA(2)), thromboxane-prostanoid (called TP), which is highly expressed in immature thymocytes. TXA(2) has been implicated in thymocyte apoptosis. We found that Lsc(-/-) mice on a BALB/c background show thymic hyperplasia due to increased numbers of thymocytes and that these numbers further increase with the age of the mice. To investigate a role for Lsc in TXA(2) signaling, we analyzed activation of primary thymocytes by TXA(2) in vitro. TXA(2)-induced apoptosis of double-positive thymocytes and Rho activation required Lsc, and TXA(2) stimulation of actin polymerization and cofilin phosphorylation required both Lsc and Rho kinase (ROCK). Additionally, in the absence of Lsc, phosphorylation of the survival kinase Akt in response to TXA(2) was greatly enhanced. Together, these data demonstrate that Lsc is essential for mediating TXA(2 )signaling involved in apoptosis and actin organization and suggest that TXA(2) regulates thymic cellularity via Lsc.

Thromboxane A receptor-mediated cell proliferation, survival and gene expression in oligodendrocytes

Thromboxane A(2) receptors (TP) were previously localized to discrete regions in the rat brain on myelinated fiber tracts and oligodendrocytes (OLGs). The present studies extended these findings and investigated the effects of TP signaling on cell proliferation, survival, and gene expression in OLG progenitor cells (OPCs) and OLGs. It was found that the TP agonist, U46619 stimulated the proliferation of OPCs and promoted the survival of mature OLGs. Examination of the early gene expression events involved in OPC proliferation, revealed that c-fos expression was substantially increased by U46619 stimulation. Treatment of OPCs or OLGs with U46619 caused activation of the mitogen-activated protein kinases (MAPK) ERK 1/2. In OPCs this activation was blocked by inhibition of src. However, in OLGs this phosphorylation was not only blocked by inhibition of src but also by inhibition of protein kinase C (PKC). Furthermore, U46619 was found to increase CREB phosphorylation in both OPCs and OLGs. Similar to ERK 1/2 activation, there was a divergence in the mechanism of the TP-mediated CREB response for each cell type. Specifically, U46619 activation was attenuated by src and protein kinase A (PKA) inhibition in OPCs, whereas in OLGs this effect was blocked by inhibition of src, PKA as well as by inhibition of PKC. Collectively, these results provide the first demonstration that TP-activated nuclear signaling events are involved in the proliferation of OPCs, the survival of mature OLGs, and the stimulation of gene expression.

Arachidonic acid cascade in endothelial pathobiology

Arachidonic acid (AA) and its metabolites (eicosanoids) represent powerful mediators, used by organisms to induce and suppress inflammation as a part of the innate response to disturbances. Several cell types participate in the synthesis and release of AA metabolites, while many cell types represent the targets for eicosanoid action. Endothelial cells (EC), forming a semi-permeable barrier between the interior space of blood vessels and underlying tissues, are of particular importance for the development of inflammation, since endothelium controls such diverse processes as vascular tone, homeostasis, adhesion of platelets and leukocytes to the vascular wall, and permeability of the vascular wall for cells and fluids. Proliferation and migration of endothelial cells contribute significantly to new vessel development (angiogenesis). This review discusses endothelial-specific synthesis and action of arachidonic acid derivatives with a particular focus on the mechanisms of signal transduction and associated intracellular protein targets.

Thromboxane A2 (TP) receptor in the non-pregnant porcine myometrium and its role in regulation of spontaneous contractile activity

Although there are species-related differences in uterine prostanoid receptor subtypes, functional prostanoid receptors in the porcine uterus are similar with those in the human uterus (FP, TP, EP(1), EP(2), EP(3), DP and IP) except for the TP receptor. These similarities promoted us to determine whether TP receptors are present in the non-pregnant porcine uterus. For this purpose, the effects of TP receptor agonists and antagonists were investigated by a contraction study and by a binding study. 9,11-Dideoxy-9 alpha, 11 alpha-methanoepoxy-prosta-5Z,13E-dien-1-oic acid (U46619, 1 nM-10 microM), a stable thromboxane A(2) mimetic, caused tetrodotoxin-resistant contraction in both longitudinal and circular muscles of the uterine cornu. The pEC(50) value in the longitudinal muscle (6.69) was lower than that in the circular muscle (7.62), but the maximum response in the longitudinal muscle was two times larger than that in the circular muscle. The longitudinal and circular muscles of other regions (corpus and cervix) also responded to U46619, and region-related difference in contractile responses was observed only in the longitudinal muscles. 4(Z)-6-(2-o-Chlorophenyl-4-o-hydroxyphenyl-1,3-dioxan-cis-5-yl) hexenoic acid (ICI192605) and 7-[3-[[2-[(phenylamino)carbonyl] hydrazino]methyl]7-oxabicyclo[2.2.1]hept-2-yl]-,[1S-[1 alpha,2 alpha(Z),3 alpha,4 alpha]]-]5-heptenoic acid (SQ29548) inhibited the contractile responses to U46619 competitively. The longitudinal and circular muscles in the cornu contained a single class of [3H]SQ29548 binding site with similar K(d) values (30 nM), but B(max) in the circular muscle (90.9+/-8.6 fmol/mg protein) was two times higher than that in the longitudinal muscle (58.2+/-8.6 fmol/mg protein). The ranking order of competition by TP receptor agonists and antagonists (with pK(i) values in parentheses) was [1S-[1,2(Z),3(1E,3S*),4]]-7-[3-[3-Hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (I-BOP, 7.70)>SQ29548 (7.39)>7-[3-(3-Hydroxy-1-octenyl)bicycle[3.1.1]hept-2-yl]-,[2S-[2 alpha(Z),3 beta(1E,3R*)]]-5-heptenoic acid (CTA(2), 6.55)>7-[3-(3-hydroxy-1-octenyl)-6,6-dimethylbicyclo[3.1.1]hept-2-yl-,[1S-[1 alpha,2 beta(Z),3 alpha(1E,3R*),5 alpha]]-5-heptenoic acid (PTA(2), 6.50)>U46619 (6.41)>7-[5-(3-hydroxy-1-octenyl)-2-oxabicyclo[2.2.1] hept-6yl]-,[1S-[1 alpha,4 alpha,5 alpha(1E,3R*),6 beta(Z)]]-5-heptenoic acid (U44069, 6.34), and this order is consistent with current TP receptors. Treatment with indomethacin (100 nM) and N-tert-butyl-N cent -[(2-cyclohexylamino-5-nitrobenzene) sulfonyl] urea (BM-531, 10 microM) inhibited the spontaneous contractile activities of both longitudinal and circular muscles. The present results indicate that contractile TP receptors are present in the non-pregnant porcine uterus. Therefore, the prostanoid receptor subtypes that exist in the porcine uterus (TP, IP, DP, FP, EP(1), EP(2) and EP(3)) are the same as those present in the human uterus. The distribution of TP receptors in the porcine uterus differed depending on the type of myometrium (longitudinal and circular muscles) and region of the uterus. The endogenous thromboxane A(2)-TP receptor pathway is thought to play a physiological role in regulation of spontaneous contractile activity in the porcine uterus.

Thromboxane receptor stimulation associated with loss of SKCa activity and reduced EDHF responses in the rat isolated mesenteric artery

1. The possibility that thromboxane (TXA(2)) receptor stimulation causes differential block of the SK(Ca) and IK(Ca) channels which underlie EDHF-mediated vascular smooth muscle hyperpolarization and relaxation was investigated in the rat isolated mesenteric artery. 2. Acetylcholine (30 nm-3 microm ACh) or cyclopiazonic acid (10 microm CPA, SERCA inhibitor) were used to stimulate EDHF-evoked smooth muscle hyperpolarization. In each case, this led to maximal hyperpolarization of around 20 mV, which was sensitive to block with 50 nm apamin and abolished by repeated stimulation of mesenteric arteries with the thromboxane mimetic, U46619 (30 nm-0.1 microm), but not the alpha(1)-adrenoceptor agonist phenylephrine (PE). 3. The ability of U46619 to abolish EDHF-evoked smooth muscle hyperpolarization was prevented by prior exposure of mesenteric arteries to the TXA(2) receptor antagonist 1 microm SQ29548. 4. Similar-sized smooth muscle hyperpolarization evoked with the SK(Ca) activator 100 microm riluzole was also abolished by prior stimulation with U46619, while direct muscle hyperpolarization in response to either levcromakalim (1 microm, K(ATP) activator) or NS1619 (40 microm, BK(Ca) activator) was unaffected. 5. During smooth muscle contraction and depolarization to either PE or U46619, ACh evoked concentration-dependent hyperpolarization (to -67 mV) and complete relaxation. These responses were well maintained during repeated stimulation with PE, but with U46619 there was a progressive decline, so that during a third exposure to U46619 maximum hyperpolarization only reached -52 mV and relaxation was reduced by 20%. This relaxation could now be blocked with charybdotoxin alone. The latter responses could be mimicked with 300 microm 1-EBIO (IK(Ca) activator), an action not modified by exposure to U46619. 6. An early consequence of TXA(2) receptor stimulation is a reduction in the arterial hyperpolarization and relaxation attributed to EDHF. This effect appears to reflect a loss of SK(Ca) activity.

Genetic loci that control vascular endothelial growth factor-induced angiogenesis

Angiogenesis is regulated by the balance between angiogenic stimulators and inhibitors. Numerous reports have demonstrated that tumors induce aggressive angiogenesis by up-regulating the production of angiogenesis stimulating growth factors to overcome the baseline levels of endogenous inhibitors. However, the possibility of large differences in the host's responsiveness to angiogenic factors has been largely overlooked. Using the corneal micropocket neovascularization assay, we have observed >10-fold differences in responsiveness to either basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF) among various mouse strains. The inheritance pattern observed for these traits supported a QTL (quantitative trait locus) approach to mapping the genes responsible for the differences in angiogenic responsiveness. To overcome variability in the assay, we used recombinant inbred lines to map this phenotype. In the BXD series of recombinant inbred mouse strains, we have mapped the regions responsible for regulating VEGF-induced angiogenesis using both composite interval mapping and multiple interval mapping. Both approaches link VEGF responsiveness to regions on chromosomes 2 (near D2Mit6) and 10 (near D10Mit20). Candidate angiogenesis-related genes in these regions include those for collagen XVIII/endostatin, matrix metalloproteinase 11, integrin beta2, prostaglandin D2 synthase, and interleukin-1 receptor antagonist.

Inhibition of Akt phosphorylation by thrombin, histamine and lysophosphatidylcholine in endothelial cells. Differential role of protein kinase C

The protein kinase Akt is involved in embryonic vascular development and neoangiogenesis as well as in several endothelial cell functions, including activation of endothelial NO-synthase (eNOS) and promotion of endothelial cell survival. We have examined the effects of G-protein activators thrombin and histamine as well as lysophosphatidylcholine (LPC) on Akt phosphorylation in cultured human umbilical vein endothelial cells (HUVEC). Akt phosphorylation was analyzed with the phosphospecific Akt (Ser473) antibody by Western blotting. While epidermal growth factor (EGF) was a potent stimulator of Akt phosphorylation histamine, thrombin and LPC blocked its activation when used in cotreatment with EGF. Following inhibition or downregulation of protein kinase C (PKC), the inhibitory effect of both histamine and thrombin on the endothelial response to EGF was prevented. Furthermore, stimulation of PKC, using short-term 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment, markedly inhibited the stimulatory effects of EGF on Akt phosphorylation. Rottlerin, an inhibitor of the PKCdelta, but not Gö6976, which is an inhibitor of alpha, beta, gamma and isoforms, reversed the inhibitory effects of histamine. Conversely, inhibition or downregulation of PKC did not prevent the inhibitory effect of LPC. Akt phosphorylation was also increased by sphingosine 1-phosphate (S1P) treatment and this activity was influenced by the various cotreatments in the same way as the activation by EGF. Overall, this study demonstrated that the G-protein activators thrombin and histamine inhibited both EGF- and S1P-mediated Akt phosphorylation in HUVEC by activation of PKCdelta, while the inhibitory effects of LPC were independent of PKCdelta.