Pressure stress delays cyclooxygenase-2 expression induced by interleukin-1β in cultured human pulmonary artery smooth muscle cells

Introduction

Pulmonary artery smooth muscle cells (PASMCs) play an important role in the sequence of events leading to the formation of pulmonary hypertension (PH). However, little is known about the direct effects of high pressure on the function and intercellular signaling pathways of PASMCs. The aim of this study was to evaluate the effect of pressure stress that simulates PH on interleukin (IL)-1β- or angiotensin II-induced cyclooxygenase-2 (COX-2) expression in cultured human PASMCs.

Methods

Either 20 or 60 mmHg atmospheric pressure was applied to PASMCs by a pressure-loading apparatus. Protein expression and phosphorylation were analyzed by western blotting. mRNA expression was analyzed by quantitative real-time reverse transcription-polymerase chain reaction.

Results

IL-1β-induced COX-2 protein expression peaked at 6 h in non-pressurized cells, whereas COX-2 expression was delayed, peaking at 12 h, in 20 and 60 mmHg pressurized cells. Both pressures also delayed the time to peak COX-2 mRNA expression induced by IL-1β. In addition, pressure stress delayed the time to peak mitogen-activated protein kinase (MAPK) phosphorylation induced by IL-1β. In contrast, angiotensin II-induced transient COX-2 mRNA expression and MAPK phosphorylation were not affected by pressure stress.

Conclusion

These results suggest that pressure stress delays IL-1β-induced COX-2 expression via the delayed activation of MAPKs in PASMCs, and the effects of pressure stress differ according to the bioactive substance being stimulated. Our results demonstrate that the application of pressure stress to PASMCs directly alters cell function, which may provide a basic insight into our understanding of the pathogenesis of PH.

Natural Products and Small Molecules Targeting Cellular Ceramide Metabolism to Enhance Apoptosis in Cancer Cells

Molecular targeting strategies have been used for years in order to control cancer progression and are often based on targeting various enzymes involved in metabolic pathways. Keeping this in mind, it is essential to determine the role of each enzyme in a particular metabolic pathway. In this review, we provide in-depth information on various enzymes such as ceramidase, sphingosine kinase, sphingomyelin synthase, dihydroceramide desaturase, and ceramide synthase which are associated with various types of cancers. We also discuss the physicochemical properties of well-studied inhibitors with natural product origins and their related structures in terms of these enzymes. Targeting ceramide metabolism exhibited promising mono- and combination therapies at preclinical stages in preventing cancer progression and cemented the significance of sphingolipid metabolism in cancer treatments. Targeting ceramide-metabolizing enzymes will help medicinal chemists design potent and selective small molecules for treating cancer progression at various levels.

Sphingosine Kinase 2 Inhibitors: Rigid Aliphatic Tail Derivatives Deliver Potent and Selective Analogues

Sphingosine 1-phosphate (S1P) is a pleiotropic signaling molecule that interacts with five native G-protein coupled receptors (S1P1–5) to regulate cell growth, survival, and proliferation. S1P has been implicated in a variety of pathologies including cancer, kidney fibrosis, and multiple sclerosis. As key mediators in the synthesis of S1P, sphingosine kinase (SphK) isoforms 1 and 2 have attracted attention as viable targets for pharmacologic intervention. In this report, we describe the design, synthesis, and biological evaluation of sphingosine kinase 2 (SphK2) inhibitors with a focus on systematically introducing rigid structures in the aliphatic lipid tail present in existing SphK2 inhibitors. Experimental as well as molecular modeling studies suggest that conformationally restricted “lipophilic tail” analogues bearing a bulky terminal moiety or an internal phenyl ring are useful to complement the “J”-shaped sphingosine binding pocket of SphK2. We identified 14c (SLP9101555) as a potent SphK2 inhibitor (K_i = 90 nM) with 200-fold selectivity over SphK1. Molecular docking studies indicated key interactions: the cyclohexyl ring binding in the cleft deep in the pocket, a trifluoromethyl group fitting in a small side cavity, and a hydrogen bond between the guanidino group and Asp308 (amino acid numbering refers to human SphK2 (isoform c) orthologue). In vitro studies using U937 human histiocytic lymphoma cells showed marked decreases in extracellular S1P levels in response to our SphK2 inhibitors. Administration of 14c (dose: 5 mg/kg) to mice resulted in a sustained increase of circulating S1P levels, suggesting target engagement.

Abnormal Pressure Stress Reduces Interleukin-1β-Induced Cyclooxygenase-2 Expression in Cultured Rat Vascular Smooth Muscle Cells

Elevated mechanical stress on blood vessels associated with hypertension has a direct effect on the function of vascular endothelial cells and vascular smooth muscle cells (VSMCs). In the present study, we have identified the effect of pulsatile pressure stress on cyclooxygenase-2 (COX-2) expression induced by interleukin (IL)-1β in cultured rat VSMCs. VSMCs were isolated from aortic media of Wistar rats and cultured. Pulsatile pressure applied to VSMCs was repeatedly given between either 80 and 160 mmHg, which simulates systolic hypertension, or 80 and 120 mmHg, which simulates normal blood pressure, at a frequency of 4 cycles per min using our original apparatus. Pressure loading that simulates systolic hypertension reduced IL-1β-induced COX-2 expression. The pressure also inhibited the rapid and transient phosphorylation of extracellular signal-regulated kinase (ERK) induced by IL-1β. IL-1β-induced COX-2 expression was significantly inhibited by a specific conventional protein kinase C (PKC) inhibitor. Pressure loading that simulates systolic hypertension also reduced phorbol myristate 13-acetate (PMA) (a PKC activator)-induced COX-2 expression and the rapid and transient phosphorylation of ERK. Pressure loading that simulates normal blood pressure had no effect on IL-1β- and PMA-induced COX-2 expression. The present study shows that pressure stress between 80 and 160 mmHg, which simulates systolic hypertension reduces IL-1β-induced COX-2 expression by affecting a mechanism involving PKC and ERK signaling pathways. Downregulation of COX-2 expression in VSMCs by abnormal pressure stress may further worsen local vascular injury associated with hypertension.

Increased Reactive Oxygen Species Generation Contributes to the Atherogenic Activity of the B2 Bradykinin Receptor

Atherosclerosis and ensuing cardiovascular disease are major causes of death with insufficient treatment options. In search for pathomechanisms of atherosclerosis, we investigated the impact of the B2 bradykinin receptor, Bdkrb2, on atherosclerotic lesion formation, because to date it is not clear whether the B2 bradykinin receptor is atheroprotective or atherogenic. As a model of atherosclerosis, we used hypercholesterolemic ApoE-deficient (apolipoprotein E-deficient) mice, which develop atherosclerotic lesions in the aorta with increasing age. The role of Bdkrb2 in atherosclerosis was studied in ApoE-deficient mice, which were either Bdkrb2-deficient, or had moderately increased aortic B2 bradykinin receptor protein levels induced by transgenic BDKRB2 expression under control of the ubiquitous CMV promoter. We found that Bdkrb2 deficiency led to a significantly decreased atherosclerotic plaque area whereas transgenic BDKRB2 expression enhanced atherosclerotic lesion formation in the aorta of ApoE-deficient mice at an age of 8 months. Concomitantly, the aortic content of reactive oxygen species (ROS) was higher in BDKRB2-expressing mice whereas Bdkrb2 deficiency decreased aortic ROS levels of ApoE-deficient mice. In addition, aortic nitrate as a marker of nitric oxide activity and the endothelial nitric oxide synthase (eNOS) co-factor, tetrahydrobiopterin (BH4) were reduced in BDKRB2-expressing ApoE-deficient mice. The decreased aortic BH4 content could be a consequence of increased ROS generation and down-regulated aortic expression of the BH4-synthesizing enzyme, Gch1 (GTP cyclohydrolase 1). In agreement with a causal involvement of decreased BH4 levels in the atherogenic function of BDKRB2, we found that treatment with the BH4 analog, sapropterin, significantly retarded atherosclerotic plaque formation in BDKRB2-expressing ApoE-deficient mice. Together our data show that the B2 bradykinin receptor is atherogenic, and the atherosclerosis-promoting function of BDKRB2 is partially caused by decreased aortic BH4 levels, which could account for eNOS uncoupling and further enhancement of ROS generation.

Analysis of Vascular Cell Response to Hypertension Induced by Pressure Loading and Its Application as a Tool for Exploring Pharmacological Modes of Action

Inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression is induced by interleukin-1β (IL-1β) stimulation in vascular smooth muscle cells (VSMCs), resulting in the production of nitric oxide and prostaglandins such as PGI₂. The expression of iNOS and COX-2 in cultured VSMCs isolated from 6-7-week-old stroke-prone spontaneously hypertensive rats (SHRSP) is significantly lower than in cells of normotensive Wistar Kyoto rats (WKY). These reductions are also found in cells exposed to pulsatile atmospheric pressure between 80-160 mmHg at a rate of 4 cycles/min, which simulates systolic hypertension. Docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid, potentiates IL-1β-induced iNOS and COX-2 expression in VSMCs isolated from WKY, but not those from SHRSP. In response to endothelial injury at a local site, iNOS and COX-2 induction in VSMCs may function primarily as a defensive and compensatory mechanism for endothelial dysfunction by preventing the development of pathological conditions. Thus, in certain pathological conditions associated with hypertension, vascular walls with reduced iNOS and COX-2 expression may aggravate or initiate further vascular injury. In this situation, DHA may contribute to maintaining homeostasis in VSMCs by potentiating iNOS and COX-2 expression. Using cells isolated from a genetic pathological animal model alongside cells exposed to experimental pathological conditions can be an effective tool for the analysis of cell response to hypertension and exploring pharmacological modes of action in vitro.

Cellular function and signaling pathways of vascular smooth muscle cells modulated by sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) plays important roles in cardiovascular pathophysiology. S1P₁ and/or S1P₃, rather than S1P₂ receptors, seem to be predominantly expressed in vascular endothelial cells, while S1P₂ and/or S1P₃, rather than S1P₁ receptors, seem to be predominantly expressed in vascular smooth muscle cells (VSMCs). S1P has multiple actions, such as proliferation, inhibition or stimulation of migration, and vasoconstriction or release of vasoactive mediators. S1P induces an increase of the intracellular Ca²⁺ concentration in many cell types, including VSMCs. Activation of S1P₃ seems to play an important role in Ca²⁺ mobilization. S1P induces cyclooxygenase-2 expression in VSMCs via both S1P₂ and S1P₃ receptors. S1P₂ receptor activation in VSMCs inhibits inducible nitric oxide synthase (iNOS) expression. At the local site of vascular injury, vasoactive mediators such as prostaglandins and NO produced by VSMCs are considered primarily as a defensive and compensatory mechanism for the lack of endothelial function to prevent further pathology. Therefore, selective S1P₂ receptor antagonists may have the potential to be therapeutic agents, in view of their antagonism of iNOS inhibition by S1P. Further progress in studies of the precise mechanisms of S1P may provide useful knowledge for the development of new S1P-related drugs for the treatment of cardiovascular diseases.

Sphingosine kinase 1/sphingosine 1-phosphate signalling pathway as a potential therapeutic target of pulmonary hypertension

Pulmonary hypertension is characterized by extensive vascular remodelling, leading to increased pulmonary vascular resistance and eventual death due to right heart failure. The pathogenesis of pulmonary hypertension involves vascular endothelial dysfunction and disordered vascular smooth muscle cell (VSMC) proliferation and migration, but the exact processes remain unknown. Sphingosine 1-phosphate (S1P) is a bioactive lysophospholipid involved in a wide spectrum of biological processes. S1P has been shown to regulate VSMC proliferation and migration and vascular tension via a family of five S1P G-protein-coupled receptors (S1P1-SIP5). S1P has been shown to have both a vasoconstrictive and vasodilating effect. The S1P receptors S1P1 and S1P3 promote, while S1P2 inhibits VSMC proliferation and migration in vitro in response to S1P. Moreover, it has been reported recently that sphingosine kinase 1 and S1P2 inhibitors might be useful therapeutic agents in the treatment of empirical pulmonary hypertension. The sphingosine kinase 1/S1P signalling pathways may play a role in the pathogenesis of pulmonary hypertension. Modulation of this pathway may offer novel therapeutic strategies.

Pressure stress reduces inducible NO synthase expression by interleukin-1β stimulation in cultured rat vascular smooth muscle cells

Elevated mechanical stress applied to vascular walls is well known to modulate vascular remodeling. We investigated the effect of pulsatile pressure stress on nitric oxide (NO) production and inducible NO synthase (iNOS) expression by interleukin-1β (IL-1β) stimulation in rat vascular smooth muscle cells (VSMCs). VSMCs were enzymatically isolated from aortic media of Wistar rats. Pulsatile pressure applied to VSMCs was repeatedly given between 80 and 160 mm Hg at a frequency of 4 cycles per min using an original apparatus. Protein expression and activation were evaluated by Western blot analysis. mRNA expression was evaluated by real-time reverse transcription-polymerase chain reaction. The pulsatile pressure reduced IL-1β-induced NO production, iNOS protein, and mRNA expression. The pressure also reduced GTP cyclohydrolase I mRNA expression. Furthermore, the pressure reduced phosphorylation of IL-1β-induced extracellular signal-regulated kinase (ERK), nuclear factor-κB (NF-κB) p65, and I-κBα. The pressure had no effect on I-κBβ degradation by IL-1β stimulation. The present study shows for the first time that pressure stress reduces IL-1β-induced iNOS expression via a mechanism involving the ERK-NF-κB signaling pathway.

Sphingosine 1-phosphate increases an intracellular Ca(2+) concentration via S1P3 receptor in cultured vascular smooth muscle cells

OBJECTIVE

We investigated the effect of sphingosine 1-phosphate (S1P) on intracellular Ca(2+) dynamics in rat vascular smooth muscle cells (VSMCs).

METHODS

Intracellular Ca(2+) concentration ([Ca(2+) ]i) was determined using a fluorescence dye fura-2/AM. Small interfering RNAs (siRNA) were transfected into VSMCs to deplete the expression of S1P2 and S1P3 receptors.

KEY FINDINGS

S1P induced a rapid and transient elevation in [Ca(2+) ]i, which was maximal 1 min after the stimulation, followed by a sustained increase. When extracellular Ca(2+) was removed, a decrease in resting level and a small and transient increase in [Ca(2+) ]i by S1P stimulation were observed. siRNA targeted for the S1P3 receptor almost completely inhibited the S1P-induced increase in [Ca(2+) ]i. The rapid and transient increase in [Ca(2+) ]i was significantly inhibited by diltiazem at a high concentration. Pertussis toxin and a phospholipase C (PLC) inhibitor inhibited the S1P-induced increase in [Ca(2+) ]i regardless of the presence of extracellular Ca(2+) . Furthermore, S1P activated store-operated and receptor-operated Ca(2+) entry.

CONCLUSIONS

These results suggest that S1P increases [Ca(2+) ]i via the S1P3 receptor by inducing an influx of extracellular Ca(2+) partially through the voltage-dependent Ca(2+) channels, as well as by mobilizing Ca(2+) from its intracellular stores. S1P3 receptor-coupled Gi/o protein and PLC activation mediate the mechanisms.

Control of metabolism and signaling of simple bioactive sphingolipids: Implications in disease

Simple bioactive sphingolipids include ceramide, sphingosine and their phosphorylated forms sphingosine 1-phosphate and ceramide 1-phosphate. These molecules are crucial regulators of cell functions. In particular, they play important roles in the regulation of angiogenesis, apoptosis, cell proliferation, differentiation, migration, and inflammation. Decoding the mechanisms by which these cellular functions are regulated requires detailed understanding of the signaling pathways that are implicated in these processes. Most importantly, the development of inhibitors of the enzymes involved in their metabolism may be crucial for establishing new therapeutic strategies for treatment of disease.