Sphingosine 1-phosphate attenuates H2O2-induced apoptosis in endothelial cells

A Rheostat of Ceramide and Sphingosine-1-Phosphate as a Determinant of Oxidative Stress-Mediated Kidney Injury

Reactive oxygen species (ROS) modulate sphingolipid metabolism, including enzymes that generate ceramide and sphingosine-1-phosphate (S1P), and a ROS-antioxidant rheostat determines the metabolism of ceramide-S1P. ROS induce ceramide production by activating ceramide-producing enzymes, leading to apoptosis, while they inhibit S1P production, which promotes survival by suppressing sphingosine kinases (SphKs). A ceramide-S1P rheostat regulates ROS-induced mitochondrial dysfunction, apoptotic/anti-apoptotic Bcl-2 family proteins and signaling pathways, leading to apoptosis, survival, cell proliferation, inflammation and fibrosis in the kidney. Ceramide inhibits the mitochondrial respiration chain and induces ceramide channel formation and the closure of voltage-dependent anion channels, leading to mitochondrial dysfunction, altered Bcl-2 family protein expression, ROS generation and disturbed calcium homeostasis. This activates ceramide-induced signaling pathways, leading to apoptosis. These events are mitigated by S1P/S1P receptors (S1PRs) that restore mitochondrial function and activate signaling pathways. SphK1 promotes survival and cell proliferation and inhibits inflammation, while SphK2 has the opposite effect. However, both SphK1 and SphK2 promote fibrosis. Thus, a ceramide-SphKs/S1P rheostat modulates oxidant-induced kidney injury by affecting mitochondrial function, ROS production, Bcl-2 family proteins, calcium homeostasis and their downstream signaling pathways. This review will summarize the current evidence for a role of interaction between ROS-antioxidants and ceramide-SphKs/S1P and of a ceramide-SphKs/S1P rheostat in the regulation of oxidative stress-mediated kidney diseases.

Mechanism of cell death of endothelial cells regulated by mechanical forces

Cell death of endothelial cells (ECs) is a common devastating consequence of various vascular-related diseases. Atherosclerosis, hypertension, sepsis, diabetes, cerebral ischemia and cardiac ischemia/reperfusion injury, and chronic kidney disease remain major causes of morbidity and mortality worldwide, in which ECs are constantly subjected to a great amount of dynamic changed mechanical forces including shear stress, extracellular matrix stiffness, mechanical stretch and microgravity. A thorough understanding of the regulatory mechanisms by which the mechanical forces controlled the cell deaths including apoptosis, autophagy, and pyroptosis is crucial for the development of new therapeutic strategies. In the present review, experimental and clinical data highlight that nutrient depletion, oxidative stress, tumor necrosis factor-α, high glucose, lipopolysaccharide, and homocysteine possess cytotoxic effects in many tissues and induce apoptosis of ECs, and that sphingosine-1-phosphate protects ECs. Nevertheless, EC apoptosis in the context of those artificial microenvironments could be enhanced, reduced or even reversed along with the alteration of patterns of shear stress. An appropriate level of autophagy diminishes EC apoptosis to some extent, in addition to supporting cell survival upon microenvironment challenges. The intervention of pyroptosis showed a profound effect on atherosclerosis. Further cell and animal studies are required to ascertain whether the alterations in the levels of cell deaths and their associated regulatory mechanisms happen at local lesion sites with considerable mechanical force changes, for preventing senescence and cell deaths in the vascular-related diseases.

An adiponectin-S1P axis protects against lipid induced insulin resistance and cardiomyocyte cell death via reduction of oxidative stress

BACKGROUND

Adiponectin exerts several beneficial cardiovascular effects, however their specific molecular mechanisms require additional understanding. This study investigated the mechanisms of adiponectin action in the heart during high fat diet (HFD) feeding or in palmitate (PA) treated H9c2 cardiomyoblasts.

METHODS

6-week-old male adiponectin knock out (Ad-KO) mice were fed chow or 60% HFD for 6 weeks then received saline or recombinant adiponectin (3μg/g body weight) for an additional 2 weeks. After acute insulin stimulation (4 U/kg), tissue and serum samples were collected for analysis. H9c2 cardiomyocytes were treated ±0.1 mM PA, the adiponectin receptor agonist AdipoRon, or the antioxidant MnTBAP then assays to analyze reactive oxygen species (ROS) production and cell death were conducted. To specifically determine the mechanistic role of S1P, gain and loss of function studies were conducted with adding S1P to cells or the inhibitors THI and SKI-II, respectively.

RESULTS

HFD feeding induced cardiac insulin resistance in Ad-KO mice, which was reversed following replenishment of normal circulating adiponectin levels. In addition, myocardial total triglyceride was elevated by HFD and lipidomic analysis showed increased levels of ceramides and sphingosine-1-phosphate (S1P), with only the latter being corrected by adiponectin administration. Similarly, treatment of H9C2 cardiomyoblasts with PA led to a significant increase of intracellular S1P but not in conditioned media whereas AdipoRon significantly increased S1P production and secretion from cells. AdipoRon or the antioxidant MnTBAP significantly reduced PA-induced cell death. Gain and loss of function studies suggested S1P secretion and autocrine receptor activation mediated the effect of AdipoRon to attenuate PA-induced ROS production and cell death.

CONCLUSION

Our data establish adiponectin signaling-mediated increase in S1P secretion as a mechanism via which HFD or PA induced cardiomyocyte lipotoxicity, leading to insulin resistance and cell death, is attenuated.

S1PR2 antagonist alleviates oxidative stress-enhanced brain endothelial permeability by attenuating p38 and Erk1/2-dependent cPLA2 phosphorylation

Both sphingosine-1-phosphate receptor-2 (S1PR2) and cytosolic phospholipase A₂ (cPLA₂) are implicated in the disruption of cerebrovascular integrity in experimental stroke. However, the role of S1PR2 in induction of cPLA₂ phosphorylation during cerebral ischemia-induced endothelial dysfunction remains unknown. This study investigated the effect of S1PR2 blockade on oxidative stress-induced cerebrovascular endothelial barrier impairment and explored the possible mechanisms. In bEnd3 cells, cPLA₂ inhibitor CAY10502 as well as S1PR2 antagonist JTE013 profoundly suppressed hydrogen peroxide (H₂O₂)-induced changes of paracellular permeability and ZO-1 localization. Besides p38, extracellular signal-regulated kinase (Erk) 1/2 is required for H₂O₂-increased cPLA₂ phosphorylation and endothelial permeability. Pharmacological and genetic inhibition of S1PR2 significantly suppressed their phosphorylation in response to H₂O₂. Especially lentivirus-mediated knockdown of S1PR2 inhibited H₂O₂-induced ZO-1 redistribution and paracellular hyperpermeability. Using the permanent middle cerebral artery occlusion (pMCAO) mouse model, we found JTE013 pretreatment markedly reduced Evans blue dye (EBD) extravasation and reversed the decrease in VE-cadherin, occludin, claudin-5 and CD31 expression in infarcted hemisphere. Lentivirus-mediated S1PR2 knockdown also attenuated EBD extravasation. Furthermore, JTE013 pretreatment attenuated neurological deficit, brain edema and infarction volume. Therefore, our findings suggest the protective effect of JTE013 on brain endothelial barrier integrity is likely mediated by suppressing p38 and Erk1/2-dependent cPLA₂ phosphorylation under oxidative stress.

The protective effects of a novel synthetic β-elemene derivative on human umbilical vein endothelial cells against oxidative stress-induced injury: Involvement of antioxidation and PI3k/Akt/eNOS/NO signaling pathways

Antioxidant therapy is considered as promising strategy for treating oxidative stress-induced cardiovascular disease. Bis (β-elemene-13-yl) glutarate (BEG) is a novel β-elemene derivative. Herein, we examined the antioxidant activity of BEG on human umbilical vein endothelial cells (HUVECs) after injury with hydrogen peroxide (H₂O₂) and investigated the mechanism involved. HUVECs were divided into the following groups: control group (untreated cells); treated groups (cells treated with 0.1, 1, 10 μmol/L of BEG); positive control group (cells treated with 0.1 mM Vitamin E); model group (cells treated with 0.5 mM H₂O₂ alone). Cells were pre-incubated with or without BEG for 24 h and then incubated for a further 2 h with 0.5 mM H₂O₂. Our results showed that BEG significantly reduced H₂O₂ induced loss in endothelial cell viability, reactive oxygen species (ROS) production, reduced lactate dehydrogenase (LDH) release, and malonyldialdehyde (MDA) level in a concentration-dependent manner. Also, BEG increased the cellular the superoxide dismutase (SOD) activity. Moreover, we found that H₂O₂ decreased Akt and eNOS phosphorylation, which perhaps, indirectly reduced nitric oxide (NO) production. These effects induced by H₂O₂, however, were reduced by pre-treatment with BEG. BEG effects were inhibited by a PI3K inhibitor (wortmannin) and eNOS inhibitor (L-NAME). In conclusion, the present study demonstrated that BEG has antioxidant activity. Furthermore, BEG reduced H₂O₂-induced endothelial cells injury by the involvement of antioxidation and PI3K/Akt/eNOS/NO signaling pathways.

Curcumin protects rabbit articular chondrocytes against sodium nitroprusside-induced apoptosis in vitro

The preventive and therapeutic effects of curcumin on degeneration of articular (joint) cartilage diseases have rarely been investigated. In the present study, the protective effects of curcumin against sodium nitroprusside (SNP)-induced chondrocyte apoptosis were evaluated and the underlying molecular mechanisms were elucidated. Curcumin was used to as a co-treatment with SNP in chondrocytes, and changes occurring in the cells were observed and evaluated. It was shown using a cell counting kit-8 (CCK-8) assay that curcumin protected the viability of chondrocytes against SNP damage. NO (nitric oxide) from SNP could be scavenged by curcumin. Flow cytometry and Hoechst 33342 staining showed that curcumin not only inhibited the cell apoptosis in a concentration-dependent pattern but also ameliorated the SNP-induced nuclear chromatin damage and reduction of the mitochondrial membrane potential in chondrocytes. In SNP-treated chondrocytes, curcumin downregulated the expression of Bax and cleaved caspase-3 but upregulated the expression of Bcl-2, as shown by western blot. Meanwhile, curcumin administration also protected extracellular matrix (ECM) synthesis and prevented its degradation. Taken together, these results support the hypothesis that curcumin exerts its protective effect on chondrocytes against SNP-induced apoptosis, at least partly, via blocking the mitochondrial-dependent apoptotic pathway and maintaining the metabolic balance of ECM. Thus, curcumin may be a potential candidate to be used as a unique biological agent for the prevent and treatment of osteoarthritis (OA).

Treatment with a JNK inhibitor increases, whereas treatment with a p38 inhibitor decreases, H2O2-induced calf pulmonary arterial endothelial cell death

Oxidative stress induces apoptosis in endothelial cells (ECs). Reactive oxygen species (ROS) promote cell death by regulating the activity of various mitogen-activated protein kinases (MAPKs) in ECs. The present study investigated the effects of MAPK inhibitors on cell survival and glutathione (GSH) levels upon H₂O₂ treatment in calf pulmonary artery ECs (CPAECs). H₂O₂ treatment inhibited the growth and induced the death of CPAECs, as well as causing GSH depletion and the loss of mitochondrial membrane potential (MMP). While treatment with the MEK or JNK inhibitor impaired the growth of H₂O₂-treated CPAECs, treatment with the p38 inhibitor attenuated this inhibition of growth. Additionally, JNK inhibitor treatment increased the proportion of sub-G₁ phase cells in H₂O₂-treated CPAECs and further decreased the MMP. However, treatment with a p38 inhibitor reversed the effects of H₂O₂ treatment on cell growth and the MMP. Similarly, JNK inhibitor treatment further increased, whereas p38 inhibitor treatment decreased, the proportion of GSH-depleted cells in H₂O₂-treated CPAECs. Each of the MAPK inhibitors affected cell survival, and ROS or GSH levels differently in H₂O₂-untreated, control CPAECs. The data suggest that the exposure of CPAECs to H₂O₂ caused the cell growth inhibition and cell death through GSH depletion. Furthermore, JNK inhibitor treatment further enhanced, whereas p38 inhibitors attenuated, these effects. Thus, the results of the present study suggest a specific protective role for the p38 inhibitor, and not the JNK inhibitor, against H₂O₂-induced cell growth inhibition and cell death.

Demyelination induced by oxidative stress is regulated by sphingosine 1-phosphate receptors

Oxidative stress is a pathological condition defined as an imbalance between production and removal of reactive oxygen species. This process causes structural cell damage, disrupts DNA repair and induces mitochondrial dysfunction. Many in vitro studies have used direct bolus application of H₂ O₂ to investigate the role of oxidative stress in cell culture. In this study, using mouse organotypic cerebellar slice cultures, the effects of H₂ O₂ -induced oxidative stress on myelination state were examined, using bolus concentrations of H₂ O₂ (0.1-1 mM) and low-continuous H₂ O₂ (∼20 μM) generated from glucose oxidase and catalase (GOX-CAT). Using these models, the potential therapeutic effects of pFTY720, an oral therapy used in multiple sclerosis, was also examined. We found bolus treatment of H₂ O₂ (0.5 mM) and, for the first time, low-continuous H₂ O₂ (GOX-CAT) to induce demyelination in organotypic slices. Both bolus H₂ O₂ and GOX-CAT treatments significantly decreased vimentin expression in these slice cultures as well as increased cell death in isolated astrocyte cultures. Importantly, pre-treatment with pFTY720 significantly attenuated both bolus H₂ O₂ and GOX-CAT-induced demyelination and the GOX-CAT-induced decrease in vimentin in cerebellar slices, without altering levels of the proinflammatory cytokines such as IL-6 and CX3CL1. We also observed increased SMI-32 immunoreactivity in the white matter tract induced by GOX-CAT indicating axonal damage, which was remarkably attenuated by pFTY720. Taken together, this data establishes a novel GOX-CAT model of demyelination and demonstrates that pFTY720 can act independently of inflammatory cytokines to attenuate decreases in vimentin, as well as axonal damage and demyelination induced by oxidative stress.

HDL-associated ApoM is anti-apoptotic by delivering sphingosine 1-phosphate to S1P1 & S1P3 receptors on vascular endothelium

Background

High-density Lipoprotein (HDL) attenuates endothelial cell apoptosis induced by different cell-death stimuli such as oxidation or growth factor deprivation. HDL is the main plasma carrier of the bioactive lipid sphingosine 1-phosphate (S1P), which it is a signaling molecule that promotes cell survival in response to several apoptotic stimuli. In HDL, S1P is bound to Apolipoprotein M (ApoM), a Lipocalin that is only present in around 5% of the HDL particles. The goal of this study is to characterize ApoM-bound S1P role in endothelial apoptosis protection and the signaling pathways involved.

Methods

Human umbilical vein endothelial cells (HUVEC) cultures were switched to serum/grow factor deprivation medium to induce apoptosis and the effect caused by the addition of ApoM and S1P analyzed.

Results

The addition of HDL^+ApoM or recombinant ApoM-bound S1P promoted cell viability and blocked apoptosis, whereas HDL^-ApoM had no protective effect. Remarkably, S1P exerted a more potent anti-apoptotic effect when carried by ApoM as compared to albumin, or when added as free molecule. Mechanistically, cooperation between S1P1 and S1P3 was required for the HDL/ApoM/S1P-mediated anti-apoptotic ability. Furthermore, AKT and ERK phosphorylation was also necessary to achieve the anti-apoptotic effect of the HDL/ApoM/S1P complex.

Conclusions

Altogether, our results indicate that ApoM and S1P are key elements of the anti-apoptotic activity of HDL and promote optimal endothelial function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-017-0429-2) contains supplementary material, which is available to authorized users.

Role of lipid phosphate phosphatase 3 in human aortic endothelial cell function

AIMS

Lipid phosphate phosphatase 3; type 2 phosphatidic acid phosphatase β (LPP3; PPAP2B) is a transmembrane protein dephosphorylating and thereby terminating signalling of lipid substrates including lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P). Human LPP3 possesses a cell adhesion motif that allows interaction with integrins. A polymorphism (rs17114036) in PPAP2B is associated with coronary artery disease, which prompted us to investigate the possible role of LPP3 in human endothelial dysfunction, a condition promoting atherosclerosis.

METHODS AND RESULTS

To study the role of LPP3 in endothelial cells we used human primary aortic endothelial cells (HAECs) in which LPP3 was silenced or overexpressed using either wild type or mutated cDNA constructs. LPP3 silencing in HAECs enhanced secretion of inflammatory cytokines, leucocyte adhesion, cell survival, and migration and impaired angiogenesis, whereas wild-type LPP3 overexpression reversed these effects and induced apoptosis. We also demonstrated that LPP3 expression was negatively correlated with vascular endothelial growth factor expression. Mutations in either the catalytic or the arginine-glycine-aspartate (RGD) domains impaired endothelial cell function and pharmacological inhibition of S1P or LPA restored it. LPA was not secreted in HAECs under silencing or overexpressing LPP3. However, the intra- and extra-cellular levels of S1P tended to be correlated with LPP3 expression, indicating that S1P is probably degraded by LPP3.

CONCLUSIONS

We demonstrated that LPP3 is a negative regulator of inflammatory cytokines, leucocyte adhesion, cell survival, and migration in HAECs, suggesting a protective role of LPP3 against endothelial dysfunction in humans. Both the catalytic and the RGD functional domains were involved and S1P, but not LPA, might be the endogenous substrate of LPP3.

Berberine Protects Human Umbilical Vein Endothelial Cells against LPS-Induced Apoptosis by Blocking JNK-Mediated Signaling

Endothelial dysfunction is a critical factor during the initiation of atherosclerosis. Berberine has a beneficial effect on endothelial function; however, the underlying mechanisms remain unclear. In this study, we investigated the effects of berberine on lipopolysaccharide- (LPS-) induced apoptosis in human umbilical vein endothelial cells (HUVECs) and the molecular mechanisms mediating the effect. The effects of berberine on LPS-induced cell apoptosis and viability were measured with 5-ethynyl-2′-deoxyuridine staining, flow cytometry, and Cell Counting Kit-8 assays. The expression and/or activation of proapoptotic and antiapoptotic proteins or signaling pathways, including caspase-3, poly(ADP-ribose) polymerase, myeloid cell leukemia-1 (MCL-1), p38 mitogen-activated protein kinase, C-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase, were determined with western blotting. The malondialdehyde levels, superoxide dismutase (SOD) activity, and production of proinflammatory cytokines were measured with enzyme-linked immunosorbent assays. The results demonstrated that berberine pretreatment protected HUVECs from LPS-induced apoptosis, attenuated LPS-induced injury, inhibited LPS-induced JNK phosphorylation, increased MCL-1 expression and SOD activity, and decreased proinflammatory cytokine production. The effects of berberine on LPS-treated HUVECs were prevented by SP600125, a JNK-specific inhibitor. Thus, berberine might be a potential candidate in the treatment of endothelial cell injury-related vascular diseases.

FTY720, a sphingosine-1-phosphate (S1P) receptor modulator, protects sinusoid endothelial cells from radiation injury in vitro

PURPOSE

To determine whether FTY720, a sphingosine-1-phosphate (S1P) receptor modulator, would protect sinusoid endothelial cells (SECs) from radiation injury in vitro.

MATERIALS AND METHODS

The effect of FTY720 on the viability of irradiated human liver SECs were examined by MTT assay or FACS analysis. The effect of FTY720 on the survival of hepatocellular carcinoma cell line, HepG2 and McA-RH7777, were determined by clonogenic assays. The activation of Akt pathway was tested by western bolt.

RESULTS

FTY720 increases the survival of irradiated SECs; in contrast, it does not appear to be radioprotective of tumor cells. Furthermore, the activation of Akt pathway was confirmed in the protective effect of FTY720 on SECs.

CONCLUSION

These results suggest that FTY720 will be a potential therapeutic protector for the SEC apoptosis during RILD.

Roles of sphingosine-1-phosphate in reproduction

Sphingosine-1-phosphate (S1P) plays crucial roles in the regulation of cell growth, proliferation, differentiation, cell survival, migration, and angiogenesis. In the reproductive system, S1P protects mammalian germ cells from irradiation or chemotherapy-induced cell death in vivo and in vitro. Moreover, S1P could improve the survival rate of thawed ovary and transplanted ovary. Furthermore, S1P could improve the developmental potential of oocyte and preimplantation embryo. In conclusion, S1P plays important roles in reproduction.

Sphingosine-1-phosphate: distribution, metabolism and role in the regulation of cellular functions

The role of sphingosine-1-phosphate (S1P) in regulation of cellular functions and cell protection is reviewed. S1P, along with other sphingolipid metabolites, is believed to act as an intracellular second messenger and as an extracellular mediator molecule. S1P chemistry, production and metabolism are described. Cellular receptors for S1P and their tissue specificity are described. Platelets and erythrocytes have a crucial significance in blood transport of S1P. Hypoxic conditions induce an increase in S1P, which initiates a set of cytoprotective events via its cellular receptors. S1P involvement in regulation of cell migration, myogenesis, control of skeletal muscle function is described. It is shown that S1P balance disturbances may mediate pathological state. S1P system implication in regulation of the most important cellular functions allows considering it as a prospective remedial target.

Lipid phosphate phosphatase (LPP3) and vascular development

Lipid phosphate phosphatases (LPP) are integral membrane proteins with broad substrate specificity that dephosphorylate lipid substrates including phosphatidic acid, lysophosphatidic acid, ceramide 1-phosphate, sphingosine 1-phosphate, and diacylglycerol pyrophosphate. Although the three mammalian enzymes (LPP1-3) demonstrate overlapping catalytic activities and substrate preferences in vitro, the phenotypes of mice with targeted inactivation of the Ppap2 genes encoding the LPP enzymes reveal nonredundant functions. A specific role for LPP3 in vascular development has emerged from studies of mice lacking Ppap2b. A meta-analysis of multiple, large genome-wide association studies identified a single nucleotide polymorphism in PPAP2B as a novel predictor of coronary artery disease. In this review, we will discuss the evidence that links LPP3 to vascular development and disease and evaluate potential molecular mechanisms. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Differential roles of JNK, ERK1/2, and p38 mitogen-activated protein kinases on endothelial cell tissue repair functions in response to tumor necrosis factor-α

Tumor necrosis factor (TNF)-α can alter tissue repair functions in a variety of cells including endothelial cells. However, the mechanism by which TNF-α mediates these functional changes has not fully been studied. We investigated the role of mitogen-activated protein kinases (MAPKs) on mediating the regulatory effect of TNF-α on the tissue repair functions of human pulmonary artery endothelial cells (HPAECs). TNF-α protected HPAECs from undergoing apoptosis induced by serum and growth factor deprivation, augmented collagen gel contraction, and stimulated wound closure. TNF-α activated c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases 1 and 2 (ERK1/2), and p38. Inhibitors of JNK (SP600125, 5 µM) or ERK1/2 (PD98059, 5 µM) significantly inhibited TNF-α-stimulated cell survival, contraction of collagen gels, and wound closure. In contrast, the p38 inhibitor SB203580 (5 µM) further amplified all of the TNF-α effects on HPAECs. TNF-α specifically activated p38α but not other p38 isoforms and suppression of p38α by an siRNA resulted in further amplification of the TNF-α effect. These results suggest that TNF-α stimulates tissue repair functions of HPAECs, and this may be mediated, at least in part, positively via JNK and ERK1/2, and negatively through p38α. MAPKs may play a role in endothelial cell-mediated tissue repair, especially in an inflammatory milieu where TNF-α is present.

Sphingosine kinase 1 is required for mesothelioma cell proliferation: role of histone acetylation

Background

Malignant pleural mesothelioma (MPM) is a devastating disease with an overall poor prognosis. Despite the recent advances in targeted molecular therapies, there is a clear and urgent need for the identification of novel mesothelioma targets for the development of highly efficacious therapeutics.

Methodology/Principal Findings

In this study, we report that the expression of Sphingosine Kinase 1 (SphK1) protein was preferentially elevated in MPM tumor tissues (49 epithelioid and 13 sarcomatoid) compared to normal tissue (n = 13). In addition, we also observed significantly elevated levels of SphK1 and SphK2 mRNA and SphK1 protein expression in MPM cell lines such as H2691, H513 and H2461 compared to the non-malignant mesothelial Met5 cells. The underlying mechanism appears to be mediated by SphK1 induced upregulation of select gene transcription programs such as that of CBP/p300 and PCAF, two histone acetyl transferases (HAT), and the down regulation of cell cycle dependent kinase inhibitor genes such as p27Kip1 and p21Cip1. In addition, using immunoprecipitates of anti-acetylated histone antibody from SphK inhibitor, SphK-I2 treated Met5A and H2691 cell lysates, we also showed activation of other cell proliferation related genes, such as Top2A (DNA replication), AKB (chromosome remodeling and mitotic spindle formation), and suppression of p21 CIP1 and p27KIP1. The CDK2, HAT1 and MYST2 were, however, unaffected in the above study. Using SphK inhibitor and specific siRNA targeting either SphK1 or SphK2, we also unequivocally established that SphK1, but not SphK2, promotes H2691 mesothelioma cell proliferation. Using a multi-walled carbon nanotubes induced peritoneal mesothelioma mouse model, we showed that the SphK1−/− null mice exhibited significantly less inflammation and granulamatous nodules compared to their wild type counterparts.

Conclusions/Significance

The lipid kinase SphK1 plays a positive and essential role in the growth and development of malignant mesothelioma and is therefore a likely therapeutic target.

The effects of ginsenoside Rb1 on JNK in oxidative injury in cardiomyocytes

Reactive oxygen species (ROS) can induce oxidative injury via iron interactions (i.e. Fenton chemistry and hydroxyl radical formation). Our prior work suggested that American ginseng berry extract and ginsenoside Re were highly cardioprotective against oxidant stress. To extend this study, we evaluated the protective effect of protopanaxadiol-type ginsenoside Rb1 (gRb1) on H(2)O(2)-induced oxidative injury in cardiomyocytes and explored the ROS-mediated intracellular signaling mechanism. Cultured embryonic chick cardiomyocytes (4-5 day) were used. Cell death was assessed by propidium iodide and lactate dehydrogenase release. Pretreatment with gRb1 (0.01, 0.1, or 1 μM) for 2 h and concurrent treatment with H(2)O(2) (0.5 mM) for 2 h resulted in a dose-dependent reduction of cell death, 36.6 ± 2.9% (n = 12, p < 0.05), 30.5 ± 5.1% (n = 12, p < 0.05) and 28.6 ± 3.1% (n = 12, p < 0.01) respectively, compared to H(2)O(2)-exposed cells (48.2 ± 3.3%, n = 12). This cardioprotective effect of gRb1 was associated with attenuated intracellular ROS generation as measured by 6-carboxy-2', 7'-dichlorodihydrofluorescein diacetate, preserved the mitochondrial membrane potential as determined using JC-1. In the ESR study, gRb1 exhibited the scavenging DPPH and hydroxyl radical activities. Furthermore, our data showed the increased JNK phosphorylation (p-JNK) in H(2)O(2)-exposed cells was suppressed by the pretreatment with gRb 1 (1 μM) (p < 0.01). Co-treatment of gRb1 with a specific inhibitor of JNK SP600125 (10 μM) further reduced the p-JNK and enhanced the cell survival after H(2)O(2) exposure. Collectively, our results suggest that gRb1 conferred cardioprotection that was mediated via attenuating ROS and suppressing ROS-induced JNK activation.

Sphingosine-1-phosphate inhibits H2O2-induced granulosa cell apoptosis via the PI3K/Akt signaling pathway

OBJECTIVE

To investigate the protective effect of sphingosine-1-phosphate (S1P) against H(2)O(2)-induced apoptosis in human granulosa cell cultures with freshly harvested granulosa cells.

DESIGN

Experimental study.

SETTING

Academic medical center for reproductive medicine.

PATIENT(S)

Cultures of primary granulosa cells isolated from women undergoing in vitro fertilization (IVF).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Cell apoptosis and Western blot analysis of signaling pathway proteins.

RESULT(S)

We found that S1P (1 and 10 mM) statistically significantly decreased granulosa cell apoptosis after H(2)O(2) treatment. The decreased cell apoptosis induced by S1P was abolished after treatment with VPC23019, an inhibitor of S1P1 and S1P3 receptors, W146, an inhibitor of S1P1 receptors, and CAY10444, an inhibitor of S1P3 receptors. A Western blot analysis revealed that the level of phospho-Akt increased and peaked at 10 minutes after 10 mM S1P exposure.

CONCLUSION(S)

Treatment with S1P can inhibit the apoptosis of granulosa cells in response to oxidative stress induced by H(2)O(2). The protective effect of S1P is mediated by activating the PI3K/Akt pathway, and the antiapoptotic effect of S1P is mainly mediated through the S1P1 and S1P3 receptor.

Redox balance dynamically regulates vascular growth and remodeling

Vascular growth and remodeling responses entail several complex biochemical, molecular, and cellular responses centered primarily on endothelial cell activation and function. Recent studies reveal that changes in endothelial cell redox status critically influence numerous cellular events that are important for vascular growth under different conditions. It has been known for some time that oxidative stress actively participates in many aspects of angiogenesis and vascular remodeling. Initial studies in this field were largely exploratory with minimal insight into specific molecular mechanisms and how these responses could be regulated. However, it is now clear that intracellular redox mechanisms involving hypoxia, NADPH oxidases (NOX), xanthine oxidase (XO), nitric oxide and its synthases, and intracellular antioxidant defense pathways collectively orchestrate a redox balance system whereby reactive oxygen and nitrogen species integrate cues controlling vascular growth and remodeling. In this review, we discuss key redox regulation pathways that are centrally important for vascular growth in tissue health and disease. Important unresolved questions and issues are also addressed that requires future investigation.

Isoflurane protects against human endothelial cell apoptosis by inducing sphingosine kinase-1 via ERK MAPK

Endothelial dysfunction is a major clinical problem affecting virtually every patient requiring critical care. Volatile anesthetics are frequently used during the perioperative period and protect the heart and kidney against ischemia and reperfusion injury. We aimed to determine whether isoflurane, the most commonly used volatile anesthetic in the USA, protects against endothelial apoptosis and necrosis and the mechanisms involved in this protection. Human endothelial EA.hy926 cells were pretreated with isoflurane or carrier gas (95% room air + 5% CO₂) then subjected to apoptosis with tumor necrosis factor-α or to necrosis with hydrogen peroxide. DNA laddering and in situ Terminal Deoxynucleotidyl Transferase Biotin-dUTP Nick-End Labeling (TUNEL) staining determined EA.hy926 cell apoptosis and percent LDH released determined necrosis. We also determined whether isoflurane modulates the expression and activity of sphingosine kinase-1 (SK1) and induces the phosphorylation of extracellular signal regulated kinase (ERK MAPK) as both enzymes are known to protect against cell death. Isoflurane pretreatment significantly decreased apoptosis in EA.hy926 cells as evidenced by reduced TUNEL staining and DNA laddering without affecting necrosis. Mechanistically, isoflurane induces the phosphorylation of ERK MAPK and increased SK1 expression and activity in EA.hy926 cells. Finally, selective blockade of SK1 (with SKI-II) or S1P₁ receptor (with W146) abolished the anti-apoptotic effects of isoflurane. Taken together, we demonstrate that isoflurane, in addition to its potent analgesic and anesthetic properties, protects against endothelial apoptosis most likely via SK1 and ERK MAPK activation. Our findings have significant clinical implication for protection of endothelial cells during the perioperative period and patients requiring critical care.

The p38 mitogen-activated protein kinases modulate endothelial cell survival and tissue repair

OBJECTIVE AND DESIGN

This study is designed to investigate the role of p38 MAPK in modulating human pulmonary artery endothelial cells (HPAECs) survival and tissue repair functions.

METHODS

HPAECs (passage 8-12) were used for all experiments. Cells were treated with IL-1β (0.5 or 2 ng/ml) or p38 inhibitor (SB203580 or SB220025, 5 μM each). Cells were also transfected with 50 nM siRNAs. Cell length was measured using ImageJ software. Collagen gel contraction and wound close assay were performed to evaluate tissue repair functions.

RESULTS

IL-1β activated p38 MAPK and induced morphologic change of HPAECs. The p38 inhibitors further augmented IL-1β-induced cell morphologic change, prevented cell death, and augmented collagen gel contraction. Suppression of p38α, γ, or δ, but not p38β resulted in cell morphologic alteration, and suppressing any one of p38 isoforms by siRNAs increased cell survival. Suppression of p38α or δ augmented gel contraction. While p38α suppression stimulated cell migration, suppressing the rest of three isoforms inhibit cell migration. Nuclear factor p65-siRNA blocked IL-1β-induced cell morphologic change, but did not affect p38 inhibitor-induced change.

CONCLUSION

These findings suggest that p38 MAPK may negatively modulate tissue repair functions of endothelial cells via p65 independent pathway.

Pharmacological relevance and potential of sphingosine 1-phosphate in the vascular system

Sphingosine-1-phosphate (S1P) was identified as a crucial molecule for regulating immune responses, inflammatory processes as well as influencing the cardiovascular system. S1P mediates differentiation, proliferation and migration during vascular development and homoeostasis. S1P is a naturally occurring lipid metabolite and is present in human blood in nanomolar concentrations. S1P is not only involved in physiological but also in pathophysiological processes. Therefore, this complex signalling system is potentially interesting for pharmacological intervention. Modulation of the system might influence inflammatory, angiogenic or vasoregulatory processes. S1P activates G-protein coupled receptors, namely S1P(1-5) , whereas only S1P(1-3) is present in vascular cells. S1P can also act as an intracellular signalling molecule. This review highlights the pharmacological potential of S1P signalling in the vascular system by giving an overview of S1P-mediated processes in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). After a short summary of S1P metabolism and signalling pathways, the role of S1P in EC and VSMC proliferation and migration, the cause of relaxation and constriction of arterial blood vessels, the protective functions on endothelial apoptosis, as well as the regulatory function in leukocyte adhesion and inflammatory responses are summarized. This is followed by a detailed description of currently known pharmacological agonists and antagonists as new tools for mediating S1P signalling in the vasculature. The variety of effects influenced by S1P provides plenty of therapeutic targets currently under investigation for potential pharmacological intervention.

Roles of sphingosine 1-phosphate on tumorigenesis

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid with a variety of biological activities. It is generated from the conversion of ceramide to sphingosine by ceramidase and the subsequent conversion of sphingosine to S1P, which is catalyzed by sphingosine kinases. Through increasing its intracellular levels by sphingolipid metabolism and binding to its cell surface receptors, S1P regulates several physiological and pathological processes, including cell proliferation, migration, angiogenesis and autophagy. These processes are responsible for tumor growth, metastasis and invasion and promote tumor survival. Since ceramide and S1P have distinct functions in regulating in cell fate decision, the balance between the ceramide/sphingosine/S1P rheostat becomes a potent therapeutic target for cancer cells. Herein, we summarize our current understanding of S1P signaling on tumorigenesis and its potential as a target for cancer therapy.

Sphingosine-1-phosphate activates the AKT pathway to protect small intestines from radiation-induced endothelial apoptosis

A previous in vitro study showed that sphingosine-1-phosphate (S1P), a ceramide antagonist, preserved endothelial cells in culture from radiation-induced apoptosis. We proposed to validate the role of S1P in tissue radioprotection by inhibiting acute gastrointestinal (GI) syndrome induced by endothelial cell apoptosis after high dose of radiation. Retro-orbital S1P was injected in mice exposed to 15 Gy, a dose-inducing GI syndrome within 10 days. Overall survival and apoptosis on intestines sections were studied. Intestinal cell type targeted by S1P and early molecular survival pathways were researched using irradiated in vitro cell models and in vivo mouse models. We showed that retro-orbital S1P injection before irradiation prevented GI syndrome by inhibiting endothelium collapse. We defined endothelium as a specific therapeutic target because only these cells and not intestinal epithelial cells, or B and T lymphocytes, were protected. Pharmacologic approaches using AKT inhibitor and pertussis toxin established that S1P affords endothelial cell protection in vitro and in vivo through a mechanism involving AKT and 7-pass transmembrane receptors coupled to Gi proteins. Our results provide strong pharmacologic and mechanistic proofs that S1P protects endothelial cells against acute radiation enteropathy.

Transforming growth factor-β1 downregulates caveolin-1 expression and enhances sphingosine 1-phosphate signaling in cultured vascular endothelial cells

In vascular endothelial cells, specialized microdomains of plasma membrane termed caveolae modulate various receptor signal transduction pathways regulated by caveolin-1, a resident protein of caveolae. We examined whether transforming growth factor-β1 (TGF-β1), a multifunctional cytokine, alters expression levels of caveolin-1 and influences heterologous receptor signaling. Treatment of cultured bovine aortic endothelial cells (BAEC) with TGF-β1 induces marked decreases in caveolin-1 expression in a time- and dose-dependent fashion at both levels of protein and mRNA. A pharmacological inhibitor of activin receptor-like kinase 5 (ALK-5) counteracts caveolin-1 downregulation by TGF-β1, indicating the involvement of ALK-5 receptor subtype for TGF-β1. Sphingosine 1-phosphate (S1P) is a serum-borne angiogenic lipid growth factor that exerts a wide variety of biological actions. S1P modulates G protein-coupled S1P receptors, activating downstream molecules kinases AMP-activated protein kinase (AMPK), and Akt as well as a small G protein Rac1, ultimately to promote migration. Because S1P receptor signaling is associated with caveolae/caveolin-1, we examined whether pretreatment with TGF-β1 enhances effects of S1P on BAEC. Whereas S1P alone evokes robust BAEC responses to S1P, pretreatment with TGF-β1 leads to even higher magnitudes of S1P-elicited signaling responses and cell migration. Conversely, genetic knockdown of caveolin-1 using small interfering RNA mimics TGF-β1-induced promotion of BAEC responses to S1P. Collectively, these data demonstrate that TGF-β1 downregulates caveolin-1 of cultured endothelial cells, involving ALK-5 receptor subtype. Because downregulation of caveolin-1 by TGF-β1 promotes subsequent heterologous receptor signaling by S1P, these results may also identify novel point of cross-talk between cytokines and sphingolipids within endothelial signal transduction machineries.

The effect of tetramethylpyrazine on hydrogen peroxide-induced oxidative damage in human umbilical vein endothelial cells

Tetramethylpyrazine has been widely used in traditional Chinese medicine to treat cardiovascular diseases such as atherosclerosis and hypertension. The underlying mechanism of cardioprotective effects, however, remains to be elucidated. Here, using human umbilical vein endothelial cells (HUVECs), we have assessed the protective effect of tetramethylpyrazine on H(2)O(2)-induced oxidative damage. After pre-incubation with tetramethylpyrazine (50, 100 and 150 microg/ml) for 24 hr., viability loss in H(2)O(2)-induced HUVECs (76.5% of the control level, p < 0.05, at 400 microM of H(2)O(2) for 12 hr.) was restored in a concentration-dependent manner, and the maximal recovery (88.7% of the control level, p < 0.05) was achieved with tetramethylpyrazine at 150 microg/ml. The production of reactive oxygen species was suppressed by measuring fluorescent intensity of 2',7'-dichorofluorescein (83.1% of the H(2)O(2)-treated group, p < 0.05, at 150 microg/ml of tetramethylpyrazine). Tetramethylpyrazine also increased activities of superoxide dismutase and glutathione peroxidase (144.1% and 118.3% of the H(2)O(2)-treated group, respectively, p < 0.05, at 150 microg/ml of tetramethylpyrazine). In addition, tetramethylpyrazine reduced levels of malonaldehyde, intracellular nitric oxide and nitric oxide synthase (83.8%, 91.2% and 78.7% of the H(2)O(2)-treated group, respectively, p < 0.05, at 150 microg/ml of tetramethylpyrazine). Furthermore, pre-incubation of tetramethylpyrazine with HUVECs for 24 hr. resulted in reduction of apoptosis and removal of cell cycle arrest in the S phase (56.6% and 59.7% of the H(2)O(2)-treated group, respectively, p < 0.01, at 150 microg/ml of tetramethylpyrazine). Altogether, these results suggest that tetramethylpyrazine has a protective effect on H(2)O(2)-induced oxidative damage in HUVECs due to its antioxidant and antiapoptotic properties.

Up-regulation of calcium-dependent proteolysis in human myoblasts under acute oxidative stress

The reduced regenerative potential of muscle fibres, most likely due to a decreased number and/or function of satellite cells, could play a significant role in the progression of muscle ageing. Accumulation of reactive oxygen species has been clearly correlated to sarcopenia and could contribute to the impairment of satellite cell function. In this work we have investigated the effect of oxidative stress generated by hydrogen peroxide in cultured human skeletal muscle satellite cells. We specifically focused on the activity and regulation of calpains. These calcium-dependent proteases are known to regulate many transduction pathways including apoptosis and play a critical role in satellite cell function. In our experimental conditions, which induce an increase in calcium concentration, protein oxidation and apoptotic cell death, a significant up-regulation of calpain expression and activity were observed and ATP synthase, a major component of the respiratory chain, was identified as a calpain target. Interestingly we were able to protect the cells from these H(2)O(2)-induced effects and prevent calpain up-regulation with a natural antioxidant extracted from pine bark (Oligopin). These data strongly suggest that oxidative stress could impair satellite cell functionality via calpain-dependent pathways and that an antioxidant such as Oligopin could prevent apoptosis and calpain activation.