Arachidonic acid-derived oxidation products initiate apoptosis in vascular smooth muscle cells

Advanced age protects resistance arteries of mouse skeletal muscle from oxidative stress through attenuating apoptosis induced by hydrogen peroxide

KEY POINTS

Vascular oxidative stress increases with advancing age. We hypothesized that resistance vessels develop resilience to oxidative stress to protect functional integrity and tested this hypothesis by exposing isolated pressurized superior epigastric arteries (SEAs) of old and young mice to H₂ O₂ . H₂ O₂ -induced death was greater in smooth muscle cells (SMCs) than endothelial cells (ECs) and lower in SEAs from old vs. young mice; the rise in vessel wall [Ca²⁺ ]_i induced by H₂ O₂ was attenuated with ageing, as was the decline in noradrenergic vasoconstriction; genetic deletion of IL-10 mimicked the effects of advanced age on cell survival. Inhibiting NO synthase or scavenging peroxynitrite reduced SMC death; endothelial denudation or inhibiting gap junctions increased SMC death; delocalization of cytochrome C activated caspases 9 and 3 to induce apoptosis. Vascular cells develop resilience to H₂ O₂ during ageing by preventing Ca²⁺ overload and endothelial integrity promotes SMC survival.

ABSTRACT

Advanced age is associated with elevated oxidative stress and can protect the endothelium from cell death induced by H₂ O₂ . Whether such protection occurs for intact vessels or differs between smooth muscle cell (SMC) and endothelial cell (EC) layers is unknown. We tested the hypothesis that ageing protects SMCs and ECs during acute exposure to H₂ O₂ (200 µm, 50 min). Mouse superior epigastric arteries (SEAs; diameter, ∼150 µm) were isolated and pressurized to 100 cmH₂ O at 37˚C. For SEAs from young (4 months) mice, H₂ O₂ killed 57% of SMCs and 11% of ECs in males vs. 8% and 2%, respectively, in females. Therefore, SEAs from males were studied to resolve the effect of ageing and experimental interventions. For old (24 months) mice, SMC death was reduced to 10% with diminished accumulation of [Ca²⁺ ]_i in the vessel wall during H₂ O₂ exposure. In young mice, genetic deletion of IL-10 mimicked the protective effect of ageing on cell death and [Ca²⁺ ]_i accumulation. Whereas endothelial denudation or gap junction inhibition (carbenoxolone; 100 µm) increased SMC death, inhibiting NO synthase (l-NAME, 100 µm) or scavenging peroxynitrite (FeTPPS, 5 µm) reduced SMC death along with [Ca²⁺ ]_i . Despite NO toxicity via peroxynitrite formation, endothelial integrity protects SMCs. Caspase inhibition (Z-VAD-FMK, 50 µm) attenuated cell death with immunostaining for annexin V, cytochrome C, and caspases 3 and 9 pointing to induction of intrinsic apoptosis during H₂ O₂ exposure. We conclude that advanced age reduces Ca²⁺ influx that triggers apoptosis, thereby promoting resilience of the vascular wall during oxidative stress.

Moderate levels of dietary arachidonic acid reduced lipid accumulation and tended to inhibit cell cycle progression in the liver of Japanese seabass Lateolabrax japonicus

To investigate the physiological roles of dietary arachidonic acid (ARA) in fish, a feeding trial with Japanese seabass was conducted, followed by a hepatic transcriptome assay. Six experimental diets differing basically in ARA level (0.05%, 0.22%, 0.37%, 0.60%, 1.38% and 2.32% of dry matter) were used in the feeding trial. Liver samples from fish fed diets with 0.05% and 0.37% ARA were subjected to transcriptomic assay, generating a total of 139 differently expressed unigenes, which were primarily enriched in lipid metabolism and cell cycle-related signaling pathways. Then, qRT-PCR validation on lipid metabolism and cell cycle-related genes as well as corresponding enzyme-linked immunosorbent assay of selected proteins were conducted with liver samples from all six groups. Moderated ARA levels reduced lipogenesis and stimulated β-oxidation concurrently, but high ARA levels seemed to affect lipid metabolism in complicated ways. Both gene expression and protein concentration of cell cycle-related proteins were decreased by moderate levels of dietary ARA. The lipid content and fatty acid composition in fish confirmed the transcription and protein concentration results related to lipid metabolism. In conclusion, moderate levels of dietary ARA (0.37% and 0.60%) reduced lipid accumulation and tended to inhibit cell cycle progression in the liver of Japanese seabass.

Circulating membrane-derived microvesicles in redox biology

Microparticles or microvesicles (MVs) are subcellular membrane blebs shed from all cells in response to various stimuli. MVs carry a battery of signaling molecules, many of them related to redox-regulated processes. The role of MVs, either as a cause or as a result of cellular redox signaling, has been increasingly recognized over the past decade. This is in part due to advances in flow cytometry and its detection of MVs. Notably, recent studies have shown that circulating MVs from platelets and endothelial cells drive reactive species-dependent angiogenesis; circulating MVs in cancer alter the microenvironment and enhance invasion through horizontal transfer of mutated proteins and nucleic acids and harbor redox-regulated matrix metalloproteinases and procoagulative surface molecules; and circulating MVs from red blood cells and other cells modulate cell-cell interactions through scavenging or production of nitric oxide and other free radicals. Although our recognition of MVs in redox-related processes is growing, especially in the vascular biology field, much remains unknown regarding the various biologic and pathologic functions of MVs. Like reactive oxygen and nitrogen species, MVs were originally believed to have a solely pathological role in biology. And like our understanding of reactive species, it is now clear that MVs also play an important role in normal growth, development, and homeostasis. We are just beginning to understand how MVs are involved in various biological processes-developmental, homeostatic, and pathological-and the role of MVs in redox signaling is a rich and exciting area of investigation.

Therapeutic implications of disorders of cell death signalling: membranes, micro-environment, and eicosanoid and docosanoid metabolism

Disruptions of cell death signalling occur in pathological processes, such as cancer and degenerative disease. Increased knowledge of cell death signalling has opened new areas of therapeutic research, and identifying key mediators of cell death has become increasingly important. Early triggering events in cell death may provide potential therapeutic targets, whereas agents affecting later signals may be more palliative in nature. A group of primary mediators are derivatives of the highly unsaturated fatty acids (HUFAs), particularly oxygenated metabolites such as prostaglandins. HUFAs, esterified in cell membranes, act as critical signalling molecules in many pathological processes. Currently, agents affecting HUFA metabolism are widely prescribed in diseases involving disordered cell death signalling. However, partly due to rapid metabolism, their role in cell death signalling pathways is poorly characterized. Recently, HUFA-derived mediators, the resolvins/protectins and endocannabinoids, have added opportunities to target selective signals and pathways. This review will focus on the control of cell death by HUFA, eicosanoid (C20 fatty acid metabolites) and docosanoid (C22 metabolites), HUFA-derived lipid mediators, signalling elements in the micro-environment and their potential therapeutic applications. Further therapeutic approaches will involve cell and molecular biology, the multiple hit theory of disease progression and analysis of system plasticity. Advances in the cell biology of eicosanoid and docosanoid metabolism, together with structure/function analysis of HUFA-derived mediators, will be useful in developing therapeutic agents in pathologies characterized by alterations in cell death signalling.

Interactions between CB(1) receptors and TRPV1 channels mediated by 12-HPETE are cytotoxic to mesencephalic dopaminergic neurons

BACKGROUND AND PURPOSES

We recently proposed the existence of neurotoxic interactions between the cannabinoid type 1 (CB(1)) receptor and transient receptor potential vanilloid 1 (TRPV1) channels in rat mesencephalic cultures. This study seeks evidence for the mediator(s) and mechanisms underlying the neurotoxic interactions between CB(1) receptors and TRPV1 in vitro and in vivo.

EXPERIMENTAL APPROACH

The mediator(s) and mechanism(s) for the interactions between CB(1) receptors and TRPV1 were evaluated by cell viability assays, immunocytochemistry, Fura-2 calcium imaging, mitochondrial morphology assay, ELISA and Western blot assay in vitro in neuron-enriched mesencephalic cultures. Injections into the substantia nigra and subsequent cell counts were also used to confirm these interactions in vivo.

KEY RESULTS

The neurotoxic interactions were mediated by 12(S)-hydroperoxyeicosatetraenoic acid (12(S)-HPETE), an endogenous TRPV1 agonist. CB(1) receptor agonists (HU210 and WIN55,212-2) increased the level of 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), a downstream metabolite of 12(S)-HPETE, which stimulates TRPV1-mediated death of mesencephalic neurons, both in vitro and in vivo. The neurotoxicity was mediated by increased intracellular Ca(2+) concentration ([Ca(2+)](i)) through TRPV1, consequently leading to mitochondrial damage and was attenuated by baicalein, a 12-lipoxygenase inhibitor.

CONCLUSION AND IMPLICATIONS

Activation of CB(1) receptors in rat mesencephalic neurons was associated with biosynthesis of 12(S)-HPETE, which in turn stimulated TRPV1 activity, leading to increased [Ca(2+)](i), mitochondrial damage and neuronal death.

Identification of a new functional splice variant of the enzyme methionine sulphoxide reductase A (MSRA) expressed in rat vascular smooth muscle cells

Reactive oxygen species contribute to ageing of the vascular system and development of cardiovascular disease. Methionine-S-sulphoxide, an oxidized form of methionine, is repaired by the enzyme methionine sulphoxide reductase A (MSRA). The enzyme, targeted to mitochondria or the cytosol by alternative splicing, is vital for oxidative stress resistance. This study was designed to examine the endogenous expression and intracellular localization of MSRA in rat aortic vascular smooth muscle cells (VSMCs). We detected robust MSRA immunoreactivity exclusively in mitochondria. Sequence analysis of msrA transcripts revealed the presence of a novel mitochondrial splice variant, msrA2a, in cultured rat VSMCs as well as in aortic tissue preparations. The enzymatic activity of a recombinant MSRA2a protein was confirmed by the reduction of methionine sulphoxide in a model substrate peptide. We conclude that multiple MSRA variants participate in the repair of oxidized proteins in VSMC mitochondria, but that other protective mechanisms may exist in the cytoplasmic compartment.

Herpes simplex virus type 1 infection induces oxidative stress and the release of bioactive lipid peroxidation by-products in mouse P19N neural cell cultures

To determine whether herpes simplex virus type 1 (HSV-1) infection causes oxidative stress and lipid peroxidation in cultured neural cells, mouse P19 embryonal carcinoma cells were differentiated into cells with neural phenotypes (P19N cells) by retinoic acid and were then infected with HSV-1. Cellular levels of reactive oxygen species (ROS) and the release of lipid peroxidation by-products into the tissue culture medium were then measured by the generation of fluorescent markers hydroxyphenyl fluorescein and a stable chromophore produced by lipid peroxidation products, malondialdehyde (MDA) and hydroxyalkenals (4-HAEs; predominantly 4-hydroxy-2-nonenal [HNE]), respectively. HSV-1 infection increased ROS levels in neural cells as early as 1 h post infection (p.i.) and ROS levels remained elevated at 24 h p.i. This viral effect required viral entry and replication as heat- and ultraviolet light-inactivated HSV-1 were ineffective. HSV-1 infection also was associated with increased levels of MDA/HAE in the culture medium at 2 and 4 h p.i., but MDA/HAE levels were not different from those detected in mock infected control cultures at 1, 6, and 24 h p.i. HSV-1 replication in P19N cells was inhibited by the antioxidant compound ebselen and high concentrations of HNE added to the cultures, but was increased by low concentrations of HNE. These findings indicate that HSV-1 infection of neural cells causes oxidative stress that is required for efficient viral replication. Furthermore, these observations raise the possibility that soluble, bioactive lipid peroxidation by-products generated in infected neural cells may be important regulators of HSV-1 pathogenesis in the nervous system.

Mediation of apoptosis by oxidized phospholipids

Free radical-mediated oxidation of (poly)unsaturated glycerophospholipids in membranes and lipoproteins leads to the formation of a plethora of products. Some of these oxidized phospholipids, especially the truncated forms, induce apoptosis depending on their chemical structure, concentration and cell type. Depending on the phospholipid and the cell type, two pathways have so far been identified for the intracellular transmission of the apoptotic signals. One pathway involves activation of acid sphingomyelinase, which gives rise to the formation of ceramide and is followed by phosphorylation of pro-apoptotic mitogen-activated protein kinases. Alternatively, oxidized phospholipids act directly on mitochondria leading to efflux of pro-apoptotic effectors in endothelial cells. During the execution of the apoptotic program additional oxidized phospholipids are generated. The apoptotic cascade itself leads to oxidation and exposure of e.g. membrane phosphatidylserine. Oxidized phospholipids on the outer leaflet of the plasma membrane can form surface lipid patterns that specifically bind to phagocytic cells, e.g. macrophages.In this manuscript we review the recent literature reporting on apoptosis-inducing glycerophospholipids. In addition, we describe the cellular processes that lead to phospholipid oxidation as part of the apoptotic mode of cell death and are likely to enhance the recognition of apoptotic cells by phagocytic macrophages.

Oxidized phospholipids: From molecular properties to disease

Oxidized lipids are generated from (poly)unsaturated diacyl- and alk(en)ylacyl glycerophospholipids under conditions of oxidative stress. The great variety of reaction products is defined by the degree of modification, hydrophobicity, chemical reactivity, physical properties and biological activity. The biological activities of these compounds may depend on both, the recognition of the particular molecular structures by specific receptors and on the unspecific physical and chemical effects on their target systems (membranes, proteins). In this review, we aim at highlighting the molecular features that are essential for the understanding of the biological actions of pure oxidized phospholipids. Firstly, their chemical structures are described as a basis for an understanding of their physical and (bio)chemical properties in membrane- and protein-bound form. Secondly, the biological activities of oxidized phospholipids are discussed in terms of their unspecific effects on the membrane level as well as their potential interactions with specific targets (receptors) affecting a large set of (signaling) molecules. Finally, the role of oxidized phospholipids as important mediators in pathophysiology is discussed with emphasis on atherosclerosis.

Localization of lipids in the aortic wall with imaging TOF-SIMS

Time-of-flight secondary-ion-mass-spectrometry (TOF-SIMS) was utilized to address the issue of localization of lipids and inorganic ions in healthy rat aorta and human atherosclerotic plaque. Pieces of rat aorta were high pressure frozen, freeze-fractured and freeze dried. The samples were analyzed by imaging TOF-SIMS equipped with a Bi(1-7)(+)-source. Reference lipid samples were analyzed and compared to data obtained by analysis of the rat aorta samples. Fatty acids, cholesterol, oxysterol and diacylglycerols were detected and localized. A heterogeneous lipid distribution could be shown in the aorta, where the lamellae of the aorta, distinguished by imaging of CN(-), appeared enriched in cholesterol, oxysterol and diacylglycerols, while the smooth muscle tissue, identified by imaging of PO(3), appeared enriched in phosphocholine. Palmitic/palmitoleic acid and stearic/oleic acid appeared to be heterogeneously distributed over the aorta with high concentration areas located especially in the tunica media region of the aorta. Human atherosclerotic plaque showed an irregular cholesterol distribution mainly located in spots in the intima region with elongated diacylglycerol regions located mainly in the media region.

Affinity Adhesion of Carbohydrate Particles and Yeast Cells to Boronate-Containing Polymer Brushes Grafted onto Siliceous Supports

Cross-linked agarose particles (Sepharose CL-6B) and baker's yeast cells were found to adhere to siliceous supports end-grafted with boronate-containing copolymers (BCCs) of N,N-dimethylacrylamide at pH> or =7.5, due to boronate interactions with surface carbohydrates of the particles and the cells. These interactions were registered both on macroscopic and on molecular levels: the BCCs spontaneously adsorbed on the agarose gel at pH> or =7.5, with adsorption increasing with pH. Agarose particles and yeast cells stained with Procion Red HE-3B formed stable, monolayer-like structures at pH 8.0, whereas at pH 7.0-7.8 the structures on the copolymer-grafted supports were less stable and more random. At pH 9.0, 50 % saturation of the surface with adhering cells was attained in 2 min. Stained cells formed denser and more stable layers on the copolymer-grafted supports than they did on supports modified with self-assembled organosilane layers derivatized with low-molecular-weight boronate, presumably due to a higher reactivity of the grafted BCCs. Quantitative detachment of adhered particles and cells could be achieved by addition of 20 mM fructose--a strong competitor for binding to boronates--at pH 7.0-9.0. Regeneration of the grafted supports allowed several sequential adhesion and detachment cycles with stained yeast cells. Affinity adhesion of micron-sized carbohydrate particles to boronate-containing polymer brushes fixed on solid supports is discussed as a possible model system suggesting a new approach to isolation and separation of living cells.

Enhanced 15-HPETE production during oxidant stress induces apoptosis of endothelial cells

Oxidant stress plays an important role in the etiology of vascular diseases by increasing rates of endothelial cell apoptosis, but few data exist on the mechanisms involved. Using a unique model of oxidative stress based on selenium deficiency (-Se), the effects of altered eicosanoid production on bovine aortic endothelial cells (BAEC) apoptosis was evaluated. Oxidant stress significantly increased the immediate oxygenation product of arachidonic acid metabolized by the 15-lipoxygenase pathway, 15-hydroxyperoxyeicosatetraenoic acid (15-HPETE). Treatment of -Se BAEC with TNFalpha/cyclohexamide (CHX) exhibited elevated levels of apoptosis, which was significantly reduced by the addition of a specific 15-lipoxygenase inhibitor PD146176. Furthermore, the addition of 15-HPETE to PD146176-treated BAEC, partially restored TNF/CHX-induced apoptosis. Increased exposure to 15-HPETE induced apoptosis, as determined by internucleosomal DNA fragmentation, chromatin condensation, caspase-3 activation, and caspase-9 activation, which suggests mitochondrial dysfunction. The expression of Bcl-2 protein also was decreased in -Se BAEC. Addition of a caspase-9 inhibitor (LEHD-fmk) completely blocked 15-HPETE-induced chromatin condensation in -Se BAEC, suggesting that 15-HPETE-induced apoptosis is caspase-9 dependent. Increased apoptosis of BAEC as a result of oxidant stress and subsequent production of 15-HPETE may play a critical role in a variety of inflammatory based diseases.

Implications of oxidative stress in the cytotoxicity of Pseudomonas aeruginosa ExoU

ExoU PLA2-like activity has been shown to account for membrane lysis and acute death of infected cells. Translocation of effector proteins by the type III secretion systems depends on close contact between microbial and host cells. Our finding that both the ExoU-producing PA103 Pseudomonas aeruginosa and its mutant obtained by deletion of exoU adhered poorly to endothelial cells (EC) led to the hypothesis that, in some cells, the amount of injected toxin may not be enough to induce cell lysis but cells would suffer from a long-term effect of ExoU intoxication. To address this question, cells were exposed to both bacteria for 1 h and then treated with gentamicin-containing medium, to eliminate infecting microorganisms. After 24 h, the percentage of viable EC in PA103-infected cultures was significantly lower than in cultures exposed to the mutant, as determined by the MTT assay. Cell death was not likely to depend on the ExoU lytic activity since cell labeling with propidium iodide was similar in cultures infected with both bacterial strains. Bacterial cytotoxicity was significantly reduced by MAFP, a specific inhibitor of cPLA2 and iPLA2. Since the PLA2 activity on membrane phospholipids generates free fatty acid, including arachidonic acid (AA), we next compared the bacterial ability to release AA from infected EC. PA103 was shown to induce a potent AA release that was inhibited by MAFP. AA oxidation by oxygenases generates eicosanoids, known to induce both cell death and proliferation. However neither inhibitors of cyclooxygenases (ibuprofen) nor lipoxygenases (NDGA) reduced the ExoU toxicity. Since non-enzymatic oxidation of AA generates reactive radicals, we next investigated the PA103 ability to induce oxidative stress in infected cells. FACS analysis of cell labeling with the C-11 fluor probe and with anti-4-hydroxynonel antibody revealed a significant peroxidation of cell membrane lipids. These results, together with our finding that PA103-infected EC death was significantly attenuated by alpha-tocopherol, led to the conclusion that AA-induced oxidative stress may be another mechanism of cell damage in the course of infection by ExoU-producing P. aeruginosa.

Hydrogen peroxide induces apoptosis in cerebral vascular smooth muscle cells: possible relation to neurodegenerative diseases and strokes

Recently, reactive oxygen species (ROS) have been suggested as important mediators of brain damage in a number of disease states, including traumatic brain injury, neurodegenerative diseases and strokes. Apoptosis has been suggested to play an important role in neurodegenerative diseases, traumatic brain injury and strokes. The aim of this study was to determine whether or not cerebral vascular smooth muscle cells (CVSMCs) undergo apoptosis following treatment with hydrogen peroxide (H2O2). Herein, we demonstrate, for the first time, that H2O2 can induce apoptosis in a concentration-dependent manner in primary cultured CVSMCs, as measured by several morphological and biochemical criteria. H2O2-induced apoptosis may be initiated by stimulating Ca2+-dependent endonuclease activity. The present new data suggest that apoptosis in cerebral VSMCs, induced by ROS, such as H2O2, could play important roles in neruodegenerative processes, traumatic brain injury and strokes.