Group II phospholipase A2 mRNA synthesis is stimulated by two distinct mechanisms in rat vascular smooth muscle cells

Modulation of immunity by the secreted phospholipase A2 family

Among the phospholipase A2 (PLA2 ) superfamily, which typically catalyzes the sn-2 hydrolysis of phospholipids to yield fatty acids and lysophospholipids, the secreted PLA2 (sPLA2 ) family contains 11 isoforms in mammals. Individual sPLA2 s have unique enzymatic specificity toward fatty acids and polar heads of phospholipid substrates and display distinct tissue/cellular distributions, suggesting their distinct physiological functions. Recent studies using knockout and/or transgenic mice for a full set of sPLA2 s have revealed their roles in modulation of immunity and related disorders. Application of mass spectrometric lipidomics to these mice has enabled to identify target substrates and products of individual sPLA2 s in given tissue microenvironments. sPLA2 s hydrolyze not only phospholipids in the plasma membrane of activated, damaged or dying mammalian cells, but also extracellular phospholipids such as those in extracellular vesicles, microbe membranes, lipoproteins, surfactants, and dietary phospholipids, thereby exacerbating or ameliorating various diseases. The actions of sPLA2 s are dependent on, or independent of, the generation of fatty acid- or lysophospholipid-derived lipid mediators according to the pathophysiological contexts. In this review, we make an overview of our current understanding of the roles of individual sPLA2 s in various immune responses and associated diseases.

Group IIA secreted phospholipase A2 (PLA2G2A) augments adipose tissue thermogenesis

Group IIA secreted phospholipase A2 (PLA2G2A) hydrolyzes glycerophospholipids at the sn-2 position resulting in the release of fatty acids and lysophospholipids. C57BL/6 mice do not express Pla2g2a due to a frameshift mutation (wild-type [WT] mice). We previously reported that transgenic expression of human PLA2G2A in C57BL/6 mice (IIA+ mice) protects against weight gain and insulin resistance, in part by increasing total energy expenditure. Additionally, we found that brown and white adipocytes from IIA+ mice have increased expression of mitochondrial uncoupling markers, such as uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor-gamma coactivator, and PR domain containing 16, suggesting that the energy expenditure phenotype might be due to an increased thermogenic capacity in adipose tissue. Here, we further characterize the impact of PLA2G2A on thermogenic mechanisms in adipose tissue. Metabolic analysis of WT and IIA+ mice revealed that even when housed within their thermoneutral zone, IIA+ mice have elevated energy expenditure compared to WT littermates. Increased energy expenditure in IIA+ mice is associated with increased citrate synthase activity in brown adipose tissue (BAT) and increased mitochondrial respiration in both brown and white adipocytes. We also observed that direct addition of recombinant PLA2G2A enzyme to in vitro cultured adipocytes results in the marked induction of UCP1 protein expression. Finally, we report that PLA2G2A induces the expression of numerous transcripts related to energy substrate transport and metabolism in BAT, suggestive of an increase in substrate flux to fuel BAT activity. These data demonstrate that PLA2G2A enhances adipose tissue thermogenesis, in part, through elevated substrate delivery and increased mitochondrial content in BAT.

The effect of ω-fatty acids on the expression of phospholipase A2 group 2A in human gastric cancer patients

Background:

Studies show that polyunsaturated fatty acids (PUFAs) may have an inhibitory role in carcinogenesis. It was previously shown that PLA2 group 2A (PLA2G2A) messenger RNA (mRNA) expression is associated with less frequent metastasis and longer survival in gastric adenocarcinoma. This study intends to investigate the effect of PUFAs on the expression of PLA2G2A in patients with gastric cancer.

Materials and Methods:

Thirty-four patients with gastric cancer (GC) were randomly divided into two groups. The first group received cisplatin medication. The second group received cisplatin medication and supplements of ω-fatty acids for three courses. The total RNA was extracted from the tissues and cDNA was synthesized. The gene expression of PLA2G2A was evaluated by the real-time polymerase chain reaction (PCR) method. To confirm the changes in gene expression, frozen section was utilized. The frozen tissue samples were sectioned and stained using the immunohistochemistry technique.

Results:

After chemotherapy and chemotherapy plus supplement, the relative mean of PLA2G2A gene expression increased 1.5 ± 0.5-fold and 7.4 ± 2.6-fold, respectively (P = 0.006). The relative mean of gene expression in patients who received cisplatin and ω-fatty acids supplement increased more significantly (7.5 ± 3.3-fold) than in patients who received only cisplatin (P = 0.016).

Conclusion:

It was found that PUFAs increased the gene and protein expression of PLA2G2A in gastric cancer. Concerning the fact that studies reveal protective function of PLA2G2A in gastric cancer, it is suggested that increased expression of PLA2G2A is helpful. Furthermore, PUFAs can be considered as a useful therapeutic supplement for patients with gastric cancer.

Antisense inhibition of secretory and cytosolic phospholipase A2 reduces the mortality in rats with sepsis*

OBJECTIVE

Phospholipase A(2) has been implicated to play a pivotal role in the pathogenesis of sepsis syndrome. The two major forms of phospholipase A(2) isoenzymes, secretory phospholipase A(2) and cytosolic phospholipase A(2), are overexpressed during sepsis. The objective of this study was to test the hypothesis that inhibition of the overexpressed secretory phospholipase A(2) and cytosolic phospholipase A(2) during sepsis benefits the disease's eventual outcome.

DESIGN

Short-chain antisense oligonucleotide molecules were designed with the aid of computer software programs, and their in vitro efficacies were assessed in cell culture systems based on inhibition of target protein expression. The in vivo efficacies were determined in intact sepsis rats using 35-day survival rate as a primary efficacy end point.

SETTING

Animal research laboratory at a university.

SUBJECTS

Male Sprague-Dawley rats (180-200 g).

INTERVENTIONS

Sepsis was induced by cecal ligation and puncture. Antibiotics were administered subcutaneously once daily at 12 mg/kg, for 20 days. Oligonucleotides (antisense or mismatch) were administered intravenously once daily at 2 mg/kg to 0.8 mg/kg in a decreasing order, for 20 days.

MEASUREMENTS AND MAIN RESULTS

In cell culture systems, 21 of the 105 antisense constructs were found to be efficacious in inhibiting secretory phospholipase A(2) IIa and cytosolic phospholipase A(2) IVa protein expression. In sepsis rats, antisense oligonucleotides were capable of reducing their target protein expression by 18%-61% in major organs such as liver, heart, and kidney. In animal experiments, sepsis without any treatment (Group 1) had a median survival time of 2 days and a zero (0) percent survival rate at day 14. Sepsis with antibiotic treatment (Group 2) had a median survival time of 6 days and a 35-day survival rate of 28%. Sepsis with cotreatment of antibiotics and antisense oligonucleotides (one against secretory phospholipase A2 IIa and the other against cytosolic phospholipase A(2) IVa) (Group 4) increased the median survival time from 6 to 35 days and the 35-day survival rate from 28% to 58.8% as compared with antibiotics alone (Group 4 vs. Group 2; p <.05). Sepsis with cotreatment of antibiotics and mismatch oligonucleotides (Group 3) did not affect the median survival time and the 35-day survival rate as compared to antibiotics alone (Group 3 vs. Group 2; p >.05).

CONCLUSIONS

The results demonstrate that antisense strategy against secretory phospholipase A(2) IIa and cytosolic phospholipase A(2) IVa can inhibit their target protein expression in major organs and greatly improve the clinical outcome, i.e., an absolute reduction in 35-day mortality of 30.8%, in rats with sepsis. Our studies, thus, provide an improved method for the treatment of sepsis by targeting multiple forms of phospholipase A(2) isoenzymes with DNA antisense oligomers.

Trafficking of endogenous smooth muscle cell cholesterol: a role for serum amyloid A and interleukin-1β

OBJECTIVE

Intracellular cholesterol distribution impacts cell function; however, processes influencing endogenous cholesterol trafficking remain largely unknown. Atherosclerosis is associated with vascular inflammation and these studies address the role of inflammatory mediators on smooth muscle cell cholesterol trafficking.

METHODS AND RESULTS

Interestingly, in the absence of an exogenous cholesterol source, serum amyloid A increased [(14)C] oleic acid incorporation into cholesteryl ester in rat smooth muscle cells, suggesting endogenous cholesterol trafficking to the endoplasmic reticulum. [(3)H] cholesteryl ester accumulated in cells prelabeled with [(3)H] cholesterol, confirming that serum amyloid A mediated the movement of endogenous cholesterol. Cholesterol movement was dependent upon functional endolysosomes. The cholesterol oxidase-sensitive pool of cholesterol decreased in serum amyloid A-treated cells. Furthermore, the mechanism whereby serum amyloid A induced cholesterol trafficking was determined to be via activation of expression of secretory phospholipase A(2), group IIA (sPLA(2)) and sPLA(2)-dependent activation of sphingomyelinase. Interestingly, although neither tumor necrosis factor-α nor interferon-γ induced cholesterol trafficking, interleukin-1β induced [(14)C] cholesteryl ester accumulation that was also dependent upon sPLA(2) and sphingomyelinase activities. Serum amyloid A activates smooth muscle cell interleukin-1β expression, and although the interleukin-1-receptor antagonist inhibited the interleukin-1β-induced cholesterol trafficking, it had no effect on the movement of cholesterol mediated by serum amyloid A.

CONCLUSIONS

These data support a role for inflammation in endogenous smooth muscle cell cholesterol trafficking from the plasma membrane to the endoplasmic reticulum.

Inhibition of aldose reductase prevents endotoxin-induced inflammation by regulating the arachidonic acid pathway in murine macrophages

The bacterial endotoxin lipopolysaccharide (LPS) is known to induce release of arachidonic acid (AA) and its metabolic products, which play important roles in the inflammatory process. We have shown earlier that LPS-induced signals in macrophages are mediated by aldose reductase (AR). Here we have investigated the role of AR in LPS-induced release of AA metabolites and their modulation using a potent pharmacological inhibitor, fidarestat, and AR siRNA ablation in RAW264.7 macrophages and AR-knockout mouse peritoneal macrophages and heart tissue. Inhibition or genetic ablation of AR prevented the LPS-induced synthesis and release of AA metabolites such as PGE2, TXB, PGI2, and LTBs in macrophages. LPS-induced activation of cPLA2 was also prevented by AR inhibition. Similarly, AR inhibition also prevented the calcium ionophore A23187-induced cPLA2 and LTB4 in macrophages. Further, AR inhibition by fidarestat prevented the expression of AA-metabolizing enzymes such as COX-2 and LOX-5 in RAW264.7 cells and AR-knockout mouse-derived peritoneal macrophages. LPS-induced expression of AA-metabolizing enzymes and their catalyzed metabolic products was significantly lower in peritoneal macrophages and heart tissue from AR-knockout mice. LPS-induced activation of redox-sensitive signaling intermediates such as MAPKs, transcription factor NF-κB, and EGR-1, a transcriptional regulator of mPGES-1, which in collaboration with COX-2 leads to the production of PGE2, was also significantly prevented by AR inhibition. Taken together, our results indicate that AR mediates LPS-induced inflammation by regulating the AA-metabolic pathway and thus provide a novel role for AR inhibition in preventing inflammatory complications such as sepsis.

A lytic mechanism based on soluble phospholypases A2 (sPLA2) and β-galactoside specific lectins is exerted by Ciona intestinalis (ascidian) unilocular refractile hemocytes against K562 cell line and mammalian erythrocytes

Hemocytes from the ascidian Ciona intestinalis exert in vitro Ca²+-dependent cytotoxic activity toward mammalian erythrocytes and K562 cells. To examine the lytic mechanism, hemocyte populations were separated (B1-B6 bands) through a Percoll discontinuous density gradient, the hemocyte cytotoxic activity (HCA) and the lytic activity of the hemocyte lysate supernatant (HLS) were assayed. In addition the separated hemocytes were cultured and the cell-free culture medium (CFM) assayed after 3 h culture. Results support that unilocular refractile hemocytes (URGs), enriched in B5, are cytotoxic. The B5-HLS contains lysins and the activity of B5-CFM shows that lysins can be released into a culture medium. The B5 activity was blocked by D-galactose, α-lactose, lactulose, LacNAc, thiodigalactoside (TDG), L-fucose, D-mannose, D-glucose, sphingomyelin (SM), and soluble phospholipase A2 (sPLA2) inhibitors (dibucain, quinacrine). Accordingly, HLS chemico-physical properties (alkaline medium, high thermostability, Ca²+-dependence, trypsin treatment, protease inhibitors) and SEM observations of the affected targets suggested that sPLA2 could be responsible for changes and large alterations of the target cell membrane. An apoptotic activity, as recorded by a caspase 3, 7 assay, was found by treating K562 cells with very diluted HLS. A lytic mechanism involving sPLA2 and lectins promptly released by URGs and morula cells respectively is suggested, whereas target cell membrane SM could be a modulator of the enzyme activity.

Recent progress in phospholipase A₂ research: from cells to animals to humans

Mammalian genomes encode genes for more than 30 phospholipase A₂s (PLA₂s) or related enzymes, which are subdivided into several classes including low-molecular-weight secreted PLA₂s (sPLA₂s), Ca²+-dependent cytosolic PLA₂s (cPLA₂s), Ca²+-independent PLA₂s (iPLA₂s), platelet-activating factor acetylhydrolases (PAF-AHs), lysosomal PLA₂s, and a recently identified adipose-specific PLA. Of these, the intracellular cPLA₂ and iPLA₂ families and the extracellular sPLA₂ family are recognized as the "big three". From a general viewpoint, cPLA₂α (the prototypic cPLA₂ plays a major role in the initiation of arachidonic acid metabolism, the iPLA₂ family contributes to membrane homeostasis and energy metabolism, and the sPLA₂ family affects various biological events by modulating the extracellular phospholipid milieus. The cPLA₂ family evolved along with eicosanoid receptors when vertebrates first appeared, whereas the diverse branching of the iPLA₂ and sPLA₂ families during earlier eukaryote development suggests that they play fundamental roles in life-related processes. During the past decade, data concerning the unexplored roles of various PLA₂ enzymes in pathophysiology have emerged on the basis of studies using knockout and transgenic mice, the use of specific inhibitors, and information obtained from analysis of human diseases caused by mutations in PLA₂ genes. This review focuses on current understanding of the emerging biological functions of PLA₂s and related enzymes.

Secretory phospholipase A2, group IIA is a novel serum amyloid A target gene: activation of smooth muscle cell expression by an interleukin-1 receptor-independent mechanism

Atherosclerosis is a multifactorial vascular disease characterized by formation of inflammatory lesions. Elevated circulating acute phase proteins indicate disease risk. Serum amyloid A (SAA) is one such marker but its function remains unclear. To determine the role of SAA on aortic smooth muscle cell gene expression, a preliminary screen of a number of genes was performed and a strong up-regulation of expression of secretory phospholipase A(2), group IIA (sPLA(2)) was identified. The SAA-induced increase in sPLA(2) was validated by real time PCR, Western blot analysis, and enzyme activity assays. Demonstrating that SAA increased expression of sPLA(2) heteronuclear RNA and that inhibiting transcription eliminated the effect of SAA on sPLA(2) mRNA suggested that the increase was transcriptional. Transient transfections and electrophoretic mobility shift assays identified CAAT enhancer-binding protein (C/EBP) and nuclear factor kappaB (NFkappaB) as key regulatory sites mediating the induction of sPLA(2). Moreover, SAA activated the inhibitor of NF-kappaB kinase (IKK) in cultured smooth muscle cells. Previous reports showed that interleukin (IL)-1beta up-regulates Pla2g2a gene transcription via C/EBPbeta and NFkappaB. Interestingly, SAA activated smooth muscle cell IL-1beta mRNA expression, however, blocking IL-1 receptors had no effect on SAA-mediated activation of sPLA(2) expression. Thus, the observed changes in sPLA(2) expression were not secondary to SAA-induced IL-1 receptor activation. The association of SAA with high density lipoprotein abrogated the SAA-induced increase in sPLA(2) expression. These data suggest that during atherogenesis, SAA can amplify the involvement of smooth muscle cells in vascular inflammation and that this can lead to deposition of sPLA(2) and subsequent local changes in lipid homeostasis.

Thrombin and activated protein C inhibit the expression of secretory group IIA phospholipase A(2) in the TNF-alpha-activated endothelial cells by EPCR and PAR-1 dependent mechanisms

INTRODUCTION

Thrombin and tumor necrosis factor (TNF)-alpha up-regulate the expression of proinflammatory molecules in human umbilical vein endothelial cells (HUVECs). However, activated protein C (APC) down-regulates the expression of the same molecules. The expression level of secretory group IIA phospholipase A(2) (sPLA(2)-IIA) is known to be elevated in inflammatory disorders including in sepsis. Here, we investigated the effects of APC and thrombin on the expression of sPLA(2)-IIA and extracellular signal-regulated kinase (ERK) in HUVECs.

MATERIALS AND METHODS

The expression level of sPLA(2)-IIA was quantitatively measured by an enzyme-linked-immunosorbent-assay following stimulation of HUVECs with either thrombin or TNF-alpha in the absence and presence of the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor LY294002 and the cholesterol-depleting drug methyl-beta-cyclodextrin (MbetaCD).

RESULTS AND CONCLUSIONS

Thrombin had no effect on the expression of sPLA(2)-IIA in HUVECs, however, TNF-alpha potently induced its expression. The prior treatment of cells with APC inhibited expression of sPLA(2)-IIA through the EPCR-dependent cleavage of PAR-1. Further studies revealed that if HUVECs were pretreated with the zymogen protein C to occupy EPCR, thrombin also inhibited the TNF-alpha-mediated expression of sPLA(2)-IIA through the cleavage of PAR-1. The EPCR-dependent cleavage of PAR-1 by both APC and thrombin increased the phosphorylation of ERK 1/2. Pretreatment of cells with either LY294002 or MbetaCD abolished the inhibitory activity of both APC and thrombin against sPLA(2)-IIA expression, suggesting that the protein C occupancy of EPCR confers a PI3-kinase dependent protective activity for thrombin such that its cleavage of the lipid-raft localized PAR-1 inhibits the TNF-alpha-mediated expression of sPLA(2)-IIA in HUVECs.

Notch3 and IL-1beta exert opposing effects on a vascular smooth muscle cell inflammatory pathway in which NF-kappaB drives crosstalk

Atherogenesis begins with the transfer of monocytes from the lumen to the intimal layer of arteries. The paracrine activity acquired by these monocytes shifts vascular smooth muscle cells from a contractile-quiescent to a secretory-proliferative phenotype, allowing them to survive and migrate in the intima. Transformed and relocated, they also start to produce and/or secrete inflammatory enzymes, converting them into inflammatory cells. Activation of the Notch pathway, a crucial determinant of cell fate, regulates some of the new features acquired by these cells as it triggers vascular smooth muscle cells to grow and inhibits their death and migration. Here, we evaluate whether and how the Notch pathway regulates the cell transition towards an inflammatory or de-differentiated state. Activation of the Notch pathway by the notch ligand Delta1, as well as overexpression of the active form of Notch3, prevents this phenomenon [initiated by interleukin 1beta (IL-1beta)], whereas inhibiting the Notch pathway enhances the transition. IL-1beta decreases the expression of Notch3 and Notch target genes. As shown by using an IkappaBalpha-mutated form, the decrease of Notch3 signaling elements occurs subsequent to dissociation of the NF-kappaB complex. These results demonstrate that the Notch3 pathway is attenuated through NF-kappaB activation, allowing vascular smooth muscle cells to switch into an inflammatory state.

Secretory and cytosolic phospholipase A2 activities and expression are regulated by oxytocin and estradiol during labor

The release of arachidonic acid from membrane glycerophospholipids through the action of phospholipases (PLs) is the first step in the biosynthesis of prostaglandins (PGs). In reproductive tissues, the most important PLs are cytosolic PLA2(cPLA2) and types IIA and V of the secretory isoform (sPLA2). The aim of this work was to investigate the role of ovarian steroid hormones and oxytocin (OT) in the regulation of rat uterine PLA2activity and expression during pregnancy and labor. The activity of sPLA2increased near labor, whereas cPLA2activity augmented towards the end of gestation. The levels of sPLA2IIA and cPLA2mRNA showed an increase before labor (P<0.05, day 21), whereas sPLA2V mRNA was not regulated during pregnancy. The administration of atosiban (synthetic OT antagonist) together with tamoxifen (antagonist of estrogen receptors) was able to decrease cytosolic and secretory PLA2activities, diminish the expression of sPLA2IIA and cPLA2, as well as decrease PGF2αproduction before the onset of labor (P<0.01). The ovarian steroid did not affect PLA2during pregnancy. Collectively, these findings indicate that in the rat uterus, both 17β-estradiol and OT could be regulating the activity and the expression of the secretory and the cytosolic isoforms of PLA2, thus controlling PGF2αsynthesis prior to the onset of labor.

Effect of chronic CB1 cannabinoid receptor antagonism on livers of rats with biliary cirrhosis

Recent studies have shown that the activated endocannabinoid system participates in the increase in IHR (intrahepatic resistance) in cirrhosis. The increased hepatic production of vasoconstrictive eicosanoids is involved in the effect of endocannabinoids on the hepatic microcirculation in cirrhosis; however, the mechanisms of these effects are still unknown. The aim of the present study was to investigate the effects of chronic CB(1) (cannabinoid 1) receptor blockade in the hepatic microcirculation of CBL (common bile-duct-ligated) cirrhotic rats. After 1 week of treatment with AM251, a specific CB(1) receptor antagonist, IHR, SMA (superior mesenteric artery) blood flow and hepatic production of eicosanoids [TXB(2) (thromboxane B(2)), 6-keto PGF(1alpha) (prostaglandin F(1alpha)) and Cys-LTs (cysteinyl leukotrienes)] were measured. Additionally, the protein levels of hepatic COX (cyclo-oxygenase) isoforms, 5-LOX (5-lipoxygenase), CB(1) receptor, TGF-beta(1) (transforming growth factor beta(1)), cPLA(2) [cytosolic PLA(2) (phospholipase A(2))], sPLA(2) (secreted PLA(2)) and collagen deposition were also measured. In AM251-treated cirrhotic rats, a decrease in portal venous pressure was associated with the decrease in IHR and SMA blood flow. Additionally, the protein levels of hepatic CB(1) receptor, TGF-beta(1), cPLA(2) and hepatic collagen deposition, and the hepatic levels of 5-LOX and COX-2 and the corresponding production of TXB(2) and Cys-LTs in perfusates, were significantly decreased after 1 week of AM251 treatment in cirrhotic rats. Furthermore, acute infusion of AM251 resulted in a decrease in SMA blood flow and an increase in SMA resistance in CBL rats. In conclusion, the chronic effects of AM251 treatment on the intrahepatic microcirculation were, at least partly, mediated by the inhibition of hepatic TGF-beta(1) activity, which was associated with decreased hepatic collagen deposition and the activated PLA(2)/eicosanoid cascade in cirrhotic livers.

Angiotensin II type 1-receptor antagonism prevents type IIA secretory phospholipase A2-dependent lipid peroxidation

Accumulation and modification of low density lipoproteins (LDL) within the vessel wall represent key events in atherogenesis. Secretory phospholipase A2 type IIA (sPLA2-IIA) modulates the enzymatic process of LDL-modification and was recently identified as an independent predictor of coronary events in patients with coronary artery disease (CAD). Angiotensin II (ANG II) type 1 (AT1)-receptor blockade reduces LDL-modification and atherosclerotic plaque formation in rodent and primate models of atherosclerosis. Therefore, we assessed whether ANG II via its AT1-receptor enhances sPLA2-IIA-dependent lipid peroxidation in vitro and in patients with CAD. Stimulation of rat aortic smooth muscle cells with ANG II (10(-7) mol/L) enhanced sPLA2-IIA protein expression, activity as well as LDL-peroxidation, determined by western blot, activity assay and malondialdehyde (MDA)-assay and diene formation, respectively, and were blunted by AT1-receptor blockade (Losartan, 10(-5) mol/L). In addition, ANG II-induced sPLA2 activity and LDL-peroxidation were abolished by the sPLA2-IIa activity inhibitor LY311727 (10(-5) mol/L). To evaluate a potential clinical implication, patients (n=18) with angiographically documented CAD were treated with the AT1-receptor blocker Irbesartan (IRB; 300 mg/d) for 12 weeks. Blood samples were obtained from patients pre- and post-treatment and from healthy volunteers. SPLA2-IIA serum level and activity, circulating antibodies against oxidized LDL (oxLDL), oxLDL and MDA were determined in patients and found to be significantly increased compared to healthy volunteers. IRB therapy reduced these markers of inflammation, whereas total cholesterol, HDL- and LDL-fractions remained unchanged. ANG II may elicit pro-atherosclerotic effects via type IIA sPLA2-dependent LDL-modifications. Chronical AT1-receptor blockade reduces sPLA2-IIA level and activity and subsequently lipid peroxidation. Theses findings represent a novel anti-atherosclerotic mechanism and imply that AT1-receptor blockade elicits anti-atherosclerotic potencies even in the absence of plasma cholesterol reduction.

PGE2 amplifies the effects of IL-1beta on vascular smooth muscle cell de-differentiation: a consequence of the versatility of PGE2 receptors 3 due to the emerging expression of adenylyl cyclase 8

Transition of vascular smooth muscle cells from a contractile/quiescent to a secretory/proliferative phenotype is one of the critical steps in atherosclerosis and is instigated by pro-inflammatory cytokines released from macrophages that have infiltrated into the vascular wall. In most inflammatory diseases, cell activation induced by these compounds leads to a massive production of type E2 prostaglandin (PGE2) which often takes over and even potentiates the pro-inflammatory cytokine-related effects. To evaluate PGE2 incidence on atheroma plaque development, we investigated whether and how this compound could enhance the dedifferentiation of smooth muscle cells initially induced by interleukin-1beta (IL-1beta). To address this issue, we took advantage of vascular smooth muscle cells in primary culture and tracked two markers: PLA2 secretion and alpha-actin filament disorganization. In such a context, we found that PGE2 synergizes with IL-1beta to further enhance the phenotype transition of smooth muscle cells, through cAMP-protein kinase A. As indicated by pharmacological studies, the full PGE2-dependent potentiation of IL-1beta induced PLA2 secretion is associated with a change of regulation exerted by the subtypes 3 G(i)-coupled PGE2 receptors toward adenylyl cyclase(s) activated by the subtype 4 G(s)-linked PGE2 receptor. Whereas on contractile cells, stimulated subtypes 3 inhibit type 4-dependent PLA2 secretion, this negative regulation is switched to positive on IL-1beta-treated cells. Using real time PCR, pharmacological tools and small interfering RNA (siRNA), we demonstrated that the different integration of PGE2 signals depends on the upregulation of calcium/calmodulin stimulable adenylyl cyclase 8.

Secretory phospholipase A2 of group IIA: Is it an offensive or a defensive player during atherosclerosis and other inflammatory diseases?

Since its discovery in the serum of patients with severe inflammation and in rheumatoid arthritic fluids, the secretory phospholipase A2 of group IIA (sPLA2-IIA) has been chiefly considered as a proinflammatory enzyme, the result of which has been very intense interest in selective inhibitors of sPLA2-IIA in the hope of developing new and efficient therapies for inflammatory diseases. The recent discovery of the antibacterial properties of sPLA2-IIA, however, has raised the question of whether the upregulation of sPLA2-IIA during inflammation is to be considered uniformly negative and the hindrance of sPLA2-IIA in every instance beneficial. The aim of this review is for this reason, along with the results of various investigations which argue for the proinflammatory and proatherogenic effects of an upregulation of sPLA2-IIA, also to array data alongside which point to a protective function of sPLA2-IIA during inflammation. Thus, it could be shown that sPLA2-IIA, apart from the bactericidal effects, possesses also antithrombotic properties and indeed plays a possible role in the resolution of inflammation and the accelerated clearance of oxidatively modified lipoproteins during inflammation via the liver and adrenals. Based on these multipotent properties the knowledge of the function of sPLA2-IIA during inflammation is a fundamental prerequisite for the development and establishment of new therapeutic strategies to prevent and treat severe inflammatory diseases up to and including sepsis.

Statins potentiate the IFN-γ-induced upregulation of group IIA phospholipase A2 in human aortic smooth muscle cells and HepG2 hepatoma cells

The present study shows that the incubation of human aortic smooth muscle cells (HASMC) and HepG2 cells with atorvastatin and mevastatin as HMG-CoA reductase inhibitors potentiated the interferon-gamma (INF-gamma)-induced group IIA phospholipase A(2) (sPLA(2)-IIA) expression in a dose- and time-dependent manner. The effect of statins on sPLA(2)-IIA expression was reduced by mevalonate, farnesyl pyrophosphate and geranylgeranyl pyrophosphate. Inversely, inhibitors of the farnesyl transferase and geranylgeranyl transferase-I mimicked the effects of statins. Clostridium difficile toxin B (TcdB), Y-27632 and H-1152, functioning as inhibitors of Rho proteins and Rho-associated kinase, also augmented the sPLA(2)-IIA expression in combination with IFN-gamma. The same effects were observed when inhibitors of mitogen-activated/extracellular response protein kinase kinase (MEK), PD98059 or U0126 were used. Further, the Janus kinase-2 (Jak2)-specific inhibitor, AG-490 and inhibitors of nuclear factor-kappaB (NFkappaB) abrogated the sPLA(2)-IIA elevating effects of statins, TcdB and PD98059 in the presence of IFN-gamma. This cytokine alone increased the NFkappaB p65 and CAAT-enhancer-binding protein-beta (C/EBP-beta) activity in HASMC nuclear extract, but only C/EBP-beta was further augmented when the cells were incubated in addition to IFN-gamma with atorvastatin, H-1152, PD98059 or U0126. Moreover, after the incubation of cells with atorvastatin and IFN-gamma the stability of sPLA-(2)IIA mRNA significantly increased in comparison to those after incubation with IFN-gamma alone. In conclusion, the obtained data suggest that (i) the expression of sPLA(2)-IIA is negatively regulated by RhoA/Rho-associated kinase and MEK/ERK signaling pathways and (ii) statins, because of their ability to down-regulate these pathways, can potentiate the IFN-gamma-induced sPLA(2)-II expression at transcriptional and post-transcriptional levels.

Emerging drugs in migraine treatment

Ergot alkaloids have been the mainstay of acute migraine therapy for most of the 20th century. They have been supplanted by sumatriptan-like drugs ('triptans'), which, while keeping some of the ergotś mechanisms of action, show improved safety profiles due to their increased receptor selectivity. However, triptans are still far from being perfect drugs: they can constrict human coronary arteries at therapeutic doses and, therefore, are contra-indicated in the presence of cardiovascular disease. Another problem with these agents is recurrence of moderate-to-severe pain within 24 h of initial headache relief. While mechanism-driven drug design has led to the development of various novel, albeit still imperfect, acute antimigraine medications, only a few new prophylactic agents have been made available to migraine clinicians. The efficacy of most, if not all of them has been discovered serendipitously. This is probably due to the fact that, while the pathophysiology of a migraine attack is now reasonably understood, the mechanisms leading to an attack are still mostly unknown. This update analyses the profile of some antimigraine drugs in clinical trials, their mode of action and their potential advantages or drawbacks over already available agents.

Phospholipase A2 isozymes in pregnancy and parturition

Mammalian cells contain several structurally different phospholipase (PLA2) enzymes that exhibit distinct localisation, function and mechanisms of regulation. PLA2 isozymes have been postulated to play significant roles in the parturition process. Both secretory and cytosolic PLA2 isozymes have been identified in human gestational tissues, and there is differential expression of these PLA2 isozymes in human fetal membranes and placenta obtained at preterm and term. The aims of this commentary are: (1) to review recent data concerning the expression, role and regulation of PLA2 isozymes in human gestational tissues; and (2) to present novel data demonstrating the regulation of PLA2 isozymes in human gestational tissues by nuclear factor-kappa B (NF-kappaB) and peroxisome proliferator-activated receptor (PPAR)-g.

Relation of Secretory Phospholipase A2 and High-Sensitivity C-Reactive Protein to Chlamydia Pneumoniae Infection in Acute Coronary Syndromes

BACKGROUND

Recently it has become clear that inflammatory changes play a part in the development of atherosclerosis, including coronary artery disease, and Chlamydia pneumoniae (C. pneumoniae) is thought to be a proinflammatory factor. The plasma concentration of high-sensitive C-reactive protein (hs-CRP) is a potential predictor of outcome in atherosclerotic diseases. Recent interest has focused on secretory group IIA phospholipase A(2) (sPLA (2)) in regard to the progression of atherosclerotic disease.

METHODS AND RESULTS

The concentrations of sPLA(2), hs-CRP, and the titers of C. pneumoniae IgG and IgA antibodies were measured in blood samples. The study groups were an acute coronary syndrome (ACS) group, old myocardial infarction/angina pectoris (OMI/AP) group, and a control group. The concentrations of sPLA(2) and hs-CRP in the ACS group and the OMI/AP group were higher than in the control group. The titers of C. pneumoniae IgG and IgA were higher in the ACS group than in the control group. The sPLA(2) concentration was higher in those who were positive to C. pneumoniae IgG/IgA than in those who were negative.

CONCLUSION

Increased concentrations of sPLA(2) reflect participation in the progression of coronary artery disease. The sPLA(2) concentration was higher in patients positive for C. pneumoniae than in those negative for C. pneumoniae, so C. pneumoniae infection poses a greater risk for ACS in those individuals than in those who are free of such infection.

Amyloidosis modifier genes in the less amyloidogenic a/j mouse strain

Apolipoprotein A-II is deposited as an amyloid fibril in aged mice (senile AApoAII amyloidosis). Although mouse strains with the apolipoprotein A-II c allele (Apoa2(c)) generally develop early-onset and severe senile amyloidosis, the A/J strain shows significantly less amyloid deposition. To identify genes that modify spontaneous amyloidosis development in the A/J mouse, we performed a genome-wide screening using hybrid mice derived from A/J and SAMP1 mice, which have Apoa2(c) and age-associated severe amyloid deposition. Our genetic analysis revealed that the lower levels of amyloidosis in the A/J strain were polygenically controlled. We found two chromosome locations associated with amyloidosis. One of these regions was in the chromosome 19 telomeric region, where the A/J alleles modify amyloidosis in an additive manner. The second region was in the chromosome 4 telomeric region, where the A/J alleles modify amyloidosis in a dominant manner. Perlecan and group II secretory phospholipase A2, located on the significantly linked region of chromosome 4, were compared in this study. These findings are for understanding the genetic mechanism of amyloidosis-related diseases and their prevention.

New phospholipase A(2) isozymes with a potential role in atherosclerosis

PURPOSE OF REVIEW

Inflammation is an integral feature of atherosclerosis, in which inflammatory processes contribute to the initiation, progression and rupture of lipid-rich atherosclerotic plaques. Recent studies have suggested the involvement of the proinflammatory secretory phospholipase A2 (sPLA2)-IIA in the development of atherosclerosis. This enzyme has been proposed to hydrolyze phosphatidylcholine (PC) in lipoproteins to liberate lyso-PC and free fatty acids in the arterial wall, thereby facilitating the accumulation of bioactive lipids and modified lipoproteins in atherosclerotic foci. However, the recent discovery of several novel sPLA2 isozymes has raised the question of which types of sPLA2 truly contribute to the atherosclerotic process.

RECENT FINDINGS

Amongst the 10 mammalian sPLA2 isozymes, sPLA2-X, -V, -IIF and -III exhibit much more potent PC-hydrolyzing activity than do the others, and can release free fatty acids and lysophospholipids from the PC-rich outer leaflet of the cellular plasma membrane. In particular, sPLA2-X and sPLA2-V hydrolyze PC in lipoproteins far more efficiently than does sPLA2-IIA. Moreover, sPLA2-X promotes foam cell formation in vitro and is expressed in the atherosclerotic arterial walls of apolipoprotein E deficient mice in vivo.

SUMMARY

PC-hydrolyzing sPLA2 isozymes, particularly sPLA2-V and sPLA2-X, are attractive candidates for proatherosclerotic factors that may act in place of sPLA2-IIA. However, their expression in human atherosclerotic lesions requires confirmation by specific methods that can distinguish between the different sPLA2 isozymes.

Anti-cytokine therapeutics and infections

In view of the increasing use of anti-cytokine-based therapies to treat autoimmune diseases, the role of specific cytokines in host defense against infection has become a highly relevant area of investigation. There are over 300,000 patients worldwide being treated with agents that specifically block the biological activities of interleukin-1 (IL-1) or tumor necrosis factor (TNF) for reducing the severity of autoimmune diseases such as rheumatoid arthritis, Crohn's disease or psoriasis. Those patients receiving anti-TNF-alpha or IL-1 blocking therapies are treated on a chronic basis. Studies suggest that other chronic inflammatory diseases will benefit from anti-cytokine therapies. However, there is a growing body of clinical evidence that neutralization of TNF-alpha is associated with an increased risk of opportunistic infections, including mycobacterial diseases. Blockade of IL-1 activity with the IL-1 receptor antagonist (IL-1Ra) appears, at present, to be relatively safe. However, because of physician under reporting (some estimates of reporting being less than 5% of these infections), the true incidence of infections, both serious and non-serious, will remain unknown. Does the increase in infections associated with anti-cytokine-based therapies come as a surprise? Of the two components of host defense, the innate and the acquired responses, which are affected by anti-cytokine therapies? From a wealth of rodent studies using live infection models, the following conclusions can be drawn: (1) neutralization or gene deletion for TNF-alpha is frequently associated with reduction of host defense in models of live Gram-positive or Gram-negative infections as well as infection by intracellular microbes such as Salmonella and Listeria; (2) absence of the IL-1 receptor can also result in decreased resistance to Listeria or Gram-positive bacteria and (3) TNF-alpha and IFN-gamma are required for defense against infection caused by Mycobacterium tuberculosis.

Pertussis toxin-sensitive secretory phospholipase A2 expression and motility in activated primary human keratinocytes

Secretory phospholipase A2 and cycloxygenase-2 are coexpressed in activated primary keratinocytes. These proteins are known to be functionally linked, mediating proliferation of human keratinocytes during epidermal wound repair. Primary human keratinocytes grown at low densities (15-30%; nonconfluent) produce high levels of prostaglandin E2 important for proliferation and are a good model for studying activated keratinocytes after injury. In this study, we used this model to assess the role of secretory phospholipase A2 and cycloxygenase-2 in keratinocyte motility. Initial work showed 24 h pretreatment with 20 ng pertussis toxin per ml, an inhibitor of the inhibitory G-protein, decreased prostaglandin E2 production and both secretory phospholipase A2 and cycloxygenase-2 protein expression. This suggested that inhibitory G-protein may be involved in mediating expression of these proteins. Pertussis toxin also caused changes in cell morphology, actin organization, and keratinocyte motility. Pretreatment with 5 microm 12-epi-scalaradial, a secretory phospholipase A2 inhibitor, caused similar changes in cell motility and actin organization; however, the specific cycloxygenase-2 inhibitor, SC-58236 (20 nm) was much less effective. These results suggested that secretory phospholipase A2 plays a part in keratinocyte motility that is independent of its functional linkage to cycloxygenase-2 and prostaglandin E2 biosynthesis.

Transcriptional regulation of the rat type IIA phospholipase A2 gene by cAMP and interleukin-1beta in vascular smooth muscle cells: interplay of the CCAAT/enhancer binding protein (C/EBP), nuclear factor-kappaB and Ets transcription factors

The abundant secretion of type IIA secreted phospholipase A(2) (sPLA(2)) is a major feature of the inflammatory process of atherosclerosis. sPLA(2) is crucial for the development of inflammation, as it catalyses the production of lipid mediators and induces the proliferation of smooth muscle cells. We have analysed the activation of sPLA(2) transcription by cAMP and interleukin-1beta (IL-1beta), and shown that the 500 bp region upstream of the transcription start site of the rat sPLA(2) gene is implicated in activation by synergistically acting cAMP and IL-1beta. We transiently transfected and stimulated rat smooth muscle cells in primary culture and measured the promoter activities of serial and site-directed deletion mutants of sPLA(2)-luciferase constructs. A distal region, between -488 and -157 bp, bearing a CAAT/enhancer binding protein (C/EBP)-responsive element (-242 to -223) was sufficient for cAMP/protein kinase A-mediated sPLA(2) promoter activation. We find evidence for the first time that activation of the sPLA(2) promoter by IL-1beta requires activation of an Ets-responsive element in the -184 to -180 region of the distal promoter via the Ras pathway and a nuclear factor-kappaB site at positions -141 to -131 of the proximal promoter. We also used electrophoretic mobility shift assays to identify five binding sites for the Sp1 factor; a specific inhibitor of Sp1, mithramycin A, showed that this factor is crucial for the basal activity of the sPLA(2) promoter.

Biological effects of secretory phospholipase A(2) group IIA on lipoproteins and in atherogenesis

Secretory phospholipase A(2) group IIA(sPLA(2) IIA) can be produced and secreted by various cell types either constitutionally or as an acute-phase reactant upon stimulation by proinflammatory cytokines. The enzyme prefers phosphatidylethanolamine and phosphatidylserine as substrates. One important biological function may be the hydrolytic destruction of bacterial membranes. It has been demonstrated, however, that sPLA(2) can also hydrolyse the phospholipid monolayers of high density lipoprotein (HDL) and low density lipoprotein (LDL) in vitro. Secretory phospholipase A(2)-modified LDL show increased affinity to glycosaminoglycans and proteoglycans, a tendency to aggregate, and an enhanced ability to deliver cholesterol to cells. Incubation of cultured macrophages with PLA(2)-treated LDL and HDL is associated with increased intracellular lipid accumulation, resulting in the formation of foam cells. Elevated sPLA(2)(IIA) activity in blood serum leads to an increased clearance of serum cholesterol. Secretory phospholipase A(2)(IIA) can also be detected in the intima, adventitia and media of the atherosclerotic wall not only in developed lesions but also in very early stages of atherosclerosis. The presence of DNA of Chlamydia pneumoniae, herpes simplex virus, and cytomegalovirus was found to be associated with sPLA(2)(IIA) expression and other signs of local inflammation. Thus, sPLA(2)(IIA) appears to be one important link between the lipid and the inflammation hypothesis of atherosclerosis.

Deficiency in sPLA(2) does not affect HDL levels or atherosclerosis in mice

Secretory non-pancreatic phospholipase A(2) (sPLA(2)) has been implicated in inflammation and has been found in human atherosclerotic lesions. To test the effect of sPLA(2) deficiency on atherosclerosis, C57BL/Ks mice (apoE(+/+) and PLA(2)(++) were bred with C57BL/6 apoE knockout mice which are sPLA(2)(--) due to a spontaneous mutation. Sibling pairs of mice (apoE(--)/sPLA(2)(++) and apoE(--)/sPLA(2)(--)) on high fat Western diets were dissected at 22 weeks. In vitro enzyme assays confirmed higher serum sPLA(2) activity in the sPLA(2)(++) compared to sPLA(2)(--) for both sexes, while sPLA(2)(--) males had slightly higher serum cholesterol and phospholipids. Analysis of lipoprotein profiles by FPLC showed no effect of sPLA(2) genotype on any measured parameters. Atherosclerosis was quantitated by assaying cholesterol in aortic extracts. Male sPLA(2) trended slightly higher than sPLA(2)(++) with no statistical significance. Female sPLA(2)(++) and sPLA(2)(--) mice showed no significant differences in any of the measured parameters. These results suggest that the endogenous mouse sPLA(2) gene does not significantly affect HDL or atherosclerosis in mice.

CCAAT/enhancer binding proteins: do they possess intrinsic cAMP-inducible activity?

CCAAT/enhancer binding proteins (C/EBPs) are transcription factors that are enriched in tissues which play a central role in energy metabolism, such as adipose and liver. Structure/function analyses of these proteins have identified several transactivation domains, some of which can physically interact with general transcription factors present in the preinitiation complex. C/EBPs are generally considered to be constitutively-acting factors, unlike other transcription factors whose activities can be regulated by covalent modification, binding of a specific ligand, etc. However, studies of the regulatory property of the phosphoenolpyruvate carboxykinase gene promoter have uncovered a role for C/EBPs in mediating cAMP responsiveness, and identified specific domains within the proteins, which mediate this effect. Interestingly, a number of other gene promoters that are activated in response to cAMP also contain binding sites for C/EBP, and these binding sites are often located within the region of the promoter that is responsible for mediating the acute responsiveness to cAMP. The evidence presented in this review provides compelling support for the hypothesis that C/EBPs have both constitutive and cAMP-inducible activities, and should be considered as a cAMP-responsive nuclear regulator.

Cellular localization of group IIA phospholipase A2 in rats

It has been known that group II phospholipase A2 (PLA2) mRNA and protein are present in the homogenates of the spleen, lung, liver, and kidney in normal rats, but the cellular origin of this enzyme has not been yet identified. At present, five subtypes of group II PLA2 have been identified in mammals. Antibodies or mRNA probes previously used for detecting group II PLA2 need to be evaluated to identify the subtypes of group II PLA2. In this study we tried to identify group IIA PLA2-producing cells in normal rat tissues by in situ hybridization (ISH) using an almost full-length RNA probe for rat group IIA enzyme. Group IIA PLA2 mRNA was detected in megakaryocytes in the spleen and Paneth cells in the intestine by ISH. These cells were also immunopositive for an antibody raised against group IIA PLA(2) isolated from rat platelets. Group IIA PLA2 mRNA-positive cells were not detected in lung, liver, kidney, and pancreas. Under normal conditions, group IIA PLA2-producing cells are splenic megakaryocytes and intestinal Paneth cells in rats.

Interleukin-1beta-induced type IIA secreted phospholipase A2 gene expression and extracellular activity in rat vascular endothelial cells

Two phospholipase A2 (PLA2) isoforms, secretory and cytosolic, have been implicated in inflammation. Secretory type IIA PLA2 (sPLA2-IIA), which hydrolyzes fatty acids bound at the sn-2 position of glycerophospholipids, has been detected universally in a variety of mammalian tissues and cells. The expression of the sPLA2-IIA gene and its extracellular activity were shown to be regulated by different factors such as hypoxia, cytokines and phorbol esters. In the present study, we examined the effects of interleukin-1beta (IL-1beta) on the expression of the 14kDa sPLA2-IIA, determined using reverse transcription polymerase chain reaction and radiometric Escherichia coli enzyme assay in primary cultures of rat endothelial cells and in two different rat endothelial cell lines (SVAREC and RBE4). These experiments revealed that IL-1beta induces sPLA2-IIa gene expression and secretion of the enzyme in endothelial cells in a dose- and time-dependent manner. The cAMP-elevator forskolin did not augment the cytokine-induced elevation of sPLA2-IIa enzyme activity but significantly increased the IL-1beta-stimulated sPLA2-IIa mRNA contents in endothelial cells.

Type II phospholipase A2 in preterm human gestational tissues

Maternal genital tract infections and the associated inflammatory response may contribute to the onset of many cases of preterm labour. Type II phospholipase A(2)(PLA2) hydrolyses glycerophospholipids, releasing free fatty acid for conversion into potent biological mediators, such as prostaglandins, which play a significant role in both the onset and progression of human labour and the activation of inflammatory reactions. The aim of this study was to quantify immunoreactive (ir) Type II PLA2 in placenta, amnion and choriodecidua collected from women delivering prematurely or due to histological chorioamnionitis, and to compare levels to those at term. Tissues were assayed for ir Type II PLA2 by ELISA and expressed as ng/mg tissue protein. Ir Type II PLA2 tissue content was significantly higher in preterm (n=26) amnion and choriodecidua, but not in the placenta when compared to tissues obtained at term (n=42). When the data were stratified with respect to labour status, ir Type II PLA2 content was significantly higher in the preterm not-in-labour group (NIL, n=17) than the preterm in labour group (IL, n=9) in the amnion. When the NIL group was analysed with respect to membrane rupture, women who had spontaneously ruptured membranes (n=6) expressed significantly greater ir Type II PLA2 than those that had intact membranes (n=11) in both the amnion and choriodecidua but not in the placenta. No significant difference was observed between the preterm IL group (n=9) and the group with histological chorioamnionitis (n=14). The data obtained in this study support a role for Type II PLA2 in association with spontaneous rupture of membranes.

Protein kinase A-dependent stimulation of rat type II secreted phospholipase A(2) gene transcription involves C/EBP-beta and -delta in vascular smooth muscle cells

Type II secreted phospholipase A(2) (sPLA(2)) releases precursors of important inflammatory lipid mediators from phospholipids. Some observations have indicated that the sPLA(2), which has been implicated in chronic inflammatory conditions such as arthritis, contributes to atherosclerosis in the arterial wall. sPLA(2) was not detected in control vascular smooth muscle cells (VSMC). Treatment of VSMC with agents that increase intracellular cAMP (eg, forskolin, dibutyryl [db]-cAMP) resulted in a time- and concentration-dependent increase in sPLA(2) gene expression. Semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) showed a marked dose-dependent inhibition of forskolin-induced mRNA by protein kinase A inhibitor. Electrophoretic mobility shift analysis of nuclear proteins from forskolin-treated and db-cAMP-treated VSMC with C/EBP consensus oligonucleotides and C/EBP oligonucleotides from the rat promoter revealed greater binding than in control VSMC. Incubation of VSMC with H89, a specific protein kinase inhibitor, also blocked the binding of nuclear C/EBP to the C/EBP site of the rat promoter induced by db-cAMP and forskolin. Binding was unchanged with the use of CRE consensus oligonucleotides. Antibodies revealed the specific formation of C/EBP/DNA complexes, the majority of which were supershifted by C/EBP-ss and -delta antibodies. Functional activation of C/EBP was confirmed by a luciferase reporter gene assay. A construct comprising 4 tandem repeat copies of the C/EBP element from the rat sPLA(2) promoter linked to luciferase was transcriptionally activated in VSMC by cotransfection with expression vector for the protein kinase A catalytic subunit. It was also significantly activated in transfected VSMC treated by forskolin or db-cAMP. H89 inhibited this activations. We therefore conclude that the increases in sPLA(2) mRNA and enzyme activity produced by cAMP-elevating agents is controlled by a mechanism involving nuclear C/EBP-ss and -delta acting through a protein kinase A signaling pathway.

Structure, function, and regulation of group V phospholipase A(2)

The hydrolysis of membrane phospholipid by phospholipase A(2) (PLA(2)) is a key step in the production of inflammatory eicosanoids. Recent cell studies have shown that secretory group V PLA(2) (gVPLA(2)) is involved in agonist-induced eicosanoid biosynthesis in mouse P388D1 cell line, mast cells, and transfected HEK 293 cells. gVPLA(2) is homologous to other group II PLA(2) family members but has distinctive enzymatic properties, including its activity to effectively hydrolyze phosphatidylcholine (PC) vesicles and the outer plasma membrane of mammalian cells. Mutational studies showed that gVPLA(2) has a unique structure that allows effective binding to PC membranes and efficient catalysis of an active-site-bound PC substrate. Thanks to this unique structure and activity, exogenously added gVPLA(2) can induce the eicosanoid biosynthesis in unstimulated inflammatory cells, including human neutrophils and eosinophils, suggesting that it might be able to trigger inflammatory responses under certain physiological conditions. Extensive structure-function and cell studies showed that gVPLA(2) could act directly on the outer plasma membranes of neutrophils and eosinophils. The release of fatty acids and lysophospholipids from the cell surfaces induces the translocation and activation of cytosolic PLA(2) and 5-lipoxygenase, resulting in the leukotriene synthesis. In case of neutrophils, induction of leukotriene B(4) synthesis by gVPLA(2) leads to the phosphorylation of cytosolic PLA(2) by a leukotriene B(4) receptor and MAP kinase-mediated mechanism. Finally, heparan sulfate proteoglycans in neutrophils appear to play a role of internalizing and degrading the cell surface-bound gVPLA(2) to protect the cells from extensive lipolytic damage.

Transcriptional regulation of inflammatory secreted phospholipases A(2)

Secreted phospholipases A(2) is a family of small molecular weight and calcium-dependent enzymes of which the members list is presently growing. Among these enzymes, the synovial type IIA and the type V phospholipases A(2) are involved in inflammation. Although their actual mechanism is still a subject of debate, new therapeutic strategies can result from the knowledge of the regulations of their gene expression. The human genes of the type IIA and type V phospholipases A(2) are located on the chromosome 1 at close positions and transcribed in reverse orientations. These genes can therefore be regulated by common elements but only the regulation of the type IIA phospholipase A(2) gene expression has been extensively studied. Pro-inflammatory cytokines upregulate while the growth factors downregulate the type IIA phospholipase A(2) gene expression. Interleukin-6 and interleukin-1beta exert their effects at least partially at the transcriptional level. The transcriptional regulation of the type IIA phospholipase A(2) gene is cell- and species-specific. The activity of the human promoter is controlled by the CAAT-enhancer binding protein (C/EBP) factors while that of the rat promoter is regulated by nuclear factor kappaB (NF-kappaB) and C/EBPs. Furthermore, the human promoter is constitutively repressed in hepatocytes by single strand DNA binding proteins whose effects are relieved by C/EBP factors while the glucocorticoid receptor interacts with C/EBPs in chondrocytes to achieve full basal and interleukin-1beta-stimulated transcription activity. Other factors like CTF/NF1 and Sp1 might be involved in the regulation of both the rat and human promoter. Peroxisome proliferator-activated receptors could contribute to the stimulation of the rat promoter by NF-kappaB in vascular smooth muscle cells. The study of the coactivators and coinhibitors associated to these transcription factors will give a better understanding of the diversity and complexity of the transcriptional regulations of the type IIA phospholipase A(2) gene.

Prognostic value of plasma levels of secretory type II phospholipase A2 in patients with unstable angina pectoris

Plasma levels of secretory nonpancreatic type II phospholipase A2 (sPLA2) are increased in various chronic inflammatory diseases; this increase is correlated with disease severity. sPLA2 plays a possible role in atherogenesis and is highly expressed in atheromatous plaques. Thus, this study prospectively examined whether plasma levels of sPLA2 may have a prognostic value in patients with unstable angina, which is known to have inflammatory features. Plasma levels of sPLA2 were measured in 52 patients with unstable angina, in 107 patients with stable angina, and in 96 control subjects by radioimmunoassay. sPLA2 levels were significantly higher in patients with unstable angina than in those with stable angina and in control subjects. sPLA2 remained elevated after stabilization of disease. The levels were not increased in the blood in the coronary sinus. Kaplan-Meier analysis demonstrated that patients with unstable angina and with the higher sPLA2 levels had a significantly higher probability of developing clinical coronary events during a follow-up period of 2 years compared with those with the lower levels. In multivariate Cox hazard analysis, the higher levels of sPLA2 were a significant predictor of developing coronary events in patients with unstable angina, independent of other risk factors, including C-reactive protein levels, an established inflammatory predictor. In conclusion, the increase in circulating levels of sPLA2 predicts clinical coronary events independently of other risk factors in patients with unstable angina. sPLA2 levels were persistently elevated but the elevated levels may not be derived from coronary circulation.

Interferon-gamma induces secretory group IIA phospholipase A2 in human arterial smooth muscle cells. Involvement of cell differentiation, STAT-3 activation, and modulation by other cytokines

Increased expression of secretory non-pancreatic phospholipase A(2) (sPLA(2)-IIA) could be part of the inflammatory reaction in atherosclerosis. However, the factors controlling sPLA(2)-IIA production in human vascular cells are unknown. We investigated regulation of sPLA(2)-IIA expression and secretion by human arterial smooth muscle cells in culture (HASMC). SPLA(2)-IIA was induced after 3-14 days of culture in non-proliferating conditions. SPLA(2)-IIA was co-expressed with heavy caldesmon, a cytoskeleton protein, and p27, a G(1) cyclin inhibitor, proteins characteristically expressed by differentiated cells. Further incubation with 50-500 units/ml of interferon (IFN)-gamma significantly increased sPLA(2)-IIA mRNA and secretion. IFN-gamma-induced sPLA(2)-IIA was found to be active in cell media and associated with cell membrane proteoglycans. IFN-gamma induced sPLA(2)-IIA expression was antagonized by tumor necrosis factor (TNF)-alpha and interleukin (IL)-10. TNF-alpha added individually induced a significant but transient (4 h) increase in sPLA(2)-IIA secretion. IL-10 by itself did not affect sPLA(2)-IIA expression and secretion. IFN-gamma-stimulated sPLA(2)-IIA transcription involved STAT-3 protein. Interestingly, IL-6 but not IFN-gamma up-regulated the sPLA(2)-IIA expression in HepG2 cells, thus sPLA(2)-IIA induction by IFN-gamma response appears to be cell specific. In summary, conditions leading to cell differentiation induced sPLA(2)-IIA expression in HASMC and further exposure to IFN-gamma can up-regulate sPLA(2)-IIA transcription and secretion. This IFN-gamma stimulatory effect can be modulated by other cytokines.

Are the anti-inflammatory effects of dexamethasone responsible for inhibition of the induction of enzymes involved in prostanoid formation in rat carrageenin-induced pleurisy?

Since anti-inflammatory steroids modulate multiple gene expression, including the expression of prostaglandin H synthase-2 and phospholipase A(2), at the molecular level, we studied the effects of dexamethasone on rat carrageenin-induced pleurisy to elucidate whether regulation of phospholipase A(2) and prostaglandin H synthase-2 expression is the primary mechanism of its anti-inflammatory action. Suppression of plasma exudation by a lower dose of dexamethasone (0.3 mg/kg) was almost equal to that by aspirin (100 mg/kg), but that by higher dexamethasone doses (3 and 30 mg/kg) was considerably stronger, suggesting the involvement of effects other than that on prostanoid formation. The lower dose of dexamethasone also significantly reduced the pleural exudate neutrophil count and prostanoid levels. However, this dose affected neither the prostaglandin H synthase-2 level nor the phospholipase A(2) activity in the exudate cells. The prostaglandin H synthase-2 level was affected only at the higher doses, while phospholipase A(2) activity was not. These results suggest that the anti-inflammatory effects of dexamethasone in acute inflammation cannot be ascribed to direct interference with prostanoid formation via suppression of phospholipase A(2) and prostaglandin H synthase-2 expression.

Overexpression of secretory phospholipase A(2) causes rapid catabolism and altered tissue uptake of high density lipoprotein cholesteryl ester and apolipoprotein A-I

Plasma levels of high density lipoprotein (HDL) cholesterol and its major protein component apolipoprotein (apo) A-I are significantly reduced in both acute and chronic inflammatory conditions, but the basis for this phenomenon is not well understood. We hypothesized that secretory phospholipase A(2) (sPLA(2)), an acute phase protein that has been found in association with HDL, promotes HDL catabolism. A series of HDL metabolic studies were performed in transgenic mice that specifically overexpress human sPLA(2) but have no evidence of local or systemic inflammation. We found that HDL isolated from these mice have a significantly lower phospholipid and cholesteryl ester and significantly greater triglyceride content. The fractional catabolic rate (FCR) of (125)I-HDL was significantly faster in sPLA(2) transgenic mice (4.08 +/- 0.01 pools/day) compared with control wild-type littermates (2.16 +/- 0.48 pools/day). (125)I-HDL isolated from sPLA(2) transgenic mice was catabolized significantly faster than (131)I-HDL isolated from wild-type mice after injection in wild-type mice (p < 0.001). Injection of (125)I-tyramine-cellobiose-HDL demonstrated significantly greater degradation of HDL apolipoproteins in the kidneys of sPLA(2) transgenic mice compared with control mice (p < 0.05). The fractional catabolic rate of [(3)H]cholesteryl ether HDL was significantly faster in sPLA(2)-overexpressing mice (6.48 +/- 0.24 pools/day) compared with controls (4.80 +/- 0.72 pools/day). Uptake of [(3)H] cholesteryl ether into the livers and adrenals of sPLA(2) transgenic mice was significantly enhanced compared with control mice. In summary, these data demonstrate that overexpression of sPLA(2) alone in the absence of inflammation causes profound alterations of HDL metabolism in vivo and are consistent with the hypothesis that sPLA(2) may promote HDL catabolism in acute and chronic inflammatory conditions.

Circulating levels of secretory type II phospholipase A(2) predict coronary events in patients with coronary artery disease

Background-The circulating levels of secretory nonpancreatic type II phospholipase A(2) (sPLA(2)) are increased in various chronic inflammatory diseases and the increase in the levels correlates with the disease severity. sPLA(2) may possibly play a role in atherogenesis and is highly expressed in atherosclerotic arterial walls that are known to have inflammatory features. Thus, this study prospectively examined whether circulating levels of sPLA(2) may have a significant risk and prognostic values in patients with coronary artery disease (CAD). Methods and Results-Plasma levels of sPLA(2) were measured in 142 patients with CAD and in 93 control subjects by a radioimmunoassay. The sPLA(2) levels had a significant and positive relations with serum levels of C-reactive protein, a marker of systemic inflammation, and with the number of the traditional coronary risk factors associated with individuals. Multivariate logistic regression analysis showed that higher levels of sPLA(2) (>246 ng/dL; 75th percentile of sPLA(2) distribution in controls) were a significant and independent risk factor for the presence of CAD. In multivariate Cox hazard analysis, the higher levels of sPLA(2) were a significant predictor of developing coronary events (ie, coronary revascularization, myocardial infarction, coronary death) during a 2-year follow-up period in patients with CAD independent of other risk factors, including CRP levels, an established inflammatory predictor. Conclusions-The increase in circulating levels of sPLA(2) is a significant risk factor for the presence of CAD and predicts clinical coronary events independent of other risk factors in patients with CAD; these results may reflect possible relation of sPLA(2) levels with inflammatory activity in atherosclerotic arteries.

Cloning and characterization of novel mouse and human secretory phospholipase A(2)s

Mammalian secretory phospholipase A(2)s (sPLA(2)s) are classified into several groups according to molecular structure and the localization of intramolecular disulfide bridges. Among them, group IIA sPLA(2) has been thought to be one of the key enzymes in the pathogenesis of inflammatory diseases owing to its augmented expression under various inflammatory conditions. However, in a number of inbred mouse strains, the group IIA sPLA(2) gene is naturally disrupted by a frameshift mutation. Here, we report the cloning of a cDNA encoding a novel sPLA(2) expressed in the spleen of group IIA sPLA(2)-deficient mouse. We also cloned its human homolog and mapped its gene location on chromosome 1p36.12 near the loci of group IIA and V sPLA(2) genes. The human mature sPLA(2) protein consists of 125 amino acids (M(r) = 14,500) preceded by a 20-residue prepeptide and is most similar to group IIA sPLA(2) with respect to the number and positions of cysteine residues as well as overall identity (48%). Based on these structural properties, the novel sPLA(2) should be categorized into group II, called group IID to follow the already identified IIA to IIC sPLA(2)s. When the cDNA was expressed in COS-7 cells, PLA(2) activity preferentially accumulated in the culture medium. It is maximally active at neutral to alkaline pH and with 2 mM Ca(2+). In assays with individual substrates, L-alpha-1-palmitoyl-2-linoleoyl phosphatidylethanolamine was more efficiently hydrolyzed than the other phospholipids examined. An RNA blot hybridized with the cDNA exhibited two transcripts (2.0 and 1.0 kb) in human spleen, thymus, and colon. The expression of a novel sPLA(2) mRNA was elevated in the thymus after treatment with endotoxin in rats as well as in group IIA sPLA(2)-deficient mice, suggesting its functional role in the progression of the inflammatory process.

Interleukin 1beta induces type II-secreted phospholipase A(2) gene in vascular smooth muscle cells by a nuclear factor kappaB and peroxisome proliferator-activated receptor-mediated process

Type II-secreted phospholipase A(2) (type II-sPLA(2)) is expressed in smooth muscle cells during atherosclerosis or in response to interleukin-1beta. The present study shows that the induction of type II-sPLA(2) gene by interleukin-1beta requires activation of the NFkappaB pathway and cytosolic PLA(2)/PPARgamma pathway, which are both necessary to achieve the transcriptional process. Interleukin-1beta induced type II-sPLA(2) gene dose- and time-dependently and increased the binding of NFkappaB to a specific site of type II-sPLA(2) promoter. This effect was abolished by proteinase inhibitors that block the proteasome machinery and NFkappaB nuclear translocation. Type II-sPLA(2) induction was also obtained by free arachidonic acid and was blocked by either AACOCF(3), a specific cytosolic-PLA(2) inhibitor, PD98059, a mitogen-activated protein kinase kinase inhibitor which prevents cytosolic PLA(2) activation, or nordihydroguaiaretic acid, a lipoxygenase inhibitor, but not by the cyclooxygenase inhibitor indomethacin, suggesting a role for a lipoxygenase product. Type II-sPLA(2) induction was obtained after treatment of the cells by 15-deoxy-Delta(12,14)-dehydroprostaglandin J(2), carbaprostacyclin, and 9-hydroxyoctadecadienoic acid, which are ligands of peroxisome proliferator-activated receptor (PPAR) gamma, whereas PPARalpha ligands were ineffective. Interleukin-1beta as well as PPARgamma-ligands stimulated the activity of a reporter gene containing PPARgamma-binding sites in its promoter. Binding of both NFkappaB and PPARgamma to their promoter is required to stimulate the transcriptional process since inhibitors of each class block interleukin-1beta-induced type II-sPLA(2) gene activation. We therefore suggest that NFkappaB and PPARgamma cooperate at the enhanceosome-coactivator level to turn on transcription of the proinflammatory type II-sPLA(2) gene.

A role for phospholipase A2 in ARDS pathogenesis

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury that is characterized by arterial hypoxemia and noncardiogenic pulmonary oedema. One feature of ARDS is an alteration of pulmonary surfactant that increases surface tension at the air-liquid interface and results in alveolar collapse and the impairment of gas exchange. Type-II secretory phospholipase A2 (sPLA2-II) plays a major role in the hydrolysis of surfactant phospholipids and its expression is inhibited by surfactant. Here, we discuss the evidence that in pathological situations, such as ARDS, in which surfactant is altered, sPLA2-II production is exacerbated, leading to further surfactant alteration and the establishment of a vicious cycle.

Phospholipase A2: its usefulness in laboratory diagnostics

Phospholipase A2 (PLA2) is an enzyme that catalyzes the hydrolysis of membrane phospholipids. This article reviews the source and structure of PLA2, the involvement of the enzyme in various biological and pathological phenomena, and the usefulness of PLA2 assays in laboratory diagnostics. Of particular importance is the role of PLA2 in the cellular production of mediators of inflammatory response to various stimuli. Assays for PLA2 activity and mass concentration are discussed, and the results of enzyme determinations in plasma from patients with different pathological conditions are presented. The determination of activity and mass concentration in plasma is particularly useful in the diagnosis and prognosis of pancreatitis, multiple organ failure, septic shock, and rheumatoid arthritis. A very important result is the demonstration that PLA2 is an acute phase protein, like CRP. Indeed, there is a close correlation between PLA2 mass concentration and CRP levels in several pathological conditions. Although the determination of C-reactive protein is much easier to perform and is routinely carried out in most clinical laboratories, the assessment of PLA2 activity or mass concentration has to be considered as a reliable approach to obtain a deeper understanding of some pathological conditions and may offer additional information concerning the prognosis of several disorders.

COX-2 and cytosolic PLA2 mediate IL-1beta-induced cAMP production in human vascular smooth muscle cells

Interleukin (IL)-1 is a potent vasodilator that causes prolonged induction of prostacyclin (PGI2) and cAMP synthesis in human vascular smooth muscle cells (HVSMC). The present study investigated IL-1 induction of PG synthetic enzymes in HVSMC and tested their respective roles in PGI2 and cAMP production. Cyclooxygenase (COX)-1 mRNA was not detectable in either control or IL-1-treated HVSMC, as assessed by RT-PCR. In contrast, COX-2 mRNA was detectable in control HVSMC, increased markedly (16-fold) after 1 h of IL-1 exposure, and increased further (52-fold) after 24 h. COX-2 protein levels, assessed by Western analysis, were increased concomitantly. HVSMC contained mRNA encoding both the secreted and cytosolic forms of phospholipase A2 (sPLA2 and cPLA2, respectively). IL-1 stimulation did not affect sPLA2 mRNA levels, but cPLA2 mRNA levels increased at 8 h, after the initial induction of PG synthesis. HVSMC constitutively expressed PGI2 synthase mRNA, and its levels were not affected by IL-1. A selective COX-2 inhibitor, NS-398, reversed IL-1-induced PGI2 and cAMP production, supporting a role of COX-2 in mediating increased PG synthesis. IL-1-induced cAMP was also reversed by a selective cPLA2 inhibitor, AACOCF3, but not by thioetheramide phosphorylcholine, which inhibits sPLA2 preferentially over cPLA2, supporting a requirement for cPLA2-derived arachidonic acid in IL-1-induced PG synthesis. The delayed induction of cPLA2 mRNA was also attenuated by NS-398, suggesting that it was secondary to the initial COX-2-induced PG synthesis. Together, the results support the hypothesis that IL-1 induces intracellular PG synthesis in HVSMC via rapid upregulation of COX-2, which utilizes cPLA2-derived arachidonic acid to generate PG metabolites that regulate adenylate cyclase.

Plasma levels of type II phospholipase A2 and nitrite/nitrate in patients with burns

Type II phospholipase A2 (type II PLA2), nitrite/nitrate (NOx), tumor necrosis factor-alpha (TNF-alpha) and endotoxin were studied in burn patients. Type II PLA2 values and NOx values were both significantly higher in the group that died, the group with shock as a complication and the group with multiple organ dysfunction syndrome (MODS) as a complication, than in the group that survived, the group without shock as a complication and the group without MODS as a complication, respectively. The results suggested that type II PLA2 and nitric oxide (NO) may play a major role in the pathology of burn patients. Significant correlations were found between TNF-alpha and type II PLA2 values and between type II PLA2 and NOx values, suggesting the possibility of involvement in each other's production.

Regulation of the cellular expression of secretory and cytosolic phospholipases A2, and cyclooxygenase-2 by peptide growth factors

Secretory group II (sPLA2) and cytosolic (cPLA2) phospholipases A2 and cyclooxygenase-2 (Cox-2) play a pivotal role in release of proinflammatory eicosanoids. Excessive activity of sPLA2 per se can also propagate inflammation. Endogenous control of the above enzymes has not been completely elucidated. We investigated the combined impact of promoting cytokines and inhibitory peptide growth factors on the expression of mRNA of the above enzymes, on protein content and extracellular release of sPLA2 and on PGE2 production in osteoblasts (FRCO). The synthesis and release of sPLA2 were enhanced by about 20-fold by 0.5 ng/ml IL-1beta or by 50 ng/ml of TNFalpha. Coaddition of both cytokines resulted in synergistic 150-fold increase in the release of sPLA2 implying the existence of two paths of induction. IL-1beta and TNFalpha markedly enhanced the transcription of sPLA2 mRNA. Kinetic study showed that IL-1/TNF initiated sPLA2 release after 12 h, reaching maximum at 48 h. IL-1alpha was a weak stimulator of sPLA2 release, whereas IL-6, IL-8, IGF, IFN-gamma, growth hormone, insulin and GM-CSF were not stimulatory. Peptide growth hormones TGFbeta, PDGF-BB, EGF and bFGF markedly inhibited the extracellular release of sPLA2. TGFbeta and PDGF-BB significantly reduced the level of sPLA2 mRNA, thus acting upon transcription whereas EGF and bFGF were not inhibitory, acting rather upon the translational or posttranslational steps. IL-1/TNF and growth factors had no significant effect on cPLA2 mRNA expression. Cox-2 mRNA expression was markedly enhanced by IL-1/TNF and suppressed by all growth factors tested. Cytokines enhanced the extracellular release of PGE2 and further enhancement was induced by growth factors with the exception of TGFbeta. Cycloheximide abolished completely the release of sPLA2 and markedly reduced the release of PGE2 from cytokine-stimulated FRCO, regardless of whether growth factors were present or not. NS-398, a specific inhibitor of Cox-2 abolished almost completely the release of PGE2 from cytokine-stimulated cells, regardless of the presence of growth factors. Thus, different signalling mechanisms are involved in the impact of growth factors on mRNA expression of sPLA2, cPLA2 and Cox-2. The differences between the impact on FRCO sPLA2 and that reported in other cells, imply that endogenous control of arachidonic acid cascade is cell-specific.

Expression of mRNA for phospholipase A2, cyclooxygenases, and lipoxygenases in cultured human umbilical vascular endothelial and smooth muscle cells and in biopsies from umbilical arteries and veins

Arachidonic acid (AA) is released by phospholipase A2 (PLA2) and then converted into vasoactive and inflammatory eicosanoids by cyclooxygenases (COX) and lipoxygenases (LOX). These eicosanoids are important paracrine regulators of vascular permeability, blood flow, local pro- and anticoagulant activity and they play a major role in the local inflammatory response. We have investigated the presence of mRNAs for PLA2 and for isoforms of COX and LOX in both human endothelial cells (EC) and in human smooth muscle cells (SMC) in culture and in vascular biopsies of human umbilical veins (HUVB) and arteries (HUAB) by using the reversed transcription-polymerase chain reaction (RT-PCR) technique. Results show detectable levels of PLA2 type IV (cPLA2) in cultured EC and SMC and in vascular wall biopsies from HUAB and HUVB. The cultured EC and SMC demonstrate higher levels of both COX-1 and COX-2 with PCR analyses than do vascular wall biopsies from HUAB and HUVB. This indicates a difference in the native expression of COX-1 and COX-2 in cultures of EC and SMC compared to that in biopsies from intact vessel walls. The EC and SMC in culture do not express mRNA for 5-LOX, that was, however, expressed in the vascular wall biopsies. This speaks in favour of a constitutive, i.e. in vivo expression of 5-LOX in SMC in the vascular wall of both umbilical vein and arteries. Thus results from in vitro studies of constitutive COX and LOX expression in EC and vascular SMC in culture cannot simply be extrapolated to represent in vivo conditions.