Phospholipase A2 structure/function, mechanism, and signaling

Eicosanoids, prostacyclin and cyclooxygenase in the cardiovascular system

Eicosanoids represent a diverse family of lipid mediators with fundamental roles in physiology and disease. Within the eicosanoid superfamily are prostanoids, which are specifically derived from arachidonic acid by the enzyme cyclooxygenase (COX). COX has two isoforms; COX-1 and COX-2. COX-2 is the therapeutic target for the nonsteroidal anti-inflammatory drug (NSAID) class of pain medications. Of the prostanoids, prostacyclin, first discovered by Sir John Vane in 1976, remains amongst the best studied and retains an impressive pedigree as one of the fundamental cardiovascular protective pathways. Since this time, we have learnt much about how eicosanoids, COX enzymes and prostacyclin function in the cardiovascular system, knowledge that has allowed us, for example, to harness the power of prostacyclin as therapy to treat pulmonary arterial hypertension and peripheral vascular disease. However, there remain many unanswered questions in our basic understanding of the pathways, and how they can be used to improve human health. Perhaps, the most important and controversial outstanding question in the field remains; 'how do NSAIDs produce their much publicized cardiovascular side-effects?' This review summarizes the history, biology and cardiovascular function of key eicosanoids with particular focus on prostacyclin and other COX products and discusses how our knowledge of these pathways can applied in future drug discovery and be used to explain the cardiovascular side-effects of NSAIDs. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

cPLA2a correlates with metastasis and poor prognosis of osteosarcoma by facilitating epithelial-mesenchymal transition

BACKGROUND

Osteosarcoma (OS) patients with metastasis have very dismal prognoses, and lack effective target therapies. Overexpression of cytosolic phospholipase A2 (cPLA₂) has been shown to promote progression in several types of cancers, but its functions in OS have not been investigated.

MATERIALS AND METHODS

In our study, the expression of cPLA₂a was detected with immunohistochemistry in 102 cases of OS. The clinical significance of cPLA₂a was evaluated by analyzing its correlation with clinicopathological factors. The prognostic significance of cPLA₂a was estimated by univariate and multivariate analysis. The oncogenic functions of cPLA₂a on cell proliferation and invasion were investigated by MTT assay and tranwell assay respectively. Western blotting was applied to detect the markers of epithelial-mesenchymal transition (EMT) after silencing cPLA₂a expression or inhibiting its activity by a specific antagonist.

RESULTS

In our study, high expression of cPLA₂a was significantly associated with metastasis and advanced Enneking stage. High cPLA₂a expression was significantly associated with poor prognosis and it was an independent prognostic biomarker of OS. By silencing cPLA₂a or inhibiting its activity by a specific antagonist, we demonstrated that cPLA₂a promoted cell invasion of OS cells via inducing the EMT process.

CONCLUSIONS

High cPLA₂a expression was an independent prognostic biomarker of OS, and cPLA₂a could promote OS cell invasion via inducing the EMT process, indicating that cPLA₂a was an independent prognostic biomarker and may be an effective drug target for OS.

Mechanosensitive Ion Channels: TRPV4 and P2X7 in Disseminating Cancer Cells

Cancer metastasis is the second leading cause of death in the United States. Despite its morbidity, metastasis is an inefficient process that few cells can survive. However, cancer cells can overcome these metastatic barriers via cellular responses to microenvironmental cues, such as through mechanotransduction. This review focuses on the mechanosensitive ion channels TRPV4 and P2X7, and their roles in metastasis, as both channels have been shown to significantly affect tumor cell dissemination. Upon activation, these channels help form tumor neovasculature, promote transendothelial migration, and increase cell motility. Conversely, they have also been linked to forms of cancer cell death dependent upon levels of activation, implying the complex functionality of mechanosensitive ion channels. Understanding the roles of TRPV4, P2X7 and other mechanosensitive ion channels in these processes may reveal new possible drug targets that modify channel function to reduce a tumor's metastatic potential.

Molecular docking and dynamic studies of crepiside E beta glucopyranoside as an inhibitor of snake venom PLA2

Alternative treatments from plant-derived small molecules for neutralizing the venom lethality in snake envenomation are prevalent now. Elephantopus scaber, a tropical plant species has been recognized for its various pharmacological activities and especially anti-snake venom property; however, the molecular basis for this property is not understood. It is reported that snake venom PLA2 is a toxic factor with pharmacological effects independent of their catalytic activity. Here we report the inhibition of catalytic property of Cobra and Viper (group I and group II) snake venom PLA2 by the phytocompounds from E. scaber through molecular docking and dynamics studies. Initially, Lipinski's rule, ADMET, and molecular docking studies were carried out. Our results show that among 124 phytocompounds, crepiside E (deacylcynaropicrin-3' beta-glucopyranoside) has shown interactions with the conserved catalytic active site residues, His 48 and Asp 49, in both the PLA2s. Further, molecular dynamic simulations for 60 ns confirmed the stability of crepiside E in the active site of PLA2s and were found to be stable throughout the simulation. In order to understand the drug-likeness of crepiside E, pIC50 and MMGBSA scores were correlated by performing a linear regression analysis. Crepiside E was found to have similar chemical features to that of doxycycline, a known PLA2 inhibitor as indicated by a similarity score of 64.15%. Hence, it is concluded that crepiside E beta glucopyranoside present in Elephantopus scaber contributes to neutralizing the snake venom.

Long chain lipid hydroperoxides increase the glutathione redox potential through glutathione peroxidase 4

BACKGROUND

Peroxidation of PUFAs by a variety of endogenous and xenobiotic electrophiles is a recognized pathophysiological process that can lead to adverse health effects. Although secondary products generated from peroxidized PUFAs have been relatively well studied, the role of primary lipid hydroperoxides in mediating early intracellular oxidative events is not well understood.

METHODS

Live cell imaging was used to monitor changes in glutathione (GSH) oxidation in HAEC expressing the fluorogenic sensor roGFP during exposure to 9-hydroperoxy-10E,12Z-octadecadienoic acid (9-HpODE), a biologically important long chain lipid hydroperoxide, and its secondary product 9-hydroxy-10E,12Z-octadecadienoic acid (9-HODE). The role of hydrogen peroxide (H₂O₂) was examined by direct measurement and through catalase interventions. shRNA-mediated knockdown of glutathione peroxidase 4 (GPx4) was utilized to determine its involvement in the relay through which 9-HpODE initiates the oxidation of GSH.

RESULTS

Exposure to 9-HpODE caused a dose-dependent increase in GSH oxidation in HAEC that was independent of intracellular or extracellular H₂O₂ production and was exacerbated by NADPH depletion. GPx4 was involved in the initiation of GSH oxidation in HAEC by 9-HpODE, but not that induced by exposure to H₂O₂ or the low molecular weight alkyl tert-butyl hydroperoxide (TBH).

CONCLUSIONS

Long chain lipid hydroperoxides can directly alter cytosolic E_GSH independent of secondary lipid oxidation products or H₂O₂ production. NADPH has a protective role against 9-HpODE induced E_GSH changes. GPx4 is involved specifically in the reduction of long-chain lipid hydroperoxides, leading to GSH oxidation.

SIGNIFICANCE

These results reveal a previously unrecognized consequence of lipid peroxidation, which may provide insight into disease states involving lipid peroxidation in their pathogenesis.

Non-Mammalian Prdx6 Enzymes (Proteins with 1-Cys Prdx Mechanism) Display PLA₂ Activity Similar to the Human Orthologue

Mammalian peroxiredoxin class 6 (Prdx6) are bifunctional enzymes. Non-mammalian Prdx6 enzymes display Cys-based peroxidase activity, but to date their putative phospholipase A₂ (PLA₂ activities) has not been experimentally investigated. Initially, we observed that five non-mammalian Prdx6 enzymes (enzymes from Arabidopsis thaliana (AtPER1), Triticum aestivum (TaPER1), Pseudomonas aeruginosa (PaLsfA) and Aspergillus fumigatus (AfPrx1 and AfPrxC)) present features compatible with PLA₂ activities in mammalian Prdx6 by amino acid sequences alignment and tertiary structure modeling. Employing unilamellar liposomes with tracer amounts of [³H]-1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and thin layer chromatography, all the tested non-mammalian Prdx6 enzymes displayed PLA₂ activities, with values ranging from 3.4 to 6.1 nmol/min/mg protein. It was previously shown that Thr177 phosphorylation of human Prdx6 increases its PLA₂ activity, especially at neutral pH. Therefore, we investigated if human Erk2 kinase could also phosphorylate homologous Thr residues in non-mammalian Prdx6 proteins. We observed phosphorylation of the conserved Thr in three out of the five non-mammalian Prdx enzymes by mass spectrometry. In the case of the mitochondrial Prdx6 from A. fumigatus (AfPrxC), we also observed phosphorylation by western blot, and as a consequence, the PLA₂ activity was increased in acidic and neutral conditions by the human Erk2 kinase treatment. The possible physiological meanings of these PLA₂ activities described open new fields for future research.

Conodipine-P1-3, the First Phospholipases A2 Characterized from Injected Cone Snail Venom

The phospholipase A₂ (PLA₂s) superfamily are ubiquitous small enzymes that catalyze the hydrolysis of phospholipids at the sn-2 ester bond. PLA₂s in the venom of cone snails (conodipines, Cdpi) are composed of two chains termed as alpha and beta subunits. Conodipines are categorized within the group IX of PLA₂s. Here we describe the purification and biochemical characterization of three conodipines (Cdpi-P1, -P2 and -P3) isolated from the injected venom of Conus purpurascens Using proteomics methods, we determined the full sequences of all three conodipines. Conodipine-P1-3 have conserved consensus catalytic domain residues, including the Asp/His dyad. Additionally, these enzymes are expressed as a mixture of proline hydroxylated isoforms. The activities of the native Conodipine-Ps were evaluated by conventional colorimetric and by MS-based methods, which provide the first detailed cone snail venom conodipine activity monitored by mass spectrometry. Conodipines can have medicinal applications such inhibition of cancer proliferation, bacterial and viral infections among others.

Dysregulation of lipid metabolism induced by airway exposure to polycyclic aromatic hydrocarbons in C57BL/6 mice

Polycyclic aromatic hydrocarbons (PAHs), originated from cigarette smoke and fine particle matter (PM2.5), are important inducers of lung cancer. Lipid metabolic disorder is an important biological feature in the progression of lung cancer. However, the dysregulation of lipid metabolism induced by airway exposure to PAHs remains unknown. In this study, an untargeted lipidomics approach was performed to characterize the effects of airway exposure to benzo[a]pyrene (BaP) on lipid metabolism of C57BL/6 mice. Lipidome of serum samples were analyzed with an ultra-performance liquid chromatography coupled with quadrupole-orbitrap mass spectrometer. Lipid profiling and multivariate statistical analysis results demonstrated that airway exposure to BaP mainly disturbed glycerophospholipid metabolism of mice. Moreover, sex-dependent and time-dependent effects of BaP exposure on lipids profile of mice were observed. Several phosphatidylcholines (PCs), Lysophosphatidylcholines (LysoPCs), phosphatidylethanolamines (PEs), Lysophosphatidylethanolamines (LysoPEs) and phosphatidylinositols (PIs) were significantly down-regulated in mice serum after BaP exposure. Meanwhile, these altered lipids showed different susceptibility and change trends in male and female mice. Our results are corresponding with the lipid metabolic alterations induced by cigarette smoke and PM2.5 in animals or human. Compared with the dysregulation of lipid metabolism in patients with lung cancer, these results indicated that the lipid metabolism response to PAHs airway exposure may contribute to the lung cancer progression.

Conditions for Analysis of Native Protein Structures Using Uniform Field Drift Tube Ion Mobility Mass Spectrometry and Characterization of Stable Calibrants for TWIM-MS

Determination of collisional cross sections (CCS) by travelling wave ion mobility mass spectrometry (TWIM-MS) requires calibration against standards for which the CCS has been measured previously by drift tube ion mobility mass spectrometry (DTIM-MS). The different extents of collisional activation in TWIM-MS and DTIM-MS can give rise to discrepancies in the CCS of calibrants across the two platforms. Furthermore, the conditions required to ionize and transmit large, folded proteins and assemblies may variably affect the structure of the calibrants and analytes. Stable hetero-oligomeric phospholipase A₂ (PDx) and its subunits were characterized as calibrants for TWIM-MS. Conditions for acquisition of native-like TWIM (Synapt G1 HDMS) and DTIM (Agilent 6560 IM-Q-TOF) mass spectra were optimized to ensure the spectra exhibited similar charge state distributions. CCS measurements (DTIM-MS) for ubiquitin, cytochrome c, holo-myoglobin, serum albumin and glutamate dehydrogenase were in good agreement with other recent results determined using this and other DTIM-MS instruments. PDx and its β and γ subunits were stable across a wide range of cone and trap voltages in TWIM-MS and were stable in the presence of organic solvents. The CCS of PDx and its subunits were determined by DTIM-MS and were used as calibrants in determination of CCS of native-like cytochrome c, holo-myoglobin, carbonic anhydrase, serum albumin and haemoglobin in TWIM-MS. The CCS values were in good agreement with those measured by DTIM-MS where available. These experiments demonstrate conditions for analysis of native-like proteins using a commercially available DTIM-MS instrument, characterize robust calibrants for TWIM-MS, and present CCS values determined by DTIM-MS and TWIM-MS for native proteins to add to the current literature database. Graphical Abstract ᅟ.

Dynamic structural biology at the protein membrane interface

Since I started doing scientific research, I've been fascinated by the interplay of protein structure and dynamics and how they together mediate protein function. A particular area of interest has been in understanding the mechanistic basis of how lipid-signaling enzymes function on membrane surfaces. In this award lecture article, I will describe my laboratory's studies on the structure and dynamics of lipid-signaling enzymes on membrane surfaces. This is important, as many lipid-signaling enzymes are regulated through dynamic regulatory mechanisms that control their enzymatic activity. This article will discuss my continued enthusiasm in using a synergistic application of hydrogen-deuterium exchange MS (HDX-MS) with other structural biology techniques to probe the mechanistic basis for how membrane-localized signaling enzymes are regulated and how these approaches can be used to understand how they are misregulated in disease. I will discuss specific examples of how we have used HDX-MS to study phosphoinositide kinases and the protein kinase Akt. An important focus will be on a description of how HDX-MS can be used as a powerful tool to optimize the design of constructs for X-ray crystallography and EM. The use of a diverse toolbox of biophysical methods has revealed novel insight into the complex and varied regulatory networks that control the function of lipid-signaling enzymes and enabled unique insight into the mechanics of membrane recruitment.

Cytosolic group IVA phospholipase A2 inhibitors, AVX001 and AVX002, ameliorate collagen-induced arthritis

Background

Cytosolic phospholipase A2 group IVA (cPLA2α)-deficient mice are resistant to collagen-induced arthritis, suggesting that cPLA2α is an important therapeutic target. Here, the anti-inflammatory effects of the AVX001 and AVX002 cPLA2α inhibitors were investigated.

Methods

In vitro enzyme activity was assessed by a modified Dole assay. Effects on inhibiting IL-1β-induced release of arachidonic acid (AA) and prostaglandin E2 (PGE2) were measured using SW982 synoviocyte cells. In vivo effects were studied in prophylactic and therapetic murine collagen-induced arthritis models and compared to methotrexate (MTX) and Enbrel, commonly used anti-rheumatic drugs. The in vivo response to treatment was evaluated in terms of the arthritis index (AI), histopathology scores and by plasma levels of PGE2 following 14 and 21 days of treatment.

Results

Both cPLA2α inhibitors are potent inhibitors of cPLA2α in vitro. In synoviocytes, AVX001 and AVX002 reduce, but do not block, release of AA or PGE2 synthesis. In both CIA models, the AI and progression of arthritis were significantly lower in the mice treated with AVX001, AVX002, Enbrel and MTX than in non- treated mice. Several histopathology parameters of joint damage were found to be significantly reduced by AVX001 and AVX002 in both prophylactic and therapeutic study modes; namely articular cavity and peripheral tissue inflammatory cell infiltration; capillary and synovial hyperplasia; articular cartilage surface damage; and periostal and endochondral ossification. In comparison, MTX did not significantly improve any histopathology parameters and Enbrel only improved ossification. Finally, as a biomarker of inflammation and as an indication that AVX001 and AVX002 blocked the cPLA2α target, we determined that plasma levels of PGE2 were significantly reduced in response to the AVX inhibitors and MTX, but not Enbrel.

Conclusions

AVX001 and AVX002 display potent anti-inflammatory activity and disease-modifying properties in cellular and in vivo models. The in vivo effects of AVX001 and AVX002 were comparable to, or superior, to those of MTX and Enbrel. Taken together, this study suggests that cPLA2α inhibitors AVX001 and AVX002 are promising small molecule disease-modifying anti-rheumatic therapies.

Naja annulifera Snake: New insights into the venom components and pathogenesis of envenomation

Background

Naja annulifera is a medically important venomous snake occurring in some of the countries in Sub-Saharan Africa. Accidental bites result in severe coagulation disturbances, systemic inflammation and heart damage, as reported in dogs, and death, by respiratory arrest, in humans. Despite the medical importance of N. annulifera, little is known about its venom composition and the pathogenesis of envenomation. In this paper, the toxic, inflammatory and immunogenic properties of N. annulifera venom were analyzed.

Methodology/Principal findings

Venom proteomic analysis identified 79 different proteins, including Three Finger Toxins, Cysteine Rich Secretory Proteins, Metalloproteinases, Phospholipases A₂ (PLA₂), Hyaluronidase, L-amino-acid oxidase, Cobra Venom Factor and Serine Proteinase. The presence of PLA₂, hyaluronidase, fibrinogenolytic and anticoagulant activities was detected using functional assays. The venom was cytotoxic to human keratinocytes. In an experimental murine model of envenomation, it was found that the venom induced local changes, such as swelling, which was controlled by anti-inflammatory drugs. Moreover, the venom caused death, which was preceded by systemic inflammation and pulmonary hemorrhage. The venom was shown to be immunogenic, inducing a strong humoral immune response, with the production of antibodies able to recognize venom components with high molecular weight and to neutralize its lethal activity.

Conclusions/Significance

The results obtained in this study demonstrate that N. annulifera venom contains toxins able to induce local and systemic inflammation, which can contribute to lung damage and death. Moreover, the venom is immunogenic, an important feature that must be considered during the production of a therapeutic anti-N. annulifera antivenom.

N. annulifera is a dangerous snake that belongs to the Elapidae family. It is found in some of the countries in Sub-Saharan Africa and has caused accidents in humans and dogs. In this study, we characterized some of the biochemical, toxic and immunogenic properties of N. annulifera venom. We showed that the venom is composed of several proteins, some of which display enzymatic activities, such as phospholipase A2, hyaluronidase, metalloproteinases and serine proteinases. The venom promoted disturbances in the human coagulation system and was cytotoxic to human epidermal cells. Using a mouse model, we showed that the venom promotes local reactions that were reduced with anti-inflammatory drugs. The venom caused systemic inflammation, lung hemorrhage and death. Further, the venom stimulated production of high antibody titers when injected into mice and the antiserum produced was able to inhibit venom-induced death. This study demonstrated that N. annulifera venom contains toxins that trigger inflammatory process, which may contribute to the envenomation pathology. Moreover, the venom is immunogenic, an important aspect for the production of an efficient N. annulifera antivenom.

Reversed phase UHPLC/ESI-MS determination of oxylipins in human plasma: a case study of female breast cancer

The ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC/MS) method was optimized and validated for the determination of oxylipins in human plasma using the targeted approach with selected reaction monitoring (SRM) in the negative-ion electrospray ionization (ESI) mode. Reversed phase UHPLC separation on an octadecylsilica column enabled the analysis of 63 oxylipins including numerous isomeric species within 12-min run time. The method was validated (calibration curve, linearity, limit of detection, limit of quantification, carry-over, precision, accuracy, recovery rate, and matrix effect) and applied to 40 human female plasma samples from breast cancer patients and age-matched healthy volunteers (control). Thirty-six oxylipins were detected in human plasma with concentrations above the limit of detection, and 21 of them were quantified with concentrations above the limit of quantitation. The concentrations determined in healthy controls are in a good agreement with previously reported data on human plasma. Quantitative data were statistically evaluated by multivariate data analysis (MDA) methods including principal component analysis (PCA) and orthogonal partial least square discriminant analysis (OPLS-DA). S-plot and box plots showed that 13-HODE, 9-HODE, 13-HOTrE, 9-HOTrE, and 12-HHTrE were the most upregulated oxylipin species in plasma of breast cancer patients.

Overexpression of PGE2 synthase by in vivo transient expression enhances immunocompetency along with fitness cost in a lepidopteran insect

Prostaglandins (PGs) mediate various physiological functions in insects. Especially, PGE2 is known to mediate immunity and egg-laying behavior in the beet armyworm, Spodoptera exigua. A PGE2 synthase 2 (Se-PGES2) has been identified to catalyze the final step to produce PGE2 in S. exigua. Its expression is inducible in response to immune challenge. Inhibition of the gene expression results in immunosuppression. On the other hand, any physiological alteration induced by its uncontrolled overexpression was not recognized in insects. This study used in vivo transient expression (IVTE) technique to induce overexpression and assessed subsequent physiological alteration in S. exigua. Se-PGES2 was cloned into a eukaryotic expression vector and transfected to Sf9 cells to monitor its heterologous expression. The Sf9 cells expressed the recombinant Se-PGES2 (rSe-PGES2) at an expected size (∼47 kDa), which was localized in cytoplasm. The recombinant expression vector was then used to transfect larvae of S. exigua. Hemocytes collected from the larvae treated with IVTE expressed rSe-PGES2 gene for at least 48 h. The larvae treated with IVTE exhibited an enhanced competency in cellular immune response measured by hemocyte nodule formation. In addition, IVTE treatment of Se-PGES2 induced gene expression of antimicrobial peptides without any immune challenge. The larvae treated with IVTE became significantly resistant to infection of an entomopathogenic nematode, Steinernema monticolum or to infection to its symbiotic bacterium, Xenorhabdus hominickii. However, IVTE-treated S. exigua larvae suffered from reduced pupal size and fecundity.

Identification of Small Peptides that Inhibit NADPH Oxidase (Nox2) Activation

Nicotinamide adenine phosphate (NADPH) oxidase type 2 (Nox2), a major source of reactive oxygen species in lungs, plays an important role in tissue damage associated with acute inflammatory diseases. The phospholipase A₂ (PLA₂) activity of peroxiredoxin 6 (Prdx6), called aiPLA₂, is required for Nox2 activation through its role in the cellular generation of Rac, a key cytosolic component of the activation cascade. Lung surfactant protein A (SP-A) binds to Prdx6, inhibits its aiPLA₂ activity, and prevents activation of Nox2. Based on protein docking software, we previously identified a 16 amino acid (aa) peptide derived from rat SP-A as the Prdx6 binding motif. We now identify the minimal effective sequences of rat/mouse and human SP-A as 9-aa sequences that we have called PLA₂-inhibitory peptide (PIP).These sequences are PIP-1, rat/mouse; PIP-2, human; and PIP-3, a hybrid of PIPs 1&2. aiPLA₂ activity in vitro was inhibited by 50% with ~7⁻10 µg PIP/µg Prdx6. Inhibition of the aiPLA₂ activity and Nox2 activation of lungs in vivo was similar for intratracheal (IT) and intravenous (IV) administration of PIP-2, but required its incorporation into liposomes as a delivery vehicle; tissue ½ time for decrease of the in vivo inhibition of aiPLA₂ activity after PIP-2 administration was ~50 h. These properties suggest that PIP-2 could be an effective therapeutic agent to prevent tissue injury associated with lung inflammation.

Characterization of the Intrinsic Phospholipase A1 Activity of Bordetella pertussis Adenylate Cyclase Toxin

Adenylate cyclase toxin (ACT, CyaA) is one of the important virulence factors secreted by the whooping cough bacterium Bordetella pertussis, and it is essential for the colonization of the human respiratory tract by this bacterium. Cytotoxicity by ACT results from the synergy between toxin's two main activities, production of supraphysiological cAMP levels by its N-terminal adenylate cyclase domain (AC domain), and cell membrane permeabilization, induced by its C-terminal pore-forming domain (hemolysin domain), which debilitate the host defenses. In a previous study we discovered that purified ACT is endowed with intrinsic phospholipase A1 (PLA) activity and that Ser in position 606 of the ACT polypeptide is a catalytic site for such hydrolytic activity, as part of G-X-S-X-G catalytic motif. Recently these findings and our conclusions have been directly questioned by other authors who claim that ACT-PLA activity does not exist. Here we provide new data on ACT phospholipase A1 characteristics. Based on our results we reaffirm our previous conclusions that ACT is endowed with PLA activity; that our purified ACT preparations are devoid of any impurity with phospholipase A activity; that ACT-S606A is a PLA-inactive mutant and thus, that Ser606 is a catalytic site for the toxin hydrolytic activity on phospholipids, and that ACT-PLA activity is involved in AC translocation.

A non-venomous sPLA2 of a lepidopteran insect: Its physiological functions in development and immunity

Eicosanoids are oxygenated C20 polyunsaturated fatty acids that mediate various physiological processes in insects. Eicosanoid biosynthesis begins with a C20 precursor, arachidonic acid (5,8,11,14-eicosatetraenoic acid: AA). AA is usually released from phospholipids at sn-2 position by catalytic activity of phospholipase A₂ (PLA₂). Although various PLA₂s classified into 16 gene families (= Groups) are known in various biological systems, few PLA₂s are known in insects. Only two PLA₂s involved in intracellular calcium independent PLA₂ (iPLA₂) group have been identified in lepidopteran insects with well known eicosanoid physiology. This study reports the first secretory PLA₂ (sPLA₂) in lepidopteran insects. A partial open reading frame (ORF) of PLA₂ was obtained by interrogating Spodoptera exigua transcriptome. Subsequent 3'-RACE resulted in a full ORF (Se-sPLA2A) encoding 194 amino acid sequence containing signal peptide, calcium-binding domain, and catalytic site. Phylogenetic analysis indicated that Se-sPLA₂A was clustered with other Group III sPLA₂s. Se-sPLA₂A was expressed in most larval instars except late last instar. Its expression was inducible by immune challenge and juvenile hormone analog injection. RNA interference of Se-sPLA₂A significantly suppressed cellular immunity and impaired larval development. These results suggest that non-venomous sPLA₂ plays a crucial role in immune and developmental processes in S. exigua, a lepidopteran insect.

Clinical workup of fatty liver for the primary care provider

Nonalcoholic fatty liver disease (NAFLD) is quickly emerging as a global epidemic in parallel with the rise in obesity and the Metabolic Syndrome. NAFLD, once seen simply as a passive consequence of the Metabolic Syndrome (MetS), has been found to interact with other features of MetS to exacerbate insulin resistance, diabetes, and cardiovascular disease. NAFLD is also becoming the top indication for liver transplant and an important risk factor for hepatocellular carcinoma. Treatment of this disorder is limited mainly to lifestyle modifications to promote weight loss along with consideration for off-label use of certain medications, but recent progression in clinical trials means more effective treatments are on the horizon. Therefore, the primary care provider must be prepared to recognize and determine the severity of this disorder in order to optimize management. In this review, we will discuss risk factors for NAFLD, workup and differential, and finally, offer recommendations on screening.

Comprehensive analysis of oxylipins in human plasma using reversed-phase liquid chromatography-triple quadrupole mass spectrometry with heatmap-assisted selection of transitions

Oxylipins, a subclass of lipid mediators, are metabolites of various polyunsaturated fatty acids with crucial functions in regulation of systemic inflammation. Elucidation of their roles in pathological conditions requires accurate quantification of their levels in biological samples. We refined an ultra-performance liquid chromatography-multiple reaction monitoring-mass spectrometry (UPLC-MRM-MS)-based workflow for comprehensive and specific quantification of 131 endogenous oxylipins in human plasma, in which we optimized LC mobile phase additives, column, and gradient conditions. We employed heatmap-assisted strategy to identify unique transitions to improve the assay selectivity and optimized solid phase extraction procedures to achieve better analyte recovery. The method was validated according to FDA guidelines. Overall, 94.4% and 95.7% of analytes at tested concentrations were within acceptable accuracy (80-120%) and precision (CV < 15%), respectively. Good linearity for most analytes was obtained with R² > 0.99. The method was also validated using a standard reference material-SRM 1950 frozen human plasma to demonstrate inter-lab compatibility. Graphical abstract ᅟ.

iPLA2β and its role in male fertility, neurological disorders, metabolic disorders, and inflammation

The Ca²⁺-independent phospholipases, designated as group VI iPLA₂s, also referred to as PNPLAs due to their shared homology with patatin, include the β, γ, δ, ε, ζ, and η forms of the enzyme. The iPLA₂s are ubiquitously expressed, share a consensus GXSXG catalytic motif, and exhibit organelle/cell-specific localization. Among the iPLA₂s, iPLA₂β has received wide attention as it is recognized to be involved in membrane remodeling, cell proliferation, cell death, and signal transduction. Ongoing studies implicate participation of iPLA₂β in a variety of disease processes including cancer, cardiovascular abnormalities, glaucoma, and peridonditis. This review will focus on iPLA₂β and its links to male fertility, neurological disorders, metabolic disorders, and inflammation.

Flow Cytometry Has a Significant Impact on the Cellular Metabolome

The characterization of specialized cell subpopulations in a heterogeneous tissue is essential for understanding organ function in health and disease. A popular method of cell isolation is fluorescence-activated cell sorting (FACS) based on probes that bind surface or intracellular markers. In this study, we analyze the impact of FACS on the cell metabolome of mouse peritoneal macrophages. Compared with directly pelleted macrophages, FACS-treated cells had an altered content of metabolites related to the plasma membrane, activating a mechanosensory signaling cascade causing inflammation-like stress. The procedure also triggered alterations related to energy consumption and cell damage. The observed changes mostly derive from the physical impact on cells during their passage through the instrument. These findings provide evidence of FACS-induced biochemical changes, which should be taken into account in the design of robust metabolic assays of cells separated by flow cytometry.

Impact of Dietary Fats on Brain Functions

BACKGROUND

Adequate dietary intake and nutritional status have important effects on brain functions and on brain health. Energy intake and specific nutrients excess or deficiency from diet differently affect cognitive processes, emotions, behaviour, neuroendocrine functions and synaptic plasticity with possible protective or detrimental effects on neuronal physiology. Lipids, in particular, play structural and functional roles in neurons. Here the importance of dietary fats and the need to understand the brain mechanisms activated by peripheral and central metabolic sensors. Thus, the manipulation of lifestyle factors such as dietary interventions may represent a successful therapeutic approach to maintain and preserve brain health along lifespan.

METHODS

This review aims at summarizing the impact of dietary fats on brain functions.

RESULTS

Starting from fat consumption, nutrient sensing and food-related reward, the impact of gut-brain communications will be discussed in brain health and disease. A specific focus will be on the impact of fats on the molecular pathways within the hypothalamus involved in the control of reproduction via the expression and the release of Gonadotropin-Releasing Hormone. Lastly, the effects of specific lipid classes such as polyunsaturated fatty acids and of the "fattest" of all diets, commonly known as "ketogenic diets", on brain functions will also be discussed.

CONCLUSION

Despite the knowledge of the molecular mechanisms is still a work in progress, the clinical relevance of the manipulation of dietary fats is well acknowledged and such manipulations are in fact currently in use for the treatment of brain diseases.

Lipidomics in Major Depressive Disorder

Omic sciences coupled with novel computational approaches such as machine intelligence offer completely new approaches to major depressive disorder (MDD) research. The complexity of MDD's pathophysiology is being integrated into studies examining MDD's biology within the omic fields. Lipidomics, as a late-comer among other omic fields, is increasingly being recognized in psychiatric research because it has allowed the investigation of global lipid perturbations in patients suffering from MDD and indicated a crucial role of specific patterns of lipid alterations in the development and progression of MDD. Combinatorial lipid-markers with high classification power are being developed in order to assist MDD diagnosis, while rodent models of depression reveal lipidome changes and thereby unveil novel treatment targets for depression. In this systematic review, we provide an overview of current breakthroughs and future trends in the field of lipidomics in MDD research and thereby paving the way for precision medicine in MDD.

Functional role of peroxiredoxin 6 in the eye

Peroxiredoxin 6 (Prdx6) is the only mammalian 1-Cys member of the Prdx family, a group of enzymes which share the ability to reduce peroxides. In addition to its peroxidase function, Prdx6 also demonstrates phospholipase A₂ and lysophosphatidylcholine acyl transferase (LPCAT) activities. These enzymatic activities play an important role in regenerating oxidized membrane phospholipids and maintaining an appropriate balance of intracellular reactive oxygen species. Development of clinical pathologies, including those within the eye, have been linked to dysregulation of Prdx6 function. Interplay between external stressors like exposure to UV light, transforming growth factor β (TGF-β), and hyperglycemia in conjunction with diminished Prdx6 levels and loss of redox balance is associated with cellular changes in a variety of ophthalmic pathologies including cataracts, glaucoma, and retinal degeneration. Many of these cellular abnormalities can be rescued through supplementation with exogenous Prdx6. Additionally, corneal endothelial cells have been found to express high levels of Prdx6 in the plasma membrane. These findings highlight the importance of Prdx6 as an essential regulator of oxidative stress in the eye.

Endogenous Fatty Acids Are Essential Signaling Factors of Pancreatic β-Cells and Insulin Secretion

The secretion of insulin from β-cells depends on extracellular factors, in particular glucose and other small molecules, some of which act on G-protein-coupled receptors. Fatty acids (FAs) have been discussed as exogenous secretagogues of insulin for decades, especially after the FA receptor GPR40 (G-protein-coupled receptor 40) was discovered. However, the role of FAs as endogenous signaling factors has not been investigated until now. In the present work, we demonstrate that lowering endogenous FA levels in β-cell medium by stringent washing or by the application of FA-free (FAF) BSA immediately reduced glucose-induced oscillations of cytosolic Ca²⁺ ([Ca²⁺]_i oscillations) in MIN6 cells and mouse primary β-cells, as well as insulin secretion. Mass spectrometry confirmed BSA-mediated removal of FAs, with palmitic, stearic, oleic, and elaidic acid being the most abundant species. [Ca²⁺]_i oscillations in MIN6 cells recovered when BSA was replaced by buffer or as FA levels in the supernatant were restored. This was achieved by recombinant lipase-mediated FA liberation from membrane lipids, by the addition of FA-preloaded FAF-BSA, or by the photolysis of cell-impermeant caged FAs. Our combined data support the hypothesis of FAs as essential endogenous signaling factors for β-cell activity and insulin secretion.

Harnessing snake venom phospholipases A2 to novel approaches for overcoming antibiotic resistance

The emergence of antibiotic resistance drives an essential race against time to reveal new molecular structures capable of addressing this alarming global health problem. Snake venoms are natural catalogs of multifunctional toxins and privileged frameworks, which serve as potential templates for the inspiration of novel treatment strategies for combating antibiotic resistant bacteria. Phospholipases A₂ (PLA₂ s) are one of the main classes of antibacterial biomolecules, with recognized therapeutic value, found in these valuable secretions. Recently, a number of biomimetic oligopeptides based on small fragments of primary structure from PLA₂ toxins has emerged as a meaningful opportunity to overcome multidrug-resistant clinical isolates. Thus, this review will highlight the biochemical and structural properties of antibacterial PLA₂ s and peptides thereof, as well as their possible molecular mechanisms of action and key roles in development of effective therapeutic strategies. Chemical strategies possibly useful to convert antibacterial peptides from PLA₂ s to efficient drugs will be equally addressed.

Mitochondrial uncoupling reveals a novel therapeutic opportunity for p53-defective cancers

There are considerable challenges in directly targeting the mutant p53 protein, given the large heterogeneity of p53 mutations in the clinic. An alternative approach is to exploit the altered fitness of cells imposed by loss-of-wild-type p53. Here we identify niclosamide through a HTS screen for compounds selectively killing p53-deficient cells. Niclosamide impairs the growth of p53-deficient cells and of p53 mutant patient-derived ovarian xenografts. Metabolome profiling reveals that niclosamide induces mitochondrial uncoupling, which renders mutant p53 cells susceptible to mitochondrial-dependent apoptosis through preferential accumulation of arachidonic acid (AA), and represents a first-in-class inhibitor of p53 mutant tumors. Wild-type p53 evades the cytotoxicity by promoting the transcriptional induction of two key lipid oxygenation genes, ALOX5 and ALOX12B, which catalyzes the dioxygenation and breakdown of AA. Therefore, we propose a new paradigm for targeting cancers defective in the p53 pathway, by exploiting their vulnerability to niclosamide-induced mitochondrial uncoupling.

Several challenges are involved in direct targeting of mutant p53, while targeting altered fitness of cells with loss of wild type p53 is an alternative approach. Here they identify niclosamide to be selectively toxic to p53 deficient cells through a previously unknown mitochondrial uncoupling mechanism.

Roles of secreted phospholipase A2 group IIA in inflammation and host defense

Among all members of the secreted phospholipase A₂ (sPLA₂) family, group IIA sPLA₂ (sPLA₂-IIA) is possibly the most studied enzyme. Since its discovery, many names have been associated with sPLA₂-IIA, such as "non-pancreatic", "synovial", "platelet-type", "inflammatory", and "bactericidal" sPLA_2. Whereas the different designations indicate comprehensive functions or sources proposed for this enzyme, the identification of the precise roles of sPLA₂-IIA has remained a challenge. This can be attributed to: the expression of the enzyme by various cells of different lineages, its limited activity towards the membranes of immune cells despite its expression following common inflammatory stimuli, its ability to interact with certain proteins independently of its catalytic activity, and its absence from multiple commonly used mouse models. Nevertheless, elevated levels of the enzyme during inflammatory processes and associated consistent release of arachidonic acid from the membrane of extracellular vesicles suggest that sPLA₂-IIA may contribute to inflammation by using endogenous substrates in the extracellular milieu. Moreover, the remarkable potency of sPLA₂-IIA towards bacterial membranes and its induced expression during the course of infections point to a role for this enzyme in the defense of the host against invading pathogens. In this review, we present current knowledge related to mammalian sPLA₂-IIA and its roles in sterile inflammation and host defense.

Lysophosphatidylinositols in inflammation and macrophage activation: Altered levels and anti-inflammatory effects

Lysophosphatidylinositols (LPI) are bioactive lipids that are implicated in several pathophysiological processes such as cell proliferation, migration and tumorigenesis and were shown to play a role in obesity and metabolic disorders. Often, these effects of LPI were due to activation of the G protein-coupled receptor GPR55. However, the role of LPI and GPR55 in inflammation and macrophage activation remains unclear. Therefore, we thought to study the effect of macrophage activation and inflammation on LPI levels and metabolism. To do so, we used J774 and BV2 cells in culture activated with lipopolysaccharides (LPS, 100 ng/mL) as well as primary mouse alveolar and peritoneal macrophages. We also quantified LPI levels in the cerebellum, lung, liver, spleen and colon of mice with a systemic inflammation induced by LPS (300 μg/kg) and in the colon of mice with acute colitis induced by dextran sulfate sodium (DSS) or trinitrobenzene sulfonic acid (TNBS) and chronic DSS-induced colitis. Our data show that LPS-induced macrophage activation leads to altered LPI levels in both the cells and culture medium. We also show that cytosolic phospholipase A2α (cPLA2α) and α/β‑hydrolase domain 6 (ABHD6) are among the enzymes implicated in LPI metabolism in J774 macrophages. Indeed, ABHD6 and cPLA2α inhibition increased 20:4-LPI levels in LPS-activated macrophages. Furthermore, incubation of LPS-activated cells with LPI decreased J774 activation in a GPR55-dependent manner. In vivo, LPI levels were altered by inflammation in the liver, spleen and colon. These alterations are tissue dependent and could highlight a potential role for LPI in inflammatory processes.

Crystal structure of phospholipase A2 in complex with 1-naphthaleneacetic acid

Phospholipase A₂ (PLA₂ ) is one of the rate limiting enzymes involved in the production of arachidonic acid, a potent inflammatory mediator. PLA₂ is widely distributed all over the animal kingdom. It is also seen in inflammatory exudation and venoms of different organisms. The studies demonstrated that PLA₂ inhibitors have broad spectrum activities that they can either be used against inflammation or envenomation. In this study, the inhibitory activity of 1-napthaleneacetic acid (NAA) against porcine pancreatic PLA₂ has been explained through isothermal titration calorimetry and enzyme kinetics studies. The atomic level of interactions of NAA with PLA₂ was also studied using X-ray crystallography. Apart from these findings, the theoretical binding affinities and mode of interactions of two naphthalene-based NSAIDs such as naproxen (NAP) and nabumetone (NAB) were studied through molecular modeling. The studies proved that the selected ligands are binding at the doorway of the active site cleft and hindering the substrate entry to the active site. The study brings out a potential scaffold for the designing of broad spectrum PLA₂ inhibitors which can be used for inflammation or envenomation. © 2018 IUBMB Life, 70(10):995-1001, 2018.

Edema Induced by a Crotalus durissus terrificus Venom Serine Protease (Cdtsp 2) Involves the PAR Pathway and PKC and PLC Activation

Snake venom serine proteases (SVSPs) represent an essential group of enzymatic toxins involved in several pathophysiological effects on blood homeostasis. Some findings suggest the involvement of this class of enzymatic toxins in inflammation. In this paper, we purified and isolated a new gyroxin isoform from the Crotalus durissus terrificus (Cdt) venom, designated as Cdtsp 2, which showed significant proinflammatory effects in a murine model. In addition, we performed several studies to elucidate the main pathway underlying the edematogenic effect induced by Cdtsp 2. Enzymatic assays and structural analysis (primary structure analysis and three-dimensional modeling) were closely performed with pharmacological assays. The determination of edematogenic activity was performed using Cdtsp 2 isolated from snake venom, and was applied to mice treated with protein kinase C (PKC) inhibitor, phospholipase C (PLC) inhibitor, dexamethasone (Dexa), antagonists for protease-activated receptors (PARs), or saline (negative control). Additionally, we measured the levels of cyclooxygenase 2 (COX-2), malondialdehyde (MDA), and prostaglandin E2 (PGE2). Cdtsp 2 is characterized by an approximate molecular mass of 27 kDa, an isoelectric point (pI) of 4.5, and significant fibrinolytic activity, as well as the ability to hydrolyze Nα-benzoyl-l-arginine 4-nitroanilide (BAPNA). Its primary and three-dimensional structures revealed Cdtsp 2 as a typical snake venom serine protease that induces significant edema via the metabolism of arachidonic acid (AA), involving PARs, PKC, PLC, and COX-2 receptors, as well as inducing a significant increase in MDA levels. Our results showed that Cdtsp 2 is a serine protease with significant enzymatic activity, and it may be involved in the degradation of PAR1 and PAR2, which activate PLC and PKC to mobilize AA, while increasing oxidative stress. In this article, we provide a new perspective for the role of SVSPs beyond their effects on blood homeostasis.

Lysosomal phospholipase A2

Lysosomal phospholipase A2 (PLA2G15) is a ubiquitous enzyme uniquely characterized by a subcellular localization to the lysosome and late endosome. PLA2G15 has an acidic pH optimum, is calcium independent, and acts as a transacylase in the presence of N-acetyl-sphingosine as an acceptor. Recent studies aided by the delineation of the crystal structure of PLA2G15 have clarified further the catalytic mechanism, sn-1 versus sn-2 specificity, and the basis whereby cationic amphiphilic drugs inhibit its activity. PLA2G15 has recently been shown to hydrolyze short chain oxidized phospholipids which access the catalytic site directly based on their aqueous solubility. Studies on the PLA2G15 null mouse suggest a role for the enzyme in the catabolism of pulmonary surfactant. PLA2G15 may also have a role in host defense and in the processing of lipid antigens for presentation by CD1 proteins. This article is part of a Special Issue entitled Novel functions of phospholipase A2 Guest Editors: Makoto Murakami and Gerard Lambeau.

Signaling pathways activated by resolvin E1 to stimulate mucin secretion and increase intracellular Ca2+ in cultured rat conjunctival goblet cells

Glycoconjugate mucin secretion from conjunctival goblet cells is tightly regulated by nerves and specialized pro-resolving mediators (SPMs) to maintain ocular surface health. Here we investigated the actions of the SPM resolvin E1 (RvE1) on cultured rat conjunctival goblet cell glycoconjugate secretion and intracellular [Ca2+] ([Ca2+]i) and the signaling pathways used by RvE1. Goblet cells were cultured from rat conjunctiva in RPMI medium. The amount of RvE1-stimulated glycoconjugate mucin secretion was determined using an enzyme-linked lectin assay with Ulex Europaeus Agglutinin 1 lectin. Cultured goblet cells were also incubated with the Ca2+ indicator dye fura 2/AM and [Ca2+]i was measured. Cultured goblet cells were incubated with inhibitors to phospholipase (PL-) C, D, and A2 signaling pathways. RvE1 stimulated glycoconjugate secretion in a concentration dependent manner and was inhibited with the Ca2+ chelator BAPTA. The Ca2+i response was also increased in a concentration manner when stimulated by RvE1. Inhibition of PLC, PLD, and PLA2, but not Ca2+/calmodulin-dependent kinase blocked RvE1-stimulated increase in [Ca2+]i and glycoconjugate secretion. We conclude that under normal, physiological conditions RvE1 stimulates multiple pathways to increase glycoconjugate secretion and [Ca2+]i. RvE1 could be an important regulator of goblet cell glycoconjugate mucin secretion to maintain ocular surface health.

Label-free quantitative proteomics of rat hypothalamus under fever induced by LPS and PGE2

Fever is a brain-mediated increase in body temperature mainly during inflammatory or infectious challenges. Although there is considerable data regarding the inflammation pathways involved in fever, metabolic alterations necessary to orchestrate the complex inflammatory response are not totally understood. We performed proteomic analysis of rat hypothalamus using label-free LC-MS/MS in a model of fever induced by lipopolysaccharide (LPS) or prostaglandin E₂ (PGE₂). In total, 7021 proteins were identified. As far as we know, this is the largest rat hypothalamus proteome dataset available to date. Pathway analysis showed proteins from both stimuli associated with inflammatory and metabolic pathways. Concerning metabolic pathways, rats exposed to LPS or PGE₂ presented lower relative abundance of proteins involved in glycolysis, pentose phosphate pathway and tricarboxylic acid cycle. Mitochondrial function may also be altered by both stimuli because significant downregulation of several proteins was found, mainly in complexes I and IV. LPS was able to induce downregulation of important proteins in the enzymatic antioxidant system, thereby contributing to oxidative stress. The results offered comprehensive information about fever responses and helped to reveal new insights into proteins potentially involved in inflammatory signaling and metabolic changes in the hypothalamus during systemic LPS and central PGE₂ administration.

SIGNIFICANCE

The evolutionary persistence of fever, despite the elevated cost for maintenance of this response, suggests that elevation in core temperature may represent an interesting strategy for survival. Fever response is achieved through the integrated behavioral, physiological, immunological and biochemical processes that determine the balance between heat generation and elimination. The development of such complex response arouses interest in studying how the cell metabolism responds or even contributes to promote fever. Our results offered comprehensive information about fever responses, including metabolic and inflammatory pathways, providing new insights into candidate proteins potentially involved in inflammatory signaling and metabolic changes in the hypothalamus during fever induced by systemic LPS and central PGE₂ perturbation.

Sevoflurane attenuates ventilator‑induced lung injury by regulating c‑PLA2 expression

The aim of the present study was to investigate the potential role of club cell secretory protein (CCSP), an endogenous modulator, in reducing pulmonary inflammation induced by sevoflurane following one‑lung ventilation (OLV). Healthy Japanese white rabbits were randomly assigned to six groups: Sham‑operated group (group S); respiratory management of OLV group (group O); OLV + sevoflurane treated group (group OF), club cells exfoliated + sham‑operated group (group NA), club cells exfoliated + OLV group (group NAO); and club cells exfoliated + OLV + sevoflurane treated group (group NAOF). At the end of the experimental observation, all animals in the different groups were sacrificed and lung injury was evaluated according to the lung wet/dry weight ratio and histological scoring system. Lung homogenates were harvested to detect the mRNA and protein expression of cytosolic phospholipase A2 (c‑PLA2) and CCSP. The content of arachidonic acid was measured using an ELISA. Following OLV treatment, c‑PLA2 expression was increased, CCSP expression was decreased and lung injury scores were significantly increased. Sevoflurane inhalation in the OLV‑treated group induced an upregulation of CCSP and a downregulation of c‑PLA2 expression. In the group NAO, in which the club cells were simultaneously exfoliated, OLV caused more severe lung damage and induced higher expression of c‑PLA2 compared with that in group O. However, sevoflurane inhalation reduced the extent of lung injury and the expression of c‑PLA2, even when the endogenous modulator of lung inflammation, CCSP, was exfoliated (group NAOF). These results indicated that OLV promoted lung inflammation through the CCSP and c‑PLA2 pathway. However, the results from the club cells exfoliated group indicated that the CCSP may not be involved in the protective effect exerted by sevoflurane inhalation.

Selectivity of phospholipid hydrolysis by phospholipase A2 enzymes in activated cells leading to polyunsaturated fatty acid mobilization

Phospholipase A₂s are enzymes that hydrolyze the fatty acid at the sn-2 position of the glycerol backbone of membrane glycerophospholipids. Given the asymmetric distribution of fatty acids within phospholipids, where saturated fatty acids tend to be present at the sn-1 position, and polyunsaturated fatty acids such as those of the omega-3 and omega-6 series overwhelmingly localize in the sn-2 position, the phospholipase A₂ reaction is of utmost importance as a regulatory checkpoint for the mobilization of these fatty acids and the subsequent synthesis of proinflammatory omega-6-derived eicosanoids on one hand, and omega-3-derived specialized pro-resolving mediators on the other. The great variety of phospholipase A₂s, their differential substrate selectivity under a variety of pathophysiological conditions, as well as the different compartmentalization of each enzyme and accessibility to substrate, render this class of enzymes also key to membrane phospholipid remodeling reactions, and the generation of specific lipid mediators not related with canonical metabolites of omega-6 or omega-3 fatty acids. This review highlights novel findings regarding the selective hydrolysis of phospholipids by phospholipase A₂s and the influence this may have on the ability of these enzymes to generate distinct lipid mediators with essential functions in biological processes. This brings a new understanding of the cellular roles of these enzymes depending upon activation conditions.

α-Synuclein and Polyunsaturated Fatty Acids: Molecular Basis of the Interaction and Implication in Neurodegeneration

α-Synuclein (α-syn) is a 140-amino acid protein, the physiological function of which has yet to be clarified. It is involved in several neurodegenerative disorders, and the interaction of the protein with brain lipids plays an important role in the pathogenesis of Parkinson’s disease (PD). Polyunsaturated fatty acids (PUFA) are highly abundant in the brain where they play critical roles in neuronal membrane fluidity and permeability, serve as energy reserves and function as second messengers in cell signaling. PUFA concentration and composition in the brain are altered with age when also an increase of lipid peroxidation is observed. Considering that PD is clearly correlated with oxidative stress, PUFA abundance and composition became of great interest in neurodegeneration studies because of PUFA’s high propensity to oxidize. The high levels of the PUFA docosahexaenoic acid (DHA) in brain areas containing α-syn inclusions in patients with PD further support the hypothesis of possible interactions between α-syn and DHA. Additionally, a possible functional role of α-syn in sequestering the early peroxidation products of fatty acids was recently proposed. Here, we provide an overview of the current knowledge regarding the molecular interactions between α-syn and fatty acids and the effect exerted by the protein on their oxidative state. We highlight recent findings supporting a neuroprotective role of the protein, linking α-syn, altered lipid composition in neurodegenerative disorders and PD development.

Ultrastructural variability of mitochondrial cristae induced in vitro by bee (Apis mellifera) venom and its derivatives, melittin and phospholipase A2, in isolated rat adrenocortical mitochondria

We tested the ability of bee venom (BV), melittin (Mlt), and phospholipase A2 (PLA) - used in 5 concentrations each (5, 10, 15, 20 and 40 μg/100 μl) - to promote ultrastructural changes and reorganization of cristae in vitro in mitochondria isolated from rat adrenal cortex after a protocol optimized by us. Thus, apart from two control grups (CI and CS), in which the mitochondria were suspended into saline buffer and isolation medium respectively, 15 more groups of mitochondria were constituted, corresponding to the five different doses of the three substance tested (BV5 to M40; M5 to M40 and P5 to P40). The ultrastructural effects were quantified on transmission electron micrographs using a morphometry software. Values of 84.49 nm and 95.45 nm were calculated for median diameters of mitochondrial cristae in two control groups. Large and very large vesicular cristae, many with 2 or 3 membranes, were generated depending on dose among normal cristae in all treated groups. In the BV and Mlt treated groups, after an initial increase (up to 127.27 nm in V15 group and 151.2 nm in M10 group) due to stimulation of cristae fusion, the cristae diameter diminished as the doses increased, mainly by the collapse of the cristae. In the PLA treated groups, the cristae diameter increased continuously from 83.84 nm to 136.01 nm, by stimulated fusion of cristae, only the two largest doses promoting the collapse of cristae in some mitochondria. The highest percentage of abnormal cristae was found in the Mlt treated groups and next in BV treated groups. All substances tested produced pronounced ultrastructural variability of mitochondrial cristae in vitro: they also changed (depending on dose) mitochondrial shapes, generated matrix debris and the highest concentrations of BV and Mlt were responsible for mitochondrial breakdown. These ultrastructural alterations of mitochondrial criste in the presence of the BV molecules suggest a reduced capacity of adrenocortical mitochondria to synthetize steroid hormones consequently to BV envenomations and partially explain the toxic effects of the BV.

Strong and sustained activation of the anticipatory unfolded protein response induces necrotic cell death

The endoplasmic reticulum stress sensor, the unfolded protein response (UPR), regulates intracellular protein homeostasis. While transient activation of the reactive UPR by unfolded protein is protective, prolonged and sustained activation of the reactive UPR triggers CHOP-mediated apoptosis. In the recently characterized, evolutionarily conserved anticipatory UPR, mitogenic hormones and other effectors pre-activate the UPR; how strong and sustained activation of the anticipatory UPR induces cell death was unknown. To characterize this cell death pathway, we used BHPI, a small molecule that activates the anticipatory UPR through estrogen receptor α (ERα) and induces death of ERα⁺ cancer cells. We show that sustained activation of the anticipatory UPR by BHPI kills cells by inducing depletion of intracellular ATP, resulting in classical necrosis phenotypes, including plasma membrane disruption and leakage of intracellular contents. Unlike reactive UPR activation, BHPI-induced hyperactivation of the anticipatory UPR does not induce apoptosis or sustained autophagy. BHPI does not induce CHOP protein or PARP cleavage, and two pan-caspase inhibitors, or Bcl2 overexpression, have no effect on BHPI-induced cell death. Moreover, BHPI does not increase expression of autophagy markers, or work through recently identified programmed-necrosis pathways, such as necroptosis. Opening of endoplasmic reticulum IP₃R calcium channels stimulates cell swelling, cPLA2 activation, and arachidonic acid release. Notably, cPLA2 activation requires ATP depletion. Importantly, blocking rapid cell swelling or production of arachidonic acid does not prevent necrotic cell death. Rapid cell death is upstream of PERK activation and protein synthesis inhibition, and results from strong and sustained activation of early steps in the anticipatory UPR. Supporting a central role for ATP depletion, reversing ATP depletion blocks rapid cell death, and the onset of necrotic cell death is correlated with ATP depletion. Necrotic cell death initiated by strong and sustained activation of the anticipatory UPR is a newly discovered role of the UPR.

Eicosanoid-mediated immunity in insects

Eicosanoid is a collective term for oxygenated metabolites of C20 polyunsaturated fatty acids. As seen in mammals, eicosanoids play crucial roles in mediating various physiological processes, including immune responses, in insects. Upon microbial pathogen infection, non-self recognition signals are propagated to nearly immune effectors such as hemocytes and fat body using various immune mediators, in which eicosanoid signals act as the ultimate downstream mediator. The chemical diversity of eicosanoids may operate to mediate various immune responses. Some entomopathogenic bacteria suppress eicosanoid biosynthesis, which inhibits host insect immunity and promotes their pathogenicity. This review introduces immune responses mediated by various eicosanoids. Then it explains the cross-talks of eicosanoids with other immune mediators including cytokines, biogenic monoamines, and nitric oxide to clarify the complexity of insect immune mediation. Finally, we highlight the biological significance of eicosanoids by demonstrating bacterial pathogenicity inhibiting a key enzyme - phospholipase A₂ - in eicosanoid biosynthesis using their secondary metabolites to defend host insect immune attack.

The role of the LTB4-BLT1 axis in chemotactic gradient sensing and directed leukocyte migration

Directed leukocyte migration is a hallmark of inflammatory immune responses. Leukotrienes are derived from arachidonic acid and represent a class of potent lipid mediators of leukocyte migration. In this review, we summarize the essential steps leading to the production of LTB₄ in leukocytes. We discuss the recent findings on the exosomal packaging and transport of LTB₄ in the context of chemotactic gradients formation and regulation of leukocyte recruitment. We also discuss the dynamic roles of the LTB₄ receptors, BLT1 and BLT2, in mediating chemotactic signaling in leukocytes and contrast them to other structurally related leukotrienes that bind to distinct GPCRs. Finally, we highlight the specific roles of the LTB₄-BLT1 axis in mediating signal-relay between chemotaxing neutrophils and its potential contribution to a wide variety of inflammatory conditions including tumor progression and metastasis, where LTB₄ is emerging as a key signaling component.

Differential immunosuppression by inhibiting PLA2 affects virulence of Xenorhabdus hominickii and Photorhabdus temperata temperata

Immunity negatively influences bacterial pathogenicity. Eicosanoids mediate both cellular and humoral immune responses in insects. This study tested a hypothesis that differential bacterial virulence of Xenorhabdus/Photorhabdus is dependent on their inhibitory activity against phospholipase A₂ (PLA₂) activity. P. temperata subsp. temperata ('Ptt') was more than 40 times more potent than X. hominickii ('Xh'). Although both bacteria suppressed cellular immune responses, Ptt infection suppressed hemocyte nodule formation much more than Xh infection. Their differential immunosuppression appeared to be induced by their secondary metabolites because organic extracts of Ptt-cultured broth exhibited higher inhibitory activities against cellular immune responses than Xn-cultured broth extracts. Humoral immune responses were analyzed by measuring expression levels of 11 antimicrobial peptide (AMP) genes. Among inducible AMPs in hemocytes and fat body, higher number and more kinds of AMPs exhibited lower expression levels in Ptt infection than those in Xh infection. Suppressed immune responses induced by Ptt or Xh infection were significantly rescued by the addition of a catalytic product of PLA₂, suggesting that PLA₂ was a common inhibitory target. In fact, Ptt infection inhibited PLA₂ activity more strongly than Xh infection. RNA interference of a PLA₂ gene decreased its expression and significantly increased bacterial virulence. Moreover, addition of PLA₂ inhibitor to Xh infection enhanced its virulence, similar to virulence level of Ptt infection. These results suggest that variation in Xenorhabdus/Photorhabdus bacterial virulence can be explained by their differential inhibitory activities against host insect PLA₂.

The phospholipase A2 activity of peroxiredoxin 6

Peroxiredoxin 6 (Prdx6) is a Ca²⁺-independent intracellular phospholipase A₂ (called aiPLA₂) that is localized to cytosol, lysosomes, and lysosomal-related organelles. Activity is minimal at cytosolic pH but is increased significantly with enzyme phosphorylation, at acidic pH, and in the presence of oxidized phospholipid substrate; maximal activity with phosphorylated aiPLA₂ is ∼2 µmol/min/mg protein. Prdx6 is a "moonlighting" protein that also expresses glutathione peroxidase and lysophosphatidylcholine acyl transferase activities. The catalytic site for aiPLA₂ activity is an S32-H26-D140 triad; S32-H26 is also the phospholipid binding site. Activity is inhibited by a serine "protease" inhibitor (diethyl p-nitrophenyl phosphate), an analog of the PLA₂ transition state [1-hexadecyl-3-(trifluoroethyl)-sn-glycero-2-phosphomethanol (MJ33)], and by two naturally occurring proteins (surfactant protein A and p67^phox), but not by bromoenol lactone. aiPLA₂ activity has important physiological roles in the turnover (synthesis and degradation) of lung surfactant phospholipids, in the repair of peroxidized cell membranes, and in the activation of NADPH oxidase type 2 (NOX2). The enzyme has been implicated in acute lung injury, carcinogenesis, neurodegenerative diseases, diabetes, male infertility, and sundry other conditions, although its specific roles have not been well defined. Protein mutations and animal models are now available to further investigate the roles of Prdx6-aiPLA₂ activity in normal and pathological physiology.