Group X Secreted Phospholipase A2 Limits the Development of Atherosclerosis in LDL Receptor–Null Mice

Up-regulated PLA2G10 in cancer impairs T cell infiltration to dampen immunity

T cells are often absent from human cancer tissues during both spontaneously induced immunity and therapeutic immunotherapy, even in the presence of a functional T cell-recruiting chemokine system, suggesting the existence of T cell exclusion mechanisms that impair infiltration. Using a genome-wide in vitro screening platform, we identified a role for phospholipase A2 group 10 (PLA2G10) protein in T cell exclusion. PLA2G10 up-regulation is widespread in human cancers and is associated with poor T cell infiltration in tumor tissues. PLA2G10 overexpression in immunogenic mouse tumors excluded T cells from infiltration, resulting in resistance to anti-PD-1 immunotherapy. PLA2G10 can hydrolyze phospholipids into small lipid metabolites, thus inhibiting chemokine-mediated T cell mobility. Ablation of PLA2G10's enzymatic activity enhanced T cell infiltration and sensitized PLA2G10-overexpressing tumors to immunotherapies. Our study implicates a role for PLA2G10 in T cell exclusion from tumors and suggests a potential target for cancer immunotherapy.

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.

Response of gut microbiota and ileal transcriptome to inulin intervention in HFD induced obese mice

Inulin, as a dietary fiber, exerted prominent anti-obesity effects by modulating gut microbiota. However, the possible relationship and interplay of gut microbiome and function of distal intestine is still unclear now. This study aimed to investigate the possible targets of microbes and the related intestinal genes mediated by inulin. C57 BL/6 male mice were randomly allocated to chow diet (Chow) group, high-fat diet (HFD) group, and HFD supplemented with 3 % inulin (Inulin) group. Compared with HFD treatment, inulin supplementation significantly decreased the body weight, fat deposition, and fasting blood glucose level. In addition, mice treated with inulin had a remarkable alteration in the structure of cecal microbiota and transcriptomic profiling of ileum. In particular, inulin supplementation significantly reversed the HFD induced expression of Bacteroides, Allobaculum and nonrank_f_Bacteroidates_S24-7_group, and reversed the expression of genes belonging to phospholipase A2 (PLA2) family and cytochrome P450 (CYP450) family. In summary, inulin might alleviate HFD-induced fat deposition and metabolic disorders via regulating lipid metabolism of ileum, while the interaction between the sPLA2s and gut microbes might play important roles in the process.

Regulatory Roles of Phospholipase A2 Enzymes and Bioactive Lipids in Mast Cell Biology

Lipids play fundamental roles in life as an essential component of cell membranes, as a major source of energy, as a body surface barrier, and as signaling molecules that transmit intracellular and intercellular signals. Lipid mediators, a group of bioactive lipids that mediates intercellular signals, are produced via specific biosynthetic enzymes and transmit signals via specific receptors. Mast cells, a tissue-resident immune cell population, produce several lipid mediators that contribute to exacerbation or amelioration of allergic responses and also non-allergic inflammation, host defense, cancer and fibrosis by controlling the functions of microenvironmental cells as well as mast cell themselves in paracrine and autocrine fashions. Additionally, several bioactive lipids produced by stromal cells regulate the differentiation, maturation and activation of neighboring mast cells. Many of the bioactive lipids are stored in membrane phospholipids as precursor forms and released spatiotemporally by phospholipase A₂ (PLA₂) enzymes. Through a series of studies employing gene targeting and lipidomics, several enzymes belonging to the PLA₂ superfamily have been demonstrated to participate in mast cell-related diseases by mobilizing unique bioactive lipids in multiple ways. In this review, we provide an overview of our current understanding of the regulatory roles of several PLA₂-driven lipid pathways in mast cell biology.

Old but New: Group IIA Phospholipase A2 as a Modulator of Gut Microbiota

Among the phospholipase A₂ (PLA₂) superfamily, the secreted PLA₂ (sPLA₂) family contains 11 mammalian isoforms that exhibit unique tissue or cellular distributions and enzymatic properties. Current studies using sPLA₂-deficient or -overexpressed mouse strains, along with mass spectrometric lipidomics to determine sPLA₂-driven lipid pathways, have revealed the diverse pathophysiological roles of sPLA₂s in various biological events. In general, individual sPLA₂s exert their specific functions within tissue microenvironments, where they are intrinsically expressed through hydrolysis of extracellular phospholipids. Recent studies have uncovered a new aspect of group IIA sPLA₂ (sPLA₂-IIA), a prototypic sPLA₂ with the oldest research history among the mammalian PLA₂s, as a modulator of the gut microbiota. In the intestine, Paneth cell-derived sPLA₂-IIA acts as an antimicrobial protein to shape the gut microbiota, thereby secondarily affecting inflammation, allergy, and cancer in proximal and distal tissues. Knockout of intestinal sPLA₂-IIA in BALB/c mice leads to alterations in skin cancer, psoriasis, and anaphylaxis, while overexpression of sPLA₂-IIA in Pla2g2a-null C57BL/6 mice induces systemic inflammation and exacerbates arthritis. These phenotypes are associated with notable changes in gut microbiota and fecal metabolites, are variable in different animal facilities, and are abrogated after antibiotic treatment, co-housing, or fecal transfer. These studies open a new mechanistic action of this old sPLA₂ and add the sPLA₂ family to the growing list of endogenous factors capable of affecting the microbe–host interaction and thereby systemic homeostasis and diseases.

Gowda SG, Ikeda K, Arita M, Murakami M. Group IIA secreted phospholipase A2 controls skin carcinogenesis and psoriasis by shaping the gut microbiota

Besides promoting inflammation by mobilizing lipid mediators, group IIA secreted phospholipase A₂ (sPLA₂-IIA) prevents bacterial infection by degrading bacterial membranes. Here, we show that, despite the restricted intestinal expression of sPLA₂-IIA in BALB/c mice, its genetic deletion leads to amelioration of cancer and exacerbation of psoriasis in distal skin. Intestinal expression of sPLA₂-IIA is reduced after treatment with antibiotics or under germ-free conditions, suggesting its upregulation by gut microbiota. Metagenome, transcriptome, and metabolome analyses have revealed that sPLA₂-IIA deficiency alters the gut microbiota, accompanied by notable changes in the intestinal expression of genes related to immunity and metabolism, as well as in the levels of various blood metabolites and fecal bacterial lipids, suggesting that sPLA₂-IIA contributes to shaping of the gut microbiota. The skin phenotypes in Pla2g2a^–/– mice are lost (a) when they are cohoused with littermate WT mice, resulting in the mixing of the microbiota between the genotypes, or (b) when they are housed in a more stringent pathogen-free facility, where Pla2g2a expression in WT mice is low and the gut microbial compositions in both genotypes are nearly identical. Thus, our results highlight a potentially new aspect of sPLA₂-IIA as a modulator of gut microbiota, perturbation of which affects distal skin responses.

Lipid Droplets, Phospholipase A2, Arachidonic Acid, and Atherosclerosis

Lipid droplets, classically regarded as static storage organelles, are currently considered as dynamic structures involved in key processes of lipid metabolism, cellular homeostasis and signaling. Studies on the inflammatory state of atherosclerotic plaques suggest that circulating monocytes interact with products released by endothelial cells and may acquire a foamy phenotype before crossing the endothelial barrier and differentiating into macrophages. One such compound released in significant amounts into the bloodstream is arachidonic acid, the common precursor of eicosanoids, and a potent inducer of neutral lipid synthesis and lipid droplet formation in circulating monocytes. Members of the family of phospholipase A₂, which hydrolyze the fatty acid present at the sn-2 position of phospholipids, have recently emerged as key controllers of lipid droplet homeostasis, regulating their formation and the availability of fatty acids for lipid mediator production. In this paper we discuss recent findings related to lipid droplet dynamics in immune cells and the ways these organelles are involved in regulating arachidonic acid availability and metabolism in the context of atherosclerosis.

RNA sequencing of blood in coronary artery disease: involvement of regulatory T cell imbalance

BACKGROUND

Cardiovascular disease had a global prevalence of 523 million cases and 18.6 million deaths in 2019. The current standard for diagnosing coronary artery disease (CAD) is coronary angiography. Surprisingly, despite well-established clinical indications, up to 40% of the one million invasive cardiac catheterizations return a result of 'no blockage'. The present studies employed RNA sequencing of whole blood to identify an RNA signature in patients with angiographically confirmed CAD.

METHODS

Whole blood RNA was depleted of ribosomal RNA (rRNA) and analyzed by single-molecule sequencing of RNA (RNAseq) to identify transcripts associated with CAD (TRACs) in a discovery group of 96 patients presenting for elective coronary catheterization. The resulting transcript counts were compared between groups to identify differentially expressed genes (DEGs).

RESULTS

Surprisingly, 98% of DEGs/TRACs were down-regulated ~ 1.7-fold in patients with mild to severe CAD (> 20% stenosis). The TRACs were independent of comorbid risk factors for CAD, such as sex, hypertension, and smoking. Bioinformatic analysis identified an enrichment in transcripts such as FoxP1, ICOSLG, IKZF4/Eos, SMYD3, TRIM28, and TCF3/E2A that are likely markers of regulatory T cells (Treg), consistent with known reductions in Tregs in CAD. A validation cohort of 80 patients confirmed the overall pattern (92% down-regulation) and supported many of the Treg-related changes. TRACs were enriched for transcripts associated with stress granules, which sequester RNAs, and ciliary and synaptic transcripts, possibly consistent with changes in the immune synapse of developing T cells.

CONCLUSIONS

These studies identify a novel mRNA signature of a Treg-like defect in CAD patients and provides a blueprint for a diagnostic test for CAD. The pattern of changes is consistent with stress-related changes in the maturation of T and Treg cells, possibly due to changes in the immune synapse.

Imaging and Targeting Coronary Artery Inflammation

Significance: Coronary artery disease (CAD) continues to be a leading cause of morbidity and mortality across the world despite significant progress in the prevention, diagnosis, and treatment of atherosclerotic disease. Recent Advances: The focus of the cardiovascular community has shifted toward seeking a better understanding of the inflammatory mechanisms driving residual CAD risk that is not modulated by current therapies. Significant progress has been achieved in revealing both proinflammatory and anti-inflammatory mechanisms, and how shift of the balance in favor of the former can drive the development of disease. Critical Issues: Advances in the noninvasive detection of coronary artery inflammation have been forthcoming. These advances include multiple imaging modalities, with novel applications of computed tomography both with and without positron emission tomography, and experimental ultrasound techniques. These advances will enable better selection of patients for anti-inflammatory treatments and assessment of treatment response. The rapid advancement in pharmaceutical design has enabled the production of specific antibodies against inflammatory pathways of atherosclerosis, with modest success to date. The pursuit of demonstrating the efficacy and safety of novel anti-inflammatory and/or proinflammatory resolution therapies for atherosclerotic CAD has become a major focus. Future Directions: This review seeks to provide an update of the latest evidence of all three of these highly related but disparate areas of inquiry: Our current understanding of the key mechanisms by which inflammation contributes to coronary artery atherosclerosis, the evidence for noninvasive assessment of coronary artery inflammation, and finally, the evidence for targeted therapies to treat coronary inflammation for the reduction of CAD risk. Antioxid. Redox Signal. 34, 1217-1243.

Lysophosphatidylcholine in phospholipase A2-modified LDL triggers secretion of angiopoietin 2

BACKGROUND AND AIMS

Secretory phospholipase A₂ (PLA₂) hydrolyzes LDL phospholipids generating modified LDL particles (PLA₂-LDL) with increased atherogenic properties. Exocytosis of Weibel-Palade bodies (WPB) releases angiopoietin 2 (Ang2) and externalizes P-selectin, which both play important roles in vascular inflammation. Here, we investigated the effects of PLA₂-LDL on exocytosis of WPBs.

METHODS

Human coronary artery endothelial cells (HCAECs) were stimulated with PLA₂- LDL, and its uptake and effect on Ang2 release, leukocyte adhesion, and intracellular calcium levels were measured. The effects of PLA₂-LDL on Ang2 release and WPB exocytosis were measured in and ex vivo in mice.

RESULTS

Exposure of HCAECs to PLA₂-LDL triggered Ang2 secretion and promoted leukocyte-HCAEC interaction. Lysophosphatidylcholine was identified as a critical component of PLA₂-LDL regulating the WPB exocytosis, which was mediated by cell-surface proteoglycans, phospholipase C, intracellular calcium, and cytoskeletal remodeling. PLA₂-LDL also induced murine endothelial WPB exocytosis in blood vessels in and ex vivo, as evidenced by secretion of Ang2 in vivo, P-selectin translocation to plasma membrane in intact endothelial cells in thoracic artery and tracheal vessels, and reduced Ang2 staining in tracheal endothelial cells. Finally, in contrast to normal human coronary arteries, in which Ang2 was present only in the endothelial layer, at sites of advanced atherosclerotic lesions, Ang2 was detected also in the intima, media, and adventitia.

CONCLUSIONS

Our studies reveal PLA₂-LDL as a potent agonist of endothelial WPB exocytosis, resulting in increased secretion of Ang2 and translocation of P-selectin. The results provide mechanistic insight into PLA₂-LDL-dependent promotion of vascular inflammation and atherosclerosis.

On the present and future role of Lp-PLA2 in atherosclerosis-related cardiovascular risk prediction and management

Circulating concentration and activity of secretory phospholipase A₂ (sPLA₂) and lipoprotein-associated phospholipase A₂ (Lp-PLA₂) have been proven as biomarkers of increased risk of atherosclerosis-related cardiovascular disease (ASCVD). Lp-PLA₂ might be part of the atherosclerotic process and may contribute to plaque destabilisation through inflammatory activity within atherosclerotic lesions. However, all attempts to translate the inhibition of phospholipase into clinically beneficial ASCVD risk reduction, including in randomised studies, by either non-specific inhibition of sPLA₂ (by varespladib) or specific Lp-PLA₂ inhibition by darapladib, unexpectedly failed. This gives us a strong imperative to continue research aimed at a better understanding of how Lp-PLA₂ and sPLA₂ regulate vascular inflammation and atherosclerotic plaque development. From the clinical viewpoint there is a need to establish and validate the existing and emerging novel anti-inflammatory therapeutic strategies to fight against ASCVD development, by using potentially better animal models and differently designed clinical trials in humans.

Updating Phospholipase A2 Biology

The phospholipase A2 (PLA2) superfamily contains more than 50 enzymes in mammals that are subdivided into several distinct families on a structural and biochemical basis. In principle, PLA2 has the capacity to hydrolyze the sn-2 position of glycerophospholipids to release fatty acids and lysophospholipids, yet several enzymes in this superfamily catalyze other reactions rather than or in addition to the PLA2 reaction. PLA2 enzymes play crucial roles in not only the production of lipid mediators, but also membrane remodeling, bioenergetics, and body surface barrier, thereby participating in a number of biological events. Accordingly, disturbance of PLA2-regulated lipid metabolism is often associated with various diseases. This review updates the current state of understanding of the classification, enzymatic properties, and biological functions of various enzymes belonging to the PLA2 superfamily, focusing particularly on the novel roles of PLA2s in vivo.

Group V secreted phospholipase A2 plays a protective role against aortic dissection

Aortic dissection is a life-threatening aortopathy involving separation of the aortic wall, whose underlying mechanisms are still incompletely understood. Epidemiological evidence suggests that unsaturated fatty acids improve cardiovascular health. Here, using quantitative RT-PCR, histological analyses, magnetic cell sorting and flow cytometry assays, and MS-based lipidomics, we show that the activity of a lipid-metabolizing enzyme, secreted phospholipase A₂ group V (sPLA₂-V), protects against aortic dissection by endogenously mobilizing vasoprotective lipids. Global and endothelial cell-specific sPLA₂-V-deficient mice frequently developed aortic dissection shortly after infusion of angiotensin II (AT-II). We observed that in the AT-II-treated aorta, endothelial sPLA₂-V mobilized oleic and linoleic acids, which attenuated endoplasmic reticulum stress, increased the expression of lysyl oxidase, and thereby stabilized the extracellular matrix in the aorta. Of note, dietary supplementation with oleic or linoleic acid reversed the increased susceptibility of sPLA₂-V-deficient mice to aortic dissection. These findings reveal an unexplored functional link between sPLA₂-driven phospholipid metabolism and aortic stability, possibly contributing to the development of improved diagnostic and/or therapeutic strategies for preventing aortic dissection.

Group IIA Secretory Phospholipase A2, Vascular Inflammation, and Incident Cardiovascular Disease

Objective- Inflammation is a causal risk factor for cardiovascular disease (CVD). sPLA₂-IIA (group IIA secretory phospholipase A₂) plays an integral role in regulating vascular inflammation. Although studies investigated sPLA₂-IIA in secondary prevention, we prospectively evaluated sPLA₂-IIA mass and genetic variants with CVD events in a primary prevention population with chronic inflammation. Approach and Results- The JUPITER trial (Justification for the Use of Statins in Prevention: An Intervention Trial Evaluating Rosuvastatin) randomized participants with LDL (low-density lipoprotein) <130 mg/dL and hsCRP (high-sensitivity C-reactive protein) ≥2 mg/L to high-intensity rosuvastatin versus placebo. Baseline and 1-year plasma sPLA₂-IIA mass was measured (N=11 269 baseline; N=9620 1 year). We also identified genetic variants influencing sPLA₂-IIA using genome-wide association and examined them with CVD. Three hundred thirteen incident CVD events occurred during follow-up. Baseline sPLA₂-IIA mass (median, 25th-75th percentile: 3.81, 2.49-6.03 ng/mL) was associated with increased risk of CVD: risk factor-adjusted hazard ratio (95% CI; P) per SD increment: 1.22 (1.08-1.38; P=0.002). This remained significant (1.18; 1.04-1.35; P=0.01) after incrementally adjusting for hsCRP. Similar estimates were observed in rosuvastatin and placebo groups ( P treatment interaction>0.05). The rs11573156C variant in PLA2G2A (encoding sPLA₂-IIA) had the strongest effect on sPLA₂-II: median (25th-75th percentile, ng/mL) for CC and GG genotypes: 2.79 (1.97-4.01) and 7.38 (5.38-10.19), respectively; and had nonsignificant trend for higher CVD risk (hazard ratio, 1.11; 95% CI, 0.89-1.38; P=0.34). Conclusions- In the JUPITER population recruited on chronic inflammation, sPLA₂-IIA mass was associated with CVD risk relating to vascular inflammation not fully reflected by hsCRP. Additional studies, including larger functional genetic and clinical studies, are needed to determine whether sPLA₂-IIA may be a potential pharmacological target for primary prevention of CVD. Clinical Trial Registration- URL: http://www.clinicaltrials.gov . Unique identifier: NCT00239681.

Antimalarial Activity of Human Group IIA Secreted Phospholipase A2 in Relation to Enzymatic Hydrolysis of Oxidized Lipoproteins

The level of human group IIA secreted phospholipase A₂ (hGIIA sPLA₂) is increased in the plasma of malaria patients, but its role is unknown. In parasite culture with normal plasma, hGIIA is inactive against Plasmodium falciparum, contrasting with hGIIF, hGV, and hGX sPLA₂s, which readily hydrolyze plasma lipoproteins, release nonesterified fatty acids (NEFAs), and inhibit parasite growth. Here, we revisited the anti-Plasmodium activity of hGIIA under conditions closer to those of malaria physiopathology where lipoproteins are oxidized. In parasite culture containing oxidized lipoproteins, hGIIA sPLA₂ was inhibitory, with a 50% inhibitory concentration value of 150.0 ± 40.8 nM, in accordance with its capacity to release NEFAs from oxidized particles. With oxidized lipoproteins, hGIIF, hGV, and hGX sPLA₂s were also more potent, by 4.6-, 2.1-, and 1.9-fold, respectively. Using specific immunoassays, we found that hGIIA sPLA₂ is increased in plasma from 41 patients with malaria over levels for healthy donors (median [interquartile range], 1.6 [0.7 to 3.4] nM versus 0.0 [0.0 to 0.1] nM, respectively; P < 0.0001). Other sPLA₂s were not detected. Malaria plasma, but not normal plasma, contains oxidized lipoproteins and was inhibitory to P. falciparum when spiked with hGIIA sPLA₂ Injection of recombinant hGIIA into mice infected with P. chabaudi reduced the peak of parasitemia, and this was effective only when the level of plasma peroxidation was increased during infection. In conclusion, we propose that malaria-induced oxidation of lipoproteins converts these into a preferential substrate for hGIIA sPLA₂, promoting its parasite-killing effect. This mechanism may contribute to host defense against P. falciparum in malaria where high levels of hGIIA are observed.

HDL Phospholipids, but Not Cholesterol Distinguish Acute Coronary Syndrome From Stable Coronary Artery Disease

Background Although acute coronary syndromes (ACS) are a major cause of morbidity and mortality, relationships with biologically active lipid species potentially associated with plaque disruption/erosion in the context of their lipoprotein carriers are indeterminate. The aim was to characterize lipid species within lipoprotein particles which differentiate ACS from stable coronary artery disease. Methods and Results Venous blood was obtained from 130 individuals with de novo presentation of an ACS (n=47) or stable coronary artery disease (n=83) before coronary catheterization. Lipidomic measurements (533 lipid species; liquid chromatography electrospray ionization/tandem mass spectrometry) were performed on whole plasma as well as 2 lipoprotein subfractions: apolipoprotein A1 (apolipoprotein A, high-density lipoprotein) and apolipoprotein B. Compared with stable coronary artery disease, ACS plasma was lower in phospholipids including lyso species and plasmalogens, with the majority of lipid species differing in abundance located within high-density lipoprotein (high-density lipoprotein, 113 lipids; plasma, 73 lipids). Models including plasma lipid species alone improved discrimination between the stable and ACS groups by 0.16 (C-statistic) compared with conventional risk factors. Models utilizing lipid species either in plasma or within lipoprotein fractions had a similar ability to discriminate groups, though the C-statistic was highest for plasma lipid species (0.80; 95% CI, 0.75-0.86). Conclusions Multiple lysophospholipids, but not cholesterol, featured among the lipids which were present at low concentration within high-density lipoprotein of those presenting with ACS. Lipidomics, when applied to either whole plasma or lipoprotein fractions, was superior to conventional risk factors in discriminating ACS from stable coronary artery disease. These associative mechanistic insights elucidate potential new preventive, prognostic, and therapeutic avenues for ACS which require investigation in prospective analyses.

Group IID, IIE, IIF and III secreted phospholipase A2s

Among the 11 members of the secreted phospholipase A₂ (sPLA₂) family, group IID, IIE, IIF and III sPLA₂s (sPLA₂-IID, -IIE, -IIF and -III, respectively) are “new” isoforms in the history of sPLA₂ research. Relative to the better characterized sPLA₂s (sPLA₂-IB, -IIA, -V and -X), the enzymatic properties, distributions, and functions of these “new” sPLA₂s have remained obscure until recently. Our current studies using knockout and transgenic mice for a nearly full set of sPLA₂s, in combination with comprehensive lipidomics, have revealed unique and distinct roles of these “new” sPLA₂s in specific biological events. Thus, sPLA₂-IID is involved in immune suppression, sPLA₂-IIE in metabolic regulation and hair follicle homeostasis, sPLA₂-IIF in epidermal hyperplasia, and sPLA₂-III in male reproduction, anaphylaxis, colonic diseases, and possibly atherosclerosis. In this article, we overview current understanding of the properties and functions of these sPLA₂s and their underlying lipid pathways in vivo.

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.

Design of Selective sPLA2-X Inhibitor (-)-2-{2-[Carbamoyl-6-(trifluoromethoxy)-1H-indol-1-yl]pyridine-2-yl}propanoic Acid

A lead generation campaign identified indole-based sPLA₂-X inhibitors with a promising selectivity profile against other sPLA₂ isoforms. Further optimization of sPLA₂ selectivity and metabolic stability resulted in the design of (-)-17, a novel, potent, and selective sPLA₂-X inhibitor with an exquisite pharmacokinetic profile characterized by high absorption and low clearance, and low toxicological risk. Compound (-)-17 was tested in an ApoE^-/- murine model of atherosclerosis to evaluate the effect of reversible, pharmacological sPLA₂-X inhibition on atherosclerosis development. Despite being well tolerated and achieving adequate systemic exposure of mechanistic relevance, (-)-17 did not significantly affect circulating lipid and lipoprotein biomarkers and had no effect on coronary function or histological markers of atherosclerosis.

Association between polymorphisms in SLC15A1 and PLA2G16 genes and development of obesity in Chinese subjects

INTRODUCTION

The small peptide transporter 1 (PepT-1) and adipose phospholipase A2 (AdPLA) play a key role in the development of obesity. However, there are no data assessing the impact of PepT-1 (SLC15A1) and AdPLA (PLA2G16) variants on obesity susceptibility. Therefore, we assessed the contribution of 9 single-nucleotide polymorphisms (SNPs) between these two genes on obesity susceptibility in Chinese subjects.

MATERIALS AND METHODS

A total of 611 participants were enrolled in the study, and 9 SNPs in the SLC15A1 and PLA2G16 genes were selected. Blood samples were collected for genotyping. Overweight and obesity were established by body mass index. Regression analyses were performed to test for any association of genetic polymorphisms with weight abnormality.

RESULTS

The genotype frequencies (P=0.04 for rs9557029, P=0.027 for rs1289389) were significantly different between obese or overweight subjects and healthy controls. However, no significant difference in allele was found between these three groups (P>0.05). Further logistic regression analyses adjusted for age and sex also failed to reveal significant associations between overweight, obesity, and the selected SNPs (P>0.05).

CONCLUSION

Data indicate that the selected 9 SNPs in SLC15A1 and PLA2G16 genes were not related to obesity susceptibility in the Han Chinese population.

Secretory phospholipase A2 modified HDL rapidly and potently suppresses platelet activation

Levels of secretory phospholipases A₂ (sPLA₂) highly increase under acute and chronic inflammatory conditions. sPLA₂ is mainly associated with high-density lipoproteins (HDL) and generates bioactive lysophospholipids implicated in acute and chronic inflammatory processes. Unexpectedly, pharmacological inhibition of sPLA₂ in patients with acute coronary syndrome was associated with an increased risk of myocardial infarction and stroke. Given that platelets are key players in thrombosis and inflammation, we hypothesized that sPLA₂-induced hydrolysis of HDL-associated phospholipids (sPLA₂-HDL) generates modified HDL particles that affect platelet function. We observed that sPLA₂-HDL potently and rapidly inhibited platelet aggregation induced by several agonists, P-selectin expression, GPIIb/IIIa activation and superoxide production, whereas native HDL showed little effects. sPLA₂-HDL suppressed the agonist-induced rise of intracellular Ca²⁺ levels and phosphorylation of Akt and ERK1/2, which trigger key steps in promoting platelet activation. Importantly, sPLA₂ in the absence of HDL showed no effects, whereas enrichment of HDL with lysophosphatidylcholines containing saturated fatty acids (the main sPLA₂ products) mimicked sPLA₂-HDL activities. Our findings suggest that sPLA₂ generates lysophosphatidylcholine-enriched HDL particles that modulate platelet function under inflammatory conditions.

The Therapeutic Potential of Anti-Inflammatory Exerkines in the Treatment of Atherosclerosis

Although many cardiovascular (CVD) medications, such as antithrombotics, statins, and antihypertensives, have been identified to treat atherosclerosis, at most, many of these therapeutic agents only delay its progression. A growing body of evidence suggests physical exercise could be implemented as a non-pharmacologic treatment due to its pro-metabolic, multisystemic, and anti-inflammatory benefits. Specifically, it has been discovered that certain anti-inflammatory peptides, metabolites, and RNA species (collectively termed “exerkines”) are released in response to exercise that could facilitate these benefits and could serve as potential therapeutic targets for atherosclerosis. However, much of the relationship between exercise and these exerkines remains unanswered, and there are several challenges in the discovery and validation of these exerkines. This review primarily highlights major anti-inflammatory exerkines that could serve as potential therapeutic targets for atherosclerosis. To provide some context and comparison for the therapeutic potential of exerkines, the anti-inflammatory, multisystemic benefits of exercise, the basic mechanisms of atherosclerosis, and the limited efficacies of current anti-inflammatory therapeutics for atherosclerosis are briefly summarized. Finally, key challenges and future directions for exploiting these exerkines in the treatment of atherosclerosis are discussed.

Targeting inflammation to reduce cardiovascular disease risk: a realistic clinical prospect?

Data from basic science experiments is overwhelmingly supportive of the causal role of immune-inflammatory response(s) at the core of atherosclerosis, and therefore, the theoretical potential to manipulate the inflammatory response to prevent cardiovascular events. However, extrapolation to humans requires care and we still lack definitive evidence to show that interfering in immune-inflammatory processes may safely lessen clinical atherosclerosis. In this review, we discuss key therapeutic targets in the treatment of vascular inflammation, placing basic research in a wider clinical perspective, as well as identifying outstanding questions.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Mendelian Randomization Analyses for Selection of Therapeutic Targets for Cardiovascular Disease Prevention: a Note of Circumspection

Genetic factors identified from genome-wide association studies have been used to understand causative variants for complex diseases. Studies conducted on large populations of individuals from many geographical regions have provided insights into genetic pathways involved in the causal pathway for atherosclerotic cardiovascular disease. A single genetic trait may ineffectively evaluate the pathway of interest, and it may not account for other complementary genetic pathways that may be activated at various stages of the disease process or evidence-based therapies that alter the molecular and cellular milieu.

Immune-mediated mechanisms of atherosclerosis and implications for the clinic

INTRODUCTION

A large body of evidence supports the inflammatory hypothesis of atherosclerosis, and both innate and adaptive immune responses play important roles in all disease stages. Areas covered: Here, we review our understanding of the role of the immune response in atherosclerosis, focusing on the pathways currently amenable to therapeutic modulation. We also discuss the advantages or undesirable effects that may be foreseen from targeting the immune response in patients at high cardiovascular risk, suggesting new avenues for research. Expert commentary: There is an extraordinary opportunity to directly test the inflammatory hypothesis of atherosclerosis in the clinic using currently available therapeutics. However, a more balanced interpretation of the experimental and translational data is needed, which may help address and identify in more detail the appropriate settings where an immune pathway can be targeted with minimal risk.

The Roles of the Secreted Phospholipase A2 Gene Family in Immunology

Within the phospholipase A₂ (PLA₂) family that hydrolyzes phospholipids to yield fatty acids and lysophospholipids, secreted PLA₂ (sPLA₂) enzymes comprise the largest group containing 11 isoforms in mammals. Individual sPLA₂s exhibit unique tissue or cellular distributions and enzymatic properties, suggesting their distinct biological roles. Although PLA₂ enzymes, particularly cytosolic PLA₂ (cPLA₂α), have long been implicated in inflammation by driving arachidonic acid metabolism, the precise biological roles of sPLA₂s have remained a mystery over the last few decades. Recent studies employing mice gene-manipulated for individual sPLA₂s, in combination with mass spectrometric lipidomics to identify their target substrates and products in vivo, have revealed their roles in diverse biological events, including immunity and associated disorders, through lipid mediator-dependent or -independent processes in given microenvironments. In this review, we summarize our current knowledge of the roles of sPLA₂s in various immune responses and associated diseases.

Group X Secreted Phospholipase A2 Releases ω3 Polyunsaturated Fatty Acids, Suppresses Colitis, and Promotes Sperm Fertility

Within the secreted phospholipase A2(sPLA2) family, group X sPLA2(sPLA2-X) has the highest capacity to hydrolyze cellular membranes and has long been thought to promote inflammation by releasing arachidonic acid, a precursor of pro-inflammatory eicosanoids. Unexpectedly, we found that transgenic mice globally overexpressing human sPLA2-X (PLA2G10-Tg) displayed striking immunosuppressive and lean phenotypes with lymphopenia and increased M2-like macrophages, accompanied by marked elevation of free ω3 polyunsaturated fatty acids (PUFAs) and their metabolites. Studies usingPla2g10-deficient mice revealed that endogenous sPLA2-X, which is highly expressed in the colon epithelium and spermatozoa, mobilized ω3 PUFAs or their metabolites to protect against dextran sulfate-induced colitis and to promote fertilization, respectively. In colitis, sPLA2-X deficiency increased colorectal expression of Th17 cytokines, and ω3 PUFAs attenuated their production by lamina propria cells partly through the fatty acid receptor GPR120. In comparison, cytosolic phospholipase A2(cPLA2α) protects from colitis by mobilizing ω6 arachidonic acid metabolites, including prostaglandin E2 Thus, our results underscore a previously unrecognized role of sPLA2-X as an ω3 PUFA mobilizerin vivo, segregated mobilization of ω3 and ω6 PUFA metabolites by sPLA2-X and cPLA2α, respectively, in protection against colitis, and the novel role of a particular sPLA2-X-driven PUFA in fertilization.

The role of group IIF-secreted phospholipase A2 in epidermal homeostasis and hyperplasia

Yamamoto et al. report that PLA2G2F represents a previously unrecognized regulator of skin pathophysiology, and point to this enzyme as a novel drug target for epidermal-hyperplasic diseases.

Epidermal lipids are important for skin homeostasis. However, the entire picture of the roles of lipids, particularly nonceramide lipid species, in epidermal biology still remains obscure. Here, we report that PLA2G2F, a functionally orphan-secreted phospholipase A₂ expressed in the suprabasal epidermis, regulates skin homeostasis and hyperplasic disorders. Pla2g2f^−/− mice had a fragile stratum corneum and were strikingly protected from psoriasis, contact dermatitis, and skin cancer. Conversely, Pla2g2f-overexpressing transgenic mice displayed psoriasis-like epidermal hyperplasia. Primary keratinocytes from Pla2g2f^−/− mice showed defective differentiation and activation. PLA2G2F was induced by calcium or IL-22 in keratinocytes and preferentially hydrolyzed ethanolamine plasmalogen-bearing docosahexaenoic acid secreted from keratinocytes to give rise to unique bioactive lipids (i.e., protectin D1 and 9S-hydroxyoctadecadienoic acid) that were distinct from canonical arachidonate metabolites (prostaglandins and leukotrienes). Ethanolamine lysoplasmalogen, a PLA2G2F-derived marker product, rescued defective activation of Pla2g2f^−/− keratinocytes both in vitro and in vivo. Our results highlight PLA2G2F as a previously unrecognized regulator of skin pathophysiology and point to this enzyme as a novel drug target for epidermal-hyperplasic diseases.

Deciphering the Causal Role of sPLA2s and Lp-PLA2 in Coronary Heart Disease

Over the last 10 to 15 years, animal and human observational studies have identified elevated levels of both proinflammatory secretory phospholipase A2-IIA and lipoprotein-associated phospholipase A2 as potential risk factors for coronary heart disease. However, Mendelian randomization, a genetic tool to test causality of a biomarker, and phase III randomized controlled trials of inhibitors of theses enzymes (varespladib and darapladib) converged to indicate that elevated levels are unlikely to be themselves causal of coronary heart disease and that inhibition had little or no clinical utility. The concordance of findings from Mendelian randomization and clinical trials suggests that for these 2 drugs, and for other novel biomarkers in future, validation of potential therapeutic targets by genetic studies (such as Mendelian randomization) before embarking on costly phase III randomized controlled trials could increase efficiency and offset the high risk of drug development, thereby facilitating discovery of new therapeutics and mitigating against the exuberant costs of drug development.

PLA2G10 Gene Variants, sPLA2 Activity, and Coronary Heart Disease Risk

Background—

Observational studies report that secretory phospholipase A2 (sPLA2) activity is a marker for coronary heart disease (CHD) risk, and activity measures are thought to represent the composite activity of sPLA2-IIA, -V, and -X. The aim of this study was to use genetic variants of PLA2G10 , encoding sPLA2-X, to investigate the contribution of sPLA2-X to the measure of sPLA2 activity and coronary heart disease (CHD) risk traits and outcome.

Methods and Results—

Three PLA2G10 tagging single-nucleotide polymorphisms (rs72546339, rs72546340, and rs4003232) and a previously studied PLA2G10 coding single-nucleotide polymorphism rs4003228, R38C, were genotyped in a nested case: control cohort drawn from the prospective EPIC-Norfolk Study (2175 cases and 2175 controls). Meta-analysis of rs4003228 (R38C) and CHD was performed using data from the Northwick Park Heart Study II and 2 published cohorts AtheroGene and SIPLAC, providing in total an additional 1884 cases and 3119 controls. EPIC-Norfolk subjects in the highest tertile of sPLA2 activity were older and had higher inflammatory markers compared with those in the lowest tertile for sPLA2 activity. None of the PLA2G10 tagging single-nucleotide polymorphism nor R38C, a functional variant, were significantly associated with sPLA2 activity, intermediate CHD risk traits, or CHD risk. In meta-analysis, the summary odds ratio for R38C was odds ratio=0.97 (95% confidence interval, 0.77–1.22).

Conclusions—

PLA2G10 variants are not significantly associated with plasma sPLA2 activity or with CHD risk.

Matrix metalloproteinase-2 negatively regulates cardiac secreted phospholipase A2 to modulate inflammation and fever

Background

Matrix metalloproteinase (MMP)‐2 deficiency makes humans and mice susceptible to inflammation. Here, we reveal an MMP‐2–mediated mechanism that modulates the inflammatory response via secretory phospholipase A₂ (sPLA₂), a phospholipid hydrolase that releases fatty acids, including precursors of eicosanoids.

Methods and Results

Mmp2^−/− (and, to a lesser extent, Mmp7^−/− and Mmp9^−/−) mice had between 10‐ and 1000‐fold elevated sPLA₂ activity in plasma and heart, increased eicosanoids and inflammatory markers (both in the liver and heart), and exacerbated lipopolysaccharide‐induced fever, all of which were blunted by adenovirus‐mediated MMP‐2 overexpression and varespladib (pharmacological sPLA₂ inhibitor). Moreover, Mmp2 deficiency caused sPLA₂‐mediated dysregulation of cardiac lipid metabolic gene expression. Compared with liver, kidney, and skeletal muscle, the heart was the single major source of the Ca²⁺‐dependent, ≈20‐kDa, varespladib‐inhibitable sPLA₂ that circulates when MMP‐2 is deficient. PLA2G5, which is a major cardiac sPLA₂ isoform, was proinflammatory when Mmp2 was deficient. Treatment of wild‐type (Mmp2^+/+) mice with doxycycline (to inhibit MMP‐2) recapitulated the Mmp2^−/− phenotype of increased cardiac sPLA₂ activity, prostaglandin E₂ levels, and inflammatory gene expression. Treatment with either indomethacin (to inhibit cyclooxygenase‐dependent eicosanoid production) or varespladib (which inhibited eicosanoid production) triggered acute hypertension in Mmp2^−/− mice, revealing their reliance on eicosanoids for blood pressure homeostasis.

Conclusions

A heart‐centric MMP‐2/sPLA₂ axis may modulate blood pressure homeostasis, inflammatory and metabolic gene expression, and the severity of fever. This discovery helps researchers to understand the cardiovascular and systemic effects of MMP‐2 inhibitors and suggests a disease mechanism for human MMP‐2 gene deficiency.

A new era of secreted phospholipase A₂

Among more than 30 members of the phospholipase A2 (PLA2) superfamily, secreted PLA2 (sPLA2) enzymes represent the largest family, being Ca(2+)-dependent low-molecular-weight enzymes with a His-Asp catalytic dyad. Individual sPLA2s exhibit unique tissue and cellular distributions and enzymatic properties, suggesting their distinct biological roles. Recent studies using transgenic and knockout mice for nearly a full set of sPLA2 subtypes, in combination with sophisticated lipidomics as well as biochemical and cell biological studies, have revealed distinct contributions of individual sPLA2s to various pathophysiological events, including production of pro- and anti-inflammatory lipid mediators, regulation of membrane remodeling, degradation of foreign phospholipids in microbes or food, or modification of extracellular noncellular lipid components. In this review, we highlight the current understanding of the in vivo functions of sPLA2s and the underlying lipid pathways as revealed by a series of studies over the last decade.

Anti-inflammatory therapies for atherosclerosis

The view of atherosclerosis as an inflammatory disease has emerged from observations of immune activation and inflammatory signalling in human atherosclerotic lesions, from the definition of inflammatory biomarkers as independent risk factors for cardiovascular events, and from evidence of low-density lipoprotein-induced immune activation. Studies in animal models of hyperlipidaemia have also supported the beneficial effects of countering inflammation to delay atherosclerosis progression. Specific inflammatory pathways with relevance to human diseases have been identified, and inhibitors of these pathways are either already in use for the treatment of other diseases, or are under development and evaluation. These include 'classic' drugs (such as allopurinol, colchicine, and methotrexate), biologic therapies (for example tumour necrosis factor inhibitors and IL-1 neutralization), as well as targeting of lipid mediators (such as phospholipase inhibitors and antileukotrienes) or intracellular pathways (inhibition of NADPH oxidase, p38 mitogen-activated protein kinase, or phosphodiesterase). The evidence supporting the use of anti-inflammatory therapies for atherosclerosis is mainly based on either observational or small interventional studies evaluating surrogate markers of disease activity. Nevertheless, these data are crucial to understand the role of inflammation in atherosclerosis, and to design randomized controlled studies to evaluate the effect of specific anti-inflammatory strategies on cardiovascular outcomes.

Induction of dendritic cell-mediated T-cell activation by modified but not native low-density lipoprotein in humans and inhibition by annexin a5: involvement of heat shock proteins

OBJECTIVE

Atherosclerosis is an inflammatory disease, where activated immunocompetent cells, including dendritic cells (DCs) and T cells are abundant in plaques. Low-density lipoprotein modified either by oxidation (oxLDL) or by human group X-secreted phospholipase A2 (LDLx) and heat shock proteins (HSP), especially HSP60 and 90, have been implicated in atherosclerosis. We previously reported that Annexin A5 inhibits inflammatory effects of phospholipids, decreases vascular inflammation and improves vascular function in apolipoprotein E(-/-) mice. Here, we focus on the LDLx effects on human DCs and T cells.

APPROACH AND RESULTS

Human DCs were differentiated from peripheral blood monocytes, stimulated by oxLDL or LDLx. Naive autologous T cells were cocultured with pretreated DCs. oxLDL and LDLx, in contrast to LDL, induced DC-activation and T-cell proliferation. T cells exposed to LDLx-treated DCs produced interferon-γ, interleukin (IL)-17 but not IL-4 and IL-10. Annexin A5 abrogated LDLx effects on DCs and T cells and increased production of transforming growth factor-β and IL-10. Furthermore, IL-10 producing T cells suppressed primary T-cell activation via soluble IL-10, transforming growth factor-β, and cell-cell contact. Lentiviral-mediated shRNA knock-down HSP60 and 90 in DCs attenuated the effect of LDLx on DCs and subsequent T-cell proliferation. Experiments on DC and T cells derived from carotid atherosclerotic plaques gave similar results.

CONCLUSIONS

Our data show that modified forms of LDL such as LDLx but not native LDL activate human T cells through DCs. HSP60 and 90 contribute to such T-cell activation. Annexin A5 promotes induction of regulatory T cells and is potentially interesting as a therapeutic agent.

Emerging roles of secreted phospholipase A2 enzymes: the 3rd edition

Within the phospholipase A2 (PLA2) superfamily, secreted PLA2 (sPLA2) enzymes comprise the largest family that contains 11 to 12 mammalian isoforms with a conserved His-Asp catalytic dyad. Individual sPLA2s exhibit unique tissue and cellular localizations and specific enzymatic properties, suggesting distinct biological roles. Individual sPLA2s are involved in diverse biological events through lipid mediator-dependent or -independent processes and act redundantly or non-redundantly in a given microenvironment. In the past few years, new biological aspects of sPLA2s have been clarified using their transgenic and knockout mouse lines in combination with mass spectrometric lipidomics to unveil their target substrates and products in vivo. In the 3rd edition of this review series, we highlight the newest understanding of the in vivo functions of sPLA2s in pathophysiological conditions in the context of immunity and metabolism. We will also describe the latest knowledge on PLA2R1, the best known sPLA2 receptor, which may serve either as a clearance or signaling receptor for sPLA2 or may even act independently of sPLA2 function.

Lipoproteins as biomarkers and therapeutic targets in the setting of acute coronary syndrome

The period following an acute coronary syndrome (ACS) represents a critical time frame with a high risk for recurrent events and death. The pathogenesis of this increase in clinical cardiovascular disease events after ACS is complex, with molecular mechanisms including increased thrombosis and inflammation. Dyslipoproteinemia is common in patients with ACS and predictive of recurrent cardiovascular disease events after presentation with an ACS event. Although randomized clinical trials have provided fairly convincing evidence that high-dose statins reduce the risk of recurrent cardiovascular events after ACS, there remain questions about how aggressively to reduce low-density lipoprotein cholesterol levels in ACS. Furthermore, no other lipid-related interventions have yet been proven to be effective in reducing major cardiovascular events after ACS. Here, we review the relationship of lipoproteins as biomarkers to cardiovascular risk after ACS, the evidence for lipid-targeted interventions, and the potential for novel therapeutic approaches in this arena.

DNA methylation map of human atherosclerosis

BACKGROUND

Epigenetic alterations may contribute to the development of atherosclerosis. In particular, DNA methylation, a reversible and highly regulated DNA modification, could influence disease onset and progression because it functions as an effector for environmental influences, including diet and lifestyle, both of which are risk factors for cardiovascular diseases.

METHODS AND RESULTS

To address the role of DNA methylation changes in atherosclerosis, we compared a donor-matched healthy and atherosclerotic human aorta sample using whole-genome shotgun bisulfite sequencing. We observed that the atherosclerotic portion of the aorta was hypermethylated across many genomic loci in comparison with the matched healthy counterpart. Furthermore, we defined specific loci of differential DNA methylation using a set of donor-matched aortic samples and a high-density (>450 000 CpG sites) DNA methylation microarray. The functional importance in the disease was corroborated by crossing the DNA methylation signature with the corresponding expression data of the same samples. Among the differentially methylated CpGs associated with atherosclerosis onset, we identified genes participating in endothelial and smooth muscle functions. These findings provide new clues toward a better understanding of the molecular mechanisms of atherosclerosis.

CONCLUSIONS

Our data identify an atherosclerosis-specific DNA methylation profile that highlights the contribution of different genes and pathways to the disorder. Interestingly, the observed gain of DNA methylation in the atherosclerotic lesions justifies efforts to develop DNA demethylating agents for therapeutic benefit.

The adipocyte-inducible secreted phospholipases PLA2G5 and PLA2G2E play distinct roles in obesity

Metabolic disorders, including obesity and insulin resistance, have their basis in dysregulated lipid metabolism and low-grade inflammation. In a microarray search of unique lipase-related genes whose expressions are associated with obesity, we found that two secreted phospholipase A2s (sPLA2s), PLA2G5 and PLA2G2E, were robustly induced in adipocytes of obese mice. Analyses of Pla2g5(-/-) and Pla2g2e(-/-) mice revealed distinct roles of these sPLA2s in diet-induced obesity. PLA2G5 hydrolyzed phosphatidylcholine in fat-overladen low-density lipoprotein to release unsaturated fatty acids, which prevented palmitate-induced M1 macrophage polarization. As such, PLA2G5 tipped the immune balance toward an M2 state, thereby counteracting adipose tissue inflammation, insulin resistance, hyperlipidemia, and obesity. PLA2G2E altered minor lipoprotein phospholipids, phosphatidylserine and phosphatidylethanolamine, and moderately facilitated lipid accumulation in adipose tissue and liver. Collectively, the identification of "metabolic sPLA2s" adds this gene family to a growing list of lipolytic enzymes that act as metabolic coordinators.

The (G>A) rs11573191 polymorphism of PLA2G5 gene is associated with premature coronary artery disease in the Mexican Mestizo population: the genetics of atherosclerotic disease Mexican study

Coronary artery disease (CAD) is a multifactorial disorder that results from an excessive inflammatory response. Secretory phospholipase A₂-V (sPLA₂-V) encoded by PLA2G5 gene promotes diverse proinflammatory processes. The aim of the present study was to analyze if PLA2G5 gene polymorphisms are associated with premature CAD. Three PLA2G5 polymorphisms (rs11573187, rs2148911, and rs11573191) were analyzed in 707 patients with premature CAD and 749 healthy controls. Haplotypes were constructed after linkage disequilibrium analysis. Under dominant, recessive, and additive models, the rs11573191 polymorphism was associated with increased risk of premature CAD (OR = 1.51, P_dom = 3.5 × 10⁻³; OR = 2.95, P_rec = 0.023; OR = 1.51, P_add = 1.2 × 10⁻³). According to the informatics software, this polymorphism had a functional effect modifying the affinity of the sequence by the MZF1 transcription factor. PLA2G5 polymorphisms were in linkage disequilibrium and the CGA haplotype was associated with increased risk of premature CAD (OR = 1.49, P = 0.0023) and with hypertension in these patients (OR = 1.75, P = 0.0072). Our results demonstrate the association of the PLA2G5 rs11573191 polymorphism with premature CAD. In our study, it was possible to distinguish one haplotype associated with increased risk of premature CAD and hypertension.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.