Group 1B phospholipase A₂ deficiency protects against diet-induced hyperlipidemia in mice

Identifying potential targets for preventing cancer progression through the PLA2G1B recombinant protein using bioinformatics and machine learning methods

Lung cancer is the deadliest and most aggressive malignancy in the world. Preventing cancer is crucial. Therefore, the new molecular targets have laid the foundation for molecular diagnosis and targeted therapy of lung cancer. PLA2G1B plays a key role in lipid metabolism and inflammation. PLA2G1B has selective substrate specificity. In this paper, the recombinant protein molecular structure of PLA2G1B was studied and novel therapeutic interventions were designed to disrupt PLA2G1B activity and impede tumor growth by targeting specific regions or residues in its structure. Construct protein-protein interaction networks and core genes using R's "STRING" program. LASSO, SVM-RFE and RF algorithms identified important genes associated with lung cancer. 282 deg were identified. Enrichment analysis showed that these genes were mainly related to adhesion and neuroactive ligand-receptor interaction pathways. PLA2G1B was subsequently identified as developing a preventative feature. GSEA showed that PLA2G1B is closely related to α-linolenic acid metabolism. Through the analysis of LASSO, SVM-RFE and RF algorithms, we found that PLA2G1B gene may be a preventive gene for lung cancer.

PLA2G12A protects against diet-induced obesity and insulin resistance by enhancing energy expenditure and clearance of circulating triglycerides

Secreted phospholipase A2s are involved in the development of obesity, type 2 diabetes mellitus (T2DM) and cardiovascular disease, which have become serious and growing health concerns worldwide. Integration of genome-wide association study and gene co-expression networks analysis showed that the secreted phospholipase A2 group XIIA (PLA2G12A) may participate in hepatic lipids metabolism. Nevertheless, the role of PLA2G12A in lipid metabolism and its potential mechanism remain elusive. Here, we used AAV9 vector carrying human PLA2G12A gene to exogenously express hPLA2G12A in the liver of mice. We demonstrated that the overexpression of hPLA2G12A resulted in a significant decrease in serum lipid levels in wild-type mice fed with chow diet or high-fat diet (HFD). Moreover, hPLA2G12A treatment protected against diet-induced obesity and insulin resistance in mice fed a HFD. Notably, we found that hPLA2G12A treatment confers protection against obesity and hyperlipidemia independent of its enzymatic activity, but rather by increasing physical activity and energy expenditure. Furthermore, we demonstrated that hPLA2G12A treatment induced upregulation of ApoC2 and Cd36 and downregulation of Angptl8, which contributed to the increase in clearance of circulating triglycerides and hepatic uptake of fatty acids without affecting hepatic de novo lipogenesis, very low-density lipoprotein secretion, or intestinal lipid absorption. Our study highlights the potential of PLA2G12A gene therapy as a promising approach for treating obesity, insulin resistance and T2DM.

Inactivation of Group 1B Phospholipase A2 Enhances Disease Recovery and Reduces Experimental Colitis in Mice

Phospholipase A2 (PLA2) enzymes influence inflammatory bowel disease in both positive and negative manners depending on the type of PLA2 that is expressed. This study explored the influence of the abundantly expressed Group 1B PLA2 (PLA2G1B) on ulcerative colitis. Wild-type C57BL/6J mice and Pla2g1b-/- mice were treated with dextran sulfate sodium (DSS) for 5 days to induce epithelial injury, followed by another 5 days without DSS for recovery. The Pla2g1b-/- mice displayed significantly less body weight loss, colitis pathology, and disease activity indexes compared to the wild-type mice. The differences in colitis were not due to differences in the colonic lysophospholipid levels, but higher numbers of stem and progenitor cells were found in the intestines of Pla2g1b-/- mice compared to the wild-type mice. The DSS-treated Pla2g1b-/- mice also showed higher expressions of genes that are responsible for epithelial repair and lower expressions of proinflammatory cytokine genes in the colon, as well as reduced inflammatory cytokine levels in the plasma. In vitro experiments revealed the PLA2G1B stimulation of inflammatory cytokine expression by myeloid cells. PLA2G1B inactivation protects against DSS-induced colitis in mice by increasing the intestinal stem cell reservoir for epithelial repair and reducing myeloid cell inflammation in the diseased colon. Thus, PLA2G1B may be a target for colitis management.

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.

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.

Transcriptome analysis provides insights into the anti-diabetic mechanism of theaflavins in high-fat diet and streptozotocin-induced mice

Black tea exhibits potential to improve hyperglycemia and insulin resistance, and theaflavins (TFs) are one of its characteristic components. The aim of this study was to explore the anti-diabetic mechanism...

Phospholipase A2, a nonnegligible enzyme superfamily in gastrointestinal diseases

Gastrointestinal tract is important for digestion, absorption, detoxification and immunity. Gastrointestinal diseases are mainly caused by the imbalance of protective and attacking factors in gastrointestinal mucosa, which can seriously harm human health. Phospholipase A₂ (PLA₂) is a large family closely involved in lipid metabolism and is found in almost all human cells. A growing number of studies have revealed that its metabolites are deeply implicated in various inflammatory pathways and also regulates the maintenance of numerous biological events such as dietary digestion, membrane remodeling, barrier action, and host immunity. In addition to their phospholipase activity, some members of the superfamily also have other catalytic activities. Based on the in-depth effects of phospholipase A2 on bioactive lipid metabolism and inflammatory cytokines, PLA₂ and its metabolites are likely to be involved in the pathogenesis, development or prevention of gastrointestinal diseases. Therefore, this review will focus on the physiological and pathogenic roles of several important PLA₂ enzymes in the gastrointestinal tract, and reveals the potential of PLA₂ as a therapeutic target for gastrointestinal diseases.

The interaction between brain and liver regulates lipid metabolism in the TBI pathology

To shed light on the impact of systemic physiology on the pathology of traumatic brain injury (TBI), we examine the effects of TBI (concussive injury) and dietary fructose on critical aspects of lipid homeostasis in the brain and liver of young-adult rats. Lipids are integral components of brain structure and function, and the liver has a role on the synthesis and metabolism of lipids. Fructose is mainly metabolized in the liver with potential implications for brain function. Lipidomic analysis accompanied by unbiased sparse partial least squares discriminant analysis (sPLS-DA) identified lysophosphatidylcholine (LPC) and cholesterol ester (CE) as the top lipid families impacted by TBI and fructose in the hippocampus, and only LPC (16:0) was associated with hippocampal-dependent memory performance. Fructose and TBI elevated liver pro-inflammatory markers, interleukin-1α (IL-1α), Interferon-γ (IFN-γ) that correlated with hippocampal-dependent memory dysfunction, and monocyte chemoattractant protein-1 (MCP-1) positively correlated with LPC levels in the hippocampus. The effects of fructose were more pronounced in the liver, in agreement with the role of liver on fructose metabolism and suggest that fructose could exacerbate liver inflammation caused by TBI. The overall results indicate that TBI and fructose interact to influence systemic and central inflammation by engaging liver lipids. The impact of TBI and fructose diet on the periphery provides a therapeutic target to counteract the TBI pathogenesis.

Secretory Phospholipase A2s in Insulin Resistance and Metabolism

The phospholipases A₂ (PLA₂) superfamily encompasses enzymes commonly found in mammalian tissues and snake venom. Many of these enzymes have unique tissue distribution, function, and substrate specificity suggesting distinct biological roles. In the past, much of the research on secretory PLA₂s has analyzed their roles in inflammation, anti-bacterial actions, and atherosclerosis. In recent studies utilizing a variety of mouse models, pancreatic islets, and clinical trials, a role for many of these enzymes in the control of metabolism and insulin action has been revealed. In this review, this research, and the unique contributions of the PLA₂ enzymes in insulin resistance and metabolism.

The phospholipase A2 family's role in metabolic diseases: Focus on skeletal muscle

The prevalence of obesity and type 2 diabetes has increased substantially in recent years creating a global health burden. In obesity, skeletal muscle, the main tissue responsible for insulin-mediated glucose uptake, exhibits dysregulation of insulin signaling, glucose uptake, lipid metabolism, and mitochondrial function, thus, promoting type 2 diabetes. The phospholipase A2 (PLA2) enzyme family mediates lipid signaling and membrane remodeling and may play an important role in metabolic disorders such as obesity, diabetes, hyperlipidemia, and fatty liver disease. The PLA2 family consists of 16 members clustered in four groups. PLA2s hydrolyze the sn-2 ester bond of phospholipids generating free fatty acids and lysophospholipids. Differential tissue and subcellular PLA2 expression patterns and the abundance of distinct fatty acyl groups in the target phospholipid determine the impact of individual family members on metabolic functions and, potentially, diseases. Here, we update the current knowledge of the role of the PLA2 family in skeletal muscle, with a view to their potential for therapeutic targeting in metabolic diseases.

Cytotoxic, Antioxidant, and Metabolic Enzyme Inhibitory Activities of Euphorbia cyparissias Extracts

Plants of the Euphorbia genus present a wide range of therapeutic applications. This study is aimed at investigating new antidigestive enzyme agents from Euphorbia cyparissias through inhibition of lipid and carbohydrate absorption, to evaluate their potential applications for the treatment of metabolic syndrome. Lipase, phospholipase, protease, α-amylase, β-glucosidase, and xanthine oxidase activities under treatment with aqueous and ethanolic extracts of Euphorbia cyparissias were observed to evaluate the inhibitory effect of these extracts, as well as their antioxidant and cytotoxic effects. Results showed that ethanolic and aqueous extracts exhibited important inhibitory activity in a concentration-related manner on digestive enzymes, which is more effective than the commercial drugs used as controls. Results also showed that, out of the two extracts tested, the ethanolic extract presented the most promising results in inhibiting the activities of all digestive enzymes used. Moreover, the two extracts displayed a higher reducing power than that of the positive control used. The obtained results, together with previous reports in the literature, strongly suggest that Euphorbia cyparissias extracts may be natural inhibitors of the digestive enzymes and thus a potential new drug for metabolic syndrome treatment.

Rescue of Hepatic Phospholipid Remodeling Defectin iPLA2β-Null Mice Attenuates Obese but Not Non-Obese Fatty Liver

Polymorphisms of group VIA calcium-independent phospholipase A2 (iPLA₂β or PLA2G6) are positively associated with adiposity, blood lipids, and Type-2 diabetes. The ubiquitously expressed iPLA₂β catalyzes the hydrolysis of phospholipids (PLs) to generate a fatty acid and a lysoPL. We studied the role of iPLA₂β on PL metabolism in non-alcoholic fatty liver disease (NAFLD). By using global deletion iPLA₂β-null mice, we investigated three NAFLD mouse models; genetic Ob/Ob and long-term high-fat-diet (HFD) feeding (representing obese NAFLD) as well as feeding with methionine- and choline-deficient (MCD) diet (representing non-obese NAFLD). A decrease of hepatic PLs containing monounsaturated- and polyunsaturated fatty acids and a decrease of the ratio between PLs and cholesterol esters were observed in all three NAFLD models. iPLA₂β deficiency rescued these decreases in obese, but not in non-obese, NAFLD models. iPLA₂β deficiency elicited protection against fatty liver and obesity in the order of Ob/Ob › HFD » MCD. Liver inflammation was not protected in HFD NAFLD, and that liver fibrosis was even exaggerated in non-obese MCD model. Thus, the rescue of hepatic PL remodeling defect observed in iPLA₂β-null mice was critical for the protection against NAFLD and obesity. However, iPLA₂β deletion in specific cell types such as macrophages may render liver inflammation and fibrosis, independent of steatosis protection.

sPLA2-IB Level Correlates with Hyperlipidemia and the Prognosis of Idiopathic Membranous Nephropathy

Recent studies suggested that serum secretory phospholipase A2 group IB (sPLA2-IB) was increased in idiopathic membranous nephropathy (IMN). However, the interference of high lipemia on the sPLA2-IB levels was not taken into account in these studies. The present study aimed to investigate the correlation between sPLA2-IB and lipemia, and the clinical merit of sPLA2-IB in the prediction of prognosis of IMN patients. A total of 64 IMN patients, 39 immunoglobulin A nephropathy (IgAN) patients and 64 healthy controls were included in the study. The levels of serum sPLA2-IB, lipemia and proteinuria were measured. Fifty IMN patients were followed up for 6 months. Pathologic stages were made for all IgAN and IMN patients. The results showed that the levels of serum sPLA2-IB, cholesterol and low-density lipoprotein cholesterol (LDL-C) were significantly higher, and the levels of albumin and high-density lipoprotein cholesterol (HDL-C) were significantly lower in IMN patients than in healthy controls and IgAN patients. Serum sPLA2-IB levels were also found to be higher in IgAN patients than in heathy controls, but the association of serum sPLA2-IB levels with proteinuria, cholesterol and albumin was only shown in IMN patients. Antibody against M-type receptor for secretory phospholipase A2 (PLA2R1) was positive in 81.3% IMN patients. Glomerular sPLA2-IB deposition, podocyte fused processes, and density deposition on thickened basement membrane were seen in IMN patients, but not in IgAN patients. IMN patients with lower sPLA2-IB and proteinuria levels were found to have better outcome after the 6-month follow-up. In IMN patients, sPLA2-IB levels were significantly increased in both serum and renal tissue. In conclusion, serum sPLA2-IB was closely correlated with proteinuria, albumin and cholesterol, and IMN patients with lower sPLA2-IB levels were more likely to achieve a better outcome.

A Genome-Wide Association Study on Feed Efficiency Related Traits in Landrace Pigs

Feed efficiency (FE) traits in pigs are of utmost economic importance. Genetic improvement of FE related traits in pigs might significantly reduce production cost and energy consumption. Hence, our study aimed at identifying SNPs and candidate genes associated with FE related traits, including feed conversion ratio (FCR), average daily gain (ADG), average daily feed intake (ADFI), and residual feed intake (RFI). A genome-wide association study (GWAS) was performed for the four FE related traits in 296 Landrace pigs genotyped with PorcineSNP50 BeadChip. Two different single-trait methods, single SNP linear model GWAS (LM-GWAS) and single-step GWAS (ssGWAS), were implemented. Our results showed that the two methods showed high consistency with respect to SNP identification. A total of 32 common significant SNPs associated with the four FE related traits were identified. Bioinformatics analysis revealed eight common QTL regions, of which three QTL regions related to ADFI and RFI traits were overlapped. Gene ontology analysis revealed six common candidate genes (PRELID2, GPER1, PDX1, TEX2, PLCL2, ICAM2) relevant for the four FE related traits. These genes are involved in the processes of fat synthesis and decomposition, lipid transport process, insulin metabolism, among others. Our results provide, new insights into the genetic mechanisms and candidate function genes of FE related traits in pigs. However, further investigations to validate these results are warranted.

The Vitamin D Receptor Regulates Glycerolipid and Phospholipid Metabolism in Human Hepatocytes

The vitamin D receptor (VDR) must be relevant to liver lipid metabolism because VDR deficient mice are protected from hepatosteatosis. Therefore, our objective was to define the role of VDR on the overall lipid metabolism in human hepatocytes. We developed an adenoviral vector for human VDR and performed transcriptomic and metabolomic analyses of cultured human hepatocytes upon VDR activation by vitamin D (VitD). Twenty percent of the VDR responsive genes were related to lipid metabolism, including MOGAT1, LPGAT1, AGPAT2, and DGAT1 (glycerolipid metabolism); CDS1, PCTP, and MAT1A (phospholipid metabolism); and FATP2, SLC6A12, and AQP3 (uptake of fatty acids, betaine, and glycerol, respectively). They were rapidly induced (4–6 h) upon VDR activation by 10 nM VitD or 100 µM lithocholic acid (LCA). Most of these genes were also upregulated by VDR/VitD in mouse livers in vivo. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS) metabolomics demonstrated intracellular accumulation of triglycerides, with concomitant decreases in diglycerides and phosphatidates, at 8 and 24 h upon VDR activation. Significant alterations in phosphatidylcholines, increases in lyso-phosphatidylcholines and decreases in phosphatidylethanolamines and phosphatidylethanolamine plasmalogens were also observed. In conclusion, active VitD/VDR signaling in hepatocytes triggers an unanticipated coordinated gene response leading to triglyceride synthesis and to important perturbations in glycerolipids and phospholipids.

The role of the small intestine in modulating metabolism and inflammation in atherosclerosis and cancer

PURPOSE OF REVIEW

To discuss recent findings on the importance of the small intestine in modulating metabolism and inflammation in atherosclerosis and cancer.

RECENT FINDINGS

Integrin β7 natural gut intraepithelial T cells modulated metabolism and accelerated atherosclerosis in mice. Reducing the generation of lysophospholipids in the small intestine mimicked bariatric surgery and improved diabetes. Enterocyte-specific knockdown of stearoyl-CoA desaturase-1 significantly improved dyslipidemia in LDL receptor null (Ldlr) mice fed a Western diet. Adding a concentrate of tomatoes transgenic for the apolipoprotein A-I mimetic peptide 6F to the chow of wild-type mice altered lipid metabolism in the small intestine, preserved Notch signaling and reduced tumor burden in mouse models. The phospholipid-remodeling enzyme Lpcat3 regulated intestinal stem cells and progenitor cells by stimulating cholesterol biosynthesis; increasing cholesterol in the diet or through genetic manipulation promoted tumorigenesis in Apc mice.

SUMMARY

The small intestine is important for regulating metabolism and inflammation in animal models of both atherosclerosis and cancer.

Pancreatic and mucosal enzymes in choline phospholipid digestion

The digestion of choline phospholipids is important for choline homeostasis, lipid signaling, postprandial lipid and energy metabolism, and interaction with intestinal bacteria. The digestion is mediated by the combined action of pancreatic and mucosal enzymes. In the proximal small intestine, hydrolysis of phosphatidylcholine (PC) to 1-lyso-PC and free fatty acid (FFA) by the pancreatic phospholipase A₂ IB coincides with the digestion of the dietary triacylglycerols by lipases, but part of the PC digestion is extended and must be mediated by other enzymes as the jejunoileal brush-border phospholipase B/lipase and mucosal secreted phospholipase A₂ X. Absorbed 1-lyso-PC is partitioned in the mucosal cells between degradation and reacylation into chyle PC. Reutilization of choline for hepatic bile PC synthesis, and the reacylation of 1-lyso-PC into chylomicron PC by the lyso-PC-acyl-CoA-acyltransferase 3 are important features of choline recycling and postprandial lipid metabolism. The role of mucosal enzymes is emphasized by sphingomyelin (SM) being sequentially hydrolyzed by brush-border alkaline sphingomyelinase (alk-SMase) and neutral ceramidase to sphingosine and FFA, which are well absorbed. Ceramide and sphingosine-1-phosphate are generated and are both metabolic intermediates and important lipid messengers. Alk-SMase has anti-inflammatory effects that counteract gut inflammation and tumorigenesis. These may be mediated by multiple mechanisms including generation of sphingolipid metabolites and suppression of autotaxin induction and lyso-phosphatidic acid formation. Here we summarize current knowledge on the roles of pancreatic and mucosal enzymes in PC and SM digestion, and its implications in intestinal and liver diseases, bacterial choline metabolism in the gut, and cholesterol absorption.

Epithelial-Cell-Derived Phospholipase A2 Group 1B Is an Endogenous Anthelmintic

Immunity to intestinal helminth infections has been well studied, but the mechanism of helminth killing prior to expulsion remains unclear. Here we identify epithelial-cell-derived phospholipase A₂ group 1B (PLA₂g1B) as a host-derived endogenous anthelmintic. PLA₂g1B is elevated in resistant mice and is responsible for killing tissue-embedded larvae. Despite comparable activities of other essential type-2-dependent immune mechanisms, Pla2g1b^−/− mice failed to expel the intestinal helminths Heligmosomoides polygyrus or Nippostrongylus brasiliensis. Expression of Pla2g1b by epithelial cells was dependent upon intestinal microbiota, adaptive immunity, and common-gamma chain-dependent signaling. Notably, Pla2g1b was downregulated in susceptible mice and inhibited by IL-4R-signaling in vitro, uncoupling parasite killing from expulsion mechanisms. Resistance was restored in Pla2g1b^−/− mice by treating infective H. polygyrus L3 larvae with PLA₂g1B, which reduced larval phospholipid abundance. These findings uncover epithelial-cell-derived Pla2g1b as an essential mediator of helminth killing, highlighting a previously overlooked mechanism of anti-helminth immunity.

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Pla2g1b expression correlated with resistance to intestinal helminth infection

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PLA₂g1B is essential for resistance to intestinal helminth infection in mice

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PLA₂g1B directly reduces phospholipid abundance in infective larvae

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Pla2g1b is expressed by epithelial cells and is negatively regulated by IL-4Rα

Group 1B phospholipase A2 in metabolic and inflammatory disease modulation

The group 1B phospholipase A₂ (PLA2G1B) is a secreted phospholipase that catalyzes the hydrolytic removal of the sn-2 fatty acyl moiety from phospholipids. This enzyme is synthesized most abundantly in the pancreas and is also expressed in the lung. The first part of this review article focuses on the role of pancreatic-derived PLA2G1B in mediating lipid absorption and discusses how the PLA2G1B-derived metabolic product contributes to cardiometabolic diseases, including obesity, hyperinsulinemia, hyperlipidemia, and atherosclerosis. The anti-helminth properties of PLA2G1B will also be discussed. The second part of this review will focus on PLA2G1B expressed in the lung, and in vitro data suggest that how this enzyme may modulate lung inflammation via both hydrolytic activity-dependent and -dependent mechanisms. Finally, recent studies revealing a relationship between PLA2G1B and cancer will also be discussed. This article is part of a Special Issue entitled Novel functions of phospholipase A2 Guest Editors: Makoto Murakami and Gerard Lambeau.

Genes involved in leukotriene synthesis pathway are dynamically regulated during lung development in Rhesus monkeys

BACKGROUND

Leukotrienes play critical roles in many inflammatory lung diseases and several antagonists of their receptors have been used in the clinical settings. However, the physiological functions of leukotrienes in lung development are still unclear.

METHOD

The expression levels of 34 genes involved in leukotriene synthesis and function pathway in the lungs of Rhesus monkey during different developmental time points were determined on a MiSeq platform and analyzed by the reads per kilobase of transcript per million mapped reads (RPKM) method.

RESULTS

The results showed that the expression levels of PLA2G1B, PLA2G10, PLA2G2D, ALOX5, and ALOX5AP increased dramatically in the lung of Rhesus monkey, reflecting the changes in the pulmonary environment after delivery. Additionally, the different expression patterns between molecules related to LTB4 and LTC4 synthesis suggested distinct roles of LTB4 and LTC4 in lung development. Finally, the constant expression of CysLT1 during the development process provided new information to the pharmaceutical basis of the use of leukotriene receptor antagonists in the clinical setting.

CONCLUSION

The expression levels of several key genes involved in leukotriene synthesis changed dramatically during lung development in Rhesus monkeys, suggesting the potential roles of leukotrienes in lung development in this animal model.

Enzymatic hydrolysate from velvet antler suppresses adipogenesis in 3T3-L1 cells and attenuates obesity in high-fat diet-fed mice

The purpose of the current study was to investigate the potential anti-obesity activity of an enzymatic hydrolysate of velvet antler in inhibiting adipogenesis in 3T3-L1 cells and in high-fat diet (HFD)-fed obese mice. The enzymatic hydrolysate was prepared using the commercial food grade protease, Protamex. The velvet antler Protamex hydrolysate (VAPH) indicated profound inhibitory effects on adipogenesis dose-dependently by decreasing the accumulation of triglycerides and down-regulating expression levels of adipogenesis-related proteins C/EBPα, SREBP-1, and PPARγ. In a mouse model of HFD-induced obesity, oral administration of VAPH (100 and 300 mg/kg for 13 weeks) significantly reduced the body weight gain that had resulted from the HFD. VAPH treatment also lowered the serum glucose and triglyceride levels, while increasing the HDL-C level. Furthermore, the treatment greatly reduced hepatic lipid droplet accumulation as well as the size of adipocytes. Current findings demonstrate that VAPH has profound anti-obesity effects and could be an effective candidate for preventing obesity and obesity-related chronic diseases.

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.

Liver-specific overexpression of LPCAT3 reduces postprandial hyperglycemia and improves lipoprotein metabolic profile in mice

Previous studies have shown that group 1B phospholipase A2-mediated absorption of lysophospholipids inhibits hepatic fatty acid β-oxidation and contributes directly to postprandial hyperglycemia and hyperlipidemia, leading to increased risk of cardiometabolic disease. The current study tested the possibility that increased expression of lysophosphatidylcholine acyltransferase-3 (LPCAT3), an enzyme that converts lysophosphatidylcholine to phosphatidylcholine in the liver, may alleviate the adverse effects of lysophospholipids absorbed after a lipid-glucose mixed meal. The injection of an adenovirus vector harboring the human LPCAT3 gene into C57BL/6 mice increased hepatic LPCAT3 expression fivefold compared with mice injected with a control LacZ adenovirus. Postprandial glucose tolerance tests after feeding these animals with a bolus lipid-glucose mixed meal revealed that LPCAT3 overexpression improved postprandial hyperglycemia and glucose tolerance compared with control mice with LacZ adenovirus injection. Mice with LPCAT3 overexpression also showed reduced very low density lipoprotein production and displayed elevated levels of the metabolic- and cardiovascular-protective large apoE-rich high density lipoproteins in plasma. The mechanism underlying the metabolic benefits of LPCAT3 overexpression was shown to be due to the alleviation of lysophospholipid inhibition of fatty acid β-oxidation in hepatocytes. Taken together, these results suggest that specific LPCAT3 induction in the liver may be a viable strategy for cardiometabolic disease intervention.

Forty five years with membrane phospholipids, phospholipases and lipid mediators: A historical perspective

Phospholipases play a key role in the metabolism of phospholipids and in cell signaling. They are also a very useful tool to explore phospholipid structure and metabolism as well as membrane organization. They are at the center of this review, covering a period starting in 1971 and focused on a number of subjects in which my colleagues and I have been involved. Those include determination of phospholipid asymmetry in the blood platelet membrane, biosynthesis of lysophosphatidic acid, biochemistry of platelet-activating factor, first attempts to define the role of phosphoinositides in cell signaling, and identification of novel digestive (phospho)lipases such as pancreatic lipase-related protein 2 (PLRP2) or phospholipase B. Besides recalling some of our contributions to those various fields, this review makes an appraisal of the impressive and often unexpected evolution of those various aspects of membrane phospholipids and lipid mediators. It is also the occasion to propose some new working hypotheses.

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.

Consequences of periodic α-to-β(3) residue replacement for immunological recognition of peptide epitopes

Oligomers that contain both α- and β-amino acid residues, or "α/β-peptides", have emerged as promising mimics of signal-bearing polypeptides that can inhibit or augment natural protein-protein interactions. α/β-Peptides that contain a sufficient proportion of β residues evenly distributed along the sequence can be highly resistant to enzymatic degradation, which is favorable with regard to in vivo applications. Little is known, however, about recognition of α/β-peptides by the immune system. Prior studies have focused almost entirely on examples that contain a single β residue; such α/β-peptides frequently retain the immunological profile of the analogous α-peptide. We have conducted α-peptide vs α/β-peptide comparisons involving higher β residue content, focusing on molecules with αααβ and ααβαααβ backbone repeat patterns. Among analogues of an 18-mer derived from the Bim BH3 domain and an 8-mer derived from secreted phospholipase-2 (sPLA2), we find that recognition by antibodies raised against the prototype α-peptide is suppressed by periodic α → β replacements. Complementary studies reveal that antibodies raised against Bim BH3- or sPLA2-derived α/β-peptides fail to recognize prototype α-peptides displaying identical side chain repertoires. Because polypeptides containing d-α-amino acid residues are of growing interest for biomedical applications, we included the enantiomer of the sPLA2-derived α-peptide in these studies; this d-peptide is fully competent as a hapten, but the resulting antibodies do not cross react with the enantiomeric peptide. Among analogues of the 9-mer CD8(+) T-cell viral epitope GP33, we observe that periodic α → β replacements suppress participation in the MHC I + peptide + T-cell receptor ternary complexes that activate cytotoxic T-lymphocytes, due in part to disruption of MHC binding.

Source and role of intestinally derived lysophosphatidic acid in dyslipidemia and atherosclerosis

We previously reported that i) a Western diet increased levels of unsaturated lysophosphatidic acid (LPA) in small intestine and plasma of LDL receptor null (LDLR(-/-)) mice, and ii) supplementing standard mouse chow with unsaturated (but not saturated) LPA produced dyslipidemia and inflammation. Here we report that supplementing chow with unsaturated (but not saturated) LPA resulted in aortic atherosclerosis, which was ameliorated by adding transgenic 6F tomatoes. Supplementing chow with lysophosphatidylcholine (LysoPC) 18:1 (but not LysoPC 18:0) resulted in dyslipidemia similar to that seen on adding LPA 18:1 to chow. PF8380 (a specific inhibitor of autotaxin) significantly ameliorated the LysoPC 18:1-induced dyslipidemia. Supplementing chow with LysoPC 18:1 dramatically increased the levels of unsaturated LPA species in small intestine, liver, and plasma, and the increase was significantly ameliorated by PF8380 indicating that the conversion of LysoPC 18:1 to LPA 18:1 was autotaxin dependent. Adding LysoPC 18:0 to chow increased levels of LPA 18:0 in small intestine, liver, and plasma but was not altered by PF8380 indicating that conversion of LysoPC 18:0 to LPA 18:0 was autotaxin independent. We conclude that i) intestinally derived unsaturated (but not saturated) LPA can cause atherosclerosis in LDLR(-/-) mice, and ii) autotaxin mediates the conversion of unsaturated (but not saturated) LysoPC to LPA.

Insights from human congenital disorders of intestinal lipid metabolism

The intestine must challenge the profuse daily flux of dietary fat that serves as a vital source of energy and as an essential component of cell membranes. The fat absorption process takes place in a series of orderly and interrelated steps, including the uptake and translocation of lipolytic products from the brush border membrane to the endoplasmic reticulum, lipid esterification, Apo synthesis, and ultimately the packaging of lipid and Apo components into chylomicrons (CMs). Deciphering inherited disorders of intracellular CM elaboration afforded new insight into the key functions of crucial intracellular proteins, such as Apo B, microsomal TG transfer protein, and Sar1b GTPase, the defects of which lead to hypobetalipoproteinemia, abetalipoproteinemia, and CM retention disease, respectively. These "experiments of nature" are characterized by fat malabsorption, steatorrhea, failure to thrive, low plasma levels of TGs and cholesterol, and deficiency of liposoluble vitamins and essential FAs. After summarizing and discussing the functions and regulation of these proteins for reader's comprehension, the current review focuses on their specific roles in malabsorptions and dyslipidemia-related intestinal fat hyperabsorption while dissecting the spectrum of clinical manifestations and managements. The influence of newly discovered proteins (proprotein convertase subtilisin/kexin type 9 and angiopoietin-like 3 protein) on fat absorption has also been provided. Finally, it is stressed how the overexpression or polymorphism status of the critical intracellular proteins promotes dyslipidemia and cardiometabolic disorders.

Beneficial effects of phosphatidylcholine on high-fat diet-induced obesity, hyperlipidemia and fatty liver in mice

AIMS

Soybean-derived PC is an essential cell membrane phospholipid that is composed of unsaturated fatty acids, including oleic acid. The present study aimed to evaluate the potential alleviation effects of soybean PC on high fat diet (HFD)-induced obesity and its related complications.

MAIN METHODS

We fed C57BL/6 mice a HFD for 12 weeks and administered PC orally for 8 or 12 weeks at different doses. At the end of the experiment, blood was prepared for biochemical analysis and leptin ELISA. Aorta, epididymal and mesenteric fat and liver were removed surgically, weighed and observed for histological or immunohistochemical changes.

KEY FINDINGS

PC significantly prevented body weight gain and lipid accumulation and alleviated hyperlipidemia by decreasing triglyceride (TG) and total cholesterol (TC) levels and the atherogenic index in serum or by increasing the HDL/TC ratio. Aortic apoE expression and serum leptin levels were suppressed by PC treatment in the HFD-induced obese mouse model. Elevated serum aspartate aminotransferase and alanine aminotransferase levels in HFD-fed mice were decreased in the PC groups. PC treatment significantly decreased HFD-induced liver weight and hepatic lipid accumulation.

SIGNIFICANCE

PC treatment alleviated HFD-induced obese status and obesity-related complications such as hyperlipidemic changes that induce cardiovascular disease and NAFLD.

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.

Group 1B phospholipase A₂ inactivation suppresses atherosclerosis and metabolic diseases in LDL receptor-deficient mice

OBJECTIVE

Previous studies have shown that inactivation of the group 1B phospholipase A2 (Pla2g1b) suppresses diet-induced obesity, hyperglycemia, insulin resistance, and hyperlipidemia in C57BL/6 mice. A possible influence of Pla2g1b inactivation on atherosclerosis has not been addressed previously. The current study utilized LDL receptor-deficient (Ldlr(-/-)) mice with plasma lipid levels and distribution similar to hyperlipidemic human subjects as a preclinical animal model to test the effectiveness of Pla2g1b inactivation on atherosclerosis.

METHODS AND RESULTS

The Pla2g1b(+/+)Ldlr(-/-) and Pla2g1b(-/-)Ldlr(-/-) mice were fed a low fat chow diet or a hypercaloric diet with 58.5 kcal% fat and 25 kcal% sucrose for 10 weeks. Minimal differences were observed between Pla2g1b(+/+)Ldlr(-/-) and Pla2g1b(-/-)Ldlr(-/-) mice when the animals were maintained on the low fat chow diet. However, when the animals were maintained on the hypercaloric diet, the Pla2g1(+/+)Ldlr(-/-) mice showed the expected body weight gain but the Pla2g1b(-/-)Ldlr(-/-) mice were resistant to diet-induced body weight gain. The Pla2g1b(-/-)Ldlr(-/-) mice also displayed lower fasting glucose, insulin, and plasma lipid levels compared to the Pla2g1b(+/+)Ldlr(-/-) mice, which displayed robust hyperglycemia, hyperinsulinemia, and hyperlipidemia in response to the hypercaloric diet. Importantly, atherosclerotic lesions in the aortic roots were also reduced 7-fold in the Pla2g1b(-/-)Ldlr(-/-) mice.

CONCLUSION

The effectiveness of Pla2g1b inactivation to suppress diet-induced body weight gain and reduce diabetes and atherosclerosis in LDL receptor-deficient mice suggests that pharmacological inhibition of Pla2g1b may be a viable strategy to decrease diet-induced obesity and the risk of diabetes and atherosclerosis in humans.

Micromolar changes in lysophosphatidylcholine concentration cause minor effects on mitochondrial permeability but major alterations in function

Mice deficient in group 1b phospholipase A2 have decreased plasma lysophosphatidylcholine and increased hepatic oxidation that is inhibited by intraperitoneal lysophosphatidylcholine injection. This study sought to identify a mechanism for lysophosphatidylcholine-mediated inhibition of hepatic oxidative function. Results showed that in vitro incubation of isolated mitochondria with 40-200μM lysophosphatidylcholine caused cyclosporine A-resistant swelling in a concentration-dependent manner. However, when mitochondria were challenged with 220μM CaCl2, cyclosporine A protected against permeability transition induced by 40μM, but not 80μM lysophosphatidylcholine. Incubation with 40-120μM lysophosphatidylcholine also increased mitochondrial permeability to 75μM CaCl2 in a concentration-dependent manner. Interestingly, despite incubation with 80μM lysophosphatidylcholine, the mitochondrial membrane potential was steady in the presence of succinate, and oxidation rates and respiratory control indices were similar to controls in the presence of succinate, glutamate/malate, and palmitoyl-carnitine. However, mitochondrial oxidation rates were inhibited by 30-50% at 100μM lysophosphatidylcholine. Finally, while 40μM lysophosphatidylcholine has no effect on fatty acid oxidation and mitochondria remained impermeable in intact hepatocytes, 100μM lysophosphatidylcholine inhibited fatty acid stimulated oxidation and caused intracellular mitochondrial permeability. Taken together, these present data demonstrated that LPC concentration dependently modulates mitochondrial microenvironment, with low micromolar concentrations of lysophosphatidylcholine sufficient to change hepatic oxidation rate whereas higher concentrations are required to disrupt mitochondrial integrity.

Non-systemic drugs: a critical review

Non-systemic drugs act within the intestinal lumen without reaching the systemic circulation. The first generation included polymeric resins that sequester phosphate ions, potassium ions, or bile acids for the treatment of electrolyte imbalances or hypercholesteremia. The field has evolved towards non-absorbable small molecules or peptides targeting luminal enzymes or transporters for the treatment of mineral metabolism disorders, diabetes, gastrointestinal (GI) disorders, and enteric infections. From a drug design and development perspective, non-systemic agents offer novel opportunities to address unmet medical needs while minimizing toxicity risks, but also present new challenges, including developing a better understanding and control of non-transcellular leakage pathways into the systemic circulation. The pharmacokinetic-pharmacodynamic relationship of drugs acting in the GI tract can be complex due to the variability of intestinal transit, interaction with chyme, and the complex environment of the surface epithelia. We review the main classes of nonabsorbable agents at various stages of development, and their therapeutic potential and limitations. The rapid progress in the identification of intestinal receptors and transporters, their functional characterization and role in metabolic and inflammatory disorders, will undoubtedly renew interest in the development of novel, safe, non-systemic therapeutics.

Phospholipase A(2) enzymes in metabolic and cardiovascular diseases

PURPOSE OF REVIEW

The phospholipase A2 (PLA2) family of proteins includes lipolytic enzymes that liberate the sn-2 fatty acyl chains from phospholipids to yield nonesterified fatty acids and lysophospholipids. The purpose of this review is to discuss recent findings showing distinct roles of several of these PLA2 enzymes in inflammatory metabolic diseases such as diabetes and atherosclerosis.

RECENT FINDINGS

The group 1B PLA2 digestion of phospholipids in the intestinal lumen facilitates postprandial lysophospholipid absorption, which suppresses hepatic fatty acid oxidation leading to increased VLDL synthesis, decreased glucose tolerance, and promotion of tissue lipid deposition to accentuate diet-induced hyperlipidemia, diabetes, and obesity. Other secretory PLA2s promote inflammatory metabolic diseases by generating bioactive lipid metabolites to induce inflammatory cytokine production, whereas the major intracellular PLA2s, cPLA2α, and iPLA2, generate arachidonic acid and lysophosphatic acid in response to extracellular stimuli to activate leukocyte chemotactic response.

SUMMARY

Each member of the PLA2 family of enzymes serves a distinct role in generating active lipid metabolites that promote inflammatory metabolic diseases including atherosclerosis, hyperlipidemia, obesity, and diabetes. The development of specific drugs that target one or more of these PLA2 enzymes may be novel strategies for treatment of these chronic inflammatory metabolic disorders.