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Platelet-activating factor (PAF) is a potent classical lipid mediator that plays a critical role in various diseases such as allergy and nervous system disorders. In the realm of allergy, previous studies suggested that PAF is generated in response to extracellular stimuli and contributes to allergic reactions via PAF receptor (PAFR). However, the sources of endogenous PAF and its pathophysiological dynamics remain largely elusive in vivo. Here, we report that rapid and local PAF generation completely depends on lysophospholipid acyltransferase 9 (LPLAT9, also known as LPCAT2) expressed in mast cells in IgE-mediated passive cutaneous anaphylaxis. However, we found that LPLAT9 knockout (KO) mice did not display attenuated vascular leakage. Additionally, decreased vascular leakage was observed in PAFR KO mice, but not in endothelial cell-specific mice in this model. These divergences highlight a yet unsolved complexity of the biological functions of PAF and PAFR in a pathophysiological process., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Patatin-like phospholipase domain-containing lipase 8 (PNPLA8), one of the calcium-independent phospholipase A2 enzymes, is involved in various physiological processes through the maintenance of membrane phospholipids. Biallelic variants in PNPLA8 have been associated with a range of paediatric neurodegenerative disorders. However, the phenotypic spectrum, genotype-phenotype correlations and the underlying mechanisms are poorly understood. Here, we newly identified 14 individuals from 12 unrelated families with biallelic ultra-rare variants in PNPLA8 presenting with a wide phenotypic spectrum of clinical features. Analysis of the clinical features of current and previously reported individuals (25 affected individuals across 20 families) showed that PNPLA8-related neurological diseases manifest as a continuum ranging from variable developmental and/or degenerative epileptic-dyskinetic encephalopathy to childhood-onset neurodegeneration. We found that complete loss of PNPLA8 was associated with the more profound end of the spectrum, with congenital microcephaly. Using cerebral organoids generated from human induced pluripotent stem cells, we found that loss of PNPLA8 led to developmental defects by reducing the number of basal radial glial cells and upper-layer neurons. Spatial transcriptomics revealed that loss of PNPLA8 altered the fate specification of apical radial glial cells, as reflected by the enrichment of gene sets related to the cell cycle, basal radial glial cells and neural differentiation. Neural progenitor cells lacking PNPLA8 showed a reduced amount of lysophosphatidic acid, lysophosphatidylethanolamine and phosphatidic acid. The reduced number of basal radial glial cells in patient-derived cerebral organoids was rescued, in part, by the addition of lysophosphatidic acid. Our data suggest that PNPLA8 is crucial to meet phospholipid synthetic needs and to produce abundant basal radial glial cells in human brain development., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Guarantors of Brain.)

The gut microbiota influences physiological functions of the host, ranging from the maintenance of local gut homeostasis to systemic immunity and metabolism. Secreted phospholipase A 2 group X (sPLA 2 -X) is abundantly expressed in colonic epithelial cells but is barely detectable in metabolic and immune tissues. Despite this distribution, sPLA 2 -X-deficient (Pla2g10 -/- ) mice displayed variable obesity-related phenotypes that were abrogated after treatment with antibiotics or cohousing with Pla2g10 +/+ mice, suggesting the involvement of the gut microbiota. Under housing conditions where Pla2g10 -/- mice showed aggravation of diet-induced obesity and insulin resistance, they displayed increased colonic inflammation and epithelial damage, reduced production of polyunsaturated fatty acids (PUFAs) and lysophospholipids, decreased abundance of several Clostridium species, and reduced levels of short-chain fatty acids (SCFAs). These obesity-related phenotypes in Pla2g10 -/- mice were reversed by dietary supplementation with ω3 PUFAs or SCFAs. Thus, colonic sPLA 2 -X orchestrates ω3 PUFA-SCFA interplay via modulation of the gut microbiota, thereby secondarily affecting systemic metabolism., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Interaction of mast cells (MCs) with fibroblasts is essential for MC maturation within tissue microenvironments, although the underlying mechanism is incompletely understood. Through a phenotypic screening of >30 mouse lines deficient in lipid-related genes, we found that deletion of the lysophosphatidic acid (LPA) receptor LPA 1 , like that of the phospholipase PLA2G3, the prostaglandin D 2 (PGD 2 ) synthase L-PGDS, or the PGD 2 receptor DP1, impairs MC maturation and thereby anaphylaxis. Mechanistically, MC-secreted PLA2G3 acts on extracellular vesicles (EVs) to supply lysophospholipids, which are converted by fibroblast-derived autotaxin (ATX) to LPA. Fibroblast LPA 1 then integrates multiple pathways required for MC maturation by facilitating integrin-mediated MC-fibroblast adhesion, IL-33-ST2 signaling, L-PGDS-driven PGD 2 generation, and feedforward ATX-LPA 1 amplification. Defective MC maturation resulting from PLA2G3 deficiency is restored by supplementation with LPA 1 agonists or PLA2G3-modified EVs. Thus, the lipid-orchestrated paracrine circuit involving PLA2G3-driven lysophospholipid, eicosanoid, integrin, and cytokine signaling fine-tunes MC-fibroblast communication, ensuring MC maturation., Competing Interests: Declaration of interests J.C. has an employment relationship with Neurocrine Biosciences, Inc. as a Distinguished Scholar, unrelated to the current manuscript., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Current treatments of eosinophilic chronic rhinosinusitis (ECRS) involve corticosteroids with various adverse effects and costly therapies such as dupilumab, highlighting the need for improved treatments. However, because of the lack of a proper mouse ECRS model that recapitulates human ECRS, molecular mechanisms underlying this disease are incompletely understood. ECRS is often associated with aspirin-induced asthma, suggesting that dysregulation of lipid mediators in the nasal mucosa may underlie ECRS pathology. We herein found that the expression of microsomal PGE synthase-1 (encoded by PTGES ) was significantly lower in the nasal mucosa of ECRS patients than that of non-ECRS subjects. Histological, transcriptional, and lipidomics analyses of Ptges -deficient mice revealed that defective PGE 2 biosynthesis facilitated eosinophil recruitment into the nasal mucosa, elevated expression of type-2 cytokines and chemokines, and increased pro-allergic and decreased anti-allergic lipid mediators following challenges with Aspergillus protease and ovalbumin. A nasal spray containing agonists for the PGE 2 receptor EP2 or EP4, including omidenepag isopropyl that has been clinically used for treatment of glaucoma, markedly reduced intranasal eosinophil infiltration in Ptges -deficient mice. These results suggest that the present model using Ptges -deficient mice is more relevant to human ECRS than are previously reported models and that eosinophilic inflammation in the nasal mucosa can be efficiently blocked by activation of the PGE 2 -EP2 pathway. Furthermore, our findings suggest that drug repositioning of omidenepag isopropyl may be useful for treatment of patients with ECRS., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Horikiri, Taketomi, Kondo, Yamasoba and Murakami.)

Asthma is a chronic inflammatory disease of the airways characterized by recurrent episodes of airway obstruction, hyperresponsiveness, remodeling, and eosinophilia. Phospholipase A 2 s (PLA 2 s), which release fatty acids and lysophospholipids from membrane phospholipids, have been implicated in exacerbating asthma by generating pro-asthmatic lipid mediators, but an understanding of the association between individual PLA 2 subtypes and asthma is still incomplete. Here, we show that group III-secreted PLA 2 (sPLA 2 -III) plays an ameliorating, rather than aggravating, role in asthma pathology. In both mouse and human lungs, sPLA 2 -III was expressed in bronchial epithelial cells and decreased during the asthmatic response. In an ovalbumin (OVA)-induced asthma model, Pla2g3 -/- mice exhibited enhanced airway hyperresponsiveness, eosinophilia, OVA-specific IgE production, and type 2 cytokine expression as compared to Pla2g3 +/+ mice. Lipidomics analysis showed that the pulmonary levels of several lysophospholipids, including lysophosphatidylcholine, lysophosphatidylethanolamine, and lysophosphatidic acid (LPA), were decreased in OVA-challenged Pla2g3 -/- mice relative to Pla2g3 +/+ mice. LPA receptor 2 (LPA 2 ) agonists suppressed thymic stromal lymphopoietin (TSLP) expression in bronchial epithelial cells and reversed airway hyperresponsiveness and eosinophilia in Pla2g3 -/- mice, suggesting that sPLA 2 -III negatively regulates allergen-induced asthma at least by producing LPA. Thus, the activation of the sPLA 2 -III-LPA pathway may be a new therapeutic target for allergic asthma., (© 2024 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)

Macrophages are essential for the proper inflammatory and reparative processes that lead to regeneration of skeletal muscle after injury. Recent studies have demonstrated close links between the function of activated macrophages and their cellular metabolism. Sterol regulatory element-binding protein 1 (SREBP1) is a key regulator of lipid metabolism and has been shown to affect the activated states of macrophages. However, its role in tissue repair and regeneration is poorly understood. Here we show that systemic deletion of Srebf1 , encoding SREBP1, or macrophage-specific deletion of Srebf1a , encoding SREBP1a, delays resolution of inflammation and impairs skeletal muscle regeneration after injury. Srebf1 deficiency impairs mitochondrial function in macrophages and suppresses the accumulation of macrophages at sites of muscle injury. Lipidomic analyses showed the reduction of major phospholipid species in Srebf1 -/- muscle myeloid cells. Moreover, diet supplementation with eicosapentaenoic acid restored the accumulation of macrophages and their mitochondrial gene expression and improved muscle regeneration. Collectively, our results demonstrate that SREBP1 in macrophages is essential for repair and regeneration of skeletal muscle after injury and suggest that SREBP1-mediated fatty acid metabolism and phospholipid remodeling are critical for proper macrophage function in tissue repair., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Oishi, Koike, Kumagami, Nakagawa, Araki, Taketomi, Miki, Matsuda, Kim, Matsuzaka, Ozawa, Shimano, Murakami and Manabe.)

The brain is generally resistant to regeneration after damage. The cerebral endogenous mechanisms triggering brain self-recovery have remained unclarified to date. We here discovered that the secreted phospholipase PLA2G2E from peri-infarct neurons generated dihomo-γ-linolenic acid (DGLA) as necessary for triggering brain-autonomous neural repair after ischemic brain injury. Pla2g2e deficiency diminished the expression of peptidyl arginine deiminase 4 (Padi4), a global transcriptional regulator in peri-infarct neurons. Single-cell RNA sequencing (scRNA-seq) and epigenetic analysis demonstrated that neuronal PADI4 had the potential for the transcriptional activation of genes associated with recovery processes after ischemic stroke through histone citrullination. Among various DGLA metabolites, we identified 15-hydroxy-eicosatrienoic acid (15-HETrE) as the cerebral metabolite that induced PADI4 in peri-infarct-surviving neurons. Administration of 15-HETrE enhanced functional recovery after ischemic stroke. Thus, our research clarifies the promising potential of brain-autonomous neural repair triggered by the specialized lipids that initiate self-recovery processes after brain injury., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Metabolic fluxes involving fatty acid biosynthesis play essential roles in controlling the differentiation of T helper 17 (T H 17) cells. However, the exact enzymes and lipid metabolites involved, as well as their link to promoting the core gene transcriptional signature required for the differentiation of T H 17 cells, remain largely unknown. From a pooled CRISPR-based screen and unbiased lipidomics analyses, we identified that 1-oleoyl-lysophosphatidylethanolamine could act as a lipid modulator of retinoid-related orphan receptor gamma t (RORγt) activity in T H 17 cells. In addition, we specified five enzymes, including Gpam , Gpat3 , Lplat1 , Pla2g12a , and Scd2 , suggestive of the requirement of glycerophospholipids with monounsaturated fatty acids being required for the transcription of Il17a . 1-Oleoyl-lysophosphatidylethanolamine was reduced in Pla2g12a -deficient T H 17 cells, leading to the abolition of interleukin-17 (IL-17) production and disruption to the core transcriptional program required for the differentiation of T H 17 cells. Furthermore, mice with T cell-specific deficiency of Pla2g12a failed to develop disease in an experimental autoimmune encephalomyelitis model of multiple sclerosis. Thus, our data indicate that 1-oleoyl-lysophosphatidylethanolamine is a lipid metabolite that promotes RORγt-induced T H 17 cell differentiation and the pathogenicity of T H 17 cells.

Among the phospholipase A 2 (PLA 2 ) superfamily, which typically catalyzes the sn-2 hydrolysis of phospholipids to yield fatty acids and lysophospholipids, the secreted PLA 2 (sPLA 2 ) family contains 11 isoforms in mammals. Individual sPLA 2 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 sPLA 2 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 sPLA 2 s in given tissue microenvironments. sPLA 2 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 sPLA 2 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 sPLA 2 s in various immune responses and associated diseases., (© 2023 The Authors. Immunological Reviews published by John Wiley & Sons Ltd.)

The in vivo roles of lysophospholipase, which cleaves a fatty acyl ester of lysophospholipid, remained unclear. Recently, we have unraveled a previously unrecognized physiological role of the lysophospholipase PNPLA7, a member of the Ca 2+ -independent phospholipase A 2 (iPLA 2 ) family, as a key regulator of the production of glycerophosphocholine (GPC), a precursor of endogenous choline, whose methyl groups are preferentially fluxed into the methionine cycle in the liver. PNPLA7 deficiency in mice markedly decreases hepatic GPC, choline, and several metabolites related to choline/methionine metabolism, leading to various symptoms reminiscent of methionine shortage. Overall metabolic alterations in the liver of Pnpla7 -null mice in vivo largely recapitulate those in methionine-deprived hepatocytes in vitro. Reduction of the methyl donor S -adenosylmethionine (SAM) after methionine deprivation decreases the methylation of the PNPLA7 gene promoter, relieves PNPLA7 expression, and thereby increases GPC and choline levels, likely as a compensatory adaptation. In line with the view that SAM prevents the development of liver cancer, the expression of PNPLA7, as well as several enzymes in the choline/methionine metabolism, is reduced in human hepatocellular carcinoma. These findings uncover an unexplored role of a lysophospholipase in hepatic phospholipid catabolism coupled with choline/methionine metabolism.

Choline supplies methyl groups for regeneration of methionine and the methyl donor S-adenosylmethionine in the liver. Here, we report that the catabolism of membrane phosphatidylcholine (PC) into water-soluble glycerophosphocholine (GPC) by the phospholipase/lysophospholipase PNPLA8-PNPLA7 axis enables endogenous choline stored in hepatic PC to be utilized in methyl metabolism. PNPLA7-deficient mice show marked decreases in hepatic GPC, choline, and several metabolites related to the methionine cycle, accompanied by various signs of methionine insufficiency, including growth retardation, hypoglycemia, hypolipidemia, increased energy consumption, reduced adiposity, increased fibroblast growth factor 21 (FGF21), and an altered histone/DNA methylation landscape. Moreover, PNPLA8-deficient mice recapitulate most of these phenotypes. In contrast to wild-type mice fed a methionine/choline-deficient diet, both knockout strains display decreased hepatic triglyceride, likely via reductions of lipogenesis and GPC-derived glycerol flux. Collectively, our findings highlight the biological importance of phospholipid catabolism driven by PNPLA8/PNPLA7 in methyl group flux and triglyceride synthesis in the liver., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Sepsis is a systemic response to infection with life-threatening consequences. Our understanding of the impact of sepsis across organs of the body is rudimentary. Here, using mouse models of sepsis, we generate a dynamic, organism-wide map of the pathogenesis of the disease, revealing the spatiotemporal patterns of the effects of sepsis across tissues. These data revealed two interorgan mechanisms key in sepsis. First, we discover a simplifying principle in the systemic behavior of the cytokine network during sepsis, whereby a hierarchical cytokine circuit arising from the pairwise effects of TNF plus IL-18, IFN-γ, or IL-1β explains half of all the cellular effects of sepsis on 195 cell types across 9 organs. Second, we find that the secreted phospholipase PLA2G5 mediates hemolysis in blood, contributing to organ failure during sepsis. These results provide fundamental insights to help build a unifying mechanistic framework for the pathophysiological effects of sepsis on the body.

Background: Although hypercholesterolemia reportedly counteracts lymphocyte trafficking across lymphatic vessels, the roles of lymphatic endothelial cells (LECs) in the lymphocyte regulations remain unclear. Previous studies showed that calpain-an intracellular modulatory protease-interferes with leukocyte dynamics in the blood microcirculation and is associated with hypercholesterolemic dysfunction in vascular endothelial cells., Methods: This study investigated whether the calpain systems in LECs associate with the LEC-lymphocyte interaction under hypercholesterolemia using gene-targeted mice., Results: Lipidomic analysis in hypercholesterolemic mice showed that several lysophospholipids, including lysophosphatidic acid, accumulated in the lymphatic environment. Lysophosphatidic acid enables the potentiation of calpain systems in cultured LECs, which limits their ability to stabilize regulatory T cells (Treg) without altering Th1/Th2 (T helper type1/2) subsets. This occurs via the proteolytic degradation of MEKK1 (mitogen-activated protein kinase kinase kinase 1) and the subsequent inhibition of TGF (transforming growth factor)-β1 production in LECs. Targeting calpain systems in LECs expanded Tregs in the blood circulation and reduced aortic atherosclerosis in hypercholesterolemic mice, concomitant with the reduction of proinflammatory macrophages in the lesions. Treg expansion in the blood circulation and atheroprotection in calpain-targeted mice was prevented by the administration of TGF-β type-I receptor inhibitor. Moreover, lysophosphatidic acid-induced calpain overactivation potentiated the IL (interleukin)-18/NF-κB (nuclear factor κB)/VCAM1 (vascular cell adhesion molecule 1) axis in LECs, thereby inhibiting lymphocyte mobility on the cells. Indeed, VCAM1 in LECs was upregulated in hypercholesterolemic mice and human cases of coronary artery disease. Neutralization of VCAM1 or targeting LEC calpain systems recovered afferent Treg transportation via lymphatic vessels in mice., Conclusions: Calpain systems in LECs have a key role in controlling Treg stability and trafficking under hypercholesterolemia.

Milk lipids are an important energy source for infants, but the composition of milk lipids has not yet been clarified in detail. In this study, we analyzed free fatty acids and their metabolites in milk from humans and cows. In comparison to cow milk, human milk showed a higher content of free fatty acids including polyunsaturated fatty acids, especially ω-3 fatty acids and their metabolites. Polyunsaturated fatty acids were enriched at an early period of lactation, while saturated fatty acids did not change significantly over the period. Moreover, human milk contained high levels of ω-3 fatty acid metabolites, particularly 18-hydroxyeicosapentaenoic acid, an eicosapentaenoic acid-derived metabolite with anti-inflammatory activity. In comparison with human normal milk, thromboxane B 2 and protectin D1 levels were significantly elevated in milk from individuals with mastitis, suggesting that these lipid mediators could be potential biomarkers of obstructive mastitis. Overall, the unique lipid profile of human milk supports the efficacy of breast-feeding for supply of more nutritional and bioactive lipids in comparison to artificial or cow milk to infants, in whom digestive and absorptive functions are still immature., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the reported work., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Among the phospholipase A 2 (PLA 2 ) superfamily, group IVA cytosolic PLA 2 (cPLA 2 α) is currently attracting much attention as a central regulator of arachidonic acid (AA) metabolism linked to eicosanoid biosynthesis. Following cell activation, cPLA 2 α selectively releases AA, a precursor of a variety of eicosanoids, from phospholipids in perinuclear membrane compartments. cPLA 2 α-null mice display various phenotypes that could be largely explained by reduced eicosanoid signaling. In contrast, group IVE cPLA 2 ε, another member of the cPLA 2 family, acts as a Ca 2+ -dependent N-acyltransferase rather than a PLA 2 , thereby regulating the biosynthesis of N-acylethanolamines (NAEs), a unique class of lipid mediators with an anti-inflammatory effect. In response to Ca 2+ signaling, cPLA 2 ε translocates to phosphatidylserine-rich organelle membranes in the endocytic/recycling pathway. In vivo, cPLA 2 ε is induced in keratinocytes of psoriatic skin, and its genetic deletion exacerbates psoriatic inflammation due to a marked reduction of NAE-related lipids. cPLA 2 ε also contributes to NAE generation in several if not all mouse tissues. Thus, the two members of the cPLA 2 family, cPLA 2 α and cPLA 2 ε, catalyze distinct enzymatic reactions to mobilize distinct sets of lipid mediators, thereby differently regulating pathophysiological events in health and disease. Such segregation of the cPLA 2 α-eicosanoid and cPLA 2 ε-NAE pathways represents a new paradigm of research on PLA 2 s and lipid mediators., (Copyright © 2022. Published by Elsevier Inc.)

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 A 2 (PLA 2 ) enzymes. Through a series of studies employing gene targeting and lipidomics, several enzymes belonging to the PLA 2 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 PLA 2 -driven lipid pathways in mast cell biology., Competing Interests: The authors declare that the research was conducted in the absence of any commercial and financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Taketomi and Murakami.)

Phospholipids in the membrane consist of diverse pairs of fatty acids bound to a glycerol backbone. The biological significance of the diversity, however, remains mostly unclear. Part of this diversity is due to lysophospholipid acyltransferases (LPLATs), which introduce a fatty acid into lysophospholipids. The human genome has 14 LPLATs and most of them are highly conserved in vertebrates. Here, we analyzed the function of one of these enzymes, lysophosphatidylglycerol acyltransferase 1 (Lpgat1), in zebrafish. We found that the reproduction of heterozygous (lpgat1 +/- ) male mutants was abnormal. Crosses between heterozygous males and wild-type females produced many eggs with no obvious cleavage, whereas eggs produced by crosses between heterozygous females and wild-type males cleaved normally. Consistent with this, spermatozoa from heterozygous males had reduced motility and abnormal morphology. We also found that the occurrence of lpgat1 homozygous (lpgat1 -/- ) mutants was far lower than expected. In addition, downregulation of lpgat1 by morpholino antisense oligonucleotides resulted in severe developmental defects. Lipidomic analysis revealed that selective phospholipid species with stearic acid and docosahexaenoic acid were reduced in homozygous larvae and spermatozoa from heterozygotes. These results suggest that the specific phospholipid molecular species produced by Lpgat1 have an essential role in sperm fertilization and in embryonic development., (© 2022. The Author(s).)

Psoriasis is an inflammatory disorder characterized by keratinocyte hyper-proliferation and Th17-type immune responses. However, the roles of bioactive lipids and the regulation of their biosynthesis in this chronic skin disease are not fully understood. Herein, we show that group IVE cytosolic phospholipase A 2 (cPLA 2 ε/PLA2G4E) plays a counterregulatory role against psoriatic inflammation by producing the anti-inflammatory lipid N-acylethanolamine (NAE). Lipidomics analysis of mouse skin revealed that NAE species and their precursors (N-acyl-phosphatidylethanolamine and glycerophospho-N-acylethanolamine) were robustly increased in parallel with the ongoing process of imiquimod (IMQ)-induced psoriasis, accompanied by a marked upregulation of cPLA 2 ε in epidermal keratinocytes. Genetic deletion of cPLA 2 ε exacerbated IMQ-induced ear swelling and psoriatic marker expression, with a dramatic reduction of NAE-related lipids in IMQ-treated, and even normal, skin. Stimulation of cultured human keratinocytes with psoriatic cytokines concomitantly increased PLA2G4E expression and NAE production, and supplementation with NAEs significantly attenuated the cytokine-induced upregulation of the psoriatic marker S100A9. Increased expression of cPLA 2 ε was also evident in the epidermis of psoriatic patients. These findings reveal for the first time the in vivo role of cPLA 2 ε, which is highly induced in the keratinocytes of the psoriatic skin, promotes the biosynthesis of NAE-related lipids, and contributes to limiting psoriatic inflammation., (© 2022 Federation of American Societies for Experimental Biology.)

Among the phospholipase A 2 (PLA 2 ) superfamily, the secreted PLA 2 (sPLA 2 ) family contains 11 mammalian isoforms that exhibit unique tissue or cellular distributions and enzymatic properties. Current studies using sPLA 2 -deficient or -overexpressed mouse strains, along with mass spectrometric lipidomics to determine sPLA 2 -driven lipid pathways, have revealed the diverse pathophysiological roles of sPLA 2 s in various biological events. In general, individual sPLA 2 s 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 sPLA 2 (sPLA 2 -IIA), a prototypic sPLA 2 with the oldest research history among the mammalian PLA 2 s, as a modulator of the gut microbiota. In the intestine, Paneth cell-derived sPLA 2 -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 sPLA 2 -IIA in BALB/c mice leads to alterations in skin cancer, psoriasis, and anaphylaxis, while overexpression of sPLA 2 -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 sPLA 2 and add the sPLA 2 family to the growing list of endogenous factors capable of affecting the microbe-host interaction and thereby systemic homeostasis and diseases.

The effects of a crowded environment on DNA-mediated electron transfer were evaluated using a pyrene-modified oligonucleotide containing a hole-trapping nucleobase in poly(ethylene glycol) mixed solutions. Rapid decompositions of hole-trapping bases in condensed and noncondensed DNA showed that more efficient electron transfer occurred under crowded conditions than in dilute solutions.

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.

Tissue-resident mast cells (MCs) have important roles in IgE-associated and -independent allergic reactions. Although microenvironmental alterations in MC phenotypes affect the susceptibility to allergy, understanding of the regulation of MC maturation is still incomplete. We previously reported that group III secreted phospholipase A 2 (sPLA 2 -III) released from immature MCs is functionally coupled with lipocalin-type prostaglandin D 2 (PGD 2 ) synthase in neighboring fibroblasts to supply a microenvironmental pool of PGD 2 , which in turn acts on the PGD 2 receptor DP1 on MCs to promote their proper maturation. In the present study, we reevaluated the role of sPLA 2 -III in MCs using a newly generated MC-specific Pla2g3 -deficient mouse strain. Mice lacking sPLA 2 -III specifically in MCs, like those lacking the enzyme in all tissues, had immature MCs and displayed reduced local and systemic anaphylactic responses. Furthermore, MC-specific Pla2g3 -deficient mice, as well as MC-deficient Kit W-sh mice reconstituted with MCs prepared from global Pla2g3- null mice, displayed a significant reduction in irritant contact dermatitis (ICD) and an aggravation of contact hypersensitivity (CHS). The increased CHS response by Pla2g3 deficiency depended at least partly on the reduced expression of hematopoietic PGD 2 synthase and thereby reduced production of PGD 2 due to immaturity of MCs. Overall, our present study has confirmed that MC-secreted sPLA 2 -III promotes MC maturation, thereby facilitating acute anaphylactic and ICD reactions and limiting delayed CHS response.

Autophagy is an intracellular degradation system, but its physiological functions in vertebrates are not yet fully understood. Here, we show that autophagy is required for inflation of air-filled organs: zebrafish swim bladder and mouse lung. In wild-type zebrafish swim bladder and mouse lung type II pulmonary epithelial cells, autophagosomes are formed and frequently fuse with lamellar bodies. The lamellar body is a lysosome-related organelle that stores a phospholipid-containing surfactant complex that lines the air-liquid interface and reduces surface tension. We find that autophagy is critical for maturation of the lamellar body. Accordingly, atg-deficient zebrafish fail to maintain their position in the water, and type-II-pneumocyte-specific Fip200-deficient mice show neonatal lethality with respiratory failure. Autophagy suppression does not affect synthesis of the surfactant phospholipid, suggesting that autophagy supplies lipids and membranes to lamellar bodies. These results demonstrate an evolutionarily conserved role of autophagy in lamellar body maturation., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

The phospholipase A 2 (PLA 2 ) superfamily contains more than 50 enzymes in mammals that are subdivided into several distinct families on a structural and biochemical basis. In principle, PLA 2 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 PLA 2 reaction. PLA 2 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 PLA 2 -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 PLA 2 superfamily, focusing particularly on the novel roles of PLA 2 s in vivo.

Lipolysis, the breakdown of triglyceride storage in white adipose tissue, supplies fatty acids to other tissues as a fuel under fasting conditions. In morbid obesity, fibrosis limits adipocyte expandability, resulting in enforced lipolysis, ectopic fat distribution, and ultimately insulin resistance. Although basal levels of lipolysis persist even after feeding, the regulatory mechanisms of basal lipolysis remain unclear. Here, we show the important role of adipocyte prostaglandin (PG) E 2 -EP4 receptor signaling in controlling basal lipolysis, fat distribution, and collagen deposition during feeding-fasting cycles. The PGE 2 -synthesis pathway in adipocytes, which is coupled with lipolysis, is activated by insulin during feeding. By regulating the lipolytic key players, the PGE 2 -EP4 pathway sustains basal lipolysis as a negative feedback loop of insulin action, and perturbation of this process leads to "metabolically healthy obesity." The potential role of the human EP4 receptor in lipid regulation was also suggested through genotype-phenotype association analyses., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

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 A 2 group V (sPLA 2 -V), protects against aortic dissection by endogenously mobilizing vasoprotective lipids. Global and endothelial cell-specific sPLA 2 -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 sPLA 2 -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 sPLA 2 -V-deficient mice to aortic dissection. These findings reveal an unexplored functional link between sPLA 2 -driven phospholipid metabolism and aortic stability, possibly contributing to the development of improved diagnostic and/or therapeutic strategies for preventing aortic dissection., Competing Interests: Conflict of interest—The authors declare that they have no conflicts of interest with the contents of this article., (© 2020 Watanabe et al.)

Polyunsaturated fatty acids (PUFAs) confer health benefits by preventing inflammation and obesity and by increasing thermogenesis in brown and beige adipocytes. As well as being supplied exogenously as nutrients, PUFAs are largely stored in membrane glycerophospholipids and released by phospholipase A 2 s (PLA 2 s). However, the molecular identity of the PLA 2 subtype(s) that supplies endogenous PUFAs for metabolic homeostasis remains unclear. Here we show that PLA2G2D, a secreted PLA 2 isoform, is constitutively expressed in M2-type macrophages in white adipose tissue (WAT) and shows a reciprocal correlation with obesity. Studies using global and macrophage-specific Pla2g2d-deficient mice reveal that PLA2G2D increases energy expenditure and thermogenesis by facilitating adipocyte browning, thereby ameliorating diet-induced obesity, insulin resistance, and WAT inflammation. Mechanistically, PLA2G2D constitutively supplies a pool of PUFAs, ω3 in particular, in WAT. Thus, our present findings underscore the contribution of the macrophage-driven PLA2G2D-ω3 PUFA axis to metabolic health., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background: The upregulation of the cyclooxygenase and lipoxygenase pathways of arachidonic acid is thought to be involved in the development of rheumatoid arthritis. Recently, the presence of specialized pro-resolving lipid mediators in synovial tissues from patients with osteoarthritis has been reported., Objective: To clarify the quantitative and qualitative changes in lipid mediators in the synovium of severe rheumatoid arthritis patients, we compared the profiles of lipid mediators in synovial fluid obtained from patients with severe rheumatoid arthritis and from those with severe osteoarthritis., Methods: We enrolled 18 patients with rheumatoid arthritis and 26 patients with osteoarthritis. All the patients had undergone total knee replacement surgery. Synovial fluid samples had been obtained during the surgery. Lipid profiling in the synovial fluid from these patients was performed using liquid chromatography-tandem mass spectrometry/mass spectrometry., Results: Among the 150 oxidized fatty acids examined so far, 119 were substantially detected in synovial fluid from the patients. Not only the concentrations of pro-inflammatory lipid mediators such as prostaglandins and leukotrienes, but also those of specialized pro-resolving lipid mediators such as lipoxins, resolvins, and protectin D1 were significantly higher in synovial fluid obtained from rheumatoid arthritis patients than from synovial fluid obtained from osteoarthritis patients., Conclusion: The activation of both inflammation and resolution pathways of lipid mediators might be a fatty acid signature in the synovial fluid of patients with severe rheumatoid arthritis. Inflammatory, anti-inflammatory and pro-resolving mediators in synovial fluid could be good biomarkers for differentiating between severe rheumatoid arthritis and severe osteoarthritis., Competing Interests: Conflict of Interest: The authors have no financial conflicts of interest., (Copyright © 2020. Asia Pacific Association of Allergy, Asthma and Clinical Immunology.)

Among the 11 members of the secreted phospholipase A 2 (sPLA 2 ) family, group IID, IIE, IIF and III sPLA 2 s (sPLA 2 -IID, -IIE, -IIF and -III, respectively) are "new" isoforms in the history of sPLA 2 research. Relative to the better characterized sPLA 2 s (sPLA 2 -IB, -IIA, -V and -X), the enzymatic properties, distributions, and functions of these "new" sPLA 2 s have remained obscure until recently. Our current studies using knockout and transgenic mice for a nearly full set of sPLA 2 s, in combination with comprehensive lipidomics, have revealed unique and distinct roles of these "new" sPLA 2 s in specific biological events. Thus, sPLA 2 -IID is involved in immune suppression, sPLA 2 -IIE in metabolic regulation and hair follicle homeostasis, sPLA 2 -IIF in epidermal hyperplasia, and sPLA 2 -III in male reproduction, anaphylaxis, colonic diseases, and possibly atherosclerosis. In this article, we overview current understanding of the properties and functions of these sPLA 2 s and their underlying lipid pathways in vivo., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The skin represents one of the tissues that are most profoundly influenced by alterations in the quality of lipids (lipoquality). Lipids not only constitute cellular membranes, but also serve as bioactive lipid mediators and essential components of the skin barrier. Phospholipase A 2 (PLA 2 ) enzymes supply fatty acids and lysophospholipids from membrane phospholipids, thereby variably affecting cutaneous homeostasis. Accordingly, perturbation of particular PLA 2 -driven lipid pathways can be linked to various forms of skin disease. In this review article, we highlight the roles of several PLA 2 subtypes in cutaneous pathophysiology, as revealed by transgenic/knockout studies in combination with comprehensive lipidomics. We focus mainly on secreted PLA 2 group IIF (sPLA 2 -IIF), which is associated with epidermal hyperplasia through mobilization of a unique lipid metabolite. We also address the distinct roles of sPLA 2 -IIE in hair follicles and sPLA 2 -IID in lymphoid immune cells that secondarily affect cutaneous inflammation, and provide some insights into species differences in sPLA 2 s. Additionally, we briefly overview the patatin-like phospholipase PNPLA1, which belongs to the Ca 2+ -independent PLA 2 (iPLA 2 ) family, as a key regulator of skin barrier function through catalysis of a unique non-PLA 2 reaction. These knowledges on lipid metabolism driven by various PLA 2 subtypes will open novel opportunities for translated studies toward diagnosis and therapy of human skin diseases., Competing Interests: Not applicable.Not applicable.The authors declare that they have no competing interests.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Critical to the function of mast cells in immune responses including allergy is their production of lipid mediators, among which only omega-6 (ω-6) arachidonate-derived eicosanoids have been well characterized. Here, by employing comprehensive lipidomics, we identify omega-3 (ω-3) fatty acid epoxides as new mast cell-derived lipid mediators and show that they are produced by PAF-AH2, an oxidized-phospholipid-selective phospholipase A2. Genetic or pharmacological deletion of PAF-AH2 reduced the steady-state production of ω-3 epoxides, leading to attenuated mast cell activation and anaphylaxis following FcɛRI cross-linking. Mechanistically, the ω-3 epoxides promote IgE-mediated activation of mast cells by downregulating Srcin1, a Src-inhibitory protein that counteracts FcɛRI signaling, through a pathway involving PPARg. Thus, the PAF-AH2-ω-3 epoxide-Srcin1 axis presents new potential drug targets for allergic diseases.

Lipid mediators play pivotal roles in colorectal cancer and colitis, but only a limited member of the phospholipase A 2 (PLA 2 ) subtypes, which lie upstream of various lipid mediators, have been implicated in the positive or negative regulation of these diseases. Clinical and biochemical evidence suggests that secreted PLA 2 group III (sPLA 2 -III) is associated with colorectal cancer, although its precise role remains obscure. Here we have found that sPLA 2 -III-null (Pla2g3 -/- ) mice are highly resistant to colon carcinogenesis. Furthermore, Pla2g3 -/- mice are less susceptible to dextran sulfate-induced colitis, implying that the amelioration of colonic inflammation by sPLA 2 -III ablation may underlie the protective effect against colon cancer. Lipidomics analysis of the colon revealed significant reduction of pro-inflammatory/pro-tumorigenic lysophosholipids as well as unusual steady-state elevation of colon-protective fatty acids and their oxygenated metabolites in Pla2g3 -/- mice. Overall, our results establish a role of sPLA 2 -III in the promotion of colorectal inflammation and cancer, expand our understanding of the divergent roles of multiple PLA 2 enzymes in the gastrointestinal tract, and point to sPLA 2 -III as a novel druggable target for colorectal diseases.

During pregnancy, up-regulation of heparin-binding (HB-) EGF and cyclooxygenase-2 (COX-2) in the uterine epithelium contributes to decidualization, a series of uterine morphological changes required for placental formation and fetal development. Here, we report a key role for the lipid mediator lysophosphatidic acid (LPA) in decidualization, acting through its G-protein-coupled receptor LPA 3 in the uterine epithelium. Knockout of Lpar3 or inhibition of the LPA-producing enzyme autotaxin (ATX) in pregnant mice leads to HB-EGF and COX-2 down-regulation near embryos and attenuates decidual reactions. Conversely, selective pharmacological activation of LPA 3 induces decidualization via up-regulation of HB-EGF and COX-2. ATX and its substrate lysophosphatidylcholine can be detected in the uterine epithelium and in pre-implantation-stage embryos, respectively. Our results indicate that ATX-LPA-LPA 3 signaling at the embryo-epithelial boundary induces decidualization via the canonical HB-EGF and COX-2 pathways., (© 2017 The Authors. Published under the terms of the CC BY 4.0 license.)

The secreted phospholipase A 2 (sPLA 2 ) family contains 10 catalytically active isoforms. Current in vitro biochemical studies have shown that individual sPLA 2 s have distinct substrate selectivity in terms of the polar head groups or sn-2 fatty acids of their substrate phospholipids. Importantly, transgenic or knockout mice for distinct sPLA 2 s display nonoverlapping phenotypes, arguing that they do act on different phospholipid substrates and mobilize unique lipid metabolites in vivo. In an effort to comprehensively understand lipid metabolism driven by individual sPLA 2 s under pathophysiological conditions, we took advantages of mass spectrometric lipidomics technology to monitor the spatiotemporal changes in phospholipids (substrates) and products (fatty acids, lysophospholipids, and their metabolites) in tissues or cells of sPLA 2 -transgenic or knockout mice. The in vivo lipidomic data were compared with the in vitro activity of recombinant sPLA 2 s toward phospholipid mixtures extracted from the target tissues, cells, or extracellular membrane components on which sPLA 2 s may intrinsically act. These approaches reveal that the overall tendency in in vitro assays using natural membranes is recapitulated in several in vivo systems, often with even more selective patterns of hydrolysis. In this chapter, we will summarize current understanding of the in vivo substrate specificity of sPLA 2 s toward natural membrane phospholipids., (© 2017 Elsevier Inc. All rights reserved.)

Mast cells originate from hematopoietic stem cells and undergo terminal maturation in the extravascular tissues, in which they are ultimately resident. Mast maturation, phenotype, and function are dictated by the local microenvironment, which has a significant influence on the ability of mast cells to recognize and respond to stimuli. Activation of mast cells can lead to the release of three distinct classes of mediators, including preformed mediators stored in secretory granules, newly transcribed cytokines and chemokines, and de novo-synthesized bioactive lipid mediators. It is currently recognized that bioactive lipids such as arachidonic acid metabolites (prostaglandins and leukotrienes) released from mast cells modulate innate and adaptive immune responses both directly and indirectly through communication with other microenvironmental immune cells or stroma cells. Moreover, mast cells express a variety of lipid receptors and, if activated by bioactive lipids such as arachidonic acid, ω3 fatty acids, lysophospholipids, and their metabolites, can alter the release and production of other mediators including histamine, cytokines, and chemokines, and thereby alter homeostatic or pathophysiological responses. This review focuses on newly identified functional aspects of bioactive lipids with regard to their immune regulation and functional outcomes in both homeostasis and allergic disease.

Although pneumococcal infection is a serious problem worldwide and has a high mortality rate, the molecular mechanisms underlying the lethality caused by pneumococcus remain elusive. Here, we show that BLT2, a G protein-coupled receptor for leukotriene B 4 and 12(S)-hydroxyheptadecatrienoic acid (12-HHT), protects mice from lung injury caused by a pneumococcal toxin, pneumolysin (PLY). Intratracheal injection of PLY caused lethal acute lung injury (ALI) in BLT2-deficient mice, with evident vascular leakage and bronchoconstriction. Large amounts of cysteinyl leukotrienes (cysLTs), classically known as a slow reactive substance of anaphylaxis, were detected in PLY-treated lungs. PLY-dependent vascular leakage, bronchoconstriction, and death were markedly ameliorated by treatment with a CysLT1 receptor antagonist. Upon stimulation by PLY, mast cells produced cysLTs that activated CysLT1 expressed in vascular endothelial cells and bronchial smooth muscle cells, leading to lethal vascular leakage and bronchoconstriction. Treatment of mice with aspirin or loxoprofen inhibited the production of 12-HHT and increased the sensitivity toward PLY, which was also ameliorated by the CysLT1 antagonist. Thus, the present study identifies the molecular mechanism underlying PLY-dependent ALI and suggests the possible use of CysLT1 antagonists as a therapeutic tool to protect against ALI caused by pneumococcal infection.

Psoriasis is a chronic inflammatory skin disease marked by aberrant tissue repair. Mutant mice modeling psoriasis skin characteristics have provided useful information relevant to molecular mechanisms and could serve to evaluate therapeutic strategies. Here, we found that epidermal ANGPTL6 expression was markedly induced during tissue repair in mice. Analysis of mice overexpressing ANGPTL6 in keratinocytes (K14-Angptl6 Tg mice) revealed that epidermal ANGPTL6 activity promotes aberrant epidermal barrier function due to hyperproliferation of prematurely differentiated keratinocytes. Moreover, skin tissues of K14-Angptl6 Tg mice showed aberrantly activated skin tissue inflammation seen in psoriasis. Levels of the proteins S100A9, recently proposed as therapeutic targets for psoriasis, also increased in skin tissue of K14-Angptl6 Tg mice, but psoriasis-like inflammatory phenotypes in those mice were not rescued by S100A9 deletion. This finding suggests that decreasing S100A9 levels may not ameliorate all cases of psoriasis and that diverse mechanisms underlie the condition. Finally, we observed enhanced levels of epidermal ANGPTL6 in tissue specimens from some psoriasis patients. We conclude that the K14-Angptl6 Tg mouse is useful to investigate psoriasis pathogenesis and for preclinical testing of new therapeutics. Our study also suggests that ANGPTL6 activation in keratinocytes enhances psoriasis susceptibility.

Phospholipase A2 enzymes have long been implicated in the promotion of inflammation by mobilizing pro-inflammatory lipid mediators, yet recent evidence suggests that they also contribute to anti-inflammatory or pro-resolving programs. Group IID-secreted phospholipase A2 (sPLA2-IID) is abundantly expressed in dendritic cells in lymphoid tissues and resolves the Th1 immune response by controlling the steady-state levels of anti-inflammatory lipids such as docosahexaenoic acid and its metabolites. Here, we show that psoriasis and contact dermatitis were exacerbated in Pla2g2d-null mice, whereas they were ameliorated in Pla2g2d-overexpressing transgenic mice, relative to littermate wild-type mice. These phenotypes were associated with concomitant alterations in the tissue levels of ω3 polyunsaturated fatty acid (PUFA) metabolites, which had the capacity to reduce the expression of pro-inflammatory and Th1/Th17-type cytokines in dendritic cells or lymph node cells. In the context of cancer, however, Pla2g2d deficiency resulted in marked attenuation of skin carcinogenesis, likely because of the augmented anti-tumor immunity. Altogether, these results underscore a general role of sPLA2-IID as an immunosuppressive sPLA2 that allows the microenvironmental lipid balance toward an anti-inflammatory state, exerting beneficial or detrimental impact depending upon distinct pathophysiological contexts in inflammation and cancer., (© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.)

Recent studies using knock-out mice for various secreted phospholipase A2 (sPLA2) isoforms have revealed their non-redundant roles in diverse biological events. In the skin, group IIF sPLA2 (sPLA2-IIF), an "epidermal sPLA2" expressed in the suprabasal keratinocytes, plays a fundamental role in epidermal-hyperplasic diseases such as psoriasis and skin cancer. In this study, we found that group IIE sPLA2 (sPLA2-IIE) was expressed abundantly in hair follicles and to a lesser extent in basal epidermal keratinocytes in mouse skin. Mice lacking sPLA2-IIE exhibited skin abnormalities distinct from those in mice lacking sPLA2-IIF, with perturbation of hair follicle ultrastructure, modest changes in the steady-state expression of a subset of skin genes, and no changes in the features of psoriasis or contact dermatitis. Lipidomics analysis revealed that sPLA2-IIE and -IIF were coupled with distinct lipid pathways in the skin. Overall, two skin sPLA2s, hair follicular sPLA2-IIE and epidermal sPLA2-IIF, play non-redundant roles in distinct compartments of mouse skin, underscoring the functional diversity of multiple sPLA2s in the coordinated regulation of skin homeostasis and diseases., (© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.)

Within the phospholipase A 2 (PLA 2 ) superfamily that hydrolyzes phospholipids to yield fatty acids and lysophospholipids, the secreted PLA 2 (sPLA 2 ) enzymes comprise the largest family that contains 11 isoforms in mammals. Individual sPLA 2 s exhibit unique distributions and specific enzymatic properties, suggesting their distinct biological roles. While sPLA 2 s have long been implicated in inflammation and atherosclerosis, it has become evident that they are involved in diverse biological events through lipid mediator-dependent or mediator-independent processes in a given microenvironment. In recent years, new biological aspects of sPLA 2 s have been revealed using their transgenic and knockout mouse models in combination with mass spectrometric lipidomics to unveil their target substrates and products in vivo. In this review, we summarize our current knowledge of the roles of sPLA 2 s in metabolic disorders including obesity, hepatic steatosis, diabetes, insulin resistance, and adipose tissue inflammation.

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., (© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.)

Background: IgE/Ag-stimulated mast cells release various pro-allergic inflammatory mediators, including histamine, eicosanoids, and pro-inflammatory cytokines. NecroX-5, a cell permeable necrosis inhibitor, showed cytoprotective effects in both in vitro and in vivo models. However, the anti-allergic effect of NecroX-5 has not yet been investigated. The aims of this study were to evaluate the anti-allergic activity of NecroX-5 in vivo and to investigate the underlying mechanism in vitro., Methods: The anti-allergic activity of NecroX-5 was evaluated in vitro using bone marrow-derived mast cells (BMMCs) and IgE receptor-bearing RBL-2H3 or KU812 cells and in vivo using a mouse model of passive anaphylaxis. The levels of histamine, eicosanoids (PGD2 and LTC4 ), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) were measured using enzyme immunoassay kits. The mechanism underlying the action of NecroX-5 was investigated using immunoblotting, immunoprecipitation, and gene knockdown techniques., Results: NecroX-5 markedly inhibited mast cell degranulation and the synthesis of eicosanoids, TNF-α, and IL-6 by suppressing the activation of Syk, LAT, phospholipase Cγ1, MAP kinases, the Akt/NF-κB pathway, and intracellular Ca(2+) mobilization via the activation of phosphatase SHP-1. Oral administration of NecroX-5 effectively suppressed mast cell-dependent passive cutaneous and systemic anaphylactic reactions in a dose-dependent manner., Conclusions: NecroX-5 might be a potential candidate for the development of a novel anti-allergic agent that suppresses IgE-dependent mast cells signaling., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Within the phospholipase A 2 (PLA 2 ) family that hydrolyzes phospholipids to yield fatty acids and lysophospholipids, secreted PLA 2 (sPLA 2 ) enzymes comprise the largest group containing 11 isoforms in mammals. Individual sPLA 2 s exhibit unique tissue or cellular distributions and enzymatic properties, suggesting their distinct biological roles. Although PLA 2 enzymes, particularly cytosolic PLA 2 (cPLA 2 α), have long been implicated in inflammation by driving arachidonic acid metabolism, the precise biological roles of sPLA 2 s have remained a mystery over the last few decades. Recent studies employing mice gene-manipulated for individual sPLA 2 s, 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 sPLA 2 s in various immune responses and associated diseases., (© 2016 Elsevier Inc. All rights reserved.)

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., (© 2015 Yamamoto et al.)

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., (Copyright © 2015 by the American Society for Biochemistry and Molecular Biology, Inc.)

Distortion of primary cilium formation is increasingly recognized as a key event in many human pathologies. One of the underlying mechanisms involves aberrant activation of the lipogenic transcription factor sterol regulatory element-binding protein 1c (SREBP1c), as observed in cancer cells. To gain more insight into the molecular pathways by which SREBP1c suppresses primary ciliogenesis, we searched for overlap between known ciliogenesis regulators and targets of SREBP1. One of the candidate genes that was consistently up-regulated in cellular models of SREBP1c-induced cilium repression was phospholipase A2 group III (PLA2G3), a phospholipase that hydrolyzes the sn-2 position of glycerophospholipids. Use of RNA interference and a chemical inhibitor of PLA2G3 rescued SREBP1c-induced cilium repression. Cilium repression by SREBP1c and PLA2G3 involved alterations in endosomal recycling and vesicular transport toward the cilium, as revealed by aberrant transferrin and Rab11 localization, and was largely mediated by an increase in lysophosphatidylcholine and lysophosphatidylethanolamine levels. Together these findings indicate that aberrant activation of SREBP1c suppresses primary ciliogenesis by PLA2G3-mediated distortion of vesicular trafficking and suggest that PLA2G3 is a novel potential target to normalize ciliogenesis in SREBP1c-overexpressing cells, including cancer cells., (© 2015 Gijs et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).)

Background: Although secretory phospholipase A2 (sPLA2) has been shown to be involved in various biological processes, its specific roles in sub-types of cancer development remain to be elucidated., Materials and Methods: We examined the expression of sPLA2 group III (GIII) in 142 patients with colorectal cancer using immunohistochemistry, and its correlation with clinicopathological features and outcomes. In addition, we examined the co-expression of sPLA2GIII and sPLA2GX using serial tissue sections to clarify the roles of both proteins in colorectal carcinogenesis., Results: In 66 cases, diffuse staining of sPLA2GIII was seen; this was defined as the group with high expression. High expression was associated with a significantly higher rate of lymph node metastasis (p=0.02) and poorer survival (p=0.03) compared with low expression. Patients with low sPLA2GIII and high sPLA2GX expression had a significantly higher survival rate than those with high sPLA2GIII and low sPLA2GX expression (p=0.038)., Conclusion: sPLA2GIII expression may be used as a risk factor for lymph node metastasis and a prognostic marker in colorectal cancer. In addition, sPLA2GIII and sPLA2GX may play opposing roles in colorectal carcinogenesis., (Copyright© 2015 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved.)

Rationale: Janus kinase/signal transducer and activator of transcription (JAK/STAT) signals and their endogenous inhibitor, suppressor of cytokine signaling 3 (SOCS3), in vascular endothelial cells (ECs) reportedly dominate the pathological angiogenesis. However, how these inflammatory signals are potentiated during pathological angiogenesis has not been fully elucidated. We suspected that an intracellular protease calpain, which composes the multifunctional proteolytic systems together with its endogenous inhibitor calpastatin (CAST), contributes to the JAK/STAT regulations., Objective: To specify the effect of EC calpain/CAST systems on JAK/STAT signals and their relationship with pathological angiogenesis., Methods and Results: The loss of CAST, which is ensured by several growth factor classes, was detectable in neovessels in murine allograft tumors, some human malignant tissues, and oxygen-induced retinopathy lesions in mice. EC-specific transgenic introduction of CAST caused downregulation of JAK/STAT signals, upregulation of SOCS3 expression, and depletion of vascular endothelial growth factor (VEGF)-C, thereby counteracting unstable pathological neovessels and disease progression in tumors and oxygen-induced retinopathy lesions in mice. Neutralizing antibody against VEGF-C ameliorated pathological angiogenesis in oxygen-induced retinopathy lesions. Small interfering RNA-based silencing of endogenous CAST in cultured ECs facilitated μ-calpain-induced proteolytic degradation of SOCS3, leading to VEGF-C production through amplified interleukin-6-driven STAT3 signals. Interleukin-6-induced angiogenic tube formation in cultured ECs was accelerated by CAST silencing, which is suppressible by pharmacological inhibition of JAK/STAT signals, antibody-based blockage of VEGF-C, and transfection of calpain-resistant SOCS3, whereas transfection of wild-type SOCS3 exhibited modest angiostatic effects., Conclusions: Loss of CAST in angiogenic ECs facilitates μ-calpain-induced SOCS3 degradation, which amplifies pathological angiogenesis through interleukin-6/STAT3/VEGF-C axis., (© 2015 American Heart Association, Inc.)