Hepatic phosphatidylcholine catabolism driven by PNPLA7 and PNPLA8 supplies endogenous choline to replenish the methionine cycle with methyl groups

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.

Lipid Profiles of Human Serum Fractions Enhanced with CD9 Antibody-Immobilized Magnetic Beads

Blood samples are minimally invasive and can be collected repeatedly, but they are far from the site of disease and the target molecules are diluted by the large amount of blood. Therefore, we performed lipidomics using immunoprecipitation as a method to enrich specific fractions of serum. In this study, a CD9 antibody was immobilized on magnetic beads to enrich CD9-containing components in the serum for lipidomics. The percentages of phospholipids recovered from serum by methanol and isopropanol extractions were not significantly different, but triglycerides were barely recovered from serum by methanol extraction, requiring the use of isopropanol. However, once the serum was enriched with CD9 magnetic beads, triglycerides, and phospholipids were recovered at similar levels in both methanol and isopropanol extractions. Therefore, it is possible that the triglyceride fraction of the whole serum and the triglyceride fraction were enriched in CD9 magnetic beads differ in localization and properties. In addition, the variation per disease was small in general serum lipidomics; however, the difference per disease appeared larger when CD9 magnetic bead enrichment was employed.

Lipidomic Analyses Reveal Specific Alterations of Phosphatidylcholine in Dystrophic Mdx Muscle

In Duchenne muscular dystrophy (DMD), lack of dystrophin increases the permeability of myofiber plasma membranes to ions and larger macromolecules, disrupting calcium signaling and leading to progressive muscle wasting. Although the biological origin and meaning are unclear, alterations of phosphatidylcholine (PC) are reported in affected skeletal muscles of patients with DMD that may include higher levels of fatty acid (FA) 18:1 chains and lower levels of FA 18:2 chains, possibly reflected in relatively high levels of PC 34:1 (with 16:0_18:1 chain sets) and low levels of PC 34:2 (with 16:0_18:2 chain sets). Similar PC alterations have been reported to occur in the mdx mouse model of DMD. However, altered ratios of PC 34:1 to PC 34:2 have been variably reported, and we also observed that PC 34:2 levels were nearly equally elevated as PC 34:1 in the affected mdx muscles. We hypothesized that experimental factors that often varied between studies; including muscle types sampled, mouse ages, and mouse diets; may strongly impact the PC alterations detected in dystrophic muscle of mdx mice, especially the PC 34:1 to PC 34:2 ratios. In order to test our hypothesis, we performed comprehensive lipidomic analyses of PC and phosphatidylethanolamine (PE) in several muscles (extensor digitorum longus, gastrocnemius, and soleus) and determined the mdx-specific alterations. The alterations in PC 34:1 and PC 34:2 were closely monitored from the neonate period to the adult, and also in mice raised on several diets that varied in their fats. PC 34:1 was naturally high in neonate’s muscle and decreased until age ∼3-weeks (disease onset age), and thereafter remained low in WT muscles but was higher in regenerated mdx muscles. Among the muscle types, soleus showed a distinctive phospholipid pattern with early and diminished mdx alterations. Diet was a major factor to impact PC 34:1/PC 34:2 ratios because mdx-specific alterations of PC 34:2 but not PC 34:1 were strictly dependent on diet. Our study identifies high PC 34:1 as a consistent biochemical feature of regenerated mdx-muscle and indicates nutritional approaches are also effective to modify the phospholipid compositions.

TRPV4 is activated by mechanical stimulation to induce prostaglandins release in trabecular meshwork, lowering intraocular pressure

Trabecular meshwork constitutes the conventional outflow pathway and controls intraocular pressure by regulating aqueous outflow. Mechanical stimulation has been studied as one of the triggers to regulate aqueous outflow in trabecular meshwork, but it is not well understood. We investigated that how transient receptor potential cation channel subfamily V member 4 (TRPV4) functions in human trabecular meshwork cells (HTMC) and affects intraocular pressure (IOP). HTMC were treated with TRPV4 siRNA, followed by incubation for 24 hours. We confirmed the suppression of TRPV4 mRNA expression and the reduction of Ca²⁺ influx by the TRPV4 agonist GSK1016790A in TRPV4 siRNA-treated HTMC. TRPV4 siRNA-treated HTMC exhibited a significant reduction in Ca²⁺ influx and production of arachidonic acid and prostaglandin (PG) E₂ induced by mechanical stretch, and direct activation of TRPV4 by GSK1016790A increased production of arachidonic acid, PGE₂, and PGD₂ and inhibited gel contraction. Furthermore, TRPV4-deficient mice had higher IOP than wild-type mice, and GSK1016790A administration lowered IOP. These results suggest that TRPV4 mediates the cellular response induced by trabecular meshwork stretch, leading to IOP reduction through the production of prostaglandins and inhibition of cell contraction. Targeting TRPV4 may have therapeutic benefits that lead to lowering IOP in glaucoma patients.

LimeMap: a comprehensive map of lipid mediator metabolic pathways

Lipid mediators are major factors in multiple biological functions and are strongly associated with disease. Recent lipidomics approaches have made it possible to analyze multiple metabolites and the associations of individual lipid mediators. Such systematic approaches have enabled us to identify key changes of biological relevance. Against this background, a knowledge-based pathway map of lipid mediators would be useful to visualize and understand the overall interactions of these factors. Here, we have built a precise map of lipid mediator metabolic pathways (LimeMap) to visualize the comprehensive profiles of lipid mediators that change dynamically in various disorders. We constructed the map by focusing on ω-3 and ω-6 fatty acid metabolites and their respective metabolic pathways, with manual curation of referenced information from public databases and relevant studies. Ultimately, LimeMap comprises 282 factors (222 mediators, and 60 enzymes, receptors, and ion channels) and 279 reactions derived from 102 related studies. Users will be able to modify the map and visualize measured data specific to their purposes using CellDesigner and VANTED software. We expect that LimeMap will contribute to elucidating the comprehensive functional relationships and pathways of lipid mediators.

Development of Tandem Mass Tag Labeling Method for Lipid Molecules Containing Carboxy and Phosphate Groups, and Their Stability in Human Serum

In clinical lipidomics, it is a challenge to measure a large number of samples and to reproduce the quantitative results. We expanded the range of application of the tandem mass tag (TMT) method, which is widely used in proteomics, to lipidomic fields. There are various types of lipid molecule, for example, eicosanoids have a carboxyl group and phosphatidic acid has a phosphate group. We modified these functional groups simultaneously with TMT. This approach allows for a single analysis by mixing six samples and using one of the six samples as a bridging sample; the quantitative data can be easily normalized even if the number of measurements increases. To accommodate a large number of samples, we utilize a pooled serum sample of 300 individuals as a bridging sample. The stability of these lipid molecules in serum was examined as an analytical validation for the simultaneous TMT labeling. It was found that the stability of these lipid molecules in serum differs greatly depending on the lipid species. These findings reaffirmed the importance of proper sample preparation and storage to obtain reliable data. The TMT labeling method is expected to be a useful method for lipidomics with high-throughput and reliable reproducibility.

Limitations of deuterium-labeled internal standards for quantitative electrospray ionization mass spectrometry analysis of fatty acid metabolites

RATIONALE

The electrospray ionization mass spectrometry (ESI-MS) methodology often shows poor ionization reproducibility in the analysis of biological samples. Therefore, normalization of the measured peak intensities is essential. It is believed that quantitative data with high reproducibility can be obtained by adding a constant amount of an internal standard (IS) material labeled with stable isotopes to each sample, thus allowing the correction of the quantitative value of the target compound by that of the IS. We investigated whether the presence or absence of a labeled IS improves the accuracy of these quantitative values.

METHODS

Triple quadrupole MS coupled with liquid chromatography was used to analyze fatty acid metabolites in biological samples as target compounds. Two independent systems were used to provide a measure of reproducibility in two different laboratories.

RESULTS

Data having poor reproducibility in the raw peak areas were efficiently normalized using the IS, but, crucially, the IS method using stable isotopes was not always necessary. In some cases, the reproducibility was relatively good even without using the IS. In a contaminant matrix, the MS response behavior of the target compound and its stable isotope-labeled material was complicated. Since ion suppression by matrix contaminants was dependent on the concentration of the target compound, the added amounts of the ISs were also important, Furthermore, an equivalent normalization effect was obtained by using a pooled quality control sample as an external standard, thus obviating the need for labeled IS samples, which are often expensive and sometimes not commercially available.

CONCLUSIONS

Our results raise the question as to whether the quantitative method using stable-isotope-labeled ISs is always necessary and beneficial. However, the results obtained in this study cannot be generalized because only fatty acid metabolites were examined using ESI-MS and only a highly substituted deuterium-labeled IS was used.

Quantification of Fatty Acids in Mammalian Tissues by Gas Chromatography-Hydrogen Flame Ionization Detection

In mammalian organisms, fatty acids (FAs) exist mostly in esterified forms, as building blocks of phospholipids, triglycerides, and cholesteryl esters, while some exist as non-esterified free FAs. The absolute quantification of FA species in total lipids or in a specific lipid class is critical in lipid-metabolism studies. To quantify FAs in biological samples, gas chromatography-hydrogen flame ionization detection (GC-FID)-based methods have been used as highly robust and reliable techniques. Prior to GC-FID analysis, FAs need to be derivatized to volatile FA methyl esters (FAMEs). The derivatization of unsaturated FAs using classical derivatization methods that rely on high reaction temperature requires skill; consequently, the quantification results are often unreliable. The recently available FA-methylation procedure rapidly and reliably derivatizes a variety of FA species, including poly-unsaturated FAs (PUFAs). To analyze FAs in mammalian tissue samples, lipid extraction and fractionation are also critical for robust analysis. In this report, we describe a whole protocol for the GC-FID-based FA quantification of mammalian tissue samples, including lipid extraction, fractionation, derivatization, and quantification. The protocol is useful when various FAs, especially unsaturated FAs, need to be reliably quantified.

The COX-2/PGE2 pathway suppresses apical elimination of RasV12-transformed cells from epithelia

At the initial stage of carcinogenesis, when RasV12-transformed cells are surrounded by normal epithelial cells, RasV12 cells are apically extruded from epithelia through cell competition with the surrounding normal cells. In this study, we demonstrate that expression of cyclooxygenase (COX)-2 is upregulated in normal cells surrounding RasV12-transformed cells. Addition of COX inhibitor or COX-2-knockout promotes apical extrusion of RasV12 cells. Furthermore, production of Prostaglandin (PG) E2, a downstream prostanoid of COX-2, is elevated in normal cells surrounding RasV12 cells, and addition of PGE2 suppresses apical extrusion of RasV12 cells. In a cell competition mouse model, expression of COX-2 is elevated in pancreatic epithelia harbouring RasV12-exressing cells, and the COX inhibitor ibuprofen promotes apical extrusion of RasV12 cells. Moreover, caerulein-induced chronic inflammation substantially suppresses apical elimination of RasV12 cells. These results indicate that intrinsically or extrinsically mediated inflammation can promote tumour initiation by diminishing cell competition between normal and transformed cells.

Isobaric mass tagging and triple quadrupole mass spectrometry to determine lipid biomarker candidates for Alzheimer's disease

The isobaric tagging method widely used in proteomic and lipidomic fields, with the multiple reaction monitoring (MRM) approach using a triple quadrupole mass spectrometer, was applied to identify biomarker candidates from plasma samples for Alzheimer’s disease (AD). We focused on the following phospholipids that have amino groups as the functional group: phosphatidylethanolamine (PE), Lyso-PE, phosphatidylserine, and Lyso-phosphatidylserine. We also investigated fatty acids that have a carboxy group. A sixplex tandem mass tag (TMT) was used for the isobaric tagging method in this study. The TMT reaction had high reproducibility in human plasma. A total of 196 human plasma samples from three AD cohorts were used for the study, and compared to pooled plasma quality control (QC) samples. The described method required only 40 MRM measurements, including the pooled QC samples, for a full comparison of the data. We found that the content of free fatty acids increased in AD samples in all the three cohorts, alkenyl PEs (ePEs) decreased over a one-year interval in AD patients, and ePEs weakly correlated with amyloid peptide (a-beta) 1–42 in cerebrospinal fluid. In conclusion, total free fatty acids in plasma are a risk factor for AD, and ePEs monitor candidates for AD. Therefore, TMT-lipidomics is a powerful approach for the determination of plasma biomarkers because of the high sample throughput.

Characterization of supported liquid extraction as a sample pretreatment method for eicosanoids and related metabolites in biological fluids

Sample pretreatment is an important process in liquid chromatography-mass spectrometry-based quantitative lipidomics. Reversed-phase solid phase extraction (RP-SPE) has been widely used for analyzing various types of samples, including aqueous samples such as cell culture media, plasma, serum, urine, and other biological fluids. Because lipid mediators are often protein-bound, prior deproteinization is necessary for their effective recovery. Deproteinization is typically performed by the addition of organic solvents, which requires time-consuming evaporation-reconstitution, or dilution with aqueous solvents before RP-SPE; however, both of these approaches compromise the analytical performance. As a potential alternative, we attempted to utilize supported liquid extraction (SLE), an automation-compatible variant of liquid-liquid extraction, for the determination of eicosanoids and related metabolites in aqueous samples. We screened 81 different sample diluent-eluent conditions and found that the use of 0.1% formic acid-water as the diluent and 0.1% formic acid-methyl acetate as the eluent enabled the optimum recovery of a variety of eicosanoids, except for peptide leukotrienes. The optimized SLE method efficiently removed protein from human plasma, while phospholipids and neutral lipids were modestly recovered. Moreover, the proposed method exhibited a quantitative performance comparable to that of typical ordinary RP-SPE method in the analysis of human platelets stimulated with thrombin receptor-activating peptide 6. Thus, we propose SLE as an attractive option for rapid lipid mediator extraction from aqueous samples.

Polyunsaturated fatty acids promote Plasmodium falciparum gametocytogenesis

The molecular triggers of sexual differentiation into gametocytes by blood stage Plasmodium falciparum, the most malignant human malaria parasites, are subject of much investigation for potential transmission-blocking strategies. The parasites are readily grown in vitro with culture media supplemented by the addition of human serum (10%) or by a commercially available substitute (0.5% AlbuMAX). We found better gametocytemia with serum than AlbuMAX, suggesting suboptimal concentrations of some components in the commercial product; consistent with this hypothesis, substantial concentration differences of multiple fatty acids were detected between serum- and AlbuMAX-supplemented media. Mass spectroscopy analysis distinguished the lipid profiles of gametocyte- and asexual stage-parasite membranes. Delivery of various combinations of unsaturated fatty-acid-containing phospholipids to AlbuMAX-supported gametocyte cultures improved gametocyte production to the levels achieved with human-serum-supplemented media. Maturing gametocytes readily incorporated externally supplied d5-labeled glycerol with fatty acids into unsaturated phospholipids. Phospholipids identified in this work thus may be taken up from extracellular sources or generated internally for important steps of gametocyte development. Further study of polyunsaturated fatty-acid metabolism and phospholipid profiles will improve understanding of gametocyte development and malaria parasite transmission.

Monoacylglycerol lipase deficiency affects diet-induced obesity, fat absorption, and feeding behavior in CB1 cannabinoid receptor-deficient mice

Excess energy intake causes obesity, which leads to insulin resistance and various other complications of metabolic syndrome, including diabetes, atherosclerosis, dyslipidemia, and nonalcoholic fatty liver disease. Although recent studies have depicted altered lipid metabolism as an underlying feature, the detailed mechanisms are still unclear. Here we describe a possible role in high-fat diet (HFD)-induced obesity for monoacylglycerol lipase (MGL), an enzyme that is also known to hydrolyze the endocannabinoid 2-arachidonoylglycerol in brain. MGL-deficient [MGL-knockout (KO)] mice fed a HFD gained less body weight than wild-type mice and were protected from insulin resistance and hepatic steatosis. Food intake and energy expenditure were not altered in MGL-KO mice, but blood triglyceride levels after oral olive oil gavage were suppressed, indicating a role for MGL in intestinal fat absorption. Experiments with cannabinoid receptor type 1 (CB₁)/MGL double-KO mice revealed that these phenotypes may include mechanisms that are independent of CB₁-receptor-mediated endocannabinoid functions. We also noted that MGL-KO mice had less preference for HFD over normal chow diet. Oral but not intraperitoneal lipid administration strongly suppressed the appetites of MGL-KO and CB₁/MGL double-KO mice, but not of wild-type and CB₁-KO mice. Appetite suppression was reversed by vagotomy, suggesting involvement of MGL in the gut-brain axis regulation of appetite. Our results provide mechanistic insights of MGL's role in diet-induced obesity, lipid metabolic disorder, and regulation of appetite.-Yoshida, K., Kita, Y., Tokuoka, S. M., Hamano, F., Yamazaki, M., Sakimura, K., Kano, M., Shimizu, T. Monoacylglycerol lipase deficiency affects diet-induced obesity, fat absorption, and feeding behavior in CB₁ cannabinoid receptor-deficient mice.

LPAAT3 incorporates docosahexaenoic acid into skeletal muscle cell membranes and is upregulated by PPARδ activation

Adaption of skeletal muscle to endurance exercise includes PPARδ- and AMP-activated protein kinase (AMPK)/PPARγ coactivator 1α-mediated transcriptional responses that result in increased oxidative capacity and conversion of glycolytic to more oxidative fiber types. These changes are associated with whole-body metabolic alterations including improved glucose handling and resistance to obesity. Increased DHA (22:6n-3) content in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) is also reported in endurance exercise-trained glycolytic muscle; however, the DHA-metabolizing enzymes involved and the biological significance of the enhanced DHA content are unknown. In the present study, we identified lysophosphatidic acid acyltransferase (LPAAT)3 as an enzyme that was upregulated in myoblasts during in vitro differentiation and selectively incorporated DHA into PC and PE. LPAAT3 expression was increased by pharmacological activators of PPARδ or AMPK, and combination treatment led to further increased LPAAT3 expression and enhanced incorporation of DHA into PC and PE. Our results indicate that LPAAT3 was upregulated by exercise-induced signaling pathways and suggest that LPAAT3 may also contribute to the enhanced phospholipid-DHA content of endurance-trained muscles. Identification of DHA-metabolizing enzymes in the skeletal muscle will help to elucidate broad metabolic effects of DHA.

Multiplex quantitative analysis of eicosanoid mediators in human plasma and serum: Possible introduction into clinical testing

Eicosanoid mediators play important roles in maintaining the physiological and pathophysiological homeostasis in the body. Their measurements, however, are rarely performed in clinical practice. In the present study, we analyzed 30 varieties of eicosanoid mediators that were detectable in human plasma and serum collected from healthy donors, using liquid chromatography-tandem mass spectrometry from the viewpoint of the clinical application of the multiplex quantitation of eicosanoid mediators. Wider variety of eicosanoid mediators were detected in serum (27 out of 30) than in plasma (14 out of 30), since the serum was thought to contain lipid mediators released from activated platelets. Larger inter-individual variations were observed in the plasma and serum eicosanoid levels. On the other hand, the concentrations of eicosanoids were not affected by the platelet count but were affected by the concentration of arachidonic acid (AA) within the reference interval (17.4-40.5×10¹⁰/L). When serum samples from patients with hematological disorders were analyzed, the concentrations of AA were positively correlated with the platelet count. When the patients underwent ASA therapy, a marked decrease in the concentrations of thromboxane B₂ (TXB₂) and 12-hydroxyl-heptadecatrienoic acid (12-HHT) was observed. Considering the availability of serum samples in clinical settings, the serum analysis of eicosanoids may be clinically useful.

Glycerol kinase of African trypanosomes possesses an intrinsic phosphatase activity

BACKGROUND

In general, glycerol kinases (GKs) are transferases that catalyze phospho group transfer from ATP to glycerol, and the mechanism was suggested to be random bi-bi. The reverse reaction i.e. phospho transfer from glycerol 3-phosphate (G3P) to ADP is only physiologically feasible by the African trypanosome GK. In contrast to other GKs the mechanism of Trypanosoma brucei gambiense glycerol kinase (TbgGK) was shown to be in an ordered fashion, and proceeding via autophosphorylation. From the unique reaction mechanism of TbgGK, we envisaged its potential to possess phosphatase activity in addition to being a kinase.

METHODS

Our hypothesis was tested by spectrophotometric and LC-MS/MS analyses using paranitrophenyl phosphate (pNPP) and TbgGK's natural substrate, G3P respectively. Furthermore, protein X-ray crystallography and site-directed mutagenesis were performed to examine pNPP binding, catalytic residues, and the possible reaction mechanism.

RESULTS

In addition to its widely known and expected phosphotransferase (class II) activity, TbgGK can efficiently facilitate the hydrolytic cleavage of phosphoric anhydride bonds (a class III property). This phosphatase activity followed the classical Michaelis-Menten pattern and was competitively inhibited by ADP and G3P, suggesting a common catalytic site for both activities (phosphatase and kinase). The structure of the TGK-pNPP complex, and structure-guided mutagenesis implicated T276 to be important for the catalysis. Remarkably, we captured a crystallographic molecular snapshot of the phosphorylated T276 reaction intermediate.

CONCLUSION

We conclude that TbgGK has both kinase and phosphatase activities.

GENERAL SIGNIFICANCE

This is the first report on a bifunctional kinase/phosphatase enzyme among members of the sugar kinase family.

Relief from neuropathic pain by blocking of the platelet-activating factor-pain loop

Neuropathic pain resulting from peripheral neuronal damage is largely resistant to treatment with currently available analgesic drugs. Recently, ATP, lysophosphatidic acid, and platelet-activating factor (PAF) have been reported to play important inductive roles in neuropathic pain. In the present study, we found that pain-like behaviors resulting from partial sciatic nerve ligation (PSL) were largely attenuated by deficiency of lysophosphatidylcholine acyltransferase (LPCAT)2, which is one of the PAF biosynthetic enzymes. By contrast, deficiency of the other PAF biosynthetic enzyme, LPCAT1, did not ameliorate neuropathic pain. With regard to the mechanism of the observed effects, LPCAT2 was detected in wild-type spinal cord microglia, and the absence of LPCAT2 expression precluded spinal PAF expression in LPCAT2-knockout mice. Furthermore, ATP-stimulated PAF biosynthesis in macrophages was decreased by pretreatment with the PAF receptor antagonist ABT-491, indicating the existence of a positive feedback loop of PAF biosynthesis, which we designated the PAF-pain loop. In conclusion, LPCAT2 is a novel therapeutic target for newly categorized analgesic drugs; in addition, our data call for the re-evaluation of the clinical utility of PAF receptor antagonists.-Shindou, H., Shiraishi, S., Tokuoka, S. M., Takahashi Y., Harayama, T., Abe, T., Bando, K., Miyano, K., Kita, Y., Uezono, Y., Shimizu, T. Relief from neuropathic pain by blocking of the platelet-activating factor-pain loop.

Imaging of intracellular fatty acids by scanning X-ray fluorescence microscopy

Fatty acids are taken up by cells and incorporated into complex lipids such as neutral lipids and glycerophospholipids. Glycerophospholipids are major constituents of cellular membranes. More than 1000 molecular species of glycerophospholipids differ in their polar head groups and fatty acid compositions. They are related to cellular functions and diseases and have been well analyzed by mass spectrometry. However, intracellular imaging of fatty acids and glycerophospholipids has not been successful due to insufficient resolution using conventional methods. Here, we developed a method for labeling fatty acids with bromine (Br) and applied scanning X-ray fluorescence microscopy (SXFM) to obtain intracellular Br mapping data with submicrometer resolution. Mass spectrometry showed that cells took up Br-labeled fatty acids and metabolized them mainly into glycerophospholipids in CHO cells. Most Br signals observed by SXFM were in the perinuclear region. Higher resolution revealed a spot-like distribution of Br in the cytoplasm. The current method enabled successful visualization of intracellular Br-labeled fatty acids. Single-element labeling combined with SXFM technology facilitates the intracellular imaging of fatty acids, which provides a new tool to determine dynamic changes in fatty acids and their derivatives at the single-cell level.—Shimura, M., Shindou, H., Szyrwiel, L., Tokuoka, S. M., Hamano, F., Matsuyama, S., Okamoto, M., Matsunaga, A., Kita, Y., Ishizaka, Y., Yamauchi, K., Kohmura, Y., Lobinski, R., Shimizu, I., Shimizu, T. Imaging of intracellular fatty acids by scanning X-ray fluorescence microscopy.

Fever Is Mediated by Conversion of Endocannabinoid 2-Arachidonoylglycerol to Prostaglandin E2

Fever is a common response to inflammation and infection. The mechanism involves prostaglandin E2 (PGE2)-EP3 receptor signaling in the hypothalamus, which raises the set point of hypothalamic thermostat for body temperature, but the lipid metabolic pathway for pyretic PGE2 production remains unknown. To reveal the molecular basis of fever initiation, we examined lipopolysaccharides (LPS)-induced fever model in monoacylglycerol lipase (MGL)-deficient (Mgll-/-) mice, CB1 receptor-MGL compound-deficient (Cnr1-/-Mgll-/-) mice, cytosolic phospholipase A2α (cPLA2α)-deficient (Pla2g4a-/-) mice, and diacylglycerol lipase α (DGLα)-deficient (Dagla-/-) mice. Febrile reactions were abolished in Mgll-/- and Cnr1-/-Mgll-/- mice, whereas Cnr1-/-Mgll+/+, Pla2g4a-/- and Dagla-/- mice responded normally, demonstrating that MGL is a critical enzyme for fever, which functions independently of endocannabinoid signals. Intracerebroventricular administration of PGE2 caused fever similarly in Mgll-/- and wild-type control mice, suggesting a lack of pyretic PGE2 production in Mgll-/- hypothalamus, which was confirmed by lipidomics analysis. Normal blood cytokine responses after LPS administration suggested that MGL-deficiency does not affect pyretic cytokine productions. Diurnal body temperature profiles were normal in Mgll-/- mice, demonstrating that MGL is unrelated to physiological thermoregulation. In conclusion, MGL-dependent hydrolysis of endocannabinoid 2-arachidonoylglycerol is necessary for pyretic PGE2 production in the hypothalamus.

Fatty acid remodeling by LPCAT3 enriches arachidonate in phospholipid membranes and regulates triglyceride transport

Polyunsaturated fatty acids (PUFAs) in phospholipids affect the physical properties of membranes, but it is unclear which biological processes are influenced by their regulation. For example, the functions of membrane arachidonate that are independent of a precursor role for eicosanoid synthesis remain largely unknown. Here, we show that the lack of lysophosphatidylcholine acyltransferase 3 (LPCAT3) leads to drastic reductions in membrane arachidonate levels, and that LPCAT3-deficient mice are neonatally lethal due to an extensive triacylglycerol (TG) accumulation and dysfunction in enterocytes. We found that high levels of PUFAs in membranes enable TGs to locally cluster in high density, and that this clustering promotes efficient TG transfer. We propose a model of local arachidonate enrichment by LPCAT3 to generate a distinct pool of TG in membranes, which is required for normal directionality of TG transfer and lipoprotein assembly in the liver and enterocytes.

DOI:http://dx.doi.org/10.7554/eLife.06328.001

Membranes made of molecules called lipids surround every living cell and also form compartments inside the cell. There are hundreds of different lipid molecules that can be found in membranes. The amount of each type within the membrane can vary, which affects the flexibility and other physical properties of the membrane.

One type of lipid found in membranes is called arachidonic acid. It is involved in cell communication and other processes, and is required for young animals to grow and develop properly. An enzyme called LPCAT3 is thought to incorporate arachidonic acid into membranes, but this has not yet been proven to occur in living animals.

Here, Hashidate-Yoshida, Harayama et al. studied the role of LPCAT3 in newborn mice. The experiments show that this enzyme is found at high levels in the intestine and liver. Mice that lacked LPCAT3 had much lower levels of arachidonic acid compared with normal mice. These mice also showed signs of severe intestinal damage due to the build up of lipids from their mother's milk, and died within a few days of being born.

The mice that lacked LPCAT3 had different amounts of another type of lipid—called triacylglycerols—in their intestine and liver. Normally, these lipids would be assembled into larger molecules called lipoproteins that are released into the blood stream and used in the muscles and other parts of the body. However, Hashidate-Yoshida, Harayama et al. found that in the mice missing LPCAT3, the triacylglycerols did not get assembled into lipoproteins and so they accumulated inside the intestine and liver cells.

The experiments also show that high levels of arachidonic acid and other similar lipids in the membrane enable triacylglycerol molecules to cluster together, which increases the production of lipoproteins. Hashidate-Yoshida, Harayama et al.'s findings suggest that LPCAT3 incorporates arachidonic acid into the membrane of intestine and liver cells, which enables triacylglycerols to be assembled into lipoproteins. The next challenge will be to find out if LPCAT3 is also important for the production of lipoproteins in humans. If it is, then developing new therapies that alter the activity of this enzyme might be beneficial for patients with abnormal levels of lipids in the blood (known as dyslipidemia).

DOI:http://dx.doi.org/10.7554/eLife.06328.002

Selective ablation of mast cells or basophils reduces peanut-induced anaphylaxis in mice

BACKGROUND

Studies with c-kit mutant mast cell (MC)-deficient mice and antibody-mediated depletion of basophils suggest that both MCs and basophils can contribute to peanut-induced anaphylaxis (PIA). However, interpretation of data obtained by using such approaches is complicated because c-kit mutant mice have several phenotypic abnormalities in addition to MC deficiency and because basophil-depleting antibodies can also react with MCs.

OBJECTIVE

We analyzed (1) the changes in the features of PIA in mice after the selective and inducible ablation of MCs or basophils and (2) the possible importance of effector cells other than MCs and basophils in the PIA response.

METHODS

Wild-type and various mutant mice were orally sensitized with peanut extract and cholera toxin weekly for 4 weeks and challenged intraperitoneally with peanut extract 2 weeks later.

RESULTS

Peanut-challenged, MC-deficient Kit(W-sh/W-sh) mice had reduced immediate hypothermia, as well as a late-phase decrease in body temperature that was abrogated by antibody-mediated depletion of neutrophils. Diphtheria toxin-mediated selective depletion of MCs or basophils in Mcpt5-Cre;iDTR and Mcpt8(DTR) mice, respectively, and treatment of wild-type mice with the basophil-depleting antibody Ba103 significantly reduced peanut-induced hypothermia. Non-c-kit mutant MC- and basophil-deficient Cpa3-Cre;Mcl-1(fl/fl) mice had reduced but still significant responses to peanut.

CONCLUSION

Inducible and selective ablation of MCs or basophils in non-c-kit mutant mice can significantly reduce PIA, but partial responses to peanut can still be observed in the virtual absence of both cell types. The neutrophilia in Kit(W-sh/W-sh) mice might influence the responses of these mice in this PIA model.

The mood stabilizer valproate inhibits both inositol- and diacylglycerol-signaling pathways in Caenorhabditis elegans

The antiepileptic valproate (VPA) is widely used in the treatment of bipolar disorder, although the mechanism of its action in the disorder is unclear. We show here that VPA inhibits both inositol phosphate and diacylglycerol (DAG) signaling in Caenorhabditis elegans. VPA disrupts two behaviors regulated by the inositol-1,4,5-trisphosphate (IP(3)): defecation and ovulation. VPA also inhibits two activities regulated by DAG signaling: acetylcholine release and egg laying. The effects of VPA on DAG signaling are relieved by phorbol ester, a DAG analogue, suggesting that VPA acts to inhibit DAG production. VPA reduces levels of DAG and inositol-1-phosphate, but phosphatidylinositol-4,5-bisphosphate (PIP(2)) is slightly increased, suggesting that phospholipase C-mediated hydrolysis of PIP(2) to form DAG and IP(3) is defective in the presence of VPA.

Recruitment of katanin p60 by phosphorylated NDEL1, an LIS1 interacting protein, is essential for mitotic cell division and neuronal migration

LIS1 is mutated in the human neuronal migration defect lissencephaly and along with NDEL1 (formerly NUDEL) participates in the regulation of cytoplasmic dynein function during neuronal development. Targeted disruption of Ndel1 suggested that NDEL1 could have other molecular targets that regulate microtubule organization for proper neuronal migration. To further understanding the molecular mechanism of LIS1 and lissencephaly, we identified the katanin p60 microtubule-severing protein as an additional molecular target of NDEL1. We demonstrate that phosphorylation of NDEL1 by Cdk5 facilitates interaction between NDEL1 and p60, suggesting that P-NDEL1 regulates the distribution of katanin p60. Abnormal accumulation of p60 in nucleus of Ndel1 null mutants supports an essential role of NDEL1 in p60 regulation. Complete loss of NDEL1 or expression of dominant negative mutants of p60 in migrating neurons results in defective migration and elongation of nuclear-centrosomal distance. Our results suggest that NDEL1 is essential for mitotic cell division and neuronal migration not only via regulation of cytoplasmic dynein function but also by modulation of katanin p60 localization and function.

Involvement of platelet-activating factor and LIS1 in neuronal migration

Platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a biologically active lipid mediator. We have previously shown the expression of PAF receptor in neurons and microglia. PAF is produced in the brain from its precursor, and degraded by the enzyme PAF acetylhydrolase. LIS1 is a regulatory subunit of PAF acetylhydrolase, and is identical to a gene whose deletion causes the human neuronal migration disorder, type I lissencephaly. Indeed, Lis1 mutant mice display defects in neuronal migration and layering in vivo, and also in cerebellar granule cell migration in vitro. However, the roles of PAF and the PAF receptor in the neuronal migration remain to be determined. Here, we show that PAF receptor-deficient mice exhibited histological abnormalities in the embryonic cerebellum. PAF receptor-deficient cerebellar granule neurons migrated more slowly in vitro than wild-type neurons, consistent with the observation that a PAF receptor antagonist reduced the migration of wild-type neurons in vitro. Synergistic reduction of neuronal migration was observed in a double mutant of PAF receptor and LIS1. Unexpectedly, PAF affected the migration of PAF receptor-deficient neurons, suggesting a receptor-independent pathway for PAF action. The PAF receptor-independent response to PAF was abolished in granule neurons derived from the double mutant mice. Thus, our results suggest that the migration of cerebellar granule cells is regulated by PAF through receptor-dependent and receptor-independent pathways, and that LIS1 is a pivotal molecule that links PAF action and neuronal cell migration both in vivo and in vitro.