Human lysophosphatidic acid acyltransferase. cDNA cloning, expression, and localization to chromosome 9q34.3

Systematic crosstalk in plasmalogen and diacyl lipid biosynthesis for their differential yet concerted molecular functions in the cell

Plasmalogen is a major phospholipid of mammalian cell membranes. Recently it is becoming evident that the sn-1 vinyl-ether linkage in plasmalogen, contrasting to the ester linkage in the counterpart diacyl glycerophospholipid, yields differential molecular characteristics for these lipids especially related to hydrocarbon-chain order, so as to concertedly regulate biological membrane processes. A role played by NMR in gaining information in this respect, ranging from molecular to tissue levels, draws particular attention. We note here that a broad range of enzymes in de novo synthesis pathway of plasmalogen commonly constitute that of diacyl glycerophospholipid. This fact forms the basis for systematic crosstalk that not only controls a quantitative balance between these lipids, but also senses a defect causing loss of lipid in either pathway for compensation by increase of the counterpart lipid. However, this inherent counterbalancing mechanism paradoxically amplifies imbalance in differential effects of these lipids in a diseased state on membrane processes. While sharing of enzymes has been recognized, it is now possible to overview the crosstalk with growing information for specific enzymes involved. The overview provides a fundamental clue to consider cell and tissue type-dependent schemes in regulating membrane processes by plasmalogen and diacyl glycerophospholipid in health and disease.

An ER phospholipid hydrolase drives ER-associated mitochondrial constriction for fission and fusion

Mitochondria are dynamic organelles that undergo cycles of fission and fusion at a unified platform defined by endoplasmic reticulum (ER)-mitochondria membrane contact sites (MCSs). These MCSs or nodes co-localize fission and fusion machinery. We set out to identify how ER-associated mitochondrial nodes can regulate both fission and fusion machinery assembly. We have used a promiscuous biotin ligase linked to the fusion machinery, Mfn1, and proteomics to identify an ER membrane protein, ABHD16A, as a major regulator of node formation. In the absence of ABHD16A, fission and fusion machineries fail to recruit to ER-associated mitochondrial nodes, and fission and fusion rates are significantly reduced. ABHD16A contains an acyltransferase motif and an α/β hydrolase domain, and point mutations in critical residues of these regions fail to rescue the formation of ER-associated mitochondrial hot spots. These data suggest a mechanism whereby ABHD16A functions by altering phospholipid composition at ER-mitochondria MCSs. Our data present the first example of an ER membrane protein that regulates the recruitment of both fission and fusion machineries to mitochondria.

Update and nomenclature proposal for mammalian lysophospholipid acyltransferases which create membrane phospholipid diversity

The diversity of glycerophospholipid species in cellular membranes is immense and affects various biological functions. Glycerol-3-phosphate acyltransferases (GPATs) and lysophospholipid acyltransferases (LPLATs), in concert with phospholipase A_1/2s enzymes, contribute to this diversity via selective esterification of fatty acyl chains at the sn-1 or sn-2 positions of membrane phospholipids. These enzymes are conserved across all kingdoms, and in mammals four GPATs of the 1-acylglycerol-3-phosphate O-acyltransferase (AGPAT) family and at least 14 LPLATs, either of the AGPAT or the membrane-bound O-acyltransferase (MBOAT) families, have been identified. Here we provide an overview of the biochemical and biological activities of these mammalian enzymes, including their predicted structures, involvements in human diseases, and essential physiological roles as revealed by gene-deficient mice. Recently, the nomenclature used to refer to these enzymes has generated some confusion due to the use of multiple names to refer to the same enzyme and instances of the same name being used to refer to completely different enzymes. Thus, this review proposes a more uniform LPLAT enzyme nomenclature, as well as providing an update of recent advances made in the study of LPLATs, continuing from our JBC mini review in 2009.

Biosynthetic Enzymes of Membrane Glycerophospholipid Diversity as Therapeutic Targets for Drug Development

Biophysical properties of membranes are dependent on their glycerophospholipid compositions. Lysophospholipid acyltransferases (LPLATs) selectively incorporate fatty chains into lysophospholipids to affect the fatty acid composition of membrane glycerophospholipids. Lysophosphatidic acid acyltransferases (LPAATs) of the 1-acylglycerol-3-phosphate O-acyltransferase (AGPAT) family incorporate fatty chains into phosphatidic acid during the de novo glycerophospholipid synthesis in the Kennedy pathway. Other LPLATs of both the AGPAT and the membrane bound O-acyltransferase (MBOAT) families further modify the fatty chain compositions of membrane glycerophospholipids in the remodeling pathway known as the Lands' cycle. The LPLATs functioning in these pathways possess unique characteristics in terms of their biochemical activities, regulation of expressions, and functions in various biological contexts. Essential physiological functions for LPLATs have been revealed in studies using gene-deficient mice, and important roles for several enzymes are also indicated in human diseases where their mutation or dysregulation causes or contributes to the pathological condition. Now several LPLATs are emerging as attractive therapeutic targets, and further understanding of the mechanisms underlying their physiological and pathological roles will aid in the development of novel therapies to treat several diseases that involve altered glycerophospholipid metabolism.

Evolution, dynamic expression changes and regulatory characteristics of gene families involved in the glycerophosphate pathway of triglyceride synthesis in chicken (Gallus gallus)

It is well documented that four gene families, including the glycerophosphate acyltransferases (GPATs), acylglycerophosphate acyltransferases (AGPATs), lipid phosphate phosphohydrolases (LPINs) and diacylglycerol acyltransferases (DGATs), are involved in the glycerophosphate pathway of de novo triglyceride (TG) biosynthesis in mammals. However, no systematic analysis has been conducted to characterize the gene families in poultry. In this study, the sequences of gene family members in the glycerophosphate pathway were obtained by screening the public databases. The phylogenetic tree, gene structures and conserved motifs of the corresponding proteins were evaluated. Dynamic expression changes of the genes at different developmental stages were analyzed by qRT-PCR. The regulatory characteristics of the genes were analyzed by in vivo experiments. The results showed that the GPAT, AGPAT and LPIN gene families have 2, 7 and 2 members, respectively, and they were classified into 2, 4 and 2 cluster respectively based on phylogenetic analysis. All of the genes except AGPAT1 were extensively expressed in various tissues. Estrogen induction upregulated the expression of GPAM and AGPAT2, downregulated the expression of AGPAT3, AGPAT9, LPIN1 and LPIN2, and had no effect on the expression of the other genes. These findings provide a valuable resource for further investigation of lipid metabolism in liver of chicken.

What lipodystrophies teach us about the metabolic syndrome

Lipodystrophies are the result of a range of inherited and acquired causes, but all are characterized by perturbations in white adipose tissue function and, in many instances, its mass or distribution. Though patients are often nonobese, they typically manifest a severe form of the metabolic syndrome, highlighting the importance of white fat in the "safe" storage of surplus energy. Understanding the molecular pathophysiology of congenital lipodystrophies has yielded useful insights into the biology of adipocytes and informed therapeutic strategies. More recently, genome-wide association studies focused on insulin resistance have linked common variants to genes implicated in adipose biology and suggested that subtle forms of lipodystrophy contribute to cardiometabolic disease risk at a population level. These observations underpin the use of aligned treatment strategies in insulin-resistant obese and lipodystrophic patients, the major goal being to alleviate the energetic burden on adipose tissue.

Identification of an intrinsic lysophosphatidic acid acyltransferase activity in the lipolytic inhibitor G0/G1 switch gene 2 (G0S2)

G₀/G₁ switch gene 2 (G0S2) is a specific inhibitor of adipose triglyceride lipase (ATGL), the rate-limiting enzyme for intracellular lipolysis. Recent studies show that G0S2 plays a critical role in promoting triacylglycerol (TG) accumulation in the liver, and its encoding gene is a direct target of a major lipogenic transcription factor liver X receptor (LXR)α. Here we sought to investigate a lipolysis-independent role of G0S2 in hepatic triglyceride synthesis. Knockdown of G0S2 decreased hepatic TG content in mice with ATGL ablation. Conversely, overexpression of G0S2 promoted fatty acid incorporation into TGs and diacylglycerols in both wild-type and ATGL-deficient hepatocytes. Biochemical characterization showed that G0S2 mediates phosphatidic acid synthesis from lysophosphatidic acid (LPA) and acyl-coenzyme A. In response to a high-sucrose lipogenic diet, G0S2 is up-regulated via LXRα and required for the increased TG accumulation in liver. Furthermore, deletion of a distinct 4-aa motif necessary for the LPA-specific acyltransferase (LPAAT) activity impaired G0S2's ability to mediate TG synthesis both in vitro and in vivo. These studies identify G0S2 as a dual-function regulator of lipid metabolism as well as a novel mechanism whereby hepatic TG storage is promoted in response to lipogenic stimulation. In addition to its role as a lipolytic inhibitor, G0S2 is capable of directly promoting TG synthesis by acting as a lipid-synthesizing enzyme.-Zhang, X., Xie, X., Heckmann, B. L., Saarinen, A. M., Gu, H., Zechner, R., Liu, J. Identification of an intrinsic lysophosphatidic acid acyltransferase activity in the lipolytic inhibitor G₀/G₁ switch gene 2 (G0S2).

Substrate channeling in the glycerol-3-phosphate pathway regulates the synthesis, storage and secretion of glycerolipids

The successive acylation of glycerol-3-phosphate (G3P) by glycerol-3-phosphate acyltransferases and acylglycerol-3-phosphate acyltransferases produces phosphatidic acid (PA), a precursor for CDP-diacylglycerol-dependent phospholipid synthesis. PA is further dephosphorylated by LIPINs to produce diacylglycerol (DG), a substrate for the synthesis of triglyceride (TG) by DG acyltransferases and a precursor for phospholipid synthesis via the CDP-choline and CDP-ethanolamine (Kennedy) pathways. The channeling of fatty acids into TG for storage in lipid droplets and secretion in lipoproteins or phospholipids for membrane biogenesis is dependent on isoform expression, activity and localization of G3P pathway enzymes, as well as dietary and hormonal and tissue-specific factors. Here, we review the mechanisms that control partitioning of substrates into lipid products of the G3P pathway.

Phospholipid Remodeling in Physiology and Disease

Phospholipids are major constituents of biological membranes. The fatty acyl chain composition of phospholipids determines the biophysical properties of membranes and thereby affects their impact on biological processes. The composition of fatty acyl chains is also actively regulated through a deacylation and reacylation pathway called Lands' cycle. Recent studies of mouse genetic models have demonstrated that lysophosphatidylcholine acyltransferases (LPCATs), which catalyze the incorporation of fatty acyl chains into the sn-2 site of phosphatidylcholine, play important roles in pathophysiology. Two LPCAT family members, LPCAT1 and LPCAT3, have been particularly well studied. LPCAT1 is crucial for proper lung function due to its role in pulmonary surfactant biosynthesis. LPCAT3 maintains systemic lipid homeostasis by regulating lipid absorption in intestine, lipoprotein secretion, and de novo lipogenesis in liver. Mounting evidence also suggests that changes in LPCAT activity may be potentially involved in pathological conditions, including nonalcoholic fatty liver disease, atherosclerosis, viral infections, and cancer. Pharmacological manipulation of LPCAT activity and membrane phospholipid composition may provide new therapeutic options for these conditions.

Roles of lysophosphatidic acid and sphingosine-1-phosphate in stem cell biology

Stem cells are unique in their ability to self-renew and differentiate into various cell types. Because of these features, stem cells are key to the formation of organisms and play fundamental roles in tissue regeneration and repair. Mechanisms controlling their fate are thus fundamental to the development and homeostasis of tissues and organs. Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are bioactive phospholipids that play a wide range of roles in multiple cell types, during developmental and pathophysiological events. Considerable evidence now demonstrates the potent roles of LPA and S1P in the biology of pluripotent and adult stem cells, from maintenance to repair. Here we review their roles for each main category of stem cells and explore how those effects impact development and physiopathology.

Lpaatδ/Agpat4 deficiency impairs maximal force contractility in soleus and alters fibre type in extensor digitorum longus muscle

Lysophosphatidic acid acyltransferase (LPAAT) δ/acylglycerophosphate acyltransferase 4 is a mitochondrial enzyme and one of five homologues that catalyze the acyl-CoA-dependent synthesis of phosphatidic acid (PA) from lysophosphatidic acid. We studied skeletal muscle LPAATδ and found highest levels in soleus, a red oxidative fibre-type that is rich in mitochondria, and lower levels in extensor digitorum longus (EDL) (white glycolytic) and gastrocnemius (mixed fibre-type). Using Lpaatδ-deficient mice, we found no change in soleus or EDL mass, or in treadmill time-to-exhaustion compared to wildtype littermates. There was, however, a significant reduction in the proportion of type I and type IIA fibres in EDL but, surprisingly, not soleus, where these fibre-types predominate. Also unexpectedly, there was no impairment in force generation by EDL, but a significant reduction by soleus. Oxidative phosphorylation and activity of complexes I, I + II, III, and IV in soleus mitochondria was unchanged and therefore could not explain this effect. However, pyruvate dehydrogenase activity was significantly reduced in Lpaatδ^-/- soleus and EDL. Analysis of cellular lipids indicated no difference in soleus triacylglycerol, but specific elevations in soleus PA and phosphatidylethanolamine levels, likely due to a compensatory upregulation of Lpaatβ and Lpaatε in Lpaatδ^-/- mice. An anabolic effect for PA as an activator of skeletal muscle mTOR has been reported, but we found no change in serine 2448 phosphorylation, indicating reduced soleus force generation is unlikely due to the loss of mTOR activation by a specific pool of LPAATδ-derived PA. Our results identify an important role for LPAATδ in soleus and EDL.

Triglyceride Metabolism in the Liver

Triglyceride molecules represent the major form of storage and transport of fatty acids within cells and in the plasma. The liver is the central organ for fatty acid metabolism. Fatty acids accrue in liver by hepatocellular uptake from the plasma and by de novo biosynthesis. Fatty acids are eliminated by oxidation within the cell or by secretion into the plasma within triglyceride-rich very low-density lipoproteins. Notwithstanding high fluxes through these pathways, under normal circumstances the liver stores only small amounts of fatty acids as triglycerides. In the setting of overnutrition and obesity, hepatic fatty acid metabolism is altered, commonly leading to the accumulation of triglycerides within hepatocytes, and to a clinical condition known as nonalcoholic fatty liver disease (NAFLD). In this review, we describe the current understanding of fatty acid and triglyceride metabolism in the liver and its regulation in health and disease, identifying potential directions for future research. Advances in understanding the molecular mechanisms underlying the hepatic fat accumulation are critical to the development of targeted therapies for NAFLD. © 2018 American Physiological Society. Compr Physiol 8:1-22, 2018.

Is hepatic lipogenesis fundamental for NAFLD/NASH? A focus on the nuclear receptor coactivator PGC-1β

Non-alcoholic fatty liver diseases are the hepatic manifestation of metabolic syndrome. According to the classical pattern of NAFLD progression, de novo fatty acid synthesis has been incriminated in NAFLD progression. However, this hypothesis has been challenged by the re-evaluation of NAFLD development mechanisms together with the description of the role of lipogenic genes in NAFLD and with the recent observation that PGC-1β, a nuclear receptor/transcription factor coactivator involved in the transcriptional regulation of lipogenesis, displays protective effects against NAFLD/NASH progression. In this review, we focus on the implication of lipogenesis and triglycerides synthesis on the development of non-alcoholic fatty liver diseases and discuss the involvement of these pathways in the protective role of PGC-1β toward these hepatic manifestations.

<i>AGPAT6</i> gene EX1_303T > C and EX12_299G > A mutations and associations with economic traits of Chinese Simmental-cross cattle

Abstract. One of the 11 members in the family of 1-acylglycerol-3-phosphate-O- acyltransferases (AGPATs), AGPAT6, is responsible for the second step in the biosynthesis of triacylglycerol in eukaryotes. The AGPAT6 gene is highly expressed in brown adipose tissue, mammary gland epithelial cells and many other tissues. In this study, the PCR-restriction fragment length polymorphism technique was applied to detect sites of polymorphism in the bovine AGPAT6 gene, and two single nucleotide polymorphisms (SNPs) were detected in the exon 1 and exon 12. Thirty-three traits associated with the meat quality and the carcass were also measured in Chinese Simmental-cross steers. The association between the two SNPs and the traits was then analyzed. The polymorphism site EX1_303T > C was significantly associated with the omasum weight, liver weight, pH value of the beef (carcass), fat coverage rate of the carcass, fat color score, kidney weight and back fat thickness. The polymorphism site EX12_299G > A was significantly associated with bone net weight, forehoof weight, hind feet weight, the fat coverage rate of the carcass, the head and heart weight and the marbling score. Thus, the polymorphisms in the AGPAT6 gene might be important genetic factors that influence the carcass yield and meat quality of beef cattle and may be useful markers of meat quality traits in future marker-assisted selection programs for the breeding and production of beef cattle.

AGPAT2 is essential for postnatal development and maintenance of white and brown adipose tissue

Objective

Characterize the cellular and molecular events responsible for lipodystrophy in AGPAT2 deficient mice.

Methods

Adipose tissue and differentiated MEF were assessed using light and electron microscopy, followed by protein (immunoblots) and mRNA analysis (qPCR). Phospholipid profiling was determined by electrospray ionization tandem mass spectrometry (ESI-MS/MS).

Results

In contrast to adult Agpat2^−/− mice, fetuses and newborn Agpat2^−/− mice have normal mass of white and brown adipose tissue. Loss of both the adipose tissue depots occurs during the first week of postnatal life as a consequence of adipocyte death and inflammatory infiltration of the adipose tissue. At the ultrastructural level, adipose tissue of newborn Agpat2^−/− mice is virtually devoid of caveolae and has abnormal mitochondria and lipid droplets. Autophagic structures are also abundant. Consistent with these findings, differentiated Agpat2^−/− mouse embryonic fibroblasts (MEFs) also have impaired adipogenesis, characterized by a lower number of lipid-laden cells and ultrastructural abnormalities in lipid droplets, mitochondria and plasma membrane. Overexpression of PPARγ, the master regulator of adipogenesis, increased the number of Agpat2^−/− MEFs that differentiated into adipocyte-like cells but did not prevent morphological abnormalities and cell death. Furthermore, differentiated Agpat2^−/− MEFs have abnormal phospholipid compositions with 3-fold increased levels of phosphatidic acid.

Conclusion

We conclude that lipodystrophy in Agpat2^−/− mice results from postnatal cell death of adipose tissue in association with acute local inflammation. It is possible that AGPAT2 deficient adipocytes have an altered lipid filling or a reduced capacity to adapt the massive lipid availability associated with postnatal feeding.

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Post weaning Agpat2^−/− mice are lipodystrophic.

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However, they are born with normal mass of white and brown adipose tissue.

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Adipose tissue in Agpat2^−/− mice undergoes postnatal inflammatory cell death.

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Differentiated Agpat2^−/− MEFs recapitulate abnormalities of Agpat2^−/− adipocytes.

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Abnormal phospholipid composition might underlies lipodystrophy in Agpat2^−/− mice.

PGC-1α-mediated changes in phospholipid profiles of exercise-trained skeletal muscle

Exercise training influences phospholipid fatty acid composition in skeletal muscle and these changes are associated with physiological phenotypes; however, the molecular mechanism of this influence on compositional changes is poorly understood. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a nuclear receptor coactivator, promotes mitochondrial biogenesis, the fiber-type switch to oxidative fibers, and angiogenesis in skeletal muscle. Because exercise training induces these adaptations, together with increased PGC-1α, PGC-1α may contribute to the exercise-mediated change in phospholipid fatty acid composition. To determine the role of PGC-1α, we performed lipidomic analyses of skeletal muscle from genetically modified mice that overexpress PGC-1α in skeletal muscle or that carry KO alleles of PGC-1α. We found that PGC-1α affected lipid profiles in skeletal muscle and increased several phospholipid species in glycolytic muscle, namely phosphatidylcholine (PC) (18:0/22:6) and phosphatidylethanolamine (PE) (18:0/22:6). We also found that exercise training increased PC (18:0/22:6) and PE (18:0/22:6) in glycolytic muscle and that PGC-1α was required for these alterations. Because phospholipid fatty acid composition influences cell permeability and receptor stability at the cell membrane, these phospholipids may contribute to exercise training-mediated functional changes in the skeletal muscle.

The Peanut (Arachis hypogaea L.) Gene AhLPAT2 Increases the Lipid Content of Transgenic Arabidopsis Seeds

Lysophosphatidic acid acyltransferase (LPAT), which converts lysophosphatidic acid (LPA) to phosphatidic acid (PA), catalyzes the addition of fatty acyl moieties to the sn-2 position of the LPA glycerol backbone in triacylglycerol (TAG) biosynthesis. We recently reported the cloning and temporal-spatial expression of a peanut (Arachis hypogaea) AhLPAT2gene, showing that an increase in AhLPAT2 transcript levels was closely correlated with an increase in seed oil levels. However, the function of the enzyme encoded by the AhLPAT2 gene remains unclear. Here, we report that AhLPAT2 transcript levels were consistently higher in the seeds of a high-oil cultivar than in those of a low-oil cultivar across different seed developmental stages. Seed-specific overexpression of AhLPAT2 in Arabidopsis results in a higher percentage of oil in the seeds and greater-than-average seed weight in the transgenic plants compared with the wild-type plants, leading to a significant increase in total oil yield per plant. The total fatty acid (FA) content and the proportion of unsaturated FAs also increased. In the developing siliques of AhLPAT2-overexpressing plants, the expression levels of genes encoding crucial enzymes involved in de novo FA synthesis, acetyl-CoA subunit (AtBCCP2) and acyl carrier protein 1 (AtACP1) were elevated. AhLPAT2 overexpression also promoted the expression of several key genes related to TAG assembly, sucrose metabolism, and glycolysis. These results demonstrate that the expression of AhLPAT2 plays an important role in glycerolipid production in peanuts.

Glycerophosphate/Acylglycerophosphate acyltransferases

Acyl-CoA:glycerol-3-phosphate acyltransferase (GPAT) and acyl-CoA: 1-acyl-glycerol-3-phosphate acyltransferase (AGPAT) are involved in the de novo synthesis of triacylglycerol (TAG) and glycerophospholipids. Many enzymes belonging to the GPAT/AGPAT family have recently been identified and their physiological or pathophysiological roles have been proposed. The roles of GPAT/AGPAT in the synthesis of TAG and obesity-related diseases were revealed through the identification of causative genes of these diseases or analyses of genetically manipulated animals. Recent studies have suggested that some isoforms of GPAT/AGPAT family enzymes are involved in the fatty acid remodeling of phospholipids. The enzymology of GPAT/AGPAT and their physiological/pathological roles in the metabolism of glycerolipids have been described and discussed in this review.

Genome-wide identification and evolutionary analysis of algal LPAT genes involved in TAG biosynthesis using bioinformatic approaches

Lysophosphatidyl acyltransferase (LPAT) is one of the major triacylglycerol synthesis enzymes, controlling the metabolic flow of lysophosphatidic acid to phosphatidic acid. Experimental studies in Arabidopsis have shown that LPAT activity is exhibited primarily by three distinct isoforms, namely the plastid-located LPAT1, the endoplasmic reticulum-located LPAT2, and the soluble isoform of LPAT (solLPAT). In this study, 24 putative genes representing all LPAT isoforms were identified from the analysis of 11 complete genomes including green algae, red algae, diatoms and higher plants. We observed LPAT1 and solLPAT genes to be ubiquitously present in nearly all genomes examined, whereas LPAT2 genes to have evolved more recently in the plant lineage. Phylogenetic analysis indicated that LPAT1, LPAT2 and solLPAT have convergently evolved through separate evolutionary paths and belong to three different gene families, which was further evidenced by their wide divergence at gene structure and sequence level. The genome distribution supports the hypothesis that each gene encoding a LPAT is not duplicated. Mapping of exon-intron structure of LPAT genes to the domain structure of proteins across different algal and plant species indicates that exon shuffling plays no role in the evolution of LPAT genes. Besides the previously defined motifs, several conserved consensus sequences were discovered which could be useful to distinguish different LPAT isoforms. Taken together, this study will enable the generation of experimental approximations to better understand the functional role of algal LPAT in lipid accumulation.

Towards a mechanistic understanding of lipodystrophy and seipin functions

CGL (Congenital generalized lipodystrophy) is a genetic disorder characterized by near complete loss of adipose tissue along with increased ectopic fat storage in other organs including liver and muscle. Of the four CGL types, BSCL2 (Berardinelli-Seip Congenital lipodystrophy type 2), resulting from mutations in the BSCL2/seipin gene, exhibits the most severe lipodystrophic phenotype with loss of both metabolic and mechanical adipose depots. The majority of Seipin mutations cause C-terminal truncations, along with a handful of point mutations. Seipin localizes to the ER and is composed of a conserved region including a luminal loop and two transmembrane domains, plus cytosolic N- and C-termini. Animal models deficient in seipin recapitulate the human lipodystrophic phenotype. Cells isolated from seipin knockout mouse models also exhibit impaired adipogenesis. Mechanistically, seipin appears to function as a scaffolding protein to bring together interacting partners essential for lipid metabolism and LD (lipid droplet) formation during adipocyte development. Moreover, cell line and genetic studies indicate that seipin functions in a cell-autonomous manner. Here we will provide a brief overview of the genetic association of the CGLs, and focus on the current understanding of differential contributions of distinct seipin domains to lipid storage and adipogenesis. We will also discuss the roles of seipin-interacting partners, including lipin 1 and 14-3-3β, in mediating seipin-dependent regulation of cellular pathways such as actin cytoskeletal remodelling.

Differentially localized acyl-CoA synthetase 4 isoenzymes mediate the metabolic channeling of fatty acids towards phosphatidylinositol

The acyl-CoA synthetase 4 (ACSL4) has been implicated in carcinogenesis and neuronal development. Acyl-CoA synthetases are essential enzymes of lipid metabolism, and ACSL4 is distinguished by its preference for arachidonic acid. Two human ACSL4 isoforms arising from differential splicing were analyzed by ectopic expression in COS cells. We found that the ACSL4_v1 variant localized to the inner side of the plasma membrane including microvilli, and was also present in the cytosol. ACSL4_v2 contains an additional N-terminal hydrophobic region; this isoform was located at the endoplasmic reticulum and on lipid droplets. A third isoform was designed de novo by appending a mitochondrial targeting signal. All three ACSL4 variants showed the same specific enzyme activity. Overexpression of the isoenzymes increased cellular uptake of arachidonate to the same degree, indicating that the metabolic trapping of fatty acids is independent of the subcellular localization. Remarkably, phospholipid metabolism was changed by ACSL4 expression. Labeling with arachidonate showed that the amount of newly synthesized phosphatidylinositol was increased by all three ACSL4 isoenzymes but not by ACSL1. This was dependent on the expression level and the localization of the ACSL4 isoform. We conclude that in our model system exogenous fatty acids are channeled preferentially towards phosphatidylinositol by ACSL4 overexpression. The differential localization of the endogenous isoenzymes may provide compartment specific precursors of this anionic phospholipid important for many signaling processes.

Diversity and function of membrane glycerophospholipids generated by the remodeling pathway in mammalian cells

Cellular membranes are composed of numerous kinds of glycerophospholipids with different combinations of polar heads at the sn-3 position and acyl moieties at the sn-1 and sn-2 positions, respectively. The glycerophospholipid compositions of different cell types, organelles, and inner/outer plasma membrane leaflets are quite diverse. The acyl moieties of glycerophospholipids synthesized in the de novo pathway are subsequently remodeled by the action of phospholipases and lysophospholipid acyltransferases. This remodeling cycle contributes to the generation of membrane glycerophospholipid diversity and the production of lipid mediators such as fatty acid derivatives and lysophospholipids. Furthermore, specific glycerophospholipid transporters are also important to organize a unique glycerophospholipid composition in each organelle. Recent progress in this field contributes to understanding how and why membrane glycerophospholipid diversity is organized and maintained.

Chemical modulation of glycerolipid signaling and metabolic pathways

Thirty years ago, glycerolipids captured the attention of biochemical researchers as novel cellular signaling entities. We now recognize that these biomolecules occupy signaling nodes critical to a number of physiological and pathological processes. Thus, glycerolipid-metabolizing enzymes present attractive targets for new therapies. A number of fields-ranging from neuroscience and cancer to diabetes and obesity-have elucidated the signaling properties of glycerolipids. The biochemical literature teems with newly emerging small molecule inhibitors capable of manipulating glycerolipid metabolism and signaling. This ever-expanding pool of chemical modulators appears daunting to those interested in exploiting glycerolipid-signaling pathways in their model system of choice. This review distills the current body of literature surrounding glycerolipid metabolism into a more approachable format, facilitating the application of small molecule inhibitors to novel systems. This article is part of a Special Issue entitled Tools to study lipid functions.

Identification and characterization of a gene encoding a putative lysophosphatidyl acyltransferase from Arachis hypogaea

Lysophosphatidyl acyltransferase (LPAT) is the important enzyme responsible for the acylation of lysophosphatidic acid (LPA), leading to the generation of phosphatidic acid (PA) in plant. Its encoding gene is an essential candidate for oil crops to improve oil composition and increase seed oil content through genetic engineering. In this study, a full length AhLPAT4 gene was isolated via cDNA library screening and rapid amplification of cDNA ends (RACE); our data demonstrated that AhLPAT4 had 1631 nucleotides, encoding a putative 43.8 kDa protein with 383 amino acid residues. The deduced protein included a conserved acyltransferase domain and four motifs (I–IV) with putative LPA and acyl-CoA catalytic and binding sites. Bioinformatic analysis indicated that AhLPAT4 contained four transmembrane domains (TMDs), localized to the endoplasmic reticulum (ER) membrane; detailed analysis indicated that motif I and motifs II–III in AhLPAT4 were separated by the third TMD, which located on cytosolic and ER luminal side respectively, and hydrophobic residues on the surface of AhLPAT4 protein fold to form a hydrophobic tunnel to accommodate the acyl chain. Subcellular localization analysis confirmed that AhLPAT4 was a cytoplasm protein.Phylogenetic analysis revealed that AhLPAT4 had a high homology (63.7–78.3%) with putative LPAT4 proteins from Glycine max, Arabidopsis thaliana and Ricinus communis. AhLPAT4 was ubiquitously expressed in diverse tissues except in flower, which is almost undetectable. The expression analysis in different developmental stages in peanut seeds indicated that AhLPAT4 did not coincide with oil accumulation.

Identification of a novel nonsense mutation and a missense substitution in the AGPAT2 gene causing congenital generalized lipodystrophy type 1

Congenital generalized lipodystrophy (CGL) is an autosomal recessive disease characterized by the generalized scant of adipose tissue. CGL type 1 is caused by mutations in gene encoding 1-acylglycerol-3-phosphate O-acyltransferase-2 (AGPAT2). A clinical and molecular genetic investigation was performed in affected and unaffected members of two families with CGL type 1. The AGPAT2 coding region was sequenced in index cases of the two families. The presence of the identified mutations in relevant parents was tested. We identified a novel nonsense mutation (c.685G>T, p.Glu229*) and a missense substitution (c.514G>A, p.Glu172Lys). The unaffected parents in both families were heterozygous carrier of the relevant mutation. The results expand genotype-phenotype spectrum in CGL1 and will have applications in prenatal and early diagnosis of the disease. This is the first report of Persian families identified with AGPAT2 mutations.

LPIAT1 regulates arachidonic acid content in phosphatidylinositol and is required for cortical lamination in mice

Arachidonic acid (AA) is remarkably enriched in phosphatidylinositol (PI). Studies using knockout mice of lysophosphatidylinositol acyltransferase 1, which selectively incorporates AA into PI, reveal that AA-containing PI plays a crucial role in cortical lamination and neuronal migration during brain development.

Dietary arachidonic acid (AA) has roles in growth, neuronal development, and cognitive function in infants. AA is remarkably enriched in phosphatidylinositol (PI), an important constituent of biological membranes in mammals; however, the physiological significance of AA-containing PI remains unknown. In an RNA interference–based genetic screen using Caenorhabditis elegans, we recently cloned mboa-7 as an acyltransferase that selectively incorporates AA into PI. Here we show that lysophosphatidylinositol acyltransferase 1 (LPIAT1, also known as MBOAT7), the closest mammalian homologue, plays a crucial role in brain development in mice. Lpiat1^−/− mice show almost no LPIAT activity with arachidonoyl-CoA as an acyl donor and show reduced AA contents in PI and PI phosphates. Lpiat1^−/− mice die within a month and show atrophy of the cerebral cortex and hippocampus. Immunohistochemical analysis reveals disordered cortical lamination and delayed neuronal migration in the cortex of E18.5 Lpiat1^−/− mice. LPIAT1 deficiency also causes disordered neuronal processes in the cortex and reduced neurite outgrowth in vitro. Taken together, these results demonstrate that AA-containing PI/PI phosphates play an important role in normal cortical lamination during brain development in mice.

Common variation in fatty acid genes and resuscitation from sudden cardiac arrest

BACKGROUND

Fatty acids provide energy and structural substrates for the heart and brain and may influence resuscitation from sudden cardiac arrest (SCA). We investigated whether genetic variation in fatty acid metabolism pathways was associated with SCA survival.

METHODS AND RESULTS

Subjects (mean age, 67 years; 80% male, white) were out-of-hospital SCA patients found in ventricular fibrillation in King County, WA. We compared subjects who survived to hospital admission (n=664) with those who did not (n=689), and subjects who survived to hospital discharge (n=334) with those who did not (n=1019). Associations between survival and genetic variants were assessed using logistic regression adjusting for age, sex, location, time to arrival of paramedics, whether the event was witnessed, and receipt of bystander cardiopulmonary resuscitation. Within-gene permutation tests were used to correct for multiple comparisons. Variants in 5 genes were significantly associated with SCA survival. After correction for multiple comparisons, single-nucleotide polymorphisms in ACSL1 and ACSL3 were significantly associated with survival to hospital admission. Single-nucleotide polymorphisms in ACSL3, AGPAT3, MLYCD, and SLC27A6 were significantly associated with survival to hospital discharge.

CONCLUSIONS

Our findings indicate that variants in genes important in fatty acid metabolism are associated with SCA survival in this population.

Human 1-acylglycerol-3-phosphate O-acyltransferase isoforms 1 and 2: biochemical characterization and inability to rescue hepatic steatosis in Agpat2(-/-) gene lipodystrophic mice

Loss-of-function mutations in 1-acylglycerol-3-phosphate O-acyltransferase (AGPAT) 2 in humans and mice result in loss of both the white and brown adipose tissues from birth. AGPAT2 generates precursors for the synthesis of glycerophospholipids and triacylglycerols. Loss of adipose tissue, or lipodystrophy, results in hyperinsulinemia, diabetes mellitus, and severe hepatic steatosis. Here, we analyzed biochemical properties of human AGPAT2 and its close homolog, AGPAT1, and we studied their role in liver by transducing their expression via recombinant adenoviruses in Agpat2(-/-) mice. The in vitro substrate specificities of AGPAT1 and AGPAT2 are quite similar for lysophosphatidic acid and acyl-CoA. Protein homology modeling of both the AGPATs with glycerol-3-phosphate acyltransferase 1 (GPAT1) revealed that they have similar tertiary protein structure, which is consistent with their similar substrate specificities. When co-expressed, both isoforms co-localize to the endoplasmic reticulum. Despite such similarities, restoring AGPAT activity in liver by overexpression of either AGPAT1 or AGPAT2 in Agpat2(-/-) mice failed to ameliorate the hepatic steatosis. From these studies, we suggest that the role of AGPAT1 or AGPAT2 in liver lipogenesis is minimal and that accumulation of liver fat is primarily a consequence of insulin resistance and loss of adipose tissue in Agpat2(-/-) mice.

Liver X Receptor: an oxysterol sensor and a major player in the control of lipogenesis

De novo fatty acid biosynthesis is also called lipogenesis. It is a metabolic pathway that provides the cells with fatty acids required for major cellular processes such as energy storage, membrane structures and lipid signaling. In this article we will review the role of the Liver X Receptors (LXRs), nuclear receptors that sense oxysterols, in the transcriptional regulation of genes involved in lipogenesis.

Enzymatic activities of the human AGPAT isoform 3 and isoform 5: localization of AGPAT5 to mitochondria

The enzyme 1-acylglycerol-3-phosphate-O-acyltransferase (AGPAT) converts lysophosphatidic acid (LPA) to phosphatidic acid (PA). In this study, we show enzymatic properties, tissue distribution, and subcellular localization of human AGPAT3 and AGPAT5. In cells overexpressing these isoforms, the proteins were detected in the nuclear envelope and the endoplasmic reticulum. AGPAT5-GFP fusion protein was localized in the mitochondria of both Chinese hamster ovary and human epithelial cervical cancer cells. Using lysates of AD293 cells infected with AGPAT3 and AGPAT5 recombinant adenovirus, we show that AGPAT3 and AGPAT5 proteins have AGPAT activity. Both the isoforms have similar apparent V(max) of 6.35 and 2.42 nmol/min/mg protein, respectively, for similar LPA. The difference between the two isoforms is in their use of additional lysophospholipids. AGPAT3 shows significant esterification of lysophosphatidylinositol (LPI) in the presence of C20:4 fatty acid, whereas AGPAT5 demonstrates significant acyltransferase activity toward lysophosphatidylethanolamine (LPE) in the presence of C18:1 fatty acid. The AGPAT3 mRNA is ubiquitously expressed in human tissues with several-fold differences in the expression pattern compared with the closely related AGPAT4. In summary, we show that in the presence of different fatty acids, AGPAT3 and AGPAT5 prefer different lysophospholipids as acyl acceptors. More importantly, localization of overexpressed AGPAT5 (this study) as well as GPAT1 and 2 (previous studies) in mitochondria supports the idea that the mitochondria might be capable of synthesizing some of their own glycerophospholipids.

Lysophosphatidic acid acyltransferase β (LPAATβ) promotes the tumor growth of human osteosarcoma

Background

Osteosarcoma is the most common primary malignancy of bone with poorly characterized molecular pathways important in its pathogenesis. Increasing evidence indicates that elevated lipid biosynthesis is a characteristic feature of cancer. We sought to investigate the role of lysophosphatidic acid acyltransferase β (LPAATβ, aka, AGPAT2) in regulating the proliferation and growth of human osteosarcoma cells. LPAATβ can generate phosphatidic acid, which plays a key role in lipid biosynthesis as well as in cell proliferation and survival. Although elevated expression of LPAATβ has been reported in several types of human tumors, the role of LPAATβ in osteosarcoma progression has yet to be elucidated.

Methodology/Principal Findings

Endogenous expression of LPAATβ in osteosarcoma cell lines is analyzed by using semi-quantitative PCR and immunohistochemical staining. Adenovirus-mediated overexpression of LPAATβ and silencing LPAATβ expression is employed to determine the effect of LPAATβ on osteosarcoma cell proliferation and migration in vitro and osteosarcoma tumor growth in vivo. We have found that expression of LPAATβ is readily detected in 8 of the 10 analyzed human osteosarcoma lines. Exogenous expression of LPAATβ promotes osteosarcoma cell proliferation and migration, while silencing LPAATβ expression inhibits these cellular characteristics. We further demonstrate that exogenous expression of LPAATβ effectively promotes tumor growth, while knockdown of LPAATβ expression inhibits tumor growth in an orthotopic xenograft model of human osteosarcoma.

Conclusions/Significance

Our results strongly suggest that LPAATβ expression may be associated with the aggressive phenotypes of human osteosarcoma and that LPAATβ may play an important role in regulating osteosarcoma cell proliferation and tumor growth. Thus, targeting LPAATβ may be exploited as a novel therapeutic strategy for the clinical management of osteosarcoma. This is especially attractive given the availability of selective pharmacological inhibitors.

VE-statin/egfl7 expression in endothelial cells is regulated by a distal enhancer and a proximal promoter under the direct control of Erg and GATA-2

Angiogenesis is the process by which new blood vessels arise from existing ones by the budding out of endothelial cell capillaries from the luminal side of blood vessels. Blood vessel formation is essential for organ development during embryogenesis and is associated with several physiological and pathological processes, such as wound healing and tumor development. The VE-statin/egfl7 gene is specifically expressed in endothelial cells during embryonic development and in the adult. We studied here the regulatory mechanisms that control this tissue-specific expression. RT-qPCR analyses showed that the specificity of expression of VE-statin/egfl7 in endothelial cells is not shared with its closest neighbor genes notch1 and agpat2 on the mouse chromosome 2. Chromatin-immunoprecipitation analysis of histone modifications at the VE-statin/egfl7 locus showed that the chromatin is specifically opened in endothelial cells, but not in fibroblasts at the transcription start sites. A 13 kb genomic fragment of promoter was cloned and analyzed by gene reporter assays which showed that two conserved regions are important for the specific expression of VE-statin/egfl7 in endothelial cells; a −8409/−7563 enhancer and the −252/+38 region encompassing the exon-1b transcription start site. The latter contains essential GATA and ETS-binding sites, as assessed by linker-scanning analysis and site-directed mutagenesis. An analysis of expression of the ETS and GATA transcription factors showed that Erg, Fli-1 and GATA-2 are the most highly expressed factors in endothelial cells. Erg and GATA-2 directly control the expression of the endogenous VE-statin/egfl7 while Fli-1 probably exerts an indirect control, as assessed by RNA interference and chromatin immunoprecipitation. This first detailed analysis of the mechanisms that govern the expression of the VE-statin/egfl7 gene in endothelial cells pinpoints the specific importance of ETS and GATA factors in the specific regulation of genes in this cell lineage.

Role of lysophosphatidic acid acyltransferase 3 for the supply of highly polyunsaturated fatty acids in TM4 Sertoli cells

Sertoli cells supply germ cells with nutrients, including highly polyunsaturated fatty acids (hPUFAs), which are essential for testicular function. We have previously reported high expression of lysophosphatidic acid acyltransferase (LPAAT)3 in mature mouse testis and suggested an arachidonoyl-transferase activity to LPA. To investigate the role of LPAAT3 in the storage and release of PUFAs, TM4 Sertoli cells were stably transfected with LPAAT3-small hairpin (sh)RNA. Arachidonoyl-, eicosapentaenoyl-, and docosapentaenoyl-containing phosphatidylcholine (PC) and linoleoyl-containing phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylglycerol were significantly decreased as determined by liquid chromatography coupled to electrospray ionization mass spectrometry. Expression of murine LPAAT3 in Chinese hamster ovary (CHO)-K1 cells had essentially an opposite effect. The level of polyunsaturated PC correlated with cellular levels of free docosapentaenoic acid and eicosapentaenoic acid in TM4 and CHO-K1 cells, respectively. Activity assays using microsomal preparations as a source of LPAAT3 revealed an excessive PA synthesis from LPA acceptors for docosahexaenoyl-, arachidonoyl- and less pronounced for linoleoyl-CoA. We propose that the efficient incorporation of hPUFAs into PA-the precursor of several phospholipids, including PC-and the selective increase of the polyunsaturated PC pool in TM4 Sertoli cells might be required for the controlled release of hPUFAs and their supply to germ cells.

Functional characterization of the human 1-acylglycerol-3-phosphate-O-acyltransferase isoform 10/glycerol-3-phosphate acyltransferase isoform 3

Synthesis of phospholipids can occur de novo or via remodeling of the existing phospholipids. Synthesis of triglycerides, a form of energy storage in cells, is an end product of these pathways. Several 1-acylglycerol-3-phosphate-O-acyltransferases (AGPATs) acylate lysophosphatidic acid (LPA) at the sn-2 (carbon 2) position to produce phosphatidic acid (PA). These enzymes are involved in phospholipids and triglyceride synthesis through an evolutionary conserved process involving serial acylations of glycerol-3-phosphate. We cloned a cDNA predicted to be an AGPAT isoform (AGPAT10). This cDNA has been recently identified as glycerol-3-phosphate-O-acyltransferase isoform 3 (GPAT3). When this AGPAT10/GPAT3 cDNA was expressed in Chinese Hamster ovary cells, the protein product localizes to the endoplasmic reticulum. In vitro enzymatic activity using lysates of human embryonic kidney-293 cells infected with recombinant AGPAT10/GPAT3 adenovirus show that the protein has a robust AGPAT activity with an apparent V(max) of 2 nmol/min per mg protein, but lacks GPAT enzymatic activity. This AGPAT has similar substrate specificities for LPA and acyl-CoA as shown for another known isoform, AGPAT2. We further show that when overexpressed in human Huh-7 cells depleted of endogenous AGPAT activity by sh-RNA-AGPAT2-lentivirus, the protein again demonstrates AGPAT activity. These observations strongly suggest that the cDNA previously identified as GPAT3 has AGPAT activity and thus we prefer to identify this clone as AGPAT10 as well.

Biochemistry, physiology, and genetics of GPAT, AGPAT, and lipin enzymes in triglyceride synthesis

Triacylglycerol (TAG) synthesis and storage in tissues such as adipose tissue and liver have important roles in metabolic homeostasis. The molecular identification of genes encoding enzymes that catalyze steps in TAG biosynthesis from glycerol 3-phosphate has revealed an unexpected number of protein isoforms of the glycerol phosphate acyltransferase (GPAT), acylglycerolphosphate acyltransferase (AGPAT), and lipin (phosphatidate phosphatase) families that appear to catalyze similar biochemical reactions. However, on the basis of available data for a few members in which genetic deficiencies in mouse and/or human have been studied, we postulate that each GPAT, AGPAT, and lipin family member likely has a specialized role that may be uncovered through careful biochemical and physiological analyses.

Characterization of mouse lysophosphatidic acid acyltransferase 3: an enzyme with dual functions in the testis

Glycerophospholipids are structural and functional components of cellular membranes as well as precursors of various lipid mediators. Using acyl-CoAs as donors, glycerophospholipids are formed by the de novo pathway (Kennedy pathway) and modified in the remodeling pathway (Lands' cycle). Various acyltransferases, including two lysophosphatidic acid acyltransferases (LPAATs), have been discovered from a 1-acylglycerol-3-phosphate O-acyltransferase (AGPAT) family. Proteins of this family contain putative acyltransferase motifs, but their biochemical properties and physiological roles are not completely understood. Here, we demonstrated that mouse LPAAT3, previously known as mouse AGPAT3, possesses strong LPAAT activity and modest lysophosphatidylinositol acyltransferase activity with a clear preference for arachidonoyl-CoA as a donor. This enzyme is highly expressed in the testis, where CDP-diacylglycerol synthase 1 preferring 1-stearoyl-2-arachidonoyl-phosphatidic acid as a substrate is also highly expressed. Since 1-stearoyl-2-arachidonoyl species are the main components of phosphatidylinositol, mouse LPAAT3 may function in both the de novo and remodeling pathways and contribute to effective biogenesis of 1-stearoyl-2-arachidonoyl-phosphatidylinositol in the testis. Additionally, the expression of this enzyme in the testis increases significantly in an age-dependent manner, and beta-estradiol may be an important regulator of this enzyme's induction. Our findings identify this acyltransferase as an alternative important enzyme to produce phosphatidylinositol in the testis.

The microsomal cardiolipin remodeling enzyme acyl-CoA lysocardiolipin acyltransferase is an acyltransferase of multiple anionic lysophospholipids

Phospholipids are subjected to remodeling through the Lands cycle to attain appropriate FA compositions. In recent years, at least two families of lysophospholipid acyltransferases have been identified. Acyl-CoA lysocardiolipin acyltransferase 1 (ALCAT1) was initially identified as a microsomal lysocardiolipin acyltransferase. However, the physiological relevance of how this enzyme is involved in cardiolipin remodeling has not been elucidated. We report in this study that ALCAT1 possesses acyltransferase activities toward lysophosphatidylinositol (LPI) and lysophosphatidylglycerol (LPG). Membrane preparations from human embryonic kidney 293 (HEK293) cells overexpressing human ALCAT1 demonstrated significant increases in LPI acyltransferase (LPIAT) and LPG acyltransferase (LPGAT) activities using a variety of fatty acyl-CoAs. The enzyme affinities toward LPI and LPG were determined through kinetic studies suggesting that the LPI binding affinity to ALCAT1 depends on fatty acyl-CoA. Reduced expression of ALCAT1 in Hela cells resulted in significant reductions of LPIAT and LPGAT activities, but not ALCAT activity. Through structural and functional studies, we have identified critical amino acids D168 and L169 within ALCAT1 that are potentially involved in lysophospholipid substrate binding. Our studies provide the molecular basis for future investigations of the physiological function of ALCAT1 and offer evidence of critical amino acids involved in substrate binding for the family of glycerolipid acyltransferases.

31P MRS analysis of the phospholipid composition of the peripheral blood mononuclear cells (PBMC) and bone marrow mononuclear cells (BMMC) of patients with acute leukemia (AL)

The aim of this study was to evaluate the phospholipid concentration in acute leukemia (AL) blast cells from peripheral blood (PBMC) and bone marrow (BMMC). In vitro 31P Nuclear Magnetic Resonance Spectroscopy (31P MRS) was used. The integral intensities of the resonant peaks and the phospholipid concentrations in PBMC and BMMC were analyzed. Differences in the phospholipid concentrations in cells from myeloblastic or lymphoblastic lines were also evaluated. This investigation was carried out on phospholipid extracts from PBMC and BMMC from 15 healthy volunteers and 77 patients with AL (samples taken at the moment of diagnosis). A significant decrease in sphingomyelin (SM) and phosphtidylserine (PS) was observed in the PBMC of patients with AL relative to the results for the healthy volunteers. For ALL, we found a significant decrease in the concentration of phosphatidylcholine plasmalogen (CPLAS), SM, PI+PE (phosphatidylinositol + phosphatidylethanolamine) and PS in comparison with the results for healthy volunteers and patients with AML. Experiments with BMMC cells revealed a significant decrease in the concentration of CPLAS, SM, PI+PE, and PS in ALL relative to AML. Additionally, a significant decrease in phosphatidylcholine (PC) concentration was observed in ALL compared to AML. If the phospholipid extracts were taken simultaneously from the same patient, there were no significant differences in the integral intensities and phospholipid concentrations between PBMC and BMMC.

Acyl-CoA:lysophospholipid acyltransferases

Cell membranes contain several classes of glycerophospholipids, which have numerous structural and functional roles in the cells. Polyunsaturated fatty acids, including arachidonic acid and eicosapentaenoic acid, are located at the sn-2 (but not sn-1)-position of glycerophospholipids in an asymmetrical manner. Using acyl-CoAs as donors, glycerophospholipids are formed by a de novo pathway (Kennedy pathway) and modified by a remodeling pathway (Lands' cycle) to generate membrane asymmetry and diversity. Both pathways were reported in the 1950s. Whereas enzymes involved in the Kennedy pathway have been well characterized, including enzymes in the 1-acylglycerol-3-phosphate O-acyltransferase family, little is known about enzymes involved in the Lands' cycle. Recently, several laboratories, including ours, isolated enzymes working in the remodeling pathway. These enzymes were discovered not only in the 1-acylglycerol-3-phosphate O-acyltransferase family but also in the membrane-bound O-acyltransferase family. In this review, we summarize recent studies on cloning and characterization of lysophospholipid acyltransferases that contribute to membrane asymmetry and diversity.

Lysophospholipid acyltransferases: novel potential regulators of the inflammatory response and target for new drug discovery

Molecular and biochemical analyses of membrane phospholipids have revealed that, in addition to their physico-chemical properties, the metabolites of phospholipids play a crucial role in the recognition, signalling and responses of cells to a variety of stimuli. Such responses are mediated in large part by the removal and/or addition of different acyl chains to provide different phospholipid molecular species. The reacylation reactions, catalysed by specific acyltransferases control phospholipid composition and the availability of the important mediators free arachidonic acid and lysophospholipids. Lysophospholipid acyltransferases are therefore key control points for cellular responses to a variety of stimuli including inflammation. Regulation or manipulation of lysophospholipid acyltransferases may thus provide important mechanisms for novel anti-inflammatory therapies. This review will highlight mammalian lysophospholipid acyltransferases with particular reference to the potential role of lysophosphatidylcholine acyltransferase and its substrates in sepsis and other inflammatory conditions and as a potential target for novel anti-inflammatory therapies.

Genetic disorders of adipose tissue development, differentiation, and death

Lack of adipose tissue, either complete or partial, is the hallmark of disorders known as lipodystrophies. Patients with lipodystrophies suffer from metabolic complications similar to those associated with obesity, including insulin resistance, type 2 diabetes, hypertriglyceridemia, and hepatic steatosis. The loss of body fat in inherited lipodystrophies can be caused by defects in the development and/or differentiation of adipose tissue as a consequence of mutations in a number of genes, including PPARG (encoding a nuclear hormone receptor), AGPAT2 (encoding an enzyme involved in the biosynthesis of triglyceride and phospholipids), AKT2 (encoding a protein involved in insulin signal transduction), and BSCL2 (encoding seipin, whose role in the adipocyte biology remains unclear). The loss of body fat can also be caused by the premature death of adipocytes due to mutations in lamin A/C, nuclear lamina proteins, and ZMPSTE24, which modifies the prelamin A post-translationally. In this review, we focus on the molecular basis of inherited lipodystrophies as they relate to adipocyte biology and their associated phenotypic manifestations.

The bone microenvironment in metastasis; what is special about bone?

The skeleton is a common destination for many cancer metastases including breast and prostate cancer. There are many characteristics of bone that make it an ideal environment for cancer cell migration and colonization. Metaphyseal bone, found at the ends of long bone, in ribs, and in vertebrae, is comprised of trabecular bone interspersed with marrow and rich vasculature. The specialized microvasculature is adapted for the easy passage of cells in and out of the bone marrow. Moreover, the metasphyseal regions of bone are constantly undergoing remodeling, a process that releases growth factors from the matrix. Bone turnover also involves the production of numerous cytokines and chemokines that provide a means of communication between osteoblasts and osteoclasts, but co-incidentally can also attract and support metastatic cells. Once in the marrow, cancer cells can interact directly and indirectly with osteoblasts and osteclasts, as well as hematopoietic and stromal cells. Cancer cells secrete factors that affect the network of cells in the bone microenvironment as well as interact with other cytokines. Additionally, transient cells of the immune system may join the local mileau to ultimately support cancer cell growth. However, most metastasized cells that enter the bone marrow are transient; a few may remain in a dormant state for many years. Advances in understanding the bone cell-tumor cell interactions are key to controlling, if not preventing metastasis to bone.