CTP:phosphocholine cytidylyltransferase

Investigating the effects of dexamethasone on pulmonary surfactant lipids based on lipidomics studies

Dexamethasone, a glucocorticoid commonly used in pediatric patients, has potent anti-inflammatory and immunosuppressive properties. However, it is associated with side effects such as reduced lung function and decreased immunity. Pulmonary surfactant lipids are closely linked to lung disease and play a role in reducing surface tension, immune response and antiviral activity. The dysregulation of lipid metabolism is closely associated with lung disease. Hence, untargeted lipidomics may be instrumental in elucidating the effects of dexamethasone on pulmonary surfactant lipids. We obtained surfactant lipid samples from the bronchoalveolar lavage fluid of young mice injected subcutaneously with dexamethasone and conducted a comprehensive lipidomic analysis, comparing them with a control group. We observed a decrease in lipids, such as phosphatidylcholine, phosphatidylglycerol and phosphatidylethanolamine, and an increase in ceramide, fatty acid, diacylglycerol and monoglyceride, which may impact lung health. This study revealed the influence of dexamethasone on pulmonary surfactant lipids, offering new insights into adverse reactions in clinical settings.

Single-cell atlas of ABCA7 loss-of-function reveals impaired neuronal respiration via choline-dependent lipid imbalances

Loss-of-function (LoF) variants in the lipid transporter ABCA7 significantly increase the risk of Alzheimer's disease (odds ratio ∼2), yet the pathogenic mechanisms and the neural cell types affected by these variants remain largely unknown. Here, we performed single-nuclear RNA sequencing of 36 human post-mortem samples from the prefrontal cortex of 12 ABCA7 LoF carriers and 24 matched non-carrier control individuals. ABCA7 LoF was associated with gene expression changes in all major cell types. Excitatory neurons, which expressed the highest levels of ABCA7, showed transcriptional changes related to lipid metabolism, mitochondrial function, cell cycle-related pathways, and synaptic signaling. ABCA7 LoF-associated transcriptional changes in neurons were similarly perturbed in carriers of the common AD missense variant ABCA7 p.Ala1527Gly (n = 240 controls, 135 carriers), indicating that findings from our study may extend to large portions of the at-risk population. Consistent with ABCA7's function as a lipid exporter, lipidomic analysis of isogenic iPSC-derived neurons (iNs) revealed profound intracellular triglyceride accumulation in ABCA7 LoF, which was accompanied by a relative decrease in phosphatidylcholine abundance. Metabolomic and biochemical analyses of iNs further indicated that ABCA7 LoF was associated with disrupted mitochondrial bioenergetics that suggested impaired lipid breakdown by uncoupled respiration. Treatment of ABCA7 LoF iNs with CDP-choline (a rate-limiting precursor of phosphatidylcholine synthesis) reduced triglyceride accumulation and restored mitochondrial function, indicating that ABCA7 LoF-induced phosphatidylcholine dyshomeostasis may directly disrupt mitochondrial metabolism of lipids. Treatment with CDP-choline also rescued intracellular amyloid β -42 levels in ABCA7 LoF iNs, further suggesting a link between ABCA7 LoF metabolic disruptions in neurons and AD pathology. This study provides a detailed transcriptomic atlas of ABCA7 LoF in the human brain and mechanistically links ABCA7 LoF-induced lipid perturbations to neuronal energy dyshomeostasis. In line with a growing body of evidence, our study highlights the central role of lipid metabolism in the etiology of Alzheimer's disease.

Shotgun lipidomics of human subretinal fluids under rod-dominant retina reveals cone-dominated lipids

Subretinal fluid (SRF) accumulates between photoreceptor outer segments and retinal pigment epithelium during rhegmatogenous retinal detachment. Biomolecular components such as lipids originate from cells surrounding the SRF. Knowledge of the composition of these molecules in SRF potentially provides mechanistic insight into the physiologic transfer of lipids between retinal tissue compartments. Using mass spectrometry and tandem mass spectrometry analysis on an electrospray ionization quadrupole-time-of-flight mass spectrometer, we identified a total of 115 lipid molecular species of 11 subclasses and 9 classes in two samples from two patients with rhegmatogenous retinal detachment. These included 47 glycerophosphocholines, 6 glycerophosphoethanolamines, 1 glycerophosphoinositol, 18 sphingomyelins, 9 cholesteryl esters, free cholesterol, 3 ceramides, 22 triacylglycerols and 8 free fatty acids. Glycerophosphocholines were of the highest intensity. By minimizing the formation of different adduct forms or clustering ions of different adducts, we determined the relative intensity of lipid molecular species within the same subclasses. The profiles were compared with those of retinal cells available in the published literature. The glycerophosphocholine profile of SRF was similar to that of cone outer segments, suggesting that outer segment degradation products are constitutively released into the interphotoreceptor matrix, appearing in SRF during detachment. This hypothesis was supported by the retinal distributions of corresponding lipid synthases' mRNA expression obtained from an online resource based on publicly available single-cell sequencing data. In contrast, based on lipid profiles and relevant gene expression in this study, the sources of free cholesterol and cholesteryl esters in SRF appeared more ambiguous, possibly reflecting that outer retina takes up plasma lipoproteins. Further studies to identify and quantify lipids in SRF will help better understand etiology of diseases relevant to outer retina.

Dietary choline activates the Ampk/Srebp signaling pathway and decreases lipid levels in Pacific white shrimp (Litopenaeus vannamei)

An 8-week feeding trial was conducted in Pacific white shrimp (Litopenaeus vannamei) to evaluate the effects of dietary choline supplementation on choline transport and metabolism, hepatopancreas histological structure and fatty acid profile, and regulation of lipid metabolism. Six isonitrogenous and isolipidic diets were formulated to contain different choline levels of 2.91 (basal diet), 3.85, 4.67, 6.55, 10.70 and 18.90 g/kg, respectively. A total of 960 shrimp (initial weight, 1.38 ± 0.01 g) were distributed randomly into twenty-four 250-L cylindrical fiber-glass tanks, with each diet assigned randomly to 4 replicate tanks. The results indicated that dietary choline significantly promoted the deposition of choline, betaine and carnitine (P < 0.05). The diameters and areas of R cells, total lipid and triglyceride contents in hepatopancreas, and triglyceride and non-esterified fatty acid contents in hemolymph were negatively correlated with dietary choline level. The contents of functional fatty acids in hepatopancreas, the activity of acetyl-CoA carboxylase (Acc), and the mRNA expression of fas, srebp and acc were highest in shrimp fed the diet containing 4.67 g/kg choline, and significantly higher than those fed the diet containing 2.91 g/kg, the lowest level of choline (P < 0.05). The number of R cells, content of very low-density lipoprotein (VLDL), activities of carnitine palmitoyl-transferase (Cpt1), lipoprotein lipase and hepatic lipase, and the mRNA expression levels of cpt1, fabp, fatp, ldlr, and ampk in hepatopancreas increased significantly as dietary choline increased (P < 0.05). In addition, hepatopancreas mRNA expression levels of ctl1, ctl2, oct1, badh, bhmt, ck, cept, and cct were generally up-regulated as dietary choline level increased (P < 0.01). In conclusion, dietary choline promoted the deposition of choline and its metabolites by up-regulating genes related to choline transport and metabolism. Moreover, appropriate dietary choline level promoted the development of hepatopancreas R cells and maintained the normal accumulation of lipids required for development, while high dietary choline not only promoted hepatopancreas lipid export by enhancing VLDL synthesis, but also promoted fatty acid β-oxidation and inhibited de novo fatty acid synthesis by activating the Ampk/Srebp signaling pathway. These findings provided further insight and understanding of the mechanisms by which dietary choline regulated lipid metabolism in L. vannamei.

The Role of Cytosolic Lipid Droplets in Hepatitis C Virus Replication, Assembly, and Release

The hepatitis C virus (HCV) causes chronic hepatitis by establishing a persistent infection. Patients with chronic hepatitis frequently develop hepatic cirrhosis, which can lead to liver cancer-the progressive liver damage results from the host's immune response to the unresolved infection. The HCV replication process, including the entry, replication, assembly, and release stages, while the virus circulates in the bloodstream, it is intricately linked to the host's lipid metabolism, including the dynamic of the cytosolic lipid droplets (cLDs). This review article depicts how this interaction regulates viral cell tropism and aids immune evasion by coining viral particle characteristics. cLDs are intracellular organelles that store most of the cytoplasmic components of neutral lipids and are assumed to play an increasingly important role in the pathophysiology of lipid metabolism and host-virus interactions. cLDs are involved in the replication of several clinically significant viruses, where viruses alter the lipidomic profiles of host cells to improve viral life cycles. cLDs are involved in almost every phase of the HCV life cycle. Indeed, pharmacological modulators of cholesterol synthesis and intracellular trafficking, lipoprotein maturation, and lipid signaling molecules inhibit the assembly of HCV virions. Likewise, small-molecule inhibitors of cLD-regulating proteins inhibit HCV replication. Thus, addressing the molecular architecture of HCV replication will aid in elucidating its pathogenesis and devising preventive interventions that impede persistent infection and prevent disease progression. This is possible via repurposing the available therapeutic agents that alter cLDs metabolism. This review highlights the role of cLD in HCV replication.

Combination of biomarkers for neoadjuvant systemic chemotherapy before cystectomy in patients with urinary bladder cancer

Clinical utility of cisplatin based neoadjuvant chemotherapy (NAC) prior to radical cystectomy is limited because of lack of tools that can guide for a better patient selection. We aim to explore if a combination of biomarkers is superior to a single marker. Pretreatment tumor specimens and clinical data from two randomized trials including 250 patients with T2-T4 urothelial bladder cancer, were used. The information on the expressions on tumor tissue of four biomarkers; CCTα, emmprin, survivin, and BCL-2, detected by immunohistochemistry in our previous studies, was used. Cox proportional hazard models, including treatment-by-biomarker interaction terms, were used to assess the predictive value of the biomarkers for efficacy of NAC on overall survival. CCTα provided predictive information about the efficacy of NAC (interaction P=0.009). None of the other biomarkers provided statistically significant information additional to CCTα. The adjusted hazard ratio for NAC treated versus no-NAC was 0.42 (95% CI: 0.27-0.64) for patients with negative CCTα expression, when adding information about emmprin it decreased to 0.33 (95% CI: 0.19-0.56) for patients with both negative CCTα and emmprin. This corresponds to a decrease in number needed to treat from 4 to 3 patients. The combination of CCTα with survivin or BCL-2 yielded similar results. In a group of patients with muscle invasive bladder cancer a combination of two biomarkers might improve the possibility to identify patients most likely to benefit from the use of NAC. Further studies designed to have sufficient power to detect an interaction effect are needed.

Choline Kinase Alpha Is a Novel Transcriptional Target of the Brg1 in Hepatocyte: Implication in Liver Regeneration

Liver regeneration is a key compensatory process in response to liver injury serving to contain damages and to rescue liver functions. Hepatocytes, having temporarily exited the cell cycle after embryogenesis, resume proliferation to regenerate the injured liver parenchyma. In the present study we investigated the transcriptional regulation of choline kinase alpha (Chka) in hepatocytes in the context of liver regeneration. We report that Chka expression was significantly up-regulated in the regenerating livers in the partial hepatectomy (PHx) model and the acetaminophen (APAP) injection model. In addition, treatment with hepatocyte growth factor (HGF), a strong pro-proliferative cue, stimulated Chka expression in primary hepatocytes. Chka depletion attenuated HGF-induced proliferation of hepatocytes as evidenced by quantitative PCR and Western blotting measurements of pro-proliferative genes as well as EdU incorporation into replicating DNA. Of interest, deletion of Brahma-related gene 1 (Brg1), a chromatin remodeling protein, attenuated Chka induction in the regenerating livers in mice and in cultured hepatocytes. Further analysis revealed that Brg1 interacted with hypoxia-inducible factor 1 alpha (HIF-1α) to directly bind to the Chka promoter and activate Chka transcription. Finally, examination of human acute liver failure (ALF) specimens identified a positive correlation between Chka expression and Brg1 expression. In conclusion, our data suggest that Brg1-dependent trans-activation of Chka expression may contribute to liver regeneration.

IGF-1 induces IRE1-XBP1-dependent endoplasmic reticulum biogenesis in bovine mammary epithelial cells

Insulin-like growth factor-1 (IGF-1) plays a key role in proliferation and galactopoiesis in mammary epithelial cells (MEC), but its definitive functions on endoplasmic reticulum (ER) during protein synthesis remain unknown. The present study aimed to elucidate the effects of IGF-1 on ER biogenesis in MEC in vitro and examined the expression of ER biogenesis-associated genes in the mammary gland during early lactation. We treated mammary alveolar cells-large T antigen cells (immortalized bovine MEC line established via stable transfection with simian virus-40 large T-antigen) with IGF-1 and examined ER biogenesis using the fluorescence intensity of an ER tracker and quantitative real-time PCR. We found IGF-1 significantly increased ER tracker staining and upregulated mRNA levels of ER biogenesis-related genes, such as CHKA (choline kinase α), PCYT1A (choline-phosphate cytidylyltransferase A), and SURF4 (surfeit locus protein 4). We focused on unfolded protein response to explore molecular mechanisms by which IGF-1 induces ER biogenesis. We found IGF-1 significantly increased mRNA levels of the XBP1 splicing form (XBP1s). Based on western blot analysis, IGF-1 induced the expression of (inositol-requiring kinase 1 α) protein, upstream of XBP1s, and phosphorylated-IRE1α. The inhibition of IRE1 endoribonuclease activity with 4-methylumbelliferone 8-carbaldehyde (4μ8C) significantly suppressed the increase in ER tracker fluorescence and ER biogenesis-related gene expression induced by IGF-1. Also, IGF-1-induced XBP1s and ER biogenesis-associated gene expression was inhibited by rapamycin, an inhibitor of mTORC1 (mammalian target of rapamycin complex 1), indicating that IRE1-XBP1 activation by IGF-1 is mediated by mTORC1. Moreover, to clarify the expression of XBP1s and ER biogenesis-associated genes expression under normal physiological conditions, mammary gland tissue from biopsies of dairy cows during late gestation and lactation were analyzed. In vivo data highlighted the significant increases in the mRNA levels of XBP1s and ER biogenesis-related genes in mammary gland tissue immediately after calving through 6 wk of lactation. The mRNA levels of IGF1R (IGF-1 receptor) in mammary glands increased during 6 wk of lactation. Therefore, the present study indicated for the first time that IGF-1 induces ER biogenesis by activating the IRE1-XBP1 axis under the regulation of mTORC1 in bovine MEC line.

Lipid Droplet Contact Sites in Health and Disease

After having been disregarded for a long time as inert fat drops, lipid droplets (LDs) are now recognized as ubiquitous cellular organelles with key functions in lipid biology and beyond. The identification of abundant LD contact sites, places at which LDs are physically attached to other organelles, has uncovered an unexpected level of communication between LDs and the rest of the cell. In recent years, many disease factors mutated in hereditary disorders have been recognized as LD contact site proteins. Furthermore, LD contact sites are dramatically rearranged in response to infections with intracellular pathogens, as well as under pathological metabolic conditions such as hepatic steatosis. Collectively, it is emerging that LD-organelle contacts are important players in development and progression of disease.

Identification and characterization of CTP:phosphocholine cytidylyltransferase CpCCT1 in the resurrection plant Craterostigma plantagineum

Phosphatidylcholine is a major phospholipid which is shown to be involved in stress adaptation. Phosphatidylcholine increased during dehydration in Craterostigma plantagineum, and therefore we characterized CTP:phosphocholine cytidylyltransferase (CpCCT1), a key regulatory enzyme for phosphatidylcholine synthesis in plants. The CpCCT1 gene from the resurrection plant C. plantagineum was cloned and the amino acid sequence was compared with homologs from other species including yeast and rat. CCT proteins have conserved catalytic and membrane-binding domains while the N-terminal and C-terminal domains have diverged. The tissue specific expression analysis indicated that CpCCT1 is expressed in all tested tissues and it is induced by dehydration and in response to 0.5 M NaCl solutions. In plants exposed to low temperature in the dark, the CpCCT1 transcript increased after 4 h at 4 °C. CpCCT1 expression also increased during mannitol and sorbitol treatments in a concentration dependent manner. Phytohormones such as abscisic acid and indole-3-acetic acid also trigged transcript accumulation. Comparisons of transcript and protein accumulations for different treatments (except for dehydration) suggest transcriptional and translational control mechanisms. Analysis of promoter activity and polysome occupancy suggest that CpCCT1 gene expression is mainly under translational regulation during dehydration.

Development of a new and reliable assay for choline kinase using 31P NMR

Choline kinase catalyzes the conversion of choline to phosphocholine (PC) by transferring a phosphate group from adenosine triphosphate (ATP) as the first step in the biosynthetic pathway for the membrane phospholipid phosphatidylcholine, an essential pathway in the Leishmania parasitic protozoan. Commonly used methods for kinetically quantifying the enzyme include a radioisotope assay utilizing labeled choline and a coupled spectrophotometric assay with multiple enzymes and substrates that indirectly measures choline kinase activity. When testing potential inhibitors with the coupled assay, results can cast doubt on whether choline kinase is being inhibited or one of the coupled enzymes. Therefore, ³¹P NMR spectroscopy was used to quantitatively measure the formation of the key product, phosphocholine, and to evaluate choline kinase activity. Interrogation of ³¹P NMR spectroscopy offers a number of benefits. Since this isotope is 100% abundant and has a relatively large gyromagnetic ratio, it is considered one of the more sensitive nuclides. As such, the need for costly isotopic enriched phosphorous is not required and detection of the ³¹P signal is possible even at relatively low concentrations. The enzymatic activity of Leishmania infantum choline kinase was able to be directly measured via integration of the ³¹P resonance associated with the phosphocholine product (δ = 3.94 ppm). These initial studies reveal that a ³¹P NMR spectroscopic-based assay could be used for testing substrate or transition state analogs as competitive inhibitors of Leishmania choline kinase that may prevent phosphatidylcholine synthesis in the parasite.

Diapause-associated changes in the lipid and metabolite profiles of the Asian tiger mosquito, Aedes albopictus

Diapause is an alternative life-history strategy that allows organisms to enter developmental arrest in anticipation of unfavorable conditions. Diapause is widespread among insects and plays a key role in enhancing overwinter survival as well as defining the seasonal and geographic distributions of populations. Next-generation sequencing has greatly advanced our understanding of the transcriptional basis for this crucial adaptation but less is known about the regulation of embryonic diapause physiology at the metabolite level. Here, we characterized the lipid and metabolite profiles of embryonic diapause in the Asian tiger mosquito, Aedes albopictus We used an untargeted approach to capture the relative abundance of 250 lipids and 241 metabolites. We observed adjustments associated with increased energy storage, including an accumulation of lipids, the formation of larger lipid droplets and increased lipogenesis, as well as metabolite shifts suggesting reduced energy utilization. We also found changes in neuroregulatory- and insulin-associated metabolites with potential roles in diapause regulation. Finally, we detected a group of unidentified, diapause-specific metabolites which have physical properties similar to those of steroids/steroid derivatives and may be associated with the ecdysteroidal regulation of embryonic diapause in A.albopictus Together, these results deepen our understanding of the metabolic regulation of embryonic diapause and identify key targets for future investigations.

A pair of phospho-base methyltransferases important for phosphatidylcholine biosynthesis in Arabidopsis

Phosphatidylcholine (PtdCho) is a predominant membrane lipid class in eukaryotes. Phospho-base N-methyltransferase (PMT) catalyzes a critical step in PtdCho biosynthesis. However, in Arabidopsis thaliana, the discovery of involvement of the specific PMT isoform in PtdCho biosynthesis remains elusive. Here, we show that PMT1 and PMT3 redundantly play an essential role in phosphocholine (PCho) biosynthesis, a prerequisite for PtdCho production. A pmt1 pmt3 double mutant was devoid of PCho, which affected PtdCho biosynthesis in vivo, showing severe growth defects in post-embryonic development. PMT1 and PMT3 were both highly expressed in the vasculature. The pmt1 pmt3 mutants had specifically affected leaf vein development and showed pale-green seedlings that were rescued by exogenous supplementation of PCho. We suggest that PMT1 and PMT3 are the primary enzymes for PCho biosynthesis and are involved in PtdCho biosynthesis and vascular development in Arabidopsis seedlings.

Localization and expression of CTP: Phosphocholine cytidylyltransferase in rat brain following cocaine exposure

Phosphatidylcholine (PC) is a primary phospholipid and major source of secondary lipid messengers and also serves as a biosynthetic precursor for other membrane phospholipids. Phosphocholine cytidylyltransferase (CCT) is the rate-limiting enzyme responsible for catalyzing the formation of PC. Changes in CCT activity have been associated with lipid dysregulation across various neurological disorders. Additionally, intermediates in PC synthesis, such as CDP-choline, have been suggested to attenuate drug craving during cocaine addiction. Recent work from our group demonstrated that cocaine exposure and conditioning alter the level of PC in the brain, specifically in the cerebellum and hippocampus. The present study examines the role of CCT expression in the brain and determines the effect of cocaine exposure on CCT expression. Immunohistochemical analysis (IHC) was performed to assess region-specific expression of CCT, including both of its isoforms; alpha (CCTα) and beta (CCTβ). IHC did not detect any staining of CCTα throughout the rat brain. In contrast, CCTβ expression was detected in the Purkinje cells of the cerebellum with decreases in expression following cocaine exposure. Collectively, these data demonstrate the region- and cell-specific localization of CCTα and CCTβ in the rat brain, as well as the altered expression of CCTβ in the cerebellum following cocaine exposure.

Unfolded Protein Response-Dependent Communication and Contact among Endoplasmic Reticulum, Mitochondria, and Plasma Membrane

The function of the endoplasmic reticulum (ER) can be impaired by changes to the extra- and intracellular environment, such as disruption of calcium homeostasis, expression of mutated proteins, and oxidative stress. In response to disruptions to ER homeostasis, eukaryotic cells activate canonical branches of signal transduction cascades, collectively termed the unfolded protein response (UPR). The UPR functions to remove or recover the activity of misfolded proteins that accumulated in the ER and to avoid irreversible cellular damage. Additionally, the UPR plays unique physiological roles in the regulation of diverse cellular events, including cell differentiation and development and lipid biosynthesis. Recent studies have shown that these important cellular events are also regulated by contact and communication among organelles. These reports suggest strong involvement among the UPR, organelle communication, and regulation of cellular homeostasis. However, the precise mechanisms for the formation of contact sites and the regulation of ER dynamics by the UPR remain unresolved. In this review, we summarize the current understanding of how the UPR regulates morphological changes to the ER and the formation of contact sites between the ER and other organelles. We also review how UPR-dependent connections between the ER and other organelles affect cellular and physiological functions.

Zn Stimulates the Phospholipids Biosynthesis via the Pathways of Oxidative and Endoplasmic Reticulum Stress in the Intestine of Freshwater Teleost Yellow Catfish

The hypothesis of our study was that waterborne Zn exposure evoked phospholipids (PL) biosynthesis to compensate for the loss of membrane integrity, and the pathways of oxidative stress and endoplasmic reticulum (ER) stress mediated the Zn-evoked changes of PL biosynthesis. Thus, we conducted RNA sequencing to analyze the differences in the intestinal transcriptomes between the control and Zn-treated P. fulvidraco. The 56-day Zn exposure increased the intestinal Zn accumulation, and mRNA levels of 816 genes were markedly up-regulated, while that of 263 genes were down-regulated. Many differentially expressed genes in the pathways of PL biosynthesis and protein processing in ER were identified. Their expression profiles indicated that waterborne Zn exposure injured protein metabolism, induced PL biosynthesis caused oxidative stress and ER stress, and activated the unfolded protein response. Then, using the primary enterocytes, we identified the mechanism of oxidative and ER stress mediating Zn-induced PL biosynthesis, and indicated that the activation of these pathways constituted adaptive mechanisms to reduce Zn toxicity. Our study demonstrated that Zn exposure via the water increased Zn accumulation and PL biosynthesis, and that oxidative stress and ER stress were interdependent and mediated the Zn-induced PL biosynthesis of the intestine in the freshwater teleost.

The folding, stability and function of lactose permease differ in their dependence on bilayer lipid composition

Lipids play key roles in Biology. Mechanical properties of the lipid bilayer influence their neighbouring membrane proteins, however it is unknown whether different membrane protein properties have the same dependence on membrane mechanics, or whether mechanics are tuned to specific protein processes of the protein. We study the influence of lipid lateral pressure and electrostatic effects on the in vitro reconstitution, folding, stability and function of a representative of the ubiquitous major facilitator transporter superfamily, lactose permease. Increasing the outward chain lateral pressure in the bilayer, through addition of lamellar phosphatidylethanolamine lipids, lowers lactose permease folding and reconstitution yields but stabilises the folded state. The presence of phosphatidylethanolamine is however required for correct folding and function. An increase in headgroup negative charge through the addition of phosphatidylglycerol lipids favours protein reconstitution but is detrimental to topology and function. Overall the in vitro folding, reconstitution, topology, stability and function of lactose permease are found to have different dependences on bilayer composition. A regime of lipid composition is found where all properties are favoured, even if suboptimal. This lays ground rules for rational control of membrane proteins in nanotechnology and synthetic biology by manipulating global bilayer properties to tune membrane protein behaviour.

Insights into the phosphatidylcholine and phosphatidylethanolamine biosynthetic pathways in Leishmania parasites and characterization of a choline kinase from Leishmania infantum

The protozoan parasite Leishmania infantum is a causative agent of the disease visceral leishmaniasis, which can be fatal if not properly treated. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) biosynthesis pathways are attractive targets for new antileishmanial compounds since these Leishmania cell membrane phospholipids are important for parasite morphology and physiology. In this work we observed Leishmania synthesize PC and PE from extracellular choline and ethanolamine, respectively, suggesting the presence of CDP-choline and CDP-ethanolamine pathways. In addition, Leishmania converted PE to PC, indicating the parasite possesses phosphatidylethanolamine N-methyltransferase (PEMT) activity. The first step in the biosynthesis of PC or PE requires the phosphorylation of choline or ethanolamine by a kinase. We cloned the gene encoding a putative choline/ethanolamine kinase from Leishmania infantum and expressed and purified the encoded recombinant protein. The enzyme possesses choline kinase activity with a V_max of 3.52μmol/min/mg and an apparent K_m value of 0.089mM with respect to choline. The enzyme can also phosphorylate ethanolamine in vitro, but the apparent K_m for ethanolamine is 850-fold greater than for choline. In an effort to probe requirements for small molecule inhibition of Leishmania choline kinase, the recombinant enzyme was evaluated for the ability to be inhibited by novel quaternary ammonium salts. The most effective inhibitor was N-iodomethyl-N,N,-dimethyl-N-(6,6-diphenyl hex-5-en-1-yle) ammonium iodide, denoted compound C6. In the presence of 4mM compound C6, the V_max/K_m decreased to approximately 1% of the wild-type catalytic efficiency. In addition, in Leishmania cells treated with compound C6 choline transport was inhibited.

Lung surfactant metabolism: early in life, early in disease and target in cell therapy

Lung surfactant is a complex mixture of lipids and proteins lining the alveolar epithelium. At the air-liquid interface, surfactant lowers surface tension, avoiding alveolar collapse and reducing the work of breathing. The essential role of lung surfactant in breathing and therefore in life, is highlighted by surfactant deficiency in premature neonates, which causes neonatal respiratory distress syndrome and results in early death after birth. In addition, defects in surfactant metabolism alter lung homeostasis and lead to disease. Special attention should be paid to two important key cells responsible for surfactant metabolism: alveolar epithelial type II cells (AE2C) and alveolar macrophages (AM). On the one hand, surfactant deficiency coming from abnormal AE2C function results in high surface tension, promoting alveolar collapse and mechanical stress in the epithelium. This epithelial injury contributes to tissue remodeling and lung fibrosis. On the other hand, impaired surfactant catabolism by AM leads to accumulation of surfactant in air spaces and the associated altered lung function in pulmonary alveolar proteinosis (PAP). We review here two recent cell therapies that aim to recover the activity of AE2C or AM, respectively, therefore targeting the restoring of surfactant metabolism and lung homeostasis. Applied therapies successfully show either transplantation of healthy AE2C in fibrotic lungs, to replace injured AE2C cells and surfactant, or transplantation of bone marrow-derived macrophages to counteract accumulation of surfactant lipid and proteinaceous material in the alveolar spaces leading to PAP. These therapies introduce an alternative treatment with great potential for patients suffering from lung diseases.

Characterization of cytidylyltransferase enzyme activity through high performance liquid chromatography

The cytidylyltransferases are a family of enzymes that utilize cytidine 5'-triphosphate (CTP) to synthesize molecules that are typically precursors to membrane phospholipids. The most extensively studied cytidylyltransferase is CTP:phosphocholine cytidylyltransferase (CCT), which catalyzes conversion of phosphocholine and CTP to cytidine diphosphocholine (CDP-choline), a step critical for synthesis of the membrane phospholipid phosphatidylcholine (PC). The current method used to determine catalytic activity of CCT measures production of radiolabeled CDP-choline from (14)C-labeled phosphocholine. The goal of this research was to develop a CCT enzyme assay that employed separation of non-radioactive CDP-choline from CTP. A C18 reverse phase column with a mobile phase of 0.1 M ammonium bicarbonate (98%) and acetonitrile (2%) (pH 7.4) resulted in separation of solutions of the substrate CTP from the product CDP-choline. A previously characterized truncated version of rat CCTα (denoted CCTα236) was used to test the HPLC enzyme assay by measuring CDP-choline product formation. The Vmax for CCTα236 was 3850 nmol/min/mg and K0.5 values for CTP and phosphocholine were 4.07 mM and 2.49 mM, respectively. The HPLC method was applied to glycerol 3-phosphate cytidylyltransferase (GCT) and CTP:2-C-methyl-D-erythritol-4-phosphate cytidylyltransferase synthetase (CMS), members of the cytidylyltransferase family that produce CDP-glycerol and CDP-methylerythritol, respectively.

Participation of prostaglandin D2 in the mobilization of the nuclear-localized CTP:phosphocholine cytidylyltransferase alpha in renal epithelial cells

Phosphatidylcholine (PC) is the main constituent of mammalian cell membranes. Consequently, preservation of membrane PC content and composition - PC homeostasis - is crucial to maintain cellular life. PC biosynthetic pathway is generally controlled by CTP:phosphocholine cytidylyltransferase (CCT), which is considered the rate-limiting enzyme. CCTα is an amphitropic protein, whose enzymatic activity is commonly associated with endoplasmic reticulum redistribution. However, most of the enzyme is located inside the nuclei. Here, we demonstrate that CCTα is the most abundant isoform in renal collecting duct cells, and its redistribution is dependent on endogenous prostaglandins. Previously we have demonstrated that PC synthesis was inhibited by indomethacin (Indo) treatment, and this effect was reverted by exogenous PGD(2). In this work we found that Indo induced CCTα distribution into intranuclear Lamin A/C foci. Exogenous PGD(2) reverted this effect by inducing CCTα redistribution to nuclear envelope, suggesting that PGD(2) maintains PC synthesis by CCTα mobilization. Interestingly, we found that the effect of PGD(2) was dependent on ERK1/2 activation. In conclusion, our previous observations and the present results lead us to suggest that papillary cells possess the ability to maintain their structural integrity through the synthesis of their own survival molecule, PGD(2), by modulating CCTα intracellular location.

Membrane lipid compositional sensing by the inducible amphipathic helix of CCT

The amphipathic helical (AH) membrane binding motif is recognized as a major device for lipid compositional sensing. We explore the function and mechanism of sensing by the lipid biosynthetic enzyme, CTP:phosphocholine cytidylyltransferase (CCT). As the regulatory enzyme in phosphatidylcholine (PC) synthesis, CCT contributes to membrane PC homeostasis. CCT directly binds and inserts into the surface of bilayers that are deficient in PC and therefore enriched in lipids that enhance surface charge and/or create lipid packing voids. These two membrane physical properties induce the folding of the CCT M domain into a ≥60 residue AH. Membrane binding activates catalysis by a mechanism that has been partially deciphered. We review the evidence for CCT compositional sensing, and the membrane and protein determinants for lipid selective membrane-interactions. We consider the factors that promote the binding of CCT isoforms to the membranes of the ER, nuclear envelope, or lipid droplets, but exclude CCT from other organelles and the plasma membrane. The CCT sensing mechanism is compared with several other proteins that use an AH motif for membrane compositional sensing. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.

CTP:phosphocholine cytidylyltransferase: Function, regulation, and structure of an amphitropic enzyme required for membrane biogenesis

CTP:phosphocholine cytidylyltransferase (CCT) catalyzes a rate-limiting and regulated step in the CDP-choline pathway for the synthesis of phosphatidylcholine (PC) and PC-derived lipids. Control of CCT activity is multi-layered, and includes direct regulation by reversible membrane binding involving a built-in lipid compositional sensor. Thus CCT contributes to phospholipid compositional homeostasis. CCT also modifies the curvature of its target membrane. Knowledge of CCT structure and regulation of its catalytic function are relatively advanced compared to many lipid metabolic enzymes, and are reviewed in detail. Recently the genetic origins of two human developmental and lipogenesis disorders have been traced to mutations in the gene for CCTα.

The metabolic responses to hepatitis B virus infection shed new light on pathogenesis and targets for treatment

Chronic infection caused by the hepatitis B virus (HBV), is strongly associated with hepatitis, fatty liver and hepatocellular carcinoma. To investigate the underlying mechanisms, we characterize the metabolic features of host cells infected with the virus using systems biological approach. The results show that HBV replication induces systematic metabolic alterations in host cells. HBV infection up-regulates the biosynthesis of hexosamine and phosphatidylcholine by activating glutamine-fructose-6-phosphate amidotransferase 1 (GFAT1) and choline kinase alpha (CHKA) respectively, which were reported for the first time for HBV infection. Importantly suppressing hexosamine biosynthesis and phosphatidylcholine biosynthesis can inhibit HBV replication and expression. In addition, HBV induces oxidative stress and stimulates central carbon metabolism and nucleotide synthesis. Our results also indicate that HBV associated hepatocellular carcinoma could be attributed to GFAT1 activated hexosamine biosynthesis and CHKA activated phosphatidylcholine biosynthesis. This study provides further insights into the pathogenesis of HBV-induced diseases, and sheds new light on drug target for treating HBV infection.

Near-isogenic lines of Triticum aestivum with distinct modes of resistance exhibit dissimilar transcriptional regulation during Diuraphis noxia feeding

Russian wheat aphid (Diuraphis noxia, Kurdjumov) feeding on susceptible Triticum aestivum L. leads to leaf rolling, chlorosis and plant death - symptoms not present in resistant lines. Although the effects of several D. noxia (Dn) resistance genes are known, none have been isolated or characterized. Wheat varieties expressing different Dn genes exhibit distinct modes of D. noxia resistance, such as antibiosis (Dn1), tolerance (Dn2), and antixenosis (Dn5). However, the mechanism whereby feeding aphids are perceived, and how subsequent transcriptional responses are partitioned into resistance categories, remains unclear. Here we report on downstream events in near-isogenic wheat lines containing different Dn genes after D. noxia biotype SA1 feeding. Transcripts involved in stress, signal transduction, photosynthesis, metabolism and gene regulation were differentially regulated during D. noxia feeding. Expression analyses using RT-qPCR and RNA hybridization, as well as enzyme activity profiling, provide evidence that the timing and intensity of pathways induced are critical in the development of particular modes of resistance. Pathways involved include the generation of kinase signalling cascades that lead to a sustained oxidative burst, and a hypersensitive response that is active during antibiosis. Tolerance is a passive resistance mechanism that acts through repair or de novo synthesis of photosystem proteins. Results further suggest that ethylene-mediated pathways are possibly involved in generating volatile compounds and cell wall fortification during the antixenosic response.

Pre-conditioning with CDP-choline attenuates oxidative stress-induced cardiac myocyte death in a hypoxia/reperfusion model

Background. CDP-choline is a key intermediate in the biosynthesis of phosphatidylcholine, which is an essential component of cellular membranes, and a cell signalling mediator. CDP-choline has been used for the treatment of cerebral ischaemia, showing beneficial effects. However, its potential benefit for the treatment of myocardial ischaemia has not been explored yet. Aim. In the present work, we aimed to evaluate the potential use of CDP-choline as a cardioprotector in an in vitro model of ischaemia/reperfusion injury. Methods. Neonatal rat cardiac myocytes were isolated and subjected to hypoxia/reperfusion using the coverslip hypoxia model. To evaluate the effect of CDP-choline on oxidative stress-induced reperfusion injury, the cells were incubated with H₂O₂ during reperfusion. The effect of CDP-choline pre- and postconditioning was evaluated using the cell viability MTT assay, and the proportion of apoptotic and necrotic cells was analyzed using the Annexin V determination by flow cytometry. Results. Pre- and postconditioning with 50 mg/mL of CDP-choline induced a significant reduction of cells undergoing apoptosis after hypoxia/reperfusion. Preconditioning with CDP-choline attenuated postreperfusion cell death induced by oxidative stress. Conclusion. CDP-choline administration reduces cell apoptosis induced by oxidative stress after hypoxia/reperfusion of cardiac myocytes. Thus, it has a potential as cardioprotector in ischaemia/reperfusion-injured cardiomyocytes.

Expression of phosphatidylcholine biosynthetic enzymes during early embryogenesis in the amphibian Bufo arenarum

In the principal route of phosphatidylcholine (PC) synthesis the regulatory steps are catalysed by CTP:phosphocholine cytidylyltransferase (CCT) and choline kinase (CK). Knock-out mice in Pcyt1a (CCT gene) and Chka1 (CK gene) resulted in preimplantation embryonic lethality, demonstrating the essential role of this pathway. However, there is still a lack of detailed CCT and CK expression analysis during development. The aim of the current work was to study the expression during early development of both enzymes in the external-fertilization vertebrate Bufo arenarum. Reverse transcription polymerase chain reaction (RT-PCR) and western blot confirmed their presence in unfertilized eggs. Analysis performed in total extracts from staged embryos showed constant protein levels of both enzymes until the 32-cell stage: then they decreased, reaching a minimum in the gastrula before starting to recover. CTP:phosphocholine cytidylyltransferase is an amphitropic enzyme that inter-converts between cytosolic inactive and membrane-bound active forms. Immunoblot analysis demonstrated that the cytosolic:total CCT protein ratio does not change throughout embryogenesis, suggesting a progressive decline of CCT activity in early development. However, PC (and phosphatidylethanolamine) content per egg/embryo remained constant throughout the stages analysed. In conclusion, the current data for B. arenarum suggest that net synthesis of PC mediated by CCT and CK is not required in early development and that supplies for membrane biosynthesis are fulfilled by lipids already present in the egg/embryo reservoirs.

Cell cycle dependent changes in membrane stored curvature elastic energy: evidence from lipidomic studies

One of the most developed theories of phospholipid homeostasis is the intrinsic curvature hypothesis, which, in broad terms, postulates that cells regulate their lipid composition so as to keep constant the membrane stored curvature elastic energy. The implication of this hypothesis is that lipid composition is determined by a ratio control function consisting of the weighted sum of concentrations of type II lipids in the numerator and the weighted sum of concentrations of Type 0 lipids in the denominator. In previous work we used a data-driven approach, based on lipidomic data from asynchronous cell cultures, to determine a criterion that allows the different lipid species to be assigned to the set of type 0 or of type II lipids, and hence construct a ratio control function that serves as a proxy for the lipid contribution to total membrane stored curvature elastic energy in vivo. Here we apply the curvature elastic energy proxy to the analysis of lipid composition data from synchronous HeLa cells as they traverse the cell cycle. Our analysis suggests HeLa cells modify their membrane stored elastic energy through the cell cycle. In S-phase type 0 lipids are the most abundant, whilst in G2 type II lipids are most abundant. Changes in our proxy for membrane stored elastic energy correlate with membrane curvature dependent processes in the HeLa cell around division, providing some insights into the interplay between the individual lipid and protein contributions to membrane free energy.

The role of phosphatidylcholine and choline metabolites to cell proliferation and survival

The reorganization of metabolic pathways in cancer facilitates the flux of carbon and reducing equivalents into anabolic pathways at the expense of oxidative phosphorylation. This provides rapidly dividing cells with the necessary precursors for membrane, protein and nucleic acid synthesis. A fundamental metabolic perturbation in cancer is the enhanced synthesis of fatty acids by channeling glucose and/or glutamine into cytosolic acetyl-CoA and upregulation of key biosynthetic genes. This lipogenic phenotype also extends to the production of complex lipids involved in membrane synthesis and lipid-based signaling. Cancer cells display sensitivity to ablation of fatty acid synthesis possibly as a result of diminished capacity to synthesize complex lipids involved in signaling or growth pathways. Evidence has accrued that phosphatidylcholine, the major phospholipid component of eukaryotic membranes, as well as choline metabolites derived from its synthesis and catabolism, contribute to both proliferative growth and programmed cell death. This review will detail our current understanding of how coordinated changes in substrate availability, gene expression and enzyme activity lead to altered phosphatidylcholine synthesis in cancer, and how these changes contribute directly or indirectly to malignant growth. Conversely, apoptosis targets key steps in phosphatidylcholine synthesis and degradation that are linked to disruption of cell cycle regulation, reinforcing the central role that phosphatidylcholine and its metabolites in determining cell fate.

Comparative kinetic analysis of glycerol 3-phosphate cytidylyltransferase from Enterococcus faecalis and Listeria monocytogenes

BACKGROUND

Glycerol 3-phosphate cytidylyltransferase (GCT) is an enzyme central to the synthesis of teichoic acids, components of the cell wall in gram positive bacteria. Catalysis by GCT from Enterococcus faecalis and Listeria monocytogenes has been investigated and catalytic properties compared.

MATERIAL/METHODS

The genes encoding GCT were cloned from genomic DNA and recombinant proteins expressed in E. coli and purified. Enzyme assays were used to determine kinetic constants kcat and Km. Chemical crosslinking provided a means to assess quaternary structure of each GCT.

RESULTS

Recombinant Enterococcus faecalis GCT had an apparent kcat value of 1.51 s⁻¹ and apparent Km values of 2.42 mM and 4.03 mM with respect to substrates cytidine 5'-triphosphate (CTP) and glycerol phosphate. Listeria monocytogenes GCT had an apparent kcat value of 4.15 s⁻¹ and apparent Km values of 1.52 mM and 6.56 mM with respect to CTP and glycerol phosphate. This resulted in kcat/Km values of 0.62 s⁻¹mM⁻¹ and 0.37 s⁻¹mM⁻¹ for E. faecalis GCT and 2.73 s⁻¹mM⁻¹ and 0.63 s⁻¹mM⁻¹ for L. monocytogenes GCT with respect to CTP and glycerol phosphate, respectively.

CONCLUSIONS

The genome of both Enterococcus faecalis and Listeria monocytogenes contain a gene that encodes a functional GCT. The genes are 67% identical at the nucleotide level and the encoded proteins exhibit a 63% amino acid identity. The purified, recombinant enzymes each appear to be dimeric and display similar kinetic characteristics. Studying the catalytic characteristics of GCT isoforms from pathogenic bacteria provides information important for the future development of potential antibacterial agents.

Phospholipids: "greasing the wheels" of humoral immunity

Phospholipids are major structural components of all cellular membranes. In addition, certain phospholipids execute regulatory activities that affect cell behavior, function and fate in critically important physiological settings. The influence of phospholipids is especially obvious in the adaptive immune system, where these macromolecules mediate both intrinsic and extrinsic effects on B and T lymphocytes. This review article highlights the action of lysophospholipid sphingosine-1-phosphate as a lymphocyte chemoattractant, the function of phosphatidylinositol phosphates as signaling conduits in lymphocytes and the role of phospholipids as raw materials for membrane assembly and organelle biogenesis in activated B lymphocytes. Special emphasis is placed on the means by which these three processes push humoral immune responses forward. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.

An in vivo ratio control mechanism for phospholipid homeostasis: evidence from lipidomic studies

While it is widely accepted that the lipid composition of eukaryotic membranes is under homeostatic control, the mechanisms through which cells sense lipid composition are still the subject of debate. It has been postulated that membrane curvature elastic energy is the membrane property that is regulated by cells, and that lipid composition is maintained by a ratio control function derived from the concentrations of type II and type 0 lipids, weighted appropriately. We assess this proposal by seeking a signature of ratio control in quantified lipid composition data obtained by electrospray ionization mass spectrometry from over 40 independent asynchronous cell populations. Our approach revealed the existence of a universal 'pivot' lipid, which marks the boundary between type 0 lipids and type II lipids, and which is invariant between different cell types or cells grown under different conditions. The presence of such a pivot species is a distinctive signature of the operation in vivo, in human cell lines, of a control function that is consistent with the hypothesis that membrane elastic energy is homeostatically controlled.

Surfactant phospholipid metabolism

Pulmonary surfactant is essential for life and is composed of a complex lipoprotein-like mixture that lines the inner surface of the lung to prevent alveolar collapse at the end of expiration. The molecular composition of surfactant depends on highly integrated and regulated processes involving its biosynthesis, remodeling, degradation, and intracellular trafficking. Despite its multicomponent composition, the study of surfactant phospholipid metabolism has focused on two predominant components, disaturated phosphatidylcholine that confers surface-tension lowering activities, and phosphatidylglycerol, recently implicated in innate immune defense. Future studies providing a better understanding of the molecular control and physiological relevance of minor surfactant lipid components are needed. This article is part of a Special Issue entitled Phospholipids and Phospholipid Metabolism.

Metabolic consequences of treatment with AKT inhibitor perifosine in breast cancer cells

Activation of the PI3K/Akt pathway is associated with the development of numerous human cancers. As a result, many emerging therapies target this pathway. Previous studies have shown that targeting the PI3K/Akt pathway at the level of PI3K is associated with a drop in phosphocholine (PCho) and a reduction in hyperpolarized lactate production. However, the consequences of targeting downstream of PI3K at the level of Akt have not been investigated. Perifosine is an anticancer alkylphospholipid used in clinical trials. It acts by inhibiting phosphorylation of Akt and has been shown to inhibit CTP-phosphocholine cytidyltransferase (CT). The goal of this study was to identify the MRS-detectable metabolic consequences of treatment with perifosine in MCF-7 breast cancer cells. We found that perifosine treatment led to a 51 ± 5% drop in PCho from 30 ± 5 to 15 ± 1 fmol/cell and a comparable drop in de novo synthesized PCho. This was associated with a drop in choline kinase (ChoK) activity and ChoKα expression. CT inhibition could not be ruled out but likely did not contribute to the change in PCho. We also found that intracellular lactate levels decreased from 2.7 ± 0.5 to 1.5 ± 0.3 fmol/cell and extracellular lactate levels dropped by a similar extent. These findings were consistent with a drop in lactate dehydrogenase expression and associated with a drop in activity of the hypoxia inducible factor (HIF)-1α. The drops in PCho and lactate production following perifosine treatment are therefore mediated downstream of Akt by the drop in HIF-1α, which serves as the transcription factor for both ChoK and lactate dehydrogenase. The metabolic changes were confirmed in a second breast cancer cell line, MDA-MB-231. Taken together, these findings indicate that PCho and lactate can serve as noninvasive metabolic biomarkers for monitoring the effects of inhibitors that target the PI3K/Akt pathway, independent of the step that leads to inhibition of HIF-1α.

Choline metabolism in malignant transformation

Abnormal choline metabolism is emerging as a metabolic hallmark that is associated with oncogenesis and tumour progression. Following transformation, the modulation of enzymes that control anabolic and catabolic pathways causes increased levels of choline-containing precursors and breakdown products of membrane phospholipids. These increased levels are associated with proliferation, and recent studies emphasize the complex reciprocal interactions between oncogenic signalling and choline metabolism. Because choline-containing compounds are detected by non-invasive magnetic resonance spectroscopy (MRS), increased levels of these compounds provide a non-invasive biomarker of transformation, staging and response to therapy. Furthermore, enzymes of choline metabolism, such as choline kinase, present novel targets for image-guided cancer therapy.

UPR-Mediated Membrane Biogenesis in B Cells

The unfolded protein response (UPR) can coordinate the regulation of gene transcription and protein translation to balance the load of client proteins with the protein folding and degradative capacities of the ER. Increasing evidence also implicates the UPR in the regulation of lipid synthesis and membrane biogenesis. The differentiation of B lymphocytes into antibody-secreting cells is marked by significant expansion of the ER, the site for antibody synthesis and assembly. In activated B cells, the demand for membrane protein and lipid components leads to activation of the UPR transcriptional activator XBP1(S) which, in turn, initiates a cascade of biochemical events that enhance supplies of phospholipid precursors and build machinery for the synthesis, maturation, and transport of secretory proteins. The alterations in lipid metabolism that occur during this developmental transition and the impact of membrane phospholipid restriction on B cell secretory characteristics are discussed in this paper.

Proteomic analysis of an Aedes albopictus cell line infected with Dengue serotypes 1 and 3 viruses

Background

Proteomic analysis was performed to identify proteins regulated during infection by Dengue serotypes 1 and 3 in an Aedes albopictus cell line. The potential of these viruses to cause severe disease at primary infection is of interest although few studies have been performed with these two Dengue serotypes.

Results

The most relevant observation of our study is the significant overexpression of proteins involved in the cellular stress response and the glycolysis pathway after 48 hours of infection. Viral infection activates the translation of some host genes, which may result in stress due to responses involving unfolded proteins.

Conclusions

Therefore, the oxidation reduction and glycolytic mechanisms could participate in the antiviral response against Dengue virus. The results of our study should help to improve our knowledge of the virus-mosquito interaction at a cellular level with the aim of designing efficient strategies for the control of Dengue virus.

Short-term administration of uridine increases brain membrane phospholipid precursors in healthy adults: a 31-phosphorus magnetic resonance spectroscopy study at 4T

OBJECTIVES

  Altered metabolism of membrane phospholipids has been implicated in bipolar disorder. In humans, uridine is an important precursor of cytidine diphosphate (CDP)-choline, which plays a critical role in phospholipid synthesis and is currently being evaluated as a potential treatment for bipolar depression.

METHODS

  A total of 17 healthy males (mean age ± SD: 32.73 ± 7.2 years; range: 21.8-46.4 years) were enrolled in this study. Subjects underwent a 31-phosphorus magnetic resonance spectroscopy ((31) P-MRS) acquisition at baseline and then again after seven days of either 2 g of uridine or placebo administration. A two-dimensional chemical shift imaging (31) P-MRS acquisition collected spectral data from a 4 × 4 cluster of voxels acquired in the axial plane encompassing the subcortical structures as well as frontal-temporal cortical gray and white matter. The slab thickness was 3 cm and the approximate total volume of brain sampled was 432 cm(3) . The spectra obtained were analyzed using a fully automated in-house fitting algorithm. A population-averaged generalized estimating equation was used to evaluate changes both in phosphomonoesters (PME) [phosphocholine (PCho) and phosphoethanolamine (PEtn)] and phosphodiesters (PDE) [glycerophosphocholine (GPCho) and glycerophosphethanolamine (GPEtn)]. Metabolite ratios were reported with respect to the total integrated (31) P resonance area.

RESULTS

  The uridine group had significantly increased total PME and PEtn levels over the one-week period [6.32 and 7.17% for PME and PEtn, respectively (p<0.001)]. Other metabolite levels such as PCho, PDE, GPEtn and GPCho showed no significant changes following either uridine or placebo (all p>0.05).

CONCLUSIONS

  This is the first study to report a direct effect of uridine on membrane phospholipid precursors in healthy adults using (31) P-MRS. Sustained administration of uridine appears to increase PME in healthy subjects. Further investigation is required to clarify the effects of uridine in disorders with altered phospholipid metabolism such as bipolar disorder.

The rate-limiting enzyme in phosphatidylcholine synthesis is associated with nuclear speckles under stress conditions

Phosphatidylcholine (PtdCho) is the most abundant phospholipid in eukaryotic membranes and its biosynthetic pathway is generally controlled by CTP:Phosphocholine Cytidylyltransferase (CCT), which is considered the rate-limiting enzyme. CCT is an amphitropic protein, whose enzymatic activity is commonly associated with endoplasmic reticulum (ER) translocation; however, most of the enzyme is intranuclearly located. Here we demonstrate that CCTα is concentrated in the nucleoplasm of MDCK cells. Confocal immunofluorescence revealed that extracellular hypertonicity shifted the diffuse intranuclear distribution of the enzyme to intranuclear domains in a foci pattern. One population of CCTα foci colocalised and interacted with lamin A/C speckles, which also contained the pre-mRNA processing factor SC-35, and was resistant to detergent and salt extraction. The lamin A/C silencing allowed us to visualise a second more labile population of CCTα foci that consisted of lamin A/C-independent foci non-resistant to extraction. We demonstrated that CCTα translocation is not restricted to its redistribution from the nucleus to the ER and that intranuclear redistribution must thus be considered. We suggest that the intranuclear organelle distribution of CCTα is a novel mechanism for the regulation of enzyme activity.

Phosphatidylcholine biosynthesis during neuronal differentiation and its role in cell fate determination

Neuronal differentiation is characterized by neuritogenesis and neurite outgrowth, processes that are dependent on membrane biosynthesis. Thus, the production of phosphatidylcholine (PtdCho), the major membrane phospholipid, should be stimulated during neuronal differentiation. We demonstrate that during retinoic acid (RA)-induced differentiation of Neuro-2a cells, PtdCho synthesis was promoted by an ordered and sequential activation of choline kinase alpha (CK(alpha)) and choline cytidylyltransferase alpha (CCT(alpha)). Early after RA stimulation, the increase in PtdCho synthesis is mainly governed by the biochemical activation of CCT(alpha). Later, the transcription of CK(alpha)- and CCT(alpha)-encoding genes was induced. Both PtdCho biosynthesis and neuronal differentiation are dependent on ERK activation. A novel mechanism is proposed by which PtdCho biosynthesis is coordinated during neuronal differentiation. Enforced expression of either CK(alpha) or CCTalpha increased the rate of synthesis and the amount of PtdCho, and these cells initiated differentiation without RA stimulation, as evidenced by cell morphology and the expression of genes associated with neuritogenesis. The differentiation resulting from enforced expression of CCT(alpha) or CK(alpha) was dependent on persistent ERK activation. These results indicate that elevated PtdCho synthesis could mimic the RA signals and thus determine neuronal cell fate. Moreover, they could explain the key role that PtdCho plays during neuronal regeneration.

Specific induction of TaAAPT1, an ER- and Golgi-localized ECPT-type aminoalcoholphosphotransferase, results in preferential accumulation of the phosphatidylethanolamine membrane phospholipid during cold acclimation in wheat

Cold acclimation requires substantial alteration in membrane property. In contrast to well-documented fatty acid unsaturation during cold acclimation, changes in phospholipid biosynthesis during cold acclimation are less understood. Here, we isolated and characterized two aminoalcoholphosphotransferase (AAPT) cDNAs, TaAAPT1 and TaAAPT2, from wheat. AAPTs utilize diacylglycerols and CDP-choline/ethanolamine as substrates and catalyze the final step of the CDP-choline/ethanolamine pathway for phosphatidylcholine (PC)/phosphatidylethanolamine (PE) synthesis, respectively. Functionality of TaAAPT1 and TaAAPT2 was demonstrated by heterologous expression in a yeast cpt1Delta ept1Delta double mutant that lacks both AAPT activities. Detailed characterization of AAPT activities from the transformed mutant cells indicated that TaAAPT1 is an ECPT-type enzyme with higher ethanolamine phosphotransferase (EPT) activity than choline phosphotransferase (CPT) activity, while TaAAPT2 is a CEPT-type with the opposite substrate preference. Transient expression of GFP-fused TaAAPT1 and TaAAPT2 proteins in wheat and onion cells indicated they are localized to both the endoplasmic reticulum and Golgi apparatus, suggesting that the final synthesis of PE and PC via the CDP-choline/ethanolamine pathway occurs in these organella. Quantitative PCR analyses revealed that TaAAPT1 expression is strongly induced by cold, while TaAAPT2 was constitutively expressed at lower levels. Measurement of phospholipid content in wheat leaves indicated that PE is more prominently increased in response to cold than PC and accordingly PE/PC ratio increased from 0.385 to 0.530 during 14 days of cold acclimation. Together, these data suggested that an increase in the PE/PC ratio during cold acclimation is regulated at the final step of the biosynthetic pathway.

Specific interaction between E2F1 and Sp1 regulates the expression of murine CTP:phosphocholine cytidylyltransferase alpha during the S phase

CTP:phosphocholine cytidylyltransferase alpha (CCTalpha) is a key enzyme for phosphatidylcholine biosynthesis in mammalian cells. This enzyme plays an essential role in all processes that require membrane biosynthesis such as cell proliferation and viability. Thus, CCTalpha activity and expression fluctuate during the cell cycle to achieve PtdCho requirements. We demonstrated, for the first time, that CCTalpha is localized in the nucleus in cells transiting the S phase, whereas it is localized in the cytoplasm of G(0)-arrested cells, suggesting a specific role of nuclear CCTalpha during the S phase. We also investigated how E2F1 influences the regulation of the CCTalpha-promoter during the S phase; we demonstrated that E2F1 is necessary, but not sufficient, to activate CCTalpha expression when this factor is over-expressed. However, when E2F1 and Sp1 were over-expressed, the transcription from the CCTalpha-promoter reporter construct was super-activated. Transient transfection studies demonstrated that E2F1 could super-activate Sp1-dependent transcription in a promoter containing only the Sp1 binding sites "B" or "C", and that Sp1 could activate Sp1-dependent transcription in a promoter containing the E2F site, thus, further demonstrating a functional interaction of these factors. In conclusion, the present results allowed us to portray the clearest picture of the CCTalpha-gene expression in proliferating cells, and understand the mechanism by which cells coordinate cell cycle progression with the requirement for phosphatidylcholine.

Over-expression of pemt2 into rat hepatoma cells contributes to the mitochondrial apoptotic pathway

We previously established a line of phosphatidylethanolamine N-methyltransferase 2 (pemt2) -stably transfected CBRH-7919 hepatoma cells, and showed that pemt2 over-expression inhibited cell proliferation and induced apoptosis. This study was aimed to further elucidate the cellular mechanisms leading to this apoptosis in these cells. Fatty acid compositions of phosphatidylcholine (PC) in pemt2 over-expressed cells and control cells, and the location of PC synthesized by PEMT2 pathway were analyzed with lipid extraction, high-performance thin layer chromatography, high-performance gas chromatography (HPGC), and [(3)H]-ethanolamine tracing. The effects of pemt2 over-expression on the mitochondrial membrane fluidity, the release of cytochrome C from mitochondria, and the activity of caspases were determined by Western blot. Newly synthesized PC by PEMT2 contained more acyl groups of oleic acid (P < 0.01) and was mainly located in mitochondria; pemt2 over-expression increased the mitochondrial membrane fluidity and the release of cytochrome C from the mitochondria into the cytoplasma, which in turn activated caspase-9 and caspase-3, the key molecules in the mitochondrial apoptotic pathway. We demonstrated that, in rat hepatoma cells, PEMT2-induced apoptosis proceeds through mitochondria.

Identification of hydrophobic amino acids required for lipid activation of C. elegans CTP:phosphocholine cytidylyltransferase

CTP:phosphocholine cytidylyltransferase (CCT), critical for phosphatidylcholine biosynthesis, is activated by translocation to the membrane surface. The lipid activation region of Caenorhabditis elegans CCT is between residues 246 and 266 of the 347 amino acid polypeptide, a region proposed to form an amphipathic alpha helix. When leucine 246, tryptophan 249, isoleucine 256, isoleucine 257, or phenylalanine 260, on the hydrophobic face of the helix, were changed individually to serine low activity was observed in the absence of lipid vesicles, similar to wild-type CCT, while lipid stimulated activity was reduced compared to wild-type CCT. Mutational analysis of phenylalanine 260 implicated this residue as a contributor to auto-inhibition of CCT while mutation of L246, W249, I256, and I257 simultaneously to serine resulted in significantly higher activity in the absence of lipid vesicles and an enzyme that was not lipid activated. These results support a concerted mechanism of lipid activation that requires multiple residues on the hydrophobic face of the putative amphipathic alpha helix.

Depletion of phosphatidylcholine affects endoplasmic reticulum morphology and protein traffic at the Golgi complex

The mutant Chinese hamster ovary cell line MT58 contains a thermosensitive mutation in CTP:phosphocholine cytidylyltransferase, the regulatory enzyme in the CDP-choline pathway. As a result, MT58 cells have a 50% decrease in their phosphatidylcholine (PC) level within 24 h when cultured at the nonpermissive temperature (40 degrees C). This is due to a relative rapid breakdown of PC that is not compensated for by the inhibition of de novo PC synthesis. Despite this drastic decrease in cellular PC content, cells are viable and can proliferate by addition of lysophosphatidylcholine. By [(3)H]oleate labeling, we found that the FA moiety of the degraded PC is recovered in triacylglycerol. In accordance with this finding, an accumulation of lipid droplets is seen in MT58 cells. Analysis of PC-depleted MT58 cells by electron and fluorescence microscopy revealed a partial dilation of the rough endoplasmic reticulum, resulting in spherical structures on both sites of the nucleus, whereas the morphology of the plasma membrane, mitochondria, and Golgi complex was unaffected. In contrast to these morphological observations, protein transport from the ER remains intact. Surprisingly, protein transport at the level of the Golgi complex is impaired. Our data suggest that the transport processes at the Golgi complex are regulated by distal changes in lipid metabolism.

Polymorphism located between CPT1B and CHKB, and HLA-DRB1*1501-DQB1*0602 haplotype confer susceptibility to CNS hypersomnias (essential hypersomnia)

Background

SNP rs5770917 located between CPT1B and CHKB, and HLA-DRB1*1501-DQB1*0602 haplotype were previously identified as susceptibility loci for narcolepsy with cataplexy. This study was conducted in order to investigate whether these genetic markers are associated with Japanese CNS hypersomnias (essential hypersomnia: EHS) other than narcolepsy with cataplexy.

Principal Findings

EHS was significantly associated with SNP rs5770917 (P_allele = 3.6×10⁻³; OR = 1.56; 95% c.i.: 1.12–2.15) and HLA-DRB1*1501-DQB1*0602 haplotype (P_positivity = 9.2×10⁻¹¹; OR = 3.97; 95% c.i.: 2.55–6.19). No interaction between the two markers (SNP rs5770917 and HLA-DRB1*1501-DQB1*0602 haplotype) was observed in EHS.

Conclusion

CPT1B, CHKB and HLA are candidates for susceptibility to CNS hypersomnias (EHS), as well as narcolepsy with cataplexy.