Yeast as a model system for studying lipid homeostasis and function

Structures, Antioxidant Properties, and Antimicrobial Properties of Eu(III), Gd(III), and Dy(III) Caffeinates and p-Coumarates

In this study, we investigated the structures of lanthanide (Eu(III), Dy(III), and Gd(III)) complexes with p-coumaric (p-CAH2) and caffeic (CFAH3) acids using the FTIRKBr, FTIRATR, and Raman spectroscopic methods. The compositions of the solid phase caffeinates and p-coumarates were obtained on the basis of the amounts of hydrogen and carbon determined using an elemental analysis. The degree of hydration and the thermal decomposition of each compound were examined via a thermal analysis of TG, DTG, and DSC. Antioxidant spectroscopic tests were performed using the DPPH (1,1-diphenyl-2-picrylhydrazyl radical), FRAP (ferric reducing antioxidant activity), and ABTS (2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (diammonium salt radical cation) methods. The antimicrobial activity of each compound against Escherichia coli, Bacillus subtilis, and Candida albicans was investigated. The electrical properties of the liposomes which mimicked the microbial surfaces formed in the electrolyte containing the tested compounds were also investigated. The above biological properties of the obtained complexes were compared with the activities of p-CAH2 and CFAH3. The obtained data suggest that lanthanide complexes are much more thermally stable and have higher antimicrobial and antioxidant properties than the ligands (with the exception of CFAH3 in the case of antioxidant activity tests). The Gd(III) complexes revealed the highest biological activity among the studied lanthanide complexes.

Harnessing Clickable Acylated Glycerol Probes as Chemical Tools for Tracking Glycerolipid Metabolism

We report the use of clickable monoacylglycerol (MAG) analogs as probes for the labeling of glycerolipids during lipid metabolism. Incorporation of azide tags onto the glycerol region was pursued to develop probes that would label glycerolipids, in which the click tag would not be removed through processes including acyl chain and headgroup remodeling. Analysis of clickable MAG probes containing acyl chains of different length resulted in widely variable cell imaging and cytotoxicity profiles. Based on these results, we focused on a probe bearing a short acyl chain (C4 -MAG-N3 ) that was found to infiltrate natural lipid biosynthetic pathways to produce click-tagged versions of both neutral and phospholipid products. Alternatively, strategic blocking of the glycerol sn-3 position in probe C4 -MEG-N3 served to deactivate phospholipid tagging and focus labeling on neutral lipids. This work shows that lipid metabolic labeling profiles can be tuned based on probe structures and provides valuable tools for evaluating alterations to lipid metabolism in cells.

The foundations and development of lipidomics

For over a century, the importance of lipid metabolism in biology was recognized but difficult to mechanistically understand due to the lack of sensitive and robust technologies for identification and quantification of lipid molecular species. The enabling technological breakthroughs emerged in the 1980s with the development of soft ionization methods (Electrospray Ionization and Matrix Assisted Laser Desorption/Ionization) that could identify and quantify intact individual lipid molecular species. These soft ionization technologies laid the foundations for what was to be later named the field of lipidomics. Further innovative advances in multistage fragmentation, dramatic improvements in resolution and mass accuracy, and multiplexed sample analysis fueled the early growth of lipidomics through the early 1990s. The field exponentially grew through the use of a variety of strategic approaches, which included direct infusion, chromatographic separation, and charge-switch derivatization, which facilitated access to the low abundance species of the lipidome. In this Thematic Review, we provide a broad perspective of the foundations, enabling advances, and predicted future directions of growth of the lipidomics field.

Yeast YPK9 deficiency results in shortened replicative lifespan and sensitivity to hydrogen peroxide

YPK9/YOR291W of Saccharomyces cerevisiae encodes a vacuolar membrane protein. Previous research has suggested that Ypk9p is similar to the yeast P5-type ATPase Spf1p and that it plays a role in the sequestration of heavy metals. In addition, bioinformatics analysis has suggested that Ypk9p is a homolog of human ATP13A2, which encodes a protein of the subfamily of P5 ATPases. However, no specific function of Ypk9p has been described to date. In this study, we found, for the first time, that YPK9 is involved in the oxidative stress response and modulation of the replicative lifespan (RLS). We found that YPK9 deficiency confers sensitivity to the oxidative stress inducer hydrogen peroxide accompanied by increased intracellular ROS levels, decreased mitochondrial membrane potential, abnormal mitochondrial function, and increased incidence of early apoptosis in budding yeast. More importantly, YPK9 deficiency can lead to a shortened RLS. In addition, we found that overexpression of the catalase-encoding gene CTA1 can reverse the phenotypic abnormalities of the ypk9Δ yeast strain. Collectively, these findings highlight the involvement of Ypk9p in the oxidative stress response and modulation of RLS.

Sec14 family of lipid transfer proteins in yeasts

The hydrophobicity of lipids prevents their free movement across the cytoplasm. To achieve highly heterogeneous and precisely regulated lipid distribution in different cellular membranes, lipids are transported by lipid transfer proteins (LTPs) in addition to their transport by vesicles. Sec14 family is one of the most extensively studied groups of LTPs. Here we provide an overview of Sec14 family of LTPs in the most studied yeast Saccharomyces cerevisiae as well as in other selected non-Saccharomyces yeasts-Schizosaccharomyces pombe, Kluyveromyces lactis, Candida albicans, Candida glabrata, Cryptococcus neoformans, and Yarrowia lipolytica. Discussed are specificities of Sec14-domain LTPs in various yeasts, their mode of action, subcellular localization, and physiological function. In addition, quite few Sec14 family LTPs are target of antifungal drugs, serve as modifiers of drug resistance or influence virulence of pathologic yeasts. Thus, they represent an important object of study from the perspective of human health.

FSH1 encodes lysophospholipase activity in Saccharomyces cerevisiae

OBJECTIVES

To elucidate the role of FSH1 (family of serine hydrolase) in lipid homeostasis.

RESULTS

Proteins in various species containing alpha/beta hydrolase domain are known to be involved in lipid metabolism. In silico analysis of the FSH1 gene in Saccharomyces cerevisiae revealed the presence of alpha/beta hydrolase domain (ABHD) and a lipase motif (GXSXG), however its function in lipid metabolism remained elusive. The overexpression of FSH1 in WT and fsh1Δ cells showed a significant reduction in the cellular phospholipid levels and an increase in the triacylglycerol levels and lipid droplet (LD) number. Furthermore, the purified recombinant protein Fsh1p was identified as a lysophospholipase that specifically acts on lysophosphatidylserine (LPS) and impacts the lipid homeostasis in S. cerevisiae.

CONCLUSIONS

These results depicted that Fsh1p has a role on lipid homeostasis and is a lysophospholipase that hydrolyzes lysophosphatidylserine (LPS).

Water soluble lipid precursor contaminants in yeast culture medium ingredients

The presence of the water soluble glycerophospholipid precursors choline and inositol in culture media highly affects lipid biosynthesis and regulation thereof. We report that widely used media ingredients contain trace amounts of choline and inositol that are not mentioned on the product label, influencing experimental outcome.

redLips: a comprehensive mechanistic model of the lipid metabolic network of yeast

Over the last decades, yeast has become a key model organism for the study of lipid biochemistry. Because the regulation of lipids has been closely linked to various physiopathologies, the study of these biomolecules could lead to new diagnostics and treatments. Before the field can reach this point, however, sufficient tools for integrating and analyzing the ever-growing availability of lipidomics data will need to be developed. To this end, genome-scale models (GEMs) of metabolic networks are useful tools, though their large size and complexity introduces too much uncertainty in the accuracy of predicted outcomes. Ideally, therefore, a model for studying lipids would contain only the pathways required for the proper analysis of these biomolecules, but would not be an ad hoc reduction. We hereby present a metabolic model that focuses on lipid metabolism constructed through the integration of detailed lipid pathways into an already existing GEM of Saccharomyces cerevisiae. Our model was then systematically reduced around the subsystems defined by these pathways to provide a more manageable model size for complex studies. We show that this model is as consistent and inclusive as other yeast GEMs regarding the focus and detail on the lipid metabolism, and can be used as a scaffold for integrating lipidomics data to improve predictions in studies of lipid-related biological functions.

Spatial compartmentalization of lipid droplet biogenesis

Lipid droplets (LDs) are ubiquitous organelles that store metabolic energy in the form of neutral lipids (typically triacylglycerols and steryl esters). Beyond being inert energy storage compartments, LDs are dynamic organelles that participate in numerous essential metabolic functions. Cells generate LDs de novo from distinct sub-regions at the endoplasmic reticulum (ER), but what determines sites of LD formation remains a key unanswered question. Here, we review the factors that determine LD formation at the ER, and discuss how they work together to spatially and temporally coordinate LD biogenesis. These factors include lipid synthesis enzymes, assembly proteins, and membrane structural requirements. LDs also make contact with other organelles, and these inter-organelle contacts contribute to defining sites of LD production. Finally, we highlight emerging non-canonical roles for LDs in maintaining cellular homeostasis during stress.

Lipid transfer proteins: the lipid commute via shuttles, bridges and tubes

Lipids are distributed in a highly heterogeneous fashion in different cellular membranes. Only a minority of lipids achieve their final intracellular distribution through transport by vesicles. Instead, the bulk of lipid traffic is mediated by a large group of lipid transfer proteins (LTPs), which move small numbers of lipids at a time using hydrophobic cavities that stabilize lipid molecules outside membranes. Although the first LTPs were discovered almost 50 years ago, most progress in understanding these proteins has been made in the past few years, leading to considerable temporal and spatial refinement of our understanding of the function of these lipid transporters. The number of known LTPs has increased, with exciting discoveries of their multimeric assembly. Structural studies of LTPs have progressed from static crystal structures to dynamic structural approaches that show how conformational changes contribute to lipid handling at a sub-millisecond timescale. A major development has been the finding that many intracellular LTPs localize to two organelles at the same time, forming a shuttle, bridge or tube that links donor and acceptor compartments. The understanding of how different lipids achieve their final destination at the molecular level allows a better explanation of the range of defects that occur in diseases associated with lipid transport and distribution, opening up the possibility of developing therapies that specifically target lipid transfer.

Sphingolipidomic Analysis of C. elegans reveals Development- and Environment-dependent Metabolic Features

Sphingolipids (SLs) serve as structural and signaling molecules in regulating various cellular events and growth. Given that SLs contain various bioactive species possessing distinct roles, quantitative analysis of sphingolipidome is essential for elucidating their differential requirement during development. Herein we developed a comprehensive sphingolipidomic profiling approach using liquid chromatography-mass spectrometry coupled with multiple reaction monitoring mode (LC-MS-MRM). SL profiling of C. elegans revealed organism-specific, development-dependent and environment-driven metabolic features. We showed for the first time the presence of a series of sphingoid bases in C. elegans sphingolipid profiles, although only C17-sphingoid base is used for generating complex SLs. Moreover, we successfully resolved growth-, temperature- and nutrition-dependent SL profiles at both individual metabolite-level and network-level. Sphingolipidomic analysis uncovered significant SL composition changes throughout development, with SMs/GluCers ratios dramatically increasing from larva to adult stage whereas total sphingolipid levels exhibiting opposing trends. We also identified a temperature-dependent alteration in SMs/GluCers ratios, suggesting an organism-specific strategy for environmental adaptation. Finally, we found serine-biased GluCer increases between serine- versus alanine-supplemented worms. Our study builds a “reference” resource for future SL analysis in the worm, provides insights into natural variability and plasticity of eukaryotic multicellular sphingolipid composition and is highly valuable for investigating their functional significance.

The hypoxic transcription factor KlMga2 mediates the response to oxidative stress and influences longevity in the yeast Kluyveromyces lactis

Hypoxia is defined as the decline of oxygen availability, depending on environmental supply and cellular consumption rate. The decrease in O2 results in reduction of available energy in facultative aerobes. The response and/or adaptation to hypoxia and other changing environmental conditions can influence the properties and functions of membranes by modifying lipid composition. In the yeast Kluyveromyces lactis, the KlMga2 gene is a hypoxic regulatory factor for lipid biosynthesis—fatty acids and sterols—and is also involved in glucose signaling, glucose catabolism and is generally important for cellular fitness.

In this work we show that, in addition to the above defects, the absence of the KlMGA2 gene caused increased resistance to oxidative stress and extended lifespan of the yeast, associated with increased expression levels of catalase and SOD genes. We propose that KlMga2 might also act as a mediator of the oxidative stress response/adaptation, thus revealing connections among hypoxia, glucose signaling, fatty acid biosynthesis and ROS metabolism in K. lactis.

Lipid composition in fungal membrane models: effect of lipid fluidity

The creation of effective fungal membrane models for neutron and X-ray reflectometry experiments is a key step in the development of new antifungal pharmaceuticals and agrochemicals to allow in vitro investigation of their mode of interaction with target cells. The structure of the obtained models depends on the properties of the lipids used and the final composition of the leaflets, and can be subject to the spontaneous translocation of phospholipids across the bilayer. The effect of phospholipid acyl-chain unsaturation and the presence of steroids in the membrane on the bilayer asymmetry were examined by means of neutron reflectometry. The measurements showed that membrane stability was higher if a zwitterionic, saturated acyl-chain phospholipid is present as the inner leaflet. Furthermore, membrane asymmetry was higher in the case of fully saturated lipid systems. As a result, membrane models consisting of fully saturated acyl chains within the inner leaflet are recommended as the starting point for subsequent studies of antifungal interactions owing to the simplicity of the models and their relative stability, thus allowing better control over the exact lipid composition facing the tested antifungal.

Guidelines and recommendations on yeast cell death nomenclature

Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cel-lular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the defi-nition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differ-ential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death rou-tines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the au-thors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the pro-gress of this vibrant field of research.

Cultivation and quantitative single-cell analysis of Saccharomyces cerevisiae on a multifunctional microfluidic device

Here, we present a multifunctional microfluidic device whose integrative design enables to combine cell culture studies and quantitative single cell biomolecule analysis. The platform consists of 32 analysis units providing two key features; first, a micrometer-sized trap for hydrodynamic capture of a single Saccharomyces cerevisiae (S. cerevisiae) yeast cell; second, a convenient double-valve configuration surrounding the trap. Actuating of the outer valve with integrated opening results in a partial isolation in a volume of 11.8 nL, i.e. the cell surrounding fluid can be exchanged diffusion-based without causing shear stress or cell loss. Actuation of the inner ring-shaped valve isolates the trapped cell completely in a small analysis volume of 230 pL. The device was used to determine the growth rate of yeast cells (S. cerevisiae) under under optimum and oxidative stress conditions. In addition, we successfully quantified the cofactor beta-nicotinamide adenine dinucleotide phosphate (NAD(P)H) in single and few cells exposed to the different microenvironments. In conclusion, the microdevice enables to analyze the influence of an external stress factor on the cellular fitness in a fast and more comprehensive way as cell growth and intracellular biomolecule levels can be investigated.

ERG6 gene deletion modifies Kluyveromyces lactis susceptibility to various growth inhibitors

The ERG6 gene encodes an S-adenosylmethionine dependent sterol C-24 methyltransferase in the ergosterol biosynthetic pathway. In this work we report the results of functional analysis of the Kluyveromyces lactis ERG6 gene. We cloned the KlERG6 gene, which was able to complement the erg6Δ mutation in both K. lactis and Saccharomyces cerevisiae. The lack of ergosterol in the Klerg6 deletion mutant was accompanied by increased expression of genes encoding the last steps of the ergosterol biosynthesis pathway as well as the KlPDR5 gene encoding an ABC transporter. The Klerg6Δ mutation resulted in reduced cell susceptibility to amphotericin B, nystatin and pimaricin and increased susceptibility to azole antifungals, fluphenazine, terbinafine, brefeldin A and caffeine. The susceptibility phenotype was suppressed by the KlPDR16 gene encoding one of the phosphatidylinositol transfer proteins belonging to the Sec14 family. Decreased activity of KlPdr5p in Klerg6Δ mutant (measured as the ability to efflux rhodamine 6G) together with increased amount of KlPDR5 mRNA suggest that the zymosterol which accumulates in the Klerg6Δ mutant may not fully compensate for ergosterol in the membrane targeting of efflux pumps. These results point to the fact that defects in sterol transmethylation appear to cause a multitude of physiological effects in K. lactis cells. Copyright © 2016 John Wiley & Sons, Ltd.

Making Sense of the Yeast Sphingolipid Pathway

Sphingolipids (SL) and their metabolites play key roles both as structural components of membranes and as signaling molecules. Many of the key enzymes and regulators of SL metabolism were discovered using the yeast Saccharomyces cerevisiae, and based on the high degree of conservation, a number of mammalian homologs were identified. Although yeast continues to be an important tool for SL research, the complexity of SL structure and nomenclature often hampers the ability of new researchers to grasp the subtleties of yeast SL biology and discover new modulators of this intricate pathway. Moreover, the emergence of lipidomics by mass spectrometry has enabled the rapid identification of SL species in yeast and rendered the analysis of SL composition under various physiological and pathophysiological conditions readily amenable. However, the complex nomenclature of the identified species renders much of the data inaccessible to non-specialists. In this review, we focus on parsing both the classical SL nomenclature and the nomenclature normally used during mass spectrometry analysis, which should facilitate the understanding of yeast SL data and might shed light on biological processes in which SLs are involved. Finally, we discuss a number of putative roles of various yeast SL species.

A method for analysis and design of metabolism using metabolomics data and kinetic models: Application on lipidomics using a novel kinetic model of sphingolipid metabolism

We present a model-based method, designated Inverse Metabolic Control Analysis (IMCA), which can be used in conjunction with classical Metabolic Control Analysis for the analysis and design of cellular metabolism. We demonstrate the capabilities of the method by first developing a comprehensively curated kinetic model of sphingolipid biosynthesis in the yeast Saccharomyces cerevisiae. Next we apply IMCA using the model and integrating lipidomics data. The combinatorial complexity of the synthesis of sphingolipid molecules, along with the operational complexity of the participating enzymes of the pathway, presents an excellent case study for testing the capabilities of the IMCA. The exceptional agreement of the predictions of the method with genome-wide data highlights the importance and value of a comprehensive and consistent engineering approach for the development of such methods and models. Based on the analysis, we identified the class of enzymes regulating the distribution of sphingolipids among species and hydroxylation states, with the D-phospholipase SPO14 being one of the most prominent. The method and the applications presented here can be used for a broader, model-based inverse metabolic engineering approach.

Wnt directs the endosomal flux of LDL-derived cholesterol and lipid droplet homeostasis

The Wnt pathway, which controls crucial steps of the development and differentiation programs, has been proposed to influence lipid storage and homeostasis. In this paper, using an unbiased strategy based on high-content genome-wide RNAi screens that monitored lipid distribution and amounts, we find that Wnt3a regulates cellular cholesterol. We show that Wnt3a stimulates the production of lipid droplets and that this stimulation strictly depends on endocytosed, LDL-derived cholesterol and on functional early and late endosomes. We also show that Wnt signaling itself controls cholesterol endocytosis and flux along the endosomal pathway, which in turn modulates cellular lipid homeostasis. These results underscore the importance of endosome functions for LD formation and reveal a previously unknown regulatory mechanism of the cellular programs controlling lipid storage and endosome transport under the control of Wnt signaling.

ROG1 encodes a monoacylglycerol lipase in Saccharomyces cerevisiae

Lipid metabolism is extensively studied in Saccharomyces cerevisiae. Here, we report that revertant of glycogen synthase kinase mutation-1 (Rog1p) possesses monoacylglycerol (MAG) lipase activity in S. cerevisiae. The lipase activity of Rog1p was confirmed in two ways: through analysis of a strain with a double deletion of ROG1 and monoglyceride lipase YJU3 (yju3Δrog1Δ) and by site-directed mutagenesis of the ROG1 lipase motif (GXSXG). Rog1p is localized in both the cytosol and the nucleus. Overexpression of ROG1 in a ROG1-deficient strain resulted in an accumulation of reactive oxygen species. These results suggest that Rog1p is a MAG lipase that regulates lipid homeostasis.

Systematic lipidomic analysis of yeast protein kinase and phosphatase mutants reveals novel insights into regulation of lipid homeostasis

The regulatory pathways required to maintain eukaryotic lipid homeostasis are largely unknown. We developed a systematic approach to uncover new players in the regulation of lipid homeostasis. Through an unbiased mass spectrometry-based lipidomic screening, we quantified hundreds of lipid species, including glycerophospholipids, sphingolipids, and sterols, from a collection of 129 mutants in protein kinase and phosphatase genes of Saccharomyces cerevisiae. Our approach successfully identified known kinases involved in lipid homeostasis and uncovered new ones. By clustering analysis, we found connections between nutrient-sensing pathways and regulation of glycerophospholipids. Deletion of members of glucose- and nitrogen-sensing pathways showed reciprocal changes in glycerophospholipid acyl chain lengths. We also found several new candidates for the regulation of sphingolipid homeostasis, including a connection between inositol pyrophosphate metabolism and complex sphingolipid homeostasis through transcriptional regulation of AUR1 and SUR1. This robust, systematic lipidomic approach constitutes a rich, new source of biological information and can be used to identify novel gene associations and function.

A neurotoxic glycerophosphocholine impacts PtdIns-4, 5-bisphosphate and TORC2 signaling by altering ceramide biosynthesis in yeast

Unbiased lipidomic approaches have identified impairments in glycerophosphocholine second messenger metabolism in patients with Alzheimer's disease. Specifically, we have shown that amyloid-β42 signals the intraneuronal accumulation of PC(O-16:0/2:0) which is associated with neurotoxicity. Similar to neuronal cells, intracellular accumulation of PC(O-16:0/2:0) is also toxic to Saccharomyces cerevisiae, making yeast an excellent model to decipher the pathological effects of this lipid. We previously reported that phospholipase D, a phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P₂)-binding protein, was relocalized in response to PC(O-16:0/2:0), suggesting that this neurotoxic lipid may remodel lipid signaling networks. Here we show that PC(O-16:0/2:0) regulates the distribution of the PtdIns(4)P 5-kinase Mss4 and its product PtdIns(4,5)P₂ leading to the formation of invaginations at the plasma membrane (PM). We further demonstrate that the effects of PC(O-16:0/2:0) on the distribution of PM PtdIns(4,5)P₂ pools are in part mediated by changes in the biosynthesis of long chain bases (LCBs) and ceramides. A combination of genetic, biochemical and cell imaging approaches revealed that PC(O-16:0/2:0) is also a potent inhibitor of signaling through the Target of rampamycin complex 2 (TORC2). Together, these data provide mechanistic insight into how specific disruptions in phosphocholine second messenger metabolism associated with Alzheimer's disease may trigger larger network-wide disruptions in ceramide and phosphoinositide second messenger biosynthesis and signaling which have been previously implicated in disease progression.

Accelerated cognitive decline in Alzheimer's patients is associated with distinct changes in the abundance of choline-containing lipids belonging to the platelet activating factor family. In particular, PC(O-16:0/2:0) or C16:0 platelet activating factor (PAF), is specifically elevated in brains of Alzheimer's patients. Since elevated intraneuronal levels of PC(O-16:0/2:0) are thought to contribute to the loss of neuronal cells it is imperative to identify the underlying mechanisms contributing to the toxic effects of PC(O-16:0/2:0). In this study, we have determined that elevated levels of PC(O-16:0/2:0) has negative effects upon the distribution of phosphoinositides at the plasma membrane leading to a potent inhibition of target of rapamycin (TOR) signaling. We further show that the changes in phosphoinositide distribution are due to changes in ceramide metabolism. In conclusion, our study suggests that the toxicity associated with aberrant metabolism of glycerophosphocholine lipids species is likely due to the remodeling of phosphoinositide and ceramide metabolism and that therapeutic strategies which target these disruptions may be effective in ameliorating Alzheimer's Disease pathology.

The natural diyne-furan fatty acid EV-086 is an inhibitor of fungal delta-9 fatty acid desaturation with efficacy in a model of skin dermatophytosis

Human fungal infections represent a therapeutic challenge. Although effective strategies for treatment are available, resistance is spreading, and many therapies have unacceptable side effects. A clear need for novel antifungal targets and molecules is thus emerging. Here, we present the identification and characterization of the plant-derived diyne-furan fatty acid EV-086 as a novel antifungal compound. EV-086 has potent and broad-spectrum activity in vitro against Candida, Aspergillus, and Trichophyton spp., whereas activities against bacteria and human cell lines are very low. Chemical-genetic profiling of Saccharomyces cerevisiae deletion mutants identified lipid metabolic processes and organelle organization and biogenesis as targets of EV-086. Pathway modeling suggested that EV-086 inhibits delta-9 fatty acid desaturation, an essential process in S. cerevisiae, depending on the delta-9 fatty acid desaturase OLE1. Delta-9 unsaturated fatty acids-but not saturated fatty acids-antagonized the EV-086-mediated growth inhibition, and transcription of the OLE1 gene was strongly upregulated in the presence of EV-086. EV-086 increased the ratio of saturated to unsaturated free fatty acids and phosphatidylethanolamine fatty acyl chains, respectively. Furthermore, EV-086 was rapidly taken up into the lipid fraction of the cell and incorporated into phospholipids. Together, these findings demonstrate that EV-086 is an inhibitor of delta-9 fatty acid desaturation and that the mechanism of inhibition might involve an EV-086-phospholipid. Finally, EV-086 showed efficacy in a guinea pig skin dermatophytosis model of topical Trichophyton infection, which demonstrates that delta-9 fatty acid desaturation is a valid antifungal target, at least for dermatophytoses.

Sphingolipids and lifespan regulation

Diseases including cancer, type 2 diabetes, cardiovascular and immune dysfunction and neurodegeneration become more prevalent as we age, and combined with the increase in average human lifespan, place an ever increasing burden on the health care system. In this chapter we focus on finding ways of modulating sphingolipids to prevent the development of age-associated diseases or delay their onset, both of which could improve health in elderly, fragile people. Reducing the incidence of or delaying the onset of diseases of aging has blossomed in the past decade because of advances in understanding signal transduction pathways and cellular processes, especially in model organisms, that are largely conserved in most eukaryotes and that can be modulated to reduce signs of aging and increase health span. In model organisms such interventions must also increase lifespan to be considered significant, but this is not a requirement for use in humans. The most encouraging interventions in model organisms involve lowering the concentration of one or more sphingolipids so as to reduce the activity of key signaling pathways, one of the most promising being the Target of Rapamycin Complex 1 (TORC1) protein kinase pathway. Other potential ways in which modulating sphingolipids may contribute to improving the health profile of the elderly is by reducing oxidative stresses, inflammatory responses and growth factor signaling. Lastly, perhaps the most interesting way to modulate sphingolipids and promote longevity is by lowering the activity of serine palmitoyltransferase, the first enzyme in the de novo sphingolipid biosynthesis pathway. Available data in yeasts and rodents are encouraging and as we gain insights into molecular mechanisms the strategies for improving human health by modulating sphingolipids will become more apparent. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Fusarium verticillioides and maize interaction in vitro: relationship between oxylipin cross-talk and fumonisin synthesis

Fusarium verticillioides is one of the most important fungal pathogens causing ear and stalk rot in maize. Even if frequently asymptomatic, it can produce a harmful series of compounds named fumonisins. Plant and fungal oxylipins play a crucial role in determining the outcome of the interaction between the pathogen and its host. Moreover, oxylipins are factors able to modulate the secondary metabolism in fungi. To uncover the existence of the relationship between oxylipin production and fumonisin synthesis in F. verticillioides, we analysed some molecular and physiological parameters, such as the expression of genes whose products are related to oxylipin synthesis (i.e. lipoxygenase, diol synthases and fatty acid oxidase), the oxylipin profile of both cracked maize and the pathogen by using a lipidomic approach (i.e. combining LC-TOF and LC-MS/MS approaches with a robust statistical analysis) and the synthesis of fumonisin B1. The results suggested a close relationship between the modification of the pathogen oxylipin profile with the fumonisin synthesis. Notably, a modification of the oxylipin profile of the pathogen during its growth on cracked maize can be demonstrated. The switch in oxylipin synthesis could indicate that the ‘presence’ of maize determinants (e.g. plant cell wall fragments and/or lipids) was able to promote the modification of the pathogen lifestyle, also by adapting the secondary metabolism, notably fumonisin synthesis.

Key role of lipids in heat stress management

Heat stress is a common and, therefore, an important environmental impact on cells and organisms. While much attention has been paid to severe heat stress, moderate temperature elevations are also important. Here we discuss temperature sensing and how responses to heat stress are not necessarily dependent on denatured proteins. Indeed, it is clear that membrane lipids have a pivotal function. Details of membrane lipid changes and the associated production of signalling metabolites are described and suggestions made as to how the interconnected signalling network could be modified for helpful intervention in disease.

Differential pathways of claudin oligomerization and integration into tight junctions

Tight junctions are the critical intercellular structure required to establish an epithelial barrier. Among the several classes of proteins required to form tight junctions are the tetraspan transmembrane proteins known as claudins that directly determine paracellular permeability. Considerable progress has been made in understanding how incorporation of different claudins into tight junctions increase or decrease paracellular permeability and ion selectivity. However, it has proven difficult to identify discrete steps in claudin assembly and whether claudins exist in distinct oligomerization states prior to tight junction assembly. Studies of homomeric and heteromeric claudin-claudin interactions using complementary techniques suggest a diversity of pathways used by different claudins to oligomerize and integrate into tight junctions.