Disruption of the Saccharomyces cerevisiae FAT1 gene decreases very long-chain fatty acyl-CoA synthetase activity and elevates intracellular very long-chain fatty acid concentrations

Proteome-scale movements and compartment connectivity during the eukaryotic cell cycle

Cell cycle progression relies on coordinated changes in the composition and subcellular localization of the proteome. By applying two distinct convolutional neural networks on images of millions of live yeast cells, we resolved proteome-level dynamics in both concentration and localization during the cell cycle, with resolution of ∼20 subcellular localization classes. We show that a quarter of the proteome displays cell cycle periodicity, with proteins tending to be controlled either at the level of localization or concentration, but not both. Distinct levels of protein regulation are preferentially utilized for different aspects of the cell cycle, with changes in protein concentration being mostly involved in cell cycle control and changes in protein localization in the biophysical implementation of the cell cycle program. We present a resource for exploring global proteome dynamics during the cell cycle, which will aid in understanding a fundamental biological process at a systems level.

Definition of fatty acid transport protein-2 (FATP2) structure facilitates identification of small molecule inhibitors for the treatment of diabetic complications

Diabetes is a major public health problem due to morbidity and mortality associated with end organ complications. Uptake of fatty acids by Fatty Acid Transport Protein-2 (FATP2) contributes to hyperglycemia, diabetic kidney and liver disease pathogenesis. Because FATP2 structure is unknown, a homology model was constructed, validated by AlphaFold2 prediction and site-directed mutagenesis, and then used to conduct a virtual drug discovery screen. In silico similarity searches to two low-micromolar IC50 FATP2 inhibitors, followed by docking and pharmacokinetics predictions, narrowed a diverse 800,000 compound library to 23 hits. These candidates were further evaluated for inhibition of FATP2-dependent fatty acid uptake and apoptosis in cells. Two compounds demonstrated nanomolar IC50, and were further characterized by molecular dynamic simulations. The results highlight the feasibility of combining a homology model with in silico and in vitro screening, to economically identify high affinity inhibitors of FATP2, as potential treatment for diabetes and its complications.

Fatty Acyl Coenzyme A Synthetase Fat1p Regulates Vacuolar Structure and Stationary-Phase Lipophagy in Saccharomyces cerevisiae

During yeast stationary phase, a single spherical vacuole (lysosome) is created by the fusion of several small ones. Moreover, the vacuolar membrane is reconstructed into two distinct microdomains. Little is known, however, about how cells maintain vacuolar shape or regulate their microdomains. Here, we show that Fat1p, a fatty acyl coenzyme A (acyl-CoA) synthetase and fatty acid transporter, and not the synthetases Faa1p and Faa4p, is essential for vacuolar shape preservation, the development of vacuolar microdomains, and cell survival in stationary phase of the yeast Saccharomyces cerevisiae. Furthermore, Fat1p negatively regulates general autophagy in both log- and stationary-phase cells. In contrast, Fat1p promotes lipophagy, as the absence of FAT1 limits the entry of lipid droplets into the vacuole and reduces the degradation of liquid droplet (LD) surface proteins. Notably, supplementing with unsaturated fatty acids or overexpressing the desaturase Ole1p can reverse all aberrant phenotypes caused by FAT1 deficiency. We propose that Fat1p regulates stationary phase vacuolar morphology, microdomain differentiation, general autophagy, and lipophagy by controlling the degree of fatty acid saturation in membrane lipids. IMPORTANCE The ability to sense environmental changes and adjust the levels of cellular metabolism is critical for cell viability. Autophagy is a recycling process that makes the most of already-existing energy resources, and the vacuole/lysosome is the ultimate autophagic processing site in cells. Lipophagy is an autophagic process to select degrading lipid droplets. In yeast cells in stationary phase, vacuoles fuse and remodel their membranes to create a single spherical vacuole with two distinct membrane microdomains, which are required for yeast lipophagy. In this study, we discovered that Fat1p was capable of rapidly responding to changes in nutritional status and preserving cell survival by regulating membrane lipid saturation to maintain proper vacuolar morphology and the level of lipophagy in the yeast S. cerevisiae. Our findings shed light on how cells maintain vacuolar structure and promote the differentiation of vacuole surface microdomains for stationary-phase lipophagy.

The Advancements and Prospects of Nervonic Acid Production

Nervonic acid (NA) is a monounsaturated very long-chain fatty acid (VLCFA) and has been identified with critical biological functions in medical and health care for brain development and injury repair. Yet, the approaches to producing NA from the sources of plants or animals continue to pose challenges to meet increasing market demand, as they are generally associated with high costs, a lack of natural resources, a long life cycle, and low production efficiency. The recent technological advance in metabolic engineering allows us to precisely engineer oleaginous microbes to develop high-content NA-producing strains, which has the potential to provide a possible solution to produce NA on a commercial fermentation scale. In this Review, the biosynthetic pathway, natural sources, and metabolic engineering of NA are summarized. The strategies of metabolic engineering that could be adopted to modify oleaginous yeast to produce NA are discussed in detail, providing the prospecting views for the microbial cells producing NA.

Two AMP-Binding Domain Proteins from Rhizophagus irregularis Involved in Import of Exogenous Fatty Acids

Arbuscular mycorrhizal fungi (AMF) colonize roots, where they provide nutrients in exchange for sugars and lipids. Because AMF lack genes for cytosolic fatty acid de novo synthase (FAS), they depend on host-derived fatty acids. AMF colonization is accompanied by expression of specific lipid genes and synthesis of sn-2 monoacylglycerols (MAGs). It is unknown how host-derived fatty acids are taken up by AMF. We describe the characterization of two AMP-binding domain protein genes from Rhizophagus irregularis, RiFAT1 and RiFAT2, with sequence similarity to Saccharomyces cerevisiae fatty acid transporter 1 (FAT1). Uptake of ¹³C-myristic acid (14:0) and, to a lesser extent, ¹³C-palmitic acid (16:0) was enhanced after expression of RiFAT1 or RiFAT2 in S. cerevisiae Δfat1 cells. The uptake of ²H-labeled fatty acids from ²H-myristoylglycerol or ²H-palmitoylglycerol was also increased after RiFAT1 and RiFAT2 expression in Δfat, but intact ²H-MAGs were not detected. RiFAT1 and RiFAT2 expression was induced in colonized roots compared with extraradical mycelium. ¹³C-label in the AMF-specific palmitvaccenic acid (16:1Δ11) and eicosatrienoic acid (20:3) were detected in colonized roots only when ¹³C₂-acetate was supplemented but not ¹³C-fatty acids, demonstrating that de novo synthesized, host-derived fatty acids are rapidly taken up by R. irregularis from the roots. The results show that RiFAT1 and RiFAT2 are involved in the uptake of myristic acid (14:0) and palmitic acid (16:0), while fatty acids from MAGs are only taken up after hydrolysis. Therefore, the two proteins might be involved in fatty acid import into the fungal arbuscules in colonized roots.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Fatty acid transport protein 2 interacts with ceramide synthase 2 to promote ceramide synthesis

Dihydroceramide is a lipid molecule generated via the action of (dihydro)ceramide synthases (CerSs), which use two substrates, namely sphinganine and fatty acyl-CoAs. Sphinganine is generated via the sequential activity of two integral membrane proteins located in the endoplasmic reticulum. Less is known about the source of the fatty acyl-CoAs, although a number of cytosolic proteins in the pathways of acyl-CoA generation modulate ceramide synthesis via direct or indirect interaction with the CerSs. In this study, we demonstrate, by proteomic analysis of immunoprecipitated proteins, that fatty acid transporter protein 2 (FATP2) (also known as very long-chain acyl-CoA synthetase) directly interacts with CerS2 in mouse liver. Studies in cultured cells demonstrated that other members of the FATP family can also interact with CerS2, with the interaction dependent on both proteins being catalytically active. In addition, transfection of cells with FATP1, FATP2, or FATP4 increased ceramide levels although only FATP2 and 4 increased dihydroceramide levels, consistent with their known intracellular locations. Finally, we show that lipofermata, an FATP2 inhibitor which is believed to directly impact tumor cell growth via modulation of FATP2, decreased de novo dihydroceramide synthesis, suggesting that some of the proposed therapeutic effects of lipofermata may be mediated via (dihydro)ceramide rather than directly via acyl-CoA generation. In summary, our study reinforces the idea that manipulating the pathway of fatty acyl-CoA generation will impact a wide variety of down-stream lipids, not least the sphingolipids, which utilize two acyl-CoA moieties in the initial steps of their synthesis.

The Effect of FATP1 on Adipocyte Differentiation in Qinchuan Beef Cattle

Simple Summary

Previous research found that FATP1 plays an important role in the regulation of fatty acid metabolism and lipid accumulation in pig and chicken, but its function has not been explored in bovine adipocyte yet. In this study, we investigated the effect of FATP1 expression on preadipocyte differentiation in Qinchuan cattle using overexpression and interference assays. Our results reveal that FATP1 overexpression promoted preadipocyte differentiation, lipid droplet formation, and the expression of LPL and PPARγ, while FATP1 interference had the opposite effects on adipocyte differentiation and fat deposition. Following FATP1 overexpression and FATP1 interference in adipocytes, RNA-seq analysis identified that SLPI, STC1, SEMA6A, TNFRSF19, SLN, PTGS2, ADCYP1, FADS2, and SCD genes were differentially expressed. Pathway analysis revealed that the PPAR signaling pathway, AMPK signal pathway, and Insulin signaling pathway were enriched with differentially expressed genes. We propose that the FATP1 gene may affect the beef quality by involving adipocyte differentiation and lipid deposition, and may shed new light on the formation mechanisms of adipose tissues.

Abstract

FATP1 plays an important role in the regulation of fatty acid metabolism and lipid accumulation. In this study, we investigated the patterns of FATP1 expression in various tissues obtained from calf and adult Qinchuan cattle, and in differentiating adipocytes. Next, we investigated the effect of FATP1 expression on preadipocyte differentiation in Qinchuan cattle using overexpression and interference assays. We also identified the differentially expressed genes (DEGs) and pathways associated with FATP1 overexpression/interference. Our results reveal that FATP1 was broadly expressed in heart, kidney, muscle, small intestine, large intestine, and perirenal fat tissues. While FATP1 overexpression promoted preadipocyte differentiation, fat deposition, and the expression of several genes involved in fat metabolism, FATP1 interference had the opposite effects on adipocyte differentiation. Following FATP1 overexpression and FATP1 interference in adipocytes, RNA-seq analysis was performed to identify DEGs related to fat metabolism. The DEGs identified include SLPI, STC1, SEMA6A, TNFRSF19, SLN, PTGS2, ADCYP1, FADS2, and SCD. Pathway analysis revealed that the DEGs were enriched in the PPAR signaling pathway, AMPK signal pathway, and Insulin signaling pathway. Our results provide an in-depth understanding of the function and regulation mechanism of FAPT1 in fat metabolism.

Integrating transcriptomic and metabolomic analysis of the oleaginous yeast Rhodosporidium toruloides IFO0880 during growth under different carbon sources

Rhodosporidium toruloides is an oleaginous yeast capable of producing a variety of biofuels and bioproducts from diverse carbon sources. Despite numerous studies showing its promise as a platform microorganism, little is known about its metabolism and physiology. In this work, we investigated the central carbon metabolism in R. toruloides IFO0880 using transcriptomics and metabolomics during growth on glucose, xylose, acetate, or soybean oil. These substrates were chosen because they can be derived from plants. Significant changes in gene expression and metabolite concentrations were observed during growth on these four substrates. We mapped these changes onto the governing metabolic pathways to better understand how R. toruloides reprograms its metabolism to enable growth on these substrates. One notable finding concerns xylose metabolism, where poor expression of xylulokinase induces a bypass leading to arabitol production. Collectively, these results further our understanding of central carbon metabolism in R. toruloides during growth on different substrates. They may also help guide the metabolic engineering and development of better models of metabolism for R. toruloides.Key points• Gene expression and metabolite concentrations were significantly changed.• Reduced expression of xylulokinase induces a bypass leading to arabitol production.• R. toruloides reprograms its metabolism to allow growth on different substrates.

Quantitative live-cell PALM reveals nanoscopic Faa4 redistributions and dynamics on lipid droplets during metabolic transitions of yeast

Lipid droplets (LDs) are dynamic organelles for lipid storage and homeostasis. Cells respond to metabolic changes by regulating the spatial distribution of LDs and enzymes required for LD growth and turnover. The small size of LDs precludes the observation of their associated enzyme densities and dynamics with conventional fluorescence microscopy. Here we employ quantitative photo-activated localization microscopy to study the density of the fatty acid (FA) activating enzyme Faa4 on LDs in live yeast cells with single-molecule sensitivity and 30 nm resolution. During the log phase LDs colocalize with the endoplasmic reticulum (ER) where their emergence and expansion are mediated by the highest observed Faa4 densities. During transition to the stationary phase, LDs with a ∼2-fold increased surface area translocate to the vacuolar surface and lumen and exhibit a ∼2.5-fold increase in Faa4 density. The increased Faa4 density on LDs further suggests its role in LD expansion, is caused by its ∼5-fold increased expression level, and is specific to exogenous FA chain-lengths. When lipolysis is induced by refreshed medium, Faa4 shuttles through ER- and lipophagy to the vacuole, where it may activate FAs for membrane expansion and degrade Faa4 to reset its cellular abundance to levels in the log phase.

Aspergillus niger uses the peroxisomal CoA-dependent β-oxidative genes to degrade the hydroxycinnamic acids caffeic acid, ferulic acid, and p-coumaric acid

Abstract

Aromatic compounds are important molecules which are widely applied in many industries and are mainly produced from nonrenewable sources. Renewable sources such as plant biomass are interesting alternatives for the production of aromatic compounds. Ferulic acid and p-coumaric acid, a precursor for vanillin and p-vinyl phenol, respectively, can be released from plant biomass by the fungus Aspergillus niger. The degradation of hydroxycinnamic acids such as caffeic acid, ferulic acid, and p-coumaric acid has been observed in many fungi. In A. niger, multiple metabolic pathways were suggested for the degradation of hydroxycinnamic acids. However, no genes were identified for these hydroxycinnamic acid metabolic pathways. In this study, several pathway genes were identified using whole-genome transcriptomic data of A. niger grown on different hydroxycinnamic acids. The genes are involved in the CoA-dependent β-oxidative pathway in fungi. This pathway is well known for the degradation of fatty acids, but not for hydroxycinnamic acids. However, in plants, it has been shown that hydroxycinnamic acids are degraded through this pathway. We identified genes encoding hydroxycinnamate-CoA synthase (hcsA), multifunctional β-oxidation hydratase/dehydrogenase (foxA), 3-ketoacyl CoA thiolase (katA), and four thioesterases (theA-D) of A. niger, which were highly induced by all three tested hydroxycinnamic acids. Deletion mutants revealed that these genes were indeed involved in the degradation of several hydroxycinnamic acids. In addition, foxA and theB are also involved in the degradation of fatty acids. HcsA, FoxA, and KatA contained a peroxisomal targeting signal and are therefore predicted to be localized in peroxisomes.

Key points

• Metabolism of hydroxycinnamic acid was investigated in Aspergillus niger

• Using transcriptome data, multiple CoA-dependent β-oxidative genes were identified.

• Both foxA and theB are involved in hydroxycinnamate but also fatty acid metabolism.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11311-0.

The role of FATP1 in lipid accumulation: a review

Lipid accumulation in mammals has been widely studied for decades due to its significant association with obesity in humans and meat quality in livestock animals. Fatty acid transport 1 (FATP1) is an evolutionarily conserved protein that localizes to the plasma membrane to enhance the transportation of fatty acids (FAs). In line with this function, FATP1 is involved in the metabolism of FAs, including their esterification and oxidation. In addition, the expression of FATP1 can be regulated by several energy-related factors, such as insulin and PPAR activators and transcription factors. These events connect FATP1 with cellular lipid accumulation. Recently, several studies have suggested that FATP1 acts as a facilitator in cellular lipid accumulation, whereas others hold a contrary view. Here, we will review these data and probe the possibility that FATP1 acts as a regulator in lipid accumulation, which will provide effective information for studies on the relationship between FATP1 and obesity in humans and meat quality in livestock animals.

The role of very long chain fatty acids in yeast physiology and human diseases

Fatty acids (FAs) are a highly diverse class of molecules that can have variable chain length, number of double bonds and hydroxylation sites. FAs with 22 or more carbon atoms are described as very long chain fatty acids (VLCFAs). VLCFAs are synthesized in the endoplasmic reticulum (ER) through a four-step elongation cycle by membrane embedded enzymes. VLCFAs are precursors for the synthesis of sphingolipids (SLs) and glycerophospholipids. Besides their role as lipid constituents, VLCFAs are also found as precursors of lipid mediators. Mis-regulation of VLCFA metabolism can result in a variety of inherited diseases ranging from ichthyosis, to myopathies and demyelination. The enzymes for VLCFA biosynthesis are evolutionary conserved and many of the pioneering studies were performed in the model organism Saccharomyces cerevisiae. A growing body of evidence suggests that VLCFA metabolism is intricately regulated to maintain lipid homeostasis. In this review we will describe the metabolism of VLCFAs, how they are synthesized, transported and degraded and how these processes are regulated, focusing on budding yeast. We will review how lipid metabolism and membrane properties are affected by VLCFAs and which impact mutations in the biosynthetic genes have on physiology. We will also briefly describe diseases caused by mis-regulation of VLCFAs in human cells.

NIX-Mediated Mitophagy Promotes Effector Memory Formation in Antigen-Specific CD8+ T Cells

Autophagy plays a critical role in the maintenance of immunological memory. However, the molecular mechanisms involved in autophagy-regulated effector memory formation in CD8⁺ T cells remain unclear. Here we show that deficiency in NIX-dependent mitophagy leads to metabolic defects in effector memory T cells. Deletion of NIX caused HIF1α accumulation and altered cellular metabolism from long-chain fatty acid to short/branched-chain fatty acid oxidation, thereby compromising ATP synthesis during effector memory formation. Preventing HIF1α accumulation restored long-chain fatty acid metabolism and effector memory formation in antigen-specific CD8⁺ T cells. Our study suggests that NIX-mediated mitophagy is critical for effector memory formation in T cells.

Gupta et al. demonstrate that mitophagy mediated by NIX, a mitochondrial outer membrane protein, plays a critical role in CD8⁺ T cell effector memory formation by regulating mitochondrial superoxide-dependent HIF1α protein accumulation and fatty acid metabolism. These findings elucidate the molecular mechanisms regulating T cell effector memory formation against viruses.

A conserved evolutionary mechanism permits Δ9 desaturation of very-long-chain fatty acyl lipids

Δ9 fatty acyl desaturases introduce a cis-double bond between C9 and C10 of saturated fatty acyl chains. From the crystal structure of the mouse stearoyl-CoA desaturase (mSCD1) it was proposed that Tyr-104, a surface residue located at the distal end of the fatty acyl binding pocket plays a key role in specifying 18C selectivity. We created mSCD1-Y104G to test the hypothesis that eliminating this bulky side chain would create an opening and permit the substrate's methyl end to protrude through the enzyme into the lipid bilayer, facilitating the desaturation of very-long-chain (VLC) substrates. Consistent with this hypothesis, Y104G acquired the ability to desaturate 24C and 26C acyl-CoAs while maintaining its Δ9-regioselectivity. We also investigated two distantly related very-long-chain fatty acyl (VLCFA) desaturases from Arabidopsis, ADS1.2 and ADS1.4, which have Ala and Gly, respectively, in place of the gatekeeping Tyr found in mSCD1. Substitution of Tyr for Ala and Gly in ADS1.2 and ADS1.4, respectively, blocked their ability to desaturate VLCFAs. Further, we identified a pair of fungal desaturase homologs which contained either an Ile or a Gly at this location and showed that only the Gly-containing desaturase was capable of very-long-chain desaturation. The conserved desaturase architecture wherein a surface residue with a single bulky side chain forms the end of the substrate binding cavity predisposes them to single amino acid substitutions that enable a switch between long- and very-long-chain selectivity. The data presented here show that such changes have independently occurred multiple times during evolution.

Dysregulation of very-long-chain fatty acid metabolism causes membrane saturation and induction of the unfolded protein response

The unfolded protein response (UPR) senses defects in the endoplasmic reticulum (ER) and orchestrates a complex program of adaptive cellular remodeling. Increasing evidence suggests an important relationship between lipid homeostasis and the UPR. Defects in the ER membrane induce the UPR, and the UPR in turn controls the expression of some lipid metabolic genes. Among lipid species, the very-long-chain fatty acids (VLCFAs) are relatively rare and poorly understood. Here, we show that loss of the VLCFA-coenzyme A synthetase Fat1, which is essential for VLCFA utilization, results in ER stress with compensatory UPR induction. Comprehensive lipidomic analyses revealed a dramatic increase in membrane saturation in the fat1Δ mutant, likely accounting for UPR induction. In principle, this increased membrane saturation could reflect adaptive membrane remodeling or an adverse effect of VLCFA dysfunction. We provide evidence supporting the latter, as the fat1Δ mutant showed defects in the function of Ole1, the sole fatty acyl desaturase in yeast. These results indicate that VLCFAs play essential roles in protein quality control and membrane homeostasis and suggest an unexpected requirement for VLCFAs in Ole1 function.

Neuronal Lipid Metabolism: Multiple Pathways Driving Functional Outcomes in Health and Disease

Lipids are a fundamental class of organic molecules implicated in a wide range of biological processes related to their structural diversity, and based on this can be broadly classified into five categories; fatty acids, triacylglycerols (TAGs), phospholipids, sterol lipids and sphingolipids. Different lipid classes play major roles in neuronal cell populations; they can be used as energy substrates, act as building blocks for cellular structural machinery, serve as bioactive molecules, or a combination of each. In amyotrophic lateral sclerosis (ALS), dysfunctions in lipid metabolism and function have been identified as potential drivers of pathogenesis. In particular, aberrant lipid metabolism is proposed to underlie denervation of neuromuscular junctions, mitochondrial dysfunction, excitotoxicity, impaired neuronal transport, cytoskeletal defects, inflammation and reduced neurotransmitter release. Here we review current knowledge of the roles of lipid metabolism and function in the CNS and discuss how modulating these pathways may offer novel therapeutic options for treating ALS.

Long-chain bases of sphingolipids are transported into cells via the acyl-CoA synthetases

Transport of dietary lipids into small-intestinal epithelial cells is pathologically and nutritionally important. However, lipid uptake remains an almost unexplored research area. Although we know that long-chain bases (LCBs), constituents of sphingolipids, can enter into cells efficiently, the molecular mechanism of LCB uptake is completely unclear. Here, we found that the yeast acyl-CoA synthetases (ACSs) Faa1 and Faa4 are redundantly involved in LCB uptake. In addition to fatty acid-activating activity, transporter activity toward long-chain fatty acids (LCFAs) has been suggested for ACSs. Both LCB and LCFA transports were largely impaired in faa1Δ faa4Δ cells. Furthermore, LCB and LCFA uptakes were mutually competitive. However, the energy dependency was different for their transports. Sodium azide/2-deoxy-D-glucose treatment inhibited import of LCFA but not that of LCB. Furthermore, the ATP-AMP motif mutation FAA1 S271A largely impaired the metabolic activity and LCFA uptake, while leaving LCB import unaffected. These results indicate that only LCFA transport requires ATP. Since ACSs do not metabolize LCBs as substrates, Faa1 and Faa4 are likely directly involved in LCB transport. Furthermore, we revealed that ACSs are also involved in LCB transport in mammalian cells. Thus, our findings provide strong support for the hypothesis that ACSs directly transport LCFAs.

Fatty Acid Transport Proteins: Targeting FATP2 as a Gatekeeper Involved in the Transport of Exogenous Fatty Acids

The fatty acid transport proteins (FATP) are classified as members of the Solute Carrier 27 (Slc27) family of proteins based on their ability to function in the transport of exogenous fatty acids. These proteins, when localized to the plasma membrane or at intracellular membrane junctions with the endoplasmic reticulum, function as a gate in the regulated transport of fatty acids and thus represent a therapeutic target to delimit the acquisition of fatty acids that contribute to disease as in the case of fatty acid overload. To date, FATP1, FATP2, and FATP4 have been used as targets in the selection of small molecule inhibitors with the goal of treating insulin resistance and attenuating dietary absorption of fatty acids. Several studies targeting FATP1 and FATP4 were based on the intrinsic acyl CoA synthetase activity of these proteins and not on transport directly. While several classes of compounds were identified as potential inhibitors of fatty acid transport, in vivo studies using a mouse model failed to provide evidence these compounds were effective in blocking or attenuating fatty acid transport. Studies targeting FATP2 employed a naturally occurring splice variant, FATP2b, which lacks intrinsic acyl CoA synthetase due to the deletion of exon 3, yet is fully functional in fatty acid transport. These studies identified two compounds, 5'-bromo-5-phenyl-spiro[3H-1,3,4-thiadiazole-2,3'-indoline]-2'-one), now referred to as Lipofermata, and 2-benzyl-3-(4-chlorophenyl)-5-(4-nitrophenyl)pyrazolo[1,5-a]pyrimidin-7(4H)-one, now called Grassofermata, that are effective fatty acid transport inhibitors both in vitro using a series of model cell lines and in vivo using a mouse model.

Integration and Validation of the Genome-Scale Metabolic Models of Pichia pastoris: A Comprehensive Update of Protein Glycosylation Pathways, Lipid and Energy Metabolism

Motivation

Genome-scale metabolic models (GEMs) are tools that allow predicting a phenotype from a genotype under certain environmental conditions. GEMs have been developed in the last ten years for a broad range of organisms, and are used for multiple purposes such as discovering new properties of metabolic networks, predicting new targets for metabolic engineering, as well as optimizing the cultivation conditions for biochemicals or recombinant protein production. Pichia pastoris is one of the most widely used organisms for heterologous protein expression. There are different GEMs for this methylotrophic yeast of which the most relevant and complete in the published literature are iPP668, PpaMBEL1254 and iLC915. However, these three models differ regarding certain pathways, terminology for metabolites and reactions and annotations. Moreover, GEMs for some species are typically built based on the reconstructed models of related model organisms. In these cases, some organism-specific pathways could be missing or misrepresented.

Results

In order to provide an updated and more comprehensive GEM for P. pastoris, we have reconstructed and validated a consensus model integrating and merging all three existing models. In this step a comprehensive review and integration of the metabolic pathways included in each one of these three versions was performed. In addition, the resulting iMT1026 model includes a new description of some metabolic processes. Particularly new information described in recently published literature is included, mainly related to fatty acid and sphingolipid metabolism, glycosylation and cell energetics. Finally the reconstructed model was tested and validated, by comparing the results of the simulations with available empirical physiological datasets results obtained from a wide range of experimental conditions, such as different carbon sources, distinct oxygen availability conditions, as well as producing of two different recombinant proteins. In these simulations, the iMT1026 model has shown a better performance than the previous existing models.

Fatty acid transport proteins in disease: New insights from invertebrate models

The dysregulation of lipid metabolism has been implicated in various diseases, including diabetes, cardiopathies, dermopathies, retinal and neurodegenerative diseases. Mouse models have provided insights into lipid metabolism. However, progress in the understanding of these pathologies is hampered by the multiplicity of essential cellular processes and genes that modulate lipid metabolism. Drosophila and Caenorhabditis elegans have emerged as simple genetic models to improve our understanding of these metabolic diseases. Recent studies have characterized fatty acid transport protein (fatp) mutants in Drosophila and C. elegans, establishing new models of cardiomyopathy, retinal degeneration, fat storage disease and dermopathies. These models have generated novel insights into the physiological role of the Fatp protein family in vivo in multicellular organisms, and are likely to contribute substantially to progress in understanding the etiology of various metabolic disorders. Here, we describe and discuss the mechanisms underlying invertebrate fatp mutant models in the light of the current knowledge relating to FATPs and lipid disorders in vertebrates.

Involvement of acyl-CoA synthetase genes in n-alkane assimilation and fatty acid utilization in yeast Yarrowia lipolytica

Here, we investigated the roles of YAL1 (FAA1) and FAT1 encoding acyl-CoA synthetases (ACSs) and three additional orthologs of ACS genes FAT2-FAT4 of the yeast Yarrowia lipolytica in the assimilation or utilization of n-alkanes and fatty acids. ACS deletion mutants were generated to characterize their function. The FAT1 deletion mutant exhibited decreased growth on n-alkanes of 10-18 carbons, whereas the FAA1 mutant showed growth reduction on n-alkane of 16 carbons. However, FAT2-FAT4 deletion mutants did not show any growth defects, suggesting that FAT1 and FAA1 are involved in the activation of fatty acids produced during the metabolism of n-alkanes. In contrast, deletions of FAA1 and FAT1-FAT4 conferred no defect in growth on fatty acids. The wild-type strain grew in the presence of cerulenin, an inhibitor of fatty acid synthesis, by utilizing exogenously added fatty acid or fatty acid derived from n-alkane when oleic acid or n-alkane of 18 carbons was supplemented. However, the FAA1 deletion mutant did not grow, indicating a critical role for FAA1 in the utilization of fatty acids. Fluorescent microscopic observation and biochemical analyses suggested that Fat1p is present in the peroxisome and Faa1p is localized in the cytosol and to membranes.

Insulin sensitivity is independent of lipid binding protein trafficking at the plasma membrane in human skeletal muscle: effect of a 3-day, high-fat diet

The aim of the present study was to investigate lipid-induced regulation of lipid binding proteins in human skeletal muscle and the impact hereof on insulin sensitivity. Eleven healthy male subjects underwent a 3-day hypercaloric and high-fat diet regime. Muscle biopsies were taken before and after the diet intervention, and giant sarcolemmal vesicles were prepared. The high-fat diet induced decreased insulin sensitivity, but this was not associated with a relocation of FAT/CD36 or FABPpm protein to the sarcolemma. However, FAT/CD36 and FABPpm mRNA, but not the proteins, were upregulated by increased fatty acid availability. This suggests a time dependency in the upregulation of FAT/CD36 and FABPpm protein during high availability of plasma fatty acids. Furthermore, we did not detect FATP1 and FATP4 protein in giant sarcolemmal vesicles obtained from human skeletal muscle. In conclusion, this study shows that a short-term lipid-load increases mRNA content of key lipid handling proteins in human muscle. However, decreased insulin sensitivity after a high-fat diet is not accompanied with relocation of FAT/CD36 or FABPpm protein to the sarcolemma. Finally, FATP1 and FATP4 protein was located intracellularly but not at the sarcolemma in humans.

A peroxisomal long-chain acyl-CoA synthetase from Glycine max involved in lipid degradation

Seed storage oil, in the form of triacylglycerol (TAG), is degraded to provide carbon and energy during germination and early seedling growth by the fatty acid β-oxidation in the peroxisome. Although the pathways for lipid degradation have been uncovered, understanding of the exact involved enzymes in soybean is still limited. Long-chain acyl-CoA synthetase (ACSL) is a critical enzyme that activates free fatty acid released from TAG to form the fatty acyl-CoA. Recent studies have shown the importance of ACSL in lipid degradation and synthesis, but few studies were focused on soybean. In this work, we cloned a ACSL gene from soybean and designated it as GmACSL2. Sequence analysis revealed that GmACSL2 encodes a protein of 733 amino acid residues, which is highly homologous to the ones in other higher plants. Complementation test showed that GmACSL2 could restore the growth of an ACS-deficient yeast strain (YB525). Co-expression assay in Nicotiana benthamiana indicated that GmACSL2 is located at peroxisome. Expression pattern analysis showed that GmACSL2 is highly expressed in germinating seedling and strongly induced 1 day after imbibition, which indicate that GmACSL2 may take part in the seed germination. GmACSL2 overexpression in yeast and soybean hairy root severely reduces the contents of the lipids and fatty acids, compared with controls in both cells, and enhances the β-oxidation efficiency in yeast. All these results suggest that GmACSL2 may take part in fatty acid and lipid degradation. In conclusion, peroxisomal GmACSL2 from Glycine max probably be involved in the lipid degradation during seed germination.

Regulatory and functional diversity of methylmercaptopropionate coenzyme A ligases from the dimethylsulfoniopropionate demethylation pathway in Ruegeria pomeroyi DSS-3 and other proteobacteria

The organosulfur compound dimethylsulfoniopropionate (DMSP) is produced by phytoplankton and is ubiquitous in the surface ocean. Once released from phytoplankton, marine bacteria degrade DMSP by either the cleavage pathway to form the volatile gas dimethylsulfide (DMS) or the demethylation pathway, yielding methanethiol (MeSH), which is readily assimilated or oxidized. The enzyme DmdB, a methylmercaptopropionate (MMPA)-coenzyme A (CoA) ligase, catalyzes the second step in the demethylation pathway and is a major regulatory point. The two forms of DmdB present in the marine roseobacter Ruegeria pomeroyi DSS-3, RPO_DmdB1 and RPO_DmdB2, and the single form in the SAR11 clade bacterium "Candidatus Pelagibacter ubique" HTCC1062, PU_DmdB1, were characterized in detail. DmdB enzymes were also examined from Ruegeria lacuscaerulensis ITI-1157, Pseudomonas aeruginosa PAO1, and Burkholderia thailandensis E264. The DmdB enzymes separated into two phylogenetic clades. All enzymes had activity with MMPA and were sensitive to inhibition by salts, but there was no correlation between the clades and substrate specificity or salt sensitivity. All Ruegeria species enzymes were inhibited by physiological concentrations (70 mM) of DMSP. However, ADP reversed the inhibition of RPO_DmdB1, suggesting that this enzyme was responsive to cellular energy charge. MMPA reversed the inhibition of RPO_DmdB2 as well as both R. lacuscaerulensis ITI-1157 DmdB enzymes, suggesting that a complex regulatory system exists in marine bacteria. In contrast, the DmdBs of the non-DMSP-metabolizing P. aeruginosa PAO1 and B. thailandensis E264 were not inhibited by DMSP, suggesting that DMSP inhibition is a specific adaptation of DmdBs from marine bacteria.

The yeast sphingolipid signaling landscape

Sphingolipids are recognized as signaling mediators in a growing number of pathways, and represent potential targets to address many diseases. The study of sphingolipid signaling in yeast has created a number of breakthroughs in the field, and has the potential to lead future advances. The aim of this article is to provide an inclusive view of two major frontiers in yeast sphingolipid signaling. In the first section, several key studies in the field of sphingolipidomics are consolidated to create a yeast sphingolipidome that ranks nearly all known sphingolipid species by their level in a resting yeast cell. The second section presents an overview of most known phenotypes identified for sphingolipid gene mutants, presented with the intention of illuminating not yet discovered connections outside and inside of the field.

Fatty acid transporters in skin development, function and disease

Fatty acids in the epidermis can be incorporated into complex lipids or exist in a free form, and they are crucial to proper functions of the epidermis and its appendages, such as sebaceous glands. Epidermal fatty acids can be synthesized de novo by keratinocytes or taken up from extracutaneous sources in a process that likely involves protein transporters. Several proteins that are expressed in the epidermis have been proposed to facilitate the uptake of long-chain fatty acids (LCFA) in mammalian cells, including fatty acid translocase/CD36, fatty acid binding protein, and fatty acid transport protein (FATP)/very long-chain acyl-CoA synthetase. In this review, we will discuss the mechanisms by which these candidate transporters facilitate the uptake of fatty acids. We will then discuss the clinical implications of defects in these transporters and relevant animal models, including the FATP4 animal models and ichthyosis prematurity syndrome, a congenital ichthyosis caused by FATP4 deficiency. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

SLC27 fatty acid transport proteins

The uptake and metabolism of long chain fatty acids (LCFA) are critical to many physiological and cellular processes. Aberrant accumulation or depletion of LCFA underlie the pathology of numerous metabolic diseases. Protein-mediated transport of LCFA has been proposed as the major mode of LCFA uptake and activation. Several proteins have been identified to be involved in LCFA uptake. This review focuses on the SLC27 family of fatty acid transport proteins, also known as FATPs, with an emphasis on the gain- and loss-of-function animal models that elucidate the functions of FATPs in vivo and how these transport proteins play a role in physiological and pathological situations.

Physiological role of Acyl coenzyme A synthetase homologs in lipid metabolism in Neurospora crassa

Acyl coenzyme A (CoA) synthetase (ACS) enzymes catalyze the activation of free fatty acids (FAs) to CoA esters by a two-step thioesterification reaction. Activated FAs participate in a variety of anabolic and catabolic lipid metabolic pathways, including de novo complex lipid biosynthesis, FA β-oxidation, and lipid membrane remodeling. Analysis of the genome sequence of the filamentous fungus Neurospora crassa identified seven putative fatty ACSs (ACS-1 through ACS-7). ACS-3 was found to be the major activator for exogenous FAs for anabolic lipid metabolic pathways, and consistent with this finding, ACS-3 localized to the endoplasmic reticulum, plasma membrane, and septa. Double-mutant analyses confirmed partial functional redundancy of ACS-2 and ACS-3. ACS-5 was determined to function in siderophore biosynthesis, indicating alternative functions for ACS enzymes in addition to fatty acid metabolism. The N. crassa ACSs involved in activation of FAs for catabolism were not specifically defined, presumably due to functional redundancy of several of ACSs for catabolism of exogenous FAs.

Lipid droplets and peroxisomes: key players in cellular lipid homeostasis or a matter of fat--store 'em up or burn 'em down

Lipid droplets (LDs) and peroxisomes are central players in cellular lipid homeostasis: some of their main functions are to control the metabolic flux and availability of fatty acids (LDs and peroxisomes) as well as of sterols (LDs). Both fatty acids and sterols serve multiple functions in the cell—as membrane stabilizers affecting membrane fluidity, as crucial structural elements of membrane-forming phospholipids and sphingolipids, as protein modifiers and signaling molecules, and last but not least, as a rich carbon and energy source. In addition, peroxisomes harbor enzymes of the malic acid shunt, which is indispensable to regenerate oxaloacetate for gluconeogenesis, thus allowing yeast cells to generate sugars from fatty acids or nonfermentable carbon sources. Therefore, failure of LD and peroxisome biogenesis and function are likely to lead to deregulated lipid fluxes and disrupted energy homeostasis with detrimental consequences for the cell. These pathological consequences of LD and peroxisome failure have indeed sparked great biomedical interest in understanding the biogenesis of these organelles, their functional roles in lipid homeostasis, interaction with cellular metabolism and other organelles, as well as their regulation, turnover, and inheritance. These questions are particularly burning in view of the pandemic development of lipid-associated disorders worldwide.

Genetic engineering of microorganisms for biodiesel production

Biodiesel, as one type of renewable energy, is an ideal substitute for petroleum-based diesel fuel and is usually made from triacylglycerides by transesterification with alcohols. Biodiesel production based on microbial fermentation aiming to establish more efficient, less-cost and sustainable biodiesel production strategies is under current investigation by various start-up biotechnology companies and research centers. Genetic engineering plays a key role in the transformation of microbes into the desired cell factories with high efficiency of biodiesel production. Here, we present an overview of principal microorganisms used in the microbial biodiesel production and recent advances in metabolic engineering for the modification required. Overexpression or deletion of the related enzymes for de novo synthesis of biodiesel is highlighted with relevant examples.

Neutral lipid metabolism influences phospholipid synthesis and deacylation in Saccharomyces cerevisiae

Establishment and maintenance of equilibrium in the fatty acid (FA) composition of phospholipids (PL) requires both regulation of the substrate available for PL synthesis (the acyl-CoA pool) and extensive PL turnover and acyl editing. In the present study, we utilize acyl-CoA synthetase (ACS) deficient cells, unable to recycle FA derived from lipid deacylation, to evaluate the role of several enzymatic activities in FA trafficking and PL homeostasis in Saccharomyces cerevisiae. The data presented show that phospholipases B are not contributing to constitutive PL deacylation and are therefore unlikely to be involved in PL remodeling. In contrast, the enzymes of neutral lipid (NL) synthesis and mobilization are central mediators of FA trafficking. The phospholipid:DAG acyltransferase (PDAT) Lro1p has a substantial effect on FA release and on PL equilibrium, emerging as an important mediator in PL remodeling. The acyl-CoA dependent biosynthetic activities of NL metabolism are also involved in PL homeostasis through active modulation of the substrate available for PL synthesis. In addition TAG mobilization makes an important contribution, especially in cells from stationary phase, to FA availability. Beyond its well-established role in the formation of a storage pool, NL metabolism could play a crucial role as a mechanism to uncouple the pools of PL and acyl-CoAs from each other and thereby to allow independent regulation of each one.

Lipidome and proteome of lipid droplets from the methylotrophic yeast Pichia pastoris

Lipid droplets (LD) are the main depot of non-polar lipids in all eukaryotic cells. In the present study we describe isolation and characterization of LD from the industrial yeast Pichia pastoris. We designed and adapted an isolation procedure which allowed us to obtain this subcellular fraction at high purity as judged by quality control using appropriate marker proteins. Components of P. pastoris LD were characterized by conventional biochemical methods of lipid and protein analysis, but also by a lipidome and proteome approach. Our results show several distinct features of LD from P. pastoris especially in comparison to Saccharomyces cerevisiae. P. pastoris LD are characterized by their high preponderance of triacylglycerols over steryl esters in the core of the organelle, the high degree of fatty acid (poly)unsaturation and the high amount of ergosterol precursors. The high phosphatidylinositol to phosphatidylserine of ~ 7.5 ratio on the surface membrane of LD is noteworthy. Proteome analysis revealed equipment of the organelle with a small but typical set of proteins which includes enzymes of sterol biosynthesis, fatty acid activation, phosphatidic acid synthesis and non-polar lipid hydrolysis. These results are the basis for a better understanding of P. pastoris lipid metabolism and lipid storage and may be helpful for manipulating cell biological and/or biotechnological processes in this yeast.

Metabolism and regulation of glycerolipids in the yeast Saccharomyces cerevisiae

Due to its genetic tractability and increasing wealth of accessible data, the yeast Saccharomyces cerevisiae is a model system of choice for the study of the genetics, biochemistry, and cell biology of eukaryotic lipid metabolism. Glycerolipids (e.g., phospholipids and triacylglycerol) and their precursors are synthesized and metabolized by enzymes associated with the cytosol and membranous organelles, including endoplasmic reticulum, mitochondria, and lipid droplets. Genetic and biochemical analyses have revealed that glycerolipids play important roles in cell signaling, membrane trafficking, and anchoring of membrane proteins in addition to membrane structure. The expression of glycerolipid enzymes is controlled by a variety of conditions including growth stage and nutrient availability. Much of this regulation occurs at the transcriptional level and involves the Ino2–Ino4 activation complex and the Opi1 repressor, which interacts with Ino2 to attenuate transcriptional activation of UAS_INO-containing glycerolipid biosynthetic genes. Cellular levels of phosphatidic acid, precursor to all membrane phospholipids and the storage lipid triacylglycerol, regulates transcription of UAS_INO-containing genes by tethering Opi1 to the nuclear/endoplasmic reticulum membrane and controlling its translocation into the nucleus, a mechanism largely controlled by inositol availability. The transcriptional activator Zap1 controls the expression of some phospholipid synthesis genes in response to zinc availability. Regulatory mechanisms also include control of catalytic activity of glycerolipid enzymes by water-soluble precursors, products and lipids, and covalent modification of phosphorylation, while in vivo function of some enzymes is governed by their subcellular location. Genome-wide genetic analysis indicates coordinate regulation between glycerolipid metabolism and a broad spectrum of metabolic pathways.

Peroxisomal acyl-CoA synthetases

Peroxisomes carry out many essential lipid metabolic functions. Nearly all of these functions require that an acyl group-either a fatty acid or the acyl side chain of a steroid derivative-be thioesterified to coenzyme A (CoA) for subsequent reactions to proceed. This thioesterification, or "activation", reaction, catalyzed by enzymes belonging to the acyl-CoA synthetase family, is thus central to cellular lipid metabolism. However, despite our rather thorough understanding of peroxisomal metabolic pathways, surprisingly little is known about the specific peroxisomal acyl-CoA synthetases that participate in these pathways. Of the 26 acyl-CoA synthetases encoded by the human and mouse genomes, only a few have been reported to be peroxisomal, including ACSL4, SLC27A2, and SLC27A4. In this review, we briefly describe the primary peroxisomal lipid metabolic pathways in which fatty acyl-CoAs participate. Then, we examine the evidence for presence and functions of acyl-CoA synthetases in peroxisomes, much of which was obtained before the existence of multiple acyl-CoA synthetase isoenzymes was known. Finally, we discuss the role(s) of peroxisome-specific acyl-CoA synthetase isoforms in lipid metabolism.

Arabidopsis long-chain acyl-CoA synthetase 1 (LACS1), LACS2, and LACS3 facilitate fatty acid uptake in yeast

The plant cuticle is a lipid-based barrier on the aerial surfaces of plants that plays a variety of protective roles. The cuticle is comprised largely of long-chain and very-long-chain fatty acids and their derivatives. In Arabidopsis, LONG-CHAIN ACYL-COA SYNTHETASE1 (LACS1), LACS2, and LACS3 are known or suspected cuticle biosynthetic genes. Very-long-chain acyl-coenzyme A (CoA) synthetase activity has been demonstrated for LACS1 and LACS2, although the role for such an activity in cuticle biosynthesis is currently unclear. In yeast and mammalian systems, some very-long-chain acyl-CoA synthetases are also called fatty acid transport proteins (FATPs) due to a second function of mediating transmembrane movement of fatty acids. We sought to determine if LACS1-3 also have this dual functionality. A yeast fat1Δ mutant is deficient in both very-long-chain acyl-CoA synthetase activity and exogenous fatty acid uptake. We demonstrate that heterologous expression of LACS1, 2, or 3 is able to complement both of these deficiencies. Furthermore, expression of each LACS enzyme in yeast resulted in uptake of the long-chain fatty acid analogue, C(1)-BODIPY-C(12). Only expression of LACS1 resulted in uptake of the very-long-chain fatty acid analogue, BODIPY-C(16). These results demonstrate that LACS1, LACS2, and LACS3 have the dual functionality of yeast and mammalian FATP enzymes. These findings have implications in the transmembrane transport and intracellular trafficking of plant lipids destined for export to the cuticle.

Enhanced fatty acid oxidation and FATP4 protein expression after endurance exercise training in human skeletal muscle

FATP1 and FATP4 appear to be important for the cellular uptake and handling of long chain fatty acids (LCFA). These findings were obtained from loss- or gain of function models. However, reports on FATP1 and FATP4 in human skeletal muscle are limited. Aerobic training enhances lipid oxidation; however, it is not known whether this involves up-regulation of FATP1 and FATP4 protein. Therefore, the aim of this project was to investigate FATP1 and FATP4 protein expression in the vastus lateralis muscle from healthy human individuals and to what extent FATP1 and FATP4 protein expression were affected by an increased fuel demand induced by exercise training. Eight young healthy males were recruited to the study. All subjects were non smokers and did not participate in regular physical activity (<1 time per week for the past 6 months, VO_2peak 3.4±0.1 l O₂ min⁻¹). Subjects underwent an 8 week supervised aerobic training program. Training induced an increase in VO_2peak from 3.4±0.1 to 3.9±0.1 l min⁻¹ and citrate synthase activity was increased from 53.7±2.5 to 80.8±3.7 µmol g⁻¹ min⁻¹. The protein content of FATP4 was increased by 33%, whereas FATP1 protein content was reduced by 20%. Interestingly, at the end of the training intervention a significant association (r² = 0.74) between the observed increase in skeletal muscle FATP4 protein expression and lipid oxidation during a 120 min endurance exercise test was observed. In conclusion, based on the present findings it is suggested that FATP1 and FATP4 proteins perform different functional roles in handling LCFA in skeletal muscle with FATP4 apparently more important as a lipid transport protein directing lipids for lipid oxidation.

The SUN protein Mps3 is required for spindle pole body insertion into the nuclear membrane and nuclear envelope homeostasis

The budding yeast spindle pole body (SPB) is anchored in the nuclear envelope so that it can simultaneously nucleate both nuclear and cytoplasmic microtubules. During SPB duplication, the newly formed SPB is inserted into the nuclear membrane. The mechanism of SPB insertion is poorly understood but likely involves the action of integral membrane proteins to mediate changes in the nuclear envelope itself, such as fusion of the inner and outer nuclear membranes. Analysis of the functional domains of the budding yeast SUN protein and SPB component Mps3 revealed that most regions are not essential for growth or SPB duplication under wild-type conditions. However, a novel dominant allele in the P-loop region, MPS3-G186K, displays defects in multiple steps in SPB duplication, including SPB insertion, indicating a previously unknown role for Mps3 in this step of SPB assembly. Characterization of the MPS3-G186K mutant by electron microscopy revealed severe over-proliferation of the inner nuclear membrane, which could be rescued by altering the characteristics of the nuclear envelope using both chemical and genetic methods. Lipid profiling revealed that cells lacking MPS3 contain abnormal amounts of certain types of polar and neutral lipids, and deletion or mutation of MPS3 can suppress growth defects associated with inhibition of sterol biosynthesis, suggesting that Mps3 directly affects lipid homeostasis. Therefore, we propose that Mps3 facilitates insertion of SPBs in the nuclear membrane by modulating nuclear envelope composition.

Fatty acid transport into the brain: of fatty acid fables and lipid tails

The blood-brain barrier formed by the brain capillary endothelial cells provides a protective barrier between the systemic blood and the extracellular environment of the central nervous system. Brain capillaries are a continuous layer of endothelial cells with highly developed tight junctional complexes and a lack of fenestrations. The presence of these tight junctions in the cerebral microvessel endothelial cells aids in the restriction of movement of molecules and solutes into the brain. Fatty acids are important components of biological membranes, are precursors for the biosynthesis of phospholipids and sphingolipids and are utilized for mitochondrial β-oxidation. The brain is capable of synthesizing only a few fatty acids. Hence, most fatty acids must enter into the brain from the blood. Here we review current mechanisms of transport of free fatty acids into cells and describe how free fatty acids move from the blood into the brain. We discuss both diffusional as well as protein-mediated movement of fatty acids across biological membranes.

Microautophagy of the nucleus coincides with a vacuolar diffusion barrier at nuclear-vacuolar junctions

Nuclei bind yeast vacuoles via nucleus-vacuole (NV) junctions. Under nutrient restriction, NV junctions invaginate and release vesicles filled with nuclear material into vacuoles, resulting in piecemeal microautophagy of the nucleus (PMN). We show that the electrochemical gradient across the vacuolar membrane promotes invagination of NV junctions. Existing invaginations persist independently of the gradient, but final release of PMN vesicles requires again V-ATPase activity. We find that NV junctions form a diffusion barrier on the vacuolar membrane that excludes V-ATPase but is enriched in the VTC complex and accessible to other membrane-integral proteins. V-ATPase exclusion depends on the NV junction proteins Nvj1p,Vac8p, and the electrochemical gradient. It also depends on factors of lipid metabolism, such as the oxysterol binding protein Osh1p and the enoyl-CoA reductase Tsc13p, which are enriched in NV junctions, and on Lag1p and Fen1p. Our observations suggest that NV junctions form in two separable steps: Nvj1p and Vac8p suffice to establish contact between the two membranes. The electrochemical potential and lipid-modifying enzymes are needed to establish the vacuolar diffusion barrier, invaginate NV junctions, and form PMN vesicles.

Ypk1, the yeast orthologue of the human serum- and glucocorticoid-induced kinase, is required for efficient uptake of fatty acids

Fatty acids constitute an important energy source for various tissues. The mechanisms that mediate and control uptake of free fatty acids from the circulation, however, are poorly understood. Here we show that efficient fatty-acid uptake by yeast cells requires the protein kinase Ypk1, the orthologue of the human serum- and glucocorticoid-induced kinase Sgk1. ypk1Delta mutant cells fail to grow under conditions that render cells auxotrophic for fatty acids, show a reduced uptake of radiolabelled or fluorescently labelled fatty acids, lack the facilitated component of the uptake activity, and have elevated levels of fatty acids in a bovine serum albumin (BSA) back-extractable compartment. Efficient fatty-acid uptake and/or incorporation requires the protein-kinase activity of Ypk1, because a kinase-dead point-mutant allele of YPK1 is defective in this process. This function of Ypk1 in fatty-acid uptake and/or incorporation is functionally conserved, because expression of the human Sgk1 kinase rescues ypk1Delta mutant yeast. These observations suggest that Ypk1 and possibly the human Sgk1 kinase affect fatty-acid uptake and thus energy homeostasis through regulating endocytosis. Consistent with such a proposition, mutations that block early steps of endocytosis display reduced levels of fatty-acid uptake.

Membrane Fatty Acid Transporters as Regulators of Lipid Metabolism: Implications for Metabolic Disease

Long-chain fatty acids and lipids serve a wide variety of functions in mammalian homeostasis, particularly in the formation and dynamic properties of biological membranes and as fuels for energy production in tissues such as heart and skeletal muscle. On the other hand, long-chain fatty acid metabolites may exert toxic effects on cellular functions and cause cell injury. Therefore, fatty acid uptake into the cell and intracellular handling need to be carefully controlled. In the last few years, our knowledge of the regulation of cellular fatty acid uptake has dramatically increased. Notably, fatty acid uptake was found to occur by a mechanism that resembles that of cellular glucose uptake. Thus, following an acute stimulus, particularly insulin or muscle contraction, specific fatty acid transporters translocate from intracellular stores to the plasma membrane to facilitate fatty acid uptake, just as these same stimuli recruit glucose transporters to increase glucose uptake. This regulatory mechanism is important to clear lipids from the circulation postprandially and to rapidly facilitate substrate provision when the metabolic demands of heart and muscle are increased by contractile activity. Studies in both humans and animal models have implicated fatty acid transporters in the pathogenesis of diseases such as the progression of obesity to insulin resistance and type 2 diabetes. As a result, membrane fatty acid transporters are now being regarded as a promising therapeutic target to redirect lipid fluxes in the body in an organ-specific fashion.

Arabidopsis CER8 encodes LONG-CHAIN ACYL-COA SYNTHETASE 1 (LACS1) that has overlapping functions with LACS2 in plant wax and cutin synthesis

Plant cuticle is an extracellular lipid-based matrix of cutin and waxes, which covers aerial organs and protects them from many forms of environmental stress. We report here the characterization of CER8/LACS1, one of nine Arabidopsis long-chain acyl-CoA synthetases thought to activate acyl chains. Mutations in LACS1 reduced the amount of wax in all chemical classes on the stem and leaf, except in the very long-chain fatty acid (VLCFA) class wherein acids longer than 24 carbons (C(24)) were elevated more than 155%. The C(16) cutin monomers on lacs1 were reduced by 37% and 22%, whereas the C(18) monomers were increased by 28% and 20% on stem and leaf, respectively. Amounts of wax and cutin on a lacs1-1 lacs2-3 double mutant were much lower than on either parent, and lacs1-1 lacs2-3 had much higher cuticular permeability than either parent. These additive effects indicate that LACS1 and LACS2 have overlapping functions in both wax and cutin synthesis. We demonstrated that LACS1 has synthetase activity for VLCFAs C(20)-C(30), with highest activity for C(30) acids. LACS1 thus appears to function as a very long-chain acyl-CoA synthetase in wax metabolism. Since C(16) but not C(18) cutin monomers are reduced in lacs1, and C(16) acids are the next most preferred acid (behind C(30)) by LACS1 in our assays, LACS1 also appears to be important for the incorporation of C(16) monomers into cutin polyester. As such, LACS1 defines a functionally novel acyl-CoA synthetase that preferentially modifies both VLCFAs for wax synthesis and long-chain (C(16)) fatty acids for cutin synthesis.

Methods to monitor Fatty Acid transport proceeding through vectorial acylation

The process of fatty acid transport across the plasma membrane occurs by several mechanisms that involve distinct membrane-bound and membrane-associated proteins and enzymes. Among these are the fatty acid transport proteins (FATP) and long-chain acyl CoA synthetases (Acsl). Previous studies in yeast and adipocytes have shown FATP and Acsl form a physical complex at the plasma membrane and are required for fatty acid transport, which proceeds through a coupled process-linking transport with metabolic activation termed vectorial acylation. At present, six isoforms of FATP and five isoforms of ACSL have been identified in mice and man. In addition, there are a number of splice variants of different FATP and Acsl isoforms. The different FATP and Acsl isoforms have distinct tissue expression profiles and different cellular locations suggesting they function in the channeling of fatty acids into discrete metabolic pools. The concerted activity of these proteins is proposed to allow cells to discriminate different classes of fatty acids and provides the mechanistic basis underpinning the selectivity and specificity of the fatty acid transport process.

Transcriptome analysis reveals new insight into appressorium formation and function in the rice blast fungus Magnaporthe oryzae

BACKGROUND

Rice blast disease is caused by the filamentous Ascomycetous fungus Magnaporthe oryzae and results in significant annual rice yield losses worldwide. Infection by this and many other fungal plant pathogens requires the development of a specialized infection cell called an appressorium. The molecular processes regulating appressorium formation are incompletely understood.

RESULTS

We analyzed genome-wide gene expression changes during spore germination and appressorium formation on a hydrophobic surface compared to induction by cAMP. During spore germination, 2,154 (approximately 21%) genes showed differential expression, with the majority being up-regulated. During appressorium formation, 357 genes were differentially expressed in response to both stimuli. These genes, which we refer to as appressorium consensus genes, were functionally grouped into Gene Ontology categories. Overall, we found a significant decrease in expression of genes involved in protein synthesis. Conversely, expression of genes associated with protein and amino acid degradation, lipid metabolism, secondary metabolism and cellular transportation exhibited a dramatic increase. We functionally characterized several differentially regulated genes, including a subtilisin protease (SPM1) and a NAD specific glutamate dehydrogenase (Mgd1), by targeted gene disruption. These studies revealed hitherto unknown findings that protein degradation and amino acid metabolism are essential for appressorium formation and subsequent infection.

CONCLUSION

We present the first comprehensive genome-wide transcript profile study and functional analysis of infection structure formation by a fungal plant pathogen. Our data provide novel insight into the underlying molecular mechanisms that will directly benefit efforts to identify fungal pathogenicity factors and aid the development of new disease management strategies.