Lipids and Trehalose Actively Cooperate in Heat Stress Management of Schizosaccharomyces pombe

Homeostatic maintenance of the physicochemical properties of cellular membranes is essential for life. In yeast, trehalose accumulation and lipid remodeling enable rapid adaptation to perturbations, but their crosstalk was not investigated. Here we report about the first in-depth, mass spectrometry-based lipidomic analysis on heat-stressed Schizosaccharomyces pombe mutants which are unable to synthesize (tps1Δ) or degrade (ntp1Δ) trehalose. Our experiments provide data about the role of trehalose as a membrane protectant in heat stress. We show that under conditions of trehalose deficiency, heat stress induced a comprehensive, distinctively high-degree lipidome reshaping in which structural, signaling and storage lipids acted in concert. In the absence of trehalose, membrane lipid remodeling was more pronounced and increased with increasing stress dose. It could be characterized by decreasing unsaturation and increasing acyl chain length, and required de novo synthesis of stearic acid (18:0) and very long-chain fatty acids to serve membrane rigidification. In addition, we detected enhanced and sustained signaling lipid generation to ensure transient cell cycle arrest as well as more intense triglyceride synthesis to accommodate membrane lipid-derived oleic acid (18:1) and newly synthesized but unused fatty acids. We also demonstrate that these changes were able to partially substitute for the missing role of trehalose and conferred measurable stress tolerance to fission yeast cells.

Membrane lipid and osmolyte readjustment in the alkaliphilic micromycete Sodiomyces tronii under cold, heat and osmotic shocks

Previously, we showed for the first time that alkaliphilic fungi, in contrast to alkalitolerant fungi, accumulated trehalose under extremely alkaline conditions, and we have proposed its key role in alkaliphilia. We propose that high levels of trehalose in the mycelium of alkaliphiles may promote adaptation not only to alkaline conditions, but also to other stressors. Therefore, we studied changes in the composition of osmolytes, and storage and membrane lipids under the action of cold (CS), heat (HS) and osmotic (OS) shocks in the obligate alkaliphilic micromycete Sodiomyces tronii. During adaptation to CS, an increase in the degree of unsaturation of phospholipids was observed while the composition of osmolytes, membrane and storage lipids remained the same. Under HS conditions, a twofold increase in the level of trehalose and an increase in the proportion of phosphatidylethanolamines were observed against the background of a decrease in the proportion of phosphatidic acids. OS was accompanied by a decrease in the amount of membrane lipids, while their ratio remained unchanged, and an increase in the level of polyols (arabitol and mannitol) in the fungal mycelium, which suggests their role for adaptation to OS. Thus, the observed consistency of the composition of membrane lipids suggests that trehalose can participate in adaptation not only to extremely alkaline conditions, but also to other stressors – HS, CS and OS. Taken together, the data obtained indicate the adaptability of the fungus to the action of various stressors, which can point to polyextremotolerance.

The Unfolded Protein Response as a Guardian of the Secretory Pathway

The endoplasmic reticulum (ER) is the major site of membrane biogenesis in most eukaryotic cells. As the entry point to the secretory pathway, it handles more than 10,000 different secretory and membrane proteins. The insertion of proteins into the membrane, their folding, and ER exit are affected by the lipid composition of the ER membrane and its collective membrane stiffness. The ER is also a hotspot of lipid biosynthesis including sterols, glycerophospholipids, ceramides and neural storage lipids. The unfolded protein response (UPR) bears an evolutionary conserved, dual sensitivity to both protein-folding imbalances in the ER lumen and aberrant compositions of the ER membrane, referred to as lipid bilayer stress (LBS). Through transcriptional and non-transcriptional mechanisms, the UPR upregulates the protein folding capacity of the ER and balances the production of proteins and lipids to maintain a functional secretory pathway. In this review, we discuss how UPR transducers sense unfolded proteins and LBS with a particular focus on their role as guardians of the secretory pathway.

The Unfolded Protein Response as Guardian of the Secretory Pathway

The endoplasmic reticulum (ER) is the major site of membrane biogenesis in most eukaryotic cells. As the entry point to the secretory pathway, it handles more than 10.000 different secretory and membrane proteins. The membrane insertion of proteins, their folding, and ER exit are affected by the lipid composition of the ER membrane and its collective membrane stiffness. The ER is also a hotspot of lipid metabolism for membrane lipids including sterols, glycerophospholipids, ceramides and neural storage lipids. The unfolded protein response (UPR) bears an evolutionary conserved, dual sensitivity to both protein folding-imbalances in the ER lumen and aberrant compositions of the ER membrane, referred to as lipid bilayer stress (LBS). Through transcriptional and non-transcriptional mechanisms, the UPR upregulates the protein folding capacity of the ER and balances the production of proteins and lipids to maintain a functional secretory pathway. In this review, we discuss how UPR transducers sense unfolded proteins and LBS with a particular focus on their role as guardians of the secretory pathway.

Lipidomic profiling reveals biosynthetic relationships between phospholipids and diacylglycerol ethers in the deep-sea soft coral Paragorgia arborea

The cold-water gorgonian coral Paragorgia arborea is considered as a foundation species of deep-sea ecosystems in the northern Atlantic and Pacific oceans. To advance lipidomic studies of deep-sea corals, molecular species compositions of diacylglycerol ethers (DAGE), which are specific storage lipids of corals, and structural glycerophospholipids (GPL) including ethanolamine, choline, inositol and serine GPL (PE, PC, PI, and PS, respectively) were analyzed in P. arborea by HPLC and tandem mass spectrometry. In DAGE molecules, alkyl groups (16:0, 14:0, and 18:1), polyunsaturated fatty acids (PUFA), and monounsaturated FA are mainly substituted the glycerol moiety at position sn-1, sn-2, and sn-3, respectively. The ether form (1-O-alkyl-2-acyl) predominates in PE and PC, while PI is comprised of the 1,2-diacyl form. Both ether and diacyl forms were observed in PS. At position sn-2, C20 PUFA are mainly attached to PC, but C24 PUFA, soft coral chemotaxonomic markers, concentrate in PS, PI, and PE. A comparison of non-polar parts of molecules has shown that DAGE, ether PE, and ether PC can originate from one set of 1-O-alkyl-2-acyl-sn-glycerols. Ether PE may be converted to ether PS by the base-exchange reaction. A diacylglycerol unit generated from phosphatidic acid can be a precursor for diacyl PS, PC, and PI. Thus, a lipidomic approach has confirmed the difference in biosynthetic origins between ether and diacyl lipids of deep-sea gorgonians.

Different DGAT1s show different TAG synthesis abilities and a specific amino acid substitution enhances oil accumulation

Triacylglycerols (TAGs) are the major component of plant storage lipids. Acyl-CoA:diacylglycerol acyltransferase (DGAT) catalyzes the final step of the Kennedy pathway, and responsible for plant oil accumulation. We previously found DGAT activity of Vernonia galamensis DGAT1 was distinctively higher than that of Arabidopsis thaliana DGAT1 and soybean DGAT1 in a yeast microsome assay. In this study, the DGAT1 cDNAs of Arabidopsis, Vernonia, soybean, and castor were introduced into Arabidopsis (ecotype Col-0). All Vernonia DGAT1 expressing lines showed a significantly higher oil content (average 49% relative increase compared to the wild type) followed by soybean, and castor. Most Arabidopsis DGAT1 over-expressing lines did not show a significant increase. In addition to these four DGAT1s, sunflower, Jatropha and sesame DGAT1 genes were introduced into the TAG biosynthesis defective yeast mutant (H1246). In the yeast expression culture, DGAT1s from Arabidopsis, castor, and soybean only slightly increased TAG content, however, DGAT1s from Vernonia, sunflower, Jatropha, and sesame remarkably increased TAG content more than 10 times higher than the former three DGAT1s. Three amino acid residues were characteristically common in the latter four DGAT1s. Using soybean DGAT1, these amino acid substitutions by site-directed mutagenesis was performed and analyzed. These substitutions substantially increased the TAG content.HighlightDGAT1s from several plant species were tested their TAG accumulation promotion in Arabidopsis and yeast. They were divided into high and low function and single amino acid substitution enhanced function

The Role of Sch9 and the V-ATPase in the Adaptation Response to Acetic Acid and the Consequences for Growth and Chronological Lifespan

Studies with Saccharomyces cerevisiae indicated that non-physiologically high levels of acetic acid promote cellular acidification, chronological aging, and programmed cell death. In the current study, we compared the cellular lipid composition, acetic acid uptake, intracellular pH, growth, and chronological lifespan of wild-type cells and mutants lacking the protein kinase Sch9 and/or a functional V-ATPase when grown in medium supplemented with different acetic acid concentrations. Our data show that strains lacking the V-ATPase are especially more susceptible to growth arrest in the presence of high acetic acid concentrations, which is due to a slower adaptation to the acid stress. These V-ATPase mutants also displayed changes in lipid homeostasis, including alterations in their membrane lipid composition that influences the acetic acid diffusion rate and changes in sphingolipid metabolism and the sphingolipid rheostat, which is known to regulate stress tolerance and longevity of yeast cells. However, we provide evidence that the supplementation of 20 mM acetic acid has a cytoprotective and presumable hormesis effect that extends the longevity of all strains tested, including the V-ATPase compromised mutants. We also demonstrate that the long-lived sch9Δ strain itself secretes significant amounts of acetic acid during stationary phase, which in addition to its enhanced accumulation of storage lipids may underlie its increased lifespan.

The role of lipid droplets in microbial pathogenesis

The nonpolar lipids present in cells are mainly triacylglycerols and steryl esters. When cells are provided with an abundance of nutrients, these storage lipids accumulate. As large quantities of nonpolar lipids cannot be integrated into membranes, they are isolated from the cytosolic environment in lipid droplets. As specialized, inducible cytoplasmic organelles, lipid droplets have functions beyond the regulation of lipid metabolism, in cell signalling and activation, membrane trafficking and control of inflammatory mediator synthesis and secretion. Pathogens, including fungi, viruses, parasites, or intracellular bacteria can induce and may benefit from lipid droplets in infected cells. Here we review biogenesis of lipid droplets as well as the role of lipid droplets in the pathogenesis of selected viruses, bacteria, protists and yeasts.