Molecular species composition of plant cardiolipin determined by liquid chromatography mass spectrometry

Electrophoresis-enhanced paper spray mass spectrometry

The development of ambient ionization methods, such as paper spray (PS), has streamlined the transition from a collection of molecules in a condensed-phase sample to the gas-phase ions represented in a mass spectrum. In many cases, time and resources are saved by omitting chromatography and sample preparation; yet this strategy also eliminates the opportunity to process mixtures in the condensed phase. We here report a PS method that, without additional hardware or expertise, enhances mass spectrometry (MS) analysis of mixtures through electrophoresis. By loading analyte solution onto pre-wetted paper and applying spray potential, analytes were spatiotemporally processed according to their electrophoretic mobility before being subjected to MS. The fundamental and analytical aspects of this electrophoresis-enhanced PS (EePS) were probed with polarity switching, pH changes, complex environmental matrices, and a variety of analytes, including natural products obtained directly from plant material, without chromatography. EePS provides only modest separations but exhibits wide pH tolerance, high compatibility with complex environmental matrices, excellent robustness, superb cost-effectiveness, and is amenable to novel mass analysis strategies using portable mass spectrometers in situ.

Qualitative and quantitative lipidomic profiling of cardiolipin, oxidized cardiolipin, and monolysocardiolipin from human skeletal muscle by UPLC-Orbitrap-MSn

BACKGROUND

Cardiolipins (CL) are a mitochondria-specific family of phospholipids that play central roles in mitochondrial function. Imbalance in CL metabolism, especially excessive CL oxidation, leads to mitochondrial dysfunction, apoptosis, and inflammation, contributing to age-related diseases. As of yet no comprehensive methods have been developed to assess CL, oxidized CL (oxCL), and monolyso-CL (MLCL) species.

RESULTS

To fill this critical research gap, we combined untargeted and targeted lipidomic approaches to analyze CL species in human skeletal muscle samples. The method enabled in-depth structural characterization using exact mass measurement followed by multistage fragmentation (MSn) to achieve unequivocal structural elucidation at the molecular species level and sn-position level for some species. This novel methodology identified intact mono- and di-oxygenated L4CL species and allowed the differentiation of isomeric 9/13-HODE-L3CL and 9(10)/12(13)-EpOME-L3CL with unprocessed total lipid extracts. Overall, 220 molecular species (125 CL, 30 oxCL, and 65 MLCL) were detected. Our method includes a quantitation strategy that leveraged on establishing three-leveled matrix-matched calibration curves normalized by using internal standard M4CL and its isotopologues M+1 (13C-M4CL) and M+3 (13C3-M4CL) respectively. The analytical performance was also evaluated and found to be highly sensitive with LLOQs at fmol levels and reproducible with precision RSD <20 % for the majority.

SIGNIFICANCE AND NOVELTY

This is the first reported method to simultaneously provide broad coverage of CL, oxCL, and MLCL species from a single injection of total lipid extract in a complex biological sample. This method is also the first to demonstrate the presence of sn-positional isomers of CL in human skeletal muscle. It has been successfully applied to a pilot study of skeletal muscle biopsies and provided meaningful results. We anticipate the methodology will facilitate investigations of the cardiolipin lipidome leading to a better understanding of the complex and highly interactive biological processes that regulate mitochondria function and expand minor cardiolipin targets including oxCL and MLCL for biomarker discovery.

Lipidomic profiling reveals the protective mechanism of nitrogen-controlled atmosphere on brown rice quality during storage

Rice, a globally important staple, requires effective preservation methods to maintain its quality during extended storage. This study explored the efficacy of nitrogen-controlled atmosphere (NCA) storage in preserving the quality of brown rice during a one-year period using UHPLC-MS/MS based lipidomic profiling. A total of 1013 lipids were identified and categorized into five main groups. Specific lipids including triglycerides (TG), diglycerides (DG), phosphatidylethanolamines (PE), cardiolipins (CL), and ceramides (Cer), were highlighted as potential biomarkers for assessing rice rancidity. NCA storage significantly suppressed lipase and lipoxygenase activities, reducing lipid hydrolysis and oxidation to effectively delayed rice quality deterioration. Furthermore, NCA regulated glycerolipid and glycerophospholipid metabolisms, promoting lipid remodeling while reducing the degradation of TGs and phospholipids. This regulation preserved cellular membrane integrity, limited fatty acid release, and mitigate rancidity and quality loss during storage. These findings elucidate the mechanism by which NCA storage delays deterioration and extends the stored rice shelf-life.

Ferrostatin supplementation improves microalgal activities and nutrient removal in wastewater under high temperature shock: From ferroptosis-like inhibition to enhanced oxidation resistance

High temperature (HT) shock is one of environmental stressors suppressing microalgal activities in microalgal wastewater bioremediation system. However, its inhibition mechanism and how to alleviate such suppression remain inadequately understood. This study confirmed a transient ferroptosis as a novel form of programmed cell death in a wastewater-indigenous Chlorella sp., responding to a 30-minute HT (50 °C) exposure, through the systematically physiological, metabolomic and transcriptomic analysis. Specifically, the HT-induced ferroptosis could be supported by both the growth and physiological indicators. These include the suppressed growth (76.05 %), suppressed nutrient removals (NH4+-N by 76.22 %, PO43--P by 64.15 %), accumulated intracellular Fe3+ concentrations (7.75-fold), enhanced oxidative stress (e.g., increased levels of reactive oxygen species (159.97 %)), activated antioxidant defense system (e.g., increased activities of superoxide dismutase (24.83 %) and catalase (5.03-fold)), and obvious membrane damage (e.g., increased levels of malondialdehyde (1.67-fold)). Further metabolomic analysis indicated that such HT-induced ferroptosis was also largely related to the significant alternations of lipid remodeling in three aspects: varied abundance of certain lipids specific to chloroplast membrane or mitochondria, accumulation of certain lipids with lower unsaturation, and formation of lipid peroxides disrupting membrane integrity. Moreover, the key genes involved in ferroptosis correspondingly responded, especially those associated with lipid metabolism (e.g., ACSL), antioxidant defense system (e.g., GSS, GPX and GSR), mitochondrial normal functioning (e.g., SEL1L), autophagy regulation (e.g., ATG9, ATG11, ATG13) and protein folding (e.g., HSPA5, HSPA1s, HSP90B). In addition, the supplementation of the typical ferroptosis inhibitor Ferrostatin-1 effectively mitigated lipid peroxide accumulation and suppressed the onset of ferroptosis, accelerating subsequent recovery of NH4+-N removal by 60.66 %. These findings update current understandings of microalgal ferroptosis-like inhibition, offering Ferrostatin-1 supplementation as a potential strategy for system resistance to heat stress in microalgae-based bioremediation system.

Setting the curve: the biophysical properties of lipids in mitochondrial form and function

Mitochondrial membranes are defined by their diverse functions, complex geometries, and unique lipidomes. In the inner mitochondrial membrane, highly curved membrane folds known as cristae house the electron transport chain and are the primary sites of cellular energy production. The outer mitochondrial membrane is flat by contrast, but is critical for the initiation and mediation of processes key to mitochondrial physiology: mitophagy, interorganelle contacts, fission and fusion dynamics, and metabolite transport. While the lipid composition of both the inner mitochondrial membrane and outer mitochondrial membrane have been characterized across a variety of cell types, a mechanistic understanding for how individual lipid classes contribute to mitochondrial structure and function remains nebulous. In this review, we address the biophysical properties of mitochondrial lipids and their related functional roles. We highlight the intrinsic curvature of the bulk mitochondrial phospholipid pool, with an emphasis on the nuances surrounding the mitochondrially-synthesized cardiolipin. We also outline emerging questions about other lipid classes - ether lipids, and sterols - with potential roles in mitochondrial physiology. We propose that further investigation is warranted to elucidate the specific properties of these lipids and their influence on mitochondrial architecture and function.

Impact of acute heat stress on mitochondrial function, ultrastructure and cardiolipin distribution in Arabidopsis

Besides providing energy to sustain life, mitochondria also play crucial roles in stress response and programmed cell death. The mitochondrial hallmark lipid, cardiolipin (CL), is essential to the maintenance of mitochondrial structure and function. However, how mitochondria and CL are involved in stress response is not as well defined in plants as in animal and yeast cells. We previously revealed a role for CL in mitochondrial fission and in heat stress response in Arabidopsis. To further determine the involvement of mitochondria and CL in plant heat response, here we treated Arabidopsis seedlings with varied lengths of acute heat stress. These treatments resulted in decreases in mitochondrial membrane potential, disruption of mitochondrial ultrastructure, accumulation of mitochondrial reactive-oxygen species (ROS), and redistribution of CL to the outer mitochondrial membrane and to a novel type of vesicle. The level of the observed changes correlated with the severeness of the heat stress, indicating the strong relevance of these processes to stress response. Our findings provide the basis for studying mechanisms underpinning the role of mitochondria and CL in plant stress response.

Analysis of glycosylated cardiolipins from thermophilic bacteria using GC-MS and LC-ESI-MS/MS methods

Unusual glucose-substituted cardiolipins (Glcx-CLs) in three genera of thermophilic bacteria, having more than one glycosidically linked glucose to the hydroxyl of the central glycerol of Glcx-CLs were identified for the first time in thermophilic bacteria of the genera Geobacillus, Meiothermus, and Thermus. The number of glucoses reached up to five units. The structure of glycosidically linked oligosaccharides was determined based on shotgun analysis MS (electrospray high-resolution tandem mass spectrometry), partially methylated alditol acetates were identified by GC-MS, both electron ionization (EI) and positive chemical ionization (PCI), hydrophilic interaction liquid chromatography (HILIC) separation and identification of CLs glycosides by high resolution MS-ESI, and digestion by specific glycosidases.

Can cardiolipins be used as a biomarker for arbuscular mycorrhizal fungi?

Specific biomarker molecules are increasingly being used for detection and quantification in plant and soil samples of arbuscular mycorrhizal (AM) fungi, an important and widespread microbial guild heavily implicated in transfers of nutrients and carbon between plants and soils and in the maintenance of soil physico-chemical properties. Yet, concerns have previously been raised as to the validity of a range of previously used approaches (e.g., microscopy, AM-specific fatty acids, sterols, glomalin-like molecules, ribosomal DNA sequences), justifying further research into novel biomarkers for AM fungal abundance and/or functioning. Here, we focused on complex polar lipids contained in pure biomass of Rhizophagus irregularis and in nonmycorrhizal and mycorrhizal roots of chicory (Cichorium intybus), leek (Allium porrum), and big bluestem (Andropogon gerardii). The lipids were analyzed by shotgun lipidomics using a high-resolution hybrid mass spectrometer. Size range between 1350 and 1550 Da was chosen for the detection of potential biomarkers among cardiolipins (1,3-bis(sn-3'-phosphatidyl)-sn-glycerols), a specific class of phospholipids. The analysis revealed a variety of molecular species, including cardiolipins containing one or two polyunsaturated fatty acids with 20 carbon atoms each, i.e., arachidonic and/or eicosapentaenoic acids, some of them apparently specific for the mycorrhizal samples. Although further verification using a greater variety of AM fungal species and samples from various soils/ecosystems/environmental conditions is needed, current results suggest the possibility to identify novel biochemical signatures specific for AM fungi within mycorrhizal roots. Whether they could be used for quantification of both root and soil colonization by the AM fungi merits further scrutiny.

Cytidine diphosphate diacylglycerol synthase is essential for mitochondrial structure and energy production in Arabidopsis thaliana

Cytidine diphosphate diacylglycerol (CDP-DAG), an important intermediate for glycerolipid biosynthesis, is synthesized under the catalytic activity of CDP-DAG synthase (CDS) to produce anionic phosphoglycerolipids such as phosphatidylglycerol (PG) and cardiolipin (CL). Previous studies showed that Arabidopsis CDSs are encoded by a small gene family, termed CDS1-CDS5, the members of which are integral membrane proteins in endoplasmic reticulum (ER) and in plastids. However, the details on how CDP-DAG is provided for mitochondrial membrane-specific phosphoglycerolipids are missing. Here we present the identification of a mitochondrion-specific CDS, designated CDS6. Enzymatic activity of CDS6 was demonstrated by the complementation of CL synthesis in the yeast CDS-deficient tam41Δ mutant. The Arabidopsis cds6 mutant lacking CDS6 activity showed decreased mitochondrial PG and CL biosynthesis capacity, a severe growth deficiency finally leading to plant death. These defects were rescued partly by complementation with CDS6 or supplementation with PG and CL. The ultrastructure of mitochondria in cds6 was abnormal, missing the structures of cristae. The degradation of triacylglycerol (TAG) in lipid droplets and starch in chloroplasts in the cds6 mutant was impaired. The expression of most differentially expressed genes involved in the mitochondrial electron transport chain was upregulated, suggesting an energy-demanding stage in cds6. Furthermore, the contents of polar glycerolipids in cds6 were dramatically altered. In addition, cds6 seedlings lost the capacity for cell proliferation and showed a higher oxidase activity. Thus, CDS6 is indispensable for the biosynthesis of PG and CL in mitochondria, which is critical for establishing mitochondrial structure, TAG degradation, energy production and seedling development.

Cardiolipin released by microglia can act on neighboring glial cells to facilitate the uptake of amyloid-β (1-42)

Cardiolipin is a mitochondrial phospholipid that is also detected in serum inferring its extracellular release; however, this process has not been directly demonstrated for any of the brain cell types. Nevertheless, extracellular cardiolipin has been shown to modulate several neuroimmune functions of microglia and astrocytes, including upregulation of their endocytic activity. Low cardiolipin levels are associated with brain aging, and may thus hinder uptake of amyloid-β (Αβ) in Alzheimer's disease. We hypothesized that glial cells are one of the sources of extracellular cardiolipin in the brain parenchyma where this phospholipid interacts with neighboring cells to upregulate the endocytosis of Αβ. Liquid chromatography-mass spectrophotometry identified 31 different species of cardiolipin released from murine BV-2 microglial cells and revealed this process was accelerated by exposure to Aβ42. Extracellular cardiolipin upregulated internalization of fluorescently-labeled Aβ42 by primary murine astrocytes, human U118 MG astrocytic cells, and murine BV-2 microglia. Increased endocytic activity in the presence of extracellular cardiolipin was also demonstrated by studying uptake of Aβ42 and pHrodo™ Bioparticles™ by human induced pluripotent stem cells (iPSCs)-derived microglia, as well as iPSC-derived human brain organoids containing microglia, astrocytes, oligodendrocytes and neurons. Our observations indicate that Aβ42 augments the release of cardiolipin from microglia into the extracellular space, where it can act on microglia and astrocytes to enhance their endocytosis of Aβ42. Our observations suggest that the reduced glial uptake of Aβ due to the decreased levels of cardiolipin could be at least partially responsible for the extracellular accumulation of Aβ in aging and Alzheimer's disease.

Exogenous fatty acids affect membrane properties and cold adaptation of Listeria monocytogenes

Listeria monocytogenes is a food-borne pathogen that can grow at very low temperatures close to the freezing point of food and other matrices. Maintaining cytoplasmic membrane fluidity by changing its lipid composition is indispensable for growth at low temperatures. Its dominant adaptation is to shorten the fatty acid chain length and, in some strains, increase in addition the menaquinone content. To date, incorporation of exogenous fatty acid was not reported for Listeria monocytogenes. In this study, the membrane fluidity grown under low-temperature conditions was affected by exogenous fatty acids incorporated into the membrane phospholipids of the bacterium. Listeria monocytogenes incorporated exogenous fatty acids due to their availability irrespective of their melting points. Incorporation was demonstrated by supplementation of the growth medium with polysorbate 60, polysorbate 80, and food lipid extracts, resulting in a corresponding modification of the membrane fatty acid profile. Incorporated exogenous fatty acids had a clear impact on the fitness of the Listeria monocytogenes strains, which was demonstrated by analyses of the membrane fluidity, resistance to freeze-thaw stress, and growth rates. The fatty acid content of the growth medium or the food matrix affects the membrane fluidity and thus proliferation and persistence of Listeria monocytogenes in food under low-temperature conditions.

In-silico-library-based method enables rapid and comprehensive annotation of cardiolipins and cardiolipin oxidation products using high resolution tandem mass spectrometer

Accumulated evidences suggest that cardiolipins (CLs) and cardiolipin oxidation products (oxCLs) are a class of essential molecules that play critical roles in many physiological functions. Diversity of four acyl chains leads to high structure complexity for cardiolipin species including CLs, monolysocardiolipins (MLCLs) and their oxCLs. The ability to rapidly identify CL species can be implemented by the match of mass spectrometry (MS)-based in-silico spectral database. In this study, after optimizing the chromatography conditions and MS detection, an in-silico library containing 377,754 simulated tandem mass spectra deducing from 31,578 CLs to 52,160 of MLCLs was successfully augmented based on LipidBlast templates. For the construction of the oxCLs' library, twenty-five fatty acyls oxidation products relating to nine oxidation types were permuted and combined. A total of 42,180 oxCL spectra were predicted based on the experimental measurements of oxCLs forming by artificially oxidation. Applying the in-silico database to murine mitochondria and cell samples enabled the sensitive and comprehensive annotation of 86 MLCLs, 307 CLs and 112 oxCLs with high annotation confidence. Compared to the conventional method, our proposed in-silico database provides a more comprehensive interpretation for CL species' characterization with high throughput and sensitivity in nontarget lipidomic study.

The biosynthesis of phospholipids is linked to the cell cycle in a model eukaryote

The structural challenges faced by eukaryotic cells through the cell cycle are key for understanding cell viability and proliferation. We tested the hypothesis that the biosynthesis of structural lipids is linked to the cell cycle. If true, this would suggest that the cell's structure is important for progress through and perhaps even control of the cell cycle. Lipidomics (31P NMR and MS), proteomics (Western immunoblotting) and transcriptomics (RT-qPCR) techniques were used to profile the lipid fraction and characterise aspects of its metabolism at seven stages of the cell cycle of the model eukaryote, Desmodesmus quadricauda. We found considerable, transient increases in the abundance of phosphatidylethanolamine during the G1 phase (+35%, ethanolamine phosphate cytidylyltransferase increased 2·5×) and phosphatidylglycerol (+100%, phosphatidylglycerol synthase increased 22×) over the G1/pre-replication phase boundary. The relative abundance of phosphatidylcholine fell by ~35% during the G1. N-Methyl transferases for the conversion of phosphatidylethanolamine into phosphatidylcholine were not found in the de novo transcriptome profile, though a choline phosphate transferase was found, suggesting that the Kennedy pathway is the principal route for the synthesis of PC. The fatty acid profiles of the four most abundant lipids suggested that these lipids were not generally converted between one another. This study shows for the first time that there are considerable changes in the biosynthesis of the three most abundant phospholipid classes in the normal cell cycle of D. quadricauda, by margins large enough to elicit changes to the physical properties of membranes.

Detailed structural characterization of cardiolipins from various biological sources using a complex analytical strategy comprising fractionation, hydrolysis and chiral chromatography

Cardiolipins (1,3-bis(sn-3'-phosphatidyl)-sn-glycerol) (CLs) are widespread in many organisms, from bacteria to higher green plants and mammals. CLs were observed in Gram-positive bacterium of the genus Kocuria, brewer's yeast Saccharomyces, the green alga Chlamydomonas, spinach and beef heart. A mixture of molecular species of CLs was obtained from total lipids by hydrophilic interaction liquid chromatography (HILIC), and these were further separated and identified by reversed phase LC/MS with negative tandem electrospray ionization. The majority of CLs molecular species from each organism were cleaved using phospholipase C from Bacillus cereus. This phospholipase cleaves CLs into 1,2-diglycerols and phosphatidylglycerol 3-phosphates, which were then separated. After CLs cleavage, diacylglycerols such as sn-1,2-diacyl-3-acetyl-glycerols (i.e., triacylglycerols) were separated and identified by chiral chromatography/MS-positive tandem ESI. Significant differences in the composition of the molecular species between the 3-(3-sn-phosphatidyl) and 1-(3-sn-phosphatidyl) moieties of CLs were found in all organisms tested. Molecular species of CLs that contained four different fatty acids were identified in all five samples, and CLs containing very long chain fatty acids were identified in yeast. In addition, CLs containing both enantiomers (at the sn-2 carbon) were present in the bacterium tested. These findings were further supported by data already published in GenBank where, in the same family - Micrococcaceae - both enzymes responsible for chirality in the sn-2 position, glycerol-3-phosphate and glycerol-1-phosphate dehydrogenases, were present.

Membrane dynamics during individual and combined abiotic stresses in plants and tools to study the same

The plasma membrane (PM) is possibly the most diverse biological membrane of plant cells; it separates and guards the cell against its external environment. It has an extremely complex structure comprising a mosaic of lipids and proteins. The PM lipids are responsible for maintaining fluidity, permeability and integrity of the membrane and also influence the functioning of membrane proteins. However, the PM is the primary target of environmental stress, which affects its composition, conformation and properties, thereby disturbing the cellular homeostasis. Maintenance of integrity and fluidity of the PM is a prerequisite for ensuring the survival of plants during adverse environmental conditions. The ability of plants to remodel membrane lipid and protein composition plays a crucial role in adaptation towards varying abiotic environmental cues, including high or low temperature, drought, salinity and heavy metals stress. The dynamic changes in lipid composition affect the functioning of membrane transporters and ultimately regulate the physical properties of the membrane. Plant membrane-transport systems play a significant role in stress adaptation by cooperating with the membrane lipidome to maintain the membrane integrity under stressful conditions. The present review provides a holistic view of stress responses and adaptations in plants, especially the changes in the lipidome and proteome of PM under individual or combined abiotic stresses, which cause alterations in the activity of membrane transporters and modifies the fluidity of the PM. The tools to study the varying lipidome and proteome of the PM are also discussed.

Targeted Analysis of the Plant Lipidome by UPLC-NanoESI-MS/MS

The plant lipidome is highly complex and changes dynamically under the influence of various biotic and abiotic stresses. Targeted analyses based on mass spectrometry enable the detection and characterization of the plant lipidome. It can be analyzed in plant tissues of different developmental stages and from isolated cellular organelles and membranes. Here, we describe a sensitive method to establish the relative abundance of molecular lipid species belonging to three lipid categories: glycerolipids, sphingolipids, and sterol lipids. The method is based on a monophasic lipid extraction and includes the derivatization of a few rare and low-abundant lipid classes. The molecular lipid species are resolved by lipid class-specific reverse-phase liquid chromatography and detected by nanoelectrospray ionization coupled with tandem mass spectrometry. The triple quadrupole analyzer is used for detection with multiple reaction monitoring (MRM). Mass transition lists are constructed based on the knowledge of organism-specific lipid building blocks. They are initially determined by classical lipid analytical methods and then used for combinative assembly of all possible lipid structures. The targeted analysis enables detailed and comprehensive profiling of the entire lipid content and composition of plants.

Liquid Chromatography-Mass Spectrometry (LC-MS)-Based Analysis for Lipophilic Compound Profiling in Plants

Lipids are fascinating due to their chemical diversity, which is especially vast in the plant kingdom thanks to the high plasticity of the plant biosynthetic machinery. Lipidomic studies aim to simultaneously analyze a large number of lipid compounds of diverse classes in a given sample. The method presented here uses liquid chromatography-mass spectrometry (LC-MS)-based lipidomic profiling in a relatively fast, robust, and high-throughput manner for high-coverage quantification and annotation of lipophilic compounds. Protocols cover sample preparation, LC-MS-based measurement, and data extraction and annotation. An extensive lipid library for triacylglycerols, galactolipids, and phospholipids is provided. The extended profiling described here could be used in a range of applications and is suitable for integration with other omic datasets. © 2020 by John Wiley & Sons, Inc. Basic Protocol 1: Sample preparation and metabolite extraction Basic Protocol 2: Liquid chromatography-mass spectrometry (LC-MS) analysis Basic Protocol 3: Data extraction, annotation, and quantification.

Towards model-driven characterization and manipulation of plant lipid metabolism

Plant lipids have versatile applications and provide essential fatty acids in human diet. Therefore, there has been a growing interest to better characterize the genetic basis, regulatory networks, and metabolic pathways that shape lipid quantity and composition. Addressing these issues is challenging due to context-specificity of lipid metabolism integrating environmental, developmental, and tissue-specific cues. Here we systematically review the known metabolic pathways and regulatory interactions that modulate the levels of storage lipids in oilseeds. We argue that the current understanding of lipid metabolism provides the basis for its study in the context of genome-wide plant metabolic networks with the help of approaches from constraint-based modeling and metabolic flux analysis. The focus is on providing a comprehensive summary of the state-of-the-art of modeling plant lipid metabolic pathways, which we then contrast with the existing modeling efforts in yeast and microalgae. We then point out the gaps in knowledge of lipid metabolism, and enumerate the recent advances of using genome-wide association and quantitative trait loci mapping studies to unravel the genetic regulations of lipid metabolism. Finally, we offer a perspective on how advances in the constraint-based modeling framework can propel further characterization of plant lipid metabolism and its rational manipulation.

Extracción e identificación de lípidos polares de las microalgas Nannochloropsis oceanica y Desmodesmus asymmetricus

Los lípidos polares de las microalgas son de gran interés debido a su aplicación como ingredientes naturales novedosos para las industrias cosmética, nutricional y farmacéutica. Por ello, el presente trabajo buscó determinar el efecto de los principales factores en la extracción e identificación de los lípidos polares de las microalgas Nannochloropsis oceanica y Desmodesmus asymmetricus, mediante el diseño de superficie de respuesta de Box-Behnken y el diseño factorial completo, respectivamente. Estas cepas del Banco de Germoplasma de Organismos Acuáticos (BGOA – IMARPE) fueron cultivadas en un invernadero, en biorreactores de 30 litros, centrifugadas y liofilizadas. Los lípidos fueron extraídos con cloroformo-metanol, fraccionados y analizados con un espectrómetro de masas Waters Xevo G2-XS QTOF. La maximización de la extracción de los lípidos totales determinó un valor óptimo de la relación masa-solvente de 25 mg/3 mL, una proporción 1:1 de cloroformo-metanol, aproximadamente, y un tiempo del baño de ultrasonido entre 10 y 30 min. Los principales lípidos polares identificados para N. oceanica fueron lisofosfatidilcolina (LPC), diacilgliceril-N,N,N-trimetilhomoserina (DGTS), digalactosil diacilglicerol (DGDG) y monogalactosil diacilglicerol (MGDG) y para D. asymmetricus fueron sulfoquinovosil diacilglicerol (SQDG), LDGTS, DGTS, DGDG y MGDG.

Rapid Affinity Purification of Tagged Plant Mitochondria (Mito-AP) for Metabolome and Proteome Analyses

The isolation of organelles facilitates the focused analysis of subcellular protein and metabolite pools. Here we present a technique for the affinity purification of plant mitochondria (Mito-AP). The stable ectopic expression of a mitochondrial outer membrane protein fused to a GFP:Strep tag in Arabidopsis (Arabidopsis thaliana) exclusively decorates mitochondria, enabling their selective affinity purification using magnetic beads coated with Strep-Tactin. With Mito-AP, intact mitochondria from 0.5 g plant material were highly enriched in 30-60 min, considerably faster than with conventional gradient centrifugation. Combining gradient centrifugation and Mito-AP techniques resulted in high purity of >90% mitochondrial proteins in the lysate. Mito-AP supports mitochondrial proteome analysis by shotgun proteomics. The relative abundances of proteins from distinct mitochondrial isolation methods were correlated. A cluster of 619 proteins was consistently enriched by all methods. Among these were several proteins that lack subcellular localization data or that are currently assigned to other compartments. Mito-AP is also compatible with mitochondrial metabolome analysis by triple-quadrupole and orbitrap mass spectrometry. Mito-AP preparations showed a strong enrichment with typical mitochondrial lipids like cardiolipins and demonstrated the presence of several ubiquinones in Arabidopsis mitochondria. Affinity purification of organelles is a powerful tool for reaching higher spatial and temporal resolution for the analysis of metabolomic and proteomic dynamics within subcellular compartments. Mito-AP is small scale, rapid, economic, and potentially applicable to any organelle or to organelle subpopulations.

Insights Into Oxidized Lipid Modification in Barley Roots as an Adaptation Mechanism to Salinity Stress

Lipidomics is an emerging technology, which aims at the global characterization and quantification of lipids within biological matrices including biofluids, cells, whole organs and tissues. The changes in individual lipid molecular species in stress treated plant species and different cultivars can indicate the functions of genes affecting lipid metabolism or lipid signaling. Mass spectrometry-based lipid profiling has been used to track the changes of lipid levels and related metabolites in response to salinity stress. We have developed a comprehensive lipidomics platform for the identification and direct qualification and/or quantification of individual lipid species, including oxidized lipids, which enables a more systematic investigation of peroxidation of individual lipid species in barley roots under salinity stress. This new lipidomics approach has improved with an advantage of analyzing the composition of acyl chains at the molecular level, which facilitates to profile precisely the 18:3-containing diacyl-glycerophosphates and allowed individual comparison of lipids across varieties. Our findings revealed a general decrease in most of the galactolipids in plastid membranes, and an increase of glycerophospholipids and acylated steryl glycosides, which indicate that plastidial and extraplastidial membranes in barley roots ubiquitously tend to form a hexagonal II (HII) phase under salinity stress. In addition, salt-tolerant and salt-sensitive cultivars showed contrasting changes in the levels of oxidized membrane lipids. These results support the hypothesis that salt-induced oxidative damage to membrane lipids can be used as an indication of salt stress tolerance in barley.

Saturation of acyl chains converts cardiolipin from an antagonist to an activator of Toll-like receptor-4

Cardiolipins (CLs) are tetra-acylated diphosphatidylglycerols found in bacteria, yeast, plants, and animals. In healthy mammals, CLs are unsaturated, whereas saturated CLs are found in blood cells from Barth syndrome patients and in some Gram-positive bacteria. Here, we show that unsaturated but not saturated CLs block LPS-induced NF-κB activation, TNF-α and IP-10 secretion in human and murine macrophages, as well as LPS-induced TNF-α and IL-1β release in human blood mononuclear cells. Using HEK293 cells transfected with Toll-like receptor 4 (TLR4) and its co-receptor Myeloid Differentiation 2 (MD2), we demonstrate that unsaturated CLs compete with LPS for binding TLR4/MD2 preventing its activation, whereas saturated CLs are TLR4/MD2 agonists. As a consequence, saturated CLs induce a pro-inflammatory response in macrophages characterized by TNF-α and IP-10 secretion, and activate the alternative NLRP3 inflammasome pathway in human blood-derived monocytes. Thus, we identify that double bonds discriminate between anti- and pro-inflammatory properties of tetra-acylated molecules, providing a rationale for the development of TLR4 activators and inhibitors for use as vaccine adjuvants or in the treatment of TLR4-related diseases.

Plant lipidomics at the crossroads: From technology to biology driven science

The identification and quantification of lipids from plant tissues have become commonplace and many researchers now incorporate lipidomics approaches into their experimental studies. Plant lipidomics research continues to involve technological developments such as those in mass spectrometry imaging, but in large part, lipidomics approaches have matured to the point of being accessible to the novice. Here we review some important considerations for those planning to apply plant lipidomics to their biological questions, and offer suggestions for appropriate tools and practices. This article is part of a Special Issue entitled: BBALIP_Lipidomics Opinion Articles edited by Sepp Kohlwein.

Cardiolipin Supports Respiratory Enzymes in Plants in Different Ways

In eukaryotes the presence of the dimeric phospholipid cardiolipin (CL) is limited to the mitochondrial membranes. It resides predominantly in the inner membrane where it interacts with components of the mitochondrial electron transfer chain. CL deficiency has previously been shown to affect abundances of the plant NADH-dehydrogenase complex and its association with dimeric cyctochrome c reductase. Using an Arabidopsis thaliana knock-out mutant for the final enzyme of CL biosynthesis we here extend current knowledge on the dependence of plant respiration on CL. By correlating respiratory enzyme abundances with enzymatic capacities in mitochondria isolated from wild type, CL deficient and CL complemented heterotrophic cell culture lines a new picture of the participation of CL in plant respiration is emerging. Data indicate a loss of a general reduction of respiratory capacity in CL deficient mitochondria which cannot solely be attributed to decreased abundances or capacities of mitochondrial electron transfer protein complexes and supercomplexes. Instead, it most likely is the result of a loss of the mobile electron carrier cytochrome c. Furthermore, enzymes of the tricarboxylic acid cycle are found to have lower maximum activities in the mutant, including the succinate dehydrogenase complex. Interestingly, abundance of the latter is not altered, indicative of a direct impact of CL deficiency on the enzymatic capacity of this electron transfer chain protein complex.

Glycerolipid synthesis and lipid trafficking in plant mitochondria

Lipid trafficking between mitochondria and other organelles is required for mitochondrial membrane biogenesis and signaling. This lipid exchange occurs by poorly understood nonvesicular mechanisms. In yeast and mammalian cells, this lipid exchange is thought to take place at contact sites between mitochondria and the ER or vacuolar membranes. Some proteins involved in the tethering between membranes or in the transfer of lipids in mitochondria have been identified. However, in plants, little is known about the synthesis of mitochondrial membranes. Mitochondrial membrane biogenesis is particularly important and noteworthy in plants as the lipid composition of mitochondrial membranes is dramatically changed during phosphate starvation and other stresses. This review focuses on the principal pathways involved in the synthesis of the most abundant mitochondrial glycerolipids in plants and the lipid trafficking that is required for plant mitochondria membrane biogenesis.