Enzymatic measurement of phosphatidylglycerol and cardiolipin in cultured cells and mitochondria

Teflubenzuron effects on springtail life history traits explained from impairment of its lipid metabolism

This study investigated how the insecticide teflubenzuron disrupts lipid metabolism in the springtail Folsomia candida, revealing significant alterations in lipid profiles. F. candida was exposed to sub-lethal concentrations of teflubenzuron (0, 0.006, 0.014, 0.035 mg a.s. kg-1 soil dry weight). Untargeted lipidomics was used to study the dynamic changes in lipid profiles in the springtail over exposure intervals of 2, 7, and 14 days exposure intervals. Teflubenzuron induced shifts in lipid profiles, affecting lipid pathways crucial for energy storage, membrane integrity, and signaling, which are essential for survival, reproduction, and stress responses in this springtail. Diacylglycerols (DG) and Triacylglycerols (TG), which play crucial roles in energy storage and lipid-mediated signaling, were substantially affected by teflubenzuron. Decreased levels of DG and TG suggest a shift in priorities from reproduction to maintenance functions, implying disruptions in cholesterol homeostasis and vitellogenesis in response to teflubenzuron exposure. Furthermore, increased levels of fatty acids and N-acylethanolamines in response to teflubenzuron exposure indicated increased energy production and potential oxidative stress, highlighting the springtails' response to pesticide exposure. Certain lipid alterations (N-palmitoylethanolamine (NAE 16:0) and N-stearoylethanolamine (NAE 18:0)), known for their anti-inflammatory properties, point towards inflammation and mitochondrial membrane remodeling (alternations in cardiolipin lipids), indicating broader impacts on physiological functions. Ether glycerophospholipids, such as lysophosphatidylethanolamine and phosphatidylethanolamine, linked to peroxisomes and the endoplasmic reticulum, underscore their potential antioxidative role in response to oxidative stress. The study shows the significance of incorporating life cycle events into ecotoxicological assessments to comprehensively understand pesticide impacts on organisms. The integration of lipidomics into environmental risk assessments offers a more informed approach to pesticide regulation and environmental stewardship.

Constitutively active mTORC1 signaling modifies the skeletal muscle metabolome and lipidome response to exercise

A chronic increase in the Mammalian Target of Rapamycin Complex 1 (mTORC1) signaling is implicated in reduced longevity, altered metabolism, and mitochondrial dysfunction. Abnormal mTORC1 signaling may also be involved in the etiology of sarcopenia. To better understand the role of mTORC1 signaling in the regulation of muscle metabolism, we developed an inducible muscle-specific knockout model of DEP domain-containing 5 protein (DEPDC5 mKO), which results in constitutively active mTORC1 signaling. We hypothesized that constitutively active mTORC1 signaling in skeletal muscle would alter the metabolomic and lipidomic response to an acute bout of exercise. Wild-type (WT) and DEPDC5 muscle-specific knockout (KO) mice were studied at rest and following a 1 h bout of treadmill exercise. Acute exercise induced an increased reliance on glycolytic and pentose phosphate pathway (PPP) metabolites in the muscle of mice with hyperactive mTORC1. Lipidomic analysis showed an increase in triglycerides (TGs) in KO mice. Although exercise had a pronounced effect on muscle metabolism, the genotype effect was larger, indicating that constitutively active mTORC1 signaling exerts a dominant influence on metabolic and lipidomic regulation. We conclude that increased mTORC1 signaling shifts muscle metabolism toward greater reliance on nonoxidative energy sources in response to exercise. Understanding the mechanisms responsible for these effects may lead to the development of strategies for restoring proper mTORC1 signaling in conditions such as aging and sarcopenia.NEW & NOTEWORTHY This study demonstrates that hyperactive mTORC1 alters the muscle metabolomic and lipidomic response to exercise, with genotype having a larger effect than exercise. Knockout mice exhibited an increase in reliance on glycolysis and pentose phosphate pathway and an increase in triglyceride turnover. Wild-type mice primarily showed an increase in utilization of TCA cycle and lipid metabolism intermediates.

Lipid metabolism, remodelling and intercellular transfer in the CNS

Lipid metabolism encompasses the catabolism and anabolism of lipids, and is fundamental for the maintenance of cellular homeostasis, particularly within the lipid-rich CNS. Increasing evidence further underscores the importance of lipid remodelling and transfer within and between glial cells and neurons as key orchestrators of CNS lipid homeostasis. In this Review, we summarize and discuss the complex landscape of processes involved in lipid metabolism, remodelling and intercellular transfer in the CNS. Highlighted are key pathways, including those mediating lipid (and lipid droplet) biogenesis and breakdown, lipid oxidation and phospholipid metabolism, as well as cell-cell lipid transfer mediated via lipoproteins, extracellular vesicles and tunnelling nanotubes. We further explore how the dysregulation of these pathways contributes to the onset and progression of neurodegenerative diseases, and examine the homeostatic and pathogenic impacts of environment, diet and lifestyle on CNS lipid metabolism.

Chikungunya Replication and Infection Is Dependent upon and Alters Cellular Hexosylceramide Levels in Vero Cells

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, causes significant global morbidity, including fever, rash, and persistent arthralgia. Utilizing untargeted lipidomics, we investigated how CHIKV infection alters host cell lipid metabolism in Vero cells. CHIKV infection induced marked catabolism of hexosylceramides, reducing their levels while increasing ceramide byproducts. Functional studies revealed a reliance on fatty acid synthesis, β-oxidation, and glycosphingolipid biosynthesis. Notably, inhibition of uridine diphosphate glycosyltransferase 8 (UGT8), essential for galactosylceramide production, significantly impaired CHIKV replication and entry in Vero cells. Sensitivity of CHIKV to UGT8 inhibition was reproduced in a disease-relevant cell line, mouse hepatocytes (Hepa1-6). CHIKV was also sensitive to evacetrapib, a cholesterol ester transfer protein (CETP) inhibitor, though the mechanism of inhibition appeared independent of CETP itself, suggesting an off-target effect. These findings highlight specific lipid pathways, particularly glycosphingolipid metabolism, as critical for CHIKV replication and further refine our understanding of how CHIKV exploits host lipid networks. This study provides new insights into CHIKV biology and suggests that targeted investigation of host lipid pathways may inform future therapeutic strategies.

A New Perspective on the Role of Alterations in Mitochondrial Proteins Involved in ATP Synthesis and Mobilization in Cardiomyopathies

The heart requires a continuous energy supply to sustain its unceasing contraction-relaxation cycle. Mitochondria, a double-membrane organelle, generate approximately 90% of cellular energy as adenosine triphosphate (ATP) through oxidative phosphorylation, utilizing the electrochemical gradient established by the respiratory chain. Mitochondrial function is compromised by damage to mitochondrial DNA, including point mutations, deletions, duplications, or inversions. Additionally, disruptions to proteins associated with mitochondrial membranes regulating metabolic homeostasis can impair the respiratory chain's efficiency. This results in diminished ATP production and increased generation of reactive oxygen species. This review provides an overview of mutations affecting mitochondrial transporters and proteins involved in mitochondrial energy synthesis, particularly those involved in ATP synthesis and mobilization, and it examines their role in the pathogenesis of specific cardiomyopathies.

Synthetic Lipid Biology

Cells contain thousands of different lipids. Their rapid and redundant metabolism, dynamic movement, and many interactions with other biomolecules have justly earned lipids a reputation as a vexing class of molecules to understand. Further, as the cell's hydrophobic metabolites, lipids assemble into supramolecular structures─most commonly bilayers, or membranes─from which they carry out myriad biological functions. Motivated by this daunting complexity, researchers across disciplines are bringing order to the seeming chaos of biological lipids and membranes. Here, we formalize these efforts as "synthetic lipid biology". Inspired by the idea, central to synthetic biology, that our abilities to understand and build biological systems are intimately connected, we organize studies and approaches across numerous fields to create, manipulate, and analyze lipids and biomembranes. These include construction of lipids and membranes from scratch using chemical and chemoenzymatic synthesis, editing of pre-existing membranes using optogenetics and protein engineering, detection of lipid metabolism and transport using bioorthogonal chemistry, and probing of lipid-protein interactions and membrane biophysical properties. What emerges is a portrait of an incipient field where chemists, biologists, physicists, and engineers work together in proximity─like lipids themselves─to build a clearer description of the properties, behaviors, and functions of lipids and membranes.

Sparassis latifolia polysaccharide alleviated lipid metabolism abnormalities in kidney of lead-exposed mice by regulating oxidative stress-mediated inflammation and autophagy based on multi-omics

Lead is a common environmental pollutant which can accumulate in the kidney and cause renal injury. However, regulatory effects and mechanisms of Sparassis latifolia polysaccharide (SLP) on lipid metabolism abnormality in kidney exposed to lead are not clarified. In this study, mice were used to construct an animal model to observe the histopathological changes in kidney, measure lead content, damage indicators, differentially expressed metabolites (DEMs) and genes (DEGs) in key signaling pathways that cause lipid metabolism abnormalities based on lipidomics and transcriptomics, which were later validated using qPCR and western blotting. Co-treatment of Pb and N-acetylcysteine (NAC) were used to verify the link between SLP and oxidative stress. Our results indicated that treatment with SLP identified 276 DEMs (including metabolism of glycerophospholipid, sphingolipid, glycerolipid and fatty acid) and 177 DEGs (including genes related to oxidative stress, inflammation, autophagy and lipid metabolism). Notably, regulatory effects of SLP on abnormal lipid metabolism in kidney were mainly associated with oxidative stress, inflammation and autophagy; SLP could regulate abnormal lipid metabolism in kidney by reducing oxidative stress and affecting its downstream-regulated autophagy and inflammatory to alleviate renal injury caused by lead exposure. This study provides a theoretical basis for SLP intervention in lead injury.

A change in metal cation switches selectivity of a phospholipid sensor from phosphatidic acid to phosphatidylserine

Phosphatidic acid and phosphatidylserine are anionic phospholipids with emerging signalling roles in cells. Determination of how phosphatidic acid and phosphatidylserine change location and quantity in cells over time requires selective fluorescent sensors that can distinguish these two anionic phospholipids. However, the design of such synthetic sensors that can selectively bind and respond to a single phospholipid within the complex membrane milieu remains challenging. In this work, we present a simple and robust strategy to control the selectivity of synthetic sensors for phosphatidic acid and phosphatidylserine. By changing the coordination metal of a dipicolylamine (DPA) ligand from Zn(II) to Ni(II) on the same synthetic sensor with a peptide backbone, we achieve a complete switch in selectivity from phosphatidic acid to phosphatidylserine in model lipid membranes. Furthermore, this strategy was largely unaffected by the choice and the position of the fluorophores. We envision that this strategy will provide a platform for the rational design of targeted synthetic phospholipid sensors to probe plasma and intracellular membranes.

Phospholipid biomarkers of coronary heart disease

Coronary heart disease, also known as ischemic heart disease, is induced by atherosclerosis, which is initiated by subendothelial retention of lipoproteins. Plasma lipoproteins, including high density lipoprotein, low density lipoprotein (LDL), very low density lipoprotein, and chylomicron, are composed of a surface monolayer containing phospholipids and cholesterol and a hydrophobic core containing triglycerides and cholesteryl esters. Phospholipids play a crucial role in the binding of apolipoproteins and enzymes to lipoprotein surfaces, thereby regulating lipoprotein metabolism. High LDL-cholesterol is a well-known risk factor for coronary heart disease, and statins reduce the risk of coronary heart disease by lowering LDL-cholesterol levels. In contrast, the relationships of phospholipids in plasma lipoproteins with coronary heart disease have not yet been established. To further clarify the physiological and pathological roles of phospholipids, we have developed the simple high-throughput assays for quantifying all major phospholipid classes, namely phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidic acid, phosphatidylinositol, phosphatidylglycerol + cardiolipin, and sphingomyelin, using combinations of specific enzymes and a fluorogenic probe. These enzymatic fluorometric assays will be helpful in elucidating the associations between phospholipid classes in plasma lipoproteins and coronary heart disease and in identifying phospholipid biomarkers. This review describes recent progress in the identification of phospholipid biomarkers of coronary heart disease.

Exploring the Relationship Among Lipid Profile Changes, Growth, and Reproduction in Folsomia candida Exposed to Teflubenzuron Over Time

The integration of untargeted lipidomics approaches in ecotoxicology has emerged as a strategy to enhance the comprehensiveness of environmental risk assessment. Although current toxicity tests with soil microarthropods focus on species performance, that is, growth, reproduction, and survival, understanding the mechanisms of toxicity across all levels of biological organization, from molecule to community is essential for informed decision-making. Our study focused on the impacts of sublethal concentrations of the insecticide teflubenzuron on the springtail Folsomia candida. Untargeted lipidomics was applied to link changes in growth, reproduction, and the overall stress response with lipid profile changes over various exposure durations. The accumulation of teflubenzuron in organisms exposed to the highest test concentration (0.035 mg a.s. kg-1 soil dry wt) significantly impacted reproductive output without compromising growth. The results suggested a resource allocation shift from reproduction to size maintenance. This hypothesis was supported by lipid shifts on day 7, at which point reductions in triacylglycerol and diacylglycerol content corresponded with decreased offspring production on day 21. The hypermetabolism of fatty acids and N-acylethanolamines on days 2 and 7 of exposure indicated oxidative stress and inflammation in the animals in response to teflubenzuron bioaccumulation, as measured using high-performance liquid chromatography-tandem mass spectrometry. Overall, the changes in lipid profiles in comparison with phenotypic adverse outcomes highlight the potential of lipid analysis as an early-warning tool for reproductive disturbances caused by pesticides in F. candida. Environ Toxicol Chem 2024;00:1-12. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Lipidomic landscape of lipokines in adipose tissue derived extracellular vesicles

Introduction: Adipose tissue-derived extracellular vesicles (EVs-AT) are recognized as critical mediators of metabolic alterations in obesity-related diseases. However, few studies have focused on the role of lipids within EVs-AT in the development of obesity-related diseases. Methods: In this study, we performed a targeted lipidomic analysis to compare the lipidome of EVs secreted by inguinal white adipose tissue (EVs-iWAT), epididymal white adipose tissue (EVs-eWAT), and interscapular brown adipose tissue (EVs-BAT) in lean and obese mice. Results: We uncovered a comprehensive lipidomic map, revealing the diversity and specific lipid sorting in EVs-iWAT, EVs-eWAT, and EVs-BAT in obesity. Biological function analyses suggested that lipids encapsulated within EVs-AT of obese individuals might correlate with metabolism, pro-inflammatory response, and insulin resistance. These effects were particularly pronounced in EVs-eWAT and EVs-BAT. Conclusion: Our findings indicated that EVs-AT serves as novel carriers for lipokines, thereby mediating the biological functions of EVs-AT. This study holds promise for the identification of new biomarkers for obesity-related diseases and the development of new strategies to combat metabolic diseases.

Characterization of lipid signatures in the plasma and insulin-sensitive tissues of the C57BL/6J mice fed on obesogenic diets

Diet-induced obesity mouse models are widely utilized to investigate the underlying mechanisms of dyslipidemia, glucose intolerance, insulin resistance, hepatic steatosis, and type 2 diabetes mellitus (T2DM), as well as for screening potential drug compounds. However, there is limited knowledge regarding specific signature lipids that accurately reflect dietary disorders. In this study, we aimed to identify key lipid signatures using LC/MS-based untargeted lipidomics in the plasma, liver, adipose tissue (AT), and skeletal muscle tissues (SKM) of male C57BL/6J mice that were fed chow, LFD, or obesogenic diets (HFD, HFHF, and HFCD) for a duration of 20 weeks. Furthermore, we conducted a comprehensive lipid analysis to assess similarities and differences with human lipid profiles. The mice fed obesogenic diets exhibited weight gain, glucose intolerance, elevated BMI, glucose and insulin levels, and a fatty liver, resembling characteristics of T2DM and obesity in humans. In total, we identified approximately 368 lipids in plasma, 433 in the liver, 493 in AT, and 624 in SKM. Glycerolipids displayed distinct patterns across the tissues, differing from human findings. However, changes in sphingolipids, phospholipids, and the expression of inflammatory and fibrotic genes showed similarities to reported human findings. Significantly modulated pathways in the obesogenic diet-fed groups included ceramide de novo synthesis, sphingolipid remodeling, and the carboxylesterase pathway, while lipoprotein-mediated pathways were minimally affected.

Lipidomic Profiling of Colorectal Lesions for Real-Time Tissue Recognition and Risk-Stratification Using Rapid Evaporative Ionization Mass Spectrometry

OBJECTIVE

Rapid evaporative ionization mass spectrometry (REIMS) is a metabolomic technique analyzing tissue metabolites, which can be applied intraoperatively in real-time. The objective of this study was to profile the lipid composition of colorectal tissues using REIMS, assessing its accuracy for real-time tissue recognition and risk-stratification.

SUMMARY BACKGROUND DATA

Metabolic dysregulation is a hallmark feature of carcinogenesis; however, it remains unknown if this can be leveraged for real-time clinical applications in colorectal disease.

METHODS

Patients undergoing colorectal resection were included, with carcinoma, adenoma and paired-normal mucosa sampled. Ex vivo analysis with REIMS was conducted using monopolar diathermy, with the aerosol aspirated into a Xevo G2S QToF mass spectrometer. Negatively charged ions over 600 to 1000 m/z were used for univariate and multivariate functions including linear discriminant analysis.

RESULTS

A total of 161 patients were included, generating 1013 spectra. Unique lipidomic profiles exist for each tissue type, with REIMS differentiating samples of carcinoma, adenoma, and normal mucosa with 93.1% accuracy and 96.1% negative predictive value for carcinoma. Neoplasia (carcinoma or adenoma) could be predicted with 96.0% accuracy and 91.8% negative predictive value. Adenomas can be risk-stratified by grade of dysplasia with 93.5% accuracy, but not histological subtype. The structure of 61 lipid metabolites was identified, revealing that during colorectal carcinogenesis there is progressive increase in relative abundance of phosphatidylglycerols, sphingomyelins, and mono-unsaturated fatty acid-containing phospholipids.

CONCLUSIONS

The colorectal lipidome can be sampled by REIMS and leveraged for accurate real-time tissue recognition, in addition to riskstratification of colorectal adenomas. Unique lipidomic features associated with carcinogenesis are described.

Staphylococcal phosphatidylglycerol antigens activate human T cells via CD1a

Expressed on epidermal Langerhans cells, CD1a presents a range of self-lipid antigens found within the skin; however, the extent to which CD1a presents microbial ligands from bacteria colonizing the skin is unclear. Here we identified CD1a-dependent T cell responses to phosphatidylglycerol (PG), a ubiquitous bacterial membrane phospholipid, as well as to lysylPG, a modified PG, present in several Gram-positive bacteria and highly abundant in Staphylococcus aureus. The crystal structure of the CD1a-PG complex showed that the acyl chains were buried within the A'- and F'-pockets of CD1a, while the phosphoglycerol headgroup remained solvent exposed in the F'-portal and was available for T cell receptor contact. Using lysylPG and PG-loaded CD1a tetramers, we identified T cells in peripheral blood and in skin that respond to these lipids in a dose-dependent manner. Tetramer+CD4+ T cell lines secreted type 2 helper T cell cytokines in response to phosphatidylglycerols as well as to co-cultures of CD1a+ dendritic cells and Staphylococcus bacteria. The expansion in patients with atopic dermatitis of CD4+ CD1a-(lysyl)PG tetramer+ T cells suggests a response to lipids made by bacteria associated with atopic dermatitis and provides a link supporting involvement of PG-based lipid-activated T cells in atopic dermatitis pathogenesis.

Mitochondrial Fission Process 1 controls inner membrane integrity and protects against heart failure

Mitochondria are paramount to the metabolism and survival of cardiomyocytes. Here we show that Mitochondrial Fission Process 1 (MTFP1) is an inner mitochondrial membrane (IMM) protein that is dispensable for mitochondrial division yet essential for cardiac structure and function. Constitutive knockout of cardiomyocyte MTFP1 in mice resulted in a fatal, adult-onset dilated cardiomyopathy accompanied by extensive mitochondrial and cardiac remodeling during the transition to heart failure. Prior to the onset of disease, knockout cardiac mitochondria displayed specific IMM defects: futile proton leak dependent upon the adenine nucleotide translocase and an increased sensitivity to the opening of the mitochondrial permeability transition pore, with which MTFP1 physically and genetically interacts. Collectively, our data reveal new functions of MTFP1 in the control of bioenergetic efficiency and cell death sensitivity and define its importance in preventing pathogenic cardiac remodeling.

Comparisons of High Intensity Interval Training and Continuous Training on Metabolomic Alteration and Cardiac Function in Male Adolescent Rats

Background: Comparisons between high intensity interval training (HIIT) and continuous training (CT) regarding improvements of adolescents’ cardiac function are scarce and the preferred intensity for cardiac improvement with restricted myocardial damage remains unknown. This study conducted a 4-weeks training in male adolescent rats under moderate (MI) or high intensity (HI) HIIT and CT programs, aiming to discover and compare exercise-induced myocardial adaptations towards these two training methods.

Methods: 39 male adolescent Sprague-Dawley rats (aged 4 weeks) were randomly assigned to high intensity HIIT (HI-HIIT, n = 8), moderate intensity HIIT (MI-HIIT, n = 8), high intensity CT (HI-CT, n = 8), moderate intensity CT (MI-CT, n = 8) and sedentary control (SC, n = 7) groups. Rats in training groups were trained for 4 weeks and echocardiography was performed at baseline and after the final training. Serum creatine kinase myocardial band (CK-MB), cardiac troponin T (cTn-T) and untargeted metabolomics analysis were measured from blood samples collected 24 h after the final training.

Results: HIIT groups had greater cardiac output improvement than CT groups while no significant difference was found between the HI-HIIT and the MI-HIIT groups. HI-CT group showed higher serum CK-MB and cTn-T levels compared to MI-HIIT, MI-CT and control groups. Untargeted metabolomics analysis identified eleven HI-HIIT-related metabolites, five MI-HIIT-related metabolites and two HICT-related metabolites. The majority of the identified metabolites were phospholipid-related. Phosphatidylglyceride 18 level was significantly different between the HI-CT and MI-CT groups, and was negatively associated with cTn-T in CT groups.

Conclusion: HIIT and CT improve cardiac function of adolescent rats while the HIIT demonstrates better improvement and less myocardial damage. High and moderate training intensities in HIIT exert similar cardiac benefits. HI-CT induced myocardial damage might be associated with serum phospholipids.

Determination of Glycerophospholipids in Biological Material Using High-Performance Liquid Chromatography with Charged Aerosol Detector HPLC-CAD-A New Approach for Isolation and Quantification

The method of using high-performance liquid chromatography with a charged aerosol detector method (HPLC-CAD) was developed for the separation and determination of phospholipids isolated from cell membranes. The established cell lines—normal and neoplastic prostate cells and normal skin fibroblasts and melanoma cells—were selected for the study. Chromatographic separation was performed in the diol stationary phase using a gradient elution based on a mixture of n-hexane, isopropanol and water with the addition of triethylamine and acetic acid as buffer additives. Taking the elements of the Folch and Bligh–Dyer methods, an improved procedure for lipid isolation from biological material was devised. Ultrasound-assisted extraction included three extraction steps and changed the composition of the extraction solvent, which led to higher recovery of the tested phospholipids. This method was validated by assessing the analytical range, precision, intermediate precision and accuracy. The analytical range was adjusted to the expected concentrations in cell extracts of various origins (from 40 µg/mL for PS up to 10 mg/mL for PC). Both precision and intermediate precision were at a similar level and ranged from 3.5% to 9.0%. The recovery for all determined phospholipids was found to be between 95% and 110%. The robustness of the method in terms of the use of equivalent columns was also confirmed. Due to the curvilinear response of CAD, the quantification was based on an internal standard method combined with a power function transformation of the normalized peak areas, allowing the linearization of the signal with an R² greater than 0.996. The developed method was applied for the isolation and determination of glycerophospholipids from cell membranes, showing that the profile of the tested substances was characteristic of various types of cells. This method can be used to assess changes in metabolism between normal cells and neoplastic cells or cells with certain pathologies or genetic changes.

Integrated application of multi-omics approach and biochemical assays provides insights into physiological responses to saline-alkaline stress in the gills of crucian carp (Carassius auratus)

Given the decline of freshwater resources in recent years, the accessible space for freshwater aquaculture is rapidly shrinking, and aquaculture in saline-alkaline water has become a critical approach to meet the rising demand. However, the molecular mechanism behind the adverse effects of saline-alkaline water on fish and the regulatory mechanism in fish tolerance remains unclear. Here, adult crucian carp (Carassius auratus) were exposed to 60 mmol/L NaHCO₃ for 30 days. It was observed that long-term carbonate alkalinity (CA) exposure not only caused gill oxidative stress but also changed the levels of several physiological parameters associated with ammonia transport, including blood ammonia, urea nitrogen (BUN), glutamine (Gln), and glutamine synthetase (GS). According to the metabolomics study, differential metabolites (DMs) engaged in various metabolic pathways, such as glycerophospholipid metabolism, sphingolipid metabolism, and arachidonic acid metabolism. In addition, transcriptomics data showed that differentially expressed genes (DEGs) were closely related to ammonia transport, apoptosis, and immunological response. In general, comprehensive multi-omics and biochemical analysis revealed that crucian carp might adopt Rh glycoprotein as a carrier to mediate ammonia transport and increase glutamine and urea synthesis under long-term high saline-alkaline stress to mitigate the adverse effects of blocked ammonia excretion. Simultaneously, saline-alkaline stress caused the destruction of the antioxidant system and the disorder of lipid metabolism in the crucian carp gills, which induced apoptosis and immunological response. To our knowledge, this is the first study to investigate fish's molecular and metabolic mechanisms under saline-alkaline stress using integrated metabolomics, transcriptomics, and biochemical assays. Overall, the results of this study provided new insights into the molecular mechanism behind the adverse effects of saline-alkaline water on fish and the regulatory mechanism in fish tolerance.

A Peptide-Based Fluorescent Sensor for Anionic Phospholipids

Anionic phospholipids are key cell signal mediators. The distribution of these lipids on the cell membrane and intracellular organelle membranes guides the recruitment of signaling proteins leading to the regulation of cellular processes. Hence, fluorescent sensors that can detect anionic phospholipids within living cells can provide a handle into revealing molecular mechanisms underlying lipid-mediated signal regulation. A major challenge in the detection of anionic phospholipids is related to the presence of these phospholipids mostly in the inner leaflet of the plasma membrane and in the membranes of intracellular organelles. Hence, cell-permeable sensors would provide an advantage by enabling the rapid detection and tracking of intracellular pools of anionic phospholipids. We have developed a peptide-based, cell-permeable, water-soluble, and ratiometric fluorescent sensor that entered cells within 15 min of incubation via the endosomal machinery and showed punctate labeling in the cytoplasm. The probe could also be introduced into living cells via lipofection, which allows bypassing of endosomal uptake, to image anionic phospholipids in the cell membrane. We validated the ability of the sensor toward detection of intracellular anionic phospholipids by colocalization studies with a fluorescently tagged lipid and a protein-based anionic phospholipid sensor. Further, the sensor could image the externalization of anionic phospholipids during programmed cell death, indicating the ability of the probe toward detection of both intra- and extracellular anionic phospholipids based on the biological context.

Phospholipid Profiles for Phenotypic Characterization of Adipose-Derived Multipotent Mesenchymal Stromal Cells

Multipotent mesenchymal stromal cells (MSC) have emerged as therapeutic tools for a wide range of pathological conditions. Yet, the still existing deficits regarding MSC phenotype characterization and the resulting heterogeneity of MSC used in different preclinical and clinical studies hamper the translational success. In search for novel MSC characterization approaches to complement the traditional trilineage differentiation and immunophenotyping assays reliably across species and culture conditions, this study explored the applicability of lipid phenotyping for MSC characterization and discrimination. Human peripheral blood mononuclear cells (PBMC), human fibroblasts, and human and equine adipose-derived MSC were used to compare different mesodermal cell types and MSC from different species. For MSC, cells cultured in different conditions, including medium supplementation with either fetal bovine serum or platelet lysate as well as culture on collagen-coated dishes, were additionally investigated. After cell harvest, lipids were extracted by chloroform/methanol according to Bligh and Dyer. The lipid profiles were analysed by an untargeted approach using liquid chromatography coupled to mass spectrometry (LC-MS) with a reversed phase column and an ion trap mass spectrometer. In all samples, phospholipids and sphingomyelins were found, while other lipids were not detected with the current approach. The phospholipids included different species of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI) and phosphatidylserine (PS) in all cell types, whereas phosphatidylglycerol (PG) species were only present in MSC. MSC from both species showed a higher phospholipid species diversity than PBMC and fibroblasts. Few differences were found between MSC from different culture conditions, except that human MSC cultured with platelet lysate exhibited a unique phenotype in that they exclusively featured PE O-40:4, PG 38:6 and PG 40:6. In search for specific and inclusive candidate MSC lipid markers, we identified PE O-36:3 and PG 40:7 as potentially suitable markers across culture conditions, at which PE O-36:3 might even be used across species. On that basis, phospholipid phenotyping is a highly promising approach for MSC characterization, which might condone some heterogeneity within the MSC while still achieving a clear discrimination even from fibroblasts. Particularly the presence or absence of PG might emerge as a decisive criterion for future MSC characterization.

Multi-Omics Analysis of Mammary Metabolic Changes in Dairy Cows Exposed to Hypoxia

Hypoxia exposure can cause a series of physiological and biochemical reactions in the organism and cells. Our previous studies found the milk fat rate increased significantly in hypoxic dairy cows, however, its specific metabolic mechanism is unclear. In this experiment, we explored and verified the mechanism of hypoxia adaptation based on the apparent and omics results of animal experiments and in vitro cell model. The results revealed that hypoxia exposure was associated with the elevation of AGPAT2-mediated glycerophospholipid metabolism. These intracellular metabolic disorders consequently led to the lipid disorders associated with apoptosis. Our findings update the existing understanding of increased adaptability of dairy cows exposure to hypoxia at the metabolic level.

Fat of the Gut: Epithelial Phospholipids in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) comprise a distinct set of clinical symptoms resulting from chronic inflammation within the gastrointestinal (GI) tract. Despite the significant progress in understanding the etiology and development of treatment strategies, IBD remain incurable for thousands of patients. Metabolic deregulation is indicative of IBD, including substantial shifts in lipid metabolism. Recent data showed that changes in some phospholipids are very common in IBD patients. For instance, phosphatidylcholine (PC)/phosphatidylethanolamine (PE) and lysophosphatidylcholine (LPC)/PC ratios are associated with the severity of the inflammatory process. Composition of phospholipids also changes upon IBD towards an increase in arachidonic acid and a decrease in linoleic and a-linolenic acid levels. Moreover, an increase in certain phospholipid metabolites, such as lysophosphatidylcholine, sphingosine-1-phosphate and ceramide, can result in enhanced intestinal inflammation, malignancy, apoptosis or necroptosis. Because some phospholipids are associated with pathogenesis of IBD, they may provide a basis for new strategies to treat IBD. Current attempts are aimed at controlling phospholipid and fatty acid levels through the diet or via pharmacological manipulation of lipid metabolism.

Mass spectrometry-based untargeted lipidomics reveals new compositional insights into membrane dynamics of Candida albicans under magnesium deprivation

AIMS

There is growing appreciation in adopting new approaches to disrupt multidrug resistance in human fungal pathogen, Candida albicans. The plasma membrane of C. albicans comprises potential lipid moieties that contribute towards the survival of pathogen and could be utilized as antifungal targets. Considering promising applications of developments in mass spectrometry (MS)-based lipidomics technology, the aim of the study was to analyse lipidome profile and expose lipid-dependent changes in response to Mg deprivation.

METHODS AND RESULTS

We found that both phosphatidylcholine (PC) and lysophosphatidylcholine (LysoPC) were decreased. Increased flip (inward translocation) in the fluorophore labelled NBD-PC was ascribed to enhanced PC-specific flippase activity. Furthermore, a decrease in phosphatidylethanolamine (PE) leading to altered membrane fluidity and loss of cellular material was prominent. Additionally, we observed decreased phosphatidylglycerol (PG) and phosphatidylinositol (PI) leading to genotoxic stress. Besides, we could detect enhanced levels of phosphatidylserine (PS), diacylglycerol (DAG) and triacylglycerides (TAG). The altered gene expressions of lipid biosynthetic pathway by RT-PCR correlated with the lipidome profile. Lastly, we explored abrogated ionic (Na⁺ and K⁺ ) transport across the plasma membrane.

CONCLUSIONS

We propose that C. albicans exposed to Mg deprivation could reorganize plasma membrane (lipid species, membrane fluidity and ionic transport), and possibly redirected carbon flux to store energy in TAGs as an adaptive stress response. This work unravels several vulnerable targets governing lipid metabolism in C. albicans and pave way for better antifungal strategies.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates that magnesium availability is important when one considers dissecting drug resistance mechanisms in Candida albicans. Through mass spectrometry (MS)-based lipidomics technology, the study analyses lipidome profile and exposes lipid-dependent changes that are vulnerable to magnesium availability and presents an opportunity to employ this new information in improving treatment strategies.

Untargeted Lipidomics for Determining Cellular and Subcellular Responses in Zebrafish (Danio rerio) Liver Cells Following Exposure to Complex Mixtures in U.S. Streams

Surface waters often contain a variety of chemical contaminants potentially capable of producing adverse outcomes in both humans and wildlife due to impacts from industrial, urban, and agricultural activity. Here, we report the results of a zebrafish liver (ZFL) cell-based lipidomics approach to assess the potential ecotoxicological effects of complex contaminant mixtures using water collected from eight impacted streams across the United States mainland and Puerto Rico. We initially characterized the ZFL lipidome using high resolution mass spectrometry, resulting in the annotation of 508 lipid species covering 27 classes. We then identified lipid changes induced by all streamwater samples (nonspecific stress indicators) as well as those unique to water samples taken from specific streams. Subcellular impacts were classified based on organelle-specific lipid changes, including increased lipid saturation (endoplasmic reticulum stress), elevated bis(monoacylglycero)phosphate (lysosomal overload), decreased ubiquinone (mitochondrial dysfunction), and elevated ether lipids (peroxisomal stress). Finally, we demonstrate how these results can uniquely inform environmental monitoring and risk assessments of surface waters.

Application of enzymatic fluorometric assays to quantify phosphatidylcholine, phosphatidylethanolamine and sphingomyelin in human plasma lipoproteins

Phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SM) are important surface components of plasma lipoproteins, including very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL) and high-density lipoproteins (HDL). However, the pathophysiological roles of PC, PE and SM in lipoproteins have not been well characterized owing to the difficulties in quantifying phospholipid classes in lipoproteins. In this study, we assessed the precision and accuracy of the enzymatic fluorometric assays for measuring PC, PE and SM in VLDL, LDL and HDL, which were isolated from human plasma by ultracentrifugation. The within-run coefficients of variation (CV) for the measurements of PC, PE and SM in lipoproteins were 1.5-2.8 %, 1.1-2.4 % and 0.9-2.3 %, respectively, whereas the between-run CVs for the PC, PE and SM assays were 2.7-4.7 %, 2.1-4.5 % and 1.6-3.3 %, respectively. Excellent linearity and almost complete recovery were achieved for all assays measuring PC, PE and SM in VLDL, LDL and HDL. Our preliminary results using these enzymatic fluorometric assays suggested that the phospholipid compositions were different among VLDL, LDL and HDL. In conclusion, we established high-throughput enzymatic fluorometric assays to quantify PC, PE and SM in human plasma VLDL, LDL and HDL, which will be useful for further investigation of pathophysiological roles of phospholipids in lipoproteins.

Novel Molecular Insights into Human Lipid-Mediated T Cell Immunity

T cells represent a critical arm of our immune defense against pathogens. Over the past two decades, considerable inroads have been made in understanding the fundamental principles underpinning the molecular presentation of peptide-based antigens by the Major Histocompatibility Complex molecules (MHC-I and II), and their molecular recognition by specialized subsets of T cells. However, some T cells can recognize lipid-based antigens presented by MHC-I-like molecules that belong to the Cluster of Differentiation 1 (CD1) family. Here, we will review the advances that have been made in the last five years to understand the molecular mechanisms orchestrating the presentation of novel endogenous and exogenous lipid-based antigens by the CD1 glycoproteins and their recognition by specific populations of CD1-reactive T cells.

Alterations in cellular and organellar phospholipid compositions of HepG2 cells during cell growth

The human hepatoblastoma cell line, HepG2, has been used for investigating a wide variety of physiological and pathophysiological processes. However, less information is available about the phospholipid metabolism in HepG2 cells. In the present report, to clarify the relationship between cell growth and phospholipid metabolism in HepG2 cells, we examined the phospholipid class compositions of the cells and their intracellular organelles by using enzymatic fluorometric methods. In HepG2 cells, the ratios of all phospholipid classes, but not the ratio of cholesterol, markedly changed with cell growth. Of note, depending on cell growth, the phosphatidic acid (PA) ratio increased and phosphatidylcholine (PC) ratio decreased in the nuclear membranes, the sphingomyelin (SM) ratio increased in the microsomal membranes, and the phosphatidylethanolamine (PE) ratio increased and the phosphatidylserine (PS) ratio decreased in the mitochondrial membranes. Moreover, the mRNA expression levels of enzymes related to PC, PE, PS, PA, SM and cardiolipin syntheses changed during cell growth. We suggest that the phospholipid class compositions of organellar membranes are tightly regulated by cell growth. These findings provide a basis for future investigations of cancer cell growth and lipid metabolism.

Lipid Diversity in Cells and Tissue Using Imaging SIMS

Lipids are an important class of biomolecules with many roles within cells and tissue. As targets for study, they present several challenges. They are difficult to label, as many labels lack the specificity to the many different lipid species or the labels maybe larger than the lipids themselves, thus severely perturbing the natural chemical environment. Mass spectrometry provides exceptional specificity and is often used to examine lipid extracts from different samples. However, spatial information is lost during extraction. Of the different imaging mass spectrometry methods available, secondary ion mass spectrometry (SIMS) is unique in its ability to analyze very small features, with probe sizes <50 nm available. It also offers high surface sensitivity and 3D imaging capability on a subcellular scale. This article reviews the current capabilities and some remaining challenges associated with imaging the diverse lipids present in cell and tissue samples. We show how the technique has moved beyond show-and-tell, proof-of-principle analysis and is now being used to address real biological challenges. These include imaging the microenvironment of cancer tumors, probing the pathophysiology of traumatic brain injury, or tracking the lipid composition through bacterial membranes.

Lipid metabolism adaptations are reduced in human compared to murine Schwann cells following injury

Mammals differ in their regeneration potential after traumatic injury, which might be caused by species-specific regeneration programs. Here, we compared murine and human Schwann cell (SC) response to injury and developed an ex vivo injury model employing surgery-derived human sural nerves. Transcriptomic and lipid metabolism analysis of murine SCs following injury of sural nerves revealed down-regulation of lipogenic genes and regulator of lipid metabolism, including Pparg (peroxisome proliferator-activated receptor gamma) and S1P (sphingosine-1-phosphate). Human SCs failed to induce similar adaptations following ex vivo nerve injury. Pharmacological PPARg and S1P stimulation in mice resulted in up-regulation of lipid gene expression, suggesting a role in SCs switching towards a myelinating state. Altogether, our results suggest that murine SC switching towards a repair state is accompanied by transcriptome and lipidome adaptations, which are reduced in humans.

In situ metabolite and lipid analysis of GluN2D-/- and wild-type mice after ischemic stroke using MALDI MSI

The N-methyl-D-aspartate (NMDA) receptor is a crucial mediator of pathological glutamate-driven excitotoxicity and subsequent neuronal death in acute ischemic stroke. Although the roles of the NMDAR's composite GluN2A-C subunits have been investigated in this phenomenon, the relative importance of the GluN2D subunit has yet to be evaluated. Herein, GluN2D^-/- mice were studied in a model of ischemic stroke using MALDI FT-ICR mass spectrometry imaging to investigate the role of the GluN2D subunit of the NMDA receptor in brain ischemia. GluN2D^-/- mice underwent middle cerebral artery occlusion (MCAO) and brain tissue was subsequently harvested, frozen, and cryosectioned. Tissue sections were analyzed via MALDI FT-ICR mass spectrometry imaging. MALDI analyses revealed increases in several calcium-related species, namely vitamin D metabolites, LysoPC, and several PS species, in wild-type mouse brain tissue when compared to wild type. In addition, GluN2D^-/- mice also displayed an increase in PC, as well as a decrease in DG, suggesting reduced free fatty acid release from brain ischemia. These trends indicate that GluN2D^-/- mice show enhanced rates of neurorecovery and neuroprotection from ischemic strokes compared to wild-type mice. The cause of neuroprotection may be the result of an increase in PGP in knockout mice, contributing to greater cardiolipin synthesis and decreased sensitivity to apoptotic signals. Graphical abstract.

Protocols for Enzymatic Fluorometric Assays to Quantify Phospholipid Classes

Phospholipids, consisting of a hydrophilic head group and two hydrophobic acyl chains, are essential for the structures of cell membranes, plasma lipoproteins, biliary mixed micelles, pulmonary surfactants, and extracellular vesicles. Beyond their structural roles, phospholipids have important roles in numerous biological processes. Thus, abnormalities in the metabolism and transport of phospholipids are involved in many diseases, including dyslipidemia, atherosclerosis, cholestasis, drug-induced liver injury, neurological diseases, autoimmune diseases, respiratory diseases, myopathies, and cancers. To further clarify the physiological, pathological, and molecular mechanisms and to identify disease biomarkers, we have recently developed enzymatic fluorometric assays for quantifying all major phospholipid classes, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidic acid, phosphatidylinositol, phosphatidylglycerol + cardiolipin, and sphingomyelin. These assays are specific, sensitive, simple, and high-throughput, and will be applicable to cells, intracellular organelles, tissues, fluids, lipoproteins, and extracellular vesicles. In this review, we present the detailed protocols for the enzymatic fluorometric measurements of phospholipid classes in cultured cells.

Lipid class composition of membrane and raft fractions from brains of individuals with Alzheimer's disease

Perturbation of the homeostasis of brain membrane lipids has been implicated in the pathomechanism of Alzheimer's disease (AD). The ε4 allele of the apolipoprotein E gene (APOE) confers an increased risk, in a dosage-dependent manner, for brain amyloid-β accumulation and the development of sporadic AD. An effect of the APOE genotype on brain lipid homeostasis may underlie the AD risk associated with the ε4 allele. In this research, we examined an effect of APOE ε4 on the lipid class composition of crude membranes and raft-enriched fractions of brains. We applied enzymatic reaction-based methods for the quantification of phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidic acid, and sphingomyelin. Our results indicate that brain lipid class composition was neither significantly altered in AD subjects nor affected by the presence of the APOE ε4 allele.

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No change was found in the composition of lipid classes of brains with Alzheimer's disease.

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The APOE ε4 allele did not affect lipid class composition of the brain membrane or rafts.

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The enzymatic measurement of phospholipids is applicable to brain tissues.

The MYC Oncogene Cooperates with Sterol-Regulated Element-Binding Protein to Regulate Lipogenesis Essential for Neoplastic Growth

Lipid metabolism is frequently perturbed in cancers, but the underlying mechanism is unclear. We present comprehensive evidence that oncogene MYC, in collaboration with transcription factor sterol-regulated element-binding protein (SREBP1), regulates lipogenesis to promote tumorigenesis. We used human and mouse tumor-derived cell lines, tumor xenografts, and four conditional transgenic mouse models of MYC-induced tumors to show that MYC regulates lipogenesis genes, enzymes, and metabolites. We found that MYC induces SREBP1, and they collaborate to activate fatty acid (FA) synthesis and drive FA chain elongation from glucose and glutamine. Further, by employing desorption electrospray ionization mass spectrometry imaging (DESI-MSI), we observed in vivo lipidomic changes upon MYC induction across different cancers, for example, a global increase in glycerophosphoglycerols. After inhibition of FA synthesis, tumorigenesis was blocked, and tumors regressed in both xenograft and primary transgenic mouse models, revealing the vulnerability of MYC-induced tumors to the inhibition of lipogenesis.

Enzymatic fluorometric assays for quantifying all major phospholipid classes in cells and intracellular organelles

Cell membrane phospholipids regulate various biological functions. We previously reported enzymatic fluorometric methods for quantifying phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, sphingomyelin, phosphatidylglycerol and cardiolipin. In the present report, a new enzymatic fluorometric assay was developed for quantifying phosphatidylinositol. These simple, sensitive and high-throughput methods enabled us to quantify all major phospholipid classes in cultured cells and intracellular organelles. By conducting comprehensive quantitative analyses of major phospholipid classes, we demonstrated that the contents of phospholipid classes in HEK293 cells changed with cell density and that overexpression of phosphatidylinositol synthase or CDP-diacylglycerol synthase significantly affected the phospholipid compositions of microsomal and mitochondrial membranes. These enzymatic fluorometric assays for measuring all major phospholipid classes may be applicable to tissues, fluids, lipoproteins, extracellular vesicles and intracellular organelles of many organisms and will further our understanding of cellular, physiological and pathological processes.

Energy metabolism in cachexia

Cachexia is a wasting disorder that accompanies many chronic diseases including cancer and results from an imbalance of energy requirements and energy uptake. In cancer cachexia, tumor-secreted factors and/or tumor-host interactions cause this imbalance, leading to loss of adipose tissue and skeletal and cardiac muscle, which weakens the body. In this review, we discuss how energy enters the body and is utilized by the different organs, including the gut, liver, adipose tissue, and muscle, and how these organs contribute to the energy wasting observed in cachexia. We also discuss futile cycles both between the organs and within the cells, which are often used to fine-tune energy supply under physiologic conditions. Ultimately, understanding the complex interplay of pathologic energy-wasting circuits in cachexia can bring us closer to identifying effective treatment strategies for this devastating wasting disease.

Site-directed mutagenesis of two amino acid residues in cytochrome b559 α subunit that interact with a phosphatidylglycerol molecule (PG772) induces quinone-dependent inhibition of photosystem II activity

X-ray crystallographic analysis (1.9-Å resolution) of the cyanobacterial photosystem II (PSII) dimer showed the presence of five phosphatidylglycerol (PG) molecules per reaction center. One of the PG molecules, PG772, is located in the vicinity of the Q_B-binding site. To investigate the role of PG772 in PSII, we performed site-directed mutagenesis in the cytochrome (Cyt) b₅₅₉ α subunit of Synechocystis sp. PCC 6803 to change two amino acids, Thr-5 and Ser-11, which interact with PG772. The photosynthetic activity of intact cells was slightly lower in all mutants than that of cells in the control strain; however, the oxygen-evolving PSII activity was decreased markedly in cells of mutants, as measured using artificial quinones (such as p-benzoquinone). Furthermore, electron transport from Q_A to Q_B was inhibited in mutants incubated with quinones, particularly under high-intensity light conditions. Lipid analysis of purified PSII showed approximately one PG molecule per reaction center, presumably PG772, was lost in the PSII dimer from the T5A and S11A mutants compared with that in the PSII dimer from the control strain. In addition, protein analysis of monomer and dimer showed decreased levels of PsbV and PsbU extrinsic proteins in the PSII monomer purified from T5A and S11A mutants. These results suggest that site-directed mutagenesis of Thr-5 and Ser-11, which presumably causes the loss of PG772, induces quinone-dependent inhibition of PSII activity under high-intensity light conditions and destabilizes the binding of extrinsic proteins to PSII.

Spectrophotometric versus spectrofluorometric assessment in the study of the relationships between lipid peroxidation and metabolic dysregulation

Reactive oxygen species are crucial to normal cell function, but are also part of the pathogenesis of multiple modern maladies. As such, sensitive, fast, and reliable methods of appreciating redox status are needed. We aimed to optimize the Amplex Red (AR) and ferric-xylenol orange (FOX) methods using human serum samples, rat tissue homogenates, and mitochondrial preparations. For AR, we intended to reduce probe concentration, maintaining method sensitivity, as well as extending its use from isolated lipoproteins samples, and readjust it for a high-throughput application. Also, we evaluated the usefulness of a modified xylenol orange-based spectrophotometric protocol, comparing and contrasting these methods in terms of clinical relevance and suitability for their further use in assessing redox status of various biological samples in different pathological conditions. Our results show that these optimized protocols are suitable for complex in vivo studies, as they require low quantities of sample and reagents, and are sensitive, rapid, and economical, with the option of adapting them for high-throughput analysis. For a better assessment of oxidative status of serum-derived samples, the two methods can be used concurrently, while for tissue-derived ones, either can be employed for the measurement of a global redox status.

The intricacies of self-lipid antigen presentation by CD1b

The CD1 family of glycoproteins are MHC class I-like molecules that present a wide array of self and foreign lipid antigens to T-cell receptors (TCRs) on T-cells. Humans express three classes of CD1 molecules, denoted as Group 1 (CD1a, CD1b, and CD1c), Group 2 (CD1d), and Group 3 (CD1e). Of the CD1 family of molecules, CD1b exhibits the largest and most complex antigen binding groove; allowing it the capabilities to present a broad spectrum of lipid antigens. While its role in foreign-lipid presentation in the context of mycobacterial infection are well characterized, understanding the roles of CD1b in autoreactivity are recently being elucidated. While the mechanisms governing proliferation of CD1b-restricted autoreactive T cells, regulation of CD1 gene expression, and the processes controlling CD1+ antigen presenting cell maturation are widely undercharacterized, the exploration of self-lipid antigens in the context of disease have recently come into focus. Furthermore, the recently expanded pool of CD1b crystal structures allow the opportunity to further analyze the molecular mechanisms of T-cell recognition and self-lipid presentation; where the intricacies of the two-compartment system, that accommodate both the presented self-lipid antigen and scaffold lipids, are scrutinized. This review delves into the immunological and molecular mechanisms governing presentation and T-cell recognition of the broad self-lipid repertoire of CD1b; with evidence mounting pointing towards a role in diseases such as microbial infection, autoimmune diseases, and cancer.

Differential Pattern of Phospholipid Profile in the Temporal Cortex from E280A-Familiar and Sporadic Alzheimer's Disease Brains

Lipids are considered important factors in the pathogenesis of Alzheimer's disease (AD). In this study, we realized a comparative analysis of the phospholipid profile and phospholipid composition of the temporal cortex from E280A-familiar AD (FAD), sporadic AD (SAD), and healthy human brains. Findings showed a significant decrease of lysophosphatidylcholine and phosphatidylethanolamine formed by low levels of polyunsaturated fatty acids (20 : 4, 22 : 6) in AD brains. However, phosphatidylethanolamine-ceramide and phosphoglycerol were significantly increased in SAD, conformed by high levels of (18 : 0/18 : 1) and (30/32/36 : 0/1/2), respectively. Together, the findings suggest a deficiency in lysophosphacholine and phosphatidylethanolamine, and alteration in the balance between poly- and unsaturated fatty acids in both types of AD, and a differential pattern of phospholipid profile and fatty acid composition between E280A FAD and SAD human brains.

A molecular basis of human T cell receptor autoreactivity toward self-phospholipids

Human T cell autoreactivity toward lipid antigens presented by CD1 proteins can manifest in numerous diseases, including psoriasis, contact hypersensitivities, and allergies. However, the molecular mechanisms for regulating T cell autoreactivity toward lipid antigens remain unclear. We determined the basis for T cell receptor (TCR) autoreactivity toward CD1b bound to self-phospholipids. The spectrum of self-antigens captured by CD1b skews toward abundant membrane phospholipids such as phosphatidylcholine and phosphatidylethanolamine. However, TCRs can specifically recognize rare phospholipids, including phosphatidylglycerol (PG). The structure of an autoreactive TCR bound to CD1b-PG shows that discrimination occurs through a marked induced fit movement of PG so that its polar head group fits snugly into the cationic cup of the TCR. Conversely, TCR binding toward ubiquitous self-phospholipids was sterically or electrostatically repelled. Accordingly, we describe a mechanism of TCR autoreactivity toward rare phospholipids and avoidance of autoreactivity to the most abundant self-phospholipids.

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.

Human Carboxylesterase 2 Reverses Obesity-Induced Diacylglycerol Accumulation and Glucose Intolerance

Serine hydrolases are a large family of multifunctional enzymes known to influence obesity. Here, we performed activity-based protein profiling to assess the functional level of serine hydrolases in liver biopsies from lean and obese humans in order to gain mechanistic insight into the pathophysiology of metabolic disease. We identified reduced hepatic activity of carboxylesterase 2 (CES2) and arylacetamide deacetylase (AADAC) in human obesity. In primary human hepatocytes, CES2 knockdown impaired glucose storage and lipid oxidation. In mice, obesity reduced CES2, whereas adenoviral delivery of human CES2 reversed hepatic steatosis, improved glucose tolerance, and decreased inflammation. Lipidomic analysis identified a network of CES2-regulated lipids altered in human and mouse obesity. CES2 possesses triglyceride and diacylglycerol lipase activities and displayed an inverse correlation with HOMA-IR and hepatic diacylglycerol concentrations in humans. Thus, decreased CES2 is a conserved feature of obesity and plays a causative role in the pathogenesis of obesity-related metabolic disturbances.

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Obesity decreases hepatic activity of AADAC and CES2 in humans

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CES2 depletion impairs lipid and glucose metabolism in primary human hepatocytes

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Human CES2 expression reverses hepatic steatosis and glucose intolerance in mice

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CES2 controls a hepatic lipid network dysregulated in human and mouse obesity

Phosphatidic acid: biosynthesis, pharmacokinetics, mechanisms of action and effect on strength and body composition in resistance-trained individuals

The mechanistic target of rapamycin complex 1 (mTORC1) has received much attention in the field of exercise physiology as a master regulator of skeletal muscle hypertrophy. The multiprotein complex is regulated by various signals such as growth factors, energy status, amino acids and mechanical stimuli. Importantly, the glycerophospholipid phosphatidic acid (PA) appears to play an important role in mTORC1 activation by mechanical stimulation. PA has been shown to modulate mTOR activity by direct binding to its FKBP12-rapamycin binding domain. Additionally, it has been suggested that exogenous PA activates mTORC1 via extracellular conversion to lysophosphatidic acid and subsequent binding to endothelial differentiation gene receptors on the cell surface. Recent trials have therefore evaluated the effects of PA supplementation in resistance-trained individuals on strength and body composition. As research in this field is rapidly evolving, this review attempts to provide a comprehensive overview of its biosynthesis, pharmacokinetics, mechanisms of action and effect on strength and body composition in resistance-trained individuals.

Human autoreactive T cells recognize CD1b and phospholipids

In contrast with the common detection of T cells that recognize MHC, CD1a, CD1c, or CD1d proteins, CD1b autoreactive T cells have been difficult to isolate in humans. Here we report the development of polyvalent complexes of CD1b proteins and carbohydrate backbones (dextramers) and their use in identifying CD1b autoreactive T cells from human donors. Activation is mediated by αβ T-cell receptors (TCRs) binding to CD1b-phospholipid complexes, which is sufficient to activate autoreactive responses to CD1b-expressing cells. Using mass spectrometry and T-cell responses to scan through the major classes of phospholipids, we identified phosphatidylglycerol (PG) as the immunodominant lipid antigen. T cells did not discriminate the chemical differences that distinguish mammalian PG from bacterial PG. Whereas most models of T-cell recognition emphasize TCR discrimination of differing self and foreign structures, CD1b autoreactive T cells recognize lipids with dual self and foreign origin. PG is rare in the cellular membranes that carry CD1b proteins. However, bacteria and mitochondria are rich in PG, so these data point to a more general mechanism of immune detection of infection- or stress-associated lipids.

Crystallographic Identification of Lipid as an Integral Component of the Epitope of HIV Broadly Neutralizing Antibody 4E10

Numerous studies of the anti-HIV-1 envelope glycoprotein 41 (gp41) broadly neutralizing antibody 4E10 suggest that 4E10 also interacts with membrane lipids, but the antibody regions contacting lipids and its orientation with respect to the viral membrane are unknown. Vaccine immunogens capable of re-eliciting these membrane proximal external region (MPER)-like antibodies may require a lipid component to be successful. We performed a systematic crystallographic study of lipid binding to 4E10 to identify lipids bound by the antibody and the lipid-interacting regions. We identified phosphatidic acid, phosphatidylglycerol, and glycerol phosphate as specific ligands for 4E10 in the crystal structures. 4E10 used its CDRH1 loop to bind the lipid head groups, while its CDRH3 interacted with the hydrophobic lipid tails. Identification of the lipid binding sites on 4E10 may aid design of immunogens for vaccines that include a lipid component in addition to the MPER on gp41 for generation of broadly neutralizing antibodies.