Innate immune detection of lipid oxidation as a threat assessment strategy.

Oxidized phospholipids that result from tissue injury operate as immunomodulatory signals that, depending on the context, lead to proinflammatory or anti-inflammatory responses. In this Perspective, we posit that cells of the innate immune system use the presence of oxidized lipids as a generic indicator of threat to the host. Similarly to how pathogen-associated molecular patterns represent general indicators of microbial encounters, oxidized lipids may be the most common molecular feature of an injured tissue. Therefore, microbial detection in the absence of oxidized lipids may indicate encounters with avirulent microorganisms. By contrast, microbial detection and detection of oxidized lipids would indicate encounters with replicating microorganisms, thereby inducing a heightened inflammatory and defensive response. Here we review recent studies supporting this idea. We focus on the biology of oxidized phosphocholines, which have emerged as context-dependent regulators of immunity. We highlight emerging functions of oxidized phosphocholines in dendritic cells and macrophages that drive unique inflammasome and migratory activities and hypermetabolic states. We describe how these lipids hyperactivate dendritic cells to stimulate antitumour CD8+ T cell immunity and discuss the potential implications of the newly described activities of oxidized phosphocholines in host defence.

Dynamics of Choline-Containing Phospholipids in Traumatic Brain Injury and Associated Comorbidities.

The incidences of traumatic brain injuries (TBIs) are increasing globally because of expanding population and increased dependencies on motorized vehicles and machines. This has resulted in increased socio-economic burden on the healthcare system, as TBIs are often associated with mental and physical morbidities with lifelong dependencies, and have severely limited therapeutic options. There is an emerging need to identify the molecular mechanisms orchestrating these injuries to life-long neurodegenerative disease and a therapeutic strategy to counter them. This review highlights the dynamics and role of choline-containing phospholipids during TBIs and how they can be used to evaluate the severity of injuries and later targeted to mitigate neuro-degradation, based on clinical and preclinical studies. Choline-based phospholipids are involved in maintaining the structural integrity of the neuronal/glial cell membranes and are simultaneously the essential component of various biochemical pathways, such as cholinergic neuronal transmission in the brain. Choline or its metabolite levels increase during acute and chronic phases of TBI because of excitotoxicity, ischemia and oxidative stress; this can serve as useful biomarker to predict the severity and prognosis of TBIs. Moreover, the effect of choline-replenishing agents as a post-TBI management strategy has been reviewed in clinical and preclinical studies. Overall, this review determines the theranostic potential of choline phospholipids and provides new insights in the management of TBI.

Link between Lipid Second Messengers and Osmotic Stress in Plants.

Plants are subject to different types of stress, which consequently affect their growth and development. They have developed mechanisms for recognizing and processing an extracellular signal. Second messengers are transient molecules that modulate the physiological responses in plant cells under stress conditions. In this sense, it has been shown in various plant models that membrane lipids are substrates for the generation of second lipid messengers such as phosphoinositide, phosphatidic acid, sphingolipids, and lysophospholipids. In recent years, research on lipid second messengers has been moving toward using genetic and molecular approaches to reveal the molecular setting in which these molecules act in response to osmotic stress. In this sense, these studies have established that second messengers can transiently recruit target proteins to the membrane and, therefore, affect protein conformation, activity, and gene expression. This review summarizes recent advances in responses related to the link between lipid second messengers and osmotic stress in plant cells.

The Role of Lipids in Legionella-Host Interaction.

Legionella are Gram-stain-negative rods associated with water environments: either natural or man-made systems. The inhalation of aerosols containing Legionella bacteria leads to the development of a severe pneumonia termed Legionnaires' disease. To establish an infection, these bacteria adapt to growth in the hostile environment of the host through the unusual structures of macromolecules that build the cell surface. The outer membrane of the cell envelope is a lipid bilayer with an asymmetric composition mostly of phospholipids in the inner leaflet and lipopolysaccharides (LPS) in the outer leaflet. The major membrane-forming phospholipid of Legionella spp. is phosphatidylcholine (PC)-a typical eukaryotic glycerophospholipid. PC synthesis in Legionella cells occurs via two independent pathways: the N-methylation (Pmt) pathway and the Pcs pathway. The utilisation of exogenous choline by Legionella spp. leads to changes in the composition of lipids and proteins, which influences the physicochemical properties of the cell surface. This phenotypic plasticity of the Legionella cell envelope determines the mode of interaction with the macrophages, which results in a decrease in the production of proinflammatory cytokines and modulates the interaction with antimicrobial peptides and proteins. The surface-exposed O-chain of Legionella pneumophila sg1 LPS consisting of a homopolymer of 5-acetamidino-7-acetamido-8-O-acetyl-3,5,7,9-tetradeoxy-l-glycero-d-galacto-non-2-ulosonic acid is probably the first component in contact with the host cell that anchors the bacteria in the host membrane. Unusual in terms of the structure and function of individual LPS regions, it makes an important contribution to the antigenicity and pathogenicity of Legionella bacteria.

Mapping the electrostatic profiles of cellular membranes.

Anionic phospholipids can confer a net negative charge on biological membranes. This surface charge generates an electric field that serves to recruit extrinsic cationic proteins, can alter the disposition of transmembrane proteins and causes the local accumulation of soluble counterions, altering the local pH and the concentration of physiologically important ions such as calcium. Because the phospholipid compositions of the different organellar membranes vary, their surface charges are similarly expected to diverge. Yet, despite the important functional implications, remarkably little is known about the electrostatic properties of the individual organellar membranes. We therefore designed and implemented approaches to estimate the surface charges of the cytosolic membranes of various organelles in situ in intact cells. Our data indicate that the inner leaflet of the plasma membrane is most negative, with a surface potential of approximately -35 mV, followed by the Golgi complex > lysosomes > mitochondria ≈ peroxisomes > endoplasmic reticulum, in decreasing order.

Inducible intracellular membranes: molecular aspects and emerging applications.

Membrane remodeling and phospholipid biosynthesis are normally tightly regulated to maintain the shape and function of cells. Indeed, different physiological mechanisms ensure a precise coordination between de novo phospholipid biosynthesis and modulation of membrane morphology. Interestingly, the overproduction of certain membrane proteins hijack these regulation networks, leading to the formation of impressive intracellular membrane structures in both prokaryotic and eukaryotic cells. The proteins triggering an abnormal accumulation of membrane structures inside the cells (or membrane proliferation) share two major common features: (1) they promote the formation of highly curved membrane domains and (2) they lead to an enrichment in anionic, cone-shaped phospholipids (cardiolipin or phosphatidic acid) in the newly formed membranes. Taking into account the available examples of membrane proliferation upon protein overproduction, together with the latest biochemical, biophysical and structural data, we explore the relationship between protein synthesis and membrane biogenesis. We propose a mechanism for the formation of these non-physiological intracellular membranes that shares similarities with natural inner membrane structures found in α-proteobacteria, mitochondria and some viruses-infected cells, pointing towards a conserved feature through evolution. We hope that the information discussed in this review will give a better grasp of the biophysical mechanisms behind physiological and induced intracellular membrane proliferation, and inspire new applications, either for academia (high-yield membrane protein production and nanovesicle production) or industry (biofuel production and vaccine preparation).

Nontuberculous Mycobacteria Show Differential Infectivity and Use Phospholipids to Antagonize LL-37.

Comparisons of infectivity among the clinically important nontuberculous mycobacteria (NTM) species have not been explored in great depth. Rapid-growing mycobacteria, including Mycobacterium abscessus and M. porcinum, can cause indolent but progressive lung disease. Slow-growing members of the M. avium complex are the most common group of NTM to cause lung disease, and molecular approaches can now distinguish between several distinct species of M. avium complex including M. intracellulare, M. avium, M. marseillense, and M. chimaera. Differential infectivity among these NTM species may, in part, account for differences in clinical outcomes and response to treatment; thus, knowing the relative infectivity of particular isolates could increase prognostication accuracy and enhance personalized treatment. Using human macrophages, we investigated the infectivity and virulence of nine NTM species, as well as multiple isolates of the same species. We also assessed their capacity to evade killing by the antibacterial peptide cathelicidin (LL-37). We discovered that the ability of different NTM species to infect macrophages varied among the species and among isolates of the same species. Our biochemical assays implicate modified phospholipids, which may include a phosphatidylinositol or cardiolipin backbone, as candidate antagonists of LL-37 antibacterial activity. The high variation in infectivity and virulence of NTM strains suggests that more detailed microbiological and biochemical characterizations are necessary to increase our knowledge of NTM pathogenesis.

Phospholipases in neuronal function: A role in learning and memory?

Despite the human brain being made of nearly 60% fat, the vast majority of studies on the mechanisms of neuronal communication which underpin cognition, memory and learning, primarily focus on proteins and/or (epi)genetic mechanisms. Phospholipids are the main component of all cellular membranes and function as substrates for numerous phospholipid-modifying enzymes, including phospholipases, which release free fatty acids (FFAs) and other lipid metabolites that can alter the intrinsic properties of the membranes, recruit and activate critical proteins, and act as lipid signalling molecules. Here, we will review brain specific phospholipases, their roles in membrane remodelling, neuronal function, learning and memory, as well as their disease implications. In particular, we will highlight key roles of unsaturated FFAs, particularly arachidonic acid, in neurotransmitter release, neuroinflammation and memory. In light of recent findings, we will also discuss the emerging role of phospholipase A1 and the creation of saturated FFAs in the brain.

Hopanoids, like sterols, modulate dynamics, compaction, phase segregation and permeability of membranes.

In recent years, hopanoids, a group of pentacyclic compounds found in bacterial membranes, are in the spotlight since it was proposed that they induce order in lipid membranes in a similar way cholesterol do in eukaryotes, despite their structural differences. We studied here whether diplopterol (an abundant hopanoid) promoted similar effects on model membranes as sterols do. We analyzed the compaction, dynamics, phase segregation, permeability and compressibility of model membranes containing diplopterol, and compared with those containing sterols from animals, plants and fungi. We also tested the effect that the incubation with diplopterol had on hopanoid-lacking bacteria. Our results show that diplopterol induces phase segregation, increases lipid compaction, and decreases permeability on phospholipid membranes, while retaining membrane fluidity and compressibility. Furthermore, the exposition to this hopanoid decreases the permeability of the opportunistic pathogen Pseudomonas aeruginosa and increases the resistance to antibiotics. All effects promoted by diplopterol were similar to those generated by the sterols. Our observations add information on the functional significance of hopanoids as molecules that play an important role in membrane organization and dynamics in model membranes and in a bacterial system.

Can Yellow Stripe Scad Compete with Salmon on Its Role in Platelet Phospholipid Membrane and Its Cardiovascular Benefits?

This review article stresses the effective role of dietary fish fillet docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) on overweight as a risk factor of cardiovascular disease (CVD) via platelet phospholipid modification. Several reports have demonstrated that saturated fat in overweight evokes systemic inflammation and more importantly predisposes it to cardiovascular disorder. Prospective studies have shown that saturated fat is directly proportional to the level of arachidonic acids (AA), precursor of thromboxane in the platelet phospholipid membrane as omega-6 fatty acid in overweight and obese people. Some literature has demonstrated that omega-3 fatty acid from fish fillet ameliorates inflammation, reduces proinflammatory cytokine, inhibits signaling pathway, and regulates the physical composition of inflammatory leukocytes and free radicals (ROS). Yellow stripe scad (YSS) is a local Malaysian fish that has been shown to contain a comparable level of EPA/DHA content as observed in salmon. This review article will focus on the dietary role of fish fillet that will balance the omega-6 fatty acid/omega-3 fatty acid ratio in platelet phospholipid from YSS to manage and prevent healthy overweight/obesity-related risk factor of CVD and to avoid the risk orthodox drug treatment.

[Systemic membrane-destabilizing distress syndrome in surgery: concept, pathogenesis, diagnosis]. / Sistemnyi membranodestabiliziruiushchii distress-sindrom v khirurgii: poniatie, patogenez, diagnostika.

AIM: To justify the concept of systemic membrane-destabilizing distress syndrome in surgery via analysis of phospholipid bilayer of cell membranes of various organs in urgent surgical abdominal diseases. MATERIAL AND METHODS: Experimental research on dogs (n=90) included modeling of peritonitis, pancreatitis, intestinal obstruction, obstructive jaundice, and post-hemorrhagic anemia. Clinical and laboratory studies were performed in patients (n=119) with acute peritonitis, severe pancreatitis, intestinal obstruction, post-hemorrhagic anemia, acute cholecystitis, gastrointestinal bleeding, benign mechanical jaundice. Lipid profile in tissues and blood cells was determined by extraction, fractionation and densitometry. Moreover, we assessed intensity of lipid peroxidation and phospholipase activity, endogenous intoxication, functional state of organs and blood cells. RESULTS: It was revealed that all above-mentioned acute abdominal diseases are followed by significant changes of lipid bilayer and dysfunction of tissues in target organs, blood cells and other organs (liver, kidney, colon and small intestine, heart, lungs, spleen, brain). Changes of phospholipid bilayer are correlated with severity and course of the disease. These data were used to determine a new complex in surgery - systemic membrane-destabilizing distress syndrome. Its concept, pathogenesis, and diagnosis are presented. It was analyzed its role in development and progression of dysregulation pathology and thanatogenesis. Evidence of its importance in the pathogenesis of surgical aggression was obtained.

Genome-Wide Analysis of Phospholipase D Gene Family and Profiling of Phospholipids under Abiotic Stresses in Brassica napus.

Oil crop Brassica napus is subjected to environmental stresses such as drought, cold and salt. Phospholipase Ds (PLDs) have vital roles in regulation of plant growth, development and stress tolerance. In this study, 32 BnaPLD genes were identified and classified into six subgroups depending on the conserved protein structures. High similarity in gene and protein structures exists between BnaPLDs and AtPLDs. Gene expression analysis showed that BnaPLDα1s and BnaPLDδs had higher expression than other PLDs. BnaPLDα1 and BnaPLDδ were significantly induced by abiotic stresses including dehydration, NaCl, abscisic acid (ABA) and 4�C. Lipidomic analysis showed that the content of main membrane phospholipids decreased gradually under stresses, except phosphatidylglycerol increased under the treatment of ABA and phosphatidylethanolamine increased under 4�C. Correspondingly, their product of phosphatidic acid increased often with a transient peak at 8 h. The plant height of mutants of PLDα1 was significantly reduced. Agronomic traits such as yield, seed number, silique number and branches were significantly impaired in PLDα1 mutants. These results indicate that there is a large family of PLD genes in B. napus, especially BnaPLDα1s and BnaPLDδs may play important roles in membrane lipids remodeling and maintaining of the growth and stress tolerance of B. napus.

Phospholipid effects on SGLT1-mediated glucose transport in rabbit ileum brush border membrane vesicles.

In small intestine, sodium-glucose cotransporter SGLT1 provides the main mechanism for sugar uptake. We investigated the effect of membrane phospholipids (PL) on this transport in rabbit ileal brush border membrane vesicles (BBMV). For this, PL of different charge, length, and saturation were incorporated into BBMV. Transport was measured related to (i) membrane surface charge (membrane-bound MC540 fluorescence), (ii) membrane thickness (PL incorporation of different acyl chain length), and (iii) membrane fluidity (r12AS, fluorescence anisotropy of 12-AS). Compared to phosphatidylcholine (PC) carrying a neutral head group, inhibition of SGLT1 increased considerably with the acidic phosphatidic acid (PA) and phosphatidylinositol (PI) that increase membrane negative surface charge. The order of PL potency was PI>PA > PE = PS > PC. Inhibition by acidic PA-oleate was 5-times more effective than with neutral PE (phosphatidylethanolamine)-oleate. Lineweaver-Burk plot indicated uncompetitive inhibition of SGLT1 by PA. When membrane thickness was increased by neutral PC of varying acyl chain length, transport was increasingly inhibited by 16:1 PC to 22:1 PC. Even more pronounced inhibition was observed with mono-unsaturated instead of saturated acyl chains which increased membrane fluidity (indicated by decreased r12AS). In conclusion, sodium-dependent glucose transport of rabbit ileal BBMV is modulated by (i) altered membrane surface charge, (ii) length of acyl chains via membrane thickness, and (iii) saturation of PL acyl chains altering membrane fluidity. Transport was attenuated by charged PL with longer and unsaturated acyl residues. Alterations of PL may provide a principle for attenuating dietary glucose uptake.

Enzymatically oxidized phospholipids assume center stage as essential regulators of innate immunity and cell death.

Enzymatically oxidized phospholipids (eoxPLs) are formed through regulated processes by which eicosanoids or prostaglandins are attached to phospholipids (PLs) in immune cells. These eoxPLs comprise structurally diverse families of biomolecules with potent bioactivities, and they have important immunoregulatory roles in both health and disease. The formation of oxPLs through enzymatic pathways and their signaling capabilities are emerging concepts. This paradigm is changing our understanding of eicosanoid, prostaglandin, and PL biology in health and disease. eoxPLs have roles in cellular events such as ferroptosis, apoptosis, and blood clotting and diseases such as arthritis, diabetes, and cardiovascular disease. They are increasingly recognized as endogenous bioactive mediators and potential targets for drug development. This review will describe recent evidence that places eoxPLs and their biosynthetic pathways center stage in immunoregulation.

Neisseria gonorrhoeae MlaA influences gonococcal virulence and membrane vesicle production.

The six-component maintenance of lipid asymmetry (Mla) system is responsible for retrograde transport of phospholipids, ensuring the barrier function of the Gram-negative cell envelope. Located within the outer membrane, MlaA (VacJ) acts as a channel to shuttle phospholipids from the outer leaflet. We identified Neisseria gonorrhoeae MlaA (ngo2121) during high-throughput proteomic mining for potential therapeutic targets against this medically important human pathogen. Our follow-up phenotypic microarrays revealed that lack of MlaA results in a complex sensitivity phenome. Herein we focused on MlaA function in cell envelope biogenesis and pathogenesis. We demonstrate the existence of two MlaA classes among 21 bacterial species, characterized by the presence or lack of a lipoprotein signal peptide. Purified truncated N. gonorrhoeae MlaA elicited antibodies that cross-reacted with a panel of different Neisseria. Little is known about MlaA expression; we provide the first evidence that MlaA levels increase in stationary phase and under anaerobiosis but decrease during iron starvation. Lack of MlaA resulted in higher cell counts during conditions mimicking different host niches; however, it also significantly decreased colony size. Antimicrobial peptides such as polymyxin B exacerbated the size difference while human defensin was detrimental to mutant viability. Consistent with the proposed role of MlaA in vesicle biogenesis, the ΔmlaA mutant released 1.7-fold more membrane vesicles. Comparative proteomics of cell envelopes and native membrane vesicles derived from ΔmlaA and wild type bacteria revealed enrichment of TadA-which recodes proteins through mRNA editing-as well as increased levels of adhesins and virulence factors. MlaA-deficient gonococci significantly outcompeted (up to 16-fold) wild-type bacteria in the murine lower genital tract, suggesting the growth advantage or increased expression of virulence factors afforded by inactivation of mlaA is advantageous in vivo. Based on these results, we propose N. gonorrhoeae restricts MlaA levels to modulate cell envelope homeostasis and fine-tune virulence.

Oxidized phospholipids in Doxorubicin-induced cardiotoxicity.

Doxorubicin (Dox), a widely used chemotherapy drug, can also cause cardiotoxic effects leading to heart failure. The excessive oxidative stress caused by Dox results in the modification of a variety of cellular molecules, including phospholipids. In cardiomyocytes, Dox increases oxidation of a species of phospholipids, phosphatidylcholine, which has been associated with increased cell death. Oxidized phospholipids (Ox-PL) are involved in development and progression of various pathologies, including atherosclerosis, thrombosis, and tissue inflammation. Moreover, Ox-PL and excess iron are associated with ferroptosis, a form of regulated cell death. Neutralizing Ox-PL increases resistance to ischemia-reperfusion injuries which is linked to preservation of the mitochondrial membrane potential. This review aims to discuss the potential role of Ox-PL in Dox-induced pathology and supports the notion that a better understanding of the field could point to new strategies to prevent cardiotoxicity.

Phospholipid regulation of innate immunity and respiratory viral infection.

Toll-like receptors (TLRs) coupled to intracellular signaling cascades function as central elements of innate immunity that control transcription of numerous pro-inflammatory genes. Two minor anionic phospholipids present in the pulmonary surfactant complex, palmitoyl-oleoyl-phosphatidylglycerol (POPG) and phosphatidylinositol (PI), antagonize the cognate ligand activation of TLRs 2 and 4. The lipids block recognition of activating ligands by the TLRs, either directly or via the TLR4 coreceptors CD14 and MD2. Antagonism of TLR activation results in inhibition of the initiating step of the pro-inflammatory signaling pathways. Evidence for this mechanism of action comes from direct binding studies between CD14 and MD2 with POPG and PI. Additional evidence for this mechanism of antagonism also comes from monitoring the reduction of protein phosphorylation events that characterize the intracellular signaling by activated TLRs. The pathogenesis of respiratory syncytial virus (RSV) and influenza A virus (IAV) have been linked to TLR4 activation, and we examined the action of POPG and PI as potential antagonists of the pathology of these viruses. Surprisingly, POPG and PI dramatically curtail infection, in addition to inhibiting inflammatory sequelae associated with RSV and IAV infections. The mechanism of action by the lipids is disruption of virus particle binding to host cell plasma membrane receptors, required for viral uptake. The antagonism of activation of TLRs and virus binding to the alveolar epithelium by resident constituents of the pulmonary surfactant system suggests that POPG and PI function in homeostasis, to prevent inflammatory processes that result in reductions in gas exchange within the alveolar compartment.

The phospholipid flippase DnfD localizes to late Golgi and is involved in asexual differentiation in Aspergillus nidulans.

The maintenance of cell shape requires finely tuned and robust vesicle trafficking in order to provide sufficient plasma membrane materials. The hyphal cells of filamentous fungi are an extreme example of cell shape maintenance due to their ability to grow rapidly and respond to the environment while keeping a relatively consistent shape. We have previously shown that two phospholipid flippases, which regulate the asymmetry of specific phospholipids within the plasma membrane, are important for hyphal growth in Aspergillus nidulans. Here, we examine the rest of the phospholipid flippases encoded by A. nidulans by obtaining single and double deletions of all four family members, dnfA, dnfB, dnfC, and dnfD. We find that deleting dnfC does not impart a noticeable phenotype, by itself or with other deletions, but that dnfD, the homolog of the essential yeast gene neo1, is important for conidiation. dnfD deletion mutants form misshapen conidiophore vesicles that are defective in metulae formation. We localize DnfD to late Golgi equivalents, where it appears just before dissociation of this organelle. We propose that DnfD functions in a trafficking process that is specifically required for the morphological changes that take place during conidiation.

Natural phospholipids: Occurrence, biosynthesis, separation, identification, and beneficial health aspects.

During the last years, phospholipids (PLs) have attracted great attention because of their crucial roles in providing nutritional values, technological and medical applications. There are considerable proofs that PLs have unique nutritional benefits on human health, such as reducing cholesterol absorption, improving liver functions, and decreasing the risk of cardiovascular diseases. PLs are the main structural lipid components of cell and organelle membranes in all living organisms, and therefore, they occur in all organisms and the derived food products. PLs are distinguished by the presence of a hydrophilic head and a hydrophobic tail, consequently they possess amphiphilic features. Due to their unique characteristics, the extraction, separation, and identification of PLs are critical issues to be concerned. This review is focused on the content of PLs classes in several sources (including milk, vegetable oils, egg yolk, and mitochondria). As well, it highlights PLs biosynthesis, and the methodologies applied for PLs extraction and separation, such as solvent extraction and solid-phase extraction. In addition, the determination and quantification of PLs classes by using thin layer chromatography, high-performance liquid chromatography coupled with different detectors, and nuclear magnetic resonance spectroscopy techniques.

Articular cartilage. Strong adsorption and cohesion of phospholipids with the quaternary ammonium cations providing satisfactory lubrication of natural joints.

Much evidence supports the hypothesis that surface-active phospholipid (SAPL) molecules on articular cartilage (AC) adsorbed to negatively-charged proteoglycan matrix form phospholipid (membrane), are negatively charged surface (-PO4-) and hydrophilic. In Hills cartilage model (1984) phospholipids adsorbed to cartilage surface act as boundary lubricants making the surface extremely hydrophobic. Hydrophobic surface of AC has gained no support in all experimental facts presented in this paper and the current literature showing that AC is amphoteric and hydrophilic with the negatively charged surface (-PO4-). The interfacial energy of the model membrane of spherical lipid bilayers evident from phosphatidylcholine "bell-shaped curve" has amphoteric character and lowest energy in lubrication at a pH 7.4 ± 1 of the natural joint.