Biophysical properties of lipids and dynamic membranes

The autophagy protein ATG-9 regulates lysosome function and integrity

The transmembrane autophagy protein ATG9 has multiple functions essential for autophagosome formation. Here, we uncovered a novel function of ATG-9 in regulating lysosome biogenesis and integrity in Caenorhabditis elegans. Through a genetic screen, we identified that mutations attenuating the lipid scrambling activity of ATG-9 suppress the autophagy defect in epg-5 mutants, in which non-degradative autolysosomes accumulate. The scramblase-attenuated ATG-9 mutants promote lysosome biogenesis and delivery of lysosome-localized hydrolases and also facilitate the maintenance of lysosome integrity. Through manipulation of phospholipid levels, we found that a reduction in phosphatidylethanolamine (PE) also suppresses the autophagy defects and lysosome damage associated with impaired lysosomal degradation. Our results reveal that modulation of phospholipid composition and distribution, e.g., by attenuating the scramblase activity of ATG-9 or reducing the PE level, regulates lysosome function and integrity.

Reprograming gene expression in 'hibernating' C. elegans involves the IRE-1/XBP-1 pathway

In nature, many animals respond to cold by entering hibernation, while in clinical settings, controlled cooling is used in transplantation and emergency medicine. However, the molecular mechanisms that enable cells to survive severe cold are still not fully understood. One key aspect of cold adaptation is the global downregulation of protein synthesis. Studying it in the nematode Caenorhabditis elegans, we find that the translation of most mRNAs continues in the cold, albeit at a slower rate, and propose that cold-specific gene expression is regulated primarily at the transcription level. Supporting this idea, we found that the transcription of certain cold-induced genes is linked to the activation of unfolded protein response (UPR) through the conserved IRE-1/XBP-1 signaling pathway. Our findings suggest that this pathway is triggered by cold-induced perturbations in proteins and lipids within the endoplasmic reticulum, and that its activation is beneficial for cold survival.

Temporal oscillation of phospholipids promotes metabolic efficiency

Biological timing is a fundamental aspect of life, facilitating efficient resource use and adaptation to environmental changes. In this study, we unveil robust temporal oscillations in phospholipid abundance as a function of the yeast metabolic cycle (YMC). These fluctuations, occurring throughout the cell division cycle, demonstrate a systematic segregation of various phospholipid species over time. Such segregation corresponds logically with their physical properties, generating entropic forces for membrane dynamics and biogenesis. Within the YMC, the temporal oscillations in phosphatidylethanolamine and phosphatidylcholine levels require biosynthesis from triacylglycerol as a crucial lipid reservoir, with phosphatidylinositol and phosphatidylserine synthesized primarily de novo. The orchestrated regulation of gene expression in biosynthesis pathways ensures precise temporal control of phospholipid dynamics, ultimately promoting metabolic efficiency.

Unlocking the power of membrane biophysics: enhancing the study of antimicrobial peptides activity and selectivity

The application of membrane-active antimicrobial peptides (AMPs) is considered to be a viable alternative to conventional antibiotics for treating infections caused by multidrug-resistant pathogenic microorganisms. In vitro and in silico biophysical approaches are indispensable for understanding the underlying molecular mechanisms of membrane-active AMPs. Lipid bilayer models are widely used to mimic and study the implication of various factors affecting these bio-active molecules, and their relationship with the physical parameters of the different membranes themselves. The quality and resemblance of these models to their target is crucial for elucidating how these AMPs work. Unfortunately, over the last few decades, no notable efforts have been made to improve or refine membrane mimetics, as it pertains to the elucidation of AMPs molecular mechanisms. In this review, we discuss the importance of improving the quality and resemblance of target membrane models, in terms of lipid composition and distribution, which ultimately directly influence physical parameters such as charge, fluidity, and thickness. In conjunction, membrane and peptide properties determine the global effect of selectivity, activity, and potency. It is therefore essential to define these interactions, and to do so, more refined lipid models are necessary. In this review, we focus on the significant advancements in promoting biomimetic membranes that closely resemble native ones, for which thorough biophysical characterization is key. This includes utilizing more complex lipid compositions that mimic various cell types. Additionally, we discuss important considerations to be taken into account when working with more complex systems.

Cellular Signaling at the Nano-Bio Interface: Spotlighting Membrane Curvature

No longer viewed as a passive consequence of cellular activities, membrane curvature-the physical shape of the cell membrane-is now recognized as an active constituent of biological processes. Nanoscale topographies on extracellular matrices or substrate surfaces impart well-defined membrane curvatures on the plasma membrane. This review examines biological events occurring at the nano-bio interface, the physical interface between the cell membrane and surface nanotopography, which activates intracellular signaling by recruiting curvature-sensing proteins. We encompass a wide range of biological processes at the nano-bio interface, including cell adhesion, endocytosis, glycocalyx redistribution, regulation of mechanosensitive ion channels, cell migration, and differentiation. Despite the diversity of processes, we call attention to the critical role of membrane curvature in each process. We particularly highlight studies that elucidate molecular mechanisms involving curvature-sensing proteins with the hope of providing comprehensive insights into this rapidly advancing area of research.

Fumonisin B1 Exerts Immunosuppressive Effects Through Cytoskeleton Remodeling and Function Attenuation of Mature Dendritic Cells

Fumonisin B1 (FB1) is one of the most toxic mycotoxins and is harmful to humans and animals due to its hepatotoxicity, immunotoxicity and carcinogenicity. However, the mechanism of its immunosuppressive effect is still under investigation. Dendritic cells (DCs) are the most potent professional antigen-presenting cells, and their differentiation, maturation and immunomodulatory functions are closely related to the immunotoxicity of certain mycotoxins. Migratory capacity is a prerequisite for mature DCs (mDCs) to move and present antigens in secondary lymphoid tissue, whereas the mechanical properties and cytoskeletal structure are critical for their migration and immune functions. Therefore, the effects of FB1 on the cell viability, mechanical characteristics, cytoskeletal structure and its binding proteins, migration, co-stimulatory molecules and the immune functions of mDCs were investigated to explore the potential mechanisms of immunotoxicity. The results showed that FB1 could impair the chemotactic migratory capability, the expression of co-stimulatory molecules and the ability of DCs to stimulate T cell proliferation. Further analyses elucidated that the mechanical properties of mDCs were changed, the cytoskeletal structures were reorganized and the expressions of cytoskeleton-binding proteins were regulated. In conclusion, the attenuated migration and immune functions of mDCs caused by FB1 may be related to their altered mechanical properties and cytoskeleton remodeling, which may be one of the action modes for FB1 to exert its immunosuppressive effect.

Host Immune Cell Membrane Deformability Governs the Uptake Route of Malaria-Derived Extracellular Vesicles

The malaria parasite, Plasmodium falciparum, secretes extracellular vesicles (EVs) to facilitate its growth and to communicate with the external microenvironment, primarily targeting the host's immune cells. How parasitic EVs enter specific immune cell types within the highly heterogeneous pool of immune cells remains largely unknown. Using a combination of imaging flow cytometry and advanced fluorescence analysis, we demonstrated that the route of uptake of parasite-derived EVs differs markedly between host T cells and monocytes. T cells, which are components of the adaptive immune system, internalize parasite-derived EVs mainly through an interaction with the plasma membrane, whereas monocytes, which function in the innate immune system, take up these EVs via endocytosis. The membranal/endocytic balance of EV internalization is driven mostly by the amount of endocytic incorporation. Integrating atomic force microscopy with fluorescence data analysis revealed that internalization depends on the biophysical properties of the cell membrane rather than solely on molecular interactions. In support of this, altering the cholesterol content in the cell membrane tilted the balance in favor of one uptake route over another. Our results provide mechanistic insights into how P. falciparum-derived EVs enter into diverse host cells. This study highlights the sophisticated cell-communication tactics used by the malaria parasite.

Phospholipid biosynthesis modulates nucleotide metabolism and reductive capacity

Phospholipid and nucleotide syntheses are fundamental metabolic processes in eukaryotic organisms, with their dysregulation implicated in various disease states. Despite their importance, the interplay between these pathways remains poorly understood. Using genetic and metabolic analyses in Saccharomyces cerevisiae, we elucidate how cytidine triphosphate usage in the Kennedy pathway for phospholipid synthesis influences nucleotide metabolism and redox balance. We find that deficiencies in the Kennedy pathway limit nucleotide salvage, prompting compensatory activation of de novo nucleotide synthesis and the pentose phosphate pathway. This metabolic shift enhances the production of antioxidants such as NADPH and glutathione. Moreover, we observe that the Kennedy pathway for phospholipid synthesis is inhibited during replicative aging, indicating its role in antioxidative defense as an adaptive mechanism in aged cells. Our findings highlight the critical role of phospholipid synthesis pathway choice in the integrative regulation of nucleotide metabolism, redox balance and membrane properties for cellular defense.

Membrane structure-responsive lipid scrambling by TMEM63B to control plasma membrane lipid distribution

Phospholipids are asymmetrically distributed in the plasma membrane (PM), with phosphatidylcholine and sphingomyelin abundant in the outer leaflet. However, the mechanisms by which their distribution is regulated remain unclear. Here, we show that transmembrane protein 63B (TMEM63B) functions as a membrane structure-responsive lipid scramblase localized at the PM and lysosomes, activating bidirectional lipid translocation upon changes in membrane curvature and thickness. TMEM63B contains two intracellular loops with palmitoylated cysteine residue clusters essential for its scrambling function. TMEM63B deficiency alters phosphatidylcholine and sphingomyelin distributions in the PM. Persons with heterozygous mutations in TMEM63B are known to develop neurodevelopmental disorders. We show that V44M, the most frequent substitution, confers constitutive scramblase activity on TMEM63B, disrupting PM phospholipid asymmetry. We determined the cryo-electron microscopy structures of TMEM63B in its open and closed conformations, uncovering a lipid translocation pathway formed in response to changes in the membrane environment. Together, our results identify TMEM63B as a membrane structure-responsive scramblase that controls PM lipid distribution and we reveal the molecular basis for lipid scrambling and its biological importance.

Proton diffusion on the surface of mixed lipid membranes highlights the role of membrane composition

Proton circuits within biological membranes, the foundation of natural bioenergetic systems, are significantly influenced by the lipid compositions of different biological membranes. In this study, we investigate the influence of mixed lipid membrane composition on the proton transfer (PT) properties on the surface of the membrane. We track the excited-state PT (ESPT) process from a tethered probe to the membrane with timescales and length scales of PT relevant to bioenergetic systems. Two processes can happen during ESPT: the initial PT from the probe to the membrane at short timescales, followed by diffusion of dissociated protons around the probe on the membrane, and the possible geminate recombination with the probe at longer timescales. Here, we use membranes composed of mixtures of phosphatidylcholine (PC) and phosphatidic acid (PA). We show that the changes in the ESPT properties are not monotonous with the concentration of the lipid mixture; at a low concentration of PA in PC, we find that the membrane is a poor proton acceptor. Molecular dynamics simulations indicate that the membrane is more structured at this specific lipid mixture, with the least number of defects. Accordingly, we suggest that the structure of the membrane is an important factor in facilitating PT. We further show that the composition of the membrane affects the geminate proton diffusion around the probe, whereas, on a timescale of tens of nanoseconds, the dissociated proton is mostly lateral restricted to the membrane plane in PA membranes, while in PC, the diffusion is less restricted by the membrane.

A tuneable minimal cell membrane reveals that two lipid species suffice for life

All cells are encapsulated by a lipid membrane that facilitates their interactions with the environment. How cells manage diverse mixtures of lipids, which dictate membrane property and function, is experimentally challenging to address. Here, we present an approach to tune and minimize membrane lipid composition in the bacterium Mycoplasma mycoides and its derived 'minimal cell' (JCVI-Syn3A), revealing that a two-component lipidome can support life. Systematic reintroduction of phospholipids with different features demonstrates that acyl chain diversity is more important for growth than head group diversity. By tuning lipid chirality, we explore the lipid divide between Archaea and the rest of life, showing that ancestral lipidomes could have been heterochiral. However, in these simple organisms, heterochirality leads to impaired cellular fitness. Thus, our approach offers a tunable minimal membrane system to explore the fundamental lipidomic requirements for life, thereby extending the concept of minimal life from the genome to the lipidome.

Decoding the role of mycobacterial lipid remodelling and membrane dynamics in antibiotic tolerance

Current treatments for tuberculosis primarily target Mycobacterium tuberculosis (Mtb) infections, often neglecting the emerging issue of latent tuberculosis infection (LTBI) which are characterized by reduced susceptibility to antibiotics. The bacterium undergoes multiple adaptations during dormancy within host granulomas, leading to the development of antibiotic-tolerant strains. The mycobacterial membrane plays a crucial role in drug permeability, and this study aims to characterize membrane lipid deviations during dormancy through extensive lipidomic analysis of bacteria cultivated in distinct media and growth stages. The results revealed that specific lipids localize in different regions of the membrane envelope, allowing the bacterium to adapt to granuloma conditions. These lipid modifications were then correlated with the biophysical properties of the mycomembrane, which may affect interactions with antibiotics. Overall, our findings offer a deeper understanding of the bacterial adaptations during dormancy, highlighting the role of lipids in modulating membrane behaviour and drug permeability, ultimately providing the groundwork for the development of more effective treatments tailored to combat latent infections.

A tuneable minimal cell membrane reveals that two lipid species suffice for life

All cells are encapsulated by a lipid membrane which facilitates the interaction between life and its environment. How life exploits the diverse mixtures of lipids that dictate membrane property and function has been experimentally challenging to address. We introduce an approach to tune and minimize lipidomes in Mycoplasma mycoides and the Minimal Cell (JCVI-Syn3A) revealing that a 2-component lipidome can support life. Systematically reintroducing phospholipid features demonstrated that acyl chain diversity is more critical for growth than head group diversity. By tuning lipid chirality, we explored the lipid divide between Archaea and the rest of life, showing that ancestral lipidomes could have been heterochiral. Our approach offers a tunable minimal membrane system to explore the fundamental lipidomic requirements for life, thereby extending the concept of minimal life from the genome to the lipidome.

Structure-function relationship of phase-separated liposomes containing diacylglycerol analogues

The composition and morphology of lipid-based nanoparticles can influence their overall in vivo behavior. Previously, we demonstrated that phase separation in liposomes composed of DSPC and a diacylglycerol lipid analogue (DOaG) drives the in vivo biodistribution towards a specific subset of endothelial cells in zebrafish embryos. In the absence of traditional targeting functionalities (e.g., antibodies, ligands), this selectivity is mediated solely by the unique liposome morphology and composition, characterized by a DOaG-rich lipid droplet within the DSPC-rich phospholipid bilayer. The phase separation is induced due to the geometry of DOaG lipid and its ability to create non-bilayer phases in lipid membranes. To investigate the underlying principles of phase separation and to optimize the liposome colloidal stability, we performed a structure-function relationship study by synthesizing a library of DOaG analogues with varying molecular properties, such as the number, length and sn-position of the acyl chains, as well as the degree of saturation or carbonyl substituents. We assessed the ability of these lipid analogues to assemble into phase-separated liposomes and studied their morphology, colloidal stability, and in vivo biodistribution in zebrafish embryos. We found that analogues containing unsaturated, medium length (C16-C18) fatty acids were required to obtain colloidally stable, phase-separated liposomes with cell-specific biodistribution patterns. Moreover, we observed that using the pure DOaG isomer, with acyl chains at the sn-1,3 positions, leads to more colloidally stable liposomes than when a mixture of sn-1,2 and sn-1,3 isomers is used. Similarly, we observed that incorporating a DOaG analogue with fatty tails shorter than DSPC, as well as PEGylation, endows liposomes with long term stability while retaining cell-selective biodistribution. Diacylglycerols are known to promote fusion, lipid polymorphism, signaling and protein recruitment on lipid membranes. In this study, we showed that diacylglycerol derivatives can induce phase separation in liposomes, unlocking the potential for cell-specific targeting in vivo. We believe that these findings can be the foundation for future use of diacylglycerols in lipid-based nanomedicines and could lead to the development of novel targeted delivery strategies.

Comparison of human breast milk vs commercial formula-induced early trophic enteral nutrition during postoperative prolonged starvation in an animal model

The present study aimed to characterize the changes in macromolecular composition and structure in ileal tissue induced by postoperative prolonged starvation (PS), human breast milk feeding (HM) and commercial formula feeding (CF) for 48 and 72 h (h). Forty-two Wistar albino rats underwent an ileal transection and primary anastomosis and were then divided into six subgroups. Two groups of seven rats were food-deprived for 48 and 72 h with free access to water only in metabolic cages (48 h PS, 72 h PS). Then, two groups of seven rats received early enteral trophic nutrition (EEN) either using HM, and CF at 48 h post-operation (48 h HM, 48 h CF). The other two groups of seven rats received the same trophic enteral nutrition at 72 h post-operation (72 h HM, 72 h CF). An additional seven rats were fed normal rat chow (control), after which the ileal tissues were harvested and freeze-dried overnight. Then sample spectra were recorded by Fourier transform infrared (FTIR) spectroscopy. PS at 48 and 72 h resulted in an increase in the concentration of lipids and a decrease in the concentration of proteins. CF and HM trophic feeding induced a decrease in membrane fluidity and an increase in lipid order. Ileal tissues showed similar compositional and structural changes in lipids and proteins in the PS and CF groups after 48 and 72 h. A marked decrease in nucleic acid concentration was seen in CF at 48 h compared to HM. The human milk feeding groups did not induce any significant alterations and showed compositional and structural data similar to the controls. In conclusion, EEN application seems to be safer when introduced at 48 h rather than 72 h and time of this nutrition is crucial to maintain ileum structure and therefore immunity and well-being. HM-induced trophic nutrition is seen to protect the ileal tissue from significant alterations within lipid and protein compositions, whereas CF caused notable changes. HM is absolutely the best nutritional source for gut health in this animal model.

GMP affected assembly behaviors of phosphatidylethanolamine monolayers elucidated by multi-resolved SFG-VS and BAM

The interaction between nucleotide molecules and lipid molecules plays important roles in cell activities, but the molecular mechanism is very elusive. In the present study, a small but noticeable interaction between the negatively charged phosphatidylethanolamine (PE) and Guanosine monophosphate (GMP) molecules was observed from the PE monolayer at the air/water interface. As shown by the sum frequency generation (SFG) spectra and Pi-A isotherm of the PE monolayer, the interaction between the PE and GMP molecules imposes very small changes to the PE molecules. However, the Brewster angle microscopy (BAM) technique revealed that the assembly conformations of PE molecules are significantly changed by the adsorption of GMP molecules. By comparing the SFG spectra of PE monolayers after the adsorption of GMP, guanosine and guanine, it is also shown that the hydrogen bonding effect plays an important role in the nucleotide-PE interactions. These results provide fundamental insight into the structure changes during the nucleotide-lipid interaction, which may shed light on the molecular mechanism of viral infection, DNA drug delivery, and cell membrane curvature control in the brain or neurons.

Probing membrane deformation energy by KcsA potassium channel gating under varied membrane thickness and tension

This study investigated how membrane thickness and tension modify the gating of KcsA potassium channels when simultaneously varied. The KcsA channel undergoes global conformational changes upon gating: expansion of the cross-sectional area and longitudinal shortening upon opening. Thus, membranes impose differential effects on the open and closed conformations, such as hydrophobic mismatches. Here, the single-channel open probability was recorded in the contact bubble bilayer, by which variable thickness membranes under a defined tension were applied. A fully open channel in thin membranes turned to sporadic openings in thick membranes, where the channel responded moderately to tension increase. Quantitative gating analysis prompted the hypothesis that tension augmented the membrane deformation energy when hydrophobic mismatch was enhanced in thick membranes.

Identification of lipid-specific proteins with high-density lipid-immobilized beads

In biological membranes, lipids often interact with membrane proteins (MPs), regulating the localization and activity of MPs in cells. Although elucidating lipid-MP interactions is critical to comprehend the physiological roles of lipids, a systematic and comprehensive identification of lipid-binding proteins has not been adequately established. Therefore, we report the development of lipid-immobilized beads where lipid molecules were covalently immobilized. Owing to the detergent tolerance, these beads enable screening of water-soluble proteins and MPs, the latter of which typically necessitate surfactants for solubilization. Herein, two sphingolipid species-ceramide and sphingomyelin-which are major constituents of lipid rafts, were immobilized on the beads. We first showed that the density of immobilized lipid molecules on the beads was as high as that of biological lipid membranes. Subsequently, we confirmed that these beads enabled the selective pulldown of known sphingomyelin- or ceramide-binding proteins (lysenin, p24, and CERT) from protein mixtures, including cell lysates. In contrast, commercial sphingomyelin beads, on which lipid molecules are sparsely immobilized through biotin-streptavidin linkage, failed to capture lysenin, a well-known protein that recognizes clustered sphingomyelin molecules. This clearly demonstrates the applicability of our beads for obtaining proteins that recognize not only a single lipid molecule but also lipid clusters or lipid membranes. Finally, we demonstrated the screening of lipid-binding proteins from Neuro2a cell lysates using these beads. This method is expected to significantly contribute to the understanding of interactions between lipids and proteins and to unravel the complexities of lipid diversity.

Piezo 1 and Piezo 2 in the Chemosensory Organs of Zebrafish (Danio rerio)

The ion channels Piezo 1 and Piezo 2 have been identified as membrane mechano-proteins. Studying mechanosensitive channels in chemosensory organs could help in understanding the mechanisms by which these channels operate, offering new therapeutic targets for various disorders. This study investigates the expression patterns of Piezo proteins in zebrafish chemosensory organs. For the first time, Piezo protein expression in adult zebrafish chemosensory organs is reported. In the olfactory epithelium, Piezo 1 immunolabels kappe neurons, microvillous cells, and crypt neurons, while Calretinin is expressed in ciliated sensory cells. The lack of overlap between Piezo 1 and Calretinin confirms Piezo 1's specificity for kappe neurons, microvillous cells, and crypt neurons. Piezo 2 shows intense immunoreactivity in kappe neurons, one-ciliated sensory cells, and multi-ciliated sensory cells, with overlapping Calretinin expression, indicating its olfactory neuron nature. In taste buds, Piezo 1 immunolabels Merkel-like cells at the bases of cutaneous and pharyngeal taste buds and the light and dark cells of cutaneous and oral taste buds. It also marks the dark cells of pharyngeal taste buds and support cells in oral taste buds. Piezo 2 is found in the light and dark cells of cutaneous and oral taste buds and isolated chemosensory cells. These findings provide new insights into the distribution of Piezo channels in zebrafish chemosensory organs, enhancing our understanding of their sensory processing and potential therapeutic applications.

Membrane Epilipidome-Lipid Modifications, Their Dynamics, and Functional Significance

Lipids are characterized by extremely high structural diversity translated into a wide range of physicochemical properties. As such, lipids are vital for many different functions including organization of cellular and organelle membranes, control of cellular and organismal energy metabolism, as well as mediating multiple signaling pathways. To maintain the lipid chemical diversity and to achieve rapid lipid remodeling required for the responsiveness and adaptability of cellular membranes, living systems make use of a network of chemical modifications of already existing lipids that complement the rather slow biosynthetic pathways. Similarly to biopolymers, which can be modified epigenetically and posttranscriptionally (for nucleic acids) or posttranslationally (for proteins), lipids can also undergo chemical alterations through oxygenation, nitration, phosphorylation, glycosylation, etc. In this way, an expanded collective of modified lipids that we term the "epilipidome," provides the ultimate level of complexity to biological membranes and delivers a battery of active small-molecule compounds for numerous regulatory processes. As many lipid modifications are tightly controlled and often occur in response to extra- and intracellular stimuli at defined locations, the emergence of the epilipidome greatly contributes to the spatial and temporal compartmentalization of diverse cellular processes. Accordingly, epilipid modifications are observed in all living organisms and are among the most consistent prerequisites for complex life.

Docosahexaenoic Acid Controls Pulmonary Macrophage Lipid Raft Size and Inflammation

BACKGROUND

Docosahexaenoic acid (DHA) controls the biophysical organization of plasma membrane sphingolipid/cholesterol-enriched lipid rafts to exert anti-inflammatory effects, particularly in lymphocytes. However, the impact of DHA on the spatial arrangement of alveolar macrophage lipid rafts and inflammation is unknown.

OBJECTIVES

The primary objective was to determine how DHA controls lipid raft organization and function of alveolar macrophages. As proof-of-concept, we also investigated DHA's anti-inflammatory effects on select pulmonary inflammatory markers with a murine influenza model.

METHODS

MH-S cells, an alveolar macrophage line, were treated with 50 μM DHA or vehicle control and were used to study plasma membrane molecular organization with fluorescence-based methods. Biomimetic membranes and coarse grain molecular dynamic (MD) simulations were employed to investigate how DHA mechanistically controls lipid raft size. qRT-PCR, mass spectrometry, and ELISAs were used to quantify downstream inflammatory signaling transcripts, oxylipins, and cytokines, respectively. Lungs from DHA-fed influenza-infected mice were analyzed for specific inflammatory markers.

RESULTS

DHA increased the size of lipid rafts while decreasing the molecular packing of the MH-S plasma membrane. Adding a DHA-containing phospholipid to a biomimetic lipid raft-containing membrane led to condensing, which was reversed with the removal of cholesterol. MD simulations revealed DHA nucleated lipid rafts by driving cholesterol and sphingomyelin into rafts. Downstream of the plasma membrane, DHA lowered the concentration of select inflammatory transcripts, oxylipins, and IL-6 secretion. DHA lowered pulmonary Il6 and Tnf-α mRNA expression and increased anti-inflammatory oxylipins of influenza-infected mice.

CONCLUSIONS

The data suggest a model in which the localization of DHA acyl chains to nonrafts is driving sphingomyelin and cholesterol molecules into larger lipid rafts, which may serve as a trigger to impede signaling and lower inflammation. These findings also identify alveolar macrophages as a target of DHA and underscore the anti-inflammatory properties of DHA for lung inflammation.

FIT2 proteins and lipid droplet emergence, an interplay between phospholipid synthesis, surface tension, and membrane curvature

Lipid droplets (LDs) serve as intracellular compartments primarily dedicated to the storage of metabolic energy in the form of neutral lipids. The processes that regulate and control LD biogenesis are being studied extensively and are gaining significance due to their implications in major metabolic disorders, including type 2 diabetes and obesity. A protein of particular interest is Fat storage-Inducing Transmembrane 2 (FIT2), which affects the emergence step of LD biogenesis. Instead of properly emerging towards the cytosol, LDs in FIT2-deficient cells remain embedded within the membrane of the endoplasmic reticulum (ER). In vitro studies revealed the ability of FIT2 to bind both di- and triacylglycerol (DAG/TAG), key players in lipid storage, and its activity to cleave acyl-CoA. However, the translation of these in vitro functions to the observed embedding of LDs in FIT2 deficient cells remains to be established. To understand the role of FIT2 in vivo, we discuss the parameters that affect LD emergence. Our focus centers on the role that membrane curvature and surface tension play in LD emergence, as well as the impact that the lipid composition exerts on these key parameters. In addition, we discuss hypotheses on how FIT2 could function locally to modulate lipids at sites of LD emergence.

Deciphering the functional role of clinical mutations in ABCB1, ABCC1, and ABCG2 ABC transporters in endometrial cancer

ATP-binding cassette transporters represent a superfamily of dynamic membrane-based proteins with diverse yet common functions such as use of ATP hydrolysis to efflux substrates across cellular membranes. Three major transporters-P-glycoprotein (P-gp or ABCB1), multidrug resistance protein 1 (MRP1 or ABCC1), and breast cancer resistance protein (BCRP or ABCG2) are notoriously involved in therapy resistance in cancer patients. Despite exhaustive individual characterizations of each of these transporters, there is a lack of understanding in terms of the functional role of mutations in substrate binding and efflux, leading to drug resistance. We analyzed clinical variations reported in endometrial cancers for these transporters. For ABCB1, the majority of key mutations were present in the membrane-facing region, followed by the drug transport channel and ATP-binding regions. Similarly, for ABCG2, the majority of key mutations were located in the membrane-facing region, followed by the ATP-binding region and drug transport channel, thus highlighting the importance of membrane-mediated drug recruitment and efflux in ABCB1 and ABCG2. On the other hand, for ABCC1, the majority of key mutations were present in the inactive nucleotide-binding domain, followed by the drug transport channel and membrane-facing regions, highlighting the importance of the inactive nucleotide-binding domain in facilitating indirect drug efflux in ABCC1. The identified key mutations in endometrial cancer and mapped common mutations present across different types of cancers in ABCB1, ABCC1, and ABCG2 will facilitate the design and discovery of inhibitors targeting unexplored structural regions of these transporters and re-engineering of these transporters to tackle chemoresistance.

Dysregulation of cellular membrane homeostasis as a crucial modulator of cancer risk

Cellular membranes serve as an epicentre combining extracellular and cytosolic components with membranous effectors, which together support numerous fundamental cellular signalling pathways that mediate biological responses. To execute their functions, membrane proteins, lipids and carbohydrates arrange, in a highly coordinated manner, into well-defined assemblies displaying diverse biological and biophysical characteristics that modulate several signalling events. The loss of membrane homeostasis can trigger oncogenic signalling. More recently, it has been documented that select membrane active dietaries (MADs) can reshape biological membranes and subsequently decrease cancer risk. In this review, we emphasize the significance of membrane domain structure, organization and their signalling functionalities as well as how loss of membrane homeostasis can steer aberrant signalling. Moreover, we describe in detail the complexities associated with the examination of these membrane domains and their association with cancer. Finally, we summarize the current literature on MADs and their effects on cellular membranes, including various mechanisms of dietary chemoprevention/interception and the functional links between nutritional bioactives, membrane homeostasis and cancer biology.

Nanoscale Structure of Lipid-Gemini Surfactant Mixed Monolayers Resolved with AFM and KPFM Microscopy

Drug delivery vehicles composed of lipids and gemini surfactants (GS) are promising in gene therapy. Tuning the composition and properties of the delivery vehicle is important for the efficient load and delivery of DNA fragments (genes). In this paper, we studied novel gene delivery systems composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-3-phosphocholine (DPPC), and GS of the type N,N-bis(dimethylalkyl)-α,ω-alkanediammonium dibromide at different ratios. The nanoscale properties of the mixed DOPC-DPPC-GS monolayers on the surface of the gene delivery system were studied using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We demonstrate that lipid-GS mixed monolayers result in the formation of nanoscale domains that vary in size, height, and electrical surface potential. We show that the presence of GS can impart significant changes to the domain topography and electrical surface potential compared to monolayers composed of lipids alone.

Oleic Acid Could Act as a Channel Blocker in the Inhibition of nAChR: Insights from Molecular Dynamics Simulations

The activation of the muscular nicotinic acetylcholine receptor (nAChR) produces the opening of the channel, with the consequent increase in the permeability of cations, triggering an excitatory signal. Free fatty acids (FFA) are known to modulate the activity of the receptor as noncompetitive antagonists, acting at the membrane-AChR interface. We present molecular dynamics simulations of a model of nAChR in a desensitized closed state embedded in a lipid bilayer in which distinct membrane phospholipids were replaced by two different monounsaturated FFA that differ in the position of a double bond. This allowed us to detect and describe that the cis-18:1ω-9 FFA were located at the interface between the transmembrane segments of α2 and γ subunits diffused into the channel lumen with the consequent potential ability to block the channel to the passage of ions.

Protective Effects of High-Density Lipoprotein on Cancer Risk: Focus on Multiple Myeloma

Lipid metabolism is intrinsically linked to tumorigenesis. And one of the most important characteristics of cancer is the modification of lipid metabolism and its correlation with oncogenic signaling pathways within the tumors. Because lipids function as signaling molecules, membrane structures, and energy sources, lipids are essential to the development of cancer. Above all, the proper immune response of tumor cells depends on the control of lipid metabolism. Changes in metabolism can modify systems that regulate carcinogenesis, such as inflammation, oxidative stress, and angiogenesis. The dependence of various malignancies on lipid metabolism varies. This review delves into the modifications to lipid metabolism that take place in cancer, specifically focusing on multiple myeloma. The review illustrates how changes in different lipid pathways impact the growth, survival, and drug-responsiveness of multiple myeloma cells, in addition to their interactions with other cells within the tumor microenvironment. The phenotype of malignant plasma cells can be affected by lipid vulnerabilities, and these findings offer a new avenue for understanding this process. Additionally, they identify novel druggable pathways that have a major bearing on multiple myeloma care.

Towards a Unitary Hypothesis of Alzheimer's Disease Pathogenesis

The "amyloid cascade" hypothesis of Alzheimer's disease (AD) pathogenesis invokes the accumulation in the brain of plaques (containing the amyloid-β protein precursor [AβPP] cleavage product amyloid-β [Aβ]) and tangles (containing hyperphosphorylated tau) as drivers of pathogenesis. However, the poor track record of clinical trials based on this hypothesis suggests that the accumulation of these peptides is not the only cause of AD. Here, an alternative hypothesis is proposed in which the AβPP cleavage product C99, not Aβ, is the main culprit, via its role as a regulator of cholesterol metabolism. C99, which is a cholesterol sensor, promotes the formation of mitochondria-associated endoplasmic reticulum (ER) membranes (MAM), a cholesterol-rich lipid raft-like subdomain of the ER that communicates, both physically and biochemically, with mitochondria. We propose that in early-onset AD (EOAD), MAM-localized C99 is elevated above normal levels, resulting in increased transport of cholesterol from the plasma membrane to membranes of intracellular organelles, such as ER/endosomes, thereby upregulating MAM function and driving pathology. By the same token, late-onset AD (LOAD) is triggered by any genetic variant that increases the accumulation of intracellular cholesterol that, in turn, boosts the levels of C99 and again upregulates MAM function. Thus, the functional cause of AD is upregulated MAM function that, in turn, causes the hallmark disease phenotypes, including the plaques and tangles. Accordingly, the MAM hypothesis invokes two key interrelated elements, C99 and cholesterol, that converge at the MAM to drive AD pathogenesis. From this perspective, AD is, at bottom, a lipid disorder.

Cardiolipin binding enhances KcsA channel gating via both its specific and dianion-monoanion interchangeable sites

KcsA is a potassium channel with a plethora of structural and functional information, but its activity in the KcsA-producing actinomycete membranes remains elusive. To determine lipid species involved in channel-modulation, a surface plasmon resonance (SPR)-based methodology, characterized by immobilization of membrane proteins under a membrane environment, was applied. Dianionic cardiolipin (CL) showed extremely higher affinity for KcsA than monoanionic lipids. The SPR experiments further demonstrated that CL bound not only to the N-terminal M0 helix, a lipid-sensor domain, but to the M0 helix-deleted mutant. In contrast, monoanionic lipids interacted primarily with the M0 helix. This indicates the presence of an alternative CL-binding site, plausibly in the transmembrane domain. Single-channel recordings demonstrated that CL enhanced channel opening in an M0-independent manner. Taken together, the action of monoanionic lipids is exclusively mediated by the M0 helix, while CL binds both the M0 helix and its specific site, further enhancing the channel activity.

The asymmetric plasma membrane-A composite material combining different functionalities?: Balancing Barrier Function and Fluidity for Effective Signaling

One persistent puzzle in the life sciences is the asymmetric lipid composition of the cellular plasma membrane: while the exoplasmic leaflet is enriched in lipids carrying predominantly saturated fatty acids, the cytoplasmic leaflet hosts preferentially lipids with (poly-)unsaturated fatty acids. Given the high energy requirements necessary for cells to maintain this asymmetry, the question naturally arises regarding its inherent benefits. In this paper, we propose asymmetry to represent a potential solution for harmonizing two conflicting requirements for the plasma membrane: first, the need to build a barrier for the uncontrolled influx or efflux of substances; and second, the need to form a fluid and dynamic two-dimensional substrate for signaling processes. We hence view here the plasma membrane as a composite material, where the exoplasmic leaflet is mainly responsible for the functional integrity of the barrier and the cytoplasmic leaflet for fluidity. We reinforce the validity of the proposed mechanism by presenting quantitative data from the literature, along with multiple examples that bolster our model.

Sample Preparation Method for MALDI Mass Spectrometry Imaging of Fresh-Frozen Spines

Technologies assessing the lipidomics, genomics, epigenomics, transcriptomics, and proteomics of tissue samples at single-cell resolution have deepened our understanding of physiology and pathophysiology at an unprecedented level of detail. However, the study of single-cell spatial metabolomics in undecalcified bones faces several significant challenges, such as the fragility of bone, which often requires decalcification or fixation leading to the degradation or removal of lipids and other molecules. As such, we describe a method for performing mass spectrometry imaging on undecalcified spine that is compatible with other spatial omics measurements. In brief, we use fresh-frozen rat spines and a system of carboxyl methylcellulose embedding, cryofilm, and polytetrafluoroethylene rollers to maintain tissue integrity while avoiding signal loss from variations in laser focus and artifacts from traditional tissue processing. This reveals various tissue types and lipidomic profiles of spinal regions at 10 μm spatial resolutions using matrix-assisted laser desorption/ionization mass spectrometry imaging. We expect this method to be adapted and applied to the analysis of the spinal cord, shedding light on the mechanistic aspects of cellular heterogeneity, development, and disease pathogenesis underlying different bone-related conditions and diseases. This study furthers the methodology for high spatial metabolomics of spines and adds to the collective efforts to achieve a holistic understanding of diseases via single-cell spatial multiomics.

ATG9A regulates the dissociation of recycling endosomes from microtubules to form liquid influenza A virus inclusions

It is now established that many viruses that threaten public health establish condensates via phase transitions to complete their lifecycles, and knowledge on such processes may offer new strategies for antiviral therapy. In the case of influenza A virus (IAV), liquid condensates known as viral inclusions, concentrate the 8 distinct viral ribonucleoproteins (vRNPs) that form IAV genome and are viewed as sites dedicated to the assembly of the 8-partite genomic complex. Despite not being delimited by host membranes, IAV liquid inclusions accumulate host membranes inside as a result of vRNP binding to the recycling endocytic marker Rab11a, a driver of the biogenesis of these structures. We lack molecular understanding on how Rab11a-recycling endosomes condensate specifically near the endoplasmic reticulum (ER) exit sites upon IAV infection. We show here that liquid viral inclusions interact with the ER to fuse, divide, and slide. We uncover that, contrary to previous indications, the reported reduction in recycling endocytic activity is a regulated process rather than a competition for cellular resources involving a novel role for the host factor ATG9A. In infection, ATG9A mediates the removal of Rab11a-recycling endosomes carrying vRNPs from microtubules. We observe that the recycling endocytic usage of microtubules is rescued when ATG9A is depleted, which prevents condensation of Rab11a endosomes near the ER. The failure to produce viral inclusions accumulates vRNPs in the cytosol and reduces genome assembly and the release of infectious virions. We propose that the ER supports the dynamics of liquid IAV inclusions, with ATG9A facilitating their formation. This work advances our understanding on how epidemic and pandemic influenza genomes are formed. It also reveals the plasticity of recycling endosomes to undergo condensation in response to infection, disclosing new roles for ATG9A beyond its classical involvement in autophagy.

Review of Eukaryote Cellular Membrane Lipid Composition, with Special Attention to the Fatty Acids

Biological membranes, primarily composed of lipids, envelop each living cell. The intricate composition and organization of membrane lipids, including the variety of fatty acids they encompass, serve a dynamic role in sustaining cellular structural integrity and functionality. Typically, modifications in lipid composition coincide with consequential alterations in universally significant signaling pathways. Exploring the various fatty acids, which serve as the foundational building blocks of membrane lipids, provides crucial insights into the underlying mechanisms governing a myriad of cellular processes, such as membrane fluidity, protein trafficking, signal transduction, intercellular communication, and the etiology of certain metabolic disorders. Furthermore, comprehending how alterations in the lipid composition, especially concerning the fatty acid profile, either contribute to or prevent the onset of pathological conditions stands as a compelling area of research. Hence, this review aims to meticulously introduce the intricacies of membrane lipids and their constituent fatty acids in a healthy organism, thereby illuminating their remarkable diversity and profound influence on cellular function. Furthermore, this review aspires to highlight some potential therapeutic targets for various pathological conditions that may be ameliorated through dietary fatty acid supplements. The initial section of this review expounds on the eukaryotic biomembranes and their complex lipids. Subsequent sections provide insights into the synthesis, membrane incorporation, and distribution of fatty acids across various fractions of membrane lipids. The last section highlights the functional significance of membrane-associated fatty acids and their innate capacity to shape the various cellular physiological responses.

Arabidopsis flippase ALA3 is required for adjustment of early subcellular trafficking in plant response to osmotic stress

To compensate for their sessile lifestyle, plants developed several responses to exogenous changes. One of the previously investigated and not yet fully understood adaptations occurs at the level of early subcellular trafficking, which needs to be rapidly adjusted to maintain cellular homeostasis and membrane integrity under osmotic stress conditions. To form a vesicle, the membrane needs to be deformed, which is ensured by multiple factors, including the activity of specific membrane proteins, such as flippases from the family of P4-ATPases. The membrane pumps actively translocate phospholipids from the exoplasmic/luminal to the cytoplasmic membrane leaflet to generate curvature, which might be coupled with recruitment of proteins involved in vesicle formation at specific sites of the donor membrane. We show that lack of the AMINOPHOSPHOLIPID ATPASE3 (ALA3) flippase activity caused defects at the plasma membrane and trans-Golgi network, resulting in altered endocytosis and secretion, processes relying on vesicle formation and movement. The mentioned cellular defects were translated into decreased intracellular trafficking flexibility failing to adjust the root growth on osmotic stress-eliciting media. In conclusion, we show that ALA3 cooperates with ARF-GEF BIG5/BEN1 and ARF1A1C/BEX1 in a similar regulatory pathway to vesicle formation, and together they are important for plant adaptation to osmotic stress.

Spatial lipidomics of fresh-frozen spines

Technologies assessing the lipidomics, genomics, epigenomics, transcriptomics, and proteomics of tissue samples at single-cell resolution have deepened our understanding of physiology and pathophysiology at an unprecedented level of detail. However, the study of single-cell spatial metabolomics in undecalcified bones faces several significant challenges, such as the fragility of bone which often requires decalcification or fixation leading to the degradation or removal of lipids and other molecules and. As such, we describe a method for performing mass spectrometry imaging on undecalcified spine that is compatible with other spatial omics measurements. In brief, we use fresh-freeze rat spines and a system of carboxyl methylcellulose embedding, cryofilm, and polytetrafluoroethylene rollers to maintain tissue integrity, while avoiding signal loss from variations in laser focus and artifacts from traditional tissue processing. This reveals various tissue types and lipidomic profiles of spinal regions at 10 μm spatial resolutions using matrix-assisted laser desorption/ionization mass spectrometry imaging. We expect this method to be adapted and applied to the analysis of spinal cord, shedding light on the mechanistic aspects of cellular heterogeneity, development, and disease pathogenesis underlying different bone-related conditions and diseases. This study furthers the methodology for high spatial metabolomics of spines, as well as adds to the collective efforts to achieve a holistic understanding of diseases via single-cell spatial multi-omics.

Exploring the Potent Anticancer Activity of Essential Oils and Their Bioactive Compounds: Mechanisms and Prospects for Future Cancer Therapy

Cancer is one of the leading causes of death worldwide, affecting millions of people each year. Fortunately, the last decades have been marked by considerable advances in the field of cancer therapy. Researchers have discovered many natural substances, some of which are isolated from plants that have promising anti-tumor activity. Among these, essential oils (EOs) and their constituents have been widely studied and shown potent anticancer activities, both in vitro and in vivo. However, despite the promising results, the precise mechanisms of action of EOs and their bioactive compounds are still poorly understood. Further research is needed to better understand these mechanisms, as well as their effectiveness and safety in use. Furthermore, the use of EOs as anticancer drugs is complex, as it requires absolute pharmacodynamic specificity and selectivity, as well as an appropriate formulation for effective administration. In this study, we present a synthesis of recent work on the mechanisms of anticancer action of EOs and their bioactive compounds, examining the results of various in vitro and in vivo studies. We also review future research prospects in this exciting field, as well as potential implications for the development of new cancer drugs.

Cholesterol and Sphingomyelin Polarize at the Leading Edge of Migrating Myoblasts and Involve Their Clustering in Submicrometric Domains

Myoblast migration is crucial for myogenesis and muscular tissue homeostasis. However, its spatiotemporal control remains elusive. Here, we explored the involvement of plasma membrane cholesterol and sphingolipids in this process. In resting C2C12 mouse myoblasts, those lipids clustered in sphingomyelin/cholesterol/GM1 ganglioside (SM/chol/GM1)- and cholesterol (chol)-enriched domains, which presented a lower stiffness than the bulk membrane. Upon migration, cholesterol and sphingomyelin polarized at the front, forming cholesterol (chol)- and sphingomyelin/cholesterol (SM/chol)-enriched domains, while GM1-enriched domains polarized at the rear. A comparison of domain proportion suggested that SM/chol- and GM1-enriched domains originated from the SM/chol/GM1-coenriched domains found at resting state. Modulation of domain proportion (through cholesterol depletion, combined or not with actin polymerization inhibition, or sphingolipid synthesis inhibition) revealed that the higher the chol- and SM/chol-enriched domains, the higher the myoblast migration. At the front, chol- and SM/chol-enriched domains were found in proximity with F-actin fibers and the lateral mobility of sphingomyelin in domains was specifically restricted in a cholesterol- and cytoskeleton-dependent manner while domain abrogation impaired F-actin and focal adhesion polarization. Altogether, we showed the polarization of cholesterol and sphingomyelin and their clustering in chol- and SM/chol-enriched domains with differential properties and roles, providing a mechanism for the spatial and functional control of myoblast migration.

Changes in Electrical Capacitance of Cell Membrane Reflect Drug Partitioning-Induced Alterations in Lipid Bilayer

The plasma membrane is a lipid bilayer that establishes the outer boundary of a living cell. The composition of the lipid bilayer influences the membrane's biophysical properties, including fluidity, thickness, permeability, phase behavior, charge, elasticity, and formation of flat sheet or curved structures. Changes in the biophysical properties of the membrane can be occasioned when new entities, such as drug molecules, are partitioned in the bilayer. Therefore, assessing drugs for their effect on the biophysical properties of the lipid bilayer of a cell membrane is critical to understanding specific and non-specific drug action. Previously, we reported a non-invasive technique for real-time characterization of cellular dielectric properties, such as membrane capacitance and cytoplasmic conductivity. In this study, we discuss the potential application of the technique in assessing the biophysical properties of the cell membrane in response to interaction with amiodarone compared to aspirin/acetylsalicylic acid and glucose. Amiodarone is a potent drug used to treat cardiac arrhythmia, but it also exerts various non-specific effects. Compared to aspirin and glucose, we measured a rapid and higher magnitude increase in membrane capacitance on cells under amiodarone treatment. Increased membrane capacitance induced by aspirin and glucose quickly returned to baseline in 15 s, while amiodarone-induced increased capacitance sustained and decreased slowly, approaching baseline or another asymptotic limit in ~2.5 h. Because amiodarone has a strong lipid partitioning property, we reason that drug partitioning alters the lipid bilayer context and subsequently reduces bilayer thickness, leading to an increase in the electrical capacitance of the cell membrane. The presented microfluidic system promises a new approach to assess drug-membrane interactions and delineate specific and non-specific actions of the drug on cells.

The ERAD system is restricted by elevated ceramides

Misfolded proteins in the endoplasmic reticulum (ER) are removed through a process known as ER-associated degradation (ERAD). ERAD occurs through an integral membrane protein quality control system that recognizes substrates, retrotranslocates the substrates across the membrane, and ubiquitinates and extracts the substrates from the membrane for degradation at the cytosolic proteasome. While ERAD systems are known to regulate lipid biosynthetic enzymes, the regulation of ERAD systems by the lipid composition of cellular membranes remains unexplored. Here, we report that the ER membrane composition influences ERAD function by incapacitating substrate extraction. Unbiased lipidomic profiling revealed that elevation of specific very-long-chain ceramides leads to a marked increase in the level of ubiquitinated substrates in the ER membrane and concomitantly reduces extracted substrates in the cytoplasm. This work reveals a previously unrecognized mechanism in which ER membrane lipid remodeling changes the activity of ERAD.

Anisotropic 3D confinement of MCF-7 cells induces directed cell-migration and viscoelastic anisotropy of cell-membrane

Tumor-associated collagen signature-3 (TACS-3) is a prognostic indicator for breast cancer survival. It is characterized by highly organized, parallel bundles of collagen fibers oriented perpendicular to the tumor boundary, serving as directional, confining channels for cancer cell invasion. Here we design a TACS-3-mimetic anisotropic, confined collagen I matrix and examine the relation between anisotropy of matrix, directed cellular migration, and anisotropy of cell membrane-the first direct contact between TACS-3 and cell-using Michigan Cancer Foundation-7 (MCF-7) cells as cancer-model. Using unidirectional freezing, we generated ∼50 μm-wide channels filled with collagen I. Optical tweezer (OT) microrheology shows that anisotropic confinement increases collagen viscoelasticity by two orders of magnitude, and the elastic modulus is significantly greater along the direction of anisotropic confinement compared to that along the orthogonal direction, thus establishing matrix anisotropy. Furthermore, MCF-7 cells embedded in anisotropic collagen I, exhibit directionality in cellular morphology and migration. Finally, using customized OT to trap polystyrene probes bound to cell-membrane (and not to ECM) of either free cells or cells under anisotropic confinement, we quantified the effect of matrix anisotropy on membrane viscoelasticity, both in-plane and out-of-plane, vis-à-vis the membrane. Both bulk and viscous modulus of cell-membrane of MCF-7 cells exhibit significant anisotropy under anisotropic confinement. Moreover, the cell membrane of MCF-7 cells under anisotropic confinement is significantly softer (both in-plane and out-of-plane moduli) despite their local environment being five times stiffer than free cells. In order to test if the coupling between anisotropy of extracellular matrix and anisotropy of cell-membrane is regulated by cell-cytoskeleton, actin cytoskeleton was depolymerized for both free and confined cells. Results show that cell membrane viscoelasticity of confined MCF-7 cells is unaffected by actin de-polymerization, in contrast to free cells. Together, these findings suggest that anisotropy of ECM induces directed migration and correlates with anisotropy of cell-membrane viscoelasticity of the MCF-7 cells in an actin-independent manner.

Studying the Role of Lipid Geometry in COPI Vesicle Formation

The Coat Protein I (COPI) complex forms vesicles from Golgi membrane for retrograde transport among the Golgi stacks, and also from the Golgi to the endoplasmic reticulum (ER). We have been elucidating the mechanistic details of COPI vesicle formation through a reconstitution system that involves the incubation of Golgi membrane with purified components. This approach has enabled us recently to gain new insight into how certain lipids are critical for the fission stage of COPI vesicle formation. Lipid geometry has been proposed to act in the formation of transport carriers by promoting membrane curvature. However, evidence for this role has come from studies using simplified membranes, while confirmation in the more physiologic setting of native membranes has been challenging, as such membranes contain a complex composition of lipids and proteins. We have recently refined the COPI reconstitution system to overcome this experimental obstacle. This has led us to identify an unanticipated type of lipid geometry needed for COPI vesicle fission. This chapter describes the approach that we have developed to enable this discovery. The methodologies include: (i) preparation Golgi membrane from cells that are deficient in a particular lipid enzyme activity and (ii) functional rescue of this deficiency by introducing the product of the lipid enzyme, with experiments being performed at the in vitro level to gain mechanistic clarity and at the in vivo level to confirm physiologic relevance.

Uncovering mechanisms of brain inflammation in Alzheimer's disease with APOE4: Application of single cell-type lipidomics

A chronic state of unresolved inflammation in Alzheimer's disease (AD) is intrinsically involved with the remodeling of brain lipids. This review highlights the effect of carrying the apolipoprotein E ε4 allele (APOE4) on various brain cell types in promoting an unresolved inflammatory state. Among its pleotropic effects on brain lipids, we focus on APOE4's activation of Ca²⁺ -dependent phospholipase A2 (cPLA2) and its effects on arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid signaling cascades in the brain. During the process of neurodegeneration, various brain cell types, such as astrocytes, microglia, and neurons, together with the neurovascular unit, develop distinct inflammatory phenotypes that impact their functions and have characteristic lipidomic fingerprints. We propose that lipidomic phenotyping of single cell-types harvested from brains differing by age, sex, disease severity stage, and dietary and genetic backgrounds can be employed to probe mechanisms of neurodegeneration. A better understanding of the brain cellular inflammatory/lipidomic response promises to guide the development of nutritional and drug interventions for AD dementia.

Model Lipid Raft Membranes for Embedding Integral Membrane Proteins: Reconstitution of HMG-CoA Reductase and Its Inhibition by Statins

For the first time, HMG-CoA reductase, the membrane protein responsible for cholesterol synthesis, was incorporated into a lipid membrane consisting of DOPC:Chol:SM at a 1:1:1 molar ratio, which mimics the lipid rafts of cell membranes. The membrane containing the protein was generated in the form of either a proteoliposomes or a film obtained by spreading the proteoliposomes at the air-water interface to prepare a protein-rich and stable lipid layer over time. The lipid vesicle parameters were characterized using dynamic light scattering (DLS) and fluorescence microscopy. The incorporation of HMG-CoA reductase was reflected in the increased size of the proteoliposomes compared to that of the empty liposomes of model rafts. Enzyme reconstitution was confirmed by measuring the activity of NADPH, which participates in the catalytic process. The thin lipid raft films formed by spreading liposomes and proteoliposomes at the air-water interface were investigated using the Langmuir technique. The activities of the HMG-CoA reductase films were preserved over time, and the two lipid raft systems, nanoparticles and films, were exposed to solutions of fluvastatin, a HMG-CoA reductase inhibitor commonly used in the treatment of hypercholesterolemia. Both lipid raft systems constructed were useful membrane models for the determination of reductase activity and for monitoring the statin inhibitory effects and may be used for investigating other integral membrane proteins during exposure to inhibitors/activators considered to be potential drugs.

Pleiotropic Roles of Cholesteryl Sulfate during Entamoeba Encystation: Involvement in Cell Rounding and Development of Membrane Impermeability

Entamoeba histolytica, a protozoan parasite, causes amoebiasis, which is a global public health problem. The major route of infection is oral ingestion of cysts, the only form that is able to transmit to a new host. Cysts are produced by cell differentiation from proliferative trophozoites in a process termed "encystation." During encystation, cell morphology is markedly changed; motile amoeboid cells become rounded, nonmotile cells. Concomitantly, cell components change and significant fluctuations of metabolites occur. Cholesteryl sulfate (CS) is a crucial metabolite for encystation. However, its precise role remains uncertain. To address this issue, we used in vitro culture of Entamoeba invadens as the model system for the E. histolytica encystation study and identified serum-free culture conditions with CS supplementation at concentrations similar to intracellular CS concentrations during natural encystation. Using this culture system, we show that CS exerts pleiotropic effects during Entamoeba encystation, affecting cell rounding and development of membrane impermeability. CS dose dependently induced and maintained encysting cells as spherical maturing cysts with almost no phagocytosis activity. Consequently, the percentage of mature cysts was increased. CS treatment also caused time- and dose-dependent development of membrane impermeability in encysting cells via induction of de novo synthesis of dihydroceramides containing very long N-acyl chains (≥26 carbons). These results indicate that CS-mediated morphological and physiological changes are necessary for the formation of mature cysts and the maintenance of the Entamoeba life cycle. Our findings also reveal important morphological aspects of the process of dormancy and the control of membrane structure. IMPORTANCE Entamoeba histolytica causes a parasitic infectious disease, amoebiasis. Amoebiasis is a global public health problem with a high occurrence of infection and inadequate clinical options. The parasite alternates its form between a proliferative trophozoite and a dormant cyst that enables the parasite to adapt to new environments. The transition stage in which trophozoites differentiate into cysts is termed "encystation." Cholesteryl sulfate is essential for encystation; however, its precise role remains to be determined. Here, we show that cholesteryl sulfate is a multifunctional metabolite exerting pleiotropic roles during Entamoeba encystation, including the rounding of cells and the development of membrane impermeability. Such morphological and physiological changes are required for Entamoeba to produce cysts that are transmissible to a new host, which is essential for maintenance of the Entamoeba life cycle. Our findings are therefore relevant not only to Entamoeba biology but also to general cell and lipid biology.

Four Cholesterol-Recognition Motifs in the Pore-Forming and Translocation Domains of Adenylate Cyclase Toxin Are Essential for Invasion of Eukaryotic Cells and Lysis of Erythrocytes

Adenylate Cyclase Toxin (ACT or CyaA) is one of the important virulence factors secreted by Bordetella pertussis, the bacterium causative of whooping cough. ACT debilitates host defenses by production of unregulated levels of cAMP into the cell cytosol upon delivery of its N-terminal domain with adenylate cyclase activity (AC domain) and by forming pores in the plasma membrane of macrophages. Binding of soluble toxin monomers to the plasma membrane of target cells and conversion into membrane-integrated proteins are the first and last step for these toxin activities; however, the molecular determinants in the protein or the target membrane that govern this conversion to an active toxin form are fully unknown. It was previously reported that cytotoxic and cytolytic activities of ACT depend on membrane cholesterol. Here we show that ACT specifically interacts with membrane cholesterol, and find in two membrane-interacting ACT domains, four cholesterol-binding motifs that are essential for AC domain translocation and lytic activities. We hypothesize that direct ACT interaction with membrane cholesterol through those four cholesterol-binding motifs drives insertion and stabilizes the transmembrane topology of several helical elements that ultimately build the ACT structure for AC delivery and pore-formation, thereby explaining the cholesterol-dependence of the ACT activities. The requirement for lipid-mediated stabilization of transmembrane helices appears to be a unifying mechanism to modulate toxicity in pore-forming toxins.

Assessment of a combination of plasma anti-histone autoantibodies and PLA2/PE ratio as potential biomarkers to clinically predict autism spectrum disorders

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficiencies in social interaction and repetitive behaviors. Multiple studies have reported abnormal cell membrane composition and autoimmunity as known mechanisms associated with the etiopathogenesis of ASD. In this study, multiple regression and combined receiver operating characteristic (ROC) curve as statistic tools were done to clarify the relationship between phospholipase A2 and phosphatidylethanolamine (PE) ratio (PLA2/PE) as marker of lipid metabolism and membrane fluidity, and antihistone-autoantibodies as marker of autoimmunity in the etiopathology of ASD. Furthermore, the study intended to define the linear combination that maximizes the partial area under an ROC curve for a panel of markers. Forty five children with ASD and forty age- and sex-matched controls were enrolled in the study. Using ELISA, the levels of antihistone-autoantibodies, and PLA2 were measured in the plasma of both groups. PE was measured using HPLC. Statistical analyses using ROC curves and multiple and logistic regression models were performed. A notable rise in the area under the curve was detected using combined ROC curve models. Additionally, higher specificity and sensitivity of the combined markers were documented. The present study indicates that the measurement of the predictive value of selected biomarkers related to autoimmunity and lipid metabolism in children with ASD using a ROC curve analysis should lead to a better understanding of the pathophysiological mechanism of ASD and its link with metabolism. This information may enable the early diagnosis and intervention.

Measles and Nipah virus assembly: Specific lipid binding drives matrix polymerization

Measles virus, Nipah virus, and multiple other paramyxoviruses cause disease outbreaks in humans and animals worldwide. The paramyxovirus matrix (M) protein mediates virion assembly and budding from host cell membranes. M is thus a key target for antivirals, but few high-resolution structures of paramyxovirus M are available, and we lack the clear understanding of how viral M proteins interact with membrane lipids to mediate viral assembly and egress that is needed to guide antiviral design. Here, we reveal that M proteins associate with phosphatidylserine and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] at the plasma membrane. Using x-ray crystallography, electron microscopy, and molecular dynamics, we demonstrate that PI(4,5)P2 binding induces conformational and electrostatic changes in the M protein surface that trigger membrane deformation, matrix layer polymerization, and virion assembly.

Exploring TRPC3 Interaction with Cholesterol through Coarse-Grained Molecular Dynamics Simulations

Transient receptor potential canonical 3 (TRPC3) channel belongs to the superfamily of transient receptor potential (TRP) channels which mediate Ca2+ influx into the cell. These channels constitute essential elements of cellular signalling and have been implicated in a wide range of diseases. TRPC3 is primarily gated by lipids and its surface expression has been shown to be dependent on cholesterol, yet a comprehensive exploration of its interaction with this lipid has thus far not emerged. Here, through 80 µs of coarse-grained molecular dynamics simulations, we show that cholesterol interacts with multiple elements of the transmembrane machinery of TRPC3. Through our approach, we identify an annular binding site for cholesterol on the pre-S1 helix and a non-annular site at the interface between the voltage-sensor-like domain and pore domains. Here, cholesterol interacts with exposed polar residues and possibly acts to stabilise the domain interface.

Archaeal Lipids Regulating the Trimeric Structure Dynamics of Bacteriorhodopsin for Efficient Proton Release and Uptake

S-TGA-1 and PGP-Me are native archaeal lipids associated with the bacteriorhodopsin (bR) trimer and contribute to protein stabilization and native dynamics for proton transfer. However, little is known about the underlying molecular mechanism of how these lipids regulate bR trimerization and efficient photocycling. Here, we explored the specific binding of S-TGA-1 and PGP-Me with the bR trimer and elucidated how specific interactions modulate the bR trimeric structure and proton release and uptake using long-term atomistic molecular dynamic simulations. Our results showed that S-TGA-1 and PGP-Me are essential for stabilizing the bR trimer and maintaining the coherent conformational dynamics necessary for proton transfer. The specific binding of S-TGA-1 with W80 and K129 regulates proton release on the extracellular surface by forming a “Glu-shared” model. The interaction of PGP-Me with K40 ensures proton uptake by accommodating the conformation of the helices to recruit enough water molecules on the cytoplasmic side. The present study results could fill in the theoretical gaps of studies on the functional role of archaeal lipids and could provide a reference for other membrane proteins containing similar archaeal lipids.

The yellow brick road to nuclear membrane mechanotransduction

The nuclear membrane may function as a mechanosensory surface alongside the plasma membrane. In this Review, we discuss how this idea emerged, where it currently stands, and point out possible implications, without any claim of comprehensiveness.