Effects of ceramide and other simple sphingolipids on membrane lateral structure

Bending the rules: Molecular dynamics of hydroxylated sphingolipid membranes with 2-hydroxyoleic acid

In this study, we introduce a novel method for quantifying the mechanical properties of lipid membranes-bending rigidity (κ), Gaussian rigidity (κG), and surface tension (γ) using molecular dynamics (MD) simulations. Our approach is applied to membranes incorporating 2-hydroxyoleic acid (2OHOA), a synthetic oleic acid derivative currently under clinical investigation for its anticancer properties. 2OHOA modifies the plasma membrane composition in cancer cells and activates sphingomyelin synthase 1 (SMS1), an enzyme critical for maintaining sphingolipid levels in the plasma membrane. This research focuses on how the integration of 2OHOA into ceramide and sphingomyelin alters the mechanical and biophysical properties of these membranes. We employed MD simulations to analyze structural parameters such as lipid area, volume, and bilayer thickness. Additionally, by constructing a system of linear equations based on the Helfrich-Seifert model, we estimated the mechanical properties of hydroxylated versus non-hydroxylated membranes. Our findings reveal significant membrane rigidity and curvature changes due to hydroxylation, affecting membrane-protein interactions and cellular processes like vesiculation. This work provides critical insights into the molecular mechanisms by which hydroxylation influences membrane elasticity, with implications for both fundamental biophysics and therapeutic applications in cancer treatment.

Polar lipids and proteins in milk fat globule membranes as players in spontaneous lipolysis in cow's milk

A study of the lipidome and proteome was performed on milk fat globule membranes (MFGM) originating from milk samples from high (HL) and low (LL) lipolysis groups of cows. Combined univariate and multivariate statistical analyses proposed a set of variables highly associated to contrasted samples with regard to milk lipolysis. Milk from HL group were related to 4 phosphatidylinositols, 8 phosphatidylcholines, 1 sphingomyelin and 27 proteins, among them the phosphatidylcholine/phosphatidylethanolamine ratio and ORM1 may contribute to the membrane remodeling of the MFGM. The abundance of CP, CHI3L1, NECTIN2, A2M were strongly positively correlated with HL. Conversely, 3 phosphatidylinositols, 1 phosphatidylcholine and 2 phosphatidylethanolamines were assigned to the LL group. The HL group in cows is associated with a specific MFGM phospholipids and proteins profile, suggesting an impact on membrane fluidity and lipid rafts composition intervening in LPL anchoring and activation, as well as on pro-inflammatory lipids and proteins.

The potential therapeutic effect of human umbilical cord mesenchymal stem cell-derived exosomes in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of preterm infants, with its incidence rising due to improved survival rates of these infants. BPD results from a combination of prenatal and postnatal factors, such as mechanical ventilation, oxygen toxicity, and infections, all of which significantly impact the prognosis and growth of affected infants. Current treatment options for BPD are largely supportive and do not address the underlying pathology. Exosomes are cell-derived bilayer-enclosed membrane structures enclosing proteins, lipids, RNAs, growth factors, cytokines and metabolites. They have become recognized as crucial regulators of intercellular communication in various physiological and pathological processes. Previous studies have revealed the therapeutic potential of human umbilical cord mesenchymal stem cells-derived exosomes (HUCMSCs-Exos) in promoting tissue repair and regeneration. Therefore, HUCMSCs-Exos maybe a promising and effective therapeutic modality for BPD. In this review, we firstly provide a comprehensive overview of BPD, including its etiology and the mechanisms of lung injury. Then we detail the isolation, characterization, and contents of HUCMSCs-Exos, and discuss their potential mechanisms of HUCMSCs-Exos in BPD treatment. Additionally, we summarize current clinical trials and discuss the challenges in translating these findings from bench to bedside. This review aims to lay the groundwork for future clinical applications of HUCMSCs-Exos in treating BPD.

Ceramide regulation of autophagy: A biophysical approach

Specific membrane lipids play unique roles in (macro)autophagy. Those include phosphatidylethanolamine, to which LC3/GABARAP autophagy proteins become covalently bound in the process, or cardiolipin, an important effector in mitochondrial autophagy (or mitophagy). Ceramide (Cer), or N-acyl sphingosine, is one of the simplest sphingolipids, known as a stress signal in the apoptotic pathway. Moreover, Cer is increasingly being recognized as an autophagy activator, although its mechanism of action is unclear. In the present review, the proposed Cer roles in autophagy are summarized, together with some biophysical properties of Cer in membranes. Possible pathways for Cer activation of autophagy are discussed, including specific protein binding of the lipid, and Cer-dependent perturbation of bilayer properties. Cer generation of lateral inhomogeneities (domain formation) is given special attention. Recent biophysical results, including fluorescence and atomic force microscopy data, show Cer-promoted enhanced binding of LC3/GABARAP to lipid bilayers. These observations could be interpreted in terms of the putative formation of Cer-rich nanodomains.

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.

Relevance of multilamellar and multicompartmental vesicles in biological fluids: understanding the significance of proportional variations and disease correlation

Extracellular vesicles (EVs) have garnered significant interest in the field of biomedical science due to their potential applications in therapy and diagnosis. These vesicles participate in cell-to-cell communication and carry a diverse range of bioactive cargo molecules, such as nucleic acids, proteins, and lipids. These cargoes play essential roles in various signaling pathways, including paracrine and endocrine signaling. However, our understanding of the morphological and structural features of EVs is still limited. EVs could be unilamellar or multilamellar or even multicompartmental structures. The relative proportions of these EV subtypes in biological fluids have been associated with various human diseases; however, the mechanism remains unclear. Cryo-electron microscopy (cryo-EM) holds great promise in the field of EV characterization due to high resolution properties. Cryo-EM circumvents artifacts caused by fixation or dehydration, allows for the preservation of native conformation, and eliminates the necessity for staining procedures. In this review, we summarize the role of EVs biogenesis and pathways that might have role on their structure, and the role of cryo-EM in characterization of EVs morphology in different biological samples and integrate new knowledge of the alterations of membranous structures of EVs which could be used as biomarkers to human diseases.

A Review of Extracellular Vesicles in COVID-19 Diagnosis, Treatment, and Prevention

The 2019 novel coronavirus disease (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is ongoing, and has necessitated scientific efforts in disease diagnosis, treatment, and prevention. Interestingly, extracellular vesicles (EVs) have been crucial in these developments. EVs are a collection of various nanovesicles which are delimited by a lipid bilayer. They are enriched in proteins, nucleic acids, lipids, and metabolites, and naturally released from different cells. Their natural material transport properties, inherent long-term recycling ability, excellent biocompatibility, editable targeting, and inheritance of parental cell properties make EVs one of the most promising next-generation drug delivery nanocarriers and active biologics. During the COVID-19 pandemic, many efforts have been made to exploit the payload of natural EVs for the treatment of COVID-19. Furthermore, strategies that use engineered EVs to manufacture vaccines and neutralization traps have produced excellent efficacy in animal experiments and clinical trials. Here, the recent literature on the application of EVs in COVID-19 diagnosis, treatment, damage repair, and prevention is reviewed. And the therapeutic value, application strategies, safety, and biotoxicity in the production and clinical applications of EV agents for COVID-19 treatment, as well as inspiration for using EVs to block and eliminate novel viruses are discussed.

Extracellular Vesicles in Hepatobiliary Health and Disease

Extracellular vesicles (EVs) are membrane-bound nanoparticles released by cells and are an important means of intercellular communication in physiological and pathological states. We provide an overview of recent advances in the understanding of EV biogenesis, cargo selection, recipient cell effects, and key considerations in isolation and characterization techniques. Studies on the physiological role of EVs have relied on cell-based model systems due to technical limitations of studying endogenous nanoparticles in vivo . Several recent studies have elucidated the mechanistic role of EVs in liver diseases, including nonalcoholic fatty liver disease, viral hepatitis, cholestatic liver disease, alcohol-associated liver disease, acute liver injury, and liver cancers. Employing disease models and human samples, the biogenesis of lipotoxic EVs downstream of endoplasmic reticulum stress and microvesicles via intracellular activation stress signaling are discussed in detail. The diverse cargoes of EVs including proteins, lipids, and nucleic acids can be enriched in a disease-specific manner. By carrying diverse cargo, EVs can directly confer pathogenic potential, for example, recruitment and activation of monocyte-derived macrophages in NASH and tumorigenicity and chemoresistance in hepatocellular carcinoma. We discuss the pathogenic role of EVs cargoes and the signaling pathways activated by EVs in recipient cells. We review the literature that EVs can serve as biomarkers in hepatobiliary diseases. Further, we describe novel approaches to engineer EVs to deliver regulatory signals to specific cell types, and thus use them as therapeutic shuttles in liver diseases. Lastly, we identify key lacunae and future directions in this promising field of discovery and development. © 2023 American Physiological Society. Compr Physiol 13:4631-4658, 2023.

Extracellular vesicles in the glioblastoma microenvironment: A diagnostic and therapeutic perspective

Glioblastoma (GBM), is the most malignant form of gliomas and the most common and lethal primary brain tumor in adults. Conventional cancer treatments have limited to no efficacy on GBM. GBM cells respond and adapt to the surrounding brain parenchyma known as tumor microenvironment (TME) to promote tumor preservation. Among specific TME, there are 3 of particular interest for GBM biology: the perivascular niche, the subventricular zone neurogenic niche, and the immune microenvironment. GBM cells and TME cells present a reciprocal feedback which results in tumor maintenance. One way that these cells can communicate is through extracellular vesicles. These vesicles include exosomes and microvesicles that have the ability to carry both cancerous and non-cancerous cargo, such as miRNA, RNA, proteins, lipids, and DNA. In this review we will discuss the booming topic that is extracellular vesicles, and how they have the novelty to be a diagnostic and targetable vehicle for GBM.

Impact of sphingolipids on protein membrane trafficking

Membrane trafficking is essential to maintain the spatiotemporal control of protein and lipid distribution within membrane systems of eukaryotic cells. To achieve their functional destination proteins are sorted and transported into lipid carriers that construct the secretory and endocytic pathways. It is an emerging theme that lipid diversity might exist in part to ensure the homeostasis of these pathways. Sphingolipids, a chemical diverse type of lipids with special physicochemical characteristics have been implicated in the selective transport of proteins. In this review, we will discuss current knowledge about how sphingolipids modulate protein trafficking through the endomembrane systems to guarantee that proteins reach their functional destination and the proposed underlying mechanisms.

Lipids in Mitochondrial Macroautophagy: Phase Behavior of Bilayers Containing Cardiolipin and Ceramide

Cardiolipin (CL) is a key lipid for damaged mitochondrial recognition by the LC3/GABARAP human autophagy proteins. The role of ceramide (Cer) in this process is unclear, but CL and Cer have been proposed to coexist in mitochondria under certain conditions. Varela et al. showed that in model membranes composed of egg sphingomyelin (eSM), dioleoyl phosphatidylethanolamine (DOPE), and CL, the addition of Cer enhanced the binding of LC3/GABARAP proteins to bilayers. Cer gave rise to lateral phase separation of Cer-rich rigid domains but protein binding took place mainly in the fluid continuous phase. In the present study, a biophysical analysis of bilayers composed of eSM, DOPE, CL, and/or Cer was attempted to understand the relevance of this lipid coexistence. Bilayers were studied by differential scanning calorimetry, confocal fluorescence microscopy, and atomic force microscopy. Upon the addition of CL and Cer, one continuous phase and two segregated ones were formed. In bilayers with egg phosphatidylcholine instead of eSM, in which the binding of LC3/GABARAP proteins hardly increased with Cer in the former study, a single segregated phase was formed. Assuming that phase separation at the nanoscale is ruled by the same principles acting at the micrometer scale, it is proposed that Cer-enriched rigid nanodomains, stabilized by eSM:Cer interactions formed within the DOPE- and CL-enriched fluid phase, result in structural defects at the rigid/fluid nanointerfaces, thus hypothetically facilitatingLC3/GABARAP protein interaction.

Structural diversity of photoswitchable sphingolipids for optodynamic control of lipid microdomains

Sphingolipids are a structurally diverse class of lipids predominantly found in the plasma membrane of eukaryotic cells. These lipids can laterally segregate with other rigid lipids and cholesterol into liquid-ordered domains that act as organizing centers within biomembranes. Owing the vital role of sphingolipids for lipid segregation, controlling their lateral organization is of utmost significance. Hence, we made use of the light-induced trans-cis isomerization of azobenzene-modified acyl chains to develop a set of photoswitchable sphingolipids with different headgroups (hydroxyl, galactosyl, phosphocholine) and backbones (sphingosine, phytosphingosine, tetrahydropyran-blocked sphingosine) that are able to shuttle between liquid-ordered and liquid-disordered regions of model membranes upon irradiation with UV-A (λ = 365 nm) and blue (λ = 470 nm) light, respectively. Using combined high-speed atomic force microscopy, fluorescence microscopy, and force spectroscopy, we investigated how these active sphingolipids laterally remodel supported bilayers upon photoisomerization, notably in terms of domain area changes, height mismatch, line tension, and membrane piercing. Hereby, we show that the sphingosine-based (Azo-β-Gal-Cer, Azo-SM, Azo-Cer) and phytosphingosine-based (Azo-α-Gal-PhCer, Azo-PhCer) photoswitchable lipids promote a reduction in liquid-ordered microdomain area when in the UV-adapted cis-isoform. In contrast, azo-sphingolipids having tetrahydropyran groups that block H-bonding at the sphingosine backbone (lipids named Azo-THP-SM, Azo-THP-Cer) induce an increase in the liquid-ordered domain area when in cis, accompanied by a major rise in height mismatch and line tension. These changes were fully reversible upon blue light-triggered isomerization of the various lipids back to trans, pinpointing the role of interfacial interactions for the formation of stable liquid-ordered domains.

Effect of Cisplatin and Its Cationic Analogues in the Phase Behavior and Permeability of Model Lipid Bilayers

Increasing evidence suggests a critical role of lipids in both the mechanisms of toxicity and resistance of cells to platinum(II) complexes. In particular, cisplatin and other analogues were reported to interact with lipids and transiently promote lipid phase changes both in the bulk membranes and in specific membrane domains. However, these processes are complex and not fully understood. In this work, cisplatin and its cationic species formed at pH 7.4 in low chloride concentrations were tested for their ability to induce phase changes in model membranes with different lipid compositions. Fluorescent probes that partition to different lipid phases were used to report on the fluidity of the membrane, and a leakage assay was performed to evaluate the effect of cisplatin in the permeability of these vesicles. The results showed that platinum(II) complex effects on membrane fluidity depend on membrane lipid composition and properties, promoting a stronger decrease in the fluidity of membranes containing gel phase. Moreover, at high concentration, these complexes were prone to alter the permeability of lipid membranes without inducing their collapse or aggregation.

Preeclampsia and syncytiotrophoblast membrane extracellular vesicles (STB-EVs)

Preeclampsia (PE) is a hypertensive complication of pregnancy that affects 2-8% of women worldwide and is one of the leading causes of maternal deaths and premature birth. PE can occur early in pregnancy (<34 weeks gestation) or late in pregnancy (>34 weeks gestation). Whilst the placenta is clearly implicated in early onset PE (EOPE), late onset PE (LOPE) is less clear with some believing the disease is entirely maternal whilst others believe that there is an interplay between maternal systems and the placenta. In both types of PE, the syncytiotrophoblast (STB), the layer of the placenta in direct contact with maternal blood, is stressed. In EOPE, the STB is oxidatively stressed in early pregnancy (leading to PE later in gestation- the two-stage model) whilst in LOPE the STB is stressed because of villous overcrowding and senescence later in pregnancy. It is this stress that perturbs maternal systems leading to the clinical manifestations of PE. Whilst some of the molecular species driving this stress have been identified, none completely explain the multisystem nature of PE. Syncytiotrophoblast membrane vesicles (STB-EVs) are a potential contributor to this multisystem disorder. STB-EVs are released into the maternal circulation in increasing amounts with advancing gestational age, and this release is further exacerbated with stress. There are good in vitro evidence that STB-EVs are taken up by macrophages and liver cells with additional evidence supporting endothelial cell uptake. STB-EV targeting remains in the early stages of discovery. In this review, we highlight the role of STB-EVs in PE. In relation to current research, we discuss different protocols for ex vivo isolation of STB-EVs, as well as specific issues involving tissue preparation, isolation (some of which may be unique to STB-EVs), and methods for their analysis. We suggest potential solutions for these challenges.

Neuronal activity induces glucosylceramide that is secreted via exosomes for lysosomal degradation in glia

Recessive variants in GBA1 cause Gaucher disease, a prevalent form of lysosome storage disease. GBA1 encodes a lysosomal enzyme that hydrolyzes glucosylceramide (GlcCer) into glucose and ceramide. Its loss causes lysosomal dysfunction and increased levels of GlcCer. We generated a null allele of the Drosophila ortholog Gba1b by inserting the Gal4 using CRISPR-Cas9. Here, we show that Gba1b is expressed in glia but not in neurons. Glial-specific knockdown recapitulates the defects found in Gba1b mutants, and these can be rescued by glial expression of human GBA1. We show that GlcCer is synthesized upon neuronal activity, and it is transported from neurons to glia through exosomes. Furthermore, we found that glial TGF-β/BMP induces the transfer of GlcCer from neurons to glia and that the White protein, an ABCG transporter, promotes GlcCer trafficking to glial lysosomes for degradation.

Influence of ceramide on lipid domain stability studied with small-angle neutron scattering: The role of acyl chain length and unsaturation

Ceramides and diacylglycerols are groups of lipids capable of nucleating and stabilizing ordered lipid domains, structures that have been implicated in a range of biological processes. Previous studies have used fluorescence reporter molecules to explore the influence of ceramide acyl chain structure on sphingolipid-rich ordered phases. Here, we use small-angle neutron scattering (SANS) to examine the ability of ceramides and diacylglycerols to promote lipid domain formation in the well-characterized domain-forming mixture DPPC/DOPC/cholesterol. SANS is a powerful, probe-free technique for interrogating membrane heterogeneity, as it is differentially sensitive to hydrogen's stable isotopes protium and deuterium. Specifically, neutron contrast is generated through selective deuteration of lipid species, thus enabling the detection of nanoscopic domains enriched in deuterated saturated lipids dispersed in a matrix of protiated unsaturated lipids. Using large unilamellar vesicles, we found that upon replacing 10 mol% DPPC with either C16:0 or C18:0 ceramide, or 16:0 diacylglycerol (dag), lipid domains persisted to higher temperatures. However, when DPPC was replaced with short chain (C6:0 or C12:0) or very long chain (C24:0) ceramides, or ceramides with unsaturated acyl chains of any length (C6:1(3), C6:1(5), C18:1, and C24:1), as well as C18:1-dag, lipid domains were destabilized, melting at lower temperatures than those in the DPPC/DOPC/cholesterol system. These results show how ceramide acyl chain length and unsaturation influence lipid domains and have implications for how cell membranes might modify their function through the generation of different ceramide species.

Different Sourced Extracellular Vesicles and Their Potential Applications in Clinical Treatments

Extracellular vesicles (EVs) include a heterogeneous group of natural cell-derived nanostructures that are increasingly regarded as promising biotherapeutic agents and drug delivery vehicles in human medicine. Desirable intrinsic properties of EVs including the ability to bypass natural membranous barriers and to deliver their unique biomolecular cargo to specific cell populations position them as fiercely competitive alternatives for currently available cell therapies and artificial drug delivery platforms. EVs with distinct characteristics can be released from various cell types into the extracellular environment as a means of transmitting bioactive components and altering the status of the target cell. Despite the existence of a large number of preclinical studies confirming the therapeutic efficacy of different originated EVs for treating several pathological conditions, in this review, we first provide a brief overview of EV biophysical properties with an emphasis on their intrinsic therapeutic benefits over cell-based therapies and synthetic delivery systems. Next, we describe in detail different EVs derived from distinct cell sources, compare their advantages and disadvantages, and recapitulate their therapeutic effects on various human disorders to highlight the progress made in harnessing EVs for clinical applications. Finally, knowledge gaps and concrete hurdles that currently hinder the clinical translation of EV therapies are debated with a futuristic perspective.

Quality-controlled ceramide-based GPI-anchored protein sorting into selective ER exit sites

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) exit the endoplasmic reticulum (ER) through a specialized export pathway in the yeast Saccharomyces cerevisiae. We have recently shown that a very-long acyl chain (C26) ceramide present in the ER membrane drives clustering and sorting of GPI-APs into selective ER exit sites (ERES). Now, we show that this lipid-based ER sorting also involves the C26 ceramide as a lipid moiety of GPI-APs, which is incorporated into the GPI anchor through a lipid-remodeling process after protein attachment in the ER. Moreover, we also show that a GPI-AP with a C26 ceramide moiety is monitored by the GPI-glycan remodelase Ted1, which, in turn, is required for receptor-mediated export of GPI-APs. Therefore, our study reveals a quality-control system that ensures lipid-based sorting of GPI-APs into selective ERESs for differential ER export, highlighting the physiological need for this specific export pathway.

Biogenesis of JC polyomavirus associated extracellular vesicles

JC polyomavirus (JCPyV) is a small, non-enveloped virus that persists in the kidney in about half the adult population. In severely immune-compromised individuals JCPyV causes the neurodegenerative disease progressive multifocal leukoencephalopathy (PML) in the brain. JCPyV has been shown to infect cells by both direct and indirect mechanisms, the latter involving extracellular vesicle (EV) mediated infection. While direct mechanisms of infection are well studied indirect EV mediated mechanisms are poorly understood. Using a combination of chemical and genetic approaches we show that several overlapping intracellular pathways are responsible for the biogenesis of virus containing EV. Here we show that targeting neutral sphingomyelinase 2 (nSMase2) with the drug cambinol decreased the spread of JCPyV over several viral life cycles. Genetic depletion of nSMase2 by either shRNA or CRISPR/Cas9 reduced EV-mediated infection. Individual knockdown of seven ESCRT-related proteins including HGS, ALIX, TSG101, VPS25, VPS20, CHMP4A, and VPS4A did not significantly reduce JCPyV associated EV (JCPyV(+) EV) infectivity, whereas knockdown of the tetraspanins CD9 and CD81 or trafficking and/or secretory autophagy-related proteins RAB8A, RAB27A, and GRASP65 all significantly reduced the spread of JCPyV and decreased EV-mediated infection. These findings point to a role for exosomes and secretory autophagosomes in the biogenesis of JCPyV associated EVs with specific roles for nSMase2, CD9, CD81, RAB8A, RAB27A, and GRASP65 proteins.

An Overview of Cell Membrane Perforation and Resealing Mechanisms for Localized Drug Delivery

Localized and reversible plasma membrane disruption is a promising technique employed for the targeted deposition of exogenous therapeutic compounds for the treatment of disease. Indeed, the plasma membrane represents a significant barrier to successful delivery, and various physical methods using light, sound, and electrical energy have been developed to generate cell membrane perforations to circumvent this issue. To restore homeostasis and preserve viability, localized cellular repair mechanisms are subsequently triggered to initiate a rapid restoration of plasma membrane integrity. Here, we summarize the known emergency membrane repair responses, detailing the salient membrane sealing proteins as well as the underlying cytoskeletal remodeling that follows the physical induction of a localized plasma membrane pore, and we present an overview of potential modulation strategies that may improve targeted drug delivery approaches.

Emerging Roles of Ceramide in Cardiovascular Diseases

Ceramide is a core molecule of sphingolipid metabolism that causes selective insulin resistance and dyslipidemia. Research on its involvement in cardiovascular diseases has grown rapidly. In resting cells, ceramide levels are extremely low, while they rapidly accumulate upon encountering external stimuli. Recently, the regulation of ceramide levels under pathological conditions, including myocardial infarction, hypertension, and atherosclerosis, has drawn great attention. Increased ceramide levels are strongly associated with adverse cardiovascular risks and events while inhibiting the synthesis of ceramide or accelerating its degradation improves a variety of cardiovascular diseases. In this article, we summarize the role of ceramide in cardiovascular disease, investigate the possible application of ceramide as a new diagnostic biomarker and a therapeutic target for cardiovascular disorders, and highlight the remaining problems.

Activation of Sphingomyelinase-Ceramide-Pathway in COVID-19 Purposes Its Inhibition for Therapeutic Strategies

Effective treatment strategies for severe coronavirus disease (COVID-19) remain scarce. Hydrolysis of membrane-embedded, inert sphingomyelin by stress responsive sphingomyelinases is a hallmark of adaptive responses and cellular repair. As demonstrated in experimental and observational clinical studies, the transient and stress-triggered release of a sphingomyelinase, SMPD1, into circulation and subsequent ceramide generation provides a promising target for FDA-approved drugs. Here, we report the activation of sphingomyelinase-ceramide pathway in 23 intensive care patients with severe COVID-19. We observed an increase of circulating activity of sphingomyelinase with subsequent derangement of sphingolipids in serum lipoproteins and from red blood cells (RBC). Consistent with increased ceramide levels derived from the inert membrane constituent sphingomyelin, increased activity of acid sphingomyelinase (ASM) accurately distinguished the patient cohort undergoing intensive care from healthy controls. Positive correlational analyses with biomarkers of severe clinical phenotype support the concept of an essential pathophysiological role of ASM in the course of SARS-CoV-2 infection as well as of a promising role for functional inhibition with anti-inflammatory agents in SARS-CoV-2 infection as also proposed in independent observational studies. We conclude that large-sized multicenter, interventional trials are now needed to evaluate the potential benefit of functional inhibition of this sphingomyelinase in critically ill patients with COVID-19.

Molecular and mesoscopic geometries in autophagosome generation. A review

Autophagy is an essential process in cell self-repair and survival. The centre of the autophagic event is the generation of the so-called autophagosome (AP), a vesicle surrounded by a double membrane (two bilayers). The AP delivers its cargo to a lysosome, for degradation and re-use of the hydrolysis products as new building blocks. AP formation is a very complex event, requiring dozens of specific proteins, and involving numerous instances of membrane biogenesis and architecture, including membrane fusion and fission. Many stages of AP generation can be rationalised in terms of curvature, both the molecular geometry of lipids interpreted in terms of 'intrinsic curvature', and the overall mesoscopic curvature of the whole membrane, as observed with microscopy techniques. The present contribution intends to bring together the worlds of biophysics and cell biology of autophagy, in the hope that the resulting cross-pollination will generate abundant fruit.

Preparation of Nitrogen Analogues of Ceramide and Studies of Their Aggregation in Sphingomyelin Bilayers

Ceramides can regulate biological processes probably through the formation of laterally segregated and highly packed ceramide-rich domains in lipid bilayers. In the course of preparation of its analogues, we found that a hydrogen-bond-competent functional group in the C1 position is necessary to form ceramide-rich domains in lipid bilayers [Matsufuji; Langmuir 2018]. Hence, in the present study, we newly synthesized three ceramide analogues: CerN₃, CerNH₂, and CerNHAc, in which the 1-OH group of ceramide is substituted with a nitrogen functionality. CerNH₂ and CerNHAc are capable of forming hydrogen bonds in their headgroups, whereas CerN₃ is not. Fluorescent microscopy observation and differential scanning calorimetry analysis disclosed that these ceramide analogues formed ceramide-rich phases in sphingomyelin bilayers, although their thermal stability was slightly inferior to that of normal ceramides. Moreover, wide-angle X-ray diffraction analysis showed that the chain packing structure of ceramide-rich phases of CerNHAc and CerN₃ was similar to that of normal ceramide, while the CerNH₂-rich phase showed a slightly looser chain packing due to the formation of CerNH₃⁺. Although the domain formation of CerN₃ was unexpected because of the lack of hydrogen-bond capability in the headgroup, it may become a promising tool for investigating the mechanistic link between the ceramide-rich phase and the ceramide-related biological functions owing to its Raman activity and applicability to click chemistry.

Comparative Metabolomics Analysis Reveals Sterols and Sphingolipids Play a Role in Cotton Fiber Cell Initiation

Cotton fiber is a seed trichome that protrudes from the outer epidermis of cotton ovule on the day of anthesis (0 day past anthesis, 0 DPA). The initial number and timing of fiber cells are closely related to fiber yield and quality. However, the mechanism underlying fiber initiation is still unclear. Here, we detected and compared the contents and compositions of sphingolipids and sterols in 0 DPA ovules of Xuzhou142 lintless-fuzzless mutants (Xufl) and Xinxiangxiaoji lintless-fuzzless mutants (Xinfl) and upland cotton wild-type Xuzhou142 (XuFL). Nine classes of sphingolipids and sixty-six sphingolipid molecular species were detected in wild-type and mutants. Compared with the wild type, the contents of Sphingosine-1-phosphate (S1P), Sphingosine (Sph), Glucosylceramide (GluCer), and Glycosyl-inositol-phospho-ceramides (GIPC) were decreased in the mutants, while the contents of Ceramide (Cer) were increased. Detail, the contents of two Cer molecular species, d18:1/22:0 and d18:1/24:0, and two Phyto-Cer molecular species, t18:0/22:0 and t18:0/h22:1 were significantly increased, while the contents of all GluCer and GIPC molecular species were decreased. Consistent with this result, the expression levels of seven genes involved in GluCer and GIPC synthesis were decreased in the mutants. Furthermore, exogenous application of a specific inhibitor of GluCer synthase, PDMP (1-phenyl-2-decanoylamino-3-morpholino-1-propanol), in ovule culture system, significantly inhibited the initiation of cotton fiber cells. In addition, five sterols and four sterol esters were detected in wild-type and mutant ovules. Compared with the wild type, the contents of total sterol were not significantly changed. While the contents of stigmasterol and campesterol were significantly increased, the contents of cholesterol were significantly decreased, and the contents of total sterol esters were significantly increased. In particular, the contents of campesterol esters and stigmasterol esters increased significantly in the two mutants. Consistently, the expression levels of some sterol synthase genes and sterol ester synthase genes were also changed in the two mutants. These results suggested that sphingolipids and sterols might have some roles in the initiation of fiber cells. Our results provided a novel insight into the regulatory mechanism of fiber cell initiation.

Schwann cell-derived exosomes: Janus-faced mediators of regeneration and disease

The phenotypic plasticity of Schwann cells (SCs) has contributed to the regenerative potential of the peripheral nervous system (PNS), but also pathological processes. This double-sided effect has led to an increasing attention to the role of extracellular vesicles (EVs) or exosomes in SCs to examine the intercellular communication between SCs and their surroundings. Here, we first describe the current knowledge of SC and EV biology, which forms the basis for the updates on advances in SC-derived exosomes research. We seek to explore in-depth the exosome-mediated molecular mechanisms involved in the regulation of SCs and their microenvironment. This review concludes with potential applications of SC-derived exosomes as delivery vehicles for therapeutics and biomarkers. The goal of this review is to emphasize the crucial role of SC-derived exosomes in the functional integration of the PNS, highlighting an emerging area in which there is much to explore and re-explore.

Role of ceramide/sphingomyelin (SM) balance regulated through "SM cycle" in cancer

Sphingomyelin synthase (SMS), which comprises of two isozymes, SMS1 and SMS2, is the only enzyme that generates sphingomyelin (SM) by transferring phosphocholine of phosphatidylcholine to ceramide in mammals. Conversely, ceramide is generated from SM hydrolysis via sphingomyelinases (SMases), ceramide de novo synthesis, and the salvage pathway. The biosynthetic pathway for SM and ceramide content by SMS and SMase, respectively, is called "SM cycle." SM forms a SM-rich microdomain on the cell membrane to regulate signal transduction, such as proliferation/survival, migration, and inflammation. On the other hand, ceramide acts as a lipid mediator by forming a ceramide-rich platform on the membrane, and ceramide exhibits physiological actions such as cell death, cell cycle arrest, and autophagy induction. Therefore, the regulation of ceramide/SM balance by SMS and SMase is responsible for diverse cell functions not only in physiological cells but also in cancer cells. This review outlines the implications of ceramide/SM balance through "SM cycle" in cancer progression and prevention. In addition, the possible involvement of "SM cycle" is introduced in anti-cancer tumor immunity, which has become a hot topic to innovate a more effective and safer way to conquer cancer in recent years.

Metabolic Depletion of Sphingolipids Does Not Alter Cell Cycle Progression in Chinese Hamster Ovary Cells

The cell cycle is a sequential multi-step process essential for growth and proliferation of cells comprising multicellular organisms. Although a number of proteins are known to modulate the cell cycle, the role of lipids in regulation of cell cycle is still emerging. In our previous work, we monitored the role of cholesterol in cell cycle progression in CHO-K1 cells. Since sphingolipids enjoy a functionally synergistic relationship with membrane cholesterol, in this work, we explored whether sphingolipids could modulate the eukaryotic cell cycle using CHO-K1 cells. Sphingolipids are essential components of eukaryotic cell membranes and are involved in a number of important cellular functions. To comprehensively monitor the role of sphingolipids on cell cycle progression, we carried out metabolic depletion of sphingolipids in CHO-K1 cells using inhibitors (fumonisin B₁, myriocin, and PDMP) that block specific steps of the sphingolipid biosynthetic pathway and examined their effect on individual cell cycle phases. Our results show that metabolic inhibitors led to significant reduction in specific sphingolipids, yet such inhibition in sphingolipid biosynthesis did not show any effect on cell cycle progression in CHO-K1 cells. We speculate that any role of sphingolipids on cell cycle progression could be context and cell-type dependent, and cancer cells could be a better choice for monitoring such regulation, since sphingolipids are differentially modulated in these cells.

CHO/LY-B cell growth under limiting sphingolipid supply: Correlation between lipid composition and biophysical properties of sphingolipid-restricted cell membranes

Sphingolipids (SL) are ubiquitous in mammalian cell membranes, yet there is little data on the behavior of cells under SL-restriction conditions. LY-B cells derive from a CHO linein whichserine palmitoyl transferase (SPT), thus de novo SL synthesis, is suppressed, while maintaining the capacity of taking up and metabolizing exogenous sphingoid bases from the culture medium. In this study, LY-B cells were adapted to grow in a fetal bovine serum (FBS)-deficient medium to avoid external uptake of lipids. The lowest FBS concentration that allowed LY-B cell growth, though at a slow rate, under our conditions was 0.04%, that is, 250-fold less than the standard (10%) concentration. Cells grown under limiting SL concentrations remained viable for at least 72 hours. Enriching with sphingomyelin the SL-deficient medium allowed the recovery of growth rates analogous to those of control LY-B cells. Studies including whole cells, plasma membrane preparations, and derived lipid vesicles were carried out. Laurdan fluorescence was recorded to measure membrane molecular order, showing a significant decrease in the rigidity of LY-B cells, not only in plasma membrane but also in whole cell lipid extract, as a result of SL limitation in the growth medium. Plasma membrane preparations and whole cell lipid extracts were also studied using atomic force microscopy in the force spectroscopy mode. Force measurements demonstrated that lower breakthrough forces were required to penetrate samples obtained from SL-poor LY-B cells than those obtained from control cells. Mass-spectroscopic analysis was also a helpful tool to understand the rearrangement undergone by the LY-B cell lipid metabolism. The most abundant SL in LY-B cells, sphingomyelin, decreased by about 85% as a result of SL limitation in the medium, the bioactive lipid ceramide and the ganglioside precursor hexosylceramide decreased similarly, together with cholesterol. Quantitative SL analysis showed that a 250-fold reduction in sphingolipid supply to LY-B cells led only to a sixfold decrease in membrane sphingolipids, underlining the resistance to changes in composition of these cells. Plasma membrane compositions exhibited similar changes, at least qualitatively, as the whole cells with SL restriction. A linear correlation was observed between the sphingomyelin concentration in the membranes, the degree of lipid order as measured by laurdan fluorescence, and membrane breakthrough forces assessed by atomic force microscopy. Smaller, though significant, changes were also detected in glycerophospholipids under SL-restriction conditions.

pH dependent electrical properties of the inner- and outer- leaflets of biomimetic cell membranes

Composition and asymmetry of lipid membranes provide a means for regulation of trans-membrane permeability of ions and small molecules. The pH dependence of these processes plays an important role in the functioning and survival of cells. In this work, we study the pH dependence of membrane electrical resistance and capacitance using electrochemical impedance spectroscopy (EIS), surface plasmon resonance (SPR) and neutron reflectometry (NR) measurements of biomimetic tethered bilayer lipid membranes (tBLMs). tBLMs were prepared with single-component phospholipid compositions, as well as mixtures of phospholipids (phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, sphingomyelin and cholesterol) that mimic the inner- and outer- leaflets of plasma cell membranes. We found that all studied tBLMs have a resistance maximum at pHs near the pK_as of the phospholipids. SPR and NR indicated that surface concentration of phospholipids and the thickness of the hydrophobic part of the membrane did not change versus pH. We postulate that these maxima are the result of protonation of the phosphate oxygen of the phospholipids and that hydronium ions play a major role in the conductance at pHs < pK_as while sodium ions play the major role at pHs > pK_as. An additional sharp resistance maximum of the PE tBLMs found at pH 5.9 and most likely represents the phosphatidylethanolamine's isoelectric point. The data show the key roles of the characteristic parts of phospholipid molecules: terminal group (choline, carboxyl, amine), phosphate, glycerol and ester oxygens on the permeability and selectivity of ions through the membrane. The interactions between these groups lead to significant differences in the electrical properties of biomimetic models of inner- and outer- leaflets of the plasma cell membranes.

Chemical and genetic rescue of in vivo progranulin-deficient lysosomal and autophagic defects

In 2006, GRN mutations were first linked to frontotemporal dementia (FTD), the leading cause of non-Alzheimer dementias. While much research has been dedicated to understanding the genetic causes of the disease, our understanding of the mechanistic impacts of GRN deficiency has only recently begun to take shape. With no known cure or treatment available for GRN-related FTD, there is a growing need to rapidly advance genetic and/or small-molecule therapeutics for this disease. This issue is complicated by the fact that, while lysosomal dysfunction seems to be a key driver of pathology, the mechanisms linking a loss of GRN to a pathogenic state remain unclear. In our attempt to address these key issues, we have turned to the nematode, Caenorhabditis elegans, to model, study, and find potential therapies for GRN-deficient FTD. First, we show that the loss of the nematode GRN ortholog, pgrn-1, results in several behavioral and molecular defects, including lysosomal dysfunction and defects in autophagic flux. Our investigations implicate the sphingolipid metabolic pathway in the regulation of many of the in vivo defects associated with pgrn-1 loss. Finally, we utilized these nematodes as an in vivo tool for high-throughput drug screening and identified two small molecules with potential therapeutic applications against GRN/pgrn-1 deficiency. These compounds reverse the biochemical, cellular, and functional phenotypes of GRN deficiency. Together, our results open avenues for mechanistic and therapeutic research into the outcomes of GRN-related neurodegeneration, both genetic and molecular.

Aberrant sphingomyelin 31P-NMR signatures in giant cell tumour of bone

An understanding of the biochemistry of the giant cell tumour of bone (GCTB) provides an opportunity for the development of prognostic markers and identification of therapeutic targets. Based on metabolomic analysis, we proposed glycerophospholipid metabolism as the altered pathway in GCTB and the objective of this study was to identify these altered metabolites. Using phosphorus-31 nuclear magnetic resonance spectroscopy (³¹P-NMR), sphingomyelin was determined as the most dysregulated phospholipid in tissue samples from six patients with GCTB; subsequently, enzymes related to its biosynthesis and hydrolysis were examined using immunodetection techniques. High expression of sphingomyelin synthases 1 and 2, but low expression of neutral sphingomyelinase 2 (nSMase2), was found in GCTB tissues compared to non-neoplastic bone tissues. Sphingomyelin/ ceramide biosynthesis is dysregulated in GCTB due to alterations in the expression of SMS1, SMS2, and nSMase2.

The fine-tuning of cell membrane lipid bilayers accentuates their compositional complexity

Cell membranes are now emerging as finely tuned molecular systems, signifying that re-evaluation of our understanding of their structure is essential. Although the idea that cell membrane lipid bilayers do little more than give shape and form to cells and limit diffusion between cells and their environment is totally passé, the structural, compositional, and functional complexity of lipid bilayers often catches cell and molecular biologists by surprise. Models of lipid bilayer structure have developed considerably since the heyday of the fluid mosaic model, principally by the discovery of the restricted diffusion of membrane proteins and lipids within the plane of the bilayer. In reviewing this field, we now suggest that further refinement of current models is necessary and propose that describing lipid bilayers as "finely-tuned molecular assemblies" best portrays their complexity and function. Also see the video abstract here: https://www.youtube.com/watch?v=ddkP-QRZTl8.

Effect of irradiation treatment on the lipid composition and nutritional quality of goat meat

The knowledge of the changes in the lipid species in irradiated goat meat is expected to clarify the beneficial effects of irradiation on meat preservation. This study explored the characteristic lipid composition and the changes in irradiated goat meat based on quantitative lipidomics strategy by LC-MS. Totally, 12 subclasses of 174 lipids were identified with significant differences (p < 0.05, VIP > 1), and the absolute quantitative analysis of characteristic lipids was achieved. Significant lipid variables were involved in the major pathways of glycerophospholipid and sphingolipid metabolism. Moreover, significant increases during irradiation were found in total TG, PC, PE, LPE, Cer, LPC and SPH, while the total DG, PS, PG, PI and SM decreased after irradiation. Noteworthily, DHA-enriched PC (18:4/22:6) + H, a core nutrient for human health, exhibited an increase in the irradiated group. These results provide a basis for lipid quantitative alterations in irradiated goat meat and application of irradiation in meat preservation.

The Role of Cardiolipin as a Scaffold Mitochondrial Phospholipid in Autophagosome Formation: In Vitro Evidence

Cardiolipin (CL) is a hallmark phospholipid localized within the inner mitochondrial membrane. Upon several mitochondrial stress conditions, CL is translocated to specialized platforms, where it may play a role in signaling events to promote mitophagy and apoptosis. Recent studies characterized the molecular composition of MAM-associated lipid microdomains and their implications in regulating the autophagic process. In this study we analyzed the presence of CL within MAMs following autophagic stimulus and the possible implication of raft-like microdomains enriched in CL as a signaling platform in autophagosome formation. Human 2FTGH fibroblasts and SKNB-E-2 cells were stimulated under nutrient deprivation with HBSS. MAM fraction was obtained by an ultracentrifugation procedure and analyzed by HPTLC immunostaining. CL interactions with mitofusin2 (MFN2), calnexin (CANX) and AMBRA1 were analyzed by scanning confocal microscopy and coimmunoprecipitation. The analysis revealed that CL accumulates in MAMs fractions following autophagic stimulus, where it interacts with MFN2 and CANX. It associates with AMBRA1, which in turn interacts with BECN1 and WIPI1. This study demonstrates that CL is present in MAM fractions following autophagy triggering and interacts with the multimolecular complex (AMBRA1/BECN1/WIPI1) involved in autophagosome formation. It may have both structural and functional implications in the pathophysiology of neurodegenerative disease(s).

The versatile role of exosomes in human retroviral infections: from immunopathogenesis to clinical application

Eukaryotic cells produce extracellular vesicles (EVs) mediating intercellular communication. These vesicles encompass many bio-molecules such as proteins, nucleic acids, and lipids that are transported between cells and regulate pathophysiological actions in the recipient cell. Exosomes originate from multivesicular bodies inside cells and microvesicles shed from the plasma membrane and participate in various pathological conditions. Retroviruses such as Human Immunodeficiency Virus -type 1 (HIV-1) and Human T-cell leukemia virus (HTLV)-1 engage exosomes for spreading and infection. Exosomes from virus-infected cells transfer viral components such as miRNAs and proteins that promote infection and inflammation. Additionally, these exosomes deliver virus receptors to target cells that make them susceptible to virus entry. HIV-1 infected cells release exosomes that contribute to the pathogenesis including neurological disorders and malignancy. Exosomes can also potentially carry out as a modern approach for the development of HIV-1 and HTLV-1 vaccines. Furthermore, as exosomes are present in most biological fluids, they hold the supreme capacity for clinical usage in the early diagnosis and prognosis of viral infection and associated diseases. Our current knowledge of exosomes' role from virus-infected cells may provide an avenue for efficient retroviruses associated with disease prevention. However, the exact mechanism involved in retroviruses infection/ inflammation remains elusive and related exosomes research will shed light on the mechanisms of pathogenesis.

Extracellular Vesicles and Their Roles in Cancer Progression

Extracellular vesicles (EVs) produced by cancer cells function as a unique form of intercellular communication that can promote cell growth and survival, help shape the tumor microenvironment, and increase invasive and metastatic activity. There are two major classes of EVs, microvesicles (MVs) and exosomes, and they differ in how they are formed. MVs are generated by the outward budding and fission of the plasma membrane. On the other hand, exosomes are derived as multivesicular bodies (MVBs) fuse with the plasma membrane and release their contents. What makes EVs especially interesting is how they mediate their effects. Both MVs and exosomes have been shown to contain a wide-variety of bioactive cargo, including cell surface, cytosolic, and nuclear proteins, as well as RNA transcripts, micro-RNAs (miRNAs), and even fragments of DNA. EVs, and their associated cargo, can be transferred to other cancer cells, as well as to normal cell types, causing the recipient cells to undergo phenotypic changes that promote different aspects of cancer progression. These findings, combined with those demonstrating that the amounts and contents of EVs produced by cancer cells can vary depending on their cell of origin, stage of development, or response to therapies, have raised the exciting possibility that EVs can be used for diagnostic purposes. Moreover, the pharmaceutical community is aggressively pursuing the use of EVs as a potential drug delivery platform. Here, in this chapter, we will highlight what is currently known about how EVs are generated, how they impact cancer progression, and the different ways they are being exploited for clinical applications.

Cooperation and Interplay between EGFR Signalling and Extracellular Vesicle Biogenesis in Cancer

Epidermal growth factor receptor (EGFR) takes centre stage in carcinogenesis throughout its entire cellular trafficking odyssey. When loaded in extracellular vesicles (EVs), EGFR is one of the key proteins involved in the transfer of information between parental cancer and bystander cells in the tumour microenvironment. To hijack EVs, EGFR needs to play multiple signalling roles in the life cycle of EVs. The receptor is involved in the biogenesis of specific EV subpopulations, it signals as an active cargo, and it can influence the uptake of EVs by recipient cells. EGFR regulates its own inclusion in EVs through feedback loops during disease progression and in response to challenges such as hypoxia, epithelial-to-mesenchymal transition and drugs. Here, we highlight how the spatiotemporal rules that regulate EGFR intracellular function intersect with and influence different EV biogenesis pathways and discuss key regulatory features and interactions of this interplay. We also elaborate on outstanding questions relating to EGFR-driven EV biogenesis and available methods to explore them. This mechanistic understanding will be key to unravelling the functional consequences of direct anti-EGFR targeted and indirect EGFR-impacting cancer therapies on the secretion of pro-tumoural EVs and on their effects on drug resistance and microenvironment subversion.

Extracellular Vesicles in Viral Infections: Two Sides of the Same Coin?

Extracellular vesicles are small membrane structures containing proteins and nucleic acids that are gaining a lot of attention lately. They are produced by most cells and can be detected in several body fluids, having a huge potential in therapeutic and diagnostic approaches. EVs produced by infected cells usually have a molecular signature that is very distinct from healthy cells. For intracellular pathogens like viruses, EVs can have an even more complex function, since the viral biogenesis pathway can overlap with EV pathways in several ways, generating a continuum of particles, like naked virions, EVs containing infective viral genomes and quasi-enveloped viruses, besides the classical complete viral particles that are secreted to the extracellular space. Those particles can act in recipient cells in different ways. Besides being directly infective, they also can prime neighbor cells rendering them more susceptible to infection, block antiviral responses and deliver isolated viral molecules. On the other hand, they can trigger antiviral responses and cytokine secretion even in uninfected cells near the infection site, helping to fight the infection and protect other cells from the virus. This protective response can also backfire, when a massive inflammation facilitated by those EVs can be responsible for bad clinical outcomes. EVs can help or harm the antiviral response, and sometimes both mechanisms are observed in infections by the same virus. Since those pathways are intrinsically interlinked, understand the role of EVs during viral infections is crucial to comprehend viral mechanisms and respond better to emerging viral diseases.

Dexosomes as a cell-free vaccine for cancer immunotherapy

Dendritic cells (DCs) secrete vast quantities of exosomes termed as dexosomes. Dexosomes are symmetric nanoscale heat-stable vesicles that consist of a lipid bilayer displaying a characteristic series of lipid and protein molecules. They include tetraspanins and all established proteins for presenting antigenic material such as the major histocompatibility complex class I/II (MHC I/II) and CD1a, b, c, d proteins and CD86 costimulatory molecule. Dexosomes contribute to antigen-specific cellular immune responses by incorporating the MHC proteins with antigen molecules and transferring the antigen-MHC complexes and other associated molecules to naïve DCs. A variety of ex vivo and in vivo studies demonstrated that antigen-loaded dexosomes were able to initiate potent antitumor immunity. Human dexosomes can be easily prepared using monocyte-derived DCs isolated by leukapheresis of peripheral blood and treated ex vivo by cytokines and other factors. The feasibility of implementing dexosomes as therapeutic antitumor vaccines has been verified in two phase I and one phase II clinical trials in malignant melanoma and non small cell lung carcinoma patients. These studies proved the safety of dexosome administration and showed that dexosome vaccines have the capacity to trigger both the adaptive (T lymphocytes) and the innate (natural killer cells) immune cell recalls. In the current review, we will focus on the perspective of utilizing dexosome vaccines in the context of cancer immunotherapy.

Mechanisms of Action of EGFR Tyrosine Kinase Receptor Incorporated in Extracellular Vesicles

EGFR and some of the cognate ligands extensively traffic in extracellular vesicles (EVs) from different biogenesis pathways. EGFR belongs to a family of four homologous tyrosine kinase receptors (TKRs). This family are one of the major drivers of cancer and is involved in several of the most frequent malignancies such as non-small cell lung cancer, breast cancer, colorectal cancer and ovarian cancer. The carrier EVs exert crucial biological effects on recipient cells, impacting immunity, pre-metastatic niche preparation, angiogenesis, cancer cell stemness and horizontal oncogene transfer. While EV-mediated EGFR signalling is important to EGFR-driven cancers, little is known about the precise mechanisms by which TKRs incorporated in EVs play their biological role, their stoichiometry and associations to other proteins relevant to cancer pathology and EV biogenesis, and their means of incorporation in the target cell. In addition, it remains unclear whether different subtypes of EVs incorporate different complexes of TKRs with specific functions. A raft of high spatial and temporal resolution methods is emerging that could solve these and other questions regarding the activity of EGFR and its ligands in EVs. More importantly, methods are emerging to block or mitigate EV activity to suppress cancer progression and drug resistance. By highlighting key findings and areas that remain obscure at the intersection of EGFR signalling and EV action, we hope to cross-fertilise the two fields and speed up the application of novel techniques and paradigms to both.

Exploring polar headgroup interactions between sphingomyelin and ceramide with infrared spectroscopy

Ceramide is a major actor in the sphingolipid signaling pathway elicited by various kinds of cell stress. Under those conditions ceramide (Cer) is produced in the plasma membrane as a product of sphingomyelin (SM) hydrolysis, and this may lead to apoptosis. Thus, SM and Cer coexist in the membrane for some time, and they are known to separate laterally from the (more abundant) glycerolipids, giving rise to highly rigid domains or platforms. The properties of these domains/platforms are rather well understood, but the underlying SM:Cer molecular interactions have not been explored in detail. Infrared (IR) spectroscopy is a powerful analytical technique that provides information on all the chemical groupings in a molecule, and that can be applied to membranes and lipid bilayers in aqueous media. IR spectra can be conveniently retrieved as a function of temperature, thus revealing the thermotropic transitions of SM and its mixtures with Cer. Four regions of the IR spectrum of these sphingolipids have been examined, two of them dominated by the hydrophobic regions in the molecules, namely the C–H stretching vibrations (2800–3000 cm⁻¹), and the CH₂ scissoring vibrations (1455–1485 cm⁻¹), and two others arising from chemical groups at the lipid-water interface, the sphingolipid amide I band (1600–1680 cm⁻¹), and the phosphate vibrations in the 1000–1110 cm⁻¹ region. The latter two regions have been rarely studied in the past. The IR data from the hydrophobic components show a gel (or ripple)-fluid transition of SM at 40 °C, that is shifted up to about 70 °C when Cer is added to the bilayers, in agreement with previous studies using a variety of techniques. IR information concerning the polar parts is more interesting. The amide I (carbonyl) band of pure SM exhibits a maximum at 1638 cm⁻¹ at room temperature, and its position is shifted by about 10 cm⁻¹ in the presence of Cer. Cer causes also a change in the overall band shape, but no signs of band splitting are seen, suggesting that SM and Cer carbonyl groups are interacting tightly, presumably through H-bonds. The 1086 cm⁻¹ band, corresponding to PO₂⁻ vibrations, appears more stable in SM than in DPPC, and it is further stabilized by Cer, again suggesting an important role of H-bonds in the formation of SM:Cer clusters. Thus, SM and Cer can interact through their polar headgroups, in a way that is not accessible to other lipid classes.

Aberrant Membrane Composition and Biophysical Properties Impair Erythrocyte Morphology and Functionality in Elliptocytosis

Red blood cell (RBC) deformability is altered in inherited RBC disorders but the mechanism behind this is poorly understood. Here, we explored the molecular, biophysical, morphological, and functional consequences of α-spectrin mutations in a patient with hereditary elliptocytosis (pEl) almost exclusively expressing the Pro260 variant of SPTA1 and her mother (pElm), heterozygous for this mutation. At the molecular level, the pEI RBC proteome was globally preserved but spectrin density at cell edges was increased. Decreased phosphatidylserine vs. increased lysophosphatidylserine species, and enhanced lipid peroxidation, methemoglobin, and plasma acid sphingomyelinase (aSMase) activity were observed. At the biophysical level, although membrane transversal asymmetry was preserved, curvature at RBC edges and rigidity were increased. Lipid domains were altered for membrane:cytoskeleton anchorage, cholesterol content and response to Ca²⁺ exchange stimulation. At the morphological and functional levels, pEl RBCs exhibited reduced size and circularity, increased fragility and impaired membrane Ca²⁺ exchanges. The contribution of increased membrane curvature to the pEl phenotype was shown by mechanistic experiments in healthy RBCs upon lysophosphatidylserine membrane insertion. The role of lipid domain defects was proved by cholesterol depletion and aSMase inhibition in pEl. The data indicate that aberrant membrane content and biophysical properties alter pEl RBC morphology and functionality.

Evidence of the Mechanism by Which Polyomaviruses Exploit the Extracellular Vesicle Delivery System during Infection

Increasing evidence suggests that human viruses can hijack extracellular vesicles (EVs) to deliver proteins, mRNAs, microRNAs (miRNAs) and whole viral particles during viral persistence in the host. Human polyomavirus (PyV) miRNAs, which downregulate large T-antigen expression and target host factors, help the virus escape immune elimination and may have roles in the success of viral persistence/replication and the development of diseases. In this context, several investigations have detected PyV miRNAs in EVs obtained from cell culture supernatants after viral infection, demonstrating the ability of these vesicles to deliver miRNAs to uninfected cells, potentially counteracting new viral infection. Additionally, PyV miRNAs have been identified in EVs derived from the biological fluids of clinical samples obtained from patients with or at risk of severe PyV-associated diseases and from asymptomatic control healthy subjects. Interestingly, PyV miRNAs were found to be circulating in blood, urine, cerebrospinal fluid, and saliva samples from patients despite their PyV DNA status. Recently, the association between EVs and PyV viral particles was reported, demonstrating the ability of PyV viral particles to enter the cell without natural receptor-mediated entry and evade antibody-mediated neutralization or to be neutralized at a step different from that of the neutralization of naked whole viral particles. All these data point toward a potential role of the association between PyVs with EVs in viral persistence, suggesting that further work to define the implication of this interaction in viral reactivation is warranted.

Unraveling the mechanisms that specify molecules for secretion in extracellular vesicles

Extracellular vesicles (EVs) are small membrane-bound organelles naturally released from cells and potentially function as vehicles of intercellular communication. Cells release numerous sub-species of EVs, including exosomes and microvesicles, which are formed via distinct cellular pathways and molecular machineries and contain specific proteins, RNAs and lipids. Accumulating evidence indicates that the repertoire of molecules packaged into EVs is shaped by both the physiological state of the cell and the EV biogenesis pathway involved. Although these observations intimate that precisely regulated pathways sort molecules into EVs, the underlying molecular mechanisms that direct molecules for secretion remain poorly defined. Recently, with the advancement of mass spectrometry, next-generation sequencing techniques and molecular biology tools, several mechanisms contributing to EV cargo selection are beginning to be unraveled. This review examines strategies employed to reveal how specific proteins, RNAs and lipids are directed for secretion via EVs.

The Contrasting Role of Extracellular Vesicles in Vascular Inflammation and Tissue Repair

Extracellular vesicles are a heterogeneous family of vesicles, generated from different subcellular compartments and released into the extracellular space. Composed of a lipid bilayer encompassing both soluble cytosolic material and nuclear components, these organelles have been recently described as novel regulators of intercellular communication between adjacent and remote cells. Due to their diversified composition and biological content, they portray specific signatures of cellular activation and pathological processes, their potential as diagnostic and prognostic biomarkers has raised significant interest in cardiovascular diseases. Circulating vesicles, especially those released from platelets, leukocytes, and endothelial cells are found to play a critical role in activating several fundamental cells within the vasculature, including endothelial cells and vascular smooth muscle cells. Their intrinsic activity and immunomodulatory properties lends them to not only promote vascular inflammation, but also enhance tissue regeneration, vascular repair, and indeed resolution. In this review we aim to recapitulate the recent findings concerning the roles played by EVs that originate from different circulating cells, with particular reference to their action on the endothelium. We focus herein, on the interaction of platelet and leukocyte EVs with the endothelium. In addition, their potential biological function in promoting tissue resolution and vascular repair will also be discussed.

Tumorigenesis, diagnosis, and therapeutic potential of exosomes in liver cancer

Hepatocellular carcinoma (HCC, also called primary liver cancer) is one of the most fatal cancers in the world. Due to the insidiousness of the onset of HCC and the lack of effective treatment methods, the prognosis of HCC is extremely poor, and the 5-year average survival rate is less than 10%. Exosomes are nano-sized microvesicle and contain various components such as nucleic acids, proteins, and lipids. Exosomes are important carriers for signal transmission or transportation of material from cell to cell or between cells and tissues. In recent years, exosomes have been considered as potential therapeutic targets of HCC. A large number of reports indicate that exosomes play a key role in the establishment of an HCC microenvironment, as well as the development, progression, invasion, metastasis, and even the diagnosis, treatment, and prognosis of HCC. However, the exact molecular mechanisms and roles of exosomes in these processes remain unclear. We believe that elucidation of the regulatory mechanism of HCC-related exosomes and its signaling pathway and analysis of its clinical applications in the diagnosis and treatment of HCC can provide useful clues for future treatment regimens for HCC. This article discusses and summarizes the research progress of HCC-related exosomes and their potential clinical applications.

Mixing brain cerebrosides with brain ceramides, cholesterol and phospholipids

The properties of bilayers composed of pure brain cerebroside (bCrb) or of binary mixtures of bCrb with brain ceramide, cholesterol, egg phosphatidylcholine or brain sphingomyelin have been studied using a combination of physical techniques. Pure bCrb exhibits a rather narrow gel-fluid transition centred at ≈65 °C, with a half-width at half-height T1/2 ≈ 3 °C. bCrb mixes well with both fluid and gel phospholipids and ceramide, and it rigidifies bilayers of egg phosphatidylcholine or brain sphingomyelin when the latter are in the fluid state. Cholesterol markedly widens the bCrb gel-fluid transition, while decreasing the associated transition enthalpy, in the manner of cholesterol mixtures with saturated phosphatidylcholines, or sphingomyelins. Laurdan and DPH fluorescence indicate the formation of fluid ordered phases in the bCrb:cholesterol mixtures. Macroscopic phase separation of more and less fluid domains is observed in giant unilamellar vesicles consisting of bCrb:egg phosphatidylcholine or bCrb:sphingomyelin. Crb capacity to induce bilayer permeabilization or transbilayer (flip-flop) lipid motion is much lower than those of ceramides. The mixtures explored here contained mostly bCrb concentrations >50 mol%, mimicking the situation of cell membranes in Gaucher's disease, or of the Crb-enriched microdomains proposed to exist in healthy cell plasma membranes.

Lateral Segregation of Palmitoyl Ceramide-1-Phosphate in Simple and Complex Bilayers

Ceramide-1-phosphate is a minor sphingolipid with important functions in cell signaling. In this study, we examined the propensity of palmitoyl ceramide-1-phosphate (Cer-1P) to segregate laterally into ordered domains in different bilayer compositions at 23 and 37°C and compared this with segregation of palmitoyl ceramide (PCer) and palmitoyl sphingomyelin (PSM). The ordered-domain formation in the fluid phosphatidylcholine bilayers was determined using the emission lifetime changes of trans-parinaric acid and from differential scanning calorimetry thermograms. The lateral segregation of Cer-1P was examined when hydrated to bilayers in Tris buffer (50 mM Tris, 140 mM NaCl (pH 7.4)). At this pH, Cer-1P was negatively charged. The lateral segregation propensity of Cer-1P in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers was intermediate between PCer and PSM. Based on differential scanning calorimetry analysis, we observed that the gel domains formed by Cer-1P in POPC bilayers (POPC:Cer-1P 70:30 by mol) were less stable (melting interval 16-37°C) than the corresponding POPC and PCer gel domains at equal composition (melting interval 20-55°C). The gel-phase melting enthalpy was also much lower in Cer-1P (1.5 kcal/mol) than in the PCer-containing POPC bilayers (9 kcal/mol). Cer-1P appeared to be at least partially miscible with PCer domains in POPC bilayers. Cer-1P domains were stabilized in the presence of PSM (POPC:PSM 85:15), similarly as seen with PCer-rich domains. In bilayers at 37°C, with an approximate outer-leaflet cell membrane composition (sphingomyelin and cholesterol enriched, aminophospholipid poor), Cer-1P segregation did not lead to the formation of ordered domains, at least when compared with PCer segregation. In bilayers with an approximate inner-leaflet composition (sphingomyelin poor, cholesterol and aminophospholipid enriched), Cer-1P also failed to form ordered domains. PCer segregated into ordered domains only after the PCer/cholesterol ratio exceeded an approximate equimolar ratio.