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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Antivesiculation and Complete Unbinding of Tail-Tethered Lipids

Here, we report the effect of tail-tethering on vesiculation and complete unbinding of bilayered membranes. Amphiphilic molecules of a bolalipid, resembling the tail-tethered molecular structure of archaeal lipids, with two identical zwitterionic phosphatidylcholine headgroups self-assemble into a large flat lamellar membrane, in contrast to the multilamellar vesicles (MLVs) observed in its counterpart, monopolar nontethered zwitterionic lipids. The antivesiculation is confirmed by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cyro-TEM). With the net charge of zero and higher bending rigidity of the membrane (confirmed by neutron spin echo (NSE) spectroscopy), the current membrane theory would predict that membranes should stack with each other (aka “bind”) due to dominant van der Waals attraction, while the outcome of the nonstacking (“unbinding”) membrane suggests that the theory needs to include entropic contribution for the nonvesicular structures. This report pioneers an understanding of how the tail-tethering of amphiphiles affects the structure, enabling better control over the final nanoscale morphology.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Deciphering Melatonin-Stabilized Phase Separation in Phospholipid Bilayers

Lipid bilayers are fundamental building blocks of cell membranes, which contain the machinery needed to perform a range of biological functions, including cell–cell recognition, signal transduction, receptor trafficking, viral budding, and cell fusion. Importantly, many of these functions are thought to take place in the laterally phase-separated regions of the membrane, commonly known as lipid rafts. In this paper, we provide experimental evidence for the “stabilizing” effect of melatonin, a naturally occurring hormone produced by the brain’s pineal gland, on phase-separated model membranes mimicking the outer leaflet of plasma membranes. Specifically, we show that melatonin stabilizes the liquid-ordered/liquid-disordered phase coexistence over an extended range of temperatures. The melatonin-mediated stabilization effect is observed in both nanometer- and micrometer-sized liposomes using small angle neutron scattering (SANS), confocal fluorescence microscopy, and differential scanning calorimetry. To experimentally detect nanoscopic domains in 50 nm diameter phospholipid vesicles, we developed a model using the Landau–Brazovskii approach that may serve as a platform for detecting the existence of nanoscopic lateral heterogeneities in soft matter and biological materials with spherical and planar geometries.

42 ENGINEERING↗
DOE OSTI2019

Minireview - Microtubules and Tubulin Oligomers: Shape Transitions and Assembly by Intrinsically Disordered Protein Tau and Cationic Biomolecules

In this minireview, which is part of a special issue in honor of Jacob N. Israelachvili’s remarkable research career on intermolecular forces and interfacial science, we present studies of structures, phase behavior, and forces in reaction mixtures of microtubules (MTs) and tubulin oligomers with either intrinsically disordered protein (IDP) Tau, cationic vesicles, or the polyamine spermine (4+). Bare MTs consist of 13 protofilaments (PFs), on average, where each PF is made of a linear stack of αβ-tubulin dimers (i.e., tubulin oligomers). We begin with a series of experiments which demonstrate the flexibility of PFs toward shape changes in response to local environmental cues. First, studies show that MT-associated protein (MAP) Tau controls the diameter of microtubules upon binding to the outer surface, implying a shape change in the cross-sectional area of PFs forming the MT perimeter. The diameter of a MT may also be controlled by the charge density of a lipid bilayer membrane that coats the outer surface. We further describe an experimental study where it is unexpectedly found that the biologically relevant polyamine spermine (+4e) is able to depolymerize taxol-stabilized microtubules with efficiency that increases with decreasing temperature. This MT destabilization drives a dynamical structural transition where inside-out curving of PFs, during the depolymerization peeling process, is followed by reassembly of ring-like curved PF building blocks into an array of helical inverted tubulin tubules. We finally turn to a very recent study on pressure–distance measurements in bundles of MTs employing the small-angle X-ray scattering (SAXS)-osmotic pressure technique, which complements the surface-forces-apparatus technique developed by Jacob N. Israelachvili. Furthermore, these latter studies are among the very few which are beginning to shed light on the precise nature of the interactions between MTs mediated by MAP Tau in 37 °C reaction mixtures containing GTP and lacking taxol.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Halogenation-Dependent Effects of the Chlorosulfolipids of Ochromonas danica on Lipid Bilayers

The chlorosulfolipids are amphiphilic natural products with stereochemically complex patterns of chlorination and sulfation. Despite their role in toxic shellfish poisoning, potential pharmacological activities, and unknown biological roles, they remain understudied due to the difficulties in purifying them from natural sources. The structure of these molecules, with a charged sulfate group in the middle of the hydrophobic chain, appears incompatible with the conventional lipid bilayer structure. Questions about chlorosulfolipids remain unanswered partly due to the unavailability of structural analogues with which to conduct structure–function studies. Here, we approach this problem by combining enantioselective total synthesis and membrane biophysics. Using a combination of Langmuir pressure–area isotherms of lipid monolayers, fluorescence imaging of vesicles, mass spectrometry imaging, natural product isolation, small-angle X-ray scattering, and cryogenic electron microscopy, we show that danicalipin A (1) likely inserts into lipid bilayers in the headgroup region and alters their structure and phase behavior. Specifically, danicalipin A (1) thins the bilayer and fluidizes it, allowing even saturated lipid to form fluid bilayers. Lipid monolayers show similar fluidizing upon insertion of danicalipin A (1). Furthermore, we show that the halogenation of the molecule is critical for its membrane activity, likely due to sterically controlled conformational changes. Synthetic unchlorinated and monochlorinated analogues do not thin and fluidize lipid bilayers to the same extent as the natural product. Overall, this study sheds light on how amphiphilic small molecules interact with lipid bilayers and the importance of stereochemistry and halogenation for this interaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Nanotubes Growth by Self-Assembly of DNA Strands at Room Temperature

Artificial biomolecular nanotubes are a promising approach to building materials mimicking the capacity of the cellular cytoskeleton to grow and self-organize dynamically. Nucleic acid nanotechnology has demonstrated a variety of self-assembling nanotubes with programmable, robust features and morphological similarities to actual cytoskeleton components. However, their production typically requires thermal annealing, which not only poses a general constraint on their potential applications but is also incompatible with physiological conditions. Here, we demonstrate that DNA nanotubes can self-assemble from a simple mixture of five short DNA strands at constant room temperature, growing for extended periods of time in bulk conditions as well as under confinement. Assembly is achieved using a monovalent salt buffer, which ensures a faithful nanoscale arrangement and avoids nanotube aggregation. We observe the formation of individual nanotubes up to 20 days with a diameter of 22 ± 4 nm and length of several tens of micrometers. We finally encapsulate the strands in microsized compartments, such as water-in-oil microdroplets and giant unilamellar vesicles serving as simple cell models. Notably, nanotubes not only isothermally self-assemble directly inside the microcompartments but also self-organize into dynamic higher-order structures resembling rings and dynamic networks. Our study provides an advantageous method for in situ assembly of programmable biomolecular scaffolds and materials using synthetic DNA strands without requirements of thermal treatment.

Chemistry↗
DOE OSTI2023

A Genome-Scale Atlas Reveals Complex Interplay of Transcription and Translation in an Archaeon

The scale of post-transcriptional regulation and the implications of its interplay with other forms of regulation in environmental acclimation are underexplored for organisms of the domain Archaea. Here, we have investigated the scale of post-transcriptional regulation in the extremely halophilic archaeon Halobacterium salinarum NRC-1 by integrating the transcriptome-wide locations of transcript processing sites (TPSs) and SmAP1 binding, the genome-wide locations of antisense RNAs (asRNAs), and the consequences of RNase_2099C knockout on the differential expression of all genes. This integrated analysis has discovered that 54% of all protein-coding genes in the genome of this haloarchaeon are likely targeted by multiple mechanisms for putative post-transcriptional processing and regulation, with about 20% of genes likely being regulated by combinatorial schemes involving SmAP1, asRNAs, and RNase_2099C. Comparative analysis of mRNA levels (transcriptome sequencing [RNA-Seq]) and protein levels (sequential window acquisition of all theoretical fragment ion spectra mass spectrometry [SWATH-MS]) for 2,579 genes over four phases of batch culture growth in complex medium generated additional evidence for the conditional post-transcriptional regulation of 7% of all protein-coding genes. We demonstrate that post-transcriptional regulation may act to fine-tune specialized and rapid acclimation to stressful environments, e.g., as a switch to turn on gas vesicle biogenesis to promote vertical relocation under anoxic conditions and modulate the frequency of transposition by insertion sequence (IS) elements of the IS200/IS605, IS4, and ISH3 families. Findings from this study are provided as an atlas in a public Web resource (https://halodata.systemsbiology.net).

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Endogenous Retroviral Elements Generate Pathologic Neutrophils in Pulmonary Arterial Hypertension

Rationale: The role of neutrophils and their extracellular vesicles (EVs) in the pathogenesis of pulmonary arterial hypertension is unclear. Objectives: To relate functional abnormalities in pulmonary arterial hypertension neutrophils and their EVs to mechanisms uncovered by proteomic and transcriptomic profiling. Methods: Production of elastase, release of extracellular traps, adhesion, and migration were assessed in neutrophils from patients with pulmonary arterial hypertension and control subjects. Proteomic analyses were applied to explain functional perturbations, and transcriptomic data were used to find underlying mechanisms. CD66b-specific neutrophil EVs were isolated from plasma of patients with pulmonary arterial hypertension, and we determined whether they produce pulmonary hypertension in mice. Measurements and Main Results: Neutrophils from patients with pulmonary arterial hypertension produce and release increased neutrophil elastase, associated with enhanced extracellular traps. They exhibit reduced migration and increased adhesion attributed to elevated β1-integrin and vinculin identified by proteomic analysis and previously linked to an antiviral response. This was substantiated by a transcriptomic IFN signature that we related to an increase in human endogenous retrovirus K envelope protein. Transfection of human endogenous retrovirus K envelope in a neutrophil cell line (HL-60) increases neutrophil elastase and IFN genes, whereas vinculin is increased by human endogenous retrovirus K deoxyuridine triphosphate diphosphatase that is elevated in patient plasma. Neutrophil EVs from patient plasma contain increased neutrophil elastase and human endogenous retrovirus K envelope and induce pulmonary hypertension in mice, mitigated by elafin, an elastase inhibitor. Conclusions: Elevated human endogenous retroviral elements and elastase link a neutrophil innate immune response to pulmonary arterial hypertension.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Astronauts Plasma-Derived Exosomes Induced Aberrant EZH2-Mediated H3K27me3 Epigenetic Regulation of the Vitamin D Receptor

There are unique stressors in the spaceflight environment. Exposure to such stressors may be associated with adverse effects on astronauts' health, including increased cancer and cardiovascular disease risks. Small extracellular vesicles (sEVs, i.e., exosomes) play a vital role in intercellular communication and regulate various biological processes contributing to their role in disease pathogenesis. To assess whether spaceflight alters sEVs transcriptome profile, sEVs were isolated from the blood plasma of 3 astronauts at two different time points: 10 days before launch (L-10) and 3 days after return (R+3) from the Shuttle mission. AC16 cells (human cardiomyocyte cell line) were treated with L-10 and R+3 astronauts-derived exosomes for 24 h. Total RNA was isolated and analyzed for gene expression profiling using Affymetrix microarrays. Enrichment analysis was performed using Enrichr. Furthermore, transcription factor (TF) enrichment analysis using the ENCODE/ChEA Consensus TF database identified gene sets related to the polycomb repressive complex 2 (PRC2) and Vitamin D receptor (VDR) in AC16 cells treated with R+3 compared to cells treated with L-10 astronauts-derived exosomes. Further analysis of the histone modifications using datasets from the Roadmap Epigenomics Project confirmed enrichment in gene sets related to the H3K27me3 repressive mark. Interestingly, analysis of previously published H3K27me3–chromatin immunoprecipitation sequencing (ChIP-Seq) ENCODE datasets showed enrichment of H3K27me3 in the VDR promoter. Collectively, our results suggest that astronaut-derived sEVs may epigenetically repress the expression of the VDR in human adult cardiomyocytes by promoting the activation of the PRC2 complex and H3K27me3 levels.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Spaceflight-Associated Changes of snoRNAs in Peripheral Blood Mononuclear Cells and Plasma Exosomes—A Pilot Study

During spaceflight, astronauts are exposed to various physiological and psychological stressors that have been associated with adverse health effects. Therefore, there is an unmet need to develop novel diagnostic tools to predict early alterations in astronauts’ health. Small nucleolar RNA (snoRNA) is a type of short non-coding RNA (60–300 nucleotides) known to guide 2'-O-methylation (Nm) or pseudouridine (ψ) of ribosomal RNA (rRNA), small nuclear RNA (snRNA), or messenger RNA (mRNA). Emerging evidence suggests that dysregulated snoRNAs may be key players in regulating fundamental cellular mechanisms and in the pathogenesis of cancer, heart, and neurological disease. Therefore, we sought to determine whether the spaceflight-induced snoRNA changes in astronaut’s peripheral blood (PB) plasma extracellular vesicles (PB-EV) and peripheral blood mononuclear cells (PBMCs). Using unbiased small RNA sequencing (sRNAseq), we evaluated changes in PB-EV snoRNA content isolated from astronauts (n = 5/group) who underwent median 12-day long Shuttle missions between 1998 and 2001. Using stringent cutoff (fold change > 2 or log 2 -fold change >1, FDR < 0.05), we detected 21 down-and 9—up-regulated snoRNAs in PB-EVs 3 days after return (R + 3) compared to 10 days before launch (L-10). qPCR validation revealed that SNORA74A was significantly down-regulated at R + 3 compared to L-10. We next determined snoRNA expression levels in astronauts’ PBMCs at R + 3 and L-10 (n = 6/group). qPCR analysis further confirmed a significant increase in SNORA19 and SNORA47 in astronauts’ PBMCs at R + 3 compared to L-10. Notably, many downregulated snoRNA-guided rRNA modifications, including four Nms and five ψs. Our findings revealed that spaceflight induced changes in PB-EV and PBMCs snoRNA expression, thus suggesting snoRNAs may serve as potential novel biomarkers for monitoring astronauts’ health.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Non-Invasive Biophysical Techniques to Monitor the Structural Plasticity of the Photosynthetic Machinery of Live Diatom Cells

The photosynthetic performance of diatoms depends largely on the organization and structural flexibility of their thylakoid membranes, the densely packed, highly organized membrane vesicles in which light reactions of photosynthesis occur. Different regulatory mechanisms that fine tune the photosynthetic functions affect the organization of the photosynthetic machinery at different levels of structural complexity, from the level of individual protein complexes to the macroarray of membrane proteins and the remodeling of the entire thylakoid membrane system. To monitor these reorganizations, non-invasive techniques are of special value. In this chapter, we focus our attention on three of these techniques, which have been demonstrated to provide unique and useful information on the structure and structural and functional plasticity of live diatom cells: (i) circular dichroism (CD) spectroscopy, which has provided unique information on the chiral (macro-)organization of protein complexes and on their rapid, reversible reorganizations, fine-tuning the light-harvesting processes, as well as on variations in the short-range excitonic interactions in the antenna complexes; (ii) small-angle neutron scattering (SANS), which has been used to determine the periodic organization of the thylakoid membranes and to monitor reversible ultrastructural changes on the time-scale of minutes, induced by variations in the environmental conditions such as changes in temperature or light intensity; and (iii) electrochromic shift absorbance transients (ΔA ECS ), a spectroscopic tool which has been shown to be capable of identifying distinct functional groups of the light-harvesting carotenoid fucoxanthin in different diatoms and in cells exposed to different light intensities. Future use of these techniques will most certainly contribute to the deeper understanding of key regulatory mechanisms of photosynthesis in diatoms.

Szabo, Milan↗
DOE OSTI2021

Head on Comparison of Self- and Nano-Assemblies of Gamma Peptide Nucleic Acid Amphiphiles

Peptide nucleic acids (PNAs) are nucleic acid analogs with hybridization properties and enzymatic stability superior to that of DNA. In addition to gene targeting applications, PNAs have garnered significant attention as bio-polymers due to the Watson–Crick-based molecular recognition and flexibility of synthesis. Here, in this work, PNA amphiphiles are engineered using chemically modified gamma PNA (8 mer in length) containing hydrophilic diethylene glycol units at the gamma position and covalently conjugated lauric acid (C12) as a hydrophobic moiety. Gamma PNA ($\gamma$PNA) amphiphiles self-assemble into spherical vesicles. Further, nano-assemblies (NA) are formulated using the amphiphilic $\gamma$PNA as a polymer via ethanol injection-based protocols. Comprehensive head-on comparison of the physicochemical and cellular uptake properties of PNA derived self- and NA is performed. Small-angle neutron and X-ray scattering analysis reveal ellipsoidal morphology of $\gamma$PNA NA that results in superior cellular delivery compate to the spherical self-assembly. Next, the functional activities of $\gamma$PNA self-and NA in lymphoma cells via multiple endpoints, including gene expression, cell viability, and apoptosis-based assays are compared. Overall, it is established that $\gamma$PNA amphiphile is a functionally active bio-polymer to formulate NA for a wide range of biomedical applications.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Reversible Photoswitching in Poly(2-oxazoline) Nanoreactors

This contribution reports light responsive catalytic nanoreactors based on poly(2-oxazoline) diblock copolymers. The hydrophobic block of the copolymer is a random copolymer consisting of a spiropyran functionalized 2-oxazoline (SPOx) and 2-(but-3-yn-1-yl)-4,5-dihydrooxazole (ButynOx), while the hydrophilic block is based on 2-methyl-2-oxazoline (MeOx). The block copolymer is terminated with tris(2-aminoethyl) amine (TREN) that serves as catalyst in a Knoevenagel condensation. Four block copolymers with different ButynOx/SPOx and hydrophilic/hydrophobic ratios are synthesized and self-assembled through solvent exchange. Micelles and vesicles of various sizes are observed by TEM, which undergo morphological and size changes in response to irradiation with UV light. We hypothesize that these transformations in the nanostructures are caused by increases in the hydrophilicity of the hydrophobic block when spiropyran (SP) isomerizes to merocyanine (MC) in the presence of UV light. The reversible transition from micellar to vesicular nanoreactors resulted in increased reaction kinetics through improved substrate accessibility to the catalytic site, or termination of the catalytic reaction due to polymer precipitation. Furthermore, these nanoreactors present a promising platform towards photoregulating reaction outcomes based on changes in nanostructure morphology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Macrophage-derived MLKL in alcohol-associated liver disease: Regulation of phagocytosis

Mixed lineage kinase domain-like pseudokinase (MLKL), a key terminal effector of necroptosis, also plays a role in intracellular vesicle trafficking that is critical for regulating liver inflammation and injury in alcohol-associated liver disease (ALD). Although receptor interacting protein kinase 3 (Rip3) -/- mice are completely protected from ethanol-induced liver injury, Mlkl -/- mice are only partially protected. Therefore, we hypothesized that cell-specific functions of MLKL may contribute to ethanol-induced injury. Bone marrow transplants between Mlkl -/- mice and littermates were conducted to distinguish the role of myeloid versus nonmyeloid Mlkl in the Gao-binge model of ALD. Ethanol-induced hepatic injury, steatosis, and inflammation were exacerbated in Mlkl -/- →wild-type (WT) mice, whereas Mlkl deficiency in nonmyeloid cells (WT→Mlkl -/- ) had no effect on Gao-binge ethanol-induced injury. Importantly, Mlkl deficiency in myeloid cells exacerbated ethanol-mediated bacterial burden and accumulation of immune cells in livers. Mechanistically, challenging macrophages with lipopolysaccharide (LPS) induced signal transducer and activator of transcription 1–mediated expression and phosphorylation of MLKL, as well as translocation and oligomerization of MLKL to intracellular compartments, including phagosomes and lysosomes but not plasma membrane. Importantly, pharmacological or genetic inhibition of MLKL suppressed the phagocytic capability of primary mouse Kupffer cells (KCs) at baseline and in response to LPS with/without ethanol as well as peripheral monocytes isolated from both healthy controls and patients with alcohol-associated hepatitis. Further, in vivo studies revealed that KCs of Mlkl -/- mice phagocytosed fewer bioparticles than KCs of WT mice. Together, these data indicate that myeloid MLKL restricts ethanol-induced liver inflammation and injury by regulating hepatic immune cell homeostasis and macrophage phagocytosis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

In vivo localization of iron starvation induced proteins under variable iron supplementation regimes in Phaeodactylum tricornutum

Abstract The model pennate diatom Phaeodactylum tricornutum is able to assimilate a range of iron sources. It therefore provides a platform to study different mechanisms of iron processing concomitantly in the same cell. In this study, we follow the localization of three iron starvation induced proteins (ISIPs) in vivo, driven by their native promoters and tagged by fluorophores in an engineered line of P. tricornutum . We find that the localization patterns of ISIPs are dynamic and variable depending on the overall iron status of the cell and the source of iron it is exposed to. Notwithstanding, a shared destination of the three ISIPs both under ferric iron and siderophore‐bound iron supplementation is a globular compartment in the vicinity of the chloroplast. In a proteomic analysis, we identify that the cell engages endocytosis machinery involved in the vesicular trafficking as a response to siderophore molecules, even when these are not bound to iron. Our results suggest that there may be a direct vesicle traffic connection between the diatom cell membrane and the periplastidial compartment (PPC) that co‐opts clathrin‐mediated endocytosis and the “cytoplasm to vacuole” (Cvt) pathway, for proteins involved in iron assimilation. Proteomics data are available via ProteomeXchange with identifier PXD021172. Highlight The marine diatom P. tricornutum engages a vesicular network to traffic siderophores and phytotransferrin from the cell membrane directly to a putative iron processing site in the vicinity of the chloroplast.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Torsional twist of the SARS ‐ CoV and SARS ‐ CoV ‐2 SUD ‐N and SUD ‐M domains

Abstract Coronavirus non‐structural protein 3 (nsp3) forms hexameric crowns of pores in the double membrane vesicle that houses the replication–transcription complex. Nsp3 in SARS‐like viruses has three unique domains absent in other coronavirus nsp3 proteins. Two of these, SUD‐N (Macrodomain 2) and SUD‐M (Macrodomain 3), form two lobes connected by a peptide linker and an interdomain disulfide bridge. We resolve the first complete x‐ray structure of SARS‐CoV SUD‐N/M as well as a mutant variant of SARS‐CoV‐2 SUD‐N/M modified to restore cysteines for interdomain disulfide bond naturally lost by evolution. Comparative analysis of all structures revealed SUD‐N and SUD‐M are not rigidly associated but rather have significant rotational flexibility. Phylogenetic analysis supports that the potential to form the disulfide bond is common across betacoronavirus isolates from many bat species and civets, but also one or both of the cysteines that form the disulfide bond are absent across isolates from bats and pangolins. The absence of these cysteines does not impact viral replication or protein translation.

Rosas‐Lemus, Monica [Department of Microbiology‐Im↗
DOE OSTI2024

Submicron immunoglobulin particles exhibit FcγRII-dependent toxicity linked to autophagy in TNFα-stimulated endothelial cells

In intravenous immunoglobulins (IVIG), and some other immunoglobulin products, protein particles have been implicated in adverse events. Role and mechanisms of immunoglobulin particles in vascular adverse effects of blood components and manufactured biologics have not been elucidated. We have developed a model of spherical silica microparticles (SiMPs) of distinct sizes 200–2000 nm coated with different IVIG- or albumin (HSA)-coronas and investigated their effects on cultured human umbilical vein endothelial cells (HUVEC). IVIG products (1–20 mg/mL), bare SiMPs or SiMPs with IVIG-corona, did not display significant toxicity to unstimulated HUVEC. In contrast, in TNFα-stimulated HUVEC, IVIG-SiMPs induced decrease of HUVEC viability compared to HSA-SiMPs, while no toxicity of soluble IVIG was observed. 200 nm IVIG-SiMPs after 24 h treatment further increased ICAM1 (intercellular adhesion molecule 1) and tissue factor surface expression, apoptosis, mammalian target of rapamacin (mTOR)-dependent activation of autophagy, and release of extracellular vesicles, positive for mitophagy markers. Toxic effects of IVIG-SiMPs were most prominent for 200 nm SiMPs and decreased with larger SiMP size. Using blocking antibodies, toxicity of IVIG-SiMPs was found dependent on FcγRII receptor expression on HUVEC, which increased after TNFα-stimulation. Similar results were observed with different IVIG products and research grade IgG preparations. In conclusion, submicron particles with immunoglobulin corona induced size-dependent toxicity in TNFα-stimulated HUVEC via FcγRII receptors, associated with apoptosis and mTOR-dependent activation of autophagy. Testing of IVIG toxicity in endothelial cells prestimulated with proinflammatory cytokines is relevant to clinical conditions. Our results warrant further studies on endothelial toxicity of sub-visible immunoglobulin particles.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Interdigitation-Induced Order and Disorder in Asymmetric Membranes

We studied the transleaflet coupling of compositionally asymmetric liposomes in the fluid phase. The vesicles were produced by cyclodextrin-mediated lipid exchange and contained dipalmitoyl phosphatidylcholine (DPPC) in the inner leaflet and different mixed-chain phosphatidylcholines (PCs) as well as milk sphingomyelin (MSM) in the outer leaflet. In order to jointly analyze the obtained small-angle neutron and X-ray scattering data, we adapted existing models of trans-bilayer structures to measure the overlap of the hydrocarbon chain termini by exploiting the contrast of the terminal methyl ends in X-ray scattering. In all studied systems, the bilayer-asymmetry has large effects on the lipid packing density. Fully saturated mixed-chain PCs interdigitate into the DPPC-containing leaflet and evoke disorder in one or both leaflets. The long saturated acyl chains of MSM penetrate even deeper into the opposing leaflet, which in turn has an ordering effect on the whole bilayer. These results are qualitatively understood in terms of a balance of entropic repulsion of fluctuating hydrocarbon chain termini and van der Waals forces, which is modulated by the interdigitation depth. Monounsaturated PCs in the outer leaflet also induce disorder in DPPC despite vestigial or even absent interdigitation. Instead, the transleaflet coupling appears to emerge here from a matching of the inner leaflet lipids to the larger lateral lipid area of the outer leaflet lipids.

59 BASIC BIOLOGICAL SCIENCES↗