Membrane fusion

Research progress of paclitaxel nanodrug delivery system in the treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, characterized by the loss or low expression of estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2) and progesterone receptor (PR). Due to the lack of clear therapeutic targets, paclitaxel (PTX) is often used as a first-line standard chemotherapy drug for the treatment of high-risk and locally advanced TNBC. PTX is a diterpenoid alkaloid extracted and purified from Taxus plants, functioning as an anticancer agent by inducing and promoting tubulin polymerization, inhibiting spindle formation in cancer cells, and preventing mitosis. However, its clinical application is limited by low solubility and high toxicity. Nanodrug delivery system (NDDS) is one of the feasible methods to improve the water solubility of PTX and reduce side effects. In this review, we summarize the latest advancements in PTX-targeted NDDS, as well as its combination with other codelivery therapies for TNBC treatment. NDDS includes passive targeting, active targeting, stimuli-responsive, codelivery, and multimode strategies. These systems have good prospects in improving the bioavailability of PTX, enhancing tumor targeting, reducing toxicity, controlling drug release, and reverse tumor multidrug resistance (MDR). This review provides valuable insights into the clinical development and application of PTX-targeted NDDS in the treatment of TNBC.

Recalibration of MARTINI-3 Parameters for Improved Interactions between Peripheral Proteins and Lipid Bilayers

The MARTINI force field is one of the most used coarse-grained models for biomolecular simulations. Many limitations of the model including the protein-protein overaggregation have been improved in its latest version, MARTINI-3. In this study, we investigate the efficacy of the MARTINI-3 parameters for capturing the interactions of peripheral proteins with model plasma membranes. Particularly, we consider two classes of proteins, namely, annexin and epsin, which are known to generate negative and positive membrane curvatures, respectively. We find that current MARTINI-3 parameters are not able to correctly describe the protein-membrane interface and the protein-induced membrane curvatures for any of these proteins. The problem arises due to the lack of proper hydrophobic interactions between the protein residues and lipid tails. Making systematic adjustments, we show that a combination of reduction in the protein-water interactions and enhancement of protein-lipid hydrophobic interactions is essential for accurate prediction of the interfacial structure including the protein-induced membrane curvature. Next, we apply our model to a couple of other peripheral proteins, namely, Snf7, a core component of the ESCRT-III complex, and the PH domain of evectin-2. We find that our model captures the protein-membrane interfacial structure much more accurately than the MARTINI-3 model for all of the peripheral proteins considered in this study. However, the strategy described in this study may not be suitable for oligomeric transmembrane proteins where protein-protein hydrophobic interactions should be increased instead of protein-lipid hydrophobic interactions.

Mechanisms of extracellular vesicle uptake and implications for the design of cancer therapeutics

The translation of pre-clinical anti-cancer therapies to regulatory approval has been promising, but slower than hoped. While innovative and effective treatments continue to achieve or seek approval, setbacks are often attributed to a lack of efficacy, failure to achieve clinical endpoints, and dose-limiting toxicities. Successful efforts have been characterized by the development of therapeutics designed to specifically deliver optimal and effective dosing to tumour cells while minimizing off-target toxicity. Much effort has been devoted to the rational design and application of synthetic nanoparticles to serve as targeted therapeutic delivery vehicles. Several challenges to the successful application of this modality as delivery vehicles include the induction of a protracted immune response that results in their rapid systemic clearance, manufacturing cost, lack of stability, and their biocompatibility. Extracellular vesicles (EVs) are a heterogeneous class of endogenous biologically produced lipid bilayer nanoparticles that mediate intercellular communication by carrying bioactive macromolecules capable of modifying cellular phenotypes to local and distant cells. By genetic, chemical, or metabolic methods, extracellular vesicles (EVs) can be engineered to display targeting moieties on their surface while transporting specific cargo to modulate pathological processes following uptake by target cell populations. This review will survey the types of EVs, their composition and cargoes, strategies employed to increase their targeting, uptake, and cargo release, and their potential as targeted anti-cancer therapeutic delivery vehicles.

SMARTINI3 parametrization of multi-scale membrane models via unsupervised learning methods

In this study, we utilize genetic algorithms to develop a realistic implicit solvent ultra-coarse-grained (ultra-CG) membrane model comprising only three interaction sites. The key philosophy of the ultra-CG membrane model SMARTINI3 is its compatibility with realistic membrane proteins, for example, modeled within the Martini coarse-grained (CG) model, as well as with the widely used GROMACS software for molecular simulations. Our objective is to parameterize this ultra-CG model to accurately reproduce the experimentally observed structural and thermodynamic properties of Phosphatidylcholine (PC) membranes in real units, including properties such as area per lipid, area compressibility, bending modulus, line tension, phase transition temperature, density profile, and radial distribution function. In our example, we specifically focus on the properties of a POPC membrane, although the developed membrane model could be perceived as a generic model of lipid membranes. To optimize the performance of the model (the fitness), we conduct a series of evolutionary runs with diverse random initial population sizes (ranging from 96 to 384). We demonstrate that the ultra-CG membrane model we developed exhibits authentic lipid membrane behaviors, including self-assembly into bilayers, vesicle formation, membrane fusion, and gel phase formation. Moreover, we demonstrate compatibility with the Martini coarse-grained model by successfully reproducing the behavior of a transmembrane domain embedded within a lipid bilayer. This facilitates the simulation of realistic membrane proteins within an ultra-CG bilayer membrane, enhancing the accuracy and applicability of our model in biophysical studies.

In Situ Synthesis and Visualization of Membrane SNAP25 Nano-Organization

Cryo-electron tomography (cryo-ET) can provide insights into the structure and states of natural membrane environments to explore the role of SNARE proteins at membrane fusion and understand the relationship between their subcellular localization/formation and action mechanism. Nevertheless, the identification of individual molecules in crowded and low signal-to-noise ratio membrane environments remains a significant challenge. In this study, cryo-ET is employed to image near-physiological state 293T cell membranes, specifically utilizing in situ synthesized gold nanoparticles (AuNPs) bound with cysteine-rich protein tags to single-molecularly labeled synaptosomal-associated protein 25 (SNAP25) on the membrane surface. The high-resolution images reveal that SNAP25 is predominantly located in regions of high molecular density within the cell membrane and aggregates into smaller clusters, which may increase the fusion efficiency. Remarkably, a zigzag arrangement of SNAP25 is observed on the cell membrane. These findings provide valuable insights into the functional mechanisms of SNARE proteins.

Developing peptide-based fusion inhibitors as an antiviral strategy utilizing coronin 1 as a template

Enveloped viruses enter the host cells by endocytosis and subsequently fuse with the endosomal membranes, or fuse with the plasma membrane at the cell surface. The crucial stage of viral infection, regardless of the route taken to enter the host cell, is membrane fusion. The present work aims to develop a peptide-based fusion inhibitor that prevents membrane fusion by modifying the properties of the participating membranes, without targeting a protein. This would allow us to develop a fusion inhibitor that might work against a larger spectrum of enveloped viruses as it does not target any specific viral fusion protein. With this goal in mind, we have designed a novel peptide by modifying a native sequence derived from coronin 1, a phagosomal protein, that helps to avoid lysosomal degradation of mycobacterium-loaded phagosomes. The designed peptide, mTG-23, inhibits ∼30-40% fusion between small unilamellar vesicles containing varying amounts of cholesterol by modulating the biophysical properties of the participating bilayers. As a proof of principle, we have further demonstrated that the mTG-23 inhibits Influenza A virus infection in A549 and MDCK cells (with ∼EC50 of 20.45 μM and 21.55 μM, respectively), where viral envelope and endosomal membrane fusion is a crucial step. Through a gamut of biophysical and biochemical methods, we surmise that mTG-23 inhibits viral infection by inhibiting viral envelope and endosomal membrane fusion. We envisage that the proposed antiviral strategy can be extended to other viruses that employ a similar modus operandi, providing a novel pan-antiviral approach.

Quantitative assessment of the nanoanatomy of the contractile vacuole complex in Trypanosoma cruzi

Trypanosoma cruzi uses various mechanisms to cope with osmotic fluctuations during infection, including the remodeling of organelles such as the contractile vacuole complex (CVC). Little is known about the morphological changes of the CVC during pulsation cycles occurring upon osmotic stress. Here, we investigated the structure-function relationship between the CVC and the flagellar pocket domain where fluid discharge takes place-the adhesion plaque-during the CVC pulsation cycle. Using TcrPDEC2 and TcVps34 overexpressing mutants, known to have low and high efficiency for osmotic responses, we described a structural phenotype for the CVC that matches their corresponding physiological responses. Quantitative tomography provided data on the volume of the CVC and spongiome connections. Changes in the adhesion plaque during the pulsation cycle were also quantified and a dense filamentous network was observed. Together, the results suggest that the adhesion plaque mediates fluid discharge from the central vacuole, revealing new aspects of the osmoregulatory system in T. cruzi.

Strategic Design of Tryptophan-Aspartic Acid-Containing Peptide Inhibitors Using Coronin 1 as a Template: Inhibition of Fusion by Enhancing Acyl Chain Order

Enveloped viruses enter the host cell by fusing at the cell membrane or entering the cell via endocytosis and fusing at the endosome. Conventional inhibitors target the viral fusion protein to inactivate it for inducing fusion. These target-specific vis-à-vis virus-specific inhibitors fail to display their inhibitory efficacy against emerging and remerging viral infections. This necessitates the need to develop broad-spectrum entry inhibitors that are effective irrespective of the virus. Using a broad range of targeting techniques, the fusion inhibitors can modify the physical characteristics of the viral membrane, making it less prone to fusion. We have previously shown that two tryptophan-aspartic acid (WD)-containing hydrophobic peptides, TG-23 and GG-21, from coronin 1, a phagosomal protein, inhibit membrane fusion by modulating membrane organization and dynamics. In the present work, we designed two WD-containing hydrophilic peptides, QG-22 and AG-22, using coronin 1 as a template and evaluated their fusion inhibitory efficacies in the absence and presence of membrane cholesterol. Our results demonstrate that QG-22 and AG-22 inhibit membrane fusion irrespective of the concentration of membrane cholesterol. Our measurements of depth-dependent membrane organization and dynamics reveal that they impede fusion by enhancing the acyl chain order. Overall, our results validate the hypothesis of designing fusion inhibitors by modulating the membrane's physical properties. In addition, it demonstrates that chain hydrophobicity might not be a critical determinant for the development of peptide-based fusion inhibitors.

Optical and molecular features of negatively curved surfaces created by POPE lipids: A crucial role of the initial conditions

Membrane fusion is closely related to plasma membrane domains rich in cone-shaped phosphatidylethanolamine (PE) lipids that can reverse membrane curvature under certain conditions. The phase transition of PE-based lipid membranes from the lamellar fluid phase (Lα) to the inverse hexagonal phase (HII) is commonly taken as a general model in reconstructing the membrane fusion pathway, and whose structural features have been mostly described so far using structural and microscopic techniques. The aim of this paper is to decipher the optical and molecular features of Lβ → Lα and especially of Lα → HII transition of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) lipids at pH = 7.0 when they are initially prepared in the form of both multi- and unilamellar liposomes (MLVs and LUVs). The distinction between optical properties of MLS- and LUVs-derived HII phase, provided from turbidity-sensitive temperature-dependent UV-Vis spectra, was attributed to different formation mechanisms of HII phase. Most importantly, from FTIR spectroscopic data of POPE lipids in Lβ (15 °C), Lα (50 °C) and HII (85 °C) phases we identified the changes in molecular features of POPE lipids during phase transitions. Among the latter, by far the most significant is different hydration pattern of POPE lipids in MLVs- and LUVs-derived HII phase which extends from the polar-apolar interface all the way to the terminal amino group of the POPE lipid, along with the changes in the conformation of glycerol backbone as evidenced by the signature of α-methylene groups. Molecular dynamics simulations confirmed higher water penetration in HII phase and provided insight into hydrogen bonding patterns.

Hemifusomes and Interacting Proteolipid Nanodroplets: Formation of a Novel Cellular Organelle Complex

Within cells, vesicle fusion, scission, and the formation of intraluminal vesicles are critical processes that facilitate traffic, degradation, and recycling of cellular components, and maintenance of cellular homeostasis. Despite significant advancements in elucidating the molecular mechanisms that drive these dynamic processes, the direct in situ visualization of membrane remodeling intermediates remains challenging. Here, through the application of cryo-electron tomography in mammalian cells, we have identified a previously undescribed vesicular organelle complex with unique membrane topology: heterotypic hemifused vesicles that share extended hemifusion diaphragms (HDs) with a 42 nm proteolipid nanodroplet (PND) at their rim. We have termed these organelle complexes "hemifusomes". The HDs of hemifusomes exhibit a range of sizes and curvatures, including the formation of lens-shaped compartments encapsulated within the membrane bilayer. The morphological diversity of the lens-shaped vesicle aligns with a step-wise process of their intraluminal budding, ultimately leading to their scission and the generation of intraluminal vesicles. We propose that hemifusomes function as versatile platforms for protein and lipid sorting and as central hubs for the biogenesis of intraluminal vesicles and the formation of multivesicular bodies.

Extracellular vesicles (EVs)' journey in recipient cells: from recognition to cargo release

Extracellular vesicles (EVs) are nano-sized bilayer vesicles that are shed or secreted by virtually every cell type. A variety of biomolecules, including proteins, lipids, coding and non-coding RNAs, and mitochondrial DNA, can be selectively encapsulated into EVs and delivered to nearby and distant recipient cells, leading to alterations in the recipient cells, suggesting that EVs play an important role in intercellular communication. EVs play effective roles in physiology and pathology and could be used as diagnostic and therapeutic tools. At present, although the mechanisms of exosome biogenesis and secretion in donor cells are well understood, the molecular mechanism of EV recognition and uptake by recipient cells is still unclear. This review summarizes the current understanding of the molecular mechanisms of EVs' biological journey in recipient cells, from recognition to uptake and cargo release. Furthermore, we highlight how EVs escape endolysosomal degradation after uptake and thus release cargo, which is crucial for studies applying EVs as drug-targeted delivery vehicles. Knowledge of the cellular processes that govern EV uptake is important to shed light on the functions of EVs as well as on related clinical applications.

Functionalized extracellular nanovesicles as advanced CRISPR delivery systems

The clustered regularly interspaced short palindromic repeat (CRISPR) system, an emerging tool for genome editing, has garnered significant public interest for its potential in treating genetic diseases. Despite the rapid advancements in CRISPR technology, the progress in developing effective delivery strategies lags, impeding its clinical application. Extracellular nanovesicles (EVs), either in their endogenous forms or with engineered modifications, have emerged as a promising solution for CRISPR delivery. These EVs offer several advantages, including high biocompatibility, biological permeability, negligible immunogenicity, and straightforward production. Herein, we first summarize various types of functional EVs for CRISPR delivery, such as unmodified, modified, engineered virus-like particles (VLPs), and exosome-liposome hybrid vesicles, and examine their distinct intracellular pathways. Then, we outline the cutting-edge techniques for functionalizing extracellular vesicles, involving producer cell engineering, vesicle engineering, and virus-like particle engineering, emphasizing the diverse CRISPR delivery capabilities of these nanovesicles. Lastly, we address the current challenges and propose rational design strategies for their clinical translation, offering future perspectives on the development of functionalized EVs.

α-Synuclein and Mitochondria: Probing the Dynamics of Disordered Membrane-protein Regions Using Solid-State Nuclear Magnetic Resonance

The characterization of intrinsically disordered regions (IDRs) in membrane-associated proteins is of crucial importance to elucidate key biochemical processes, including cellular signaling, drug targeting, or the role of post-translational modifications. These protein regions pose significant challenges to powerful analytical techniques of molecular structural investigations. We here applied magic angle spinning solid-state nuclear magnetic resonance to quantitatively probe the structural dynamics of IDRs of membrane-bound α-synuclein (αS), a disordered protein whose aggregation is associated with Parkinson's disease (PD). We focused on the mitochondrial binding of αS, an interaction that has functional and pathological relevance in neuronal cells and that is considered crucial for the underlying mechanisms of PD. Transverse and longitudinal 15N relaxation revealed that the dynamical properties of IDRs of αS bound to the outer mitochondrial membrane (OMM) are different from those of the cytosolic state, thus indicating that regions generally considered not to interact with the membrane are in fact affected by the spatial proximity with the lipid bilayer. Moreover, changes in the composition of OMM that are associated with lipid dyshomeostasis in PD were found to significantly perturb the topology and dynamics of IDRs in the membrane-bound state of αS. Taken together, our data underline the importance of characterizing IDRs in membrane proteins to achieve an accurate understanding of the role that these elusive protein regions play in numerous biochemical processes occurring on cellular surfaces.

Nanoparticle induced fusion of lipid membranes

Membrane fusion is crucial for infection of enveloped viruses, cellular transport, and drug delivery via liposomes. Nanoparticles can serve as fusogenic agents facilitating such membrane fusion for direct transmembrane transport. However, the underlying mechanisms of nanoparticle-induced fusion and the ideal properties of such nanoparticles remain largely unknown. Here, we used molecular dynamics simulations to investigate the efficacy of spheroidal nanoparticles with different size, prolateness, and ligand interaction strengths to enhance fusion between vesicles. By systematically varying nanoparticle properties, we identified how each parameter affects the fusion process and determined the optimal parameter range that promotes fusion. These findings provide valuable insights for the design and optimization of fusogenic nanoparticles with potential biotechnological and biomedical applications.

Control of artificial membrane fusion in physiological ionic solutions beyond the limits of electroformation

Membrane fusion, merging two lipid bilayers, is crucial for fabricating artificial membrane structures. Over the past 40 years, in contrast to precise and controllable membrane fusion in-vivo through specific molecules such as SNAREs, controlling the fusion in-vitro while fabricating artificial membrane structures in physiological ionic solutions without fusion proteins has been a challenge, becoming a significant obstacle to practical applications. We present an approach consisting of an electric field and a few kPa hydraulic pressure as an additional variable to physically control the fusion, enabling tuning of the shape and size of the 3D freestanding lipid bilayers in physiological ionic solutions. Mechanical model analysis reveals that pressure-induced parallel/normal tensions enhance fusion among membranes in the microwell. In-vitro peptide-membrane assay, mimicking vesicular transport via pressure-assisted fusion, and stability of 38 days with in-chip pressure control via pore size-regulated hydrogel highlight the potential for diverse biological applications.

A Coronin 1-Derived Peptide Inhibits Membrane Fusion by Modulating Membrane Organization and Dynamics

Membrane fusion is considered the first step in the entry of enveloped viruses into the host cell. Several targeted strategies have been implemented to block viral entry by limiting the fusion protein to form a six-helix bundle, which is a prerequisite for fusion. Nonetheless, the development of broad-spectrum fusion inhibitors is essential to combat emerging and re-emerging viral infections. TG-23, a coronin 1, a tryptophan-aspartate-rich phagosomal protein-derived peptide, demonstrated inhibition of fusion between small unilamellar vesicles (SUVs) by modulating the membrane's physical properties. However, its inhibitory efficacy reduces with an increasing concentration of membrane cholesterol. The present work aims to develop a fusion inhibitor whose efficacy would be unaltered in the presence of membrane cholesterol. A stretch of the tryptophan-aspartic acid-containing peptide with a similar secondary structure and hydrophobicity profile of TG-23 from coronin 1 was synthesized, and its ability to inhibit SUV-SUV fusion with varying concentrations of membrane cholesterol was evaluated. Our results demonstrate that the GG-21 peptide inhibits fusion irrespective of the cholesterol content of the membrane. We have further evaluated the peptide-induced change in the membrane organization and dynamics utilizing arrays of steady-state and time-resolved fluorescence measurements and correlated these results with their effect on fusion. Interestingly, GG-21 displays inhibitory efficacy in a wide variety of lipid compositions despite having a secondary structure and physical properties similar to those of TG-23. Overall, our results advocate that the secondary structure and physical properties of the peptide may not be sufficient to predict its inhibitory efficacy.

In Situ Detection of Nucleic Acids in Extracellular Vesicles via Membrane Fusion

Extracellular vesicles (EVs) carry diverse biomolecules (e. g., nucleic acids, proteins) for intercellular communication, serving as important markers for diseases. Analyzing nucleic acids derived from EVs enables non-invasive disease diagnosis and prognosis evaluation. Membrane fusion, a fundamental cellular process wherein two lipid membranes merge, facilitates cell communication and cargo transport. Building on this natural phenomenon, recent years have witnessed the emergence of membrane fusion-based strategies for the detection of nucleic acids within EVs. These strategies entail the encapsulation of detection probes within either artificial or natural vesicles, followed by the induction of membrane fusion with EVs to deliver probes. This innovative approach not only enables in situ detection of nucleic acids within EVs but also ensures the maintenance of structural integrity of EVs, thus preventing nucleic acid degradation and minimizing the interference from free nucleic acids. This concept categorizes approaches into universal and targeted membrane fusion strategies, and discusses their application potential, and challenges and future prospects.

An antifouling membrane-fusogenic liposome for effective intracellular delivery in vivo

The membrane-fusion-based internalization without lysosomal entrapment is advantageous for intracellular delivery over endocytosis. However, protein corona formed on the membrane-fusogenic liposome surface converts its membrane-fusion performance to lysosome-dependent endocytosis, causing poorer delivery efficiency in biological conditions. Herein, we develop an antifouling membrane-fusogenic liposome for effective intracellular delivery in vivo. Leveraging specific lipid composition at an optimized ratio, such antifouling membrane-fusogenic liposome facilitates fusion capacity even in protein-rich conditions, attributed to the copious zwitterionic phosphorylcholine groups for protein-adsorption resistance. Consequently, the antifouling membrane-fusogenic liposome demonstrates robust membrane-fusion-mediated delivery in the medium with up to 38% fetal bovine serum, outclassing two traditional membrane-fusogenic liposomes effective at 4% and 6% concentrations. When injected into mice, antifouling membrane-fusogenic liposomes can keep their membrane-fusion-transportation behaviors, thereby achieving efficient luciferase transfection and enhancing gene-editing-mediated viral inhibition. This study provides a promising tool for effective intracellular delivery under complex physiological environments, enlightening future nanomedicine design.

Tomosyns attenuate SNARE assembly and synaptic depression by binding to VAMP2-containing template complexes

Tomosyns are widely thought to attenuate membrane fusion by competing with synaptobrevin-2/VAMP2 for SNARE-complex assembly. Here, we present evidence against this scenario. In a novel mouse model, tomosyn-1/2 deficiency lowered the fusion barrier and enhanced the probability that synaptic vesicles fuse, resulting in stronger synapses with faster depression and slower recovery. While wild-type tomosyn-1m rescued these phenotypes, substitution of its SNARE motif with that of synaptobrevin-2/VAMP2 did not. Single-molecule force measurements indeed revealed that tomosyn's SNARE motif cannot substitute synaptobrevin-2/VAMP2 to form template complexes with Munc18-1 and syntaxin-1, an essential intermediate for SNARE assembly. Instead, tomosyns extensively bind synaptobrevin-2/VAMP2-containing template complexes and prevent SNAP-25 association. Structure-function analyses indicate that the C-terminal polybasic region contributes to tomosyn's inhibitory function. These results reveal that tomosyns regulate synaptic transmission by cooperating with synaptobrevin-2/VAMP2 to prevent SNAP-25 binding during SNARE assembly, thereby limiting initial synaptic strength and equalizing it during repetitive stimulation.

Myomerger Induces Membrane Hemifusion and Regulates Fusion Pore Expansion

Membrane fusion is a crucial mechanism in a wide variety of important events in cell biology from viral infection to exocytosis. However, despite many efforts and much progress, cell-cell fusion has remained elusive to our understanding. Along the life of the fusion pore, large conformational changes take place from the initial lipid bilayer bending, passing through the hemifusion intermediates, and ending with the formation of the first nascent fusion pore. In this sense, computer simulations are an ideal technique for describing such complex lipid remodeling at the molecular level. In this work, we studied the role played by the muscle-specific membrane protein Myomerger during the formation of the fusion pore. We have conducted μs length atomistic and coarse-grained molecular dynamics, together with free-energy calculations using ad hoc collective variables. Our results show that Myomerger favors the hemifusion diaphragm-stalk transition, reduces the nucleation-expansion energy difference, and promotes the formation of nonenlarging fusion pores.

Munc18c accelerates SNARE-dependent membrane fusion in the presence of regulatory proteins α-SNAP and NSF

Intracellular vesicle fusion is driven by the soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and their cofactors, including Sec1/Munc18 (SM), α-SNAP, and NSF. α-SNAP and NSF play multiple layers of regulatory roles in the SNARE assembly, disassembling the cis-SNARE complex and the prefusion SNARE complex. How SM proteins coupled with NSF and α-SNAP regulate SNARE-dependent membrane fusion remains incompletely understood. Munc18c, an SM protein involved in the exocytosis of the glucose transporter GLUT4, binds and activates target (t-) SNAREs to accelerate the fusion reaction through a SNARE-like peptide (SLP). Here, using an in vitro reconstituted system, we discovered that α-SNAP blocks the GLUT4 SNAREs-mediated membrane fusion. Munc18c interacts with t-SNAREs to displace α-SNAP, which overcomes the fusion inhibition. Furthermore, Munc18c shields the trans-SNARE complex from NSF/α-SNAP-mediated disassembly and accelerates SNARE-dependent fusion kinetics in the presence of NSF and α-SNAP. The SLP in domain 3a is indispensable in Munc18c-assisted resistance to NSF and α-SNAP. Together, our findings demonstrate that Munc18c protects the prefusion SNARE complex from α-SNAP and NSF, promoting SNARE-dependent membrane fusion through its SLP.

A practical guide for fast implementation of SNARE-mediated liposome fusion

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNAER) family proteins are the engines of most intra-cellular and exocytotic membrane fusion pathways (Jahn and Scheller 2006). Over the past two decades, in-vitro liposome fusion has been proven to be a powerful tool to reconstruct physiological SNARE-mediated membrane fusion processes (Liu et al. 2017). The reconstitution of the membrane fusion process not only provides direct evidence of the capability of the cognate SNARE complex in driving membrane fusion but also allows researchers to study the functional mechanisms of regulatory proteins in related pathways (Wickner and Rizo 2017). Heretofore, a variety of delicate methods for in-vitro SNARE-mediated liposome fusion have been established (Bao et al. 2018; Diao et al. 2012; Duzgunes 2003; Gong et al. 2015; Heo et al. 2021; Kiessling et al. 2015; Kreye et al. 2008; Kyoung et al. 2013; Liu et al. 2017; Scott et al. 2003). Although technological advances have made reconstitution more physiologically relevant, increasingly elaborate experimental procedures, instruments, and data processing algorithms nevertheless hinder the non-experts from setting up basic SNARE-mediated liposome fusion assays. Here, we describe a low-cost, timesaving, and easy-to-handle protocol to set up a foundational in-vitro SNARE-mediated liposome fusion assay based on our previous publications (Liu et al. 2023; Wang and Ma 2022). The protocol can be readily adapted to assess various types of SNARE-mediated membrane fusion and the actions of fusion regulators by using appropriate alternative additives (e.g., proteins, macromolecules, chemicals, etc.). The total time required for one round of the assay is typically two days and could be extremely compressed into one day.

New insights into plant autophagy: molecular mechanisms and roles in development and stress responses

Autophagy is an evolutionarily conserved eukaryotic intracellular degradation process. Although the molecular mechanisms of plant autophagy share similarities with those in yeast and mammals, certain unique mechanisms have been identified. Recent studies have highlighted the importance of autophagy during vegetative growth stages as well as in plant-specific developmental processes, such as seed development, germination, flowering, and somatic reprogramming. Autophagy enables plants to adapt to and manage severe environmental conditions, such as nutrient starvation, high-intensity light stress, and heat stress, leading to intracellular remodeling and physiological changes in response to stress. In the past, plant autophagy research lagged behind similar studies in yeast and mammals; however, recent advances have greatly expanded our understanding of plant-specific autophagy mechanisms and functions. This review summarizes current knowledge and latest research findings on the mechanisms and roles of plant autophagy with the objective of improving our understanding of this vital process in plants.

CRISPR-Cas12a powered hybrid nanoparticle for extracellular vesicle aggregation and in-situ microRNA detection

Efficient extracellular vesicle (EV) enrichment and timely internal RNA detection for cancer diagnostics are highly desirable and remain a challenge. Here, we report a rapid EV aggregation induced in-situ microRNA detection technology based on cationic lipid-polymer hybrid nanoparticles encapsulating cascade system of catalytic hairpin assembly and CRISPR-Cas12a (CLHN-CCC), allowing for EV enrichment in three-dimensional space and in-situ detection of internal microRNAs in one step within 30 min. The enrichment efficiency (>90%) of CLHN-CCC is demonstrated in artificial EVs, cell-secreted EVs and serum EVs, which is 5-fold higher than that of traditional ultracentrifugation. The sensitive detection of artificial EVs and internal miR-1290 was achieved with the limit of detection of 10 particles/μL and 0.07 amol, respectively. After lyophilization, CLHN-CCC shows no obvious loss of performance within 6 months, making it much more robust and user friendly. This technique could sensitively (sensitivity = 92.9%) and selectively (selectivity = 85.7%) identify low amount miR-1290 in serum EVs, distinguishing early-stage pancreatic cancer patients from healthy subjects, showing high potential for clinical applications.

Methods for Studying Fusion of Bacterial Extracellular Vesicles with Intact Bacteria and Host Cells

Bacterial extracellular vesicles (BEVs) are nano- or micrometer-sized membrane-bound lipid vesicles released from both Gram-negative and Gram-positive bacteria. Cellular transport, communication, pathogenesis, and host-pathogen interactions are some of the major biological processes impacted by BEVs. Among these, host-pathogen interactions and bacterial pathogenesis are emerging as highly important targetable avenues underlined by the issues of antimicrobial resistance, thus demanding novel targets and approaches to treat bacterial infections. In this aspect, the study of the interaction of BEVs with bacteria and/or host cells becomes imperative and brings the membrane fusion process to the forefront. Furthermore, membrane fusion also underscores the performance of BEVs as nano-therapeutic delivery platforms. Here, we report methods to study fusion kinetics between mycobacteria-derived extracellular vesicles, which we refer to as MEVs, and intact mycobacteria or MEVs themselves. We also discuss the isolation of MEVs and their characterization. We outline critical factors that affect fusion kinetics by MEVs. The same principle can be extended for studying fusion between BEVs and mammalian host cells important for understanding how BEVs influence host-pathogen crosstalk.

The Regulation of Exosome Generation and Function in Physiological and Pathological Processes

Exosomes, a type of extracellular vesicle with a diameter of approximately 100 nm that is secreted by all cells, regulate the phenotype and function of recipient cells by carrying molecules such as proteins, nucleic acids, and lipids and are important mediators of intercellular communication. Exosomes are involved in various physiological and pathological processes such as immunomodulation, angiogenesis, tumorigenesis, metastasis, and chemoresistance. Due to their excellent properties, exosomes have shown their potential application in the clinical diagnosis and treatment of disease. The functions of exosomes depend on their biogenesis, uptake, and composition. Thus, a deeper understanding of these processes and regulatory mechanisms can help to find new targets for disease diagnosis and therapy. Therefore, this review summarizes and integrates the recent advances in the regulatory mechanisms of the entire biological process of exosomes, starting from the formation of early-sorting endosomes (ESCs) by plasma membrane invagination to the release of exosomes by fusion of multivesicular bodies (MVBs) with the plasma membrane, as well as the regulatory process of the interactions between exosomes and recipient cells. We also describe and discuss the regulatory mechanisms of exosome production in tumor cells and the potential of exosomes used in cancer diagnosis and therapy.

Host antiviral factors hijack furin to block SARS-CoV-2, ebola virus, and HIV-1 glycoproteins cleavage

Viral envelope glycoproteins are crucial for viral infections. In the process of enveloped viruses budding and release from the producer cells, viral envelope glycoproteins are presented on the viral membrane surface as spikes, promoting the virus's next-round infection of target cells. However, the host cells evolve counteracting mechanisms in the long-term virus-host co-evolutionary processes. For instance, the host cell antiviral factors could potently suppress viral replication by targeting their envelope glycoproteins through multiple channels, including their intracellular synthesis, glycosylation modification, assembly into virions, and binding to target cell receptors. Recently, a group of studies discovered that some host antiviral proteins specifically recognized host proprotein convertase (PC) furin and blocked its cleavage of viral envelope glycoproteins, thus impairing viral infectivity. Here, in this review, we briefly summarize several such host antiviral factors and analyze their roles in reducing furin cleavage of viral envelope glycoproteins, aiming at providing insights for future antiviral studies.

The explicit role of interfacial hydration during polyethylene glycol induced lipid fusion: a THz spectroscopic investigation

While the phenomenon of excipient mediated membrane fusion has been studied widely, the inherent role of interfacial hydration involved in the process has mostly remained unaddressed. Here we report the experimental validation of the fact that PEG-induced membrane fusion is associated with the dehydration of the membrane(s). We explore the explicit hydration behavior at three different lipids (DOPC, POPC and DPPC) membranes with different aliphatic tails as they undergo fusogenic transition in the presence of PEG of average molecular weight of 4000 using THz-FTIR spectroscopy in the frequency window of 1.5-13.5 THz. Dynamic light scattering and electron microscopic measurements confirm the formation of different intermediate steps of the liposomes during the fusion process: bilayer aggregation, destabilization and finally lipid fusion. We observe that membrane hydration follows a systematic trend with the lipid specificity as the fusion process sets in.

Qa-SNARE syntaxin 18 mediates lipid droplet fusion with SNAP23 and SEC22B

Lipid droplets (LDs) are dynamic lipid storage organelles that can sense and respond to changes in systemic energy balance. The size and number of LDs are controlled by complex and delicate mechanisms, among which, whether and which SNARE proteins mediate LD fusion, and the mechanisms governing this process remain poorly understood. Here we identified a SNARE complex, syntaxin 18 (STX18)-SNAP23-SEC22B, that is recruited to LDs to mediate LD fusion. STX18 targets LDs with its transmembrane domain spanning the phospholipid monolayer twice. STX18-SNAP23-SEC22B complex drives LD fusion in adiposome lipid mixing and content mixing in vitro assays. CIDEC/FSP27 directly binds STX18, SEC22B, and SNAP23, and promotes the lipid mixing of SNAREs-reconstituted adiposomes by promoting LD clustering. Knockdown of STX18 in mouse liver via AAV resulted in smaller liver and reduced LD size under high-fat diet conditions. All these results demonstrate a critical role of the SNARE complex STX18-SNAP23-SEC22B in LD fusion.

A supramolecular system mimicking the infection process of an enveloped virus through membrane fusion

Membrane fusion is an essential step for the entry of enveloped viruses, such as human immunodeficiency virus and influenza virus, into the host cell, often triggered by the binding of membrane proteins on the viral envelope to host cell membrane. Recently, external stimuli was shown to trigger membrane fusion in an artificial system. Direct observation of artificial membrane fusion using a giant unilamellar vesicle (GUV), which is similar in size to a cell, is useful as a biological model system. However, there are no model systems for studying membrane fusion of enveloped viruses with host cells. Here, we report a supramolecular model system for viral entry into a GUV or cell through membrane fusion. The system was constructed by complexing a cationic lipid bilayer on an anionic artificial viral capsid, self-assembled from viral β-annulus peptides. We demonstrate that the cationic enveloped artificial viral capsid electrostatically interacts with the anionic GUV or cell, and the capsid enters the GUV or cell through membrane fusion. The model system established in this study will be important for analyzing membrane fusion during infection of a natural virus.

A palisade-shaped membrane reservoir is required for rapid ring cell inflation in Drechslerella dactyloides

Fusion of individual vesicles carrying membrane-building materials with the plasma membrane (PM) enables gradual cell expansion and shape change. Constricting ring (CR) cells of carnivorous fungi triple in size within 0.1-1 s to capture passing nematodes. Here, we investigated how a carnivorous fungus, Drechslerella dactyloides, executes rapid and irreversible PM expansion during CR inflation. During CR maturation, vesicles carrying membrane-building materials accumulate and fuse, forming a structure named the Palisade-shaped Membrane-building Structure (PMS) around the rumen side of ring cells. After CR inflation, the PMS disappears, with partially inflated cells displaying wavy PM and fully inflated cells exhibiting smooth PM, suggesting that the PMS serves as the reservoir for membrane-building materials to enable rapid and extensive PM expansion. The DdSnc1, a v-SNARE protein, accumulates at the inner side of ring cells and is necessary for PMS formation and CR inflation. This study elucidates the unique cellular mechanisms underpinning rapid CR inflation.

Dynamic Fusion of Nucleic Acid Functionalized Nano-/Micro-Cell-Like Containments: From Basic Concepts to Applications

Membrane fusion processes play key roles in biological transformations, such as endocytosis/exocytosis, signal transduction, neurotransmission, or viral infections, and substantial research efforts have been directed to emulate these functions by artificial means. The recognition and dynamic reconfiguration properties of nucleic acids provide a versatile means to induce membrane fusion. Here we address recent advances in the functionalization of liposomes or membranes with structurally engineered lipidated nucleic acids guiding the fusion of cell-like containments, and the biophysical and chemical parameters controlling the fusion of the liposomes will be discussed. Intermembrane bridging by duplex or triplex nucleic acids and light-induced activation of membrane-associated nucleic acid constituents provide the means for spatiotemporal fusion of liposomes or nucleic acid modified liposome fusion with native cell membranes. The membrane fusion processes lead to exchange of loads in the fused containments and are a means to integrate functional assemblies. This is exemplified with the operation of biocatalytic cascades and dynamic DNA polymerization/nicking or transcription machineries in fused protocell systems. Membrane fusion processes of protocell assemblies are found to have important drug-delivery, therapeutic, sensing, and biocatalytic applications. The future challenges and perspectives of DNA-guided fused containments and membranes are addressed.

Phosphate-dependent regulation of vacuolar trafficking of OsSPX-MFSs is critical for maintaining intracellular phosphate homeostasis in rice

Vacuolar storage of inorganic phosphate (Pi) is essential for Pi homeostasis in plants. The SPX-MFS family proteins have been demonstrated to be vacuolar Pi transporters in many plant species. Transcriptional regulation of the predominant transporter among rice SPX-MFSs, OsSPX-MFS3, was only moderately suppressed by Pi starvation. Thus, post-transcriptional mechanisms were hypothesized to regulate the activity of OsSPX-MFS3. In this study, we found that the tonoplast localization of OsSPX-MFSs is inhibited under Pi-depleted conditions, resulting in their retention in the pre-vacuolar compartments (PVCs). A yeast two-hybrid screen identified that two SNARE proteins, OsSYP21 and OsSYP22, interact with the MFS domain of OsSPX-MFS3. Further genetic and cytological analyses indicate that OsSYP21 and OsSYP22 facilitate trafficking of OsSPX-MFS3 from PVCs to the tonoplast. Although a homozygous frameshift mutation in OsSYP22 appeared to be lethal, tonoplast localization of OsSPX-MFS3 was significantly inhibited in transgenic plants expressing a negative-dominant form of OsSYP22 (OsSYP22-ND), resulting in reduced vacuolar Pi concentrations in OsSYP22-ND plants. Under Pi-depleted conditions, the interaction between OsSYP22 and OsSPX-MFS3 was disrupted, and this process depended on the presence of the SPX domain. Deleting the SPX domains of OsSPX-MFSs resulted in their tonoplast localization under both Pi-depleted and Pi-replete conditions. Complementation of the osspx-mfs1/2/3 triple mutants with the MFS domain or the SPX domain of OsSPX-MFS3 confirmed that the MFS and SPX domains are responsive to Pi transport activity and Pi-dependent regulation, respectively. These data indicated that the SPX domains of OsSPX-MFSs sense cellular Pi (InsP) levels and, under Pi-depleted conditions, inhibit the interaction between OsSPX-MFSs and OsSYP21/22 and subsequent trafficking of OsSPX-MFSs from PVCs to the tonoplast.

Insights into the role of the membranes in Rab GTPase regulation

Rab GTPases are molecular switches with essential roles in mediating vesicular trafficking and establishing organelle identity. The conversion from the inactive, cytosolic to the membrane-bound, active species and back is tightly controlled by regulatory proteins. Recently, the roles of membrane properties and lipid composition of different target organelles in determining the activity state of Rabs have come to light. The investigation of several Rab guanine nucleotide exchange factors (GEFs) has revealed principles of how the recruitment via lipid interactions and the spatial confinement on the membrane surface contribute to spatiotemporal specificity in the Rab GTPase network. This paints an intricate picture of the control mechanisms in Rab activation and highlights the importance of the membrane lipid code in the organization of the endomembrane system.

A Frame-by-Frame Glance at Membrane Fusion Mechanisms: From Viral Infections to Fertilization

Viral entry and fertilization are distinct biological processes that share a common mechanism: membrane fusion. In viral entry, enveloped viruses attach to the host cell membrane, triggering a series of conformational changes in the viral fusion proteins. This results in the exposure of a hydrophobic fusion peptide, which inserts into the host membrane and brings the viral and host membranes into close proximity. Subsequent structural rearrangements in opposing membranes lead to their fusion. Similarly, membrane fusion occurs when gametes merge during the fertilization process, though the exact mechanism remains unclear. Structural biology has played a pivotal role in elucidating the molecular mechanisms underlying membrane fusion. High-resolution structures of the viral and fertilization fusion-related proteins have provided valuable insights into the conformational changes that occur during this process. Understanding these mechanisms at a molecular level is essential for the development of antiviral therapeutics and tools to influence fertility. In this review, we will highlight the biological importance of membrane fusion and how protein structures have helped visualize both common elements and subtle divergences in the mechanisms behind fusion; in addition, we will examine the new tools that recent advances in structural biology provide researchers interested in a frame-by-frame understanding of membrane fusion.

Simulation study of membrane bending by protein crowding: a case study with the epsin N-terminal homology domain

The mechanisms by which peripheral membrane proteins generate curvature is currently an active area of research. One of the proposed mechanisms is amphipathic insertion or the 'wedge' mechanism in which the protein shallowly inserts an amphipathic helix inside the membrane to drive the curvature. However, recent experimental studies have challenged the efficiency of the 'wedge' mechanism as it requires unusual protein densities. These studies proposed an alternative mechanism, namely 'protein-crowding', in which the lateral pressure generated by the random collisions among the membrane bound proteins drives the bending. In this study, we employ atomistic and coarse-grained molecular dynamics simulations to investigate the effects of amphipathic insertion and protein crowding on the membrane surface. Considering epsin N-terminal homology (ENTH) domain as a model protein, we show that amphipathic insertion is not essential for membrane bending. Our results suggest that ENTH domains can aggregate on the membrane surface by employing another structured region (H₃ helix). And this protein crowding decreases the cohesive energy of the lipid tails which causes a significant decrease in the membrane bending rigidity. The ENTH domain can generate a similar degree of membrane curvature irrespective of the activity of its H₀ helix. Our results are consistent with the recent experimental results.

Cholesterol-Containing Liposomes Decorated With Au Nanoparticles as Minimal Tunable Fusion Machinery

Membrane fusion is essential for the basal functionality of eukaryotic cells. In physiological conditions, fusion events are regulated by a wide range of specialized proteins, operating with finely tuned local lipid composition and ionic environment. Fusogenic proteins, assisted by membrane cholesterol and calcium ions, provide the mechanical energy necessary to achieve vesicle fusion in neuromediator release. Similar cooperative effects must be explored when considering synthetic approaches for controlled membrane fusion. We show that liposomes decorated with amphiphilic Au nanoparticles (AuLips) can act as minimal tunable fusion machinery. AuLips fusion is triggered by divalent ions, while the number of fusion events dramatically changes with, and can be finely tuned by, the liposome cholesterol content. We combine quartz-crystal-microbalance with dissipation monitoring (QCM-D), fluorescence assays, and small-angle X-ray scattering (SAXS) with molecular dynamics (MD) at coarse-grained (CG) resolution, revealing new mechanistic details on the fusogenic activity of amphiphilic Au nanoparticles (AuNPs) and demonstrating the ability of these synthetic nanomaterials to induce fusion regardless of the divalent ion used (Ca²⁺ or Mg²⁺ ). The results provide a novel contribution to developing new artificial fusogenic agents for next-generation biomedical applications that require tight control of the rate of fusion events (e.g., targeted drug delivery).

Effect of Cell Membrane-cloaked Nanoparticle Elasticity on Nano-Bio Interaction

Cell membrane-cloaked nanoparticles are exploited as a promising drug carrier to enhance circulation, accumulation, penetration into tumor sites and cellular internalization. However, the effect of physicochemical properties (e.g., size, surface charge, shape, and elasticity) of cell membrane-cloaked nanoparticles on nano-bio interaction is rarely studied. In the present study, keeping the other parameters constant, erythrocyte membrane (EM)-cloaked nanoparticles (nanoEMs) with different Young's moduli are fabricated by altering different kinds of nano-core (i.e., aqueous phase core, gelatin nanoparticles, and platinum nanoparticles). The designed nanoEMs are used to investigate the effect of nanoparticle elasticity on nano-bio interaction including cellular internalization, tumor penetration, biodistribution, blood circulation, and so on. The results demonstrate that the nanoEMs with intermediate elasticity (≈95 MPa) have a relatively higher increase in cellular internalization and inhibition of tumor cells migration than the soft (≈11 MPa) and stiff (≈173 MPa) ones. Furthermore, in vivo studies show that nanoEMs with intermediate elasticity preferentially accumulate and penetrate into tumor sites than the soft and stiff ones, while in circulation, softer nanoEMs show a longer blood circulation time. This work provides an insight for optimizing the design of biomimetic carriers and may further contribute to the selection of nanomaterials on biomedical application.

Botulinum neurotoxin A modulates the axonal release of pathological tau in hippocampal neurons

Pathological tau aggregates propagate across functionally connected neuronal networks in human neurodegenerative pathologies, such as Alzheimer's disease. However, the mechanism underlying this process is poorly understood. Several studies have showed that tau release is dependent on neuronal activity and that pathological tau is found in the extracellular space in free form, as well as in the lumen of extracellular vesicles. We recently showed that metabotropic glutamate receptor activity and SNAP25 integrity modulate the release of pathological tau from human and mouse synaptosomes. Here, we have leveraged botulinum neurotoxins (BoNTs), which impair neurotransmitter release by cleaving specific synaptic SNARE proteins, to dissect molecular mechanisms related to tau release at synapses. In particular, we have tested the effect of botulinum neurotoxin A (BoNT/A) on the synaptic release of tau in primary mouse neurons. Hippocampal neurons were grown in microfluidic chambers and transduced with lentiviruses expressing human tau (hTau). We found that neuronal stimulation significantly increases the release of mutant hTau, whereas wild-type hTau is unaffected. Importantly, BoNT/A blocks mutant hTau release, indicating that this process is controlled by SNAP25, a component of the SNARE complex, in intact neurons. These results suggest that BoNTs are potent tools to study the spreading of pathological proteins in neurodegenerative diseases and could play a central role in identifying novel molecular targets for the development of therapeutic interventions to treat tauopathies.

Quantifying DNA-mediated liposome fusion kinetics with a fluidic trap

Self-assembly of synthetic lipid vesicles via lipid membrane fusion is a versatile tool for creating biomimetic nano- and micron-sized particles. These so-called liposomes are used in the development of biosensing platforms, design of drug delivery schemes, and for investigating protein-mediated fusion of biological membranes. This work demonstrates DNA-induced liposome fusion in a nanofluidic trap where the reaction occurs in a 15 femtoliter volume at homogeneous mixing. In contrast to current methods for fusion in bulk, we show that the fusion reaction follows second-order kinetics with a fusion rate of (170 ± 30)/(M^-1s^-1) times the square number of DNA molecules per liposome. The nanofluidic trapping gives a full characterization of the size and charge of the liposomes before and after fusion. The chip-based approach limits the amount of sample (down to 440 vesicles) and can be parallelized for systematic studies in synthetic biology, diagnostics, and drug delivery.

Differential Behavior of Eicosapentaenoic and Docosahexaenoic Acids on the Organization, Dynamics, and Fusion of Homogeneous and Heterogeneous Membranes

Membrane fusion is a common course in innumerable biological processes that helps in the survival of eukaryotes. Enveloped viruses utilize this process to enter the host cells. Generally, the membrane lipid compositions play an important role in membrane fusion by modulating the membrane's physical properties and the behavior of membrane proteins in the cellular milieu. In this work, we have demonstrated the role of polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, on the organization, dynamics, and fusion of homogeneous and heterogeneous membranes. We have exploited arrays of steady-state and time-resolved fluorescence spectroscopic methods and polyethylene glycol-induced membrane fusion assay to elucidate the behavior of EPA and DHA on dioleoyl phosphatidylcholine (DOPC)/cholesterol (CH) homogeneous and DOPC/sphingomyelin/CH heterogeneous membranes. Our results suggest that EPA and DHA display differential effects on two different membranes. The effects of PUFAs in homogeneous membranes are majorly attributed to their flexible chain dynamics, whereas the ability of PUFA-induced cholesterol transfer from the l_o to the l_d phase rules their behavior in heterogeneous membranes. Overall, our results provide detailed information on the effect of PUFAs on homogeneous and heterogeneous membranes.

The Role of Exosomes in Pancreatic Ductal Adenocarcinoma Progression and Their Potential as Biomarkers

Pancreatic ductal adenocarcinoma (PDAC), the most common pancreatic malignancy, is an aggressive and lethal cancer with a dismal five-year survival rate. Despite remarkable improvements in cancer therapeutics, the clinical outcome of PDAC patients remains poor due to late diagnosis of the disease. This highlights the importance of early detection, wherein biomarker evaluation including exosomes would be helpful. Exosomes, small extracellular vesicles (sEVs), are cell-secreted entities with diameters ranging from 50 to 150 nm that deliver cellular contents (e.g., proteins, lipids, and nucleic acids) from parent cells to regulate the cellular processes of targeted cells. Recently, an increasing number of studies have reported that exosomes serve as messengers to facilitate stromal-immune crosstalk within the PDAC tumor microenvironment (TME), and their contents are indicative of disease progression. Moreover, evidence suggests that exosomes with specific surface markers are capable of distinguishing patients with PDAC from healthy individuals. Detectable exosomes in bodily fluids (e.g., blood, urine, saliva, and pancreatic juice) are omnipresent and may serve as promising biomarkers for improving early detection and evaluating patient prognosis. In this review, we shed light on the involvement of exosomes and their cargos in processes related to disease progression, including chemoresistance, angiogenesis, invasion, metastasis, and immunomodulation, and their potential as prognostic markers. Furthermore, we highlight feasible clinical applications and the limitations of exosomes in liquid biopsies as tools for early diagnosis as well as disease monitoring. Taking advantage of exosomes to improve diagnostic capacity may provide hope for PDAC patients, although further investigation is urgently needed.

Rab GTPases, tethers, and SNAREs work together to regulate Arabidopsis cell plate formation

Cell plates are transient structures formed by the fusion of vesicles at the center of the dividing plane; furthermore, these are precursors to new cell walls and are essential for cytokinesis. Cell plate formation requires a highly coordinated process of cytoskeletal rearrangement, vesicle accumulation and fusion, and membrane maturation. Tethering factors have been shown to interact with the Ras superfamily of small GTP binding proteins (Rab GTPases) and soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), which are essential for cell plate formation during cytokinesis and are fundamental for maintaining normal plant growth and development. In Arabidopsis thaliana, members of the Rab GTPases, tethers, and SNAREs are localized in cell plates, and mutations in the genes encoding these proteins result in typical cytokinesis-defective phenotypes, such as the formation of abnormal cell plates, multinucleated cells, and incomplete cell walls. This review highlights recent findings on vesicle trafficking during cell plate formation mediated by Rab GTPases, tethers, and SNAREs.

Effect of polyunsaturated free fatty acids on the membrane fusion mechanism

Membrane fusion is one of the important processes for the survival of eukaryotic cells and the entry of enveloped viruses into the host cells. Lipid composition plays a crucial role by modulating the organization and dynamics of the membrane, as well as the structure and conformation of membrane proteins. The diversity of the lipid acyl chain in its length and degree of unsaturation originates from the variation in free fatty acids (FFAs). We have studied the effect of linoleic (LA) and alpha-linolenic (ALA) acids on the depth-dependent organization, dynamics, and fusion of DOPC/DOPE (70/30 mol%) membranes utilizing steady-state and time-resolved fluorescence spectroscopic methods. Our results suggest that membranes with 5 mol% LA stabilize the stalk-intermediate and promote lipid mixing at the early stage of the process, i.e., the fusion follows the classical stalk model. Conversely, the extents of lipid and content mixing at the stalk intermediate are similar in the presence of 5 mol% of ALA, indicating the fusion mechanism as a nonclassical one like in the DOPC/DOPE (70/30 mol%) membranes. Our results provide an in-depth insight into the effect of the increasing degree of fatty acid tail unsaturation on membrane organization and dynamics and their impact on the membrane fusion mechanism.

Intercellular communication in the cumulus-oocyte complex during folliculogenesis: A review

During folliculogenesis, the oocyte and surrounding cumulus cells form an ensemble called the cumulus-oocyte complex (COC). Due to their interdependence, research on the COC has been a hot issue in the past few decades. A growing body of literature has revealed that intercellular communication is critical in determining oocyte quality and ovulation. This review provides an update on the current knowledge of COC intercellular communication, morphology, and functions. Transzonal projections (TZPs) and gap junctions are the most described structures of the COC. They provide basic metabolic and nutrient support, and abundant molecules for signaling pathways and regulations. Oocyte-secreted factors (OSFs) such as growth differentiation factor 9 and bone morphogenetic protein 15 have been linked with follicular homeostasis, suggesting that the communications are bidirectional. Using advanced techniques, new evidence has highlighted the existence of other structures that participate in intercellular communication. Extracellular vesicles can carry transcripts and signaling molecules. Microvilli on the oocyte can induce the formation of TZPs and secrete OSFs. Cell membrane fusion between the oocyte and cumulus cells can lead to sharing of cytoplasm, in a way making the COC a true whole. These findings give us new insights into related reproductive diseases like polycystic ovary syndrome and primary ovarian insufficiency and how to improve the outcomes of assisted reproduction.

Snapshots from within the cell: Novel trafficking and non trafficking functions of Snap29 during tissue morphogenesis

Membrane trafficking is a core cellular process that supports diversification of cell shapes and behaviors relevant to morphogenesis during development and in adult organisms. However, how precisely trafficking components regulate specific differentiation programs is incompletely understood. Snap29 is a multifaceted Soluble N-ethylmaleimide-sensitive factor Attachment protein Receptor, involved in a wide range of trafficking and non-trafficking processes in most cells. A body of knowledge, accrued over more than two decades since its discovery, reveals that Snap29 is essential for establishing and maintaining the operation of a number of cellular events that support cell polarity and signaling. In this review, we first summarize established functions of Snap29 and then we focus on novel ones in the context of autophagy, Golgi trafficking and vesicle fusion at the plasma membrane, as well as on non-trafficking activities of Snap29. We further describe emerging evidence regarding the compartmentalisation and regulation of Snap29. Finally, we explore how the loss of distinct functions of human Snap29 may lead to the clinical manifestations of congenital disorders such as CEDNIK syndrome and how altered SNAP29 activity may contribute to the pathogenesis of cancer, viral infection and neurodegenerative diseases.

SNARE Proteins in Synaptic Vesicle Fusion

Neurotransmitters are stored in small membrane-bound vesicles at synapses; a subset of synaptic vesicles is docked at release sites. Fusion of docked vesicles with the plasma membrane releases neurotransmitters. Membrane fusion at synapses, as well as all trafficking steps of the secretory pathway, is mediated by SNARE proteins. The SNAREs are the minimal fusion machinery. They zipper from N-termini to membrane-anchored C-termini to form a 4-helix bundle that forces the apposed membranes to fuse. At synapses, the SNAREs comprise a single helix from syntaxin and synaptobrevin; SNAP-25 contributes the other two helices to complete the bundle. Unc13 mediates synaptic vesicle docking and converts syntaxin into the permissive "open" configuration. The SM protein, Unc18, is required to initiate and proofread SNARE assembly. The SNAREs are then held in a half-zippered state by synaptotagmin and complexin. Calcium removes the synaptotagmin and complexin block, and the SNAREs drive vesicle fusion. After fusion, NSF and alpha-SNAP unwind the SNAREs and thereby recharge the system for further rounds of fusion. In this chapter, we will describe the discovery of the SNAREs, their relevant structural features, models for their function, and the central role of Unc18. In addition, we will touch upon the regulation of SNARE complex formation by Unc13, complexin, and synaptotagmin.

The Architecture of the Presynaptic Release Site

The architecture of the presynaptic release site is exquisitely designed to facilitate and regulate synaptic vesicle exocytosis. With the identification of some of the building blocks of the active zone and the advent of super resolution imaging techniques, we are beginning to understand the morphological and functional properties of synapses in great detail. Presynaptic release sites consist of the plasma membrane, the cytomatrix, and dense projections. These three components are morphologically distinct but intimately connected with each other and with postsynaptic specializations, ensuring the fidelity of synaptic vesicle tethering, docking, and fusion, as well as signal detection. Although the morphology and molecular compositions of active zones may vary among species, tissues, and cells, global architectural design of the release sites is highly conserved.

A comprehensive investigation of human endogenous retroviral syncytin proteins and their receptors in men with normozoospermia and impaired semen quality

PURPOSE

The study aims to investigate first the presence of Syncytin 2 and its receptor, MFSD2, in human sperm, and second whether the expressions of Syncytin 1, Syncytin 2, and their receptors, SLC1A5 and MFSD2, differ between normozoospermic, asthenozoospermic, oligozoospermic, and oligoasthenozoospermic human sperm samples.

METHODS

The localization patterns and expression levels of syncytins and their receptors were evaluated in normozoospermic (concentration = 88.9 ± 5.5 × 10⁶, motility = 79.2 ± 3.15%, n = 30), asthenozoospermic (concentration = 51.7 ± 7.18 × 10⁶, motility = 24.0 ± 3.12%, n = 15), mild oligozoospermic (concentration = 13.5 ± 2.17 × 10⁶, motility = 72.1 ± 6.5%, n = 15), moderate oligozoospermic (concentration = 8.4 ± 3.21 × 10⁶, motility = 65.1 ± 8.9%, n = 15), severe oligozoospermic (concentration = 2.1 ± 1.01 × 10⁶, motility = 67.5 ± 3.2%, n = 15), and oligoasthenozoospermic (concentration = 5.5 ± 3.21 × 10⁶, motility = 18.5 ± 1.2%, n = 15) samples by immunofluorescence staining and western blot.

RESULTS

Syncytins and their receptors visualized by immunofluorescence showed similar staining patterns with slight staining of the tail in all spermatozoa regardless of normozoospermia, asthenozoospermia, oligozoospermia, or oligoasthenozoospermia. The localization patterns were categorized as equatorial segment, midpiece region, acrosome, and post-acrosomal areas. The combined staining patterns were also detected as acrosomal cap plus post acrosomal region, the midpiece plus equatorial segment, and midpiece plus acrosomal region. However, some sperm cells were categorized as non-stained. Both syncytin proteins were most intensely localized in the midpiece region, while their receptors were predominantly present in the midpiece plus acrosomal region. Conspicuously, syncytins and their receptors showed decreased expression in asthenozospermic, oligozoospermic, and oligoasthenozoospermic samples compared to normozoospermic samples.

CONCLUSION

The expression patterns of HERV-derived syncytins and their receptors were identical regardless of the spermatozoa in men with normozoospermia versus impaired semen quality. Further, asthenozoospermia, oligozoospermia, and oligoasthenozoospermia as male fertility issues are associated with decreased expression of both syncytins and their receptors.

Studying membrane fusion using supported lipid bilayers on superparamagnetic beads

The fusion between two lipid membranes is a ubiquitous mechanism in cell traffic and pathogens invasion. Yet it is not well understood how two distinct bilayers overcome the energy barriers towards fusion and reorganize themselves to form a unique continuous bilayer. The magnitudes and numbers of these energy barriers are themselves an open question. To tackle these issues, we developed a new tool that allows to control the forces applied between two supported lipid bilayers (SLBs) deposited on superparamagnetic beads. By applying a magnetic field, the beads self-organize along field lines in chains of beads and compress the two membranes on the contact zone. Using the diffusion of fluorescently labelled lipids from one bilayer to the other allows us to identify fusion of the bilayers in contact. We applied increasing forces on SLBs and increased the occurrence of fusion. This experimental system allows the simultaneous study of tens of facing bilayers in a single experiment and mitigates the stochasticity of the fusion process. It is thus a powerful tool to test the various parameters involved in the membrane fusion process.