Fusion Pathway Research Articles

Cardiac specific PPAR alpha knock-down protects against cardiac lipid accumulation during metabolic stress

A dysregulated lipid metabolism contributes to the pathological development of a wide array of diseases including Type 2 Diabetes and associated cardiovascular diseases. One main regulator of cardiac lipid metabolism is the transcription factor Peroxisome Proliferator Activated Receptor α (PPARα). PPARα has been shown to have regulatory effects on many proteins that are integral for the proper regulation of lipid metabolism including those involved in fatty acid oxidation, mitochondria, and lipid droplets. After triglycerides (TG) accumulate and are stored in lipid droplets, the fat is then transferred from lipid droplets to mitochondria where the fatty acids undergo fatty acid oxidation and are used for ATP synthesis. In this research we aimed to determine how cardiac PPARα regulates lipid metabolism and the organelles responsible for its homeostasis in the heart during metabolic stress in the context of obesity. To study this, we used our tamoxifen-inducible cardiomyocyte specific PPARα knockout (cPPARα -/- ) mouse. To induce obesity, we fed Control and cPPARα -/- mice a high fat diet (HFD) for 5 weeks. Our results show that the TG content is lower in hearts from cPPARα -/- vs Control mice fed the HFD. cPPARα -/- vs Control hearts also had a lower expression of Plin2 (a key lipid droplet protein) when fed a HFD. also agrees with our previous findings in fasted/fed hearts. Interestingly, this agrees with our previous findings that the hearts in cPPARα -/- mice were protected against the elevation in TG that normally occurs in response to short term fasting (16 hr fast). Therefore, a reduction in cardiac PPARα protects against lipid accumulation in the heart. As mitochondrial dysfunction has been linked to the cardiac dysfunction present in diabetic hearts and may be involved in regulating lipid accumulation, we next wanted to test whether cPPARα -/- affected mitochondrial function. Measurements of mitochondrial stress proteins have not suggested any elevation in mitochondrial dysfunction in the cPPARα -/- hearts either at baseline or in response to the HFD or 16 hr fast. Interestingly, cPPARα -/- hearts had a higher expression of the uncut ATF6 protein than the control hearts when fasted which suggests that the cPPARα -/- hearts may have less mitochondrial stress due to less excess ROS in the heart. In agreement with this, echocardiography measurements have so far not indicated any reduction in the cardiac function of cPPARα -/- vs control mice. In the future it will be important to look into mitochondrial dysfunction in greater depth including the regulation of mitochondrial fission and fusion pathways. Overall, this suggests that cardiac PPARα may protect against cardiac lipid accumulation in obesity and that this may be through the regulation of Plin2 and mitochondrial stress pathways. ND EPSCoR This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Structural dynamics reveal subtype-specific activation and inhibition of influenza virus hemagglutinin

Influenza hemagglutinin (HA) is a prototypical class 1 viral entry glycoprotein, responsible for mediating receptor binding and membrane fusion. Structures of its prefusion and postfusion forms, embodying the beginning and endpoints of the fusion pathway, have been extensively characterized. Studies probing HA dynamics during fusion have begun to identify intermediate states along the pathway, enhancing our understanding of how HA becomes activated and traverses its conformational pathway to complete fusion. HA is also the most variable, rapidly evolving part of influenza virus, and it is not known whether mechanisms of its activation and fusion are conserved across divergent viral subtypes. Here, we apply hydrogen-deuterium exchange mass spectrometry to compare fusion activation in two subtypes of HA, H1 and H3. Our data reveal subtype-specific behavior in the regions of HA that undergo structural rearrangement during fusion, including the fusion peptide and HA1/HA2 interface. In the presence of an antibody that inhibits the conformational change (FI6v3), we observe that acid-induced dynamic changes near the epitope are dampened, but the degree of protection at the fusion peptide is different for the two subtypes investigated. These results thus provide new insights into variation in the mechanisms of influenza HA's dynamic activation and its inhibition.

Abstract 5498: SHP2 inhibition enhances antitumor effect of mirdametinib in a pediatric brain tumor model bearing CDC42SE2BRAF fusion by rewiring the proteome and phosphoproteome landscape

Abstract Pediatric gliomas are the most common type of pediatric brain tumors representing wide range of molecularly and clinically heterogenous subtypes. The hyperactivity of mitogen-activated protein kinases (MAPK) pathway has been identified in the majority of pediatric glioma suggesting its therapeutic potential. However, pharmacologic targeting single MAPK pathway’s component is limited due to the development of drug resistance and differential response associated with tumor molecular landscape. Therefore, effective combination strategy in the framework of precision medicine is needed. Here we report combination benefit and molecular underpinning therapeutic response of brain penetrant MEK inhibitor (mirdametinib) and SHP2 inhibitor (SHP099) in a pediatric patient derived xenograft (PDX) and xenoline developed at our institution. Our model was derived from a pediatric patient who was diagnosed with rare high-grade subtype of glioma, anaplastic pleomorphic xanthoastrocytoma, and did not respond to MEK inhibitor, trametinib. Integrative multi-omics revealed molecular fidelity between our model and its patient tumor counterpart including the presence of 7q35 fusion, CDC52SE2-BRAF, CDKN2A/B loss, and MAPK pathway hyperactivation. In vitro studies using our xenoline IU-X128 demonstrated synergy between SHP099 and mirdametinib to curtail cell proliferation (p<0.05). Moreover, this combination was well tolerated in our PDX, IU-RHT128, and potentiated anti-tumor effect of the single agent within clinically achievable doses. Reverse Phase Proteome Array (RPPA) identified MAPK reactivation via Mushasi RNA binding protein-PI3K-AKT crosstalk as a potential innate resistance mechanism to single agent MEK inhibitor in the PDX tumor. Further, tandem mass tags (TMT)-LC-MS/MS profiling on tumor treated with single agent SHP099 or mirdametinib and their combination revealed that combination therapy does not only revert certain proteome and phosphoproteome reprogramming from single agent treatment but also created a novel landscape which can be associated with anti-tumor effect. In this case, kinase network reprograming leading to MAPK reactivation was identified in mirdametinib treated tumor which was attenuated in the combination treatment. In summary, our results demonstrated that combination SHP099 and mirdametinib is superior to single agent alone in the pediatric A-PXA brain tumor model with proteome and phosphoproteome reprogramming of multiple networks as potential molecular mechanisms underlying therapeutic benefit of combination therapy. Ultimately, clinical translation of this finding will potentially benefit patient of this malignant rare pediatric glioma subset which currently does not have standard therapy. Citation Format: Nur P. Damayanti, Anthony Alfonso, Josue D. Ordaz, Erika Dobrota, M. Reza Saadatzadeh, Pankita Pandya, Barbara J. Bailey, Khadijeh Bijangi-Vishehsaraei, Harlan E. Shannon, Kathy Coy, Melissa Trowbridge, Anthony L. Sinn, Rosa Gallager, Julia Wulfkuhle, Emanuel Petricoin, Amber Mosley, Mark S. Marshall, Alex Lion, Michael J. Fergusson, Karl Balsara, Karen E. Pollok. SHP2 inhibition enhances antitumor effect of mirdametinib in a pediatric brain tumor model bearing CDC42SE2BRAF fusion by rewiring the proteome and phosphoproteome landscape. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5498.

The SARS-CoV-2 fusion domain preferentially initiates fusion in the late endosome.

SARS-CoV-2 can enter target cells via both the plasma and endosomal membranes. This ability to utilize either pathway increases the likelihood by which viral entry will succeed in delivering the viral genetic information, a vital component of the viral lifecycle. Most other viruses only utilize one or the other fusion pathway, partly due to vastly different environmental factors such as pH and membrane lipid composition. The coronavirus spike glycoprotein is responsible for facilitating viral entry by first binding to the receptor followed by membrane fusion, the latter of which is initiated by the fusion domain (FD). Improving our understanding of how the FD initiates fusion in both pathways, and whether or not one is preferred over the other, will help to elucidate the molecular mechanisms involved in the membrane fusion process of SARS-CoV-2. Through a FRET-based lipid mixing assay, the SARS-CoV-2 FD (S816-F855) displays a biphasic relationship between pH and fusion, with a pH similar to that of the late endosome (∼pH5.5-4.5) demonstrating the highest fusogenic activity. Intriguingly, when assessing the structure of the FD at pH7.4 and pH5.0 in dodecylphosphocholine, only minor conformational changes occur. This change in conformation results in the elongation of an α-helix within the fusion peptide, which alongside the fusion loop, are the two structural components of the FD that are found to be critical for full functionality of the peptide. Furthermore, the FD also favors the lipid environment of the late endosome to elicit fusion, with a specificity for the endosomal lipid BMP observed. In conclusion, the SARS-CoV-2 FD displays an α-helical extension at low pH when compared to neutral pH, that allows it to preferentially initiate fusion in a lipid and pH environment resembling that of the late endosome.

On the role of membrane embedding, protein rigidity and transmembrane length in lipid membrane fusion.

The fusion of biological membranes is ubiquitous in natural processes like exo- and endocytosis, intracellular trafficking and viral entry. Membrane fusion is also utilized in artificial biomimetic fusion systems, e.g. for drug delivery. Both the natural and the biomimetic fusion systems rely on a wide range of (artificial) proteins mediating the fusion process. Although the exact mechanisms of these proteins differ, clear analogies in their general behavior can be observed in bringing the membranes in close proximity and mediating the fusion reaction. In our study, we use molecular dynamics simulations with coarse grained models, mimicking the general behavior of fusion proteins (spikes), to systematically examine the effects of specific characteristics of these proteins on the fusion process. The protein characteristics considered are (i) the type of membrane embedding, i.e., either transmembrane or not, (ii) the rigidity, and (iii) the transmembrane domain (TMD) length. The results show essential differences in fusion pathway between monotopic and transmembrane spikes, in which transmembrane spikes seem to inhibit the formation of hemifusion diaphragms, leading to a faster fusion development. Furthermore, we observed that an increased rigidity and a decreased TMD length both proved to contribute to a faster fusion development. Finally, we show that a single spike may suffice to successfully induce a fusion reaction, provided that the spike is sufficiently rigid and attractive. Not only does this shed light on biological fusion of membranes, it also provides clear design rules for artificial membrane fusion systems.

Convolutional Transformer Fusion Blocks for Multi-Modal Gesture Recognition

Gesture recognition defines an important information channel in human-computer interaction. Intuitively, combining inputs from multiple modalities improves the recognition rate. In this work, we explore multi-modal video-based gesture recognition tasks by fusing spatio-temporal representation of relevant distinguishing features from different modalities. We present a self-attention based transformer fusion architecture to distill the knowledge from different modalities in two-stream convolutional neural networks (CNNs). For this, we introduce convolutions into the self-attention function and design the Convolutional Transformer Fusion Blocks (CTFB) for multi-modal data fusion. These fusion blocks can be easily added at different abstraction levels of the feature hierarchy in existing two-stream CNNs. In addition, the information exchange between two-stream CNNs along the feature hierarchy has so far been barely explored. We propose and evaluate different architectures for multi-level fusion pathways using CTFB to gain insights into the information flow between both streams. Our method achieves state-of-the-art or competitive performance on three benchmark gesture recognition datasets: a) IsoGD, b) NVGesture, and c) IPN hand. Extensive evaluation demonstrates the effectiveness of the proposed CTFB both in terms of recognition rate as well as resource efficiency.

Crowded Environment Regulates the Coacervation of Biopolymers via Nonspecific Interactions.

The membrane-less organelles (MLOs) with subcompartments are formed via liquid-liquid phase separation (LLPS) in the crowded cell interior whose background molecules are up to 400 mg/mL. It is still a puzzle how the background molecules regulate the formation, dynamics, and functions of MLOs. Using biphasic coacervate droplets formed by poly(l-lysine) (PLL), quaternized dextran (Q-dextran), and single-stranded oligonucleotides (ss-oligo) as a model of MLO, we online monitored the LLPS process in Bovine Serine Albumin (BSA) solution up to 200.0 mg/mL. Negatively charged BSA is able to form complex or coacervate with positively charged PLL and Q-dextran and thus participates in the LLPS via nonspecific interactions. Results show that BSA effectively regulates the LLPS by controlling the phase distribution, morphologies, and kinetics. With increasing BSA concentration, the spherical biphasic droplets evolve in sequence into phase-inverted flower-like structure, worm-like chains, network structures, and confined coacervates. Each kind of morphology is formed via its own specific growth and fusion pathway. Our work suggests that MLOs could be controlled solely by the crowded environment and provides a further step toward understanding the life process in cell.

Fusion assays for screening of fusion inhibitors targeting SARS-CoV-2 entry and syncytia formation.

Virus fusion process is evolutionarily conserved and provides a promising pan-viral target. Cell-cell fusion leads to syncytial formation and has implications in pathogenesis, virus spread and immune evasion. Drugs that target these processes can be developed into anti-virals. Here, we have developed sensitive, rapid, adaptable fusion reporter gene assays as models for plasma membrane and alternative fusion pathways as well as syncytial fusion in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and have confirmed their specificity using neutralizing antibodies and specific protease inhibitors. The fusion report gene assays are more sensitive and unbiased than morphological fusion assay. The fusion assays can differentiate between transmembrane serine protease 2 (TMPRSS2)-dependency in TMPRSS2(+) cells and trypsin-dependency in angiotensin-converting enzyme 2 (ACE2)(+)TMPRSS2(-) cells. Moreover, we have identified putative novel fusion processes that are triggered by an acidic pH with and without trypsin. Coupled with morphological fusion criteria, we have found that syncytia formation is enhanced by TMPRSS2 or trypsin. By testing against our top drug hits previously shown to inhibit SARS-CoV-2 pseudovirus infection, we have identified several fusion inhibitors including structurally related lopsided kite-shaped molecules. Our results have important implications in the development of universal blockers and synergistic therapeutics and the small molecule inhibitors can provide important tools in elucidating the fusion process.

Intermediates in SARS-CoV-2 spike-mediated cell entry.

SARS-CoV-2 cell entry is completed after viral spike (S) protein–mediated membrane fusion between viral and host cell membranes. Stable prefusion and postfusion S structures have been resolved by cryo–electron microscopy and cryo–electron tomography, but the refolding intermediates on the fusion pathway are transient and have not been examined. We used an antiviral lipopeptide entry inhibitor to arrest S protein refolding and thereby capture intermediates as S proteins interact with hACE2 and fusion-activating proteases on cell-derived target membranes. Cryo–electron tomography imaged both extended and partially folded intermediate states of S2, as well as a novel late-stage conformation on the pathway to membrane fusion. The intermediates now identified in this dynamic S protein–directed fusion provide mechanistic insights that may guide the design of CoV entry inhibitors.

Visualization of conformational changes and membrane remodeling leading to genome delivery by viral class-II fusion machinery

Chikungunya virus (CHIKV) is a human pathogen that delivers its genome to the host cell cytoplasm through endocytic low pH-activated membrane fusion mediated by class-II fusion proteins. Though structures of prefusion, icosahedral CHIKV are available, structural characterization of virion interaction with membranes has been limited. Here, we have used cryo-electron tomography to visualize CHIKV’s complete membrane fusion pathway, identifying key intermediary glycoprotein conformations coupled to membrane remodeling events. Using sub-tomogram averaging, we elucidate features of the low pH-exposed virion, nucleocapsid and full-length E1-glycoprotein’s post-fusion structure. Contrary to class-I fusion systems, CHIKV achieves membrane apposition by protrusion of extended E1-glycoprotein homotrimers into the target membrane. The fusion process also features a large hemifusion diaphragm that transitions to a wide pore for intact nucleocapsid delivery. Our analyses provide comprehensive ultrastructural insights into the class-II virus fusion system function and direct mechanistic characterization of the fundamental process of protein-mediated membrane fusion.

Long-lived mitochondrial proteins and why they exist.

Intracellular long-lived proteins (LLPs) provide structural support for several highly stable protein complexes and assemblies that play essential roles in ensuring cellular homeostasis and function. Recently, mitochondrial long-lived proteins (mt-LLPs) were discovered within inner mitochondria membranes (IMMs) and cristae invagination in tissues with old postmitotic cells. This observation is at odds with the fact that mitochondria are highly dynamic organelles that are continually remodeled through processes of fission, fusion, biogenesis, and multiple quality control pathways. In this opinion article, we propose that a subset of the mitochondrial proteome persists over long time frames and these mt-LLPs provide key structural support for the lifelong maintenance of mitochondrial structure.

Weight-guided dual-direction-fusion feature pyramid network for prohibited item detection in x-ray images

Accurate and robust detection of prohibited items in x-ray images has been playing a significant role in protecting public safety. However, large-scale variation of prohibited items and diverse backgrounds in x-ray images bring in many challenges to the detection. We propose an effective weight-guided dual-direction-fusion feature pyramid network (WDFPN), making full use of multilevel features to solve the scale variation problem in cluttered backgrounds. Specifically, our WDFPN mainly consists of weight-guided upsample fusion pathway (WUFP), attention-based connection (AC), and downsample fusion pathway (DFP). WUFP uses channel-wise weights generated from high-level features to weight low-level features, reducing invalid information redundancy. AC transfers enhanced low-level detail information to DFP. Subsequently, DFP improves the localization capacity of the entire features pyramid by the bottom-up fusion pathway. Extensive experiments on the security inspection x-ray and occluded prohibited items x-ray datasets demonstrate the superiority of our WDFPN in detecting prohibited items.

Sensitivity to Vaccines, Therapeutic Antibodies, and Viral Entry Inhibitors and Advances To Counter the SARS-CoV-2 Omicron Variant.

SUMMARYSevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) keeps evolving and mutating into newer variants over time, which gain higher transmissibility, disease severity, and spread in communities at a faster rate, resulting in multiple waves of surge in Coronavirus Disease 2019 (COVID-19) cases. A highly mutated and transmissible SARS-CoV-2 Omicron variant has recently emerged, driving the extremely high peak of infections in almost all continents at an unprecedented speed and scale. The Omicron variant evades the protection rendered by vaccine-induced antibodies and natural infection, as well as overpowers the antibody-based immunotherapies, raising the concerns of current effectiveness of available vaccines and monoclonal antibody-based therapies. This review outlines the most recent advancements in studying the virology and biology of the Omicron variant, highlighting its increased resistance to current antibody-based therapeutics and its immune escape against vaccines. However, the Omicron variant is highly sensitive to viral fusion inhibitors targeting the HR1 motif in the spike protein, enzyme inhibitors, involving the endosomal fusion pathway, and ACE2-based entry inhibitors. Omicron variant-associated infectivity and entry mechanisms of Omicron variant are essentially distinct from previous characterized variants. Innate sensing and immune evasion of SARS-CoV-2 and T cell immunity to the virus provide new perspectives of vaccine and drug development. These findings are important for understanding SARS-CoV-2 viral biology and advances in developing vaccines, antibody-based therapies, and more effective strategies to mitigate the transmission of the Omicron variant or the next SARS-CoV-2 variant of concern.

Competition for dominance within replicating quasispecies during prolonged SARS-CoV-2 infection in an immunocompromised host.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) emerge for their capability to better adapt to the human host aimed and enhance human-to-human transmission. Mutations in spike largely contributed to adaptation. Viral persistence is a prerequisite for intra-host virus evolution, and this likely occurred in immunocompromised patients who allow intra-host long-term viral replication. The underlying mechanism leading to the emergence of variants during viral persistence in the immunocompromised host is still unknown. Here, we show the existence of an ensemble of minor mutants in the early biological samples obtained from an immunocompromised patient and their dynamic interplay with the master mutant during a persistent and productive long-term infection. In particular, after 222 days of active viral replication, the original master mutant, named MB610, was replaced by a minor quasispecies (MB61222) expressing two critical mutations in spike, namely Q493K and N501T. Isolation of the two viruses allowed us to show that MB61222 entry into target cells occurred mainly by the fusion at the plasma membrane (PM), whereas endocytosis characterized the entry mechanism used by MB610. Interestingly, coinfection of two human cell lines of different origin with the SARS-CoV-2 isolates highlighted the early and dramatic predominance of MB61222 over MB610 replication. This finding may be explained by a faster replicative activity of MB61222 as compared to MB610 as well as by the capability of MB61222 to induce peculiar viral RNA-sensing mechanisms leading to an increased production of interferons (IFNs) and, in particular, of IFN-induced transmembrane protein 1 (IFITM1) and IFITM2. Indeed, it has been recently shown that IFITM2 is able to restrict SARS-CoV-2 entry occurring by endocytosis. In this regard, MB61222 may escape the antiviral activity of IFITMs by using the PM fusion pathway for entry into the target cell, whereas MB610 cannot escape this host antiviral response during MB61222 coinfection, since it has endocytosis as the main pathway of entry. Altogether, our data support the evidence of quasispecies fighting for host dominance by taking benefit from the cell machinery to restrict the productive infection of competitors in the viral ensemble. This finding may explain, at least in part, the extraordinary rapid worldwide turnover of VOCs that use the PM fusion pathway to enter into target cells over the original pandemic strain.

High-throughput drug screening allowed identification of entry inhibitors specifically targeting different routes of SARS-CoV-2 Delta and Omicron/BA.1

The Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS-CoV-2) has continuously evolved, resulting in the emergence of several variants of concern (VOCs). To study mechanisms of viral entry and potentially identify specific inhibitors, we pseudotyped lentiviral vectors with different SARS-CoV-2 VOC spike variants (D614G, Alpha, Beta, Delta, Omicron/BA.1), responsible for receptor binding and membrane fusion. These SARS-CoV-2 lentiviral pseudoviruses were applied to screen 774 FDA-approved drugs. For the assay we decided to use CaCo2 cells, since they equally allow cell entry through both the direct membrane fusion pathway mediated by TMPRSS2 and the endocytosis pathway mediated by cathepsin-L. The active molecules which showed stronger differences in their potency to inhibit certain SARS-CoV-2 VOCs included antagonists of G-protein coupled receptors, like phenothiazine-derived antipsychotic compounds such as Chlorpromazine, with highest activity against the Omicron pseudovirus. In general, our data showed that the various VOCs differ in their preferences for cell entry, and we were able to identify synergistic combinations of inhibitors. Notably, Omicron singled out by relying primarily on the endocytosis pathway while Delta preferred cell entry via membrane fusion. In conclusion, our data provide new insights into different entry preferences of SARS-CoV-2 VOCs, which might help to identify new drug targets.

SARS-CoV-2突变背景下的病毒入侵机制研究进展与干预策略

<p indent="0mm">Since coronavirus disease 2019 (COVID-19) was reported in late 2019, its causative agent, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been spreading worldwide for more than two years, and the trend continues unabated. SARS-CoV-2 is a single positive-stranded RNA virus from the same β-coronavirus family as SARS-CoV, which caused a severe acute respiratory syndrome (SARS) epidemic in 2003. Entry into the cell is mediated by the binding of the spike glycoprotein on the envelope to angiotensin converting enzyme 2 (ACE2) on the host cell, possibly with the help of co-receptors, adhesion factors, or alternative receptors. During the process of virus assembly, release, cell adhesion, and entry into the host cell, the SARS-CoV-2 spike protein must undergo a series of structural changes, including cleavage and conformational changes, to achieve membrane fusion function. After binding to cell surface receptors, SARS-CoV-2 has two invasion pathways: (i) The direct fusion pathway at the cell membrane interface, and (ii) the clathrin-mediated endocytosis pathway. In both cases, the SARS-CoV-2 spike protein must be cleaved by furin-like proteins at the S1/S2 site. Host proteases, mainly TMPRSS-2 or cathepsin, are involved in cleavage at the S2′ site, corresponding to pathway (i) or (ii). The entire entry process ends when the viral genome enters the cytosol. During the replication cycle of SARS-CoV-2, genomic RNA can be mutated. Accumulation of mutations, particularly in the spike protein, may result in new variants that differ in infectivity, transmissibility, virulence, and/or immune escape capability. These changes can alter the prevailing lineage in circulation, trigger a new wave of public health events, and threaten scientific research, clinical prevention, and treatment. The World Health Organization (WHO) has identified five mutant strains as variants of concern (VOCs) by assessing their public health significance worldwide: Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), and Omicron (B.1.1.529). The Omicron variant is currently in circulation. The entry-related characteristics of VOCs may indicate global epidemiological trends and shed light on future pandemic dynamics. The entry mechanism of SARS-CoV-2, the first and crucial step in the establishment of a viral infection, has been extensively studied over the past two years. As the molecular mechanisms involved in entry are gradually being elucidated, interventions in key events may prevent viral entry and provide information for drug development and clinical treatment. Because the cellular entry mechanism of coronaviruses is relatively conserved, the first step in interrupting viral infection—blocking the entry process—is a promising target for the development of new preventive and therapeutic drugs against COVID-19 and even pan-coronavirus inhibitors, including small molecules, peptides, and monoclonal antibodies. Researchers have identified potential drug targets involved in the SARS-CoV-2 entry process, such as spike proteins, ACE2, and host proteases. Inhibition of the viral entry process is expected to reduce viral load in patients, thereby alleviating symptoms and improving prognosis. Recently, computer-aided drug design has emerged as a powerful and productive tool for drug discovery, in addition to experimental methods in the wet lab. In future anti-SARS-CoV-2 drug discovery, the flexible combination and optimized design of drug discovery strategies to improve the efficiency of drug development will be the trend. In this review, we outline the mechanism of SARS-CoV-2 entry into cells, describe the entry properties of VOCs currently defined by the WHO, and present the progress in the discovery of SARS-CoV-2 entry inhibitors.

The complexin C-terminal amphipathic helix stabilizes the fusion pore open state by sculpting membranes.

Neurotransmitter release is mediated by proteins that drive synaptic vesicle fusion with the presynaptic plasma membrane. While soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs) form the core of the fusion apparatus, additional proteins play key roles in the fusion pathway. Here, we report that the C-terminal amphipathic helix of the mammalian accessory protein, complexin (Cpx), exerts profound effects on membranes, including the formation of pores and the efficient budding and fission of vesicles. Using nanodisc-black lipid membrane electrophysiology, we demonstrate that the membrane remodeling activity of Cpx modulates the structure and stability of recombinant exocytic fusion pores. Cpx had particularly strong effects on pores formed by small numbers of SNAREs. Under these conditions, Cpx increased the current through individual pores 3.5-fold, and increased the open time fraction from roughly 0.1 to 1.0. We propose that the membrane sculpting activity of Cpx contributes to the phospholipid rearrangements that underlie fusion by stabilizing highly curved membrane fusion intermediates.

Trypsin enhances SARS-CoV-2 infection by facilitating viral entry.

Coronaviruses infect cells by cytoplasmic or endosomal membrane fusion, driven by the spike (S) protein, which must be primed by proteolytic cleavage at the S1/S2 furin cleavage site (FCS) and the S2′ site by cellular proteases. Exogenous trypsin as a medium additive facilitates isolation and propagation of several coronaviruses in vitro. Here, we show that trypsin enhances severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in cultured cells and that SARS-CoV-2 enters cells via either a non-endosomal or an endosomal fusion pathway, depending on the presence of trypsin. Interestingly, trypsin enabled viral entry at the cell surface and led to more efficient infection than trypsin-independent endosomal entry, suggesting that trypsin production in the target organs may trigger a high level of replication of SARS-CoV-2 and cause severe tissue injury. Extensive syncytium formation and enhanced growth kinetics were observed only in the presence of exogenous trypsin when cell-adapted SARS-CoV-2 strains were tested. During 50 serial passages without the addition of trypsin, a specific R685S mutation occurred in the S1/S2 FCS (681PRRAR685) that was completely conserved but accompanied by several mutations in the S2 fusion subunit in the presence of trypsin. These findings demonstrate that the S1/S2 FCS is essential for proteolytic priming of the S protein and fusion activity for SARS-CoV-2 entry but not for viral replication. Our data can potentially contribute to the improvement of SARS-CoV-2 production for the development of vaccines or antivirals and motivate further investigations into the explicit functions of cell-adaptation-related genetic drift in SARS-CoV-2 pathogenesis.

Neuroprotective Effects of a Small Mitochondrially-Targeted Tetrapeptide Elamipretide in Neurodegeneration.

Neural mitochondrial dysfunction, neural oxidative stress, chronic neuroinflammation, toxic protein accumulation, and neural apoptosis are common causes of neurodegeneration. Elamipretide, a small mitochondrially-targeted tetrapeptide, exhibits therapeutic effects and safety in several mitochondria-related diseases. In neurodegeneration, extensive studies have shown that elamipretide enhanced mitochondrial respiration, activated neural mitochondrial biogenesis via mitochondrial biogenesis regulators (PCG-1α and TFAM) and the translocate factors (TOM-20), enhanced mitochondrial fusion (MNF-1, MNF-2, and OPA1), inhibited mitochondrial fission (Fis-1 and Drp-1), as well as increased mitophagy (autophagy of mitochondria). In addition, elamipretide has been shown to attenuate neural oxidative stress (hydrogen peroxide, lipid peroxidation, and ROS), neuroinflammation (TNF, IL-6, COX-2, iNOS, NLRP3, cleaved caspase-1, IL-1β, and IL-18), and toxic protein accumulation (Aβ). Consequently, elamipretide could prevent neural apoptosis (cytochrome c, Bax, caspase 9, and caspase 3) and enhance neural pro-survival (Bcl2, BDNF, and TrkB) in neurodegeneration. These findings suggest that elamipretide may prevent the progressive development of neurodegenerative diseases via enhancing mitochondrial respiration, mitochondrial biogenesis, mitochondrial fusion, and neural pro-survival pathway, as well as inhibiting mitochondrial fission, oxidative stress, neuroinflammation, toxic protein accumulation, and neural apoptosis. Elamipretide or mitochondrially-targeted peptide might be a targeted agent to attenuate neurodegenerative progression.

“I could have a proper ankle” – a qualitative study of patients’ perceptions of total ankle replacement and ankle fusion surgery

BackgroundEnd-stage ankle osteoarthritis typically causes severe pain and impaired function. Surgical treatment involves total ankle replacement (TAR) or ankle fusion. Definitive evidence about which procedure is optimal is lacking. No previous studies have thoroughly explored patients’ experiences across the entire TAR/ankle fusion pathway. This study aimed to address this gap by exploring perceptions of surgery, education, rehabilitation and outcomes among patients who had undergone TAR or ankle fusion.MethodsSeven participants were purposively selected from an orthopaedic centre in northern England (3 females, 4 males). Participants had undergone primary TAR without revision (n = 2), TAR requiring revision (n = 3) or ankle fusion (n = 2). Each participant completed a single semi-structured interview. Interviews were digitally recorded, transcribed verbatim and analysed thematically.ResultsThree themes, each with two subthemes, were identified: decision-making (seeking help; surgical options), perceptions of support (information/education; clinical support) and impact on the individual (personal circumstances and beliefs; post-operative outcomes). Pain affecting participants’ valued activities was key to their decision to seek help. Participants’ decision between TAR and ankle fusion was influenced by multiple factors. Concerns regarding the lack of joint flexibility following fusion were highlighted, with some participants perceiving TAR as a “proper ankle” that would enable them to avoid limping. Participants obtained information from various sources, with most feeling that the education from their care team was inadequate. Participants’ individual circumstances and beliefs influenced their decision-making and perceptions of their post-operative outcomes. Finally, whilst most participants were pleased with their outcomes, some experienced substantial ongoing problems such as difficulty walking and chronic pain.ConclusionsThis study demonstrates the importance of providing adequate education about TAR and ankle fusion to enable patients to make informed decisions. Most participants felt that the education and clinical support they received did not fully meet their needs. Participants’ personal circumstances and beliefs had a strong influence on their decision-making and perceptions of their post-operative outcomes, highlighting the need to personally tailor education and clinical support. Future work with a larger sample of patients and other key stakeholders is required to develop consensus-based guidelines on pre- and post-operative support for patients undergoing TAR/ankle fusion.