Extracellular Vimentin as a Target Against SARS-CoV-2 Host Cell Invasion

Research progress of vimentin in viral infections

Vimentin, a type III intermediate filament protein, has become a focal point in the research of viral infections. It participates in multiple crucial processes during the viral life cycle and the host's antiviral response. During viral entry, it may function as a receptor or co-receptor and interact with viral entry proteins, also influencing endocytic pathways. Furthermore, vimentin engages with replication complexes and modulates the intracellular environment in viral replication. Moreover, vimentin plays significant roles in immune responses and inflammatory reactions during viral infections. This review thoroughly analyzes the recent progress in understanding vimentin's functions during viral infections, covering aspects such as viral entry, replication, and the immune response to achieve a cohesive comprehension of the underlying mechanisms. The antiviral strategies based on vimentin are also discussed, aiming to promote the development of more effective preventive and treatment strategies for viral diseases.

The unconventional role of vimentin intermediate filaments

Vimentin, a type III intermediate filament (IF) protein, is well-recognized for its role at the intersection of structural biology and cellular dynamics, influencing various pathways that determine cell fate and function. While these functions have been extensively characterized, there is still limited understanding of vimentin's broader impact beyond its traditional cytoskeletal roles in regulating a spectrum of cellular processes. This review explores the novel and unconventional roles of vimentin, with a focus on its extracellular functions, membrane receptor properties, and regulatory influence on gene expression and cellular metabolism.

Extracellular vimentin is a damage-associated molecular pattern protein serving as an agonist of TLR4 in human neutrophils

BACKGROUND

Vimentin is a type III intermediate filament protein that plays an important role in cytoskeletal mechanics. It is now known that vimentin also has distinct functions outside the cell. Recent studies show the controlled release of vimentin into the extracellular environment, where it functions as a signaling molecule. Such observations are expanding our current knowledge of vimentin as a structural cellular component towards additional roles as an active participant in cell signaling.

METHODS

Our study investigates the immunological roles of extracellular vimentin (eVim) and its citrullinated form (CitVim) as a damage-associated molecular pattern (DAMP) engaging the Toll-like receptor 4 (TLR4) of human neutrophils. We used in vitro assays to study neutrophil migration through endothelial cell monolayers and activation markers such as NADPH oxidase subunit 2 (NOX2/gp91phox). The comparison of eVim with CitVim and its effect on human neutrophils was extended to the induction of extracellular traps (NETs) and phagocytosis of pathogens.

RESULTS

Both eVim and CitVim interact with and trigger TLR4, leading to increased neutrophil migration and adhesion. CitVim stimulated the enhanced migratory ability of neutrophils, activation of NF-κB, and induction of NET formation mainly mediated through reactive oxygen species (ROS)-dependent and TLR4-dependent pathways. In contrast, neutrophils exposed to non-citrullinated vimentin exhibited higher efficiency in favoring pathogen phagocytosis, such as Escherichia coli and Candida albicans, compared to CitVim.

CONCLUSIONS

Our study identifies new functions of eVim in its native and modified forms as an extracellular matrix DAMP and highlights its importance in the modulation of immune system functions. The differential effects of eVim and CitVim on neutrophil functions highlight their potential as new molecular targets for therapeutic strategies aimed at regulation of neutrophil activity in different pathological conditions. This, in turn, opens new windows of therapeutic intervention in inflammatory and immunological diseases characterized by immune system dysfunction, in which eVim and CitVim play a key role.

Cytoskeletal Vimentin Directs Cell-Cell Transmission of Hepatitis C Virus

Hepatitis C virus (HCV) is a major human pathogen causing liver diseases. Although direct-acting antiviral agents effectively inhibit HCV infection, cell-cell transmission remains a critical venue for HCV persistence in vivo. However, the underlying mechanism of how HCV spreads intercellularly remains elusive. Here, we demonstrated that vimentin, a host intermediate filaments protein, is dispensable for HCV infection in cell models but essential for simulated in vivo infection in differentiated hepatocytes. Genetic removal of vimentin markedly and specifically disrupts HCV cell-cell transmission without influencing cell-free infection. Through mutual co-immunoprecipitation screening, we identified that the N-terminal 1-95 amino acids of vimentin exclusively interact with the HCV envelope protein E1. Introducing either full-length or head region of vimentin is capable of restoring the cell-cell transmission deficiency in vimentin-knockout cells. Moreover, we showed that it is vimentin on the plasma membrane of recipient cells that orchestrates HCV cell-cell transmission. Consequently, vimentin antibody, either applied individually or in combination with HCV neutralizing antibody, exerts pronounced inhibition of HCV cell-cell transmission. Together, the results unveil an unrecognized function of vimentin as a unique venue dominating viral transmission, providing novel insights into propelling advancements in vimentin-targeted anti-HCV therapies.

Vimentin as a universal receptor for pseudorabies virus infection in pig and human cells

Pseudorabies virus (PRV), known to infect pigs and found in various species, including humans, shows zoonotic potential. This study identified vimentin (VIM), a highly conserved intermediate filament protein expressed in multiple mammalian species and tissues, as a universal receptor for PRV infections in human and porcine cells. The adsorption of PRV is positively correlated with the level of VIM expressed in different cells. Overexpression and knockdown of VIM significantly increase and decrease PRV adsorption in cells, respectively. Dot blot assay and VOPBA showed that purified VIM can directly bind to PRV virions efficiently in a dose-dependent manner. PRV and VIM are co-localized at the cell membrane of PRV-infected cells. Moreover, PRV mainly binds to host VIM via its conserved amino acid residues in PRV gD (W98, G162, Y164, C205) and gH (C439) and the Rod domain (residues 96-404) of VIM. In addition, regulating the expression of VIM also influences the entry, replication, and release of PRV, which has a similar result to the adsorption. These results demonstrate that VIM, as a universal receptor, can facilitate PRV infection in multiple stages in human and porcine cells, highlighting the zoonosis characteristics of PRV and the need for more attention.

Toosi B, Ghorbanifaraz P, Mahmoudiasl GR, Aliaghaei A, Faghihi Hosseinabadi H, Paktinat S, Abdollahifar MA. Vimentin as a contributing factor in SARS-CoV-2-induced orchitis on postmortem testicular autopsy of COVID-19 cases: A case-control study

Background

Coronavirus disease 2019 (COVID-19) was identified in China in late December 2019 and led to a pandemic that resulted in millions of confirmed cases and deaths. The causative agent, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), uses distinct receptors and co-receptors to enter host cells. Vimentin has emerged as a potential co-receptor for SARS-CoV-2 due to the high level of vimentin expression in testis tissue.

Objective

The present study investigated the link between vimentin expression level and SARS-CoV-2-induced orchitis.

Materials and Methods

In this case-control study, testis autopsy samples were collected immediately after the death of both COVID-19 cases and a control group that included individuals who died due to accidental causes. Gene expression and immunohistochemical assays were conducted to evaluate the level of vimentin expression, cell proliferation, and leukocyte infiltration.

Results

A significant expression of vimentin and infiltration of immune cells (CD68+, CD38+, and CD138+) in the testicular tissue of COVID-19 cases, along with extensive immunoglobulin G precipitation and reduced inhibin expression (p = 0.001) were observed. Additionally, gene expression analysis revealed increased expression of vimentin and decreased expression of the proliferation markers Ki67 and proliferating cell nuclear antigen, suggesting that SARS-CoV-2 may disrupt spermatogenesis through immune responses and the arrest of cell proliferation.

Conclusion

There may be a strong link between vimentin expression and COVID-19-induced orchitis. Further studies are needed to confirm these findings. Considering some limitations, vimentin can be used as a biomarker option for testicular damage following COVID-19-induced orchitis.

Mycoplasma synoviae surface-located elongation factor G functions as a cytoadhesin to promote adhesion to synovial sheath cells through binding to vimentin

Mycoplasma synoviae infection has caused serious economic losses to the poultry industry worldwide. The molecular mechanism by which M. synoviae colonizes the synovium and induces synovitis is unclear. In this study, desthiobiotin pull-down and liquid chromatography-tandem mass spectrometry analyses were used to screen M. synoviae membrane proteins that bind the membrane proteins of synovial sheath cells (SSCs). Among the 128 screened proteins, elongation factor G (EF-G) of M. synoviae was identified as a surface-located protein using colony blotting and dual fluorescence analyses. The immunogenicity of EF-G was confirmed by the preparation of a rabbit polyclonal antibody. EF-G was identified as a cytoadhesin that directly binds to SSCs using indirect immunofluorescence assay and ELISA plate binding assay. In addition, antibody adhesion inhibition and protein adhesion inhibition demonstrated that EF-G could significantly promote the adhesion of M. synoviae to SSCs. Co-IP, GST pull-down, bacterial two-hybridization, and ELISA plate binding assays were performed to demonstrate the binding of EF-G and vimentin in vivo and in vitro. Antibody adhesion inhibition, protein adhesion inhibition, and siRNA interference adhesion inhibition assays demonstrated that vimentin significantly affected M. synoviae adhesion to SSCs. These studies indicate that two interacting proteins, EF-G, a novel cytoadhesin, and vimentin, an important cell surface receptor, play important roles in the adhesion of M. synoviae to SSCs, laying a foundation for subsequent studies on the mechanism of M. synoviae-induced synovitis and providing meaningful targets for screening target drugs against M. synoviae infection.

Cellular vimentin interacts with VP70 protein of goose astrovirus genotype 2 and acts as a structural organizer to facilitate viral replication

The fatal gouty disease caused by goose astrovirus genotype 2 (GAstV-2) still seriously endangers the goose industry in China, causing great economic losses. However, research on its infection mechanism has progressed relatively slowly. VP70 is the structural protein of GAstV-2 and is closely related to virus invasion and replication. To better understand the role of VP70 during GAstV-2 infection, we used immunoprecipitation and mass spectrometry to identify host proteins that interact with VP70. Here, we report that cellular vimentin (VIM) is a host binding partner of VP70. Site-directed mutagenesis showed that amino acid residues 399 to 413 of VP70 interacted with VIM. Using reverse genetics, we found that VP70 mutation disrupts the interaction of VP70 with VIM, which is essential for viral replication. Overexpression of VIM significantly promoted GAstV-2 replication, while knockdown of VIM significantly inhibited GAstV-2 replication. Laser confocal microscopy showed that VP70 protein expression induced the rearrangement of VIM, gradually aggregating from the original uniform grid to the side of the nucleus, and aggregated the originally dispersed GAstV-2 RNA in VIM. This rearrangement was associated with increased VIM phosphorylation caused by GAstV-2. Meanwhile, blocking VIM rearrangement with acrylamide substantially inhibited viral replication. These results indicate that VIM interacts with VP70 and positively regulates GAstV-2 replication, and VIM-VP70 interaction and an intact VIM network are needed for GAstV-2 replication. This study provides a theoretical basis and novel perspective for the further characterization of the pathogenic mechanism of GAstV-2-induced gouty disease in goslings.

Intermediate filaments at a glance

Intermediate filaments (IFs) comprise a large family of versatile cytoskeletal proteins, divided into six subtypes with tissue-specific expression patterns. IFs have a wide repertoire of cellular functions, including providing structural support to cells, as well as active roles in mechanical support and signaling pathways. Consequently, defects in IFs are associated with more than 100 diseases. In this Cell Science at a Glance article, we discuss the established classes of IFs and their general features, their functions beyond structural support, and recent advances in the field. We also highlight their involvement in disease and potential use as clinical markers of pathological conditions. Finally, we provide our view on current knowledge gaps and the future directions of the IF field.

Mechanisms of Gut-Related Viral Persistence in Long COVID

Long COVID (post-acute sequelae of COVID-19-PASC) is a consequence of infection by SARS-CoV-2 that continues to disrupt the well-being of millions of affected individuals for many months beyond their first infection. While the exact mechanisms underlying PASC remain to be defined, hypotheses regarding the pathogenesis of long COVID are varied and include (but are not limited to) dysregulated local or systemic inflammatory responses, autoimmune mechanisms, viral-induced hormonal imbalances, skeletal muscle abnormalities, complement dysregulation, novel abzymes, and long-term persistence of virus and/or fragments of viral RNA or proteins. This review article is based on a comprehensive review of the wide range of symptoms most often observed in long COVID and an attempt to integrate that information into a plausible hypothesis for the pathogenesis of PASC. In particular, it is proposed that long-term dysregulation of the gut in response to viral persistence could lead to the myriad of symptoms observed in PASC.

Cytoskeleton-modulating nanomaterials and their therapeutic potentials

The cytoskeleton, an intricate network of protein fibers within cells, plays a pivotal role in maintaining cell shape, enabling movement, and facilitating intracellular transport. Its involvement in various pathological states, ranging from cancer proliferation and metastasis to the progression of neurodegenerative disorders, underscores its potential as a target for therapeutic intervention. The exploration of nanotechnology in this realm, particularly the use of nanomaterials for cytoskeletal modulation, represents a cutting-edge approach with the promise of novel treatments. Inorganic nanomaterials, including those derived from gold, metal oxides, carbon, and black phosphorus, alongside organic variants such as peptides and proteins, are at the forefront of this research. These materials offer diverse mechanisms of action, either by directly interacting with cytoskeletal components or by influencing cellular signaling pathways that, in turn, modulate the cytoskeleton. Recent advancements have introduced magnetic field-responsive and light-responsive nanomaterials, which allow for targeted and controlled manipulation of the cytoskeleton. Such precision is crucial in minimizing off-target effects and enhancing therapeutic efficacy. This review explores the importance of research into cytoskeleton-targeting nanomaterials for developing therapeutic interventions for a range of diseases. It also addresses the progress made in this field, the challenges encountered, and future directions for using nanomaterials to modulate the cytoskeleton. The continued exploration of nanomaterials for cytoskeleton modulation holds great promise for advancing therapeutic strategies against a broad spectrum of diseases, marking a significant step forward in the intersection of nanotechnology and medicine.

Mechanobiology in Metabolic Dysfunction-Associated Steatotic Liver Disease and Obesity

With the ongoing obesity epidemic, the prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) is expected to rise and necessitates a greater understanding of how the disease proceeds from benign excess lipid in hepatocytes to liver fibrosis and eventually to liver cancer. MASLD is caused, at least in part, by hepatocytes' storage of free fatty acids (FAs) that dysfunctional adipocytes are no longer able to store, and therefore, MASLD is a disease that involves both the liver and adipose tissues. The disease progression is not only facilitated by biochemical signals, but also by mechanical cues such as the increase in stiffness often seen with fibrotic fatty livers. The change in stiffness and accumulation of excess lipid droplets impact the ability of a cell to mechanosense and mechanotranduce, which perpetuates the disease. A mechanosensitive protein that is largely unexplored and could serve as a potential therapeutic target is the intermediate filament vimentin. In this review, we briefly summarize the recent research on hepatocyte and adipocyte mechanobiology and provide a synopsis of studies on the varied, and sometimes contradictory, roles of vimentin. This review is intended to benefit and encourage future studies on hepatocyte and adipocyte mechanobiology in the context of MASLD and obesity.

Targeting vimentin: a multifaceted approach to combatting cancer metastasis and drug resistance

This comprehensive review explores vimentin as a pivotal therapeutic target in cancer treatment, with a primary focus on mitigating metastasis and overcoming drug resistance. Vimentin, a key player in cancer progression, is intricately involved in processes such as epithelial-to-mesenchymal transition (EMT) and resistance mechanisms to standard cancer therapies. The review delves into diverse vimentin inhibition strategies. Precision tools, including antibodies and nanobodies, selectively neutralize vimentin's pro-tumorigenic effects. DNA and RNA aptamers disrupt vimentin-associated signaling pathways through their adaptable binding properties. Innovative approaches, such as vimentin-targeted vaccines and microRNAs (miRNAs), harness the immune system and post-transcriptional regulation to combat vimentin-expressing cancer cells. By dissecting vimentin inhibition strategies across these categories, this review provides a comprehensive overview of anti-vimentin therapeutics in cancer treatment. It underscores the growing recognition of vimentin as a pivotal therapeutic target in cancer and presents a diverse array of inhibitors, including antibodies, nanobodies, DNA and RNA aptamers, vaccines, and miRNAs. These multifaceted approaches hold substantial promise for tackling metastasis and overcoming drug resistance, collectively presenting new avenues for enhanced cancer therapy.

Extracellular vimentin as a modulator of the immune response and an important player during infectious diseases

Vimentin, an intermediate filament protein primarily recognized for its intracellular role in maintaining cellular structure, has recently garnered increased attention and emerged as a pivotal extracellular player in immune regulation and host-pathogen interactions. While the functions of extracellular vimentin were initially overshadowed by its cytoskeletal role, accumulating evidence now highlights its significance in diverse physiological and pathological events. This review explores the multifaceted role of extracellular vimentin in modulating immune responses and orchestrating interactions between host cells and pathogens. It delves into the mechanisms underlying vimentin's release into the extracellular milieu, elucidating its unconventional secretion pathways and identifying critical molecular triggers. In addition, the future perspectives of using extracellular vimentin in diagnostics and as a target protein in the treatment of diseases are discussed.

Salivary IgA and vimentin differentiate in vitro SARS-CoV-2 infection: A study of 290 convalescent COVID-19 patients

SARS-CoV-2 initially infects cells in the nasopharynx and oral cavity. The immune system at these mucosal sites plays a crucial role in minimizing viral transmission and infection. To develop new strategies for preventing SARS-CoV-2 infection, this study aimed to identify proteins that protect against viral infection in saliva. We collected 551 saliva samples from 290 healthcare workers who had tested positive for COVID-19, before vaccination, between June and December 2020. The samples were categorized based on their ability to block or enhance infection using in vitro assays. Mass spectrometry and enzyme-linked immunosorbent assay experiments were used to identify and measure the abundance of proteins that specifically bind to SARS-CoV-2 antigens. Immunoglobulin (Ig)A specific to SARS-CoV-2 antigens was detectable in over 83% of the convalescent saliva samples. We found that concentrations of anti-receptor-binding domain IgA >500 pg/µg total protein in saliva correlate with reduced viral infectivity in vitro. However, there is a dissociation between the salivary IgA response to SARS-CoV-2, and systemic IgG titers in convalescent COVID-19 patients. Then, using an innovative technique known as spike-baited mass spectrometry, we identified novel spike-binding proteins in saliva, most notably vimentin, which correlated with increased viral infectivity in vitro and could serve as a therapeutic target against COVID-19.

Desmin and its molecular chaperone, the αB-crystallin: How post-translational modifications modulate their functions in heart and skeletal muscles?

Maintenance of the highly organized striated muscle tissue requires a cell-wide dynamic network through protein-protein interactions providing an effective mechanochemical integrator of morphology and function. Through a continuous and complex trans-cytoplasmic network, desmin intermediate filaments ensure this essential role in heart and in skeletal muscle. Besides their role in the maintenance of cell shape and architecture (permitting contractile activity efficiency and conferring resistance towards mechanical stress), desmin intermediate filaments are also key actors of cell and tissue homeostasis. Desmin participates to several cellular processes such as differentiation, apoptosis, intracellular signalisation, mechanotransduction, vesicle trafficking, organelle biogenesis and/or positioning, calcium homeostasis, protein homeostasis, cell adhesion, metabolism and gene expression. Desmin intermediate filaments assembly requires αB-crystallin, a small heat shock protein. Over its chaperone activity, αB-crystallin is involved in several cellular functions such as cell integrity, cytoskeleton stabilization, apoptosis, autophagy, differentiation, mitochondria function or aggresome formation. Importantly, both proteins are known to be strongly associated to the aetiology of several cardiac and skeletal muscles pathologies related to desmin filaments disorganization and a strong disturbance of desmin interactome. Note that these key proteins of cytoskeleton architecture are extensively modified by post-translational modifications that could affect their functional properties. Therefore, we reviewed in the herein paper the impact of post-translational modifications on the modulation of cellular functions of desmin and its molecular chaperone, the αB-crystallin.

Interaction of species A rotavirus VP4 with the cellular proteins vimentin and actin related protein 2 discovered by a proximity interactome assay

IMPORTANCE

Rotavirus (RV) is an important zoonosis virus, which can cause severe diarrhea and extra-intestinal infection. To date, some proteins or carbohydrates have been shown to participate in the attachment or internalization of RV, including HGBAs, Hsc70, and integrins. This study attempted to indicate whether there were other proteins that would participate in the entry of RV; thus, the RV VP4-interacting proteins were identified by proximity labeling. After analysis and verification, it was found that VIM and ACTR2 could significantly promote the proliferation of RV in intestinal cells. Through further viral binding assays after knockdown, antibody blocking, and recombinant protein overexpression, it was revealed that both VIM and ACTR2 could promote RV replication.

A natural product YSK-A blocks SARS-CoV-2 propagation by targeting multiple host genes

Natural products and herbal medicine have been widely used in drug discovery for treating infectious diseases. Recent outbreak of COVID-19 requires various therapeutic strategies. Here, we used YSK-A, a mixture of three herbal components Boswellia serrata, Commiphora myrrha, and propolis, to evaluate potential antiviral activity against SARS-CoV-2. We showed that YSK-A inhibited SARS-CoV-2 propagation with an IC50 values of 12.5 µg/ml and 15.42 µg/ml in Vero E6 and Calu-3 cells, respectively. Using transcriptome analysis, we further demonstrated that YSK-A modulated various host gene expressions in Calu-3 cells. Among these, we selected 9 antiviral- or immune-related host genes for further study. By siRNA-mediated knockdown experiment, we verified that MUC5AC, LIF, CEACAM1, and GDF15 host genes were involved in antiviral activity of YSK-A. Therefore, silencing of these genes nullified YSK-A-mediated inhibition of SARS-CoV-2 propagation. These data indicate that YSK-A displays an anti-SARS-CoV-2 activity by targeting multiple antiviral genes. Although the exact antiviral mechanism of each constituent has not been verified yet, our data indicate that YSK-A has an immunomodulatory effect on SARS-CoV-2 and thus it may represent a novel natural product-derived therapeutic agent for treating COVID-19.

Extracellular vimentin: Battle between the devil and the angel

Vimentin, an intracellular cytoskeletal protein, can be secreted by various cells in response to conditions such as injury, stress, senescence, and cancer. Once vimentin is secreted outside of the cell, it is called extracellular vimentin. This extracellular vimentin is significantly involved in pathological conditions, particularly in the areas of viral infection, cancer, immune response, and wound healing. The effects of extracellular vimentin can be either positive or negative, for example it can enhance axonal repair but also mediates SARS-CoV-2 infection. In this review, we categorize the functional implications of extracellular vimentin based on its localization outside the cell. Specifically, we classify extracellular vimentin into two distinct forms: surface vimentin, which remains bound to the cell surface, and secreted vimentin, which refers to the free form that is completely released outside the cell. Overall, extracellular vimentin has a dual nature that encompasses both beneficial and detrimental effects on the functionality of cells, organs and whole organisms. Here, we summarize its effects in viral infection, cancer, immune response and wound healing. We find that surface vimentin is often associated with negative consequences, whereas secreted vimentin manifests predominantly with positive influences. We found that the observed effects of extracellular vimentin strongly depend on the specific circumstances under which its expression occurs in cells.

Vimentin takes a hike - Emerging roles of extracellular vimentin in cancer and wound healing

Vimentin is a cytoskeletal protein important for many cellular processes, including proliferation, migration, invasion, stress resistance, signaling, and many more. The vimentin-deficient mouse has revealed many of these functions as it has numerous severe phenotypes, many of which are found only following a suitable challenge or stress. While these functions are usually related to vimentin as a major intracellular protein, vimentin is also emerging as an extracellular protein, exposed at the cell surface in an oligomeric form or secreted to the extracellular environment in soluble and vesicle-bound forms. Thus, this review explores the roles of the extracellular pool of vimentin (eVIM), identified in both normal and pathological states. It focuses specifically on the recent advances regarding the role of eVIM in wound healing and cancer. Finally, it discusses new technologies and future perspectives for the clinical application of eVIM.

The molecular biophysics of extracellular vimentin and its role in pathogen-host interactions

Vimentin, an intermediate filament protein typically located in the cytoplasm of mesenchymal cells, can also be secreted as an extracellular protein. The organization of extracellular vimentin strongly determines its functions in physiological and pathological conditions, making it a promising target for future therapeutic interventions. The extracellular form of vimentin has been found to play a role in the interaction between host cells and pathogens. In this review, we first discuss the molecular biophysics of extracellular vimentin, including its structure, secretion, and adhesion properties. We then provide a general overview of the role of extracellular vimentin in mediating pathogen-host interactions, with a focus on its interactions with viruses and bacteria. We also discuss the implications of these findings for the development of new therapeutic strategies for combating infectious diseases.

Transmit and protect: The mechanical functions of intermediate filaments

New aspects of the unique mechanical properties of intermediate filaments (IFs) continue to emerge from studies that illuminate the structure and mechanical response of single filaments, the interaction of intermediate filaments with each other or with other cytoskeletal elements, and the viscoelasticity of the networks that these intermediate filaments form. The relation of purified IF network mechanics to the role of IFs in cells and tissues is a particularly active area, with several new demonstrations of the unique and essential role that intermediate filament networks play in determining the mechanical response of biological materials, especially to large deformations, and the mechanisms by which intermediate filaments protect the nucleus from mechanical stresses that cells and tissues encounter in vivo.

Cellular vimentin regulates the infectivity of Newcastle disease virus through targeting of the HN protein

The haemagglutinin-neuraminidase (HN) protein plays a crucial role in the infectivity and virulence of Newcastle disease virus (NDV). In a previous study, the mutant HN protein was identified as a crucial virulence factor for the velogenic variant NDV strain JS/7/05/Ch, which evolved from the prototypic vaccine strain Mukteswar. Furthermore, macrophages are the main susceptible target cells of NDV. However, the possible involvement of cellular molecules in viral infectivity remains unclear. Herein, we elucidate the crucial role of vimentin, an intermediate filament protein, in regulating NDV infectivity through targeting of the HN protein. Using LC‒MS/MS mass spectrometry and coimmunoprecipitation assays, we identified vimentin as a host protein that differentially interacted with prototypic and mutant HN proteins. Further analysis revealed that the variant NDV strain induced more significant rearrangement of vimentin fibres compared to the prototypic NDV strain and showed an interdependence between vimentin rearrangement and virus replication. Notably, these mutual influences were pronounced in HD11 chicken macrophages. Moreover, vimentin was required for multiple infection processes of the variant NDV strain in HD11 cells, including viral internalization, fusion, and release, while it was not necessary for those of the prototypic NDV strain. Collectively, these findings underscore the pivotal role of vimentin in NDV infection through targeting of the HN protein, providing novel targets for antiviral treatment strategies for NDV.

Specific pupylation as IDEntity reporter (SPIDER) for the identification of protein-biomolecule interactions

Protein-biomolecule interactions play pivotal roles in almost all biological processes. For a biomolecule of interest, the identification of the interacting protein(s) is essential. For this need, although many assays are available, highly robust and reliable methods are always desired. By combining a substrate-based proximity labeling activity from the pupylation pathway of Mycobacterium tuberculosis and the streptavidin (SA)-biotin system, we developed the Specific Pupylation as IDEntity Reporter (SPIDER) method for identifying protein-biomolecule interactions. Using SPIDER, we validated the interactions between the known binding proteins of protein, DNA, RNA, and small molecule. We successfully applied SPIDER to construct the global protein interactome for m6A and mRNA, identified a variety of uncharacterized m6A binding proteins, and validated SRSF7 as a potential m6A reader. We globally identified the binding proteins for lenalidomide and CobB. Moreover, we identified SARS-CoV-2-specific receptors on the cell membrane. Overall, SPIDER is powerful and highly accessible for the study of protein-biomolecule interactions.

Extracellular vimentin is sufficient to promote cell attachment, spreading, and motility by a mechanism involving N-acetyl glucosamine-containing structures

Vimentin intermediate filaments form part of the cytoskeleton of mesenchymal cells, but under pathological conditions often associated with inflammation, vimentin filaments depolymerize as the result of phosphorylation or citrullination, and vimentin oligomers are secreted or released into the extracellular environment. In the extracellular space, vimentin can bind surfaces of cells and the extracellular matrix, and the interaction between extracellular vimentin and cells can trigger changes in cellular functions, such as activation of fibroblasts to a fibrotic phenotype. The mechanism by which extracellular vimentin binds external cell membranes and whether vimentin alone can act as an adhesive anchor for cells is largely uncharacterized. Here, we show that various cell types (normal and vimentin null fibroblasts, mesenchymal stem cells, and A549 lung carcinoma cells) attach to and spread on polyacrylamide hydrogel substrates covalently linked to vimentin. Using traction force microscopy and spheroid expansion assays, we characterize how different cell types respond to extracellular vimentin. Cell attachment to and spreading on vimentin-coated surfaces is inhibited by hyaluronic acid degrading enzymes, hyaluronic acid synthase inhibitors, soluble heparin or N-acetyl glucosamine, all of which are treatments that have little or no effect on the same cell types binding to collagen-coated hydrogels. These studies highlight the effectiveness of substrate-bound vimentin as a ligand for cells and suggest that carbohydrate structures, including the glycocalyx and glycosylated cell surface proteins that contain N-acetyl glucosamine, form a novel class of adhesion receptors for extracellular vimentin that can either directly support cell adhesion to a substrate or fine-tune the glycocalyx adhesive properties.

Physicochemical Nature of SARS-CoV-2 Spike Protein Binding to Human Vimentin

Vimentin, a protein that builds part of the cytoskeleton and is involved in many aspects of cellular function, was recently identified as a cell surface attachment site for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The present study investigated the physicochemical nature of the binding between the SARS-CoV-2 S1 glycoprotein receptor binding domain (S1 RBD) and human vimentin using atomic force microscopy and a quartz crystal microbalance. The molecular interactions of S1 RBD and vimentin proteins were quantified using vimentin monolayers attached to the cleaved mica or a gold microbalance sensor as well as in its native extracellular form present on the live cell surface. The presence of specific interactions between vimentin and S1 RBD was also confirmed using in silico studies. This work provides new evidence that cell-surface vimentin (CSV) functions as a site for SARS-CoV-2 virus attachment and is involved in the pathogenesis of Covid-19, providing a potential target for therapeutic countermeasures.

Vimentin: from a cytoskeletal protein to a critical modulator of immune response and a target for infection

Vimentin is an intermediate filament protein that plays a role in cell processes, including cell migration, cell shape and plasticity, or organelle anchorage. However, studies from over the last quarter-century revealed that vimentin can be expressed at the cell surface and even secreted and that its implications in cell physiology largely exceed structural and cytoskeletal functions. Consequently, vimentin contributes to several pathophysiological conditions such as cancer, autoimmune and inflammatory diseases, or infection. In this review, we aimed at covering these various roles and highlighting vimentin implications in the immune response. We also provide an overview of how some microbes including bacteria and viruses have acquired the ability to circumvent vimentin functions in order to interfere with host responses and promote their uptake, persistence, and egress from host cells. Lastly, we discuss the therapeutic approaches associated with vimentin targeting, leading to several beneficial effects such as preventing infection, limiting inflammatory responses, or the progression of cancerous events.

Peptide-Drug Conjugate Targeting Keratin 1 Inhibits Triple-Negative Breast Cancer in Mice

Selective delivery of chemotherapy to the tumor site while sparing healthy cells and tissues is an attractive approach for cancer treatment. Carriers such as peptides can facilitate selective tumor targeting and payload delivery. Peptides with specific affinity for the overexpressed cell-surface receptors in cancer cells are conjugated to chemotherapy to afford peptide-drug conjugates (PDCs) that show selective uptake by cancer cells. Using a 10-mer linear peptide (WxEAAYQrFL) called 18-4 that targets and binds breast cancer cells, we designed a peptide 18-4-doxorubicin (Dox) conjugate with high specific toxicity toward triple-negative breast cancer (TNBC) MDA-MB-231 cells and 30-fold lower toxicity to normal breast MCF10A epithelial cells. Here, we elucidate the in vivo activity of this potent and tumor-selective peptide 18-4-Dox conjugate in mice bearing orthotopic MDA-MB-231 tumors. Mice treated with four weekly injections of the conjugate showed significantly lower tumor volumes compared to mice treated with free Dox at an equivalent Dox dose. Immunohistochemical (IHC) analysis of mice tissues revealed that treatment with a low dose of PDC (2.5 mg/kg of Dox equiv) reduced the expression of proliferation markers (PCNA and Ki-67) and increased apoptosis (evidenced by increased caspase-3 expression). At the same dose of free Dox (2.5 mg/kg), the expression of these markers was similar to that of saline treatment. Accordingly, significantly more Dox accumulated in tumors of conjugate-treated mice (7-fold) compared to the Dox-treated mice, while lower levels of Dox were observed in the liver, heart, and lungs of peptide-Dox conjugate-treated mice (up to 3-fold less) than Dox-treated mice. The IHC analysis of keratin 1 (K1), the receptor for peptide 18-4, revealed K1 upregulation in tumors and low levels in normal mammary fat pad and liver tissues from mice, suggesting preferential uptake of PDCs by TNBC to be K1 receptor-mediated. Taken together, our data support the use of a PDC approach to deliver chemotherapy selectively to the TNBC to inhibit tumor growth.

Excess KLHL24 Impairs Skin Wound Healing through the Degradation of Vimentin

Start codon variants in ubiquitin ligase KLHL24 lead to a gain-of-function mutant KLHL24-ΔN28, which mediates the excessive degradation of keratin 15, desmin, and keratin 14, resulting in alopecia, cardiopathy, and epidermolysis bullosa syndrome. Patients with alopecia, cardiopathy, and epidermolysis bullosa syndrome normally present atrophic scars after wounds heal, which is rare in KRT14-related epidermolysis bullosa. The mechanisms underlying the formation of atrophic scars in epidermolysis bullosa of patients with alopecia, cardiopathy, and epidermolysis bullosa syndrome remain unclear. This study showed that KLHL24-ΔN28 impaired skin wound healing by excessively degrading vimentin. Heterozygous Klhl24c.3G>T knock-in mice displayed delayed wound healing and decreased wound collagen deposition. We identified vimentin as an unreported substrate of KLHL24. KLHL24-ΔN28 mediated the excessive degradation of vimentin, which failed to maintain efficient fibroblast proliferation and activation during wound healing. Furthermore, by mediating vimentin degradation, KLHL24 can hinder myofibroblast activation, which attenuated bleomycin-induced skin fibrosis. These findings showed the function of KLHL24 in regulating tissue remodeling, atrophic scarring, and fibrosis.

Independent Membrane Binding Properties of the Caspase Generated Fragments of the Beaded Filament Structural Protein 1 (BFSP1) Involves an Amphipathic Helix

BACKGROUND

BFSP1 (beaded filament structural protein 1) is a plasma membrane, Aquaporin 0 (AQP0/MIP)-associated intermediate filament protein expressed in the eye lens. BFSP1 is myristoylated, a post-translation modification that requires caspase cleavage at D433. Bioinformatic analyses suggested that the sequences 434-452 were α-helical and amphipathic.

METHODS AND RESULTS

By CD spectroscopy, we show that the addition of trifluoroethanol induced a switch from an intrinsically disordered to a more α-helical conformation for the residues 434-467. Recombinantly produced BFSP1 fragments containing this amphipathic helix bind to lens lipid bilayers as determined by surface plasmon resonance (SPR). Lastly, we demonstrate by transient transfection of non-lens MCF7 cells that these same BFSP1 C-terminal sequences localise to plasma membranes and to cytoplasmic vesicles. These can be co-labelled with the vital dye, lysotracker, but other cell compartments, such as the nuclear and mitochondrial membranes, were negative. The N-terminal myristoylation of the amphipathic helix appeared not to change either the lipid affinity or membrane localisation of the BFSP1 polypeptides or fragments we assessed by SPR and transient transfection, but it did appear to enhance its helical content.

CONCLUSIONS

These data support the conclusion that C-terminal sequences of human BFSP1 distal to the caspase site at G433 have independent membrane binding properties via an adjacent amphipathic helix.

Long COVID: pathophysiological factors and abnormalities of coagulation

Acute COVID-19 infection is followed by prolonged symptoms in approximately one in ten cases: known as Long COVID. The disease affects ~65 million individuals worldwide. Many pathophysiological processes appear to underlie Long COVID, including viral factors (persistence, reactivation, and bacteriophagic action of SARS CoV-2); host factors (chronic inflammation, metabolic and endocrine dysregulation, immune dysregulation, and autoimmunity); and downstream impacts (tissue damage from the initial infection, tissue hypoxia, host dysbiosis, and autonomic nervous system dysfunction). These mechanisms culminate in the long-term persistence of the disorder characterized by a thrombotic endothelialitis, endothelial inflammation, hyperactivated platelets, and fibrinaloid microclots. These abnormalities of blood vessels and coagulation affect every organ system and represent a unifying pathway for the various symptoms of Long COVID.

Evidence of SARS-CoV-2 infection in postmortem lung, kidney, and liver samples, revealing cellular targets involved in COVID-19 pathogenesis

There is an urgent need to understand severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-host interactions involved in virus spread and pathogenesis, which might contribute to the identification of new therapeutic targets. In this study, we investigated the presence of SARS-CoV-2 in postmortem lung, kidney, and liver samples of patients who died with coronavirus disease (COVID-19) and its relationship with host factors involved in virus spread and pathogenesis, using microscopy-based methods. The cases analyzed showed advanced stages of diffuse acute alveolar damage and fibrosis. We identified the SARS-CoV-2 nucleocapsid (NC) in a variety of cells, colocalizing with mitochondrial proteins, lipid droplets (LDs), and key host proteins that have been implicated in inflammation, tissue repair, and the SARS-CoV-2 life cycle (vimentin, NLRP3, fibronectin, LC3B, DDX3X, and PPARγ), pointing to vimentin and LDs as platforms involved not only in the viral life cycle but also in inflammation and pathogenesis. SARS-CoV-2 isolated from a patient´s nasal swab was grown in cell culture and used to infect hamsters. Target cells identified in human tissue samples included lung epithelial and endothelial cells; lipogenic fibroblast-like cells (FLCs) showing features of lipofibroblasts such as activated PPARγ signaling and LDs; lung FLCs expressing fibronectin and vimentin and macrophages, both with evidence of NLRP3- and IL1β-induced responses; regulatory cells expressing immune-checkpoint proteins involved in lung repair responses and contributing to inflammatory responses in the lung; CD34⁺ liver endothelial cells and hepatocytes expressing vimentin; renal interstitial cells; and the juxtaglomerular apparatus. This suggests that SARS-CoV-2 may directly interfere with critical lung, renal, and liver functions involved in COVID-19-pathogenesis.

N-acetylglucosamine-bearing polymers mimicking O-GlcNAc-modified proteins elicit anti-fibrotic activities in myofibroblasts and activated stellate cells

O-linked β-N-acetylglucosamine (O-GlcNAc)-modified proteins are post-translationally modified with GlcNAc conjugated to serine and threonine residues. This modification is associated with various physiological functions such as serine and threonine phosphorylation and Notch signaling. Here, we demonstrated that O-GlcNAc-modified proteins leaked from dead cells and GlcNAc-bearing polymers mimicking the multivalent GlcNAc moiety of these proteins induced anti-fibrotic activities, such as the suppression of α-smooth muscle actin and collagen and the induction of matrix metalloprotease 1 in myofibroblasts. We have previously reported that O-GlcNAc-modified proteins and GlcNAc-bearing polymers could interact with cell surface vimentin and desmin. In the current study, it was demonstrated that a multivalent GlcNAc moiety structure of these molecules activated PI3K/Akt and p38MAPK pathway and elicited these anti-fibrotic activities in myofibroblasts by interacting with cell surface vimentin. Since the interaction of O-GlcNAc-modified proteins with desmin was observed in the fibrotic liver of carbon tetrachloride-treated mice via an in situ proximity ligation assay, it was assumed that the activated stellate cells could bind to the O-GlcNAc-modified proteins from the damaged hepatocytes. In addition, the administration of anti-O-GlcNAc antibody to inhibit the interaction exacerbated liver fibrosis in the mice. Moreover, administration of the GlcNAc-bearing polymers into carbon tetrachloride-treated mice could ameliorate liver fibrosis. Thus, O-GlcNAc-modified proteins leaked from dead cells can interact with myofibroblasts and activated stellate cells and function as fibrosis suppressors. Moreover, we anticipate that GlcNAc-bearing polymers mimicking O-GlcNAc-modified proteins will be applied as novel therapeutic tools for fibrosis.

Coronavirus and the Cytoskeleton of Virus-Infected Cells

The cytoskeleton, which includes actin filaments, microtubules, and intermediate filaments, is one of the most important networks in the cell and undertakes many fundamental life activities. Among them, actin filaments are mainly responsible for maintaining cell shape and mediating cell movement, microtubules are in charge of coordinating all cargo transport within the cell, and intermediate filaments are mainly thought to guard against external mechanical pressure. In addition to this, cytoskeleton networks are also found to play an essential role in multiple viral infections. Due to the COVID-19 epidemic, including SARS-CoV-2, SARS-CoV and MERS-CoV, so many variants have caused wide public concern, that any virus infection can potentially bring great harm to human beings and society. Therefore, it is of great importance to study coronavirus infection and develop antiviral drugs and vaccines. In this chapter, we summarize in detail how the cytoskeleton responds and participates in coronavirus infection by analyzing the possibility of the cytoskeleton and its related proteins as antiviral targets, thereby providing ideas for finding more effective treatments.

Recombinant human plasma gelsolin reverses increased permeability of the blood-brain barrier induced by the spike protein of the SARS-CoV-2 virus

BACKGROUND

Plasma gelsolin (pGSN) is an important part of the blood actin buffer that prevents negative consequences of possible F-actin deposition in the microcirculation and has various functions during host immune response. Recent reports reveal that severe COVID-19 correlates with reduced levels of pGSN. Therefore, using an in vitro system, we investigated whether pGSN could attenuate increased permeability of the blood-brain barrier (BBB) during its exposure to the portion of the SARS-CoV-2 spike protein containing the receptor binding domain (S1 subunit).

MATERIALS AND METHODS

Two- and three-dimensional models of the human BBB were constructed using the human cerebral microvascular endothelial cell line hCMEC/D3 and exposed to physiologically relevant shear stress to mimic perfusion in the central nervous system (CNS). Trans-endothelial electrical resistance (TEER) as well as immunostaining and Western blotting of tight junction (TJ) proteins assessed barrier integrity in the presence of the SARS-CoV-2 spike protein and pGSN. The IncuCyte Live Imaging system evaluated the motility of the endothelial cells. Magnetic bead-based ELISA was used to determine cytokine secretion. Additionally, quantitative real-time PCR (qRT-PCR) revealed gene expression of proteins from signaling pathways that are associated with the immune response.

RESULTS

pGSN reversed S1-induced BBB permeability in both 2D and 3D BBB models in the presence of shear stress. BBB models exposed to pGSN also exhibited attenuated pro-inflammatory signaling pathways (PI3K, AKT, MAPK, NF-κB), reduced cytokine secretion (IL-6, IL-8, TNF-α), and increased expression of proteins that form intercellular TJ (ZO-1, occludin, claudin-5).

CONCLUSION

Due to its anti-inflammatory and protective effects on the brain endothelium, pGSN has the potential to be an alternative therapeutic target for patients with severe SARS-CoV-2 infection, especially those suffering neurological complications of COVID-19.

PEDOT:PSS in Solution Form Exhibits Strong Potential in Inhibiting SARS-CoV-2 Infection of the Host Cells by Targeting Viruses and Also the Host Cells

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a global pandemic with over 5 million fatalities. Vaccines against this virus have been globally administered; however, SARS-CoV-2 variants with spike protein mutations are continuously identified with strong capability to escape vaccine-elicited protection. Due to the high mutation rate and transmission ability, the development of a broad-spectrum SARS-CoV-2 inhibitor is highly in demand. In this study, the effect of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) against SARS-CoV-2 was investigated. The treatment of pseudoviruses carrying the SARS-CoV-2 spike protein with PEDOT:PSS strongly blocked SARS-CoV-2 pseudovirus infection in human ACE2-expressing cells without causing cytotoxicity. Specifically, PEDOT:PSS showed great potential in both inactivating viruses and rendering antiviral activity to the treated cells. The effects of other PEDOT:PSS solutions with different chemical ratios and properties were also validated to find the high inhibition capacity against SARS-CoV-2 pseudovirus infection. The transcriptomic data reveal that PEDOT:PSS-treated cells were endowed with transcriptional alteration, and it could be reverted after the removal of PEDOT:PSS from the culture medium. Importantly, PEDOT:PSS also exhibited broad-spectrum inhibition effects on the pseudovirus carrying the spike protein isolated from different variants. In combination with the advantage of high biocompatibility, PEDOT:PSS could thus be considered a potential therapeutic and prophylactic material against SARS-CoV-2.

Extracellular vimentin is expressed at the rear of activated macrophage-like cells: Potential role in enhancement of migration and phagocytosis

Macrophages have a vital role in the immune system through elimination of cell debris and microorganisms by phagocytosis. The activation of macrophages by tumour necrosis factor-α induces expression of extracellular cell-surface vimentin and promotes release of this vimentin into the extracellular environment. Vimentin is a cytoskeletal protein that is primarily located in the cytoplasm of cells. However, under circumstances like injury, stress, senescence and activation, vimentin can be expressed on the extracellular cell surface, or it can be released into the extracellular space. The characteristics of this extracellular vimentin, and its implications for the functional role of macrophages and the mechanism of secretion remain unclear. Here, we demonstrate that vimentin is released mainly from the back of macrophage-like cells. This polarisation is strongly enhanced upon macrophage activation. One-dimensional patterned lines showed that extracellular cell-surface vimentin is localised primarily at the back of activated macrophage-like cells. Through two-dimensional migration and phagocytosis assays, we show that this extracellular vimentin enhances migration and phagocytosis of macrophage-like cells. We further show that this extracellular vimentin forms agglomerates on the cell surface, in contrast to its intracellular filamentous form, and that it is released into the extracellular space in the form of small fragments. Taken together, we provide new insights into the release of extracellular cell-surface vimentin and its implications for macrophage functionality.

Autoimmune Effect of Antibodies against the SARS-CoV-2 Nucleoprotein

COVID-19 caused by SARS-CoV-2 is continuing to spread around the world and drastically affect our daily life. New strains appear, and the severity of the course of the disease itself seems to be decreasing, but even people who have been ill on an outpatient basis suffer post-COVID consequences. Partly, it is associated with the autoimmune reactions, so debates about the development of new vaccines and the need for vaccination/revaccination continue. In this study we performed an analysis of the antibody response of patients with COVID-19 to linear and conformational epitopes of viral proteins using ELISA, chip array and western blot with analysis of correlations between antibody titer, disease severity, and complications. We have shown that the presence of IgG antibodies to the nucleoprotein can deteriorate the course of the disease, induce multiple direct COVID-19 symptoms, and contribute to long-term post-covid symptoms. We analyzed the cross reactivity of antibodies to SARS-CoV-2 with own human proteins and showed that antibodies to the nucleocapsid protein can bind to human proteins. In accordance with the possibility of HLA presentation, the main possible targets of the autoantibodies were identified. People with HLA alleles A01:01; A26:01; B39:01; B15:01 are most susceptible to the development of autoimmune processes after COVID-19.

SARS-CoV-2 and Emerging Variants: Unmasking Structure, Function, Infection, and Immune Escape Mechanisms

As of April 1, 2022, over 468 million COVID-19 cases and over 6 million deaths have been confirmed globally. Unlike the common coronavirus, SARS-CoV-2 has highly contagious and attracted a high level of concern worldwide. Through the analysis of SARS-CoV-2 structural, non-structural, and accessory proteins, we can gain a deeper understanding of structure-function relationships, viral infection mechanisms, and viable strategies for antiviral therapy. Angiotensin-converting enzyme 2 (ACE2) is the first widely acknowledged SARS-CoV-2 receptor, but researches have shown that there are additional co-receptors that can facilitate the entry of SARS-CoV-2 to infect humans. We have performed an in-depth review of published papers, searching for co-receptors or other auxiliary membrane proteins that enhance viral infection, and analyzing pertinent pathogenic mechanisms. The genome, and especially the spike gene, undergoes mutations at an abnormally high frequency during virus replication and/or when it is transmitted from one individual to another. We summarized the main mutant strains currently circulating global, and elaborated the structural feature for increased infectivity and immune evasion of variants. Meanwhile, the principal purpose of the review is to update information on the COVID-19 outbreak. Many countries have novel findings on the early stage of the epidemic, and accruing evidence has rewritten the timeline of the outbreak, triggering new thinking about the origin and spread of COVID-19. It is anticipated that this can provide further insights for future research and global epidemic prevention and control.

Elucidating Design Principles for Engineering Cell-Derived Vesicles to Inhibit SARS-CoV-2 Infection

The ability of pathogens to develop drug resistance is a global health challenge. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) presents an urgent need wherein several variants of concern resist neutralization by monoclonal antibody (mAb) therapies and vaccine-induced sera. Decoy nanoparticles-cell-mimicking particles that bind and inhibit virions-are an emerging class of therapeutics that may overcome such drug resistance challenges. To date, quantitative understanding as to how design features impact performance of these therapeutics is lacking. To address this gap, this study presents a systematic, comparative evaluation of various biologically derived nanoscale vesicles, which may be particularly well suited to sustained or repeated administration in the clinic due to low toxicity, and investigates their potential to inhibit multiple classes of model SARS-CoV-2 virions. A key finding is that such particles exhibit potent antiviral efficacy across multiple manufacturing methods, vesicle subclasses, and virus-decoy binding affinities. In addition, these cell-mimicking vesicles effectively inhibit model SARS-CoV-2 variants that evade mAbs and recombinant protein-based decoy inhibitors. This study provides a foundation of knowledge that may guide the design of decoy nanoparticle inhibitors for SARS-CoV-2 and other viral infections.

Cell surface detection of vimentin, ACE2 and SARS-CoV-2 Spike proteins reveals selective colocalization at primary cilia

The SARS-CoV-2 Spike protein mediates docking of the virus onto cells prior to viral invasion. Several cellular receptors facilitate SARS-CoV-2 Spike docking at the cell surface, of which ACE2 plays a key role in many cell types. The intermediate filament protein vimentin has been reported to be present at the surface of certain cells and act as a co-receptor for several viruses; furthermore, its potential involvement in interactions with Spike proteins has been proposed. Nevertheless, the potential colocalization of vimentin with Spike and its receptors on the cell surface has not been explored. Here we have assessed the binding of Spike protein constructs to several cell types. Incubation of cells with tagged Spike S or Spike S1 subunit led to discrete dotted patterns at the cell surface, which consistently colocalized with endogenous ACE2, but sparsely with a lipid raft marker. Vimentin immunoreactivity mostly appeared as spots or patches unevenly distributed at the surface of diverse cell types. Of note, vimentin could also be detected in extracellular particles and in the cytoplasm underlying areas of compromised plasma membrane. Interestingly, although overall colocalization of vimentin-positive spots with ACE2 or Spike was moderate, a selective enrichment of the three proteins was detected at elongated structures, positive for acetylated tubulin and ARL13B. These structures, consistent with primary cilia, concentrated Spike binding at the top of the cells. Our results suggest that a vimentin-Spike interaction could occur at selective locations of the cell surface, including ciliated structures, which can act as platforms for SARS-CoV-2 docking.

SARS-CoV-2: Receptor and Co-receptor Tropism Probability

The recent pandemic which arose from China, is caused by a pathogenic virus named "severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2)". Its rapid global expansion has inflicted an extreme public health concern. The attachment of receptor-binding domains (RBD) of the spike proteins (S) to the host cell's membrane, with or without the help of other cellular components such as proteases and especially co-receptors, is required for the first stage of its pathogenesis. In addition to humans, angiotensin-converting enzyme 2 (ACE2) is found on a wide range of vertebrate host's cellular surface. SARS-CoV-2 has a broad spectrum of tropism; thus, it can infect a vast range of tissues, organs, and hosts; even though the surface amino acids of the spike protein conflict in the receptor-binding region. Due to the heterogeneous ACE2 distribution and the presence of different domains on the SARS-CoV-2 spike protein for binding, the virus entry into diverse host cell types may depend on the host cells' receptor presentation with or without co-receptors. This review investigates multiple current types of receptor and co-receptor tropisms, with other molecular factors alongside their respective mechanisms, which facilitate the binding and entry of SARS-CoV-2 into the cells, extending the severity of the coronavirus disease 2019 (COVID-19). Understanding the pathogenesis of COVID-19 from this perspective can effectively help prevent this disease and provide more potent treatment strategies, particularly in vulnerable people with various cellular-level susceptibilities.

Vimentin Intermediate Filaments Mediate Cell Morphology on Viscoelastic Substrates

The ability of cells to take and change shape is a fundamental feature underlying development, wound repair, and tissue maintenance. Central to this process is physical and signaling interactions between the three cytoskeletal polymeric networks: F-actin, microtubules, and intermediate filaments (IFs). Vimentin is an IF protein that is essential to the mechanical resilience of cells and regulates cross-talk among the cytoskeleton, but its role in how cells sense and respond to the surrounding extracellular matrix is largely unclear. To investigate vimentin's role in substrate sensing, we designed polyacrylamide hydrogels that mimic the elastic and viscoelastic nature of in vivo tissues. Using wild-type and vimentin-null mouse embryonic fibroblasts, we show that vimentin enhances cell spreading on viscoelastic substrates, even though it has little effect in the limit of purely elastic substrates. Our results provide compelling evidence that vimentin modulates how cells sense and respond to their environment and thus plays a key role in cell mechanosensing.

Update of the keratin gene family: evolution, tissue-specific expression patterns, and relevance to clinical disorders

Intermediate filament (IntFil) genes arose during early metazoan evolution, to provide mechanical support for plasma membranes contacting/interacting with other cells and the extracellular matrix. Keratin genes comprise the largest subset of IntFil genes. Whereas the first keratin gene appeared in sponge, and three genes in arthropods, more rapid increases in keratin genes occurred in lungfish and amphibian genomes, concomitant with land animal-sea animal divergence (~ 440 to 410 million years ago). Human, mouse and zebrafish genomes contain 18, 17 and 24 non-keratin IntFil genes, respectively. Human has 27 of 28 type I "acidic" keratin genes clustered at chromosome (Chr) 17q21.2, and all 26 type II "basic" keratin genes clustered at Chr 12q13.13. Mouse has 27 of 28 type I keratin genes clustered on Chr 11, and all 26 type II clustered on Chr 15. Zebrafish has 18 type I keratin genes scattered on five chromosomes, and 3 type II keratin genes on two chromosomes. Types I and II keratin clusters-reflecting evolutionary blooms of keratin genes along one chromosomal segment-are found in all land animal genomes examined, but not fishes; such rapid gene expansions likely reflect sudden requirements for many novel paralogous proteins having divergent functions to enhance species survival following sea-to-land transition. Using data from the Genotype-Tissue Expression (GTEx) project, tissue-specific keratin expression throughout the human body was reconstructed. Clustering of gene expression patterns revealed similarities in tissue-specific expression patterns for previously described "keratin pairs" (i.e., KRT1/KRT10, KRT8/KRT18, KRT5/KRT14, KRT6/KRT16 and KRT6/KRT17 proteins). The ClinVar database currently lists 26 human disease-causing variants within the various domains of keratin proteins.

Exogenous Vimentin Supplementation Transiently Affects Early Steps during HPV16 Pseudovirus Infection

Understanding and modulating the early steps in oncogenic Human Papillomavirus (HPV) infection has great cancer-preventative potential, as this virus is the etiological agent of virtually all cervical cancer cases and is associated with many other anogenital and oropharyngeal cancers. Previous work from our laboratory has identified cell-surface-expressed vimentin as a novel HPV16 pseudovirus (HPV16-PsVs)-binding molecule modulating its infectious potential. To further explore its mode of inhibiting HPV16-PsVs internalisation, we supplemented it with exogenous recombinant human vimentin and show that only the globular form of the molecule (as opposed to the filamentous form) inhibited HPV16-PsVs internalisation in vitro. Further, this inhibitory effect was only transient and not sustained over prolonged incubation times, as demonstrated in vitro and in vivo, possibly due to full-entry molecule engagement by the virions once saturation levels have been reached. The vimentin-mediated delay of HPV16-PsVs internalisation could be narrowed down to affecting multiple steps during the virus’ interaction with the host cell and was found to affect both heparan sulphate proteoglycan (HSPG) binding as well as the subsequent entry receptor complex engagement. Interestingly, decreased pseudovirus internalisation (but not infection) in the presence of vimentin was also demonstrated for oncogenic HPV types 18, 31 and 45. Together, these data demonstrate the potential of vimentin as a modulator of HPV infection which can be used as a tool to study early mechanisms in infectious internalisation. However, further refinement is needed with regard to vimentin’s stabilisation and formulation before its development as an alternative prophylactic means.