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

Annexin A2 Contributes to Release of Extracellular Vimentin in Response to Inflammation

Vimentin, an abundant intracellular cytoskeletal protein, is secreted into the extracellular space, where it can amplify tissue destruction in inflammatory diseases. The mechanisms by which inflammation promotes the release of extracellular vimentin (ECV) are not defined. In human subjects, we found > twofold higher levels of ECV in gingival crevicular fluid from periodontitis sites with inflammation compared with healthy sites. In cultures of human gingival fibroblasts (hGFs) treated with 1% serum or IL-1β (10 ng/mL) to model tissue injury or inflammation, respectively, we found that 1% serum increased ECV release > 11-fold while IL-1β further enhanced release 17-fold. Mass spectrometry of vimentin immunoprecipitates identified Annexin A2 (AnxA2), a Ca2+-dependent phospholipid-binding protein, as a potential binding protein of ECV, which was confirmed by immunoprecipitation of cultured hGFs and immunostaining of inflamed human gingiva. IL-1β treatment enhanced the abundance of AnxA2 and vimentin in membrane fractions prepared by sucrose gradients of hGF lysates. IL-1β increased colocalization of ECV and AnxA2 at the outer aspect of the plasma membrane of intact hGFs. Knockdown of AnxA2 with siRNA or inhibition of the unconventional secretory pathway reduced ECV release from hGFs. These findings indicate that the production of ECV by hGFs in response to inflammation is mediated by an AnxA2-dependent, unconventional secretory pathway that may play a role in amplification of the inflammatory response.

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.

The Cancer Chimera: Impact of Vimentin and Cytokeratin Co-Expression in Hybrid Epithelial/Mesenchymal Cancer Cells on Tumor Plasticity and Metastasis

The epithelial-mesenchymal transition (EMT) program is critical to metastatic cancer progression. EMT results in the expression of mesenchymal proteins and enhances migratory and invasive capabilities. In a small percentage of cells, EMT results in the expression of stemness-associated genes that provide a metastatic advantage. Although EMT had been viewed as a binary event, it has recently become clear that the program leads to a spectrum of phenotypes, including hybrid epithelial/mesenchymal (E/M) cells that have significantly greater metastatic capability than cells on the epithelial or mesenchymal ends of the spectrum. As hybrid E/M cells are rarely observed in physiological, non-diseased states in the adult human body, these cells are potential biomarkers and drug targets. Hybrid E/M cells are distinguished by the co-expression of epithelial and mesenchymal proteins, such as the intermediate filament proteins cytokeratin (CK; epithelial) and vimentin (VIM; mesenchymal). Although these intermediate filaments have been extensively used for pathological characterization and detection of aggressive carcinomas, little is known regarding the interactions between CK and VIM when co-expressed in hybrid E/M cells. This review describes the characteristics of hybrid E/M cells with a focus on the unique co-expression of VIM and CK. We will discuss the structures and functions of these two intermediate filament proteins and how they may interact when co-expressed in hybrid E/M cells. Additionally, we review what is known about cell-surface expression of these intermediate filament proteins and discuss their potential as predictive biomarkers and therapeutic targets.

Septin 9 expression regulates 'don't eat me' signals and identifies an immune-epithelial class of intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (iCCA) is a highly heterogeneous and aggressive liver cancer with limited therapeutic options. Precise classification and immunotherapy are perspectives to improve the treatments. We reported the role of septin 9 in apico-basal polarity and epithelial-to-mesenchymal transition (EMT). Here, we aim to elucidate its role in iCCA. We analyzed single-cell transcriptomes from human iCCA tumor cells based on phenotype and cell state. Knockdown of the septin 9 gene (SEPT9) was done using small interfering RNA (siRNA); interferon-γ (IFN-γ) stimulation was performed using different CCA cells; gene expressions were analyzed by reverse transcription and real-time PCR analysis (RT-qPCR); and immunofluorescence, immunoblotting, and flow cytometry were performed to assess the expression of proteins. The differential distributions of SEPT9 and vimentin (VIM) gene expressions allowed us to define specific cellular trajectories of malignant cells and thus identified distinct clusters of iCCA cells. One cluster was enriched in VIM and extracellular-matrix (ECM) remodeling molecules, and another had high expression of SEPT9 and genes from the 'don't eat me' signal involved in immune escape. This antagonism between SEPT9 and VIM was confirmed by in vitro experiments. Notably, SEPT9 and 'don't eat me' gene expressions were inversely correlated to those of vimentin and the EMT markers. SEPT9 expression was upregulated by IFN-γ and SEPT9 knockdown decreased expression of 'don't eat me' signal genes and increased expression of mesenchymal markers. Cancer Cell Line Encyclopedia (CCLE) transcriptome database analyses confirmed that iCCA cells enriched in septin 9 exhibit epithelial-like features. This study revealed septin 9 as a cytoskeleton element of iCCA epithelial-like cells and a regulator of the immune system response. It also brings new insights into the enigmatic relationship between EMT and immune response. Notably, we decoded a potential mechanism that could sensitize patients to immunotherapies.

Vimentin regulates mitochondrial ROS production and inflammatory responses of neutrophils

The intermediate filament vimentin is present in immune cells and is implicated in proinflammatory immune responses. Whether and how it supports antimicrobial activities of neutrophils are not well established. Here, we developed an immortalized neutrophil model to examine the requirement of vimentin. We demonstrate that vimentin restricts the production of proinflammatory cytokines and reactive oxygen species (ROS), but enhances phagocytosis and swarming. We observe that vimentin is dispensable for neutrophil extracellular trap (NET) formation, degranulation, and inflammasome activation. Moreover, gene expression analysis demonstrated that the presence of vimentin was associated with changes in expression of multiple genes required for mitochondrial function and ROS overproduction. Treatment of wild-type cells with rotenone, an inhibitor for complex I of the electron transport chain, increases the ROS levels. Likewise, treatment with mitoTEMPO, a SOD mimetic, rescues the ROS production in cells lacking vimentin. Together, these data show vimentin regulates neutrophil antimicrobial functions and alters ROS levels through regulation of mitochondrial activity.

Inflammatory, metabolic, and sex-dependent gene-regulatory dynamics of microglia and macrophages in neonatal hippocampus after hypoxia-ischemia

Neonatal hypoxia-ischemia (HI) is a major cause of perinatal death and long-term disabilities worldwide. Post-ischemic neuroinflammation plays a pivotal role in HI pathophysiology. In the present study, we investigated the temporal dynamics of microglia (CX3CR1GFP/+) and infiltrating macrophages (CCR2RFP/+) in the hippocampi of mice subjected to HI at postnatal day 9. Using inflammatory pathway and transcription factor (TF) analyses, we identified a distinct post-ischemic response in CCR2RFP/+ cells characterized by differential gene expression in sensome, homeostatic, matrisome, lipid metabolic, and inflammatory molecular signatures. Three days after injury, transcriptomic signatures of CX3CR1GFP/+ and CCR2RFP/+ cells isolated from hippocampi showed a partial convergence. Interestingly, microglia-specific genes in CX3CR1GFP/+ cells showed a sexual dimorphism, where expression returned to control levels in males but not in females during the experimental time frame. These results highlight the importance of further investigations on metabolic rewiring to pave the way for future interventions in asphyxiated neonates.

Vimentin regulates mitochondrial ROS production and inflammatory responses of neutrophils

The intermediate filament vimentin is present in immune cells and is implicated in proinflammatory immune responses. Whether and how it supports antimicrobial activities of neutrophils is not well established. Here, we developed an immortalized neutrophil model to examine the requirement of vimentin. We demonstrate that vimentin restricts the production of proinflammatory cytokines and reactive oxygen species (ROS), but enhances phagocytosis and swarming. We observe that vimentin is dispensable for neutrophil extracellular trap (NET) formation, degranulation, and inflammasome activation. Moreover, gene expression analysis demonstrated that the presence of vimentin was associated with changes in expression of multiple genes required for mitochondrial function and ROS overproduction. Treatment of wild-type cells with rotenone, an inhibitor for complex I of the electron transport chain, increases the ROS levels. Likewise, treatment with mitoTEMPO, a SOD mimetic, rescues the ROS production in cells lacking vimentin. Together, these data show vimentin regulates neutrophil antimicrobial functions and alters ROS levels through regulation of mitochondrial activity.

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.

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.

Extracellular vimentin as a versatile immune suppressive protein in cancer

The interest in finding new targets in the tumor microenvironment for anti-cancer therapy has increased rapidly over the years. More specifically, the tumor-associated blood vessels are a promising target. We recently found that the intermediate filament protein vimentin is externalized by endothelial cells of the tumor vasculature. Extracellular vimentin was shown to sustain angiogenesis by mimicking VEGF and supporting cell migration, as well as endothelial cell anergy, the unresponsiveness of the endothelium to proinflammatory cytokines. The latter hampers immune cell infiltration and subsequently provides escape from tumor immunity. Other studies showed that extracellular vimentin plays a role in sustained systemic and local inflammation. Here we will review the reported roles of extracellular vimentin with a particular emphasis on its involvement in the interactions between immune cells and the endothelium in the tumor microenvironment. To this end, we discuss the different ways by which extracellular vimentin modulates the immune system. Moreover, we review how this protein can alter immune cell-vessel wall adhesion by altering the expression of adhesion proteins, attenuating immune cell infiltration into the tumor parenchyma. Finally, we discuss how vimentin-targeting therapy can reverse endothelial cell anergy and promote immune infiltration, supporting anti-tumor immunity.

AXL-initiated paracrine activation of pSTAT3 enhances mesenchymal and vasculogenic supportive features of tumor-associated macrophages

Tumor-associated macrophages (TAMs) are integral to the development of complex tumor microenvironments (TMEs) and can execute disparate cellular programs in response to extracellular cues. However, upstream signaling processes underpinning this phenotypic plasticity remain to be elucidated. Here, we report that concordant AXL-STAT3 signaling in TAMs is triggered by lung cancer cells or cancer-associated fibroblasts in the cytokine milieu. This paracrine action drives TAM differentiation toward a tumor-promoting "M2-like" phenotype with upregulation of CD163 and putative mesenchymal markers, contributing to TAM heterogeneity and diverse cellular functions. One of the upregulated markers, CD44, mediated by AXL-IL-11-pSTAT3 signaling cascade, enhances macrophage ability to interact with endothelial cells and facilitate formation of primitive vascular networks. We also found that AXL-STAT3 inhibition can impede the recruitment of TAMs in a xenograft mouse model, thereby suppressing tumor growth. These findings suggest the potential application of AXL-STAT3-related markers to quantitatively assess metastatic potential and inform therapeutic strategies in lung cancer.

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.

A low-cost alternative method of generating fibronectin micropatterned lines for cellular applications

The cellular microenvironment contributes to the architecture, differentiation, polarity, mechanics and functions of the cell [1]. Spatial confinement of cells using micropatterning techniques allows to alter and regulate the cellular microenvironment for a better understanding of cellular mechanisms [2]. However, commercially available micropatterned consumables such as coverslips, dishes, plates etc. are expensive. These methods are complex and based on deep UV patterning [3,4]. In this study, we establish a low-cost method for effective micropatterning using Polydimethylsiloxane (PDMS) chips.•We demonstrate this method by generating fibronectin-coated micropatterned lines (width, 5 µm) on a glass bottom dish.•As a proof of concept, we culture macrophages on these lines. We additionally show that this method allows to determine the cellular polarity by measuring the position of the nucleus within a cell on a micropatterned line.