Soluble CD44 interacts with intermediate filament protein vimentin on endothelial cell surface

An Investigation into the In Vitro Targeted Killing of CD44-Expressing Triple-Negative Breast Cancer Cells Using Recombinant Photoimmunotherapeutics Compared to Auristatin-F-Based Antibody-Drug Conjugates

Triple-negative breast cancer (TNBC) is the deadliest form of breast cancer with limited treatment options. The persistence of highly tumorigenic CD44-expressing subpopulation referred to as cancer stem cells (CSCs), endowed with the self-renewal capacity, has been associated with therapeutic resistance, hence clinical relapses. To mitigate these undesired events, targeted immunotherapies using antibody-photoconjugate (APC) or antibody-drug conjugate (ADC), were developed to specifically release cytotoxic payloads within targeted cells overexpressing cognate antigen receptors. Therefore, an αCD44(scFv)-SNAP-tag antibody fusion protein was engineered through genetic fusion of a single-chain antibody fragment (scFv) to a SNAPf-tag fusion protein, capable of self-conjugating with benzylguanine-modified light-sensitive near-infrared (NIR) phthalocyanine dye IRDye700DX (BG-IR700) or the small molecule toxin auristatin-F (BG-AURIF). Binding of the αCD44(scFv)-SNAPf-IR700 photoimmunoconjugate to antigen-positive cells was demonstrated by confocal microscopy and flow cytometry. By switching to NIR irradiation, CD44-expressing TNBC was selectively killed through induced phototoxic activities. Likewise, the αCD44(scFv)-SNAPf-AURIF immunoconjugate was able to selectively accumulate within targeted cells and significantly reduced cell viability through antimitotic activities at nano- to micromolar drug concentrations. This study provides an in vitro proof-of-concept for a future strategy to selectively destroy light-accessible superficial CD44-expressing TNBC tumors and their metastatic lesions which are inaccessible to therapeutic light.

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.

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.

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.

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.

Human isogenic cells of the neurovascular unit exert transcriptomic cell type-specific effects on a blood-brain barrier in vitro model of late-onset Alzheimer disease

BACKGROUND

The function of the blood-brain barrier (BBB) is impaired in late-onset Alzheimer disease (LOAD), but the associated molecular mechanisms, particularly with respect to the high-risk APOE4/4 genotype, are not well understood. For this purpose, we developed a multicellular isogenic model of the neurovascular unit (NVU) based on human induced pluripotent stem cells.

METHODS

The human NVU was modeled in vitro using isogenic co-cultures of astrocytes, brain capillary endothelial-like cells (BCECs), microglia-like cells, neural stem cells (NSCs), and pericytes. Physiological and pathophysiological properties were investigated as well as the influence of each single cell type on the characteristics and function of BCECs. The barriers established by BCECs were analyzed for specific gene transcription using high-throughput quantitative PCR.

RESULTS

Co-cultures were found to tighten the barrier of BCECs and alter its transcriptomic profile under both healthy and disease conditions. In vitro differentiation of brain cell types that constitute the NVU was not affected by the LOAD background. The supportive effect of NSCs on the barrier established by BCECs was diminished under LOAD conditions. Transcriptomes of LOAD BCECs were modulated by different brain cell types. NSCs were found to have the strongest effect on BCEC gene regulation and maintenance of the BBB. Co-cultures showed cell type-specific functional contributions to BBB integrity under healthy and LOAD conditions.

CONCLUSIONS

Cell type-dependent transcriptional effects on LOAD BCECs were identified. Our study suggests that different brain cell types of the NVU have unique roles in maintaining barrier integrity that vary under healthy and LOAD conditions. .

Automated Image Analysis for Characterization of Circulating Tumor Cells and Clusters Sorted by Magnetic Levitation

Magnetic levitation-based sorting technologies have revolutionized the detection and isolation of rare cells, including circulating tumor cells (CTCs) and circulating tumor cell clusters (CTCCs). Manual counting and quantification of these cells are prone to time-consuming processes, human error, and inter-observer variability, particularly challenging when heterogeneous cell types in 3D clusters are present. To overcome these challenges, we developed "Fastcount," an in-house MATLAB-based algorithm for precise, automated quantification and phenotypic characterization of CTCs and CTCCs, in both 2D and 3D. Fastcount is 120 times faster than manual counting and produces reliable results with a ±7.3% deviation compared to a trained laboratory technician. By analyzing 400 GB of fluorescence imaging data, we showed that Fastcount outperforms manual counting and commercial software when cells are aggregated in 3D or staining artifacts are present, delivering more accurate results. We further employed Fastcount for automated analysis of 3D image stacks obtained from CTCCs isolated from colorectal adenocarcinoma and renal cell carcinoma blood samples. Interestingly, we observed a highly heterogeneous spatial cellular composition within CTCCs, even among clusters from the same patient. Overall, Fastcount can be employed for various applications with lab-chip devices, such as CTC detection, CTCC analysis in 3D and cell detection in biosensors.

Vimentin-mediated myosin 10 aggregation at tips of cell extensions drives MT1-MMP-dependent collagen degradation in colorectal cancer

Colorectal cancer (CRC) is a high prevalence adenocarcinoma with progressive increases in metastasis-related mortality, but the mechanisms governing the extracellular matrix (ECM) degradation important for metastasis in CRC are not well-defined. We investigated a functional relationship between vimentin (Vim) and myosin 10 (Myo10), and whether this relationship is associated with cancer progression. We tested the hypothesis that Vim regulates the aggregation of Myo10 at the tips of cell extensions, which increases membrane-type 1 matrix metalloproteinase (MT1-MMP)-associated local collagen proteolysis and ECM degradation. Analysis of CRC samples revealed colocalization of Vim with Myo10 and MT1-MMP in cell extensions adjacent to sites of collagen degradation, suggesting an association with local cell invasion. We analyzed cultured CRC cells and fibroblasts and found that Vim accelerates aggregation of Myo10 at cell tips, which increases the cell extension rate. Vim stabilizes the interaction of Myo10 with MT1-MMP, which in turn increases collagenolysis. Vim depletion reduced the aggregation of Myo10 at the cell extension tips and MT1-MMP-dependent collagenolysis. We propose that Vim interacts with Myo10, which in turn associates with MT1-MMP to facilitate the transport of these molecules to the termini of cell extensions and there enhance cancer invasion of soft connective tissues.

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.

Septin and actin contributions to endothelial cell-cell junctions and monolayer integrity

Septins in endothelial cells (ECs) have important roles supporting the integrity of the endothelial monolayer. Cell-cell junctions in EC monolayers are highly dynamic, with continuous retractions and protrusions. Depletion of septins in ECs leads to disruption of cell-cell junctions, which are composed of VE-cadherin and other junctional proteins. In EC monolayers, septins are concentrated at the plasma membrane at sites of cell-cell contact, in curved- and scallop-shaped patterns. These membrane-associated septin accumulations are located in regions of positive membrane curvature, and those regions are often associated with and immediately adjacent to actin-rich protrusions with negative membrane curvature. EC septins associate directly with plasma membrane lipids, based on findings with site-specific mutations of septins in ECs, which is consistent with biochemical and cell biological studies in other systems. Loss of septins leads to disruption of the EC monolayer, and gaps form between cells. The number and breadth of cell-cell contacts and junctions decreases, and the number and frequency of retractions, ruffles, and protrusions at cell edges also decreases. In addition, loss of septins leads to decreased amounts of F-actin at the cortical membrane, along with increased amounts of F-actin in stress fibers of the cytoplasm. Endothelial monolayer disruption from loss of septins is also associated with decreased transendothelial electric resistance (TEER) and increased levels of transendothelial migration (TEM) by immune and cancer cells, owing to the gaps in the monolayer. A current working model is that assembly of septin filaments at regions of positive membrane curvature contributes to a mechanical footing or base for actin-based protrusive forces generated at adjoining regions of the membrane. Specific molecular interactions between the septin and actin components of the cytoskeleton may also be important contributors. Regulators of actin assembly may promote and support the assembly of septin filaments at the membrane, as part of a molecular feedback loop between the assembly of septin and actin filaments.

Anti-vimentin antibodies are associated with higher severity of Sjögren's disease

Vimentin is a ubiquitously present Type III intermediate filament protein, often targeted by autoimmune responses in multiple rheumatic disorders. Although previous studies have reported anti-vimentin antibodies in Sjögren's disease (SjD) patients, the clinical significance of such antibodies is unknown. To address this issue, the presence of anti-vimentin antibodies was determined in serum samples from a well-characterized cohort of primary SjD patients, non-SjD Sicca, and healthy controls. The occurrence of anti-vimentin antibodies and their association with different clinical features of the disease were evaluated. Anti-vimentin antibodies were detected in 24% of primary SjD patients, compared to 4% in non-SjD sicca patients and 3% in healthy controls. In primary SjD patients, higher levels of anti-vimentin antibodies were significantly associated with reduced saliva and tear flow and severe ocular surface damage indicators. The anti-vimentin antibody levels did not show significant associations with the presence or absence of other autoantibodies like ANA, RF, and anti-Ro/La. Our data suggest that the anti-vimentin antibody specificity arises in a subset of primary SjD patients and is associated with oral and ocular features of the disease. Anti-vimentin can potentially serve as a novel biomarker for evaluating the severity of salivary and lacrimal gland dysfunction in primary SjD.

A novel interaction between extracellular vimentin and fibrinogen in fibrin formation

INTRODUCTION

Thrombosis is frequently manifested in critically ill patients with systemic inflammation, including sepsis and COVID-19. The coagulopathy in systemic inflammation is often associated with increased levels of fibrinogen and D-dimer. Because elevated levels of vimentin have been detected in sepsis, we sought to investigate the relationship between vimentin and the increased fibrin formation potential observed in these patients.

MATERIALS AND METHODS

This hypothesis was examined by using recombinant human vimentin, anti-vimentin antibodies, plasma derived from healthy and critically ill patients, confocal microscopy, co-immunoprecipitation assays, and size exclusion chromatography.

RESULTS

The level of vimentin in plasma derived from critically ill subjects with systemic inflammation was on average two-fold higher than that of healthy volunteers. We determined that vimentin directly interacts with fibrinogen and enhances fibrin formation. Anti-vimentin antibody effectively blocked fibrin formation ex vivo and caused changes in the fibrin structure in plasma. Additionally, confocal imaging demonstrated plasma vimentin enmeshed in the fibrin fibrils. Size exclusion chromatography column and co-immunoprecipitation assays demonstrated a direct interaction between extracellular vimentin and fibrinogen in plasma from critically ill patients but not in healthy plasma.

CONCLUSIONS

The results describe that extracellular vimentin engages fibrinogen in fibrin formation. In addition, the data suggest that elevated levels of an apparent aberrant extracellular vimentin potentiate fibrin clot formation in critically ill patients with systemic inflammation; consistent with the notion that plasma vimentin contributes to the pathogenesis of thrombosis.

Interoperability of RTN1A in dendrite dynamics and immune functions in human Langerhans cells

Skin is an active immune organ where professional antigen-presenting cells such as epidermal Langerhans cells (LCs) link innate and adaptive immune responses. While Reticulon 1A (RTN1A) was recently identified in LCs and dendritic cells in cutaneous and lymphoid tissues of humans and mice, its function is still unclear. Here, we studied the involvement of this protein in cytoskeletal remodeling and immune responses toward pathogens by stimulation of Toll-like receptors (TLRs) in resident LCs (rLCs) and emigrated LCs (eLCs) in human epidermis ex vivo and in a transgenic THP-1 RTN1A+ cell line. Hampering RTN1A functionality through an inhibitory antibody induced significant dendrite retraction of rLCs and inhibited their emigration. Similarly, expression of RTN1A in THP-1 cells significantly altered their morphology, enhanced aggregation potential, and inhibited the Ca2+ flux. Differentiated THP-1 RTN1A+ macrophages exhibited long cell protrusions and a larger cell body size in comparison to wild-type cells. Further, stimulation of epidermal sheets with bacterial lipoproteins (TLR1/2 and TLR2 agonists) and single-stranded RNA (TLR7 agonist) resulted in the formation of substantial clusters of rLCs and a significant decrease of RTN1A expression in eLCs. Together, our data indicate involvement of RTN1A in dendrite dynamics and structural plasticity of primary LCs. Moreover, we discovered a relation between activation of TLRs, clustering of LCs, and downregulation of RTN1A within the epidermis, thus indicating an important role of RTN1A in LC residency and maintaining tissue homeostasis.

Extracellular vimentin mimics VEGF and is a target for anti-angiogenic immunotherapy

Anti-angiogenic cancer therapies possess immune-stimulatory properties by counteracting pro-angiogenic molecular mechanisms. We report that tumor endothelial cells ubiquitously overexpress and secrete the intermediate filament protein vimentin through type III unconventional secretion mechanisms. Extracellular vimentin is pro-angiogenic and functionally mimics VEGF action, while concomitantly acting as inhibitor of leukocyte-endothelial interactions. Antibody targeting of extracellular vimentin shows inhibition of angiogenesis in vitro and in vivo. Effective and safe inhibition of angiogenesis and tumor growth in several preclinical and clinical studies is demonstrated using a vaccination strategy against extracellular vimentin. Targeting vimentin induces a pro-inflammatory condition in the tumor, exemplified by induction of the endothelial adhesion molecule ICAM1, suppression of PD-L1, and altered immune cell profiles. Our findings show that extracellular vimentin contributes to immune suppression and functions as a vascular immune checkpoint molecule. Targeting of extracellular vimentin presents therefore an anti-angiogenic immunotherapy strategy against cancer.

The pro-tumorigenic effects of vimentin have been attributed to intracellular functions in tumour cells so far. Here, the authors show that tumour endothelial cells can secrete vimentin as a pro-angiogenic factor and that targeting of vimentin can be used as an immunotherapeutic strategy.

Serum vimentin predicts mortality in pediatric severe sepsis: A prospective observational study

OBJECTIVES

Vascular hyperpermeability by loss of endothelial barrier integrity is a hallmark of sepsis. Vimentin is involved in the regulation of the endothelial function and inflammatory response. However, the serum level of vimentin and its clinical relevance in pediatric severe sepsis (PSS) remain unknown.

METHODS

We conducted a prospective study of PSS cases who were admitted to the pediatric intensive care unit (PICU) from January 2018 to December 2020.

RESULTS

A total of 108 patients with PSS with a median age of 19.5 month were enrolled. The hospital mortality rate was 19.44% (21/108). Comparing with healthy controls, serum vimentin levels on PICU admission were significantly higher in patients with PSS (P < 0.001). The area under the ROC curve for vimentin to predict the hospital mortality was 0.712 (95% CI: 0.578-846) with a sensitivity of 71.43% and a specificity of 70.11%. Moreover, hospital mortality was significantly higher in patients with vimentin level over the cutoff value of 24.53 ng/ml than in patients with vimentin level below 24.53 ng/ml (P < 0.001).

CONCLUSIONS

Serum vimentin level as an indicator of endothelial injury is associated with the prognosis of PSS, and serum vimentin level ≥24.53 ng/ml on PICU admission predicts high risk for hospital mortality in PSS.

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.

The "Third Violin" in the Cytoskeleton Orchestra-The Role of Intermediate Filaments in the Endothelial Cell's Life

The endothelium plays an important role in the transcytosis of lipoproteins. According to one of the theories, endothelial injury is a triggering factor for the development of atherosclerosis, and intracellular structures, including components of the endotheliocyte cytoskeleton (microtubules, actin, and intermediate filaments), are involved in its development. In contrast to the proteins of tubulin-based microtubules and actin microfilaments, intermediate filaments are comprised of various tissue-specific protein members. Vimentin, the main protein of endothelial intermediate filaments, is one of the most well-studied of these and belongs to type-III intermediate filaments, commonly found in cells of mesenchymal origin. Vimentin filaments are linked mechanically or by signaling molecules to microfilaments and microtubules by which coordinated cell polarisation and migration are carried out, as well as control over several endotheliocyte functions. Moreover, the soluble vimentin acts as an indicator of the state of the cardiovascular system, and the involvement of vimentin in the development and course of atherosclerosis has been demonstrated. Here we discuss current concepts of the participation of vimentin filaments in the vital activity and functioning of endothelial cells, as well as the role of vimentin in the development of inflammatory processes and atherosclerosis.

Extracellular vimentin is an attachment factor that facilitates SARS-CoV-2 entry into human endothelial cells

SARS-CoV-2 entry into host cells is a crucial step for virus tropism, transmission, and pathogenesis. Angiotensin-converting enzyme 2 (ACE2) has been identified as the primary entry receptor for SARS-CoV-2; however, the possible involvement of other cellular components in the viral entry has not yet been fully elucidated. Here we describe the identification of vimentin (VIM), an intermediate filament protein widely expressed in cells of mesenchymal origin, as an important attachment factor for SARS-CoV-2 on human endothelial cells. Using liquid chromatography-tandem mass spectrometry, we identified VIM as a protein that binds to the SARS-CoV-2 spike (S) protein. We showed that the S-protein receptor binding domain (RBD) is sufficient for S-protein interaction with VIM. Further analysis revealed that extracellular VIM binds to SARS-CoV-2 S-protein and facilitates SARS-CoV-2 infection, as determined by entry assays performed with pseudotyped viruses expressing S and with infectious SARS-CoV-2. Coexpression of VIM with ACE2 increased SARS-CoV-2 entry in HEK-293 cells, and shRNA-mediated knockdown of VIM significantly reduced SARS-CoV-2 infection of human endothelial cells. Moreover, incubation of A549 cells expressing ACE2 with purified VIM increased pseudotyped SARS-CoV-2-S entry. CR3022 antibody, which recognizes a distinct epitope on SARS-CoV-2-S-RBD without interfering with the binding of the spike with ACE2, inhibited the binding of VIM with CoV-2 S-RBD, and neutralized viral entry in human endothelial cells, suggesting a key role for VIM in SARS-CoV-2 infection of endothelial cells. This work provides insight into the pathogenesis of COVID-19 linked to the vascular system, with implications for the development of therapeutics and vaccines.

Vimentin as a Cap of Invisibility: Proposed Role of Vimentin in Rabbit Hemorrhagic Disease Virus (RHDV) Infection

Vimentin is an intermediate filament, a cytoskeleton protein expressed mainly in cells of mesenchymal origin. Increasing evidence indicates that vimentin could play a key role in viral infections. Therefore, changes in tissue and extracellular vimentin expression and associated signal trails may determine/protect the fate of cells and the progression of disease caused by viral infection. Rabbit hemorrhagic disease virus (RHDV), genotype GI.1, is an etiological agent that causes a severe and highly lethal disease—RHD (rabbit hemorrhagic disease). This article evaluates the gene and protein expression of vimentin in the tissues (liver, lungs, spleen, and kidneys) and serum of rabbits experimentally infected with two RHDV variants (GI.1a). The VIM mRNA expression levels in the tissues were determined using reverse transcription quantitative real-time PCR (RT-qPCR). In addition, the amount of vimentin protein in the serum was analyzed by an ELISA test. We observed significantly elevated expression levels of VIM mRNA and protein in the liver and kidney tissues of infected rather than healthy rabbits. In addition, VIM mRNA expression was increased in the lung tissues; meanwhile, we observed only protein-enhanced vimentin in the spleen. The obtained results are significant and promising, as they indicate the role of vimentin in RHDV infection and the course of RHD. The role of vimentin in RHDV infection could potentially rely on the one hand, on creating a cap of invisibility against the intracellular viral spread, or, on the other hand, after the damage of cells, vimentin could act as a signal of tissue damage.

Role of Intermediate Filaments in Blood-Brain Barrier in Health and Disease

The blood–brain barrier (BBB) is a highly selective cellular monolayer unique to the microvasculature of the central nervous system (CNS), and it mediates the communication of the CNS with the rest of the body by regulating the passage of molecules into the CNS microenvironment. Limitation of passage of substances through the BBB is mainly due to tight junctions (TJ) and adherens junctions (AJ) between brain microvascular endothelial cells. The importance of actin filaments and microtubules in establishing and maintaining TJs and AJs has been indicated; however, recent studies have shown that intermediate filaments are also important in the formation and function of cell–cell junctions. The most common intermediate filament protein in endothelial cells is vimentin. Vimentin plays a role in blood–brain barrier permeability in both cell–cell and cell–matrix interactions by affecting the actin and microtubule reorganization and by binding directly to VE-cadherin or integrin proteins. The BBB permeability increases due to the formation of stress fibers and the disruption of VE–cadherin interactions between two neighboring cells in various diseases, disrupting the fiber network of intermediate filament vimentin in different ways. Intermediate filaments may be long ignored key targets in regulation of BBB permeability in health and disease.

Vimentin regulates the assembly and function of matrix adhesions

The intermediate filament protein vimentin is a widely used phenotypic marker for identifying cells of the mesenchymal linkage such as fibroblasts and myofibroblasts, but the full repertoire of vimentin's functional attributes has not been fully explored. Here we consider how vimentin, in addition to its contributions to mechanical stabilization of cell structure, also helps to control the assembly of cell adhesions and migration through collagen matrices. While the assembly and function of matrix adhesions are critical for the differentiation of myofibroblasts and many other types of adherent cells, a potential mechanism that explains how vimentin affects the recruitment and abundance of centrally important proteins in cell adhesions has been elusive. Here we review recent data indicating that vimentin plays a central regulatory role in the assembly of focal adhesions which form in response to the attachment to collagen. We show that in particular, vimentin is a key organizer of the β1 integrin adhesive machinery, which affects cell migration through collagen. This review provides a comprehensive picture of the surprisingly broad array of processes and molecules with which vimentin interacts to affect cell function in the context of fibroblast and myofibroblast adhesion and migration on collagen.

CD44 and Tumor-Derived Extracellular Vesicles (TEVs). Possible Gateway to Cancer Metastasis

Cancer metastasis, the final stage of tumor progression, is a complex process governed by the interplay of multiple types of cells and the tumor microenvironment. One of the aspects of this interplay involves the release of various factors by the tumor cells alone or by forcing other cells to do so. As a consequence of these actions, tumor cells are prepared in favorable conditions for their dissemination and spread to other sites/organs, which guarantees their escape from immunosurveillance and further progression. Tumor-derived extracellular vesicles (TEVs) represent a heterogeneous population of membrane-bound vesicles that are being actively released by different tumors. The array of proteins (i.e., receptors, cytokines, chemokines, etc.) and nucleic acids (i.e., mRNA, miR, etc.) that TEVs can transfer to other cells is often considered beneficial for the tumor’s survival and proliferation. One of the proteins that is associated with many different tumors as well as their TEVs is a cluster of differentiation 44 in its standard (CD44s) and variant (CD44v) form. This review covers the present information regarding the TEVs-mediated CD44s/CD44v transfer/interaction in the context of cancer metastasis. The content and the impact of the transferred cargo by this type of TEVs also are discussed with regards to tumor cell dissemination.

Mechanical and Non-Mechanical Functions of Filamentous and Non-Filamentous Vimentin

Intermediate filaments (IFs) formed by vimentin are less understood than their cytoskeletal partners, microtubules and F-actin, but the unique physical properties of IFs, especially their resistance to large deformations, initially suggest a mechanical function. Indeed, vimentin IFs help regulate cell mechanics and contractility, and in crowded 3D environments they protect the nucleus during cell migration. Recently, a multitude of studies, often using genetic or proteomic screenings show that vimentin has many non-mechanical functions within and outside of cells. These include signaling roles in wound healing, lipogenesis, sterol processing, and various functions related to extracellular and cell surface vimentin. Extracellular vimentin is implicated in marking circulating tumor cells, promoting neural repair, and mediating the invasion of host cells by viruses, including SARS-CoV, or bacteria such as Listeria and Streptococcus. These findings underscore the fundamental role of vimentin in not only cell mechanics but also a range of physiological functions. Also see the video abstract here https://youtu.be/YPfoddqvz-g.

Single-Cell Profiling of AKI in a Murine Model Reveals Novel Transcriptional Signatures, Profibrotic Phenotype, and Epithelial-to-Stromal Crosstalk

BACKGROUND

Current management of AKI, a potentially fatal disorder that can also initiate or exacerbate CKD, is merely supportive. Therefore, deeper understanding of the molecular pathways perturbed in AKI is needed to identify targets with potential to lead to improved treatment.

METHODS

We performed single-cell RNA sequencing (scRNA-seq) with the clinically relevant unilateral ischemia-reperfusion murine model of AKI at days 1, 2, 4, 7, 11, and 14 after AKI onset. Using real-time quantitative PCR, immunofluorescence, Western blotting, and both chromogenic and single-molecule in situ hybridizations, we validated AKI signatures in multiple experiments.

RESULTS

Our findings show the time course of changing gene expression patterns for multiple AKI stages and all renal cell types. We observed elevated expression of crucial injury response factors-including kidney injury molecule-1 (Kim1), lipocalin 2 (Lcn2), and keratin 8 (Krt8)-and of several novel genes (Ahnak, Sh3bgrl3, and Col18a1) not previously examined in kidney pathologies. AKI induced proximal tubule dedifferentiation, with a pronounced nephrogenic signature represented by Sox4 and Cd24a. Moreover, AKI caused the formation of "mixed-identity cells" (expressing markers of different renal cell types) that are normally seen only during early kidney development. The injured tubules acquired a proinflammatory and profibrotic phenotype; moreover, AKI dramatically modified ligand-receptor crosstalk, with potential pathologic epithelial-to-stromal interactions. Advancing age in AKI onset was associated with maladaptive response and kidney fibrosis.

CONCLUSIONS

The scRNA-seq, comprehensive, cell-specific profiles provide a valuable resource for examining molecular pathways that are perturbed in AKI. The results fully define AKI-associated dedifferentiation programs, potential pathologic ligand-receptor crosstalk, novel genes, and the improved injury response in younger mice, and highlight potential targets of kidney injury.

Vimentin as a Multifaceted Player and Potential Therapeutic Target in Viral Infections

Vimentin is an intermediate filament protein that plays key roles in integration of cytoskeletal functions, and therefore in basic cellular processes such as cell division and migration. Consequently, vimentin has complex implications in pathophysiology. Vimentin is required for a proper immune response, but it can also act as an autoantigen in autoimmune diseases or as a damage signal. Although vimentin is a predominantly cytoplasmic protein, it can also appear at extracellular locations, either in a secreted form or at the surface of numerous cell types, often in relation to cell activation, inflammation, injury or senescence. Cell surface targeting of vimentin appears to associate with the occurrence of certain posttranslational modifications, such as phosphorylation and/or oxidative damage. At the cell surface, vimentin can act as a receptor for bacterial and viral pathogens. Indeed, vimentin has been shown to play important roles in virus attachment and entry of severe acute respiratory syndrome-related coronavirus (SARS-CoV), dengue and encephalitis viruses, among others. Moreover, the presence of vimentin in specific virus-targeted cells and its induction by proinflammatory cytokines and tissue damage contribute to its implication in viral infection. Here, we recapitulate some of the pathophysiological implications of vimentin, including the involvement of cell surface vimentin in interaction with pathogens, with a special focus on its role as a cellular receptor or co-receptor for viruses. In addition, we provide a perspective on approaches to target vimentin, including antibodies or chemical agents that could modulate these interactions to potentially interfere with viral pathogenesis, which could be useful when multi-target antiviral strategies are needed.

Extracellular Vimentin/VWF (von Willebrand Factor) Interaction Contributes to VWF String Formation and Stroke Pathology

Background and Purpose- VWF (von Willebrand factor) strings mediate spontaneous platelet adhesion in the vascular lumen, which may lead to microthrombi formation and contribute to stroke pathology. However, the mechanism of VWF string attachment at the endothelial surface is unknown. We tested the novel hypothesis that VWF strings are tethered to the endothelial surface through an interaction between extracellular vimentin and the A2 domain of VWF. We further explored the translational value of blocking this interaction in a model of ischemic stroke. Methods- Human endothelial cells and pressurized cerebral arteries were stimulated with histamine to elicit VWF string formation. Recombinant proteins and antibodies were used to block VWF string formation. Mice underwent transient middle cerebral artery occlusion with reperfusion. Just before recanalization, mice were given either vehicle or A2 protein (recombinant VWF A2 domain) to disrupt the vimentin/VWF interaction. Laser speckle contrast imaging was used to monitor cortical perfusion. Results- Pressurized cerebral arteries produced VWF strings following histamine stimulation, which were reduced in arteries from Vim KO (vimentin knockout) mice. VWF string formation was significantly reduced in endothelial cells incubated with A2 protein or antivimentin antibodies. Lastly, A2 protein treatment significantly improved cortical reperfusion after middle cerebral artery occlusion. Conclusions- We provide the first direct evidence of cerebral VWF strings and demonstrate that extracellular vimentin significantly contributes to VWF string formation via A2 domain binding. Lastly, we show that pharmacologically targeting the vimentin/VWF interaction through the A2 domain can promote improved reperfusion after ischemic stroke. Together, these studies demonstrate the critical role of VWF strings in stroke pathology and offer new therapeutic targets for treatment of ischemic stroke.

A versatile theranostic nanoplatform based on mesoporous silica

A versatile of mesoporous silica is designed and operated, including ion doping, surface modify and pore adsorption, based on aqueous well-dispersed. Thus, a multifunctional theranostic nanoplatform is obtained through endowing some functional materials. Detailedly, Gd ions is introduced to mesoporous silica (GM nanoparticles) via a co-assemble process, which is used as prime carrier with MRI. Furthermore, the surface graft of hyaluronic acid (HA) molecule makes contribution to lymph system-targeted delivery (GMH nanoparticles). Additionally, the introduction of functional molecules including Iopamidol (IGMH nanoparticles) and DOX (DGMH nanoparticles) could combine the diagnosis and therapy with CT and sustained drug release. We present evidence that the IGMH and DGMH nanoparticles are highly targeted to lymph system in vitro and in vivo, and highlight CT and MR imaging of IGMH nanoparticles in lymph system, and chemotherapy and MR imaging of DGMH nanoparticles in lymph cancer. Our results provide a new universal manufacture for mesoporous silica to obtain a multifunctional theranostic nanoplatform, has great potential for use in biological applications.

A Binding Potency Assay for Pritumumab and Ecto-Domain Vimentin

Pritumumab, a natural human IgG1kappa mAb, was isolated from the regional lymph node of a patient with cervical cancer. This antibody has been reported to bind the cytoskeletal protein vimentin, and to cell surface expressed vimentin referred to as ecto-domain vimentin (EDV). Here, we report details of the development of a potency of binding assay for pritumumab as a prerequisite before pursuing clinical trials. The enzyme linked immunosorbent assay (ELISA) to detect antibody-binding antigen can serve as a potency assay for release of manufactured samples to be used in clinical studies. Several layers of controls for this assay along with suitability testing for reagents and components of the assay must be developed before the assay can be incorporated for stability testing and release of manufatured samples.

Vimentin Diversity in Health and Disease

Vimentin is a protein that has been linked to a large variety of pathophysiological conditions, including cataracts, Crohn's disease, rheumatoid arthritis, HIV and cancer. Vimentin has also been shown to regulate a wide spectrum of basic cellular functions. In cells, vimentin assembles into a network of filaments that spans the cytoplasm. It can also be found in smaller, non-filamentous forms that can localise both within cells and within the extracellular microenvironment. The vimentin structure can be altered by subunit exchange, cleavage into different sizes, re-annealing, post-translational modifications and interacting proteins. Together with the observation that different domains of vimentin might have evolved under different selection pressures that defined distinct biological functions for different parts of the protein, the many diverse variants of vimentin might be the cause of its functional diversity. A number of review articles have focussed on the biology and medical aspects of intermediate filament proteins without particular commitment to vimentin, and other reviews have focussed on intermediate filaments in an in vitro context. In contrast, the present review focusses almost exclusively on vimentin, and covers both ex vivo and in vivo data from tissue culture and from living organisms, including a summary of the many phenotypes of vimentin knockout animals. Our aim is to provide a comprehensive overview of the current understanding of the many diverse aspects of vimentin, from biochemical, mechanical, cellular, systems biology and medical perspectives.

In wound repair vimentin mediates the transition of mesenchymal leader cells to a myofibroblast phenotype

Following injury, mesenchymal repair cells are activated to function as leader cells that modulate wound healing. These cells have the potential to differentiate to myofibroblasts, resulting in fibrosis and scarring. The signals underlying these differing pathways are complex and incompletely understood. The ex vivo mock cataract surgery cultures are an attractive model with which to address this question. With this model we study, concurrently, the mechanisms that control mesenchymal leader cell function in injury repair within their native microenvironment and the signals that induce this same cell population to acquire a myofibroblast phenotype when these cells encounter the environment of the adjacent tissue culture platform. Here we show that on injury, the cytoskeletal protein vimentin is released into the extracellular space, binds to the cell surface of the mesenchymal leader cells located at the wound edge in the native matrix environment, and supports wound closure. In profibrotic environments, the extracellular vimentin pool also links specifically to the mesenchymal leader cells and has an essential role in signaling their fate change to a myofibroblast. These findings suggest a novel role for extracellular, cell-surface–associated vimentin in mediating repair-cell function in wound repair and in transitioning these cells to a myofibroblast phenotype.

Matrix stiffness modulates infection of endothelial cells by Listeria monocytogenes via expression of cell surface vimentin

Extracellular matrix stiffness (ECM) is one of the many mechanical forces acting on mammalian adherent cells and an important determinant of cellular function. While the effect of ECM stiffness on many aspects of cellular behavior has been studied previously, how ECM stiffness might mediate susceptibility of host cells to infection by bacterial pathogens is hitherto unexplored. To address this open question, we manufactured hydrogels of varying physiologically relevant stiffness and seeded human microvascular endothelial cells (HMEC-1) on them. We then infected HMEC-1 with the bacterial pathogen Listeria monocytogenes (Lm) and found that adhesion of Lm to host cells increases monotonically with increasing matrix stiffness, an effect that requires the activity of focal adhesion kinase (FAK). We identified cell surface vimentin as a candidate surface receptor mediating stiffness-dependent adhesion of Lm to HMEC-1 and found that bacterial infection of these host cells is decreased when the amount of surface vimentin is reduced. Our results provide the first evidence that ECM stiffness can mediate the susceptibility of mammalian host cells to infection by a bacterial pathogen.

Recombinant Human Vimentin Binds to P-Selectin and Blocks Neutrophil Capture and Rolling on Platelets and Endothelium

Leukocyte adhesion to vascular endothelium and platelets is an early step in the acute inflammatory response. The initial process is mediated through P-selectin glycoprotein ligand-1 (PSGL-1) on leukocytes binding to platelets adhered to endothelium and the endothelium itself via P-selectin. Although these interactions are generally beneficial, pathologic inflammation may occur in undesirable circumstances, such as in acute lung injury (ALI) and ischemia and reperfusion injury. Therefore, the development of novel therapies to attenuate inflammation may be beneficial. In this article, we describe the potential benefit of using a recombinant human vimentin (rhVim) on reducing human leukocyte adhesion to vascular endothelium and platelets under shear stress. The addition of rhVim to whole blood and isolated neutrophils decreased leukocyte adhesion to endothelial and platelet monolayers. Furthermore, rhVim blocked neutrophil adhesion to P-selectin-coated surfaces. Binding assays showed that rhVim binds specifically to P-selectin and not to its counterreceptor, PSGL-1. Finally, in an endotoxin model of ALI in C57BL/6J mice, treatment with rhVim significantly decreased histologic findings of ALI. These data suggest a potential role for rhVim in attenuating inflammation through blocking P-selectin-PSGL-1 interactions.

Osteopontin promotes epithelial-mesenchymal transition of hepatocellular carcinoma through regulating vimentin

Our previous studies have found that osteopontin (OPN) is a promoter for hepatocellular carcinoma (HCC) progression. However, the molecular mechanism by which OPN enhances HCC metastasis remains elusive. Epithelial-mesenchymal transition (EMT) of cancer cells plays a pivotal role in promoting metastatic process. In this study, we demonstrated that OPN promotes HCC metastasis by inducing an EMT-like, more aggressive cellular phenotype in vitro and in vivo. Furthermore, OPN was identified to interact with vimentin by reciprocal OPN and vimentin immunoprecipitation as well as co-immunofluorescence examination. By using deletion mutants, we found that the residues between 246 and 406 in vimentin are required for binding to OPN. Importantly, OPN significantly increased vimentin stability through inhibition of its protein degradation. Knockdown of vimentin neutralized the EMT induced by OPN both in vitro and in vivo. Moreover, a significant correlation between OPN and vimentin levels was found in clinical HCC specimens and their combination had a worse prognosis with shorter overall survival (OS) and time to recurrence (TTR). In multivariate analysis, OPN and their combination were demonstrated to be independent prognostic indicators for OS and TTR of HCC patients. Collectively, this study indicates that OPN can induce EMT of HCC cells through increasing vimentin stability, which provides more in-depth understanding about the molecular mechanisms of OPN in promoting HCC metastasis and opens tantalizing therapeutic possibilities in HCC.

A Consensus Definitive Classification of Scavenger Receptors and Their Roles in Health and Disease

Scavenger receptors constitute a large family of proteins that are structurally diverse and participate in a wide range of biological functions. These receptors are expressed predominantly by myeloid cells and recognize a diverse variety of ligands including endogenous and modified host-derived molecules and microbial pathogens. There are currently eight classes of scavenger receptors, many of which have multiple names, leading to inconsistencies and confusion in the literature. To address this problem, a workshop was organized by the United States National Institute of Allergy and Infectious Diseases, National Institutes of Health, to help develop a clear definition of scavenger receptors and a standardized nomenclature based on that definition. Fifteen experts in the scavenger receptor field attended the workshop and, after extensive discussion, reached a consensus regarding the definition of scavenger receptors and a proposed scavenger receptor nomenclature. Scavenger receptors were defined as cell surface receptors that typically bind multiple ligands and promote the removal of nonself or altered-self targets. They often function by mechanisms that include endocytosis, phagocytosis, adhesion, and signaling that ultimately lead to the elimination of degraded or harmful substances. Based on this definition, nomenclature and classification of these receptors into 10 classes were proposed. This classification was discussed at three national meetings and input from participants at these meetings was requested. The following manuscript is a consensus statement that combines the recommendations of the initial workshop and incorporates the input received from the participants at the three national meetings.

The Rho ADP-ribosylating C3 exoenzyme binds cells via an Arg-Gly-Asp motif

The Rho ADP-ribosylating C3 exoenzyme (C3bot) is a bacterial protein toxin devoid of a cell-binding or -translocation domain. Nevertheless, C3 can efficiently enter intact cells, including neurons, but the mechanism of C3 binding and uptake is not yet understood. Previously, we identified the intermediate filament vimentin as an extracellular membranous interaction partner of C3. However, uptake of C3 into cells still occurs (although reduced) in the absence of vimentin, indicating involvement of an additional host cell receptor. C3 harbors an Arg–Gly–Asp (RGD) motif, which is the major integrin-binding site, present in a variety of integrin ligands. To check whether the RGD motif of C3 is involved in binding to cells, we performed a competition assay with C3 and RGD peptide or with a monoclonal antibody binding to β1-integrin subunit and binding assays in different cell lines, primary neurons, and synaptosomes with C3-RGD mutants. Here, we report that preincubation of cells with the GRGDNP peptide strongly reduced C3 binding to cells. Moreover, mutation of the RGD motif reduced C3 binding to intact cells and also to recombinant vimentin. Anti-integrin antibodies also lowered the C3 binding to cells. Our results indicate that the RGD motif of C3 is at least one essential C3 motif for binding to host cells and that integrin is an additional receptor for C3 besides vimentin.

Analysis of tick-borne encephalitis virus-induced host responses in human cells of neuronal origin and interferon-mediated protection

Tick-borne encephalitis virus (TBEV) is a member of the genus Flavivirus. It can cause serious infections in humans that may result in encephalitis/meningoencephalitis. Although several studies have described the involvement of specific genes in the host response to TBEV infection in the central nervous system (CNS), the overall network remains poorly characterized. Therefore, we investigated the response of DAOY cells (human medulloblastoma cells derived from cerebellar neurons) to TBEV (Neudoerfl strain, Western subtype) infection to characterize differentially expressed genes by transcriptome analysis. Our results revealed a wide panel of interferon-stimulated genes (ISGs) and pro-inflammatory cytokines, including type III but not type I (or II) interferons (IFNs), which are activated upon TBEV infection, as well as a number of non-coding RNAs, including long non-coding RNAs. To obtain a broader view of the pathways responsible for eliciting an antiviral state in DAOY cells we examined the effect of type I and III IFNs and found that only type I IFN pre-treatment inhibited TBEV production. The cellular response to TBEV showed only partial overlap with gene expression changes induced by IFN-β treatment - suggesting a virus-specific signature - and we identified a group of ISGs that were highly up-regulated following IFN-β treatment. Moreover, a high rate of down-regulation was observed for a wide panel of pro-inflammatory cytokines upon IFN-β treatment. These data can serve as the basis for further studies of host-TBEV interactions and the identification of ISGs and/or lncRNAs with potent antiviral effects in cases of TBEV infection in human neuronal cells.

An anti vimentin antibody promotes tube formation

In recent years, there has been an increasing appreciation of the importance of secreted and extracellular proteins that traditionally have been considered as intracellular components. Vimentin is a highly abundant intermediate filament protein, and its intracellular functions have been investigated in a large number of studies. Recently, however, vimentin has been shown to take part in significant processes outside the cell. Our understanding of the functions of extracellular vimentin is, however, limited. In this study we demonstrate that a vimentin specific antibody, obtained by phage antibody technology, promotes tube formation of endothelial cells in a 2D matrigel assay. By binding vimentin, the antibody increases the tube formation by 21% after 5 hours of incubation. Addition of the antibody directly to cultured endothelial cells does not influence endothelial cell migration or proliferation. The enhanced tube formation can be seen for up to 10 hours where after the effect decreases. It is shown that the antibody-binding site is located on the coil 2 domain of vimentin. To our knowledge this is the first study that demonstrates an enhanced tube formation by binding vimentin in a 2D matrigel assay under normoxic conditions.

Intermediate Filaments and the Plasma Membrane

A variety of intermediate filament (IF) types show intricate association with plasma membrane proteins, including receptors and adhesion molecules. The molecular basis of linkage of IFs to desmosomes at sites of cell-cell interaction and hemidesmosomes at sites of cell-matrix adhesion has been elucidated and involves IF-associated proteins. However, IFs also interact with focal adhesions and cell-surface molecules, including dystroglycan. Through such membrane interactions, it is well accepted that IFs play important roles in the establishment and maintenance of tissue integrity. However, by organizing cell-surface complexes, IFs likely regulate, albeit indirectly, signaling pathways that are key to tissue homeostasis and repair.

Anaplasma phagocytophilum-Occupied Vacuole Interactions with the Host Cell Cytoskeleton

Anaplasma phagocytophilum is an obligate intracellular bacterial pathogen of humans and animals. The A. phagocytophium-occupied vacuole (ApV) is a critical host-pathogen interface. Here, we report that the intermediate filaments, keratin and vimentin, assemble on the ApV early and remain associated with the ApV throughout infection. Microtubules localize to the ApV to a lesser extent. Vimentin, keratin-8, and keratin-18 but not tubulin expression is upregulated in A. phagocytophilum infected cells. SUMO-2/3 but not SUMO-1 colocalizes with vimentin filaments that surround ApVs. PolySUMOylation of vimentin by SUMO-2/3 but not SUMO-1 decreases vimentin solubility. Consistent with this, more vimentin exists in an insoluble state in A. phagocytophilum infected cells than in uninfected cells. Knocking down the SUMO-conjugating enzyme, Ubc9, abrogates vimentin assembly at the ApV but has no effect on the bacterial load. Bacterial protein synthesis is dispensable for maintaining vimentin and SUMO-2/3 at the ApV. Withaferin A, which inhibits soluble vimentin, reduces vimentin recruitment to the ApV, optimal ApV formation, and the bacterial load when administered prior to infection but is ineffective once vimentin has assembled on the ApV. Thus, A. phagocytophilum modulates cytoskeletal component expression and co-opts polySUMOylated vimentin to aid construction of its vacuolar niche and promote optimal survival.

Regulation of CD44E by DARPP-32-dependent activation of SRp20 splicing factor in gastric tumorigenesis

Objective

CD44E is a frequently overexpressed variant of CD44 in gastric cancer. Mechanisms that regulate CD44 splicing and expression in gastric cancer remain unknown. Herein, we investigated the role of DARPP-32 (dopamine and cAMP-regulated phosphoprotein, Mr 32000) in promoting tumor growth through regulation of CD44 splicing.

Design

Quantitative luciferase reporter, quantitative real-time RT-PCR (qRT-PCR), Western blot, co-immunoprecipitation, ubiquitination, and tumor xenograft experiments were performed.

Results

Western blot and qRT-PCR results indicated that knockdown of endogenous DARPP-32 markedly reduces expression of CD44 V8-V10 (CD44E). Using a quantitative splicing luciferase reporter system, we detected a significant increase in the reporter activity following DARPP-32 overexpression (p < 0.001). Conversely, knocking down endogenous DARPP-32 significantly attenuated the splicing activity (p < 0.001). Further experiments showed that DARPP-32 regulates the expression of SRp20 splicing factor and co-exists with it in the same protein complex. Inhibition of alternative splicing with digitoxin followed by immunoprecipitation and immunoblotting indicated that DARPP-32 plays an important role in regulating SRp20 protein stability. The knockdown of endogenous DARPP-32 confirmed that DARPP-32 regulates the SRp20-dependent CD44E splicing. Using tumor xenograft mouse model, knocking down endogenous DARPP-32 markedly reduced SRp20 and CD44E protein levels with a decreased tumor growth. The reconstitution of SRp20 expression in these cells rescued tumor growth. In addition, we also demonstrated frequent co-overexpression and positive correlation of DARPP-32, SRp20 and CD44E expression levels in human gastric primary tumors.

Conclusion

Our novel findings establish for the first time the role of DARPP-32 in regulating splicing factors in gastric cancer cells. The DARPP-32–SRp20 axis plays a key role in regulating the CD44E splice variant that promotes gastric tumorigenesis.

A recombinant fragment of von Willebrand factor reduces fibrin-rich microthrombi formation in mice with endotoxemia

INTRODUCTION

Disseminated fibrin deposition in the microvasculature such as in disseminated intravascular coagulation (DIC) arises from uninhibited activated coagulation secondary to sustained systemic inflammation. Currently there is no treatment for DIC. Treating the underlying trigger and supportive care are the current recommendations to manage DIC. This study aims at using recombinant von Willebrand factor (VWF) A2 domain polypeptide to inhibit VWF-mediated platelet adhesion to fibrin and prevent DIC.

MATERIALS AND METHODS

We use flow chamber assay to test the capacity of purified A2 protein to inhibit platelet adhesion to immobilized fibrin(ogen) and platelet-fibrin clot formation. We use a murine model of lipopolysaccharide-induced DIC to examine the effect of A2 protein on DIC.

RESULTS

The A2 protein blocked flow-dependent platelet adhesion to fibrin, delayed fibrin polymerization, and inhibited platelet-fibrin clot formation in vitro. The infusion of the purified A2 protein to the endotoxin-treated mice prevented fibrin-rich microthrombi formation in brain, lung, kidney, and liver. It also attenuated levels of inflammatory mediators, and markedly reduced mortality rates at 96hours.

CONCLUSIONS

The A2 protein inhibited platelet interaction with fibrin(ogen). Furthermore, A2 prevented disseminated fibrin-rich microthrombi and decrease mortality in a lipopolysaccharide-induced DIC murine model. A2 could provide a novel therapeutic approach in critically ill patients with uninhibited activated coagulation and disseminated fibrin deposition such as DIC.

Platelet adhesion involves a novel interaction between vimentin and von Willebrand factor under high shear stress

The interaction between platelet receptor glycoprotein Ibα and the A1 domain of von Willebrand factor (VWF) mediates tethering/translocation of platelets to sites of vascular injury. Unexpectedly, we observed platelets translocating over A1A2A3 domains protein slower than on A1 domain at high shear stress. This observation suggests an additional interaction between A domains and an adhesive receptor. We investigated vimentin because we have data showing the interaction of vimentin with the A2 domain of VWF. Moreover, vimentin is expressed on the platelet surface. This novel interaction was analyzed by using purified VWF, recombinant proteins, anti-vimentin antibodies, parallel flow chamber adhesion assays, flow cytometry, and vimentin-deficient murine platelets. The active form of VWF bound to vimentin, and the purified A2 domain blocked that binding. The interaction of a gain-of-function A1A2A3 mutant with platelet was reduced using anti-vimentin antibody. Platelet adhesion to wild-type (WT) A1A2A3 protein, collagen, and fibrin(ogen) was inhibited (32-75%) by anti-vimentin antibody under high shear stress. Compared with WT mice, platelets from vimentin-deficient mice had a reduced flow-dependent adhesion to both collagen and purified murine VWF. Last, the vimentin knockout mice had a prolonged tail bleeding time. The results describe that platelet vimentin engages VWF during platelet adhesion under high shear stress.

Purification, characterization and plasma half-life of PEGylated soluble recombinant non-HA-binding CD44

BACKGROUND AND OBJECTIVES

The aim of this study was to increase the serum half-life of recombinant CD44 hyaluronan (HA) binding domain by PEGylation. We have previously found that recombinant soluble CD44 HA binding domain (CD44HABD) and its non-HA-binding triple mutant CD44HABD(R41AY78SY79S) (CD44-3MUT) inhibits angiogenesis and subcutaneous tumor growth. However, this ~12 kDa recombinant protein displays a high serum clearance rate.

METHODS

Here, we report the purification of monomeric CD44-3MUT from urea solubilized inclusion bodies using weak anion exchange chromatography and gel filtration. To increase the serum residence time of CD44-3MUT we PEGylated the resulting protein using 20 kDa methoxy-PEG-propionaldehyde.

RESULTS

PEGylation of CD44-3MUT prolonged its in vivo serum half-life about 70-fold from 0.03 to 1.8 hours. Along with extended plasma residence time, PEGylation also increased the systemic exposure. By cell impedance assay we confirmed that PEGylated CD44-3MUT maintained its in vitro function. The results from the impedance assay additionally demonstrate that the CD44-3MUT effect on endothelial cells is mediated by vimentin.

CONCLUSIONS

In summary, we have developed a purification protocol for large-scale production of CD44-3MUT and generated a PEGylated form of CD44-3MUT. HA binding domain of CD44(CD44HABD) and its modified non-HA binding form (CD44-3MUT) inhibit angiogenesis and tumor growth in vivo without disturbing HA-binding functions. CD44-3MUT has been PEGylated for use as a new type of anti-angiogenic human drug. PEGylation of CD44-3MUT improved pharmacokinetic properties but retains its functional activity.

Hyaluronan accumulates with high-fat feeding and contributes to insulin resistance

Increased deposition of specific extracellular matrix (ECM) components is a characteristic of insulin-resistant skeletal muscle. Hyaluronan (HA) is a major constituent of the ECM. The hypotheses that 1) HA content is increased in the ECM of insulin-resistant skeletal muscle and 2) reduction of HA in the muscle ECM by long-acting pegylated human recombinant PH20 hyaluronidase (PEGPH20) reverses high-fat (HF) diet-induced muscle insulin resistance were tested. We show that muscle HA was increased in HF diet-induced obese (DIO) mice and that treatment of PEGPH20, which dose-dependently reduced HA in muscle ECM, decreased fat mass, adipocyte size, and hepatic and muscle insulin resistance in DIO mice at 10 mg/kg. Reduced muscle insulin resistance was associated with increased insulin signaling, muscle vascularization, and percent cardiac output to muscle rather than insulin sensitization of muscle per se. Dose-response studies revealed that PEGPH20 dose-dependently increased insulin sensitivity in DIO mice with a minimally effective dose of 0.01 mg/kg. PEGPH20 at doses of 0.1 and 1 mg/kg reduced muscle HA to levels seen in chow-fed mice, decreased fat mass, and increased muscle glucose uptake. These findings suggest that ECM HA is a target for treatment of insulin resistance.

Identification of endothelial cell surface antigens encoded by genes other than HLA. A combined immunoprecipitation and proteomic approach for the identification of antigens recognized by antibodies against endothelial cells in transplant recipients

It has been known for some time that transplant recipients may have antibodies to endothelial cells which are not detected on lymphocytes. However, little progress has been made in the analysis of these endothelial antigens. In the present experiments we have attempted to characterize endothelial cell surface antigens to which antibodies were produced during graft rejection. We have used a panel of endothelial cells from umbilical cord veins and found that antibodies with a polymorphic pattern in the panel appeared to correlate with transplant failure of kidney allografts and with the development of transplant-related coronary artery disease (TCAD) in heart transplant recipients. Among 39 patients with kidney allografts, 21 were negative for antibodies to endothelial cells and did well and 18 were positive and had frequent transplant loss (p=0.001). In 18 patients with TCAD and 20 patients of a comparator group without TCAD, association of coronary disease with endothelial cell antibodies was observed (p<0.02). To characterize the endothelial antigens responsible for these serologic reactions we performed immunoprecipitation of reactive antibodies with the corresponding endothelial cell surface antigens, followed by protein identification of the target antigens. Nine proteins were identified in these experiments, 5 were non-polymorphic and appeared to represent autoantigens. Four of the isolated proteins appeared to be polymorphic. They were the Human Major Histocompatibility Complex class I chain-related gene A (MICA), already known to be associated with antibody production and graft failure, human keratin 1, a protein known to be polymorphic and expressed on the surface of endothelial cells, eukaryotic translation initiation factor (EIF) 2A and ErbB3-binding protein 1. The possible role of keratin 1 and the other antigens in allograft rejection requires further investigation.

All-thermoplastic nanoplasmonic microfluidic device for transmission SPR biosensing

Early and accurate disease diagnosis still remains a major challenge in clinical settings. Biomarkers could potentially provide useful tools for the detection and monitoring of disease progression, treatment safety and efficacy. Recent years have witnessed prodigious advancement in biosensor development with research directed towards rapid, real-time, label-free and sensitive biomarker detection. Among emerging techniques, nanoplasmonic biosensors pose tremendous potential to accelerate clinical diagnosis with real-time multiplexed analysis, rapid and miniaturized assays, low sample consumption and high sensitivity. In order to translate these technologies from the proof-of-principle concept level to point of care clinical diagnosis, integrated, portable devices having small footprint cartridges that house low-cost disposable consumables are sought. Towards this goal, we developed an all-polymeric nanoplasmonic microfluidic (NMF) transmission surface plasmon resonance (SPR) biosensor. The device was fabricated in thermoplastics using a simple, single step and cost-effective hot embossing technique amenable to mass production. The novel 3D hierarchical mold fabrication process enabled monolithic integration of blazed nanogratings within the detection chambers of a multichannel microfluidic system. Consequently, a single hard thermoplastic bottom substrate comprising plasmonic and fluidic features allowed integration of active fluidic elements, such as pneumatic valves, in the top soft thermoplastic cover, increasing device functionality. A simple and compact transmission-based optical setup was employed with multiplexed end-point or dual-channel kinetic detection capability which did not require stringent angular accuracy. The sensitivity, specificity and reproducibility of the transmission SPR biosensor was demonstrated through label-free immunodetection of soluble cell-surface glycoprotein sCD44 at clinically relevant picomolar to nanomolar concentrations.