Structure and binding mechanism of vascular endothelial cadherin: a divergent classical cadherin

Cadherin Expression Is Regulated by Mechanical Phenotypes of Fibroblasts in the Perivascular Matrix

INTRODUCTION

The influence of mechanical forces generated by stromal cells in the perivascular matrix is thought to be a key regulator in controlling blood vessel growth. Cadherins are mechanosensors that facilitate and maintain cell-cell interactions and blood vessel integrity, but little is known about how stromal cells regulate cadherin signaling in the vasculature. Our objective was to investigate the relationship between mechanical phenotypes of stromal cells with cadherin expression in 3D tissue engineering models of vascular growth.

METHODS

Stromal cell lines were subjected to a bead displacement assay to track matrix distortions and characterize mechanical phenotypes in 3D microtissue models. These cells included human ventricular cardiac (NHCF), dermal (NHDF), lung (NHLF), breast cancer-associated (CAF), and normal breast fibroblasts (NBF). Cells were embedded in a fibrin matrix (10 mg/mL) with fluorescent tracker beads; images were collected every 30 min. We also studied endothelial cells (ECs) in co-culture with mechanically active or inactive stromal cells and quantified N-Cad, OB-Cad, and VE-Cad expression using immunofluorescence.

RESULTS

Bead displacement studies identified mechanically active stromal cells (CAFs, NHCFs, NHDFs) that generate matrix distortions and mechanically inactive cells (NHLFs, NBFs). CAFs, NHCFs, and NHDFs displaced the matrix with an average magnitude of 3.17 ± 0.11 μm, 3.13 ± 0.06 μm, and 2.76 ± 0.05 μm, respectively, while NHLFs and NBFs displaced the matrix with an average of 1.82 ± 0.05 μm and 2.66 ± 0.06 μm in fibrin gels. Compared to ECs only, CAFs + ECs as well as NBFs + ECs in 3D co-culture significantly decreased expression of VE-Cad; in addition, Pearson's Correlation Coefficient for N-Cad and VE-Cad showed a strong correlation (>0.7), suggesting cadherin colocalization. Using a microtissue model, we demonstrated that mechanical phenotypes associated with increased matrix deformations correspond to enhanced angiogenic growth. The results could suggest a mechanism to control tight junction regulation in developing vascular beds for tissue engineering scaffolds or understanding vascular growth during developmental processes.

CONCLUSION

Our studies provide novel data for how mechanical phenotype of stromal cells in combination with secreted factor profiles is related to cadherin regulation, localization, and vascularization potential in 3D microtissue models.

Controlling nanoparticle-induced endothelial leakiness with the protein corona

Understanding nanoparticle-cell interaction is essential for advancing research in nanomedicine and nanotoxicology. Apart from the transcytotic pathway mediated by cellular recognition and energetics, nanoparticles (including nanomedicines) may harness the paracellular route for their transport by inducing endothelial leakiness at cadherin junctions. This phenomenon, termed as NanoEL, is correlated with the physicochemical properties of the nanoparticles in close association with cellular signalling, membrane mechanics, as well as cytoskeletal remodelling. However, nanoparticles in biological systems are transformed by the ubiquitous protein corona and yet the potential effect of the protein corona on NanoEL remains unclear. Using confocal fluorescence microscopy, biolayer interferometry, transwell, toxicity, and molecular inhibition assays, complemented by molecular docking, here we reveal the minimal to significant effects of the anionic human serum albumin and fibrinogen, the charge neutral immunoglobulin G as well as the cationic lysozyme on negating gold nanoparticle-induced endothelial leakiness in vitro and in vivo. This study suggests that nanoparticle-cadherin interaction and hence the extent of NanoEL may be partially controlled by pre-exposing the nanoparticles to plasma proteins of specific charge and topology to facilitate their biomedical applications.

Prediction of interactions between cell surface proteins by machine learning

Cells detect changes in their external environments or communicate with each other through proteins on their surfaces. These cell surface proteins form a complicated network of interactions in order to fulfill their functions. The interactions between cell surface proteins are highly dynamic and, thus, challenging to detect using traditional experimental techniques. Here, we tackle this challenge using a computational framework. The primary focus of the framework is to develop new tools to identify interactions between domains in the immunoglobulin (Ig) fold, which is the most abundant domain family in cell surface proteins. These interactions could be formed between ligands and receptors from different cells or between proteins on the same cell surface. In practice, we collected all structural data on Ig domain interactions and transformed them into an interface fragment pair library. A high-dimensional profile can then be constructed from the library for a given pair of query protein sequences. Multiple machine learning models were used to read this profile so that the probability of interaction between the query proteins could be predicted. We tested our models on an experimentally derived dataset that contains 564 cell surface proteins in humans. The cross-validation results show that we can achieve higher than 70% accuracy in identifying the PPIs within this dataset. We then applied this method to a group of 46 cell surface proteins in Caenorhabditis elegans. We screened every possible interaction between these proteins. Many interactions recognized by our machine learning classifiers have been experimentally confirmed in the literature. In conclusion, our computational platform serves as a useful tool to help identify potential new interactions between cell surface proteins in addition to current state-of-the-art experimental techniques. The tool is freely accessible for use by the scientific community. Moreover, the general framework of the machine learning classification can also be extended to study the interactions of proteins in other domain superfamilies.

Endothelial leakiness elicited by amyloid protein aggregation

Alzheimer's disease (AD) is a major cause of dementia debilitating the global ageing population. Current understanding of the AD pathophysiology implicates the aggregation of amyloid beta (Aβ) as causative to neurodegeneration, with tauopathies, apolipoprotein E and neuroinflammation considered as other major culprits. Curiously, vascular endothelial barrier dysfunction is strongly associated with Aβ deposition and 80-90% AD subjects also experience cerebral amyloid angiopathy. Here we show amyloid protein-induced endothelial leakiness (APEL) in human microvascular endothelial monolayers as well as in mouse cerebral vasculature. Using signaling pathway assays and discrete molecular dynamics, we revealed that the angiopathy first arose from a disruption to vascular endothelial (VE)-cadherin junctions exposed to the nanoparticulates of Aβ oligomers and seeds, preceding the earlier implicated proinflammatory and pro-oxidative stressors to endothelial leakiness. These findings were analogous to nanomaterials-induced endothelial leakiness (NanoEL), a major phenomenon in nanomedicine depicting the paracellular transport of anionic inorganic nanoparticles in the vasculature. As APEL also occurred in vitro with the oligomers and seeds of alpha synuclein, this study proposes a paradigm for elucidating the vascular permeation, systemic spread, and cross-seeding of amyloid proteins that underlie the pathogeneses of AD and Parkinson's disease.

Structural basis of molecular recognition among classical cadherins mediating cell adhesion

Cadherins are type-I membrane glycoproteins that primarily participate in calcium-dependent cell adhesion and homotypic cell sorting in various stages of embryonic development. Besides their crucial role in cellular and physiological processes, increasing studies highlight their involvement in pathophysiological functions ranging from cancer progression and metastasis to being entry receptors for pathogens. Cadherins mediate these cellular processes through homophilic, as well as heterophilic interactions (within and outside the superfamily) by their membrane distal ectodomains. This review provides an in-depth structural perspective of molecular recognition among type-I and type-II classical cadherins. Furthermore, this review offers structural insights into different dimeric assemblies like the 'strand-swap dimer' and 'X-dimer' as well as mechanisms relating these dimer forms like 'two-step adhesion' and 'encounter complex'. Alongside providing structural details, this review connects structural studies to bond mechanics merging crystallographic and single-molecule force spectroscopic findings. Finally, the review discusses the recent discoveries on dimeric intermediates that uncover prospects of further research beyond two-step adhesion.

Dynamics and functions of E-cadherin complexes in epithelial cell and tissue morphogenesis

Cell-cell adhesion is at the center of structure and dynamics of epithelial tissue. E-cadherin-catenin complexes mediate Ca2+-dependent trans-homodimerization and constitute the kernel of adherens junctions. Beyond the basic function of cell-cell adhesion, recent progress sheds light the dynamics and interwind interactions of individual E-cadherin-catenin complex with E-cadherin superclusters, contractile actomyosin and mechanics of the cortex and adhesion. The nanoscale architecture of E-cadherin complexes together with cis-interactions and interactions with cortical actomyosin adjust to junctional tension and mechano-transduction by reinforcement or weakening of specific features of the interactions. Although post-translational modifications such as phosphorylation and glycosylation have been implicated, their role for specific aspects of in E-cadherin function has remained unclear. Here, we provide an overview of the E-cadherin complex in epithelial cell and tissue morphogenesis focusing on nanoscale architectures by super-resolution approaches and post-translational modifications from recent, in particular in vivo, studies. Furthermore, we review the computational modelling in E-cadherin complexes and highlight how computational modelling has contributed to a deeper understanding of the E-cadherin complexes.

Prediction of Interactions between Cell Surface Proteins by Machine Learning

Cells detect changes of external environments or communicate with each other through proteins on their surfaces. These cell surface proteins form a complicated network of interactions in order to fulfill their functions. The interactions between cell surface proteins are highly dynamic and thus challenging to detect using traditional experimental techniques. Here we tackle this challenge by a computational framework. The primary focus of the framework is to develop new tools to identify interactions between domains in immunoglobulin (Ig) fold, which is the most abundant domain family in cell surface proteins. These interactions could be formed between ligands and receptors from different cells, or between proteins on the same cell surface. In practice, we collected all structural data of Ig domain interactions and transformed them into an interface fragment pair library. A high dimensional profile can be then constructed from the library for a given pair of query protein sequences. Multiple machine learning models were used to read this profile, so that the probability of interaction between the query proteins can be predicted. We tested our models to an experimentally derived dataset which contains 564 cell surface proteins in human. The cross-validation results show that we can achieve higher than 70% accuracy in identifying the PPIs within this dataset. We then applied this method to a group of 46 cell surface proteins in C elegans. We screened every possible interaction between these proteins. Many interactions recognized by our machine learning classifiers have been experimentally confirmed in the literatures. In conclusion, our computational platform serves a useful tool to help identifying potential new interactions between cell surface proteins in addition to current state-of-the-art experimental techniques. The tool is freely accessible for use by the scientific community. Moreover, the general framework of the machine learning classification can also be extended to study interactions of proteins in other domain superfamilies.

Molecular Mechanisms of Endothelialitis in SARS-CoV-2 Infection: Evidence for VE-Cadherin Cleavage by ACE2

Long COVID-19 syndrome appears after Severe Acute Respiratory Syndrome-Corona Virus (SARS-CoV-2) infection with acute damage to microcapillaries, microthrombi, and endothelialitis. However, the mechanisms involved in these processes remain to be elucidated. All blood vessels are lined with a monolayer of endothelial cells called vascular endothelium, which provides a the major function is to prevent coagulation. A component of endothelial cell junctions is VE-cadherin, which is responsible for maintaining the integrity of the vessels through homophilic interactions of its Ca++-dependent adhesive extracellular domain. Here we provide the first evidence that VE-cadherin is a target in vitro for ACE2 cleavage because its extracellular domain (hrVE-ED) contains two amino acid sequences for ACE2 substrate recognition at the positions 256P-F257 and 321PMKP-325L. Indeed, incubation of hrVE-ED with the active ectopeptidase hrACE2 for 16 hrs in the presence of 10 μM ZnCl2 showed a dose-dependent (from 0.2 ng/μL to 2 ng/μL) decrease of the VE-cadherin immunoreactive band. In vivo, in the blood from patients having severe COVID-19 we detected a circulating form of ACE2 with an apparent molecular mass of 70 kDa, which was barely detectable in patients with mild COVID-19. Of importance, in the patients with severe COVID-19 disease, the presence of three soluble fragments of VE-cadherin (70, 62, 54 kDa) were detected using the antiEC1 antibody while only the 54 kDa fragment was present in patients with mild disease. Altogether, these data clearly support a role for ACE2 to cleave VE-cadherin, which leads to potential biomarkers of SARS-CoV-2 infection related with the vascular disease in "Long COVID-19".

Coordinated linear and rotational movements of endothelial cells compartmentalized by VE-cadherin drive angiogenic sprouting

Angiogenesis is a sequential process to extend new blood vessels from preexisting ones by sprouting and branching. During angiogenesis, endothelial cells (ECs) exhibit inhomogeneous multicellular behaviors referred to as "cell mixing," in which ECs repetitively exchange their relative positions, but the underlying mechanism remains elusive. Here we identified the coordinated linear and rotational movements potentiated by cell-cell contact as drivers of sprouting angiogenesis using in vitro and in silico approaches. VE-cadherin confers the coordinated linear motility that facilitated forward sprout elongation, although it is dispensable for rotational movement, which was synchronous without VE-cadherin. Mathematical modeling recapitulated the EC motility in the two-cell state and angiogenic morphogenesis with the effects of VE-cadherin-knockout. Finally, we found that VE-cadherin-dependent EC compartmentalization potentiated branch elongations, and confirmed this by mathematical simulation. Collectively, we propose a way to understand angiogenesis, based on unique EC behavioral properties that are partially dependent on VE-cadherin function.

Dengue Virus Infection Alters Inter-Endothelial Junctions and Promotes Endothelial-Mesenchymal-Transition-Like Changes in Human Microvascular Endothelial Cells

Dengue virus (DENV) is a pathogenic arbovirus that causes human disease. The most severe stage of the disease (severe dengue) is characterized by vascular leakage, hypovolemic shock, and organ failure. Endothelial dysfunction underlies these phenomena, but the causal mechanisms of endothelial dysfunction are poorly characterized. This study investigated the role of c-ABL kinase in DENV-induced endothelial dysfunction. Silencing c-ABL with artificial miRNA or targeting its catalytic activity with imatinib revealed that c-ABL is required for the early steps of DENV infection. DENV-2 infection and conditioned media from DENV-infected cells increased endothelial expression of c-ABL and CRKII phosphorylation, promoted expression of mesenchymal markers, e.g., vimentin and N-cadherin, and decreased the levels of endothelial-specific proteins, e.g., VE-cadherin and ZO-1. These effects were reverted by silencing or inhibiting c-ABL. As part of the acquisition of a mesenchymal phenotype, DENV infection and treatment with conditioned media from DENV-infected cells increased endothelial cell motility in a c-ABL-dependent manner. In conclusion, DENV infection promotes a c-ABL-dependent endothelial phenotypic change that leads to the loss of intercellular junctions and acquisition of motility.

Transcriptomic Modulation Reveals the Specific Cellular Response in Chinese Sea Bass (Lateolabrax maculatus) Gills under Salinity Change and Alkalinity Stress

Salinity and alkalinity are among the important factors affecting the distribution, survival, growth and physiology of aquatic animals. Chinese sea bass (Lateolabrax maculatus) is an important aquaculture fish species in China that can widely adapt to diverse salinities from freshwater (FW) to seawater (SW) but moderately adapt to highly alkaline water (AW). In this study, juvenile L. maculatus were exposed to salinity change (SW to FW) and alkalinity stress (FW to AW). Coordinated transcriptomic responses in L. maculatus gills were investigated and based on the weighted gene co-expression network analysis (WGCNA), 8 and 11 stress-responsive modules (SRMs) were identified for salinity change and alkalinity stress, respectively, which revealed a cascade of cellular responses to oxidative and osmotic stress in L. maculatus gills. Specifically, four upregulated SRMs were enriched with induced differentially expressed genes (DEGs) for alkalinity stress, mainly corresponding to the functions of "extracellular matrix" and "anatomical structure", indicating a strong cellular response to alkaline water. Both "antioxidative activity" and "immune response" functions were enriched in the downregulated alkaline SRMs, which comprised inhibited alkaline specific DEGs, revealing the severely disrupted immune and antioxidative functions under alkalinity stress. These alkaline-specific responses were not revealed in the salinity change groups with only moderately inhibited osmoregulation and induced antioxidative response in L. maculatus gills. Therefore, the results revealed the diverse and correlated regulation of the cellular process and stress response in saline-alkaline water, which may have arisen through the functional divergence and adaptive recruitment of the co-expression genes and will provide vital insights for the development of L. maculatus cultivation in alkaline water.

Hsa_circ_0074158 regulates the endothelial barrier function in sepsis and its potential value as a biomarker

Background: Sepsis is one of the main causes of death in critically ill patients with high morbidity and mortality. Circular RNAs (CircRNAs) are aberrantly expressed, and play significant regulatory roles in many diseases. However, the expression profiles and functions of circRNAs in sepsis have not yet been fully clarified.

Methods: Our present study performed an RNA sequencing (RNA-seq) analysis to assess the expression profiles of circRNAs in vitro. We applied the quantitative real-time polymerase chain reaction (RT-qPCR) to verify the RNA-seq results. The analyses of Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, the competitive endogenous RNA (ceRNA) regulatory networks, were performed to explore the potential mechanism in sepsis. And then, significantly up-regulated differentially expressed (DE) circRNA, hsa_circ_0074158, was selected for further study. Hsa_circ_0074158 was silenced to investigate its regulatory function in sepsis, and the barrier function was also examined in vitro. Endothelial cell junctions were valued using Vascular endothelial cadherin (VE-cadherin), which was detected by immunofluorescence staining. We measured endothelial permeability by transendothelial electrical resistance (TEER) and fluorescein isothiocyanate (FITC)-dextran extravasation.

Results: In total, 203 significantly DE circRNAs, including 77 up-regulated and 126 down-regulated, were identified. In vitro, the RT-qPCR assay showed that the expression pattern of hsa_circ_0074158, hsa_circ_RSBN1L_11059, hsa_circ_0004188, and hsa_circ_0005564 were consistent with the results from RNA-seq analysis. The expression of hsa_circ_0074158 detected by RT-qPCR in vivo was also consistent with the RNA-seq results. The ceRNA networks, GO enrichment, and the KEGG pathway analyses revealed that circRNAs may be related to the barrier function in sepsis. The immunofluorescence assay showed that the suppression of hsa_circ_0074158 expression significantly enhanced the expression of VE-cadherin, which was suppressed in lipopolysaccharide (LPS)-induced sepsis. Additionally, hsa_circ_0074158 knockdown could partially reverse the LPS-induced TEER reduction and FITC-dextran extravasation elevation in sepsis.

Conclusion: In conclusion, we have found DE circRNAs could serve as potential biomarkers and therapeutic targets for sepsis. Hsa_circ_0074158 plays a vital role in sepsis and is related to the disruption of the endothelial barrier.

Anionic nanoplastic exposure induces endothelial leakiness

The global-scale production of plastics has been instrumental in advancing modern society, while the rising accumulation of plastics in landfills, oceans, and anything in between has become a major stressor on environmental sustainability, climate, and, potentially, human health. While mechanical and chemical forces of man and nature can eventually break down or recycle plastics, our understanding of the biological fingerprints of plastics, especially of nanoplastics, remains poor. Here we report on a phenomenon associated with the nanoplastic forms of anionic polystyrene and poly(methyl methacrylate), where their introduction disrupted the vascular endothelial cadherin junctions in a dose-dependent manner, as revealed by confocal fluorescence microscopy, signaling pathways, molecular dynamics simulations, as well as ex vivo and in vivo assays with animal model systems. Collectively, our results implicated nanoplastics-induced vasculature permeability as primarily biophysical-biochemical in nature, uncorrelated with cytotoxic events such as reactive oxygen species production, autophagy, and apoptosis. This uncovered route of paracellular transport has opened up vast avenues for investigating the behaviour and biological effects of nanoplastics, which may offer crucial insights for guiding innovations towards a sustainable plastics industry and environmental remediation.

The transcriptome landscapes of allantochorion and vitelline-chorion in equine day 30 conceptus

During equine early gestation, trophectoderm forms chorion tissue, which is composed of two parts that one is covering allantoin, called allantochorion (AC) and another is covering yolk sac, which here we call vitelline-chorion (VC). Given that little is known about the equine trophoblast-derived chorion differentiation at an early stage, we first compared the transcriptome of AC and VC of day 30 equine conceptus based on RNA-sequencing. As a result, we found that compared to VC, there are 484 DEGs, including 305 up- and 179 down-regulated genes in AC. GO and KEGG analysis indicated that up-regulated genes in AC are mainly cell proliferation and cell adhesion-related genes, participating in allantois expansion and allantochorionic-placenta formation; dominant genes in VC are extracellular exosome and other cell adhesion-related genes implicated in direct and indirect conceptus-maternal communication. Additionally, as for the progenitor chorion tissue of equine chorionic gonadotropin secreting endometrium cup-the chorionic girdle (CG), which locates at the junction of the dilating AC and regressing VC, we revealed its unique gene expression pattern and the gene regulation during its further differentiation in vitro. Collectively, this study sheds light on the molecular events regarding the trophoblast differentiation and function at an early stage of the equine preimplantation conceptus.

Endothelial Transcytosis in Acute Lung Injury: Emerging Mechanisms and Therapeutic Approaches

Acute Lung Injury (ALI) is characterized by widespread inflammation which in its severe form, Acute Respiratory Distress Syndrome (ARDS), leads to compromise in respiration causing hypoxemia and death in a substantial number of affected individuals. Loss of endothelial barrier integrity, pneumocyte necrosis, and circulating leukocyte recruitment into the injured lung are recognized mechanisms that contribute to the progression of ALI/ARDS. Additionally, damage to the pulmonary microvasculature by Gram-negative and positive bacteria or viruses (e.g., Escherichia coli, SARS-Cov-2) leads to increased protein and fluid permeability and interstitial edema, further impairing lung function. While most of the vascular leakage is attributed to loss of inter-endothelial junctional integrity, studies in animal models suggest that transendothelial transport of protein through caveolar vesicles, known as transcytosis, occurs in the early phase of ALI/ARDS. Here, we discuss the role of transcytosis in healthy and injured endothelium and highlight recent studies that have contributed to our understanding of the process during ALI/ARDS. We also cover potential approaches that utilize caveolar transport to deliver therapeutics to the lungs which may prevent further injury or improve recovery.

Potential Therapeutic Applications of N-Cadherin Antagonists and Agonists

This review focuses on the cell adhesion molecule (CAM), known as neural (N)-cadherin (CDH2). The molecular basis of N-cadherin-mediated intercellular adhesion is discussed, as well as the intracellular signaling pathways regulated by this CAM. N-cadherin antagonists and agonists are then described, and several potential therapeutic applications of these intercellular adhesion modulators are considered. The usefulness of N-cadherin antagonists in treating fibrotic diseases and cancer, as well as manipulating vascular function are emphasized. Biomaterials incorporating N-cadherin modulators for tissue regeneration are also presented. N-cadherin antagonists and agonists have potential for broad utility in the treatment of numerous maladies.

Comprehensive Statistical and Bioinformatics Analysis in the Deciphering of Putative Mechanisms by Which Lipid-Associated GWAS Loci Contribute to Coronary Artery Disease

The study was designed to evaluate putative mechanisms by which lipid-associated loci identified by genome-wide association studies (GWAS) are involved in the molecular pathogenesis of coronary artery disease (CAD) using a comprehensive statistical and bioinformatics analysis. A total of 1700 unrelated individuals of Slavic origin from the Central Russia, including 991 CAD patients and 709 healthy controls were examined. Sixteen lipid-associated GWAS loci were selected from European studies and genotyped using the MassArray-4 system. The polymorphisms were associated with plasma lipids such as total cholesterol (rs12328675, rs4846914, rs55730499, and rs838880), LDL-cholesterol (rs3764261, rs55730499, rs1689800, and rs838880), HDL-cholesterol (rs3764261) as well as carotid intima-media thickness/CIMT (rs12328675, rs11220463, and rs1689800). Polymorphisms such as rs4420638 of APOC1 (p = 0.009), rs55730499 of LPA (p = 0.0007), rs3136441 of F2 (p < 0.0001), and rs6065906 of PLTP (p = 0.002) showed significant associations with the risk of CAD, regardless of sex, age, and body mass index. A majority of the observed associations were successfully replicated in large independent cohorts. Bioinformatics analysis allowed establishing (1) phenotype-specific and shared epistatic gene–gene and gene–smoking interactions contributing to all studied cardiovascular phenotypes; (2) lipid-associated GWAS loci might be allele-specific binding sites for transcription factors from gene regulatory networks controlling multifaceted molecular mechanisms of atherosclerosis.

Mechanobiology of Microvascular Function and Structure in Health and Disease: Focus on the Coronary Circulation

The coronary microvasculature plays a key role in regulating the tight coupling between myocardial perfusion and myocardial oxygen demand across a wide range of cardiac activity. Short-term regulation of coronary blood flow in response to metabolic stimuli is achieved via adjustment of vascular diameter in different segments of the microvasculature in conjunction with mechanical forces eliciting myogenic and flow-mediated vasodilation. In contrast, chronic adjustments in flow regulation also involve microvascular structural modifications, termed remodeling. Vascular remodeling encompasses changes in microvascular diameter and/or density being largely modulated by mechanical forces acting on the endothelium and vascular smooth muscle cells. Whereas in recent years, substantial knowledge has been gathered regarding the molecular mechanisms controlling microvascular tone and how these are altered in various diseases, the structural adaptations in response to pathologic situations are less well understood. In this article, we review the factors involved in coronary microvascular functional and structural alterations in obstructive and non-obstructive coronary artery disease and the molecular mechanisms involved therein with a focus on mechanobiology. Cardiovascular risk factors including metabolic dysregulation, hypercholesterolemia, hypertension and aging have been shown to induce microvascular (endothelial) dysfunction and vascular remodeling. Additionally, alterations in biomechanical forces produced by a coronary artery stenosis are associated with microvascular functional and structural alterations. Future studies should be directed at further unraveling the mechanisms underlying the coronary microvascular functional and structural alterations in disease; a deeper understanding of these mechanisms is critical for the identification of potential new targets for the treatment of ischemic heart disease.

Extracellular domains of E-cadherin determine key mechanical phenotypes of an epithelium through cell- and non-cell-autonomous outside-in signaling

Cadherins control intercellular adhesion in most metazoans. In vertebrates, intercellular adhesion differs considerably between cadherins of type-I and type-II, predominantly due to their different extracellular regions. Yet, intercellular adhesion critically depends on actomyosin contractility, in which the role of the cadherin extracellular region is unclear. Here, we dissect the roles of the Extracellular Cadherin (EC) Ig-like domains by expressing chimeric E-cadherin with E-cadherin and cadherin-7 Ig-like domains in cells naturally devoid of cadherins. Using cell-cell separation, cortical tension measurement, tissue stretching and migration assays, we show that distinct EC repeats in the extracellular region of cadherins differentially modulate epithelial sheet integrity, cell-cell separation forces, and cell cortical tension with the Cdc42 pathway, which further differentially regulate epithelial tensile strength, ductility, and ultimately collective migration. Interestingly, dissipative processes rather than static adhesion energy mostly dominate cell-cell separation forces. We provide a framework for the emergence of epithelial phenotypes from cell mechanical properties dependent on EC outside-in signaling.

Transcriptional and Epigenetic Bioinformatic Analysis of Claudin-9 Regulation in Gastric Cancer

Gastric cancer is a heterogeneous disease that represents 5% to 10% of all new cancer cases worldwide. Advances in histological diagnosis and the discovery of new genes have admitted new genomic classifications. Nevertheless, the bioinformatic analysis of gastric cancer databases has favored the detection of specific differentially expressed genes with biological significance. Claudins, a family of proteins involved in tight junction physiology, have emerged as the key regulators of cellular processes, such as growth, proliferation, and migration, associated with cancer progression. The expression of Claudin-9 in the gastric cancer tissue has been linked to poor prognosis, however, its transcriptional and epigenetic regulations demand a more comprehensive analysis. Using the neural network promoter prediction, TransFact, Uniprot-KB, Expasy-SOPMA, protein data bank, proteomics DB, Interpro, BioGRID, String, and the FASTA protein sequence databases and software, we found the following: (1) the promoter sequence has an unconventional structure, including different transcriptional regulation elements distributed throughout it, (2) GATA 4, GATA 6, and KLF5 are the key regulators of Claudin-9 expression, (3) Oct1, NF-κB, AP-1, c-Ets-1, and HNF-3β have the higher binding affinity to the CLDN9 promoter, (4) Claudin-9 interacts with cell differentiation and development proteins, (5) CLDN9 is highly methylated, and (6) Claudin-9 expression is associated with poor survival. In conclusion, Claudin-9 is a protein that should be considered a diagnostic marker as its gene promoter region binds to the transcription factors associated with the deregulation of cell control, enhanced cell proliferation, and metastasis.

Heterophilic and homophilic cadherin interactions in intestinal intermicrovillar links are species dependent

Enterocytes are specialized epithelial cells lining the luminal surface of the small intestine that build densely packed arrays of microvilli known as brush borders. These microvilli drive nutrient absorption and are arranged in a hexagonal pattern maintained by intermicrovillar links formed by 2 nonclassical members of the cadherin superfamily of calcium-dependent cell adhesion proteins: protocadherin-24 (PCDH24, also known as CDHR2) and the mucin-like protocadherin (CDHR5). The extracellular domains of these proteins are involved in heterophilic and homophilic interactions important for intermicrovillar function, yet the structural determinants of these interactions remain unresolved. Here, we present X-ray crystal structures of the PCDH24 and CDHR5 extracellular tips and analyze their species-specific features relevant for adhesive interactions. In parallel, we use binding assays to identify the PCDH24 and CDHR5 domains involved in both heterophilic and homophilic adhesion for human and mouse proteins. Our results suggest that homophilic and heterophilic interactions involving PCDH24 and CDHR5 are species dependent with unique and distinct minimal adhesive units.

A Framework of Paracellular Transport via Nanoparticles-Induced Endothelial Leakiness

Nanomaterial-induced endothelial leakiness (NanoEL) is an interfacial phenomenon denoting the paracellular transport of nanoparticles that is pertinent to nanotoxicology, nanomedicine and biomedical engineering. While the NanoEL phenomenon is complementary to the enhanced permeability and retention effect in terms of their common applicability to delineating the permeability and behavior of nanoparticles in tumoral environments, these two effects significantly differ in scope, origin, and manifestation. In the current study, the descriptors are fully examined of the NanoEL phenomenon elicited by generic citrate-coated gold nanoparticles (AuNPs) of changing size and concentration, from microscopic gap formation and actin reorganization down to molecular signaling pathways and nanoscale interactions of AuNPs with VE-cadherin and its intra/extracellular cofactors. Employing synergistic in silico methodologies, for the first time the molecular and statistical mechanics of cadherin pair disruption, especially in response to AuNPs of the smallest size and highest concentration are revealed. This study marks a major advancement toward establishing a comprehensive NanoEL framework for complementing the understanding of the transcytotic pathway and for guiding the design and application of future nanomedicines harnessing the myriad functions of the mammalian vasculature.

Crystal structure of the nonclassical cadherin-17 N-terminus and implications for its adhesive binding mechanism

The cadherin superfamily of calcium-dependent cell-adhesion proteins has over 100 members in the human genome. All members of the superfamily feature at least a pair of extracellular cadherin (EC) repeats with calcium-binding sites in the EC linker region. The EC repeats across family members form distinct complexes that mediate cellular adhesion. For instance, classical cadherins (five EC repeats) strand-swap their N-termini and exchange tryptophan residues in EC1, while the clustered protocadherins (six EC repeats) use an extended antiparallel `forearm handshake' involving repeats EC1-EC4. The 7D-cadherins, cadherin-16 (CDH16) and cadherin-17 (CDH17), are the most similar to classical cadherins and have seven EC repeats, two of which are likely to have arisen from gene duplication of EC1-2 from a classical ancestor. However, CDH16 and CDH17 lack the EC1 tryptophan residue used by classical cadherins to mediate adhesion. The structure of human CDH17 EC1-2 presented here reveals features that are not seen in classical cadherins and that are incompatible with the EC1 strand-swap mechanism for adhesion. Analyses of crystal contacts, predicted glycosylation and disease-related mutations are presented along with sequence alignments suggesting that the novel features in the CDH17 EC1-2 structure are well conserved. These results hint at distinct adhesive properties for 7D-cadherins.

Autoregulatory "Multitasking" at Endothelial Cell Junctions by Junction-Associated Intermittent Lamellipodia Controls Barrier Properties

Vascular endothelial cell (EC) junctions are key structures controlling tissue homeostasis in physiology. In the last three decades, excellent studies have addressed many aspects of this complex and highly dynamic regulation, including cell signaling, remodeling processes of the proteins of tight junctions, adherens junctions, and gap junctions, the cytoskeleton, and post-transcriptional modifications, transcriptional activation, and gene silencing. In this dynamic process, vascular endothelial cadherin (VE-cadherin) provides the core structure of EC junctions mediating the physical adhesion of cells as well as the control of barrier function and monolayer integrity via remodeling processes, regulation of protein expression and post-translational modifications. In recent years, research teams have documented locally restricted dynamics of EC junctions in which actin-driven protrusions in plasma membranes play a central role. In this regard, our research group showed that the dynamics of VE-cadherin is driven by small (1-5 μm) actin-mediated protrusions in plasma membranes that, due to this specific function, were named "junction-associated intermittent lamellipodia" (JAIL). JAIL form at overlapping, adjacent cells, and exactly at this site new VE-cadherin interactions occur, leading to new VE-cadherin adhesion sites, a process that restores weak or lost VE-cadherin adhesion. Mechanistically, JAIL formation occurs locally restricted (1-5 μm) and underlies autoregulation in which the local VE-cadherin concentration is an important parameter. A decrease in the local concentration of VE-cadherin stimulates JAIL formation, whereas an increase in the concentration of VE-cadherin blocks it. JAIL mediated VE-cadherin remodeling at the subjunctional level have been shown to be of crucial importance in angiogenesis, wound healing, and changes in permeability during inflammation. The concept of subjunctional regulation of EC junctions is strongly supported by permeability assays, which can be employed to quantify actin-driven subjunctional changes. In this brief review, we summarize and discuss the current knowledge and concepts of subjunctional regulation in the endothelium.

Interactions of Influenza and SARS-CoV-2 with the Lung Endothelium: Similarities, Differences, and Implications for Therapy

Respiratory viruses such as influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are a constant threat to public health given their ability to cause global pandemics. Infection with either virus may lead to aberrant host responses, such as excessive immune cell recruitment and activation, dysregulated inflammation, and coagulopathy. These may contribute to the development of lung edema and respiratory failure. An increasing amount of evidence suggests that lung endothelial cells play a critical role in the pathogenesis of both viruses. In this review, we discuss how infection with influenza or SARS-CoV-2 may induce endothelial dysfunction. We compare the effects of infection of these two viruses, how they may contribute to pathogenesis, and discuss the implications for potential treatment. Understanding the differences between the effects of these two viruses on lung endothelial cells will provide important insight to guide the development of therapeutics.

How Does Endothelial Permeability Affect the Development of Juvenile Idiopathic Arthritis? Vascular Endothelial Cadherin as a Promising New Tool Helpful in the Diagnostic Process

Introduction

Vascular endothelial cadherin (VE-cadherin) is a calcium-dependent protein essential for stabilization of the adherens junctions of the endothelial cells. Through vasculogenic mimicry, VE-cadherin may influence angiogenesis in synovial fibroblast-like cells. The soluble extracellular domain of VE-cadherin may be considered an indicator of endothelial dysfunction. Its potential as a diagnostic biomarker in rheumatic diseases, including juvenile idiopathic arthritis (JIA), needs to be investigated.

Materials and Methods

The study group included 80 patients diagnosed with JIA. In 53 individuals, blood samples were obtained twice with an average interval of 102.4 ± 4.6 days. Results from the study group were compared to 29 age- and sex-matched healthy children.

Results

Serum levels of VE-cadherin were significantly higher in JIA patients than in healthy controls. In such comparison, VE-cadherin had 87.5% sensitivity and 69.0% specificity for the cutoff level 4.36 ng/ml (Youden index 0.56, area under the curve 0.724). VE-cadherin concentrations negatively correlated with the disease activity score. However, such finding may be a false result because of the downregulation of VE-cadherin induced by glucocorticosteroids.

Conclusions

VE-cadherin may become a promising diagnostic biomarker of early stages of JIA. Its predictive significance may be decreased by utilization of glucocorticosteroids. A multicentre study including patients with other arthritides is recommended for further evaluation of this protein.

Direct visualization of the extracellular binding structure of E-cadherins in liquid

E-cadherin is a key Ca-dependent cell adhesion molecule, which is expressed on many cell surfaces and involved in cell morphogenesis, embryonic development, EMT, etc. The fusion protein E-cad-Fc consists of the extracellular domain of E-cadherin and the IgG Fc domain. On plates coated with this chimeric protein, ES/iPS cells are cultivated particularly well and induced to differentiate. The cells adhere to the plate via E-cad-Fc in the presence of Ca2+ and detach by a chelating agent. For the purpose of clarifying the structures of E-cad-Fc in the presence and absence of Ca2+, we analyzed the molecular structure of E-cad-Fc by AFM in liquid. Our AFM observations revealed a rod-like structure of the entire extracellular domain of E-cad-Fc in the presence of Ca2+ as well as trans-binding of E-cad-Fc with adjacent molecules, which may be the first, direct confirmation of trans-dimerization of E-cadherin. The observed structures were in good agreement with an X-ray crystallographic model. Furthermore, we succeeded in visualizing the changes in the rod-like structure of the EC domains with and without calcium. The biomatrix surface plays an important role in cell culture, so the analysis of its structure and function may help promote cell engineering based on cell recognition.

Coronary Collateral Microcirculation Reserve Becomes Vestigial with Aging

INTRODUCTION

Our previous study indicated that coronary collateral microcirculation reserve (CCMR), native collaterals, transports blood flow to an ischemic area to reduce ischemic tissue injury. This study aimed to observe the changes of CCMR in the hearts of different month-old rats.

METHODS

We selected 2-, 8-, 16-, and 24-month-old rats as the research objects to monitor the changes of CCMR in rats with aging. After acute myocardial infarction, lectin-FITC was injected into the femoral vein vessels of rats to mark CCMR vessels in the ischemic area.

RESULTS

Results of the lectin-FITC perfusion experiment indicated that the number and collagen IV coverage of CCMR vessels declined with aging. Moreover, data suggested a correlation between endothelial nitric oxide synthase and a decline in the number of CCMR vessels.

CONCLUSION

Aging causes CCMR decline in rats.

Homophilic and Heterophilic Interactions of Type II Cadherins Identify Specificity Groups Underlying Cell-Adhesive Behavior

Type II cadherins are cell-cell adhesion proteins critical for tissue patterning and neuronal targeting but whose molecular binding code remains poorly understood. Here, we delineate binding preferences for type II cadherin cell-adhesive regions, revealing extensive heterophilic interactions between specific pairs, in addition to homophilic interactions. Three distinct specificity groups emerge from our analysis with members that share highly similar heterophilic binding patterns and favor binding to one another. Structures of adhesive fragments from each specificity group confirm near-identical dimer topology conserved throughout the family, allowing interface residues whose conservation corresponds to specificity preferences to be identified. We show that targeted mutation of these residues converts binding preferences between specificity groups in biophysical and co-culture assays. Our results provide a detailed understanding of the type II cadherin interaction map and a basis for defining their role in tissue patterning and for the emerging importance of their heterophilic interactions in neural connectivity.

Identification of an adhesive interface for the non-clustered δ1 protocadherin-1 involved in respiratory diseases

Cadherins form a large family of calcium-dependent adhesive proteins involved in morphogenesis, cell differentiation, and neuronal connectivity. Non-clustered δ1 protocadherins form a cadherin subgroup of proteins with seven extracellular cadherin (EC) repeats and cytoplasmic domains distinct from those of classical cadherins. Non-clustered δ1 protocadherins mediate homophilic adhesion and have been implicated in various diseases including asthma, autism, and cancer. Here we present X-ray crystal structures of human Protocadherin-1 (PCDH1), a δ1-protocadherin member essential for New World Hantavirus infection that is typically expressed in the brain, airway epithelium, skin keratinocytes, and lungs. The structures suggest a binding mode that involves antiparallel overlap of repeats EC1 to EC4. Mutagenesis combined with binding assays and biochemical experiments validated this mode of adhesion. Overall, these results reveal the molecular mechanism underlying adhesiveness of PCDH1 and δ1-protocadherins, also shedding light on PCDH1's role in maintaining airway epithelial integrity, the loss of which causes respiratory diseases.

A Biomimetic Lipid Membrane Device Reveals the Interaction of Cancer Biomarkers with Human Serum Lipidic Moieties

A major problem for the detection of cancer biomarkers in plasma or serum is that common clinical practice does not require the patient to be in a fasting state. Considering that lipoproteins are the main population affected by food intake, the authors hypothesized that biomarkers could be embedded in lipid particles and thereby opens a new avenue for detection. Using the recently published biomarker, soluble VE-cadherin (sVE), the authors tested our hypothesis using techniques of biophysics, biochemistry and the tools of nanobiotechnology on serum samples from kidney cancer patients (n = 106). Optical density as well as contact angle measurements of serum revealed heterogeneity in the particle content of the serum samples. Isolation of the lipidic moieties by ultracentrifugation showed that sVE was detected in this compartment. Further, isolation of lipoprotein subclasses by precipitation with sodium phosphotungstate and MgCl₂ , showed that HDL carried the majority of sVE. Immunoprecipitation of sVE confirmed that it was associated with Apolipoprotein A1, a major compound of HDL. Using a biomimetic lipid bilayer membrane coupled with impedance spectroscopy the authors quantified, in real-time, that the sVE adsorbed to the lipid bilayer membrane without altering its structure. Taken together, these results show for the first time a direct interaction of a cancer biomarker with lipids. The authors anticipate these results to prompt fasting for future blood tests for large-scale studies in the biomarkers research field.

Effect of melatonin on EGF- and VEGF-induced monolayer permeability of HUVECs

Melatonin is a natural hormone involved in the regulation of circadian rhythm, immunity, and cardiovascular function. In the present study, we focused on the mechanism of melatonin in the regulation of vascular permeability. We found that melatonin could inhibit both VEGF- and EGF-induced monolayer permeability of human umbilical vein endothelial cells (HUVECs) and change the tyrosine phosphorylation of vascular-endothelial (VE-)cadherin, which was related to endothelial barrier function. In addition, phospho-AKT (Ser⁴⁷³) and phospho-ERK(1/2) played significant roles in the regulation of VE-cadherin phosphorylation. Both the phosphatidylinositol 3-kinase/AKT inhibitor LY49002 and MEK/ERK inhibitor U0126 could inhibit the permeability of HUVECs, but with different effects on tyrosine phosphorylation of VE-cadherin. Melatonin can influence the two growth factor-induced phosphorylation of AKT (Ser⁴⁷³) but not ERK(1/2). Our results show that melatonin can inhibit growth factor-induced monolayer permeability of HUVECs by influencing the phosphorylation of AKT and VE-cadherin. Melatonin can be a potential treatment for diseases associated with abnormal vascular permeability. NEW & NOTEWORTHY We found that melatonin could inhibit both EGF- and VEGF-induced monolayer permeability of human umbilical vein endothelial cells, which is related to phosphorylation of vascular-endothelial cadherin. Blockade of phosphatidylinositol 3-kinase/AKT and MEK/ERK pathways could inhibit the permeability of human umbilical vein endothelial cells, and phosphorylation of AKT (Ser⁴⁷³) might be a critical event in the changing of monolayer permeability and likely has cross-talk with the MEK/ERK pathway.

A Mechanically Weak Extracellular Membrane-Adjacent Domain Induces Dimerization of Protocadherin-15

The cadherin superfamily of proteins is defined by the presence of extracellular cadherin (EC) "repeats" that engage in protein-protein interactions to mediate cell-cell adhesion, cell signaling, and mechanotransduction. The extracellular domains of nonclassical cadherins often have a large number of EC repeats along with other subdomains of various folds. Protocadherin-15 (PCDH15), a protein component of the inner-ear tip link filament essential for mechanotransduction, has 11 EC repeats and a membrane adjacent domain (MAD12) of atypical fold. Here we report the crystal structure of a pig PCDH15 fragment including EC10, EC11, and MAD12 in a parallel dimeric arrangement. MAD12 has a unique molecular architecture and folds as a ferredoxin-like domain similar to that found in the nucleoporin protein Nup54. Analytical ultracentrifugation experiments along with size-exclusion chromatography coupled to multiangle laser light scattering and small-angle x-ray scattering corroborate the crystallographic dimer and show that MAD12 induces parallel dimerization of PCDH15 near its membrane insertion point. In addition, steered molecular dynamics simulations suggest that MAD12 is mechanically weak and may unfold before tip-link rupture. Sequence analyses and structural modeling predict the existence of similar domains in cadherin-23, protocadherin-24, and the "giant" FAT and CELSR cadherins, indicating that some of them may also exhibit MAD-induced parallel dimerization.

EpCAM homo-oligomerization is not the basis for its role in cell-cell adhesion

Cell-surface tumor marker EpCAM plays a key role in proliferation, differentiation and adhesion processes in stem and epithelial cells. It is established as a cell-cell adhesion molecule, forming intercellular interactions through homophilic association. However, the mechanism by which such interactions arise has not yet been fully elucidated. Here, we first show that EpCAM monomers do not associate into oligomers that would resemble an inter-cellular homo-oligomer, capable of mediating cell-cell adhesion, by using SAXS, XL-MS and bead aggregation assays. Second, we also show that EpCAM forms stable dimers on the surface of a cell with pre-formed cell-cell contacts using FLIM-FRET; however, no inter-cellular homo-oligomers were detectable. Thus, our study provides clear evidence that EpCAM indeed does not function as a homophilic cell adhesion molecule and therefore calls for a significant revision of its role in both normal and cancerous tissues. In the light of this, we strongly support the previously suggested name Epithelial Cell Activating Molecule instead of the Epithelial Cell Adhesion Molecule.

Mussel adhesive protein fused with VE-cadherin domain specifically triggers endothelial cell adhesion

Endothelium is the only known completely non-thrombogenic material. In the present study, a strategy to mimic the adhesive interactions of endothelial cells (ECs) to alter the vascular microenvironment was established and applied to directing the behaviour of cells. To facilitate the regeneration of a functional endothelium in vascular lesions, we designed a recombinant mussel foot protein (Mfp-5) fused with the VE-cadherin extracellular domain EC1-2, termed VE-M. Surface coating analysis showed that recombinant VE-M successfully formed a coating on substrate materials with uniform nanorods, low roughness, and sufficient hydrophilicity. We then evaluated the effects of VE-M on the adhesion of ECs and the capture of endothelial progenitor cells (EPCs). The result demonstrated that VE-M efficiently promoted the adhesion of ECs and EPCs. The number of ECs and EPCs on VE-M was 5.5- and 1.8-fold higher, respectively, than that on bare 316L SS under static conditions, whereas there was no significant difference in the number of captured smooth muscle cells (SMCs) between VE-M and other substrates. In addition, the number of EPCs captured by VE-M was approximately four times higher than that captured by 316L SS under dynamic conditions. In particular, the result of the neutralization test indicated that VE-M specifically triggered ECs' adhesion via the interaction of VE-cadherin EC1-2. Further investigation showed that VE-M significantly increased the levels of endogenous VE-cadherin in HUVECs as well as the endothelial eNOS content, with little or no endothelial inflammation. Our results showed that VE-M could be a promising biomimetic modification for accelerating endothelialization and vascularization in tissue engineering.

Atorvastatin enhances endothelial adherens junctions through promoting VE-PTP gene transcription and reducing VE-cadherin-Y731 phosphorylation

Vascular endothelial protein tyrosine phosphatase (VE-PTP) is essential for endothelial cells (ECs) adherens junction and vascular homeostasis; however, the regulatory mechanism of VE-PTP transcription is unknown, and a drug able to promote VE-PTP expression in ECs has not yet been reported in the literature. In this study, we used human ECs as a model to explore small molecule compounds able to promote VE-PTP expression, and found that atorvastatin, a HMG-CoA reductase inhibitor widely used in the clinic to treat hypercholesterolemia-related cardiovascular diseases, strongly promoted VE-PTP transcription in ECs through activating the VE-PTP promoter and upregulating the expression of the transcription factor, specificity protein 1 (SP1). Additionally, atorvastatin markedly reduced VE-cadherin-Y731 phosphorylation induced by cigarette smoke extract and significantly enhanced stability of endothelial adherens junctions. Together, our findings reveal that atorvastatin up-regulates VE-PTP expression, increases VE-cadherin protein levels, and decreases VE-cadherin-Y731 phosphorylation to strengthen EC adherens junctions and maintain vascular cell monolayer integrity, offering a new mechanism of atorvastatin against CSE-induced disruption of vascular integrity and relevant cardio-cerebrovascular disease.

An alternative conformation of human TrpRS suggests a role of zinc in activating non-enzymatic function

Tryptophanyl-tRNA synthetase (TrpRS) in vertebrates contains a N-terminal extension in front of the catalytic core. Proteolytic removal of the N-terminal 93 amino acids gives rise to T2-TrpRS, which has potent anti-angiogenic activity mediated through its extracellular interaction with VE-cadherin. Zinc has been shown to have anti-angiogenic effects and can bind to human TrpRS. However, the connection between zinc and the anti-angiogenic function of TrpRS has not been explored. Here we report that zinc binding can induce structural relaxation in human TrpRS to facilitate the proteolytic generation of a T2-TrpRS-like fragment. The zinc-binding site is likely to be contained within T2-TrpRS, and the zinc-bound conformation of T2-TrpRS is mimicked by mutation H130R. We determined the crystal structure of H130R T2-TrpRS at 2.8 Å resolution, which reveals drastically different conformation from that of wild-type (WT) T2-TrpRS. The conformational change creates larger binding surfaces for VE-cadherin as suggested by molecular dynamic simulations. Surface plasmon resonance analysis indicates more than 50-fold increase in binding affinity of H130R T2-TrpRS for VE-cadherin, compared to WT T2-TrpRS. The enhanced interaction is also confirmed by a cell-based binding analysis. These results suggest that zinc plays an important role in activating TrpRS for angiogenesis regulation.

A potential new, stable state of the E-cadherin strand-swapped dimer in solution

E-cadherin is a transmembrane glycoprotein that facilitates inter-cellular adhesion in the epithelium. The ectodomain of the native structure is comprised of five repeated immunoglobulin-like domains. All E-cadherin crystal structures show the protein in one of three alternative conformations: a monomer, a strand-swapped trans homodimer and the so-called X-dimer, which is proposed to be a kinetic intermediate to forming the strand-swapped trans homodimer. However, previous studies have indicated that even once the trans strand-swapped dimer is formed, the complex is highly dynamic and the E-cadherin monomers may reorient relative to each other. Here, molecular dynamics simulations have been used to investigate the stability and conformational flexibility of the human E-cadherin trans strand-swapped dimer. In four independent, 100 ns simulations, the dimer moved away from the starting structure and converged to a previously unreported structure, which we call the Y-dimer. The Y-dimer was present for over 90% of the combined simulation time, suggesting that it represents a stable conformation of the E-cadherin dimer in solution. The Y-dimer conformation is stabilised by interactions present in both the trans strand-swapped dimer and X-dimer crystal structures, as well as additional interactions not found in any E-cadherin dimer crystal structures. The Y-dimer represents a previously unreported, stable conformation of the human E-cadherin trans strand-swapped dimer and suggests that the available crystal structures do not fully capture the conformations that the human E-cadherin trans homodimer adopts in solution.

Protein Interactions at Endothelial Junctions and Signaling Mechanisms Regulating Endothelial Permeability

The monolayer of endothelial cells lining the vessel wall forms a semipermeable barrier (in all tissue except the relatively impermeable blood-brain and inner retinal barriers) that regulates tissue-fluid homeostasis, transport of nutrients, and migration of blood cells across the barrier. Permeability of the endothelial barrier is primarily regulated by a protein complex called adherens junctions. Adherens junctions are not static structures; they are continuously remodeled in response to mechanical and chemical cues in both physiological and pathological settings. Here, we discuss recent insights into the post-translational modifications of junctional proteins and signaling pathways regulating plasticity of adherens junctions and endothelial permeability. We also discuss in the context of what is already known and newly defined signaling pathways that mediate endothelial barrier leakiness (hyperpermeability) that are important in the pathogenesis of cardiovascular and lung diseases and vascular inflammation.

Structural determinants of adhesion by Protocadherin-19 and implications for its role in epilepsy

Non-clustered δ-protocadherins are homophilic cell adhesion molecules essential for the development of the vertebrate nervous system, as several are closely linked to neurodevelopmental disorders. Mutations in protocadherin-19 (PCDH19) result in a female-limited, infant-onset form of epilepsy (PCDH19-FE). Over 100 mutations in PCDH19 have been identified in patients with PCDH19-FE, about half of which are missense mutations in the adhesive extracellular domain. Neither the mechanism of homophilic adhesion by PCDH19, nor the biochemical effects of missense mutations are understood. Here we present a crystallographic structure of the minimal adhesive fragment of the zebrafish Pcdh19 extracellular domain. This structure reveals the adhesive interface for Pcdh19, which is broadly relevant to both non-clustered δ and clustered protocadherin subfamilies. In addition, we show that several PCDH19-FE missense mutations localize to the adhesive interface and abolish Pcdh19 adhesion in in vitro assays, thus revealing the biochemical basis of their pathogenic effects during brain development.

DOI:http://dx.doi.org/10.7554/eLife.18529.001

As the brain develops, its basic building blocks – cells called neurons – need to form the correct connections with one another in order to give rise to neural circuits. A mistake that leads to the formation of incorrect connections can result in a number of disorders or brain abnormalities.

Proteins called cadherins that are present on the surface of neurons enable them to stick to their correct partners like Velcro. One of these proteins is called Protocadherin-19. However, it was not fully understood how this protein forms an adhesive bond with other Protocadherin-19 molecules, or how some of the proteins within the cadherin family are able to distinguish between one another.

Cooper et al. used X-ray crystallography to visualize the molecular structure of Protocadherin-19 taken from zebrafish in order to better understand the adhesive bond that these proteins form with each other. In addition, the new structure showed the sites of the mutations that cause a form of epilepsy in infant females. From this, Cooper et al. could predict how the mutations would disrupt Protocadherin-19’s shape and function.

The structures revealed that Protocadherin-19 molecules from adjacent cells engage in a “forearm handshake” to form the bond that connects neurons. Some of the mutations that cause epilepsy occur in the region responsible for this Protocadherin-19 forearm handshake. Laboratory experiments confirmed that these mutations impair the formation of the adhesive bond, revealing the molecular basis for some of the mutations that underlie Protocadherin-19-female-limited epilepsy.

Other cadherin molecules may interact via a similar forearm handshake; this could be investigated in future experiments. It also remains to be discovered how brain wiring depends on Protocadherin-19 adhesion in animal development, and how altering these proteins can rewire developing brain circuits.

DOI:http://dx.doi.org/10.7554/eLife.18529.002

Molecular basis of sidekick-mediated cell-cell adhesion and specificity

Sidekick (Sdk) 1 and 2 are related immunoglobulin superfamily cell adhesion proteins required for appropriate synaptic connections between specific subtypes of retinal neurons. Sdks mediate cell-cell adhesion with homophilic specificity that underlies their neuronal targeting function. Here we report crystal structures of Sdk1 and Sdk2 ectodomain regions, revealing similar homodimers mediated by the four N-terminal immunoglobulin domains (Ig1-4), arranged in a horseshoe conformation. These Ig1-4 horseshoes interact in a novel back-to-back orientation in both homodimers through Ig1:Ig2, Ig1:Ig1 and Ig3:Ig4 interactions. Structure-guided mutagenesis results show that this canonical dimer is required for both Sdk-mediated cell aggregation (via trans interactions) and Sdk clustering in isolated cells (via cis interactions). Sdk1/Sdk2 recognition specificity is encoded across Ig1-4, with Ig1-2 conferring the majority of binding affinity and differential specificity. We suggest that competition between cis and trans interactions provides a novel mechanism to sharpen the specificity of cell-cell interactions.

Divergence of structural strategies for homophilic E-cadherin binding among bilaterians

Homophilic binding of E-cadherins through their ectodomains is fundamental to epithelial cell-cell adhesion. Despite this, E-cadherin ectodomains have evolved differently in the vertebrate and insect lineages. Of the five rod-like, tandemly aligned extracellular cadherin domains of vertebrate E-cadherin, the tip extracellular cadherin domain plays a pivotal role in binding interactions. Comparatively, the six consecutive N-terminal extracellular cadherin domains of Drosophila E-cadherin, DE-cadherin (also known as Shotgun), can mediate adhesion; however, the underlying mechanism is unknown. Here, we report atomic force microscopy imaging of DE-cadherin extracellular cadherin domains. We identified a tightly folded globular structure formed by the four N-terminal-most extracellular cadherin domains stabilized by the subsequent two extracellular cadherin domains. Analysis of hybrid cadherins from different insects indicated that the E-cadherin globular portion is associated with determining homophilic binding specificity. The second to fourth extracellular cadherin domains were identified as the minimal portion capable of mediating exclusive homophilic binding specificity. Our findings suggest that the N-terminal-most four extracellular cadherin domains of insect E-cadherin are functionally comparable with the N-terminal-most single extracellular cadherin domain of vertebrate E-cadherin, but that their mechanisms might significantly differ. This work illuminates the divergence of structural strategies for E-cadherin homophilic binding among bilaterians.

Structural basis of adhesive binding by desmocollins and desmogleins

Desmosomes are intercellular adhesive junctions that impart strength to vertebrate tissues. Their dense, ordered intercellular attachments are formed by desmogleins (Dsgs) and desmocollins (Dscs), but the nature of trans-cellular interactions between these specialized cadherins is unclear. Here, using solution biophysics and coated-bead aggregation experiments, we demonstrate family-wise heterophilic specificity: All Dsgs form adhesive dimers with all Dscs, with affinities characteristic of each Dsg:Dsc pair. Crystal structures of ectodomains from Dsg2 and Dsg3 and from Dsc1 and Dsc2 show binding through a strand-swap mechanism similar to that of homophilic classical cadherins. However, conserved charged amino acids inhibit Dsg:Dsg and Dsc:Dsc interactions by same-charge repulsion and promote heterophilic Dsg:Dsc interactions through opposite-charge attraction. These findings show that Dsg:Dsc heterodimers represent the fundamental adhesive unit of desmosomes and provide a structural framework for understanding desmosome assembly.

Integrated Data Set of microRNAs and mRNAs Involved in Severe Intrauterine Adhesion

BACKGROUND

Adhesion tissue is formed following injury to the uterine basal layer. Currently, there is no effective treatment for severe intrauterine adhesion (IUA), which causes loss of reproductive function. Enhanced understanding of the molecular mechanisms driving severe IUA would be beneficial for the treatment.

METHODS

Differentially expressed microRNAs (miRNAs) and messenger RNAs (mRNAs) in severe IUA (n = 3) and normal (n = 3) endometrium were analyzed by high-throughput microarray analysis. Subsequently, the target genes of the differentially expressed miRNAs were predicted and found to overlap with the differentially expressed mRNAs. Gene Ontology and pathway analyses were performed for the intersecting genes. Three of the significantly dysregulated miRNAs and 4 of their target mRNAs were further assessed using quantitative real-time polymerase chain reaction (PCR) in 10 severe IUA and 10 normal endometrium samples.

RESULTS

Microarray analysis indicated that 26 miRNAs and 1180 mRNAs were significantly different between the 2 groups. Of these, 16 miRNAs and 54 mRNAs overlapped with putative miRNA target genes and prediction of target gene. Real-time PCR revealed upregulation of hsa-miR-513a-5p and has-miR-135a-3p and downregulation of hsa-miR-543 and their corresponding target genes, plus downregulation of ADAM9 (a disintegrin-containing and metalloproteinases) and lysyl oxidase and upregulation of CDH2 (N-cadherin) and COL16A1 (collagen 16A1). Both CDH2 and COL16A1 were bioinformatically predicted and confirmed in vitro as target genes of miR-543.

CONCLUSION

This study provides an integrated data set of the miRNA and mRNA profiles in severe IUA, showing involvement of many miRNAs and their target genes. Further analysis of these genes will help in understanding of the molecular mechanism of IUA formation.

Ankyrin-G Inhibits Endocytosis of Cadherin Dimers

Dynamic regulation of endothelial cell adhesion is central to vascular development and maintenance. Furthermore, altered endothelial adhesion is implicated in numerous diseases. Therefore, normal vascular patterning and maintenance require tight regulation of endothelial cell adhesion dynamics. However, the mechanisms that control junctional plasticity are not fully understood. Vascular endothelial cadherin (VE-cadherin) is an adhesive protein found in adherens junctions of endothelial cells. VE-cadherin mediates adhesion through trans interactions formed by its extracellular domain. Trans binding is followed by cis interactions that laterally cluster the cadherin in junctions. VE-cadherin is linked to the actin cytoskeleton through cytoplasmic interactions with β- and α-catenin, which serve to increase adhesive strength. Furthermore, p120-catenin binds to the cytoplasmic tail of cadherin and stabilizes it at the plasma membrane. Here we report that induced cis dimerization of VE-cadherin inhibits endocytosis independent of both p120 binding and trans interactions. However, we find that ankyrin-G, a protein that links membrane proteins to the spectrin-actin cytoskeleton, associates with VE-cadherin and inhibits its endocytosis. Ankyrin-G inhibits VE-cadherin endocytosis independent of p120 binding. We propose a model in which ankyrin-G associates with and inhibits the endocytosis of VE-cadherin cis dimers. Our findings support a novel mechanism for regulation of VE-cadherin endocytosis through ankyrin association with cadherin engaged in lateral interactions.

Rac1 functions as a reversible tension modulator to stabilize VE-cadherin trans-interaction

The role of the RhoGTPase Rac1 in stabilizing mature endothelial adherens junctions (AJs) is not well understood. In this paper, using a photoactivatable probe to control Rac1 activity at AJs, we addressed the relationship between Rac1 and the dynamics of vascular endothelial cadherin (VE-cadherin). We demonstrated that Rac1 activation reduced the rate of VE-cadherin dissociation, leading to increased density of VE-cadherin at AJs. This response was coupled to a reduction in actomyosin-dependent tension across VE-cadherin adhesion sites. We observed that inhibiting myosin II directly or through photo-release of the caged Rho kinase inhibitor also reduced the rate of VE-cadherin dissociation. Thus, Rac1 functions by stabilizing VE-cadherin trans-dimers in mature AJs by counteracting the actomyosin tension. The results suggest a new model of VE-cadherin adhesive interaction mediated by Rac1-induced reduction of mechanical tension at AJs, resulting in the stabilization of VE-cadherin adhesions.

Cadherin-11 in poor prognosis malignancies and rheumatoid arthritis: common target, common therapies

Cadherin-11 (CDH11), associated with epithelial to mesenchymal transformation in development, poor prognosis malignancies and cancer stem cells, is also a major therapeutic target in rheumatoid arthritis (RA). CDH11 expressing basal-like breast carcinomas and other CDH11 expressing malignancies exhibit poor prognosis. We show that CDH11 is increased early in breast cancer and ductal carcinoma in-situ. CDH11 knockdown and antibodies effective in RA slowed the growth of basal-like breast tumors and decreased proliferation and colony formation of breast, glioblastoma and prostate cancer cells. The repurposed arthritis drug celecoxib, which binds to CDH11, and other small molecules designed to bind CDH11 without inhibiting COX-2 preferentially affect the growth of CDH11 positive cancer cells in vitro and in animals. These data suggest that CDH11 is important for malignant progression, and is a therapeutic target in arthritis and cancer with the potential for rapid clinical translation

Modulation of intercellular junctions by cyclic-ADT peptides as a method to reversibly increase blood-brain barrier permeability

It is challenging to deliver molecules to the brain for diagnosis and treatment of brain diseases. This is primarily because of the presence of the blood-brain barrier (BBB), which restricts the entry of many molecules into the brain. In this study, cyclic-ADT peptides (ADTC1, ADTC5, and ADTC6) have been shown to modify the BBB to enhance the delivery of marker molecules [e.g., (14) C-mannitol, gadolinium-diethylenetriaminepentacetate (Gd-DTPA)] to the brain via the paracellular pathways of the BBB. The hypothesis is that these peptides modulate cadherin interactions in the adherens junctions of the vascular endothelial cells forming the BBB to increase paracellular drug permeation. In vitro studies indicated that ADTC5 had the best profile to inhibit adherens junction resealing in Madin-Darby canine kidney cell monolayers in a concentration-dependent manner (IC50 = 0.3 mM) with a maximal response at 0.4 mM. Under the current experimental conditions, ADTC5 improved the delivery of (14) C-mannitol to the brain about twofold compared with the negative control in the in situ rat brain perfusion model. Furthermore, ADTC5 peptide increased in vivo delivery of Gd-DTPA to the brain of Balb/c mice when administered intravenously. In conclusion, ADTC5 has the potential to improve delivery of diagnostic and therapeutic agents to the brain.