Rho-GTPase signaling in leukocyte extravasation: an endothelial point of view

Rhogef17: A novel target for endothelial barrier function

ARHGEF17 encodes the protein RhoGEF17, which is highly expressed in vascular endothelial cells. It is a guanine nucleotide exchange factor (GEF) that accelerates the exchange of GDP with GTP on many small GTPases through its Dbl homology (DH) domain, enabling the activation of Rho-GTPases such as RhoA, RhoB, and RhoC. Rho GTPase-regulated changes in the actin cytoskeleton and cell adhesion kinetics are the main mechanisms mediating many endothelial cell (EC) alterations, including cell morphology, migration, and division changes, which profoundly affect EC barrier function. This review focuses on ARHGEF17 expression, activation and biological functions in ECs, linking its regulation of cellular morphology, migration, mitosis and other cellular behaviors to disease onset and progression. Understanding ARHGEF17 mechanisms of action will contribute to the design of therapeutic approaches targeting RhoGEF17, a potential drug target for the treatment of various endothelium-related diseases, Such as vascular inflammation, carcinogenesis and transendothelial metastasis of tumors.

Prenyltransferase gene expression reveals an essential role of prenylation for the inflammatory response in human gingival fibroblasts

BACKGROUND

Prenyltrasferases (PTases) are a class of enzymes known to be responsible for promoting posttranslational modification at the carboxyl terminus of proteins containing a so-called CaaX-motif. The process is responsible for proper membrane localization and the appropriate function of several intracellular signaling proteins. Current research demonstrating the pathomechanistic importance of prenylation in inflammatory illnesses emphasizes the requirement to ascertain the differential expression of PT genes under inflammatory settings, particularly in periodontal disease.

METHODS

Telomerase-immortalized human gingival fibroblasts (HGF-hTert) were cultured and treated with either inhibitors of prenylation (PTI) lonafarnib, tipifarnib, zoledronic acid, or atorvastatin at concentrations of 10 μM in combination with or without 10 μg Porphyromonas gingivalis lipopolysaccharide (LPS) for 24 h. Prenyltransferase genes FNTB, FNTA, PGGT1B, RABGGTA, RABGGTB, and PTAR1 as well as inflammatory marker genes MMP1 and IL1B were detected using quantitative real-time polymerase chain reaction (RT-qPCR). Immunoblot and protein immunoassay were used to confirm the results on the protein level.

RESULTS

RT-qPCR experiments revealed significant upregulation of IL1B, MMP1, FNTA, and PGGT1B upon LPS treatment. PTase inhibitors caused significant downregulation of the inflammatory cytokine expression. Interestingly, FNTB expression was significantly upregulated in response to any PTase inhibitor in combination with LPS, but not upon LPS treatment only, indicating a vital role of protein farnesyltransferase in the proinflammatory signaling cascade.

CONCLUSIONS

In this study, distinct PTase gene expression patterns in pro-inflammatory signaling were discovered. Moreover, PTase inhibiting drugs ameliorated inflammatory mediator expression by a significant margin, indicating that prenylation is a major pre-requisite for innate immunity in periodontal cells.

Intercellular Adhesion Molecule 1: More than a Leukocyte Adhesion Molecule

Intercellular adhesion molecule 1 (ICAM-1) is a transmembrane protein in the immunoglobulin superfamily expressed on the surface of multiple cell populations and upregulated by inflammatory stimuli. It mediates cellular adhesive interactions by binding to the β2 integrins macrophage antigen 1 and leukocyte function-associated antigen 1, as well as other ligands. It has important roles in the immune system, including in leukocyte adhesion to the endothelium and transendothelial migration, and at the immunological synapse formed between lymphocytes and antigen-presenting cells. ICAM-1 has also been implicated in the pathophysiology of diverse diseases from cardiovascular diseases to autoimmune disorders, certain infections, and cancer. In this review, we summarize the current understanding of the structure and regulation of the ICAM1 gene and the ICAM-1 protein. We discuss the roles of ICAM-1 in the normal immune system and a selection of diseases to highlight the breadth and often double-edged nature of its functions. Finally, we discuss current therapeutics and opportunities for advancements.

HAM/TSP Pathogenesis: The Transmigration Activity of HTLV-1-Infected T Cells into Tissues

Slowly progressive spastic paraparesis with bladder dysfunction, the main clinical feature of human T-cell leukemia virus-1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP), is induced by chronic inflammation in the spinal cord, mainly the lower thoracic cord. A long-standing bystander mechanism, such as the destruction of surrounding tissues by inflammatory cytokines, etc., induced under the interaction between infiltrated HTLV-1-infected CD4⁺ T cells and HTLV-1-specific CD8⁺ cytotoxic T cells, has been considered implicated for the induction of chronic inflammation. As this bystander mechanism is triggered conceivably by the transmigration of HTLV-1-infected CD4⁺ T cells to the spinal cord, heightened transmigrating activity of HTLV-1-infected CD4⁺ T cells to the spinal cord might play a crucial role as the first responder in the development of HAM/TSP. This review evaluated the functions of HTLV-1-infected CD4⁺ T cells in HAM/TSP patients as the prerequisite for the acquisition of the activity such as adhesion molecule expression changes, small GTPases activation, and expression of mediators involved in basement membrane disruption. The findings suggest that HTLV-1-infected CD4⁺ T cells in HAM/TSP patients have enough potential to facilitate transmigration into the tissues. Future HAM/TSP research should clarify the molecular mechanisms leading to the establishment of HTLV-1-infected CD4⁺ T cells as the first responder in HAM/TSP patients. In addition, a regimen with an inhibitory activity against the transmigration of HTLV-1-infected CD4⁺ T cells into the spinal cord might be recommended as one of the therapeutic strategies against HAM/TSP patients.

Mechanosensation by endothelial PIEZO1 is required for leukocyte diapedesis

The extravasation of leukocytes is a critical step during inflammation which requires the localized opening of the endothelial barrier. This process is initiated by the close interaction of leukocytes with various adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) on the surface of endothelial cells. Here we reveal that mechanical forces generated by leukocyte-induced clustering of ICAM-1 synergistically with fluid shear stress exerted by the flowing blood increase endothelial plasma membrane tension to activate the mechanosensitive cation channel PIEZO1. This leads to increases in [Ca2+]i and activation of downstream signaling events including phosphorylation of SRC, PYK2 and myosin light chain resulting in opening of the endothelial barrier. Mice with endothelium-specific Piezo1 deficiency show decreased leukocyte extravasation in different inflammation models. Thus, leukocytes and the hemodynamic microenvironment synergize to mechanically activate endothelial PIEZO1 and subsequent downstream signaling to initiate leukocyte diapedesis.

Role of Semaphorins in Ischemic Stroke

Ischemic stroke is one of the major causes of neurological morbidity and mortality in the world. Although the management of ischemic stroke has been improved significantly, it still imposes a huge burden on the health and property. The integrity of the neurovascular unit (NVU) is closely related with the prognosis of ischemic stroke. Growing evidence has shown that semaphorins, a family of axon guidance cues, play a pivotal role in multiple pathophysiological processes in NVU after ischemia, such as regulating the immune system, angiogenesis, and neuroprotection. Modulating the NVU function via semaphorin signaling has a potential to develop a novel therapeutic strategy for ischemic stroke. We, therefore, review recent progresses on the role of semphorin family members in neurons, glial cells and vasculature after ischemic stroke.

Ebola Virus GP Activates Endothelial Cells via Host Cytoskeletal Signaling Factors

Ebola virus disease (EVD) is a lethal disease caused by the highly pathogenic Ebola virus (EBOV), and its major symptoms in severe cases include vascular leakage and hemorrhage. These symptoms are caused by abnormal activation and disruption of endothelial cells (ECs) whose mediators include EBOV glycoprotein (GP) without the need for viral replication. However, the detailed molecular mechanisms underlying virus-host interactions remain largely unknown. Here, we show that EBOV-like particles (VLPs) formed by GP, VP40, and NP activate ECs in a GP-dependent manner, as demonstrated by the upregulation of intercellular adhesion molecules-1 (ICAM-1) expression. VLPs-mediated ECs activation showed a different kinetic pattern from that of TNF-α-mediated activation and was associated with apoptotic ECs disruption. In contrast to TNF-α, VLPs induced ICAM-1 overexpression at late time points. Furthermore, screening of host cytoskeletal signaling inhibitors revealed that focal adhesion kinase inhibitors were found to be potent inhibitors of ICAM-1 expression mediated by both TNF-α and VLPs. Our results suggest that EBOV GP stimulates ECs to induce endothelial activation and dysfunction with the involvement of host cytoskeletal signaling factors, which represent potential therapeutic targets for EVD.

Where the Action Is-Leukocyte Recruitment in Atherosclerosis

Atherosclerosis is the leading cause of death worldwide and leukocyte recruitment is a key element of this phenomenon, thus allowing immune cells to enter the arterial wall. There, in concert with accumulating lipids, the invading leukocytes trigger a plethora of inflammatory responses which promote the influx of additional leukocytes and lead to the continued growth of atherosclerotic plaques. The recruitment process follows a precise scheme of tethering, rolling, firm arrest, crawling and transmigration and involves multiple cellular and subcellular players. This review aims to provide a comprehensive up-to-date insight into the process of leukocyte recruitment relevant to atherosclerosis, each from the perspective of endothelial cells, monocytes and macrophages, neutrophils, T lymphocytes and platelets. In addition, therapeutic options targeting leukocyte recruitment into atherosclerotic lesions-or potentially arising from the growing body of insights into its precise mechanisms-are highlighted.

Prediction of adverse effects of effluents containing phenolic compounds in the Ba River on the ovary of fish (Hemiculter leucisculus) using transcriptomic and metabolomic analyses

The aim of this work was to evaluate the endocrine disrupting effects on the ovarian development of sharpbelly (Hemiculter leucisculus) caused by effluents containing phenolic compounds. This was achieved using integrated transcriptomic and metabolomic analyses, along with histopathological examinations. Sharpbelly, an indigenous freshwater fish widely distributed in East Asia, were collected by pole fishing from three sampling sites in the Ba River. These sampling sites include a mid-stream site near a wastewater outfall and a reference site located upstream and a far field comparison site located downstream. In sharpbelly collected near the wastewater discharge, the oocyte development was activated, compared to the other two sites. Histopathological alterations in the fish ovaries were likely due to the upregulated steroid hormone biosynthesis process, as suggested by the differentially expressed genes (e.g., hsd3b, hsd17b1) and differentially accumulated metabolites (e.g., pregnenolone). Additionally, under the stress of effluents containing phenolic compounds, genes related to the signaling pathways for oxidative phosphorylation and leukocyte transendothelial migration were dysregulated, suggesting the potential induction of inflammation and several ovarian diseases. Overall, these findings suggest that effluents containing phenolic compounds influence ovary development and reproductive function of female sharpbelly. Whether there is any resulting dysfunction of folliculogenesis, abnormality of ovulation, production of premature eggs and/or potential induction of ovarian cancers remains to be determined by further studies, for a better evaluation on effluents containing phenolic compounds to the fish fertility and the health of their offspring, and even the stability of the wild fish population. Notably, the integration of transcriptomics and metabolomics can complement the routine chemical analysis to comprehensively monitor the effects of wastewater treatment plant effluents on the health of wild fish.

Rho GTPase signalling networks in cancer cell transendothelial migration

Rho GTPases are small signalling G-proteins that are central regulators of cytoskeleton dynamics, and thereby regulate many cellular processes, including the shape, adhesion and migration of cells. As such, Rho GTPases are also essential for the invasive behaviour of cancer cells, and thus involved in several steps of the metastatic cascade, including the extravasation of cancer cells. Extravasation, the process by which cancer cells leave the circulation by transmigrating through the endothelium that lines capillary walls, is an essential step for metastasis towards distant organs. During extravasation, Rho GTPase signalling networks not only regulate the transmigration of cancer cells but also regulate the interactions between cancer and endothelial cells and are involved in the disruption of the endothelial barrier function, ultimately allowing cancer cells to extravasate into the underlying tissue and potentially form metastases. Thus, targeting Rho GTPase signalling networks in cancer may be an effective approach to inhibit extravasation and metastasis. In this review, the complex process of cancer cell extravasation will be discussed in detail. Additionally, the roles and regulation of Rho GTPase signalling networks during cancer cell extravasation will be discussed, both from a cancer cell and endothelial cell point of view.

The RhoGEF Trio: A Protein with a Wide Range of Functions in the Vascular Endothelium

Many cellular processes are controlled by small GTPases, which can be activated by guanine nucleotide exchange factors (GEFs). The RhoGEF Trio contains two GEF domains that differentially activate the small GTPases such as Rac1/RhoG and RhoA. These small RhoGTPases are mainly involved in the remodeling of the actin cytoskeleton. In the endothelium, they regulate junctional stabilization and play a crucial role in angiogenesis and endothelial barrier integrity. Multiple extracellular signals originating from different vascular processes can influence the activity of Trio and thereby the regulation of the forementioned small GTPases and actin cytoskeleton. This review elucidates how various signals regulate Trio in a distinct manner, resulting in different functional outcomes that are crucial for endothelial cell function in response to inflammation.

Endothelial junctional membrane protrusions serve as hotspots for neutrophil transmigration

Upon inflammation, leukocytes rapidly transmigrate across the endothelium to enter the inflamed tissue. Evidence accumulates that leukocytes use preferred exit sites, alhough it is not yet clear how these hotspots in the endothelium are defined and how they are recognized by the leukocyte. Using lattice light sheet microscopy, we discovered that leukocytes prefer endothelial membrane protrusions at cell junctions for transmigration. Phenotypically, these junctional membrane protrusions are present in an asymmetric manner, meaning that one endothelial cell shows the protrusion and the adjacent one does not. Consequently, leukocytes cross the junction by migrating underneath the protruding endothelial cell. These protrusions depend on Rac1 activity and by using a photo-activatable Rac1 probe, we could artificially generate local exit-sites for leukocytes. Overall, we have discovered a new mechanism that uses local induced junctional membrane protrusions to facilitate/steer the leukocyte escape/exit from inflamed vessel walls.

Visualizing endogenous Rho activity with an improved localization-based, genetically encoded biosensor

Rho GTPases are regulatory proteins, which orchestrate cell features such as morphology, polarity and movement. Therefore, probing Rho GTPase activity is key to understanding processes such as development and cell migration. Localization-based reporters for active Rho GTPases are attractive probes to study Rho GTPase-mediated processes in real time with subcellular resolution in living cells and tissue. Until now, relocation Rho biosensors (sensors that relocalize to the native location of active Rho GTPase) seem to have been only useful in certain organisms and have not been characterized well. In this paper, we systematically examined the contribution of the fluorescent protein and Rho-binding peptides on the performance of localization-based sensors. To test the performance, we compared relocation efficiency and specificity in cell-based assays. We identified several improved localization-based, genetically encoded fluorescent biosensors for detecting endogenous Rho activity. This enables a broader application of Rho relocation biosensors, which was demonstrated by using the improved biosensor to visualize Rho activity during several cellular processes, such as cell division, migration and G protein-coupled receptor signaling. Owing to the improved avidity of the new biosensors for Rho activity, cellular processes regulated by Rho can be better understood.

This article has an associated First Person interview with the first author of the paper.

Summary: The dT-2xrGBD location-based Rho biosensor relocalizes more efficiently than other sensors of this type, and this sensor enables the observation of endogenous Rho activity in cultured cells.

Endothelial Focal Adhesions Are Functional Obstacles for Leukocytes During Basolateral Crawling

An inflammatory response requires leukocytes to migrate from the circulation across the vascular lining into the tissue to clear the invading pathogen. Whereas a lot of attention is focused on how leukocytes make their way through the endothelial monolayer, it is less clear how leukocytes migrate underneath the endothelium before they enter the tissue. Upon finalization of the diapedesis step, leukocytes reside in the subendothelial space and encounter endothelial focal adhesions. Using TIRF microscopy, we show that neutrophils navigate around these focal adhesions. Neutrophils recognize focal adhesions as physical obstacles and deform to get around them. Increasing the number of focal adhesions by silencing the small GTPase RhoJ slows down basolateral crawling of neutrophils. However, apical crawling and diapedesis itself are not affected by RhoJ depletion. Increasing the number of focal adhesions drastically by expressing the Rac1 GEF Tiam1 make neutrophils to avoid migrating underneath these Tiam1-expressing endothelial cells. Together, our results show that focal adhesions mark the basolateral migration path of neutrophils.

Proteomic Profiling of Leukocytes Reveals Dysregulation of Adhesion and Integrin Proteins in Chronic Kidney Disease-Related Atherosclerosis

A progressive loss of functional nephrons defines chronic kidney disease (CKD). Complications related to cardiovascular disease (CVD) are the principal causes of mortality in CKD; however, the acceleration of CVD in CKD remains unresolved. Our study used a complementary proteomic approach to assess mild and advanced CKD patients with different atherosclerosis stages and two groups of patients with different classical CVD progression but without renal dysfunction. We utilized a label-free approach based on LC-MS/MS and functional bioinformatic analyses to profile CKD and CVD leukocyte proteins. We revealed dysregulation of proteins involved in different phases of leukocytes' diapedesis process that is very pronounced in CKD's advanced stage. We also showed an upregulation of apoptosis-related proteins in CKD as compared to CVD. The differential abundance of selected proteins was validated by multiple reaction monitoring, ELISA, Western blotting, and at the mRNA level by ddPCR. An increased rate of apoptosis was then functionally confirmed on the cellular level. Hence, we suggest that the disturbances in leukocyte extravasation proteins may alter cell integrity and trigger cell death, as demonstrated by flow cytometry and microscopy analyses. Our proteomics data set has been deposited to the ProteomeXchange Consortium via the PRIDE repository with the data set identifier PXD018596.

Integrating Network Pharmacology and Experimental Validation to Decipher the Mechanism of Action of Huanglian Jiedu Decoction in Treating Atherosclerosis

Background

This study used network pharmacology, molecular docking and experimental validation to assess the effects of Huanglian Jiedu Decoction (HLJDD) on atherosclerosis (AS).

Methods

The components and targets of HLJDD were analyzed using the Traditional Chinese Medicine Systems Pharmacology database, and information on the genes associated with AS was retrieved from the GeneCards and OMIM platforms. Protein–protein interactions were analyzed using the STRING platform. A component–target–disease network was constructed using Cytoscape. GO and KEGG analyses were performed to identify molecular biological processes and signaling pathways, and the predictions were verified experimentally. Molecular docking was conducted with ChemOffice software, PyMOL software and Vina to verify the correlation of targets and compounds.

Results

HLJDD contained 31 active compounds, with quercetin, kaempferol, moupinamide and 5-hydroxy-7-methoxy-2-(3,4,5-trimethoxyphenyl)chromone as the core compounds. The most important biotargets of HLJDD in AS were ICAM-1, CD31 and RAM-11. The molecular docking results showed that the molecular docking interaction energy between the 3 key targets and the 4 high-degree components were much less than −5 kJ∙mol⁻¹. The experimental validation results showed that HLJDD might treat AS mainly by reducing TC, TG and LDL-C and increasing HDL-C, upregulating CD31 expression, reducing ICAM-1 and RAM-11 expression, and downregulating inflammatory factors, including CRP, IL-6 and TNF-α. These results support the network pharmacology data and demonstrate that HLJDD affects the expression of core genes and alters the leukocyte transendothelial migration signaling pathway.

Conclusion

Based on network pharmacology and experimental validation, our study indicated that HLJDD exerted anti-AS effect through upregulating CD31 expression and reducing the expression of ICAM-1 and RAM-11. HLJDD may be a potential therapeutic drug to the prevention of AS.

Elucidating the Biomechanics of Leukocyte Transendothelial Migration by Quantitative Imaging

Leukocyte transendothelial migration is crucial for innate immunity and inflammation. Upon tissue damage or infection, leukocytes exit blood vessels by adhering to and probing vascular endothelial cells (VECs), breaching endothelial cell-cell junctions, and transmigrating across the endothelium. Transendothelial migration is a critical rate-limiting step in this process. Thus, leukocytes must quickly identify the most efficient route through VEC monolayers to facilitate a prompt innate immune response. Biomechanics play a decisive role in transendothelial migration, which involves intimate physical contact and force transmission between the leukocytes and the VECs. While quantifying these forces is still challenging, recent advances in imaging, microfabrication, and computation now make it possible to study how cellular forces regulate VEC monolayer integrity, enable efficient pathfinding, and drive leukocyte transmigration. Here we review these recent advances, paying particular attention to leukocyte adhesion to the VEC monolayer, leukocyte probing of endothelial barrier gaps, and transmigration itself. To offer a practical perspective, we will discuss the current views on how biomechanics govern these processes and the force microscopy technologies that have enabled their quantitative analysis, thus contributing to an improved understanding of leukocyte migration in inflammatory diseases.

Functional and Therapeutic Relevance of Rho GTPases in Innate Immune Cell Migration and Function during Inflammation: An In Silico Perspective

Systematic regulation of leukocyte migration to the site of infection is a vital step during immunological responses. Improper migration and localization of immune cells could be associated with disease pathology as seen in systemic inflammation. Rho GTPases act as molecular switches during inflammatory cell migration by cycling between Rho-GDP (inactive) to Rho-GTP (active) forms and play an essential role in the precise regulation of actin cytoskeletal dynamics as well as other immunological functions of leukocytes. Available reports suggest that the dysregulation of Rho GTPase signaling is associated with various inflammatory diseases ranging from mild to life-threatening conditions. Therefore, it is crucial to understand the step-by-step activation and inactivation of GTPases and the functioning of different Guanine Nucleotide Exchange Factors (GEFs) and GTPase-Activating Proteins (GAPs) that regulate the conversion of GDP to GTP and GTP to GDP exchange reactions, respectively. Here, we describe the molecular organization and activation of various domains of crucial elements associated with the activation of Rho GTPases using solved PDB structures. We will also present the latest evidence available on the relevance of Rho GTPases in the migration and function of innate immune cells during inflammation. This knowledge will help scientists design promising drug candidates against the Rho-GTPase-centric regulatory molecules regulating inflammatory cell migration.

Paracellular and Transcellular Leukocytes Diapedesis Are Divergent but Interconnected Evolutionary Events

Infiltration of the endothelial layer of the blood-brain barrier by leukocytes plays a critical role in health and disease. When passing through the endothelial layer during the diapedesis process lymphocytes can either follow a paracellular route or a transcellular one. There is a debate whether these two processes constitute one mechanism, or they form two evolutionary distinct migration pathways. We used artificial intelligence, phylogenetic analysis, HH search, ancestor sequence reconstruction to investigate further this intriguing question. We found that the two systems share several ancient components, such as RhoA protein that plays a critical role in controlling actin movement in both mechanisms. However, some of the key components differ between these two transmigration processes. CAV1 genes emerged during Trichoplax adhaerens, and it was only reported in transcellular process. Paracellular process is dependent on PECAM1. PECAM1 emerged from FASL5 during Zebrafish divergence. Lastly, both systems employ late divergent genes such as ICAM1 and VECAM1. Taken together, our results suggest that these two systems constitute two different mechanical sensing mechanisms of immune cell infiltrations of the brain, yet these two systems are connected. We postulate that the mechanical properties of the cellular polarity is the main driving force determining the migration pathway. Our analysis indicates that both systems coevolved with immune cells, evolving to a higher level of complexity in association with the evolution of the immune system.

A Window of Opportunity: Targeting Cancer Endothelium to Enhance Immunotherapy

Vascular abnormalities in tumors have a major impact on the immune microenvironment in tumors. The consequences of abnormal vasculature include increased hypoxia, acidosis, high intra-tumoral fluid pressure, and angiogenesis. This introduces an immunosuppressive microenvironment that alters immune cell maturation, activation, and trafficking, which supports tumor immune evasion and dissemination of tumor cells. Increasing data suggests that cancer endothelium is a major barrier for traveling leukocytes, ranging from a partial blockade resulting in a selective endothelial barrier, to a complete immune infiltration blockade associated with immune exclusion and immune desert cancer phenotypes. Failed immune cell trafficking as well as immunosuppression within the tumor microenvironment limits the efficacy of immunotherapeutic approaches. As such, targeting proteins with key roles in angiogenesis may potentially reduce immunosuppression and might restore infiltration of anti-tumor immune cells, creating a therapeutic window for successful immunotherapy. In this review, we provide a comprehensive overview of established as well as more controversial endothelial pathways that govern selective immune cell trafficking across cancer endothelium. Additionally, we discuss recent insights and strategies that target tumor vasculature in order to increase infiltration of cytotoxic immune cells during the therapeutic window of vascular normalization hereby improving the efficacy of immunotherapy.

Stiffness-Induced Endothelial DLC-1 Expression Forces Leukocyte Spreading through Stabilization of the ICAM-1 Adhesome

Leukocytes follow the well-defined steps of rolling, spreading, and crawling prior to diapedesis through endothelial cells (ECs). We found increased expression of DLC-1 in stiffness-associated diseases like atherosclerosis and pulmonary arterial hypertension. Depletion of DLC-1 in ECs cultured on stiff substrates drastically reduced cell stiffness and mimicked leukocyte transmigration kinetics observed for ECs cultured on soft substrates. Mechanistic studies revealed that DLC-1-depleted ECs or ECs cultured on soft substrates failed to recruit the actin-adaptor proteins filamin B, α-actinin-4, and cortactin to clustered ICAM-1, thereby preventing the ICAM-1 adhesome formation and impairing leukocyte spreading. This was rescued by overexpressing DLC-1, resulting in ICAM-1 adhesome stabilization and leukocyte spreading. Our results reveal an essential role for substrate stiffness-regulated endothelial DLC-1, independent of its GAP domain, in locally stabilizing the ICAM-1 adhesome to promote leukocyte spreading, essential for efficient leukocyte transendothelial migration.

Defining the molecular evolution of extrauterine high grade serous carcinoma

OBJECTIVE

High grade serous carcinoma (HGSC) is the most common and most aggressive, subtype of epithelial ovarian cancer. It presents as advanced stage disease with poor prognosis. Recent pathological evidence strongly suggests HGSC arises from the fallopian tube via the precursor lesion; serous tubal intraepithelial carcinoma (STIC). However, further definition of the molecular evolution of HGSC has major implications for both clinical management and research. This study aims to more clearly define the molecular pathogenesis of HGSC.

METHODS

Six cases of HGSC were identified at the Northern Ireland Gynaecological Cancer Centre (NIGCC) that each contained ovarian HGSC (HGSC), omental HGSC (OMT), STIC, normal fallopian tube epithelium (FTE) and normal ovarian surface epithelium (OSE). The relevant formalin-fixed paraffin embedded (FFPE) tissue samples were retrieved from the pathology archive via the Northern Ireland Biobank following attaining ethical approval (NIB11:005). Full microarray-based gene expression profiling was performed on the cohort. The resulting data was analysed bioinformatically and the results were validated in a HGSC-specific in-vitro model.

RESULTS

The carcinogenesis of HGSC was investigated and showed the molecular profile of HGSC to be more closely related to normal FTE than OSE. STIC lesions also clustered closely with HGSC, indicating a common molecular origin.

CONCLUSION

This study provides strong evidence suggesting that extrauterine HGSC arises from the fimbria of the distal fallopian tube. Furthermore, several potential pathways were identified which could be targeted by novel therapies for HGSC. These findings have significant translational relevance for both primary prevention and clinical management of the disease.

Passing the Vascular Barrier: Endothelial Signaling Processes Controlling Extravasation

A central function of the vascular endothelium is to serve as a barrier between the blood and the surrounding tissue of the body. At the same time, solutes and cells have to pass the endothelium to leave or to enter the bloodstream to maintain homeostasis. Under pathological conditions, for example, inflammation, permeability for fluid and cells is largely increased in the affected area, thereby facilitating host defense. To appropriately function as a regulated permeability filter, the endothelium uses various mechanisms to allow solutes and cells to pass the endothelial layer. These include transcellular and paracellular pathways of which the latter requires remodeling of intercellular junctions for its regulation. This review provides an overview on endothelial barrier regulation and focuses on the endothelial signaling mechanisms controlling the opening and closing of paracellular pathways for solutes and cells such as leukocytes and metastasizing tumor cells.

Endothelial Nanomechanics in the Context of Endothelial (Dys)function and Inflammation

SIGNIFICANCE

Stiffness of endothelial cells is closely linked to the function of the vasculature as it regulates the release of vasoactive substances such as nitric oxide (NO) and reactive oxygen species. The outer layer of endothelial cells, consisting of the glycocalyx above and the cortical zone beneath the plasma membrane, is a vulnerable compartment able to adapt its nanomechanical properties to any changes of forces exerted by the adjacent blood stream. Sustained stiffening of this layer contributes to the development of endothelial dysfunction and vascular pathologies. Recent Advances: The development of specific techniques to quantify the mechanical properties of cells enables the detailed investigation of the mechanistic link between structure and function of cells.

CRITICAL ISSUES

Challenging the mechanical stiffness of cells, for instance, by inflammatory mediators can lead to the development of endothelial dysfunction. Prevention of sustained stiffening of the outer layer of endothelial cells in turn improves endothelial function.

FUTURE DIRECTIONS

The mechanical properties of cells can be used as critical marker and test system for the proper function of the vascular system. Pharmacological substances, which are able to improve endothelial nanomechanics and function, could take a new importance in the prevention and treatment of vascular diseases. Thus, detailed knowledge acquisition about the structure/function relationship of endothelial cells and the underlying signaling pathways should be promoted.

Vascular Endothelial (VE)-Cadherin, Endothelial Adherens Junctions, and Vascular Disease

Endothelial cell-cell adherens junctions (AJs) supervise fundamental vascular functions, such as the control of permeability and transmigration of circulating leukocytes, and the maintenance of existing vessels and formation of new ones. These processes are often dysregulated in pathologies. However, the evidence that links dysfunction of endothelial AJs to human pathologies is mostly correlative. In this review, we present an update of the molecular organization of AJ complexes in endothelial cells (ECs) that is mainly based on observations from experimental models. Furthermore, we report in detail on a human pathology, cerebral cavernous malformation (CCM), which is initiated by loss-of-function mutations in the genes that encode the three cytoplasmic components of AJs (CCM1, CCM2, and CCM3). At present, these represent a unique example of mutations in components of endothelial AJs that cause human disease. We describe also how studies into the defects of AJs in CCM are shedding light on the crucial regulatory mechanisms and signaling activities of these endothelial structures. Although these observations are specific for CCM, they support the concept that dysfunction of endothelial AJs can directly contribute to human pathologies.

Increasing spatial resolution of photoregulated GTPases through immobilized peripheral membrane proteins

Light-induced dimerizing systems, e.g. iLID, are an increasingly utilized optogenetics tool to perturb cellular signaling. The major benefit of this technique is that it allows external spatiotemporal control over protein localization with sub-cellular specificity. However, when it comes to local recruitment of signaling components to the plasmamembrane, this precision in localization is easily lost due to rapid diffusion of the membrane anchor. In this study, we explore different approaches of countering the diffusion of peripheral membrane anchors, to the point where we detect immobilized fractions with iFRAP on a timescale of several minutes. One method involves simultaneous binding of the membrane anchor to a secondary structure, the microtubules. The other strategy utilizes clustering of the anchor into large immobile structures, which can also be interlinked by employing tandem recruitable domains. For both approaches, the anchors are peripheral membrane constructs, which also makes them suitable for in vitro use. Upon combining these slower diffusing anchors with recruitable guanine exchange factors (GEFs), we show that we can elicit much more localized morphological responses from Rac1 and Cdc42 as compared to a regular CAAX-box based membrane anchor in living cells. Thanks to these new slow diffusing anchors, more precisely defined membrane recruitment experiments are now possible.

Tetraspanin CD9: A Key Regulator of Cell Adhesion in the Immune System

The tetraspanin CD9 is expressed by all the major subsets of leukocytes (B cells, CD4⁺ T cells, CD8⁺ T cells, natural killer cells, granulocytes, monocytes and macrophages, and immature and mature dendritic cells) and also at a high level by endothelial cells. As a typical member of the tetraspanin superfamily, a prominent feature of CD9 is its propensity to engage in a multitude of interactions with other tetraspanins as well as with different transmembrane and intracellular proteins within the context of defined membranal domains termed tetraspanin-enriched microdomains (TEMs). Through these associations, CD9 influences many cellular activities in the different subtypes of leukocytes and in endothelial cells, including intracellular signaling, proliferation, activation, survival, migration, invasion, adhesion, and diapedesis. Several excellent reviews have already covered the topic of how tetraspanins, including CD9, regulate these cellular processes in the different cells of the immune system. In this mini-review, however, we will focus particularly on describing and discussing the regulatory effects exerted by CD9 on different adhesion molecules that play pivotal roles in the physiology of leukocytes and endothelial cells, with a particular emphasis in the regulation of adhesion molecules of the integrin and immunoglobulin superfamilies.

Curcumin modulates endothelial permeability and monocyte transendothelial migration by affecting endothelial cell dynamics

Curcumin is a phenolic compound that exhibits beneficial properties for cardiometabolic health. We previously showed that curcumin reduced the infiltration of immune cells into the vascular wall and prevented atherosclerosis development in mice. This study aimed to investigate the effect of curcumin on monocyte adhesion and transendothelial migration (TEM) and to decipher the underlying mechanisms of these actions. Human umbilical vein endothelial cells (HUVECs) were exposed to curcumin (0.5-1μM) for 3h prior to their activation by Tumor Necrosis Factor alpha (TNF-α). Endothelial permeability, monocyte adhesion and transendothelial migration assays were conducted under static condition and shear stress that mimics blood flow. We further investigated the impact of curcumin on signaling pathways and on the expression of genes using macroarrays. Pre-exposure of endothelial cells to curcumin reduced monocyte adhesion and their transendothelial migration in both static and shear stress conditions. Curcumin also prevented changes in both endothelial permeability and the area of HUVECs when induced by TNF-α. We showed that curcumin modulated the expression of 15 genes involved in the control of cytoskeleton and endothelial junction dynamic. Finally, we showed that curcumin inhibited NF-κB signaling likely through an antagonist interplay with several kinases as suggested by molecular docking analysis. Our findings demonstrate the ability of curcumin to reduce monocyte TEM through a multimodal regulation of the endothelial cell dynamics with a potential benefit on the vascular endothelial function barrier.

Endothelial cell-cell adhesion and signaling

Endothelial cells line blood vessels and provide a dynamic interface between the blood and tissues. They remodel to allow leukocytes, fluid and small molecules to enter tissues during inflammation and infections. Here we compare the signaling networks that contribute to endothelial permeability and leukocyte transendothelial migration, focusing particularly on signals mediated by small GTPases that regulate cell adhesion and the actin cytoskeleton. Rho and Rap GTPase signaling is important for both processes, but they differ in that signals are activated locally under leukocytes, whereas endothelial permeability is a wider event that affects the whole cell. Some molecules play a unique role in one of the two processes, and could therefore be targeted to selectively alter either endothelial permeability or leukocyte transendothelial migration.

Endothelial CD2AP Binds the Receptor ICAM-1 To Control Mechanosignaling, Leukocyte Adhesion, and the Route of Leukocyte Diapedesis In Vitro

Inflammation is driven by excessive transmigration (diapedesis) of leukocytes from the blood to the tissue across the endothelial cell monolayer that lines blood vessels. Leukocyte adhesion, crawling, and transmigration are regulated by clustering of the endothelial mechanosensitive receptor intercellular adhesion molecule-1 (ICAM-1). Whereas several proteins are known to promote ICAM-1 function, the molecular mechanisms that limit ICAM-1-mediated adhesion to prevent excessive leukocyte transmigration remain unknown. We identify the endothelial actin-binding protein CD2-associated protein (CD2AP) as a novel interaction partner of ICAM-1. Loss of CD2AP stimulates the dynamics of ICAM-1 clustering, which facilitates the formation of ICAM-1 complexes on the endothelial cell surface. Consequently, neutrophil adhesion is increased, but crawling is decreased. In turn, this promotes the neutrophil preference for the transcellular over the paracellular transmigration route. Mechanistically, CD2AP is required for mechanosensitive ICAM-1 downstream signaling toward activation of the PI3K, and recruitment of F-actin and of the actin-branching protein cortactin. Moreover, CD2AP is necessary for ICAM-1-induced Rac1 recruitment and activation. Mechanical force applied on ICAM-1 impairs CD2AP binding to ICAM-1, suggesting that a tension-induced negative feedback loop promotes ICAM-1-mediated neutrophil crawling and paracellular transmigration. To our knowledge, these data show for the first time that the mechanoreceptor ICAM-1 is negatively regulated by an actin-binding adaptor protein, i.e., CD2AP, to allow a balanced and spatiotemporal control of its adhesive function. CD2AP is important in kidney dysfunction that is accompanied by inflammation. Our findings provide a mechanistic basis for the role of CD2AP in inflamed vessels, identifying this adaptor protein as a potential therapeutic target.

VCAM1 acts in parallel with CD69 and is required for the initiation of oligodendrocyte myelination

Oligodendrocytes differentiate to wrap their plasma membranes around axons, forming the myelin sheath. A neuronal cue is one of the regulator elements controlling this process. Here, we demonstrate that VCAM1, which plays a key role throughout the immune system, is also expressed in oligodendrocytes, where it regulates the initiation of myelination. VCAM1 knockout mice exhibit reduced myelin thickness. Decreased myelin thickness is also observed in mutant mice of α4 integrin, which is a neuronal VCAM1 ligand. Furthermore, CD69 is identified as one of the transcripts downregulated when VCAM1 is knocked down in oligodendrocytes. Knockdown of CD69 in mice indicates its role in myelination. Therefore, VCAM1 contributes not only to the initiation of myelination but also to its regulation through controlling the abundance of CD69, demonstrating that an intercellular molecule whose primary role is in the immune system can also play an unexpected role in the CNS.

The vascular cell adhesion molecule VCAM1 plays a role in the immune system but is also expressed in oligodendrocytes. Here, the authors find VCAM1 interacts with neuronal α4 integrin to regulate oligodendrocyte differentiation and thereby myelination, an effect mediated by downstream CD69 signalling.

EphA2 promotes cell adhesion and spreading of monocyte and monocyte/macrophage cell lines on integrin ligand-coated surfaces

Eph signaling, which arises following stimulation by ephrins, is known to induce opposite cell behaviors such as promoting and inhibiting cell adhesion as well as promoting cell-cell adhesion and repulsion by altering the organization of the actin cytoskeleton and influencing the adhesion activities of integrins. However, crosstalk between Eph/ephrin with integrin signaling has not been fully elucidated in leukocytes, including monocytes and their related cells. Using a cell attachment stripe assay, we have shown that, following stimulation with ephrin-A1, kinase-independent EphA2 promoted cell spreading/elongation as well as adhesion to integrin ligand-coated surfaces in cultured U937 (monocyte) and J774.1 (monocyte/macrophage) cells as well as sublines of these cells expressing dominant negative EphA2 that lacks most of the intracellular region. Moreover, a pull-down assay showed that dominant negative EphA2 is recruited to the β2 integrin/ICAM1 and β2 integrin/VCAM1 molecular complexes in the subline cells following stimulation with ephrin-A1-Fc. Notably, this study is the first comprehensive analysis of the effects of EphA2 receptors on integrin-mediated cell adhesion in monocytic cells. Based on these findings we propose that EphA2 promotes cell adhesion by an unknown signaling pathway that largely depends on the extracellular region of EphA2 and the activation of outside-in integrin signaling.

Leukocyte transendothelial migration: A local affair

Inflammation is part of the complex biological response of body tissues to harmful stimuli, such as pathogens. It serves as a protective response that involves leukocytes, blood vessels and molecular mediators with the purpose to eliminate the initial cause of cell injury and to initiate tissue repair. Inflammation is tightly regulated by the body and is associated with transient crossing of leukocytes through the blood vessel wall, a process called transendothelial migration (TEM) or diapedesis. TEM is a close collaboration between leukocytes on one hand and the endothelium on the other. Limiting vascular leakage during TEM but also when the leukocyte has crossed the endothelium is essential for maintaining vascular homeostasis. Although many details have been uncovered during the recent years, the molecular mechanisms from the vascular part that drive TEM still shows significant gaps in our understanding. This review will focus on the local signals that are induced in the endothelium that regulate leukocyte TEM and simultaneous preservation of endothelial barrier function.

Matrix stiffness exerts biphasic control over monocyte-endothelial adhesion via Rho-mediated ICAM-1 clustering

Leukocyte-endothelial adhesion is a critical early step in chronic vascular inflammation associated with diabetes, emphysema, and aging. Importantly, these conditions are also marked by abnormal subendothelial matrix crosslinking (stiffness). Yet, whether and how abnormal matrix stiffness contributes to leukocyte-endothelial adhesion remains poorly understood. Using a co-culture of human monocytic cells and human microvascular endothelial cells (ECs) grown on matrices of tunable stiffness, we demonstrate that matrix stiffness exerts biphasic control over monocyte-EC adhesion, with both matrix softening and stiffening eliciting a two-fold increase in this adhesive interaction. This preferential endothelial adhesivity on softer and stiffer matrices was consistent with a significant increase in α-actinin-4-associated endothelial ICAM-1 clustering, a key determinant of monocyte-EC adhesion. Further, the enhanced ICAM-1 clustering on soft and stiff matrices correlated strongly with an increase in Rho activity and ROCK2 expression. Importantly, inhibition of Rho/ROCK activity blocked the effects of abnormal matrix stiffness on ICAM-1 clustering and monocyte-EC adhesion. Thus, these findings implicate matrix stiffness-dependent ICAM-1 clustering as an important regulator of vascular inflammation and provide the rationale for closely examining mechanotransduction pathways as new molecular targets for anti-inflammatory therapy.

Angiopellosis as an Alternative Mechanism of Cell Extravasation

Stem cells possess the ability to home in and travel to damaged tissue when injected intravenously. For the cells to exert their therapeutic effect, they must cross the blood vessel wall and enter the surrounding tissues. The mechanism of extravasation injected stem cells employ for exit has yet to be characterized. Using intravital microscopy and a transgenic zebrafish line Tg(fli1a:egpf) with GFP-expressing vasculature, we documented the detailed extravasation processes in vivo for injected stem cells in comparison to white blood cells (WBCs). While WBCs left the blood vessels by the standard diapedesis process, injected cardiac and mesenchymal stem cells underwent a distinct method of extravasation that was markedly different from diapedesis. Here, the vascular wall undergoes an extensive remodeling to allow the cell to exit the lumen, while the injected cell remains distinctively passive in activity. We termed this process Angio-pello-sis, which represents an alternative mechanism of cell extravasation to the prevailing theory of diapedesis. Stem Cells 2017;35:170-180 Video Highlight: https://youtu.be/i5EI-ZvhBps.

The effect of hypothermia on influx of leukocytes in the digital lamellae of horses with oligofructose-induced laminitis

Sepsis-related laminitis (SRL) is a common complication in the septic/endotoxemic critically-ill equine patient, in which lamellar injury and failure commonly lead to crippling distal displacement of the distal phalanx. Similar to organ injury in human sepsis, lamellar injury in SRL has been associated with inflammatory events, including the influx of leukocytes into the lamellar tissue and markedly increased expression of a wide array of inflammatory mediators at the onset of Obel grade 1 (OG1) laminitis. The only treatment reported both clinically and experimentally to protect the lamellae in SRL, local hypothermia ("cryotherapy"), has been demonstrated to effectively inhibit lamellar expression of multiple inflammatory mediators when initiated at the time of administration of a carbohydrate overload in experimental models of SRL. However, the effect of hypothermia on leukocyte influx into affected tissue has not been assessed. We hypothesized that cryotherapy inhibits leukocyte emigration into the digital lamellae in SRL. Immunohistochemical staining using leukocyte markers MAC387 (marker of neutrophils, activated monocytes) and CD163 (monocyte/macrophage-specific marker) was performed on archived lamellar tissue samples from an experimental model of SRL in which one forelimb was maintained at ambient temperature (AMB) and one forelimb was immersed in ice water (ICE) immediately following enteral oligofructose administration (10g/kg, n=14 horses). Lamellae were harvested at 24h post-oligofructose administration (DEV, n=7) or at the onset of OG1 laminitis (OG1, n=7). Both MAC387-positive and CD163-positive cells were counted by a single blinded investigator on images [n=10 (40× fields/digit for MAC387 and 20x fields/digit for CD163)] obtained using Aperio microscopy imaging analysis software. Data were assessed for normality and analyzed with a paired t-test and one-way ANOVA with significance set at p<0.05. MAC387-positive cells were present in low numbers in the lamellar tissue and were decreased in the hypothermic limbs (vs. AMB limbs, p<0.05) in the OG1 group; no change in CD163-positive cell numbers was noted across the conditions of the model. This study demonstrated that hypothermia of the distal limbs instituted early in the disease process in the horse at risk of SRL significantly attenuates the increase of MAC387-positive leukocytes in the digital lamellae, but has minimal effect on increases in lamellar concentrations of the major leukocyte cell type present in that tissue, CD163-positive mononuclear cells.

Rho Kinases in Health and Disease: From Basic Science to Translational Research

Rho-associated kinases ROCK1 and ROCK2 are key regulators of actin cytoskeleton dynamics downstream of Rho GTPases that participate in the control of important physiologic functions, S including cell contraction, migration, proliferation, adhesion, and inflammation. Several excellent review articles dealing with ROCK function and regulation have been published over the past few years. Although a brief overview of general molecular, biochemical, and functional properties of ROCKs is included, an effort has been made to produce an original work by collecting and synthesizing recent studies aimed at translating basic discoveries from cell and experimental models into knowledge of human physiology, pathophysiological mechanisms, and medical therapeutics. This review points out the specificity and distinct roles of ROCK1 and ROCK2 isoforms highlighted in the last few years. Results obtained from genetically modified mice and genetic analysis in humans are discussed. This review also addresses the involvement of ROCKs in human diseases and the potential use of ROCK activity as a biomarker or a pharmacological target for specific inhibitors.

Recent insights into endothelial control of leukocyte extravasation

In the process of leukocyte migration from the circulation across the vascular wall, the crosstalk with endothelial cells that line the blood vessels is essential. It is now firmly established that in endothelial cells important signaling events are initiated upon leukocyte adhesion that impinge on the regulation of cell-cell contact and control the efficiency of transendothelial migration. In addition, several external factors such as shear force and vascular stiffness were recently identified as important regulators of endothelial signaling and, consequently, leukocyte transmigration. Here, I review recent insights into endothelial signaling events that are linked to leukocyte migration across the vessel wall. In this field, protein phosphorylation and Rho-mediated cytoskeletal dynamics are still widely studied using increasingly sophisticated mouse models. In addition, activation of tyrosine phosphatases, changes in endothelial cell stiffness as well as different vascular beds have all been established as important factors in endothelial signaling and leukocyte transmigration. Finally, I address less-well-studied but interesting components in the endothelium that also control transendothelial migration, such as the ephrins and their Eph receptors, that provide novel insights in the complexity associated with this process.

Tension on JAM-A activates RhoA via GEF-H1 and p115 RhoGEF

Forces on JAM-A activate RhoA to increase cell stiffness. Activation of RhoA requires GEF-H1 and p115 RhoGEF activation downstream of FAK/ERK and Src family kinases, respectively.

Junctional adhesion molecule A (JAM-A) is a broadly expressed adhesion molecule that regulates cell–cell contacts and facilitates leukocyte transendothelial migration. The latter occurs through interactions with the integrin LFA-1. Although we understand much about JAM-A, little is known regarding the protein’s role in mechanotransduction or as a modulator of RhoA signaling. We found that tension imposed on JAM-A activates RhoA, which leads to increased cell stiffness. Activation of RhoA in this system depends on PI3K-mediated activation of GEF-H1 and p115 RhoGEF. These two GEFs are further regulated by FAK/ERK and Src family kinases, respectively. Finally, we show that phosphorylation of JAM-A at Ser-284 is required for RhoA activation in response to tension. These data demonstrate a direct role of JAM-A in mechanosignaling and control of RhoA and implicate Src family kinases in the regulation of p115 RhoGEF.

F-actin-rich contractile endothelial pores prevent vascular leakage during leukocyte diapedesis through local RhoA signalling

During immune surveillance and inflammation, leukocytes exit the vasculature through transient openings in the endothelium without causing plasma leakage. However, the exact mechanisms behind this intriguing phenomenon are still unknown. Here we report that maintenance of endothelial barrier integrity during leukocyte diapedesis requires local endothelial RhoA cycling. Endothelial RhoA depletion in vitro or Rho inhibition in vivo provokes neutrophil-induced vascular leakage that manifests during the physical movement of neutrophils through the endothelial layer. Local RhoA activation initiates the formation of contractile F-actin structures that surround emigrating neutrophils. These structures that surround neutrophil-induced endothelial pores prevent plasma leakage through actomyosin-based pore confinement. Mechanistically, we found that the initiation of RhoA activity involves ICAM-1 and the Rho GEFs Ect2 and LARG. In addition, regulation of actomyosin-based endothelial pore confinement involves ROCK2b, but not ROCK1. Thus, endothelial cells assemble RhoA-controlled contractile F-actin structures around endothelial pores that prevent vascular leakage during leukocyte extravasation.

Endothelial cells can support leukocyte extravasation without causing vascular leakage, but the exact mechanism underlying this process has not been fully elucidated. Here the authors show that it is regulated through actomyosin-based endothelial pore confinement, which requires local endothelial RhoA activation.

Nanoscale Imaging Reveals a Tetraspanin-CD9 Coordinated Elevation of Endothelial ICAM-1 Clusters

Endothelial barriers have a central role in inflammation as they allow or deny the passage of leukocytes from the vasculature into the tissue. To bind leukocytes, endothelial cells form adhesive clusters containing tetraspanins and ICAM-1, so-called endothelial adhesive platforms (EAPs). Upon leukocyte binding, EAPs evolve into docking structures that emanate from the endothelial surface while engulfing the leukocyte. Here, we show that TNF-α is sufficient to induce apical protrusions in the absence of leukocytes. Using advanced quantitation of atomic force microscopy (AFM) recordings, we found these structures to protrude by 160 ± 80 nm above endothelial surface level. Confocal immunofluorescence microscopy proved them positive for ICAM-1, JAM-A, tetraspanin CD9 and f-actin. Microvilli formation was inhibited in the absence of CD9. Our findings indicate that stimulation with TNF-α induces nanoscale changes in endothelial surface architecture and that—via a tetraspanin CD9 depending mechanism—the EAPs rise above the surface to facilitate leukocyte capture.

Genome Wide Identification of SARS-CoV Susceptibility Loci Using the Collaborative Cross

New systems genetics approaches are needed to rapidly identify host genes and genetic networks that regulate complex disease outcomes. Using genetically diverse animals from incipient lines of the Collaborative Cross mouse panel, we demonstrate a greatly expanded range of phenotypes relative to classical mouse models of SARS-CoV infection including lung pathology, weight loss and viral titer. Genetic mapping revealed several loci contributing to differential disease responses, including an 8.5Mb locus associated with vascular cuffing on chromosome 3 that contained 23 genes and 13 noncoding RNAs. Integrating phenotypic and genetic data narrowed this region to a single gene, Trim55, an E3 ubiquitin ligase with a role in muscle fiber maintenance. Lung pathology and transcriptomic data from mice genetically deficient in Trim55 were used to validate its role in SARS-CoV-induced vascular cuffing and inflammation. These data establish the Collaborative Cross platform as a powerful genetic resource for uncovering genetic contributions of complex traits in microbial disease severity, inflammation and virus replication in models of outbred populations.

Rho GTPase signalling in cell migration

Cells migrate in multiple different ways depending on their environment, which includes the extracellular matrix composition, interactions with other cells, and chemical stimuli. For all types of cell migration, Rho GTPases play a central role, although the relative contribution of each Rho GTPase depends on the environment and cell type. Here, I review recent advances in our understanding of how Rho GTPases contribute to different types of migration, comparing lamellipodium-driven versus bleb-driven migration modes. I also describe how cells migrate across the endothelium. In addition to Rho, Rac and Cdc42, which are well known to regulate migration, I discuss the roles of other less-well characterized members of the Rho family.

Rho GTPase signalling in cell migration

Cells migrate in multiple different ways depending on their environment, which includes the extracellular matrix composition, interactions with other cells, and chemical stimuli. For all types of cell migration, Rho GTPases play a central role, although the relative contribution of each Rho GTPase depends on the environment and cell type. Here, I review recent advances in our understanding of how Rho GTPases contribute to different types of migration, comparing lamellipodium-driven versus bleb-driven migration modes. I also describe how cells migrate across the endothelium. In addition to Rho, Rac and Cdc42, which are well known to regulate migration, I discuss the roles of other less-well characterized members of the Rho family.

CD100 and plexins B2 and B1 mediate monocyte-endothelial cell adhesion and might take part in atherogenesis

Leukocyte migration is essential for the function of the immune system. Their recruitment from the vessels to the tissues involves sequential molecular interactions between leukocytes and endothelial cells (ECs). Many adhesion molecules involved in this process have already been described. However, additional molecules may be important in this interaction, and here we explore the potential role for CD100 and plexins in monocyte-EC binding. CD100 was shown to be involved in platelet-endothelial cell interaction, an important step in atherogenesis and thrombus formation. In a recent work we have described CD100 expression in monocytes and in macrophages and foam cells of human atherosclerotic plaques. In the present work, we have identified plexin B2 as a putative CD100 receptor in these cells. We have detected CD100 expression in the endothelium as well as in in vitro cultured endothelial cells. Blocking of CD100, plexin B1 and/or B2 in adhesion experiments have shown that both CD100 and plexins act as adhesion molecules involved in monocyte-endothelial cell binding. This effect may be mediated by CD100 expressed in both cell types, probably coupled to the receptors endothelial plexin B1 and monocytic plexin B2. These results can bring new insights about a possible biological activity of CD100 in monocyte adhesion and atherosclerosis, as well as a future candidate for targeting therapeutics.

The physiological roles of ICAM-1 and ICAM-2 in neutrophil migration into tissues

PURPOSE OF REVIEW

Neutrophil extravasation from the blood into tissues is initiated by tethering and rolling of neutrophils on endothelial cells, followed by neutrophil integrin activation and shear resistant arrest, crawling, diapedesis and breaching the endothelial basement membrane harbouring pericytes. Endothelial intercellular cell adhesion molecule (ICAM)-1 and ICAM-2, in conjunction with ICAM-1 on pericytes, critically contribute to each step. In addition, epithelial ICAM-1 is involved in neutrophil migration to peri-epithelial sites. The most recent findings on the role of ICAM-1 and ICAM-2 for neutrophil migration into tissues will be reviewed here.

RECENT FINDINGS

Signalling via endothelial ICAM-1 and ICAM-2 contributes to stiffness of the endothelial cells at sites of chronic inflammation and junctional maturation, respectively. Endothelial ICAM-2 contributes to neutrophil crawling and initiation of paracellular diapedesis, which then proceeds independent of ICAM-2. Substantial transcellular neutrophil diapedesis across the blood-brain barrier is strictly dependent on endothelial ICAM-1 and ICAM-2. Endothelial ICAM-1 or ICAM-2 is involved in neutrophil-mediated plasma leakage. ICAM-1 on pericytes assists the final step of neutrophil extravasation. Epithelial ICAM-1 rather indirectly promotes neutrophil migration to peri-epithelial sites.

SUMMARY

ICAM-1 and ICAM-2 are involved in each step of neutrophil extravasation, and have redundant but also distinct functions. Analysis of the role of endothelial ICAM-1 requires simultaneous consideration of ICAM-2.

Identifying genes related with rheumatoid arthritis via system biology analysis

Rheumatoid arthritis (RA) is a chronic, inflammatory joint disease that mainly attacks synovial joints. However, the underlying systematic relationship among different genes and biological processes involved in the pathogenesis are still unclear. By analyzing and comparing the transcriptional profiles from RA, OA (osteoarthritis) patients as well as ND (normal donors) with bioinformatics methods, we tend to uncover the potential molecular networks and critical genes which play important roles in RA and OA development. Initially, hierarchical clustering was performed to classify the overall transcriptional profiles. Differentially expressed genes (DEGs) between ND and RA and OA patients were identified. Furthermore, PPI networks were constructed, functional modules were extracted, and functional annotation was also applied. Our functional analysis identifies 22 biological processes and 2 KEGG pathways enriched in the commonly-regulated gene set. However, we found that number of set of genes differentially expressed genes only between RA and ND reaches up to 244, indicating this gene set may specifically accounts for processing to disease of RA. Additionally, 142 biological processes and 19 KEGG pathways are over-represented by these 244 genes. Meanwhile, although another 21 genes were differentially expressed only in OA and ND, no biological process nor pathway is over-represented by them.