Rap1 potentiates endothelial cell junctions by spatially controlling myosin II activity and actin organization

MRCK-1 activates non-muscle myosin for outgrowth of a unicellular tube in Caenorhabditis elegans

The formation and patterning of unicellular biological tubes is essential for metazoan development. It is well established that vascular tubes and neurons use similar guidance cues to direct their development, but the downstream mechanisms that promote the outgrowth of biological tubes are not well characterized. We show that the conserved kinase MRCK-1 and its substrate the regulatory light chain of non-muscle myosin, MLC-4, are required for outgrowth of the unicellular excretory canal in C. elegans. Ablation of MRCK-1 or MLC-4 in the canal causes severe truncations with unlumenized projections of the basal membrane. Structure-function analysis of MRCK-1 indicates that the kinase domain, but not the small GTPase-binding CRIB domain, is required for canal outgrowth. Expression of a phosphomimetic form of MLC-4 rescues canal truncations in mrck-1 mutants and shows enrichment at the growing canal tip. Moreover, our work reveals a previously unreported function for non-muscle myosin downstream of MRCK-1 in excretory canal outgrowth that may be conserved in the development of seamless tubes in other organisms.

Initiation of lumen formation from junctions via differential actomyosin contractility regulated by dynamic recruitment of Rasip1

De novo lumen formation necessitates the precise segregation of junctional proteins from apical surfaces, yet the underlying mechanisms remain unclear. Using a zebrafish model, we develop a series of molecular reporters, photo-convertible and optogenetic tools to study the establishment of apical domains. Our study identifies Rasip1 as one of the earliest apical proteins recruited, which suppresses actomyosin contractility at junctional patches by inhibiting NMII, thereby allowing for the sustained outward flow of junctional complexes. Following the establishment of apical compartments, Rasip1 shuttles between junctions and the apical compartments in response to local high tension. Rasip1 confines Cdh5 to junctions by suppressing apical contractility. Conversely, the recruitment of Rasip1 to junctions is regulated by Heg1 and Krit1 to modulate contractility along junctions. Overall, de novo lumen formation and maintenance depend on the precise control of contractility within apical compartments and junctions, orchestrated by the dynamic recruitment of Rasip1.

AAMP and MTSS1 Are Novel Negative Regulators of Endothelial Barrier Function Identified in a Proteomics Screen

Cell-cell adhesion in endothelial monolayers is tightly controlled and crucial for vascular integrity. Recently, we reported on the importance of fast protein turnover for maintenance of endothelial barrier function. Specifically, continuous ubiquitination and degradation of the Rho GTPase RhoB is crucial to preserve quiescent endothelial integrity. Here, we sought to identify other barrier regulators, which are characterized by a short half-life, using a proteomics approach. Following short-term inhibition of ubiquitination with E1 ligase inhibitor MLN7243 or Cullin E3 ligase inhibitor MLN4924 in primary human endothelial cells, we identified sixty significantly differentially expressed proteins. Intriguingly, our data showed that AAMP and MTSS1 are novel negative regulators of endothelial barrier function and that their turnover is tightly controlled by ubiquitination. Mechanistically, AAMP regulates the stability and activity of RhoA and RhoB, and colocalizes with F-actin and cortactin at membrane ruffles, possibly regulating F-actin dynamics. Taken together, these findings demonstrate the critical role of protein turnover of specific proteins in the regulation of endothelial barrier function, contributing to our options to target dysregulation of vascular permeability.

Molecular Mechanisms Regulating Vascular Endothelial Permeability

Vascular endothelial cells form a monolayer in the vascular lumen and act as a selective barrier to control the permeability between blood and tissues. To maintain homeostasis, the endothelial barrier function must be strictly integrated. During acute inflammation, vascular permeability temporarily increases, allowing intravascular fluid, cells, and other components to permeate tissues. Moreover, it has been suggested that the dysregulation of endothelial cell permeability may cause several diseases, including edema, cancer, and atherosclerosis. Here, we reviewed the molecular mechanisms by which endothelial cells regulate the barrier function and physiological permeability.

Quantitative proteomics reveals CLR interactome in primary human cells

The G protein-coupled receptor (GPCR) calcitonin receptor-like receptor (CLR) mediates essential functions in several cell types and is implicated in cardiovascular pathologies, skin diseases, migraine, and cancer. To date, the network of proteins interacting with CLR ("CLR interactome") in primary cells, where this GPCR is expressed at endogenous (physiologically relevant) levels, remains unknown. To address this knowledge gap, we established a novel integrative methodological workflow/approach for conducting a comprehensive/proteome-wide analysis of Homo sapiens CLR interactome. We used primary human dermal lymphatic endothelial cells and combined immunoprecipitation utilizing anti-human CLR antibody with label-free quantitative nano LC-MS/MS and quantitative in situ proximity ligation assay. By using this workflow, we identified 37 proteins interacting with endogenously expressed CLR amongst 4902 detected members of the cellular proteome (by quantitative nano LC-MS/MS) and revealed direct interactions of two kinases and two transporters with this GPCR (by in situ proximity ligation assay). All identified interactors have not been previously reported as members of CLR interactome. Our approach and findings uncover the hitherto unrecognized compositional complexity of the interactome of endogenously expressed CLR and contribute to fundamental understanding of the biology of this GPCR. Collectively, our study provides a first-of-its-kind integrative methodological approach and datasets as valuable resources and robust platform/springboard for advancing the discovery and comprehensive characterization of physiologically relevant CLR interactome at a proteome-wide level in a range of cell types and diseases in future studies.

Establishment of the deuterium oxide dilution method as a new possibility for determining the transendothelial water permeability

Increase in transendothelial water permeability is an essential etiological factor in a variety of diseases like edema and shock. Despite the high clinical relevance, there has been no precise method to detect transendothelial water flow until now. The deuterium oxide (D2O) dilution method, already established for measuring transepithelial water transport, was used to precisely determine the transendothelial water permeability. It detected appropriate transendothelial water flow induced by different hydrostatic forces. This was shown in four different endothelial cell types. The general experimental setup was verified by gravimetry and absorbance spectroscopy. Determination of transendothelial electrical resistance (TEER) and immunocytochemical staining for proteins of the cell-cell contacts were performed to ensure that no damage to the endothelium occurred because of the measurements. Furthermore, endothelial barrier function was modulated. Measurement of transendothelial water flux was verified by measuring the TEER, the apparent permeability coefficient and the electrical capacity. The barrier-promoting substances cyclic adenosine monophosphate and iloprost reduced TEER and electrical capacity and increased permeability. This was accompanied by a reduced transendothelial water flux. In contrast, the barrier-damaging substances thrombin, histamine and bradykinin reduced TEER and electrical capacity, but increased permeability. Here, an increased water flow was shown. This newly established in vitro method for direct measurement of transendothelial water permeability was verified as a highly precise technique in various assays. The use of patient-specific endothelial cells enables individualized precision medicine in the context of basic edema research, for example regarding the development of barrier-protective pharmaceuticals.

Mechanisms of pulmonary endothelial barrier dysfunction in acute lung injury and acute respiratory distress syndrome

Endothelial cells (ECs) form a semi-permeable barrier between the interior space of blood vessels and the underlying tissues. Pulmonary endothelial barrier integrity is maintained through coordinated cellular processes involving receptors, signaling molecules, junctional complexes, and protein-regulated cytoskeletal reorganization. In acute lung injury (ALI) or its more severe form acute respiratory distress syndrome (ARDS), the loss of endothelial barrier integrity secondary to endothelial dysfunction caused by severe pulmonary inflammation and/or infection leads to pulmonary edema and hypoxemia. Pro-inflammatory agonists such as histamine, thrombin, bradykinin, interleukin 1β, tumor necrosis factor α, vascular endothelial growth factor, angiopoietin-2, and platelet-activating factor, as well as bacterial toxins and reactive oxygen species, cause dynamic changes in cytoskeletal structure, adherens junction disorganization, and detachment of vascular endothelial cadherin (VE-cadherin) from the actin cytoskeleton, leading to an increase in endothelial permeability. Endothelial interactions with leukocytes, platelets, and coagulation enhance the inflammatory response. Moreover, inflammatory infiltration and the associated generation of pro-inflammatory cytokines during infection cause EC death, resulting in further compromise of the structural integrity of lung endothelial barrier. Despite the use of potent antibiotics and aggressive intensive care support, the mortality of ALI is still high, because the mechanisms of pulmonary EC barrier disruption are not fully understood. In this review, we summarized recent advances in the studies of endothelial cytoskeletal reorganization, inter-endothelial junctions, endothelial inflammation, EC death, and endothelial repair in ALI and ARDS, intending to shed some light on the potential diagnostic and therapeutic targets in the clinical management of the disease.

A Focus on the Pathophysiology of Adrenomedullin Expression: Endothelitis and Organ Damage in Severe Viral and Bacterial Infections

Adrenomedullin (ADM) is a peptide hormone produced primarily in the adrenal glands, playing a crucial role in various physiological processes. As well as improving vascular integrity and decreasing vascular permeability, ADM acts as a vasodilator, positive inotrope, diuretic, natriuretic and bronchodilator, antagonizing angiotensin II by inhibiting aldosterone secretion. ADM also has antihypertrophic, anti-apoptotic, antifibrotic, antioxidant, angiogenic and immunoregulatory effects and antimicrobial properties. ADM expression is upregulated by hypoxia, inflammation-inducing cytokines, viral or bacterial substances, strength of shear stress, and leakage of blood vessels. These pathological conditions are established during systemic inflammation that can result from infections, surgery, trauma/accidents or burns. The ability to rapidly identify infections and the prognostic, predictive power makes it a valuable tool in severe viral and bacterial infections burdened by high incidence and mortality. This review sheds light on the pathophysiological processes that in severe viral or bacterial infections cause endothelitis up to the development of organ damage, the resulting increase in ADM levels dosed through its more stable peptide mid-regional proadrenomedullin (MR-proADM), the most significant studies that attest to its diagnostic and prognostic accuracy in highlighting the severity of viral or bacterial infections and appropriate therapeutic insights.

Semmaphorin 3 A causes immune suppression by inducing cytoskeletal paralysis in tumour-specific CD8+ T cells

Semaphorin-3A (SEMA3A) functions as a chemorepulsive signal during development and can affect T cells by altering their filamentous actin (F-actin) cytoskeleton. The exact extent of these effects on tumour-specific T cells are not completely understood. Here we demonstrate that Neuropilin-1 (NRP1) and Plexin-A1 and Plexin-A4 are upregulated on stimulated CD8+ T cells, allowing tumour-derived SEMA3A to inhibit T cell migration and assembly of the immunological synapse. Deletion of NRP1 in both CD4+ and CD8+ T cells enhance CD8+ T-cell infiltration into tumours and restricted tumour growth in animal models. Conversely, over-expression of SEMA3A inhibit CD8+ T-cell infiltration. We further show that SEMA3A affects CD8+ T cell F-actin, leading to inhibition of immune synapse formation and motility. Examining a clear cell renal cell carcinoma patient cohort, we find that SEMA3A expression is associated with reduced survival, and that T-cells appear trapped in SEMA3A rich regions. Our study establishes SEMA3A as an inhibitor of effector CD8+ T cell tumour infiltration, suggesting that blocking NRP1 could improve T cell function in tumours.

Endothelial cells regulate alveolar morphogenesis by constructing basement membranes acting as a scaffold for myofibroblasts

Alveologenesis is a spatially coordinated morphogenetic event, during which alveolar myofibroblasts surround the terminal sacs constructed by epithelial cells and endothelial cells (ECs), then contract to form secondary septa to generate alveoli in the lungs. Recent studies have demonstrated the important role of alveolar ECs in this morphogenetic event. However, the mechanisms underlying EC-mediated alveologenesis remain unknown. Herein, we show that ECs regulate alveologenesis by constructing basement membranes (BMs) acting as a scaffold for myofibroblasts to induce septa formation through activating mechanical signaling. Rap1, a small GTPase of the Ras superfamily, is known to stimulate integrin-mediated cell adhesions. EC-specific Rap1-deficient (Rap1iECKO) mice exhibit impaired septa formation and hypo-alveolarization due to the decreased mechanical signaling in myofibroblasts. In Rap1iECKO mice, ECs fail to stimulate integrin β1 to recruit Collagen type IV (Col-4) into BMs required for myofibroblast-mediated septa formation. Consistently, EC-specific integrin β1-deficient mice show hypo-alveolarization, defective mechanical signaling in myofibroblasts, and disorganized BMs. These data demonstrate that alveolar ECs promote integrin β1-mediated Col-4 recruitment in a Rap1-dependent manner, thereby constructing BMs acting as a scaffold for myofibroblasts to induce mechanical signal-mediated alveologenesis. Thus, this study unveils a mechanism of organ morphogenesis mediated by ECs through intrinsic functions.

Cdc42 activity in the trailing edge is required for persistent directional migration of keratinocytes

Fibroblasts migrate discontinuously by generating transient leading-edge protrusions and irregular, abrupt retractions of a narrow trailing edge. In contrast, keratinocytes migrate persistently and directionally via a single, stable, broad protrusion paired with a stable trailing-edge. The Rho GTPases Rac1, Cdc42 and RhoA are key regulators of cell protrusions and retractions. However, how these molecules mediate cell-type specific migration modes is still poorly understood. In fibroblasts, all three Rho proteins are active at the leading edge, suggesting short-range coordination of protrusive Rac1 and Cdc42 signals with RhoA retraction signals. Here, we show that Cdc42 was surprisingly active in the trailing-edge of migrating keratinocytes. Elevated Cdc42 activity colocalized with the effectors MRCK and N-WASP suggesting that Cdc42 controls both myosin activation and actin polymerization in the back. Indeed, Cdc42 was required to maintain the highly dynamic contractile acto-myosin retrograde flow at the trailing edge of keratinocytes, and its depletion induced ectopic protrusions in the back, leading to decreased migration directionality. These findings suggest that Cdc42 is required to stabilize the dynamic cytoskeletal polarization in keratinocytes, to enable persistent, directional migration.

Rap1 small GTPase is essential for maintaining pulmonary endothelial barrier function in mice

Vascular permeability is dynamically but tightly controlled by vascular endothelial (VE)-cadherin-mediated endothelial cell-cell junctions to maintain homeostasis. Thus, impairments of VE-cadherin-mediated cell adhesions lead to hyperpermeability, promoting the development and progression of various disease processes. Notably, the lungs are a highly vulnerable organ wherein pulmonary inflammation and infection result in vascular leakage. Herein, we showed that Rap1, a small GTPase, plays an essential role for maintaining pulmonary endothelial barrier function in mice. Endothelial cell-specific Rap1a/Rap1b double knockout mice exhibited severe pulmonary edema. They also showed vascular leakage in the hearts, but not in the brains. En face analyses of the pulmonary arteries and 3D-immunofluorescence analyses of the lungs revealed that Rap1 potentiates VE-cadherin-mediated endothelial cell-cell junctions through dynamic actin cytoskeleton reorganization. Rap1 inhibits formation of cytoplasmic actin bundles perpendicularly binding VE-cadherin adhesions through inhibition of a Rho-ROCK pathway-induced activation of cytoplasmic nonmuscle myosin II (NM-II). Simultaneously, Rap1 induces junctional NM-II activation to create circumferential actin bundles, which anchor and stabilize VE-cadherin at cell-cell junctions. We also showed that the mice carrying only one allele of either Rap1a or Rap1b out of the two Rap1 genes are more vulnerable to lipopolysaccharide (LPS)-induced pulmonary vascular leakage than wild-type mice, while activation of Rap1 by administration of 007, an activator for Epac, attenuates LPS-induced increase in pulmonary endothelial permeability in wild-type mice. Thus, we demonstrate that Rap1 plays an essential role for maintaining pulmonary endothelial barrier functions under physiological conditions and provides protection against inflammation-induced pulmonary vascular leakage.

MRCK activates mouse oocyte myosin II for spindle rotation and male pronucleus centration

Asymmetric meiotic divisions in oocytes rely on spindle positioning in close vicinity to the cortex. In metaphase II mouse oocytes, eccentric spindle positioning triggers cortical polarization, including the build-up of an actin cap surrounded by a ring of activated myosin II. While the role of the actin cap in promoting polar body formation is established, ring myosin II activation mechanisms and functions have remained elusive. Here, we show that ring myosin II activation requires myotonic dystrophy kinase-related Cdc42-binding kinase (MRCK), downstream of polarized Cdc42. MRCK inhibition resulted in spindle rotation defects during anaphase II, precluding polar body extrusion. Remarkably, disengagement of segregated chromatids from the anaphase spindle could rescue rotation. We further show that the MRCK/myosin II pathway is activated in the fertilization cone and is required for male pronucleus migration toward the center of the zygote. These findings provide novel insights into the mechanism of myosin II activation in oocytes and its role in orchestrating asymmetric division and pronucleus centration.

Classical cadherins in the testis: how are they regulated?

Cadherins (CDH) are crucial intercellular adhesion molecules, contributing to morphogenesis and creating tissue barriers by regulating cells' movement, clustering and differentiation. In the testis, classical cadherins such as CDH1, CDH2 and CDH3 are critical to gonadogenesis by promoting the migration and the subsequent clustering of primordial germ cells with somatic cells. While CDH2 is present in both Sertoli and germ cells in rodents, CDH1 is primarily detected in undifferentiated spermatogonia. As for CDH3, its expression is mainly found in germ and pre-Sertoli cells in developing gonads until the establishment of the blood-testis barrier (BTB). This barrier is made of Sertoli cells forming intercellular junctional complexes. The restructuring of the BTB allows the movement of early spermatocytes toward the apical compartment as they differentiate during a process called spermatogenesis. CDH2 is among many junctional proteins participating in this process and is regulated by several pathways. While cytokines promote the disassembly of the BTB by enhancing junctional protein endocytosis for degradation, testosterone facilitates the assembly of the BTB by increasing the recycling of endocytosed junctional proteins. Mitogen-activated protein kinases (MAPKs) are also mediators of the BTB kinetics in many chemically induced damages in the testis. In addition to regulating Sertoli cell functions, follicle stimulating hormone can also regulate the expression of CDH2. In this review, we discuss the current knowledge on regulatory mechanisms of cadherin localisation and expression in the testis.

Rap1 promotes epithelial integrity and cell viability in a growing tissue

Having intact epithelial tissues is critical for embryonic development and adult homeostasis. How epithelia respond to damaging insults or tissue growth while still maintaining intercellular connections and barrier integrity during development is poorly understood. The conserved small GTPase Rap1 is critical for establishing cell polarity and regulating cadherin-catenin cell junctions. Here, we identified a new role for Rap1 in maintaining epithelial integrity and tissue shape during Drosophila oogenesis. Loss of Rap1 activity disrupted the follicle cell epithelium and the shape of egg chambers during a period of major growth. Rap1 was required for proper E-Cadherin localization in the anterior epithelium and for epithelial cell survival. Both Myo-II and the adherens junction-cytoskeletal linker protein α-Catenin were required for normal egg chamber shape but did not strongly affect cell viability. Blocking the apoptotic cascade failed to rescue the cell shape defects caused by Rap1 inhibition. One consequence of increased cell death caused by Rap1 inhibition was the loss of polar cells and other follicle cells, which later in development led to fewer cells forming a migrating border cell cluster. Our results thus indicate dual roles for Rap1 in maintaining epithelia and cell survival in a growing tissue during development.

Necroptosis in apical periodontitis: A programmed cell death with multiple roles

Programmed cell death (PCD) has been a research focus for decades and different mechanisms of cell death, such as necroptosis, pyroptosis, ferroptosis, and cuproptosis have been discovered. Necroptosis, a form of inflammatory PCD, has gained increasing attention in recent years due to its critical role in disease progression and development. Unlike apoptosis, which is mediated by caspases and characterized by cell shrinkage and membrane blebbing, necroptosis is mediated by mixed lineage kinase domain-like protein (MLKL) and characterized by cell enlargement and plasma membrane rupture. Necroptosis can be triggered by bacterial infection, which on the one hand represents a host defense mechanism against the infection, but on the other hand can facilitate bacterial escape and worsen inflammation. Despite its importance in various diseases, a comprehensive review on the involvement and roles of necroptosis in apical periodontitis is still lacking. In this review, we tried to provide an overview of recent progresses in necroptosis research, summarized the pathways involved in apical periodontitis (AP) activation, and discussed how bacterial pathogens induce and regulated necroptosis and how necroptosis would inhibit bacteria. Furthermore, the interplay between various types of cell death in AP and the potential treatment strategy for AP by targeting necroptosis were also discussed.

Rap1 coordinates cell-cell adhesion and cytoskeletal reorganization to drive collective cell migration in vivo

Collective cell movements contribute to tissue development and repair and spread metastatic disease. In epithelia, cohesive cell movements require reorganization of adherens junctions and the actomyosin cytoskeleton. However, the mechanisms that coordinate cell-cell adhesion and cytoskeletal remodeling during collective cell migration in vivo are unclear. We investigated the mechanisms of collective cell migration during epidermal wound healing in Drosophila embryos. Upon wounding, the cells adjacent to the wound internalize cell-cell adhesion molecules and polarize actin and the motor protein non-muscle myosin II to form a supracellular cable around the wound that coordinates cell movements. The cable anchors at former tricellular junctions (TCJs) along the wound edge, and TCJs are reinforced during wound closure. We found that the small GTPase Rap1 was necessary and sufficient for rapid wound repair. Rap1 promoted myosin polarization to the wound edge and E-cadherin accumulation at TCJs. Using embryos expressing a mutant form of the Rap1 effector Canoe/Afadin that cannot bind Rap1, we found that Rap1 signals through Canoe for adherens junction remodeling, but not for actomyosin cable assembly. Instead, Rap1 was necessary and sufficient for RhoA/Rho1 activation at the wound edge. The RhoGEF Ephexin localized to the wound edge in a Rap1-dependent manner, and Ephexin was necessary for myosin polarization and rapid wound repair, but not for E-cadherin redistribution. Together, our data show that Rap1 coordinates the molecular rearrangements that drive embryonic wound healing, promoting actomyosin cable assembly through Ephexin-Rho1, and E-cadherin redistribution through Canoe, thus enabling rapid collective cell migration in vivo.

MRCKα/β positively regulates Gli protein activity

Posttranslational modifications (PTMs) are key regulatory events for the majority of signaling pathways. Transcription factors are often phosphorylated on multiple residues, which regulates their trafficking, stability, or transcriptional activity. Gli proteins, transcription factors that respond to the Hedgehog pathway, are regulated by phosphorylation, but the sites and the kinases involved have been only partially described. We identified three novel kinases: MRCKα, MRCKβ, and MAP4K5 which physically interact with Gli proteins and directly phosphorylate Gli2 on multiple sites. We established that MRCKα/β kinases regulate Gli proteins, which impacts the transcriptional output of the Hedgehog pathway. We showed that double knockout of MRCKα/β affects Gli2 ciliary and nuclear localization and reduces Gli2 binding to the Gli1 promoter. Our research fills a critical gap in our understanding of the regulation of Gli proteins by describing their activation mechanisms through phosphorylation.

Mechanisms of pulmonary endothelial permeability and inflammation caused by extracellular histone subunits H3 and H4

Extracellular DNA-binding proteins such as histones are danger-associated molecular pattern released by the injured tissues in trauma and sepsis settings, which trigger host immune response and vascular dysfunction. Molecular events leading to histone-induced endothelial cell (EC) dysfunction remain poorly understood. This study performed comparative analysis of H1, H2A, H2B, H3, and H4 histone subunits effects on human pulmonary EC permeability and inflammatory response. Analysis of transendothelial electrical resistance and EC monolayer permeability for macromolecues revealed that H3 and H4, but not H1, H2A, or H2B caused dose-dependent EC permeability accompanied by disassembly of adherens junctions. At higher doses, H3 and H4 activated nuclear factor kappa B inflammatory cascade leading to upregulation EC adhesion molecules ICAM1, VCAM1, E-selectin, and release of inflammatory cytokines. Inhibitory receptor analysis showed that toll-like receptor (TLR) 4 but not TLR1/2 or receptor for advanced glycation end inhibition significantly attenuated deleterious effects of H3 and H4 histones. Inhibitor of Rho-kinase was without effect, while inhibition of Src kinase caused partial preservation of cell-cell junctions, H3/H4-induced permeability and inflammation. Deleterious effects of H3/H4 were blocked by heparin. Activation of Epac-Rap1 signaling restored EC barrier properties after histone challenge. Intravenous injection of histones in mice caused elevation of inflammatory markers and increased vascular leak. Post-treatment with pharmacological Epac/Rap1 activator suppressed injurious effects of histones in vitro and in vivo. These results identify H3 and H4 as key histone subunits exhibiting deleterious effects on pulmonary vascular endothelium via TLR4-dependent mechanism. In conclusion, elevation of circulating histones may represent a serious risk of exacerbated acute lung injury (ALI) and multiple organ injury during severe trauma and infection.

Regulation and Dysregulation of Endothelial Permeability during Systemic Inflammation

Systemic inflammation can be triggered by infection, surgery, trauma or burns. During systemic inflammation, an overshooting immune response induces tissue damage resulting in organ dysfunction and mortality. Endothelial cells make up the inner lining of all blood vessels and are critically involved in maintaining organ integrity by regulating tissue perfusion. Permeability of the endothelial monolayer is strictly controlled and highly organ-specific, forming continuous, fenestrated and discontinuous capillaries that orchestrate the extravasation of fluids, proteins and solutes to maintain organ homeostasis. In the physiological state, the endothelial barrier is maintained by the glycocalyx, extracellular matrix and intercellular junctions including adherens and tight junctions. As endothelial cells are constantly sensing and responding to the extracellular environment, their activation by inflammatory stimuli promotes a loss of endothelial barrier function, which has been identified as a hallmark of systemic inflammation, leading to tissue edema formation and hypotension and thus, is a key contributor to lethal outcomes. In this review, we provide a comprehensive summary of the major players, such as the angiopoietin-Tie2 signaling axis, adrenomedullin and vascular endothelial (VE-) cadherin, that substantially contribute to the regulation and dysregulation of endothelial permeability during systemic inflammation and elucidate treatment strategies targeting the preservation of vascular integrity.

Exploring the ovine sperm transcriptome by RNAseq techniques. I Effect of seasonal conditions on transcripts abundance

Understanding the cell molecular changes occurring as a results of climatic circumstances is crucial in the current days in which climate change and global warming are one of the most serious challenges that living organisms have to face. Sperm are one of the mammals’ cells most sensitive to heat, therefore evaluating the impact of seasonal changes in terms of its transcriptional activity can contribute to elucidate how these cells cope with heat stress events. We sequenced the total sperm RNA from 64 ejaculates, 28 collected in summer and 36 collected in autumn, from 40 Manchega rams. A highly rich transcriptome (11,896 different transcripts) with 90 protein coding genes that exceed an average number of 5000 counts were found. Comparing transcriptome in the summer and autumn ejaculates, 236 significant differential abundance genes were assessed, most of them (228) downregulated. The main functions that these genes are related to sexual reproduction and negative regulation of protein metabolic processes and kinase activity. Sperm response to heat stress supposes a drastic decrease of the transcriptional activity, and the upregulation of only a few genes related with the basic functions to maintain the organisms’ homeostasis and surviving. Rams’ spermatozoids carry remnant mRNAs which are retrospectively indicators of events occurring along the spermatogenesis process, including abiotic factors such as environmental temperature.

Endothelial cells of pulmonary origin display unique sensitivity to the bacterial endotoxin lipopolysaccharide

Acute respiratory distress syndrome (ARDS) is a major clinical problem without available therapies. Known risks for ARDS include severe sepsis, SARS-CoV-2, gram-negative bacteria, trauma, pancreatitis, and blood transfusion. During ARDS, blood fluids and inflammatory cells enter the alveoli, preventing oxygen exchange from air into blood vessels. Reduced pulmonary endothelial barrier function, resulting in leakage of plasma from blood vessels, is one of the major determinants in ARDS. It is, however, unknown why systemic inflammation particularly targets the pulmonary endothelium, as endothelial cells (ECs) line all vessels in the vascular system of the body. In this study, we examined ECs of pulmonary, umbilical, renal, pancreatic, and cardiac origin for upregulation of adhesion molecules, ability to facilitate neutrophil (PMN) trans-endothelial migration (TEM) and for endothelial barrier function, in response to the gram-negative bacterial endotoxin LPS. Interestingly, we found that upon LPS stimulation, pulmonary ECs showed increased levels of adhesion molecules, facilitated more PMN-TEM and significantly perturbed the endothelial barrier, compared to other types of ECs. These observations could partly be explained by a higher expression of the adhesion molecule ICAM-1 on the pulmonary endothelial surface compared to other ECs. Moreover, we identified an increased expression of Cadherin-13 in pulmonary ECs, for which we demonstrated that it aids PMN-TEM in pulmonary ECs stimulated with LPS. We conclude that pulmonary ECs are uniquely sensitive to LPS, and intrinsically different, compared to ECs from other vascular beds. This may add to our understanding of the development of ARDS upon systemic inflammation.

Transendothelial migration induces differential migration dynamics of leukocytes in tissue matrix

Leukocyte extravasation into inflamed tissue is a complex process that is difficult to capture as a whole in vitro. We employed a blood-vessel-on-a-chip model in which human endothelial cells were cultured in a tube-like lumen in a collagen-1 matrix. The vessels are leak tight, creating a barrier for molecules and leukocytes. Addition of inflammatory cytokine TNF-α (also known as TNF) caused vasoconstriction, actin remodelling and upregulation of ICAM-1. Introducing leukocytes into the vessels allowed real-time visualization of all different steps of the leukocyte transmigration cascade, including migration into the extracellular matrix. Individual cell tracking over time distinguished striking differences in migratory behaviour between T-cells and neutrophils. Neutrophils cross the endothelial layer more efficiently than T-cells, but, upon entering the matrix, neutrophils display high speed but low persistence, whereas T-cells migrate with low speed and rather linear migration. In conclusion, 3D imaging in real time of leukocyte extravasation in a vessel-on-a-chip enables detailed qualitative and quantitative analysis of different stages of the full leukocyte extravasation process in a single assay. This article has an associated First Person interview with the first authors of the paper.

Exploring the therapeutic promise of targeting Rho kinase in rheumatoid arthritis

Rheumatoid arthritis (RA) is a prevalent systemic autoimmune disease caused by dysregulated inflammatory reactions, T lymphocyte invasion into the joints, and articular thickening. Immune cells, primarily tumor necrosis factor-alpha (TNF-α) and chemokines (interleukin or IL-1), which are predominantly generated by activated macrophages cells, have also been involved with the pathogenesis of rheumatoid arthritis. Rho GTPases are integral factors of biochemical cascades utilized by antigens, and also by cellular receptors, cytokines, and chemokines, to modulate inflammatory reactions, according to growing data. The Rho family is a group of G proteins that govern a variety of biological and physiological activities such as mobility, actin stress fiber production, growth, and polarity. Research suggests that the Rho A and Rho-associated coiled-coil kinase (ROCK) regulatory cascade could be essential in several autoimmune conditions, including RA. ROCK is activated in the synovial of rheumatoid arthritis patients, while the blocking of ROCK with fasudil could also decrease IL-6, TNF-α, and IL-1. This review covers current developments in understanding the overactivation of Rho enzyme activity in RA suppressed by ROCK inhibitors which can be utilized for the treatment of autoimmune disease. We offer an outline of the function of ROCK inhibitors in immune cells and discuss findings which emphasize the rising participation of this category of kinases within the pathological process of autoimmune disorders. Assuming the potential ability of ROCK as a therapeutic, we define approaches that might be used to inhibit Rho kinase activity in rheumatoid disorders.

Gene transfer of MRCKα rescues lipopolysaccharide-induced acute lung injury by restoring alveolar capillary barrier function

Acute Lung Injury/Acute Respiratory Distress Syndrome (ALI/ARDS) is characterized by alveolar edema accumulation with reduced alveolar fluid clearance (AFC), alveolar-capillary barrier disruption, and substantial inflammation, all leading to acute respiratory failure. Enhancing AFC has long been considered one of the primary therapeutic goals in gene therapy treatments for ARDS. We previously showed that electroporation-mediated gene delivery of the Na⁺, K⁺-ATPase β1 subunit not only increased AFC, but also restored alveolar barrier function through upregulation of tight junction proteins, leading to treatment of LPS-induced ALI in mice. We identified MRCKα as an interaction partner of β1 which mediates this upregulation in cultured alveolar epithelial cells. In this study, we investigate whether electroporation-mediated gene transfer of MRCKα to the lungs can attenuate LPS-induced acute lung injury in vivo. Compared to mice that received a non-expressing plasmid, those receiving the MRCKα plasmid showed attenuated LPS-increased pulmonary edema and lung leakage, restored tight junction protein expression, and improved overall outcomes. Interestingly, gene transfer of MRCKα did not alter AFC rates. Studies using both cultured microvascular endothelial cells and mice suggest that β1 and MRCKα upregulate junctional complexes in both alveolar epithelial and capillary endothelial cells, and that one or both barriers may be positively affected by our approach. Our data support a model of treatment for ALI/ARDS in which improvement of alveolar-capillary barrier function alone may be of more benefit than improvement of alveolar fluid clearance.

Rap1 Small GTPase Regulates Vascular Endothelial-Cadherin-Mediated Endothelial Cell-Cell Junctions and Vascular Permeability

The vascular permeability of the endothelium is finely controlled by vascular endothelial (VE)-cadherin-mediated endothelial cell-cell junctions. In the majority of normal adult tissues, endothelial cells in blood vessels maintain vascular permeability at a relatively low level, while in response to inflammation, they limit vascular barrier function to induce plasma leakage and extravasation of immune cells as a defense mechanism. Thus, the dynamic but also simultaneously tight regulation of vascular permeability by endothelial cells is responsible for maintaining homeostasis and, as such, impairments of its underlying mechanisms result in hyperpermeability, leading to the development and progression of various diseases including coronavirus disease 2019 (COVID-19), a newly emerging infectious disease. Recently, increasing numbers of studies have been unveiling the important role of Rap1, a small guanosine 5'-triphosphatase (GTPase) belonging to the Ras superfamily, in the regulation of vascular permeability. Rap1 enhances VE-cadherin-mediated endothelial cell-cell junctions to potentiate vascular barrier functions via dynamic reorganization of the actin cytoskeleton. Importantly, Rap1 signaling activation reportedly improves vascular barrier function in animal models of various diseases associated with vascular hyperpermeability, suggesting that Rap1 might be an ideal target for drugs intended to prevent vascular barrier dysfunction. Here, we describe recent progress in understanding the mechanisms by which Rap1 potentiates VE-cadherin-mediated endothelial cell-cell adhesions and vascular barrier function. We also discuss how alterations in Rap1 signaling are related to vascular barrier dysfunction in diseases such as acute pulmonary injury and malignancies. In addition, we examine the possibility of Rap1 signaling as a target of drugs for treating diseases associated with vascular hyperpermeability.

cAMP Signaling Pathway Prevents Dasatinib-Induced Vascular Hyperpermeability

Dasatinib is a first-line pharmacotherapeutic treatment for chronic myeloid leukemia (CML). It is more effective than traditional treatments but causes adverse effects such as pleural effusion that limits its effective treatment cycle. Since pleural effusion is caused by vascular hyperpermeability and causes discontinuation of treatment with dasatinib, it is important to explore the mechanism of pleural effusion caused by dasatinib and how to prevent it. In this study, we investigated how dasatinib increase vascular permeability, and how it can be prevented. Cytotoxicity was observed in vascular endothelial cells or epithelial cells were exposed to high concentrations of dasatinib. Thus, it was observed in vascular endothelial cells such as human umbilical vascular endothelial cell (HUVEC). Vascular endothelial (VE)-cadherin is one of the important factors that control vascular permeability. When VE-cadherin expression decreases, vascular permeability increases, but it did not change with tyrosine kinase inhibitor exposure. Monolayer permeability significantly increased only with high concentration of dasatinib, but this increase was prevented by cAMP activation. Furthermore, dasatinib affects the cell morphology of HUVEC, with increased inter celluar space compared to control and bosutinib, which were also attenuated by cAMP activation. Dasatinib significantly affected permeability control of vascular endothelial cells compared to bosutinib and imatinib. These results indicated that the cAMP signaling pathway may be involved in the pleural effusion caused by dasatinib in CML patients.

Faciogenital Dysplasia 5 supports cancer stem cell traits in basal-like breast cancer by enhancing EGFR stability

Most basal-like breast cancers (BLBCs) are triple-negative breast cancers (TNBCs), which have the worst prognosis and distant metastasis-free survival among breast cancer subtypes. Now, no targeted therapies are available for patients with BLBC due to the lack of reliable and effective molecular targets. Here, we performed the BLBC tissue microarray-based immunohistochemical analysis and showed that Faciogenital Dysplasia 5 (FGD5) abundance is associated with poor prognosis in BLBCs. FGD5 deletion decreased the proliferation, invasion, and tumorsphere formation capacity of BLBC cells. Furthermore, genetic inhibition of Fgd5 in mouse mammary epithelial cells attenuated BLBC initiation and progression by reducing the self-renewal ability of tumor-initiating cells. In addition, FGD5 abundance was positively correlated with the abundance of epidermal growth factor receptor (EGFR) in BLBCs. FGD5 ablation decreased EGFR abundance by reducing EGFR stability in TNBC cells in 2D and 3D culture conditions. Mechanistically, FGD5 binds to EGFR and interferes with basal EGFR ubiquitination and degradation induced by the E3 ligase ITCH. Impaired EGFR degradation caused BLBC cell proliferation and promoted invasive properties and self-renewal. To verify the role of the FGD5-EGFR interaction in the regulation of EGFR stability, we screened a cell-penetrating α-helical peptide PER3 binding with FGD5 to disrupt the interaction. Treatment of BLBC patient-derived xenograft-bearing mice with the peptide PER3 disrupting the FGD5-EGFR interaction either with or without chemotherapy reduced BLBC progression. Our study identified FGD5 as a positive modulator of tumor-initiating cells and suggests a potential therapeutic option for the BLBC subtype of breast cancer.

Therapeutic Hypothermia Mitigates the Sepsis-Increased Permeability in EA. hy926 Cells by Preserving Rap1 Expression

To determine the effect and potential mechanisms of therapeutic hypothermia (TH) on the permeability of septic cells. Human EA. hy926 cells were transfected with, or without, control or ras-proximate-1 (Rap1)-specific siRNA and treated with 2 μg/mL of lipopolysaccharide (LPS). The cells were cultured in normal temperature (NT) or a temporary TH for 10 hours. The cellular permeability of each group of cells was determined by transwell permeability assay. The relative levels of Rap1, RhoA (a small GTP enzyme of the Rho family), VE-cadherin expression, and myosin light chain (MLC) phosphorylation were quantified by Western blot and immunofluorescent assays. Compared with the control group, LPS stimulation increased cellular permeability in EA. hy926 cells under an NT condition, but significantly mitigated by TH. The effect of TH decreased after Rap1 silencing. Furthermore, LPS upregulated RhoA expression and MLC phosphorylation, but reduced Rap1 and VE-cadherin expression, which were also enhanced by Rap1 silencing, but significantly mitigated by TH. Immunofluorescent analyses indicated that LPS significantly increased phosphorylated MLC, but decreased VE-cadherin expression, which were further deteriorated by Rap1 silencing, but significantly mitigated by TH in EA. hy926 cells. TH significantly mitigated the sepsis-increased permeability of EA. hy926 cells by enhancing the Rap1 expression to attenuate the RhoA/MLC signaling.

Vascular Endothelial Protein Tyrosine Phosphatase Regulates Endothelial Function

Vascular endothelial protein tyrosine phosphatase (VE-PTP) is a receptor-type PTP (RPTP), predominantly expressed in vascular endothelial cells. It regulates embryonic and tumor angiogenesis and controls vascular permeability and homeostasis in inflammation. Major substrates are the tyrosine kinase receptor Tie-2 and the adhesion molecule VE-cadherin. This review describes how VE-PTP controls vascular functions by its various substrates and the therapeutic potential of VE-PTP in various pathophysiological settings.

Fgd5 is a Rac1-specific Rho GEF that is selectively inhibited by aurintricarboxylic acid

Rho proteins are signalling molecules that control cellular dynamics, movement and morphological changes. They are activated by Rho guanine-nucleotide exchange factors (Rho GEFs) that transduce upstream signals into Rho-mediated activation of downstream processes. Fgd5 is a Rho GEF involved in angiogenesis and its target Rho protein for this process has been linked to Cdc42 activation. Here, we examined the function of purified Fgd5, specifically, which Rho proteins it activates and pinpoint the structural domains required for enzymatic activity. Using a GEF enzyme assay, we found that purified Fgd5 showed preferential activation of Rac1 and direct binding of Rac1 in pull-down and co-immunoprecipitation assays. Structural comparisons showed that the Fgd5 DH domain is highly similar to the Rac1 GEF, TrioN, supporting a role for Fgd5 as a Rac1 GEF. Compounds that bind to purified Fgd5 DH-PH protein were identified by screening a small molecule library via surface plasmon resonance. The effects of eleven ligands were further examined for their ability to inhibit the Fgd5 GEF enzymatic activity and Rac1 interaction. From these studies, we found that the compound aurintricarboxylic acid, and to a lesser extent mitoxantrone dihydrochloride, inhibited both Fgd5 GEF activation of Rac1 and their interaction. Aurintricarboxylic acid had no effect on the activity or binding of the Rac1 GEF, TrioN, thus demonstrating the feasibility of selectively disrupting Rho GEF activators. Abbreviations: a.a.: amino acid; ATA: aurintricarboxylic acid; DH: Dbl homology; DOCK: dictator of cytokinesis; Fgd: faciogenital dysplasia; GEF: guanine-nucleotide exchange factor; GST: glutathione S-transferase; LOPAC: library of pharmacologically active compounds; PH: pleckstrin homology; PDB: protein data bank; s.e.m.: standard error of the mean; SPR: surface plasmon resonance.

The Na+, K+-ATPase β1 subunit regulates epithelial tight junctions via MRCKα

An intact lung epithelial barrier is essential for lung homeostasis. The Na⁺, K⁺-ATPase (NKA), primarily serving as an ion transporter, also regulates epithelial barrier function via modulation of tight junctions. However, the underlying mechanism is not well understood. Here, we show that overexpression of the NKA β1 subunit upregulates the expression of tight junction proteins, leading to increased alveolar epithelial barrier function by an ion transport–independent mechanism. Using IP and mass spectrometry, we identified a number of unknown protein interactions of the β1 subunit, including a top candidate, myotonic dystrophy kinase–related cdc42-binding kinase α (MRCKα), which is a protein kinase known to regulate peripheral actin formation. Using a doxycycline-inducible gene expression system, we demonstrated that MRCKα and its downstream activation of myosin light chain is required for the regulation of alveolar barrier function by the NKA β1 subunit. Importantly, MRCKα is expressed in both human airways and alveoli and has reduced expression in patients with acute respiratory distress syndrome (ARDS), a lung illness that can be caused by multiple direct and indirect insults, including the infection of influenza virus and SARS-CoV-2. Our results have elucidated a potentially novel mechanism by which NKA regulates epithelial tight junctions and have identified potential drug targets for treating ARDS and other pulmonary diseases that are caused by barrier dysfunction.

Plexin-B2 facilitates glioblastoma infiltration by modulating cell biomechanics

Infiltrative growth is a major cause of high lethality of malignant brain tumors such as glioblastoma (GBM). We show here that GBM cells upregulate guidance receptor Plexin-B2 to gain invasiveness. Deletion of Plexin-B2 in GBM stem cells limited tumor spread and shifted invasion paths from axon fiber tracts to perivascular routes. On a cellular level, Plexin-B2 adjusts cell adhesiveness, migratory responses to different matrix stiffness, and actomyosin dynamics, thus empowering GBM cells to leave stiff tumor bulk and infiltrate softer brain parenchyma. Correspondingly, gene signatures affected by Plexin-B2 were associated with locomotor regulation, matrix interactions, and cellular biomechanics. On a molecular level, the intracellular Ras-GAP domain contributed to Plexin-B2 function, while the signaling relationship with downstream effectors Rap1/2 appeared variable between GBM stem cell lines, reflecting intertumoral heterogeneity. Our studies establish Plexin-B2 as a modulator of cell biomechanics that is usurped by GBM cells to gain invasiveness.

High Endothelial Venules Accelerate Naive T Cell Recruitment by Tumor Necrosis Factor-Mediated R-Ras Upregulation

Recruitment of naive T cells to lymph nodes is essential for the development of adaptive immunity. Upon pathogen infection, lymph nodes promptly increase the influx of naive T cells from the circulation in order to screen and prime the T cells. The precise contribution of the lymph node vasculature to the regulation of this process remains unclear. Here we show a role for the Ras GTPase, R-Ras, in the functional adaptation of high endothelial venules to increase naive T cell trafficking to the lymph nodes. R-Ras is transiently up-regulated in the endothelium of high endothelial venules by the inflammatory cytokine tumor necrosis factor (TNF) within 24 hours of pathogen inoculation. TNF induces R-Ras upregulation in endothelial cells via JNK and p38 mitogen-activated protein kinase but not NF-κB. Studies of T cell trafficking found that the loss of function of endothelial R-Ras impairs the rapid acceleration of naive T cell recruitment to the lymph nodes upon inflammation. This defect diminished the ability of naive OT-1 T cells to develop antitumor activity against ovalbumin-expressing melanoma. Proteomic analyses suggest that endothelial R-Ras facilitates TNF-dependent transendothelial migration (diapedesis) of naive T cells by modulating molecular assembly the at T cell-endothelial cell interface. These findings give new mechanistic insights into the functional adaptation of high endothelial venules to accelerate naive T cell recruitment to the lymph nodes.

The CDC42 effector protein MRCKβ autophosphorylates on Threonine 1108

The CDC42 small GTPase is a major influence on actin-myosin cytoskeleton organization and dynamics, signalling via effector proteins including the Myotonic dystrophy related CDC42-binding protein kinases (MRCK) α and β. We previously identified Serine 1003 of MRCKα as a site of autophosphorylation, and showed that a phosphorylation-sensitive antibody raised against this site could be used as a surrogate indicator of kinase activity. In this study, a kinase-dead version of MRCKβ was established by mutation of the conserved Lysine 105 to Methionine (K105M), which was then used for mass spectrometry analysis to identify phosphorylation events that occurred in catalytically-competent MRCKβ but not in the kinase-dead form. A total of ten phosphorylations were identified on wild-type MRCKβ, of which the previously undescribed Threonine 1108 (Thr1108) was not found on kinase-dead MRCKβ K105M, consistent with this being due to autophosphorylation. Mutation of Thr1108 to non-phosphorylatable Alanine (T1108A) or phosphomimetic Glutamate (T1108E) did not affect the ability of MRCKβ to phosphorylate recombinant myosin light chain in vitro, or observably alter the subcellular localization of green fluorescent protein (GFP)-tagged MRCKβ expressed in MDA MB 231 human breast cancer cells. Although phosphorylation of Thr1108 did not appear to contribute to MRCKβ function or regulation, the identification of this phosphorylation does make it possible to characterize whether this site could be used as a surrogate biomarker of kinase activity and inhibitor efficacy as we previously demonstrated for Ser 1003 in MRCKα.

Epac1 Is Crucial for Maintenance of Endothelial Barrier Function through A Mechanism Partly Independent of Rac1

Epac1 (exchange protein activated by cAMP) stabilizes the endothelial barrier, but detailed studies are limited by the side effects of pharmacological Epac1 modulators and transient transfections. Here, we compare the key properties of barriers between endothelial cells derived from wild-type (WT) and Epac1-knockout (KO) mice myocardium. We found that KO cell layers, unlike WT layers, had low and cAMP-insensitive trans-endothelial resistance (TER). They also had fragmented VE-cadherin staining despite having augmented cAMP levels and increased protein expression of Rap1, Rac1, RhoA, and VE-cadherin. The simultaneous direct activation of Rac1 and RhoA by CN04 compensated Epac1 loss, since TER was increased. In KO-cells, inhibition of Rac1 activity had no additional effect on TER, suggesting that other mechanisms compensate the inhibition of the Rac1 function to preserve barrier properties. In summary, Epac1 is crucial for baseline and cAMP-mediated barrier stabilization through mechanisms that are at least partially independent of Rac1.

Double-Hit-Induced Leukocyte Extravasation Driven by Endothelial Adherens Junction Destabilization

During inflammation, endothelial cells are bombarded with cytokines and other stimuli from surrounding cells. Leukocyte extravasation and vascular leakage are both prominent but believed to be uncoupled as they occur in separate spatiotemporal patterns. In this study, we investigated a "double-hit" approach on primary human endothelial cells primed with LPS followed by histamine. Using neutrophil transendothelial migration (TEM) under physiological flow assays, we found that an LPS-primed endothelium synergistically enhanced neutrophil TEM when additionally treated with histamine, whereas the effects on neutrophil TEM of the individual stimuli were moderate to undetectable. Interestingly, the double-hit-induced TEM increase was not due to decreased endothelial barrier, increased adhesion molecule expression, or Weibel-Palade body release. Instead, we found that it was directly correlated with junctional remodeling. Compounds that increased junctional "linearity" (i.e., stability) counteracted the double-hit effect on neutrophil TEM. We conclude that a compound, in this case histamine (which has a short primary effect on vascular permeability), can have severe secondary effects on neutrophil TEM in combination with an inflammatory stimulus. This effect is due to synergic modifications of the endothelial cytoskeleton and junctional remodeling. Therefore, we hypothesize that junctional linearity is a better and more predictive readout than endothelial resistance for compounds aiming to attenuate inflammation.

Lupeol inhibits migration and invasion of colorectal cancer cells by suppressing RhoA-ROCK1 signaling pathway

Metastasis is the main cause of death in colorectal cancer (CRC) patients. However, current treatment options for CRC metastasis are very limited. Lupeol, a triterpene that is widely found in vegetables and fruits, has been reported to possess the cancer-preventive and anti-inflammatory functions. However, the roles of Lupeol in the migration and invasion of colorectal cancer remain unclear. Here, we evaluated the effect of Lupeol treatment on colorectal cancer cell lines, HCT116 and SW620, and delineated its underlying mechanisms. Our results showed that Lupeol induced a dose-dependent inhibition of HCT116 and SW620 cells viability, measured by CCK8 assay. Wound healing and Transwell migration and invasion assays revealed that Lupeol significantly suppressed the migration and invasion of CRC cells. Using laser confocal microscope, we observed that the pseudopods and protrusions of HCT116 and SW620 cells decreased and disrupted after treatment with Lupeol. In addition, the quantitative real-time PCR and Western blotting results showed that Lupeol downregulated the expression of RhoA and RhoC, and their downstream effectors ROCK1, Cofilin, p-MLC, and the associated regulatory protein Cyclin A2. Interestingly, the migration and invasion capacity of CRC cells was reduced after RhoA knockdown. And there were no additional changes in CRC cells with RhoA knockdown to treat with Lupeol. These findings demonstrate that Lupeol can suppress the migration and invasion of colorectal cancer cells by remodeling the actin cytoskeleton via RhoA-ROCK1 pathway inhibition, which may provide an effective anti-metastatic agent for CRC patients.

Rap1 is Involved in Angiopoietin-1-Induced Cell-Cell Junction Stabilization and Endothelial Cell Sprouting

Angiopoietin-1 (Ang-1) is an important proangiogenic factor also involved in the maintenance of endothelial-barrier integrity. The small GTPase Rap1 is involved in the regulation of adherens junctions through VE-cadherin-mediated adhesion, and in endothelial permeability. While many studies established that Rap1 activation is critical for endothelial cell–cell adhesions, its roles in the antipermeability effects of Ang-1 are ill-defined. Thus, we determined the contribution of Rap1 to Ang-1-stimulated angiogenic effects on endothelial cells (ECs). We found that Rap1 is activated following Ang-1 stimulation and is required for the antipermeability effects of Ang-1 on EC monolayers. Our results also revealed that Rap1 is necessary for EC sprouting stimulated by Ang-1 but had no significant effect on Ang-1-induced EC migration and adhesion. In contrast, downregulation of VE-cadherin markedly increased the adhesiveness of ECs to the substratum, which resulted in inhibition of Ang-1-stimulated migration. These results revealed that Rap1 is central to the effects of Ang-1 at intercellular junctions of ECs, whereas VE-cadherin is also involved in the adhesion of ECs to the extracellular matrix.

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.

Identification of guanine nucleotide exchange factors that increase Cdc42 activity in primary human endothelial cells

The Rho GTPase family is involved in actin dynamics and regulates the barrier function of the endothelium. One of the main barrier-promoting Rho GTPases is Cdc42, also known as cell division control protein 42 homolog. Currently, regulation of Cdc42-based signalling networks in endothelial cells (ECs) lack molecular details. To examine these, we focused on a subset of 15 Rho guanine nucleotide exchange factors (GEFs), which are expressed in the endothelium. By performing single cell FRET measurements with Rho GTPase biosensors in primary human ECs, we monitored GEF efficiency towards Cdc42 and Rac1. A new, single cell-based analysis was developed and used to enable the quantitative comparison of cellular activities of the overexpressed full-length GEFs. Our data reveal GEF dependent activation of Cdc42, with the most efficient Cdc42 activation induced by PLEKHG2, FGD1, PLEKHG1 and PREX1 and the highest selectivity for FGD1. Additionally, we generated truncated GEF constructs that comprise only the catalytic dbl homology (DH) domain or together with the adjacent pleckstrin homology domain (DHPH). The DH domain by itself did not activate Cdc42, whereas the DHPH domain of ITSN1, ITSN2 and PLEKHG1 showed activity towards Cdc42. Together, our study characterized endothelial GEFs that may directly or indirectly activate Cdc42, which will be of great value for the field of vascular biology.

Combination of Gentiana rhodantha and Gerbera anandria in the BL02 formula as therapeutics to non-small cell lung carcinoma acting via Rap1/cdc42 signaling: A transcriptomics/ bio-informatics biological validation approach

BACKGROUND

Non-small cell lung cancer (NSCLC) ranks the most commonly diagnosed and highest mortality-leading cancer worldwide despite a variety of treatment strategies are available. The highly heterogeneous and aggressive property of NSCLC as well as its poor prognosis indicates the need for novel therapeutic targets identification. The objective of this study is to identify potential targets from the adjuvant herbal formula BL02 using a combined approach of high throughput transcriptomics and network pharmacology.

METHODS

The quality and stability of BL02 were assessed by UHPLC analysis. The inhibitory effect of BL02 on NSCLC was measured by in vivo orthotopic intrathoracic mouse model and in vitro cellular models. EGFR-mutant HCC827 and wild type A549 cell lines were employed. Transcriptomics analysis was introduced to profile the gene expression of NSCLC cells treated with BL02; Network pharmacology and molecular docking analyses predicted the interaction of compounds and NSCLC targets. Immuno-blotting and pull-down assays verified the putative targets.

RESULTS

The UHPLC analysis revealed that BL02 was relatively stable between batches of production and for 24 months of storage. Orally administration of BL02 was safe and effective to inhibit pulmonary NSCLC growth in mice implanted with A549 and HCC827-generated tumors. BL02 exhibited relatively low cytotoxicity to NSCLC cells in vitro, but potently suppressed NSCLC cell motility. The transcriptomic analysis illustrated that EGFR and cellular adhesion-related signaling is involved in BL02 action. Further bioinformatics analysis validated BL02 activity is mediated by cdc42-regulated signaling. BL02 depolymerized the actin cytoskeleton through suppressing cdc42 and deactivating its upstream molecule Rap1. These effects may be primarily mediated by the direct binding of 5-methylcoumarin-4-cellobioside and mangiferin from BL02 to Rap1 protein.

CONCLUSION

Our study proposes an integration model of experimental, transcriptomic and bioinformatics analyses in the identification of novel therapeutic target of NSCLC from an adjuvant herbal formula BL02. Our findings revealed that inhibition of Rap1/cdc42 signaling by active compounds 5-methylcoumarin-4-cellobioside and mangiferin from BL02 might be potentially effective therapy for NSCLC.

Small GTPase Rap1A/B Is Required for Lymphatic Development and Adrenomedullin-Induced Stabilization of Lymphatic Endothelial Junctions

Objective- Maintenance of lymphatic permeability is essential for normal lymphatic function during adulthood, but the precise signaling pathways that control lymphatic junctions during development are not fully elucidated. The G_s-coupled AM (adrenomedullin) signaling pathway is required for embryonic lymphangiogenesis and the maintenance of lymphatic junctions during adulthood. Thus, we sought to elucidate the downstream effectors mediating junctional stabilization in lymphatic endothelial cells. Approach and Results- We knocked-down both Rap1A and Rap1B isoforms in human neonatal dermal lymphatic cells (human lymphatic endothelial cells) and genetically deleted the mRap1 gene in lymphatic endothelial cells by producing 2 independent, conditional Rap1a/b knockout mouse lines. Rap1A/B knockdown caused disrupted junctional formation with hyperpermeability and impaired AM-induced lymphatic junctional tightening, as well as rescue of histamine-induced junctional disruption. Less than 60% of lymphatic- Rap1a/b knockout embryos survived to E13.5 exhibiting interstitial edema, blood-filled lymphatics, disrupted lymphovenous valves, and defective lymphangiogenesis. Consistently, inducible lymphatic- Rap1a/b deletion in adult animals prevented AM-rescue of histamine-induced lymphatic leakage and dilation. Conclusions- Rap1 (Ras-related protein) serves as the dominant effector downstream of AM to stabilize lymphatic junctions. Rap1 is required for maintaining lymphatic permeability and driving normal lymphatic development.

VE-PTP inhibition stabilizes endothelial junctions by activating FGD5

Inhibition of VE-PTP, an endothelial receptor-type tyrosine phosphatase, triggers phosphorylation of the tyrosine kinase receptor Tie-2, which leads to the suppression of inflammation-induced vascular permeability. Analyzing the underlying mechanism, we show here that inhibition of VE-PTP and activation of Tie-2 induce tyrosine phosphorylation of FGD5, a GTPase exchange factor (GEF) for Cdc42, and stimulate its translocation to cell contacts. Interfering with the expression of FGD5 blocks the junction-stabilizing effect of VE-PTP inhibition in vitro and in vivo. Likewise, FGD5 is required for strengthening cortical actin bundles and inhibiting radial stress fiber formation, which are each stimulated by VE-PTP inhibition. We identify Y820 of FGD5 as the direct substrate for VE-PTP. The phosphorylation of FGD5-Y820 is required for the stabilization of endothelial junctions and for the activation of Cdc42 by VE-PTP inhibition but is dispensable for the recruitment of FGD5 to endothelial cell contacts. Thus, activation of FGD5 is a two-step process that comprises membrane recruitment and phosphorylation of Y820. These steps are necessary for the junction-stabilizing effect stimulated by VE-PTP inhibition and Tie-2 activation.

Robo2 regulates synaptic oxytocin content by affecting actin dynamics

The regulation of neuropeptide level at the site of release is essential for proper neurophysiological functions. We focused on a prominent neuropeptide, oxytocin (OXT) in the zebrafish as an in vivo model to visualize and quantify OXT content at the resolution of a single synapse. We found that OXT-loaded synapses were enriched with polymerized actin. Perturbation of actin filaments by either cytochalasin-D or conditional Cofilin expression resulted in decreased synaptic OXT levels. Genetic loss of robo2 or slit3 displayed decreased synaptic OXT content and robo2 mutants displayed reduced mobility of the actin probe Lifeact-EGFP in OXT synapses. Using a novel transgenic reporter allowing real-time monitoring of OXT-loaded vesicles, we show that robo2 mutants display slower rate of vesicles accumulation. OXT-specific expression of dominant-negative Cdc42, which is a key regulator of actin dynamics and a downstream effector of Robo2, led to a dose-dependent increase in OXT content in WT, and a dampened effect in robo2 mutants. Our results link Slit3-Robo2-Cdc42, which controls local actin dynamics, with the maintenance of synaptic neuropeptide levels.

Balance of mechanical forces drives endothelial gap formation and may facilitate cancer and immune-cell extravasation

The formation of gaps in the endothelium is a crucial process underlying both cancer and immune cell extravasation, contributing to the functioning of the immune system during infection, the unfavorable development of chronic inflammation and tumor metastasis. Here, we present a stochastic-mechanical multiscale model of an endothelial cell monolayer and show that the dynamic nature of the endothelium leads to spontaneous gap formation, even without intervention from the transmigrating cells. These gaps preferentially appear at the vertices between three endothelial cells, as opposed to the border between two cells. We quantify the frequency and lifetime of these gaps, and validate our predictions experimentally. Interestingly, we find experimentally that cancer cells also preferentially extravasate at vertices, even when they first arrest on borders. This suggests that extravasating cells, rather than initially signaling to the endothelium, might exploit the autonomously forming gaps in the endothelium to initiate transmigration.

Neuroinflammation During RNA Viral Infections

Neurotropic RNA viruses continue to emerge and are increasingly linked to diseases of the central nervous system (CNS) despite viral clearance. Indeed, the overall mortality of viral encephalitis in immunocompetent individuals is low, suggesting efficient mechanisms of virologic control within the CNS. Both immune and neural cells participate in this process, which requires extensive innate immune signaling between resident and infiltrating cells, including microglia and monocytes, that regulate the effector functions of antiviral T and B cells as they gain access to CNS compartments. While these interactions promote viral clearance via mainly neuroprotective mechanisms, they may also promote neuropathology and, in some cases, induce persistent alterations in CNS physiology and function that manifest as neurologic and psychiatric diseases. This review discusses mechanisms of RNA virus clearance and neurotoxicity during viral encephalitis with a focus on the cytokines essential for immune and neural cell inflammatory responses and interactions. Understanding neuroimmune communications in the setting of viral infections is essential for the development of treatments that augment neuroprotective processes while limiting ongoing immunopathological processes that cause ongoing CNS disease.

Mechanosensitive Rap1 activation promotes barrier function of lung vascular endothelium under cyclic stretch

Mechanical ventilation remains an imperative treatment for the patients with acute respiratory distress syndrome, but can also exacerbate lung injury. We have previously described a key role of RhoA GTPase in high cyclic stretch (CS)-induced endothelial cell (EC) barrier dysfunction. However, cellular mechanotransduction complexes remain to be characterized. This study tested a hypothesis that recovery of a vascular EC barrier after pathologic mechanical stress may be accelerated by cell exposure to physiologic CS levels and involves Rap1-dependent rearrangement of endothelial cell junctions. Using biochemical, molecular, and imaging approaches we found that EC pre- or postconditioning at physiologically relevant low-magnitude CS promotes resealing of cell junctions disrupted by pathologic, high-magnitude CS. Cytoskeletal remodeling induced by low CS was dependent on small GTPase Rap1. Protective effects of EC preconditioning at low CS were abolished by pharmacological or molecular inhibition of Rap1 activity. In vivo, using mice exposed to mechanical ventilation, we found that the protective effect of low tidal volume ventilation against lung injury caused by lipopolysaccharides and ventilation at high tidal volume was suppressed in Rap1 knockout mice. Taken together, our results demonstrate a prominent role of Rap1-mediated signaling mechanisms activated by low CS in acceleration of lung vascular EC barrier restoration.

C3G dynamically associates with nuclear speckles and regulates mRNA splicing

The first example of a Ras family GTPase and its exchange factor C3G localizing to nuclear speckles and regulating mRNA splicing is presented.

C3G (Crk SH3 domain binding guanine nucleotide releasing factor) (Rap guanine nucleotide exchange factor 1), essential for mammalian embryonic development, is ubiquitously expressed and undergoes regulated nucleocytoplasmic exchange. Here we show that C3G localizes to SC35-positive nuclear speckles and regulates splicing activity. Reversible association of C3G with speckles was seen on inhibition of transcription and splicing. C3G shows partial colocalization with SC35 and is recruited to a chromatin and RNase-sensitive fraction of speckles. Its presence in speckles is dependent on intact cellular actin cytoskeleton and is lost on expression of the kinase Clk1. Rap1, a substrate of C3G, is also present in nuclear speckles, and inactivation of Rap signaling by expression of GFP-Rap1GAP alters speckle morphology and number. Enhanced association of C3G with speckles is seen on glycogen synthase kinase 3 beta inhibition or differentiation of C2C12 cells to myotubes. CRISPR/Cas9-mediated knockdown of C3G resulted in altered splicing activity of an artificial gene as well as endogenous CD44. C3G knockout clones of C2C12 as well as MDA-MB-231 cells showed reduced protein levels of several splicing factors compared with control cells. Our results identify C3G and Rap1 as novel components of nuclear speckles and a role for C3G in regulating cellular RNA splicing activity.