Dynamics between actin and the VE-cadherin/catenin complex: novel aspects of the ARP2/3 complex in regulation of endothelial junctions

Adherent junctions: Physiology, role in hydrocephalus and potential therapeutic targets

In all epithelial cells, the adherent junctions (AJs) with cadherin as the core play an important role in the maintenance of the connection and the formation of apical-basal polarity. The ependymal cells close to the ventricular system rely on AJs with N-cadherin at the core to maintain their normal morphology and function. Therefore, it has an important impact on the function and disease of the central nervous system. Hydrocephalus is a pathological phenomenon of excessive cerebrospinal fluid accumulating in the ventricular system accompanied by continuous ventricular dilatation, which can be divided into obstructive hydrocephalus and communicating hydrocephalus according to the pathogenesis. Obstructive hydrocephalus is often associated with excessive ependymal cells produced by differentiation of radial glial cells. The etiology of communicating hydrocephalus is mainly related to the dyskinesia of cerebrospinal fluid. In addition, the damage of the brain barrier can lead to brain edema and aggravate the symptoms. At present, the researches on the pathogenesis of hydrocephalus are mainly focused on the development of ependymal cells and cilia, while less attention has been paid to molecules such as AJs, which play an important role in maintaining the polarity of ependymal cells. This paper discusses the formation and function of AJs and their role in preventing hydrocephalus by preserving the polarity of ependymal cilia, regulating the number of ependymal cells, and upholding the brain barrier integrity to impede hydrocephalus exacerbation, which provides a new direction for the study of hydrocephalus.

A specific role for endothelial EPLIN-isoform-regulated actin dynamics in neutrophil transmigration

Proinflammatory cytokines such as TNF-α or IL-1β activate the endothelium promoting leukocyte transendothelial migration (TEM) via expression of cell adhesion molecules (CAM) and cause actin remodelling. However, the function of endothelial actin remodelling in TEM remains elusive, despite its involvement in the formation of docking structures, diapedesis pores and pore resealing. Here, we establish EPLIN-isoforms, EPLIN-β and EPLIN-α, as differential regulators of TNF-α-inducedactin-remodelling significantly affecting TEM. We find EPLIN-β-induced stress fiber formation upon TNF-α-treatment weakens endothelial junctions, upregulates junctional dynamics and facilitates intercellular gaps for TEM. Increased junctional dynamics involves branched actin filaments under the control of EPLIN-α, including docking structure formation and transmigratory pore closure. We further establish by EPLIN deletion and re-expression studies that EPLIN-α-mediated termination of branched actin filaments maintains TNF-α-induced junctional dynamics and intercellular gaps facilitating TEM. These findings highlight the critical role of TNF-α-induced differential actin dynamics, controlled by EPLIN isoforms, in TEM. These results also offer a wider understanding of inflammation-induced TEM by incorporating altered junctional dynamics alongside upregulation of cell adhesion molecules.

Revealing Mechanopathology Induced by Dengue NS1 Using Organ Chips and Single-Cell Force Spectroscopy

Capillary leakage is a hallmark of severe dengue, yet its precise mechanisms remain elusive. Emerging evidence highlights the dengue virus's targeting of mechanically active endothelial cells as a key contributor to dengue shock syndrome. The viral nonstructural protein 1 (NS1) has been identified as a central player, disrupting endothelial integrity and inducing vascular hyperpermeability independently of pro-inflammatory cytokines. This study provides a direct assessment of NS1-induced endothelial pathology by combining single-cell force spectroscopy and a microvessel-on-a-chip platform. We demonstrate that NS1 significantly alters endothelial cell mechanics, reducing cell stiffness and compromising junctional integrity, thereby directly linking these mechanical alterations to vascular dysfunction. These findings establish a framework for understanding the mechano-pathology of dengue and offer a platform for developing targeted therapeutic strategies to mitigate severe disease outcomes.

Spatial Transcriptomics and Proteomics Profiling After Ischemic Stroke Reperfusion: Insights Into Vascular Alterations

BACKGROUND

More than half of patients with ischemic stroke experience futile reperfusion, increasing the risk of death and disabilities despite a successful recanalization. The reason behind this is debated, and we aim to investigate cerebrovascular changes toward a broader understanding of these conditions. We hypothesize that ischemic stroke reperfusion modifies the expression profile in the microvasculature in a spatial manner toward peri-infarct brain edema and circulatory failure.

METHODS

We investigated the early (24-hour) changes in spatial gene expression in the brain parenchymal endothelial cells and mural cells following ischemia stroke reperfusion in 13- to 14-week-old C57BL/6JRj male mice (n=5). Ischemia was induced by occlusion of the middle cerebral artery for 60 minutes, and Nissl staining was used to validate infarct size. Spatial transcriptomics complemented by bulk proteomics was conducted in the peri-infarct cortex region and validated with immunohistochemical semiquantification of proteins of interest. To avoid individual biological variations, changes in the peri-infarct cortex region were expressed relatively to the matching contralateral hemisphere region.

RESULTS

Ischemic stroke reperfusion impaired the blood-brain barrier integrity through junctional Cldn5 (claudin-5) downregulation, changes of the actin cytoskeleton adhesion, and high expression of the proinflammatory Il-6 (interleukin-6). Molecules important for extracellular Ca2+ influx and intracellular Ca2+ release, Cacna1e (R-type Ca2+ channels), Orai2, Ryr3, Itpr1, and Itpka (inositol-trisphosphate 3-kinase A), were markedly reduced. Furthermore, reduced Grm5 (glutamate receptor 5) associated with upregulated Nfatc3 and Stat3 implicates suppression of the contractile phenotype, suggesting reduced poststroke vascular resistance due to loss of mural cell tone. The complete spatial transcriptomics map over the ipsilateral and contralateral hemispheres is available online as a Web tool.

CONCLUSIONS

Emphasizing the spatial molecular pattern behind blood-brain barrier disruption and loss of the vascular tone in the acute phase following ischemic stroke reperfusion suggests the gene expression contribution for a therapeutic target in ischemia-reperfusion abnormalities.

The endothelium at the interface between tissues and Staphylococcus aureus in the bloodstream

SUMMARYStaphylococcus aureus is a major human pathogen. It can cause many types of infections, in particular bacteremia, which frequently leads to infective endocarditis, osteomyelitis, sepsis, and other debilitating diseases. The development of secondary infections is based on the bacterium's ability to associate with endothelial cells lining blood vessels. The success of endothelial colonization and infection by S. aureus relies on its ability to express a wide array of cell wall-anchored and secreted virulence factors. Establishment of endothelial infection by the pathogen is a multistep process involving adhesion, invasion, extravasation, and dissemination of the bacterium into surrounding tissues. The process is dependent on the type of endothelium in different organs (tissues) and pathogenetic potential of the individual strains. In this review, we report an update on the organization of the endothelium in the vessels, the structure and function of the virulence factors of S. aureus, and the several aspects of bacteria-endothelial cell interactions. After these sections, we will discuss recent advances in understanding the specific mechanisms of infections that develop in the heart, bone and joints, lung, and brain. Finally, we describe how neutrophils bind to endothelial cells, migrate to the site of infection to kill bacteria in the tissues, and how staphylococci counteract neutrophils' actions. Knowledge of the molecular details of S. aureus-endothelial cell interactions will promote the development of new therapeutic strategies and tools to combat this formidable pathogen.

An Integrated Microcurrent Delivery System Facilitates Human Parathyroid Hormone Delivery for Enhancing Osteoanabolic Effect

Human parathyroid hormone (1-34) (PTH) exhibits osteoanabolic and osteocatabolic effects, with shorter plasma exposure times favoring bone formation. Subcutaneous injection (SCI) is the conventional delivery route for PTH but faces low delivery efficiency due to limited passive diffusion and the obstruction of the vascular endothelial barrier, leading to prolonged drug exposure times and reduced osteoanabolic effects. In this work, a microcurrent delivery system (MDS) based on multimicrochannel microneedle arrays (MMAs) is proposed, achieving high efficiency and safety for PTH transdermal delivery. The internal microchannels of the MMAs are fabricated using high-precision 3D printing technology, providing a concentrated and safe electric field that not only accelerates the movement of PTH but also reversibly increases vascular endothelial permeability by regulating the actin cytoskeleton and interendothelial junctions through Ca2+-dependent cAMP signaling, ultimately promoting PTH absorption and shortening exposure times. The MDS enhances the osteoanabolic effect of PTH in an osteoporosis model by inhibiting osteoclast differentiation on the bone surface compared to SCI. Moreover, histopathological analysis of the skin and organs demonstrated the good safety of PTH delivered by MDS in vivo. In addition to PTH, the MDS shows broad prospects for the high-efficiency transdermal delivery of macromolecular drugs.

Dragon's blood attenuates LPS-induced intestinal epithelial barrier dysfunction via upregulation of FAK-DOCK180-Rac1-WAVE2-Arp3 and downregulation of TLR4/NF-κB signaling pathways

Inflammation-induced intestinal epithelial barrier (IEB) dysfunction is one of the important reasons for the occurrence and development of intestinal inflammatory-related diseases, including ulcerative colitis (UC), Crohn's disease and necrotizing enterocolitis (NEC). Dragon's blood (DB) is a traditional Chinese medicine and has been clinically used to treat UC. However, the protective mechanism of DB on intestinal inflammatory-related diseases has still not been elucidated. The present study aimed to explore the protection mechanism of DB on IEB dysfunction in rat ileum and human colorectal adenocarcinoma cells (Caco-2)/human umbilical vein endothelial cells (HUVECs) coculture system induced by lipopolysaccharide (LPS). DB could ameliorate rat ileum mucosa morphological injury, reduce the accumulation of lipid-peroxidation products and increase the expression of junction proteins. DB also alleviated LPS-induced Caco-2 cells barrier integrity destruction in Caco-2/ HUVECs coculture system, leading to increased trans-endothelial electrical resistance (TEER), reduced cell permeability, and upregulation of expressions of F-actin and junction proteins. DB contributed to the assembly of actin cytoskeleton by upregulating the FAK-DOCK180-Rac1-WAVE2-Arp3 pathway and contributed to the formation of intercellular junctions by downregulating TLR4-MyD88-NF-κB pathway, thus reversing LPS-induced IEB dysfunction. These novel findings illustrated the potential protective mechanism of DB on intestinal inflammatory-related diseases and might be useful for further clinical application of DB.

Characterization of Photo-Crosslinked Methacrylated Type I Collagen as a Platform to Investigate the Lymphatic Endothelial Cell Response

Despite chronic fibrosis occurring in many pathological conditions, few in vitro studies examine how fibrosis impacts lymphatic endothelial cell (LEC) behavior. This study examined stiffening profiles of PhotoCol®-commercially available methacrylated type I collagen-photo-crosslinked with the photoinitiators: Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), Irgacure 2959 (IRG), and Ruthenium/Sodium Persulfate (Ru/SPS) prior to evaluating PhotoCol® permeability and LEC response to PhotoCol® at stiffnesses representing normal and fibrotic tissues. Ru/SPS produced the highest stiffness (~6 kilopascal (kPa)) for photo-crosslinked PhotoCol®, but stiffness did not change with burst light exposures (30 and 90 s). The collagen fibril area fraction increased, and dextran permeability (40 kilodalton (kDa)) decreased with photo-crosslinking, showing the impact of photo-crosslinking on microstructure and molecular transport. Human dermal LECs on softer, uncrosslinked PhotoCol® (~0.5 kPa) appeared smaller with less prominent vascular endothelial (VE)-cadherin (cell-cell junction) expression compared to LECs on stiffer PhotoCol® (~6 kPa), which had increased cell size, border irregularity, and VE-cadherin thickness (junction zippering) that is consistent with LEC morphology in fibrotic tissues. Our quantitative morphological analysis demonstrates our ability to produce LECs with a fibrotic phenotype, and the overall study shows that PhotoCol® with Ru/SPS provides the necessary physical properties to systematically study LEC responses related to capillary growth and function under fibrotic conditions.

SOX4 induces cytoskeleton remodeling and promotes cell motility via N-wasp/ARP2/3 pathway in colorectal cancer cells

Filopodia are thin, actin-rich projection from the plasma membrane that promote cancer cell invasion and migration. Sex-determining region Y-related high-mobility group-box 4 (SOX4) is a crucial transcription factor that plays a role in the development and metastasis of colorectal cancer (CRC). However, the involvement of SOX4 in cytoskeleton remodeling in CRC remains unknown. For the first time, we demonstrate that SOX4 is a potent regulator of filopodia formation in CRC cells. Overexpression of SOX4 protein enhances both migration and invasion ability of HCT116, and CACO2 cells, which is relevant to the metastasis. Furthermore, through phalloidin staining, cytoskeleton re-assembly was observed in SOX4-modified cell lines. Enhanced expression of SOX4 increased the number and length of filopodia on cell surface. In contrast, silencing SOX4 in SW620 cells with higher endogenous expression of SOX4, impeded the filopodia formation. Moreover, SOX4 was found to be positively regulating the expression of central regulators of actin cytoskeleton - N-Wiskott-Aldrich syndrome protein (N-WASP); WAVE2; Actin related proteins, ARP2 and ARP3. Inhibiting the N-WASP/ARP2/3 pathway diminishes the filopodia formation and the migration of CRC cells. These results indicate the crucial role of SOX4 in the regulation of filopodia formation mediated by N-WASP/ARP2/3 pathway in CRC cells.

Single-cell dissection of the human motor and prefrontal cortices in ALS and FTLD

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) share many clinical, pathological, and genetic features, but a detailed understanding of their associated transcriptional alterations across vulnerable cortical cell types is lacking. Here, we report a high-resolution, comparative single-cell molecular atlas of the human primary motor and dorsolateral prefrontal cortices and their transcriptional alterations in sporadic and familial ALS and FTLD. By integrating transcriptional and genetic information, we identify known and previously unidentified vulnerable populations in cortical layer 5 and show that ALS- and FTLD-implicated motor and spindle neurons possess a virtually indistinguishable molecular identity. We implicate potential disease mechanisms affecting these cell types as well as non-neuronal drivers of pathogenesis. Finally, we show that neuron loss in cortical layer 5 tracks more closely with transcriptional identity rather than cellular morphology and extends beyond previously reported vulnerable cell types.

DNA-PKcs Phosphorylates Cofilin2 to Induce Endothelial Dysfunction and Microcirculatory Disorder in Endotoxemic Cardiomyopathy

The presence of endotoxemia is strongly linked to the development of endothelial dysfunction and disruption of myocardial microvascular reactivity. These factors play a crucial role in the progression of endotoxemic cardiomyopathy. Sepsis-related multiorgan damage involves the participation of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs). However, whether DNA-PKcs contributes to endothelial dysfunction and myocardial microvascular dysfunction during endotoxemia remains unclear. Hence, we conducted experiments in mice subjected to lipopolysaccharide (LPS)-induced endotoxemic cardiomyopathy, as well as assays in primary mouse cardiac microvascular endothelial cells. Results showed that endothelial-cell-specific DNA-PKcs ablation markedly attenuated DNA damage, sustained microvessel perfusion, improved endothelial barrier function, inhibited capillary inflammation, restored endothelium-dependent vasodilation, and improved heart function under endotoxemic conditions. Furthermore, we show that upon LPS stress, DNA-PKcs recognizes a TQ motif in cofilin2 and consequently induces its phosphorylation at Thr25. Phosphorylated cofilin2 shows increased affinity for F-actin and promotes F-actin depolymerization, resulting into disruption of the endothelial barrier integrity, microvascular inflammation, and defective eNOS-dependent vasodilation. Accordingly, cofilin2-knockin mice expressing a phospho-defective (T25A) cofilin2 mutant protein showed improved endothelial integrity and myocardial microvascular function upon induction of endotoxemic cardiomyopathy. These findings highlight a novel mechanism whereby DNA-PKcs mediates cofilin2Thr25 phosphorylation and subsequent F-actin depolymerization to contribute to endotoxemia-related cardiac microvascular dysfunction.

Endothelial IL17RD promotes Western diet-induced aortic myeloid cell infiltration

The Interleukin-17 (IL17) family is a group of cytokines implicated in the etiology of several inflammatory diseases. Interleukin-17 receptor D (IL17RD), also known as Sef (similar expression to fibroblast growth factor) belonging to the family of IL17 receptors, has been shown to modulate IL17A-associated inflammatory phenotypes. The objective of this study was to test the hypothesis that IL17RD promotes endothelial cell activation and consequent leukocyte adhesion. We utilized primary human aortic endothelial cells and demonstrated that RNAi targeting of IL17RD suppressed transcript levels by 83 % compared to non-targeted controls. Further, RNAi knockdown of IL17RD decreased the adhesion of THP-1 monocytic cells onto a monolayer of aortic endothelial cells in response to IL17A. Additionally, we determined that IL17A did not significantly enhance the activation of canonical MAPK and NFκB pathways in endothelial cells, and further did not significantly affect the expression of VCAM-1 and ICAM-1 in aortic endothelial cells, which is contrary to previous findings. We also determined the functional relevance of our findings in vivo by comparing the expression of endothelial VCAM-1 and ICAM-1 and leukocyte infiltration in the aorta in Western diet-fed Il17rd null versus wild-type mice. Our results showed that although Il17rd null mice do not have significant alteration in aortic expression of VCAM-1 and ICAM-1 in endothelial cells, they exhibit decreased accumulation of proinflammatory monocytes and neutrophils, suggesting that endothelial IL17RD induced in vivo myeloid cell accumulation is not dependent on upregulation of VCAM-1 and ICAM-1 expression. We further performed proteomics analysis to identify potential molecular mediators of the IL17A/IL17RD signaling axis. Collectively, our results underscore a critical role for Il17rd in the regulation of aortic myeloid cell infiltration in the context of Western diet feeding.

Helical vasculogenesis driven by cell chirality

The cellular helical structure is well known for its crucial role in development and disease. Nevertheless, the underlying mechanism governing this phenomenon remains largely unexplored, particularly in recapitulating it in well-controlled engineering systems. Leveraging advanced microfluidics, we present compelling evidence of the spontaneous emergence of helical endothelial tubes exhibiting robust right-handedness governed by inherent cell chirality. To strengthen our findings, we identify a consistent bias toward the same chirality in mouse vascular tissues. Manipulating endothelial cell chirality using small-molecule drugs produces a dose-dependent reversal of the handedness in engineered vessels, accompanied by non-monotonic changes in vascular permeability. Moreover, our three-dimensional cell vertex model provides biomechanical insights into the chiral morphogenesis process, highlighting the role of cellular torque and tissue fluidity in its regulation. Our study unravels an intriguing mechanism underlying vascular chiral morphogenesis, shedding light on the broader implications and distinctive perspectives of tubulogenesis within biological systems.

Role of cell rearrangement and related signaling pathways in the dynamic process of tip cell selection

Angiogenesis is a complex, highly-coordinated and multi-step process of new blood vessel formation from pre-existing blood vessels. When initiated, the sprouting process is spearheaded by the specialized endothelial cells (ECs) known as tip cells, which guide the organization of accompanying stalk cells and determine the function and morphology of the finally-formed blood vessels. Recent studies indicate that the orchestration and coordination of angiogenesis involve dynamic tip cell selection, which is the competitive selection of cells to lead the angiogenic sprouts. Therefore, this review attempt to summarize the underlying mechanisms involved in tip cell specification in a dynamic manner to enable readers to gain a systemic and overall understanding of tip cell formation, involving cooperative interaction of cell rearrangement with Notch and YAP/TAZ signaling. Various mechanical and chemical signaling cues are integrated to ensure the right number of cells at the right place during angiogenesis, thereby precisely orchestrating morphogenic functions that ensure correct patterning of blood vessels. Video Abstract.

Imaging and Analysis of the Dynamics of Filamentous Actin Structures in Live Endothelial Cells

The ability to view and record the movements of subcellular structures is a powerful tool that has accelerated the discovery and understanding of signaling mechanisms that control microvascular functions such as the control of endothelial permeability. Advances in molecular biology over the past few decades have facilitated the generation of fusion proteins in which fluorescent reporters based upon the structure of green fluorescent protein can be linked to proteins found in human endothelial cells, such as VE-cadherin or β-actin. These fusion proteins have been found to incorporate into structures alongside their native protein counterparts, allowing the dynamic visualization of how these subcellular structures are modified when cells are challenged with stimuli such as inflammatory mediators. The result of such studies has been a much more advanced view of the complex mechanisms by which endothelial cells maintain barrier properties than previously obtained by only viewing fixed cells labeled by immunofluorescence. Here, we describe our protocols that we have used to view the dynamics of actin filaments using time-lapse microscopy to record endothelial cells expressing GFP-actin and the analysis tools available to quantify dynamics of subcellular structures.

Magneto-Mechanical Actuation Induces Endothelial Permeability

Cancer treatment is one of the major health problems that burden our society. According to the American Cancer Society, over 1.9 million new cancer cases and ∼0.6 million deaths from cancer are expected in the US in 2023. Therapeutic targeting is considered to be the gold standard in cancer treatment. However, when a tumor grows beyond a critical size, its vascular system differentiates abnormally and erratically, creating a heterogeneous endothelial barrier that further restricts drug delivery into tumors. While several methods exist, these prompt tumor migration and the appearance of new metastatic sites. Herein, we propose an innovative method based on magneto-mechanical actuation (MMA) to induce endothelial permeability. This method employs FDA-approved PEGylated superparamagnetic iron oxide nanoparticles (PEG-SPIONs) and alternating nonheating magnetic fields. MMA lies in the translation of magnetic forces into mechanical agitation. As a proof of concept, we developed a 2D cell culture model based on human umbilical vein endothelial cells (HUVEC), which were incubated with PEG-SPIONs and then exposed to different magnetic doses. After adjusting the particle concentration, incubation times, and parameters (amplitude, frequency, and exposure time) of the magnetic field generator, we induced actin filament remodeling and subsequent vascular endothelial-cadherin junction disruption. This led to transient gaps in cell monolayers, through which fluorescein isothiocyanate-dextran was translocated. We observed no cell viability reduction for 3 h of particle incubation up to a concentration of 100 μg/mL in the presence and absence of magnetic fields. For optimal permeability studies, the magnetic field parameters were adjusted to 100 mT, 65 Hz, and 30 min in a pulse mode with 5 min OFF intervals. We found that the endothelial permeability reached the highest value (33%) when 2 h postmagnetic field treatment was used. To explain these findings, a magneto-mechanical transduced stress mechanism mediated by intracellular forces was proposed. This method can open new avenues for targeted drug delivery into anatomic regions within the body for a broad range of disease interventions.

TIMP2 ameliorates blood-brain barrier disruption in traumatic brain injury by inhibiting Src-dependent VE-cadherin internalization

Blood-brain barrier (BBB) disruption is a serious pathological consequence of traumatic brain injury (TBI), for which there are limited therapeutic strategies. Tissue inhibitor of metalloproteinase-2 (TIMP2), a molecule with dual functions of inhibiting MMP activity and displaying cytokine-like activity through receptor binding, has been reported to inhibit VEGF-induced vascular hyperpermeability. Here, we investigate the ability of TIMP2 to ameliorate BBB disruption in TBI and the underlying molecular mechanisms. Both TIMP2 and AlaTIMP2, a TIMP2 mutant without MMP-inhibiting activity, attenuated neurological deficits and BBB leakage in TBI mice; they also inhibited junctional protein degradation and translocation to reduce paracellular permeability in human brain microvascular endothelial cells (ECs) exposed to hypoxic plus inflammatory insult. Mechanistic studies revealed that TIMP2 interacted with α3β1 integrin on ECs, inhibiting Src activation-dependent VE-cadherin phosphorylation, VE-cadherin/catenin complex destabilization, and subsequent VE-cadherin internalization. Notably, localization of VE-cadherin on the membrane was critical for TIMP2-mediated EC barrier integrity. Furthermore, TIMP2-mediated increased membrane localization of VE-cadherin enhanced the level of active Rac1, thereby inhibiting stress fiber formation. All together, our studies have identified an MMP-independent mechanism by which TIMP2 regulates EC barrier integrity after TBI. TIMP2 may be a therapeutic agent for TBI and other neurological disorders involving BBB breakdown.

VE-CADHERIN is expressed transiently in early ISL1+ cardiovascular progenitor cells and facilitates cardiac differentiation

Adherens junctions (AJs) provide adhesive properties through cadherins and associated cytoplasmic catenins and participate in morphogenetic processes. We examined AJs formed between ISL1+ cardiovascular progenitor cells during differentiation of embryonic stem cells (ESCs) in vitro and in mouse embryogenesis in vivo. We found that, in addition to N-CADHERIN, a percentage of ISL1+ cells transiently formed vascular endothelial (VE)-CADHERIN-mediated AJs during in vitro differentiation on days 4 and 5, and the same pattern was observed in vivo. Fluorescence-activated cell sorting (FACS) analysis extended morphological data showing that VE-CADHERIN+/ISL1+ cells constitute a significant percentage of cardiac progenitors on days 4 and 5. The VE-CADHERIN+/ISL1+ cell population represented one-third of the emerging FLK1+/PDGFRa+ cardiac progenitor cells (CPCs) for a restricted time window (days 4-6). Ablation of VE-CADHERIN during ESC differentiation results in severe inhibition of cardiac differentiation. Disruption of all classic cadherins in the VE-CADHERIN+ population via a cadherin dominant-negative mutant's expression resulted in a dramatic decrease in the ISL1+ population and inhibition of cardiac differentiation.

Characterization of LIMA1 and its emerging roles and potential therapeutic prospects in cancers

Actin is the most abundant and highly conserved cytoskeletal protein present in all eukaryotic cells. Remodeling of the actin cytoskeleton is controlled by a variety of actin-binding proteins that are extensively involved in biological processes such as cell motility and maintenance of cell shape. LIM domain and actin-binding protein 1 (LIMA1), as an important actin cytoskeletal regulator, was initially thought to be a tumor suppressor frequently downregulated in epithelial tumors. Importantly, the deficiency of LIMA1 may be responsible for dysregulated cytoskeletal dynamics, altered cell motility and disrupted cell-cell adhesion, which promote tumor proliferation, invasion and migration. As research progresses, the roles of LIMA1 extend from cytoskeletal dynamics and cell motility to cell division, gene regulation, apical extrusion, angiogenesis, cellular metabolism and lipid metabolism. However, the expression of LIMA1 in malignant tumors and its mechanism of action have not yet been elucidated, and many problems and challenges remain to be addressed. Therefore, this review systematically describes the structure and biological functions of LIMA1 and explores its expression and regulatory mechanism in malignant tumors, and further discusses its clinical value and therapeutic prospects.

Inhibition of Exchange Proteins Directly Activated by cAMP (EPAC) as a Strategy for Broad-Spectrum Antiviral Development

The recent SARS-CoV-2 and mpox outbreaks have highlighted the need to expand our arsenal of broad-spectrum antiviral agents for future pandemic preparedness. Host-directed antivirals are an important tool to accomplish this as they typically offer protection against a broader range of viruses than direct-acting antivirals and have a lower susceptibility to viral mutations that cause drug resistance. In this study, we investigate the Exchange Protein Activated by cAMP (EPAC) as a target for broad-spectrum antiviral therapy. We find that the EPAC-selective inhibitor, ESI-09 provides robust protection against a variety of viruses, including SARS-CoV-2 and Vaccinia (VACV) - an orthopoxvirus from the same family as mpox. We show, using a series of immunofluorescence experiments, that ESI-09 remodels the actin cytoskeleton through Rac1/Cdc42 GTPases and the Arp2/3 complex, impairing internalization of viruses that use clathrin-mediated endocytosis (e.g. VSV) or micropinocytosis (e.g. VACV). Additionally, we find that ESI-09 disrupts syncytia formation and inhibits cell-to-cell transmission of viruses such as measles and VACV. When administered to immune-deficient mice in an intranasal challenge model, ESI-09 protects mice from lethal doses of VACV and prevents formation of pox lesions. Altogether, our finding show that EPAC antagonists such as ESI-09 are promising candidates for broad-spectrum antiviral therapy that can aid in the fight against ongoing and future viral outbreaks.

Nuclear SUN1 stabilizes endothelial cell junctions via microtubules to regulate blood vessel formation

Endothelial cells line all blood vessels, where they coordinate blood vessel formation and the blood-tissue barrier via regulation of cell-cell junctions. The nucleus also regulates endothelial cell behaviors, but it is unclear how the nucleus contributes to endothelial cell activities at the cell periphery. Here, we show that the nuclear-localized linker of the nucleoskeleton and cytoskeleton (LINC) complex protein SUN1 regulates vascular sprouting and endothelial cell-cell junction morphology and function. Loss of murine endothelial Sun1 impaired blood vessel formation and destabilized junctions, angiogenic sprouts formed but retracted in SUN1-depleted sprouts, and zebrafish vessels lacking Sun1b had aberrant junctions and defective cell-cell connections. At the cellular level, SUN1 stabilized endothelial cell-cell junctions, promoted junction function, and regulated contractility. Mechanistically, SUN1 depletion altered cell behaviors via the cytoskeleton without changing transcriptional profiles. Reduced peripheral microtubule density, fewer junction contacts, and increased catastrophes accompanied SUN1 loss, and microtubule depolymerization phenocopied effects on junctions. Depletion of GEF-H1, a microtubule-regulated Rho activator, or the LINC complex protein nesprin-1 rescued defective junctions of SUN1-depleted endothelial cells. Thus, endothelial SUN1 regulates peripheral cell-cell junctions from the nucleus via LINC complex-based microtubule interactions that affect peripheral microtubule dynamics and Rho-regulated contractility, and this long-range regulation is important for proper blood vessel sprouting and junction integrity.

Contribution of Blood Vessel Activation, Remodeling and Barrier Function to Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs) consist of a group of chronic inflammatory disorders with a complex etiology, which represent a clinical challenge due to their often therapy-refractory nature. In IBD, inflammation of the intestinal mucosa is characterized by strong and sustained leukocyte infiltration, resulting in the loss of epithelial barrier function and subsequent tissue destruction. This is accompanied by the activation and the massive remodeling of mucosal micro-vessels. The role of the gut vasculature in the induction and perpetuation of mucosal inflammation is receiving increasing recognition. While the vascular barrier is considered to offer protection against bacterial translocation and sepsis after the breakdown of the epithelial barrier, endothelium activation and angiogenesis are thought to promote inflammation. The present review examines the respective pathological contributions of the different phenotypical changes observed in the microvascular endothelium during IBD, and provides an overview of potential vessel-specific targeted therapy options for the treatment of IBD.

ZNF185 prevents stress fiber formation through the inhibition of RhoA in endothelial cells

Signaling through cAMP/protein kinase A (PKA) promotes endothelial barrier function to prevent plasma leakage induced by inflammatory mediators. The discovery of PKA substrates in endothelial cells increases our understanding of the molecular mechanisms involved in vessel maturation. In this study, we evaluate a cAMP inducer, forskolin, and a phospho-PKA substrate antibody to identify ZNF185 as a PKA substrate. ZNF185 interacts with PKA and colocalizes with F-actin in endothelial cells. Both ZNF185 and F-actin accumulate in the plasma membrane region in response to forskolin to stabilize the cortical actin structure. By contrast, ZNF185 knockdown disrupts actin filaments and promotes stress fiber formation without inflammatory mediators. Constitutive activation of RhoA is induced by ZNF185 knockdown, which results in forskolin-resistant endothelial barrier dysfunction. Knockout of mouse Zfp185 which is an orthologous gene of human ZNF185 increases vascular leakage in response to inflammatory stimuli in vivo. Thrombin protease is used as a positive control to assemble stress fibers via RhoA activation. Unexpectedly, ZNF185 is cleaved by thrombin, resulting in an N-terminal actin-targeting domain and a C-terminal PKA-interacting domain. Irreversible dysfunction of ZNF185 protein potentially causes RhoA-dependent stress fiber formation by thrombin.

Critical role of Rho proteins in myosin light chain di-phosphorylation during early phase of endothelial barrier disruption

We previously reported the Rho-associated coiled-coil containing protein kinase (ROCK)-mediated di-phosphorylation of myosin light chain (MLC) and actin bundle formation at the cell periphery as early events of the endothelial barrier disruption. We herein examined the role of RhoA during early events of barrier disruption. Treatment of cultured porcine aortic endothelial cells with simvastatin prevented the decrease in trans-endothelial electrical resistance, MLC di-phosphorylation and peripheral actin bundle formation seen 3 min after thrombin stimulation. Co-treatment with geranylgeranyl pyrophosphate rescued the thrombin-induced events. Thrombin increased a GTP-bound form of RhoA and phosphorylation of myosin phosphatase target subunit 1 (MYPT1) at the ROCK site. The intracellular introduction of the inhibitory protein of RhoA inhibited the thrombin-induced di-phosphorylation of MLC. However, knockdown of either one of RhoA, RhoB or RhoC failed to inhibit thrombin-induced MLC di-phosphorylation. The findings suggest that Rho proteins play a critical role during early events of thrombin-induced barrier disruption.

Feedback between mechanosensitive signaling and active forces governs endothelial junction integrity

The formation and recovery of gaps in the vascular endothelium governs a wide range of physiological and pathological phenomena, from angiogenesis to tumor cell extravasation. However, the interplay between the mechanical and signaling processes that drive dynamic behavior in vascular endothelial cells is not well understood. In this study, we propose a chemo-mechanical model to investigate the regulation of endothelial junctions as dependent on the feedback between actomyosin contractility, VE-cadherin bond turnover, and actin polymerization, which mediate the forces exerted on the cell-cell interface. Simulations reveal that active cell tension can stabilize cadherin bonds, but excessive RhoA signaling can drive bond dissociation and junction failure. While actin polymerization aids gap closure, high levels of Rac1 can induce junction weakening. Combining the modeling framework with experiments, our model predicts the influence of pharmacological treatments on the junction state and identifies that a critical balance between RhoA and Rac1 expression is required to maintain junction stability. Our proposed framework can help guide the development of therapeutics that target the Rho family of GTPases and downstream active mechanical processes.

p73 is required for vessel integrity controlling endothelial junctional dynamics through Angiomotin

Preservation of blood vessel integrity, which is critical for normal physiology and organ function, is controlled at multiple levels, including endothelial junctions. However, the mechanism that controls the adequate assembly of endothelial cell junctions is not fully defined. Here, we uncover TAp73 transcription factor as a vascular architect that orchestrates transcriptional programs involved in cell junction establishment and developmental blood vessel morphogenesis and identify Angiomotin (AMOT) as a TAp73 direct transcriptional target. Knockdown of p73 in endothelial cells not only results in decreased Angiomotin expression and localization at intercellular junctions, but also affects its downstream function regarding Yes-associated protein (YAP) cytoplasmic sequestration upon cell–cell contact. Analysis of adherens junctional morphology after p73-knockdown in human endothelial cells revealed striking alterations, particularly a sharp increase in serrated junctions and actin bundles appearing as stress fibers, both features associated with enhanced barrier permeability. In turn, stabilization of Angiomotin levels rescued those junctional defects, confirming that TAp73 controls endothelial junction dynamics, at least in part, through the regulation of Angiomotin. The observed defects in monolayer integrity were linked to hyperpermeability and reduced transendothelial electric resistance. Moreover, p73-knockout retinas showed a defective sprout morphology coupled with hemorrhages, highlighting the physiological relevance of p73 regulation in the maintenance of vessel integrity in vivo. We propose a new model in which TAp73 acts as a vascular architect integrating transcriptional programs that will impinge with Angiomotin/YAP signaling to maintain junctional dynamics and integrity, while balancing endothelial cell rearrangements in angiogenic vessels.

TWEAK and TNFα, Both TNF Ligand Family Members and Multiple Sclerosis-Related Cytokines, Induce Distinct Gene Response in Human Brain Microvascular Endothelial Cells

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the TNF ligand family involved in various diseases including brain inflammatory pathologies such as multiple sclerosis. It has been demonstrated that TWEAK can induce cerebrovascular permeability in an in vitro model of the blood-brain barrier. The molecular mechanisms playing a role in TWEAK versus TNFα signaling on cerebral microvascular endothelial cells are not well defined. Therefore, we aimed to identify gene expression changes in cultures of human brain microvascular endothelial cells (hCMEC/D3) to address changes initiated by TWEAK exposure. Taken together, our studies highlighted that gene involved in leukocyte extravasation, notably claudin-5, were differentially modulated by TWEAK and TNFα. We identified differential gene expression of hCMEC/D3 cells at three timepoints following TWEAK versus TNFα stimulation and also found distinct modulations of several canonical pathways including the actin cytoskeleton, vascular endothelial growth factor (VEGF), Rho family GTPases, and phosphatase and tensin homolog (PTEN) pathways. To our knowledge, this is the first study to interrogate and compare the effects of TWEAK versus TNFα on gene expression in brain microvascular endothelial cells.

Neutrophil Elastase Increases Vascular Permeability and Leukocyte Transmigration in Cultured Endothelial Cells and Obese Mice

Neutrophil elastase (NE) plays a pivotal role in inflammation. However, the mechanism underlying NE-mediated inflammation in obesity remains unclear. Here, we report that NE activates protease-activated receptor-2 (PAR2), stimulates actin filament (F-actin) formation, decreases intercellular junction molecule VE-cadherin expression, and increases the permeability of human arterial endothelial cells (hECs). NE also prompts degradation of VE-cadherin and its binding proteins p120- and β-catenins via MG132-sensitive proteasomes. NE stimulates phosphorylation of myosin light-chain (MLC) and its regulator myosin phosphatase target subunit-1 (MYPT1), a target of Rho kinase (ROCK). Inhibitors of PAR2 and ROCK prohibit NE-induced F-actin formation, MLC phosphorylation, and VE-cadherin reduction in hECs, and impede monocyte transmigration through hEC monolayer pretreated with either neutrophils or NE. Further, administration of an NE inhibitor GW311616A significantly attenuates vascular leakage, leukocyte infiltration, and the expression of proinflammatory cytokines in the white adipose tissue from high-fat diet (HFD)-induced obese mice. Likewise, NE-deficient mice are resistant to HFD-induced vascular leakage in the heart. Together, NE regulates actomyosin cytoskeleton activity and VE-cadherin expression by activating PAR2 signaling in the endothelial cells, leading to increased vascular permeability and leukocyte extravasation. Hence, inhibition of NE is a potential approach to mitigate vascular injury and leukocyte infiltration in obesity-related systemic inflammation.

Nuclear Mechanosensation and Mechanotransduction in Vascular Cells

Vascular cells are constantly subjected to physical forces associated with the rhythmic activities of the heart, which combined with the individual geometry of vessels further imposes oscillatory, turbulent, or laminar shear stresses on vascular cells. These hemodynamic forces play an important role in regulating the transcriptional program and phenotype of endothelial and smooth muscle cells in different regions of the vascular tree. Within the aorta, the lesser curvature of the arch is characterized by disturbed, oscillatory flow. There, endothelial cells become activated, adopting pro-inflammatory and athero-prone phenotypes. This contrasts the descending aorta where flow is laminar and endothelial cells maintain a quiescent and atheroprotective phenotype. While still unclear, the specific mechanisms involved in mechanosensing flow patterns and their molecular mechanotransduction directly impact the nucleus with consequences to transcriptional and epigenetic states. The linker of nucleoskeleton and cytoskeleton (LINC) protein complex transmits both internal and external forces, including shear stress, through the cytoskeleton to the nucleus. These forces can ultimately lead to changes in nuclear integrity, chromatin organization, and gene expression that significantly impact emergence of pathology such as the high incidence of atherosclerosis in progeria. Therefore, there is strong motivation to understand how endothelial nuclei can sense and respond to physical signals and how abnormal responses to mechanical cues can lead to disease. Here, we review the evidence for a critical role of the nucleus as a mechanosensor and the importance of maintaining nuclear integrity in response to continuous biophysical forces, specifically shear stress, for proper vascular function and stability.

Testing 3D printed biological platform for advancing simulated microgravity and space mechanobiology research

The advancement of microgravity simulators is helping many researchers better understanding the impact of the mechanically unloaded space environment on cellular function and disfunction. However, performing microgravity experiments on Earth, using simulators such as the Random Positioning Machine, introduces some unique practical challenges, including air bubble formation and leakage of growth medium from tissue culture flask and plates, all of which limit research progress. Here, we developed an easy-to-use hybrid biological platform designed with the precision of 3D printing technologies combined with PDMS microfluidic fabrication processes to facilitate reliable and reproducible microgravity cellular experiments. The system has been characterized for applications in the contest of brain cancer research by exposing glioblastoma and endothelial cells to 24 h of simulated microgravity condition to investigate the triggered mechanosensing pathways involved in cellular adaptation to the new environment. The platform demonstrated compatibility with different biological assays, i.e., proliferation, viability, morphology, protein expression and imaging of molecular structures, showing advantages over the conventional usage of culture flask. Our results indicated that both cell types are susceptible when the gravitational vector is disrupted, confirming the impact that microgravity has on both cancer and healthy cells functionality. In particular, we observed deactivation of Yap-1 molecule in glioblastoma cells and the remodeling of VE-Cadherin junctional protein in endothelial cells. The study provides support for the application of the proposed biological platform for advancing space mechanobiology research, also highlighting perspectives and strategies for developing next generation of brain cancer molecular therapies, including targeted drug delivery strategies.

Semen Ziziphi Spinosae attenuates blood-brain barrier dysfunction induced by lipopolysaccharide by targeting the FAK-DOCK180-Rac1-WAVE2-Arp3 signaling pathway

Semen Ziziphi Spinosae (SZS) has been extensively used in the daily diet as a functional food for neuroprotective health-benefit in China for many years. However, the neuroprotective mechanism of SZS associated with blood–brain barrier (BBB) integrity remains unexplored. The present study suggests SZS could protect against lipopolysaccharide (LPS)-induced BBB dysfunction. Proteomics indicate that 135 proteins in rat brain are significantly altered by SZS. These differentially expressed proteins are mainly clustered into cell–cell adhesion and adherens junctions, which are closely related with BBB integrity. SZS reversed LPS-induces BBB breakdown by activating the FAK-DOCK180-Rac1-WAVE2-Arp3 pathway. Molecular docking between signaling pathway proteins and identified SZS components in rat plasma reveals that 6”‘-feruloylspinosin, spinosin, and swertisin strongly binds to signaling proteins at multiple amino acid sites. These novel findings suggest a health benefit of SZS in prevention of cerebral diseases and contributes to the further application of SZS as a functional food.

Vinculin controls endothelial cell junction dynamics during vascular lumen formation

Blood vessel morphogenesis is driven by coordinated endothelial cell behaviors. Active remodeling of cell-cell junctions promotes cellular plasticity while preserving vascular integrity. Here, we analyze the dynamics of endothelial adherens junctions during lumen formation in angiogenic sprouts in vivo. Live imaging in zebrafish reveals that lumen expansion is accompanied by the formation of transient finger-shaped junctions. Junctional fingers are positively regulated by blood pressure, whereas flow inhibition prevents their formation. Using fluorescent reporters, we show that junctional fingers contain the mechanotransduction protein vinculin. Furthermore, genetic deletion of vinculin prevents finger formation, a junctional defect that could be rescued by transient endothelial expression of vinculin. Our findings suggest a mechanism whereby lumen expansion leads to an increase in junctional tension, triggering recruitment of vinculin and formation of junctional fingers. We propose that endothelial cells employ force-dependent junctional remodeling to counteract external forces in order to maintain vascular integrity during sprouting angiogenesis.

Human Vascular Wall Microfluidic Model for Preclinical Evaluation of Drug-Induced Vascular Injury

Drug-induced vascular injury (DIVI) in preclinical animal models often leads to candidate compound termination during drug development. DIVI has not been documented in human clinical trials with drugs that cause DIVI in preclinical animals. A robust human preclinical assay for DIVI is needed as an early vascular injury screen. A human vascular wall microfluidic tissue chip was developed with a human umbilical vein endothelial cell (HUVEC)-umbilical artery smooth muscle cell (vascular smooth muscle cell, VSMC) bilayer matured under physiological shear stress. Optimized temporal flow profiles produced HUVEC-VSMC bilayers with quiescent endothelial cell (EC) monolayers, EC tight junctions, and contractile VSMC morphology. Dose-response testing (3-30 μM concentration) was conducted with minoxidil and tadalafil vasodilators. Both drugs have demonstrated preclinical DIVI but lack clinical evidence. The permeability of severely damaged engineered bilayers (30 μM tadalafil) was 4.1 times that of the untreated controls. Immunohistochemical protein assays revealed contrasting perspectives on tadalafil and minoxidil-induced damage. Tadalafil impacted the endothelial monolayer with minor injury to the contractile VSMCs, whereas minoxidil demonstrated minor EC barrier injury but damaged VSMCs and activated ECs in a dose-response manner. This proof-of-concept human vascular wall bilayer model of DIVI is a critical step toward developing a preclinical human screening assay for drug development. Impact statement More than 90% of drug candidates fail during clinical trials due to human efficacy and toxicity concerns. Preclinical studies rely heavily on animal models, although animal toxicity and drug metabolism responses often differ from humans. During the drug development process, perfused in vitro human tissue chips could model the clinical drug response and potential toxicity of candidate compounds. Our long-term objective is to develop a human vascular wall tissue chip to screen for drug-induced vascular injury. Its application could ultimately reduce drug development delays and costs, and improve patient safety.

Aberrant stromal tissue factor localisation and mycolactone-driven vascular dysfunction, exacerbated by IL-1β, are linked to fibrin formation in Buruli ulcer lesions

Buruli ulcer (BU) is a neglected tropical disease caused by subcutaneous infection with Mycobacterium ulcerans and its exotoxin mycolactone. BU displays coagulative necrosis and widespread fibrin deposition in affected skin tissues. Despite this, the role of the vasculature in BU pathogenesis remains almost completely unexplored. We hypothesise that fibrin-driven ischemia can be an ‘indirect’ route to mycolactone-dependent tissue necrosis by a mechanism involving vascular dysfunction. Here, we tracked >900 vessels within contiguous tissue sections from eight BU patient biopsies. Our aim was to evaluate their vascular and coagulation biomarker phenotype and explore potential links to fibrin deposition. We also integrated this with our understanding of mycolactone’s mechanism of action at Sec61 and its impact on proteins involved in maintaining normal vascular function. Our findings showed that endothelial cell dysfunction is common in skin tissue adjacent to necrotic regions. There was little evidence of primary haemostasis, perhaps due to mycolactone-dependent depletion of endothelial von Willebrand factor. Instead, fibrin staining appeared to be linked to the extrinsic pathway activator, tissue factor (TF). There was significantly greater than expected fibrin staining around vessels that had TF staining within the stroma, and this correlated with the distance it extended from the vessel basement membrane. TF-induced fibrin deposition in these locations would require plasma proteins outside of vessels, therefore we investigated whether mycolactone could increase vascular permeability in vitro. This was indeed the case, and leakage was further exacerbated by IL-1β. Mycolactone caused the loss of endothelial adherens and tight junctions by the depletion of VE-cadherin, TIE-1, TIE-2 and JAM-C; all Sec61-dependent proteins. Taken together, our findings suggest that both vascular and lymphatic vessels in BU lesions become “leaky” during infection, due to the unique action of mycolactone, allowing TF-containing structures and plasma proteins into skin tissue, ultimately leading to local coagulopathy and tissue ischemia.

To date, the debilitating skin disease Buruli ulcer remains a public health concern and financial burden in low or middle-income countries, especially in tropical regions. Late diagnosis is frequent in remote areas, perhaps due to the painlessness of the disease. Hence patients often present with large, destructive opened ulcers leading to delayed wound closure or even lifelong disability. The infectious agent produces a toxin called mycolactone that drives the disease. We previously found evidence that the vascular system is disrupted by mycolactone in these lesions, and now we have further explored potential explanations for these findings by looking at the expression of vascular markers in BU. In a detailed analysis of patient skin punch biopsies, we identified distinct expression patterns of certain proteins and found that tissue factor, which initiates the so-called extrinsic pathway of blood clotting, is particularly important. Mycolactone is able to disrupt the barrier function of the endothelium, further aggravating the diseased phenotype, which may explain how clotting factors access the tissue. Altogether, such localised hypercoagulation in Buruli ulcer skin lesions may contribute to the development of the lesion.

CCL4 induces inflammatory signalling and barrier disruption in the neurovascular endothelium

Background

During neuroinflammation many chemokines alter the function of the blood-brain barrier (BBB) that regulates the entry of macromolecules and immune cells into the brain. As the milieu of the brain is altered, biochemical and structural changes contribute to the pathogenesis of neuroinflammation and may impact on neurogenesis. The chemokine CCL4, previously known as MIP-1β, is upregulated in a wide variety of central nervous system disorders, including multiple sclerosis, where it is thought to play a key role in the neuroinflammatory process. However, the effect of CCL4 on BBB endothelial cells (ECs) is unknown.

Materials and methods

Expression and distribution of CCR5, phosphorylated p38, F-actin, zonula occludens-1 (ZO-1) and vascular endothelial cadherin (VE-cadherin) were analysed in the human BBB EC line hCMEC/D3 by Western blot and/or immunofluorescence in the presence and absence of CCL4. Barrier modulation in response to CCL4 using hCMEC/D3 monolayers was assessed by measuring molecular flux of 70 ​kDa RITC-dextran and transendothelial lymphocyte migration. Permeability changes in response to CCL4 in vivo were measured by an occlusion technique in pial microvessels of Wistar rats and by fluorescein angiography in mouse retinae.

Results

CCR5, the receptor for CCL4, was expressed in hCMEC/D3 cells. CCL4 stimulation led to phosphorylation of p38 and the formation of actin stress fibres, both indicative of intracellular chemokine signalling. The distribution of junctional proteins was also altered in response to CCL4: junctional ZO-1 was reduced by circa 60% within 60 ​min. In addition, surface VE-cadherin was redistributed through internalisation. Consistent with these changes, CCL4 induced hyperpermeability in vitro and in vivo and increased transmigration of lymphocytes across monolayers of hCMEC/D3 cells.

Conclusion

These results show that CCL4 can modify BBB function and may contribute to disease pathogenesis.

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The chemokine CCL4 induced phosphorylation of P38 in an in vitro model of the blood-brain barrier (BBB).

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CCL4 treatment resulted in reduction of plasma membrane VE-cadherin and junctional ZO-1.

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CCL4 induced neurovascular barrier breakdown in vitro and in vivo.

Epithelial protein lost in neoplasm (EPLIN) and prostate cancer: lessons learned from the ARCaP model

Confucius said, "Good tools are prerequisite to the successful execution of a job". Among his many groundbreaking achievements, Dr. Leland W. K. Chung established several widely used prostate cancer (PCa) cell lines, including C4-2, C4-2B, and ARCaP. These cellular models have been pivotal tools to enhance our understanding of the biology of PCa progression and assist in the discovery of new strategies to treat metastatic, castration-resistant PCa. Recent studies in the ARCaP PCa progression model uncovered epithelial protein lost in neoplasm (EPLIN), an actin-binding protein with an indispensable role in the maintenance of epithelial structures, as a negative regulator of epithelial-mesenchymal transition. Clinical evidence further supports the potential role of EPLIN in controlling metastasis in PCa and other solid tumors. In this article, we review the current understanding of the biology of EPLIN and the ARCaP model in the discovery of new agents for the prevention and treatment of PCa metastasis.

Treponema pallidum Disrupts VE-Cadherin Intercellular Junctions and Traverses Endothelial Barriers Using a Cholesterol-Dependent Mechanism

Treponema pallidum subspecies pallidum, the causative agent of syphilis, traverses the vascular endothelium to gain access to underlying tissue sites. Herein, we investigate the mechanisms associated with T. pallidum traversal of endothelial barriers. Immunofluorescence microscopy reveals that a subpopulation of T. pallidum localizes to intercellular junctions and that viable T. pallidum, as well as a T. pallidum vascular adhesin (Tp0751), disrupts the architecture of the main endothelial junctional protein VE-cadherin. Intriguingly, in this study we show that T. pallidum traverses endothelial barriers with no disruption in barrier permeability. Furthermore, barrier traversal by T. pallidum is reduced by pretreatment of endothelial cells with filipin, an inhibitor that blocks cholesterol-mediated endocytosis. Collectively, these results suggest that T. pallidum can use a cholesterol-dependent, lipid raft-mediated endocytosis mechanism to traverse endothelial barriers. Further, treponemal localization to, and disruption of, intercellular junctions suggests that a paracellular route may also be utilized, a dual traversal strategy that has also been observed to occur for leukocytes and other invasive bacteria.

Photodynamic Priming Modulates Endothelial Cell-Cell Junction Phenotype for Light-activated Remote Control of Drug Delivery

The blood-brain barrier (BBB) remains a major obstacle for drug delivery to the central nervous system. In particular, the tight and adherens junctions that join the brain capillary endothelial cells limit the diffusion of various molecules from the bloodstream into the brain. Photodynamic priming (PDP) is a non-cytotoxic modality that involves light activation of photosensitizers to photochemically modulate nearby molecules without killing the cells. Here we investigate the effects of sub-lethal photochemistry on junction phenotype (i.e., continuous, punctate, or perpendicular), as well as the BBB permeability in a transwell model of human brain microvascular endothelial cells (HBMECs). We showed that PDP decreases the continuous junction architecture by ~20%, increases the perpendicular junction architecture by ~40%, and has minimal impact on cell morphology in HBMECs. Furthermore, transwell permeability assay revealed that PDP improves the HBMEC permeability to dextran or nanoliposomes by up to 30-fold for 6-9 days. These results suggest that PDP could safely reverse the mature brain endothelial junctions without killing the HBMECs. This study not only emphasizes the critical roles of PDP in the modulation junction phenotype, but also highlights the opportunity to further develop PDP-based combinations that opens the cerebrum endothelium for enhanced drug transporter across the BBB.

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

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

Rac1/Wave2/Arp3 Pathway Mediates Rat Blood-Brain Barrier Dysfunction under Simulated Microgravity Based on Proteomics Strategy

The blood-brain barrier (BBB) is critical to maintaining central nervous system (CNS) homeostasis. However, the effects of microgravity (MG) on the BBB remain unclear. This study aimed to investigate the influence of simulated MG (SMG) on the BBB and explore its potential mechanism using a proteomic approach. Rats were tail-suspended to simulate MG for 21 days. SMG could disrupt the BBB, including increased oxidative stress levels, proinflammatory cytokine levels, and permeability, damaged BBB ultrastructure, and downregulated tight junctions (TJs) and adherens junctions (AJs) protein expression in the rat brain. A total of 554 differentially expressed proteins (DEPs) induced by SMG were determined based on the label-free quantitative proteomic strategy. The bioinformatics analysis suggested that DEPs were mainly enriched in regulating the cell–cell junction and cell–extracellular matrix biological pathways. The inhibited Ras-related C3 botulinum toxin substrate 1 (Rac1)/Wiskott–Aldrich syndrome protein family verprolin-homologous protein 2 (Wave2)/actin-related protein 3 (Arp3) pathway and the decreased ratio of filamentous actin (F-actin) to globular actin contributed to BBB dysfunction induced by SMG. In the human brain microvascular endothelial cell (HBMECs), SMG increased the oxidative stress levels and proinflammatory cytokine levels, promoted apoptosis, and arrested the cell cycle phase. Expression of TJs and AJs proteins were downregulated and the distribution of F-actin was altered in SMG-treated HBMECs. The key role of the Rac1/Wave2/Arp3 pathway in BBB dysfunction was confirmed in HBMECs with a specific Rac1 agonist. This study demonstrated that SMG induced BBB dysfunction and revealed that Rac1/Wave2/Arp3 could be a potential signaling pathway responsible for BBB disruption under SMG. These results might shed a novel light on maintaining astronaut CNS homeostasis during space travel.

Orai-vascular endothelial-cadherin signaling complex regulates high-glucose exposure-induced increased permeability of mouse aortic endothelial cells

INTRODUCTION

Diabetes-associated endothelial barrier function impairment might be linked to disturbances in Ca²⁺ homeostasis. To study the role and molecular mechanism of Orais-vascular endothelial (VE)-cadherin signaling complex and its downstream signaling pathway in diabetic endothelial injury using mouse aortic endothelial cells (MAECs).

RESEARCH DESIGN AND METHODS

The activity of store-operated Ca²⁺ entry (SOCE) was detected by calcium imaging after 7 days of high-glucose (HG) or normal-glucose (NG) exposure, the expression levels of Orais after HG treatment was detected by western blot analysis. The effect of HG exposure on the expression of phosphorylated (p)-VE-cadherin and VE-cadherin on cell membrane was observed by immunofluorescence assay. HG-induced transendothelial electrical resistance was examined in vitro after MAECs were cultured in HG medium. FD-20 permeability was tested in monolayer aortic endothelial cells through transwell permeability assay. The interactions between Orais and VE-cadherin were detected by co-immunoprecipitation and immunofluorescence technologies. Immunohistochemical experiment was used to detect the expression changes of Orais, VE-cadherin and p-VE-cadherin in aortic endothelium of mice with diabetes.

RESULTS

(1) The expression levels of Orais and activity of SOCE were significantly increased in MAECs cultured in HG for 7 days. (2) In MAECs cultured in HG for 7 days, the ratio of p-VE-cadherin to VE-cadherin expressed on the cell membrane and the FD-20 permeability in monolayer endothelial cells increased, indicating that intercellular permeability increased. (3) Orais and VE-cadherin can interact and enhance the interaction ratio through HG stimulation. (4) In MAECs cultured with HG, the SOCE activator ATP enhanced the expression level of p-VE-cadherin, and the SOCE inhibitor BTP2 decreased the expression level of p-VE-cadherin. (5) Significantly increased expression of p-VE-cadherin and Orais in the aortic endothelium of mice with diabetes.

CONCLUSION

HG exposure stimulated increased expression of Orais in endothelial cells, and increased VE-cadherin phosphorylation through Orais-VE-cadherin complex and a series of downstream signaling pathways, resulting in disruption of endothelial cell junctions and initiation of atherosclerosis.

Biomechanical Characterization of Endothelial Cells Exposed to Shear Stress Using Acoustic Force Spectroscopy

Characterizing mechanical properties of cells is important for understanding many cellular processes, such as cell movement, shape, and growth, as well as adaptation to changing environments. In this study, we explore the mechanical properties of endothelial cells that form the biological barrier lining blood vessels, whose dysfunction leads to development of many cardiovascular disorders. Stiffness of living endothelial cells was determined by Acoustic Force Spectroscopy (AFS), by pull parallel multiple functionalized microspheres located at the cell-cell periphery. The unique configuration of the acoustic microfluidic channel allowed us to develop a long-term dynamic culture protocol exposing cells to laminar flow for up to 48 h, with shear stresses in the physiological range (i.e., 6 dyn/cm2). Two different Endothelial cells lines, Human Aortic Endothelial Cells (HAECs) and Human Umbilical Vein Endothelial Cells (HUVECs), were investigated to show the potential of this tool to capture the change in cellular mechanical properties during maturation of a confluent endothelial monolayer. Immunofluorescence microscopy was exploited to follow actin filament rearrangement and junction formation over time. For both cell types we found that the application of shear-stress promotes the typical phenotype of a mature endothelium expressing a linear pattern of VE-cadherin at the cell-cell border and actin filament rearrangement along the perimeter of Endothelial cells. A staircase-like sequence of increasing force steps, ranging from 186 pN to 3.5 nN, was then applied in a single measurement revealing the force-dependent apparent stiffness of the membrane cortex in the kPa range. We also found that beads attached to cells cultured under dynamic conditions were harder to displace than cells cultured under static conditions, showing a stiffer membrane cortex at cell periphery. All together these results demonstrate that the AFS can identify changes in cell mechanics based on force measurements of adherent cells under conditions mimicking their native microenvironment, thus revealing the shear stress dependence of the mechanical properties of neighboring endothelial cells.

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

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

Blood-Brain Barrier Damage in Ischemic Stroke and Its Regulation by Endothelial Mechanotransduction

Ischemic stroke, a major cause of mortality in the United States, often contributes to disruption of the blood-brain barrier (BBB). The BBB along with its supportive cells, collectively referred to as the “neurovascular unit,” is the brain’s multicellular microvasculature that bi-directionally regulates the transport of blood, ions, oxygen, and cells from the circulation into the brain. It is thus vital for the maintenance of central nervous system homeostasis. BBB disruption, which is associated with the altered expression of tight junction proteins and BBB transporters, is believed to exacerbate brain injury caused by ischemic stroke and limits the therapeutic potential of current clinical therapies, such as recombinant tissue plasminogen activator. Accumulating evidence suggests that endothelial mechanobiology, the conversion of mechanical forces into biochemical signals, helps regulate function of the peripheral vasculature and may similarly maintain BBB integrity. For example, the endothelial glycocalyx (GCX), a glycoprotein-proteoglycan layer extending into the lumen of bloods vessel, is abundantly expressed on endothelial cells of the BBB and has been shown to regulate BBB permeability. In this review, we will focus on our understanding of the mechanisms underlying BBB damage after ischemic stroke, highlighting current and potential future novel pharmacological strategies for BBB protection and recovery. Finally, we will address the current knowledge of endothelial mechanotransduction in BBB maintenance, specifically focusing on a potential role of the endothelial GCX.

TIMP1 preserves the blood-brain barrier through interacting with CD63/integrin 1 complex and regulating downstream FAK/RhoA signaling

Blood-brain barrier (BBB) breakdown and the associated microvascular hyperpermeability are hallmark features of several neurological disorders, including traumatic brain injury (TBI). However, there is no viable therapeutic strategy to rescue BBB function. Tissue inhibitor of metalloproteinase-1 (TIMP1) has been considered to be beneficial for vascular integrity, but the molecular mechanisms underlying the functions of TIMP1 remain elusive. Here, we report that TIMP1 executes a protective role on neuroprotective function via ameliorating BBB disruption in mice with experimental TBI. In human brain microvessel endothelial cells (HBMECs) exposed to hypoxia and inflammation injury, the recombinant TIMP1 (rTIMP1) treatment maintained integrity of junctional proteins and trans-endothelial tightness. Mechanistically, TIMP1 interacts with CD63/integrin β1 complex and activates downstream FAK signaling, leading to attenuation of RhoA activation and F-actin depolymerization for endothelial cells structure stabilization. Notably, these effects depend on CD63/integrin β1 complex, instead of the MMP-inhibitory function. Together, our results identified a novel MMP-independent function of TIMP1 in regulating endothelial barrier integrity. Therapeutic interventions targeting TIMP1 and its downstream signaling may be beneficial to protect BBB function following brain injury and neurological disorders.

Human brain microvascular endothelial cell pairs model tissue-level blood-brain barrier function

The blood-brain barrier plays a critical role in delivering oxygen and nutrients to the brain while preventing the transport of neurotoxins. Predicting the ability of potential therapeutics and neurotoxicants to modulate brain barrier function remains a challenge due to limited spatial resolution and geometric constraints offered by existing in vitro models. Using soft lithography to control the shape of microvascular tissues, we predicted blood-brain barrier permeability states based on structural changes in human brain endothelial cells. We quantified morphological differences in nuclear, junction, and cytoskeletal proteins that influence, or indicate, barrier permeability. We established a correlation between brain endothelial cell pair structure and permeability by treating cell pairs and tissues with known cytoskeleton-modulating agents, including a Rho activator, a Rho inhibitor, and a cyclic adenosine monophosphate analog. Using this approach, we found that high-permeability cell pairs showed nuclear elongation, loss of junction proteins, and increased actin stress fiber formation, which were indicative of increased contractility. We measured traction forces generated by high- and low-permeability pairs, finding that higher stress at the intercellular junction contributes to barrier leakiness. We further tested the applicability of this platform to predict modulations in brain endothelial permeability by exposing cell pairs to engineered nanomaterials, including gold, silver-silica, and cerium oxide nanoparticles, thereby uncovering new insights into the mechanism of nanoparticle-mediated barrier disruption. Overall, we confirm the utility of this platform to assess the multiscale impact of pharmacological agents or environmental toxicants on blood-brain barrier integrity.

Silica nanomaterials induce organ injuries by Ca2+-ROS-initiated disruption of the endothelial barrier and triggering intravascular coagulation

Background

The growing use of silica nanoparticles (SiNPs) in many fields raises human toxicity concerns. We studied the toxicity of SiNP-20 (particle diameter 20 nm) and SiNP-100 (100 nm) and the underlying mechanisms with a focus on the endothelium both in vitro and in vivo.

Methods

The study was conducted in cultured human umbilical vein endothelial cells (HUVECs) and adult female Balb/c mice using several techniques.

Results

In vitro, both SiNP-20 and SiNP-100 decreased the viability and damaged the plasma membrane of cultured HUVECs. The nanoparticles also inhibited HUVECs migration and tube formation in a concentration-dependent manner. Both SiNPs induced significant calcium mobilization and generation of reactive oxygen species (ROS), increased the phosphorylation of vascular endothelial (VE)-cadherin at the site of tyrosine 731 residue (pY731-VEC), decreased the expression of VE-cadherin expression, disrupted the junctional VE-cadherin continuity and induced F-actin re-assembly in HUVECs. The injuries were reversed by blocking Ca²⁺ release activated Ca²⁺ (CRAC) channels with YM58483 or by eliminating ROS with N-acetyl cysteine (NAC). In vivo, both SiNP-20 and SiNP-100 (i.v.) induced multiple organ injuries of Balb/c mice in a dose (range 7–35 mg/kg), particle size, and exposure time (4–72 h)-dependent manner. Heart injuries included coronary endothelial damage, erythrocyte adhesion to coronary intima and coronary coagulation. Abdominal aorta injury exhibited intimal neoplasm formation. Lung injuries were smaller pulmonary vein coagulation, bronchiolar epithelial edema and lumen oozing and narrowing. Liver injuries included multifocal necrosis and smaller hepatic vein congestion and coagulation. Kidney injuries involved glomerular congestion and swelling. Macrophage infiltration occurred in all of the observed organ tissues after SiNPs exposure. SiNPs also decreased VE-cadherin expression and altered VE-cadherin spatial distribution in multiple organ tissues in vivo. The largest SiNP (SiNP-100) and longest exposure time exerted the greatest toxicity both in vitro and in vivo.

Conclusions

SiNPs, administrated in vivo, induced multiple organ injuries, including endothelial damage, intravascular coagulation, and secondary inflammation. The injuries are likely caused by upstream Ca²⁺-ROS signaling and downstream VE-cadherin phosphorylation and destruction and F-actin remodeling. These changes led to endothelial barrier disruption and triggering of the contact coagulation pathway.

Interrogating the ccm-3 Gene Network

Cerebral cavernous malformations (CCMs) are neurovascular lesions caused by mutations in one of three genes (CCM1-3). Loss of CCM3 causes the poorest prognosis, and little is known about how it regulates vascular integrity. The C. elegans ccm-3 gene regulates the development of biological tubes that resemble mammalian vasculature, and in a genome-wide reverse genetic screen, we identified more than 500 possible CCM-3 pathway genes. With a phenolog-like approach, we generated a human CCM signaling network and identified 29 genes in common, of which 14 are required for excretory canal extension and membrane integrity, similar to ccm-3. Notably, depletion of the MO25 ortholog mop-25.2 causes severe defects in tube integrity by preventing CCM-3 localization to apical membranes. Furthermore, loss of MO25 phenocopies CCM3 ablation by causing stress fiber formation in endothelial cells. This work deepens our understanding of how CCM3 regulates vascular integrity and may help identify therapeutic targets for treating CCM3 patients.

Reversible Cavitation-Induced Junctional Opening in an Artificial Endothelial Layer

Targeting pharmaceuticals through the endothelial barrier is crucial for drug delivery. In this context, cavitation-assisted permeation shows promise for effective and reversible opening of intercellular junctions. A vessel-on-a-chip is exploited to investigate and quantify the effect of ultrasound-excited microbubbles-stable cavitation-on endothelial integrity. In the vessel-on-a-chip, the endothelial cells form a complete lumen under physiological shear stress, resulting in intercellular junctions that exhibit barrier functionality. Immunofluorescence microscopy is exploited to monitor vascular integrity following vascular endothelial cadherin staining. It is shown that microbubbles amplify the ultrasound effect, leading to the formation of interendothelial gaps that cause barrier permeabilization. The total gap area significantly increases with pressure amplitude compared to the control. Gap opening is fully reversible with gap area distribution returning to the control levels 45 min after insonication. The proposed integrated platform allows for precise and repeatable in vitro measurements of cavitation-enhanced endothelium permeability and shows potential for validating irradiation protocols for in vivo applications.