Ca(2+) signalling and PKCalpha activate increased endothelial permeability by disassembly of VE-cadherin junctions

Role of blood-brain barrier dysfunction in the development of poststroke epilepsy

Stroke is a major contributor to mortality and morbidity worldwide and the most common cause of epilepsy in the elderly in high income nations. In recent years, it has become increasingly evident that both ischemic and hemorrhagic strokes induce dysfunction of the blood-brain barrier (BBB), and that this impairment can contribute to epileptogenesis. Nevertheless, studies directly comparing BBB dysfunction and poststroke epilepsy (PSE) are largely absent. Therefore, this review summarizes the role of BBB dysfunction in the development of PSE in animal models and clinical studies. There are multiple mechanisms whereby stroke induces BBB dysfunction, including increased transcytosis, tight junction dysfunction, spreading depolarizations, astrocyte and pericyte loss, reactive astrocytosis, angiogenesis, matrix metalloproteinase activation, neuroinflammation, adenosine triphosphate depletion, oxidative stress, and finally cell death. The degree to which these effects occur is dependent on the severity of the ischemia, whereby cell death is a more prominent mechanism of BBB disruption in regions of critical ischemia. BBB dysfunction can contribute to epileptogenesis by increasing the risk of hemorrhagic transformation, increasing stroke size and the amount of cerebral vasogenic edema, extravasation of excitatory compounds, and increasing neuroinflammation. Furthermore, albumin extravasation after BBB dysfunction contributes to epileptogenesis primarily via increased transforming growth factor β signaling. Finally, seizures themselves induce BBB dysfunction, thereby contributing to epileptogenesis in a cyclical manner. In repairing this BBB dysfunction, pericyte migration via platelet-derived growth factor β signaling is indispensable and required for reconstruction of the BBB, whereby astrocytes also play a role. Although animal stroke models have their limitations, they provide valuable insights into the development of potential therapeutics designed to restore the BBB after stroke, with the ultimate goal of improving outcomes and minimizing the occurrence of PSE. In pursuit of this goal, rapamycin, statins, losartan, semaglutide, and metformin show promise, whereby modulation of pericyte migration could also be beneficial.

Honokiol targeting ankyrin repeat domain of TRPV4 ameliorates endothelial permeability in mice inflammatory bowel disease induced by DSS

ETHNOPHARMACOLOGICAL RELEVANCE

As a classic traditional Chinese medicine, Magnolia officinalis (M. officinalis) is widely used in digestive diseases. It has rich gastrointestinal activity including inflammatory bowel disease (IBD) treatment, but the mechanism is not clear.

AIM OF THE STUDY

In recent years, there has been a growing interest in investigating the regulatory effects of herbal compounds on transient receptor potential (TRP) channel proteins. Transient receptor potential vanilloid 4 (TRPV4), a subtype involved in endothelial permeability regulation, was discussed as the target of M. officinalis in the treatment of IBD in the study. Based on the targeting effect of TRPV4, this study investigated the active ingredients and mechanism of M. officinalis extract in treating IBD.

MATERIALS AND METHODS

To reveal the connection between the active ingredients in M. officinalis and TRPV4, a bioactivity-guided high performance liquid chromatography system coupled with mass spectrometry identification was utilized to screen for TRPV4 antagonists. TRPV4 siRNA knockdown experiment was employed to validate the significance of TRPV4 as a crucial target in regulating endothelial permeability by honokiol (HON). The interaction of the active ingredient representing HON with TRPV4 was confirmed by molecular docking, fluorescence-based thermal shift and live cell calcium imaging experiments. The potential binding sites and inhibitory mechanisms of HON in TRPV4 were analyzed by molecular dynamics simulation and microscale thermophoresis. The therapeutic effect of HON based on TRPV4 was discussed in DSS-IBD mice.

RESULTS

Our finding elucidated that the inhibitory activity of M. officinalis against TRPV4 is primarily attributed to HON analogues. The knockdown of TRPV4 expression significantly impaired the calcium regulation and permeability protection in endothelial cells. The mechanism study revealed that HON specifically targets the Q239 residue located in the ankyrin repeat domain of TRPV4, and competitively inhibits channel opening with adenosine triphosphate (ATP) binding. The immunofluorescence assay demonstrated that the administration of HON enhances the expression and location of VE-Cadherin to protect the endothelial barrier and attenuates immune cell infiltration.

CONCLUSIONS

The finding suggested that HON alleviates IBD by improving endothelial permeability through TRPV4. The discovery provides valuable insights into the potential therapeutic strategy of active natural products for alleviating IBD.

Empagliflozin prevents oxidative stress in human coronary artery endothelial cells via the NHE/PKC/NOX axis

BACKGROUND

Empagliflozin (EMPA) ameliorates reactive oxygen species (ROS) generation in human endothelial cells (ECs) exposed to 10 % stretch, but the underlying mechanisms are still unclear. Pathological stretch is supposed to stimulate protein kinase C (PKC) by increasing intracellular calcium (Ca2+), therefore activating nicotinamide adenine dinucleotide phosphate oxidase (NOX) and promoting ROS production in human ECs. We hypothesized that EMPA inhibits stretch-induced NOX activation and ROS generation through preventing PKC activation.

METHODS

Human coronary artery endothelial cells (HCAECs) were pre-incubated for 2 h before exposure to cyclic stretch (5 % or 10 %) with either vehicle, EMPA or the PKC inhibitor LY-333531 or PKC siRNA. PKC activity, NOX activity and ROS production were detected after 24 h. Furthermore, the Ca2+ chelator BAPTA-AM, NCX inhibitor ORM-10962 or NCX siRNA, sodium/potassium pump inhibitor ouabain and sodium hydrogen exchanger (NHE) inhibitor cariporide were applied to explore the involvement of the NHE/Na+/NCX/Ca2+ in the ROS inhibitory capacity of EMPA.

RESULTS

Compared to 5 % stretch, 10 % significantly increased PKC activity, which was reduced by EMPA and PKC inhibitor LY-333531. EMPA and LY-333531 showed a similar inhibitory capacity on NOX activity and ROS generation induced by 10 % stretch, which was not augmented by combined treatment with both drugs. PKC-β knockdown inhibits the NOX activation induced by Ca2+ and 10 % stretch. BAPTA, pharmacologic or genetic NCX inhibition and cariporide reduced Ca2+ in static HCAECs and prevented the activation of PKC and NOX in 10%-stretched cells. Ouabain increased ROS generation in cells exposed to 5 % stretch.

CONCLUSION

EMPA reduced NOX activity via attenuation of the NHE/Na+/NCX/Ca2+/PKC axis, leading to less ROS generation in HCAECs exposed to 10 % stretch.

Benidipine impairs innate immunity converting sublethal to lethal infections in a murine model of spotted fever rickettsiosis

Spotted fever group rickettsiae are tick-borne obligate intracellular bacteria that infect microvascular endothelial cells. Humans and mammalian infection results in endothelial cell barrier dysfunction and increased vascular permeability. We previously demonstrated that treatment of Rickettsia parkeri-infected cells with the calcium channel blocker benidipine significantly delayed vascular barrier permeability. Thus, we hypothesized that benidipine, known to be safe and effective for other clinical processes, could reduce rickettsia-induced vascular permeability in vivo in an animal model of spotted fever rickettsiosis. Based on liver, lung and brain vascular FITC-dextran extravasation studies, benidipine did not reliably impact vascular permeability. However, it precipitated a deleterious effect on responses to control sublethal R. parkeri infection. Animals treated with benidipine alone had no clinical signs or changes in histopathology and splenic immune cell distributions. Benidipine-treated infected animals had marked increases in tissue and blood bacterial loads, more extensive inflammatory histopathologic injury, and changes in splenic architecture and immune cell distributions potentially reflecting diminished Ca2+ signaling, reduced innate immune cell activation, and loss of rickettsial propagation control. Impaired T cell activation by R. parkeri antigen in the presence of benidipine was confirmed in vitro with the use of NKT cell hybridomas. The unexpected findings stand in stark contrast to recent discussions of the benefits of calcium channel blockers for viral infections and chronic infectious or inflammatory diseases. A role for calcium channel blockers in exacerbation of human rickettsiosis and acute inflammatory infections should be evaluated by a retrospective review of patient's outcomes and medications.

Depletion of Endothelial-Derived 2-AG Reduces Blood-Endothelial Barrier Integrity via Alteration of VE-Cadherin and the Phospho-Proteome

Mounting evidence supports the role of the endocannabinoid system in neurophysiology, including blood-brain barrier (BBB) function. Recent work has demonstrated that activation of endocannabinoid receptors can mitigate insults to the BBB during neurological disorders like traumatic brain injury, cortical spreading depression, and stroke. As alterations to the BBB are associated with worsening clinical outcomes in these conditions, studies herein sought to examine the impact of endocannabinoid depletion on BBB integrity. Barrier integrity was investigated in vitro via bEnd.3 cell monolayers to assess endocannabinoid synthesis, barrier function, calcium influx, junctional protein expression, and proteome-wide changes. Inhibition of 2-AG synthesis using DAGLα inhibition and siRNA inhibition of DAGLα led to loss of barrier integrity via altered expression of VE-cadherin, which could be partially rescued by exogenous application of 2-AG. Moreover, the deleterious effects of DAGLα inhibition on BBB integrity showed both calcium and PKC (protein kinase C)-dependency. These data indicate that disruption of 2-AG homeostasis in brain endothelial cells, in the absence of insult, is sufficient to disrupt BBB integrity thus supporting the role of the endocannabinoid system in neurovascular disorders.

Everolimus-induced hyperpermeability of endothelial cells causes lung injury

The mammalian target of rapamycin (mTOR) inhibitors, everolimus (but not dactolisib), is frequently associated with lung injury in clinical therapies. However, the underlying mechanisms remain unclear. Endothelial cell barrier dysfunction plays a major role in the pathogenesis of the lung injury. This study hypothesizes that everolimus increases pulmonary endothelial permeability, which leads to lung injury. We tested the effects of everolimus on human pulmonary microvascular endothelial cell (HPMEC) permeability and a mouse model of intraperitoneal injection of everolimus was established to investigate the effect of everolimus on pulmonary vascular permeability. Our data showed that everolimus increased human pulmonary microvascular endothelial cell (HPMEC) permeability which was associated with MLC phosphorylation and F-actin stress fiber formation. Furthermore, everolimus induced an increasing concentration of intracellular calcium Ca2+ leakage in HPMECs and this was normalized with ryanodine pretreatment. In addition, ryanodine decreased everolimus-induced phosphorylation of PKCα and MLC, and barrier disruption in HPMECs. Consistent with in vitro data, everolimus treatment caused a visible lung-vascular barrier dysfunction, including an increase in protein in BALF and lung capillary-endothelial permeability, which was significantly attenuated by pretreatment with an inhibitor of PKCα, MLCK, and ryanodine. This study shows that everolimus induced pulmonary endothelial hyper-permeability, at least partly, in an MLC phosphorylation-mediated EC contraction which is influenced in a Ca2+-dependent manner and can lead to lung injury through mTOR-independent mechanisms.

Stroke-induced damage on the blood-brain barrier

The blood-brain barrier (BBB) is a functional phenotype exhibited by the neurovascular unit (NVU). It is maintained and regulated by the interaction between cellular and non-cellular matrix components of the NVU. The BBB plays a vital role in maintaining the dynamic stability of the intracerebral microenvironment as a barrier layer at the critical interface between the blood and neural tissues. The large contact area (approximately 20 m2/1.3 kg brain) and short diffusion distance between neurons and capillaries allow endothelial cells to dominate the regulatory role. The NVU is a structural component of the BBB. Individual cells and components of the NVU work together to maintain BBB stability. One of the hallmarks of acute ischemic stroke is the disruption of the BBB, including impaired function of the tight junction and other molecules, as well as increased BBB permeability, leading to brain edema and a range of clinical symptoms. This review summarizes the cellular composition of the BBB and describes the protein composition of the barrier functional junction complex and the mechanisms regulating acute ischemic stroke-induced BBB disruption.

Edema and lymphatic clearance: molecular mechanisms and ongoing challenges

Resolution of edema remains a significant clinical challenge. Conditions such as traumatic shock, sepsis, or diabetes often involve microvascular hyperpermeability, which leads to tissue and organ dysfunction. Lymphatic insufficiency due to genetic causes, surgical removal of lymph nodes, or infections, leads to varying degrees of tissue swelling that impair mobility and immune defenses. Treatment options are limited to management of edema as there are no specific therapeutics that have demonstrated significant success for ameliorating microvascular leakage or impaired lymphatic function. This review examines current knowledge about the physiological, cellular, and molecular mechanisms that control microvascular permeability and lymphatic clearance, the respective processes for interstitial fluid formation and removal. Clinical conditions featuring edema, along with potential future directions are discussed.

Microparticle Phosphatidylserine Mediates Coagulation: Involvement in Tumor Progression and Metastasis

Tumor progression and cancer metastasis has been linked to the release of microparticles (MPs), which are shed upon cell activation or apoptosis and display parental cell antigens, phospholipids such as phosphatidylserine (PS), and nucleic acids on their external surfaces. In this review, we highlight the biogenesis of MPs as well as the pathophysiological processes of PS externalization and its involvement in coagulation activation. We review the available evidence, suggesting that coagulation factors (mainly tissue factor, thrombin, and fibrin) assist in multiple steps of tumor dissemination, including epithelial-mesenchymal transition, extracellular matrix remodeling, immune escape, and tumor angiogenesis to support the formation of the pre-metastatic niche. Platelets are not just bystander cells in circulation but are functional players in primary tumor growth and metastasis. Tumor-induced platelet aggregation protects circulating tumor cells (CTCs) from the blood flow shear forces and immune cell attack while also promoting the binding of CTCs to endothelial cells and extravasation, which activates tumor invasion and sustains metastasis. Finally, in terms of therapy, lactadherin can inhibit coagulation by competing effectively with coagulation factors for PS binding sites and may similarly delay tumor progression. Furthermore, we also investigate the therapeutic potential of coagulation factor inhibitors within the context of cancer treatment. The development of multiple therapies targeting platelet activation and platelet-tumor cell interactions may not only reduce the lethal consequences of thrombosis but also impede tumor growth and spread.

Multimodal CRISPR perturbations of GWAS loci associated with coronary artery disease in vascular endothelial cells

Genome-wide association studies have identified >250 genetic variants associated with coronary artery disease (CAD), but the causal variants, genes and molecular mechanisms remain unknown at most loci. We performed pooled CRISPR screens to test the impact of sequences at or near CAD-associated genetic variants on vascular endothelial cell functions. Using CRISPR knockout, inhibition and activation, we targeted 1998 variants at 83 CAD loci to assess their effect on three adhesion proteins (E-selectin, ICAM1, VCAM1) and three key endothelial functions (nitric oxide and reactive oxygen species production, calcium signalling). At a false discovery rate ≤10%, we identified significant CRISPR perturbations near 42 variants located within 26 CAD loci. We used base editing to validate a putative causal variant in the promoter of the FES gene. Although a few of the loci include genes previously characterized in endothelial cells (e.g. AIDA, ARHGEF26, ADAMTS7), most are implicated in endothelial dysfunction for the first time. Detailed characterization of one of these new loci implicated the RNA helicase DHX38 in vascular endothelial cell senescence. While promising, our results also highlighted several limitations in using CRISPR perturbations to functionally dissect GWAS loci, including an unknown false negative rate and potential off-target effects.

IL-33 via PKCμ/PRKD1 Mediated α-Catenin Phosphorylation Regulates Endothelial Cell-Barrier Integrity and Ischemia-Induced Vascular Leakage

Angiogenesis, neovascularization, and vascular remodeling are highly dynamic processes, where endothelial cell-cell adhesion within the vessel wall controls a range of physiological processes, such as growth, integrity, and barrier function. The cadherin-catenin adhesion complex is a key contributor to inner blood-retinal barrier (iBRB) integrity and dynamic cell movements. However, the pre-eminent role of cadherins and their associated catenins in iBRB structure and function is not fully understood. Using a murine model of oxygen-induced retinopathy (OIR) and human retinal microvascular endothelial cells (HRMVECs), we try to understand the significance of IL-33 on retinal endothelial barrier disruption, leading to abnormal angiogenesis and enhanced vascular permeability. Using electric cell-substrate impedance sensing (ECIS) analysis and FITC-dextran permeability assay, we observed that IL-33 at a 20 ng/mL concentration induced endothelial-barrier disruption in HRMVECs. The adherens junction (AJs) proteins play a prominent role in the selective diffusion of molecules from the blood to the retina and in maintaining retinal homeostasis. Therefore, we looked for the involvement of adherens junction proteins in IL-33-mediated endothelial dysfunction. We observed that IL-33 induces α-catenin phosphorylation at serine/threonine (Ser/Thr) residues in HRMVECs. Furthermore, mass-spectroscopy (MS) analysis revealed that IL-33 induces the phosphorylation of α-catenin at Thr654 residue in HRMVECs. We also observed that PKCμ/PRKD1-p38 MAPK signaling regulates IL-33-induced α-catenin phosphorylation and retinal endothelial cell-barrier integrity. Our OIR studies revealed that genetic deletion of IL-33 resulted in reduced vascular leakage in the hypoxic retina. We also observed that the genetic deletion of IL-33 reduced OIR-induced PKCμ/PRKD1-p38 MAPK-α-catenin signaling in the hypoxic retina. Therefore, we conclude that IL-33-induced PKCμ/PRKD1-p38 MAPK-α-catenin signaling plays a significant role in endothelial permeability and iBRB integrity.

Oxidative stress-induced MMP- and γ-secretase-dependent VE-cadherin processing is modulated by the proteasome and BMP9/10

Classical cadherins, including vascular endothelial (VE)-cadherin, are targeted by matrix metalloproteinases (MMPs) and γ-secretase during adherens junction (AJ) disassembly, a mechanism that might have relevance for endothelial cell (EC) integrity and vascular homeostasis. Here, we show that oxidative stress triggered by H₂O₂ exposure induced efficient VE-cadherin proteolysis by MMPs and γ-secretase in human umbilical endothelial cells (HUVECs). The cytoplasmic domain of VE-cadherin produced by γ-secretase, VE-Cad/CTF2-a fragment that has eluded identification so far-could readily be detected after H₂O₂ treatment. VE-Cad/CTF2, released into the cytosol, was tightly regulated by proteasomal degradation and was sequentially produced from an ADAM10/17-generated C-terminal fragment, VE-Cad/CTF1. Interestingly, BMP9 and BMP10, two circulating ligands critically involved in vascular maintenance, significantly reduced VE-Cad/CTF2 levels during H₂O₂ challenge, as well as mitigated H₂O₂-mediated actin cytoskeleton disassembly during VE-cadherin processing. Notably, BMP9/10 pretreatments efficiently reduced apoptosis induced by H₂O₂, favoring endothelial cell recovery. Thus, oxidative stress is a trigger of MMP- and γ-secretase-mediated endoproteolysis of VE-cadherin and AJ disassembly from the cytoskeleton in ECs, a mechanism that is negatively controlled by the EC quiescence factors, BMP9 and BMP10.

Mechanisms of Arsenic Exposure-Induced Hypertension and Atherosclerosis: an Updated Overview

Arsenic is an abundant element in the earth's crust. In the environment and within the human body, this toxic element can be found in both organic and inorganic forms. Chronic exposure to arsenic can predispose humans to cardiovascular diseases including hypertension, stroke, atherosclerosis, and blackfoot disease. Oxidative damage induced by reactive oxygen species is a major player in arsenic-induced toxicity, and it can affect genes expression, inflammatory responses, and/or nitric oxide homeostasis. Exposure to arsenic in drinking water can lead to vascular endothelial dysfunction which is reflected by an imbalance between vascular relaxation and contraction. Arsenic has been shown to inactivate endothelial nitric oxide synthase leading to a reduction of the generation and bioavailability of nitric oxide. Ultimately, these effects increase the risk of vascular diseases such as hypertension and atherosclerosis. The present article reviews how arsenic exposure contributes to hypertension and atherosclerosis development.

The release of osteoclast-stimulating factors on supraphysiological loading by osteoprogenitors coincides with expression of genes associated with inflammation and cytoskeletal arrangement

Supraphysiological loading induced by unstable orthopedic implants initiates osteoclast formation, which results in bone degradation. We aimed to investigate which mechanosensitive cells in the peri-implant environment produce osteoclast-stimulating factors and how the production of these factors is stimulated by supraphysiological loading. The release of osteoclast-stimulating factors by different types of isolated bone marrow-derived hematopoietic and mesenchymal stem cells from six osteoarthritic patients was analyzed after one hour of supraphysiological loading (3.0 ± 0.2 Pa, 1 Hz) by adding their conditioned medium to osteoclast precursors. Monocytes produced factors that enhanced osteoclastogenesis by 1.6 ± 0.07-fold and mesenchymal stem cells by 1.4 ± 0.07-fold. Medium from osteoprogenitors and pre-osteoblasts enhanced osteoclastogenesis by 1.3 ± 0.09-fold and 1.4 ± 0.03-fold, respectively, where medium from four patients elicited a response and two did not. Next generation sequencing analysis of osteoprogenitors revealed that genes encoding for inflammation-related pathways and cytoskeletal rearrangements were regulated differently between responders and non-responders. Our data suggest that released osteoclast-stimulating soluble factors by progenitor cells in the bone marrow after supraphysiological loading may be related to cytoskeletal arrangement in an inflammatory environment. This connection could be relevant to better understand the aseptic loosening process of orthopedic implants.

Protective role of Cav-1 in pneumolysin-induced endothelial barrier dysfunction

Pneumolysin (PLY) is a bacterial pore forming toxin and primary virulence factor of Streptococcus pneumonia, a major cause of pneumonia. PLY binds cholesterol-rich domains of the endothelial cell (EC) plasma membrane resulting in pore assembly and increased intracellular (IC) Ca2+ levels that compromise endothelial barrier integrity. Caveolae are specialized plasmalemma microdomains of ECs enriched in cholesterol. We hypothesized that the abundance of cholesterol-rich domains in EC plasma membranes confers cellular susceptibility to PLY. Contrary to this hypothesis, we found increased PLY-induced IC Ca2+ following membrane cholesterol depletion. Caveolin-1 (Cav-1) is an essential structural protein of caveolae and its regulation by cholesterol levels suggested a possible role in EC barrier function. Indeed, Cav-1 and its scaffolding domain peptide protected the endothelial barrier from PLY-induced disruption. In loss of function experiments, Cav-1 was knocked-out using CRISPR-Cas9 or silenced in human lung microvascular ECs. Loss of Cav-1 significantly enhanced the ability of PLY to disrupt endothelial barrier integrity. Rescue experiments with re-expression of Cav-1 or its scaffolding domain peptide protected the EC barrier against PLY-induced barrier disruption. Dynamin-2 (DNM2) is known to regulate caveolar membrane endocytosis. Inhibition of endocytosis, with dynamin inhibitors or siDNM2 amplified PLY induced EC barrier dysfunction. These results suggest that Cav-1 protects the endothelial barrier against PLY by promoting endocytosis of damaged membrane, thus reducing calcium entry and PLY-dependent signaling.

Trauma-induced hypocalcemia

BACKGROUND

Trauma-induced hypocalcemia is an underappreciated complication of severe injury but is well known to result in the derangement of an array of physiological regulatory mechanisms. Existing literature provides a compelling link between hypocalcemia and worse trauma-induced coagulopathy and increased mortality after injury.

STUDY DESIGN AND METHODS

This narrative review evaluates available data related to the risk factors, mechanisms, and treatment of hypocalcemia after severe injury. The authors did not perform a systemic review or meta-analysis.

RESULTS AND DISCUSSION

The interplay of acidosis, hypothermia, and coagulopathy with hypocalcemia potentiates the bloody vicious cycle of hemorrhagic shock which has been the paradigm of trauma resuscitation for over half a century. However, current screening and treatment of postinjury hypocalcemia are relegated to a secondary consideration in trauma resuscitation. We conclude calcium supplementation should be a primary tier intervention for life-threatening injury.

Impact of surface chemistry of ultrasmall superparamagnetic iron oxide nanoparticles on protein corona formation and endothelial cell uptake, toxicity, and barrier function

Ultrasmall superparamagnetic iron oxide nanoparticles (USPION) have been investigated for biomedical applications, including novel contrast agents, magnetic tracers for tumor imaging, targeted drug delivery vehicles, and magneto-mechanical actuators for hyperthermia and thrombolysis. Despite significant progress, recent clinical reports have raised concerns regarding USPION safety related to endothelial cell dysfunction; however, there is limited information on factors contributing to these clinical responses. The influence of USPION surface chemistry on nanoparticle interactions with proteins may impact endothelial cell function leading to adverse responses. Therefore, the goal of this study was to assess the effects of carboxyl-functionalized USPION (CU) or amine-functionalized USPION (AU) (∼30 nm diameter) on biological responses in human coronary artery endothelial cells. Increased protein adsorption was observed for AU compared to CU after exposure to serum proteins. Exposure to CU, but not AU, resulted in a concentration-dependent decrease in cell viability and perinuclear accumulation inside cytoplasmic vesicles. Internalization of CU was correlated with endothelial cell functional changes under non-cytotoxic conditions, as evidenced by a marked decreased expression of endothelial-specific adhesion proteins (e.g., VE-cadherin and PECAM-1) and increased endothelial permeability. Evaluation of downstream signaling indicated endothelial permeability is associated with actin cytoskeleton remodeling, possibly elicited by intracellular events involving reactive oxygen species, calcium ions, and the nanoparticle cellular uptake pathway. This study demonstrated that USPION surface chemistry significantly impacts protein adsorption and endothelial cell uptake, viability, and barrier function. This information will advance the current toxicological profile of USPION and improve development, safety assessment, and clinical outcomes of USPION-enabled medical products.

Dichotomous Role of Tumor Necrosis Factor in Pulmonary Barrier Function and Alveolar Fluid Clearance

Alveolar-capillary leak is a hallmark of the acute respiratory distress syndrome (ARDS), a potentially lethal complication of severe sepsis, trauma and pneumonia, including COVID-19. Apart from barrier dysfunction, ARDS is characterized by hyper-inflammation and impaired alveolar fluid clearance (AFC), which foster the development of pulmonary permeability edema and hamper gas exchange. Tumor Necrosis Factor (TNF) is an evolutionarily conserved pleiotropic cytokine, involved in host immune defense against pathogens and cancer. TNF exists in both membrane-bound and soluble form and its mainly -but not exclusively- pro-inflammatory and cytolytic actions are mediated by partially overlapping TNFR1 and TNFR2 binding sites situated at the interface between neighboring subunits in the homo-trimer. Whereas TNFR1 signaling can mediate hyper-inflammation and impaired barrier function and AFC in the lungs, ligand stimulation of TNFR2 can protect from ventilation-induced lung injury. Spatially distinct from the TNFR binding sites, TNF harbors within its structure a lectin-like domain that rather protects lung function in ARDS. The lectin-like domain of TNF -mimicked by the 17 residue TIP peptide- represents a physiological mediator of alveolar-capillary barrier protection. and increases AFC in both hydrostatic and permeability pulmonary edema animal models. The TIP peptide directly activates the epithelial sodium channel (ENaC) -a key mediator of fluid and blood pressure control- upon binding to its α subunit, which is also a part of the non-selective cation channel (NSC). Activity of the lectin-like domain of TNF is preserved in complexes between TNF and its soluble TNFRs and can be physiologically relevant in pneumonia. Antibody- and soluble TNFR-based therapeutic strategies show considerable success in diseases such as rheumatoid arthritis, psoriasis and inflammatory bowel disease, but their chronic use can increase susceptibility to infection. Since the lectin-like domain of TNF does not interfere with TNF's anti-bacterial actions, while exerting protective actions in the alveolar-capillary compartments, it is currently evaluated in clinical trials in ARDS and COVID-19. A more comprehensive knowledge of the precise role of the TNFR binding sites versus the lectin-like domain of TNF in lung injury, tissue hypoxia, repair and remodeling may foster the development of novel therapeutics for ARDS.

A generic model based on the properties of nanoparticles and cells for predicting cellular uptake

Nanoparticles (NPs) are widely used in industry and technology due to their small size and versatility, which makes them easy to enter organisms and pose threats to human and ecological health. Given the particularity and complex structure of NPs, statistical models alone cannot reliably predict uptake. Hence, we developed a generic model for predicting the cellular uptake of NPs with organic coatings, based on physicochemical interactions underlying uptake. The model utilized the concentration, experimental conditions and properties of NPs viz. size, surface coating and coverage. These parameters were converted to surface energy components and surface potentials, and combined with the components and potential for a cell membrane. For NPs uptake, we constructed energetic profiles and barriers for adsorption and permeation onto/through cell membranes. The relationships derived were compared to experimental uptake data. The model provided accurate and robust uptake estimates for neutrally charged unhalogenated NPs and six different cell types. We envision that the model provides a reference for cellular accumulation of neutral NPs and (ecological/human) risk assessment of NPs or microparticles.

The Role of TRPM2 in Endothelial Function and Dysfunction

The transient receptor potential (TRP) melastatin-like subfamily member 2 (TRPM2) is a non-selective calcium-permeable cation channel. It is expressed by many mammalian tissues, including bone marrow, spleen, lungs, heart, liver, neutrophils, and endothelial cells. The best-known mechanism of TRPM2 activation is related to the binding of ADP-ribose to the nudix-box sequence motif (NUDT9-H) in the C-terminal domain of the channel. In cells, the production of ADP-ribose is a result of increased oxidative stress. In the context of endothelial function, TRPM2-dependent calcium influx seems to be particularly interesting as it participates in the regulation of barrier function, cell death, cell migration, and angiogenesis. Any impairments of these functions may result in endothelial dysfunction observed in such conditions as atherosclerosis or hypertension. Thus, TRPM2 seems to be an attractive therapeutic target for the conditions connected with the increased production of reactive oxygen species. However, before the application of TRPM2 inhibitors will be possible, some issues need to be resolved. The main issues are the lack of specificity, poor membrane permeabilization, and low stability in in vivo conditions. The article aims to summarize the latest findings on a role of TRPM2 in endothelial cells. We also show some future perspectives for the application of TRPM2 inhibitors in cardiovascular system diseases.

Baicalin Protects Vascular Tight Junctions in Piglets During Glaesserella parasuis Infection

Glaesserella parasuis (G. parasuis) can cause Glässer's disease and severely affect swine industry worldwide. This study is an attempt to address the issue of the capability of G. parasuis to damage the vascular barrier and the effects of baicalin on vascular tight junctions (TJ) in order to investigate the interactions between the pathogen and the porcine vascular endothelium. Piglets were challenged with G. parasuis and treated with or without baicalin. The expressions of vascular TJ genes were examined using RT-PCR. The distribution patterns of TJ proteins were detected by immunofluorescence. The involved signaling pathways were determined by Western blot assays on related proteins. G. parasuis can downregulate TJ expression and disrupt the distribution of TJ proteins. Baicalin can alleviate the downregulation of vascular TJ mRNA, maintain the distribution, and prevent the abnormalities of TJ. These results provide ample evidence that baicalin has the capacity to protect vascular TJ damaged by G. parasuis through inhibiting PKC and MLCK/MLC pathway activation. As a result, baicalin is a promising candidate for application as a natural agent for the prevention and control of G. parasuis infection.

Effects of Alzheimer's Disease-Related Proteins on the Chirality of Brain Endothelial Cells

Introduction

Cell chirality is an intrinsic cellular property that determines the directionality of cellular polarization along the left-right axis. We recently show that endothelial cell chirality can influence intercellular junction formation and alter trans-endothelial permeability, depending on the uniformity of the chirality of adjacent cells, which suggests a potential role for cell chirality in neurodegenerative diseases with blood-brain barrier (BBB) dysfunctions, such as Alzheimer's disease (AD). In this study, we determined the effects of AD-related proteins amyloid-β (Aβ), tau, and apolipoprotein E4 (ApoE4) on the chiral bias of the endothelial cell component in BBB.

Methods

We first examined the chiral bias and effects of protein kinase C (PKC)-mediated chiral alterations of human brain microvascular endothelial cells (hBMECs) using the ring micropattern chirality assay. We then investigated the effects of Aβ, tau, and ApoE4 on hBMEC chirality using chirality assay and biased organelle positions.

Results

The hBMECs have a strong clockwise chiral bias, which can be reversed by protein kinase C (PKC) activation. Treatment with tau significantly disrupted the chiral bias of hBMECs with altered cellular polarization. In contrast, neither ApoE4 nor Aβ-42 caused significant changes in cell chirality.

Conclusions

We conclude that tau might cause BBB dysfunction by disrupting cell polarization and chiral morphogenesis, while the effects of ApoE4 and Aβ-42 on BBB integrity might be chirality-independent. The potential involvement of chiral morphogenesis in tau-mediated BBB dysfunction in AD provides a novel perspective in vascular dysfunction in tauopathies such as AD, chronic traumatic encephalopathy, progressive supranuclear palsy, and frontotemporal dementia.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-021-00669-w.

Protein kinase Cα regulates the nucleocytoplasmic shuttling of KRIT1

KRIT1 is a scaffolding protein that regulates multiple molecular mechanisms, including cell-cell and cell-matrix adhesion, and redox homeostasis and signaling. However, rather little is known about how KRIT1 is itself regulated. KRIT1 is found in both the cytoplasm and the nucleus, yet the upstream signaling proteins and mechanisms that regulate KRIT1 nucleocytoplasmic shuttling are not well understood. Here, we identify a key role for protein kinase C (PKC) in this process. In particular, we found that PKC activation promotes the redox-dependent cytoplasmic localization of KRIT1, whereas inhibition of PKC or treatment with the antioxidant N-acetylcysteine leads to KRIT1 nuclear accumulation. Moreover, we demonstrated that the N-terminal region of KRIT1 is crucial for the ability of PKC to regulate KRIT1 nucleocytoplasmic shuttling, and may be a target for PKC-dependent regulatory phosphorylation events. Finally, we found that silencing of PKCα, but not PKCδ, inhibits phorbol 12-myristate 13-acetate (PMA)-induced cytoplasmic enrichment of KRIT1, suggesting a major role for PKCα in regulating KRIT1 nucleocytoplasmic shuttling. Overall, our findings identify PKCα as a novel regulator of KRIT1 subcellular compartmentalization, thus shedding new light on the physiopathological functions of this protein.

The Role of MSC Therapy in Attenuating the Damaging Effects of the Cytokine Storm Induced by COVID-19 on the Heart and Cardiovascular System

The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) has led to 47 m infected cases and 1. 2 m (2.6%) deaths. A hallmark of more severe cases of SARS-CoV-2 in patients with acute respiratory distress syndrome (ARDS) appears to be a virally-induced over-activation or unregulated response of the immune system, termed a "cytokine storm," featuring elevated levels of pro-inflammatory cytokines such as IL-2, IL-6, IL-7, IL-22, CXCL10, and TNFα. Whilst the lungs are the primary site of infection for SARS-CoV-2, in more severe cases its effects can be detected in multiple organ systems. Indeed, many COVID-19 positive patients develop cardiovascular complications, such as myocardial injury, myocarditis, cardiac arrhythmia, and thromboembolism, which are associated with higher mortality. Drug and cell therapies targeting immunosuppression have been suggested to help combat the cytokine storm. In particular, mesenchymal stromal cells (MSCs), owing to their powerful immunomodulatory ability, have shown promise in early clinical studies to avoid, prevent or attenuate the cytokine storm. In this review, we will discuss the mechanistic underpinnings of the cytokine storm on the cardiovascular system, and how MSCs potentially attenuate the damage caused by the cytokine storm induced by COVID-19. We will also address how MSC transplantation could alleviate the long-term complications seen in some COVID-19 patients, such as improving tissue repair and regeneration.

The vital role for nitric oxide in intraocular pressure homeostasis

Catalyzed by endothelial nitric oxide (NO) synthase (eNOS) activity, NO is a gaseous signaling molecule maintaining endothelial and cardiovascular homeostasis. Principally, NO regulates the contractility of vascular smooth muscle cells and permeability of endothelial cells in response to either biochemical or biomechanical cues. In the conventional outflow pathway of the eye, the smooth muscle-like trabecular meshwork (TM) cells and Schlemm's canal (SC) endothelium control aqueous humor outflow resistance, and therefore intraocular pressure (IOP). The mechanisms by which outflow resistance is regulated are complicated, but NO appears to be a key player as enhancement or inhibition of NO signaling dramatically affects outflow function; and polymorphisms in NOS3, the gene that encodes eNOS modifies the relation between various environmental exposures and glaucoma. Based upon a comprehensive review of past foundational studies, we present a model whereby NO controls a feedback signaling loop in the conventional outflow pathway that is sensitive to changes in IOP and its oscillations. Thus, upon IOP elevation, the outflow pathway tissues distend, and the SC lumen narrows resulting in increased SC endothelial shear stress and stretch. In response, SC cells upregulate the production of NO, relaxing neighboring TM cells and increasing permeability of SC's inner wall. These IOP-dependent changes in the outflow pathway tissues reduce the resistance to aqueous humor drainage and lower IOP, which, in turn, diminishes the biomechanical signaling on SC. Similar to cardiovascular pathogenesis, dysregulation of the eNOS/NO system leads to dysfunctional outflow regulation and ocular hypertension, eventually resulting in primary open-angle glaucoma.

IGF-1 Deficiency Rescue and Intracellular Calcium Blockade Improves Survival and Corresponding Mechanisms in a Mouse Model of Acute Kidney Injury

This study was undertaken to test two therapies for acute kidney injury (AKI) prevention, IGF-1, which is renal protective, and BTP-2, which is a calcium entry (SOCE) inhibitor. We utilized lipopolysaccharide (LPS) IP, as a systemic model of AKI and studied in five groups of animals. Three experiments showed that at 7 days: (1) LPS significantly reduced serum IGF-1 and intramuscular IGF-I in vivo gene therapy rescued this deficiency. (2) Next, at the 7-day time point, our combination therapy, compared to the untreated group, caused a significant increase in survival, which was noteworthy because all of the untreated animals died in 72 h. (3) The four pathways associated with inflammation, including (A) increase in cytosolic calcium, (B) elaboration of proinflammatory cytokines, (C) impairment of vascular integrity, and (D) cell injury, were adversely affected in renal tissue by LPS, using a sublethal dose of LPS. The expression of several genes was measured in each of the above pathways. The combined therapy of IGF-1 and BTP-2 caused a favorable gene expression response in all four pathways. Our current study was an AKI study, but these pathways are also involved in other types of severe inflammation, including sepsis, acute respiratory distress syndrome, and probably severe coronavirus infection.

Regulation of Vessel Permeability by TRP Channels

The vascular endothelium constitutes a semi-permeable barrier between blood and interstitial fluids. Since an augmented endothelial permeability is often associated to pathological states, understanding the molecular basis for its regulation is a crucial biomedical and clinical challenge. This review focuses on the processes controlling paracellular permeability that is the permeation of fluids between adjacent endothelial cells (ECs). Cytosolic calcium changes are often detected as early events preceding the alteration of the endothelial barrier (EB) function. For this reason, great interest has been devoted in the last decades to unveil the molecular mechanisms underlying calcium fluxes and their functional relationship with vessel permeability. Beyond the dicotomic classification between store-dependent and independent calcium entry at the plasma membrane level, the search for the molecular components of the related calcium-permeable channels revealed a difficult task for intrinsic and technical limitations. The contribution of redundant channel-forming proteins including members of TRP superfamily and Orai1, together with the very complex intracellular modulatory pathways, displays a huge variability among tissues and along the vascular tree. Moreover, calcium-independent events could significantly concur to the regulation of vascular permeability in an intricate and fascinating multifactorial framework.

Ca2+ release-activated Ca2+ channels are responsible for histamine-induced Ca2+ entry, permeability increase, and interleukin synthesis in lymphatic endothelial cells

The lymphatic functions in maintaining lymph transport, and immune surveillance can be impaired by infections and inflammation, thereby causing debilitating disorders, such as lymphedema and inflammatory bowel disease. Histamine is a key inflammatory mediator known to trigger vasodilation and vessel hyperpermeability upon binding to its receptors and evoking intracellular Ca²⁺ ([Ca²⁺]_i) dynamics for downstream signal transductions. However, the exact molecular mechanisms beneath the [Ca²⁺]_i dynamics and the downstream cellular effects have not been elucidated in the lymphatic system. Here, we show that Ca²⁺ release-activated Ca²⁺ (CRAC) channels, formed by Orai1 and stromal interaction molecule 1 (STIM1) proteins, are required for the histamine-elicited Ca²⁺ signaling in human dermal lymphatic endothelial cells (HDLECs). Blockers or antagonists against CRAC channels, phospholipase C, and H₁R receptors can all significantly diminish the histamine-evoked [Ca²⁺]_i dynamics in lymphatic endothelial cells (LECs), while short interfering RNA-mediated knockdown of endogenous Orai1 or STIM1 also abolished the Ca²⁺ entry upon histamine stimulation in LECs. Furthermore, we find that histamine compromises the lymphatic endothelial barrier function by increasing the intercellular permeability and disrupting vascular endothelial-cadherin integrity, which is remarkably attenuated by CRAC channel blockers. Additionally, the upregulated expression of inflammatory cytokines, IL-6 and IL-8, after histamine stimulation was abolished by silencing Orai1 or STIM1 with RNAi in LECs. Taken together, our data demonstrated the essential role of CRAC channels in mediating the [Ca²⁺]_i signaling and downstream endothelial barrier and inflammatory functions induced by histamine in the LECs, suggesting a promising potential to relieve histamine-triggered vascular leakage and inflammatory disorders in the lymphatics by targeting CRAC channel functions.

Impact of Bacterial Toxins in the Lungs

Bacterial toxins play a key role in the pathogenesis of lung disease. Based on their structural and functional properties, they employ various strategies to modulate lung barrier function and to impair host defense in order to promote infection. Although in general, these toxins target common cellular signaling pathways and host compartments, toxin- and cell-specific effects have also been reported. Toxins can affect resident pulmonary cells involved in alveolar fluid clearance (AFC) and barrier function through impairing vectorial Na⁺ transport and through cytoskeletal collapse, as such, destroying cell-cell adhesions. The resulting loss of alveolar-capillary barrier integrity and fluid clearance capacity will induce capillary leak and foster edema formation, which will in turn impair gas exchange and endanger the survival of the host. Toxins modulate or neutralize protective host cell mechanisms of both the innate and adaptive immunity response during chronic infection. In particular, toxins can either recruit or kill central players of the lung's innate immune responses to pathogenic attacks, i.e., alveolar macrophages (AMs) and neutrophils. Pulmonary disorders resulting from these toxin actions include, e.g., acute lung injury (ALI), the acute respiratory syndrome (ARDS), and severe pneumonia. When acute infection converts to persistence, i.e., colonization and chronic infection, lung diseases, such as bronchitis, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) can arise. The aim of this review is to discuss the impact of bacterial toxins in the lungs and the resulting outcomes for pathogenesis, their roles in promoting bacterial dissemination, and bacterial survival in disease progression.

Downregulation of S1P Lyase Improves Barrier Function in Human Cerebral Microvascular Endothelial Cells Following an Inflammatory Challenge

Sphingosine 1-phosphate (S1P) is a key bioactive lipid that regulates a myriad of physiological and pathophysiological processes, including endothelial barrier function, vascular tone, vascular inflammation, and angiogenesis. Various S1P receptor subtypes have been suggested to be involved in the regulation of these processes, whereas the contribution of intracellular S1P (iS1P) through intracellular targets is little explored. In this study, we used the human cerebral microvascular endothelial cell line HCMEC/D3 to stably downregulate the S1P lyase (SPL-kd) and evaluate the consequences on endothelial barrier function and on the molecular factors that regulate barrier tightness under normal and inflammatory conditions. The results show that in SPL-kd cells, transendothelial electrical resistance, as a measure of barrier integrity, was regulated in a dual manner. SPL-kd cells had a delayed barrier build up, a shorter interval of a stable barrier, and, thereafter, a continuous breakdown. Contrariwise, a protection was seen from the rapid proinflammatory cytokine-mediated barrier breakdown. On the molecular level, SPL-kd caused an increased basal protein expression of the adherens junction molecules PECAM-1, VE-cadherin, and β-catenin, increased activity of the signaling kinases protein kinase C, AMP-dependent kinase, and p38-MAPK, but reduced protein expression of the transcription factor c-Jun. However, the only factors that were significantly reduced in TNFα/SPL-kd compared to TNFα/control cells, which could explain the observed protection, were VCAM-1, IL-6, MCP-1, and c-Jun. Furthermore, lipid profiling revealed that dihydro-S1P and S1P were strongly enhanced in TNFα-treated SPL-kd cells. In summary, our data suggest that SPL inhibition is a valid approach to dampenan inflammatory response and augmente barrier integrity during an inflammatory challenge.

Differential Regulation of LPS-Mediated VE-Cadherin Disruption in Human Endothelial Cells and the Underlying Signaling Pathways: A Mini Review

Endothelial cells lining the inner vascular wall form a monolayer that contributes to the selective permeability of endothelial barrier. This selective permeability is mainly regulated by an endothelium-specific adherens junctional protein, known as vascular endothelial-cadherin (VE-cadherin). In endothelial cells, the adherens junction comprises of VE-cadherin and its associated adhesion molecules such as p120, α-catenin, and β-catenin, in which α-catenin links cytoplasmic tails of VE-cadherin to actin cytoskeleton through β-catenin. Proinflammatory stimuli such as lipopolysaccharide (LPS) are capable of attenuating vascular integrity through the disruption of VE-cadherin adhesion in endothelial cells. To date, numerous studies demonstrated the disruption of adherens junction as a result of phosphorylation-mediated VE-cadherin disruption. However, the outcomes from these studies were inconsistent and non-conclusive as different cell fractions were used to examine the effect of LPS on the disruption of VE-cadherin. By using Western Blot, some studies utilized total protein lysate and reported decreased protein expression while some studies reported unchanged expression. Other studies which used membrane and cytosolic fractions of protein extract demonstrated decreased and increased VE-cadherin expression, respectively. Despite the irregularities, the results of immunofluorescence staining are consistent with the formation of intercellular gap. Besides that, the overall underlying disruptive mechanisms of VE-cadherin remain largely unknown. Therefore, this mini review will focus on different experiment approaches in terms of cell fractions used in different human endothelial cell studies, and relate these differences to the results obtained in Western blot and immunofluorescence staining in order to give some insights into the overall differential regulatory mechanisms of LPS-mediated VE-cadherin disruption and address the discrepancy in VE-cadherin expression.

Nafamostat mesylate attenuates the pathophysiologic sequelae of neurovascular ischemia

Nafamostat mesylate, an apparent soi-disant panacea of sorts, is widely used to anticoagulate patients undergoing hemodialysis or cardiopulmonary bypass, mitigate the inflammatory response in patients diagnosed with acute pancreatitis, and reverse the coagulopathy of patients experiencing the commonly preterminal disseminated intravascular coagulation in the Far East. The serine protease inhibitor nafamostat mesylate exhibits significant neuroprotective effects in the setting of neurovascular ischemia. Nafamostat mesylate generates neuroprotective effects by attenuating the enzymatic activity of serine proteases, neuroinflammatory signaling cascades, and the endoplasmic reticulum stress responses, downregulating excitotoxic transient receptor membrane channel subfamily 7 cationic currents, modulating the activity of intracellular signal transduction pathways, and supporting neuronal survival (brain-derived neurotrophic factor/TrkB/ERK1/2/CREB, nuclear factor kappa B. The effects collectively reduce neuronal necrosis and apoptosis and prevent ischemia mediated disruption of blood-brain barrier microarchitecture. Investigational clinical applications of these compounds may mitigate ischemic reperfusion injury in patients undergoing cardiac, hepatic, renal, or intestinal transplant, preventing allograft rejection, and treating solid organ malignancies. Neuroprotective effects mediated by nafamostat mesylate support the wise conduct of randomized prospective controlled trials in Western countries to evaluate the clinical utility of this compound.

Endothelial Cell Calcium Signaling during Barrier Function and Inflammation

Calcium is an essential second messenger in endothelial cells and plays a pivotal role in regulating a number of physiologic processes, including cell migration, angiogenesis, barrier function, and inflammation. An increase in intracellular Ca²⁺ concentration can trigger a number of diverse signaling pathways under both physiologic and pathologic conditions. In this review, we discuss how calcium signaling pathways in endothelial cells play an essential role in affecting barrier function and facilitating inflammation. Inflammatory mediators, such as thrombin and histamine, increase intracellular calcium levels. This calcium influx causes adherens junction disassembly and cytoskeletal rearrangements to facilitate endothelial cell retraction and increased permeability. During inflammation endothelial cell calcium entry and the calcium-related signaling events also help facilitate several leukocyte-endothelial cell interactions, such as leukocyte rolling, adhesion, and ultimately transendothelial migration.

BmK NT1-induced neurotoxicity is mediated by PKC/CaMKⅡ-dependent ERK1/2 and p38 activation in primary cultured cerebellar granule cells

Voltage-gated sodium channels (VGSCs) represent molecular targets for a number of potent neurotoxins that affect the ion permeation or gating kinetics. BmK NT1, an α-scorpion toxin purified from Buthus martensii Karch (BMK), induces excitatory neurotoxicity by activation of VGSCs with subsequent overloading of intracellular Ca²⁺ in cerebellar granule cells (CGCs). In the current study, we further investigated signaling pathways responsible for BmK NT1-induced neurotoxicity in CGCs. BmK NT1 exposure induced neuronal death in different development stages of CGCs with similar potencies ranging from 0.21-0.48 μM. The maximal neuronal death induced by BmK NT1 gradually increased from 25.6% at 7 days in vitro (DIVs) to 42.1%, 47.8%, and 67.2% at 10, 13, and 16 DIVs, respectively, suggesting that mature CGCs are more vulnerable to BmK NT1 exposure. Application of Ca²⁺/calmodulin-dependent protein kinase Ⅱ (CaMKⅡ) inhibitors, KN-62 or KN-93, but not Ca²⁺/calmodulin-dependent protein kinase kinase (CaMKK) inhibitor, STO-609, completely abolished BmK NT1-induced neuronal death. Moreover, BmK NT1 exposure stimulated CaMKⅡ phosphorylation. BmK NT1 also stimulated extracellular regulated protein kinases 1/2 (ERK1/2) and p38 phosphorylation which was abolished by tetrodotoxin demonstrating the role of VGSCs on BmK NT1-induced ERK1/2 and p38 phosphorylation. However, BmK NT1 didn't affect c-Jun N-terminal kinase (JNK) phosphorylation. In addition, both ERK1/2 inhibitor, U0126 and p38 inhibitor, SB203580 attenuated BmK NT1-induced neuronal death. Both PKC inhibitor, Gö 6983 and CaMKⅡ inhibitor, KN-62 abolished BmK NT1-induced ERK1/2 and p38 phosphorylation. Considered together, these data demonstrate that BmK NT1-induced neurotoxicity is through PKC/CaMKⅡ mediated ERK1/2 and p38 activation.

Protein Phosphatase 2A: More Than a Passenger in the Regulation of Epithelial Cell-Cell Junctions

Cell–cell adhesion plays a key role in the maintenance of the epithelial barrier and apicobasal cell polarity, which is crucial for homeostasis. Disruption of cell–cell adhesion is a hallmark of numerous pathological conditions, including invasive carcinomas. Adhesion between apposing cells is primarily regulated by three types of junctional structures: desmosomes, adherens junctions, and tight junctions. Cell junctional structures are highly regulated multiprotein complexes that also serve as signaling platforms to control epithelial cell function. The biogenesis, integrity, and stability of cell junctions is controlled by complex regulatory interactions with cytoskeletal and polarity proteins, as well as modulation of key component proteins by phosphorylation/dephosphorylation processes. Not surprisingly, many essential signaling molecules, including protein Ser/Thr phosphatase 2A (PP2A) are associated with intercellular junctions. Here, we examine how major PP2A enzymes regulate epithelial cell–cell junctions, either directly by associating with and dephosphorylating component proteins, or indirectly by affecting signaling pathways that control junctional integrity and cytoskeletal dynamics. PP2A deregulation has severe consequences on the stability and functionality of these structures, and disruption of cell–cell adhesion and cell polarity likely contribute to the link between PP2A dysfunction and human carcinomas.

Unloading of intercellular tension induces the directional translocation of PKCα

The migration of endothelial cells (ECs) is closely associated with a Ca²⁺ -dependent protein, protein kinase Cα (PKCα). The disruption of intercellular adhesion by single-cell wounding has been shown to induce the directional translocation of PKCα. We hypothesized that this translocation of PKCα is induced by mechanical stress, such as unloading of intercellular tension, or by intercellular communication, such as gap junction-mediated and paracrine signaling. In the current study, we found that the disruption of intercellular adhesion induced the directional translocation of PKCα even when gap junction-mediated and paracrine signaling were inhibited. Conversely, it did not occur when the mechanosensitive channel was inhibited. In addition, the strain field of substrate attributable to the disruption of intercellular adhesion tended to be larger at the areas corresponding with PKCα translocation. Recently, we found that a direct mechanical stimulus induced the accumulation of PKCα at the stimulus area, involving Ca ²⁺ influx from extracellular space. These results indicated that the unloading of intercellular tension induced directional translocation of PKCα, which required Ca ²⁺ influx from extracellular space. The results of this study indicate the involvement of PKCα in the Ca ²⁺ signaling pathway in response to mechanical stress in ECs.

Cell chirality regulates intercellular junctions and endothelial permeability

Cell chirality is a newly discovered intrinsic property of the cell, reflecting the bias of the cell to polarize in the left-right axis. Despite increasing evidence on its substantial role in the asymmetric development of embryos, little is known about implications of cell chirality in physiology and disease. We demonstrate that cell chirality accounts for the nonmonotonic, dose-response relationship between endothelial permeability and protein kinase C (PKC) activation. The permeability of the endothelial cell layer is tightly controlled in our body, and dysregulation often leads to tissue inflammation and diseases. Our results show that low-level PKC activation is sufficient to reverse cell chirality through phosphatidylinositol 3-kinase/AKT signaling and alters junctional protein organization between cells with opposite chirality, leading to an unexpected substantial change in endothelial permeability. Our findings suggest that cell chirality regulates intercellular junctions in important ways, providing new opportunities for drug delivery across tightly connected semipermeable cellular sheets.

Endothelial Protrusions in Junctional Integrity and Barrier Function

Endothelial cells of the microcirculation form a semi-permeable diffusion barrier between the blood and tissues. This permeability of the endothelium, particularly in the capillaries and postcapillary venules, is a normal physiological function needed for blood-tissue exchange in the microcirculation. During inflammation, microvascular permeability increases dramatically and can lead to tissue edema, which in turn can lead to dysfunction of tissues and organs. The molecular mechanisms that control the barrier function of endothelial cells have been under investigation for several decades and remain an important topic due to the potential for discovery of novel therapeutic strategies to reduce edema. This review highlights current knowledge of the cellular and molecular mechanisms that lead to endothelial hyperpermeability during inflammatory conditions associated with injury and disease. This includes a discussion of recent findings demonstrating temporal protrusions by endothelial cells that may contribute to intercellular junction integrity between endothelial cells and affect the diffusion distance for solutes via the paracellular pathway.

5,6-DiHETE attenuates vascular hyperpermeability by inhibiting Ca2+ elevation in endothelial cells

Although more than 100 lipid metabolites have been identified, their bioactivities remain unknown. In a previous study, we discovered that the production of several lipid metabolites in the intestines dramatically changed in colitis. Of these metabolites, 5,6-dihydroxyeicosatetraenoic acid (DiHETE) possesses novel anti-inflammatory activity in the vasculature. In this study, we used mouse and human umbilical vein endothelial cell (HUVEC) models to elucidate the mechanisms underlying the vascular activity of lipid metabolites, particularly those related to the release of histamine, a major proinflammatory mediator that stimulates endothelial cells to produce NO, a mediator of vascular relaxation and hyperpermeability, by activating intracellular Ca²⁺ concentration-dependent signaling. In a mouse ear, the administration of 5,6-DiHETE did not induce inflammatory reactions, and pretreatment with 5,6-DiHETE inhibited histamine-induced inflammation, specifically vascular dilation and hyperpermeability. In an isolated mouse aorta, 5,6-DiHETE treatment did not influence vascular contraction but attenuated acetylcholine-induced vascular relaxation. In HUVECs, treatment with 5,6-DiHETE inhibited histamine-induced endothelial barrier disruption and inhibited the production of NO. Most notably, 5,6-DiHETE inhibited histamine-induced increases in intracellular Ca²⁺ concentrations in HUVECs. Our findings suggest that 5,6-DiHETE attenuates vascular hyperpermeability during inflammation by inhibiting endothelial Ca²⁺ elevation, which might lead to a novel pharmacological strategy against inflammatory diseases.

TRPV4 Blockade Preserves the Blood-Brain Barrier by Inhibiting Stress Fiber Formation in a Rat Model of Intracerebral Hemorrhage

Blood–brain barrier (BBB) disruption and subsequent brain edema play important roles in the secondary neuronal death and neurological dysfunction that are observed following intracerebral hemorrhage (ICH). In previous studies, transient receptor potential vanilloid 4 (TRPV4), a calcium-permeable mechanosensitive channel, was shown to induce cytotoxicity in many types of cells and to play a role in orchestrating barrier functions. In the present study, we explored the role of TRPV4 in ICH-induced brain injury, specifically investigating its effect on BBB disruption. Autologous arterial blood was injected into the basal ganglia of rats to mimic ICH. Adult male Sprague Dawley rats were randomly assigned to sham and experimental groups for studies on the time course of TRPV4 expression after ICH. The selective TRPV4 antagonist HC-067047 and TRPV4 siRNA were administered to evaluate the effects of TRPV4 inhibition. GSK1016790A, a TRPV4 agonist, was administered to naive rats to verify the involvement of TRPV4-induced BBB disruption. A PKC inhibitor, dihydrochloride (H7), and a selective RhoA inhibitor, C3 transferase, were administered to clarify the involvement of the PKCα/RhoA/MLC2 pathway following ICH. Post-ICH assessments including functional tests, brain edema measurements, Evans blue extravasation, western blotting and immunohistochemical assays were performed. TRPV4 inhibition remarkably ameliorated neurological symptoms, brain edema, and neuronal death, as well as BBB disruption, 24–72 h following ICH. Meanwhile, TRPV4 blockade preserved the expression of adherens and tight junction proteins, as well as BBB integrity, by inhibiting stress fiber formation, which might be correlated with the regulation of components of the PKCα/RhoA/MLC2 pathway. Furthermore, adherens and tight junction protein degradation induced by GSK1016790A treatment in naive rats was also related to PKCα/RhoA/MLC2-pathway-mediated stress fiber formation. Based on these findings, therapeutic interventions targeting TRPV4 may represent a novel approach to ameliorate secondary brain injury following ICH.

Phosphorylation of E-cadherin at threonine 790 by protein kinase Cδ reduces β-catenin binding and suppresses the function of E-cadherin

Proper control of cell-cell adhesion is crucial for embryogenesis and tissue homeostasis. In this study, we show that protein kinase C (PKC)δ, a member of the novel PKC subfamily, localizes at cell-cell contacts of epithelial cells through its C2-like domain in an F-actin-dependent manner. Upon hepatocyte growth factor stimulation, PKCδ is phosphorylated and activated by Src, which then phosphorylates E-cadherin at Thr790. Phosphorylation of E-cadherin at Thr790 diminishes its interaction with β-catenin and impairs the homophilic interaction between the ectodomains of E-cadherin. The suppression of PKCδ by its dominant-negative mutants or specific short-hairpin RNA inhibits the disruption of cell-cell adhesions induced by hepatocyte growth factor. Elevated PKCδ expression in cancer cells is correlated with increased phosphorylation of E-cadherin at Thr790, reduced binding of E-cadherin to β-catenin, and poor homophilic interaction between E-cadherin. Analysis of surgical specimens confirmed that PKCδ is overexpressed in cervical cancer tissues, accompanied by increased phosphorylation of E-cadherin at Thr790. Together, our findings unveil a negative role for PKCδ in cell-cell adhesion through phosphorylation of E-cadherin.

Protective role of FKBP51 in calcium entry-induced endothelial barrier disruption

Pulmonary artery endothelial cells (PAECs) express a cation current, I_SOC (store-operated calcium entry current), which when activated permits calcium entry leading to inter-endothelial cell gap formation. The large molecular weight immunophilin FKBP51 inhibits I_SOC but not other calcium entry pathways in PAECs. However, it is unknown whether FKBP51-mediated inhibition of I_SOC is sufficient to protect the endothelial barrier from calcium entry-induced disruption. The major objective of this study was to determine whether FKBP51-mediated inhibition of I_SOC leads to decreased calcium entry-induced inter-endothelial gap formation and thus preservation of the endothelial barrier. Here, we measured the effects of thapsigargin-induced I_SOC on the endothelial barrier in control and FKBP51 overexpressing PAECs. FKBP51 overexpression decreased actin stress fiber and inter-endothelial cell gap formation in addition to attenuating the decrease in resistance observed with control cells using electric cell-substrate impedance sensing. Finally, the thapsigargin-induced increase in dextran flux was abolished in FKBP51 overexpressing PAECs. We then measured endothelial permeability in perfused lungs of FKBP51 knockout (FKBP51^–/–) mice and observed increased calcium entry-induced permeability compared to wild-type mice. To begin to dissect the mechanism underlying the FKBP51-mediated inhibition of I_SOC, a second goal of this study was to determine the role of the microtubule network. We observed that FKBP51 overexpressing PAECs exhibited increased microtubule polymerization that is critical for inhibition of I_SOC by FKBP51. Overall, we have identified FKBP51 as a novel regulator of endothelial barrier integrity, and these findings are significant as they reveal a protective mechanism for endothelium against calcium entry-induced disruption.

IP3 receptor signaling and endothelial barrier function

The endothelium, a monolayer of endothelial cells lining vessel walls, maintains tissue-fluid homeostasis by restricting the passage of the plasma proteins and blood cells into the interstitium. The ion Ca²⁺, a ubiquitous secondary messenger, initiates signal transduction events in endothelial cells that is critical to control of vascular tone and endothelial permeability. The ion Ca²⁺ is stored inside the intracellular organelles and released into the cytosol in response to environmental cues. The inositol 1,4,5-trisphosphate (IP₃) messenger facilitates Ca²⁺ release through IP₃ receptors which are Ca²⁺-selective intracellular channels located within the membrane of the endoplasmic reticulum. Binding of IP₃ to the IP₃Rs initiates assembly of IP₃R clusters, a key event responsible for amplification of Ca²⁺ signals in endothelial cells. This review discusses emerging concepts related to architecture and dynamics of IP₃R clusters, and their specific role in propagation of Ca²⁺ signals in endothelial cells.

Pyk2 phosphorylation of VE-PTP downstream of STIM1-induced Ca2+ entry regulates disassembly of adherens junctions

Vascular endothelial protein tyrosine phosphatase (VE-PTP) stabilizes endothelial adherens junctions (AJs) through constitutive dephosphorylation of VE-cadherin. Here we investigated the role of stromal interaction molecule 1 (STIM1) activation of store-operated Ca²⁺ entry (SOCE) in regulating AJ assembly. We observed that SOCE induced by STIM1 activated Pyk2 in human lung microvascular endothelial cells (ECs) and induced tyrosine phosphorylation of VE-PTP at Y1981. Pyk2-induced tyrosine phosphorylation of VE-PTP promoted Src binding to VE-PTP, Src activation, and subsequent VE-cadherin phosphorylation and thereby increased the endothelial permeability response. The increase in permeability was secondary to disassembly of AJs. Pyk2-mediated responses were blocked in EC-restricted Stim1 knockout mice, indicating the requirement for STIM1 in initiating the signaling cascade. A peptide derived from the Pyk2 phosphorylation site on VE-PTP abolished the STIM1/SOCE-activated permeability response. Thus Pyk2 activation secondary to STIM1-induced SOCE causes tyrosine phosphorylation of VE-PTP, and VE-PTP, in turn, binds to and activates Src, thereby phosphorylating VE-cadherin to increase endothelial permeability through disassembly of AJs. Our results thus identify a novel signaling mechanism by which STIM1-induced Ca²⁺ signaling activates Pyk2 to inhibit the interaction of VE-PTP and VE-cadherin and hence increase endothelial permeability. Therefore, targeting the Pyk2 activation pathway may be a potentially important anti-inflammatory strategy.

Thrombin-unique coagulation system protein with multifaceted impacts on cancer and metastasis

The association between blood coagulation and cancer development is well recognized. Thrombin, the pleiotropic enzyme best known for its contribution to fibrin formation and platelet aggregation during vascular hemostasis, may also trigger cellular events through protease-activated receptors, PAR-1 and PAR-4, leading to cancer progression. Our pioneering findings provided evidence that thrombin contributes to cancer metastasis by increasing adhesive potential of malignant cells. However, there is evidence that thrombin regulates every step of cancer dissemination: (1) cancer cell invasion, detachment from primary tumor, migration; (2) entering the blood vessel; (3) surviving in vasculature; (4) extravasation; (5) implantation in host organs. Recent studies have provided new molecular data about thrombin generation in cancer patients and the mechanisms by which thrombin contributes to transendothelial migration, platelet/tumor cell interactions, angiogenesis, and other processes. Though a great deal is known regarding the role of thrombin in cancer dissemination, there are new data for multiple thrombin-mediated events that justify devoting focus to this topic with a comprehensive approach.

The VE-cadherin cytoplasmic domain undergoes proteolytic processing during endocytosis

VE-cadherin is cleaved by calpain to remove the β-catenin–binding domain upon entry into clathrin-enriched membrane domains. Calpain cleavage of VE-cadherin cytoplasmic tail appears to fate cadherin for degradation rather than recycling and thus alters the cadherin trafficking itinerary after endocytosis.

VE-cadherin trafficking to and from the plasma membrane has emerged as a critical mechanism for regulating cadherin surface levels and adhesion strength. In addition, proteolytic processing of cadherin extracellular and cytoplasmic domains has been reported to regulate cadherin adhesion and signaling. Here we provide evidence that VE-cadherin is cleaved by calpain upon entry into clathrin-enriched domains. This cleavage event occurs between the β-catenin and p120-binding domains within the cadherin cytoplasmic tail. Of interest, VE-cadherin mutants that are resistant to endocytosis are similarly resistant to cleavage. Furthermore, p120-catenin overexpression blocks cadherin internalization and cleavage, coupling entry into the endocytic pathway with proteolytic processing. Of importance, the cleavage of the VE-cadherin tail alters the postendocytic trafficking itinerary of the cadherin, resulting in a higher turnover rate due to decreased recycling and increased degradation. In conclusion, this study identifies a novel proteolytic event that regulates the trafficking of VE-cadherin after endocytosis.

Biomimetic carriers mimicking leukocyte plasma membrane to increase tumor vasculature permeability

Recent advances in the field of nanomedicine have demonstrated that biomimicry can further improve targeting properties of current nanotechnologies while simultaneously enable carriers with a biological identity to better interact with the biological environment. Immune cells for example employ membrane proteins to target inflamed vasculature, locally increase vascular permeability, and extravasate across inflamed endothelium. Inspired by the physiology of immune cells, we recently developed a procedure to transfer leukocyte membranes onto nanoporous silicon particles (NPS), yielding Leukolike Vectors (LLV). LLV are composed of a surface coating containing multiple receptors that are critical in the cross-talk with the endothelium, mediating cellular accumulation in the tumor microenvironment while decreasing vascular barrier function. We previously demonstrated that lymphocyte function-associated antigen (LFA-1) transferred onto LLV was able to trigger the clustering of intercellular adhesion molecule 1 (ICAM-1) on endothelial cells. Herein, we provide a more comprehensive analysis of the working mechanism of LLV in vitro in activating this pathway and in vivo in enhancing vascular permeability. Our results suggest the biological activity of the leukocyte membrane can be retained upon transplant onto NPS and is critical in providing the particles with complex biological functions towards tumor vasculature.

Regulation of pulmonary endothelial barrier function by kinases

The pulmonary endothelium is the target of continuous physiological and pathological stimuli that affect its crucial barrier function. The regulation, defense, and repair of endothelial barrier function require complex biochemical processes. This review examines the role of endothelial phosphorylating enzymes, kinases, a class with profound, interdigitating influences on endothelial permeability and lung function.

Calcium Signaling Is Dispensable for Receptor Regulation of Endothelial Barrier Function

Endothelial barrier function is tightly regulated by plasma membrane receptors and is crucial for tissue fluid homeostasis; its dysfunction causes disease, including sepsis and inflammation. The ubiquitous activation of Ca²⁺ signaling upon phospholipase C-coupled receptor ligation leads quite naturally to the assumption that Ca²⁺ signaling is required for receptor-regulated endothelial barrier function. This widespread hypothesis draws analogy from smooth muscle and proposes the requirement of G protein-coupled receptor (GPCR)-generated Ca²⁺ signaling in activating the endothelial contractile apparatus and generating interendothelial gaps. Notwithstanding endothelia being non-excitable in nature, the hypothesis of Ca²⁺-induced endothelial contraction has been invoked to explain actions of GPCR agonists that either disrupt or stabilize endothelial barrier function. Here, we challenge this correlative hypothesis by showing a lack of causal link between GPCR-generated Ca²⁺ signaling and changes in human microvascular endothelial barrier function. We used three endogenous GPCR agonists: thrombin and histamine, which disrupt endothelial barrier function, and sphingosine-1-phosphate, which stabilizes barrier function. The qualitatively different effects of these three agonists on endothelial barrier function occur independently of Ca²⁺ entry through the ubiquitous store-operated Ca²⁺ entry channel Orai1, global Ca²⁺ entry across the plasma membrane, and Ca²⁺ release from internal stores. However, disruption of endothelial barrier function by thrombin and histamine requires the Ca²⁺ sensor stromal interacting molecule-1 (STIM1), whereas sphingosine-1-phosphate-mediated enhancement of endothelial barrier function occurs independently of STIM1. We conclude that although STIM1 is required for GPCR-mediated disruption of barrier function, a causal link between GPCR-induced cytoplasmic Ca²⁺ increases and acute changes in barrier function is missing. Thus, the cytosolic Ca²⁺-induced endothelial contraction is a cum hoc fallacy that should be abandoned.