Brain Microvascular Endothelial Cell Monolayers Research Articles

Measurement of Transendothelial Electrical Resistance in Blood-Brain Barrier Endothelial Cells.

The integrity of the blood-brain barrier (BBB), the protective barrier of the brain, is key to maintaining normal microvascular permeability and brain homeostasis. Brain microvascular endothelial cells are primary components of the blood-brain barrier. Transendothelial electrical resistance (TEER) is the electrical resistance across a cellular monolayer such as the brain microvascular endothelial cell monolayers. Measurement of TEER is considered a sensitive, reliable, and noninvasive method for evaluating barrier integrity and permeability of an endothelial cell monolayer under in vitro conditions. Measurement of TEER is also helpful for studying various cellular and molecular changes and signaling events that regulate barrier functions in endothelial monolayers. One of the in vitro endothelial cell barrier models that have been commonly used for measuring TEER is the BBB model using human or rodent brain microvascular endothelial cells grown as a monolayer. In this protocol, we describe how TEER is measured in brain microvascular endothelial cell monolayers, to determine blood-brain barrier integrity under in vitro conditions.

Lung infection by Pseudomonas aeruginosa induces neuroinflammation and blood–brain barrier dysfunction in mice

BackgroundSevere lung infection can lead to brain dysfunction and neurobehavioral disorders. The mechanisms that regulate the lung-brain axis of inflammatory response to respiratory infection are incompletely understood. This study examined the effects of lung infection causing systemic and neuroinflammation as a potential mechanism contributing to blood–brain barrier (BBB) leakage and behavioral impairment.MethodsLung infection in mice was induced by instilling Pseudomonas aeruginosa (PA) intratracheally. We determined bacterial colonization in tissue, microvascular leakage, expression of cytokines and leukocyte infiltration into the brain.ResultsLung infection caused alveolar-capillary barrier injury as indicated by leakage of plasma proteins across pulmonary microvessels and histopathological characteristics of pulmonary edema (alveolar wall thickening, microvessel congestion, and neutrophil infiltration). PA also caused significant BBB dysfunction characterized by leakage of different sized molecules across cerebral microvessels and a decreased expression of cell–cell junctions (VE-cadherin, claudin-5) in the brain. BBB leakage peaked at 24 h and lasted for 7 days post-inoculation. Additionally, mice with lung infection displayed hyperlocomotion and anxiety-like behaviors. To test whether cerebral dysfunction was caused by PA directly or indirectly, we measured bacterial load in multiple organs. While PA loads were detected in the lungs up to 7 days post-inoculation, bacteria were not detected in the brain as evidenced by negative cerebral spinal fluid (CSF) cultures and lack of distribution in different brain regions or isolated cerebral microvessels. However, mice with PA lung infection demonstrated increased mRNA expression in the brain of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), chemokines (CXCL-1, CXCL-2) and adhesion molecules (VCAM-1 and ICAM-1) along with CD11b + CD45+ cell recruitment, corresponding to their increased blood levels of white cells (polymorphonuclear cells) and cytokines. To confirm the direct effect of cytokines on endothelial permeability, we measured cell–cell adhesive barrier resistance and junction morphology in mouse brain microvascular endothelial cell monolayers, where administration of IL-1β induced a significant reduction of barrier function coupled with tight junction (TJ) and adherens junction (AJ) diffusion and disorganization. Combined treatment with IL-1β and TNFα augmented the barrier injury.ConclusionsLung bacterial infection is associated with BBB disruption and behavioral changes, which are mediated by systemic cytokine release.

Trypanosoma brucei rhodesiense Inhibitor of Cysteine Peptidase (ICP) Is Required for Virulence in Mice and to Attenuate the Inflammatory Response.

The protozoan Trypanosoma brucei rhodesiense causes Human African Trypanosomiasis, also known as sleeping sickness, and penetrates the central nervous system, leading to meningoencephalitis. The Cathepsin L-like cysteine peptidase of T. b. rhodesiense has been implicated in parasite penetration of the blood-brain barrier and its activity is modulated by the chagasin-family endogenous inhibitor of cysteine peptidases (ICP). To investigate the role of ICP in T. b. rhodesiense bloodstream form, ICP-null (Δicp) mutants were generated, and lines re-expressing ICP (Δicp:ICP). Lysates of Δicp displayed increased E-64-sensitive cysteine peptidase activity and the mutant parasites traversed human brain microvascular endothelial cell (HBMEC) monolayers in vitro more efficiently. Δicp induced E-selectin in HBMECs, leading to the adherence of higher numbers of human neutrophils. In C57BL/6 mice, no Δicp parasites could be detected in the blood after 6 days, while mice infected with wild-type (WT) or Δicp:ICP displayed high parasitemia, peaking at day 12. In mice infected with Δicp, there was increased recruitment of monocytes to the site of inoculation and higher levels of IFN-γ in the spleen. At day 14, mice infected with Δicp exhibited higher preservation of the CD4+, CD8+, and CD19+ populations in the spleen, accompanied by sustained high IFN-γ, while NK1.1+ populations receded nearly to the levels of uninfected controls. We propose that ICP helps to downregulate inflammatory responses that contribute to the control of infection.

Simple and efficient protocol to isolate and culture brain microvascular endothelial cells from newborn mice.

The neurovascular unit (NVU) is a multicellular structure comprising of neurons, glial cells, and non-neural cells, and it is supported by a specialized extracellular matrix, the basal lamina. Astrocytes, brain microvascular endothelial cells (BMECs), pericytes, and smooth muscle cells constitute the blood–brain barrier (BBB). BMECs have a mesodermal origin and invade the nervous system early in neural tube development, forming the BBB anatomical core. BMECs are connected by adherent junction complexes composed of integral membrane and cytoplasmic proteins. In vivo and in vitro studies have shown that, given the proximity and relationship with neural cells, BMECs acquire a unique gene expression profile, proteome, and specific mechanical and physical properties compared to endothelial cells from the general vasculature. BMECs are fundamental in maintaining brain homeostasis by regulating transcellular and paracellular transport of fluids, molecules, and cells. Therefore, it is essential to gain in-depth knowledge of the dynamic cellular structure of the cells in the NVU and their interactions with health and disease. Here we describe a significantly improved and simplified protocol using C57BL/6 newborn mice at postnatal day 1 (PND1) to isolate, purify, and culture BMECs monolayers in two different substrates (glass coverslips and transwell culture inserts). In vitro characterization and validation of the BMEC primary culture monolayers seeded on glass or insert included light microscopy, immunolabeling, and gene expression profile. Transendothelial electrical resistance (TEER) measurement and diffusion test were used as functional assays for adherent junction complexes and integrity and permeability of BMECs monolayers. The protocol presented here for the isolation and culture of BMECs is more straightforward than previously published protocols and yields a high number of purified cells. Finally, we tested BMECs function using the oxygen–glucose deprivation (OGD) model of hypoxia. This protocol may be suitable as a bioscaffold for secondary cell seeding allowing the study and better understanding of the NVU.

Flavivirus NS1 Triggers Tissue-Specific Disassembly of Intercellular Junctions Leading to Barrier Dysfunction and Vascular Leak in a GSK-3β-Dependent Manner.

The flavivirus nonstructural protein 1 (NS1) is secreted from infected cells and contributes to endothelial barrier dysfunction and vascular leak in a tissue-dependent manner. This phenomenon occurs in part via disruption of the endothelial glycocalyx layer (EGL) lining the endothelium. Additionally, we and others have shown that soluble DENV NS1 induces disassembly of intercellular junctions (IJCs), a group of cellular proteins critical for maintaining endothelial homeostasis and regulating vascular permeability; however, the specific mechanisms by which NS1 mediates IJC disruption remain unclear. Here, we investigated the relative contribution of five flavivirus NS1 proteins, from dengue (DENV), Zika (ZIKV), West Nile (WNV), Japanese encephalitis (JEV), and yellow fever (YFV) viruses, to the expression and localization of the intercellular junction proteins β-catenin and VE-cadherin in endothelial cells from human umbilical vein and brain tissues. We found that flavivirus NS1 induced the mislocalization of β-catenin and VE-cadherin in a tissue-dependent manner, reflecting flavivirus disease tropism. Mechanistically, we observed that NS1 treatment of cells triggered internalization of VE-cadherin, likely via clathrin-mediated endocytosis, and phosphorylation of β-catenin, part of a canonical IJC remodeling pathway during breakdown of endothelial barriers that activates glycogen synthase kinase-3β (GSK-3β). Supporting this model, we found that a chemical inhibitor of GSK-3β reduced both NS1-induced permeability of human umbilical vein and brain microvascular endothelial cell monolayers in vitro and vascular leakage in a mouse dorsal intradermal model. These findings provide insight into the molecular mechanisms regulating NS1-mediated endothelial dysfunction and identify GSK-3β as a potential therapeutic target for treatment of vascular leakage during severe dengue disease.

C-Type Natriuretic Peptide Ameliorates Vascular Injury and Improves Neurological Outcomes in Neonatal Hypoxic-Ischemic Brain Injury in Mice.

C-type natriuretic peptide (CNP) is an important vascular regulator that is present in the brain. Our previous study demonstrated the innate neuroprotectant role of CNP in the neonatal brain after hypoxic-ischemic (HI) insults. In this study, we further explored the role of CNP in cerebrovascular pathology using both in vivo and in vitro models. In a neonatal mouse HI brain injury model, we found that intracerebroventricular administration of recombinant CNP dose-dependently reduces brain infarct size. CNP significantly decreases brain edema and immunoglobulin G (IgG) extravasation into the brain tissue, suggesting a vasculoprotective effect of CNP. Moreover, in primary brain microvascular endothelial cells (BMECs), CNP dose-dependently protects BMEC survival and monolayer integrity against oxygen-glucose deprivation (OGD). The vasculoprotective effect of CNP is mediated by its innate receptors NPR2 and NPR3, in that inhibition of either NPR2 or NPR3 counteracts the protective effect of CNP on IgG leakage after HI insult and BMEC survival under OGD. Of importance, CNP significantly ameliorates brain atrophy and improves neurological deficits after HI insults. Altogether, the present study indicates that recombinant CNP exerts vascular protection in neonatal HI brain injury via its innate receptors, suggesting a potential therapeutic target for the treatment of neonatal HI brain injury.

Abstract 2984: Building an in vitro blood brain barrier model to test the influence of tight junction gene alleles on disruption by focused ultrasound to treat brain tumors

Abstract Treating primary or metastatic tumors in the brain (glioblastomas, melanoma, lung cancer, breast cancer) proves challenging by virtue of the protective function of the blood brain barrier (BBB). Recently, it has been shown that low intensity focused ultrasonic (LIFU) waves stably cavitate infused microbubbles which then mechanically disrupt the tight junctions of the BBB. This leads to temporary, recoverable opening of the BBB, and passage of otherwise disqualified cancer-therapeutic drugs at precise locations targeted by the focused ultrasound. To date, potential genetic influences on the durability and vulnerability of tight junctions to LIFU have not been elucidated, nor have the determinants of tight junction repair post LIFU been thoroughly investigated. We report the development of an ultrasound transparent organ-on-chip model to test LIFU with microbubble infusion treatment on a cell-engineered BBB. The BBB is developed using brain-specific endothelial cells derived from genomically characterized immortalized pluripotent stem cells (iPSC). Furthermore, to test genetic variation effects we propose that alleles coding for the proteins involved in tight junction assembly contribute to LIFU disruption variability. Developing preclinical models of the BBB to accommodate cell sources with tight junction genes of different allele makeup will shed light on how individuals will respond to different ultrasound frequencies. The in vitro BBB device is composed of two orthogonally stacked fluidic channels formed by top and bottom polydimethylsiloxane (PDMS) membranes and a middle polyester membrane with 3 µm pores. An ultrasound system is constructed with a waveform generator, amplifier, and 1MHz ultrasound transducer. A 0.5 MHz receiving transducer and a digital storage oscilloscope are used for stable cavitation monitoring. Nanobubbles (FUS Instruments) transduce the LIFU into a mechanical vibration force to disrupt the BBB. To deliver the ultrasonic waves, the device is submerged in degassed DI water in a custom tank. Fluid flow was achieved, and subharmonic ultrasound signal is observed using the digital oscilloscope with Fast Fourier Transform (FFT). Preliminary results convey stable cavitation with LIFU and the formation of tight junctions in a brain microvascular endothelial cell monolayer in the device, eventually leading to a versatile platform to evaluate genetic-based vulnerability of the BBB. Citation Format: Jayashree Iyer, Adam Akkad, Nanyun Tang, Michael E. Berens, Frederic Zenhausern, Jian Gu. Building an in vitro blood brain barrier model to test the influence of tight junction gene alleles on disruption by focused ultrasound to treat brain tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2984.

Transcellular Model for Neutral and Charged Nanoparticles Across an In Vitro Blood-Brain Barrier.

PurposeThe therapeutic drug-loaded nanoparticles (NPs, 20–100 nm) have been widely used to treat brain disorders. To improve systemic brain delivery efficacy of these NPs, it is necessary to quantify their transport parameters across the blood–brain barrier (BBB) and understand the underlying transport mechanism.MethodsPermeability of an in vitro BBB, bEnd3 (mouse brain microvascular endothelial cells) monolayer, to three neutral NPs with the representative diameters was measured using an automated fluorometer system. To elucidate the transport mechanism of the neutral NPs across the in vitro BBB, and that of positively charged NPs whose BBB permeability was measured in a previous study, we developed a novel transcellular model, which incorporates the charge of the in vitro BBB, the mechanical property of the cell membrane, the ion concentrations of the surrounding salt solution and the size and charge of the NPs.ResultsOur model indicates that the negative charge of the surface glycocalyx and basement membrane of the BBB plays a pivotal role in the transcelluar transport of NPs with diameter 20-100 nm across the BBB. The electrostatic force between the negative charge at the in vitro BBB and the positive charge at NPs greatly enhances NP permeability. The predictions from our transcellular model fit very well with the measured BBB permeability for both neutral and charged NPs.ConclusionOur model can be used to predict the optimal size and charge of the NPs and the optimal charge of the BBB for an optimal systemic drug delivery strategy to the brain.

Site-specific opening of the blood-brain barrier by extracellular histones

BackgroundIncreased extracellular histones in the bloodstream are known as a biomarker for vascular dysfunction associated with severe trauma or sepsis. There is limited information regarding the pathogenic role of circulating histones in neuroinflammation and cerebrovascular endothelial injury. Particularly, it remains unclear whether histones affect the blood-brain barrier (BBB) permeability function.MethodsThe direct effects of unfractionated histones on endothelial barrier properties were first assessed in brain microvascular endothelial cell monolayers by measuring transendothelial electrical resistance and solute flux. This was followed by in vivo mouse experiments, where BBB function was assessed by quantifying brain tissue accumulation of intravenously injected tracers of different molecular sizes, and comparison was made in mice receiving a sublethal dose of histones versus sterile saline. In parallel, the endothelial barrier ultrastructure was examined in histone- and saline-injected animals under transmission electron microscopy, corresponding to the expression of tight junction and adherens junction proteins.ResultsHistones increased paracellular permeability to sodium fluorescein and reduced barrier resistance at 100 μg/mL; these responses were accompanied by discontinuous staining of the tight junction proteins claudin-5 and zona ocludens-1. Interestingly, the effects of histones did not seem to result from cytotoxicity, as evidenced by negative propidium iodide staining. In vivo, histones increased the paracellular permeability of the BBB to small tracers of < 1-kDa, whereas tracers larger than 3-kDa remained impermeable across brain microvessels. Further analysis of different brain regions showed that histone-induced tracer leakage and loss of tight junction protein expression mainly occurred in the hippocampus, but not in the cerebral cortex. Consistently, opening of tight junctions was found in hippocampal capillaries from histone-injected animals. Protein expression levels of GFAP and iBA1 remained unchanged in histone-injected mice indicating that histones did not affect reactive gliosis. Moreover, cell membrane surface charge alterations are involved in histone-induced barrier dysfunction and tight junction disruption.ConclusionsExtracellular histones cause a reversible, region-specific increase in BBB permeability to small molecules by disrupting tight junctions in the hippocampus. We suggest that circulating histones may contribute to cerebrovascular injury or brain dysfunction by altering BBB structure and function.

Structural, Functional, and Metabolic Alterations in Human Cerebrovascular Endothelial Cells during Toxoplasma gondii Infection and Amelioration by Verapamil In Vitro.

Toxoplasma gondii (T. gondii), the causative agent of toxoplasmosis, is a frequent cause of brain infection. Despite its known ability to invade the brain, there is still a dire need to better understand the mechanisms by which this parasite interacts with and crosses the blood–brain barrier (BBB). The present study revealed structural and functional changes associated with infection and replication of T. gondii within human brain microvascular endothelial cells (BMECs) in vitro. T. gondii proliferated within the BMECs and disrupted the integrity of the cerebrovascular barrier through diminishing the cellular viability, disruption of the intercellular junctions and increasing permeability of the BMEC monolayer, as well as altering lipid homeostasis. Proton nuclear magnetic resonance (1H NMR)-based metabolomics combined with multivariate data analysis revealed profiles that can be attributed to infection and variations in the amounts of certain metabolites (e.g., amino acids, fatty acids) in the extracts of infected compared to control cells. Notably, treatment with the Ca2+ channel blocker verapamil rescued BMEC barrier integrity and restricted intracellular replication of the tachyzoites regardless of the time of treatment application (i.e., prior to infection, early- and late-infection). This study provides new insights into the structural and functional changes that accompany T. gondii infection of the BMECs, and sheds light upon the ability of verapamil to inhibit the parasite proliferation and to ameliorate the adverse effects caused by T. gondii infection.

Assessment of Macrophage and Blood‐Brain Barrier Function in the Resilient C57BL/6 Mouse and Non‐Resilient Balb/c Mouse

Macrophage activation disrupts the blood‐brain barrier (BBB) in neurological and psychological diseases. However, the contribution of individual differences in macrophage and BBB phenotype in people’s susceptibility to these illnesses is largely unknown. We proposed to use a mouse model of psychological resilience to understand the role of macrophage and BBB function in disease susceptibility. In this model, the adoptive transfer of macrophages between Balb/c and C57BL/6 mice confers susceptibility or resistance, respectively, to development of depressive behaviors, thus highlighting the role of individual differences in macrophage function in brain‐related disorders.Our objective was to determine BBB function (permeability of brain microvascular endothelial cell (BMEC) monolayer), BBB response to endotoxin challenge (E. colilipopolysaccharide (LPS)), and macrophage activation (via LPS) in C57BL/6 mice and Balb/c mice. We hypothesized that 1) Balb/c BMEC monolayer will be innately more permeable than C57BL/6 BMEC monolayer, 2) Balb/c BMECs will be more sensitive to LPS, and 3) LPS‐activated bone‐marrow derived macrophages (BMMs) of Balb/c mice will induce greater disruption of BMECs than C57BL/6 BMMs.BMECs derived from C57BL/6 and Balb/c mice were seeded on 96‐well plates outfitted with electrodes to measure transendothelial electrical resistance (TEER) by Electric Cell‐substrate Impedance Sensing (Applied Biophysics, Inc.). After a stable monolayer was established, cells were treated with LPS (0, 25, 50, 75 or 100 ng/mL), or media conditioned by Balb/c or C57BL/6 BMMs plated at a density of 20,000 cells/cm2. BMMs were treated with 100 ng/mL of LPS (activated) or plain media (non‐activated). After 24 hours, the media was exchanged with fresh plain media, and collected after an additional 24 hours. Experiments were performed on three different days to obtain N=3/group.C57BL/6 BMEC monolayers displayed higher maximal TEER than Balb/c BMEC monolayer (24684 ± 1291 versus 19950 ± 1462 ohms cm2), and were significantly more sensitive to the TEER‐reducing effects of LPS after 12 hours of LPS exposure (FStrain(1, 20) = 7.4, P = 0.01). Media conditioned with LPS‐activated Balb/c BMMs induced significant disruption of C57BL/6 BMECs for up to 24 hours (FStrain(1,20) = 18.9, P = 0.0003), but had no effect on Balb/c BMECs. Media conditioned with non‐activated Balb/c BMMs, or activated or non‐activated C57BL/6 BMMs had no effect on TEER of either types of BMECs.Our study demonstrated that C57BL/6 mice have a less permeable BBB that is more sensitive to endotoxin challenge compared to BBB of Balb/c mice. C57BL/6 mice also possess macrophages that, when activated, are less capable of inducing BBB leakiness compared to Balb/c mice. The innate differences in macrophage and BBB function between the resilient C57BL/6 mouse and the non‐resilient Balb/c mouse likely play a role in their susceptibility to neurological/psychological disorders. We postulate that people’s susceptibility to brain‐related disorders is partly due to the interaction of their genetically‐determined BBB and macrophage phenotypes.Support or Funding InformationThe views expressed in this abstract are those of the authors and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the U.S. Government.

Endothelial surface glycocalyx (ESG) components and ultra-structure revealed by stochastic optical reconstruction microscopy (STORM).

In order to play different roles in vascular functions as a mechanosensor to blood flows and as a barrier to transvascular exchange, the endothelial surface glycocalyx (ESG) should have an organized structure. Due to the limitations of optical and electron microscopy, the ultra-structure of ESG has not been revealed until the recent development of super-resolution optical microscopy, STORM. To investigate the ESG components and their organization on bEnd3 (mouse brain microvascular endothelial cells) monolayer. ESG was immunolabeled with anti-heparan sulfate (HS), followed by an ATTO488 conjugated goat anti-mouse IgG, and with biotinylated hyaluronic acid (HA) binding protein, followed by an AF647 conjugated anti-biotin. The ESG was then imaged by the STORM. HA is a long molecule weaving into a network which covers the endothelial luminal surface. In contrast, HS is a shorter molecule, perpendicular to the cell surface. HA and HS are partially overlapped with each other at the endothelial luminal surface. We also quantified the length, diameter, orientation, and density of HS at the top, middle and bottom regions of the endothelial surface. Our results suggest that HS plays a major role in mechanosensing and HA plays a major role in the molecular sieve.

Interplay of Plasmodium falciparum and thrombin in brain endothelial barrier disruption

Recent concepts suggest that both Plasmodium falciparum factors and coagulation contribute to endothelial activation and dysfunction in pediatric cerebral malaria (CM) pathology. However, there is still limited understanding of how these complex inflammatory stimuli are integrated by brain endothelial cells. In this study, we examined how mature-stage P. falciparum infected erythrocytes (IE) interact with tumor necrosis factor α (TNFα) and thrombin in the activation and permeability of primary human brain microvascular endothelial cell (HBMEC) monolayers. Whereas trophozoite-stage P. falciparum-IE have limited effect on the viability of HBMEC or the secretion of pro-inflammatory cytokines or chemokines, except at super physiological parasite-host cell ratios, schizont-stage P. falciparum-IE induced low levels of cell death. Additionally, schizont-stage parasites were more barrier disruptive than trophozoite-stage P. falciparum-IE and prolonged thrombin-induced barrier disruption in both resting and TNFα-activated HBMEC monolayers. These results provide evidence that parasite products and thrombin may interact to increase brain endothelial permeability.

Tumor Cell Mechanosensing During Incorporation into the Brain Microvascular Endothelium.

Tumor metastasis to the brain occurs in approximately 20% of all cancer cases and often occurs due to tumor cells crossing the blood-brain barrier (BBB). The brain microenvironment is comprised of a soft hyaluronic acid (HA)-rich extracellular matrix with an elastic modulus of 0.1-1kPa, whose crosslinking is often altered in disease states. To explore the effects of HA crosslinking on breast tumor cell migration, we developed a biomimetic model of the human brain endothelium, consisting of brain microvascular endothelial cell (HBMEC) monolayers on HA and gelatin (HA/gelatin) films with different degrees of crosslinking, as established by varying the concentration of the crosslinker Extralink. Metastatic breast tumor cell migration speed, diffusion coefficient, spreading area, and aspect ratio increased with decreasing HA crosslinking, a mechanosensing trend that correlated with tumor cell actin organization but not CD44 expression. Meanwhile, breast tumor cell incorporation into endothelial monolayers was independent of HA crosslinking density, suggesting that alterations in HA crosslinking density affect tumor cells only after they exit the vasculature. Tumor cells appeared to exploit both the paracellular and transcellular routes of trans-endothelial migration. Quantitative phenotyping of HBMEC junctions via a novel Python software revealed a VEGF-dependent decrease in punctate VE-cadherin junctions and an increase in continuous and perpendicular junctions when HBMECs were treated with tumor cell-secreted factors. Overall, our quantitative results suggest that a combination of biochemical and physical factors promote tumor cell migration through the BBB.

A streptococcal Fic domain-containing protein disrupts blood-brain barrier integrity by activating moesin in endothelial cells.

Streptococcus equi subsp. zooepidemicus (SEZ) is a zoonotic pathogen capable of causing meningitis in humans. The mechanisms that enable pathogens to traverse the blood-brain barrier (BBB) are incompletely understood. Here, we investigated the role of a newly identified Fic domain-containing protein, BifA, in SEZ virulence. BifA was required for SEZ to cross the BBB and to cause meningitis in mice. BifA also enhanced SEZ translocation across human Brain Microvascular Endothelial Cell (hBMEC) monolayers. Purified BifA or its Fic domain-containing C-terminus alone were able to enter into hBMECs, leading to disruption of monolayer barrier integrity. A SILAC-based proteomic screen revealed that BifA binds moesin. BifA’s Fic domain was required for its binding to this regulator of host cell cytoskeletal processes. BifA treatment of hBMECs led to moesin phosphorylation and downstream RhoA activation. Inhibition of moesin activation or moesin depletion in hBMEC monolayers abrogated BifA-mediated increases in barrier permeability and SEZ’s capacity to translocate across monolayers. Thus, BifA activation of moesin appears to constitute a key mechanism by which SEZ disrupts endothelial monolayer integrity to penetrate the BBB.

Dopamine Regulates Blood‐Brain Barrier Endothelial Cell Hyperpermeability

Blood‐Brain Barrier (BBB) dysfunction leading to hyperpermeability is one of the major causes of brain edema following conditions such as traumatic and ischemic brain injury. The BBB consists of microvascular endothelial cells that are linked to each other by tight junction and adherens junction proteins and are intracellularly linked to actin cytoskeletal assembly of the cell mainly via zonula occludens‐1 (ZO‐1). Recent studies suggest that the activation of the NLRP3 inflammasome pathway has a major role promoting various pathologies associated with brain injury. An inflammasome is a multiprotein complex that is responsible for the activation of inflammatory responses in the body. Recent studies show that the neurotransmitter, dopamine (DA) is an inhibitor of this pathway. Dopamine regulates bodily functions such as movement, behavior and many systemic functions, but also connects the nervous and immune system in the body. In this study we investigated the effects of DA for its protective effect against oxidative stress‐induced BBB dysfunction and hyperpermeability. In the experiments, hydrogen peroxide (H2O2) was used to induce oxidative stress in rat brain microvascular endothelial cells. Oxidative stress due to increased reactive oxygen species (ROS) formation occurs following trauma and ischemia. Rat brain microvascular endothelial cell monolayers were exposed to H2O2 alone (100μM; 2 hour) or in presence of DA (10μg/ml; 30min) or dopamine D1 receptor agonist (A68930; 10μg/ml; 30min). The changes in tight junction integrity and cytoskeletal assembly were studied using ZO‐1 and β‐catenin immunofluorescence and rhodamine phalloidin staining for F‐actin respectively. Cell viability was studied using Calcein AM cell viability assay. Changes in the formation ROS were studied using 2′, 7′‐dichlorofluorescien diacetate. H2O2 (100μM) treatment resulted in significant increase in monolayer permeability (p&lt;0.05), ROS formation (p&lt;0.05), disruption of the endothelial tight/adherens junctions and induced F‐actin stress fiber formation. Dopamine and A68930 treatment resulted in a decrease in H2O2‐induced monolayer hyperpermeability significantly (p&lt;0.05). Furthermore, DA protected tight junction integrity and actin cytoskeletal assembly. DA and A68930 had no effect on H2O2‐induced ROS formation. The cell viability assay showed that H2O2‐induced barrier disruption is independent of cell death. Our results suggest that one of the major mechanisms for DA‐mediated protection against barrier dysfunction/hyperpermeability may be mediated via inhibiting the NLRP3 inflammasome pathway and not by inhibiting increased ROS formation.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Oxygen-Glucose Deprivation/Reoxygenation-Induced Barrier Disruption at the Human Blood-Brain Barrier is Partially Mediated Through the HIF-1 Pathway.

The blood-brain barrier (BBB) plays an important role in brain homeostasis. Hypoxia/ischemia constitutes an important stress factor involved in several neurological disorders by inducing the disruption of the BBB, ultimately leading to cerebral edema formation. Yet, our current understanding of the cellular and molecular mechanisms underlying the BBB disruption following cerebral hypoxia/ischemia remains limited. Stem cell-based models of the human BBB present some potentials to address such issues. Yet, such models have not been validated in regard of its ability to respond to hypoxia/ischemia as existing models. In this study, we investigated the cellular response of two iPSC-derived brain microvascular endothelial cell (BMEC) monolayers to respond to oxygen-glucose deprivation (OGD) stress, using two induced pluripotent stem cells (iPSC) lines. iPSC-derived BMECs responded to prolonged (24h) and acute (6h) OGD by showing a decrease in the barrier function and a decrease in tight junction complexes. Such iPSC-derived BMECs responded to OGD stress via a partial activation of the HIF-1 pathway, whereas treatment with anti-angiogenic pharmacological inhibitors (sorafenib, sunitinib) during reoxygenation worsened the barrier function. Taken together, our results suggest such models can respond to hypoxia/ischemia similarly to existing in vitro models and support the possible use of this model as a screening platform for identifying novel drug candidates capable to restore the barrier function following hypoxic/ischemic injury.

MiR-27a-3p protects against blood–brain barrier disruption and brain injury after intracerebral hemorrhage by targeting endothelial aquaporin-11

Previous studies have reported that miR-27a-3p is down-regulated in the serum of patients with intracerebral hemorrhage (ICH), but the implication of miR-27a-3p down-regulation in post-ICH complications remains elusive. Here we verified miR-27a-3p levels in the serum of ICH patients by real-time PCR and observed that miR-27a-3p is also significantly reduced in the serum of these patients. We then further investigated the effect of miR-27a-3p on post-ICH complications by intraventricular administration of a miR-27a-3p mimic in rats with collagenase-induced ICH. We found that the hemorrhage markedly reduced miR-27a-3p levels in the hematoma, perihematomal tissue, and serum and that intracerebroventricular administration of the miR-27a-3p mimic alleviated behavioral deficits 24 h after ICH. Moreover, ICH-induced brain edema, vascular leakage, and leukocyte infiltration were also attenuated by this mimic. Of note, miR-27a-3p mimic treatment also inhibited neuronal apoptosis and microglia activation in the perihematomal zone. We further observed that the miR-27a-3p mimic suppressed the up-regulation of aquaporin-11 (AQP11) in the perihematomal area and in rat brain microvascular endothelial cells (BMECs). Moreover, miR-27a-3p down-regulation increased BMEC monolayer permeability and impaired BMEC proliferation and migration. In conclusion, miR-27a-3p down-regulation contributes to brain edema, blood-brain barrier disruption, neuron loss, and neurological deficits following ICH. We conclude that application of exogenous miR-27a-3p may protect against post-ICH complications by targeting AQP11 in the capillary endothelial cells of the brain.

A passive diffusion model of fluorescein derivatives in an in vitro human brain microvascular endothelial cell (HBMEC) monolayer

Eukaryotic cells have a protective plasma membrane, which restricts the free movement of molecules from the external environment to the internal environment. This study aims to computationally model the transport of fluorescein derivatives across the monolayer of human brain microvascular endothelial cells (HBMEC). The determination of plausible effective diffusion constants (Deff) will allow models to be built that could be useful beyond in vitro experimentation. Fluorescein-5-isothiocyanate (FITC) modeling produced a Deff range of 1E-20 to 5E-20 cm2/s at a 1 µm cell monolayer thickness and a Deff constant near 5E-29 cm2/s at a 5 µm cell monolayer thickness. Both fluorescein and sodium fluorescein (NaFl) modeling at the 1 and 5 µm thicknesses did not produce simulations that closely resembled the HBMEC in vitro model. Overall, it is possible that the fluorescent intensity noted with fluorescein and NaFl may be better explained by a mechanism other than passive diffusion. Simulations of FITC diffusion produced a narrow range of Deff constants that closely matched the in vitro HBMEC fluorescent intensity.

Gliotoxin penetrates and impairs the integrity of the human blood-brain barrier in vitro.

Cerebral fungal infections represent an important public health concern, where a key element of pathophysiology is the ability of the fungi to cross the blood-brain barrier (BBB). Yet the mechanism used by micro-organisms to cross such a barrier and invade the brain parenchyma remains unclear. This study investigated the effects of gliotoxin (GTX), a mycotoxin secreted by Aspergillus fumigatus, on the BBB using brain microvascular endothelial cells (BMECs) derived from induced pluripotent stem cells (iPSCs). We observed that both acute (2h) and prolonged (24h) exposure to GTX at the level of 1μM or higher compromised BMECs monolayer integrity. Notably, acute exposure was sufficient to disrupt the barrier function in iPSC-derived BMECs, resulting in decreased transendothelial electrical resistance (TEER) and increased fluorescein permeability. Further, our data suggest that such disruption occurred without affecting tight junction complexes, via alteration of cell-matrix interactions, alterations in F-actin distribution, through a protein kinase C-independent signaling. In addition to its effect on the barrier function, we have observed a low permeability of GTX across the BBB. This fact can be partially explained by possible interactions of GTX with membrane proteins. Taken together, this study suggests that GTX may contribute in cerebral invasion processes of Aspergillus fumigatus by altering the blood-brain barrier integrity without disrupting tight junction complexes.