Viral entry and translation in brain endothelia provoke influenza-associated encephalopathy

Influenza-associated encephalopathy (IAE) is extremely acute in onset, with high lethality and morbidity within a few days, while the direct pathogenesis by influenza virus in this acute phase in the brain is largely unknown. Here we show that influenza virus enters into the cerebral endothelium and thereby induces IAE. Three-weeks-old young mice were inoculated with influenza A virus (IAV). Physical and neurological scores were recorded and temporal-spatial analyses of histopathology and viral studies were performed up to 72 h post inoculation. Histopathological examinations were also performed using IAE human autopsy brains. Viral infection, proliferation and pathogenesis were analyzed in cell lines of endothelium and astrocyte. The effects of anti-influenza viral drugs were tested in the cell lines and animal models. Upon intravenous inoculation of IAV in mice, the mice developed encephalopathy with brain edema and pathological lesions represented by micro bleeding and injured astrocytic process (clasmatodendrosis) within 72 h. Histologically, massive deposits of viral nucleoprotein were observed as early as 24 h post infection in the brain endothelial cells of mouse models and the IAE patients. IAV inoculated endothelial cell lines showed deposition of viral proteins and provoked cell death, while IAV scarcely amplified. Inhibition of viral transcription and translation suppressed the endothelial cell death and the lethality of mouse models. These data suggest that the onset of encephalopathy should be induced by cerebral endothelial infection with IAV. Thus, IAV entry into the endothelium, and transcription and/or translation of viral RNA, but not viral proliferation, should be the key pathogenesis of IAE.

Subcellular trafficking and transcytosis efficacy of different receptor types for therapeutic antibody delivery at the blood‒brain barrier

Here, we report an experimental setup to benchmark different receptors for targeted therapeutic antibody delivery at the blood-brain barrier. We used brain capillary endothelial-like cells derived from induced pluripotent stem cells (hiPSC-BECs) as a model system and compared them to colon epithelial Caco-2 cells. This approach helped to identify favourable receptors for transport into the cell layer itself or for directing transport for transcytosis across the cell layer. The sorting receptors transferrin receptor and sortilin were shown to be efficient as antibody cargo receptors for intracellular delivery to the cell layer. In contrast, the cell surface receptors CD133 and podocalyxin were identified as static and inefficient receptors for delivering cargo antibodies. Similar to in vivo studies, the hiPSC-BECs maintained detectable transcytotic transport via transferrin receptor, while transcytosis was restricted using sortilin as a cargo receptor. Based on these findings, we propose the application of sortilin as a cargo receptor for delivering therapeutic antibodies into the brain microvascular endothelium.

Chronic kidney disease promotes cerebral microhemorrhage formation

BACKGROUND

Chronic kidney disease (CKD) is increasingly recognized as a stroke risk factor, but its exact relationship with cerebrovascular disease is not well-understood. We investigated the development of cerebral small vessel disease using in vivo and in vitro models of CKD.

METHODS

CKD was produced in aged C57BL/6J mice using an adenine-induced tubulointerstitial nephritis model. We analyzed brain histology using Prussian blue staining to examine formation of cerebral microhemorrhage (CMH), the hemorrhagic component of small vessel disease and the neuropathological substrate of MRI-demonstrable cerebral microbleeds. In cell culture studies, we examined effects of serum from healthy or CKD patients and gut-derived uremic toxins on brain microvascular endothelial barrier.

RESULTS

CKD was induced in aged C57BL/6J mice with significant increases in both serum creatinine and cystatin C levels (p < 0.0001) without elevation of systolic or diastolic blood pressure. CMH was significantly increased and positively correlated with serum creatinine level (Spearman r = 0.37, p < 0.01). Moreover, CKD significantly increased Iba-1-positive immunoreactivity by 51% (p < 0.001), induced a phenotypic switch from resting to activated microglia, and enhanced fibrinogen extravasation across the blood-brain barrier (BBB) by 34% (p < 0.05). On analysis stratified by sex, the increase in CMH number was more pronounced in male mice and this correlated with greater creatinine elevation in male compared with female mice. Microglial depletion with PLX3397 diet significantly decreased CMH formation in CKD mice without affecting serum creatinine levels. Incubation of CKD serum significantly reduced transendothelial electrical resistance (TEER) (p < 0.01) and increased sodium fluorescein permeability (p < 0.05) across the endothelial monolayer. Uremic toxins (i.e., indoxyl sulfate, p-cresyl sulfate, and trimethylamine-N-oxide) in combination with urea and lipopolysaccharide induced a marked drop in TEER compared with the control group (p < 0.0001).

CONCLUSIONS

CKD promotes the development of CMH in aged mice independent of blood pressure but directly proportional to the degree of renal impairment. These effects of CKD are likely mediated in part by microglia and are associated with BBB impairment. The latter is likely related to gut-derived bacteria-dependent toxins classically associated with CKD. Overall, these findings demonstrate an important role of CKD in the development of cerebral small vessel disease.

Apicobasal transferrin receptor localization and trafficking in brain capillary endothelial cells

The detailed mechanisms by which the transferrin receptor (TfR) and associated ligands traffic across brain capillary endothelial cells (BECs) of the CNS-protective blood-brain barrier constitute an important knowledge gap within maintenance and regulation of brain iron homeostasis. This knowledge gap also presents a major obstacle in research aiming to develop strategies for efficient receptor-mediated drug delivery to the brain. While TfR-mediated trafficking from blood to brain have been widely studied, investigation of TfR-mediated trafficking from brain to blood has been limited. In this study we investigated TfR distribution on the apical and basal plasma membranes of BECs using expansion microscopy, enabling sufficient resolution to separate the cellular plasma membranes of these morphological flat cells, and verifying both apical and basal TfR membrane domain localization. Using immunofluorescence-based transcellular transport studies, we delineated endosomal sorting of TfR endocytosed from the apical and basal membrane, respectively, as well as bi-directional TfR transcellular transport capability. The findings indicate different intracellular sorting mechanisms of TfR, depending on the apicobasal trafficking direction across the BBB, with the highest transcytosis capacity in the brain-to-blood direction. These results are of high importance for the current understanding of brain iron homeostasis. Also, the high level of TfR trafficking from the basal to apical membrane of BECs potentially explains the low transcytosis which are observed for the TfR-targeted therapeutics to the brain parenchyma.

Development of a multicellular in vitro model of the meningeal blood-CSF barrier to study Neisseria meningitidis infection

Background

Bacterial meningitis is a life-threatening disease that occurs when pathogens such as Neisseria meningitidis cross the meningeal blood cerebrospinal fluid barrier (mBCSFB) and infect the meninges. Due to the human-specific nature of N. meningitidis, previous research investigating this complex host–pathogen interaction has mostly been done in vitro using immortalized brain endothelial cells (BECs) alone, which often do not retain relevant barrier properties in culture. Here, we developed physiologically relevant mBCSFB models using BECs in co-culture with leptomeningeal cells (LMCs) to examine N. meningitidis interaction.

Methods

We used BEC-like cells derived from induced pluripotent stem cells (iBECs) or hCMEC/D3 cells in co-culture with LMCs derived from tumor biopsies. We employed TEM and structured illumination microscopy to characterize the models as well as bacterial interaction. We measured TEER and sodium fluorescein (NaF) permeability to determine barrier tightness and integrity. We then analyzed bacterial adherence and penetration of the cell barrier and examined changes in host gene expression of tight junctions as well as chemokines and cytokines in response to infection.

Results

Both cell types remained distinct in co-culture and iBECs showed characteristic expression of BEC markers including tight junction proteins and endothelial markers. iBEC barrier function as determined by TEER and NaF permeability was improved by LMC co-culture and remained stable for seven days. BEC response to N. meningitidis infection was not affected by LMC co-culture. We detected considerable amounts of BEC-adherent meningococci and a relatively small number of intracellular bacteria. Interestingly, we discovered bacteria traversing the BEC-LMC barrier within the first 24 h post-infection, when barrier integrity was still high, suggesting a transcellular route for N. meningitidis into the CNS. Finally, we observed deterioration of barrier properties including loss of TEER and reduced expression of cell-junction components at late time points of infection.

Conclusions

Here, we report, for the first time, on co-culture of human iPSC derived BECs or hCMEC/D3 with meningioma derived LMCs and find that LMC co-culture improves barrier properties of iBECs. These novel models allow for a better understanding of N. meningitidis interaction at the mBCSFB in a physiologically relevant setting.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00379-z.

Engineering Extracellular Vesicles to Modulate Their Innate Mitochondrial Load

Introduction

Extracellular vesicles (EVs) are promising carriers for the delivery of biotherapeutic cargo such as RNA and proteins. We have previously demonstrated that the innate EV mitochondria in microvesicles (MVs), but not exosomes (EXOs) can be transferred to recipient BECs and mouse brain slice neurons. Here, we sought to determine if the innate EV mitochondrial load can be further increased via increasing mitochondrial biogenesis in the donor cells. We hypothesized that mitochondria-enriched EVs ("mito-EVs") may increase the recipient BEC ATP levels to a greater extent than naïve MVs.

Methods

We treated NIH/3T3, a fibroblast cell line and hCMEC/D3, a human brain endothelial cell (BEC) line using resveratrol to activate peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), the central mediator of mitochondrial biogenesis. Naïve EVs and mito-EVs isolated from the non-activated and activated donor cells were characterized using transmission electron microscopy, dynamic light scattering and nanoparticle tracking analysis. The effect of mito-EVs on resulting ATP levels in the recipient BECs were determined using Cell Titer Glo ATP assay. The uptake of Mitotracker Red-stained EVs into recipient BECs and their colocalization with recipient BEC mitochondria were studied using flow cytometry and fluorescence microscopy.

Results

Resveratrol treatment increased PGC-1α expression in the donor cells. Mito-MVs but not mito-EXOs showed increased expression of mitochondrial markers ATP5A and TOMM20 compared to naïve MVs. TEM images showed that a greater number of mito-MVs contained mitochondria compared to naïve MVs. Mito-MVs but not mito-EXOs showed a larger particle diameter compared to their naïve EV counterparts from the non-activated cells suggesting increased mitochondria incorporation. Mito-EVs were generated at higher particle concentrations compared to naïve EVs from non-activated cells. Mito-EVs increased the cellular ATP levels and transferred their mitochondrial load into the recipient BECs. Mito-MV mitochondria also colocalized with recipient BEC mitochondria.

Conclusions

Our results suggest that the pharmacological modulation of mitochondrial biogenesis in the donor cells can change the mitochondrial load in the secreted MVs. Outcomes of physicochemical characterization studies and biological assays confirmed the superior effects of mito-MVs compared to naïve MVs-suggesting their potential to improve mitochondrial function in neurovascular and neurodegenerative diseases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-022-00738-8.

Structurally related (-)-epicatechin metabolites and gut microbiota derived metabolites exert genomic modifications via VEGF signaling pathways in brain microvascular endothelial cells under lipotoxic conditions: Integrated multi-omic study

Dysfunction of blood-brain barrier formed by endothelial cells of cerebral blood vessels, plays a key role in development of neurodegenerative disorders. Epicatechin exerts vasculo-protective effects through genomic modifications, however molecular mechanisms of action, particularly on brain endothelial cells, are largely unknow. This study aimed to use a multi-omic approach (transcriptomics of mRNA, miRNAs and lncRNAs, and proteomics), to provide novel in-depth insights into molecular mechanisms of how metabolites affect brain endothelial cells under lipid-stressed (as a model of BBB dysfunction) at physiological concentrations. We showed that metabolites can simultaneously modulate expression of protein-coding, non-coding genes and proteins. Integrative analysis revealed interactions between different types of RNAs and form functional groups of genes involved in regulation of processing like VEGF-related functions, cell signaling, cell adhesion and permeability. Molecular modeling of genomics data predicted that metabolites decrease endothelial cell permeability, increased by lipotoxic stress. Correlation analysis between genomic modifications observed and genomic signature of patients with vascular dementia and Alzheimer's diseases showed opposite gene expression changes. Taken together, this study describes for the first time a multi-omic mechanism of action by which (-)-epicatechin metabolites could preserve brain vascular endothelial cell integrity and reduce the risk of neurodegenerative diseases. SIGNIFICANCE: Dysfunction of the blood-brain barrier (BBB), characterized by dysfunction of endothelial cells of cerebral blood vessels, result in an increase in permeability and neuroinflammation which constitute a key factor in the development neurodegenerative disorders. Even though it is suggested that polyphenols can prevent or delay the development of these disorders, their impact on brain endothelial cells and underlying mechanisms of actions are unknow. This study aimed to use a multi-omic approach including analysis of expression of mRNA, microRNA, long non-coding RNAs, and proteins to provide novel global in-depth insights into molecular mechanisms of how (-)-epicatechin metabolites affect brain microvascular endothelial cells under lipid-stressed (as a model of BBB dysfunction) at physiological relevant conditions. The results provide basis of knowledge on the capacity of polyphenols to prevent brain endothelial dysfunction and consequently neurodegenerative disorders.

Argonaute-2 protects the neurovascular unit from damage caused by systemic inflammation

BACKGROUND

The brain vasculature plays a pivotal role in the inflammatory process by modulating the interaction between blood cells and the neurovascular unit. Argonaute-2 (Ago2) has been suggested as essential for endothelial survival but its role in the brain vasculature or in the endothelial-glial crosstalk has not been addressed. Thus, our aim was to clarify the significance of Ago2 in the inflammatory responses elicited by these cell types.

METHODS

Mouse primary cultures of brain endothelial cells, astrocytes and microglia were used to evaluate cellular responses to the modulation of Ago2. Exposure of microglia to endothelial cell-conditioned media was used to assess the potential for in vivo studies. Adult mice were injected intraperitoneally with lipopolysaccharide (LPS) (2 mg/kg) followed by three daily intraperitoneal injections of Ago2 (0.4 nM) to assess markers of endothelial disruption, glial reactivity and neuronal function.

RESULTS

Herein, we demonstrated that LPS activation disturbed the integrity of adherens junctions and downregulated Ago2 in primary brain endothelial cells. Exogenous treatment recovered intracellular Ago2 above control levels and recuperated vascular endothelial-cadherin expression, while downregulating LPS-induced nitric oxide release. Primary astrocytes did not show a significant change in Ago2 levels or response to the modulation of the Ago2 system, although endogenous Ago2 was shown to be critical in the maintenance of tumor necrosis factor-α basal levels. LPS-activated primary microglia overexpressed Ago2, and Ago2 silencing contained the inflammatory response to some extent, preventing interleukin-6 and nitric oxide release. Moreover, the secretome of Ago2-modulated brain endothelial cells had a protective effect over microglia. The intraperitoneal injection of LPS impaired blood-brain barrier and neuronal function, while triggering inflammation, and the subsequent systemic administration of Ago2 reduced or normalized endothelial, glial and neuronal markers of LPS damage. This outcome likely resulted from the direct action of Ago2 over the brain endothelium, which reestablished glial and neuronal function.

CONCLUSIONS

Ago2 could be regarded as a putative therapeutic agent, or target, in the recuperation of the neurovascular unit in inflammatory conditions.

Selegiline Protects Against Lipopolysaccharide (LPS)-Induced Impairment of the Blood-Brain Barrier Through Regulating the NF-κB/MLCK/p-MLC Signaling Pathway

Disruption of the blood-brain barrier (BBB) is an important hallmark of sepsis-associated encephalopathy (SAE). Selegiline, a selective and irreversible inhibitor of monoamine oxidase type B, has been applied for the treatment of nervous disorders. In this study, we aimed to investigate whether selegiline has a protective capacity in the impairment of the BBB in both in vivo and in vitro experiments. In a sepsis mouse model, administration of selegiline ameliorated lipopolysaccharide (LPS)-induced impairment of BBB integrity. Additionally, treatment with selegiline increased the expression of the tight junction protein junctional adhesion molecule A (JAM-A) against LPS. Also, we found that selegiline inhibited the production of the proinflammatory cytokines tumor necrosis factor (TNF)-α and interleukin (IL)-1β. In an in vitro experimental model, bEnd.3 brain endothelial cells were exposed to LPS. Results indicate that stimulation with LPS significantly increased the permeability of bEnd.3 cells and reduced the expression of JAM-A, both of which were rescued by treatment with selegiline. Additionally, selegiline prevented the activation of the NF-κB/MLCK/p-MLC signaling pathway in LPS-challenged bEnd.3 cells. These results indicate that selegiline exerted a protective effect on BBB dysfunction, which might be attributed to the inhibition of the NF-κB/MLCK/p-MLC signaling pathway. These findings provide a basis for further research into the neuroprotective mechanism of selegiline.

Induced Pluripotent Stem Cell (iPSC)-Derived Endothelial Cells to Study Bacterial-Brain Endothelial Cell Interactions

Bacterial meningitis is a serious infection of the central nervous system (CNS) that occurs when blood-borne bacteria are able to exit the cerebral vasculature and cause inflammation. The blood-brain barrier (BBB) and the meningeal blood-CSF barrier (mBCSFB) are composed of highly specialized brain endothelial cells (BECs) that possess unique phenotypes when compared to their peripheral endothelial counterparts. To cause meningitis, bacterial pathogens must be able to interact and penetrate these specialized BECs to gain access to the CNS. In vitro models have been employed to study bacterial-BEC interactions; however, many lack BEC phenotypes. Induced pluripotent stem cell (iPSC) technologies have enabled the derivation of brain endothelial-like cells that phenocopy BECs in culture. Recently, these iPSC-BECs have been employed to examine the host-pathogen interaction at the endothelial brain barriers. Using two clinically relevant human meningeal pathogens, this chapter describes the use of iPSC-BECs to study various aspects of BEC-bacterial interaction.

An In Vitro Blood-Brain Barrier Model to Study Firm Shear Stress-Resistant Leukocyte Adhesion to Human Brain Endothelial Cells

Adhesion between leukocytes and brain endothelial cells, which line cerebral blood vessels, is a key event in both physiological and pathological conditions such as neuroinflammatory diseases. Leukocyte recruitment from blood into tissues is described as a multistep process involving leukocyte rolling on endothelial cells, adhesion, crawling, and diapedesis under hemodynamic shear stress. In neuroinflammatory conditions, there is an increase in leukocyte adhesion to the brain endothelial cells, activated by proinflammatory molecules such as cytokines. Here, we describe an in vitro technique to study the interaction between human leukocytes with human brain endothelial cells under shear stress mimicking the blood flow in vivo, coupled to live-cell imaging.

Ramelteon Mitigates Free Fatty Acid (FFA)-Induced Attachment of Monocytes to Brain Vascular Endothelial Cells

Acute ischemic stroke is a challenging disease that threatens the life of older people. Dysfunction of brain endothelial cells is reported to be involved in the pathogenesis of acute ischemic stroke. Ramelteon is a novel agonist of melatonin receptor developed for the treatment of insomnia. Recently, the promising protective effect of Ramelteon on brain injury has been widely reported. The present study aims to investigate the protective effect of Ramelteon against free fatty acid (FFA)-induced damages in brain vascular endothelial cells and the underlying mechanism. Firstly, we discovered that Ramelteon administration remarkably reversed the decreased cell viability, increased LDH release, activated oxidative stress, and excessive released inflammatory factors caused by FFAs. Secondly, Ramelteon extensively suppressed the attachment of U937 monocytes to bEnd.3 brain endothelial cells induced by FFAs. In addition, the elevated expression of E-selectin and the reduced expression of KLF2 induced by FFAs were pronouncedly alleviated by Ramelteon. Lastly, silencing of KLF2 abolished the protective effects of Ramelteon against FFA-induced expression of E-selectin and the attachment of U937 monocytes to bEnd.3 brain endothelial cells. In conclusion, Ramelteon mitigated FFA-induced attachment of monocytes to brain vascular endothelial cells by increasing the expression of KLF2 and reducing the expression of E-selectin.

Characterization of the blood-brain barrier in genetically diverse laboratory mouse strains

Background

Genetic variation in a population has an influence on the manifestation of monogenic as well as multifactorial disorders, with the underlying genetic contribution dependent on several interacting variants. Common laboratory mouse strains used for modelling human disease lack the genetic variability of the human population. Therefore, outcomes of rodent studies show limited relevance to human disease. The functionality of brain vasculature is an important modifier of brain diseases. Importantly, the restrictive interface between blood and brain—the blood–brain barrier (BBB) serves as a major obstacle for the drug delivery into the central nervous system (CNS). Using genetically diverse mouse strains, we aimed to investigate the phenotypic and transcriptomic variation of the healthy BBB in different inbred mouse strains.

Methods

We investigated the heterogeneity of brain vasculature in recently wild-derived mouse strains (CAST/EiJ, WSB/EiJ, PWK/PhJ) and long-inbred mouse strains (129S1/SvImJ, A/J, C57BL/6J, DBA/2J, NOD/ShiLtJ) using different phenotypic arms. We used immunohistochemistry and confocal laser microscopy followed by quantitative image analysis to determine vascular density and pericyte coverage in two brain regions—cortex and hippocampus. Using a low molecular weight fluorescence tracer, sodium fluorescein and spectrophotometry analysis, we assessed BBB permeability in young and aged mice of selected strains. For further phenotypic characterization of endothelial cells in inbred mouse strains, we performed bulk RNA sequencing of sorted endothelial cells isolated from cortex and hippocampus.

Results

Cortical vessel density and pericyte coverage did not differ among the investigated strains, except in the cortex, where PWK/PhJ showed lower vessel density compared to NOD/ShiLtJ, and a higher pericyte coverage than DBA/2J. The vascular density in the hippocampus differed among analyzed strains but not the pericyte coverage. The staining patterns of endothelial arteriovenous zonation markers were similar in different strains. BBB permeability to a small fluorescent tracer, sodium fluorescein, was also similar in different strains, except in the hippocampus where the CAST/EiJ showed higher permeability than NOD/ShiLtJ. Transcriptomic analysis of endothelial cells revealed that sex of the animal was a major determinant of gene expression differences. In addition, the expression level of several genes implicated in endothelial function and BBB biology differed between wild-derived and long-inbred mouse strains. In aged mice of three investigated strains (DBA/2J, A/J, C57BL/6J) vascular density and pericyte coverage did not change—expect for DBA/2J, whereas vascular permeability to sodium fluorescein increased in all three strains.

Conclusions

Our analysis shows that although there were no major differences in parenchymal vascular morphology and paracellular BBB permeability for small molecular weight tracer between investigated mouse strains or sexes, transcriptomic differences of brain endothelial cells point to variation in gene expression of the intact BBB. These baseline variances might be confounding factors in pathological conditions that may lead to a differential functional outcome dependent on the sex or genetic polymorphism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00269-w.

The Protective Effects of Ramelteon Against Isoflurane-Induced Insults and Inflammatory Response in Brain Microvascular Endothelial Cells

Anesthetic-induced cognitive impairment has been observed clinically. The mechanism underlying anesthetic-induced cognitive impairment is closely associated with neuronal apoptosis and neuroinflammation. Ramelteon is a potent and highly selective melatonin receptor agonist that has been used for the treatment of insomnia and has been reported to have an anti-inflammatory effect. In this study, we aimed to investigate the protective effects of Ramelteon against the cytotoxicity induced by isoflurane in brain microvascular endothelial cells. Our results show that Ramelteon ameliorated oxidative stress by suppressing the generation of mitochondrial reactive oxygen species (ROS) in human brain microvascular endothelial cells (HBMVECs). In addition, Ramelteon displayed a robust anti-inflammatory capacity against isoflurane-induced insults and inflammation by reducing the generation of interleukin-1β (IL-1β), transforming growth factor-β (TGF-β), monocyte chemotactic protein 1 (MCP-1), stromal cell-derived factor-1 (SDF-1), matrix metalloproteinase-2 (MMP-2), and MMP-9. Furthermore, Ramelteon reduced the expression of cell adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) and E-selectin. Importantly, Ramelteon downregulated the activation of the p38MAPK/NF-κB signaling pathway, which is the key transcriptional regulator in the inflammation process. Our findings in the present study provide new evidence for the use of Ramelteon in the prevention of isoflurane-induced insults in brain endothelial cells.

Vesicular Transport Machinery in Brain Endothelial Cells: What We Know and What We Do not

The vesicular transport machinery regulates numerous essential functions in cells such as cell polarity, signaling pathways, and the transport of receptors and their cargoes. From a pharmaceutical perspective, vesicular transport offers avenues to facilitate the uptake of therapeutic agents into cells and across cellular barriers. In order to improve receptor-mediated transcytosis of biologics across the blood-brain barrier and into the diseased brain, a detailed understanding of intracellular transport mechanisms is essential. The vesicular transport machinery is a highly complex network and involves an array of protein complexes, cytosolic adaptor proteins, and the subcellular structures of the endo-lysosomal system. The endo-lysosomal system includes several types of vesicular entities such as early, late, and recycling endosomes, exosomes, ectosomes, retromer-coated vesicles, lysosomes, trans-endothelial channels, and tubules. While extensive research has been done on the trafficking system in many cell types, little is known about vesicular trafficking in brain endothelial cells. Consequently, assumptions on the transport system in endothelial cells are based on findings in polarised epithelial cells, although recent studies have highlighted differences in the endothelial system. This review highlights aspects of the vesicular trafficking machinery in brain endothelial cells, including recent findings, limitations, and opportunities for further studies.

Protective effect of neuropeptide Y2 receptor activation against methamphetamine-induced brain endothelial cell alterations

Methamphetamine (METH) consumption is a health problem that leads to neurological and psychiatric disturbances. The cellular alterations behind these conditions have been extensively investigated and it is now well-established that METH causes cerebrovascular alterations being a key feature in drug-induced neuropathology. Although promising advances in understanding the blood-brain barrier (BBB) alterations induced by METH, there is still no available approach to counteract or diminish such effects. Interestingly, several studies show that neuropeptide Y (NPY) has an important protective role against METH-induced neuronal and glial toxicity, as well as behavioral deficits. Despite these beneficial effects of the NPY system, nothing is known about its role in brain endothelial cells under conditions of METH exposure. Thus, our aim was to unravel the effect of NPY and its receptors against METH-induced endothelial cell dysfunction. For that, we used a human brain microvascular endothelial cell line (hCMEC/D3) and our results demonstrate that endothelial cells express both NPY Y1 (Y1R) and Y2 (Y2R) receptors, but only Y2R is upregulated after METH exposure. Moreover, this drug of abuse induced endothelial cell death and elicited the production of reactive oxygen species (ROS) by these cells, which were prevented by the activation of Y2R. Additional, cell death and oxidative stress triggered by METH were dependent on the concentration of the drug. In sum, with the present study we identified for the first time the NPY system, and particularly the Y2R subtype, as a promising target to protect against METH-induced neurovascular dysfunction.

Sleep loss disrupts pericyte-brain endothelial cell interactions impairing blood-brain barrier function

Sleep loss in the rat increases blood-brain barrier permeability to circulating molecules by disrupting interendothelial tight junctions. Despite the description of the ultrastructure of cerebral microvessels and the evidence of an apparent pericyte detachment from capillary wall in sleep restricted rats the effect of sleep loss on pericytes is unknown. Here we characterized the interactions between pericytes and brain endothelial cells after sleep loss using male Wistar rats. Animals were sleep-restricted 20 h daily with 4 h sleep recovery for 10 days. At the end of the sleep restriction, brain microvessels (MVs) were isolated from cerebral cortex and hippocampus and processed for Western blot and immunocytochemistry to evaluate markers of pericyte-endothelial cell interaction (connexin 43, PDGFR-β), tight junction proteins, and proinflammatory mediator proteins (MMP9, A_2A adenosine receptor, CD73, NFκB). Sleep restriction reduced PDGFR-β and connexin 43 expression in MVs; in addition, scanning electron microscopy micrographs showed that pericytes were detached from capillary walls, but did not undergo apoptosis (as depicted by a reduced active caspase-3 expression). Sleep restriction also decreased tight junction protein expression in MVs and increased BBB permeability to low- and high-molecular weight tracers in in vivo permeability assays. Those alterations seemed to depend on a low-grade inflammatory status as reflected by the increased expression of phosphorylated NFκB and A_2A adenosine receptor in brain endothelial cells from the sleep-restricted rats. Our data show that pericyte-brain endothelial cell interaction is altered by sleep restriction; this evidence is essential to understand the role of sleep in regulating blood-brain barrier function.

Effects of Antimalarial Drugs on Neuroinflammation-Potential Use for Treatment of COVID-19-Related Neurologic Complications

The SARS-CoV-2 virus that is the cause of coronavirus disease 2019 (COVID-19) affects not only peripheral organs such as the lungs and blood vessels, but also the central nervous system (CNS)—as seen by effects on smell, taste, seizures, stroke, neuropathological findings and possibly, loss of control of respiration resulting in silent hypoxemia. COVID-19 induces an inflammatory response and, in severe cases, a cytokine storm that can damage the CNS. Antimalarials have unique properties that distinguish them from other anti-inflammatory drugs. (A) They are very lipophilic, which enhances their ability to cross the blood-brain barrier (BBB). Hence, they have the potential to act not only in the periphery but also in the CNS, and could be a useful addition to our limited armamentarium against the SARS-CoV-2 virus. (B) They are non-selective inhibitors of phospholipase A₂ isoforms, including cytosolic phospholipase A₂ (cPLA₂). The latter is not only activated by cytokines but itself generates arachidonic acid, which is metabolized by cyclooxygenase (COX) to pro-inflammatory eicosanoids. Free radicals are produced in this process, which can lead to oxidative damage to the CNS. There are at least 4 ways that antimalarials could be useful in combating COVID-19. (1) They inhibit PLA_2. (2) They are basic molecules capable of affecting the pH of lysosomes and inhibiting the activity of lysosomal enzymes. (3) They may affect the expression and Fe²⁺/H⁺ symporter activity of iron transporters such as divalent metal transporter 1 (DMT1), hence reducing iron accumulation in tissues and iron-catalysed free radical formation. (4) They could affect viral replication. The latter may be related to their effect on inhibition of PLA₂ isoforms. Inhibition of cPLA₂ impairs an early step of coronavirus replication in cell culture. In addition, a secretory PLA₂ (sPLA₂) isoform, PLA2G2D, has been shown to be essential for the lethality of SARS-CoV in mice. It is important to take note of what ongoing clinical trials on chloroquine and hydroxychloroquine can eventually tell us about the use of antimalarials and other anti-inflammatory agents, not only for the treatment of COVID-19, but also for neurovascular disorders such as stroke and vascular dementia.

Nrf2-regulated redox signaling in brain endothelial cells adapted to physiological oxygen levels: Consequences for sulforaphane mediated protection against hypoxia-reoxygenation

Ischemic stroke is associated with a surge in reactive oxygen species generation during reperfusion. The narrow therapeutic window for the delivery of intravenous thrombolysis and endovascular thrombectomy limits therapeutic options for patients. Thus, understanding the mechanisms regulating neurovascular redox defenses are key for improved clinical translation. Our previous studies in a rodent model of ischemic stroke established that activation of Nrf2 defense enzymes by pretreatment with sulforaphane (SFN) affords protection against neurovascular and neurological deficits. We here further investigate SFN mediated protection in mouse brain microvascular endothelial cells (bEnd.3) adapted long-term (5 days) to hyperoxic (18 kPa) and normoxic (5 kPa) O₂ levels. Using an O₂-sensitive phosphorescent nanoparticle probe, we measured an intracellular O₂ level of 3.4 ± 0.1 kPa in bEnd 3 cells cultured under 5 kPa O₂. Induction of HO-1 and GCLM by SFN (2.5 μM) was significantly attenuated in cells adapted to 5 kPa O₂, despite nuclear accumulation of Nrf2. To simulate ischemic stroke, bEnd.3 cells were adapted to 18 or 5 kPa O₂ and subjected to hypoxia (1 kPa O₂, 1 h) and reoxygenation. In cells adapted to 18 kPa O₂, reoxygenation induced free radical generation was abrogated by PEG-SOD and significantly attenuated by pretreatment with SFN (2.5 μM). Silencing Nrf2 transcription abrogated HO-1 and NQO1 induction and led to a significant increase in reoxygenation induced free radical generation. Notably, reoxygenation induced oxidative stress, assayed using the luminescence probe L-012 and fluorescence probes MitoSOX™ Red and FeRhoNox™-1, was diminished in cells cultured under 5 kPa O₂, indicating an altered redox phenotype in brain microvascular cells adapted to physiological normoxia. As redox and other intracellular signaling pathways are critically affected by O₂, the development of antioxidant therapies targeting the Keap1-Nrf2 defense pathway in treatment of ischemia-reperfusion injury in stroke, coronary and renal disease will require in vitro studies conducted under well-defined O₂ levels.

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Physiological normoxia alters the redox phenotype of murine microvascular brain endothelial cells.

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Intracellular GSH levels are lower in bEnd.3 cells adapted to 5 kPa versus 18 kPa O₂.

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Nrf2 activated HO-1 and GCLM expression is attenuated under physiological normoxia.

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Sulforaphane protects against reoxygenation induced reactive oxygen species generation via Nrf2.

Mapping Receptor Antibody Endocytosis and Trafficking in Brain Endothelial Cells

Drug delivery to the brain is a tremendous problem for the academic society and the industry. One solution with a huge potential is to use endocytic receptors as carriers. Here we describe how endocytic activity and subcellular trafficking of a specific receptor in brain endothelial cells can be characterized in three steps. (1) Labeling, endocytosis, and trafficking of a specific receptor at given time points in a pulse-chase experiment. (2) Fixed antibody labeling and co-staining of subcellular markers for image acquisition. (3) Analysis and quantification of co-localization between the receptor and subcellular markers in ImageJ.

Selective Regional Isolation of Brain Microvessels

The study of the regionalized function of the blood-brain barrier at the level of brain endothelial cells and pericytes is essential to understand the biological properties and molecular mechanisms regulating this biological barrier. The isolation of blood vessels from specific brain regions will allow to understand regional differences in susceptibility to pathological phenomena such as ischemia, traumatic brain injury, and neurodegenerative diseases, such as Alzheimer disease. Here, we propose an efficient and fast method to isolate brain endothelial cells and pericytes from a specific cerebral region. The isolated brain endothelial cells and pericytes are viable to perform conventional molecular and histological techniques such as Western blots, immunocytofluorescence, and scanning electron microscopy.

Brain Endothelial Cell-Derived Exosomes Induce Neuroplasticity in Rats with Ischemia/Reperfusion Injury

Exosomes derived from the cerebral endothelial cells play essential roles in protecting neurons from hypoxia injury, but little is known regarding the biological effects and mechanisms of exosomes on brain plasticity. In this study, exosomes were isolated from rodent cerebral endothelial cells (bEnd.3 cells) by ultracentrifugation, either endothelial cell-derived exosomes (EC-Exo) or PBS was injected intraventricularly 2 h after the middle cerebral artery occlusion/reperfusion (MCAO/R) model surgery in the Exo group and control group, respectively. Sham group rats received the same surgical but not ischemic procedure. We evaluated the motor function of rats after MCAO/R, and the foot-fault rate of the Exo group was significantly lower than that of the control group within 23 days (p < 0.05); the Catwalk analysis also showed gait difference between two groups (p < 0.05). On day 28 after MCAO/R, we euthanized the rats, removed the motor cortex from the brain, and then sequenced the genes by using GO and KEGG to find transcriptome analysis of biological terms and functional annotations: The pathway enrichment revealed that the function of synaptic transmission, regulation of synaptic plasticity, and regulation of synaptic vesicle cycle was significantly enriched with the Exo group than control group. Furthermore, the upregulation of synapsin-I expression in the motor cortex (p < 0.05) as well as the increase of the length of the dendrites were found in the Exo group (p < 0.05) than the control group. We determined the content of exosome microRNA levels, and microRNA-126-3p was the highest (TPM) by transcriptome analysis. Moreover, the microRNA-126-3p protected PC12 cells from apoptosis and increased neurite outgrowth, illustrating the mechanism of how exosomes play a role in altering brain plasticity. This study demonstrated that EC-Exo promoted functional motor recovery in the MCAO/R model, exosomes were critical for the reconstruction of synaptic function in ischemic brain injury, and microRNA-126-3p from EC-Exo could serve as a treatment for nerve damage.

Models of the blood-brain barrier using iPSC-derived cells

The blood-brain barrier (BBB) constitutes the interface between the blood and the brain tissue. Its primary function is to maintain the tightly controlled microenvironment of the brain. Models of the BBB are useful for studying the development and maintenance of the BBB as well as diseases affecting it. Furthermore, BBB models are important tools in drug development and support the evaluation of the brain-penetrating properties of novel drug molecules. Currently used in vitro models of the BBB include immortalized brain endothelial cell lines and primary brain endothelial cells of human and animal origin. Unfortunately, many cell lines and primary cells do not recreate physiological restriction of transport in vitro. Human-induced pluripotent stem cell (iPSC)-derived brain endothelial cells have proven a promising alternative source of brain endothelial-like cells that replicate tight cell layers with low paracellular permeability. Given the possibility to generate large amounts of human iPSC-derived brain endothelial cells they are a feasible alternative when modelling the BBB in vitro. iPSC-derived brain endothelial cells form tight cell layers in vitro and their barrier properties can be enhanced through coculture with other cell types of the BBB. Currently, many different models of the BBB using iPSC-derived cells are under evaluation to study BBB formation, maintenance, disruption, drug transport and diseases affecting the BBB. This review summarizes important functions of the BBB and current efforts to create iPSC-derived BBB models in both static and dynamic conditions. In addition, it highlights key model requirements and remaining challenges for human iPSC-derived BBB models in vitro.

Effects of the synthetic cannabinoid XLR-11 on the viability and migration rates of human brain microvascular endothelial cells in a clinically-relevant model

BACKGROUND

Synthetic cannabinoids (SCs) are a group of newly-developed drugs that bind and activate endocannabinoid system receptors. Angiogenesis is a biological process in which new blood vessels are formed from preexistent blood vessels. It plays a vital role in tissue growth, wound healing, and embryogenesis. This study aims to investigate the effects of the synthetic cannabinoid XLR-11 on specific cellular functions such as viability and angiogenesis in vitro.

METHODS

Human brain microvascular endothelial cells (HBMECs) were cultured in DMEM/F12 medium supplemented with an endothelial cell growth kit. The MTT assay was used to investigate the viability of endothelial cells. An endothelial cell migration assay was used to investigate migration ability, while a tube formation assay was used to investigate the angiogenic capacity of the endothelial cells.

RESULTS

XLR-11 was found to enhance the viability of HBMECs. Moreover, the migration rate and angiogenic capacity significantly increased in the presence of various concentrations of XLR-11 compared to the control.

CONCLUSION

The current study shows that XLR-11 increases the viability of human brain microvascular endothelial cells and enhances angiogenesis in the brain in vitro, suggesting that XLR-11 could potentially be used as a therapeutic angiogenic drug in human brain injury treatment.

The pivotal role of micro-environmental cells in a human blood-brain barrier in vitro model of cerebral ischemia: functional and transcriptomic analysis

Background

The blood–brain barrier (BBB) is altered in several diseases of the central nervous system. For example, the breakdown of the BBB during cerebral ischemia in stroke or traumatic brain injury is a hallmark of the diseases’ progression. This functional damage is one key event which is attempted to be mimicked in in vitro models. Recent studies showed the pivotal role of micro-environmental cells such as astrocytes for this barrier damage in mouse stroke in vitro models. The aim of this study was to evaluate the role of micro-environmental cells for the functional, paracellular breakdown in a human BBB cerebral ischemia in vitro model accompanied by a transcriptional analysis.

Methods

Transwell models with human brain endothelial cell line hCMEC/D3 in mono-culture or co-culture with human primary astrocytes and pericytes or rat glioma cell line C6 were subjected to oxygen/glucose deprivation (OGD). Changes of transendothelial electrical resistance (TEER) and FITC-dextran 4000 permeability were recorded as measures for paracellular tightness. In addition, qPCR and high-throughput qPCR Barrier chips were applied to investigate the changes of the mRNA expression of 38 relevant, expressed barrier targets (tight junctions, ABC-transporters) by different treatments.

Results

In contrast to the mono-culture, the co-cultivation with human primary astrocytes/pericytes or glioma C6 cells resulted in a significantly increased paracellular permeability after 5 h OGD. This indicated the pivotal role of micro-environmental cells for BBB breakdown in the human model. Hierarchical cluster analysis of qPCR data revealed differently, but also commonly regulated clustered targets dependent on medium exchange, serum reduction, hydrocortisone addition and co-cultivations.

Conclusions

The co-cultivation with micro-environmental cells is necessary to achieve a functional breakdown of the BBB in the cerebral ischemia model within an in vivo relevant time window. Comprehensive studies by qPCR revealed that distinct expression clusters of barrier markers exist and that these are regulated by different treatments (even by growth medium change) indicating that controls for single cell culture manipulation steps are crucial to understand the observed effects properly.

Simvastatin, edaravone and dexamethasone protect against kainate-induced brain endothelial cell damage

BACKGROUND

Excitotoxicity is a central pathological pathway in many neurological diseases with blood-brain barrier (BBB) dysfunction. Kainate, an exogenous excitotoxin, induces epilepsy and BBB damage in animal models, but the direct effect of kainate on brain endothelial cells has not been studied in detail. Our aim was to examine the direct effects of kainate on cultured cells of the BBB and to test three anti-inflammatory and antioxidant drugs used in clinical practice, simvastatin, edaravone and dexamethasone, to protect against kainate-induced changes.

METHODS

Primary rat brain endothelial cell, pericyte and astroglia cultures were used to study cell viability by impedance measurement. BBB permeability was measured on a model made from the co-culture of the three cell types. The production of nitrogen monoxide and reactive oxygen species was followed by fluorescent probes. The mRNA expression of kainate receptors and nitric oxide synthases were studied by PCR.

RESULTS

Kainate damaged brain endothelial cells and made the immunostaining of junctional proteins claudin-5 and zonula occludens-1 discontinuous at the cell border indicating the opening of the barrier. The permeability of the BBB model for marker molecules fluorescein and albumin and the production of nitric oxide in brain endothelial cells were increased by kainate. Simvastatin, edaravone and dexamethasone protected against the reduced cell viability, increased permeability and the morphological changes in cellular junctions caused by kainate. Dexamethasone attenuated the elevated nitric oxide production and decreased the inducible nitric oxide synthase (NOS2/iNOS) mRNA expression increased by kainate treatment.

CONCLUSION

Kainate directly damaged cultured brain endothelial cells. Simvastatin, edaravone and dexamethasone protected the BBB model against kainate-induced changes. Our results confirmed the potential clinical usefulness of these drugs to attenuate BBB damage.

Zafirlukast protects blood-brain barrier integrity from ischemic brain injury

Stroke has been considered the second leading cause of death worldwide, and ischemic stroke accounts for the vast majority of stroke cases. Some of the main features of ischemic stroke are increased brain permeability, ischemia/reperfusion injury, oxidative stress, and acute inflammation. Antagonism of cysLT1R has been shown to provide cardiovascular and neural benefits. In the present study, we investigated the effects of the cysLT1R antagonist zafirlukast both in vivo and in vitro using a middle cerebral artery occlusion (MCAO) mouse model and human brain microvascular endothelial cells (HBMVECs). In vivo, we found that zafirlukast pretreatment could reduce MCAO-induced increased brain permeability by rescuing the expression levels of the tight junction proteins occludin and ZO-1. In vitro, we found that zafirlukast could suppress the increase in endothelial monolayer permeability induced by OGD/R via rescue of occludin and ZO-1 expression; additionally, we found that zafirlukast prevented OGD/R-induced degradation of the extracellular matrix via inhibition of MMP-2 and MMP-9 expression. Finally, we found that zafirlukast could also inhibit OGD/R-induced activation of the critical proinflammatory regulator NF-κB by preventing phosphorylation and nuclear translocation of p65 protein. Together, our findings demonstrate a promising role for zafirlukast in preventing damage induced by ischemic stroke and reperfusion injury.

Nanomechanical insights: Amyloid beta oligomer-induced senescent brain endothelial cells

Senescent cells accumulate in various peripheral tissues during aging and have been shown to exacerbate age-related inflammatory responses. We recently showed that exposure to neurotoxic amyloid β (Aβ1-42) oligomers can readily induce a senescence phenotype in human brain microvascular endothelial cells (HBMECs). In the present work, we used atomic force microscopy (AFM) to further characterize the morphological properties such as cell membrane roughness and cell height and nanomechanical properties such as Young's modulus of the membrane (membrane stiffness) and adhesion resulting from the interaction between AFM tip and cell membrane in Aβ1-42 oligomer-induced senescent human brain microvascular endothelial cells. Morphological imaging studies showed a flatter and spread-out nucleus in the senescent HBMECs, both characteristic features of a senescent phenotype. Furthermore, the mean cell body roughness and mean cell height were lower in senescent HBMECs compared to untreated normal HBMECs. We also observed increased stiffness and alterations in the adhesion properties in Aβ1-42 oligomer-induced senescent endothelial cells compared to the untreated normal HBMECs suggesting dynamic reorganization of cell membrane. We then show that vascular endothelial growth factor receptor 1 (VEGFR-1) knockdown or overexpression of Rho GTPase Rac 1 in the endothelial cells inhibited senescence and reversed these nanomechanical alterations, confirming a direct role of these pathways in the senescent brain endothelial cells. These results illustrate that nanoindentation and topographic analysis of live senescent brain endothelial cells can provide insights into cerebrovascular dysfunction in neurodegenerative diseases such as Alzheimer's disease.

Hydroxyethylstarch (130/0.4) tightens the blood-brain barrier in vitro

In order to prevent cerebral vasospasm after a subarachnoid hemorrhage (SAH), the so-called triple H-therapy (hypertension, hypervolemia, hemodilution) could be applied. In these cases, colloidal solutions containing Hydroxyethylstarch (HES) are used to induce hypervolemia. The administration of HES is very much under debate for the mentioned use, because in general the application of HES for the treatment of critical ill patients has been reduced tremendously in the last years due to its nephrotoxic effects. In this context, there are limited data investigating the influence of HES on the blood-brain barrier. These data might help to assess if a transient administration of HES is possibly justifiable to prevent cerebral ischemia during vasospasm despite the risk of an acute kidney injury. To address this question, a mouse blood-brain barrier in vitro model based on cell line cerebEND was exposed to different HES concentrations and compared to NaCl-containing control solutions. In order to assess the effects of HES on blood-brain barrier properties, cell viability, transendothelial electrical resistance, permeability of carboxyfluorescein, mRNA and protein expression and localization of tight junction proteins were determined. In summary, 1.5-4% HES attenuated cell viability in a mild, concentration dependent manner compared to the NaCl control solution (0% HES). At the mRNA level 1% and 4% HES significantly increased the expression of tight junction associated proteins (ZO-1 and occludin) and the glucose transporter Glut-1 (Slc2a1). In correspondence to this, 4% HES inhibited breakdown of the paracellular barrier in comparison to the control NaCl group (0% HES) shown by transendothelial electrical resistance values and the permeability of the paracellular marker carboxyfluorescein. These effects at the functional level were confirmed by immunofluorescence microscopic images of junctional proteins. The obtained in vitro data showed a potential for HES to counteract blood-brain barrier damage. Future studies are needed to reveal the applicability of HES as a blood-brain barrier stabilizing agent.

Oligodendrocytes upregulate blood-brain barrier function through mechanisms other than the PDGF-BB/PDGFRα pathway in the barrier-tightening effect of oligodendrocyte progenitor cells

White matter lesions are associated with impairment of the blood-brain barrier (BBB), an essential component of the cerebrovasculature. The BBB allows the brain to maintain its highly specialized microenvironment by restricting entry of blood-borne substances including molecules that induce myelin damage. Accumulating evidence suggests that interactions between brain endothelial cells and neighboring cells, including oligodendrocyte progenitor cells (OPCs), are required for the induction and maintenance of BBB function. Here, we compared the ability of OPCs and oligodendrocytes to modulate BBB integrity using co-cultures of rat brain endothelial cells with OPCs or oligodendrocytes. We found that OPCs lowered the brain endothelial permeability to sodium fluorescein, and this enhancement of BBB function was prevented by treatment with AG1296 (a PDGFRα inhibitor). Oligodendrocytes also enhanced BBB integrity. Pharmacological inhibition of PDGFRα did not affect the oligodendrocyte-induced BBB facilitation. These data indicate that oligodendrocytes enhance BBB integrity through pathways other than PDGF-BB/PDGFRα signaling triggered by the brain endothelial cell-derived PDGF-BB. Therefore, our findings suggest that oligodendrocytes constitutively support BBB integrity through soluble factors. Crosstalk between brain endothelial cells and oligodendrocytes could play a facilitatory role in maintaining BBB integrity in the white matter.

Streptococcus agalactiae disrupts P-glycoprotein function in brain endothelial cells

Bacterial meningitis is a serious life threatening infection of the CNS. To cause meningitis, blood-borne bacteria need to interact with and penetrate brain endothelial cells (BECs) that comprise the blood-brain barrier. BECs help maintain brain homeostasis and they possess an array of efflux transporters, such as P-glycoprotein (P-gp), that function to efflux potentially harmful compounds from the CNS back into the circulation. Oftentimes, efflux also serves to limit the brain uptake of therapeutic drugs, representing a major hurdle for CNS drug delivery. During meningitis, BEC barrier integrity is compromised; however, little is known about efflux transport perturbations during infection. Thus, understanding the impact of bacterial infection on P-gp function would be important for potential routes of therapeutic intervention. To this end, the meningeal bacterial pathogen, Streptococcus agalactiae, was found to inhibit P-gp activity in human induced pluripotent stem cell-derived BECs, and live bacteria were required for the observed inhibition. This observation was correlated to decreased P-gp expression both in vitro and during infection in vivo using a mouse model of bacterial meningitis. Given the impact of bacterial interactions on P-gp function, it will be important to incorporate these findings into analyses of drug delivery paradigms for bacterial infections of the CNS.

Cysteinyl leukotriene receptor type 1 antagonist montelukast protects against injury of blood-brain barrier

The blood-brain barrier (BBB) is formed by tightly connected cerebrovascular endothelial cells. Injury of human brain endothelial cells can cause disruption of the BBB and severe injury to brain tissue. Signals mediated cysteinyl leukotrienes (cysLTs) and their receptors are involved in a variety of pathological conditions. In the current study, our results show that oxygen glucose-deprivation/reoxygenation (OGD/R) induced the expression of leukotriene receptor type 1 (cysLT1R) in brain endothelial cells. Blockage of cysLT1R by its specific antagonist montelukast suppressed OGD/R-induced altered permeability of the human brain endothelial cell (EC) monolayer. Mechanistically, montelukast treatment reversed OGD/R-induced reduction of the tight junction proteins occludin and zonula occludens-1 (ZO-1). Montelukast also ameliorated OGD/R-induced reduction of inhibitors of matrix metalloproteinases (TIMPs), such as TIMP-1 and TIMP-2. On the other hand, montelukast suppressed the expression and production of matrix metalloproteinases (MMPs) and cytokines including MMP-2, MMP-9, interleukin 1β (IL-1β), tumor necrosis factor-α (TNF-α), and interleukin 6 (IL-6). Using a murine middle cerebral artery occlusion brain injury model, we demonstrated that the administration of montelukast improved the surgery-induced brain injury and protected against disruption of brain endothelial junction proteins such as occludin and ZO-1. Collectively, our data suggest that montelukast might confer protective roles against injury in brain endothelial cells.

Neurolymphatic biomarkers of brain endothelial inflammatory activation: Implications for multiple sclerosis diagnosis

AIMS

Multiple sclerosis (MS) is the leading cause of non-traumatic neurological disability in young adults, and its diagnosis is often delayed due to the lack of diagnostic markers. Initiation of disease -modifying therapy in the early stages of MS is especially critical because currently available therapy mostly target relapsing-remitting MS, and is less effective as disease progresses into the more chronic form of secondary-progressive MS. Therefore, exploring specific and sensitive biomarkers will facilitate an expedited and more accurate diagnosis to allow currently available therapies to be more effective.

MAIN METHODS

Western blotting was conducted to detect the expression of neurolymphatic proteins in human brain endothelial cells in culture. Additionally, using a cohort of 150 patients with relapsing remitting MS, 26 with secondary progressive MS, and 60 healthy control samples, neurolymphatic protein expression was detected in serum samples using dot blot analysis.

KEY FINDINGS

Human brain microvascular endothelial cells express neurolymphatic markers. Neurolymphatic protein abundance increases with tumor necrosis factor (TNF)-α stimulation but decreases with interferon (IFN)- γ or combined (TNF + IFN) treatment. Circulating neurolymphatic protein levels is significantly lower in MS patients. Further, one of the markers, FOXC2, is associated with the clinical stages of MS, with significantly lower expression in secondary progressive MS compared to relapsing remitting MS.

SIGNIFICANCE

Our findings describe brain endothelial expression of neurolymphatic proteins, which is altered under inflammatory stress, and provide a possibility of using a collective pool of circulating neurolymphatic proteins as a diagnostic and prognostic biomarker of MS.

Lidocaine turns the surface charge of biological membranes more positive and changes the permeability of blood-brain barrier culture models

The surface charge of brain endothelial cells forming the blood-brain barrier (BBB) is highly negative due to phospholipids in the plasma membrane and the glycocalyx. This negative charge is an important element of the defense systems of the BBB. Lidocaine, a cationic and lipophilic molecule which has anaesthetic and antiarrhytmic properties, exerts its actions by interacting with lipid membranes. Lidocaine when administered intravenously acts on vascular endothelial cells, but its direct effect on brain endothelial cells has not yet been studied. Our aim was to measure the effect of lidocaine on the charge of biological membranes and the barrier function of brain endothelial cells. We used the simplified membrane model, the bacteriorhodopsin (bR) containing purple membrane of Halobacterium salinarum and culture models of the BBB. We found that lidocaine turns the negative surface charge of purple membrane more positive and restores the function of the proton pump bR. Lidocaine also changed the zeta potential of brain endothelial cells in the same way. Short-term lidocaine treatment at a 10 μM therapeutically relevant concentration did not cause major BBB barrier dysfunction, substantial change in cell morphology or P-glycoprotein efflux pump inhibition. Lidocaine treatment decreased the flux of a cationic lipophilic molecule across the cell layer, but had no effect on the penetration of hydrophilic neutral or negatively charged markers. Our observations help to understand the biophysical background of the effect of lidocaine on biological membranes and draws the attention to the interaction of cationic drug molecules at the level of the BBB.

Human ES-derived MSCs correct TNF-α-mediated alterations in a blood-brain barrier model

Background

Immune cell trafficking into the CNS is considered to contribute to pathogenesis in MS and its animal model, EAE. Disruption of the blood–brain barrier (BBB) is a hallmark of these pathologies and a potential target of therapeutics. Human embryonic stem cell-derived mesenchymal stem/stromal cells (hES-MSCs) have shown superior therapeutic efficacy, compared to bone marrow-derived MSCs, in reducing clinical symptoms and neuropathology of EAE. However, it has not yet been reported whether hES-MSCs inhibit and/or repair the BBB damage associated with neuroinflammation that accompanies EAE.

Methods

BMECs were cultured on Transwell inserts as a BBB model for all the experiments. Disruption of BBB models was induced by TNF-α, a pro-inflammatory cytokine that is a hallmark of acute and chronic neuroinflammation.

Results

Results indicated that hES-MSCs reversed the TNF-α-induced changes in tight junction proteins, permeability, transendothelial electrical resistance, and expression of adhesion molecules, especially when these cells were placed in direct contact with BMEC.

Conclusions

hES-MSCs and/or products derived from them could potentially serve as novel therapeutics to repair BBB disturbances in MS.

Electronic supplementary material

The online version of this article (10.1186/s12987-019-0138-5) contains supplementary material, which is available to authorized users.

Pericytic Laminin Maintains Blood-Brain Barrier Integrity in an Age-Dependent Manner

Brain pericytes synthesize and deposit laminin at the blood-brain barrier (BBB). The function of pericyte-derived laminin in BBB maintenance remains largely unknown. In a previous study, we generated pericytic laminin conditional knockout (PKO) mice, which developed BBB breakdown and hydrocephalus in a mixed genetic background. However, since hydrocephalus itself can compromise BBB integrity, it remains unclear whether BBB disruption in these mutants is due to loss of pericytic laminin or secondary to hydrocephalus. Here, we report that, in C57Bl6 dominant background, the PKO mice fail to show hydrocephalus, have a normal lifespan, and develop BBB breakdown in an age-dependent manner. Further mechanistic studies demonstrate that abnormal paracellular transport, enhanced transcytosis, decreased pericyte coverage, and diminished AQP4 level are responsible for BBB disruption in PKO mice. These results suggest that pericyte-derived laminin plays an indispensable and age-dependent role in the maintenance of BBB integrity under homeostatic conditions.

Monomeric α-synuclein induces blood-brain barrier dysfunction through activated brain pericytes releasing inflammatory mediators in vitro

Blood-brain barrier (BBB) disruption is often mediated by neuroinflammation, and occurs during various neurodegenerative diseases including Parkinson's disease (PD). PD is characterized by loss of dopaminergic neurons and aggregated α-synuclein protein in inclusions known as Lewy bodies. Misfolded α-synuclein has been implicated in neurodegeneration and neuroinflammation through activation of microglia and astrocytes. Pericytes are a key cellular regulator of the BBB, although it is not known if they participate in α-synuclein-associated PD pathology. Here, we investigated the impact of pericytes on BBB integrity in response to α-synuclein using rat brain endothelial cells (RBECs) co-cultured with rat brain pericytes (RBEC/pericyte co-culture). In RBEC/pericyte co-cultures, α-synuclein added to the abluminal chamber (where pericytes were grown) significantly increased RBEC permeability to sodium fluorescein. In contrast, it had no marked effect when added to the luminal chamber. In the absence of pericytes, both luminal and abluminal addition of α-synuclein failed to affect permeability of the RBEC monolayer. α-Synuclein did not self-assemble in culture media within 24 h, suggesting that monomeric α-synuclein can disrupt the BBB by interacting with pericytes. We found that in response to α-synuclein, pericytes, but not RBECs, released interleukin (IL)-1β, IL-6, monocyte chemotactic protein (MCP)-1, tumor necrosis factor (TNF)-α, and matrix metalloproteinase-9 (MMP-9). α-Synuclein did not affect platelet-derived growth factor (PDGF)-BB release from RBECs and PDGF receptor-β expression in pericytes. These results suggest that pericytes are more sensitive to monomeric α-synuclein than RBECs regarding release of various inflammatory cytokines/chemokines and MMP-9. Thus, monomeric α-synuclein-activated pericytes may contribute to BBB breakdown in patients with PD.

Canonical Wnt Pathway Maintains Blood-Brain Barrier Integrity upon Ischemic Stroke and Its Activation Ameliorates Tissue Plasminogen Activator Therapy

Stroke induces blood-brain barrier (BBB) breakdown, which promotes complications like oedema and hemorrhagic transformation. Administration of recombinant tissue plasminogen activator (rtPA) within a therapeutic time window of 4.5 h after stroke onset constitutes the only existing treatment. Beyond this time window, rtPA worsens BBB breakdown. Canonical Wnt pathway induces BBB formation and maturation during ontogeny. We hypothesized that the pathway is required to maintain BBB functions after stroke; thus, its activation might improve rtPA therapy. Therefore, we first assessed pathway activity in the brain of mice subjected to transient middle cerebral artery occlusion (MCAo). Next, we evaluated the effect of pathway deactivation early after stroke onset on BBB functions. Finally, we assessed the impact of pathway activation on BBB breakdown associated to delayed administration of rtPA. Our results show that pathway activity is induced predominately in endothelial cells early after ischemic stroke. Early deactivation of the pathway using a potent inhibitor, XAV939, aggravates BBB breakdown and increases hemorrhagic transformation incidence. On the other hand, pathway activation using a potent activator, 6-bromoindirubin-3'-oxime (6-BIO), reduces the incidence of hemorrhagic transformation associated to delayed rtPA administration by attenuating BBB breakdown via promotion of tight junction formation and repressing endothelial basal permeability independently of rtPA proteolytic activity. BBB preservation upon pathway activation limited the deleterious effects of delayed rtPA administration. Our study demonstrates that activation of the canonical Wnt pathway constitutes a clinically relevant strategy to extend the therapeutic time window of rtPA by attenuating BBB breakdown via regulation of BBB-specific mechanisms.

The neurovascular protective effect of alogliptin in murine MCAO model and brain endothelial cells

Endothelial damage and blood brain barrier disruption contribute to ischemic stroke and brain injury. Gliptins are a novel class of treatment agents for diabetes, and recent studies have linked the use of gliptins to neuroprotection. Alogliptin is a type of orally available gliptin that was approved for clinical use by the FDA in 2013. In this study, we investigated the neurovascular protective effects of alogliptin both in vivo and in vitro. In a murine middle cerebral artery occlusion (MCAO) stroke model, administration of alogliptin ameliorated cerebral infarction and disruption of brain vascular permeability, and restored expression of the endothelial tight junction proteins occludin and zona occludens 1 (ZO-1). In brain vascular endothelial cells exposed to oxygen and glucose deprivation/reperfusion (OGD/R), alogliptin prevented OGD/R-induced high permeability of the endothelial monolayer. Alogliptin treatment recovered the reduction in occludin and ZO-1 induced by OGD/R. Moreover, alogliptin treatment prevented OGD/R-induced induction of metalloproteinase (MMP)-2 and MMP-9, and restored expression of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2. Collectively, our data indicate that alogliptin can improve neurovascular integrity and exerts neuroprotective effects.

A bidirectional crosstalk between glioblastoma and brain endothelial cells potentiates the angiogenic and proliferative signaling of sphingosine-1-phosphate in the glioblastoma microenvironment

Glioblastoma is one of the most malignant, angiogenic, and incurable tumors in humans. The aberrant communication between glioblastoma cells and tumor microenvironment represents one of the major factors regulating glioblastoma malignancy and angiogenic properties. Emerging evidence implicates sphingosine-1-phosphate signaling in the pathobiology of glioblastoma and angiogenesis, but its role in glioblastoma-endothelial crosstalk remains largely unknown. In this study, we sought to determine whether the crosstalk between glioblastoma cells and brain endothelial cells regulates sphingosine-1-phosphate signaling in the tumor microenvironment. Using human glioblastoma and brain endothelial cell lines, as well as primary brain endothelial cells derived from human glioblastoma, we report that glioblastoma-co-culture promotes the expression, activity, and plasma membrane enrichment of sphingosine kinase 2 in brain endothelial cells, leading to increased cellular level of sphingosine-1-phosphate, and significant potentiation of its secretion. In turn, extracellular sphingosine-1-phosphate stimulates glioblastoma cell proliferation, and brain endothelial cells migration and angiogenesis. We also show that, after co-culture, glioblastoma cells exhibit enhanced expression of S1P₁ and S1P₃, the sphingosine-1-phosphate receptors that are of paramount importance for cell growth and invasivity. Collectively, our results envision glioblastoma-endothelial crosstalk as a multi-compartmental strategy to enforce pro-tumoral sphingosine-1-phosphate signaling in the glioblastoma microenvironment.

Extracellular vesicles: mediators and biomarkers of pathology along CNS barriers

Extracellular vesicles (EVs) are heterogeneous, nano-sized vesicles that are shed into the blood and other body fluids, which disperse a variety of bioactive molecules (e.g., protein, mRNA, miRNA, DNA and lipids) to cellular targets over long and short distances. EVs are thought to be produced by nearly every cell type, however this review will focus specifically on EVs that originate from cells at the interface of CNS barriers. Highlighted topics include, EV biogenesis, the production of EVs in response to neuroinflammation, role in intercellular communication and their utility as a therapeutic platform. In this review, novel concepts regarding the use of EVs as biomarkers for BBB status and as facilitators for immune neuroinvasion are also discussed. Future directions and prospective are covered along with important unanswered questions in the field of CNS endothelial EV biology.

Zika virus crosses an in vitro human blood brain barrier model

Zika virus (ZIKV) is a flavivirus that is highly neurotropic causing congenital abnormalities and neurological damage to the central nervous systems (CNS). In this study, we used a human induced pluripotent stem cell (iPSC)-derived blood brain barrier (BBB) model to demonstrate that ZIKV can infect brain endothelial cells (i-BECs) without compromising the BBB barrier integrity or permeability. Although no disruption to the BBB was observed post-infection, ZIKV particles were released on the abluminal side of the BBB model and infected underlying iPSC-derived neural progenitor cells (i-NPs). AXL, a putative ZIKV cellular entry receptor, was also highly expressed in ZIKV-susceptible i-BEC and i-NPs. This iPSC-derived BBB model can help elucidate the mechanism by which ZIKV can infect BECs, cross the BBB and gain access to the CNS.

Protection of cultured brain endothelial cells from cytokine-induced damage by α-melanocyte stimulating hormone

The blood–brain barrier (BBB), an interface between the systemic circulation and the nervous system, can be a target of cytokines in inflammatory conditions. Pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) induce damage in brain endothelial cells and BBB dysfunction which contribute to neuronal injury. The neuroprotective effects of α-melanocyte stimulating hormone (α-MSH) were investigated in experimental models, but there are no data related to the BBB. Based on our recent study, in which α-MSH reduced barrier dysfunction in human intestinal epithelial cells induced by TNF-α and IL-1β, we hypothesized a protective effect of α-MSH on brain endothelial cells. We examined the effect of these two pro-inflammatory cytokines, and the neuropeptide α-MSH on a culture model of the BBB, primary rat brain endothelial cells co-cultured with rat brain pericytes and glial cells. We demonstrated the expression of melanocortin-1 receptor in isolated rat brain microvessels and cultured brain endothelial cells by RT-PCR and immunohistochemistry. TNF-α and IL-1β induced cell damage, measured by impedance and MTT assay, which was attenuated by α-MSH (1 and 10 pM). The peptide inhibited the cytokine-induced increase in brain endothelial permeability, and restored the morphological changes in cellular junctions visualized by immunostaining for claudin-5 and β-catenin. Elevated production of reactive oxygen species and the nuclear translocation of NF-κB were also reduced by α-MSH in brain endothelial cells stimulated by cytokines. We demonstrated for the first time the direct beneficial effect of α-MSH on cultured brain endothelial cells, indicating that this neurohormone may be protective at the BBB.

Papain-based Single Cell Isolation of Primary Murine Brain Endothelial Cells Using Flow Cytometry

Brain endothelial cells (BECs) form the integral component of the blood-brain barrier (BBB) which separates the systemic milieu from the brain parenchyma and protects the brain from pathogens and circulating factors. In order to study BEC biology, it was of particular interest to establish a method that enables researchers to investigate and understand the underlying molecular mechanisms regulating their function during homeostasis, aging and disease. Furthermore, due to the heterogeneity of the cerebrovasculature and different vessel types that comprise the BBB, it is of particular interest to isolate primary BECs for single cell analysis from various subregions of the brain, such as the neurogenic and highly vascularized hippocampus and to enrich for specific vessel types. In the past, approaches to isolate endothelial cells were dependent on transgenic mice and often resulted in insufficiently pure cell populations and poor yield. This protocol describes a technique that allows single-cell isolation of highly pure brain endothelial cell populations using fluorescence activated cell sorting (FACS). Briefly, after perfusion and careful removal of the meninges, and dissection of the cortex/hippocampus, the brain tissue is mechanically homogenized and enzymatically digested resulting in a single cell suspension. Cells are stained with fluorochrome-conjugated antibodies identifying CD31⁺ brain endothelial cells, as well as CD45⁺CD11b⁺ myeloid cells for exclusion. Using flow cytometry, cell populations are separated and CD31⁺BECs are sorted in bulk into RNA later or as single cells directly into either RNA lysis buffer for single or bulk RNA-Seq analyses. The protocol does not require the expression of a transgene to label brain endothelial cells and thus, may be applied to any mouse model. In our hands, the protocol has been highly reproducible with an average yield of 1 × 10⁵ cells isolated from an adult mouse cortex/hippocampus.

Effects of erythropoietin on astrocytes and brain endothelial cells in primary culture during anoxia depend on simultaneous signaling by other cytokines and on duration of anoxia

Studies on animals revealed neuroprotective effects of exogenously applied erythropoietin (EPO) during cerebral ischemia/hypoxia. Yet, application of exogenous EPO in stroke patients often lead to haemorrhagic transformation. To clarify potential mechanism of this adverse effect we explored effects of EPO on viabilities of astrocytes and brain endothelial cells (BECs) in primary culture during anoxia of various durations, in the presence or absence of vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1), which are cytokines that are also released from the neurovascular unit during hypoxia. Anoxia (2-48 h) exerted marginal effects on BECs' viability and significant reductions in viability of astrocytes. Astrocyte-conditioned medium did not exert effects and exerted detrimental effects on BECs during 2 h and 24 h anoxia, respectively. This was partially reversed by inhibition of Janus kinase (Jak)2/signal transducer and activator of transcription (STAT)5 activation. Addition of rat recombinant EPO (rrEPO) during 2 h-6h anoxia was protective for astrocytes, but had no effect on BECs. Addition of rrEPO significantly reduced viability of BECs and astrocytes after 48 h anoxia and after 24 h-48 h anoxia, respectively, which was attenuated by inhibition of Jak2/STAT5 activation. Simultaneous addition of rrEPO and VEGFA (1-165) caused marginal effects on BECs, but a highly significant protective effects on astrocytes during 24-48 h anoxia, which were attenuated by inhibition of Jak2/STAT5 activation. Simultaneous addition of EPO, VEGFA 1-165 and Ang1 exerted protective effects on BECs during 24 h-48 h anoxia, which were attenuated by addition of soluble Tie2 receptor. These data revealed that EPO could exert protective, but also injurious effects on BECs and astrocytes during anoxia, which depended on the duration of anoxia and on simultaneous signaling by VEGF and Ang1. If these injurious effects occur in stroke patients, they could enhance vascular damage and haemorrhagic transformation.

Blood-brain barrier transport and neuroprotective potential of blackberry-digested polyphenols: an in vitro study

PURPOSE

Epidemiological and intervention studies have attempted to link the health effects of a diet rich in fruits and vegetables with the consumption of polyphenols and their impact in neurodegenerative diseases. Studies have shown that polyphenols can cross the intestinal barrier and reach concentrations in the bloodstream able to exert effects in vivo. However, the effective uptake of polyphenols into the brain is still regarded with some reservations. Here we describe a combination of approaches to examine the putative transport of blackberry-digested polyphenols (BDP) across the blood-brain barrier (BBB) and ultimate evaluation of their neuroprotective effects.

METHODS

BDP was obtained by in vitro digestion of blackberry extract and BDP major aglycones (hBDP) were obtained by enzymatic hydrolysis. Chemical characterization and BBB transport of extracts were evaluated by LC-MSⁿ. BBB transport and cytoprotection of both extracts was assessed in HBMEC monolayers. Neuroprotective potential of BDP was assessed in NT2-derived 3D co-cultures of neurons and astrocytes and in primary mouse cerebellar granule cells. BDP-modulated genes were evaluated by microarray analysis.

RESULTS

Components from BDP and hBDP were shown to be transported across the BBB. Physiologically relevant concentrations of both extracts were cytoprotective at endothelial level and BDP was neuroprotective in primary neurons and in an advanced 3D cell model. The major canonical pathways involved in the neuroprotective effect of BDP were unveiled, including mTOR signaling and the unfolded protein response pathway. Genes such as ASNS and ATF5 emerged as novel BDP-modulated targets.

CONCLUSIONS

BBB transport of BDP and hBDP components reinforces the health benefits of a diet rich in polyphenols in neurodegenerative disorders. Our results suggest some novel pathways and genes that may be involved in the neuroprotective mechanism of the BDP polyphenol components.

Reduced glucose transporter-1 in brain derived circulating endothelial cells in mild Alzheimer's disease patients

Patients with Alzheimer's disease (AD) have blood-brain barrier (BBB) dysfunction. Methods to study cells of the BBB in vivo would facilitate analyses of neurovascular damage in early AD. Thus, we conducted a pilot study to investigate if brain-derived endothelial cells (BDCECs) could be identified from a cell population of circulating endothelial cells (CECs). Peripheral blood was sampled from early AD patients (n = 9), patients with vascular diseases (myocardial infarction (n = 8) and ischemic stroke (n = 8)), and healthy controls (n = 8). We enumerated CD34⁺/CD146⁺/CD45^- cells (CECs) and Glucose transporter-1 (Glut1⁺ CECs (BDCECs)) by flow cytometry. We found that BDCECs formed a separate, aggregate cell population. Glut1 expression on BDCECs, measured by the median fluorescence intensity, was significantly decreased in patients with AD compared to both the healthy controls and patients with myocardial infarction ((p < .05, Kruskal-Wallis, Dunn's post hoc test). We found no significant differences in cell numbers. Our study shows that isolation of BDCECs offers a promising non-invasive tool to investigate cells derived from the BBB. Downregulation of Glut1 at the mild stages of AD suggests that agents that increase Glut1 levels may be therapeutic candidates to improve energy availability to the brain.

Recombinant tissue plasminogen activator enhances microparticle release from mouse brain-derived endothelial cells through plasmin

Thrombolysis with recombinant tissue plasminogen activator (rt-PA) is currently the only approved pharmacological strategy for acute ischemic stroke. However, rt-PA exhibits vascular toxicity mainly due to endothelial damage. To investigate the mechanisms underlying rt-PA-induced endothelial alterations, we assessed the role of rt-PA in the generation of endothelial microparticles (EMPs), emerging biological markers and effectors of endothelial dysfunction. The mouse brain-derived endothelial cell line bEnd.3 was used. Cells were treated with rt-PA at 20, 40 or 80μg/ml for 15 or 24h, and EMPs were quantified in the culture media using Annexin-V staining coupled with flow cytometry. Rt-PA enhanced EMP release from bEnd.3 cells with a maximal increase at the 40μg/ml dose for 24h (+78% compared to controls). Using tranexamic acid and aprotinin we demonstrated that plasmin is responsible for rt-PA-induced EMP release. The p38 MAPK inhibitor SB203580 and the poly(ADP-ribose)polymerase (PARP) inhibitor PJ34 also reduced rt-PA-induced EMP production, suggesting that p38 MAPK and PARP are downstream intracellular effectors of rt-PA/plasmin. Rt-PA also altered through plasmin the morphology and the confluence of bEnd.3 cells. By contrast, these changes did not implicate p38 MAPK and PARP. This study demonstrates that rt-PA induces the production of microparticles by cerebral endothelial cells, through plasmin, p38 MAPK and PARP pathways. Determining the phenotype of these EMPs to clarify their role on the endothelium in ischemic conditions could thus be of particular interest.

In-silico analysis of claudin-5 reveals novel putative sites for post-translational modifications: Insights into potential molecular determinants of blood-brain barrier breach during HIV-1 infiltration

The blood-brain barrier (BBB) poses a huge challenge and is a serious issue in deciphering the pathophysiology of central nervous system disorders. Endothelial tight junctions play an essential role in maintaining the integrity of the BBB. Post-translational modifications (PTMs) in endothelial tight junction proteins are known to cause deleterious functional impairment and possible disruptions in BBB integrity. PTMs in tight junction proteins play an important role in human immunodeficiency virus type 1 (HIV-1) entry through the BBB. Human claudin-5 is one of the highly expressed brain endothelial tight junction protein and various PTMs in claudin-5 are expected to aid HIV-1 in crossing the BBB. A precise characterization of PTMs in claudin-5 is important for understanding its role in HIV-1 brain infiltration. In this study, we have examined post-translational crosstalk between phosphorylation, O-glycosylation, palmitoylation and methylation sites in claudin-5, which could alter claudin-5's ability to maintain BBB integrity. To the best of our knowledge, this is the first report on claudin-5 protein that suggests a novel interplay between potential PTM sites. PTMs of predicted residues in claudin-5, suggested in this study, can serve as compelling targets for potential therapeutic agents against HIV-1 induced neuropathogenesis. Further site-specific experimental studies in this aspect are highly recommended.

Interleukin-1β induced activation of the hypothalamus-pituitary-adrenal axis is dependent on interleukin-1 receptors on non-hematopoietic cells

The proinflammatory cytokine interleukin-1β (IL-1β) plays a major role in the signal transduction of immune stimuli from the periphery to the central nervous system, and has been shown to be an important mediator of the immune-induced stress hormone release. The signaling pathway by which IL-1β exerts this function involves the blood-brain-barrier and induced central prostaglandin synthesis, but the identity of the blood-brain-barrier cells responsible for this signal transduction has been unclear, with both endothelial cells and perivascular macrophages suggested as critical components. Here, using an irradiation and transplantation strategy, we generated mice expressing IL-1 type 1 receptors (IL-1R1) either in hematopoietic or non-hematopoietic cells and subjected these mice to peripheral immune challenge with IL-1β. Following both intraperitoneal and intravenous administration of IL-1β, mice lacking IL-1R1 in hematopoietic cells showed induced expression of the activity marker c-Fos in the paraventricular hypothalamic nucleus, and increased plasma levels of ACTH and corticosterone. In contrast, these responses were not observed in mice with IL-1R1 expression only in hematopoietic cells. Immunoreactivity for IL-1R1 was detected in brain vascular cells that displayed induced expression of the prostaglandin synthesizing enzyme cyclooxygenase-2 and that were immunoreactive for the endothelial cell marker CD31, but was not seen in cells positive for the brain macrophage marker CD206. These results imply that activation of the HPA-axis by IL-1β is dependent on IL-1R1s on non-hematopoietic cells, such as brain endothelial cells, and that IL-1R1 on perivascular macrophages are not involved.