Death receptors DR6 and TROY regulate brain vascular development

IL-1β disrupts the initiation of blood-brain barrier development by inhibiting endothelial Wnt/β-catenin signaling

During neuroinflammation, the proinflammatory cytokine interleukin-1β (IL-1β) impacts blood-brain barrier (BBB) function by disrupting brain endothelial tight junctions, promoting vascular permeability, and increasing transmigration of immune cells. Here, we examined the effects of Il-1β on the in vivo initiation of BBB development. We generated doxycycline-inducible transgenic zebrafish to secrete Il-1β in the CNS. To validate the utility of our model, we showed Il-1β dose-dependent mortality, recruitment of neutrophils, and expansion of microglia. Using live imaging, we discovered that Il-1β causes a significant reduction in CNS angiogenesis and barriergenesis. To demonstrate specificity, we rescued the Il-1β induced phenotypes by targeting the zebrafish il1r1 gene using CRISPR-Cas9. Mechanistically, we determined that Il-1β disrupts the initiation of BBB development by decreasing Wnt/β-catenin transcriptional activation in brain endothelial cells. Given that several neurodevelopmental disorders are associated with inflammation, our findings support further investigation into the connections between proinflammatory cytokines, neuroinflammation, and neurovascular development.

Endothelial DR6 in blood-brain barrier malfunction in Alzheimer's disease

The impairment of the blood-brain barrier (BBB) has been increasingly recognised as a critical element in the early pathogenesis of Alzheimer's disease (AD), prompting a focus on brain endothelial cells (BECs), which serve as the primary constituents of the BBB. Death receptor 6 (DR6) is highly expressed in brain vasculature and acts downstream of the Wnt/β-catenin pathway to promote BBB formation during development. Here, we found that brain endothelial DR6 levels were significantly reduced in a murine model of AD (APPswe/PS1dE9 mice) at the onset of amyloid-β (Aβ) accumulation. Toxic Aβ25-35 oligomer treatment recapitulated the reduced DR6 in cultured BECs. We further showed that suppressing DR6 resulted in BBB malfunction in the presence of Aβ25-35 oligomers. In contrast, overexpressing DR6 increased the level of BBB functional proteins through the activation of the Wnt/β-catenin and JNK pathways. More importantly, DR6 overexpression in BECs was sufficient to rescue BBB dysfunction in vitro. In conclusion, our findings provide new insight into the role of endothelial DR6 in AD pathogenesis, highlighting its potential as a therapeutic target to tackle BBB dysfunction in early-stage AD progression.

IL-1β disrupts blood-brain barrier development by inhibiting endothelial Wnt/β-catenin signaling

During neuroinflammation, the proinflammatory cytokine Interleukin-1β (IL-1β) impacts blood-brain barrier (BBB) function by disrupting brain endothelial tight junctions, promoting vascular permeability, and increasing transmigration of immune cells. Here, we examined the effects of Il-1β on the in vivo development of the BBB. We generated a doxycycline-inducible transgenic zebrafish model that drives secretion of Il-1β in the CNS. To validate the utility of our model, we showed Il-1β dose-dependent mortality, recruitment of neutrophils, and expansion of microglia. Using live imaging, we discovered that Il-1β causes a significant reduction in CNS angiogenesis and barriergenesis. To demonstrate specificity, we rescued the Il-1β induced phenotypes by targeting the zebrafish il1r1 gene using CRISPR/Cas9. Mechanistically, we determined that Il-1β disrupts BBB development by decreasing Wnt/β-catenin transcriptional activation in brain endothelial cells. Given that several neurodevelopmental disorders are associated with inflammation, our findings support further investigation into the connections between proinflammatory cytokines, neuroinflammation, and neurovascular development.

Integrative multi-omic profiling of adult mouse brain endothelial cells and potential implications in Alzheimer's disease

The blood-brain barrier (BBB) is primarily manifested by a variety of physiological properties of brain endothelial cells (ECs), but the molecular foundation for these properties remains incompletely clear. Here, we generate a comprehensive molecular atlas of adult brain ECs using acutely purified mouse ECs and integrated multi-omics. Using RNA sequencing (RNA-seq) and proteomics, we identify the transcripts and proteins selectively enriched in brain ECs and demonstrate that they are partially correlated. Using single-cell RNA-seq, we dissect the molecular basis of functional heterogeneity of brain ECs. Using integrative epigenomics and transcriptomics, we determine that TCF/LEF, SOX, and ETS families are top-ranked transcription factors regulating the BBB. We then validate the identified brain-EC-enriched proteins and transcription factors in normal mouse and human brain tissue and assess their expression changes in mice with Alzheimer's disease. Overall, we present a valuable resource with broad implications for regulation of the BBB and treatment of neurological disorders.

Trans-Compartmental Regulation of Tight Junction Barrier Function

Tight junctions (TJs) are the most apical components of junctional complexes in epithelial and endothelial cells. Barrier function is one of the major functions of TJ, which restricts the ions and small water-soluble molecules from passing through the paracellular pathway. Adherens junctions (AJs) play an important role in cell-cell adhesion and cell signaling. Gap junctions (GJs) are intercellular channels regulating electrical and metabolic signals between cells. It is well known that TJ integral membrane proteins, such as claudins and occludins, are the molecular building blocks responsible for TJ barrier function. However, recent studies demonstrate that proteins of other junctional complexes can influence and regulate TJ barrier function. Therefore, the crosstalk between different cell junctions represents a common means to modulate cellular activities. In this review, we will discuss the interactions among TJ, AJ, and GJ by focusing on how AJ and GJ proteins regulate TJ barrier function in different biological systems.

The secreted neuronal signal Spock1 promotes blood-brain barrier development

The blood-brain barrier (BBB) is a unique set of properties of the brain vasculature which severely restrict its permeability to proteins and small molecules. Classic chick-quail chimera studies have shown that these properties are not intrinsic to the brain vasculature but rather are induced by surrounding neural tissue. Here, we identify Spock1 as a candidate neuronal signal for regulating BBB permeability in zebrafish and mice. Mosaic genetic analysis shows that neuronally expressed Spock1 is cell non-autonomously required for a functional BBB. Leakage in spock1 mutants is associated with altered extracellular matrix (ECM), increased endothelial transcytosis, and altered pericyte-endothelial interactions. Furthermore, a single dose of recombinant SPOCK1 partially restores BBB function in spock1 mutants by quenching gelatinase activity and restoring vascular expression of BBB genes including mcamb. These analyses support a model in which neuronally secreted Spock1 initiates BBB properties by altering the ECM, thereby regulating pericyte-endothelial interactions and downstream vascular gene expression.

Shaping the brain vasculature in development and disease in the single-cell era

The CNS critically relies on the formation and proper function of its vasculature during development, adult homeostasis and disease. Angiogenesis - the formation of new blood vessels - is highly active during brain development, enters almost complete quiescence in the healthy adult brain and is reactivated in vascular-dependent brain pathologies such as brain vascular malformations and brain tumours. Despite major advances in the understanding of the cellular and molecular mechanisms driving angiogenesis in peripheral tissues, developmental signalling pathways orchestrating angiogenic processes in the healthy and the diseased CNS remain incompletely understood. Molecular signalling pathways of the 'neurovascular link' defining common mechanisms of nerve and vessel wiring have emerged as crucial regulators of peripheral vascular growth, but their relevance for angiogenesis in brain development and disease remains largely unexplored. Here we review the current knowledge of general and CNS-specific mechanisms of angiogenesis during brain development and in brain vascular malformations and brain tumours, including how key molecular signalling pathways are reactivated in vascular-dependent diseases. We also discuss how these topics can be studied in the single-cell multi-omics era.

Brain endothelial cells acquire blood-brain barrier properties in the absence of Vegf-dependent CNS angiogenesis

During neurovascular development, brain endothelial cells (BECs) respond to secreted signals from the neuroectoderm that regulate CNS angiogenesis, the formation of new blood vessels in the brain, and barriergenesis, the acquisition of blood-brain barrier (BBB) properties. Wnt/β-catenin signaling and Vegf signaling are both required for CNS angiogenesis; however, the relationship between these pathways is not understood. Furthermore, while Wnt/β-catenin signaling is essential for barriergenesis, the role of Vegf signaling in this vital process remains unknown. Here, we provide the first direct evidence, to our knowledge, that Vegf signaling is not required for barriergenesis and that activation of Wnt/β-catenin in BECs is independent of Vegf signaling during neurovascular development. Using double transgenic glut1b:mCherry and plvap:EGFP zebrafish (Danio rerio) to visualize the developing brain vasculature, we performed a forward genetic screen and identified a new mutant allele of kdrl, an ortholog of mammalian Vegfr2. The kdrl mutant lacks CNS angiogenesis but, unlike the Wnt/β-catenin pathway mutant gpr124, acquires BBB properties in BECs. To examine Wnt/β-catenin pathway activation in BECs, we chemically inhibited Vegf signaling and found robust expression of the Wnt/β-catenin transcriptional reporter line 7xtcf-Xla.Siam:EGFP. Taken together, our results establish that Vegf signaling is essential for CNS angiogenesis but is not required for Wnt/β-catenin-dependent barriergenesis. Given the clinical significance of either inhibiting pathological angiogenesis or stimulating neovascularization, our study provides valuable new insights that are critical for the development of effective therapies that target the vasculature in neurological disorders.

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.

Peptide Shuttles for Blood–Brain Barrier Drug Delivery

The blood–brain barrier (BBB) limits the delivery of therapeutics to the brain but also represents the main gate for nutrient entrance. Targeting the natural transport mechanisms of the BBB offers an attractive route for brain drug delivery. Peptide shuttles are able to use these mechanisms to increase the transport of compounds that cannot cross the BBB unaided. As peptides are a group of biomolecules with unique physicochemical and structural properties, the field of peptide shuttles has substantially evolved in the last few years. In this review, we analyze the main classifications of BBB–peptide shuttles and the leading sources used to discover them.

Developmental regulation of barrier- and non-barrier blood vessels in the CNS

The blood-brain barrier (BBB) is essential for creating and maintaining tissue homeostasis in the central nervous system (CNS), which is key for proper neuronal function. In most vertebrates, the BBB is localized to microvascular endothelial cells that acquire barrier properties during angiogenesis of the neuroectoderm. Complex and continuous tight junctions, and the lack of fenestrae combined with low pinocytotic activity render the BBB endothelium a tight barrier for water-soluble molecules that may only enter the CNS via specific transporters. The differentiation of these unique endothelial properties during embryonic development is initiated by endothelial-specific flavours of the Wnt/β-catenin pathway in a precise spatiotemporal manner. In this review, we summarize the currently known cellular (neural precursor and endothelial cells) and molecular (VEGF and Wnt/β-catenin) mechanisms mediating brain angiogenesis and barrier formation. Moreover, we introduce more recently discovered crosstalk with cellular and acellular elements within the developing CNS such as the extracellular matrix. We discuss recent insights into the downstream molecular mechanisms of Wnt/β-catenin in particular, the recently identified target genes like Foxf2, Foxl2, Foxq1, Lef1, Ppard, Zfp551, Zic3, Sox17, Apcdd1 and Fgfbp1 that are involved in refining and maintaining barrier characteristics in the mature BBB endothelium. Additionally, we elute to recent insight into barrier heterogeneity and differential endothelial barrier properties within the CNS, focussing on the circumventricular organs as well as on the neurogenic niches in the subventricular zone and the hippocampus. Finally, open questions and future BBB research directions are highlighted in the context of taking benefit from understanding BBB development for strategies to modulate BBB function under pathological conditions.

Analytical Approaches for the Segmentation of the Zebrafish Brain Vasculature

With advancements in imaging techniques, data visualization allows new insights into fundamental biological processes of development and disease. However, although biomedical science is heavily reliant on imaging data, interpretation of datasets is still often based on subjective visual assessment rather than rigorous quantitation. This overview presents steps to validate image processing and segmentation using the zebrafish brain vasculature data acquired with light sheet fluorescence microscopy as a use case. Blood vessels are of particular interest to both medical and biomedical science. Specific image enhancement filters have been developed that enhance blood vessels in imaging data prior to segmentation. Using the Sato enhancement filter as an example, we discuss how filter application can be evaluated and optimized. Approaches from the medical field such as simulated, experimental, and augmented datasets can be used to gain the most out of the data at hand. Using such datasets, we provide an overview of how biologists and data analysts can assess the accuracy, sensitivity, and robustness of their segmentation approaches that allow extraction of objects from images. Importantly, even after optimization and testing of a segmentation workflow (e.g., from a particular reporter line to another or between immunostaining processes), its generalizability is often limited, and this can be tested using double-transgenic reporter lines. Lastly, due to the increasing importance of deep learning networks, a comparative approach can be adopted to study their applicability to biological datasets. In summary, we present a broad methodological overview ranging from image enhancement to segmentation with a mixed approach of experimental, simulated, and augmented datasets to assess and validate vascular segmentation using the zebrafish brain vasculature as an example. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. HIGHLIGHTS: Simulated, experimental, and augmented datasets provide an alternative to overcome the lack of segmentation gold standards and phantom models for zebrafish cerebrovascular segmentation. Direct generalization of a segmentation approach to the data for which it was not optimized (e.g., different transgenics or antibody stainings) should be treated with caution. Comparison of different deep learning segmentation methods can be used to assess their applicability to data. Here, we show that the zebrafish cerebral vasculature can be segmented with U-Net-based architectures, which outperform SegNet architectures.

Both the Complexity of Tight Junctions and Endothelial Transcytosis Are Increased During BBB Postnatal Development in Rats

The blood-brain barrier (BBB) comprises a single layer of endothelial cells and maintains a safe and homeostatic environment for proper neuronal function and synaptic transmission. BBB is not a discrete physical barrier, but a complex, dynamic, and adaptable interface. BBB continues to mature under the influence of the neural environment within a short period of time after birth. However, the basic mechanism of BBB formation and maintenance remains a mystery. Early studies have identified two structural characteristics of microvascular endothelium: special tight junctions (TJs) and a very low transcellular vesicle transport rate. Previous studies believed that BBB damage was mainly due to the destruction of tight junctions, and the role of vesicle transcytosis was neglected, so there was a lack of research on its impact on blood-brain barrier. It is urgent to get a better clarification of the unique structural and functional characteristics of the BBB endothelium to explain the role of BBB injury in neurological diseases. RNA sequencing was used to study the molecular characterization of cerebral cortex vascular endothelium by isolating them from neonatal, adolescent and adult rats. For investigation the maintenance mechanism of the BBB, we focused on the cellular and molecular regulation of barrier formation and the two characteristics of microvascular endothelial cells. Interestingly, we found that during the development of the blood-brain barrier, although the tight junctions gradually mature, endothelial cell transcytosis is gradually enhanced, resulting in an increase in the permeability of the blood-brain barrier. This study suggested that under physiological conditions, low vesicle transport is playing an important role in maintaining the integrity of the blood-brain barrier. This study not only summarized the unique characteristics of microvascular endothelial cells, but also illustrated a clarified mechanism of the development and maintenance of BBB which can provide new therapeutic opportunities for central nervous system drug delivery. Raw data of RNA sequencing were deposited in NCBI Sequence Read Archive database (PRJNA790676).

A Structural and Functional Perspective of Death Receptor 6

As a member of the tumor necrosis factor receptor superfamily (TNFRSF), death receptor 6 (DR6) has a similar structural architecture to other family members. The extracellular region of DR6 contains four cysteine-rich domains, followed by a single-pass transmembrane domain and an intracellular region. Since its discovery, DR6 has become an orphan receptor ubiquitously expressed to transduce unique signaling pathways. Although the free ectodomains of β-amyloid precursor protein (APP) can bind to DR6 to induce apoptotic signals, the natural ligands of DR6 still remain largely unknown. In this review, we focus on recent research progress of structural and functional studies on DR6 for better understanding DR6-mediated signaling and the treatment of DR6-related diseases.

Addressing Blood–Brain Barrier Impairment in Alzheimer’s Disease

The blood–brain barrier (BBB) plays a vital role in maintaining the specialized microenvironment of the brain tissue. It facilitates communication while separating the peripheral circulation system from the brain parenchyma. However, normal aging and neurodegenerative diseases can alter and damage the physiological properties of the BBB. In this review, we first briefly present the essential pathways maintaining and regulating BBB integrity, and further review the mechanisms of BBB breakdown associated with normal aging and peripheral inflammation-causing neurodegeneration and cognitive impairments. We also discuss how BBB disruption can cause or contribute to Alzheimer’s disease (AD), the most common form of dementia and a devastating neurological disorder. Next, we document overlaps between AD and vascular dementia (VaD) and briefly sum up the techniques for identifying biomarkers linked to BBB deterioration. Finally, we conclude that BBB breakdown could be used as a biomarker to help diagnose cognitive impairment associated with normal aging and neurodegenerative diseases such as AD.

VPS28 regulates brain vasculature by controlling neuronal VEGF trafficking through extracellular vesicle secretion

Extracellular vesicles (EVs) participate in intercellular communication and contribute to the angiogenesis. However, the understanding of the mechanisms underlying EVs secretion by neurons and their action on the vascular system of the central nervous system (CNS) remain rudimentary. Here, we show that vacuolar protein sorting 28 (Vps28) is essential for the sprouting of brain central arteries (CtAs) and for the integrity of blood-brain barrier (BBB) in zebrafish. Disruption of neuron-enriched Vps28 significantly decreased EVs secretion by regulating the formation of intracellular multivesicular bodies (MVBs). EVs derived from zebrafish embryos or mouse cortical neurons partially rescued the brain vasculature defect and brain leakage. Further investigations revealed that neuronal EVs containing vascular endothelial growth factor A (VEGF-A) are key regulators in neurovascular communication. Our results indicate that Vps28 acts as an intercellular endosomal regulator mediating the secretion of neuronal EVs, which in turn communicate with endothelial cells to mediate angiogenesis through VEGF-A trafficking.

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Vps28 is highly expressed in neurons and involved in the secretion of neuronal EVs

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Vps28, as a subunit of ESCRT-1 complexes, participates in the formation of MVB

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Vps28 plays an important role in VEGFA transport and promotes neurovascular communication

Zebrafish vascular quantification: a tool for quantification of three-dimensional zebrafish cerebrovascular architecture by automated image analysis

Zebrafish transgenic lines and light sheet fluorescence microscopy allow in-depth insights into three-dimensional vascular development in vivo. However, quantification of the zebrafish cerebral vasculature in 3D remains highly challenging. Here, we describe and test an image analysis workflow for 3D quantification of the total or regional zebrafish brain vasculature, called zebrafish vasculature quantification (ZVQ). It provides the first landmark- or object-based vascular inter-sample registration of the zebrafish cerebral vasculature, producing population average maps allowing rapid assessment of intra- and inter-group vascular anatomy. ZVQ also extracts a range of quantitative vascular parameters from a user-specified region of interest, including volume, surface area, density, branching points, length, radius and complexity. Application of ZVQ to 13 experimental conditions, including embryonic development, pharmacological manipulations and morpholino-induced gene knockdown, shows that ZVQ is robust, allows extraction of biologically relevant information and quantification of vascular alteration, and can provide novel insights into vascular biology. To allow dissemination, the code for quantification, a graphical user interface and workflow documentation are provided. Together, ZVQ provides the first open-source quantitative approach to assess the 3D cerebrovascular architecture in zebrafish.

Summary: An image analysis workflow pipeline for 3D quantification of the total or regional zebrafish brain vasculature, called zebrafish vasculature quantification or ZVQ.

Treating Metastatic Brain Cancers With Stem Cells

Stem cell therapy may present an effective treatment for metastatic brain cancer and glioblastoma. Here we posit the critical role of a leaky blood-brain barrier (BBB) as a key element for the development of brain metastases, specifically melanoma. By reviewing the immunological and inflammatory responses associated with BBB damage secondary to tumoral activity, we identify the involvement of this pathological process in the growth and formation of metastatic brain cancers. Likewise, we evaluate the hypothesis of regenerating impaired endothelial cells of the BBB and alleviating the damaged neurovascular unit to attenuate brain metastasis, using the endothelial progenitor cell (EPC) phenotype of bone marrow-derived mesenchymal stem cells. Specifically, there is a need to evaluate the efficacy for stem cell therapy to repair disruptions in the BBB and reduce inflammation in the brain, thereby causing attenuation of metastatic brain cancers. To establish the viability of stem cell therapy for the prevention and treatment of metastatic brain tumors, it is crucial to demonstrate BBB repair through augmentation of vasculogenesis and angiogenesis. BBB disruption is strongly linked to metastatic melanoma, worsens neuroinflammation during metastasis, and negatively influences the prognosis of metastatic brain cancer. Using stem cell therapy to interrupt inflammation secondary to this leaky BBB represents a paradigm-shifting approach for brain cancer treatment. In this review article, we critically assess the advantages and disadvantages of using stem cell therapy for brain metastases and glioblastoma.

Transcriptome analysis of human dorsal striatum implicates attenuated canonical WNT signaling in neuroinflammation and in age-related impairment of striatal neurogenesis and synaptic plasticity

BACKGROUND

Motor and cognitive decline as part of the normal aging process is linked to alterations in synaptic plasticity and reduction of adult neurogenesis in the dorsal striatum. Neuroinflammation, particularly in the form of microglial activation, is suggested to contribute to these age-associated changes.

OBJECTIVE AND METHODS

To explore the molecular basis of alterations in striatal function during aging we analyzed RNA-Seq data for 117 postmortem human dorsal caudate samples and 97 putamen samples acquired through GTEx.

RESULTS

Increased expression of neuroinflammatory transcripts including TREM2, MHC II molecules HLA-DMB, HLA-DQA2, HLA-DPA1, HLA-DPB1, HLA-DMA and HLA-DRA, complement genes C1QA, C1QB, CIQC and C3AR1, and MHCI molecules HLA-B and HLA-F was identified. We also identified down-regulation of transcripts involved in neurogenesis, synaptogenesis, and synaptic pruning, including DCX, CX3CL1, and CD200, and the canonical WNTs WNT7A, WNT7B, and WNT8A. The canonical WNT signaling pathway has previously been shown to mediate adult neurogenesis and synapse formation and growth. Recent findings also highlight the link between WNT/β-catenin signaling and inflammation pathways.

CONCLUSIONS

These findings suggest that age-dependent attenuation of canonical WNT signaling plays a pivotal role in regulating striatal plasticity during aging. Dysregulation of WNT/β-catenin signaling via astrocyte-microglial interactions is suggested to be a novel mechanism that drives the decline of striatal neurogenesis and altered synaptic connectivity and plasticity, leading to a subsequent decrease in motor and cognitive performance with age. These findings may aid in the development of therapies targeting WNT/β-catenin signaling to combat cognitive and motor impairments associated with aging.

Cadmium-induced dysfunction of the blood-brain barrier depends on ROS-mediated inhibition of PTPase activity in zebrafish

Increasing evidence has demonstrated that cadmium accumulation in the blood increases the risk of neurological diseases. However, how cadmium breaks through the blood-brain barrier (BBB) and is transferred from the blood circulation into the central nervous system is still unclear. In this study, we examined the toxic effect of cadmium chloride (CdCl₂) on the development and function of BBB in zebrafish. CdCl₂ exposure induced cerebral hemorrhage, increased BBB permeability and promoted abnormal vascular formation by promoting VEGF production in zebrafish brain. Furthermore, in vivo and in vitro experiments showed that CdCl₂ altered cell-cell junctional morphology by disrupting the proper localization of VE-cadherin and ZO-1. The potential mechanism involved in the inhibition of protein tyrosine phosphatase (PTPase) mediated by cadmium-induced ROS was confirmed with diphenylene iodonium (DPI), a ROS production inhibitor. Together, these data indicate that BBB is a critical target of cadmium toxicity and provide in vivo etiological evidence of cadmium-induced neurovascular disease in a zebrafish BBB model.

Basigin Antibodies with Capacity for Drug Delivery Across Brain Endothelial Cells

The blood-brain barrier (BBB) poses challenges for delivering antibody-based therapeutics to the brain and is a main obstacle for the successful application of biotherapeutics for the treatment of brain disorders. As only a small fraction of monoclonal antibodies (mAbs) is penetrating the BBB, high doses of therapeutics are required to elicit a pharmacological effect. This limitation has evoked research to improve transport across the BBB through receptor-mediated transcytosis, and several receptors have been explored for mediating this process. A recently suggested candidate is the brain endothelial cells (BECs) expressed basigin. Here, we explore the transcytosis capacity of different basigin mAbs targeting distinct epitopes using the porcine in vitro BBB models and provide data showing the intracellular vesicle sorting of these basigin mAbs in porcine BECs. Our data suggest that basigin mAbs avoid the lysosomal degradation pathway and are internalized to vesicles used by recycling receptors. Engagement of basigin mAbs with basigin led to the translocation of the mAbs across the tight BECs into the astrocytes in our in vitro BBB co-culture model. Although mAbs with higher binding affinity to basigin showed a greater astrocyte internalization, based on our experiments, it is not clear whether the transcytosis is affinity- or epitope-dependent or a combination of both. Overall, this study provides information about the intra- and intercellular fate of basigin mAbs in BECs, which are valuable for the future design of basigin-mediated drug delivery platforms.

In-vivo 3D imaging of Zebrafish's intersegmental vessel development by a bi-directional light-sheet illumination microscope

Precise quantification of vascular developments in Zebrafish requires continuous in-vivo 3D imaging. Here we employed a bi-directional light-sheet illumination microscope to characterize the development process of Zebrafish's intersegmental vessels. A Virtual Reality-based method was used to measure the lengths of intersegmental vessels (ISVs). The quantified growth rates of typical ISVs can be plotted, and unusual growth of some specific vessels was also observed.

Human Induced Pluripotent Stem Cell-Derived Brain Endothelial Cells: Current Controversies

Brain microvascular endothelial cells (BMECs) possess unique properties that are crucial for many functions of the blood-brain-barrier (BBB) including maintenance of brain homeostasis and regulation of interactions between the brain and immune system. The generation of a pure population of putative brain microvascular endothelial cells from human pluripotent stem cell sources (iBMECs) has been described to meet the need for reliable and reproducible brain endothelial cells in vitro. Human pluripotent stem cells (hPSCs), embryonic or induced, can be differentiated into large quantities of specialized cells in order to study development and model disease. These hPSC-derived iBMECs display endothelial-like properties, such as tube formation and low-density lipoprotein uptake, high transendothelial electrical resistance (TEER), and barrier-like efflux transporter activities. Over time, the de novo generation of an organotypic endothelial cell from hPSCs has aroused controversies. This perspective article highlights the developments made in the field of hPSC derived brain endothelial cells as well as where experimental data are lacking, and what concerns have emerged since their initial description.

Nradd Acts as a Negative Feedback Regulator of Wnt/β-Catenin Signaling and Promotes Apoptosis

Wnt/β-catenin signaling controls many biological processes for the generation and sustainability of proper tissue size, organization and function during development and homeostasis. Consequently, mutations in the Wnt pathway components and modulators cause diseases, including genetic disorders and cancers. Targeted treatment of pathway-associated diseases entails detailed understanding of the regulatory mechanisms that fine-tune Wnt signaling. Here, we identify the neurotrophin receptor-associated death domain (Nradd), a homolog of p75 neurotrophin receptor (p75NTR), as a negative regulator of Wnt/β-catenin signaling in zebrafish embryos and in mammalian cells. Nradd significantly suppresses Wnt8-mediated patterning of the mesoderm and neuroectoderm during zebrafish gastrulation. Nradd is localized at the plasma membrane, physically interacts with the Wnt receptor complex and enhances apoptosis in cooperation with Wnt/β-catenin signaling. Our functional analyses indicate that the N-glycosylated N-terminus and the death domain-containing C-terminus regions are necessary for both the inhibition of Wnt signaling and apoptosis. Finally, Nradd can induce apoptosis in mammalian cells. Thus, Nradd regulates cell death as a modifier of Wnt/β-catenin signaling during development.

Brain vascular biology

The complex development of the brain vascular system can be broken down by embryonic stages and anatomic locations, which are tightly regulated by different factors and pathways in time and spatially. The adult brain is relatively quiescent in angiogenesis. However, under disease conditions, such as trauma, stroke, or tumor, angiogenesis can be activated in the adult brain. Disruption of any of the factors or pathways may lead to malformed vessel development. In this chapter, we will discuss factors and pathways involved in normal brain vasculogenesis and vascular maturation, and the pathogenesis of several brain vascular malformations.

Characterization of basigin monoclonal antibodies for receptor-mediated drug delivery to the brain

The brain uptake of biotherapeutics for brain diseases is hindered by the blood–brain barrier (BBB). The BBB selectively regulates the transport of large molecules into the brain and thereby maintains brain homeostasis. Receptor-mediated transcytosis (RMT) is one mechanism to deliver essential proteins into the brain parenchyma. Receptors expressed in the brain endothelial cells have been explored to ferry therapeutic antibodies across the BBB in bifunctional antibody formats. In this study, we generated and characterized monoclonal antibodies (mAbs) binding to the basigin receptor, which recently has been proposed as a target for RMT across the BBB. Antibody binding properties such as affinity have been demonstrated to be important factors for transcytosis capability and efficiency. Nevertheless, studies of basigin mAb properties' effect on RMT are limited. Here we characterize different basigin mAbs for their ability to associate with and subsequently internalize human brain endothelial cells. The mAbs were profiled to determine whether receptor binding epitope and affinity affected receptor-mediated uptake efficiency. By competitive epitope binning studies, basigin mAbs were categorized into five epitope bins. mAbs from three of the epitope bins demonstrated properties required for RMT candidates judged by binding characteristics and their superior level of internalization in human brain endothelial cells.

Angiomodulin (IGFBP7) is a cerebral specific angiocrine factor, but is probably not a blood-brain barrier inducer

BACKGROUND

Several secreted factors have been identified as drivers of cerebral vasculature development and inducers of blood-brain barrier (BBB) differentiation. Vascular endothelial growth factor A (VEGF-A) is central for driving cerebral angiogenesis and Wnt family factors (Wnt7a, Wnt7b and norrin) are central for induction and maintenance of barrier properties. Expressed by developing neural tissue (neuron and glia progenitors), they influence the formation of central nervous system (CNS) vascular networks. Another type of factors are tissue-specific paracrine factors produced by endothelial cells (ECs), also known as 'angiocrine' factors, that provide instructive signals to regulate homeostatic and regenerative processes. Very little is known about CNS angiocrine factors and their role in BBB development. Angiomodulin (AGM) was reported to be expressed by developing vasculature and by pathological tumor vasculature. Here we investigated AGM in the developing CNS and its function as a potential BBB inducer.

METHODS

We analyzed microarray data to identify potential angiocrine factors specifically expressed at early stages of barrier formation. We then tested AGM expression with immunofluorescence and real-time PCR in various organs during development, post-natal and in adults. Permeability induction with recombinant proteins (Miles assay) was used to test potential interaction of AGM with VEGF-A.

RESULTS

Several angiocrine factors are differentially expressed by CNS ECs and AGM is a prominent CNS-specific angiocrine candidate. Contrary to previous reports, we found that AGM protein expression is specific to developing CNS endothelium and not to highly angiogenic developing vasculature in general. In skin vasculature we found that AGM antagonizes VEGF-A-induced vascular hyperpermeability. Finally, CNS AGM expression is not specific to BBB vasculature and AGM is highly expressed in non-BBB choroid-plexus vasculature.

CONCLUSIONS

We propose AGM as a developmental CNS vascular-specific marker. AGM is not a pan-endothelial marker, nor a general marker for developing angiogenic vasculature. Thus, AGM induction in the developing CNS might be distinct from its induction in pathology. While AGM is able to antagonize VEGF-A-induced vascular hyperpermeability in the skin, its high expression levels in non-BBB CNS vasculature does not support its potential role as a BBB inducer. Further investigation including loss-of-function approaches might elucidate AGM function in the developing CNS.

Identification of a combination of transcription factors that synergistically increases endothelial cell barrier resistance

Endothelial cells (ECs) display remarkable plasticity during development before becoming quiescent and functionally mature. EC maturation is directed by several known transcription factors (TFs), but the specific set of TFs responsible for promoting high-resistance barriers, such as the blood-brain barrier (BBB), have not yet been fully defined. Using expression mRNA data from published studies on ex vivo ECs from the central nervous system (CNS), we predicted TFs that induce high-resistance barrier properties of ECs as in the BBB. We used our previously established method to  generate ECs from human pluripotent stem cells (hPSCs), and then we overexpressed the candidate TFs in hPSC-ECs and measured barrier resistance and integrity using electric cell-substrate impedance sensing, trans-endothelial electrical resistance and FITC-dextran permeability assays. SOX18 and TAL1 were the strongest EC barrier-inducing TFs, upregulating Wnt-related signaling and EC junctional gene expression, respectively, and downregulating EC proliferation-related genes. These TFs were combined with SOX7 and ETS1 that together effectively induced EC barrier resistance, decreased paracellular transport and increased protein expression of tight junctions and induce mRNA expression of several genes involved in the formation of EC barrier and transport. Our data shows identification of a transcriptional network that controls barrier resistance in ECs. Collectively this data may lead to novel approaches for generation of in vitro models of the BBB.

The impact of endothelial cell death in the brain and its role after stroke: A systematic review

The supply of oxygen and nutrients to the brain is vital for its function and requires a complex vascular network that, when disturbed, results in profound neurological dysfunction. As part of the pathology in stroke, endothelial cells die. As endothelial cell death affects the surrounding cellular environment and is a potential target for the treatment and prevention of neurological disorders, we have systematically reviewed important aspects of endothelial cell death with a particular focus on stroke. After screening 2876 publications published between January 1, 2010 and August 7, 2019, we identified 154 records to be included. We found that endothelial cell death occurs rapidly as well as later after the onset of stroke conditions. Among the different cell death mechanisms, apoptosis was the most widely investigated (92 records), followed by autophagy (20 records), while other, more recently defined mechanisms received less attention, such as lysosome-dependent cell death (2 records) and necroptosis (2 records). We also discuss the differential vulnerability of brain cells to injury after stroke and the role of endothelial cell death in the no-reflow phenomenon with a special focus on the microvasculature. Further investigation of the different cell death mechanisms using novel tools and biomarkers will greatly enhance our understanding of endothelial cell death. For this task, at least two markers/criteria are desirable to determine cell death subroutines according to the recommendations of the Nomenclature Committee on Cell Death.

TNFRSF21 mutations cause high myopia

Background

High myopia (HM) is one of the leading causes of vision impairment worldwide, accompanied by a series of pathological ocular complications. Studies have shown that genetic factors play an important role in the pathogenesis of HM. The aim of our study is to identify a candidate gene for a large family with non-syndromic HM.

Methods

A large Chinese family, including 12 patients with non-syndromic HM, and 220 unrelated patients with HM, were recruited from the Department of Ophthalmology, Peking Union Medical College Hospital. Three affected subjects from the large family were selected to perform whole exome sequencing (WES). Rare heterozygous variants shared by all three subjects were retained and then Sanger sequencing was used to determine whether any of the remaining variants cosegregated with the disease phenotype. Furthermore, all coding regions of the candidate genes were analysed in 220 unrelated patients with HM. Immunofluorescence assay was used to detect the expression of the candidate gene in the eye. Annexin V/PI staining and flow cytometry were applied to detect cell apoptotic changes.

Results

WES identified a novel TNF receptor superfamily member 21 (TNFRSF21) variant, P146A, in a large Chinese family with HM, and another three rare heterozygous variants (P202L, E240* and A440G) in TNFRSF21 were found in 220 unrelated cases with HM. Immunofluorescence assay indicated that it is strongly expressed in the mouse eye. Compared with the wild type, the P146A variant could significantly increase adult retinal pigment epithelial cell line-19 cell apoptotic levels.

Conclusions

Variants in TNFRSF21 cause non-syndromic HM in Chinese population.

Clostridium perfringens Epsilon Toxin Compromises the Blood-Brain Barrier in a Humanized Zebrafish Model

Clostridium perfringens epsilon toxin (ETX) is hypothesized to mediate blood-brain barrier (BBB) permeability by binding to the myelin and lymphocyte protein (MAL) on the luminal surface of endothelial cells (ECs). However, the kinetics of this interaction and a general understanding of ETX's behavior in a live organism have yet to be appreciated. Here we investigate ETX binding and BBB breakdown in living Danio rerio (zebrafish). Wild-type zebrafish ECs do not bind ETX. When zebrafish ECs are engineered to express human MAL (hMAL), proETX binding occurs in a time-dependent manner. Injection of activated toxin in hMAL zebrafish initiates BBB leakage, hMAL downregulation, blood vessel stenosis, perivascular edema, and blood stasis. We propose a kinetic model of MAL-dependent ETX binding and neurovascular pathology. By generating a humanized zebrafish BBB model, this study contributes to our understanding of ETX-induced BBB permeability and strengthens the proposal that MAL is the ETX receptor.

Disruption of the Extracellular Matrix Progressively Impairs Central Nervous System Vascular Maturation Downstream of β-Catenin Signaling

Supplemental Digital Content is available in the text.

Objective—

The Wnt/β-catenin pathway orchestrates development of the blood-brain barrier, but the downstream mechanisms involved at different developmental windows and in different central nervous system (CNS) tissues have remained elusive.

Approach and Results—

Here, we create a new mouse model allowing spatiotemporal investigations of Wnt/β-catenin signaling by induced overexpression of Axin1, an inhibitor of β-catenin signaling, specifically in endothelial cells (Axin1^iEC−^OE). AOE (Axin1 overexpression) in Axin1^iEC−^OE mice at stages following the initial vascular invasion of the CNS did not impair angiogenesis but led to premature vascular regression followed by progressive dilation and inhibition of vascular maturation resulting in forebrain-specific hemorrhage 4 days post-AOE. Analysis of the temporal Wnt/β-catenin driven CNS vascular development in zebrafish also suggested that Axin1^iEC−^OE led to CNS vascular regression and impaired maturation but not inhibition of ongoing angiogenesis within the CNS. Transcriptomic profiling of isolated, β-catenin signaling-deficient endothelial cells during early blood-brain barrier–development (E11.5) revealed ECM (extracellular matrix) proteins as one of the most severely deregulated clusters. Among the 20 genes constituting the forebrain endothelial cell-specific response signature, 8 (Adamtsl2, Apod, Ctsw, Htra3, Pglyrp1, Spock2, Ttyh2, and Wfdc1) encoded bona fide ECM proteins. This specific β-catenin-responsive ECM signature was also repressed in Axin1^iEC−^OE and endothelial cell-specific β-catenin–knockout mice (Ctnnb1-KO^iEC) during initial blood-brain barrier maturation (E14.5), consistent with an important role of Wnt/β-catenin signaling in orchestrating the development of the forebrain vascular ECM.

Conclusions—

These results suggest a novel mechanism of establishing a CNS endothelium-specific ECM signature downstream of Wnt-β-catenin that impact spatiotemporally on blood-brain barrier differentiation during forebrain vessel development.

A signature of circulating inflammatory proteins and development of end-stage renal disease in diabetes

Chronic inflammation is postulated to be involved in development of end stage renal disease (ESRD) in diabetes, but which specific circulating inflammatory proteins contribute to this risk remains unknown. To study this we examined 194 circulating inflammatory proteins in subjects from three independent cohorts with Type 1 and Type 2 diabetes. In each cohort we identified an extremely robust Kidney Risk Inflammatory Signature (KRIS) consisting of 17 novel proteins enriched for TNF Receptor Superfamily members that was associated with a 10-year risk of ESRD. All these proteins had a systemic, non-kidney source. Our prospective study findings provide strong evidence that KRIS proteins contribute to the inflammatory process underlying ESRD development in both types of diabetes. These proteins may be used as new therapeutic targets, new prognostic tests for high risk of ESRD and as surrogate outcome measures where changes in KRIS levels during intervention can reflect the tested therapy’s effectiveness.

Proteomic profiling of circulating proteins in subjects from three independent cohorts with type 1 and type 2 diabetes, identified an extremely robust inflammatory signature, consisting of 17 proteins enriched for TNF Receptor Superfamily members that was associated with a 10-year risk of end-stage renal disease.

Postnatal development of the astrocyte perivascular MLC1/GlialCAM complex defines a temporal window for the gliovascular unit maturation

Astrocytes, the most abundant glial cells of the central nervous system are morphologically complex. They display numerous processes interacting with synapses and blood vessels. At the vascular interface, astrocyte endfeet-terminated processes almost entirely cover the blood vessel surface and participate to the gliovascular unit where important vascular properties of the brain are set such as the blood-brain barrier (BBB) integrity. How specific morphological and functional interactions between astrocytes and the vascular compartment develop has not been fully investigated. Here, we elaborated an original experimental strategy to study the postnatal development of astrocyte perivascular endfeet. Using purified gliovascular units, we focused on the postnatal expression of MLC1 and GlialCAM, two transmembrane proteins forming a complex enriched at the junction between mature astrocyte perivascular endfeet. We showed that MLC1 and GlialCAM were enriched and assembled into mature complexes in astrocyte perivascular endfeet between postnatal days 10 and 15, after the formation of astrocyte perivascular Aquaporin 4 water channels. These events correlated with the increased expression of Claudin-5 and P-gP, two endothelial-specific BBB components. These results illustrate for the first time that astrocyte perivascular endfeet differentiation is a complex and progressive process which correlates with BBB maturation. Moreover, our results suggest that maturation of the astrocyte endfeet MLC1/GlialCAM complex between postnatal days 10 and 15 might be a key event in the gliovascular unit maturation.

Enhancement and Segmentation Workflow for the Developing Zebrafish Vasculature

Zebrafish have become an established in vivo vertebrate model to study cardiovascular development and disease. However, most published studies of the zebrafish vascular architecture rely on subjective visual assessment, rather than objective quantification. In this paper, we used state-of-the-art light sheet fluorescence microscopy to visualize the vasculature in transgenic fluorescent reporter zebrafish. Analysis of image quality, vascular enhancement methods, and segmentation approaches were performed in the framework of the open-source software Fiji to allow dissemination and reproducibility. Here, we build on a previously developed image processing pipeline; evaluate its applicability to a wider range of data; apply and evaluate an alternative vascular enhancement method; and, finally, suggest a work-flow for successful segmentation of the embryonic zebrafish vasculature.

Blood-Brain Barrier: From Physiology to Disease and Back

The blood-brain barrier (BBB) prevents neurotoxic plasma components, blood cells, and pathogens from entering the brain. At the same time, the BBB regulates transport of molecules into and out of the central nervous system (CNS), which maintains tightly controlled chemical composition of the neuronal milieu that is required for proper neuronal functioning. In this review, we first examine molecular and cellular mechanisms underlying the establishment of the BBB. Then, we focus on BBB transport physiology, endothelial and pericyte transporters, and perivascular and paravascular transport. Next, we discuss rare human monogenic neurological disorders with the primary genetic defect in BBB-associated cells demonstrating the link between BBB breakdown and neurodegeneration. Then, we review the effects of genes underlying inheritance and/or increased susceptibility for Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease, and amyotrophic lateral sclerosis (ALS) on BBB in relation to other pathologies and neurological deficits. We next examine how BBB dysfunction relates to neurological deficits and other pathologies in the majority of sporadic AD, PD, and ALS cases, multiple sclerosis, other neurodegenerative disorders, and acute CNS disorders such as stroke, traumatic brain injury, spinal cord injury, and epilepsy. Lastly, we discuss BBB-based therapeutic opportunities. We conclude with lessons learned and future directions, with emphasis on technological advances to investigate the BBB functions in the living human brain, and at the molecular and cellular level, and address key unanswered questions.

TROY interacts with RKIP to promote glioma development

TROY is a component of the Nogo receptor complex and plays the key role in neuronal survival, migration, and differentiation. Here, we show the up-regulation of TROY in human glioma tissues and cells. Inhibition of TROY expression slowed glioma development in vivo and in vitro. Raf kinase inhibitor (RKIP) was found to interact with TROY. The physical interaction of TROY/RKIP was confirmed via co-immunoprecipitation (co-IP) assays. Furthermore, we found that the TROY/RKIP interaction was enhanced by fetal bovine serum (FBS) exposure, and TROY knockdown also led to down-regulation of NF-κB. Finally, disruption of the TROY/RKIP interaction using the TAT-TROY (234–371 aa) protein reduced the glioma development in xenografted mice. This suggests the TROY/RKIP interaction is a potential target for therapy of gliomas.

Erythro-myeloid progenitors contribute endothelial cells to blood vessels

The earliest blood vessels in mammalian embryos are formed when endothelial cells differentiate from angioblasts and coalesce into tubular networks. Thereafter, the endothelium is thought to expand solely by proliferation of pre-existing endothelial cells. Here we show that a complementary source of endothelial cells is recruited into pre-existing vasculature after differentiation from the earliest precursors of erythrocytes, megakaryocytes and macrophages, the erythro-myeloid progenitors (EMPs) that are born in the yolk sac. A first wave of EMPs contributes endothelial cells to the yolk sac endothelium, and a second wave of EMPs colonizes the embryo and contributes endothelial cells to intraembryonic endothelium in multiple organs, where they persist into adulthood. By demonstrating that EMPs constitute a hitherto unrecognized source of endothelial cells, we reveal that embryonic blood vascular endothelium expands in a dual mechanism that involves both the proliferation of pre-existing endothelial cells and the incorporation of endothelial cells derived from haematopoietic precursors.

Death receptor 6 promotes ovarian cancer cell migration through KIF11

The expression of death receptor 6 (DR6) is abnormal in some cancer types, but the function and underlying molecular mechanisms of DR6 in tumor progression are not yet clear. In the present study, our analysis of ovarian cancer RNA sequencing data from The Cancer Genome Atlas revealed that DR6 is upregulated in human ovarian cancer. We confirmed that the expression level of DR6 is upregulated in ovarian cancer tissues when compared with matched adjacent normal tissues. In addition, DR6 enhanced ovarian carcinoma cell migration ability, and decreased expression of DR6 inhibited the expression of matrix metalloprotease (MMP) 2 and MMP9, and increased the expression of E‐cadherin. Additionally, DR6 shRNA caused a significant decrease in phosphoinositide‐3‐kinase (PI3K), phospho (p) ‐AKT, p‐extracellular signal‐regulated kinase (ERK), and p‐mitogen‐activated protein kinase kinase expression in SKOV3 cells. These results suggested that DR6 can enhance ovarian carcinoma cell migration ability through the mitogen‐activated protein kinase/ERK and PI3K/AKT pathways. Notably, mass spectrometric analysis indicated that DR6 co‐purified with kinesin family member 11 (KIF11), and we verified the interaction between KIF11 and DR6 by co‐immunoprecipitation and glutathione S‐transferase pull‐down. Furthermore, we demonstrated that DR6 can bind tumor necrosis factor receptor‐associated factor 4 (TRAF4) with co‐immunoprecipitation. Overexpression of KIF11 or TRAF4 eliminated the suppression of carcinoma cell migration by DR6 knockdown. We also found that TRAF4 and KIF11 were upregulated in ovarian carcinomas and that their level of expression was positively correlated with that of DR6. The findings above suggest that DR6 may play a notable oncogenic role in ovarian malignancy by interacting with TRAF4 and KIF11, and that DR6 may be an effective therapeutic target in ovarian cancer.

Bridging barriers: a comparative look at the blood-brain barrier across organisms

This review by O'Brown et al. discusses the cellular nature of the blood–brain barrier (BBB) and the conservation and variation of BBB function across taxa. It compares the BBB across organisms in order to provide insight into the human BBB both under normal physiological conditions and in neurological diseases.

The blood–brain barrier (BBB) restricts free access of molecules between the blood and the brain and is essential for regulating the neural microenvironment. Here, we describe how the BBB was initially characterized and how the current field evaluates barrier properties. We next detail the cellular nature of the BBB and discuss both the conservation and variation of BBB function across taxa. Finally, we examine our current understanding of mouse and zebrafish model systems, as we expect that comparison of the BBB across organisms will provide insight into the human BBB under normal physiological conditions and in neurological diseases.

Neurovascular Communication during CNS Development

A precise communication between the nervous and the vascular systems is crucial for proper formation and function of the central nervous system (CNS). Interestingly, this communication does not only occur by neural cells regulating the growth and properties of the vasculature, but new studies show that blood vessels actively control different neurodevelopmental processes. Here, we review the current knowledge on how neurons in particular influence growing blood vessels during CNS development and on how vessels participate in shaping the neural compartment. We also review the identified molecular mechanisms of this bidirectional communication.

Blood–brain barrier and its function during inflammation and autoimmunity

The blood–brain barrier (BBB) is an important physiologic barrier that separates CNS from soluble inflammatory mediators and effector immune cells from peripheral circulation. The optimum function of the BBB is necessary for the homeostasis, maintenance, and proper neuronal function. The clinical and experimental findings have shown that BBB dysfunction is an early hallmark of various neurologic disorders ranging from inflammatory autoimmune, neurodegenerative, and traumatic diseases to neuroinvasive infections. Significant progress has been made in the understanding of the regulation of BBB function under homeostatic and neuroinflammatory conditions. Several neurologic disease-modifying drugs have shown to improve the BBB function. However, they have a broad-acting immunomodulatory function and can increase the risk of life-threatening infections. The recent development of in vitro multicomponent 3-dimensional BBB models coupled with fluidics chamber as well as a cell-type specific reporter and knockout mice gave a new boost to our understanding of the dynamics of the BBB. In the review, we discuss the current understanding of BBB composition and recent findings that illustrate the critical regulatory elements of the BBB function under physiologic and inflammatory conditions, and also suggested the strategies to control BBB structure and function.

Blood–brain barrier and its function during inflammation and autoimmunity

The blood–brain barrier (BBB) is an important physiologic barrier that separates CNS from soluble inflammatory mediators and effector immune cells from peripheral circulation. The optimum function of the BBB is necessary for the homeostasis, maintenance, and proper neuronal function. The clinical and experimental findings have shown that BBB dysfunction is an early hallmark of various neurologic disorders ranging from inflammatory autoimmune, neurodegenerative, and traumatic diseases to neuroinvasive infections. Significant progress has been made in the understanding of the regulation of BBB function under homeostatic and neuroinflammatory conditions. Several neurologic disease-modifying drugs have shown to improve the BBB function. However, they have a broad-acting immunomodulatory function and can increase the risk of life-threatening infections. The recent development of in vitro multicomponent 3-dimensional BBB models coupled with fluidics chamber as well as a cell-type specific reporter and knockout mice gave a new boost to our understanding of the dynamics of the BBB. In the review, we discuss the current understanding of BBB composition and recent findings that illustrate the critical regulatory elements of the BBB function under physiologic and inflammatory conditions, and also suggested the strategies to control BBB structure and function.

Blood–brain barrier and its function during inflammation and autoimmunity

The blood–brain barrier (BBB) is an important physiologic barrier that separates CNS from soluble inflammatory mediators and effector immune cells from peripheral circulation. The optimum function of the BBB is necessary for the homeostasis, maintenance, and proper neuronal function. The clinical and experimental findings have shown that BBB dysfunction is an early hallmark of various neurologic disorders ranging from inflammatory autoimmune, neurodegenerative, and traumatic diseases to neuroinvasive infections. Significant progress has been made in the understanding of the regulation of BBB function under homeostatic and neuroinflammatory conditions. Several neurologic disease-modifying drugs have shown to improve the BBB function. However, they have a broad-acting immunomodulatory function and can increase the risk of life-threatening infections. The recent development of in vitro multicomponent 3-dimensional BBB models coupled with fluidics chamber as well as a cell-type specific reporter and knockout mice gave a new boost to our understanding of the dynamics of the BBB. In the review, we discuss the current understanding of BBB composition and recent findings that illustrate the critical regulatory elements of the BBB function under physiologic and inflammatory conditions, and also suggested the strategies to control BBB structure and function.

Blood–brain barrier and its function during inflammation and autoimmunity

The blood–brain barrier (BBB) is an important physiologic barrier that separates CNS from soluble inflammatory mediators and effector immune cells from peripheral circulation. The optimum function of the BBB is necessary for the homeostasis, maintenance, and proper neuronal function. The clinical and experimental findings have shown that BBB dysfunction is an early hallmark of various neurologic disorders ranging from inflammatory autoimmune, neurodegenerative, and traumatic diseases to neuroinvasive infections. Significant progress has been made in the understanding of the regulation of BBB function under homeostatic and neuroinflammatory conditions. Several neurologic disease-modifying drugs have shown to improve the BBB function. However, they have a broad-acting immunomodulatory function and can increase the risk of life-threatening infections. The recent development of in vitro multicomponent 3-dimensional BBB models coupled with fluidics chamber as well as a cell-type specific reporter and knockout mice gave a new boost to our understanding of the dynamics of the BBB. In the review, we discuss the current understanding of BBB composition and recent findings that illustrate the critical regulatory elements of the BBB function under physiologic and inflammatory conditions, and also suggested the strategies to control BBB structure and function.

Blood–brain barrier and its function during inflammation and autoimmunity

The blood–brain barrier (BBB) is an important physiologic barrier that separates CNS from soluble inflammatory mediators and effector immune cells from peripheral circulation. The optimum function of the BBB is necessary for the homeostasis, maintenance, and proper neuronal function. The clinical and experimental findings have shown that BBB dysfunction is an early hallmark of various neurologic disorders ranging from inflammatory autoimmune, neurodegenerative, and traumatic diseases to neuroinvasive infections. Significant progress has been made in the understanding of the regulation of BBB function under homeostatic and neuroinflammatory conditions. Several neurologic disease-modifying drugs have shown to improve the BBB function. However, they have a broad-acting immunomodulatory function and can increase the risk of life-threatening infections. The recent development of in vitro multicomponent 3-dimensional BBB models coupled with fluidics chamber as well as a cell-type specific reporter and knockout mice gave a new boost to our understanding of the dynamics of the BBB. In the review, we discuss the current understanding of BBB composition and recent findings that illustrate the critical regulatory elements of the BBB function under physiologic and inflammatory conditions, and also suggested the strategies to control BBB structure and function.

Blood–brain barrier and its function during inflammation and autoimmunity

The blood–brain barrier (BBB) is an important physiologic barrier that separates CNS from soluble inflammatory mediators and effector immune cells from peripheral circulation. The optimum function of the BBB is necessary for the homeostasis, maintenance, and proper neuronal function. The clinical and experimental findings have shown that BBB dysfunction is an early hallmark of various neurologic disorders ranging from inflammatory autoimmune, neurodegenerative, and traumatic diseases to neuroinvasive infections. Significant progress has been made in the understanding of the regulation of BBB function under homeostatic and neuroinflammatory conditions. Several neurologic disease-modifying drugs have shown to improve the BBB function. However, they have a broad-acting immunomodulatory function and can increase the risk of life-threatening infections. The recent development of in vitro multicomponent 3-dimensional BBB models coupled with fluidics chamber as well as a cell-type specific reporter and knockout mice gave a new boost to our understanding of the dynamics of the BBB. In the review, we discuss the current understanding of BBB composition and recent findings that illustrate the critical regulatory elements of the BBB function under physiologic and inflammatory conditions, and also suggested the strategies to control BBB structure and function.

Blood–brain barrier and its function during inflammation and autoimmunity

The blood–brain barrier (BBB) is an important physiologic barrier that separates CNS from soluble inflammatory mediators and effector immune cells from peripheral circulation. The optimum function of the BBB is necessary for the homeostasis, maintenance, and proper neuronal function. The clinical and experimental findings have shown that BBB dysfunction is an early hallmark of various neurologic disorders ranging from inflammatory autoimmune, neurodegenerative, and traumatic diseases to neuroinvasive infections. Significant progress has been made in the understanding of the regulation of BBB function under homeostatic and neuroinflammatory conditions. Several neurologic disease-modifying drugs have shown to improve the BBB function. However, they have a broad-acting immunomodulatory function and can increase the risk of life-threatening infections. The recent development of in vitro multicomponent 3-dimensional BBB models coupled with fluidics chamber as well as a cell-type specific reporter and knockout mice gave a new boost to our understanding of the dynamics of the BBB. In the review, we discuss the current understanding of BBB composition and recent findings that illustrate the critical regulatory elements of the BBB function under physiologic and inflammatory conditions, and also suggested the strategies to control BBB structure and function.