The Serine Protease Homolog, Scarface, Is Sensitive to Nutrient Availability and Modulates the Development of the Drosophila Blood-Brain Barrier.

The adaptable transcriptional response to changes in food availability not only ensures animal survival but also lets embryonic development progress. Interestingly, the CNS is preferentially protected from periods of malnutrition, a phenomenon known as "brain sparing." However, the mechanisms that mediate this response remain poorly understood. To get a better understanding of this, we used Drosophila melanogaster as a model, analyzing the transcriptional response of neural stem cells (neuroblasts) and glia of the blood-brain barrier (BBB) from larvae of both sexes during nutrient restriction using targeted DamID. We found differentially expressed genes in both neuroblasts and glia of the BBB, although the effect of nutrient deficiency was primarily observed in the BBB. We characterized the function of a nutritional sensitive gene expressed in the BBB, the serine protease homolog, scarface (scaf). Scaf is expressed in subperineurial glia in the BBB in response to nutrition. Tissue-specific knockdown of scaf increases subperineurial glia endoreplication and proliferation of perineurial glia in the blood-brain barrier. Furthermore, neuroblast proliferation is diminished on scaf knockdown in subperineurial glia. Interestingly, reexpression of Scaf in subperineurial glia is able to enhance neuroblast proliferation and brain growth of animals in starvation. Finally, we show that loss of scaf in the blood-brain barrier increases sensitivity to drugs in adulthood, suggesting a physiological impairment. We propose that Scaf integrates the nutrient status to modulate the balance between neurogenesis and growth of the BBB, preserving the proper equilibrium between the size of the barrier and the brain.SIGNIFICANCE STATEMENT The Drosophila BBB separates the CNS from the open circulatory system. The BBB glia are not only acting as a physical segregation of tissues but participate in the regulation of the metabolism and neurogenesis during development. Here we analyze the transcriptional response of the BBB glia to nutrient deprivation during larval development, a condition in which protective mechanisms are switched on in the brain. Our findings show that the gene scarface reduces growth in the BBB while promoting the proliferation of neural stem, assuring the balanced growth of the larval brain. Thus, Scarface would link animal nutrition with brain development, coordinating neurogenesis with the growth of the BBB.

[Central Nervous System Developmental Regulation of Microglia via Cytokines and Chemokines].

Microglia are immune cells resident in the central nervous system (CNS). It has been gradually clarified that microglia play various roles at the developmental stage of the CNS. From embryonic to early postnatal age, microglia remove apoptotic cells by phagocytosis and refine the neural circuits by synaptic pruning. In addition, microglia promote the proliferation and differentiation of neural stem cells by releasing physiologically active substances. Our group has focused on the physiological actions of microglia via cytokines and chemokines at the early postnatal developmental stage. We found that a large number of activated microglia accumulate in the early postnatal subventricular zone (SVZ). We demonstrated that the these SVZ microglia facilitate neurogenesis and oligodendrogenesis via inflammatory cytokines including IL-1ß, TNFα, IL-6, IFNγ. We have also found that microglia regulate the functional maturation of the blood brain barrier (BBB) and identified the cytokines and chemokines involved in the effects of microglia. These findings indicate that microglia are physiologically more important than ever thought to reveal robust brain functions. Furthermore, the new mode of microglial action may lead to the discovery of drug targets of the incurable CNS diseases.

Contribution of brain pericytes in blood-brain barrier formation and maintenance: a transcriptomic study of cocultured human endothelial cells derived from hematopoietic stem cells.

Formation, maintenance, and repair of the blood-brain barrier (BBB) are critical for central nervous system homeostasis. The interaction of endothelial cells (ECs) with brain pericytes is known to induce BBB characteristics in brain ECs during embryogenesis and can be used to differentiate human ECs from stem cell source in in vitro BBB models. However, the molecular events involved in BBB maturation are not fully understood. To this end, human ECs derived from hematopoietic stem cells were cultivated with either primary bovine or cell line-derived human brain pericytes to induce BBB formation. Subsequently, the transcriptomic profiles of solocultured vs. cocultured ECs were analysed over time by Massive Analysis of cDNA Ends (MACE) technology. This RNA sequencing method is a 3'-end targeted, tag-based, reduced representation transcriptome profiling technique, that can reliably quantify all polyadenylated transcripts including those with low expression. By analysing the generated transcriptomic profiles, we can explore the molecular processes responsible for the functional changes observed in ECs in coculture with brain pericytes (e.g. barrier tightening, changes in the expression of transporters and receptors). Our results identified several up- and downregulated genes and signaling pathways that provide a valuable data source to further delineate complex molecular processes that are involved in BBB formation and BBB maintenance. In addition, this data provides a source to identify novel targets for central nervous system drug delivery strategies.

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.

Basal Sodium-Dependent Vitamin C Transporter 2 polarization in choroid plexus explant cells in normal or scorbutic conditions.

Vitamin C is incorporated into the cerebrospinal fluid (CSF) through choroid plexus cells. While the transfer of vitamin C from the blood to the brain has been studied functionally, the vitamin C transporter, SVCT2, has not been detected in the basolateral membrane of choroid plexus cells. Furthermore, it is unknown how its expression is induced in the developing brain and modulated in scurvy conditions. We concluded that SVCT2 is intensely expressed in the second half of embryonic brain development and postnatal stages. In postnatal and adult brain, SVCT2 is highly expressed in all choroidal plexus epithelial cells, shown by colocalization with GLUT1 in the basolateral membranes and without MCT1 colocalization, which is expressed in the apical membrane. We confirmed that choroid plexus explant cells (in vitro) form a sealed epithelial structure, which polarized basolaterally, endogenous or overexpressed SVCT2. These results are reproduced in vivo by injecting hSVCT2wt-EYFP lentivirus into the CSF. Overexpressed SVCT2 incorporates AA (intraperitoneally injected) from the blood to the CSF. Finally, we observed in Guinea pig brain under scorbutic condition, that normal distribution of SVCT2 in choroid plexus may be regulated by peripheral concentrations of vitamin C. Additionally, we observed that SVCT2 polarization also depends on the metabolic stage of the choroid plexus cells.

Development and Cell Biology of the Blood-Brain Barrier.

The vertebrate vasculature displays high organotypic specialization, with the structure and function of blood vessels catering to the specific needs of each tissue. A unique feature of the central nervous system (CNS) vasculature is the blood-brain barrier (BBB). The BBB regulates substance influx and efflux to maintain a homeostatic environment for proper brain function. Here, we review the development and cell biology of the BBB, focusing on the cellular and molecular regulation of barrier formation and the maintenance of the BBB through adulthood. We summarize unique features of CNS endothelial cells and highlight recent progress in and general principles of barrier regulation. Finally, we illustrate why a mechanistic understanding of the development and maintenance of the BBB could provide novel therapeutic opportunities for CNS drug delivery.

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.

Tissue linkage through adjoining basement membranes: The long and the short term of it.

Basement membranes (BMs) are thin dense sheets of extracellular matrix that surround most tissues. When the BMs of neighboring tissues come into contact, they usually slide along one another and act to separate tissues and organs into distinct compartments. However, in certain specialized regions, the BMs of neighboring tissues link, helping to bring tissues together. These BM connections can be transient, such as during tissue fusion events in development, or long-term, as with adult tissues involved with filtration, including the blood brain barrier and kidney glomerulus. The transitory nature of these connections in development and the complexity of tissue filtration systems in adults have hindered the understanding of how juxtaposed BMs fasten together. The recent identification of a BM-BM adhesion system in C. elegans, termed B-LINK (BM linkage), however, is revealing cellular and extracellular matrix components of a nascent tissue adhesion system. We discuss insights gained from studying the B-LINK tissue adhesion system in C. elegans, compare this adhesion with other BM-BM connections in Drosophila and vertebrates, and outline important future directions towards elucidating this fascinating and poorly understood mode of adhesion that joins neighboring tissues.

Interplay of the Norrin and Wnt7a/Wnt7b signaling systems in blood-brain barrier and blood-retina barrier development and maintenance.

ß-Catenin signaling controls the development and maintenance of the blood-brain barrier (BBB) and the blood-retina barrier (BRB), but the division of labor and degree of redundancy between the two principal ligand-receptor systems-the Norrin and Wnt7a/Wnt7b systems-are incompletely defined. Here, we present a loss-of-function genetic analysis of postnatal BBB and BRB maintenance in mice that shows striking threshold and partial redundancy effects. In particular, the combined loss of Wnt7a and Norrin or Wnt7a and Frizzled4 (Fz4) leads to anatomically localized BBB defects that are far more severe than observed with loss of Wnt7a, Norrin, or Fz4 alone. In the cerebellum, selective loss of Wnt7a in glia combined with ubiquitous loss of Norrin recapitulates the phenotype observed with ubiquitous loss of both Wnt7a and Norrin, implying that glia are the source of Wnt7a in the cerebellum. Tspan12, a coactivator of Norrin signaling in the retina, is also active in BBB maintenance but is less potent than Norrin, consistent with a model in which Tspan12 enhances the amplitude of the Norrin signal in vascular endothelial cells. Finally, in the context of a partially impaired Norrin system, the retina reveals a small contribution to BRB development from the Wnt7a/Wnt7b system. Taken together, these experiments define the extent of CNS region-specific cooperation for several components of the Norrin and Wnt7a/Wnt7b systems, and they reveal substantial regional heterogeneity in the extent to which partially redundant ligands, receptors, and coactivators maintain the BBB and BRB.

Wnt/ß-catenin signaling regulates VE-cadherin-mediated anastomosis of brain capillaries by counteracting S1pr1 signaling.

Canonical Wnt signaling is crucial for vascularization of the central nervous system and blood-brain barrier (BBB) formation. BBB formation and modulation are not only important for development, but also relevant for vascular and neurodegenerative diseases. However, there is little understanding of how Wnt signaling contributes to brain angiogenesis and BBB formation. Here we show, using high resolution in vivo imaging and temporal and spatial manipulation of Wnt signaling, different requirements for Wnt signaling during brain angiogenesis and BBB formation. In the absence of Wnt signaling, premature Sphingosine-1-phosphate receptor (S1pr) signaling reduces VE-cadherin and Esama at cell-cell junctions. We suggest that Wnt signaling suppresses S1pr signaling during angiogenesis to enable the dynamic junction formation during anastomosis, whereas later S1pr signaling regulates BBB maturation and VE-cadherin stabilization. Our data provides a link between brain angiogenesis and BBB formation and identifies Wnt signaling as coordinator of the timing and as regulator of anastomosis.

Glutathione Conjugation at the Blood-CSF Barrier Efficiently Prevents Exposure of the Developing Brain Fluid Environment to Blood-Borne Reactive Electrophilic Substances.

Exposure of the developing brain to toxins, drugs, or deleterious endogenous compounds during the perinatal period can trigger alterations in cell division, migration, differentiation, and synaptogenesis, leading to lifelong neurological impairment. The brain is protected by cellular barriers acting through multiple mechanisms, some of which are still poorly explored. We used a combination of enzymatic assays, live tissue fluorescence microscopy, and an in vitro cellular model of the blood-CSF barrier to investigate an enzymatic detoxification pathway in the developing male and female rat brain. We show that during the early postnatal period the choroid plexus epithelium forming the blood-CSF barrier and the ependymal cell layer bordering the ventricles harbor a high detoxifying capacity that involves glutathione S-transferases. Using a functional knock-down rat model for choroidal glutathione conjugation, we demonstrate that already in neonates, this metabolic pathway efficiently prevents the penetration of blood-borne reactive compounds into CSF. The versatility of the protective mechanism results from the multiplicity of the glutathione S-transferase isoenzymes, which are differently expressed between the choroidal epithelium and the ependyma. The various isoenzymes display differential substrate specificities, which greatly widen the spectrum of molecules that can be inactivated by this pathway. In conclusion, the blood-CSF barrier and the ependyma are identified as key cellular structures in the CNS to protect the brain fluid environment from different chemical classes of potentially toxic compounds during the postnatal period. This metabolic neuroprotective function of brain interfaces ought to compensate for the liver postnatal immaturity.SIGNIFICANCE STATEMENT Brain homeostasis requires a stable and controlled internal environment. Defective brain protection during the perinatal period can lead to lifelong neurological impairment. We demonstrate that the choroid plexus forming the blood-CSF barrier is a key player in the protection of the developing brain. Glutathione-dependent enzymatic metabolism in the choroidal epithelium inactivates a broad spectrum of noxious compounds, efficiently preventing their penetration into the CSF. A second line of detoxification is located in the ependyma separating the CSF from brain tissue. Our study reveals a novel facet of the mechanisms by which the brain is protected at a period of high vulnerability, at a time when the astrocytic network is still immature and liver xenobiotic metabolism is limited.

Variant cell cycles regulated by Notch signaling control cell size and ensure a functional blood-brain barrier.

Regulation of cell size is crucial in development. In plants and animals two cell cycle variants are employed to generate large cells by increased ploidy: the endocycle and endomitosis. The rationale behind the choice of which of these cycles is implemented is unknown. We show that in the Drosophila nervous system the subperineurial glia (SPG) are unique in using both the endocycle and endomitosis to grow. In the brain, the majority of SPG initially endocycle, then switch to endomitosis during larval development. The Notch signaling pathway and the String Cdc25 phosphatase are crucial for the endocycle versus endomitosis choice, providing the means experimentally to change cells from one to the other. This revealed fundamental insights into the control of cell size and the properties of endomitotic cells. Endomitotic cells attain a higher ploidy and larger size than endocycling cells, and endomitotic SPG are necessary for the blood-brain barrier. Decreased Notch signaling promotes endomitosis even in the ventral nerve cord SPG that normally are mononucleate, but not in the endocycling salivary gland cells, revealing tissue-specific cell cycle responses.

A role for sex and a common HFE gene variant in brain iron uptake.

HFE (high iron) is an essential protein for regulating iron transport into cells. Mutations of the HFE gene result in loss of this regulation causing accumulation of iron within the cell. The mutated protein has been found increasingly in numerous neurodegenerative disorders in which increased levels of iron in the brain are reported. Additionally, evidence that these mutations are associated with elevated brain iron challenges the paradigm that the brain is protected by the blood-brain barrier. While much has been studied regarding the role of HFE in cellular iron uptake, it has remained unclear what role the protein plays in the transport of iron into the brain. We investigated regulation of iron transport into the brain using a mouse model with a mutation in the HFE gene. We demonstrated that the rate of radiolabeled iron (59Fe) uptake was similar between the two genotypes despite higher brain iron concentrations in the mutant. However, there were significant differences in iron uptake between males and females regardless of genotype. These data indicate that brain iron status is consistently maintained and tightly regulated at the level of the blood-brain barrier.

Investigation of the Safety of Focused Ultrasound-Induced Blood-Brain Barrier Opening in a Natural Canine Model of Aging.

Rationale: Ultrasound-mediated opening of the Blood-Brain Barrier(BBB) has shown exciting potential for the treatment of Alzheimer's disease(AD). Studies in transgenic mouse models have shown that this approach can reduce plaque pathology and improve spatial memory. Before clinical translation can occur the safety of the method needs to be tested in a larger brain that allows lower frequencies be used to treat larger tissue volumes, simulating clinical situations. Here we investigate the safety of opening the BBB in half of the brain in a large aged animal model with naturally occurring amyloid deposits. Methods: Aged dogs naturally accumulate plaques and show associated cognitive declines. Low-frequency ultrasound was used to open the BBB unilaterally in aged beagles (9-11yrs, n=10) in accordance with institutionally approved protocols. Animals received either a single treatment or four weekly treatments. Magnetic resonance imaging(MRI) was used to guide the treatments and assess the tissue effects. The animals underwent neurological testing during treatment follow-up, and a follow-up MRI exam 1 week following the final treatment. Results: The permeability of the BBB was successfully increased in all animals (mean enhancement: 19±11% relative to untreated hemisphere). There was a single adverse event in the chronic treatment group that resolved within 24 hrs. Follow-up MRI showed the BBB to be intact with no evidence of tissue damage in all animals. Histological analysis showed comparable levels of microhemorrhage between the treated and control hemispheres in the prefrontal cortex (single/repeat treatment: 1.0±1.4 vs 0.4±0.5/5.2±1.8 vs. 4.0±2.0). No significant differences were observed in beta-amyloid load (single/repeat: p=0.31/p=0.98) although 3/5 animals in each group showed lower Aß loads in the treated hemisphere. Conclusion: Whole-hemisphere opening of the BBB was well tolerated in the aged large animal brain. The treatment volumes and frequencies used are clinically relevant and indicate safety for clinical translation. Further study is warranted to determine if FUS has positive effects on naturally occurring amyloid pathology.

The blood brain barrier: Insights from development and ageing.

The blood brain barrier is a necessity for cerebral homeostasis and response to environmental insult, thus loss in functionality with age creates opportunities for disease to arise in the aged brain. Understanding how the barrier is developed and maintained throughout the earlier years of adult life can identify key processes that may have beneficial applications in the restoration of the aged brain. With an unprecedented increasing global aged population, the prevention and treatment of age-associated disorders has become a rising healthcare priority demanding novel approaches for the development of therapeutic strategies. The aging cardiovascular system has long been recognised to be a major factor in age-associated diseases such as stroke, atherosclerosis and cardiac arrest. Changes in the highly specialised cerebral vasculature may similarly drive neurodegenerative and neuropsychiatric disease.

[Iron and Neurodevelopment]. / Fer et neurodéveloppement.

In the central nervous system, iron is a cofactor of many metabolic processes and synthesis of aminergic neurotransmitters. Iron plays an major function on brain development from the prenatal period to teenage years. The blood-brain barrier modulates concentration of iron in the brain. In case of iron deficiency in the child, the negative impact on the myelinogenesis and synaptogenesis are well proven, with negative effects on psychomotor and cognitive functions. Iron supplementation has a beneficial effect, even if there is no anemia. The consequences of iron deficiency are more harmful as deficiency is early. The main mechanisms involved about iron and brain are reviewed.

Differential Effects of Retinoic Acid Concentrations in Regulating Blood-Brain Barrier Properties.

The blood-brain barrier (BBB) is a multifaceted property of the brain vasculature that protects the brain and maintains homeostasis by tightly regulating the flux of ions, molecules, and cells across the vasculature. Blood vessels in the brain are formed by endothelial cells that acquire barrier properties, such as tight and adherens junctions, soon after the brain vasculature is formed. Endothelial WNT signaling is crucial to induce these BBB properties by regulating their expression and stabilization. Recent studies have implicated retinoic acid (RA) signaling in BBB development and shown that pharmacological concentrations of RA (≥5 µm) can induce BBB properties in cultured brain endothelial cells. However, a recent study demonstrated that RA inhibits endothelial WNT signaling during brain development, suggesting that RA does not promote BBB properties. We therefore investigated whether RA plays a physiological role in BBB development. We found that BBB function and junctional protein expression was unaffected in mouse mutants that have a reduced capacity to synthesize RA (Rdh10 mutants). Furthermore, embryos exposed to a RA-enriched diet did not enhance BBB protein expression. Together, our data indicate that RA is not capable of inducing, nor is it required for, BBB protein expression in vivo. Like other studies, we found that pharmacological concentrations of RA induce BBB genes in cultured murine brain endothelial cells, and this may involve activation of the LXR/RXR signaling pathway. Our data do not support a role for RA in BBB development, but confirm reports that pharmacological RA is a robust tool to induce BBB properties in culture.

Brain uptake of deltamethrin in rats as a function of plasma protein binding and blood-brain barrier maturation.

Pyrethroids, including permethrin and deltamethrin (DLM), are very widely used of insecticides. It was hypothesized that lower plasma binding and increased blood-brain barrier (BBB) penetration of DLM in immature rats contribute to the higher brain concentrations of DLM and more pronounced neurotoxicity reported in this age group. The left brain of anesthetized adult rats was perfused for 2min via a carotid artery with 1µM 14C-DLM in: 2-5% human serum albumin (HSA); plasma from adult and 15- and 21-d-old rats; and plasma from human donors of: birth-1 week, 1-4 weeks, 4 weeks-1 year, 1-3 years and adults. The fraction of DLM bound and brain uptake of DLM did not vary significantly with the HSA concentration nor with the age of rat or human plasma donors. One, 10 and 50µM 14C-DLM were perfused into the left-brain of anesthetized adult, 15- and 21-d-old rats. DLM deposition in the brain was linear over this range of concentrations and inversely related to age. The results of this investigation indicate that increased BBB permeability in the youngest rats enhances brain deposition of the insecticide. Plasma protein binding of DLM in immature rats and humans is not sufficiently diminished to impact its brain uptake.

Blood-brain barrier-supported neurogenesis in healthy and diseased brain.

Adult neurogenesis is one of the most important mechanisms contributing to brain development, learning, and memory. Alterations in neurogenesis underlie a wide spectrum of brain diseases. Neurogenesis takes place in highly specialized neurogenic niches. The concept of neurogenic niches is becoming widely accepted due to growing evidence of the important role of the microenvironment established in the close vicinity to stem cells in order to provide adequate control of cell proliferation, differentiation, and apoptosis. Neurogenic niches represent the platform for tight integration of neurogenesis and angiogenesis supported by specific properties of cerebral microvessel endothelial cells contributing to establishment of partially compromised blood-brain barrier (BBB) for the adjustment of local conditions to the current metabolic needs of stem and progenitor cells. Here, we review up-to-date data on microvascular dynamics in activity-dependent neurogenesis, specific properties of BBB in neurogenic niches, endothelial-driven mechanisms of clonogenic activity, and future perspectives for reconstructing the neurogenic niches in vitro.

Brain microvasculature defects and Glut1 deficiency syndrome averted by early repletion of the glucose transporter-1 protein.

Haploinsufficiency of the SLC2A1 gene and paucity of its translated product, the glucose transporter-1 (Glut1) protein, disrupt brain function and cause the neurodevelopmental disorder, Glut1 deficiency syndrome (Glut1 DS). There is little to suggest how reduced Glut1 causes cognitive dysfunction and no optimal treatment for Glut1 DS. We used model mice to demonstrate that low Glut1 protein arrests cerebral angiogenesis, resulting in a profound diminution of the brain microvasculature without compromising the blood-brain barrier. Studies to define the temporal requirements for Glut1 reveal that pre-symptomatic, AAV9-mediated repletion of the protein averts brain microvasculature defects and prevents disease, whereas augmenting the protein late, during adulthood, is devoid of benefit. Still, treatment following symptom onset can be effective; Glut1 repletion in early-symptomatic mutants that have experienced sustained periods of low brain glucose nevertheless restores the cerebral microvasculature and ameliorates disease. Timely Glut1 repletion may thus constitute an effective treatment for Glut1 DS.