Sensory-related neural activity regulates the structure of vascular networks in the cerebral cortex

Neuronal enhancers fine-tune adaptive circuit plasticity

Neuronal activity-regulated gene expression plays a crucial role in sculpting neural circuits that underpin adaptive brain function. Transcriptional enhancers are now recognized as key components of gene regulation that orchestrate spatiotemporally precise patterns of gene transcription. We propose that the dynamics of enhancer activation uniquely position these genomic elements to finely tune activity-dependent cellular plasticity. Enhancer specificity and modularity can be exploited to gain selective genetic access to specific cell states, and the precise modulation of target gene expression within restricted cellular contexts enabled by targeted enhancer manipulation allows for fine-grained evaluation of gene function. Mounting evidence also suggests that enduring stimulus-induced changes in enhancer states can modify target gene activation upon restimulation, thereby contributing to a form of cell-wide metaplasticity. We advocate for focused exploration of activity-dependent enhancer function to gain new insight into the mechanisms underlying brain plasticity and cognitive dysfunction.

Neural Regulation of Vascular Development: Molecular Mechanisms and Interactions

As a critical part of the circulatory system, blood vessels transport oxygen and nutrients to every corner of the body, nourishing each cell, and also remove waste and toxins. Defects in vascular development and function are closely associated with many diseases, such as heart disease, stroke, and atherosclerosis. In the nervous system, the nervous and vascular systems are intricately connected in both development and function. First, peripheral blood vessels and nerves exhibit parallel distribution patterns. In the central nervous system (CNS), nerves and blood vessels form a complex interface known as the neurovascular unit. Second, the vascular system employs similar cellular and molecular mechanisms as the nervous system for its development. Third, the development and function of CNS vasculature are tightly regulated by CNS-specific signaling pathways and neural activity. Additionally, vascular endothelial cells within the CNS are tightly connected and interact with pericytes, astrocytes, neurons, and microglia to form the blood-brain barrier (BBB). The BBB strictly controls material exchanges between the blood and brain, maintaining the brain's microenvironmental homeostasis, which is crucial for the normal development and function of the CNS. Here, we comprehensively summarize research on neural regulation of vascular and BBB development and propose directions for future research.

Glutamatergic neuronal activity regulates angiogenesis and blood-retinal barrier maturation via Norrin/β-catenin signaling

Interactions among neuronal, glial, and vascular components are crucial for retinal angiogenesis and blood-retinal barrier (BRB) maturation. Although synaptic dysfunction precedes vascular abnormalities in many retinal pathologies, how neuronal activity, specifically glutamatergic activity, regulates retinal angiogenesis and BRB maturation remains unclear. Using in vivo genetic studies in mice, single-cell RNA sequencing (scRNA-seq), and functional validation, we show that deep plexus angiogenesis and paracellular BRB maturation are delayed in Vglut1-/- retinas where neurons fail to release glutamate. By contrast, deep plexus angiogenesis and paracellular BRB maturation are accelerated in Gnat1-/- retinas, where constitutively depolarized rods release excessive glutamate. Norrin expression and endothelial Norrin/β-catenin signaling are downregulated in Vglut1-/- retinas and upregulated in Gnat1-/- retinas. Pharmacological activation of endothelial Norrin/β-catenin signaling in Vglut1-/- retinas rescues defects in deep plexus angiogenesis and paracellular BRB maturation. Our findings demonstrate that glutamatergic neuronal activity regulates retinal angiogenesis and BRB maturation by modulating endothelial Norrin/β-catenin signaling.

Pathology-based brain arterial disease phenotypes and their radiographic correlates

INTRODUCTION

Brain arterial diseases, including atherosclerosis, vasculitis, and dissections, are major contributors to cerebrovascular morbidity and mortality worldwide. These diseases not only increase the risk of stroke but also play a significant role in neurodegeneration and dementia. Clear and unambiguous terminology and classification of brain arterial disease phenotypes is crucial for research and clinical practice.

MATERIAL AND METHODS

This review aims to summarize and harmonize the terminology used for brain large and small arterial phenotypes based on pathology studies and relate them to imaging phenotypes used in medical research and clinical practice.

CONCLUSIONS AND RESULTS

Arteriosclerosis refers to hardening of the arteries but does not specify the underlying etiology. Specific terms such as atherosclerosis, calcification, or non-atherosclerotic fibroplasia are preferred. Atherosclerosis is defined pathologically by an atheroma. Other brain arterial pathologies occur and should be distinguished from atherosclerosis given therapeutic implications. On brain imaging, intracranial arterial luminal stenosis is usually attributed to atherosclerosis in the presence of atherosclerotic risk factors but advanced high-resolution arterial wall imaging has the potential to more accurately identify the underlying pathology. Regarding small vessel disease, arteriosclerosis is ambiguous and arteriolosclerosis is often used to denote the involvement of arterioles rather than arteries. Lipohyalinosis is sometimes used synonymously with arteriolosclerosis, but less accurately describes this common small vessel thickening which uncommonly shows lipid. Specific measures of small vessel wall thickness, the relationship to the lumen as well as changes in the layer composition might convey objective, measurable data regarding the status of brain small vessels.

Modeling oxygen transport in the brain: An efficient coarse-grid approach to capture perivascular gradients in the parenchyma

Recent progresses in intravital imaging have enabled highly-resolved measurements of periarteriolar oxygen gradients (POGs) within the brain parenchyma. POGs are increasingly used as proxies to estimate the local baseline oxygen consumption, which is a hallmark of cell activity. However, the oxygen profile around a given arteriole arises from an interplay between oxygen consumption and delivery, not only by this arteriole but also by distant capillaries. Integrating such interactions across scales while accounting for the complex architecture of the microvascular network remains a challenge from a modelling perspective. This limits our ability to interpret the experimental oxygen maps and constitutes a key bottleneck toward the inverse determination of metabolic rates of oxygen. We revisit the problem of parenchymal oxygen transport and metabolism and introduce a simple, conservative, accurate and scalable direct numerical method going beyond canonical Krogh-type models and their associated geometrical simplifications. We focus on a two-dimensional formulation, and introduce the concepts needed to combine an operator-splitting and a Green's function approach. Oxygen concentration is decomposed into a slowly-varying contribution, discretized by Finite Volumes over a coarse cartesian grid, and a rapidly-varying contribution, approximated analytically in grid-cells surrounding each vessel. Starting with simple test cases, we thoroughly analyze the resulting errors by comparison with highly-resolved simulations of the original transport problem, showing considerable improvement of the computational-cost/accuracy balance compared to previous work. We then demonstrate the model ability to flexibly generate synthetic data reproducing the spatial dynamics of oxygen in the brain parenchyma, with sub-grid resolution. Based on these synthetic data, we show that capillaries distant from the arteriole cannot be overlooked when interpreting POGs, thus reconciling recent measurements of POGs across cortical layers with the fundamental idea that variations of vascular density within the depth of the cortex may reveal underlying differences in neuronal organization and metabolic load.

Brain artery diameters and risk of dementia and stroke

INTRODUCTION

We tested the association of brain artery diameters with dementia and stroke risk in three distinct population-based studies using conventional T2-weighted brain magnetic resonance imaging (MRI) images.

METHODS

We included 8420 adults > 40 years old from three longitudinal population-based studies with brain MRI scans. We estimated and meta-analyzed the hazard ratios (HRs) of the brain and carotids and basilar diameters associated with dementia and stroke.

RESULT

Overall and carotid artery diameters > 95th percentile increased the risk for dementia by 1.74 (95% confidence interval [CI], 1.13-2.68) and 1.48 (95% CI, 1.12-1.96) fold, respectively. For stroke, meta-analyses yielded HRs of 1.59 (95% CI, 1.04-2.42) for overall arteries and 2.11 (95% CI, 1.45-3.08) for basilar artery diameters > 95th percentile.

DISCUSSION

Individuals with dilated brain arteries are at higher risk for dementia and stroke, across distinct populations. Our findings underline the potential value of T2-weighted brain MRI-based brain diameter assessment in estimating the risk of dementia and stroke.

A Vascular-Centric Approach to Autism Spectrum Disorders

Brain development and function are highly reliant on adequate establishment and maintenance of vascular networks. Early impairments in vascular health can impact brain maturation and energy metabolism, which may lead to neurodevelopmental anomalies. Our recent work not only provides novel insights into the development of cerebrovascular networks but also emphasizes the importance of their well-being for proper brain maturation. In particular, we have demonstrated that endothelial dysfunction in autism spectrum disorders (ASD) mouse models is causally related to altered behavior and brain metabolism. In the prenatal human brain, vascular cells change metabolic states in the second trimester. Such findings highlight the need to identify new cellular and molecular players in neurodevelopmental disorders, raising awareness about the importance of a healthy vasculature for brain development. It is thus essential to shift the mostly neuronal point of view in research on ASD and other neurodevelopmental disorders to also include vascular and metabolic features.

Cone cell dysfunction attenuates retinal neovascularization in oxygen-induced retinopathy mouse model

Aberrant neovascularization is the most common feature in retinopathy of prematurity (ROP), which leads to the retinal detachment and visual defects in neonates with a low gestational age eventually. Understanding the regulation of inappropriate angiogenic signaling benefits individuals at-risk. Recently, neural activity originating from the specific neural activity has been considered to contribute to retinal angiogenesis. Here, we explored the impact of cone cell dysfunction on oxygen-induced retinopathy (OIR), a mouse model commonly employed to understand retinal diseases associated with abnormal blood vessel growth, using the Gnat2cpfl3 (cone photoreceptor function loss-3) strain of mice (regardless of the sex), which is known for its inherent cone cell dysfunction. We found that the retinal avascular area, hypoxic area, and neovascular area were significantly attenuated in Gnat2cpfl3 OIR mice compared to those in C57BL/6 OIR mice. Moreover, the HIF-1α/VEGF axis was also reduced in Gnat2cpfl3 OIR mice. Collectively, our results indicated that cone cell dysfunction, as observed in Gnat2cpfl3 OIR mice, leads to attenuated retinal neovascularization. This finding suggests that retinal neural activity may precede and potentially influence the onset of pathological neovascularization.

Involvement of neuronal factors in tumor angiogenesis and the shaping of the cancer microenvironment

Emerging evidence suggests that nerves within the tumor microenvironment play a crucial role in regulating angiogenesis. Neurotransmitters and neuropeptides released by nerves can interact with nearby blood vessels and tumor cells, influencing their behavior and modulating the angiogenic response. Moreover, nerve-derived signals may activate signaling pathways that enhance the production of pro-angiogenic factors within the tumor microenvironment, further supporting blood vessel growth around tumors. The intricate network of communication between neural constituents and the vascular system accentuates the potential of therapeutically targeting neural-mediated pathways as an innovative strategy to modulate tumor angiogenesis and, consequently, neoplastic proliferation. Hereby, we review studies that evaluate the precise molecular interplay and the potential clinical ramifications of manipulating neural elements for the purpose of anti-angiogenic therapeutics within the scope of cancer treatment.

Implementation of the neuro-glia-vascular unit through co-culture of adult neural stem cells and vascular cells and transcriptomic analysis of diverse Aβ assembly types

BACKGROUND

The blood-brain barrier (BBB) is a specialized layer between blood vessels and tissue in the brain, which is comprised of a neuro-glia-vascular (NGV) unit, thus play a vital role in various brain diseases.

NEW METHOD

We developed the in vitro NGV units by co-culturing brain microvascular endothelial cells (BMECs; bEnd.3) and primary neural stem cells extracted from subventricular zone of adult mice. This approach was designed to mimic the RNA profile conditions found in the microvessels of a mouse brain and confirmed through various comparative transcriptome analyses.

RESULTS

Optimal NGV unit development was achieved by adjusting cell density-dependent co-culture ratios. Specifically, the morphogenic development and neuronal association of astrocyte endfeet were well observed in the contact region with BMECs in the NGV unit. Through transcriptome analysis, we compared co-cultured bEnd.3/NSCs with monocultured bEnd.3 or NSCs and additionally compared them with previously reported mouse brain vascular tissue to show that this NGV unit model is a suitable in vitro model for neurological disease such as Alzheimer's disease (AD).

COMPARISON WITH EXISTING METHOD(S)

This in vitro NGV unit was formed from neural stem cells and vascular cells in the brain of adult mice, not embryos. It is very useful for studying brain disease mechanisms by identifying proteins and genes associated with diseases progress.

CONCLUSIONS

We suggest that this simple in vitro NGV model is appropriate to investigate the relationship between BBB changes and pathological factors in the fields of neurovascular biology and cerebrovascular diseases including AD.

Glutamatergic neuronal activity regulates angiogenesis and blood-retinal barrier maturation via Norrin/β-catenin signaling

Interactions among neuronal, glial and vascular components are crucial for retinal angiogenesis and blood-retinal barrier (BRB) maturation. Although synaptic dysfunction precedes vascular abnormalities in many retinal pathologies, how neuronal activity, specifically glutamatergic activity, regulates retinal angiogenesis and BRB maturation remains unclear. Using in vivo genetic studies in mice, single-cell RNA-sequencing and functional validation, we show that deep plexus angiogenesis and paracellular BRB maturation are delayed in Vglut1 -/- retinas where neurons fail to release glutamate. In contrast, deep plexus angiogenesis and paracellular BRB maturation are accelerated in Gnat1 -/- retinas where constitutively depolarized rods release excessive glutamate. Norrin expression and endothelial Norrin/β-catenin signaling are downregulated in Vglut1 -/- retinas, and upregulated in Gnat1 -/- retinas. Pharmacological activation of endothelial Norrin/β-catenin signaling in Vglut1 -/- retinas rescued defects in deep plexus angiogenesis and paracellular BRB maturation. Our findings demonstrate that glutamatergic neuronal activity regulates retinal angiogenesis and BRB maturation by modulating endothelial Norrin/β-catenin signaling.

Sex, hormones and cerebrovascular function: from development to disorder

Proper cerebrovascular development and neurogliovascular unit assembly are essential for brain growth and function throughout life, ensuring the continuous supply of nutrients and oxygen. This involves crucial events during pre- and postnatal stages through key pathways, including vascular endothelial growth factor (VEGF) and Wnt signaling. These pathways are pivotal for brain vascular growth, expansion, and blood-brain barrier (BBB) maturation. Interestingly, during fetal and neonatal life, cerebrovascular formation coincides with the early peak activity of the hypothalamic-pituitary-gonadal axis, supporting the idea of sex hormonal influence on cerebrovascular development and barriergenesis.Sex hormonal dysregulation in early development has been implicated in neurodevelopmental disorders with highly sexually dimorphic features, such as autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD). Both disorders show higher prevalence in men, with varying symptoms between sexes, with boys exhibiting more externalizing behaviors, such as aggressivity or hyperactivity, and girls displaying higher internalizing behaviors, including anxiety, depression, or attention disorders. Indeed, ASD and ADHD are linked to high prenatal testosterone exposure and reduced aromatase expression, potentially explaining sex differences in prevalence and symptomatology. In line with this, high estrogen levels seem to attenuate ADHD symptoms. At the cerebrovascular level, sex- and region-specific variations of cerebral blood flow perfusion have been reported in both conditions, indicating an impact of gonadal hormones on the brain vascular system, disrupting its ability to respond to neuronal demands.This review aims to provide an overview of the existing knowledge concerning the impact of sex hormones on cerebrovascular formation and maturation, as well as the onset of neurodevelopmental disorders. Here, we explore the concept of gonadal hormone interactions with brain vascular and BBB development to function, with a particular focus on the modulation of VEGF and Wnt signaling. We outline how these pathways may be involved in the underpinnings of ASD and ADHD. Outstanding questions and potential avenues for future research are highlighted, as uncovering sex-specific physiological and pathological aspects of brain vascular development might lead to innovative therapeutic approaches in the context of ASD, ADHD and beyond.

Impaired neuronal activity as a potential factor contributing to the underdeveloped cerebrovasculature in a young Parkinson's disease mouse model

Misfolding of α-synuclein (α-Syn) in the brain causes cellular dysfunction, leading to cell death in a group of neurons, and consequently causes the progression of Parkinson's disease (PD). Although many studies have demonstrated the pathological connections between vascular dysfunction and neurodegenerative diseases, it remains unclear how neuronal accumulation of α-Syn affects the structural and functional aspects of the cerebrovasculature to accelerate early disease progression. Here, we demonstrated the effect of aberrant α-Syn expression on the brain vasculature using a PD mouse model expressing a familial mutant form of human α-Syn selectively in neuronal cells. We showed that young PD mice have an underdeveloped cerebrovasculature without significant α-Syn accumulation in the vasculature. During the early phase of PD, toxic α-Syn was selectively increased in neuronal cells, while endothelial cell proliferation was decreased in the absence of vascular cell death or neuroinflammation. Instead, we observed altered neuronal activation and minor changes in the activity-dependent gene expression in brain endothelial cells (ECs) in young PD mice. These findings demonstrated that neuronal expression of mutant α-Syn in the early stage of PD induces abnormal neuronal activity and contributes to vascular patterning defects, which could be associated with a reduced angiogenic potential of ECs.

Synaptic plasticity through a naturalistic lens

From the myriad of studies on neuronal plasticity, investigating its underlying molecular mechanisms up to its behavioral relevance, a very complex landscape has emerged. Recent efforts have been achieved toward more naturalistic investigations as an attempt to better capture the synaptic plasticity underpinning of learning and memory, which has been fostered by the development of in vivo electrophysiological and imaging tools. In this review, we examine these naturalistic investigations, by devoting a first part to synaptic plasticity rules issued from naturalistic in vivo-like activity patterns. We next give an overview of the novel tools, which enable an increased spatio-temporal specificity for detecting and manipulating plasticity expressed at individual spines up to neuronal circuit level during behavior. Finally, we put particular emphasis on works considering brain-body communication loops and macroscale contributors to synaptic plasticity, such as body internal states and brain energy metabolism.

Stroke-induced damage on the blood-brain barrier

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

Involvement of brain metabolism in neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) affect a significant portion of the global population and have a substantial social and economic impact worldwide. Most NDDs manifest in early childhood and are characterized by deficits in cognition, communication, social interaction and motor control. Due to a limited understanding of the etiology of NDDs, current treatment options primarily focus on symptom management rather than on curative solutions. Moreover, research on NDDs is problematic due to its reliance on a neurocentric approach. However, recent studies are broadening the scope of research on NDDs, to include dysregulations within a diverse network of brain cell types, including vascular and glial cells. This review aims to summarize studies from the past few decades on potential new contributions to the etiology of NDDs, with a special focus on metabolic signatures of various brain cells. In particular, we aim to convey how the metabolic functions are intimately linked to the onset and/or progression of common NDDs such as autism spectrum disorders, fragile X syndrome, Rett syndrome and Down syndrome.

Astroglial Hmgb1 regulates postnatal astrocyte morphogenesis and cerebrovascular maturation

Astrocytes are intimately linked with brain blood vessels, an essential relationship for neuronal function. However, astroglial factors driving these physical and functional associations during postnatal brain development have yet to be identified. By characterizing structural and transcriptional changes in mouse cortical astrocytes during the first two postnatal weeks, we find that high-mobility group box 1 (Hmgb1), normally upregulated with injury and involved in adult cerebrovascular repair, is highly expressed in astrocytes at birth and then decreases rapidly. Astrocyte-selective ablation of Hmgb1 at birth affects astrocyte morphology and endfoot placement, alters distribution of endfoot proteins connexin43 and aquaporin-4, induces transcriptional changes in astrocytes related to cytoskeleton remodeling, and profoundly disrupts endothelial ultrastructure. While lack of astroglial Hmgb1 does not affect the blood-brain barrier or angiogenesis postnatally, it impairs neurovascular coupling and behavior in adult mice. These findings identify astroglial Hmgb1 as an important player in postnatal gliovascular maturation.

Diversity of cells and signals in the cardiovascular system

This white paper is the outcome of the seventh UC Davis Cardiovascular Research Symposium on Systems Approach to Understanding Cardiovascular Disease and Arrhythmia. This biannual meeting aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The theme of the 2022 Symposium was 'Cell Diversity in the Cardiovascular System, cell-autonomous and cell-cell signalling'. Experts in the field contributed their experimental and mathematical modelling perspectives and discussed emerging questions, controversies, and challenges in examining cell and signal diversity, co-ordination and interrelationships involved in cardiovascular function. This paper originates from the topics of formal presentations and informal discussions from the Symposium, which aimed to develop a holistic view of how the multiple cell types in the cardiovascular system integrate to influence cardiovascular function, disease progression and therapeutic strategies. The first section describes the major cell types (e.g. cardiomyocytes, vascular smooth muscle and endothelial cells, fibroblasts, neurons, immune cells, etc.) and the signals involved in cardiovascular function. The second section emphasizes the complexity at the subcellular, cellular and system levels in the context of cardiovascular development, ageing and disease. Finally, the third section surveys the technological innovations that allow the interrogation of this diversity and advancing our understanding of the integrated cardiovascular function and dysfunction.

Hearing loss and its link to cognitive impairment and dementia

Hearing loss is an important risk factor for the development of dementia, particularly Alzheimer's disease (AD). Mid-life hearing loss increases the risk of developing dementia by double any other single factor. However, given this strong connection between hearing loss and AD, the mechanisms responsible for this link are still unknown. Data from observational studies relating hearing loss and cognitive impairment, measured with standardized questionnaires, has shown a strong relationship between them. Similar findings have emerged from animal studies, showing that the induction of hearing loss via prolonged loud sound exposure or ear canal blocking, can impair cognitive abilities. Interestingly, patients with age-related hearing impairment exhibit increased phosphorylated tau in the cerebrospinal fluid, but no such relationship has been identified for amyloid-β. In addition, hearing loss predisposes to social isolation precipitating the development of dementia through a supposed reduction in cognitive load and processing requirements. Given this link between hearing loss and dementia, the question arises whether the restoration of hearing might mitigate against the onset or progress of AD. Indeed, there is a growing body of research that suggests that those who wear hearing aids for age-related hearing problems maintain better cognitive function over time than those who do not. These are compelling findings, as they suggest the use of hearing aids has the potential to be a cost-effective treatment for those with hearing loss both prior (for those at high risk for AD) and after the development of symptoms. This review aims to summarize the current theories that relate hearing loss and cognitive decline, present the key findings of animal studies, observational studies and summarize the gaps and limitations that need to be addressed in this topic. Through this, we suggest directions for future studies to tackle the lack of adequately randomized control trials in the field. This omission is responsible for the inability to provide a conclusive verdict on whether to use hearing interventions to target hearing-loss related cognitive decline.

Endothelial structure contributes to heterogeneity in brain capillary diameter

The high metabolic demand of brain tissue is supported by a constant supply of blood through dense microvascular networks. Capillaries are the smallest class of vessels and vary in diameter between ∼2 to 5 μm in the brain. This diameter range plays a significant role in the optimization of blood flow resistance, blood cell distribution, and oxygen extraction. The control of capillary diameter has largely been ascribed to pericyte contractility, but it remains unclear if endothelial wall architecture also contributes to capillary diameter heterogeneity. Here, we use public, large-scale volume electron microscopy data from mouse cortex (MICrONS Explorer, Cortical MM^3) to examine how endothelial cell number, endothelial cell thickness, and pericyte coverage relates to microvascular lumen size. We find that transitional vessels near the penetrating arteriole and ascending venule are composed of 2 to 5 interlocked endothelial cells, while the numerous capillary segments intervening these zones are composed of either 1 or 2 endothelial cells, with roughly equal proportions. The luminal area and diameter is on average slightly larger with capillary segments composed of 2 interlocked endothelial cells versus 1 endothelial cell. However, this difference is insufficient to explain the full range of capillary diameters seen in vivo. This suggests that both endothelial structure and other influences, such as pericyte tone, contribute to the basal diameter and optimized perfusion of brain capillaries.

Bi-allelic variants in the ESAM tight-junction gene cause a neurodevelopmental disorder associated with fetal intracranial hemorrhage

The blood-brain barrier (BBB) is an essential gatekeeper for the central nervous system and incidence of neurodevelopmental disorders (NDDs) is higher in infants with a history of intracerebral hemorrhage (ICH). We discovered a rare disease trait in thirteen individuals, including four fetuses, from eight unrelated families associated with homozygous loss-of-function variant alleles of ESAM which encodes an endothelial cell adhesion molecule. The c.115del (p.Arg39Glyfs∗33) variant, identified in six individuals from four independent families of Southeastern Anatolia, severely impaired the in vitro tubulogenic process of endothelial colony-forming cells, recapitulating previous evidence in null mice, and caused lack of ESAM expression in the capillary endothelial cells of damaged brain. Affected individuals with bi-allelic ESAM variants showed profound global developmental delay/unspecified intellectual disability, epilepsy, absent or severely delayed speech, varying degrees of spasticity, ventriculomegaly, and ICH/cerebral calcifications, the latter being also observed in the fetuses. Phenotypic traits observed in individuals with bi-allelic ESAM variants overlap very closely with other known conditions characterized by endothelial dysfunction due to mutation of genes encoding tight junction molecules. Our findings emphasize the role of brain endothelial dysfunction in NDDs and contribute to the expansion of an emerging group of diseases that we propose to rename as "tightjunctionopathies."

Caspase-3 Inhibition toward Perinatal Protection of the Developing Brain from Environmental Stress

Throughout our lives, we are exposed to a variety of hazards, such as environmental pollutants and chemical substances that affect our health, and viruses and bacteria that cause infectious diseases. These external factors that are undesirable to an organism are called environmental stress. During the perinatal period, when neural networks are drastically reorganized and refined, the tolerance of the developing brain to various environmental stresses is lower than in adulthood. Thus, exposure to environmental stress during this vulnerable period is strongly associated with cognitive and behavioral deficits in later life. Recent studies have uncovered various mechanisms underlying the adverse impacts of environmental stress during the perinatal period on brain development. In this mini-review, we will present the findings from these studies, focusing on caspase-mediated apoptotic and nonapoptotic effects of environmental stress, and discuss several compounds that mitigate these caspase-mediated effects as examples of potential therapeutic approaches.

Endothelial structure contributes to heterogeneity in brain capillary diameter

The high metabolic demand of brain tissue is supported by a constant supply of blood flow through dense microvascular networks. Capillaries are the smallest class of vessels in the brain and their lumens vary in diameter between ~2 and 5 μm. This diameter range plays a significant role in optimizing blood flow resistance, blood cell distribution, and oxygen extraction. The control of capillary diameter has largely been ascribed to pericyte contractility, but it remains unclear if the architecture of the endothelial wall also contributes to capillary diameter. Here, we use public, large-scale volume electron microscopy data from mouse cortex (MICrONS Explorer, Cortical mm3) to examine how endothelial cell number, endothelial cell thickness, and pericyte coverage relates to microvascular lumen size. We find that transitional vessels near the penetrating arteriole and ascending venule are composed of two to six interlocked endothelial cells, while the capillaries intervening these zones are composed of either one or two endothelial cells, with roughly equal proportions. The luminal area and diameter are on average slightly larger with capillary segments composed of two interlocked endothelial cells vs one endothelial cell. However, this difference is insufficient to explain the full range of capillary diameters seen in vivo. This suggests that both endothelial structure and other influences, including pericyte tone, contribute to the basal diameter and optimized perfusion of brain capillaries.

Inhibition of VEGF receptors induces pituitary apoplexy: An experimental study in mice

Anti-vascular endothelial growth factor (VEGF) therapy has been developed for the treatment of a variety of cancers. Although this therapy may be a promising alternative treatment for refractory pituitary adenomas and pituitary carcinomas, the effects of anti-VEGF agents on the pituitary gland are not yet well understood. Here, we found that mice administered with OSI-930, an inhibitor of receptor tyrosine kinases including VEGF receptor 1 and 2, frequently exhibited hemorrhage in the pituitary gland. This is the first report that anti-VEGF therapy can cause pituitary apoplexy. C57BL/6 mice were daily injected intraperitoneally with 100 mg/kg body weight of OSI-930 for one to six days. Pituitary glands were immunohistochemically examined. Four of six mice treated for three days and all of five mice treated for six days exhibited hemorrhage in the pituitary gland. In all cases, the hemorrhage occurred just around Rathke's cleft. In OSI-930-administered mice, the vascular coverage and branching were reduced in the anterior lobe, and capillary networks were also decreased in the intermediate lobe in a treatment-day dependent manner. Few blood vessels around Rathke's cleft of the intermediate lobe express VE-cadherin and are covered with platelet-derived growth factor receptor-β (PDGFR-β)-positive cells, which suggests that capillaries around Rathke's cleft of the intermediate lobe were VE-cadherin-negative and not covered with pericytes. The reduction of capillary plexus around Rathke's cleft was observed at the site where hemorrhage occurred, suggesting a causal relationship with the pathogenesis of pituitary hemorrhage. Our study demonstrates that anti-VEGF agents have a risk of pituitary apoplexy. Pituitary apoplexy should be kept in mind as an adverse effect of anti-VEGF therapy.

Neurovascular responses to neuronal activity during sensory development

Understanding the development of intercellular communication in sensory regions is relevant to elucidate mechanisms of physiological and pathological responses to oxygen shortage in the newborn brain. Decades of studies in laboratory rodents show that neuronal activity impacts sensory maturation during two periods of postnatal development distinguished by the maturation of accessory structures at the sensory periphery. During the first of these developmental periods, angiogenesis is modulated by neuronal activity, and physiological levels of neuronal activity cause local tissue hypoxic events. This correlation suggests that neuronal activity is upstream of the production of angiogenic factors, a process that is mediated by intermittent hypoxia caused by neuronal oxygen consumption. In this perspective article we address three theoretical implications based on this hypothesis: first, that spontaneous activity of sensory neurons has properties that favor the generation of intermittent tissue hypoxia in neonate rodents; second, that intermittent hypoxia promotes the expression of hypoxia inducible transcription factors (HIFs) in sensory neurons and astrocytes; and third, that activity-dependent production of angiogenic factors is involved in pathological oxygen contexts.

An analysis of the influence of transfer learning when measuring the tortuosity of blood vessels

BACKGROUND AND OBJECTIVE

Convolutional Neural Networks (CNNs) can provide excellent results regarding the segmentation of blood vessels. One important aspect of CNNs is that they can be trained on large amounts of data and then be made available, for instance, in image processing software. The pre-trained CNNs can then be easily applied in downstream blood vessel characterization tasks, such as the calculation of the length, tortuosity, or caliber of the blood vessels. Yet, it is still unclear if pre-trained CNNs can provide robust, unbiased, results in downstream tasks involving the morphological analysis of blood vessels. Here, we focus on measuring the tortuosity of blood vessels and investigate to which extent CNNs may provide biased tortuosity values even after fine-tuning the network to a new dataset under study.

METHODS

We develop a procedure for quantifying the influence of CNN pre-training in downstream analyses involving the measurement of morphological properties of blood vessels. Using the methodology, we compare the performance of CNNs that were trained on images containing blood vessels having high tortuosity with CNNs that were trained on blood vessels with low tortuosity and fine-tuned on blood vessels with high tortuosity. The opposite situation is also investigated.

RESULTS

We show that the tortuosity values obtained by a CNN trained from scratch on a dataset may not agree with those obtained by a fine-tuned network that was pre-trained on a dataset having different tortuosity statistics. In addition, we show that improving the segmentation accuracy does not necessarily lead to better tortuosity estimation. To mitigate the aforementioned issues, we propose the application of data augmentation techniques even in situations where they do not improve segmentation performance. For instance, we found that the application of elastic transformations was enough to prevent an underestimation of 8% of blood vessel tortuosity when applying CNNs to different datasets.

CONCLUSIONS

The results highlight the importance of developing new methodologies for training CNNs with the specific goal of reducing the error of morphological measurements, as opposed to the traditional approach of using segmentation accuracy as a proxy metric for performance evaluation.

The barrier and interface mechanisms of the brain barrier, and brain drug delivery

Three different barriers are formed between the cerebrovascular and the brain parenchyma: the blood-brain barrier (BBB), the blood-cerebrospinal fluid barrier (BCSFB), and the cerebrospinal fluid-brain barrier (CBB). The BBB is the main regulator of blood and central nervous system (CNS) material exchange. The semipermeable nature of the BBB limits the passage of larger molecules and hydrophilic small molecules, Food and Drug Administration (FDA)-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Although the complexity of the BBB affects CNS drug delivery, understanding the composition and function of the BBB can provide a platform for the development of new methods for CNS drug delivery. This review summarizes the classification of the brain barrier, the composition and role of the basic structures of the BBB, and the transport, barrier, and destruction mechanisms of the BBB; discusses the advantages and disadvantages of different drug delivery methods and prospects for future drug delivery strategies.

Critical Role of Neuronal Vps35 in Blood Vessel Branching and Maturation in Developing Mouse Brain

Vps35 (vacuolar protein sorting 35), a key component of retromer, plays a crucial role in selective retrieval of transmembrane proteins from endosomes to trans-Golgi networks. Dysfunctional Vps35/retromer is a risk factor for the development of neurodegenerative diseases. Vps35 is highly expressed in developing pyramidal neurons, both in the mouse neocortex and hippocampus, Although embryonic neuronal Vps35’s function in promoting neuronal terminal differentiation and survival is evident, it remains unclear whether and how neuronal Vps35 communicates with other types of brain cells, such as blood vessels (BVs), which are essential for supplying nutrients to neurons. Dysfunctional BVs contribute to the pathogenesis of various neurodegenerative disorders. Here, we provide evidence for embryonic neuronal Vps35 as critical for BV branching and maturation in the developing mouse brain. Selectively knocking out (KO) Vps35 in mouse embryonic, not postnatal, neurons results in reductions in BV branching and density, arteriole diameter, and BV-associated pericytes and microglia but an increase in BV-associated reactive astrocytes. Deletion of microglia by PLX3397 enhances these BV deficits in mutant mice. These results reveal the function of neuronal Vps35 in neurovascular coupling in the developing mouse brain and implicate BV-associated microglia as underlying this event.

Signaling Pathways in Neurovascular Development

During development, the central nervous system (CNS) vasculature grows to precisely meet the metabolic demands of neurons and glia. In addition, the vast majority of the CNS vasculature acquires a unique set of molecular and cellular properties-collectively referred to as the blood-brain barrier-that minimize passive diffusion of molecules between the blood and the CNS parenchyma. Both of these processes are controlled by signals emanating from neurons and glia. In this review, we describe the nature and mechanisms-of-action of these signals, with an emphasis on vascular endothelial growth factor (VEGF) and beta-catenin (canonical Wnt) signaling, the two best-understood systems that regulate CNS vascular development. We highlight foundational discoveries, interactions between different signaling systems, the integration of genetic and cell biological studies, advances that are of clinical relevance, and questions for future research.

The Influence of Neural Activity and Neural Cytoarchitecture on Cerebrovascular Arborization: A Computational Model

Normal functioning of the brain relies on a continual and efficient delivery of energy by a vast network of cerebral blood vessels. The bidirectional coupling between neurons and blood vessels consists of vasodilatory energy demand signals from neurons to blood vessels, and the retrograde flow of energy substrates from the vessels to neurons, which fuel neural firing, growth and other housekeeping activities in the neurons. Recent works indicate that, in addition to the functional coupling observed in the adult brain, the interdependence between the neural and vascular networks begins at the embryonic stage, and continues into subsequent developmental stages. The proposed Vascular Arborization Model (VAM) captures the effect of neural cytoarchitecture and neural activity on vascular arborization. The VAM describes three important stages of vascular tree growth: (i) The prenatal growth phase, where the vascular arborization depends on the cytoarchitecture of neurons and non-neural cells, (ii) the post-natal growth phase during which the further arborization of the vasculature depends on neural activity in addition to neural cytoarchitecture, and (iii) the settling phase, where the fully grown vascular tree repositions its vascular branch points or nodes to ensure minimum path length and wire length. The vasculature growth depicted by VAM captures structural characteristics like vascular volume density, radii, mean distance to proximal neurons in the cortex. VAM-grown vasculature agrees with the experimental observation that the neural densities do not covary with the vascular density along the depth of the cortex but predicts a high correlation between neural areal density and microvascular density when compared over a global scale (across animals and regions). To explore the influence of neural activity on vascular arborization, the VAM was used to grow the vasculature in neonatal rat whisker barrel cortex under two conditions: (i) Control, where the whiskers were intact and (ii) Lesioned, where one row of whiskers was cauterized. The model captures a significant reduction in vascular branch density in lesioned animals compared to control animals, concurring with experimental observation.

Reinforced thinned-skull window for repeated imaging of the neonatal mouse brain

Significance: Two-photon microscopy is a powerful tool for in vivo imaging of the mammalian brain at cellular to subcellular resolution. However, resources that describe methods for imaging live newborn mice have remained sparse. Aim: We describe a non-invasive cranial window procedure for longitudinal imaging of neonatal mice. Approach: We demonstrate construction of the cranial window by iterative shaving of the calvarium of P0 to P12 mouse pups. We use the edge of a syringe needle and scalpel blades to thin the bone to ∼ 15 - μ m thickness. The window is then reinforced with cyanoacrylate glue and a coverslip to promote stability and optical access for at least a week. The head cap also includes a light-weight aluminum flange for head-fixation during imaging. Results: The resulting chronic thinned-skull window enables in vivo imaging to a typical cortical depth of ∼ 200    μ m without disruption of the intracranial environment. We highlight techniques to measure vascular structure and blood flow during development, including use of intravenous tracers and transgenic mice to label the blood plasma and vascular cell types, respectively. Conclusions: This protocol enables direct visualization of the developing neurogliovascular unit in the live neonatal brain during both normal and pathological states.

Toward an integrative neurovascular framework for studying brain networks

Brain functional connectivity based on the measure of blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals has become one of the most widely used measurements in human neuroimaging. However, the nature of the functional networks revealed by BOLD fMRI can be ambiguous, as highlighted by a recent series of experiments that have suggested that typical resting-state networks can be replicated from purely vascular or physiologically driven BOLD signals. After going through a brief review of the key concepts of brain network analysis, we explore how the vascular and neuronal systems interact to give rise to the brain functional networks measured with BOLD fMRI. This leads us to emphasize a view of the vascular network not only as a confounding element in fMRI but also as a functionally relevant system that is entangled with the neuronal network. To study the vascular and neuronal underpinnings of BOLD functional connectivity, we consider a combination of methodological avenues based on multiscale and multimodal optical imaging in mice, used in combination with computational models that allow the integration of vascular information to explain functional connectivity.

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.

Unbiased analysis of mouse brain endothelial networks from two- or three-dimensional fluorescence images

Significance: A growing body of research supports the significant role of cerebrovascular abnormalities in neurological disorders. As these insights develop, standardized tools for unbiased and high-throughput quantification of cerebrovascular structure are needed. Aim: We provide a detailed protocol for performing immunofluorescent labeling of mouse brain vessels, using thin ( 25    μ m ) or thick (50 to 150    μ m ) tissue sections, followed respectively by two- or three-dimensional (2D or 3D) unbiased quantification of vessel density, branching, and tortuosity using digital image processing algorithms. Approach: Mouse brain sections were immunofluorescently labeled using a highly selective antibody raised against mouse Cluster of Differentiation-31 (CD31), and 2D or 3D microscopy images of the mouse brain vasculature were obtained using optical sectioning. An open-source toolbox, called Pyvane, was developed for analyzing the imaged vascular networks. The toolbox can be used to identify the vasculature, generate the medial axes of blood vessels, represent the vascular network as a graph, and calculate relevant measurements regarding vascular morphology. Results: Using Pyvane, vascular parameters such as endothelial network density, number of branching points, and tortuosity are quantified from 2D and 3D immunofluorescence micrographs. Conclusions: The steps described in this protocol are simple to follow and allow for reproducible and unbiased analysis of mouse brain vascular structure. Such a procedure can be applied to the broader field of vascular biology.

Vascular network expansion, integrity of blood-brain interfaces, and cerebrospinal fluid cytokine concentration during postnatal development in the normal and jaundiced rat

BACKGROUND

Severe neonatal jaundice resulting from elevated levels of unconjugated bilirubin in the blood induces dramatic neurological impairment. Central oxidative stress and an inflammatory response have been associated with the pathophysiological mechanism. Cells forming the blood-brain barrier and the choroidal blood-CSF barrier are the first CNS cells exposed to increased plasma levels of unconjugated bilirubin. These barriers are key regulators of brain homeostasis and require active oxidative metabolism to fulfill their protective functions. The choroid plexus-CSF system is involved in neuroinflammatory processes. In this paper, we address the impact of neonatal hyperbilirubinemia on some aspects of brain barriers. We describe physiological changes in the neurovascular network, blood-brain/CSF barriers integrities, and CSF cytokine levels during the postnatal period in normobilirubinemic animals, and analyze these parameters in parallel in Gunn rats that are deficient in bilirubin catabolism and develop postnatal hyperbilirubinemia.

METHODS

Gunn rats bearing a mutation in UGT1a genes were used. The neurovascular network was analyzed by immunofluorescence stereomicroscopy. The integrity of the barriers was evaluated by [14C]-sucrose permeability measurement. CSF cytokine levels were measured by multiplex immunoassay. The choroid plexus-CSF system response to an inflammatory challenge was assessed by enumerating CSF leukocytes.

RESULTS

In normobilirubinemic animals, the neurovascular network expands postnatally and displays stage-specific regional variations in its complexity. Network expansion is not affected by hyperbilirubinemia. Permeability of the blood-brain and blood-CSF barriers to sucrose decreases between one- and 9-day-old animals, and does not differ between normobilirubinemic and hyperbilirubinemic rats. Cytokine profiles differ between CSF and plasma in all 1-, 9-, and 18-day-old animals. The CSF cytokine profile in 1-day-old animals is markedly different from that established in older animals. Hyperbilirubinemia perturbs these cytokine profiles only to a very limited extent, and reduces CSF immune cell infiltration triggered by systemic exposure to a bacterial lipopeptide.

CONCLUSION

The data highlight developmental specificities of the blood-brain barrier organization and of CSF cytokine content. They also indicate that a direct effect of bilirubin on the vascular system organization, brain barriers morphological integrity, and inflammatory response of the choroid plexus-CSF system is not involved in the alteration of brain functions induced by severe neonatal jaundice.

Blood-brain barrier leakage in Alzheimer's disease: From discovery to clinical relevance

Alzheimer's disease (AD) is the most common form of dementia. AD brain pathology starts decades before the onset of clinical symptoms. One early pathological hallmark is blood-brain barrier dysfunction characterized by barrier leakage and associated with cognitive decline. In this review, we summarize the existing literature on the extent and clinical relevance of barrier leakage in AD. First, we focus on AD animal models and their susceptibility to barrier leakage based on age and genetic background. Second, we re-examine barrier dysfunction in clinical and postmortem studies, summarize changes that lead to barrier leakage in patients and highlight the clinical relevance of barrier leakage in AD. Third, we summarize signaling mechanisms that link barrier leakage to neurodegeneration and cognitive decline in AD. Finally, we discuss clinical relevance and potential therapeutic strategies and provide future perspectives on investigating barrier leakage in AD. Identifying mechanistic steps underlying barrier leakage has the potential to unravel new targets that can be used to develop novel therapeutic strategies to repair barrier leakage and slow cognitive decline in AD and AD-related dementias.

Behavioral and Neural Activity-Dependent Recanalization of Plugged Capillaries in the Brain of Adult and Aged Mice

The capillaries of the brain, owing to their small diameter and low perfusion pressure, are vulnerable to interruptions in blood flow. These tiny occlusions can have outsized consequences on angioarchitecture and brain function; especially when exacerbated by disease states or accumulate with aging. A distinctive feature of the brain’s microvasculature is the ability for active neurons to recruit local blood flow. The coupling of neural activity to blood flow could play an important role in recanalizing obstructed capillaries. To investigate this idea, we experimentally induced capillary obstructions in mice by injecting fluorescent microspheres and then manipulated neural activity levels though behavioral or pharmacologic approaches. We show that engaging adult and aged mice with 12 h exposure to an enriched environment (group housing, novel objects, exercise wheels) was sufficient to significantly reduce the density of obstructed capillaries throughout the forebrain. In order to more directly manipulate neural activity, we pharmacologically suppressed or increased neuronal activity in the somatosensory cortex. When we suppressed cortical activity, recanalization was impaired given the density of obstructed capillaries was significantly increased. Conversely, increasing cortical activity improved capillary recanalization. Since systemic cardiovascular factors (changes in heart rate, blood pressure) could explain these effects on recanalization, we demonstrate that unilateral manipulations of neural activity through whisker trimming or injection of muscimol, still had significant and hemisphere specific effects on recanalization, even in mice exposed to enrichment where cardiovascular effects would be evident in both hemispheres. In summary, our studies reveal that neural activity bi-directionally regulates the recanalization of obstructed capillaries. Further, we show that stimulating brain activity through behavioral engagement (i.e., environmental enrichment) can promote vascular health throughout the lifespan.

CfDNA Measurement as a Diagnostic Tool for the Detection of Brain Somatic Mutations in Refractory Epilepsy

Epilepsy is a neurological disorder that affects more than 50 million people. Its etiology is unknown in approximately 60% of cases, although the existence of a genetic factor is estimated in about 75% of these individuals. Hundreds of genes involved in epilepsy are known, and their number is increasing progressively, especially with next-generation sequencing techniques. However, there are still many cases in which the results of these molecular studies do not fully explain the phenotype of the patients. Somatic mutations specific to brain tissue could contribute to the phenotypic spectrum of epilepsy. Undetectable in the genomic DNA of blood cells, these alterations can be identified in cell-free DNA (cfDNA). We aim to review the current literature regarding the detection of somatic variants in cfDNA to diagnose refractory epilepsy, highlighting novel research directions and suggesting further studies.

Central auditory deficits associated with genetic forms of peripheral deafness

Since the 1990s, the study of inherited hearing disorders, mostly those detected at birth, in the prelingual period or in young adults, has led to the identification of their causal genes. The genes responsible for more than 140 isolated (non-syndromic) and about 400 syndromic forms of deafness have already been discovered. Studies of mouse models of these monogenic forms of deafness have provided considerable insight into the molecular mechanisms of hearing, particularly those involved in the development and/or physiology of the auditory sensory organ, the cochlea. In parallel, studies of these models have also made it possible to decipher the pathophysiological mechanisms underlying hearing impairment. This has led a number of laboratories to investigate the potential of gene therapy for curing these forms of deafness. Proof-of-concept has now been obtained for the treatment of several forms of deafness in mouse models, paving the way for clinical trials of cochlear gene therapy in patients in the near future. Nevertheless, peripheral deafness may also be associated with central auditory dysfunctions and may extend well beyond the auditory system itself, as a consequence of alterations to the encoded sensory inputs or involvement of the causal deafness genes in the development and/or functioning of central auditory circuits. Investigating the diversity, causes and underlying mechanisms of these central dysfunctions, the ways in which they could impede the expected benefits of hearing restoration by peripheral gene therapy, and determining how these problems could be remedied is becoming a research field in its own right. Here, we provide an overview of the current knowledge about the central deficits associated with genetic forms of deafness.

Maternal high-fat diet in mice induces cerebrovascular, microglial and long-term behavioural alterations in offspring

Various environmental exposures during pregnancy, like maternal diet, can compromise, at critical periods of development, the neurovascular maturation of the offspring. Foetal exposure to maternal high-fat diet (mHFD), common to Western societies, has been shown to disturb neurovascular development in neonates and long-term permeability of the neurovasculature. Nevertheless, the effects of mHFD on the offspring’s cerebrovascular health remains largely elusive. Here, we sought to address this knowledge gap by using a translational mouse model of mHFD exposure. Three-dimensional and ultrastructure analysis of the neurovascular unit (vasculature and parenchymal cells) in mHFD-exposed offspring revealed major alterations of the neurovascular organization and metabolism. These alterations were accompanied by changes in the expression of genes involved in metabolism and immunity, indicating that neurovascular changes may result from abnormal brain metabolism and immune regulation. In addition, mHFD-exposed offspring showed persisting behavioural alterations reminiscent of neurodevelopmental disorders, specifically an increase in stereotyped and repetitive behaviours into adulthood.

In order to advance our understanding of the effects of maternal high-fat diet (mHFD) on the cerebrovascular health of offspring, Bordeleau et al. use a translational mouse model of mHFD exposure. They demonstrate that mHFD induces cerebrovascular and microglial changes in the offspring as well as behavioural alterations that are reminiscent of neurodevelopmental disorders associated with repetitive behaviours at adulthood.

Effects of Hypoxia on Cerebral Microvascular Angiogenesis: Benefits or Damages?

Cerebrovascular microcirculation is essential for maintaining the physiological functions of the brain. The brain can be protected from stress injury by remodeling the microcirculation network. Angiogenesis is a type of cerebral vascular remodeling. It is an effective approach to improve the blood flow of the cerebral microcirculation, which is necessary for preventing and treating various neurological disorders. Hypoxia is one of the most important regulators of angiogenesis, affecting the sprouting, proliferation, and maturation stages of angiogenesis. Moreover, hypoxia negatively affects cerebral vascular tissue by impairing the structural and functional integrity of the blood-brain barrier and vascular-nerve decoupling. Therefore, hypoxia has a dual effect on blood vessels and is affected by confounding factors including oxygen concentration, hypoxia duration, and hypoxia frequency and extent. Establishing an optimal model that promotes cerebral microvasculogenesis without causing vascular injury is essential. In this review, we first elaborate on the effects of hypoxia on blood vessels from two different perspectives: (1) the promotion of angiogenesis and (2) cerebral microcirculation damage. We further discuss the factors influencing the dual role of hypoxia and emphasize the benefits of moderate hypoxic irritation and its potential application as an easy, safe, and effective treatment for multiple nervous system disorders.

ACTA2-Related Dysgyria: An Under-Recognized Malformation of Cortical Development

BACKGROUND AND PURPOSE

Pathogenic variants in the ACTA2 gene cause a distinctive arterial phenotype that has recently been described to be associated with brain malformation. Our objective was to further characterize gyral abnormalities in patients with ACTA2 pathogenic variants as per the 2020 consensus recommendations for the definition and classification of malformations of cortical development.

MATERIALS AND METHODS

We performed a retrospective, multicentric review of patients with proved ACTA2 pathogenic variants, searching for the presence of malformations of cortical development. A consensus read was performed for all patients, and the type and location of cortical malformation were noted in each. The presence of the typical ACTA2 arterial phenotype as well as demographic and relevant clinical data was obtained.

RESULTS

We included 13 patients with ACTA2 pathogenic variants (Arg179His mutation, n = 11, and Arg179Cys mutation, n = 2). Ninety-two percent (12/13) of patients had peri-Sylvian dysgyria, 77% (10/13) had frontal dysgyria, and 15% (2/13) had generalized dysgyria. The peri-Sylvian location was involved in all patients with dysgyria (12/12). All patients with dysgyria had a characteristic arterial phenotype described in ACTA2 pathogenic variants. One patient did not have dysgyria or the characteristic arterial phenotype.

CONCLUSIONS

Dysgyria is common in patients with ACTA2 pathogenic variants, with a peri-Sylvian and frontal predominance, and was seen in all our patients who also had the typical ACTA2 arterial phenotype.

A review of bioeffects induced by focused ultrasound combined with microbubbles on the neurovascular unit

Focused ultrasound combined with circulating microbubbles (FUS+MB) can transiently enhance blood-brain barrier (BBB) permeability at targeted brain locations. Its great promise in improving drug delivery to the brain is reflected by a rapidly growing number of clinical trials using FUS+MB to treat various brain diseases. As the clinical applications of FUS+MB continue to expand, it is critical to have a better understanding of the molecular and cellular effects induced by FUS+MB to enhance the efficacy of current treatment and enable the discovery of new therapeutic strategies. Existing studies primarily focus on FUS+MB-induced effects on brain endothelial cells, the major cellular component of BBB. However, bioeffects induced by FUS+MB expand beyond the BBB to cells surrounding blood vessels, including astrocytes, microglia, and neurons. Together these cell types comprise the neurovascular unit (NVU). In this review, we examine cell-type-specific bioeffects of FUS+MB on different NVU components, including enhanced permeability in endothelial cells, activation of astrocytes and microglia, as well as increased intraneuron protein metabolism and neuronal activity. Finally, we discuss knowledge gaps that must be addressed to further advance clinical applications of FUS+MB.

Parallels between the Developing Vascular and Neural Systems: Signaling Pathways and Future Perspectives for Regenerative Medicine

Neurovascular disorders, which involve the vascular and nervous systems, are common. Research on such disorders usually focuses on either vascular or nervous components, without looking at how they interact. Adopting a neurovascular perspective is essential to improve current treatments. Therefore, comparing molecular processes known to be involved in both systems separately can provide insight into promising areas of future research. Since development and regeneration share many mechanisms, comparing signaling molecules involved in both the developing vascular and nervous systems and shedding light to those that they have in common can reveal processes, which have not yet been studied from a regenerative perspective, yet hold great potential. Hence, this review discusses and compares processes involved in the development of the vascular and nervous systems, in order to provide an overview of the molecular mechanisms, which are most promising with regards to treatment for neurovascular disorders. Vascular endothelial growth factor, semaphorins, and ephrins are found to hold the most potential, while fibroblast growth factor, bone morphogenic protein, slits, and sonic hedgehog are shown to participate in both the developing vascular and nervous systems, yet have not been studied at the neurovascular level, therefore being of special interest for future research.

3D hydrogel models of the neurovascular unit to investigate blood-brain barrier dysfunction

The neurovascular unit (NVU), consisting of neurons, glial cells, vascular cells (endothelial cells, pericytes and vascular smooth muscle cells (VSMCs)) together with the surrounding extracellular matrix (ECM), is an important interface between the peripheral blood and the brain parenchyma. Disruption of the NVU impacts on blood-brain barrier (BBB) regulation and underlies the development and pathology of multiple neurological disorders, including stroke and Alzheimer's disease (AD). The ability to differentiate induced pluripotent stem cells (iPSCs) into the different cell types of the NVU and incorporate them into physical models provides a reverse engineering approach to generate human NVU models to study BBB function. To recapitulate the in vivo situation such NVU models must also incorporate the ECM to provide a 3D environment with appropriate mechanical and biochemical cues for the cells of the NVU. In this review, we provide an overview of the cells of the NVU and the surrounding ECM, before discussing the characteristics (stiffness, functionality and porosity) required of hydrogels to mimic the ECM when incorporated into in vitro NVU models. We summarise the approaches available to measure BBB functionality and present the techniques in use to develop robust and translatable models of the NVU, including transwell models, hydrogel models, 3D-bioprinting, microfluidic models and organoids. The incorporation of iPSCs either without or with disease-specific genetic mutations into these NVU models provides a platform in which to study normal and disease mechanisms, test BBB permeability to drugs, screen for new therapeutic targets and drugs or to design cell-based therapies.

Experience-dependent myelination following stress is mediated by the neuropeptide dynorphin

Emerging evidence implicates experience-dependent myelination in learning and memory. However, the specific signals underlying this process remain unresolved. We demonstrate that the neuropeptide dynorphin, which is released from neurons upon high levels of activity, promotes experience-dependent myelination. Following forced swim stress, an experience that induces striatal dynorphin release, we observe increased striatal oligodendrocyte precursor cell (OPC) differentiation and myelination, which is abolished by deleting dynorphin or blocking its endogenous receptor, kappa opioid receptor (KOR). We find that dynorphin also promotes developmental OPC differentiation and myelination and demonstrate that this effect requires KOR expression specifically in OPCs. We characterize dynorphin-expressing neurons and use genetic sparse labeling to trace their axonal projections. Surprisingly, we find that they are unmyelinated normally and following forced swim stress. We propose a new model whereby experience-dependent and developmental myelination is mediated by unmyelinated, neuropeptide-expressing neurons that promote OPC differentiation for the myelination of neighboring axons.