Cerebrovascular plasticity: Processes that lead to changes in the architecture of brain microvessels

Vascular Aging in Ischemic Stroke

Cellular senescence, a permanent halt in cell division due to stress, spurs functional and structural changes, contributing to vascular aging characterized by endothelial dysfunction and vascular remodeling. This process raises the risk of ischemic stroke (IS) in older individuals, with its mechanisms still not completely understood despite ongoing research efforts. In this review, we have analyzed the impact of vascular aging on increasing susceptibility and exacerbating the pathology of IS. We have emphasized the detrimental effects of endothelial dysfunction and vascular remodeling influenced by oxidative stress and inflammatory response on vascular aging and IS. Our goal is to aid the understanding of vascular aging and IS pathogenesis, particularly benefiting older adults with high risk of IS.

Nano/micro-plastic, an invisible threat getting into the brain

Due to weather and working/operational conditions, plastic degradation produces toxic and non-biodegradable nano and microplastics (N/M-Ps, ranging from 10 nm to 5 mm), and over time these N/M-Ps have integrated with the human cycle through ingestion and inhalation. These N/M-Ps, as serious emerging pollutants, are causing considerable adverse health issues due to up-taken by the cells, tissue, and organs, including the brain. It has been proven that N/M-Ps can cross the blood-brain barrier (via olfactory and blood vessels) and affect the secretion of neuroinflammatory (cytokine and chemokine), transporters, and receptor markers. Neurotoxicity, neuroinflammation, and brain injury, which may result in such scenarios are a serious concern and may cause brain disorders. However, the related pathways and pathogenesis are not well-explored but are the focus of upcoming emerging research. Therefore, as a focus of this editorial, well-organized multidisciplinary research is required to explore associated pathways and pathogenesis, leading to brain mapping and nano-enabled therapeutics in acute and chronic N/M - Ps exposure.

Transcriptomic changes in the posterior pallium of male zebra finches associated with social niche conformance

Animals plastically adjust their physiological and behavioural phenotypes to conform to their social environment-social niche conformance. The degree of sexual competition is a critical part of the social environment to which animals adjust their phenotypes, but the underlying genetic mechanisms are poorly understood. We conducted a study to investigate how differences in sperm competition risk affect the gene expression profiles of the testes and two brain areas (posterior pallium and optic tectum) in breeding male zebra finches (Taeniopygia castanotis). In this pre-registered study, we investigated a large sample of 59 individual transcriptomes. We compared two experimental groups: males held in single breeding pairs (low sexual competition) versus those held in two pairs (elevated sexual competition) per breeding cage. Using weighted gene co-expression network analysis (WGCNA), we observed significant effects of the social treatment in all three tissues. However, only the treatment effects found in the pallium were confirmed by an additional randomisation test for statistical robustness. Likewise, the differential gene expression analysis revealed treatment effects only in the posterior pallium (ten genes) and optic tectum (six genes). No treatment effects were found in the testis at the single gene level. Thus, our experiments do not provide strong evidence for transcriptomic adjustment specific to manipulated sperm competition risk. However, we did observe transcriptomic adjustments to the manipulated social environment in the posterior pallium. These effects were polygenic rather than based on few individual genes with strong effects. Our findings are discussed in relation to an accompanying paper using the same animals, which reports behavioural results consistent with the results presented here.

Thromboembolic Events After the Coverage of Anterior Cerebral Artery with Flow Diversion: A Single Institution Series and Systematic Review

BACKGROUND

Advances in the use of flow diversion (FD) now extend to bifurcation aneurysms; herein, we compare thromboembolic events in patients with internal carotid artery (ICA) aneurysms treated with and without exclusion of the anterior cerebral artery (ACA).

METHODS

Retrospective analysis of aneurysms in the terminal ICA treated with FD from 2013 to 2023 at a single-center study. Procedures were classified according to the coverage at the origin of the ACA and compared through bivariate-analysis. A review was also carried on PubMed, Web of Science, and EMBASE until April 2024, adhering to the PRISMA reporting guidelines.

RESULTS

Ninety-five patients harboring 113 aneurysms treated in 102 procedures were evaluated. Fifty-eight were treated covering the ACA origin. Dual antiplatelet regimens included aspirin-clopidogrel (50%), aspirin-ticagrelor (44.1%), and aspirin-prasugrel (4.9%). Thromboembolic events occurred in 6 patients (5.9%), all of which presented with large vessel occlusion of the ICA, but without reaching statistical difference in the 2 treated cohorts (P = 0.46). At a median clinical follow-up of 5.95 months, there were no differences in the functional outcomes in the 2 groups (P = 0.22). Contralateral angiographic runs post-treatment after covering the ACA origin demonstrated increase in the A1 (median: 0.45 mm; IQR = 0.4-1.2) and ICA diameter (median: 0.55 mm; IQR = 0.1-1.2). After pooling data from literature and our cohort, complete side branch occlusion after the coverage of ACA was seen in 25% of branches (95%CI = 0.16-0.36), and thromboembolic events were observed after 3% (95%CI = 0.01-0.04) of procedures.

CONCLUSIONS

Thromboembolic events can occur in distal ICA aneurysms treated with FD, but no significant association was seen with covering the ACA origin.

3D Visualization of Whole Brain Vessels and Quantification of Vascular Pathology in a Chronic Hypoperfusion Model Causing White Matter Damage

Chronic cerebral hypoperfusion is an important pathological factor in many neurodegenerative diseases, such as cerebral small vessel disease (CSVD). One of the most used animal models for chronic cerebral hypoperfusion is the bilateral common carotid artery stenosis (BCAS) mouse. For the therapy of CSVD and other diseases, it will be beneficial to understand the pathological alterations of the BCAS mouse, particularly vascular pathological changes. A mouse model of BCAS was used, and 8 weeks later, cognitive function of the mice was examined by using novel object recognition test and eight-arm radial maze test. 11.7 T magnetic resonance imaging (MRI) and luxol fast blue staining were used to evaluate the injury of the corpus callosum (CC), anterior commissure (AC), internal capsule (IC), and optic tract (Opt) in the cerebral white matter of mice. Three-dimensional vascular images of the whole brain of mice were acquired using fluorescence micro-optical sectioning tomography (fMOST) with a high resolution of 0.32 × 0.32 × 1.00 μm3. Then, the damaged white matter regions were further extracted to analyze the vessel length density, volume fraction, tortuosity, and the number of vessels of different internal diameters. The mouse cerebral caudal rhinal vein was also extracted and analyzed for its branch number and divergent angle in this study. BCAS modeling for 8 weeks resulted in impaired spatial working memory, reduced brain white matter integrity, and myelin degradation in mice, and CC showed the most severe white matter damage. 3D revascularization of the whole mouse brain showed that the number of large vessels was reduced and the number of small vessels was increased in BCAS mice. Further analysis revealed that the vessel length density and volume fraction in the damaged white matter region of BCAS mice were significantly reduced, and the vascular lesions were most noticeable in the CC. At the same time, the number of small vessels in the above white matter regions was significantly reduced, while the number of microvessels was significantly increased in BCAS mice, and the vascular tortuosity was also significantly increased. In addition, the analysis of caudal rhinal vein extraction revealed that the number of branches and the average divergent angle in BCAS mice were significantly reduced. The BCAS modeling for 8 weeks will lead to vascular lesions in whole brain of mice, and the caudal nasal vein was also damaged, while BCAS mice mainly mitigated the damages by increasing microvessels. What is more, the vascular lesions in white matter of mouse brain can cause white matter damage and spatial working memory deficit. These results provide evidence for the vascular pathological alterations caused by chronic hypoperfusion.

Cerebral blood flow and structural connectivity after working memory or physical training in paediatric cancer survivors - Exploratory findings

Paediatric cancer survivors often suffer from cognitive long-term difficulties. Consequently, strengthening cognition is of major clinical relevance. This study investigated cerebral changes in relation to cognition in non-brain tumour paediatric cancer survivors after working memory or physical training compared to a control group. Thirty-four children (≥one-year post-treatment) either underwent eight weeks of working memory training (n = 10), physical training (n = 11), or a waiting period (n = 13). Cognition and MRI, including arterial spin labelling and diffusion tensor imaging, were assessed at three time points (baseline, post-training, and three-month follow-up). Results show lower cerebral blood flow immediately after working memory training (z = -2.073, p = .038) and higher structural connectivity at the three-month follow-up (z = -2.240, p = .025). No cerebral changes occurred after physical training. Short-term changes in cerebral blood flow correlated with short-term changes in cognitive flexibility (r = -.667, p = .049), while long-term changes in structural connectivity correlated with long-term changes in working memory (r = .786, p = .021). Despite the caution given when interpreting data from small samples, this study suggests a link between working memory training and neurophysiological changes. Further research is needed to validate these findings.

Melanocortin Derivatives Induced Vascularization and Neuroglial Proliferation in the Rat Brain under Conditions of Cerebral Ischemia

Stroke remains the second leading cause of death worldwide. The development of new therapeutic agents focused on restoring vascular function and neuroprotection of viable tissues is required. In this study the neuroprotective activity of melanocortin-like ACTH(4-7)PGP and ACTH(6-9)PGP peptides was investigated in rat brain at 24 h after transient middle cerebral artery occlusion (tMCAO). The severity of ischemic damage, changes in the proliferative activity of neuroglial cells and vascularization of rat brain tissue were analyzed. The administration of peptides resulted in a significant increase in the volume density of neurons in the perifocal zone of infarction compared to rats subjected to ischemia and receiving saline. Immunohistochemical analysis of the proliferative activity of neuroglia cells using PCNA antibodies showed a significant increase in the number of proliferating cells in the penumbra and in the intact cerebral cortex of rats receiving peptide treatment. The effect of peptides on vascularization was examined using CD31 antibodies under tMCAO conditions, revealing a significant increase in the volume density of vessels and their sizes in the penumbra after administration of ACTH(4-7)PGP and ACTH(6-9)PGP. These findings confirm the neuroprotective effect of peptides due to the activation of neuroglia proliferation and the enhancement of collateral blood flow.

The influence of physiological and pathological perturbations on blood-brain barrier function

The blood-brain barrier (BBB) is located at the interface between the vascular system and the brain parenchyma, and is responsible for communication with systemic circulation and peripheral tissues. During life, the BBB can be subjected to a wide range of perturbations or stresses that may be endogenous or exogenous, pathological or therapeutic, or intended or unintended. The risk factors for many diseases of the brain are multifactorial and involve perturbations that may occur simultaneously (e.g., two-hit model for Alzheimer's disease) and result in different outcomes. Therefore, it is important to understand the influence of individual perturbations on BBB function in isolation. Here we review the effects of eight perturbations: mechanical forces, temperature, electromagnetic radiation, hypoxia, endogenous factors, exogenous factors, chemical factors, and pathogens. While some perturbations may result in acute or chronic BBB disruption, many are also exploited for diagnostic or therapeutic purposes. The resultant outcome on BBB function depends on the dose (or magnitude) and duration of the perturbation. Homeostasis may be restored by self-repair, for example, via processes such as proliferation of affected cells or angiogenesis to create new vasculature. Transient or sustained BBB dysfunction may result in acute or pathological symptoms, for example, microhemorrhages or hypoperfusion. In more extreme cases, perturbations may lead to cytotoxicity and cell death, for example, through exposure to cytotoxic plaques.

A framework of transient hypercapnia to achieve an increased cerebral blood flow induced by nasal breathing during aerobic exercise

During exercise, cerebral blood flow (CBF) is expected to only increase to a maximal volume up to a moderate intensity aerobic effort, suggesting that CBF is expected to decline past 70 % of a maximal aerobic effort. Increasing CBF during exercise permits an increased cerebral metabolic activity that stimulates neuroplasticity and other key processes of cerebral adaptations that ultimately improve cognitive health. Recent work has focused on utilizing gas-induced exposure to intermittent hypoxia during aerobic exercise to maximize the improvements in cognitive function compared to those seen under normoxic conditions. However, it is postulated that exercising by isolating breathing only to the nasal route may provide a similar effect by stimulating a transient hypercapnic condition that is non-gas dependent. Because nasal breathing prevents hyperventilation during exercise, it promotes an increase in the partial arterial pressure of CO2. The rise in systemic CO2 stimulates hypercapnia and permits the upregulation of hypoxia-related genes. In addition, the rise in systemic CO2 stimulates cerebral vasodilation, promoting a greater increase in CBF than seen during normoxic conditions. While more research is warranted, nasal breathing might also promote benefits related to improved sleep, greater immunity, and body fat loss. Altogether, this narrative review presents a theoretical framework by which exercise-induced hypercapnia by utilizing nasal breathing during moderate-intensity aerobic exercise may promote greater health adaptations and cognitive improvements than utilizing oronasal breathing.

Review of Major Social Determinants of Health in Schizophrenia-Spectrum Psychotic Disorders: III. Biology

BACKGROUND

Social determinants of health (SDoHs) are nonmedical factors that significantly impact health and longevity. We found no published reviews on the biology of SDoHs in schizophrenia-spectrum psychotic disorders (SSPD).

STUDY DESIGN

We present an overview of pathophysiological mechanisms and neurobiological processes plausibly involved in the effects of major SDoHs on clinical outcomes in SSPD.

STUDY RESULTS

This review of the biology of SDoHs focuses on early-life adversities, poverty, social disconnection, discrimination including racism, migration, disadvantaged neighborhoods, and food insecurity. These factors interact with psychological and biological factors to increase the risk and worsen the course and prognosis of schizophrenia. Published studies on the topic are limited by cross-sectional design, variable clinical and biomarker assessments, heterogeneous methods, and a lack of control for confounding variables. Drawing on preclinical and clinical studies, we propose a biological framework to consider the likely pathogenesis. Putative systemic pathophysiological processes include epigenetics, allostatic load, accelerated aging with inflammation (inflammaging), and the microbiome. These processes affect neural structures, brain function, neurochemistry, and neuroplasticity, impacting the development of psychosis, quality of life, cognitive impairment, physical comorbidities, and premature mortality. Our model provides a framework for research that could lead to developing specific strategies for prevention and treatment of the risk factors and biological processes, thereby improving the quality of life and increasing the longevity of people with SSPD.

CONCLUSIONS

Biology of SDoHs in SSPD is an exciting area of research that points to innovative multidisciplinary team science for improving the course and prognosis of these serious psychiatric disorders.

The extent of damage to the blood-brain barrier in the hypercholesterolemic LDLR-/-/Apo E-/- double knockout mice depends on the animal's age, duration of pathology and brain area

One of the effects of hypercholesterolemia (Hch) exerted on the central nervous system (CNS) is damage to the blood-brain barrier (BBB). Increased permeability of BBB results from structural changes in the vascular wall, loss of the tight junctions and barrier function, as well as alterations in the concentration of proteins located in the layers of the vascular wall. These changes occur in the course of metabolic and neurodegenerative diseases. The important role in the course of these processes is attributed to agrin, matrix metalloproteinase-9, and aquaporin-4. In this study, we aimed to determine: 1) the extent of Hch-induced damage to the BBB during maturation, and 2) the distribution of the above-mentioned markers in the vascular wall. Immunohistochemical staining and confocal microscopy were used for vascular wall protein assessment. The size of BBB damage was studied based on perivascular leakage of fluorescently labeled dextran. Three- and twelve-month-old male LDLR^-/-/Apo E^-/- double knockout mice (EX) developing Hch were used in the study. Age-matched male wild-type (WT) C57BL/6 mice were used as a control group. Differences in the concentration of studied markers coexisted with BBB disintegration, especially in younger mice. A relationship between the maturation of the vascular system and reduction of the BBB damage was also observed. We conclude that the extent of BBB permeability depends on animal age, duration of Hch, and brain region. These may explain different susceptibility of various brain areas to Hch, and different presentation of this pathology depending on age and its duration.

Modeling angiogenesis in the human brain in a tissue-engineered post-capillary venule

Angiogenesis plays an essential role in embryonic development, organ remodeling, wound healing, and is also associated with many human diseases. The process of angiogenesis in the brain during development is well characterized in animal models, but little is known about the process in the mature brain. Here, we use a tissue-engineered post-capillary venule (PCV) model incorporating stem cell derived induced brain microvascular endothelial-like cells (iBMECs) and pericyte-like cells (iPCs) to visualize the dynamics of angiogenesis. We compare angiogenesis under two conditions: in response to perfusion of growth factors and in the presence of an external concentration gradient. We show that both iBMECs and iPCs can serve as tip cells leading angiogenic sprouts. More importantly, the growth rate for iPC-led sprouts is about twofold higher than for iBMEC-led sprouts. Under a concentration gradient, angiogenic sprouts show a small directional bias toward the high growth factor concentration. Overall, pericytes exhibited a broad range of behavior, including maintaining quiescence, co-migrating with endothelial cells in sprouts, or leading sprout growth as tip cells.

Vessel Distance Mapping: A novel methodology for assessing vascular-induced cognitive resilience

The association between cerebral blood supply and cognition has been widely discussed in the recent literature. One focus of this discussion has been the anatomical variability of the circle of Willis, with morphological differences being present in more than half of the general population. While previous studies have attempted to classify these differences and explore their contribution to hippocampal blood supply and cognition, results have been controversial. To disentangle these previously inconsistent findings, we introduce Vessel Distance Mapping (VDM) as a novel methodology for evaluating blood supply, which allows for obtaining vessel pattern metrics with respect to the surrounding structures, extending the previously established binary classification into a continuous spectrum. To accomplish this, we manually segmented hippocampal vessels obtained from high-resolution 7T time-of-flight MR angiographic imaging in older adults with and without cerebral small vessel disease, generating vessel distance maps by computing the distances of each voxel to its nearest vessel. Greater values of VDM-metrics, which reflected higher vessel distances, were associated with poorer cognitive outcomes in subjects affected by vascular pathology, while this relation was not observed in healthy controls. Therefore, a mixed contribution of vessel pattern and vessel density is proposed to confer cognitive resilience, consistent with previous research findings. In conclusion, VDM provides a novel platform, based on a statistically robust and quantitative method of vascular mapping, for addressing a variety of clinical research questions.

Differences in total cognition and cerebrovascular function in female breast cancer survivors and cancer-free women

Reduced cognition is often reported by breast cancer patients and survivors, but the mechanisms for this decline are yet to be determined. We compared the differences in cerebrovascular function and cognition in breast cancer survivors (n = 15) and cancer-free women (n = 15) matched by age and body mass index. Participants undertook anthropometric, mood, cardiovascular, exercise performance, strength, cerebrovascular, and cognitive measurements. Transcranial Doppler ultrasound was used to measure the cerebrovascular responsiveness (CVR) to physiological (hypercapnia; 5% carbon dioxide) and psychological stimuli. Breast cancer survivors had a lower CVR to hypercapnia (21.5 ± 12.8 vs 66.0 ± 20.9%, P < 0.001), CVR to cognitive stimuli (15.1 ± 1.5 vs 23.7 ± 9.0%, P < 0.001) and total composite cognitive score (100 ± 12 vs. 113 ± 7, P = 0.003) than cancer-free women. These parameters remained statistically different between the groups following adjustments for covariates using an analysis of co-variance. We observed significant correlations between multiple measures and exercise capacity the only variable positively correlated to all primary measures (CVR to hypercapnia, r = 0.492, P = 0.007; CVR to cognitive stimuli r = 0.555, P = 0.003; and total composite cognitive score, r = 0.625, P < 0.001). In this study, breast cancer survivors had lower cerebrovascular and cognitive function than age-matched cancer-free women, which may be attributable to the effects of cancer and cancer treatment on brain health.

Transient Receptor Potential Mucolipin-1 Participates in Intracerebral Hemorrhage-Induced Secondary Brain Injury by Inducing Neuroinflammation and Neuronal Cell Death

Transient receptor potential mucolipin-1 (TRPML1) is the most abundantly and widely expressed channel protein in the TRP family. While numerous studies have been conducted involving many aspects of TRPML1, such as its role in cell biology, oncology, and neurodegenerative diseases, there are limited reports about what role it plays in intracerebral hemorrhage (ICH)-induced secondary brain injury (SBI). Here we examined the function of TRPML1 in ICH-induced SBI. The caudal arterial blood of rats was injected into the caudate nucleus of basal ganglia to establish an experimental ICH model. We observed that lentivirus downregulated the expression level of TRPML1 and chemical agonist promoted the enzyme activity of TRPML1. The results indicated that the protein levels of TRPML1 in brain tissues increased 24 h after ICH. These results suggested that downregulated TRPML1 could significantly reduce inflammatory cytokines, and ICH induced the production of LDH and ROS. Furthermore, TRPML1 knockout relieved ICH-induced neuronal cell death and degeneration, and declines in learning and memory after ICH could be improved by downregulating the expression of TRPML1. In addition, chemical agonist-expressed TRPML1 showed the opposite effect and exacerbated SBI after ICH. In summary, this study demonstrated that TRPML1 contributed to brain injury after ICH, and downregulating TRPML1 could improve ICH-induced SBI, suggesting a potential target for ICH therapy.

Electroacupuncture ameliorates cerebrovascular impairment in Alzheimer's disease mice via melatonin signaling

AIMS

Cerebrovascular impairment contributes to the pathogenesis of Alzheimer's disease (AD). However, it still lacks effective intervention in clinical practice. Here, we investigated the efficacy of electroacupuncture (EA) in cerebrovascular repair in 3xTg-AD mice and its mechanism.

METHODS

3xTg-AD mice were employed to evaluate the protective effect of EA at ST36 acupoint (EAST36). Behavioral tests were performed to assess neurological disorders. Laser speckle contrast imaging, immunostaining, and Western blot were applied to determine EAST36-boosted cerebrovascular repair. The mechanism was explored in 3xTg mice and endothelial cell cultures by melatonin signaling modulation.

RESULTS

EAST36 at 20/100 Hz effectively alleviated the olfactory impairment and anxiety behavior and boosted cerebrovascular repair in AD mice. EAST36 attenuated cerebral microvascular degeneration in AD mice by modulating endothelial cell viability and injury. Consequently, the Aβ deposits and neural damage in AD mice were reversed after EAST36. Mechanistically, we revealed that EAST36 restored melatonin levels in AD mice. Melatonin supplement mimicked the EAST36 effect on cerebrovascular protection in AD mice and endothelial cell cultures. Importantly, blockage of melatonin signaling by antagonist blunted EAST36-induced cerebrovascular recovery and subsequent neurological improvement.

CONCLUSIONS

These findings provided strong evidence to support EAST36 as a potential nonpharmacological therapy against cerebrovascular impairment in AD. Further study is necessary to better understand how EAST36 treatment drives melatonin signaling.

Three-dimensional microenvironment regulates gene expression, function, and tight junction dynamics of iPSC-derived blood-brain barrier microvessels

The blood-brain barrier (BBB) plays a pivotal role in brain health and disease. In the BBB, brain microvascular endothelial cells (BMECs) are connected by tight junctions which regulate paracellular transport, and express specialized transporter systems which regulate transcellular transport. However, existing in vitro models of the BBB display variable accuracy across a wide range of characteristics including gene/protein expression and barrier function. Here, we use an isogenic family of fluorescently-labeled iPSC-derived BMEC-like cells (iBMECs) and brain pericyte-like cells (iPCs) within two-dimensional confluent monolayers (2D) and three-dimensional (3D) tissue-engineered microvessels to explore how 3D microenvironment regulates gene expression and function of the in vitro BBB. We show that 3D microenvironment (shear stress, cell-ECM interactions, and cylindrical geometry) increases BBB phenotype and endothelial identity, and alters angiogenic and cytokine responses in synergy with pericyte co-culture. Tissue-engineered microvessels incorporating junction-labeled iBMECs enable study of the real-time dynamics of tight junctions during homeostasis and in response to physical and chemical perturbations.

Mechanism of acteoside-activated let-7g-5P attenuating Aβ-induced increased permeability and apoptosis of brain microvascular endothelial cells based on experimental and network pharmacology

OBJECTIVES

Amyloid β-protein (Aβ)-induced apoptosis and oxidative stress of human brain microvascular endothelial cells(BMECs) are contributors to the development of Alzheimer's disease (AD). Acteoside has shown its therapeutic potential for AD treatment. Therefore, this study investigated the effect of acteoside on Aβ-induced blood-brain barrier damage, oxidative stress and apoptosis as well as to explore the underlying mechanisms through network pharmacology.

METHODS

The study used Aβ to induce human BMECs to construct an in-vitro injury model. Following treatment with acteoside, transendothelial electrical resistance (TEER), RT-qPCR and Western blot were used to evaluate the permeability of BMECs. The apoptosis level was detected by TUNEL and Western blot, ROS assay kit was used for the detection of reactive oxygen species (ROS) expression. The let-7g-5p expression level was detected by RT-qPCR. After additional treatment with let-7g-5p inhibitor, corresponding assays were performed again. Finally, network pharmacology was used to verify the mechanism.

RESULTS

Acteoside decreased the permeability, oxidative stress and cell apoptosis of Aβ-stimulated cells. More importantly, acteoside-activated let-7g-5p and additional treatment with let-7g-5p inhibitor abated the effects of acteoside on Aβ-induced permeability, oxidative stress and apoptosis of Aβ-stimulated BMECs. According to network pharmacology, 233 targeted genes of acteoside and 122 potential targets of let-7g-5p were determined by screening several databases, and two targets called Casp-3 and ITGB3 were obtained after taking the intersection.

CONCLUSION

In conclusion, these results reveal that acteoside-activated let-7g-5p attenuating Aβ-induced increased permeability and apoptosis of human BMECs.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Prolonged release of VEGF and Ang1 from intralesionally implanted hydrogel promotes perilesional vascularization and functional recovery after experimental ischemic stroke

Injectable hydrogels can generate and support pro-repair environments in injured tissue. Here we used a slow-releasing drug carrying in situ-forming hydrogel to promote post-stroke recovery in a rat model. Release kinetics were measured in vitro and in vivo with MRI, using gadolinium-labeled albumin (Galbumin), which demonstrated prolonged release over multiple weeks. Subsequently, this hydrogel was used for long-term delivery of vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1) (Gel VEGF + Ang1, n = 14), in a photothrombotically induced cortical stroke lesion in rats. Control stroke animals were intralesionally injected with saline (Saline, n = 10), non-loaded gel (Gel, n = 10), or a single bolus of VEGF + Ang1 in saline (Saline VEGF + Ang1, n = 10). MRI was executed to guide hydrogel injection. Functional recovery was assessed with sensorimotor function tests, while tissue status and vascularization were monitored by serial in vivo MRI. Significant recovery from sensorimotor deficits from day 28 onwards was only measured in the Gel VEGF + Ang1 group. This was accompanied by significantly increased vascularization in the perilesional cortex. Histology confirmed (re)vascularization and neuronal sparing in perilesional areas. In conclusion, intralesional injection of in situ-forming hydrogel loaded with pro-angiogenic factors can support prolonged brain tissue regeneration and promote functional recovery in the chronic phase post-stroke.

Effect of Cardiotonic Steroid Marinobufagenin on Vascular Remodeling and Cognitive Impairment in Young Dahl-S Rats

The hypertensive response in Dahl salt-sensitive (DSS) rats on a high-salt (HS) diet is accompanied by central arterial stiffening (CAS), a risk factor for dementia, and heightened levels of a prohypertensive and profibrotic factor, the endogenous Na/K-ATPase inhibitor marinobufagenin (MBG). We studied the effect of the in vivo administration of MBG or HS diet on blood pressure (BP), CAS, and behavioral function in young DSS rats and normotensive Sprague-Dawley rats (SD), the genetic background for DSS rats. Eight-week-old male SD and DSS rats were given an HS diet (8% NaCl, n = 18/group) or a low-salt diet (LS; 0.1% NaCl, n = 14-18/group) for 8 weeks or MBG (50 µg/kg/day, n = 15-18/group) administered via osmotic minipumps for 4 weeks in the presence of the LS diet. The MBG-treated groups received the LS diet. The systolic BP (SBP); the aortic pulse wave velocity (aPWV), a marker of CAS; MBG levels; spatial memory, measured by a water maze task; and tissue collection for the histochemical analysis were assessed at the end of the experiment. DSS-LS rats had higher SBP, higher aPWV, and poorer spatial memory than SD-LS rats. The administration of stressors HS and MBG increased aPWV, SBP, and aortic wall collagen abundance in both strains vs. their LS controls. In SD rats, HS or MBG administration did not affect heart parameters, as assessed by ECHO vs. the SD-LS control. In DSS rats, impaired whole-heart structure and function were observed after HS diet administration in DSS-HS vs. DSS-LS rats. MBG treatment did not affect the ECHO parameters in DSS-MBG vs. DSS-LS rats. The HS diet led to an increase in endogenous plasma and urine MBG levels in both SD and DSS groups. Thus, the prohypertensive and profibrotic effect of HS diet might be partially attributed to an increase in MBG. The prohypertensive and profibrotic functions of MBG were pronounced in both DSS and SD rats, although quantitative PCR revealed that different profiles of profibrotic genes in DSS and SD rats was activated after MBG or HS administration. Spatial memory was not affected by HS diet or MBG treatment in either SD or DSS rats. Impaired cognitive function was associated with higher BP, CAS, and cardiovascular remodeling in young DSS-LS rats, as compared to young SD-LS rats. MBG and HS had similar effects on the cardiovascular system and its function in DSS and SD rats, although the rate of change in SD rats was lower than in DSS rats. The absence of a cumulative effect of increased aPWV and BP on spatial memory can be explained by the cerebrovascular and brain plasticity in young rats, which help the animals to tolerate CAS elevated by HS and MBG and to counterbalance the profibrotic effect of heightened MBG.

Non-Linear Frequency Dependence of Neurovascular Coupling in the Cerebellar Cortex Implies Vasodilation-Vasoconstriction Competition

Neurovascular coupling (NVC) is the process associating local cerebral blood flow (CBF) to neuronal activity (NA). Although NVC provides the basis for the blood oxygen level dependent (BOLD) effect used in functional MRI (fMRI), the relationship between NVC and NA is still unclear. Since recent studies reported cerebellar non-linearities in BOLD signals during motor tasks execution, we investigated the NVC/NA relationship using a range of input frequencies in acute mouse cerebellar slices of vermis and hemisphere. The capillary diameter increased in response to mossy fiber activation in the 6-300 Hz range, with a marked inflection around 50 Hz (vermis) and 100 Hz (hemisphere). The corresponding NA was recorded using high-density multi-electrode arrays and correlated to capillary dynamics through a computational model dissecting the main components of granular layer activity. Here, NVC is known to involve a balance between the NMDAR-NO pathway driving vasodilation and the mGluRs-20HETE pathway driving vasoconstriction. Simulations showed that the NMDAR-mediated component of NA was sufficient to explain the time course of the capillary dilation but not its non-linear frequency dependence, suggesting that the mGluRs-20HETE pathway plays a role at intermediate frequencies. These parallel control pathways imply a vasodilation-vasoconstriction competition hypothesis that could adapt local hemodynamics at the microscale bearing implications for fMRI signals interpretation.

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.

The role of hypoxia in stem cell regulation of the central nervous system: From embryonic development to adult proliferation

Hypoxia is involved in the regulation of various cell functions in the body, including the regulation of stem cells. The hypoxic microenvironment is indispensable from embryonic development to the regeneration and repair of adult cells. In addition to embryonic stem cells, which need to maintain their self-renewal properties and pluripotency in a hypoxic environment, adult stem cells, including neural stem cells (NSCs), also exist in a hypoxic microenvironment. The subventricular zone (SVZ) and hippocampal dentate gyrus (DG) are the main sites of adult neurogenesis in the brain. Hypoxia can promote the proliferation, migration, and maturation of NSCs in these regions. Also, because most neurons in the brain are non-regenerative, stem cell transplantation is considered as a promising strategy for treating central nervous system (CNS) diseases. Hypoxic treatment also increases the effectiveness of stem cell therapy. In this review, we firstly describe the role of hypoxia in different stem cells, such as embryonic stem cells, NSCs, and induced pluripotent stem cells, and discuss the role of hypoxia-treated stem cells in CNS diseases treatment. Furthermore, we highlight the role and mechanisms of hypoxia in regulating adult neurogenesis in the SVZ and DG and adult proliferation of other cells in the CNS.

Comparative study of two isothiazolinone biocides, 1,2-benzisothiazolin-3-one (BIT) and 4,5-dichloro-2-n-octyl-isothiazolin-3-one (DCOIT), on barrier function and mitochondrial bioenergetics using murine brain endothelial cell line (bEND.3)

Isothiazolinone (IT) biocides are potent antibacterial substances used as preservatives and disinfectants. These biocides exert differing biocidal effects and display environmental stability based upon chemical structure. In agreement with our recent study reporting that 2-n-octyl-4-isothiazolin-3-one (OIT) induced dysfunction of the blood-brain barrier (BBB), the potential adverse health effects of two IT biocides 1,2-benzisothiazolin-3-one (BIT) and 4,5-dichloro-2-n-octyl-isothiazolin-3-one (DCOIT) were compared using brain endothelial cells (ECs) derived from murine brain endothelial cell line (bEND.3). BIT possesses an unchlorinated IT ring structure and used as a preservative in cleaning products. DCOIT contains a chlorinated IT ring structure and employed as an antifouling agent in paints. Data demonstrated that DCOIT altered cellular metabolism at a lower concentration than BIT. Both BIT and DCOIT increased reactive oxygen species (ROS) generation at the mitochondrial and cellular levels. However, the effect of DCOIT on glutathione (GSH) levels appeared to be greater than BIT. While mitochondrial membrane potential (MMP) was decreased in both BIT- and DCOIT-exposed cells, direct disturbance in mitochondrial bioenergetic flux was only observed in BIT-treated ECs. Taken together, IT biocides produced toxicity in brain EC and barrier dysfunction, but at different concentration ranges suggesting distinct differing mechanisms related to chemical structure.

Lactate as Potential Mediators for Exercise-Induced Positive Effects on Neuroplasticity and Cerebrovascular Plasticity

The accumulated evidence from animal and human studies supports that exercise is beneficial to physical health. Exercise can upregulate various neurotrophic factors, activate neuroplasticity, and play a positive role in improving and enhancing cerebrovascular function. Due to its economy, convenience, and ability to prevent or ameliorate various aging-related diseases, exercise, a healthy lifestyle, is increasingly popularized by people. However, the mechanism by which exercise performs this function and how it is transmitted from muscles to the brain remains incompletely understood. Here, we review the beneficial effects of exercise with different intensities on the brain with a focus on the positive effects of lactate on neuroplasticity and cerebrovascular plasticity. Based on these recent studies, we propose that lactate, a waste previously misunderstood as a by-product of glycolysis in the past, may be a key signal molecule that regulates the beneficial adaptation of the brain caused by exercise. Importantly, we speculate that a central protective mechanism may underlie the cognitive benefits induced by exercise.

Artificial neurovascular network (ANVN) to study the accuracy vs. efficiency trade-off in an energy dependent neural network

Artificial feedforward neural networks perform a wide variety of classification and function approximation tasks with high accuracy. Unlike their artificial counterparts, biological neural networks require a supply of adequate energy delivered to single neurons by a network of cerebral microvessels. Since energy is a limited resource, a natural question is whether the cerebrovascular network is capable of ensuring maximum performance of the neural network while consuming minimum energy? Should the cerebrovascular network also be trained, along with the neural network, to achieve such an optimum? In order to answer the above questions in a simplified modeling setting, we constructed an Artificial Neurovascular Network (ANVN) comprising a multilayered perceptron (MLP) connected to a vascular tree structure. The root node of the vascular tree structure is connected to an energy source, and the terminal nodes of the vascular tree supply energy to the hidden neurons of the MLP. The energy delivered by the terminal vascular nodes to the hidden neurons determines the biases of the hidden neurons. The "weights" on the branches of the vascular tree depict the energy distribution from the parent node to the child nodes. The vascular weights are updated by a kind of "backpropagation" of the energy demand error generated by the hidden neurons. We observed that higher performance was achieved at lower energy levels when the vascular network was also trained along with the neural network. This indicates that the vascular network needs to be trained to ensure efficient neural performance. We observed that below a certain network size, the energetic dynamics of the network in the per capita energy consumption vs. classification accuracy space approaches a fixed-point attractor for various initial conditions. Once the number of hidden neurons increases beyond a threshold, the fixed point appears to vanish, giving place to a line of attractors. The model also showed that when there is a limited resource, the energy consumption of neurons is strongly correlated to their individual contribution to the network's performance.

Blood-brain barrier opening by intracarotid artery hyperosmolar mannitol induces sterile inflammatory and innate immune responses

Intracarotid arterial hyperosmolar mannitol (ICAHM) blood-brain barrier disruption (BBBD) is effective and safe for delivery of therapeutics for central nervous system malignancies. ICAHM osmotically alters endothelial cells and tight junction integrity to achieve BBBD. However, occurrence of neuroinflammation following hemispheric BBBD by ICAHM remains unknown. Temporal proteomic changes in rat brains following ICAHM included increased damage-associated molecular patterns, cytokines, chemokines, trophic factors, and cell adhesion molecules, indicative of a sterile inflammatory response (SIR). Proteomic changes occurred within 5 min of ICAHM infusion and returned to baseline by 96 h. Transcriptomic analyses following ICAHM BBBD further supported an SIR. Immunohistochemistry revealed activated astrocytes, microglia, and macrophages. Moreover, proinflammatory proteins were elevated in serum, and proteomic and histological findings from the contralateral hemisphere demonstrated a less pronounced SIR, suggesting neuroinflammation beyond regions of ICAHM infusion. Collectively, these results demonstrate ICAHM induces a transient SIR that could potentially be harnessed for neuroimmunomodulation.

Aβ (Amyloid Beta) and Tau Tangle Pathology Modifies the Association Between Small Vessel Disease and Cortical Microinfarcts

BACKGROUND AND PURPOSE

There is increasing recognition of the importance of cortical microinfarcts to overall brain health, cognition, and Alzheimer dementia. Cerebral small vessel pathologies are associated with microinfarcts and frequently coexist with Alzheimer disease; however, the extent to which Aβ (amyloid beta) and tau pathology modulates microvascular pathogenesis is not fully understood. Study objective was to examine the relationship of small vessel pathologies, arteriolosclerosis, and cerebral amyloid angiopathy, with cortical microinfarcts in people with differing levels of Aβ or tau tangle burden.

METHODS

Participants were 1489 autopsied older people (mean age at death, 89 years; 67% women) from 1 of 3 ongoing clinical-pathological cohort studies of aging. Neuropathological evaluation identified cortical Aβ and tau tangle burden using immunohistochemistry in 8 brain regions, provided semiquantitative grading of cerebral vessel pathologies, and identified the presence of cortical microinfarcts. Logistic regression models adjusted for demographics and atherosclerosis and examined whether Aβ or tau tangle burden modified relations between small vessel pathologies and cortical microinfarcts.

RESULTS

Cortical microinfarcts were present in 17% of older people, moderate-to-severe cerebral amyloid angiopathy pathology in 36%, and arteriolosclerosis in 34%. In logistic regression models, we found interactions with Aβ and tau tangles, reflecting that the association between arteriolosclerosis and cortical microinfarcts was stronger in the context of greater Aβ (estimate, 0.15; SE=0.07; P=0.02) and tau tangle burden (estimate, 0.13; SE=0.06; P=0.02). Interactions also emerged for cerebral amyloid angiopathy, suggesting that the association between cerebral amyloid angiopathy and cortical microinfarcts is more robust in the presence of higher Aβ (estimate, 0.27; SE=0.07; P<0.001) and tangle burden (estimate, 0.16; SE=0.06; P=0.005).

CONCLUSIONS

These findings suggest that in the presence of elevated Aβ or tangle pathology, small vessel pathologies are associated with greater microvascular tissue injury, highlighting a potential link between neurodegenerative and vascular mechanisms.

Ultrastructural studies of the neurovascular unit reveal enhanced endothelial transcytosis in hyperglycemia‐enhanced hemorrhagic transformation after stroke

Aims

Pre‐existing hyperglycemia (HG) aggravates the breakdown of blood–brain barrier (BBB) and increases the risk of hemorrhagic transformation (HT) after acute ischemic stroke in both animal models and patients. To date, HG‐induced ultrastructural changes of brain microvascular endothelial cells (BMECs) and the mechanisms underlying HG‐enhanced HT after ischemic stroke are poorly understood.

Methods

We used a mouse model of mild brain ischemia/reperfusion to investigate HG‐induced ultrastructural changes of BMECs that contribute to the impairment of BBB integrity after stroke. Adult male mice received systemic glucose administration 15 min before middle cerebral artery occlusion (MCAO) for 20 min. Ultrastructural characteristics of BMECs were evaluated using two‐dimensional and three‐dimensional electron microscopy and quantitatively analyzed.

Results

Mice with acute HG had exacerbated BBB disruption and larger brain infarcts compared to mice with normoglycemia (NG) after MCAO and 4 h of reperfusion, as assessed by brain extravasation of the Evans blue dye and microtubule‐associated protein 2 immunostaining. Electron microscopy further revealed that HG mice had more endothelial vesicles in the striatal neurovascular unit than NG mice, which may account for their deterioration of BBB impairment. In contrast with enhanced endothelial transcytosis, paracellular tight junction ultrastructure was not disrupted after this mild ischemia/reperfusion insult or altered upon HG. Consistent with the observed increase of endothelial vesicles, transcytosis‐related proteins caveolin‐1, clathrin, and hypoxia‐inducible factor (HIF)‐1α were upregulated by HG after MCAO and reperfusion.

Conclusion

Our study provides solid structural evidence to understand the role of endothelial transcytosis in HG‐elicited BBB hyperpermeability. Enhanced transcytosis occurs prior to the physical breakdown of BMECs and is a promising therapeutic target to preserve BBB integrity.

Three-dimensional induced pluripotent stem-cell models of human brain angiogenesis

During brain development, chemical cues released by developing neurons, cellular signaling with pericytes, and mechanical cues within the brain extracellular matrix (ECM) promote angiogenesis of brain microvascular endothelial cells (BMECs). Angiogenesis is also associated with diseases of the brain due to pathological chemical, cellular, and mechanical signaling. Existing in vitro and in vivo models of brain angiogenesis have key limitations. Here, we develop a high-throughput in vitro blood-brain barrier (BBB) bead assay of brain angiogenesis utilizing 150 μm diameter beads coated with induced pluripotent stem-cell (iPSC)-derived human BMECs (dhBMECs). After embedding the beads within a 3D matrix, we introduce various chemical cues and extracellular matrix components to explore their effects on angiogenic behavior. Based on the results from the bead assay, we generate a multi-scale model of the human cerebrovasculature within perfusable three-dimensional tissue-engineered blood-brain barrier microvessels. A sprouting phenotype is optimized in confluent monolayers of dhBMECs using chemical treatment with vascular endothelial growth factor (VEGF) and wnt ligands, and the inclusion of pro-angiogenic ECM components. As a proof-of-principle that the bead angiogenesis assay can be applied to study pathological angiogenesis, we show that oxidative stress can exert concentration-dependent effects on angiogenesis. Finally, we demonstrate the formation of a hierarchical microvascular model of the human blood-brain barrier displaying key structural hallmarks. We develop two in vitro models of brain angiogenesis: the BBB bead assay and the tissue-engineered BBB microvessel model. These platforms provide a tool kit for studies of physiological and pathological brain angiogenesis, with key advantages over existing two-dimensional models.

Modeling hyperosmotic blood-brain barrier opening within human tissue-engineered in vitro brain microvessels

As the majority of therapeutic agents do not cross the blood-brain barrier (BBB), transient BBB opening (BBBO) is one strategy to enable delivery into the brain for effective treatment of CNS disease. Intra-arterial infusion of the hyperosmotic agent mannitol reversibly opens the BBB; however, widespread clinical use has been limited due to the variability in outcomes. The current model for mannitol-induced BBBO assumes a transient but homogeneous increase in permeability; however, the details are poorly understood. To elucidate the mechanism of hyperosmotic opening at the cellular level, we developed a tissue-engineered microvessel model using stem cell-derived human brain microvascular endothelial cells (BMECs) perturbed with clinically relevant mannitol doses. This model recapitulates physiological shear stress, barrier function, microvessel geometry, and cell-matrix interactions. Using live-cell imaging, we show that mannitol results in dose-dependent and spatially heterogeneous increases in paracellular permeability through the formation of transient focal leaks. Additionally, we find that the degree of BBB opening and subsequent recovery is modulated by treatment with basic fibroblast growth factor. These results show that tissue-engineered BBB models can provide insight into the mechanisms of BBBO and hence improve the reproducibility of hyperosmotic therapies for treatment of CNS disease.

Insights into the dual role of angiogenesis following stroke

Stroke remains a major cause of serious disability due to the brain's limited capacity to regenerate. Current treatments focus on acute recanalization of the occluded blood vessels; however, currently there are no approved therapy options to regenerate neural circuits and reduce stroke-related disability. To promote recovery, therapeutic angiogenesis has been proposed as a promising target. Although restoration of blood vessels providing oxygen and nutrients to the peri-infarct regions may be beneficial, newly generated capillaries may also carry pathophysiological risk factors that need to be considered. One major concern are adverse effects including edema formation and haemorrhagic transformation due to the comprised endothelial barrier function during vascular remodelling. This brief opinion article will discuss the challenges and the newest advancements of angiogenesis as a therapeutic strategy for ischemic stroke.

Aging Impairs Cerebrovascular Reactivity at Preserved Resting Cerebral Arteriolar Tone and Vascular Density in the Laboratory Rat

The age-related (mal)adaptive modifications of the cerebral microvascular system have been implicated in cognitive impairment and worse outcomes after ischemic stroke. The magnitude of the hyperemic response to spreading depolarization (SD), a recognized principle of ischemic lesion development has also been found to be reduced by aging. Here, we set out to investigate whether the SD-coupled reactivity of the pial arterioles is subject to aging, and whether concomitant vascular rarefaction may contribute to the age-related insufficiency of the cerebral blood flow (CBF) response. CBF was assessed with laser-speckle contrast analysis (LASCA), and the tone adjustment of pial arterioles was followed with intrinsic optical signal (IOS) imaging at green light illumination through a closed cranial window created over the parietal cortex of isoflurane-anesthetized young (2 months old) and old (18 months old) male Sprague-Dawley rats. Global forebrain ischemia and later reperfusion were induced by the bilateral occlusion and later release of both common carotid arteries. SDs were elicited repeatedly with topical 1M KCl. Pial vascular density was measured in green IOS images of the brain surface, while the density and resting diameter of the cortical penetrating vasculature was estimated with micro-computed tomography of paraformaldehyde-fixed cortical samples. Whilst pial arteriolar dilation in response to SD or ischemia induction were found reduced in the old rat brain, the density and resting diameter of pial cortical vessels, and the degree of SD-related oligemia emerged as variables unaffected by age in our experiments. Spatial flow distribution analysis identified an age-related shift to a greater representation of higher flow ranges in the reperfused cortex. According to our data, impairment of functional arteriolar dilation, at preserved vascular density and resting vascular tone, may be implicated in the age-related deficit of the CBF response to SD, and possibly in the reduced efficacy of neurovascular coupling in the aging brain. SD has been recognized as a potent pathophysiological contributor to ischemic lesion expansion, in part because of the insufficiency of the associated CBF response. Therefore, the age-related impairment of cerebral vasoreactivity as shown here is suggested to contribute to the age-related acceleration of ischemic lesion development.

Tissue-engineered blood-brain barrier models via directed differentiation of human induced pluripotent stem cells

Three-dimensional (3D) tissue-engineered models of the blood-brain barrier (BBB) recapitulate in vivo shear stress, cylindrical geometry, and cell-ECM interactions. Here we address four issues associated with BBB models: cell source, barrier function, cryopreservation, and matrix stiffness. We reproduce a directed differentiation of brain microvascular endothelial cells (dhBMECs) from two fluorescently labeled human induced pluripotent stem cell lines (hiPSCs) and demonstrate physiological permeability of Lucifer yellow over six days. Microvessels formed from cryopreserved dhBMECs show expression of BBB markers and maintain physiological barrier function comparable to non-cryopreserved cells. Microvessels displaying physiological barrier function are formed in collagen I hydrogels with stiffness matching that of human brain. The dilation response of microvessels was linear with increasing transmural pressure and was dependent on matrix stiffness. Together these results advance capabilities for tissue-engineered BBB models.