Revisiting the neurovascular unit

Neuropathological links between T2DM and LOAD: systematic review and meta-analysis

Recent decades have described parallel neuropathological mechanisms increasing the risk for developing late-onset Alzheimer's dementia (LOAD) in type 2 diabetes mellitus (T2DM); however, still little is known of the role of diabetic encephalopathy and brain atrophy in LOAD. The aim of this systematic review is to provide a comprehensive view on diabetic encephalopathy/cerebral atrophy, taking into account neuroimaging data, neuropathology, metabolic and endocrine mechanisms, amyloid formation, brain perfusion impairments, neuroimmunology, and inflammasome activation. Key switches were identified, to further meta-analyze genomic candidate loci and epigenetic modifications. For the qualitative meta-analysis of genomic bases extracted, human linkage studies were examined; for epigenetic mechanisms, data from both human and animal studies are described. For the systematic review of pathophysiological mechanisms, 1,259 publications were evaluated and 93 gene loci extracted for candidate risk linkages. Sixty-six publications were evaluated for genomic association and descriptions of epigenomic modifications. Overall accumulated results highlight the insulin signaling system, vascular markers, inflammation and inflammasome pathways, amylin interactions, and glycosylation mechanisms. The protocol was registered with PROSPERO (ID: CRD42023440535).

Long-term nucleus basalis cholinergic lesions alter the structure of cortical vasculature, astrocytic density and microglial activity in Wistar rats

Basal forebrain cholinergic neurons (BFCNs) are the sole source of cholinergic innervation to the cerebral cortex and hippocampus in humans and the primary source in rodents. This system undergoes early degeneration in Alzheimer's disease. BFCNs terminal synapses are involved in the regulation of the cerebral blood flow by making classical synaptic contacts with other neurons. Additionally, they are located in proximity to cortical cerebral blood vessels, forming connections with various cell types of the neurovascular unit (NVU), including vascular smooth muscle cells, endothelial cells, and astrocytic end-feet. However, the effects of the BFCNs input on NVU components remain unresolved. To address this issue, we immunolesioned the nucleus basalis by administering bilateral stereotaxic injections of the cholinergic immunotoxin 192-IgG-Saporin in 2.5-month-old Wistar rats. Seven months post-lesion, we observed a significant reduction in cortical vesicular acetylcholine transporter-immunoreactive synapses. This was accompanied by changes in the diameter of cortical capillaries and precapillary arterioles, as well as lower levels of vascular endothelial growth factor A (VEGF-A). Additionally, the cholinergic immunolesion increased the density of cortical astrocytes and microglia in the cortex. At these post-BFCN-lesion stages, astrocytic end-feet exhibited an increased co-localization with arterioles. The number of microglia in the parietal cortex correlated with cholinergic loss and exhibited morphological changes indicative of an intermediate activation state. This was supported by decreased levels of proinflammatory mediators IFN-γ, IL-1β, and KC/GRO (CXCL1), and by increased expression of M2 markers SOCS3, IL4Rα, YM1, ARG1, and Fizz1. Our findings offer a novel insight: that the loss of nucleus basalis cholinergic input negatively impacts cortical blood vessels, NVU components, and microglia phenotype.

Nanoparticles targeting the central circadian clock: Potential applications for neurological disorders

Circadian rhythms and their involvement with various human diseases, including neurological disorders, have become an intense area of research for the development of new pharmacological treatments. The location of the circadian clock machinery in the central nervous system makes it challenging to reach molecular targets at therapeutic concentrations. In addition, a timely administration of the therapeutic agents is necessary to efficiently modulate the circadian clock. Thus, the use of nanoparticles in circadian clock dysfunctions may accelerate their clinical translation by addressing these two key challenges: enhancing brain penetration and/or enabling their formulation in chronodelivery systems. This review describes the implications of the circadian clock in neurological pathologies, reviews potential molecular targets and their modulators and suggests how the use of nanoparticle-based formulations could improve their clinical success. Finally, the potential integration of nanoparticles into chronopharmaceutical drug delivery systems will be described.

The Cells of the Vasculature: Advances in the Regulation of Vascular Tone in the Brain and Periphery

The vasculature is a complex tissue in which multiple cell types coordinate the regulation of tissue perfusion in response to hemodynamic and biochemical signals. Advances in this field are continuing to deepen our understanding of the relative importance of these cell types through the body. In the peripheral vasculature, tone is generated primarily by smooth muscle cells and regulated by endothelial cells, and neurons. In the brain parenchyma, unique cell types including pericytes, perivascular astrocytes and microglia, also contribute to the regulation of arterial and capillary tone. Here, we provide a cell-by-cell review of the regulation of vascular tone and highlight recent advances in the regulation of vascular tone in both the periphery and cerebral vasculature.

Unlocking the potential of photobiomodulation therapy for brain neurovascular coupling: The biological effects and medical applications

Photobiomodulation (PBM) therapy stands as an innovative neurostimulation modality that has demonstrated both efficacy and safety in improving brain function. This therapy exerts multifaceted influences on neurons, blood vessels, and their intricate interplay known as neurovascular coupling (NVC). Growing evidence indicates that NVC may present a promising target for PBM intervention. However, the detailed mechanisms underlying its therapeutic benefits remain to be fully understood. This review aims to elucidate the potential metabolic pathways and signaling cascades involved in the modulatory effects of PBM, while also exploring the extensive repertoire of PBM applications in neurologic and psychiatric conditions. The prospects of PBM within the realm of NVC investigation are intensively considered, providing deeper insights into the powerful capabilities of PBM therapy and its potential to revolutionize neurostimulation treatments.

Spatially and temporally mismatched blood flow and neuronal activity by high-intensity intracortical microstimulation

INTRODUCTION

Intracortial microstimulation (ICMS) is widely used in neuroprosthetic brain-machine interfacing, particularly in restoring lost sensory and motor functions. Spiking neuronal activity requires increased cerebral blood flow to meet local metabolic demands, a process conventionally denoted as neurovascular coupling (NVC). However, it is unknown precisely how and to what extent ICMS elicits NVC and how the neuronal and blood flow responses to ICMS correlate. Suboptimal NVC by ICMS may compromise oxygen and energy delivery to the activated neurons thus impair neuroprosthetic functionality.

MATERIAL AND METHOD

We used wide-field imaging (WFI), laser speckle imaging (LSI) and two-photon microscopy (TPM) to study living, transgenic mice expressing calcium (Ca2+) fluorescent indicators in either neurons or vascular mural cells (VMC), as well as to measure vascular inner lumen diameters.

RESULT

By testing a range of stimulation amplitudes and examining cortical tissue responses at different distances from the stimulating electrode tip, we found that high stimulation intensities (≥ 50 μA) elicited a spatial and temporal neurovascular decoupling in regions most adjacent to electrode tip (< 200 μm), with significantly delayed onset times of blood flow responses to ICMS and compromised maximum blood flow increases. We attribute these effects respectively to delayed Ca2+ signalling and decreased Ca2+ sensitivity in VMCs.

CONCLUSION

Our study offers new insights into ICMS-associated neuronal and vascular physiology with potentially critical implications towards the optimal design of ICMS in neuroprosthetic therapies: low intensities preserve NVC; high intensities disrupt NVC responses and potentially precipitate blood supply deficits.

Dexmedetomidine Promotes Angiogenesis After Ischemic Stroke Through the NRF2/HO-1/VEGF Pathway

Neurological dysfunction following stroke presents a significant challenge for patients. Recent studies suggest that angiogenesis can improve neurological function and enhance neuronal survival after ischemic stroke. Dexmedetomidine exhibits neuroprotective effects through various mechanisms; therefore, this study aimed to investigate whether it promotes angiogenesis and improves neurological function after stroke. A mouse model of ischemic stroke was developed by embolizing the middle cerebral arteries. Neurological function was assessed using scoring methods, the water maze test, and histological analyses, including Nissl and hematoxylin and eosin staining, to evaluate neuronal survival in the ischemic penumbra. Angiogenesis was observed through immunofluorescence staining, whereas pathway protein expression was analyzed via western blotting. Additionally, a model of oxygen-glucose deprivation/reoxygenation was established in mouse cerebral microvascular cells to conduct angiogenesis-related experiments. Dexmedetomidine reduced cerebral infarction size, alleviated neurological damage, promoted angiogenesis in the ischemic penumbra, and decreased neuronal death through the Nrf2/HO-1/VEGF pathway. However, these neuroprotective effects were reversed by the NRF2 inhibitor ML385. In vitro, dexmedetomidine enhanced the proliferation, migration, and tube-formation of cerebral microvascular cells in mice. ML385 also reversed the protective effects of dexmedetomidine against hypoxia and glucose deprivation-induced axonal damage. Dexmedetomidine enhances angiogenesis, reduces neuronal damage, and promotes cerebral microvascular cell migration and tube formation in the ischemic penumbra of an ischemic stroke mouse model through the Nrf2/HO-1/VEGF pathway.

Imaging the cerebral vasculature at different scales: translational tools to investigate the neurovascular interfaces

The improvements in imaging technology opened up the possibility to investigate the structure and function of cerebral vasculature and the neurovascular unit with unprecedented precision and gaining deep insights not only on the morphology of the vessels but also regarding their function and regulation related to the cerebral activity. In this review, we will dissect the different imaging capabilities regarding the cerebrovascular tree, the neurovascular unit, the haemodynamic response function, and thus, the vascular-neuronal coupling. We will discuss both clinical and preclinical setting, with a final discussion on the current scenery in cerebrovascular imaging where magnetic resonance imaging and multimodal microscopy emerge as the most potent and versatile tools, respectively, in the clinical and preclinical context.

Transcranial brain-wide functional ultrasound and ultrasound localization microscopy in mice using multi-array probes

Functional ultrasound imaging (fUS) and ultrasound localization microscopy (ULM) are advanced ultrasound imaging modalities for assessing both functional and anatomical characteristics of the brain. However, the application of these techniques at a whole-brain scale has been limited by technological challenges. While conventional linear acoustic probes provide a narrow 2D field of view and matrix probes lack sufficient sensitivity for 3D transcranial fUS, multi-array probes have been developed to combine high sensitivity to blood flow with fast 3D acquisitions. In this study, we present a novel approach for the combined implementation of transcranial whole-brain fUS and ULM in mice using a motorized multi-array probe. This technique provides high-resolution, non-invasive imaging of neurovascular dynamics across the entire brain. Our findings reveal a significant correlation between absolute cerebral blood volume (ΔCBV) increases and microbubble speed, indicating vessel-level dependency of the evoked response. However, the lack of correlation with relative CBV (rCBV) suggests that fUS cannot distinguish functional responses alterations across different arterial vascular compartments. This methodology holds promise for advancing our understanding of neurovascular coupling and could be applied in brain disease diagnostics and therapeutic monitoring.

Blood pressure and the brain: the conundrum of hypertension and dementia

As the population ages, the anticipated rates of dementia worldwide are likely to increase dramatically, especially in low- and middle-income countries; thus, any opportunity to modify dementia risk is especially critical. Hypertension is one risk factor that is highly prevalent, consistently important for late-life brain health, and which could represent a target for prevention of dementia. Furthermore, hypertension is the most significant modifiable risk factor for stroke. This review will summarize existing literature linking hypertension with dementia and brain health more broadly, will discuss potential mechanisms linking hypertension with brain health, and will consider specific factors that may impact not only the relationship between hypertension and the brain but also the importance of treatment, including different associations over the life course.

Mapping the transcriptional and epigenetic landscape of organotypic endothelial diversity in the developing and adult mouse

The vascular endothelium features unique molecular and functional properties across different vessel types, such as between arteries, veins and capillaries, as well as between different organs, such as the leaky sinusoidal endothelium of the liver versus the impermeable vessels of the brain. However, the transcriptional networks governing endothelial organ specialization remain unclear. Here we profile the accessible chromatin and transcriptional landscapes of the endothelium from the mouse liver, lung, heart, kidney, brain and retina, across developmental time, to identify potential transcriptional regulators of endothelial heterogeneity. We then determine which of these putative regulators are conserved in human brain endothelial cells, and using single-cell transcriptomic profiling, we define which regulatory networks are active during brain maturation. Finally, we show that the putative transcriptional regulators identified by these three approaches molecularly and functionally reprogram naive endothelial cells. Thus, this resource can be used to identify potential transcriptional regulators controlling the establishment and maintenance of organ-specific endothelial specialization.

STING immune activation of microglia aggravating neurovascular unit damage in diabetic retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness and is pathologically characterized by neuroinflammation and neovascularization. Retinal homeostasis is critically maintained by the retinal neurovascular unit (NVU), which can be disrupted by abnormal activation of microglia in DR. However, the underlying mechanism remains unclear. Here, we provide the first evidence of upregulated stimulator of interferon genes (STING) in microglia within fibrovascular membranes (FVMs) and retinas from oxygen-induced retinopathy (OIR) and streptozotocin (STZ)-induced diabetic mice. Furthermore, we identified STING upregulation in BV2 cells stimulated with high glucose (HG) or hypoxia, accompanied by mitochondrial dysfunction and cytoplasmic leakage of damaged mitochondrial DNA (mtDNA). Pharmacologic or genetic inhibition of STING in microglia prevented their activation and polarization. Next, we demonstrated that STING-deficient BV2 cells reversed the proangiogenic behavior of endothelial cells and protected retinal ganglion cells (RGCs) from oxidative stress. Finally, intravitreal injection of AAV-STING alleviated retinal neurovascular pathologies in both OIR and STZ mice. This study demonstrated that the release of mtDNA mediates STING immune activation of microglia, which further exacerbates NVU damage in DR. In contrast, immunosuppressing STING in microglia could serve as a potential therapeutic strategy.

Glial vascular Unit as a bridge between Blood-Brain Barrier and glymphatic System: Roles in sepsis-associated encephalopathy

This article underscores the Glial Vascular Unit (GVU) 's possible role in bridging the Blood-Brain Barrier (BBB) and Glymphatic System in Sepsis-associated encephalopathy (SAE). Future studies should prioritize understanding the mechanistic underpinnings of GVU dysfunction in sepsis and explore interventions aimed at modulating BBB permeability, astrocytic function, and glymphatic clearance. Understanding these complex mechanisms is crucial for developing therapeutic strategies aimed at mitigating the neurological impact of sepsis and improving outcomes for patients with SAE.

Changes in cerebrovascular reactivity within functional networks in older adults with long-COVID

Introduction

Cognitive symptoms are reported in the vast majority of individuals with long-COVID and there is growing support to suggest neurovascular mechanisms may play a role. Older adults are at increased risk for developing complications associated with COVID-19, including heightened risk for cognitive decline. Cerebrovascular Reactivity (CVR), a marker of neurovascular health, has been linked to age related cognitive decline and may play a role in long-COVID, however, this has not yet been explored.

Methods

The present study examined group differences in CVR in 31 older adults with long-COVID compared to 31 cognitively unimpaired older adults without long-COVID symptoms. Follow up analyses were conducted to examine how CVR was associated with both subjective cognitive symptoms and neuropsychological (NP) test performance. A subject-specific approach, Distribution-Corrected Z-scores (DisCo-Z), was used.

Results

Analyses revealed the long-COVID group demonstrated significantly greater incidence of extreme CVR clusters within the brain (>100 voxels) and within functional networks thought to drive attention and executive function. Extreme positive CVR clusters were positively associated with greater number of subjective cognitive symptoms and negatively correlated with NP performance.

Discussion

These findings are among the first to provide a link between cognitive functioning in long-COVID and neurovascular changes relevant for aging and mechanistic studies of long-COVID.

Loss of endothelial CD2AP causes sex-dependent cerebrovascular dysfunction

Polymorphisms in CD2-associated protein (CD2AP) predispose to Alzheimer's disease (AD), but the underlying mechanisms remain unknown. Here, we show that loss of CD2AP in cerebral blood vessels is associated with cognitive decline in AD subjects and that genetic downregulation of CD2AP in brain vascular endothelial cells impairs memory function in male mice. Animals with reduced brain endothelial CD2AP display altered blood flow regulation at rest and during neurovascular coupling, defects in mural cell activity, and an abnormal vascular sex-dependent response to Aβ. Antagonizing endothelin-1 receptor A signaling partly rescues the vascular impairments, but only in male mice. Treatment of CD2AP mutant mice with reelin glycoprotein that mitigates the effects of CD2AP loss function via ApoER2 increases resting cerebral blood flow and even protects male mice against the noxious effect of Aβ. Thus, endothelial CD2AP plays critical roles in cerebrovascular functions and represents a novel target for sex-specific treatment in AD.

Unlocking the therapeutic potential of tumor-derived EVs in ischemia-reperfusion: a breakthrough perspective from glioma and stroke

Clinical studies have revealed a bidirectional relationship between glioma and ischemic stroke, with evidence of spatial overlap between the two conditions. This connection arises from significant similarities in their pathological processes, including the regulation of cellular metabolism, inflammation, coagulation, hypoxia, angiogenesis, and neural repair, all of which involve common biological factors. A significant shared feature of both diseases is the crucial role of extracellular vesicles (EVs) in mediating intercellular communication. Extracellular vesicles, with their characteristic bilayer structure, encapsulate proteins, lipids, and nucleic acids, shielding them from enzymatic degradation by ribonucleases, deoxyribonucleases, and proteases. This structural protection facilitates long-distance intercellular communication in multicellular organisms. In gliomas, EVs are pivotal in intracranial signaling and shaping the tumor microenvironment. Importantly, the cargos carried by glioma-derived EVs closely align with the biological factors involved in ischemic stroke, underscoring the substantial impact of glioma on stroke pathology, particularly through the crucial roles of EVs as key mediators in this interaction. This review explores the pathological interplay between glioma and ischemic stroke, addressing clinical manifestations and pathophysiological processes across the stages of hypoxia, stroke onset, progression, and recovery, with a particular focus on the crucial role of EVs and their cargos in these interactions.

Collateral blood vessels in stroke and ischemic disease: Formation, physiology, rarefaction, remodeling

Collateral blood vessels are unique, naturally occurring endogenous bypass vessels that provide alternative pathways for oxygen delivery in obstructive arterial conditions and diseases. Surprisingly however, the capacity of the collateral circulation to provide protection varies greatly among individuals, resulting in a significant fraction having poor collateral circulation in their tissues. We recently reviewed evidence that the presence of naturally-occurring polymorphisms in genes that determine the number and diameter of collaterals that form during development (ie, genetic background), is a major contributor to this variation. The purpose of this review is to summarize current understanding of the other determinants of collateral blood flow, drawing on both animal and human studies. These include the level of smooth muscle tone in collaterals, hemodynamic forces, how collaterals form during development (collaterogenesis), de novo formation of additional new collaterals during adulthood, loss of collaterals with aging and cardiovascular risk factor presence (rarefaction), and collateral remodeling (structural lumen enlargement). We also review emerging evidence that collaterals not only provide protection in ischemic conditions but may also serve a physiological function in healthy individuals. Primary focus is on studies conducted in brain, however relevant findings in other tissues are also reviewed, as are questions for future investigation.

Edaravone dexborneol for ischemic stroke with sufficient recanalization after thrombectomy: a randomized phase II trial

This phase II, randomized, double blinded, multi-center study aims to explore whether intravenous edaravone dexborneol (ED) could improve clinical outcomes in patients with anterior circulation stroke with successful endovascular reperfusion (ClinicalTrials.gov: NCT04667637). Eligible patients were randomly (1:1) assigned into ED, which received intravenous ED (37.5 mg, 2/day, for 12 days) or control group, which received placebo. The primary endpoint was favorable functional outcome (a modified Rankin Scale [mRS] of 0-2 at 90 days). Two hundred patients were enrolled, including 97 in ED group and 103 in control group. The proportion of patients with 90-day mRS (0-2) was 58.7% (54/92) in ED group and 52.1% (49/94) in control group (unadjusted odds ratio 1.37, [95% CI 0.76-2.44], P = 0.29). This work suggests that intravenous ED is safe, but do not statistically improve 90-day functional outcomes in patients with anterior circulation stroke with successful endovascular reperfusion.

Disrupted Calcium Dynamics in Reactive Astrocytes Occur with Endfeet-Arteriole Decoupling in an Amyloid Mouse Model of Alzheimer's Disease

While cerebrovascular dysfunction and reactive astrocytosis are extensively characterized hallmarks of Alzheimer's disease (AD) and related dementias, the dynamic relationship between reactive astrocytes and cerebral vessels remains poorly understood. Here, we used jGCaMP8f and two photon microscopy to investigate Ca2+ signaling in multiple astrocyte subcompartments, concurrent with changes in cerebral arteriole activity, in fully awake eight-month-old male and female 5xFAD mice, a model for AD-like pathology, and wild-type (WT) littermates. In the absence of movement, spontaneous Ca2+ transients in barrel cortex occurred more frequently in astrocyte somata, processes, and perivascular regions of 5xFAD mice. However, evoked arteriole dilations (in response to air puff stimulation of contralateral whiskers) and concurrent Ca2+ transients across astrocyte compartments were reduced in 5xFAD mice relative to WTs. Synchronous activity within multi-cell astrocyte networks was also impaired in the 5xFAD group. Using a custom application to assess functional coupling between astrocyte endfeet and immediately adjacent arteriole segments, we detected deficits in Ca2+ response probability in 5xFAD mice. Moreover, endfeet Ca2+ transients following arteriole dilations exhibited a slower onset, reduced amplitude, and lacked relative proportionality to vasomotive activity compared to WTs. The results reveal nuanced alterations in 5xFAD reactive astrocytes highlighted by impaired signaling fidelity between astrocyte endfeet and cerebral arterioles. The results have important implications for the mechanistic underpinnings of brain hypometabolism and the disruption of neurophysiological communication found in AD and other neurodegenerative conditions.

A Proposed Role for Lymphatic Supermicrosurgery in the Management of Alzheimer's Disease: A Primer for Reconstructive Microsurgeons

The relatively recent discovery of a novel lymphatic system within the brain meninges has spurred interest in how waste products generated by neurons and glial cells-including proteins associated with Alzheimer's disease (AD) pathology such as amyloid beta (Aβ) and tau-are disposed of. Evidence is building that suggests disease progression in AD and other cognitive impairments could be explained by dysfunction in the brain's lymphatic system or obstruction of drainage. An interesting implication of this hypothesis is that, by relieving the obstruction of flow, lymphatic reconstruction along the drainage pathway could serve as a potential novel treatment. Should this concept prove true, it could represent a surgical solution to a problem for which only medical solutions have thus far been considered. This study is meant to serve as a primer for reconstructive microsurgeons, introducing the topic and current hypotheses about the potential role of lymphatic drainage in AD. A preview of current research evaluating the feasibility of lymphatic reconstruction as a surgical approach to improving Aβ clearance is provided, with the aim of inspiring others to design robust preclinical and clinical investigations into this intriguing hypothesis.

Shocking insights for neurovascular coupling: Electrical signals ignite calcium dynamics in brain capillaries

Brain capillaries contribute to neurovascular coupling (NVC) by sensing neural activity and coordinating upstream arteriole dilation. However, the mechanisms underlying conducted vasodilation remain incompletely understood. Recent findings (PNAS, 2024) identify a novel process, "electrocalcium coupling," in which hyperpolarizing signals from K+ channels drive long-range Ca²⁺ signaling in capillaries, revealing new insights into the integration of vasodilatory signals in the brain.

Endothelial cells as key players in cerebral small vessel disease

Cerebral small vessel disease (SVD) is a vascular disorder that increases the risk of stroke and dementia and is diagnosed through brain MRI. Current primary prevention and secondary treatment of SVD are focused on lifestyle interventions and vascular risk factor control, including blood pressure reduction. However, these interventions have limited effects, a proportion of individuals with sporadic SVD do not have hypertension, and SVD shows strong familial and genetic underpinnings. Here, we describe the increasing evidence that cerebral endothelial cell dysfunction is a key mechanism of SVD. Dysfunctional endothelial cells can cause cerebral blood vessel dysfunction, alter blood-brain barrier integrity and interfere with cell-cell interactions in the neuro-glial-vascular unit, thereby causing damage to adjacent brain tissue. Endothelial cells in SVD may become dysfunctional through intrinsic mechanisms via genetic vulnerability to SVD and/or via extrinsic factors such as hypertension, smoking and diabetes. Drugs that act on endothelial pathways are already looking promising in clinical trials, and understanding their action on endothelial cells and the surrounding brain may lead to the development of other therapies to limit disease progression and improve outcomes for individuals with SVD.

Fibrillar tau alters cerebral endothelial cell metabolism, vascular inflammatory activation, and barrier function in vitro and in vivo

INTRODUCTION

The presence of tau aggregates in and around the brain vasculature in Alzheimer's disease (AD) and tauopathies suggests its possible pathogenicity to cerebral endothelial cells (ECs).

METHODS

We used an in vitro model of the blood-brain barrier (BBB) to understand the mechanisms of fibrillar tau-mediated cerebral EC and BBB pathology, confirming our findings in 3-month-old P301S mice brains and extracted microvessels.

RESULTS

Protofibrillar and fibrillar tau species induce endothelial barrier permeability through an increase in glycolysis, which activates ECs toward a pro-inflammatory phenotype, inducing loss of junction protein expression and localization. The Warburg-like metabolic shift toward glycolysis and increased vascular pathological phenotypes are also present in young P301S mice.

DISCUSSION

In sum, our work reveals that fibrillar tau species, by enhancing endothelial glycolytic metabolism, promote vascular inflammatory phenotypes and loss of BBB function, highlighting the importance of addressing and targeting early tau-mediated neurovascular damage in AD and tauopathies.

HIGHLIGHTS

We improve the understanding of the mechanisms of vascular pathology in tauopathies. Fibrillar tau mediates vascular metabolic changes, inflammation, and blood-brain barrier (BBB) dysfunction. These events are replicated at early stages in a tauopathy mouse model. Inhibiting altered glycolysis reduces BBB permeability and endothelial activation.

Alzheimer's, Parkinson's, Frontotemporal Lobar Degeneration, and Amyotrophic Lateral Sclerosis Start in Pediatric Ages: Ultrafine Particulate Matter and Industrial Nanoparticles Are Key in the Early-Onset Neurodegeneration: Time to Invest in Preventive Medicine

Billions of people are exposed to fine particulate matter (PM2.5) levels above the USEPA's annual standard of 9 μg/m3. Common emission sources are anthropogenic, producing complex aerosolized toxins. Ultrafine particulate matter (UFPM) and industrial nanoparticles (NPs) have major detrimental effects on the brain, but the USA does not measure UFPM on a routine basis. This review focuses on the development and progression of common neurodegenerative diseases, as diagnosed through neuropathology, among young residents in Metropolitan Mexico City (MMC). MMC is one of the most polluted megacities in the world, with a population of 22 million residents, many of whom are unaware of the brain effects caused by their polluted atmosphere. Fatal neurodegenerative diseases (such as Alzheimer's and Parkinson's) that begin in childhood in populations living in air polluted environments are preventable. We conclude that UFPM/NPs are capable of disrupting neural homeostasis and give rise to relentless neurodegenerative processes throughout the entire life of the highly exposed population in MMC. The paradigm of reaching old age to have neurodegeneration is no longer supported. Neurodegenerative changes start early in pediatric ages and are irreversible. It is time to invest in preventive medicine.

A higher vertebrobasilar pulsatility index is associated with lower parietal perfusion in Alzheimer's disease

BACKGROUND

While cerebrovascular hemodynamics exhibits critical interplay with the pathogenesis of dementia, limited articles have examined the impact of vertebrobasilar (VB) hemodynamics on cerebral blood flow (CBF), and to what extent it varies by dementia subtypes.

OBJECTIVE

To explore the associations between VB hemodynamics and CBF by dementia subtypes.

METHODS

This research recruited a total of 120 dementia patients [43 subcortical ischemic vascular dementia (SIVD); 59 Alzheimer's disease (AD); 18 mixed dementia] and 40 older adults with normal cognition and compared their transcranial doppler (TCD) flow parameters and arterial spin labeling-measured CBF. Using the partial correlation analysis, the associations between TCD parameters and CBF values were explored among the defined subgroups.

RESULTS

A higher VB pulsatility index (PI) was related to lower parietal CBF and lower VB end-diastolic velocity (EDV). Moreover, the significance of flow parameters in the basilar artery (BA) to parietal CBF was identified: peak-systolic velocity (PSV) unanimously showed positive correlations among all subgroups except SIVD, and both PSV and EDV showed positive correlations in AD. Of note, there were more noticeable "BA flow-frontoparietal CBF" associations among the high than low VB PI group, and AD than SIVD group.

CONCLUSIONS

The findings indicate that VB-resistance-related parietal vulnerability and topological CBF associations vary by dementia subtypes. Given VB hemodynamics-CBF relationships, the current research extends our understanding of the vasocognopathic effects among dementia patients.

The Triad of Blood-Brain Barrier Integrity: Endothelial Cells, Astrocytes, and Pericytes in Perinatal Stroke Pathophysiology

Pediatric stroke, a significant cause of long-term neurological deficits in children, often arises from disruptions within neurovascular unit (NVU) components. The NVU, a dynamic ensemble of astrocytes, endothelial cells, pericytes, and microglia, is vital for maintaining cerebral homeostasis and regulating vascular brain development. Its structural integrity, particularly at the blood-brain barrier (BBB), depends on intercellular junctions and the basement membrane, which together restrict paracellular transport and shield the brain from systemic insults. Dysfunction in this intricate system is increasingly linked to pediatric stroke and related cerebrovascular conditions. Mutations disrupting endothelial cell adhesion or pericyte-endothelial interactions can compromise BBB stability, leading to pathological outcomes such as intraventricular hemorrhage in the germinal matrix, a hallmark of vascular brain immaturity. Additionally, inflammation, ferroptosis, necroptosis, and autophagy are key cellular processes influencing brain damage and repair. Excessive activation of these mechanisms can exacerbate NVU injury, whereas targeted therapeutic modulation offers potential pathways to mitigate damage and support recovery. This review explores the cellular and molecular mechanisms underlying NVU dysfunction, BBB disruption, and subsequent brain injury in pediatric stroke. Understanding the interplay between genetic mutations, environmental stressors, and NVU dynamics provides new insights into stroke pathogenesis. The susceptibility of the germinal matrix to vascular rupture further emphasizes the critical role of NVU integrity in early brain development. Targeting inflammatory pathways and cell death mechanisms presents promising strategies to preserve NVU function and improve outcomes for affected neonates.

Neurovascular Decoupling Is Associated With Lobar Intracerebral Hemorrhages and White Matter Hyperintensities

BACKGROUND

Neurovascular coupling is a fundamental aspect of brain function by regulating cerebral blood flow in response to regional neuronal activity. Increasing evidence suggest neurovascular decoupling occurs early in the progression of Alzheimer disease (AD), potentially reflecting early vascular damage. Therefore, understanding the relationship between neurovascular coupling and established vascular risk factors for AD is essential to gain deeper insights into the vascular mechanisms underlying AD.

METHODS

This cross-sectional observational study investigated the association between neurovascular coupling and vascular risk factors for AD, specifically small vessel disease magnetic resonance imaging markers, cardiovascular risk factors, and the apolipoprotein E genotype. The cohort included 119 participants diagnosed with subjective cognitive impairment, mild cognitive impairment, and AD-related dementia, as well as individuals without cognitive complaints. Neurovascular coupling was measured by blood-oxygen-level-dependent functional magnetic resonance imaging amplitude in response to visual stimulation.

RESULTS

Our findings revealed that decreased neurovascular coupling is linked to structural brain changes typically seen in small vessel disease; specifically we found an association between neurovascular coupling and white matter hyperintensities load (β=-0.199, P=0.030) and presence of lobar intracerebral hemorrhage (β=-0.228, P=0.011).

CONCLUSIONS

This raises the suggestion that a decreased neurovascular coupling in the disease process of AD is related to comorbid small vessel disease.

An Update on Neuroaging on Earth and in Spaceflight

Over 400 articles on the pathophysiology of brain aging, neuroaging, and neurodegeneration were reviewed, with a focus on epigenetic mechanisms and numerous non-coding RNAs. In particular, this review the accent is on microRNAs, the discovery of whose pivotal role in gene regulation was recognized by the 2024 Nobel Prize in Physiology or Medicine. Aging is not a gradual process that can be easily modeled and described. Instead, multiple temporal processes occur during aging, and they can lead to mosaic changes that are not uniform in pace. The rate of change depends on a combination of external and internal factors and can be boosted in accelerated aging. The rate can decrease in decelerated aging due to individual structural and functional reserves created by cognitive, physical training, or pharmacological interventions. Neuroaging can be caused by genetic changes, epigenetic modifications, oxidative stress, inflammation, lifestyle, and environmental factors, which are especially noticeable in space environments where adaptive changes can trigger aging-like processes. Numerous candidate molecular biomarkers specific to neuroaging need to be validated to develop diagnostics and countermeasures.

Arousal as a universal embedding for spatiotemporal brain dynamics

Neural activity in awake organisms shows widespread and spatiotemporally diverse correlations with behavioral and physiological measurements. We propose that this covariation reflects in part the dynamics of a unified, multidimensional arousal-related process that regulates brain-wide physiology on the timescale of seconds. By framing this interpretation within dynamical systems theory, we arrive at a surprising prediction: that a single, scalar measurement of arousal (e.g., pupil diameter) should suffice to reconstruct the continuous evolution of multidimensional, spatiotemporal measurements of large-scale brain physiology. To test this hypothesis, we perform multimodal, cortex-wide optical imaging and behavioral monitoring in awake mice. We demonstrate that spatiotemporal measurements of neuronal calcium, metabolism, and brain blood-oxygen can be accurately and parsimoniously modeled from a low-dimensional state-space reconstructed from the time history of pupil diameter. Extending this framework to behavioral and electrophysiological measurements from the Allen Brain Observatory, we demonstrate the ability to integrate diverse experimental data into a unified generative model via mappings from an intrinsic arousal manifold. Our results support the hypothesis that spontaneous, spatially structured fluctuations in brain-wide physiology-widely interpreted to reflect regionally-specific neural communication-are in large part reflections of an arousal-related process. This enriched view of arousal dynamics has broad implications for interpreting observations of brain, body, and behavior as measured across modalities, contexts, and scales.

Neurovascular unit impairment in iron deficiency anemia

Iron is one of the crucial elements for CNS development and function and its deficiency (ID) is the most common worldwide nutrient deficit in the world. Iron deficiency anemia (IDA) in pregnant women and infants is a worldwide health problem due to its high prevalence and its irreversible long-lasting effects on brain development. Even with iron supplementation, IDA during pregnancy and/or breastfeeding can result in irreversible cognitive, motor, and behavioral impairments. The neurovascular unit (NVU) plays an important role in iron transport within the CNS as well as in the blood brain-barrier (BBB) formation and maturation, vasculogenesis/angiogenesis, neurovascular coupling and metabolic waste clearance. In animal models of IDA, significant changes have been observed at the capillary level, including alterations in iron transport, vasculogenesis, astrocyte endfeet, and pericytes. Despite these findings, the role of the NVU in IDA remains poorly understood. This review summarizes the potential effects of ID/IDA on brain development, myelination and neuronal function and discusses the role of NVU cells in iron metabolism, BBB, vasculogenesis/angiogenesis, neurovascular coupling and metabolic waste clearance. Furthermore, it emphasizes the need to view the NVU as a whole and as a potential target for ID/IDA. However, it remains unclear to what extent NVU alterations contribute to neuronal dysfunction, myelination abnormalities, and synaptic disturbances described in IDA.

Rosuvastatin mitigates blood-brain barrier disruption in sepsis-associated encephalopathy by restoring occludin levels

BACKGROUND

Blood-brain barrier (BBB) disruption is a key pathological feature of sepsis-associated encephalopathy (SAE). Rosuvastatin, a third-generation statin, exhibits diverse pharmacological functions beyond its lipid-lowering capacity. However, its potential neuroprotective role in SAE remains unclear.

MATERIALS AND METHODS

SAE models were established using the cecal ligation and puncture (CLP) method. BBB integrity was evaluated using NaF, and endothelial permeability was assessed by fluorescein isothiocyanate (FITC)-dextran assays.

RESULTS

Rosuvastatin significantly attenuated neuroinflammation in the brains of septic mice by reducing the expression of the pro-inflammatory cytokines interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factor α (TNF-α). It also ameliorated vascular injury in the brain cortex of septic mice by decreasing the levels of vascular cell adhesion molecule-1 (VCAM-1) and E-selectin. Furthermore, Rosuvastatin preserved BBB integrity in septic mice by enhancing the expression of the tight junction protein occludin. In vitro studies demonstrated that Rosuvastatin alleviated endothelial permeability and increased transendothelial electrical resistance (TEER) in lipopolysaccharide (LPS)-stimulated human brain microvascular endothelial cells (HBMECs). Additionally, Rosuvastatin prevented the LPS-induced reduction of occludin and Krüppel-like factor 2 (KLF2) in HBMECs. Importantly, silencing KLF2 abrogated Rosuvastatin's protective effects on endothelial permeability and occludin expression.

CONCLUSIONS

These findings indicate that Rosuvastatin may be a promising therapeutic candidate for mitigating BBB dysfunction associated with SAE.

Normative Cerebral Perfusion Across the Lifespan

Cerebral perfusion plays a crucial role in maintaining brain function and is tightly coupled with neuronal activity. While previous studies have examined cerebral perfusion trajectories across development and aging, precise characterization of its lifespan dynamics has been limited by small sample sizes and methodological inconsistencies. In this study, we construct the first comprehensive normative model of cerebral perfusion across the human lifespan (birth to 85 years) using a large multi-site dataset of over 12,000 high-quality arterial spin labeling (ASL) MRI scans. Leveraging generalized additive models for location, scale, and shape (GAMLSS), we mapped nonlinear growth trajectories of cerebral perfusion at global, network, and regional levels. We observed a rapid postnatal increase in cerebral perfusion, peaking at approximately 7.1 years, followed by a gradual decline into adulthood. Sex differences were evident, with distinct regional maturation patterns rather than uniform differences across all brain regions. Beyond normative modeling, we quantified individual deviations from expected CBF patterns in neurodegenerative and psychiatric conditions, identifying disease-specific perfusion abnormalities across four brain disorders. Using longitudinal data, we established typical and atypical cerebral perfusion trajectories, highlighting the prognostic value of perfusion-based biomarkers for detecting disease progression. Our findings provide a robust normative framework for cerebral perfusion, facilitating precise characterization of brain health across the lifespan and enhancing the early identification of neurovascular dysfunction in clinical populations.

Type-I nNOS neurons orchestrate cortical neural activity and vasomotion

It is unknown how the brain orchestrates coordination of global neural and vascular dynamics. We sought to uncover the role of a sparse but unusual population of genetically-distinct interneurons known as type-I nNOS neurons, using a novel pharmacological strategic to unilaterally ablate these neurons from the somatosensory cortex of mice. Region-specific ablation produced changes in both neural activity and vascular dynamics, decreased power in the delta-band of the local field potential, reduced sustained vascular responses to prolonged sensory stimulation, and abolished the post-stimulus undershoot in cerebral blood volume. Coherence between the left and right somatosensory cortex gamma-band power envelope and blood volume at ultra-low frequencies was decreased, suggesting type-1 nNOS neurons integrate long-range coordination of brain signals. Lastly, we observed decreases in the amplitude of resting-state blood volume oscillations and decreased vasomotion following the ablation of type-I nNOS neurons. This demonstrates that a small population of nNOS-positive neurons are indispensable for regulating both neural and vascular dynamics in the whole brain and implicates disruption of these neurons in diseases ranging from neurodegeneration to sleep disturbances.

Species-specific blood-brain barrier permeability in amphibians

BACKGROUND

The blood-brain barrier (BBB) is a semipermeable interface that prevents the non-selective transport into the central nervous system. It controls the delivery of macromolecules fueling the brain metabolism and the immunological surveillance. The BBB permeability is locally regulated depending on the physiological requirements, maintaining the tissue homeostasis and influencing pathological conditions. Given its relevance in vertebrate CNS, it is surprising that little is known about the BBB in Amphibians, some of which are capable of adult CNS regeneration.

RESULTS

The BBB size threshold of the anuran Xenopus laevis (African clawed toad), as well as two urodele species, Ambystoma mexicanum (axolotl) and Pleurodeles waltl (Iberian ribbed newt), was evaluated under physiological conditions through the use of synthetic tracers. We detected important differences between the analyzed species. Xenopus exhibited a BBB with characteristics more similar to those observed in mammals, whereas the BBB of axolotl was found to be permeable to the 1 kDa tracer. The permeability of the 1 kDa tracer measured in Pleurodeles showed values in between axolotl and Xenopus vesseks. We confirmed that these differences are species-specific and not related to metamorphosis. In line with these results, the tight junction protein Claudin-5 was absent in axolotl, intermediate in Pleurodeles and showed full-coverage in Xenopus vessels. Interestingly, electron microscopy analysis and the retention pattern of the larger tracers (3 and 70 kDa) demonstrated that axolotl endothelial cells exhibit higher rates of macropinocytosis, a non-regulated type of transcellular transport.

CONCLUSIONS

Our study demonstrated that, under physiological conditions, the blood-brain barrier exhibited species-specific variations, including permeability threshold, blood vessel coverage, and macropinocytosis rate. Future studies are needed to test whether the higher permeability observed in salamanders could have metabolic and immunological consequences contributing to their remarkable regenerative capacity.

Western diet since adolescence impairs brain functional hyperemia at adulthood in mice: rescue by a balanced ω-3:ω-6 polyunsaturated fatty acids ratio

BACKGROUND/OBJECTIVE

Obesity is a devastating worldwide metabolic disease, with the highest prevalence in children and adolescents. Obesity impacts neuronal function but the fate of functional hyperemia, a vital mechanism making possible cerebral blood supply to active brain areas, is unknown in organisms fed a high-caloric Western Diet (WD) since adolescence.

SUBJECTS/METHODS

We mapped changes in cerebral blood volume (CBV) in the somatosensory cortex in response to whisker stimulation in adolescent, adult, and middle-aged mice fed a WD since adolescence. To this aim, we used non-invasive and high-resolution functional ultrasound imaging (fUS).

RESULTS

We efficiently mimicked the metabolic syndrome of adolescents in young mice with early weight gain, dysfunctional glucose homeostasis, and insulinemia. Functional hyperemia is compromised as early as 3 weeks of WD and remains impaired after that in adolescent mice. These findings highlight the cerebrovascular vulnerability to WD during adolescence. In WD, ω-6:ω-3 polyunsaturated fatty acids (PUFAs) ratio is unbalanced towards proinflammatory ω-6. A balanced ω-6:ω-3 PUFAs ratio in WD achieved by docosahexaenoic acid supplementation efficiently restores glucose homeostasis and functional hyperemia in adults.

CONCLUSIONS

WD triggers a rapid impairment in cerebrovascular activity in adolescence, which is maintained at older ages, and can be rescued by a PUFA-based nutraceutical approach.

Neuroregulation during Bone Formation and Regeneration: Mechanisms and Strategies

The skeleton is highly innervated by numerous nerve fibers. These nerve fibers, in addition to transmitting information within the bone and mediating bone sensations, play a crucial role in regulating bone tissue formation and regeneration. Traditional bone tissue engineering (BTE) often fails to achieve satisfactory outcomes when dealing with large-scale bone defects, which is frequently related to the lack of effective reconstruction of the neurovascular network. In recent years, increasing research has revealed the critical role of nerves in bone metabolism. Nerve fibers regulate bone cells through neurotransmitters, neuropeptides, and peripheral glial cells. Furthermore, nerves also coordinate with the vascular and immune systems to jointly construct a microenvironment favorable for bone regeneration. As a signaling driver of bone formation, neuroregulation spans the entire process of bone physiological activities from the embryonic formation to postmaturity remodeling and repair. However, there is currently a lack of comprehensive summaries of these regulatory mechanisms. Therefore, this review sketches out the function of nerves during bone formation and regeneration. Then, we elaborate on the mechanisms of neurovascular coupling and neuromodulation of bone immunity. Finally, we discuss several novel strategies for neuro-bone tissue engineering (NBTE) based on neuroregulation of bone, focusing on the coordinated regeneration of nerve and bone tissue.

Exploring Endothelial Cell Dysfunction's Impact on the Brain-Retina Microenvironment Connection: Molecular Mechanisms and Implications

The intricate linking between the health of blood vessels and the functioning of neurons has attracted growing attention in the context of disorders that affect the neurological environment. Endothelial cells, forming the blood-brain barrier and blood-retinal barrier, play a fundamental role in maintaining the integrity of the brain-retina microenvironment connection. This review explores the molecular foundations of endothelial cell dysfunction and its implications for the brain-retina interaction. A comprehensive analysis of the complex factors contributing to endothelial dysfunction is presented, including oxidative stress, inflammation, reduced nitric oxide signaling, and disrupted vascular autoregulation. The significance of endothelial dysfunction extends to neurovascular coupling, synaptic plasticity, and trophic support. To our knowledge, there is currently no existing literature review addressing endothelial microvascular dysfunction and its interplay with the brain-retina microenvironment. The review also explains bidirectional communication between the brain and retina, highlighting how compromised endothelial function can disrupt this vital crosstalk and inhibit normal physiological processes. As neurodegenerative diseases frequently exhibit vascular involvement, a deeper comprehension of the interaction between endothelial cells and neural tissue holds promise for innovative therapeutic strategies. By targeting endothelial dysfunction, we may enhance our ability to preserve the intricate dynamics of the brain-retina microenvironment connection and ameliorate the progression of neurological disorders.

Advances in the Study of Necroptosis in Vascular Dementia: Focus on Blood-Brain Barrier and Neuroinflammation

BACKGROUND

Vascular dementia (VaD) includes a group of brain disorders that are characterized by cerebrovascular pathology.Neuroinflammation, disruption of the blood-brain barrier (BBB) permeability, white matter lesions, and neuronal loss are all significant pathological manifestations of VaD and play a key role in disease progression. Necroptosis, also known asprogrammed necrosis, is a mode of programmed cell death distinct from apoptosis and is closely associated with ischemic injury and neurodegenerative diseases. Recent studies have shown that necroptosis in VaD exacerbates BBB destruction, activates neuroinflammation, promotes neuronal loss, and severely affects VaD prognosis.

RESULTS AND CONCLUSIONS

In this review, we outline the significant roles of necroptosis and its molecular mechanisms in the pathological process of VaD, with a particular focus on the role of necroptosis in modulating neuroinflammation and exacerbating the disruption of BBB permeability in VaD, and elaborate on the molecular regulatory mechanisms and the centrally involved cells of necroptosis mediated by tumor necrosis factor-α in neuroinflammation in VaD. We also analyze the possibility and specific strategy that targeting necroptosis would help inhibit neuroinflammation and BBB destruction in VaD. With a focus on necroptosis, this study delved into its impact on the pathological changes and prognosis of VaD to provide new treatment ideas.

Simulation of Conducted Responses in Microvascular Networks: Role of Gap Junction Current Rectification

OBJECTIVE

Local control of blood flow depends on signaling to arterioles via upstream conducted responses. Here, the objective is to examine how electrical properties of gap junctions between endothelial cells (EC) affect the spread of conducted responses in microvascular networks of the brain cortex, using a theoretical model based on EC electrophysiology.

METHODS

Modeled EC currents are an inward-rectifying potassium current, a non-voltage-dependent potassium current, a leak current, and a gap junction current between adjacent ECs. Effects of varying gap junction conductance are considered, including asymmetric conductance, with higher conductance for forward currents (positive currents from upstream to downstream, based on blood flow direction). The response is initiated by a local increase in extracellular potassium concentration. The model is applied to a 45-segment synthetic network and a 4881-segment network from mouse brain cortex.

RESULTS

The conducted response propagates preferentially to upstream arterioles when the conductance for forward currents is at least 20 times that for backward currents. The response depends strongly on the site of stimulation. With symmetric gap junction conductance, the network acts as a syncytium and the conducted response is dissipated.

CONCLUSIONS

Upstream propagation of conducted responses may depend on the asymmetric conductance of EC gap junctions.

Cell-specific transcriptional signatures of vascular cells in Alzheimer's disease: perspectives, pathways, and therapeutic directions

Alzheimer's disease (AD) is a debilitating neurodegenerative disease that is marked by profound neurovascular dysfunction and significant cell-specific alterations in the brain vasculature. Recent advances in high throughput single-cell transcriptomics technology have enabled the study of the human brain vasculature at an unprecedented depth. Additionally, the understudied niche of cerebrovascular cells, such as endothelial and mural cells, and their subtypes have been scrutinized for understanding cellular and transcriptional heterogeneity in AD. Here, we provide an overview of rich transcriptional signatures derived from recent single-cell and single-nucleus transcriptomic studies of human brain vascular cells and their implications for targeted therapy for AD. We conducted an in-depth literature search using Medline and Covidence to identify pertinent AD studies that utilized single-cell technologies in human post-mortem brain tissue by focusing on understanding the transcriptional differences in cerebrovascular cell types and subtypes in AD and cognitively normal older adults. We also discuss impaired cellular crosstalk between vascular cells and neuroglial units, as well as astrocytes in AD. Additionally, we contextualize the findings from single-cell studies of distinct endothelial cells, smooth muscle cells, fibroblasts, and pericytes in the human AD brain and highlight pathways for potential therapeutic interventions as a concerted multi-omic effort with spatial transcriptomics technology, neuroimaging, and neuropathology. Overall, we provide a detailed account of the vascular cell-specific transcriptional signatures in AD and their crucial cellular crosstalk with the neuroglial unit.

Microglia modulate the cerebrovascular reactivity through ectonucleotidase CD39

Microglia and the border-associated macrophages contribute to the modulation of cerebral blood flow, but the mechanisms have remained uncertain. Here, we show that microglia regulate the cerebral blood flow baseline and the responses to whisker stimulation or intra-cisternal magna injection of adenosine triphosphate, but not intra-cisternal magna injection of adenosine in mice model. Notably, microglia repopulation corrects these cerebral blood flow anomalies. The microglial-dependent regulation of cerebral blood flow requires the adenosine triphosphate-sensing P2RY12 receptor and ectonucleotidase CD39 that initiates the dephosphorylation of extracellular adenosine triphosphate into adenosine in both male and female mice. Pharmacological inhibition or CX3CR1-CreER-mediated deletion of CD39 mimics the cerebral blood flow anomalies in microglia-deficient mice and reduces the upsurges of extracellular adenosine following whisker stimulation. Together, these results suggest that the microglial CD39-initiated breakdown of extracellular adenosine triphosphate co-transmitter is an important step in neurovascular coupling and the regulation of cerebrovascular reactivity.

The immunology of stroke and dementia

Ischemic stroke and vascular cognitive impairment, caused by a sudden arterial occlusion or more subtle but protracted vascular insufficiency, respectively, are leading causes of morbidity and mortality worldwide with limited therapeutic options. Innate and adaptive immunity have long been implicated in neurovascular injury, but recent advances in methodology and new experimental approaches have shed new light on their contributions. A previously unappreciated dynamic interplay of brain-resident, meningeal, and systemic immune cells with the ischemic brain and its vasculature has emerged, and new insights into the frequent overlap between vascular and Alzheimer pathology have been provided. Here, we critically review these recent findings, place them in the context of current concepts on neurovascular pathologies and Alzheimer's disease, and highlight their impact on recent stroke and Alzheimer therapies.

Temporal dynamics of neurovascular unit changes following blood-brain barrier opening in the putamen of non-human primates

Low-intensity focused ultrasound (LIFU) combined with intravenously circulating microbubbles has recently emerged as a novel approach for increasing delivery through the blood-brain barrier (BBB). This technique safely and transiently enables therapeutic agents to overcome the BBB, which typically poses a significant obstacle for treatment of brain disorders. However, the full impact of LIFU on the entire neurovascular unit (NVU), as well as the mechanisms and factors involved in restoring BBB integrity still require further elucidation. We conducted immunohistochemical analyses of the putamen in non-human primates to monitor changes over time [immediately post-treatment (3 h) and at 7- and 30-days post-BBB opening] in vascular, glial, and immune cells. Additionally, we examined the dynamic interactions among these elements and their role in the restorative process at the BBB level. A mild inflammatory response primarily involving microglia, astrocytes, and T- and B-lymphocytes was observed in the treated putamen acutely after BBB opening. These cells, recruited in response to the vascular changes, stimulate upregulation of PDGFRβ, a pericyte-specific marker, and VEGF-A, a pro-angiogenic factor. This was associated with vascular sprouting by 7 days post-BBB opening. Importantly, no notable long-term alterations were observed in the NVU 30 days post-BBB opening. These results offer further evidence regarding the efficacy and safety of LIFU in achieving BBB opening in the primate brain, indicating that nearly all changes in the NVU revert to baseline within 30 days post-treatment. This also suggests that angiogenesis may play an important role in restoring vascular integrity after BBB opening.

Characterizing astrocyte-mediated neurovascular coupling by combining optogenetics and biophysical modeling

Vasoactive signaling from astrocytes is an important contributor to the neurovascular coupling (NVC), which aims at providing energy to neurons during brain activation by increasing blood perfusion in the surrounding vasculature. Pharmacological manipulations have been previously combined with experimental techniques (e.g., transgenic mice, uncaging, and multiphoton microscopy) and stimulation paradigms to isolate in vivo individual pathways of the astrocyte-mediated NVC. Unfortunately, these pathways are highly nonlinear and non-additive. To separate these pathways in a unified framework, we combine a comprehensive biophysical model of vasoactive signaling from astrocytes with a unique optogenetic stimulation method that selectively induces astrocytic Ca2+ signaling in a large population of astrocytes. We also use a sensitivity analysis and an optimization technique to estimate key model parameters. Optogenetically-induced Ca2+ signals in astrocytes cause a cerebral blood flow (CBF) response with two major components. Component-1 was rapid and smaller (ΔCBF∼13%, 18 seconds), while component-2 was slowest and highest (ΔCBF ∼18%, 45 seconds). The proposed biophysical model was adequate in reproducing component-2, which was validated with a pharmacological manipulation. Model's predictions were not in contradiction with previous studies. Finally, we discussed scenarios accounting for the existence of component-1, which once validated might be included in our model.

A multimodal neuroimaging study of cerebrovascular regulation: protocols and insights of combining electroencephalography, functional near-infrared spectroscopy, transcranial Doppler ultrasound, and physiological parameters

Objective. The current paper describes the creation of a simultaneous trimodal neuroimaging protocol. The authors detail their methodological design for a subsequent large-scale study, demonstrate the ability to obtain the expected physiologically induced responses across cerebrovascular domains, and describe the pitfalls experienced when developing this approach.Approach. Electroencephalography (EEG), functional near-infrared spectroscopy (fNIRS), and transcranial Doppler ultrasound (TCD) were combined to provide an assessment of neuronal activity, microvascular oxygenation, and upstream artery velocity, respectively. Real-time blood pressure, capnography, and heart rate were quantified to control for the known confounding influence of cardiorespiratory variables. The EEG-fNIRS-TCD protocol was attached to a 21 year-old male who completed neurovascular coupling/functional hyperemia (finger tapping and 'Where's Waldo/Wally?'), dynamic cerebral autoregulation (squat-stand maneuvers), and cerebrovascular reactivity tasks (end-tidal clamping during hypocapnia/hypercapnia).Main results. In a pilot participant, the Waldo task produced robust hemodynamic responses within the occipital microvasculature and the posterior cerebral artery. A ∼90% decrease in alpha band power was seen in the occipital cortical region compared between the eyes closed and eyes opened protocol, compared to the frontal, central, and parietal regions (∼80% reduction). A modest increase in motor oxygenated hemoglobin was seen during the finger tapping task, with a harmonious alpha decrease of ∼15% across all cortical regions. No change in the middle or posterior cerebral arteries were noted during finger tapping. During cerebral autoregulatory challenges, sinusoidal oscillations were produced in hemodynamics at 0.05 and 0.10 Hz, while a decrease and increase in TCD and fNIRS metrics were elicited during hypocapnia and hypercapnia protocols, respectively.Significance. All neuroimaging modalities have their inherent limitations; however, these can be minimized by employing multimodal neuroimaging approaches. This EEG-fNIRS-TCD protocol enables a comprehensive assessment of cerebrovascular regulation across the association between electrical activity and cerebral hemodynamics during tasks with a mild degree of body and/or head movement.

The pathobiology of neurovascular aging

As global life expectancy increases, age-related brain diseases such as stroke and dementia have become leading causes of death and disability. The aging of the neurovasculature is a critical determinant of brain aging and disease risk. Neurovascular cells are particularly vulnerable to aging, which induces significant structural and functional changes in arterial, venous, and lymphatic vessels. Consequently, neurovascular aging impairs oxygen and glucose delivery to active brain regions, disrupts endothelial transport mechanisms essential for blood-brain exchange, compromises proteostasis by reducing the clearance of potentially toxic proteins, weakens immune surveillance and privilege, and deprives the brain of key growth factors required for repair and renewal. In this review, we examine the effects of neurovascular aging on brain function and its role in stroke, vascular cognitive impairment, and Alzheimer's disease. Finally, we discuss key unanswered questions that must be addressed to develop neurovascular strategies aimed at promoting healthy brain aging.

Neuroprotective Effects of Eugenol Acetate Against Ischemic Stroke

Objective

To explore the neuroprotective effect of Eugenol Acetate (EA) on post-stroke neuroinflammation and investigate the underlying mechanisms.

Methods

For in vitro experiments, primary microglia were pre-incubated with EA for 2 hours, followed by lipopolysaccharide (LPS) stimulation for 24 hours or Oxygen-Glucose Deprivation (OGD) treatment for 4 hours. Real-time quantitative PCR, enzyme-linked immunosorbent assay (ELISA) and Western blot were performed to examine the expression levels of inflammatory cytokines in primary microglia. The activation of NF-κB signaling pathway was evaluated by immunofluorescence staining and Western blot. For in vivo experiments, middle cerebral artery occlusion (MCAO) was constructed to mimic ischemic brain injury on 8-week-old male C57BL/6J mice. The mice were continuously injected intraperitoneally with EA or vehicle after MCAO. Neurobehavioral tests and TTC staining were conducted to estimate the neurological deficits and infarct area. Moreover, the white matter integrity after MCAO was observed via immunofluorescence staining.

Results

EA significantly reduced the expression of pro-inflammatory cytokines in LPS or OGD treated primary microglia, and inhibited LPS-induced activation of the NF-κB signaling pathway. In addition, EA alleviated ischemic brain injury and improved neuromotor function of MCAO mice. Furthermore, long-term neurological deficits and white matter integrity were improved by EA treatment after MCAO.

Conclusion

EA alleviated ischemic injury and restored white matter integrity in MCAO mice, which might be associated with the inhibition of NF-κB signaling pathway in microglia. Therefore, EA might be a promising candidate for the treatment of ischemic stroke.

Semaglutide restores astrocyte-vascular interactions and blood-brain barrier integrity in a model of diet-induced metabolic syndrome

INTRODUCTION

Metabolic syndrome (MetS) is a metabolic disorder related to obesity and insulin resistance and is the primary determinant of the development of low-intensity chronic inflammation. This continuous inflammatory response culminates in neuroimmune-endocrine dysregulation responsible for the metabolic abnormalities and morbidities observed in individuals with MetS. Events such as the accumulation of visceral adipose tissue, increased plasma concentrations of free fatty acids, tissue hypoxia, and sympathetic hyperactivity in individuals with MetS may contribute to the activation of the innate immune response, which compromises cerebral microcirculation and the neurovascular unit, leading to the onset or progression of neurodegenerative diseases.

OBJECTIVE

This study aimed to evaluate the effects of chronic treatment with a GLP-1 receptor agonist (semaglutide) on cerebral microcirculation and neurovascular unit (NVU) integrity.

METHODS

C57BL/6 mice were fed a standard normolipidic diet or a high-fat diet (HFD) for 24 weeks and then treated for 4 weeks with semaglutide (HFD SEMA) or saline solution (HFD SAL). At the end of pharmacological treatment, biochemical analyses, immunohistochemistry analysis, and intravital microscopy of the brain microcirculation were carried out to quantify leukocyte-endothelium interactions and to assess structural capillary density, astrocyte coverage on cerebral vessels and microglial activation.

RESULTS

We observed that SEMA attenuates high-fat diet-induced metabolic alterations in mice fed with HFD for 24 weeks. SEMA also reversed cerebral microcirculation effects of HFD by reducing capillary rarefaction and the interaction of leukocytes in postcapillary brain venules. The HFD-SEMA group exhibited improved astrocyte coverage on vessels. However, SEMA did not reverse microglial activation.

CONCLUSIONS

Semaglutide can reverse microvascular rarefaction in metabolic syndrome by restoring the integrity of the neurovascular unit. Adverse dietary stimuli can compromise microglial homeostasis that is not reversed by semaglutide.

The role of the neurovascular unit in vascular cognitive impairment: Current evidence and future perspectives

Vascular cognitive impairment (VCI) is a progressive cognitive impairment caused by cerebrovascular disease or vascular risk factors. It is the second most common type of cognitive impairment after Alzheimer's disease. The pathogenesis of VCI is complex, and neurovascular unit destruction is one of its important mechanisms. The neurovascular unit (NVU) is responsible for combining blood flow with brain activity and includes endothelial cells, pericytes, astrocytes and many regulatory nerve terminals. The concept of an NVU emphasizes that interactions between different types of cells are essential for maintaining brain homeostasis. A stable NVU is the basis of normal brain function. Therefore, understanding the structure and function of the neurovascular unit and its role in VCI development is crucial for gaining insights into its pathogenesis. This article reviews the structure and function of the neurovascular unit and its contribution to VCI, providing valuable information for early diagnosis and prevention.