Neuronal Activity Regulates Blood-Brain Barrier Efflux Transport through Endothelial Circadian Genes

Chronopharmacokinetics of the antidepressant paroxetine: An in vitro and in vivo approach

The circadian rhythm influences homeostatic functions such as sleep, physical activity and food intake as well as pharmacotherapy, namely pharmacokinetics. To investigate the impact of the circadian rhythm on the pharmacokinetics of paroxetine, in vitro synchronized permeability studies were carried out in a tri-culture blood-brain barrier model. Paroxetine demonstrated lower apparent permeability when the cells were incubated at 24 h post-synchronization than at 36 h. Additionally, in vivo chronopharmacokinetic studies were performed in CD-1 female mice administered with paroxetine (5 mg/kg) by intranasal route in the early morning or evening. Paroxetine exposure in the brain was higher when it was administered at the beginning of the active phase (ZT13) compared with the rest phase (ZT1) (p < 0.001), probably owing to the lower levels of P-glycoprotein expressed in the brain at the active phase (p < 0.05). Since melatonin production depends on serotonin, its plasma concentrations were also assessed in vivo. The results demonstrated that melatonin concentrations increased 12 h after paroxetine nasal instillation at ZT13 (p < 0.05), but remained unchanged at ZT1, suggesting that the drug effect is influenced by administration time. In conclusion, the circadian rhythm impacted the pharmacokinetics of paroxetine, especially its distribution into the brain, the target organ. This emphasizes the importance of the time of administration in antidepressant dosing, highlighting its relevance for future studies.

Challenges and material innovations in drug delivery to central nervous system tumors

Central nervous system (CNS) tumors, encompassing a diverse array of neoplasms in the brain and spinal cord, pose significant therapeutic challenges due to their intricate anatomy and the protective presence of the blood-brain barrier (BBB). The primary treatment obstacle is the effective delivery of therapeutics to the tumor site, which is hindered by multiple physiological, biological, and technical barriers, including the BBB. This comprehensive review highlights recent advancements in material science and nanotechnology aimed at surmounting these delivery challenges, with a focus on the development and application of nanomaterials. Nanomaterials emerge as potent tools in designing innovative drug delivery systems that demonstrate the potential to overcome the limitations posed by CNS tumors. The review delves into various strategies, including the use of lipid nanoparticles, polymeric nanoparticles, and inorganic nanoparticles, all of which are engineered to enhance drug stability, BBB penetration, and targeted tumor delivery. Additionally, this review highlights the burgeoning role of theranostic nanoparticles, integrating therapeutic and diagnostic functionalities to optimize treatment efficacy. The exploration extends to biocompatible materials like biodegradable polymers, liposomes, and advanced material-integrated delivery systems such as implantable drug-eluting devices and microfabricated devices. Despite promising preclinical results, the translation of these material-based strategies into clinical practice necessitates further research and optimization.

Nanomedicine for targeting brain Neurodegeneration: Critical barriers and circadian rhythm Considerations

The development of novel therapies for central nervous system (CNS) diseases, particularly neurodegenerative disorders like Alzheimer's disease (AD), is a critical global health priority. Biotherapeutics, such as monoclonal antibodies (mAbs) and RNA-based therapies, have shown potential for treating brain disorders. However, their clinical progress is limited by their difficult access to their brain targets. At the preclinical level, nanotechnology has been shown, to help these molecules overcome the biological barriers that imped their adequate brain delivery. This review highlights advances in this area and the challenges for the translation to the clinic. Key nanotechnology-based strategies, such as surface modifications utilizing endogenous protein corona, functionalization with targeting ligands, therapeutic ultrasound-mediated microbubble oscillation were particularly analyzed. Additionally, in line with the focus of the Special Issue, this review integrates the concept of chronotherapy, with a focus on AD treatment, highlighting the idea that, by aligning nanoparticle (NP)-based drug delivery with circadian rhythms, it may be possible to improve therapeutic outcomes. Finally, the article analyzes current strategies in CNS drug delivery in clinical trials and provides future directions within this frame, notably in the area of AD.

Regulation of blood-brain barrier integrity by brain microvascular endothelial cells in ischemic stroke: A therapeutic opportunity

Stroke is the second leading cause of death from cardiovascular diseases. Brain microvascular endothelial cells (BMECs) are crucial in the treatment of cerebral ischemic stroke, as their functional status directly affects the integrity of the blood-brain barrier (BBB). This review systematically discusses the central role of BMECs in ischemia. The mitochondrial dysfunction and activation of apoptosis/necrosis pathways in BMECs directly disrupt the integrity of the BBB and the degradation of junctional complexes (such as TJs and AJs) further exacerbates its permeability. In the neurovascular unit (NVU), astrocytes, microglia, and pericytes regulate the function of BMECs by secreting cytokines (such as TGF-β and VEGF), showing dual effects of promoting repair and damage. The dynamic changes of transporters, including those from the ATP-binding cassette and solute carrier families, as well as ion channels and exchangers, such as potassium and calcium channels, offer novel insights for the development of targeted drug delivery systems.

Biological Fluid Flows: Signaling Mediums for Circadian Timing

While there is extensive literature on both the neuronal circuitry of rhythms and the intracellular molecular clock, there is a large component of signaling that has been understudied: interstitial fluid (ISF)-fluid that surrounds the cells in the extracellular space of tissue. In this review, we highlight evidence in the circadian literature supporting ISF signaling as key to circadian synchronization and entrainment and propose new mechanisms of how fluid movement between the brain and periphery may act as zeitgebers by examining the main ISF pathways of the body, focusing on circadian regulation of the glymphatic and lymphatic systems. We identify key pieces of circadian research that point to ISF as an important timing medium, expand on the basics of cerebrospinal fluid (CSF) and ISF production, and outline the basic structure and function of the glymphatic and lymphatic systems.

Protocol for isolation of endothelial cells from adult mouse brain

Brain endothelial cells (ECs) line blood vessel walls and form the blood-brain barrier (BBB), facilitating interactions between the brain and the periphery. Here, we present a protocol for isolating purified ECs from adult mouse brains using fluorescence-activated cell sorting (FACS) for downstream analyses, such as RNA sequencing. We describe the steps for brain dissection, enzymatic tissue digestion, trituration, myelin removal, and FACS. Furthermore, we detail adaptations of this protocol for isolating ECs from brain subregions, such as the hippocampus. For complete details on the use and execution of this protocol, please refer to Munji et al.1 and Pulido et al.2.

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.

Interaction of mercury exposure and DNA methylation with sustained attention in children in a novel analysis of epigenetic susceptibility

The etiology of attention-deficit/hyperactivity disorder (ADHD) remains poorly understood, despite it being one of the most common neurodevelopmental disorders worldwide. Past research suggests methylmercury exposure and DNA methylation (DNAm) levels are each associated with ADHD in children, yet whether they interact to affect ADHD is unknown. Leveraging data from a longitudinal cohort of children in Mexico, this novel epigenetic-environment interaction study identified significant interactions between childhood mercury exposure (measured at 6-12 years of age) and adolescent blood leukocyte DNAm in their association with sustained attention [quantified via the Conners continuous performance test, 3rd edition (CPT3)] measured on average 5.6 ± 0.99 years later. Using adjusted linear regression, we assessed associations between hair and urine mercury concentrations and CPT3 scores reflecting inattention, impulsivity, vigilance, and sustained attention (N = 399). We then tested the interaction between mercury and DNAm at loci previously associated with the CPT3 outcomes (N = 374). Significant associations between mercury and CPT3 differed in magnitude and direction depending on the mercury biomarker and CPT3 variable. These associations often differed by gender. For example, urine mercury was positively associated with vigilance scores in males [β = 1.31(SE = 0.65), P = .045] but not in females [β = -0.20 (SE = 0.81), P = .80). In all children, three significant mercury-DNAm interactions were identified for either inattention or vigilance outcomes. Among females, 155 significant interaction terms were identified for the inattention models. In males, three significant interactions were identified for the impulsivity model. Overall, results suggest in some cases DNAm can influence the association between mercury exposure and ADHD-like symptoms.

Sleep Alterations and Cognitive Decline

Sleep disturbances and cognitive decline are intricately connected, and both are prevalent in aging populations and individuals with neurodegenerative disorders such as Alzheimer's disease (AD) and other dementias. Sleep is vital for cognitive functions including memory consolidation, executive function, and attention. Disruption in these processes is associated with cognitive decline, although causal evidence is mixed. This review delves into the bidirectional relationship between alterations in sleep and cognitive impairment, exploring key mechanisms such as amyloid-β accumulation, tau pathology, synaptic homeostasis, neurotransmitter dysregulation, oxidative stress, and vascular contributions. Evidence from both experimental research and population-based studies underscores the necessity of early interventions targeting sleep to mitigate risks of neurodegenerative diseases. A deeper understanding of the interplay between sleep and cognitive health may pave the way for innovative strategies to prevent or reduce cognitive decline through improved sleep management.

Global Clock Coordination by the Brain Clock in the Suprachiasmatic Nucleus Through Relay and Amplification of Diffusible and Neural Signaling

The brain clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus receives direct retinal input, thereby providing the entire body with an internal representation of external solar time. The pathways by which this small nucleus signals so broadly involve co-occurring nervous and diffusible output signals, although the latter are less understood. Portal pathways, such as the well-known pituitary portal pathway, provide a mechanism, whereby signals of neural origin can reach local, specialized targets without suffering dilution in the systemic blood supply. Newly discovered vascular pathways involve direct connections between each of the sensory circumventricular nuclei at its point of attachment to the brain. These nuclei line the brain's ventricles, and their leaky blood vessels and large perivascular spaces represent a route, whereby secretions from the SCN can be relayed and then amplified, providing a pathway to achieve global coordination of circadian clock signaling. This review provides a narrative that incorporates our understanding of SCN neural and diffusible output signals, with particular emphasis on the contribution of brain fluidic compartments and the fluids therein.

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.

Molecular and cellular characteristics of cerebrovascular cell types and their contribution to neurodegenerative diseases

Many diseases and disorders of the nervous system suffer from a lack of adequate therapeutics to halt or slow disease progression, and to this day, no cure exists for any of the fatal neurodegenerative diseases. In part this is due to the incredible diversity of cell types that comprise the brain, knowledge gaps in understanding basic mechanisms of disease, as well as a lack of reliable strategies for delivering new therapeutic modalities to affected areas. With the advent of single cell genomics, it is now possible to interrogate the molecular characteristics of diverse cell populations and their alterations in diseased states. More recently, much attention has been devoted to cell populations that have historically been difficult to profile with bulk single cell technologies. In particular, cell types that comprise the cerebrovasculature have become increasingly better characterized in normal and neurodegenerative disease contexts. In this review, we describe the current understanding of cerebrovasculature structure, function, and cell type diversity and its role in the mechanisms underlying various neurodegenerative diseases. We focus on human and mouse cerebrovasculature studies and discuss both origins and consequences of cerebrovascular dysfunction, emphasizing known cell type-specific vulnerabilities in neuronal and cerebrovascular cell populations. Lastly, we highlight how novel insights into cerebrovascular biology have impacted the development of modern therapeutic approaches and discuss outstanding questions in the field.

Deciphering the Blood-Brain Barrier Paradox in Brain Metastasis Development and Therapy

Gatekeeper or accomplice? That is the paradoxical role of the blood-brain barrier (BBB) in developing brain metastasis (BM). BM occurs when cancerous cells from primary cancer elsewhere in the body gain the ability to metastasize and invade the brain parenchyma despite the formidable defense of the BBB. These metastatic cells manipulate the BBB's components, changing them from gatekeepers of the brain to accomplices that aid in their progression into the brain tissue. This dual role of the BBB-as both a protective system and a potential facilitator of metastatic cells-highlights its complexity. Even with metastasis therapy such as chemotherapy, BM usually recurs due to the BBB limiting the crossing of drugs via the efflux transporters; therefore, treatment efficacy is limited. The pathophysiology is also complex, and our understanding of the paradoxical interplay between the BBB components and metastatic cells still needs to be improved. However, advancements in clinical research are helping to bridge the knowledge gap, which is essential for developing effective metastasis therapy. By targeting the BBB neurovascular unit components such as the polarization of microglia, astrocytes, and pericytes, or by utilizing technological tools like focused ultrasound to transiently disrupt the BBB and therapeutic nanoparticles to improve drug delivery efficiency to BM tissue, we can better address this pathology. This narrative review delves into the latest literature to analyze the paradoxical role of the BBB components in the manifestation of BM and explores potential therapeutic avenues targeting the BBB-tumor cell interaction.

Molecular Rhythmicity in Glia: Importance for Brain Health and Relevance to Psychiatric Disease

Circadian rhythms are approximate 24-hour rhythms present in nearly all aspects of human physiology, including proper brain function. These rhythms are produced at the cellular level through a transcriptional-translational feedback loop known as the molecular clock. Diurnal variation in gene expression has been demonstrated in brain tissue from multiple species, including humans, in both cortical and subcortical regions. Interestingly, these rhythms in gene expression have been shown to be disrupted across psychiatric disorders and may be implicated in their underlying pathophysiology. However, little is known regarding molecular rhythms in specific cell types in the brain and how they might be involved in psychiatric disease. Although glial cells (e.g., astrocytes, microglia, and oligodendrocytes) have been historically understudied compared to neurons, evidence of the molecular clock is found within each of these cell subtypes. Here, we review the current literature, which suggests that molecular rhythmicity is essential to functional physiologic outputs from each glial subtype. Furthermore, disrupted molecular rhythms within these cells and the resultant functional deficits may be relevant to specific phenotypes across psychiatric illnesses. Given that circadian rhythm disruptions have been so integrally tied to psychiatric disease, the molecular mechanisms governing these associations could represent exciting new avenues for future research and potential novel pharmacologic targets for treatment.

Microglia drive diurnal variation in susceptibility to inflammatory blood-brain barrier breakdown

The blood-brain barrier (BBB) is critical for maintaining brain homeostasis but is susceptible to inflammatory dysfunction. While transporter-dependent efflux of some lipophilic substrates across the BBB shows circadian variation due to rhythmic transporter expression, basal transporter-independent permeability and leakage is nonrhythmic. Whether daily timing influences BBB permeability in response to inflammation is unknown. Here, we induced systemic inflammation through repeated LPS injections either in the morning (ZT1) or evening (ZT13) under standard lighting conditions; we then examined BBB permeability to a polar molecule that is not a transporter substrate, sodium fluorescein. We observed clear diurnal variation in inflammatory BBB permeability, with a striking increase in paracellular leak across the BBB specifically following evening LPS injection. Evening LPS led to persisting glia activation as well as inflammation in the brain that was not observed in the periphery. The exaggerated evening neuroinflammation and BBB disruption were suppressed by microglial depletion or through keeping mice in constant darkness. Our data show that diurnal rhythms in microglial inflammatory responses to LPS drive daily variability in BBB breakdown and reveal time of day as a key regulator of inflammatory BBB disruption.

Brain-to-blood transport of fluorescein in vitro

Investigating blood-brain barrier (BBB) dysfunction has become a pre-clinical and clinical research focus as it accompanies many neurological disorders. Nevertheless, knowledge of how diagnostic BBB tracers cross the endothelium from blood-to-brain or vice versa often remains incomplete. In particular, brain-to-blood transport (efflux) may reduce tracer extravasation of intravascularly (i.v.) applied tracers. Conversely, impaired efflux could mimic phenotypic extravasation. Both processes would affect conclusions on BBB properties primarily attributed to blood-to-brain leakage. Here, we specifically investigated efflux of fluorescent BBB tracers, focusing on the most common non-toxic marker, sodium fluorescein, which is applicable in patients. We used acute neocortical slices from mice and applied fluorescein, sulforhodamine-B, rhodamine-123, FITC dextran to the artificial cerebrospinal fluid. Anionic low molecular weight (MW) fluorescein and sulforhodamine-B, but not ~ 10-fold larger FITC-dextran and cationic low MW rhodamine-123, showed efflux into the lumen of blood vessels. Our data suggest that fluorescein efflux depends on organic anion transporter polypeptides (Oatp) rather than P-glycoprotein. Furthermore, sodium-potassium ATPase inhibition and incomplete oxygen-glucose deprivation (OGD, 20% O2) reduced fluorescein efflux, while complete OGD (0% O2) abolished efflux. We provide evidence for active efflux of fluorescein in vitro. Impaired efflux of fluorescein could thus contribute to the frequently observed BBB dysfunction in neuropathologies in addition to blood-to-brain leakage.

miR126-mediated impaired vascular integrity in Rett syndrome

Rett syndrome (RTT) is a neurodevelopmental disorder that is caused by mutations in melty-CpG binding protein 2 (MeCP2). MeCP2 is a non-cell type-specific DNA binding protein, and its mutation influences not only neural cells but also non-neural cells in the brain, including vasculature associated with endothelial cells. Vascular integrity is crucial for maintaining brain homeostasis, and its alteration may be linked to the pathology of neurodegenerative disease, but a non-neurogenic effect, especially the relationship between vascular alternation and Rett syndrome pathogenesis, has not been shown. Here, we recapitulate a microvascular network using Rett syndrome patient-derived induced pluripotent stem (iPS) cells that carry MeCP2[R306C] mutation to investigate early developmental vascular impact. To expedite endothelial cell differentiation, doxycycline (DOX)-inducible ETV2 expression vectors were inserted into the AAVS1 locus of Rett syndrome patient-derived iPS cells and its isogenic control by CRISPR/Cas9. With these endothelial cells, we established a disease microvascular network (Rett-dMVNs) and observed higher permeability in the Rett-dMVNs compared to isogenic controls, indicating altered barrier function by MeCP2 mutation. Furthermore, we unveiled that hyperpermeability is involved in the upregulation of miR126-3p in Rett syndrome patient-derived endothelial cells by microRNA profiling and RNAseq, and rescue of miR126-3p level can recover their phenotype. We discover miR126-3p-mediated vascular impairment in Rett syndrome patients and suggest the potential application of these findings for translational medicine.

Melatonin and brain barriers: The protection conferred by melatonin to the blood-brain barrier and blood-cerebrospinal fluid barrier

The blood-brain barrier and the blood-cerebrospinal fluid barrier separate the blood from brain tissue and cerebrospinal fluid. These brain barriers are important to maintain homeostasis and complex functions by protecting the brain from xenobiotics and harmful endogenous compounds. The disruption of brain barriers is a characteristic of neurologic diseases. Melatonin is a lipophilic hormone that is mainly produced by the pineal gland. The blood-brain barrier and the blood-cerebrospinal fluid barriers are melatonin-binding sites. Among the several melatonin actions, the most characteristic one is the regulation of sleep-wake cycles, melatonin has anti-inflammatory and antioxidant properties. Since brain barriers disruption can arise from inflammation and oxidative stress, knowing the influence of melatonin on the integrity of brain barriers is extremely important. Therefore, the objective of this review is to gather and discuss the available literature about the regulation of brain barriers by melatonin.

Endothelial Myosin IIA Is Required for the Maintenance of Blood-Brain Barrier Integrity

Brain endothelial cells (ECs) are essential elements of the blood-brain barrier (BBB), maintaining its integrity through both paracellular junctions and transcellular transport systems. Myosin IIA, a multifunctional protein, plays a significant role in various cellular processes, including cytoskeletal maintenance, cell division, and signal transduction. While Myosin IIA has been implicated in bleeding and ischemic stroke, its role in regulating BBB integrity under physiological conditions remains unclear. In this study, we investigated the impact of Myosin IIA deficiency on BBB integrity using intravenous tracer injections and models of epilepsy. Flow cytometry, Western blot, and real-time PCR were employed to isolate brain cells and assess changes in protein and mRNA levels. Additionally, immunofluorescence staining and electron microscopy were used to explore alterations in protein expression and the structure of BBB. Our results demonstrate that endothelial Myosin IIA deficiency increased BBB permeability and exacerbated symptoms in BBB-related diseases. Mechanistically, we found that Myosin IIA modulates β-catenin transcription and protein interactions. The overexpression of β-catenin in brain endothelial Myosin IIA deficiency mice improved BBB integrity and reduced disease severity. This study establishes Myosin IIA as a critical regulator of BBB integrity and suggests new therapeutic targets for vascular diseases.

Microglia are not necessary for maintenance of blood-brain barrier properties in health, but PLX5622 alters brain endothelial cholesterol metabolism

Microglia, the resident immune cells of the central nervous system, are intimately involved in the brain's most basic processes, from pruning neural synapses during development to preventing excessive neuronal activity throughout life. Studies have reported both helpful and harmful roles for microglia at the blood-brain barrier (BBB) in the context of disease. However, less is known about microglia-endothelial cell interactions in the healthy brain. To investigate the role of microglia at a healthy BBB, we used the colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 to deplete microglia and analyzed the BBB ultrastructure, permeability, and transcriptome. Interestingly, we found that, despite their direct contact with endothelial cells, microglia are not necessary for the maintenance of BBB structure, function, or gene expression in the healthy brain. However, we found that PLX5622 treatment alters brain endothelial cholesterol metabolism. This effect was independent from microglial depletion, suggesting that PLX5622 has off-target effects on brain vasculature.

Neural Regulation of Vascular Development: Molecular Mechanisms and Interactions

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

Gene therapy for CNS disorders: modalities, delivery and translational challenges

Gene therapy is emerging as a powerful tool to modulate abnormal gene expression, a hallmark of most CNS disorders. The transformative potentials of recently approved gene therapies for the treatment of spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS) and active cerebral adrenoleukodystrophy are encouraging further development of this approach. However, most attempts to translate gene therapy to the clinic have failed to make it to market. There is an urgent need not only to tailor the genes that are targeted to the pathology of interest but to also address delivery challenges and thereby maximize the utility of genetic tools. In this Review, we provide an overview of gene therapy modalities for CNS diseases, emphasizing the interconnectedness of different delivery strategies and routes of administration. Important gaps in understanding that could accelerate the clinical translatability of CNS genetic interventions are addressed, and we present lessons learned from failed clinical trials that may guide the future development of gene therapies for the treatment and management of CNS disorders.

Circadian Regulation of the Lactate Metabolic Kinetics in Mice Using the [1H-13C]-NMR Technique

Lactate is not only the energy substrate of neural cells, but also an important signal molecule in brain. In modern societies, disturbed circadian rhythms pose a global challenge. Therefore, exploring the influence of circadian period on lactate and its metabolic kinetics is essential for the advancement of neuroscientific research. In the present study, the different groups of mice (L: 8:00 a.m.; D: 20:00 p.m.; SD: 20:00 p.m. with 12 h acute sleep deprivation) were infused with [3-13C] lactate through the lateral tail vein for a duration of 2 min. After 30-min lactate metabolism, the animals were euthanized and the tissues of brain and liver were obtained and extracted, and then, the [1H-13C] NMR technology was employed to investigate the kinetic information of lactate metabolism in different brain regions and liver to detect the enrichment of various metabolic kinetic information. Results revealed the fluctuating lactate concentrations in the brain throughout the day, with lower levels during light periods and higher levels during dark periods. Most metabolites displayed strong sensitivity to circadian rhythm, exhibiting significant day-night variations. Conversely, only a few metabolites showed changes after acute sleep deprivation, primarily in the temporal brain region. Interestingly, in contrast to brain lactate metabolism, liver lactate metabolism exhibited a significant increase following acute sleep deprivation. This study explored the kinetics of lactate metabolism, hinted at potential clinical implications for disorders involving circadian rhythm disturbances, and providing a new research basis for clinical exploration of brain and liver lactate metabolism.

Cortical plasticity is associated with blood-brain barrier modulation

Brain microvessels possess the unique properties of a blood-brain barrier (BBB), tightly regulating the passage of molecules from the blood to the brain neuropil and vice versa. In models of brain injury, BBB dysfunction and the associated leakage of serum albumin to the neuropil have been shown to induce pathological plasticity, neuronal hyper-excitability, and seizures. The effect of neuronal activity on BBB function and whether it plays a role in plasticity in the healthy brain remain unclear. Here we show that neuronal activity induces modulation of microvascular permeability in the healthy brain and that it has a role in local network reorganization. Combining simultaneous electrophysiological recording and vascular imaging with transcriptomic analysis in rats, and functional and BBB-mapping MRI in human subjects, we show that prolonged stimulation of the limb induces a focal increase in BBB permeability in the corresponding somatosensory cortex that is associated with long-term synaptic plasticity. We further show that the increased microvascular permeability depends on neuronal activity and involves caveolae-mediated transcytosis and transforming growth factor β signaling. Our results reveal a role of BBB modulation in cortical plasticity in the healthy brain, highlighting the importance of neurovascular interactions for sensory experience and learning.

A circadian clock regulates the blood-brain barrier across phylogeny

As the central regulatory system of an organism, the brain is responsible for overseeing a wide variety of physiological processes essential for an organism's survival. To maintain the environment necessary for neurons to function, the brain requires highly selective uptake and elimination of specific molecules through the blood-brain barrier (BBB). As an organism's activities vary throughout the day, how does the BBB adapt to meet the changing needs of the brain? A mechanism is through temporal regulation of BBB permeability via its circadian clock, which will be the focal point of this chapter. To comprehend the circadian clock's role within the BBB, we will first examine the anatomy of the BBB and the transport mechanisms enabling it to fulfill its role as a restrictive barrier. Next, we will define the circadian clock, and the discussion will encompass an introduction to circadian rhythms, the Transcription-Translation Feedback Loop (TTFL) as the mechanistic basis of circadian timekeeping, and the organization of tissue clocks found in organisms. Then, we will cover the role of the circadian rhythms in regulating the cellular mechanisms and functions of the BBB. We discuss the implications of this regulation in influencing sleep behavior, the progression of neurodegenerative diseases, and finally drug delivery for treatment of neurological diseases.

Improving drug delivery to the brain: the prodrug approach

INTRODUCTION

The prodrug approach has been thought to be a simple solution to improve brain drug delivery for decades. Nevertheless, it still comes as a surprise that there is relatively little success in the field. The best example anti-parkinsonian drug levodopa has been serendipitously discovered to be a transporter-utilizing brain-delivered prodrug rather than a rationally developed one.

AREAS COVERED

The lack of success can mainly be explained by the insufficient understanding of the role of membrane proteins that can facilitate drug delivery at dynamic barriers, such as the blood-brain barrier (BBB), but also by the sparse knowledge of prodrug bioconverting enzymes in the brain. This review summarizes the current status of the prodrug attempts that have been developed in the past to improve brain drug delivery.

EXPERT OPINION

With the expandingly improved analytical and computational technologies, it is anticipated that enhanced brain drug delivery will be eventually achieved for most of the central nervous system (CNS) acting drugs. However, this requires that carrier-mediated (pro)drug delivery methods are implemented in the very early phases of the drug development processes and not as a last step to survive a problematic investigational drug candidate.

Obesity-induced blood-brain barrier dysfunction: phenotypes and mechanisms

Obesity, a burgeoning global health issue, is increasingly recognized for its detrimental effects on the central nervous system, particularly concerning the integrity of the blood-brain barrier (BBB). This manuscript delves into the intricate relationship between obesity and BBB dysfunction, elucidating the underlying phenotypes and molecular mechanisms. We commence with an overview of the BBB's critical role in maintaining cerebral homeostasis and the pathological alterations induced by obesity. By employing a comprehensive literature review, we examine the structural and functional modifications of the BBB in the context of obesity, including increased permeability, altered transport mechanisms, and inflammatory responses. The manuscript highlights how obesity-induced systemic inflammation and metabolic dysregulation contribute to BBB disruption, thereby predisposing individuals to various neurological disorders. We further explore the potential pathways, such as oxidative stress and endothelial cell dysfunction, that mediate these changes. Our discussion culminates in the summary of current findings and the identification of knowledge gaps, paving the way for future research directions. This review underscores the significance of understanding BBB dysfunction in obesity, not only for its implications in neurodegenerative diseases but also for developing targeted therapeutic strategies to mitigate these effects.

Blood-brain barrier biomarkers

The blood-brain barrier (BBB) is a dynamic interface that regulates the exchange of molecules and cells between the brain parenchyma and the peripheral blood. The BBB is mainly composed of endothelial cells, astrocytes and pericytes. The integrity of this structure is essential for maintaining brain and spinal cord homeostasis and protection from injury or disease. However, in various neurological disorders, such as traumatic brain injury, Alzheimer's disease, and multiple sclerosis, the BBB can become compromised thus allowing passage of molecules and cells in and out of the central nervous system parenchyma. These agents, however, can serve as biomarkers of BBB permeability and neuronal damage, and provide valuable information for diagnosis, prognosis and treatment. Herein, we provide an overview of the BBB and changes due to aging, and summarize current knowledge on biomarkers of BBB disruption and neurodegeneration, including permeability, cellular, molecular and imaging biomarkers. We also discuss the challenges and opportunities for developing a biomarker toolkit that can reliably assess the BBB in physiologic and pathophysiologic states.

Microglia drive diurnal variation in susceptibility to inflammatory blood-brain barrier breakdown

The blood-brain barrier (BBB) is critical for maintaining brain homeostasis but is susceptible to inflammatory dysfunction. Permeability of the BBB to lipophilic molecules shows circadian variation due to rhythmic transporter expression, while basal permeability to polar molecules is non-rhythmic. Whether daily timing influences BBB permeability in response to inflammation is unknown. Here, we induced systemic inflammation through repeated lipopolysaccharide (LPS) injections either in the morning (ZT1) or evening (ZT13) under standard lighting conditions, then examined BBB permeability to a polar molecule, sodium fluorescein. We observed clear diurnal variation in inflammatory BBB permeability, with a striking increase in paracellular leak across the BBB specifically following evening LPS injection. Evening LPS led to persisting glia activation and inflammation in the brain that was not observed in the periphery. The exaggerated evening neuroinflammation and BBB disruption were suppressed by microglial depletion or through keeping mice in constant darkness. Our data show that diurnal rhythms in microglial inflammatory responses to LPS drive daily variability in BBB breakdown and reveals time-of-day as a key regulator of inflammatory BBB disruption.

Circadian Rhythms of the Blood-Brain Barrier and Drug Delivery

The blood-brain barrier (BBB) is a critical interface separating the central nervous system from the peripheral circulation, ensuring brain homeostasis and function. Recent research has unveiled a profound connection between the BBB and circadian rhythms, the endogenous oscillations synchronizing biological processes with the 24-hour light-dark cycle. This review explores the significance of circadian rhythms in the context of BBB functions, with an emphasis on substrate passage through the BBB. Our discussion includes efflux transporters and the molecular timing mechanisms that regulate their activities. A significant focus of this review is the potential implications of chronotherapy, leveraging our knowledge of circadian rhythms for improving drug delivery to the brain. Understanding the temporal changes in BBB can lead to optimized timing of drug administration, to enhance therapeutic efficacy for neurological disorders while reducing side effects. By elucidating the interplay between circadian rhythms and drug transport across the BBB, this review offers insights into innovative therapeutic interventions.

Circadian and Diurnal Regulation of Cerebral Blood Flow

Circadian and diurnal variation in cerebral blood flow directly contributes to the diurnal variation in the risk of stroke, either through factors that trigger stroke or due to impaired compensatory mechanisms. Cerebral blood flow results from the integration of systemic hemodynamics, including heart rate, cardiac output, and blood pressure, with cerebrovascular regulatory mechanisms, including cerebrovascular reactivity, autoregulation, and neurovascular coupling. We review the evidence for the circadian and diurnal variation in each of these mechanisms and their integration, from the detailed evidence for mechanisms underlying the nocturnal nadir and morning surge in blood pressure to identifying limited available evidence for circadian and diurnal variation in cerebrovascular compensatory mechanisms. We, thus, identify key systemic hemodynamic factors related to the diurnal variation in the risk of stroke but particularly identify the need for further research focused on cerebrovascular regulatory mechanisms.

Hypertension: Causes and Consequences of Circadian Rhythms in Blood Pressure

Hypertension is extremely common, affecting approximately 1 in every 2 adults globally. Chronic hypertension is the leading modifiable risk factor for cardiovascular disease and premature mortality worldwide. Despite considerable efforts to define mechanisms that underlie hypertension, a potentially major component of the disease, the role of circadian biology has been relatively overlooked in both preclinical models and humans. Although the presence of daily and circadian patterns has been observed from the level of the genome to the whole organism, the functional and structural impact of biological rhythms, including mechanisms such as circadian misalignment, remains relatively poorly defined. Here, we review the impact of daily rhythms and circadian systems in regulating blood pressure and the onset, progression, and consequences of hypertension. There is an emphasis on the impact of circadian biology in relation to vascular disease and end-organ effects that, individually or in combination, contribute to complex phenotypes such as cognitive decline and the loss of cardiac and brain health. Despite effective treatment options for some individuals, control of blood pressure remains inadequate in a substantial portion of the hypertensive population. Greater insight into circadian biology may form a foundation for novel and more widely effective molecular therapies or interventions to help in the prevention, treatment, and management of hypertension and its related pathophysiology.

Circadian Biology and the Neurovascular Unit

Mammalian physiology and cellular function are subject to significant oscillations over the course of every 24-hour day. It is likely that these daily rhythms will affect function as well as mechanisms of disease in the central nervous system. In this review, we attempt to survey and synthesize emerging studies that investigate how circadian biology may influence the neurovascular unit. We examine how circadian clocks may operate in neural, glial, and vascular compartments, review how circadian mechanisms regulate cell-cell signaling, assess interactions with aging and vascular comorbidities, and finally ask whether and how circadian effects and disruptions in rhythms may influence the risk and progression of pathophysiology in cerebrovascular disease. Overcoming identified challenges and leveraging opportunities for future research might support the development of novel circadian-based treatments for stroke.

Circadian Mechanisms in Brain Fluid Biology

The brain is a complex organ, fundamentally changing across the day to perform basic functions like sleep, thought, and regulating whole-body physiology. This requires a complex symphony of nutrients, hormones, ions, neurotransmitters and more to be properly distributed across the brain to maintain homeostasis throughout 24 hours. These solutes are distributed both by the blood and by cerebrospinal fluid. Cerebrospinal fluid contents are distinct from the general circulation because of regulation at brain barriers including the choroid plexus, glymphatic system, and blood-brain barrier. In this review, we discuss the overlapping circadian (≈24-hour) rhythms in brain fluid biology and at the brain barriers. Our goal is for the reader to gain both a fundamental understanding of brain barriers alongside an understanding of the interactions between these fluids and the circadian timing system. Ultimately, this review will provide new insight into how alterations in these finely tuned clocks may lead to pathology.

Neuronal dynamics direct cerebrospinal fluid perfusion and brain clearance

The accumulation of metabolic waste is a leading cause of numerous neurological disorders, yet we still have only limited knowledge of how the brain performs self-cleansing. Here we demonstrate that neural networks synchronize individual action potentials to create large-amplitude, rhythmic and self-perpetuating ionic waves in the interstitial fluid of the brain. These waves are a plausible mechanism to explain the correlated potentiation of the glymphatic flow1,2 through the brain parenchyma. Chemogenetic flattening of these high-energy ionic waves largely impeded cerebrospinal fluid infiltration into and clearance of molecules from the brain parenchyma. Notably, synthesized waves generated through transcranial optogenetic stimulation substantially potentiated cerebrospinal fluid-to-interstitial fluid perfusion. Our study demonstrates that neurons serve as master organizers for brain clearance. This fundamental principle introduces a new theoretical framework for the functioning of macroscopic brain waves.

Impact of Sleep Disorders and Disturbed Sleep on Brain Health: A Scientific Statement From the American Heart Association

Accumulating evidence supports a link between sleep disorders, disturbed sleep, and adverse brain health, ranging from stroke to subclinical cerebrovascular disease to cognitive outcomes, including the development of Alzheimer disease and Alzheimer disease-related dementias. Sleep disorders such as sleep-disordered breathing (eg, obstructive sleep apnea), and other sleep disturbances, as well, some of which are also considered sleep disorders (eg, insomnia, sleep fragmentation, circadian rhythm disorders, and extreme sleep duration), have been associated with adverse brain health. Understanding the causal role of sleep disorders and disturbances in the development of adverse brain health is complicated by the common development of sleep disorders among individuals with neurodegenerative disease. In addition to the role of sleep disorders in stroke and cerebrovascular injury, mechanistic hypotheses linking sleep with brain health and biomarker data (blood-based, cerebrospinal fluid-based, and imaging) suggest direct links to Alzheimer disease-specific pathology. These potential mechanisms and the increasing understanding of the "glymphatic system," and the recognition of the importance of sleep in poststroke recovery, as well, support a biological basis for the indirect (through the worsening of vascular disease) and direct (through specific effects on neuropathology) connections between sleep disorders and brain health. Given promising evidence for the benefits of treatment and prevention, sleep disorders and disturbances represent potential targets for early treatment that may improve brain health more broadly. In this scientific statement, we discuss the evidence supporting an association between sleep disorders and disturbances and poor brain health ranging from stroke to dementia and opportunities for prevention and early treatment.

Audiovisual gamma stimulation for the treatment of neurodegeneration

Alzheimer's disease (AD) is the most common type of neurodegenerative disease and a health challenge with major social and economic consequences. In this review, we discuss the therapeutic potential of gamma stimulation in treating AD and delve into the possible mechanisms responsible for its positive effects. Recent studies reveal that it is feasible and safe to induce 40 Hz brain activity in AD patients through a range of 40 Hz multisensory and noninvasive electrical or magnetic stimulation methods. Although research into the clinical potential of these interventions is still in its nascent stages, these studies suggest that 40 Hz stimulation can yield beneficial effects on brain function, disease pathology, and cognitive function in individuals with AD. Specifically, we discuss studies involving 40 Hz light, auditory, and vibrotactile stimulation, as well as noninvasive techniques such as transcranial alternating current stimulation and transcranial magnetic stimulation. The precise mechanisms underpinning the beneficial effects of gamma stimulation in AD are not yet fully elucidated, but preclinical studies have provided relevant insights. We discuss preclinical evidence related to both neuronal and nonneuronal mechanisms that may be involved, touching upon the relevance of interneurons, neuropeptides, and specific synaptic mechanisms in translating gamma stimulation into widespread neuronal activity within the brain. We also explore the roles of microglia, astrocytes, and the vasculature in mediating the beneficial effects of gamma stimulation on brain function. Lastly, we examine upcoming clinical trials and contemplate the potential future applications of gamma stimulation in the management of neurodegenerative disorders.

Current progress and challenges in the development of brain tissue models: How to grow up the changeable brain in vitro?

In vitro modeling of brain tissue is a promising but not yet resolved problem in modern neurobiology and neuropharmacology. Complexity of the brain structure and diversity of cell-to-cell communication in (patho)physiological conditions make this task almost unachievable. However, establishment of novel in vitro brain models would ultimately lead to better understanding of development-associated or experience-driven brain plasticity, designing efficient approaches to restore aberrant brain functioning. The main goal of this review is to summarize the available data on methodological approaches that are currently in use, and to identify the most prospective trends in development of neurovascular unit, blood-brain barrier, blood-cerebrospinal fluid barrier, and neurogenic niche in vitro models. The manuscript focuses on the regulation of adult neurogenesis, cerebral microcirculation and fluids dynamics that should be reproduced in the in vitro 4D models to mimic brain development and its alterations in brain pathology. We discuss approaches that are critical for studying brain plasticity, deciphering the individual person-specific trajectory of brain development and aging, and testing new drug candidates in the in vitro models.

In Vitro Blood-Brain Barrier Models for Neuroinfectious Diseases: A Narrative Review

The blood-brain barrier (BBB) is a complex, dynamic, and adaptable barrier between the peripheral blood system and the central nervous system. While this barrier protects the brain and spinal cord from inflammation and infection, it prevents most drugs from reaching the brain tissue. With the expanding interest in the pathophysiology of BBB, the development of in vitro BBB models has dramatically evolved. However, due to the lack of a standard model, a range of experimental protocols, BBB-phenotype markers, and permeability flux markers was utilized to construct in vitro BBB models. Several neuroinfectious diseases are associated with BBB dysfunction. To conduct neuroinfectious disease research effectively, there stems a need to design representative in vitro human BBB models that mimic the BBB's functional and molecular properties. The highest necessity is for an in vitro standardised BBB model that accurately represents all the complexities of an intact brain barrier. Thus, this in-depth review aims to describe the optimization and validation parameters for building BBB models and to discuss previous research on neuroinfectious diseases that have utilized in vitro BBB models. The findings in this review may serve as a basis for more efficient optimisation, validation, and maintenance of a structurally- and functionally intact BBB model, particularly for future studies on neuroinfectious diseases.

CNS Drug Delivery in Stroke: Improving Therapeutic Translation From the Bench to the Bedside

Drug development for ischemic stroke is challenging as evidenced by the paucity of therapeutics that have advanced beyond a phase III trial. There are many reasons for this lack of clinical translation including factors related to the experimental design of preclinical studies. Often overlooked in therapeutic development for ischemic stroke is the requirement of effective drug delivery to the brain, which is critical for neuroprotective efficacy of several small and large molecule drugs. Advancing central nervous system drug delivery technologies implies a need for detailed comprehension of the blood-brain barrier (BBB) and neurovascular unit. Such knowledge will permit the innate biology of the BBB/neurovascular unit to be leveraged for improved bench-to-bedside translation of novel stroke therapeutics. In this review, we will highlight key aspects of BBB/neurovascular unit pathophysiology and describe state-of-the-art approaches for optimization of central nervous system drug delivery (ie, passive diffusion, mechanical opening of the BBB, liposomes/nanoparticles, transcytosis, intranasal drug administration). Additionally, we will discuss how endogenous BBB transporters represent the next frontier of drug delivery strategies for stroke. Overall, this review will provide cutting edge perspective on how central nervous system drug delivery must be considered for the advancement of new stroke drugs toward human trials.

Blood-brain barrier dysfunction mediated by the EZH2-Claudin-5 axis drives stress-induced TNF-α infiltration and depression-like behaviors

Growing evidence suggests that neurovascular dysfunction characterized by blood-brain barrier (BBB) breakdown underlies the development of psychiatric disorders, such as major depressive disorder (MDD). Tight junction (TJ) proteins are critical modulators of homeostasis and BBB integrity. TJ protein Claudin-5 is the most dominant BBB component and is downregulated in numerous depression models; however, the underlying mechanisms remain elusive. Here, we demonstrate a molecular basis of BBB breakdown that links stress and depression. We implemented an animal model of depression, chronic unpredictable mild stress (CUMS) in male C57BL/6 mice, and showed that hippocampal BBB breakdown was closely associated with stress vulnerability. Concomitantly, we found that dysregulated Cldn5 level coupled with repression of the histone methylation signature at its promoter contributed to stress-induced BBB dysfunction and depression. Moreover, histone methyltransferase enhancer of zeste homolog 2 (EZH2) knockdown improved Cldn5 expression and alleviated depression-like behaviors by suppressing the tri-methylation of lysine 27 on histone 3 (H3K27me3) in chronically stressed mice. Furthermore, the stress-induced excessive transfer of peripheral cytokine tumor necrosis factor-α (TNF-α) into the hippocampus was prevented by Claudin-5 overexpression and EZH2 knockdown. Interestingly, antidepressant treatment could inhibit H3K27me3 deposition at the Cldn5 promoter, reversing the loss of the encoded protein and BBB damage. Considered together, these findings reveal the importance of the hippocampal EZH2-Claudin-5 axis in regulating neurovascular function and MDD development, providing potential therapeutic targets for this psychiatric illness.

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

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

An arrayed CRISPR knockout screen identifies genetic regulators of GLUT1 expression

Glucose, a primary fuel source under homeostatic conditions, is transported into cells by membrane transporters such as glucose transporter 1 (GLUT1). Due to its essential role in maintaining energy homeostasis, dysregulation of GLUT1 expression and function can adversely affect many physiological processes in the body. This has implications in a wide range of disorders such as Alzheimer's disease (AD) and several types of cancers. However, the regulatory pathways that govern GLUT1 expression, which may be altered in these diseases, are poorly characterized. To gain insight into GLUT1 regulation, we performed an arrayed CRISPR knockout screen using Caco-2 cells as a model cell line. Using an automated high content immunostaining approach to quantify GLUT1 expression, we identified more than 300 genes whose removal led to GLUT1 downregulation. Many of these genes were enriched along signaling pathways associated with G-protein coupled receptors, particularly the rhodopsin-like family. Secondary hit validation confirmed that removal of select genes, or modulation of the activity of a corresponding protein, yielded changes in GLUT1 expression. Overall, this work provides a resource and framework for understanding GLUT1 regulation in health and disease.

The Drosophila blood-brain barrier regulates sleep via Moody G protein-coupled receptor signaling

Sleep is vital for most animals, yet its mechanism and function remain unclear. We found that permeability of the BBB (blood-brain barrier)-the organ required for the maintenance of homeostatic levels of nutrients, ions, and other molecules in the brain-is modulated by sleep deprivation (SD) and can cell-autonomously effect sleep changes. We observed increased BBB permeability in known sleep mutants as well as in acutely sleep-deprived animals. In addition to molecular tracers, SD-induced BBB changes also increased the penetration of drugs used in the treatment of brain pathologies. After chronic/genetic or acute SD, rebound sleep or administration of the sleeping aid gaboxadol normalized BBB permeability, showing that SD effects on the BBB are reversible. Along with BBB permeability, RNA levels of the BBB master regulator moody are modulated by sleep. Conversely, altering BBB permeability alone through glia-specific modulation of moody, gαo, loco, lachesin, or neuroglian-each a well-studied regulator of BBB function-was sufficient to induce robust sleep phenotypes. These studies demonstrate a tight link between BBB permeability and sleep and indicate a unique role for the BBB in the regulation of sleep.

Dynamic rewiring of neurovasculature in health and disease

Brain vasculature is chiefly considered a support network responsible for delivering signaling molecules and nutrients to neural cells. Several central disorders exhibit disruptions in functional and structural plasticity of this network. Considering this vasculature as structurally dynamic, it challenges the field's view and may be important for brain-directed therapeutic strategies.

Development of circadian neurovascular function and its implications

The neurovascular system forms the interface between the tissue of the central nervous system (CNS) and circulating blood. It plays a critical role in regulating movement of ions, small molecules, and cellular regulators into and out of brain tissue and in sustaining brain health. The neurovascular unit (NVU), the cells that form the structural and functional link between cells of the brain and the vasculature, maintains the blood-brain interface (BBI), controls cerebral blood flow, and surveils for injury. The neurovascular system is dynamic; it undergoes tight regulation of biochemical and cellular interactions to balance and support brain function. Development of an intrinsic circadian clock enables the NVU to anticipate rhythmic changes in brain activity and body physiology that occur over the day-night cycle. The development of circadian neurovascular function involves multiple cell types. We address the functional aspects of the circadian clock in the components of the NVU and their effects in regulating neurovascular physiology, including BBI permeability, cerebral blood flow, and inflammation. Disrupting the circadian clock impairs a number of physiological processes associated with the NVU, many of which are correlated with an increased risk of dysfunction and disease. Consequently, understanding the cell biology and physiology of the NVU is critical to diminishing consequences of impaired neurovascular function, including cerebral bleeding and neurodegeneration.

Blood-Brain Barrier Breakdown in Neuroinflammation: Current In Vitro Models

The blood-brain barrier, which is formed by tightly interconnected microvascular endothelial cells, separates the brain from the peripheral circulation. Together with other central nervous system-resident cell types, including pericytes and astrocytes, the blood-brain barrier forms the neurovascular unit. Upon neuroinflammation, this barrier becomes leaky, allowing molecules and cells to enter the brain and to potentially harm the tissue of the central nervous system. Despite the significance of animal models in research, they may not always adequately reflect human pathophysiology. Therefore, human models are needed. This review will provide an overview of the blood-brain barrier in terms of both health and disease. It will describe all key elements of the in vitro models and will explore how different compositions can be utilized to effectively model a variety of neuroinflammatory conditions. Furthermore, it will explore the existing types of models that are used in basic research to study the respective pathologies thus far.

The Role of Biological Rhythms in New Drug Formulations to Cross the Brain Barriers

For brain protection, the blood-brain barrier and blood-cerebrospinal fluid barrier limit the traffic of molecules between blood and brain tissue and between blood and cerebrospinal fluid, respectively. Besides their protective function, brain barriers also limit the passage of therapeutic drugs to the brain, which constitutes a great challenge for the development of therapeutic strategies for brain disorders. This problem has led to the emergence of novel strategies to treat neurological disorders, like the development of nanoformulations to deliver therapeutic agents to the brain. Recently, functional molecular clocks have been identified in the blood-brain barrier and in the blood-cerebrospinal fluid barrier. In fact, circadian rhythms in physiological functions related to drug disposition were also described in brain barriers. This opens the possibility for chronobiological approaches that aim to use time to improve drug efficacy and safety. The conjugation of nanoformulations with chronobiology for neurological disorders is still unexplored. Facing this, here, we reviewed the circadian rhythms in brain barriers, the nanoformulations studied to deliver drugs to the brain, and the nanoformulations with the potential to be conjugated with a chronobiological approach to therapeutic strategies for the brain.

Day-night fluctuations in choroid plexus transcriptomics and cerebrospinal fluid metabolomics

The cerebrospinal fluid (CSF) provides mechanical protection for the brain and serves as a brain dispersion route for nutrients, hormones, and metabolic waste. The CSF secretion rate is elevated in the dark phase in both humans and rats, which could support the CSF flow along the paravascular spaces that may be implicated in waste clearance. The similar diurnal CSF dynamics pattern observed in the day-active human and the nocturnal rat suggests a circadian regulation of this physiological variable, rather than sleep itself. To obtain a catalog of potential molecular drivers that could provide the day-night-associated modulation of the CSF secretion rate, we determined the diurnal fluctuation in the rat choroid plexus transcriptomic profile with RNA-seq and in the CSF metabolomics with ultraperformance liquid chromatography combined with mass spectrometry. We detected significant fluctuation of 19 CSF metabolites and differential expression of 2,778 choroid plexus genes between the light and the dark phase, the latter of which encompassed circadian rhythm-related genes and several choroid plexus transport mechanisms. The fluctuating components were organized with joint pathway analysis, of which several pathways demonstrated diurnal regulation. Our results illustrate substantial transcriptional and metabolic light-dark phase-mediated changes taking place in the rat choroid plexus and its encircling CSF. The combined data provide directions toward future identification of the molecular pathways governing the fluctuation of this physiological process and could potentially be harnessed to modulate the CSF dynamics in pathology.