Activation of NMDA receptors in brain endothelial cells increases transcellular permeability

The role of endothelial frequency in the cerebral blood flow control during neonatal asphyxia: a retrospective longitudinal study

BACKGROUND

Cerebral blood flow dynamics can be explored through analysis of endothelial frequencies. Our hypothesis posits a disparity in endothelial activity among neonates with perinatal asphyxia, stratified by the presence or absence of neuronal lesions.

METHODS

We conducted a retrospective longitudinal study involving newborns treated with hypothermia for moderate to severe asphyxia. Participants were grouped based on the presence or absence of neuronal damage to investigate temporal endothelial involvement in cerebral blood flow regulation. Regional cerebral oxygen saturation (rScO2) was measured using near-infrared spectroscopy (NIRS), and temporal series were analyzed in the frequency domain, utilizing the original frequency of the INVOS™ device.

RESULTS

The study included 88 patients, with 53% (47/88) being male and 33% (29/88) demonstrating brain lesions on magnetic resonance imaging. Among them, 86% (76/88) had a gestational age exceeding 37 weeks according to the Ballard scale, and 81% (71/88) had a birth weight exceeding 2500 g. Cohen's d effect size was calculated to assess differences in endothelial frequency between groups, indicating a small effect size based on cerebral MRI findings (Cohen's d values for Day 2 = 0.2351 and Day 3 = 0.2325).

CONCLUSION

NIRS represents a valuable tool for monitoring cerebral autoregulation in neonates affected by perinatal asphyxia, underscoring the utility of assessing endothelial frequency or energy on rScO2 measured by NIRS using the original INVOS™ device frequency.

NMDARs in Alzheimer's Disease: Between Synaptic and Extrasynaptic Membranes

N-methyl-D-aspartate receptors (NMDARs) are glutamate receptors with key roles in synaptic communication and plasticity. The activation of synaptic NMDARs initiates plasticity and stimulates cell survival. In contrast, the activation of extrasynaptic NMDARs can promote cell death underlying a potential mechanism of neurodegeneration occurring in Alzheimer's disease (AD). The distribution of synaptic versus extrasynaptic NMDARs has emerged as an important parameter contributing to neuronal dysfunction in neurodegenerative diseases including AD. Here, we review the concept of extrasynaptic NMDARs, as this population is present in numerous neuronal cell membranes but also in the membranes of various non-neuronal cells. Previous evidence regarding the membranal distribution of synaptic versus extrasynaptic NMDRs in relation to AD mice models and in the brains of AD patients will also be reviewed.

H2S prevents the disruption of the blood-brain barrier in rats with prenatal hyperhomocysteinemia

Elevation of the homocysteine concentration in the plasma called hyperhomocysteinemia (hHCY) during pregnancy causes a number of pre- and postnatal developmental disorders. The aim of our study was to analyze the effects of H2S donors -NaHS and N-acetylcysteine (NAC) on blood-brain barrier (BBB) permeability in rats with prenatal hHCY. In rats with mild hHCY BBB permeability assessed by Evans Blue extravasation in brain increased markedly throughout life. Administration of NaHS or NAC during pregnancy attenuated hHCY-associated damage and increased endogenous concentrations of sulfides in brain tissues. Acute application of dl-homocysteine thiolactone induced BBB leakage, which was prevented by the NMDA receptor antagonist MK-801 or H2S donors. Rats with hHCY demonstrated high levels of NO metabolite - nitrites and proinflammatory cytokines (IL-1β, TNF-α, IL-6) in brain. Lactate dehydrogenase (LDH) activity in the serum was higher in rats with hHCY. Mitochondrial complex-I activity was lower in brain of hHCY rats. NaHS treatment during pregnancy restored levels of proinflammatory cytokines, nitrites and activity of the respiratory chain complex in brain as well as the LDH activity in serum. Our data suggest that H2S has neuroprotective effects against prenatal hHCY-associated BBB disturbance providing a potential strategy for the prevention of developmental impairments in newborns.

Inhibiting Caveolin-1-Related Akt/mTOR Signaling Pathway Protects Against N-methyl-D-Aspartate Receptor Activation-Mediated Dysfunction of Blood-Brain Barrier in vitro

BACKGROUND

The aim of this study was to further explore the role of caveolin-1 (Cav-1) related Akt/mTOR signaling pathway in blood brain barrier (BBB) dysfunction caused by NMDAR activation.

METHODS

The cell localization of NMDAR GluN1 subunit and Cav-1 was observed on human brain microvascular HBEC-5i cells after immunofluorescence double staining. The transendothelial resistance (TEER) of BBB in vitro was measured by Millicell-ERS cell resistance meter. Sodium fluorescein (SF) was used to measure the permeability of BBB in vitro. A stable Cav-1-silenced HBEC-5i cell line was established by infecting the cells with a lentivirus encoding Cav-1 shRNA. The changes of the protein and mRNA of MMP9 and Occludin induced by NMDA were detected by Western blot (WB) and real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), respectively. The phosphorylated proteins of Cav-1, Akt, and mTOR were detected by WB.

RESULTS

NMDAR GluN1 was expressed in the cytoplasm and part of the cell membrane of the HBEC-5i cell line. NMDAR activation decreased TEER and increased the SF of BBB in vitro. HBEC-5i cells incubated with NMDA enhanced the phosphorylation of Cav-1, Akt, and mTOR, also promoting the expression of MMP9 along with the degradation of Occludin. These effects could be reversed by pretreatment with NMDAR antagonist (MK801) or Cav-1 antagonist (Daidzein), or Akt antagonist (LY294002), respectively. Further silencing Cav-1 with LV-Cav-1-RNAi also played a similar protective effect.

CONCLUSION

Caveolin-1 (Cav-1) related Akt/mTOR signaling probably contributes to BBB dysfunction by activating NMDAR on human brain microvascular cells.

Multi-omics Study of Hypoxic-Ischemic Brain Injury After Cardiopulmonary Resuscitation in Swine

BACKGROUND

Hypoxic-ischemic brain injury is a common cause of mortality after cardiac arrest (CA) and cardiopulmonary resuscitation; however, the specific underlying mechanisms are unclear. This study aimed to explore postresuscitation changes based on multi-omics profiling.

METHODS

A CA swine model was established, and the neurological function was assessed at 24 h after resuscitation, followed by euthanizing animals. Their fecal, blood, and hippocampus samples were collected to analyze gut microbiota, metabolomics, and transcriptomics.

RESULTS

The 16S ribosomal DNA sequencing showed that the microbiota composition and diversity changed after resuscitation, in which the abundance of Akkermansia and Muribaculaceae_unclassified increased while the abundance of Bifidobacterium and Romboutsia decreased. A relationship was observed between CA-related microbes and metabolites via integrated analysis of gut microbiota and metabolomics, in which Escherichia-Shigella was positively correlated with glycine. Combined metabolomics and transcriptomics analysis showed that glycine was positively correlated with genes involved in apoptosis, interleukin-17, mitogen-activated protein kinases, nuclear factor kappa B, and Toll-like receptor signal pathways.

CONCLUSIONS

Our results provided novel insight into the mechanism of hypoxic-ischemic brain injury after resuscitation, which is envisaged to help identify potential diagnostic and therapeutic markers.

Brain microvascular endothelial cell metabolism and its ties to barrier function

Brain microvascular endothelial cells, which lie at the interface between blood and brain, are critical to brain energetics. These cells must precisely balance metabolizing nutrients for their own demands with transporting nutrients into the brain to sustain parenchymal cells. It is essential to understand this integrated metabolism and transport so that we can develop better diagnostics and therapeutics for neurodegenerative diseases such as Alzheimer's disease, multiple sclerosis, and traumatic brain injury. In this chapter, we first describe brain microvascular endothelial cell metabolism and how these cells regulate both blood flow and nutrient transport. We then explain the impact of brain microvascular endothelial cell metabolism on the integrity of the blood-brain barrier, as well as how metabolites produced by the endothelial cells impact other brain cells. We detail some ways that cell metabolism is typically measured experimentally and modeled computationally. Finally, we describe changes in brain microvascular endothelial cell metabolism in aging and neurodegenerative diseases. At the end of the chapter, we highlight areas for future research in brain microvascular endothelial cell metabolism. The goal of this chapter is to underscore the importance of nutrient metabolism and transport at the brain endothelium for cerebral health and neurovascular disease treatment.

Hopping the Hurdle: Strategies to Enhance the Molecular Delivery to the Brain through the Blood-Brain Barrier

Modern medicine has allowed for many advances in neurological and neurodegenerative disease (ND). However, the number of patients suffering from brain diseases is ever increasing and the treatment of brain diseases remains an issue, as drug efficacy is dramatically reduced due to the existence of the unique vascular structure, namely the blood-brain barrier (BBB). Several approaches to enhance drug delivery to the brain have been investigated but many have proven to be unsuccessful due to limited transport or damage induced in the BBB. Alternative approaches to enhance molecular delivery to the brain have been revealed in recent studies through the existence of molecular delivery pathways that regulate the passage of peripheral molecules. In this review, we present recent advancements of the basic research for these delivery pathways as well as examples of promising ventures to overcome the molecular hurdles that will enhance therapeutic interventions in the brain and potentially save the lives of millions of patients.

Excitotoxic Storms of Ischemic Stroke: A Non-neuronal Perspective

Numerous neurological disorders share a fatal pathologic process known as glutamate excitotoxicity. Among which, ischemic stroke is the major cause of mortality and disability worldwide. For a long time, the main idea of developing anti-excitotoxic neuroprotective agents was to block glutamate receptors. Despite this, there has been little successful clinical translation to date. After decades of "neuron-centered" views, a growing number of studies have recently revealed the importance of non-neuronal cells. Glial cells, cerebral microvascular endothelial cells, blood cells, and so forth are extensively engaged in glutamate synthesis, release, reuptake, and metabolism. They also express functional glutamate receptors and can listen and respond for fast synaptic transmission. This broadens the thoughts of developing excitotoxicity antagonists. In this review, the critical contribution of non-neuronal cells in glutamate excitotoxicity during ischemic stroke will be emphasized in detail, and the latest research progress as well as corresponding therapeutic strategies will be updated at length, aiming to reconceptualize glutamate excitotoxicity in a non-neuronal perspective.

Anoxia-induced hippocampal LTP is regeneratively produced by glutamate and nitric oxide from the neuro-glial-endothelial axis

Transient anoxia causes amnesia and neuronal death. This is attributed to enhanced glutamate release and modeled as anoxia-induced long-term potentiation (aLTP). aLTP is mediated by glutamate receptors and nitric oxide (·NO) and occludes stimulation-induced LTP. We identified a signaling cascade downstream of ·NO leading to glutamate release and a glutamate-·NO loop regeneratively boosting aLTP. aLTP in entothelial ·NO synthase (eNOS)-knockout mice and blocking neuronal NOS (nNOS) activity suggested that both nNOS and eNOS contribute to aLTP. Immunostaining result showed that eNOS is predominantly expressed in vascular endothelia. Transient anoxia induced a long-lasting Ca2+ elevation in astrocytes that mirrored aLTP. Blocking astrocyte metabolism or depletion of the NMDA receptor ligand D-serine abolished eNOS-dependent aLTP, suggesting that astrocytic Ca2+ elevation stimulates D-serine release from endfeet to endothelia, thereby releasing ·NO synthesized by eNOS. Thus, the neuro-glial-endothelial axis is involved in long-term enhancement of glutamate release after transient anoxia.

Two Signaling Modes Are Better than One: Flux-Independent Signaling by Ionotropic Glutamate Receptors Is Coming of Age

Glutamate is the major excitatory neurotransmitter in the central nervous system. Glutamatergic transmission can be mediated by ionotropic glutamate receptors (iGluRs), which mediate rapid synaptic depolarization that can be associated with Ca2+ entry and activity-dependent change in the strength of synaptic transmission, as well as by metabotropic glutamate receptors (mGluRs), which mediate slower postsynaptic responses through the recruitment of second messenger systems. A wealth of evidence reported over the last three decades has shown that this dogmatic subdivision between iGluRs and mGluRs may not reflect the actual physiological signaling mode of the iGluRs, i.e., α-amino-3-hydroxy-5-methyl-4-isoxasolepropionic acid (AMPA) receptors (AMPAR), kainate receptors (KARs), and N-methyl-D-aspartate (NMDA) receptors (NMDARs). Herein, we review the evidence available supporting the notion that the canonical iGluRs can recruit flux-independent signaling pathways not only in neurons, but also in brain astrocytes and cerebrovascular endothelial cells. Understanding the signaling versatility of iGluRs can exert a profound impact on our understanding of glutamatergic synapses. Furthermore, it may shed light on novel neuroprotective strategies against brain disorders.

NMDA Receptor Antagonist Memantine Ameliorates Experimental Autoimmune Encephalomyelitis in Aged Rats

Aging is closely related to the main aspects of multiple sclerosis (MS). The average age of the MS population is increasing and the number of elderly MS patients is expected to increase. In addition to neurons, N-methyl-D-aspartate receptors (NMDARs) are also expressed on non-neuronal cells, such as immune cells. The aim of this study was to investigate the role of NMDARs in experimental autoimmune encephalomyelitis (EAE) in young and aged rats. Memantine, a non-competitive NMDAR antagonist, was administered to young and aged Dark Agouti rats from day 7 after immunization. Antagonizing NMDARs had a more favourable effect on clinical disease, reactivation, and apoptosis of CD4+ T cells in the target organ of aged EAE rats. The expression of the fractalkine receptor CX3CR1 was increased in memantine-treated rats, but to a greater extent in aged rats. Additionally, memantine increased Nrf2 and Nrf2-regulated enzymes' mRNA expression in brain tissue. The concentrations of superoxide anion radicals, malondialdehyde, and advanced oxidation protein products in brain tissue were consistent with previous results. Overall, our results suggest that NMDARs play a more important role in the pathogenesis of EAE in aged than in young rats.

Anti-NMDAR antibodies, the blood-brain barrier, and anti-NMDAR encephalitis

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is an antibody-related autoimmune encephalitis. It is characterized by the existence of antibodies against NMDAR, mainly against the GluN1 subunit, in cerebrospinal fluid (CSF). Recent research suggests that anti-NMDAR antibodies may reduce NMDAR levels in this disorder, compromising synaptic activity in the hippocampus. Although anti-NMDAR antibodies are used as diagnostic indicators, the origin of antibodies in the central nervous system (CNS) is unclear. The blood-brain barrier (BBB), which separates the brain from the peripheral circulatory system, is crucial for antibodies and immune cells to enter or exit the CNS. The findings of cytokines in this disorder support the involvement of the BBB. Here, we aim to review the function of NMDARs and the relationship between anti-NMDAR antibodies and anti-NMDAR encephalitis. We summarize the present knowledge of the composition of the BBB, especially by emphasizing the role of BBB components. Finally, we further provide a discussion on the impact of BBB dysfunction in anti-NMDAR encephalitis.

The Emerging Role of N-Methyl-D-Aspartate (NMDA) Receptors in the Cardiovascular System: Physiological Implications, Pathological Consequences, and Therapeutic Perspectives

N-methyl-D-aspartate receptors (NMDARs) are ligand-gated ion channels that are activated by the neurotransmitter glutamate, mediate the slow component of excitatory neurotransmission in the central nervous system (CNS), and induce long-term changes in synaptic plasticity. NMDARs are non-selective cation channels that allow the influx of extracellular Na⁺ and Ca²⁺ and control cellular activity via both membrane depolarization and an increase in intracellular Ca²⁺ concentration. The distribution, structure, and role of neuronal NMDARs have been extensively investigated and it is now known that they also regulate crucial functions in the non-neuronal cellular component of the CNS, i.e., astrocytes and cerebrovascular endothelial cells. In addition, NMDARs are expressed in multiple peripheral organs, including heart and systemic and pulmonary circulations. Herein, we survey the most recent information available regarding the distribution and function of NMDARs within the cardiovascular system. We describe the involvement of NMDARs in the modulation of heart rate and cardiac rhythm, in the regulation of arterial blood pressure, in the regulation of cerebral blood flow, and in the blood-brain barrier (BBB) permeability. In parallel, we describe how enhanced NMDAR activity could promote ventricular arrhythmias, heart failure, pulmonary artery hypertension (PAH), and BBB dysfunction. Targeting NMDARs could represent an unexpected pharmacological strategy to reduce the growing burden of several life-threatening cardiovascular disorders.

Blood tissue Plasminogen Activator (tPA) of liver origin contributes to neurovascular coupling involving brain endothelial N-Methyl-D-Aspartate (NMDA) receptors

BACKGROUND

Regulation of cerebral blood flow (CBF) directly influence brain functions and dysfunctions and involves complex mechanisms, including neurovascular coupling (NVC). It was suggested that the serine protease tissue-type plasminogen activator (tPA) could control CNV induced by whisker stimulation in rodents, through its action on N-methyl-D-Aspartate receptors (NMDARs). However, the origin of tPA and the location and mechanism of its action on NMDARs in relation to CNV remained debated.

METHODS

Here, we answered these issues using tPA^Null mice, conditional deletions of either endothelial tPA (VECad-Cre^ΔtPA) or endothelial GluN1 subunit of NMDARs (VECad-Cre^ΔGluN1), parabioses between wild-type and tPA^Null mice, hydrodynamic transfection-induced deletion of liver tPA, hepatectomy and pharmacological approaches.

RESULTS

We thus demonstrate that physiological concentrations of vascular tPA, achieved by the bradykinin type 2 receptors-dependent production and release of tPA from liver endothelial cells, promote NVC, through a mechanism dependent on brain endothelial NMDARs.

CONCLUSIONS

These data highlight a new mechanism of regulation of NVC involving both endothelial tPA and NMDARs.