Role In Blood-brain Barrier Integrity Research Articles

Effect of advanced maternal age on ischemic stroke vulnerability in aged rats: Investigating on blood-brain barrier permeability and gene expression

BackgroundAdvanced maternal age (AMA), commonly defined as pregnancy at or above 35 years old. Based on the evidence, this trend has raised concerns about potential health consequences for mothers, particularly in relation to ischemic stroke. Studies suggest that AMA may be associated with a higher risk of ischemic stroke in women due to physiological changes that impact vascular health and increase cardiovascular risk factors. The aim of this study was to investigate the effect of AMA on the extent of damage after ischemic stroke in aged rats. MethodsFemale rats that gave birth at an old age (10 months) and at a young age (4 months) were subjected to ischemic stroke in old age (20 months) and subsequently compared.We assessed neurological deficits, infarct volume, blood–brain barrier (BBB) permeability, TNF-alpha levels, total oxidant capacity, and gene expressions that play a role in BBB integrity (VEGF, Occludin, and MMP-9) following ischemic stroke. ResultsThere were significantly elevated levels of MMP-9 expression and reduced levels of occludin in AMA rats. Additionally, AMA rats had significantly higher levels of TNF-alpha and total oxidant capacity after experiencing an ischemic stroke. AMA rats showed significantly higher brain water content (BBB permeability), infarct volume, and neurological deficits compared to young-aged pregnancies. DiscussionComplex relationship between pregnancy-related physiological changes, aging, vascular gene expression, and inflammatory factors may play a role in the increased vulnerability observed in older pregnant rats. The similarities between pregnancy-related alterations and aging highlight the influence of advanced maternal age on susceptibility to ischemic stroke.

Chloroquine Protects Hypoxia/Ischemia-Induced Neonatal Brain Injury in Rats by Mitigating Blood-Brain Barrier Disruption.

Neonatal hypoxic-ischemic (H/I) brain damage (HIBD) is a devastating condition for which there are presently no effective therapeutic strategies against its severe neurological deficits in neonates and young children. Traditionally, H/I induces the compromise of the blood-brain barrier (BBB), which causes neuronal cell death, eventually resulting in brain secondary injury. In addition to neonatal HIBD, chloroquine (CQ) has been proved to exert a protective effect on BBB disruption in several brain injury models. The main purpose of this research was to study whether CQ protects the BBB from H/I insult and confers beneficial neuroprotection in the neonatal Rice-Vannucci rat model. Herein, we reported that CQ administration significantly reduced brain damage and improved behavioral dysplasia after H/I injury. Moreover, we demonstrated the protective effects of CQ on BBB integrity, evidenced by ameliorating brain edema and Evans blue extravasation, inhibiting the degeneration of the tight junction and adherens junction proteins, and improving pericyte survival in neonatal rats after HIBD. These findings indicated that CQ administration protected the BBB against H/I injury, thereby ameliorating brain damage and promoting neurofunctional recovery. Collectively, our data demonstrated that CQ played a crucial role in BBB integrity after neonatal H/I injury, which sheds light on the development of therapeutic agents to treat HIBD.

The Neuroinflammatory Role of Pericytes in Epilepsy.

Pericytes are a component of the blood–brain barrier (BBB) neurovascular unit, in which they play a crucial role in BBB integrity and are also implicated in neuroinflammation. The association between pericytes, BBB dysfunction, and the pathophysiology of epilepsy has been investigated, and links between epilepsy and pericytes have been identified. Here, we review current knowledge about the role of pericytes in epilepsy. Clinical evidence has shown an accumulation of pericytes with altered morphology in the cerebral vascular territories of patients with intractable epilepsy. In vitro, proinflammatory cytokines, including IL-1β, TNFα, and IL-6, cause morphological changes in human-derived pericytes, where IL-6 leads to cell damage. Experimental studies using epileptic animal models have shown that cerebrovascular pericytes undergo redistribution and remodeling, potentially contributing to BBB permeability. These series of pericyte-related modifications are promoted by proinflammatory cytokines, of which the most pronounced alterations are caused by IL-1β, a cytokine involved in the pathogenesis of epilepsy. Furthermore, the pericyte-glial scarring process in leaky capillaries was detected in the hippocampus during seizure progression. In addition, pericytes respond more sensitively to proinflammatory cytokines than microglia and can also activate microglia. Thus, pericytes may function as sensors of the inflammatory response. Finally, both in vitro and in vivo studies have highlighted the potential of pericytes as a therapeutic target for seizure disorders.

MicroRNA-182 exacerbates blood-brain barrier (BBB) disruption by downregulating the mTOR/FOXO1 pathway in cerebral ischemia.

Cerebral ischemia causes damage to the structure and function of the blood-brain barrier (BBB) and alleviating BBB destruction will be of great significance for the treatment and prognosis of ischemic stroke. Recently, microRNAs have been shown to play a critical role in BBB integrity. However, the potential mechanism by which microRNA-182 (miR-182) affects the BBB in ischemic stroke remains unclear. We demonstrated for the first time that cerebral ischemia leads to a significant progressive increase in miR-182 after pMCAO, and bEnd.3 cells are the primary target cells of miR-182. In miR-182 KD transgenic mice, infarct volume, and BBB permeability were attenuated, and tight junction (TJ) proteins increased. Inhibition of miR-182 with an antagomir reduced OGD-induced apoptosis of bEnd.3 cells and the loss of ZO-1 and Occludin. To further explore the mechanism by which miR-182 regulates BBB integrity, we detected the apoptotic proteins Bcl-2/Bax and demonstrated that mTOR and FOXO1 were the targets of miR-182. Inhibition of mTOR/FOXO1 by rapamycin/AS1842856 decreased the ratio of Bcl-2/Bax and exacerbated TJ protein loss. Taken together, inhibition of miR-182 protects BBB integrity by reducing endothelial cell apoptosis through the mTOR/FOXO1 pathway. Thus, miR-182 may be a potential target for the treatment of BBB disruption during cerebral ischemia.

O-(2-[18F]-Fluoroethyl)-L-Tyrosine (FET) in Neurooncology: A Review of Experimental Results.

In recent years, PET using radiolabelled amino acids has gained considerable interest as an additional tool besides MRI to improve the diagnosis of cerebral gliomas and brain metastases. A very successful tracer in this field is O-(2-[18F]fluoroethyl)-L-tyrosine (FET) which in recent years has replaced short-lived tracers such as [11C]-methyl-L-methionine in many neuro-oncological centers in Western Europe. FET can be produced with high efficiency and distributed in a satellite concept like 2- [18F]fluoro-2-deoxy-D-glucose. Many clinical studies have demonstrated that FET PET provides important diagnostic information regarding the delineation of cerebral gliomas for therapy planning, an improved differentiation of tumor recurrence from treatment-related changes and sensitive treatment monitoring. In parallel, a considerable number of experimental studies have investigated the uptake mechanisms of FET on the cellular level and the behavior of the tracer in various benign lesions in order to clarify the specificity of FET uptake for tumor tissue. Further studies have explored the effects of treatment related tissue alterations on tracer uptake such as surgery, radiation and drug therapy. Finally, the role of blood-brain barrier integrity for FET uptake which presents an important aspect for PET tracers targeting neoplastic lesions in the brain has been investigated in several studies. Based on a literature research regarding experimental FET studies and corresponding clinical applications this article summarizes the knowledge on the uptake behavior of FET, which has been collected in more than 30 experimental studies during the last two decades and discusses the role of these results in the clinical context.

Wip1 regulates blood-brain barrier function and neuro-inflammation induced by lipopolysaccharide via the sonic hedgehog signaling signaling pathway

The blood brain barrier (BBB) is a diffusion barrier that maintains the brain environment. Wip1 is a nuclear phosphatase induced by many factors and involved in various stresses, tumorigenesis, organismal aging, and neurogenesis. Wip1’s role in BBB integrity has not been thoroughly investigated. The purpose of the present study was to investigate the effect and mechanism of Wip1 on lipopolysaccharide (LPS)-induced BBB dysfunction and inflammation in an in vitro BBB model. The in vitro BBB model was established by co-culturing human brain-microvascular endothelial cells and human astrocytes and then exposing them to 1μg/ml LPS for 6, 12, 18, 24, and 48h. Wip1 expression was significantly elevated by LPS treatment. Knockdown of Wip1 aggravated the increased permeability and decreased transepithelial electrical resistance, protein expression of ZO-1, and occludin induced by LPS. Wip1 silencing augmented the elevated inflammatory cytokines TNF-α, IL-1β, IL-12, and IL-6 of the BBB induced by LPS, whereas overexpression of Wip1 showed a contrary effect. Sonic hedgehog signaling (SHH) was activated by Wip1 overexpression and inhibited by Wip1 silencing. Additionally, activating or inhibiting the SHH pathway by purmorphamine or cyclopamine, respectively, abolished the Wip1-induced changes in transepithelial electrical resistance and permeability and inflammatory responses in the LPS-injured BBB model. Our results demonstrate that Wip1 may protect the BBB against LPS-induced integrity disruption and inflammatory response through the SHH signaling pathway.

Transitory loss of glia and the subsequent modulation in inflammatory cytokines/chemokines regulate paracellular claudin-5 expression in endothelial cells.

Signaling mechanisms involved in regulating blood-brain barrier (BBB) integrity during central nervous system (CNS) inflammation remain unclear. We show that an imbalance between pro-/anti-inflammatory cytokines/chemokines alters claudin-5 expression. In vivo, gliotoxin-induced changes in glial populations and an imbalance between pro-/anti-inflammatory cytokine/chemokine expression occurred as BBB integrity was compromised. The balance was restored as BBB integrity was re-established. In vitro, TNF-α, IL-6, and MCP-1 induced paracellular claudin-5 expression loss. TNF-α- and IL-6- effects were mediated through the PI3K pathway and IL-10 attenuated TNF-α's effect. This study shows that pro-/anti-inflammatory modulators play a critical role in BBB integrity during CNS inflammation.

Characterization of HDAC9 isoforms in brain microvessel bEnd.3 cells upon oxygen and glucose deprivation–reperfusion injury

Histone deacetylases (HDACs) and their inhibitors affect the integrity of blood–brain barrier (BBB) which plays an important role in pathological conditions of the central nervous system (CNS). In this study, expression of HDACs was examined in bEnd.3 endothelial cells subjected to oxygen and glucose deprivation (OGD)–reperfusion injury. Expression of histone deacetylase-related protein (HDRP) produced by alternative splicing of HDAC9 was found to increase significantly in bEnd.3 cells upon OGD–reperfusion injury. HDRP was primarily localized in the nucleus. To investigate potential target genes of HDRP, its transcript was depleted by RNA interference and gene expression was determined. We found that FAS and GADD45a gene expression was up-regulated in HDRP-depleted bEnd.3 cells subjected to OGD–reperfusion injury. Interestingly, these genes are known to be involved in apoptosis and permeability of vascular endothelial cells. Our study suggests that HDRP may play a significant role in BBB integrity after CNS damage.

Chronic systemic IL-1β exacerbates central neuroinflammation independently of the blood-brain barrier integrity.

Peripheral circulating cytokines are involved in immune to brain communication and systemic inflammation is considered a risk factor for flaring up the symptoms in most neurodegenerative diseases. We induced both central inflammatory demyelinating lesion, and systemic inflammation with an interleukin-1β expressing adenovector. The peripheral pro-inflammatory stimulus aggravated the ongoing central lesion independently of the blood-brain barrier (BBB) integrity. This model allows studying the role of specific molecules and cells (neutrophils) from the innate immune system, in the relationship between central and peripheral communication, and on relapsing episodes of demyelinating lesions, along with the role of BBB integrity.

α1-Acid glycoprotein induced effects in rat brain microvessel endothelial cells

α1-Acid glycoprotein (AGP) is a positive acute phase protein which is elevated 1–10 times during inflammation. Whereas AGP has been reported to have immunomodulatory properties, other biological functions of this protein such as its effects on the blood–brain barrier (BBB) endothelium are unknown. Tight junction (TJ) proteins (ZO-1 and occludin) are crucial in maintaining BBB integrity and brain homeostasis. As inflammatory cytokines have been shown to alter BBB integrity and TJ protein expression, we hypothesized that AGP changes BBB function by stimulating inflammatory cytokines and/or directly modulating TJ protein expression.We used primary rat brain microvessel endothelial cells (RBMECs) as an in vitro BBB model to study the direct effects of AGP on the brain microvasculature. No change in cytokine levels was detected in supernatant from AGP-treated RBMECs, despite increased mRNA expression by the cells. Paracellular permeability was decreased up to 20%, across RBMEC monolayers following treatment with AGP, suggesting its role in enhancing BBB integrity. RBMECs showed a biphasic response of increased occludin protein expression following AGP treatment while ZO-1 expression changed in a dose- and time-dependent manner. These changes in TJ proteins suggest that AGP induced changes in occludin related to enhanced barrier properties while the change in ZO-1 may play a secondary role in BBB integrity and/or as an intracellular signaling molecule. AGP significantly changed transcription factor activator protein 1 (AP-1) DNA‐binding activity which provides evidence of the potential cell signaling pathways that contribute to the effect of AGP in RBMECs. Together, this supports our hypothesis that AGP has a direct effect in brain microvasculature and may play an important role in altering BBB integrity in inflammatory-related diseases.

The Role of VWF In BBB Permeability Associated with Hypoxia/Reoxygenation

AbstractAbstract 2102Aberrant blood brain barrier (BBB) permeability is a hallmark pathology in many diseases of the central nervous system (CNS) including hypoxia, epilepsy, multiple sclerosis and ischemic stroke. Generalized hypoxia is a pathological condition in which the body as a whole is deprived of adequate oxygen supply. Hypoxia occurs in healthy people when they ascend to high altitudes, where it can cause altitude sickness, often manifested by headache, leading to potentially fatal complications such as high altitude cerebral edema (HACE). Hypoxia followed by reoxygenation (H/R) is also commonly used as a model to investigate pathology associated with ischemia/reperfusion as the latter condition is present in several disease states including stroke. In animal models, H/R has been shown to cause tight junction protein abnormalities, increased BBB paracellular permeability and edema. von Willebrand Factor (VWF) is a glycoprotein that is synthesized exclusively by endothelial cells and megakaryocytes. Endothelial cell-derived VWF is secreted constitutively and stored in Weibel-Palade bodies (WPB) from where it is released by regulated secretion into the plasma and subendothelium in response to endothelial activation. It has been demonstrated in vitro that exposure of cultured endothelial cells to hypoxia results in WPB exocytosis and VWF secretion. While it is known that VWF is expressed abundantly by cerebral endothelial cells, very little is known about the role of VWF in endothelial biology, particularly, in regulation of the BBB under stressful conditions. Several studies have shown that VWF protein is up regulated in plasma of patients with several neurological conditions involving BBB disruption such as stroke, severe head injury, cerebral malaria and cerebral venous sinus thrombosis. As it is known that C57BL/6 (wild-type) mice have increased BBB permeability induced by H/R, we investigated the status of BBB integrity in VWF-deficient mice (also on the C57BL/6 background). For these experiments, we used a mouse model of normobaric hypoxia (24 hours of 6% oxygen) followed by reoxygenation (1 hour ~21% oxygen). VWF antigen levels were measured by ELISA and BBB permeability was assessed by quantification of Evan's blue dye leakage into the brain. Our data indicate that plasma VWF levels in wild-type mice are significantly increased after hypoxia when compared to normoxic controls. Upon comparison with wild-type mice, we have determined that VWF-deficient mice have significantly less BBB permeability after H/R suggesting that VWF plays a role in BBB integrity under stressful conditions. We have previously reported that VWF-deficient mice have a defect in regulated P-selectin secretion (Denis et al., PNAS, 2001). To determine if the maintenance of BBB integrity found in VWF-deficient mice was due to lack of P-selectin we utilized an aptamer which inhibits P-selectin (Archemix). Inhibition of P-selectin in wild-type animals resulted in similar BBB permeability when compared to controls. Our findings suggest a critical role for VWF in BBB permeability after hypoxia/reoxygenation that is independent of P-selectin. Disclosures:No relevant conflicts of interest to declare.