Circular RNA circPLOD2 regulates pericyte function by targeting the transcription factor KLF4.

Circular RNAs are generated by backsplicing and control cellular signaling and phenotypes. Pericytes stabilize capillary structures and play important roles in the formation and maintenance of blood vessels. Here, we characterize hypoxia-regulated circular RNAs (circRNAs) in human pericytes and show that the circular RNA of procollagen-lysine,2-oxoglutarate 5-dioxygenase-2 (circPLOD2) is induced by hypoxia and regulates pericyte functions. Silencing of circPLOD2 affects pericytes and increases proliferation, migration, and secretion of soluble angiogenic proteins, thereby enhancing endothelial migration and network capability. Transcriptional and epigenomic profiling of circPLOD2-depleted cells reveals widespread changes in gene expression and identifies the transcription factor krüppel-like factor 4 (KLF4) as a key effector of the circPLOD2-mediated changes. KLF4 depletion mimics circPLOD2 silencing, whereas KLF4 overexpression reverses the effects of circPLOD2 depletion on proliferation and endothelial-pericyte interactions. Together, these data reveal an important function of circPLOD2 in controlling pericyte proliferation and capillary formation and show that the circPLOD2-mediated regulation of KLF4 significantly contributes to the transcriptional response to hypoxia.

A Non-Interventional Study of Tiotropium/Olodaterol versus Any Triple Combination Therapy for Chronic Obstructive Pulmonary Disease: The EVELUT® Study Protocol.

Background: The Global Initiative for Chronic Obstructive Lung Disease 2020 report recommends that patients with chronic obstructive pulmonary disease (COPD) suffering from persistent dyspnea, despite long-acting ß2-agonist (LABA)/inhaled corticosteroid (ICS) maintenance therapy, are switched to either a long-acting muscarinic antagonist (LAMA)/LABA combination regimen or LAMA/LABA/ICS triple therapy. However, to date, no studies have investigated the direct switch from LABA/ICS to LAMA/LABA therapy-instead of switching to triple therapy-in a prospective, real-world, non-interventional setting. Methods: EVELUT® (NCT03954132) is an ongoing, prospective, open-label, multicenter, non-interventional study comparing the once-daily fixed-dose combination of tiotropium and olodaterol (tio/olo) versus any triple therapy (LAMA/LABA/ICS) in patients with COPD who are symptomatic despite LABA/ICS maintenance therapy. Patients with acute or frequent COPD exacerbations are excluded from the study. Participants will receive LABA/ICS maintenance treatment until Visit 1, followed by switching of treatment to tio/olo or LAMA/LABA/ICS. The primary endpoints are changes in modified Medical Research Council (mMRC) and COPD Assessment Test (CAT®) scores after approximately 12 weeks of treatment. Secondary endpoints are change in the patients' general condition according to the Physician's Global Evaluation score, the proportion of responders with a change in mMRC score of ≥1 and in CAT® score of ≥2, and patient satisfaction with the inhaler and therapy. The study is expected to enroll approximately 900 patients. Conclusion: EVELUT results are expected to add to the current real-world evidence informing therapeutic decisions for COPD in everyday clinical practice. Trial Registration: The European Union electronic Register of Post-authorisation Studies (EU PAS Register): EUPAS29784; the Federal Institute for Drugs and Medical Devices (BfArM): NIS Study No 7305; Clinicaltrials.gov: NCT03954132.

Long Noncoding RNA TYKRIL Plays a Role in Pulmonary Hypertension via the p53-mediated Regulation of PDGFRß.

Rationale: Long noncoding RNAs (lncRNAs) are emerging as important regulators of diverse biological functions. Their role in pulmonary arterial hypertension (PAH) remains to be explored.Objectives: To elucidate the role of TYKRIL (tyrosine kinase receptor-inducing lncRNA) as a regulator of p53/ PDGFRß (platelet-derived growth factor receptor ß) signaling pathway and to investigate its role in PAH.Methods: Pericytes and pulmonary arterial smooth muscle cells exposed to hypoxia and derived from patients with idiopathic PAH were analyzed with RNA sequencing. TYKRIL knockdown was performed in above-mentioned human primary cells and in precision-cut lung slices derived from patients with PAH.Measurements and Main Results: Using RNA sequencing data, TYKRIL was identified to be consistently upregulated in pericytes and pulmonary arterial smooth muscles cells exposed to hypoxia and derived from patients with idiopathic PAH. TYKRIL knockdown reversed the proproliferative (n = 3) and antiapoptotic (n = 3) phenotype induced under hypoxic and idiopathic PAH conditions. Owing to the poor species conservation of TYKRIL, ex vivo studies were performed in precision-cut lung slices from patients with PAH. Knockdown of TYKRIL in precision-cut lung slices decreased the vascular remodeling (n = 5). The number of proliferating cell nuclear antigen-positive cells in the vessels was decreased and the number of terminal deoxynucleotide transferase-mediated dUTP nick end label-positive cells in the vessels was increased in the LNA (locked nucleic acid)-treated group compared with control. Expression of PDGFRß, a key player in PAH, was found to strongly correlate with TYKRIL expression in the patient samples (n = 12), and TYKRIL knockdown decreased PDGFRß expression (n = 3). From the transcription factor-screening array, it was observed that TYKRIL knockdown increased the p53 activity, a known repressor of PDGFRß. RNA immunoprecipitation using various p53 mutants demonstrated that TYKRIL binds to the N-terminal of p53 (an important region for p300 interaction with p53). The proximity ligation assay revealed that TYKRIL interferes with the p53-p300 interaction (n = 3) and regulates p53 nuclear translocation.Conclusions: TYKRIL plays an important role in PAH by regulating the p53/PDGFRß axis.

Identification and Functional Characterization of Hypoxia-Induced Endoplasmic Reticulum Stress Regulating lncRNA (HypERlnc) in Pericytes.

RATIONALE: Pericytes are essential for vessel maturation and endothelial barrier function. Long noncoding RNAs regulate many cellular functions, but their role in pericyte biology remains unexplored. OBJECTIVE: Here, we investigate the effect of hypoxia-induced endoplasmic reticulum stress regulating long noncoding RNAs (HypERlnc, also known as ENSG00000262454) on pericyte function in vitro and its regulation in human heart failure and idiopathic pulmonary arterial hypertension. METHODS AND RESULTS: RNA sequencing in human primary pericytes identified hypoxia-regulated long noncoding RNAs, including HypERlnc. Silencing of HypERlnc decreased cell viability and proliferation and resulted in pericyte dedifferentiation, which went along with increased endothelial permeability in cocultures consisting of human primary pericyte and human coronary microvascular endothelial cells. Consistently, Cas9-based transcriptional activation of HypERlnc was associated with increased expression of pericyte marker genes. Moreover, HypERlnc knockdown reduced endothelial-pericyte recruitment in Matrigel assays (P<0.05). Mechanistically, transcription factor reporter arrays demonstrated that endoplasmic reticulum stress-related transcription factors were prominently activated by HypERlnc knockdown, which was confirmed via immunoblotting for the endoplasmic reticulum stress markers IRE1α (P<0.001), ATF6 (P<0.01), and soluble BiP (P<0.001). Kyoto encyclopedia of genes and gene ontology pathway analyses of RNA sequencing experiments after HypERlnc knockdown indicate a role in cardiovascular disease states. Indeed, HypERlnc expression was significantly reduced in human cardiac tissue from patients with heart failure (P<0.05; n=19) compared with controls. In addition, HypERlnc expression significantly correlated with pericyte markers in human lungs derived from patients diagnosed with idiopathic pulmonary arterial hypertension and from donor lungs (n=14). CONCLUSIONS: Here, we show that HypERlnc regulates human pericyte function and the endoplasmic reticulum stress response. In addition, RNA sequencing analyses in conjunction with reduced expression of HypERlnc in heart failure and correlation with pericyte markers in idiopathic pulmonary arterial hypertension indicate a role of HypERlnc in human cardiopulmonary disease.

Shear stress-regulated miR-27b controls pericyte recruitment by repressing SEMA6A and SEMA6D.

AIMS: Vessel maturation involves the recruitment of mural cells such as pericytes and smooth muscle cells. Laminar shear stress is a major trigger for vessel maturation, but the molecular mechanisms by which shear stress affects recruitment of pericytes are unclear. MicroRNAs (miRs) are small non-coding RNAs, which post-transcriptionally control gene expression. The aim of the present study was to unveil the mechanism by which shear stress-regulated microRNAs contribute to vessel maturation. METHODS AND RESULTS: Here, we show that laminar shear stress increased miR-27a and miR-27b expression in vitro and in ex vivo in mouse femoral artery explants. Overexpression of miR-27b in endothelial cells increased pericyte adhesion and pericyte recruitment in vitro. In vitro barrier function of endothelial-pericyte co-cultures was augmented by miR-27b overexpression, whereas inhibition of miR-27a/b reduced adhesion and pericyte coverage and decreased barrier functions. In vivo, pharmacological inhibition of miR-27a/b by locked nucleic acid antisense oligonucleotides significantly reduced pericyte coverage and increased water content in the murine uterus. MiR-27b overexpression repressed semaphorins (SEMA), which mediate repulsive signals, and the vessel destabilizing human but not mouse Angiopoietin-2 (Ang-2). Silencing of SEMA6A and SEMA6D rescued the reduced pericyte adhesion by miR-27 inhibition. Furthermore, inhibition of SEMA6D increased barrier function of an endothelial-pericyte co-culture in vitro. CONCLUSION: The present study demonstrates for the first time that shear stress-regulated miR-27b promotes the interaction of endothelial cells with pericytes, partly by repressing SEMA6A and SEMA6D.

JMJD8 Regulates Angiogenic Sprouting and Cellular Metabolism by Interacting With Pyruvate Kinase M2 in Endothelial Cells.

OBJECTIVE: Jumonji C (JmjC) domain-containing proteins modify histone and nonhistone proteins thereby controlling cellular functions. However, the role of JmjC proteins in angiogenesis is largely unknown. Here, we characterize the expression of JmjC domain-containing proteins after inducing endothelial differentiation of murine embryonic stem cells and study the function of JmjC domain-only proteins in endothelial cell (EC) functions. APPROACH AND RESULTS: We identified a large number of JmjC domain-containing proteins regulated by endothelial differentiation of murine embryonic stem cells. Among the family of JmjC domain-only proteins, Jmjd8 was significantly upregulated on endothelial differentiation. Knockdown of Jmjd8 in ECs significantly decreased in vitro network formation and sprouting in the spheroid assay. JMJD8 is exclusively detectable in the cytoplasm, excluding a function as a histone-modifying enzyme. Mass spectrometry analysis revealed JMJD8-interacting proteins with known functions in cellular metabolism like pyruvate kinase M2. Accordingly, knockdown of pyruvate kinase M2 in human umbilical vein ECs decreased endothelial sprouting in the spheroid assay. Knockdown of JMJD8 caused a reduction of EC metabolism as measured by Seahorse Bioscience extracellular flux analysis. Conversely, overexpression of JMJD8 enhanced cellular oxygen consumption rate of ECs, reflecting an increased mitochondrial respiration. CONCLUSIONS: Jmjd8 is upregulated during endothelial differentiation and regulates endothelial sprouting and metabolism by interacting with pyruvate kinase M2.

Mild systemic inflammation and moderate hypoxia transiently alter neuronal excitability in mouse somatosensory cortex.

During the perinatal period, the brain is highly vulnerable to hypoxia and inflammation, which often cause white matter injury and long-term neuronal dysfunction such as motor and cognitive deficits or epileptic seizures. We studied the effects of moderate hypoxia (HYPO), mild systemic inflammation (INFL), or the combination of both (HYPO+INFL) in mouse somatosensory cortex induced during the first postnatal week on network activity and compared it to activity in SHAM control animals. By performing in vitro electrophysiological recordings with multi-electrode arrays from slices prepared directly after injury (P8-10), one week after injury (P13-16), or in young adults (P28-30), we investigated how the neocortical network developed following these insults. No significant difference was observed between the four groups in an extracellular solution close to physiological conditions. In extracellular 8mM potassium solution, slices from the HYPO, INFL, and HYPO+INFL group were more excitable than SHAM at P8-10 and P13-16. In these two age groups, the number and frequency of spontaneous epileptiform events were significantly increased compared to SHAM. The frequency of epileptiform events was significantly reduced by the NMDA antagonist D-APV in HYPO, INFL, and HYPO+INFL, but not in SHAM, indicating a contribution of NMDA receptors to this pathophysiological activity. In addition, the AMPA/kainate receptor antagonist CNQX suppressed the remaining epileptiform activity. Electrical stimulation evoked prominent epileptiform activity in slices from HYPO, INFL and HYPO+INFL animals. Stimulation threshold to elicit epileptiform events was lower in these groups than in SHAM. Evoked events spread over larger areas and lasted longer in treated animals than in SHAM. In addition, the evoked epileptiform activity was reduced in the older (P28-30) group indicating that cortical dysfunction induced by hypoxia and inflammation was transient and compensated during early development.

Traumatic brain injury results in rapid pericyte loss followed by reactive pericytosis in the cerebral cortex.

Accumulating evidence suggests a pivotal role of PDGFRß positive cells, a specific marker for central nervous system (CNS) pericytes, in tissue scarring. Identification of cells that contribute to tissue reorganization in the CNS upon injury is a crucial step to develop novel treatment strategies in regenerative medicine. It has been shown that pericytes contribute to scar formation in the spinal cord. It is further known that ischemia initially triggers pericyte loss in vivo, whilst brain trauma is capable of inducing pericyte detachment from cerebral vessels. These data point towards a significant role of pericytes in CNS injury. The temporal and spatial dynamics of PDGFRß cells and their responses in traumatic brain injury are poorly understood. Here we show that PDGFRß positive cells initially decline in the acute phase following experimental traumatic brain injury. However, PDGFRß positive cells increase significantly in the trauma zone days after brain injury. Using various pericyte markers we identify these cells to be pericytes that are demarcated by reactive gliosis. Our data indicate that brain trauma causes a biphasic response of pericytes in the early phase of brain trauma that may be of relevance for the understanding of pathological cellular responses in traumatic brain injury.

Multifaceted effects of oligodendroglial exosomes on neurons: impact on neuronal firing rate, signal transduction and gene regulation.

Exosomes are small membranous vesicles of endocytic origin that are released by almost every cell type. They exert versatile functions in intercellular communication important for many physiological and pathological processes. Recently, exosomes attracted interest with regard to their role in cell-cell communication in the nervous system. We have shown that exosomes released from oligodendrocytes upon stimulation with the neurotransmitter glutamate are internalized by neurons and enhance the neuronal stress tolerance. Here, we demonstrate that oligodendroglial exosomes also promote neuronal survival during oxygen-glucose deprivation, a model of cerebral ischaemia. We show the transfer from oligodendrocytes to neurons of superoxide dismutase and catalase, enzymes which are known to help cells to resist oxidative stress. Additionally, we identify various effects of oligodendroglial exosomes on neuronal physiology. Electrophysiological analysis using in vitro multi-electrode arrays revealed an increased firing rate of neurons exposed to oligodendroglial exosomes. Moreover, gene expression analysis and phosphorylation arrays uncovered differentially expressed genes and altered signal transduction pathways in neurons after exosome treatment. Our study thus provides new insight into the broad spectrum of action of oligodendroglial exosomes and their effects on neuronal physiology. The exchange of extracellular vesicles between neural cells may exhibit remarkable potential to impact brain performance.

A neurovascular blood-brain barrier in vitro model.

The cerebral microvasculature possesses certain cellular features that constitute the blood-brain barrier (BBB) (Abbott et al., Neurobiol Dis 37:13-25, 2010). This dynamic barrier separates the brain parenchyma from peripheral blood flow and is of tremendous clinical importance: for example, BBB breakdown as in stroke is associated with the development of brain edema (Rosenberg and Yang, Neurosurg Focus 22:E4, 2007), inflammation (Kuhlmann et al., Neurosci Lett 449:168-172, 2009; Coisne and Engelhardt, Antioxid Redox Signal 15:1285-1303, 2011), and increased mortality. In vivo, the BBB consists of brain endothelial cells (BEC) that are embedded within a precisely regulated environment containing astrocytes, pericytes, smooth muscle cells, and glial cells. These cells experience modulation by various pathways of intercellular communication and by pathophysiological processes, e.g., through neurovascular coupling (Attwell et al., Nature 468:232-243, 2010), cortical spreading depression (Gursoy-Ozdemir et al., J Clin Invest 113:1447-1455, 2004), or formation of oxidative stress (Yemisci et al., Nat Med 15:1031-1037, 2009). Hence, this interdependent assembly of cells is referred to as the neurovascular unit (NVU) (Zlokovic, Nat Med 16:1370-1371, 2010; Zlokovic, Neuron 57:178-201, 2008). Experimental approaches to investigate the BBB in vitro are highly desirable to study the cerebral endothelium in health and disease. However, due to the complex interactions taking place within the NVU in vivo, it is difficult to mimic this interplay in vitro.Here, we describe a murine blood-brain barrier coculture model consisting of cortical organotypic slice cultures and brain endothelial cells that includes most of the cellular components of the NVU including neurons, astrocytes, and brain endothelial cells. This model allows the experimental analysis of several crucial BBB parameters such as transendothelial electrical resistance or tight junction protein localization by immunohistochemistry and live cell imaging of reactive oxygen species.

Moderate hypoxia followed by reoxygenation results in blood-brain barrier breakdown via oxidative stress-dependent tight-junction protein disruption.

Re-canalization of cerebral vessels in ischemic stroke is pivotal to rescue dysfunctional brain areas that are exposed to moderate hypoxia within the penumbra from irreversible cell death. Goal of the present study was to evaluate the effect of moderate hypoxia followed by reoxygenation (MHR) on the evolution of reactive oxygen species (ROS) and blood-brain barrier (BBB) integrity in brain endothelial cells (BEC). BBB integrity was assessed in BEC in vitro and in microvessels of the guinea pig whole brain in situ preparation. Probes were exposed to MHR (2 hours 67-70 mmHg O2, 3 hours reoxygenation, BEC) or towards occlusion of the arteria cerebri media (MCAO) with or without subsequent reperfusion in the whole brain preparation. In vitro BBB integrity was evaluated using trans-endothelial electrical resistance (TEER) and transwell permeability assays. ROS in BEC were evaluated using 2',7'-dichlorodihydrofluorescein diacetate (DCF), MitoSox and immunostaining for nitrotyrosine. Tight-junction protein (TJ) integrity in BEC, stainings for nitrotyrosine and FITC-albumin extravasation in the guinea pig brain preparation were assessed by confocal microscopy. Diphenyleneiodonium (DPI) was used to investigate NADPH oxidase dependent ROS evolution and its effect on BBB parameters in BEC. MHR impaired TJ proteins zonula occludens 1 (ZO-1) and claudin 5 (Cl5), decreased TEER, and significantly increased cytosolic ROS in BEC. These events were blocked by the NADPH oxidase inhibitor DPI. MCAO with or without subsequent reoxygenation resulted in extravasation of FITC-albumin and ROS generation in the penumbra region of the guinea pig brain preparation and confirmed BBB damage. BEC integrity may be impaired through ROS in MHR on the level of TJ and the BBB is also functionally impaired in moderate hypoxic conditions followed by reperfusion in a complex guinea pig brain preparation. These findings suggest that the BBB is susceptible towards MHR and that ROS play a key role in this process.

Developmental switch in neurovascular coupling in the immature rodent barrel cortex.

Neurovascular coupling (NVC) in the adult central nervous system (CNS) is a mechanism that provides regions of the brain with more oxygen and glucose upon increased levels of neural activation. Hemodynamic changes that go along with neural activation evoke a blood oxygen level-dependent (BOLD) signal in functional magnetic resonance imaging (fMRI) that can be used to study brain activity non-invasively. A correct correlation of the BOLD signal to neural activity is pivotal to understand this signal in neuronal development, health and disease. However, the function of NVC during development is largely unknown. The rodent whisker-to-barrel cortex is an experimentally well established model to study neurovascular interdependences. Using extracellular multi-electrode recordings and laser-Doppler-flowmetry (LDF) we show in the murine barrel cortex of postnatal day 7 (P7) and P30 mice in vivo that NVC undergoes a physiological shift during the first month of life. In the mature CNS it is well accepted that cortical sensory processing results in a rise in regional cerebral blood flow (rCBF). We show in P7 animals that rCBF decreases during prolonged multi-whisker stimulation and goes along with multi unit activity (MUA) fatigue. In contrast at P30, MUA remains stable during repetitive stimulation and is associated with an increase in rCBF. Further we characterize in both age groups the responses in NVC to single sensory stimuli. We suggest that the observed shift in NVC is an important process in cortical development that may be of high relevance for the correct interpretation of brain activity e.g. in fMRI studies of the immature central nervous system (CNS).

A novel in vitro model to study pericytes in the neurovascular unit of the developing cortex.

Cortical function is impaired in various disorders of the central nervous system including Alzheimer's disease, autism and schizophrenia. Some of these disorders are speculated to be associated with insults in early brain development. Pericytes have been shown to regulate neurovascular integrity in development, health and disease. Hence, precisely controlled mechanisms must have evolved in evolution to operate pericyte proliferation, repair and cell fate within the neurovascular unit (NVU). It is well established that pericyte deficiency leads to NVU injury resulting in cognitive decline and neuroinflammation in cortical layers. However, little is known about the role of pericytes in pathophysiological processes of the developing cortex. Here we introduce an in vitro model that enables to precisely study pericytes in the immature cortex and show that moderate inflammation and hypoxia result in caspase-3 mediated pericyte loss. Using heterozygous EYFP-NG2 mouse mutants we performed live imaging of pericytes for several days in vitro. In addition we show that pericytes maintain their capacity to proliferate which may allow cell-based therapies like reprogramming of pericytes into induced neuronal cells in the presented approach.

A simple and novel method to monitor breathing and heart rate in awake and urethane-anesthetized newborn rodents.

Rodents are most useful models to study physiological and pathophysiological processes in early development, because they are born in a relatively immature state. However, only few techniques are available to monitor non-invasively heart frequency and respiratory rate in neonatal rodents without restraining or hindering access to the animal. Here we describe experimental procedures that allow monitoring of heart frequency by electrocardiography (ECG) and breathing rate with a piezoelectric transducer (PZT) element without hindering access to the animal. These techniques can be easily installed and are used in the present study in unrestrained awake and anesthetized neonatal C57/Bl6 mice and Wistar rats between postnatal day 0 and 7. In line with previous reports from awake rodents we demonstrate that heart rate in rats and mice increases during the first postnatal week. Respiratory frequency did not differ between both species, but heart rate was significantly higher in mice than in rats. Further our data indicate that urethane, an agent that is widely used for anesthesia, induces a hypoventilation in neonates whilst heart rate remains unaffected at a dose of 1 g per kg body weight. Of note, hypoventilation induced by urethane was not detected in rats at postnatal 0/1. To verify the detected hypoventilation we performed blood gas analyses. We detected a respiratory acidosis reflected by a lower pH and elevated level in CO2 tension (pCO2) in both species upon urethane treatment. Furthermore we found that metabolism of urethane is different in P0/1 mice and rats and between P0/1 and P6/7 in both species. Our findings underline the usefulness of monitoring basic cardio-respiratory parameters in neonates during anesthesia. In addition our study gives information on developmental changes in heart and breathing frequency in newborn mice and rats and the effects of urethane in both species during the first postnatal week.

Volatile anesthetics influence blood-brain barrier integrity by modulation of tight junction protein expression in traumatic brain injury.

Disruption of the blood-brain barrier (BBB) results in cerebral edema formation, which is a major cause for high mortality after traumatic brain injury (TBI). As anesthetic care is mandatory in patients suffering from severe TBI it may be important to elucidate the effect of different anesthetics on cerebral edema formation. Tight junction proteins (TJ) such as zonula occludens-1 (ZO-1) and claudin-5 (cl5) play a central role for BBB stability. First, the influence of the volatile anesthetics sevoflurane and isoflurane on in-vitro BBB integrity was investigated by quantification of the electrical resistance (TEER) in murine brain endothelial monolayers and neurovascular co-cultures of the BBB. Secondly brain edema and TJ expression of ZO-1 and cl5 were measured in-vivo after exposure towards volatile anesthetics in native mice and after controlled cortical impact (CCI). In in-vitro endothelial monocultures, both anesthetics significantly reduced TEER within 24 hours after exposure. In BBB co-cultures mimicking the neurovascular unit (NVU) volatile anesthetics had no impact on TEER. In healthy mice, anesthesia did not influence brain water content and TJ expression, while 24 hours after CCI brain water content increased significantly stronger with isoflurane compared to sevoflurane. In line with the brain edema data, ZO-1 expression was significantly higher in sevoflurane compared to isoflurane exposed CCI animals. Immunohistochemical analyses revealed disruption of ZO-1 at the cerebrovascular level, while cl5 was less affected in the pericontusional area. The study demonstrates that anesthetics influence brain edema formation after experimental TBI. This effect may be attributed to modulation of BBB permeability by differential TJ protein expression. Therefore, selection of anesthetics may influence the barrier function and introduce a strong bias in experimental research on pathophysiology of BBB dysfunction. Future research is required to investigate adverse or beneficial effects of volatile anesthetics on patients at risk for cerebral edema.

Caspase-3 contributes to ZO-1 and Cl-5 tight-junction disruption in rapid anoxic neurovascular unit damage.

BACKGROUND: Tight-junction (TJ) protein degradation is a decisive step in hypoxic blood-brain barrier (BBB) breakdown in stroke. In this study we elucidated the impact of acute cerebral ischemia on TJ protein arrangement and the role of the apoptotic effector protease caspase-3 in this context. METHODOLOGY/PRINCIPAL FINDINGS: We used an in vitro model of the neurovascular unit and the guinea pig whole brain preparation to analyze with immunohistochemical methods the BBB properties and neurovascular integrity. In both methodological approaches we observed rapid TJ protein disruptions after 30 min of oxygen and glucose deprivation or middle cerebral artery occlusion, which were accompanied by strong caspase-3 activation in brain endothelial cells (BEC). Surprisingly only few DNA-fragmentations were detected with TUNEL stainings in BEC. Z-DEVD-fmk, an irreversible caspase-3 inhibitor, partly blocked TJ disruptions and was protective on trans-endothelial electrical resistance. CONCLUSIONS/SIGNIFICANCE: Our data provide evidence that caspase-3 is rapidly activated during acute cerebral ischemia predominantly without triggering DNA-fragmentation in BEC. Further we detected fast TJ protein disruptions which could be partly blocked by caspase-3 inhibition with Z-DEVD-fmk. We suggest that the basis for clinically relevant BBB breakdown in form of TJ disruptions is initiated within minutes during ischemia and that caspase-3 contributes to this process.

Fine-tuning DNA/albumin polyelectrolyte interactions to produce the efficient transfection agent cBSA-147.

We present the preparation and isolation of different chemically modified BSA species with varying numbers of primary amino groups at the surface. Highly cationic albumin proteins with increased numbers of amino groups were achieved and complex formation with plasmid DNA was carefully investigated. We compare the transfection results, polyelectrolyte complexes morphologies with their impact on complex stabilities, cytotoxicities and DNA accessibility. This knowledge-driven approach led to the identification of the efficient non-viral DNA delivery agent cBSA-147, which showed high transfection efficacies and stability.

Oxidative stress upregulates the NMDA receptor on cerebrovascular endothelium.

N-methyl-d-aspartate receptor (NMDA-R)-mediated oxidative stress has been implicated in blood-brain barrier (BBB) disruption in a variety of neuropathological diseases. Although some interactions between both phenomena have been elucidated, possible influences of reactive oxygen species (ROS) on the NMDA-R itself have so far been neglected. The objective of this study was to examine how the cerebroendothelial NMDA-R is affected by exposure to oxidative stress and to assess possible influences on BBB integrity. RT-PCR confirmed several NMDA-R subunits (NR1, NR2B-D) expressed in the bEnd3 cell line (murine cerebrovascular endothelial cells). NR1 protein expression after exposure to ROS was observed via in-cell Western. The functionality of the expressed NMDA-R was determined by measuring DiBAC fluorescence in ROS-preexposed cells upon stimulation with the specific agonist NMDA. Finally, the effects on barrier integrity were evaluated using the ECIS system to detect changes in monolayer impedance upon NMDA-R stimulation after exposure to ROS. The expression of NR1 significantly (p<0.001) increased 72 h after 30 min exposure to superoxide (+33.8+/-7.5%), peroxynitrite (+84.9+/-10.7%), or hydrogen peroxide (+92.8+/-7.6%), resulting in increased cellular response to NMDA-R stimulation and diminished monolayer impedance. We conclude that oxidative stress upregulates NMDA-R on cerebrovascular endothelium and thus heightens susceptibility to glutamate-induced BBB disruption.

Studying the neurovascular unit: an improved blood-brain barrier model.

The blood-brain barrier (BBB) closely interacts with the neuronal parenchyma in vivo. To replicate this interdependence in vitro, we established a murine coculture model composed of brain endothelial cell (BEC) monolayers with cortical organotypic slice cultures. The morphology of cell types, expression of tight junctions, formation of reactive oxygen species, caspase-3 activity in BECs, and alterations of electrical resistance under physiologic and pathophysiological conditions were investigated. This new BBB model allows the application of techniques such as laser scanning confocal microscopy, immunohistochemistry, fluorescent live cell imaging, and electrical cell substrate impedance sensing in real time for studying the dynamics of BBB function under defined conditions.

MK801 blocks hypoxic blood-brain-barrier disruption and leukocyte adhesion.

The aim of the present study was to examine the signaling pathways of hypoxia followed by reoxygenation (H/R)-induced disruption of the blood-brain-barrier (BBB) in a co-culture of astrocytes and brain endothelial cells (BEC) in vitro. We analyzed the possible stabilizing effect of MK801, a highly selective N-methyl-d-aspartate receptor (NMDAR) antagonist, on BBB integrity. Levels of reactive oxygen species (ROS), glutamate (Glut) release and monocyte adhesion were measured under normoxia and H/R. BBB integrity was monitored measuring the trans-endothelial electrical resistance (TEER). TEER values dropped under H/R conditions which was abolished by MK801. Glut release from astrocytes, but not from endothelial cells was significantly increased under H/R, as were ROS levels and monocyte adhesion. The oxidative stress was blocked by MK801 and the NAD(P)H-oxidase inhibitor apocynin. We observed that calcium (Ca(2+)) signaling plays a crucial role during ROS generation and monocyte adhesion under H/R. ROS levels were decreased by applying ryanodine, a blocker of Ca(2+) release from the endoplasmic reticulum (ER) and by lowering the extracellular Ca(2+) concentration. Xestospongin C, which blocks IP(3) mediated Ca(2+) release from the ER did not alter ROS production under H/R conditions. These findings indicate that both extracellular Ca(2+) influx and ryanodine-mediated intracellular Ca(2+) release from the ER during H/R contribute to ROS formation at the BBB. Blocking ROS or Ca(2+) signaling prevented H/R-induced monocyte adhesion to BEC. We conclude, that the activation of NMDAR under H/R by Glut increases intracellular Ca(2+) levels, contributes to BBB disruption, ROS generation and monocyte adhesion.