Characterization of Blood-Brain Barrier Opening Induced by Transcranial Histotripsy in Murine Brains

OBJECTIVE

Transcranial histotripsy has shown promise as a non-invasive neurosurgical tool, as it has the ability to treat a wide range of locations in the brain without overheating the skull. One important effect of histotripsy in the brain is the blood-brain barrier (BBB) opening (BBBO) at the ablation site, but there is a knowledge gap concerning the extent of histotripsy-induced BBBO. Here we describe induction of BBBO by transcranial histotripsy and use of magnetic resonance imaging (MRI) and histology to quantify changes in BBBO at the periphery of the histotripsy ablation zone over time in the healthy mouse brain.

METHODS

An eight-element, 1 MHz histotripsy transducer with a focal distance of 32.5 mm was used to treat the brains of 23 healthy female BL6 mice. T1-gadolinium (T1-Gd) MR images were acquired immediately following histotripsy treatment and during each of the subsequent 4 wk to quantify the size and intensity of BBB leakage.

RESULTS

The T1-Gd MRI results revealed that the hyperintense BBBO volume increased over the first week and subsided gradually over the following 3 wk. Histology revealed complete loss of tight junction proteins and blood vessels in the center of the ablation region immediately after histotripsy, partial recovery in the periphery of the ablation zone 1 wk following histotripsy and near-complete recovery of tight junction complex after 4 wk.

CONCLUSION

These results provide the first evidence of transcranial histotripsy-induced BBBO and repair at the periphery of the ablation zone.

20 kDa isoform of connexin-43 augments spatial reorganization of the brain endothelial junctional complex and lesion leakage in cerebral cavernous malformation type-3

Cerebral cavernous malformation type-3 (CCM3) is a type of brain vascular malformation caused by mutations in programmed cell death protein-10 (PDCD10). It is characterized by early life occurrence of hemorrhagic stroke and profound blood-brain barrier defects. The pathogenic mechanisms responsible for microvascular hyperpermeability and lesion progression in CCM3 are still largely unknown. The current study examined brain endothelial barrier structural defects formed in the absence of CCM3 in vivo and in vitro that may lead to CCM3 lesion leakage. We found significant upregulation of a 20 kDa isoform of connexin 43 (GJA1-20 k) in brain endothelial cells (BEC) in both non-leaky and leaky lesions, as well as in an in vitro CCM3 knockdown model (CCM3KD-BEC). Morphological, biochemical, FRET, and FRAP analyses of CCM3KD-BEC found GJA1-20 k regulates full-length GJA1 biogenesis, prompting uncontrolled gap junction growth. Furthermore, by binding to a tight junction scaffolding protein, ZO-1, GJA1-20 k interferes with Cx43/ZO-1 interactions and gap junction/tight junction crosstalk, promoting ZO-1 dissociation from tight junction complexes and diminishing claudin-5/ZO-1 interaction. As a consequence, the tight junction complex is destabilized, allowing "replacement" of tight junctions with gap junctions leading to increased brain endothelial barrier permeability. Modifying cellular levels of GJA1-20 k rescued brain endothelial barrier integrity re-establishing the spatial organization of gap and tight junctional complexes. This study highlights generation of potential defects at the CCM3-affected brain endothelial barrier which may underlie prolonged vascular leakiness.

A tissue chip with integrated digital immunosensors: In situ brain endothelial barrier cytokine secretion monitoring

Organ-on-a-chip platforms have potential to offer more cost-effective, ethical, and human-resembling models than animal models for disease study and drug discovery. Particularly, the Blood-Brain-Barrier-on-a-chip (BBB-oC) has emerged as a promising tool to investigate several neurological disorders since it promises to provide a model of the multifunctional tissue working as an important node to control pathogen entry, drug delivery and neuroinflammation. A comprehensive understanding of the multiple physiological functions of the tissue model requires biosensors detecting several tissue-secreted substances in a BBB-oC system. However, current sensor-integrated BBB-oC platforms are only available for tissue membrane integrity characterization based on permeability measurement. Protein secretory pathways are closely associated with the tissue's various diseased conditions. At present, no biosensor-integrated BBB-oC platform exists that permits in situ tissue protein secretion analysis over time, which prohibits researchers from fully understanding the time-evolving pathology of a tissue barrier. Herein, the authors present a platform named "Digital Tissue-BArrier-CytoKine-counting-on-a-chip (DigiTACK)," which integrates digital immunosensors into a tissue chip system and demonstrates on-chip multiplexed, ultrasensitive, longitudinal cytokine secretion profiling of cultured brain endothelial barrier tissues. The integrated digital sensors utilize a novel beadless microwell format to perform an ultrafast "digital fingerprinting" of the analytes while achieving a low limit of detection (LoD) around 100-500 fg/mL for mouse MCP1 (CCL2), IL-6 and KC (CXCL1). The DigiTACK platform is extensively applicable to profile temporal cytokine secretion of other barrier-related organ-on-a-chip systems and can provide new insight into the secretory dynamics of the BBB by sequentially controlled experiments.

Blood-Brain Barrier Dysfunction in Normal Aging and Neurodegeneration: Mechanisms, Impact, and Treatments

Cerebral endothelial cells and their linking tight junctions form a unique, dynamic and multi-functional interface, the blood-brain barrier (BBB). The endothelium is regulated by perivascular cells and components forming the neurovascular unit. This review examines BBB and neurovascular unit changes in normal aging and in neurodegenerative disorders, particularly focusing on Alzheimer disease, cerebral amyloid angiopathy and vascular dementia. Increasing evidence indicates BBB dysfunction contributes to neurodegeneration. Mechanisms underlying BBB dysfunction are outlined (endothelium and neurovascular unit mediated) as is the BBB as a therapeutic target including increasing the uptake of systemically delivered therapeutics across the BBB, enhancing clearance of potential neurotoxic compounds via the BBB, and preventing BBB dysfunction. Finally, a need for novel biomarkers of BBB dysfunction is addressed.

Epigenetics and stroke: role of DNA methylation and effect of aging on blood-brain barrier recovery

Incomplete recovery of blood-brain barrier (BBB) function contributes to stroke outcomes. How the BBB recovers after stroke remains largely unknown. Emerging evidence suggests that epigenetic factors play a significant role in regulating post-stroke BBB recovery. This study aimed to evaluate the epigenetic and transcriptional profile of cerebral microvessels after thromboembolic (TE) stroke to define potential causes of limited BBB recovery. RNA-sequencing and reduced representation bisulfite sequencing (RRBS) analyses were performed using microvessels isolated from young (6 months) and old (18 months) mice seven days poststroke compared to age-matched sham controls. DNA methylation profiling of poststroke brain microvessels revealed 11,287 differentially methylated regions (DMR) in old and 9818 DMR in young mice, corresponding to annotated genes. These DMR were enriched in genes encoding cell structural proteins (e.g., cell junction, and cell polarity, actin cytoskeleton, extracellular matrix), transporters and channels (e.g., potassium transmembrane transporter, organic anion and inorganic cation transporters, calcium ion transport), and proteins involved in endothelial cell processes (e.g., angiogenesis/vasculogenesis, cell signaling and transcription regulation). Integrated analysis of methylation and RNA sequencing identified changes in cell junctions (occludin), actin remodeling (ezrin) as well as signaling pathways like Rho GTPase (RhoA and Cdc42ep4). Aging as a hub of aberrant methylation affected BBB recovery processes by profound alterations (hypermethylation and repression) in structural protein expression (e.g., claudin-5) as well as activation of a set of genes involved in endothelial to mesenchymal transformation (e.g., Sox9, Snai1), repression of angiogenesis and epigenetic regulation. These findings revealed that DNA methylation plays an important role in regulating BBB repair after stroke, through regulating processes associated with BBB restoration and prevalently with processes enhancing BBB injury.

Systemic Delivery of an Adjuvant CXCR4-CXCL12 Signaling Inhibitor Encapsulated in Synthetic Protein Nanoparticles for Glioma Immunotherapy

Glioblastoma (GBM) is an aggressive primary brain cancer, with a 5 year survival of ∼5%. Challenges that hamper GBM therapeutic efficacy include (i) tumor heterogeneity, (ii) treatment resistance, (iii) immunosuppressive tumor microenvironment (TME), and (iv) the blood-brain barrier (BBB). The C-X-C motif chemokine ligand-12/C-X-C motif chemokine receptor-4 (CXCL12/CXCR4) signaling pathway is activated in GBM and is associated with tumor progression. Although the CXCR4 antagonist (AMD3100) has been proposed as an attractive anti-GBM therapeutic target, it has poor pharmacokinetic properties, and unfavorable bioavailability has hampered its clinical implementation. Thus, we developed synthetic protein nanoparticles (SPNPs) coated with the transcytotic peptide iRGD (AMD3100-SPNPs) to target the CXCL2/CXCR4 pathway in GBM via systemic delivery. We showed that AMD3100-SPNPs block CXCL12/CXCR4 signaling in three mouse and human GBM cell cultures in vitro and in a GBM mouse model in vivo. This results in (i) inhibition of GBM proliferation, (ii) reduced infiltration of CXCR4⁺ monocytic myeloid-derived suppressor cells (M-MDSCs) into the TME, (iii) restoration of BBB integrity, and (iv) induction of immunogenic cell death (ICD), sensitizing the tumor to radiotherapy and leading to anti-GBM immunity. Additionally, we showed that combining AMD3100-SPNPs with radiation led to long-term survival, with ∼60% of GBM tumor-bearing mice remaining tumor free after rechallenging with a second GBM in the contralateral hemisphere. This was due to a sustained anti-GBM immunological memory response that prevented tumor recurrence without additional treatment. In view of the potent ICD induction and reprogrammed tumor microenvironment, this SPNP-mediated strategy has a significant clinical translation applicability.

Transcriptomic Profile of Blood–Brain Barrier Remodeling in Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA) is a small vessel disease characterized by amyloid β (Aβ) peptide deposition within the walls of medium to small-caliber blood vessels, cerebral microhemorrhage, and blood–brain barrier (BBB) leakage. It is commonly associated with late-stage Alzheimer’s disease. BBB dysfunction is indicated as a pathological substrate for CAA progression with hyperpermeability, enhancing the extravasation of plasma components and inducing neuroinflammation, further worsening BBB injury and contributing to cognitive decline. Although significant effort has been made in defining the gene mutations and risk factors involved in microvascular alterations with vascular dementia and Alzheimer’s disease, the intra- and intercellular pathogenic mechanisms responsible for vascular hyperpermeability are still largely unknown. The present study aimed to elucidate the transcriptional profile of the cerebral microvessels (BBB) in a murine model with CAA vasculopathy to define potential causes and underlying mechanisms of BBB injury. A comprehensive RNA sequencing analysis was performed of CAA vasculopathy in Tg-SwDI mice at 6 and 18 months in comparison to age-matched wildtype controls to examine how age and amyloid accumulation impact the transcriptional signature of the BBB. Results indicate that Aβ has a critical role in triggering brain endothelial cell and BBB dysfunction in CAA vasculopathy, causing an intense proinflammatory response, impairing oxidative metabolism, altering the coagulation status of brain endothelial cells, and remodeling barrier properties. The proinflammatory response includes both adaptive and innate immunity, with pronounced induction of genes that regulate macrophage/microglial activation and chemokines/adhesion molecules that support T and B cell transmigration. Age has an important impact on the effects of Aβ, increasing the BBB injury in CAA vasculopathy. However, early inflammation, particularly microglia/macrophage activation and the mediators of B lymphocytes’ activities are underlying processes of BBB hyperpermeability and cerebral microbleeds in the early stage of CAA vasculopathy. These findings reveal a specific profile of the CAA-associated BBB injury that leads to a full progression of CAA.

Cerebral Cavernous Malformation Pathogenesis: Investigating Lesion Formation and Progression with Animal Models

Cerebral cavernous malformation (CCM) is a cerebromicrovascular disease that affects up to 0.5% of the population. Vessel dilation, decreased endothelial cell-cell contact, and loss of junctional complexes lead to loss of brain endothelial barrier integrity and hemorrhagic lesion formation. Leakage of hemorrhagic lesions results in patient symptoms and complications, including seizures, epilepsy, focal headaches, and hemorrhagic stroke. CCMs are classified as sporadic (sCCM) or familial (fCCM), associated with loss-of-function mutations in KRIT1/CCM1, CCM2, and PDCD10/CCM3. Identifying the CCM proteins has thrust the field forward by (1) revealing cellular processes and signaling pathways underlying fCCM pathogenesis, and (2) facilitating the development of animal models to study CCM protein function. CCM animal models range from various murine models to zebrafish models, with each model providing unique insights into CCM lesion development and progression. Additionally, these animal models serve as preclinical models to study therapeutic options for CCM treatment. This review briefly summarizes CCM disease pathology and the molecular functions of the CCM proteins, followed by an in-depth discussion of animal models used to study CCM pathogenesis and developing therapeutics.

An In Vivo Mouse Model to Study Blood-Brain Barrier Destabilization in the Chronic Phase of Stroke

Cerebral ischemic injury evokes a complex cascade of pathophysiological events at the blood-vascular-parenchymal interface. These evolve over time and space and result in progressive neurological damage. Emerging evidence suggests that blood-brain barrier (BBB) recovery and reestablishment of BBB impermeability are incomplete and that these could influence stroke injury recovery, increase the risk of new stroke occurrence, and be a solid substrate for developing vascular dementia. Recent work from the author's laboratory has established the existence of incomplete BBB recovery in chronic stroke conditions that was induced by structural alterations to brain endothelial junctional complexes and persistent BBB leakage. The experimental methodology presented here is focused on modelling chronic stroke injury using an in vivo thromboembolic mouse stroke model and how to evaluate the kinetics and magnitude of BBB hyperpermeability in chronic stroke conditions using a combination of magnetic resonance imaging, tracer studies, and immunohistochemistry.

Tight junctions in the blood-brain barrier promote edema formation and infarct size in stroke - Ambivalent effects of sealing proteins

The outcome of stroke is greatly influenced by the state of the blood-brain barrier (BBB). The BBB endothelium is sealed paracellularly by tight junction (TJ) proteins, i.e., claudins (Cldns) and the redox regulator occludin. Functions of Cldn3 and occludin at the BBB are largely unknown, particularly after stroke. We address the effects of Cldn3 deficiency and stress factors on the BBB and its TJs. Cldn3 tightened the BBB for small molecules and ions, limited endothelial endocytosis, strengthened the TJ structure and controlled Cldn1 expression. After middle cerebral artery occlusion (MCAO) and 3-h reperfusion or hypoxia of isolated brain capillaries, Cldn1, Cldn3 and occludin were downregulated. In Cldn3 knockout mice (C3KO), the reduction in Cldn1 was even greater and TJ ultrastructure was impaired; 48 h after MCAO of wt mice, infarct volumes were enlarged and edema developed, but endothelial TJs were preserved. In contrast, junctional localization of Cldn5 and occludin, TJ density, swelling and infarction size were reduced in affected brain areas of C3KO. Taken together, Cldn3 and occludin protect TJs in stroke, and this keeps the BBB intact. However, functional Cldn3, Cldn3-regulated TJ proteins and occludin promote edema and infarction, which suggests that TJ modulation could improve the outcome of stroke.

Modeling blood-brain barrier pathology in cerebrovascular disease in vitro: current and future paradigms

The complexity of the blood–brain barrier (BBB) and neurovascular unit (NVU) was and still is a challenge to bridge. A highly selective, restrictive and dynamic barrier, formed at the interface of blood and brain, the BBB is a “gatekeeper” and guardian of brain homeostasis and it also acts as a “sensor” of pathological events in blood and brain. The majority of brain and cerebrovascular pathologies are associated with BBB dysfunction, where changes at the BBB can lead to or support disease development. Thus, an ultimate goal of BBB research is to develop competent and highly translational models to understand mechanisms of BBB/NVU pathology and enable discovery and development of therapeutic strategies to improve vascular health and for the efficient delivery of drugs. This review article focuses on the progress being made to model BBB injury in cerebrovascular diseases in vitro.

Endothelial Targets in Stroke: Translating Animal Models to Human

Cerebral ischemia (stroke) induces injury to the cerebral endothelium that may contribute to parenchymal injury and worsen outcome. This review focuses on current preclinical studies examining how to prevent ischemia-induced endothelial dysfunction. It particularly focuses on targets at the endothelium itself. Those include endothelial tight junctions, transcytosis, endothelial cell death, and adhesion molecule expression. It also examines how such studies are being translated to the clinic, especially as adjunct therapies for preventing intracerebral hemorrhage during reperfusion of the ischemic brain. Identification of endothelial targets may prove valuable in a search for combination therapies that would specifically protect different cell types in ischemia.

Involvement of Epigenetic Mechanisms and Non-coding RNAs in Blood-Brain Barrier and Neurovascular Unit Injury and Recovery After Stroke

Cessation of blood flow leads to a complex cascade of pathophysiological events at the blood-vascular-parenchymal interface which evolves over time and space, and results in damage to neural cells and edema formation. Cerebral ischemic injury evokes a profound and deleterious upregulation in inflammation and triggers multiple cell death pathways, but it also induces a series of the events associated with regenerative responses, including vascular remodeling, angiogenesis, and neurogenesis. Emerging evidence suggests that epigenetic reprograming could play a pivotal role in ongoing post-stroke neurovascular unit (NVU) changes and recovery. This review summarizes current knowledge about post-stroke recovery processes at the NVU, as well as epigenetic mechanisms and modifiers (e.g., DNA methylation, histone modifying enzymes and microRNAs) associated with stroke injury, and NVU repair. It also discusses novel drug targets and therapeutic strategies for enhancing post-stroke recovery.

Decline in Sirtuin-1 expression and activity plays a critical role in blood-brain barrier permeability in aging

Accumulating evidence suggest that cerebral microvascular disease increases with advancing age and is associated with lacunar stroke, leukoaraiosis, vascular dementia and Alzheimer disease. Increased blood brain barrier (BBB) permeability/leakage takes "center stage" in ongoing age-related vascular/brain parenchymal injury. Although significant effort has been made in defining the gene mutations and risk factors involved in microvascular alterations in vascular dementia and Alzheimer disease, the intra- and intercellular pathogenic mechanisms responsible for vascular hyperpermeability are still largely unknown. The present study aimed to reveal the ongoing senescence process in brain endothelial cells and its effect on BBB integrity in healthy/non-disease conditions. An analysis of BBB integrity during the life span of C56Bl6 mice (young, 2-6 months; middle-aged, 6-12, months; old, 16-22 months) showed increased BBB permeability for different molecular sized tracers (sodium fluorescein, inulin and 20 kDa dextran) in aged mice which was accompanied by modifications in tight junction (TJ) complex organization, manifested as altered TJ protein expression (particularly claudin-5). A gene screening analysis of aging associated markers in brain microvessels isolated from "aged" mice (C56Bl6, 18-20 months) and human brain samples showed a significant decline in sirtuin-1 expression (Sirt1; ~2.8-fold) confirmed at mRNA and protein levels and by activation assay. Experiments in Sirt1 transgenic mice and brain endothelial cell-specific Sirt1 knockout mice indicated that Sirt1 affects BBB integrity, with loss increasing permeability. Similarly, in vitro, overexpressing Sirt1 or increasing Sirt1 activity with an agonist (Sirt1720) protected against senescence-induced brain endothelial barrier hyperpermeability, stabilized claudin-5/ZO-1 interactions and rescued claudin-5 expression. These findings reveal a novel role of Sirt1 in modulating aging-associated BBB persistent leakage.

Is there a central role for the cerebral endothelium and the vasculature in the brain response to conditioning stimuli?

A variety of conditioning stimuli (e.g. ischemia or hypoxia) can protect against stroke-induced brain injury. While most attention has focused on the effects of conditioning on parenchymal injury, there is considerable evidence that such stimuli also protect the cerebrovasculature, including the blood-brain barrier. This review summarizes the data on the cerebrovascular effects of ischemic/hypoxic pre-, per- and post-conditioning and the mechanisms involved in protection. It also addresses some important questions: Are the cerebrovascular effects of conditioning just secondary to reduced parenchymal injury? How central is endothelial conditioning to overall brain protection? For example, is endothelial conditioning sufficient or necessary for the induction of brain protection against stroke? Is the endothelium crucial as a sensor/transducer of conditioning stimuli?

Brain endothelial cell junctions after cerebral hemorrhage: Changes, mechanisms and therapeutic targets

Vascular disruption is the underlying cause of cerebral hemorrhage, including intracerebral, subarachnoid and intraventricular hemorrhage. The disease etiology also involves cerebral hemorrhage-induced blood-brain barrier (BBB) disruption, which contributes an important component to brain injury after the initial cerebral hemorrhage. BBB loss drives vasogenic edema, allows leukocyte extravasation and may lead to the entry of potentially neurotoxic and vasoactive compounds into brain. This review summarizes current information on changes in brain endothelial junction proteins in response to cerebral hemorrhage (and clot-related factors), the mechanisms underlying junction modification and potential therapeutic targets to limit BBB disruption and, potentially, hemorrhage occurrence. It also addresses advances in the tools that are now available for assessing changes in junctions after cerebral hemorrhage and the potential importance of such junction changes. Recent studies suggest post-translational modification, conformational change and intracellular trafficking of junctional proteins may alter barrier properties. Understanding how cerebral hemorrhage alters BBB properties beyond changes in tight junction protein loss may provide important therapeutic insights to prevent BBB dysfunction and restore normal function.

Connexin 43 gap junctions contribute to brain endothelial barrier hyperpermeability in familial cerebral cavernous malformations type III by modulating tight junction structure

Familial cerebral cavernous malformations type III (fCCM3) is a disease of the cerebrovascular system caused by loss-of-function mutations in ccm3 that result in dilated capillary beds that are susceptible to hemorrhage. Before hemorrhage, fCCM3 lesions are characterized by a hyperpermeable blood-brain barrier (BBB), the key pathologic feature of fCCM3. We demonstrate that connexin 43 (Cx43), a gap junction (GJ) protein that is incorporated into the BBB junction complex, is up-regulated in lesions of a murine model of fCCM3. Small interfering RNA-mediated ccm3 knockdown (CCM3KD) in brain endothelial cells in vitro increased Cx43 protein expression, GJ plaque size, GJ intracellular communication (GJIC), and barrier permeability. CCM3KD hyperpermeability was rescued by GAP27, a peptide gap junction and hemichannel inhibitor of Cx43 GJIC. Tight junction (TJ) protein, zonula occludens 1 (ZO-1), accumulated at Cx43 GJs in CCM3KD cells and displayed fragmented staining at TJs. The GAP27-mediated inhibition of Cx43 GJs in CCM3KD cells restored ZO-1 to TJ structures and reduced plaque accumulation at Cx43 GJs. The TJ protein, Claudin-5, was also fragmented at TJs in CCM3KD cells, and GAP27 treatment lengthened TJ-associated fragments and increased Claudin 5-Claudin 5 transinteraction. Overall, we demonstrate that Cx43 GJs are aberrantly increased in fCCM3 and regulate barrier permeability by a TJ-dependent mechanism.-Johnson, A. M., Roach, J. P., Hu, A., Stamatovic, S. M., Zochowski, M. R., Keep, R. F., Andjelkovic, A. V. Connexin 43 gap junctions contribute to brain endothelial barrier hyperpermeability in familial cerebral cavernous malformations type III by modulating tight junction structure.

Blood-brain barrier dysfunction and recovery after ischemic stroke

The blood-brain barrier (BBB) plays a vital role in regulating the trafficking of fluid, solutes and cells at the blood-brain interface and maintaining the homeostatic microenvironment of the CNS. Under pathological conditions, such as ischemic stroke, the BBB can be disrupted, followed by the extravasation of blood components into the brain and compromise of normal neuronal function. This article reviews recent advances in our knowledge of the mechanisms underlying BBB dysfunction and recovery after ischemic stroke. CNS cells in the neurovascular unit, as well as blood-borne peripheral cells constantly modulate the BBB and influence its breakdown and repair after ischemic stroke. The involvement of stroke risk factors and comorbid conditions further complicate the pathogenesis of neurovascular injury by predisposing the BBB to anatomical and functional changes that can exacerbate BBB dysfunction. Emphasis is also given to the process of long-term structural and functional restoration of the BBB after ischemic injury. With the development of novel research tools, future research on the BBB is likely to reveal promising potential therapeutic targets for protecting the BBB and improving patient outcome after ischemic stroke.

Cross-over endocytosis of claudins is mediated by interactions via their extracellular loops

Claudins (Cldns) are transmembrane tight junction (TJ) proteins that paracellularly seal endo- and epithelial barriers by their interactions within the TJs. However, the mechanisms allowing TJ remodeling while maintaining barrier integrity are largely unknown. Cldns and occludin are heterophilically and homophilically cross-over endocytosed into neighboring cells in large, double membrane vesicles. Super-resolution microscopy confirmed the presence of Cldns in these vesicles and revealed a distinct separation of Cldns derived from opposing cells within cross-over endocytosed vesicles. Colocalization of cross-over endocytosed Cldn with the autophagosome markers as well as inhibition of autophagosome biogenesis verified involvement of the autophagosomal pathway. Accordingly, cross-over endocytosed Cldns underwent lysosomal degradation as indicated by lysosome markers. Cross-over endocytosis of Cldn5 depended on clathrin and caveolin pathways but not on dynamin. Cross-over endocytosis also depended on Cldn-Cldn-interactions. Amino acid substitutions in the second extracellular loop of Cldn5 (F147A, Q156E) caused impaired cis- and trans-interaction, as well as diminished cross-over endocytosis. Moreover, F147A exhibited an increased mobility in the membrane, while Q156E was not as mobile but enhanced the paracellular permeability. In conclusion, the endocytosis of TJ proteins depends on their ability to interact strongly with each other in cis and trans, and the mobility of Cldns in the membrane is not necessarily an indicator of barrier permeability. TJ-remodeling via cross-over endocytosis represents a general mechanism for the degradation of transmembrane proteins in cell-cell contacts and directly links junctional membrane turnover to autophagy.

Endocytosis of tight junction proteins and the regulation of degradation and recycling

Internalization of tight junction (TJ) proteins from the plasma membrane is a pivotal mechanism regulating TJ plasticity and function in both epithelial and endothelial barrier tissues. Once internalized, the TJ proteins enter complex vesicular machinery, where further trafficking is directly dependent on the initiating stimulus and downstream signaling pathways that regulate the sorting and destiny of TJ proteins, as well as on cell and barrier responses. The destiny of internalized TJ proteins is recycling to the plasma membrane or sorting to late endosomes and degradation. This review highlights recent advances in our knowledge of endocytosis and vesicular trafficking of TJ proteins in both epithelial and endothelial cells. A greater understanding of these processes may allow for the development of methods to modulate barrier permeability for drug delivery or prevent barrier dysfunction in disease states.

Junctional proteins of the blood-brain barrier: New insights into function and dysfunction

The blood-brain barrier (BBB) is a highly complex and dynamic barrier. It is formed by an interdependent network of brain capillary endothelial cells, endowed with barrier properties, and perivascular cells (astrocytes and pericytes) responsible for inducing and maintaining those properties. One of the primary properties of the BBB is a strict regulation of paracellular permeability due to the presence of junctional complexes (tight, adherens and gap junctions) between the endothelial cells. Alterations in junction assembly and function significantly affect BBB properties, particularly barrier permeability. However, such alterations are also involved in remodeling the brain endothelial cell surface and regulating brain endothelial cell phenotype. This review summarizes the characteristics of brain endothelial tight, adherens and gap junctions and highlights structural and functional alterations in junctional proteins that may contribute to BBB dysfunction.

Organ distribution of histones after intravenous infusion of FITC histones or after sepsis

Histones appear in plasma during infectious or non-infectious sepsis and are associated with multiorgan injury. In the current studies, intravenous infusion of histones resulted in their localization in major organs. In vitro exposure of mouse macrophages to histones caused a buildup of histones on cell membranes followed by localization into cytosol and into the nucleus. After polymicrobial sepsis (cecal ligation and puncture), histones appeared in plasma as well as in a multiorgan pattern, peaking at 8 h followed by decline. In lungs, histones and neutrophils appeared together, with evidence for formation of neutrophil extracellular traps (NETs), which represent an innate immune response to trap and kill bacteria and other infectious agents. In liver, there was intense NET formation, featuring linear patterns containing histones and strands of DNA. When neutrophils were activated in vitro with C5a or phorbol myristate acetate, NET formation ensued. While formation of NETs represents entrapment and killing of infectious agents, the simultaneous release from neutrophils of histones often results in tissue/organ damage.

PDCD10 (CCM3) regulates brain endothelial barrier integrity in cerebral cavernous malformation type 3: role of CCM3-ERK1/2-cortactin cross-talk

Impairment of brain endothelial barrier integrity is critical for cerebral cavernous malformation (CCM) lesion development. The current study investigates changes in tight junction (TJ) complex organization when PDCD10 (CCM3) is mutated/depleted in human brain endothelial cells. Analysis of lesions with CCM3 mutation and brain endothelial cells transfected with CCM3 siRNA (CCM3-knockdown) showed little or no increase in TJ transmembrane and scaffolding proteins mRNA expression, but proteins levels were generally decreased. CCM3-knockdown cells had a redistribution of claudin-5 and occludin from the membrane to the cytosol with no alterations in protein turnover but with diminished protein-protein interactions with ZO-1 and ZO-1 interaction with the actin cytoskeleton. The most profound effect of CCM3 mutation/depletion was on an actin-binding protein, cortactin. CCM3 depletion caused cortactin Ser-phosphorylation, dissociation from ZO-1 and actin, redistribution to the cytosol and degradation. This affected cortical actin ring organization, TJ complex stability and consequently barrier integrity, with constant hyperpermeability to inulin. A potential link between CCM3 depletion and altered cortactin was tonic activation of MAP kinase ERK1/2. ERK1/2 inhibition increased cortactin expression and incorporation into the TJ complex and improved barrier integrity. This study highlights the potential role of CCM3 in regulating TJ complex organization and brain endothelial barrier permeability.

Vascular disruption and blood-brain barrier dysfunction in intracerebral hemorrhage

This article reviews current knowledge of the mechanisms underlying the initial hemorrhage and secondary blood-brain barrier (BBB) dysfunction in primary spontaneous intracerebral hemorrhage (ICH) in adults. Multiple etiologies are associated with ICH, for example, hypertension, Alzheimer's disease, vascular malformations and coagulopathies (genetic or drug-induced). After the initial bleed, there can be continued bleeding over the first 24 hours, so-called hematoma expansion, which is associated with adverse outcomes. A number of clinical trials are focused on trying to limit such expansion. Significant progress has been made on the causes of BBB dysfunction after ICH at the molecular and cell signaling level. Blood components (e.g. thrombin, hemoglobin, iron) and the inflammatory response to those components play a large role in ICH-induced BBB dysfunction. There are current clinical trials of minimally invasive hematoma removal and iron chelation which may limit such dysfunction. Understanding the mechanisms underlying the initial hemorrhage and secondary BBB dysfunction in ICH is vital for developing methods to prevent and treat this devastating form of stroke.

Critical role for the NLRP3 inflammasome during acute lung injury

The inflammasome is a key factor in innate immunity and senses soluble pathogen and danger-associated molecular patterns as well as biological crystals (urate, cholesterol, etc.), resulting in expression of IL-1β and IL-18. Using a standard model of acute lung injury (ALI) in mice featuring airway instillation of LPS, ALI was dependent on availability of NLRP3 as well as caspase-1, which are known features of the NLRP3 inflammasome. The appearance of IL-1β, a product of NLRP3 inflammasome activation, was detected in bronchoalveolar lavage fluids (BALF) in a macrophage- and neutrophil-dependent manner. Neutrophil-derived extracellular histones appeared in the BALF during ALI and directly activated the NLRP3 inflammasome. Ab-mediated neutralization of histones significantly reduced IL-1β levels in BALF during ALI. Inflammasome activation by extracellular histones in LPS-primed macrophages required NLRP3 and caspase-1 as well as extrusion of K(+), increased intracellular Ca(2+) concentration, and generation of reactive oxygen species. NLRP3 and caspase-1 were also required for full extracellular histone presence during ALI, suggesting a positive feedback mechanism. Extracellular histone and IL-1β levels in BALF were also elevated in C5a-induced and IgG immune complex ALI models, suggesting a common inflammatory mechanism. These data indicate an interaction between extracellular histones and the NLRP3 inflammasome, resulting in ALI. Such findings suggest novel targets for treatment of ALI, for which there is currently no known efficacious drug.

Inhibition of junctional adhesion molecule-A/LFA interaction attenuates leukocyte trafficking and inflammation in brain ischemia/reperfusion injury

Proinflammatory mediators trigger intensive postischemic inflammatory remodeling of the blood-brain barrier (BBB) including extensive brain endothelial cell surface and junctional complex changes. Junctional adhesion molecule-A (JAM-A) is a component of the brain endothelial junctional complex with dual roles: paracellular route occlusion and regulating leukocyte docking and migration. The current study examined the contribution of JAM-A to the regulation of leukocyte (neutrophils and monocytes/macrophages) infiltration and the postischemic inflammatory response in brain ischemia/reperfusion (I/R injury). Brain I/R injury was induced by transient middle cerebral artery occlusion (MCAO) for 30min in mice followed by reperfusion for 0-5days, during which time JAM-A antagonist peptide (JAM-Ap) was administered. The peptide, which inhibits JAM-A/leukocyte interaction by blocking the interaction of the C2 domain of JAM-A with LFA on neutrophils and monocytes/macrophages, attenuated I/R-induced neutrophil and monocyte infiltration into brain parenchyma. Consequently, mice treated with JAM-A peptide during reperfusion had reduced expression (~3-fold) of inflammatory mediators in the ischemic penumbra, reduced infarct size (94±39 vs 211±38mm3) and significantly improved neurological score. BBB hyperpermeability was also reduced. Collectively, these results indicate that JAM-A has a prominent role in regulating leukocyte infiltration after brain I/R injury and could be a new target in limiting post-ischemic inflammation.

Treatment with a histone deacetylase inhibitor, valproic acid, is associated with increased platelet activation in a large animal model of traumatic brain injury and hemorrhagic shock

BACKGROUND

We have previously shown that resuscitation with fresh frozen plasma (FFP) in a large animal model of traumatic brain injury (TBI) and hemorrhagic shock (HS) decreases the size of the brain lesion, and that addition of a histone deacetylase inhibitor, valproic acid (VPA), provides synergistic benefits. In this study, we hypothesized that VPA administration would be associated with a conservation of platelet function as measured by increased platelet activation after resuscitation.

MATERIALS AND METHODS

Ten swine (42-50 kg) were subjected to TBI and HS (40% blood loss). Animals were left in shock for 2 h before resuscitation with either FFP or FFP+VPA (300 mg/kg). Serum levels of platelet activation markers transforming growth factor beta, CD40 L, P-selectin, and platelet endothelial cell adhesion molecule (PECAM) 1 were measured at baseline, postresuscitation, and after a 6-h observation period. Platelet activation markers were also measured in the brain whole cell lysates and immunohistochemistry.

RESULTS

Circulating P-selectin levels were significantly higher in the FFP+VPA group compared with the FFP alone group (70.85±4.70 versus 48.44±7.28 ng/mL; P<0.01). Likewise, immunohistochemistry data showed elevated P-selectin in the VPA treatment group (22.30±10.39% versus 8.125±3.94%, P<0.01). Serum sCD40L levels were also higher in the FFP+VPA group (3.21±0.124 versus 2.38±0.124 ng/mL; P<0.01), as was brain sCD40L levels (1.41±0.15 versus 1.22±0.12 ng/mL; P=0.05). Circulating transforming growth factor beta levels were elevated in the FFP+VPA group, but this did not reach statistical significance (11.20±1.46 versus 8.09±1.41 ng/mL; P=0.17). Brain platelet endothelial cell adhesion molecule 1 levels were significantly lower in the FFP+VPA group compared with the FFP group (5.22±2.00 pg/mL versus 7.99±1.13 pg/mL; P=0.03).

CONCLUSIONS

In this clinically relevant large animal model of combined TBI+HS, the addition of VPA to FFP resuscitation results in an early upregulation of platelet activation in the circulation and the brain. The previously observed neuroprotective effects of VPA may be due to a conservation of platelet function as measured by a higher platelet activation response after resuscitation.

Zonulin as prehaptoglobin2 regulates lung permeability and activates the complement system

Zonulin is a protein involved in the regulation of tight junctions (TJ) in epithelial or endothelial cells. Zonulin is known to affect TJ in gut epithelial cells, but little is known about its influences in other organs. Prehaptoglobin2 has been identified as zonulin and is related to serine proteases (MASPs, C1qrs) that activate the complement system. The current study focused on the role of zonulin in development of acute lung injury (ALI) in C57BL/6 male mice following intrapulmonary deposition of IgG immune complexes. A zonulin antagonist (AT-1001) and a related peptide with permeability agonist activities (AT-1002) were employed and given intratracheally or intravenously. Also, zonulin was blocked in lung with a neutralizing antibody. In a dose-dependent manner, AT-1001 or zonulin neutralizing antibody attenuated the intensity of ALI (as quantitated by albumin leak, neutrophil accumulation, and proinflammatory cytokines). A similar pattern was found using the bacterial lipopolysaccharide model of ALI. Using confocal microscopy on sections of injured lungs, staining patterns for TJ proteins were discontinuous, reduced, and fragmented. As expected, the leak of blood products into the alveolar space confirmed the passage of 3 and 20 kDa dextran, and albumin. In contrast to AT-1001, application of the zonulin agonist AT-1002 intensified ALI. Zonulin both in vitro and in vivo induced generation of complement C3a and C5a. Collectively, these data suggest that zonulin facilitates development of ALI both by enhancing albumin leak and complement activation as well as increased buildup of neutrophils and cytokines during development of ALI.

Abstract TP435: Junctional Adhesion Molecule-a Deficiency Attenuate Leukocytes Trafficking And Inflammation In Brain Ischemic /reperfusion Injury

Background: Brain ischemic reperfusion (I/R) injury elicits an intense inflammatory response that causes secondary brain damage. Proinflammatory mediators trigger intensive inflammatory remodeling of the blood-brain barrier (BBB) that includes extensive changes of the brain endothelial cell surface and alteration of junctional complex in order to “receive and support” leukocyte migration into the brain parenchyma. Junctional adhesion molecule-A (JAM-A) is component of the brain endothelial junctional complex with dual role: the occlusion of the paracellular route and regulation of leukocyte docking and migration. In this study we have examined contribution of JAM-A in developing the postischemic inflammatory response.

Method: Brain I/R injury was induced by transient occlusion of middle cerebral artery (tMCAO) for 30 min followed by reperfusion for 0-7 days. JAM-A role in brain I/R injury was investigated in condition of presence JAM-A on brain endothelial cells, JAM-A absence (JAM-A knockout -KO- mice) or in condition of inhibition via administration of JAM-A antagonist peptide (JAM-Ap, 1mg/ml), 6 hrs after tMCAO and for 6 consecutive days. Leukocytes infiltration was estimated by FACS analysis. The inflammatory mediators expression was evaluated by protein array, RT-PCR and ELISA.

Result: I/R-induced neutrophils transmigration was attenuated in both JAM-A-KO mice as well as in mice treated with JAM-Ap whereas transmigration of monocytes and T cells was JAM-A independent. Consequently with that, expression of inflammatory mediators was reduced in area of penumbra. JAM-A-KO and mice treated with JAM-Ap showed the reduction of infarct size and significantly improved neurological score. BBB permeability was reduced by the treatment with JAM-Ap.

Conclusion: JAM-A has a prominent role in regulation of neutrophils infiltration after brain I/R injury and could be a new target in limiting the postischemic inflammation.

Claudin-derived peptides are internalized via specific endocytosis pathways

Claudin proteins are involved in the paracellular tightening of epithelia and endothelia. Their internalization, which can be modulated by extracellular stimuli, for example, proinflammatory cytokines, is a prerequisite for the regulation of the paracellular barrier to allow, for instance, cell migration or drug delivery. The internalization of peptide sequences of claudins is completely unknown. Here, we studied the internalization of two peptides, TAMRA-claudin-1 and TAMRA-claudin-5, derivatives of the extracellular loop of claudin-1 and -5, respectively, in either epithelial or endothelial cells. The cellular uptake of the claudin-1 peptide follows the clathrin-mediated endocytosis as indicated by inhibitors and respective tracers for colocalization. In addition, macropinocytosis and caveolae-mediated endocytosis of the peptide was observed. In contrast, the claudin-5 peptide is mainly internalized via the caveolae-mediated endocytosis evidenced by the colocalization with respective tracers and vesicle markers, whereas the nonselective macropinocytosis seems to be involved in a less effective manner. In conclusion, the assumption is supported that claudin peptides can be internalized by specific and nonspecific pathways.

Nicotine aggravates the brain postischemic inflammatory response

A substantial body of evidence suggests that nicotine adversely affects cerebral blood flow and the blood-brain barrier and is a risk factor for stroke. The present study investigated the effect of nicotine on cerebrovascular endothelium under basal and ischemia/reperfusion injury under in vivo condition. Nicotine (2 mg/kg sc) was administered to mice over 14 days, which resulted in plasma nicotine levels of ∼100 ng/ml, reflecting plasma concentrations in average to heavy smokers. An analysis of the phenotype of isolated brain microvessels after nicotine exposure indicated higher expression of inflammatory mediators, cytokines (IL-1β, TNF-α, and IL-18), chemokines (CCL2 and CX(3)CL1), and adhesion molecules (ICAM-1, VCAM-1, and P-selectins), and this was accompanied by enhanced leukocyte infiltration into brain during ischemia/reperfusion (P < 0.01). Nicotine had a profound effect on ischemia/reperfusion injury; i.e., increased brain infarct size (P < 0.01), worse neurological deficits, and a higher mortality rate. These experiments illuminate, for the first time, how nicotine regulates brain endothelial cell phenotype and postischemic inflammatory response at the brain-vascular interface.

Brain endothelial cell-cell junctions: how to "open" the blood brain barrier

The blood-brain barrier (BBB) is a highly specialized structural and biochemical barrier that regulates the entry of blood-borne molecules into brain, and preserves ionic homeostasis within the brain microenvironment. BBB properties are primarily determined by junctional complexes between the cerebral endothelial cells. These complexes are comprised of tight and adherens junctions. Such restrictive angioarchitecture at the BBB reduces paracellular diffusion, while minimal vesicle transport activity in brain endothelial cells limits transcellular transport. Under normal conditions, this largely prevents the extravasation of large and small solutes (unless specific transporters are present) and prevents migration of any type of blood-borne cell. However, this is changed in many pathological conditions. There, BBB disruption (“opening”) can lead to increased paracellular permeability, allowing entry of leukocytes into brain tissue, but also contributing to edema formation. In parallel, there are changes in the endothelial pinocytotic vesicular system resulting in the uptake and transfer of fluid and macromolecules into brain parenchyma. This review highlights the route and possible factors involved in BBB disruption in a variety of neuropathological disorders (e.g. CNS inflammation, Alzheimer’s disease, Parkinson’s disease, epilepsy). It also summarizes proposed signal transduction pathways that may be involved in BBB “opening”.

Insulin and IGF-1 receptors, nitrotyrosin and cerebral neuronal deficits in two young patients with diabetic ketoacidosis and fatal brain edema

Gray and white matter structural deficits may accompany type 1 diabetes. Earlier experimental studies have demonstrated neuronal deficits associated with impaired neurotrophic support, inflammation and oxidative stress. In this study we demonstrate in two patients with histories of poorly controlled type 1 diabetes and fatal brain edema of ketoacidosis neuronal deficits associated with a decreased presence of insulin and IGF-1 receptors and accumulation of nitrotyrosin in neurons of affected areas and the choroid plexus. The findings add support to the suggested genesis of T1DM encephalopathy due to compromised neurotrophic protection, oxidative stress, inflammation and neuronal deficits, as demonstrated in T1DM encephalopathy in the BB/Wor-rat.

Intact and injured endothelial cells differentially modulate postnatal murine forebrain neural stem cells

Neural stem cells (NSCs) persist in the forebrain subventricular zone (SVZ) within a niche containing endothelial cells. Evidence suggests that endothelial cells stimulate NSC expansion and neurogenesis. Experimental stroke increases neurogenesis and angiogenesis, but how endothelial cells influence stroke-induced neurogenesis is unknown. We hypothesized intact or oxygen-glucose deprived (OGD) endothelial cells secrete factors that enhance neurogenesis. We co-cultured mouse SVZ neurospheres (NS) with endothelial cells, or differentiated NS in endothelial cell-conditioned medium (ECCM). NS also were expanded in ECCM from OGD-exposed (OGD-ECCM) endothelial cells to assess injury effects. ECCM significantly increased NS production. NS co-cultured with endothelial cells or ECCM generated more immature-appearing neurons and oligodendrocytes, and astrocytes with radial glial-like/reactive morphology than controls. OGD-ECCM stimulated neuroblast migration and yielded neurons with longer processes and more branching. These data indicate that intact and injured endothelial cells exert differing effects on NSCs, and suggest targets for stimulating regeneration after brain insults.

Caveolae-mediated internalization of occludin and claudin-5 during CCL2-induced tight junction remodeling in brain endothelial cells

Disturbance of the tight junction (TJ) complexes between brain endothelial cells leads to increased paracellular permeability, allowing leukocyte entry into inflamed brain tissue and also contributing to edema formation. The current study dissects the mechanisms by which a chemokine, CCL2, induces TJ disassembly. It investigates the potential role of selective internalization of TJ transmembrane proteins (occludin and claudin-5) in increased permeability of the brain endothelial barrier in vitro. To map the internalization and intracellular fate of occludin and claudin-5, green fluorescent protein fusion proteins of these TJ proteins were generated and imaged by fluorescent microscopy with simultaneous measurement of transendothelial electrical resistance. During CCL2-induced reductions in transendothelial electrical resistance, claudin-5 and occludin became internalized via caveolae and further processed to early (EEA1+) and recycling (Rab4+) endosomes but not to late endosomes. Western blot analysis of fractions collected from a sucrose gradient showed the presence of claudin-5 and occludin in the same fractions that contained caveolin-1. For the first time, these results suggest an underlying molecular mechanism by which the pro-inflammatory chemokine CCL2 mediates brain endothelial barrier disruption during CNS inflammation.

IL-12- and IL-23-modulated T cells induce distinct types of EAE based on histology, CNS chemokine profile, and response to cytokine inhibition

The interleukin (IL)-12p40 family of cytokines plays a critical role in the development of experimental autoimmune encephalomyelitis (EAE). However, the relative contributions of IL-12 and IL-23 to the pathogenic process remain to be elucidated. Here, we show that activation of uncommitted myelin-reactive T cells in the presence of either IL-12p70 or IL-23 confers encephalogenicity. Adoptive transfer of either IL-12p70– or IL-23–polarized T cells into naive syngeneic hosts resulted in an ascending paralysis that was clinically indistinguishable between the two groups. However, histological and reverse transcription–polymerase chain reaction analysis of central nervous system (CNS) tissues revealed distinct histopathological features and immune profiles. IL-12p70–driven disease was characterized by macrophage-rich infiltrates and prominent NOS2 up-regulation, whereas neutrophils and granulocyte–colony-stimulating factor (CSF) were prominent in IL-23–driven lesions. The monocyte-attracting chemokines CXCL9, 10, and 11 were preferentially expressed in the CNS of mice injected with IL-12p70–modulated T cells, whereas the neutrophil-attracting chemokines CXCL1 and CXCL2 were up-regulated in the CNS of mice given IL-23–modulated T cells. Treatment with anti–IL-17 or anti–granulocyte/macrophage-CSF inhibited EAE induced by transfer of IL-23–polarized, but not IL-12p70–polarized, cells. These findings indicate that autoimmunity can be mediated by distinct effector populations that use disparate immunological pathways to achieve a similar clinical outcome.

Absence of the chemokine receptor CCR2 protects against cerebral ischemia/reperfusion injury in mice

BACKGROUND AND PURPOSE

The chemokine, monocyte chemoattractant protein-1 (CCL2), is a major factor driving leukocyte infiltration into the brain parenchyma in a variety of neuropathologic conditions associated with inflammation, including stroke. In addition, recent studies indicate that CCL2 and its receptor (CCR2) could have an important role in regulating blood-brain barrier (BBB) permeability. This study evaluated the role of the CCL2/CCR2 axis in regulating postischemic inflammation, BBB breakdown, and vasogenic edema formation.

METHODS

CCR2(-/-) and CCR2(+/+) mice were subjected to focal transient cerebral ischemia. BBB permeability and brain edema formation were observed at days 1 and 5 of reperfusion by evaluating the product surface area for fluorescein isothiocyanate-albumin and measuring water and electrolyte contents. Immunohistochemistry was used to assess leukocyte infiltration. cDNA gene and protein arrays for inflammatory cytokines were used to assess inflammatory profiles in CCR2(+/+) and CCR2(-/-) mice.

RESULTS

CCR2(-/-) mice had reduced infarct sizes and significantly reduced BBB permeability and brain edema formation in the affected ischemic hemisphere compared with CCR2(+/+) mice. This reduction in injury was closely associated with reduced infiltration of not only monocytes but also neutrophils (7- and 4-fold decreases, respectively). In addition, CCR2(-/-) mice had reduced expression/production of inflammatory cytokines during reperfusion.

CONCLUSIONS

These data suggest that inhibiting the CCL2/CCR2 axis affects brain reperfusion outcome by reducing brain edema, leukocyte infiltration, and inflammatory mediator expression.

CCL2 Regulates Angiogenesis via Activation of Ets-1 Transcription Factor

Although recent studies have suggested that CC chemokine CCL2 may directly affect the angiogenesis, the signaling events involved in such regulation remain to be determined. This study investigated a potential signal mechanism involved in CCL2-induced angiogenesis. Our in vitro and in vivo (hemangioma model of angiogenesis) experiments confirmed earlier findings that CCL2 can induce angiogenesis directly. Using a gene array analysis, CCL2 was found to induce expression of several angiogenic factors in brain endothelial cells. Among the most prominent was an up-regulation in Ets-1 transcription factor. CCL2 induced a significant increase in Ets-1 mRNA and protein expression as well as Ets-1 DNA-binding activity. Importantly, Ets-1 antisense oligonucleotide markedly abrogated in vitro CCL2-induced angiogenesis, suggesting that Ets-1 is critically involved in this process. Activation of Ets-1 by CCL2 further regulated some of Ets-1 target molecules including beta(3) integrins. CCL2 induced significant up-regulation of beta(3) mRNA and protein expression, and this effect of CCL2 was prevented by the Ets-1 antisense oligonucleotide. The functional regulation of Ets-1 activity by CCL2 was dependent on ERK-1/2 cascade. Inhibition of ERK1/2 activity by PD98509 prevented CCL2-induced increases in Ets-1 DNA-binding activity and Ets-1 mRNA expression. Based on these findings, we suggest that Ets-1 transcription factor plays a critical role in CCL2 actions on brain endothelial cells and CCL2-induced angiogenesis.

Effects of the chemokine CCL2 on blood-brain barrier permeability during ischemia-reperfusion injury

The chemokine CCL2 is considered as one of the main effectors driving postischemic infiltration of monocytes into the brain parenchyma. New experimental data, however, suggest that CCL2 could also participate in blood-brain barrier (BBB) 'opening' during the transmigration of monocytes. The current study examines the role of CCL2 in regulating BBB permeability after ischemia in vitro. To address this issue, an in vitro BBB model (coculture of astrocytes and brain endothelial cells) was subjected to 5 h of oxygen glucose deprivation, followed by reoxgenation (in vitro ischemia/reperfusion (I/R)) for 0 to 48 h. During reperfusion, there was a biphasic enhancement of barrier permeability, with a 200-fold increase in barrier permeability to FITC-albumin at 6 h and a further period of disruption around 24 h. The latter coincided with increased secretion of CCL2 by both astrocytes and brain endothelial cells and increased levels of the CCL2 receptor, CCR2. Applying antisense oligonucleotide or neutralizing antibody to block CCL2 significantly decreased I/R-induced enhancement of BBB permeability (approximately twofold) and redistribution of tight-junction (TJ) proteins (occludin, zonula occluden-1, 2, claudin-5). Similarly, absence of CCR2 from endothelial cells caused stabilization of TJ complexes and decreased the permeability of brain endothelial barrier during in vitro I/R. These data suggest CCL2/CCR2 has an important role in regulating brain endothelial permeability and might be a potential novel therapeutic target for stroke.

Protein Kinase Cα-RhoA Cross-talk in CCL2-induced Alterations in Brain Endothelial Permeability

Monocyte chemoattractant protein-1 (MCP-1 or CCL2) regulates blood-brain barrier permeability by inducing morphological and biochemical alterations in the tight junction (TJ) complex between brain endothelial cells. The present study used cultured brain endothelial cells to examine the signaling networks involved in the redistribution of TJ proteins (occludin, ZO-1, ZO-2, claudin-5) by CCL2. The CCL2-induced alterations in the brain endothelial barrier were associated with de novo Ser/Thr phosphorylation of occludin, ZO-1, ZO-2, and claudin-5. The phosphorylated TJ proteins were redistributed/localized in Triton X-100-soluble as well as Triton X-100-insoluble cell fractions. Two protein kinase C (PKC) isoforms, PKCalpha and PKCzeta, had a significant impact on this event. Inhibition of their activity using dominant negative mutants PKCalpha-DN and PKCzeta-DN diminished CCL2 effects on brain endothelial permeability. Previous data indicate that Rho/Rho kinase signaling is involved in CCL2 regulation of brain endothelial permeability. The interactions between the PKC and Rho/Rho kinase pathways were therefore examined. Rho, PKCalpha, and PKCzeta activities were knocked down using dominant negative mutants (T17Rho, PKCalpha-DN, and PKCzeta-DN, respectively). PKCalpha and Rho, but not PKCzeta and Rho, interacted at the level of Rho, with PKCalpha being a downstream target for Rho. Double transfection experiments using dominant negative mutants confirmed that this interaction is critical for CCL2-induced redistribution of TJ proteins. Collectively these data suggest for the first time that CCL2 induces brain endothelial hyperpermeability via Rho/PKCalpha signal pathway interactions.

Inflammation and brain edema: new insights into the role of chemokines and their receptors

Brain edema is associated with a variety of neuropathological conditions such as brain trauma, ischemic and hypoxic brain injury, central nervous system infection, acute attacks of multiple sclerosis, and brain tumors. A common finding is an inflammatory response, which may have a significant impact on brain edema formation. One critical event in the development of brain edema is blood-brain barrier (BBB) breakdown, which may be initiated and regulated by several proinflammatory mediators (oxidative mediators, adhesion molecules, cytokines, chemokines). These mediators not only regulate the magnitude of leukocyte extravasation into brain parenchyma, but also act directly on brain endothelial cells causing the loosening of junction complexes between endothelial cells, increasing brain endothelial barrier permeability, and causing vasogenic edema. Here we review junction structure at the BBB, the effects of pro-inflammatory mediators on that structure, and focus on the effects of chemokines at the BBB. New evidence indicates that chemokines (chemoattractant cytokines) do not merely direct leukocytes to areas of injury. They also have direct and indirect effects on the BBB leading to BBB disruption, facilitating entry of leukocytes into brain, and inducing vasogenic brain edema formation. Chemokine inhibition may be a new therapeutic target to reduce vasogenic brain edema.

Monocyte chemoattractant protein-1 regulation of blood-brain barrier permeability

The present study was designed to elucidate the effects of the chemokine monocyte chemoattractant protein (MCP-1) on blood-brain barrier (BBB) permeability. Experiments were conducted under in vitro conditions (coculture of brain endothelial cells and astrocytes) to study the cellular effects of MCP-1 and under in vivo conditions (intracerebral and intracerebroventricular administration of MCP-1) to study the potential contribution of MCP-1 to BBB disruption in vivo. Our results showed that MCP-1 induces a significant increase in the BBB permeability surface area product for fluorescein isothiocyanate (FITC)-albumin under in vivo conditions, particularly during prolonged (3 or 7 days) exposure (0.096+/-0.008 versus 0.031+/-0.005 microL/g min in controls at 3 days, P<0.001). Monocyte chemoattractant protein-1 also enhanced (17-fold compared with control) the permeability of the in vitro BBB (coculture) model. At the cellular level, MCP-1 causes alteration of tight junction (TJ) proteins in endothelial cells (redistribution of TJ proteins determined by Western blotting and loss of immunostaining for occludin, claudin-5, ZO-1, ZO-2). Monocyte chemoattractant protein-1-induced alterations in BBB permeability are mostly realized through the CCR2 receptor. Absence of CCR2 diminishes any effect of MCP-1 on BBB permeability in vitro and in vivo. The permeability surface area product for FITC-albumin after 3 days exposure to MCP-1 was 0.096+/-0.006 and 0.032+/-0.007 microL/g min, in CCR2+/+ and CCR2-/- mice, respectively (P<0.001). Monocytes/macrophages also participate in MCP-1-induced alterations in BBB permeability in vivo. Monocytes/macrophages depletion (by clodronate liposomes) reduced the effect of MCP-1 on BBB permeability in vivo approximately 2 fold. Our results suggest that, besides its main function of recruiting leukocytes at sites of inflammation, MCP-1 also plays a role in 'opening' the BBB.

Ischemia-induced endothelial cell dysfunction

Hemorrhagic transformation upon reperfusion therapy has focused attention on ischemia-induced endothelial dysfunction. This study examined whether hyperglycemia may induce hemorrhagic transformation by enhancing endothelial mitochondrial damage during ischemia and whether preconditioning (PC) stimuli may limit ischemia-induced endothelial damage. In vivo, rats received 2.8 M D-glucose or arabinose (1 ml/100 g; i.p.) prior to undergoing two hours of middle cerebral artery occlusion and transcardiac fixation for electron microscopy. In vitro, brain endothelial cells were exposed to a PC impulse (short-term oxygen glucose deprivation; OGD) prior to an injurious event (5 hours OGD). Endothelial injury was assessed by measuring lactate dehydrogenase release. Hyperglycemia during cerebral ischemia resulted in marked changes in endothelial morphology and mitochondrial swelling. Thus, in the ischemic hemisphere, there was no evidence of endothelial mitochondrial swelling in normoglycemic rats (mean profile width 0.22 +/- 0.04 vs. 0.17 +/- 0.01 microm in contralateral hemisphere) but there was marked swelling in hyperglycemic rats (0.44 +/- 0.02 microm). In vitro, cells preconditioned with one hour of OGD one day prior to 5 hours of OGD, showed reduced lactate dehydrogenase release (p < 0.05). In conclusion, hyperglycemia may have specific adverse effects on endothelial cell mitochondria during ischemia. Preventing those effects may help to ameliorate blood-brain barrier disruption on reperfusion. Insights into how to prevent endothelial injury may come from determining the mechanisms involved in endothelial preconditioning.

Potential role of MCP-1 in endothelial cell tight junction 'opening': signaling via Rho and Rho kinase

The expression of the monocyte chemoattractant protein-1 (MCP-1) receptor CCR2 by brain endothelial cells suggests that MCP-1 may have other functions than purely driving leukocyte migration into brain parenchyma during inflammation. This study examines one of these potential novel roles of MCP-1 regulation of endothelial permeability using primary cultures of mouse brain endothelial cells. MCP-1 induces reorganization of actin cytoskeleton (stress fiber formation) and redistribution of tight junction proteins, ZO-1, ZO-2 occludin and claudin-5, from the Triton X-100-soluble to the Triton X-100-insoluble fractions. These morphological changes are associated with a decrease in transendothelial electrical membrane resistance and an increase in [14C]inulin permeability. MCP-1 did not induce these events in brain endothelial cells prepared from mice genotype CCR2-/-. The Rho kinase inhibitor Y27632 and inhibition of Rho (C3 exoenzyme, and dominant negative mutant of Rho, RhoT19N) prevented MCP-1-induced stress fiber assembly, reorganization of tight junction proteins and alterations in endothelial permeability. In all, this suggests that a small GTPase Rho and Rho kinase have a pivotal role in MCP-1-induced junction disarrangement. These data are the first to strongly suggest that MCP-1, via CCR2 present on brain endothelial cells, contributes to increased brain endothelial permeability.