Rapid disruption of an astrocyte interaction with the extracellular matrix mediated by integrin alpha 6 beta 4 during focal cerebral ischemia/reperfusion

Endothelial Cell Integrin α6 Regulates Vascular Remodeling Through the PI3K/Akt-eNOS-VEGFA Axis After Stroke

The angiogenic response is essential for the repair of ischemic brain tissue. Integrin α6 (Itga6) expression has been shown to increase under hypoxic conditions and is expressed exclusively in vascular structures; however, its role in post-ischemic angiogenesis remains poorly understood. In this study, we demonstrate that mice with endothelial cell-specific knockout of Itga6 exhibit reduced neovascularization, reduced pericyte coverage on microvessels, and accelerated breakdown of microvascular integrity in the peri-infarct area. In vitro, endothelial cells with ITGA6 knockdown display reduced proliferation, migration, and tube-formation. Mechanistically, we demonstrated that ITGA6 regulates post-stroke angiogenesis through the PI3K/Akt-eNOS-VEGFA axis. Importantly, the specific overexpression of Itga6 in endothelial cells significantly enhanced neovascularization and enhanced the integrity of microvessels, leading to improved functional recovery. Our results suggest that endothelial cell Itga6 plays a crucial role in key steps of post-stroke angiogenesis, and may represent a promising therapeutic target for promoting recovery after stroke.

Increasing reproducibility in preclinical stroke research: the correlation of immunofluorescence intensity measurements and Western blot analyses strongly depends on antibody clonality and tissue pre-treatment in a mouse model of focal cerebral ischemia

In the setting of stroke, ischemia not only impairs neuronal function, but also detrimentally affects the different components of the neurovascular unit, which are shown to be involved in the transition from reversible to long-lasting tissue damage. In this context, the glial proteins myelin basic protein (MBP) and the 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNP) as well as the vasculature-associated basement membrane proteins laminin and collagen IV have been identified as ischemia-sensitive elements. However, available data from immunofluorescence and Western blot analyses are often found to be contradictory, which renders interpretation of the respective data rather difficult. Therefore, the present study investigates the impact of tissue pre-treatment and antibody clonality on immunofluorescence measurements of the mentioned proteins in a highly reproducible model of permanent middle cerebral artery occlusion. Here, immunofluorescence labeling using polyclonal antibodies revealed an increased immunofluorescence intensity of MBP, CNP, laminin and collagen IV in ischemic areas, although Western blot analyses did not reveal increased protein levels. Importantly, contrary to polyclonal antibodies, monoclonal ones did not provide increased fluorescence intensities in ischemic areas. Further, we were able to demonstrate that different ways of tissue pre-treatment including paraformaldehyde fixation and antigen retrieval may not only impact on fluorescence intensity measurements in general, but rather one-sidedly affect either ischemic or unaffected tissue. Therefore, immunofluorescence intensity measurements do not necessarily correlate with the actual protein levels, especially in ischemia-affected tissue and should always be complemented by different techniques to enhance reproducibility and to hopefully overcome the translational roadblock from bench to bedside.

Aging Effects on Optic Nerve Neurodegeneration

Common risk factors for many ocular pathologies involve non-pathologic, age-related damage to the optic nerve. Understanding the mechanisms of age-related changes can facilitate targeted treatments for ocular pathologies that arise at any point in life. In this review, we examine these age-related, neurodegenerative changes in the optic nerve, contextualize these changes from the anatomic to the molecular level, and appreciate their relationship with ocular pathophysiology. From simple structural and mechanical changes at the optic nerve head (ONH), to epigenetic and biochemical alterations of tissue and the environment, multiple age-dependent mechanisms drive extracellular matrix (ECM) remodeling, retinal ganglion cell (RGC) loss, and lowered regenerative ability of respective axons. In conjunction, aging decreases the ability of myelin to preserve maximal conductivity, even with "successfully" regenerated axons. Glial cells, however, regeneratively overcompensate and result in a microenvironment that promotes RGC axonal death. Better elucidating optic nerve neurodegeneration remains of interest, specifically investigating human ECM, RGCs, axons, oligodendrocytes, and astrocytes; clarifying the exact processes of aged ocular connective tissue alterations and their ultrastructural impacts; and developing novel technologies and pharmacotherapies that target known genetic, biochemical, matrisome, and neuroinflammatory markers. Management models should account for age-related changes when addressing glaucoma, diabetic retinopathy, and other blinding diseases.

Cell-specific expression and function of laminin at the neurovascular unit

Laminin, a major component of the basal lamina (BL), is a heterotrimeric protein with many isoforms. In the CNS, laminin is expressed by almost all cell types, yet different cells synthesize distinct laminin isoforms. By binding to its receptors, laminin exerts a wide variety of important functions. However, due to the reciprocal and cell-specific expression of laminin in different cells at the neurovascular unit, its functions in blood-brain barrier (BBB) maintenance and BBB repair after injury are not fully understood. In this review, we focus on the expression and functions of laminin and its receptors in the neurovascular unit under both physiological and pathological conditions. We first briefly introduce the structures of laminin and its receptors. Next, the expression and functions of laminin and its receptors in the CNS are summarized in a cell-specific manner. Finally, we identify the knowledge gap in the field and discuss key questions that need to be answered in the future. Our goal is to provide a comprehensive overview on cell-specific expression of laminin and its receptors in the CNS and their functions on BBB integrity.

Laminin regulates oligodendrocyte development and myelination

Oligodendrocytes are the cells that myelinate axons and provide trophic support to neurons in the CNS. Their dysfunction has been associated with a group of disorders known as demyelinating diseases, such as multiple sclerosis. Oligodendrocytes are derived from oligodendrocyte precursor cells, which differentiate into premyelinating oligodendrocytes and eventually mature oligodendrocytes. The development and function of oligodendrocytes are tightly regulated by a variety of molecules, including laminin, a major protein of the extracellular matrix. Accumulating evidence suggests that laminin actively regulates every aspect of oligodendrocyte biology, including survival, migration, proliferation, differentiation, and myelination. How can laminin exert such diverse functions in oligodendrocytes? It is speculated that the distinct laminin isoforms, laminin receptors, and/or key signaling molecules expressed in oligodendrocytes at different developmental stages are the reasons. Understanding molecular targets and signaling pathways unique to each aspect of oligodendrocyte biology will enable more accurate manipulation of oligodendrocyte development and function, which may have implications in the therapies of demyelinating diseases. Here in this review, we first introduce oligodendrocyte biology, followed by the expression of laminin and laminin receptors in oligodendrocytes and other CNS cells. Next, the functions of laminin in oligodendrocyte biology, including survival, migration, proliferation, differentiation, and myelination, are discussed in detail. Last, key questions and challenges in the field are discussed. By providing a comprehensive review on laminin's roles in OL lineage cells, we hope to stimulate novel hypotheses and encourage new research in the field.

Neuroinflammation and fibrosis in stroke: The good, the bad and the ugly

Stroke is the leading cause of death and the main cause of disability in surviving patients. The detrimental interaction between immune cells, glial cells, and matrix components in stroke pathology results in persistent inflammation that progresses to fibrosis. A substantial effort is being directed toward understanding the exact neuroinflammatory events that take place as a result of stroke. The initiation of a potent cytokine response, along with immune cell activation and infiltration in the ischemic core, has massive acute deleterious effects, generally exacerbated by comorbid inflammatory conditions. There is secondary neuroinflammation that promotes further injury, resulting in cell death, but conversely plays a beneficial role, by promoting recovery. This highlights the need for a better understanding of the neuroinflammatory and fibrotic processes, as well as the need to identify new mechanisms and potential modulators. In this review, we summarize several aspects of stroke-induced inflammation, fibrosis, and include a discussion of cytokine inhibitors/inducers, immune cells, and fibro-inflammation signaling inhibitors in order to identify new pharmacological means of intervention.

The Diversity of Intermediate Filaments in Astrocytes

Despite the remarkable complexity of the individual neuron and of neuronal circuits, it has been clear for quite a while that, in order to understand the functioning of the brain, the contribution of other cell types in the brain have to be accounted for. Among glial cells, astrocytes have multiple roles in orchestrating neuronal functions. Their communication with neurons by exchanging signaling molecules and removing molecules from extracellular space takes place at several levels and is governed by different cellular processes, supported by multiple cellular structures, including the cytoskeleton. Intermediate filaments in astrocytes are emerging as important integrators of cellular processes. Astrocytes express five types of intermediate filaments: glial fibrillary acidic protein (GFAP); vimentin; nestin; synemin; lamins. Variability, interactions with different cellular structures and the particular roles of individual intermediate filaments in astrocytes have been studied extensively in the case of GFAP and vimentin, but far less attention has been given to nestin, synemin and lamins. Similarly, the interplay between different types of cytoskeleton and the interaction between the cytoskeleton and membranous structures, which is mediated by cytolinker proteins, are understudied in astrocytes. The present review summarizes the basic properties of astrocytic intermediate filaments and of other cytoskeletal macromolecules, such as cytolinker proteins, and describes the current knowledge of their roles in normal physiological and pathological conditions.

Systems-wide analysis unravels the new roles of CCM signal complex (CSC)

Cerebral cavernous malformations (CCMs) are characterized by abnormally dilated intracranial capillaries that result in increased susceptibility to stroke. Three genes have been identified as causes of CCMs; KRIT1 (CCM1), MGC4607 (CCM2) and PDCD10 (CCM3); one of them is disrupted in most CCM cases. It was demonstrated that both CCM1 and CCM3 bind to CCM2 to form a CCM signaling complex (CSC) to modulate angiogenesis. In this report, we deployed both RNA-seq and proteomic analysis of perturbed CSC after depletion of one of three CCM genes to generate interactomes for system-wide studies. Our results demonstrated a unique portrait detailing alterations in angiogenesis and vascular integrity. Interestingly, only in-direct overlapped alterations between RNA and protein levels were detected, supporting the existence of multiple layers of regulation in CSC cascades. Notably, this is the first report identifying that both β4 integrin and CAV1 signaling are downstream of CSC, conveying the angiogenic signaling. Our results provide a global view of signal transduction modulated by the CSC, identifies novel regulatory signaling networks and key cellular factors associated with CSC.

The post-cardiac arrest syndrome: A case for lung-brain coupling and opportunities for neuroprotection

Systemic inflammation and multi-organ failure represent hallmarks of the post-cardiac arrest syndrome (PCAS) and predict severe neurological injury and often fatal outcomes. Current interventions for cardiac arrest focus on the reversal of precipitating cardiac pathologies and the implementation of supportive measures with the goal of limiting damage to at-risk tissue. Despite the widespread use of targeted temperature management, there remain no proven approaches to manage reperfusion injury in the period following the return of spontaneous circulation. Recent evidence has implicated the lung as a moderator of systemic inflammation following remote somatic injury in part through effects on innate immune priming. In this review, we explore concepts related to lung-dependent innate immune priming and its potential role in PCAS. Specifically, we propose and investigate the conceptual model of lung-brain coupling drawing from the broader literature connecting tissue damage and acute lung injury with cerebral reperfusion injury. Subsequently, we consider the role that interventions designed to short-circuit lung-dependent immune priming might play in improving patient outcomes following cardiac arrest and possibly other acute neurological injuries.

Angioneurins - Key regulators of blood-brain barrier integrity during hypoxic and ischemic brain injury

The loss of blood-brain barrier (BBB) integrity leading to vasogenic edema and brain swelling is a common feature of hypoxic/ischemic brain diseases such as stroke, but is also central to the etiology of other CNS disorders. In the past decades, numerous proteins, belonging to the family of angioneurins, have gained increasing attention as potential therapeutic targets for ischemic stroke, but also other CNS diseases attributed to BBB dysfunction. Angioneurins encompass mediators that affect both neuronal and vascular function. Recently, increasing evidence has been accumulated that certain angioneurins critically determine disease progression and outcome in stroke among others through multifaceted effects on the compromised BBB. Here, we will give a concise overview about the family of angioneurins. We further describe the most important cellular and molecular components that contribute to structural integrity and low permeability of the BBB under steady-state conditions. We then discuss BBB alterations in ischemic stroke, and highlight underlying cellular and molecular mechanisms. For the most prominent angioneurin family members including vascular endothelial growth factors, angiopoietins, platelet-derived growth factors and erythropoietin, we will summarize current scientific literature from experimental studies in animal models, and if available from clinical trials, on the following points: (i) spatiotemporal expression of these factors in the healthy and hypoxic/ischemic CNS, (ii) impact of loss- or gain-of-function during cerebral hypoxia/ischemia for BBB integrity and beyond, and (iii) potential underlying molecular mechanisms. Moreover, we will highlight novel therapeutic strategies based on the activation of endogenous angioneurins that might improve BBB dysfuntion during ischemic stroke.

Laminins and their receptors in the CNS

Laminin, an extracellular matrix protein, is widely expressed in the central nervous system (CNS). By interacting with integrin and non-integrin receptors, laminin exerts a large variety of important functions in the CNS in both physiological and pathological conditions. Due to the existence of many laminin isoforms and their differential expression in various cell types in the CNS, the exact functions of each individual laminin molecule in CNS development and homeostasis remain largely unclear. In this review, we first briefly introduce the structure and biochemistry of laminins and their receptors. Next, the dynamic expression of laminins and their receptors in the CNS during both development and in adulthood is summarized in a cell-type-specific manner, which allows appreciation of their functional redundancy/compensation. Furthermore, we discuss the biological functions of laminins and their receptors in CNS development, blood-brain barrier (BBB) maintenance, neurodegeneration, stroke, and neuroinflammation. Last, key challenges and potential future research directions are summarized and discussed. Our goals are to provide a synthetic review to stimulate future studies and promote the formation of new ideas/hypotheses and new lines of research in this field.

Tissue linkage through adjoining basement membranes: The long and the short term of it

Basement membranes (BMs) are thin dense sheets of extracellular matrix that surround most tissues. When the BMs of neighboring tissues come into contact, they usually slide along one another and act to separate tissues and organs into distinct compartments. However, in certain specialized regions, the BMs of neighboring tissues link, helping to bring tissues together. These BM connections can be transient, such as during tissue fusion events in development, or long-term, as with adult tissues involved with filtration, including the blood brain barrier and kidney glomerulus. The transitory nature of these connections in development and the complexity of tissue filtration systems in adults have hindered the understanding of how juxtaposed BMs fasten together. The recent identification of a BM-BM adhesion system in C. elegans, termed B-LINK (BM linkage), however, is revealing cellular and extracellular matrix components of a nascent tissue adhesion system. We discuss insights gained from studying the B-LINK tissue adhesion system in C. elegans, compare this adhesion with other BM-BM connections in Drosophila and vertebrates, and outline important future directions towards elucidating this fascinating and poorly understood mode of adhesion that joins neighboring tissues.

Roles of blood-brain barrier integrins and extracellular matrix in stroke

Ischemicstroke is a leading cause of death and disability in the United States, but recent advances in treatments [i.e., endovascular thrombectomy and tissue plasminogen activator (t-PA)] that target the stroke-causing blood clot, while improving overall stroke mortality rates, have had much less of an impact on overall stroke morbidity. This may in part be attributed to the lack of therapeutics targeting reperfusion-induced injury after the blood clot has been removed, which, if left unchecked, can expand injury from its core into the surrounding at risk tissue (penumbra). This occurs in two phases of increased permeability of the blood-brain barrier, a physical barrier that under physiologic conditions regulates brain influx and efflux of substances and consists of tight junction forming endothelial cells (and transporter proteins), astrocytes, pericytes, extracellular matrix, and their integrin cellular receptors. During, embryonic development, maturity, and following stroke reperfusion, cerebral vasculature undergoes significant changes including changes in expression of integrins and degradation of surrounding extracellular matrix. Integrins, heterodimers with α and β subunits, and their extracellular matrix ligands, a collection of proteoglycans, glycoproteins, and collagens, have been modestly studied in the context of stroke compared with other diseases (e.g., cancer). In this review, we describe the effect that various integrins and extracellular matrix components have in embryonic brain development, and how this changes in both maturity and in the poststroke environment. Particular focus will be on how these changes in integrins and the extracellular matrix affect blood-brain barrier components and their potential as diagnostic and therapeutic targets for ischemic stroke.

Transcriptomic Study Reveals Recovery of Impaired Astrocytes Contribute to Neuroprotective Effects of Danhong Injection Against Cerebral Ischemia/Reperfusion-Induced Injury

Danhong Injection (DHI) is widely used in clinics for treating cardiovascular and cerebrovascular diseases in China. However, the mode of action of DHI for neuroprotection remains unclear. In the present study, we deemed to investigate the effects of DHI on a rat model of cerebral ischemia/reperfusion injury (IRI) with an emphasis on its regulated gene profile obtained from microarray assays. Firstly, we showed that a 14-day DHI treatment effectively ameliorated severity of neurological deficits, reduced size of ischemic damage, improved status of oxidation stress, as well as systemic inflammation for IRI rats, along with which was a pronounced reduced cell infiltration in the area of periaqueductal gray matter. Secondly, bioinformatic analyses for the 429 differentially expressed genes (DEGs) regulated by DHI treatment pointed out ECM–receptor interaction, neuroactive ligand–receptor interaction, and endocytosis as the top three biological processes, while Toll-like recptor 4 (TLR4) as the most relavant singaling molecule. Lastly, we provided evidences showing that DHI might directly protect primary astrocytes from oxygen and glucose deprivation/re-oxygenation (OGD/Re) injury, the effects of which was associated with LAMC2 and ADRB3, two DEGs related to the top three biological processes according to transcriptomic analysis. In conlusion, we reported that DHI might work through maintaining the integrity for brain–blood barrier and to regulate TLR4-related signaling pathway to diminish the inflammation, therefore, effectively improved the outcomes of IRI. Our findings suggested that the attenuated astrocytic dysfunction could be a novel mechanism contributing to the neuroprotective effects of DHI against cerebral ischemia/reperfusion-induced damage.

Astrocytes in Migration

Cell migration is a fundamental phenomenon that underlies tissue morphogenesis, wound healing, immune response, and cancer metastasis. Great progresses have been made in research methodologies, with cell migration identified as a highly orchestrated process. Brain is considered the most complex organ in the human body, containing many types of neural cells with astrocytes playing crucial roles in monitoring normal functions of the central nervous system. Astrocytes are mostly quiescent under normal physiological conditions in the adult brain but become migratory after injury. Under most known pathological conditions in the brain, spinal cord and retina, astrocytes are activated and become hypertrophic, hyperplastic, and up-regulating GFAP based on the grades of severity. These three observations are the hallmark in glia scar formation-astrogliosis. The reactivation process is initiated with structural changes involving cell process migration and ended with cell migration. Detailed mechanisms in astrocyte migration have not been studied extensively and remain largely unknown. Here, we therefore attempt to review the mechanisms in migration of astrocytes.

β4 integrin is not essential for localization of hemidesmosome proteins plectin and CD151 in cerebral vessels

Objective:

In the central nervous system (CNS), β4 integrin is predominantly expressed by endothelial cells lining arterioles. As β4 integrin plays an essential role in epithelial tissues, organizing structural proteins into specialized adhesive structures called hemidesmosomes (HD), the aim of this study was to determine whether it plays a similar role in CNS endothelium.

Methods:

Dual-immunofluorescence was used to examine the relationship between β4 integrin expression and co-expression of the HD proteins plectin and CD151 in frozen sections of mouse brain, both under normoxic (control) conditions and following chronic mild hypoxia. The requirement of β4 integrin for the localization of HD proteins was examined in transgenic mice lacking β4 integrin expression specifically in endothelial cells (β4-EC-KO mice).

Results:

Immunofluorescence revealed that in the normal adult CNS, plectin and CD151 strongly co-localized with β4 integrin in arterioles. However, in the chronic mild hypoxia model, in which extensive cerebrovascular remodeling is observed, plectin and CD151 were strongly upregulated on all cerebral vessels, but surprisingly, in capillaries, this occurred in a β4 integrin-independent manner. Unexpectedly, absence of endothelial β4 integrin (in β4-EC-KO mice) had no impact on the expression level or distribution pattern of plectin and CD151 within stable or remodeling cerebral vessels.

Conclusions:

These results demonstrate that the HD proteins plectin and CD151 are closely associated with β4 integrin on arterioles in normal brain, and are strongly upregulated on remodeling blood vessels. However, unlike its described role in the epidermis, β4 integrin is not essential for localization or regulation of expression of plectin and CD151 in cerebral vessels.

Factors controlling permeability of the blood-brain barrier

As the primary protective barrier for neurons in the brain, the blood-brain barrier (BBB) exists between the blood microcirculation system and the brain parenchyma. The normal BBB integrity is essential in protecting the brain from systemic toxins and maintaining the necessary level of nutrients and ions for neuronal function. This integrity is mediated by structural BBB components, such as tight junction proteins, integrins, annexins, and agrin, of a multicellular system including endothelial cells, astrocytes, pericytes, etc. BBB dysfunction is a significant contributor to the pathogeneses of a variety of brain disorders. Many signaling factors have been identified to be able to control BBB permeability through regulating the structural components. Among those signaling factors are inflammatory mediators, free radicals, vascular endothelial growth factor, matrix metalloproteinases, microRNAs, etc. In this review, we provide a summary of recent progress regarding these structural components and signaling factors, relating to their roles in various brain disorders. Attention is also devoted to recent research regarding impact of pharmacological agents such as isoflurane on BBB permeability and how iron ion passes across BBB. Hopefully, a better understanding of the factors controlling BBB permeability helps develop novel pharmacological interventions of BBB hyperpermeability under pathological conditions.

Cross-species Transcriptomic Comparison of In Vitro and In Vivo Mammalian Neural Cells

The mammalian brain is characterized by distinct classes of cells that differ in morphology, structure, signaling, and function. Dysregulation of gene expression in these cell populations leads to various neurological disorders. Neural cells often need to be acutely purified from animal brains for research, which requires complicated procedure and specific expertise. Primary culture of these cells in vitro is a viable alternative, but the differences in gene expression of cells grown in vitro and in vivo remain unclear. Here, we cultured three major neural cell classes of rat brain (ie, neurons, astrocytes, and oligodendrocyte precursor cells [OPCs]) obtained from commercial sources. We measured transcript abundance of these cell types by RNA sequencing (RNA-seq) and compared with their counterparts acutely purified from mouse brains. Cross-species RNA-seq data analysis revealed hundreds of genes that are differentially expressed between the cultured and acutely purified cells. Astrocytes have more such genes compared to neurons and OPCs, indicating that signaling pathways are greatly perturbed in cultured astrocytes. This dataset provides a powerful resource to demonstrate the similarities and differences of biological processes in mammalian neural cells grown in vitro and in vivo at the molecular level.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Blood-letting punctures at twelve Jing-Well points of the hand can treat cerebral ischemia in a similar manner to mannitol

A rat model of middle cerebral artery permanent occlusion was established using the modified Longa method. Successfully established model animals were treated by blood-letting puncture at twelve Jing-Well points of the hand, and/or by injecting mannitol into the caudal vein twice daily. Brain tissue was collected at 24, 48 and 72 hours after modeling, and blood was collected through the retinal vein before Evans blue was injected, approximately 1 hour prior to harvesting of brain tissue. Results showed that Evans blue leakage into brain tissue and serum nitric oxide synthase activity were significantly increased in model rats. Treatment with blood-letting punctures at twelve Jing-Well points of the hand and/or injection of mannitol into the caudal vein reduced the amount of Evans blue leakage into the brain tissue and serum nitric oxide synthase activity to varying degrees. There was no significant difference between single treatment and combined treatment. Experimental findings indicate that blood-letting punctures at twelve Jing-Well points of the hand can decrease blood-brain barrier permeability and serum nitric oxide synthase activity in rats following middle cerebral artery occlusion, and its effect is similar to that of mannitol injection alone and Jing-Well points plus mannitol injection.

Pathophysiogenesis of mesial temporal lobe epilepsy: is prevention of damage antiepileptogenic?

Temporal lobe epilepsy (TLE) is frequently associated with hippocampal sclerosis, possibly caused by a primary brain injury that occurred a long time before the appearance of neurological symptoms. This type of epilepsy is characterized by refractoriness to drug treatment, so to require surgical resection of mesial temporal regions involved in seizure onset. Even this last therapeutic approach may fail in giving relief to patients. Although prevention of hippocampal damage and epileptogenesis after a primary event could be a key innovative approach to TLE, the lack of clear data on the pathophysiological mechanisms leading to TLE does not allow any rational therapy. Here we address the current knowledge on mechanisms supposed to be involved in epileptogenesis, as well as on the possible innovative treatments that may lead to a preventive approach. Besides loss of principal neurons and of specific interneurons, network rearrangement caused by axonal sprouting and neurogenesis are well known phenomena that are integrated by changes in receptor and channel functioning and modifications in other cellular components. In particular, a growing body of evidence from the study of animal models suggests that disruption of vascular and astrocytic components of the blood-brain barrier takes place in injured brain regions such as the hippocampus and piriform cortex. These events may be counteracted by drugs able to prevent damage to the vascular component, as in the case of the growth hormone secretagogue ghrelin and its analogues. A thoroughly investigation on these new pharmacological tools may lead to design effective preventive therapies.

Extracellular proteolytic pathophysiology in the neurovascular unit after stroke

The NINDS Stroke Progress Review Group recommended a shift in emphasis from a purely neurocentric view of cell death towards a more integrative approach whereby responses in all brain cells and matrix are considered. The neurovascular unit (fundamentally comprising endothelium, astrocyte, and neuron) provides a conceptual framework where cell-cell and cell-matrix signaling underlies the overall tissue response to stroke and its treatments. Here, we briefly review recent data on extracellular proteolytic dysfunction in the neurovascular unit after a stroke. The breakdown of neurovascular matrix initiates blood-brain barrier disruption with edema and/or hemorrhage. Endothelial dysfunction amplifies inflammatory responses. Perturbation of cell-matrix homeostasis triggers multiple cell death pathways. Interactions between the major classes of extracellular proteases from the plasminogen and matrix metalloprotease families may underlie processes responsible for some of the hemorrhagic complications of thrombolytic stroke therapy. Targeting the proteolytic imbalance within the neurovascular unit may provide new approaches for improving the safety and efficacy of thrombolytic reperfusion therapy for stroke.

Regulation and dysregulation of astrocyte activation and implications in tumor formation

Astrocytic activation is a cellular response to disturbances of the central nervous system (CNS). Recent advances in cellular and molecular biology have demonstrated the remarkable changes in molecular signaling, morphology, and metabolism that occur during astrocyte activation. Based on these studies, it has become clear that the astrocyte activation process is regulated by a variety of signaling pathways, which result in metabolic support, wound healing and scar formation. While normal astrocyte activation pathways drive homeostasis and/or repair in the CNS, dysregulation of these pathways can lead to astrocyte abnormalities, including glioma formation with similar phenotypes as reactive astrocytes. We review the principle pathways responsible for astrocytic activation, as well as their potential contribution to tumor formation in the CNS.

Hemostasis and alterations of the central nervous system

Modulation of coagulation has been successfully applied to ischemic disorders of the central nervous system (CNS). Some components of the coagulation system have been identified in the CNS, yet with limited exception their functions have not been clearly defined. Little is known about how events within the cerebral tissues affect hemostasis. Nonetheless, the interaction between cerebral cells and vascular hemostasis and the possibility that endogenous coagulation factors can participate in functions within the neurovascular unit provide intriguing possibilities for deeper insight into CNS functions and the potential for treatment of CNS injuries. Here, we consider the expression of coagulation factors in the CNS, the coagulopathy associated with focal cerebral ischemia (and its relationship to hemorrhagic transformation), the use of recombinant tissue plasminogen activator (rt-PA) in ischemic stroke and its study in animal models, the impact of rt-PA on neuron and CNS structure and function, and matrix protease generation and matrix degradation and hemostasis. Interwoven among these topics is evidence for interactions of coagulation factors with and within the CNS. How activation of hemostasis occurs in the cerebral tissues and how the brain responds are difficult questions that offer many research possibilities.

Glial influence on the blood brain barrier

The Blood Brain Barrier (BBB) is a specialized vascular structure tightly regulating central nervous system (CNS) homeostasis. Endothelial cells are the central component of the BBB and control of their barrier phenotype resides on astrocytes and pericytes. Interactions between these cells and the endothelium promote and maintain many of the physiological and metabolic characteristics that are unique to the BBB. In this review we describe recent findings related to the involvement of astroglial cells, including radial glial cells, in the induction of barrier properties during embryogenesis and adulthood. In addition, we describe changes that occur in astrocytes and endothelial cells during injury and inflammation with a particular emphasis on alterations of the BBB phenotype. GLIA 2013;61:1939–1958

Long-term remodeling of rat pial microcirculation after transient middle cerebral artery occlusion and reperfusion

OBJECTIVE

The aim of this study was to assess the in vivo structural and functional remodeling of pial arteriolar networks in the ischemic area of rats submitted to transient middle cerebral artery occlusion (MCAO) and different time intervals of reperfusion.

METHODS AND RESULTS

Two closed cranial windows were implanted above the left and right parietal cortex to observe pial microcirculation by fluorescence microscopy. The geometric characteristics of pial arteriolar networks, permeability increase, leukocyte adhesion and capillary density were analyzed after 1 h or 1, 7, 14 or 28 days of reperfusion. MCAO and 1-hour reperfusion caused marked microvascular changes in pial networks. The necrotic core was devoid of vessels, while the penumbra area presented a few arterioles, capillaries and venules with severe neuronal damage. Penumbra microvascular permeability and leukocyte adhesion were pronounced. At 7 days of reperfusion, new pial arterioles were organized in anastomotic vessels, overlapping the ischemic core and in penetrating pial arterioles. Vascular remodeling caused different arteriolar rearrangement up to 28 days of reperfusion and animals gradually regained their motor and sensory functions.

CONCLUSIONS

Transient MCAO-induced pial-network remodeling is characterized by arteriolar anastomotic arcades. Remodeling mechanisms appear to be accompanied by an increased expression of nitric oxide synthases.

Laminins containing the β2 and γ3 chains regulate astrocyte migration and angiogenesis in the retina

Pathologies of retinal blood vessels are among the major causes of blindness worldwide. A key cell type that regulates retinal vascular development is the astrocyte. Generated extrinsically to the retina, astrocytes migrate into the retina through the optic nerve head. Even though there is a strong correlation between astrocyte distribution and retinal vascular development, the factors that guide astrocytes into the retina remain unclear. In this study, we show that astrocytes migrate within a laminin-containing basement membrane - the inner limiting membrane. Genetic deletion of the laminin β2 and γ3 chains affects astrocyte migration and spatial distribution. We show that laminins act as haptotactic factors in vitro in an isoform-specific manner, inducing astrocyte migration and promoting astrocyte differentiation. The addition of exogenous laminins to laminin-null retinal explants rescues astrocyte migration and spatial patterning. Furthermore, we show that the loss of laminins reduces β1 integrin expression in astrocytes. Culturing laminin-null retinal astrocytes on laminin substrates restores focal localization of β1 integrin. Finally, we show that laminins containing β2 and γ3 chains regulate subsequent retinal blood vessel growth and maintain vascular integrity. These in vivo and in vitro studies demonstrate clearly that laminins containing β2 and γ3 chains are indispensable for migration and spatial organization of astrocytes and that they play a crucial role during retinal angiogenesis in vivo.

Magnetic resonance imaging of ischemia viability thresholds and the neurovascular unit

Neuroimaging has improved our understanding of the evolution of stroke at discreet time points helping to identify irreversibly damaged and potentially reversible ischemic brain. Neuroimaging has also contributed considerably to the basic premise of acute stroke therapy which is to salvage some portion of the ischemic region from evolving into infarction, and by doing so, maintaining brain function and improving outcome. The term neurovascular unit (NVU) broadens the concept of the ischemic penumbra by linking the microcirculation with neuronal-glial interactions during ischemia reperfusion. Strategies that attempt to preserve the individual components (endothelium, glia and neurons) of the NVU are unlikely to be helpful if blood flow is not fully restored to the microcirculation. Magnetic resonance imaging (MRI) is the foremost imaging technology able to bridge both basic science and the clinic via non-invasive real time high-resolution anatomical delineation of disease manifestations at the molecular and ionic level. Current MRI based technologies have focused on the mismatch between perfusion-weighted imaging (PWI) and diffusion weighted imaging (DWI) signals to estimate the tissue that could be saved if reperfusion was achieved. Future directions of MRI may focus on the discordance of recanalization and reperfusion, providing complimentary pathophysiological information to current compartmental paradigms of infarct core (DWI) and penumbra (PWI) with imaging information related to cerebral blood flow, BBB permeability, inflammation, and oedema formation in the early acute phase. In this review we outline advances in our understanding of stroke pathophysiology with imaging, transcending animal stroke models to human stroke, and describing the potential translation of MRI to image important interactions relevant to acute stroke at the interface of the neurovascular unit.

Endothelial β4 integrin is predominantly expressed in arterioles, where it promotes vascular remodeling in the hypoxic brain

OBJECTIVE

Laminin is a major component of the vascular basal lamina, implying that laminin receptors, such as α6β1 and α6β4 integrins, may regulate vascular remodeling and homeostasis. Previous studies in the central nervous system have shown that β4 integrin is expressed by only a fraction of cerebral vessels, but defining the vessel type and cellular source of β4 integrin has proved controversial. The goal of this study was to define the class of vessel and cell type expressing β4 integrin in cerebral vessels and to examine its potential role in vascular remodeling.

APPROACH AND RESULTS

Dual-immunofluorescence showed that β4 integrin is expressed predominantly in arterioles, both in the central nervous system and in peripheral organs. Cell-specific knockouts of β4 integrin revealed that β4 integrin expression in cerebral vessels is derived from endothelial cells, not astrocytes or smooth muscle cells. Lack of endothelial β4 integrin had no effect on vascular development, integrity, or endothelial proliferation, but in the hypoxic central nervous system, its absence led to defective arteriolar remodeling and associated transforming growth factor-β signaling.

CONCLUSIONS

These results define high levels of β4 integrin in arteriolar endothelial cells and demonstrate a novel link among β4 integrin, transforming growth factor-β signaling, and arteriolar remodeling in cerebral vessels.

Disruption of dystroglycan-laminin interactions modulates water uptake by astrocytes

Cerebral edema is a serious complication of ischemic brain injury. Cerebral edema includes accumulation of extracellular fluid due to leakage of the brain's microvessel permeability barrier, and swelling of astrocytes as they absorb water from the extracellular space. Expression of matrix adhesion receptors in brain microvessels decreases in ischemic stroke; this contributes to increased microvessel permeability and detachment of astrocytes from the extracellular matrix (ECM). Since loss of the astrocyte adhesion receptor dystroglycan has been associated with disrupted polarization of ion and water channels, we hypothesized that adhesion of astrocytes to the ECM contributes to regulation of water uptake, and that disruption of matrix adhesion impairs the ability of astrocytes to direct water transport. To test this hypothesis, the capacity of astrocytes to take up water was measured using a fluorescence self-quenching assay under both oxygen/glucose deprivation (OGD) and direct antibody-mediated blockade of α-dystroglycan. Both conditions decreased the rate of water uptake. Moreover, inhibiting proteolytic cleavage of dystroglycan that occurs in OGD abrogated the effect of OGD, but not direct blockade of α-dystroglycan, indicating that interfering with dystroglycan-matrix binding itself affects water uptake. Activation of extracellular signal-related kinase (ERK) by OGD was dependent on α-dystroglycan binding, and inhibition of ERK activity with U0126 abrogated the loss of water uptake following OGD. These studies demonstrate for the first time that water uptake in astrocytes is regulated by dystroglycan-dependent signaling associated with matrix adhesion. This presents a novel potential approach to the treatment of cerebral edema.

Aging and the neurovascular unit

With the demonstration that acute recanalization of obstructed symptomatic cerebral arteries during ischemic stroke can result in substantial improvement in clinical outcome, the variability in clinical responses, and in hemorrhagic transformation, requires attention. This short review addresses the effect of aging and amyloid deposition disease on microvessel integrity, interactions within the neurovascular unit, cerebral tissue susceptibility to ischemic injury, and postischemic inflammation, and ultimately on the outcomes and safety of acute recanalization during ischemic stroke. Microvessels and neighboring neurons respond simultaneously to focal ischemia. The cellular components and matrix barriers of the neurovascular unit all respond to ischemia; however, their coordinate interactions are not understood. Furthermore, there is little known about the cell-cell and cell-matrix interactions within the unit, or about the effect of β-amyloid on microvessel responses during ischemia. These considerations indicate the need for a coordinated research effort to understand the origins of the variability in recanalization outcome.

Vulnerability of the developing brain to hypoxic-ischemic damage: contribution of the cerebral vasculature to injury and repair?

As clinicians attempt to understand the underlying reasons for the vulnerability of different regions of the developing brain to injury, it is apparent that little is known as to how hypoxia-ischemia may affect the cerebrovasculature in the developing infant. Most of the research investigating the pathogenesis of perinatal brain injury following hypoxia-ischemia has focused on excitotoxicity, oxidative stress and an inflammatory response, with the response of the developing cerebrovasculature receiving less attention. This is surprising as the presentation of devastating and permanent injury such as germinal matrix-intraventricular haemorrhage (GM-IVH) and perinatal stroke are of vascular origin, and the origin of periventricular leukomalacia (PVL) may also arise from poor perfusion of the white matter. This highlights that cerebrovasculature injury following hypoxia could primarily be responsible for the injury seen in the brain of many infants diagnosed with hypoxic-ischemic encephalopathy (HIE). Interestingly the highly dynamic nature of the cerebral blood vessels in the fetus, and the fluctuations of cerebral blood flow and metabolic demand that occur following hypoxia suggest that the response of blood vessels could explain both regional protection and vulnerability in the developing brain. However, research into how blood vessels respond following hypoxia-ischemia have mostly been conducted in adult models of ischemia or stroke, further highlighting the need to investigate how the developing cerebrovasculature responds and the possible contribution to perinatal brain injury following hypoxia. This review discusses the current concepts on the pathogenesis of perinatal brain injury, the development of the fetal cerebrovasculature and the blood brain barrier (BBB), and key mediators involved with the response of cerebral blood vessels to hypoxia.

Extracellular matrix and matrix receptors in blood-brain barrier formation and stroke

The blood-brain barrier (BBB) is formed primarily to protect the brain microenvironment from the influx of plasma components, which may disturb neuronal functions. The BBB is a functional unit that consists mainly of specialized endothelial cells (ECs) lining the cerebral blood vessels, astrocytes, and pericytes. The BBB is a dynamic structure that is altered in neurologic diseases, such as stroke. ECs and astrocytes secrete extracellular matrix (ECM) proteins to generate and maintain the basement membranes (BMs). ECM receptors, such as integrins and dystroglycan, are also expressed at the brain microvasculature and mediate the connections between cellular and matrix components in physiology and disease. ECM proteins and receptors elicit diverse molecular signals that allow cell adaptation to environmental changes and regulate growth and cell motility. The composition of the ECM is altered upon BBB disruption and directly affects the progression of neurologic disease. The purpose of this review is to discuss the dynamic changes of ECM composition and integrin receptor expression that control BBB functions in physiology and pathology.

Inflammation modulates expression of laminin in the central nervous system following ischemic injury

BACKGROUND

Ischemic stroke induces neuronal death in the core of the infarct within a few hours and the secondary damage in the surrounding regions over a long period of time. Reduction of inflammation using pharmacological reagents has become a target of research for the treatment of stroke. Cyclooxygenase 2 (COX-2), a marker of inflammation, is induced during stroke and enhances inflammatory reactions through the release of enzymatic products, such as prostaglandin (PG) E2.

METHODS

Wild-type (WT) and COX-2 knockout (COX-2KO) mice were subjected to middle cerebral artery occlusion (MCAO). Additionally, brain slices derived from these mice or brain microvascular endothelial cells (BMECs) were exposed to oxygen-glucose deprivation (OGD) conditions. The expression levels of extracellular matrix (ECM) proteins were assessed and correlated with the state of inflammation.

RESULTS

We found that components of the ECM, and specifically laminin, are transiently highly upregulated on endothelial cells after MCAO or OGD. This upregulation is not observed in COX-2KO mice or WT mice treated with COX-2 inhibitor, celecoxib, suggesting that COX-2 is associated with changes in the levels of laminins.

CONCLUSIONS

Taken together, we report that transient ECM remodeling takes place early after stroke and suggest that this increase in ECM protein expression may constitute an effort to revascularize and oxygenate the tissue.

The neurovascular unit and combination treatment strategies for stroke

Tissue plasminogen activator (tPA) administered within 4.5h of symptom onset restores cerebral blood flow (CBF) and promotes neurological recovery of stroke patients. However, the narrow therapeutic time window and the risk of intracerebral hemorrhage after tPA treatment pose major hurdles to its clinical usage. In light of the failures of neuroprotective therapies in clinical trials, emerging concepts suggest that neuroprotection alone without restoration of tissue perfusion and vascular integrity may not be adequate for treatment of acute stroke. Here we review evidence of the use of adjuvant pharmacological agents to extend the therapeutic window for tPA via targeting the neurovascular unit and the underlying mechanisms of the combination therapy in experimental stroke.

Use of Cre-lox technology to analyze integrin functions in astrocytes

Astrocytes communicate with the vascular endothelium via direct cell-cell contacts as well as a variety of secreted growth factors and extracellular matrix (ECM) proteins. Integrins are heterodimeric cell surface receptors for ECM protein ligands, and many integrin subunits are expressed in astrocytes. Here, we will discuss gene deletion strategies in mice that have deciphered functions for specific integrins in astrocyte-endothelial cell adhesion and signaling. Specifically, we will detail how Cre-lox molecular genetic techniques have revealed important roles for integrin αvβ8 in regulating cerebral blood vessel development and homeostasis. First, we will detail how to generate Cre-lox mutant mouse models that our group and others have used to study αvβ8 integrin in embryonic astroglial progenitors and postnatal astrocytes. Second, we will discuss how viral-delivered Cre can be used to acutely delete integrin genes in astrocytes within defined anatomic regions of the brain. Third, detailed in vivo methods to verify Cre-mediated gene recombination in astrocytes will be presented. Lastly, we will present one experimental strategy to determine how integrin gene deletion affects astrocyte-endothelial cell coupling in the CNS. While this review focuses on the generation and characterization of mice lacking αvβ8 integrin, these experimental strategies can be expanded to analyze other cell adhesion and signaling genes important for astroglial-mediated regulation of blood vessel development and homeostasis.

Polymorphisms of integrin, alpha 6 contribute to the development and neurologic symptoms of intracerebral hemorrhage in korean population

OBJECTIVE

The extracellular matrix (ECM) and cell adhesion molecules play crucial roles in angiogenesis, apoptosis, thrombosis, and inflammation, and also contribute to the pathogenesis of stroke. Integrin, alpha 6 (ITGA6) is a member of ECM adhesion receptors. We investigated whether two single nucleotide polymorphisms (SNPs) (rs11895564, Ala380Thr; rs2293649, Asp694Asp) of ITGA6 were associated with the development and clinical phenotypes of intracerebral hemorrhage (ICH) and ischemic stroke (IS).

METHODS

We enrolled 199 stroke (78 ICH and 121 IS) and 291 control subjects. Stroke patients were divided into subgroups according to the scores of the National Institutes of Health Stroke Survey (NIHSS, <6 and ≥6) and Modified Barthel Index (MBI, <60 and ≥60). SNPStats, SNPAnalyzer, and Helixtree programs were used to calculate odds ratios, 95% confidence intervals, and p values. Multiple logistic regression models were used to analyze genetic data.

RESULTS

A missense SNP rs11895564 was associated with the development of ICH (p=0.026 in codominant2, p=0.013 in recessive, p=0.02 in log-additive models; p=0.041 in allele distributions). The A allele frequency of rs11895564 was higher in the ICH group (13.5%) than in the control group (8.1%). In the clinical phenotypes, rs11895564 and rs2293649 showed significant associations in the MBI scores of IS (p=0.014 in codominant1 model; p=0.02 in allele distributions) and NIHSS scores of ICH (p=0.017 in codominant2, p=0.035 in recessive, p=0.035 in log-additive models), respectively.

CONCLUSION

These results suggest that ITGA6 may be associated with the development and clinical phenotypes of stroke in Korean population.

Neuroinflammation and cerebrovascular disease in old age: a translational medicine perspective

The incidence of cerebrovascular disease is highest in the elderly population. However, the pathophysiological mechanisms of brain response to cerebral ischemia in old age are currently poorly understood. Ischemic changes in the commonly used young animal stroke models do not reflect the molecular changes associated with the aged brain. Neuroinflammation and oxidative stress are important pathogenic processes occurring during the acute phase of cerebral ischemia. Free radical generation is also implicated in the aging process, and the combination of these effects in elderly stroke patients could explain the higher risk of morbidity and mortality. A better understanding of stroke pathophysiology in the elderly patient would assist in the development of new therapeutic strategies for this vulnerable age group. With the increasing use of reperfusion therapies, inflammatory pathways and oxidative stress remain attractive therapeutic targets for the development of adjuvant neuroprotective agents. This paper will discuss these molecular aspects of acute stroke and senescence from a bench-to-bedside research perspective.

Upregulation of fibronectin and the α5β1 and αvβ3 integrins on blood vessels within the cerebral ischemic penumbra

Following focal cerebral ischemia, blood vessels in the ischemic border, or penumbra, launch an angiogenic response. In light of the critical role for fibronectin in angiogenesis, and the observation that fibronectin and its integrin receptors are strongly upregulated on angiogenic vessels in the hypoxic CNS, the aim of this study was to establish whether angiogenic vessels in the ischemic CNS also show this response. Focal cerebral ischemia was established in C57/Bl6 mice by middle cerebral artery occlusion (MCA:O), and brain tissue analyzed 7 days following re-perfusion, a time at which angiogenesis is ongoing. Within the ischemic core, immunofluorescent (IF) studies demonstrated vascular expression of MECA-32, a marker of leaky cerebral vessels, and vascular breakdown, defined by loss of staining for the endothelial marker, CD31, and the vascular adhesion molecules, laminin, dystroglycan and α6 integrin. Within the ischemic penumbra, dual-IF with CD31 and Ki67 revealed the presence of proliferating endothelial cells, indicating ongoing angiogenesis. Significantly, vessels in the ischemic penumbra showed strong upregulation of fibronectin and the fibronectin receptors, α5β1 and αvβ3 integrins. Taken together with our recent finding that the α5β1 integrin plays an important role in promoting cerebral angiogenesis in response to hypoxia, these results suggest that stimulation of the fibronectin-α5β1 integrin signaling pathway may provide a novel approach to amplifying the intrinsic angiogenic response to cerebral ischemia.

Heterogeneity in the penumbra

Original experimental studies in nonhuman primate models of focal ischemia showed flow-related changes in evoked potentials that suggested a circumferential zone of low regional cerebral blood flow with normal K(+) homeostasis, around a core of permanent injury in the striatum or the cortex. This became the basis for the definition of the ischemic penumbra. Imaging techniques of the time suggested a homogeneous core of injury, while positing a surrounding 'penumbral' region that could be salvaged. However, both molecular studies and observations of vascular integrity indicate a more complex and dynamic situation in the ischemic core that also changes with time. The microvascular, cellular, and molecular events in the acute setting are compatible with heterogeneity of the injury within the injury center, which at early time points can be described as multiple 'mini-cores' associated with multiple 'mini-penumbras'. These observations suggest the progression of injury from many small foci to a homogeneous defect over time after the onset of ischemia. Recent observations with updated imaging techniques and data processing support these dynamic changes within the core and the penumbra in humans following focal ischemia.

Early micro vascular changes after subarachnoid hemorrhage

During the last decade much effort has been invested in understanding the events that occur early after SAH. It is now widely accepted that these early events not only participate in the early ischemic injury but also set the stage for the pathogenesis of delayed vasospasm. That early cerebral ischemia occurs after SAH is documented in both experimental SAH and in human autopsy studies; however, angiographic evidence for vasoconstriction early after SAH is lacking and the source of early ischemic injury is therefore unclear. Recently, the cerebral microvasculature has been identified as an early target of SAH. Changes in the anatomical structure of cerebral microvessels, sufficient to cause functional deficits, are found early after experimental SAH. These changes may explain cerebral ischemia in human in the absence of angiographic evidence of large vessel vasoconstriction. This paper summarizes known alterations in cerebral microvasculature during the first 48 h after SAH.

Dynamics of dystroglycan complex proteins and laminin changes due to angiogenesis in rat cerebral hypoperfusion

Permanent bilateral carotid occlusion is a well known cerebral hypoperfusion model in rats. The aim of our study was to investigate the different stages of vascular reaction by detecting changes in the extracellular martix proteins and to examine their relationship to angiogenesis after occlusion. Experiments were performed on adult male rats. Brain samples were investigated from day 1 to day 30 post-surgery. Immunohistochemical analysis was performed on the whole hippocampus and on the adjacent cortex in order to investigate extracellular martix proteins, such as the markers of dystroglycan complex (β-dystroglycan, α-dystrobrevin and utrophin) and a marker of basal lamina (laminin). The levels of the proteins were estimated by western blot analysis. Vascular density as well as blood-brain barrier permeability were studied on brain slices from the same regions. Our results showed altered laminin and β-dystroglycan immunoreactivity beginning 2 days after the onset of occlusion followed by an increased utrophin immunoreactivity without blood-brain barrier disruption 5 days later. By day 30 of hypoperfusion, when increased vascular density was detected, all changes returned to baseline levels. Western blot analysis showed significant differences in β-dystroglycan and utrophin expression. Our results indicate that the different stages of neovascularisation resulting from cerebral hypoperfusion can be well defined by the markers laminin, β-dystroglycan, and utrophin and that these markers are more likely to correlate with glio-vascular decoupling than does altered blood-brain barrier function.