Brain microvascular endothelial cells and leukocytes derived from patients with multiple sclerosis exhibit increased adhesion capacity

Cellular and molecular distribution of thyroid-specific proteins, thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG) in the central nervous system

The widespread extra-thyroidal localisation of thyroid-specific proteins, thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG), has been well documented. However, more recent years has seen the focus of this research area shift to the distribution of these thyroid-specific proteins, in the central nervous system (CNS). This is largely attributed to the well-known associations between thyroid auto-immunity and neuro-psychiatric disorders. Although these associations have not yet been well defined, there are several studies that demonstrate the presence of TSH-R and TG proteins in CNS regions and its cellular structures. In addition, there is an emerging body of evidence to describe the potential functional roles of these thyroid proteins in various regions of the CNS. In this review, the neural distribution of TSH-R and TG as well as their possible physiological implications in various regions of human and non-human brain is discussed.

Effect of Insulin Receptor-Knockdown on the Expression Levels of Blood-Brain Barrier Functional Proteins in Human Brain Microvascular Endothelial Cells

PURPOSE

The insulin receptor (INSR) mediates insulin signaling to modulate cellular functions. Although INSR is expressed at the blood-brain barrier (BBB), its role in the modulation of BBB function is poorly understood. Therefore, in this study, we aimed to analyze the effect of INSR knockdown on the expression levels of functional proteins at the BBB.

METHODS

We established the INSR-knockdown cell line (shINSR) using human cerebral microvascular endothelial cells (hCMEC/D3). The cellular proteome was analyzed using quantitative proteomics.

RESULTS

INSR mRNA and protein expressions were decreased in shINSR cells. The suppression of INSR-mediated signaling in shINSR cells was evaluated. The proteins involved in glycolysis and glycogenolysis were suppressed in shINSR cells. As amyloid-β peptide-related proteins, the expressions of presenilin-1 was increased, and those of the insulin-degrading enzyme and neprilysin were decreased. The expressions of BBB transporters, including the ABCB1/MDR1, ABCG2/BCRP, and SLCO2A1/OATP2A1 were significantly decreased by more than 50% in shINSR cells. The efflux activity of ABCB1/MDR1 was also suppressed. The expressions of the low-density lipoprotein receptor-related protein 1 were significantly increased, and those of the transferrin receptor were significantly decreased in shINSR cells. The expression of claudin-5 was also suppressed in shINSR cells.

CONCLUSIONS

The present study suggests that INSR-mediated signaling is involved in the regulation of functional protein expression at the BBB and contributes to the maintenance of BBB function. Changes in the expressions of amyloid-β peptide-related proteins may contribute to the development of cerebral amyloid angiopathy via the suppression of INSR-mediated signaling.

The effect of insomnia on development of Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia and a neurodegenerative disorder characterized by memory deficits especially forgetting recent information, recall ability impairment, and loss of time tracking, problem-solving, language, and recognition difficulties. AD is also a globally important health issue but despite all scientific efforts, the treatment of AD is still a challenge. Sleep has important roles in learning and memory consolidation. Studies have shown that sleep deprivation (SD) and insomnia are associated with the pathogenesis of Alzheimer's disease and may have an impact on the symptoms and development. Thus, sleep disorders have decisive effects on AD; this association deserves more attention in research, diagnostics, and treatment, and knowing this relation also can help to prevent AD through screening and proper management of sleep disorders. This study aimed to show the potential role of SD and insomnia in the pathogenesis and progression of AD.

Bipolar limbic expression of auto-immune thyroid targets: thyroglobulin and thyroid-stimulating hormone receptor

The associations between thyroid auto-immunity and neuro-psychiatric disorders are well-documented. However, there exists limited literature specifically linking auto-immune thyroid disease (AITD) to bipolar disorder (BD). Thus, we investigated the likely association between Hashimoto's disease and BD through the extra-thyroidal localisation of thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG) in limbic regions of normal and bipolar human adult brain. Further, we hypothesised that changes in thyroid expression in bipolar limbic cortex may contribute to mood dysregulation associated with BD. Immuno-chemistry and in-situ PCR were used to localise TSH-R/TG within the amygdala, cingulate gyrus and frontal cortex of normal (n = 5) and bipolar (n = 5) brains. Reverse-transcriptase qPCR provided fold-change differences in TSH-R gene expression. The results demonstrated reduced thyroid protein expression in bipolar limbic regions; these novel results correlate with other neuro-imaging reports that describe reduced cortico-limbic tissue volumes and neuro-physiological activity during BD. We also demonstrated TG-like proteins exclusive to bipolar amygdala neurons, and which relates to previous neuro-imaging studies of amygdala hyperactivity and enhanced emotional sensitivity in BD. Indeed, reduced TSH-R/TG in limbic regions may predispose to, or bear relevance in the pathophysiology of mood dysregulation and symptoms of BD. Further, we attribute mood dysregulation in BD to limbic-derived TSH-R, which probably provides potential targets for thyroid auto-immune factors during Hashimoto's disease. Consequently, this may lead to inactivated and/or damaged neurons. The neuro-pathology of diminished neuronal functioning or neuronal atrophy suggests a novel neuro-degeneration mechanism in BD.

Aggregatibacter actinomycetemcomitans Leukotoxin (LtxA; Leukothera®): Mechanisms of Action and Therapeutic Applications

Aggregatibacter actinomycetemcomitans is an oral pathogen that produces the RTX toxin, leukotoxin (LtxA; Leukothera^®). A. actinomycetemcomitans is strongly associated with the development of localized aggressive periodontitis. LtxA acts as a virulence factor for A. actinomycetemcomitans to subvert the host immune response by binding to the β₂ integrin lymphocyte function-associated antigen-1 (LFA-1; CD11a/CD18) on white blood cells (WBCs), causing cell death. In this paper, we reviewed the state of knowledge on LtxA interaction with WBCs and the subsequent mechanisms of induced cell death. Finally, we touched on the potential therapeutic applications of LtxA (trade name Leukothera^®) toxin therapy for the treatment of hematological malignancies and immune-mediated diseases.

Expression of thyroid-stimulating hormone receptors and thyroglobulin in limbic regions in the adult human brain

Expression of the human thyroid-specific proteins, thyroid-stimulating hormone receptor (TSH-R) and thyroglobulin (TG) in non-thyroid tissue is well-documented. TSH-R has been identified in the heart, kidney, bone, pituitary, adipose tissue, skin and astrocyte cultures. TG has been identified in the skin, thymus and kidney. However, none of those previous studies had identified TSH-R or TG in specific human brain regions. Previously, a pilot study conducted by our group on normal adult human brain demonstrated TSH-R and TG in cortical neurons and cerebral vasculature, respectively, within various brain areas. In the present study, we extend this investigation of thyroid proteins specifically in limbic regions of normal human brain. Forensic human samples of amygdalae, cingulate gyrii, frontal cortices, hippocampii, hypothalamii, and thalamii were obtained from five individuals who had died of causes unrelated to head injury and had no evidence of brain disease or psychological abnormality. Tissues were probed with commercial polyclonal antibodies against human TSH-R and TG which resulted in the significant demonstration of neuronal TSH-R in all limbic regions examined. Other novel results demonstrated TG in vascular smooth muscle of all limbic regions and in some neurons. Finding thyroid proteins in limbic areas of the human brain is unique, and this study demonstrates that cerebro-limbic localisation of thyroid proteins may have potential roles in neuro-psycho-pharmacology.

FRET based quantification and screening technology platform for the interactions of leukocyte function-associated antigen-1 (LFA-1) with intercellular adhesion molecule-1 (ICAM-1)

The interaction between leukocyte function-associated antigen-1(LFA-1) and intercellular adhesion molecule-1 (ICAM-1) plays a pivotal role in cellular adhesion including the extravasation and inflammatory response of leukocytes, and also in the formation of immunological synapse. However, irregular expressions of LFA-1 or ICAM-1 or both may lead to autoimmune diseases, metastasis cancer, etc. Thus, the LFA-1/ICAM-1 interaction may serve as a potential therapeutic target for the treatment of these diseases. Here, we developed one simple 'in solution' steady state fluorescence resonance energy transfer (FRET) technique to obtain the dissociation constant (Kd) of the interaction between LFA-1 and ICAM-1. Moreover, we developed the assay into a screening platform to identify peptides and small molecules that inhibit the LFA-1/ICAM-1 interaction. For the FRET pair, we used Alexa Fluor 488-LFA-1 conjugate as donor and Alexa Fluor 555-human recombinant ICAM-1 (D1-D2-Fc) as acceptor. From our quantitative FRET analysis, the Kd between LFA-1 and D1-D2-Fc was determined to be 17.93±1.34 nM. Both the Kd determination and screening assay were performed in a 96-well plate platform, providing the opportunity to develop it into a high-throughput assay. This is the first reported work which applies FRET based technique to determine Kd as well as classifying inhibitors of the LFA-1/ICAM-1 interaction.

iPSC-derived neural precursors exert a neuroprotective role in immune-mediated demyelination via the secretion of LIF

The possibility of generating neural stem/precursor cells (NPCs) from induced pluripotent stem cells (iPSCs) has opened a new avenue of research that might nurture bench-to-bedside translation of cell transplantation protocols in central nervous system myelin disorders. Here we show that mouse iPSC-derived NPCs (miPSC-NPCs)-when intrathecally transplanted after disease onset-ameliorate clinical and pathological features of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. Transplanted miPSC-NPCs exert the neuroprotective effect not through cell replacement, but through the secretion of leukaemia inhibitory factor that promotes survival, differentiation and the remyelination capacity of both endogenous oligodendrocyte precursors and mature oligodendrocytes. The early preservation of tissue integrity limits blood-brain barrier damage and central nervous system infiltration of blood-borne encephalitogenic leukocytes, ultimately responsible for demyelination and axonal damage. While proposing a novel mechanism of action, our results further expand the therapeutic potential of NPCs derived from iPSCs in myelin disorders.

Nanoparticles for brain drug delivery

The central nervous system, one of the most delicate microenvironments of the body, is protected by the blood-brain barrier (BBB) regulating its homeostasis. BBB is a highly complex structure that tightly regulates the movement of ions of a limited number of small molecules and of an even more restricted number of macromolecules from the blood to the brain, protecting it from injuries and diseases. However, the BBB also significantly precludes the delivery of drugs to the brain, thus, preventing the therapy of a number of neurological disorders. As a consequence, several strategies are currently being sought after to enhance the delivery of drugs across the BBB. Within this review, the recently born strategy of brain drug delivery based on the use of nanoparticles, multifunctional drug delivery systems with size in the order of one-billionth of meters, is described. The review also includes a brief description of the structural and physiological features of the barrier and of the most utilized nanoparticles for medical use. Finally, the potential neurotoxicity of nanoparticles is discussed, and future technological approaches are described. The strong efforts to allow the translation from preclinical to concrete clinical applications are worth the economic investments.

Depression after myocardial infarction: TNF-α-induced alterations of the blood-brain barrier and its putative therapeutic implications

Patients experiencing an acute myocardial infarction (AMI) have a three times higher chance to develop depression. Vice versa, depressive symptoms increase the risk of cardiovascular events. The co-existence of both conditions is associated with substantially worse prognosis. Although the underlying mechanism of the interaction is largely unknown, inflammation is thought to be of pivotal importance. AMI-induced peripheral cytokines release may cause cerebral endothelial leakage and hence induces a neuroinflammatory reaction. The neuroinflammation may persist even long after the initial peripheral inflammation has subsided. Among those selected brain regions that are prone to blood-brain barrier dysfunction, the paraventricular nucleus of the hypothalamus (PVN), a major center for cardiovascular autonomic regulation, is indicated to play a mediating role. Optimal cardiovascular therapy improves cardiovascular prognosis without major effects on depression. By the same token, antidepressant therapy in cardiovascular disease is associated with modest improvement in depressive symptoms, however without improvement in cardiac outcome. The failure of current antidepressants and the growing number of patients suffering from both conditions legitimize the search for better antidepressive therapies, from patients as well as society perspectives. Though we appreciate the mutual character of the interaction between depression and AMI, the present review focuses on the side of AMI induced depression and discusses the role of inflammation, represented by the proinflammatory cytokine TNF-α, as potential underlying mechanism. It is conceivable that inhibition of the inflammatory response post-AMI, through targeted anti-inflammatory pharmacotherapeutical agents may prevent the development of depressive symptoms and ultimately may improve cardiovascular outcomes.

Breakdown of the blood-brain barrier during tick-borne encephalitis in mice is not dependent on CD8+ T-cells

Tick-borne encephalitis (TBE) virus causes severe encephalitis with serious sequelae in humans. The disease is characterized by fever and debilitating encephalitis that can progress to chronic illness or fatal infection. In this study, changes in permeability of the blood-brain barrier (BBB) in two susceptible animal models (BALB/c, and C57Bl/6 mice) infected with TBE virus were investigated at various days after infection by measuring fluorescence in brain homogenates after intraperitoneal injection of sodium fluorescein, a compound that is normally excluded from the central nervous system. We demonstrate here that TBE virus infection, in addition to causing fatal encephalitis in mice, induces considerable breakdown of the BBB. The permeability of the BBB increased at later stages of TBE infection when high virus load was present in the brain (i.e., BBB breakdown was not necessary for TBE virus entry into the brain), and at the onset of the first severe clinical symptoms of the disease, which included neurological signs associated with sharp declines in body weight and temperature. The increased BBB permeability was in association with dramatic upregulation of proinflammatory cytokine/chemokine mRNA expression in the brain. Breakdown of the BBB was also observed in mice deficient in CD8⁺ T-cells, indicating that these cells are not necessary for the increase in BBB permeability that occurs during TBE. These novel findings are highly relevant to the development of future therapies designed to control this important human infectious disease.

Resistance to experimental autoimmune encephalomyelitis and impaired IL-17 production in protein kinase C theta-deficient mice

The protein kinase C theta (PKC theta) serine/threonine kinase has been implicated in signaling of T cell activation, proliferation, and cytokine production. However, the in vivo consequences of ablation of PKC theta on T cell function in inflammatory autoimmune disease have not been thoroughly examined. In this study we used PKC theta-deficient mice to investigate the potential involvement of PKC theta in the development of experimental autoimmune encephalomyelitis, a prototypic T cell-mediated autoimmune disease model of the CNS. We found that PKC theta-/- mice immunized with the myelin oligodendrocyte glycoprotein (MOG) peptide MOG(35-55) were completely resistant to the development of clinical experimental autoimmune encephalomyelitis compared with wild-type control mice. Flow cytometric and histopathological analysis of the CNS revealed profound reduction of both T cell and macrophage infiltration and demyelination. Ex vivo MOG(35-55) stimulation of splenic T lymphocytes from immunized PKC theta-/- mice revealed significantly reduced production of the Th1 cytokine IFN-gamma as well as the T cell effector cytokine IL-17 despite comparable levels of IL-2 and IL-4 and similar cell proliferative responses. Furthermore, IL-17 expression was dramatically reduced in the CNS of PKC theta-/- mice compared with wild-type mice during the disease course. In addition, PKC theta-/- T cells failed to up-regulate LFA-1 expression in response to TCR activation, and LFA-1 expression was also significantly reduced in the spleens of MOG(35-55)-immunized PKC theta-/- mice as well as in in vitro-stimulated CD4+ T cells compared with wild-type mice. These results underscore the importance of PKC theta in the regulation of multiple T cell functions necessary for the development of autoimmune disease.

Suppression of experimental autoimmune encephalomyelitis by extracellular adherence protein of Staphylococcus aureus

Multiple sclerosis (MS) is a devastating inflammatory disorder of the central nervous system (CNS). A major hallmark of MS is the infiltration of T cells reactive against myelin components. T cell infiltration is mediated by the interaction of integrins of the beta1 and beta2 family expressed by lymphocytes with their endothelial counter-receptors, vascular cell adhesion molecule 1 and intercellular adhesion molecule (ICAM)-1, respectively. We have reported previously that extracellular adherence protein (Eap) of Staphylococcus aureus exerts antiinflammatory activities by interacting with ICAM-1 and blocking beta2-integrin-dependent neutrophil recruitment. Here, we report that Eap inhibits experimental autoimmune encephalomyelitis (EAE) in mice. In vitro, Eap reduced adhesion of peripheral blood T cells to immobilized ICAM-1 as well as their adhesion and transmigration of TNF-activated human endothelium under static and shear flow conditions. These inhibitory effects were corroborated in two mouse models of inflammation. In a delayed-type hypersensitivity model, both T cell infiltration and the corresponding tissue edema were significantly reduced by Eap. In addition, Eap administration prevented the development of EAE and markedly decreased infiltration of inflammatory cells into the CNS. Strikingly, intervention with Eap after the onset of EAE suppressed the disease. Collectively, our findings indicate that Eap represents an attractive treatment for autoimmune neuroinflammatory disorders such as MS.

Blood-Brain Barrier Imaging and Therapeutic Potentials

Much work has been done in the last several decades to improve the understanding of the molecular composition of the blood-brain barrier (BBB). Advances in magnetic resonance imaging have resulted in development of dynamic magnetic resonance imaging techniques to quantify permeability measurements across the brain endothelium. This review describes the basic anatomical and biochemical concepts of a BBB and the various techniques for magnetic resonance measurement of BBB permeability. To date, BBB permeability data have been shown to be useful in preoperative brain tumor grading and potentially also in determining the effectiveness of selective types of therapy. Explorative studies are evaluating new strategies for safe and effective altering of the BBB permeability to improve local drug delivery into brain tumors. As new antiangiogenesis drugs become available, BBB permeability imaging may also become critical as a surrogate angiogenesis marker to monitor tumor response to these agents. Finally, BBB permeability data may also prove useful in future applications to guide therapy in other nontumoral disease processes such as acute cerebral ischemia and inflammatory processes such as multiple sclerosis.

Ultrastructural and immunohistochemical similarities of two distinct entities; multiple sclerosis and hereditary motor sensory neuropathy

In the present study, we present the ultrastructural and immunohistochemical properties of the sural nerves of two patients, one of whom was diagnosed as having multiple sclerosis with involvement of the peripheral nervous system (PNS), and the other as having hereditary motor sensory neuropathy type-I with involvement of the central nervous system (CNS). Expression of several extracellular matrix (ECM) proteins (fibronectin, laminin, and collagen type-IV), intermediate filaments (vimentin) and S-100 protein (marker for the axon-Schwann cell interface) was investigated by means of immunohistochemical methods. In addition, the tissue samples were evaluated ultrastructurally. Immunohistochemical staining revealed increased expression of the ECM molecules mentioned above in relation with the sural nerves of the patients. We hypothesize that this enhanced expression is due to Schwann cell-axon interactions. Vimentin expression was different in Schwann cells and S-100 immunostaining was decreased near the Schwann cell-axon interface. Myelin fragmentation, axon vacuolization, onion bulbs, tomoculous formation, axonal degeneration were found to occur. These results suggest that there is active ECM reorganization in the sural nerve of these patients, and some ultrastructural changes are similar in the damaged axonal organization and in Schwann cells although the changes are not completely the same in the two patients. In conclusion, our study demonstrates that there is an association between the demyelinization process in the CNS and the PNS even though they are affected by different mechanisms.

Pharmacological Targeting of ICAM-1 Signaling in Brain Endothelial Cells: Potential for Treating Neuroinflammation

(1) The vasculature of the blood-brain barrier allows only comparatively few leukocytes to enter and survey the healthy central nervous system (CNS). However, during pathological CNS inflammation, the number of leukocytes adhering to and penetrating the CNS vasculature increases strongly. (2) Endothelial adhesion molecules do not only mediate firm adhesion of leukocyte to vascular beds but also trigger signaling cascades within the endothelial cell, which play a crucial role in modulating subsequent leukocyte diapedesis. (3) Signaling through endothelial intercellular adhesion molecule-1 (ICAM-1, CD54) has been shown to induce changes of the endothelial cytoskeleton, transcription, and interendothelial junctions, all of which may be important in modulating endothelial disposition to infiltrating leukocytes. Furthermore, a number of recent reports document that drugs interfering with endothelial ICAM-1 signaling, efficiently reduce leukocyte migration both in vitro and in animal models of CNS inflammation. (4) These approaches are novel in as much as they target vascular beds rather than the penetrating leukocytes. Since endothelial ICAM-1 signaling appears to differ between different vascular beds we propose that such compounds could potentially be used as exquisite drugs in the treatment of neuroinflammatory diseases.

The blood-brain barrier: an overview: structure, regulation, and clinical implications

The blood-brain barrier (BBB) is a diffusion barrier, which impedes influx of most compounds from blood to brain. Three cellular elements of the brain microvasculature compose the BBB-endothelial cells, astrocyte end-feet, and pericytes (PCs). Tight junctions (TJs), present between the cerebral endothelial cells, form a diffusion barrier, which selectively excludes most blood-borne substances from entering the brain. Astrocytic end-feet tightly ensheath the vessel wall and appear to be critical for the induction and maintenance of the TJ barrier, but astrocytes are not believed to have a barrier function in the mammalian brain. Dysfunction of the BBB, for example, impairment of the TJ seal, complicates a number of neurologic diseases including stroke and neuroinflammatory disorders. We review here the recent developments in our understanding of the BBB and the role of the BBB dysfunction in CNS disease. We have focused on intraventricular hemorrhage (IVH) in premature infants, which may involve dysfunction of the TJ seal as well as immaturity of the BBB in the germinal matrix (GM). A paucity of TJs or PCs, coupled with incomplete coverage of blood vessels by astrocyte end-feet, may account for the fragility of blood vessels in the GM of premature infants. Finally, this review describes the pathogenesis of increased BBB permeability in hypoxia-ischemia and inflammatory mechanisms involving the BBB in septic encephalopathy, HIV-induced dementia, multiple sclerosis, and Alzheimer disease.

A simple method for isolation and characterization of mouse brain microvascular endothelial cells

Brain endothelial cells, a site of the blood-brain barrier in vivo, regulate a number of physiological and pathophysiological processes in the brain including transport of nutrients, export of critical toxins, transmigration of circulating leukocytes and formation of new blood vessels. In this report, we describe a simple and reproducible method to isolate pure (>99%), functionally active endothelial cells from small quantities of adult mouse brain tissue. In vitro, these cells express typical phenotypic markers of differentiated brain endothelium such as von Willebrand factor, multiple drug resistant protein and glucose transporter-1, demonstrate uptake of acetylated low-density lipoprotein, and possess morphological and ultrastructural characteristics of microvascular endothelium. They form tight junctions and capillary-like tubes when stimulated by growth factors in an in vitro angiogenesis assay. In response to tumor necrosis factor-alpha, isolated mouse brain endothelial cells (MBEC) express vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). The protocol described here provides an effective and reliable method to isolate pure cerebral endothelium from adult mouse brain that should offer a useful tool for studying the role of altered vascular biology in mice with genetically manipulated brain disorders.

Targeting ICAM-1/LFA-1 interaction for controlling autoimmune diseases: designing peptide and small molecule inhibitors

This review describes the role of modulation of intracellular adhesion molecule-1 (ICAM-1)/leukocyte function-associated antigen-1 (LFA-1) interaction in controlling autoimmune diseases or inducing immunotolerance. ICAM-1/LFA-1 interaction is essential for T-cell activation as well as for migration of T-cells to target tissues. This interaction also functions, along with Signal-1, as a co-stimulatory signal (Signal-2) for T-cell activation, which is delivered by the T-cell receptors (TCR)-major histocompatibility complex (MHC)-peptide complex. Therefore, blocking ICAM-1/LFA-1 interaction can suppress T-cell activation in autoimmune diseases and organ transplantation. Many types of inhibitors (i.e. antibodies, peptides, small molecules) have been developed to block ICAM-1/LFA-1 interactions, and some of these molecules have reached clinical trials. Peptides derived from ICAM-1 and LFA-1 sequences have been shown to inhibit T-cell adhesion and activation. In addition, these inhibitors have been useful in elucidating the mechanism of ICAM-1/LFA-1 interaction. Besides binding to LFA-1, the ICAM-1 peptide can be internalized by LFA-1 receptors into the cytoplasmic domain of T-cells. Therefore, this ICAM-1 peptide can be utilized to selectively target toxic drugs to T-cells, thus avoiding harmful side effects. Finally, bi-functional inhibitory peptide (BPI), which is made by conjugating the antigenic peptide and an LFA-1 peptide, can alter the T-cell commitment from T-helper-1 (Th1) to T-helper-2 (Th2)-like cells, suggesting that this peptide may have a role in blocking the formation of the "immunological synapse."

The adhesion molecule ICAM-1 and its regulation in relation with the blood-brain barrier

The blood-brain barrier (BBB) is formed by high resistance tight junctions within the capillary endothelium perfusing the vertebrate brain. Normal BBB maintains a unique microenvironment within the central nervous system (CNS). In neurodegenerative disorders (for example multiple sclerosis, MS), the BBB becomes impaired. Perivascular cells (astrocytes, macrophages and microglial cells) and brain microvascular endothelial cells (BMEC) produce various inflammatory factors that affect the BBB permeability and the expression of adhesion molecules. Indeed, cytokines can stimulate the expression of several adhesion molecules on brain microvascular endothelial cells. Among these adhesion molecules, the intercellular adhesion molecule-1 (ICAM-1) binds to its leukocyte ligands and allows activated leukocytes entry into the CNS. This review is dealing with the expression and regulation of ICAM-1 in relation with several properties of the BBB. Particularly, the role of ICAM-1 in the control of the leukocyte traffic into the CNS, as well as in cerebral malaria and in CNS infection by viruses, is discussed.

Inhibition of LFA-1/ICAM-1 and VLA-4/VCAM-1 as a therapeutic approach to inflammation and autoimmune diseases

This review focuses on providing insights into the structural basis and clinical relevance of LFA-1 and VLA-4 inhibition by peptides and small molecules as adhesion-based therapeutic strategies for inflammation and autoimmune diseases. Interactions of cell adhesion molecules (CAM) play central roles in mediating immune and inflammatory responses. Leukocyte function-associated antigen (LFA-1, alpha(L)beta(2), and CD11a/CD18) and very late antigen (VLA-4, alpha(4)beta(1), and CD49d/CD29) are members of integrin-type CAM that are predominantly involved in leukocyte trafficking and extravasation. LFA-1 is exclusively expressed on leukocytes and interacts with its ligands ICAM-1, -2, and -3 to promote a variety of homotypic and heterotypic cell adhesion events required for normal and pathologic functions of the immune systems. VLA-4 is expressed mainly on lymphocyte, monocytes, and eosinophils, but is not found on neutrophils. VLA-4 interacts with its ligands VCAM-1 and fibronectin (FN) CS1 during chronic inflammatory diseases, such as rheumatoid arthritis, asthma, psoriasis, transplant-rejection, and allergy. Blockade of LFA-1 and VLA-4 interactions with their ligands is a potential target for immunosuppression. LFA-1 and VLA-4 antagonists (antibodies, peptides, and small molecules) are being developed for controlling inflammation and autoimmune diseases. The therapeutic intervention of mostly mAb-based has been extensively studied. However, due to the challenging relative efficacy/safety ratio of mAb-based therapy application, especially in terms of systemic administration and immunogenic potential, strategic alternatives in the forms of peptide, peptide mimetic inhibitors, and small molecule non-peptide antagonists are being sought. Linear and cyclic peptides derived from the sequences of LFA-1, ICAM-1, ICAM-2, VCAM-1, and FN C1 have been shown to have inhibitory effects in vitro and in vivo. Finally, understanding the mechanism of LFA-1 and VLA-4 binding to their ligands has become a fundamental basis in developing therapeutic agents for inflammation and autoimmune diseases.

Studies on single-cell adhesion probability between lymphocytes and endothelial cells with micropipette technique

An in vitro model with micropipette technique was used to investigate single-cell adhesion probability between lymphocytes and endothelial cells. The basal adhesion probability between lymphocytes and endothelial cells was low and was significantly increased when either lymphocytes were activated by phytohemagglutinin (PHA) or endothelial cells were stimulated by tumor necrosis factor. The adhesion probability of lymphocytes to human umbilical vein endothelial cells was similar to that of lymphocytes to human brain microvascular endothelial cells (HB-MVEC). However, lymphocyte adhesion probability was higher in HB-MVEC than in mouse brain microvascular endothelial cells (MB-MVEC) under both resting and activated conditions. Furthermore, lymphocytes preincubated with monoclonal antibodies to lymphocyte function-associated antigen-1 (LFA-1) or HB-MVEC preincubated with monoclonal antibodies to intercellular adhesion molecule 1 (ICAM-1) significantly down-regulated the adhesion probability between lymphocytes and endothelial cells, indicating that the adhesion probability is related to the expression of LFA-1 on lymphocytes and to the expression of ICAM-1 on endothelial cells. Lymphocytes isolated from patients with cerebral stroke exhibited increased adhesion probability to HB-MVEC as compared with lymphocytes from healthy donors. Preincubation of lymphocytes with tetramethylpyrazine (TMP), an extract from a Chinese traditional herb, effectively inhibited the adhesion probability to HB-MVEC, suggesting that TMP has a potential therapeutic value. These results indicate that the micropipette technique is a useful model for investigating single-cell adhesion probability between lymphocytes and endothelial cells in vitro.

Molecular physiology and pathophysiology of tight junctions in the blood-brain barrier

Disruption of the tight junctions (TJs) of the blood-brain barrier (BBB) is a hallmark of many CNS pathologies, including stroke, HIV encephalitis, Alzheimer's disease, multiple sclerosis and bacterial meningitis. Furthermore, systemic-derived inflammation has recently been shown to cause BBB tight junctional disruption and increased paracellular permeability. The BBB is capable of rapid modulation in response to physiological stimuli at the cytoskeletal level, which enables it to protect the brain parenchyma and maintain a homeostatic environment. By allowing the "loosening" of TJs and an increase in paracellular permeability, the BBB is able to "bend without breaking"; thereby, maintaining structural integrity.

Glial cell influence on the human blood-brain barrier

The blood-brain barrier (BBB) is a specialized structure of the central nervous system (CNS) that restricts immune cell migration and soluble molecule diffusion from the systemic compartment into the CNS. Astrocytes and microglia are resident cells of the CNS that contribute to the formation of the BBB. In this article, we consider the influence of these glial cells on the immune regulatory functions of the microvascular endothelium, with special emphasis on the human BBB. A series of in vitro studies demonstrate that soluble factors produced by glial cells, under basal culture conditions, help restrict development of inflammation within the CNS. These soluble factor effects include upregulating expression of molecules including HT7, UEA-1 lectin-binding sites, and angiotensin receptors that help define the phenotype of endothelial cells. These factors also induce tight junction formation between brain endothelial cells, contributing to the restricted permeability of the BBB. In contrast, these factors have little effect on expression of molecules by ECs that either promote lymphocyte migration, such as chemokines and adhesion molecules or molecules that are required for competent antigen presentation, such as MHC and co-stimulatory molecules. Glial cells that become activated in response to signals derived from the immune system or generated within the CNS, produce an array of inflammatory molecules that increase permeability and promote lymphocyte trafficking and persistence. These observations emphasize the bidirectional nature of neural-immune interactions; this dynamic system should be amenable to therapeutic interventions.

LFA-1 expression on CD4(+)CD45RO(+) peripheral blood T-lymphocytes in RR MS: effects induced by rIFNbeta-1a

We investigate the in vivo and in vitro effects of short-term treatment with recombinant Interferon beta-1a (rIFNbeta-1a) on CD4(+)CD45RO(+) activated/memory peripheral blood T-lymphocytes (PBTLs) expressing Leukocyte Function Antigen-1 (LFA-1; CD11a/CD18) in relapsing-remitting (RR) Multiple Sclerosis (MS) patients. Blood samples were obtained from 10 RR MS patients before and after 2, 4 and 6 months of rIFNbeta-1a (Avonex) treatment. For each sample, the percentage of CD4(+)CD45RO(+)CD11a(+) (CD11a(dim) and CD11a(bright)) T-cells was evaluated in in vivo PBTLs and in untreated or rIFNbeta-1a (1000 U/ml) or recombinant soluble Intercellular Adhesion Molecule-1 (ICAM-1, the ligand for LFA-1) (400 ng/ml) treated cultured PBTLs by triple fluorescence flow-cytometry (FACS analysis). Soluble ICAM-1 (sICAM-1) serum levels were evaluated by ELISA. In vivo, the percentage of CD4(+)CD45RO(+), CD4(+)CD45RO(+)CD11a(+), CD4(+)CD45RO(+)CD11a(dim) PBTLs increased after 4 and 6 months of rIFNbeta-1a treatment compared to pretreatment and 2 months of treatment (p<0.05). The CD11a expression per se did not change during the time course. Soluble ICAM-1 (sICAM-1) serum levels also increased (p<0.05) after 4 and 6 months of treatment. When T-cells, obtained from the blood of the same patients before and during in vivo treatment, were cultured either untreated or treated with rIFNbeta-1a, they showed an increase in the percentage of CD4(+)CD45RO(+) T-cells expressing CD11a(bright) (p<0.05). The addition of recombinant sICAM-1 to untreated cultures decreased the percentage of CD4(+)CD45RO(+) T-cells expressing CD11a. This last finding seems to support an indirect effect in vivo of rIFNbeta-1a via sICAM-1 on this T-cell subset, since the ICAM-1 soluble form, induced in vivo in serum by rIFNbeta-1a but lacking in in vitro conditions, keeps the percentage of CD11a(+) unchanged within CD4(+)CD45RO(+) T-cells and induces their expression of CD11a(dim), probably preventing T-cells from transmigrating.

Immunological profile of patients with primary progressive multiple sclerosis. Expression of adhesion molecules

Adhesion molecules are important in the trafficking of peripheral leucocytes into the central nervous system, a major event in the pathogenesis of multiple sclerosis, which is an inflammatory and demyelinating disease. The latest MRI evidence supports clinical divergence between forms of multiple sclerosis with relapses and the primary progressive form without relapses, which shows fewer and smaller inflammatory lesions. With the aim of elucidating whether different pathogenic mechanisms are involved in primary progressive multiple sclerosis, we compared membrane expression of the adhesion molecules ICAM-1 (CD54), LFA-1alpha (CD11a), VLA-4 [alpha(4)/beta(1) integrin (CD49d/CD29)], L-selectin (CD62L) and ICAM-3 (CD50) in peripheral blood and the serum-soluble forms ICAM-1, L-selectin, VCAM-1 and ICAM-3 in 89 patients (39 with the primary progressive form, 25 with the secondary progressive form and 25 with the relapsing-remitting form) and 38 healthy controls. We found a significant decrease in leucocyte surface expression of most of the adhesion molecules tested and an increase in soluble ICAM-1 and L-selectin levels in secondary progressive and relapsing-remitting multiple sclerosis compared with primary progressive multiple sclerosis, which gave results similar to those in controls. These results, which are supported by MRI evidence, show that trafficking of autoreactive leucocytes through the blood-brain barrier is crucial to the pathogenesis of secondary progressive and relapsing-remitting forms of multiple sclerosis, whereas other mechanisms leading to progressive axonal damage would account for primary progressive forms of the disease.

Neuroglial activation repertoire in the injured brain: graded response, molecular mechanisms and cues to physiological function

Damage to the central nervous system (CNS) leads to cellular changes not only in the affected neurons but also in adjacent glial cells and endothelia, and frequently, to a recruitment of cells of the immune system. These cellular changes form a graded response which is a consistent feature in almost all forms of brain pathology. It appears to reflect an evolutionarily conserved program which plays an important role in the protection against infectious pathogens and the repair of the injured nervous system. Moreover, recent work in mice that are genetically deficient for different cytokines (MCSF, IL1, IL6, TNFalpha, TGFbeta1) has begun to shed light on the molecular signals that regulate this cellular response. Here we will review this work and the insights it provides about the biological function of the neuroglial activation in the injured brain.

TNF alpha and IL-1beta mediate intercellular adhesion molecule-1 induction via microglia-astrocyte interaction in CNS radiation injury

Radiation injury to the central nervous system (CNS) results in glial activation accompanied by expression of pro-inflammatory cytokines and adhesion molecules. In this study we demonstrate intercellular adhesion molecule-1 (ICAM-1) induction in the irradiated mouse brain at the mRNA and protein levels. Immunocytochemical analysis revealed that ICAM-1 protein was primarily expressed in endothelial cells and microglia. In vitro, ionizing radiation significantly induces TNF alpha, IL-1beta and ICAM-1 mRNA in primary microglia cultures. Interestingly, although ionizing radiation activated primary astrocyte cultures, it did not induce ICAM-1 expression. However, exposure of astrocytes to conditioned medium collected from irradiated microglia resulted in ICAM-1 induction, which was abrogated when the conditioned medium was pre-incubated with neutralizing antibodies raised against murine TNF alpha and IL-1beta. These results indicate that pro-inflammatory cytokines may be necessary for ICAM-1 expression in astrocytes in CNS radiation injury.

Platelet activating factor is elevated in cerebral spinal fluid and plasma of patients with relapsing-remitting multiple sclerosis

Platelet-activating factor (PAF) is a phospholipid mediator of inflammation with a wide range of biological activities, including the alteration of barrier function of endothelium. A biological assay combined with high pressure liquid chromatography-tandem mass spectrometry showed that plasma and cerebral spinal fluid (CSF) PAF levels in 20 patients with relapsing/remitting or secondary progressive multiple sclerosis (MS) studied by magnetic resonance imaging (MRI) were significantly higher than in healthy controls (plasma: 3.29+/-4.52 vs. 0.48+/-0.36 ng/ml, p < 0.002; CSF: 4.95+/-6.22 ng/ml vs. 0.01+/-0.04 ng/ml, p < 0.0001). Values were also significantly higher in relapsing/remitting than in secondary progressive (plasma: 5.10+/-4.97 vs. 0.52+/-0.85 ng/ml, p < 0.005; CSF: 8.59+/-6.39 vs. 0.55+/-0.68 ng/ml, p < 0.002). It was also found that both plasma (R2: 0.65) and CSF (R2:0.72) levels were correlated with the MRI number of gadolinium enhancing lesions, which are markers of blood-brain barrier (BBB) injury, whereas their peaks were not correlated with the MRI number of white matter lesions, nor with the expanded disability status score (EDSS) according to Kurtze [Kurtze, J.F., 1983. Rating neurological impairment in multiple sclerosis: an expanded disability scale (EDSS). Neurology 33, 1444-1452]. Both plasma and CSF in patients with relapsing/remitting MS and marked gadolinium enhancement contained the two major molecular species of PAF: 1-0-hexadecyl- (C16:O) and 1-0-octadecyl-sn-glycero-3-phosphocholine (C18:O). The ratio of the two molecular species was different in the two biological fluids, being PAF C18:0 more abundant in CSF and PAF C16:0 in plasma, indicating a different cellular origin of PAF or different enzymatic processing. These findings suggest that PAF is a significant mediator of BBB injury in the early stages of MS, rather than a marker of its progression and severity.

Transcriptional regulation of the intercellular adhesion molecule-1 gene by proinflammatory cytokines in human astrocytes

Intercellular adhesion molecule-1 (ICAM-1) expression is upregulated by cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and interferon-gamma (IFN-gamma) in numerous cell types including the astrocyte, which functions as an immunoregulatory cell within the central nervous system. We investigated the mechanism by which ICAM-1 is transcriptionally regulated by proinflammatory cytokines in human fetal astrocytes. TNF-alpha and IL-1beta enhanced ICAM-1 expression at both the mRNA and protein levels, while IFN-gamma had a modest enhancing effect. However, a synergistic response was noted when IFN-gamma was added with either TNF-alpha or IL-1beta. Using human ICAM-1 deletion constructs and linker scanning mutants, we determined that the NF-kappaB element (-186 bp region) is critical for both TNF-alpha- and IL-1beta-mediated ICAM-1 expression, while the IFN-gamma activation sequence (GAS) element at -75 bp region is important for IFN-gamma stimulation. The synergistic effect between TNF-alpha and IFN-gamma is dependent on both NF-kappaB and GAS elements. Upon TNF-alpha and IL-1beta stimulation, p65 homodimers and p65/p50 heterodimers bind to the NF-kappaB site, and STAT-1alpha homodimers bind to the GAS element upon IFN-gamma stimulation. Transient transfection assays demonstrated that overexpression of the p65 protein transactivated the promoter activity of an ICAM-1 reporter construct, while p50 overexpression inhibited, in a dose-dependent manner, p65-mediated ICAM-1 expression. These data collectively suggest that in human astrocytes, the p65 homodimer is responsible for ICAM-1 upregulation upon TNF-alpha or IL-1beta stimulation, and that IFN-gamma enhancement of ICAM-1 involves activation of STAT-1alpha homodimers.

Transcriptional regulation of intercellular adhesion molecule-1 in astrocytes involves NF-kappaB and C/EBP isoforms

ICAM-1 is an inducible cell surface protein that is involved in cell extravasation into inflamed tissues as well as immune responses. ICAM-1 expression is upregulated by proinflammatory cytokines such as TNF-alpha and IL-1beta in numerous cell types including the astrocyte, which functions as an immune effector cell in the central nervous system (CNS). We investigated the mechanism by which the ICAM-1 gene is transcriptionally regulated in astrocytes in response to TNF-alpha and IL-1beta. Human ICAM-1 promoter constructs linked to the reporter gene luciferase were transiently transfected into astrocytes, stimulated with TNF-alpha and IL-1beta, and ICAM-1 promoter activity examined. We determined that binding sites for both NF-kappaB (-186 bp region) and C/EBP (-198 bp region) are involved in TNF-alpha and IL-1beta-mediated ICAM-1 upregulation. Electrophoretic mobility shift assays using antibodies against NF-kappaB and C/EBP isoforms showed that p65 homodimers and p65/p50 heterodimers bind to the NF-kappaB site, and C/EBPdelta homodimers and C/EBPbeta/delta heterodimers bind to the C/EBP site. Transient transfection assays demonstrated that overexpression of p65 could transactivate the promoter activity of ICAM-1 reporter constructs. p50 overexpression had no effect on the basal levels of ICAM-1 transcription, but inhibited, in a dose dependent manner, p65 mediated transcription. Overexpression of C/EBPbeta slightly inhibited basal levels of ICAM-1 promoter activity, however, when C/EBPbeta and p65 were cotransfected, C/EBPbeta completely abolished the transactivating effects of p65. These results demonstrate that cytokine-induced ICAM-1 expression in astrocytes is regulated by interactions between NF-kappaB and C/EBP transcription factors.

Crucial role of tumor necrosis factor (TNF) receptor 2 and membrane-bound TNF in experimental cerebral malaria

Tumor necrosis factor (TNF) has been implicated in the pathogenesis of experimental cerebral malaria (CM), but the respective role of its two types of receptors has not been established. A significant increase in the expression of TNF-receptor 2 (TNFR2, p75), but not of TNFR1 (p55), was found on brain microvessels at the time of CM in susceptible animals. Moreover, mice genetically deficient for TNFR2 (Tnfr2null) were significantly protected from experimental CM, in contrast to TNFR1-deficient (Tnfr1null) mice, which were as susceptible as wild-type mice. To identify the factors involved in the protection from CM conferred by the lack of TNFR2, we assessed in both knockout and control mice the serum concentrations of mediators that are critical for the development of CM, as well as the up-regulation of intercellular adhesion molecule-1 (ICAM-1) in the brain microvessels. No significant difference in serum levels of TNF and interferon-gamma was found between infected wild-type and Tnfr1null or Tnfr2null mice. Interestingly, the pronounced ICAM-1 up-regulation and leukocyte sequestration, typically occurring in brain microvessels of CM-susceptible animals, was detected in infected control and Tnfr1null mice-both of which developed CM-whereas no such ICAM-1 up-regulation or leukocyte sequestration was observed in Tnfr2null mice, which were protected from CM. Making use of microvascular endothelium cells (MVEC) isolated from wild-type, Tnfr1null or Tnfr2null mice, we show that soluble TNF requires the presence of both TNF receptors, whereas membrane-bound TNF only needs TNFR2 for TNF-mediated ICAM-1 up-regulation in brain MVEC. Thus, only in MVEC lacking TNFR2, neither membrane-bound nor soluble TNF cause the up-regulation of ICAM-1 in vitro. In conclusion, these results indicate that the interaction between membrane TNF and TNFR2 is crucial in the development of this neurological syndrome.

Modulation of soluble and membrane-bound TNF-induced phenotypic and functional changes of human brain microvascular endothelial cells by recombinant TNF binding protein I

In this study, the effects of TNF binding protein I (TBP I) on TNF-induced changes of human brain microvascular endothelial cells (MVEC) were investigated. TBP I completely abolished TNF-induced IL-6 production and E-selectin induction, while it partially inhibited TNF-induced IL-8 production and up-regulation of ICAM-1 and VCAM-1. Moreover, TBP I significantly inhibited TNF-induced cytotoxicity and leukocyte adherence on human brain MVEC. The inhibitory activity of TBP I for TNF was dose-dependent and related to the time of administration after TNF stimulation. In addition, TBP I inhibited membrane-bound TNF induced activation of human brain MVEC, but the concentration required was about 10-fold higher than that for soluble TNF. These results indicate a therapeutic potential for TBP I in diseases of the central nervous system associated with TNF overproduction.