Pathophysiology of the blood-brain barrier

Association of FAK activation with lentivirus-induced disruption of blood-brain barrier tight junction-associated ZO-1 protein organization

Expression of tight junction proteins between brain microvascular endothelial cells (BMECs) of the blood-brain barrier (BBB) is lost during development of human immunodeficiency virus (HIV) encephalitis (HIVE). Although many studies have focused on the strains of virus that induce neurological sequelae or on the macrophages/microglia that are associated with development of encephalitis, the molecular signaling pathways within the BMECs involved have yet to be resolved. We have previously shown that there is activation and disruption of an in vitro BBB model using lentivirus-infected CEMx174 cells. We and others have shown similar disruption in vivo. Therefore, it was of interest to determine if the presence of infected cells could disrupt intact cerebral microvessels immediately ex vivo, and if so, which signaling pathways were involved. The present data demonstrate that disruption of tight junctions between BMECs is mediated through activation of focal adhesion kinase (FAK) by phosphorylation at TYR-397. Inhibition of FAK activation is sufficient to prevent tight junction disruption. Thus, it may be possible to inhibit the development of HIVE by using inhibitors of FAK.

Marcação imunoistoquímica da expressão astrocitária de proteína glial fibrilar ácida e de vimentina no sistema nervoso central de cães com cinomose

Uma vez que muitos dos aspectos envolvidos na patogenia dos processos desmielinizantes do sistema nervoso central (SNC) são ainda pouco esclarecidos e que os astrócitos parecem estar envolvidos na mediação de tais processos, este estudo analisou morfologicamente a participação astrocitária na desmielinização do SNC por meio da marcação imunoistoquímica de duas proteínas dos filamentos intermediários astrocitários - a proteína glial fibrilar ácida (GFAP) e a vimentina (VIM) -, comparando amostras de cerebelo e de tronco encefálico de oito cães com cinomose e de dois cães normais, de diferentes raças e com idades entre um e quatro anos. Cortes histológicos dos tecidos foram submetidos à marcação pelo método indireto da avidina-biotina-peroxidase (ABC) e a reatividade astrocitária, observada em microscopia de luz, foi quantificada em um sistema computacional de análise de imagens. Observou-se, na maioria dos cortes de animais doentes, a presença de lesões degenerativas compatíveis com desmielinização. A marcação para a GFAP e para a VIM foi mais intensa nos animais com cinomose do que nos animais normais, especialmente nas regiões circunventriculares e nas adjacentes às áreas de degeneração tecidual. Não houve diferença significativa entre a imunomarcação (GFAP e VIM) dos animais com cinomose com e sem infiltração inflamatória da substância branca do cerebelo. O aumento da imunorreatividade dos astrócitos para a GFAP e a reexpressão de VIM nas áreas lesionais indicam o envolvimento astrocitário na resposta do tecido nervoso às lesões desmielinizantes induzidas pelo vírus da cinomose (CDV) no SNC.

The contribution of protease-activated receptor 1 to neuronal damage caused by transient focal cerebral ischemia

The serine proteases tissue plasminogen activator, plasmin, and thrombin and their receptors have previously been suggested to contribute to neuronal damage in certain pathological situations. Here we demonstrate that mice lacking protease-activated receptor 1 (PAR1) have a 3.1-fold reduction in infarct volume after transient focal cerebral ischemia. Intracerebroventricular injection of PAR1 antagonist BMS-200261 reduced infarct volume 2.7-fold. There are no detectable differences between PAR1-/- and WT mice in cerebrovascular anatomy, capillary density, or capillary diameter, demonstrating that the neuroprotective phenotype is not likely related to congenital abnormalities in vascular development. We also show that the exogenously applied serine proteases thrombin, plasmin, and tissue plasminogen activator can activate PAR1 signaling in brain tissue. These data together suggest that if blood-derived serine proteases that enter brain tissue in ischemic situations can activate PAR1, this sequence of events may contribute to the harmful effects observed. Furthermore, PAR1 immunoreactivity is present in human brain, suggesting that inhibition of PAR1 may provide a novel potential therapeutic strategy for decreasing neuronal damage associated with ischemia and blood-brain barrier breakdown.

Serial analysis of soluble intercellular adhesion molecule-1 level in relapsing-remitting multiple sclerosis patients during IFN-beta1b treatment

In this controlled study, we investigated the serum and cerebrospinal fluid (CSF) levels of soluble intercellular adhesion molecule-1 (sICAM-1) in relapsing-remitting multiple sclerosis (RRMS) patients and changes in the levels of this adhesion molecule during interferon-beta1b (IFN-beta1b) treatment. We also investigated the changes in the levels of sICAM-1 in correlation with disease activity and with findings on magnetic resonance images (MRI). The study included 24 patients (16 females and 8 males) who were confirmed to have RRMS based on the criteria of Poser et al. Sixteen of the patients received IFN-beta1b (Betaseron, Berlex Laboratories, Schering AG Germany, Berlin) treatment, and 8 did not receive this therapy. The levels of sICAM-1 in the MS patients' serum and CSF were significantly higher than levels in individuals with noninflammatory neurologic disease (p = 0.0081 and p = 0.0001, respectively). In the first 3 months of the study, MS patients treated with IFN-beta1b showed a significant rise in sICAM-1 levels (p = 0.0023), whereas their untreated counterparts showed no significant change. Neither of the groups showed a significant correlation between sICAM-1 level and disease activity demonstrated by MRI or between sICAM-1 level and clinical disease activity. The findings suggest that IFN-beta1b treatment may have a short-term upregulating effect on sICAM-1.

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.

Expression and function of lysophosphatidic acid receptors in cultured rodent microglial cells

Microglia are the resident tissue macrophages of the central nervous system. They are rapidly activated by a variety of insults; and recently, receptors linked to cytoplasmic Ca(2+) signals have been implicated in such events. One potential class of receptors are those recognizing lysophosphatidic acid (LPA). LPA is a phospholipid signaling molecule that has been shown to cause multiple cellular responses, including increases in cytoplasmic calcium. We examined whether any of the known LPA receptor genes (lp(A1)/Edg2, lp(A2)/Edg4, and lp(A3)/Edg7) are expressed by cultured mouse or rat microglia. Reverse transcriptase-polymerase chain reaction indicated that mouse microglia predominantly expressed the lp(A1) gene, whereas rat microglia predominantly expressed lp(A3). Although LPA induced increases in the cytoplasmic Ca(2+) concentration in both microglial preparations, the responses differed substantially. The Ca(2+) signal in rat microglia occurred primarily through Ca(2+) influx via the plasma membrane, whereas the Ca(2+) signal in mouse microglia was due to release from intracellular stores. Only at high concentrations was an additional influx component recruited. Additionally, LPA induced increased metabolic activity in mouse (but not rat) microglial cells. Our findings provide evidence for functional LPA receptors on microglia. Thus, LPA might play an important role as a mediator of microglial activation in response to central nervous system injury.

Thrombin-induced activation of cultured rodent microglia

Microglia are the resident immune cells of the CNS. Upon brain damage, these cells are rapidly activated and function as tissue macrophages. The first steps in this activation still remain unclear, but it is widely believed that substances released from damaged brain tissue trigger this process. In this article, we describe the effects of the blood coagulation factor thrombin on cultured rodent microglial cells. Thrombin induced a transient Ca(2+) increase in microglial cells, which persisted in Ca(2+)-free media. It was blocked by thapsigargin, indicating that thrombin caused a Ca(2+) release from internal stores. Preincubation with pertussis toxin did not alter the thrombin-induced [Ca(2+)](i) signal, whereas it was blocked by hirudin, a blocker of thrombin's proteolytic activity. Incubation with thrombin led to the production of nitric oxide and the release of the cytokines tumor necrosis factor-alpha, interleukin-6, interleukin-12, the chemokine KC, and the soluble tumor necrosis factor-alpha receptor II and had a significant proliferative effect. Our findings indicate that thrombin, a molecule that enters the brain at sites of injury, rapidly triggered microglial activation.

Blood-cerebrospinal fluid barrier impairment as indicator for an immune process in schizophrenia

An impairment of the blood-cerebrospinal fluid barrier (BCB) has repeatedly been described in schizophrenic patients. A BCB impairment can be due to vascular leakage during an inflammatory process, or to neuroleptic treatment. The soluble intercellular adhesion molecule-1 (sICAM-1) has been demonstrated to be a reliable marker for an inflammatory process causing an BCB impairment. To clarify the basis of a BCB impairment in schizophrenic patients, we measured the sICAM-1 levels in CSF of 40 schizophrenic patients. High concentrations of sICAM-1 were found to be related to high concentrations of albumin, IgG and total protein in CSF. A BCB impairment was associated with high levels of sICAM-1. Our data indicate an inflammatory mechanism of BCB impairment in schizophrenics and should enrich the discussion on an expanded immunological diagnosis in schizophrenia.

Luciferase: a sensitive and quantitative probe for blood-brain barrier disruption

A novel method for quantitative analysis of blood-brain barrier (BBB) disruption is described, using luciferase as a probe in a murine model system. Purified luciferase was delivered to mouse brain by osmotic BBB disruption with hypertonic mannitol; control animals received an intracarotid inoculation of saline prior to infusion of luciferase. Delivery of luciferase to brain tissue was then assessed by enzyme assay of tissue extracts, and by immunohistochemical staining. Luciferase activity in the brain of mannitol-treated animals was found to be significantly elevated (approx. sevenfold), when compared to activity in control (saline-treated) mice. This finding was confirmed by quantitative immunohistochemical staining of tissue sections, using a luciferase-specific antibody. These studies showed that there was an eight-fold elevation in the level of extravascular luciferase particles within the brain of mannitol-treated animals, as compared to controls. Taken together these data show that purified recombinant luciferase can be used as a sensitive probe, with which to study the integrity of the BBB.

Multiple sclerosis: the increased frequency of the ICAM-1 exon 6 gene point mutation genetic type K469

Intracellular adhesion molecule-1 (ICAM-1) plays an important role in the cascade of adhesion events in the homing of inflammatory cells to the central nervous system (CNS) in experimental autoimmune encephalomyelitis (EAE) and in multiple sclerosis (MS). Two single-base ICAM-1 polymorphisms have been described, in exons 4 and 6, changing codons 241 and 469 in the ICAM-1 gene, respectively. Both polymorphisms result in amino acid changes and can potentially lead to different interactions of ICAM-1 with its ligands. To detect ICAM-1 gene polymorphisms in MS, we have developed a highly sensitive and site-specific, two-stage, nested polymerase chain reaction. Genomic DNA was extracted from blood cells of 79 MS patients and 68 control subjects. The results were confirmed by direct dideoxy chain termination sequencing. The frequency of exon 6 allele T was found to be significantly higher in MS patients than in controls (68% vs 49%). Most interesting, the frequency of exon 6 homozygote K469 was significantly higher in MS patients than in controls (53% vs 34%). Higher frequency of the K469 genotype was found to be independent of possible linkage with the previously described MS susceptibility factor, the HLA class II DR2 allele. In the present study, we have shown for the first time the ICAM-1 gene polymorphisms in MS. The results indicate increased frequency of ICAM-1 exon 6 allele T in MS patients, which may contribute to the MS genetics background.