Microglial tissue plasminogen activator (tPA) triggers neuronal apoptosis in vitro

Fibrinolytic and Non-fibrinolytic Roles of Tissue-type Plasminogen Activator in the Ischemic Brain

The neurovascular unit (NVU) is assembled by endothelial cells (ECs) and pericytes, and encased by a basement membrane (BM) surveilled by microglia and surrounded by perivascular astrocytes (PVA), which in turn are in contact with synapses. Cerebral ischemia induces the rapid release of the serine proteinase tissue-type plasminogen activator (tPA) from endothelial cells, perivascular astrocytes, microglia and neurons. Owning to its ability to catalyze the conversion of plasminogen into plasmin, in the intravascular space tPA functions as a fibrinolytic enzyme. In contrast, the release of astrocytic, microglial and neuronal tPA have a plethora of effects that not always require the generation of plasmin. In the ischemic brain tPA increases the permeability of the NVU, induces microglial activation, participates in the recycling of glutamate, and has various effects on neuronal survival. These effects are mediated by different receptors, notably subunits of the N-methyl-D-aspartate receptor (NMDAR) and the low-density lipoprotein receptor-related protein-1 (LRP-1). Here we review data on the role of tPA in the NVU under non-ischemic and ischemic conditions, and analyze how this knowledge may lead to the development of potential strategies for the treatment of acute ischemic stroke patients.

Proteomic profiling of interferon-responsive reactive astrocytes in rodent and human

Astrocytes are a heterogeneous population of central nervous system glial cells that respond to pathological insults and injury by undergoing a transformation called "reactivity." Reactive astrocytes exhibit distinct and context-dependent cellular, molecular, and functional state changes that can either support or disturb tissue homeostasis. We recently identified a reactive astrocyte sub-state defined by interferon-responsive genes like Igtp, Ifit3, Mx1, and others, called interferon-responsive reactive astrocytes (IRRAs). To further this transcriptomic definition of IRRAs, we wanted to define the proteomic changes that occur in this reactive sub-state. We induced IRRAs in immunopanned rodent astrocytes and human iPSC-differentiated astrocytes using TNF, IL1α, C1Q, and IFNβ and characterized their proteomic profile (both cellular and secreted) using unbiased quantitative proteomics. We identified 2335 unique cellular proteins, including IFIT2/3, IFITM3, OASL1/2, MX1/2/3, and STAT1. We also report that rodent and human IRRAs secrete PAI1, a serine protease inhibitor which may influence reactive states and functions of nearby cells. Finally, we evaluated how IRRAs are distinct from neurotoxic reactive astrocytes (NRAs). While NRAs are described by expression of the complement protein C3, it was not upregulated in IRRAs. Instead, we found ~90 proteins unique to IRRAs not identified in NRAs, including OAS1A, IFIT3, and MX1. Interferon signaling in astrocytes is critical for the antiviral immune response and for regulating synaptic plasticity and glutamate transport mechanisms. How IRRAs contribute to these functions is unknown. This study provides the basis for future experiments to define the functional roles of IRRAs in the context of neurodegenerative disorders.

Thrombolysis by PLAT/tPA increases serum free IGF1 leading to a decrease of deleterious autophagy following brain ischemia

Cerebral ischemia is a pathology involving a cascade of cellular mechanisms, leading to the deregulation of proteostasis, including macroautophagy/autophagy, and finally to neuronal death. If it is now accepted that cerebral ischemia induces autophagy, the effect of thrombolysis/energy recovery on proteostasis remains unknown. Here, we investigated the effect of thrombolysis by PLAT/tPA (plasminogen activator, tissue) on autophagy and neuronal death. In two in vitro models of hypoxia reperfusion and an in vivo model of thromboembolic stroke with thrombolysis by PLAT/tPA, we found that ischemia enhances neuronal deleterious autophagy. Interestingly, PLAT/tPA decreases autophagy to mediate neuroprotection by modulating the PI3K-AKT-MTOR pathways both in vitro and in vivo. We identified IGF1R (insulin-like growth factor I receptor; a tyrosine kinase receptor) as the effective receptor and showed in vitro, in vivo and in human stroke patients and that PLAT/tPA is able to degrade IGFBP3 (insulin-like growth factor binding protein 3) to increase IGF1 (insulin-like growth factor 1) bioavailability and thus IGF1R activation.Abbreviations: AKT/protein kinase B: thymoma viral proto-oncogene 1; EGFR: epidermal growth factor receptor; Hx: hypoxia; IGF1: insulin-like growth factor 1; IGF1R: insulin-like growth factor I receptor; IGFBP3: insulin-like growth factor binding protein 3; Ka: Kainate; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAPK/ERK: mitogen-activated protein kinase; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; OGD: oxygen and glucose deprivation; OGD_reox: oxygen and glucose deprivation + reoxygentation; PepA: pepstatin A1; PI3K: phosphoinositide 3-kinase; PLAT/tPA: plasminogen activator, tissue; PPP: picropodophyllin; SCH77: SCH772984; ULK1: unc-51 like kinase 1; Wort: wortmannin.

Enhanced expression of P2X4 purinoceptors in pyramidal neurons of the rat hippocampal CA1 region may be involved ischemia-reperfusion injury

Ischemic stroke is the most serious disease that harms human beings. In principle, its treatment is to restore blood flow supply as soon as possible. However, after the blood flow is restored, it will lead to secondary brain injury, that is, ischemia-reperfusion injury. The mechanism of ischemia-reperfusion injury is very complicated. This study showed that P2X4 receptors in the pyramidal neurons of rat hippocampus were significantly upregulated in the early stage of ischemia-reperfusion injury. Neurons with high expression of P2X4 receptors are neurons that are undergoing apoptosis. Intraventricular injection of the P2X4 receptor antagonist 5-(3-bromophenyl)-1,3-dihydro-2H-benzofuro[3,2-e]-1,4-diazepin-2-one (5-BDBD) and PSB-12062 can partially block neuronal apoptosis, to promote the survival of neurons, indicating that ATP through P2X4 receptors is involved in the process of cerebral ischemia-reperfusion injury. Therefore, identifying the mechanism of neuronal degeneration induced by extracellular ATP via P2X4 receptors after ischemia-reperfusion will likely find new targets for the treatment of ischemia-reperfusion injury, and will provide a useful theoretical basis for the treatment of ischemia-reperfusion injury.

Central Nervous System Neuron-Glia co-Culture Models and Application to Neuroprotective Agents

Glial cell activation plays an important role in the pathogenesis of various neurodegenerative disorders. This article presents a protocol for the preparation of cultures consisting of rat embryonic cortical neurons grown in the presence of cortical microglia, in which the glia are present in physical contact with the neurons or separated by a semipermeable membrane barrier. An example of how such systems can be used to evaluate potential neuroprotective agents will also be described.

11β-HSD1 in Human Fetal Membranes as a Potential Therapeutic Target for Preterm Birth

Human parturition is a complex process involving interactions between the myometrium and signals derived from the placenta, fetal membranes, and fetus. Signals originating from fetal membranes are crucial components that trigger parturition, which is clearly illustrated by the labor-initiating consequence of membrane rupture. It has been recognized for a long time that among fetal tissues in late gestation the fetal membranes possess the highest capacity for cortisol regeneration by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). However, the exact role of this unique feature remains a mystery. Accumulating evidence indicates that this extra-adrenal source of cortisol may serve as an upstream signal for critical events in human parturition, including enhanced prostaglandin and estrogen synthesis as well as extracellular matrix remodeling. This may explain why such high capacity for cortisol regeneration develops in human fetal membranes at late gestation. Therefore, inhibition of 11β-HSD1 may provide a potential therapeutic target for prevention of preterm birth. This review summarizes the current understanding of the functional role of cortisol regeneration by 11β-HSD1 in human fetal membranes.

White matter pathways as both a target and mediator of health behaviors

Health behaviors arise from the dynamics of highly interconnected networks in the brain and variability in these networks drives individual differences in behavior. In this review, we show how many factors that predict the physical health of the body also correlate with variability of the myelinated fascicles, called white matter, that connect brain regions together. The general pattern present in the literature is that as predictors of physical health decline, there is often a coincident reduction in the integrity of major white matter pathways. We also highlight a plausible mechanism, inflammatory pathways, whereby health-related activation of the immune system can impact the myelin sheath, a protective tissue that facilitates long range communication in the brain. The growing body of evidence supports the hypothesis that degrading health in the periphery may disrupt the communication efficiency of the macroscopic neural circuits that mediate complex behaviors, which can in turn contribute to poorer physical health.

Myelin basic protein stimulates plasminogen activation via tissue plasminogen activator following binding to independent l-lysine-containing domains

Myelin basic protein (MBP) is a key component of myelin, the specialized lipid membrane that encases the axons of all neurons. Both plasminogen (Pg) and tissue-type plasminogen activator (t-PA) bind to MBP with high affinity. We investigated the kinetics and mechanisms involved in this process using immobilized MBP and found that Pg activation by t-PA is significantly stimulated by MBP. This mechanism involves the binding of t-PA via a lysine-dependent mechanism to the Lys⁹¹ residue of the MBP NH₂-terminal region Asp⁸² -Pro⁹⁹, and the binding of Pg via a lysine-dependent mechanism to the Lys¹²² residue of the MBP COOH-terminal region Leu¹⁰⁹-Gly¹²⁶. In this context, MBP mimics fibrin and because MBP is a plasmin substrate, our results suggest direct participation of the Pg activation system on MBP physiology.

Morphine Withdrawal Increases Brain-Derived Neurotrophic Factor Precursor

Morphine has been shown to increase the expression of brain-derived neurotrophic factor (BDNF) in the brain. However, little is known about the effect of morphine withdrawal on BDNF and its precursor protein, or proBDNF, which induces neuronal apoptosis. In this work, we examined whether BDNF and proBDNF levels change in rats chronically injected with escalating doses of morphine and those who undergo spontaneous withdrawal for 60 h. We observed, in the frontal cortex and striatum, that the ratio of BDNF to proBDNF changed depending upon the experimental paradigm. Morphine treatment and morphine withdrawal increased both BDNF and proBDNF levels. However, the increase in proBDNF immunoreactivity in withdrawal rats was more robust than that observed in morphine-treated rats. proBDNF is processed either intracellularly by furin or extracellularly by the tissue plasminogen activator (tPA)/plasminogen system or matrix metalloproteases (MMPs). To examine the mechanisms whereby chronic morphine treatment and morphine withdrawal differentially affects BDNF/proBDNF, the levels MMP-3 and MMP-7, furin, and tPA were analyzed. We found that morphine increases tPA levels, whereas withdrawal causes a decrease. To confirm the involvement of tPA in the morphine-mediated effect on BDNF/proBDNF, we exposed cortical neurons to morphine in the presence of the tPA inhibitor plasminogen activator inhibitor-1 (PAI-1). This inhibitor reversed the morphine-mediated decrease in proBDNF, supporting the hypothesis that morphine increases the availability of BDNF by promoting the extracellular processing of proBDNF by tPA. Because proBDNF could negatively influence synaptic repair, preventing withdrawal is crucial for reducing neurotoxic mechanisms associated with opioid abuse.

Induction of Amnion Epithelial Apoptosis by Cortisol via tPA/Plasmin System

Rupture of fetal membranes (ROM) can initiate parturition at both term and preterm birth. Apoptosis of the amnion epithelium plays a key role in structural remodeling of the membranes preceding ROM. However, the causative factors for apoptosis remain unidentified. Toward the end of gestation, a feed-forward regeneration of cortisol via 11β-hydroxysteroid dehydrogenase 1 exists in the fetal membranes. Here, we have examined whether cortisol accumulation is a causative factor for amnion cells apoptosis. By using primary human amnion epithelial and fibroblast cells, we demonstrated cortisol induced apoptosis specifically in epithelial cells but not in fibroblasts via reciprocal regulation of tissue-type plasminogen activator (tPA)/plasmin system. Cortisol increased PLAT expression, the gene encoding tPA, via glucocorticoid receptor binding to a glucocorticoid response element in PLAT promoter, thereby increasing plasmin activity in epithelial cells. Further study revealed that a Fas-mediated extrinsic apoptotic pathway was involved in the induction of epithelial cells apoptosis by cortisol, which was blocked by inhibiting either tPA or plasmin. Consistently, cortisol increased cleaved-caspase-3 and tPA abundance in amnion tissue explants. Moreover, the abundance of cortisol, cleaved-caspase-3, and tPA was significantly increased in amnion tissue after labor-initiated spontaneous rupture of membranes. In conclusion, local accumulation of cortisol is a causative factor for amnion epithelial apoptosis via activation of tPA/plasmin system toward the end of gestation. This may contribute to the ROM at both term and preterm birth.

Ginsenoside Rg1 protects against sepsis-associated encephalopathy through beclin 1-independent autophagy in mice

BACKGROUND

Sepsis-associated encephalopathy (SAE), a commonly complicated syndrome, is associated with increased mortality in patients with sepsis. Currently, no specific diagnostic test or effective intervention exists to improve long-term consequences on cerebral function. Ginsenoside Rg1 (Rg1), a major component in ginseng, was reported to have pleiotropic properties including anti-inflammation and neuroprotection. The aim of our study was to investigate the protective effect of Rg1 on SAE and the potential mechanism.

MATERIALS AND METHODS

SAE model was prepared by inducing cecal ligation and puncture (CLP) in mice. Rg1 was injected 1 h before the CLP operation. Survival rate within 7 d after operation was analyzed. Surviving mice were subjected to Morris water maze tests and the brains were collected for histopathologic evaluation and immunohistochemistry. The hippocampus was obtained for Western blot, real time polymerase chain reaction, and enzyme-linked immunosorbent assay analysis.

RESULTS

Rg1 improved the postoperative survival rate and protected against sepsis-associated learning and memory impairments (Morris water maze). Besides, Rg1 was able to attenuate brain histopathologic changes (hematoxylin and eosin staining), suppress Iba1 activation, decrease the expressions of inflammatory cytokines (tumor necrosis factor α, interleukin 1β, and interleukin 6), and reduce neuronal apoptosis (cleaved caspase 3 activation) in hippocampus. Furthermore, the mechanism study showed that Rg1 suppressed the expressions of light chain 3-II and p62 in hippocampus but not beclin 1.

CONCLUSIONS

These findings suggested that Rg1 improved the survival rate and ameliorated cognitive impairments partially through regulating cerebral inflammation and apoptosis. In addition, the action mechanism might be noncanonical beclin 1-independent autophagy pathway. Rg1 may be a promising treatment strategy for SAE.

Microglia-blood vessel interactions: a double-edged sword in brain pathologies

Microglia are long-living resident immune cells of the brain, which secure a stable chemical and physical microenvironment necessary for the proper functioning of the central nervous system (CNS). These highly dynamic cells continuously scan their environment for pathogens and possess the ability to react to damage-induced signals in order to protect the brain. Microglia, together with endothelial cells (ECs), pericytes and astrocytes, form the functional blood-brain barrier (BBB), a specialized endothelial structure that selectively separates the sensitive brain parenchyma from blood circulation. Microglia are in bidirectional and permanent communication with ECs and their perivascular localization enables them to survey the influx of blood-borne components into the CNS. Furthermore, they may stimulate the opening of the BBB, extravasation of leukocytes and angiogenesis. However, microglia functioning requires tight control as their dysregulation is implicated in the initiation and progression of numerous neurological diseases. Disruption of the BBB, changes in blood flow, introduction of pathogens in the sensitive CNS niche, insufficient nutrient supply, and abnormal secretion of cytokines or expression of endothelial receptors are reported to prime and attract microglia. Such reactive microglia have been reported to even escalate the damage of the brain parenchyma as is the case in ischemic injuries, brain tumors, multiple sclerosis, Alzheimer's and Parkinson's disease. In this review, we present the current state of the art of the causes and mechanisms of pathological interactions between microglia and blood vessels and explore the possibilities of targeting those dysfunctional interactions for the development of future therapeutics.

The combination of astragalus membranaceus and ligustrazine ameliorates micro-haemorrhage by maintaining blood-brain barrier integrity in cerebrally ischaemic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Haemorrhagic transformation is an asymptomatic event that frequently occurs after following ischaemic stroke, particularly when pharmaceutical thrombolysis is used. However, the mechanism responsible for haemorrhagic transformation remains unknown, and therapeutics have not been identified. In this study, we administered a combination of astragalus membranaceus and ligustrazine to rats with cerebral ischaemia that had undergone thrombolysis. We analysed the effect of this combination on the attenuation of haemorrhagic transformation and the maintenance of blood-brain barrier integrity.

METHODS

A rat model of focal cerebral ischaemia was induced with autologous blood clot injections. Thrombolysis was performed via the intravenous injection of rt-PA. Astragalus membranaceus, ligustrazine or a combination of Astragalus membranaceus and ligustrazine was administered immediately after the clot injection. The cerebral infarct area, neurological deficits, blood-brain barrier integrity, and cerebral haemorrhage status were determined after 3, 6 and 24h of ischaemia. The ultrastructure of the blood-brain barrier was examined with a transmission electron microscope. The expression of tight junction proteins, including claudin-1, claudin-5, occludin, and zonula occludens-1, and matrix metallopeptidase-9 activation was further evaluated in terms of their roles in the protective effects of the combination drug on the integrity of the blood-brain barrier.

RESULTS

Ischaemia-induced Evans blue leakage and cerebral haemorrhage were markedly reduced in the combination drug-treated rats compared to the rats treated with either astragalus membranaceus or ligustrazine alone (p<0.05). The disruption of the ultrastructure of the blood-brain barrier and the neurological deficits were ameliorated by the combination treatment (p<0.05). The reductions in the expression of laudin-1, claudin-5, occludin, and ZO-1 were smaller in the rats that received the combination treatment. In addition, MMP-9 activity was suppressed in the combination-treated rats compared to the controls (p<0.05).

CONCLUSIONS

Treatment with a combination of astragalus membranaceus and ligustrazine alleviated ischaemia-induced micro-haemorrhage transformation by maintaining the integrity of the blood-brain barrier.

Fractalkine (CX3CL1) enhances hippocampal N-methyl-D-aspartate receptor (NMDAR) function via D-serine and adenosine receptor type A2 (A2AR) activity

BACKGROUND

N-Methyl-D-aspartate receptors (NMDARs) play fundamental roles in basic brain functions such as excitatory neurotransmission and learning and memory processes. Their function is largely regulated by factors released by glial cells, including the coagonist d-serine. We investigated whether the activation of microglial CX3CR1 induces the release of factors that modulate NMDAR functions.

METHODS

We recorded the NMDAR component of the field excitatory postsynaptic potentials (NMDA-fEPSPs) elicited in the CA1 stratum radiatum of mouse hippocampal slices by Shaffer collateral stimulation and evaluated D-serine content in the extracellular medium of glial primary cultures by mass spectrometry analysis.

RESULTS

We demonstrated that CX3CL1 increases NMDA-fEPSPs by a mechanism involving the activity of the adenosine receptor type A2 (A2AR) and the release of the NMDAR coagonist D-serine. Specifically (1) the selective A2AR blocker 7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH58261) and the genetic ablation of A2AR prevent CX3CL1 action while the A2AR agonist 5-(6-amino-2-(phenethylthio)-9H-purin-9-yl)-N-ethyl-3,4-dihydroxytetrahydrofuran-2-carboxamide (VT7) mimics CX3CL1 effect, and (2) the selective blocking of the NMDAR glycine (and D-serine) site by 5,7-dicholorokynurenic acid (DCKA), the enzymatic degradation of D-serine by D-amino acid oxidase (DAAO) and the saturation of the coagonist site by D-serine, all block the CX3CL1 effect. In addition, mass spectrometry analysis demonstrates that stimulation of microglia and astrocytes with CX3CL1 or VT7 increases D-serine release in the extracellular medium.

CONCLUSIONS

CX3CL1 transiently potentiates NMDAR function though mechanisms involving A2AR activity and the release of D-serine.

Plasminogen activator inhibitor-1 is increased in colonic epithelial cells from patients with colitis-associated cancer

BACKGROUND

Patients with long-term ulcerative colitis are at risk for developing colorectal cancer.

METHODS

Archival formalin-fixed paraffin-embedded tissue from ulcerative colitis patients who underwent a colectomy for high-grade dysplasia or carcinoma was examined for changes in expression of plasminogen activator inhibitor-1 (PAI-1) as well as other mediators of inflammation-associated cancer. Epithelia from areas of colons that showed histologic evidence of carcinoma, high-grade dysplasia, and epithelia that were not dysplastic or malignant but did contain evidence of prior inflammation (quiescent colitis) was microdissected using laser capture microscopy. mRNA was extracted from the microdissected tissue and PCR array analysis was performed. To extend our findings, PAI-1 protein levels were determined using immunohistochemistry.

RESULTS

The mRNA expression of PAI-1 is increased 6-fold (p=0.02) when comparing the carcinoma group to the quiescent colitis group; increases were also observed in NFKB2, REL, SRC, and VEGFA. The protein levels of PAI-1 are increased by 50% (p<0.001) in high-grade dysplasia and by 60% (p<0.001) in carcinoma when compared to the quiescent colitis group.

CONCLUSIONS

The increase in PAI-1 in high-grade dysplasia and carcinoma suggests a functional role for PAI-1 in malignant transformation in colitis-associated cancer. PAI-1 could also prove a useful diagnostic marker to identify patients at risk for neoplasia and it may be a useful therapeutic target to treat colitis-associated cancer.

Light-induced degeneration and microglial response in the retina of an epibenthonic pigmented teleost: age-dependent photoreceptor susceptibility to cell death

Constant intense light causes apoptosis of photoreceptors in the retina of albino fish. However, very few studies have been performed on pigmented species. Tench (Tinca tinca) is a teleost inhabiting dimly lit environments that has a predominance of rods within the photoreceptor layer. To test the hypothesis that constant high intensity light can result in retinal damage in such pigmented epibenthonic teleost species, photodegeneration of the retina was investigated in the larvae and in juveniles of tench to assess whether any damage may also be dependent on fish age. We exposed both groups of animals to 5 days of constant darkness, followed by 4 days of constant 20,000 lx light, and then by 6 days of recovery in a 14 h light:10 h dark cycle. The results showed that the retina of the larvae group exhibited abundant photoreceptor cell apoptosis during the time of exposition to intense light, whereas that of juveniles was indifferent to it. Damaged retinas showed a strong TUNEL signal in photoreceptor nuclei, and occasionally a weak cytoplasmic TUNEL signal in Müller glia. Specific labelling of microglial cells with Griffonia simplicifolia lectin (GSL) histochemistry revealed that photoreceptor cell death alerts microglia in the degenerating retina, leading to local proliferation, migration towards the injured outer nuclear layer (ONL), and enhanced phagocytosis of photoreceptor debris. During the first days of intense light treatment, Müller cells phagocytosed dead photoreceptor cells but, once microglial cells became activated, there was a progressive increase in the phagocytic capacity of the microglia.

Activators and inhibitors of the plasminogen system in Alzheimer's disease

Accumulation and deposition of Aβ is one of the main neuropathological hallmarks of Alzheimer's disease (AD) and impaired Aβ degradation may be one mechanism of accumulation. Plasmin is the key protease of the plasminogen system and can cleave Aβ. Plasmin is activated from plasminogen by tissue plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). The activators are regulated by inhibitors which include plasminogen activator inhibitor-1 (PAI-1) and neuroserpin. Plasmin is also regulated by inhibitors including α2-antiplasmin and α2-macroglobulin. Here, we investigate the mRNA levels of the activators and inhibitors of the plasminogen system and the protein levels of tPA, neuroserpin and α2-antiplasmin in post-mortem AD and control brain tissue. Distribution of the activators and inhibitors in human brain sections was assessed by immunoperoxidase staining. mRNA measurements were made in 20 AD and 20 control brains by real-time PCR. In an expanded cohort of 38 AD and 38 control brains tPA, neuroserpin and α2-antiplasmin protein levels were measured by ELISA. The activators and inhibitors were present mainly in neurons and α2-antiplasmin was also associated with Aβ plaques in AD brain tissue. tPA, uPA, PAI-1 and α2-antiplasmin mRNA were all significantly increased in AD compared to controls, as were tPA and α2-antiplasmin protein, whereas neuroserpin mRNA and protein were significantly reduced. α2-macroglobulin mRNA was not significantly altered in AD. The increases in tPA, uPA, PAI-1 and α2-antiplasmin may counteract each other so that plasmin activity is not significantly altered in AD, but increased tPA may also affect synaptic plasticity, excitotoxic neuronal death and apoptosis.

Mild hypothermia of 34°C reduces side effects of rt-PA treatment after thromboembolic stroke in rats

BACKGROUND

Hypothermia is neuroprotective in experimental stroke and may extend the so far limited therapeutic time window for thrombolysis. Therefore, hypothermia of 34°C and its effects on delayed thrombolysis including reperfusion-associated injury were investigated in a model of thromboembolic stroke (TE).

METHODS

Male Wistar rats (n = 48) were subjected to TE. The following treatment groups were investigated: control group - normothermia (37°C); thrombolysis group - rt-PA 90 min after TE; hypothermia by 34°C applied 1.5 to 5 hours after TE; combination therapy- hypothermia and rt-PA. After 24 hours infarct size, brain edema and neuroscore were assessed. Protein markers for inflammation and adhesion, gelatinase activity, and blood brain barrier (BBB) disruption were determined. MRI-measurements investigated infarct evolution and blood flow parameters.

RESULTS

The infarct volume and brain swelling were smaller in the hypothermia group compared to the other groups (p < 0.05 to p < 0.01). Thrombolysis resulted in larger infarct and brain swelling than all others. Hypothermia in combination with thrombolysis reduced these parameters compared to thrombolysis (p < 0.05). Moreover, the neuroscore improved in the hypothermia group compared to control and thrombolysis. Animals of the combination therapy performed better than after thrombolysis alone (p < 0.05). Lower serum concentration of sICAM-1, and TIMP-1 were shown for hypothermia and combination therapy. Gelatinase activity was decreased by hypothermia in both groups.

CONCLUSIONS

Therapeutic hypothermia reduced side-effects of rt-PA associated treatment and reperfusion in our model of TE.

Microglia and neuronal cell death

Microglia, the brain's innate immune cell type, are cells of mesodermal origin that populate the central nervous system (CNS) during development. Undifferentiated microglia, also called ameboid microglia, have the ability to proliferate, phagocytose apoptotic cells and migrate long distances toward their final destinations throughout all CNS regions, where they acquire a mature ramified morphological phenotype. Recent studies indicate that ameboid microglial cells not only have a scavenger role during development but can also promote the death of some neuronal populations. In the mature CNS, adult microglia have highly motile processes to scan their territorial domains, and they display a panoply of effects on neurons that range from sustaining their survival and differentiation contributing to their elimination. Hence, the fine tuning of these effects results in protection of the nervous tissue, whereas perturbations in the microglial response, such as the exacerbation of microglial activation or lack of microglial response, generate adverse situations for the organization and function of the CNS. This review discusses some aspects of the relationship between microglial cells and neuronal death/survival both during normal development and during the response to injury in adulthood.

Central nervous system neuron-glia co-culture models

Glial cell activation plays an important role in the pathogenesis of various neurodegenerative disorders. This article presents a protocol for the preparation of cultures consisting of rat embryonic cortical neurons grown in the presence of cortical microglia, in which the glia are present in physical contact with the neurons or separated by a semi-permeable membrane barrier.

tPA in the injured central nervous system: different scenarios starring the same actor?

When in 1947, Astrup and Permin reported that animal tissues contain fibrinokinase, a plasminogen activator, and when Pennica and colleagues (Pennica et al., 1983) cloned and expressed human tissue plasminogen activator (tPA) in Escherichia coli in 1983, they might did not realize how much their pioneer work would impact the life of millions of patients suffering from myocardial infarction or ischemic stroke. Some years after, accumulating evidence shows that tPA is not just a plasminogen activator of endothelial origin. Indeed, the main function of tPA released from the endothelium is to convert fibrin-bound plasminogen into active plasmin, thus dissolving the fibrin meshwork of blood clots. But this serine protease is also expressed by several cell types, and its beneficial and deleterious actions stand beyond fibrinolysis or even proteolysis. We will review here the reported effects and mechanisms of action of tPA in the course of three different pathologies of the central nervous system (CNS): spinal cord injury, ischemic stroke and multiple sclerosis. While these three disorders have distinct aetiologies, they share some pathogenic mechanisms. We will depict the main "good" and "bad" sides of tPA described to date during each of these pathological situations, as well as the proposed mechanisms explaining these effects. We speculate that due to common pathogenic pathways, tPA's actions described in one particular disease could in fact occur in the others. Finally, we will evaluate if tPA could be a therapeutic target for these pathologies. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

Neurotoxic factors released by stimulated human monocytes and THP-1 cells

Activated monocytes/macrophages are known to release toxic materials. Identification of these materials is important for developing more effective treatments for inflammatory disorders where self attack occurs. We stimulated human monocytes and THP-1 cells with LPS/IFNγ and measured the toxic effects of their conditioned media against differentiated human NT-2 cells. Their cytotoxicity, as measured by LDH release, was reduced by half when their conditioned media was passed through a 3kDa cutoff filter, indicating an equal division between high and low molecular weight materials. When the high molecular weight components tumor necrosis factor-α (TNFα), interleukin-1β (IL-1β), and IL-6 were removed from the conditioned medium by specific antibodies, the toxicity was reduced by 37-38%. When prostaglandin production was blocked by treatment with the COX inhibitors acetylsalicylic acid and ibuprofen, toxicity was reduced by 15-16%. When oxygen free radical production was blocked by the NADPH inhibitor diphenylene iodonium (DPI) the toxicity was reduced by 17-18%. Treatment with the nitric oxide scavenger carboxy-phenyl-tetramethylimidazolineoxyl-oxide, or the NOS inhibitor N(G)-monomethylene-l-arginine, attenuated the toxicity by about 20%. Removal of released glutamate by glutamate decarboxylase also attenuated the toxicity by 12-13%. In combination, these treatments reduced the toxicity by approximately 50% accounting for the low molecular weight component toxicity. About 10% of the overall toxicity, which was associated with the high molecular weight component, was not identified. Optimal antiinflammatory therapy may require combined suppression of these identified toxin-generating pathways as well as relatively minor pathways yet to be identified.

Association between neuroserpin and molecular markers of brain damage in patients with acute ischemic stroke

BACKGROUND

Neuroserpin has shown neuroprotective effects in animal models of cerebral ischemia and has been associated with functional outcome after ischemic stroke. Our aim was to study whether neuroserpin serum levels could be associated to biomarkers of excitotoxicity, inflammation and blood brain barrier disruption.

METHODS

We prospectively included 129 patients with ischemic stroke (58.1% male; mean age, 72.4 ± 9.6 years) not treated with tPA within 12 hours (h) of symptoms onset (mean time, 4.7 ± 2.1 h). Poor functional outcome at 3 months was considered as a modified Rankin scale score >2. Serum levels of neuroserpin, Interleukin 6 (IL-6), Intercellular adhesion molecule-1 (ICAM-1), active Matrix metalloproteinase 9 (MMP-9), and cellular fibronectin (cFn) (determined by ELISA) and glutamate (determined by HPLC) were measured on admission, 24 and 72 h. The main variable was considered the decrease of neuroserpin levels within the first 24 h. ROC analysis was used to select the best predictive value for neuroserpin to predict poor functional outcome due to a lack of linearity.

RESULTS

The decrease of neuroserpin levels within the first 24 h was negatively correlated with serum levels at 24 hours of glutamate (r = -0.642), IL-6 (r = -0.678), ICAM-1 (r = -0.345), MMP-9 (r = -0.554) and cFn (r = -0.703) (all P < 0.0001). In the multivariate analysis, serum levels of glutamate (OR, 1.04; CI95%, 1.01-1.06, p = 0.001); IL-6 (OR, 1.4; CI95%, 1.1-1.7, p = 0.001); and cFn (OR, 1.3; CI95%, 1.1-1.6, p = 0.002) were independently associated with a decrease of neuroserpin levels <70 ng/mL at 24 h after adjusting for confounding factors.

CONCLUSIONS

These findings suggest that neuroprotective properties of neuroserpin may be related to the inhibition of excitotoxicity, inflammation, as well as blood brain barrier disruption that occur after acute ischemic stroke.

Direct protection of cultured neurons from ischemia-like injury by minocycline

Minocycline, a tetracycline antibiotic, is now known to protect cells via an anti-inflammatory mechanism. We further explored this effect using an in vitro model of ischemia-like injury to neurons. Coculturing neurons with microglia, the brain's resident immune cell, modestly increased cell death due to oxygen and glucose deprivation (OGD), compared to neurons alone. Treatment of cocultures with minocycline decreased cell death to a level significantly lower than that of neurons alone. Treatment of cocultures with minocycline or inhibitors of various immune mediators, also led to decreased cell death. Importantly, treatment of neuron cultures without added microglia with these same inhibitors of tissue plasminogen activator, matrix metalloproteinases, TNF-alpha and inducible nitric oxide synthase as well as minocycline also led to decreased cell death. Thus, anti-inflammatory treatments appear to be directly protective of neurons from in vitro ischemia.

The TGF-beta1/upstream stimulatory factor-regulated PAI-1 gene: potential involvement and a therapeutic target in Alzheimer's disease

Amyloid peptide (Aβ) aggregates, derived from initial β-site proteolytic processing of the amyloid precursor protein (APP), accumulate in the brains of Alzheimer's disease patients. The plasmin-generating cascade appears to serve a protective role in the central nervous system since plasmin-mediated proteolysis of APP utilizes the α site, eventually generating nontoxic peptides, and plasmin also degrades Aβ. The conversion of plasminogen to plasmin by tissue-type plasminogen activator in the brain is negatively regulated by plasminogen activator inhibitor type-1 (PAI-1) resulting in attenuation of plasmin-dependent substrate degradation with resultant accumulation of Aβ. PAI-1 and its major physiological inducer TGF-β1, moreover, are increased in models of Alzheimer's disease and have been implicated in the etiology and progression of human neurodegenerative disorders. This review highlights the potential role of PAI-1 and TGF-β1 in this process. Current molecular events associated with TGF-β1-induced PAI-1 transcription are presented with particular relevance to potential targeting of PAI-1 gene expression as a molecular approach to the therapy of neurodegenerative diseases associated with increased PAI-1 expression such as Alzheimer's disease.

The time-dependent effect of lipopolysaccharide on kainic acid-induced neuronal death in hippocampal CA3 region: possible involvement of cytokines via glucocorticoid

It has been reported that glucocorticoid (Gc) can induce neuronal cell toxicity in the hippocampus. In addition, we examined that serum Gc increased by restraint stress aggravated kainic acid (KA)-induced neuronal death in hippocampal CA3 region. However, the effect of other stressful stimulus like lipopolysaccharide (LPS) increasing serum Gc on KA-induced neuronal death was not elucidated until now. Thus, we examined the time course effect of LPS on KA-induced neuronal death in the hippocampal CA3 region of mice, especially to address the role of Gc and inflammatory mediators. In the present study, we found that an aggravating effect of LPS on KA-induced neuronal death was correlated with an alteration of hippocampal IL-1beta mRNA level at all time points, and the serum Gc and hippocampal IL-1beta mRNA level was peak at 90 min after LPS treatment (LPS 90 min) when the aggravating effect of LPS on KA-induced neuronal death was maximum. In addition, RU38486 (glucocorticoid receptor antagonist) decreased the hippocampal IL-1beta mRNA level and abolished the aggravating effect of LPS on KA-induced neuronal death at LPS 90 min and 24 h. In the immunohistochemical study, we found activated and ramified microglia (OX-42) and astrocyte (GFAP) at 24 h after LPS treatment (LPS 24 h) in the hippocampus. These results suggest that Gc itself, cytokines triggered by Gc, or both appears to be involved in the LPS effect depending on LPS pretreatment time.

Inflammation and NFkappaB activation is decreased by hypothermia following global cerebral ischemia

We previously showed that hypothermia attenuates inflammation in focal cerebral ischemia (FCI) by suppressing activating kinases of nuclear factor-kappa B (NFkappaB). Here we characterize the inflammatory response in global cerebral ischemia (GCI), and the influence of mild hypothermia. Rodents were subjected to GCI by bilateral carotid artery occlusion. The inflammatory response was accompanied by microglial activation, but not neutrophil infiltration, or blood brain barrier disruption. Mild hypothermia reduced CA1 damage, decreased microglial activation and decreased nuclear NFkappaB translocation and activation. Similar anti-inflammatory effects of hypothermia were observed in a model of pure brain inflammation that does not cause brain cell death. Primary microglial cultures subjected to oxygen glucose deprivation (OGD) or stimulated with LPS under hypothermic conditions also experienced less activation and less NFkappaB translocation. However, NFkappaB regulatory proteins were not affected by hypothermia. The inflammatory response following GCI and hypothermia's anti-inflammatory mechanism is different from that observed in FCI.

Tissue-type plasminogen activator as a therapeutic target in stroke

BACKGROUND

Ischemic stroke is a leading cause of morbidity and mortality worldwide and recombinant human tissue-type plasminogen activator (tPA) is the prominent therapeutic among very few therapeutics used in its treatment. Due to complications attributed to the drug, most notably transformation of ischemia to hemorrhage, tPA is only used in a small number of ischemic stroke cases, albeit significantly more often in specialized stroke centers.

OBJECTIVE

What are the mechanisms of tPA action and side effects in ischemic stroke, and can the knowledge about these mechanisms aid in making tPA a more efficacious and safe therapeutic or in developing alternative therapeutics?

METHODS

tPA use and alternative/combination therapies in acute ischemic stroke treatment are summarized. The review focuses on literature concerning tPA neurotoxicity and its implications for further development of tPA as a stroke therapeutic.

RESULTS/CONCLUSION

Exogenously administered recombinant tPA and endogenous tPA have both turned into promising therapeutic targets for the stroke patient.

Enhanced poly(ADP-ribose) polymerase-1 activation contributes to recombinant tissue plasminogen activator-induced aggravation of ischemic brain injury in vivo

Recombinant tissue plasminogen activator (rt-PA) treatment improves functional outcome after acute ischemic stroke, inducing reperfusion by its thrombolytic activity. Conversely, there is evidence that rt-PA can mediate neuronal damage after ischemic brain injury in vivo. In addition to other mechanisms, enhancement of N-methyl-D-aspartate (NMDA) receptor signalling has been proposed to underlie rt-PA-mediated neurotoxicity. However, the role of poly(ADP-ribose) polymerase-1 (PARP-1) activation, which mediates postischemic excitotoxic cell death, in rt-PA-mediated aggravation of ischemic brain injury has not been established and was therefore addressed in this study. After permanent focal cerebral ischemia, intravenous rt-PA application significantly increased early postischemic PARP-1 activation within ischemic hemispheres and infarct volumes compared with control mice without affecting cerebral blood flow. Rt-PA induced increase in PARP-1 activation, and infarct volumes could be blocked by the PARP inhibitor 3-aminobenzamide. Moreover, the rt-PA-induced increase in PARP-1 activation was also prevented by the NMDA antagonist MK-801. In summary, we demonstrate that rt-PA treatment enhances postischemic PARP-1 activation, which contributes to rt-PA induced aggravation of ischemic brain injury in vivo. Furthermore, we provide evidence that NMDA receptor activation is required for rt-PA-mediated effects on postischemic PARP-1 activation.

Combination Therapy Using tPA and Edaravone Improves the Neurotoxic Effect of tPA

SUMMARY

In acute ischemic stroke patients, administration of tissue plasminogen activator (tPA) was proven to improve clinical outcome. On the other hand, neurotoxic effects of tPA have been reported in animal experimental studies. Using a rat thromboembolic stroke model, we examined whether or not the free radical scavenger, edaravone, could attenuate such neurotoxic effect of tPA administered for the purpose of fibrinolysis. Even when early recanalization was induced by administering tPA at 30 minutes after the onset of ischemia, significant amount of tPA was extravasated through the cerebral vessels. Edaravone significantly attenuated extravasation of tPA. Combination therapy using tPA and edaravone appears to be a promising strategy for diminishing the negative effects of tPA.

Addition of intravenous N-methyl-D-aspartate receptor antagonists to local fibrinolytic therapy for the optimal treatment of experimental intracerebral hemorrhages

OBJECT

Fibrinolytic therapy with recombinant tissue plasminogen activator (rtPA) is considered a treatment option in patients with deep-seated intracerebral hemorrhage (ICH). Nevertheless, the results of animal experiments have shown that tPA exerts pleiotropic actions in the brain, including regulation of vasoactivity, amplification of calcium conductance by cleavage of the N-methyl-D-aspartate (NMDA) receptor subunit, and activation of metalloproteinases, which increase excitotoxicity, damage the blood-brain barrier, and worsen edema. The authors investigated whether the noncompetitive NMDA receptor antagonist MK801 can be used as an adjuvant therapy in combination with rtPA to attenuate the unfavorable delayed edema formation and inflammation observed following rtPA therapy in an experimental porcine model of ICH.

METHODS

Twenty pigs were used in this study; MK801 (0.3 mg/kg) was administered to each pig intravenously immediately after hematoma induction and on the 1st and 3rd day after hematoma induction. Ten of the 20 pigs were randomly assigned to fibrinolytic therapy with rtPA (MK801-tPA group), whereas in the remaining 10 control animals (MK801 group) the hematomas were allowed to follow their natural courses of resorption. The extent of edema formation was evaluated using magnetic resonance (MR) imaging volumetry on Days 0, 4, and 10 after hematoma induction and was compared with histopathological changes found at necropsy. The mean edema volumes in these two groups were also compared with that in the group of nine pigs examined in a preceding experimental series, in which the animals' hematomas were only treated with rtPA (tPA group). In the 10 animals in the MK801-tPA group, the mean perihematoma edema volume on MR images had not significantly increased by Day 4 (p < 0.08) or Day 10 (p < 0.35) after hematoma induction. In the 10 animals in the MK801 group, the increase in mean perifocal edema size was significant after 4 days (p < 0.001) and nonsignificant after 10 days (p < 0.09). In the nine animals in the tPA group, the mean edema volume significantly increased by Days 4 (p < 0.002) and 10 (p < 0.03).

CONCLUSIONS

As suggested by the reduction in delayed edema volume and the inflammatory response, MK801 modifies the neurotoxic properties of rtPA but not those of blood degradation products. Possibly, fibrinolytic therapy of ICH is more beneficial if combined with agents such as MK801.

Kainate induces rapid redistribution of the actin cytoskeleton in ameboid microglia

Microglia are key mediators of the immune response in the central nervous system (CNS). They are closely related to macrophages and undergo dramatic morphological and functional changes after CNS trauma or excitotoxic lesions. Microglia can be directly stimulated by excitatory neurotransmitters and are known to express many neurotransmitter receptors. The role of these receptors, however, is not clear. This study describes the microglial response to the glutamate receptor agonist kainate (KA) and shows via immunochemistry that the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate receptor subunit GluR1 is present on cultured microglia. In the presence of 100 microM or 1 mM KA, cultured microglia underwent dramatic morphological and cytoskeletal changes as observed by time-lapse photography and quantitative confocal analysis of phalloidin labeling. KA-stimulated microglia showed condensation of cytoplasmic actin filaments, rapid de- and repolymerization, and cytoplasmic redistribution of condensed actin bundles. Rearrangement of actin filaments-thought to be involved in locomotion and phagocytosis and to indicate an increased level of activation (for reviews see Greenberg [ 1995] Trends Cell Biol. 5:93-99; Imai and Kohsaka [ 2002] Glia 40:164-174)-was significantly increased in treated vs. control cultures. Morphological plasticity and membrane ruffling were also seen. These findings suggest direct microglial excitation via glutamate receptor pathways. Thus, neurotransmitter release after brain or spinal cord injury might directly modulate the inflammatory response.

The glutamate-glutamine cycle as an inducible, protective face of macrophage activation

Neuronal damage in HIV infection results mainly from chronic activation of brain tissue and involves inflammation, oxidative stress, and glutamate-related neurotoxicity. Glutamate toxicity acts via two distinct pathways: an excitotoxic one, in which glutamate receptors are hyperactivated, and an oxidative one, in which cystine uptake is inhibited, resulting in glutathione depletion, oxidative stress, and cell degeneration. A number of studies have shown that astrocytes normally take up glutamate, keeping extracellular glutamate concentration low in the brain and preventing excitotoxicity. They, in turn, provide the trophic amino acid glutamine via their expression of glutamine synthetase. These protective and trophic actions are inhibited in HIV infection, probably as a result of the effects of inflammatory mediators and viral proteins. In vitro and in vivo studies have demonstrated that activated microglia and brain macrophages (AMM) express the transporters and enzymes of the glutamate cycle. This suggests that in addition to their recognized neurotoxic properties in HIV infection, these cells exhibit some neuroprotective properties, which may partly compensate for the inhibited astrocytic function. This hypothesis might explain the discrepancy between microglial activation, which occurs early in the disease, and neuronal apoptosis and neuronal loss, which are late events. In this review, we discuss the possible neuroprotective and neurotrophic roles of AMM and their relationships with inflammation and oxidative stress.

MAPK-activated Protein Kinase 2 Deficiency in Microglia Inhibits Pro-inflammatory Mediator Release and Resultant Neurotoxicity

MAPK-activated protein kinase 2 (MAPKAP K2 or MK2) is one of several kinases directly regulated by p38 MAPK. A role for p38 MAPK in the pathology of Alzheimer disease (AD) has previously been suggested. Here, we provide evidence to suggest that MK2 also plays a role in neuroinflammatory and neurodegenerative pathology of relevance to AD. MK2 activation and expression were increased in lipopolysaccharide (LPS) + interferon gamma-stimulated microglial cells, implicating a role for MK2 in eliciting a pro-inflammatory response. Microglia cultured ex vivo from MK2-deficient (MK2-/-) mice demonstrated significant inhibition in release of tumor necrosis factor alpha, KC (mouse chemokine with highest sequence identity to human GROs and interleukin-8), and macrophage inflammatory protein 1alpha on stimulation with LPS + interferon gamma or amyloid-beta peptide (1-42) compared with MK2+/+ wild-type microglia. Consistent with an inhibition in pro-inflammatory mediator release, cortical neurons co-cultured with LPS + interferon gamma-stimulated or amyloid-beta peptide (1-42)-stimulated MK2-/- microglia were protected from microglial-mediated neuronal cell toxicity. In a transgenic mouse model of AD in which amyloid precursor protein and presenilin-1 harboring familial AD mutations are overexpressed in specific regions of the brain, elevated activation and expression of MK2 correlated with beta-amyloid deposition, microglial activation, and up-regulation of tumor necrosis factor alpha, macrophage inflammatory protein 1alpha, and KC gene expression in the same brain regions. Our data propose a role for MK2 in AD brain pathology, for which neuroinflammation involving cytokines and chemokines and overt neuronal loss have been documented.

Microglia potentiate damage to blood-brain barrier constituents: improvement by minocycline in vivo and in vitro

BACKGROUND

Blood-brain barrier (BBB) disruption after stroke can worsen ischemic injury by increasing edema and causing hemorrhage. We determined the effect of microglia on the BBB and its primary constituents, endothelial cells (ECs) and astrocytes, after ischemia using in vivo and in vitro models.

METHODS AND RESULTS

Primary astrocytes, ECs, or cocultures were prepared with or without added microglia. Primary ECs were more resistant to oxygen-glucose deprivation/reperfusion than astrocytes. ECs plus astrocytes showed intermediate vulnerability. Microglia added to cocultures nearly doubled cell death. This increase was prevented by minocycline and apocynin. In vivo, minocycline reduced infarct volume and neurological deficits and markedly reduced BBB disruption and hemorrhage in mice after experimental stroke.

CONCLUSIONS

Inhibition of microglial activation may protect the brain after ischemic stroke by improving BBB viability and integrity. Microglial inhibitors may prove to be an important treatment adjunct to fibrinolysis.

LRP and alphavbeta3 mediate tPA activation of smooth muscle cells

Tissue-type plasminogen activator (tPA) regulates vascular contractility through the low-density lipoprotein-related receptor (LRP), and this effect is inhibited by plasminogen activator inhibitor type 1 (PAI-1). We now report that tPA-mediated vasocontraction also requires the integrin alphavbeta3. tPA-induced contraction of rat aortic rings is inhibited by the Arg-Gly-Asp (RGD) peptide and by monoclonal anti-alphavbeta3 antibody. tPA induces the formation of a complex between LRP and alphavbeta3 in vascular smooth muscle cells. The three proteins are internalized within 10 min, causing the cells to become refractory to the readdition of tPA. LRP and alphavbeta3 return to the cell surface by 90 min, restoring cell responsiveness to tPA. PAI-1 and the PAI-1-derived hexapeptide EEIIMD abolish the vasocontractile activity of tPA and inhibit the tPA-mediated interaction between LRP and alphavbeta3. tPA induces calcium mobilization from intracellular stores in vascular smooth muscle cells, and this effect is inhibited by PAI-1, RGD, and antibodies to both LRP and alphavbeta3. These data indicate that tPA-mediated vasocontraction involves the coordinated interaction of LRP with alphavbeta3. Delineating the mechanism underlying these interactions and the nature of the signals transduced may provide new tools to regulate vascular tone and other consequences of tPA-mediated signaling.

Potentiation of the NMDA receptor-mediated responses through the activation of the glycine site by microglia secreting soluble factors

We have previously reported that both transferred microglia and microglia-conditioned medium (MCM) potentiated the N-methyl-D-aspatate (NMDA) receptor-mediated synaptic responses in cortical neurons. To elucidate the mechanism underlying the potentiation of NMDA receptor-mediated responses by microglia, we examined the effects of MCM on NMDA-induced inward currents in mechanically dissociated hippocampal CA1 neurons under whole-cell patch recordings. MCM potentiated the amplitude of NMDA-induced currents up to 10-fold in a dose-dependent manner, and this effect of MCM remained even after boiling or cutting off molecules with a molecular mass more than 3 kDa. In the presence of glycine with a concentration sufficient to saturate the NMDA receptor glycine site, MCM failed to further potentiate the NMDA-induced currents. The glycine site antagonist 5, 7-dichrolokynurenic acid, significantly inhibited the effects of MCM. The effect of MCM was still observed even after treatment with D-amino acid oxidase, a D-serine degrading enzyme. On the other hand, MCM had no significant effect on the voltage-dependent Mg(2+) blockade of NMDA receptors. Furthermore, MCM enhanced the formation of the long-term potentiation in the Schaffer collateral pathway-CA1 pyramidal cell synapses. Using a high performance liquid chromatography system, we found the levels of both glycine and L-serine in MCM to be significantly higher than those in the control medium. It was also noted that an increased glycine productivity of microglia was observed in the hippocampus in the acute phase of neuronal injury. These observations strongly suggest that glycine is a major causative molecule released from microglia that potentiates the NMDA-induced currents.

Inflammation following stroke

Stroke is one of the leading causes of mortality and morbidity. The stroke process triggers an inflammatory reaction that may last up to several months. Suppression of inflammation using a variety of drugs reduces infarct volume and improves clinical outcomes in animal models of stroke. This benefit occurs even with the initiation of therapy after 3 hours of onset of stroke, beyond the therapeutic window for thrombolysis with tPA. The use of neuroprotectants to suppress inflammation may widen the therapeutic time window for tPA while lessening its side-effects. Suppression of inflammation may also improve outcomes in animal models of haemorrhagic stroke. To date, clinical trials with anti-inflammatory agents in acute ischaemic stroke have failed to improve clinical outcomes. However, because of the potential for broader applicability across all aspects of stroke, a better understanding of anti-inflammatory mechanisms is important.

Tissue-type plasminogen activator acts as a cytokine that triggers intracellular signal transduction and induces matrix metalloproteinase-9 gene expression

Tissue-type plasminogen activator (tPA), a serine protease well known for generating plasmin, has been demonstrated to induce matrix metalloproteinase-9 (MMP-9) gene expression and protein secretion in renal interstitial fibroblasts. However, exactly how tPA transduces its signal into the nucleus to control gene expression is unknown. This study investigated the mechanism by which tPA induces MMP-9 gene expression. Both wild-type and non-enzymatic mutant tPA were found to induce MMP-9 expression in rat kidney interstitial fibroblasts (NRK-49F), indicating that the actions of tPA are independent of its proteolytic activity. tPA bound to the low density lipoprotein receptor-related protein-1 (LRP-1) in NRK-49F cells, and this binding was competitively abrogated by the LRP-1 antagonist, the receptor-associated protein. In mouse embryonic fibroblasts (PEA-13) lacking LRP-1, tPA failed to induce MMP-9 expression. Furthermore, tPA induced rapid tyrosine phosphorylation on the beta subunit of LRP-1, which was followed by the activation of Mek1 and its downstream Erk-1 and -2. Blockade of Erk-1/2 activation by the Mek1 inhibitor abolished MMP-9 induction by tPA in NRK-49F cells. Conversely, overexpression of constitutively activated Mek1 induced Erk-1/2 phosphorylation and MMP-9 expression. In mouse obstructed kidney, tPA, LRP-1, and MMP-9 were concomitantly induced in the renal interstitium. Collectively, these results suggest that besides its classical proteolytic activity, tPA acts as a cytokine that binds to the cell membrane receptor LRP-1, induces its tyrosine phosphorylation, and triggers intracellular signal transduction, thereby inducing specific gene expression in renal interstitial fibroblasts.

Attenuation of extravasation of tissue plasminogen activator by the free radical scavenger, edaravone: evaluation in a rat thromboembolic stroke model

OBJECTIVES AND METHODS

Deleterious effects of tissue plasminogen activator (tPA) have been described recently in experimental studies. For example, tPA can aggravate ischemic neuronal damage through its proteolytic activity. The present study was undertaken to examine whether or not the free radical scavenger, edaravone, could prevent the extravasation of tPA administered for the purpose of fibrinolysis in a rat model of thromboembolic stroke.

RESULTS

Significant amounts of tPA were extravasated through the cerebral vessels even when early recanalization was induced by administering tPA at 30 minutes after the onset of schema. Edaravone significantly attenuated such extravasation of tPA.

CONCLUSION

In acute ischemic stroke patients, combination therapy using tPA with edaravone appears to be a reasonable strategy for diminishing the negative effects of tPA.

Investigations with cultured human microglia on pathogenic mechanisms of Alzheimer's disease and other neurodegenerative diseases

Inflammation-mediated mechanisms for human neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD) have evolved from being on the fringe of medical hypotheses to mainstream thinking. Pioneering immunopathology studies with human brain tissues identified microglia associated with neuropathologic hallmarks of these diseases. As activated macrophages were known to produce many potential toxic products, this gave rise to the hypothesis that activated microglia (brain resident macrophages) could be contributing to the degeneration of key target neurons in these diseases, as well as potential vascular dysfunction. Studies with microglia derived from different sources, including human brains, have confirmed that activated microglia can mediate neuronal cell death. Based on these theories, a number of human clinical trials with antiinflammatory agents have been carried out on AD patients. Results to date have indicated a lack of effectiveness at slowing disease progression and have begun to cast doubt on the significance of inflammation in AD. It has been shown recently that activating microglia through immunization of amyloid plaque-developing mice with amyloid beta peptide (Abeta) has promise as a therapeutic strategy and despite some setbacks, has potential as a treatment for AD patients. This article will consider experimental data with microglia to determine whether the additional targets need to be investigated. The use of human microglia cultures, in particular those derived from elderly diseased human brains, offers an experimental system that can closely model the cell type activated in human neurodegenerative diseases. Experimental data produced by our laboratory and others is reviewed to determine the contribution of this unique experimental model to understanding disease mechanisms and possibly discovering new therapeutic targets.

Cell-autonomous death of cerebellar purkinje neurons with autophagy in Niemann-Pick type C disease

Niemann-Pick type C is a neurodegenerative lysosomal storage disorder caused by mutations in either of two genes, npc1 and npc2. Cells lacking Npc1, which is a transmembrane protein related to the Hedgehog receptor Patched, or Npc2, which is a secreted cholesterol-binding protein, have aberrant organelle trafficking and accumulate large quantities of cholesterol and other lipids. Though the Npc proteins are produced by all cells, cerebellar Purkinje neurons are especially sensitive to loss of Npc function. Since Niemann-Pick type C disease involves circulating molecules such as sterols and steroids and a robust inflammatory response within the brain parenchyma, it is crucial to determine whether external factors affect the survival of Purkinje cells (PCs). We investigated the basis of neurodegeneration in chimeric mice that have functional npc1 in only some cells. Death of mutant npc1 cells was not prevented by neighboring wild-type cells, and wild-type PCs were not poisoned by surrounding mutant npc1 cells. PCs undergoing cell-autonomous degeneration have features consistent with autophagic cell death. Chimeric mice exhibited a remarkable delay and reduction of wasting and ataxia despite their substantial amount of mutant tissue and dying cells, revealing a robust mechanism that partially compensates for massive PC death.

Niemann-Pick disease type C is a deadly neurodegenerative disease that is most often due to mutations in a gene called npc1. As a consequence of intracellular lipid trafficking defects, patients with Niemann-Pick type C, and mice with the same disease, lose an important class of cerebellar neurons called Purkinje cells (PCs). Npc1 (the protein coded by npc1) might be needed in other cell types to produce substances that nourish PCs or within the PCs themselves. To see which is true, the researchers constructed genetically mosaic mice in which some cells have mutant Npc1 and some have normal Npc1 function. In the cerebella of these mosaic mice, PCs lacking Npc1 continued to die even while surrounded by normal cells, while normal PCs appeared unaffected by their partially mutant surroundings. From these findings, the researchers concluded that the neurodegeneration is due to a problem within PCs and not due to a lack of supporting factors provided by other cells or an extrinsic toxic or inflammatory insult. Npc1 probably functions within PCs to allow critical transport processes necessary for cell survival. The researchers also found that the degenerating PCs undergo a complex process called autophagy in which the cells sense a lack of key nutrients and start to break down their own structures to feed themselves. By identifying exactly which cells require Npc1 function, the researchers set the stage for investigating the exact molecular roles of Npc1 protein in the cells where it is most needed.

Macrophages and neurodegeneration

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). Demyelination is a classical feature of MS lesions, and neurological deficits are often ascribed to the reduced signal conduction by demyelinated axons. However, recent studies emphasize that axonal loss is an important factor in MS pathogenesis and disease progression. Axonal loss is found in association with cellular infiltrates in MS lesions. In this review, we discuss the possible contribution of the innate immune system in this process. In particular, we describe how infiltrated macrophages may contribute to axonal loss in MS and in experimental autoimmune encephalomyelitis (EAE), the animal model for MS. An overview is given of the possible effects of mediators, which are produced by activated macrophages, such as such as pro-inflammatory cytokines, free radicals, glutamate and metalloproteases, on axonal integrity. We conclude that infiltrated macrophages, which are activated to produce pro-inflammatory mediators, may be interesting targets for therapeutic approaches aimed to prevent or reduce axonal loss during exacerbation of inflammation. Interference with the process of infiltration and migration of monocytes across the blood-brain barrier is one of the possibilities to reduce the damage by activated macrophages.