Focal cerebral ischemia induces active proteases that degrade microvascular matrix

High t-PA release by neonate brain microvascular endothelial cells under glutamate exposure affects neuronal fate

Glutamate excitotoxicity is a consolidated hypothesis in neonatal brain injuries and tissue plasminogen activator (t-PA) participates in the processes through proteolytic and receptor mediated effects. In brain microvascular endothelial cell (nBMEC) cultures from neonates, t-PA content and release upon glutamate are higher than in adult (aBMECs) cultures. Owing to the variety of t-PA substrates and receptor targets, the study was aimed at determining the putative roles of endothelial t-PA in the neonatal brain parenchyma under glutamate challenge. Basal t-PA release was 4.4 fold higher in nBMECs vs aBMECs and glutamate was 20 fold more potent to allow Evans blue vascular permeability in neonate microvessels indicating that, under noxious glutamate (50 μM) exposure, high amounts of endothelial t-PA stores may be mobilized and may access the nervous parenchyma. Culture media from nBMECS or aBMECs challenged by excitotoxic glutamate were applied to neuron cultures at DIV 11. While media from adult cells did not evoke more LDH release in neuronal cultures that under glutamate alone, media from nBMECs enhanced 2.2 fold LDH release. This effect was not observed with media from t-PA(-/-) nBMECs and was inhibited by hr-PAI-1. In Cortical slices from 10 day-old mice, hrt-PA associated with glutamate evoked neuronal necrosis in deeper (more mature) layers, an effect reversed by NMDA receptor GluN1 amino-terminal domain antibody capable of inhibiting t-PA potentiation of the receptor. In superficial layers (less mature), hrt-PA alone inhibited apoptosis, an effect reversed by the EGF receptor antagonist AG1478. Applied to immature neurons in culture (DIV5), media from nBMEC rescued 85.1% of neurons from cell death induced by serum deprivation. In cortical slices, the anti-apoptotic effect of t-PA fitted with age dependent localization of less mature neurons. These data suggest that in the immature brain, propensity of vessels to release high amounts of t-PA may not only impact vascular integrity but may also influence neuronal fate, via regulation of apoptosis in immature cells and, as in adult by potentiating glutamate toxicity in mature neurons. The data point out putative implication of microvessels in glutamate neurotoxicity in the development, and justify research towards vessel oriented neuroprotection strategies in neonates.

Perlecan Domain V induces VEGf secretion in brain endothelial cells through integrin α5β1 and ERK-dependent signaling pathways

Perlecan Domain V (DV) promotes brain angiogenesis by inducing VEGF release from brain endothelial cells (BECs) following stroke. In this study, we define the specific mechanism of DV interaction with the α₅β₁ integrin, identify the downstream signal transduction pathway, and further investigate the functional significance of resultant VEGF release. Interestingly, we found that the LG3 portion of DV, which has been suggested to possess most of DV’s angio-modulatory activity outside of the brain, binds poorly to α₅β₁ and induces less BEC proliferation compared to full length DV. Additionally, we implicate DV’s DGR sequence as an important element for the interaction of DV with α₅β₁. Furthermore, we investigated the importance of AKT and ERK signaling in DV-induced VEGF expression and secretion. We show that DV increases the phosphorylation of ERK, which leads to subsequent activation and stabilization of eIF4E and HIF-1α. Inhibition of ERK activity by U0126 suppressed DV-induced expression and secretion of VEGR in BECs. While DV was capable of phosphorylating AKT we show that AKT phosphorylation does not play a role in DV’s induction of VEGF expression or secretion using two separate inhibitors, LY294002 and Akt IV. Lastly, we demonstrate that VEGF activity is critical for DV increases in BEC proliferation, as well as angiogenesis in a BEC-neuronal co-culture system. Collectively, our findings expand our understanding of DV’s mechanism of action on BECs, and further support its potential as a novel stroke therapy.

DIDS prevents ischemic membrane degradation in cultured hippocampal neurons by inhibiting matrix metalloproteinase release

During stroke, cells in the infarct core exhibit rapid failure of their permeability barriers, which releases ions and inflammatory molecules that are deleterious to nearby tissue (the penumbra). Plasma membrane degradation is key to penumbral spread and is mediated by matrix metalloproteinases (MMPs), which are released via vesicular exocytosis into the extracellular fluid in response to stress. DIDS (4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid) preserves membrane integrity in neurons challenged with an in vitro ischemic penumbral mimic (ischemic solution: IS) and we asked whether this action was mediated via inhibition of MMP activity. In cultured murine hippocampal neurons challenged with IS, intracellular proMMP-2 and -9 expression increased 4–10 fold and extracellular latent and active MMP isoform expression increased 2–22 fold. MMP-mediated extracellular gelatinolytic activity increased ∼20–50 fold, causing detachment of 32.1±4.5% of cells from the matrix and extensive plasma membrane degradation (>60% of cells took up vital dyes and >60% of plasma membranes were fragmented or blebbed). DIDS abolished cellular detachment and membrane degradation in neurons and the pathology-induced extracellular expression of latent and active MMPs. DIDS similarly inhibited extracellular MMP expression and cellular detachment induced by the pro-apoptotic agent staurosporine or the general proteinase agonist 4-aminophenylmercuric acetate (APMA). Conversely, DIDS-treatment did not impair stress-induced intracellular proMMP production, nor the intracellular cleavage of proMMP-2 to the active form, suggesting DIDS interferes with the vesicular extrusion of MMPs rather than directly inhibiting proteinase expression or activation. In support of this hypothesis, an antagonist of the V-type vesicular ATPase also inhibited extracellular MMP expression to a similar degree as DIDS. In addition, in a proteinase-independent model of vesicular exocytosis, DIDS prevented stimulus-evoked release of von Willebrand Factor from human umbilical vein endothelial cells. We conclude that DIDS inhibits MMP exocytosis and through this mechanism preserves neuronal membrane integrity during pathological stress.

Computational analysis reveals increased blood deposition following repeated mild traumatic brain injury

Mild traumatic brain injury (mTBI) has become an increasing public health concern as subsequent injuries can exacerbate existing neuropathology and result in neurological deficits. This study investigated the temporal development of cortical lesions using magnetic resonance imaging (MRI) to assess two mTBIs delivered to opposite cortical hemispheres. The controlled cortical impact model was used to produce an initial mTBI on the right cortex followed by a second injury induced on the left cortex at 3 (rmTBI 3d) or 7 (rmTBI 7d) days later. Histogram analysis was combined with a novel semi-automated computational approach to perform a voxel-wise examination of extravascular blood and edema volumes within the lesion. Examination of lesion volume 1d post last injury revealed increased tissue abnormalities within rmTBI 7d animals compared to other groups, particularly at the site of the second impact. Histogram analysis of lesion T2 values suggested increased edematous tissue within the rmTBI 3d group and elevated blood deposition in the rm TBI 7d animals. Further quantification of lesion composition for blood and edema containing voxels supported our histogram findings, with increased edema at the site of second impact in rmTBI 3d animals and elevated blood deposition in the rmTBI 7d group at the site of the first injury. Histological measurements revealed spatial overlap of regions containing blood deposition and microglial activation within the cortices of all animals. In conclusion, our findings suggest that there is a window of tissue vulnerability where a second distant mTBI, induced 7d after an initial injury, exacerbates tissue abnormalities consistent with hemorrhagic progression.

Perlecan and the blood-brain barrier: beneficial proteolysis?

The cerebral microvasculature is important for maintaining brain homeostasis. This is achieved via the blood-brain barrier (BBB), composed of endothelial cells with specialized tight junctions, astrocytes, and a basement membrane (BM). Prominent components of the BM extracellular matrix (ECM) include fibronectin, laminin, collagen IV, and perlecan, all of which regulate cellular processes via signal transduction through various cell membrane bound ECM receptors. Expression and proteolysis of these ECM components can be rapidly altered during pathological states of the central nervous system. In particular, proteolysis of perlecan, a heparan sulfate proteoglycan, occurs within hours following ischemia induced by experimental stroke. Proteolysis of ECM components following stroke results in the degradation of the BM and further disruption of the BBB. While it is clear that such proteolysis has negative consequences for the BBB, we propose that it also may lead to generation of ECM protein fragments, including the C-terminal domain V (DV) of perlecan, that potentially have a positive influence on other aspects of CNS health. Indeed, perlecan DV has been shown to be persistently generated after stroke and beneficial as a neuroprotective molecule and promoter of post-stroke brain repair. This mini-review will discuss beneficial roles of perlecan protein fragment generation within the brain during stroke.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Clinical assessment, neuroimaging and immunomarkers in Chagas disease study (CLINICS): Rationale, study design and preliminary findings

Chagas disease (CD) is an important cause of cardiomyopathy and stroke in Brazil. Brain infarcts and atrophy seem to occur independently of cardiomyopathy severity and cognitive impairment is understudied.

OBJECTIVE

Compare the prevalence of brain magnetic resonance imaging abnormalities between patients with or without CD; determine if inflammatory biomarkers are increased in CD; and determine the efficacy of aspirin in reducing the rate of microembolization in these patients.

METHODS

500 consecutive patients with heart failure will undergo a structured cognitive evaluation, biomarker collection and search for microembolic signals on transcranial Doppler. The first 90 patients are described, evaluated with cognitive tests and brain magnetic resonance imaging to measure N-acetyl aspartate (NAA), choline (Cho), myo-inositol (MI) and creatine (Cr).

RESULTS

Mean age was 55±11 years, 51% female, 38 (42%) with CD. Mean NAA/Cr ratio was lower in patients with CD as compared to other cardiomyopathies. Long-term memory and clock-drawing test were also significantly worse in CD patients. In the multivariable analysis correcting for ejection fraction, age, sex and educational level, reduced NAA/Cr (p=0.006) and cognitive dysfunction (long-term memory, p=0.023; clock-drawing test, p=0.015) remained associated with CD.

CONCLUSION

In this preliminary sample, CD was associated with cognitive impairment and decreased NAA/Cr independently of cardiac function or educational level.

N-methyl D-aspartate (NMDA) receptor antagonists and memantine treatment for Alzheimer's disease, vascular dementia and Parkinson's disease

Memantine, a partial antagonist of N-methyl-D-aspartate receptor (NMDAR), approved for moderate to severe Alzheimer's disease (AD) treatment within the U.S. and Europe under brand name Namenda (Forest), Axura and Akatinol (Merz), and Ebixa and Abixa (Lundbeck), may have potential in alleviating additional neurological conditions, such as vascular dementia (VD) and Parkinson's disease (PD). In various animal models, memantine has been reported to be a neuroprotective agent that positively impacts both neurodegenerative and vascular processes. While excessive levels of glutamate result in neurotoxicity, in part through the over-activation of NMDARs, memantine-as a partial NMDAR antagonist, blocks the NMDA glutamate receptors to normalize the glutamatergic system and ameliorate cognitive and memory deficits. The key to memantine's therapeutic action lies in its uncompetitive binding to the NMDAR through which low affinity and rapid off-rate kinetics of memantine at the level of the NMDAR-channel preserves the physiological function of the receptor, underpinning memantine's tolerability and low adverse event profile. As the biochemical pathways evoked by NMDAR antagonism also play a role in PD and since no other drug is sufficiently effective to substitute for the first-line treatment of L-dopa despite its side effects, memantine may be useful in PD treatment with possibly fewer side effects. In spite of the relative modest nature of its adverse effects, memantine has been shown to provide only a moderate decrease in clinical deterioration in AD and VD, and hence efforts are being undertaken in the design of new and more potent memantine-based drugs to hopefully provide greater efficacy.

Matrix metalloproteinase-12 deficiency ameliorates the clinical course and demyelination in Theiler's murine encephalomyelitis

Matrix metalloproteinases (MMPs) are a family of extracellular proteases involved in the pathogenesis of demyelinating diseases like multiple sclerosis (MS). The aim of the present study was to investigate whether MMPs induce direct myelin degradation, leukocyte infiltration, disruption of the blood-brain barrier (BBB), and/or extracellular matrix remodeling in the pathogenesis of Theiler's murine encephalomyelitis (TME), a virus-induced model of MS. During the demyelinating phase of TME, the highest transcriptional upregulation was detected for Mmp12, followed by Mmp3. Mmp12 (-/-) mice showed reduced demyelination, macrophage infiltration, and motor deficits compared with wild-type- and Mmp3 knock-out mice. However, BBB remained unaltered, and the amount of extracellular matrix deposition was similar in knock-out mice and wild-type mice. Furthermore, stereotaxic injection of activated MMP-3, -9, and -12 into the caudal cerebellar peduncle of adult mice induced a focally extensive primary demyelination prior to infiltration of inflammatory cells, as well as a reduction in the number of oligodendrocytes and a leakage of BBB. All these results demonstrate that MMP-12 plays an essential role in the pathogenesis of TME, most likely due to its primary myelin- or oligodendrocyte-toxic potential and its role in macrophage extravasation, whereas there was no sign of BBB damage or alterations to extracellular matrix remodeling/deposition. Thus, interrupting the MMP-12 cascade may be a relevant therapeutic approach for preventing chronic progressive demyelination.

Impaired blood-brain/spinal cord barrier in ALS patients

Vascular pathology, including blood-brain/spinal cord barrier (BBB/BSCB) alterations, has recently been recognized as a key factor possibly aggravating motor neuron damage, identifying a neurovascular disease signature for ALS. However, BBB/BSCB competence in sporadic ALS (SALS) is still undetermined. In this study, BBB/BSCB integrity in postmortem gray and white matter of medulla and spinal cord tissue from SALS patients and controls was investigated. Major findings include (1) endothelial cell damage and pericyte degeneration, (2) severe intra- and extracellular edema, (3) reduced CD31 and CD105 expressions in endothelium, (4) significant accumulation of perivascular collagen IV, and fibrin deposits (5) significantly increased microvascular density in lumbar spinal cord, (6) IgG microvascular leakage, (7) reduced tight junction and adhesion protein expressions. Microvascular barrier abnormalities determined in gray and white matter of the medulla, cervical, and lumbar spinal cord of SALS patients are novel findings. Pervasive barrier damage discovered in ALS may have implications for disease pathogenesis and progression, as well as for uncovering novel therapeutic targets.

Hyperthermia worsens ischaemic brain injury through destruction of microvessels in an embolic model in rats

PURPOSE

Basal lamina is a major part of the microvascular wall and plays a critical role in the integrity of microvasculature. The aim of this study is to determine whether hyperthermia worsens the destruction of microvascular integrity in the ischaemic injured brain.

MATERIALS AND METHODS

Focal cerebral ischaemia was induced by embolising a pre-formed clot into the middle cerebral artery (MCA). Rats received either normothermic or hyperthermic treatment. Neurological score and infarct size were evaluated at 24 h after the MCA occlusion. Microvascular collagen type IV and laminin were measured with fluorescence microscopy. The activities of matrix metalloproteinases (MMP-2 and MMP-9) and plasminogen activators (tPA and uPA) were determined by zymography.

RESULTS

Treatment with hyperthermia significantly increased infarct volume (p<0.01), cortex swelling (p<0.01), striatum swelling (p<0.05) and neurologic score (p<0.01) at 24 h after the MCA occlusion. Compared to the normothermic groups, hyperthermia significantly worsened the losses of microvascular basal lamina structure proteins, collagen type IV and laminin, at 6 h (p<0.001) and 24 h (p<0.01) after MCA occlusion. Hyperthermia increased the MMP-9 activity at 6 and 24 h after MCA occlusion compared with normothermia (p<0.05), whereas increased the MMP-2 activity at 6 h only (p<0.05). Hyperthermia also elevated uPA activity significantly at 6 and 24 h after MCA occlusion compared to normothermia (p<0.05).

CONCLUSIONS

These results demonstrate that hyperthermia exacerbates the destruction of microvascular integrity possibly by increasing the activities of MMP-2, MMP-9 and uPA in the ischaemic cerebral tissues.

Microglial cell activation is a source of metalloproteinase generation during hemorrhagic transformation

Hemorrhage and edema accompany evolving brain tissue injury after ischemic stroke. In patients, these events have been associated with metalloproteinase (MMP)-9 in plasma. Both the causes and cellular sources of MMP-9 generation in this setting have not been defined. MMP-2 and MMP-9 in nonhuman primate tissue in regions of plasma leakage, and primary murine microglia and astrocytes, were assayed by immunocytochemistry, zymography, and real-time RT-PCR. Ischemia-related hemorrhage was associated with microglial activation in vivo, and with the leakage of plasma fibronectin and vitronectin into the surrounding tissue. In strict serum-depleted primary cultures, by zymography, pro-MMP-9 was generated by primary murine microglia when exposed to vitronectin and fibronectin. Protease secretion was enhanced by experimental ischemia (oxygen-glucose deprivation, OGD). Primary astrocytes, on each matrix, generated only pro-MMP-2, which decreased during OGD. Microglia-astrocyte contact enhanced pro-MMP-9 generation in a cell density-dependent manner under normoxia and OGD. Compatible with observations in a high quality model of focal cerebral ischemia, microglia, but not astrocytes, respond to vitronectin and fibronectin, found when plasma extravasates into the injured region. Astrocytes alone do not generate pro-MMP-9. These events explain the appearance of MMP-9 antigen in association with ischemia-induced cerebral hemorrhage and edema.

Matrix metalloproteinases 2 and 9 increase permeability of sheep pleura in vitro

BACKGROUND

Matrix metalloproteinases (MMPs) 2 and 9 are two gelatinase members which have been found elevated in exudative pleural effusions. In endothelial cells these MMPs increase paracellular permeability via the disruption of tight junction (TJ) proteins occludin and claudin. In the present study it was investigated if MMP2 and MMP9 alter permeability properties of the pleura tissue by degradation of TJ proteins in pleural mesothelium.

RESULTS

In the present study the transmesothelial resistance (RTM) of sheep pleura tissue was recorded in Ussing chambers after the addition of MMP2 or MMP9. Both enzymes reduced RTM of the pleura, implying an increase in pleural permeability. The localization and expression of TJ proteins, occludin and claudin-1, were assessed after incubation with MMPs by indirect immunofluorescence and western blot analysis. Our results revealed that incubation with MMPs did not alter neither proteins localization at cell periphery nor their expression.

CONCLUSIONS

MMP2 and MMP9 increase the permeability of sheep pleura and this finding suggests a role for MMPs in pleural fluid formation. Tight junction proteins remain intact after incubation with MMPs, contrary to previous studies which have shown TJ degradation by MMPs. Probably MMP2 and MMP9 augment pleural permeability via other mechanisms.

Acute UV irradiation increases heparan sulfate proteoglycan levels in human skin

Glycosaminoglycans are important structural components in the skin and exist as various proteoglycan forms, except hyaluronic acid. Heparan sulfate (HS), one of the glycosaminoglycans, is composed of repeated disaccharide units, which are glucuronic acids linked to an N-acetyl-glucosamine or its sulfated forms. To investigate acute ultraviolet (UV)-induced changes of HS and HS proteoglycans (HSPGs), changes in levels of HS and several HSPGs in male human buttock skin were examined by immunohistochemistry and real-time quantitative polymerase chain reaction (qPCR) after 2 minimal erythema doses (MED) of UV irradiation (each n = 4-7). HS staining revealed that 2 MED of UV irradiation increased its expression, and staining for perlecan, syndecan-1, syndecan-4, CD44v3, and CD44 showed that UV irradiation increased their protein levels. However, analysis by real-time qPCR showed that UV irradiation did not change mRNA levels of CD44 and agrin, and decreased perlecan and syndecan-4 mRNA levels, while increased syndecan-1 mRNA level. As HS-synthesizing or -degrading enzymes, exostosin-1 and heparanase mRNA levels were increased, but exostosin-2 was decreased by UV irradiation. UV-induced matrix metalloproteinase-1 expression was confirmed for proper experimental conditions. Acute UV irradiation increases HS and HSPG levels in human skin, but their increase may not be mediated through their transcriptional regulation.

A broad-spectrum matrix metalloproteinase inhibitor prevents hemorrhagic complications induced by tissue plasminogen activator in mice

Delayed activation of tissue plasminogen activator (tPA) can lead to the disruption of the blood-brain barrier (BBB), resulting in hemorrhagic complications. In the present study, we focused on tight junction proteins (TJPs), occludin, zona occludens (ZO)-1, and claudin-5, which are important structural components of the BBB, and investigated whether inhibition of matrix metalloproteinases (MMPs) provides a protective effect against hemorrhagic complications induced by tPA. We subjected mice to 6-h filamental middle cerebral artery occlusion (MCAO) with vehicle, delayed tPA alone, or combined tPA (10 mg/kg, i.v.) plus GM6001 (100 mg/kg, i.p.), a broad-spectrum MMP inhibitor. We evaluated brain hemoglobin and the expression of MMP-9 and TJPs by immunoblotting. GM6001 significantly reduced tPA-elevated brain hemoglobin, MMP-9, and inhibited the degradation of occludin and ZO-1 induced by tPA, but not claudin-5. Treatment with GM6001 also significantly prevented the decrease in the survival rate and the reduction in locomotor activity caused by tPA at 7 days after ischemia/reperfusion. Furthermore, GM6001 treatment also significantly prevented cell damage, determined by release of lactase dehydrogenase (LDH) activity, and the decrease in transendothelial electrical resistance (TEER) induced by tPA. These findings indicate that GM6001 prevented the hemorrhagic complications and improved the behavioral abnormalities induced by tPA, partly via protection of TJPs. This suggests that GM6001 may be a useful candidate for combination therapy against the hemorrhagic complications induced by tPA.

Oxygen-glucose deprivation (OGD) and interleukin-1 (IL-1) differentially modulate cathepsin B/L mediated generation of neuroprotective perlecan LG3 by neurons

Brain extracellular matrix (ECM) is highly degraded after cerebral ischemia. The perlecan c-terminal fragment LG3 is generated at increased levels by proteolytic processing as long as 3 days after ischemia. It has previously been shown that oxygen-glucose deprivation (OGD), reperfusion and interleukin-1 α (IL-1α) stimulate brain cells to yield increased levels of LG3. This LG3, in turn, is neuroprotective against OGD, and may therefore represent one of the brain's defenses against ischemic injury. Here, we investigate whether, in neurons, this increased LG3 is the result of increased perlecan generation and cellular release, increased protease release (to generate LG3 from previous extracellularly deposited perlecan) or both. We found that pre-synthesized perlecan may be exocytosed by neurons during OGD and de novo synthesis of perlecan is increased during reperfusion, even 24 h after OGD. Furthermore, while cathepsin L activity was seen to be marginally important to generate LG3 during normoxic conditions, cathepsin B activity was found to be important to generate increased levels of LG3 following OGD and reperfusion. On the other hand, IL-1α treatment raised levels of cathepsin L in neuronal media, and both cathepsin L and cathepsin B were demonstrated to be important for increasing LG3 levels after IL-1α treatment.

Doxycycline-mediated protective effect against focal cerebral ischemia-reperfusion injury through the modulation of tight junctions and PKCδ signaling in rats

The strategy for the development of effective and safe neuroprotective agents has great potential to reduce cerebral ischemia-reperfusion injury and improve the functional outcome in stroke patients. Recently, doxycycline, a tetracycline antibiotic, has been shown to have neuroprotective efficiency in reduction of a variety of ischemia-reperfusion injuries as well as ischemic brain damage. We used the rat models of middle cerebral artery occlusion (MCAO) and reperfusion to investigate the effects of treatments with doxycycline against the blood-brain barrier (BBB) leakage at 3, 12, 72, and 120 h of reperfusion. Male Sprague-Dawley rats were subjected to MCAO for 2 h followed by reperfusion for 3, 12, 72, and 120 h and received either doxycycline (45 mg/kg) or saline. The results showed that the treatment of doxycycline significantly reduced the BBB leakage and cerebral infarct volume, which were proved by Evans blue assay and TTC staining. Real-time PCR, immunohistochemistry, and western blot assay verified that the administration of doxycycline significantly up-regulated the expression of tight junction claudin-5, occludin, and ZO-1 from 3 to 120 h after reperfusion. The results of real-time PCR, western blot, and gelatin zymography analyses revealed that the gene and protein expression and activities of matrix metalloproteinases (MMPs) MMP-2 and MMP-9 were significantly elevated in a different time-dependent manner after ischemia-reperfusion but significantly inhibited by doxycycline treatment. Moreover, doxycycline could also significantly down-regulate the expression of PKCδ mRNA and protein after ischemia-reperfusion. These results suggested that the protective effects of doxycycline against BBB damage induced by reperfusion might be related to the up-regulation of tight junction proteins and inhibition of MMP-2, MMP-9, and PKCδ.

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'.

Oxygen-glucose deprivation and interleukin-1α trigger the release of perlecan LG3 by cells of neurovascular unit

Two of the main stresses faced by cells at the neurovascular unit (NVU) as an immediate result of cerebral ischemia are oxygen-glucose deprivation (OGD)/reperfusion and inflammatory stress caused by up regulation of IL-1. As a result of these stresses, perlecan, an important component of the NVU extracellular matrix, is highly proteolyzed. In this study, we describe that focal cerebral ischemia in rats results in increased generation of laminin globular domain 3 (LG3), the c-terminal bioactive fragment of perlecan. Further, in vitro study of the cells of the NVU was performed to locate the source of this increased perlecan-LG3. Neurons, astrocytes, brain endothelial cells and pericytes were exposed to OGD/reperfusion and IL-1α/β. It was observed that neurons and pericytes showed increased levels of LG3 during OGD in their culture media. During in vitro reperfusion, neurons, astrocytes and pericytes showed elevated levels of LG3, but only after exposure to brief durations of OGD. IL-1α and IL-1β treatment tended to have opposite effects on NVU cells. While IL-1α increased or had minimal to no effect on LG3 generation, high concentrations of IL-1β decreased it in most cells studied. Finally, LG3 was determined to be neuroprotective and anti-proliferative in brain endothelial cells, suggesting a possible role for the generation of LG3 in the ischemic brain.

Interendothelial claudin-5 expression depends on cerebral endothelial cell-matrix adhesion by β(1)-integrins

The hypothesis tested by these studies states that in addition to interendothelial cell tight junction proteins, matrix adhesion by β(1)-integrin receptors expressed by endothelial cells have an important role in maintaining the cerebral microvessel permeability barrier. Primary brain endothelial cells from C57 BL/6 mice were incubated with β(1)-integrin function-blocking antibody (Ha2/5) or isotype control and the impacts on claudin-5 expression and microvessel permeability were quantified. Both flow cytometry and immunofluorescence studies demonstrated that the interendothelial claudin-5 expression by confluent endothelial cells was significantly decreased in a time-dependent manner by Ha2/5 exposure relative to isotype. Furthermore, to assess the barrier properties, transendothelial electrical resistance and permeability measurements of the monolayer, and stereotaxic injection into the striatum of mice were performed. Ha2/5 incubation reduced the resistance of endothelial cell monolayers significantly, and significantly increased permeability to 40 and 150  kDa dextrans. Ha2/5 injection into mouse striatum produced significantly greater IgG extravasation than the isotype or the control injections. This study demonstrates that blockade of β(1)-integrin function changes interendothelial claudin-5 expression and increases microvessel permeability. Hence, endothelial cell-matrix interactions via β(1)-integrin directly affect interendothelial cell tight junction claudin-5 expression and brain microvascular permeability.

Contribution of matrix metalloproteinase-9 to cerebral edema and functional outcome following experimental subarachnoid hemorrhage

BACKGROUND

Cerebral edema is an important risk factor for death and poor outcome following subarachnoid hemorrhage (SAH). However, underlying mechanisms are still poorly understood. Matrix metalloproteinase (MMP)-9 is held responsible for the degradation of microvascular basal lamina proteins leading to blood-brain barrier dysfunction and, thus, formation of vasogenic cerebral edema. The current study was conducted to clarify the role of MMP-9 for the development of cerebral edema and for functional outcome after SAH.

METHODS

SAH was induced in FVB/N wild-type (WT) or MMP-9 knockout (MMP-9(-/-)) mice by endovascular puncture. Intracranial pressure (ICP), regional cerebral blood flow (rCBF), and mean arterial blood pressure (MABP) were continuously monitored up to 30 min after SAH. Mortality was quantified for 7 days after SAH. In an additional series neurological function and body weight were assessed for 3 days after SAH. Subsequently, ICP and brain water content were quantified.

RESULTS

Acute ICP, rCBF, and MABP did not differ between WT and MMP-9(-/-) mice, while 7 days' mortality was lower in MMP-9(-/-) mice (p = 0.03; 20 vs. 60%). MMP-9(-/-) mice also exhibited better neurological recovery, less brain edema formation, and lower chronic ICP.

CONCLUSIONS

The results of the current study suggest that MMP-9 contributes to the development of early brain damage after SAH by promoting cerebral edema formation. Hence, MMP- 9 may represent a novel molecular target for the treatment of SAH.

MMPs 2 and 9 are essential for coronary collateral growth and are prominently regulated by p38 MAPK

Transient, repetitive ischemia (RI) stimulates coronary collateral growth (CCG) in normal, healthy (SD) rats, which requires p38 MAPK activation. In contrast, RI does not induce CCG in the metabolic syndrome (JCR) rats, which is associated with lack of p38 MAPK activation. The functional consequences of p38 MAPK activation in CCG remain unknown. Theoretically, effective collateral growth would require extracellular matrix remodeling; however, direct assessment as well as identification of proteases responsible for this degradation are lacking. In this study, we investigated the role of p38 MAPK in the regulation of matrix metalloproteinases 2 and 9 (MMPs 2 and 9) and their requirement for CCG in SD vs. JCR rats. The rats underwent the RI protocol (8 LAD occlusions, 40s each, every 20min, in 8h cycles for 0, 3, 6, or 9days). MMP expression was measured in the ischemic, collateral-dependent zone (CZ) and the normal zone (NZ) by Western blot, and MMP activity by zymography. Expression and activation of MMP 2 and 9 were significantly increased (~3.5 fold) on day 3 of RI in the CZ of SD rats. In vivo p38 MAPK inhibition completely blocked RI-induced MMP 2 and 9 expression and activation. MMP activation correlated with increased degradation of components of the basement membrane and the vascular elastic laminae: elastin (~3 fold), laminin (~3 fold) and type IV collagen (~2 fold). This was blocked by MMP 2 and 9 inhibition, which also abolished RI-induced CCG. In contrast, in JCR rats, RI did not induce expression or activation of MMP 2 or 9 and there was no associated degradation of elastin, laminin or type IV collagen. In conclusion, MMP 2 and 9 activation is essential for CCG and is mediated, in part, by p38 MAPK. Furthermore, compromised CCG in the metabolic syndrome may be partially due to the lack of p38 MAPK-dependent activation of MMP 2 and 9 and resultant decreased extracellular matrix degradation.

Perlecan domain V is neuroprotective and proangiogenic following ischemic stroke in rodents

Stroke is the leading cause of long-term disability and the third leading cause of death in the United States. While most research thus far has focused on acute stroke treatment and neuroprotection, the exploitation of endogenous brain self-repair mechanisms may also yield therapeutic strategies. Here, we describe a distinct type of stroke treatment, the naturally occurring extracellular matrix fragment of perlecan, domain V, which we found had neuroprotective properties and enhanced post-stroke angiogenesis, a key component of brain repair, in rodent models of stroke. In both rat and mouse models, Western blot analysis revealed elevated levels of perlecan domain V. When systemically administered 24 hours after stroke, domain V was well tolerated, reached infarct and peri-infarct brain vasculature, and restored stroke-affected motor function to baseline pre-stroke levels in these multiple stroke models in both mice and rats. Post-stroke domain V administration increased VEGF levels via a mechanism involving brain endothelial cell α5β1 integrin, and the subsequent neuroprotective and angiogenic actions of domain V were in turn mediated via VEGFR. These results suggest that perlecan domain V represents a promising approach for stroke treatment.

Matrix metalloproteinases as drug targets in ischemia/reperfusion injury

Deficient blood supply (ischemia) is a common consequence of some surgical procedures and certain pathologies. Once blood circulation is re-established (reperfusion), a complex series of events results in recruitment of inflammatory cells, rearrangement of the extracellular matrix and induction of cell death, which lead to organ dysfunction. Although ischemia/reperfusion (I/R) injury is an important cause of death, there is no effective therapy targeting the molecular mechanism of disease progression. Matrix metalloproteinases (MMPs), which are important regulators of many cellular activities, have a central role in disease progression after I/R injury, as suggested by numerous studies using MMP inhibitors or MMP-deficient mice. Here, we review the involvement of MMP activity in the various processes following I/R injury and the therapeutic potential of MMP inhibition.

Early outcome and blood-brain barrier integrity after co-administered thrombolysis and hyperbaric oxygenation in experimental stroke

BACKGROUND

After promising results in experimental stroke, normobaric (NBO) or hyperbaric oxygenation (HBO) have recently been discussed as co-medication with tissue plasminogen activator (tPA) for improving outcome. This study assessed the interactions of hyperoxia and tPA, focusing on survival, early functional outcome and blood-brain barrier (BBB) integrity following experimental stroke.

METHODS

Rats (n = 109) underwent embolic middle cerebral artery occlusion or sham surgery. Animals were assigned to: Control, NBO (60-minute pure oxygen), HBO (60-minute pure oxygen at 2.4 absolute atmospheres), tPA, or HBO+tPA. Functional impairment was assessed at 4 and 24 hours using Menzies score, followed by intravenous application of FITC-albumin as a BBB permeability marker, which was allowed to circulate for 1 hour. Further, blood sampling was performed at 5 and 25 hours for MMP-2, MMP-9, TIMP-1 and TIMP-2 concentration.

RESULTS

Mortality rates did not differ significantly between groups, whereas functional improvement was found for NBO, tPA and HBO+tPA. NBO and HBO tended to stabilize BBB and to reduce MMP-2. tPA tended to increase BBB permeability with corresponding MMP and TIMP elevation. Co-administered HBO failed to attenuate these early deleterious effects, independent of functional improvement.

CONCLUSIONS

The long-term consequences of simultaneously applied tPA and both NBO and HBO need to be addressed by further studies to identify therapeutic potencies in acute stroke, and to avoid unfavorable courses following combined treatment.

Matrix metalloproteinase inhibitors attenuate neuroinflammation following focal cerebral ischemia in mice

The aim of this study was to investigate whether matrix metalloproteinase (MMP) inhibitors attenuate neuroinflammation in an ischemic brain following photothrombotic cortical ischemia in mice. Male C57BL/6 mice were anesthetized, and Rose Bengal was systemically administered. Permanent focal ischemia was induced in the medial frontal and somatosensory cortices by irradiating the skull with cold white light. MMP inhibitors, such as doxycycline, minocycline, and batimastat, significantly reduced the cerebral infarct size, and the expressions of monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), and indoleamine 2,3-dioxygenase (IDO). However, they had no effect on the expressions of heme oxygenase-1 and neuroglobin in the ischemic cortex. These results suggest that MMP inhibitors attenuate ischemic brain injury by decreasing the expression levels of MCP-1, TNF-α, and IDO, thereby providing a therapeutic benefit against cerebral ischemia.

Vascularization of cytochrome oxidase-rich blobs in the primary visual cortex of squirrel and macaque monkeys

The close correlation between energy supply by blood vessels and energy consumption by cellular processes in the brain is the basis of blood flow-related functional imaging techniques. Regional differences in vascular density can be detected using high-resolution functional magnetic resonance imaging. Therefore, inhomogeneities in vascularization might help to identify anatomically distinct areas noninvasively in vivo. It was reported previously that cytochrome oxidase-rich blobs in the striate cortex of squirrel monkeys are characterized by a notably higher vascular density (42% higher than interblob regions). However, blobs have so far never been identified in vivo on the basis of their vascular density. Here, we analyzed blobs of the primary visual cortex of squirrel monkeys and macaques with respect to the relationship between vascularization and cytochrome oxidase activity. By double staining with cytochrome oxidase enzyme histochemistry to define the blobs and collagen type IV immunohistochemistry to quantify the blood vessels, a close correlation between oxidative metabolism and vascularization was confirmed and quantified in detail. The vascular length density in cytochrome oxidase blobs was on average 4.5% higher than in the interblob regions, a difference almost one order of magnitude smaller than previously reported. Thus, the vascular density that is closely associated with local average metabolic activity is a structural equivalent of cerebral metabolism and blood flow. However, the quantitative differences in vascularization between blob and interblob regions are small and below the detectability threshold of the noninvasive hemodynamic imaging methods of today.

The neurovascular unit, matrix proteases, and innate inflammation

In the central nervous system, microvessel-neuron interactions appear highly coordinated. The rapid simultaneous responses of the microvasculature, neurons, and glia to focal ischemia in experimental ischemic stroke suggest that these responses could be viewed in a unitary fashion, rather than as individual components. The "neurovascular unit" consists of microvessels (endothelial cells-basal lamina matrix-astrocyte end-feet [and pericytes]), astrocytes, neurons and their axons, and other supporting cells that are likely to modulate the function of the "unit." Each cell component generates an inflammatory response to ischemia. Matrix metalloproteinase (MMP)-9 was first associated with hemorrhagic transformation following focal ischemia in an experimental model. A series of studies of ischemic stroke patients also suggests a relationship between MMP-9 levels and several consequences of ischemic injury, including hemorrhagic transformation. Recent experimental work suggests specific cell sources for MMP-9 generation and for matrix proteases from four distinct families that could impact neurovascular unit integrity.

The asparaginyl endopeptidase legumain after experimental stroke

Various proteases in the brain contribute to ischemic brain injury. We investigated the involvement of the asparaginyl endopeptidase legumain after experimental stroke. On the basis of gene array studies and in situ hybridizations, we observed an increase of legumain expression in the peri-infarct area of rats after transient occlusion of the middle cerebral artery (MCAO) for 120 mins with a maximum expression at 24 and 48 h. Immunohistochemical analyses revealed the expression of legumain in Iba1(+) microglial cells and glial fibrillary acidic protein-positive astrocytes of the peri-infarct area in mice after MCAO. Post-stroke recovery was also studied in aged legumain-deficient mice (45 to 58 weeks old). Legumain-deficient mice did not show any differences in physiologic parameters compared with respective littermates before, during MCAO (45 mins), and the subsequent recovery period of 8 days. Moreover, legumain deficiency had no effect on mortality, infarct volume, and the neurologic deficit determined by the rotating pole test, a standardized grip strength test, and the pole test. However, a reduced number of invading CD74(+) cells in the ischemic hemisphere indicates an involvement in post-stroke inflammation. We conclude that legumain is not essential for the functional deficit after MCAO but may be involved in mechanisms of immune cell invasion.

Improvement in recovery after experimental intracerebral hemorrhage using a selective cathepsin B and L inhibitor

OBJECT

This study investigates a potential novel application of a selective cathepsin B and L inhibitor in experimental intracerebral hemorrhage (ICH) in rats.

METHODS

Forty adult male Wistar rats received an ICH by stereotactic injection of 100 μl of autologous blood or sham via needle insertion into the right striatum. The rats were treated with a selective cathepsin B and L inhibitor (CP-1) or 1% dimethyl sulfoxide sterile saline intravenously at 2 and 4 hours after injury. Modified neurological severity scores were obtained and corner turn tests were performed at 1, 4, 7, and 14 days after ICH. The rats were sacrificed at 3 and 14 days after ICH for immunohistological analysis of tissue loss, neurogenesis, angiogenesis, and apoptosis.

RESULTS

The animals treated with CP-1 demonstrated significantly reduced apoptosis as well as tissue loss compared with controls (p < 0.05 for each). Neurological function as assessed by modified neurological severity score and corner turn tests showed improvement after CP-1 treatment at 7 and 14 days (p < 0.05). Angiogenesis and neurogenesis parameters demonstrated improvement after CP-1 treatment compared with controls (p < 0.05) at 14 days.

CONCLUSIONS

This study is the first report of treatment of ICH with a selective cathepsin B and L inhibitor. Cathepsin B and L inhibition has been shown to be beneficial after cerebral ischemia, likely because of its upstream regulation of the other prominent cysteine proteases, calpains, and caspases. While ICH may not induce a major component of ischemia, the cellular stress in the border zone may activate these proteolytic pathways. The observation that cathepsin B and L blockade is efficacious in this model is provocative for further investigation.

Adhesion to the extracellular matrix is required for interleukin-1 beta actions leading to reactive phenotype in rat astrocytes

The extracellular matrix (ECM) of the brain is essential for homeostasis and normal functions, but is rapidly remodelled during acute brain injury alongside the development of an inflammatory response driven by the cytokine interleukin (IL)-1. Whether the ECM regulates IL-1 actions in astrocytes is completely unknown. The aim of this study was to test the hypothesis that cellular attachment to the ECM is a critical mediator of IL-1beta-induced signalling pathways and development of reactive phenotype in astrocytes. Primary rat astrocytes adhered to fibronectin, laminin and fibrillin-1 in an integrin-dependent manner. Attachment to these ECM molecules significantly increased IL-1beta-induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and inhibition of RhoA and Rho kinase (ROCK), coincident with loss of focal adhesions and cellular morphological changes. Our data demonstrate that the ECM regulates IL-1 actions in astrocytes via cross-talk mechanisms between ERK1/2 and RhoA/ROCK, which could have important implications in brain inflammatory disorders.

Hypertension-induced vascular remodeling contributes to reduced cerebral perfusion and the development of spontaneous stroke in aged SHRSP rats

Stroke in spontaneously-hypertensive, stroke-prone (SHRSP) rats is of particular interest because the pathogenesis is believed to be similar to that in the clinical setting. In this study, we employed multi-modal MRI-ASL, DWI, T(2), GRE, T(1) (pre/post contrast)-to investigate the natural history of spontaneous cerebral infarction and the specific role of cerebral perfusion in disease development. Twelve female SHRSP rats (age: approximately 1 year) were imaged within 1 to 3 days of symptom onset. The distribution of ischemic lesions was the following: 28.1% visual, 21.9% striatal, 18.8% motorsensory, 12.5% thalamic, 12.5% auditory, 3.1% frontal/prelimbic, and 3.1% multiple areas. Ischemic lesions had significantly reduced blood flow in comparison with healthy tissue. Ischemic lesions were characterized by hyperplastic, thrombosed, and compressed vessels. These findings suggest that ischemic lesion development is related to hypertension-induced vascular remodeling and persistent hypoperfusion. This model should be useful for studying the relationship between chronic hypertension and subsequent stroke, both in terms of primary and secondary prevention.

Mast cells as early responders in the regulation of acute blood-brain barrier changes after cerebral ischemia and hemorrhage

The inflammatory response triggered by stroke has been viewed as harmful, focusing on the influx and migration of blood-borne leukocytes, neutrophils, and macrophages. This review hypothesizes that the brain and meninges have their own resident cells that are capable of fast host response, which are well known to mediate immediate reactions such as anaphylaxis, known as mast cells (MCs). We discuss novel research suggesting that by acting rapidly on the cerebral vessels, this cell type has a potentially deleterious role in the very early phase of acute cerebral ischemia and hemorrhage. Mast cells should be recognized as a potent inflammatory cell that, already at the outset of ischemia, is resident within the cerebral microvasculature. By releasing their cytoplasmic granules, which contain a host of vasoactive mediators such as tumor necrosis factor-alpha, histamine, heparin, and proteases, MCs act on the basal membrane, thus promoting blood-brain barrier (BBB) damage, brain edema, prolonged extravasation, and hemorrhage. This makes them a candidate for a new pharmacological target in attempts to even out the inflammatory responses of the neurovascular unit, and to stabilize the BBB after acute stroke.

Protective effects of natrii sulfas on cerebral focal ischemia induced by MCAO in rats

This study examined the effect of Natrii sulfas, a treatment for stroke patients suffering constipation in Oriental medicine, on the physiological indices and brain edema of rats. Brain edema was induced by a middle cerebral artery occlusion (MCAO), Natrii sulfas was administered after the MCAO. At 3, 6, 15, 24, and 48 hours after reperfusion, the physiological indices such as the fecal weight, urine volume and water content in the stools were assessed. The edema index was measured 48 hours after reperfusion. At 48 hours, the expressions of iNOS, MMP9, VEGF, GFAP, Bax, Bcl-2, c-Fos, and HSP72 positive astrocytes were observed on the brain tissues by immunohistochemistry. Natrii sulfas significantly improved the decrease in fecal weight, urine volume and water content in the stool caused by the ischemic insult (p < 0.05) and attenuated the brain edema caused by the ischemia insult (p < 0.05). Natrii sulfas significantly down-regulated iNOS and MMP9 expressions and attenuated the astrocyte swelling due to brain edema in the penumbra of the cerebral cortex of MCAO rats. Natrii sulfas reduced the excess Bax and HSP72 expressions in ischemic brain, which was statistically significant in the penumbra of the cerebral cortex but not in the caudate putamen. These results suggest Natrii sulfas has a protective effect on ischemia-induced brain edema and improves the physiological symptoms.

The neurovascular unit in the setting of stroke

Microvessels and neurons respond rapidly and simultaneously in focal regions of ischaemic injury in such a way as to suggest that the responses could be coordinated. The ability of neurons to modulate cerebral blood flow in regions of activation results from neurovascular coupling. But little is known about the microvessel-to-neuron direction of the relationship. The presence and participation of intervening glial cells implies the association of microvessels, glia, and neurons in a 'neurovascular unit'. The interdependent functions of the cellular and matrix components of this theoretical unit have not been rigorously explored, except under conditions of injury where, for the most part, only single components or tissue samples have been studied. Whereas maintenance or timely re-establishment of flow reduces tissue and neuron injury in both humans and animal models, protection of neuron function in humans has not prevented the evolution of injury despite the inherent mechanisms of neurovascular coupling. However, occlusion of flow to the brain rapidly identifies regions of neuron-vascular vulnerability within the vascular territory-at-risk. These coalesce to become the mature ischaemic lesion. The failure, so far, of clinical trials of neuron protectant agents to achieve detectable tissue salvage could be explained by the vulnerability (and lack of protection) of essential components of the 'unit'. This presentation summarizes evidence and thoughts on this topic. These support the need to understand component interactions within the neurovascular unit.

Early activation of matrix metalloproteinase-9 is associated with blood-brain barrier disruption after photothrombotic cerebral ischemia in rats

BACKGROUND

The activation of matrix metalloproteinases (MMPs) is a critical event for disruption of the blood-brain barrier (BBB) during cerebral ischemia. Among the MMPs, MMP-2, and MMP-9 expression were reported to be significantly elevated after the onset of ischemia. The aim of this study was to investigate which one is more significant for BBB disruption in the photothrombotic cerebral ischemia.

MATERIALS AND METHODS

Male Sprague-Dawley rats weighing 250-300 g received focal cerebral ischemia by photothrombosis. MMP-2 and MMP-9 activities were assessed by gelatin zymography at various times from 2 h to 7 days. The BBB integrity was assessed using Evans blue dye with a spectrophotometric assay.

FINDINGS

The Evans blue extravasation was increased within 2 h after cerebral ischemia, and was maximal at 12 and 24 h after the injury, and then gradually decreased. MMP-9 protein activity was detected as early as 2 h after the focal ischemic event; it rapidly increased at 6 h after ischemia, and reached a maximum level 48 h after the ischemic event. Thereafter, the MMP-9 level abruptly decreased and returned to the baseline at 72 h after the insult. By contrast, the MMP-2 protein activity was up-regulated at 6 h after the focal ischemic insult, and reached a maximum level at 72 h after the event. The elevated MMP-2 levels persisted for 7 days after the injury.

CONCLUSIONS

The early activation of MMP-9 was correlated with the increase in the permeability of the BBB. Our findings suggest that MMP-9 is the key factor involved in BBB disruption and subsequent brain injury after photothrombotic cerebral ischemia in rats.

Astrocyte-neuron interactions in neurological disorders

Astrocytes have long been considered as just providing trophic support for neurons in the central nervous system, but recently several studies have highlighted their importance in many functions such as neurotransmission, metabolite and electrolyte homeostasis, cell signaling, inflammation, and synapse modulation. Astrocytes are, in fact, part of a bidirectional crosstalk with neurons. Moreover, increasing evidence is stressing the emerging role of astrocyte dysfunction in the pathophysiology of neurological disorders, including neurodegenerative disease, stroke, epilepsy, migraine, and neuroinflammatory diseases.

Molecular mechanisms of ischemic cerebral edema: role of electroneutral ion transport

The brain achieves homeostasis of its intracellular and extracellular fluids by precisely regulating the transport of solute and water across its major cellular barriers: endothelia of the blood-brain barrier (BBB), choroid plexus epithelia, and neuroglial cell membranes. Cerebral edema, the pathological accumulation of fluid in the brain's intracellular and extracellular spaces, is a major cause of morbidity and mortality following stroke and other forms of ischemic brain injury. Until recently, mechanisms of cerebral edema formation have been obscure; consequently, its treatment has been empiric and suboptimal. Here, we provide a paradigm for understanding ischemic cerebral edema, showing that its molecular pathogenesis is a complex yet step-wise process that results largely from impaired astrocytic cell volume regulation and permeability alterations in the cerebral microvasculature, both of which arise from pathological changes in the activities of specific ion channels and transporters. Recent data has implicated the bumetanide-sensitive NKCC1, an electroneutral cotransporter expressed in astrocytes and the BBB, in cerebral edema formation in several different rodent models of stroke. Pharmacological inhibition or genetic deficiency of NKCC1 decreases ischemia-induced cell swelling, BBB breakdown, cerebral edema, and neurotoxicity. Combination pharmacological strategies that include NKCC1 as a target might thus prove beneficial for the treatment of ischemic, and potentially other types of, cerebral edema.

Matrix metalloproteinase-9 potentiates early brain injury after subarachnoid hemorrhage

OBJECTIVE

This study investigated the role of matrix metalloproteinase-9 (MMP-9) in early brain injury after subarachnoid hemorrhage (SAH).

METHOD

Sprague-Dawley male rats (n=36) weighing between 250 and 300 g were used. SAH was produced by injecting autologous arterial blood into the pre-chiasmatic cistern. MMP-9 protein expression and activity were measured by Western blot and zymogram; laminin expression and neuronal cell in hippocampus were studied by immunohistochemistry and TUNEL staining at 24 hours after SAH in the presence or absence of a selective MMP-9 inhibitor SB-3CT.

RESULT

MMP-9 was activated by SAH and inhibited by SB-3CT at 24 hours after SAH (p<0.01). Laminin, the substrate of MMP-9, was decreased at 24 hours after SAH, and SB-3CT prevented laminin degradation. The number of TUNEL-positive neurons in hippocampus was increased after SAH and decreased by SB-3CT (p<0.01). In addition, brain water content and neurological functional abnormalities were attenuated by SB-3CT.

CONCLUSION

MMP-9 may be involved in early brain injury through degradation of laminin and neuronal death, and inhibition of MMP-9 may be a potential direction for brain protection after SAH.

2008 Landis Award lecture. Inflammation and the autodigestion hypothesis

Although long recognized in microvascular research, an increasing body of evidence suggests that inflammatory markers are present in human diseases. Since the inflammatory cascade serves as a repair mechanism, the presence of inflammatory markers in patient groups has raised an important question about the mechanisms that initiate the inflammatory cascade (i.e., the mechanisms that cause tissue injury). Using a severe form of inflammation, shock, and multiorgan failure, for which there is no accepted injury mechanism, we summarize studies that suggest that the powerful pancreatic digestive enzymes play a central role in the destruction of the intestine and other tissues if their compartmentalization in the lumen of the intestine and in the pancreas is compromised. Further, we summarize evidence that uncontrolled degrading enzyme activity in plasma causes proteolytic cleavage of the extracellular domain of membrane receptors and loss of associated cell functions. For example, in a model of metabolic disease with type II diabetes, proteolytic cleavage of the insulin receptor causes the inability of insulin to signal glucose transport across membranes. The evidence suggests that uncontrolled proteolytic and lipolytic enzyme activity may trigger the mechanism for tissue injury. The significance of such mechanisms remain to be explored in human diseases.

Neurovascular mechanisms and blood-brain barrier disorder in Alzheimer's disease

Vascular dysfunction has a critical role in Alzheimer's disease (AD). Recent data from brain imaging studies in humans and animal models suggest that cerebrovascular dysfunction may precede cognitive decline and onset of neurodegenerative changes in AD and AD models. Cerebral hypoperfusion and impaired amyloid beta-peptide (Abeta) clearance across the blood-brain barrier (BBB) may contribute to the onset and progression of dementia AD type. Decreased cerebral blood flow (CBF) negatively affects the synthesis of proteins required for memory and learning, and may eventually lead to neuritic injury and neuronal death. Impaired clearance of Abeta from the brain by the cells of the neurovascular unit may lead to its accumulation on blood vessels and in brain parenchyma. The accumulation of Abeta on the cerebral blood vessels, known as cerebral amyloid angiopathy (CAA), is associated with cognitive decline and is one of the hallmarks of AD pathology. CAA can severely disrupt the integrity of the blood vessel wall resulting in micro or macro intracerebral bleedings that exacerbates neurodegenerative process and inflammatory response and may lead to hemorrhagic stroke, respectively. Here, we review the role of the neurovascular unit and molecular mechanisms in vascular cells behind AD and CAA pathogenesis. First, we discuss apparent vascular changes, including the cerebral hypoperfusion and vascular degeneration that contribute to different stages of the disease process in AD individuals. We next discuss the role of the low-density lipoprotein receptor related protein-1 (LRP), a key Abeta clearance receptor at the BBB and along the cerebrovascular system, whose expression is suppressed early in AD. We also discuss how brain-derived apolipoprotein E isoforms may influence Abeta clearance across the BBB. We then review the role of two interacting transcription factors, myocardin and serum response factor, in cerebral vascular cells in controlling CBF responses and LRP-mediated Abeta clearance. Finally, we discuss the role of microglia and perivascular macrophages in Abeta clearance from the brain. The data reviewed here support an essential role of neurovascular and BBB mechanisms in contributing to both, onset and progression of AD.

Newborn- and adult-derived brain microvascular endothelial cells show age-related differences in phenotype and glutamate-evoked protease release

Few data are available on the involvement of brain microvascular endothelial cells (BMECs) in excitotoxic neonatal brain lesions. Therefore, we developed an original approach for investigating mouse-derived BMECs in vitro. We hypothesized that newborn and adult BMEC cultures would show age-related differences in phenotype and sensitivity to glutamate. Expression of the monocarboxylate transporter, MCT1, was higher in neonatal than in adult BMECs, whereas expression of the glucose transporter, GLUT1, was higher in adult than in neonatal BMECs that overexpressed the N-methyl-D-aspartate receptor NR1 subunit (NMDAR1) compared with adult BMECs. The ability of neonatal and adult BMECs to be activated by glutamate was confirmed through intracellular calcium ([Ca2+]i) recording. The glutamate-induced [Ca2+]i increase was blocked by the selective NMDAR antagonist, MK-801. Significant glutamate-evoked concentration-dependent release of tissue-type plasminogen activator (t-PA) and matrix metalloproteinases (MMPs) activities was found in supernatants of neonatal, but not in adult BMECs. The glutamate-mediated release of t-PA, MMP-2, and MMP-9 proteolytic activities in neonatal BMECs was blocked by MK-801. Conceivably, this protease release from neonatal BMECs may participate in neonatal brain lesions.

Course of matrix metalloproteinase-9 isoforms after the administration of uric acid in patients with acute stroke: a proof-of-concept study

Oxidative stress as well as expression and activity of matrix metalloproteinase 9 (MMP-9) are rapidly enhanced after cerebral ischemia. The magnitude of these effects is related to stroke outcome. In human stroke, the extent of oxidative stress correlates well with increased MMP-9 expression. The aim of this study was to evaluate whether treatment with the antioxidant molecule uric acid (UA) decreased the levels of MMP-9 in stroke patients treated with rtPA. The patients were part of a pilot, double-blind, randomized, vehicle-controlled study of patients with acute stroke treated with rtPA (< 3 h) and randomized to receive an intravenous infusion of UA (n = 16) or vehicle (n = 8). Total matrix metalloproteinase (tMMP)-9 and active (aMMP-9) levels were measured in serum at baseline (< 3 h), at the end of study treatment infusion (< 5.5 h), and at 48 hours. Total MMP-9 and aMMP-9 increased very early after stroke onset in patients allocated vehicle after rtPA therapy. Lower increments of aMMP-9 were associated with better outcome at 3 months. UA treatment was associated with reduced levels of aMMP-9 at T1 (p < 0.02) in multivariate models adjusted for age, NIHSS score, and baseline aMMP-9 levels. The decline of aMMP-9 attained after UA administration supports further clinical assessment of UA therapy in patients with acute stroke.

Relationship of neurovascular elements to neuron injury during ischemia

Occlusion of flow to the brain regions identifies regions of vulnerability within the vascular territory at risk, which coalesce to become the mature ischemic lesion. A large number of unsuccessful clinical trials have focused on neuron and extravascular targets in humans that have shown apparent salvage in preclinical models. However, the observation that microvessel and neuron responses to ischemia occur simultaneously in these regions suggest that the responses could be coordinated. This presentation examines evidence in support of the conceptual 'neurovascular unit' and its application to the setting of acute intervention trials in ischemic stroke. There are no uniform reasons for which nonvascular interventions, as a class, have not been successful in clinical trials, but both the clinical observations and the hypothesis imply the need to understand interactions with the neurovascular unit as a prelude to further neuron protectant trials.