Neutrophil infiltration increases matrix metalloproteinase-9 in the ischemic brain after occlusion/reperfusion of the middle cerebral artery in rats

Essential role of program death 1-ligand 1 in regulatory T-cell-afforded protection against blood-brain barrier damage after stroke

BACKGROUND AND PURPOSE

Our recent research revealed that adoptively transferred regulatory T cells (Tregs) reduced acute ischemic brain injury by inhibiting neutrophil-derived matrix metalloproteinase-9 (MMP-9) and protecting against blood-brain barrier damage. The mechanisms underlying Treg interactions with neutrophils remain elusive. This study evaluates the contribution of program death 1-ligand 1 (PD-L1) to Treg-mediated neutrophil inhibition and neuroprotection after cerebral ischemia.

METHODS

In vitro experiments were performed using a transwell system or a coculture system allowing cell-to-cell contact. Focal cerebral ischemia was induced in mice for 60 minutes. Tregs (2×10(6)) isolated from donor animals (wild-type or PD-L1-/-) were intravenously injected into ischemic recipients 2 hours after middle cerebral artery occlusion (MCAO). MMP-9 production, blood-brain barrier permeability, and brain infarct were assessed at 1 or 3 days after MCAO.

RESULTS

In vitro experiments reveal that Treg-mediated inhibition of neutrophil MMP-9 required direct cell-to-cell contact. The suppression of MMP-9 was abolished when Tregs were pretreated with PD-L1 neutralizing antibodies or when neutrophils were pretreated with PD-1 antibodies. In vivo studies confirmed that intravenous administration of Tregs pretreated with PD-L1 antibodies or Tregs isolated from PD-L1-deficient mice failed to inhibit MMP-9 production by blood neutrophils 1 day after 60 minutes MCAO. Furthermore, the blood-brain barrier damage after MCAO was greatly ameliorated in PD-L1-competent Treg-treated mice but not in PD-L1-compromised Treg-treated mice. Consequently, PD-L1 dysfunction abolished Treg-mediated brain protection and neurological improvements 3 days after MCAO.

CONCLUSIONS

PD-L1 plays an essential role in the neuroprotection afforded by Tregs against cerebral ischemia by mediating the suppressive effect of Tregs on neutrophil-derived MMP-9.

Hemorrhagic transformation after ischemic stroke in animals and humans

Hemorrhagic transformation (HT) is a common complication of ischemic stroke that is exacerbated by thrombolytic therapy. Methods to better prevent, predict, and treat HT are needed. In this review, we summarize studies of HT in both animals and humans. We propose that early HT (<18 to 24 hours after stroke onset) relates to leukocyte-derived matrix metalloproteinase-9 (MMP-9) and brain-derived MMP-2 that damage the neurovascular unit and promote blood-brain barrier (BBB) disruption. This contrasts to delayed HT (>18 to 24 hours after stroke) that relates to ischemia activation of brain proteases (MMP-2, MMP-3, MMP-9, and endogenous tissue plasminogen activator), neuroinflammation, and factors that promote vascular remodeling (vascular endothelial growth factor and high-moblity-group-box-1). Processes that mediate BBB repair and reduce HT risk are discussed, including transforming growth factor beta signaling in monocytes, Src kinase signaling, MMP inhibitors, and inhibitors of reactive oxygen species. Finally, clinical features associated with HT in patients with stroke are reviewed, including approaches to predict HT by clinical factors, brain imaging, and blood biomarkers. Though remarkable advances in our understanding of HT have been made, additional efforts are needed to translate these discoveries to the clinic and reduce the impact of HT on patients with ischemic stroke.

Molecular dialogs between the ischemic brain and the peripheral immune system: dualistic roles in injury and repair

Immune and inflammatory responses actively modulate the pathophysiological processes of acute brain injuries such as stroke. Soon after the onset of stroke, signals such as brain-derived antigens, danger-associated molecular patterns (DAMPs), cytokines, and chemokines are released from the injured brain into the systemic circulation. The injured brain also communicates with peripheral organs through the parasympathetic and sympathetic branches of the autonomic nervous system. Many of these diverse signals not only activate resident immune cells in the brain, but also trigger robust immune responses in the periphery. Peripheral immune cells then migrate toward the site of injury and release additional cytokines, chemokines, and other molecules, causing further disruptive or protective effects in the ischemic brain. Bidirectional communication between the injured brain and the peripheral immune system is now known to regulate the progression of stroke pathology as well as tissue repair. In the end, this exquisitely coordinated crosstalk helps determine the fate of animals after stroke. This article reviews the literature on ischemic brain-derived signals through which peripheral immune responses are triggered, and the potential impact of these peripheral responses on brain injury and repair. Pharmacological strategies and cell-based therapies that target the dialog between the brain and peripheral immune system show promise as potential novel treatments for stroke.

Leg ischaemia before circulatory arrest alters brain leucocyte count and respiratory chain redox state

OBJECTIVES

Remote ischaemic preconditioning and its neuroprotective abilities are currently under investigation and the method has shown significant effects in several small and large animal studies. In our previous studies, leucocyte filtration during cardiopulmonary bypass reduced cerebrocortical adherent leucocyte count and mitigated cerebral damage after hypothermic circulatory arrest (HCA) in piglets. This study aimed to obtain and assess direct visual data of leucocyte behaviour in cerebral vessels after hypothermic circulatory arrest following remote ischaemic preconditioning.

METHODS

Twelve native stock piglets were randomized into a remote ischaemic preconditioning group (n = 6) and a control group (n = 6). The intervention group underwent hind-leg ischaemia, whereas the control group received a sham-treatment before a 60-min period of hypothermic circulatory arrest. An intravital microscope was used to obtain measurements from the cerebrocortical vessel in vivo. It included three sets of filters: a violet filter to visualize microvascular perfusion and vessel diameter, a green filter for visualization of rhodamine-labelled leucocytes and an ultraviolet filter for reduced nicotinamide adenine dinucleotide (NADH) analysis. The final magnification on the microscope was 400. After the experiment, cerebral and cerebellar biopsies were collected and analysed with transmission electron microscope by a blinded analyst.

RESULTS

In the transmission electron microscope analysis, the entire intervention group had normal, unaffected rough endoplasmic reticulum's in their cerebellar tissue, whereas the control group had a mean score of 1.06 (standard deviation 0.41) (P = 0.026). The measured amount of adherent leucocytes was lower in the remote ischaemic preconditioning group. The difference was statistically significant at 5, 15 and 45 min after circulatory arrest. Statistically significant differences were seen also in the recovery phase at 90 and 120 min after reperfusion. Nicotinamide adenine dinucleotide autofluorescence had statistically significant differences at 10 min after cooling and at 120 and 180 min after hypothermic circulatory arrest.

CONCLUSIONS

Remote ischaemic preconditioning seems to provide better mitochondrial respiratory chain function as indicated by the higher NADH content. It simultaneously provides a reduction of adherent leucocytes in cerebral vessels after hypothermic circulatory arrest. Additionally, it might provide some degree of cellular organ preservation as implied by the electron microscopy results.

Neuroinflammation in ischemic brain injury as an adaptive process

Cerebral ischaemia triggers various physiological processes, some of which have been considered deleterious and others beneficial. These processes have been characterized in one influential model as being part of a transition from injury to repair processes. We argue that another important distinction is between dysregulated and regulated processes. Although intervening in the course of dysregulated processes may be neuroprotective, this is unlikely to be true for regulated processes. This is because from an evolutionary perspective, regulated complex processes that are conserved across many species are likely to be adaptive and provide a survival advantage. We argue that the neuroinflammatory cascade is an adaptive process in this sense, and contrast this with a currently popular theory which we term the maladaptive immune response theory. We review the evidence from clinical and preclinical pharmacology with respect to this theory, and deduced that the evidence is inconclusive at best, and probably falsifies the theory. We argue that this is why there are no anti-inflammatory treatments for cerebral ischaemia, despite 30 years of seemingly promising preclinical results. We therefore propose an opposing theory, which we call the adaptive immune response hypothesis.

Molecular contributions to neurovascular unit dysfunctions after brain injuries: lessons for target-specific drug development

The revised 'expanded' neurovascular unit (eNVU) is a physiological and functional unit encompassing endothelial cells, pericytes, smooth muscle cells, astrocytes and neurons. Ischemic stroke and traumatic brain injury are acute brain injuries directly affecting the eNVU with secondary damage, such as blood-brain barrier (BBB) disruption, edema formation and hypoperfusion. BBB dysfunctions are observed at an early postinjury time point, and are associated with eNVU activation of proteases, such as tissue plasminogen activator and matrix metalloproteinases. BBB opening is accompanied by edema formation using astrocytic AQP4 as a key protein regulating water movement. Finally, nitric oxide dysfunction plays a dual role in association with BBB injury and dysregulation of cerebral blood flow. These mechanisms are discussed including all targets of eNVU encompassing endothelium, glial cells and neurons, as well as larger blood vessels with smooth muscle. In fact, the feeding blood vessels should also be considered to treat stroke and traumatic brain injury. This review underlines the importance of the eNVU in drug development aimed at improving clinical outcome after stroke and traumatic brain injury.

RNA in blood is altered prior to hemorrhagic transformation in ischemic stroke

OBJECTIVE

Hemorrhagic transformation (HT) is a major complication of ischemic stroke that worsens outcomes and increases mortality. Disruption of the blood-brain barrier is a central feature of HT pathogenesis, and leukocytes may contribute to this process. We sought to determine whether ischemic strokes that develop HT have differences in RNA expression in blood within 3 hours of stroke onset prior to treatment with thrombolytic therapy.

METHODS

Stroke patient blood samples were obtained prior to treatment with thrombolysis, and leukocyte RNA was assessed by microarray analysis. Strokes that developed HT (n = 11) were compared to strokes without HT (n = 33) and controls (n = 14). Genes were identified (corrected p < 0.05, fold change ≥|1.2|), and functional analysis was performed. RNA prediction of HT in stroke was evaluated using cross-validation, and in a second stroke cohort (n = 52).

RESULTS

Ischemic strokes that developed HT had differential expression of 29 genes in circulating leukocytes prior to treatment with thrombolytic therapy. A panel of 6 genes could predict strokes that later developed HT with 80% sensitivity and 70.2% specificity. Key pathways involved in HT of human stroke are described, including amphiregulin, a growth factor that regulates matrix metalloproteinase-9; a shift in transforming growth factor-β signaling involving SMAD4, INPP5D, and IRAK3; and a disruption of coagulation factors V and VIII.

INTERPRETATION

Identified genes correspond to differences in inflammation and coagulation that may predispose to HT in ischemic stroke. Given the adverse impact of HT on stroke outcomes, further evaluation of the identified genes and pathways is warranted to determine their potential as therapeutic targets to reduce HT and as markers of HT risk.

Temporal profile of matrix metalloproteinases and their inhibitors in a human endothelial cell culture model of cerebral ischemia

BACKGROUND

Matrix metalloproteinases (MMPs) are key players in proteolytic blood-brain barrier (BBB) disruption during ischemic stroke, leading to vascular edema, hemorrhagic transformation and infiltration by leukocytes. Their effect is dampened by the endogenous tissue inhibitors of metalloproteinases (TIMPs). The respective cellular source of specific MMPs and TIMPs during BBB breakdown is still under investigation.

METHODS

We analyzed the MMP and TIMP release of human brain microvascular endothelial cells (BMECs) under oxygen glucose deprivation (OGD). Cultured human BMECs (the hCMEC/D3 cell line) were subjected to OGD (6, 12, 18 and 24 h). Gene expression of MMP-2, MMP-9, TIMP-1 and TIMP-2 were serially measured by quantitative real time-PCR and compared to ELISA-detected cell culture medium levels.

RESULTS

OGD induced a significant and long-lasting increase in MMP-2 gene expression, reaching a plateau after 12 h. Medium protein levels of MMP-2 were correspondingly elevated at 12 h of OGD. The MMP-9 synthesis rate was detectable at very low levels and remained unaffected by OGD. TIMP-1 gene expression and secretion declined under OGD, whereas both expression and secretion of TIMP-2 remained stable. Contrary to the respective gene expression rate, medium levels of MMP-2, TIMP-1 and TIMP-2 started a simultaneous decline after 12 h of OGD. This is most likely due to an impaired synthesis and enhanced consumption rate under OGD.

CONCLUSIONS

The objective of our study was to determine the contribution of human BMECs to the MMP metabolism under in vitro OGD conditions simulating ischemic stroke. Our results suggest that human BMECs switch to a proinflammatory state by means of an enhanced production of MMP-2, attenuated release of TIMP-1, and unaffected production of TIMP-2. Thus, human BMECs might participate in the MMP-mediated BBB breakdown during ischemic stroke. However, our data does not support human BMECs to be a source of MMP-9.

Adoptive regulatory T-cell therapy protects against cerebral ischemia

OBJECTIVE

Recent evidence suggests that functional deficiency in regulatory T cells (Tregs), an innate immunomodulator, exacerbates brain damage after cerebral ischemia. We therefore evaluated the effect of Treg transfer in rodent models of ischemic stroke and further investigated the mechanism underlying Treg-afforded neuroprotection.

METHODS

We examined the therapeutic potential of Tregs and the mechanisms of neuroprotection in vivo in 2 rodent models of ischemic stroke and in vitro in Treg-neutrophil cocultures using a combined approach including cell-specific depletion, gene knockout mice, and bone marrow chimeras.

RESULTS

Systemic administration of purified Tregs at 2, 6, or even 24 hours after middle cerebral artery occlusion resulted in a marked reduction of brain infarct and prolonged improvement of neurological functions lasting out to 4 weeks. Treg-afforded neuroprotection was accompanied by attenuated blood-brain barrier (BBB) disruption during early stages of ischemia, decreased cerebral inflammation, and reduced infiltration of peripheral inflammatory cells into the lesioned brain. Surprisingly, Tregs exerted early neuroprotection without penetrating into the brain parenchyma or inhibiting the activation of residential microglia. Rather, both in vivo and in vitro studies demonstrated that Tregs suppressed peripheral neutrophil-derived matrix metallopeptidase-9 production, thus preventing proteolytic damage of the BBB. In addition to its potent central neuroprotection, Treg treatment was shown to ameliorate poststroke lymphopenia, suggesting a beneficial effect on immune status.

INTERPRETATION

Our study suggests that Treg adoptive therapy is a novel and potent cell-based therapy targeting poststroke inflammatory dysregulation and neurovascular disruption.

Matrix metalloproteinases and blood-brain barrier disruption in acute ischemic stroke

Ischemic stroke continues to be one of the most challenging diseases in translational neurology. Tissue plasminogen activator (tPA) remains the only approved treatment for acute ischemic stroke, but its use is limited to the first hours after stroke onset due to an increased risk of hemorrhagic transformation over time resulting in enhanced brain injury. In this review we discuss the role of matrix metalloproteinases (MMPs) in blood-brain barrier (BBB) disruption as a consequence of ischemic stroke. MMP-9 in particular appears to play an important role in tPA-associated hemorrhagic complications. Reactive oxygen species can enhance the effects of tPA on MMP activation through the loss of caveolin-1 (cav-1), a protein encoded in the cav-1 gene that serves as a critical determinant of BBB permeability. This review provides an overview of MMPs' role in BBB breakdown during acute ischemic stroke. The possible role of MMPs in combination treatment of acute ischemic stroke is also examined.

High-density lipoproteins limit neutrophil-induced damage to the blood-brain barrier in vitro

Breakdown of the blood-brain barrier (BBB) is a key step associated with ischemic stroke and its increased permeability causes extravasation of plasma proteins and circulating leukocytes. Polymorphonuclear neutrophil (PMN) proteases may participate in BBB breakdown. We investigated the role of PMNs in ischemic conditions by testing their effects on a model of BBB in vitro, under oxygen-glucose deprivation (OGD) to mimic ischemia, supplemented or not with high-density lipoproteins (HDLs) to assess their potential protective effects. Human cerebral endothelial cells cultured on transwells were incubated for 4 hours under OGD conditions with or without PMNs and supplemented or not with HDLs or alpha-1 antitrypsin (AAT, an elastase inhibitor). The integrity of the BBB was then assessed and the effect of HDLs on PMN-induced proteolysis of extracellular matrix proteins was evaluated. The release of myeloperoxidase and matrix metalloproteinase 9 (MMP-9) by PMNs was quantified. Polymorphonuclear neutrophils significantly increased BBB permeability under OGD conditions via proteolysis of extracellular matrix proteins. This was associated with PMN degranulation. Addition of HDLs or AAT limited the proteolysis and associated increased permeability by inhibiting PMN activation. Our results suggest a deleterious, elastase-mediated role of activated PMNs under OGD conditions leading to BBB disruption that could be inhibited by HDLs.

Increased accumulation of regulatory granulocytic myeloid cells in mannose receptor C type 1-deficient mice correlates with protection in a mouse model of neurocysticercosis

Neurocysticercosis (NCC) is a central nervous system (CNS) infection caused by the metacestode stage of the parasite Taenia solium. During NCC, the parasites release immunodominant glycan antigens in the CNS environment, invoking immune responses. The majority of the associated pathogenesis is attributed to the immune response against the parasites. Glycans from a number of pathogens, including helminths, act as pathogen-associated molecular pattern molecules (PAMPs), which are recognized by pattern recognition receptors (PRRs) known as C-type lectin receptors (CLRs). Using a mouse model of NCC by infection with the related parasite Mesocestoides corti, we have investigated the role of mannose receptor C type 1 (MRC1), a CLR which recognizes high-mannose-containing glycan antigens. Here we show that MRC1(-/-) mice exhibit increased survival times after infection compared with their wild-type (WT) counterparts. The decreased disease severity correlates with reduced levels of expression of markers implicated in NCC pathology, such as interleukin-1β (IL-1β), IL-6, CCL5, and matrix metalloproteinase 9 (MMP9), in addition to induction of an important repair marker, fibroblast growth factor 2 (FGF2). Furthermore, the immune cell subsets that infiltrate the brain of MRC1(-/-) mice are dramatically altered and characterized by reduced numbers of T cells and the accumulation of granulocytic cells with an immune phenotype resembling granulocytic myeloid-dependent suppressor cells (gMDSCs). The results suggest that MRC1 plays a critical role in myeloid plasticity, which in turn affects the adaptive immune response and immunopathogenesis during murine NCC.

Post-ischemic vascular adhesion protein-1 inhibition provides neuroprotection in a rat temporary middle cerebral artery occlusion model

We examined the neuroprotective efficacy associated with post-ischemic vascular adhesion protein-1 (VAP-1) blockade in rats subjected to transient (1 h) middle cerebral artery occlusion (MCAo). We compared saline-treated control rats to rats treated with a highly selective VAP-1 inhibitor, LJP-1586 [Z-3-fluoro-2-(4-methoxybenzyl) allylamine hydrochloride]. Initial intraperitoneal LJP-1586 (or saline control) treatments were delayed until 6 h or 12 h reperfusion. At 72-h reperfusion, LJP-1586-treated rats displayed 51% and 33% smaller infarct volumes, relative to their controls, in the 6- and 12-h treatment groups, respectively. However, only in the 6-h treatment group was the infarct volume reduction significant (p < 0.05). On the other hand, we observed significantly improved neurologic functions in both 6- and 12-h treatment groups, versus their matched controls (p < 0.05). Also, the effect of 6-h LJP-1586 treatment on post-ischemic leukocyte trafficking in pial venules overlying the ischemic cortex was evaluated using intravital microscopy. These experiments revealed that: 1) LJP-1586 did not affect intravascular leukocyte (largely neutrophil) adhesion, at least out to 12-h reperfusion; and 2) the onset of neutrophil extravasation, which occurred between 6-8-h reperfusion in control rats, was prevented by LJP-1586-treatment. In conclusion, in rats subjected to transient MCAo, selective VAP-1 pharmacologic blockade provided neuroprotection, with a prolonged therapeutic window of 6-12-h reperfusion.

Putative role of prostaglandin receptor in intracerebral hemorrhage

Each year, approximately 795,000 people experience a new or recurrent stroke. Of all strokes, 84% are ischemic, 13% are intracerebral hemorrhage (ICH) strokes, and 3% are subarachnoid hemorrhage strokes. Despite the decreased incidence of ischemic stroke, there has been no change in the incidence of hemorrhagic stroke in the last decade. ICH is a devastating disease 37–38% of patients between the ages of 45 and 64 die within 30 days. In an effort to prevent ischemic and hemorrhagic strokes we and others have been studying the role of prostaglandins and their receptors. Prostaglandins are bioactive lipids derived from the metabolism of arachidonic acid. They sustain homeostatic functions and mediate pathogenic mechanisms, including the inflammatory response. Most prostaglandins are produced from specific enzymes and act upon cells via distinct G-protein coupled receptors. The presence of multiple prostaglandin receptors cross-reactivity and coupling to different signal transduction pathways allow differentiated cells to respond to prostaglandins in a unique manner. Due to the number of prostaglandin receptors, prostaglandin-dependent signaling can function either to promote neuronal survival or injury following acute excitotoxicity, hypoxia, and stress induced by ICH. To better understand the mechanisms of neuronal survival and neurotoxicity mediated by prostaglandin receptors, it is essential to understand downstream signaling. Several groups including ours have discovered unique roles for prostaglandin receptors in rodent models of ischemic stroke, excitotoxicity, and Alzheimer disease, highlighting the emerging role of prostaglandin receptor signaling in hemorrhagic stroke with a focus on cyclic-adenosine monophosphate and calcium (Ca²⁺) signaling. We review current ICH data and discuss future directions notably on prostaglandin receptors, which may lead to the development of unique therapeutic targets against hemorrhagic stroke and brain injuries alike.

Monocyte chemotactic protein-1 as a potential biomarker for early anti-thrombotic therapy after ischemic stroke

Inflammation following ischemic brain injury is correlated with adverse outcome. Preclinical studies indicate that treatment with acetylsalicylic acid + extended-release dipyridamole (ASA + ER-DP) has anti-inflammatory and thereby neuroprotective effects by inhibition of monocyte chemotactic protein-1 (MCP-1) expression. We hypothesized that early treatment with ASA + ER-DP will reduce levels of MCP-1 also in patients with ischemic stroke. The EARLY trial randomized patients with ischemic stroke or TIA to either ASA + ER-DP treatment or ASA monotherapy within 24 h following the event. After 7 days, all patients were treated for up to 90 days with ASA + ER-DP. MCP-1 was determined from blood samples taken from 425 patients on admission and day 8. The change in MCP-1 from admission to day 8 did not differ between patients treated with ASA + ER-DP and ASA monotherapy (p > 0.05). Comparisons within MCP-1 baseline quartiles indicated that patients in the highest quartile (>217–973 pg/mL) showed improved outcome at 90 days if treated with ASA + ER-DP in comparison to treatment with ASA alone (p = 0.004). Our data does not provide any evidence that treatment with ASA + ER-DP lowers MCP-1 in acute stroke patients. However, MCP-1 may be a useful biomarker for deciding on early stroke therapy, as patients with high MCP-1 at baseline appear to benefit from early treatment with ASA + ER-DP.

The immunology of acute stroke

Recent clinical and experimental studies have highlighted a complex role for the immune system in the pathophysiological changes that occur after acute stroke. Sensors of the innate immune system such as Toll-like receptors, or effectors such as the lectin pathway of complement activation and innate immune cells, are activated by brain ischaemia and tissue damage, leading to amplification of the inflammatory cascade. Activation of the adaptive arm of the immune system, mediated by lymphocyte populations including T and B cells, regulatory T cells, and γδT cells, in response to stroke can lead to deleterious antigen-specific autoreactive responses but can also have cytoprotective effects. Increased incidence of infections is observed after acute stroke, and might result from activation of long-distance feedback loops between the CNS and peripheral immune organs, which are thought to play a part in stroke-induced immunodepression. Ongoing clinical trials are investigating whether the preventive use of antibiotics improves functional outcome after stroke. This Review discusses the multifaceted role of the immune system in the pathophysiology of acute stroke.

Spatio-temporal course of macrophage-like cell accumulation after experimental embolic stroke depending on treatment with tissue plasminogen activator and its combination with hyperbaric oxygenation

Inflammation following ischaemic stroke attracts high priority in current research, particularly using human-like models and long-term observation periods considering translational aspects. The present study aimed on the spatio-temporal course of macrophage-like cell accumulation after experimental thromboembolic stroke and addressed microglial and astroglial reactions in the ischaemic border zone. Further, effects of tissue plasminogen activator (tPA) as currently best treatment for stroke and the potentially neuroprotective co-administration of hyperbaric oxygen (HBO) were investigated. Rats underwent middle cerebral artery occlusion and were assigned to control, tPA or tPA+HBO. Twenty-four hours, 7, 14 and 28 days were determined as observation time points. The accumulation of macrophage-like cells was semiquantitatively assessed by CD68 staining in the ischaemic area and ischaemic border zone, and linked to the clinical course. CD11b, ionized calcium binding adaptor molecule 1 (Iba), glial fibrillary acidic protein (GFAP) and Neuronal Nuclei (NeuN) were applied to reveal delayed glial and neuronal alterations. In all groups, the accumulation of macrophage-like cells increased distinctly from 24 hours to 7 days post ischaemia. tPA+HBO tended to decrease macrophage-like cell accumulation at day 14 and 28. Overall, a trend towards an association of increased accumulation and pronounced reduction of the neurological deficit was found. Concerning delayed inflammatory reactions, an activation of microglia and astrocytes with co-occurring neuronal loss was observed on day 28. Thereby, astrogliosis was found circularly in contrast to microglial activation directly in the ischaemic area. This study supports previous data on long-lasting inflammatory processes following experimental stroke, and additionally provides region-specific details on glial reactions. The tendency towards a decreasing macrophage-like cell accumulation after tPA+HBO needs to be discussed critically since neuroprotective properties were recently ascribed to long-term inflammatory processes.

Bone marrow chimeras in the study of experimental stroke

Inflammation is known to contribute to stroke evolution, and poststroke immune responses have been documented to emanate from the brain via microglia. However, circulating immune cells are increasingly recognized to play a significant role as well. Recent work has demonstrated the importance of the peripheral circulation and stroke pathogenesis. Understanding how the peripheral circulation contributes to ischemic brain injury may reveal important therapeutic targets and strategies. The use of bone marrow chimeras can be a useful tool in understanding the relative contributions of brain resident and peripheral inflammatory responses.

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.

Neutrophil depletion reduces edema formation and tissue loss following traumatic brain injury in mice

Background

Brain edema as a result of secondary injury following traumatic brain injury (TBI) is a major clinical concern. Neutrophils are known to cause increased vascular permeability leading to edema formation in peripheral tissue, but their role in the pathology following TBI remains unclear.

Methods

In this study we used controlled cortical impact (CCI) as a model for TBI and investigated the role of neutrophils in the response to injury. The outcome of mice that were depleted of neutrophils using an anti-Gr-1 antibody was compared to that in mice with intact neutrophil count. The effect of neutrophil depletion on blood-brain barrier function was assessed by Evan's blue dye extravasation, and analysis of brain water content was used as a measurement of brain edema formation (24 and 48 hours after CCI). Lesion volume was measured 7 and 14 days after CCI. Immunohistochemistry was used to assess cell death, using a marker for cleaved caspase-3 at 24 hours after injury, and microglial/macrophage activation 7 days after CCI. Data were analyzed using Mann-Whitney test for non-parametric data.

Results

Neutrophil depletion did not significantly affect Evan's blue extravasation at any time-point after CCI. However, neutrophil-depleted mice exhibited a decreased water content both at 24 and 48 hours after CCI indicating reduced edema formation. Furthermore, brain tissue loss was attenuated in neutropenic mice at 7 and 14 days after injury. Additionally, these mice had a significantly reduced number of activated microglia/macrophages 7 days after CCI, and of cleaved caspase-3 positive cells 24 h after injury.

Conclusion

Our results suggest that neutrophils are involved in the edema formation, but not the extravasation of large proteins, as well as contributing to cell death and tissue loss following TBI in mice.

Matrix metalloproteinase-9 is associated with acute inflammation after olfactory injury

We previously reported an increase in matrix metalloproteinase-9 (MMP-9) levels in the olfactory bulb immediately after nerve transection; however, its role remains unknown. In this study, we determined the source of MMP-9 by monitoring the infiltration of inflammatory leukocytes in the olfactory bulb after nerve transection. We used myeloperoxidase to identify neutrophils and CD68 to identify macrophages at days 1, 7, and 10. MMP-9 colocalized with neutrophils at all three time points but was not contained in macrophages. This is the first study to demonstrate that MMP-9 is associated with early inflammatory response after olfactory injury, and provides insight into mechanisms underlying olfactory injury and recovery processes.

Increased cerebral matrix metalloprotease-9 activity is associated with compromised recovery in the diabetic db/db mouse following a stroke

Diabetes is a major risk factor of stroke and is associated with increased frequency of stroke and a poorer prognosis for recovery. In earlier studies we have utilized type 2 diabetic mouse models of stroke and demonstrated that diabetic db/db and ob/ob mice experience larger infarct volumes and impaired recovery associated with greater infiltration of macrophage following hypoxic-ischemic (H/I) insult than their heterozygous non-diabetic db/+ and ob/+ littermates. To obtain a better understanding of the pathogenesis of the impaired recovery, we have investigated the role of matrix metalloproteases and their endogenous inhibitors in the breakdown of the blood-brain barrier (BBB) following H/I. Diabetic db/db mice showed a significant and more rapid increase in matrix metalloprotease (MMP)-9 mRNA, protein and gelatinolytic activity compared with db/+, which resulted in an increased degradation of occludin and collagen IV and subsequently, an increased BBB permeability and greater infiltration of neutrophils into the infarct area. The expression of the MMPs, especially in the db/+ mice, is preceded by an elevated expression of their endogenous tissue inhibitors of metalloproteases (TIMPs) 1, 2, and 3, whereas in the db/db mice, a lower expression of the TIMPs is associated with greater MMP 3 and 9 expression. These results suggest that an imbalance in the MMPs/TIMPs cascade in the diabetic mouse, particularly MMP-9, results in a greater neutrophil invasion, a compromised BBB and consequently a greater insult.

Reduction of neutrophil activity decreases early microvascular injury after subarachnoid haemorrhage

Background

Subarachnoid haemorrhage (SAH) elicits rapid pathological changes in the structure and function of parenchymal vessels (≤ 100 μm). The role of neutrophils in these changes has not been determined. This study investigates the role of neutrophils in early microvascular changes after SAH

Method

Rats were either untreated, treated with vinblastine or anti-polymorphonuclear (PMN) serum, which depletes neutrophils, or treated with pyrrolidine dithiocarbamate (PDTC), which limits neutrophil activity. SAH was induced by endovascular perforation. Neutrophil infiltration and the integrity of vascular endothelium and basement membrane were assessed immunohistochemically. Vascular collagenase activity was assessed by in situ zymography.

Results

Vinblastine and anti-PMN serum reduced post-SAH accumulation of neutrophils in cerebral vessels and in brain parenchyma. PDTC increased the neutrophil accumulation in cerebral vessels and decreased accumulation in brain parenchyma. In addition, each of the three agents decreased vascular collagenase activity and post-SAH loss of vascular endothelial and basement membrane immunostaining.

Conclusions

Our results implicate neutrophils in early microvascular injury after SAH and indicate that treatments which reduce neutrophil activity can be beneficial in limiting microvascular injury and increasing survival after SAH.

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.

Quercetin reduces the elevated matrix metalloproteinases-9 level and improves functional outcome after cerebral focal ischemia in rats

BACKGROUND

Blood-brain barrier (BBB) disruption mediated by matrix metalloproteinase (MMPs) activation is a critical event during cerebral ischemia. The inhibition of MMP might be a potential approach to protect against secondary injury. The present study was designed to determine the effects of quercetin on BBB disruption and MMP activity, in a focal ischemia model induced by photothrombosis, in rats.

METHODS

Adult male Sprague-Dawley rats received focal ischemia by photothrombosis. The injured animals were divided into two groups: one group received 25 μmol/kg of quercetin intraperitoneally, starting 1 h after injury with continued treatment at 12-h intervals for 3 days, while animals in the control group received weight-adjusted doses of a saline vehicle. The effects of quercetin on BBB disruption, brain edema, MMP activities, and neurological deficits were determined.

FINDINGS

Quercetin treatment markedly reduced ischemia-induced up-regulation of MMP-9 at 24 and 48 h after ischemic injury. No significant change in MMP-2 activity was observed throughout the experimental period. Post-ischemic increase in BBB permeability and brain edema were significantly reduced in the quercetin-treated group compared to the vehicle-treated ischemia control. Quercetin treatment significantly improved the functional outcomes assessed by the accelerating rotarod test.

CONCLUSIONS

The results of this study demonstrated that quercetin attenuated BBB disruption during focal ischemia through inhibitory effects on MMP-9 activity. These results suggest that quercetin might have a potential role in the protection against neuronal injury in patients with focal ischemic stroke.

Decreased myeloperoxidase expressing cells in the aged rat brain after excitotoxic damage

Brain aging is associated to several morphological and functional alterations that influence the evolution and outcome of CNS damage. Acute brain injury such as an excitotoxic insult induces initial tissue damage followed by associated inflammation and oxidative stress, partly attributed to neutrophil recruitment and the expression of oxidative enzymes such as myeloperoxidase (MPO), among others. However, to date, very few studies have focused on how age can influence neutrophil infiltration after acute brain damage. Therefore, to evaluate the age-dependent pattern of neutrophil cell infiltration following an excitotoxic injury, intrastriatal injection of N-methyl-d-aspartate was performed in young and aged male Wistar rats. Animals were sacrificed at different times between 12h post-lesion (hpl) to 14 days post-lesion (dpl). Cryostat sections were processed for myeloperoxidase (MPO) immunohistochemistry, and double labeling for either neuronal cells (NeuN), astrocytes (GFAP), perivascular macrophages (ED-2), or microglia/macrophages (tomato lectin histochemistry). Our observations showed that MPO + cells were observed in the injured striatum from 12 hpl (when maximum values were found) until 7 dpl, when cell density was strongly diminished. However, at all survival times analyzed, the overall density of MPO + cells was lower in the aged versus the adult injured striatum. MPO + cells were mainly identified as neutrophils (especially at 12 hpl and 1 dpl), but it should be noted that MPO + neurons and microglia/macrophages were also found. MPO + neurons were most commonly observed at 12 hpl and reduced in the aged. MPO + microglia/macrophages were the main population expressing MPO from 3 dpl, when density was also reduced in aged subjects. These results point to neutrophil infiltration as another important factor contributing to the different responses of the adult and aged brain to damage, highlighting the need of using aged animals for the study of acute age-related brain insults.

Pathways for ischemic cytoprotection: role of sirtuins in caloric restriction, resveratrol, and ischemic preconditioning

Caloric restriction (CR), resveratrol, and ischemic preconditioning (IPC) have been shown to promote protection against ischemic injury in the heart and brain, as well as in other tissues. The activity of sirtuins, which are enzymes that modulate diverse biologic processes, seems to be vital in the ability of these therapeutic modalities to prevent against cellular dysfunction and death. The protective mechanisms of the yeast Sir2 and the mammalian homolog sirtuin 1 have been extensively studied, but the involvement of other sirtuins in ischemic protection is not yet clear. We examine the roles of mammalian sirtuins in modulating protective pathways against oxidative stress, energy depletion, excitotoxicity, inflammation, DNA damage, and apoptosis. Although many of these sirtuins have not been directly implicated in ischemic protection, they may have unique roles in enhancing function and preventing against stress-mediated cellular damage and death. This review will include in-depth analyses of the roles of CR, resveratrol, and IPC in activating sirtuins and in mediating protection against ischemic damage in the heart and brain.

Matrix metalloproteinase-β19 expressed in cerebral amyloid angiopathy

BACKGROUND

Cerebral amyloid angiopathy (CAA) is a frequent finding in the brains of patients with Alzheimer's disease (AD). CAA may be complicated with CAA-associated intracerebral haemorrhage (CAAH). Previous studies have revealed matrix metalloproteinase (MMP) expression in a mouse model of CAA and in human intracerebral haemorrhage. Here we studied the involvement of MMPs in human CAA and CAAH.

MATERIAL AND METHODS

To investigate the putative expression of MMPs in human CAA and CAAH (Step 1), immunohistochemistry (IHC) against MMPs-1, -2, -7, -9, -19 and -26 was applied on tissue microarray (TMA) constructed of cerebral samples from 29 individuals with AD, 15 with CAAH and 2 controls. The findings in TMA were confirmed (Step 2) in tissue samples from 64 individuals, 45 presenting with CAA (including 36 with CAAH) and 19 without CAA (including 11 with hypertensive cerebral haemorrhage).

RESULTS

In Step 1, immunoreactivity against MMPs-19 and -26 was detected in cerebral blood vessels in CAA. The results were confirmed in Step 2, where CAA (p<0.001) and intracerebral haemorrhage (p=0.045) were associated with vascular immunoreactivity against MMP-19. Multivariate analysis showed that the association between vascular MMP-19 and intracerebral haemorrhage was dependent from CAA. MMP-26 associated with CAA (p=0.021) but not with intracerebral haemorrhage.

CONCLUSION

This is the first human study showing local MMP-19 immunoreactivity in the Aβ-amyloid-laden blood vessels in CAA, suggesting that MMPs may be involved in CAA.

Metalloproteinase and stroke infarct size: role for anti-inflammatory treatment?

Deregulation of matrix metalloproteinases (MMPs), the largest class of human proteases, has been implicated in brain damage in both animal and human studies. Some MMPs are elevated after stroke (both in plasma and in brain tissue), and their expression is enhanced by t-PA during thrombolysis related to hemorrhagic transformation events. Although the exact cellular source of MMPs remains unknown, brain endothelium, astrocytes, neurons, and inflammatory-activated cells, such as neutrophils, may release MMP-2, MMP-3, MMP-8, MMP-9, MMP-10, and/or MMP-13. Neurovascular perturbations occurring after stroke lead to blood-brain barrier leakage, edema, hemorrhage, leukocyte infiltration, and progressive inflammatory reactions to brain injury over hours or even days after the initial stroke. Synthesized MMP inhibitors and several compounds used for stroke secondary prevention, such as anti-inflammatory drugs, might decrease MMPs and improve the acute treatment of human brain ischemia without compromising the beneficial effects of matrix plasticity during stroke recovery.

The dual role of the neuroinflammatory response after ischemic stroke: modulatory effects of hypothermia

Neuroinflammation is a key element in the ischemic cascade after cerebral ischemia that results in cell damage and death in the subacute phase. However, anti-inflammatory drugs do not improve outcome in clinical settings suggesting that the neuroinflammatory response after an ischemic stroke is not entirely detrimental. This review describes the different key players in neuroinflammation and their possible detrimental and protective effects in stroke. Because of its inhibitory influence on several pathways of the ischemic cascade, hypothermia has been introduced as a promising neuroprotective strategy. This review also discusses the influence of hypothermia on the neuroinflammatory response. We conclude that hypothermia exerts both stimulating and inhibiting effects on different aspects of neuroinflammation and hypothesize that these effects are key to neuroprotection.

Inflammation and brain injury: acute cerebral ischaemia, peripheral and central inflammation

Inflammation is a classical host defence response to infection and injury that has many beneficial effects. However, inappropriate (in time, place and magnitude) inflammation is increasingly implicated in diverse disease states, now including cancer, diabetes, obesity, atherosclerosis, heart disease and, most relevant here, CNS disease. A growing literature shows strong correlations between inflammatory status and the risk of cerebral ischaemia (CI, most commonly stroke), as well as with outcome from an ischaemic event. Intervention studies to demonstrate a causal link between inflammation and CI (or its consequences) are limited but are beginning to emerge, while experimental studies of CI have provided direct evidence that key inflammatory mediators (cytokines, chemokines and inflammatory cells) contribute directly to ischaemic brain injury. However, it remains to be determined what the relative importance of systemic (largely peripheral) versus CNS inflammation is in CI. Animal models in which CI is driven by a CNS intervention may not accurately reflect the clinical condition; stroke being typically induced by atherosclerosis or cardiac dysfunction, and hence current experimental paradigms may underestimate the contribution of peripheral inflammation. Experimental studies have already identified a number of potential anti-inflammatory therapeutic interventions that may limit ischaemic brain damage, some of which have been tested in early clinical trials with potentially promising results. However, a greater understanding of the contribution of inflammation to CI is still required, and this review highlights some of the key mechanism that may offer future therapeutic targets.

Oxygen-sensitive outcomes and gene expression in acute ischemic stroke

Acute ischemic stroke (AIS) results in focal deprivation of blood-borne factors, one of them being oxygen. The purpose of this study was two-fold: (1) to identify therapeutic conditions for supplemental oxygen in AIS and (2) to use transcriptome-wide screening toward uncovering oxygen-sensitive mechanisms. Transient MCAO in rodents was used to delineate the therapeutic potential of normobaric (NBO, 100% O(2), 1ATA) and hyperbaric oxygen (HBO, 100% O(2), 2ATA) during ischemia (iNBO, iHBO) and after reperfusion (rNBO, rHBO). Stroke lesion was quantified using 4.7 T MRI at 48 h. Supplemental oxygen during AIS significantly attenuated percent stroke hemisphere lesion volume as compared with that in room air (RA) controls, whereas identical treatment immediately after reperfusion exacerbated lesion volume (RA=22.4+/-1.8, iNBO=9.9+/-3.6, iHBO=6.6+/-4.8, rNBO=29.8+/-3.6, rHBO=35.4+/-7.6). iNBO and iHBO corrected penumbra tissue pO(2) during AIS as measured by EPR oxymetry. Unbiased query of oxygen-sensitive transcriptome in stroke-affected tissue identified 5,769 differentially expressed genes. Candidate genes were verified by real-time PCR using neurons laser-captured from the stroke-affected somatosensory cortex. Directed microarray analysis showed that supplemental oxygen limited leukocyte accumulation to the infarct site by attenuation of stroke-inducible proinflammatory chemokine response. The findings provide key information relevant to understanding oxygen-dependent molecular mechanisms in the AIS-affected brain.

Protective effect of high-density lipoprotein-based therapy in a model of embolic stroke

BACKGROUND AND PURPOSE

High-density lipoprotein (HDL) levels are inversely associated with stroke incidence, suggesting a protective effect. Using a rat model, we tested the hypothesis that HDL exerts direct vasculo-/neuroprotective effects when administered during the acute phase of embolic stroke.

METHODS

After embolic occlusion, Sprague-Dawley rats were randomly treated intravenously with purified HDL versus saline immediately (2, 10 mg/kg) or 3 or 5 hours (10 mg/kg) after stroke. The effects of HDL were assessed blindly 24 hours later by evaluating neurological deficit score and measuring the infarct volume and blood-brain barrier breakdown. Protease activities and neutrophil infiltration were also evaluated.

RESULTS

HDL injection immediately after stroke (10 mg/kg) reduced by 68% the mortality at 24 hours (P=0.015). HDL administration immediately or at 3 or 5 hours after stroke also reduced cerebral infarct volume by 74%, 68%, and 70.7%, respectively (P=0.0003, P=0.011, and P=0.019; n=17 per group). The neurological deficit at 24 hours in the HDL-treated group was decreased versus the saline-treated group (P=0.015). Ischemia-induced blood-brain barrier breakdown was significantly reduced in HDL-treated rats versus controls (P=0.0045). Neuroprotective effects of HDL were associated with decreased neutrophil recruitment in the infarct area (P=0.0027) accompanied by reduced matrix metalloproteinase gelatinase activity. Immunostaining showed that HDL was associated with endothelial and glial cells, and also that intercellular adhesion molecule-1 expression was decreased in vessels within the infarct area.

CONCLUSIONS

Administration of HDL is neuroprotective when performed up to 5 hours after experimental stroke. This effect may be attributed to the ability of HDL to protect the blood-brain barrier and limit neutrophil recruitment.

Matrix metalloproteinase 2 in reduced-size liver transplantation: beyond the matrix

We studied the contribution of matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9) to the beneficial effects of preconditioning (PC) in reduced-size orthotopic liver transplantation (ROLT). We also examined the role of c-Jun N-terminal kinase (JNK) and whether it regulates MMP2 in these conditions. Animals were subjected to ROLT with or without PC and pharmacological modulation, and liver tissue samples were then analyzed. We found that MMP2, but notMMP9, is involved in the beneficial effects of PC in ROLT. MMP2 reduced hepatic injury and enhanced liver regeneration. Moreover, inhibition of MMP2 in PC reduced animal survival after transplantation. JNK inhibition in the PC group decreased hepatic injury and enhanced liver regeneration. Furthermore, JNK upregulated MMP2 in PC. In addition, we showed that Tissue inhibitors of matrix metalloproteinases 2 (TIMP2) was also upregulated in PC and that JNK modulation also altered its levels in ROLT and PC. Our results open up new possibilities for therapeutic treatments to reduce I/R injury and increase liver regeneration after ROLT, which are the main limitations in living-donor transplantation.

Molecular insights and therapeutic targets for blood-brain barrier disruption in ischemic stroke: critical role of matrix metalloproteinases and tissue-type plasminogen activator

Blood-brain barrier (BBB) disruption, mediated through matrix metalloproteinases (MMPs) and other mechanisms, is a critical event during ischemic stroke. Tissue plasminogen activator (tPA) is the only FDA-approved thrombolytic therapy for acute ischemic stroke, but the efficacy and safety of its therapeutic application are limited by narrow treatment time windows and side effects. Thus, there is a pressing need to develop combinational therapy that could offset tPA side effects and improve efficacy in clinical practice. Recent experimental studies indicate that tPA has previously unidentified functions in the brain beyond its well-established thrombolytic activity, which might contribute to tPA-related side effects through MMPs (mainly MMP-9) and several signaling pathways involved in LDL receptor-related protein (LRP), activated protein C (APC) and protease-activated receptor 1 (PAR-1), platelet-derived growth factor C (PDGF-C), and N-methyl-d-aspartate (NMDA) receptor. Therapeutic targeting of MMPs and/or tPA-related signaling pathways might offer promising new approaches to combination therapies for ischemic stroke. This review provides an overview of the relationship between structural components and function of the BBB/neurovascular unit with respect to ischemic stroke. We discuss how MMPs and tPA contribute to BBB disruption during ischemic stroke and highlight recent findings of molecular signaling pathways involved in neurotoxicity of tPA therapy.

Cyclooxygenases-1 and -2 differentially modulate leukocyte recruitment into the inflamed brain

Peripheral leukocyte recruitment in neuroinflammatory conditions can exacerbate brain tissue damage by releasing cytotoxic mediators and by increasing vascular permeability. Cyclooxygenase (COX)-derived prostaglandins promote the migration of several immune cells in vitro, however, the specific roles of COX-1 and -2 on leukocyte recruitment in vivo have not been investigated. To examine the specific effects of COX-1 or COX-2 deficiency on neuroinflammation-induced leukocyte infiltration, we used a model of intracerebroventricular lipopolysaccharide (LPS)-induced neuroinflammation in COX-1(-/-), COX-2(-/-), and their respective wild-type (WT) ((+/+)) mice. After LPS, leukocyte infiltration and inflammatory response were attenuated in COX-1(-/-) and increased in COX-2(-/-) mice, compared with their respective WT controls. This influx of leukocytes was accompanied by a marked disruption of blood-brain barrier and differential expression of chemokines. These results indicate that COX-1 and COX-2 deletion differentially modulate leukocyte recruitment during neuroinflammation, and suggest that inhibition of COX-1 activity is beneficial, whereas COX-2 inhibition is detrimental, during a primary neuroinflammatory response.

Vascular MMP-9/TIMP-2 and neuronal MMP-10 up-regulation in human brain after stroke: a combined laser microdissection and protein array study

Matrix Metalloproteinases (MMPs) play an important role in brain injury after ischemic stroke. In the present study, we aimed to assess the global expression of MMP-Family proteins in the human brain after stroke by using a combination of Searchlight Protein Array and Laser Microdissection to determine their cellular origin. This study demonstrated that MMP-1, MMP-2, MMP-3, MMP-8, MMP-9, MMP-10, MMP-13, and TIMP-1 were upregulated in the infarcted tissue compared to healthy control areas. Using laser microdissection we obtained specific neuronal and vascular populations from both infarcted and control areas. From these fractions, we showed that MMP-9 and TIMP-2 were highly produced in brain microvessels while MMP-10 was notably increased in neurons of the ischemic brain but not in healthy areas. These findings demonstrate a selective cell-dependent MMP secretion, opening the possibility of selectively targeting specific MMPs for neuroprotection or vasculoprotection following stroke.

Bone marrow-derived cells are the major source of MMP-9 contributing to blood-brain barrier dysfunction and infarct formation after ischemic stroke in mice

Matrix metalloproteinase (MMP)-9 has been shown to contribute to blood-brain barrier (BBB) disruption, infarct formation, and hemorrhagic transformation after ischemic stroke. The cellular source of MMP-9 detectable in the ischemic brain remains controversial since extracellular molecules in the brain may be derived from blood. We here demonstrate that bone marrow-derived cells are the major source of MMP-9 in the ischemic brain. We made bone marrow chimeric mice with MMP-9 null and wild-type as donor and recipient. After 90 min of transient focal cerebral ischemia, MMP-9 null mice receiving wild-type bone marrow showed comparable outcomes to wild-type in brain MMP-9 levels and BBB disruption (endogenous albumin extravasation) at 1 h post-reperfusion and infarct size at 24 h post-reperfusion. In contrast, wild-type animals replaced with MMP-9 null bone marrow showed barely detectable levels of MMP-9 in the ischemic brain, with attenuations in BBB disruption and infarct size. MMP-9 null mice receiving wild-type bone marrow showed enhanced Evans blue extravasation as early as 1 h post-reperfusion compared to wild-type mice replaced with MMP-9 null bone marrow. These findings suggest that MMP-9 released from bone marrow-derived cells influences the progression of BBB disruption in the ischemic brain.

In vivo near-infrared fluorescence imaging of matrix metalloproteinase activity after cerebral ischemia

Matrix metalloproteinases (MMPs) have been implicated in the pathophysiology of cerebral ischemia. In this study, we explored whether MMP activity can be visualized by noninvasive near-infrared fluorescence (NIRF) imaging using an MMP-activatable probe in a mouse model of stroke. C57Bl6 mice were subjected to transient middle cerebral artery occlusion (MCAO) or sham operation. Noninvasive NIRF imaging was performed 24 h after probe injection, and target-to-background ratios (TBRs) between the two hemispheres were determined. TBRs were significantly higher in MCAO mice injected with the MMP-activatable probe than in sham-operated mice and in MCAO mice that were injected with the nonactivatable probe as controls. Treatment with an MMP inhibitor resulted in significantly lower TBRs and lesion volumes compared to injection of vehicle. To test the contribution of MMP-9 to the fluorescence signal, MMP9-deficient (MMP9(-/-)) mice and wild-type controls were subjected to MCAO of different durations to attain comparable lesion volumes. TBRs were significantly lower in MMP9(-/-) mice, suggesting a substantial contribution of MMP-9 activity to the signal. Our study shows that MMP activity after cerebral ischemia can be imaged noninvasively with NIRF using an MMP-activatable probe, which might be a useful tool to study MMP activity in the pathophysiology of the disease.

Neutrophils contribute to intracerebral haemorrhages after treatment with recombinant tissue plasminogen activator following cerebral ischaemia

BACKGROUND AND PURPOSE

Polymorphonuclear neutrophils (PMNs) contribute to the vascular damage caused by transient cerebral ischaemia. Here we have evaluated the role of PMNs in intracerebral haemorrhage (ICH) induced in a model of thrombolysis with recombinant tissue plasminogen activator (t-PA) during the acute phase of cerebral ischaemia.

EXPERIMENTAL APPROACH

The middle cerebral artery (MCA) of male spontaneously hypertensive rats was occluded for 1 h followed by reperfusion and, 5 h later, infusion of thrombolytic products (generated in vitro by t-PA on autologous clots). Effects of pretreatment (before the MCA occlusion) with vinblastine (4 days before; 0.5 mg.kg(-1)), monoclonal anti-neutrophil antibody (mAbRP3; 12 h, 0.3 mg.kg(-1)) or saline on ICH, neutrophil infiltration, MCA vascular reactivity and brain infarct volume were assessed, 24 h after the beginning of reperfusion.

KEY RESULTS

Depletion of circulating neutrophils significantly reduced t-PA-induced ICH (vinblastine, 4.6 +/- 1.0; mAbRP3, 5.2 +/- 1.0 vs. saline, 10.8 +/- 2.7 haemorrhages; P < 0.05). This depletion was associated with a decrease in cerebral infiltration by neutrophils and a decrease of endothelium-dependent, vascular dysfunction in isolated MCA, induced by the ischaemia/reperfusion and t-PA treatment. Brain infarct volume was significantly decreased after vinblastine treatment (159 +/- 13 mm(3) vs. 243 +/- 16 mm(3) with saline; P < 0.01) but not after depletion with mAbRP3 (221 +/- 22 mm(3)).

CONCLUSIONS AND IMPLICATIONS

Our results showed that pharmacological depletion of PMNs prevented t-PA-induced ICH, in parallel with a decrease in cerebral infiltration by PMNs and a decreased endothelial dysfunction in cerebral blood vessels.

Matrix metalloproteinase-13 is activated and is found in the nucleus of neural cells after cerebral ischemia

Matrix metalloproteinases (MMPs) have been implicated in the pathophysiology of ischemic stroke. In this study, we investigated the time course of gelatinolytic activation in a rat model of permanent ischemia. We observed an activation of MMPs as early as 30 mins after the ischemic insult, mainly in the nuclei of brain cells. Besides, we explored MMP-13 expression in brain samples of the animal model and stroke deceased patients. We observed an upregulation of active MMP-13 in rat brains (P<0.05) after 90 mins of cerebral ischemia. Human infarct/periinfarct samples also showed higher levels of active MMP-13 (P<0.05) compared with contralateral ones. Interestingly, we found that MMP-13 colocalized with 46-diamidino-2-phenyl indole signal by immunohistochemistry in both humans and rats, suggesting an intranuclear localization for MMP-13. Immunohistochemistry also revealed that MMP-13 was mainly produced by neurons, in both species, but also by oligodendrocytes in rats, and by astrocytes in humans. Finally we subjected a rat primary neuronal culture to oxygen and glucose deprivation (OGD) and we reproduced the nuclear translocation of MMP-13 in vitro. Nuclear extracts from cells confirmed upregulation of active MMP-13 after OGD (P<0.05). These results suggest that MMP-13 activation and its nuclear translocation is an early consequence of an ischemic stimulus.

The role of leukocyte biology in laminitis

The underlying pathogenesis of laminitis clearly depends importantly on inflammatory processes that recruit leukocytes at an early stage in disease. The role of leukocytes in the initiation of laminitis, or as an intermediary factor is currently being investigated using a limited array of models, and future studies require both new reagent and model systems if we are to clearly define how leukocytes propagate this disease. The opportunities presented by this type of research could easily include new and powerful treatment and preventative modalities.