Multiple roles for MMPs and TIMPs in cerebral ischemia

Post-treatment with amphetamine enhances reinnervation of the ipsilateral side cortex in stroke rats

Amphetamine (AM) treatment has been shown to alter behavioral recovery after ischemia caused by embolism, permanent unilateral occlusion of the common carotid and middle cerebral arteries, or unilateral sensorimotor cortex ablation in rats. However, the behavioral results are inconsistent possibly due to difficulty controlling the size of the lesion before treatment. There is also evidence that AM promotes neuroregeneration in the cortex contralateral to the infarction; however, the effects of AM in the ipsilateral cortex remain unclear. The purpose of this study was to employ T2-weighted imaging (T2WI) to establish controlled criteria for AM treatment and to examine neuroregenerative effects in both cortices after stroke. Adult rats were anesthetized, and the right middle cerebral artery was ligated for 90 min to generate lesions in the ipsilateral cortex. Animals were separated into two equal treatment groups (AM or saline) according to the size of infarction, measured by T2WI at 2days after stroke. AM or saline was administered to stroke rats every third day starting on day 3 for 4weeks. AM treatment significantly reduced neurological deficits, as measured by body asymmetry and Bederson's score. T2WI and diffusion tensor imaging (DTI) were used to examine the size of infarction and axonal reinnervation, respectively, before and following treatment on days 2, 10 and 25 after stroke. AM treatment reduced the volume of tissue loss on days 10 and 25. A significant increase in fractional anisotropy ratio was found in the ipsilateral cortex after repeated AM administration, suggesting a possible increase in axonal outgrowth in the lesioned side cortex. Western analysis indicated that AM significantly increased the expression of synaptophysin ipsilaterally and neurofilament bilaterally. AM also enhanced matrix metalloproteinase (MMP) enzymatic activity, determined by MMP zymography in the lesioned side cortex. qRT-PCR was used to examine the expression of trophic factors after the 1st and 2nd doses of AM or saline injection. The expression of BDNF, but not BMP7 or CART, was significantly enhanced by AM in the lesioned side cortex. In conclusion, post-stroke treatment with AM facilitates behavioral recovery, which is associated with an increase in fractional anisotropy activity, enhanced fiber growth in tractography, synaptogenesis, upregulation of BDNF, and MMP activity mainly in the lesioned cortex. Our data suggest that the ipsilateral cortex may be the major target of action in stroke brain after AM treatment.

Inhibition of matrix metalloproteinases reduces ischemia-reperfusion acute kidney injury

Matrix metalloproteinases (MMPs) are endopeptidases that degrade extracellular matrix and involved in ischemic organ injuries. The present study was designed to determine the role of MMP-2 in the development of ischemic acute kidney injury (AKI). AKI was induced in MMP-2 wild-type (MMP-2(+/+)) mice by 30, 60, 90, and 120 min renal ischemia and reperfusion. Renal histology, expression and activity of MMP-2 and MMP-9, and renal function were examined during the development of AKI. AKI was also induced in MMP-2-deficient (MMP-2(-/-)) mice and MMP-2(+/+) mice treated with inhibitor of MMPs (minocycline and synthetic peptide MMP inhibitor). In MMP-2(+/+) mice, MMP-2 and MMP-9 activities increased significantly at 2 to 24 h, peaked at 6 h, after reperfusion. Immunohistochemical analysis identified MMP-2 in the interstitium around tubules and peritubular capillaries in the outer medulla. Acute tubular injury (ATI), including apoptosis and necrosis, was evident in the outer medulla at 24 h, along with renal dysfunction. As ischemia period increases, MMP-2 and MMP-9 activities at 6 h and severity of AKI at 24 h increased depending on the duration of ischemia between 30 and 120 min. However, the kidneys of MMP-2(-/-) mice showed minimal ATI; serum creatinine 24 h after reperfusion was significantly low in these mice. Inhibitors of MMPs reduced ATI and improved renal dysfunction at 24 h. We conclude that MMPs, especially MMP-2 have a pathogenic role in ischemia-reperfusion AKI, and that inhibitors of MMPs can protect against ischemic AKI.

Neuroprotective effect of neuroserpin in rat primary cortical cultures after oxygen and glucose deprivation and tPA

Besides its role as a thrombolytic agent, tissue plasminogen activator (tPA) triggers harmful effects in the brain parenchyma after stroke, such as inflammation, excitotoxicity and basal lamina degradation. Neuroserpin, a natural inhibitor of tPA, has shown neuroprotective effects in animal models of brain infarct. However, the molecular mechanisms of neuroserpin-mediated neuroprotection after brain ischemia remain to be well characterized. Then, our aim was to investigate such mechanisms in primary mixed cortical cell cultures after oxygen and glucose deprivation (OGD). Primary rat mixed cortical cultures containing both astrocytes and neurons were subjected to OGD for 150min and subsequently treated with either tPA (5μg/mL), neuroserpin (0.125, 0.25, 0.5 or 1μM), and tPA together with neuroserpin at the mentioned doses. Twenty-four hours after treatment, LDH release, caspase-3 activity, MCP-1, MIP-2, active MMP-9, GRO/KC and COX-2 were measured. Statistical differences were analyzed using Student's t-test or one-way ANOVA as appropriate. Treatment with tPA after OGD increased LDH release, active MMP-9, MCP-1 and MIP-2 (all p≤0.05), but not caspase-3, GRO/KC or COX-2 compared to control. Treatment with neuroserpin after OGD decreased LDH release and active MMP-9 (all p≤0.05). It had no effect on caspase-3 activity, or on MCP-1, MIP-2, GRO/KC or COX-2 expression compared to control. Administration of tPA together with neuroserpin decreased LDH release, active MMP-9 and MIP-2 (all p≤0.05) and showed no effect on MCP-1, GRO/KC or COX-2 compared to control. Our results suggest that neuroprotective activity of neuroserpin involves attenuation on tPA-mediated mechanisms of inflammation and BBB disruption after brain ischemia.

Association of tumor necrosis factor-α and matrix metalloproteinase-3 gene variants with stroke

BACKGROUND AND PURPOSE

  There is increasing evidence that the genetic variation in the genes coding for pro-inflammatory markers and matrix metalloproteinase may play an important role in the pathogenesis of various human diseases including stroke. The aim of this study was to evaluate the association of genetic variants within the genes encoding tumor necrosis factor-α (TNF-α) and matrix metalloproteinase-3 (MMP-3), with stroke.

METHODS

  Five hundred and twenty-five ischemic stroke patients and 500 age- and sex-matched controls were included in this study. We analyzed +488 G/A polymorphism in TNF-α gene and -1612 5A/6A polymorphism in MMP-3 gene. The genotypes were determined by Amplification Refractory Mutation System PCR. The strength of association between genotypes and stroke was measured by the odds ratio with 95% confidence interval (CI) and chi-squared analysis.

RESULTS

  Allelic and genotypic frequencies of TNF-α G/A polymorphism differed significantly between patients and healthy controls (P < 0.001). A stepwise logistic regression analysis confirmed these findings (P < 0.001). Further, evaluating the association of this polymorphism with stroke subtypes, we found significant association with intracranial large artery atherosclerosis, extracranial large artery atherosclerosis, and stroke of undetermined etiology. As far as MMP-3-1612 5A/6A polymorphism is concerned, there was no significant difference in genotypic distribution and allelic frequency between the patients and healthy controls (P = 0.5 and 0.9, respectively). We tested the gene-gene interaction between TNF-α and MMP-3 genes using the logistic regression model. However, there was no evidence for a gene-gene interaction between TNF-α and MMP-3.

CONCLUSION

  TNF-α +488 G/A variant is an important risk factor for ischemic stroke in the South Indians from Andhra Pradesh, whereas MMP-3-1612 5A/6A polymorphism is not associated with stroke in the same population.

Mechanisms of early brain injury after SAH: matrix metalloproteinase 9

Subarachnoid hemorrhage (SAH) is an important cause of death and disability worldwide. To date, there is not a definitive treatment that completely prevents brain injury after SAH. Recently, early brain injury (EBI) has been pointed out to be the primary cause of mortality in SAH patients. Apoptosis that occurs in neuronal tissues and cerebral vasculature after SAH plays an essential role in EBI. Matrix metalloproteinase 9 (MMP-9) has been found to increase in many cerebral vascular diseases. There have been reports that MMP-9 can mediate apoptosis, which called anoikis in cerebral ischemia models, through cleaving main components of the extracellular matrix (ECM), especially laminin. Therefore, minocycline, which has been found to inhibit MMP-9, may be protective to brain injury after SAH. We based our hypothesis on the fact that SAH possesses some aspects that are similar to those of cerebral ischemia. It is conceivable that MMP-9 may also be involved in the pathological process of EBI after SAH, and minocycline can relieve anoikis and improve EBI after SAH.

Blockade of the MEK/ERK pathway with a raf inhibitor prevents activation of pro-inflammatory mediators in cerebral arteries and reduction in cerebral blood flow after subarachnoid hemorrhage in a rat model

Cerebral ischemia that develops after subarachnoid hemorrhage (SAH) carries high morbidity and mortality. Inflammatory mediators are involved in the development of cerebral ischemia through activation of the mitogen-activated protein kinase pathway. We hypothesized that blockade of the MAPkinase/ERK (MEK)/extracellular signal-regulated kinase (ERK) pathway upstream with a specific raf inhibitor would prevent SAH-induced activation of the cerebrovascular inflammatory response. The raf inhibitor SB-386023-b was injected intracisternally in our rat model at 0, 6, or 12 hours after the SAH. After 48 hours, cerebral arteries were harvested, and iNOS, interleukin (IL)-6, IL-1β, matrix metalloproteinase (MMP)-9, tissue inhibitors of metalloproteinase (TIMP)-1, and phosphorylated ERK1/2 were investigated by immunofluorescence, real-time polymerase chain reaction (PCR), and Western blot analysis. Cerebral blood flow (CBF) was measured using autoradiography. Protein levels of MMP-9, TIMP-1, iNOS, IL-6, and IL-1β were increased after SAH, as were mRNA levels of IL-6, MMP-9, and TIMP-1. After SAH, pERK1/2 was increased, but CBF was reduced. Treatment with SB-386023-b at 0 or 6 hours after SAH normalized CBF and prevented SAH-induced upregulation of MMPs, pro-inflammatory cytokines, and pERK1/2 proteins. These results suggested that inhibition of MEK/ERK signal transduction by a specific raf inhibitor administered up to 6 hours after SAH normalized the expression of pro-inflammatory mediators and extracellular matrix-related genes.

Multiple roles of metalloproteinases in neurological disorders

Once thought to mainly act in brain to remodel the extracellular matrix, the family of metalloproteinases is important in many normal and pathological processes in the nervous system. Matrix metalloproteinases (MMPs) and A disintegrin and metalloproteinases (ADAMs) are the two major families of metalloproteinases in the brain. MMPs are comprised of several related enzymes that act on extracellular molecules. Normally, they are important in angiogenesis and neurogenesis in development. In neuroinflammatory illnesses, they disrupt the basal lamina and tight junction proteins to open the blood-brain barrier (BBB). ADAMs are important in neuroinflammation through activation of tumor necrosis factor-α (TNF-α) and their action as secretases that modulate the action of receptors on the cell surface. Four tissue inhibitors of metalloproteinases (TIMPs) are the main inhibitors of the MMPs and ADAMs. Recently, MMPs were found to affect DNA repair processes by an unexpected intranuclear action. MMPs and ADAMs have been implicated in the pathophysiology of neurodegenerative diseases such as Alzheimer's disease and vascular cognitive impairment. Growing literature on the functions of MMPs and ADAMs in the central nervous system is opening up new and exciting areas of research that may lead to novel approaches to treatment of neurological diseases.

Valproic acid attenuates blood-brain barrier disruption in a rat model of transient focal cerebral ischemia: the roles of HDAC and MMP-9 inhibition

Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, is known to protect against cerebral ischemia. The effects of VPA on blood-brain barrier (BBB) disruption were investigated in rats subjected to transient middle cerebral artery occlusion (MCAO). Postischemic VPA treatment remarkably attenuated MCAO-induced BBB disruption and brain edema. Meanwhile, VPA significantly reduced MCAO-induced elevation of matrix metalloproteinase-9 (MMP-9), degradation of tight junction proteins, and nuclear translocation of nuclear factor-κB (NF-κB). Sodium butyrate, another HDAC inhibitor, mimicked these effects of VPA. Our findings suggest that BBB protection by VPA involves HDAC inhibition-mediated suppression of NF-κB activation, MMP-9 induction, and tight junction degradation.

Morphology and properties of brain endothelial cells

The molecular advances in various aspects of brain endothelial cell function in steady states are considerable and difficult to summarize in one chapter. Therefore, this chapter focuses on endothelial permeability mechanisms in steady states and disease namely vasogenic edema. The morphology and properties of caveolae and tight junctions that are involved in endothelial permeability to macromolecules are reviewed. Endothelial transport functions are briefly reviewed. Diseases with alterations of endothelial permeability are mentioned and details are provided of the molecular alterations in caveolae and tight junctions in vasogenic edema. Other factors involved in increased endothelial permeability such as the matrix metalloproteinases are briefly discussed. Of the modulators of endothelial permeability, angioneurins such as the vascular endothelial growth factors and angiopoietins are discussed. The chapter concludes with a brief discussion on delivery of therapeutic substances across endothelium.

Vasopressin amplifies the production of proinflammatory mediators in traumatic brain injury

Arginine vasopressin (AVP) has previously been shown to promote disruption of the blood-brain barrier, exacerbate edema, and augment the loss of neural tissue in various forms and models of brain injury. However, the mechanisms underlying these AVP actions are not well understood. These mechanisms were studied in AVP-deficient Brattleboro rats (Avp(di/di)), and their parental Long-Evans strain, using a controlled cortical impact model of traumatic brain injury (TBI). The increased influx of inflammatory cells into the injured cortex in wild-type versus Avp(di/di) rats was associated with higher levels of cortical synthesis of the CXC and CC chemokines found in wild-type versus Avp(di/di) rats. These chemokines were predominantly produced by the cerebrovascular endothelium and astrocytes. In astrocyte and brain endothelial cell cultures, AVP acted synergistically with tumor necrosis factor-alpha (TNF-alpha) to increase the TNF-alpha-dependent production of CXC and CC chemokines. These AVP actions were mediated by c-Jun N-terminal kinase (JNK), as shown by Western blotting and pharmacological inhibition of JNK activity. The activity of JNK was increased in response to injury, and the differences in the magnitude of its post-traumatic activation between Avp(di/di) and wild-type rats were observed. These data demonstrate that AVP plays an important role in exacerbating the brain inflammatory response to injury.

Peroxynitrite decomposition catalyst prevents matrix metalloproteinase activation and neurovascular injury after prolonged cerebral ischemia in rats

Matrix metalloproteinases (MMPs) play an important role in reperfusion-induced brain injury following ischemia. To define the effects of peroxynitrite decomposition catalyst on MMP activation and neurovascular reperfusion injury, 5,10,15,20-tetrakis (2,4,6-trimethyl-3,5-disulfonatophenyl)-porphyrin iron (III) (FeTMPyP) was administered intravenously 30 min prior to reperfusion following a middle cerebral artery occlusion. Activation of MMP was assessed by in situ and gel zymography. Neurovascular injury was assessed using endothelial barrier antigen, collagen IV immunohistochemistry and Cresyl violet staining. Results were compared with sham and ischemia alone groups. We found that administration of FeTMPyP just before reperfusion after ischemia inhibited MMP-9 activation and total MMP-2 increases in the cortex and decreased active MMP-9 along with the total amounts of active MMP-9 and active MMP-2 in the striatum. Reperfusion-induced injury to the basal lamina of collagen IV-immunopositive microvasculature and neural cells in cortex and striatum was ameliorated by FeTMPyP. Losses of blood vessel endothelium produced by ischemia or reperfusion were also decreased in the cortex. These results suggest that administration of FeTMPy prior to reperfusion decreases MMP activation and neurovascular injury after prolonged cerebral ischemia. This strategy may be useful for future therapies targeted at preventing breakdown of the blood-brain barrier and hemorrhagic transformation.

P2X7 receptor regulates leukocyte infiltrations in rat frontoparietal cortex following status epilepticus

BACKGROUND

In the present study, we investigated the roles of P2X7 receptor in recruitment and infiltration of neutrophil during epileptogenesis in rat epilepsy models.

METHODS

Status epilepticus (SE) was induced by pilocarpine in rats that were intracerebroventricularly infused with either saline, 2',3'-O-(4-benzoylbenzoyl)-adenosine 5'-triphosphate (BzATP), adenosine 5'-triphosphate-2',3'-dialdehyde (OxATP), or IL-1Ra (interleukin 1 receptor antagonist) prior to SE induction. Thereafter, we performed immunohistochemical studies for myeloperoxidase (MPO), CD68, interleukin-1β (IL-1β), monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2).

RESULTS

In saline-infused animals, neutrophils and monocytes were observed in frontoparietal cortex (FPC) at 1 day and 2 days after SE, respectively. In BzATP-infused animals, infiltrations of neutrophils and monocytes into the FPC were detected at 12 hr and 1 day after SE, respectively. In OxATP-infused animals, neutrophils and monocytes infiltrated into the FPC at 1 day and 2 days after SE, respectively. However, the numbers of both classes of leukocytes were significantly lower than those observed in the saline-infused group. In piriform cortex (PC), massive leukocyte infiltration was detected in layers III/IV of saline-infused animals at 1-4 days after induction of SE. BzATP or OxATP infusion did not affect neutrophil infiltration in the PC. In addition, P2X7 receptor-mediated MCP-1 (released from microglia)/MIP-2 (released from astrocytes) regulation was related to SE-induced leukocyte infiltration in an IL-1β-independent manner.

CONCLUSIONS

Our findings suggest that selective regulation of P2X7 receptor-mediated neutrophil infiltration may provide new therapeutic approaches to SE or epilepsy.

Targeting astrocytes for stroke therapy

Stroke remains a major health problem and is a leading cause of death and disability. Past research and neurotherapeutic clinical trials have targeted the molecular mechanisms of neuronal cell death during stroke, but this approach has uniformly failed to reduce stroke-induced damage or to improve functional recovery. Beyond the intrinsic molecular mechanisms inducing neuronal death during ischemia, survival and function of astrocytes is absolutely required for neuronal survival and for functional recovery after stroke. Many functions of astrocytes likely improve neuronal viability during stroke. For example, uptake of glutamate and release of neurotrophins enhances neuronal viability during ischemia. Under certain conditions, however, astrocyte function may compromise neuronal viability. For example, astrocytes may produce inflammatory cytokines or toxic mediators, or may release glutamate. The only clinical neurotherapeutic trial for stroke that specifically targeted astrocyte function focused on reducing release of S-100β from astrocytes, which becomes a neurotoxin when present at high levels. Recent work also suggests that astrocytes, beyond their influence on cell survival, also contribute to angiogenesis, neuronal plasticity, and functional recovery in the several days to weeks after stroke. If these delayed functions of astrocytes could be targeted for enhancing stroke recovery, it could contribute importantly to improving stroke recovery. This review focuses on both the positive and the negative influences of astrocytes during stroke, especially as they may be targeted for translation to human trials.

A novel quantification of blood-brain barrier damage and histochemical typing after embolic stroke in rats

Treatment strategies in acute ischemic stroke are still limited. Considering numerous translation failures, research is tending to a preferred use of human-like animal models, and a more-complex perspective of tissue salvaging involving endothelial, glial and neuronal components according to the neurovascular unit (NVU) concept. During ischemia, blood-brain barrier (BBB) alterations lead to brain edema and hemorrhagic transformation affecting NVU components. The present study aims on a novel quantification method of BBB damage and affected tissue following experimental cerebral ischemia, closely to the human condition. Wistar rats underwent embolic middle cerebral artery occlusion, followed by an intravenous application of fluorescein isothiocyanate (FITC)-tagged albumin (≈70kDa) and/or biotinylated rat IgG (≈150kDa) as BBB permeability markers. Both fluorescent agents revealed similar leakage and allow quantification of BBB permeability by fluorescence microscopy, and after immunohistochemical conversion into a permanent diaminobenzidine label at light-microscopical level. The following markers were identified for sufficient detection of NVU components: Rat endothelial cell antigen-1 (RECA) and laminin for vessels, Lycopersicon esculentum and Griffonia simplicifolia agglutinin for vessels and microglial subpopulations, ionized calcium binding adaptor molecule 1 (Iba1), CD68 and CD11b for macrophages, activated microglia, monocytes and neutrophils, S100β for astroglia, as well as NeuN and HuC/D for neurons. This is the first report confirming the usefulness of simultaneously applied FITC-albumin and biotinylated rat IgG as BBB permeability markers in experimental stroke, and, specifying antibodies and lectins for multiple fluorescence labeling of NVU components. Newly elaborated protocols might facilitate a more-complex outcome measurement in drug development for cerebral ischemia.

Preclinical and clinical research on inflammation after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is one of the most lethal stroke subtypes. Despite the high morbidity and mortality associated with ICH, its pathophysiology has not been investigated as well as that of ischemic stroke. Available evidence from preclinical and clinical studies suggests that inflammatory mechanisms are involved in the progression of ICH-induced secondary brain injury. For example, in preclinical ICH models, microglial activation has been shown to occur within 1h, much earlier than neutrophil infiltration. Recent advances in our understanding of neuroinflammatory pathways have revealed several new molecular targets, and related therapeutic strategies have been tested in preclinical ICH models. This review summarizes recent progress made in preclinical models of ICH, surveys preclinical and clinical studies of inflammatory cells (leukocytes, macrophages, microglia, and astrocytes) and inflammatory mediators (matrix metalloproteinases, nuclear factor erythroid 2-related factor 2, heme oxygenase, and iron), and highlights the emerging areas of therapeutic promise.

The effect of umbilical cord blood cells on outcomes after experimental traumatic spinal cord injury

STUDY DESIGN

A cytokine expression profile of umbilical cord blood (UCB) derived multipotential stem cells (MPSC) was produced. We then transplanted MPSCs into a rat model of spinal cord injury (SCI) and assessed neurologic function as well as spinal cord histology.

OBJECTIVE

To determine if MPSCs transplanted into a rat model of acute SCI would lead to a beneficial neurologic effect.

SUMMARY OF BACKGROUND DATA

Conditioned medium from UCB contains factors that could promote healing of endogenous neural tissues. Previously, our laboratory has demonstrated that UCB hematopoietic cells can develop into MPSCs capable of differentiating into multiple cell types including oligodendrocyte-like cells.

METHODS

We cultured MPSCs from UCB cells using fibroblast growth factor 4, stem cell factor and fms-like tyrosine kinase receptor-3 ligand supplemented serum-free medium. Using a cytokine antibody array, we produced a cytokines expression profile of MPSCs. We then transplanted MPSCs into an immunosuppressed rat model of SCI and assessed neurologic function weekly for 6 weeks by the Basso, Beattie, and Bresnahan locomotor test. The spinal cords were examined histologically and lesion areas quantified.

RESULTS

We detected elevated levels of cytokines and growth factors with known neuroprotective, angiogenic, and anti-inflammatory effects in the MPSC conditioned media. The SCI rats treated with MPSCs showed a significant improvement in Basso, Beattie, and Bresnahan scores after 6 weeks compared with the group that received vehicle only. Immunohistochemistry revealed transplanted human cells were present in the injured spinal cord after 1 week, but were no longer present by 6 weeks. There was a trend for the lesion size in treated rats to be smaller than that of the control group.

CONCLUSION

We conclude that UCB MPSCs improve neurologic function of rats with acute SCI, possibly by the release of factors that reduce secondary injury.

The comparison of mouse full metallothionein-1 versus alpha and beta domains and metallothionein-1-to-3 mutation following traumatic brain injury reveals different biological motifs

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, but current therapies are limited. Previously it has been shown that the antioxidant proteins metallothioneins (MTs) are potent neuroprotective factors in animal models of brain injury. The exogenous administration of MTs causes effects consistent with the roles proposed from studies in knock-out mice. We herewith report the results comparing full mouse MT-1 with the independent alpha and beta domains, alone or together, in a cryoinjury model. The lesion of the cortex caused the mice to perform worse in the horizontal ladder beam and the rota-rod tests; all the proteins showed a modest effect in the former test, while only full MT-1 improved the performance of animals in the rota-rod, and the alpha domain showed a rather detrimental effect. Gene expression analysis by RNA protection assay demonstrated that all proteins may alter the expression of host-response genes such as GFAP, Mac1 and ICAM, in some cases being the beta domain more effective than the alpha domain or even the full MT-1. A MT-1-to-MT-3 mutation blunted some but not all the effects caused by the normal MT-1, and in some cases increased its potency. Thus, splitting the two MT-1 domains do not seem to eliminate all MT functions but certainly modifies them, and different motifs seem to be present in the protein underlying such functions.

Looking at the blood-brain barrier: molecular anatomy and possible investigation approaches

The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.

Matrix metalloproteinases cleave the beta2-adrenergic receptor in spontaneously hypertensive rats

We recently observed the enhanced serine and matrix metalloproteinase (MMP) activity in the spontaneously hypertensive rat (SHR) compared with its normotensive Wistar-Kyoto (WKY) rat and the cleavage of membrane receptors in the SHR by MMPs. We demonstrate in vivo that MMP-7 and MMP-9 injection leads to a vasoconstrictor response in microvessels of rats that is blocked by a specific MMP inhibitor (GM-6001, 1 microM). Multiple pathways may be responsible. Since the beta(2)-adrenergic receptor (beta(2)-AR) is susceptible to the action of endogenous MMPs, we hypothesize that MMPs in the plasma of SHRs are able to cleave the extracellular domain of the beta(2)-AR. SHR arterioles respond in an attenuated fashion to beta(2)-AR agonists and antagonists. Aorta and heart muscle of control Wistar rats were exposed for 24 h (37 degrees C) to fresh plasma of male Wistar and WKY rats and SHRs with and without doxycycline (30 microM) and EDTA (10 mM) to reduce MMP activity. The density of extracellular and intracellular domains of beta(2)-AR was determined by immunohistochemistry. The density of the extracellular domain of beta(2)-AR is reduced in aortic endothelial cells and cardiac microvessels of SHRs compared with that of WKY or Wistar rats. Treatment of the aorta and the heart of control Wistar rats with plasma from SHRs, but not from WKY rats, reduced the number of extracellular domains, but not intracellular domains, of beta(2)-AR in aortic endothelial cells and cardiac microvessels. MMP inhibitors (EDTA and doxycycline) prevented the cleavage of the extracellular domain. Thus MMPs may contribute to the reduced density of the extracellular domain of beta(2)-AR in blood vessels and to the increased arteriolar tone of SHRs compared with normotensive rats.

Matrix metalloproteinase-9 mediates hypoxia-induced vascular leakage in the brain via tight junction rearrangement

Blood-brain barrier (BBB) disruption, resulting from loss of tight junctions (TJ) and activation of matrix metalloproteinases (MMPs), is associated with edema formation in ischemic stroke. Cerebral edema develops in a phasic manner and consists of both vasogenic and cytotoxic components. Although it is contingent on several independent mechanisms, involving hypoxic and inflammatory responses, the single effect of prolonged hypoxia on BBB integrity in vivo was not addressed so far. Exposing mice to normobaric hypoxia (8% oxygen for 48 h) led to a significant increase in vascular permeability associated with diminished expression of the TJ protein occludin. Immunofluorescence studies revealed that hypoxia resulted in disrupted continuity of occludin and zonula occludens-1 (Zo-1) staining with significant gap formation. Hypoxia increased gelatinolytic activity specifically in vascular structures and gel zymography identified MMP-9 as enzymatic source. Treatment with an MMP inhibitor reduced vascular leakage and attenuated disorganization of TJ. Inhibition of vascular endothelial growth factor (VEGF) attenuated vascular leakage and MMP-9 activation induced by hypoxia. In conclusion, our data suggest that hypoxia-induced edema formation is mediated by MMP-9-dependent TJ rearrangement by a mechanism involving VEGF. Therefore, inhibition of MMP-9 might provide the basis for therapeutic strategies to treat brain edema.

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.

Cellular and molecular regulation of spiral artery remodelling: lessons from the cardiovascular field

A number of important changes take place in the maternal uterine vasculature during the first few weeks of pregnancy resulting in increased blood flow to the intervillous space. Vascular endothelial and smooth muscle cells are lost from the spiral arteries and are replaced by fetal trophoblast cells. Failure of the vessels to remodel sufficiently is a common feature of pregnancy pathologies such as early pregnancy loss, intrauterine growth restriction and pre-eclampsia. There is evidence to suggest that some vascular changes occur prior to trophoblast invasion, however, in the absence of trophoblasts remodelling of the spiral arteries is reduced. Until recently our knowledge of these events has been obtained from immunohistochemical studies which, although extremely useful, can give little insight into the mechanisms involved. With the development of more complex in vitro models a picture of events at a cellular and molecular level is beginning to emerge, although some caution is required in extrapolating to the in vivo situation. Trophoblasts synthesise and release a plethora of cytokines and growth factors including members of the tumour necrosis factor family. Studies suggest that these factors may be important in regulating the remodelling process by inducing both endothelial and vascular smooth muscle cell apoptosis. In addition, it is evident from studies in other vascular beds that the structure of the vessel is influenced by factors such as flow, changes in the composition of the extracellular matrix, the phenotype of the vascular cells and the local immune cell environment. It is the aim of this review to present our current knowledge of the mechanisms involved in spiral artery remodelling and explore other possible pathways and cellular interactions that may be involved, informed by studies in the cardiovascular field.

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.

The Janus-faced effects of hypoxia on astrocyte function

Astrocytes are increasingly recognized for their impact on neuronal function and viability in health and disease. Hypoxia has Janus-faced influences on astrocytes and their ability to support neuronal viability. For example, hypoxia induces astrocyte-dependent protection of neurons following hypoxia preconditioning. Yet, hypoxia induces processes in astrocytes that augment neuronal death in other situations, such as the coincidence of hypoxia with inflammatory signaling. A complex array of gene expression is induced by hypoxia within astrocytes and neurons through multiple transcription factors and intracellular molecular pathways. The hypoxia inducible factors (HIFs) are transcription factors that are likely instrumental in orchestrating adaptive and pathological functions of astrocytes. As such, the HIFs are postulated to mediate both adaptive and pathological functions during hypoxia/ ischemia. Identifying the conditions under which hypoxia induces signaling in astrocytes that alters autonomous or neuronal survival will undoubtedly have important implications regarding the development of new strategies for stroke treatment.

Accumulation of macromolecules in brain parenchyma in acute phase of cerebral infarction/reperfusion

Ischemia-reperfusion injury is induced by recovery of blood flow after ischemia. This phenomenon is a main cause of ischemic brain injury. The integrity of the blood-brain barrier (BBB) fails after cerebral ischemia and reperfusion. Further elucidation of this phenomenon promotes to develop treatment strategies for ischemia-reperfusion injury. In the present study, we attempted to examine the time-dependent change of ischemia-reperfusion injury in relation to BBB disorders at acute phase in a transient middle cerebral artery occlusion (t-MCAO) model rat as a cerebral infarction and reperfusion model. Brain cell damage after the reperfusion was assessed by 2, 3, 5-triphenyltetrazolium chloride (TTC) staining. To clarify a time-dependent change of the integrity of BBB, fluorescein isothiocyanate (FITC)-dextran (150 kDa) was injected intravenously into t-MCAO rats, and time-dependent localization of FITC-dextran was monitored in ex vivo. As a result, obvious brain damage was firstly observed at 3 h after reperfusion following 1 h of MCAO. In contrast, the leakage of FITC-dextran from cerebral vessels was observed immediately after the reperfusion. The present data suggest that the integrity of BBB failed prior to the occurrence of serious brain damage induced by ischemia-reperfusion, and that macromolecules such as water-soluble polymers and proteins which cannot pass through the BBB under normal condition would reach brain parenchyma at early stage after reperfusion. These findings would be useful to establish a novel treatment strategy for reperfusion injury after cerebral infarction.

Spontaneous intracerebral hemorrhage during acute and chronic hypertension in mice

Oxidative stress and matrix metalloproteinases (MMPs) contribute to hemorrhagic transformation after ischemic stroke and brain injury after intracerebral hemorrhage (ICH). The goal of this study was to develop a new model of spontaneous ICH, based on the hypothesis that acute, superimposed on chronic, hypertension produces ICH. We hypothesized that increases in angiotensin II (AngII)-mediated oxidative stress and activation of MMPs are associated with, and may precede, spontaneous ICH during hypertension. In C57BL/6 mice, chronic hypertension was produced with AngII infusion and an inhibitor of nitric oxide synthase. During chronic hypertension, mice with acute hypertension from injections of AngII developed ICH. Oxidative stress and MMP levels increased in the brain even before developing ICH. Active MMPs colocalized with a marker of oxidative stress, especially on cerebral vessels that appeared to lead toward regions with ICH. Incidence of ICH and levels of oxidative stress and MMP-9 were greater in mice with acute hypertension produced by AngII than by norepinephrine. In summary, we have developed an experimental model of ICH during hypertension that may facilitate studies in genetically altered mice. We speculate that acute hypertension, especially when induced by AngII, may be critical in spontaneous ICH during chronic hypertension, possibly through oxidative stress and MMP-9.

Role of matrix metalloproteinase-9 in apoptosis of hippocampal neurons in rats during early brain injury after subarachnoid hemorrhage

This study investigated the possible involvement of matrix metalloproteinase 9 (MMP-9) in early brain injury (EBI) of subarachnoid hemorrhage (SAH) in rats. MMP-9 activities in hippocampus were examined at 6, 12, 24, 48 and 72 h after SAH. Laminin was detected by immunohistochemistry. Apoptosis of neurons in hippocampus was observed by TUNEL. Brain water content was also examined. MMP-9 activity and the number of apoptotic neurons increased from 12 to 72 h with a peak at 24 h. Laminin was found to decrease at 12 h, reached minimum at 24 h and began to increase from 48 h, which had a negative correlation with apoptotic neurons. The changes of brain water content were found to be coincidence with that of neuronal apoptosis. Our findings suggest that MMP-9 is probably involved in the pathophysiological events of EBI after SAH, through degrading laminin which leads to neuronal anoikis of hippocampus.

Reversal of West Nile virus-induced blood-brain barrier disruption and tight junction proteins degradation by matrix metalloproteinases inhibitor

Though compromised blood-brain barrier (BBB) is a pathological hallmark of WNV-associated neurological sequelae, underlying mechanisms are unclear. We characterized the expression of matrix metalloproteinases (MMP) in WNV-infected human brain microvascular endothelial cells (HBMVE) and human brain cortical astrocytes (HBCA), components of BBB and their role in BBB disruption. Expression of multiple MMPs was significantly induced in WNV-infected HBCA cells. Naïve HBMVE cells incubated with the supernatant from WNV-infected HBCA cells demonstrated loss of tight junction proteins, which were rescued in the presence of MMP inhibitor, GM6001. Further, supernatant from WNV-infected HBCA cells compromised the in vitro BBB model integrity. Our data suggest astrocytes as one of the sources of MMP in the brain, which mediates BBB disruption allowing unrestricted entry of immune cells into the brain, thereby contributing to WNV neuropathogenesis. Because of the unavailability of WNV antivirals and vaccines, use of MMP inhibitors as an adjunct therapy to ameliorate WNV disease progression is warranted.

Targeting eNOS and beyond: emerging heterogeneity of the role of endothelial Rho proteins in stroke protection

Currently available modalities for the treatment of acute ischemic stroke are aimed at preserving or augmenting cerebral blood flow. Experimental evidence suggests that statins, which show 25-30% reduction of stroke incidence in clinical trials, confer stroke protection by upregulation of eNOS and increasing cerebral blood flow. The upregulation of eNOS by statins is mediated by inhibition of small GTP-binding protein RhoA. Our recent study uncovered a unique role for a Rho-family member Rac1 in stroke protection. Rac1 in endothelium does not affect cerebral blood flow. Instead, inhibition of endothelial Rac1 leads to broad upregulation of the genes relevant to neurovascular protection. Intriguingly, inhibition of endothelial Rac1 enhances neuronal cell survival through endothelium-derived neurotrophic factors, including artemin. This review discusses the emerging therapeutic opportunities to target neurovascular signaling beyond the BBB, with special emphasis on the novel role of endothelial Rac1 in stroke protection.

Increased intranuclear matrix metalloproteinase activity in neurons interferes with oxidative DNA repair in focal cerebral ischemia

Increased matrix metalloproteinase (MMP) activity is implicated in proteolysis of extracellular matrix in ischemic stroke. We recently observed intranuclear MMP activity in ischemic brain neurons at early reperfusion, suggesting a possible role in nuclear matrix proteolysis. Nuclear proteins, poly-ADP-ribose polymerase-1 (PARP-1) and X-ray cross-complementary factor 1 (XRCC1), as well as DNA repair enzymes, are important in DNA fragmentation and cell apoptosis. We hypothesized that intranuclear MMP activity facilitates oxidative injury in neurons during early ischemic insult by cleaving PARP-1 and XRCC1, interfering with DNA repair. We induced a 90-min middle cerebral artery occlusion in rats. Increase activity of MMP-2 and -9, detected in the ischemic neuronal nuclei at 3 h, was associated with DNA fragmentation at 24 and 48 h reperfusion. The intranuclear MMPs cleaved PARP-1. Treatment of the rats with a broad-spectrum MMP inhibitor, BB1101, significantly attenuated ischemia-induced PARP-1 cleavage, increasing its activity. Degradation of XRCC1 caused by ischemic insult in rat brain was also significantly attenuated by BB1101. We found elevation of oxidized DNA, apurinic/apyrimidinic sites, and 8-hydroxy-2'-deoxyguanosine, in ischemic brain cells at 3 h reperfusion. BB1101 markedly attenuated the early increase of oxidized DNA. Using tissue from stroke patients, we found increased intranuclear MMP expression. Our data suggest that intranuclear MMP activity cleaves PARP-1 and XRCC1, interfering with oxidative DNA repair. This novel role for MMPs could contribute to neuronal apoptosis in ischemic injuries.

Rosiglitazone alone or in combination with tissue plasminogen activator improves ischemic brain injury in an embolic model in rats

In this study, we examined whether rosiglitazone, a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, is neuroprotective in focal ischemic brain injury, and whether rosiglitazone can enhance the protective action of tissue plasminogen activator (tPA), an agent used clinically for thrombolytic therapy. Rats were subjected to ischemic brain injury by embolizing preformed clots into the middle cerebral artery (MCA). Treatment with rosiglitazone reduced infarction and improved functional recovery; it also enhanced the neuroprotective action of tPA and lengthened the time window for initiating tPA treatment. Occlusion of MCA resulted in a loss of collagen type IV, a major structural protein of the microvascular basal lamina, and tPA treatment worsened this loss. Rosiglitazone treatment prevented the reduction of collagen type IV in the ischemic injured brain by inhibiting the activation of matrix metallopeptidase-9 (MMP-9). In addition, rosiglitazone treatment reduced inflammatory reactions in the ischemic injured brain. Rosiglitazone either alone or in combination with tPA is an effective agent in the reduction of ischemic brain injury. The reduction of microvascular damage and inflammation contributes to the beneficial actions of rosiglitazone.

Transcriptional activation of endothelial cells by TGFβ coincides with acute microvascular plasticity following focal spinal cord ischaemia/reperfusion injury

Microvascular dysfunction, loss of vascular support, ischaemia and sub-acute vascular instability in surviving blood vessels contribute to secondary injury following SCI (spinal cord injury). Neither the precise temporal profile of the cellular dynamics of spinal microvasculature nor the potential molecular effectors regulating this plasticity are well understood. TGFβ (transforming growth factor β) isoforms have been shown to be rapidly increased in response to SCI and CNS (central nervous system) ischaemia, but no data exist regarding their contribution to microvascular dysfunction following SCI. To examine these issues, in the present study we used a model of focal spinal cord ischaemia/reperfusion SCI to examine the cellular response(s) of affected microvessels from 30 min to 14 days post-ischaemia. Spinal endothelial cells were isolated from affected tissue and subjected to focused microarray analysis of TGFβ-responsive/related mRNAs 6 and 24 h post-SCI. Immunohistochemical analyses of histopathology show neuronal disruption/loss and astroglial regression from spinal microvessels by 3 h post-ischaemia, with complete dissolution of functional endfeet (loss of aquaporin-4) by 12 h post-ischaemia. Coincident with this microvascular plasticity, results from microarray analyses show 9 out of 22 TGFβ-responsive mRNAs significantly up-regulated by 6 h post-ischaemia. Of these, serpine 1/PAI-1 (plasminogen-activator inhibitor 1) demonstrated the greatest increase (>40-fold). Furthermore, uPA (urokinase-type plasminogen activator), another member of the PAS (plasminogen activator system), was also significantly increased (>7.5-fold). These results, along with other select up-regulated mRNAs, were confirmed biochemically or immunohistochemically. Taken together, these results implicate TGFβ as a potential molecular effector of the anatomical and functional plasticity of microvessels following SCI.

Does inflammation after stroke affect the developing brain differently than adult brain?

The immature brain is prone to hypoxic-ischemic encephalopathy and stroke. The incidence of arterial stroke in newborns is similar to that in the elderly. However, the pathogenesis of ischemic brain injury is profoundly affected by age at the time of the insult. Necrosis is a dominant type of neuronal cell death in adult brain, whereas widespread neuronal apoptosis is unique for the early postnatal synaptogenesis period. The inflammatory response, in conjunction with excitotoxic and oxidative responses, is the major contributor to ischemic injury in both the immature and adult brain, but there are several areas where these responses diverge. We discuss the contribution of various inflammatory mechanisms to injury and repair after cerebral ischemia in the context of CNS immaturity. In particular, we discuss the role of lower expression of selectins, a more limited leukocyte transmigration, undeveloped complement pathways, a more rapid microglial activation, differences in cytokine and chemokine interplay, and a different threshold to oxidative stress in the immature brain. We also discuss differences in activation of intracellular pathways, especially nuclear factor kappaB and mitogen-activated protein kinases. Finally, we discuss emerging data on both the supportive and adverse roles of inflammation in plasticity and repair after stroke.

Pathology and new players in the pathogenesis of brain edema

Brain edema continues to be a major cause of mortality after diverse types of brain pathologies such as major cerebral infarcts, hemorrhages, trauma, infections and tumors. The classification of edema into vasogenic, cytotoxic, hydrocephalic and osmotic has stood the test of time although it is recognized that in most clinical situations there is a combination of different types of edema during the course of the disease. Basic information about the types of edema is provided for better understanding of the expression pattern of some of the newer molecules implicated in the pathogenesis of brain edema. These molecules include the aquaporins, matrix metalloproteinases and growth factors such as vascular endothelial growth factors A and B and the angiopoietins. The potential of these agents in the treatment of edema is discussed. Since many molecules are involved in the pathogenesis of brain edema, effective treatment cannot be achieved by a single agent but will require the administration of a "magic bullet" containing a variety of agents released at different times during the course of edema in order to be successful.

Brain angiogenesis in developmental and pathological processes: neurovascular injury and angiogenic recovery after stroke

Pathophysiologic responses in brain after stroke are highly complex. Thus far, a singular focus on saving neurons alone has not revealed any clinically effective neuroprotectants. To address this limitation, the concept of a neurovascular unit was developed. Within this conceptual framework, brain function and dysfunction are manifested at the level of cell-cell signaling between neuronal, glial and vascular elements. For stroke, coordinated responses at the neurovascular interface will mediate acute as well as chronic events in ischemic and hemorrhagic brain tissue. In this minireview, we briefly survey two representative examples of neurovascular responses in stroke. During the early acute phase of neurovascular injury, blood-brain barrier perturbations should predominate with key roles for various matrix proteases. During the delayed phase, brain angiogenesis may provide the critical neurovascular substrates for neuronal remodeling. In this minireview, we propose the hypothesis that the biphasic nature of neurovascular responses represents an endogenous attempt by damaged parenchyma to trigger brain angiogenesis and repair. This phenomenon may allow acute deleterious signals to transition into beneficial effects during stroke recovery. Understanding how neurovascular signals and substrates make the transition from initial injury to angiogenic recovery will be important if we are to find new therapeutic approaches for stroke.

Role of tumor necrosis factor-alpha and matrix metalloproteinase-9 in blood-brain barrier disruption after peripheral thermal injury in rats

OBJECT

A relationship has been found between peripheral thermal injury and cerebral complications leading to injury and death. In the present study, the authors examined whether tumor necrosis factor-alpha (TNF-alpha) and matrix metalloproteinase-9 (MMP-9) play a causative role in blood-brain barrier (BBB) disruption after peripheral thermal injury.

METHODS

Thirty-two male Sprague-Dawley rats were subjected to thermal injury. One hour later, 8 rats were injected with TNF-alpha neutralizing antibody, and 8 were injected with doxycycline, an inhibitor of the MMP family proteins; 16 rats did not receive any treatment. Brain tissue samples obtained 7 hours after injury in the treated animals were examined for BBB function by using fluorescein isothiocyanate-dextran and by assessing parenchymal water content. Protein expression of basement membrane components (collagen IV, laminin, and fibronectin) was quantified on Western blot analysis, and MMP-9 protein expression and enzyme activity were determined using Western blot and gelatin zymography. Thermally injured rats that did not receive treatment were killed at 3, 7, or 24 hours after injury and tested for BBB functioning at each time point. Histological analysis for basement membrane proteins was also conducted in untreated rats killed at 7 hours after injury. Results of testing in injured rats were compared with those obtained in a control group of rats that did not undergo thermal injury.

RESULTS

At 7 hours after thermal injury, a significant increase in the fluorescein isothiocyanate-dextran and water content of the brain was found (p < 0.05), but BBB dysfunction was significantly decreased in the rats that received TNF-alpha antibody or doxycycline (p < 0.05). In addition, the components of the basal lamina were significantly decreased at 7 hours after thermal injury (p < 0.01), and there were significant increases in MMP-9 protein expression and enzyme activity (p < 0.05). The basal lamina damage was reversed by inhibition of TNF-alpha and MMP-9, and the increase in MMP-9 protein was reduced in the presence of doxycycline (p < 0.05). The authors found that MMP-9 enzyme activity was significantly increased after thermal injury (p < 0.01) but decreased in the presence of either TNF-alpha antibody or doxycycline (p < 0.01).

CONCLUSIONS

The dual, inhibitory activity of both TNF-alpha and MMP-9 in brain injury suggests that a TNF-alpha and MMP-9 cascade may play a key role in BBB disruption. These results offer a better understanding of the pathophysiology of burn injuries, which may open new avenues for burn treatment beyond the level of current therapies.

Psychoneuroimmunology of stroke

Stroke is the major cause of disability in the Western world and is the third greatest cause of death, but there are no widely effective treatments to prevent the devastating effects of stroke. Extensive and growing evidence implicates inflammatory and immune processes in the occurrence of stroke and particularly in the subsequent injury. Several inflammatory mediators have been identified in the pathogenesis of stroke including specific cytokines, adhesion molecules, matrix metalloproteinases, and eicosanoids. An early clinical trial suggests that inhibiting interleukin-1 may be of benefit in the treatment of acute stroke.

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.

Neuroinflammation and MMPs: potential therapeutic targets in neonatal hypoxic-ischemic injury

Exposure to hypoxic-ischemic insults during the neonatal or perinatal developmental periods produces various forms of pathology. Injuries that occur in response to these events often manifest as severe cognitive and/or motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of hypoxic-ischemic injury, there is a growing need for effective therapies that can be delivered at delayed time points. Much of the research into mechanisms of neural injury has focused on molecular targets associated with excitotoxicity and free oxygen radicals. Despite repeated success in animal models, these compounds have failed to show efficacy in clinical trials. Increasing evidence indicates that hypoxic-ischemic injury in the neonate is progressive, and the resulting neuropathies are linked to the activation of neuroinflammatory processes that occur in response to the initial wave of cell death. Understanding this latter response, therefore, will be critical in the development of novel therapies to block the progression of the injury. In this review, we summarize emerging concepts from rodent models concerning the regulation of various cytokines, chemokines, and matrix metalloproteinases in response to ischemia, and the various ways in which the delayed neuroinflammatory response may contribute to the progressive nature of neonatal hypoxic-ischemic injury in rat. Finally, we discuss data that supports the potential to target these neuroinflammatory signals at clinically relevant time points.

Progesterone exerts neuroprotective effects by inhibiting inflammatory response after stroke

OBJECTIVE AND DESIGN

We evaluated the inhibitory effects of progesterone (PROG) on inflammatory response and its influence on the structure of blood-brain barrier in a permanent model of stroke.

MATERIAL

One hundred and twenty adult male Sprague-Dawley rats were used in this study.

TREATMENTS

PROG was dissolved in 22.5% 2-hydroxypropyl-bcyclodextrin and given in a dose of 15 mg/kg by intraperitoneal injection 1 h after permanent occlusion of middle cerebral artery (pMCAO). Additional injections of 15 mg/kg were administered subcutaneously 6, 24, and 48 h after pMCAO.

METHODS

The expression of tumor necrosis factor-alpha (TNF-alpha) and claudin5 was measured by immunohistochemistry and western blot technique. Brain water content was determined by the dry-wet weight method.

RESULTS

TNF-alpha were increased, but claudin5 were reduced in vehicle-treated rats after pMCAO. PROG-treated rats showed a substantial reduction in the expression of TNF-alpha compared to vehicle controls. In addition, there was significant increase in the expression of claudin5 in the pMCAO rats treated with PROG compared to vehicle. Examination of the water content of the brain also revealed that administration of PROG significantly attenuated the amount of water compared to vehicle in the ipsilateral hemispheres.

CONCLUSIONS

These data indicate that PROG is beneficial in this animal model, and may warrant further test in future clinical trials for human stroke.

Rac1 is a critical mediator of endothelium-derived neurotrophic activity

The therapeutic potential of neurotrophic factors has been hampered by their inability to achieve adequate tissue penetration. Brain blood vessels, however, could be an alternative target for neurosalvage therapies by virtue of their close proximity to neurons. Here we show that hemizygous deletion of Rac1 in mouse endothelial cells (ECs) attenuates brain injury and edema after focal cerebral ischemia. Microarray analysis of Rac1(+/-) ECs revealed enrichment of stress response genes, basement membrane components, and neurotrophic factors that could affect neuronal survival. Consistent with these expression profiles, endothelial Rac1 hemizygosity enhanced antioxidative and endothelial barrier capacities and potentiated paracrine neuroprotective activities through the up-regulation of the neurotrophic factor, artemin. Endothelial Rac1, therefore, could be an important therapeutic target for promoting endothelial barrier integrity and neurotrophic activity.

Synapse loss regulated by matrix metalloproteinases in traumatic brain injury is associated with hypoxia inducible factor-1alpha expression

The present study assessed the role of matrix metalloproteinase-2 (MMP-2) and -9 in synapse loss after traumatic brain injury (TBI) and the role of hypoxia inducible factor-1alpha (HIF-1alpha), a transcription factor up-regulated during hypoxia, in the regulation of MMP-2 and -9 expression post-TBI. Adult male Sprague-Dawley rats (n=6 per group, 400 g-425 g) were injured using Marmarou's closed-head acceleration impact model and allowed to survive for 1, 4, 24 and 48 h. In another set of experiments, 30 min after TBI, animals were treated with Minocycline (inhibitor of MMPs), or 2-Methoxyestradiol (2ME2, inhibitor of HIF-1alpha) and sacrificed at 4 h after injury. Relative amounts of synaptophysin, a presynaptic vesicular protein, HIF-1alpha, as well as MMP-2 and -9 were assessed by real-time PCR and Western blotting. Activity levels of MMP-2 and -9 were determined by zymography. Synaptophysin expression was significantly (p<0.05) decreased at 1 h through 48 h after TBI. A significant increase in gene and protein expressions of HIF-1alpha, MMP-2 and -9, as well as enzyme activity of MMP-2 and -9 at the same time points was also detected. Inhibition of either MMPs or HIF-1alpha significantly reversed the TBI-induced decrease in synaptophysin. Inhibition of HIF-1alpha reduced expression of MMP-2 and -9. This study showed an early detection of a correlation between synaptic loss and MMP expression after TBI. The data also supports a role for HIF-1alpha in the MMP regulatory cascade in synapse loss after TBI, suggesting potential targets for reducing loss of synaptic terminals.

Inhibition of gelatinase activity reduces neural injury in an ex vivo model of hypoxia-ischemia

Perinatal hypoxia-ischemia (H-I) often manifests as cognitive and/or motor disturbances that appear early in development. Growing evidence indicates that neuroinflammation may exacerbate H-I injury. Resident microglia release proinflammatory cytokines and proteases in response to ischemia. Matrix metalloproteinases (MMPs), in particular, activate cytokines and degrade basement membrane proteins. These actions ultimately permit entry of peripheral leukocytes into the CNS neuropil, enhancing neuroinflammation and cell death. Currently, the relative contributions of resident and peripheral immune cells to ischemic brain injury are unclear. The present study employed an ex vivo model of H-I through oxygen glucose deprivation (OGD) to identify the cellular localization of MMP-9 in organotypic hippocampal slices from rat, and to determine whether inhibiting gelatin-degrading MMPs affords neuroprotection in the absence of peripheral immune cells. Immunohistochemistry revealed ubiquitous neuronal MMP-9 expression in both normoxic and hypoxic slices. Increased MMP-9 expression was detected in CD11b-positive microglia after 48 h exposure to OGD relative to normoxic controls. Consistent with these data, in situ zymography showed increased gelatinolytic activity after OGD. Gelatin-cleaved fluorescence localized to astrocytic processes and somata of various cellular morphologies. Treatment with either the MMP inhibitor AG3340 (prinomastat) or minocycline dampened OGD-induced gelatinolytic activity and neural injury, as measured by Fluoro-Jade staining, relative to vehicle controls. These results show that resident microglia, in the absence of peripheral immune cells, were sufficient to enhance neural injury after OGD in the organotypic hippocampal slice. Additionally, these effects were associated with upregulation or secretion of MMP-9, and were blocked after treatment with either the gelatinase-selective compound AG3340 or the anti-inflammatory compound minocycline. These data, coupled with the effectiveness of these compounds previously shown in vivo, support the selective targeting of gelatin-degrading MMPs and activated microglia as potential therapeutic approaches to combat neonatal H-I injury.

Matrix metalloproteinase-9 deficiency leads to prolonged foreign body response in the brain associated with increased IL-1beta levels and leakage of the blood-brain barrier

Matrix metalloproteinases (MMPs) are enzymes with specificity towards extracellular matrix (ECM) components. MMPs, especially MMP-9, have been shown to degrade components of the basal lamina and disrupt the blood-brain barrier (BBB) and thus, contribute to neuroinflammation. In the present study we examined the role of MMP-9 in the foreign body response in the brain. Millipore filters of mixed cellulose ester were implanted into the brain cortex of wild type and MMP-9-null mice for a period of 2 d to 8 wks and the response was analyzed by histology and immunohistochemistry. We observed enhanced and prolonged neuroinflammation in MMP-9-null mice, evidenced by persistence of neutrophils, macrophages/microglia, and reactive astrocytes up to 8 wks post-implantation. In addition, blood vessel density around implants was increased in MMP-9-null mice and detection of mouse serum albumin (MSA) indicated that vessels were leaky. Immunohistochemical and western blot analyses indicated that this defect was associated with the absence of tight junction proteins zonula occludens-1 (ZO-1) and ZO-2 from vessels in proximity to implants. Analysis of brain sections and brain protein extracts revealed that the levels of the pro-inflammatory cytokine interleukin-1beta (IL-1beta), which is a substrate for MMP-9, were significantly higher in MMP-9-null mice at 8wks post-implantation. Collectively, our studies suggest that increased levels of IL-1beta and the delayed repair of BBB are associated with prolongation of the FBR in MMP-9-null mice.

Tissue inhibitor of matrix metalloproteinases-3 (TIMP-3) lacks involvement in bacterial collagenase-induced intracerebral hemorrhage in mouse

Intracerebral hemorrhage (ICH) leads to delayed cell death in the regions around the hemorrhagic mass. Apoptosis has been identified in the dying cells, but the mechanism involved is unclear. Others and us have shown that matrix metalloproteinases (MMPs) are increased in ICH and could directly contribute to cell death. Tissue inhibitor to metalloproteinases-3 (TIMP-3) facilitates apoptosis in cancer cells and neurons by inhibiting the shedding of tumor necrosis factor-alpha (TNF-alpha) death receptors, Fas and p55TNF receptor 1, by MMP-3 and TNF-alpha converting enzyme (TACE), respectively. Therefore, TIMP-3 may contribute to cell death in ICH. We adapted the bacterial collagenase-induced hemorrhage (CIH) model to the mouse. Adult C57Bl/6 and Timp-3 knockout mice had CIH. Expression of mRNA for TIMP-3 was determined by real-time PCR. Hemorrhage volume and numbers of apoptotic cells were measured by unbiased stereology. Timp-3 mRNA was similar in the knockout and wild-type mice prior to injury and induction of CIH failed to cause an increase in Timp-3 mRNA in the wild-type. Furthermore, there were no differences found in the hemorrhage size or in the numbers of apoptotic cells between the Timp-3 knockout or wild-type. We were unable to prove the hypothesis that TIMP-3 is involved cell death in CIH in the mouse.

Association of carotid artery atherosclerosis with circulating biomarkers of extracellular matrix remodeling: the Framingham Offspring Study

OBJECTIVE

We sought to relate circulating biomarkers of extracellular matrix turnover to site-specific measures of carotid artery atherosclerosis on duplex ultrasound.

BACKGROUND

Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) regulate extracellular matrix remodeling, a key feature of atherosclerosis, and their circulating concentrations can be assayed. MMP-9, TIMP-1, and protocollagen-III n-terminal propeptide (PIIINP) may relate differentially to the severity of atherosclerosis at different carotid artery sites. However, data examining this premise are sparse.

METHODS

We related circulating MMP-9, TIMP-1, and/or PIIINP concentrations to carotid atherosclerosis on duplex ultrasound in 1006 Framingham offspring (mean age 58 years, 56% women) who attended a routine examination from 1995 to 1998. We used multivariable regression to relate MMP-9 (detectable v undetectable), TIMP-1, and PIIINP (age- and sex-specific quartiles) to internal carotid artery (IC) stenosis (>25%) and log-transformed common carotid artery and IC intima-media thickness (IMT).

RESULTS

Detectable MMP-9 was associated with carotid stenosis (odds ratio [OR] 1.71, P = .032) but not with IMT. Higher TIMP-1 was associated with carotid stenosis (OR for Quartiles (Q)4 v Q1-3, 1.63, P = .022) and a higher IC IMT (beta 0.057 +/- 0.025, Q4 v Q1-3, P = .023). Higher PIIINP (Q4 v Q1-3) showed a borderline association with carotid stenosis (OR 1.45 for Q4 v Q1-3, P = .095) but not with IMT. TIMP-1 was not associated with common carotid artery IMT.

CONCLUSIONS

In our community-based sample of middle-aged to older adults, higher circulating biomarkers of matrix remodeling were associated with a greater prevalence of carotid stenosis and subclinical atherosclerosis in the IC. Our findings are consistent with regional differences in matrix remodeling in the carotid artery.