Metalloproteinases: mediators of pathology and regeneration in the CNS

MMPs initiate Schwann cell-mediated MBP degradation and mechanical nociception after nerve damage

Matrix metalloproteinases (MMPs) emerge as modulators of neuropathic pain. Because myelin protects Abeta afferents from ectopic hyperexcitability and nociception from innocuous mechanical stimuli (or mechanical allodynia), we analyzed the role of MMPs in the development of mechanical allodynia through myelin protein degradation after rat and MMP-9-/- mouse L5 spinal nerve crush (L5 SNC). MMPs were shown to promote selective degradation of myelin basic protein (MBP), with MMP-9 regulating initial Schwann cell-mediated MBP processing after L5 SNC. Acute and long-term therapy with GM6001 (broad-spectrum MMP inhibitor) protected from injury-induced MBP degradation, caspase-mediated apoptosis, macrophage infiltration in the spinal nerve and inhibited astrocyte activation in the spinal cord. The effect of GM6001 therapy on attenuation of mechanical allodynia was robust, immediate and sustained through the course of L5 SNC. In conclusion, MMPs mediate the initiation and maintenance of mechanical nociception through Schwann cell-mediated MBP processing and support of neuroinflammation.

Contributions of multiple proteases to neurotoxicity in a mouse model of intracerebral haemorrhage

Proteases such as matrix metalloproteinases (MMPs) and thrombin are implicated in intracerebral haemorrhage (ICH) but their interactions amongst one another and interdependency remain to be defined. The latter is important since proteases acting through different mechanisms to inflict neurotoxicity would require separate targeting compared with proteases acting through the same cascade. We reported recently that MMP-9 and thrombin combined to promote neurotoxicity in ICH; however, as there was still substantial injury when both MMP-9 and thrombin were inhibited, we sought other factors that also contribute to ICH pathology. MMP-3, another member of the MMP family, has been correlated with poor prognosis in ICH in humans and it has been shown to increase rapidly after ICH in animals. Moreover, MMP-3 can convert the MMP-9 zymogen to its active form. Thus, we have examined whether MMP-3 is neurotoxic and addressed whether its potential effect in ICH is dependent on, or additional to, damage inflicted by MMP-9 and thrombin. We report that cultured neurons are killed by MMP-3 and that neuronal death is most marked when all three proteases, MMP-3, MMP-9 and thrombin, are combined. In vivo, the injection of autologous blood into the right striatum to produce ICH injury resulted in MMP-3 expression within 3 h. The blood-induced lesion and neuronal death was significantly reduced in MMP-3 or MMP-9 null mice compared with wild-type counterparts, and MMP-3 and -9 double null mice had even less brain damage. Significantly, pathological destruction after ICH was least in MMP-3 and -9 double null mice treated with a thrombin antagonist, hirudin. These results provide insights into molecules that inflict neurotoxicity in ICH and demonstrate that multiple proteases would need to be targeted simultaneously to successfully reduce ICH neurotoxicity.

Matrix metalloproteinase-1 treatment of muscle fibrosis

The onset of scarring after injury may impede the regeneration and functional recovery of skeletal muscle. Matrix metalloproteinase-1 (MMP-1) hydrolyzes type I collagen and thus may improve muscle regeneration by resolving fibrotic tissue. We examined the effect of recombinant human MMP-1 on fibrosis in the lacerated gastrocnemius muscle of NOD/scid mice, allowing treatment potential to be ascertained in isolation from immune response. The efficacy of proMMP-1 and active MMP-1 were compared with or without poly(ethylene glycol) (PEG) modification, which was intended to increase the enzyme's stability. Active MMP-1 was most effective in reducing fibrosis, although treatment with proMMP-1 was also beneficial relative to controls. PEG-modified MMP-1 had minimal activity in vivo, despite retaining activity towards a thioester substrate. Moreover, the modified enzyme was inactivated by trypsin and subtilisin at rates comparable to that of native MMP-1. These results and those of computational structural studies suggest that modification occurs at the C-terminal hemopexin domain of MMP-1, which plays a critical role in collagen turnover. Site-specific modifications that spares catalytic and substrate binding sites while protecting susceptible proteolytic digestion sites may be beneficial. We conclude that active MMP-1 can effectively reduce muscle scarring and that its activity is related to the ability of the enzyme to digest collagen, thereby facilitating remodeling of the injured muscle.

Ephrin-B2-induced cleavage of EphB2 receptor is mediated by matrix metalloproteinases to trigger cell repulsion

EphB receptors provide crucial adhesive and repulsive signals during cell migration and axon guidance, but it is unclear how they switch between these opposing responses. Here we provide evidence of an important role for matrix metalloproteinases (MMPs) in repulsive EphB2 signaling. We found that EphB2 is cleaved by MMPs both in vitro and in vivo, and that this cleavage is induced by interaction with its ligand ephrin-B2. Our findings demonstrate that MMP-2/MMP-9-specific inhibition or cleavage-resistant mutations in the ectodomain of EphB2 can prevent EphB2-mediated cell-cell repulsion in HEK293 cells, and block ephrin-B1-induced growth cone withdrawal in cultured hippocampal neurons. Transient expression of wtEphB2, but not noncleavable EphB2-4/5 mutant, restored ephrin-B1-induced growth cone collapse and withdrawal in EphB-deficient neurons. The inhibition of EphB2 cleavage also had potent regulatory effects on EphB2 activity. This study provides the first evidence that MMP-mediated cleavage of EphB2 is induced by receptor-ligand interactions at the cell surface and that this event triggers cell-repulsive responses.

Brain extracellular matrix in neurodegeneration

The role of extracellular matrix (ECM) in neurological development, function and degeneration has evolved from a simplistic physical adhesion to a system of intricate cellular signaling. While most cells require ECM adhesion to survive, it is now clear that differentiated function is intimately dependent upon cellular interaction with the ECM. Therefore, it is not surprising that the ECM is increasingly found to be involved in the enigmatic process of neurodegeneration. Descriptive studies of human neurodegenerative disorders and experimental studies of animal models of neurodegeneration have begun to define potential mechanisms of ECM disruption that can lead to synaptic and neuronal loss.

Matrix metalloproteinase 9 facilitates West Nile virus entry into the brain

West Nile virus (WNV) is the most-common cause of mosquito-borne encephalitis in the United States. Invasion of the brain by WNV is influenced by viral and host factors, and the molecular mechanism underlying disruption of the blood-brain barrier is likely multifactorial. Here we show that matrix metalloproteinase 9 (MMP9) is involved in WNV entry into the brain by enhancing blood-brain barrier permeability. Murine MMP9 expression was induced in the circulation shortly after WNV infection, and the protein levels remained high even when viremia subsided. In the murine brain, MMP9 expression and its enzymatic activity were upregulated and MMP9 was shown to partly localize to the blood vessels. Interestingly, we also found that cerebrospinal fluid from patients suffering from WNV contained increased MMP9 levels. The peripheral viremia and expression of host cytokines were not altered in MMP9(-/-) mice; however, these animals were protected from lethal WNV challenge. The resistance of MMP9(-/-) mice to WNV infection correlated with an intact blood-brain barrier since immunoglobulin G, Evans blue leakage into brain, and type IV collagen degradation were markedly reduced in the MMP9(-/-) mice compared with their levels in controls. Consistent with this, the brain viral loads, selected inflammatory cytokines, and leukocyte infiltrates were significantly reduced in the MMP9(-/-) mice compared to their levels in wild-type mice. These data suggest that MMP9 plays a role in mediating WNV entry into the central nervous system and that strategies to interrupt this process may influence the course of West Nile encephalitis.

A novel intracellular role of matrix metalloproteinase-3 during apoptosis of dopaminergic cells

We have previously demonstrated that the active form of matrix metalloproteinase-3 (actMMP-3) is released from dopamine(DA)rgic neurons undergoing apoptosis. Herein, whether actMMP-3 might be generated intracellularly, and if so, whether it is involved in apoptosis of DArgic neurons itself was investigated in primary cultured DArgic neurons of wild-type, MMP-3 knockout animals, and CATH.a cells. During apoptosis, gene expression of MMP-3 is induced, specifically among the various classes of MMPs, generating the proform (55 kDa) which is subsequently cleaved to the catalytically active actMMP-3 (48 kDa) involving a serine protease. Intracellular actMMP-3 activity is directly linked to apoptotic signaling in DArgic cells: (i) Pharmacologic inhibition of enzymatic activity, repression of gene expression by siRNA, and gene deficiency all lead to protection; (ii) pharmacologic inhibition causes attenuation of DNA fragmentation and caspase 3 activation, the indices of apoptosis; and (iii) inhibition of the pro-apoptotic enzyme c-Jun N-terminal protein kinase leads to repression of MMP-3 induction. Under the cell stress condition, MMP-3 is released as actMMP-3 rather than the proform (proMMP-3), and catalytically active MMP-3 added to the medium does not cause cell death. Thus, actMMP-3 seems to have a novel intracellular role in apoptotic DArgic cells and this finding provides an insight into the pathogenesis of Parkinson's disease.

Diverse roles of matrix metalloproteinases and tissue inhibitors of metalloproteinases in neuroinflammation and cerebral ischemia

Regulation of the extracellular matrix by proteases and protease inhibitors is a fundamental biological process for normal growth, development and repair in the CNS. Matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs) are the major extracellular-degrading enzymes. Two other enzyme families, a disintegrin and metalloproteinase (ADAM), and the serine proteases, plasminogen/plasminogen activator (P/PA) system, are also involved in extracellular matrix degradation. Normally, the highly integrated action of these enzyme families remodels all of the components of the matrix and performs essential functions at the cell surface involved in signaling, cell survival, and cell death. During the inflammatory response induced in infection, autoimmune reactions and hypoxia/ischemia, abnormal expression and activation of these proteases lead to breakdown of the extracellular matrix, resulting in the opening of the blood-brain barrier (BBB), preventing normal cell signaling, and eventually leading to cell death. There are several key MMPs and ADAMs that have been implicated in neuroinflammation: gelatinases A and B (MMP-2 and -9), stromelysin-1 (MMP-3), membrane-type MMP (MT1-MMP or MMP-14), and tumor necrosis factor-alpha converting enzyme (TACE). In addition, TIMP-3, which is bound to the cell surface, promotes cell death and impedes angiogenesis. Inhibitors of metalloproteinases are available, but balancing the beneficial and detrimental effects of these agents remains a challenge.

Interactions between APP secretases and inflammatory mediators

There is now a large body of evidence linking inflammation to Alzheimer's disease (AD). This association manifests itself neuropathologically in the presence of activated microglia and astrocytes around neuritic plaques and increased levels of inflammatory mediators in the brains of AD patients. It is considered that amyloid-β peptide (Aβ), which is derived from the processing of the longer amyloid precursor protein (APP), could be the most important stimulator of this response, and therefore determining the role of the different secretases involved in its generation is essential for a better understanding of the regulation of inflammation in AD. The finding that certain non-steroidal anti-inflammatory drugs (NSAIDs) can affect the processing of APP by inhibiting β- and γ-secretases, together with recent revelations that these enzymes may be regulated by inflammation, suggest that they could be an interesting target for anti-inflammatory drugs. In this review we will discuss some of these issues and the role of the secretases in inflammation, independent of their effect on Aβ formation.

High resolution in situ zymography reveals matrix metalloproteinase activity at glutamatergic synapses

Synaptic plasticity involves remodeling of extracellular matrix. This is mediated, in part, by enzymes of the matrix metalloproteinase (MMP) family, in particular by gelatinase MMP-9. Accordingly, there is a need of developing methods to visualize gelatinolytic activity at the level of individual synapses, especially in the context of neurotransmitters receptors. Here we present a high-resolution fluorescent in situ zymography (ISZ), performed in thin sections of the alcohol-fixed and polyester wax-embedded brain tissue of the rat (Rattus norvegicus), which is superior to the current ISZ protocols. The method allows visualization of structural details up to the resolution-limit of light microscopy, in conjunction with immunofluorescent labeling. We used this technique to visualize and quantify gelatinolytic activity at the synapses in control and seizure-affected rat brain. In particular, we demonstrated, for the first time, frequent colocalization of gelatinase(s) with synaptic N-methyl-D-aspartic acid (NMDA)- and AMPA-type glutamate receptors. We believe that our method represents a valuable tool to study extracellular proteolytic processes at the synapses, it could be used, as well, to investigate proteinase involvement in a range of physiological and pathological phenomena in the nervous system.

Tissue plasminogen activator (tPA) and matrix metalloproteinases in the pathogenesis of stroke: therapeutic strategies

Today there exists only one FDA-approved treatment for ischemic stroke; i.e., the serine protease tissue-type plasminogen activator (tPA). In the aftermath of the failed stroke clinical trials with the nitrone spin trap/radical scavenger, NXY-059, a number of articles raised the question: are we doing the right thing? Is the animal research truly translational in identifying new agents for stroke treatment? This review summarizes the current state of affairs with plasminogen activators in thrombolytic therapy. In addition to therapeutic value, potential side effects of tPA also exist that aggravate stroke injury and offset the benefits provided by reperfusion of the occluded artery. Thus, combinational options (ultrasound alone or with microspheres/nanobubbles, mechanical dissociation of clot, activated protein C (APC), plasminogen activator inhibitor-1 (PAI-1), neuroserpin and CDP-choline) that could offset tPA toxic side effects and improve efficacy are also discussed here. Desmoteplase, a plasminogen activator derived from the saliva of Desmodus rotundus vampire bat, antagonizes vascular tPA-induced neurotoxicity by competitively binding to low-density lipoprotein related-receptors (LPR) at the blood-brain barrier (BBB) interface, minimizing the tPA uptake into brain parenchyma. tPA can also activate matrix metalloproteinases (MMPs), a family of endopeptidases comprised of 24 mammalian enzymes that primarily catalyze the turnover and degradation of the extracellular matrix (ECM). MMPs have been implicated in BBB breakdown and neuronal injury in the early times after stroke, but also contribute to vascular remodeling, angiogenesis, neurogenesis and axonal regeneration during the later repair phase after stroke. tPA, directly or by activation of MMP-9, could have beneficial effects on recovery after stroke by promoting neurovascular repair through vascular endothelial growth factor (VEGF). However, any treatment regimen directed at MMPs must consider their pleiotropic nature and the likelihood of either beneficial or detrimental effects that might depend on the timing of the treatment in relation to the stage of brain injury.

Spatial and temporal distribution of laminins in permanent focal ischemic brain damage of the adult rat

Laminins are extracellular matrix glycoproteins with multiple functions in the central nervous system, including maintenance of the blood-brain barrier. Because ischemic brain damage results in rapid degradation of extracellular matrix, we used immunocytochemistry on rat central nervous system after permanent focal ischemia to identify laminins involved in pathophysiology of stroke. At 24 hr after stroke, laminin-1 is transiently expressed by neurons inside the ischemic core, but from 2-3 days to 28 days it is expressed only in basement membrane structures. During the first 24 hr, alpha1, alpha5, beta1, and gamma1 laminins are transiently expressed in neurons within the ischemic core as an acute reaction of the brain to ischemia. Rapid induction of gamma1 laminin but no other laminin in reactive astrocytes surrounding the ischemic core is clear at 24 hr, and importantly, expression of gamma1 laminin in astrocytes surrounding the ischemic core intensifies during the first days and persists up to 28 days after stroke. At 2-3 days, gamma1 laminin immunoreactive barrier of reactive astrocytes is already fully formed, isolating the ischemic area from the healthy brain. Similar to gamma1 laminin, its KDI domain localizes in reactive astrocytes isolating the ischemic core. Results indicate that gamma1 laminin and its KDI domain are rapidly induced in glial cells after stroke and their expression persists, forming a molecular barrier between the healthy and the damaged brain. Thus, gamma1 laminin is involved in pathology of stroke and is likely to serve a protective function, considering its potent neuroprotective role after spinal cord injury and in neurodegenerative disorders.

Chemokines in and out of the central nervous system: much more than chemotaxis and inflammation

Actions of chemokines and the interaction with specific receptors go beyond their original, defined role of recruiting leukocytes to inflamed tissues. Chemokine receptor expression in peripheral elements and resident cells of the central nervous system (CNS) represents a relevant communication system during neuroinflammatory conditions. The following examples are described in this review: Chemokine receptors play important homeostatic properties by regulating levels of specific ligands in blood and tissues during healthy and pathological conditions; chemokines and their receptors are clearly involved in leukocyte extravasation and recruitment to the CNS, and current studies are directed toward understanding the interaction between chemokine receptors and matrix metalloproteinases in the process of blood brain barrier breakdown. We also propose novel functions of chemokine receptors during demyelination/remyelination, and developmental processes.

Important role of matrix metalloproteinase 9 in epileptogenesis

Temporal lobe epilepsy (TLE) is a devastating disease in which aberrant synaptic plasticity plays a major role. We identify matrix metalloproteinase (MMP) 9 as a novel synaptic enzyme and a key pathogenic factor in two animal models of TLE: kainate-evoked epilepsy and pentylenetetrazole (PTZ) kindling–induced epilepsy. Notably, we show that the sensitivity to PTZ epileptogenesis is decreased in MMP-9 knockout mice but is increased in a novel line of transgenic rats overexpressing MMP-9. Immunoelectron microscopy reveals that MMP-9 associates with hippocampal dendritic spines bearing asymmetrical (excitatory) synapses, where both the MMP-9 protein levels and enzymatic activity become strongly increased upon seizures. Further, we find that MMP-9 deficiency diminishes seizure-evoked pruning of dendritic spines and decreases aberrant synaptogenesis after mossy fiber sprouting. The latter observation provides a possible mechanistic basis for the effect of MMP-9 on epileptogenesis. Our work suggests that a synaptic pool of MMP-9 is critical for the sequence of events that underlie the development of seizures in animal models of TLE.

Peak in matrix metaloproteinases-2 levels observed during recovery from olfactory nerve injury

Matrix metalloproteineases are associated with extracellular remodeling that occurs in injury and repair processes in the central nervous system (CNS). We examined the role of MMP-2 in a model of olfactory nerve injury and found that MMP-2 levels increased several hours following injury, peaked at day 7 and then decreased rapidly. We previously reported a rapid increase in MMP-9, within 5 h after nerve injury, corresponding to neuronal degeneration and increased glial activity. In this study, we show that MMP-2 peaks later than MMP-9, at the onset of neuronal regeneration and repair. Using MMP-9 knockout mice, we determined that the MMP-2 increase is independent of MMP-9. Our data suggest that MMP-2 and MMP-9 may play different roles in the injury and repair processes.

Matrix metalloproteinase-3 induction in rat brain astrocytes: focus on the role of two AP-1 elements

Many brain cells secrete MMPs (matrix metalloproteinases), and increased or misregulated MMP levels are found in neurodegenerative disorders. Here we report that MMP-3 transcription and protein secretion were increased in rat brain astrocytes stimulated with lipopolysaccharide, gangliosides or interferon-gamma. Sequential deletion of the MMP-3 promoter revealed that sequences between -0.5 kb and the start codon were crucial for the transcriptional induction of MMP-3. In addition, experiments using pharmacological inhibitors of individual mitogen-activated protein kinases revealed that MMP-3 induction and promoter activity involved Jun N-terminal kinase, a representative upstream signal of AP-1 (activator protein-1). Sequence analyses of the region of the MMP-3 promoter 500 bp from the start codon indicated the presence of three AP-1 binding sequences. Among them, electrophoretic-mobility-shift assays as well as site-directed mutagenesis of individual AP-1 sequences revealed that distal and middle, but not proximal, sequences largely mediated its induction. Together, these results indicate that AP-1 could control MMP-3 induction in brain astrocytes and that its regulation through specific AP-1 elements could be exploited in the treatment of brain pathologies in which increased expression of MMP-3 plays crucial roles.

Psychological factors in asthma

Asthma has long been considered a condition in which psychological factors have a role. As in many illnesses, psychological variables may affect outcome in asthma via their effects on treatment adherence and symptom reporting. Emerging evidence suggests that the relation between asthma and psychological factors may be more complex than that, however. Central cognitive processes may influence not only the interpretation of asthma symptoms but also the manifestation of measurable changes in immune and physiologic markers of asthma. Furthermore, asthma and major depressive disorder share several risk factors and have similar patterns of dysregulation in key biologic systems, including the neuroendocrine stress response, cytokines, and neuropeptides. Despite the evidence that depression is common in people with asthma and exerts a negative impact on outcome, few treatment studies have examined whether improving symptoms of depression do, in fact, result in better control of asthma symptoms or improved quality of life in patients with asthma.

Distinct roles of matrix metalloproteases in the early- and late-phase development of neuropathic pain

Treatment of neuropathic pain, triggered by multiple insults to the nervous system, is a clinical challenge because the underlying mechanisms of neuropathic pain development remain poorly understood. Most treatments do not differentiate between different phases of neuropathic pain pathophysiology and simply focus on blocking neurotransmission, producing transient pain relief. Here, we report that early- and late-phase neuropathic pain development in rats and mice after nerve injury require different matrix metalloproteinases (MMPs). After spinal nerve ligation, MMP-9 shows a rapid and transient upregulation in injured dorsal root ganglion (DRG) primary sensory neurons consistent with an early phase of neuropathic pain, whereas MMP-2 shows a delayed response in DRG satellite cells and spinal astrocytes consistent with a late phase of neuropathic pain. Local inhibition of MMP-9 by an intrathecal route inhibits the early phase of neuropathic pain, whereas inhibition of MMP-2 suppresses the late phase of neuropathic pain. Further, intrathecal administration of MMP-9 or MMP-2 is sufficient to produce neuropathic pain symptoms. After nerve injury, MMP-9 induces neuropathic pain through interleukin-1beta cleavage and microglial activation at early times, whereas MMP-2 maintains neuropathic pain through interleukin-1beta cleavage and astrocyte activation at later times. Inhibition of MMP may provide a novel therapeutic approach for the treatment of neuropathic pain at different phases.

Potential conversion of adult clavicle-derived chondrocytes into neural lineage cells in vitro

Neural stem cells (NSC) can be isolated from a variety of adult tissues and become a valuable cell source for the repair of peripheral and central nervous diseases. However, their origin and identity remain controversial because of possible de-differentiation/trans-differentiation or contaminations by hematopoietic stem cells (HSCs) or mesenchymal stem cells (MSCs). We hypothesize that the commonly used NSC culture medium can induce committed cartilage chondrocytes to de-differentiate and/or trans-differentiate into neural cell lineages. Using a biological isolation and purification method with explants culture, we here show that adult rat clavicle cartilage chondrocytes migrate out from tissue blocks, form sphere-like structures, possess the capability of self-renewal, express nestin and p75NTR, markers for neural crest progenitors, and differentiate into neurons, glia, and smooth muscle cells. Comparing with adult cartilage, the spherical-forming neural crest cell-like cells downregulate the chondrocytic marker genes, including collagen II, collagen X, and sox9, as well as neural-lineage repressors/silencers REST and coREST, but upregulate a set of well-defined genes related to neural crest cells and pro-neural potential. Nerve growth factor (NGF) and glial growth factor (GGF) increase glial and neuronal differentiation, respectively. These results suggest that chondrocytes derived from adult clavicle cartilage can become neural crest stem-like cells and acquire neuronal phenotypes in vitro. The possible de-differentiation/trans-differentiation mechanisms underlying the conversion were discussed.

Matrix metalloproteinases in brain development and remodeling: synaptic functions and targets

Matrix metalloproteinases (MMPs) play critical roles in egg fertilization, embryonic development, wound repair, cancer, and inflammatory and neurologic diseases. This subfamily of metzincin peptidases can cleave extracellular matrix (ECM) and pericellular proteins that have profound effects on cell behavior. Among known MMP substrates are several proteins that play important roles in synaptogenesis, synaptic plasticity, and long-term potentiation (LTP). In this Mini-Review we discuss how MMP-directed cleavage of these proteins can impact the formation and function of synapses within the brain. Pyramidal neurons in the hippocampus, and other large neurons, are surrounded by perineuronal nets that are composed of brevican, tenascin-R, and laminin, each of which is subject to proteolytic cleavage by MMPs. Tenascin-R knockout mice show deficits in learning and memory and LTP, as do at least two MMP knockouts. Impaired LTP is also seen in brain-derived neurotrophic factor (BDNF) knockout mice, which is interesting in that pro-BDNF can be processed into mature BDNF by several MMPs and thereby regulate activation of the high-affinity BDNF receptor TrkB. At the synaptic level, MMP substrates also include ephrins, Eph receptors, and cadherins, which are also involved in synapse development and plasticity. MMPs can also process membrane-bound tumor necrosis factor-alpha into a potent soluble cytokine that is increasingly implicated in neuron-glial signaling, particularly in neurologic disease. Finally, we discuss how the development of therapeutics to attenuate MMP activity in neurodegenerative disorders may become powerful tools for future studies of synaptic formation and function within the developing and mature brain.

The multiple sclerosis degradome: enzymatic cascades in development and progression of central nervous system inflammatory disease

An array of studies implicate different classes of protease and their endogenous inhibitors in multiple sclerosis (MS) pathogenesis based on expression patterns in MS lesions, sera, and/or cerebrospinal fluid (CSF). Growing evidence exists regarding their mechanistic roles in inflammatory and neurodegenerative aspects of this disease. Proteolytic events participate in demyelination, axon injury, apoptosis, and development of the inflammatory response including immune cell activation and extravasation, cytokine and chemokine activation/inactivation, complement activation, and epitope spreading. The potential significance of proteolytic activity to MS therefore relates not only to their potential use as important biomarkers of disease activity, but additionally as prospective therapeutic targets. Experimental data indicate that understanding the net physiological consequence of altered protease levels in MS development and progression necessitates understanding protease activity in the context of substrates, endogenous inhibitors, and proteolytic cascade interactions, which together make up the MS degradome. This review will focus on evidence regarding the potential physiologic role of those protease families already identified as markers of disease activity in MS; that is, the metallo-, serine, and cysteine proteases.

A 'GAG' reflex prevents repair of the damaged CNS

The extracellular matrix of the central nervous system (CNS) serves as both a supporting structure for cells and a rich source of signaling molecules that can influence cell proliferation, survival, migration and differentiation. A large proportion of this matrix is composed of proteoglycans--proteins with long chains of polysaccharides, called glycosaminoglycans (GAGs), covalently attached. Although many of the activities of proteoglycans depend on their core proteins, GAGs themselves can influence cell signaling. Here we review accumulating evidence that two GAGs, chondroitin sulfate and hyaluronan, play essential roles during nervous system development but also accumulate in chronic CNS lesions and inhibit axonal regeneration and remyelination, making them significant hindrances to CNS repair. We propose that the balance between the synthesis and degradation of these molecules dictates, in part, how regeneration and recovery from CNS damage occurs.

Matrix metalloproteinases promote motor axon fasciculation in the Drosophila embryo

Matrix metalloproteinases (MMPs) are a large conserved family of extracellular proteases, a number of which are expressed during neuronal development and upregulated in nervous system diseases. Primarily on the basis of studies using pharmaceutical inhibitors, MMPs have been proposed to degrade the extracellular matrix to allow growth cone advance during development and hence play largely permissive roles in axon extension. Here we show that MMPs are not required for axon extension in the Drosophila embryo, but rather are specifically required for the execution of several stereotyped motor axon pathfinding decisions. The Drosophila genome contains only two MMP homologs, Mmp1 and Mmp2. We isolated Mmp1 in a misexpression screen to identify molecules required for motoneuron development. Misexpression of either MMP inhibits the regulated separation/defasciculation of motor axons at defined choice points. Conversely, motor nerves in Mmp1 and Mmp2 single mutants and Mmp1 Mmp2 double mutant embryos are loosely bundled/fasciculated, with ectopic axonal projections. Quantification of these phenotypes reveals that the genetic requirement for Mmp1 and Mmp2 is distinct in different nerve branches, although generally Mmp2 plays the predominant role in pathfinding. Using both an endogenous MMP inhibitor and MMP dominant-negative constructs, we demonstrate that MMP catalytic activity is required for motor axon fasciculation. In support of the model that MMPs promote fasciculation, we find that the defasciculation observed when MMP activity is compromised is suppressed by otherwise elevating interaxonal adhesion -- either by overexpressing Fas2 or by reducing Sema-1a dosage. These data demonstrate that MMP activity is essential for embryonic motor axon fasciculation.

Expression of metalloproteinases (MMP-2, MMP-9, and TACE) and TNF-alpha in the nerves of leprosy patients

Matrix metalloproteinases (MMPs) and tumor necrosis factor alpha (TNF-alpha) play important and related roles in the pathogenesis of nerve injury. MMP-dependent and TNF-alpha-dependent processes of neurodegeneration, such as blood-nerve breakdown and immune cell recruitment, are characteristic of leprosy nerve damage. Our work has contributed to the understanding of the role of cytokines in the process, but the role of MMPs in the pathogenesis of neuritic leprosy has not been investigated. This study analyzed the changes in mRNA expression and immunodistribution of MMP-2, MMP-9, TNF-alpha-converting enzyme (TACE), TNF-alpha in nerves of 27 pure neuritic leprosy (PNL) patients, both acid-fast bacilli positive (AFB(+)) and acid-fast bacilli negative (AFB(-)), and 8 non-leprosy patients with control peripheral neuropathic conditions. MMP-2, MMP-9, and TNF-alpha mRNA expression was significantly induced in the AFB(-) relative to the AFB(+) neuritic leprosy group and nonlepritic controls; TACE levels were also elevated in the AFB(-) group, but this change was not statistically significant. Immunoreactive profiles for TNF-alpha and MMPs demonstrated strong reactivity of myelinated axons, infiltrating macrophages, Schwann cells, endothelial cells, and perineurial cells in neuritic leprosy biopsies. This study provides the evidence of the involvement of MMPs in the pathogenesis of PNL neuropathy.

Effects of anticoagulants on the activity of gelatinases

OBJECTIVES

To identify the best procedure for preanalytical blood collection in the determination of matrix metalloproteinase (MMP)-2 and -9 by testing the effects of anticoagulants on their activity.

DESIGN AND METHODS

Active forms of both gelatinases were measured by specific activity assay systems in serum, plasma EDTA, plasma-heparin and plasma-citrate obtained from 20 healthy volunteers, as well as in a pooled serum sample before and after anticoagulant treatment.

RESULTS

: Active MMP-2 and MMP-9 mean concentrations were similar in serum and in plasma-citrate, higher in plasma EDTA than in serum, in plasma-heparin and in plasma-citrate, and lower in plasma-heparin than in serum and plasma-citrate. A similar trend was observed in untreated and treated pooled serum samples.

CONCLUSIONS

Our results indicate that MMP-2 and MMP-9 in their active forms are not released by platelets during blood clotting, whereas the use of calcium chelating anticoagulants can profoundly alter the activity of endogenous gelatinases. This suggests that the determination of active forms of MMP-2 and MMP-9 in serum samples represents a suitable procedure.

Metalloproteinases and their inhibitors: regulators of wound healing

Wound healing is a dynamic process that involves a coordinated response of many cell types representing distinct tissue compartments and is fundamentally similar among tissue types. Among the many gene products that are essential for restoration of normal tissue architecture, several members of the matrix metalloproteinase (MMP) family function as positive and, at times, negative regulators of repair processes. MMPs were initially thought to only function in the resolution phase of wound healing, particularly during scar resorption; however, recent evidence suggests that they also influence other wound-healing responses, such as inflammation and re-epithelialization. In this review, we discuss what is currently known about the function of MMPs in wound healing and will provide suggestions for future research directions.

Inhibition of GSK-3beta mediates expression of MMP-9 through ERK1/2 activation and translocation of NF-kappaB in rat primary astrocyte

Glycogen synthase kinase (GSK)-3beta and extracellular signal-regulated kinase (ERK) regulate several cellular signaling pathways in common, including embryonic development, cell differentiation and apoptosis. In this study, we investigated whether GSK-3beta inhibition is involved in ERK activation, which affects the activation of NF-kappaB and induction of MMP-9 in cultured rat primary astrocytes. Here, we found that GSK-3beta inhibition using GSK-3beta inhibitor TDZD-8 increased the phosphorylation of GSK-3beta at Ser9 site as well as the phosphorylation of ERK1/2 and Akt at Ser473 site. In this condition, GSK-3beta inhibition increased MMP-9 but not MMP-2 activity in a concentration-dependent manner. In RT-PCR analysis, MMP-9 mRNA level was increased by GSK-3beta inhibition in a concentration-dependent manner. MMP-9 promoter reporter activity was similarly increased by GSK-3beta inhibition. Pretreatment of U-0126 (MEK1/2 inhibitor) completely abolished the GSK-3beta inhibition-induced phosphorylation of ERK1/2. U-0126 prevented GSK-3beta inhibition-mediated induction of MMP-9 reporter activity as well as the MMP-9 gene expression. The transcriptional activity of NF-kappaB was significantly increased by GSK-3beta inhibition, which was determined by nuclear translocation of NF-kappaB. Inhibition of ERK1/2 activity by U-0126 also completely blocked the nuclear translocation of NF-kappaB. Transfection of dominant negative plasmid (S9A) of GSK-3beta significantly decreased phosphorylation of ERK, MMP-9 expression and nuclear translocation of NF-kappaB by GSK-3beta inhibition as compared to wild type GSK-3beta. These data suggest that GSK-3beta inhibition mediates ERK1/2 activation followed by NF-kappaB activation, which directly regulates the induction of MMP-9 in rat primary astrocytes.

Association of the MMP-3 5A/6A gene polymorphism with multiple sclerosis in patients from Serbia

Matrix metalloproteinases (MMPs) are proteolytic enzymes involved in remodeling of the extracellular matrix. MMPs are suggested to play a role in the influx of inflammatory cells into the CNS, disruption of the blood brain barrier, and to degrade myelin in vitro. In this study, we have investigated the possible association of MMP-3 5A/6A gene polymorphism with MS susceptibility and/or severity in patients from Serbia. A total of 184 MS patients (150 RR, 34 SP) and 236 controls have been studied. Results show that the distribution of MMP-3 5A/6A genotype frequencies between MS patients and controls were not significantly different. In bout onset patients, carriers of MMP-3 6A/6A genotype had significantly higher mean MSSS values compared to the carriers of 5A allele (6.29+/-1.89 vs. 5.29+/-2.62, respectively, ANCOVA, p=0.01 Scheffe post-hoc test). In conclusion, our results indicate association of MMP-3 6A/6A genotype with significantly higher mean MSSS values. Thus, the obtained results suggest that it should be carefully considered during follow up of patients with MS. Further genetic and functional studies are needed to resolve the complex role of MMPs and their tissue inhibitors in MS pathology and/or regeneration.

Targeting MMPs in acute and chronic neurological conditions

The matrix metalloproteinases (MMPs) are important enzymes that regulate developmental processes, maintain normal physiology in adulthood and have reparative roles at specific stages after an insult to the nervous system. Conversely, the concordant presence and significant upregulation of several MMP members in virtually all neurological conditions result in pathology. Thus, the MMPs have diverse functions, capable of mediating repair and recovery on the one hand and being involved in producing injury on the other. Therefore, targeting MMPs in neurological conditions has become a complicated challenge. This article highlights the beneficial roles of MMPs in normal and reparative processes within the nervous system and discusses the detriments of MMPs encountered in pathology. We review the availability of MMP inhibitors for clinical use and propose that an important consideration for these inhibitors is timing and duration of their use. With acute injuries where a massive upregulation of several MMPs are observed in the early periods after the insult, early and short-term use of broad spectrum MMP inhibitors would seem logical. In chronic conditions where recurrent insults to the CNS are accompanied by prolonged upregulation of MMPs, thereby necessitating the chronic use of medications, the beneficial effects of MMPs in repair may be compromised by the long-term application of MMP inhibitors. In this review we have used spinal cord injury and multiple sclerosis as examples of acute and chronic neurological conditions, respectively, and we consider the use of MMP inhibitors in these states.

Pathologically activated therapeutics for neuroprotection

Many drugs that have been developed to treat neurodegenerative diseases fail to gain approval for clinical use because they are not well tolerated in humans. In this article, I describe a series of strategies for the development of neuroprotective therapeutics that are both effective and well tolerated. These strategies are based on the principle that drugs should be activated by the pathological state that they are intended to inhibit. This approach has already met with success, and has led to the development of the potentially neuroprotective drug memantine, an N-methyl-D-aspartate (NMDA)-type and glutamate receptor antagonist.

Matrix metalloproteinases in neuromuscular disease

Matrix metalloproteinases (MMPs), a family of zinc-dependent endoproteinases, are effector molecules in the breakdown of the blood-brain and blood-nerve barrier, and promote neural tissue invasion by leukocytes in inflammatory diseases of the central and peripheral nervous systems. Moreover, MMPs play an important role in synaptic remodeling, neuronal regeneration, and remyelination. Recent work concerning MMPs in patients with neuropathy, myopathy, spinal cord injury, and amyotrophic lateral sclerosis (ALS), and in corresponding animal models, is discussed in this review.

Synaptic localization of seizure-induced matrix metalloproteinase-9 mRNA

The phenomenon of dendritic transport and local translation of mRNA is considered to be one of the most fundamental mechanisms underlying long-term synaptic plasticity. Matrix metalloproteinase 9 (gelatinase B) (MMP-9) is a matrix metalloproteinase implicated in synaptic long-term potentiation and hippocampus-dependent memory. It was recently shown to be prominently up-regulated in the hippocampal dentate gyrus (DG) upon kainate-mediated seizures. Here, using a high resolution nonradioactive in situ hybridization at the light- and electron-microscopic levels, as well as subcellular fractionation, we provide evidence that in the rat hippocampus, MMP-9 mRNA is associated with dendrites and dendritic spines bearing asymmetric (excitatory) synapses. Moreover we observe that after kainate treatment the number of dendrites and synapses containing MMP-9 mRNA increases markedly. Our results indicate that we are observing the phenomenon of dendritic transport of seizure-induced MMP-9 mRNA.

Oral disease-modifying treatments for multiple sclerosis: the story so far

Multiple sclerosis (MS) represents the prototypic inflammatory autoimmune disorder of the CNS. It is the most common cause of neurological disability in young adults and exhibits considerable clinical, radiological and pathological heterogeneity. Increased understanding of the immunopathological processes underlying this disease, advances in biotechnology and the development of powerful magnetic resonance imaging (MRI) technologies, together with improvements in clinical trial design, have led to a variety of valuable therapeutic approaches to MS. Therapy for MS has changed dramatically over the past decade, yielding significant progress in the treatment of relapsing remitting and secondary progressive forms; however, most of the clinically relevant therapeutic approaches are not yet available as oral formulations. A substantial number of preliminary and pivotal reports have provided promising results for oral therapies, and various phase III clinical trials are currently being initiated or are already underway evaluating the efficacy of a variety of orally administered agents, including cladribine, teriflunomide, laquinimod, fingolimod and fumaric acid. It is hoped that these trials will advance the development of oral therapies for MS.

TIMP-1 abolishes MMP-9-dependent long-lasting long-term potentiation in the prefrontal cortex

BACKGROUND

Understanding of the molecular mechanisms of prefrontal cortex (PFC) plasticity is important for developing new treatment strategies for mental disorders such as depression and schizophrenia. Long-term potentiation (LTP) is a valid model for synaptic plasticity. The extracellular proteolytic system composed of matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs) has recently been shown to play major role in the hippocampal plasticity.

METHODS

We tested whether induction of hippocampal-prefrontal LTP results in accumulation of tissue inhibitor of MMP-1, TIMP-1 mRNA, in the PFC of rats and whether adenovirally driven overexpression of TIMP-1 affects LTP. Additional study of slices was done with a specific MMP-9 inhibitor.

RESULTS

The TIMP-1 is induced in the rat medial PFC by stimuli evoking late LTP; its overexpression blocks the gelatinolytic activity of the MMP family; its overexpression before tetanization blocks late LTP in vivo; and MMP-9 inhibitor prevents late LTP in vitro.

CONCLUSIONS

We suggest a novel extracellular mechanism of late LTP in the PFC, engaging TIMP-1-controlled proteolysis as an element of information integration. Our results may also be meaningful to an understanding of mental diseases and development of new treatment strategies that are based on extracellular mechanisms of synaptic plasticity.

Matrix metalloproteinase inhibitors as therapy for inflammatory and vascular diseases

Matrix metalloproteinases (MMPs) have outgrown the field of extracellular-matrix biology and have progressed towards being important regulatory molecules in cancer and inflammation. This rise in status was accompanied by the development of various classes of inhibitors. Although clinical trials with synthetic inhibitors for the treatment of cancer were disappointing, recent data indicate that the use of selective inhibitors might lead to new therapies for acute and chronic inflammatory and vascular diseases. In this Review, we compare the major classes of MMP inhibitors and advocate that future drug discovery should be based on crucial insights into the differential roles of specific MMPs in pathophysiology obtained with animal models, including knockout studies.

Death receptor expression and function at the human blood brain barrier

The blood brain barrier (BBB) is composed of specialized endothelial cells tightly anastomosed to one another and surrounded by a thick extracellular matrix, the basement membrane. Together these components restrict the diffusion of cells and molecules from the periphery into the central nervous system (CNS), providing immune privilege and homeostasis. Dysregulation of the BBB and trans-endothelial migration of immune cells are amongst the earliest CNS changes partaking in lesion formation in multiple sclerosis (MS). Death receptors are members of the tumor necrosis factor receptor (TNFR) super-family. They are expressed on a variety of tissues including endothelium, but the consequence of their triggering appears to be cell type specific. In this study, we describe the expression of death receptors TNFR1, Fas and DR5 on primary cultures of human BBB-derived endothelial cells (ECs), as well as the effects of receptor activation on human brain endothelial cell (HBEC) function. We show that HBECs are resistant to cell death mediated via TNFalpha, FasL and TRAIL and that neither receptor ligation induces cellular proliferation of HBECs. TNFR1 ligation induces NFkappaB activation and the upregulation of chemokines MCP-1 and IL-8, as well as adhesion molecules ICAM-1 and VCAM-1, while Fas and DR5 triggering activate the extracellular signal regulated kinases-1 and -2 (Erk 1/2, p42/44 MAPK) inducing the release of matrix metalloproteinase 9 (MMP9) by BBB-derived ECs.

Elevation of matrix metalloproteinases (MMPs) in multiple sclerosis and impact of immunomodulators

The matrix metalloproteinases (MMPs) are implicated in the pathology of multiple sclerosis (MS). This review summarizes the consequences of upregulation of MMP members in MS as well as in an animal model of the disease, experimental autoimmune encephalomyelitis (EAE). The pathogenic roles of MMPs are considered, especially in the transmigration of leukocytes into the CNS. We review the evidence that interferon-beta, an immunomodulator that is commonly used in MS, affects MMP expression in the disease. The potential of minocycline as a therapy in MS, based on its activity as an MMP inhibitor, is discussed. Besides affecting MMPs, minocycline may have other actions that help account for its possible utility in MS.

Cytokine regulation of MMP-9 in peripheral glia: implications for pathological processes and pain in injured nerve

Matrix metalloproteinase-9 (MMP-9) is an extracellular protease that is induced in Schwann cells hours after peripheral nerve injury and controls axonal degeneration and macrophage recruitment to the lesion. Here, we report a robust (90-fold) increase in MMP-9 mRNA within 24 h after rat sciatic nerve crush (1 to 60 days time-course). Using direct injection into a normal sciatic nerve, we identify the proinflammatory cytokines TNF-alpha and IL-1beta as potent regulators of MMP-9 expression (Taqman qPCR, zymography). Myelinating Schwann cells produced MMP-9 in response to cytokine injection and crush nerve injury. MMP-9 gene deletion reduced unstimulated neuropathic nociceptive behavior after one week post-crush and preserved myelin thickness by protecting myelin basic protein (MBP) from degradation, tested by Western blot and immunofluorescence. These data suggest that MMP-9 expression in peripheral nerve is controlled by key proinflammatory cytokine pathways, and that its removal protects nerve fibers from demyelination and reduces neuropathic pain after injury.

Matrix metalloproteinases and their inhibitors in human traumatic spinal cord injury

BACKGROUND

Matrix metalloproteinases (MMPs) are a family of extracellular endopeptidases that degrade the extracellular matrix and other extracellular proteins. Studies in experimental animals demonstrate that MMPs play a number of roles in the detrimental as well as in the beneficial events after spinal cord injury (SCI). In the present correlative investigation, the expression pattern of several MMPs and their inhibitors has been investigated in the human spinal cord.

METHODS

An immunohistochemical investigation in post mortem samples of control and lesioned human spinal cords was performed. All patients with traumatic SCI had been clinically diagnosed as having "complete" injuries and presented lesions of the maceration type.

RESULTS

In the unlesioned human spinal cord, MMP and TIMP immunoreactivity was scarce. After traumatic SCI, a lesion-induced bi-phasic pattern of raised MMP-1 levels could be found with an early up-regulation in macrophages within the lesion epicentre and a later induction in peri-lesional activated astrocytes. There was an early and brief induction of MMP-2 at the lesion core in macrophages. MMP-9 and -12 expression peaked at 24 days after injury and both molecules were mostly expressed in macrophages at the lesion epicentre. Whereas MMP-9 levels rose progressively from 1 week to 3 weeks, there was an isolated peak of MMP-12 expression at 24 days. The post-traumatic distribution of the MMP inhibitors TIMP-1, -2 and -3 was limited. Only occasional TIMP immuno-positive macrophages could be detected at short survival times. The only clear induction was detected for TIMP-3 at survival times of 8 months and 1 year in peri-lesional activated astrocytes.

CONCLUSION

The involvement of MMP-1, -2, -9 and -12 has been demonstrated in the post-traumatic events after human SCI. With an expression pattern corresponding largely to prior experimental studies, they were mainly expressed during the first weeks after injury and were most likely involved in the destructive inflammatory events of protein breakdown and phagocytosis carried out by infiltrating neutrophils and macrophages, as well as being involved in enhanced permeability of the blood spinal cord barrier. Similar to animal investigations, the strong induction of MMPs was not accompanied by an expression of their inhibitors, allowing these proteins to exert their effects in the lesioned spinal cord.

Subventricular zone-derived neuroblast migration to the olfactory bulb is modulated by matrix remodelling

In the rodent brain neural progenitor cells are born in the subventricular zone and migrate along a pathway called the rostral migratory stream (RMS) into the olfactory bulb where they differentiate into several classes of interneurones. In the adult, tangential migration in the RMS takes place in 'chains' of cells contained within glial tubes. In contrast, neonatal neuroblasts along the RMS lack these defined glial tubes and chains, migrating instead as individual cells. Time-lapse confocal microscopy of neuroblasts at each of these ages shows that individual cells migrate in a saltatory manner with bursts of high speed followed by periods of slower speed. Tangential migration within a glial tube is 20% faster than migration as individual cells. Neuroblasts may also interact and modify the extracellular matrix during migration through expression of a family of proteins, the matrix metalloproteinases (MMPs). MMPs are present and active along the subventricular zone-olfactory bulb pathway. In the presence of inhibitors of MMPs, neuroblast migration rates were reduced only when cells migrate individually. Chain migration in the adult was unaffected by MMP inhibitors. Taken together, these data suggest that MMPs only influence migration as individual cells and not as chains.

Intracerebroventricular administration of an endothelin ETB receptor agonist increases expression of tissue inhibitor of matrix metalloproteinase-1 and -3 in rat brain

Production of tissue inhibitors of matrix metalloproteinases (TIMPs), a family of secreted proteins with inhibitory actions on matrix metalloproteinases (MMPs), is up-regulated following nerve injuries and is suggested to have protective effects against MMP-mediated tissue damages. To clarify the extracellular signals involved in TIMP production in the brain, the effects of endothelins (ETs), a family of vasoconstricting peptides, were examined. I.c.v. administration of 500 pmol/day Ala(1,3,11,15)-ET-1, an ET(B) receptor agonist, increased the level of TIMP-1 mRNA in rat hippocampus, caudate-putamen and cerebrum. Ala(1,3,11,15)-ET-1 increased the level of TIMP-3 mRNA in the cerebrum, but not in the hippocampus or caudate-putamen. TIMP-2 mRNA was not affected in these brain regions. Ala(1,3,11,15)-ET-1 also stimulated the production of TIMP-1 and TIMP-3 proteins in the cerebrum. Immunohistochemical observations in the hippocampi of Ala(1,3,11,15)-ET-1-infused rats showed that NeuN-positive neurons and glial fibrillary acidic protein-positive astrocytes were immunoreactive for TIMP-1. In the cerebrum, astrocytes had TIMP-1 and TIMP3 reactivity, but neurons did not. In rat cultured astrocytes, both 100 nM Ala(1,3,11,15)-ET-1 and ET-1 increased the mRNA levels and protein release of TIMP-1 and TIMP-3 mRNAs. The effects of ET-1 on astrocytic TIMP-1 and TIMP-3 mRNAs were inhibited by BQ788, an ET(B) antagonist. These findings indicate that activation of brain ET(B) receptors causes production of TIMP-1 and TIMP-3, and suggest the involvement of astrocytes in ET-induced TIMP production.

β-Dystroglycan as a Target for MMP-9, in Response to Enhanced Neuronal Activity

Matrix metalloproteinase-9 has recently emerged as an important molecule in control of extracellular proteolysis in the synaptic plasticity. However, no synaptic targets for its enzymatic activity had been identified before. In this report, we show that beta-dystroglycan comprises such a neuronal activity-driven target for matrix metalloproteinase-9. This notion is based on the following observations. (i) Recombinant, autoactivating matrix metalloproteinase-9 produces limited proteolytic cleavage of beta-dystroglycan. (ii) In neuronal cultures, beta-dystroglycan proteolysis occurs in response to stimulation with either glutamate or bicuculline and is blocked by tissue inhibitor of metalloproteinases-1, a metalloproteinase inhibitor. (iii) Beta-dystroglycan degradation is also observed in the hippocampus in vivo in response to seizures but not in the matrix metalloproteinase-9 knock-out mice. (iv) Beta-dystroglycan cleavage correlates in time with increased matrix metalloproteinase-9 activity. (v) Finally, beta-dystroglycan and matrix metalloproteinase-9 colocalize in postsynaptic elements in the hippocampus. In conclusion, our data identify the beta-dystroglycan as a first matrix metalloproteinase-9 substrate digested in response to enhanced synaptic activity. This demonstration may help to understand the possible role of both proteins in neuronal functions, especially in synaptic plasticity, learning, and memory.

Vasogenic edema due to tight junction disruption by matrix metalloproteinases in cerebral ischemia

Cerebral ischemia causes cell swelling and breakdown of the blood-brain barrier (BBB). Cytotoxic edema results from energy failure, and vasogenic edema occurs when the blood vessels are damaged. Proteases and free radicals are the end result of a molecular injury cascade. Matrix metalloproteinases (MMPs) are a gene family of extracellular matrix-degrading enzymes that disrupt the BBB. Tight junction proteins (TJPs), occludin and claudin-5, which form the endothelial barrier, are vulnerable to attack by MMPs. Basal lamina proteins, such as fibronectin, laminin, and heparan sulfate, are also degraded by MMPs. Reperfusion injury leads to a biphasic opening of the BBB, with the early opening occurring several hours after the onset of reperfusion due to activation of the constitutive enzyme gelatinase A (MMP-2). This initial opening is transient and followed 24 to 48 hours later by more intense damage to the blood vessel, which is associated with the expression and activation of gelatinase B (MMP-9) and stromelysin-1 (MMP-3). Synthetic MMP inhibitors restore the early integrity of the BBB but are ineffective in the later opening. Because these inhibitors block MMPs involved in angiogenesis and neurogenesis, they also slow recovery. The challenge is to identify agents that will protect the BBB, blocking vasogenic edema without interfering with recovery.

Inflammation after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating clinical event without effective therapies. Increasing evidence suggests that inflammatory mechanisms are involved in the progression of ICH-induced brain injury. Inflammation is mediated by cellular components, such as leukocytes and microglia, and molecular components, including prostaglandins, chemokines, cytokines, extracellular proteases, and reactive oxygen species. Better understanding of the role of the ICH-induced inflammatory response and its potential for modulation might have profound implications for patient treatment. In this review, a summary of the available literature on the inflammatory responses after ICH is presented along with discussion of some of the emerging opportunities for potential therapeutic strategies. In the near future, additional strategies that target inflammation could offer exciting new promise in the therapeutic approach to ICH.

Comparison of in vivo and in vitro gene expression profiles in subventricular zone neural progenitor cells from the adult mouse after middle cerebral artery occlusion

Stroke stimulates neurogenesis in the adult rodent brain. The molecules that mediate stroke-induced neurogenesis are not definitely known. Using microarrays containing approximately 400 known genes associated with stem cell and angiogenesis, we compared transcriptional profiles of subventricular zone (SVZ) tissue with cultured neural progenitor cells isolated from the SVZ 7 days after ischemic stroke in the adult mouse. In SVZ tissue, we found that stroke upregulated 58 genes which are involved in multiple signaling pathways during embryonic development, suggesting that stroke recaptures embryonic molecular signals. In neural progenitor cells cultured in growth medium, 23 gene expressions were increased after stroke and 8 of 23 genes overlapped with upregulated genes in stroke SVZ tissue. Expression alterations of selected genes were confirmed by real-time RT-PCR and immunohistochemistry. These in vivo and in vitro data provide new insight into the genetic program of adult SVZ neural progenitor cells after stroke and demonstrate gene expression differences between SVZ tissue and cultured SVZ cells.