The TIMPs tango with MMPs and more in the central nervous system

The matrix metalloproteinases (MMPs) are a family of zinc-dependent extracellular proteases that have been implicated in CNS development and disease. Crucial homeostatic regulation of MMPs is mediated through the expression and actions of the tissue inhibitors of metalloproteinases (TIMPs). Although the TIMPs are recognized inhibitors of the MMPs, recent studies have revealed that these proteins also can exhibit biological activities that are distinct from their interactions with or inhibition of the MMPs. With our understanding of the roles of the TIMPs in the CNS continuously emerging, this review examines the current state of knowledge regarding the multifarious and novel functions of this family of proteins, with particular attention to their increasing potential in the development, plasticity, and pathology of the CNS.     

Matrix metalloproteinase-19 is highly expressed in active multiple sclerosis lesions

Matrix metalloproteinases (MMPs) are proteases known for their capacity to degrade extracellular matrix (ECM) components. MMPs have been implicated in several central nervous system (CNS) diseases, including multiple sclerosis (MS). Microarray analysis has demonstrated significant increased mRNA levels of MMP-19 in chronic MS lesions, suggesting a role of MMP-19 in MS pathogenesis. Therefore, in this study, we investigated the expression pattern and cellular localization of MMP-19 protein in various well-characterized MS lesion stages. In normal control patient white matter, MMP-19 was constitutively expressed by microglia throughout the brain parenchyma, suggesting a physiological role for this MMP family member. Likewise, MMP-19 was expressed by microglia in (p)reactive MS lesions, albeit more intense. In highly active demyelinating MS lesions, parenchymal and perivascular myelin-laden macrophages were strongly immunoreactive for MMP-19, whereas reactive astrocytes were occasionally immunopositive. Astrocytes in chronic inactive lesions were weakly stained for MMP-19. In vitro, MMP-19 was expressed in cultures of primary human microglia, not in astrocyte cultures. As MMP-19 is able to degrade basement membrane constituents and other ECM proteins, it is conceivable that this relatively novel MMP family member contributes to MS pathology by remodelling the ECM of the CNS, thereby influencing leucocyte infiltration, axonal regeneration and astrogliosis.     

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.     

Matrix metalloproteinases: multifunctional effectors of inflammation in multiple sclerosis and bacterial meningitis

Matrix metalloproteinases (MMPs) are a family of Zn²⁺-dependent endopeptidases targeting extracellular matrix (ECM) compounds as well as a number of other proteins. Their proteolytic activity acts as an effector mechanism of tissue remodeling in physiologic and pathologic conditions, and as modulator of inflammation. In the context of neuro-inflammatory diseases, MMPs have been implicated in processes such as (a) blood–brain barrier (BBB) and blood–nerve barrier opening, (b) invasion of neural tissue by blood-derived immune cells, (c) shedding of cytokines and cytokine receptors, and (d) direct cellular damage in diseases of the peripheral and central nervous system. This review focuses on the role of MMPs in multiple sclerosis (MS) and bacterial meningitis (BM), two neuro-inflammatory diseases where current therapeutic approaches are insufficient to prevent severe disability in the majority of patients. Inhibition of enzymatic activity may prevent MMP-mediated neuronal damage due to an overactive or deviated immune response in both diseases. Downregulation of MMP release may be the molecular basis for the beneficial effect of IFN-β and steroids in MS. Instead, synthetic MMP inhibitors offer the possibility to shut off enzymatic activity of already activated MMPs. In animal models of MS and BM, they efficiently attenuated clinical disease symptoms and prevented brain damage due to excessive metalloproteinase activity. However, the required target profile for the therapeutic use of this novel group of compounds in human disease is not yet sufficiently defined and may be different depending on the type and stage of disease. Currently available MMP inhibitors show little target-specificity within the MMP family and may lead to side-effects due to interference with physiological functions of MMPs. Results from human MS and BM indicate that only a restricted number of MMPs specific for each disease is up-regulated. MMP inhibitors with selective target profiles offer the possibility of a more efficient therapy of MS and BM and may enter clinical trials in the near future.     

Chemokine modulation of matrix metalloproteinase and TIMP production in adult rat brain microglia and a human microglial cell line in vitro

Matrix metalloproteinases (MMPs) are a family of zinc-dependent enzymes, capable of degrading proteins found in the extracellular matrix. MMPs 2 and 9 are known to be produced by microglia, the resident macrophages of the central nervous system. The control of the secretion of these proteases and the activation of proenzymes by other proteases such as plasmin, as well as the balance between MMP secretion and the secretion of their natural inhibitors (TIMPs), have an important relevance in the pathogenesis of multiple sclerosis (MS). The in vitro control of MMPs 2 and 9, TIMPs 1 and 2, and urokinase-type plasminogen activator by microglia was examined in response to a panel of chemokines (chemotactic cytokines), using ELISA and zymography techniques. The chemokines MCP1, MIP1beta, RANTES, IL-8, and Fractalkine were all found significantly to increase the secretion of MMPs and TIMPs by a human foetal microglial cell line, CHME3, after 24 h stimulation. The chemokines tested, MCP1, MIP1beta, and Fractalkine, were also shown to increase MMP9 secretion by primary isolated rat brain microglia in vitro. MCP1, MIP1alpha/beta, and RANTES significantly decreased the secretion of uPA into culture supernatants in ELISA experiments. These findings suggest an important potential role for the involvement of chemokines in the breakdown of the blood-brain barrier and also the destruction of myelin basic protein in MS.     

Role of matrix metalloproteinases in the pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease whose features include a massive lymphocyte recruitment into the central nervous system and segmental demyelinization of the white matter. One of the MS development factors is an increase of matrix metalloproteinases (MMPs) activity with a coincidental decrease of tissue inhibitors of MMPs (TIMPs) activity. Investigations of serum, cerebrospinal fluid and brain tissue of patients showed an increase of MMP-1, -2, -3, -7, -9 and MMP-12 activity. MMPs disrupt the blood-brain barrier (BBB), increase lymphocyte migration into the central nervous system and are involved in degradation of myelin proteins. MMPs induce the appearance of an active form of tumor necrosis factor alpha, a strong proinflammatory cytokine. The drugs used in MS treatment decrease MMPs expression. Multiple actions of MMPs prove their involvement in the pathogenesis and treatment of MS.     

MMP7 cleaves remyelination‐impairing fibronectin aggregates and its expression is reduced in chronic multiple sclerosis lesions

Upon demyelination, transient expression of fibronectin precedes successful remyelination. However, in chronic demyelination observed in multiple sclerosis (MS), aggregates of fibronectin persist and contribute to remyelination failure. Accordingly, removing fibronectin (aggregates) would constitute an effective strategy for promoting remyelination. Matrix metalloproteinases (MMPs) are enzymes known to remodel extracellular matrix components, including fibronectin. Here, we examined the ability of MMPs to degrade fibronectin aggregates. Our findings reveal that MMP7 cleaved fibronectin aggregates resulting into a prominent 13 kDa EIIIA (16 kDa EDA)‐containing fragment. MMP7 was upregulated during lysolecithin‐induced demyelination, indicating its potential for endogenous fibronectin clearance. In contrast, the expression of proMMP7 was substantially decreased in chronic active and inactive MS lesions compared with control white matter and remyelinated MS lesions. Microglia and macrophages were major cellular sources of proMMP7 and IL‐4‐activated, but not IFNγ+LPS‐activated, microglia and macrophages secreted significant levels of proMMP7. Also, conditioned medium of IL‐4‐activated macrophages most efficiently cleaved fibronectin aggregates upon MMP‐activating conditions. Yet, coatings of MMP7‐cleaved fibronectin aggregate fragments inhibited oligodendrocyte maturation, indicating that further degradation and/or clearance by phagocytosis is essential. These findings suggest that MMP7 cleaves fibronectin aggregates, while reduced (pro)MMP7 levels in MS lesions contribute to their persistent presence. Therefore, upregulating MMP7 levels may be key to remove remyelination‐impairing fibronectin aggregates in MS lesions.     

Matrix metalloproteinases in neural development:a phylogenetically diverse perspective

The matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases originally charac-terized as secreted proteases responsible for degrading extracellular matrix proteins. Their canonical role in matrix remodelling is of signiifcant importance in neural development and regeneration, but emerging roles for MMPs, especially in signal transduction pathways, are also of obvious importance in a neural con-text. Misregulation of MMP activity is a hallmark of many neuropathologies, and members of every branch of the MMP family have been implicated in aspects of neural development and disease. However, while extraordinary research efforts have been made to elucidate the molecular mechanisms involving MMPs, methodological constraints and complexities of the research models have impeded progress. Here we discuss the current state of our understanding of the roles of MMPs in neural development using recent ex-amples and advocate a phylogenetically diverse approach to MMP research as a means to both circumvent the challenges associated with speciifc model organisms, and to provide a broader evolutionary context from which to synthesize an understanding of the underlying biology.     

Monomethylfumarate reduces in vitro migration of mononuclear cells

Migration of immunocompetent cells into the central nervous system represents a key event in the immunopathogenesis of multiple sclerosis (MS). Fumaric acid esters have recently been approved for patients with MS. Their mode of action is not fully understood so far. We analyzed the effect of monomethylfumarate (MMF), the immediate metabolite of dimethylfumarate, on migration of lymphocytes and macrophages. Peripheral blood mononuclear cells (PBMCs) were isolated from patients with MS and healthy donors. PBMCs were treated with MMF in vitro and their migratory capacity was studied in a Boyden chamber assay. In addition, expression of matrix metalloproteinases (MMPs), chemokine receptors, adhesion molecules, and molecules of the oxidative stress cascade was assessed. MMF decreased the migratory capacity of T lymphocytes, but not of macrophages. Lymphocytes as well as macrophages responded to MMF by the upregulation of oxidative stress molecules; however, no effect was seen on the expression of MMPs, chemokine receptors, and adhesion molecules. There was no difference in comparison with cells from healthy controls. MMF reduces the migratory activity of lymphocytes most likely by changing their activational state. This points to a potential novel mode of action differentiating this drug from other available immunotherapies.     

The role of metalloprotease in pathogenesis of nervous system diseases

Matrix Metalloproteases (MMPs) comprise a big family of proteolytic enzymes secreted into extracellular matrix and involved in remodelling of many tissues. The MMPs' activity is regulated on many levels. It is also determined by specific inhibitors known as tissue inhibitors of metalloproteases (TIMPs). Several studies revealed that MMPs have a role not only in physiological processes but also in pathophysiology of nervous system diseases, such as multiplex sclerosis, Guillan-Barré syndrome and strokes. Concerning demyelination MMPs are responsible for degradation of myelin components and facilitation of immune cells migration into inflammatory sites by degrading vascular basement membrane. We still investigate substances with positive clinical effect on the nervous system diseases due to MMPs inactivation.     

Matrix metalloproteinases and skeletal muscle: a brief review

Matrix metalloproteinases (MMPs) are a family of zinc- dependent proteolytic enzymes that function mainly in the extracellular matrix, where they contribute to the development, functioning, and pathology of a wide range of tissues. This mini-review describes the MMPs and tissue inhibitors of MMPs (TIMPs) in skeletal muscle, and considers their involvement in muscle development, ischemia, myonecrosis, angiogenesis, denervation, exercise-induced injuries, disuse atrophy, muscle repair and regeneration, and inflammatory myopathies and dystrophies. Despite the very limited information currently available on MMPs and their inhibitors in skeletal muscle, it is becoming increasingly clear that they have important physiological functions in maintenance of the integrity and homeostasis of muscle fibers and of the extracellular matrix. Understanding the roles of MMPs and TIMPs may lead to the development of new drug-related treatments for various muscle disorders based on suppression or upregulation of their expression.     

Elevated matrix metalloproteinase-9 and degradation of perineuronal nets in cerebrocortical multiple sclerosis plaques

Matrix metalloproteinases (MMPs) degrade extracellular matrix; MMP activity, particularly of MMP-9, is elevated in the white matter in multiple sclerosis (MS) patients. The cerebral cortical extracellular matrix includes perineuronal nets (PNs) that surround parvalbumin-positive neurons (PV-positive neurons) and are important for their function. We measured active and total MMP-9 levels in postmortem homogenates of demyelinated and nondemyelinated cerebral cortical regions from 9MS and 7 control cases and assessed Wisteria floribunda agglutin (WFA)-positive PNs in paraffin sections from 15 MS and 6 controls and PV-positive neurons in sections from 26 MS and 6 controls. Active MMP-9 levels were higher in demyelinated than in nondemyelinated or control cortex (p < 0.05). The area fraction positive for WFA was lower in demyelinated than nondemyelinated MS or control cortex; the latter difference was significant (p < 0.05). Most PV-positive neurons in demyelinated but not intact cortex lackeda PN, and some showed perikaryal phosphorylated neurofilament protein accumulation. Loss of WFA-labeled PNs was not associated with reduced PV-positive neurons numbers. Thus, elevated MMP-9 in cortical plaques is associated with loss of PNs; PV-positive neurons are preserved but show abnormal neurofilament accumulations. Matrix metalloproteinase-mediated degradation of PNs in cortical plaques may, therefore, contribute to neuronal dysfunction and degeneration in MS patients.     

Matrix metalloproteinase-12 is expressed in phagocytotic macrophages in active multiple sclerosis lesions

Matrix metalloproteinases (MMPs) are proteases involved in extracellular matrix (ECM) remodeling, leukocyte infiltration into lesions and myelin degradation in the central nervous system (CNS) disease multiple sclerosis (MS). We have investigated whether MMP-12 (macrophage metalloelastase) is expressed in MS lesions at various stages. In control patient tissue and (p)reactive MS lesions, only occasional microglial and astrocyte staining was detected. In contrast, in active demyelinating lesions, phagocytic macrophages were MMP-12 positive. A lower proportion of phagocytes was positive for MMP-12 in chronic active demyelinating lesions and inactive lesions. This suggests a role for MMP-12 during demyelination in MS.     

Oligodendrocytes utilize a matrix metalloproteinase,MMP-9, to extend processes along an astrocyte extracellular matrix

Matrix metalloproteinases (MMPs), the key effectors of extracellular matrix remodeling, have been demonstrated to regulate the extension of neurites from neuronal cell bodies. In this report we have addressed the hypothesis that oligodendrocytes (OLs) may utilize a similar mechanism in extending their processes during the initial phase of myelination. Furthermore, given our previous findings linking protein kinase C (PKC) to the OL process outgrowth, we tested the postulate that this signal transduction pathway may regulate MMPs and thus the process outgrowth phenotype. We demonstrate that in response to pharmacologic activators of PKC, cultured human OLs augment their process extension with a concomitant increase in the activity of an MMP, MMP-9, as measured by gelatin zymography. Similarly, the phorbol ester-enhanced process extension and increased MMP-9 activity were both inhibited by calphostin C, a selective PKC inhibitor. Also, MMP inhibitors such as 1,10-phenanthroline and synthetic dipeptides that inactivate the MMP catalytic site negated the 4β-phorbol-12,13-dibutyrate (PDB)-mediated process extension, further supporting the key role of MMPs in process extension in vitro. Finally, the elevation of MMP-9 protein expression in the mouse corpus callosum, a tissue rich in OL and myelin, coincided with the previously documented temporal increase in myelination that occurs postnatally. Taken together, these data suggest that MMP-9 constitutes an important mediator of OL process outgrowth, and that this protease in turn can be regulated by PKC. The results are relevant not only to the initial steps of myelination during development, but also to the attempted remyelination that has been shown to occur in pathologic conditions such as MS. GLIA 22:53–63, 1998. © 1998 Wiley-Liss, Inc.     

Matrix metalloproteinases in inflammatory demyelination: targets for treatment.

Matrix metalloproteinases (MMPs) degrade all protein components of the extracellular matrix. Functionally, they contribute to several different physiologic conditions, such as angiogenesis or bone remodeling, as well as pathologic conditions in humans, such as rheumatoid arthritis and tumor growth. MMPs seem to be important in the pathogenesis of inflammatory demyelinating diseases of the central and peripheral nervous system, especially in MS and in Guillain-Barré syndrome (GBS). Key mechanisms in the genesis of inflammatory demyelination, such as leukocyte recruitment, blood-brain barrier or blood-nerve barrier breakdown, myelin destruction, and release of disease-promoting cytokines, are considered to be MMP-dependent processes. In experimental autoimmune encephalomyelitis, an animal model of MS, and experimental autoimmune neuritis, an animal model of GBS, different synthetic inhibitors targeting MMP activity are able to suppress and even reverse ongoing disease. This evidence points to MMPs as new targets for treatment in inflammatory demyelination.     

Chemokines and matrix metalloproteinase-9 in leukocyte recruitment to the central nervous system

Chemokines and matrix metalloproteinases (MMPs) play key roles in leukocyte migration across the blood-brain barrier (BBB) in infectious and inflammatory diseases, including multiple sclerosis (MS). In MS some chemokine receptors are expressed by an increased percentage of T cells in blood, the CSF concentration of chemokine ligands for these receptors is increased, and there is accumulation of T cells expressing relevant chemokine receptors in CSF and in the CNS parenchyma. Chemokine receptor expression patterns appear to reflect disease activity and disease stage in MS. MMPs are constitutively expressed or induced by proinflammatory cytokines and chemokines in leukocytes and CNS-resident cells. Several MMPs are expressed in MS plaques, and the CSF concentration of MMP-9 is increased in MS. The CSF concentration of MMP-9 may reflect disease activity in MS, and the CSF concentration of MMP-9 is higher in patients carrying the MS-associated HLA type DRB1 1501. We review how chemokines and MMP-9 may be involved in the pathogenesis of MS by controlling leukocyte migration between different functional compartments. Measuring expression of these molecules may find use as surrogate markers of disease activity in MS, and interfering with their function holds promise as a novel therapeutic strategy in MS.     

Matrix metalloproteinases in neuroinflammation

Matrix metalloproteinases (MMPs) are a gene family of neutral proteases that are important in normal development, wound healing, and a wide variety of pathological processes, including the spread of metastatic cancer cells, arthritic destruction of joints, atherosclerosis, and neuroinflammation. In the central nervous system (CNS), MMPs have been shown to degrade components of the basal lamina, leading to disruption of the blood-brain barrier (BBB), and to contribute to the neuroinflammatory response in many neurological diseases. Brain cells express both constitutive and inducible MMPs in response to cellular stress. MMPs are tightly regulated to avoid unwanted proteolysis. Secreted as inactive enzymes, the MMPs require activation by other proteases and free radicals. The MMPs are part of a larger class of metalloproteinases (MPs), which includes the recently discovered ADAMs (a disintegrin and metalloproteinase domain) and ADAMTS (a disintegrin and metalloproteinase thrombospondin) families. MPs have complex roles at the cell surface and within the extracellular matrix. At the cell surface, they act as sheddases, releasing growth factors, death receptors, and death-inducing ligands, making them important in cell survival and death. Tissue inhibitors of metalloproteinases (TIMPs) are endogenous inhibitors that regulate the activity of the MMPs. Synthetic inhibitors have been developed for the treatment of arthritis and cancer. These hydroxymate-based compounds have been shown to reduce injury in experimental allergic encephalomyelitis (EAE), experimental allergic neuritis (EAN), cerebral ischemia, intracerebral hemorrhage, and viral and bacterial infections. MPs have both beneficial and detrimental roles; understanding their expression in various CNS insults will allow for the use of MMP inhibitors in the treatment of neurological disorders.     

The value and correlation between PRL‐3 expression and matrix metalloproteinase activity and expression in human gliomas

Local invasion of tumor cells is characteristic of most human glioma invasions. It is associated with increased motility and a potential to degrade the extracellular matrix. Matrix metalloproteinases (MMPs) have been proved to be a main process in local invasion of brain tumor. PRL‐3 is a new protein tyrosine phosphatase which would also degrade the extracellular matrix and has been proved to be expressed in liver metastases derived from colorectal cancer. In this study, we sought to investigate the expression of PRL‐3 in glioma tissues and investigate the relationship between MMPs (MMP2, MMP9, membrane‐type matrix metalloproteinase 1 [MT1‐MMP]) activity and expression in gliomas. The modifications of in situ hybridization of mRNA phosphatase of regenerating liver‐3 (PRL‐3) methods are preformed in the study of paraffin‐embedded slides. The immunohistochemistry and gelatin zymography are used to detect the expression of PRL‐3 and activity of MMPs. The results show that PRL‐3 mRNA and antibody of PRL‐3 are detected in glioma tissues mainly in grades IV and III, only a little in grade II, but not in normal brain tissue and glioma grade I. MMP2 and MMP9 are observed mainly in glioma tissues of grades IV and III in activity and expression. MT1‐MMP protein is located in glioma tissues and vessel endothelial cells. This is the first report of detecting PRL‐3 expression in gliomas, especially in grades III and IV, which may play an important role in progression of gliomas. PRL‐3, MMP2 and MT1‐MMP cooperatively contribute to gliomas invasion. Intermediate MMP2 (MT1‐MMP, TIMP‐2, MMP2 trimeric complex) is detected in high grades of glioma tissues by gelatin zymography and may be a marker indicating latent malignance of gliomas.     

Trafficking and secretion of matrix metalloproteinase‐2 in olfactory ensheathing glial cells: A role in cell migration?

Olfactory ensheathing cells (OECs) are unique glia found only in the olfactory system. They retain exceptional plasticity and support olfactory neurogenesis and retargeting across the PNS:CNS boundary in the olfactory system. OECs have been shown to improve functional outcome when transplanted into rodents with spinal cord injury. The growth-promoting properties of implanted OECs encompass their ability to migrate through the scar tissue and render it more permissive for axonal outgrowth, but the underlying molecular mechanisms remain poorly understood. OECs appear to regulate molecules of the extracellular matrix (ECM) that inhibit axonal growth. Among the proteins that have the potential to promote cell migration, axonal regeneration and remodeling of the ECM are matrix metalloproteinases (MMPs), a family of endopeptidases that cleave matrix, soluble, and membrane-bound proteins and that are regulated by their endogenous inhibitors, the tissue inhibitors of MMPs (TIMPs). Little is known about MMP/TIMP trafficking, secretion, and role in OECs. Using a combination of cell biology, biochemistry, pharmacology, and imaging techniques, we show that MMP-2 and MMP-9 are expressed and proteolytically active in the olfactory epithelium and in particular in the OECs of the lamina propria. These proteinases and regulatory proteins such as MT1-MMP and TIMP-2 are expressed in cultured OECs. MMPs exhibit nuclear localization and vesicular trafficking and secretion, with distribution along microtubules and microfilaments and co-localization with the molecular motor protein kinesin. Finally, we show that MMPs are involved in migration of OECs in vitro on different ECM substrates.