Oligodendrocyte-type 2 astrocyte progenitors use a metalloendoprotease to spread and migrate on CNS myelin

Matrix metalloproteinases shape the oligodendrocyte (niche) during development and upon demyelination

The oligodendrocyte lineage cell is crucial to proper brain function. During central nervous system development, oligodendrocyte progenitor cells (OPCs) migrate and proliferate to populate the entire brain and spinal cord, and subsequently differentiate into mature oligodendrocytes that wrap neuronal axons in an insulating myelin layer. When damage occurs to the myelin sheath, OPCs are activated and recruited to the demyelinated site, where they differentiate into oligodendrocytes that remyelinate the denuded axons. The process of OPC attraction and differentiation is influenced by a multitude of factors from the cell's niche. Matrix metalloproteinases (MMPs) are powerful and versatile enzymes that do not only degrade extracellular matrix proteins, but also cleave cell surface receptors, growth factors, signaling molecules, proteases and other precursor proteins, leading to their activation or degradation. MMPs are markedly upregulated during brain development and upon demyelinating injury, where their broad functions influence the behavior of neural progenitor cells (NPCs), OPCs and oligodendrocytes. In this review, we focus on the role of MMPs in (re)myelination. We will start out in the developing brain with describing the effects of MMPs on NPCs, OPCs and eventually oligodendrocytes. Then, we will outline their functions in oligodendrocyte process extension and developmental myelination. Finally, we will review their potential role in demyelination, describe their significance in remyelination and discuss the evidence for a role of MMPs in remyelination failure, focusing on multiple sclerosis. In conclusion, MMPs shape the oligodendrocyte (niche) both during development and upon demyelination, and thus are important players in directing the fate and behavior of oligodendrocyte lineage cells throughout their life cycle.

CLC-2 is a positive modulator of oligodendrocyte precursor cell differentiation and myelination

Oligodendrocytes (OLs) are myelin-forming cells that are present within the central nervous system. Impaired oligodendrocyte precursor cell (OPC) differentiation into mature OLs is a major cause of demyelination diseases. Therefore, identifying the underlying molecular mechanisms of OPC differentiation is crucial to understand the processes of myelination and demyelination. It has been acknowledged that various extrinsic and intrinsic factors are involved in the control of OPC differentiation; however, the function of ion channels, particularly the voltage-gated chloride channel (CLC), in OPC differentiation and myelination are not fully understood. The present study demonstrated that CLC-2 may be a positive modulator of OPC differentiation and myelination. Western blotting results revealed that CLC-2 was expressed in both OPCs and OLs. Furthermore, CLC-2 currents (I_CLC-2) were recorded in both types of cells. The inhibition of I_CLC-2 by GaTx2, a blocker of CLC-2, was demonstrated to be higher in OPCs compared with OLs, indicating that CLC-2 may serve a role in OL differentiation. The results of western blotting and immunofluorescence staining also demonstrated that the expression levels of myelin basic protein were reduced following GaTx2 treatment, indicating that the differentiation of OPCs into OLs was inhibited following CLC-2 inhibition. In addition, following western blot analysis, it was also demonstrated that the protein expression of the myelin proteins yin yang 1, myelin regulatory factor, Smad-interacting protein 1 and sex-determining region Y-box 10 were regulated by CLC-2 inhibition. Taken together, the results of the present study indicate that CLC-2 may be a positive regulator of OPC differentiation and able to contribute to myelin formation and repair in myelin-associated diseases by controlling the number and open state of CLC-2 channels.

A new in vitro mouse oligodendrocyte precursor cell migration assay reveals a role for integrin-linked kinase in cell motility

Background

The decline of remyelination in chronic multiple sclerosis (MS) is in part attributed to inadequate oligodendrocyte precursor cell (OPC) migration, a process governed by the extracellular matrix (ECM). Elucidating the mechanisms underlying OPC migration is therefore an important step towards developing new therapeutic strategies to promote myelin repair. Many seminal OPC culture methods were established using rat-sourced cells, and these often need modification for use with mouse OPCs due to their sensitive nature. It is of interest to develop mouse OPC assays to leverage the abundant transgenic lines. To this end, we developed a new OPC migration method specifically suited for use with mouse-derived cells.

Results

To validate its utility, we combined the new OPC migration assay with a conditional knockout approach to investigate the role of integrin-linked kinase (ILK) in OPC migration. ILK is a focal adhesion protein that stabilizes cellular adhesions to the extracellular matrix (ECM) by mediating a linkage between matrix-bound integrin receptors and the cytoskeleton. We identified ILK as a regulator of OPC migration on three permissive substrates. ILK loss produced an early, albeit transient, deficit in OPC migration on laminin matrix, while migration on fibronectin and polylysine was heavily reliant on ILK expression.

Conclusions

Inclusively, our work provides a new tool for studying mouse OPC migration and highlights the role of ILK in its regulation on ECM proteins relevant to MS.

Mathematical modelling of spatio-temporal glioma evolution

Background

Gliomas are the most common types of brain cancer, well known for their aggressive proliferation and the invasive behavior leading to a high mortality rate. Several mathematical models have been developed for identifying the interactions between glioma cells and tissue microenvironment, which play an important role in the mechanism of the tumor formation and progression.

Methods

Building and expanding on existing approaches, this paper develops a continuous three-dimensional model of avascular glioma spatio-temporal evolution. The proposed spherical model incorporates the interactions between the populations of four different glioma cell phenotypes (proliferative, hypoxic, hypoglychemic and necrotic) and their tissue microenvironment, in order to investigate how they affect tumor growth and invasion in an isotropic and homogeneous medium. The model includes two key variables involved in the proliferation and invasion processes of cancer cells; i.e. the extracellular matrix and the matrix-degradative enzymes concentrations inside the tumor and its surroundings. Additionally, the proposed model focuses on innovative features, such as the separate and independent impact of two vital nutrients, namely oxygen and glucose, in tumor growth, leading to the formation of cell populations with different metabolic profiles. The model implementation takes under consideration the variations of particular factors, such as the local cell proliferation rate, the variable conversion rates of cells from one category to another and the nutrient-dependent thresholds of conversion. All model variables (cell densities, ingredients concentrations) are continuous and described by reaction-diffusion equations.

Results

Several simulations were performed using combinations of growth and invasion rates, for different evolution times. The model results were evaluated by medical experts and validated on experimental glioma models available in the literature, revealing high agreement between simulated and experimental results.

Conclusions

Based on the experimental validation, as well as the evaluation by clinical experts, the proposed model may provide an essential tool for the patient-specific simulation of different tumor evolution scenarios and reliable prognosis of glioma spatio-temporal progression.

Matrix metalloproteinase-2 and -9 as promising benefactors in development, plasticity and repair of the nervous system

It has been 50 years since Gross and Lapiere discovered collagenolytic activity during tadpole tail metamorphosis, which was later on revealed as MMP-1, the founding member of the matrix metalloproteinases (MMPs). Currently, MMPs constitute a large group of endoproteases that are not only able to cleave all protein components of the extracellular matrix, but also to activate or inactivate many other signaling molecules, such as receptors, adhesion molecules and growth factors. Elevated MMP levels are associated with an increasing number of injuries and disorders, such as cancer, inflammation and auto-immune diseases. Yet, MMP upregulation has also been implicated in many physiological functions such as embryonic development, wound healing and angiogenesis and therefore, these proteinases are considered to be crucial mediators in many biological processes. Over the past decennia, MMP research has gained considerable attention in several pathologies, most prominently in the field of cancer metastasis, and more recent investigations also focus on the nervous system, with a striking emphasis on the gelatinases, MMP-2 and MMP-9. Unfortunately, the contribution of these gelatinases to neuropathological disorders, like multiple sclerosis and Alzheimer's disease, has overshadowed their potential as modulators of fundamental nervous system functions. Within this review, we wish to highlight the currently known or suggested actions of MMP-2 and MMP-9 in the developing and adult nervous system and their potential to improve repair or regeneration after nervous system injury.

Imatinib and docetaxel in combination can effectively inhibit glioma invasion in an in vitro 3D invasion assay

The main problem in the treatment of malignant astrocytomas is their invasive behaviour. Successful resection of the main tumour mass cannot prevent recurrence due to single cells invading the surrounding brain parenchyma at the time of diagnosis. The classical combination therapy, PCV (Procarbazine, CCNU and Vincristine) used for over 30 years; has shown its clinical effectiveness in the treatment of malignant astrocytomas and glioblastomas is still doubtful. Using an in vitro three dimensional invasion model, we tested the effect of the tyrosine kinase inhibitor imatinib and the microtubule inhibitor docetaxel on the invasion activity of a panel of astrocytic tumour cell lines, including two established glioma cell lines, IPSB-18 and SNB-19, and two primary cell lines, originating from glioblastomas, CLOM002 and UPHHJA, and in normal astrocytes. A dose response curve for each drug alone and in combination was determined. The half maximal inhibitory concentration (IC(50)) concentration of imatinib was between 15.7 and 18.7 μM, which did not affect invasion activity of the cell lines. The IC(50) concentration of docetaxel was between 0.7 and 19.8 nM, and at 14.9 nM docetaxel had a slight transient inhibitory effect on invasion activity of all tested cells. The combination of imatinib at 13.5 μM and docetaxel at 14.9 nM, however, synergistically inhibited cell growth and invasion activity and could not be reversed by drug removal. A combination treatment with tyrosine kinase inhibitors and cytotoxic drugs shows promise in tackling both glioma proliferation and invasion, and could present a new treatment regimen for malignant astrocytomas.

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.

Matrix metalloproteinase-2 facilitates wound healing events that promote functional recovery after spinal cord injury

Matrix metalloproteinases (MMPs) are proteolytic enzymes that are involved in both injury and repair mechanisms in the CNS. Pharmacological blockade of MMPs, limited to the first several days after spinal cord injury, improves locomotor recovery. This beneficial response is, however, lost when treatment is extended beyond the acutely injured cord to include wound healing and tissue remodeling. This suggests that some MMPs play a beneficial role in wound healing. To test this hypothesis, we investigated the role of MMP-2, which is actively expressed during wound healing, in white matter sparing and axonal plasticity, the formation of a glial scar, and locomotor recovery after spinal cord injury. MMP-2 increased between 7 and 14 d after injury, where it was immunolocalized in reactive astrocytes bordering the lesion epicenter. There was reduced white matter sparing and fewer serotonergic fibers, caudal to the lesion in injured MMP-2 null animals. MMP-2 deficiency also resulted in increased immunoreactivity to chondroitin sulfate proteoglycans and a more extensive astrocytic scar. Most importantly, locomotion in an open field, performance on a rotarod, and grid walking were significantly impaired in injured MMP-2 null mice. Our findings suggest that MMP-2 promotes functional recovery after injury by regulating the formation of a glial scar and white matter sparing and/or axonal plasticity. Thus, strategies exploiting MMPs as therapeutic targets must balance these beneficial effects during wound healing with their adverse interactions in the acutely injured spinal cord.

Matrix metalloproteinases and their inhibitors in the developing mouse brain and spinal cord: a reverse transcription quantitative polymerase chain reaction study

Matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) are essential for coordinated extracellular matrix turnover during central nervous system development. Reverse transcription quantitative polymerase chain reaction was employed to evaluate the mRNA expression of MMP-2, -3, -7, -9, -10, -11, -12, -13, -14, -15, and -24, and TIMP-1, -2, -3, and -4 in the prosencephalon, rhombencephalon, and spinal cord of 1- to 40-week-old mice. The molecular data were interpreted in the context of morphological observations. Significantly higher expression levels of MMP-2, -11, -13, -14, -15, and -24, and TIMP-1 and -3 were found in the brain and spinal cord 1 week after birth compared to later time points, while MMP-9 and TIMP-2 upregulation was restricted to the brain. This upregulation coincided with the maximal extension of the transient cerebellar external granular layer, a marker of neuronal progenitor proliferation and migration. MMP-12 was significantly upregulated at later time points and found to be positively correlated with myelination in the rhombencephalon and spinal cord. MMP-3, -7, and -10 mRNA expressions remained unchanged or were negligible. In summary, while most of the MMPs and TIMPs studied seem to be involved in cell proliferation and migration, MMP-12 might be decisive for myelination.

Neuronal overexpression of tissue-type plasminogen activator does not enhance sensory axon regeneration or locomotor recovery following dorsal hemisection of adult mouse thoracic spinal cord

CNS axons rarely regenerate spontaneously back to original targets following spinal cord injury (SCI). Neuronal expression of the serine protease tissue-type plasminogen activator (tPA) enhances axon growth in vitro and following PNS injury. Here we test the hypothesis that neuronal overexpression of tPA in adult transgenic mice promotes CNS axon regeneration and functional recovery following SCI. Adult wild-type and transgenic mouse spinal cords were subjected to dorsal hemisection at the level of the T10/T11 vertebrae. PCR confirmed incorporation of the transgene. Immunolabeling revealed overexpression of tPA in transgenic mice in neurons, including large-diameter neurons in lumbar dorsal root ganglia that contribute axons to the dorsal columns. Immunolabeling also revealed the presence of tPA protein within axons juxtaposing the injury site in transgenics but not wild types. In situ zymography revealed abundant enzymatic activity of tPA in gray matter of thoracic spinal cords of transgenics but not wild types. Rotorod locomotor testing revealed no differences between groups in locomotor function up to 21 days postinjury. Transganglionic tracer was injected into the crushed right sciatic nerve 28 days postinjury, and mice were killed 3 days later. There was no evidence for regrowth of ascending dorsal column sensory axons through or beyond the injury site. In conclusion, despite neuronal overexpression of tPA in injured neurons of transgenics, neither locomotor recovery nor regeneration of ascending sensory axons was observed following thoracic dorsal hemisection.

The expression of matrix metalloproteinase-12 by oligodendrocytes regulates their maturation and morphological differentiation

Matrix metalloproteinases (MMPs) have important roles in many processes of the developing CNS requiring proteolytic activity such as the migration of neuronal precursors, axonal outgrowth, and vascularization. Another developmental event involving proteolysis is myelin formation, whereby the extensive processes elaborated from oligodendrocytes (OLs) enwrap axons. Here we find MMP-12 transcripts to be produced by OLs in much higher levels than other MMP members examined. MMP-12 activity correlated with the ability of OLs to extend processes in vitro, suggesting a role for MMP-12 in the morphological differentiation of OLs. This was corroborated by results that OL lineage cells from MMP-12 null mice were retarded in their ability to differentiate morphologically and that this deficiency was overcome by the exogenous addition of active MMP-12. Finally, the maturation of oligodendrocyte precursor cells (OPCs) to OLs was significantly reduced in cultures from MMP-12 null mice compared with wild-type controls. We conclude that OL lineage cells express MMP-12 during their maturation and that MMP-12 activity has functional involvement both in maturation of OPCs and in the ability of OPCs and OLs to extend processes.

The potential use of MMP inhibitors to treat CNS diseases

The matrix metalloproteinases (MMPs) are considered to be the physiological mediators of extracellular matrix remodelling. MMPs are involved in a variety of functions and in the nervous system, these include angiogenesis and the extension of neuronal growth cones during development. However, it has become increasingly evident that the aberrant expression of MMPs in the nervous system contributes to diseases that include among others, multiple sclerosis, malignant gliomas, Alzheimer's disease and stroke. This review highlights the evidence that MMPs are involved in diseases of the nervous system, and provides information for the potential beneficial use of MMP inhibitors in NS disorders. However, the application of MMP inhibitors to treat CNS diseases must be balanced carefully against the beneficial roles normally played by MMPs in CNS physiology or recovery.

Role of intracellular S100A4 for migration of rat astrocytes

S100A4 is a member of the EF-hand family of calcium-binding proteins, first identified in tumor cells, and implicated in tumor invasion and metastasis. Intracellular upregulation of S100A4 is associated with increased motility of tumor cells. Extracellular application of S100A4 increases the motility of glioma cells in vitro. We showed previously that astrocytes in spinal cord and brain white matter also express S100A4. This expression is markedly increased in reactive white matter astrocytes after injury. Here, we have explored how changes in intracellular S100A4 affect migration of astrocytes. We produced cultures of white matter, S100A4 expressing astrocytes, and developed a small interfering (si) RNA approach to specifically eliminate S100A4 expression in these cells, and compared the migration of astrocytes expressing S100A4 with astrocytes transfected with S100A4 siRNA. As a "positive control" we used S100A4 expressing C6 glioma cells. In contrast to malignant cells, S100A4 expressing astrocytes increased their migration capacity after S100A4 siRNA treatment. At the same time, and in parallel with increased migration, white matter astrocytes increased their expression of metalloproteinases MMP-9 and MT1-MMP. The addition of MMP-2/MMP-9 inhibitor resulted in a significant inhibition of migration in S100A4 siRNA-treated astrocytes. These findings indicate that S100A4 has a stabilizing function in reactive white matter astrocytes, a function that may contribute to the development of a rigid, growth-inhibitory glial scar.

Ion channels and amino acid transporters support the growth and invasion of primary brain tumors

The malignant growth of glial support cells causes gliomas, highly invasive, primary brain tumors that are largely resistant to therapy. Individual tumor cells spread by active cell migration, invading diffusely into the normal brain. This process is facilitated by Cl- channels that endow glioma cells with an enhanced ability to quickly adjust their shape and cell volume to fit the narrow and tortuous extracellular brain spaces. Once satellite tumors enlarge, their growth is limited by the spatial constraints imposed by the bony cavity of the skull and spinal column. Glioma cells circumvent this limitation by active destruction of peritumoral neural tissue through the release of glutamate, inducing peritumoral seizures and ultimately excitotoxic neuronal cell death. Hence, primary brain tumors support their unusual biology by taking advantage of ion channels and transporters that are designed to support ion homeostatic functions in normal brain.

Malignant gliomas: perverting glutamate and ion homeostasis for selective advantage

The malignant transformation of astrocytes, oligodendrocytes or their progenitor cells gives rise to tumors that are collectively called gliomas. Although the vast majority of these tumors are believed to be of astrocytic origin, the actual cell of origin remains unknown. And whereas gliomas present with some genetic alterations in tumor-suppressor genes or oncogenes that are common among cancers, their biology differs significantly from other neoplasms. Most notably, they grow in a confined space defined by the bones of the skull and spinal column, and they spread by active cell migration rather than by passive, humorous spread. Recent research suggests that astrocyte-derived tumors co-opt neurotransmitters, their transporters and ion channels to support their unusual growth and invasive migration.

Expression of voltage-gated chloride channels in human glioma cells

Voltage-gated chloride channels have recently been implicated as being important for cell proliferation and invasive cell migration of primary brain tumors cells. In the present study we provide several lines of evidence that glioma Cl- currents are primarily mediated by ClC-2 and ClC-3, two genes that belong to the ClC superfamily. Transcripts for ClC-2 thru ClC-7 were detected in a human glioma cell line by PCR, whereas only ClC-2, ClC-3, and ClC-5 protein could be identified by Western blot. Prominent ClC-2, -3, and -5 channel expression was also detected in acute patient biopsies from low- and high-grade malignant gliomas. Immunogold electron microscopic studies as well as digital confocal imaging localized a portion of these ClC channels to the plasma membrane. Whole-cell patch-clamp recordings show the presence of two pharmacologically and biophysically distinct Cl- currents that could be specifically reduced by 48 hr exposure of cells to channel-specific antisense oligonucleotides. ClC-3 antisense selectively and significantly reduced the expression of outwardly rectifying current with pronounced voltage-dependent inactivation. Such currents were sensitive to DIDS (200-500 microm) and 5-nitro-2-(3-phenylpropylamino) benzoic acid (165 microm). ClC-2 antisense significantly reduced expression of inwardly rectifying currents, which were potentiated by hyperpolarizing prepulses and inhibited by Cd2+ (200-500 microm). Currents that were mediated by ClC-5 could not be demonstrated. We suggest that ClC-2 and ClC-3 channels are specifically upregulated in glioma membranes and endow glioma cells with an enhanced ability to transport Cl-. This may in turn facilitate rapid changes in cell size and shape as cells divide or invade through tortuous extracellular brain spaces.

Extracellular proteolysis in brain injury and inflammation: role for plasminogen activators and matrix metalloproteinases

The role of intracellular proteases (e.g., calpains and caspases) in the pathophysiology of neuronal cell death has been extensively investigated. More recently, accumulating data have suggested that extracellular proteolysis also plays a critical role. The two major systems that modify the extracellular matrix in brain are the plasminogen activator (PA) and matrix metalloproteinase (MMP) axes. This Mini-Review delineates major pathways of PA and MMP action after stroke, brain trauma, and chronic inflammation. Deleterious effects include the disruption of blood-brain barrier integrity, amplification of inflammatory infiltrates, demyelination, and possibly interruption of cell-cell and cell-matrix interactions that may trigger cell death. In contrast, PA-MMP actions may contribute to extracellular proteolysis that mediates parenchymal and angiogenic recovery after brain injury. As the mechanisms of deleterious vs. potentially beneficial PA and MMP actions become better defined, it is hoped that new therapeutic targets will emerge for ameliorating the sequelae of brain injury and inflammation.

The AN2 protein is a novel marker for the Schwann cell lineage expressed by immature and nonmyelinating Schwann cells

The expression of the 330 kDa AN2 glycoprotein was studied in the rodent peripheral nervous system. AN2 is expressed by immature Schwann cells in vitro and in vivo and downregulated as the cells upregulate myelin genes. A subpopulation of nonmyelinating Schwann cells in the adult sciatic nerve retains expression of AN2. In rat sciatic nerve crushes, where Schwann cell numbers increase after initial axonal loss and markers of immature Schwann cells show an upregulation, no increased expression of AN2 was observed. In contrast, AN2 expression was upregulated in nerves from peripheral myelin protein-22-transgenic rats, where immature Schwann cells expand without axonal loss. Furthermore, coculture with neurons upregulated AN2 expression on Schwann cells in vitro. Polyclonal antibodies against AN2 inhibited the migration of an immortalized Schwann cell clone in an in vitro migration assay, and the purified AN2 protein was shown to be neither inhibitory nor permissive for outgrowing dorsal root ganglion neurites. AN2 is thus a novel marker for the Schwann cell lineage. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of purified AN2 from early postnatal mouse brain demonstrated that AN2 is the murine homolog of the rat NG2 proteoglycan.

Mitogen‐activated protein kinase signalling in oligodendrocytes: a comparison of primary cultures and CG‐4

Oligodendrocytes play a significant role in the central nervous system, as these cells are responsible for myelinating axons and allowing for the efficient conduction of nerve impulses. Therefore, any understanding we can gain about the functional biology of oligodendrocytes will give us important insights into demyelinating diseases such as multiple sclerosis, where oligodendrocytes and myelin are damaged or destroyed. Currently, much attention has focussed on the role of a family of mitogen-activated protein kinases in OL. This kinase family includes the extracellular signal-regulated protein kinases (ERKs), the stress-activated c-Jun N-terminal kinase (JNK), and the 38 kDa high osmolarity glycerol response kinase (p38). The actions of mitogen-activated protein kinases in oligodendrocytes appear to range from proliferation and cell survival to differentiation and cell death. In the past, studies on oligodendrocytes have been hampered by the difficulties inherent in producing large enough quantities of these cells for experimentation. This problem arises in large part due to the post-mitotic nature of mature oligodendrocytes. Over the years, a cell line known as Central Glia-4 (CG-4) has become a popular oligodendrocyte model due to its potentially unlimited capacity for self-renewal. In this review, we will look at the suitability of the Central Glia-4 cell line as an oligodendrocyte model, specifically in respect to studies on mitogen-activated protein kinase signalling in oligodendrocytes.

Regulation of tissue inhibitor of metalloproteinase-3 (Timp-3) mRNA expression during rat CNS development

To preserve tissue integrity during the structural rearrangements that occur during central nervous system (CNS) development, an intricate balance between extracellular matrix (ECM) synthesis and degradation must be maintained. The matrix metalloproteinases (MMPs) are believed to be the main mediators of ECM degradation. Because MMPs function in the turnover of a broad-spectrum of ECM proteins their activity is tightly regulated by interaction with tissue inhibitors of metalloproteinases (TIMPs). Whereas the primary function of TIMPs is to inhibit MMP activity, evidence is mounting that TIMPs are multifunctional molecules that exert diverse cell biological functions distinct from their MMP-inhibitory activities. Although the role of MMPs and TIMPs in the morphogenesis of non-neural tissues has been investigated, to date few studies have analyzed MMP or TIMP expression during CNS development. In the present report, we demonstrate the regulation of Timp-3 mRNA expression throughout the course of CNS development. In particular, Timp-3 mRNA is expressed in embryonic ventricular zones and the postnatal subventricular zone (SVZ). In addition, Timp-3 is expressed in the rostral migratory steam (RMS) to the olfactory bulb in a pattern similar to the ECM proteoglycan brevican. These data suggest that TIMP-3 and brevican may act in concert to guide neuronal migration along the RMS.

The role of matrix metalloproteinases in autoimmune damage to the central and peripheral nervous system

Members of the family of matrix metalloproteinases (MMPs) have been implicated in the pathogenesis of inflammatory demyelination. MMPs apparently mediate important steps in the genesis of inflammatory demyelination, such as cell migration, blood-brain/nerve barrier breakdown, demyelination, and cytokine activation. This review will highlight in vitro as well as in vivo findings, which support the importance of this group of proteases in the pathogenesis of inflammatory demyelinating disorders of the central and peripheral nervous system.

Interleukin-1 is a key regulator of matrix metalloproteinase-9 expression in human neurons in culture and following mouse brain trauma in vivo

An acute trauma to the CNS rapidly results in the upregulation of inflammatory cytokines that include interleukin-1 (IL-1). We report here that the levels of several matrix metalloproteinases (MMPs) are also elevated following a corticectomy trauma injury to the mouse CNS. The delayed upregulation of MMPs compared to that for IL-1 suggests the possibility that inflammatory cytokines regulate MMP production in CNS trauma. To resolve this, we developed a method to isolate and maintain highly enriched human fetal neurons or astrocytes in culture and examined the regulation by cytokines of the activity of a subgroup of MMPs, the gelatinases (MMP-2 and -9). While both neuronal and astrocytic cultures displayed comparable MMP-2 activity, as evidenced by gelatin zymography, levels of MMP-9 were proportionately higher in neurons compared to astrocytes. Of a variety of cytokines and growth factors tested in vitro, only IL-1beta was effective in increasing the neuronal expression of MMP-9. Finally, an IL-1 receptor antagonist attenuated the increase of neuronal MMP-9 in culture and abolished the injury-induced increase of MMP-9 in the mouse brain. These results implicate IL-1beta as a key regulator of neuronal MMP-9 in culture and of the elevation of MMP-9 that occurs following mouse CNS trauma.

Differential regulation of tissue inhibitor of metalloproteinase mRNA expression in response to intracranial injury

Injury to the CNS induces complex cellular and molecular interactions referred to as reactive gliosis. Alterations in the extracellular microenvironment associated with the gliotic response are believed to be the primary cause of regenerative failure of the mature CNS. For injured neurons to reestablish severed connections their processes must explore the extracellular milieu. Thus far, experiments have focused on extracellular matrix (ECM) proteins whose expression is upregulated after CNS injury and that exert inhibitory effects on neurite outgrowth. An intricate balance between ECM synthesis and degradation must be maintained during the tissue remodeling associated with injury. Matrix metalloproteinases (MMPs) are believed to be the main mediators of ECM degradation. MMP activity is tightly regulated by interaction with tissue inhibitors of metalloproteinases (TIMPs). To determine whether TIMPs are expressed during injury-induced matrix remodeling, TIMP expression was examined during reactive gliosis. A stab injury to the mature rat brain leads to the differential regulation of TIMP mRNA expression. Timp-1 and Timp-2 mRNA are significantly upregulated after injury, while the expression of Timp-3 and Timp-4 is unaltered. The expression of Timp-1 in reactive astrocytes and Timp-2 in microglia and neurons suggests these TIMPs may serve distinct functions in response to injury.

Developmental regulation of membrane type-5 matrix metalloproteinase (MT5-MMP) expression in the rat nervous system

An intricate balance between extracellular matrix (ECM) synthesis and degradation must be maintained during developmental tissue remodeling. Matrix metalloproteinases (MMPs) are the main mediators of ECM degradation. A subset of MMPs, referred to as membrane-type MMPs, contains a transmembrane domain that restricts protease activity at the cell surface. Membrane type-5 MMP is predominantly expressed in the brain. The present report is the first to demonstrate the temporal regulation and spatial distribution of MT5-MMP mRNA during nervous system development.

N-cadherin influences migration of oligodendrocytes on astrocyte monolayers

Oligodendrocyte cell migration is required for the development of the nervous system and the repopulation of demyelinated lesions in the adult central nervous system. We have investigated the role of the calcium-dependent adhesion molecules, the cadherins, in oligodendrocyte-astrocyte interaction and oligodendrocyte progenitor migration. Immunostaining demonstrated the expression of N-cadherin on the surfaces of both oligodendrocytes and astrocytes, and oligodendrocyte-like cells adhered to and spread on N-cadherin substrates. The blocking of cadherin function by antisera or specific peptides reduced adhesion of oligodendroglia to astrocyte monolayers, diminished contact time between oligodendrocyte processes and individual astrocytes, and significantly increased the migration of oligodendrocyte-like cells on astrocyte monolayers. Furthermore, a soluble cadherin molecule without adhesive properties increased oligodendroglial proliferation on various extracellular matrix substrates. These data suggest that cadherins are at least partially responsible for the poor migration-promoting properties of astrocytes and that decreasing cell-cell adhesion might effect repopulation of demyelinated multiple sclerosis lesions by oligodendrocyte progenitors.

Matrix metalloproteinase-9/gelatinase B is required for process outgrowth by oligodendrocytes

Oligodendrocytes (OLs) extend processes to contact axons as a prerequisite step in myelin formation. As the OL processes migrate toward their axonal targets, they modify adhesion to their substrate, an event that may be regulated by matrix metalloproteinases (MMPs). In the mouse optic nerve, MMP-9/gelatinase B increases during myelin formation. Although tissue inhibitor of metalloproteinase (TIMP)-3 also increases in parallel, the developing optic nerve has focally active MMPs demonstrable by in situ zymography. The distribution of proteolytic activity is similar to that of myelin basic protein, a marker of myelin formation. OLs in culture secrete MMP-9 and express active cell-associated metalloproteinases at the growing tips of their processes. TIMP-1 and a function-perturbing anti-MMP-9 antibody attenuate outgrowth of processes by OLs, indicating a requirement for MMP-9 in process outgrowth. Process reformation is retarded significantly in OLs cultured from MMP-9 null mice, as compared with controls, providing genetic evidence that MMP-9 is necessary for process outgrowth. These data show that MMP-9 facilitates process outgrowth by OLs in vivo and in culture.

The glial scar and central nervous system repair

Damage to the central nervous system (CNS) results in a glial reaction, leading eventually to the formation of a glial scar. In this environment, axon regeneration fails, and remyelination may also be unsuccessful. The glial reaction to injury recruits microglia, oligodendrocyte precursors, meningeal cells, astrocytes and stem cells. Damaged CNS also contains oligodendrocytes and myelin debris. Most of these cell types produce molecules that have been shown to be inhibitory to axon regeneration. Oligodendrocytes produce NI250, myelin-associated glycoprotein (MAG), and tenascin-R, oligodendrocyte precursors produce NG2 DSD-1/phosphacan and versican, astrocytes produce tenascin, brevican, and neurocan, and can be stimulated to produce NG2, meningeal cells produce NG2 and other proteoglycans, and activated microglia produce free radicals, nitric oxide, and arachidonic acid derivatives. Many of these molecules must participate in rendering the damaged CNS inhibitory for axon regeneration. Demyelinated plaques in multiple sclerosis consists mostly of scar-type astrocytes and naked axons. The extent to which the astrocytosis is responsible for blocking remyelination is not established, but astrocytes inhibit the migration of both oligodendrocyte precursors and Schwann cells which must restrict their access to demyelinated axons.

"...those left behind." Biology and oncology of invasive glioma cells

Although significant technical advances in surgical and radiation treatment for brain tumors have emerged in recent years, their impact on clinical outcome for patients has been disappointing. A fundamental source of the management challenge presented by glioma patients is the insidious propensity of the malignant cells to invade into adjacent normal brain. Invasive tumor cells escape surgical removal and geographically dodge lethal radiation exposure. Recent improved understanding of the biochemistry and molecular determinants of glioma cell invasion provide valuable insight to the underlying biological features of the disease, as well as illuminating possible new therapeutic targets. Heightened commitment to migrate and invade is accompanied by a glioma cell's reduced proliferative activity. The microenvironmental manipulations coincident to invasion and migration may also impact the glioma cell's response to cytotoxic treatments. These collateral aspects of the glioma cell invasive phenotype should be further explored and exploited as novel antiglioma therapies.

Cell-surface glycoprotein of oligodendrocyte progenitors involved in migration

Myelination by oligodendrocytes in the CNS involves the migration to and recognition and ensheathment of axons. These distinct developmental phases of myelination are assumed to involve the interplay of a precisely regulated set of cell adhesion molecules expressed by both neurons and glial cells. These molecules remain largely unelucidated. In this paper we have identified a large (330 kDa) glycoprotein expressed by murine oligodendrocyte progenitor cells in vitro and in vivo that is downregulated as oligodendrocytes mature. Antigen-positive oligodendrocyte progenitor cells purified by panning develop into myelin-associated glycoprotein-positive oligodendrocytes and also adhere to cultured neurons. Polyclonal antibodies directed against the protein reduce the migration of oligodendrocyte progenitor cells. The observations suggest that the AN2 antigen may play a role in early stages of myelination.

Matrix metalloproteinases and diseases of the CNS

Matrix metalloproteinases (MMPs) are increasingly being implicated in the pathogenesis of several CNS diseases. In multiple sclerosis, MMPs could be responsible for the influx of inflammatory mononuclear cells into the CNS, contribute to myelin destruction and disrupt the integrity of the blood-brain barrier; in Alzheimer's disease, MMPs might mediate the deposition of amyloid beta-proteins; and MMPs are known to contribute to the invasiveness of malignant glioma cells and might regulate their angiogenic capacity. Nonetheless, MMPs could also have beneficial roles in recovery from CNS injury.Therefore, both the identity of the MMP and its cellular origin could determine whether disease pathogenesis or regeneration occurs, and thus synthetic MMP inhibitors might be valuable for treating some CNS diseases.