Distinct roles for matrix metalloproteinase-2 and alpha4 integrin in autoimmune T cell extravasation and residency in brain parenchyma during experimental autoimmune encephalomyelitis

Alpha4 beta7 integrin controls Th17 cell trafficking in the spinal cord leptomeninges during experimental autoimmune encephalomyelitis

Th1 and Th17 cell migration into the central nervous system (CNS) is a fundamental process in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). Particularly, leptomeningeal vessels of the subarachnoid space (SAS) constitute a central route for T cell entry into the CNS during EAE. Once migrated into the SAS, T cells show an active motility behavior, which is a prerequisite for cell-cell communication, in situ reactivation and neuroinflammation. However, the molecular mechanisms selectively controlling Th1 and Th17 cell trafficking in the inflamed leptomeninges are not well understood. By using epifluorescence intravital microscopy, we obtained results showing that myelin-specific Th1 and Th17 cells have different intravascular adhesion capacity depending on the disease phase, with Th17 cells being more adhesive at disease peak. Inhibition of αLβ2 integrin selectively blocked Th1 cell adhesion, but had no effect on Th17 rolling and arrest capacity during all disease phases, suggesting that distinct adhesion mechanisms control the migration of key T cell populations involved in EAE induction. Blockade of α4 integrins affected myelin-specific Th1 cell rolling and arrest, but only selectively altered intravascular arrest of Th17 cells. Notably, selective α4β7 integrin blockade inhibited Th17 cell arrest without interfering with intravascular Th1 cell adhesion, suggesting that α4β7 integrin is predominantly involved in Th17 cell migration into the inflamed leptomeninges in EAE mice. Two-photon microscopy experiments showed that blockade of α4 integrin chain or α4β7 integrin selectively inhibited the locomotion of extravasated antigen-specific Th17 cells in the SAS, but had no effect on Th1 cell intratissue dynamics, further pointing to α4β7 integrin as key molecule in Th17 cell trafficking during EAE development. Finally, therapeutic inhibition of α4β7 integrin at disease onset by intrathecal injection of a blocking antibody attenuated clinical severity and reduced neuroinflammation, further demonstrating a crucial role for α4β7 integrin in driving Th17 cell-mediated disease pathogenesis. Altogether, our data suggest that a better knowledge of the molecular mechanisms controlling myelin-specific Th1 and Th17 cell trafficking during EAE delevopment may help to identify new therapeutic strategies for CNS inflammatory and demyelinating diseases.

Matrix Metalloproteinases: From Molecular Mechanisms to Physiology, Pathophysiology, and Pharmacology

The first matrix metalloproteinase (MMP) was discovered in 1962 from the tail of a tadpole by its ability to degrade collagen. As their name suggests, matrix metalloproteinases are proteases capable of remodeling the extracellular matrix. More recently, MMPs have been demonstrated to play numerous additional biologic roles in cell signaling, immune regulation, and transcriptional control, all of which are unrelated to the degradation of the extracellular matrix. In this review, we will present milestones and major discoveries of MMP research, including various clinical trials for the use of MMP inhibitors. We will discuss the reasons behind the failures of most MMP inhibitors for the treatment of cancer and inflammatory diseases. There are still misconceptions about the pathophysiological roles of MMPs and the best strategies to inhibit their detrimental functions. This review aims to discuss MMPs in preclinical models and human pathologies. We will discuss new biochemical tools to track their proteolytic activity in vivo and ex vivo, in addition to future pharmacological alternatives to inhibit their detrimental functions in diseases. SIGNIFICANCE STATEMENT: Matrix metalloproteinases (MMPs) have been implicated in most inflammatory, autoimmune, cancers, and pathogen-mediated diseases. Initially overlooked, MMP contributions can be both beneficial and detrimental in disease progression and resolution. Thousands of MMP substrates have been suggested, and a few hundred have been validated. After more than 60 years of MMP research, there remain intriguing enigmas to solve regarding their biological functions in diseases.

Dynamic changes of MMP-9 plasma levels correlate with JCV reactivation and immune activation in natalizumab-treated multiple sclerosis patients

The aim of the study was to investigate the changes of matrix metalloproteinase (MMP)-2 and MMP-9 plasma levels during natalizumab treatment and their correlation with JC virus (JCV) reactivation and T-lymphocyte phenotypic modifications in peripheral blood samples from 34 relapsing-remitting multiple sclerosis (RRMS) patients. MMP-9 levels were assessed by zymography in plasma samples. JCV-DNA was detected through quantitative real time PCR in plasma samples. T-lymphocyte phenotype was assessed with flow cytometry. MMP-9 plasma levels resulted increased from 12 to 24 natalizumab infusions. Stratifying plasma samples according to JCV-DNA detection, MMP-9 plasma levels were significantly increased in JCV-DNA positive than JCV-DNA negative samples. MMP-9 plasma levels resulted positively correlated with JCV viral load. CD4 immune senescence, CD8 immune activation and CD8 effector percentages were positively correlated to MMP-9 plasma levels, whereas a negative correlation between CD8 naïve percentages and MMP-9 plasma levels was found. Our data indicate an increase of MMP-9 plasma levels between 12 and 24 natalizumab infusions and a correlation with JCV-DNA detection in plasma, T-lymphocyte immune activation and senescence. These findings could contribute to understand PML pathogenesis under natalizumab treatment, suggesting a potential role of MMP-9 as a predictive marker of PML in RRMS patients.

Decreased expression of MMP-9 in CD8+ cells in placenta with severe preeclampsia

We compared the number of CD4-positive (CD4⁺) and CD8-positive (CD8⁺) cells in severe and non-severe preeclampsia (PE), and in normal pregnancy. We also evaluated the expression of matrix metalloproteinase 9 (MMP-9) in CD4⁺ and CD8⁺ cells. Immunohistochemistry for CD4⁺ and CD8⁺ was performed on the decidua basalis of 15 severe and 13 non-severe PE women and compared to decidual tissue of 19 normal pregnancies (control group). Co-expression of MMP-9 with CD8⁺ and CD4⁺ cells was determined by double immunofluorescence staining. The median number of CD8⁺ cells/mm² was significantly lower for the severe PE group than for the normal pregnancy group, as was the number of CD4⁺ cells and MMP-9⁺CD8⁺ cells. No statistical difference was found between the non-severe PE group and the normal pregnancy group. The significant decrease of CD4⁺, CD8⁺ and MMP-9⁺CD8⁺ cells at the fetal-maternal interface only in the severe PE group suggests that immunological disorders play a role in the pathophysiology of severe PE.

Matrix metalloproteinases in the brain and blood-brain barrier: Versatile breakers and makers

Matrix metalloproteinases are versatile endopeptidases with many different functions in the body in health and disease. In the brain, matrix metalloproteinases are critical for tissue formation, neuronal network remodeling, and blood-brain barrier integrity. Many reviews have been published on matrix metalloproteinases before, most of which focus on the two best studied matrix metalloproteinases, the gelatinases MMP-2 and MMP-9, and their role in one or two diseases. In this review, we provide a broad overview of the role various matrix metalloproteinases play in brain disorders. We summarize and review current knowledge and understanding of matrix metalloproteinases in the brain and at the blood-brain barrier in neuroinflammation, multiple sclerosis, cerebral aneurysms, stroke, epilepsy, Alzheimer's disease, Parkinson's disease, and brain cancer. We discuss the detrimental effects matrix metalloproteinases can have in these conditions, contributing to blood-brain barrier leakage, neuroinflammation, neurotoxicity, demyelination, tumor angiogenesis, and cancer metastasis. We also discuss the beneficial role matrix metalloproteinases can play in neuroprotection and anti-inflammation. Finally, we address matrix metalloproteinases as potential therapeutic targets. Together, in this comprehensive review, we summarize current understanding and knowledge of matrix metalloproteinases in the brain and at the blood-brain barrier in brain disorders.

Analysis of MMP2-1306C/T and TIMP2G-418C polymorphisms with relapsing remitting multiple sclerosis

AIMS

Multiple sclerosis (MS) is an autoimmune, inflammatory disease characterized by loss of myelin forming oligodendrocytes and changes in the blood-brain barrier. Matrix metalloproteinase (MMP) -2 and -9 are known to cause disruption of the blood-brain barrier, remodeling of the basal lamina, regeneration of axons, and remyelination in MS. The imbalance between MMPs and tissue inhibitor metalloproteinases (TIMPs) may lead to the emergence of pathological processes such as MS. The roles of MMP2-1306 C/T and TIMP2-418 G/C genetic variants in MS have not been studied before. We aimed to investigate whether MMP2-1306C/T and TIMP2-418 G/C gene variants are risk factors for patients with relapsing remitting multiple sclerosis (RRMS).

METHODS

The study included 102 RRMS and 102 healthy controls. Genomic DNA was extracted from peripheral leukocytes from ethylenediaminetetraacetic acid anticoagulated blood. Genotyping of the MMP2-1306C/T and TIMP2G-418C polymorphisms was performed using real-time PCR.

RESULTS

There were significant differences in terms of distribution of genotype (MMP2-1306- CT, TT) and T allele frequency between the patients with RRMS and the control group (p<0.0001; p<0.0001). The groups were not different in terms of TIMP2G-418C polymorphisms.

CONCLUSIONS

In the RRMS group, the genotype and allele frequencies of MMP2-1306C/T polymorphism showed significant differences from the controls. These results indicate that MMP2 might play a role in the pathogenesis of MS even during the inflammation stage.

Rational design of antirheumatic prodrugs specific for sites of inflammation

Objective

Biologic drugs, such as the anti–tumor necrosis factor (anti‐TNF) antibody adalimumab, have represented a breakthrough in the treatment of rheumatoid arthritis. Yet, concerns remain over their lack of efficacy in a sizable proportion of patients and their potential for systemic side effects such as infection. Improved biologic prodrugs specifically targeted to the site of inflammation have the potential to alleviate current concerns surrounding biologic anticytokine therapies. The purpose of this study was to design, construct, and evaluate in vitro and ex vivo the targeting and antiinflammatory capacity of activatable bispecific antibodies.

Methods

Activatable dual variable domain (aDVD) antibodies were designed and constructed to target intercellular adhesion molecule 1 (ICAM‐1), which is up‐regulated at sites of inflammation, and anti‐TNF antibodies (adalimumab and infliximab). These bispecific molecules included an external arm that targets ICAM‐1 and an internal arm that comprises the therapeutic domain of an anti‐TNF antibody. Both arms were linked to matrix metalloproteinase (MMP)–cleavable linkers. The constructs were tested for their ability to bind and neutralize both in vitro and ex vivo targets.

Results

Intact aDVD constructs demonstrated significantly reduced binding and anti‐TNF activity in the prodrug formulation as compared to the parent antibodies. Human synovial fluid and physiologic concentrations of MMP enzyme were capable of cleaving the external domain of the antibody, revealing a fully active molecule. Activated antibodies retained the same binding and anti‐TNF inhibitory capacities as the parent molecules.

Conclusion

The design of a biologic prodrug with enhanced specificity for sites of inflammation (synovium) and reduced specificity for off‐target TNF is described. This construct has the potential to form a platform technology that is capable of enhancing the therapeutic index of drugs for the treatment of RA and other inflammatory diseases.

Effect of aqueous extract of Achillea millefolium on the development of experimental autoimmune encephalomyelitis in C57BL/6 mice

Objective:

Achillea millefolium (A. millefolium) is widely used as an anti-inflammatory remedy in traditional and herbal medicine. In this study, we investigated the effect of an aqueous extract from A. millefolium on experimental autoimmune encephalomyelitis (EAE) and on the serum cytokine levels in C57BL/6 mice.

Materials and Methods:

EAE was induced in 63 C57BL/6 mice weighing 20-25 g (8 weeks old). Following immunization, the treatment protocol was initiated by using different doses of an aqueous extract from A. millefolium (1, 5, and 10 mg/mouse/day). Histopathologic assessments were performed by hematoxylin and eosin (H and E) and luxol fast blue (LFB) staining. Behavioral disabilities were recorded by a camera. Serum levels of interleukin (IL)-10, IL-12, and transforming growth factor (TGF)-β were measured using enzyme-linked immunosorbent assay (ELISA).

Results:

On average, mice developed classical behavioral disabilities of EAE, 13.2 ± 1.9 days following immunization. Treatment of mice with A. millefolium led to delay the appearance of behavioral disabilities along with reduced severity of the behavioral disabilities. Treatment with A. millefolium prevented weight loss and increased serum levels of TGF-β in immunized mice with MOG35-55. EAE-induced mice, which were treated with A. millefolium, had less cerebral infiltration of inflammatory cells.

Conclusion:

The results demonstrated that treatment with aqueous extract of A. millefolium may attenuate disease severity, inflammatory responses, and demyelinating lesions in EAE-induced mice. In addition, following treatment with A. millefolium, serum levels of TGF-βwere increased in EAE-induced mice.

Matrix metalloproteinases in inflammation

BACKGROUND

Matrix metalloproteinases (MMPs) are a family of ubiquitously expressed zinc-dependent endopeptidases with broad substrate specificity and strictly regulated tissue specific expression. They are expressed in physiological situations and pathological conditions involving inflammation. MMPs regulate several functions related to inflammation including bioavailability and activity of inflammatory cytokines and chemokines. There is also evidence that MMPs regulate inflammation in tumor microenvironment, which plays an important role in cancer progression.

SCOPE OF REVIEW

Here, we discuss the current view on the role of MMPs in the regulation of inflammation.

MAJOR CONCLUSIONS

MMPs modulate inflammation by regulating bioavailability and activity of cytokines, chemokines, and growth factors, as well as integrity of physical tissue barriers. MMPs are also involved in immune evasion of tumor cells and in regulation of inflammation in tumor microenvironment.

GENERAL SIGNIFICANCE

There is increasing evidence for non-matrix substrates of MMPs that are related to regulation of inflammatory processes. New methods have been employed for identification of the substrates of MMPs in inflammatory processes in vivo. Detailed information on the substrates of MMPs may offer more specific and effective ways of inhibiting MMP function by blocking the cleavage site in substrate or by inhibition of the bioactivity of the substrate. It is expected, that more precise information on the MMP-substrate interaction may offer novel strategies for therapeutic intervention in inflammatory diseases and cancer without blocking beneficial actions of MMPs. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

A mushroom extract Piwep from Phellinus igniarius ameliorates experimental autoimmune encephalomyelitis by inhibiting immune cell infiltration in the spinal cord

The present study aimed to evaluate the therapeutic potential of a mushroom extract from Phellinus igniarius in an animal model of multiple sclerosis. The medicinal mushroom, Phellinus igniarius, contains biologically active compounds that modulate the human immune system. Experimental autoimmune encephalomyelitis (EAE) was induced by immunization with myelin oligodendrocyte glycoprotein (MOG 35-55) in C57BL/6 female mice. A water-ethanol extract of Phellinus igniarius (Piwep) was delivered intraperitoneally every other day for the entire experimental course. Three weeks after the initial immunization, demyelination and immune cell infiltration in the spinal cord were examined. Piwep injection profoundly decreased the daily incidence rate and clinical score of EAE. The Piwep-mediated inhibition of the clinical course of EAE was accompanied by suppression of demyelination and infiltration of encephalitogenic immune cells including CD4+ T cells, CD8+ T cells, macrophages, and B cells in the spinal cord. Piwep reduced expression of vascular cell adhesion molecule-1 (VCAM-1) in the spinal cord and integrin-α 4 in the lymph node of EAE mice. Piwep also inhibited proliferation of lymphocytes and secretion of interferon-γ in the lymph node of EAE mice. The results suggest that a mushroom extract, Piwep, may have a high therapeutic potential for ameliorating multiple sclerosis progression.

The significance of matrix metalloproteinases in the immunopathogenesis and treatment of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS). The major pathological outcomes of the disease are the loss of blood-brain barrier (BBB) integrity and the development of reactive astrogliosis and MS plaque. For the disease to occur, the non-resident cells must enter into the immune-privileged CNS through a breach in the relatively impermeable BBB. It has been demonstrated that matrix metalloproteinases (MMPs) play an important role in the immunopathogenesis of MS, in part through the disruption of the BBB and the recruitment of inflammatory cells into the CNS. Moreover, MMPs can also enhance the cleavage of myelin basic protein (MBP) and the demyelination process. Regarding the growing data on the roles of MMPs and their tissue inhibitors (TIMPs) in the pathogenesis of MS, this review discusses the role of different types of MMPs, including MMP-2, -3, -7, -9, -12 and -25, in the immunopathogenesis and treatment of MS.

Pyruvate administration reduces recurrent/moderate hypoglycemia-induced cortical neuron death in diabetic rats

Recurrent/moderate (R/M) hypoglycemia is common in type 1 diabetes patients. Moderate hypoglycemia is not life-threatening, but if experienced recurrently it may present several clinical complications. Activated PARP-1 consumes cytosolic NAD, and because NAD is required for glycolysis, hypoglycemia-induced PARP-1 activation may render cells unable to use glucose even when glucose availability is restored. Pyruvate, however, can be metabolized in the absence of cytosolic NAD. We therefore hypothesized that pyruvate may be able to improve the outcome in diabetic rats subjected to insulin-induced R/M hypoglycemia by terminating hypoglycemia with glucose plus pyruvate, as compared with delivering just glucose alone. In an effort to mimic juvenile type 1 diabetes the experiments were conducted in one-month-old young rats that were rendered diabetic by streptozotocin (STZ, 50mg/kg, i.p.) injection. One week after STZ injection, rats were subjected to moderate hypoglycemia by insulin injection (10U/kg, i.p.) without anesthesia for five consecutive days. Pyruvate (500mg/kg) was given by intraperitoneal injection after each R/M hypoglycemia. Three hours after last R/M hypoglycemia, zinc accumulation was evaluated. Three days after R/M hypoglycemia, neuronal death, oxidative stress, microglial activation and GSH concentrations in the cerebral cortex were analyzed. Sparse neuronal death was observed in the cortex. Zinc accumulation, oxidative injury, microglial activation and GSH loss in the cortex after R/M hypoglycemia were all reduced by pyruvate injection. These findings suggest that when delivered alongside glucose, pyruvate may significantly improve the outcome after R/M hypoglycemia by circumventing a sustained impairment in neuronal glucose utilization resulting from PARP-1 activation.

VCAM-1-targeted magnetic resonance imaging reveals subclinical disease in a mouse model of multiple sclerosis

Diagnosis of multiple sclerosis (MS) currently requires lesion identification by gadolinium (Gd)-enhanced or T(2)-weighted magnetic resonance imaging (MRI). However, these methods only identify late-stage pathology associated with blood-brain barrier breakdown. There is a growing belief that more widespread, but currently undetectable, pathology is present in the MS brain. We have previously demonstrated that an anti-VCAM-1 antibody conjugated to microparticles of iron oxide (VCAM-MPIO) enables in vivo detection of VCAM-1 by MRI. Here, in an experimental autoimmune encephalomyelitis (EAE) mouse model of MS, we have shown that presymptomatic lesions can be quantified using VCAM-MPIO when they are undetectable by Gd-enhancing MRI. Moreover, in symptomatic animals VCAM-MPIO binding was present in all regions showing Gd-DTPA enhancement and also in areas of no Gd-DTPA enhancement, which were confirmed histologically to be regions of leukocyte infiltration. VCAM-MPIO binding correlated significantly with increasing disability. Negligible MPIO-induced contrast was found in either EAE animals injected with an equivalent nontargeted contrast agent (IgG-MPIO) or in control animals injected with the VCAM-MPIO. These findings describe a highly sensitive molecular imaging tool that may enable detection of currently invisible pathology in MS, thus accelerating diagnosis, guiding treatment, and enabling quantitative disease assessment.

How do immune cells overcome the blood-brain barrier in multiple sclerosis?

The presence of the blood-brain barrier (BBB) restricts the movement of soluble mediators and leukocytes from the periphery to the central nervous system (CNS). Leukocyte entry into the CNS is nonetheless an early event in multiple sclerosis (MS), an inflammatory disorder of the CNS. Whether BBB dysfunction precedes immune cell infiltration or is the consequence of perivascular leukocyte accumulation remains enigmatic, but leukocyte migration modifies BBB permeability. Immune cells of MS subjects express inflammatory cytokines, reactive oxygen species (ROS) and enzymes that can facilitate their migration to the CNS by influencing BBB function, either directly or indirectly. In this review, we describe how immune cells from the peripheral blood overcome the BBB and promote CNS inflammation in MS through BBB disruption.

Endogenous matrix metalloproteinases 2 and 9 regulate activation of CD4+ and CD8+ T cells

We reported that inhibiting matrix metalloproteinases (MMP), known to remodel the extracellular matrix, also down-regulated antigen-specific T-cell responses. However, the direct role of MMP2 and MMP9 in regulating intracellular function in T cells is unknown. Markers of cellular activation and cytokine profiles were examined in anti-CD3-stimulated wild-type C57BL/6 mouse-derived CD4(+) or CD8(+) T cells, or MMP2- or MMP9-deficient (-/-) mice. MMP-sufficient T cells were also treated with SB-3CT, a highly selective inhibitor of MMP2 and MMP9. The effect of MMP-specific inhibition on T cell-dependent, antigen-specific murine lung injury was examined in vivo. SB-3CT induced dose-dependent reductions in anti-CD3-stimulated T-cell proliferation. Although MMP2(-/-) cells were reduced 20%, anti-CD3-induced proliferation was down-regulated 80-85% in MMP9(-/-) or in SB-3CT-treated wild-type CD4(+) and CD8(+) T cells. Intracellular calcium flux was augmented in response to MMP inhibition or deficiency in the same cells, and IL-2 production was reduced in CD4(+) and CD8(+) MMP9(-/-) T cells. SB-3CT-mediated MMP2 and MMP9 inhibition abrogated antigen-specific CD8(+) T cell-mediated lung injury in vivo. MMPs, particularly MMP9, may function intracellularly to regulate T-cell activation. T cell-targeted MMP inhibition may provide a novel approach of immune regulation in the treatment of T cell-mediated diseases.

Disruption of central nervous system barriers in multiple sclerosis

The delicate microenvironment of the central nervous system (CNS) is protected by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCB). These barriers function in distinct CNS compartments and their anatomical basis lay on the junctional proteins present in endothelial cells for the BBB and in the choroidal epithelium for the BCB. During neuroinflammatory conditions like multiple sclerosis (MS) and its murine model experimental autoimmune encephalomyelitis (EAE), activation or damage of the various cellular components of these barriers facilitate leukocyte infiltration leading to oligodendrocyte death, axonal damage, demyelination and lesion development. This manuscript will review in detail the features of these barriers under physiological and pathological conditions, particularly when focal immune activation promotes the loss of the BBB and BCB phenotype, the upregulation of cell adhesion molecules (CAMs) and the recruitment of immune cells.

The blood-brain and the blood-cerebrospinal fluid barriers: function and dysfunction

The central nervous system (CNS) is tightly sealed from the changeable milieu of blood by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier (BCSFB). While the BBB is considered to be localized at the level of the endothelial cells within CNS microvessels, the BCSFB is established by choroid plexus epithelial cells. The BBB inhibits the free paracellular diffusion of water-soluble molecules by an elaborate network of complex tight junctions (TJs) that interconnects the endothelial cells. Combined with the absence of fenestrae and an extremely low pinocytotic activity, which inhibit transcellular passage of molecules across the barrier, these morphological peculiarities establish the physical permeability barrier of the BBB. In addition, a functional BBB is manifested by a number of permanently active transport mechanisms, specifically expressed by brain capillary endothelial cells that ensure the transport of nutrients into the CNS and exclusion of blood-borne molecules that could be detrimental to the milieu required for neural transmission. Finally, while the endothelial cells constitute the physical and metabolic barrier per se, interactions with adjacent cellular and acellular layers are prerequisites for barrier function. The fully differentiated BBB consists of a complex system comprising the highly specialized endothelial cells and their underlying basement membrane in which a large number of pericytes are embedded, perivascular antigen-presenting cells, and an ensheathment of astrocytic endfeet and associated parenchymal basement membrane. Endothelial cell morphology, biochemistry, and function thus make these brain microvascular endothelial cells unique and distinguishable from all other endothelial cells in the body. Similar to the endothelial barrier, the morphological correlate of the BCSFB is found at the level of unique apical tight junctions between the choroid plexus epithelial cells inhibiting paracellular diffusion of water-soluble molecules across this barrier. Besides its barrier function, choroid plexus epithelial cells have a secretory function and produce the CSF. The barrier and secretory function of the choroid plexus epithelial cells are maintained by the expression of numerous transport systems allowing the directed transport of ions and nutrients into the CSF and the removal of toxic agents out of the CSF. In the event of CNS pathology, barrier characteristics of the blood-CNS barriers are altered, leading to edema formation and recruitment of inflammatory cells into the CNS. In this review we will describe current knowledge on the cellular and molecular basis of the functional and dysfunctional blood-CNS barriers with focus on CNS autoimmune inflammation.

Role of the extracellular matrix in lymphocyte migration

The extracellular matrix (ECM) exists in various biochemical and structural forms that can act either as a barrier to migrating leukocytes, in the case of basement membranes, or provide a physical scaffold supporting or guiding migration (interstitial matrix). This review focuses on basement membranes and our current knowledge of the way that leukocytes transmigrate this protein barrier, with emphasis on T lymphocytes. Recent data suggest that the classical concept of cell-matrix adhesion requires revision with respect to leukocyte-ECM interactions. Whereas specific receptors may be required for leukocyte recognition of ECM molecules or three-dimensional structural domains, the role of adhesion in migration as perceived from the traditional studies of adherent cell-ECM interactions is less clear. Further, the indirect effects of ECM such as the binding and presentation of cytokines or chemotactic factors may more profoundly influence the directed migration of normally non-adherent leukocytes than the migration of adherent cells such as epithelial cells or fibroblasts. Proteases (in particular matrix metalloproteinases) released at sites of inflammation can selectively process ECM, cell surface molecules or soluble factors, which may result in the release of bioactive fragments that can function as chemoattractants for different leukocyte subsets or may modulate the activity/function of resident mesenchymal and immune cells. Current findings suggest that different leukocyte types employ different mechanisms to migrate across or through the ECM; this might be determined by the composition and organization of the ECM itself.

Differential effects of shear stress and cyclic strain on Sp1 phosphorylation by protein kinase Czeta modulates membrane type 1-matrix metalloproteinase in endothelial cells

Membrane type 1-matrix metalloproteinase (MT1-MMP) plays a key role in extracellular matrix remodeling, endothelial cell (EC) migration, and angiogenesis. Whereas cyclic strain (CS) increases MT1-MMP expression, shear stress (SS) decreases MT1-MMP expression. The aim of this study was to determine if changes in levels of Sp1 phosphorylation induced by protein kinase Czeta (PKCzeta) in ECs exposed to SS but not CS are important for MT1-MMP expression. The results showed that SS increased Sp1 phosphorylation, which could be inhibited by pretreatment with PKCzeta inhibitors. In the presence of PKCzeta inhibitors, the SS-mediated decrease in MT1-MMP protein expression was also abolished. These data demonstrate that increased affinity of Sp1 for MT1-MMP's promoter site occurs as a consequence of PKCzeta-induced phosphorylation of Sp1 in response to SS, increasing Sp1 binding affinity for the promoter site, preventing Egr-1 binding, and consequently decreasing MT1-MMP expression.

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.

Characterization of key mechanisms in transmigration and invasion of mesenchymal stem cells

For successful systemic stem cell therapy, mesenchymal stem cells (MSCs) must transmigrate across the endothelium and invade their target tissue. To date, most of the underlying mechanisms of transmigration and invasion remain to be elucidated. Improving our knowledge on these core processes might elevate the efficiency of stem cell therapy. Our aim was therefore to characterize key mechanisms involved in transmigration and invasion of MSCs. Co-cultivation experiments infer that MSCs integrate into the endothelial monolayer. However, the time course of adhesion, integration and transmigration depends on the endothelial phenotype and is most effective in venous vessels of the myocardium. Thus, a variable capacity for transmigration exists within the vasculature. Additionally, three-dimensional systems reveal that MSCs penetrate the endothelium and invade the surrounding tissue via plasmic podia. Furthermore, transmigration not only requires the interaction of vascular cell adhesion molecule-1 (VCAM-1) and very late antigen-4 (VLA-4) as verified by blocking experiments, but also triggers the clustering of beta1 integrins. In addition, in situ zymographies infer the activation of gelatinases at sites of MSC invasion into myocardial tissue. As evidenced by ELISA, MSCs secrete matrix metalloproteinase (MMP)-2 but not MMP-9. Finally, media containing additional cytokines accelerate the transmigration. Concluding, key players involved in transmigration and invasion of MSCs are the endothelial phenotype, VCAM-1/VLA-4, beta1 integrins, MMP-2 secretion and cytokines.

Enhanced allograft survival and modulation of T-cell alloreactivity induced by inhibition of MMP/ADAM enzymatic activity

Recent studies have shown significantly increased expression of matrix metalloproteinases (MMP) and disintegrin-type metalloproteinases (ADAM) during allograft rejection. In this regard, our previous studies have demonstrated contrasting roles for MMP-2 and MMP-9 during allograft rejection: MMP-2-deficiency enhanced allograft survival while MMP-9-deficiency decreased allograft survival. The aim of this study was to determine the effect of broad-spectrum MMP/ADAM inhibition on the pathogenesis of allograft rejection. Toward this, heterotopic BALB/c cardiac allografts were transplanted into C57BL/6 recipients treated with MMP/ADAM inhibitors, GM6001 or doxycycline. Systemic MMP/ADAM inhibition significantly enhanced allograft survival. Functioning allografts recovered from MMP/ADAM inhibitor-treated recipients showed lower cellular infiltration and tissue remodeling than rejected allografts recovered from control recipients. In addition, decreased chemotaxis of CD4+ and CD8+ T cells, B cells and macrophages was observed in vitro in the presence of MMP/ADAM inhibitors. Enhanced T-cell alloreactivity was also observed ex vivo in MMP/ADAM inhibitor-treated recipients and in vitro in the presence of MMP/ADAM inhibitors. These observations were associated with enhanced cytokine, chemokine and growth factor production. These results indicate that MMPs and ADAMs play a critical role in the pathogenesis of allograft rejection and may represent novel therapeutic targets for the treatment and/or prevention of this disease.

Cleavage of myelin associated glycoprotein by matrix metalloproteinases

Derivative myelin associated glycoprotein (dMAG) results from proteolysis of transmembrane MAG and can inhibit axonal growth. We have tested the ability of certain matrix metalloproteinases (MMPs) elevated with inflammatory and demyelinating diseases to cleave MAG. We show MMP-2, MMP-7 and MMP-9, but not MMP-1, cleave recombinant human MAG. Cleavage by MMP-7 occurs at Leu 509, just distal to the transmembrane domain and, to a lesser extent, at Met 234. We also show that MMP-7 cleaves MAG expressed on the external surface of CHO cells, releasing fragments that accumulate in the medium over periods of up to 48 h or more and that are able to inhibit outgrowth by dorsal root ganglion (DRG) neurons. We conclude that MMPs may have the potential both to disrupt MAG dependent axon-glia communication and to generate bioactive fragments that can inhibit neurite growth.

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.

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.

Multiple sclerosis: a battle between destruction and repair

Multiple sclerosis (MS) is a chronic neurodegenerative disease of the CNS in which an unrelenting attack from the innate and adaptive arms of the immune system results in extensive demyelination, loss of oligodendrocytes and axonal degeneration. This review summarizes advances in the understanding of the cellular and molecular pathways involved in neurodegeneration following autoimmune-mediated inflammation in the CNS. The mechanisms underlying myelin and axonal destruction and the equally important interaction between degenerative and repair mechanisms are discussed. Recent studies have revealed that the failure of CNS regeneration may be in part a result of the presence of myelin-associated growth inhibitory molecules in MS lesions. Successful therapeutic intervention in MS is likely to require suppression of the inflammatory response, in concert with blockade of growth inhibitory molecules and possibly the mobilization or transplantation of stem cells for regeneration.

Region-specific regulation of inflammation and pathogenesis in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis and is characterized by an infiltrate of predominantly T cells and macrophages in the spinal cord and brain. In both the spinal cord and the cerebellum, Th1 cells direct inflammation to antigen-rich white matter tracts, and there is a TNFR1-dependent recruitment of CD11b(hi) cells in both regions. In the spinal cord, parenchymal invasion, demyelination and clinical symptoms are associated with TNFR1-dependant parenchymal induction (especially astrocytes) of VCAM-1 and CXCL2. None of these events occur in the cerebellum despite the fact that an inflammatory infiltrate accumulates in the perivascular space. Therefore regional specificity in astrocyte responses to inflammatory cytokines may regulate regional parenchymal infiltration and pathogenesis.

Reevaluation of P-selectin and alpha 4 integrin as targets for the treatment of experimental autoimmune encephalomyelitis

There has been a great deal of interest in adhesion molecules as targets for the treatment of multiple sclerosis and other inflammatory diseases. In this study, we systematically evaluate alpha(4) integrin and P-selectin as targets for therapy in murine models of multiple sclerosis-for the first time directly measuring the ability of their blockade to inhibit recruitment and relate this to clinical efficacy. Experimental autoimmune encephalomyelitis was induced in C57BL/6 or SJL/J mice and intravital microscopy was used to quantify leukocyte interactions within the CNS microvasculature. In both strains, pretreatment with blocking Abs to either alpha(4) integrin or P-selectin reduced firm adhesion to a similar extent, but did not block it completely. The combination of the Abs was more effective than either Ab alone, although the degree of improvement was more evident in SJL/J mice. Similarly, dual blockade was much more effective at preventing the subsequent accumulation of fluorescently labeled leukocytes in the tissue in both strains. Despite evidence of blockade of leukocyte recruitment mechanisms, no clinical benefit was observed with anti-adhesion molecule treatments or genetic deletion of P-selectin in the C57BL/6 model, or in a pertussis toxin-modified model in SJL/J mice. In contrast, Abs to alpha(4) integrin resulted in a significant delay in the onset of clinical signs of disease in the standard SJL/J model. Despite evidence of a similar ability to block firm adhesion, Abs to P-selectin had no effect. Importantly, combined blockade of both adhesion molecules resulted in significantly better clinical outcome than anti-alpha(4) integrin alone.

Successful ovulation in plasminogen-deficient mice treated with the broad-spectrum matrix metalloproteinase inhibitor galardin

Many studies have suggested the hypothesis that the plasminogen activator (PA) system and the matrix metalloproteinase (MMP) system, either separately or in combination, may provide the proteolytic activity that is required for rupture of the follicular wall at the time of ovulation. Our recent studies on ovulation in plasminogen (plg)-deficient mice have, however, shown that plasmin is not required for normal ovulation, leading us to the hypothesis that MMPs may be a more important source of proteolysis for this process. To investigate the role of MMPs and also the possibility of a functional overlap or synergy between the MMP and PA systems during ovulation, we have studied ovulation efficiency in wild-type and plg-deficient mice treated with the broad-spectrum MMP inhibitor galardin. We found that in both wild-type mice and heterozygous plg-deficient (plg+/-) mice that had been treated with galardin prior to ovulation, there was a mild (18-20%) reduction in ovulation efficiency. Surprisingly, galardin treatment of plg-deficient (plg-/-) mice only caused an additional 14% reduction in ovulation efficiency as compared to vehicle-treated plg-/- mice. Our data therefore suggest that although MMPs may play a role in degradation of the follicular wall, they may not be obligatory for ovulation. In contrast to previous studies on tissue remodeling during wound healing and placental development, we have demonstrated that there is no obvious functional overlap or synergy between the PA and MMP systems, which has previously been thought to be essential for the ovulatory process.

Dystroglycan is selectively cleaved at the parenchymal basement membrane at sites of leukocyte extravasation in experimental autoimmune encephalomyelitis

The endothelial cell monolayer of cerebral vessels and its basement membrane (BM) are ensheathed by the astrocyte endfeet, the leptomeningeal cells, and their associated parenchymal BM, all of which contribute to establishment of the blood-brain barrier (BBB). As a consequence of this unique structure, leukocyte penetration of cerebral vessels is a multistep event. In mouse experimental autoimmune encephalomyelitis (EAE), a widely used central nervous system inflammatory model, leukocytes first penetrate the endothelial cell monolayer and underlying BM using integrin beta1-mediated processes, but mechanisms used to penetrate the second barrier defined by the parenchymal BM and glia limitans remain uninvestigated. We show here that macrophage-derived gelatinase (matrix metalloproteinase [MMP]-2 and MMP-9) activity is crucial for leukocyte penetration of the parenchymal BM. Dystroglycan, a transmembrane receptor that anchors astrocyte endfeet to the parenchymal BM via high affinity interactions with laminins 1 and 2, perlecan and agrin, is identified as a specific substrate of MMP-2 and MMP-9. Ablation of both MMP-2 and MMP-9 in double knockout mice confers resistance to EAE by inhibiting dystroglycan cleavage and preventing leukocyte infiltration. This is the first description of selective in situ proteolytic damage of a BBB-specific molecule at sites of leukocyte infiltration.

Matrix metalloproteinase-2 (MMP-2) regulates astrocyte motility in connection with the actin cytoskeleton and integrins

Matrix Metalloproteinases (MMPs) play a role in migration of many cell types outside the central nervous system (CNS). Among neural cells, astrocytes are one of the main sources of MMPs in physiological and postlesional conditions. However, no data are available on the possible role of MMPs in astrocyte motility. Using an in vitro model of 2D migration and broad spectrum and selective MMP inhibitors, the authors demonstrated that MMP-2, but not MMP-9, is a key enzyme for astrocyte migration. In support of these data, the authors found constitutive expression of MMP-2 in astrocytes, while MMP-9 was nearly undetectable by gel zymography and immunocytochemical methods. The inhibition of migration by MMP inhibitors correlated with changes in cell morphology and in the organization of the actin cytoskeleton. In parallel, the characteristic focalized distribution of MMP-2 at the migration front observed in control cells became more diffuse and internalized by treatments that inhibited migration. The disruption of actin by cytochalasin D caused the partial recruitment of MMP-2 and gelatinolytic activity into actin aggregates, indicating a connection between the proteinase and the actin cytoskeleton. Finally, the authors found a co-localization of beta1-integrin with MMP-2 at the leading edge of migrating astrocytes. Altogether, these data provide the first evidence for the implication of MMP-2 in astrocyte motility, probably through the interaction of the proteinase with beta1-integrin that could act as a linker between pericellular proteolysis and the actin cytoskeleton.

Developing therapeutics for the treatment of multiple sclerosis

Multiple sclerosis (MS) is both a complex and chronic neurological disease of the CNS. This poses unique challenges for drug discovery in terms of delineating specific targets related to disease mechanisms and developing safe and effective molecules for clinical application. Preclinical animal models of MS provide the necessary test bed for evaluating the effects of novel therapeutic strategies. Because the clinical manifestations and pathological consequences of disease vary dramatically from individual to individual, as well as treatment response to existing therapies, this creates a significant research endeavor in terms of translating preclinical methodologies to the clinical domain. Potentially exciting treatments have emerged in the form of natalizumab (Tysabri), an alpha4 integrin antagonist, and more recently FTY720, a sphinogosine-1 phosphate receptor modulator, providing a compelling proof-of-principle from bench to bedside. However, further research is required to discharge safety concerns associated with these therapeutic avenues. Future prospects in the guise of disease-modifying therapies that target the inflammatory and neurodegenerative components of disease have come to the forefront of preclinical research with the sole aim of reducing the underlying irreversible progressive disability of MS. Significant progress with novel therapies will be made by implementing biomarker strategies that extrapolate robustly from animal models to the divergent patient populations of MS. The future therapeutic options for MS will depend on improvements in understanding the precise factors involved in disease onset and progression and subsequently the development of oral therapeutics that translate sustained benefit from the preclinical context into clinical reality.

Interaction between the immune and central nervous systems

Much of the understanding of tolerance has focused on the requirements for antigen-specific lymphocyte activation and function. However, there is increasing evidence for anatomic regulation of effector access to self antigens. Recently, a number of studies have provided evidence for tissue-specific "addressins" in chemokine/chemokine receptor pairs. The central nervous system (CNS) provides special anatomic barriers to the movement of cells from the vascular compartment to the parenchyma. Herein I raise the possibility that antigen, perhaps through specialized antigen-presenting cells, may play a role in regulating access of activated lymphocytes into the CNS parenchyma. The results suggest that a reexamination of the widely held dogma that all activated lymphocytes have access to the CNS parenchyma is necessary to understand the relationship between the immune and central nervous systems.

Defining antigen-dependent stages of T cell migration from the blood to the central nervous system parenchyma

In experimental autoimmune encephalomyelitis (EAE), intravenous transfer of activated CD4(+) myelin-specific T cells is sufficient to induce disease. Transferred T cells access the CNS parenchyma by trafficking across the blood brain barrier (BBB) vascular endothelium into the perivascular space, and then across the glial limitans that is made up of astrocytes and microglia. Flow cytometry analysis of cells isolated from CNS tissue does not distinguish between T cell populations at the various stages of migration. In this study, we have used GK1.5 (anti-CD4) treatment along with immunohistochemistry to distinguish between populations of T cells that are associated with the vasculature, T cells that have migrated into the perivascular space, and T cells in the parenchyma. We have also re-evaluated antigen specificity requirements of T cells as they are recruited to the CNS parenchyma. Activated myelin-specific T cells are restricted to the CNS vasculature for at least 24 h post transfer. MHC class II expression on the recipient is required for cells to traffic across the CNS vascular endothelium. Further, Con A-stimulated or non-CNS-specific (ovalbumin-specific) T cells fail to migrate into the perivascular space, and only enter the CNS parenchyma when co-transferred with myelin-specific T cells. Our results indicate that Th1 populations cannot accumulate in the perivascular (subarachnoid, Virchow-Robbins) space without a CNS antigen-specific signal.

MMP-2 null mice exhibit an early onset and severe experimental autoimmune encephalomyelitis due to an increase in MMP-9 expression and activity

Matrix metalloproteinase-2 (MMP-2; gelatinase A) is known to degrade a broad range of extracellular matrix components and chemokines, and has important roles in the processes of cell migration, invasion, and involution during development, as well as during tumor growth and metastasis and in inflammation and repair. To better elucidate the roles of this matrix metalloproteinase in the development and progression of experimental autoimmune encephalomyelitis, we used MMP-2-deficient (KO) mice. Surprisingly, we found that MMP-2 KO mice exhibited an earlier onset and more severe disease than did their wild-type (WT) counterparts. WT mice engrafted with MMP-2 KO bone marrow exhibited a similar earlier onset and more severe clinical disease score than WT mice engrafted with WT bone marrow. Lymphocytes derived from MMP-2 KO mice exhibited increased transmigration through endothelial cell monolayers as well as through collagen type IV and laminin-coated BD BIOCOAT inserts, which correlated with a 3-fold increase in expression of MMP-9 and was abrogated by inhibition of MMP activity. We demonstrated a correlation between expression levels of MMP-9 and MT1-MMP expression and suggest a signaling pathway involving tethering of MMP-2 to MT1-MMP as a modulator of MMP-9 expression. Last, we discuss other possible MMP-2-mediated mechanisms which may contribute to the observed phenotype.

Membrane type 1–matrix metalloproteinase is involved in migration of human monocytes and is regulated through their interaction with fibronectin or endothelium

Membrane type 1–matrix metalloproteinase (MT1-MMP) is involved in endothelial and tumor-cell migration, but its putative role in leukocyte migration has not been characterized yet. Here, we demonstrate that anti–MT1-MMP monoclonal antibody (mAb) impaired monocyte chemotactic protein-1 (MCP-1)–stimulated monocyte migration on fibronectin (FN), vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1). In addition, monocyte transmigration through tumor necrosis factor-α (TNF-α)–activated endothelium is also inhibited by anti–MT1-MMP mAb. Therefore, regulation of MT1-MMP in human peripheral blood monocytes was investigated. First, MT1-MMP clustering was observed at motility-associated membrane protrusions of MCP-1–stimulated monocytes migrating on FN, VCAM-1, or ICAM-1 and at the leading edge, together with profilin, of monocytes transmigrating through activated endothelial cells. In addition, up-regulation of MT1-MMP expression was induced in human monocytes upon attachment to FN in a manner dependent on α4β1 and α5β1 integrins. Binding of monocytes to TNF-α–activated human endothelial cells as well as to VCAM-1 or ICAM-1 also resulted in an increase of MT1-MMP expression. These findings correlated with an enhancement of MT1-MMP fibrinolytic activity in monocytes bound to FN, VCAM-1, or ICAM-1. Our data show that MT1-MMP is required during human monocyte migration and endothelial transmigration and that MT1-MMP localization, expression, and activity are regulated in monocytes upon contact with FN or endothelial ligands, pointing to a key role of MT1-MMP in monocyte recruitment during inflammation.

Inhibition of obliterative airway disease development in murine tracheal allografts by matrix metalloproteinase-9 deficiency

This study was designed to define the roles of matrix metalloproteinase (MMP)-2 and MMP-9 in obliterative airway disease (OAD) in heterotopic murine tracheal allografts, considered a suitable animal model for chronic lung allograft rejection. BALB/c tracheal allografts were transplanted into MMP-2-deficient (-/-) and MMP-9-/- mice. Also, wild-type recipients were treated with doxycycline, a nonspecific MMP inhibitor. After 10, 20 and 30 days, allografts were analyzed for OAD development, intragraft levels of MMP-2 and MMP-9 and the frequency and cytokine/chemokine production profile of alloreactive T cells. Allografts transplanted into wild-type mice developed OAD lesions within 30 days. These allografts revealed significant upregulation of both MMP-2 and MMP-9. Allografts transplanted into MMP-9-/- and doxycycline-treated recipients did not develop OAD. In contrast, allografts transplanted into MMP-2-/- mice developed OAD lesions with normal kinetics. Interestingly, MMP-9-/- recipients showed an enhanced T cell alloreactivity associated with an abnormal profile of cytokine/chemokine production. The enhanced T cell alloreactivity in MMP-9-/- mice was mediated by enhanced dendritic cell stimulatory capacity as well as enhanced T cell responsive capacity. These results suggest that MMP-9 plays an important role in the pathogenesis of OAD and may represent a target for the therapeutic intervention of chronic lung allograft rejection.

Different roles for matrix metalloproteinase-2 and matrix metalloproteinase-9 in the pathogenesis of cardiac allograft rejection

Recent studies have shown an increased expression of several matrix metalloproteinases (MMP) during cardiac, renal and pulmonary allograft rejection. To further define the roles of MMP-2 and MMP-9 in the pathogenesis of cardiac allograft rejection, BALB/c cardiac allografts were transplanted into MMP-2-deficient (-/-) and MMP-9-/- mice. Allografts rejected by wild-type mice revealed a significant increase in MMP-2 and MMP-9 expression. MMP-2-deficiency significantly prolonged allograft survival time. Functioning allografts harvested from MMP-2-/- mice showed lower cellular infiltration and fibrosis than rejected allografts harvested from MMP-2+/+ mice at the same time. In contrast, MMP-9-deficiency significantly decreased allograft survival time. Functioning allografts harvested from MMP-9+/+ mice showed lower cellular infiltration and fibrosis than rejected allografts harvested from MMP-9-/- mice at the same time. MMP-2-/- recipients showed decreased T-cell alloreactivity mediated by a defect in dendritic cell stimulatory and T-cell responsive capacities. In contrast, MMP-9-/- recipients showed increased T-cell alloreactivity mediated by a significant increased in dendritic cell stimulatory and T-cell responsive capacities. These results indicate that MMP2 and MMP-9 play significantly different roles in the process of cardiac allograft rejection.

Inhibition of MMP-dependent chemotaxis and amelioration of experimental autoimmune uveitis with a selective metalloproteinase-2 and -9 inhibitor

The chemotaxis of inflammatory cells depends on proteolytic disruption of extracellular matrix components. The metalloproteinases (MMP)-2 and -9 enable T-lymphocytes to pass through basement membranes. Selective inhibition of only MMP-2 and -9 almost completely abolished the ability of lymphocytes to digest collagen. The chemotaxis of lymphocytes was reduced 40%. In our in-vivo model of experimental autoimmune uveitis (EAU), 46% of the animals in the treated group remained disease-free, whereas all animals in the control group developed EAU. The mean activity of the disease was also statistically significantly reduced. The data suggest that selective MMP-2 and -9 inhibition might be a treatment option.

Cerebral vessel laminins and IFN-gamma define Trypanosoma brucei brucei penetration of the blood-brain barrier

Subspecies of Trypanosoma brucei cause severe brain diseases after penetration of the blood-brain barrier. We investigated whether cytokines that modulate inflammatory cell infiltration into the brain also influence T. brucei neuroinvasion. Migration of a rodent pathogenic T. brucei strain from the cerebral blood vessels into the brain parenchyma was impeded in IFN-gamma(-/-), IFN-gamma receptor(-/-) (IFN-gammaR(-/-)), IL-12p40(-/-), and recombinant activating gene-1(-/-) (RAG-1(-/-)) mice as compared with their WT littermates despite higher levels of parasitemia in the mutant strains. Parasites accumulated in the perivascular compartment, confined between the endothelial and the parenchymal basement membranes, in certain areas of the brains of IFN-gamma(-/-), IFN-gammaR(-/-), and RAG-1(-/-) mice. This accumulation occurred around endothelial basement membranes containing the laminin alpha4 chain, while blood vessels showing robust laminin alpha5 chain immunostaining were not associated with parasite infiltration. The number of CD4+ and CD8+ T cells infiltrating the brain parenchyma was also reduced in the IFN-gamma(-/-) and IFN-gammaR(-/-) mice. Our findings suggest that lymphocyte-derived IFN-gamma facilitates trypanosome penetration across cerebral blood vessels and that the site of penetration is determined by the composition of the basement membranes of these vessels.

TNFR1-dependent VCAM-1 expression by astrocytes exposes the CNS to destructive inflammation

VCAM-1 is an adhesion molecule that is important to leukocyte movement across the blood-brain barrier and is involved in the formation of destructive CNS inflammatory lesions in experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS). We examined VCAM-1 expression in the CNS of animals with passively induced EAE and found abundant expression not only on the CNS endothelium but also on astrocytes. We show that tumor necrosis factor receptor-1 (TNFR1) signaling is required for VCAM-1 expression by astrocytes, not the vascular endothelium. In addition, we demonstrate that VCAM-1 expression by astrocytes is crucial for T cell entry into the CNS parenchyma and is required for manifestation of neurological disease.

Pirfenidone inhibits obliterative airway disease in a murine heterotopic tracheal transplant model

BACKGROUND

Chronic lung allograft rejection in the form of bronchiolitis obliterans syndrome and its histopathologic correlate, obliterative bronchiolitis (OB), are a major source of morbidity and mortality after lung transplantation. Murine heterotopic tracheal transplants into fully allogeneic mismatched recipients develop obliterative airway disease (OAD), which is a suitable model of OB. Using this murine heterotopic tracheal allograft model, we evaluated the effect of pirfenidone, a novel antifibrotic agent, on the development of OAD.

METHODS

Mice transplanted with complete MHC-mismatched tracheal allografts received pirfenidone (0.5%) in pulverized food according to different schedules: daily for the first 14 days after transplantation or daily for the duration of the study beginning on posttransplantation days 0, 5, or 10.

RESULTS

Mice on a continuous daily regimen of pirfenidone failed to develop evidence of chronic allograft rejection at the termination of the study (60 days). Mice receiving pirfenidone limited to the early posttransplantation period had delayed onset of OAD to 60 days. Forty percent (2/5) of mice receiving a continuous regimen of pirfenidone beginning on day 5 after transplantation had no evidence of OAD at 28 days. However, when the drug was started on day 10, all mice developed OAD by 28 days.

CONCLUSIONS

Our results demonstrate a delay of onset or abrogation of OAD when pirfenidone is administered in the early posttransplantation period. These findings suggest that pirfenidone is a candidate drug to be evaluated for prevention of the fibrotic changes seen in OB in human recipients of lung transplants.

Le système MMP/TIMP dans le système nerveux

The matrix metalloproteinases (MMP) belong to a growing family of secreted or membrane-bound (MT-MMP) enzymes that cleave protein components of the extracellular matrix and bioactive factors involved in intercellular signaling. MMP activity is counterbalanced by their four physiological inhibitors, the tissue inhibitors of MMP (TIMPs). Together, MMP and TIMP control cell-cell and cell-matrix interactions associated with physiological processes. However, the breakdown of the protease-inhibitor balance may lead to the loss of tissue homeostasis and the development of degenerative and tumorigenic processes in various tissues. The emerging idea is that the MMP/TIMP system also plays a major role in the pathology and physiology of the nervous system and that mastering MMP activity will set the basis for new and more efficient therapeutic strategies against nervous system disorders.