Cerebrospinal fluid activity of tissue plasminogen activator in patients with neurological diseases

Spatiotemporal perturbations of the plasminogen activation system in a rat model of acute organophosphate intoxication

Neuroinflammation is widely posited to be a key pathogenic mechanism linking acute organophosphate (OP)-induced status epilepticus (SE) to persistent brain injury and abnormal electrical activity that contribute to epilepsy and cognitive impairment. The plasminogen activation system (PAS) promotes neuroinflammation in diverse neurological diseases but whether it is activated following acute OP intoxication has yet to be evaluated. To address this data gap, we characterized the spatiotemporal expression patterns of multiple components of the PAS in a rat model of acute intoxication with the OP, diisopropylfluorophosphate (DFP). Adult male Sprague Dawley rats administered DFP (4 mg/kg, sc), atropine sulfate (2 mg/kg, im) and 2-pralidoxime (25 mg/kg, im) went into SE that persisted for hours. One day after acute DFP-induced SE, plasmin activity and protein concentrations of plasminogen activator inhibitor-1 (PAI-1) in the plasma were increased, though not significantly. In contrast, acute DFP intoxication significantly increased brain levels of PAI-1, tissue-type plasminogen activator (tPA), urokinase plasminogen activator (uPA), and transcripts of TGF-β in a time- and region-dependent manner. In the cortex and hippocampus, quantification of PAI-1, tPA, and uPA by ELISA indicated significantly increased levels at 1 day post-exposure (DPE). PAI-1 and uPA returned to control values by 7 DPE while tPA protein remained elevated at 28 DPE. Immunohistochemistry detected elevated PAI-1 expression in the DFP brain up to 28 DPE. Co-localization of PAI-1 with biomarkers of neurons, microglia, and astrocytes demonstrated that PAI-1 localized predominantly to a subpopulation of astrocytes. Cytologically, PAI-1 localized to astrocytic end feet, but not adjacent neurovascular endothelium. Electron microscopy revealed neuronal metabolic stress and neurodegeneration with disruption of adjacent neurovascular units in the hippocampus post-DFP exposure. These data indicate that acute DFP intoxication altered PAS expression in the brain, with aberrant PAI-1 expression in a subset of reactive astrocyte populations.

Tissue plasminogen activator worsens experimental autoimmune encephalomyelitis by complementary actions on lymphoid and myeloid cell responses

BACKGROUND

Tissue plasminogen activator (tPA) is a serine protease involved in fibrinolysis. It is released by endothelial cells, but also expressed by neurons and glial cells in the central nervous system (CNS). Interestingly, this enzyme also contributes to pathological processes in the CNS such as neuroinflammation by activating microglia and increasing blood-brain barrier permeability. Nevertheless, its role in the control of adaptive and innate immune response remains poorly understood.

METHODS

tPA effects on myeloid and lymphoid cell response were studied in vivo in the mouse model of multiple sclerosis experimental autoimmune encephalomyelitis and in vitro in splenocytes.

RESULTS

tPA-/- animals exhibited less severe experimental autoimmune encephalomyelitis than their wild-type counterparts. This was accompanied by a reduction in both lymphoid and myeloid cell populations in the spinal cord parenchyma. In parallel, tPA increased T cell activation and proliferation, as well as cytokine production by a protease-dependent mechanism and via plasmin generation. In addition, tPA directly raised the expression of MHC-II and the co-stimulatory molecules CD80 and CD86 at the surface of dendritic cells and macrophages by a direct action dependent of the activation of epidermal growth factor receptor.

CONCLUSIONS

Our study provides new insights into the mechanisms responsible for the harmful functions of tPA in multiple sclerosis and its animal models: tPA promotes the proliferation and activation of both lymphoid and myeloid populations by distinct, though complementary, mechanisms.

Blocking PDGF-CC signaling ameliorates multiple sclerosis-like neuroinflammation by inhibiting disruption of the blood-brain barrier

Disruption of blood–brain barrier (BBB) integrity is a feature of various neurological disorders. Here we found that the BBB is differently affected during the preclinical, progression and remission phase of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). We have identified an upregulation of pro-inflammatory and pro-angiogenic factors in the BBB transcriptome and down-regulation of endothelial tight junction members coinciding with elevated BBB leakage specifically during the progression phase. These changes were antagonized by blocking PDGFRα signaling with the small tyrosine kinase inhibitor imatinib. Moreover, targeting the PDGFRα ligand PDGF-CC using a neutralizing antibody, facilitated recovery of BBB integrity and improvement of EAE symptoms. Intracerebroventricular injection of PDGF-CC induced upregulation, whereas blocking PDGF-CC during EAE led to downregulation of Tnfa and Il1a at the BBB. Our findings suggest that blocking PDGF-CC counteracts fundamental aspects of endothelial cell activation and disruption of the BBB by decreasing Tnfa and Il1a expression. We also demonstrate that both PDGF-CC and its receptor PDGFRα were upregulated in MS lesions indicating that blocking PDGF-CC may be considered a novel treatment for MS.

Identifying the Specific Subtype of Intracerebral Hemorrhage that is Indicated for Minimally Invasive Craniopuncture

BACKGROUND

Surgeries for intracerebral hemorrhage (ICH) remain controversial. Our previous study found that postoperative cerebrospinal fluid (CSF) outflow was associated with high hematoma evacuation efficiency in ICH cases with intraventricular involvement (ICHV) treated with minimally invasive craniopuncture (MIC). This study was designed to identify factors that predict postoperative CSF outflow and the specific subtype of ICHV that may benefit from MIC.

METHODS

A total of 189 MIC needles applied to 125 ICHV patients were retrospectively analyzed. Univariate and multivariate analyses were used to identify independent predictive factors of postoperative CSF outflow.

RESULTS

A density of the whole hematoma of ≤ 59 HU [odds ratio (OR) = 8.572, 95% confidence interval (CI) 3.235-22.714, P < 0.001, standardization regression coefficients B' = 0.576] and a distance between the needle tip and the ventricular tear (tip-tear distance) of 21.79-34.15 mm (OR = 25.566, 95% CI 8.707-75.074, P < 0.001, B' = 0.883) were identified as independent predictive factors of postoperative CSF outflow. The density of the hematoma within 34.15 mm of the tear (clot 3.4) showed no statistical difference from that of the whole hematoma (P = 0.571). A density of clot 3.4 ≤ 60 HU was also a predictive factor of postoperative CSF outflow (area under curve: 0.771).

CONCLUSIONS

ICHV patients who meet the following conditions may benefit from MIC: (1) The MIC needle tip can be placed in the hematoma 21.79-34.15 mm from the ventricular tear; (2) the density of the whole hematoma is low (≤ 59 HU); and (3) the density of clot 3.4 is also low (≤ 60 HU). Future perspective studies should be conducted on this specific patient subtype.

Nonionotropic Action of Endothelial NMDA Receptors on Blood-Brain Barrier Permeability via Rho/ROCK-Mediated Phosphorylation of Myosin

Increase in blood-brain barrier (BBB) permeability is a crucial step in neuroinflammatory processes. We previously showed that N Methyl D Aspartate Receptor (NMDARs), expressed on cerebral endothelial cells forming the BBB, regulate immune cell infiltration across this barrier in the mouse. Here, we describe the mechanism responsible for the action of NMDARs on BBB permeabilization. We report that mouse CNS endothelial NMDARs display the regulatory GluN3A subunit. This composition confers to NMDARs' unconventional properties: these receptors do not induce Ca²⁺ influx but rather show nonionotropic properties. In inflammatory conditions, costimulation of human brain endothelial cells by NMDA agonists (NMDA or glycine) and the serine protease tissue plasminogen activator, previously shown to potentiate NMDAR activity, induces metabotropic signaling via the Rho/ROCK pathway. This pathway leads to an increase in permeability via phosphorylation of myosin light chain and subsequent shrinkage of human brain endothelial cells. Together, these data draw a link between NMDARs and the cytoskeleton in brain endothelial cells that regulates BBB permeability in inflammatory conditions.SIGNIFICANCE STATEMENT The authors describe how NMDARs expressed on endothelial cells regulate blood-brain barrier function via myosin light chain phosphorylation and increase in permeability. They report that these non-neuronal NMDARs display distinct structural, functional, and pharmacological features than their neuronal counterparts.

Role of tissue plasminogen activator in clinical aggravation of experimental autoimmune encephalomyelitis and its therapeutic potential

Tissue plasminogen activator (tPA), a component of the plasminogen activator (PA) system, is elevated in inflammatory neurological disorders. In the present study, we explored the immunomodulatory activity of tPA in experimental autoimmune encephalomyelitis (EAE). The EAE was treated with two catalytic inactive tPA variant proteins: S(481)A and S(481)A + KHRR(296-299)AAAA. EAE-induced tPA^-/- mice presented with markedly more severe disease than wt EAE mice. Further, treatment with tPA variants, demonstrated a significant suppression of disease severity in tPA^-/- and wt mice. Immunological evaluation showed that specific T-cell reactivity was markedly reduced in the tPA^-/- animals, as indicated by decreased T-cell reactivity and reduction in T-regulatory cells. The current findings indicate that tPA plays a role in the pathogenesis of EAE. Moreover, successful amelioration of EAE was achieved by administration of tPA variant proteins. This might mean that these proteins have potential for the immunomodulation of neuroinflammation.

Coagulation Pathways in Neurological Diseases: Multiple Sclerosis

Significant progress has been made in understanding the complex interactions between the coagulation system and inflammation and autoimmunity. Increased blood-brain-barrier (BBB) permeability, a key event in the pathophysiology of multiple sclerosis (MS), leads to the irruption into the central nervous system of blood components that include virtually all coagulation/hemostasis factors. Besides their cytotoxic deposition and role as a possible trigger of the coagulation cascade, hemostasis components cause inflammatory response and immune activation, sustaining neurodegenerative events in MS. Early studies showing the contribution of altered hemostasis in the complex pathophysiology of MS have been strengthened by recent studies using methodologies that permitted deeper investigation. Fibrin(ogen), an abundant protein in plasma, has been identified as a key contributor to neuroinflammation. Perturbed fibrinolysis was found to be a hallmark of progressive MS with abundant cortical fibrin(ogen) deposition. The immune-modulatory function of the intrinsic coagulation pathway still remains to be elucidated in MS. New molecular details in key hemostasis components participating in MS pathophysiology, and particularly involved in inflammatory and immune responses, could favor the development of novel therapeutic targets to ameliorate the evolution of MS. This review article introduces essential information on coagulation factors, inhibitors, and the fibrinolytic pathway, and highlights key aspects of their involvement in the immune system and inflammatory response. It discusses how hemostasis components are (dys)regulated in MS, and summarizes histopathological post-mortem human brain evidence, as well as cerebrospinal fluid, plasma, and serum studies of hemostasis and fibrinolytic pathways in MS. Studies of disease-modifying treatments as potential modifiers of coagulation factor levels, and case reports of autoimmunity affecting hemostasis in MS are also discussed.

A Perspective of Coagulation Dysfunction in Multiple Sclerosis and in Experimental Allergic Encephalomyelitis

A key role of both coagulation and vascular thrombosis has been reported since the first descriptions of multiple sclerosis (MS). Subsequently, the observation of a close concordance between perivascular fibrin(ogen) deposition and the occurrence of clinical signs in experimental allergic encephalomyelitis (EAE), an animal model of MS, led to numerous investigations focused on the role of thrombin and fibrin(ogen). Indeed, the activation of microglia, resident innate immune cells, occurs early after fibrinogen leakage in the pre-demyelinating lesion stage of EAE and MS. Thrombin has both neuroprotective and pro-apoptotic effects according to its concentration. After exposure to high concentrations of thrombin, astrocytes become reactive and lose their neuroprotective and supportive functions, microglia proliferate, and produce reactive oxygen species, IL-1β, and TNFα. Heparin inhibits the thrombin generation and suppresses EAE. Platelets play an important role too. Indeed, in the acute phase of the disease, they begin the inflammatory response in the central nervous system by producing of IL-1alpha and triggering and amplifying the immune response. Their depletion, on the contrary, ameliorates the course of EAE. Finally, it has been proven that the use of several anticoagulant agents can successfully improve EAE. Altogether, these studies highlight the role of the coagulation pathway in the pathophysiology of MS and suggest possible therapeutic targets that may complement existing treatments.

The Coagulation Factors Fibrinogen, Thrombin, and Factor XII in Inflammatory Disorders-A Systematic Review

Background

The interaction of coagulation factors has been shown to go beyond their traditional roles in hemostasis and to affect the development of inflammatory diseases. Key molecular players, such as fibrinogen, thrombin, or factor XII have been mechanistically and epidemiologically linked to inflammatory disorders like multiple sclerosis (MS), rheumatoid arthritis (RA), and colitis.

Objectives

To systematically review the evidence for a role of coagulation factors, especially factor XII, fibrinogen, and thrombin in inflammatory disorders like MS, RA, and bowel disorders.

Methods

A systematic literature search was done in the PubMed database to identify studies about coagulation factors in inflammatory diseases. Original articles and reviews investigating the role of the kallikrein–kinin and the coagulation system in mouse and humans were included.

Results

We identified 43 animal studies dealing with inflammatory disorders and factors of the kallikrein–kinin or the coagulation system. Different immunological influences are described and novel molecular mechanisms linking coagulation and inflammation are reported.

Conclusion

A number of studies have highlighted coagulation factors to tip the balance between hemostasis and thrombosis and between protection from infection and extensive inflammation. To optimize the treatment of chronic inflammatory disorders by these factors, further studies are necessary.

[Coagulation factors and multiple sclerosis : Key factors in the pathogenesis?]

Environmental factors and genetic predisposition influence the individual risk to develop multiple sclerosis (MS). Preclinical results in animal models of MS, such as experimental autoimmune encephalomyelitis (EAE), prove a significant contribution of the corpuscular and plasmatic coagulation system for the severity of MS. It was recently shown that key molecules of the coagulation cascade, such as fibrinogen, thrombin and factor XII can influence neuroinflammatory disorders such as MS. The inhibition of both fibrinogen and factor XII led to a significantly improved disease course in animal models. Furthermore, in patients suffering from MS a dysregulation of diverse coagulation factors was demonstrated. The precise role of these changes for the pathogenesis of MS remains to be clarified. Nonetheless, the identification of molecular mechanisms between inflammation and the coagulation cascade might provide completely new perspectives for the therapy of MS; however, as most of the currently available data were obtained from animal models, this knowledge must be interpreted with an adequate degree of caution.

Can fibrinolytic system components explain cognitive impairment in multiple sclerosis?

BACKGROUND

The fibrinolytic system is capable of modulating inflammatory and degenerative events within the central nervous system. Specifically, the plasminogen activator inhibitor-1 (PAI-1) has been associated with different pathological conditions in multiple sclerosis (MS) and its role in cognitive functioning is also known.

OBJECTIVES AND METHODS

To study the association between plasma levels and the polymorphic variants of the PAI-1 gene and cognitive performance in MS. 176 patients were studied. Neuropsychological evaluation was performed with the Brief Repeatable Battery of Neuropsychological Tests (BRB-N). A Polymerase Chain Reaction (PCR) was used to determine PAI-1 4G/5G polymorphisms and quantification was performed using an Enzyme-Linked ImmunoSorbent Assay (ELISA).

RESULTS

Participants were categorized as not cognitively impaired (NCI; n=114) and cognitively impaired (CI; n=62). The NCI group had a higher percentage of heterozygous subjects but no statistical differences were found between the CI and NCI group. Neuropsychological functioning did not correlate with plasma levels of PAI-1 or its genetic polymorphism. It is noteworthy that PAI-1 plasma levels were related to neurological impairment.

DISCUSSION

Cognitive impairment in MS is due to strategic focal lesions affecting regions and tracts involved in cognitive processes and to diffuse damage in the white and gray matter. This complex etiology could explain the absence of a relationship between the cognitive functioning and PAI-1 in patients with MS that has been found in vascular dementia or Alzheimer's disease. Plasma curves of PAI-1 and its measures in cerebrospinal fluid could help elucidate the role of PAI-1 in MS.

Neuroendothelial NMDA receptors as therapeutic targets in experimental autoimmune encephalomyelitis

Multiple sclerosis is among the most common causes of neurological disability in young adults. Here we provide the preclinical proof of concept of the benefit of a novel strategy of treatment for multiple sclerosis targeting neuroendothelial N-methyl-D-aspartate glutamate receptors. We designed a monoclonal antibody against N-methyl-D-aspartate receptors, which targets a regulatory site of the GluN1 subunit of N-methyl-D-aspartate receptor sensitive to the protease tissue plasminogen activator. This antibody reverted the effect of tissue plasminogen activator on N-methyl-D-aspartate receptor function without affecting basal N-methyl-D-aspartate receptor activity (n = 21, P < 0.01). This antibody bound N-methyl-D-aspartate receptors on the luminal surface of neurovascular endothelium in human tissues and in mouse, at the vicinity of tight junctions of the blood-spinal cord barrier. Noteworthy, it reduced human leucocyte transmigration in an in vitro model of the blood-brain barrier (n = 12, P < 0.05). When injected during the effector phase of MOG-induced experimental autoimmune encephalomyelitis (n = 24), it blocked the progression of neurological impairments, reducing cumulative clinical score (P < 0.001) and mean peak score (P < 0.001). This effect was observed in wild-type animals but not in tissue plasminogen activator knock-out animals (n = 10). This therapeutic effect was associated to a preservation of the blood-spinal cord barrier (n = 6, P < 0.001), leading to reduced leucocyte infiltration (n = 6, P < 0.001). Overall, this study unveils a critical function of endothelial N-methyl-D-aspartate receptor in multiple sclerosis, and highlights the therapeutic potential of strategies targeting the protease-regulated site of N-methyl-D-aspartate receptor.

The Influence of Differentially Expressed Tissue-Type Plasminogen Activator in Experimental Autoimmune Encephalomyelitis: Implications for Multiple Sclerosis

Tissue type plasminogen activator (t-PA) has been implicated in the development of multiple sclerosis (MS) and in rodent models of experimental autoimmune encephalomyelitis (EAE). We show that levels of t-PA mRNA and activity are increased ~4 fold in the spinal cords of wild-type mice that are mice subjected to EAE. This was also accompanied with a significant increase in the levels of pro-matrix metalloproteinase 9 (pro-MMP-9) and an influx of fibrinogen. We next compared EAE severity in wild-type mice, t-PA^-/- mice and T4+ transgenic mice that selectively over-express (~14-fold) mouse t-PA in neurons of the central nervous system. Our results confirm that t-PA deficient mice have an earlier onset and more severe form of EAE. T4+ mice, despite expressing higher levels of endogenous t-PA, manifested a similar rate of onset and neurological severity of EAE. Levels of proMMP-9, and extravasated fibrinogen in spinal cord extracts were increased in mice following EAE onset regardless of the absence or over-expression of t-PA wild-type. Interestingly, MMP-2 levels also increased in spinal cord extracts of T4+ mice following EAE, but not in the other genotypes. Hence, while the absence of t-PA confers a more deleterious form of EAE, neuronal over-expression of t-PA does not overtly protect against this condition with regards to symptom onset or severity of EAE.

Stem cells downregulate the elevated levels of tissue plasminogen activator in rats after spinal cord injury

We investigated the involvement of tPA after SCI in rats and effect of treatment with human umbilical cord blood derived stem cells. tPA expression and activity were determined in vivo after SCI in rats and in vitro in rat embryonic spinal neurons in response to injury with staurosporine, hydrogen peroxide and glutamate. The activity and/or expression of tPA increased after SCI and reached peak levels on day 21 post-SCI. Notably, the tPA mRNA activity was upregulated by 310-fold compared to controls on day 21 post-SCI. As expected, MBP expression is minimal at the time of peak tPA activity and vice versa. Implantation of hUCB after SCI resulted in the downregulation of elevated tPA activity/expression in vivo in rats as well as in vitro in spinal neurons. Our results demonstrated the involvement of tPA in the secondary pathogenesis after SCI as well as the therapeutic potential of hUCB.

Expression of the urokinase plasminogen activator receptor (uPAR) and its ligand (uPA) in brain tissues of human immunodeficiency virus patients with opportunistic cerebral diseases

The urokinase plasminogen activator receptor (uPAR) and its ligand (uPA) play an important role in cell migration and extracellular proteolysis. We previously described uPAR/uPA overexpression in the cerebrospinal fluid (CSF) and brain tissues of patients with human immunodeficiency virus (HIV)-related cerebral diseases. In this study, we examined uPAR/uPA expression by immunohistochemistry (IHC) in brains of HIV patients with opportunistic cerebral lesions and in HIV-positive/negative controls. uPAR was found in macrophages/microglia with the highest levels in cytomegalovirus (CMV) encephalitis, toxoplasmosis, and lymphomas; in cryptococcosis and progressive multifocal leukoencephalopathy (PML) cases, only a few positive cells were found and no positivity was observed in controls. uPA expression was demonstrated only in a few macrophages/microglia and lymphocytes in all the cases and HIV-positive controls without different pattern of distribution; no uPA immunostaining was found in cryptococcosis and HIV-negative controls. The higher expression of uPAR/uPA in most of the opportunistic cerebral lesions supports their role in these diseases, suggesting their contribution to tissue injury.

Tissue-type plasminogen activator is a regulator of monocyte diapedesis through the brain endothelial barrier

Inflammatory cell trafficking into the brain complicates several neurological disorders including multiple sclerosis. Normally, reliable brain functioning is maintained and controlled by the blood-brain barrier (BBB), which is essential to restrict the entry of potentially harmful molecules and cells from the blood into the brain. The BBB is a selective barrier formed by dedicated brain endothelial cells and dependent on the presence of intracellular tight junctions. In multiple sclerosis, a severe dysfunction of the BBB is observed, which is key to monocyte infiltration and inflammation in the brain. Proteolytic activity has been associated with these inflammatory processes in the brain. Our studies in plasma of rats indicated that the extracellular protease tissue-type plasminogen activator (tPA) correlates with the clinical signs of experimental allergic encephalomyelitis, a rat model of multiple sclerosis. In this study, we studied the function of the tPA during diapedesis of monocytes through a rat and human brain endothelial barrier. Monocyte-brain endothelial cell coculture experiments showed that monocytes induce the release of tPA by brain endothelial cells, which subsequently activates the signal transduction protein extracellular signal related kinase (ERK1/2), both involved in monocyte diapedesis. Importantly, live imaging and immunoblot analyses of rat brain endothelial cells revealed that tPA and ERK1/2 control the breakdown of the tight junction protein occludin. These studies identify tPA as a novel and relevant pathological mediator of neuroinflammation and provide a potential mechanism for this.

Immunological aspects of axon injury in multiple sclerosis

The role of immune-mediated axonal injury in the induction of nonremitting functional deficits associated with multiple sclerosis is an area of active research that promises to substantially alter our understanding of the pathogenesis of this disease and modify or change our therapeutic focus. This review summarizes the current state of research regarding changes in axonal function during demyelination, provides evidence of axonal dysmorphia and degeneration associated with demyelination, and identifies the cellular and molecular effectors of immune-mediated axonal injury. Finally, a unifying hypothesis that links neuronal stress associated with demyelination-induced axonal dysfunction to immune recognition and immunopathology is provided in an effort to shape future experimentation.

Cerebrospinal fluid proteome profile in multiple sclerosis

Cerebrospinal fluid (CSF) proteins may provide important information about the pathomechanisms present in multiple sclerosis (MS). Although diagnostic criteria for early MS are available, there is still a need for biomarkers, predicting disease subtype and progression to improve individually tailored treatment. Using the two-dimensional difference gel electrophoresis (2-D-DIGE) technology for comparative analysis, we compared CSF samples from patients with MS of the relapse-remitting type (RRMS, n = 12) and from patients with clinically isolated syndrome (CIS, n = 12) suggestive of a first demyelinating attack with neurologically normal controls. Protein spots that showed more than two-fold difference between patients and controls were selected for further analysis with MALDI-TOF mass spectrometry. Immunoblot analysis was performed to confirm the validity of individual candidate proteins. In RRMS, we identified 1 up-regulated and 10 down-regulated proteins. In CIS, 2 up-regulated and 11 down-regulated proteins were identified. One of these proteins (Apolipoprotein A1) was confirmed by immunoblot. Though the pathophysiological role of these proteins still remains to be elucidated in detail and further validation is needed, these findings may have a relevant impact on the identification of disease-specific markers.

Modulation of microglial/macrophage activation by macrophage inhibitory factor (TKP) or tuftsin (TKPR) attenuates the disease course of experimental autoimmune encephalomyelitis

Background

Myelin Oligodendrocyte Glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) is the most commonly used mouse model for multiple sclerosis (MS). During the of progression of EAE, microglia, the immunocompetent cells of the brain, become activated and accumulate around demyelinated lesions. Microglial activation is mediated by the extracellular protease tissue Plasminogen Activator (tPA), and mice lacking tPA display altered EAE progression. In this study, we have used pharmacological inhibitors and stimulators of microglial/macrophage activation to examine the temporal requirement for microglial activation in EAE progression and to determine whether such approaches might potentially be of therapeutic value.

Results

Intervention using the tripeptide macrophage/microglia inhibitory factor MIF (TKP) and the tetrapeptide macrophage/microglial stimulator tuftsin (TKPR) attenuated EAE symptoms and revealed that the timing of macrophage/microglial activation is critical for the clinical outcome of EAE. We show that the disease progression can potentially be manipulated favorably at early stages by altering the timing of microglial activation, which in turn alters the systemic immune response to favor upregulation of T helper cell 2 genes that promote recovery from EAE.

Conclusion

Preventative and therapeutic modulation of macrophage/microglial activity significantly alters the outcome of EAE at symptomatic stages. Specific molecular targets have been identified that represent potential avenues of exploration for the treatment and prevention of MS.

A role for the plasminogen activator system in inflammation and neurodegeneration in the central nervous system during experimental allergic encephalomyelitis

Early signs of inflammatory demyelination include entry of fibrin(ogen) into the central nervous system (CNS), which is normally excluded by the blood-brain barrier, and up-regulation of components of the plasminogen activator system. Using mice deficient in tissue-type plasminogen activator (tPA-/-) and urokinase plasminogen activator receptor (uPAR-/-), we investigated the involvement of the PA system on the clinical and pathological features of experimental allergic encephalomyelitis, an animal model of multiple sclerosis. tPA-/- mice suffered an early and a more severe acute disease characterized by incomplete recovery when compared to wild-type controls, with significantly higher CNS levels of plasminogen activator inhibitor-1. This correlated with fibrin accumulation, which co-localized with nonphosphorylated neurofilament on thickened axons in experimental allergic encephalomyelitis tissue. In contrast, uPAR-/- mice had a delayed, less acute disease reflected in delayed infiltration of inflammatory cells. These animals developed chronic disease as a result of steadily increased inflammation, increased levels of urokinase-type plasminogen activator (uPA), and greater degree of demyelination. Thus, the plasminogen activator system can modulate both inflammatory and degenerative events in the CNS through the respective effects of tPA and uPAR on fibrinolysis and cell adhesion/migration, manipulation of which may have therapeutic implications for multiple sclerosis.

Tissue-Type Plasminogen Activator Crosses the Intact Blood-Brain Barrier by Low-Density Lipoprotein Receptor–Related Protein-Mediated Transcytosis

Background— Accumulating evidence demonstrates a critical involvement of tissue-type plasminogen activator (tPA) in pathological and physiological brain conditions. Determining whether and how vascular tPA can cross the blood-brain barrier (BBB) to enter the brain is thus important, not only during stroke but also in physiological conditions.

Methods and Results— In the present work, we provide evidence in vivo that intravenous injection of tPA increases NMDA-induced striatal lesion in the absence of BBB leakage. Accordingly, we show that tPA crosses the BBB both after excitotoxic lesion and in control conditions. Indeed, vascular injected tPA can be detected within the brain parenchyma and in the cerebrospinal fluid. By using an in vitro model of BBB, we have confirmed that tPA can cross the intact BBB. Its passage was blocked at 4°C, was saturable, and was independent of its proteolytic activity. We have shown that tPA crosses the BBB by transcytosis, mediated by a member of the LDL receptor–related protein family.

Conclusions— We demonstrate that blood-derived tPA can reach the brain parenchyma without alteration of the BBB. The molecular mechanism of the passage of tPA from blood to brain described here could represent an interesting target to improve thrombolysis in stroke

Expression of the urokinase plasminogen activator and its receptor in HIV-1-associated central nervous system disease

The urokinase plasminogen activator (uPA) and its receptor (uPAR) play important physiological functions in extracellular proteolysis, as well as cell adhesion and migration. Through dysregulation of these functions, the uPA/uPAR system might be involved in the pathogenesis of AIDS dementia complex (ADC), and, in fact, uPAR has been found to be overexpressed in the cerebrospinal fluid (CSF) and brain tissues of patients with ADC. On the other hand, its ligand uPA has been shown to down-regulate HIV replication in vitro. In this study, we examined uPAR and uPA expression in the brain of HIV-related lesions, as well as CSF levels of soluble uPAR (suPAR), uPA, and complexes between these two molecules (suPAR/uPA) in patients with HIV infection with or without ADC. uPAR was highly expressed by macrophages in both HIV encephalitis (HIV-E) or leukoencephalopathy (HIV-LE), with a distribution exceeding that of HIV p24 antigen. In contrast, uPA was detected only on rare cells in most of the cases. Both uPA and suPAR/uPA complex concentrations were significantly correlated with CSF suPAR levels, and CSF concentrations of both markers were higher in ADC patients than controls. However, uPA levels were substantially lower than corresponding suPAR levels. Although these findings remain correlative, they add support to the hypothesis that uPAR might be an important participant in the events leading to ADC. Additionally, these findings are consistent with a model in which overexpression of uPAR and overproduction of its soluble form may promote HIV replication via binding and removal of uPA from cell surface.

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

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

Involvement of tissue plasminogen activator in onset and effector phases of experimental allergic encephalomyelitis

Inflammation, demyelination, and neurodegeneration are pathological features of multiple sclerosis (MS). In the brains of MS patients, tissue plasminogen activator (tPA) mRNA and protein are upregulated, and changes in the levels of tPA correlate with progression of the disease. However, the role of tPA in MS is as yet unknown. tPA functions in the CNS in neuronal plasticity and cell death. tPA also mediates the activation of microglia, the CNS "immune cells." In this study, we establish that tPA activity increases during major oligodendrocyte glycoprotein-induced experimental allergic encephalomyelitis (EAE) in normal mice. To explore the role of tPA in this disease as a model for MS, we have examined the EAE course and expression of histopathological markers in mice lacking tPA (tPA(-/-)). We find that tPA(-/-) mice have a delayed onset of EAE but then exhibit increased severity and delayed recovery from the neurological dysfunction. Demyelination and axon degeneration are delayed, microglial activation is attenuated, and the production of chemokines is decreased. Our results suggest that tPA and activated microglia have complex roles in MS/EAE, and that these roles are harmful during the onset of the disease but beneficial in the recovery phase. A temporally restricted attenuation of tPA activity could have therapeutic potential in the management of MS.

Involvement of tissue plasminogen activator in onset and effector phases of experimental allergic encephalomyelitis

Inflammation, demyelination, and neurodegeneration are pathological features of multiple sclerosis (MS). In the brains of MS patients, tissue plasminogen activator (tPA) mRNA and protein are upregulated, and changes in the levels of tPA correlate with progression of the disease. However, the role of tPA in MS is as yet unknown. tPA functions in the CNS in neuronal plasticity and cell death. tPA also mediates the activation of microglia, the CNS "immune cells." In this study, we establish that tPA activity increases during major oligodendrocyte glycoprotein-induced experimental allergic encephalomyelitis (EAE) in normal mice. To explore the role of tPA in this disease as a model for MS, we have examined the EAE course and expression of histopathological markers in mice lacking tPA (tPA(-/-)). We find that tPA(-/-) mice have a delayed onset of EAE but then exhibit increased severity and delayed recovery from the neurological dysfunction. Demyelination and axon degeneration are delayed, microglial activation is attenuated, and the production of chemokines is decreased. Our results suggest that tPA and activated microglia have complex roles in MS/EAE, and that these roles are harmful during the onset of the disease but beneficial in the recovery phase. A temporally restricted attenuation of tPA activity could have therapeutic potential in the management of MS.

Blood clot resolution in human cerebrospinal fluid: evidence of first-order kinetics

OBJECTIVE

To determine the kinetics of blood clot resolution in human cerebrospinal fluid.

METHODS

Computed tomographic scans of 17 adult patients with intraventricular hemorrhages were analyzed. Intraventricular clot volume was determined and analyzed over time to determine both a standardized percentage rate and an absolute rate of clot resolution. Results were analyzed by use of regression for cross sectional time-series data. To determine the kinetics of intraventricular clot resolution, the effect of the clot volume on the percentage rate of clot resolution, clot half-life, and absolute rate of clot resolution was analyzed. The potential effect of age, sex, type of hemorrhage, and treatment with external ventricular drainage on the percentage rate of clot resolution was assessed.

RESULTS

The percentage rate of clot resolution was 10.8% per day (95% confidence interval, 9.05-12.61 %), and it was independent of initial clot volume, age, sex, type of underlying hemorrhage, and use of external ventricular drainage. The absolute rate of clot resolution varied directly with the maximal clot volume (R2 = 0.88; P < 0.001). The percentage clot resolution data are consistent with events during the first 24 to 48 hours that antagonize clot resolution.

CONCLUSION

These findings demonstrate that intraventricular blood clot resolution in patients with intraventricular hemorrhage follows first-order kinetics. The thrombolytic enzyme system responsible for intraventricular clot resolution seems to be saturated at 24 to 48 hours after the initial hemorrhage.

Characterization of a brain-related serine protease, neurosin (human kaillikrein 6), in human cerebrospinal fluid

Neurosin (also known as zyme or protease M) is a trypsin-like serine protease dominantly expressed in the human brain. According to the official nomenclature, this gene is now designated as human kallikrein 6 (KLK6) and the protein is designated hK6. To investigate the metabolism of neurosin in human brain, neurosin contained in the human cerebrospinal fluid (CSF) was analyzed. Neurosin was detected in the all CSFs tested by Western blot analysis using an anti-neurosin monoclonal antibody. We purified neurosin from CSF (CSF-neurosin) using an immunoaffinity chromatography and an anion-exchange chromatography. SDS-PAGE revealed that the purified protein has a relative mol. mass (Mr) of 25,000 Da. The observed sequence of the N-terminal amino acids, Glu-Glu-Gln-Asn-Lys, of the purified CSF-neurosin was identical to the sequence of N-terminal of the pro-enzyme form, which is presumed to have no enzyme activity. CSF-neurosin neither showed any enzyme activity to Boc-Phe-Ser-Arg-4-methylcoumaryl-7-amide, which is known to be degraded by the mature neurosin, nor cleaved gelatin. To confirm that the major portion of CSF-neurosin is present in the pro-enzyme form, Western blot analysis using antibodies specific to the pro- or mature enzyme was carried out. The antibody against the mature neurosin fragment did not react with CSF-neurosin. Only the antibody against the pro-enzyme fragment detected CSF-neurosin. Thus, our results suggest that neurosin is present as an inactive pro-enzyme in the human CSF.

Tissue plasminogen activator gene expression in multiple sclerosis brain tissue

Recent studies have implicated tissue-type plasminogen activator (tPA) in neurodegeneration. We studied multiple sclerosis (MS) brain tissue for tPA gene and protein expression in comparison with reference tissue, by in situ hybridisation and immunohistochemistry. MS is characterised by demyelination in the central nervous system. In this study, neuronal cell bodies in MS brain showed high expression of tPA mRNA and protein, while in reference brains, staining for protein and mRNA expression were very low in neurons and mostly restricted to blood vessel walls. In MS, there was an additional staining of mononuclear cells within perivascular cuffs and foamy macrophages within demyelinating plaques. In view of evidence that the final process of demyelination in MS is thought to be enzyme-mediated, our work suggests the involvement of tPA and by inference plasmin, in the demyelinating process. Blocking tPA or plasmin activity may be a potentially beneficial therapeutic approach in MS.

Plasminogen activation in human leukemia and in normal hematopoietic cells

The active process of pericellular proteolysis is central in tumor invasion, and in particular the essential role of the urokinase-type plasminogen activator (uPA) is well established. uPA-mediated plasminogen activation facilitates cell migration and invasion through extracellular matrices by dissolving connective tissue components. uPA, its receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1) are enriched in several types of tumors. The importance of proteolysis and especially plasminogen activation is less clear in hematopoietic malignancies than in solid tumors. However, patients with leukemia have an increased tendency to bleeding, not always attributable to thrombocytopenia, and tissue infiltration by leukemic cells, processes in which plasminogen activation may be involved. Several studies have indicated that plasminogen activators (PAs) are highly expressed by cultured leukemia cells. Furthermore, differing from adherent tumor cells, leukemic cells have an enhanced capacity to activate pro-uPA and mainly the active form of uPA is released to culture medium. Ex vivo studies have shown that uPAR, uPA and its inhibitors can be found on the surface of normal blood cells and on the blast cell surfaces from patients with acute leukemia as well as from plasma samples. Elevated levels of PAs and their inhibitors have been detected in leukemic cell lysates. Few studies have tried to demonstrate a correlation between prognosis of leukemia and levels of plasminogen activators. More in vivo studies are needed to show, if any of the factors of the plasminogen activation process can be used as tools in subclassification or as markers for prognosis in leukemia. This review article will focus on the in vivo studies of plasminogen activation in leukemia and will present several in vitro findings on PAs in normal leukocytes and leukemic cell lines.

Toxicity in a double-blind, placebo-controlled pilot trial with D-penicillamine and metacycline in secondary progressive multiple sclerosis

The serine proteinase tissue-type plasminogen activator (t-PA) and the metalloproteinase gelatinase B (MMP-9) have recently been demonstrated in MS lesions. Both enzymes are interconnected in an enzyme cascade which contributes to destruction of the blood brain barrier and demyelination and both enzymes are inhibited by D-penicillamine. Metacycline was shown in in vitro experiments to inhibit gelatinase B. The combination of peroral D-penicillamine plus metacycline was evaluated in a double-blind placebo-controlled way in two groups of 10 patients suffering from secondary progressive multiple sclerosis. The major objectives of this pilot trial were to examine the safety of this combination and the possibility of blinding, while the effect on disease progression was considered as a secondary endpoint. Over a follow-up period of 1 year and in this selected patient group, there was no significant improvement in the Expanded Disability Status Scale score (EDSS) as compared with that of the placebo-control group. Toxicity was too high to consider additional trials with this combination of metalloproteinase inhibitors. Although peroral treatment is by most MS patients acknowledged as a major improvement in treatment compliance, one has to await the development of more selective and efficacious protease inhibitors than those used in the combination therapy described here.

Cerebrospinal fluid plasminogen activator inhibitor-1 in patients with neurological disease

AIM

To study cerebrospinal fluid (CSF) concentrations of plasminogen activator inhibitor type-1 (PAI-1) in patients with neurological disease.

METHODS

CSF PAI-1 concentrations were measured in 51 patients with neurological disease and 20 reference subjects using an ELISA. The patient group comprised three patients with viral meningitis, 20 with encephalitis, nine with acute lymphoblastic (n = 7) and myeloid (n = 2) leukaemia (with central nervous system involvement), and 19 with multiple sclerosis.

RESULTS

Raised PAI-1 concentrations were observed in patients with leukaemia, encephalitis and multiple sclerosis. There was no difference in the mean concentrations of PAI-1 in patients with meningitis when compared with the reference subjects. The highest mean (SEM) PAI-1 concentration was found in patients with leukaemia (1.28 (0.36) ng/ml), and the next highest in those with encephalitis (1.19 (0.20) ng/ml). these values were much higher than those in patients with viral meningitis. In a previous report, raised CSF tissue-type plasminogen activator (tPA) activities were detected in patients with multiple sclerosis, leukaemia and encephalitis, with mean activities in decreasing order. PAI-1 concentrations in the same patients were the reverse of their corresponding tPA activities, being higher in those with leukaemia and encephalitis, than in patients with multiple sclerosis. There was no association between CSF PAI-1 concentrations and age in either patients or controls. Similarly, there was no association between CSF PAI-1 concentrations and urokinase-type plasminogen activator (uPA).

CONCLUSIONS

Raised CSF PAI-1 concentrations may be used as a non-specific marker of neurological disease. Moreover, PAI-1 may play an important role in regulating the functions tPA, and probably uPA, in CSF.