Tissue-type plasminogen activator is involved in the process of neuronal death induced by oxygen-glucose deprivation in culture

Associations between Huwe1 and autophagy in rat cerebral neuron oxygen‑glucose deprivation and reperfusion injury

Autophagy and the ubiquitin proteasome system (UPS) are two major protein degradation pathways involved in brain ischemia. Autophagy can compensate for UPS impairment-induced cellular dysfunction. HECT, UBA and WWE domain containing E3 ubiquitin protein ligase 1 (Huwe1), an E3 ubiquitin ligase, serves critical roles in nervous system plasticity, regeneration and disease. However, the role of Huwe1 in autophagy in brain ischemia/reperfusion (I/R) injury remains unknown. The aim of the present study was to investigate the crosstalk between autophagy and the UPS in brain ischemia. The present study established an oxygen-glucose deprivation and reperfusion (OGD/R) model in rat primary cortex neurons in vitro. Lentiviral interference was used to silence the expression of Huwe1. An autophagy promoter (rapamycin), an autophagy inhibitor (wortmannin) and a JNK pathway inhibitor (SP600125) were also used in the current study. Cellular autophagy-related proteins, including Beclin-1, autophagy related (ATG) 7, ATG5, ATG3 and microtubule associated protein 1 light chain 3 α, and apoptosis-related proteins, such as P53, cleaved caspase 3, Bax and Bcl2, were detected via western blotting and immunocytochemistry. Neuronal apoptosis was evaluated using a TUNEL assay. The results demonstrated that silencing Huwe1 increased the expression levels of autophagy-related proteins at 24 h after OGD/R. Treatment with a JNK inhibitor or cotreatment with Huwe1 shRNA significantly increased autophagy. Rapamycin increased apoptosis under OGD/R conditions. However, treatment with Huwe1 shRNA decreased the number of TUNEL-positive cells at 24 h after OGD/R. Cotreatment with Huwe1 shRNA and wortmannin alleviated neuronal apoptosis under OGD/R conditions compared with cotreatment with DMSO. Collectively, the present results suggested that silencing Huwe1 was accompanied by a compensatory induction of autophagy under OGD/R conditions. Furthermore, the JNK pathway may be a key mediator of the interaction between Huwe1 and autophagy in response to UPS impairment.

PRODUCTION AND CHARACTERIZATION OF ANTIBODIES TO TISSUE PLASMINOGEN ACTIVATOR: APPLICATION FOR THE PLATELET FLOW CYTOMETRY ASSAY

Tissue plasminogen activator (tPA) is one of the key protein of plasminogen/plasmin system that converts plasminogen in the active proteinase plasmin. Platelets are able to bind both tPA and plasminogen on their surface, thus providing stimulatory effects on activation of zymogen. The present study was aimed to produce polyclonal antibodies against tPA and characterize their immunochemical capacities for further application in flow cytometry assay to study interaction between tPA and platelets. The experimental methods involved immunization of rabbit with tPA, collection of immune serum, synthesis of tPA-containing immunoaffine sorbent, ELISA, and flow cytometry. Polyclonal monospecific antibodies against tPA with high affinity to the antigen (Кd = 4.05・10–9 М) were obtained. Flow cytometry assay based on the use of the produced antibodies showed the presence of binding sites for tPA on the plasma membrane of inactive platelets. Moreover, agonist-stimulated platelets were revealed to expose more binding sites than their resting counterparts. Certain subpopulations of platelets that differ in the ability to bind tPA on their surface were also identified. Obtained data are of significant importance for further investigation of mechanisms underlying the role of platelets to regulate fibrinolytic rates.

Hematoma Expansion Following Intracerebral Hemorrhage: Mechanisms Targeting the Coagulation Cascade and Platelet Activation

Hematoma expansion (HE), defined as a greater than 33% increase in intracerebral hemorrhage (ICH) volume within the first 24 hours, results in significant neurological deficits, and enhancement of ICH-induced primary and secondary brain injury. An escalation in the use of oral anticoagulants has led to a surge in the incidences of oral anticoagulation-associated ICH (OAT-ICH), which has been associated with a greater risk for HE and worse functional outcomes following ICH. The oral anticoagulants in use include vitamin K antagonists, and direct thrombin and factor Xa inhibitors. Fibrinolytic agents are also frequently administered. These all act via differing mechanisms and thus have varying degrees of impact on HE and ICH outcome. Additionally, antiplatelet medications have also been increasingly prescribed, and result in increased bleeding risks and worse outcomes after ICH. Aspirin, thienopyridines, and GPIIb/IIIa receptor blockers are some of the most common agents in use clinically, and also have different effects on ICH and hemorrhage growth, based on their mechanisms of action. Recent studies have found that reduced platelet activity may be more effective in predicting ICH risk, hemorrhage expansion, and outcomes, than antiplatelet agents, and activating platelets may thus be a novel target for ICH therapy. This review explores how dysfunctions or alterations in the coagulation and platelet cascades can lead to, and/or exacerbate, hematoma expansion following intracerebral hemorrhage, and describe the mechanisms behind these effects and the drugs that induce them. We also discuss potential future therapy aimed at increasing platelet activity after ICH.

Recombinant tissue plasminogen activator attenuates basal lamina antigen loss after experimental focal cerebral ischemia

BACKGROUND AND PURPOSE

The use of recombinant tissue plasminogen activator (rt-PA) is a proven therapy in acute stroke. Main concerns are based on hemorrhagic complications, which are connected with microvascular integrity loss. The aim of this study was to evaluate microvascular changes after various doses of rt-PA.

METHODS AND RESULTS

Focal cerebral ischemia for 3 hours was induced using the suture model in rats and followed by 24 hours of reperfusion. Six rats received either saline, 0.9, 9, or 18 mg rtPA/kg body weight at the end of ischemia. By immunostaining of collagen type IV the density of microvessels and the total stained area in the basal ganglia and cortex was measured. Comparison of the ischemic with the non-ischemic hemisphere showed significantly less reduction of the number of microvessels in rats treated with low-dose rt-PA than in the other groups: controls 17 +/- 3% (basal ganglia), 12 +/- 7% (cortex); 0.9 mg rt-PA, 18 +/- 3%, 10 +/- 4%; 9 mg, 21 +/- 4%, 13 +/- 7%; 18 mg, 22 +/- 4%, 15 +/- 8%. A similar effect was observed on the total stained area: control 25 +/- 4% (basal ganglia), 14 +/- 7% (cortex); 0.9 mg rt-PA, 23 +/- 2%, 7 +/- 4%; 9 mg, 28 +/- 4%, 15 +/- 4%; 18 mg, 29 +/- 4%, 17 +/- 5%, p<0.001. The significant reduction of the area of infarction after low and moderate doses of rt-PA was visualized with an MAP2-antibody, and the volume was calculated by 3-D reconstruction: control, 165.2 mm 3 +/- 21%; 0.9 mg rt-PA, 102.6 mm 3 +/- 16%; 9 mg, 101.2 mm 3 +/- 17%; 18 mg, 133.0 mm 3 +/- 24%; p < 0.001.

CONCLUSIONS

Rats exposed to low-dose rt-PA preserved basal lamina structures, and showed smaller infarct sizes. The protective effect of low-dose rt-PA might be due to an increased microvascular patency rate.

Tissue plasminogen activator deficiency promotes early phase regeneration in the olfactory epithelium after bulbectomy

BACKGROUND

Tissue type plasminogen activator (tPA) functions as a fibrinolytic factor in the blood and has unique roles in the nervous system. However, the role of tPA in the olfactory epithelium (OE) is still unclear. Generally, surgical ablation of the olfactory bulb (bulbectomy) triggers degeneration followed by regeneration of OE. In this experimental study, we investigated the role of tPA in OE regeneration.

METHODS

Wild-type (WT) mice and tPA-knockout (tPA(-/-) ) mice were subjected to bulbectomy. Reverse-transcription polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemical examination was done to detect tPA expression in the olfactory bulb and OE. Cellular proliferation and apoptosis was also monitored in the OE.

RESULTS

Before bulbectomy, tPA was found to be expressed in the olfactory bulb and OE. OE degenerated to a similar extent in both strains between 0 and 3 days after bulbectomy. However, OE was thicker and contained more cells in tPA(-/-) mice than in WT mice at 7 days after bulbectomy. Moreover, the number of apoptotic bodies was reduced and the number of proliferating cells was increased in the OE of tPA(-/-) mice compared to WT mice, after bulbectomy. Transmission electron microscopy revealed continuous degeneration of the OE for up to 7 days after bulbectomy in WT mice. In contrast, we observed some intact olfactory vesicles and almost normal supporting cells in the OE of tPA(-/-) mice, at 7 days after bulbectomy.

CONCLUSION

The current findings show that the tPA-plasmin system plays an inhibitory role in the regulation of regeneration in the OE.

Excessive fibrin deposition in nasal polyps caused by fibrinolytic impairment through reduction of tissue plasminogen activator expression

RATIONALE

Nasal polyps (NPs) are characterized by intense edema or formation of pseudocysts filled with plasma proteins, mainly albumin. However, the mechanisms underlying NP retention of plasma proteins in their submucosa remain unclear.

OBJECTIVES

We hypothesized that formation of a fibrin mesh retains plasma proteins in NPs. We assessed the fibrin deposition and expression of the components of the fibrinolytic system in patients with chronic rhinosinusitis (CRS).

METHODS

We assessed fibrin deposition in nasal tissue from patients with CRS and control subjects by means of immunofluorescence. Fibrinolytic components, d-dimer, and plasminogen activators were measured using ELISA, real-time PCR, and immunohistochemistry. We also performed gene expression and protein quantification analysis in cultured airway epithelial cells.

MEASUREMENTS AND MAIN RESULTS

Immunofluorescence data showed profound fibrin deposition in NP compared with uncinate tissue (UT) from patients with CRS and control subjects. Levels of the cross-linked fibrin cleavage product protein, d-dimer, were significantly decreased in NP compared with UT from patients with CRS and control subjects, suggesting reduced fibrinolysis (P < 0.05). Expression levels of tissue plasminogen activator (t-PA) mRNA and protein were significantly decreased in NP compared with UT from patients with CRS and control subjects (P < 0.01). Immunohistochemistry demonstrated clear reduction of t-PA in NP, primarily in the epithelium and glands. Th2 cytokine-stimulated cultured airway epithelial cells showed down-regulation of t-PA, suggesting a potential Th2 mechanism in NP.

CONCLUSIONS

A Th2-mediated reduction of t-PA might lead to excessive fibrin deposition in the submucosa of NP, which might contribute to the tissue remodeling and pathogenesis of CRS with nasal polyps.

Morphological assessment of the luminal surface of olfactory epithelium in mice deficient in tissue plasminogen activator following bulbectomy

OBJECTIVE

This study aimed to investigate the function of tissue plasminogen activator in the olfactory epithelium of mice following neural injury.

METHOD

Transmission electron microscopy was used to study the changes in the morphology of the olfactory epithelium 1-7 days after surgical ablation of the olfactory bulb (bulbectomy).

RESULTS

Prior to bulbectomy, a uniformly fine material was observed within some regions of the olfactory epithelium of mice deficient in tissue plasminogen activator. At 2-3 days after bulbectomy, there were degenerative changes in the olfactory epithelium. At 5-7 days after bulbectomy, we noted drastic differences in olfactory epithelium morphology between mice deficient in tissue plasminogen activator and wild-type mice (comparisons were made using findings from a previous study). The microvilli seemed to be normal and olfactory vesicles and receptor neuron dendrites were largely intact in the olfactory epithelium of mice deficient in tissue plasminogen activator.

CONCLUSION

The tissue plasminogen activator plasmin system may inhibit the regeneration of the olfactory epithelium in the early stages following neural injury.

Essential role of interleukin-6 in post-stroke angiogenesis

Ambivalent effects of interleukin-6 on the pathogenesis of ischaemic stroke have been reported. However, to date, the long-term actions of interleukin-6 after stroke have not been investigated. Here, we subjected interleukin-6 knockout (IL-6(-/-)) and wild-type control mice to mild brain ischaemia by 30-min filamentous middle cerebral artery occlusion/reperfusion. While ischaemic tissue damage was comparable at early time points, IL-6(-/-) mice showed significantly increased chronic lesion volumes as well as worse long-term functional outcome. In particular, IL-6(-/-) mice displayed an impaired angiogenic response to brain ischaemia with reduced numbers of newly generated endothelial cells and decreased density of perfused microvessels along with lower absolute regional cerebral blood flow and reduced vessel responsivity in ischaemic striatum at 4 weeks. Similarly, the early genomic activation of angiogenesis-related gene networks was strongly reduced and the ischaemia-induced signal transducer and activator of transcription 3 activation observed in wild-type mice was almost absent in IL-6(-/-) mice. In addition, systemic neoangiogenesis was impaired in IL-6(-/-) mice. Transplantation of interleukin-6 competent bone marrow into IL-6(-/-) mice (IL-6(chi)) did not rescue interleukin-6 messenger RNA expression or the early transcriptional activation of angiogenesis after stroke. Accordingly, chronic stroke outcome in IL-6(chi) mice recapitulated the major effects of interleukin-6 deficiency on post-stroke regeneration with significantly enhanced lesion volumes and reduced vessel densities. Additional in vitro experiments yielded complementary evidence, which showed that after stroke resident brain cells serve as the major source of interleukin-6 in a self-amplifying network. Treatment of primary cortical neurons, mixed glial cultures or immortalized brain endothelia with interleukin 6-induced robust interleukin-6 messenger RNA transcription in each case, whereas oxygen-glucose deprivation did not. However, oxygen-glucose deprivation of organotypic brain slices resulted in strong upregulation of interleukin-6 messenger RNA along with increased transcription of key angiogenesis-associated genes. In conclusion, interleukin-6 produced locally by resident brain cells promotes post-stroke angiogenesis and thereby affords long-term histological and functional protection.

Biphasic regulation of tissue plasminogen activator activity in ischemic rat brain and in cultured neural cells: essential role of astrocyte-derived plasminogen activator inhibitor-1

In brain, the serine protease tissue plasminogen activator (tPA) and its endogenous inhibitor plasminogen activator inhibitor-1 (PAI-1) have been implicated in the regulation of various neurophysiological and pathological responses. In this study, we investigated the differential role of neurons and astrocytes in the regulation of tPA/PAI-1 activity in ischemic brain. The activity of tPA peaked transiently and then decreased in cortex and striatum along with delayed induction of PAI-1 in the inflammatory stage after MCAO/reperfusion injury. In cultured primary cells, glutamate stimulation increased tPA activity in neurons but not in other cells such as microglia and astrocytes. With LPS stimulation, a model of neuroinflammatory insults, robust PAI-1 induction was observed in astrocytes but not in neurons and microglia. The upregulation of PAI-1 by LPS in astrocytes was also verified by RT-PCR analysis as well as PAI-1 promoter reporter assay. Lastly, we checked the effects of hypoxia on tPA/PAI-1 activity. Hypoxia increased tPA release from neurons without effects on microglia, while the activity of tPA in astrocyte was decreased consistent with increased PAI-1 activity in astrocyte. Taken together, the results from the present study suggest that neurons are the major source of tPA and that the glutamate-induced stimulated release is mainly governed by neurons in the acute phase. In contrast, the massive up-regulation of PAI-1 in astrocytes during subchronic and chronic inflammatory conditions, leads to decreased tPA activity in the later stages of MCAO. Differential regulation of tPA and PAI-1 in neurons, astrocytes and microglia suggest more attention is required to understand the role of local tPA activity in the vicinity of individual cell types.

Administration of free radical scavenger edaravone associated with higher frequency of hemorrhagic transformation in patients with cardiogenic embolism

Free radicals are known to activate coagulation and inhibit fibrinolysis. Edaravone, a free radical scavenger, protects vascular endothelial cells and neurons during acute brain ischemia in in vitro models. Hemorrhagic transformation and treatment outcomes were retrospectively examined in 76 patients with acute cardiogenic embolism treated with edaravone in addition to routine treatment within 24 hours of the onset of symptoms. Hemorrhagic transformation was categorized according to European Cooperative Acute Stroke Study-II. Patient characteristics were also evaluated, including evidence of hypertension, diabetes mellitus, hyperlipidemia, coronary heart disease, history of smoking, National Institutes of Health Stroke Scale on arrival, and modified Rankin scale at 3 months post-onset. Edaravone administration was one of the factors that contributed to increased frequency of hemorrhagic transformation, but had showed no significant relationship with the outcome. The present study showed that edaravone administration increased the frequency of hemorrhagic transformation with heparin in patients with cardiogenic embolism. Free radical scavenging may have promoted the coagulating conditions. Edaravone administration may allow reduction of the dose of heparin and tissue plasminogen activator in patients with acute ischemic stroke.

Deleterious effects of plasminogen activators in neonatal cerebral hypoxia-ischemia

The immature brains of newborns often respond differently from the brains of adults when exposed to similar insults. Previous studies have indicated that although hypoxia-ischemia (HI) induces persistent thrombosis in adult brains, it only modestly impairs blood perfusion in newborn brains. Here, we used the Vannucci model of HI encephalopathy to study age-related responses to cerebral HI in rat pups. We found that HI triggered fibrin deposition and impaired blood perfusion in both neonatal and adult brains. However, these effects were only transient in neonatal brains (<4 hours) and were accompanied by acute induction of both tissue-type and urinary-type plasminogen activators (tPA and uPA), which was not observed in adult brains subjected to the same insult. Interestingly, activation of the plasminogen system persisted up to 24 hours in neonatal brains, long after the clearance of fibrin-rich thrombi. Furthermore, astrocytes and macrophages outside blood vessels expressed tPA after HI, suggesting the possibility of tPA/plasmin-mediated cytotoxicity. Consistent with this hypothesis, injection of alpha2-antiplasmin into cerebral ventricles markedly ameliorated HI-induced damage to neurofilaments and white matter oligodendrocytes, providing a dose-response reduction of brain injury after 7 days of recovery. Conversely, ventricular injection of tPA increased HI-induced brain damage. Together, these results suggest that tPA/plasmin induction, which may contribute to acute fibrinolysis, is a critical component of extravascular proteolytic damage in immature brains, representing a new therapeutic target for the treatment of HI encephalopathy.

Novel actions of tissue-type plasminogen activator in chronic kidney disease

Tissue-type plasminogen activator (tPA) is traditionally viewed as a simple serine protease whose main function is to convert plasminogen into biologically active plasmin. As a protease, tPA plays a crucial role in regulating blood fibrinolysis, in maintaining the homeostasis of extracellular matrix and in modulating the post-translational activation of growth factors. However, emerging evidence indicates that tPA also functions as a cytokine that transmits its signal across the cell membrane, initiates a diverse array of intracellular signaling, and dictates gene expression in the nuclei. tPA binds to the cell membrane LDL receptor-related protein 1 (LRP-1), triggers its tyrosine phosphorylation. As a cytokine, tPA plays a pivotal role in the pathogenesis of renal interstitial fibrosis through diverse mechanisms. It facilitates tubular epithelial to mesenchymal transition, potentiates myofibroblast activation, and protects renal interstitial fibroblasts/myofibroblasts from apoptosis. Together, growing evidence has implicated tPA as a fibrogenic cytokine that promotes the progression of kidney diseases. These new findings have radically changed our conception of tPA in renal fibrogenesis and represent a paradigm shift towards uncovering its cytokine function.

Global profiling of influence of intra-ischemic brain temperature on gene expression in rat brain

Mild to moderate differences in brain temperature are known to greatly affect the outcome of cerebral ischemia. The impact of brain temperature on ischemic disorders has been mainly evaluated through pathological analysis. However, no comprehensive analyses have been conducted at the gene expression level. Using a high-density oligonucleotide microarray, we screened 24000 genes in the hippocampus under hypothermic (32 degrees C), normothermic (37 degrees C), and hyperthermic (39 degrees C) conditions in a rat ischemia-reperfusion model. When the ischemic group at each intra-ischemic brain temperature was compared to a sham-operated control group, genes whose expression levels changed more than three-fold with statistical significance could be detected. In our screening condition, thirty-three genes (some of them novel) were obtained after screening, and extensive functional surveys and literature reviews were subsequently performed. In the hypothermic condition, many neuroprotective factor genes were obtained, whereas cell death- and cell damage-associated genes were detected as the brain temperature increased. At all intra-ischemic brain temperatures, multiple molecular chaperone genes were obtained. The finding that intra-ischemic brain temperature affects the expression level of many genes related to neuroprotection or neurotoxicity coincides with the different pathological outcomes at different brain temperatures, demonstrating the utility of the genetic approach.

Tissue-type plasminogen activator as a therapeutic target in stroke

BACKGROUND

Ischemic stroke is a leading cause of morbidity and mortality worldwide and recombinant human tissue-type plasminogen activator (tPA) is the prominent therapeutic among very few therapeutics used in its treatment. Due to complications attributed to the drug, most notably transformation of ischemia to hemorrhage, tPA is only used in a small number of ischemic stroke cases, albeit significantly more often in specialized stroke centers.

OBJECTIVE

What are the mechanisms of tPA action and side effects in ischemic stroke, and can the knowledge about these mechanisms aid in making tPA a more efficacious and safe therapeutic or in developing alternative therapeutics?

METHODS

tPA use and alternative/combination therapies in acute ischemic stroke treatment are summarized. The review focuses on literature concerning tPA neurotoxicity and its implications for further development of tPA as a stroke therapeutic.

RESULTS/CONCLUSION

Exogenously administered recombinant tPA and endogenous tPA have both turned into promising therapeutic targets for the stroke patient.

Perindoprilat modulates the activity of lipoprotein receptor-related protein in human mesangial cells

Low density lipoprotein receptor-related protein (LRP) is a multifunctional endocytic receptor implicated in the modulation of a number of cellular processes, including the turnover of proteases and the degradation of extracellular matrix proteins. As such, it can play a key role in the control of fibrosis. The aim of this investigation was to ascertain whether the anti-fibrotic effects exerted by the angiotensin-converting enzyme inhibitor (ACE-I) perindoprilat on macrophage-conditioned medium (MPCM)-injured human mesangial cells can be modulated by this receptor. Addition of receptor-associated protein to MPCM-injured mesangial cells with and without ACE-I increased the amount of tissue plasminogen activator protein detected in mesangial cell culture supernatants without affecting the protein levels of plasminogen activator inhibitor-1. The ability of ACE-I to reduce fibronectin was diminished in the presence of receptor-associated protein. ACE-I induced an increase in mesangial cell MMP9 mRNA, but reduced the MMP9 enzyme activity detected in mesangial cell supernatants. Mesangial cell lysates from ACE-I-treated cells were able to bind immobilized fibronectin at higher dilutions than cell lysates from untreated cells. Flow cytometry showed that MPCM induced an increase in LRP surface expression in mesangial cells over that in control cells and that this expression was further increased by ACE-I treatment. The increase in LRP expression in response to ACE-I was also observed by Western blotting. Northern blot analysis of RNA extracted from cells following a 24-h exposure to MPCM with and without ACE-I demonstrated that there was no change in LRP mRNA expression upon ACE-I treatment. In conclusion, we show that ACE-I treatment is able to modulate mesangial cell-surface expression of LRP, providing an additional mechanism whereby ACE-Is can mediate anti-fibrotic actions independent of their hemodynamic actions.

Tissue-type plasminogen activator promotes murine myofibroblast activation through LDL receptor-related protein 1-mediated integrin signaling

The activation of interstitial fibroblasts to become alpha-SMA-positive myofibroblasts is an essential step in the evolution of chronic kidney fibrosis, as myofibroblasts are responsible for the production and deposition of the ECM components that are a hallmark of the disease. Here we describe a signaling pathway that leads to this activation. Tissue-type plasminogen activator (tPA) promoted TGF-beta1-mediated alpha-SMA and type I collagen expression in rat kidney interstitial fibroblasts. This fibrogenic effect was independent of its protease activity but required its membrane receptor, the LDL receptor-related protein 1 (LRP-1). In rat kidney fibroblasts, tPA induced rapid LRP-1 tyrosine phosphorylation and enhanced beta1 integrin recruitment by facilitating the LRP-1/beta1 integrin complex formation. Blockade or knockdown of beta1 integrin abolished type I collagen and alpha-SMA expression. Furthermore, inhibition of the integrin-linked kinase (ILK), a downstream effector of beta1 integrin, or disruption of beta1 integrin/ILK engagement, abrogated the tPA action, whereas ectopic expression of ILK mimicked tPA in promoting myofibroblast activation. In murine renal interstitium after obstructive injury, tPA and alpha-SMA colocalized with LRP-1, and tPA deficiency reduced LRP-1/beta1 integrin interaction and myofibroblast activation. These findings show that tPA induces LRP-1 tyrosine phosphorylation, which in turn facilitates the LRP-1-mediated recruitment of beta1 integrin and downstream ILK signaling, thereby leading to myofibroblast activation. This study implicates tPA as a fibrogenic cytokine that promotes the progression of kidney fibrosis.

Enhanced poly(ADP-ribose) polymerase-1 activation contributes to recombinant tissue plasminogen activator-induced aggravation of ischemic brain injury in vivo

Recombinant tissue plasminogen activator (rt-PA) treatment improves functional outcome after acute ischemic stroke, inducing reperfusion by its thrombolytic activity. Conversely, there is evidence that rt-PA can mediate neuronal damage after ischemic brain injury in vivo. In addition to other mechanisms, enhancement of N-methyl-D-aspartate (NMDA) receptor signalling has been proposed to underlie rt-PA-mediated neurotoxicity. However, the role of poly(ADP-ribose) polymerase-1 (PARP-1) activation, which mediates postischemic excitotoxic cell death, in rt-PA-mediated aggravation of ischemic brain injury has not been established and was therefore addressed in this study. After permanent focal cerebral ischemia, intravenous rt-PA application significantly increased early postischemic PARP-1 activation within ischemic hemispheres and infarct volumes compared with control mice without affecting cerebral blood flow. Rt-PA induced increase in PARP-1 activation, and infarct volumes could be blocked by the PARP inhibitor 3-aminobenzamide. Moreover, the rt-PA-induced increase in PARP-1 activation was also prevented by the NMDA antagonist MK-801. In summary, we demonstrate that rt-PA treatment enhances postischemic PARP-1 activation, which contributes to rt-PA induced aggravation of ischemic brain injury in vivo. Furthermore, we provide evidence that NMDA receptor activation is required for rt-PA-mediated effects on postischemic PARP-1 activation.

Reduction of hippocampal cell death and proteolytic responses in tissue plasminogen activator knockout mice after transient global cerebral ischemia

Knockout mice deficient in tissue plasminogen activator (tPA) are protected against hippocampal excitotoxicity. But it is unknown whether similar neuroprotection occurs after transient global cerebral ischemia, which is known to selectively affect the hippocampus. In this study, we tested the hypothesis that hippocampal cell death in tPA knockout mice would be reduced after transient global cerebral ischemia, and this neuroprotection would occur concomitantly with amelioration of both intra- and extracellular proteolytic cascades. Wild-type and tPA knockout mice were subjected to 20 min of transient bilateral occlusions of the common carotid arteries. Three days later, Nissl and terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling staining demonstrated that hippocampal cell death was significantly reduced in tPA knockout brains compared with wild-type brains. Caspase-3 and the two major brain gelatinases (matrix metalloproteinase (MMP)-9 and MMP-2) were assessed as representative measurements of intra- and extracellular proteolysis. Post-ischemic levels of caspase-3, MMP-9 and MMP-2 were similarly reduced in tPA knockouts compared with wild-type hippocampi. Taken together, these data suggest that endogenous tPA contributes to hippocampal injury after cerebral ischemia, and these pathophysiologic pathways may involve links to aberrant activation of caspases and MMPs.

Stromelysin-1 (MMP-3) is critical for intracranial bleeding after t-PA treatment of stroke in mice

BACKGROUND

Tissue-type plasminogen activator (t-PA) is approved for treatment of ischemic stroke patients, but it may increase the risk of intracranial bleeding (ICB). Matrix metalloproteinases (MMPs), which can be activated through the plasminogen/plasmin system, may contribute to ICB after ischemic stroke.

OBJECTIVES

To explore the contribution of plasminogen, MMP-3 and MMP-9 to ICB associated with t-PA treatment after ischemic stroke.

METHODS

Using a thrombotic middle cerebral artery occlusion (MCA-O) model, ICB was studied in mice with genetic deficiencies of plasminogen (Plg(-/-)), stromelysin-1 (MMP-3(-/-)), or gelatinase B (MMP-9(-/-)) and their corresponding wild-type (WT) littermates. The induction of MMP-3 and MMP-9 was also studied in C57BL/6 WT mice.

RESULTS

ICB induced by t-PA (10 mg kg(-1)) was significantly less than WT in Plg(-/-) (P < 0.05) and MMP-3(-/-) (P < 0.05) but not in MMP-9(-/-) mice. Furthermore, administration of the broad-spectrum MMP inhibitor GM6001 after t-PA treatment reduced ICB significantly (P < 0.05) in MMP-3(+/+) mice, but had no effect on MMP-3(-/-) mice. MMP-3 expression was significantly enhanced at the ischemic hemisphere; with placebo treatment, it was expressed only in neurons, whereas it was up-regulated in endothelial cells with t-PA treatment. Although MMP-9 expression was also significantly enhanced at the ischemic brain, the amount and the distribution were comparable in mice with and without t-PA treatment.

CONCLUSIONS

Our data with gene-deficient mice thus suggest that plasminogen and MMP-3 are relatively more important than MMP-9 for the increased ICB induced by t-PA treatment of ischemic stroke.

Neurotoxic effects of exogenous recombinant tissue-type plasminogen activator on the normal rat brain

Thrombolytic therapy with intravenous and intra-arterial recombinant tissue-type plasminogen activator (rtPA) has been established for the treatment of acute ischemic stroke. However, tPA has also been suggested to have neurotoxic effects. The purpose of this study was to examine direct neurotoxicity of rtPA in vivo. The animals (Wistar rats) were divided to the following three groups: low-dose (15 micromol/L) rtPA group (n = 6); high-dose (30 micromol/L) rtPA group (n = 6); and control (physiological saline) group (n = 6). The rtPA solution was perfused into the cortex via a microdialysis probe. The volume of the lesion was quantified histologically by image analysis of the lesions. Blood-brain barrier (BBB) disruption was evaluated by intravenous injection of Evans blue, and injury to the basal lamina was evaluated by immunohistochemistry using an anti-laminin antibody. In the rtPA-perfused animals, a pale lesion was produced around the probe, and microscopically, neurons showed necrotic changes. The volume of the lesions increased significantly as the concentration of perfused rtPA was increased. Marked extravasation of Evans blue was observed, and laminin immunoreactivity of blood vessels in the rtPA-induced lesions was lost. These results suggest that rtPA promotes acute direct neurotoxicity and participates in disruption of the microvascular basal lamina to cause BBB disruption, thereby increasing edema formation.

LRP and alphavbeta3 mediate tPA activation of smooth muscle cells

Tissue-type plasminogen activator (tPA) regulates vascular contractility through the low-density lipoprotein-related receptor (LRP), and this effect is inhibited by plasminogen activator inhibitor type 1 (PAI-1). We now report that tPA-mediated vasocontraction also requires the integrin alphavbeta3. tPA-induced contraction of rat aortic rings is inhibited by the Arg-Gly-Asp (RGD) peptide and by monoclonal anti-alphavbeta3 antibody. tPA induces the formation of a complex between LRP and alphavbeta3 in vascular smooth muscle cells. The three proteins are internalized within 10 min, causing the cells to become refractory to the readdition of tPA. LRP and alphavbeta3 return to the cell surface by 90 min, restoring cell responsiveness to tPA. PAI-1 and the PAI-1-derived hexapeptide EEIIMD abolish the vasocontractile activity of tPA and inhibit the tPA-mediated interaction between LRP and alphavbeta3. tPA induces calcium mobilization from intracellular stores in vascular smooth muscle cells, and this effect is inhibited by PAI-1, RGD, and antibodies to both LRP and alphavbeta3. These data indicate that tPA-mediated vasocontraction involves the coordinated interaction of LRP with alphavbeta3. Delineating the mechanism underlying these interactions and the nature of the signals transduced may provide new tools to regulate vascular tone and other consequences of tPA-mediated signaling.

Tissue-type plasminogen activator acts as a cytokine that triggers intracellular signal transduction and induces matrix metalloproteinase-9 gene expression

Tissue-type plasminogen activator (tPA), a serine protease well known for generating plasmin, has been demonstrated to induce matrix metalloproteinase-9 (MMP-9) gene expression and protein secretion in renal interstitial fibroblasts. However, exactly how tPA transduces its signal into the nucleus to control gene expression is unknown. This study investigated the mechanism by which tPA induces MMP-9 gene expression. Both wild-type and non-enzymatic mutant tPA were found to induce MMP-9 expression in rat kidney interstitial fibroblasts (NRK-49F), indicating that the actions of tPA are independent of its proteolytic activity. tPA bound to the low density lipoprotein receptor-related protein-1 (LRP-1) in NRK-49F cells, and this binding was competitively abrogated by the LRP-1 antagonist, the receptor-associated protein. In mouse embryonic fibroblasts (PEA-13) lacking LRP-1, tPA failed to induce MMP-9 expression. Furthermore, tPA induced rapid tyrosine phosphorylation on the beta subunit of LRP-1, which was followed by the activation of Mek1 and its downstream Erk-1 and -2. Blockade of Erk-1/2 activation by the Mek1 inhibitor abolished MMP-9 induction by tPA in NRK-49F cells. Conversely, overexpression of constitutively activated Mek1 induced Erk-1/2 phosphorylation and MMP-9 expression. In mouse obstructed kidney, tPA, LRP-1, and MMP-9 were concomitantly induced in the renal interstitium. Collectively, these results suggest that besides its classical proteolytic activity, tPA acts as a cytokine that binds to the cell membrane receptor LRP-1, induces its tyrosine phosphorylation, and triggers intracellular signal transduction, thereby inducing specific gene expression in renal interstitial fibroblasts.

Effects of plasminogen activator inhibitor-1 on ischemic brain injury in permanent and thrombotic middle cerebral artery occlusion models in mice

BACKGROUND AND OBJECTIVES

Tissue plasminogen activator (t-PA) improves the outcome of ischemic stroke by recanalization of occluded vessels, but has neurotoxic side effects in experimental stroke models. Here, the effect of plasminogen activator inhibitor-1 (PAI-1), an endogenous inhibitor of t-PA, on ischemic infarct volume was studied.

METHODS

After either permanent ligation or thrombotic occlusion of the middle cerebral artery (MCA), infarct volume, spontaneous reperfusion of thrombosed MCA, t-PA/PAI-1 complex level, and blood-brain barrier (BBB) permeability in the ischemic region was studied in transgenic mice with overexpression of PAI-1 and wild-type littermate controls and in mice with intracerebroventricular injection of human PAI-1.

RESULTS

Infarct volume was smaller in PAI-1 transgenic mice (2.9 +/- 3.7 mm3, mean +/- SD) than in controls (8.9 +/- 5.0 mm3, P < 0.05) after permanent MCA ligation (plasma PAI-1 level 39 +/- 23 ng mL(-1) in transgenic mice vs. 1.5 +/- 0.6 ng mL(-1) in controls), whereas after MCA thrombosis it was larger in transgenics (13.1 +/- 3.1 mm3) than in controls (8.0 +/- 3.2 mm3, P < 0.05). Spontaneous reperfusion of the thrombosed MCA was significantly delayed in transgenic vs. control mice. In the ligation model, t-PA/PAI-1 complex levels were higher and BBB disruption was more pronounced in the ischemic region. Human PAI-1 injection reduced infarct volume by about 50% in wild-type mice but not in t-PA gene deficient mice.

CONCLUSIONS

High PAI-1 levels reduced infarct volume in the permanent MCA ligation model, but enhanced it in the MCA thrombosis model.

Vampire bat salivary plasminogen activator (desmoteplase) inhibits tissue-type plasminogen activator-induced potentiation of excitotoxic injury

BACKGROUND AND PURPOSE

In contrast to tissue-type plasminogen activator (tPA), vampire bat (Desmodus rotundus) salivary plasminogen activator (desmoteplase [DSPA]) does not promote excitotoxic injury when injected directly into the brain. We have compared the excitotoxic effects of intravenously delivered tPA and DSPA and determined whether DSPA can antagonize the neurotoxic and calcium enhancing effects of tPA.

METHODS

The brain striatal region of wild-type c57 Black 6 mice was stereotaxically injected with N-methyl-d-Aspartate (NMDA); 24 hour later, mice received an intravenous injection of tPA or DSPA (10 mg/kg) and lesion size was assessed after 24 hours. Cell death and calcium mobilization studies were performed using cultures of primary murine cortical neurons.

RESULTS

NMDA-mediated injury was increased after intravenous administration of tPA, whereas no additional toxicity was seen after administration of DSPA. Unlike DSPA, tPA enhanced NMDA-induced cell death and the NMDA-mediated increase in intracellular calcium levels in vitro. Moreover, the enhancing effects of tPA were blocked by DSPA.

CONCLUSIONS

Intravenous administration of tPA promotes excitotoxic injury, raising the possibility that leakage of tPA from the vasculature into the parenchyma contributes to brain damage. The lack of such toxicity by DSPA further encourages its use as a thrombolytic agent in the treatment of ischemic stroke.

Oxygen glucose deprivation switches the transport of tPA across the blood-brain barrier from an LRP-dependent to an increased LRP-independent process

BACKGROUND AND PURPOSE

Despite uncontroversial benefit from its thrombolytic activity, the documented neurotoxic effect of tissue plasminogen activator (tPA) raises an important issue: the current emergency stroke treatment might not be optimum if exogenous tPA can enter the brain and thus add to the deleterious effects of endogenous tPA within the cerebral parenchyma. Here, we aimed at determining whether vascular tPA crosses the blood-brain barrier (BBB) during cerebral ischemia, and if so, by which mechanism.

METHODS

First, BBB permeability was assessed in vivo by measuring Evans Blue extravasation following intravenous injection at 0 or 3 hours after middle cerebral artery electrocoagulation in mice. Second, the passage of vascular tPA was investigated in an in vitro model of BBB, subjected or not to oxygen and glucose deprivation (OGD).

RESULTS

We first demonstrated that after focal permanent ischemia in mice, the BBB remains impermeable to Evans Blue in the early phase (relative to the therapeutic window of tPA), whereas at later time points massive Evans Blue extravasation occurs. Then, the passage of tPA during these 2 phases, was investigated in vitro and we show that in control conditions, tPA crosses the intact BBB by a low-density lipoprotein (LDL) receptor-related protein (LRP)-dependent transcytosis, whereas OGD leads to an exacerbation of tPA passage, which switches to a LRP-independent process.

CONCLUSIONS

We evidence 2 different mechanisms through which vascular tPA can reach the brain parenchyma, depending on the state of the BBB. As discussed, these data show the importance of taking the side effects of blood-derived tPA into account and offer a basis to improve the current thrombolytic strategy.

Ontogenic study of the influence of tissue plasminogen activator (t-PA) in neonatal excitotoxic brain insult and the subsequent microglia/macrophage activation

Intracerebral injections of ibotenic acid in neonatal mice produced white and gray matter lesions that mimic some aspects of the acquired cerebral injuries observed in human newborns (i.e. periventricular leukomalacias in preterm newborns and post-ischemic cortical necrosis in at term infants). We have evaluated the effects of tissue plasminogen activator inactivation (t-PA-/-) on the effects of ibotenic acid (0.01-20 microg), and on F4/80 labeling of microglia/macrophages at different stages. Three ontogenic periods have been identified. In mice injected the day of birth, postnatal (P) day 0, ibotenic acid induced neuronal migration disorders together with low local microglial activation in wild-type and t-PA-/- mice. In P2 and P5 mice, ibotenic acid induced diffuse microglial activation in the whole cortex and subcortical areas; e.g. caudate nucleus and septum. In wild-type mice, cystic lesions of the white matter were consistently observed, surrounded by macrophages. In t-PA-/- mice, noncystic lesions filled of macrophages were more frequent than cysts. Macrophages were virtually absent in the gray matter. White and gray matter lesions were reduced in t-PA-/- mice. The plasmin inhibitor aprotinin reduced white and gray matter lesions only in wild-type mice injected with high ibotenic acid doses (2.5-5 microg). During this period, a transient F4/80 immunoreactive cell population was detected in the cingulum. At P10, the salient lesion characteristic was a large gray matter lesion containing macrophage accumulation. Microglial activation was confined to the injection site in the white matter. t-PA-/- mice showed reduced lesion size under high doses (>5 microg) of ibotenic acid. Similarly, aprotinin diminished the lesion in wild-type animals exposed to 10 microg ibotenic acid. These data demonstrate that t-PA and microglia do not actively participate in the migration disorders induced in P0 mice. Conversely, t-PA was implicated in cyst formation in older (P2-P10) mice, and in their subsequent growth. t-PA was also involved in GM lesions, probably through an inflammatory process involving macrophages.

Effect of reduction in endogenous dopamine on extrastriatal binding of [11C]FLB 457 in rat brain—An ex vivo study

Carbon-11 labeled FLB 457 has been used successfully as a selective, high affinity PET ligand for the quantification of extrastriatal D2-like receptors in man. This study was carried out in rats to investigate regional values for maximal binding and ED50 (a measure of apparent K(d)) for the radioligand in vivo in control animals and in a group pretreated with the neuronal impulse flow inhibitor, gamma-butyrolactone. The aims were to obtain further information regarding the specific activity needed to ensure tracer kinetics and to investigate baseline occupancy by dopamine (DA), each relevant to optimal clinical use of the radioligand. Regional B(max) values were consistent with the distribution of D2-like receptors in rat brain. Of interest, 60% of the binding in cerebellum, often used as a low-binding "reference region" for PET quantification, was saturable, with B(max) only 2- to 3-fold less than that in neocortex, hippocampus, and thalamus. ED50 values were in the range 2-3 nmol/kg, confirming minimal receptor occupancy by the tracer in human PET, using high but achievable specific activities. In the majority of extrastriatal tissues, reduction in synaptic DA did not significantly decrease the apparent K(d), except in cortical regions, where the extent of the effect suggested a low ( approximately 10%), but measurable baseline receptor occupancy by DA.

The neurotoxicity of tissue plasminogen activator?

Tissue plasminogen activator (tPA), a fibrin specific activator for the conversion of plasminogen to plasmin, stimulates thrombolysis and rescues ischemic brain by restoring blood flow. However, emerging data suggests that under some conditions, both tPA and plasmin, which are broad spectrum protease enzymes, are potentially neurotoxic if they reach the extracellular space. Animal models suggest that in severe ischemia with injury to the blood brain barrier (BBB) there is injury attributed to the protease effects of this exogenous tPA. Besides clot lysis per se, tPA may have pleiotropic actions in the brain, including direct vasoactivity, cleaveage of the N-methyl-D-aspartate (NMDA) NR1 subunit, amplification of intracellular Ca++ conductance, and activation of other extracellular proteases from the matrix metalloproteinase (MMP) family, e.g. MMP-9. These effects may increase excitotoxicity, further damage the BBB, and worsen edema and cerebral hemorrhage. If tPA is effective and reverses ischemia promptly, the BBB remains intact and exogenous tPA remains within the vascular space. If tPA is ineffective and ischemia is prolonged, there is the risk that exogenous tPA will injure both the neurovascular unit and the brain. Methods of neuroprotection, which prevent tPA toxicity or additional mechanical means to open cerebral vessels, are now needed.

ACE inhibition actively promotes cell survival by altering gene expression

We tested the effect of ACE inhibition on the survival of bovine retinal (REC) and choroidal (CEC) endothelial cells (EC) in culture. The ACE inhibitor captopril delayed the apoptotic tube collapse of REC on Matrigel for >15 days. Captopril treatment of confluent monolayers (2-8 weeks) followed by slow starvation (2-4 weeks) increased EC viability by approximately 200%. Two-week captopril exposures were sufficient to confer maximal protection. Only vehicle-treated EC demonstrated apoptotic features such as membrane blebbing and DNA laddering. By RT-PCR, the starvation marker p202 was upregulated only in starved cells. In REC, captopril upregulated the pro-survival proteins mortalin-2, uPA, and uPAR while downregulating the anti-growth sprouty-4 and tPA. In CEC, captopril also upregulated tPA and its inhibitor PAI-1. Amiloride (uPA inhibitor) blocked the captopril-induced increase in EC survival, secondary sprouting, and invasion in Matrigel. The pro-survival effects of captopril involve the reprogramming of genes involved in cell survival and immortalization.

Na+/H+ exchanger inhibitor, SM-20220, is protective against excitotoxicity in cultured cortical neurons

BACKGROUND AND PURPOSE

Recently, it has been reported that Na+/H+ exchanger (NHE) inhibitors demonstrated protective effects on ischemia/reperfusion brain injury in animal models. However, the mechanisms by which the neurons were protected against ischemic insult remain unclear. To reveal the cellular mechanism of the NHE inhibitor on the neuronal death, we examined the effects of a selective NHE inhibitor, SM-20220 (N-[aminoiminomethyl]-1-methyl-1H-indole-2-carboxamide methanesulfonate), on glutamate-induced neuronal death in rat cortical culture.

METHODS

Cortical neurons were prepared from 1-day old rats, and cultured on the glass-based dishes. Glutamate-induced neuronal death was assessed by staining the cells with propidium iodide. Morphological changes in the neurons were observed with a video-enhanced contrast-differential interference contrast microscope. The intracellular calcium concentration ([Ca2+]i) and the intracellular pH (pHi) were measured by fluorescence imaging with a confocal laser microscope using fluo-3/acetoxymethylester (AM) and 2', 7'-bis-2-carboxy-ethyl-5(6)-carboxyfluorescein (BCECF)/AM as a fluorescent dye, respectively.

RESULTS

SM-20220 (0.3 to 30 nmol/L) dose-dependently attenuated glutamate (300 micromol/L)-induced neuronal death over a period of 6 hours, and inhibited the acute cellular swelling following glutamate (500 micromol/L) exposure. Dual peaks of [Ca2+]i rise were observed at 5 and 12 minutes after glutamate (500 micromol/L) exposure, followed by a persistent rise. SM-20220 suppressed the persistent [Ca2+]i increase. SM-20220 inhibited intracellular acidification following glutamate (500 micromol/L) exposure. All of the events induced by glutamate were also inhibited by the N-methyl-d-aspartate receptor antagonist, MK-801, indicating the death process was excitotoxicity.

CONCLUSIONS

NHE inhibitor is neuroprotective through inhibition of both persistent [Ca2+]i increase and acidification in excitotoxicity.

Lipoprotein receptor-mediated induction of matrix metalloproteinase by tissue plasminogen activator

Although thrombolysis with tissue plasminogen activator (tPA) is a stroke therapy approved by the US Food and Drug Administration, its efficacy may be limited by neurotoxic side effects. Recently, proteolytic damage involving matrix metalloproteinases (MMPs) have been implicated. In experimental embolic stroke models, MMP inhibitors decreased cerebral hemorrhage and injury after treatment with tPA. MMPs comprise a family of zinc endopeptidases that can modify several components of the extracellular matrix. In particular, the gelatinases MMP-2 and MMP-9 can degrade neurovascular matrix integrity. MMP-9 promotes neuronal death by disrupting cell-matrix interactions, and MMP-9 knockout mice have reduced blood-brain barrier leakage and infarction after cerebral ischemia. Hence it is possible that tPA upregulates MMPs in the brain, and that subsequent matrix degradation causes brain injury. Here we show that tPA upregulates MMP-9 in cell culture and in vivo. MMP-9 levels were lower in tPA knockouts compared with wild-type mice after focal cerebral ischemia. In human cerebral microvascular endothelial cells, MMP-9 was upregulated when recombinant tPA was added. RNA interference (RNAi) suggested that this response was mediated by the low-density lipoprotein receptor-related protein (LRP), which avidly binds tPA and possesses signaling properties. Targeting the tPA-LRP signaling pathway in brain may offer new approaches for decreasing neurotoxicity and improving stroke therapy.

Molecular mechanisms of cerebral ischemia-induced neuronal death

The mode of neuronal death caused by cerebral ischemia and reperfusion appears on the continuum between the poles of catastrophic necrosis and apoptosis: ischemic neurons exhibit many biochemical hallmarks of apoptosis but remain cytologically necrotic. The position on this continuum may be modulated by the severity of the ischemic insult. The ischemia-induced neuronal death is an active process (energy dependent) and is the result of activation of cascades of detrimental biochemical events that include perturbion of calcium homeostasis leading to increased excitotoxicity, malfunction of endoplasmic reticulum and mitochondria, elevation of oxidative stress causing DNA damage, alteration in proapoptotic gene expression, and activation of the effector cysteine proteases (caspases) and endonucleases leading to the final degradation of the genome. In spite of strong evidence showing that brain infarction can be reduced by inhibiting any one of the above biochemical events, such as targeting excitotoxicity, up-regulation of an antiapoptotic gene, or inhibition of a down-stream effector caspase, it is becoming clear that targeting a single gene or factor is not sufficient for stroke therapeutics. An effective neuroprotective therapy is likely to be a cocktail aimed at all of the above detrimental events evoked by cerebral ischemia and the success of such therapeutic intervention relies upon the complete elucidation of pathways and mechanisms of the cerebral ischemia-induced active neuronal death.

Vampire bat salivary plasminogen activator (desmoteplase): a unique fibrinolytic enzyme that does not promote neurodegeneration

BACKGROUND AND PURPOSE

Tissue-type plasminogen activator (tPA) promotes excitotoxic and ischemic injury within the brain. These findings have implications for the use of tPA in the treatment of acute ischemic stroke. The plasminogen activator from vampire bat (Desmodus rotundus) saliva (D rotundus salivary plasminogen activator [DSPA]; desmoteplase) is an effective plasminogen activator but, in contrast to tPA, is nearly inactive in the absence of a fibrin cofactor. The purpose of this study was to compare the ability of DSPA and tPA to promote kainate- and N-methyl-D-aspartate (NMDA)-induced neurodegeneration in tPA-/- mice and wild-type mice, respectively.

METHODS

tPA-/- mice were infused intracerebrally with either tPA or DSPA. The degree of neuronal survival after hippocampal injection of kainate was assessed histochemically. Wild-type mice were used to assess the extent of neuronal damage after intrastriatal injection of NMDA in the presence of tPA or DSPA. Immunohistochemistry and fibrin zymography were used to evaluate DSPA and tPA antigen or activity.

RESULTS

Infusion of tPA into tPA-/- mice restored sensitivity to kainate-mediated neurotoxicity and activation of microglia. DSPA was incapable of conferring sensitivity to kainate treatment, even when infused at 10-fold higher molar concentration than tPA. The presence of tPA also increased the lesion volume induced by NMDA injection into the striatum of wild-type mice, whereas DSPA had no effect.

CONCLUSIONS

DSPA does not promote kainate- or NMDA-mediated neurotoxicity in vivo. These results provide significant impetus to evaluate DSPA in patients with ischemic stroke.

An Na+/H+ exchanger inhibitor suppresses cellular swelling and neuronal death induced by glutamate in cultured cortical neurons

We examined the effects of a selective Na+/H+ exchanger inhibitor, SM-20220 (N-(aminoiminomethyl)-1-methyl-1H-indole-2-carboxamide methanesulfonate), on neuronal death induced by glutamate in rat cortical neurons. Morphological changes in neurons were observed with a differential interference contrast microscope, and cellular swelling was analysed. Neuronal death was assessed by staining the cell with propidium iodide. The intracellular calcium concentration ([Ca2+]i) and the intracellular pH were measured by fluorescence imaging with fluo-3/AM as an indicator for [Ca2+]i and BCECF/AM for pH, respectively. SM-20220 (0.3 to 30 nM) dose-dependently attenuated glutamate (300 microM)-induced neuronal death in a dose-dependent fashion over 6 hours, and inhibited acute cellular swelling following glutamate (100 microM) exposure. SM-20220 suppressed the persistent [Ca2+]i increase following glutamate (500 microM) exposure, and inhibited intracellular acidification induced by glutamate (1 mM). The activation of the Na+/H+ exchanger system may enhance the progress of cerebral damage and oedema following glutamate exposure. SM-20220, a Na+/H+ exchanger inhibitor, suppressed neuronal death and cellular swelling induced by glutamate through inhibition of both Ca2+ influx and acidification in neurons.

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

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