Modulation of morphological differentiation of human neuroepithelial cells by serine proteases: independence from blood coagulation

Serine Protease Inhibitors as Good Predictors of Meat Tenderness: Which Are They and What Are Their Functions?

Since years, serine proteases and their inhibitors were an enigma to meat scientists. They were indeed considered to be extracellular and to play no role in postmortem muscle proteolysis. In the 1990's, we observed that protease inhibitors levels in muscles are a better predictor of meat tenderness than their target enzymes. From a practical point of view, we therefore choose to look for serine protease inhibitors rather than their target enzymes, i.e. serine proteases and the purpose of this report was to overview the findings obtained. Fractionation of a muscle crude extract by gel filtration revealed three major trypsin inhibitory fractions designed as F1 (Mr:50-70 kDa), F2 (Mr:40-60 kDa) and F3 (Mr:10-15kD) which were analyzed separately. Besides antithrombin III, an heparin dependent thrombin inhibitor, F1 and F2 comprised a large set of closely related trypsin inhibitors encoded by at least 8 genes bovSERPINA3-1 to A3-8 and able to inhibit also strongly initiator and effector caspases. They all belong to the serpin superfamily, known to form covalent complexes with their target enzymes, were located within muscle cells and found in all tissues and fluids examined irrespective of the animal species. Potential biological functions in living and postmortem muscle were proposed for all of them. In contrast to F1 and F2 which have been more extensively investigated only preliminary findings were provided for F3. Taken together, these results tend to ascertain the onset of apoptosis in postmortem muscle. However, the exact mechanisms driving the cell towards apoptosis and how apoptosis, an energy dependent process, can be completed postmortem remain still unclear.

Upregulation of protease-activated receptor-1 in astrocytes in Parkinson disease: astrocyte-mediated neuroprotection through increased levels of glutathione peroxidase

In the present study, we investigated the expression of protease-activated receptors (PARs), receptors for thrombin, in substantia nigra pars compacta (SNpc) of Parkinson disease (PD) brains and cultures of human neurons, astrocytes, oligodendrocytes, and microglia as determined by immunocytochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR). Expression of PAR-1 was demonstrated only in glial fibrillary acidic protein-positive astrocytes in SNpc, and the number of astrocytes expressing PAR-1 increased in SNpc of PD as compared with nonneurologic control brain. Immunoreactivity for thrombin and prothrombin was stronger in astrocytes and the vessel walls in SNpc of PD brains. PAR-1 was expressed in human astrocytes and neurons, but not in oligodendrocytes or microglia as determined by RT-PCR. We investigated thrombin-mediated activation of human astrocytes. Thrombin treatment activates human astrocytes and induces morphologic change and a marked increase in proliferation of astrocytes. Increased expression of glial cell line-derived growth factor and glutathione peroxidase (GPx) but no change in the expression of nerve growth factor and inflammatory cytokines/chemokine (IL-1beta, IL-6, IL-8, MCP-1) was found in thrombin/PAR-activated astrocytes. Next, we studied the neuroprotective effect exerted by thrombin-activated astrocytes in human cerebral neuron x human neuroblastoma hybrid neurons. Although thrombin showed neurotoxicity against human hybrid neurons in a dose-dependent manner, the conditioned media derived from thrombin-pretreated astrocyte cultures promoted the survival of human hybrid neurons. The protective effect was completely inhibited with a GPx inhibitor, mercaptosuccinic acid, indicating that GPx released from thrombin/PAR-activated astrocytes is responsible for neuroprotection of hybrid neurons against thrombin cytotoxicity. The present study suggests that the increased expression of PAR-1 in astrocytes in SNpc of PD brain is the restorative move taken by the brain to provide neuroprotection against neuronal degeneration and cell death of dopaminergic neurons caused by noxious insults during the progression of PD pathology.

Inhibition of thrombin-induced vascular endothelial growth factor production in human neuroblastoma (NB-1) cells by argatroban

Thrombin, a serine protease that plays a pivotal role in blood coagulation, wound healing, and angiogenesis, has also been implicated in the mitogenesis of various cell types. Previously, we showed that thrombin and the thrombin receptor agonist peptide (TRAP-14; SFLLRNPNDKYEPF) for protease-activated receptor 1 (PAR1) induce vascular endothelial growth factor (VEGF) secretion in PC-12 cells. In this study, we show that thrombin and TRAP-14 also stimulate VEGF secretion in the human NB-1 neuroblastoma cells. In these cells, we further show that thrombin-induced VEGF secretion was blocked by cycloheximide and actinomycin D, indicating that de novo protein synthesis is essential for this process. Reduced thrombin-induced VEGF secretion upon treatment with LY294002, calphostin C, or BAPTA, further suggests that the process is dependent on phosphatidyl-inositol-3-kinase, protein kinase C, and calcium. However, the complete loss of thrombin-induced VEGF production upon treatment with argatroban, a derivative of arginine and a potent anticoagulant/antithrombin agent, supports the notion that argatroban serves as a useful therapeutic tool for thrombin-associated pathologic conditions. Here, it appears that argatroban may be effective in controlling disorders linked to thrombin-induced VEGF production in neuronal cells.

Thrombin, a mediator of neurotoxicity and memory impairment

Thrombin has been found in neuritic plaques in Alzheimer's disease (AD). Also, traumatic brain injury, where neurons are exposed to high thrombin levels, is associated with an increased incidence of AD. Our objective was to determine the effects of thrombin administered in vivo on cognitive function and neuropathology. Rats were trained using a radial eight-arm maze and then thrombin (25 or 100 nM, 0.25 microl/h, 28 days) or vehicle was delivered via intracerebroventricular infusion. Animals that received 100 nM thrombin demonstrated cognitive impairments including deficits in reference memory and an increase in task latency. Also, significant neuropathology was detected in these animals such as enlargement of cerebral ventricles, an increased number of TUNEL-positive cells, astrogliosis, and an increase in the immunoreactivity for phosphorylated neurofilament, and apolipoprotein-E fragments. Thrombin-induced changes in cognitive function and ventricular enlargement were inhibited by hirudin. These findings demonstrate that thrombin is a mediator of neurotoxicity and cognitive deficits and suggest that inhibition of thrombin may be a treatment strategy for AD- or head trauma-associated cognitive deficits.

Prothrombin overexpressed in post-natal neurones requires blood factors for activation in the mouse brain

Thrombin is thought to mediate, through protease-activated receptors, both protective as well as cytotoxic effects. As thrombin receptors are expressed in the CNS, an important question arises as to whether the intact nervous system is able to generate thrombin by activation of its precursor prothrombin, derived endogenously or only upon extravasation following brain injury. To address this question, transgenic mice that express C-terminally haemagglutinin tagged human prothrombin in post-mitotic neurones were generated. In situ hybridization and immunohistochemical analysis showed abundant and widespread cerebral expression of the transgene. Amidolytic assays of brain homogenates and hippocampal slice cultures demonstrated that activation of transgenic prothrombin required added factors, such as snake venom or blood components. This strongly suggests that any possible action of thrombin in the adult CNS depends on blood-derived factors that activate prothrombin. Furthermore, the results are consistent with the idea that in the non-pathological situation an as yet unidentified ligand activates thrombin receptors in the nervous system.

Thrombin receptor induction by injury-related factors in human skeletal muscle cells

Thrombin is involved in tissue repair through its proteolytic activation of a specific thrombin receptor (PAR-1). Previous studies have shown that serine proteases and their inhibitors are involved in neuromuscular junction plasticity. We hypothesized that thrombin could also be involved during skeletal muscle inflammation. Thus we investigated the expression of PAR-1 in human myoblasts and myotubes in vitro and its regulation by injury-related factors. The functionality of this receptor was tested by measuring thrombin's ability to elicit Ca2+ signals. Western blot analysis and immunocytochemistry demonstrated the presence of PAR-1 in myoblasts but not in myotubes unless they were treated by tumor necrosis factor-alpha (10 ng/ml), interleukin-1beta (5 ng/ml), or transforming growth factor-beta(1) (10 ng/ml). The addition of 10 nM alpha-thrombin evoked a strong Ca2+ signal in myoblasts while a limited response in myotubes was observed. However, in the additional presence of injury-related factors, the amplitude of the Ca2+ response was significantly enhanced, representing 88, 65, 48% of their respective basal level, compared to 27% of that obtained in controls. Moreover, immunochemical studies on human skeletal muscle biopsies of patients suffering from inflammatory myopathies showed an overexpression of PAR-1. These results suggest that PAR-1 synthesis may be induced in response to muscle injury, thereby implicating thrombin signaling in certain muscle inflammatory diseases.

Effects of fibronectin cleaved by neuropsin on cell adhesion and migration

Neuropsin is a serine protease cloned from the mouse hippocampus. Since neuropsin is a secreted protein which effectively cleaves fibronectin, it may affect cell adhesion or cell migration by modulating the content and/or chemical characteriscs of fibronectin in extracellular matrix (ECM). In adhesion assays, alpha5B2 cells expressing integrin alpha5beta1 bound less effectively to fibronectin teated with neuropsin than intact fibronectin. In Boyden chamber chemotaxis assays, the fibronectin-induced migration of alpha5B2 cells was not affected by neuropsin treatment. These findings suggest that neuropsin regulates the local microenvironment by modulating the interaction between cells and fibronectin in ECM.

Protease nexin I expression is up-regulated in human skeletal muscle by injury-related factors

Protease nexin I is a 43-50 kDa glycoprotein capable of inhibiting a number of serine proteases. In cultured differentiated human skeletal muscle (myotubes), we previously found that protease nexin I was localized in patches at their surface where it was active and able to inhibit thrombin. To understand the role of skeletal muscle protease nexin I after injury or in inflammatory conditions where thrombin might be extravasated by blood vessels, we examined the role of inflammatory factors on protease nexin I synthesis and secretion by myotubes in culture. By enzyme-linked immunosorbent assay (ELISA) and Western blotting, we found that this serine protease inhibitor is secreted by cultured human myotubes. Protease nexin I secretion is stimulated by tumor necrosis factor-alpha, transforming growth factor-beta and interleukin-1. Complex formation experiments with labeled thrombin reveal active protease nexin I bound to the surface of the treated cells. Secreted protease nexin I-thrombin complex was enhanced in the presence of transforming growth factor-beta and tumor necrosis factor-alpha. Protease nexin I mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis. Whatever the conditions, no significantly different levels were observed, indicating that the changes in cell and media protease nexin I concentration are elicited at the translational/posttranslational levels. Immunocytochemical studies on human skeletal muscle biopsies of patients suffering from inflammatory myopathies showed an overexpression of protease nexin I together with the above inflammatory factors. These findings suggest that skeletal muscle protease nexin I might play a role after injury or inflammatory pathologies.

Effect of thrombin inhibition in vascular dementia and silent cerebrovascular disease. An MR spectroscopy study

BACKGROUND AND PURPOSE

Silent cerebrovascular disease (CVD) has been proposed as a predisposing condition for clinically overt stroke and vascular dementia. Recently, we found increased thrombin generation in silent CVD patients. Here, we report the effect of thrombin inhibition using a potent selective thrombin inhibitor on the cerebral metabolism and function in peripheral arterial occlusive disease (PAOD) patients with or without silent CVD.

METHODS

We examined 17 mild chronic PAOD patients, including 2 cases of vascular dementia. We divided the patients into 2 groups: 1 was the advanced CVD group with multiple lacunar infarction and/or advanced periventricular hyperintensity detected by brain MRI (n=12), and the other was the no CVD group that had none of these abnormalities (n=5). We assessed the cerebral biochemical compounds in the deep white matter area and cerebellar hemisphere (8 cm3) by proton MR spectroscopy before and after infusion of argatroban (10 mg/d IV) over 2 hours for 7 days.

RESULTS

The ratio of N-acetylasparate (NAA) to total creatine (Cre) in the deep white matter area was significantly lower in the advanced CVD group than in the no CVD group, whereas there were no significant differences in this ratio in the cerebellar hemisphere between the 2 groups. In the former group, this decreased NAA/Cre ratio significantly increased after argatroban therapy, whereas there was no change in the latter group. The 2 patients with vascular dementia showed clinical improvement with marked increases in the NAA/Cre ratio and mini-mental score.

CONCLUSIONS

These results suggest that increased thrombin generation may have some pathophysiological roles in developing vascular dementia and its chronic predisposing conditions. Thrombin inhibition may break this vicious cycle and lead to clinical improvement.

Thrombin-stimulated increases in cytosolic Ca2+ level and gonadotropin-releasing hormone release in GT1-7 neurons

The effects of thrombin on cytosolic calcium levels ([Ca2+]cyt), and on gonadotropin-releasing hormone (GnRH) release, were characterized in cultured GT1-7 neurons. GnRH release from GT1-7 neurons was pulsatile with an average pulse amplitude of 14.3+/-5.8 pg x min x ml(-1) and an average pulse duration of 21.3+/-4.2 min. The [Ca2+]cyt response to 0.005 to 0.2 U/ml thrombin was saturable and concentration dependent (EC50 = 0.0268 U/ml). Ethyleneglycotetraacetic acid (EGTA) chelation of extracellular Ca2+ resulted in an approximately 70% attenuation of thrombin-stimulated increase in [Ca2+]cyt. By use of a special superfusion system, a 5-min exposure to 0.1 U/ml thrombin significantly increased the amplitude (193.2+/-67.8 pg x min x ml(-1); P = 0.001) but not the duration (22.5+/-2.4 min; P = 0.8) of GnRH release. These results suggest that thrombin increases [Ca2+]cyt and GnRH release from GT1-7 neurons via specific membrane-bound receptors.

Signaling pathways involved in thrombin-induced cell protection

This study examined the signal transduction pathways involved in thrombin-induced neuroprotection and compares these results with those of a similar study of thrombin-induced neuronal death. In thrombin-induced protection of astrocytes from hypoglycemia, pretreatment of astrocytes with tyrosine or serine/threonine kinase inhibitors, cytochalasin D, or exoenzyme C3, a potent inhibitor of the small GTPase RhoA, attenuated thrombin-induced protection. These same inhibitors were previously shown to block thrombin-induced cell death, implying a similarity in the cell death and cell-protective pathways. Biochemical assays determined that thrombin increased available RhoA activity, although more slowly and to a lesser extent than occurs in thrombin-induced cell death. A clear difference in these pathways was revealed when a time course study of thrombin-induced cell death indicated that unlike thrombin-induced protection, cells must be exposed to thrombin for >16 h to irreversibly enter the cell death pathway. Addition of lower doses of thrombin every 24 h also induced cell death. These studies indicate that exposure of cells to micromolar concentrations of thrombin alone does not induce cell death, but the continued exposure to thrombin is required. Thus the cell death and protective pathways may share initial signaling proteins, but differences in the amplitude as well as the duration of the signal may result in different final pathways.

Transcriptional regulation of the prothrombin gene in muscle

Thrombin has been shown to mediate neurite retraction in neurons and synapse elimination at the neuromuscular junction. The presence of prothrombin mRNA has been demonstrated in brain and in muscle, but extra-hepatic regulation of the prothrombin gene has not been investigated. To identify cis-acting DNA elements involved in the expression of the prothrombin gene in muscle, we have isolated and analyzed a 1.3-kilobase pair promoter region of the mouse prothrombin gene. Using a series of transiently transfected plasmid constructs in which gene segments of the prothrombin promoter were linked to the luciferase gene, we have identified a sequence, -302 to -210, essential for prothrombin promoter activity in C2-myotubes. Fine analysis revealed that deletion of nucleotides between -248 and -235 eliminated prothrombin promoter activity in C2-myotubes. Furthermore, electrophoretic mobility shift assays demonstrated that a nuclear factor present in C2-myotubes, but not in C2-myoblasts or HepG2 hepatocytes, specifically binds to the sequence -241 to -225. Substitutional mutation of nucleotides -237 to -231 abolished myotube-specific promoter activity and inhibited the nuclear factor binding. Quantitative reverse transcription polymerase chain reaction demonstrated the expression of prothrombin mRNA in myotubes, but not in myoblasts, of primary, C2, and G8 muscle cells. This result correlates with the lack of prothrombin promoter activity in C2-myoblasts. The data thus suggest that a myotube-specific nuclear factor binds to a cis-acting sequence encompassing the core nucleotides -237 to -231 and plays a critical role in muscle-specific, differentiation-dependent expression of the mouse prothrombin gene.

Characterization of recombinant and brain neuropsin, a plasticity-related serine protease

Activity-dependent changes in neuropsin gene expression in the hippocampus implies an involvement of neuropsin in neural plasticity. Since the deduced amino acid sequence of the gene contained the complete triplet (His-Asp-Ser) of the serine protease domain, the protein was postulated to have proteolytic activity. Recombinant full-length neuropsin produced in the baculovirus/insect cell system was enzymatically inactive but was readily converted to active enzyme by endoprotease processing. The activational processing of prototype neuropsin involved the specific cleavage of the Lys32-Ile33 bond near its N terminus. Native neuropsin that was purified with a purity of 1,100-fold from mouse brain had enzymatic characteristics identical to those of active-type recombinant neuropsin. Both brain and recombinant neuropsin had amidolytic activities cleaving Arg-X and Lys-X bonds in the synthetic chromogenic substrates, and the highest specific activity was found against Boc-Val-Pro-Arg-4-methylcoumaryl-7-amide. The active-type recombinant neuropsin effectively cleaved fibronectin, an extracellular matrix protein. Taken together, these results indicate that this protease, which is enzymatically novel, has significant limbic effects by changing the extracellular matrix environment.

Calcium mobilization and protease-activated receptor cleavage after thrombin stimulation in motor neurons

Thrombin, the ultimate enzyme in the blood coagulation cascade, has prominent actions on various cells, including neurons. As in platelets, thrombin increases [Ca2+]i mobilization in neurons, and also retracts neurites. Both these effects are mediated through a G protein-coupled, proteolytically activated receptor for thrombin (PAR-1). Prolonged exposure to thrombin kills neurons via apoptosis, that may also involve PAR-1 activation. Increased [Ca2+]i has been a unifying mechanism proposed for cell death in several neurodegenerative diseases. Thrombin-elevated calcium levels may activate intracellular cascades in neurons leading to cell death. Since thrombin mediates its diverse effects on cells through both heterotrimeric and monomeric G proteins, we also explored what effect altering differential G protein coupling would have on the neuronal response to thrombin. We studied calcium mobilization by thrombin in a model motor neuronal cell line, NSC19, using fluorescence image analysis. Confirming effects in other neuronal types, thrombin caused dramatic increases in [Ca2+]i levels, both transiently and after prolonged exposure, which involved activation and cleavage of the PAR-1 receptor. Using enzyme linked immunosorbent assay (ELISA) and dot-blot analysis, we found that the N-terminal fragment of PAR-1 was released into the medium after exposure to thrombin. We confirmed that PAR-1 protein and mRNA expression occurred in motor neurons. We found that cholera toxin inhibited thrombin-mediated Ca2+ influx, pertussis toxin did not significantly alter thrombin action, and lovastatin, a small 21-kDa Ras GTPase (Rho) modulator, showed a tendency to reduce the thrombin effect. These data indicate that thrombin-increased [Ca2+]i, sufficient to trigger cell death in motor neurons, might be approached in vivo by modulating thrombin signaling through PAR-1.

Characteristics of thrombin-induced calcium signals in rat astrocytes

The protease thrombin seems to play a central role in events following neural injury, whereby the enzyme can act, in concert with other molecules as a hormone or as a growth factor. In cells derived from the nervous system, thrombin induces changes in morphology and proliferation. The signalling mechanisms involved in these thrombin-activated processes are still unclear. In the present study we investigated Ca2+ signals in fura-2 loaded rat astrocytes in primary culture. Brief stimulation of astrocytes with thrombin induced a dose-dependent transient elevation of [Ca2+]i, best fitted by a double-sigmoidal curve giving two EC50 values of 3 pM and 150 pM. Continuous superfusion of cells with thrombin induced Ca2+ responses with three different types of kinetics. In 48% of the cells tested a single transient rise superimposed with fast fluctuations of [Ca2+]i was seen. The following complex long-term changes of [Ca2+]i, dependent on the presence of the agonist thrombin, were observed: i) a biphasic [Ca2+]i elevation, characterized by an initial peak followed by a sustained plateau phase (in 43% of the cells) and ii) oscillations of [Ca2+]i (in 9% of the cells). The observed Ca2+ responses were inhibited by the phospholipase C (PLC) inhibitor U-73122 and the thrombin inhibitor protease nexin-1/glia-derived nexin. The synthetic thrombin receptor activating peptide could mimic the thrombin-induced changes of [Ca2+]i. In astrocytes in Ca2+-free medium, thrombin induced a sharp single transient Ca2+ rise, without superimposed fluctuations. After depletion of intracellular Ca2+ stores with thapsigargin the Ca2+ response to thrombin was diminished or completely suppressed indicating that thrombin induces the release of Ca2+ from intracellular stores. During long-term Ca2+ responses, omission of extracellular Ca2+ resulted in a reversible interruption of the signal. In conclusion our results demonstrate that thrombin by activation of its plasma membrane receptor induces through activation of PLC different types of Ca2+ responses. The complex Ca2+ signals are generated by an interplay of InsP3-mediated Ca2+ release from intracellular stores and Ca2+ entry across the plasma membrane.

The role of thrombin-like (serine) proteases in the development, plasticity and pathology of the nervous system

There is increasing evidence suggesting that members of the serine protease family, including thrombin, chymotrypsin, urokinase plasminogen activator, and kallikrein, may play a role in normal development and/or pathology of the nervous system. Serine proteases and their cognate inhibitors have been shown to be increased in the neural parenchyma and cerebrospinal fluid following injury to the blood brain barrier. Zymogen precursors of thrombin and thrombin-like proteases as well as their receptors have also been localized in several distinct regions of the developing or adult brain. Thrombin-like proteases have been shown to exert deleterious effects, including neurite retraction and death, on different neuronal and non-neuronal cell populations in vitro. These effects appear to be mediated through cell surface receptors and can be prevented or reversed with specific serine protease inhibitors (serpins). Furthermore, we have recently shown that treatment with protease nexin-1 (a serpin that inhibits thrombin-like proteases) promotes the survival and growth of spinal motoneurons during the period of programmed cell death and following injury. Taken together, these observations suggest that thrombin-like proteases play a deleterious role, whereas serpins promote the development and maintenance of neuronal cells. Thus, changes in the balance between serine proteases and their cognate inhibitors may lead to pathological states similar to those associated with some neurodegenerative diseases such as Alzheimer's disease. The present review summarizes the current state of research involving such serine proteases and speculates on the possible role of these thrombin-like proteases in the development, plasticity and pathology of the nervous system.

Thrombin induces apoptosis in cultured neurons and astrocytes via a pathway requiring tyrosine kinase and RhoA activities

Thrombin activity is a factor in acute CNS trauma and may contribute to such chronic neurodegenerative diseases as Alzheimer's disease. Thrombin is a multifunctional serine protease that catalyses the final steps in blood coagulation. However, increasing evidence indicates that thrombin also elicits a variety of cellular and inflammatory responses, including responses from neural cells. Most recently, high concentrations of thrombin were shown to cause cell death in both astrocyte and hippocampal neuron cultures. The purpose of this study was to determine the mechanisms underlying thrombin-induced cell death. Our data show that thrombin appears to cause apoptosis as evidenced by cleavage of DNA into oligonucleosomal-sized fragments, fragmentation of nuclei, and prevention of death by inhibition of protein synthesis. Synthetic peptides that directly activate the thrombin receptor also induced apoptosis, indicating that thrombin-induced cell death occurred via activation of the thrombin receptor. The signal transduction cascade involves tyrosine and serine/threonine kinases and an intact actin cytoskeleton. Additional study revealed the involvement of the small GTP-binding protein RhoA. Thrombin induced RhoA activity in both astrocytes and hippocampal neurons, and inhibition of RhoA activity with exoenzyme C3 attenuated cell death, indicating that thrombin activation of RhoA was necessary for thrombin-induced cell death. Tyrosine kinase inhibitors blocked thrombin induction of RhoA, indicating that tyrosine kinase activity was required upstream of RhoA. These data suggest a sequential linkage of cellular events from which we propose a model for the second messenger cascade induced by thrombin in neural cells that can lead to apoptosis.

Thrombin receptor on rat primary hippocampal neurons: coupled calcium and cAMP responses

We have tested the hypothesis that hippocampal neurons respond to thrombin via a neuronal thrombin receptor. A human neuroblastoma cell line, SK-N-SH, known to be thrombin responsive morphologically, responded both to thrombin and thrombin receptor agonist peptide (TRAP 42-55) with elevation of intracellular calcium. In Western blots of membranes from SK-N-SH cells and cultured rat hippocampal neurons using an antibody against the N-terminal peptide of the human thrombin receptor, putative receptor proteins of 66 and 47 kDa were detected in both cells. Neurons were treated with thrombin and TRAP 42-55 (TRAP-14) to determine their effects on intracellular levels of calcium and cAMP. Only 10% of the neurons showed a rapid response to thrombin, but most responded rapidly to agonist peptide with a prolonged elevation of intracellular free calcium. Neuronal cAMP levels were decreased by 40% after 24 h thrombin treatment. This decrease in cAMP level could be blocked by both the Gi-protein inhibitor, pertussis toxin, and the thrombin inhibitor, hirudin, suggesting a possible involvement of Gi-protein-coupled receptor activation. Furthermore, rapid calcium and cAMP responses were apparently induced by pre-treatment of neurons with thrombin for 24 h and subsequent washout. In summary, these data indicate that rat primary hippocampal neurons have thrombin receptors whose responses to thrombin apparently are up-regulated by 24 h thrombin pre-treatment. These results may have implications for synaptic remodeling, learning and memory.

Dual effects of thrombin and a 14-amino acid peptide agonist of the thrombin receptor on septal cholinergic neurons

We have compared the effects of thrombin and of the 14-amino acid peptide agonist (TRAP-14) of the thrombin protease activated receptor (PAR) on cholinergic neurons in pure cultures of rat septal neurons and in co-cultures of septal neurons and glial cells. In pure septal cultures, low concentrations of thrombin (up to 10 nM) did not affect choline acetyltransferase (ChAT) activity, a marker of cholinergic neurons, or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reduction, an index of cell viability. However, 100 nM thrombin decreased ChAT activity and MTT reduction by 44 and 17%, respectively. In co-cultures, a low concentration of thrombin (1 nM) increased ChAT activity (+75%), whereas a high concentration (100 nM) decreased it (-83%). At this high concentration, thrombin was neurotoxic, as indicated by a large decrease in MTT reduction (-80%). Thrombin effects on ChAT activity were mimicked by TRAP-14 both in pure septal cultures (no effect at 0.1 microM and -63% at 100 microM) and in co-cultures (+25% at 0.1 microM and -28% at 100 microM). In contrast, this peptide did not affect MTT reduction. These dual effects of thrombin and TRAP-14 on ChAT activity in co-cultures, were also observed on pure cultures of septal cells supplied with NGF. The activation and inhibition by TRAP-14 of the expression of ChAT activity in septal neuron/glial cell cultures were inhibited by a 9-amino acid peptide antagonist of thrombin PAR. Thus, the effects of thrombin on cholinergic neurons seem to be mainly mediated by thrombin PAR and glial cells seem to play a major role in these thrombin actions.

A novel serpin-like protein, B-43, exists in both neurons and astrocytes: an immunohistochemical study in the parietal region of the bovine brain

The presence of a novel member of serine proteinase inhibitor, B-43, was immunohistochemically indicated in both neurons and astrocytes in the parietal region of the bovine brain. B-43-like immunoreactivity was detected in pyramidal cells in the cortex and GFAP-positive astroglial cells in the white matter. The processes of B-43 may play a cooperative role with glia-derived nexin/protease nexin-1 and alpha 1-antichymotrypsin in the brain.

Exogenous thrombin inhibits neuritogenesis in cultured neuroblastoma cells but not in rat hippocampal neurons

Thrombin has been reported to inhibit neurite outgrowth from neuroblastoma cells grown in serum-containing medium after switching to serum-free medium. A test of the serum and substrate-dependence of this inhibition became possible with the development of Neurobasal/B27 serum-free medium. Inhibition of sprouting of Nb2a neuroblastoma cells by thrombin occurred from the substrate where it was bound to material adsorbed from serum. Neuritogenesis of primary hippocampal neurons was unaffected by exogenous thrombin on polylysine substrates with or without serum treatment. However, sprouting of hippocampal neurons was stimulated by treating the substrate with hirudin, a highly specific thrombin inhibitor. This suggests that hippocampal neurons are not directly responsive to added thrombin, perhaps because they produce their own thrombin.

Plasticity of nerve afferents to nigrostriatal neurons in Parkinson's disease

Clinical symptoms in Parkinson's disease do not appear until almost total depletion of dopamine has occurred in the striatum, suggesting the existence of compensatory mechanisms to offset the loss of nigrostriatal dopaminergic neurons. This compensation has been attributed mainly to an increased turnover of dopamine in the remaining dopaminergic neurons. Besides this biochemical phenomenon intrinsic to dopaminergic neurons, we tested whether morphological changes in the nerve afferents to the dopaminergic neurons could participate in these compensatory mechanisms. The afferents to the dendrites of dopaminergic neurons were analyzed ultrastructurally in the substantia nigra of parkinsonian patients and matched controls, using simultaneous histochemical detection of acetylcholine-like cation and tyrosine hydroxylase. The size of acetylcholine-like cation-containing terminals in contact with dopaminergic dendrites increased significantly by 38% in the substantia nigra of parkinsonian patients; whereas their number per section of dopaminergic dendrite showed an increase of 60%, although not reaching statistical significance. The number of the terminals devoid of acetylcholine-like cation per section of dopaminergic dendrite decreased significantly by 52% in the substantia nigra of parkinsonian patients. These results suggest (1) a plasticity of excitatory cholinergic neurons targeting nigral dopaminergic neurons and (2) an involution of noncholinergic nerve terminals, mostly originating from inhibitory nigral, pallidal, and striatal GABAergic neurons. The findings provide evidence of a capacity for neuronal plasticity in the elderly human brain, even in the presence of neurodegenerative disorders.

Protease nexin-1, a potent thrombin inhibitor, is reduced around cerebral blood vessels in Alzheimer's disease

The clotting protease thrombin might contribute to the pathophysiology of central nervous system (CNS) injury and certain diseases by its ability to retract processes on neurons and astrocytes and to stimulate astrocyte proliferation. Protease nexin-1 (PN-1) is a 43 kDa thrombin inhibitor found predominantly in the brain where much of it resides around capillaries and large blood vessels. This location of PN-1 prompted the hypothesis that it may play a protective role against extravasated thrombin released following cerebrovascular injury or under certain pathological conditions. Recent studies indicated that the levels of PN-1 are markedly reduced in the postmortem brains of patients with Alzheimer's disease (AD). It was suggested that this reduction in PN-1 levels was due to the sequestration of PN-1 by extravasated thrombin. In the present study we examined the specific nature of this reduction by immunohistochemical staining of sections from control and AD brains using PN-1 specific antibodies. We show that the levels of PN-1 immunoreactivity around blood vessels and the number of blood vessels exhibiting PN-1 immunoreactivity were markedly reduced in the brains of patients with AD compared to age-matched controls; this reduction was reflected by a decrease in the levels of PN-1 activity and PN-1 protein. Thus an imbalance between PN-1 and thrombin may be a contributing factor in the pathology of AD.

Mouse fibroblasts defective in thrombin mitogenesis possess functional proteolytically activated receptor for thrombin: requirement for a second signaling pathway

Thrombin mitogenesis in fibroblasts requires two distinguishable subsets of signals; one generated by proteolytic cleavage, the other by high-affinity cell surface binding. Characterizing two closely related mouse embryo (ME) cell lines with high numbers of thrombin binding sites, we found that one line, B11-A, responds mitogenically to thrombin, epidermal growth factor (EGF), and serum, whereas the B11-B cell line is responsive to EGF and serum, but not to thrombin. The B11-B defect responsible for loss of thrombin responsiveness is not due to differences in the number of high-affinity binding sites, the affinity of thrombin binding to these sites, or to differences in cell surface expression of proteolytically activated receptors for thrombin (PART). The defect is also not associated with an inability of thrombin to activate PART since thrombin stimulates the cleavage-dependent induction of the proto-oncogene c-fos in both B11-A and B11-B cells. Various combinations of thrombin, synthetic thrombin receptor peptide, TRP-14 (SFFLRNPGENTFEL), platelet-derived growth factor (PDGF), and phorbol 12-myristate 13-acetate (PMA) were used to better define the defect in thrombin-mediated mitogenesis in B11-B cells. Direct activation of protein kinase C with PMA in combination with thrombin did not overcome B11-B nonresponsiveness. However, mitogenic responsiveness was regained in B11-B cells by simultaneous addition of PDGF and either thrombin or TRP-14. Therefore, the B11-B defect may involve a set of signals initiated by nonproteolytic thrombin interactions distinct from those initiated by PART, but related to the downstream signals initiated by the tyrosine kinase-associated growth factors, EGF and PDGF.

Structure around the cleavage site in the thrombin receptor determined by NMR spectroscopy

NMR spectroscopic experiments were performed to study the structure of synthetic peptides identical to two extracellular regions of the human thrombin receptor. The smaller molecule, comprising 14 amino acids, was biologically active and was equivalent to the "tethered ligand" exposed after cleavage of the receptor by thrombin. The principal structural elements were two overlapping turns (amino acids 5-8 and 6-9), the second of which was stabilized by a hydrogen bond, 6CO-9NH. The five N-terminal residues, considered to be responsible for biological activity, were essentially unstructured. A second version of this peptide, biologically inactive due to the reversal of the two N-terminal amino acids, had a very similar structure. A longer peptide (23 amino acids) covering the proposed thrombin cleavage site was found to be more highly structured. The seven residues from Pro-2 to Arg5 (the N-terminal amino acid exposed after cleavage is taken as residue 1) formed a 3(10) helix which is not present in the shorter tethered ligand peptide. The structure is partially stabilized by a charged hydrogen bond between the side chains of Arg-1 and Asp-3. The overlapping turns observed in the shorter peptides could also be distinguished in the longer molecule. On the basis of the structure determined for the peptide which encompasses the cleavage site and the determined structure of thrombin, a model is postulated for the interaction of the thrombin receptor and the protease during activation.

Glia-derived nexin/protease nexin-1 is expressed by a subset of neurons in the rat brain

Glia-derived nexin/protease nexin-1 (GDN/PN-1) is a serine protease inhibitor that is secreted by glial cells and fibroblasts in culture. In the adult mammalian nervous system it has been shown to be expressed in the olfactory system and by some glial cells in response to neuronal injury. In situ hybridization and immunocytochemical studies were performed to identify the structures expressing GDN/PN-1 in the developing and adult rat brain. In contrast to a transient widespread expression during pre- and postnatal development, some brain structures constitutively express GDN/PN-1. These include the olfactory nerve layer of the olfactory bulb, basal forebrain, striatum, pyramidal neurons of layer V in the cortex, thalamic nuclei, pars compacta of the substantia nigra, inferior and superior colliculi, and deep cerebellar nuclei. All of these parts, excluding the olfactory nerve layer, are characterized by a high neuronal cell density. Neurons in these regions were immunoreactive for GDN/PN-1. Furthermore GDN/PN-1 expression in cell lines showed that the active protein was synthesized and secreted from B104 but not from NB2a neuroblastoma cells. Although GDN/PN-1 has only been reported to be synthesized by glia, the results presented here demonstrate that in addition, a subset of neurons express this protease inhibitor.

Variable and multiple expression of Protease Nexin-1 during mouse organogenesis and nervous system development

Protease Nexin-1 (PN-1) also known as Glia-Derived Nexin (GDN) inhibits the activity of several serine proteases including thrombin, tissue (tPA)- and urokinase (uPA)-type plasminogen activators. These and other serine proteases seem to play roles in development and tissue homeostasis. To gain insight into where and when PN-1 might counteract serine protease activities in vivo, we examined its mRNA and protein expression in the mouse embryo, postnatal developing nervous system and adult tissues. These analyses revealed distinct temporal and spatial PN-1 expression patterns in developing cartilage, lung, skin, urogenital tract, and central and peripheral nervous system. In the embryonic spinal cord, PN-1 expression occurs in cells lining the neural canal that are different from the cells previously shown to express tPA. In the developing postnatal brain, PN-1 expression appears transiently in many neuronal cell populations. These findings suggest a role for PN-1 in the maturation of the central nervous system, a phase that is accompanied by the appearance of different forms of PN-1. In adults, few distinct neuronal cell populations like pyramidal cells of the layer V in the neocortex retained detectable levels of PN-1 expression. Also, mRNA and protein levels did not correspond in adult spleen and muscle tissues. The widespread and complex regulation of PN-1 expression during embryonic development and, in particular, in the early postnatal nervous system as well as in adult tissues suggests multiple roles for this serine protease inhibitor in organogenesis and tissue homeostasis.

Co-distribution of protease nexin-1 and protease nexin-2 in brains of non-human primates

The protease nexins are protease inhibitors which regulate key blood coagulation proteases and which appear to be involved in certain physiological and pathological processes in the brain. Protease nexin-1 (PN-1), a potent inhibitor of thrombin, can regulate processes on cultured neurons and astrocytes. Protease nexin-2 (PN-2), a potent inhibitor of coagulation factor XIa, is identical to the secreted form of the Alzheimer's amyloid beta-protein precursor. In the present studies, PN-1 and PN-2 were analyzed in different tissues of monkey using monoclonal antibodies for either quantitative immunoblotting or specific [125I]protease-binding assays. PN-1 was detected only in brain. PN-2 was most abundant in brain, followed by testis and to a lesser extent kidney. Other tissues examined including spinal cord, heart, pancreas, spleen, liver, lung and muscle were essentially devoid of both PN-1 and PN-2. Within the brain, the levels of PN-1 and PN-2 were highest in the parietal cortex and lowest in the cerebellum and brainstem. The thalamus and striatum contained intermediate amounts of both proteins. Aged Cebus monkey cerebral cortical tissue contained slightly lower levels of PN-1 than did the middle-aged or young monkey tissue. The co-distribution of PN-1 and PN-2 in brain, their relative abundance in brain cortex, and previous studies on their functions suggest that in the brain they may participate in the regulation of blood coagulation and cell growth and differentiation.

Enhancement of the synthesis and secretion of nerve growth factor in primary cultures of glial cells by proteases: a possible involvement of thrombin

Newborn rat brain astrocytes cultured in vitro in a chemically defined medium are shown to secrete enhanced levels of nerve growth factor (NGF) when they are exposed to various types of proteases. Proteolytic enzymes such as alpha-thrombin or collagenase induce a continuous, dose-dependent enhancement of the levels of cell-secreted NGF. Incubation of astrocytes for a 24-h period with 300 ng/ml of alpha-thrombin (approximately 9 nM, or 1 U/ml) results in an increase of the levels of cell-secreted NGF by a factor of three- to fourfold, and at doses 10 times higher, stimulation by a factor of up to four- to fivefold was observed. This phenomenon reflects an enhancement of the cellular pool of NGF mRNA, already noticeable after 3 h of treatment, which is preceded by a temporary activation of protooncogenes encoding transcription factors of the AP-1 family, such as c-fos, c-jun or junB. Trypsin, plasmin, alpha-chymotrypsin, or elastase also enhanced, to different extents, the levels of cell-secreted NGF. However, unlike alpha-thrombin or collagenase, these enzymes cause, above a critical concentration, an extensive cell detachment from the solid support, and this is accompanied by a decrease of their activity on the production of NGF, so that their dose-response curves are bell shaped. Stimulation was maximal at those concentrations that cause a limited loosening of the cell-substratum interactions, as evidenced by a retraction of some cell processes after 24 h of treatment. Studies of the effect of alpha-thrombin indicate that the proteolytic activity itself is required to enhance the production of NGF by astrocytes. Inactivation of alpha-thrombin with D-phenyl-alanyl-L-propyl-L-arginine chloromethyl ketone, phenylmethylsulfonyl fluoride, antithrombin III, or hirudin results in a marked decrease of the stimulatory effect. Furthermore, the prolonged presence of alpha-thrombin is required to elicit a maximal effect on the levels of extracellular NGF, which was observed after 48 h of treatment. It is known that some effects of alpha-thrombin require binding to the cell surface. We found that gamma-thrombin, which still has some proteolytic activity but has lost its ability to bind to the cell surface, is almost as potent as alpha-thrombin in promoting the release of NGF. It is concluded that the effect of thrombin on NGF synthesis is essentially mediated by its proteolytic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Thrombin is a regulator of astrocytic endothelin-1

Endothelin-1, a potent vasoconstrictor of cerebral vessels, is produced by rat primary astrocytes and is subject to autostimulatory regulation in these cells. In this study we examined the effect of thrombin on astrocytic endothelins and report that endothelin-1 is released into the culture fluid in response to thrombin treatment. However, increased production of endothelin-1 is not accompanied by a concomitant increase in steady-state levels of endothelin-1 mRNA as assessed by reverse transcriptase-polymerase chain reaction, even though thrombin stimulation leads to increased inositolphospholipid turnover and activation of the nuclear factor AP1. Thus, astrocytic production of endothelin-1 may be mainly post-transcriptionally regulated in response to thrombin stimulation. In addition, two endothelin receptor genes (ET(A) and ETB) were found to be transcribed simultaneously in primary astrocyte cultures, and both thrombin and endothelin-1 stimulation result in a distinct temporary decrease in ET(A) mRNA. These studies suggest a role for thrombin in the regulation of brain perfusion through astrocytic endothelin-1 expression.

Increase in cytoplasmic casein kinase II-type activity accompanies neurite outgrowth after DNA synthesis inhibition in NIA-103 neuroblastoma cells

Whereas cells from most clonal lines derived from the murine neuroblastoma C1300 tumor can be induced to differentiate by serum withdrawal from culture medium, the NIA-103 clonal cell line has been considered unable to extend axon-like processes (neurites). Neurite growth depends on microtubule protein assembly, and although NIA-103 cells have essentially the same amounts of microtubule-associated protein (MAP)-1B and the neuronal-specific class beta 3-tubulin isoform as other neuroblastoma cell lines, these proteins are not phosphorylated in NIA-103 cells on serum withdrawal. The lack of microtubule protein phosphorylation may be due to the different sorting between the nucleus and the cytoplasm of the casein kinase II-related enzyme that is possibly involved in the modification of microtubule proteins. It is interesting that addition of DNA synthesis inhibitors to serum-starved NIA-103 cell cultures induces an increase in the level of cytosolic casein kinase II, an augmented in situ phosphorylation of MAP-1B, and the extension of neurites. Thus, the level of cytoplasmic casein kinase II appears to be controlled by the growth status of neuroblastoma cells. The shift to an increased cytoplasmic concentration of casein kinase II in nonproliferating, differentiating neuroblastoma cells is consistent with its putative role in the regulation of the cytoskeletal rearrangements underlying neuronal morphogenesis and plasticity.

Thrombin as a multifunctional protein: induction of cell adhesion and proliferation

The serine protease thrombin (E.C.3.4.21.5) is well recognized for its central role in hemostasis. In addition, thrombin is unique among the enzymes participating in the clotting cascade, by virtue of its cell activation effects induced via the enzymatic pocket or via functional domains located throughout the molecule. In this review, we elaborate on "nonhemostatic" activities of thrombin among which are interactions with vessel wall components. These activities include promotion of cellular adhesion and induction of smooth muscle cell proliferation. Thrombin can exert these effects when it is in a fluid phase and when it is immobilized to extracellular matrix.

Thrombin causes neurite retraction in neuronal cells through activation of cell surface receptors

The mechanism by which thrombin induces neurite retraction was studied in NB2a mouse neuroblastoma cells. The rapid effect of thrombin (completed within minutes) appears to involve an interaction between its anion-binding exosite and the thrombin receptor. Structural alterations of this site increase the EC50 for thrombin-mediated retraction, and a hirudin C-terminal peptide that blocks this site inhibits the response. The thrombin effect was mimicked by a 14 amino acid peptide starting with Ser-42, at the proposed cleavage site of the human thrombin receptor. The protein kinase inhibitors staurosporine and H-7 blocked thrombin-induced retraction. It is therefore proposed that thrombin-mediated neurite retraction is caused by cleavage-induced activation of the thrombin receptor and involves stimulation of a protein kinase(s).

Isolation of factor Xa from chick embryo as the amniotic endoprotease responsible for paramyxovirus activation

In chick embryo, certain paramyxoviruses mainly target the chorioallantois and the allantoamnion and show no extensive further spreading in the other organs. This has been explained by the possible presence of an endoprotease activating the viral fusion glycoprotein precursor in the allantoic and the amniotic fluid, and its absence in other places or organs. We previously isolated such an endoprotease from the allantoic fluid and demonstrated its identity with the clotting factor Xa. Exactly the same endoprotease by all the criteria including the N-terminal amino acid sequence was now isolated from the amniotic fluid. Thus, the factor Xa seems to be a major host determinant of the viral tropism in chick embryo.

Modulation of Human Neurite Outgrowth by Serine Proteases: A Comparison of the Interaction of Thrombin and Prothrombin with Glia-Derived Nexin

Neurite outgrowth from cells of neuroepithelial origin is under the reciprocal control of thrombin and the thrombin inhibitor-glia-derived nexin (GDN). The neurite retraction activity of thrombin is blocked when GDN complexes with the enzyme and inhibits its proteolytic activity. However, we have previously shown that enzymically inactive proenzyme is also capable of inducing neurite retraction. We present evidence here to show that GDN does not bind to prothrombin in solution. When a mixture of prothrombin and GDN is subjected to either polyacrylamide gel electrophoresis or immunoprecipitation, a stable complex cannot be detected. This is in direct contrast to thrombin, which exhibits stable complexes with GDN under both conditions. At the cell surface, however, GDN is able to inhibit the biological activity of prothrombin. When a mixture of proenzyme and inhibitor is applied to previously differentiated transformed retinoblasts (Ad12 HER10), the ability of prothrombin to induce neurite retraction is blocked. Furthermore, following 1 h exposure to Ad12 HER10 cells, a solution of prothrombin was found to contain half the potential enzyme activity as detected by chromogenic assay. These results have been interpreted as evidence for the ability of neuronal cells to cleave prothrombin and subsequently release activated enzyme.

Primary structure of the virus activating protease from chick embryo. Its identity with the blood clotting factor Xa

Host cell proteases activating para- and orthomyxovirus fusion glycoprotein precursors play a crucial role in determining the viral tropism in infected organisms. We previously isolated such an endoprotease from the allantoic fluid of chick embryo and showed its close similarity to the activated form of blood clotting factor X (FXa) by partial amino acid sequencing. In this report, we have cloned and sequenced a cDNA of the protease, and show that it is encoded in a single gene as a preproform with all the functional and structural domains known to be characteristic of bovine or human FX, establishing the identity between the protease and FXa.

Prothrombin mRNA is expressed by cells of the nervous system

Thrombin, a serine protease of the blood coagulation system, has additional effects on cells in vitro. It is mitogenic for fibroblasts and astrocytes and contributes to the regulation of neurite outgrowth and astrocyte stellation. Until now the expression of thrombin or its precursor prothrombin in tissues other than liver has not been demonstrated conclusively because of difficulty in avoiding serum contamination. Using sensitive mRNA detection methods, we show here that prothrombin is expressed not only in the liver, but also in the brain throughout development. Polymerase chain reaction, Northern, and in situ hybridization studies demonstrate the presence of prothrombin transcripts in the olfactory bulb, the cortex, the cerebellum, and other regions of the rat and human nervous system, as well as in neural cell lines. These results support an involvement of (pro)thrombin in the regulation of cellular events in the nervous system.

Inhibitors of urokinase and thrombin in cultured neural cells

Recent studies have suggested important roles for certain proteases and protease inhibitors in the growth and development of the CNS. In the present studies, inhibitors of urokinase or thrombin in cultured neural cells and serum-free medium from the cells were identified by screening for components that formed sodium dodecyl sulfate-stable complexes with 125I-urokinase or 125I-thrombin. Rinsed glioblastoma possessed two components that complexed 125I-urokinase. One was type 1 plasminogen activator inhibitor (PAI-1), because the 125I-urokinase-containing complexes were immunoprecipitated with anti-PAI-1 antibodies. The other component formed complexes with 125I-urokinase that were not recognized by antibodies to PAI-1 or protease nexin-1 (PN-1). Its identity is unknown. In addition to these cell-bound components, the glioblastoma cells also secreted two inhibitors that formed complexes with 125I-urokinase; one was PAI-1, and the other was PN-1. The secreted PN-1 also formed complexes with 125I-thrombin. It was the only thrombin inhibitor detected in these studies. Human neuroblastoma cells did not contain components that formed detectable complexes with either 125I-urokinase or 125I-thrombin. However, human neuroblastoma cells did contain very low levels of PN-1 mRNA and PN-1 protein. Added PN-1 bound to the surface of both glioblastoma and neuroblastoma cells. This interaction accelerated the inhibition of thrombin by PN-1 and blocked the ability of PN-1 to form complexes with 125I-urokinase. Thus, cell-bound PN-1 was a specific thrombin inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Protease nexin-1. Localization in the human brain suggests a protective role against extravasated serine proteases

Protease nexin-1 (PN-1) is a potent thrombin inhibitor that is identical to the glia-derived neurite-promoting factor or glia-derived nexin. Here we report immunocytochemical studies of adult human cerebral cortex that revealed the presence of strong immunoreactivity for PN-1 in capillaries and in the smooth muscle cells of arteries and arterioles. Expression of PN-1 was also abundant in astroglial processes in the parenchyma and in perivascular astroglial endfeet of human cerebral cortex. In situ hybridization with an 35S-labeled RNA antisense probe for PN-1 resulted in significant labeling of astrocytes and blood vessels. Because thrombin is known to cause retraction of neurites and modification of astrocytic morphology at low concentrations, PN-1 around blood vessels may play a major protective role against extravasation of thrombin and possibly other serine protease into the human brain.

The selective viability of human foetal brain cells

The influence of various factors upon the survival of human foetal neurones has been examined. The viability of several brain structures was assessed using ethidium bromide and acridine orange fluorescence in both 'intact' and mechanically dispersed tissue. Striatum was least vulnerable to dissociation while cortex, mesencephalon, pons, cerebellum and cord were more vulnerable to a greater or lesser extent. Material can be preserved in vitro with greater viability in the undissociated rather than dissociated state. The effects of other factors including foetal age upon viability are discussed.