Neurite outgrowth activity of protease nexin-1 on neuroblastoma cells requires thrombin inhibition

Biased signaling in platelet G-protein coupled receptors

Platelets are small megakaryocyte-derived, anucleate, disk-like structures that play an outsized role in human health and disease. Both a decrease in the number of platelets and a variety of platelet function disorders result in petechiae or bleeding that can be life threatening. Conversely, the inappropriate activation of platelets, within diseased blood vessels, remains the leading cause of death and morbidity by affecting heart attacks and stroke. The fine balance of the platelet state in healthy individuals is controlled by a number of receptor-mediated signaling pathways that allow the platelet to rapidly respond and maintain haemostasis. G-protein coupled receptors (GPCRs) are particularly important regulators of platelet function. Here we focus on the major platelet-expressed GPCRs and discuss the roles of downstream signaling pathways (e.g., different G-protein subtypes or β-arrestin) in regulating the different phases of the platelet activation. Further, we consider the potential for selectively targeting signaling pathways that may contribute to platelet responses in disease through development of biased agonists. Such selective targeting of GPCR-mediated signaling pathways by drugs, often referred to as biased signaling, holds promise in delivering therapeutic interventions that do not present significant side effects, especially in finely balanced physiological systems such as platelet activation in haemostasis.

The Complex Work of Proteases and Secretases in Wallerian Degeneration: Beyond Neuregulin-1

After damage, axons in the peripheral nervous system (PNS) regenerate and regrow following a process termed Wallerian degeneration, but the regenerative process is often incomplete and usually the system does not reach full recovery. Key steps to the creation of a permissive environment for axonal regrowth are the trans-differentiation of Schwann cells and the remodeling of the extracellular matrix (ECM). In this review article, we will discuss how proteases and secretases promote effective regeneration and remyelination. We will detail how they control neuregulin-1 (NRG-1) activity at the post-translational level, as the concerted action of alpha, beta and gamma secretases cooperates to balance activating and inhibitory signals necessary for physiological myelination and remyelination. In addition, we will discuss the role of other proteases in nerve repair, among which A Disintegrin And Metalloproteinases (ADAMs) and gamma-secretases substrates. Moreover, we will present how matrix metalloproteinases (MMPs) and proteases of the blood coagulation cascade participate in forming newly synthetized myelin and in regulating axonal regeneration. Overall, we will highlight how a deeper comprehension of secretases and proteases mechanism of action in Wallerian degeneration might be useful to develop new therapies with the potential of readily and efficiently improve the regenerative process.

Thrombin Causes Neuronal Atrophy and Acute but not Chronic Cell Death

BACKGROUND

Brain injury after intracerebral hemorrhage (ICH) arises from numerous contributors, of which some also play essential roles. Notably, thrombin production, needed to stop bleeding, also causes acute cell death and edema. In some rodent models of ICH, peri-hematoma neurons die over weeks. Hence we evaluated whether thrombin is responsible for this chronic degeneration. Functional impairments after ICH also result from sub-lethal damage to neurons, especially the loss of dendrites. Thus, we evaluated whether thrombin infusion alone, a reductionist model of ICH, causes similar injury.

METHODS

Adult rats had a modest intra-striatal infusion of thrombin (1 U) or saline followed by a behavioral test, to verify impairment, 7 days later. After this they were euthanized and tissue stained with Golgi-Cox solution to allow the assessment of dendritic morphology in striatal neurons. In a second experiment, rats survived 7 or 60 days after thrombin infusion in order to histologically determine lesion volume.

RESULTS

Thrombin caused early cell death and considerable atrophy in surviving peri-lesion neurons, which had less than half of their usual numbers of branches. However, total tissue loss was comparable at 7 (24.1 mm3) and 60 days (25.6 mm3).

CONCLUSION

Thrombin infusion causes early cell death and neuronal atrophy in nearby surviving striatal neurons but thrombin does not cause chronic tissue loss. Thus, the chronic degeneration found after ICH in rats is not simply and solely due to acute thrombin production. Nonetheless, thrombin is an important contributor to behavioral dysfunction because it causes cell death and substantial dendritic injury.

Proteoglycans in the central nervous system: role in development, neural repair, and Alzheimer's disease

Proteoglycans (PGs) are major components of the cell surface and extracellular matrix and play critical roles in development and maintenance of the central nervous system (CNS). PGs are a family of proteins, all of which contain a core protein to which glycosaminoglycan side chains are covalently attached. PGs possess diverse physiological roles, particularly in neural development, and are also implicated in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD). The main functions of PGs in the CNS are reviewed as are the roles of PGs in brain injury and in the development or treatment of AD.

Long-term gene therapy causes transgene-specific changes in the morphology of regenerating retinal ganglion cells

Recombinant adeno-associated viral (rAAV) vectors can be used to introduce neurotrophic genes into injured CNS neurons, promoting survival and axonal regeneration. Gene therapy holds much promise for the treatment of neurotrauma and neurodegenerative diseases; however, neurotrophic factors are known to alter dendritic architecture, and thus we set out to determine whether such transgenes also change the morphology of transduced neurons. We compared changes in dendritic morphology of regenerating adult rat retinal ganglion cells (RGCs) after long-term transduction with rAAV2 encoding: (i) green fluorescent protein (GFP), or (ii) bi-cistronic vectors encoding GFP and ciliary neurotrophic factor (CNTF), brain-derived neurotrophic factor (BDNF) or growth-associated protein-43 (GAP43). To enhance regeneration, rats received an autologous peripheral nerve graft onto the cut optic nerve of each rAAV2 injected eye. After 5–8 months, RGCs with regenerated axons were retrogradely labeled with fluorogold (FG). Live retinal wholemounts were prepared and GFP positive (transduced) or GFP negative (non-transduced) RGCs injected iontophoretically with 2% lucifer yellow. Dendritic morphology was analyzed using Neurolucida software. Significant changes in dendritic architecture were found, in both transduced and non-transduced populations. Multivariate analysis revealed that transgenic BDNF increased dendritic field area whereas GAP43 increased dendritic complexity. CNTF decreased complexity but only in a subset of RGCs. Sholl analysis showed changes in dendritic branching in rAAV2-BDNF-GFP and rAAV2-CNTF-GFP groups and the proportion of FG positive RGCs with aberrant morphology tripled in these groups compared to controls. RGCs in all transgene groups displayed abnormal stratification. Thus in addition to promoting cell survival and axonal regeneration, vector-mediated expression of neurotrophic factors has measurable, gene-specific effects on the morphology of injured adult neurons. Such changes will likely alter the functional properties of neurons and may need to be considered when designing vector-based protocols for the treatment of neurotrauma and neurodegeneration.

Expression of prostasin and its inhibitors during colorectal cancer carcinogenesis

Background

Clinical trials where cancer patients were treated with protease inhibitors have suggested that the serine protease, prostasin, may act as a tumour suppressor. Prostasin is proteolytically activated by the serine protease, matriptase, which has a very high oncogenic potential. Prostasin is inhibited by protease nexin-1 (PN-1) and the two isoforms encoded by the mRNA splice variants of hepatocyte growth factor activator inhibitor-1 (HAI-1), HAI-1A, and HAI-1B.

Methods

Using quantitative RT-PCR, we have determined the mRNA levels for prostasin and PN-1 in colorectal cancer tissue (n = 116), severe dysplasia (n = 13), mild/moderate dysplasia (n = 93), and in normal tissue from the same individuals. In addition, corresponding tissues were examined from healthy volunteers (n = 23). A part of the cohort was further analysed for the mRNA levels of the two variants of HAI-1, here denoted HAI-1A and HAI-1B. mRNA levels were normalised to β-actin. Immunohistochemical analysis of prostasin and HAI-1 was performed on normal and cancer tissue.

Results

The mRNA level of prostasin was slightly but significantly decreased in both mild/moderate dysplasia (p < 0.001) and severe dysplasia (p < 0.01) and in carcinomas (p < 0.05) compared to normal tissue from the same individual. The mRNA level of PN-1 was more that two-fold elevated in colorectal cancer tissue as compared to healthy individuals (p < 0.001) and elevated in both mild/moderate dysplasia (p < 0.01), severe dysplasia (p < 0.05) and in colorectal cancer tissue (p < 0.001) as compared to normal tissue from the same individual. The mRNA levels of HAI-1A and HAI-1B mRNAs showed the same patterns of expression. Immunohistochemistry showed that prostasin is located mainly on the apical plasma membrane in normal colorectal tissue. A large variation was found in the degree of polarization of prostasin in colorectal cancer tissue.

Conclusion

These results show that the mRNA level of PN-1 is significantly elevated in colorectal cancer tissue. Future studies are required to clarify whether down-regulation of prostasin activity via up regulation of PN-1 is causing the malignant progression or if it is a consequence of it.

The multiple sclerosis degradome: enzymatic cascades in development and progression of central nervous system inflammatory disease

An array of studies implicate different classes of protease and their endogenous inhibitors in multiple sclerosis (MS) pathogenesis based on expression patterns in MS lesions, sera, and/or cerebrospinal fluid (CSF). Growing evidence exists regarding their mechanistic roles in inflammatory and neurodegenerative aspects of this disease. Proteolytic events participate in demyelination, axon injury, apoptosis, and development of the inflammatory response including immune cell activation and extravasation, cytokine and chemokine activation/inactivation, complement activation, and epitope spreading. The potential significance of proteolytic activity to MS therefore relates not only to their potential use as important biomarkers of disease activity, but additionally as prospective therapeutic targets. Experimental data indicate that understanding the net physiological consequence of altered protease levels in MS development and progression necessitates understanding protease activity in the context of substrates, endogenous inhibitors, and proteolytic cascade interactions, which together make up the MS degradome. This review will focus on evidence regarding the potential physiologic role of those protease families already identified as markers of disease activity in MS; that is, the metallo-, serine, and cysteine proteases.

Proteinases and signalling: pathophysiological and therapeutic implications via PARs and more

Proteinases like thrombin, trypsin and tissue kallikreins are now known to regulate cell signaling by cleaving and activating a novel family of G-protein-coupled proteinase-activated receptors (PARs 1-4) via exposure of a tethered receptor-triggering ligand. On their own, short synthetic PAR-selective PAR-activating peptides (PAR-APs) mimicking the tethered ligand sequences can activate PARs 1, 2 and 4 and cause physiological responses both in vitro and in vivo. Using the PAR-APs as sentinel probes in vivo, it has been found that PAR activation can affect the vascular, renal, respiratory, gastrointestinal, musculoskeletal and nervous systems (both central and peripheral nervous system) and can promote cancer metastasis and invasion. In general, responses triggered by PARs 1, 2 and 4 are in keeping with an innate immune inflammatory response, ranging from vasodilatation to intestinal inflammation, increased cytokine production and increased or decreased nociception. Further, PARs have been implicated in a number of disease states, including cancer and inflammation of the cardiovascular, respiratory, musculoskeletal, gastrointestinal and nervous systems. In addition to activating PARs, proteinases can cause hormone-like effects by other signalling mechanisms, like growth factor receptor activation, that may be as important as the activation of PARs. We, therefore, propose that the PARs themselves, their activating serine proteinases and their associated signalling pathways can be considered as attractive targets for therapeutic drug development. Thus, proteinases in general must now be considered as 'hormone-like' messengers that can signal either via PARs or other mechanisms.

A Serpin family gene, protease nexin-1 has an activity distinct from protease inhibition in early Xenopus embryos

Protease nexin-1 (PN-1)/glia-derived nexin (GDN) is a member of the Serpin (serine proteinase inhibitor) family, and can inhibit thrombin, plasmin, and plasminogen activators. PN-1 has been shown to be a neuroprotective factor in a number of assay systems, and this activity has been assumed to be a function of its protease inhibitory function. Here, we report cloning and characterization of a Xenopus orthologue of PN-1 (xPN-1). xPN-1 was isolated in a functional screen of an egg cDNA library for factors that modify early axial patterning. xPN-1 is expressed maternally through late tadpole stages, and is expressed preferentially in the notochord, the pharyngeal endoderm, the otic vesicle, and the ventral region of the brain in tailbud embryos. Over-expression of xPN-1 causes defective gastrulation, inhibits convergent extension movements in activin induced animal caps, and inhibits expression of a distinct subset of activin induced mesendodermal markers. Interestingly, expression of point or deletion mutation of the Reactive Center Loop of xPN1,which is essential for the protease inhibitory activity of all serpins, had effects on Xenopus development indistinguishable from those of wild type xPN-1. These observations suggest the possibility that xPN-1 has a novel activity in addition to its established function as an inhibitor of serine proteases.

Protease-Activated Receptor-1 (Thrombin Receptor) Is Expressed in Mesenchymal Portions of Human Hair Follicle

Protease nexin-1, a serine protease inhibitor, is expressed specifically in the dermal papilla (DP) of anagen hair follicles and is suggested to be one of the modulators of the cyclic growth of hair follicles. Accumulating evidence has shown that protease nexin-1 plays its biologic role by inhibiting thrombin action in various systems other than the hair follicle. Thrombin has various physiologic functions including blood coagulation cascade, mostly via activation of protease-activated receptors (PAR). In this study, we investigated the expression of PAR mRNA using RT-PCR in dissected human hair follicles. We showed that PAR-1 mRNA was expressed specifically in the mesenchymal portions, including DP and connective tissue sheath, of anagen hair follicles. Furthermore, immunoreactivity for PAR-1 was detected in the DP and lower portion of connective tissue sheath in the anagen and catagen phases and in the DP of telogen hair follicles. Because only a pharmacologic level (100 nM) of thrombin significantly stimulated cell proliferation and DNA synthesis of the cultured dermal papilla cells, thrombin does not seem to have a mitogenic effect on dermal papilla cells physiologically. These results raise the possibility that thrombin is involved in the cyclic hair growth through its receptor of PAR-1.

Expression and functional characterization of the serine protease inhibitor neuroserpin in endocrine cells

Serine proteases play essential roles in a wide variety of cellular processes in endocrine cells. There is a growing interest in the roles of serine protease inhibitors, or serpins, as key regulators of their activity. We have cloned two neuroserpin cDNAs from a rat pituitary cDNA library and confirmed tissue plasminogen activator as a potential target for this inhibitor. We show that neuroserpin transcripts are expressed by endocrine cells in the adrenal and pituitary glands and that immunoreactive neuroserpin is stored in densely cored secretory granules in these cells. Overexpression of neuroserpin in an anterior pituitary corticotroph cell line results in the extension of neurite-like processes, suggesting that neuroserpin may play a role in cell communication, cell adhesion, and/or cell migration.

Identifying genes involved in regulating differentiation of neuroblastoma cells

The genes regulating the induction of differentiation in neurons are not definitively known. Some neuronal tumors retain the ability to differentiate into mature, functional neurons in response to pharmacological agents, despite the presence of genetic anomalies. We hypothesized that some of the genes whose expression is altered between undifferentiated and differentiated states may be those responsible for inducing differentiation. To investigate this, we used a mouse neuroblastoma (NB) cell line, NBP(2), in which > or =90% of the cells in the culture terminally differentiate upon elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels. Gene expression was analyzed using cDNA array blots containing 588 known genes. mRNA from cultures of undifferentiated and differentiated NB cells was used to make cDNA probes for blot hybridization. We identified several genes that are predominantly expressed in either undifferentiated or differentiated NB cells. In addition, numerous genes are moderately up- or down-regulated during differentiation of NB cells. We identified the N-myc protooncogene, cyclin B1, and protease nexin 1 as genes that are expressed in undifferentiated NB cells and whose levels are significantly down-regulated upon differentiation. In contrast, the c-fes and c-fos protooncogenes and the RAG-1 gene activator are genes whose expression is significantly up-regulated during differentiation of NB cells. These findings were confirmed by RT-PCR analysis. The transcript size and expression level of N-myc, cyclin B1, protease nexin 1, c-fes, and c-fos were verified by Northern blotting. These genes may represent key mediators involved in the regulation of NB cell differentiation.

Stroke: antithrombin versus antiplatelet therapy

The success of thrombolytic therapy for acute stroke has demonstrated that neurologic outcome can be improved with timely treatment. However, the severely restricted use of thrombolytics has reinforced the need to develop alternative and complementary therapies. Antithrombin and antiplatelet agents represent promising therapeutic approaches for stroke management. Antiplatelet therapy has modestly improved outcome in both acute stroke (aspirin) and in secondary stroke prevention (aspirin with or without dipyridamole; adenosine receptor antagonists), although bleeding and other adverse events associated with antithrombin therapy have largely negated their potential benefit. These findings have prompted innovative solutions to the pharmacokinetic and pharmacodynamic challenges that are crucial to advancing these strategies for acute, primary and secondary stroke therapy. Currently, inhibitors of the platelet surface glycoprotein IIb/IIIa (GP IIb/IIIa, fibrinogen) receptor are being examined in clinical trials while antithrombin therapies focus on thrombin antagonists and inhibitors as well as inhibitors of Factor Xa. Further advances in stroke treatment will include combination therapies. Additionally, the successful design of future drug therapies will result from a more complete understanding of the activity of these agents not only on platelet function and the coagulation cascade, but also for their effects on the endothelium and within the brain parenchyma. The sum of these activities will allow for the maintenance of cerebral blood flow, blood-brain barrier integrity and neuronal function.

Binding of pigment epithelium-derived factor (PEDF) to retinoblastoma cells and cerebellar granule neurons. Evidence for a PEDF receptor

Pigment epithelium-derived factor (PEDF) has neuronal differentiation and survival activity on retinoblastoma and cerebellar granule (CG) cells. Here, we investigated the presence of PEDF receptors on retinoblastoma Y-79 and CG cells. PEDF radiolabeled with (l25)I remained biologically active and was used for radioligand binding analysis. The binding was saturable and specific to a single class of receptors on both cells and with similar affinities (K(d) = 1.7-3.6 nM, B(max) = 0.5-2.7 x 10(5) sites/Y-79 cell; and K(d) = 3.2 nM, B(max) = 1.1 x 10(3) sites/CG cell). A polyclonal antiserum to PEDF, previously shown to block the PEDF neurotrophic activity, prevented the (125)I-PEDF binding. We designed two peptides from a region previously shown to confer the neurotrophic property to human PEDF, synthetic peptides 34-mer (positions 44-77) and 44-mer (positions 78-121). Only peptide 44-mer competed for the binding to Y-79 cell receptors (EC(50) = 5 nM) and exhibited neuronal differentiating activity. PEDF affinity column chromatography of membrane proteins from both cell types revealed a PEDF-binding protein of approximately 80 kDa. These results are the first demonstration of a PEDF-binding protein with characteristics of a PEDF receptor and suggest that the region comprising amino acid positions 78-121 of PEDF might be involved in ligand-receptor interactions.

Differential cytoskeletal changes during growth cone collapse in response to hSema III and thrombin

Growth cones are known as the site of action of many factors that influence neurite growth behavior. To assess how different collapsing agents influence the growth cone cytoskeleton, we used recombinant human Semaphorin III (hSema III) and the serine protease thrombin. Embryonic chick dorsal root ganglion neurons showed a dramatic depolymerization of actin filaments within 5 min upon hSema III exposure and virtually no influence on microtubules (MT). Only at later time points (20-30 min) was the polymerization/depolymerization rate of MT significantly affected. Thrombin induced a morphologically and kinetically similar growth cone collapse. Moreover, thrombin induced an early and selective depolymerization of dynamic MT, accompanied by the formation of loops of stable MT bundles. Selective changes in the phosphorylation pattern of tau were associated with microtubule assembly in thrombin-induced responses. Our data provide evidence that different signal transduction pathways lead to distinct changes of the growth cone cytoskeleton.

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.

Thrombin perturbs neurite outgrowth and induces apoptotic cell death in enriched chick spinal motoneuron cultures through caspase activation

Increasing evidence indicates several roles for thrombin-like serine proteases and their cognate inhibitors (serpins) in normal development and/or pathology of the nervous system. In addition to its prominent role in thrombosis and/or hemostasis, thrombin inhibits neurite outgrowth in neuroblastoma and primary neuronal cells in vitro, prevents stellation of glial cells, and induces cell death in glial and neuronal cell cultures. Thrombin is known to act via a cell surface protease-activated receptor (PAR-1), and recent evidence suggests that rodent neurons express PAR-1. Previously, we have shown that the thrombin inhibitor, protease nexin-1, significantly prevents neuronal cell death both in vitro and in vivo. Here we have examined the effects of human alpha-thrombin and the presence and/or activation of PAR-1 on the survival and differentiation of highly enriched cultures of embryonic chick spinal motoneurons. We show that thrombin significantly decreased the mean neurite length, prevented neurite branching, and induced motoneuron death by an apoptosis-like mechanism in a dose-dependent manner. These effects were prevented by cotreatment with hirudin, a specific thrombin inhibitor. Treatment of the cultures with a synthetic thrombin receptor-activating peptide (SFLLRNP) mimicked the deleterious effects of thrombin on motoneurons. Furthermore, cotreatment of the cultures with inhibitors of caspase activities completely prevented the death of motoneurons induced by either thrombin or SFLLRNP. These findings indicate that (1) embryonic avian spinal motoneurons express functional PAR-1 and (2) activation of this receptor induces neuronal cell degeneration and death via stimulation of caspases. Together with previous reports, our results suggest that thrombin, its receptor(s), and endogenous thrombin inhibitors may be important regulators of neuronal cell fate during development, after injury, and in pathology of the nervous system.

Thrombin induced inhibition of neurite outgrowth from dorsal root ganglion neurons

Thrombin is a multifunctional protease. Recent studies on cultured neuronal cells have suggested a function for thrombin in the development and maintenance of the nervous system. Thrombin has been found to induce neurite retraction and reverse stellation in neuroblastoma cell lines and rat astrocytes, respectively. The major focus of our study was to investigate the potential role of thrombin in peripheral nervous system development using the rat embryonic dorsal root ganglion model. We found a dose dependent inhibition of neurite outgrowth from explant dorsal root ganglion cultures upon exposure to 2 to 200 nM thrombin. This effect was reversed by the specific thrombin inhibitor, hirudin. A synthetic peptide that imitates the fully active receptor, thrombin receptor activating peptide, was also found to inhibit neurite outgrowth from dorsal root ganglia. bis-Benzimide stained neuronal cultures did not show any evidence of cell death after exposure to thrombin or thrombin receptor activating peptides. Immunohistochemical studies revealed specific staining of the thrombin receptor on neurons, with intense labeling along neurites. Enriched neuronal cultures exposed to thrombin and thrombin receptor activating peptides revealed rapid activation of phospholipase Cgamma-1, a second messenger associated with the thrombin receptor. These findings are the first to describe the localization of the thrombin receptor to dorsal root ganglion neurons. We propose that receptor activation is associated with thrombin induced inhibition of neurite outgrowth.

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.

Changes in the expression of protease-activated receptor 1 and protease nexin-1 mRNA during rat nervous system development and after nerve lesion

HDs racI Thrombin causes profound metabolic and morphological changes in cultured neural cells via activation of the thrombin receptor, also called protease-activated receptor 1 (PAR1). PAR1 mRNA is present in the rat brain, but the role of this receptor in the nervous system remains elusive. The expression of PAR1 and the potent thrombin inhibitor protease nexin-1 (PN-1) was investigated in the developing rat brain and spinal cord and after peripheral nerve lesion. As seen by in situ hybridization, the PAR1 mRNA signal in the late embryonic and early postnatal nervous system was widespread, but generally of low intensity whereas in the adult it was more pronounced and confined to particular neuronal cells. These include the mesencephalic dopaminergic neurons, several thalamic and brainstem nuclei, the mitral cells in the olfactory bulb and the Purkinje cells in the cerebellum. In the spinal cord, PAR1 mRNA was abundant in motoneurons and a particularly high expression was detected in the preganglionic neurons of the autonomic nervous system. High PAR1 mRNA expression was also found in the dorsal root ganglia. Interestingly, strong immunoreactivity for the protease inhibitor PN-1 was present in spinal motoneuron cell bodies, although its transcript was undetectable there. In response to sciatic nerve transection, the signal intensity of PAR1 mRNA as seen by Northern analysis increased in the proximal and the distal part of the lesioned nerve and in the denervated muscle, whereas the PN-1 mRNA signal strongly increased only in the distal part of the nerve but remained unchanged in the proximal part and in the muscle. After facial nerve transection, PAR1 mRNA expression substantially decreased in facial motoneurons. No PAR1 transcript was detected in reactive astrocytes. Similar to PAR1, PN-1 mRNA which was expressed in interneurons within the facial nucleus was also decreased following facial nerve transection.

Effects of thrombin and protease nexin-1 on peripheral nerve regeneration

Thrombin and serine protease inhibitors such as protease nexin-1 (PN-1) have been implicated in neurite outgrowth activity. We compared rat sciatic nerve regeneration in 10-mm silicone tubes, bridging an 8-mm nerve gap, that were prefilled with thrombin (1.5 IU) and PN-1 (50 micrograms/mL or 1 mg/mL) to those filled with saline solution (control). Neural regeneration and fibrinoid matrix progression (deposition of extracellular matrix) were analyzed at 1, 4, 17, and 21 days after silicone tube implantation. At 1 and 4 days after implantation, thrombin reduced fibrinoid matrix length propagation from both the proximal and distal transected nerve stumps, but PN-1 and saline did not interfere with matrix progression (p < .05). Seventeen days after implantation, the number of silicone tubes containing myelinated neuronal regenerates at the mid-tube region was 1 of 6 for thrombin, 6 of 9 for PN-1, and 6 of 10 for saline solution. Twenty-one days after implantation, 11 of 11 tubes with saline solution, 9 of 11 with PN-1 at 1 mg/mL, and 7 of 9 with PN-1 at 50 micrograms/mL had myelinated neural regenerates in the mid-silicone tube region, while only 2 of 9 thrombin-containing silicone tubes contained myelinated axons. There was no statistically significant difference in myelinated neurite regenerates at 17 and 21 days after implantation among silicone tubes prefilled with saline solution and PN-1 (50 micrograms/mL or 1 mg/mL). Thrombin interfered with matrix progression and significantly reduced the number of myelinated neurite regenerates (p = .01). The PN-1 and saline solutions did not inhibit matrix progression or affect the number of myelinated axonal regenerates (p = .92).

Expression of neuroserpin, an inhibitor of tissue plasminogen activator, in the developing and adult nervous system of the mouse

Neuroserpin is a serine protease inhibitor of the serpin family that has been identified as an axonally secreted glycoprotein in neuronal cultures of chicken dorsal root ganglia. To obtain an indication for possible functions of neuroserpin, we analyzed its expression in the developing and the adult CNS of the mouse. In the adult CNS, neuroserpin was most strongly expressed in the neocortex, the hippocampal formation, the olfactory bulb, and the amygdala. In contrast, most thalamic nuclei, the caudate putamen, and the cerebellar granule cells were devoid of neuroserpin mRNA. During embryonic development, neuroserpin mRNA was not detectable in neuroepithelia, but it was expressed in the differentiating fields of most CNS regions concurrent with their appearance. In the cerebellum, the granule cells and a subgroup of Purkinje cells were neuroserpin-positive during postnatal development. As a further step toward the elucidation of neuroserpin function, we performed a study to identify potential target proteases. In vitro, neuroserpin formed SDS-stable complexes and inhibited the amidolytic activity of tissue plasminogen activator, urokinase, and plasmin. In contrast, no complex formation with or inhibition of thrombin was found. Expression pattern and inhibitory specificity implicate neuroserpin as a candidate regulator of plasminogen activators, which have been suggested to participate in the modulation or reorganization of synaptic connections in the adult. During development, neuroserpin may attenuate extracellular proteolysis related to processes such as neuronal migration, axogenesis, or the formation of mature synaptic connections.

Nervous system-specific expression of a novel serine protease: regulation in the adult rat spinal cord by excitotoxic injury

A full-length cDNA clone of a previously unidentified serine protease, myelencephalon-specific protease (MSP), has been isolated by using a PCR cloning strategy and has been shown to be expressed in a nervous system and spinal cord-specific pattern. Sequence analysis demonstrated that MSP is most similar in sequence to neuropsin, trypsin, and tissue kallikrein and is predicted to have trypsin-like substrate specificity. MSP mRNA was found to be approximately 10-fold greater in the CNS of the rat and human, as compared with most peripheral tissues, and within the CNS was found to be highest by a factor of four in the medulla oblongata and spinal cord. Levels of mRNA encoding tissue plasminogen activator (tPA) also were elevated in the spinal cord but were more widespread in peripheral tissues as compared with MSP. In the adult rat lumbosacral spinal cord, in situ localization of MSP mRNA demonstrated 2-fold higher levels in the white, as compared with the gray, matter. MSP mRNA expression was shown to increase 3-fold in the white matter and 1.5-fold in the gray laminae at 72 hr after intraperitoneal injection of the AMPA/kainate glutamate receptor-specific agonist, kainic acid (KA). MSP mRNA remained elevated in the ventral gray matter, including expression associated with the motor neurons of lamina IX, at 7 d after the initial excitotoxic insult. Together, these observations indicate that MSP is in a position to play a fundamental role in normal homeostasis and in the response of the spinal cord to injury.

Hirudin suppresses the invasion of inflammatory cells and the appearance of vimentin-positive astrocytes in the rat cerebral ablation model

Hirudin is a specific and direct-acting thrombin inhibitor superior to heparin as an anticoagulant. Thrombin is a multifunctional molecule that acts as a serine protease locally generated from prothrombin during blood coagulation related to injury and/or inflammation. We previously reported that thrombin might be involved in the inflammatory response, glial reaction, and scar formation that occurred in central nervous system (CNS). Here we studied the suppressive effects of hirudin on the inflammation, vimentin-positive astrocytes, and glial fibrillary acidic protein (GFAP)-positive astrocytes using rat cerebral ablation models. Hirudin and vehicle solution soaked in Gelform were administered to the cavity of the traumatic brain defect. Brains were examined by conventional histologic and immunohistologic technique. Antibodies for monocytes/macrophages, GFAP, and vimentin were used to assess the infiltration of inflammatory cells and reaction of astrocytes. The number of the inflammatory cells, vimentin-positive astrocytes, and GFAP-positive astrocytes were quantitatively analyzed. Hirudin suppressed the infiltration of inflammatory cells and the increase in vimentin-positive astrocytes, but had no effects on the increase in GFAP-positive astrocytes. These data suggest that thrombin may play an important role in inflammatory and glial responses to CNS injury, and that hirudin can be a candidate for the therapeutic agent that minimizes the secondary brain damage following the inflammation, and the glial reaction mediated by vimentin-positive astrocytes near the lesion site.

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.

Amyloid precursor proteins protect neurons of transgenic mice against acute and chronic excitotoxic injuries in vivo

The beta-amyloid protein precursor (APP) is well conserved across different species and may fulfill important physiological functions within the CNS. While high-level neuronal expression of amyloidogenic forms of human APP results in beta-amyloid production and neurodegeneration, lower levels of neuronal human APP expression in neurons of transgenic mice may primarily accentuate physiological functions of this molecule. To assess the neuroprotective potential of human APP in vivo, mice from seven distinct transgenic lines expressing different human APP isoforms from the neuron-specific enolase promoter were challenged with systemic kainate injections (n=30) or transgene-mediated glial expression of gp120 (n=32), an HIV-1 protein capable of inducing excitotoxic neuronal damage. To quantitate human APP-mediated neuroprotection. the area of neuropil occupied by presynaptic terminals and neuronal dendrites in the neocortex and hippocampus of each mouse was determined using laser scanning confocal microscopy of double-immunolabelled brain sections and computer-aided image analysis. Compared with gp120 singly transgenic controls, mice from three of three human APP751gp120 bigenic lines expressing the 751 amino acid form of human APP at low levels showed significant protection against degeneration of presynaptic terminals; two of these lines also showed significantly less damage to neuronal dendrites. Two of three human APP695/gp120 bigenic lines expressing human APP695 at low levels were protected against presynaptic and dendritic damage, whereas one low expressor line and a human APP695/gp120 bigenic line expressing human APP695 at higher levels showed no significant protection. In the corresponding human APP singly transgenic lines, overexpressing only specific human APP isoforms, significant protection against kainate-induced degeneration of presynaptic terminals and neuronal dendrites was found in two of three human APP751 lines and not in any of the four human APP695 lines tested. These results indicate that human APP can protect neurons against chronic and acute excitotoxic insults in vivo and that human APP isoforms differ in their neuroprotective potential, at least with respect to specific forms of neural injury. It is therefore possible that impairments of neuroprotective human APP functions or aberrant shifts in human APP isoform ratios could contribute to neurodegeneration.

Neurotrypsin, a novel multidomain serine protease expressed in the nervous system

We have cloned a novel murine cDNA encoding a multidomain serine protease, termed neurotrypsin, which exhibits an unprecedented domain composition. The deduced amino acid sequence defines a mosaic protein of 761 amino acids consisting of a kringle domain, followed by three scavenger receptor cysteine-rich repeats, and a serine protease domain. Based on comparisons of the primary structure, the protease domain belongs to the subfamily of trypsin-like serine proteases. In situ hybridization revealed that the expression of neurotrypsin in the adult murine nervous system is confined to distinct subsets of neurons. The most prominent expression was found in the cerebral cortex, the hippocampus, and the amygdala. Le., structures engaged in the processing and storage of learned behaviors and memories. Together with the recently obtained evidence that extracellular serine proteases play a role in neural plasticity, this expression pattern suggests that the extracellular proteolytic action of neurotrypsin subserves structural reorganizations associated with learning and memory operations.

Secreted glypican binds to the amyloid precursor protein of Alzheimer's disease (APP) and inhibits APP-induced neurite outgrowth

The amyloid precursor protein (APP) of Alzheimer's disease has been shown to stimulate neurite outgrowth in vitro. The effect of APP on neurite outgrowth can be enhanced if APP is presented to neurons in substrate-bound form, in the presence of heparan sulfate proteoglycans. To identify specific heparan sulfate proteoglycans that bind to APP, conditioned medium from neonatal mouse brain cells was subjected to affinity chromatography with recombinant APP695 as a ligand. Glypican bound strongly to the APP affinity column. Purified glypican bound to APP with an equilibrium dissociation constant of 2.8 nM and inhibited APP-induced neurite outgrowth from chick sympathetic neurons. The effect of glypican was specific for APP, as glypican did not inhibit laminin-induced neurite outgrowth. Furthermore, treatment of cultures with 4-methylumbelliferyl-beta-D-xyloside, a competitive inhibitor of proteoglycan glycanation, inhibited APP-induced neurite outgrowth but did not inhibit laminin-induced neurite outgrowth. This result suggests that endogenous proteoglycans are required for substrate-bound APP to stimulate neurite outgrowth. Secreted glypican may act to inhibit APP-induced neurite outgrowth in vivo by competing with endogenous proteoglycans for binding to APP.

Factors influencing mossy fiber collateral sprouting in organotypic slice cultures of neonatal mouse hippocampus

Collateral sprouting of dentate granule cell axons, the mossy fibers, occurs in response to denervation, kindling, or excitotoxic damage to the hippocampus. Organotypic slice culture of rodent hippocampal tissue is a model system for the controlled study of collateral sprouting in vitro. Organotypic roller-tube cultures were prepared from hippocampal slices derived from postnatal day 7 mice. The Timm heavy metal stain and densitometry were used to assay the degree of mossy fiber collateral sprouting in the molecular layer of the hippocampal dentate gyrus. Factors influencing mossy fiber collateral sprouting were time in culture, positional origin of the slice culture along the septotemporal axis of the hippocampus, and presence of attached subicular-entorhinal cortical tissues. Collateral sprouting in the molecular layer was first detected after 6 days in culture and increased steadily thereafter. By 2 weeks considerable sprouting was apparent, and at 3 weeks intense sprouting was observed within the molecular layer. An intrinsic septal-to-temporal gradient of collateral sprouting was apparent at 14 days in culture. To determine whether differential damage to the mossy fibers was the basis for the differences in collateral sprouting along the septotemporal axis, we made complete transections of the mossy fiber projection as it exited the dentate hilus at various levels along the septotemporal axis; no differences were found on subsequent collateral sprouting in the dentate molecular layer. Timm-stained hippocampal cultures with an attached entorhinal cortex, a major source of afferent innervation to the dentate granule cells, displayed significantly less collateral sprouting at 10 days in culture compared to that in cultures from adjacent sections without attached subicular-entorhinal tissues present. Thus, time in culture, position along the septotemporal axis, and presence of afferent cortical tissues influence aberrant neurite collateral sprouting in organotypic slice cultures of neonatal mouse hippocampus.

Ontogeny of neuropsin mRNA expression in the mouse brain

In our previous study, we found a novel gene encoding a serine protease termed neuropsin (NP) which exhibited activity-dependent gene expression or repression in the mouse hippocampus (Chen et al., 1995). In the present study, we examined the ontogeny of NP mRNA expression by in situ hybridization in the brain. Weak hybridization signals were also observed in the choroid plexus at this stage in addition to neuronal labeling. The signals continued to show this localization pattern until postnatal day 12. After embryonic day 18, the number of hybridization signals localized in the neurons of the forebrain limbic area were more predominant than those in the lower brainstem. NP gene expression spread in the anterior olfactory nucleus, hippocampus, septal nuclei, diagonal band of Broca, amygdala and limbic cortex successively from early embryonic to adult stage, though signals in the other brain regions were gradually decreased after birth. Thus, the widespread localization and two types of expression pattern, constitutive or transient, suggest that NP is a multiple functional protein involved in development, neuronal plasticity and cerebrospinal fluid production.

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.

Regulation of neurite outgrowth from differentiated human neuroepithelial cells: a comparison of the activities of prothrombin and thrombin

The mechanism by which thrombin and prothrombin control neurite retraction was studied in Ad12E1HER10 human neuroepithelial cells. Morphological changes in differentiated cells were apparent within minutes of the addition of very low concentrations of thrombin (3 pM). Higher concentrations (2 nM) of prothrombin were required to elicit a similar response. Doses of thrombin and prothrombin sufficient to cause neurite retraction stimulated protein tyrosine kinase activity. Protein tyrosine kinase activation also correlated positively with thrombin- and prothrombin-induced phosphoinositide 3-kinase activation and InsP6 dephosphorylation. However, thrombin-stimulated Ins(1,4,5)P3 generation and intracellular Ca2+ mobilization only occurred at concentrations in excess of those needed to induce retraction. No fluctuations in Ins(1,4,5)P3 were detected after stimulation with prothrombin, and no rapid synchronized release of Ca2+ was observed, even at very high concentrations. Prothrombin did, however, cause small oscillations in the intracellular Ca2+ concentration, similar to those produced by low concentrations of thrombin, after approximately 30 min. We conclude that prothrombin- and thrombin-induced neurite retractions are not dependent on PtdIns(4,5)P2 and Ca2+ mobilization, but are more probably mediated through an effector mechanism involving protein tyrosine kinase activation. No intracellular Ca2+ mobilization, protein tyrosine kinase activity or neurite retraction was observed after treatment of cells with proteolytically inactive mutant thrombin (S205-->A). Prothrombin-mediated intracellular Ca2+ mobilization and neurite retraction were inhibited by hirudin, which was shown to interact with thrombin but not prothrombin. It is concluded that cleavage of prothrombin to thrombin is a necessary prerequisite for biological activity on differentiated Ad12E1HER10 cells and that differences in agonist concentration are capable of coupling the thrombin receptor to different pathways within the cell.

Protection against HIV-1 gp120-induced brain damage by neuronal expression of human amyloid precursor protein

Expression of the HIV-1 envelope protein gp120 in brains of transgenic (tg) mice induces extensive neurodegeneration (Toggas, S. M., E. Masliah, E. M. Rockenstein, G. F. Rall, C. R. Abraham, and L. Mucke. 1994. Nature [Lond.]. 367:188-193.). To further analyze the pathogenesis of gp120-induced neurotoxicity and to assess the neuroprotective potential of human amyloid precursor proteins (hAPPs) in vivo, different hAPP isoforms were expressed in neurons of gp120/hAPP-bigenic mice: hAPP751, which contains a Kunitz-type protease inhibitor domain, or hAPP695, which lacks this domain. Bigenic mice overexpressing hAPP751 at moderate levels showed significantly less neuronal loss, synapto-dendritic degeneration, and gliosis than singly tg mice expressing gp120 alone. In contrast, higher levels of hAPP695 expression in bigenic mice failed to prevent gp120-induced brain damage. These data indicate that hAPP can exert important neuroprotective functions in vivo and that the efficiency of this protection may depend on the hAPP isoform expressed and/or on the level of neuronal hAPP expression. Hence, molecules that mimic beneficial APP activities may be useful in the prevention/treatment of HIV-1-associated nervous system damage and, perhaps, also of other types of neural injury.

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.

Tissue-type plasminogen activator (tPA) is the main plasminogen activator associated with isolated rat nerve growth cones

Different studies in tissue culture have shown the involvement of plasminogen activators (PAs) in nerve growth-cone migration. We have studied PA activity associated with isolated rat brain growth cones. Fibrin-agarose zymographies show that tissue-type PA (tPA) is the main PA associated with these structures. After fractionation of growth cones, a slightly higher tPA activity was found associated with the particulate fraction. The present findings support the requirement of this protease for neurite growth.

Granzyme A released upon stimulation of cytotoxic T lymphocytes activates the thrombin receptor on neuronal cells and astrocytes

Granzymes are a family of serine proteases that are harbored in cytoplasmic granules of activated T lymphocytes and are released upon target cell interaction. Immediate and complete neurite retraction was induced in a mouse neuronal cell line when total extracts of granule proteins were added. This activity was isolated and identified as granzyme A. This protease not only induced neurite retraction at nanomolar concentrations but also reversed the stellation of astrocytes. Both effects were critically dependent on the esterolytic activity of granzyme A. As neurite retraction is known to be induced by thrombin, possible cleavage and activation of the thrombin receptor were investigated. A synthetic peptide spanning the N-terminal thrombin receptor activation sequence was cleaved by granzyme A at the authentic thrombin cleavage site Leu-Asp-Pro-Arg-Ser. Antibodies to the thrombin receptor inhibited both thrombin and granzyme A-mediated neurite retraction. Thus, T-cell-released granzyme A induces cellular responses by activation of the thrombin receptor. As brain-infiltrating CD4+ lymphocytes are the effector cells in experimental allergic encephalomyelitis, granzyme A released in the brain may contribute to the etiology of autoimmune disorders in the nervous system.

Secreted forms of beta-amyloid precursor protein modulate dendrite outgrowth and calcium responses to glutamate in cultured embryonic hippocampal neurons

In addition to being the major excitatory neurotransmitter in the mammalian brain, glutamate is believed to play a key role in the regulation of neurite outgrowth and synaptogenesis during development. In cultured embryonic hippocampal pyramidal neurons, glutamate inhibits dendrite outgrowth by a mechanism involving elevation of intracellular-free calcium levels ([Ca2+]i). In the present study, secreted forms of the beta-amyloid precursor protein (APPss) counteracted the inhibitory effect of glutamate on dendrite outgrowth in cultured embryonic hippocampal neurons. The prolonged elevation of [Ca2+]i normally induced by glutamate was significantly attenuated in neurons that had been pretreated with 2-10 nM of APPs695 or APPs751. Immunocytochemistry with beta-amyloid precursor protein antibodies showed that immunoreactivity was concentrated in axons and, particularly, in their growth cones. Because beta-amyloid precursor proteins are axonally transported, and APPss can be released from axon terminals/growth cones in response to electrical activity, the present findings suggest that APPss may play a role in developmental and synaptic plasticity by modulating dendritic responses to glutamate.

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.

Expression of cathepsin G-like and alpha 1-antichymotrypsin-like proteins in reactive astrocytes

The central nervous system (CNS) of many different species responds to diverse neurologic injuries with an activation of astrocytes. Yet, the exact function of this reactive astrocytosis is unknown. In this report, mouse astrocytes were activated in vivo by focal penetrating brain injury. Reactive astrocytes were stained with antibodies raised against the serine protease cathepsin G (cat.G), the serine protease inhibitor alpha 1-antichymotrypsin (ACT), or the astrocytic marker glial fibrillary acidic protein (GFAP). Reactive astrocytes expressing both cat.G-like and ACT-like antigens were found around cerebral wound margins between 18 h and 13 days after neural lesions. The injury-induced immunostaining was unaltered by 900 rads of total body irradiation, suggesting that the astroglial reaction was relatively independent of bone marrow-derived cells. The in vivo immunostaining was complemented with biochemical assays on cultured primary astrocytes. A synthetic peptide was used as a substrate in combination with specific inhibitors to identify a proteolytic activity within astroglial lysates and culture supernatants that closely resembles cat.G. This activity increased substantially upon stimulation of astrocytes with dibutyryl cyclic AMP and was neutralized by antibodies raised against cat.G. In a separate report, it was shown that astrocytes also contain an ACT-like inhibitory activity. The production of ACT- and cat.G-like antigens and activities by activated astrocytes should allow these cells to participate in a number of important biologic processes. Many of these processes may benefit the CNS by assisting in early wound repair. However, astroglial proteases and their inhibitors could also contribute to the pathogenesis of certain neurologic diseases.

Characterization of "plasma proteins" secreted by cultured rat macroglial cells

The brain is isolated behind a blood-tissue barrier that restricts the access of circulating proteins to neural cells. There is evidence that some of these proteins are synthesized within the central nervous system. The present study examines the synthesis and secretion of such proteins by cultured macroglial cells. Primary glial cultures were derived from cortical and subcortical regions of neonatal rat brains, and subsequent secondary cultures were enriched in type-1 astrocytes, type-2 astrocytes, or oligodendrocytes. Newly synthesized proteins were immunoprecipitated from the culture media using antisera directed against whole rat serum. All three types of glial cells secreted a range of plasma proteins. In general, type-1 astrocytes secreted more of these proteins than did type-2 astrocytes or oligodendrocytes, although the one-dimensional polyacrylamide gel electrophoresis (PAGE) profiles were specific for each cell type. Anti-sera directed against specific plasma proteins identified three of the most abundant proteins secreted by type-1 astrocytes as transferrin, alpha-2-macroglobulin, and ceruloplasmin. Northern blot analysis of cellular RNA confirmed that type-1 astrocytes contained transferrin mRNA, and that it was more abundant in cultures derived from subcortical regions than from cortical regions. In situ hybridization studies revealed that virtually all type-1 and type-2 astrocytes contained transferrin mRNA. Since the proteins identified in this study have been proposed to have a variety of neurotrophic roles in the central nervous system, these data further extend the range of possible functions that glial cells may serve in the CNS.