Thrombin and its precursor in human cerebrospinal fluid

The blood coagulation cascade proteolytic enzyme, thrombin, affects many cell types, including neurons and astrocytes, in which it prevents process outgrowth and induces significant morphological degeneration and even cell death. Since thrombin may contribute significantly to pathological conditions in the central nervous system (CNS), where it is synthesized locally, we measured the levels of thrombin and its precursor, prothrombin, in the cerebrospinal fluid (CSF) of 67 individuals from 6 groups: non-neurologic controls (NNC); spinal degenerative disease (SDD); peripheral nerve disease (PND); cerebrovascular, neuroimmune and seizure disorders and tumor (CNSD); traumatic brain injury (TBI) and neurodegenerative disorders (NDD). We employed a sensitive chromogenic assay utilizing the thrombin specific tripeptide substrate, S-2238, to evaluate CSF levels of thrombin and prothrombin. The latter estimated after its conversion to active enzyme by the snake venom prothrombinase, ecarin. No measurable active thrombin was detected in these CSF samples. However, activatable prothrombin was measured in all groups. The mean activatable prothrombin concentrations (in nM) were 7.26 +/- 3.39 (NNC); 8.85 +/- 3.09 (SDD); 6.78 +/- 2.58 (PND); 6.33 +/- 3.87 (CNSD); 5.10 +/- 1.86 (TBI), and 7.80 +/- 3.27 (NDD). Duncan's multiple comparison test showed significant reduction (p <0.05) in prothrombin levels of the TBI group. Our data suggests that the prothrombin zymogen gains access to the CSF, likely across either an intact or compromised blood-brain barrier (BBB), in increased amounts with age. Reduced levels in TBI patients may have diagnostic and/or prognostic value.

Effect of recombinant human insulin-like growth factor-I on progression of ALS. A placebo-controlled study. The North America ALS/IGF-I Study Group

The objective of this study was to investigate the safety and efficacy of recombinant human insulinlike growth factor-I (rhIGF-I) in the treatment of sporadic ALS. A double-blind, placebo-controlled, randomized study of 266 patients was conducted at eight centers in North America. Placebo or rhIGF-I (0.05 mg/kg/day or 0.10 mg/kg/day) was administered for 9 months. The primary outcome measure was disease symptom progression, assessed by the rate of change (per patient slope) in the Appel ALS rating scale total score. The Sickness Impact Profile (SIP), a patient-perceived, health-related quality of life assessment, was a secondary outcome variable. Progression of functional impairment in patients receiving high-dose (0.10 mg/kg/day) rhIGF-I was 26% slower than in patients receiving placebo (p = 0.01). The high-dose treatment group was less likely to terminate the study due to protocol-defined markers of disease symptom progression, and members in this group exhibited a slower decline in quality of life, as assessed by the SIP. Patients receiving 0.05 mg/kg/day of rhIGF-I exhibited trends similar to those associated with high-dose treatment, suggesting a dose-dependent response. The incidence of clinically significant adverse experiences was comparable among the three treatment groups. Recombinant human insulin-like growth factor-I slowed the progression of functional impairment and the decline in health-related quality of life in patients with ALS with no medically important adverse effects.

Quantitative PCR analysis reveals novel expression of prothrombin mRNA and regulation of its levels in developing mouse muscle

Precise determination of mRNA levels is an essential element in any investigation of complex regulatory systems. Classical methodologies such as Northern hybridization suffer from requirements for significant samples of material and also a degree of nonspecificity. Recently, quantitative techniques involving PCR amplification have been devised. We have developed and applied such procedures to the determination of prothrombin messages in skeletal muscle cells during development. In addition to its role in the blood coagulation cascade, the serine protease thrombin has been shown to participate in several signaling events in the neuromuscular system. The inactive precursor, prothrombin, primarily produced in the liver, has also been shown to be synthesized and developmentally-regulated in the brain. In skeletal muscle, thrombin is a mediator of activity-dependent polyneuronal synapse elimination (ADPSE) which occurs in early postnatal development. Recent experiments showing that thrombin is released from myotubes in culture under the influence of acetylcholine suggest that locally-synthesized prothrombin may be the source of this Hebbian synaptic interaction. We have determined that prothrombin is expressed in skeletal muscle, as the likely source of thrombin involved in ADPSE, and the current results show the quantitative expression of muscle prothrombin during this time of intense synapse remodeling.

Apoptotic, injury-induced cell death in cultured mouse murine motor neurons

In order to develop in vitro models of CNS injury, astrocytes have been mechanically injured in culture to study reactive astrocytosis. However, scratch injury models of pure neuronal cultures have not yet been exploited to study programmed cell death (PCD). For this study, we examined model motor neurons (NSC19 cells) in culture and found time-dependent cell death in proximity (within 2.5 mm) to a physical scratch injury. Injury-induced cell death was apoptotic verified by positively-stained nuclei using both the in situ end-labeling (ISEL) procedure and Hoechst 33342. Unexpectedly, cells proximal to the injury site were not affected by the injury until 3 days later suggesting that adjacent motor neuron loss was dependent on a 'death signal' produced by direct injury to sister neurons. 'Executioners' in apoptosis include free radicals, cell cycle kinases and cysteine proteases (caspases). Extracellular serine proteases, such as thrombin and granzyme B, may activate such intracellular pathways and several inhibitors (serpins), such as CrmA, are effective in blocking apoptosis. Since protease nexin I (PNI), a serpin homologous with CrmA, prevents apoptosis of lumbar motor neurons and is increased after nerve injury, we examined mRNA by RT-PCR for PNI expression. Of interest, although we were unable to find significant levels of PNI message in NSC19 cells, we did detect it in the parent neuroblastoma.

Identity of neurotrophic molecules released from astroglia by vasoactive intestinal peptide

Subnanomolar concentrations of VIP elicit a survival-producing action in CNS cultures composed of both astroglia and neurons. This neurotrophic action is mediated by a complex array of substances released by VIP from astrocytes. Included in this glial protein mixture is a cytokine (interleukin-1 alpha), a serine protease inhibitor (protease nexin I), and an extracellular stress protein (activity-dependent neurotrophic factor). In dissociated spinal cord cultures, all of these substances exhibit neuroprotection from neuronal cell death produced by electrical blockade with tetrodotoxin. All these substances produce neuronal cell death when test cultures are treated with neutralizing antisera to any one of them. They are all apparently necessary for the survival of a subpopulation of neurons that are dependent on spontaneous, excitatory neurotransmission. Our view is that these substances are components of a glia-derived environment that regulates, together with target-derived growth factors, the survival fate of developing neurons. In addition, it is our belief that some of these glia-derived substances will be found to have active roles in the injury response to the CNS or in the regulation of VIP-mediated growth in other tissues. Drugs based on these substances may provide therapeutic agents for the treatment of neurodegeneration and tumor growth.

Novel expression and localization of active thrombomodulin on the surface of mouse brain astrocytes

Thrombin's potent effects on astrocytes are mediated by a specific receptor and inhibited by a serpin, protease nexin I (PNI). Thrombomodulin (TM), a membrane protein that forms complexes with thrombin, changing its enzymatic specificity, has not been studied in astrocytes. In primary astrocyte cultures, using Western blotting and immunocytochemistry, we found a 70 kDa TM band and TM localized to the surface with an anti-mouse TM monoclonal antibody. By reverse transcriptase coupled with polymerase chain reaction (RT-PCR), we found the correct sequence for mouse TM mRNA in astrocytes. Finally, we documented calcium-dependent activation of protein C by a thrombin:TM complex with thrombin added to the astrocytes. These results indicate the presence of functionally active TM at the astrocyte surface and add support to a role for thrombin signaling in the nervous system.

Neural thrombin and protease nexin I kinetics after murine peripheral nerve injury

We addressed the balance between thrombin and its serpin protease nexin I (PNI) after sciatic nerve injury in the mouse. Prothrombin levels increased twofold 24 h after nerve crush, as measured by a specific chromogenic assay, and peaked at day 3. Thrombin activity also increased 2-4 days after injury in distal sciatic nerve segments. Nerve RNA analysis using reverse transcriptase--polymerase chain reaction (RT-PCR) assay confirmed that prothrombin was synthesized locally. We also monitored PNI levels in these injured nerve samples by complex formation with an 125I-labeled target protease and found peak activity occurring later, 6-9 days after the thrombin induction. These data indicate that nerve injury first induces the synthesis of prothrombin, which is subsequently converted to active thrombin. Nerve crush-induced thrombin is followed by the generation of functionally active PNI and may be directly responsible for its induction. By immunocytochemistry with anti-PNI antibody, we found that activated Schwann cells were the source of induced PNI. These results support the concept that the balance between serine proteases and their serpins is dysregulated during nerve injury and suggests a role for its reestablishment in nerve damage repair.

A molecular mechanism for synapse elimination: novel inhibition of locally generated thrombin delays synapse loss in neonatal mouse muscle

Activity-dependent, polyneuronal synapse elimination (ADPSE) is a programmed, regressive event in the development of the nervous system and readily studied at the neuromuscular junction, where it is complete 15-20 days after birth. Local excess, or imbalanced, protease activity is one of several possible underlying mechanisms. In this regard, thrombin mediates activity-dependent synapse loss in an in vitro model of ADPSE. To test the involvement of thrombin in vivo, we locally applied the leech thrombin-specific inhibitor, hirudin. We monitored neuromuscular behavior, correlated with acetylcholinesterase and silver nitrate histochemistry at endplates, for changes in the timecourse of in vivo synapse elimination and assayed both thrombin activity and prothrombin expression in developing muscle. Hirudin retarded elimination, without altering motor performance, uniquely at Postnatal Day 5 (P5) and maximally at P9. Reverse transcription-polymerase chain reaction (PCR) showed that neonatal muscle was a source of local prothrombin, with peak expression during the first week after birth. A specific chromogenic assay revealed that local thrombin, activated from muscle-derived prothrombin, peaked during maximal synapse remodeling.

Protease nexin I (PNI) in mouse brain is expressed from the same gene as in seminal vesicle

Protease nexin I (PNI), a serine protease inhibitor (serpin), is the most potent tissue inhibitor of thrombin. In the nervous system, PNI has been shown to participate in processes related to synaptic plasticity and neuronal survival. We assigned the human gene for PNI (P17) to chromosome 2q33-35, and to syntenic regions in mouse chromosome 1. Others showed that a similar serpin was expressed in mouse seminal vesicle, which presented the possibility of a "duplicate" gene. The data also raised controversy over the quantity of PNI mRNA expressed in the brain vs peripheral tissues, such as seminal vesicle. In order to further our investigations of PNI regulation and its influence on neuronal survival and neuroprotection, it was necessary to confirm whether the nexin observed in mouse brain samples was identical to the published protease nexin I sequences. To accomplish this, we performed DNA sequence analysis of cDNAs made from RNAs isolated from mouse forebrain and hindbrain as well as from seminal vesicle. These confirmed the identity of the mouse PNI gene (SPI4) in brain and peripheral tissues. Furthermore, Northern hybridization studies indicated that the PNI message is present at lower levels in the adult brain compared to the adult seminal vesicle. Western immunoblotting showed no differences between brain and seminal vesicle PNI proteins. The PNI cDNAs generated will serve as useful probes for the continued characterization of the serpin:protease balance as it relates to nerve cell function.

Prevention of activity-dependent neuronal death: vasoactive intestinal polypeptide stimulates astrocytes to secrete the thrombin-inhibiting neurotrophic serpin, protease nexin I

Neuronal cell death occurs as a programmed, naturally occurring mechanism and is the primary regressive event in central nervous system development. Death of neurons also occurs on an injury-induced basis after trauma and in human neurodegenerative diseases. Classical neurotrophic factors can reverse this phenomenon in experimental models prompting initiation of clinical trials in conditions such as amyotrophic lateral sclerosis and Alzheimer's disease. The glial-derived protease nexin I (PNI), a known promoter of neurite outgrowth in cell culture and a potent inhibitor of serine proteases, also enhances neuronal cell survival. PNI, in nanomolar concentrations, rescues spinal cord motor neurons from both naturally-occurring programmed cell death in the chick embryo as well as following injury in the neonatal mouse. The potent neuromodulator, vasoactive intestinal polypeptide (VIP), influences neuronal survival through glial-mediated factors and also induces secretion of newly synthesized astrocyte PNI. We now report that subnanomolar amounts of PNI enhance neuronal survival in mixed spinal cord cell culture, especially when neuronal cells were made electrically silent by administration of tetrodotoxin. The mediation of this effect is by inhibition of the multifunctional serine protease, thrombin, because hirudin, a thrombin-specific inhibitor, has the same effect. In addition, spinal cord neurons are exquisitely sensitive to thrombin because picomolar and lower levels of the coagulation factor causes neuronal death. Thus, PNI is an astrocyte-derived, thrombin-inhibiting, activity-dependent neurotrophic agent, enhanced secretion of which by VIP may be one approach to treat neurological disorders.

Thrombin, its receptor and protease nexin I, its potent serpin, in the nervous system

The multifunctional serine protease, thrombin, the principal component of the blood coagulation cascade, is also active in nervous system growth and maintenance. In neural tissue culture, it prevents neurite outgrowth and modulates morphologic changes in both neurons and astrocytes. In recent studies, we found that it mediates polyneuronal synapse elimination, both in vivo and in vitro. Of relevance to neurologic disease, as well as to development, evidence also implicates thrombin in apoptosis of these cells. As with other serine proteases, thrombin is in "balance" with one or more endogenous protein inhibitors, members of the serpin superfamily of proteins. The most potent vertebrate inhibitor for thrombin is protease nexin I (PNI), which regulates thrombin's effect by forming post-translational, covalent complexes with the protease. We review some of the nervous system effects of the thrombin:PNI balance, and also present results of a recent study of this balance after peripheral nerve injury. We measured thrombin and prothrombin activity in extracts from adult mouse sciatic nerve using a specific chromogenic assay. We also performed reverse transcription polymerase chain reaction of RNA from nerve crush samples. We found a burst of activity at 3 days following injury distal to the crush site that was inhibited by thrombin specific inhibitors. It is possible that a significant fraction of the increased prothrombin in injured nerve was synthesized locally. Active PNI levels increased in these crush samples 6 to 9 days after the thrombin induction. These data suggest that nerve injury first induces the synthesis of prothrombin, which is subsequently converted to active thrombin. Nerve crush-induced thrombin is followed by the generation of functionally active PNI and may be directly responsible for its induction. These results suggest that the balance between serine proteases and their serpins is dysregulated during nerve injury and support a role for its reestablishment in nerve damage repair.

Myoblast fusion promotes the appearance of active protease nexin I on human muscle cell surfaces

Protease nexin I (PNI) is a 43- to 50-kDa glycoprotein capable of inhibiting a number of serine proteases and belongs to the serpin superfamily. PNI is identical to glia-derived nexin, a neurite outgrowth promoter by virtue of its thrombin-inhibiting activity. Of particular relevance to neuromuscular biology and pathology, PNI was the first serpin shown to be highly localized to the neuromuscular junction and it maps to precisely the same locus as autosomal recessive amyotrophic lateral sclerosis (ALSJ) at chromosome 2q33-35. In the present report, we now show that in cultures of human skeletal muscle, PNI protein is expressed only after myoblast fusion into multinuclear myotubes and is localized in patches on their surfaces. We performed complex formation experiments with labeled thrombin, another target protease for PNI, with intact human muscle cells in culture. We detected specific SDS-stable PNI/thrombin complexes in myotube extracts only, indicating that active PNI was bound to their surfaces. We studied the gene expression of PNI mRNA using a 300-bp cDNA synthesized from the published sequence of human PNI. Confirming the protein data, upregulation of PNI appears in myotubes using Northern blot analysis. The current results reinforce the hypothesis that the regulation of the balance of serine proteases and serpins, such as PNI, is involved in muscle differentiation. They also prompt us to explore PNI abnormalities in several neuromuscular diseases, including ALSJ.

Amyotrophic lateral sclerosis: current and future treatment strategies

Amyotrophic lateral sclerosis (ALS) is a fatal, enigmatic disorder characterised by relentless progression of muscle wasting and weakness until death ensues due to respiratory muscle failure. Intellectual functions are usually spared. ALS, known also as motor neuron disease (MND) in the UK, maladie de Charcot in France and Lou Gehrig's disease in the US, is usually sporadic, but between 5 and 10% of all cases are hereditary, usually inherited as autosomal dominant. Previously thought to be untreatable, as well as incurable, just in the last 3 years ALS has been the greatest clinical application of recent exciting break-throughs in preclinical neurobiology research. Although definitive information regarding the cause(s) and pathogenesis of ALS still escapes us, meaningful demonstration of intercession in the downhill course with specific therapy has been suggested, giving reason to be hopeful, if cautiously and critically optimistic. This review focuses on the recent work from the fields of growth/trophic factors, glutamate/neurotoxicity, neuroprotection and proteases and inhibitors, as well as the approaches to measuring specific effects in patients with the illness. It ends with a eye to the horizon, and the future, and where ALS treatment strategies may be heading after the millennium.

Serine proteinase inhibitors in human skeletal muscle: expression of beta-amyloid protein precursor and alpha 1-antichymotrypsin in vivo and during myogenesis in vitro

The balance of serine proteases and inhibitors in nerve and muscle is altered during programmed- and injury-induced remodeling. A serpin, alpha 1-antichymotrypsin (alpha 1-ACT), and Kunitz-inhibitor containing forms of the beta-amyloid precursor protein (beta APP) may be important components of this balance. In the present study, we analyzed their expression in primary cultures of human myogenic (satellite) cells that mimic myogenic differentiation using Western blotting and immunocytochemistry. In vitro results were compared to in vivo results from normal adult human skeletal muscle biopsies. Using an anti-alpha 1-ACT polyclonal antibody, we detected a 62 kDa immunoreactive band both in cultured human myogenic cells (mononucleated myoblasts as well as multi-nucleated myotubes) and in extracts of human muscle biopsies. With a polyclonal anti-beta APP antibody we found two bands (105 and 120 kDa) in myoblasts and myotubes in culture. However, the same antibody recognized only a single band at 92 kDa in biopsies. By immunocytochemistry, both alpha 1-ACT and beta APP were indistinctly present on localized to the surface of myoblasts in culture. In contrast, these inhibitors were dense on myotube surfaces, where they often formed distinct aggregates and frequently co-localized. In permeabilized muscle cells, alpha 1-ACT and beta APP appeared to be localized to the perikarya of both myoblasts and myotubes. Confirming previous results, both alpha 1-ACT and beta APP were present at the neuromuscular junction in human muscle sections. These developmental changes found during in vitro myogenesis for alpha 1-ACT and beta APP, both serine protease inhibitors, reinforce the hypothesis that regulation of the serine proteases and serine protease inhibitors plays an important role in neuromuscular differentiation.

Beneficial effects of insulin-like growth factor-I on wobbler mouse motoneuron disease

Recombinant human insulin-like growth factor-I (IGF-I) is being considered as a possible therapeutic agent for the treatment of motoneuron diseases like amyotrophic lateral sclerosis. The neurological mutant mouse wobbler, carries an autosomal recessive gene (wr) and has been characterized as a model of lower motoneuron disorders with associated muscle atrophy, denervation and reinnervation. The purpose of the present study was to determine the possible beneficial effect of IGF-I administration in this mouse model. Upon diagnosis at 4 weeks of age, affected mice and their control normal littermates received human recombinant IGF-I (1 mg/kg) or vehicle solution, once a day, for 6 weeks. Body weight and grip strength were evaluated periodically during the treatment period. Mean muscle fiber diameter on biceps brachii sections, choline acetyltransferase activity in muscle extracts, and motoneuron numbers in spinal cord sections were determined. IGF-I treated wobbler mice showed a marked weight increase from 3 to 6 weeks of treatment in comparison with placebo treated mutant mice. At the end of the treatment, grip strength, estimated by dynamometer resistance, was 40% higher in IGF-I treated versus placebo treated animals. Mean muscle fiber diameter which is smaller in wobbler mice than in normal mice was increased in IGF-I treated mutants. However, in this study the muscle choline acetyltransferase activity and the number of spinal cord motoneurons were unchanged. Thus, IGF-I administration mainly results in a significant effect on the behavioral and skeletal muscle histochemical parameters of the wobbler mouse mutant.

The gene for the serpin thrombin inhibitor (PI7), protease nexin I, is located on human chromosome 2q33-q35 and on syntenic regions in the mouse and sheep genomes

Protease nexin I (PNI) is the most important physiologic regulator of alpha-thrombin in tissues. PNI is highly expressed and developmentally regulated in the nervous system where it is concentrated at neuromuscular junctions and also central synapses in the hippocampus and striatum. Approximately 10% of identified proteins at mammalian neuromuscular junctions are serine protease inhibitors, consistent with their central role in balancing serine protease activity to develop, maintain, and remodel synapses. Southern blot hybridization of PNI cDNA to somatic cell hybrids placed the structural gene for PNI (locus PI7) on human chromosome 2q33-q35 and to syntenic chromosomes in the mouse (chromosome 1) and sheep (chromosome 2).

Synaptic transmission blockade increases plasminogen activator activity in mouse skeletal muscle poisoned with botulinum toxin type A

Experimental denervation, either by nerve crush or axotomy, leads to a dramatic increase in muscle plasminogen activator (PA) activity, suggesting a regulation of muscle PA levels by some neural influence (Festoff et al., 1986, J. Cell Biol., 103:1415-1421; Hantaï et al., 1990, Proc. Natl. Acad. Sci. U.S.A., 87:2926-2930). The Botulinum toxin (BoTx) type A is known to selectively interrupt the release of acetylcholine without structurally altering synaptic morphology. In the present study we have used acute BoTx poisoning of hind limb muscles to further explore the neural regulation of muscle PA activities directly after poisoning and during the process of collateral reinnervation. Electromyographic recording and study of ultraterminal sprouting after zinc iodideosmium and silver-cholinesterase staining were used to monitor "denervation" and reinnervation. Muscle choline acetyltransferase activity did not decrease, as is observed after experimental denervation, but in contrast increased and, therefore, reflected the functional integrity of intramuscular nerve endings. Within 2 days of BoTx poisoning, muscle urokinase-PA, and to a lesser extent, tissue-PA activities, rose in muscle extracts as shown by an amidolytic assay and fibrin zymography. When reinnervation occurred, muscle urokinase-PA activity decreased but did not return to baseline levels within the 80 days of our study. These results suggest that cholinergic transmission-regulated events determine activity of muscle PAs and that PAs likely have a role in neuromuscular formation and plasticity.

The insulin-like growth factor signaling system and ALS neurotrophic factor treatment strategies

Because of its multi-faceted potential as a neurotrophic factor, insulin-like growth factor I (IGF-I) has been given to hundreds of ALS patients world-wide. Unlike some patients with post-polio syndrome and fragile elderly males, it is unclear whether any of these patients possess disturbances in IGF signaling. We found that about 25% of ALS patients in a controlled trial of human growth hormone (hGH) had lower or higher than normal IGF-I serum levels. Many ALS patients do have some of the characteristics of type II diabetes mellitus, where IGF-I therapy is also under way. In addition, in type I diabetes significant increase in a circulating molecule that binds IGF-I, IGF-I binding protein 1 (IGFBP-1), occurs along with reduced IGF-I, when neuropathic complications are prominent. We have studied the response of IGFBPs in ALS patients to subcutaneous rhIGF-I and found transient induction of IGFBP-1. Studies related to the IGFBPs have not been done in familial ALS (FALS) patients. However, the gene for another IGFBP, BP-2, co-localizes with the gene for juvenile ALS (ALSJ) on chromosome 2. IGF-I has been given to several models of motor neuron degeneration in the mouse, including motor neuron disease and wobbler, with beneficial effects. However, it is also not known whether any accepted genetic mouse model of motor neuron degeneration possesses any disturbance in the IGF signaling system.

A serine protease inhibitor, protease nexin I, rescues motoneurons from naturally occurring and axotomy-induced cell death

Protease nexin I (PNI) is a member of the family of serine protease inhibitors (serpins) that have been shown to promote neurite outgrowth in vitro from different neuronal cell types. These include neuroblastoma cells, hippocampal neurons, and sympathetic neurons. Free PNI protein is markedly decreased in various anatomical brain regions, including hippocampus, of patients with Alzheimer disease. Here, we report that PNI rescued spinal motoneurons during the period of naturally occurring (programmed) cell death in the chicken in a dose-dependent fashion. Furthermore, PNI prevented axotomy-induced spinal motoneuron death in the neonatal mouse. The survival effect of PNI on motoneurons during the period of programmed cell death was not associated with increased intramuscular nerve branching. PNI also significantly increased the nuclear size of motoneurons during the period of programmed cell death and prevented axotomy-induced atrophy of surviving motoneurons. These results are consistent with the possible role of PNI as a neurotrophic agent. They also support the idea that serine proteases or, more precisely, the balance of proteases and serpins may be involved in regulating the fate of neuronal cells during development.

Alterations in serum thrombospondin in patients with amyotrophic lateral sclerosis

Thrombospondin (TSP), an endogenous extracellular matrix (ECM) glycoprotein, is secreted from platelet alpha-granules after thrombin stimulation. Alterations in blood TSP levels occur in different pathologic conditions, suggesting it is a marker for certain disorders. We previously found a marked increase in TSP deposition in the muscle ECM of patients with amyotrophic lateral sclerosis (ALS) in comparison with controls. Because the mechanism for this increase is unknown, we compared serum TSP levels in 11 patients to 15 controls using three different site-specific monoclonal antibodies (MA-I, MA-II and A6.1). We found mean serum TSP concentrations by indirect ELISA to be significantly decreased in the ALS patients. Using laser densitometry we calculated the ratio of fragmented to native TSP from Western immunoblots probed with A6.1, where a higher ratio corresponds to increased fragments. Mean values for this ratio were 6.3 +/- 4.9 and 18.3 +/- 8.2 for controls and patients, respectively. Thus significant decrease in native TSP and increase in its proteolytic fragments in ALS is consistent with increased proteolytic enzyme activity. Dysregulation of the protease: inhibitor balance in this degenerative condition may be reflected in the quantitative and qualitative changes in TSP.

Insulin-like growth factor binding protein-1 is pre-synaptic at mouse neuromuscular synapses and is transported in nerve

In a previous study, we localized insulin-like growth factor binding protein 1 (IGFBP-1) to mouse neuromuscular junctions, and intramuscular nerves. To determine if pre-synaptic accumulation of IGFBP-1 occurred, we used double ligation of sciatic nerve in adult mice at different time points. IGFBPs were detected by Western ligand blot (WLB) with 125I-IGF-I. WLB and Western immunoblot (WIB) analysis of extracts from double-ligated nerves showed a delayed (6 days) increase of IGFBP-1 in the soluble fraction between the ligatures and distal to the distal ligature. For comparison we evaluated transport of neurofilament components, using WIB and confirmed the primarily anterograde transport of these intraaxonal proteins. These data suggest that expression of IGFBP-1 is both by activated Schwann cells as well as retrograde axonal transport with likely entry into the axon at the synapse.

Proteolytic action of thrombin is required for electrical activity-dependent synapse reduction

Molecular mechanisms of activity-dependent synapse reduction were studied in an in vitro mammalian neuromuscular preparation. Synapse reduction in this model is activity-dependent and is substantially reduced by the broad-spectrum protease inhibitor, leupeptin, suggesting the role of activity-dependent proteolytic action in the process. Our present experiments show that a potent and specific thrombin inhibitor, hirudin, at nanomolar concentration completely blocked the activity-dependent synapse reduction. Furthermore, a naturally occurring serine protease inhibitor, protease nexin I (PNI), which closely colocalizes with acetylcholine receptors at the neuromuscular junction, inhibited the synapse reduction at the same low concentration. In contrast, neither cystatin, a cysteine protease inhibitor, nor aprotinin, a serine protease inhibitor that does not inhibit thrombin, blocked the synapse reduction. Similarly, neither of the inhibitors of the calcium-activated proteases calpain I and II prevented the reduction of synapses. These results strongly suggest that serine proteolytic action by thrombin or thrombin-like molecules is required for synapse reduction in our in vitro model of the mammalian neuromuscular junction.

Extravascular proteolysis and the nervous system: serine protease/serpin balance

Widely recognized as components of the blood coagulation cascade, serine proteases and their natural inhibitors, specific serpins known as the protease nexins, also regulate the maintenance of normal function in the nervous system. Increasingly, evidence has accumulated as to regulation of their synthesis and functional roles within both the CNS and peripheral nervous system. Our review focuses on the localization and activity of TH and PN I in the nervous system, as well as on the impact of the protease/inhibitor balance for the pathogenesis of neurodegenerative disorders such as AD.