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

Impact of the Reduction Time-Dependent Electrical Conductivity of Graphene Nanoplatelet-Coated Aligned Bombyx mori Silk Scaffolds on Electrically Stimulated Axonal Growth

Graphene-based nanomaterials, renowned for their outstanding electrical conductivity, have been extensively studied as electroconductive biomaterials (ECBs) for electrically stimulated tissue regeneration. However, using eco-friendly reducing agents like l-ascorbic acid (l-Aa) can result in lower conductive properties in these ECBs, limiting their full potential for smooth charge transfer in living tissues. Moreover, creating a flexible biomaterial scaffold using these materials that accurately mimics a specific tissue microarchitecture, such as nerves, poses additional challenges. To address these issues, this study developed a microfibrous scaffold of Bombyx mori (Bm) silk fibroin uniformly coated with graphene nanoplatelets (GNPs) through a vacuum coating method. The scaffold's electrical conductivity was optimized by varying the reduction period using l-Aa. The research systematically investigated how different reduction periods impact scaffold properties, focusing on electrical conductivity and its significance on electrically stimulated axonal growth in PC12 cells. Results showed that a 48 h reduction significantly increased surface electrical conductivity by 100-1000 times compared to a shorter or no reduction process. l-Aa contributed to stabilizing the reduced GNPs, demonstrated by a slow degradation profile and sustained conductivity even after 60 days in a proteolytic environment. β (III) tubulin immunostaining of PC12 cells on varied silk:GNP scaffolds under pulsed electrical stimulation (ES, 50 Hz frequency, 1 ms pulse width, and amplitudes of 100 and 300 mV/cm) demonstrates accelerated axonal growth on scaffolds exhibiting higher conductivity. This is supported by upregulated intracellular Ca2+ dynamics immediately after ES on the scaffolds with higher conductivity, subjected to a prolonged reduction period. The study showcases a sustainable reduction approach using l-Aa in combination with natural Bm silk fibroin to create a highly conductive, mechanically robust, and stable silk:GNP-based aligned fibrous scaffold. These scaffolds hold promise for functional regeneration in electrically excitable tissues such as nerves, cardiac tissue, and muscles.

Molecular Characterization of Kunitz-Type Protease Inhibitors from Blister Beetles (Coleoptera, Meloidae)

Protease inhibitors are widely studied since the unrestricted activity of proteases can cause extensive organ lesions. In particular, elastase activity is involved in the pathophysiology of acute lung injury, for example during SARS-CoV-2 infection, while serine proteases and thrombin-like proteases are involved in the development and/or pathology of the nervous system. Natural protease inhibitors have the advantage to be reversible and with few side effects and thus are increasingly considered as new drugs. Kunitz-type protease inhibitors (KTPIs), reported in the venom of various organisms, such as wasps, spiders, scorpions, and snakes, have been studied for their potent anticoagulant activity and widespread protease inhibitor activity. Putative KTPI anticoagulants have been identified in transcriptomic resources obtained for two blister beetle species, Lydus trimaculatus and Mylabris variabilis. The KTPIs of L. trimaculatus and M. variabilis were characterized by combined transcriptomic and bioinformatics methodologies. The full-length mRNA sequences were divided on the base of the sequence of the active sites of the putative proteins. In silico protein structure analyses of each group of translational products show the biochemical features of the active sites and the potential protease targets. Validation of these genes is the first step for considering these molecules as new drugs for use in medicine.

Surface Functionalized Polyaniline Nanofibers:Chitosan Nanocomposite for Promoting Neuronal-like Differentiation of Primary Adipose Derived Mesenchymal Stem Cells and Urease Activity

Bioscaffolds having electrically conducting polymers (CPs) have become increasingly relevant in tissue engineering (TE) because of their ability to regulate conductivity and promote biological function. With this in mind, the current study shows a conducting polyaniline nanofibers (PNFs) dispersed chitosan (Ch) nanocomposites scaffold with a simple one-step surface functionalization approach using glutaraldehyde for potential neural regeneration applications. According to the findings, 4 wt % PNFs dispersion in Ch matrix is an optimal concentration for achieving desirable biological functions while maintaining required physicochemical properties as evidenced by SEM, XRD, current-voltage (I-V) measurement, mechanical strength test, and in vitro biodegradability test. Surface chemical compositional analysis using XPS and ATR FT-IR confirms the incorporation of aldehyde functionality after functionalization, which is corroborated by surface energy calculations following the Van Oss-Chaudhury-Good method. Surface functionalization induced enhancement in surface hydrophilicity in terms of the polar component of surface energy (γ_i^AB) from 6.35 to 12.54 mN m^-1 along with an increase in surface polarity from 13.61 to 22.54%. Functionalized PNF:Ch scaffolds demonstrated improvement in enzyme activity from 67 to 94% and better enzyme kinetics with a reduction of Michaelis constants (K_m) from 21.55 to 13.81 mM, indicating favorable protein-biomaterial interactions and establishing them as biologically perceptible materials. Surface functionalization mediated improved cell-biomaterial interactions led to improved viability, adhesion, and spreading of primary adipose derived mesenchymal stem cells (ADMSCs) as well as improved immunocompatibility. Cytoskeletal architecture assessment under differentiating media containing 10 ng/mL of each basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) revealed significant actin remodeling with neurite-like projections on the functionalized scaffolds after 14 days. Immunocytochemistry results showed that more than 85% of cells expressed early neuron specific β III tubulin protein on the functionalized scaffolds, whereas glial fibrillary acidic protein (GFAP) expression was limited to approximately 40% of cells. The findings point to the functionalized nanocomposites' potential as a smart scaffold for electrically stimulated neural regeneration, as they are flexible enough to be designed into microchanneled or conduit-like structures that mimic the microstructures and mechanical properties of peripheral nerves.

Emerging Roles of Protease-Activated Receptors (PARs) in the Modulation of Synaptic Transmission and Plasticity

Protease-activated receptors (PARs) are a class of G protein-coupled receptors (GPCRs) with a unique mechanism of activation, prompted by a proteolytic cleavage in their N-terminal domain that uncovers a tethered ligand, which binds and stimulates the same receptor. PARs subtypes (PAR1-4) have well-documented roles in coagulation, hemostasis, and inflammation, and have been deeply investigated for their function in cellular survival/degeneration, while their roles in the brain in physiological conditions remain less appreciated. Here, we describe PARs' effects in the modulation of neurotransmission and synaptic plasticity. Available evidence, mainly concerning PAR1-mediated and PAR2-mediated regulation of glutamatergic and GABAergic transmission, supports that PARs are important modulators of synaptic efficacy and plasticity in normal conditions.

The Inter-α-Trypsin Inhibitor Family: Versatile Molecules in Biology and Pathology

Inter-α-trypsin inhibitor (IαI) family members are ancient and unique molecules that have evolved over several hundred million years of vertebrate evolution. IαI is a complex containing the proteoglycan bikunin to which heavy chain proteins are covalently attached to the chondroitin sulfate chain. Besides its matrix protective activity through protease inhibitory action, IαI family members interact with extracellular matrix molecules and most notably hyaluronan, inhibit complement, and provide cell regulatory functions. Recent evidence for the diverse roles of the IαI family in both biology and pathology is reviewed and gives insight into their pivotal roles in tissue homeostasis. In addition, the clinical uses of these molecules are explored, such as in the treatment of inflammatory conditions including sepsis and Kawasaki disease, which has recently been associated with severe acute respiratory syndrome coronavirus 2 infection in children.

Comparative Transcriptomics Reveals Gene Families Associated with Predatory Behavior in Photuris femme fatale Fireflies

Identifying the basis of phenotypic variation is a key objective of genetics. This work has been mostly limited to model systems with a plethora of genetic manipulation and functional characterization tools. With the development of high-throughput sequencing and new computational tools, it is possible to identify candidate genes related to phenotypic variation in non-model organisms. Fireflies are excellent for studying phenotypic variation because of their diverse and well-characterized behaviors. Most adult fireflies emit a single mating flash pattern and do not eat. In contrast, adult females of many species in the genus Photuris employ multiple flash patterns and prey upon mate-seeking males of other firefly species. To investigate the genetic basis for this variation, we used comparative transcriptomics to identify positively selected genes between a predatory firefly, Photuris sp., and a non-predatory relative, Photuris frontalis, controlling for genes generally under selection in fireflies by comparing to a Photinus firefly. Nine gene families were identified under positive selection in the predatory versus non-predatory Photuris comparison, including genes involved in digestion, detoxification, vision, reproduction, and neural processes. These results generate intriguing hypotheses about the genetic basis for insect behavior and highlight the utility of comparative transcriptomic tools to investigate complex behaviors in non-model systems.

Modulatory Role of Nurr1 Activation and Thrombin Inhibition in the Neuroprotective Effects of Dabigatran Etexilate in Rotenone-Induced Parkinson's Disease in Rats

Recently, it has been shown that both decreased nuclear receptor-related 1 (Nurr1) expression and thrombin accumulation are involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). The new anticoagulant dabigatran etexilate (DE) is a direct thrombin inhibitor that owns benzimidazole group, which has been proposed to activate Nurr1. In the present study, we examined the neuroprotective effects of DE in rotenone model of PD. Rotenone was injected subcutaneously at a dose of 1.5 mg/kg every other day for 21 days. An oral regimen of DE (15 mg/kg) was started after the 5th rotenone injection following the manifestations of PD. Treatment of PD rats with DE mitigated rotenone-induced neuronal degeneration and restored striatal dopamine level with motor recovery. As well, DE enhanced Nurr1 expression in substantia nigra along with increasing transcriptional activation of Nurr1-controlled genes namely tyrosine hydroxylase, vascular monoamine transporter, glial cell line-derived neurotrophic factor, and its receptor gene c-Ret, which are critical for development and maintenance of dopaminergic neurons. DE also suppressed thrombin accumulation in substantia nigra. Both effects probably contributed to repressing neurotoxic proinflammatory cytokines, which was manifested by decreased level of nuclear factor kappa beta and tumor necrosis factor alpha. In conclusion, the present results suggest that DE could possess significant neuroprotective and regenerative effects in a rotenone-induced PD animal model as consequence of Nurr1 activation and thrombin inhibition.

MMP9-sensitive polymers mediate environmentally-responsive bivalirudin release and thrombin inhibition

MMP9-responsive bivalirudin-HPMA copolymers were synthesized for direct, local administration in rat spinal cord contusion injury models. Polymer-conjugated bivalirudin peptides maintained activity while demonstrating enzyme-mediated release upon MMP9 exposure and prolonged release from hyaluronic acid/methylcellulose (HAMC) hydrogels compared to free bivalirudin peptide. Localized administration of bivalirudin copolymers in vivo at the site of rat spinal cord injury decreased cellular proliferation and astrogliosis, suggesting the bivalirudin copolymer and HAMC hydrogel system are a promising therapeutic intervention for reducing immediate inflammatory responses and long term scarring.

Expression and localization of Inter-alpha Inhibitors in rodent brain

Inter-alpha Inhibitor Proteins (IAIPs) are a family of related serine protease inhibitors. IAIPs are important components of the systemic innate immune system. We have identified endogenous IAIPs in the central nervous system (CNS) of sheep during development and shown that treatment with IAIPs reduces neuronal cell death and improves behavioral outcomes in neonatal rats after hypoxic-ischemic brain injury. The presence of IAIPs in CNS along with their exogenous neuroprotective properties suggests that endogenous IAIPs could be part of the innate immune system in CNS. The purpose of this study was to characterize expression and localization of IAIPs in CNS. We examined cellular expressions of IAIPs in vitro in cultured cortical mouse neurons, in cultured rat neurons, microglia, and astrocytes, and in vivo on brain sections by immunohistochemistry from embryonic (E) day 18 mice and postnatal (P) day 10 rats. Cultured cortical mouse neurons expressed the light chain gene Ambp and heavy chain genes Itih-1, 2, 3, 4, and 5 mRNA transcripts and IAIP proteins. IAIP proteins were detected by immunohistochemistry in cultured cells as well as brain sections from E18 mice and P10 rats. Immunoreactivity was found in neurons, microglia, astrocytes and oligodendroglia in multiple brain regions including cortex and hippocampus, as well as within both the ependyma and choroid plexus. Our findings suggest that IAIPs are endogenous proteins expressed in a wide variety of cell types and regions both in vitro and in vivo in rodent CNS. We speculate that endogenous IAIPs may represent endogenous neuroprotective immunomodulatory proteins within the CNS.

The serine protease inhibitor TLCK attenuates intrinsic death pathways in neurons upstream of mitochondrial demise

It is well-established that activation of proteases, such as caspases, calpains and cathepsins are essential components in signaling pathways of programmed cell death (PCD). Although these proteases have also been linked to mechanisms of neuronal cell death, they are dispensable in paradigms of intrinsic death pathways, e.g. induced by oxidative stress. However, emerging evidence implicated a particular role for serine proteases in mechanisms of PCD in neurons. Here, we investigated the role of trypsin-like serine proteases in a model of glutamate toxicity in HT-22 cells. In these cells glutamate induces oxytosis, a form of caspase-independent cell death that involves activation of the pro-apoptotic protein BH3 interacting-domain death agonist (Bid), leading to mitochondrial demise and ensuing cell death. In this model system, the trypsin-like serine protease inhibitor Nα-tosyl-l-lysine chloromethyl ketone hydrochloride (TLCK) inhibited mitochondrial damage and cell death. Mitochondrial morphology alterations, the impairment of the mitochondrial membrane potential and ATP depletion were prevented and, moreover, lipid peroxidation induced by glutamate was completely abolished. Strikingly, truncated Bid-induced cell death was not affected by TLCK, suggesting a detrimental activity of serine proteases upstream of Bid activation and mitochondrial demise. In summary, this study demonstrates the protective effect of serine protease inhibition by TLCK against oxytosis-induced mitochondrial damage and cell death. These findings indicate that TLCK-sensitive serine proteases play a crucial role in cell death mechanisms upstream of mitochondrial demise and thus, may serve as therapeutic targets in diseases, where oxidative stress and intrinsic pathways of PCD mediate neuronal cell death.

Crystal structure of Jararacussin-I: the highly negatively charged catalytic interface contributes to macromolecular selectivity in snake venom thrombin-like enzymes

Snake venom serine proteinases (SVSPs) are hemostatically active toxins that perturb the maintenance and regulation of both the blood coagulation cascade and fibrinolytic feedback system at specific points, and hence, are widely used as tools in pharmacological and clinical diagnosis. The crystal structure of a thrombin-like enzyme (TLE) from Bothrops jararacussu venom (Jararacussin-I) was determined at 2.48 Å resolution. This is the first crystal structure of a TLE and allows structural comparisons with both the Agkistrodon contortrix contortrix Protein C Activator and the Trimeresurus stejnegeri plasminogen activator. Despite the highly conserved overall fold, significant differences in the amino acid compositions and three-dimensional conformations of the loops surrounding the active site significantly alter the molecular topography and charge distribution profile of the catalytic interface. In contrast to other SVSPs, the catalytic interface of Jararacussin-I is highly negatively charged, which contributes to its unique macromolecular selectivity.

Thrombin enhances NGF-mediated neurite extension via increased and sustained activation of p44/42 MAPK and p38 MAPK

Rapid neurite remodeling is fundamental to nervous system development and plasticity. It involves neurite extension that is regulated by NGF through PI3K/AKT, p44/42 MAPK and p38 MAPK. It also involves neurite retraction that is regulated by the serine protease, thrombin. However, the intracellular signaling pathway by which thrombin causes neurite retraction is unknown. Using the PC12 neuronal cell model, we demonstrate that thrombin utilizes the PI3K/AKT pathway for neurite retraction in NGF-differentiated cells. Interestingly, however, we found that thrombin enhances NGF-induced neurite extension in differentiating cells. This is achieved through increased and sustained activation of p44/42 MAPK and p38 MAPK. Thus, thrombin elicits opposing effects in differentiated and differentiating cells through activation of distinct signaling pathways: neurite retraction in differentiated cells via PI3K/AKT, and neurite extension in differentiating cells via p44/42 MAPK and p38 MAPK. These findings, which also point to a novel cooperative role between thrombin and NGF, have significant implications in the development of the nervous system and the disease processes that afflicts it as well as in the potential of combined thrombin and NGF therapy for impaired learning and memory, and spinal cord injury which all require neurite extension and remodeling.

Global PROTOMAP profiling to search for biomarkers of early-recurrent hepatocellular carcinoma

This study used global protein expression profiling to search for biomarkers to predict early recurrent hepatocellular carcinoma (HCC). HCC tissues surgically resected from patients with or without recurrence within 2 years (early recurrent) after surgery were compared with adjacent nontumor tissue and with normal liver tissue. We used the PROTOMAP strategy for comparative profiling, which integrates denaturing polyacrylamide gel electrophoresis migratory rates and high-resolution, semiquantitative mass-spectrometry-based identification of in-gel-digested tryptic peptides. PROTOMAP allows examination of global changes in the size, topography, and abundance of proteins in complex tissue samples. This approach identified 8438 unique proteins from 45 708 nonredundant peptides and generated a proteome-wide map of changes in expression and proteolytic events potentially induced by intrinsic apoptotic/necrotic pathways. In the early recurrent HCC tissue, 87 proteins were differentially expressed (≥20-fold) relative to the other tissues, 46 of which were up-regulated or specifically proteolyzed and 41 of which were down-regulated. This data set consisted of proteins that fell into various functional categories, including signal transduction and cell organization and, notably, the major catalytic pathways responsible for liver function, such as the urea cycle and detoxification metabolism. We found that aberrant proteolysis appeared to occur frequently during recurrence of HCC in several key signal transducers, including STAT1 and δ-catenin. Further investigation of these proteins will facilitate the development of novel clinical applications.

Pathologies at the nexus of blood coagulation and inflammation: thrombin in hemostasis, cancer, and beyond

Thrombin is the protease involved in blood coagulation. Its deregulation can lead to hemostatic abnormalities, which range from subtle subclinical to serious life-threatening coagulopathies, i.e., during septicemia. Additionally, thrombin plays important roles in many (patho)physiological conditions that reach far beyond its well-established role in stemming blood loss and thrombosis, including embryonic development and angiogenesis but also extending to inflammatory processes, complement activation, and even tumor biology. In this review, we will address thrombin's broad roles in diverse (patho)physiological processes in an integrative way. We will also discuss thrombin as an emerging major target for novel therapies.

Plasmin Activation of Glial Cells through Protease-Activated Receptor 1

The objective of this study was to determine whether plasmin could induce morphological changes in human glial cells via PAR1. Human glioblastoma A172 cells were cultured in the presence of plasmin or the PAR1 specific activating hexapeptide, SFLLRN. Cells were monitored by flow cytometry to detect proteolytic activation of PAR1 receptor. Morphological changes were recorded by photomicroscopy and apoptosis was measured by annexinV staining. Plasmin cleaved the PAR1 receptor on glial cells at 5 minutes (P = 0.02). After 30 minutes, cellular processes had begun to retract from the basal substratum and by 4 hours glial cells had become detached. Similar results were obtained by generating plasmin de novo from plasminogen. Morphological transformation was blocked by plasmin inhibitors aprotinin or epsilon-aminocaproic acid (P = 0.03). Cell viability was unimpaired during early morphological changes, but by 24 hours following plasmin treatment 22% of glial cells were apoptotic. PAR1 activating peptide SFLLRN (but not inactive isomer FSLLRN) promoted analogous glial cell detachment (P = 0.03), proving the role for PAR1 in this process. This study has identified a plasmin/PAR1 axis of glial cell activation, linked to changes in glial cell morophology. This adds to our understanding of pathophysiological disease mechanisms of plasmin and the plasminogen system in neuroinjury.

Analysis of the landscape of biologically-derived pharmaceuticals in Europe: dominant production systems, molecule types on the rise and approval trends

A thorough sort of the human drugs approved by the European Medicines Agency (EMA) between its establishment in 1995 until June 2012 is presented herein with a focus on biologically-derived pharmaceuticals. Over 200 (33%) of the 640 approved therapeutic drugs are derived from natural sources, produced via recombinant DNA technology, or generated through virus propagation. A breakdown based on production method, type of molecule and therapeutic category is presented. Current EMA approvals demonstrate that mammalian cells are the only choice for glycoprotein drugs, with Chinese hamster ovary cells being the dominant hosts for their production. On the other hand, bacterial cells and specifically Escherichia coli are the dominant hosts for protein-based drugs, followed by the yeast Saccharomyces cerevisiae. The latter is the dominant host for recombinant vaccine production, although egg-based production is still the main platform of vaccine provision. Our findings suggest that the majority of biologically-derived drugs are prescribed for cancer and related conditions, as well as the treatment of diabetes. The approval rate for biologically-derived drugs shows a strong upward trend for monoclonal antibodies and fusion proteins since 2009, while hormones, antibodies and growth factors remain the most populous categories. Despite a clear pathway for the approval of biosimilars set by the EMA and their potential to drive sales growth, we have only found approved biosimilars for three molecules. In 2012 there appears to be a slow-down in approvals, which coincides with a reported decline in the growth rate of biologics sales.

Development and Optimization of a Thrombin Sandwich Aptamer Microarray

A sandwich microarray employing two distinct aptamers for human thrombin has been optimized for the detection of subnanomolar concentrations of the protein. The aptamer microarray demonstrates high specificity for thrombin, proving that a two-site binding assay with the TBA1 aptamer as capture layer and the TBA2 aptamer as detection layer can ensure great specificity at times and conditions compatible with standard routine analysis of biological samples. Aptamer microarray sensitivity was evaluated directly by fluorescent analysis employing Cy5-labeled TBA2 and indirectly by the use of TBA2-biotin followed by detection with fluorescent streptavidin. Sub-nanomolar LODs were reached in all cases and in the presence of serum, demonstrating that the optimized aptamer microarray can identify thrombin by a low-cost, sensitive and specific method.

Targeting proteinase-activated receptors: therapeutic potential and challenges

Proteinase-activated receptors (PARs), a family of four seven-transmembrane G protein-coupled receptors, act as targets for signalling by various proteolytic enzymes. PARs are characterized by a unique activation mechanism involving the proteolytic unmasking of a tethered ligand that stimulates the receptor. Given the emerging roles of these receptors in cancer as well as in disorders of the cardiovascular, musculoskeletal, gastrointestinal, respiratory and central nervous system, PARs have become attractive targets for the development of novel therapeutics. In this Review we summarize the mechanisms by which PARs modulate cell function and the roles they can have in physiology and diseases. Furthermore, we provide an overview of possible strategies for developing PAR antagonists.

Is Alzheimer's disease amyloidosis the result of a repair mechanism gone astray?

Here, we synthesize several lines of evidence supporting the hypothesis that at least one function of amyloid-β is to serve as a part of the acute response to brain hemodynamic disturbances intended to seal vascular leakage. Given the resilient and adhesive physicochemical properties of amyloid, an abluminal hemostatic repair system might be highly advantageous, if deployed on a limited and short-term basis, in young individuals. However, in the aged, inevitable cardiovascular dysfunction combined with brain microvascular lesions may yield global chronic hypoperfusion that may lead to continuous amyloid deposition and consequential negative effects on neuronal viability. A large body of experimental evidence supports the hypothesis of an amyloid-β rescue function gone astray. Preventing or inducing the removal of amyloid in Alzheimer's disease (AD) has been simultaneously successful and disappointing. Amyloid deposits clearly play major roles in AD, but they may not represent the preeminent factor in dementia pathogenesis. Successful application of AD preventative approaches may hinge on an accurate and comprehensive view of comorbidities, including cardiovascular disease, diabetes, and head trauma.

Physiology of microglia

Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.

Serine proteases, serine protease inhibitors, and protease-activated receptors: roles in synaptic function and behavior

Serine proteases, serine protease inhibitors, and protease-activated receptors have been intensively investigated in the periphery and their roles in a wide range of processes-coagulation, inflammation, and digestion, for example-have been well characterized (see Coughlin, 2000; Macfarlane et al., 2001; Molinari et al., 2003; Wang et al., 2008; Di Cera, 2009 for reviews). A growing number of studies demonstrate that these protein systems are widely expressed in many cell types and regions in mammalian brains. Accumulating lines of evidence suggest that the brain has co-opted the activities of these interesting proteins to regulate various processes underlying synaptic activity and behavior. In this review, we discuss emerging roles for serine proteases in the regulation of mechanisms underlying synaptic plasticity and memory formation.

Protease inhibitors: a panacea?

With the increasing evidence of protease involvement in several diseases, novel strategies for drug development involve the use of protease inhibitors (PIs). The local balance between protease inhibitors and proteases is an important determinant of the occurrence and progression of a particular disease. Hence, enzymes and their cognate inhibitors are finding their applications as diagnostic and prognostic markers. PIs are widely implicated for their use in host defense against infection, tissue repair and matrix production, blood coagulation, cancer, and they are, therefore, the current focus as therapeutic alternatives for major diseases such as AIDS and Alzheimer's diseases. This review is a brief summary of the varied role of protein protease inhibitors in controlling the activity of aberrant enzymes in several diseases afflicting mankind today.

Characterization of a caspase-3-substrate kinome using an N- and C-terminally tagged protein kinase library produced by a cell-free system

Caspase-3 (CASP3) cleaves many proteins including protein kinases (PKs). Understanding the relationship(s) between CASP3 and its PK substrates is necessary to delineate the apoptosis signaling cascades that are controlled by CASP3 activity. We report herein the characterization of a CASP3-substrate kinome using a simple cell-free system to synthesize a library that contained 304 PKs tagged at their N- and C-termini (NCtagged PKs) and a luminescence assay to report CASP3 cleavage events. Forty-three PKs, including 30 newly identified PKs, were found to be CASP3 substrates, and 28 cleavage sites in 23 PKs were determined. Interestingly, 16 out of the 23 PKs have cleavage sites within 60 residues of their N- or C-termini. Furthermore, 29 of the PKs were cleaved in apoptotic cells, including five that were cleaved near their termini in vitro. In total, approximately 14% of the PKs tested were CASP3 substrates, suggesting that CASP3 cleavage of PKs may be a signature event in apoptotic-signaling cascades. This proteolytic assay method would identify other protease substrates.

Analysis of human kallikrein 7 expression as a potential biomarker in cervical neoplasia

Overexpression of kallikrein 7, a proteolytic enzyme important for epithelial cell shedding, may be causally involved in carcinogenesis, particularly in tumor metastasis and invasion. In this study, we have evaluated hK7 (human kallikrein 7) protein levels by immunohistochemistry in 367 cervical histological samples including 35 cases of cervicitis, 31 low-grade cervical intraepithelial neoplasia, 51 high-grade cervical intraepithelial neoplasia (H-SIL), 197 squamous cervical carcinomas (SCC) and 53 cervical adenocarcinomas. We have observed that hK7 staining increased with the severity of cervical disease. Intense hK7 staining was found in 15.2% of cervicitis samples, in contrast to 55% of H-SIL and 68% of SCC. Moreover, 92.5% of adenocarcinomas also exhibited intense hK7 staining. Differences in the expression of hK7 could potentially be used as a biomarker for the characterization of different stages of cervical disease.

Mechanisms of injury to white matter adjacent to a large intraventricular hemorrhage in the preterm brain

The purpose of this article is to investigate the hyperechoic lesion seen adjacent to a lateral ventricle that contains blood but is not distended. The literature on ependymal barrier dysfunction was reviewed in search of mechanisms of injury to the white matter adjacent to an intraventricular hemorrhage. The clinical literature on the clinical diagnosis of periventricular hemorrhagic infarction was also reviewed to find out how frequently this diagnosis was made. Support was found for the possibility that the ventricular wall does not always function as an efficient barrier, allowing ventricular contents to gain access to the white matter where they cause damage. Hemorrhagic infarction may not be the only or the most frequent mechanism of white matter damage adjacent to a large intraventricular hemorrhage.

Downregulation of genes with a function in axon outgrowth and synapse formation in motor neurones of the VEGFdelta/delta mouse model of amyotrophic lateral sclerosis

Background

Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen that stimulates vasculogenesis. It has also been shown to act as a neurotrophic factor in vitro and in vivo. Deletion of the hypoxia response element of the promoter region of the gene encoding VEGF in mice causes a reduction in neural VEGF expression, and results in adult-onset motor neurone degeneration that resembles amyotrophic lateral sclerosis (ALS). Investigating the molecular pathways to neurodegeneration in the VEGF^δ/δ mouse model of ALS may improve understanding of the mechanisms of motor neurone death in the human disease.

Results

Microarray analysis was used to determine the transcriptional profile of laser captured spinal motor neurones of transgenic and wild-type littermates at 3 time points of disease. 324 genes were significantly differentially expressed in motor neurones of presymptomatic VEGF^δ/δ mice, 382 at disease onset, and 689 at late stage disease. Massive transcriptional downregulation occurred with disease progression, associated with downregulation of genes involved in RNA processing at late stage disease. VEGF^δ/δ mice showed reduction in expression, from symptom onset, of the cholesterol synthesis pathway, and genes involved in nervous system development, including axonogenesis, synapse formation, growth factor signalling pathways, cell adhesion and microtubule-based processes. These changes may reflect a reduced capacity of VEGF^δ/δ mice for maintenance and remodelling of neuronal processes in the face of demands of neural plasticity. The findings are supported by the demonstration that in primary motor neurone cultures from VEGF^δ/δ mice, axon outgrowth is significantly reduced compared to wild-type littermates.

Conclusions

Downregulation of these genes involved in axon outgrowth and synapse formation in adult mice suggests a hitherto unrecognized role of VEGF in the maintenance of neuronal circuitry. Dysregulation of VEGF may lead to neurodegeneration through synaptic regression and dying-back axonopathy.

Natural occurring polyphenols as template for drug design. Focus on serine proteases

Several major physio-pathological processes, including cancer, inflammatory states and thrombosis, are all strongly dependent upon the fine regulation of proteolytic enzyme activities, and dramatic are the consequences of unbalanced equilibria between enzymes and their cognate inhibitors. In this perspective, the discovery of small-molecule ligands able to modulate catalytic activities has a massive therapeutic potential and is a stimulating goal. Numerous recent experimental evidences revealed that proteolytic enzymes can be opportunely targeted, reporting on small ligands capable of binding to these biological macromolecules with drug-like potencies, and primarily with comparable (or even higher) efficiency with respect to their endogenous binding partner. In particular, natural occurring polyphenols and their derivatives recently disclosed these intriguing abilities, making them promising templates for drug design and development. In this review, we compared the inhibitory capacities of a set of monomeric polyphenols toward serine proteases activity, and finally summarized the data with an emphasis on the derivation of a pharmacophore model.

Microarray analysis of prothrombin knockdown in zebrafish

The serine protease thrombin is generated from its precursor, prothrombin, in the coagulation cascade and plays a central role in fibrin deposition and platelet activation mediated through the protease activated receptors. Knockdown of prothrombin in the zebrafish was previously shown to recapitulate the phenotype observed in prothrombin knockout mice, such as an absence of blood pericardial edema, and hemorrhage. However, the role of thrombin during embryogenesis is not fully understood. To find genes affected by potential thrombin signaling in embryogenesis before blood circulation, microarray analysis was performed using total RNA prepared from antisense-injected, knockdown embryos versus mismatch-injected at 20 h post fertilization. A total of 63 upregulated and downregulated genes were identified with duplicate microarrays using dye reversal and a two-fold difference limitation. Real time RT-PCR for 10 selected genes identified by the microarray confirmed the expression changes in these genes. One particular gene, phlda3, was at least eleven fold upregulated, and in situ hybridization revealed expansion of phlda3 expression in the central nervous system, branchial arches, and head endoderm in knockdown embryos. The identification of these genes regulated by thrombin according to microarray analysis should provide a greater understanding of the effects of thrombin activity in the early vertebrate embryo.

Toxic effect of blood components on perinatal rat subventricular zone cells and oligodendrocyte precursor cell proliferation, differentiation and migration in culture

The germinal matrix of human brain gives rise to oligodendrocytes and astrocytes after mid-gestation. Hemorrhage in the germinal matrix of premature infants is associated with suppressed cell proliferation. We hypothesize that soluble blood constituents have an adverse effect on the proliferation of cultured rat subventricular zone (SVZ) cells and the proliferation, migration, and differentiation of oligodendrocyte progenitor cells (OPC). Using caspase 3 activation and lactate dehydrogenase release assays, rat plasma, serum, thrombin, and kallikrein killed SVZ cells when grown in the presence (but not absence) of platelet derived growth factor. Plasma and serum killed OPC at 1:1 to 1:100 dilutions. Using a bromodeoxyuridine incorporation assay OPC proliferation was reduced by plasma, serum, thrombin and plasmin. Blood proteins also suppressed OPC migration in a concentration dependent manner. However, differentiation of OPC into myelin basic protein expressing cells was suppressed only by thrombin. We conclude that soluble blood components, particularly thrombin, have an adverse effect on maturing SVZ cells and OPC derived from newborn rat brain.

Conformational and biochemical characterization of a biologically active rat recombinant Protease Nexin-1 expressed in E. coli

Protease Nexin-1, a 43-kDa glycoprotein, is a major physiological thrombin inhibitor involved in the modulation of nerve cell plasticity. Recombinant rat Protease Nexin-1 (rPN-1) was efficiently produced in Escherichia coli using a T7 RNA polymerase based expression system and purified by heparin-sepharose affinity chromatography yielding 3 mg of protein per liter of cell culture. The purity and chemical identity of rPN-1 were assessed by SDS-PAGE, Reverse Phase- High Performance Liquid Chromatography, mass spectrometry and two-dimensional-gel electrophoresis. Conformational analysis by circular dichroism and fluorescence spectroscopy revealed the presence of mixed alpha/beta secondary structure and the prevailing localization of Trp-residues in rather polar environments. Fluorescence titration of rPN-1 with heparin indicated that rPN-1 binds heparin with high affinity. Furthermore, the formation of a SDS-stable 1:1 thrombin-rPN-1 complex, monitored by SDS-PAGE, confirmed the native-like structure of rPN-1. Finally, the cellular effects of rPN-1, such as its ability to promote neurite outgrowth in neuroblastoma cells, were found to be very similar to those elicited by natural PN-1. Altogether, our results demonstrate that glycosylation does not alter neither structure nor function of PN-1 and that E. coli is a suitable expression system for obtaining milligram quantities of pure and fully active rPN-1 for structural and functional studies.

Thrombin and brain recovery after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a common and often fatal subtype of stroke and produces severe neurological deficits in survivors. At present, there is lack of effective treatments that improve outcome in ICH. A neglected aspect of ICH research is the development of approaches that can be effectively used to improve recovery. Although previous studies have showed that thrombin induces blood-brain barrier leakage, brain edema, and neuronal death after ICH, our recent studies have shown that thrombin may have a role in brain recovery after ICH. An understanding of the mechanisms by which thrombin affects neurogenesis, angiogenesis, and plasticity may facilitate brain recovery after ICH.

Global mapping of the topography and magnitude of proteolytic events in apoptosis

Proteolysis is a key regulatory process that promotes the (in)activation, translocation, and/or degradation of proteins. As such, there is considerable interest in methods to comprehensively characterize proteolytic pathways in biological systems. Here, we describe a robust and versatile proteomic platform that enables direct visualization of the topography and magnitude of proteolytic events on a global scale. We use this method to generate a proteome-wide map of proteolytic events induced by the intrinsic apoptotic pathway. This profile contained 91 characterized caspase substrates as well as 170 additional proteins not previously known to be cleaved during apoptosis. Surprisingly, the vast majority of proteolyzed proteins, regardless of the extent of cleavage, yielded persistent fragments that correspond to discrete protein domains, suggesting that the generation of active effector proteins may be a principal function of apoptotic proteolytic cascades.

Group S8A serine proteases, including a novel enzyme cadeprin, induce long-lasting, metabotropic glutamate receptor-dependent synaptic depression in rat hippocampal slices

Long-term potentiation and long-term depression (LTD) are forms of synaptic plasticity in the central nervous system. We now report that a group of chymotrypsin-like serine proteases, especially members of the S8A subfamily, induce LTD of evoked potentials in rat hippocampal slices. The proteolytic activity of these enzymes is required for the induction of LTD, as serine protease inhibitors prevent the effect. The depression is partly mediated by the suppression of transmitter release from glutamatergic terminals but also involves an elevation of action potential threshold with no change of post-synaptic membrane potential or input resistance. We have also isolated a novel and more potent related enzyme, cadeprin, from Aspergillus. The LTD produced by all of these proteases is not dependent on receptors for several transmitter systems, including N-methyl-d-aspartate or adenosine receptors, but is prevented by blocking group I metabotropic glutamate receptors. The activity of cadeprin, subtilisin and other S8A serine proteases may shed light on the mechanisms of LTD and a related endogenous molecule could have a physiological or pathological role as a modulator of synaptic plasticity in the mammalian hippocampus.

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.

Huntingtin cleavage induced by thrombin in vitro

Huntingtin (Htt) mutation causes Huntington's disease. Sequence analysis of Htt revealed a possible thrombin cleavage site in the N-terminal region of Htt. In order to investigate if thrombin can cleave Htt, we expressed the N-terminal fragment (1-969) of wild-type (wt) Htt (Htt 1-969) in MCF-7 cells and studied its cleavage pattern by thrombin in vitro. An expression plasmid pcDNA3-Htt-18Q-969 was used to transfect MCF-cells and Htt 1-969 expression was confirmed with immunofluorescence. Cell lysates were incubated with thrombin (1 U/ml, 10 U/ml, and 30 U/ml) for 1 h in the presence or absence of hirudin, a thrombin inhibitor. Htt fragments were separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and detected with anti-Htt antibodies. An Htt fragment with molecular mass of approximately 80 kDa was produced after incubation with thrombin. The size of this Htt fragment was anticipated by molecular mass generated from thrombin-mediated cleavage at the amino acid 183 in the Htt. Production of an 80 kDa fragment was inhibited by hirudin. This study provides the first evidence that Htt is cleaved by thrombin in vitro at amino acid 183. If endogenous thrombin cleaves Htt in vivo, the physiological significance of thrombin-mediated cleavage of Htt should be further investigated.

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.

Constitutive secretion of protease nexin-1 by glial cells and its regulation by G-protein-coupled receptors

Extracellular serine proteases and their inhibitors (serpins) play a key role for synaptic plasticity in the developing and adult CNS. Serpins also counteract the extravasated proteases during brain injury. We studied the mechanisms by which one of the most important serpins, serpinE2 or protease nexin-1 (PN-1), is secreted by glial cells and how its secretion is regulated by extracellular signals. Using time-lapse videomicroscopy and biochemical methods, we demonstrate that PN-1 is constitutively secreted through small vesicles animated by a discontinuous movement using microtubules as tracks. The F-actin network underneath the plasma membrane acting as a barrier hindered PN-1 vesicle exocytosis. Vasointestinal/pituitary adenylate cyclase peptides and the G-protein activator mastoparan increased PN-1 secretion by disrupting the F-actin barrier. The receptor-mediated regulation of PN-1 constitutive secretion may be an important mechanism adapting extracellular proteolytic activity to synaptic activity.

A novel serine protease highly expressed in the pancreas is expressed in various kinds of cancer cells

We have isolated a cDNA that encodes a novel serine protease, prosemin, from human brain. The cDNA of human prosemin is 1306 bp, encoding 317 amino acids. It showed significant homology with the sequence of a chromosome 16 cosmid clone (accession no. NT_037887.4). The prosemin gene contains six exons and five introns. The amino acid sequence of prosemin shows significant homology to prostasin, gamma-tryptase, and testisin (43%, 41%, and 38% identity, respectively), the genes of which are also located on chromosome 16. Northern hybridization showed that prosemin is expressed predominantly in the pancreas and weakly in the prostate and cerebellum. However, western blot and RT-PCR analyses showed that prosemin is expressed and secreted from various kinds of cancer cells, such as glioma, pancreas, prostate, and ovarian cell lines. Prosemin is secreted in the cystic fluid of clinical ovarian cancers. Furthermore, immunohistochemistry showed prosemin protein localized in the apical parts of ovarian carcinomas. Recombinant prosemin was expressed in COS cells and was purified by immunoaffinity chromatography. Recombinant prosemin preferentially cleaved benzyloxycarbonyl (Z)-His-Glu-Lys-methylcoumaryl amidide (MCA) and t-butyloxycarbonyl (Boc)-Gln-Ala-Arg-MCA. Our results suggest that prosemin is a novel serine protease of the chromosome 16 cluster that is highly expressed in the pancreas. The usefulness of this serine protease as a candidate tumor marker should be further examined.

Study of neurotrophic activity of thrombin on the model of regenerating mouse nerve

Experiments demonstrated a dose-dependent facilitating effect of thrombin and peptide thrombin receptor agonist PAR1 (TRAP6) on regeneration of mouse peripheral nerve after its crushing. The maximum neurotrophic effect was observed at low concentrations of thrombin (10 nM) and TRAP6 (10 microM).

Hox genes and their candidate downstream targets in the developing central nervous system

1. Homeobox (Hox) genes were originally discovered in the fruit fly Drosophila, where they function through a conserved homeodomain as transcriptional regulators to control embryonic morphogenesis. Since then over 1000 homeodomain proteins have been identified in several species. In vertebrates, 39 Hox genes have been identified as homologs of the original Drosophila complex, and like their Drosophila counterparts they are organized within chromosomal clusters. Vertebrate Hox genes have also been shown to play a critical role in embryonic development as transcriptional regulators. 2. Both the Drosophila and vertebrate Hox genes have been shown to interact with various cofactors, such as the TALE homeodomain proteins, in recognition of consensus sequences within regulatory elements of their target genes. These protein-protein interactions are believed to contribute to enhancing the specificity of target gene recognition in a cell-type or tissue- dependent manner. The regulatory activity of a particular Hox protein on a specific regulatory element is highly variable and dependent on its interacting partners within the transcriptional complex. 3. In vertebrates, Hox genes display spatially restricted patterns of expression within the developing CNS, both along the anterioposterior and dorsoventral axis of the embryo. Their restricted gene expression is suggestive of a regulatory role in patterning of the CNS, as well as in cell specification. Determining the precise function of individual Hox genes in CNS morphogenesis through classical mutational analyses is complicated due to functional redundancy between Hox genes. 4. Understanding the precise mechanisms through which Hox genes mediate embryonic morphogenesis requires the identification of their downstream target genes. Although Hox genes have been implicated in the regulation of several pathways, few target genes have been shown to be under their direct regulatory control. Development of methodologies used for the isolation of target genes and for the analysis of putative targets will be beneficial in establishing the genetic pathways controlled by Hox factors. 5. Within the developing CNS various cell adhesion molecules and signaling molecules have been identified as candidate downstream target genes of Hox proteins. These targets play a role in processes such as cell migration and differentiation, and are implicated in contributing to neuronal processes such as plasticity and/or specification. Hence, Hox genes not only play a role in patterning of the CNS during early development, but may also contribute to cell specification and identity.

Expression of myelencephalon-specific protease in transient middle cerebral artery occlusion model of rat brain

Myelencephalon-specific protease (MSP) is one of the serine proteases and is expressed in the central nervous system of rats. Its function and alternation in brain injury have not yet been clarified. In this study, we investigated the expression of MSP after transient middle cerebral artery occlusion (MCAO) using in situ hybridization and immunohistochemistry. In situ localization of MSP mRNA demonstrated a higher level in the corpus callosum and around the ischemic area from 12 h to 14 days after MCA reperfusion, with the peak of expression coming 3 days after reperfusion in both regions. Immunohistochemically, the expression of protein was found 1 day after reperfusion in the same brain region that was observed for mRNA. The peak was 7 days after reperfusion in both regions. Micro-autoradiography, immunostaining and double immunohistochemical labeling revealed the expression of MSP to be located mainly in the oligodendrocytes. The present results indicate that MSP may be related to the turnover of the myelin-associated proteins and the extracellular matrix proteins after transient MCAO. The activation of MSP may play a role in remodeling processes such as neurite outgrowth and remyelination.

The microglia-activating potential of thrombin: the protease is not involved in the induction of proinflammatory cytokines and chemokines

The serine protease thrombin is known as a blood coagulation factor. Through limited cleavage of proteinase-activated receptors it can also control growth and functions in various cell types, including neurons, astrocytes, and microglia (brain macrophages). A number of previous studies indicated that thrombin induces the release of proinflammatory cytokines and chemokines from microglial cells, suggesting another important role for the protease beyond hemostasis. In the present report, we provide evidence that this effect is not mediated by any proteolytic or non-proteolytic mechanism involving thrombin proper. Inhibition of the enzymatic thrombin activity did not affect the microglial release response. Instead the cyto-/chemokine-inducing activity solely resided in a high molecular weight protein fraction that could be isolated in trace amounts even from apparently homogenous alpha- and gamma-thrombin preparations. High molecular weight material contained thrombin-derived peptides as revealed by mass spectrometry but was devoid of thrombin-like enzymatic activity. Separated from the high molecular weight fraction by fast protein liquid chromatography, enzymatically intact alpha- and gamma-thrombin failed to trigger any release. Our findings may force a revision of the notion that thrombin itself is a direct proinflammatory release signal for microglia. In addition, they could be relevant for the study of other cellular activities and their assignment to this protease.

Differential display polymerase chain reaction reveals increased expression of striatal rat glia-derived nexin following chronic clozapine treatment

Clozapine is considered a prototype of the 'so-called' atypical antipsychotic drug class. It has affinity for a broad range of receptors and, in comparison to typical antipsychotic drugs, produces less extrapyramidal side effects. However, its mechanism of action remains unclear. Differential display polymerase chain reaction (ddPCR) was implemented in this study to contribute to the current understanding of this mechanism at the genetic level and to identify novel genes regulated by clozapine. This technique generated approximately 2400 gene sequences that were analyzed for differential gene expression following protracted clozapine treatment. One of these sequences, originally termed Clozapine Regulated Gene (CRG), was shown to be significantly upregulated following the treatment. Northern hybridization confirmation of this finding revealed that chronic clozapine administration caused a five-fold increase in CRG mRNA. Elongation of the 5'- and 3'-ends of CRG indicated that the fragment was in fact rat glia-derived nexin mRNA. Western blotting demonstrated that levels of the mRNA's associated protein also increased comparably (three-fold) following chronic treatment with the antipsychotic drug. This study presents a possible neuroprotective role of nexin in clozapine treatment, particularly in the prevention of neuronal proteolytic degradation, since nexin has been shown to be a protease inhibitor.