Possible involvement of protease-activated receptor-1 in the regulation of morphine-induced dopamine release and hyperlocomotion by the tissue plasminogen activator-plasmin system

Protease-activated receptor 1 (PAR1) inhibits synaptic NMDARs in mouse nigral dopaminergic neurons

Protease-activated receptor 1 (PAR1) is a G protein-coupled receptor (GPCR), whose activation requires a proteolytic cleavage in the extracellular domain exposing a tethered ligand, which binds to the same receptor thus stimulating Gα_q/11-, Gα_i/o- and Gα_12-13 proteins. PAR1, activated by serine proteases and matrix metalloproteases, plays multifaceted roles in neuroinflammation and neurodegeneration, in stroke, brain trauma, Alzheimer's diseases, and Parkinson's disease (PD). Substantia nigra pars compacta (SNpc) is among areas with highest PAR1 expression, but current evidence on its roles herein is restricted to mechanisms controlling dopaminergic (DAergic) neurons survival, with controversial data showing PAR1 either fostering or counteracting degeneration in PD models. Since PAR1 functions on SNpc DAergic neurons activity are unknown, we investigated if PAR1 affects glutamatergic transmission in this neuronal population. We analyzed PAR1's effects on NMDARs and AMPARs by patch-clamp recordings from DAergic neurons from mouse midbrain slices. Then, we explored subunit composition of PAR1-sensitive NMDARs, with selective antagonists, and mechanisms underlying PAR1-induced NMDARs modulation, by quantifying NMDARs surface expression. PAR1 activation inhibits synaptic NMDARs in SNpc DAergic neurons, without affecting AMPARs. PAR1-sensitive NMDARs contain GluN2B/GluN2D subunits. Moreover, PAR1-mediated NMDARs hypofunction is reliant on NMDARs internalization, as PAR1 stimulation increases NMDARs intracellular levels and pharmacological limitation of NMDARs endocytosis prevents PAR1-induced NMDARs inhibition. We reveal that PAR1 regulates glutamatergic transmission in midbrain DAergic cells. This might have implications in brain's DA-dependent functions and in neurological/psychiatric diseases linked to DAergic dysfunctions.

Neuro-Immune Hemostasis: Homeostasis and Diseases in the Central Nervous System

Coagulation and the immune system interact in several physiological and pathological conditions, including tissue repair, host defense, and homeostatic maintenance. This network plays a key role in diseases of the central nervous system (CNS) by involving several cells (CNS resident cells, platelets, endothelium, and leukocytes) and molecular pathways (protease activity, complement factors, platelet granule content). Endothelial damage prompts platelet activation and the coagulation cascade as the first physiological step to support the rescue of damaged tissues, a flawed rescuing system ultimately producing neuroinflammation. Leukocytes, platelets, and endothelial cells are sensitive to the damage and indeed can release or respond to chemokines and cytokines (platelet factor 4, CXCL4, TNF, interleukins), and growth factors (including platelet-derived growth factor, vascular endothelial growth factor, and brain-derived neurotrophic factor) with platelet activation, change in capillary permeability, migration or differentiation of leukocytes. Thrombin, plasmin, activated complement factors and matrix metalloproteinase-1 (MMP-1), furthermore, activate intracellular transduction through complement or protease-activated receptors. Impairment of the neuro-immune hemostasis network induces acute or chronic CNS pathologies related to the neurovascular unit, either directly or by the systemic activation of its main steps. Neurons, glial cells (astrocytes and microglia) and the extracellular matrix play a crucial function in a “tetrapartite” synaptic model. Taking into account the neurovascular unit, in this review we thoroughly analyzed the influence of neuro-immune hemostasis on these five elements acting as a functional unit (“pentapartite” synapse) in the adaptive and maladaptive plasticity and discuss the relevance of these events in inflammatory, cerebrovascular, Alzheimer, neoplastic and psychiatric diseases. Finally, based on the solid reviewed data, we hypothesize a model of neuro-immune hemostatic network based on protein–protein interactions. In addition, we propose that, to better understand and favor the maintenance of adaptive plasticity, it would be useful to construct predictive molecular models, able to enlighten the regulating logic of the complex molecular network, which belongs to different cellular domains. A modeling approach would help to define how nodes of the network interact with basic cellular functions, such as mitochondrial metabolism, autophagy or apoptosis. It is expected that dynamic systems biology models might help to elucidate the fine structure of molecular events generated by blood coagulation and neuro-immune responses in several CNS diseases, thereby opening the way to more effective treatments.

Neuro-Coagulopathy: Blood Coagulation Factors in Central Nervous System Diseases

Blood coagulation factors and other proteins, with modulatory effects or modulated by the coagulation cascade have been reported to affect the pathophysiology of the central nervous system (CNS). The protease-activated receptors (PARs) pathway can be considered the central hub of this regulatory network, mainly through thrombin or activated protein C (aPC). These proteins, in fact, showed peculiar properties, being able to interfere with synaptic homeostasis other than coagulation itself. These specific functions modulate neuronal networks, acting both on resident (neurons, astrocytes, and microglia) as well as circulating immune system cells and the extracellular matrix. The pleiotropy of these effects is produced through different receptors, expressed in various cell types, in a dose- and time-dependent pattern. We reviewed how these pathways may be involved in neurodegenerative diseases (amyotrophic lateral sclerosis, Alzheimer's and Parkinson's diseases), multiple sclerosis, ischemic stroke and post-ischemic epilepsy, CNS cancer, addiction, and mental health. These data open up a new path for the potential therapeutic use of the agonist/antagonist of these proteins in the management of several central nervous system diseases.

Phenylmethanesulfonyl fluoride, a serine protease inhibitor, suppresses naloxone-precipitated withdrawal jumping in morphine-dependent mice

We have previously shown that intracerebroventricular (i.c.v.) administration of cysteine protease inhibitors suppresses naloxone-precipitated withdrawal jumping in morphine-dependent mice, presumably through the inhibition of dynorphin degradation (see (Tan-No, K., Sato, T., Shimoda, M., Nakagawasai, O., Niijima, F., Kawamura, S., Furuta, S., Sato, T., Satoh, S., Silberring, J., Terenius, L., Tadano, T., 2010. Suppressive effects by cysteine protease inhibitors on naloxone-precipitated withdrawal jumping in morphine-dependent mice. Neuropeptides 44, 279-283)). In the present study, we examined the effect of phenylmethanesulfonyl fluoride (PMSF), a serine protease inhibitor, on naloxone-precipitated withdrawal jumping in morphine-dependent mice. The doses of morphine (mg/kg per injection) were subcutaneously given twice daily for 2 days [day 1 (30) and day 2 (60)]. On day 3, naloxone (8 mg/kg) was intraperitoneally administered 3h after the final injection of morphine (60 mg/kg), and the number of jumps was immediately recorded for 20 min. Naloxone-precipitated withdrawal jumping was significantly suppressed by i.c.v. administration of PMSF (4 nmol), given 5 min before each morphine treatment during the induction phase, with none given on the test day. The expression of tissue plasminogen activator (tPA), a serine protease that converts plasminogen to plasmin, in the prefrontal cortex was significantly increased in morphine-dependent and -withdrawal mice, as compared with saline-treated mice. Moreover, trans-4-(aminomethyl)-cyclohexanecarboxylic acid (300 pmol), an antiplasmin agent, and (Tyr(1))-thrombin receptor activating peptide 7 (0.45 and 2 nmol), an antagonist of protease activated receptor-1 (PAR-1), significantly suppressed naloxone-precipitated withdrawal jumping. The present results suggest that PMSF suppresses naloxone-precipitated withdrawal jumping in morphine-dependent mice, presumably through the inhibition of activities of tPA and plasmin belonging to the serine proteases family, which subsequently activates PAR-1.

Protease-activated receptor-1 modulates hippocampal memory formation and synaptic plasticity

Protease-activated receptor-1 (PAR1) is an unusual G-protein coupled receptor (GPCR) that is activated through proteolytic cleavage by extracellular serine proteases. Although previous work has shown that inhibiting PAR1 activation is neuroprotective in models of ischemia, traumatic injury, and neurotoxicity, surprisingly little is known about PAR1's contribution to normal brain function. Here, we used PAR1-/- mice to investigate the contribution of PAR1 function to memory formation and synaptic function. We demonstrate that PAR1-/- mice have deficits in hippocampus-dependent memory. We also show that while PAR1-/- mice have normal baseline synaptic transmission at Schaffer collateral-CA1 synapses, they exhibit severe deficits in N-methyl-d-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP). Mounting evidence indicates that activation of PAR1 leads to potentiation of NMDAR-mediated responses in CA1 pyramidal cells. Taken together, this evidence and our data suggest an important role for PAR1 function in NMDAR-dependent processes subserving memory formation and synaptic plasticity.

Activation of post-synaptic dopamine D₁ receptors promotes the release of tissue plasminogen activator in the nucleus accumbens via PKA signaling

We have previously demonstrated that tissue plasminogen activator (tPA) plays an important role through the conversion of plasminogen to plasmin in the release of dopamine in the nucleus accumbens (NAc) evoked by depolarization or the systemic administration of drugs of abuse such as morphine and nicotine. In the present study, we examined the mechanisms by which drugs of abuse increase extracellular tPA activity in the NAc in vivo using in situ zymography. The dopamine D(1) receptor (D(1) R) agonist SKF38393, but not D(2) receptor agonist quinpirole, significantly increased extracellular tPA activity in the NAc. The effect of SKF38393 was blocked by pre-treatment with the dopamine D(1) R antagonist SCH23390. Microinjection of Rp-cAMPs, a protein kinase A inhibitor, into the NAc completely blocked the effect of SKF38393. Systemic administration of morphine and methamphetamine increased extracellular tPA activity in the NAc, and these effects were completely blocked by pre-treatment with SCH23390 and raclopride. The results suggest that activation of post-synaptic dopamine D(1) Rs in the NAc leads to an increase in extracellular tPA activity via protein kinase A signaling. Furthermore, dopamine D(2) receptors are also involved in the release of tPA induced by morphine and methamphetamine.

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.

Aripiprazole ameliorates phencyclidine-induced impairment of recognition memory through dopamine D1 and serotonin 5-HT1A receptors

RATIONALE

Cognitive deficits, including memory impairment, are regarded as a core feature of schizophrenia. Aripiprazole, an atypical antipsychotic drug, has been shown to improve disruption of prepulse inhibition and social interaction in an animal model of schizophrenia induced by phencyclidine (PCP); however, the effects of aripiprazole on recognition memory remain to be investigated.

OBJECTIVES

In this study, we examined the effect of aripiprazole on cognitive impairment in mice treated with PCP repeatedly.

MATERIALS AND METHODS

Mice were repeatedly administered PCP at a dose of 10 mg/kg for 14 days, and their cognitive function was assessed using a novel-object recognition task. We investigated the therapeutic effects of aripiprazole (0.01-1.0 mg/kg) and haloperidol (0.3 and 1.0 mg/kg) on cognitive impairment in mice treated with PCP repeatedly.

RESULTS

Single (1.0 mg/kg) and repeated (0.03 and 0.1 mg/kg, for 7 days) treatment with aripiprazole ameliorated PCP-induced impairment of recognition memory, although single treatment significantly decreased the total exploration time during the training session. In contrast, both single and repeated treatment with haloperidol (0.3 and 1.0 mg/kg) failed to attenuate PCP-induced cognitive impairment. The ameliorating effect of aripiprazole on recognition memory in PCP-treated mice was blocked by co-treatment with a dopamine D1 receptor antagonist, SCH23390, and a serotonin 5-HT1A receptor antagonist, WAY100635; however, co-treatment with a D2 receptor antagonist raclopride had no effect on the ameliorating effect of aripiprazole.

CONCLUSIONS

These results suggest that the ameliorative effect of aripiprazole on PCP-induced memory impairment is associated with dopamine D1 and serotonin 5-HT1A receptors.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Endogenous modulators for drug dependence

Drug addiction/dependence is defined as a chronically relapsing disorder that is characterized by compulsive drug taking, inability to limit intake, and intense drug cravings. The positive reinforcing/rewarding effects of drugs primarily depend on the mesocorticolimbic dopamine system innervating the nucleus accumbens while the craving for drugs is associated with activation of the prefrontal cortex. The chronic intake of drugs causes homeostatic molecular and functional changes in synapses, which may be critically associated with the development of drug dependence. Recent studies have demonstrated that various cytokines and proteinases are produced in the brain on treatment with drugs of abuse, and play a role in drug dependence. These endogenous modulators of drug dependence are classified into two groups, pro-addictive and anti-addictive factors. The former including basic fibroblast growth factor, brain-derived neurotrophic factor, tissue plasminogen activator, matrix metalloproteinase (MMP)-2 and MMP-9 act to potentiate the rewarding effects of drugs, while the latter such as tumor necrosis factor-alpha and glial cell line-derived neurotrophic factor reduce the reward. These findings suggest that an imbalance between pro-addictive and anti-addictive factors contributes to the development and relapse of drug dependence. Furthermore, targeting these endogenous modulators would provide new therapeutic approaches to the treatment of drug dependence.

The role of tissue-type plasminogen activator system in amphetamine-induced conditional place preference extinction and reinstatement

Extracellular serine proteases of the plasminogen activator family (tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) may modulate synaptic adhesion and associate with learning behavior. Psychostimulants strongly induce their expression in the mesolimbic dopaminergic pathway, but cocaine preferentially induces uPA, whereas morphine and amphetamine preferentially induce tPA. tPA-expressing animals displayed enhanced conditional place preference (CPP) for amphetamine compared with uPA-overexpressing animals. Thus, modulation of the plasminogen system in the brain might be a potential target against drugs of abuse. In the present study, we aim to identify whether tPA is involved in the acquisition/learning phase or in the expression/retrieval phase of conditioned drug preference. For this purpose, animals were injected with lentiviruses expressing or silencing tPA in the NAc and place preference was assessed. We found that tPA expression is associated with acquisition of place preference and animals overexpressing tPA spend >87% of the time in the drug-associated compartment, compared with 60% for control animals. When ectopic expression of tPA has been inhibited by doxycycline during acquisition, animals do no more associate the environment with the drug. Suppression of endogenous tPA expression in animals treated with LV-siRNA fully suppresses place preference, and these animals appear to avoid the drug-associated box. tPA overexpression delays extinction, but priming with low doses of amphetamine reinstates place preference even after full extinction. Together, these data clearly indicate that tPA plays an important role in acquisition of amphetamine-induced CPP, but its role in CPP expression does not seem important.

Role of tissue plasminogen activator in the sensitization of methamphetamine-induced dopamine release in the nucleus accumbens

We have previously demonstrated that repeated, but not acute, methamphetamine (METH) treatment increases tissue plasminogen activator (tPA) activity in the brain, which is associated with the development of behavioral sensitization to METH. In this study, we investigated whether the tPA-plasmin system is involved in the development of sensitization in METH-induced dopamine release in the nucleus accumbens (NAc). There was no difference in acute METH-induced increase in extracellular dopamine levels in the NAc between wild-type and tPA-deficient (tPA-/-) mice. Repeated METH treatment resulted in a significant enhancement of METH- induced dopamine release in wild-type mice, but not tPA-/- mice. Microinjection of exogenous tPA or plasmin into the NAc of wild-type mice significantly potentiated acute METH- induced dopamine release. Degradation of laminin was evident in brain tissues incubated with tPA plus plasminogen or plasmin in vitro although tPA or plasminogen alone had no effect. Immunohistochemical analysis revealed that microinjection of plasmin into the NAc reduced laminin immunoreactivity without neuronal damage. Our findings suggest that the tPA-plasmin system participates in the development of behavioral sensitization induced by repeated METH treatment, by regulating the processes underlying the sensitization of METH-induced dopamine release in the NAc, in which degradation of laminin by plasmin may play a role.

Overexpression of plasminogen activators in the nucleus accumbens enhances cocaine-, amphetamine- and morphine-induced reward and behavioral sensitization

Urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) are extracellular proteases that play a role in synaptic plasticity and remodeling. Psychostimulants induce both tPA and uPA in acute and chronic drug delivery, but cocaine induces preferentially uPA, whereas morphine and amphetamine induce preferentially tPA. Specific doxycline-regulatable lentiviruses expressing these extracellular proteases have been prepared and stereotaxically injected into the nucleus accumbens. We show that tPA-overexpressing animals show greater locomotor activity and behavioral sensitization upon morphine and amphetamine treatments. These effects could be fully suppressed by doxycycline or when tPA had been silenced using small interfering RNAs (siRNAs)-expressing lentiviruses. Furthermore, animals infected with lentiviruses expressing uPA show enhanced conditional place preference for cocaine compared with tPA-overexpressing animals. In contrast, tPA-overexpressing animals when administered amphetamine or morphine showed greater place preference compared with uPA-overexpressing animals. The effects are suppressed when tPA has been silenced using specific siRNAs-expressing vectors. Tissue-type plasminogen activator and uPA possibly induce distinct behaviors, which may be interpreted according to their differential pattern of activation and downstream targets. Taken together, these data add further evidence for a significant function of extracellular proteases tPA and uPA in addiction and suggest a differential role of plasminogen activators in this context.