Cynthia Marie-Claire

Importance of ERK activation in behavioral and biochemical effects induced by MDMA in mice.

Little is known about the cellular effects induced by 3,4‐methylenedioxymethamphetamine (MDMA, ecstasy), although changes in gene expression have been observed following treatments with other psychostimulants. Thus, the aim of this study was to investigate in mice, the relationships between the ras‐dependent protein kinase ERK and MDMA‐induced reinforcement using the conditioned place preference (CPP) and locomotor activity measurements. This was completed using real‐time quantitative PCR method by a study of immediate early‐genes (IEGs) transcription known to be involved in neuronal plasticity. A significant CPP was observed after repeated MDMA treatment in CD‐1 mice at a dose of 9 mg kg−1 i.p. but not at 3 and 6 mg kg−1. This rewarding effect was abolished by the selective inhibitor of ERK activation, SL327 (50 mg kg−1; i.p.). Similar results were obtained on MDMA‐induced locomotor activity, clearly suggesting a role of ERK pathway in these behavioral responses. Following acute i.p. injection, MDMA induced a strong c‐fos transcription in brain structures, such as caudate putamen, nucleus accumbens and hippocampus, whereas egr‐1 and egr‐3 transcripts were only increased in the caudate putamen. MDMA‐induced IEGs transcription was selectively suppressed by SL327 in the caudate putamen, suggesting a role for other signaling pathways in regulation of IEGs transcription in the other brain structures. In agreement with these results, MDMA‐induced c‐fos protein expression was blocked by SL327 in the caudate putamen. This study confirms and extends to mice the reported role of ERK pathway in the development of addiction‐like properties of MDMA. This could facilitate studies about the molecular mechanism of this process by using mutant mice.

Expression of drug transporters at the blood–brain barrier using an optimized isolated rat brain microvessel strategy

Quantitative RT-PCR (qRT-PCR) and Western blotting studies on transporters at the blood-brain barrier (BBB) of isolated brain microvessels have produced conflicting data on their cellular distribution. A major problem is identifying cells expressing the genes of interest, since isolated brain microvessels are composed of several cell types and may be contaminated with mRNA or proteins from astrocytes and neurons. We isolated rat brain microvessels and examined microscopically samples at each step of isolation to evaluate microvessel purity. The expression of specific markers of endothelial cells (Glut-1, Flk-1), pericytes (Ng2), neurons (synaptophysin, Syn) and astrocytes (Gfap) was measured by qRT-PCR in order to select the protocol giving the least astrocyte and neuron mRNAs and the most endothelial mRNAs. We also evaluated the gene expression of drug transporters (Mdr1a, Mdr1b, Mrp1-5, Bcrp and Oatp-2) at each step to optimize their location in cells at the BBB. The Mdr1a, Mrp4, Bcrp and Oatp-2 gene profiles were similar to those of endothelium markers. The profiles of Mrp2 and Mrp3 closely resembled that of Ng2. Mrp5 and Mrp1 expression was not increased in the microvessel-enriched fraction, suggesting that they are ubiquitously expressed throughout the cortex parenchyma. We also evaluated by Western blotting the expression of P-gp, Mrp2, Gfap and Syn in the cortex and in the purest obtained microvessel fraction. Our results showed that P-gp expression strongly increased in microvessels whereas Mrp2 was not detected in any of the fraction. Surprisingly, Gfap expression increased in isolated microvessels whereas Syn was not detected. Our results showed that the strategy consisting of identifying gene expression at different steps of the protocol is useful to identify cells containing mRNA at the BBB and give overall similar results with protein expression.

Cytoskeletal Genes Regulation by Chronic Morphine Treatment in Rat Striatum

It has been previously suggested that morphine can regulate the expression and function of some proteins of the cytoskeleton. In the present study, we used real-time quantitative polymerase chain reaction to examine the effects of chronic morphine administration, in rat striatum, on 14 proteins involved in microtubule polymerization and stabilization, intracellular trafficking, and serving as markers of neuronal growth and degeneration. Chronic morphine treatment led to modulation of the mRNA level of seven of the 14 genes tested. Glial fibrillary acidic protein (Gfap) and activity-regulated cytoskeleton-associated protein (Arc) mRNA were upregulated, while growth associated protein (Gap43), clathrin heavy chain (Cltc), α-tubulin, Tau, and stathmin were downregulated. In order to determine if the regulation of an mRNA correlates with a modulation of the expression of the corresponding protein, immunoblot analyses were performed. With the exception of Gap43, the levels of Cltc, Gfap, Tau, stathmin, and α-tubulin proteins were found to be in good agreement with those from mRNA quantification. These results demonstrate that neuroadaptation to chronic morphine administration in rat striatum implies modifications of the expression pattern of several genes and proteins of the cytoskeleton and cytoskeleton-associated components.

Fos but not Cart (cocaine and amphetamine regulated transcript) is overexpressed by several drugs of abuse: a comparative study using real-time quantitative polymerase chain reaction in rat brain.

It has been reported that cocaine and amphetamine-regulated transcript (Cart) peptides can increase locomotor activity and produce a conditioned place preference. To establish whether or not Cart can be consider as a valuable marker of addiction we performed a comparative study of the expression of Cart and Fos genes by several drugs of abuse. This was achieved using real-time quantitative polymerase chain reaction in four rat brain structures: prefrontal cortex, caudate putamen, nucleus accumbens and hippocampus. As expected, a significant induction of the immediate early gene Fos was observed after acute administration of morphine, cocaine, 3, 4-methylenedioxymethamphetamine and Delta(9)-Tetrahydrocannabinol. On the contrary none of these drugs was able to produce a significant change in Cart mRNA levels demonstrating that the expression of this gene is not modulated by drugs of abuse in these brain structures.

Intramolecular Processing of Prothermolysin

Thermolysin, an extracellular zinc endopeptidase from Bacillus thermoproteolyticus, is synthesized as a pre-proenzyme and the prosequence has been shown to assist the refolding of the denatured enzyme in vitro and to inhibit enzyme activity (O’Donohue, M. J., and Beaumont, A. (1996)J. Biol. Chem. 271, 26477–26481). To determine whether prosequence cleavage from the mature enzyme is autocatalytic and if so, whether it is an intermolecular or intramolecular process, N-terminal histidine-tagged prothermolysin was expressed inEscherichia coli. Although partial processing to mature enzyme occurred, most of the proenzyme was recovered intact from inclusion bodies. This was then solubilized in guanidinium hydrochloride, immobilized on a cobalt-containing resin, and after dialysis against renaturation buffer, was quantitatively transformed to mature enzyme. However, when a mutation was introduced into the mature sequence to inactivate thermolysin, the proenzyme was not processed either in vivo or in vitro. In addition, mutated prothermolysin was not processed by exogenous thermolysin under a variety of experimental conditions. The results demonstrate that thermolysin maturation can proceed via an autocatalytic intramolecular pathway.

General function of N-terminal propeptide on assisting protein folding and inhibiting catalytic activity based on observations with a chimeric thermolysin-like protease.

Pro-aminopeptidase processing protease (PA protease) is a thermolysin-like metalloprotease produced by Aeromonas caviae T-64. The N-terminal propeptide acts as an intramolecular chaperone to assist the folding of PA protease and shows inhibitory activity toward its cognate mature enzyme. Moreover, the N-terminal propeptide strongly inhibits the autoprocessing of the C-terminal propeptide by forming a complex with the folded intermediate pro-PA protease containing the C-terminal propeptide (MC). In order to investigate the structural determinants within the N-terminal propeptide that play a role in the folding, processing, and enzyme inhibition of PA protease, we constructed a chimeric pro-PA protease by replacing the N-terminal propeptide with that of vibriolysin, a homologue of PA protease. Our results indicated that, although the N-terminal propeptide of vibriolysin shares only 36% identity with that of PA protease, it assists the refolding of MC, inhibits the folded MC to process its C-terminal propeptide, and shows a stronger inhibitory activity toward the mature PA protease than that of PA protease. These results suggest that the N-terminal propeptide domains in these thermolysin-like proteases may have similar functions, in spite of their primary sequence diversity. In addition, the conserved regions in the N-terminal propeptides of PA protease and vibriolysin may be essential for the functions of the N-terminal propeptide.

Effect of chronic exposure to morphine on the rat blood-brain barrier : focus on the P-glycoprotein

Morphine may affect the properties of the blood–brain barrier (BBB) by modifying the expression of certain BBB markers. We have determined the effect of chronic morphine treatment on the expression and function of some BBB markers in the rat. The mRNAs of 19 selected genes encoding caveolins, endothelial transporters, receptors and tight junctions proteins in the total RNA of isolated cortex microvessels were assayed by quantitative RT‐PCR (qRT‐PCR). The expression of genes Mdr1a, Mrp1, Bcrp, Glut‐1 and Occludin, was slightly increased, while that of Flk‐1 was decreased in microvessels from morphine‐treated rats. The expression of the Mrd1a and Mdr1b genes encoding the P‐glycoprotein (P‐gp) also increased in the whole hippocampus and cortex of morphine‐treated rats. The Mdr1a gene induction (1.38‐fold) observed by qRT‐PCR was also confirmed using in situ hybridization technique (1.40‐fold). Immunoblotting revealed an increase in P‐gp expression in the hippocampus (1.8‐fold) and cortex (1.36‐fold) of morphine‐treated rats, but no effect in isolated microvessels. In contrast, morphine treatment increased by 1.48‐fold the expression of P‐gp in a large vessel‐enriched fraction. The integrity of the BBB, measured by in situ brain perfusion of [14C]‐sucrose, and the activity of P‐gp at the BBB, measured with the P‐gp substrate [3H]‐colchicine, were not modified by morphine. Immunohistofluorescence experiments revealed that P‐gp expression is restricted to large vessels and microvessels in control rats and that morphine treatment did not induce the expression of P‐gp in the brain parenchyma (astrocytes or neurons). Taken together, our results showed that chronic morphine treatment does not significantly alter BBB integrity or P‐gp activity. The impact of morphine‐mediated P‐gp induction observed in large vessels remains to be determined in terms of brain disposition of drugs that are P‐gp substrates.

Involvement of D1 dopamine receptor in MDMA-induced locomotor activity and striatal gene expression in mice

3,4-Methylenedioxymethamphetamine (MDMA), a widely used recreational drug with psychoactive properties, induces both serotonin and dopamine release in the brain. In rats and mice MDMA induces behavioural changes and has rewarding effects but little is known about its cellular effects. We have previously shown that the ERK pathway is important for the changes in gene expression observed in mice striatum after treatment with this psychostimulant. In this study we investigated the role of D1 receptors in MDMA-induced locomotor hyperactivity and regulation of immediate-early genes (Fos, Fosb, Egr1 and Egr2) mRNA levels requiring ERK activity in mice striatum. We used the selective D1 receptor antagonist, SCH23390 at a dose (0.05 mg/kg) that did not influence locomotor activity. This dose totally blocked MDMA-induced locomotor activity but only partially the increase in transcription levels of Fos, Fosb, Egr1 and Egr2 (24%, 23%, 22% and 29% respectively). In conclusion, our results showed that D1 receptors play a key role in the acute MDMA-induced hyperlocomotion and that ERK pathway is partially under D1 receptors control to induce Fos, FosB, Egr1 and Egr2 transcription.

Rnd family genes are differentially regulated by 3,4-methylenedioxymethamphetamine and cocaine acute treatment in mice brain

Drugs of abuse induce alterations in cytoskeletal and cytoskeleton associated genes in several brain areas. We have previously shown that acute MDMA regulates the mRNA level of Rnd3, a Rho GTPase involved in actin cytoskeleton regulation, in mice striatum. In this study we investigated the effects of single administration of cocaine, another psychostimulant with a slightly different mechanism of action, on the mRNA levels of the three members of the Rnd genes family (Rnd1, Rnd2 and Rnd3). Mice were treated with either MDMA (9 mg/kg) or cocaine (20 mg/jg) and brain samples (i.e. hippocampus, striatum and prefrontal cortex) were processed for quantitative real-time PCR assay 1, 2, 4 and 6 h after the injections. The expression level of Rnd2 was differentially affected depending on the drug, brain area and time point after injection. Interestingly the two drugs up-regulate Rnd3 gene expression in the three structures tested with some differences in the timing. The effects of MDMA on Rnd3 appear earlier in the hippocampus as compared to cocaine, while it is the opposite in the prefrontal cortex. However, in the dorsal striatum, the two drugs induce an early and significant up-regulation of Rnd3 expression that is longer-lasting in the case of MDMA. In the case of cocaine contrarily to what was observed with MDMA, this modulation could not be blocked with the ERK activation inhibitor SL327 suggesting that the two drugs lead to the same effect on Rnd3 by two distinct pathways.

Differences in transition state stabilization between thermolysin (EC 3.4.24.27) and neprilysin (EC 3.4.24.11)

Important homologies in the topology of the catalytic site and the mechanism of action of thermolysin and neprilysin have been evidenced by site‐directed mutagenesis. The determination of differences in transition state stabilization between these peptidases could facilitate the design of specific inhibitors. Thus, two residues of thermolysin which could be directly (Tyr157) or indirectly (Asp226) involved in the stabilization of the transition state and their putative counterparts in neprilysin (Tyr625 and Asp709) have been mutated. The results show that Tyr157 is important for thermolysin activity while Tyr625 has no functional role in neprilysin. Conversely, the mutation of Asp226 induced a slight perturbation of thermolysin activity while Asp709 in neprilysin seems crucial in neprilysin catalysis. Taken together these data seem to indicate differences in the transition state mode of stabilization in the two peptidases.