p21WAF1/Cip1 is a negative transcriptional regulator of Wnt4 expression downstream of Notch1 activation.

In keratinocytes, the cyclin/CDK inhibitor p21(WAF1/Cip1) is a direct transcriptional target of Notch1 activation; loss of either the p21 or Notch1 genes expands stem cell populations and facilitates tumor development. The Notch1 tumor-suppressor function was associated with down-regulation of Wnt signaling. Here, we show that suppression of Wnt signaling by Notch1 activation is mediated, at least in part, by down-modulation of Wnts gene expression. p21 is a negative regulator of Wnts transcription downstream of Notch1 activation, independently of effects on the cell cycle. More specifically, expression of the Wnt4 gene is under negative control of endogenous p21 both in vitro and in vivo. p21 associates with the E2F-1 transcription factor at the Wnt4 promoter and causes curtailed recruitment of c-Myc and p300, and histone hypoacetylation at this promoter. Thus, p21 acts as a selective negative regulator of transcription and links the Notch and Wnt signaling pathways in keratinocyte growth control.

Bacterial subfamily of LuxR regulators that respond to plant compounds.

Pseudomonas fluorescens are rhizobacteria known for their biocontrol properties. Several antimicrobial functions are crucial for this process, and the experiments described here investigate the modulation of their expression during the plant-bacterium interaction. The role of a LuxR family regulator in interkingdom signaling has been investigated using genome-scale transcriptome analysis, gene promoter studies in vivo and in vitro, biocontrol assays, and response to plant compounds. PsoR, a LuxR solo or orphan regulator of P. fluorescens, was identified. PsoR is solubilized and activates a lux-box-containing promoter only in the presence of macerated plants, suggesting the presence of a plant molecule(s) that most likely binds to PsoR. Gene expression profiles revealed that genes involved in the inhibition of plant pathogens were affected by PsoR, including a chitinase gene, iron metabolism genes, and biosynthetic genes of antifungal compounds. 2,4-Diacetylphloroglucinol production is PsoR dependent both in vitro and in vivo. psoR mutants were significantly reduced for their ability to protect wheat plants from root rot, and damping-off caused by Pythium ultimum infection. PsoR most likely senses a molecule(s) in the plant and modulates expression of genes that have a role in biocontrol. PsoR and related proteins form a subfamily of LuxR family regulators in plant-associated bacteria.

Efficiency and safety of bilateral contemporaneous pallidal stimulation (deep brain stimulation) in levodopa-responsive patients with Parkinson's disease with severe motor fluctuations: a 2-year follow-up review.

OBJECT: The aim of this study was to evaluate the long-term safety and efficacy of bilateral contemporaneous deep brain stimulation (DBS) in patients who have levodopa-responsive parkinsonism with untreatable motor fluctuations. Bilateral pallidotomy carries a high risk of corticobulbar and cognitive dysfunction. Deep brain stimulation offers new alternatives with major advantages such as reversibility of effects, minimal permanent lesions, and adaptability to individual needs, changes in medication, side effects, and evolution of the disease. METHODS: Patients in whom levodopa-responsive parkinsonism with untreatable severe motor fluctuations has been clinically diagnosed underwent bilateral pallidal magnetic resonance image-guided electrode implantation while receiving a local anesthetic. Pre- and postoperative evaluations at 3-month intervals included Unified Parkinson's Disease Rating Scale (UPDRS) scoring, Hoehn and Yahr staging, 24-hour self-assessments, and neuropsychological examinations. Six patients with a mean age of 55 years (mean 42-67 years), a mean duration of disease of 15.5 years (range 12-21 years), a mean "on/off' Hoehn and Yahr stage score of 3/4.2 (range 3-5), and a mean "off' time of 40% (range 20-50%) underwent bilateral contemporaneous pallidal DBS, with a minimum follow-up period lasting 24 months (range 24-30 months). The mean dose of levodopa in these patients could not be changed significantly after the procedure and pergolide was added after 12 months in five patients because of recurring fluctuations despite adjustments in stimulation parameters. All but two patients had no fluctuations until 9 months. Two of the patients reported barely perceptible fluctuations at 12 months and two at 15 months; however, two patients remain without fluctuations at 2 years. The mean improvements in the UPDRS motor score in the off time and the activities of daily living (ADL) score were more than 50%; the mean off time decreased from 40 to 10%, and the mean dyskinesia and complication of treatment scores were reduced to one-third until pergolide was introduced at 12 months. No significant improvement in "on" scores was observed. A slight worsening after 1 year was observed and three patients developed levodopa- and stimulation-resistant gait ignition failure and minimal fluctuations at 1 year. Side effects, which were controlled by modulation of stimulation, included dysarthria, dystonia, and confusion. CONCLUSIONS: Bilateral pallidal DBS is safe and efficient in patients who have levodopa-responsive parkinsonism with severe fluctuations. Major improvements in motor score, ADL score, and off time persisted beyond 2 years after the operation, but signs of decreased efficacy started to be seen after 12 months.

PDMP blocks brefeldin a-induced retrograde membrane transport from Golgi to ER: evidence for involvement of calcium homeostasis and dissociation from sphingolipid metabolism

In this study, we show that an inhibitor of sphingolipid biosynthesis, d,l-threo-1-phenyl-2- decanoylamino-3-morpholino-1-propanol (PDMP), inhibits brefeldin A (BFA)-induced retrograde membrane transport from Golgi to endoplasmic reticulum (ER). If BFA treatment was combined with or preceded by PDMP administration to cells, disappearance of discrete Golgi structures did not occur. However, when BFA was allowed to exert its effect before PDMP addition, PDMP could not ¿rescue¿ the Golgi compartment. Evidence is presented showing that this action of PDMP is indirect, which means that the direct target is not sphingolipid metabolism at the Golgi apparatus. A fluorescent analogue of PDMP, 6-(N-[7-nitro-2,1,3-benzoxadiazol-4-yl]amino)hexanoyl-PDMP (C6-NBD-PDMP), did not localize in the Golgi apparatus. Moreover, the effect of PDMP on membrane flow did not correlate with impaired C6-NBD-sphingomyelin biosynthesis and was not mimicked by exogenous C6-ceramide addition or counteracted by exogenous C6-glucosylceramide addition. On the other hand, the PDMP effect was mimicked by the multidrug resistance protein inhibitor MK571. The effect of PDMP on membrane transport correlated with modulation of calcium homeostasis, which occurred in a similar concentration range. PDMP released calcium from at least two independent calcium stores and blocked calcium influx induced by either extracellular ATP or thapsigargin. Thus, the biological effects of PDMP revealed a relation between three important physiological processes of multidrug resistance, calcium homeostasis, and membrane flow in the ER/ Golgi system.

Fluoxetine regulates the expression of neurotrophic/growth factors and glucose metabolism in astrocytes.

Rationale The pharmacological actions of most antidepressants are ascribed to the modulation of serotonergic and/or noradrenergic transmission in the brain. During therapeutic treatment for major depression, fluoxetine, one of the most commonly prescribed selective serotonin reuptake inhibitor (SSRI) antidepressants, accumulates in the brain, suggesting that fluoxetine may interact with additional targets. In this context, there is increasing evidence that astrocytes are involved in the pathophysiology of major depression.Objectives The aim of this study was to examine the effects of fluoxetine on the expression of neurotrophic/growth factors that have antidepressant properties and on glucose metabolism in cultured cortical astrocytes.Results Treatment of astrocytes with fluoxetine and paroxetine, another SSRI antidepressant, upregulated brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF), and VGF mRNA expression. In contrast, the tricyclic antidepressants desipramine and imipramine did not affect the expression of these neurotrophic/growth factors. Analysis of the effects of fluoxetine on glucose metabolism revealed that fluoxetine reduces glycogen levels and increases glucose utilization and lactate release by astrocytes. Similar data were obtained with paroxetine, whereas imipramine and desipramine did not regulate glucose metabolism in this glial cell population. Our results also indicate that the effects of fluoxetine and paroxetine on glucose utilization, lactate release, and expression of BDNF, VEGF, and VGF are not mediated by serotonin-dependent mechanisms.Conclusions These data suggest that, by increasing the expression of specific astrocyte-derived neurotrophic factors and lactate release from astrocytes, fluoxetine may contribute to normalize the trophic and metabolic support to neurons in major depression.

Uncoupling phosphate deficiency from its major effects on growth and transcriptome via PHO1 expression in Arabidopsis.

Inorganic phosphate (Pi) is one of the most limiting nutrients for plant growth in both natural and agricultural contexts. Pi-deficiency leads to a strong decrease in shoot growth, and triggers extensive changes at the developmental, biochemical and gene expression levels that are presumably aimed at improving the acquisition of this nutrient and sustaining growth. The Arabidopsis thaliana PHO1 gene has previously been shown to participate in the transport of Pi from roots to shoots, and the null pho1 mutant has all the hallmarks associated with shoot Pi deficiency. We show here that A. thaliana plants with a reduced expression of PHO1 in roots have shoot growth similar to Pi-sufficient plants, despite leaves being strongly Pi deficient. Furthermore, the gene expression profile normally triggered by Pi deficiency is suppressed in plants with low PHO1 expression. At comparable levels of shoot Pi supply, the wild type reduces shoot growth but maintains adequate shoot vacuolar Pi content, whereas the PHO1 underexpressor maintains maximal growth with strongly depleted Pi reserves. Expression of the Oryza sativa (rice) PHO1 ortholog in the pho1 null mutant also leads to plants that maintain normal growth and suppression of the Pi-deficiency response, despite the low shoot Pi. These data show that it is possible to unlink low shoot Pi content with the responses normally associated with Pi deficiency through the modulation of PHO1 expression or activity. These data also show that reduced shoot growth is not a direct consequence of Pi deficiency, but is more likely to be a result of extensive gene expression reprogramming triggered by Pi deficiency.

Heterogeneity of the induction of HLA-DR expression by human immune interferon on glioma cell lines and their clones.

The modulation of HLA-DR and HLA-A, -B, and -C by human recombinant immune interferon (IFN-gamma) was studied on 10 malignant glioma cell lines established in our laboratory, on 8 clones or subclones derived from these lines, and on a fetal astrocyte cell line. Comparative studies were performed with recombinant leukocyte interferon (IFN-alpha). The results not only confirmed the selective activity of IFN-gamma on the modulation of HLA-DR expression, as opposed to that of IFN-alpha, but also demonstrated a marked heterogeneity in the response of glioma cell lines and their clones to the two types of IFN tested. For example, all 3 clones of an inducible cell line could be modulated to express HLA-DR, whereas only 2 of 5 clones derived from a noninducible line were modulated. This heterogeneity did not seem to be due to the absence of the receptor for IFN-gamma on the surface of these cells, since almost all of the cell lines or clones tested (17 of 19) responded to IFN-gamma by the induction or enhancement of the expression for either HLA-DR or HLA-A, -B, and -C (or both). The heterogeneity of induction was also demonstrated between clones derived from a glioma line that did not express HLA-DR after IFN-gamma treatment. The production of HLA-DR by one of the clones was abundant enough to be confirmed by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis.

Role of superoxide, nitric oxide, and peroxynitrite in doxorubicin-induced cell death in vivo and in vitro.

Doxorubicin (DOX) is a potent available antitumor agent; however, its clinical use is limited because of its cardiotoxicity. Cell death is a key component in DOX-induced cardiotoxicity, but its mechanisms are elusive. Here, we explore the role of superoxide, nitric oxide (NO), and peroxynitrite in DOX-induced cell death using both in vivo and in vitro models of cardiotoxicity. Western blot analysis, real-time PCR, immunohistochemistry, flow cytometry, fluorescent microscopy, and biochemical assays were used to determine the markers of apoptosis/necrosis and sources of NO and superoxide and their production. Left ventricular function was measured by a pressure-volume system. We demonstrated increases in myocardial apoptosis (caspase-3 cleavage/activity, cytochrome c release, and TUNEL), inducible NO synthase (iNOS) expression, mitochondrial superoxide generation, 3-nitrotyrosine (NT) formation, matrix metalloproteinase (MMP)-2/MMP-9 gene expression, poly(ADP-ribose) polymerase activation [without major changes in NAD(P)H oxidase isoform 1, NAD(P)H oxidase isoform 2, p22(phox), p40(phox), p47(phox), p67(phox), xanthine oxidase, endothelial NOS, and neuronal NOS expression] and decreases in myocardial contractility, catalase, and glutathione peroxidase activities 5 days after DOX treatment to mice. All these effects of DOX were markedly attenuated by peroxynitrite scavengers. Doxorubicin dose dependently increased mitochondrial superoxide and NT generation and apoptosis/necrosis in cardiac-derived H9c2 cells. DOX- or peroxynitrite-induced apoptosis/necrosis positively correlated with intracellular NT formation and could be abolished by peroxynitrite scavengers. DOX-induced cell death and NT formation were also attenuated by selective iNOS inhibitors or in iNOS knockout mice. Various NO donors when coadministered with DOX but not alone dramatically enhanced DOX-induced cell death with concomitant increased NT formation. DOX-induced cell death was also attenuated by cell-permeable SOD but not by cell-permeable catalase, the xanthine oxidase inhibitor allopurinol, or the NADPH oxidase inhibitors apocynine or diphenylene iodonium. Thus, peroxynitrite is a major trigger of DOX-induced cell death both in vivo and in vivo, and the modulation of the pathways leading to its generation or its effective neutralization can be of significant therapeutic benefit.

Regulation of the integration of newly generated neurons in the adult hippocampus

Hippocampal adult neurogenesis results in the continuous formation of new neurons in the adult hippocampus, which participate to learning and memory. Manipulations increasing adult neurogenesis have a huge clinical potential in pathologies involving memory loss. Intringuingly, most of the newborn neurons die during their maturation. Thus, increasing newborn neuron survival during their maturation may be a powerful way to increase overall adult neurogenesis. The factors governing this neuronal death are yet poorly known. In my PhD project, we made the hypothesis that synaptogenesis and synaptic activity play a role in the survival of newborn hippocampal neurons. We studied three factors potentially involved in the regulation of the synaptic integration of adult-born neurons. First, we used propofol anesthesia to provoke a global increase in GABAergic activity of the network, and we evaluated the outcome on newborn neuron synaptic integration, morphological development and survival. Propofol anesthesia impaired the dendritic maturation and survival of adult-born neurons in an age-dependent manner. Next, we examined the development of astrocytic ensheathment on the synapses formed by newborn neurons, as we hypothesized that astrocytes are involved in their synaptic integration. Astrocytic processes ensheathed the synapses of newborn neurons very early in their development, and the processes modulated synaptic transmission on these cells. Finally, we studied the cell-autonomous effects of the overexpression of synaptic adhesion molecules on the development, synaptic integration and survival of newborn neurons, and we found that manipulating of a single adhesion molecule was sufficient to modify synaptogenesis and/or synapse function, and to modify newborn neuron survival. Together, these results suggest that the activity of the neuronal network, the modulation of glutamate transport by astrocytes, and the synapse formation and activity of the neuron itself may regulate the survival of newborn neurons. Thus, the survival of newborn neurons may depend on their ability to communicate with the network. This knowledge is crucial for finding ways to increase neurogenesis in patients. More generally, understanding how the neurogenic niche works and which factors are important for the generation, maturation and survival of neurons is fundamental to be able to maybe, one day, replace neurons in any region of the brain.

Altered brain mechanisms of emotion processing in pre-manifest Huntington's disease.

Huntington's disease is an inherited neurodegenerative disease that causes motor, cognitive and psychiatric impairment, including an early decline in ability to recognize emotional states in others. The pathophysiology underlying the earliest manifestations of the disease is not fully understood; the objective of our study was to clarify this. We used functional magnetic resonance imaging to investigate changes in brain mechanisms of emotion recognition in pre-manifest carriers of the abnormal Huntington's disease gene (subjects with pre-manifest Huntington's disease): 16 subjects with pre-manifest Huntington's disease and 14 control subjects underwent 1.5 tesla magnetic resonance scanning while viewing pictures of facial expressions from the Ekman and Friesen series. Disgust, anger and happiness were chosen as emotions of interest. Disgust is the emotion in which recognition deficits have most commonly been detected in Huntington's disease; anger is the emotion in which impaired recognition was detected in the largest behavioural study of emotion recognition in pre-manifest Huntington's disease to date; and happiness is a positive emotion to contrast with disgust and anger. Ekman facial expressions were also used to quantify emotion recognition accuracy outside the scanner and structural magnetic resonance imaging with voxel-based morphometry was used to assess the relationship between emotion recognition accuracy and regional grey matter volume. Emotion processing in pre-manifest Huntington's disease was associated with reduced neural activity for all three emotions in partially separable functional networks. Furthermore, the Huntington's disease-associated modulation of disgust and happiness processing was negatively correlated with genetic markers of pre-manifest disease progression in distributed, largely extrastriatal networks. The modulated disgust network included insulae, cingulate cortices, pre- and postcentral gyri, precunei, cunei, bilateral putamena, right pallidum, right thalamus, cerebellum, middle frontal, middle occipital, right superior and left inferior temporal gyri, and left superior parietal lobule. The modulated happiness network included postcentral gyri, left caudate, right cingulate cortex, right superior and inferior parietal lobules, and right superior frontal, middle temporal, middle occipital and precentral gyri. These effects were not driven merely by striatal dysfunction. We did not find equivalent associations between brain structure and emotion recognition, and the pre-manifest Huntington's disease cohort did not have a behavioural deficit in out-of-scanner emotion recognition relative to controls. In addition, we found increased neural activity in the pre-manifest subjects in response to all three emotions in frontal regions, predominantly in the middle frontal gyri. Overall, these findings suggest that pathophysiological effects of Huntington's disease may precede the development of overt clinical symptoms and detectable cerebral atrophy.

The caspase 8 inhibitor c-FLIP(L) modulates T-cell receptor-induced proliferation but not activation-induced cell death of lymphocytes.

The caspase 8 inhibitor c-FLIP(L) can act in vitro as a molecular switch between cell death and growth signals transmitted by the death receptor Fas (CD95). To elucidate its function in vivo, transgenic mice were generated that overexpress c-FLIP(L) in the T-cell compartment (c-FLIP(L) Tg mice). As anticipated, FasL-induced apoptosis was inhibited in T cells from the c-FLIP(L) Tg mice. In contrast, activation-induced cell death of T cells in c-FLIP(L) Tg mice was unaffected, suggesting that this deletion process can proceed in the absence of active caspase 8. Accordingly, c-FLIP(L) Tg mice differed from Fas-deficient mice by showing no accumulation of B220(+) CD4(-) CD8(-) T cells. However, stimulation of T lymphocytes with suboptimal doses of anti-CD3 or antigen revealed increased proliferative responses in T cells from c-FLIP(L) Tg mice. Thus, a major role of c-FLIP(L) in vivo is the modulation of T-cell proliferation by decreasing the T-cell receptor signaling threshold.

Origin of the spectral shifts among the early intermediates of the rhodopsin photocycle.

A combined strategy based on the computation of absorption energies, using the ZINDO/S semiempirical method, for a statistically relevant number of thermally sampled configurations extracted from QM/MM trajectories is used to establish a one-to-one correspondence between the structures of the different early intermediates (dark, batho, BSI, lumi) involved in the initial steps of the rhodopsin photoactivation mechanism and their optical spectra. A systematic analysis of the results based on a correlation-based feature selection algorithm shows that the origin of the color shifts among these intermediates can be mainly ascribed to alterations in intrinsic properties of the chromophore structure, which are tuned by several residues located in the protein binding pocket. In addition to the expected electrostatic and dipolar effects caused by the charged residues (Glu113, Glu181) and to strong hydrogen bonding with Glu113, other interactions such as π-stacking with Ala117 and Thr118 backbone atoms, van der Waals contacts with Gly114 and Ala292, and CH/π weak interactions with Tyr268, Ala117, Thr118, and Ser186 side chains are found to make non-negligible contributions to the modulation of the color tuning among the different rhodopsin photointermediates.

Novel action of a wake-promoting neuropeptide in hippocampus : inhibition of nmda receptor function at excitatory synapses through orexin-a

One of the most intriguing functions of the brain is the ability to learn and memorize. The mechanism through which memory and learning are expressed requires the activation of NMDA receptors (NMDARs). These molecular entities are placed at the postsynaptic density of excitatory synapses and their function is tightly controlled by the actions of several modulators at the extracellular, intracellular and pore sites. A large part of the intracellular modulation comes from the action of G-protein coupled receptors (GPCRs). Through intracellular cascades typically involving kinases and phosphatases, GPCRs potentiate or inhibit NMDARs, controlling the conductive state but also the trafficking within the synapse. The GPCRs are involved in the modulation of a variety of brain functions. Many of them control cognition, memory and learning performance, therefore, their effects on NMDARs are extensively studied. The orexinergic system signals through GPCRs and it is well known for the regulation of waking, feeding, reward and autonomic functions. Moreover, it is involved in potentiating hippocampus-related cognitive tasks. Orexin receptors and fibers are present within the hippocampus, but whether these directly modulate hippocampal cells and synapses has not yet been determined. During my thesis, I studied orexinergic actions on excitatory synaptic transmission via whole-cell patch-clamp recordings in rat acute hippocampal slices. I observed that exogenously applied orexin-A (ox-A) exerted a strong inhibitory action on NMDAR-mediated synaptic potentials at mossy fiber (MF)-CA3 synapses, by postsynaptically activating orexin-2 receptors, a minor inhibition at Schaffer collateral-CAl synapses and did not affect other synapses with the CA3 area. Moreover, I demonstrated that the susceptibility of NMDARs to ox- A depends on the tone of endogenous orexin known to fluctuate during the day-night cycle. In fact, in slices prepared during the active period of the rats, when endogenous orexin levels are high, NMDAR-currents were not affected by exogenously applied ox-A. The inhibitory effect of ox-A was, however, reverted when interfering with the orexinergic system through intraperitoneal injections of almorexant, a dual orexin receptor antagonist, during the active phase prior to slice preparation. This thesis work suggests that the orexinergic system regulates NMDAR-dependent information flow through select hippocampal pathways depending on the time-of-day. The specific orexinergic modulation of NMDARs at MFs dampens the excitability of the hippocampal circuit and could impede the mechanisms related to memory formation, possibly also following extended periods of waking. -- La capacité d'apprentissage et de mémorisation est une des fonctions les plus intrigantes de notre cerveau. Il a été montré qu'elles requièrent l'activation des récepteurs NMDA (NMDARs). Ces entités moléculaires sont présentes au niveau de la densité post-synaptique des synapses excitatrices et leur fonction est étroitement contrôlée par l'action de nombreux modulateurs au niveau extracellulaire, intracellulaire et membranaire de ces récepteurs. Une grande partie de la modulation intracellulaire s'effectue via l'action de récepteurs couplés aux protéines G (GPCRs). Grace à leurs cascades intracellulaires typiquement impliquant des kinases et des phosphatases, les GPCRs favorisent l'activation ou l'inhibition des NMDARs, contrôlant ainsi leur perméabilité mais aussi leur mouvement à la synapse. Les GPCRs sont impliquées dans de nombreuses fonctions cérébrales telles que la cognition, la mémoire ainsi que la capacité d'apprentissage c'est pour cela que leurs effets sur les NMDARs sont très étudiés. Le système orexinergique fait intervenir ces GPCRs et est connu par son rôle dans la régulation de fonctions physiologiques telles que l'éveil, la prise alimentaire, la récompense ainsi que d'autres fonctions du système nerveux autonome. De plus, ce système est impliqué dans la régulation de tâches cognitives liées à l'hippocampe. Bien que les fibres et les récepteurs à l'orexine soient présents dans l'hippocampe, leur mécanisme d'action sur les cellules et les synapses de l'hippocampe n'a pas encore été élucidé. Durant ma thèse, je me suis intéressée aux effets de l'orexine sur la transmission synaptique excitatrice en utilisant la méthode d'enregistrement en patch-clamp en configuration cellule entière sur des tranches aiguës d'hippocampes de rats. J'ai observé que l'application exogène d'orexine A d'une part inhibe fortement les courants synaptiques dépendants de l'activation des NMDARs au niveau de la synapse entre les fibres moussues et CA3 via l'activation post-synaptique des orexine récepteurs 2 mais d'autre part n'inhibe que de façon mineure la synapse entre les collatérales de Schaffer et CAI et n'affecte pas les autres synapses impliquant CA3. J'ai également démontré que la sensibilité des NMDARs à l'orexine A dépend de sa concentration endogène qui fluctue durant le cycle éveil-sommeil. En effet, lorsque les coupes d'hippocampes sont préparées durant la période active de l'animal correspondant à un niveau endogène d'orexine élevé, l'application exogène d'orexine A n'a aucun effet sur les courants dépendants de l'activation des NMDARs. Cependant, l'injection dans le péritoine, durant la phase active de l'animal, d'un antagoniste des orexine récepteurs, l'almorexant, va supprimer l'effet inhibiteur de l'orexine A. Les résultats de ma thèse suggèrent donc que le système orexinergique module les informations véhiculées par les NMDARs via des voies de signalisation sélectives de l'hippocampe en fonction du moment de la journée. La modulation orexinergique des NMDARs au niveau des fibres moussues diminue ainsi l'excitabilité du circuit hippocampal et pourrait entraver les mécanismes liés à la formation de la mémoire, potentiellement après de longues périodes d'éveil.

Blood pressure, cardiac, and renal responses to salt and deoxycorticosterone acetate in mice: role of Renin genes.

Several studies have demonstrated that mice are polymorphic for the number of renin genes, with some inbred strains harboring one gene (Ren-1(c)) and other strains containing two genes (Ren-1(d) and Ren-2). In this study, the effects of 1% salt and deoxycorticosterone acetate (DOCA)/salt were investigated in one- and two-renin gene mice, for elucidation of the role of renin in the modulation of BP, cardiac, and renal responses to salt and DOCA. The results demonstrated that, under baseline conditions, mice with two renin genes exhibited 10-fold higher plasma renin activity, 100-fold higher plasma renin concentrations, elevated BP (which was angiotensin II-dependent), and an increased cardiac weight index, compared with one-renin gene mice (all P < 0.01). The presence of two renin genes markedly increased the BP, cardiac, and renal responses to salt. The number of renin genes also modulated the responses to DOCA/salt. In one-renin gene mice, DOCA/salt induced significant renal and cardiac hypertrophy (P < 0.01) even in the absence of any increase in BP. Treatment with losartan, an angiotensin II AT(1) receptor antagonist, decreased BP in two-renin gene mice but not in one-renin gene mice. However, losartan prevented the development of cardiac hypertrophy in both groups of mice. In conclusion, these data demonstrate that renin genes are important determinants of BP and of the responses to salt and DOCA in mice. The results confirm that the Ren-2 gene, which controls renin production mainly in the submaxillary gland, is physiologically active in mice and is not subject to the usual negative feedback control. Finally, these data provide further evidence that mineralocorticoids promote cardiac hypertrophy even in the absence of BP changes. This hypertrophic process is mediated in part by the activation of angiotensin II AT(1) receptors.

Mice with an adipocyte-specific lipin 1 separation-of-function allele reveal unexpected roles for phosphatidic acid in metabolic regulation.

Lipin 1 is a coregulator of DNA-bound transcription factors and a phosphatidic acid (PA) phosphatase (PAP) enzyme that catalyzes a critical step in the synthesis of glycerophospholipids. Lipin 1 is highly expressed in adipocytes, and constitutive loss of lipin 1 blocks adipocyte differentiation; however, the effects of Lpin1 deficiency in differentiated adipocytes are unknown. Here we report that adipocyte-specific Lpin1 gene recombination unexpectedly resulted in expression of a truncated lipin 1 protein lacking PAP activity but retaining transcriptional regulatory function. Loss of lipin 1-mediated PAP activity in adipocytes led to reduced glyceride synthesis and increased PA content. Characterization of the deficient mice also revealed that lipin 1 normally modulates cAMP-dependent signaling through protein kinase A to control lipolysis by metabolizing PA, which is an allosteric activator of phosphodiesterase 4 and the molecular target of rapamycin. Consistent with these findings, lipin 1 expression was significantly related to adipose tissue lipolytic rates and protein kinase A signaling in adipose tissue of obese human subjects. Taken together, our findings identify lipin 1 as a reciprocal regulator of triglyceride synthesis and hydrolysis in adipocytes, and suggest that regulation of lipolysis by lipin 1 is mediated by PA-dependent modulation of phosphodiesterase 4.