Characterization of juvenile and young adult mice following induction of hydrocephalus with kaolin

Hydrocephalus is a common neurological problem in humans, Usually caused by an impairment of cerebrospinal fluid (CSF) flow or absorption. A reliable induced model of chronic hydrocephalus in mice would be useful to test hypotheses using genetic mutants. Our goal was to characterize behavioral and histological changes in juvenile and Young adult mice with kaolin (aluminum silicate) -induced hydrocephalus. Seven-day old and 7-8 week old mice received injection of kaolin into the cisterna magna. Behavior was assessed repeatedly. Seven or 14 days following kaolin, magnetic resonance (MR) imaging was used to assess ventricle size. In hydrocephalic mice, body weight was significantly lower than in age-matched saline-injected sham controls and the gait and posture score were impaired. Juvenile mice developed severe ventriculomegaly and had reduced corpus callosum thickness with gross white matter destruction by 14 days. Reactive astroglial change in white matter and cortex and reduced cellular proliferation in the subependymal zone were also apparent. Young adult mice developed only moderate ventricular enlargement without overt white matter destruction, although there was corpus callosum atrophy and mild astroglial reaction in white matter. Glial fibrillary acidic protein content was significantly higher in juvenile and young adult hydrocephalic mice at 7 and 14 days, but myelin basic protein content was not significantly altered. In conclusion, hydrocephalus induced by percutaneous injection of kaolin in juvenile and young adult mice is feasible. The associated periventricular alterations are essentially the same as those reported in rats of comparable ages. (C) 2009 Elsevier Inc. All rights reserved.

Neuronal maturation in an experimental model of brain tissue heterotopia in the lung

Neural maturation involves diverse interaction and signaling mechanisms that are essential to the development of the nervous system. However, little is known about the development of neurons in heterotopic brain tissue in the lung, a rare abnormality observed in malformed babies and fetuses. The aim of this study was to identify the neurons and to investigate their maturation in experimental brain tissue heterotopia during fetal and neonatal periods. The fetuses from 24 pregnant female Swiss mice were used to induce brain tissue heterotopia on the 15th gestational day. Briefly, the brain of one fetus of each dam was extracted, disaggregated, and injected into the right hemithorax of siblings. Six of these fetuses with pulmonary brain tissue implantation were collected on the 18th gestational day (group E18), and six others were collected on the 8th postnatal day (group P8). The brain of each fetus from dams not submitted to any experimental procedure was collected on the 18th gestational day (group CE18) and on the 8th postnatal day (group CP8) to serve as a control for neuronal quantitation and maturation. Immunohistochemical staining of NeuN was used to assess neuron quantity and maturation. The NeuN labeling index was greater in the postnatal period than in the fetal period for the experimental and control groups (138 > E18 and CP8 > CE18), although there were fewer neurons in experimental than in control groups (P8 < CP8 and El 8 < CE1 8) (P < 0.005). These results indicate that fetal neuroblasts/neurons not only survive a dramatic event such as mechanical disaggregation, in the same way as it happens in human cases, but also they retain their development in heterotopia, irrespective of local tissue influences.

Detrimental role of prolonged sleep deprivation on adult neurogenesis

Adult mammalian brains continuously generate new neurons, a phenomenon called adult neurogenesis. Both environmental stimuli and endogenous factors are important regulators of adult neurogenesis. Sleep has an important role in normal brain physiology and its disturbance causes very stressful conditions, which disrupt normal brain physiology. Recently, an influence of sleep in adult neurogenesis has been established, mainly based on sleep deprivation studies. This review provides an overview on how rhythms and sleep cycles regulate hippocampal and subventricular zone neurogenesis, discussing some potential underlying mechanisms. In addition, our review highlights some interacting points between sleep and adult neurogenesis in brain function, such as learning, memory, and mood states, and provides some insights on the effects of antidepressants and hypnotic drugs on adult neurogenesis.

Neural Mechanisms of Exercise: Anti-Depression, Neurogenesis, and Serotonin Signaling

Depression is associated with decreased serotonin metabolism and functioning in the central nervous system, evidenced by both animal models of depression and clinical patient studies. Depression is also accompanied by decreased hippocampal neurogenesis in diverse animal models. Neurogenesis is mainly defined in dentate gyrus of hippocampus as well as subventricular zone. Moreover, hypothalamus, amygdala, olfactory tubercle, and piriform cortex are reported with evidences of adult neurogenesis. Physical exercise is found to modulate adult neurogenesis significantly, and results in mood improvement. The cellular mechanism such as adult neurogenesis upregulation was considered as one major mood regulator following exercise. The recent advances in molecular mechanisms underlying exercise-regulated neurogenesis have widen our understanding in brain plasticity in physiological and pathological conditions, and therefore better management of different psychiatric disorders.

Pharmacological blockade of either cannabinoid CB1 or CB2 receptors prevents both cocaine-induced conditioned locomotion and cocaine-induced reduction of cell proliferation in the hippocampus of adult male rat.

Addiction to major drugs of abuse, such as cocaine, has recently been linked to alterations in adult neurogenesis in the hippocampus. The endogenous cannabinoid system modulates this proliferative response as demonstrated by the finding that pharmacological activation/blockade of cannabinoid CB1 and CB2 receptors not only modulates neurogenesis but also modulates cell death in the brain. In the present study, we evaluated whether the endogenous cannabinoid system affects cocaine-induced alterations in cell proliferation. To this end, we examined whether pharmacological blockade of either CB1 (Rimonabant, 3 mg/kg) or CB2 receptors (AM630, 3 mg/kg) would affect cell proliferation [the cells were labeled with 5-bromo-2'-deoxyuridine (BrdU)] in the subventricular zone (SVZ) of the lateral ventricle and the dentate subgranular zone (SGZ). Additionally, we measured cell apoptosis (as monitored by the expression of cleaved caspase-3) and glial activation [by analyzing the expression of glial fibrillary acidic protein (GFAP) and Iba-1] in the striatum and hippocampus during acute and repeated (4 days) cocaine administration (20 mg/kg). The results showed that acute cocaine exposure decreased the number of BrdU-immunoreactive (ir) cells in the SVZ and SGZ. In contrast, repeated cocaine exposure reduced the number of BrdU-ir cells only in the SVZ. Both acute and repeated cocaine exposure increased the number of cleaved caspase-3-, GFAP- and Iba1-ir cells in the hippocampus, and this effect was counteracted by AM630 or Rimonabant, which increased the number of BrdU-, GFAP-, and Iba1-ir cells in the hippocampus. These results indicate that the changes in neurogenic, apoptotic and gliotic processes that were produced by repeated cocaine administration were normalized by pharmacological blockade of CB1 and CB2. The restorative effects of cannabinoid receptor blockade on hippocampal cell proliferation were associated with the prevention of the induction of conditioned locomotion but not with the prevention of cocaine-induced sensitization.

Differential transgene expression profiles from rAAV2/1 vectors using the tetON and CMV promoters in the rat brain.

The biodistribution of transgene expression in the CNS after localized stereotaxic vector delivery is an important issue for safety of gene therapy for neurological diseases. The cellular specificity of transgene expression from rAAV2/1 vectors using the tetON expression cassette in comparison with the CMV promoter was investigated in the rat nigrostriatal pathway. After intrastriatal injection, although GFP was mainly expressed into neurons with both vectors, the relative proportions of DARPP-32+ projection neurons and parvalbumin+ interneurons were respectively 13:1 and 2:1 for the CMV and tetON vectors. DARP32+ neurons projecting to the globus pallidus were strongly GFP+ with both vectors, whereas those projecting to the substantia nigra pars reticulata (SNpr) were efficiently labeled by the CMV but poorly by the tetON vector. Numerous GFP+ cells were evidenced in the subventricular zone with both vectors. However, in the olfactory bulb (OB), GFP+ neurons were observed with the CMV but not the tetON vector. We conclude that the absence of significant amounts of transgene product in distant regions (SN and OB) constitutes a safety advantage of the AAV2/1-tetON vector for striatal gene therapy. Midbrain injections resulted in selective GFP expression in tyrosine hydroxylase+ neurons by the tetON vector whereas with the CMV vector, GFP+ cells covered a widespread area of the midbrain. The biodistribution of GFP protein corresponded to that of the transcripts and not of the viral genomes. We conclude that the rAAV2/1-tetON vector constitutes an interesting tool for specific transgene expression in midbrain dopaminergic neurons.

The role of Bmi1 in CNS development and in retinal degeneration

SUMMARY : The present work addresses several aspects of cell cycle regulation, cell fate specification and cell death in the central nervous system (CNS), specifically the cortex and the retina. More precisely, we investigated the role of Bmi1, a polycomb family gene required for stem cell proliferation and self-renewal, in the development of the cerebral cortex, as well as in the genesis of the retina. These data, together with studies published during the last two decades concerning cell cycle re-activation in apoptotic neurons in the CNS, raised the question of a possible link between regulation of the cell cycle during development and during retinal degeneration. 1. The effects of Bmi1 loss in the cerebral cortex : Consistently with our and others' observations on failure of Bmi9-/- stem cells to proliferate and self-renew in vitro, the Bmi9-/- cerebral cortex presented slight defects in proliferation in stem/progenitor cells compartments in vivo. This was in accordance with the pattern of Bmi1 expression in the developing forebrain. The modest proliferation defects, compared to the drastic consequences of Bmi9 loss in vitro, suggest that cell-extrinsic mechanisms may partially compensate for Bmi1 deletion in vivo during cortical histogenesis. Nevertheless, we observed a decreased proliferating activity in neurogenic regions of the adult telencephalon, more precisely in the subventricular zone, showing that Bmi1 controls neural stem/progenitor proliferation during adulthood in vivo. Our data also highlight an increased production of astrocytes at birth, and a generalized gliosis in the adult Bmi9-/- brain. Importantly, glial progenitors and astrocytes retained the ability to proliferate in the absence of Bmi1. 2. The effects of Bmi1 loss in the retina : The pattern of expression of Bmi1 during development and in the adult retina suggests a role for Bmi1 in cell fate specification and differentiation rather than in proliferation. While the layering and the global structure of the retina appear normal in Bmi1 /adult mice, immunohistochemìcal analysis revealed defects in the three major classes of retinal interneurons, namely: horizontal, bipolar and amacrine cells. Electroretinogram recordings in Bmi9-/- mice are coherent with the defects observed at the histological level, with a reduced b-wave and low-profile oscillatory potentials. These results show that Bmi1 controls not only proliferation, but also cell type generation, as previously observed in the cerebellum. 3. Cell cycle events and related neuroprotective strategies in retinal degeneration : In several neurodegenerative disorders, neurons re-express cell cycle proteins such as cyclin dependent kinases (Cdks) prior to apoptosis. Here, we show for the first time that this is also the case during retinal degeneration. Rd1 mice carry a recessive defect (Pdeóbrd/rd) that causes retinal degeneration and serves as a model of retinitis pigmentosa. We found that photoreceptors express Cdk4 and Cdk2, and undergo DNA synthesis prior to cell death. To interfere with the reactivation of Cdk-related pathways, we deleted E2fs or Brni1, which normally allow cell cycle progression. While deleting E2f1 (downstream of Cdk4/6) in Rd1 mice provides only temporary protection, knocking out Bmi1 (upstream of Cdks) leads to an extensive neuroprotective effect, independent of p16ink4a or p19arf, two tumor suppressors regulated by Bmi1. Analysis of Cdks and the DNA repair-related protein Ligase IV showed that Bmi1 acts downstream of DNA repair events and upstream of Cdks in this neurodegenerative mechanism. Expression of Cdks during an acute model of retinal degeneration, light damage-induced photoreceptor death, points to a role for Bmi1 and cell cycle proteins in retinal degeneration. Considering the similarity with the cell cycle-related apoptotic pathway observed in other neurodegenerative diseases, Bmi1 is a possible general target to prevent or delay neuronal death. RESUME : Ce travail aborde plusieurs aspects de la régulation du cycle cellulaire, de la spécification du devenir des cellules et de la mort cellulaire dans le système nerveux centrale (SNC), plus particulièrement dans le cortex cérébral et dans la rétine. Nous nous sommes intéressés au gène Bmi1, appartenant à la famille polycomb et nécessaire à la prolifération et au renouvellement des cellules souches. Nous avons visé à disséquer son rôle dans le développement du cortex et de la rétine. Ces données, ainsi qu'une série de travaux publiés au cours des deux dernières décennies concernant la réactivation du cycle cellulaire dans les neurones en voie d'apoptose dans le SNC, nous ont ensuite poussé à chercher un lien entre la régulation du cycle cellulaire pendant le développement et au cours de la dégénérescence rétinienne. 1. Les effets de l'inactivation de Bmi1 dans le cortex cérébral : En accord avec l'incapacité des cellules souches neurales in vitro à proliférer et à se renouveler en absence de Bmi1, le cortex cérébral des souris Bmi1-/- présente de légers défauts de prolifération dans les compartiments contenant les cellules souches neurales. Ceci est en accord avec le profil d'expression de Bmi1 dans le télencéphale. Les conséquences de la délétion de Bmi1 sont toutefois nettement moins prononcées in vivo qu'in vitro ; cette différence suggère l'existence de mécanismes pouvant partiellement compenser l'absence de Bmi1 pendant la corticogenèse. Néanmoins, l'observation d'une réduction de la prolifération dans la zone sous-ventriculaire, la zone majeure de neurogenèse dans le télencéphale adulte, montre que Bmi1 contrôle la prolifération des cellules souche/progénitrices neurales chez la souris adulte. Nos résultats démontrent par ailleurs une augmentation de la production d'astrocytes à la naissance ainsi qu'une gliose généralisée à l'état adulte chez les souris Bmi1-/-. Les progéniteurs gliaux et les astrocytes conservent donc leur capacité à proliférer en absence de Bmi1. 2. Les effets de l'inactivation de Bmi1 dans la rétine : Le profil d'expression de Bmi1 pendant fe développement ainsi que dans la rétine adulte suggère un rôle de Bmi1 dans la spécification de certains types cellulaires et dans la différentiation plutôt que dans la prolifération. Alors que la structure et la lamination de la rétine semblent normales chez les souris Bmi1-/-, l'analyse par immunohistochimie amis en évidence des défauts au niveau des trois classes d'interneurones rétiniens (les cellules horizontales, bipolaires et amacrines). Les électrorétinogrammes des souris Bmi1-/- sont cohérents avec les défauts observés au niveau histologique et montrent une réduction de l'onde « b » et des potentiels oscillatoires. Ces résultats montrent que Bmi1 contrôle la génération de certaines sous-populations de neurones, comme démontré auparavant au niveau de cervelet. 3. Réactivation du cycle cellulaire et stratégies théraoeutiaues dans les dégénérescences rétiniennes : Dans plusieurs maladies neurodégénératives, les neurones ré-expriment des protéines du cycle cellulaire telles que les kinases cycline-dépendantes (Cdk) avant d'entrer en apoptose. Nous avons démontré que c'est aussi le cas dans les dégénérescences rétiniennes. Les souris Rd1 portent une mutation récessive (Pde6brd/rd) qui induit une dégénérescence de la rétine et sont utilisées comme modèle animal de rétinite pigmentaire. Nous avons observé que les photorécepteurs expriment Cdk4 et Cdk2, et entament une synthèse d'ADN avant de mourir par apoptose. Pour interférer avec la réactivation les mécanismes Cdk-dépendants, nous avons inactivé les gènes E2f et Bmi1, qui permettent normalement la progression du cycle cellulaire. Nous avons mis en évidence que la délétion de E2f1 (en aval de Cdk4/6) dans les souris Rd1 permet une protection transitoire des photorécepteurs. Toutefois, l'inactivation de Bmi1 (en amont des Cdk) est corrélée à une neuroprotection bien plus durable et ceci indépendamment de p16ink4a et p19arf, deux suppresseurs de tumeurs normalement régulés par Bmi1. L'analyse des Cdk et de la ligase IV (une protéine impliquée dans les mécanismes de réparation de l'ADN) a montré que Bmi1 agit en aval des événements de réparation de l'ADN et en amont des Cdk dans la cascade apoptotique dans les photorécepteurs des souris Rd1. Nous avons également observé la présence de Cdk dans un modèle aigu de dégénérescence rétinienne induit par une exposition des animaux à des niveaux toxiques de lumière. Nos résultats suggèrent donc un rôle général de Bmi1 et des protéines du cycle cellulaire dans les dégénérescences de la rétine. Si l'on considère la similarité avec les événements de réactivation du cycle cellulaire observés dans d'autres maladies neurodégénératives, Bmi1 pourrait être une cible thérapeutique générale pour prévenir la mort neuronale.

Differential transgene expression profiles in rat brain, using rAAV2/1 vectors with tetracycline-inducible and cytomegalovirus promoters.

The biodistribution of transgene expression in the CNS after localized stereotaxic vector delivery is an important issue for the safety of gene therapy for neurological diseases. The cellular specificity of transgene expression from rAAV2/1 vectors (recombinant adeno-associated viral vectors pseudotyped with viral capsids from serotype 1) using the tetracycline-inducible (TetON) expression cassette in comparison with the cytomegalovirus (CMV) promoter was investigated in the rat nigrostriatal pathway. After intrastriatal injection, although green fluorescent protein (GFP) was expressed mainly in neurons with both vectors, the relative proportions of DARPP-32-positive projection neurons and parvalbumin-positive interneurons were, respectively, 13:1 and 2:1 for the CMV and TetON vectors. DARP32-positive neurons projecting to the globus pallidus were strongly GFP positive with both vectors, whereas those projecting to the substantia nigra pars reticulata (SNpr) were efficiently labeled by the CMV vector but poorly by the TetON vector. Numerous GFP-positive cells were evidenced in the subventricular zone with both vectors. However, in the olfactory bulb (OB), GFP-positive neurons were observed with the CMV vector but not the TetON vector. We conclude that the absence of significant amounts of transgene product in distant regions (SN and OB) constitutes a safety advantage of the AAV2/1-TetON vector for striatal gene therapy. Midbrain injections resulted in selective GFP expression in tyrosine hydroxylase-positive neurons by the TetON vector whereas with the CMV vector, GFP-positive cells covered a widespread area of the midbrain. The biodistribution of GFP protein corresponded to that of the transcripts and not of the viral genomes. We conclude that the rAAV2/1-TetON vector constitutes an interesting tool for specific transgene expression in midbrain dopaminergic neurons.

Reelin controls progenitor cell migration in the healty and pathological adult brain

Understanding the signals that control migration of neural progenitor cells in the adult brain may provide new therapeutic opportunities. Reelin is best known for its role in regulating cell migration during brain development, but we now demonstrate a novel function for reelin in the injured adult brain. First, we show that Reelin is upregulated around lesions. Second, experimentally increasing Reelin expression levels in healthy mouse brain leads to a change in the migratory behavior of subventricular zone-derived progenitors, triggering them to leave the rostral migratory stream (RMS) to which they are normally restricted during their migration to the olfactory bulb. Third, we reveal that Reelin increases endogenous progenitor cell dispersal in periventricular structures independently of any chemoattraction but via cell detachment and chemokinetic action, and thereby potentiates spontaneous cell recruitment to demyelination lesions in the corpus callosum. Conversely, animals lacking Reelin signaling exhibit reduced endogenous progenitor recruitment at the lesion site. Altogether, these results demonstrate that beyond its known role during brain development, Reelin is a key player in post-lesional cell migration in the adult brain. Finally our findings provide proof of concept that allowing progenitors to escape from the RMS is a potential therapeutic approach to promote myelin repair.

The Oncoprotein BCL11A Binds to Orphan Nuclear Receptor TLX and Potentiates its Transrepressive Function

Nuclear orphan receptor TLX (NR2E1) functions primarily as a transcriptional repressor and its pivotal role in brain development, glioblastoma, mental retardation and retinopathologies make it an attractive drug target. TLX is expressed in the neural stem cells (NSCs) of the subventricular zone and the hippocampus subgranular zone, regions with persistent neurogenesis in the adult brain, and functions as an essential regulator of NSCs maintenance and self-renewal. Little is known about the TLX social network of interactors and only few TLX coregulators are described. To identify and characterize novel TLX-binders and possible coregulators, we performed yeast-two-hybrid (Y2H) screens of a human adult brain cDNA library using different TLX constructs as baits. Our screens identified multiple clones of Atrophin-1 (ATN1), a previously described TLX interactor. In addition, we identified an interaction with the oncoprotein and zinc finger transcription factor BCL11A (CTIP1/Evi9), a key player in the hematopoietic system and in major blood-related malignancies. This interaction was validated by expression and coimmunoprecipitation in human cells. BCL11A potentiated the transrepressive function of TLX in an in vitro reporter gene assay. Our work suggests that BCL11A is a novel TLX coregulator that might be involved in TLX-dependent gene regulation in the brain.

The fetal hypothalamus has the potential to generate cells with a gonadotropin releasing hormone (GnRH) phenotype.

BACKGROUND: Neurospheres (NS) are colonies of neural stem and precursor cells capable of differentiating into the central nervous system (CNS) cell lineages upon appropriate culture conditions: neurons, and glial cells. NS were originally derived from the embryonic and adult mouse striatum subventricular zone. More recently, experimental evidence substantiated the isolation of NS from almost any region of the CNS, including the hypothalamus. METHODOLOGY/FINDINGS: Here we report a protocol that enables to generate large quantities of NS from both fetal and adult rat hypothalami. We found that either FGF-2 or EGF were capable of inducing NS formation from fetal hypothalamic cultures, but that only FGF-2 is effective in the adult cultures. The hypothalamic-derived NS are capable of differentiating into neurons and glial cells and most notably, as demonstrated by immunocytochemical detection with a specific anti-GnRH antibody, the fetal cultures contain cells that exhibit a GnRH phenotype upon differentiation. CONCLUSIONS/SIGNIFICANCE: This in vitro model should be useful to study the molecular mechanisms involved in GnRH neuronal differentiation.

Nolz1 promotes striatal neurogenesis through the regulation of retinoic acid signaling

Background: Nolz1 is a zinc finger transcription factor whose expression is enriched in the lateral ganglionic eminence (LGE), although its function is still unknown. Results: Here we analyze the role of Nolz1 during LGE development. We show that Nolz1 expression is high in proliferating neural progenitor cells (NPCs) of the LGE subventricular zone. In addition, low levels of Nolz1 are detected in the mantle zone, as well as in the adult striatum. Similarly, Nolz1 is highly expressed in proliferating LGE-derived NPC cultures, but its levels rapidly decrease upon cell differentiation, pointing to a role of Nolz1 in the control of NPC proliferation and/or differentiation. In agreement with this hypothesis, we find that Nolz1 over-expression promotes cell cycle exit of NPCs in neurosphere cultures and negatively regulates proliferation in telencephalic organotypic cultures. Within LGE primary cultures, Nolz1 over-expression promotes the acquisition of a neuronal phenotype, since it increases the number of β-III tubulin (Tuj1)- and microtubule-associated protein (MAP)2-positive neurons, and inhibits astrocyte generation and/or differentiation. Retinoic acid (RA) is one of the most important morphogens involved in striatal neurogenesis, and regulates Nolz1 expression in different systems. Here we show that Nolz1 also responds to this morphogen in E12.5 LGE-derived cell cultures. However, Nolz1 expression is not regulated by RA in E14.5 LGE-derived cell cultures, nor is it affected during LGE development in mouse models that present decreased RA levels. Interestingly, we find that Gsx2, which is necessary for normal RA signaling during LGE development, is also required for Nolz1 expression, which is lost in Gsx2 knockout mice. These findings suggest that Nolz1 might act downstream of Gsx2 to regulate RA-induced neurogenesis. Keeping with this hypothesis, we show that Nolz1 induces the selective expression of the RA receptor (RAR)β without altering RARα or RARγ. In addition, Nozl1 over-expression increases RA signaling since it stimulates the RA response element. This RA signaling is essential for Nolz1-induced neurogenesis, which is impaired in a RA-free environment or in the presence of a RAR inverse agonist. It has been proposed that Drosophila Gsx2 and Nolz1 homologues could cooperate with the transcriptional co-repressors Groucho-TLE to regulate cell proliferation. In agreement with this view, we show that Nolz1 could act in collaboration with TLE-4, as they are expressed at the same time in NPC cultures and during mouse development. Conclusions: Nolz1 promotes RA signaling in the LGE, contributing to the striatal neurogenesis during development.

Nolz1 promotes striatal neurogenesis through the regulation of retinoic acid signaling

Background: Nolz1 is a zinc finger transcription factor whose expression is enriched in the lateral ganglionic eminence (LGE), although its function is still unknown. Results: Here we analyze the role of Nolz1 during LGE development. We show that Nolz1 expression is high in proliferating neural progenitor cells (NPCs) of the LGE subventricular zone. In addition, low levels of Nolz1 are detected in the mantle zone, as well as in the adult striatum. Similarly, Nolz1 is highly expressed in proliferating LGE-derived NPC cultures, but its levels rapidly decrease upon cell differentiation, pointing to a role of Nolz1 in the control of NPC proliferation and/or differentiation. In agreement with this hypothesis, we find that Nolz1 over-expression promotes cell cycle exit of NPCs in neurosphere cultures and negatively regulates proliferation in telencephalic organotypic cultures. Within LGE primary cultures, Nolz1 over-expression promotes the acquisition of a neuronal phenotype, since it increases the number of β-III tubulin (Tuj1)- and microtubule-associated protein (MAP)2-positive neurons, and inhibits astrocyte generation and/or differentiation. Retinoic acid (RA) is one of the most important morphogens involved in striatal neurogenesis, and regulates Nolz1 expression in different systems. Here we show that Nolz1 also responds to this morphogen in E12.5 LGE-derived cell cultures. However, Nolz1 expression is not regulated by RA in E14.5 LGE-derived cell cultures, nor is it affected during LGE development in mouse models that present decreased RA levels. Interestingly, we find that Gsx2, which is necessary for normal RA signaling during LGE development, is also required for Nolz1 expression, which is lost in Gsx2 knockout mice. These findings suggest that Nolz1 might act downstream of Gsx2 to regulate RA-induced neurogenesis. Keeping with this hypothesis, we show that Nolz1 induces the selective expression of the RA receptor (RAR)β without altering RARα or RARγ. In addition, Nozl1 over-expression increases RA signaling since it stimulates the RA response element. This RA signaling is essential for Nolz1-induced neurogenesis, which is impaired in a RA-free environment or in the presence of a RAR inverse agonist. It has been proposed that Drosophila Gsx2 and Nolz1 homologues could cooperate with the transcriptional co-repressors Groucho-TLE to regulate cell proliferation. In agreement with this view, we show that Nolz1 could act in collaboration with TLE-4, as they are expressed at the same time in NPC cultures and during mouse development. Conclusions: Nolz1 promotes RA signaling in the LGE, contributing to the striatal neurogenesis during development.

The regulation of adult hippocampal neurogenesis by wheel running and environmental enrichment

Introduction: Chez les mammifères, la naissance de nouveaux neurones se poursuit à l’âge adulte dans deux régions du cerveau: 1) l’hippocampe et 2) la zone sous-ventriculaire du prosencéphale. La neurogenèse adulte n’est pas un processus stable et peut être affectée par divers facteurs tels que l’âge et la maladie. De plus, les modifications de la neurogenèse peuvent être à l’origine des maladies de sorte que la régulation ainsi que le rétablissement de la neurogenèse adulte doivent être considérés comme d’importants objectifs thérapeutiques. Chez la souris saine ou malade, la neurogenèse hippocampale peut être fortement régulée par l’enrichissement environnemental ainsi que par l’activité physique. Cependant, lors même que l’activité physique et l’enrichissement environnemental pourraient contribuer au traitement de certaines maladies, très peu d’études porte sur les mécanismes moléculaires et physiologiques responsables des changements qui sont en lien avec ces stimuli. Objectifs et hypothèses: Les principaux objectifs de cette étude sont de caractériser les effets de stimuli externes sur la neurogenèse et, par le fait même, d’élucider les mécanismes sous-jacents aux changements observés. En utilisant le modèle d’activité physique volontaire sur roue, cette étude teste les deux hypothèses suivantes: tout d’abord 1) qu’une période prolongée d’activité physique peut influencer la neurogenèse adulte dans le prosencéphale et l’hippocampe, et 2) que l’activité volontaire sur roue peut favoriser la neurogenèse à travers des stimuli dépendants ou indépendants de la course. Méthodes: Afin de valider la première hypothèse, nous avons utilisé un paradigme incluant une activité physique volontaire prolongée sur une durée de six semaines, ainsi que des analyses immunohistochimiques permettant de caractériser l’activité de précurseurs neuronaux dans la zone sous-ventriculaire et l’hippocampe. Ensuite, pour valider la seconde hypothèse, nous avons utlisé une version modifiée du paradigme ci-dessous, en plaçant les animaux (souris) soit dans des cages traditionnelles, soit dans des cages munies d’une roue bloquée soit dans des cages munies d’une roue fonctionnelle. Résultats: En accord avec la première hypothèse, l’activité physique prolongée volontaire a augmenté la prolifération des précurseurs neuronaux ainsi que la neurogenèse dans le gyrus dentelé de l’hippocampe comparativement aux animaux témoins, confirmant les résultats d’études antérieures. Par ailleurs, dans ce paradigme, nous avons aussi observé de la prolifération acrue au sein de la zone sous-ventriculaire du prosencéphale. De plus, en accord avec la seconde hypothèse, les souris placées dans une cage à roue bloquée ont montré une augmentation de la prolifération des précurseurs neuronaux dans l’hippocampe comparable à celle observée chez les souris ayant accès à une roue fonctionnelle (coureurs). Cependant, seuls les animaux coureurs ont présenté une augmentation de la neurogenèse hippocampale. Conclusions: Ces résultats nous ont permis de tirer deux conclusions nouvelles concernant les effets de l’activité physique (course) sur la neurogenèse. Premièrement, en plus de la prolifération et de la neurogenèse dans le gyrus dentelé de l’hippocampe, la prolifération dans la zone sous-ventriculaire du prosencéphale peut être augmentée par l’activité physique sur roue. Deuxièmement, l’environnement dans lequel l’activité physique a lieu contient différents stimuli qui peuvent influencer certains aspects de la neurogenèse hippocampale en l’absence d’activité physique sur roue (course).

Molecular mechanisms underlying deficient neurogenesis in Alzheimer’s disease

La neurogenèse est présente, dans le cerveau adulte, dans la zone sous-ventriculaire (ZSV) encadrant les ventricules latéraux et dans le gyrus dentelé (GD) de l’hippocampe, permettant l’apprentissage, la mémoire et la fonction olfactive. Ces micro-environnements possèdent des signaux contrôlant l’auto-renouvellement des cellules souches neurales (CSN), leur prolifération, leur destin et leur différenciation. Or, lors du vieillissement, les capacités régénératives et homéostatiques et la neurogenèse déclinent. Les patients atteints de la maladie d’Alzheimer (MA), comme le modèle animal reproduisant cette maladie (3xTg-AD), montrent une accélération des phénotypes liés au vieillissement dont une diminution de la neurogenèse. Notre hypothèse est que la découverte des mécanismes affectant la neurogenèse, lors du vieillissement et de la MA, pourrait fournir de nouvelles cibles thérapeutiques pour prévenir le déclin cognitif. Les études sur l’âge d’apparition et les mécanismes altérant la neurogenèse dans la MA sont contrastées et nous ont guidé vers deux études. L’examen des changements dans les étapes de la neurogenèse lors du vieillissement et du développement de la neuropathologie. Nous avons étudié la ZSV, les bulbes olfactifs et le GD de souris femelles de 11 et 18 mois, et l’apparition des deux pathologies associées à la MA : les plaques amyloïdes et les enchevêtrements neurofibrillaires. Nous avons découvert que les souris 3xTg-AD possèdent moins de cellules en prolifération, de progéniteurs et de neuroblastes, induisant une diminution de l’intégration de nouvelles cellules dans le GD et les bulbes olfactifs. Notons que le taux de neurogenèse chez ces souris de 11 mois est similaire à celui des souris de phénotype sauvage de 18 mois, indiquant une accélération des changements liés au vieillissement dans la MA. Dans la ZSV, nous avons aussi démontré une accumulation de gouttelettes lipidiques, suggérant des changements dans l’organisation et le métabolisme de la niche. Enfin, nous avons démontré que le déficit de la neurogenèse apparait lors des premières étapes de la MA, avant l’apparition des plaques amyloïdes et des enchevêtrements neurofibrillaires. A l’examen des mécanismes inhibant la neurogenèse lors de la MA, nous voyons que chez des souris de 5 mois, le déficit de la neurogenèse dans la ZSV et le GD est corrélé avec l’accumulation de lipides, qui coïncide avec l’apparition du déclin cognitif. Nous avons aussi découvert que dans le cerveau humain de patients atteints de la MA et dans les 3xTg-AD, des gouttelettes lipidiques s’accumulaient dans les cellules épendymaires, représentant le principal soutien des CSN de la niche. Ces lipides sont des triglycérides enrichis en acide oléique qui proviennent de la niche et pas d’une défaillance du système périphérique. De plus, l’infusion locale d’acide oléique chez des souris de phénotype sauvage permet de reproduire l’accumulation de triglycérides dans les cellules épendymaires, comme dans la MA. Ces gouttelettes induisent un dérèglement de la voie de signalisation Akt-FoxO3 dans les CSN, menant à l’inhibition de leur activation in vitro et in vivo. Ces résultats permettent une meilleure compréhension de la régulation de la neurogenèse par le métabolisme lipidique. Nous avons démontré un nouveau mécanisme par lequel l’accumulation des lipides dans la ZSV induit une inhibition des capacités de prolifération et de régénération des CSN lors de la MA. Les travaux futurs permettront de comprendre comment et pourquoi le métabolisme lipidique du cerveau est altéré dans la MA, ce qui pourrait offrir de nouvelles voies thérapeutiques pour la prévention et la régénération.