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Articles de revues sur le sujet "Tanyctes"
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Yoo, Sooyeon, Juhyun Kim, Pin Lyu, Thanh V. Hoang, Alex Ma, Vickie Trinh, Weina Dai et al. « Control of neurogenic competence in mammalian hypothalamic tanycytes ». Science Advances 7, no 22 (mai 2021) : eabg3777. http://dx.doi.org/10.1126/sciadv.abg3777.
Texte intégralRésumé :
Hypothalamic tanycytes, radial glial cells that share many features with neuronal progenitors, can generate small numbers of neurons in the postnatal hypothalamus, but the identity of these neurons and the molecular mechanisms that control tanycyte-derived neurogenesis are unknown. In this study, we show that tanycyte-specific disruption of the NFI family of transcription factors (Nfia/b/x) robustly stimulates tanycyte proliferation and tanycyte-derived neurogenesis. Single-cell RNA sequencing (scRNA-seq) and single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) analysis reveals that NFI (nuclear factor I) factors repress Sonic hedgehog (Shh) and Wnt signaling in tanycytes and modulation of these pathways blocks proliferation and tanycyte-derived neurogenesis in Nfia/b/x-deficient mice. Nfia/b/x-deficient tanycytes give rise to multiple mediobasal hypothalamic neuronal subtypes that can mature, fire action potentials, receive synaptic inputs, and selectively respond to changes in internal states. These findings identify molecular mechanisms that control tanycyte-derived neurogenesis, which can potentially be targeted to selectively remodel the hypothalamic neural circuitry that controls homeostatic physiological processes.
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Wittmann, Gabor, Surbhi Gahlot, Malcolm James Low et Ronald M. Lechan. « Rax Expression Identifies a Novel Cell Type in the Adult Mouse Hypothalamus ». Journal of the Endocrine Society 5, Supplement_1 (1 mai 2021) : A42. http://dx.doi.org/10.1210/jendso/bvab048.082.
Texte intégralRésumé :
Abstract Hypothalamic tanycytes are radial glia-like ependymal cells lining the ventrolateral walls and floor of the third ventricle. Recent data show that tanycytes are adult neural stem/progenitor cells, capable of generating neurons that populate the adjacent hypothalamic nuclei involved in the regulation of feeding and energy balance. Thus, the genetic fate mapping of tanycytes has become an invaluable tool to identify and study tanycyte-derived adult-born hypothalamic neurons. Perhaps the most selective tanycyte marker identified to date is the retina and anterior neural fold homeobox (Rax), that has been used as a tanycyte marker in multiple single-cell transcriptomic studies. By using in situ hybridization and immunofluorescence, we show that Rax mRNA and RAX protein are also expressed in a minor but significant population of parenchymal cells that are concentrated in the caudal arcuate nucleus. RAX-positive nuclei in the parenchyma were often observed in pairs, suggesting recent cell divisions. The morphology of these cells was studied in tamoxifen-treated Rax-CreERT2; Ai34(RCL-Syp/tdT)-D mice, in which the synaptophysin-tdTomato fusion protein permanently labels Rax-expressing cells and their progeny. While some parenchymal RAX-positive cells had tanycyte-like morphology indicative of tanycyte migration into the parenchyma, the majority had a very different morphology with extensive local processes that often encircled adjacent neurons (termed “frizzy cells”). The tdTomato labeling also revealed numerous frizzy cells that were negative for RAX, indicating downregulation of endogenous Rax expression subsequent to the induction of synaptophysin-tdTomato reporter expression. Many of these cells were distributed outside the caudal arcuate nucleus, including the rostral lateral arcuate nucleus, ventromedial and dorsomedial hypothalamic nuclei and lateral hypothalamus. RAX-negative frizzy cells were also conspicuous in the paraventricular nucleus, and occasionally observed in the preoptic region and bed nucleus of the stria terminalis. Frizzy cells were negative for the tanycyte-enriched proteins vimentin, monocarboxylate transporter 8 (MCT8) or glial fibrillary acidic protein (GFAP). These results identify a novel Rax-expressing cell type in the adult hypothalamus that differs from tanycytes in location, morphology and gene expression characteristics. Future studies are required to determine whether frizzy cells are derived from tanycytes or constitute a separate cell lineage, and whether they represent a migratory form of neural precursor cells in the adult hypothalamus.
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Bolborea, Matei, Marie-Pierre Laran-Chich, Kamontip Rasri, Herbert Hildebrandt, Piyarat Govitrapong, Valérie Simonneaux, Paul Pévet, Stephan Steinlechner et Paul Klosen. « Melatonin Controls Photoperiodic Changes in Tanycyte Vimentin and Neural Cell Adhesion Molecule Expression in the Djungarian Hamster (Phodopus sungorus) ». Endocrinology 152, no 10 (16 août 2011) : 3871–83. http://dx.doi.org/10.1210/en.2011-1039.
Texte intégralRésumé :
The Djungarian hamster displays photoperiodic variations in gonadal size synchronized to the seasons by the nightly secretion of the pineal hormone melatonin. In short photoperiod (SP), the gonads regress in size, and circulating sex steroids levels decline. Thus, the brain is subject to seasonal variations of both melatonin and sex steroids. Tanycytes are specialized glial cells located in the ependymal lining of the third ventricle. They send processes either to the meninges or to blood vessels of the medio-basal hypothalamus. Furthermore, they are known to locally modulate GnRH release in the median eminence and to display seasonal structural changes. Seasonal changes in tanycyte morphology might be mediated either through melatonin or sex steroids. Therefore, we analyzed the effects of photoperiod, melatonin, and sex steroids 1) on tanycyte vimentin expression by immunohistochemistry and 2) on the expression of the neural cell adhesion molecule (NCAM) and polysialic acid as markers of brain plasticity. Vimentin immunostaining was reduced in tanycyte cell bodies and processes in SP. Similarly, tanycytes and their processes contained lower amounts of NCAM in SP. These changes induced by SP exposure could not be restored to long photoperiod (LP) levels by testosterone supplementation. Likewise, castration in LP did not affect tanycyte vimentin or NCAM expression. By contrast, late afternoon melatonin injections mimicking a SP-like melatonin peak in LP hamsters reduced vimentin and NCAM expression. Thus, the seasonal changes in vimentin and NCAM expression in tanycytes are regulated by melatonin independently of seasonal sex steroid changes.
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de Vries, E. M., J. Kwakkel, L. Eggels, A. Kalsbeek, P. Barrett, E. Fliers et A. Boelen. « NFκB Signaling Is Essential for the Lipopolysaccharide-Induced Increase of Type 2 Deiodinase in Tanycytes ». Endocrinology 155, no 5 (1 mai 2014) : 2000–2008. http://dx.doi.org/10.1210/en.2013-2018.
Texte intégralRésumé :
The enzyme type 2 deiodinase (D2) is a major determinant of T3 production in the central nervous system. It is highly expressed in tanycytes, a specialized cell type lining the wall of the third ventricle. During acute inflammation, the expression of D2 in tanycytes is up-regulated by a mechanism that is poorly understood at present, but we hypothesized that cJun N-terminal kinase 1 (JNK1) and v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) (the 65 kD subunit of NFκB) inflammatory signal transduction pathways are involved. In a mouse model for acute inflammation, we studied the effects of lipopolysaccharide (LPS) on mRNA expression of D2, JNK1, and RelA in the periventricular area (PE) and the arcuate nucleus-median eminence of the hypothalamus. We next investigated LPS-induced D2 expression in primary tanycyte cell cultures. In the PE, the expression of D2 was increased by LPS. In the arcuate nucleus, but not in the PE, we found increased RelA mRNA expression. Likewise, LPS increased D2 and RelA mRNA expression in primary tanycyte cell cultures, whereas JNK1 mRNA expression did not change. Phosphorylation of RelA and JNK1 was increased in tanycyte cell cultures 15–60 minutes after LPS stimulation, confirming activation of these pathways. Finally, inhibition of RelA with the chemical inhibitors sulfasalazine and 4-Methyl-N1-(3-phenylpropyl)benzene-1,2-diamine (JSH-23) in tanycyte cell cultures prevented the LPS-induced D2 increase. We conclude that NFκB signaling is essential for the up-regulation of D2 in tanycytes during inflammation.
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Jawad, Haider, Muthanna Al-Kaabi et Anam Al-Salihi. « IMMUNOHISTOCHEMICAL EXPRESSION OF MONOCARBOXYLATE TRANSPORTER 1&4 IN TANYCYTE–LIKE CELLS OF THE SULCUS MEDIANUS ORGANUM ». Iraqi Journal of Medical Sciences 17, no 1 (31 mars 2019) : 83–99. http://dx.doi.org/10.22578/ijms.17.1.12.
Texte intégralRésumé :
Background: Circumventricular organs (CVOs) are specialized structures border the brain ventricles and lack the blood-brain barrier. These CVOs are lined by specialized ependymal cells (ECs) called tanycyte. The sulcus medianus organum (SMO) locates at the floor of the 4th ventricle at the rostral part of the sulcus medianus (SM). Objective: To explore the expression of the monocarboxylate transporter 1 and monocarboxylate transporter 4 (MCT1 & MCT4) in the tanycytes of the median eminence (ME) and tanycyte-like cells of the SMO to add a functional evidence for describing the SMO as another CVOs and to start a roadmap for the citing the SMO specifically as a sensory or a secretory CVO. Methods: Ten adult male rats (Rattus norvegicus albinus), aged 3-6 months with 300±50 g, were used to study the histological characteristics of ECs in ME and SMO with Hematoxylin & Eosin and to explore the immunohistochemical expression of MCT1 & MCT4 in ME and SMO. Results: The ependymal cells were arranged in in 2-3 layers in the depth of SMO region and single layer in the ME region as seen with H&E stains. Immunohistochemical expression of MCT1 & MCT4 using Aperioscope image analysis in tanycytes of the ME is higher than that in tanycyte-like cells of the SMO with significant differences between the two regions as proved by t-test. Conclusion: the SMO has different structural and functional properties compared to ME suggesting that the SMO may be a sensory CVO. Keywords: Circumventricular organs, tanycytes, sulcus medianus organum, median eminence Citation: Jawad HF, Al-Kaabi MA, Al-Salihi AR. Immunohistochemical expression of monocarboxylate transporter 1&4 in tanycyte–like cells of the sulcus medianus organum. Iraqi JMS. 2019; 17(1): 83-99. doi: 10.22578/IJMS.17.1.12
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de Seranno, Sandrine, Xavier d'Anglemont de Tassigny, Cecilia Estrella, Anne Loyens, Sergey Kasparov, Danièle Leroy, Sergio R. Ojeda, Jean-Claude Beauvillain et Vincent Prevot. « Role of Estradiol in the Dynamic Control of Tanycyte Plasticity Mediated by Vascular Endothelial Cells in the Median Eminence ». Endocrinology 151, no 4 (4 février 2010) : 1760–72. http://dx.doi.org/10.1210/en.2009-0870.
Texte intégralRésumé :
In the ever-changing physiological context of the neuroendocrine brain, the mechanisms by which cellular events involving neurons, astroglia, and vascular cells are coordinated to bring forth the appropriate neuronal signaling is not yet known but is amenable to examination. In the median eminence of the hypothalamus, endothelial cells are key players in the plasticity of tanycytes (specialized astroglia) and neuroendocrine synapse efficacy. Here we report that estradiol acts on both purified endothelial cells and isolated tanycytes to trigger endothelial-to-glial communication that leads to a sudden and massive retraction of tanycyte processes. The blockade of endothelial nitric oxide synthase by in vitro adenoviral-mediated gene transfer of a dominant-negative form of endothelial nitric oxide synthase abrogates the estradiol-induced tanycyte plasticity mediated by endothelial cells. In parallel, increases in prostaglandin-E2 (PGE2) due to changes in cyclooxygenase (COX)-1 and COX-2 expression induced by the exposure of tanycytes to estradiol promote acute tanycyte plasticity. We also demonstrate by electron microscopy that the administration of PGE2 to median eminence explants induces rapid neuroglial plasticity at the neurovascular junction of neurons that release GnRH (the neuropeptide controlling reproduction). Conversely, preventing local PGE2 synthesis in the median eminence of adult female rats with the COX inhibitor indomethacin impairs the ovarian cycle, a process that requires a pulsatile, coordinated delivery of GnRH into the hypothalamo-hypophyseal portal system. Taken together, our findings show that estradiol controls the dialog between endothelial cells and astroglia to regulate neuroglial plasticity in the neuroendocrine brain.
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Bolborea, Matei, Gisela Helfer, Francis J. P. Ebling et Perry Barrett. « Dual signal transduction pathways activated by TSH receptors in rat primary tanycyte cultures ». Journal of Molecular Endocrinology 54, no 3 (30 mars 2015) : 241–50. http://dx.doi.org/10.1530/jme-14-0298.
Texte intégralRésumé :
Tanycytes play multiple roles in hypothalamic functions, including sensing peripheral nutrients and metabolic hormones, regulating neurosecretion and mediating seasonal cycles of reproduction and metabolic physiology. This last function reflects the expression of TSH receptors in tanycytes, which detect photoperiod-regulated changes in TSH secretion from the neighbouringpars tuberalis. The present overall aim was to determine the signal transduction pathway by which TSH signals in tanycytes. Expression of the TSH receptor in tanycytes of 10-day-old Sprague Dawley rats was observed byin situhybridisation. Primary ependymal cell cultures prepared from 10-day-old rats were found by immunohistochemistry to express vimentin but not GFAP and by PCR to express mRNA forDio2,Gpr50,Darpp-32andTshreceptors that are characteristic of tanycytes. Treatment of primary tanycyte/ependymal cultures with TSH (100 IU/l) increased cAMP as assessed by ELISA and induced a cAMP-independent increase in the phosphorylation of ERK1/2 as assessed by western blot analysis. Furthermore, TSH (100 IU/l) stimulated a 2.17-fold increase inDio2mRNA expression. We conclude that TSH signal transduction in cultured tanycytes signals via Gαsto increase cAMP and via an alternative G protein to increase phosphorylation of ERK1/2.
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Sánchez, Edith, Praful S. Singru, Gábor Wittmann, Shira S. Nouriel, Perry Barrett, Csaba Fekete et Ronald M. Lechan. « Contribution of TNF-α and Nuclear Factor-κB Signaling to Type 2 Iodothyronine Deiodinase Activation in the Mediobasal Hypothalamus after Lipopolysaccharide Administration ». Endocrinology 151, no 8 (25 mai 2010) : 3827–35. http://dx.doi.org/10.1210/en.2010-0279.
Texte intégralRésumé :
To determine whether signaling through TNF and/or nuclear factor-κB contributes to bacterial lipopolysaccharide (LPS)-induced activation of type 2 iodothyronine deiodinase (D2) in tanycytes lining the floor and infralateral walls of the third ventricle, the effect of a TNF antagonist on D2 gene expression and LPS-induced Iκ-Bα expression in tanycytes were studied. Animals treated with soluble, rat, polyethylene glycol-conjugated TNF receptor type 1 (4 mg/kg body weight) before a single ip injection of LPS showed a significant reduction in circulating IL-6 levels but no effect on LPS-induced D2 mRNA in the majority of tanycytes with the exception of a subpopulation of α tanycytes in the wall of the third ventricle. LPS induced a rapid increase in Iκ-Bα mRNA in the pars tuberalis and a delayed response in α tanycytes but absent in all other tanycyte subsets. The LPS-induced increase in Iκ-Bα in the pars tuberalis was associated with increased TSHβ gene expression in this tissue, but cAMP response element-binding protein (CREB) phosphorylation was observed only in a subset of α tanycytes. These data suggest that TNF and nuclear factor-κB signaling are not the primary, initiating mechanisms mediating the LPS-induced D2 response in tanycytes, but may contribute in part to sustaining the LPS-induced D2 response in a subset of α tanycytes. We hypothesize that in addition to TSH, other factors derived from the pars tuberalis may contribute to LPS-induced D2 activation in tanycytes.
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Porniece Kumar, Marta, Anna Lena Cremer, Paul Klemm, Lukas Steuernagel, Sivaraj Sundaram, Alexander Jais, A. Christine Hausen et al. « Insulin signalling in tanycytes gates hypothalamic insulin uptake and regulation of AgRP neuron activity ». Nature Metabolism 3, no 12 (décembre 2021) : 1662–79. http://dx.doi.org/10.1038/s42255-021-00499-0.
Texte intégralRésumé :
AbstractInsulin acts on neurons and glial cells to regulate systemic glucose metabolism and feeding. However, the mechanisms of insulin access in discrete brain regions are incompletely defined. Here we show that insulin receptors in tanycytes, but not in brain endothelial cells, are required to regulate insulin access to the hypothalamic arcuate nucleus. Mice lacking insulin receptors in tanycytes (IR∆Tan mice) exhibit systemic insulin resistance, while displaying normal food intake and energy expenditure. Tanycytic insulin receptors are also necessary for the orexigenic effects of ghrelin, but not for the anorexic effects of leptin. IR∆Tan mice exhibit increased agouti-related peptide (AgRP) neuronal activity, while displaying blunted AgRP neuronal adaptations to feeding-related stimuli. Lastly, a highly palatable food decreases tanycytic and arcuate nucleus insulin signalling to levels comparable to those seen in IR∆Tan mice. These changes are rooted in modifications of cellular stress responses and of mitochondrial protein quality control in tanycytes. Conclusively, we reveal a critical role of tanycyte insulin receptors in gating feeding-state-dependent regulation of AgRP neurons and systemic insulin sensitivity, and show that insulin resistance in tanycytes contributes to the pleiotropic manifestations of obesity-associated insulin resistance.
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Barrett, Perry, Elena Ivanova, E. Scott Graham, Alexander W. Ross, Dana Wilson, Helene Plé, Julian G. Mercer et al. « Photoperiodic regulation of cellular retinoic acid-binding protein 1, GPR50 and nestin in tanycytes of the third ventricle ependymal layer of the Siberian hamster ». Journal of Endocrinology 191, no 3 (décembre 2006) : 687–98. http://dx.doi.org/10.1677/joe.1.06929.
Texte intégralRésumé :
Tanycytes in the ependymal layer of the third ventricle act both as a barrier and a communication gateway between the cerebrospinal fluid, brain and portal blood supply to the pituitary gland. However, the range, importance and mechanisms involved in the function of tanycytes remain to be explored. In this study, we have utilized a photoperiodic animal to examine the expression of three unrelated gene sequences in relation to photoperiod-induced changes in seasonal physiology and behaviour. We demonstrate that cellular retinoic acid-binding protein 1 (CRBP1), a retinoic acid transport protein, GPR50, an orphan G-protein-coupled receptor and nestin, an intermediate filament protein, are down-regulated in short-day photoperiods. The distribution of the three sequences is very similar, with expression located in cells with tanycyte morphology in the region of the ependymal layer where tanycytes are located. Furthermore, CRBP1 expression in the ependymal layer is shown to be independent of a circadian clock and altered testosterone levels associated with testicular regression in short photo-period. Pinealectomy of Siberian hamsters demonstrates CRBP1 expression is likely to be dependent on melatonin output from the pineal gland. This provides evidence that tanycytes are seasonally responsive cells and are likely to be an important part of the mechanism to facilitate seasonal physiology and behaviour in the Siberian hamster.
Thèses sur le sujet "Tanyctes"
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Bellamy, Charlotte. « Functional characterization of a novel mutation in PRKCA, the major driver of Chordoid glioma ». Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASL052.
Texte intégralRésumé :
Le gliome chordoïde (ChG) est une tumeur cérébrale rare de bas grade, caractérisée par une nouvelle mutation ponctuelle récurrente PRKCA p.D463H, une substitution dans le domaine kinase de la protéine kinase C alpha (PKCα). Cette étude démontre le rôle de cette kinase mutée dans le développement des ChG. Ici, nous montrons l'inactivation et l'effet négatif dominant de PKCαD463H via des tests d'activité in vitro et in cellulo. Nos résultats montrent que la mutation affecte la structure tertiaire, ce qui entraîne une protéine ouverte et instable. Les données de spectrométrie de masse phosphoprotéomique et de co-immunoprécipitation des cellules HEK surexprimant PKC⍺D463H montrent une diminution de phosphorylation et interaction avec les protéines impliquées dans l'adhésion cellulaire. Nous confirmons génétiquement par le RNAseq à noyau unique que les ChG dérivent de tanycytes spécialisés. En comprenant le contexte cellulaire de la tumorigenèse ainsi que les changements fonctionnels de cette mutation sur l'activité et l'interactome de PKCα, nous avons élaboré un modèle de développement des ChGs parallèlement à l'identification d'une approche thérapeutiqueChordoid glioma (ChG) is a rare low-grade brain tumor, characterised by a novel recurrent point mutation PRKCA p.D463H, a substitution in the kinase domain of Protein kinase C alpha (PKCα). This study demonstrates the role of this mutated kinase in the development of ChGs. Here we show the inactivation and dominant negative effect of PKCαD463H via in vitro and In cellulo activity assays. Our results show the mutation affects the tertiary structure, resulting in an open, unstable protein. Phosphoproteomic and Co-Immunoprecipitation mass spectrometry data from HEK cells overexpressing PKC⍺D463H show decreased phosphorylation and interaction with proteins involved in cell adhesion. We confirm genetically through single nuclei RNAseq that ChGs derive from specialised tanycytes. By understanding the cell context of tumorigenesis alongside the functional changes of this mutation on the activity and interactome of PKCα, we elaborated a model of the development of ChGs alongside the identification of a therapeutic approach
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Benford, Heather Elizabeth. « Signalling in hypothalamic tanycytes ». Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/62112/.
Texte intégralRésumé :
Hypothalamic tanycytes are a specialised type of glial cell found lining the 3rd ventricle. They possess a cell body that contacts the cerebrospinal fluid (CSF) and a single long process that projects into the hypothalamic parenchyma, some of which are known to extend into the Arcuate nucleus (ARC) and Ventromedial nucleus (VMN), two key hypothalamic regions involved in control of energy homeostasis. Owing to their unique position, it has been hypothesised that hypothalamic tanycytes may be able to detect nutrient related signals in the CSF and influence the neurons of the ARC and VMN leading to changes in food intake and body weight. Tanycytes have recently been shown to be glucosensitive, responding to brief application of glucose by generating Ca2+ waves. However the signalling pathways inducing this response remain elusive. Here we investigated the nature of tanycyte glucosensing. Using Ca2+ imaging techniques we show that tanycytes can respond to glucose and non-nutritive sweeteners implicating the sweet taste receptor as the mediator of tanycyte glucosensitivity. We further show that activation of the sweet taste receptor induces release of ATP from tanycytes via pannexin hemichannels allowing propagation of the Ca2+wave. In addition we also investigated whether hypothalamic tanycytes can communicate to secondary cells within the hypothalamus. Using multiphoton stimulation of a single tanycyte, we show that Ca2+ waves can be generated, which spread between neighbouring cells as well as along the tanycyte process towards the hypothalamic parenchyma. We also demonstrate signalling in secondary cells following tanycyte stimulation is likely the result of tanycyte communication. Thus hypothalamic tanycytes are able to detect sweet tasting compounds in the CSF via the sweet taste receptor, this induces Ca2+ signalling which may be communicated to secondary cells, including the neurons of the ARC and VMN, where it may be integrated to induce changes in energy homeostasis.
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Lazutkaite, Greta. « Amino acid sensing in hypothalamic tanycytes via umami taste receptors ». Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/109627/.
Texte intégralRésumé :
Energy homeostasis is controlled in the hypothalamus. Hypothalamic tanycytes are a type of glial cell that lie in the wall of the third ventricle, between ventricular CSF and the key nuclei controlling feeding, and are potentially linked to this regulation. Tanycytes have been found to express sweet taste receptors; similar receptors exist for amino acids and could be present in tanycytes. Therefore, the aims of this work were to understand the tanycyte amino acid signalling process, determine the impact of diet on tanycyte function, and link tanycytes to energy homeostasis. Using ratiometric Ca2+ imaging, I showed that tanycytes responded to amino acids; the responses also involved ATP release via pannexin 1 and CalHM1 from tanycyte cell bodies and down their processes towards the parenchyma. As IMP increased the amplitude of tanycyte responses to some amino acids, one of the receptors is Tas1r1/Tas1r3. The Tas1r1 subunit was expressed in mouse tanycytes, and Tas1r1-null mice showed sex-specific altered responses to arginine and lysine. mGluR4 antagonist MAP4 reduced the responses to alanine, and mGluR4 was shown to be present in mouse tanycytes. Tas1r1/Tas1r3 and mGluR4 are therefore two of the receptors responsible for tanycyte amino acid signalling. Fasting and essential amino acid deprivation increased tanycyte sensitivity to alanine. Essential amino acid-deprived diet also reduced the intake of an alanine-enriched drink. While amino acid-imbalanced diets did not have strong effects on mouse metabolism over 24 hours, increasing dietary alanine content reduced feeding and increased metabolism in the light phase. These results demonstrate for the first time that tanycytes can detect amino acids, and that they do so via two different pathways, similarly to taste receptor cells in the tongue. Tanycytes can send ATP signals to inform the hypothalamus about nutrient availability. The data also show that tanycyte amino acid sensitivity is diet-dependent. High alanine food has a satiating effect, which could be partially mediated by tanycytes, although a direct link cannot be confirmed at this stage.
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Cappellini, Prieto Monica. « Transplantation de tanycytes dans la moelle épinière de rats adultes ». Montpellier 2, 2000. http://www.theses.fr/2000MON20109.
Texte intégralRésumé :
Il a ete recemment demontre que les tanycytes, type particulier de cellules gliales present dans l'hypothalamus mediobasal, favorisent la survie et la regeneration de nombreux types de neurones centraux. Dans cette etude, nous avons voulu utiliser ces proprietes particulieres des tanycytes afin de tenter de reparer la moelle epiniere lesee en fournissant un support favorable a la regeneration des neurones supraspinaux. Dans un premier temps, nous avons greffe des tanycytes soit dans la moelle epiniere intacte de rats adultes, soit dans la moelle epiniere lesee par compression. Cette etude nous a montre que dans tous les cas, les tanycytes survivaient mal et disparaissaient des 6 h apres la transplantation. Dans un deuxieme temps nous avons donc tente d'identifier in vitro les facteurs responsables de la disparition des tanycytes implantes au niveau lesionnel. Cette etude nous a permis de montrer que contrairement aux astrocytes matures, les tanycytes tout comme les astrocytes immatures, sont sensibles aux radicaux libres generes par l'h 2o 2. Dans un troisieme temps nous avons tente de mettre en oeuvre une protection des tanycytes transplantes vis a vis des radicaux libres. Nous avons montre que les vitamines c et e protegent les tanycytes d'un stress oxydatif in vitro et in vivo lorsque les tanycytes sont transplantes dans une moelle epiniere non lesee. Dans ce cas, les cellules survivent dans le tissu lesionnel et sont envahies par de nombreuses fibres axonales nf-, 5-ht-, th- et cgrp- positives. Cependant, ce traitement ne suffit pas a proteger les tanycytes lorsqu'ils sont transplantes dans une moelle epiniere lesee par compression. Nous avons combine la protection des tanycytes transplantes par les vitamines c et e et la neuroprotection de la moelle epiniere lesee par le lazaroide anti-oxydant u74500-a. Un tel traitement nous a permis de retrouver un greffon de tanycytes, 3 semaines apres compression totale de la moelle epiniere chez 2 des 6 rats traites. Dans chacun de ces deux cas, le greffon etait envahis par de nombreuses fibres axonales 3-tubuline positives. Ceci permet de penser que lorsqu'ils sont proteges des radicaux libres, les tanycytes representent un support permettant la regeneration des axones medullaires leses.
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Balland, Églantine. « Rôle des tanycytes de l’éminence médiane dans le transport de la leptine de la périphérie vers l’hypothalamus ». Thesis, Lille 2, 2012. http://www.theses.fr/2012LIL2S053.
Texte intégralRésumé :
Le noyau arqué hypothalamique (ARH) est un composant majeur des circuits neuronaux qui régulent la balance énergétique. Cependant les mécanismes d’entrée des hormones périphériques dans l’ARH sont peu connus. L’ARH est adjacent à l’éminence médiane (ME), où des cellules épendymales hautement spécialisées appelées tanycytes son tprésentes. Les corps cellulaires des tanycytes bordent le troisième ventricule et leurs prolongements basaux contactent le plexus de capillaires fenêtrés de la ME. Récemment, il a été proposé que les tanycytes joueraient un rôle dans la régulation de la barrière sang hypothalamus métabolique. Leur localisation privilégiée à l’interface entre le sang et le cerveau suggère que ces cellules pourraient être la cible directe de nombreux signaux hormonaux périphériques, incluant l’hormone adipocytaire qu’est la leptine. La compréhension des mécanismes régissant le transport de la leptine est fondamentale car cela apporterait de nouvelles pistes pour la détermination des mécanismes cellulaires impliqués dans la résistance à la leptine accompagnant l’obésité.Le but de ce travail de thèse était de déterminer si les tanycytes de la ME pouvaient être responsable du transport de la leptine vers l’hypothalamus et dans ce cas, si ils pouvaient être impliqués dans les mécanismes de résistance à la leptine associée à l’obésité.Dans un premier temps, nous avons étudié le transport de la leptine vers l’hypothalamus à travers diverses approches. Les expériences de western-blots ont révélé que la leptine injectée en périphérie est retrouvée de manière séquentielle dans la ME puis dans le MBH, de plus le délai d’activation du récepteur à la leptine suit la même séquence. Par ailleurs, nous avons observé que la leptine s’accumule dans la ME n’atteignant pas l’hypothalamus chez les souris obèses (modèles db/db et DIO) qui ont perdu la capacité à activer le récepteur à la leptine. L’utilisation de leptine fluorescente a permis de démontrer que la leptine est internalisée de manière polarisée dans les tanycytes de la ME,l’internalisation a lieu au niveau des prolongements qui contactent les capillaires fenêtrés puis la leptine est transportée vers le pôle apical. De plus, nous avons démontré par immunohistochimie que ces tanycytes constituent le premier type cellulaire de la ME à répondre à une injection prériphérique de leptine par l’activation de P-STAT3.L’administration d’un antagoniste de la leptine a permis de mettre en évidence que l’internalisation de la leptine dans les tanycytes est dépendante de l’activation du récepteur à la leptine.L’utilisation d’un modèle in vitro, les cultures primaires de tanycytes, constitue un outil permettant l’étude détaillée des mécanismes responsables du transport de la leptine. Les expériences menées sur ces cultures ont confirmé les résultats obtenus in vivo et montrent que la libération de la leptine par les tanycytes, étape du transport qui est bloquée chez les souris obèses, est sous la dépendance de l’activation de la voie de signalisation ERK. L’utilisation d’un agent pharmacologique capable d’activer la voie de signalisation ERK dans les tanycytes permet de restaurer le transport de la leptine de la ME vers le MBH chez les souris obèses.En définitive, ces résultats apportent d’importantes informations sur la compréhension du transport central de la leptine et pourraient aider à expliquer les mécanismes responsables de la résistance à la leptine associée à l’obésitéThe arcuate nucleus of the hypothalamus (ARH) is a critical component of the neural circuits that regulate energy balance. However, little is known about how peripheral signals reach the ARH to mediate their central effects. The ARH is adjacent to the median eminence (ME), where highly specialized ependymal cells called tanycytes are found. The cell bodies of tanycytes are lining the floor of the third ventricle and their end-feet are contacting the rich capillary plexus with fenestrated endothelium of the ME. Tanycytes have recently been proposed to play a role in blood-hypothalamus barrier regulation. Their privileged location at the interface between the blood and the brain suggests that these cells might be direct target for a variety of peripheral signals, including the adipocyte-derived hormone leptin. The understanding of leptin transport mechanisms is fundamental as it may provide new insights into cellular processes involved in leptin resistance linked to obesity.The aim of this work was to determine wether tanycytes of the median eminence could be responsible for leptin entry in the hypothalamus and in this case if they could be involved in the mechanisms responsible for obesity-associated leptin resistance.We first investigated leptin uptake into the hypothalamus through several approaches in vivo. Western-blot experiments revealed that peripherally injected leptin is sequentially found in ME and later in MBH, moreover the timing of the leptin receptor activation appears to follow the same sequence. In contrast, we observed that leptin failed to reach the hypothalamus and was seen to accumulate in the ME in obese mice (db/db and DIO models) that has lost the capacity of activating LepRb signaling pathways in the ME. The use of fluorescent leptin demonstrated that leptin is internalized in ΜΕ tanycytes in a polarized manner, leptin is uptaken at the level of the basal processes contacting fenestrated capillaries and transported toward the apical pole. In addition, we showed that these tanycytes are the first cell type in the median eminence to respond to peripheral leptin injection through the activation of P-STAT3 detected by immunohistochemistry. The use of a leptin antagonist showed the dependence of leptin receptor(s) activation for leptin internalization in tanycytes. Then, the use of tanycyte primary cultures as an in vitro model system allowed us to study leptin transport mechanisms more in detail. Experiments performed on cultured tanycytes confirmed our in vivo findings and showed that the release of leptin from tanycytes, which is blocked in obese mice, depends on the activation of the X signaling pathway. The use of a pharmacological compound able to activate the X signaling pathway in tanycytes can rescue leptin transport from ME to MBH in obese mice. Altogether this data may provide valuable information in the understanding of central leptin transport and may help to explain mechanism underlying obesity-associated leptin resistance
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Barbotin, Anne-Laure. « Plasticité neuro-structurale de l’hypothalamus dans le syndrome des ovaires polykystiques ». Thesis, Lille, 2019. http://www.theses.fr/2019LILUS043.
Texte intégralRésumé :
L’hormone anti-Müllerienne (AMH) dont les taux dans le sérum sont élevés dans le Syndrome des Ovaires Polykystiques (SOPK) est connue pour augmenter la sécrétion de LH/GnRH. Comme mis en évidence récemment, cette augmentation de la sécrétion de GnRH pourrait être liée à une hyperactivité des neurones à GnRH en réponse à une action directe de l’AMH mais pourrait également s’exercer indirectement via une augmentation des afférences excitatrices sur les neurones à GnRH. Par ailleurs, les tanycytes, qui enchâssent les terminaisons des neurones à GnRH, expriment le récepteur à l’AMH et sont connus pour moduler la plasticité neuro-structurale de l’hypothalamus. Ainsi, notre objectif est de tester les deux hypothèses suivantes dans un modèle animal et chez la femme. Est-ce que la physiopathologie du SOPK : 1- Est liée à une rétraction des tanycytes provoquée par l’AMH, entraînant l’augmentation des sécrétions de GnRH / LH ? Et/ou 2- Est liée à une augmentation de l’activité des neurones à GnRH AMH-dépendante ?Nous avons étudié la modification de la plasticité morphologique de l’hypothalamus en microscopie électronique en comparant la distance entre les terminaisons des neurones à GnRH et l’espace péri-capillaire entre des éminences médianes de rates en phase de dioestrus de leur cycle oestral (au moment où ces terminaisons sont normalement enfouies par les tanycytes) traitées par de l’AMH et des contrôles. Puis, nous avons comparé cette même distance entre des éminences médianes issues d’un modèle de souris SOPK en comparaison à des contrôles. Enfin, nous avons étudié la plasticité neuro-structurale de l’hypothalamus chez des femmes SOPK et des témoins par une approche en imagerie en comparant les métabolites cérébraux.Nous avons observé une augmentation significative du nombre de terminaisons de neurones à GnRH situées à proximité de l’espace péri-capillaire dans le groupe traité par l’AMH par rapport aux contrôles et nous avons fait les mêmes observations chez les souris SOPK comparées aux contrôles. Par ailleurs, nous avons mis en évidence une augmentation de l’activité neuronale dans le noyau arqué de l’hypothalamus chez des souris SOPK. Or, cette région est particulièrement impliquée dans la régulation de la sécrétion de GnRH. Chez les femmes atteintes de SOPK, nous avons pour la première fois mis en évidence des concentrations plus élevées de GnRH mesurées par spectroscopie de masse par rapport à des femmes normo-ovulantes. Notre étude par IRM, chez les femmes SOPK et contrôles, vient conforter ce résultat en montrant une augmentation de la viabilité/activité neuronale. Cette étude translationnelle suggère que l’augmentation des sécrétions de GnRH/LH rencontrées dans le SOPK serait dépendante d’une part d’un rapprochement de terminaisons à GnRH à l’espace péri-capillaire et d’autre part d’une augmentation de l’activité neuronale hypothalamiquePolycystic ovary syndrome (PCOS) is the most common reproductive disorder (10% of women worldwide). Anti-Müllerian hormone (AMH) levels are found to be 2-3-fold higher in PCOS women than in those with normal ovaries. AMH induces LH secretion by stimulating the activation of GnRH secretion. As recently demonstrated, this increase in GnRH secretion could be related to hyperactivity of GnRH neurons in response to a direct action of AMH but could also be exerted indirectly via an increase in excitatory inputs on GnRH neurons.Our team has previously demonstrated that tanycytes, which unsheathe the terminals of GnRH neurons, regulate GnRH secretion and express AMH receptor. Thus, we aim to determine (1) whether elevated AMH could be responsible for the retraction of the tanycyte coverage leading to increased GnRH/LH secretion in PCOS and (2) whether neuronal hyperactivity in hypothalamus could contribute to higher GnRH activity in PCOS women.Firstly, we have performed ultrastructural studies in rodents’ median eminence (ME) explants challenged with AMH. Then, we compared tanycytic retraction using electron microscopy. We have performed the same experiments in a PCOS mouse model. In humans, we have used metabolic magnetic resonance imaging approaches (i.e. proton magnetic resonance spectra). In order to assess neuronal activity, we have compared N-acetyl-aspartate/creatine ratios in the hypothalamus between PCOS women versus controls.Using electron microscopy, we have shown that tanycytes displayed a significant retraction of their end-feet after AMH treatment ex vivo. This is followed by the sprouting of GnRH terminals towards the pericapillary space. Such processes could significantly favor the sustained delivery of peak levels of GnRH, which could contribute to the rise in LH levels typical of PCOS condition. We have found the same results in PCOS-mouse model with higher GnRH terminals towards the pericapillary space in PCOS mice than in controls. In addition, we found an increase in neuronal activity in the arcuate nucleus of the hypothalamus in PCOS mice. Moreover, this region is particularly involved in the regulation of GnRH secretion. For the first time, we have demonstrated that PCOS women exhibit higher concentrations of GnRH measured by mass spectroscopy than GnRH levels in normo-ovulatory women. Our proton magnetic resonance spectroscopy analysis has revealed that PCOS women exhibit higher N-acetyl aspartate/creatine ratio than controls. These results are predicted to be correlated with increased hypothalamic activity.This translational study suggests that the increase in GnRH / LH secretions found in PCOS could be explained by neurostructural hypothalamic plasticity in link with tanycytes retraction and by an increase of neuronal activity in the hypothalamus
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Mullier, Amandine. « Etude des interfaces sang/cerveau dans la région tubérale de l'hypothalamus médiobasal : rôle des tanycytes de l'éminence médiane ». Phd thesis, Université du Droit et de la Santé - Lille II, 2009. http://tel.archives-ouvertes.fr/tel-00515862.
Texte intégralRésumé :
L'hypothalamus joue un rôle critique dans la régulation des systèmes physiologiques et de l'homéostasie. Il relaie au niveau central les signaux ou hormones sécrétées en périphérie. L'intégration de ces signaux s'effectue au niveau des interfaces sang/cerveau. Trois grandes interfaces sang/cerveau sont décrites au niveau central : la barrière hémato-encéphalique, les plexus choroïdes et les organes circumventriculaires. Alors que les deux premières sont bien caractérisées, les organes circumventriculaires sont mal connus. La région tubérale de l'hypothalamus médiobasal est une région cérébrale organisée autour du troisième ventricule. Elle a la particularité de contenir à la fois des noyaux hypothalamiques impliqués dans la régulation de grandes fonctions neuroendocrines et l'éminence médiane. L'éminence médiane est un organe circumventriculaire caractérisé par la présence de capillaires fenêtrés permettant la diffusion des molécules circulantes dans le parenchyme cérébral. Cependant, l'éminence médiane est également constituée de cellules épendymogliales particulières appelées tanycytes et dont les fonctions sont encore mal connues. Une des hypothèses est que les tanycytes formeraient une interface sang/cerveau impliquée dans la régulation des échanges entre le sang porte et le liquide céphalorachidien. En accord avec cette hypothèse, des expériences d'immunohistochimie entreprises chez la souris adulte nous ont indiqué que les tanycytes expriment des protéines de jonctions serrées et que cette expression et différente selon leur localisation. En effet, les tanycytes ventraux de l'éminence médiane expriment l'occludine, zonula-occludens-1, la claudine 5 et la claudine 1. De façon intéressante, ces protéines sont organisées en forme de nids d'abeilles autour des corps cellulaires des tanycytes. A l'inverse, les tanycytes dorsaux localisés sur les parois latérales du ventricule expriment l'occludine, zonula occludens-1 et la claudine 5 mais ces protéines ne sont pas organisées en nids d'abeille. Parallèlement, des injections de bleu d'Evans ont permis de montrer que seuls les tanycytes ventraux possèdent des jonctions serrées étanches qui restreignent les échanges entre le compartiment sanguin et le liquide céphalorachidien. En revanche, les tanycytes dorsaux sont perméables à la diffusion du bleu d'Evans indiquant ainsi que les échanges entre le liquide céphalorachidien et le noyau arqué hypothalamique ne sont pas restreints. Cette expression différentielle des protéines de jonctions serrées au niveau de la région tubérale de l'hypothalamus médiobasal est retrouvée également chez le rat adulte. De façon intéressante, des études plus poussées montrent que quelque soit le niveau antéropostérieur étudié, la présence de capillaires fenêtrés est toujours corrélée à la présence de tanycytes exprimant des protéines de jonctions serrées sous forme de nids d'abeilles et qui restreignent la communication entre le sang et le liquide céphalorachidien dans l'hypothalamus médiobasal. Ces résultats suggèrent fortement l'existence d'une intercommunication entre tanycytes et cellules endothéliales impliquée dans la mise en place du phénotype de barrière des tanycytes ventraux. Enfin des résultats préliminaires indiquent que les tanycytes expriment également des protéines de jonctions serrées chez l'Homme adulte. Notre travail montre que chez l'adulte, les tanycytes de l'éminence médiane constituent une interface sang/cerveau impliquée dans la régulation des échanges entre le sang porte et le liquide céphalorachidien. En parallèle, ces résultats apportent de nouvelles informations dans la compréhension des mécanismes régulant l'accès des hormones périphériques au noyau arqué hypothalamique et indiquent que l'éminence médiane pourrait être une voie de passage privilégiée vers ce noyau.
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Chauvet, Norbert. « Rôles des tanycytes dans les mécanismes de régénération axonale des neurones du système nerveux central du rat adulte ». Montpellier 2, 1997. http://www.theses.fr/1997MON20160.
Texte intégralRésumé :
Dans le systeme nerveux central des vertebres superieurs adultes, la regeneration axonale est extremement limitee. Cependant, il est connu que les neurones de l'hypothalamus mediobasal sont capables de regenerer. Ce travail a donc ete entrepris afin de comprendre les raisons d'une telle reponse postlesionnelle des neurones hypothalamiques. Les travaux realises sur l'hypothalamus ont permis de mettre en evidence par des approches morphologiques des associations preferentielles entre les axones qui regenerent et les prolongements d'un type particulier de cellules gliales present dans l'hypothalamus mediobasal : les tanycytes. Par la suite, l'obtention de cultures enrichies en tanycytes a permis de confirmer leur influence directe sur ces mecanismes de regeneration a travers des interactions adhesives et d'etendre cette capacite vis-a-vis d'une large variete de neurones centraux. Dans la seconde partie de ce travail nous avons donc tente d'identifier certains facteurs susceptibles d'intervenir dans l'effet trophique des tanycytes. Nous avons ainsi montre que, comme les astrocytes embryonnaires (mais contrairement aux astrocytes matures), les tanycytes expriment des quantites importantes de proteines connues pour leur effet neurotrophique, telles l'app (-like), la laminine, la fibronectine, les hspgs et la ncam. Dans un dernier temps, nous avons transplante des tanycytes dans la moelle epiniere lesee, dans le but de favoriser la regeneration des axons supraspinaux. Dans quelques rares cas, la survie des tanycytes transplantes pourrait avoir permis la regeneration d'un certain nombre d'axones afferents leses. L'ensemble de ces resultats indiquent que contrairement aux astrocytes, les tanycytes constituent un support glial qui favorise la regeneration de nombreux types de neurones centraux. Ceci nous permet d'esperer une utilisation des tanycytes a des fins therapeutiques afin de favoriser la regeneration des neurones adultes leses.
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Chaker, Zayna. « Longevity gene IGF-1 and adult neurogenesis : regulation of lifelong neuronal replacement, olfactory function and metabolism ». Thesis, Paris 5, 2014. http://www.theses.fr/2014PA05T052.
Texte intégralRésumé :
Pas de résuméProduction of new neurons in the brain decreases dramatically with age due to progressive physiological depletion of stem and progenitor cell populations (NSCs). Recent studies indicate that circulating factors constitute a systemic aging milieu regulating the birth of new cells. Interestingly, some long-lived mouse strains such as Ames dwarf mutants, with low circulating levels of GH and IGF-1, show increased neurogenesis and preserved hematopoietic stem cell pool. Thus, the possibility that genes regulating lifespan and aging also quantitatively modulate stem cells in mammals is more and more explored. IGF-1 plays a pivotal role in aging in different species, and I am asking whether some of the well-known longevity effects resulting from down-regulation of this signaling pathway could be explained by local regulation of stem and progenitor cell compartments. To validate this hypothesis, I pursued a dual approach based on biological experiments and mathematical modeling. Using a novel triple transgenic mouse model, I inactivated IGF-1 signaling specifically in adult NSCs, and traced knockout cell lineages with a fluorescent reporter transgene. By analyzing the phenotype at different time points after KO induction, I could distinguish between short and long-term effects of IGF signaling on cellular regeneration and identify cumulative physiological consequences of down-regulation of this pathway using behavioral tests. In my mathematical models, the dynamics of regenerative cell populations were described by a set of differential equations depending on circulating “growth-factor like molecules” (GFs). My results suggest that in aging tissues, the optimal distribution of GFs is a function that decreases with time. In the olfactory system, I showed that inactivation of IGF signaling in adult NSCs enhanced long-term maintenance of neuroblasts and increased the overall production of neurons. Mutants started with the same number of adult-born neurons as controls one month after KO induction at 4 months of age, but ended up having significantly more differentiated cells integrating the olfactory bulb at long-term, i.e. at 16 months of age. This highly increased neurogenic activity occurred without depletion of neural stem/progenitor cell compartments. In contrast, IGF-1R deletion in adult hippocampal stem cells did not change neurogenesis dynamics, pointing out a niche-dependent effect of IGFs. The important cellular changes in the olfactory bulb led to improved olfactory memory and odor discrimination in aged mutants. Strikingly, mutants also displayed altered energy homeostasis and increased sensitivity to metabolic hormones, namely leptin and insulin. This metabolic shift could be linked to enhanced olfactory function, and to changes in hypothalamic neurogenesis. Indeed, we observed that IGF-1R deletion in hypothalamic stem cells (HySC) protected α-tanycyte pool from age-related decline and increased the number of newborn neurons in the hypothalamus. Taken together, my results validate the hypothesis that life-long inhibition of IGF signaling in adult NSCs delays age-related decline of neurogenesis, in a niche-dependent manner. These data also show that local modulation of neural cell replacement has important physiological effects at the level of the whole organism, pointing out a novel pathophysiological role for adult neurogenesis
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Milesi, Sébastien. « Rôle de la signalisation hypothalamique TSH/T3 dans la reproduction saisonnière chez les hamsters Djungariens (Phodopus sungorus) et Syriens (Mesocricetus auratus) ». Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAJ023/document.
Texte intégralRésumé :
Chez les hamsters, les jours longs activent la reproduction. Cette activation photopériodique (AP) impliquerait la mélatonine, l’hormone thyroïdienne (HT) et les RFamides hypothalamiques. Si les jours courts inhibiteurs sont maintenus au-delà de 20 semaines, une réactivation photoréfractaire (RP) de l’axe hypothalamo pituitaire gonadotrope (HPG) est déclenchée. Les mécanismes de cette RP sont inconnus. Notre analyse de la cinétique des changements moléculaires induits par l’AP et la RP montre dans les deux cas une inhibition précoce de l’expression de la Désiodinase 3 (Dio3), l’enzyme catabolisant les HT, dans les tanycytes. Associée à une inhibition tardive du transporteur MCT8 des HT, la diminution de Dio3 pourrait créer un pic d’HT dans l’hypothalamus. Dans les 2 activations, Kisspeptine et RFRP3 augmentent plusieurs semaines après l’inhibition de Dio3 et l’activation de l’HPG. Aussi, une inhibition d’RFRP3 lors de l’AP n’affecte pas l’HPG, mettant en cause le rôle du RFRP3. Nous avons donc découvert une inhibition précoce de Dio3 pouvant induire l’activation saisonnière de l’HPG. Le régulateur saisonnier précoce de Dio3 reste à découvrirIn hamsters, reproduction is activated by long days. This photoactivation (PA) supposedly involves melatonin, hypothalamic thyroid hormones (TH) and RFamide peptides. Maintaining inhibitory short days for over 20 weeks triggers a photorefractory reactivation of the hypothalamo pituito gonadotropic axis (HPG) The mechanisms of this PR are so far unknown. Our cinetic analysis of the dynamic molecular changes in PA and PR revealed a conserved early inhibition of tanycytic deiodinase 3 (Dio3), which catabolizes TH, in both activation mechanisms. Associated with a late decrease of the TH transporter MCT8, the inhibition of Dio3 could generate an early peak of hypothalamic TH. In both activations, RFamide upregulation occurs several weeks after the initial Dio3 inhibition. Also, pharmacological inhibition of RFRP3 during PA does not influence the HPG activity, questioning the role of RFRP3 in HPG activation. We have thus uncovered a so far unreported early Dio3 inhibition that could be sufficient to seasonally reactivate the gonadotropic axis. The seasonal regulator of Dio3 remains to be discovered
Chapitres de livres sur le sujet "Tanyctes"
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Lechan, Ronald M., et Csaba Fekete. « Tanycyte Regulation of Hypophysiotropic TRH Neurons ». Dans Masterclass in Neuroendocrinology, 285–307. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-62383-8_12.
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Barrett, Perry, et Peter J. Morgan. « Tanycytes and Their Pivotal Role in Seasonal Physiological Adaptations ». Dans Neuroendocrine Clocks and Calendars, 55–84. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-55643-3_3.
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Nampoothiri, Sreekala, Manon Duquenne et Vincent Prevot. « Unveiling the Importance of Tanycytes in the Control of the Dialogue Between the Brain and the Periphery ». Dans Masterclass in Neuroendocrinology, 255–84. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-62383-8_11.
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Blackshaw, Seth, Daniel A. Lee, Thomas Pak et Sooyeon Yoo. « Regulation of Body Weight and Metabolism by Tanycyte-Derived Neurogenesis in Young Adult Mice ». Dans Stem Cells in Neuroendocrinology, 51–67. Cham : Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-41603-8_5.
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Hökfelt, T., G. Foster, M. Schultzberg, B. Meister, M. Schalling, M. Goldstein, H. C. Hemmings, C. Ouimet et P. Greengard. « DARPP-32 as a Marker for D-1 Dopaminoceptive Cells in the Rat Brain : Prenatal Development and Presence in Glial Elements (Tanycytes) in the Basal Hypothalamus ». Dans Advances in Experimental Medicine and Biology, 65–82. Boston, MA : Springer US, 1988. http://dx.doi.org/10.1007/978-1-4899-2723-1_6.
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Flament-Durand, J., et J. P. Brion. « Tanycytes : Morphology and Functions : A Review ». Dans International Review of Cytology, 121–55. Elsevier, 1985. http://dx.doi.org/10.1016/s0074-7696(08)60596-3.
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Bernal, Juan. « Deiodinases in the Brain ». Dans Thyroid and Brain : Understanding the Actions of Thyroid Hormones in Brain Development and Function, 39–64. BENTHAM SCIENCE PUBLISHERS, 2024. http://dx.doi.org/10.2174/9789815274226124010007.
Texte intégralRésumé :
Deiodinases (DIO) are central to regulating thyroid hormone action in the brain because they control the tissue concentration of the active hormone triiodothyronine (T3). DIO2, the outer ring, 5’-deiodinase expressed in the brain, converts T4 to T3 and is active primarily in two glial cell types: astrocytes and tanycytes. Astrocytes produce all of brain T3 during the fetal period and a significant fraction in adults. T3 from astrocytes reaches other neural cells, mainly neurons, devoid of DIO2. The T3 produced in the tanycytes travels to hypothalamic nuclei to perform neuroendocrine functions. DIO2 is expressed in the human fetal brain’s neural stem cells, known as outer radial glia. The inner ring, 5-deiodinase DIO3, converts T4 and T3 to the inactive compounds reverse T3 (rT3) and 3,3’T2, respectively, a reaction equivalent to suppressing thyroid hormone action. Brain DIO3 is active mainly in neurons. Thyroid hormones regulate the gene expression and enzymatic activity of DIO2 and DIO3. When T4 concentrations rise, DIO2 activity falls, and when T4 goes down, DIO2 increases. T3 stimulates the DIO3 gene, and DIO3 activity increases when T3 increases. The combined actions of DIO2 and DIO3 exert a “homeostatic-like mechanism” to maintain locally appropriate bioactivity of thyroid hormone by providing individual brain cells with the optimal concentrations of T3 required at different stages of development. These mechanisms regulate thyroid hormone action with a timeline specific to different brain regions.
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RAFOLS, JOSÉ A. « EPENDYMAL TANYCYTES OF THE VENTRICULAR SYSTEM IN VERTEBRATES ». Dans Astrocytes, 131–48. Elsevier, 1986. http://dx.doi.org/10.1016/b978-0-12-250451-8.50009-6.
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Iyer, Lakshmanan K., Joshua A. Ainsley, Csaba Fekete et Ronald M. Lechan. « Digital Expression Profiling of Tanycytes Suggests Molecular Mechanisms for Their Biological Function ». Dans BASIC/TRANSLATIONAL - Pituitary Biology & ; Tumorigenesis, P1–396—P1–396. The Endocrine Society, 2011. http://dx.doi.org/10.1210/endo-meetings.2011.part2.p2.p1-396.
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Prevot, Vincent, Ruben Nogueiras et Markus Schwaninger. « Tanycytes in the infundibular nucleus and median eminence and their role in the blood–brain barrier ». Dans The Human Hypothalamus - Middle and Posterior Region, 253–73. Elsevier, 2021. http://dx.doi.org/10.1016/b978-0-12-820107-7.00016-1.
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