[Show abstract][Hide abstract] ABSTRACT: Reelin spielt als extrazelluläres Matrixprotein eine wichtige Rolle bei der Regulation der neuronalen Migration und bei der Schichtenbildung im Gehirn.
Die vorliegende Arbeit hatte das Ziel, Faktoren zu untersuchen, welche die Expression von Reelin beeinflussen könnten. Zum einen untersuchten wir, ob frühkindlicher Stress bei Mäusen auf die Reelin-Expression einwirkt; zusätzlich wurde der Einfluss von CASK, einem MAGUK-Protein, analysiert, da CASK in vitro im Verdacht steht, die Expression von Reelin regulieren zu können.
Für CASK, das als Gerüstprotein auch die Eigenschaft besitzt, in den Kern einzuwandern und dort im Komplex mit Tbr-1 und weiteren Proteinen auf die Expression verschiedener Gene regulierend einzuwirken, konnten wir zeigen, dass eine Reduktion der Proteinkonzentration im Gehirn zu regionenspezifischen Veränderungen der Reelin-Expression führt. Während im Cortex die Reduktion von CASK zu keinen messbaren Effekten führt (weder morphologisch noch auf Ebene der Expression von Reelin), wird im Hippocampus und im Kleinhirn bei einer verringerten Menge an CASK auch die Expression von Reelin reduziert. Zusätzlich kommt es zu leichten Veränderungen im Erscheinungsbild des Gehirns (Stauchung des Hippocampus bei verringertem Volumen, Verkleinerung des Cerebellums), welches ansonsten eine normale Schichtenbildung in Cortex und Hippocampus aufweist und morphologisch normal erscheint.
Frühkindlicher Stress hingegen als von außen einwirkender Faktor kann die Reelin-Expression stark beeinflussen. Je nach Manipulation der Tiere kommt es ausschließlich in männlichen Mäusen zu einer Stimulation der Reelin-Expression verglichen mit reizarm aufgewachsenen Tieren, wobei auch nach 70 Tagen die Stimulation noch anhält. Es gibt starke Hinweise darauf, dass dieser geschlechtsspezifische Effekt durch Corticosteron vermittelt wird, da das Glucocorticoid-Rezeptoren aktivierende Corticosteron nur in Schnittkulturen aus männlichen Mäusen die Expression von Reelin stimuliert - ein Effekt, der durch RU 38486, einen Antagonisten von Corticosteron am Glucocorticoid-Rezeptor, wieder ausgeschaltet werden kann.
[Show abstract][Hide abstract] ABSTRACT: Early life stress predisposes to the development of psychiatric disorders. In this context the hippocampal formation is of particular interest, because it is affected by stress on the structural and cognitive level. Since little is known how early life stress is translated on the molecular level, we mimicked early life stress in mouse models and analyzed the expression of the glycoprotein Reelin, a master molecule for development and differentiation of the hippocampus. From postnatal day 1 (P1) to P14, mouse pups were subjected to one of the following treatments: nonhandling (NH), handling (H), maternal separation (MS), and early deprivation (ED) followed by immediate (P15) or delayed (P70) real time RT-PCR analysis of reelin mRNA expression. We show that at P15, reelin mRNA levels were significantly increased in male H and ED groups when compared with the NH group. In contrast, no stress-induced alterations of reelin mRNA expression were found in female animals. This sex difference in stress-mediated stimulation of reelin expression was maintained into adulthood, since at P70 intergroup differences were still found in male, but not in female mice. On the cellular level, however, we did not find any significant differences in cell densities of Reelin-immunolabeled neurons between treatment groups or sexes, but an overall reduction of Reelin-expressing neurons in the adult hippocampus when compared to P15. To address the question whether corticosterone mediates the stress-induced up-regulation of reelin gene expression, we used age-matched hippocampal slice cultures derived from male and female mouse pups. Quantitative determination of mRNA levels revealed that corticosterone treatment significantly up-regulated reelin mRNA expression in male, but not in female hippocampi. Taken together, these results show a sex-specific regulation of reelin gene expression by early life experience, most likely mediated by corticosterone.
[Show abstract][Hide abstract] ABSTRACT: J. Neurochem. (2012) 121, 924–931.
β-Carbolines (BCs) belong to the heterogenous family of carbolines, which have been found exogenously, that is, in various fruits, meats, tobacco smoke, alcohol and coffee, but also endogenously, that is, blood, brain and CSF. These exogenous and endogenous BCs and some of their metabolites can exert neurotoxic effects, however, an unexpected stimulatory effect of 9-methyl-β-carboline (9-me-BC) on dopaminergic neurons in primary mesencephalic cultures was recently discovered. The aim of the present study was to extend our knowledge on the stimulatory effects of 9-me-BC and to test the hypothesis that 9-me-BC may act as a cognitive enhancer. We found that 10 days (but not 5 days) of pharmacological treatment with 9-me-BC (i) improves spatial learning in the radial maze, (ii) elevates dopamine levels in the hippocampal formation, and (iii) results after 10 days of treatment in elongated, more complex dendritic trees and higher spine numbers on granule neurons in the dentate gyrus of 9-me-BC-treated rats. Our results demonstrate that beyond its neuroprotective/neurorestorative and anti-inflammatory effects, 9-me-BC acts as a cognitive enhancer in a hippocampus-dependent task, and that the behavioral effects may be associated with a stimulatory impact on hippocampal dopamine levels and dendritic and synaptic proliferation.
Full-text · Article · Mar 2012 · Journal of Neurochemistry
[Show abstract][Hide abstract] ABSTRACT: The extracellular matrix protein Reelin is an essential regulator of neuronal migration and lamination in the developing and mature brain. Lack of Reelin causes severe disturbances in cerebral layering, such as the reeler phenotype and granule cell dispersion in temporal lobe epilepsy. Reelin is synthesized and secreted by Cajal-Retzius cells and GABAergic interneurons, and its function depends on proteolytic cleavage after secretion. The mechanisms regulating these processes are largely unknown. Here, we used rat hippocampal slice cultures to investigate the effect of neuronal activation and hyperexcitation on Reelin synthesis, secretion, and proteolytic processing. We show that enhanced neuronal activity does not modulate Reelin synthesis or secretion. Moreover, we found that intracellular Reelin resides predominantly in the endoplasmic reticulum before it is constitutively secreted via the early secretory pathway. Epileptiform activity, however, impairs the proteolytic processing of Reelin and leads to accumulation of Reelin in the extracellular matrix. We found that both conditions, epileptiform activity and impaired proteolytic cleavage of Reelin, cause granule cell dispersion via inhibition of metalloproteinases. Taken together, our results strongly suggest that secretion of Reelin is activity-independent and that proteolytic processing of Reelin is required for the maintenance of granule cell lamination in the dentate gyrus.
Full-text · Article · Dec 2010 · The FASEB Journal
[Show abstract][Hide abstract] ABSTRACT: CASK is a multi-domain scaffolding protein that interacts with the transcription factor TBR1 and regulates expression of genes involved in cortical development such as RELN. Here we describe a previously unreported X-linked brain malformation syndrome caused by mutations of CASK. All five affected individuals with CASK mutations had congenital or postnatal microcephaly, disproportionate brainstem and cerebellar hypoplasia, and severe mental retardation.
[Show abstract][Hide abstract] ABSTRACT: Granule cell dispersion (GCD) in the dentate gyrus is a frequent feature of Ammon's horn sclerosis (AHS) which is often associated with temporal lobe epilepsy (TLE). It has been hypothesized that GCD may be caused by an abnormal migration of newly born granule cells. To test this hypothesis, we used markers of proliferation and neurogenesis and immunocytochemical methods as well as quantitative Western blot and real-time RT-PCR analyses in surgically resected hippocampi from TLE patients and controls. Below the age of 1 year, Ki-67-immunopositive nuclei were detected in the subgranular zone of the dentate gyrus, but not in the dentate of TLE patients independent of age. The expression of the proliferation marker minichromosome maintenance protein 2 (mcm2) and of doublecortin (DCX) decreased significantly with age in controls and in TLE patients, but the expression of both proteins was independent of the degree of AHS and GCD. Quantitative real-time RT-PCR confirmed these findings at the level of gene expression. In contrast, immunocytochemistry for glial fibrillary acidic protein (GFAP) and vimentin as well as Golgi staining revealed a radially aligned glial network in the region of GCD. GFAP-positive fiber length significantly increased with the severity of GCD. These results indicate that epileptic activity does not stimulate neurogenesis in the human dentate gyrus and that GCD probably does not result from a malpositioning of newly generated granule cells, but rather from an abnormal migration of mature granule cells along a radial glial scaffold.
Full-text · Article · Mar 2007 · Experimental Neurology
[Show abstract][Hide abstract] ABSTRACT: Mesio-temporal lobe epilepsy (MTLE) is often accompanied by granule cell dispersion (GCD), a widening of the granule cell layer. The molecular determinants of GCD are poorly understood. Here, we used an animal model to study whether GCD results from an increased dentate neurogenesis associated with an abnormal migration of the newly generated granule cells. Adult mice were given intrahippocampal injections of kainate (KA) known to induce focal epileptic seizures and GCD, comparable to the changes observed in human MTLE. Ipsilateral GCD progressively developed after KA injection and was paralleled by a gradual decrease in the expression of doublecortin, a marker of newly generated granule cells, in the dentate subgranular layer. Staining with Fluoro-Jade B revealed little cell degeneration in the subgranular layer on the KA-injected side. Labeling with bromodeoxyuridine showed an early, transient increase in mitotic activity in the dentate gyrus of the KA-injected hippocampus that gave rise to microglial cells and astrocytes but not to new neurons. Moreover, at later time points, there was a virtually complete cessation of mitotic activity in the injected hippocampus (where GCD continued to develop), but not on the contralateral side (where no GCD was observed). Finally, a significant decrease in reelin mRNA synthesis in the injected hippocampus paralleled the development of GCD, and neutralization of reelin by application of the CR-50 antibody induced GCD. These results show that GCD does not result from increased neurogenesis but reflects a displacement of mature granule cells, most likely caused by a local reelin deficiency.
Full-text · Article · May 2006 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Mesio-temporal lobe epilepsy (MTLE) is often accompanied by granule cell dispersion (GCD), a widening of the granule cell layer. The molecular determinants of GCD are poorly understood. Here, we used an animal model to study whether GCD results from an increased dentate neurogenesis associated with an abnormal migration of the newly generated granule cells. Adult mice were given intrahippocampal injections of kainate (KA) known to induce focal epileptic seizures and GCD, comparable to the changes observed in human MTLE. Ipsilateral GCD progressively developed after KA injection and was paralleled by a gradual decrease in the expression of doublecortin, a marker of newly generated granule cells, in the dentate subgranular layer. Staining with Fluoro-Jade B revealed little cell degeneration in the subgranular layer on the KA-injected side. Labeling with bromodeoxyuridine showed an early, transient increase in mitotic activity in the dentate gyrus of the KA-injected hippocampus that gave rise to microglia