Delineating the Factors and Cellular Mechanisms Involved in the Survival of Cerebellar Granule Neurons

Cerebellar granule neurons (CGNs) constitute the most abundant neuronal population in the mammalian brain. Their postnatal generation and the feasibility to induce their apoptotic death in vitro make them an excellent model to study the effect of several neurotransmitters and neurotrophins. Here, we first review which factors are involved in the generation and proliferation of CGNs in the external granule layer (EGL) and in the regulation of their differentiation and migration to internal granule layer (IGL). Special attention was given to the role of several neurotrophins and the NMDA subtype of glutamate receptor. Then, using the paradigm of potassium deprivation in cultured CGNs, we address several extracellular factors that promote the survival of CGNs, with particular emphasis on the cellular mechanisms. The role of specific protein kinases leading to the regulation of transcription factors and recent data involving the small G protein family is also discussed. Finally, the participation of some members of Bcl-2 family and the inhibition of mitochondria-related apoptotic pathway is also considered. Altogether, these studies evidence that CGNs are a key model to understand the development and the survival of neuronal population

Postulated Vasoactive Neuropeptide Autoimmunity in Fatigue-Related Conditions: A Brief Review and Hypothesis

Disorders such as chronic fatigue syndrome (CFS) and gulf war syndrome (GWS) are characterised by prolonged fatigue and a range of debilitating symptoms of pain, intellectual and emotional impairment, chemical sensitivities and immunological dysfunction. Sudden infant death syndrome (SIDS) surprisingly may have certain features in common with these conditions. Post-infection sequelae may be possible contributing factors although ongoing infection is unproven. Immunological aberration may prove to be associated with certain vasoactive neuropeptides (VN) in the context of molecular mimicry, inappropriate immunological memory and autoimmunity

Etude des effets neuroprotecteurs du peptide PACAP sur la mort neuronale induite par les céramides au cours du développement du cervelet

La mort cellulaire programmée est un processus actif qui joue un rôle important au cours du développement du système nerveux central. Elle permet l élimination par apoptose des neurones générés en excès durant l embryogenèse afin d assurer un développement harmonieux du cerveau. L'apoptose observée au cours du développement met en jeu des processus similaires à ceux décrits lors de pathologies neurodégénératives. La caractérisation des mécanismes impliqués dans la régulation de l apoptose présente donc un intérêt pour le développement de stratégies thérapeutiques innovantes. Il a été montré que le pituitary adenylate cyclase-activating polypeptide (PACAP) exerce une action neuroprotectrice sur l apoptose des neurones en grain du cervelet. Parallèlement, la production de céramides par des cytokines a été décrite comme une voie d induction de l'apoptose. Ces observations suggèrent donc que le PACAP et certaines cytokines pourraient agir de façon opposée sur la décision de survie ou de mort de la cellule. Dans cette thèse, nous démontrons que le PACAP prévient l apoptose des neurones en grain du cervelet induite par les céramides et que ces effets impliquent la mitochondrie. Migration et apoptose des cellules granulaires sont intimement liées au cours du développement. Cependant, peu de données existent concernant les effets des céramides et du PACAP sur la migration des neurones et l élongation neuritique. Nous avons montré que le C2-céramide stimule la migration cellulaire et inhibe l élongation neuritique via une destructuration du cytosquelette. A l inverse, le PACAP réduit la vitesse de migration des neurones et augmente la croissance neuritique. Ces résultats montrent que le PACAP et les céramides régulent de façon opposée la différenciation et l apoptose des neurones en grain. Ils permettent de proposer de nouveaux concepts quant à l implication des cytokines et du PACAP au cours du développement et ouvrent de nouvelles perspectives thérapeutiques pour le traitement des lésions neurodégénératives.Programmed cell death is an active process which plays a key role during central nervous system ontogeny. During embryogenesis, neurons that are generated in excess are eliminated through an apoptotic process to allow harmonious brain development. Apoptosis which occurs during histogenesis involves the same mechanisms as those described during neurodegenerative injuries. The elucidation of the mechanisms regulating apoptosis is thus of crucial interest for the development of novel therapeutical strategies. It has been shown that the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) exerts neuroprotective effects on cerebellar granule cells. Concurrently, the production of the second messengers ceramides induced by cytokine has been described as a pathway inducing apoptosis. These obervations suggest that PACAP and cytokines may act in an opposite manner on cell death/survival decision.In this thesis, we demonstrate that PACAP prevents ceramide-induced cerebellar granule cell apoptosis and that these effects involve mitochondria. Migration and apoptosis of granule cells are closely linked during development. However, very few data are available concerning the effects of ceramides and PACAP on neuronal migration and neuritogenesis. We have demonstrated that C2-ceramide stimulates migration and inhibits neuritogenesis through cytoskeleton disorganization. In contrast, PACAP reduces cell migration and stimulates neurite outgrowth.These results show that PACAP and C2-ceramide exert opposite effects on differentiation and apoptosis of cerebellar granule cells. These data allow to propose new concepts concerning the involvement of cytokines and neuropeptides such as PACAP during development and open novel therapeutical perspectives for the treatment of neurodegenerative injuries.ROUEN-BU Sciences (764512102) / SudocROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Selenoprotein T is a key player in ER proteostasis, endocrine homeostasis and neuroprotection

International audienceSelenoprotein T (SELENOT, SELT) is a thioredoxin-like enzyme anchored at the endoplasmic reticulum (ER) membrane, whose primary structure is highly conserved during evolution. SELENOT is abundant in embryonic tissues and its activity is essential during development since its gene knockout in mice is lethal early during embryogenesis. Although its expression is repressed in most adult tissues, SELENOT remains particularly abundant in endocrine organs such as the pituitary, pancreas, thyroid and testis, suggesting an important role of this selenoprotein in hormone production. Our recent studies showed indeed that SELENOT plays a key function in insulin and corticotropin biosynthesis and release by regulating ER proteostasis. Although SELENOT expression is low or undetectable in most cerebral structures, its gene conditional knockout in brain provokes anatomical alterations that impact mice behavior. This suggests that SELENOT also plays an important role in brain development and function. In addition, SELENOT is induced after injury in brain or liver and exerts a cytoprotective effect. Thus, the data gathered during the last ten years of intense investigation of this newly discovered thioredoxin-like enzyme point to an essential function during development and in adult endocrine organs or lesioned brain, most likely by regulating ER redox circuits that control homeostasis and survival of cells with intense metabolic activity

Granule Cell Survival is Deficient in PAC1(-/-) Mutant Cerebellum.

International audiencePACAP exerts neuroprotective effects during development, especially in the cerebellum where PAC1 receptor and ligand are both expressed. However, while previous studies using PACAP injections in postnatal animals defined trophic effects of exogenous peptide, the role of endogenous PACAP remains unexplored. Here, we used PAC1(-/-) mice to investigate the role of PACAP receptor signaling in postnatal day 7 cerebellum. There was no difference in DNA synthesis in the cerebellar EGL of PAC1(-/-) compared to wild type animals, assessed using thymidine incorporation and BrdU immunohistochemistry. In contrast, we found that a significant proportion of newly generated neurons were eliminated before they successfully differentiated in the granule cell layer. In aggregate, these results suggest that endogenous PACAP plays an important role in cell survival during cerebellar development, through the activation of the PAC1 receptor