Les processus neuro-inflammatoires sont observés dans de nombreux troubles neurodégénératifs. Les cellules microgliales étant les principales cellules immunitaires du système nerveux central, plusieurs recherches ont été menées afin de déterminer des molécules possédant des propriétés anti-inflammatoires au niveau de ces cellules. Une famille de polyphénols, les stilbènes (des dérivés du resvératrol), présentent des activités anti-inflammatoires au niveau périphérique et central. Dans notre étude, nous avons premièrement évalué les propriétés anti-inflammatoires de 25 stilbènes en déterminant leur capacité à inhiber la libération de NO dans un modèle de cellules microgliales BV-2 activées par le LPS. Dix stilbènes inhibent significativement cette production avec des IC50 comprises entre 3,9 ± 0,7 et 23,4 ±1,0 µM. Parmi ces composés, 1 monomère (moracine M) et 2 tétramères du resvératrol (vitisines A et B) diminuent la synthèse d’iNOS, enzyme responsable à la libération de NO, au niveau transcriptionnel et traductionnel. Nous avons ensuite mis en évidence que la moracine M inhibe la phosphorylation d’ERK1/2 et JNK (deux MAPK) et d’Akt (la voie PI3K/Akt) dans des cellules BV-2 activées. Ces enzymes étant impliquées dans la signalisation de la réponse inflammatoire, elles induisent la production de plusieurs médiateurs inflammatoires. La moracine M inhibe significativement la production de certains d'entre eux (NO, TNF-α, IL-1β et PGE2). Ce stilbène attenue également la synthèse de la protéine de mPGEs-1 (enzyme impliquée à la production de PGE2). Ainsi, la moracine M pourrait être un candidat potentiel pour prévenir l’inflammation impliquée dans les maladies neurodégénératives. / Chronic neuro-inflammatory processes observed in many neurodegenerative disorders. Microglia are the main immune cells of the central nervous system. Many studies have been conducted to find molecules with anti-inflammatory properties in the central nervous system. A family of polyphénols, Stilbenoids (resveratrol derivatives), showed anti-inflammatory effects in peripheral and central levels.In this study, we have first evaluated anti-inflammatory effects of 25 stilbenes for their potential to inhibit NO release by LPS-activated BV-2 microglial cells. Ten stilbenes significantly reduced LPS-induced NO production with IC50 ranging from 3.9 ± 0.7 to 23.4 ±1.0 µM. Among these molecules 1 monomer (moracin M) and two tetramers (vitisins A and B) attenuated the expression of iNOS, a responsible enzyme for NO release on transcriptional and translational levels. Then, we have demonstrated that moracin M inhibits ERK1/2 and JNK phosphorylation of MAPK pathway and Akt phosphorylation of PI3K/Akt pathway, two signaling pathways involved in the inflammatory response in activated BV-2 cells. Indeed, the activation of these pathways leads to the production of several inflammatory mediators. We have shown that moracin M significantly inhibits the production of certain mediators such as NO, TNF-α, IL-1β and PGE2. This stilbene reduces the synthesis of mPGES-1 protein (an enzyme involved in the production of PGE2). In conclusion, we suggest that moracine M could be a potential candidate prevents the inflammation which involved in the progress of neurodegenerative diseases.

La dépression est un trouble neurologique grave et la deuxième cause d’invalidité dans le monde. Récemment, la signalisation du récepteur X aux rétinoïdes et l’inflammation chronique ont été identifiées comme facteurs génétiques et environnementaux. Au cours de ma thèse, j'ai étudié la façon dont le récepteur X gamma aux rétinoïdes (RXRg) contrôle la neuroinflammation dans deux modèles précliniques de dépression. J'ai montré que RXRg contrôle un signal spécifique lié à l'âge, entrainant la sénescence et l'hypoactivité des cellules microgliales. Ce signal impacte également la phagocytose microgliale et contribue à l'hypertrophie neuronale dans le striatum, elle-même associée à des symptômes dépressifs. De plus, j'ai pu mettre en évidence une activité antidépressive des rexinoïdes et des fibrates dans le stress de défaite sociale chronique, ainsi que leur mécanisme cellulaire. Les données obtenues pourraient permettre le développement de nouveaux traitements antidépresseurs. / Depression is severe mental disorder that is a second leading contributor to diseases burden. Recently, retinoid X receptor signaling and chronic inflammation have been identified as genetic and environmental factors. However, a cross-talk between these two factors was poorly understood. During my PhD I have studied how retinoid X receptor gamma (RXRg) controls neuroinflammation in two pre-clinical models of depression. I have shown that RXRg controls age-specific signal that drives microglial senescence and hypoactivity. The latter, impacts also microglial phagocytosis and contribute to neuronal hypertrophy in the striatum that previously was associated with depressive symptoms. Additionally, I showed antidepressant activity and cellular mechanism of rexinoids and fibrates in chronic social defeat stress. Obtained data have strong therapeutic potential that may allow for development of new antidepressant therapies.

Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine. Toll-like receptor (TLR)-mediated signalling plays a role in cerebral ischaemia/reperfusion (I/R) injury. Modulation of TLRs has been reported to protect against cerebral I/R injury. This study examined whether modulation of TLR3 with poly (I:C) will induce protection against cerebral I/R injury. Mice were treated with or without Poly (I:C) (n = 8/group) 1 hr prior to cerebral ischaemia (60 min.) followed by reperfusion (24 hrs). Poly (I:C) pre-treatment significantly reduced the infarct volume by 57.2% compared with untreated I/R mice. Therapeutic administration of Poly (I:C), administered 30 min. after cerebral ischaemia, markedly decreased infarct volume by 34.9%. However, Poly (I:C)-induced protection was lost in TLR3 knockout mice. In poly (I:C)-treated mice, there was less neuronal damage in the hippocampus compared with untreated I/R mice. Poly (I:C) treatment induced IRF3 phosphorylation, but it inhibited NF-κB activation in the brain. Poly (I:C) also decreased I/R-induced apoptosis by attenuation of Fas/FasL-mediated apoptotic signalling. In addition, Poly (I:C) treatment decreased microglial cell caspase-3 activity. In vitro data showed that Poly (I:C) prevented hypoxia/reoxygenation (H/R)-induced interaction between Fas and FADD as well as caspase-3 and -8 activation in microglial cells. Importantly, Poly (I:C) treatment induced co-association between TLR3 and Fas. Our data suggest that Poly (I:C) decreases in cerebral I/R injury via TLR3 which associates with Fas, thereby preventing the interaction of Fas and FADD, as well as microglial cell caspase-3 and -8 activities. We conclude that TLR3 modulation by Poly (I:C) could be a potential approach for protection against ischaemic stroke.

The overall aim of this thesis was to establish strategies to minimize secondary damage to the injured spinal cord. Secondary damage that follows spinal cord injury (SCI) involves inflammatory and excitotoxic pathways. Regulation of these pathways using immunomodulatory and neuroprotective substances potentially protects the injured spinal cord from further damage. We also developed and studied resorbable biomaterials to be used as carriers for potential neuroprotectants to the injured spinal cord. We used transversal spinal cord slice cultures (SCSCs) derived from postnatal mice as a model. SCSCs were maintained on different biomaterials and were studied after treatment with immunomodulatory and/or neurotrophic factors. They were further excitotoxically injured and subsequently treated with interleukin-1 receptor antagonist (IL1RA) or by neural crest stem cell (NCSC)-transplantation. The results show that biocompatible and resorbable hydrogels based on hyaluronic acid (HA) preserved neurons in SCSCs to a much higher extent than a conventional collagen-based biomaterial or standard polyethylene terephthalate (PET) membrane inserts. Glial activation was limited in the cultures maintained on HA-based hydrogel. The anti-inflammatory factor IL1RA protected SCSCs from degenerative mechanisms that occur during in vitro incubation, and IL1RA also protected SCSCs from excitotoxic injury induced by N-Methyl-d-Aspartate (NMDA). IL1RA specifically protected neurons that resided in the ventral horn, while other neuronal populations such as dorsal horn neurons and Renshaw cells did not respond to treatment. Finally, transplantation of NCSCs onto excitotoxically injured SCSCs protected from neuronal loss, apoptosis and glial activation, while NCSCs remained undifferentiated. The results presented in this thesis indicate that carriers based on HA seem to be more suitable than conventional collagen-based biomaterials since they enhance neuronal survival per se. The observed neuroprotection is likely due to biomechanical properties of HA. IL1RA protects SCSCs from spontaneous degeneration and from NMDA-induced injury, suggesting that excitotoxic mechanisms can be modulated through anti-inflammatory pathways. Different neuronal populations are affected by IL1RA to various degrees, suggesting that a combination of different neuroprotectants should be used in treatment strategies after SCI. Finally, NCSCs seem to protect SCSCs from excitotoxic injury through paracrine actions, since they remain undifferentiated and do not migrate into the tissue during in vitro incubation. It seems that combinations of neuroprotectants and carrier substances should be considered rather than one single strategy when designing future treatments for SCI. Incorporation of neuroprotectants such as IL1RA combined with stem cells in injectable biocompatible carriers based on HA is the final goal of our group in the treatment of SCI.

La MA est caractérisée par une altération progressive des fonctions cognitives, et définie par les "dégénérescences neurofibrillaires", les "plaques séniles" et une neuroinflammation impliquant les cellules microgliales. L’immunothérapie constitue une approche thérapeutique prometteuse dans la MA. Un premier essai clinique de vaccination anti-Aβ a été arrêté après la survenue de 6% de cas de méningoencéphalites imputés à l’activation de réponses T anti-Aβ pro-inflammatoires. Cependant, des études récentes suggèrent un effet bénéfique de certaines populations de cellules T CD4+ anti-Aβ. L'ensemble de ces données suggère des rôles complexes de différentes réponses lymphocytaires T au cours de la MA, et soulignent la nécessité de mieux comprendre leur implication dans la maladie et les mécanismes de leur régulation. L’objectif de ce travail a été d’étudier l’impact des Tregs sur la progression de la maladie dans un modèle murin APPPS1. Les résultats montrent que la déplétion transitoire des Tregs accélère l’apparition des troubles cognitifs, sans altérer la pathologie amyloïde. Ces observations sont corrélées avec une réduction du recrutement des cellules microgliales autour des plaques Aβ et une altération du profil d’expression, dans le cerveau des souris, de certains gènes impliqués dans la maladie. A l’inverse, l’amplification sélective des réponses Tregs entraine une augmentation du recrutement des cellules microgliales autour des plaques et une amélioration des fonctions cognitives. L’ensemble de ces résultats suggère un rôle bénéfique des Tregs au cours de la maladie d’Alzheimer et encourage le développement d’approches d’immunothérapie basées sur leur modulation. / Alzheimer’s Disease (AD) is a neurodegenerative disorder characterized by progressive loss of memory and cognitive functions. Accumulation of Aβ peptide is considered the initiating cause of pathogenic lesions, and immunotherapy strategies targeting Aβ represent promising therapeutic approaches. Vaccination against Aβ provided encouraging results in experimental mouse models and, to a lesser extent, in a subsequent clinical trial (AN1792). Although the AN1792 trial had to be interrupted due to meningoencephalitis attributed to pro-inflammatory T cell responses in 6% of the patients, preclinical murine models did not show evidence of T cell-related side effects. In addition, several reports suggest that Aβ-specific CD4+ T cells may be implicated in the natural course of AD and could have a strong therapeutic potential as well, pointing out the need for better understanding the role and regulation of T cell responses to Aβ. We previously showed that regulatory T cells (Tregs) control Aβ-specific CD4+ T cell responses in physiological and pathological settings upon vaccination. The aim of this work was to analyze the impact of Tregs on the natural course of the disease progression in a mouse model of AD. Early transient depletion of Tregs accelerated the onset of cognitive deficits in APPPS1 mice. This result was correlated with less recruitment of microglia towards amyloid deposits and altered disease-related gene expression profile. Conversely, Tregs selectively amplifying resulted in higher numbers of plaque-associated microglia and improved cognitive functions in APPPS1 mice. These data suggest a beneficial role of Tregs in the pathophysiology of AD by modulating microglial response. Our study highlithts the therapeutic potential of Treg-based immunotherapies in AD.

In der vorliegenden Arbeit wurde die Auswirkung der Behandlung muriner Mikrogliazellen mit Agonisten von TLR2, TLR4 und TLR9 untersucht. Zu diesem Zweck wurden murine Mikrogliazellkulturen angelegt. Als TLR - Agonisten dienten Pam3Cys und HKAL (TLR2), Pneumolysin und LPS (TLR4) sowie CPG (TLR9). Die Stimulation muriner Mikrogliazellen mit den verschiedenen TLR - Agonisten führte zur Freisetzung von NO und TNF-α. Durch den Einsatz unterschiedlicher Konzentrationen der TLR - Agonisten konnten Dosis - Wirkungs - Kurven für die Freisetzung von NO und TNF-α erstellt werden. Anhand der EC50 wurde die Potenz der TLR - Liganden beurteilt. Für die Freisetzung von NO wies LPS die höchste stimulatorische Potenz auf, gefolgt von Pneumolysin, CpG und Pam3Cys. Für die TNF-α - Freisetzung besaß ebenfalls LPS die höchste stimulatorische Potenz, auch hier folgten Pneumolysin und CpG. Das verwendete Pam3Cys löste sich nicht optimal, vermutlich aus diesem Grund wurde durch die Pam3Cys - Gabe keine maximale Stimulation erreicht. Darum konnte die EC50 für die TNF-α - Freisetzung fur Pam3Cys nicht ermittelt werden. Die EC50 für die TNF-a - Freisetzung war jeweils höher als die entsprechende EC50 für die Freisetzung von NO. Die Behandlung mit HKAL führte zur starken NO - und TNF-a - Freisetzung. Ein direkter Vergleich der Potenz von HKAL mit der der anderen Liganden ist nicht möglich, da die Konzentration von HKAL in Zellzahl pro ml gemessen wird. Die Konzentrationen von Pam3Cys, Pneumolysin und LPS werden jedoch in µg/l gemessen.  Die Stimulation von Mikrogliazellen über verschiedene TLR hatte eine relativ gleich starke Sezernierung von NO und TNF-a zur Folge. Die Costimulation der Mikrogliazellen mit Konzentrationen von zwei unterschiedlichen TLR - Agonisten, welche allein jeweils zur maximalen NO - Produktion geführt hatten, resultierte nicht in einer weiteren Erhöhung der NO - Freisetzung.  Niedrig dosiert zeigte die Pneumolysinbehandlung einen immunstimulatorischen Effekt. Das Maximum an Stimulation, gemessen an der Zunahme der NO - Produktion, wurde bei einer Pneumolysin - Konzentration von 0,3 µg/ml (6nM) beobachtet. Eindeutige zytotoxische Effekte anhand der signifikant geringeren NO - Freisetzung waren bei Konzentrationen von 3 µg/ml bzw. 10 µg/ml (60 nM bzw. 200 nM) nachweisbar. Durch die Isolectin-B4 - Färbung wurden bei diesen Konzentrationen pneumolysinbedingte Zellschäden dargestellt. Bei den anderen Substanzen wurde in hohen Konzentrationen keine Zytotoxität beobachtet Die Behandlung TLR4 - defizienter Mikrogliazellen mit den spezifischen TLR4 - Agonisten Pneumolysin und LPS führte zu einer signifikant geringeren Freisetzung von NO im Vergleich zu Wildtypzellen. Schlussfolgernd kann gesagt werden: Die Stimulation von Mikrogliazellen über unterschiedliche TLR resultiert in einer relativ einheitlichen Freisetzung von NO und TNF-α. Die gleichzeitige Stimulation mit zwei jeweils niedrigdosierten TLR - Agonisten führt zu einem additiven oder supraadditiven Effekt. Nicht nur bakterielle Substanzen, sondern auch endogene Stoffe sind Agonisten an TLR - Rezeptoren. Der additive Effekt durch die simultane Stimulation mehrerer TLR erhöht nicht nur die Sensitivität von Mikroglia während Infektionen, sondern kann ebenfalls Wechselwirkungen zwischen exogenen und endogenen Agonisten von TLR zur Folge haben. Dies kann ein Grund für die Exazerbation oder Induktion autoimmuner Krankheiten durch Infektionen sein.