ED Sciences de la Vie et de la Santé
PURINERGIC SIGNALING PATHWAY AND MESODERMAL AND NEURAL DIFFERENTIATION DURING EMBRYONIC DEVELOPMENT
by Fanny HARDET (Institut des Maladies Neurodégénératives)
The defense will take place at 14h00 - Amphithéâtre Broca Bordeaux Neurocampus Centre Broca Nouvelle-Aquitaine 146 rue Léo-Saignat 33076 Bordeaux Cedex
in front of the jury composed of
- Clotilde BILLOTET - Professeure des universités - Université de Bordeaux - Examinateur
- Sabine LEVI - Directrice de recherche - ESPCI Paris - Rapporteur
- Eric BELLEFROID - Professeur des universités - Université Libre de Bruxelles - Rapporteur
- Patrick AUGUSTE - Maître de conférences - Université de Bordeaux - Examinateur
The purinergic signaling pathway, involving purines, whose extracellular concentration is controlled by ectonucleotidases, as ligands for purinergic receptors P2 (P2X and P2Y) and P1 (AdorA), regulates the physiology of many organs in adult vertebrates, and its dysregulation is correlated with several human pathologies, degenerative or developmental in nature. Understanding its functions during embryonic development is essential to understanding the molecular mechanisms that are dysregulated in these pathologies. However, its embryonic roles in an in vivo context remain poorly understood. The amphibian model Xenopus laevis, due to its biological characteristics and the various genetic tools available, is a model of choice for exploring the molecular mechanisms and signaling pathways that regulate embryogenesis. Previous work by my team has shown that the kidney and nervous system are major sites of expression for the actors in this signaling pathway. Based on their expression profile, several enzymes and receptors were selected for functional studies. The objective of my thesis was to study the embryonic roles of some of these actors, namely ectonucleotidases and P2X receptors. To do this, gain-of-function and loss-of-function experiments were used in combination with histological approaches to analyze the phenotypes induced at different embryonic stages, as well as electrophysiological and behavioral approaches. My work established that the ectonucleotidase ENTPD5 is necessary and sufficient for kidney formation. This capacity is dependent on the enzymatic activity of ENTPD5, its subcellular localization, and the cellular environment. ENTPD5 also regulates the expression of master genes involved in nephrogenesis. I have thus demonstrated the conservation of molecular mechanisms, which involve an ectonucleotidase from the ENTPDase family upstream of these networks. Furthermore, as part of an international collaboration, my work has demonstrated the deleterious effects of the loss of function of the ENPP6 ectonucleotidase and that certain mutations of this gene, identified in patients with renal pathologies (CAKUT), alter the development of the pronephros. We have also characterized the electrophysiological properties of Xenopus P2X receptors in order to elucidate their role in the formation of the sensory nervous system and in nociception, for which we have developed appropriate behavioral tests. Finally, we revealed that the P2X5 receptor, described as non-functional in humans, as well as the metabolic pathways of purine biosynthesis and recycling, are involved in the formation of somites and hypaxial muscles in Xenopus. Thus, my thesis work highlights the implications of purinergic signaling during embryogenesis, improving our understanding of developmental mechanisms and paving the way for new potential therapeutic targets. Keywords: Embryogenesis, ectonucleotidases, P2X, xenopus, pronephros, muscles, sensory nervous system, nociception, electrophysiology
Digital phenotyping for an evaluative and interventional approach of sleep in the general and clinical population
by Julien COELHO (Sommeil, Addiction et Neuropsychiatrie)
The defense will take place at 14h30 - Broca 146 rue Léo Saignat
in front of the jury composed of
- Pierre PHILIP - Professeur - Université de Bordeaux - Directeur de these
- CHARLES MORIN - Professeur - Université de Laval - Rapporteur
- LAURE PETER-DEREX - Professeure des universités - praticienne hospitalière - Université Lyon 1 - Rapporteur
- XAVIER DROUOT - Professeur des universités - praticien hospitalier - Université de Poitiers - Examinateur
- MARIE-PIA D'ORTHO - Professeure des universités - Université Neurodiderot - Examinateur
Sleep, when approached from the perspective of sleep health, represents a key target for interventions aiming to evaluate and promote both physical and mental health in the general population. The amount of sleep and homeostatic pressure have been historically well studied, but more recently, circadian rhythms and their physiology have been brought back to the forefront of sleep health. These rhythms can be described along six dimensions: circadian phase, amplitude, and stability; nychthemeral timing and regularity; and sleep complaints of circadian origin. These dimensions help characterize two main types of circadian disruptions: those due to circadian misalignment (i.e., a discrepancy between nychthemeral timing and circadian phase, not compensated by sufficient amplitude or stability, and resulting in sleep complaints), and those due to a dysfunction of the biological clock (i.e., intrinsic circadian physiology alterations causing pronounced nychthemeral irregularity and associated sleep complaints). Such disruptions are particularly common in psychiatric disorders and represent an important therapeutic target to improve mental health. Digital tools present both challenges and opportunities for the assessment and promotion of circadian physiology. This theoretical framework has guided a three-pronged research approach. First, we focused on improving the measurement tools for circadian rhythms. We analyzed 14 existing questionnaires assessing circadian rhythms to examine their content, assess their homogeneity, and identify their most appropriate use. This analysis highlighted the importance of the MCTQ (Munich ChronoType Questionnaire), which we translated and validated in French, thereby providing the first French-language tool for assessing circadian misalignment. The next step is to validate a French version of the SRQ (Sleep Regularity Questionnaire) and to develop a new, holistic circadian questionnaire. Second, we sought to better characterize the relationship between circadian physiology and sleep health. We found a strong association between nychthemeral sleep behaviors (specifically sleep timing and sleep regularity) and mental health, independent of other dimensions of sleep health and consistent over time. Given the complexity of interactions among the different dimensions of circadian physiology, further investigation will require both experimental protocols and large-scale observational cohorts. Finally, we explored how digital tools can be used to optimize circadian physiology and promote sleep health. We showed that in the context of a personalized behavioral intervention delivered by an autonomous conversational agent, improvements in nychthemeral sleep regularity predicted improvements in mental health. Circadian rhythms, therefore, represent a promising target for mental health promotion. However, these tools still need to be refined and validated in clinical populations. Ideally, they should also incorporate additional dimensions of circadian physiology not addressed here, such as sensitivity to and exposure to zeitgebers (external synchronizing cues). Furthermore, consideration of social and environmental determinants, alongside individual factors, is essential for accurate characterization and optimal efficacy of circadian-targeted interventions. Greater integration of interactions with homeostatic sleep pressure is also needed. Defining circadian health, developing a corresponding questionnaire, and proposing specific biomarkers are all important future directions. Moreover, studying circadian rhythms in the context of a 24/7 society raises ethical questions that should not be overlooked. In conclusion, circadian physiology is a key determinant of both sleep and overall health. It constitutes a priority target for addressing the public health challenge posed by sleep disturbances.
ED Sciences et environnements
Impacts of urban stressors on key aquatic organisms: biofilms and thinlip mullet
by Caroline ROUX (EABX - Écosystèmes aquatiques et changements globaux)
The defense will take place at 13h30 - Amphithéâtre de Gazinet Cestas 50 Avenue de Verdun, 33610 Cestas
in front of the jury composed of
- Soizic MORIN - Directrice de recherche - Université de Bordeaux - Directeur de these
- Isabelle LAVOIE - Professeure agrégée - Université du Québec - Rapporteur
- David BENHAIM - Professeur - Hólar University - Rapporteur
- Séverine LE FAUCHEUR - Professeure - Université de Pau et des Pays de l'Adour - Examinateur
- Christel LEFRANCOIS - Maîtresse de conférences - Université de La Rochelle - Examinateur
- Patrice GONZALEZ - Directeur de recherche - Université de Bordeaux - Examinateur
- Laure CARASSOU - Chargée de recherche - Université de Bordeaux - CoDirecteur de these
Urban aquatic ecosystems are subjected to a multitude of urban stressors and host fragile communities. While the literature on the impact of artificial light at night (ALAN) on urban biodiversity is growing, its effects on aquatic biodiversity remains largely overlooked. Moreover, the combined impacts of ALAN with other types of urban stressors, particularly chemical contamination, remain unexplored. Against this background, the aim of this thesis is to use an experimental approach to address the singular and combined effects of two stressors specific of urban environments (ALAN and chemical contamination by a widespread biocide: the dodecylbenzyldimethylammonium chloride, DDBAC) on two model organisms known to interact in nature: aquatic biofilms and a grazing fish, the thinlip mullet (Chelon ramada, Mugilidae). Based on global and specific descriptors of the organisms' physiology and behavior, three mesocosm experiments were carried out. Thinlip mullets exposed to a continuous photoperiod (mimicking ALAN in highly urbanized environments) over a short exposure period (3 days), showed different swimming behaviors (distance covered, swimming speed and group cohesion), without any marked physiological stress (as determined by measurements of plasma and water cortisol levels).With regards to biofilms, exposure to the two urban stressors (ALAN and DDBAC) over one month revealed a decrease in photosynthesis in the presence of ALAN, and bioaccumulation of DDBAC in the organisms associated with an increase in fatty acid oxidation (oxylipins) in the presence of the pollutant, indicating individual impacts of the two stressors but no measurable interaction between them. Thinlip mullets exposed to the two urban stressors (ALAN and DDBAC via contaminated food) over one month showed little difference on physiological (cortisol levels) and structural (lipid and fatty acid composition) descriptors among treatments. However, after a month of light conditioning, a choice experiment conducted with a Plus-Maze device revealed differences in fish preferences for different light conditions depending on previous exposure to light and chemicals. In conclusion, the experiments carried out during this thesis showed that ALAN (via an altered photoperiod) and DDBAC (at environmental concentrations) induced differentiated responses depending on the model organism and duration of exposure. Biofilms appear to be a sensitive community through their photosynthetic and lipidic responses, while the behavior of thinlip mullets proves to be a relevant indicator, potentially more reactive than conventional physiological markers, in experimental scenarios close to realistic environmental contexts.