La mucoviscidose est la maladie génétique la plus fréquente dans la population caucasienne. Le genre Scedosporium se situe au deuxième rang parmi les champignons filamenteux isolés des expectorations dans ce contexte. Au niveau pulmonaire, les colonisations/infections entraînent le recrutement de phagocytes qui induisent un stress oxydatif normalement délétère pour les pathogènes. Pour se défendre, ceux-ci ont développé des systèmes antioxydants, notamment diverses enzymes. Ce travail de thèse visait à étudier la réponse au stress oxydatif chez Scedosporium. Tout d’abord, la capacité à germer en présence d’oxydants a été évaluée. Par la suite, trente-trois gènes potentiellement impliqués dans la défense contre le stress oxydatif ont été identifiés. Leur expression en présence d’oxydants et en co-cultures avec des phagocytes suggère un rôle majeur, notamment pour une catalase, une peroxyrédoxine et deux thiorédoxine réductases. Par ailleurs, un mutant défectif pour un gène codant une superoxyde dismutase (SOD) pariétale et spécifique des spores a été produit. L’auranofin, un inhibiteur des thiorédoxine réductases, présente une activité vis-à-vis des Scedosporium et un effet additif avec des triazolés. Un test ELISA a été développé pour le sérodiagnostic des scédosporioses, utilisant une catalase et une Cu/Zn-SOD recombinantes. Ce test sensible et spécifique permet de distinguer les infections à Scedosporium de celles à Aspergillus fumigatus et des colonisations à Scedosporium. Au final, ces résultats indiquent un rôle majeur des enzymes antioxydantes chez Scedosporium, qui pourraient être de véritables facteurs de virulence et donc de nouvelles cibles thérapeutiques. / Cystic fibrosis (CF) is the most common genetic disease in Caucasian populations. The Scedosporium genus ranks the second among the filamentous fungi colonizing the airways of CF patients. In the respiratory tract, colonizations/infections lead to the recruitment of phagocytes which produce an oxidative stress, usually deleterious for pathogens. To defend themselves, pathogens have developed protective antioxidant systems, especially various enzymes. This thesis aimed to study the oxidative stress response in Scedosporium species. First, capacity of several Scedosporium isolates to germinate upon oxidative stress conditions was evaluated. Then, thirty-three genes potentially involved in protection against the oxidative stress were identified. Their overexpression in response to oxidants and in co-cultures with phagocytes suggested a crucial role, especially for one catalase, one peroxiredoxin and the two thioredoxin reductases. A mutant defective for the gene encoding a superoxide dismutase (SOD) anchored to the cell wall and specific for the conidia was produced. Auranofin, a thioredoxin reductase inhibitor, exhibits little anti-Scedosporium activity and an additive effect with triazole drugs. An ELISA was developed for serodiagnosis of scedosporiosis, using recombinant proteins derived from one catalase and a Cu/Zn-SOD. This sensitive and specific assay allows to differentiate Scedosporium infections from Aspergillus fumigatus infections and Scedosporium colonizations. Finally, these results indicate a crucial role of antioxidant enzymes in Scedosporium species, which could therefore be considered as virulence factors and as possible new therapeutic targets.

<p> G93A SODI mice (G93A mice) are a transgenic model over-expressing a mutant human Cu/Zn-SOD gene, and are a model for amyotrophic lateral sclerosis (ALS), a predominantly motor neurodegenerative disease. Hippocampal neurogenesis in the subgranular zone (SGZ) of dentate gyms (DG) occurs throughout the life. It is regulated by many pathological and physiological processes. There is controversy with respect to the basal level of hippocampal neurogenesis and its response to exercise in neurodegenerative diseases and their mouse models. Little information regarding hippocampal neurogenesis is available in G93A mice. The present study was designed to study the impact of treadmill exercise and sex differences on hippocampal neurogenesis in this model. In addition, potential molecular mechanisms regulating hippocampal neurogenesis including growth factors (BDNF and IGFl) and oxidative stress (SOD2, catalase, 8-0Hdg, and 3-NT) were also addressed in the study. Bromodeoxyuridine (BrdU) was used to label newly generated cells. G93A and wild type (WT) mice were subjected to treadmill exercise (EX) or a sedentary (SEO) lifestyle. Immunohistochemistry was used to detect BrdU labeled newly proliferating cells, surviving cells, and their phenotype, as well as for determination of oxidative stress. BDNF and IGFl mRNA expression was assessed by in situ hybridization. Results showed that (1) G93A mice had an elevated basal level of hippocampal neurogenesis for both cell survival and neuronal differentiation, a growth factor (BDNF mRNA), and an oxidative stress marker (NT), as compared to wild type sedentary mice. (2) Treadmill running did not show any further effect on hippocampal neurogenesis, growth factors, oxidative stress, and antioxidant enzymes in G93A mice, while treadmill running promoted hippocampal neurogenes1s and expression of the growth factor (BDNF mRNA), and lowered oxidative stress (8-0Hdg) in WT mice. (3) There also were sex differences in hippocampal neurogenesis in G93A mice, whereby male G93A mice had a significant higher level of cell proliferation but a lower level of survival than female G93A mice. (4) The DG BDNF mRNA was associated with cell survival and neuronal differentiation in sedentary G93A mice, suggesting that BDNF is associated with a higher basal level of hippocampal neurogenesis in G93A mice. We conclude that G93A mice are more permissive in the context of hippocampal neurogenesis, which is associated with elevated DG BDNF mRNA expression. Running did not have impact on hippocampal neurogenesis and BDNF mRNA expression in G93A mice, probably due to a 'ceiling effect' of the already heightened basal levels of hippocampal neurogenesis and BDNF mRNA in this model. In addition, sex differences also affect hippocampal neurogenes1s, but the further study is needed to clarify the underlying molecular mechanisms. </p> / Thesis / Doctor of Philosophy (PhD)