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[Truncated abstract] Glucocorticoids are critical for the maturation of the fetus late in pregnancy. Indeed, clinical administration of glucocorticoids is used to accelerate fetal lung maturation in mothers at risk of pre-term delivery. Increased glucocorticoid exposure, however, can have detrimental effects on fetal and placental growth and increase the risk of disease in later life. Many studies have focused on the effect of an increase in the transplacental passage of glucocorticoids on both fetal growth and subsequent postnatal development. But there is a growing body of evidence to suggest that the impact of glucocorticoids on fetal growth is mediated, in part, via their direct effects on the placenta . . . Overall, these studies quantify the labyrinth zone-specific increases in placental expression of PPARG and VEGF in association with a marked increase in vascularisation observed near term. Furthermore, this study demonstrates for the first time that these increases in gene expression are prevented by maternal dexamethasone treatment which also inhibits growth of the fetal capillary network. Elevated expression of SFRP4 in the regressing basal zone late in gestation and in both placental zones after dexamethasone-induced placental growth restriction is consistent with a role for SFRP4 in glucocorticoid-mediated inhibition of wnt signalling. Collectively, the data presented in this thesis show that glucocorticoid inhibition of fetal growth is mediated in large part via effects on the placenta, specifically through inhibition of signals that promote proliferation and vascularisation.

Transforming growth factor beta 1 (TGF-beta1) ist ein multifunktionales Zytokin, welches eine Rolle in der Sepsis und in der Sepsis-induzierten Myopathie spielen könnte. Weiterhin könnten erhöhte TGF-beta1-Level zur Muskelschwäche, die mit der Intensivpflege assoziiert ist (engl. intensiv care unit-acquired weakness, ICUAW), beitragen. Der TGF-beta1- Signalweg wurde in Skelettmuskelbiopsien von ICUAW-Patienten heraufreguliert. Secreted frizzled related protein 2 (SFRP2) wurde in einer Gen-Set-Anreicherungsanalyse als das am höchsten regulierte Gen identifiziert. Im Mausmodell führten Sepsis und Hunger zu einer verringerten Sfrp2-Expression, während dies in der Denervation-induzierten Skelettmuskelatrophie nicht festzustellen war. In differenzierten C2C12-Myotuben führte TGF-beta1 zu einer verringerten Sfrp2-mRNA- und Proteinexpression. Luciferase-Assays deuteten auf eine TGF-beta1-abhängige Herunterregulation von Sfrp2 hin, welche auf Promoterebene durch mögliche negative regulatorische Elemente im Sfrp2-Promoter vermittelt wurde. Weiterhin wurde eine TGF-beta1 induzierte Muskelatrophie durch transkriptionelle Repression der myosin heavy chain Gene beobachtet. Im Gegensatz dazu veränderte TGF-beta1 nicht den proteasomalen Abbau muskulärer Proteine. Die Genexpression von Tripartite motif containing 63 und F-box only protein 32 war hingegen leicht herunterreguliert. TGF-beta1-induzierte Atrophie in differenzierten C2C12-Myotuben wurde teilweise durch rekombinantes Sfrp2 aufgehoben. Weiterhin wurde eine direkte physikalische Interaktion zwischen Sfrp2 und TGF-beta1 gefunden, welche diesen Effekt verursacht haben könnte. Zusammengefasst lässt sich feststellen, dass der TGF-beta1- Signalweg eine wichtige Rolle in der ICUAW durch Inhibition der myosin heavy chain Expression spielt. TGF-beta1-abhängige Herunterregulation von Sfrp2 könnte zu einer Feedback-Antwort, die das Ausmaß der Atrophie durch TGF-beta1 verstärkt, führen. / Transforming growth factor beta 1 (TGF-beta1) is a multifunctional cytokine that may play a role in sepsis and in sepsis-induced myopathy. Our group speculated that increased TGF-beta1 could contribute to intensive care (ICU)-acquired weakness (ICUAW), a catastrophic muscle disease in critically ill patients. We found that TGF-beta1 signaling in skeletal muscle biopsies of ICUAW patients was upregulated. Secreted frizzled related protein 2 (SFRP2) was the most regulated gene identified by gene set enrichment analysis (GSEA). I then studied the regulation and function of SFRP2 in different skeletal muscle atrophy models. In three mouse models, downregulated Sfrp2 expression was observed in sepsis and starvation, but not in denervation-induced skeletal muscle atrophy. In differentiated C2C12 myotubes, TGF-beta1 downregulated Sfrp2 expression on both mRNA and protein levels. Luciferase assays suggested that TGF-beta1-dependent downregulation of Sfrp2 was mediated at the promoter level through possible negative regulatory elements in the Sfrp2 promoter. I also observed that TGF-beta1-induced muscle atrophy was accompanied by transcriptional repression of myosin heavy chain genes. In contrast, TGF-beta1 did not increase proteasomal degradation of muscular proteins since gene expression of Tripartite motif containing 63 (Trim63) and F-box only protein (Fbxo32) was not upregulated; instead, they were slightly downregulated. TGF- beta1-induced differentiated C2C12 myotube atrophy was partially reversed by recombinant Sfrp2. This inhibitory effect could have resulted from direct interaction between Sfrp2 and TGF-beta1, since I found a physical interaction between these two proteins. Taken together, TGF-beta1 signaling pathway could play an important role in ICUAW via inhibition of myosin heavy chain expression. TGF-beta1-dependent downregulation of Sfrp2 may establish a feedback loop augmenting the atrophic effect of TGF-beta1.

L'épithélium intestinal est un tissu en constant renouvellement, grâce à des cellules souches somatiques présentes dans les cryptes intestinales. Le renouvellement perpétuel et l’homéostasie de ce tissu sont assurés par plusieurs réseaux de signalisation. Il est maintenant admis que la dérégulation de ces mêmes voies est impliquée dans le processus d’initiation et/ou de progression tumorale. Mon laboratoire a décrit l'implication des hormones thyroïdiennes (HT) et de leur récepteur nucléaire TRα1 dans le contrôle de l'homéostasie intestinale, via la régulation de la voie Wnt, jouant un rôle clé dans la physiopathologie de ce tissu. Plus précisément, TRα1 active l’expression et la stabilisation de β-caténine via un mécanisme impliquant le facteur sFRP2. Au cours de ma thèse, j’ai participé, d’une part à l’étude de souris transgéniques surexprimant TRα1 dans l’épithélium intestinal et à l’analyse des mécanismes moléculaires de la régulation croisée entre TRα1 et la voie Wnt canonique dans l’induction des tumeurs intestinales. Nous avons donc démontré un rôle oncogénique de TRα1 dans l’épithélium intestinal. De plus, le mécanisme moléculaire et fonctionnel implique les deux effecteurs de la voie canonique, β-caténine et TCF4. D’autre part, j’ai analysé la fonction de sFRP2 dans la physiopathologie intestinale, et son action sur la voie Wnt. D’une manière intéressante, l’étude de la fonction de sFRP2 nous a permis de révéler son rôle original dans la différenciation des cytotypes épithéliaux. De plus, nous avons montré que sFRP2 est un modulateur positif des voies Wnt canonique et non canonique (JNK). Par ailleurs, l’absence d’expression de sFRP2 a pour conséquence d’augmenter l’apoptose dans les cryptes intestinales et ainsi diminuer le nombre de tumeurs chez des animaux double mutants sFRP2-/-/Apc+/1638N comparé aux simple mutants Apc+/1638N. Ces résultats fournissent des éléments originaux et importants sur les relations fonctionnelles entre les voies des HT et Wnt. / The intestinal epithelium is a tissue constantly renewing through somatic stem cells located within the crypts. Several signalling pathways control this process and the homeostasis in this tissue. It is now recognized that the deregulation of these pathways is involved in the process of initiation and/or progression of intestinal tumors. My laboratory has described the involvement of thyroid hormones (TH) and their nuclear receptor TRα1 in the control of the intestinal homeostasis via the regulation of Wnt pathway, which plays a key role in the intestinal physiopathology. Specifically, TRα1 directly activates the expression of β-catenin and controls its stabilization through a mechanism involving sFRP2 (secreted frizzled-related protein 2). During my thesis, I participated to the characterization of transgenic mice overexpressing TRα1 in the intestinal epithelium. Moreover, I have been involved in the study of the molecular mechanisms of the cross-regulation between TRα1 and the canonical Wnt in the induction of intestinal tumors. We have therefore demonstrated an oncogenic role of TRα1 in the intestinal epithelium. In addition, the molecular and functional mechanisms involve both effectors of the canonical pathway, β-catenin and TCF4. On the other hand, I carried out the study of sFRP2 function in the intestinal physiopathology, and its action on the Wnt pathway. My data strongly suggest that sFRP2 plays an essential role in the differentiation of epithelial cytotypes. In addition, we showed that sFRP2 is a positive modulator of the canonical and non-canonical (JNK) Wnt. For instance, the absence of sFRP2 expression increases the apoptosis in the intestinal crypts and thus reduces the number of tumors in the double mutant sFRP2-/-/Apc+/1638N compared to simple mutant Apc+/1638N. These results provided original and important data of the functional relationships between TH and Wnt pathways.