Zebrafish Thyroid as a Model to Study Physiological Function and Pathological Implications of the H2O2-Generating System

Since its identification, numerous studies have been carried out with the aim of characterizing the physiological role of the thyroidal H2O2-generating complex. Found expressed also in other tissues, DUOXs together with their maturation factors DUOXAs are key components to ensure the normal functionality of the thyroid gland through the production of hydrogen peroxide. However, efforts are still needed to fully understand the complexity of the scenario encountered in patients harboring mutations in these proteins, as well as the possible role of unregulated production of H2O2 in the development of thyroid cancer.Given mechanisms involved in zebrafish thyroid development are comparable to mammals, to complement and expand the current knowledge in the pathophysiology of DUOX NADPH oxidase, we used zebrafish as an animal model. Preliminary studies have suggested a similar role of the zebrafish Duox/Duoxa system to that identified in mammals, but a clear characterization was still lacking at beginning of the present work. We combined the use of our transgenic line, expressing the EGFP specifically in thyroid cells, with different methods to chemically inhibit or invalidate the Duox/Duoxa system. We were able to demonstrate that the knockout of either duox or duoxa in zebrafish, induced hypothyroidism able to stimulate a TSH-mediated pituitary response, through negative feedback within the Hypothalamus-Pituitary-Thyroid axis, in a similar fashion to what was already known after exposure to Thyroperoxidase inhibitor Phenylthiourea, and to the knowledge we have for higher vertebrates. The treatment with the NOX-inhibitor VAS2870 resulted in a similar effect, suggesting that it could be considered a new goitrogenic compound capable of altering thyroid homeostasis.In addition, we generated a new transgenic model to follow the thyroidal H2O2 production during the different stages of zebrafish development, a model that would allow us to highlight the relationship between folliculogenesis and the onset of functional thyroid activity in live fish. This system could also be used in conjunction with models overexpressing the Duox-Duoxa complex in the thyroid, to study the consequences of a sustained production of H2O2 that would result in continuous oxidative stress leading to potential carcinogenic effects.Doctorat en Sciences biomédicales et pharmaceutiques (Médecine)