ETaT

Oestrogen-active endocrine disrupting compounds (EEDCs), comprising natural and pharmaceutical oestrogens, excretions from livestock, oestrogen-active industrial chemicals and pesticides are permanently released into the aquatic environment and have been identified as a major threat to the aquatic fauna. Oestrogens have wide-ranging effects throughout life. In fish, like in other vertebrates, they primarily control sexual development, sex characteristics and reproduction. However, oestrogens also interact with the immune system in general and the developing immune system in particular. In mammals, it is well known that oestrogens regulate thymic development and thymic atrophy/involution and has complex roles in the regulation of T cell lymphopoiesis and T cell phenotypes as well as humoral and cell-mediated immunity. On the one hand, oestrogens have been shown to suppress lymphopoiesis, on the other hand antibody production can be stimulated by oestrogen. Thus, the immune system of mammals appears to respond to oestrogens both with stimulation and suppression. This project aims to evaluate the role of 17a-ethinylestradiol (EE2), on thymus development and thymopoiesis in fish. It is hypothesised that (i) Variations in exogenous EE2 levels lead to precocious thymus atrophy/involution as could be observed in mammals. This will include examining which developmental stage is most sensitive to the EE2 impact. (ii) affect T cell lymphopoiesis (iii) disruption of normal thymus development and T cell lymphopoiesis has consequences on fish health by compromising immunocompetence and reducing pathogen resistance. Aspects of these questions will be investigated in two fish species with different developmental duration and reproductive strategies, the zebrafish and the seabass, respectively. Important parameters, such as sexual maturation, reproductive cycle and juvenile development will be taken into account. Stereological methods and genetic markers specific for thymocytes at different developmental stages as well as stromal cells will be employed to examine how the cellular composition within the thymus is altered by EE2. The distribution of different isoforms of oestrogen receptors (ERa, ß1, ß2 and GPER) will be detected and associated with the different thymic environments and cell types. Mechanisms of thymic atrophy will be elucidated further by testing whether EE2 acts directly on T cells and/or stromal cells via apoptosis, if maturing T cells are arrested in their development or if a loss of premature T cells from the thymus is the cause for possible decrease of cellularity. Secretome analyses on isolated stromal cells and T cells will reveal the paracrine signalling induced upon oestrogen activation of thymic cells. Eventually, it will be shown whether modifications of thymus size, structure and function following exposure to EE2 diminish the resistance of D. rerio and D. labrax to pathogen infection. This project will provide the first comprehensive analysis of possible disruptive effects of environmental EEDCs (example EE2) on thymus development and T cell differentiation in fish, as well as on the consequences for the pathogen resistance. In addition, it will be the first to test whether the immunodisruptive effects of EE2 take place in the same concentration range, which is required to cause disruptive effects in the reproductive system. In order to obtain broader insight into the immunological actions and consequences of environmental oestrogens, the project takes a comparative approach by using two fish species of contrasting life histories (zebrafish, sea bass). The project will substantially advance our understanding of risks associated with the potential immunodisruptive effects of environmental oestrogen for fish. The challenging project objectives can only be achieved through the close collaboration of three teams with mutually complementary expertise from Switzerland and France.