Fatty acids and temperature effects in fish adipogenesis and osteogenesis: in vitro and in vivo approaches = Efecte dels àcids grassos i la temperatura sobre l'adipogènesi i l'osteogènesi en peixos : enfocament in vitro i in vivo

Abstract

Aquaculture needs to develop new strategies and tools to face challenges as the reduction of fish oil use in fish feeds and climate change, to assure the obtention of a valuable high-quality product while preserving fish health, welfare and proper growth. This thesis includes the characterization of the gene expression pattern of preadipocytes during differentiation into mature adipocytes in rainbow trout, as well as during the process of osteogenesis in gilthead sea bream both, in vitro and in vivo. Moreover, it has been characterized the in vitro plasticity of the bone-derived cells to differentiate into the adipogenic linage. In addition, the effect of fatty acids derived from fish or vegetable oils has been tested in vitro on rainbow trout preadipocytes and gilthead sea bream bone-derived cells and in vivo, by oral administration in rainbow trout. In addition, it has been evaluated the effect of temperature over bone-derived cells and the in vivo skeletal development of gilthead sea bream, as well as the effect on lipid metabolism in this species when challenged with partially substituted fish oil diets by different vegetable oils. Finally, this study presents a characterization of the expression pattern of osteogenic genes in malformed skeletal structures of gilthead sea bream. Regarding the first block of studies, results demonstrate that adipogenesis and osteogenesis in fish are similar than in mammals, and in vitro gene expression patterns have reflected clear similarities with in vivo models thus, highlighting the potential tool of these cells as model systems to study their behaviour under new conditions. Furthermore, it has been demonstrated that the bone-derived cells, as seen in mammals, have the ability to differentiate into other linages, concretely into adipocyte-like cells not only with a differentiation media but also by the presence of a single fatty acid. In this context, these fatty acids showed their potential to act as inductors of adipogenesis by upregulating pparg gene expression or inducing higher lipid accumulation through transporters depending on the fatty acid oil source. The same fatty acids increased intracellular lipid accumulation and the activation of the adipogenic process in preadipocytes from rainbow trout. Moreover, the oral administration of fatty acids in the same species produced an activation of β-oxidation, lipogenesis and lipid transport in adipose tissue, whereas in liver a decrease in these processes was observed. Concerning temperature, both in vitro and in vivo affectation of the normal gene expression during differentiation and development respectively was shown, with the addition in the latter of the demonstration of a thermal imprinting existence after a temperature challenge. In this sense, an elevated temperature has been also shown to increase in gilthead sea bream somatic growth and adipogenesis as well as fatty acid oxidation in the liver. In these fish fed diets with different vegetable oil sources, it was shown that the combination of palm and rapeseed oils is the most equilibrated formulation to assure growth and balanced lipid accumulation at this warm condition. Finally, the vertebral column deformities (lordosis and LSK syndrome) have revealed a modified expression pattern for the genes related to extracellular matrix formation and mineralization and bone resorption, pointing to key genes to be used as molecular markers, whereas for the operculum, dental and jaw deformities gene markers have not been identified. Overall, the present thesis describes adipogenic factors that can be the base to found potential links with whole body energy regulation and demonstrates that nutrition and temperature influence adipose tissue and bone development and lipid metabolism in fish, providing different valuable models to evaluate new challenges for improving a sustainable aquaculture.

La acuicultura necesita desarrollar nuevas estrategias y herramientas para enfrentarse a desafíos como la reducción del uso de aceite de pescado en los alimentos para peces y el cambio climático, para asegurar la obtención de un producto valioso de alta calidad mientras se preserva la salud, el bienestar y el crecimiento adecuado de los peces. Esta tesis incluye la caracterización del patrón de expresión génica de preadipocitos durante la diferenciación en adipocitos maduros en trucha arcoíris, así como durante el proceso de osteogénesis en dorada tanto in vitro como in vivo. Además, se ha caracterizado la plasticidad in vitro de las células derivadas de hueso para diferenciarse en el linaje adipogénico. Además, el efecto de los ácidos grasos derivados de aceites de pescado o vegetales se ha probado in vitro en preadipocitos de trucha arcoíris y células derivadas de hueso de dorada e in vivo, por administración oral en la trucha. Además, se ha evaluado el efecto de la temperatura sobre las células derivadas de hueso y el desarrollo esquelético in vivo de la dorada, así como el efecto sobre el metabolismo de los lípidos en esta especie cuando se desafía con dietas de aceite de pescado parcialmente sustituidas por diferentes aceites vegetales. Finalmente, este estudio presenta una caracterización del patrón de expresión de genes osteogénicos en estructuras esqueléticas malformadas de dorada. En general, la presente tesis describe los factores adipogénicos que pueden ser la base para encontrar posibles vínculos con la regulación energética de todo el cuerpo y demuestra que la nutrición y la temperatura influyen en el desarrollo de tejido adiposo y hueso y el metabolismo de los lípidos en los peces, proporcionando diferentes modelos valiosos para evaluar nuevos desafíos para mejorar una acuicultura sostenible.