Characterising fat tissue structure and function in grey seals, an animal model of extreme fat deposition and mobilisation, using novel in vivo and in vitro approaches

Grey Atlantic seals go through dramatic seasonal changes in body mass and composition because of the spatial and temporal separation of foraging, reproduction and moulting. The regulation of fat mobilisation during these processes is therefore a key factor for their survival. In humans, the excess accumulation of body fat is accompanied by adipose tissue hypoxia, oxidative stress and inflammation that are underlying factors of its various associated health problems. Therefore, the quick change in body mass and metabolic profile suggest that seals could be a good study model for obesity and its comorbidities. This study aims to assess the structure of the blubber, inflammation state, hypoxia and oxidative stress at different blubber depths and life stages: moulting adults, females and pups in early and late lactation and weaning pups. Two blubber biopsies from each animal were taken, one snap frozen and one placed in formalin. Adipocyte number and size, fat content, vascularisation and macrophage infiltration will be analysed through histology and immunohistochemistry. The oxidative stress steady state and pathways will be tested both in vivo and in vitro. In order to elucidate how seals cope with these conditions, physiological hypoxia state and hypoxia signalling pathways will be assessed using probes in wild animals and through in vitro experiments, respectively. We hypothesise that although typical oxygen reactive species would be present and hypoxia pathways stimulated, a compensatory machinery different from humans’ will be stimulated to counterbalance their detrimental effects.