Mari Katrine Berg

Environmental pollutants with metabolic disrupting abilities are present in the Arctic. Particularly high levels of pollutants have been found in the apex predator of the Arctic marine food web, the polar bear. This species is dependent on a highly regulated metabolic system as it undergoes a distinct feasting and fasting regime due to seasonal variation in availability of food. Key regulators in consumption and storage of energy are the peroxisome proliferator-activated receptors (PPARs, NR1C), members of the nuclear receptor superfamily. PPARα and PPARγ are particularly important due to their positions in regulation of lipid metabolism and adipose cell differentiation, respectively.

The aim of this study was to clone polar bear PPARα and PPARγ, study their activation by contaminants, and locally establish a method to investigate how environmental pollutants affect lipid metabolism in vitro. Purifying RNA from polar bear tissue and cloning of polar bear PPARα and PPARγ allowed for phylogenetic comparisons and construction of plasmids. Sequence comparison with the human orthologs revealed 94 % and 98 % amino acid identity for PPARα and PPARγ, respectively. The constructed plasmids were used to establish a luciferase reporter assay (LRA) to assess PPAR activation by environmental pollutants. Activation by known ligands showed that the established LRA system was functional. Out of eleven single compounds and three synthetic POP mixtures, only PPARγ was activated by one compound, namely tetrabromobisphenol A (TBBPA). The local establishment of the preadipogenic cellline 3T3-L1 as a model for studying adipogenic capacity was completed. Preliminary exposures to mixtures of MeSO2- metabolites of POPs as identified in polar bears suggested that this mixture can increase lipid accumulation in the preadipogenic cell line both in the absence and presence of a hormonal cocktail (MDI). Cells exposed to OH-metabolites of POPs increased lipid accumulation in the absence of MDI, but decreased accumulation in its presence. This suggests that one or several compounds in the mixture has an inhibiting effect on differentiation. Due to lack of replicates in this time-limited study, experiments should be repeated before final conclusions are drawn. The established LRA and 3T3-L1 cell-line as a method for studying adipogenic potential of environmental pollutants can further be used to assess the metabolic effects of unlimited amounts of compounds, alone or in combination.

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Mari Katrine Berg handed in her thesis in molecular biology for the degree Master of Science in June 2013