Abstract
ABSTRACT
Since their discovery in the early 1990s, peroxisome proliferator-activated receptors (PPARs)
have become an extremely important set of targets for drug discovery. The ligand-induced
transcription factors that regulate the transcription of target genes in response to specific
ligands, keeps on broadening its repertoire as new knowledge are uncovered. PPARs are
nuclear lipid-activated receptors that control a vast variety of genes in several pathways of
lipid metabolism. This includes fatty acid transport, uptake by the cells, intracellular binding
and activation, as well as catabolism (â-oxidation and ù-oxidation) or storage. They are
important pharmacological targets of treatment of obesity, diabetes and lipid disorders.
Although, PPARs are among the most studied nuclear receptors, there is little knowledge of
their activity and functions in fish. Atlantic salmon- Salmo salar L. belongs to the family
Salmonidae (Salmonids) and the order Salmoniformes. Norway have traditionally been
farming Atlantic salmon since the early 1970s, and is today one of the major producers of
farmed salmon for human consumption. The quality of fish depends much on the mechanisms
that keep the fish healthy. The adipose regulations in fish are still unknown, and it is of great
interest that they are investigated.
One of the goals of this thesis was to study PPAR gene expression in Atlantic salmon. We
compared PPAR tissue distribution in various fish tissue and cell lines. The tissue distribution
of PPARs in salmon was comparable to what has been described for mammals, a higher
concentration in tissues where adipose metabolism is more relevant. We also exposed SHK-1
and ASK cells (Atlantic salmon head kidney cells) to PPAR agonist treatment and found that
when activating PPARã, an up-regulation of target genes like SR-BI and CD 36 where seen.
These target genes play a key role in regulation of cholesterol homeostasis and have
previously been shown to be up-regulated by PPARã in mammals. To further investigate
PPARã, we performed transfection studies. Although, we obtained low transfection
efficiency, the findings showed same trend in PPAR transcription activity regulation.
Highly specific antibodies against fish antigens are rare. We therefore performed assays to
test a novel anti salmon-PPARã antibody for specificity, applying methods such as
immunostaining and western blotting. If the PPARã antibody proved specific, it would
3
provide us with an important tool in PPAR studies. Unfortunately this was not the case in our
study.
Our results of PPAR activity in Atlantic salmon head kidney cells agreed in many aspects
with previous findings in mammalian cells. However, there were low effects of ligand
treatment, and it came apparent during this work that PPAR agonists could have toxic effects
on SHK-1 and ASK cells in the concentrations employed here.