Gene expression studies in Atlantic salmon (Salmo salar L.) : Effects of peroxisome proliferator-activated receptor agonists

• Main Author: Thi, Therese Mong Thuong Le
• Other Authors: Tor Gjøen
• Format: Master Thesis
• Language: English
• Published: 2007
• Subjects: PPAR-agonist SHK-1 celler celledød toksisitet; VDP::568; Norway; Atlantic salmon; Salmo salar
• Online Access: http://hdl.handle.net/10852/12189; http://urn.nb.no/URN:NBN:no-18619

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.