Antilipogenic mechanism of conjugated linoleic acid in yeast

Conjugated linoleic acid (CLA) is a mixture of linoleic acid isomers having two double bonds in conjugated position. Beneficial health effects of CLA are unique: inhibition of fat accumulation and atherosclerosis, prevention of carcinogenesis, exhibition of anti-inflammatory properties and protection from diabetes. Synthetic CLA supplements are marketed for weight-loss purposes. However, concerns of safety of CLA have emerged, because the exact antilipogenic mechanism could not been clarified despite the active research with mammalian cells in vivo and in vitro. In this thesis the potential of yeast Saccharomyces cerevisiae as a model organism for elucidating the mechanism was examined. The trans-10,cis-12 isomer, which is recognized to be responsible of the antilipogenic effect in mammals, reduced yeast triacylglycerol content when supplemented in the cultivation medium. In contrast, the cis-9,trans-11 isomer induced high triacylglycerol accumulation. Both isomers were incorporated in the yeast phospholipids and triacylglycerols and were present in minor amounts also as free fatty acids. In triacylglycerols the CLA isomers were enriched in sn-1 and sn-3 positions. In yeast, two important mechanisms for the reduced triacylglycerol content by the trans-10,cis-12 CLA emerged. After the diauxic shift the CLA treated cells used efficiently the fatty acids from the cultivation medium and triacylglycerols as carbon source to produce more biomass resulting in the lowered triacylglycerol content. Also cis-9,trans-11 CLA induced this effect. Another mechanism specific for the trans-10,cis-12 CLA was the significant inhibition of monounsaturated fatty acid accumulation. The isomer was suspected to have direct effect on the membrane bound Δ9 desaturase, because the transcription of the enzyme was not affected by the trans-10,cis-12 CLA supplementation. In contrast, the cis-9,trans-11 isomer reduced the transcription of the enzyme, but its effect on monounsaturated fatty acid content was not that remarkable and rather typical for cis-9 unsaturated fatty acids. The transcriptional inhibition of the enzymes catalyzing DAG esterification was not induced by CLA in yeast. Are2p, the enzyme catalyzing sterol ester synthesis in yeast, showed elevated transcription by the trans-10,cis-12 CLA supplementation. On the basis of these results, yeast was proven to serve as an excellent model for CLA research. Especially the impact of CLA on membrane associated processes are encouraged to study further by using yeast as a tool.