Effect of environmental temperature and dietary lipid supplement on activity and protein abundance of acetyl-CoA carboxylase and fatty acid synthase in skeletal muscle, liver and adipose tissues of sheep

To determine the effects of temperature and dietary lipid on the key enzymes regulating fatty acid synthesis, 24 wether lambs were exposed to three temperature treatments (+23 degrees C warm, 0 degrees C cold, or cold-pairfed) and fed either a control barley-based diet or a lipid supplemented diet for a 5-wk period. After slaughter, tissue samples were collected and frozen for analysis for enzyme activity and enzyme protein abundance. Thermal environment or lipid supplementation did not affect (P > 0.05) acetyl-CoA carboxylase (ACC) activity in longissimus dorsi (LD) muscle. In liver, cold exposure increased (P < 0.05) while lipid supplementation depressed (P < 0.05) ACC activity. In subcutaneous (SC) and mesenteric (MS) adipose tissue ACC activity was not affected (P > 0.05) by cold exposure. Dietary lipid supplementation increased (P < 0.05) ACC activity in both SC and MS but the increase in perirenal (PR) fat was not significant. Western-blot analysis with peroxidase-labelled streptavidin identified two isoforms of ACC (280 and 265 kDa) in LD muscle and the 280 kDa was the more abundant isoform. In liver and adipose tissues only one isoform (265 kDa) was identified but there was a poor relationship between enzyme protein abundance and activity. Neither environment nor diet affected fatty acid synthase (FAS) activity in LD or liver. Cold exposure reduced (P < 0.05) FAS activity in SC tissue of ad libitum fed animals but increased FAS activity in MS tissue of pair-fed sheep and had no effect in PR fat. Dietary lipid supplementation reduced (P < 0.05) FAS activity by 30% in all three fat depots. A single isoform of FAS with MW of 260 kDa was present in all tissues examined with cold exposure increasing FAS protein expression in all tissues. The results indicate that temperature and dietary lipid affect enzyme catalytic activity with differential responses in different tissues.