Abundant and constant expression of uncoupling protein 2 in the liver of red sea bream Pagrus major

Four overlapping cDNA fragments encoding a partial sequence for uncoupling protein 2 (UCP2) were amplified by PCR using degenerate primers from the liver of a marine teleost fish, red sea bream (Pagrus major). The partial sequence was 674 bp long, encoding 224 amino acids. The deduced amino acid sequence from the cDNA partial sequence contained the signature motifs for mitochondrial transporter protein and revealed positional identity higher than 72.8% with UCP2 from mammals. The fish UCP2 gene was highly expressed in the liver but almost undetectable in the visceral mesenteric adipose tissue. Using beta-actin as control, the UCP2 mRNA level was determined to be at least 20-fold higher in the liver than in the visceral mesenteric adipose tissues. Neither 48 h starvation nor high lipid diet had any significant effect on liver UCP2 gene expression, indicating that the abundant UCP2 gene expression was stable and might have some basic function in a fish liver that always contains high lipid content. The striking contrast of UCP2 gene expression in the two fish fat-depot organs is consistent with their large differences in oxidative capacity. We gene expression in the two fish fat suggest that the fish liver may adapt to a constantly high fat deposit by maintaining high UCP2 expression to constrain reactive oxygen species (ROS) production and protect hepatocytes from apoptosis. (C) 2003 Elsevier Inc. All rights reserved.