真鲷肝脏解偶联蛋白2 (UCP2)基因及其功能的探讨

The liver uncoupling protein 2 gene of the red sea bream (Pagrus major) with reference to its physiological function

从真鲷 (Pagrusmajor)肝脏通过简并引物PCR克隆解偶联蛋白 2 (UCP2 )cDNA部分序列。该片段长6 74bp ,编码 2 2 4个氨基酸残基。推测的此部分氨基酸序列包含线粒体载体蛋白的特征结构 ,并与其它脊椎动物UCP2氨基酸序列同源性在 72 8%以上。对变温动物鱼类UCP2组织表达调控研究表明 :与哺乳类UCP2基因不同 ,真鲷UCP2基因在肝脏大量表达 ,而在腹腔肠系膜脂肪组织则仅有痕迹量表达 ,两者表达水平相差 2 0倍以上。饲料中添加 10 %绿鳕油或 48h饥饿对真鲷肝脏UCP2基因的表达水平均无显著影响 ,表明UCP2基因在脂肪含量高的鱼类肝脏表达十分稳定 ,为维持其基本功能所必需。真鲷肝脏和腹腔肠系膜脂肪组织UCP2基因表达水平的强烈反差 ,与鱼类这两种贮脂器官完全不同的氧化活性相一致 [动物学报 49(1) :110～ 117,2 0 0 3]。

A cDNA fragment which encodes the partial sequence for uncoupling protein 2 (UCP2) was amplified by PCR using degenerate primers from the liver of a marine teleost fish. The fragment was 674 bp long, encoding 224 amino acids. The deduced amino acid sequence from the cDNA fragment contained the signature motifs for the mitochondrial transporter protein, and revealed positional identity higher than 72.8% with UCP2 from other vertebrates (including fish and mammals). Unlike the mammalian UCP2 gene, the fish UCP2 was highly expressed in the liver but was almost undetectable in the visceral mesenteric adipose tissue of this fish. Using β-actin as the control, the UCP2 mRNA level was determined to be more than 20-fold higher in the liver than in the visceral mesenteric adipose tissues. Neither dietary fish oil (10% pollack viscera oil) nor starvation (at 48 h post-feeding) had any significant effect on liver UCP2 gene expression, indicating that the abundant UCP2 gene expression in the liver is stable and might be essential to the basic function of the fish liver which always has a high lipid content. The striking contrast of UCP2 gene expression in the two fish fat-depot organs is consistent with their great distinction of their oxidative capacity. As lipids increase reactive oxygen species (ROS) and up-regulate factors that threaten hepatocyte viability in fatty liver, we suggest that fish livers may adapt to an excessive supply of lipid substrates by inducing UCP2 to facilitate substrate disposal while constraining ROS production[Acta Zoologica Sinica 49(1):110-117,2003].