THE ROLE OF THE INTESTINAL FATTY ACID BINDING PROTEIN IN INSULIN RESISTANCE

我们之前的研究发现染色体4q上的一个区域与胰岛素的作用有关。该区域的一个候选基因是编码人类肠道脂肪酸结合蛋白（IFABP）的FABP2。我们发现了该基因的多态性，该多态性导致IFABP第54氨基酸上的丙氨酸（Ala54）向苏氨酸（Thr54）取代。我们发现Thr54编码IFABP基因型（频率= 0.29）与空腹脂质氧化率升高和胰岛素抵抗之间存在显著关联，并进一步表明重组Thr54蛋白与重组Ala54蛋白相比，对长链脂肪酸具有更高的亲和力。我们进一步研究了IFABP替代的生理后果，通过分析脂肪酸在表达Ala54和Thr54 IFABP的永久转染细胞中的转运。我们发现，与表达Ala54的细胞相比，3H脂质在表达thr54的细胞中转运的速度更快。为了研究Ala54和Thr54 IFABP之间的结构差异，我们与J. Hamilton合作，利用3-D NMR分析了这两种蛋白与长链脂肪酸结合时的结构。我们目前正在分析胰岛素敏感的Ala54等位基因纯合子个体和胰岛素抵抗的Thr54等位基因纯合子个体的IFABP基因启动子。我们已经确定了几个多态性和两个缺失，这是与Ala到Thr取代的完全连锁不平衡。为了检测这些不同启动子的功能后果，我们将它们连接到荧光素酶报告基因中，并将这些载体转染到Caco- 2细胞中。我们目前正在比较它们在这些细胞中的转录活性。-胰岛素抵抗；脂肪酸结合蛋白；-人体实验对象

Our previous studies identified a region on chromosome 4q that was linked to measures of insulin action. A candidate gene in this region is FABP2 which encodes the human intestinal fatty acid binding protein (IFABP). We identified a polymorphism in this gene which results in an alanine (Ala54) to threonine (Thr54) substitution at amino acid 54 of IFABP. We found a significant association between the Thr54-encoding IFABP genotype (frequency = 0.29) and increased fasting lipid oxidation rates and insulin resistance, and have further shown that recombinant Thr54 protein has a higher affinity for long-chain fatty acids as compared to recombinant Ala54 protein. We further investigated the physiologic consequences of the IFABP substitution, by analyzing fatty acid transport across permanently transfected cells expressing either Ala54 and Thr54 IFABP. We found that 3H lipid was transported at a faster rate across the Thr54-expressing cells as compared to the Ala54- expressing cells. To investigate the structural differences between Ala54 and Thr54 IFABP, we have collaborated with J. Hamilton and utilized 3-D NMR to solve the structure of both proteins when bound to long-chain fatty acids. We are currently analyzing the promoters of the IFABP gene from individuals who are homzygous for the Ala54 allele and are insulin sensitive and individuals who are homzygous for the Thr54 allele and are insulin resistant. We have identified several polymorphisms and two deletions which are in total linkage disequilibration with the Ala to Thr substitution. To assay the functional consequences of these varied promoters, we have ligated them into luciferase reporter genes and transfected these vectors into Caco- 2 cells. We are currently comparing their transcriptional activity in these cells. - insulin resistance; fatty acid binding protein; - Human Subjects