The Role of the Intestinal Fatty Acid Binding Protein in Insulin Resistance

我们以前的研究确定了染色体4 q上的一个区域，该区域与胰岛素作用的测量有关。 该区域中的候选基因是编码人肠脂肪酸结合蛋白（IFABP）的FABP 2。 我们确定了在这个基因的多态性，导致丙氨酸（Ala 54）苏氨酸（Thr 54）取代IFABP的氨基酸54。 我们发现编码Thr 54的IFABP基因型（频率= 0.29）与空腹脂质氧化速率和胰岛素抵抗增加之间存在显著相关性，并进一步表明重组Thr 54蛋白与重组Ala 54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取代的生理后果，通过分析脂肪酸转运通过永久转染的细胞表达Ala 54和Thr 54 IFABP。 我们发现，3 H脂质转运在一个更快的速度跨越Thr 54表达细胞相比，Ala 54表达细胞。我们还分析了来自Ala 54等位基因纯合且胰岛素敏感的个体和Thr 54等位基因纯合且胰岛素抵抗的个体的IFABP基因的启动子。我们已经鉴定了几个多态性和两个缺失，它们与Ala到Thr的取代处于完全连锁不平衡。 为了分析这些不同启动子的功能结果，我们将它们连接到荧光素酶基因中，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。一旦我们确定启动子变体是否影响转录活性，我们将终止该项目。

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. We have also analyzed the promoters of the IFABP gene from individuals who are homzygous for the Ala54allele and are insulin sensitive and individuals who are homzygous for the Thr54 allele and are insulin resistant. Wehave identified several polymorphisms and two deletions whichare 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 reportergenes and transfected these vectors into Caco-2 cells. We are currently comparing their transcriptional activity in these cells. Once we have determined whether the promoter variants affect transcriptional activity, we will terminate this project.