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

我们之前的研究确定了染色体4Q上的一个区域，该区域与衡量胰岛素作用的指标有关。该区域的候选基因是编码人类肠道脂肪酸结合蛋白(IFABP)的FABP2。我们鉴定了该基因的一种多态，导致IFABP的54位氨基酸发生丙氨酸(Ala54)到苏氨酸(Thr54)的替换。我们发现编码Thr54的IFABP基因(频率=0.29)与空腹脂肪氧化率增加和胰岛素抵抗显著相关，并进一步表明与重组Ala54蛋白相比，重组Thr54蛋白对长链脂肪酸的亲和力更高。我们通过分析表达Ala54和Thr54 IFABP的永久性转基因细胞之间的脂肪酸转运，进一步研究了IFABP替换的生理学后果。我们发现，与表达Ala54的细胞相比，表达Thr54的细胞转运~3H脂质的速度更快。我们还分析了Ala54纯合子胰岛素敏感个体和Thr54纯合子胰岛素抵抗个体的IFABP基因启动子。我们已经鉴定出几个多态和两个缺失，它们与Ala到Thr的替换完全连锁不平衡。为了测试这些不同启动子的功能结果，我们将它们连接到荧光素酶报告基因，并将这些载体导入Caco-2细胞。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，我们将终止这个项目。

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.