Intestinal Fatty Acid Binding Protein In Insulin Resista

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。我们还分析了胰岛素敏感的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。在皮马印第安人的FABP2启动子中发现了7个变异。这些启动子变异的基因型彼此完全一致，并与Ala54Thr基因完全一致。因此，在皮马印第安人中只观察到两个启动子单倍型，一个是ala54相关启动子，一个是thr54相关启动子。相比之下，这些变异在高加索DNA中的基因分型显示出多个单倍型。体外报告基因分析表明，与野生型相比，皮马印第安人的thr54相关启动子活性降低了三倍。我们得出结论，FABP2存在两种功能变异-编码Ala54Thr和变异启动子。在皮马印第安人群体中，而不是在高加索人群中，这两种功能变体总是携带在同一个等位基因上。先前归因于Ala54Thr取代的一些体内表型关联可能是由于启动子变异，从而改变了蛋白质的结合特性，从而改变了表达水平。

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 Ala54 allele and are insulin sensitive and individuals who are homzygous for the Thr54 allele and are insulin resistant. Seven variations were identified in the FABP2 promoter in Pima Indians. Genotypes of these promoter variants were in complete concordance with each other, and were in complete concordance with the Ala54Thr. Therefore, only two promoter haplotypes were observed in Pima Indians, an Ala54-associated promoter and a Thr54-associated promoter. In contrast, genotyping of these variants in Caucasian DNA revealed multiple haplotypes. In vitro reporter assays indicated that the Thr54-associated promoter in Pima Indians resulted in a three-fold reduction in promoter activity as compared to wild type. We conclude that two functional variations exist in FABP2- the coding Ala54Thr and the variant promoter. In the Pima Indian population, but not in the Caucasian population, these two functional variants are always carried on the same allele. It is likely that some of the in vivo phenotypic associations previously attributed to the Ala54Thr substitution, which alters binding characteristics of the protein, could instead be due to promoter variation, which alters expression levels.