Intestinal Fatty Acid Binding Protein In Insulin Resista

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）与增加的空腹脂质氧化速率和胰岛素抗性之间存在显著关联，并且进一步表明重组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。在皮马印第安人的FABP 2启动子中鉴定出七种变异。这些启动子变体的基因型彼此完全一致，并且与Ala 54 Thr完全一致。因此，只有两个启动子单倍型，观察皮马印第安人，一个Ala 54相关的启动子和Thr 54相关的启动子。相比之下，高加索人DNA中这些变异体的基因分型揭示了多个单倍型。体外报告基因分析表明，Thr 54相关的启动子在皮马印第安人导致在启动子活性的三倍减少相比，野生型。我们的结论是，两个功能的变化存在于FABP 2-编码Ala 54 Thr和变体启动子。在皮马印第安人群体中，而不是在高加索人群体中，这两种功能变体总是携带在同一等位基因上。这是可能的，一些体内表型协会先前归因于Ala 54 Thr取代，这改变了蛋白质的结合特性，而可能是由于启动子的变化，这改变了表达水平。

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.