Identification of a novel combined hyperlipidemia gene, Hyplip1, in a mutant mouse strain by a positional cloning strategy.

摘要

Familial combined hyperlipidemia (FCHL) is a common genetic dyslipidemia predisposing to premature coronary artery disease. Characteristics of the disorder include hypertriglyceridemia, hypercholesterolemia, and elevated apolipoprotein B (apoB). The etiology is complex, with multiple environmental and genetic influences.; One powerful approach to the dissection of a complex trait is to use animal models. We identified a mutant mouse strain, HcB-19/Dem, which shares features with FCHL, including hypertriglyceridemia, hypercholesterolemia, elevated plasma apoB, and increased secretion of very low density lipoproteins. The hyperlipidemia results from spontaneous mutation at a locus, Hyplip1, which maps to distal mouse Chromosome 3. Importantly, this region is syntenic to a FCHL locus on human 1q21–q23.; In order to identify the Hyplip1 gene, a positional cloning approach was employed. First, the Hyplip1 location was narrowed to ∼160 kilobases by fine mapping. Next, a bacterial artificial chromosome (BAC) contig was constructed. Finally, select BACs were sequenced to identify candidate genes that were analyzed for expression or sequence differences by Northern and DNA sequence analyses. In HcB-19/Dem, decreased mRNA levels were observed for a gene previously described as vitamin D₃ up-regulated protein 1 (Vdup1). Sequencing of Vdup1 RT-PCR products revealed a nonsense mutation present in the hyperlipidemic HcB-19/Dem strain but absent in the normolipidemic control strain from which it was derived. No differences were found for any other candidate genes.; The Vdup1 protein, also known as thioredoxin interacting factor (Thif), binds to and inhibits thioredoxin, a ubiquitous protein with disulfide reducing activity that plays a role in multiple cellular processes. The nonsense mutation in HcB-19/Dem mice occurs at position 337 of the 1456 bp cDNA (Genbank AF173681), corresponding to amino acid 97 of the 395 amino acid protein. The truncated Vdup1 resulting from the Hyplip1 nonsense mutation will be unable to bind and inhibit thioredoxin, since residues 134–395 are crucial for this interaction.; In addition to combined hyperlipidemia, HcB-19/Dem mice also exhibit hyperketonemia, hypoglycemia, and increased plasma lactate, free fatty acid, and unesterified cholesterol levels. Preliminary evidence also indicates an increased susceptibility to hepatic carcinoma. These results reveal a novel pathway, of potential clinical significance, influencing both lipid and carbohydrate metabolism.