Common variants of APOA5 have consistently shown association with differences in plasma triglyceride (TG) levels. These single nucleotide polymorphisms (SNPs) fall into three common haplotypes: APOA5*1, with common alleles at all sites; APOA5*2, with rare alleles of ؊1131T3 C, ؊3A3 G, 751G3 T, and 1891T3 C; and APOA5*3, distinguished by the c56C3 G (S19W). Molecular modeling of the apoAV signal peptide (SP) showed an increased angle of insertion (65°) at the lipid/water interface of Trp-19 SP compared with Ser-19 SP (40°), predicting reduced translocation. This was confirmed by 50% reduction of Trp-19-encoded SP⅐secretory alkaline phosphatase (SEAP) fusion protein secreted into the medium from HepG2 cells compared with the Ser-19⅐SEAP fusion protein (p < 0.002). Considering APOA5*2 SNPs, there was no significant difference in the relative luciferase expression in Huh7 cells transiently transfected with a ؊1131T construct compared with the ؊1131C (fragments ؊1177 to ؊516 or ؊1177 to ؊3). Similarly, for the ؊3A3 G in the Kozak sequence, in vitro transcription/translation assays and primer extension inhibition assays showed no alternate AUG initiation codon usage, demonstrating that ؊3A3 G did not influence translation efficiency. Although 1891T3 C in the 3-untranslated region disrupts a putative Oct-1 transcription factor binding site, when inserted 3 of the luciferase gene the T3 C change demonstrated no significant difference in luciferase expression. Thus, association of APOA5*2 SNPs with TG levels is not due to the individual effects of any of these SNPs, although cooperativity between the SNPs cannot be excluded. Alternatively, the effect on TG levels may reflect the strong linkage disequilibrium with the functional APOC3 SNPs.There is strong evidence from clinical studies, epidemiological studies, and animal models (reviewed in Ref. 1) that apoAV plays a key role in triglyceride (TG) 1 metabolism. Transgenic and knock-out mouse models identified an inverse relationship between apoAV and plasma TG levels (2). APOA5 variants determine between individual differences in plasma TG in all ethnic groups studied to date (3, 4). The role of apoAV in TG metabolism is further supported by the recently identified rare mutation Q145X, introducing a premature termination of apoAV and resulting in apoAV deficiency and severe hypertriglyceridemia (5). However the exact function(s) of apoAV remain to be clarified. APOA5 expression is up-regulated in liver regeneration after rat hepatectomy (6), suggesting that it acts as a break on very low density lipoprotein assembly (7). ApoAV is found preferentially on high density lipoprotein but is thought to transfer to very low density lipoprotein in the postprandial state (8) and has been shown to activate lipoprotein lipase in vitro and in vivo (9).The APOA5 gene itself is relatively polymorphic. The five most common APOA5 haplotypes can be defined by seven SNPs (10). Two haplotypes, APOA5*2 and APOA5*3, are of particular interest as they show association with raised plasma TG leve...

No abstract

Upstream stimulatory factor 1 (USF 1), is a transcription factor controlling expression of several genes involved in lipid and glucose homeostasis and co-localizes with familial combined hyperlipidemia (FCHL) and type 2 diabetes on chromosome 1q22-23. We sequenced USF1 in 24 UK FCHL probands, but found no rare or common cSNPs. Three common intronic single nucleotide ploymorphisms (SNP), 306A>G, 475C>T and 1748C>T, were identified and their association was examined with fasting and postprandial lipids and after an oral glucose tolerance test (OGTT) in the European Atherosclerosis Research Study II offspring study. There were no significant differences in allelic frequencies of the SNPs between cases and controls. Individually none of the SNPs showed significant associations with any parameter. In haplotype analysis, compared with other haplotypes, 475C/1748T showed significantly higher and 475T/1748T showed lower peak glucose (P=0.004 and 0.07, respectively) during the OGTT. There was significant case-control heterogeneity in the interaction of genotype with body mass index, on fasting low density lipoprotein with 306A>G and 1748C>T, and on borderline significance with fasting glucose with 475C>T (P=0.002, 0.0007 and 0.015, respectively). Furthermore, 475C>T showed interaction with both HSL-60C>G (case-control heterogeneity P=0.0002) on AUC TG and APOC3 -482C>T on plasma apoE levels (P=0.0012). Thus, in these healthy young men, variation in USF1 was the influencing feature of both glucose and lipid homeostasis showing case-control heterogeneity.