Identification of Genetic Variants in Endothelial Lipase in Persons With Elevated High-Density Lipoprotein Cholesterol

Abstract

Background-Elevated high-density lipoprotein cholesterol (HDL-C) is associated with reduced risk of cardiovascular disease, and variation in HDL-C levels has been shown to be Ϸ50% heritable. Overexpression of endothelial lipase (EL), a member of the lipoprotein lipase gene family, markedly reduces HDL-C levels in mouse models. We hypothesized that genetic variation in EL might be associated with elevated HDL-C. Methods and Results-All exons and 1.2 kilobase of promoter of the EL gene were sequenced in 20 unrelated human subjects with high HDL-C levels. A total of 17 variants were identified. Six of these were potentially functional and were confirmed by restriction enzyme analysis. Four variants result in amino acid changes (Gly26Ser, Thr111Ile, Thr298Ser, and Asn396Ser,) and 2 variants were in the promoter (Ϫ303A/C and Ϫ410C/G). The genotype frequencies of each variant were determined in 176 black controls, 165 white controls, and 123 whites with high HDL-C. The Thr111Ile variant was the most common, with an allele frequency of 10.3% in blacks, 31.2% in white controls, and 32.6% in the high HDL-C group. The remaining variants all had allele frequencies Ͻ5.0% but differed in frequency among the 3 groups. Interestingly, Gly26Ser, Thr298Ser, and Ϫ303A/C were found in the black and high HDL-C white cohorts but were absent in the control white group. Conclusions-Six new potentially functional variants in EL were discovered through sequencing of the EL gene in subjects with high HDL-C levels. Differences in allele frequencies exist between blacks and whites and between control subjects and those with high HDL-C levels. 2 Endothelial lipase (EL) is the most recently discovered member of the LPL, or triglyceride (TG) lipase, gene family. Cloned independently by 2 groups using distinct methods, 3,4 the EL gene spans 10 exons and 9 introns and encodes a polypeptide of 500 amino acids. The EL cDNA is 45% homologous to LPL and 40% to HL. Many of the regulatory domains found in LPL and HL, such as the lipoprotein and heparin-binding domains, are highly conserved in EL. 5 Unlike LPL and HL, EL is synthesized by endothelial cells and primarily acts as a phospholipase. 6 Whereas LPL activity indirectly influences the metabolism of high-density lipoprotein cholesterol (HDL-C) levels, 7 HL directly modulates the metabolism of HDL in vivo by converting larger HDL to smaller HDL. 2 Because EL acts predominantly as a phospholipase and the phospholipid content of HDL is a major factor in determining apolipoprotein A-I (apoA-I) conformation 8 and HDL function, 9 -11 we hypothesized that HDL might be a major substrate for EL. We showed that HDL is an excellent and preferred substrate for EL ex vivo. 6 Furthermore, we demonstrated that HDL-C and apoA-I levels were markedly reduced in mice injected with an adenoviral vector encoding human EL. 3 These results suggested that EL may play a central role in HDL metabolism.At least 50% of the variation in HDL-C is genetically determined. 12,13 Genetic diversity at both the LPL and HL loci ha...

Endothelial lipase is a major genetic determinant for high-density lipoprotein concentration, structure, and metabolism

“…The association between the LIPG gene SNP and plasma HDL-c in this study is at odds with that of deLemos et al (11). The apparent discrepancy is likely the result of different study designs.…”

“…A study by deLemos et al (11) failed to find a difference in allele frequencies of EL (LIPG) gene variants between individuals with high HDL-c and those with normal HDL-c. Because allele frequency comparison between different populations is not a very sensitive method for detecting the contribution of a specific gene locus to a phenotype, we analyzed the genotype distribution of an SNP, 584C͞T, in LIPG in a well studied population (11). This SNP produces a protein variant (T111I) with a high frequency compared with other SNPs and EL protein variants, which are extremely rare (11). T111 is conserved between mouse and human EL and HL, but is not conserved in LPL.…”

“…The LCAS, which was not preselected on the basis of HDL-c, was a prospective study of 372 subjects between 35 and 75 years old who had LDL cholesterol levels of 115-190 mg͞dl and Ն1 coronary lesion causing 30-75% diameter stenosis (27). The LCAS subjects included only 27 (or 7%) African Americans, as opposed to the study of deLemos et al (11), which included 50% African Americans as the non-high HDL control for a high-HDL group consisting of 100% white subjects. Distribution of the 584C͞T genotypes among the LCAS subjects displayed Hardy-Weinberg equilibrium (P ϭ 0.91, comparing observed vs. expected genotypes), and the association between the 584C͞T genotypes and plasma levels of lipid and apolipoprotein parameters was independent of race, gender, or age.…”

“…On the other hand, Jaye et al (7) showed that massive overexpression of EL in the liver by adenovirusmediated gene transfer in mice causes marked depletion of HDL, together with a major reduction in non-HDL lipoproteins. However, McCoy et al (9) found that EL is completely inactive in vitro in the presence of serum, and deLemos et al (11) found no significant difference in allele frequencies of six polymorphisms in the EL (LIPG) gene between individuals with normal and those with high HDL cholesterol (HDL-c). Thus, the physiological role of EL in lipoprotein metabolism, if any, is unknown.…”

Lipasa endotelial y su relación con la enfermedad cardiovascular y diabetes mellitus tipo 2

“…En humanos, se han identifi cado variantes genéticas de LE en personas con c-HDL elevado 11,13,14,15 . En un estudio de 372 personas portadoras de un polimorfi smo que determina la reducción de la actividad enzimática, se encontró que los homocigotos para esta mutación tienen un colesterol HDL 14% mayor que aquellos sujetos que no presentaron la mutación o que resultaron heterocigotos para la misma 11 .…”