A novel LPL intronic variant: g.18704C>A identified by re-sequencing Kuwaiti Arab samples is associated with high-density lipoprotein, very low-density lipoprotein and triglyceride lipid levels

A Set of Proximal Regulatory Elements Contribute to the Transcriptional Activity of the Human Lipoprotein Lipase Promoter

Lipoprotein lipase (LPL) is a multifunctional protein that catalyzes the hydrolysis of plasma triglycerides, releasing free fatty acids, which play critical roles in the metabolism and transport of lipids. The transcription of LPL in response to cell types and regulatory factors is a complex process that starts with its promoter. In previous studies, several proximal regulatory elements within the human LPL promoter were individually characterized. This study was designed to characterize the effect of 12 proximal regulatory elements as a combined unit on the transcriptional activity of the LPL promoter. The hypothesis was that these proximal regulatory elements collectively result in the optimal transcriptional activity of the human LPL promoter. Full and partial LPL promoter sequences, which contained and excluded the 12 regulatory elements, respectively, were cloned and inserted into a promoterless luciferase reporter vector. The functional activities of these constructs were tested in vitro using a dual-luciferase reporter assay. Our results showed that HEK-293 cells transfected with the full LPL promoter exhibited significantly greater luciferase activity than cells transfected with partial LPL promoters. Our results indicate that the proximal regulatory elements within the LPL promoter, including four TATA boxes, two Oct-1 sites, one CT element, two C/EBPα sites, one SP1 site, and two cis-acting regions (LP-α and LP-β), are essential for its transcriptional activity.

Sequence Variant Analysis of the APOCII Locus among an Arab Cohort

Apolipoprotein CII (ApocII) plays a key role in regulating lipoprotein lipase (LPL) in lipid metabolism and transport. Numerous polymorphisms within APOCII are reportedly associated with type 2 diabetes mellitus (T2DM), dyslipidemia, and aberrant plasma lipid levels. Few studies have investigated sequence variants at APOCII loci and their association with metabolic disorders. This study aimed to identify and characterize genetic variants by sequencing the full APOCII locus and its flanking sequences in a sample of the Kuwaiti Arab population, including patients with T2DM, hypertriglyceridemia, non-Arab patients with T2DM, and healthy Arab controls. A total of 52 variants were identified in the noncoding sequences: 45 single nucleotide polymorphisms, wherein five were novel, and seven insertion deletions. The minor allele frequency (MAF) of the 47 previously reported variants was similar to the global MAF and to that reported in major populations. Sequence variant analysis predicted a conserved role for APOCII with a potential role for rs5120 in T2DM and rs7133873 as an informative ethnicity marker. This study adds to the ongoing research that attempts to identify ethnicity-specific variants in the apolipoprotein gene loci and associated LPL genes to elucidate the molecular mechanisms of metabolic disorders.

Identification and Characterization of Variants in Intron 6 of the LPL Gene Locus among a Sample of the Kuwaiti Population

Lipoprotein lipase (LPL) is responsible for the hydrolysis of lipoproteins; hence defective LPL is associated with metabolic disorders. Here, we identify certain intronic insertions and deletions (InDels) and single nucleotide polymorphisms (SNPs) in intron 6 of the LPL gene and investigate their associations with different phenotypic characteristics in a cohort of the general Kuwaiti population. Two specific regions of intron 6 of the LPL gene, which contain InDels, were amplified via Sanger sequencing in 729 subjects. Genotypic and allelic frequencies were estimated, and genetic modeling was used to investigate genetic associations of the identified variants with lipid profile, body mass index (BMI), and risk of coronary heart disease (CHD). A total of 16 variants were identified, including 2 InDels, 2 novel SNPs, and 12 known SNPs. The most common variants observed among the population were rs293, rs274, rs295, and rs294. The rs293 “A” insertion showed a significant positive correlation with elevated LDL levels, while rs295 was significantly associated with increased BMI. The rs274 and rs294 variants showed a protective effect of the minor allele with decreased CHD prevalence. These findings shed light on the possible role of LPL intronic variants on metabolic disorders.

Genetic association of LPL rs326 with BMI among the Kuwaiti population

Supplemental Digital Content is available in the text.

Lipoprotein lipase is a key enzyme in lipid metabolism with reported variants associated with obesity, hypertension, type 2 diabetes, and coronary heart disease. This study was performed to investigate the association between common lipoprotein lipase single nucleotide polymorphisms and metabolic disorders in a sample of Kuwaiti cohort (n = 494). Five lipoprotein lipase variants (rs1801177, rs295, rs326, ss2137497749, and ss2137497750) across the lipoprotein lipase gene were genotyped by real-time PCR employing the TaqMan allele discrimination assay. Genotype, allelic frequencies, and Hardy-Weinberg Equilibrium were determined for each variant in the cohort followed by multivariate and logistic regression analysis. A novel finding was observed for the G allele of single nucleotide polymorphism rs326 which was associated with increased BMI after adjusting for age and sex (β = 1.04; 95% confidence interval = 0.15–1.94; P = 0.02). Moreover, a significant difference in the distribution of the minor C allele of rs295 among coronary heart disease subjects compared with noncoronary heart disease, however, this significance was diminished after controlling for age, sex, and BMI. This study demonstrated that lipoprotein lipase rs326 may be indicative for the increased risk of obesity and possibly rs295 for coronary heart disease. The findings are also in agreement with other reports suggesting that intronic variants are important genetic markers in association studies. The findings warrant further studies in a large cohort to confirm and validate the results presented.

Association between the lipoprotein lipase rs1534649 gene polymorphism in intron one with Body Mass Index and High Density Lipoprotein-Cholesterol

Lipoprotein lipase (LPL) is an enzyme involved in lipid metabolism and distribution of fatty acids hence its role in the initiation and development of dyslipidemia and adiposity. Single nucleotide polymorphisms (SNPs) across the LPL gene have been associated with dyslipidemia, however, the association with obesity has been limited towards specific populations. This study examined the association between LPL gene polymorphisms with plasma lipid levels and body mass index (BMI) in the Kuwaiti population. We examined a total of 486 adults (303 and 183 females and males respectively) with plasma lipid levels and BMI. DNA samples were genotyped for two LPL gene polymorphisms (rs1534649 and rs28645722) using TaqMan allelic discrimination. The relationship between the genotypes with both plasma lipid levels and BMI were assessed using linear regression using “SNPassoc” package from R statistical software. Using an additive genetic model, linear regression analysis showed the T-allele of rs1534649 to be associated with increased BMI in a dose-dependent trend β = 2.13 (95% CI 1.33–2.94); p = 1.7 × 10⁻⁷. In addition, a borderline significance was observed between the T-allele and low levels of high density lipoprotein-cholesterol β = −0.04 (95% CI −0.08, −0.006); p = 0.02. There were no associations between rs28645722 and plasma lipid levels (p > 0.05). However, a trend was observed between the A-allele and increased BMI β = 1.75 (95% CI 0.14–3.35); p = 0.03. Our study shows intron one polymorphism rs1534649 to increase the risk of obesity and dyslipidemia. Our findings warrant further investigation of the mechanism of LPL on the development of obesity along with the role of intron one and its impact on LPL gene activity.

Genetic association of LPL rs1121923 and rs258 with plasma TG and VLDL levels

Lipoprotein lipase (LPL) is a rate-limiting enzyme for the hydrolysis of triglycerides (TG). Hundreds of genetic variants including single nucleotide polymorphisms have been identified across the 30Kb gene locus on chromosome 8q22. Several of these variants have been demonstrated to have genetic association with lipid level variation but many remain unresolved. Controversial reports on the genetic association of variants among different populations pose a challenge to which variants are informative. This study aimed to investigate "common" LPL variants (rs1121923, rs258, rs328, rs13702) and their possible role in plasma lipid level. Genotyping was performed using Realtime PCR. Based on the observed genotypes, the minor allele frequencies were A: 0.065 for rs1121923; C: 0.379 for rs258; G: 0.087 for rs328 and C: 0.337 for rs13702. Using linear regression, a lowering effect of rs1121923 (p = 0.024) on TG levels (-0.14 B coefficient: CI: -0.27--0.019) and rs258 (p = 0.013) on VLDL levels (B: -0.046; CI: -0.082--0.009) was observed indicating a "protective" role for the two variants. Moreover, the findings indicate the potential for including rs1121923 and rs258 in diagnostic panels for use as an estimator of "risk" scores for dyslipidemia.