Novel genes in LDL metabolism--a comprehensive overview

The association of Sort1 expression with LDL subfraction and inflammation in patients with coronary artery disease

BACKGROUND

Controversial effect of sortilin on lipoprotein metabolism in the development of atherosclerosis reveals the need for more extensive research.

OBJECTIVES

The aim of this study was to investigate the association between Sort1 gene expression and lipids, lipoprotein subfractions, and inflammation in CAD.

METHODS

The study population included 162 subjects with CAD and 49 healthy individuals. The Sort1 gene expression level was determined by qRT-PCR using Human Sortilin TaqMan Gene Expression Assays. Lipoprotein subclasses were analysed by the Lipoprint system. Serum levels of apolipoprotein and CRP were measured by autoanalyzer.

RESULTS

Sort1 gene expression and atherogenic subfraction (SdLDL) levels were significantly higher (p < 0.001) while atheroprotective subfraction (LbLDL) was lower in the subjects with CAD (p < 0.050). Also, increased Sort1 gene expression levels were observed in those with higher CRP values.

CONCLUSIONS

Our findings reveal that the high Sort1 gene expression has a prominent linear relationship with both the atherogenic LDL phenotype and proinflammation, thereby might contribute to the occurrence of CAD.

Genome-wide association study revealed novel candidate gene loci associated with soluble E-selectin levels in a Taiwanese population

BACKGROUND AND AIMS

Increase soluble E-selectin (sE-selectin) levels are associated with various inflammation and cardiometabolic disorders.

METHODS

This study aimed to investigate the genetic determinants of circulating sE-selectin levels by genome-wide association study (GWAS) in 4,525 Taiwan Biobank (TWB) participants and genotype-phenotype association analysis for sE-selectin level-determining alleles in over 80,000 TWB participants.

RESULTS

By GWAS, ABO, SELE, and FUT6 gene variants were identified as the determinants of sE-selectin levels, which reach genome-wide significance (maximum p = 3.25 × 10-271, 4.81 × 10-14, and 9.64 × 10-12, respectively). After further adjustment for the lead ABO rs2519093 genotypes, three novel gene loci, EVI5, FER and DMAC1, were associated with sE-selectin levels at p < 5 × 10-7. Three other previously reported gene loci, CELSR2, ST3GAL6-AS1, and HNF1A-AS1, also showed supportive evidence for the association with sE-selectin levels (maximum p < 0.0073). A multivariate analysis revealed age, body mass index, current smoking, hemoglobin A1C, hematocrit, leukocyte and platelet counts, serum alanine aminotransferase, triglycerides, and uric acid levels were independently associated with sE-selectin levels, in which the above ten gene loci contribute to 27.68% of the variance. For genotype-phenotype association analysis, a pleiotropic effect was demonstrated with genome-wide significant association between ABO gene variants and total and low-density-lipoprotein cholesterol levels, leukocyte counts and hematocrit.

CONCLUSIONS

Our data provide novel insight into the regulation of sE-selectin levels. These results may open new avenues in understanding the critical role of E-selectin on the pathogenesis of inflammatory and cardiometabolic disorders.

Polygenic influences on dyslipidemias

PURPOSE OF REVIEW

Rare large-effect genetic variants underlie monogenic dyslipidemias, whereas common small-effect genetic variants - single nucleotide polymorphisms (SNPs) - have modest influences on lipid traits. Over the past decade, these small-effect SNPs have been shown to cumulatively exert consistent effects on lipid phenotypes under a polygenic framework, which is the focus of this review.

RECENT FINDINGS

Several groups have reported polygenic risk scores assembled from lipid-associated SNPs, and have applied them to their respective phenotypes. For lipid traits in the normal population distribution, polygenic effects quantified by a score that integrates several common polymorphisms account for about 20-30% of genetic variation. Among individuals at the extremes of the distribution, that is, those with clinical dyslipidemia, the polygenic component includes both rare variants with large effects and common polymorphisms: depending on the trait, 20-50% of susceptibility can be accounted for by this assortment of genetic variants.

SUMMARY

Accounting for polygenic effects increases the numbers of dyslipidemic individuals who can be explained genetically, but a substantial proportion of susceptibility remains unexplained. Whether documenting the polygenic basis of dyslipidemia will affect outcomes in clinical trials or prospective observational studies remains to be determined.

Polygenic Hypercholesterolemia: Examples of GWAS Results and Their Replication in the Czech-Slavonic Population

Since 2007, the year of their first widespread use, genome-wide association studies (GWAS) have become the “gold standard” for the detection of causal genes and polymorphisms in all fields of human medicine. Cardiovascular disease (CVD), one of the major causes of morbidity and mortality, is no exception. The first GWAS focused on hypercholesterolemia and dyslipidemia as the major CVD determinants. GWAS confirm the importance of most of the previously identified genes (e.g. APOE, APOB, LDL-R) and recognize the importance of new genetic determinants (e.g. within the CILP2 or SORT1 gene clusters). Nevertheless, the results of GWAS still require confirmation by independent studies, as interethnic and interpopulation variability of SNP effects have been reported. We analyzed an association between eight variants within seven through GWAs detected loci and plasma lipid values in the Czech post-MONICA population sample (N=2,559). We confirmed an association (all P<0.01) between plasma LDL-cholesterol values and variants within the CILP2 (rs16996148), SORT1 (rs646776), APOB (rs693), APOE (rs4420638) and LDL-R (rs6511720) genes in both males (N=1,194) and females (N=1,368). In contrast, variants within the APOB (rs515135), PCSK9 (rs11206510) and HMGCoAR (rs12654264) genes did not significantly affect plasma lipid values in Czech males or females. Unweighted gene score values were linearly associated with LDL-cholesterol values both in males (P<0.0005) and females (P<0.00005). We confirmed the effects of some, but not all analyzed SNPs on LDL-cholesterol levels, reinforcing the necessity for replication studies of GWA-detected gene variants.

Shunts, channels and lipoprotein endosomal traffic: a new model of cholesterol homeostasis in the hepatocyte

The liver directs cholesterol metabolism in the organism. All the major fluxes of cholesterol within the body involve the liver: dietary cholesterol is directed to the liver; cholesterol from peripheral cells goes to the liver; the liver is a major site of cholesterol synthesis for the organism; cholesterol is secreted from the liver within the bile, within apoB lipoproteins and translocated to nascent HDL. The conventional model of cholesterol homeostasis posits that cholesterol from any source enters a common, rapidly exchangeable pool within the cell, which is in equilibrium with a regulatory pool. Increased influx of cholesterol leads rapidly to decreased synthesis of cholesterol. This model was developed based on in vitro studies in the fibroblast and validated only for LDL particles. The challenges the liver must meet in vivo to achieve cholesterol homeostasis are far more complex. Our model posits that the cholesterol derived from three different lipoproteins endosomes has three different fates: LDL-derived cholesterol is largely recycled within VLDL with most of the cholesterol shunted through the hepatocyte without entering the exchangeable pool of cholesterol; high density lipoprotein-derived CE is transcytosed into bile; and chylomicron remnant-derived cholesterol primarily enters the regulatory pool within the hepatocyte. These endosomal channels represent distinct physiological pathways and hepatic homeostasis represents the net result of the outcomes of these distinct channels. Our model takes into account the distinct physiological challenges the hepatocyte must meet, underlie the pathophysiology of many of the apoB dyslipoproteinemias and account for the sustained effectiveness of therapeutic agents such as statins.