IDOL N342S Variant, Atherosclerosis Progression and Cardiovascular Disorders in the Italian General Population

Influence of the IDOL Gene Variants on Low-Density Lipoprotein Cholesterol Levels in Turkish Patients with Familial Hypercholesterolemia

Introduction

The inducible degrader of low-density lipoprotein (IDOL) receptor, an E3 ubiquitin ligase, was recently identified as a regulator of the LDL receptor (LDLR) pathway. Shortly, IDOL stimulates LDLR degradation through ubiquitination. However, the association of IDOL gene variants with plasma lipid levels is controversial. No previous study in the Turkish population has reported the relationship between variants of the IDOL gene and low-density lipoprotein cholesterol (LDL-C) levels. Our study aims to investigate the effects of genetic variants in the human IDOL gene, which may be a therapeutic target in human cholesterol metabolism, on LDL-C levels.

Methods

We sequenced all coding, critical intronic, and untranslated regions of the IDOL gene in 125 controls (77 women, 48 men) and 125 patients (64 women, 61 men) with definite or probable familial hypercholesterolemia (FH) according to the criteria of the Dutch Lipid Clinic Network, in whom no pathogenic/likely pathogenic LDLR variants are present.

Results

We identified 12 different IDOL gene variants, including the p.(N342S) and p.(G51S), whose association with LDL-C levels has been investigated, and classified them into common and rare variants. A rare variant p.(G51S) was only detected in patients the patient group. We compared the minor allele frequency (MAF) distribution of common variants between patient and control groups and examined the association of their genotypic distribution with plasma LDL-C levels using genetic models (dominant, recessive, overdominant, codominant). There was no statistically significant difference in the parameters of the patient and control groups (p > 0.05).

Conclusion

Our findings suggest that the common IDOL variants we identified do not associate with the LDL-C level in the Turkish population. Rare variants that were not found to be statistically significant in our study, should be emphasized, and supported with further research.

Genetic polymorphism of IDOL gene was associated with the susceptibility of coronary artery disease in Han population in Xinjiang, China

Background

Coronary artery disease (CAD) is the leading cause of death worldwide. In this study, we aimed to explore whether some genetic variants of the human IDOL gene were associated with CAD among Chinese population in Xinjiang.

Methods

We designed two independent case–control studies. The first one included in the Han population (448 CAD patients and 343 controls), and the second one is the Uygur population (304 CAD patients and 318 controls). We genotyped three SNPs (rs2072783, rs2205796, and rs909562) of the IDOL gene.

Results

Our results revealed that, in the Han female subjects, for rs2205796, the distribution of alleles, dominant model (TT vs. GG + GT) and the additive model (GG + TT vs. GT) showed significant differences between CAD patients and the control subjects (P = 0.048, P = 0.014, and P = 0.032, respectively).

Conclusions

The rs2205796 polymorphism of the IDOL gene is associated with CAD in the Chinese Han female population in Xinjiang, China.

IDOL gene variant is associated with hyperlipidemia in Han population in Xinjiang, China

Hyperlipidemia is one of the main risk factors that contributed to atherosclerosis and coronary artery disease (CAD). In the present study, our objective was to explore whether some genetic variants of human IDOL gene were associated with hyperlipidemia among Han population in Xinjiang, China. We designed a case–control study. A total of 1,172 subjects (588 diagnosed hyperlipidemia cases and 584 healthy controls) of Chinese Han were recruited. We genotyped three SNPs (rs9370867, rs909562, and rs2072783) of IDOL gene in all subjects by using the improved multiplex ligation detection reaction (iMLDR) method. Our study demonstrated that the distribution of the genotypes, the dominant model (AA vs GG + GA), and the overdominant model (AA + GG vs GA) of the rs9370867 SNP had significant differences between the case group and controls (all P < 0.001). For rs909562 and rs2072783, the distribution of the genotypes, the recessive model (AA + GA vs GG) showed significant differences between the case subjects and controls (P = 0.002, P = 0.007 and P = 0.045, P = 0.02, respectively). After multivariate adjustment for several confounders, the rs9370867 SNP is still an independent risk factor for hyperlipidemia [odds ratio (OR) = 1.380, 95% confidence interval (CI) = 1.201–1.586, P < 0.001]. The rs9370867 of human IDOL gene was associated with hyperlipidemia in Han population.

IDOL G51S Variant Is Associated With High Blood Cholesterol and Increases Low-Density Lipoprotein Receptor Degradation

Objective:

A high level of LDL-C (low-density lipoprotein cholesterol) is a major risk factor for cardiovascular disease. The E3 ubiquitin ligase named IDOL (inducible degrader of the LDLR [LDL receptor]; also known as MYLIP [myosin regulatory light chain interacting protein]) mediates degradation of LDLR through ubiquitinating its C-terminal tail. But the expression profile of IDOL differs greatly in the livers of mice and humans. Whether IDOL is able to regulate LDL-C levels in humans remains to be determined.

Approach and Results:

By using whole-exome sequencing, we identified a nonsynonymous variant rs149696224 in the IDOL gene that causes a G51S (Gly-to-Ser substitution at the amino acid site 51) from a Chinese Uygur family. Large cohort analysis revealed IDOL G51S carriers (+/G51S) displayed significantly higher LDL-C levels. Mechanistically, the G51S mutation stabilized IDOL protein by inhibiting its dimerization and preventing self-ubiquitination and subsequent proteasomal degradation. IDOL(G51S) exhibited a stronger ability to promote ubiquitination and degradation of LDLR. Adeno-associated virus-mediated expression of IDOL(G51S) in mouse liver decreased hepatic LDLR and increased serum levels of LDL-C, total cholesterol, and triglyceride.

Conclusions:

Our study demonstrates that IDOL(G51S) is a gain-of-function variant responsible for high LDL-C in both humans and mice. These results suggest that IDOL is a key player regulating cholesterol level in humans.

Cholesterol in LDL receptor recycling and degradation

The SREBP2/LDLR pathway is sensitive to cholesterol content in the endoplasmic reticulum (ER), while membrane low-density lipoprotein receptor (LDLR) is influenced by sterol response element binding protein 2 (SREBP2), pro-protein convertase subtilisin/kexin type 9 (PCSK9) and inducible degrader of LDLR (IDOL). LDL-C, one of the risk factors in cardiovascular disease, is cleared through endocytosis recycling of LDLR. Therefore, we propose that a balance between LDLR endocytosis recycling and PCSK9-mediated and IDOL-mediated lysosomal LDLR degradation is responsible for cholesterol homeostasis in the ER. For statins that decrease serum LDL-C levels via cholesterol synthesis inhibition, the mechanism by which the statins increase the membrane LDLR may be regulated by cholesterol homeostasis in the ER.

The E3 ubiquitin ligase inducible degrader of the LDL receptor/myosin light chain interacting protein in health and disease

PURPOSE OF REVIEW

The RING E3 ubiquitin ligase inducible degrader of the LDL receptor (IDOL, also known as MYLIP) promotes ubiquitylation and subsequent lysosomal degradation of the LDL receptor (LDLR), thus acting to limit uptake of lipoprotein-derived cholesterol into cells. Next to the LDLR, IDOL also promotes degradation of two related receptors, the very LDL receptor (VLDLR) and apolipoprotein E receptor 2 (APOER2), which have important signaling functions in the brain. We review here the emerging role of IDOL in lipoprotein and energy metabolism, neurodegenerative diseases, and the potential for therapeutic targeting of IDOL.

RECENT FINDINGS

Genetic studies suggest an association between IDOL and lipoprotein metabolism in humans. Studies in rodents and nonhuman primates support an in-vivo role for IDOL in lipoprotein metabolism, and also uncovered an unexpected role in whole-body energy metabolism. Recent evaluation of IDOL function in the brain revealed a role in memory formation and progression of Alzheimer's disease. The report of the first IDOL inhibitor may facilitate further investigations on therapeutic strategies to target IDOL.

SUMMARY

IDOL is emerging as an important determinant of lipid and energy metabolism in metabolic disease as well as in Alzheimer's disease. IDOL targeting may be beneficial in treating these conditions.

Molecular analysis of APOB, SAR1B, ANGPTL3, and MTTP in patients with primary hypocholesterolemia in a clinical laboratory setting: Evidence supporting polygenicity in mutation-negative patients

BACKGROUND AND AIMS

Primary hypobetalipoproteinemia is generally considered a heterogenic group of monogenic, inherited lipoprotein disorders characterized by low concentrations of LDL cholesterol and apolipoprotein B in plasma. Lipoprotein disorders include abetalipoproteinemia, familial hypobetalipoproteinemia, chylomicron retention disease, and familial combined hypolipidemia. Our aim was to review and analyze the results of the molecular analysis of hypolipidemic patients studied in our laboratory over the last 15 years.

METHODS

The study included 44 patients with clinical and biochemical data. Genomic studies were performed and genetic variants were characterized by bioinformatics analysis. A weighted LDL cholesterol gene score was calculated to evaluate common variants associated with impaired lipid concentrations and their distribution among patients.

RESULTS

Twenty-three patients were genetically confirmed as affected by primary hypobetalipoproteinemia. In this group of patients, the most prevalent mutated genes were APOB (in 17 patients, with eight novel mutations identified), SAR1B (in 3 patients, with one novel mutation identified), ANGPTL3 (in 2 patients), and MTTP (in 1 patient). The other 21 patients could not be genetically diagnosed with hypobetalipoproteinemia despite presenting suggestive clinical and biochemical features. In these patients, two APOB genetic variants associated with lower LDL cholesterol were more frequent than in controls. Moreover, the LDL cholesterol gene score, calculated with 11 SNPs, was significantly lower in mutation-negative patients.

CONCLUSIONS

Around half of the patients could be genetically diagnosed. The results suggest that, in at least some of the patients without an identified mutation, primary hypobetalipoproteinemia may have a polygenic origin.

Genetic determinants of inherited susceptibility to hypercholesterolemia - a comprehensive literature review

Hypercholesterolemia is a strong determinant of mortality and morbidity associated with cardiovascular diseases and a major contributor to the global disease burden. Mutations in four genes (LDLR, APOB, PCSK9 and LDLRAP1) account for the majority of cases with familial hypercholesterolemia. However, a substantial proportion of adults with hypercholesterolemia do not have a mutation in any of these four genes. This indicates the probability of having other genes with a causative or contributory role in the pathogenesis of hypercholesterolemia and suggests a polygenic inheritance of this condition. Here in, we review the recent evidence of association of the genetic variants with hypercholesterolemia and the three lipid traits; total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C), their biological pathways and the associated pathogenetic mechanisms. Nearly 80 genes involved in lipid metabolism (encoding structural components of lipoproteins, lipoprotein receptors and related proteins, enzymes, lipid transporters, lipid transfer proteins, and activators or inhibitors of protein function and gene transcription) with single nucleotide variants (SNVs) that are recognized to be associated with hypercholesterolemia and serum lipid traits in genome-wide association studies and candidate gene studies were identified. In addition, genome-wide association studies in different populations have identified SNVs associated with TC, HDL-C and LDL-C in nearly 120 genes within or in the vicinity of the genes that are not known to be involved in lipid metabolism. Over 90% of the SNVs in both these groups are located outside the coding regions of the genes. These findings indicates that there might be a considerable number of unrecognized processes and mechanisms of lipid homeostasis, which when disrupted, would lead to hypercholesterolemia. Knowledge of these molecular pathways will enable the discovery of novel treatment and preventive methods as well as identify the biochemical and molecular markers for the risk prediction and early detection of this common, yet potentially debilitating condition.

IDOL, inducible degrader of low-density lipoprotein receptor, serves as a potential therapeutic target for dyslipidemia

Low-density lipoprotein cholesterol (LDL-C) is the hall marker for the atherosclerotic cardiovascular disease (ASCVD). It has been shown that over 70% of circulating LDL-C is metabolized through binding and activation of hepatic LDL receptor (LDLR). Genetic LDLR mutations cause hypercholesterolemia in the patients. Therefore, elevation of LDLR levels is beneficial for the treatment of dyslipidemia. LDLR expression is regulated by the SREBP2/PCSK9 pathways. Targeting SREBP2/PCSK9 pathways by statins and human monoclonal PCSK9 antibody has been shown to reduce the progression of ASVCD. Recent studies identified that inducible degrader of LDLR (IDOL) is a novel regulator of LDLR. IDOL is an E3-ubiquitin ligase regulated via liver X receptors (LXRs) binding to the upstream of translation start site of IDOL. IDOL modulates LDLR distribution through ubiquitination and degradation of LDLR in lysosomes. Genome-wide association studies (GWAS) have revealed that the nonsynonymous substitution rs9370867 of IDOL probably contributes to the variability of circulating LDL levels. Recently studies also demonstrated that IDOL influences PCSK9 expression in a LDLR/SREBP2-dependent manner. Based upon these novel findings, we hypothesize that IDOL and PCSK9 would have a synergistic effect on LDLR distribution. Specifically, loss of IDOL increases LDLR distribution in the hepatic cell, and subsequently reduces serum LDL-C levels in dyslipidemic patients. IDOL might be a potential therapeutic target for the treatment of ASCVD.