Genomic Variants and Multilevel Regulation of ABCA1, ABCG1, and SCARB1 Expression in Atherogenesis

Atheroprotective properties of human plasma high-density lipoproteins (HDLs) are determined by their involvement in reverse cholesterol transport (RCT) from the macrophage to the liver. ABCA1, ABCG1, and SR-BI cholesterol transporters are involved in cholesterol efflux from macrophages to lipid-free ApoA-I and HDL as a first RCT step. Molecular determinants of RCT efficiency that may possess diagnostic and therapeutic meaning remain largely unknown. This review summarizes the progress in studying the genomic variants of ABCA1, ABCG1, and SCARB1, and the regulation of their function at transcriptional and post-transcriptional levels in atherosclerosis. Defects in the structure and function of ABCA1, ABCG1, and SR-BI are caused by changes in the gene sequence, such as single nucleotide polymorphism or various mutations. In the transcription initiation of transporter genes, in addition to transcription factors, long noncoding RNA (lncRNA), transcription activators, and repressors are also involved. Furthermore, transcription is substantially influenced by the methylation of gene promoter regions. Post-transcriptional regulation involves microRNAs and lncRNAs, including circular RNAs. The potential biomarkers and targets for atheroprotection, based on molecular mechanisms of expression regulation for three transporter genes, are also discussed in this review.

Denaturation of human plasma high-density lipoproteins by urea studied by apolipoprotein A-I dissociation

We studied the mechanism of HDL denaturation with concomitant apoA-I dissociation with HDL preparations from 48 patients with a wide range of plasma HDL-C and evaluated the contribution of lipid-free apoA-I into cholesterol efflux from macrophage, in particular, mediated by cholesterol transporter ABCA1. We prepared HDL by precipitation of apoB-containing lipoproteins by polyethylene glycol and used the chaotropic agent urea to denature HDL preparations. Apo-I dissociation from urea-treated HDL was assessed by the increase of preβ-band fraction with agarose gel electrophoresis followed by electro transfer and immunodetection and by the increase of ABCA1-mediated efflux of fluorescent analogue BODIPY-Cholesterol from RAW 264.7 macrophages. The HDL denaturation is governed by a single transition to fully dissociated apoA-I and the transition cooperativity decreases with increasing HDL-C. The apoA-I release depends on phospholipid concentration of HDL preparation and HDL compositional and structural heterogeneity and is well described by apolipoprotein partition between aqueous and lipid phases. Dissociated apoA-I determines the increase of ABCA1-mediated efflux of BODIPY-Cholesterol from RAW 264.7 macrophages to patient HDL. The increase in apoA-I dissociation is associated with the increase of ABCA1 gene transcript in peripheral blood mononuclear cells from patients. The low level of plasma HDL particles may be compensated by their increased potency for apoA-I release, thus suggesting apoA-I dissociation as a new HDL functional property.

[Synthesis and tuberculostatic activity of fluoridized 3-Z-hydrazine-2-benzoyl acrylates and their cyclization products]

A rapid development of the resistance of drugs and their toxic and adverse reactions suggest that new antituberculous drugs should be designed. Of the greatest importance is isoniazid resistance. Testing new compounds (IIa, b) has established that the minimum inhibitory concentration of the drug (IIa), 0.39 microgram/ml suppresses the growth of Mycobacterium tuberculosis (MBT) in the macrophages up to 50%, that of the drug (IIb), 1.56 micrograms/ml, causes death in 25% of cases, which is indicative of the high activity of compounds (IIa, b) against MBT.

Differential Expression of Subsets of Genes Related to HDL Metabolism and Atherogenesis in the Peripheral Blood in Coronary Artery Disease

Differential expression of genes (DEGs) in coronary artery disease (CAD) and the association between transcript level and high-density lipoprotein cholesterol (HDL-C) were studied with 76 male patients with CAD and 63 control patients. The transcript level of genes related to HDL metabolism (24 genes) and atherosclerosis-prone (41 genes) in RNA isolated from peripheral blood mononuclear cells was measured by real-time RT-PCR. Twenty-eight DEGs were identified. The expression of cholesterol transporters, ALB, APOA1, and LCAT was down-regulated, while the expression of AMN, APOE, LDLR, LPL, PLTP, PRKACA, and CETP was up-regulated. The systemic inflammation in CAD is evidenced by the up-regulation of IL1B, TLR8, CXCL5, and TNFRSF1A. For the controls, TLR8 and SOAT1 were negative predictors of the HDL-C level. For CAD patients, PRKACG, PRKCQ, and SREBF1 were positive predictors, while PRKACB, LCAT, and S100A8 were negative predictors. For CAD patients, the efficiency of reverse cholesterol transport is 73-79%, and intracellular free cholesterol seems to accumulate at hyperalphalipoproteinemia. Both atheroprotective (via S100A8) and proatherogenic (via SREBF1, LCAT, PRKACG, PRKACB, and PRKCQ) associations of gene expression with HDL-C determine HDL functionality in CAD patients. The selected key genes and involved pathways may represent HDL-specific targets for the diagnosis and treatment of CAD and atherosclerosis.

HDL Cholesterol-Associated Shifts in the Expression of Preselected Genes Reveal both Pro-Atherogenic and Atheroprotective Effects of HDL in Coronary Artery Disease

BACKGROUND

The associations of high-density lipoprotein (HDL) level and functionality with lipid metabolism, inflammation, and innate immunity in coronary artery disease (CAD) remain controversial. The differential expression of a set of genes related to HDL metabolism (24 genes) and atherogenesis (41 genes) in peripheral blood mononuclear cells (PBMC) from CAD and control patients with varied HDL cholesterol (HDL-C) levels was compared.

METHODS

76 male patients 40-60 years old with CAD diagnosed by angiography and 63 control patients were divided into three groups with low, normal (1.0-1.4 mM), and increased HDL-C levels. Transcript levels were measured by real-time PCR. The differentially expressed genes (DEGs) and associated metabolic pathways were analyzed for three groups, with prevalent CAD as an outcome.

RESULTS

The common feature was the increased odds ratio values for liver X receptor (LXR) gene expression for three patient groups. CAD patients with low HDL-C possessed 24 DEGs with lower expression of genes involved in cholesterol efflux, and down-regulated SREBF1 and ABCG1 are suggested as gene signatures. CAD patients with normal HDL-C possessed nine DEGs with down-regulated ITGAM and ALB as gene signatures. CAD patients with increased HDL-C possessed 19 DEGs with down-regulated APOA1 and HMGCR as gene signatures. With gene expression signatures, one standard deviation higher average gene expressions were associated with 5.1-, 48.8-, and 38.9-fold fewer CAD cases for three patient groups. As HDL-C increased in CAD patients, the expression of ABCG1, CUBN, and HDLBP genes increased, while the expression of HMGCR and NPC2 genes, involved in cholesterol synthesis and trafficking, decreased. The expression of CD14, CD36, S100A8, S100A9, S100A12, TLR5, TLR8, and VEGFA genes, involved in angiogenesis and inflammation mainly via nuclear factor-κB (NF-κB), decreased.

CONCLUSIONS

The increased accumulation of cholesteryl ester in PBMC from patients with low HDL-C was suggested. This assumption contrasts with the suggested accumulation of free cholesterol in PBMC from patients with increased HDL-C, concomitant with suppression of cholesterol synthesis and traffic to the plasma membrane, and with an inflammatory state controlled by depressed CD36-mediated and upregulated apoE-mediated immunometabolic signaling. Gene signatures may be used for the diagnosis, prognosis, and treatment of CAD in dependence on HDL-C levels.