ATP-binding cassette (ABC) transporters in atherosclerosis

In Vitro Assessment of Pesticides Toxicity and Data Correlation with Pesticides Physicochemical Properties for Prediction of Toxicity in Gastrointestinal and Skin Contact Exposure

In this work, three pesticides of different physicochemical properties, namely, glyphosate (herbicide), imidacloprid (insecticide) and imazalil (fungicide), were selected to assess their cytotoxicity against distinct cell models (Caco-2, HepG2, A431, HaCaT, SK-MEL-5 and RAW 264.7 cells) to mimic gastrointestinal and skin exposure with potential systemic effect. Cells were subjected to different concentrations of selected pesticides for 24 h or 48 h. Cell viability was assessed by Alamar Blue assay, morphological changes by bright-field microscopy and the IC50 values were calculated. Cytotoxic profiles were analysed using the physico-chemical parameters of the pesticides, namely: molecular weight, water solubility, the partition coefficient in the n-octanol/water (Log Pow) system, the topological polar surface area (TPSA), and number of hydrogen-bonds (donor/acceptor) and rotatable bonds. Results showed that glyphosate did not reduce cell viability (up to 1 mM), imidacloprid induced moderate toxicity (IC50 > 1 mM for Caco-2 cells while IC50 = 305.9 ± 22.4 μM for RAW 264.7 cells) and imazalil was highly cytotoxic (IC50 > 253.5 ± 3.37 for Caco-2 cells while IC50 = 31.3 ± 2.7 μM for RAW 264.7 cells) after 24 h exposure. Toxicity was time-dependent as IC50 values at 48 h exposure were lower, and decrease in cell viability was accompanied by changes in cell morphology. Pesticides toxicity was found to be directly proportional with their Log Pow, indicating that the affinity to a lipophilic environment such as the cell membranes governs their toxicity. Toxicity is inverse to pesticides TPSA, but lower TPSA favours membrane permeation. The lower toxicity against Caco-2 cells was attributed to the physiology and metabolism of cell barriers equipped with various ABC transporters. In conclusion, physicochemical factors such as Log Pow, TPSA and H-bond are likely to be directly correlated with pesticide-induced toxicity, thus being key factors to potentially predict the toxicity of other compounds.

MiR-202-3p Inhibits Foam Cell Formation and is Associated with Coronary Heart Disease Risk in a Chinese Population

A previous study and a gene-annotation enrichment analysis for potential targets of the microRNA miR-202-3p both suggest that this microRNA might be implicated in cardiovascular and metabolic diseases. In the present study, the role of miR-202-3p in the pathogenesis of coronary heart disease (CHD) was explored. We conduct a case-control study to detect the expression levels of miR-202-3p in peripheral blood cells and found that miR-202-3p expression was significantly higher in CHD cases than in controls (P < 0.001). miR-202-3p levels were negatively correlated with platelet distribution width (r = -0.348, P = 0.002) and mean platelet volume (r = -0.29, P = 0.01). Further functional analyses suggested that stimulation with oxidized low-density lipoprotein (ox-LDL) induced miR-202-3p expression, and that this microRNA suppressed the formation of ox-LDL-induced macrophage foam cells derived from THP-1 cells in a feedback manner. In addition, miR-202-3p overexpression modulated the expression of several key genes involved in foam cell formation, including that of ABCG4, NCEH1I, and SCARB2. In summary, miR-202-3p was associated with CHD, exerting a protective role against CHD by feedback suppression of ox-LDL-induced macrophage foam cell formation.

Differences in ABCA1 R219K Polymorphisms and Serum Indexes in Alzheimer and Parkinson Diseases in Northern China

BACKGROUND ABCA1 R219K single-nucleotide polymorphisms (SNPs) was related to Alzheimer disease (AD) but not Parkinson disease (PD). Here, we analyzed the associations among ABCA1 R219K distribution, serum biomarkers, AD, and PD in a population in northern China. MATERIAL AND METHODS We used the Mini-Mental State Examination (MMSE) and the Hoehn and Yahr scale (H-Y) to evaluate AD and PD progression, separately. ABCA1 R219K was analyzed by matrix-assisted laser desorption ionization time of flight time mass spectrometry (MALDI-TOF-MS). Serum indexes were determined by enzyme-linked immunosorbent assay (ELISA). RESULTS ABCA1 R219K RR+RK genotype frequency in AD and PD patients was lower than that in normal controls (NC), while ABCA1 R219K KK genotype frequency was significantly higher. ABCA1 R219K RR genotype frequency in AD patients and NC was lower than that in PD patients, while ABCA1 R219K RK+KK genotype frequency was significantly higher. ABCA1 R219K RR genotype was positively correlated to MMSE value in AD patients, while ABCA1 R219K KK genotype was negatively correlated to H-Y value in PD patients. Serum factors were significantly different among AD and PD patients and NC. Serum ABCA1, ApoA1, ApoA2, ApoB, HDL, TC, IL-1β, IL-6, and TNF-α were significantly different between AD and PD patients. CONCLUSIONS ABCA1 R219K R allele was the risk factor inducing abnormal serum levels of ApoA2, LDL, and TG in AD patients, and abnormal levels of serum ABCA1, HDL, IL-1b, IL-6, and TNF-α in PD patients, while ABCA1 R219K K allele was the risk factor inducing lower ABCA1 in AD patients. IL-1β, IL-6, and TNF-α were negatively correlated to MMSE in AD patients but positively correlated to H-Y in PD patients, while HDL was positively related to H-Y in PD patients.

Analysis of inflammatory and lipid metabolic networks across RAW264.7 and thioglycolate-elicited macrophages

Studies of macrophage biology have been significantly advanced by the availability of cell lines such as RAW264.7 cells. However, it is unclear how these cell lines differ from primary macrophages such as thioglycolate-elicited peritoneal macrophages (TGEMs). We used the inflammatory stimulus Kdo2-lipid A (KLA) to stimulate RAW264.7 and TGEM cells. Temporal changes of lipid and gene expression levels were concomitantly measured and a systems-level analysis was performed on the fold-change data. Here we present a comprehensive comparison between the two cell types. Upon KLA treatment, both RAW264.7 and TGEM cells show a strong inflammatory response. TGEM (primary) cells show a more rapid and intense inflammatory response relative to RAW264.7 cells. DNA levels (fold-change relative to control) are reduced in RAW264.7 cells, correlating with greater downregulation of cell cycle genes. The transcriptional response suggests that the cholesterol de novo synthesis increases considerably in RAW264.7 cells, but 25-hydroxycholesterol increases considerably in TGEM cells. Overall, while RAW264.7 cells behave similarly to TGEM cells in some ways and can be used as a good model for inflammation- and immune function-related kinetic studies, they behave differently than TGEM cells in other aspects of lipid metabolism and phenotypes used as models for various disorders such as atherosclerosis.

Macrophage ABCA2 deletion modulates intracellular cholesterol deposition, affects macrophage apoptosis, and decreases early atherosclerosis in LDL receptor knockout mice

OBJECTIVE

The ABCA2 transporter shares high structural homology to ABCA1, which is crucial for the removal of excess cholesterol from macrophages and, by extension, in atherosclerosis. It has been suggested that ABCA2 sequesters cholesterol inside the lysosomes, however, little is known of the macrophage-specific role of ABCA2 in regulating lipid homeostasis in vivo and in modulating susceptibility to atherosclerosis.

METHODS

Chimeras with dysfunctional macrophage ABCA2 were generated by transplantation of bone marrow from ABCA2 knockout (KO) mice into irradiated LDL receptor (LDLr) KO mice.

RESULTS

Interestingly, lack of ABCA2 in macrophages resulted in a diminished lesion size in the aortic root (-24.5%) and descending thoracic aorta (-36.6%) associated with a 3-fold increase in apoptotic cells, as measured by both caspase 3 and TUNEL. Upon oxidized LDL exposure, macrophages from wildtype (WT) transplanted animals developed filipin-positive droplets in lysosomal-like compartments, corresponding to free cholesterol (FC) accumulation. In contrast, ABCA2-deficient macrophages displayed an abnormal diffuse distribution of FC over peripheral regions. The accumulation of neutral sterols in lipid droplets was increased in ABCA2-deficient macrophages, but primarily in cytoplasmic clusters and not in lysosomes. Importantly, apoptosis of oxLDL loaded macrophages lacking ABCA2 was increased 2.7-fold, probably as a consequence of the broad cellular distribution of FC.

CONCLUSIONS

Lack of functional ABCA2 generates abnormalities in intracellular lipid distribution/trafficking in macrophages consistent with its lysosomal sequestering role, leading to an increased susceptibility to apoptosis in response to oxidized lipids and reduced atherosclerotic lesion development.

Nutrigenetics of the lipoprotein metabolism

It is well known that lipid metabolism is a cornerstone in the development of the commonest important chronic diseases worldwide, such as obesity, cardiovascular disease, or metabolic syndrome. In this regard, the area of lipid and lipoprotein metabolism is one of the areas in which the understanding of the development and progression of those metabolic disorders has been studied in greater depth. Thus, growing evidence has demonstrated that while universal recommendations might be appropriate for the general population, in this area there is great variability among individuals, related to a combination of environmental and genetic factors. Moreover, the interaction between genetic and dietary components has helped in understanding this variability. Therefore, with further study into the interaction between the most important genetic markers or single-nucleotide polymorphisms (SNPs) and diet, it may be possible to understand the variability in lipid metabolism, which could lead to an increase in the use of personalized nutrition as the best support to combat metabolic disorders. This review discusses some of the evidence in which candidate SNPs can affect the key players of lipid metabolism and how their phenotypic manifestations can be modified by dietary intake.

ABCA1 gene variants regulate postprandial lipid metabolism in healthy men

OBJECTIVE

Genetic variants of ABCA1, an ATP-binding cassette (ABC) transporter, have been linked to altered atherosclerosis progression and fasting lipid concentration, mainly high-density lipoproteins and apolipoprotein A1; however, results from different studies have been inconsistent.

METHODS AND RESULTS

To further characterize the effects of ABCA1 variants in human postprandial lipid metabolism, we studied the influence of 3 single nucleotide polymorphisms (i27943 [rs2575875]; i48168 [rs4149272]; R219K [rs2230806]) in the postprandial lipemia of 88 normolipidemic young men who were given a fatty meal. For i27943 and i48168 single nucleotide polymorphisms, fasting and postprandial values of apolipoprotein A1 were higher and postprandial lipemia was much lower in homozygotes for the major alleles, total triglycerides in plasma, and large triglyceride-rich lipoprotein triglycerides. These persons also showed a higher apolipoprotein A1/apolipoprotein B ratio. Major allele homozygotes for i48168 and i27943 showed additionally higher high-density lipoproteins and lower postprandial apolipoprotein B.

CONCLUSION

Our work shows that major allele homozygotes for ABCA1 single nucleotide polymorphisms i27943 and i48168 have a lower postprandial response as compared to minor allele carriers. This finding may further characterize the role of ABCA1 in lipid metabolism.

Characterization of three classes of membrane proteins involved in fungal azole resistance by functional hyperexpression in Saccharomyces cerevisiae

The study of eukaryotic membrane proteins has been hampered by a paucity of systems that achieve consistent high-level functional protein expression. We report the use of a modified membrane protein hyperexpression system to characterize three classes of fungal membrane proteins (ABC transporters Pdr5p, CaCdr1p, CaCdr2p, CgCdr1p, CgPdh1p, CkAbc1p, and CneMdr1p, the major facilitator superfamily transporter CaMdr1p, and the cytochrome P450 enzyme CaErg11p) that contribute to the drug resistance phenotypes of five pathogenic fungi and to express human P glycoprotein (HsAbcb1p). The hyperexpression system consists of a set of plasmids that direct the stable integration of a single copy of the expression cassette at the chromosomal PDR5 locus of a modified host Saccharomyces cerevisiae strain, ADDelta. Overexpression of heterologous proteins at levels of up to 29% of plasma membrane protein was achieved. Membrane proteins were expressed with or without green fluorescent protein (GFP), monomeric red fluorescent protein, His, FLAG/His, Cys, or His/Cys tags. Most GFP-tagged proteins tested were correctly trafficked within the cell, and His-tagged proteins could be affinity purified. Kinetic analysis of ABC transporters indicated that the apparent K(m) value and the V(max) value of ATPase activities were not significantly affected by the addition of His tags. The efflux properties of seven fungal drug pumps were characterized by their substrate specificities and their unique patterns of inhibition by eight xenobiotics that chemosensitized S. cerevisiae strains overexpressing ABC drug pumps to fluconazole. The modified hyperexpression system has wide application for the study of eukaryotic membrane proteins and could also be used in the pharmaceutical industry for drug screening.

The ABCA5 protein: a urine diagnostic marker for prostatic intraepithelial neoplasia

PURPOSE

To develop a urine diagnostic test for preneoplastic intraepithelial neoplasia of the prostate.

EXPERIMENTAL DESIGN

We have used a DNA-binding assay and electrophoretic mobility shift assays (EMSA) to screen for novel duplexed DNA-binding sequences, which bind protein(s) overexpressed in crude protein extracts from high-grade prostatic intraepithelial neoplasia (HGPIN). EMSAs, immunohistochemistry, and ELISAs were used to measure expression of the ABCA5 protein identified as a specific marker in prostate tissue and patient urine.

RESULTS

Following screening of 4,096 sequences, an 8-bp dsDNA sequence (i.e., TCCAGCGA) was identified, which binds the ABCA5 protein, a member of the ATP-binding cassette multidrug resistant family. EMSAs showed that ABCA5 was overexpressed in HGPIN tissue (n=11/11) and in the urine of patients with HGPIN (n=18/18) but was not expressed in prostate cancer, benign prostatic hyperplasia, or stroma. Immunohistochemistry indicated that ABCA5 was overexpressed in foci of intermediate basal cells in normal glands and in HGPIN. ABCA5 was faintly expressed in prostate cancer glands. ELISAs showed in 'blinded studies' that ABCA5 was a highly sensitive (>98% sensitivity) urine diagnostic marker for HGPIN in biopsy-positive patients (n=107) at a 'cutoff' of 25 ng/mL. ABCA5 was present at very low levels (i.e., <25 ng/mL) in the urine of patients diagnosed with benign prostatic hyperplasia (n=79) or prostatitis or kidney and bladder cancer (>86% specificity).

CONCLUSIONS

The data indicate that ABCA5 might be a specific urine marker for diagnosis of patients with HGPIN.

Homozygosity for the 168His variantof the minor histocompatibility antigen HA-1is associated with reduced riskof primary Sjögren's syndrome

The genes for the human ATP-binding cassette (ABC) transporter ABCA7 and the minor histocompatibility antigen HA-1 are juxtaposed in close proximity on chromosome 19p13.3. The multispan transmembrane protein ABCA7 contains an extracellular domain that is recognized by antisera from patients with Sjögren's syndrome ("Sjögren-epitope"). Recent work from our laboratory demonstrating the involvement of ABCA7 in cellular ceramide and phosphatidylserine export suggests a role for this transporter in programmed cell death. In HA-1, a protein of unknown function, a His/Arg polymorphism (His168Arg), which constitutes the immunologic target for HA-1-specific cytotoxic T cells, has been causatively linked to graft-versus-host disease after allogeneic stem cell transplantation. Because these findings suggest a potential implication of ABCA7 and HA-1 in immune processes, we tested the hypothesis that allelic variants in both genes are associated with autoimmune disorders. We identified a total of 31 exonic single-nucleotide polymorphisms (SNP) in the ABCA7/HA-1 gene complex, nine of which represent non-synonymous nucleotide alterations. Genotypes of ABCA7 and HA-1 SNP were determined in three distinct Caucasian populations of patients with primary Sjögren's syndrome and ethnically matched controls. Comparison of allele frequencies between these groups revealed that the incidence of the HA-1 168His allele is significantly lower in Sjögren's syndrome patients than in controls (p<0.003). In contrast, the frequencies of all ABCA7 allelic variants and additional HA-1 polymorphisms were similar in patients and controls. In cohorts of patients with systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis, no significant differences in the frequencies of ABCA7 and HA-1 allelic variants were observed relative to controls. Our results suggest that the HA-1 168His variant is associated with reduced susceptibility to primary Sjögren's syndrome.

Phosphorylation by Protein Kinase CK2 Modulates the Activity of the ATP Binding Cassette A1 Transporter

In a previous characterization of the ABCA subfamily of the ATP-binding cassette (ABC) transporters, we identified potential protein kinase 2 (CK2) phosphorylation sites, which are conserved in eukaryotic and prokaryotic members of the ABCA transporters. These phosphorylation residues are located in the conserved cytoplamic R1 and R2 domains, downstream of the nucleotide binding domains NBD1 and NBD2. To study the possible regulation of the ABCA1 transporter by CK2, we expressed the recombinant cytoplasmic domains of ABCA1, NBD1+R1 and NBD2+R2. We demonstrated that in vitro ABCA1 NBD1+R1, and not NBD2+R2, is phosphorylated by CK2, and we identified Thr-1242, Thr-1243, and Ser-1255 as the phosphorylated residues in the R1 domain by mass spectrometry. We further investigated the functional significance of the threonine and serine phosphorylation sites in NBD1 by site-directed mutagenesis of the entire ABCA1 followed by transfection into Hek-293 Tet-Off cells. The ABCA1 flippase activity, apolipoprotein AI and AII binding, and cellular phospholipid and cholesterol efflux were enhanced by mutations preventing CK2 phosphorylation of the threonine and serine residues. This was confirmed by the effect of specific protein kinase CK2 inhibitors upon the activity of wild type and mutant ABCA1 in transfected Hek-293 Tet-Off cells. The activities of the mutants mimicking threonine phosphorylation were close to that of wild type ABCA1. Our data, therefore, suggest that besides protein kinase A and C, protein kinase CK2 might play an important role in vivo in regulating the function and transport activity of ABCA1 and possibly of other members of the ABCA subfamily.

Apoptotic cell death in atherosclerosis

PURPOSE OF REVIEW

Apoptosis is a critical regulator of homeostasis in many tissues, including the vasculature. Apoptosis in atherosclerotic lesions is triggered by inflammatory processes, both via cell-cell contact and by cytokines and oxidized lipids. Apoptosis of vascular smooth muscle cells, endothelial cells and macrophages may promote plaque growth and pro-coagulation and may induce rupture, the major consequence of atherosclerosis in humans.

RECENT FINDINGS

Studies over the past year have clearly demonstrated the significance of cell death in atherosclerosis. Some of the key cellular, cytokine and molecular regulators that contribute to the apoptosis of cells within the atherosclerotic lesion have been identified and their mechanism of action elucidated. Other studies have shed some light on the identity of cells whose loss by apoptosis contributes to plaque instability.

SUMMARY

The identification of which cell types undergo apoptosis within the atherosclerotic lesion, the extracellular factors that impinge on these cells, and the intracellular mechanisms that govern their demise have begun to be elucidated. This information is critical in the design of further in-vivo experiments such as the exploitation of animal models, and ultimately, in applying this knowledge to clinical practice.

ABCA1-mediated cholesterol efflux is defective in free cholesterol-loaded macrophages. Mechanism involves enhanced ABCA1 degradation in a process requiring full NPC1 activity

In advanced atherosclerosis, macrophage foam cells progressively accumulate large amounts of unesterified or "free" cholesterol (FC), a process that is thought to contribute to foam cell death and lesional necrosis. The cellular consequences of early FC accumulation, including those that lead to further FC accumulation, are poorly understood. In this context, we show that cholesterol and phospholipid efflux mediated by ABCA1, which is initially induced in the cholesterol-loaded macrophage, was inhibited by approximately 80% in pre-toxic FC-loaded macrophages. Cholesterol efflux to HDL(2), which is mediated by a non-ABCA1 pathway, was inhibited by only approximately 20% in FC-loaded macrophages. FC loading led to decreased levels of ABCA1 protein via increased degradation of ABCA1, and not by decreased transcription or translation of AbcA1 mRNA. The decrease in ABCA1 protein occurred relatively early and was not prevented by caspase inhibitors, indicating that it was not a consequence of FC-induced apoptosis. However, inhibition of proteasomal function by lactacystin largely prevented the degradation of ABCA1. Importantly, the FC-induced decrease in ABCA1 function and protein was almost entirely prevented in macrophages that had partial deficiency of npc1 or were exposed to nanomolar concentrations of U18666A, both of which lead to defective cholesterol trafficking to the endoplasmic reticulum, but leave trafficking to the plasma membrane largely intact. Thus, a relatively early event during FC loading of macrophages is increased degradation of ABCA1, which appears to require trafficking of cholesterol to a peripheral cellular site, but not bulk trafficking of excess cholesterol to the plasma membrane. These findings provide new insight into the post-translational regulation of ABCA1 and the pathobiology of the FC-loaded macrophage.

ABCA1: regulation, trafficking and association with heteromeric proteins

HDL metabolism is crucial in maintaining cellular cholesterol and phospholipid homeostasis and prevention of atherosclerosis progression. Recent work identified the ATP-binding cassette transporter A1 (ABCA1) as the major regulator of plasma high density lipoprotein (HDL) cholesterol responsible for the removal of excess cholesterol from peripheral cells and tissues. Here we discuss some novel aspects of the ABCA1 network: 1) the cellular pathways involved in cholesterol and phospholipid efflux, 2) regulation of ABCA1, 3) sulfonylurea receptor 1 (SUR1)- or cystic fibrosis transmembrane conductance regulator (CFTR)-like function of ABCA1, 4) interaction of the ABCA1 C-terminus with beta2-syntrophin, 5) ABCA1 modulation of the Rho GTPase Cdc42, 6) localization of ABCA1 in plasma membrane microdomains and intracellular sites, 7) differential effects of prebeta-HDL precursors on ABCA1 mediated alpha-HDL particle formation and 8) ABCA1 in platelets and its relation to phosphatidylserine-flippase activity. A complex regulatory network and additional antiatherogenic features that may depend on the composition of prebeta-HDL precursor particles are believed to coordinate ABCA1 function in reverse cholesterol and phospholipid transport. Distinct prebeta-HDL ligand-specific receptor-clusters are involved that may modulate specific signaling pathways with varying outcomes related to prebeta-HDL particle composition, the cell-type and the cellular response status.