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Lipids in Health and Disease Aug 2019Atherosclerosis is an inflammatory process involving activation of monocytes recruited by various chemoattractant factors, among which lipoprotein(a) and its specific...
BACKGROUND
Atherosclerosis is an inflammatory process involving activation of monocytes recruited by various chemoattractant factors, among which lipoprotein(a) and its specific apolipoprotein apo(a). Lp(a) contains a specific apolipoprotein apo(a) which size is determined by a variable number of repeats of a specific structural domain, the kringle IV type 2 (IV-2). Lp(a) plasma concentration and apo(a) size is inversely correlated, and smaller apo(a) are major risk factors for coronary heart disease.
DESIGN AND METHODS
The aim of this study was to evaluate the effect of recombinant apo(a) isoforms (containing 10, 18 or 34 kringles) on monocytes interacting with type I collagen.
RESULTS
Apo(a) isoforms stimulated reactive oxygen species (ROS) and matrix metalloproteinase-9 (MMP-9) production by monocytes, and not modified monocytes adhesion on type I collagen. This effect was specific of apo(a) since no effect was observed in the presence of plasminogen and was inversely related to apo(a) size. The lysine analogue 6-aminohexanoic acid which blocks the lysine binding sites (LBS), and carboxypeptidase B (CpB) which cleaves carboxy-terminal lysine residues, abolished apo(a)-induced ROS and MMP-9 production, highlighting an effect mediated by apo(a) lysing-binding sites.
CONCLUSIONS
These results indicate that activation of collagen-primed monocytes stimulated with apo(a) is a Kringle number-dependent effect and reinforce the hypothesis of a role for small size apo(a) isoforms in atherothrombosis.
Topics: Aminocaproic Acid; Animals; Apolipoproteins A; Collagen Type I; Fibronectins; HEK293 Cells; Humans; Matrix Metalloproteinase 9; Molecular Weight; Monocytes; Plasminogen; Primary Cell Culture; Protein Binding; Protein Isoforms; Proteolysis; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Recombinant Proteins
PubMed: 31470857
DOI: 10.1186/s12944-019-1106-4 -
The Journal of Biological Chemistry Jan 1989We examined the effects of apolipoproteins A-IV and A-I on the catabolism of whole particles by hepatoma G2 cells and cultured primary hepatocytes. For this type of...
We examined the effects of apolipoproteins A-IV and A-I on the catabolism of whole particles by hepatoma G2 cells and cultured primary hepatocytes. For this type of experiment, high density lipoprotein is unsuitable, because all of its lipid and protein components independently dissociate and exchange and hence poorly trace whole particle catabolism. We therefore used phosphatidylcholine liposomes with radioactive tracers entrapped within their aqueous cores. Apolipoproteins A-IV, A-I, or E added to liposomes became liposome-associated and produced no detectable release of encapsulated label. As a positive control, apolipoprotein E doubled the uptake of labeled liposomes by hepatoma cells, compared to apolipoprotein-free controls, and this increase could be blocked by the addition of excess unlabeled low density lipoprotein. Degradation of labeled liposomes by hepatoma cells was increased 6-fold by the addition of apolipoprotein E. In contrast, neither apolipoprotein A-IV nor A-I increased cellular uptake or degradation of the particles. Similar results were obtained with primary hepatocytes. In studies using apolipoprotein combinations, apolipoproteins A-IV and A-I were each able to displace apolipoprotein E from liposomes and thereby reduce cellular uptake. Our data indicate that apolipoproteins A-IV and A-I do not facilitate uptake or degradation of whole particles by liver-derived cells in vitro. However, these apolipoproteins may modulate receptor-mediated uptake of particles by reducing the amount of particle-bound apolipoprotein E.
Topics: Animals; Apolipoprotein A-I; Apolipoproteins A; Apolipoproteins E; Biological Transport; Cells, Cultured; Kinetics; Lipoproteins, HDL; Liposomes; Liver; Liver Neoplasms, Experimental; Phospholipids; Rats; Reference Values
PubMed: 2492020
DOI: No ID Found -
Journal of Lipid Research Sep 2017High lipoprotein (a) [Lp(a)] concentrations are an independent risk factor for cardiovascular outcomes. Concentrations are strongly influenced by apo(a) kringle IV... (Meta-Analysis)
Meta-Analysis
High lipoprotein (a) [Lp(a)] concentrations are an independent risk factor for cardiovascular outcomes. Concentrations are strongly influenced by apo(a) kringle IV repeat isoforms. We aimed to identify genetic loci associated with Lp(a) concentrations using data from five genome-wide association studies (n = 13,781). We identified 48 independent SNPs in the and 1 SNP in the gene region to be significantly associated with Lp(a) concentrations. We also adjusted for apo(a) isoforms to identify loci affecting Lp(a) levels independently from them, which resulted in 31 SNPs (30 in the , 1 in the gene region). Seven SNPs showed a genome-wide significant association with coronary artery disease (CAD) risk. A rare SNP (rs186696265; MAF ∼1%) showed the highest effect on Lp(a) and was also associated with increased risk of CAD (odds ratio = 1.73, = 3.35 × 10). Median Lp(a) values increased from 2.1 to 91.1 mg/dl with increasing number of Lp(a)-increasing alleles. We found the -determining allele of rs7412 to be significantly associated with Lp(a) concentrations ( = 3.47 × 10). Each allele decreased Lp(a) by 3.34 mg/dl corresponding to ∼15% of the population's mean values. Performing a gene-based test of association, including suspected Lp(a) receptors and regulators, resulted in one significant association of the gene with Lp(a) ( = 3.4 × 10). In summary, we identified a large number of independent SNPs in the gene region, as well as the allele, to be significantly associated with Lp(a) concentrations.
Topics: Animals; Apolipoproteins A; Genome-Wide Association Study; Humans; Lipoprotein(a); Polymorphism, Single Nucleotide; Protein Isoforms; Sex Characteristics
PubMed: 28512139
DOI: 10.1194/jlr.M076232 -
The Journal of Biological Chemistry Apr 2020Increased plasma concentrations of lipoprotein(a) (Lp(a)) are associated with an increased risk for cardiovascular disease. Lp(a) is composed of apolipoprotein(a)...
Increased plasma concentrations of lipoprotein(a) (Lp(a)) are associated with an increased risk for cardiovascular disease. Lp(a) is composed of apolipoprotein(a) (apo(a)) covalently bound to apolipoprotein B of low-density lipoprotein (LDL). Many of apo(a)'s potential pathological properties, such as inhibition of plasmin generation, have been attributed to its main structural domains, the kringles, and have been proposed to be mediated by their lysine-binding sites. However, available small-molecule inhibitors, such as lysine analogs, bind unselectively to kringle domains and are therefore unsuitable for functional characterization of specific kringle domains. Here, we discovered small molecules that specifically bind to the apo(a) kringle domains KIV-7, KIV-10, and KV. Chemical synthesis yielded compound AZ-05, which bound to KIV-10 with a of 0.8 μm and exhibited more than 100-fold selectivity for KIV-10, compared with the other kringle domains tested, including plasminogen kringle 1. To better understand and further improve ligand selectivity, we determined the crystal structures of KIV-7, KIV-10, and KV in complex with small-molecule ligands at 1.6-2.1 Å resolutions. Furthermore, we used these small molecules as chemical probes to characterize the roles of the different apo(a) kringle domains in assays. These assays revealed the assembly of Lp(a) from apo(a) and LDL, as well as potential pathophysiological mechanisms of Lp(a), including (i) binding to fibrin, (ii) stimulation of smooth-muscle cell proliferation, and (iii) stimulation of LDL uptake into differentiated monocytes. Our results indicate that a small-molecule inhibitor targeting the lysine-binding site of KIV-10 can combat the pathophysiological effects of Lp(a).
Topics: Amino Acid Sequence; Apolipoproteins A; Fibrin; High-Throughput Screening Assays; Humans; Kringles; Ligands; Models, Molecular; Protein Binding; Protein Domains; Sequence Homology; Small Molecule Libraries
PubMed: 32132173
DOI: 10.1074/jbc.RA119.011251 -
Journal of Lipid Research Oct 2013Oxidized phospholipids (OxPLs) are present on apolipoprotein (a) [apo(a)] and lipoprotein (a) [Lp(a)] but the determinants influencing their binding are not known. The...
Oxidized phospholipids (OxPLs) are present on apolipoprotein (a) [apo(a)] and lipoprotein (a) [Lp(a)] but the determinants influencing their binding are not known. The presence of OxPLs on apo(a)/Lp(a) was evaluated in plasma from healthy humans, apes, monkeys, apo(a)/Lp(a) transgenic mice, lysine binding site (LBS) mutant apo(a)/Lp(a) mice with Asp(55/57)→Ala(55/57) substitution of kringle (K)IV10)], and a variety of recombinant apo(a) [r-apo(a)] constructs. Using antibody E06, which binds the phosphocholine (PC) headgroup of OxPLs, Western and ELISA formats revealed that OxPLs were only present in apo(a) with an intact KIV10 LBS. Lipid extracts of purified human Lp(a) contained both E06- and nonE06-detectable OxPLs by tandem liquid chromatography-mass spectrometry (LC-MS/MS). Trypsin digestion of 17K r-apo(a) showed PC-containing OxPLs covalently bound to apo(a) fragments by LC-MS/MS that could be saponified by ammonium hydroxide. Interestingly, PC-containing OxPLs were also present in 17K r-apo(a) with Asp(57)→Ala(57) substitution in KIV10 that lacked E06 immunoreactivity. In conclusion, E06- and nonE06-detectable OxPLs are present in the lipid phase of Lp(a) and covalently bound to apo(a). E06 immunoreactivity, reflecting pro-inflammatory OxPLs accessible to the immune system, is strongly influenced by KIV10 LBS and is unique to human apo(a), which may explain Lp(a)'s pro-atherogenic potential.
Topics: Animals; Apolipoproteins A; Binding Sites; Enzyme-Linked Immunosorbent Assay; Gorilla gorilla; Humans; Lipoprotein(a); Macaca fascicularis; Mice; Mice, Inbred C57BL; Mice, Transgenic; Oxidation-Reduction; Pan paniscus; Pan troglodytes; Papio; Phospholipids; Protein Binding; Species Specificity; Tandem Mass Spectrometry
PubMed: 23828779
DOI: 10.1194/jlr.M040733 -
American Journal of Physiology.... Jun 2004The focus of this article is to review evidence that apolipoprotein A-IV (apo A-IV) acts as a satiety factor. Additionally, information regarding the general involvement... (Review)
Review
The focus of this article is to review evidence that apolipoprotein A-IV (apo A-IV) acts as a satiety factor. Additionally, information regarding the general involvement of apo A-IV in the regulation of food intake and body weight is stated. Apo A-IV is a glycoprotein synthesized by the human intestine. In rodents, both the small intestine and liver secrete apo A-IV, but the small intestine is the major organ responsible for circulating apo A-IV. There is now solid evidence that the hypothalamus, especially the arcuate nucleus, is another active site of apo A-IV expression. Intestinal apo A-IV synthesis is markedly stimulated by fat absorption and does not appear to be mediated by the uptake or reesterification of fatty acids to form triglycerides. Rather, the local formation of chylomicrons acts as a signal for the induction of intestinal apo A-IV synthesis. Intestinal apo A-IV synthesis is also enhanced by a factor from the ileum, probably peptide tyrosine-tyrosine (PYY). The inhibition of food intake by apo A-IV is mediated centrally. The stimulation of intestinal synthesis and secretion of apo A-IV by lipid absorption are rapid; thus apo A-IV likely plays a role in the short-term regulation of food intake. Other evidence suggests that apo A-IV may also be involved in the long-term regulation of food intake and body weight, as it is regulated by both leptin and insulin. Chronic ingestion of a high-fat diet blunts the intestinal as well as the hypothalamic apo A-IV response to lipid feeding. It also suppresses apo A-IV gene expression in the hypothalamus. Whereas it is tempting to speculate that apo A-IV may play a role in diet-induced obesity, we believe the confirmation of such a proposal awaits further experimental evidence.
Topics: Animals; Apolipoproteins A; Body Weight; Eating; Gastrointestinal Tract; Humans; Infusions, Intravenous; Injections, Intraventricular; Peptide YY; Satiety Response
PubMed: 15132947
DOI: 10.1152/ajpgi.00511.2003 -
Biochimica Et Biophysica Acta May 2012The discovery of apolipoprotein A-V (apoA-V) in 2001 has raised a number of intriguing questions about its role in lipid transport and triglyceride (TG) homeostasis.... (Review)
Review
The discovery of apolipoprotein A-V (apoA-V) in 2001 has raised a number of intriguing questions about its role in lipid transport and triglyceride (TG) homeostasis. Genome wide association studies (GWAS) have consistently identified APOA5 as a contributor to plasma TG levels. Single nucleotide polymorphisms (SNP) within the APOA5 gene locus have been shown to correlate with elevated plasma TG. Furthermore, transgenic and knockout mouse models support the view that apoA-V plays a critical role in maintenance of plasma TG levels. The present review describes recent concepts pertaining to apoA-V SNP analysis and their association with elevated plasma TG. The interaction of apoA-V with glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) is discussed relative to its postulated role in TG-rich lipoprotein catabolism. The potential role of intracellular apoA-V in regulation of TG homeostasis, as a function of its ability to associate with cytosolic lipid droplets, is reviewed. While some answers are emerging, numerous mysteries remain with regard to this low abundance, yet potent, modulator of TG homeostasis. Given the strong correlation between elevated plasma TG and heart disease, there is great scientific and public interest in deciphering the numerous biological riddles presented by apoA-V. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.
Topics: Animals; Apolipoprotein A-V; Apolipoproteins A; Carrier Proteins; Fatty Liver; Genome-Wide Association Study; Humans; Lipid Metabolism; Mice; Non-alcoholic Fatty Liver Disease; Polymorphism, Single Nucleotide; Receptors, Lipoprotein; Triglycerides
PubMed: 22209939
DOI: 10.1016/j.bbalip.2011.12.002 -
The Journal of Biological Chemistry May 1986Apolipoprotein synthesis was measured in control optic nerves and optic nerves undergoing Wallerian degeneration. After short term organ culture with radiolabeled amino...
Apolipoprotein synthesis was measured in control optic nerves and optic nerves undergoing Wallerian degeneration. After short term organ culture with radiolabeled amino acid, optic nerve extracts were reacted with antiserum to rat or chicken apolipoproteins. Immunoprecipitates were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the degenerating rat optic nerve, apo-E synthesis increased from 0.30 to 0.90% of newly synthesized protein and from 0.45 to 1.4% of secreted protein. A DNA-excess solution hybridization assay was constructed to measure the absolute amount of apo-E mRNA in control and degenerating optic nerves. Paralleling the increase in apo-E protein synthesis, the absolute amount of apo-E mRNA was elevated 3- to 4-fold after enucleation. Similar to rat apo-E, apo-A-I synthesis was increased in degenerating chicken optic nerve. Chicken apo-A-I represented 0.65 and 3.5% of newly synthesized protein from control and enucleated optic nerves, respectively. Apo-A-I increased from 0.85 to 5.5% of secreted protein following enucleation. Using in vitro translation to quantitate relative amounts of chicken apo-A-I mRNA, enucleated optic nerve apo-A-I mRNA content was increased 5-fold. These results suggest that local apolipoprotein synthesis may be involved in the mobilization of myelin cholesterol which occurs during Wallerian degeneration. The similar response of the rat and chicken to increase optic nerve apolipoprotein synthesis during degeneration supports the idea that avian peripheral apo-A-I and mammalian peripheral apo-E may be performing functions common to both classes of animals.
Topics: Animals; Apolipoprotein A-I; Apolipoproteins A; Apolipoproteins E; Chickens; Kinetics; Lipoproteins, HDL; Nerve Degeneration; Nucleic Acid Hybridization; Optic Nerve; Organ Culture Techniques; RNA, Messenger; Rats
PubMed: 3084466
DOI: No ID Found -
Atherosclerosis Apr 2009A minor allele variant (rs3798220) of apolipoprotein(a) has been reported to be associated with elevated plasma lipoprotein(a) [Lp(a)] and increased cardiovascular risk.... (Randomized Controlled Trial)
Randomized Controlled Trial
OBJECTIVE
A minor allele variant (rs3798220) of apolipoprotein(a) has been reported to be associated with elevated plasma lipoprotein(a) [Lp(a)] and increased cardiovascular risk. We investigated whether this allele was associated with elevated Lp(a) and cardiovascular risk in the Women's Health Study, a randomized trial of low-dose aspirin, and whether aspirin reduced cardiovascular risk in minor allele carriers.
METHODS AND RESULTS
Genotypes of rs3798220 were determined for 25,131 initially healthy Caucasian participants. Median Lp(a) levels at baseline were 10.0, 79.5, and 153.9mg/dL for major allele homozygotes, heterozygotes, and minor allele homozygotes, respectively (P<0.0001). During the 9.9 years of follow-up, minor allele carriers (3.7%) in the placebo group had twofold higher risk of major cardiovascular events than non-carriers (age-adjusted hazard ratio (HR)=2.21, 95% CI: 1.39-3.52). Among carriers, risk was reduced more than twofold by aspirin: for aspirin compared with placebo the age-adjusted HR was 0.44 (95% CI: 0.20-0.94); risk was not significantly reduced among non-carriers (age-adjusted HR=0.91, 95% CI: 0.77-1.08). This interaction between carrier status and aspirin allocation was significant (P=0.048).
CONCLUSIONS
In the Women's Health Study, carriers of an apolipoprotein(a) variant had elevated Lp(a), doubled cardiovascular risk, and appeared to benefit more from aspirin than non-carriers.
Topics: Alleles; Anti-Inflammatory Agents, Non-Steroidal; Apolipoproteins A; Aspirin; Cardiovascular Diseases; Female; Genotype; Heterozygote; Homozygote; Humans; Middle Aged; Polymorphism, Genetic; Proportional Hazards Models; Risk
PubMed: 18775538
DOI: 10.1016/j.atherosclerosis.2008.07.019 -
Lipids in Health and Disease Nov 2017Lipoprotein(a) [LP(a)] is implicated as a common and independent risk factor for cardiovascular diseases. The therapeutic options currently available for reducing plasma...
BACKGROUND
Lipoprotein(a) [LP(a)] is implicated as a common and independent risk factor for cardiovascular diseases. The therapeutic options currently available for reducing plasma LP(a) concentrations are limited. Diallyl disulphide (DADS), the main component of garlic, regulates lipid metabolism in hepatocytes and adipocytes through ERK1/2 signalling. This study aimed to assess the effect of DADS on apolipoprotein(a) [apo(a)] in HepG2 cells. We also determined the effects of DADS on apo(a) expression and secretion in HepG2 cells as well as the underlying mechanisms.
METHODS
We examined the role of DADS on apo(a) expression in HepG2 cells by treating cell with different concentrations of DADS (10, 20, 40 and 80 μg/mL) for 24 h or treating cells with 40 μg/mL DADS for 0, 6, 12, 24 and 48 h. Then we used quantitative real-time PCR to analysis apo(a) mRNA levels, used Western blot to analysis apo(a) protein levels and used enzyme-linked immunosorbent assay to test apo(a) secreted levels. To farther determined the role of DADS, we applied Transfection of small interfering RNA to knockdown ELK-1levels and applied PD98059, a specific inhibitor of ERK1/2, to block ERK1/2 signal.
RESULTS
The results show DADS inhibited apo(a) at both the mRNA and protein levels in HepG2 cells in a dose-dependent manner. DADS-mediated inhibition of apoa(a) expression in HepG2 cells was attenuated when the cells were cultured in medium containing PD98059 (ERK1/2 inhibitor) or were transfected with siRNAs against MEK1 or ELK-1. Overexpression of apo(a) yielded similar results.
CONCLUSIONS
This study reveals that DADS can downregulate apo(a) expression in a dose-dependent manner via the MEK-ERK12-ELK-1 pathway.
Topics: Allyl Compounds; Apolipoproteins A; Binding Sites; Drug Evaluation, Preclinical; Enzyme Activation; Gene Expression; Hep G2 Cells; Humans; Hypolipidemic Agents; MAP Kinase Kinase 1; MAP Kinase Signaling System; Phosphorylation; Promoter Regions, Genetic; Protein Processing, Post-Translational; Sulfides; ets-Domain Protein Elk-1
PubMed: 29178936
DOI: 10.1186/s12944-017-0616-1