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Journal of Lipid Research Dec 2015Elevated lipoprotein (a) [Lp(a)] levels are a causal risk factor for coronary heart disease. Accumulating evidence suggests that Lp(a) can stimulate cellular...
Elevated lipoprotein (a) [Lp(a)] levels are a causal risk factor for coronary heart disease. Accumulating evidence suggests that Lp(a) can stimulate cellular inflammatory responses through the kringle-containing apolipoprotein (a) [apo(a)] component. Here, we report that recombinant apo(a) containing 17 kringle (17K) IV domains elicits a dose-dependent increase in interleukin (IL)-8 mRNA and protein expression in THP-1 and U937 macrophages. This effect was blunted by mutation of the lysine binding site in apo(a) kringle IV type 10, which resulted in the loss of oxidized phospholipid (oxPL) on apo(a). Trypsin-digested 17K had the same stimulatory effect on IL-8 expression as intact apo(a), while enzymatic removal of oxPL from apo(a) significantly blunted this effect. Using siRNA to assess candidate receptors, we found that CD36 and TLR2 may play roles in apo(a)-mediated IL-8 stimulation. Downstream of these receptors, inhibitors of MAPKs, Jun N-terminal kinase and ERK1/2, abolished the effect of apo(a) on IL-8 gene expression. To assess the roles of downstream transcription factors, luciferase reporter gene experiments were conducted using an IL-8 promoter fragment. The apo(a)-induced expression of this reporter construct was eliminated by mutation of IL-8 promoter binding sites for either NF-κB or AP-1. Our results provide a mechanistic link between oxPL modification of apo(a) and stimulation of proinflammatory intracellular signaling pathways.
Topics: Apolipoproteins; Apolipoproteins A; Binding Sites; Cell Line; Humans; Interleukin-8; NF-kappa B; Phospholipids; RNA, Small Interfering; Transcription Factor AP-1
PubMed: 26474593
DOI: 10.1194/jlr.M060210 -
Journal of Lipid Research Feb 1986The two major apolipoproteins of badger serum, apoA-I and apoB, have been isolated and characterized. Apolipoprotein A-I was the principal protein of badger lipoproteins...
The two major apolipoproteins of badger serum, apoA-I and apoB, have been isolated and characterized. Apolipoprotein A-I was the principal protein of badger lipoproteins with density 1.063-1.21 g/ml and, in addition, was present in the lipoprotein class with density 1.006-1.063 g/ml. This apolipoprotein displayed an Mr of approximately equal to 27,000-28,000 and was polymorphic (three prominent isoproteins) on isoelectric focusing, with pI values in the range 5.38-5.55. The amino acid profile of badger apoA-I generally resembled those reported in the literature for similar proteins in dog and man. Amino terminal sequence analysis up to the 40th residue showed close homology between the badger, dog, and human proteins; badger and dog apoA-I differed only at residue 24, at which serine in the dog was substituted by glycine in the badger. Several forms of apolipoprotein B were present in badger lipoproteins with densities less than 1.063 g/ml, their distribution and apparent Mr being unaffected by the presence or absence of 1 mM PMSF during the isolation process. The components of higher Mr were essentially represented by a protein with Mr approximately equal to 530,000-550,000 (apoBH) as determined by SDS-polyacrylamide electrophoresis; this protein predominated both in lipoproteins with d 1.006-1.063 g/ml and in those with d less than 1.006 g/ml. In addition, proteins with approximate Mr values of 490,000, 450,000, and 190,000, respectively, were present as minor components. A lower Mr form (250,000, apoBL), was observed only in lipoproteins with d less than 1.006 g/ml.(ABSTRACT TRUNCATED AT 250 WORDS)
Topics: Amino Acid Sequence; Amino Acids; Animals; Apolipoprotein A-I; Apolipoproteins A; Apolipoproteins B; Carnivora; Dogs; Electrophoresis, Disc; Humans; Isoelectric Focusing; Male; Species Specificity
PubMed: 3083034
DOI: No ID Found -
The Journal of Clinical Investigation Feb 1991Low HDL-cholesterol (HDL-C) levels may elevate atherosclerosis risk, and often associate with hypertriglyceridemia (HTG); however, the metabolic causes of low HDL-C...
Low HDL-cholesterol (HDL-C) levels may elevate atherosclerosis risk, and often associate with hypertriglyceridemia (HTG); however, the metabolic causes of low HDL-C levels with or without HTG are poorly understood. We studied the turnover of radioiodinated HDL apolipoproteins, apo A-I and apo A-II, in 15 human subjects with low HDL-C, six with normal plasma TG levels (group 1) and nine with high TG (group 2), and compared them to 13 control subjects with normal HDL-C and TG levels (group 3). The fractional catabolic rate (FCR) was equally elevated in groups 1 and 2 vs. group 3 for both apo A-I (0.313 +/- 0.052 and 0.323 +/- 0.063 vs. 0.245 +/- 0.043 pools/d, P = 0.003) and apo A-II (0.213 +/- 0.036 and 0.239 +/- 0.037 vs. 0.185 +/- 0.031 pools/d, P = 0.006). Thus, high FCR characterized low HDL-C regardless of the presence or absence of HTG. In contrast, transport rate (TR) of apo A-I did not differ significantly among the groups and the apo A-II TR differed only between groups 2 and 3 (2.15 +/- 0.57, 2.50 +/- 0.39, and 1.83 +/- 0.48 mg/kg per d for groups 1 to 3, respectively, P = 0.016). Several HDL-related factors were similar in groups 1 and 2 but differed in group 3, as with FCR, including the ratio of lipoprotein lipase to hepatic lipase activity (LPL/HL) in post-heparin plasma, the ratio of the HDL-C to apo A-I plus apo A-II levels, and the percent of tracer in the d greater than 1.21 fraction. In linear regression analysis HDL-C levels correlated inversely with the FCR of apo A-I and apo A-II (r = -0.74, P less than 0.0001 for both). Major correlates of FCR were HDL-C/apo A-I + apo A-II, LPL/HL, and plasma TG levels. We hypothesize that lipase activity and plasma TG affect HDL composition which modulates FCR, which in turn regulates HDL-C. Thus, HTG is only one of several factors which may contribute to elevated FCR and low HDL-C. Given the relationship of altered HDL composition with high FCR and low HDL-C levels, factors affecting HDL composition may increase atherosclerosis susceptibility.
Topics: Apolipoprotein A-I; Apolipoprotein A-II; Apolipoproteins A; Cholesterol, HDL; Female; Humans; Hypertriglyceridemia; Kinetics; Lipase; Lipoprotein Lipase; Liver; Male
PubMed: 1899429
DOI: 10.1172/JCI115028 -
Structure (London, England : 1993) May 2012Apolipoproteins are key structural elements of lipoproteins and critical mediators of lipid metabolism. Their detergent-like properties allow them to emulsify lipid or...
Apolipoproteins are key structural elements of lipoproteins and critical mediators of lipid metabolism. Their detergent-like properties allow them to emulsify lipid or exist in a soluble lipid-free form in various states of self-association. Unfortunately, these traits have hampered high-resolution structural studies needed to understand the biogenesis of cardioprotective high-density lipoproteins (HDLs). We derived a crystal structure of the core domain of human apolipoprotein (apo)A-IV, an HDL component and important mediator of lipid absorption. The structure at 2.4 Å depicts two linearly connected 4-helix bundles participating in a helix swapping arrangement that offers a clear explanation for how the protein self-associates as well as clues to the structure of its monomeric form. This also provides a logical basis for antiparallel arrangements recently described for lipid-containing particles. Furthermore, we propose a "swinging door" model for apoA-IV lipid association.
Topics: Apolipoproteins A; Binding Sites; Crystallography, X-Ray; Dimerization; Humans; Lipid Metabolism; Models, Molecular; Protein Structure, Secondary
PubMed: 22579246
DOI: 10.1016/j.str.2012.02.020 -
The American Journal of Medicine May 1988An inverse association between low to moderate alcohol consumption and coronary heart disease has been demonstrated in epidemiologic studies of diverse design. An... (Clinical Trial)
Clinical Trial Comparative Study Randomized Controlled Trial
An inverse association between low to moderate alcohol consumption and coronary heart disease has been demonstrated in epidemiologic studies of diverse design. An attempt was made to determine if this association might be due to an effect of alcohol on apolipoproteins A-I and B and to determine if low-dose alcohol intake might have a potentially protective effect by this mechanism in persons at increased risk for coronary heart disease. To address this, an eight-week prospective randomized clinical trial of abstention versus low-dose alcohol consumption, defined as one beverage per day, was conducted in white men, aged 21 to 60 years, most of whom were patients of a preventive cardiology program. Apolipoprotein A-I levels had a mean increase of 9 mg/dl in the 28 participants who drank alcohol compared with a mean decline of 5 mg/dl in the 28 participants who abstained (p less than 0.005). This association was independent of other cardiovascular risk factors. Low-density lipoprotein (LDL)-B levels had a mean increase of 7 mg/dl in both arms of the trial (NS). However, the ratio of apolipoprotein A-I to LDL-B increased by 4 percent in the drinkers and decreased 10 percent in the abstainers (p less than 0.03). No significant changes in mean levels of total high-density lipoprotein (HDL)-, HDL2-, or HDL3-cholesterol were observed with this low dose of alcohol. This effect on apolipoprotein A-I suggests a possible mechanism by which low-dose alcohol may lower the risk of coronary heart disease.
Topics: Adult; Alcohol Drinking; Apolipoprotein A-I; Apolipoproteins A; Apolipoproteins B; Beer; Clinical Trials as Topic; Coronary Disease; Humans; Lipoproteins, HDL; Male; Middle Aged; Prospective Studies; Random Allocation; Sexual Abstinence; Sexual Behavior
PubMed: 3129938
DOI: 10.1016/0002-9343(88)90067-8 -
The Journal of Biological Chemistry Feb 1986Both cDNA and genomic clones encoding human apolipoprotein (apo-) A-IV have been isolated and characterized. Southern blot analyses of apo-A-IV gene-containing cosmids... (Comparative Study)
Comparative Study
Both cDNA and genomic clones encoding human apolipoprotein (apo-) A-IV have been isolated and characterized. Southern blot analyses of apo-A-IV gene-containing cosmids revealed that the apo-A-IV gene is linked to the apo-A-I and apo-C-III genes within a 20-kilobase span of chromosome 11 DNA. The apo-A-IV gene is located about 14 kilobases downstream from the apo-A-I gene in the same orientation, with the apo-C-III gene located between them in the opposite orientation. The nucleotide sequence of the corresponding human apo-A-IV mRNA was determined, and the derived amino acid sequence showed that mature plasma apo-A-IV contained 376 residues. Throughout most of its length, human apo-A-IV was found to contain multiple tandem 22-residue repeated segments having amphipathic, alpha-helical potential. Amino acid substitutions within these homologous segments were generally conservative in nature. A comparison of the sequences of human and rat apo-A-IV revealed a 79% identity of amino acid positions in the amino-terminal 60 residues and a 58% identity in the remainder of the sequences, with the human protein containing 5 extra residues near the carboxyl terminus. An examination of the distribution of apo-A-IV mRNA in different tissues of the rat, marmoset, and man showed that apo-A-IV mRNA was abundant in both the liver and small intestine of the rat, but abundant in both the liver and small intestine of the marmoset and man. It was expressed in only trace amounts in all other tissues that were examined. These findings on the structure and expression of apo-A-IV and the close linkage of its gene to those of apo-A-I and apo-C-III suggest a regulatory relationship between the three genes.
Topics: Amino Acid Sequence; Animals; Apolipoprotein A-I; Apolipoprotein C-III; Apolipoproteins A; Apolipoproteins C; Base Sequence; Callitrichinae; Chromosomes, Human, 6-12 and X; DNA; Genetic Linkage; Humans; RNA, Messenger; Sequence Homology, Nucleic Acid
PubMed: 3080432
DOI: No ID Found -
Journal of Epidemiology Feb 1999Lipoprotein(a) [Lp(a)] has been considered to be a predictor of premature coronary heart disease and other cardiovascular diseases. Lp(a) levels are largely genetically...
Lipoprotein(a) [Lp(a)] has been considered to be a predictor of premature coronary heart disease and other cardiovascular diseases. Lp(a) levels are largely genetically determined, but the detailed mechanism of Lp(a) elevation is uncertain. We examined the association between Lp(a) levels and apolipoprotein(a) [apo(a)] phenotypes as well as that of Lp(a) level and other various conditions. The subjects were 280 healthy Japanese (102 males and 178 females) aged 39 to 70 years who were living in a rural community in 1992. We obtained apo(a) phenotypes determined by SDS-PAGE as well as Lp(a) levels and other cardiovascular risk factors. We combined apo(a) phenotypes form 4 groups according to molecular weights (from high apo(a) molecular weight to low: I, II, III and IV). Lp(a) levels were associated with apo(a) phenotype-groups, that is, they were inversely associated with apo(a) molecular weight. Small apo(a) phenotypes were less frequent than large ones. The median Lp(a) level was higher in smoking (29.2 mg/dL) than in non-smoking subjects (18.5 mg/dL) in phenotype-group III. Adjusted means of total cholesterol and fibrinogen levels in apo(a) phenotype-group IV were the highest of all phenotype-groups. Age, apo(a) phenotype, smoking status, total cholesterol and fibrinogen were positively correlated with Lp(a) levels by multiple regression analysis. Lp(a) levels were found to be mainly associated with apo(a) phenotype, but varied broadly within the same apo(a) phenotype at various conditions, such as smoking status and high total cholesterol.
Topics: Adult; Aged; Apolipoproteins A; Environment; Female; Genetic Markers; Genetic Predisposition to Disease; Humans; Japan; Life Style; Lipoprotein(a); Male; Middle Aged; Phenotype; Population Surveillance; Protein Isoforms; Risk Factors; Smoking; Statistics as Topic
PubMed: 10098351
DOI: 10.2188/jea.9.32 -
Journal of Lipid Research Dec 2012The relationships between oxidation-specific epitopes (OSE) and lipoprotein (a) [Lp(a)] and progressive atherosclerosis and plaque rupture have not been determined....
The relationships between oxidation-specific epitopes (OSE) and lipoprotein (a) [Lp(a)] and progressive atherosclerosis and plaque rupture have not been determined. Coronary artery sections from sudden death victims and carotid endarterectomy specimens were immunostained for apoB-100, oxidized phospholipids (OxPL), apo(a), malondialdehyde-lysine (MDA), and MDA-related epitopes detected by antibody IK17 and macrophage markers. The presence of OxPL captured in carotid and saphenous vein graft distal protection devices was determined with LC-MS/MS. In coronary arteries, OSE and apo(a) were absent in normal coronary arteries and minimally present in early lesions. As lesions progressed, apoB and MDA epitopes did not increase, whereas macrophage, apo(a), OxPL, and IK17 epitopes increased proportionally, but they differed according to plaque type and plaque components. Apo(a) epitopes were present throughout early and late lesions, especially in macrophages and the necrotic core. IK17 and OxPL epitopes were strongest in late lesions in macrophage-rich areas, lipid pools, and the necrotic core, and they were most specifically associated with unstable and ruptured plaques. Specific OxPL were present in distal protection devices. Human atherosclerotic lesions manifest a differential expression of OSEs and apo(a) as they progress, rupture, and become clinically symptomatic. These findings provide a rationale for targeting OSE for biotheranostic applications in humans.
Topics: Apolipoproteins A; Atherosclerosis; Biomarkers; Carotid Artery Diseases; Epitopes; Female; Humans; Male; Middle Aged; Oxidation-Reduction; Plaque, Atherosclerotic
PubMed: 22969153
DOI: 10.1194/jlr.P030890 -
Journal of Lipid Research Nov 2019HDL-bound ApoM and albumin are protein chaperones for the circulating bioactive lipid, sphingosine 1-phosphate (S1P); in this role, they support essential extracellular...
HDL-bound ApoM and albumin are protein chaperones for the circulating bioactive lipid, sphingosine 1-phosphate (S1P); in this role, they support essential extracellular S1P signaling functions in the vascular and immune systems. We previously showed that ApoM- and albumin-bound S1P exhibit differences in receptor activation and biological functions. Whether the physiological functions of S1P require chaperones is not clear. We examined ApoM-deficient, albumin-deficient, and double-KO (DKO) mice for circulatory S1P and its biological functions. In albumin-deficient mice, ApoM was upregulated, thus enabling S1P functions in embryonic development and postnatal adult life. The DKO mice reproduced, were viable, and exhibited largely normal vascular and immune functions, which suggested sufficient extracellular S1P signaling. However, DKO mice had reduced levels (∼25%) of plasma S1P, suggesting that novel S1P chaperones exist to mediate S1P functions. In this study, we report the identification of ApoA4 as a novel S1P binding protein. Recombinant ApoA4 bound to S1P, activated multiple S1P receptors, and promoted vascular endothelial barrier function, all reflective of its function as a S1P chaperone in the absence of ApoM and albumin. We suggest that multiple S1P chaperones evolved to support complex and essential extracellular signaling functions of this lysolipid mediator in a redundant manner.
Topics: Amino Acid Sequence; Animals; Apolipoproteins A; Apolipoproteins M; Gene Knockout Techniques; Lysophospholipids; Mice; Mice, Inbred C57BL; Serum Albumin; Sphingosine; Sphingosine-1-Phosphate Receptors
PubMed: 31462513
DOI: 10.1194/jlr.RA119000277 -
Journal of Lipid Research Mar 2013During the diagnosis of three unrelated patients with severe hypertriglyceridemia, three APOA5 mutations [p.(Ser232_Leu235)del, p.Leu253Pro, and p.Asp332ValfsX4] were...
During the diagnosis of three unrelated patients with severe hypertriglyceridemia, three APOA5 mutations [p.(Ser232_Leu235)del, p.Leu253Pro, and p.Asp332ValfsX4] were found without evidence of concomitant LPL, APOC2, or GPIHBP1 mutations. The molecular mechanisms by which APOA5 mutations result in severe hypertriglyceridemia remain poorly understood, and the functional impairment/s induced by these specific mutations was not obvious. Therefore, we performed a thorough structural and functional analysis that included follow-up of patients and their closest relatives, measurement of apoA-V serum concentrations, and sequencing of the APOA5 gene in 200 nonhyperlipidemic controls. Further, we cloned, overexpressed, and purified both wild-type and mutant apoA-V variants and characterized their capacity to activate LPL. The interactions of recombinant wild-type and mutated apoA-V variants with liposomes of different composition, heparin, LRP1, sortilin, and SorLA/LR11 were also analyzed. Finally, to explore the possible structural consequences of these mutations, we developed a three-dimensional model of full-length, lipid-free human apoA-V. A complex, wide array of impairments was found in each of the three mutants, suggesting that the specific residues affected are critical structural determinants for apoA-V function in lipoprotein metabolism and, therefore, that these APOA5 mutations are a direct cause of hypertriglyceridemia.
Topics: Adolescent; Adult; Aged; Aged, 80 and over; Apolipoprotein A-V; Apolipoproteins A; Blotting, Western; Electrophoresis, Polyacrylamide Gel; Female; Humans; Hypertriglyceridemia; Liposomes; Male; Middle Aged; Mutagenesis, Site-Directed; Mutation; Young Adult
PubMed: 23307945
DOI: 10.1194/jlr.M031195