-
Molecules and Cells Jun 2015Apolipoprotein A-I and A-IV are protein constituents of high-density lipoproteins although their functional difference in lipoprotein metabolism is still unclear. To...
Apolipoprotein A-I and A-IV are protein constituents of high-density lipoproteins although their functional difference in lipoprotein metabolism is still unclear. To compare anti-atherogenic properties between apoA-I and apoA-4, we characterized both proteins in lipid-free and lipid-bound state. In lipid-free state, apoA4 showed two distinct bands, around 78 and 67 Å on native gel electrophoresis, while apoA-I showed scattered band pattern less than 71 Å. In reconstituted HDL (rHDL) state, apoA-4 showed three major bands around 101 Å and 113 Å, while apoA-I-rHDL showed almost single band around 98 Å size. Lipid-free apoA-I showed 2.9-fold higher phospholipid binding ability than apoA-4. In lipid-free state, BS3-crosslinking revealed that apoA-4 showed less multimerization tendency upto dimer, while apoA-I showed pentamerization. In rHDL state (95:1), apoA-4 was existed as dimer as like as apoA-I. With higher phospholipid content (255:1), five apoA-I and three apoA-4 were required to the bigger rHDL formation. Regardless of particle size, apoA-I-rHDL showed superior LCAT activation ability than apoA-4-rHDL. Uptake of acetylated LDL was inhibited by apoA-I in both lipid-free and lipid-bound state, while apoA-4 inhibited it only lipid-free state. ApoA-4 showed less anti-atherogenic activity with more sensitivity to glycation. In conclusion, apoA-4 showed inferior physiological functions in lipid-bound state, compared with those of apoA-I, to induce more pro-atherosclerotic properties.
Topics: Antioxidants; Apolipoprotein A-I; Apolipoproteins A; Atherosclerosis; Cell Line; Circular Dichroism; Humans; Lipoproteins, HDL; Male; Phospholipids; Structure-Activity Relationship
PubMed: 25997739
DOI: 10.14348/molcells.2015.0052 -
American Journal of Physiology.... Mar 2012Dietary fat is an important mediator of atherosclerosis and obesity. Despite its importance in mediating metabolic disease, there is still much unknown about dietary fat...
Dietary fat is an important mediator of atherosclerosis and obesity. Despite its importance in mediating metabolic disease, there is still much unknown about dietary fat absorption in the intestine and especially the detailed biological roles of intestinal apolipoproteins involved in that process. We were specifically interested in determining the physiological role of the intestinal apolipoprotein A-IV (A-IV) using A-IV knockout (KO) mice. A-IV is stimulated by fat absorption in the intestine and is secreted on nascent chylomicrons into intestinal lymph. We found that A-IV KO mice had reduced plasma triglyceride (TG) and cholesterol levels and that this hypolipidemia persisted on a high-fat diet. A-IV KO did not cause abnormal intestinal lipid absorption, food intake, or adiposity. Additionally, A-IV KO did not cause abnormal liver TG and cholesterol metabolism, as assessed by measuring hepatic lipid content, lipogenic and cholesterol synthetic gene expression, and in vivo VLDL secretion. Instead, A-IV KO resulted in the secretion of larger chylomicrons from the intestine into the lymph, and those chylomicrons were cleared from the plasma more slowly than wild-type chylomicrons. These data suggest that A-IV has a previously unknown role in mediating the metabolism of chylomicrons, and therefore may be important in regulating plasma lipid metabolism.
Topics: Adiposity; Animals; Apolipoproteins A; Body Composition; Chylomicrons; Dietary Fats; Eating; Gene Expression Regulation; Intestinal Absorption; Lipid Metabolism; Lipids; Liver; Mice; Mice, Inbred C57BL; Mice, Knockout
PubMed: 22207575
DOI: 10.1152/ajpgi.00225.2011 -
Journal of Lipid Research Oct 1990Small particles of high density lipoproteins (HDL) were isolated from fresh, fasting human plasma and from the ultracentrifugally isolated high density lipoprotein...
Small particles of high density lipoproteins (HDL) were isolated from fresh, fasting human plasma and from the ultracentrifugally isolated high density lipoprotein fraction by means of ultrafiltration through membranes of molecular weight cutoff of 70,000. These particles were found to contain cholesterol, phospholipids, and apolipoproteins A-I and A-II; moreover, they floated at a density of 1.21 kg/l. They contained 67.5% of their mass as protein and the rest as lipid. Two populations of small HDL particles were identified: one containing apolipoprotein A-I alone [(A-I)HDL] and the other containing both apolipoproteins A-I and A-II [A-I + A-II)HDL]. The molar ratio of apoA-I to apoA-II in the latter subclass isolated from plasma or HDL was 1:1. The molecular weights of these subpopulations were determined by nondenaturing gradient polyacrylamide gel electrophoresis and found to be 70,000; 1.5% of the plasma apoA-I was recovered in the plasma ultrafiltrate.
Topics: Adult; Apolipoprotein A-I; Apolipoprotein A-II; Apolipoproteins A; Cholesterol; Electrophoresis, Polyacrylamide Gel; Female; Humans; Immunoblotting; Lipoproteins, HDL; Male; Molecular Weight; Phospholipids; Ultracentrifugation
PubMed: 2127794
DOI: No ID Found -
The Indian Journal of Medical Research Apr 2018Hepatocellular carcinoma (HCC) is one of the leading causes of cancer mortality. The objective of this study was to find out the differential expression of...
BACKGROUND & OBJECTIVES
Hepatocellular carcinoma (HCC) is one of the leading causes of cancer mortality. The objective of this study was to find out the differential expression of apolipoproteins (ApoAI and ApoAIV) in HCC and cases of liver cirrhosis and chronic hepatitis (controls) without HCC and to compare ApoAI and ApoAIV expression with alpha-foetoprotein (AFP), the conventional marker in HCC.
METHODS
Fifty patients with HCC and 50 controls comprising patients with liver cirrhosis (n=25) and chronic hepatitis (n=25) without HCC were included in this study. Total proteins were precipitated using acetone precipitation method followed by albumin and IgG depletion of precipitated protein using depletion kit. Proteins were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The expression changes of ApoAI and ApoAIV were confirmed by western blotting using specific primary and secondary polyclonal antibodies followed by densitometric protein semi-quantitative estimation. ApoAI, ApoAIV and AFP were measured in the plasma samples by ELISA method.
RESULTS
Semi-quantitative densitometric image analysis of the western blot images and the comparison between HCC patients with those without HCC (control) revealed differential expression of ApoAI and ApoAIV. Levels of ApoAI were significantly higher in patients with HCC compared to controls without HCC (0.279±0.216 vs 0.171±0.091 and 0.199±0.014; P <0.001). Levels of ApoAIV were significantly lower in patients of HCC compared to controls without HCC (0.119±0.061 vs 0.208±0.07 and 0.171±0.16; P <0.01). ELISA assays of apolipoproteins (ApoAI and ApoAIV) revealed similar results of expression of ApoAI and ApoAIV as detected in western blotting densitometric image analysis.
INTERPRETATION & CONCLUSIONS
Increased expression of ApoAI and decreased expression of ApoAIV in HCC patients compared to controls without HCC revealed the abnormalities in HCC. These molecules need to be studied further for their use as potential biomarkers in the future diagnostic tools along with other conventional biomarkers for screening of HCC cases. It needs further analysis in higher number of patient population.
Topics: Apolipoprotein A-I; Apolipoproteins; Apolipoproteins A; Biomarkers, Tumor; Carcinoma, Hepatocellular; Case-Control Studies; Humans; India; Liver Cirrhosis; Liver Neoplasms
PubMed: 29998871
DOI: 10.4103/ijmr.IJMR_1358_16 -
International Journal of Molecular... Jun 2019In the presence of dietary lipids, both apolipoprotein A-IV (ApoA-IV) production and brown adipose tissue (BAT) thermogenesis are increased. The effect of dietary...
In the presence of dietary lipids, both apolipoprotein A-IV (ApoA-IV) production and brown adipose tissue (BAT) thermogenesis are increased. The effect of dietary lipid-induced AproA-IV on BAT thermogenesis and energy expenditure remains unknown. In the present study, we hypothesized that ApoA-IV knockout (ApoA-IV-KO) mice exhibited decreased BAT thermogenesis to affect energy homeostasis. To test this hypothesis, BAT thermogenesis in wildtype (WT) and ApoA-IV-KO mice fed either a standard low-fat chow diet or a high-fat diet (HFD) was investigated. When fed a chow diet, energy expenditure and food intake were comparable between WT and ApoA-IV-KO mice. After 1 week of HFD consumption, ApoA-IV-KO mice had comparable energy intake but produced lower energy expenditure relative to their WT controls in the dark phase. After an acute feeding of dietary lipids or 1-week HFD feeding, ApoA-IV-KO mice produced lower levels of uncoupling protein 1 (UCP1) and exhibited reduced expression of thermogenic genes in the BAT compared with WT controls. In response to cold exposure, however, ApoA-IV-KO mice had comparable energy expenditure and BAT temperature relative to WT mice. Thus, ApoA-IV-KO mice exhibited reduced diet-induced BAT thermogenesis and energy expenditure.
Topics: Adipose Tissue, Brown; Animals; Apolipoproteins A; Diet, High-Fat; Dietary Fats; Energy Metabolism; Male; Mice; Mice, Inbred C57BL; Thermogenesis; Uncoupling Protein 1
PubMed: 31261740
DOI: 10.3390/ijms20133176 -
Journal of Lipid Research Mar 1988Purified apolipoprotein A-I has been separated by reversed-phase high performance liquid chromatography (HPLC) into multiple peaks and these peaks have been...
Purified apolipoprotein A-I has been separated by reversed-phase high performance liquid chromatography (HPLC) into multiple peaks and these peaks have been characterized. One peak, apoA-Ib had a relatively longer retention time on HPLC but its retention time could be shortened by treatment by hydrogen peroxide. CNBr cleavage studies indicated that the differences in apoA-Ib and in its oxidation product, apoA-Ia, were due to the different oxidation states of methionine. This phenomenon was also observed in apoA-II, where methionine oxidation produced two more forms of this apolipoprotein in addition to the native form. These isomers were found to have different secondary structures and affinities for lipid. Model peptide analogs of the amphipathic helix with the same sequence but with methionine and methionine sulfoxide at the nonpolar face of the amphipathic helix were synthesized and studied. It was found that the lipid affinities of these synthetic peptide isomers were very different. They also differed in their secondary structures as studied by circular dichroism (CD). We propose that methionine oxidation introduces hydrophilic residues at the nonpolar face of the amphipathic helical domains of these apolipoproteins and, therefore, alters their secondary structure and lipid affinity.
Topics: Apolipoprotein A-I; Apolipoprotein A-II; Apolipoproteins A; Chromatography, High Pressure Liquid; Circular Dichroism; Cyanogen Bromide; Electrophoresis, Polyacrylamide Gel; Hydrogen Peroxide; Isomerism; Mercaptoethanol; Microscopy, Electron; Oxidation-Reduction; Peptides
PubMed: 3132519
DOI: No ID Found -
Molecular and Cellular Biology Nov 1986Apolipoprotein A-IV (apo A-IV) functions in conjunction with other apolipoproteins to form lipoprotein particles which are involved in lipid homeostasis. In this report... (Comparative Study)
Comparative Study
Apolipoprotein A-IV (apo A-IV) functions in conjunction with other apolipoproteins to form lipoprotein particles which are involved in lipid homeostasis. In this report we present the nucleotide sequence of the mouse apo A-IV gene and demonstrate its induction in the liver by chronically high dietary lipid. The apo A-IV gene consists of three exons and two introns. The introns separate evolutionarily conserved and functional polypeptide domains. Intron 1 divides most of the apo A-IV signal peptide from the amino terminus of the mature plasma protein. The second intron separates a highly evolutionarily conserved, variant amphipathic peptide repeat from the remainder of the mature apo A-IV protein. The 5' flanking region has several interesting features. The apo A-IV gene has variant TATA and CAT box sequences, TTTAAA and CCAACG, respectively. There are five G-rich direct repeats of 10 nucleotides and a short inverted repeat in the 5' flanking region. We speculate that these sequence elements in the 5' flanking region may be involved in the regulation of apo A-IV gene expression. We also show that chronically high dietary lipid induces liver apo A-IV levels 10-fold in C57BL/6 mice, a strain susceptible to atherosclerotic lesions, while we observed no induction in nonsusceptible BALB/c and C3H mice.
Topics: Amino Acid Sequence; Animals; Apolipoproteins A; Base Sequence; Cloning, Molecular; DNA; Dietary Fats; Exons; Genes; Humans; Mice; Promoter Regions, Genetic; Rats; Sequence Homology, Nucleic Acid; Species Specificity
PubMed: 3796595
DOI: 10.1128/mcb.6.11.3807-3814.1986 -
Journal of Lipid Research Apr 2014Apo(a), the distinguishing protein component of lipoprotein(a) [Lp(a)], exhibits sequence similarity to plasminogen and can inhibit binding of plasminogen to cell...
Apo(a), the distinguishing protein component of lipoprotein(a) [Lp(a)], exhibits sequence similarity to plasminogen and can inhibit binding of plasminogen to cell surfaces. Plasmin generated on the surface of vascular cells plays a role in cell migration and proliferation, two of the fibroproliferative inflammatory events that underlie atherosclerosis. The ability of apo(a) to inhibit pericellular plasminogen activation on vascular cells was therefore evaluated. Two isoforms of apo(a), 12K and 17K, were found to significantly decrease tissue-type plasminogen activator-mediated plasminogen activation on human umbilical vein endothelial cells (HUVECs) and THP-1 monocytes and macrophages. Lp(a) purified from human plasma decreased plasminogen activation on THP-1 monocytes and HUVECs but not on THP-1 macrophages. Removal of kringle V or the strong lysine binding site in kringle IV10 completely abolished the inhibitory effect of apo(a). Treatment with carboxypeptidase B to assess the roles of carboxyl-terminal lysines in cellular receptors leads in most cases to decreases in plasminogen activation as well as plasminogen and apo(a) binding; however, inhibition of plasminogen activation by apo(a) was unaffected. Our findings directly demonstrate that apo(a) inhibits pericellular plasminogen activation in all three cell types, although binding of apo(a) to cell-surface receptors containing carboxyl-terminal lysines does not appear to play a major role in the inhibition mechanism.
Topics: Apolipoproteins A; Cells, Cultured; Human Umbilical Vein Endothelial Cells; Humans; Leukocytes, Mononuclear; Lysine; Macrophages; Plasminogen; Plasminogen Activators; Protein Binding; Protein Interaction Domains and Motifs
PubMed: 24478033
DOI: 10.1194/jlr.M036566 -
Clinical Biochemistry Jan 2013Apolipoprotein A5 (ApoA5) is a key regulator of plasma triglycerides (TG), even though its plasma concentration is very low compared to other known apoproteins. Over the... (Review)
Review
UNLABELLED
Apolipoprotein A5 (ApoA5) is a key regulator of plasma triglycerides (TG), even though its plasma concentration is very low compared to other known apoproteins. Over the years, researchers have attempted to elucidate the molecular mechanisms by which ApoA5 regulates plasma TG in vivo. Though still under debate, two theories broadly describe how ApoA5 modulates TG levels: (i) ApoA5 enhances the catabolism of TG-rich lipoproteins and (ii) it inhibits the rate of production of very low-density lipoprotein (VLDL), the major carrier of TGs. This review will summarize the basic and clinical studies that describe the importance of ApoA5 in TG metabolism. Population studies conducted in various countries have demonstrated an association between single nucleotide polymorphisms (SNPs) in ApoA5 and the increased risk to cardiovascular disease and metabolic syndrome (including diabetes and obesity). ApoA5 is also highly expressed during liver regeneration and is an acute phase protein associated with HDL, which is independent of its effects on TG metabolism.
CONCLUSION
Despite considerable evidences available from clinical and basic research studies on the role of ApoA5 in TG metabolism and its indirect link to metabolic diseases, additional investigations are needed to understand the paradoxical role of this important apoprotein is modulated by both diet and its polymorphism variants.
Topics: Animals; Apolipoprotein A-V; Apolipoproteins A; Cardiovascular Diseases; Diabetes Mellitus; Diet; Genetic Predisposition to Disease; Humans; Metabolic Syndrome; Obesity; Polymorphism, Single Nucleotide; Triglycerides
PubMed: 23000317
DOI: 10.1016/j.clinbiochem.2012.09.007 -
Biochimica Et Biophysica Acta Apr 1988Rat luteal cells utilize high-density lipoproteins (HDL) as a source of cholesterol for steroid synthesis. Both the free and esterified cholesterol of HDL are utilized...
Rat luteal cells utilize high-density lipoproteins (HDL) as a source of cholesterol for steroid synthesis. Both the free and esterified cholesterol of HDL are utilized by these cells. In this report, we have examined the relative uptake of free and esterified cholesterol of HDL by cultured rat luteal cells. Incubation of the cells with HDL labeled with [3H]cholesterol or [3H]cholesteryl linoleate resulted in 4-6-fold greater uptake of the free cholesterol compared to esterified cholesterol. The increased uptake of free cholesterol correlated with its utilization for progestin synthesis: utilization of HDL-derived free cholesterol was 3-6-fold higher than would be expected from its concentration in HDL. The differential uptake and utilization of free and esterified cholesterol was further examined using egg phosphatidylcholine liposomes containing cholesterol or cholesteryl linoleate as a probe. Liposomes containing free cholesterol were able to deliver cholesterol to luteal cells and support steroid synthesis in the absence of apolipoproteins, and the addition of apolipoprotein A-I (apo A-I) moderately increased the uptake and steroidogenesis. Similar experiments using cholesteryl linoleate/egg phosphatidylcholine liposomes showed that inclusion of apo A-I resulted in a pronounced increase in the uptake of cholesteryl linoleate and progestin synthesis. These experiments suggest that free cholesterol from HDL may be taken up by receptor-dependent and receptor-independent processes, whereas esterified cholesterol uptake requires a receptor-dependent process mediated by apolipoproteins.
Topics: Animals; Apolipoprotein A-I; Apolipoproteins A; Cholesterol; Cholesterol Esters; Female; Lipoproteins, HDL; Ovary; Progestins; Rats
PubMed: 3128333
DOI: 10.1016/0005-2760(88)90192-0