|
|
|
|||||||
|
|||||||||
J. Biol. Chem., Vol. 279, Issue 27, 27941-27947, July 2, 2004
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ApoAV Reduces Plasma Triglycerides by Inhibiting Very Low Density Lipoprotein-Triglyceride (VLDL-TG) Production and Stimulating Lipoprotein Lipase-mediated VLDL-TG Hydrolysis*
¶||**
¶¶
From the
AMC Liver Center, Meibergdreef 69-71, 1105 BK Amsterdam, The Netherlands, ||TNO-Prevention and Health, Gaubius Laboratory, Zernikedreef 9, 2333 CK Leiden, The Netherlands, and the Departments of **General Internal Medicine, Endocrinology, Human Genetics, and ¶¶Cardiology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands
Received for publication, March 23, 2004 , and in revised form, April 15, 2004.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONREFERENCES |
|---|
ApoAV has been discovered recently as a novel modifier of triglyceride (TG) metabolism, but the pathways involved are currently unknown. To gain insight into the function of apoAV, adenovirus-mediated gene transfer of murine apoa5 to C57Bl/6 mice was employed. The injection of low doses of Ad-apoa5 (1–5 x 108 plaqueforming units/mouse) dose-dependently reduced plasma very low density lipoprotein (VLDL)-TG levels. First, we evaluated whether a reduced hepatic VLDL production contributed to the TG-lowering effect. Ad-apoa5 treatment dose-dependently diminished (29–37%) the VLDL-TG production rate without affecting VLDL particle production, suggesting that apoAV impairs the lipidation of apoB. Second, Ad-apoa5 treatment dose-dependently reduced (68–88%) the postprandial hypertriglyceridemia following an intragastric fat load, suggesting that apoAV also stimulates the lipoprotein lipase (LPL)-dependent clearance of TG-rich lipoproteins. Indeed, recombinant apoAV was found to dose-dependently stimulate LPL activity up to 2.3-fold in vitro. Accordingly, intravenously injected VLDL-like TG-rich emulsions were cleared at an accelerated rate concomitant with the increased uptake of emulsion TG-derived fatty acids by skeletal muscle and white adipose tissue in Ad-apoa5-treated mice. From these data, we conclude that apoAV is a potent stimulator of LPL activity. Thus, apoAV lowers plasma TG by both reducing the hepatic VLDL-TG production rate and by enhancing the lipolytic conversion of TG-rich lipoproteins.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONREFERENCES |
|---|
Hypertriglyceridemia is a risk factor for coronary heart disease independent from the well known risk factors such as elevated LDL1 and reduced HDL cholesterol levels (1). Recently, a novel apolipoprotein, apoAV, has been identified that strongly influences plasma triglyceride (TG) levels (2, 3). The human APOA5 gene is part of the apolipoprotein gene cluster on chromosome 11q23 that also encompasses APOA1, APOC3, and APOA4. An initial study revealed the association of three single nucleotide polymorphisms within the APOA5 locus with plasma TG levels and VLDL mass in humans (2). Importantly, these metabolic effects were not associated with a genetic marker in the nearby APOC3 gene that is also known to affect plasma TG levels (2). Subsequent studies in diverse ethnic groups uncovered additional single nucleotide polymorphisms including apoAV protein variants and further supported a role for common genetic variations in APOA5 in influencing plasma TG levels (4, 5). Interestingly, in a recent study, minor allele frequencies of 3 of 5 studied single nucleotide polymorphisms were found to be significantly higher in a hypertriglyceridemic population (4).
Mouse models confirmed the TG-modulating effects of apoAV observed in humans. Mice expressing a human APOA5 transgene showed a 65% decrease in plasma TG levels compared with control mice (2). Conversely, apoa5 knock-out mice showed a 400% increase in plasma TG concentration (2). Interestingly, the adenovirus-mediated expression of apoAV in mice resulted in a decrease of both plasma TG and total cholesterol (TC) of 70 and 40%, respectively (6).
ApoAV appears to be expressed exclusively in the liver. At present, it is unknown in what form apoAV is secreted by the liver. The circulating mature form has a predicted molecular mass of 39 kDa and is associated mainly with HDL and to a lesser extent with VLDL particles (3). This distribution is somewhat puzzling as apoAV mainly seems to affect VLDL metabolism. Initially, apoAV may be secreted along with VLDL, and as lipolytic conversion of VLDL progresses and excess surface lipids are being transferred to HDL, apoAV may end up in HDL in a similar way. Structure predictions indicate that apoAV is a very hydrophobic, highly 
-helical protein (7). At the protein level, apoAV appears most homologous (20–28% amino acid identity) with exchangeable apolipoproteins apoAI, apoAIV, and apoE, prompting the study of lipid efflux and lecithin:cholesterol acyltransferase activation properties of apoAV (8). However, no such activity could be demonstrated in in vitro experiments employing recombinant apoAV (8). Little is known regarding the regulation of apoAV levels, but peroxisome proliferator-activated receptor- and the farnesoid X receptor have been implicated in the transcriptional regulation of the APOA5 gene (9, 10).
Animal studies and genetic association studies clearly indicate a strong effect of apoAV on plasma TG levels, implicating a role for apoAV in VLDL metabolism. Based on structural analysis, it has been proposed that, at the intracellular level, apoAV may affect hepatic VLDL production (7). Alternatively, apoAV may stimulate lipolytic conversion of TG-rich lipoproteins. To address the mechanism(s) underlying the hypotriglyceridemic action of apoAV, we employed the adenovirus-mediated gene transfer of murine apoa5 to C57Bl/6 mice.
Our results show that the expression of apoAV in mice reduces plasma TG and TC levels. ApoAV dose-dependently inhibited the hepatic VLDL-TG production rate without affecting the VLDL-apoB production rate. Moreover, our present studies clearly demonstrate that apoAV accelerates the rate of LPL-mediated TG hydrolysis both in vitro and in vivo. Thus, we propose that apoAV has a dual effect on VLDL metabolism, diminishing hepatic apoB lipidation and increasing the efficiency of TG disposal from circulating lipoproteins. Interestingly, this hypotriglyceridemic effect of apoAV is associated with a decrease of plasma TC levels. These observations suggest that apoAV is an interesting target in the treatment of hypertriglyceridemia.
|
EXPERIMENTAL PROCEDURES |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONREFERENCES |
|---|
Materials—Glycerol tri[9,10(n)-3H]oleate ([3H]triolein) and [1-14C]oleate were from Amersham Biosciences. Trans35S label was from ICN. Egg yolk phosphatidylcholine was a generous gift from Lipoid. Triolein was obtained from Fluka. Hypnorm was from Janssen Pharmaceuticals, and midazolam was from Roche Applied Science. L-
-Lysophosphatidylcholine, cholesterol, cholesteryl oleate, purified bovine milk LPL, essentially free fatty acid-free bovine serum albumin, Triton WR1339 (tyloxapol), and diethyl-p-nitrophenylphosphate (paraoxon) were from Sigma. Purified human apoCII and apoCIII were from Labconsult. Olive oil was from Carbonell. Heparin was from Leo Pharmaceutical Products. SolvableTM was from Packard Bioscience. All of the other chemicals were of analytical grade and purchased from various suppliers. For the determination of lipids, commercially available kits (TG and TC (Sigma) and phospholipids (PL) (Wako Chemicals)) were used according to the manufacturer's instructions. Animals—13–17-week-old male C57Bl/6 mice were taken from the breeding colony at the University of Leiden. Mice were kept in a temperature- and humidity-controlled environment and had free access to standard laboratory chow and water. All of the animals used in the experiments received humane care, and all of the experiments were approved by the animal ethics committees from the University of Leiden and TNO-Prevention and Health.
Adenoviral Expression of ApoAV in C57Bl/6 Mice—The construction of a recombinant replication-deficient adenoviral vector expressing mouse apoAV (Ad-apoa5) has been described previously (6). 0–5 x 108 pfu of Ad-apoa5 (total viral dose adjusted to 5 x 108 with empty vector (Ad-mock)) were injected into the tail vein of the mice (n = 4 – 6/group) at 3 h after the injection of Ad-LacZ (5 x 108 pfu) to saturate the uptake of viral particles by Kupffer cells (11). Prior to injection and 4 days after injection, mice were fasted for 4 h and a blood sample for lipid determination was collected in paraoxon-coated capillaries by tail bleeding. Mice were bled by retroorbital bleeding, and serum was prepared. For each group, sera were pooled and lipoproteins were fractionated by gel permeation chromatography (Superose 6). Following exsanguination, livers were excised, rinsed briefly in phosphate-buffered saline, and immediately frozen in liquid nitrogen. For determination of hepatic gene expression, mRNA was isolated from liver samples and converted to cDNA. The expression levels of apoa5 were determined relative to cyclophilin A by real-time PCR (Taqman). Western blot analysis of serum samples was used to estimate the extent of apoAV expression as described previously (6).
Hepatic VLDL-Triglyceride Production—To determine the effect of apoAV expression on the hepatic VLDL-TG production rate, mice were injected via the tail vein with 5 x 108 pfu of Ad-apoa5 or Ad-LacZ (n = 5/group). After 4 days, a 4-h fasted blood sample was taken (t = 0). Mice were anesthetized with Hypnorm (0.1 mg/kg fentanyl citrate and 25 mg/kg fluanisone) and midazolam (12.5 mg/kg) and injected via the tail vein with Trans35S label (150 µCi/mouse). After 30 min, 12.5 mg of Triton WR1339 (10% solution in saline) was injected to block lipolysis (12). Subsequent blood samples were drawn at 10, 30, 60, and 90 min after injection via tail bleeding. At t = 120 min, mice were exsanguinated and the VLDL fraction of each mouse was isolated quantitatively from 400 µl of serum after density gradient ultracentrifugation (13). VLDL-TG was measured as described above. VLDL-apoB was precipitated selectively by 2-propanol (14) and counted for the incorporated 35S.
Preparation of Recombinant ApoAV—Rat apoAV protein was produced by transformed Escherichia coli BL21(DE3) cells as described previously (3). The N-terminally hexahistidine-tagged apoAV protein was purified from guanidinium hydrochloride-solubilized inclusion bodies by metal affinity chromatography (AP Biotech) using an fast protein liquid chromatography system. Renaturation was achieved by on-column refolding of the protein in a linear 6–0 M urea gradient. Elution was performed with a linear 20–500 mM imidazole gradient in the presence of 0.1% Triton X-100. ApoAV-containing fractions were pooled, and buffer was exchanged to phosphate-buffered saline containing 0.1% Triton X-100. Finally, preparations were filter-sterilized (0.22 µm) and stored at –20 °C. The presence of 0.1% Triton X-100 proved to be essential to prevent the precipitation of apoAV during column elution and subsequent storage. Recombinant apoAV was essentially pure as judged from SDS-PAGE analysis. Protein concentrations were determined using the bicinchoninic acid method.
Preparation of VLDL-like Emulsions—VLDL-like TG-rich emulsion particles were prepared as described previously (15). Hereto, 100 mg of total lipid at a weight ratio of triolein:egg yolk phosphatidylcholine: lysophosphatidylcholine:cholesterYl oleate:cholesterol (70:22.7:2.3:3.0: 2.0) supplemented with 50–200 µCi of [3H]triolein was sonicated using a Soniprep 150 (MSE Scientific Instruments) at an output of 10 µm. An emulsion fraction containing 80-nm sized emulsion particles was obtained by consecutive density gradient ultracentrifugation steps exactly as described previously (16). The TG content of emulsions was determined as described above.
In Vitro LPL Activity Assay—The effect of apolipoproteins on LPL activity was determined essentially as described (17). First, [3H]triolein-labeled emulsion particles (200 µg of TG) were incubated (30 min at 37 °C) with the indicated amounts of human apoCII, human apoCIII, and/or rat apoAV in 75 µl of phosphate-buffered saline. Subsequently, 0.1 M Tris·HCl pH 8.5 was added to a total volume of 200 µl. At t = 0, LPL (final concentration 3.5 units/ml) was added in 200 µl of 12% bovine serum albumin (as [3H]oleate acceptor). At t = 15, 30, 60, 90, and 120 min, [9,10-3H]oleate that was generated during lipolysis was extracted. Hereto, 50-µl samples were added to 1.5 ml of CH3OH:CHCl3: heptane:oleic acid (1410:1250:1000:1 (v/v/v/v)) and to 0.5 ml of 0.2 M NaOH. Following vigorous mixing and centrifugation (10 min at 1000 x g), 3H radioactivity in 0.5 ml of the aqueous phase was counted in 5 ml of Ultima Gold (Packard Bioscience). The recovery of [3H]oleate in the aqueous phase following organic extraction was corrected for a 78.0 ± 0.9% recovery of [1-14C]oleate internal standard. Lipolysis rates were calculated by linear regression (regression coefficients were typically greater than 0.995) and expressed as nanomole oleate released per milliliter per min. The inclusion of 1 M NaCl during incubations resulted in negligible lipolytic activity, indicating that the employed LPL preparation was not contaminated with salt-insensitive hepatic lipase.
Postprandial TG Response—To determine the effect of apoAV expression on the postprandial TG response, mice were injected via the tail vein with 1–5 x 108 pfu of Ad-apoa5 or Ad-mock (n = 5–6/group) as described above. After 5 days, the 4-h fasted blood samples were drawn and the mice received an intragastric load of 200 µl of olive oil. Additional blood samples were drawn after 1, 2, 4, and 6 h, and the resulting sera were assayed for TG as described above.
Clearance of VLDL-like Emulsions in Vivo—To determine the effect of apoAV expression on the kinetics of TG-rich emulsions in vivo, mice were injected via the tail vein with 1 x 109 pfu of Ad-apoa5 or Ad-mock (n = 4/group). At 5 days after adenoviral injection, serum clearance and tissue distribution of VLDL-like emulsion particles was studied as detailed elsewhere (16). The fed mice were anesthetized as described above, and their abdomens were opened. 200 µl of VLDL-like [3H]triolein-labeled emulsion particles was administered via the vena cava inferior at a dose (1.0 mg of TG) that exceeded the endogenous plasma TG content in both experimental groups. Venous blood was sampled at 1, 2, 5, 10, and 15 min following injection, and the respective sera were assayed for 3H radioactivity. After the last sampling, gonadal, perirenal, and intestinal white adipose tissue, heart, hind limb muscle tissue, liver, and spleen were harvested and solubilized in Solvable (overnight at 60 °C) and 3H radioactivity was determined.
Statistical Analysis—The Mann-Whitney nonparametric test for two independent samples was used to define differences between the experimental groups. The criterion for significance was set at p < 0.05.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONREFERENCES |
|---|
Plasma Lipid and Lipoprotein Levels after Adenovirus-mediated Gene Transfer of apoa5 to C57Bl/6 Mice—The injection of low doses of Ad-apoa5 (1, 2.5, and 5 x 108 pfu) dose-dependently reduced plasma TG, TC, and PL (Fig. 1). At the highest dose, plasma TG was lowered to the same extent (–65%) as in mice transgenic for the human APOA5 gene (2). In contrast with these transgenic animals, which are normocholesterolemic, we found consistent (6) lowering of plasma TC with 68% at the highest viral dose. However, moderate overexpression by injection of 1 x 108 pfu of Ad-apoa5 reduced only plasma TG levels significantly (–33%, p < 0.01 versus control virus), whereas plasma TC and PL were unaffected. Compared with mice receiving control virus, the mice that were injected with 1, 2.5, and 5 x 108 pfu of Ad-apoa5 had
10-, 20-, and 30-fold higher hepatic apoa5 mRNA levels, respectively, at day 4 post-injection (data not shown). When compared with preinjection values, apoAV protein levels in plasma were elevated 10-, 20-, and 35-fold at day 4 after the injection of 1, 2.5, and 5 x 108 pfu of Ad-apoa5, respectively (data not shown).
|
) and at 4 days after injection (
), fasted plasma was collected from the individual mice and assayed for TG (left panel), TC (middle panel), and choline PL (right panel). Values are depicted as means ± S.D. **, p < 0.01.An analysis of lipoprotein fractions separated by fast protein liquid chromatography revealed that apoAV-mediated reduction of plasma TG was mainly confined to the VLDL fraction resulting in the virtual absence of VLDL-TG at the highest viral dose (Fig. 2, left panel). Both the TG content of the intermediate density lipoprotein/LDL fraction and size of the intermediate density lipoprotein/LDL-TG peak fraction decreased in an Ad-apoa5 dose-dependent manner. In addition, Ad-apoa5 treatment reduced HDL-TG. The TC-reducing effects of apoAV overexpression were attributed mainly to the reduction of HDL, which is the main carrier of cholesterol in normolipidemic mice (Fig. 2, right panel).
|
), 2.5 (
), and 5 x 108 (Hepatic VLDL Production after Adenovirus-mediated Gene Transfer of apoa5 to C57Bl/6 Mice—To evaluate whether reduced VLDL production contributed to the TG-lowering effect of apoAV, the hepatic VLDL production rate was assessed using Triton WR1339 to block lipolysis and the clearance of VLDL. As compared with control virus, the injection of 1 x 108 or 5 x 108 pfu of Ad-apoa5 dose-dependently reduced the VLDL-TG secretion rate with 29–37% (5.08 ± 0.54, 3.63 ± 0.20, and 3.22 ± 0.68 mM/h, respectively; p < 0.01) without affecting the VLDL-[35S]apoB production rate (Fig. 3, left and right panels). Apparently, apoAV inhibits the intrahepatic lipidation of apoB without affecting VLDL particle production.
|
An analysis of VLDL isolated 2 h after Triton WR1339 injection indicated significant reductions of VLDL lipid content. The highest Ad-apoa5 dose (5 x 108 pfu) mainly affected VLDL-TG (–39%; 6.37 ± 1.39 versus 10.4 ± 1.43 mM; mean ± S.D. (Fig. 3, middle panel)), although TC (–24%; 1.10 ± 0.15 versus 1.45 ± 0.25 mM) and PL (–32%; 1.21 ± 0.25 versus 1.79 ± 0.29 mM)) also was reduced (p < 0.05 versus Ad-LacZ)). An analysis of the lipid composition of VLDL obtained from mice injected with the lowest dose of Ad-apoa5 (1 x 108 pfu) revealed a significant reduction of the TG content (–26%; 7.74 ± 0.16 versus 10.4 ± 1.43 mM), whereas the TC and PL content only tended to be lower (data not shown). The predominant effect of Ad-apoa5 on VLDL-TG levels is indicative of reduction of VLDL particle size.
Postprandial TG Response after Adenovirus-mediated Gene Transfer of apoa5 to C57Bl/6 Mice—In addition to reducing the rate of hepatic VLDL-TG secretion, we questioned whether apoAV could also enhance the lipolytic conversion of TG-rich lipoproteins. First, we studied whether apoAV affected post-prandial lipemia, anticipating enhanced catabolism of TG-rich lipoproteins if apoAV would stimulate LPL activity. For this purpose, mice were injected with adenovirus and were given an intragastric gavage of olive oil after 5 days to force rapid and extensive chylomicron production. Animals injected with Ad-apoa5 showed a dose-dependent lowering of the postprandial TG response (68, 73, and 88% reduction compared with control virus at Ad-apoa5 doses of 1 x 108, 2.5 x 108, and 5 x 108 pfu, respectively) (Fig. 4). These findings indicate that apoAV overexpression results in a rapid clearance of chylomicron-TG. Because apoAV is not expressed by the intestine, a direct effect of apoAV on intestinal lipid absorption is unlikely. Thus, these findings strongly suggest that the diminished postprandial TG response is the result of a stimulating effect of apoAV on LPL-mediated lipolysis.
|
Effect of Purified apoAV on LPL-mediated TG Hydrolysis in Vitro—To directly evaluate the effect of recombinant rat apoAV on the triacylglycerol hydrolase activity of LPL, we determined the effect of purified apoAV on LPL-mediated TG hydrolysis from [3H]triolein-labeled VLDL-like emulsions in vitro. The incubation of 80-nm sized VLDL-like protein-free emulsion particles with LPL in the presence of apoCII resulted in an apoCII dose-dependent increased rate of [3H]oleate generation from emulsion-incorporated glycerol-tri[3H]oleate (Fig. 5A) obeying initial linear kinetics up to 120 min. Preincubation of particles with 0.48 nmol of apoAV enhanced the apoCII-stimulated lipolysis rate
2-fold (Fig. 5, A and B). In the presence of apoCII, apoAV dose-dependently stimulated LPL activity up to 2.3-fold at the highest dose but it was ineffective in the absence of apoCII (Fig. 5B). Preincubation of particles with the well established LPL-inhibitor apoCIII in the presence of a small amount of cofactor (0.11 nmol of apoCII) resulted in a dose-dependent inhibition of the lipolysis rate, reaching 65% inhibition at the highest dose (Fig. 5, C and D). Importantly, the LPL-inhibitory effect of apoCIII could be overcome fully by a low concentration of apoAV (apoAV:apoCIII = 1:20, mol/mol) (Fig. 5D). Taken together, these data suggest that apoAV may act as a stimulatory modifier of apoCII-induced LPL-mediated TG hydrolysis.
|
Kinetics of VLDL-like Emulsion Clearance after Adenovirus-mediated Gene Transfer of apoa5 to C57Bl/6 Mice—To further evaluate the metabolic consequences of the LPL-activating properties of apoAV in vivo, we subsequently determined the tissue distribution of [3H]oleate derived from intravenously injected [3H]triolein-labeled VLDL-like emulsion particles. In line with the concept that apoAV stimulates LPL activity, the serum clearance of emulsion-TG was much faster in Ad-apoa5-treated mice compared with mice injected with control virus (t
= 2.2 ± 0.2 versus 7.6 ± 0.2 min, respectively; p < 0.05) (Fig. 6, left panel). The accelerated TG clearance in Ad-apoa5-treated animals was accompanied by a 2.5–3.5-fold increased uptake of 3H radioactivity by gonadal, perirenal, and intestinal white adipose tissue (p < 0.05), a 1.8-fold increased uptake by hind limb muscle tissue (p < 0.05), and a trend toward an increased uptake by the heart (Fig. 6, right panel). The uptake by the liver also was increased (57%, p < 0.05). In contrast, the uptake by the spleen, which mainly reflects whole particle uptake because the spleen does not express LPL activity, was unaffected. Collectively, these data indicate the potency of the stimulatory effect of apoAV on LPL-mediated TG-rich lipoprotein clearance in vivo.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONREFERENCES |
|---|
In this study, we have demonstrated that adenovirus-mediated gene transfer of murine apoa5 results in a dose-dependent reduction of plasma TG in mice (Fig. 1). At least two mechanisms underlie the hypotriglyceridemic effect of apoAV overexpression. First, apoAV diminishes the rate of hepatic VLDL-TG secretion. Second, apoAV increases the efficiency of LPL-mediated TG hydrolysis. We propose that the latter mechanism results in increased conversion of VLDL and chylomicrons in their respective remnants and a subsequently more efficient clearance of remnants by the liver.
Based on structural analysis, it has been proposed recently (7) that apoAV functions in VLDL metabolism by inhibiting hepatic VLDL secretion. In this study, we have provided experimental proof for such a function (Fig. 3). One could argue that the adenoviral overexpression of a secreted apolipoprotein overloads the capacity of the ER/Golgi secretory pathway and thereby interferes with apoB lipid acquisition. Studies with other adenovirally overexpressed apolipoproteins oppose this view. We have reported previously that the adenoviral overexpression of apoE strongly increases the VLDL-TG secretion rate compared with either Ad-GFP (18) or Ad-LacZ (19). In addition, we have observed recently that Ad-APOC1 does not affect the hepatic VLDL production compared with Ad-LacZ, even at a dose as high as 3.3 x 109 pfu.2 Hence, the adenoviral overexpression of an apolipoprotein does not alter the rate of VLDL-TG secretion per se. Although the underlying mechanism is unknown as yet, the lowering effect of Ad-apoa5 on VLDL-TG production is thus specific for apoAV.
VLDL assembly is a multicompartemental process proceeding in two major steps (20). First, apoB is lipidated during the translation of its mRNA in the rough ER. Second, this partially lipidated apoB particle fuses with a TG-rich particle preformed in the smooth ER. The latter step takes place in a distal compartment of the secretory pathway and results in the formation of secretion-competent mature VLDL. ApoAV, at least when overexpressed, diminishes the rate of VLDL-TG secretion without affecting the production of VLDL particles. Under the experimental conditions used, the particle levels of major VLDL lipids (i.e. TG, TC, and PL) all were found to be lowered, albeit apoAV predominantly affected the VLDL-TG content. As underlipidated apoB protein is subject to rapid degradation before exiting the ER (20), apoAV is more likely to interfere with a step in the second stage of VLDL assembly. For example, apoAV could disturb lipidation of the TG-rich particle in the smooth ER. The hepatic mRNA level for microsomal triglyceride transfer protein, which is essential for this process and for the initial lipidation of nascent apoB, does not change following Ad-apoa5 treatment (data not shown). The intrahepatic action of apoAV presumably requires the (transient) localization of apoAV to the ER/secretory pathway, which is conceivable for a secreted plasma protein.
In this study, we further demonstrated that apoAV can enhance LPL-mediated TG hydrolysis in a dose-dependent manner in vitro (Fig. 5). The molecular mechanism of LPL stimulation remains to be determined, but a role as a cofactor comparable to apoCII seems unlikely because apoAV had no enhancing effect on lipolysis in the absence of apoCII. One could speculate that a potential molecular mechanism of apoAV action is to facilitate the access of LPL to the TG molecules in the core of the lipoprotein particle (i.e. enhancing substrate availability). This is in line with the high hydrophobicity of the apoAV protein (7), placing apoAV more toward the core of the lipoprotein particle. The improved presentation of TG to LPL could subsequently lead to a higher efficiency of TG conversion. It is also possible that apoAV interacts directly with LPL and increases the efficiency of TG hydrolysis by enhancing enzymatic activity, for example, by stabilizing the LPL dimer.
Following an intragastric fat load, a diminished postprandial hypertriglyceridemia was observed in mice injected with Ad-apoa5, strongly suggesting apoAV-mediated LPL activation to occur in vivo as well (Fig. 4). Although intestinal cells do not express apoAV, an indirect effect of apoAV on intestinal lipid absorption involving biliary lipid secretion cannot be excluded. However, bypassing intestinal absorption by intravenous injection of [3H]TG-rich emulsion particles leads to a pronounced shortening of the 3H plasma half-life in Ad-apoa5-treated mice, once more indicating the stimulation of LPL-mediated lipolytic processing of TG by apoAV in vivo (Fig. 6, left panel). Indeed, apoAV expression resulted in an increased accumulation of 3H activity into LPL-expressing tissues representing increased [3H]oleate deposition (Fig. 6, right panel). In the case of the liver, increased accumulation of 3H activity may be caused in addition by increased uptake of remnant particles, which often retain some [3H]triolein. From the combined in vitro and in vivo findings, we thus can conclude that apoAV is a potent stimulator of LPL activity, contributing to the hypotriglyceridemic effect of apoAV. This mechanism can explain fully the markedly diminished postprandial TG response upon apoAV expression, because mice with muscle-specific expression of human LPL, resulting in 2.3-fold increased post-heparin LPL levels (21), also show a >90% diminished TG response upon an intragastric gavage of 200 µl of olive oil.3
Although low expression levels of apoAV predominantly affect plasma TG levels (Fig. 1), higher levels of expression also reduced TC levels, mainly by reduction of HDL. Previously, plasma TC levels were reported to be unaffected by the absence (apoa5–/– mice) or overexpression (human APOA5 transgenic mice) of apoAV (2). Moreover, whereas genetic association studies have revealed consistent association of minor APOA5 alleles with increased plasma TG levels (2, 4, 5, 21, 22), the influence of APOA5 polymorphisms on plasma TC levels is less clear. The minor allele of the APOA5 –1131T
C promoter variant has been associated with a modest decrease of HDL cholesterol in some but not all studies (21, 22) and in one study with a more pronounced increase of VLDL-cholesterol (21). Although apoAV-induced TG reduction thus may be more relevant for human lipid metabolism compared with the TC-reducing effect, the mechanism underlying the effect on HDL is intriguing.
Hepatic mRNA levels of several proteins influencing plasma cholesterol levels (i.e. scavenger receptor-BI, ABCA1, LDL receptor, and LDL receptor-related protein) were not affected by Ad-apoa5 treatment (data not shown). Moreover, preliminary studies indicate that recombinant apoAV does not interfere with apoAI- or HDL-mediated cholesterol efflux.4 Most likely, however, HDL reduction may relate simply to the LPL-stimulating effect of apoAV. First, systemic LPL activation in C57Bl/6 mice by intravenous injection of heparin (1.0 unit/g body weight) led to a rapid decline of both plasma TG levels (–55% within 10–30 min) and plasma TC levels (–30% after 1 h) as caused by HDL reduction.5 Hence, systemic LPL activation mimics the hypolipidemic effect of Ad-apoa5 treatment. Second, enhancing LPL activity in mice by overexpression also generally resulted in the reduction of plasma HDL on chow diet (23–25). Thus, systemic LPL activation in mice results in a reduction of HDL levels, and these observations are consistent with apoAV functioning as an activator of LPL. The mechanism underlying the LPL-mediated decrease in HDL also may involve scavenger receptor-BI mediated clearance. It has been shown that the capacity of HDL to deliver cholesteryl esters via the scavenger receptor-BI pathway increases with decreasing TG content (26). Thus, increased lipolytic conversion of HDL due to the apoAV-stimulated TG-hydrolase activity of LPL may enhance the hepatic clearance of HDL-cholesterol via scavenger receptor-BI. Notwithstanding the above, it is tempting to speculate that apoAV also may have additional yet undiscovered functions. For example, apoAV may influence the activity of hepatic lipase and/or endothelial lipase. Although these lipolytic enzymes do not have major effects on plasma TG metabolism (27, 28), they both act on HDL-phospholipids and are known to influence plasma TC levels.
The potent lipid-lowering effects of apoAV make the APOA5 gene an obvious target for the treatment of dyslipidemia, especially because it appears to effectively counteract the LPL-inhibiting effect of the main endogenous LPL-modulator apoCIII and to be regulated by nuclear receptors for which ligands exist and are still being developed (9, 10). In primary human hepatocytes, APOA5 mRNA levels are increased 5-fold following treatment with a peroxisome proliferator-activated receptor- agonist (10). This is in the same order of magnitude as the increase in apoa5 expression obtained after the low dose Ad-apoa5 injection (10-fold elevation). Thus, the lipid-lowering effects seen upon hepatic apoa5 overexpression in our studies probably reflect a physiologically relevant mechanism and underscore the importance of apoAV in TG metabolism.
|
FOOTNOTES |
|---|
* This work was conducted in the framework of the "Leiden Center for Cardiovascular Research LUMC-TNO" and supported in part by a Meelmeyer grant from the Amsterdam Academic Medical Center (to F. G. S.), a Gisela Thier Fellowship from Leiden University Medical Center (to P. C. N. R.), and the NWO VIDI Grant 917-36-351) (to P. C. N. R.) and NWO Program Grant 903-39-291 (to L. M. H.) from the Netherlands Organization for Scientific Research. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Both authors equally contributed to this work.
¶ To whom correspondence should be addressed. Tel.: 31-20-566-8162; Fax: 31-20-566-9190; E-mail: f.g.schaap{at}amc.uva.nl.
1 The abbreviations used are: LDL, low density lipoprotein; HDL, high density lipoprotein; LPL, lipoprotein lipase; pfu, plaque-forming unit; PL, phospholipid(s); TC, total cholesterol; TG, triglyceride(s); VLDL, very low density lipoprotein; ER, endoplasmic reticulum.
2 P. C. N. Rensen, C. C. van der Hoogt, and K. Willems van Dijk, unpublished observations.
3 P. J. Voshol, P. C. N. Rensen, L. M. Havekes, and K. Willems van Dijk, unpublished observations.
4 F. G. Schaap and A. K. Groen, unpublished observations.
5 P. C. N Rensen, J. F. P. Berbée, and L. M. Havekes, unpublished observations.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONEXPERIMENTAL PROCEDURESRESULTSDISCUSSIONREFERENCES |
|---|
- Cullen, P. (2000) Am. J. Cardiol. 86, 943–949[CrossRef][Medline] [Order article via Infotrieve]
- Pennacchio, L. A., Olivier, M., Hubacek, J. A., Cohen, J. C., Cox, D. R., Fruchart, J. C., Krauss, R. M., and Rubin, E. M. (2001) Science 294, 169–173
[Abstract/Free Full Text] - van der Vliet, H. N., Sammels, M. G., Leegwater, A. C., Levels, J. H., Reitsma, P. H., Boers, W., and Chamuleau, R. A. (2001) J. Biol. Chem. 276, 44512–44520
[Abstract/Free Full Text] - Kao, J. T., Wen, H. C., Chien, K. L., Hsu, H. C., and Lin, S. W. (2003) Hum. Mol. Genet. 12, 2533–2539
[Abstract/Free Full Text] - Pennacchio, L. A., Olivier, M., Hubacek, J. A., Krauss, R. M., Rubin, E. M., and Cohen, J. C. (2002) Hum. Mol. Genet. 11, 3031–3038
[Abstract/Free Full Text] - van der Vliet, H. N., Schaap, F. G., Levels, J. H., Ottenhoff, R., Looije, N., Wesseling, J. G., Groen, A. K., and Chamuleau, R. A. (2002) Biochem. Biophys. Res. Commun. 295, 1156–1159[CrossRef][Medline] [Order article via Infotrieve]
- Weinberg, R. B., Cook, V. R., Beckstead, J. A., Martin, D. D., Gallagher, J. W., Shelness, G. S., and Ryan, R. O. (2003) J. Biol. Chem. 278, 34438–34444
[Abstract/Free Full Text] - Beckstead, J. A., Oda, M. N., Martin, D. D., Forte, T. M., Bielicki, J. K., Berger, T., Luty, R., Kay, C. M., and Ryan, R. O. (2003) Biochemistry 42, 9416–9423[CrossRef][Medline] [Order article via Infotrieve]
- Vu-Dac, N., Gervois, P., Jakel, H., Nowak, M., Bauge, E., Dehondt, H., Staels, B., Pennacchio, L. A., Rubin, E. M., Fruchart-Najib, J., and Fruchart, J. C. (2003) J. Biol. Chem. 278, 17982–17985
[Abstract/Free Full Text] - Prieur, X., Coste, H., and Rodriguez, J. C. (2003) J. Biol. Chem. 278, 25468–25480
[Abstract/Free Full Text] - Tao, N., Gao, G. P., Parr, M., Johnston, J., Baradet, T., Wilson, J. M., Barsoum, J., and Fawell, S. E. (2001) Mol. Ther. 3, 28–35[CrossRef][Medline] [Order article via Infotrieve]
- Otway, S., and Robinson, D. S. (1967) J. Physiol. (Lond.) 190, 321–332
[Abstract/Free Full Text] - Redgrave, T. G., Roberts, D. C., and West, C. E. (1975) Anal. Biochem. 65, 42–49[CrossRef][Medline] [Order article via Infotrieve]
- Yamada, N., and Havel, R. J. (1986) J. Lipid Res. 27, 910–912[Abstract]
- Rensen, P. C., van Dijk, M. C., Havenaar, E. C., Bijsterbosch, M. K., Kruijt, J. K., and van Berkel, T. J. (1995) Nat. Med. 1, 221–225[CrossRef][Medline] [Order article via Infotrieve]
- Rensen, P. C., Herijgers, N., Netscher, M. H., Meskers, S. C., van Eck, M., and van Berkel, T. J. (1997) J. Lipid Res. 38, 1070–1084[Abstract]
- Rensen, P. C., and van Berkel, T. J. (1996) J. Biol. Chem. 271, 14791–14799
[Abstract/Free Full Text] - Kypreos, K. E., Willems van Dijk, K., van der Zee, A., Havekes, L. M., and Zannis, V. I. (2001) J. Biol. Chem. 276, 19778–19786
[Abstract/Free Full Text] - Gerritsen, G., Kypreos, K. E., van der Zee, A., Teusink, B., Zannis, V. I., Havekes, L. M., and Willems van Dijk, K. (2003) J. Lipid Res. 44, 408–414
[Abstract/Free Full Text] - Shelness, G. S., and Sellers, J. A. (2001) Curr. Opin. Lipidol. 12, 151–157[CrossRef][Medline] [Order article via Infotrieve]
- Aouizerat, B. E., Kulkarni, M., Heilbron, D., Drown, D., Raskin, S., Pullinger, C. R., Malloy, M. J., and Kane, J. P. (2003) J. Lipid Res. 44, 1167–1173
[Abstract/Free Full Text] - Endo, K., Yanagi, H., Araki, J., Hirano, C., Yamakawa-Kobayashi, K., and Tomura, S. (2002) Hum. Genet. 111, 570–572[CrossRef][Medline] [Order article via Infotrieve]
- Levak-Frank, S., Weinstock, P. H., Hayek, T., Verdery, R., Hofmann, W., Ramakrishnan, R., Sattler, W., Breslow, J. L., and Zechner, R. (1997) J. Biol. Chem. 272, 17182–17190
[Abstract/Free Full Text] - Zsigmond, E., Scheffler, E., Forte, T. M., Potenz, R., Wu, W., and Chan, L. (1994) J. Biol. Chem. 269, 18757–18766
[Abstract/Free Full Text] - Liu, M. S., Jirik, F. R., LeBoeuf, R. C., Henderson, H., Castellani, L. W., Lusis, A. J., Ma, Y., Forsythe, I. J., Zhang, H., and Kirk, E. (1994) J. Biol. Chem. 269, 11417–11424
[Abstract/Free Full Text] - Greene, D. J., Skeggs, J. W., and Morton, R. E. (2001) J. Biol. Chem. 276, 4804–4811
[Abstract/Free Full Text] - Homanics, G. E., de Silva, H. V., Osada, J., Zhang, S. H., Wong, H., Borensztajn, J., and Maeda, N. (1995) J. Biol. Chem. 270, 2974–2980
[Abstract/Free Full Text] - Ishida, T., Choi, S., Kundu, R. K., Hirata, K., Rubin, E. M., Cooper, A. D., and Quertermous, T. (2003) J. Clin. Investig. 111, 347–355[CrossRef][Medline] [Order article via Infotrieve]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  S. F. C. Vaessen, G. M. Dallinga-Thie, C. J. D. Ross, L. J. Splint, L. W. Castellani, P. C. N. Rensen, M. R. Hayden, F. G. Schaap, and J. A. Kuivenhoven Plasma apolipoprotein AV levels in mice are positively associated with plasma triglyceride levels J. Lipid Res., May 1, 2009; 50(5): 880 - 884. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. M. Forte, X. Shu, and R. O. Ryan The ins (cell) and outs (plasma) of apolipoprotein A-V J. Lipid Res., April 1, 2009; 50(Supplement): S150 - S155. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Dorfmeister, W.W. Zeng, A. Dichlberger, S.K. Nilsson, F.G. Schaap, J.A. Hubacek, M. Merkel, J.A. Cooper, A. Lookene, W. Putt, et al. Effects of Six APOA5 Variants, Identified in Patients With Severe Hypertriglyceridemia, on In Vitro Lipoprotein Lipase Activity and Receptor Binding Arterioscler. Thromb. Vasc. Biol., October 1, 2008; 28(10): 1866 - 1871. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. K. Nilsson, S. Christensen, M. K. Raarup, R. O. Ryan, M. S. Nielsen, and G. Olivecrona Endocytosis of Apolipoprotein A-V by Members of the Low Density Lipoprotein Receptor and the Vps10p Domain Receptor Families J. Biol. Chem., September 19, 2008; 283(38): 25920 - 25927. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. M. Mansouri, E. Bauge, P. Gervois, J. Fruchart-Najib, C. Fievet, B. Staels, and J.-C. Fruchart Atheroprotective Effect of Human Apolipoprotein A5 in a Mouse Model of Mixed Dyslipidemia Circ. Res., August 29, 2008; 103(5): 450 - 453. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. M.M. Ooi, G. F. Watts, D. C. Chan, M. M. Chen, P. J. Nestel, D. Sviridov, and P. H. R. Barrett Dose-Dependent Effect of Rosuvastatin on VLDL-Apolipoprotein C-III Kinetics in the Metabolic Syndrome Diabetes Care, August 1, 2008; 31(8): 1656 - 1661. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. Olano-Martin, E. C. Abraham, R. Gill-Garrison, A. M. Valdes, K. Grimaldi, F. Tang, K. G. Jackson, C. M. Williams, and A. M. Minihane Influence of apoA-V gene variants on postprandial triglyceride metabolism: impact of gender J. Lipid Res., May 1, 2008; 49(5): 945 - 953. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Gerritsen, C. C. van der Hoogt, F. G. Schaap, P. J. Voshol, K. E. Kypreos, N. Maeda, A. K. Groen, L. M. Havekes, P. C. N. Rensen, and K. W. van Dijk ApoE2-associated hypertriglyceridemia is ameliorated by increased levels of apoA-V but unaffected by apoC-III deficiency J. Lipid Res., May 1, 2008; 49(5): 1048 - 1055. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. Nelbach, X. Shu, R. J. Konrad, R. O. Ryan, and T. M. Forte Effect of apolipoprotein A-V on plasma triglyceride, lipoprotein size, and composition in genetically engineered mice J. Lipid Res., March 1, 2008; 49(3): 572 - 580. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Sundl, M. Guardiola, G. Khoschsorur, R. Sola, J. C. Vallve, G. Godas, L. Masana, M. Maritschnegg, A. Meinitzer, N. Cardinault, et al. Increased concentrations of circulating vitamin E in carriers of the apolipoprotein A5 gene 1131T>C variant and associations with plasma lipids and lipid peroxidation J. Lipid Res., November 1, 2007; 48(11): 2506 - 2513. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. J. A. Moen, A. P. Tholens, P. J. Voshol, W. de Haan, L. M. Havekes, P. Gargalovic, A. J. Lusis, K. W. van Dyk, R. R. Frants, M. H. Hofker, et al. The Hyplip2 locus causes hypertriglyceridemia by decreased clearance of triglycerides J. Lipid Res., October 1, 2007; 48(10): 2182 - 2192. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 U. Desai, E-C. Lee, K. Chung, C. Gao, J. Gay, B. Key, G. Hansen, D. Machajewski, K. A. Platt, A. T. Sands, et al. Lipid-lowering effects of anti-angiopoietin-like 4 antibody recapitulate the lipid phenotype found in angiopoietin-like 4 knockout mice PNAS, July 10, 2007; 104(28): 11766 - 11771. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Qu, G. Perdomo, D. Su, F. M. D'Souza, N. S. Shachter, and H. H. Dong Effects of apoA-V on HDL and VLDL metabolism in APOC3 transgenic mice J. Lipid Res., July 1, 2007; 48(7): 1476 - 1487. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Shu, J. Chan, R. O. Ryan, and T. M. Forte Apolipoprotein A-V association with intracellular lipid droplets J. Lipid Res., July 1, 2007; 48(7): 1445 - 1450. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. A. Beckstead, K. Wong, V. Gupta, C.-P. L. Wan, V. R. Cook, R. B. Weinberg, P. M. M. Weers, and R. O. Ryan The C Terminus of Apolipoprotein A-V Modulates Lipid-binding Activity J. Biol. Chem., May 25, 2007; 282(21): 15484 - 15489. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. G. Schaap, M. C. Nierman, J. F. P. Berbee, H. Hattori, P. J. Talmud, S. F. C. Vaessen, P. C. N. Rensen, R. A. F. M. Chamuleau, J. A. Kuivenhoven, and A. K. Groen Evidence for a complex relationship between apoA-V and apoC-III in patients with severe hypertriglyceridemia J. Lipid Res., October 1, 2006; 47(10): 2333 - 2339. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Guardiola, R. Ferre, J. Salazar, C. Alonso-Villaverde, B. Coll, S. Parra, L. Masana, and J. Ribalta Protease Inhibitor-Associated Dyslipidemia in HIV-Infected Patients Is Strongly Influenced by the APOA5-1131T->C Gene Variation Clin. Chem., October 1, 2006; 52(10): 1914 - 1919. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. F. C. Vaessen, F. G. Schaap, J.-A. Kuivenhoven, A. K. Groen, B. A. Hutten, S. M. Boekholdt, H. Hattori, M. S. Sandhu, S. A. Bingham, R. Luben, et al. Apolipoprotein A-V, triglycerides and risk of coronary artery disease: the prospective Epic-Norfolk Population Study J. Lipid Res., September 1, 2006; 47(9): 2064 - 2070. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Stedman, C. Liddle, S. Coulter, J. Sonoda, J. G. Alvarez, R. M. Evans, and M. Downes Benefit of farnesoid X receptor inhibition in obstructive cholestasis PNAS, July 25, 2006; 103(30): 11323 - 11328. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Westerterp, W. de Haan, J. F. P. Berbee, L. M. Havekes, and P. C. N. Rensen Endogenous apoC-I increases hyperlipidemia in apoE-knockout mice by stimulating VLDL production and inhibiting LPL J. Lipid Res., June 1, 2006; 47(6): 1203 - 1211. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Rip, M. C. Nierman, C. J. Ross, J. W. Jukema, M. R. Hayden, J. J.P. Kastelein, E. S.G. Stroes, and J. A. Kuivenhoven Lipoprotein Lipase S447X: A Naturally Occurring Gain-of-Function Mutation Arterioscler. Thromb. Vasc. Biol., June 1, 2006; 26(6): 1236 - 1245. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C.-Q. Lai, D. Corella, S. Demissie, L. A. Cupples, X. Adiconis, Y. Zhu, L. D. Parnell, K. L. Tucker, and J. M. Ordovas Dietary Intake of n-6 Fatty Acids Modulates Effect of Apolipoprotein A5 Gene on Plasma Fasting Triglycerides, Remnant Lipoprotein Concentrations, and Lipoprotein Particle Size: The Framingham Heart Study Circulation, May 2, 2006; 113(17): 2062 - 2070. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Elosua, J. M. Ordovas, L. A. Cupples, C.-Q. Lai, S. Demissie, C. S. Fox, J. F. Polak, P. A. Wolf, R. B. D'Agostino Sr., and C. J. O'Donnell Variants at the APOA5 locus, association with carotid atherosclerosis, and modification by obesity: the Framingham Study J. Lipid Res., May 1, 2006; 47(5): 990 - 996. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. E. Alborn, M. G. Johnson, M. J. Prince, and R. J. Konrad Definitive N-terminal protein sequence and further characterization of the novel apolipoprotein a5 in human serum. Clin. Chem., March 1, 2006; 52(3): 514 - 517. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. C. Chan, G. F. Watts, M. N. Nguyen, and P. H. R. Barrett Apolipoproteins C-III and A-V as Predictors of Very-Low-Density Lipoprotein Triglyceride and Apolipoprotein B-100 Kinetics Arterioscler. Thromb. Vasc. Biol., March 1, 2006; 26(3): 590 - 596. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
U. Hodoglugil, S. Tanyolac, D. W. Williamson, Y. Huang, and R. W. Mahley Apolipoprotein A-V: a potential modulator of plasma triglyceride levels in Turks J. Lipid Res., January 1, 2006; 47(1): 144 - 153. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. A. Ruiz-Narvaez, Y. Yang, Y. Nakanishi, J. Kirchdorfer, and H. Campos APOC3/A5 haplotypes, lipid levels, and risk of myocardial infarction in the Central Valley of Costa Rica J. Lipid Res., December 1, 2005; 46(12): 2605 - 2613. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. C.N. Rensen, K. W. van Dijk, and L. M. Havekes Apolipoprotein AV: Low Concentration, High Impact Arterioscler. Thromb. Vasc. Biol., December 1, 2005; 25(12): 2445 - 2447. [Full Text] [PDF]
|
|
|
|
 |
|
 X. Prieur, F. G. Schaap, H. Coste, and J. C. Rodriguez Hepatocyte Nuclear Factor-4{alpha} Regulates the Human Apolipoprotein AV Gene: Identification of a Novel Response Element and Involvement in the Control by Peroxisome Proliferator-Activated Receptor-{gamma} Coactivator-1{alpha}, AMP-Activated Protein Kinase, and Mitogen-Activated Protein Kinase Pathway Mol. Endocrinol., December 1, 2005; 19(12): 3107 - 3125. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Grosskopf, N. Baroukh, S.-J. Lee, Y. Kamari, D. Harats, E. M. Rubin, L. A. Pennacchio, and A. D. Cooper Apolipoprotein A-V Deficiency Results in Marked Hypertriglyceridemia Attributable to Decreased Lipolysis of Triglyceride-Rich Lipoproteins and Removal of Their Remnants Arterioscler. Thromb. Vasc. Biol., December 1, 2005; 25(12): 2573 - 2579. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. M. Krauss Dietary and Genetic Probes of Atherogenic Dyslipidemia Arterioscler. Thromb. Vasc. Biol., November 1, 2005; 25(11): 2265 - 2272. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Claudel, B. Staels, and F. Kuipers The Farnesoid X Receptor: A Molecular Link Between Bile Acid and Lipid and Glucose Metabolism Arterioscler. Thromb. Vasc. Biol., October 1, 2005; 25(10): 2020 - 2030. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Ishihara, T. Kujiraoka, T. Iwasaki, M. Nagano, M. Takano, J. Ishii, M. Tsuji, H. Ide, I. P. Miller, N. E. Miller, et al. A sandwich enzyme-linked immunosorbent assay for human plasma apolipoprotein A-V concentration J. Lipid Res., September 1, 2005; 46(9): 2015 - 2022. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. J. Talmud, J. Palmen, W. Putt, L. Lins, and S. E. Humphries Determination of the Functionality of Common APOA5 Polymorphisms J. Biol. Chem., August 5, 2005; 280(31): 28215 - 28220. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. E. Schultze, W. E. Alborn, R. K. Newton, and R. J. Konrad Administration of a PPAR{alpha} agonist increases serum apolipoprotein A-V levels and the apolipoprotein A-V/apolipoprotein C-III ratio J. Lipid Res., August 1, 2005; 46(8): 1591 - 1595. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Prieur, T. Huby, H. Coste, F. G. Schaap, M. J. Chapman, and J. C. Rodriguez Thyroid Hormone Regulates the Hypotriglyceridemic Gene APOA5 J. Biol. Chem., July 29, 2005; 280(30): 27533 - 27543. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Lookene, J. A. Beckstead, S. Nilsson, G. Olivecrona, and R. O. Ryan Apolipoprotein A-V-heparin Interactions: IMPLICATIONS FOR PLASMA LIPOPROTEIN METABOLISM J. Biol. Chem., July 8, 2005; 280(27): 25383 - 25387. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Merkel, B. Loeffler, M. Kluger, N. Fabig, G. Geppert, L. A. Pennacchio, A. Laatsch, and J. Heeren Apolipoprotein AV Accelerates Plasma Hydrolysis of Triglyceriderich Lipoproteins by Interaction with Proteoglycan-bound Lipoprotein Lipase J. Biol. Chem., June 3, 2005; 280(22): 21553 - 21560. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Lalanne, G. Lambert, M. J. A. Amar, M. Chetiveaux, Y. Zair, A.-L. Jarnoux, K. Ouguerram, J. Friburg, N. G. Seidah, H. B. Brewer Jr., et al. Wild-type PCSK9 inhibits LDL clearance but does not affect apoB-containing lipoprotein production in mouse and cultured cells J. Lipid Res., June 1, 2005; 46(6): 1312 - 1319. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S.-O. Olofsson ApoA-V: The Regulation of a Regulator of Plasma Triglycerides Arterioscler. Thromb. Vasc. Biol., June 1, 2005; 25(6): 1097 - 1099. [Full Text] [PDF]
|
|
|
|
 |
|
 I. Duivenvoorden, B. Teusink, P. C. Rensen, J. A. Romijn, L. M. Havekes, and P. J. Voshol Apolipoprotein C3 Deficiency Results in Diet-Induced Obesity and Aggravated Insulin Resistance in Mice Diabetes, March 1, 2005; 54(3): 664 - 671. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. F. P. Berbee, C. C. van der Hoogt, D. Sundararaman, L. M. Havekes, and P. C. N. Rensen Severe hypertriglyceridemia in human APOC1 transgenic mice is caused by apoC-I-induced inhibition of LPL J. Lipid Res., February 1, 2005; 46(2): 297 - 306. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. P. Oliva, L. Pisciotta, G. L. Volti, M. P. Sambataro, A. Cantafora, A. Bellocchio, A. Catapano, P. Tarugi, S. Bertolini, and S. Calandra Inherited Apolipoprotein A-V Deficiency in Severe Hypertriglyceridemia Arterioscler. Thromb. Vasc. Biol., February 1, 2005; 25(2): 411 - 417. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. J. O'Brien, W. E. Alborn, J. H. Sloan, M. Ulmer, A. Boodhoo, M. D. Knierman, A. E. Schultze, and R. J. Konrad The Novel Apolipoprotein A5 Is Present in Human Serum, Is Associated with VLDL, HDL, and Chylomicrons, and Circulates at Very Low Concentrations Compared with Other Apolipoproteins Clin. Chem., February 1, 2005; 51(2): 351 - 359. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C.-Q. Lai, S. Demissie, L. A. Cupples, Y. Zhu, X. Adiconis, L. D. Parnell, D. Corella, and J. M. Ordovas Influence of the APOA5 locus on plasma triglyceride, lipoprotein subclasses, and CVD risk in the Framingham Heart Study J. Lipid Res., November 1, 2004; 45(11): 2096 - 2105. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| All ASBMB Journals | Molecular and Cellular Proteomics |
| Journal of Lipid Research | ASBMB Today |