Adenoviral overexpression of apolipoprotein A-V reduces serum levels of triglycerides and cholesterol in mice

194

138

The recently discovered APOA5 gene has been shown in humans and mice to be important in determining plasma triglyceride levels, a major cardiovascular disease risk factor. apoAV represents the first described apolipoprotein where overexpression lowers triglyceride levels. Since fibrates represent a commonly used therapy for lowering plasma triglycerides in humans, we investigated their ability to modulate APOA5 gene expression and consequently influence plasma triglyceride levels. Human primary hepatocytes treated with Wy 14,643 or fenofibrate displayed a strong induction of APOA5 mRNA. Deletion and mutagenesis analyses of the proximal APOA5 promoter firmly demonstrate the presence of a functional peroxisome proliferator-activated receptor response element. These findings demonstrate that APOA5 is a highly responsive peroxisome proliferator-activated receptor ␣ target gene and support its role as a major mediator for how fibrates reduce plasma triglycerides in humans.Coronary heart disease continues to be a major cause of morbidity and mortality worldwide. Several epidemiological studies established that, in addition to elevated low density lipoprotein and reduced high density lipoprotein level, elevated triglycerides (TGs) 1 constitute an independent risk factor for coronary heart disease (1, 2). In addition, hypertriglyceridemia is often associated with the metabolic syndrome that characterizes diabetes and obesity (3, 4). Therefore, the identification of factors or genes affecting triglyceride metabolism is of significant medical importance for the correction of hypertriglyceridemia and associated coronary heart disease.Apolipoproteins play a determinant role in lipoprotein metabolism and in lipid homeostasis. More specifically, the APOA1/C3/A4 apolipoprotein gene cluster is tightly linked to plasma lipid profiles. Indeed, mutations in members of this cluster have been shown to cause severe dyslipidemia and heightened atherosclerosis susceptibility (5-8). A comparative genomic characterization of the APOA1/C3/A4 gene cluster flanking regions led to the recent identification of a new apolipoprotein gene, apolipoprotein A5 (APOA5), present in both mice and humans (9). apoAV shares homology with several apolipoproteins, most prominently apoAIV, and is 368 and 366 amino acids long in mice and human, respectively. This gene appears to be predominantly expressed in the liver and resides on high density lipoprotein and very low density lipoprotein particles (9, 10).The properties of apoAV were investigated by creating human APOA5 transgenic and knock-out mice and by searching for associations between human APOA5 polymorphisms and plasma lipid parameters. The Apoa5 knock-out mice display a 400% increase in plasma triglycerides compared with wild-type mice, while APOA5 transgenics exhibit triglyceride levels corresponding to one-third of those in control mice. This determinant link between APOA5 and triglycerides was supported in several separate human studies through the consistent demonstration of associations betwe...

Section: Discussionmentioning

confidence: 99%

Apolipoprotein A5, a Crucial Determinant of Plasma Triglyceride Levels, Is Highly Responsive to Peroxisome Proliferator-activated Receptor α Activators

Vu‐Dac

Gervois

Jakel

et al. 2003

194

138

“…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 ϫ 10 8 pfu of Ad-apoa5 (total viral dose adjusted to 5 ϫ 10 8 with empty vector (Ad-mock)) were injected into the tail vein of the mice (n ϭ 4 -6/group) at 3 h after the injection of Ad-LacZ (5 ϫ 10 8 pfu) to saturate the uptake of viral particles by Kupffer cells (11).…”

Section: Materials-glycerolmentioning

confidence: 99%

“…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).…”

Section: Materials-glycerolmentioning

confidence: 99%

See 1 more Smart Citation

ApoAV Reduces Plasma Triglycerides by Inhibiting Very Low Density Lipoprotein-Triglyceride (VLDL-TG) Production and Stimulating Lipoprotein Lipase-mediated VLDL-TG Hydrolysis

Schaap¹,

Rensen

Voshol

et al. 2004

271

243

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 ؋ 10 8 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.Hypertriglyceridemia is a risk factor for coronary heart disease independent from the well known risk factors such as elevated LDL 1 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 b...

“…Interestingly, the predicted amino acid sequence showed appreciable homology with apoAI and apoAIV. Evidence for the involvement of apoAV in triglyceride metabolism was obtained in mice, in which serum triglyceride concentrations were decreased to one-third when a human apoAV transgene was overexpressed (38) or adenoviral vectors expressing mouse apoAV were injected (40). Conversely, plasma triglyceride levels were 4-fold elevated in knockout mice lacking apoAV compared with their wild-type littermates (38).…”

mentioning

confidence: 99%

The Human Apolipoprotein AV Gene Is Regulated by Peroxisome Proliferator-activated Receptor-α and Contains a Novel Farnesoid X-activated Receptor Response Element

Prieur

Coste

Rodríguez

2003

172

136

The newly identified apolipoprotein AV (apoAV) gene is a key player in determining plasma triglyceride concentrations. Because hypertriglyceridemia is a major independent risk factor in coronary artery disease, the understanding of the regulation of the expression of this gene is of considerable importance. We presently characterize the structure, the transcription start site, and the promoter of the human apoAV gene. Since the peroxisome proliferator-activated receptor-␣ (PPAR␣) and the farnesoid X-activated receptor (FXR) have been shown to modulate the expression of genes involved in triglyceride metabolism, we evaluated the potential role of these nuclear receptors in the regulation of apoAV transcription. Bile acids and FXR induced the apoAV gene promoter activity. 5-Deletion, mutagenesis, and gel shift analysis identified a heretofore unknown element at positions ؊103/؊84 consisting of an inverted repeat of two consensus receptor-binding hexads separated by 8 nucleotides (IR8), which was required for the response to bile acid-activated FXR. The isolated IR8 element conferred FXR responsiveness on a heterologous promoter. On the other hand, in apoAV-expressing human hepatic Hep3B cells, transfection of PPAR␣ specifically enhanced apoAV promoter activity. By deletion, site-directed mutagenesis, and binding analysis, a PPAR␣ response element located 271 bp upstream of the transcription start site was identified. Finally, treatment with a specific PPAR␣ activator led to a significant induction of apoAV mRNA expression in hepatocytes. The identification of apoAV as a PPAR␣ target gene has major implications with respect to mechanisms whereby pharmacological PPAR␣ agonists may exert their beneficial hypotriglyceridemic actions.Recent epidemiological studies have shown that hypertriglyceridemia is a major independent risk factor for coronary heart disease, which remains as a major cause of mortality in the Western world (1-6). Understanding the factors that control plasma triglyceride levels and the genes that primarily reflect circulating concentrations of triglyceride-rich lipoproteins is thus of major importance and may provide new opportunities for therapeutic intervention in atherogenic dyslipidemia.Pharmacological activation of peroxisome proliferator-activated receptor-␣ (PPAR␣ 1 ; NR1C1) lowers plasma levels of triglyceride-rich lipoproteins markedly (7,8). PPAR␣ is a fatty acid-activated nuclear transcription factor that regulates the expression of genes involved in lipid and energy metabolism (9, 10). PPAR␣ heterodimerizes with the retinoid X receptor ␣ (RXR␣; NR2B1) and binds to specific DNA sequence elements, designated PPREs, which consist of a direct repeat of the hexanucleotide core motif PuGGTCA separated by 1 or 2 nucleotides (DR1 or DR2). PPAR␣ mediates the hypotriglyceridemic effect of fibrates by regulating the transcription of key genes associated with different intra-and extracellular metabolic pathways. Fibrates increase cellular fatty acid transport and uptake, conversion to acyl-CoA deriv...