Intravenous Injection of Apolipoprotein A-V Reconstituted High-Density Lipoprotein Decreases Hypertriglyceridemia in apoav −/− Mice and Requires Glycosylphosphatidylinositol-Anchored High-Density Lipoprotein–Binding Protein 1

Abstract

Objective-Apolipoprotein A-V (apoA-V), a minor protein associated with lipoproteins, has a major effect on triacylglycerol (TG) metabolism. We investigated whether apoA-V complexed with phospholipid in the form of a reconstituted high-density lipoprotein (rHDL) has potential utility as a therapeutic agent for treatment of hypertriglyceridemia (HTG) when delivered intravenously. Methods and Results-Intravenous injection studies were performed in genetically engineered mouse models of severe HTG, including apoavϪ/Ϫ and gpihbp1Ϫ/Ϫ mice. Administration of apoA-V rHDL to hypertriglyceridemic apoavϪ/Ϫ mice resulted in a 60% reduction in plasma TG concentration after 4 hours. This decline can be attributed to enhanced catabolism/clearance of very-low-density lipoprotein (VLDL), where VLDL TG and cholesterol were reduced Ϸ60%.ApoA-V that associated with VLDL after injection was also rapidly cleared. Site-specific mutations in the heparin-binding region of apoA-V (amino acids 186 to 227) attenuated apoA-V rHDL TG-lowering activity by 50%, suggesting that this sequence element is required for optimal TG-lowering activity in vivo. Unlike apoavϪ/Ϫ mice, injection of apoA-V rHDL into gpihbp1Ϫ/Ϫ mice had no effect on plasma TG levels, and apoA-V remained associated with plasma VLDL. Key Words: apolipoproteins Ⅲ hyperlipoproteinemia Ⅲ lipids Ⅲ lipoproteins E pidemiological studies have revealed that increased plasma triacylglycerol (TG) is an independent risk factor for coronary heart disease. 1,2 Furthermore, hypertriglyceridemia (HTG) is a hallmark of the metabolic syndrome and is often accompanied by obesity and insulin resistance. 3 Given that the metabolic syndrome confers increased risk for development of both type 2 diabetes and cardiovascular disease, 4 maintenance of plasma TG homeostasis is highly desirable. Conclusion-IntravenouslyFollowing its discovery in 2001, 5,6 apolipoprotein A-V (apoA-V) emerged as an important TG modulator. 7 In humans, APOAV is located in the APOAI/CIII/AIV/AV gene cluster on the long arm of chromosome 11. ApoA-V is expressed exclusively by liver tissue and, in plasma, is associated with high-density lipoprotein (HDL) and VLDL. 8,9 Unlike other exchangeable apolipoproteins, the plasma concentration of apoA-V in humans (Ϸ250 ng/mL) 8 and mice (Ϸ24 ng/mL) 10 is extremely low. Despite this, the contribution of apoA-V to chylomicron and VLDL metabolism is readily appreciated from genetic engineering studies in mice. 5 ApoavϪ/Ϫ mice manifested a 4-fold increase in plasma TG, whereas the concentration in APOAV transgenic mice is 1/3 that in wild-type (WT) control littermates. Furthermore, studies in humans revealed an association between truncation mutations in apoA-V and severe HTG. [11][12][13] These data strongly suggest that apoA-V plays an important physiological role in plasma TG metabolism.Previous in vivo studies demonstrated that HTG in apoA-V-deficient mice is attributable to decreased chylomicron and VLDL lipolysis and remnant removal. 14,15 On the other hand, overexpression of apoA-V ...

Structural and functional analysis of APOA5 mutations identified in patients with severe hypertriglyceridemia

“…These fi ndings are in line with the previously reported decrease in heparin affi nity by mutant p.(Arg233Glu, Lys234Gln) ( 23 ). Even more dramatic consequences might be expected for the binding to the Nterminal, highly acidic peptide of GPIHBP1, as indicated by an apoA-V mutant in which residues R233, K234, K238, and K240 were simultaneously replaced by glutamic acid or glutamine residues (56)(57)(58).…”

Static and turnover kinetic measurement of protein biomarkers involved in triglyceride metabolism including apoB48 and apoA5 by LC/MS/MS

“…Our estimated FSR ( ‫ف‬ 19.82 pools/day) suggests that apoA5 turns over rapidly. The clearance of injected recombinant apoA5 in a mouse model was very fast ( 23 ), which supports our observation. It is worth pointing out that the actual D3-leucine enrichment is the M3/M0 ratio divided by the number of leucines in the precursor to product transition.…”

Apolipoproteins E and AV mediate lipoprotein clearance by hepatic proteoglycans

“…Apoav -/-mice accumulate plasma triglycerides 4-fold, whereas transgenic mice overexpressing ApoAV have reduced plasma triglycerides (50). Apoav -/-mice have very large TRLs due to impaired lipolysis caused by diminished interactions with LPL and/or endothelial LPL receptors, such as GPIHBP1 and endothelial HSPGs (41,51,52). ApoAV has also been suggested to promote clearance of TRLs by acting as a ligand for receptor-mediated endocytosis (53).…”