HDL from apoA1 transgenic mice expressing the 4WF isoform is resistant to oxidative loss of function

Abstract

High levels of high density lipoprotein-cholesterol (HDL-C) are associated with lower risk for cardiovascular disease in epidemiological studies ( 1 ). Although several mechanisms may play a role in HDL's protective effect, HDL and its major protein constituent, apoA1, are critical components of the reverse cholesterol transport (RCT) pathway, in which cholesterol is removed from peripheral tissues and transferred to the liver for excretion. In the fi rst step of the RCT pathway, lipid-poor apoA1 acts as an acceptor for cell cholesterol and phospholipids via the cell membrane protein ABCA1, generating nascent HDL.Recently, "HDL is the good cholesterol" hypothesis has suffered several setbacks. For example, several trials of HDL-C-raising drugs, including cholesteryl ester transfer protein inhibitors and niacin, failed to demonstrate clinical benefi t ( 2-5 ). Furthermore, a Mendelian randomization study did not associate gene variants that solely alter HDL-C with coronary artery disease (CAD) incidence ( 6 ). That said, human and mouse models with defective RCT, via mutations in ABCA1, apoA1, or scavenger receptor class B type I (SR-BI), are more susceptible to atherosclerosis independent Abstract HDL functions are impaired by myeloperoxidase (MPO), which selectively targets and oxidizes human apoA1. We previously found that the 4WF isoform of human apoA1, in which the four tryptophan residues are substituted with phenylalanine, is resistant to MPO-mediated loss of function. The purpose of this study was to generate 4WF apoA1 transgenic mice and compare functional properties of the 4WF and wild-type human apoA1 isoforms in vivo . Male mice had signifi cantly higher plasma apoA1 levels than females for both isoforms of human apoA1, attributed to different production rates. With matched plasma apoA1 levels, 4WF transgenics had a trend for slightly less HDL-cholesterol versus human apoA1 transgenics. While 4WF transgenics had 31% less reverse cholesterol transport (RCT) to the plasma compartment, equivalent RCT to the liver and feces was observed. Plasma from both strains had similar ability to accept cholesterol and facilitate ex vivo cholesterol effl ux from macrophages. Furthermore, we observed that 4WF transgenic HDL was partially ( ‫ف‬ 50%) protected from MPOmediated loss of function while human apoA1 transgenic HDL lost all ABCA1-dependent cholesterol acceptor activity. In conclusion, the structure and function of HDL from 4WF transgenic mice was not different than HDL derived from human apoA1 transgenic mice. -Berisha, S.

PI(4,5)P2 Is Translocated by ABCA1 to the Cell Surface Where It Mediates Apolipoprotein A1 Binding and Nascent HDL Assembly

“…56 PIP2 carried on circulating HDL might also serve as a signaling molecule by the delivery of PIP2 to target cells via SR-BI. In wildtype mice we observed plasma PIP2 levels at ~0.4 μM; however, with plasma apoA1 of ~ 32 uM 57 , and assuming on average 2.5 apoA1 molecules per HDL, the final HDL concentration is ~13 μM. Thus, it appears that there is less than one PIP2 molecule per HDL particle in circulation.…”

Proteome Dynamics with Heavy Water — Instrumentations, Data Analysis, and Biological Applications

“…2 H 2 O labeling-based HDL turnover method also was applied to assess the effect of different isoforms of apoAI and gender on in vivo HDL function in wild-type human transgenic apoAI mice and mice with 4WF isoform of human apoAI, in which 4 tryptophan residues are substituted with phenylalanine [86]. The in vitro cholesterol efflux assay demonstrated that the 4WF isoform of apoAI was resistant to myeloperoxidase-induced loss of function while human apoA1 transgenic HDL lost all ABCA1-dependent cholesterol acceptor activity.…”

Methionine oxidized apolipoprotein A‐I at the crossroads of HDL biogenesis and amyloid formation

“…In fact, the impact of MPO‐mediated oxidation on an apoA‐I variant in which all Tyr residues were conservatively replaced with Phe was equivalent to the impact on wild‐type apoA‐I (8). In contrast, an apoA‐I variant in which all 4 Trp were conservatively replaced with Phe (4WF‐ApoA‐I) was immune to MPO‐mediated impairment of the cholesterol acceptor function (9, 18, 19). This observation indicates that MPO‐mediated oxidation of Trp plays a central role in apoA‐I loss of function (9).…”

“…In the case of ATP binding cassette transporter A1 (ABCA1)-mediated release of cellular cholesterol toward apoA-I, its extracellular recipient, the disagreement is even more pronounced (3,4,6,8,9,11,14,(16)(17)(18)(19). In vitro, chlorination levels of apoA-I Tyr residues tightly correlate with a reduction in cellular cholesterol release capacity (3,4,11) and in vivo, they correlate with the incidence of cardiovascular events and atherosclerosis (14,16,17).…”