Depletion of Pre-β-high Density Lipoprotein by Human Chymase Impairs ATP-binding Cassette Transporter A1- but Not Scavenger Receptor Class B Type I-mediated Lipid Efflux to High Density Lipoprotein

Abstract

The ATP-binding cassette transporter A1 (ABCA1) mediates the efflux of cellular unesterified cholesterol and phospholipid to lipid-poor apolipoprotein A-I. Chymase, a protease secreted by mast cells, selectively cleaves pre-␤-migrating particles from high density lipoprotein (HDL) 3 and reduces the efflux of cholesterol from macrophages. To evaluate whether this effect is the result of reduction of ABCA1-dependent or -independent pathways of cholesterol efflux, in this study we examined the efflux of cholesterol to preparations of chymase-treated HDL 3 in two types of cell: 1) in J774 murine macrophages endogenously expressing low levels of scavenger receptor class B, type I (SR-BI), and high levels of ABCA1 upon treatment with cAMP; and 2) in Fu5AH rat hepatoma cells endogenously expressing high levels of the SR-BI and low levels of ABCA1. Treatment of HDL 3 with the human chymase resulted in rapid depletion of pre-␤-HDL and a concomitant decrease in the efflux of cholesterol and phospholipid (2-fold and 3-fold, respectively) from the ABCA1-expressing J774 cells. In contrast, efflux of free cholesterol from Fu5AH to chymase-treated and to untreated HDL 3 was similar. Incubation of HDL 3 with phospholipid transfer protein led to an increase in pre-␤-HDL contents as well as in ABCA1-mediated cholesterol efflux. A decreased cholesterol efflux to untreated HDL 3 but not to chymasetreated HDL 3 was observed in ABCA1-expressing J774 with probucol, an inhibitor of cholesterol efflux to lipidpoor apoA-I. Similar results were obtained using brefeldin and gliburide, two inhibitors of ABCA1-mediated efflux. These results indicate that chymase treatment of HDL 3 specifically impairs the ABCA1-dependent pathway without influencing either aqueous or SR-BI-facilitated diffusion and that this effect is caused by depletion of lipid-poor pre-␤-migrating particles in HDL 3 . Our results are compatible with the view that HDL 3 promotes ABCA1-mediated lipid efflux entirely through its lipid-poor fraction with pre-␤ mobility.

Cellular cholesterol efflux to plasma from moderately hypercholesterolaemic type 1 diabetic patients is enhanced, and is unaffected by simvastatin treatment

“…Cholesterol efflux out of Fu5AH cells via SR-BI is largely dependent on mature HDL, and is correlated positively with HDL cholesterol, HDL phospholipids and plasma apo A-I [33,39,44], whereas lipid-poor acceptors, including pre-β HDL, are important in ABCA1-dependent cholesterol efflux [45]. The relatively higher stimulatory effect of diabetic plasma on cholesterol efflux out of Fu5AH cells, compared to fibroblasts, suggests that plasma from type 1 diabetic patients predominantly enhances SR-BI-mediated efflux.…”

Fibroblast cholesterol efflux to plasma from metabolic syndrome subjects is not defective despite low high-density lipoprotein cholesterol

“…Thus, it is most likely that several pathways including ABCA1-mediated cholesterol transport contribute to fibroblast cholesterol efflux, although their relative contribution is still unknown. It is well established that pre-b-HDL act as primary acceptors of cellular cholesterol via ABCA1 (10,12,15,16), and the relevance of this pathway is emphasized by the observation that efflux from fibroblasts that lack functional ABCA1 is strongly diminished (22,30). In our study, cholesterol efflux was positively related to pre-b-HDL formation and PLTP activity in multiple linear regression analysis, in agreement with the proposed important role of ABCA1-pre-b-HDL interaction to promote cholesterol efflux (10,12,14), as well as with previous data showing that PLTP is able to stimulate cholesterol efflux directly via ABCA1 (32).…”

“…Cellular cholesterol removal is governed by several still incompletely understood mechanisms, including aqueous diffusion, transport of cholesterol via the ATP-binding cassette (ABC) transporters, ABCA1, and ABCG1, as well as via scavenger receptor class B type 1 (SR-BI) (11)(12)(13)(14). Small, lipid-poor, or lipid-free apo A-Icontaining particles, commonly designated pre-b-HDL, are considered to be the initial acceptors of cell-derived cholesterol via the ABCA1 transporter (8,10,15,16). Among other factors, the metabolism of these particles is governed in a complex way by phospholipid transfer protein (PLTP) and cholesteryl ester transfer protein (CETP), which contribute to pre-b-HDL generation, and by lecithin:cholesterol acyltransferase (LCAT), which decreases pre-b-HDL (8,10,16,17).…”

Structure of HDL: Particle Subclasses and Molecular Components

“…Agarose gels can be stained with Coomassie blue or with anti-apolipoprotein A-I (apoA-I) antibodies, and the relative protein content of the two HDL subclasses can be determined (Favari et al 2004). The plasma preβ-HDL concentration can be also quantified using a sandwich enzyme immunoassay (Miida et al 2003).…”