出版社：American Society for Biochemistry and Molecular Biology
摘要：Cholesterol efflux occurs by different pathways, including transportmediated by specific proteins. We determined the effect of enrichingcells with free cholesterol (FC) on the release of FC to humanserum. Loading Fu5AH cells with FC had no effect on fractionalefflux, whereas enriching mouse peritoneal macrophages (MPMs)resulted in a doubling of fractional efflux. Efflux from cholesterol-normalMPM and Fu5AH cells to 15 human sera correlated well with HDLparameters. However, these relationships were reduced or lostwith cholesterol-loaded MPMs. Using macrophages from scavengerreceptor class B type I (SR-BI)-, ABCA1-, and ABCG1-knockoutmice, together with inhibitors of SR-BI- and ABCA1-mediatedefflux, we were able to quantitate efflux upon loading macrophageswith excess cholesterol and to establish the contributions ofthe various efflux pathways in cholesterol-normal and -enrichedcells. The removal of ABCA1 had essentially no effect on thetotal efflux when cell cholesterol levels were normal. However,in cholesterol-enriched cells, the removal of ABCA1 reducedefflux by 50%. Approximately 20% of the efflux stimulated byFC-loading MPM is attributable to ABCG1. The SR-BI contributionto efflux was small. Another pathway that is present in allcells is aqueous diffusion. Our studies demonstrate that thismechanism is one of the major contributors to efflux, particularlyin cholesterol-normal cells.Supplementary key words SR-BI • ABCA1 • ABCG1 • efflux
Abbreviations: AcLDL, acetylated low density lipoprotein; apoA-I, apolipoprotein A-I; BLT-1, 2-hexyl-1-cyclopentanone thiosemicarbazone; DPBS, phosphate-buffered saline with calcium and magnesium; FC, free cholesterol; KO, knockout; MPM, mouse peritoneal macrophage; PL, phospholipid; RCT, reverse cholesterol transport; SR-BI, scavenger receptor class B type I; WT, wild-type
