Effects of interactions of apolipoprotein A-II with apolipoproteins A-I or A-IV on [3H]cholesterol efflux and uptake in cell culture.
Conflicting evidence has accumulated with years regarding the putative negative effect of apolipoprotein A-II on apo A-I mediated cholesterol efflux. In this study, this question was reexamined and in addition to the interaction of apo A-II with apo A-I, its possible effect on apo E and apo A-IV was investigated as well. Free cholesterol (FC) donors were the main components of atheroma, namely, mouse peritoneal macrophages (MP), bovine aortic smooth muscle (SMC) and fibroblasts labeled with [3H]FC. Acceptors of FC were dioleoylphosphatidylcholine (DOPC) liposomes containing apo A-I, rh-apo A-IV or rh-apo E alone or together with apo A-II. When [3H]FC labeled MP were incubated for 2 or 4 h with equimolar concentrations of apo A-I, A-II, A-IV or E, the lowest [3H]cholesterol efflux occurred with apo A-II. Exposure of [3H]FC MP to liposomes containing apo A-I/A-II at 1:2 M/M (keeping the total protein concentration at 50 micrograms/ml), resulted in a lower [3H]FC efflux as compared to apo A-I alone. However, when apo A-I or apo A-IV protein concentration was kept constant and supplemented with apo A-II, a lower [3H]FC efflux was found only at 1:3 M/M of apo A-I/A-II. Apo A-II added to apo E had no effect on FC efflux. With aortic SMC and fibroblasts, no inhibitory effect of addition of apo A-II to apo A-I or apo A-IV on cholesterol efflux was seen at apo A-I/A-II of 1:1 or 1:2 M/M. The uptake of macrophage derived [3H]FC by SMC or HepG2 cells was studied using the serum-free efflux media, containing PC liposomes + apolipoproteins, from 3H-labeled macrophages. The cellular uptake of [3H]FC was higher when apo A-II had been added to apo A-I or apo A-IV than when the apolipoproteins were added alone. In conclusion, apo A-II was found to be less effective in cholesterol efflux and to interfere with the action of A-I only when the cholesterol donors were macrophages and when the relative amount of apo A-I to apo A-II was low. This was not the case when SMC or fibroblasts served as cholesterol donors. In the presence of apo A-II, enhanced [3H]cholesterol delivery to cells was seen which could contribute to the proatherogenic activity of apo A-II.
Stein
O
O
Department of Experimental Medicine and Cancer Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Dabach
Y
Y
Hollander
G
G
Ben-Naim
M
M
Oette
K
K
Stein
Y
Y
D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism*; D016633:Apolipoprotein A-II / Q000378:metabolism / Q000494:pharmacology*; D001161:Arteriosclerosis / Q000378:metabolism; D001692:Biological Transport; D002417:Cattle; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D008081:Liposomes; D008099:Liver / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D014316:Tritium
D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D008081:Liposomes; D014316:Tritium; D002784:Cholesterol