Effect of apolipoprotein A-I deficiency on lecithin:cholesterol acyltransferase activation in mouse plasma.
Plasma cholesteryl ester (CE) synthesis by lecithin cholesterol acyltransferase (LCAT) is activated by apolipoprotein (apo)A-I. We studied the effect of plasma apoA-I concentration on LCAT activation, using normal, heterozygous or homozygous apoA-I-deficient mice made by gene targeting. Plasma esterified cholesterol concentrations of mice fed chow diets were ordered (mean +/- SEM): 105 +/- 7 (normal) > 70 +/- 5 (heterozygotes) > 26 +/- 2 (homozygotes) mg/dl. Plasma free cholesterol concentrations were similar among the three genotypes. Endogenous LCAT activity, measured as the decrease in plasma free cholesterol after a 1 h incubation at 37 degrees C, was ordered: 44 +/- 3 (normal) > 21 +/- 2 (heterozygotes) > 5 +/- 1 (homozygotes) nmol CE formed/h per ml plasma. Using a recombinant exogenous substrate consisting of egg yolk phospholipid, [14C]cholesterol, and apoA-I, CE formation of normals and heterozygotes was similar (27.4 +/- 0.6 and 28.8 +/- 1.3 nmol/h per ml plasma, respectively), but was significantly less for homozygotes (19.2 +/- 1.7 nmol/h per ml plasma). However, using a small unilamellar vesicle substrate particle containing phospholipid and [14C]cholesterol, CE formation was ordered: 1.6 +/- 0.1 (normal) = 1.6 +/- 0.1 (heterozygotes) > 0.6 +/- 0.1 (homozygotes) nmol/h per ml plasma; addition of apoA-I to the plasma of homozygous animals restored CE formation to normal levels (1.6 +/- 0.1). CE fatty acid analysis demonstrated that plasma from homozygous mice contained significantly more saturated and monounsaturated and fewer polyunsaturated fatty acids compared to normal and heterozygous mice.(ABSTRACT TRUNCATED AT 250 WORDS)
Parks
J S
JS
Department of Comparative Medicine, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, NC 27157, USA.
Li
H
H
Gebre
A K
AK
Smith
T L
TL
Maeda
N
N
D000818:Animals; D016632:Apolipoprotein A-I / Q000172:deficiency*; D002788:Cholesterol Esters / Q000097:blood; D004789:Enzyme Activation / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000097:blood*
D016632:Apolipoprotein A-I; D002788:Cholesterol Esters; D007862:Phosphatidylcholine-Sterol O-Acyltransferase