Apolipoprotein A-IFIN (Leu159-->Arg) mutation affects lecithin cholesterol acyltransferase activation and subclass distribution of HDL but not cholesterol efflux from fibroblasts.
We showed earlier that the apolipoprotein A-I Leu159-->Arg mutation (apoA-IFin) results in dominantly inherited hypoalphalipoproteinemia. In the present study we investigated the effect of the apoA-IFin mutation on lipoprotein profile, apoA-I kinetics, lecithin:cholesterol acyltransferase (LCAT) activation, and cholesterol efflux in vitro. Carriers (n = 9) of the apoA-IFin mutation exhibited several lipoprotein abnormalities. The serum HDL cholesterol level was diminished to 20% of normal, and nondenaturing gradient gel electrophoresis of HDL showed disappearance of particles at the 9.0- to 12-nm size range (HDL2-type) and the presence of small 7.8- to 8.9-nm (mostly HDL3-type) particles only. HDL3-type particles from both the mutation carriers and nonaffected family members were similarly converted to large, HDL2-type particles by phospholipid transfer protein in vitro. Studies on apoA-I kinetics in four affected subjects favored accelerated catabolism of apoA-I. Experiments with reconstituted proteoliposomes showed that the capacity of apoA-IFin protein to activate LCAT was reduced to 40% of that of the wild-type apoA-I. The impact of the apoA-IFin protein on cholesterol efflux was examined in vitro using [3H]cholesterol-loaded human fibroblasts and three different cholesterol acceptors: (1) total HDL, (2) total apoA-I combined with phospholipid, and (3) apoA-I isoform (apoA-IFin or wild-type apoA-I isoform 1) combined with phospholipid. ApoA-IFin did not impair phospholipid binding or cholesterol efflux from fibroblasts to any of the acceptors used. Only one of the nine apoA-IFin carriers appears to have evidence of clinically manifested atherosclerosis. In conclusion, although the apoA-IFin mutation does not alter the properties of apoA-I involved in promotion of cholesterol efflux, its ability to activate LCAT in vitro is defective. In vivo, apoA-IFin was found to be associated with several lipoprotein composition rearrangements and increased catabolism of apoA-I.
Miettinen
H E
HE
Department of Medicine, University of Helsinki, Finland. Helena.Miettinen@helsinki.fi
Jauhiainen
M
M
Gylling
H
H
Ehnholm
S
S
Palomäki
A
A
Miettinen
T A
TA
Kontula
K
K
D000293:Adolescent; D000328:Adult; D000368:Aged; D016632:Apolipoprotein A-I / Q000235:genetics* / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D053480:Cholesterol Ester Transfer Proteins; D004789:Enzyme Activation; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D005838:Genotype; D006023:Glycoproteins; D006801:Humans; D008075:Lipoproteins, HDL / Q000145:classification / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008875:Middle Aged; D010316:Particle Size; D010375:Pedigree; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000378:metabolism; D017354:Point Mutation; D011510:Proteolipids / Q000378:metabolism
D016632:Apolipoprotein A-I; C506642:CETP protein, human; D002352:Carrier Proteins; D053480:Cholesterol Ester Transfer Proteins; D006023:Glycoproteins; D008075:Lipoproteins, HDL; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D011510:Proteolipids; C020485:proteoliposomes; D002784:Cholesterol; D007862:Phosphatidylcholine-Sterol O-Acyltransferase