Correction of hypoalphalipoproteinemia in LDL receptor-deficient rabbits by lecithin:cholesterol acyltransferase.
Familial hypercholesterolemia (FH), a disease caused by a variety of mutations in the low density lipoprotein receptor (LDLr) gene, leads not only to elevated LDL-cholesterol (C) concentrations but to reduced high density lipoprotein (HDL)-C and apolipoprotein (apo) A-I concentrations as well. The reductions in HDL-C and apoA-I are the consequence of the combined metabolic defects of increased apoA-I catabolism and decreased apoA-I synthesis. The present studies were designed to test the hypothesis that overexpression of human lecithin:cholesterol acyltransferase (hLCAT), a pivotal enzyme involved in HDL metabolism, in LDLr defective rabbits would increase HDL-C and apoA-I concentrations. Two groups of hLCAT transgenic rabbits were established: 1) hLCAT+/LDLr heterozygotes (LDLr+/-) and 2) hLCAT+/LDLr homozygotes (LDLr-/-). Data for hLCAT+ rabbits were compared to those of nontransgenic (hLCAT-) rabbits of the same LDLr status. In LDLr+/- rabbits, HDL-C and apoA-I concentrations (mg/dl), respectively, were significantly greater in hLCAT+ (62 +/- 8, 59 +/- 4) relative to hLCAT- rabbits (21 +/- 1, 26 +/- 2). This was, likewise, the case when hLCAT+/ LDLr-/- (27 +/- 2, 19 +/- 6) and hLCAT-/LDLr-/- (5 +/- 1, 6 +/- 2) rabbits were compared. Kinetic experiments demonstrated that the fractional catabolic rate (FCR, d(-1)) of apoA-I was substantially delayed in hLCAT+ (0.376 +/- 0.025) versus hLCAT- (0.588) LDLr+/- rabbits, as well as in hLCAT+ (0.666 +/- 0.033) versus hLCAT- (1.194 +/- 0.138) LDLr-/- rabbits. ApoA-I production rate (PR, mg x kg x d(-1)) was greater in both hLCAT+/LDLr+/- (10 +/- 2 vs. 6) and hLCAT+/LDLr-/- (9 +/- 1 vs. 4 +/- 1) rabbits. Significant correlations (P < 0.02) were observed between plasma LCAT activity and HDL-C (r = 0.857), apoA-I FCR (r = -0.774), and apoA-I PR (r = 0.771), while HDL-C correlated with both apoA-I FCR (-0.812) and PR (0.751). In summary, these data indicate that hLCAT overexpression in LDLr defective rabbits increases HDL-C and apoA-I concentrations by both decreasing apoA-I catabolism and increasing apoA-I synthesis, thus correcting the metabolic defects responsible for the hypoalphalipoproteinemia observed in LDLr deficiency.
Molecular Disease Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
M E
ME
Brousseau
J
J
Wang
S J
SJ
Demosky
B L
BL
Vaisman
G D
GD
Talley
S
S
Santamarina-Fojo
H B
HB
Brewer
J M
JM
Hoeg
D000818:Animals; D030801:Animals, Genetically Modified; D016632:Apolipoprotein A-I / Q000097:blood; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004195:Disease Models, Animal; D015870:Gene Expression; D015316:Genetic Therapy; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D006938:Hyperlipoproteinemia Type II / Q000097:blood / Q000235:genetics / Q000628:therapy; D007009:Hypolipoproteinemias / Q000097:blood / Q000235:genetics / Q000628:therapy*; D007700:Kinetics; D008055:Lipids / Q000097:blood; D008074:Lipoproteins / Q000097:blood; D008075:Lipoproteins, HDL / Q000097:blood*; D009154:Mutation; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000097:blood* / Q000235:genetics*; D011817:Rabbits; D011973:Receptors, LDL / Q000172:deficiency* / Q000235:genetics
D016632:Apolipoprotein A-I; D017931:DNA Primers; D008055:Lipids; D008074:Lipoproteins; D008075:Lipoproteins, HDL; D011973:Receptors, LDL; D007862:Phosphatidylcholine-Sterol O-Acyltransferase