Functional lecithin:cholesterol acyltransferase deficiency and high density lipoprotein deficiency in transgenic mice overexpressing human apolipoprotein A-II.
The concentration of high density lipoproteins (HDL) is inversely related to the risk of atherosclerosis. The two major protein components of HDL are apolipoprotein (apo) A-I and apoA-II. To study the role of apoA-II in lipoprotein metabolism and atherosclerosis, we have developed three lines of C57BL/6 transgenic mice expressing human apoA-II (lines 25.3, 21.5, and 11.1). Northern blot experiments showed that human apoA-II mRNA was present only in the liver of transgenic mice. SDS-polyacrylamide gel electrophoresis and Western blot analysis demonstrated a 17.4-kDa human apoA-II in the HDL fraction of the plasma of transgenic mice. After 3 months on a regular chow, the plasma concentrations of human apoA-II were 21 +/- 4 mg/dl in the 25.3 line, 51 +/- 6 mg/dl in the 21.5 line, and 74 +/- 4 mg/dl in the 11.1 line. The concentration of cholesterol in plasma was significantly lower in transgenic mice than in control mice because of a decrease in HDL cholesterol that was greatest in the line that expressed the most apoA-II (23 mg/dl in the 11.1 line versus 63 mg/dl in control mice). There was also a reduction in the plasma concentration of mouse apoA-I (32 +/- 2, 56 +/- 9, 91 +/- 7, and 111 +/- 2 mg/dl for lines 11.1, 21.5, 25.3, and control mice, respectively) that was inversely correlated with the amount of human apoA-II expressed. Additional changes in plasma lipid/lipoprotein profile noted in line 11.1 that expressed the highest level of human apoA-II include elevated triglyceride, increased proportion of total plasma, and HDL free cholesterol and a marked (>10-fold) reduction in mouse apoA-II. Total endogenous plasma lecithin:cholesterol acyltransferase (LCAT) activity was reduced to a level directly correlated with the degree of increased plasma human apoA-II in the transgenic lines. LCAT activity toward exogenous substrate was, however, only slightly decreased. The biochemical changes in the 11.1 line, which is markedly deficient in plasma apoA-I, an activator for LCAT, are reminiscent of those in patients with partial LCAT deficiency. Feeding the transgenic mice a high fat, high cholesterol diet maintained the mouse apoA-I concentration at a normal level (69 +/- 14 mg/dl in line 11.1 compared with 71 +/- 6 mg/dl in nontransgenic controls) and prevented the appearance of HDL deficiency. All this happened in the presence of a persistently high plasma human apoA-II (96 +/- 14 mg/dl). Paradoxical HDL elevation by high fat diets has been observed in humans and is reproduced in human apoA-II overexpressing transgenic mice but not in control mice. Finally, HDL size and morphology varied substantially in the three transgenic lines, indicating the importance of apoA-II concentration in the modulation of HDL formation. The LCAT and HDL deficiencies observed in this study indicate that apoA-II plays a dynamic role in the regulation of plasma HDL metabolism.
Marzal-Casacuberta
A
A
Department of Cell Biology, Baylor College of Medicine, Houston, Texas, 77030, USA.
Blanco-Vaca
F
F
Ishida
B Y
BY
Julve-Gil
J
J
Shen
J
J
Calvet-Márquez
S
S
González-Sastre
F
F
Chan
L
L
D000818:Animals; D016633:Apolipoprotein A-II / Q000235:genetics*; D002784:Cholesterol / Q000097:blood; D002791:Cholesterol, Dietary / Q000097:blood; D004041:Dietary Fats / Q000008:administration & dosage; D006801:Humans; D008075:Lipoproteins, HDL / Q000737:chemistry / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D010316:Particle Size; D010641:Phenotype; D002785:Sterol O-Acyltransferase / Q000097:blood / Q000187:drug effects*
D016633:Apolipoprotein A-II; D002791:Cholesterol, Dietary; D004041:Dietary Fats; D008075:Lipoproteins, HDL; D002784:Cholesterol; D002785:Sterol O-Acyltransferase