OVEREXPRESSION OF HUMAN LECITHIN-CHOLESTEROL ACYLTRANSFERASE LEADS TOHYPERALPHALIPOPROTEINEMIA IN TRANSGENIC MICE

Lecithin cholesterol acyltransferase (LCAT) is a key enzyme which cata lyzes the esterification of free cholesterol present in plasma lipopro teins. In order to evaluate the role of LCAT in HDL metabolism, a 6.2- kilobase (kb) fragment consisting of 0.851 and 1.134 kb of the 5'- and 3'-flanking regions, as well as the entire human LCAT gene, was utili zed to develop transgenic mice. Three different transgenic mouse lines overexpressing human LCAT at plasma levels 11-, 14-, and 109-fold hig her than non-transgenic mice were established, Northern blot hybridiza tion analysis demonstrated that the injected 6.2-kb fragment contained the necessary DNA sequences to direct tissue specific expression of t he human LCAT gene in mouse liver. Compared to age- and sex-matched co ntrols, total cholesterol and HDL cholesterol levels were increased in all 3 transgenic mice lines by 124-218 and 123-194%, respectively, wh ile plasma triglyceride concentrations remained similar to that of con trol animals. Fast protein liquid chromatography analysis of transgeni c mouse plasma revealed marked increases in high density lipo-sportin (HDL)-cholesteryl ester and phospholipid as well as the formation of l arger size HDL. Thus, the majority of the increase in transgenic plasm a cholesterol concentrations was due to accumulation of cholesteryl es ter in HDL consistent with enhanced esterification of free cholesterol in mouse HDL by human LCAT. Plasma concentrations of apoA-I, apoA-II, and apoE were increased in high expressor homozygote mice who also de monstrated an accumulation of an apoE-rich HDL(1). Like the mouse enzy me, human LCAT was found to be primarily associated with mouse HDL. Ou r studies demonstrate a high correlation between plasma LCAT activity and total as well as HDL cholesterol levels establishing that in mice LCAT modulates plasma HDL concentrations. Overexpression of LCAT in mi ce leads to HDL elevation as well as increased heterogeneity of the HD L lipoprotein particles, indicating that high levels of plasma LCAT ac tivity may be associated with hyperalphalipoproteinemia and enhanced r everse cholesterol transport.