Overexpression of Human Lecithin Cholesterol Acyltransferase Leads to Hyperalphalipoproteinemia in Transgenic Mice

Lecithin cholesterol acyltransferase (LCAT) is a key enzyme which catalyzes the esterification of free cholesterol present in plasma lipoproteins. 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 utilized to develop transgenic mice. Three different transgenic mouse lines overexpressing human LCAT at plasma levels 11-, 14-, and 109-fold higher than non-transgenic mice were established. Northern blot hybridization analysis demonstrated that the injected 6.2-kb fragment contained the necessary DNA sequences to direct tissue specific expression of the human LCAT gene in mouse liver. Compared to age- and sex-matched controls, total cholesterol and HDL cholesterol levels were increased in all 3 transgenic mice lines by 124-218 and 123-194%, respectively, while plasma triglyceride concentrations remained similar to that of control animals. Fast protein liquid chromatography analysis of transgenic mouse plasma revealed marked increases in high density liposportin (HDL)-cholesteryl ester and phospholipid as well as the formation of larger size HDL. Thus, the majority of the increase in transgenic plasma cholesterol concentrations was due to accumulation of cholesteryl ester 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 demonstrated an accumulation of an apoE-rich HDL1. Like the mouse enzyme, human LCAT was found to be primarily associated with mouse HDL. Our 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 mice leads to HDL elevation as well as increased heterogeneity of the HDL lipoprotein particles, indicating that high levels of plasma LCAT activity may be associated with hyperalphalipoproteinemia and enhanced reverse cholesterol transport.