Abstract 420: Lysosomal Acid Lipase Deficiency Impairs Reverse Cholesterol Transport From Macrophages in LAL-Deficient Mice

Abstract

The rate of flux of cholesterol out of lysosomes is a key regulator of oxysterol formation and subsequent activation of liver X-receptor to upregulate genes involved in reverse cholesterol transport (RCT). We previously demonstrated impaired regulation of the lipid transporter ATP-binding cassette transporter A1 (ABCA1), required to promote removal of cholesterol from cells and high density lipoprotein (HDL) particle formation, in the lysosomal cholesterol storage disorders Niemann Pick Disease Type C and Cholesteryl Ester Storage Disease, thus providing an explanation for the low plasma HDL-C seen in these diseases. To determine the importance of lysosomal acid lipase (LAL) in reverse cholesterol transport (RCT) from macrophages to feces in vivo, we performed intraperitoneal injection of immortalized peritoneal macrophages from LAL+/+ or LAL-/- mice that had been cholesterol loaded and labeled with acetylated LDL containing 3H-cholesteryl oleate into LAL+/+ and LAL-/- mice, respectively. LAL-/- macrophages exhibited reduced basal and cholesterol-stimulated ABCA1 expression in culture, and reduced ability to support RCT in LAL-/- mice (1.55 ± 0.35 % total injected 3H-cholesterol counts appearing in feces over 48 h, n=30) compared to LAL+/+ macrophages injected into LAL+/+ mice (5.38 ± 0.92 % 3H-cholesterol counts in feces at 48 hr, n=27), p < 0.001. Injection of LAL-/- macrophages into LAL+/+ mice resulted in partial correction of RCT (2.60 ± 0.46 % 3H-cholesterol counts in feces at 48 hr, n=19), p < 0.001 when compared to injection into LAL-/- mice. ABCA1 protein expression was reduced in lal-/- mouse liver and mRNA expression of several LXR-dependent genes involved in reverse cholesterol transport (ABCG1, ABCG5, ABCG8, CYP7A1, SR-B1) were differentially modulated compared to LAL+/+ controls. The results indicate a critical role of macrophage LAL in promoting ABCA1 expression and RCT in vivo, and the ability of secreted LAL to be taken up by macrophages and correct RCT in vivo. The premature atherosclerosis seen in LAL-deficient humans may therefore be reduced by correction of LAL deficiency.