ACAT1-associated Late Endosomes/Lysosomes Significantly Improve Impaired Intracellular Cholesterol Metabolism and the Survival of Niemann-Pick Type C Mice

We previously demonstrated that macrophages exhibit endoplasmic reticulum fragmentation under cholesterol-rich conditions, which results in the generation of acyl-coenzyme A: cholesterol acyltransferase 1 (ACAT1)-associated late endosomes/lysosomes (ACAT1-LE). ACAT1-LE efficiently esterify free cholesterol in loco, even with abnormal egress of free cholesterol from late endosomes. Because impaired free cholesterol transport from late endosomes results in Niemann-Pick type C disease (NPC), the induction of ACAT1-LE is a potential therapeutic intervention for NPC. To examine the effects of ACAT1-LE induction on intracellular cholesterol metabolism, we incubated bone marrow-derived macrophages possessing NPC phenotype (npc1(-/-)) with methyl-beta-cyclodextrin-cholesterol complex (mi beta CDcho), a cholesterol donor. lmmunofluorescence confocal microscopy revealed that mi beta CDcho treatment of npc1(-/-) macrophages resulted in significant colocalization of signals from ACAT1 and lysosome-associated membrane protein 2, a late endosome/lysosome marker. npc1(-/-) macrophages contained significant amounts of free cholesterol with negligible amounts of cholesteryl ester, while wild-type macrophages possessed the same amounts of both cholesterols. mi3CD-cho treatment also induced marked restoration of cholesterol esterification activity. mi3CD-cho administration in neonate npc1(-/-) mice improved survival. These results indicate that ACAT1-LE induction in npc1(-/-) mice corrects impaired intracellular cholesterol metabolism and that restoring cholesterol esterification improves prognosis of npc1(-/-). These data suggest that ACAT1-LE induction is a potential alternative therapeutic strategy for NPC.