Cholesterol Distribution in Golgi, Lysosomes and Endoplasmic Reticulum

Abstract

Insight into the effect of exogeneously derived lipoprotein cholesterol on distribution of intracellular membrane cholesterol has been gained from structural studies on normal and Niemann Pick Type C human fibroblasts. Endocytic uptake of LDL enriches Golgi cholesterol in both normal and NPC cells. However, the NPC mutation and treatment of normal cells with progesterone during LDL uptake produces abnormal accumulation of cholesterol in lysosomes and trans Golgi cisternae. This lysosomal/Golgi block in cholesterol trafficking results in the inability of endocytosed cholesterol to induce cellular homestatic responses. In addition to lysosomes and Golgi the endoplasmic reticulum can also be a site along the intracellular cholesterol transport pathway that becomes a temporary depot for cholesterol. Specific inhibition of acyl CoA: cholesterol acyltransferase with S-58035 during endocytic uptake results in a reversable accumulation of cholesterol in membranes of ER. Thus the ER, normally low in intracellular cholesterol, has the capacity to act as a sink for endocytosed cholesterol when esterification is blocked. In contrast to the lysosomal/Golgi cholesterol sequestration, ER accumulation of cholesterol does not compromise but appears to enhance the induction of cellular homeostatic responses.