OLEATE AND OTHER LONG-CHAIN FATTY-ACIDS STIMULATE LOW-DENSITY-LIPOPROTEIN RECEPTOR ACTIVITY BY ENHANCING ACYL-COENZYME A-CHOLESTEROL ACYLTRANSFERASE ACTIVITY AND ALTERING INTRACELLULAR REGULATORY CHOLESTEROL POOLS IN CULTURED-CELLS

Modification of dietary fatty acid composition results in changes in plasma cholesterol levels in man. We examined the effect of in vitro fatty acid supplementation on low density lipoprotein (LDL) receptor activity in cultured cells and questioned whether changes were related to fatty acid-induced alterations in acyl-CoA: cholesterol acyltransferase (ACAT) activity, Preincubation of cultured cells (i.e, human skin fibroblasts, J774 macrophages, and HepG2 cells) with oleic acid (oleic acid:bovine serum albumin molar ratio 2:1) at 37 degrees C for longer than 2 h resulted in a 1.2- to 1.5-fold increase in LDL cell binding at 4 degrees C and LDL cell degradation at 37 degrees C, Scatchard analysis showed that oleic acid increased LDL receptor number but not LDL affinity (K-d). Fatty acid supplementation of J774 macrophages increased both LDL receptor activity and cholesteryl ester accumulation, The ACAT inhibitor, 58-035, eliminated both effects, and increased ACAT activity preceded stimulation of LDL receptor activity by 1-2 h, Supplementation of macrophages with triolein emulsion particles also increased LDL cell binding and degradation, and addition of cholesterol to the emulsions abolished this effect. Among fatty acids tested, oleate (18:1), arachidonate (20:4), and eicosapentanoate (20:5) demonstrated the greatest effects, We hypothesize that certain fatty acids delivered to cells either in free form, or as triglyceride, first increase cellular ACAT activity, which then causes a decrease in an intracellular free cholesterol pool, signaling a need for increased LDL receptor activity. This mechanism may play a role in the effect of certain dietary fatty acids on LDL metabolism in vivo.