Scavenger receptor activity and expression of apolipoprotein E mRNA in monocyte-derived macrophages of young and old healthy men

Abstract

The aim of this study was to compare some aspects of lipid metabolism in monocyte-derived macrophages isolated from young males, aged 18–24 years, and old males, aged 74–90 years, who were found healthy in accordance with the Senieur protocol. The parameters tested were metabolism of 125I-acetylated low-density lipoproteins (LDL) and oxidized LDL, incorporation of [3H]cholesterol into cholesteryl ester and expression of apolipoprotein E (apo E) mRNA. Cell association and degradation of 125I-acetylated LDL by macrophages of old and young subjects, respectively, was 15 978±2492 and 9300±1416 ng/mg cell protein per 24 h. Incorporation of [3H]cholesterol into cellular [3H]cholesteryl ester in the presence of acetylated LDL in cells isolated from old subjects was twice that in cells from young subjects. The macrophages from both age groups metabolized less 125I-oxidized LDL than 125I-acetylated LDL. Cell association and degradation of 125I-oxidized LDL in cells from old and young subjects, respectively, was 6779±1398 and 3219±643 ng/mg cell protein per 24 h. Expression of apo E mRNA was determined by reverse transcriptase polymerase chain reaction. In the basal state, it was 5.8±0.4 and 2.4±0.2 photo-stimulated luminescence (PSL) units in cells from the old and young subjects, respectively, and increased after exposure to acetylated LDL. In conclusion, these findings suggest that a combination of high scavenger receptor activity and increased expression of apo E mRNA in macrophages could contribute to (a) enhanced metabolism of modified LDL and (b) more efficient removal of cholesterol from arteries, thus leading to healthy old age.