Retinyl esters are hydrolyzed in early endosomes of J774 macrophages

The aim of the current study was to identify the subcellular compartment(s) responsible for the hydrolysis of chylomicron remnant-retinyl esters, in J 774.1 cells. The cells were incubated with medium containing chylomicron re mnant [H-3]retinyl ester. Subcellular fractionation was used to separate ea rly endosomes from late endosomes and lysosomes. About 26% and 80% of the t otal [H-3]retinyl esters taken up by the J774 cells were hydrolyzed after 1 0 min and 60 min of chase, respectively. In the early endosomes, there was a 4-fold increase of radioactivity (nearly all radioactivity associated wit h retinyl esters) during the first 10 min of chase. The radioactivity in ea rly endosomes was reduced by 43% from 10 min to 60 min and remained stable from 60 to 180 min of chase. From 10 to 60 min the amount of retinol in ear ly endosomes increased from 44% to 82%, indicating an efficient hydrolysis of retinyl esters, Less than 10% and 5% of the total cell-associated radioa ctivity was found in the late endosomes and lysosomes during the entire cha se period. In the chase medium, 84% of the total amount of retinoid release d during 180 min was present already after 10 min. The percentage of retino l in the medium increased from 25% to 82% during incubation from 10 to 180 min. These data suggest that retinyl esters are endocytosed together with t he chylomicron remnant particle and hydrolyzed in the early endosomes in th is cell model.