Selective retinal pigment epithelial cell lipid metabolism and remodeling conserves photoreceptor docosahexaenoic acid following phagocytosis

Abstract

Retinal pigment epithelial cells (RPE) actively retrieve and recycle docosahexaenoic acid (DHA, 22:6n-3) from phagosomal phospholipids back to photoreceptor cells. Here we studied the fate of DHA in primary culture rat RPE cells after feeding with a suspension of rod outer segments (ROS) for 4 hr. Phospholipids (PLs), triacylglycerols (TAG), and free fatty acids were isolated from cells and media by thin layer chromatography (TLC), and their acyl groups quantified by gas liquid chromatography (GLC). In RPE cells, DHA-PLs increased 3. 5-fold by 4 hr, decreasing thereafter to 1.6-fold above basal by 24 hr. In contrast, 18:1-PLs were decreased by 13%-18% below RPE basal values by 8-24 hr, respectively. DHA-TAG showed the highest increase (21-fold) by 8 hr. Free DHA displayed a small increase in the cells with a preferential release and accumulation into the media by 24 hr. These results show that in rat RPE cells, photoreceptor cell DHA is transiently incorporated into TAG prior to its release and uptake into 18:1-PLs. These metabolic pathways and remodeling may be critical in the conservation of this essential, photoreceptor cell fatty acid.