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

Retinal pigment epithelial cells (RPE) actively retrieve and recycle docosa hexaenoic acid (DHA, 22:6n-3) from phagosomal phospholipids back to photore ceptor cells. Here we studied the fate of DHA in primary culture rat RPE ce lls after feeding with a suspension of rod outer segments (ROS) for 4 hr, P hospholipids (PLs), triacylglycerols (TAG), and free fatty acids were isola ted from cells and media by thin layer chromatography (TLC), and their acyl groups quantified by gas liquid chromatography (GLC). In RPE cells, DHA-PL s 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 v alues by 8-24 hr, respectively, DHA-TAG showed the highest increase (21-fol d) by 8 hr. Free DHA displayed a small increase in the cells with a prefere ntial release and accumulation into the media by 24 hr. These results show that in rat RPE cells, photoreceptor cell DHA is transiently incorporated i nto TAG prior to its release and uptake into 18:1-PLs, These metabolic path ways and remodeling may be critical in the conservation of this essential, photoreceptor cell fatty acid. (C) 1999 Wiley-Liss, Inc.