Cellular cholesterol efflux is modulated by phospholipid-derived signalingmolecules in familial HDL deficiency/Tangier disease fibroblasts

Familial HDL deficiency (FHD) is the heterozygous form of Tangier disease ( TD). Mutations of the ABCA1 gene cause FHD and TD. FHD/TD cells are unable to normally efflux cholesterol onto nascent I-IDL particles, which are rapi dly catabolized. TD fibroblasts have an;abnormal pattern of PLC and PLD act ivation following cell stimulation with HDL3 or apolipoprotein A-I (apoA-I) . We examined cellular cholesterol efflux in FHD and TD fibroblasts by phos pholipid-derived-molecules, compared with that of normal cells. We used the PKC agonist 1,2-dioctanoylglycerol (DOG) and phorbol myristate acetate (PM A) to activate PKC, calphostin C, and GO 6976, as inhibitors of PKC; phosph atidic acid (PA), which is the product of PLD, and lysophosphatidic acid (L PA), phosphatidylcholine, sphingomyelin, and beta -cyclodextrin to investig ate their potential effect in modulating cellular cholesterol efflux in [H- 3]cholesterol-labeled and cholesterol-loaded fibroblasts. Phosphatidylcholi ne, sphingomyelin, and beta -cyclodextrin promoted cholesterol efflux in an identical fashion in control, FHD, or TD fibroblasts. In a dose-dependent fashion, DOG (0-200 muM) increased apoA-I-mediated cellular cholesterol eff lux by 40% in controls, 71% in FHD, and 242% in TD cells. PMA similarly inc reased cholesterol efflux to a maximum of 256% in controls, 182% in FHD, an d 191% in TD cells. This effect was inhibited by calphostin C. PA (100 muM) also increased cholesterol efflux by 25% in control, 44% in FHD, and 100% in TD cells. Conversely, LPA reduced cholesterol efflux in a dose-dependent fashion in control and FHD cells (-50%, 200 muM) but not in TD cells, wher e efflux was increased by 140%. Propranolol (100 muM) significantly increas ed cholesterol efflux at 24 h in all three cell lines. n-Butanol partially decreased the DOG-mediated increase in cholesterol efflux. The inhibitory e ffect of calphostin C on DOG-stimulated cholesterol efflux could be partial ly overcome by propranolol, suggesting that PA is a downstream mediator of PKC-stimulated cholesterol efflux. We conclude that PLC and PLD activities are required for apoA-I-mediated cellular cholesterol efflux, and modulatin g cellular PA concentration can correct, at least partially, the cholestero l efflux defect in FHD and TD.