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 HDL particles, which are rapidly catabolized. TD fibroblasts have an abnormal pattern of PLC and
PLD activation following cell stimulation with HDL(3) or
apolipoprotein A-I (
apoA-I). We examined cellular
cholesterol efflux in
FHD and TD fibroblasts by
phospholipid-derived-molecules, compared with that of normal cells. We used the PKC agonist
1,2-dioctanoylglycerol (DOG) and
phorbol myristate acetate (PMA) to activate PKC,
calphostin C, and
GO 6976, as inhibitors of PKC;
phosphatidic acid (PA), which is the product of
PLD, and
lysophosphatidic acid (LPA),
phosphatidylcholine,
sphingomyelin, and
beta-cyclodextrin to investigate their potential effect in modulating cellular
cholesterol efflux in [(3)H]
cholesterol-labeled and
cholesterol-loaded fibroblasts.
Phosphatidylcholine,
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 microM) increased
apoA-I-mediated cellular
cholesterol efflux by 40% in controls, 71% in
FHD, and 242% in TD cells. PMA similarly increased
cholesterol efflux to a maximum of 256% in controls, 182% in
FHD, and 191% in TD cells. This effect was inhibited by
calphostin C. PA (100 microM) 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 microM) but not in TD cells, where efflux was increased by 140%.
Propranolol (100 microM) significantly increased
cholesterol efflux at 24 h in all three cell lines.
n-Butanol partially decreased the DOG-mediated increase in
cholesterol efflux. The inhibitory effect of
calphostin C on DOG-stimulated
cholesterol efflux could be partially 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 modulating cellular PA concentration can correct, at least partially, the
cholesterol efflux defect in
FHD and TD.