Intracellular cholesterol changes induced by translocator protein (18 kDa) TSPO/PBR ligands.
One of the main functions of the translocator protein (18 kDa) or TSPO, previously known as peripheral-type benzodiazepine receptor, is the regulation of cholesterol import into mitochondria for steroid biosynthesis. In this paper we show that TSPO ligands induce changes in the distribution of intracellular cholesterol in astrocytes and fibroblasts. NBD-cholesterol, a fluorescent analog of cholesterol, was rapidly removed from membranes and accumulated into lipid droplets. This change was followed by a block of cholesterol esterification, but not by modification of intracellular cholesterol synthesis. NBD-cholesterol droplets were in part released in the medium, and increased cholesterol efflux was observed in [(3)H]cholesterol-prelabeled cells. TSPO ligands also induced a prominent shrinkage and depolarization of mitochondria and depletion of acidic vesicles with cytoplasmic acidification. Consistent with NBD-cholesterol changes, MTT assay showed enhanced accumulation of formazan into lipid droplets and inhibition of formazan exocytosis after treatment with TSPO ligands. The effects of specific TSPO ligands PK 11195 and Ro5-4864 were reproduced by diazepam, which binds with high affinity both TSPO and central benzodiazepine receptors, but not by clonazepam, which binds exclusively to GABA receptor, and other amphiphilic substances such as DIDS and propranolol. All these effects and the parallel immunocytochemical detection of TSPO in potentially steroidogenic cells (astrocytes) and non-steroidogenic cells (fibroblasts) suggest that TSPO is involved in the regulation and trafficking of intracellular cholesterol by means of mechanisms not necessarily related to steroid biosynthesis.
Falchi
Angela Maria
AM
Department of Cytomorphology, Cittadella Universitaria, University of Cagliari, Monserrato, 09100 Cagliari, Italy.
Battetta
Barbara
B
Sanna
Francesca
F
Piludu
Marco
M
Sogos
Valeria
V
Serra
Mariangela
M
Melis
Marta
M
Putzolu
Martina
M
Diaz
Giacomo
G
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects; D001570:Benzodiazepinones / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D003292:Convulsants / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005089:Exocytosis / Q000187:drug effects; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D008024:Ligands; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D025261:Mitochondrial Proton-Translocating ATPases; D018079:Receptors, GABA / Q000378:metabolism*; D012235:Rhodamines / Q000378:metabolism; D013997:Time Factors
D000970:Antineoplastic Agents; D001570:Benzodiazepinones; C463819:Bzrp protein, mouse; D002352:Carrier Proteins; D003292:Convulsants; D007546:Isoquinolines; D008024:Ligands; D008565:Membrane Proteins; D018079:Receptors, GABA; D012235:Rhodamines; C401833:tetramethylrhodamine methyl ester; C028513:4'-chlorodiazepam; D002784:Cholesterol; D000251:Adenosine Triphosphatases; D025261:Mitochondrial Proton-Translocating ATPases; C020439:oligomycin sensitivity-conferring protein; C037850:PK 11195