title: The enzyme lecithin-cholesterol acyltransferase esterifies cerebrosterol and limits the toxic effect of this oxysterol on SH-SY5Y cells.
abstract: Cholesterol is mostly removed from the CNS by its conversion to cerebrosterol (24(S)-hydroxycholesterol, 24(S)OH-C), which is transported to the circulation for bile formation in liver. A neurotoxic role of this oxysterol was previously demonstrated in cell culture. Here, we provide evidence that the enzyme lecithin-cholesterol acyltransferase, long known to esterify cholesterol, also produces monoesters of 24(S)OH-C. Proteoliposomes containing apolipoprotein A-I or apolipoprotein E were used to stimulate the enzyme activity and entrap the formed esters. Proteoliposomes with apolipoprotein A-I were found to be more active than those with apolipoprotein E in stimulating the production of oxysteryl esters. Cholesterol and 24(S)OH-C were found to compete for enzyme activity. High levels of haptoglobin, as those circulating during the acute inflammatory phase, inhibited 24(S)OH-C esterification. When highly neurotoxic 24(S)OH-C was treated with enzyme and proteoliposomes before incubation with differentiated SH-SY5Y cells, the neuron survival improved. The esters of 24(S)OH-C, embedded into proteoliposomes by the enzyme and isolated from unesterified 24(S)OH-C by gel filtration chromatography, did not enter the neurons in culture. These results suggest that the enzyme, in the presence of the apolipoproteins, converts 24(S)OH-C into esters restricted to the extracellular environment, thus preventing or limiting oxysterol-induced neurotoxic injuries to neurons in culture. 24-hydroxycholesterol (24(S)OH-C) is neurotoxic. The enzyme lecithin-cholesterol acyltransferase (LCAT) synthesizes monoesters of 24(S)OH-C in reaction mixtures with proteoliposomes containing phospholipids and apolipoprotein A-I or apolipoprotein E. The esters, also produced by incubation of cerebrospinal fluid only with tritiated 24(S)OH-C, are embedded into lipoproteins that do not enter neurons in culture. The enzyme activity limits the toxicity of 24-hydroxycholesterol in neuron culture.
authors.affiliation: Dipartimento di Biologia, Università di Napoli Federico II, Napoli, Italia.
authors.forename: Valeria
authors.initials: V
authors.lastname: La Marca
authors.forename: Maria Stefania
authors.initials: MS
authors.lastname: Spagnuolo
authors.forename: Luisa
authors.initials: L
authors.lastname: Cigliano
authors.forename: Daniela
authors.initials: D
authors.lastname: Marasco
authors.forename: Paolo
authors.initials: P
authors.lastname: Abrescia
mesh_terms: D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004951:Esterification / Q000187:drug effects / Q000502:physiology; D006801:Humans; D006888:Hydroxycholesterols / Q000037:antagonists & inhibitors* / Q000378:metabolism* / Q000633:toxicity; D008297:Male; D008875:Middle Aged; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000502:physiology*
chemical_list: D006888:Hydroxycholesterols; C044563:24-hydroxycholesterol; D007862:Phosphatidylcholine-Sterol O-Acyltransferase
keywords: ApoA-I; ApoE; LCAT; cerebrosterol; haptoglobin; neuron culture