title: Secretion of sterols and the NPC2 protein from primary astrocytes.
abstract: Astrocytes secrete cholesterol in lipoprotein particles. Here we show that primary murine embryonic astrocytes secrete endogenously synthesized cholesterol but also the cholesterol precursors desmosterol and lathosterol. In astrocyte membranes, desmosterol and cholesterol were the predominant sterols. Astrocytes derived from Niemann-Pick type C lipidosis (NPC1-/-) mice displayed late endosomal cholesterol deposits, but the secretion of biosynthetic sterols from the cells was not inhibited. Both wild-type and NPC1-/- astrocytes secreted the NPC2 protein. Size-exclusion chromatography combined with electron microscopy showed that the majority of sterols were secreted separately from NPC2 in heterogeneous spherical particles with an average diameter of 20 nm. These data suggest that NPC2 and the majority of sterols secreted from astrocytes are not released together and that the secretion of neither sterols nor NPC2 requires NPC1 function. In addition, the findings reveal a complexity of sterol species in astrocytes and bring up the possibility that some of the effects assigned to astrocyte cholesterol may be attributed to its penultimate precursors.
authors.affiliation: Institute of Biotechnology, University of Helsinki, Viikinkaari 9, 00014 University of Helsinki, Finland.
authors.forename: Aino-Liisa
authors.initials: AL
authors.lastname: Mutka
authors.forename: Sari
authors.initials: S
authors.lastname: Lusa
authors.forename: Matts D
authors.initials: MD
authors.lastname: Linder
authors.forename: Eija
authors.initials: E
authors.lastname: Jokitalo
authors.forename: Outi
authors.initials: O
authors.lastname: Kopra
authors.forename: Matti
authors.initials: M
authors.lastname: Jauhiainen
authors.forename: Elina
authors.initials: E
authors.lastname: Ikonen
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000166:cytology* / Q000378:metabolism*; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D002784:Cholesterol / Q000378:metabolism; D002845:Chromatography; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D018076:DNA, Complementary / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D005838:Genotype; D006023:Glycoproteins / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D006026:Glycoside Hydrolases / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D000077296:Niemann-Pick C1 Protein; D011506:Proteins / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D012672:Semliki forest virus / Q000235:genetics; D013261:Sterols / Q000378:metabolism*; D013395:Sucrose / Q000494:pharmacology; D013696:Temperature; D013997:Time Factors; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; C104585:NPC2 protein, human; D000077296:Niemann-Pick C1 Protein; C106831:Npc1 protein, mouse; D011506:Proteins; D013261:Sterols; D033921:Vesicular Transport Proteins; D013395:Sucrose; D002784:Cholesterol; D006026:Glycoside Hydrolases