title: Regulation of fibroblast mitochondrial 27-hydroxycholesterol production by active plasma membrane cholesterol.
abstract: Side chain oxysterols are cholesterol derivatives thought to signal the abundance of cell cholesterol to homeostatic effector proteins. Here, we investigated how plasma membrane (PM) cholesterol might regulate 27-hydroxycholesterol (HC) biosynthesis in cultured fibroblasts. We showed that PM cholesterol was a major substrate for 27-HC production. Biosynthesis commenced within minutes of loading depleted cells with cholesterol, concurrent with the rapid inactivation of hydroxy-3-methylglutaryl CoA reductase (HMGR). 27-HC production rose approximately 30-fold in normal and Niemann-Pick C1 fibroblasts when PM cholesterol was increased by approximately 60%. 27-HC production was also stimulated by 1-octanol, which displaces PM cholesterol from its phospholipid complexes and thereby increases its activity (escape tendency) and elevates its intracellular abundance. Conversely, lysophosphatidylserine and U18666A inhibited 27-HC biosynthesis and the inactivation of HMGR, presumably by reducing the activity of PM cholesterol and, therefore, its circulation to mitochondria. We conclude that, in this in vitro system, excess (active) PM cholesterol rapidly reaches mitochondria where, as the rate-limiting substrate, it stimulates 27-HC biosynthesis. The oxysterol product then promotes the rapid degradation of HMGR, along with other homeostatic effects. The regulation of 27-HC production by the active excess of PM cholesterol can thus provide a feedback mechanism in the homeostasis of PM cholesterol.
authors.affiliation: Department of Pathology, Rush University Medical Center, Chicago, IL 60612, USA. ylange@rush.edu
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Lange
authors.forename: Theodore L
authors.initials: TL
authors.lastname: Steck
authors.forename: Jin
authors.initials: J
authors.lastname: Ye
authors.forename: Michael H
authors.initials: MH
authors.lastname: Lanier
authors.forename: Vasumathi
authors.initials: V
authors.lastname: Molugu
authors.forename: Daniel
authors.initials: D
authors.lastname: Ory
mesh_terms: D000736:Androstenes / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D004789:Enzyme Activation; D005347:Fibroblasts / Q000166:cytology*; D006801:Humans; D006888:Hydroxycholesterols / Q000378:metabolism*; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D007364:Intercalating Agents / Q000494:pharmacology; D007700:Kinetics; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000736:Androstenes; D006888:Hydroxycholesterols; D007364:Intercalating Agents; C006261:3-beta-(2-(diethylamino)ethoxy)androst-5-en-17-one; C076996:27-hydroxycholesterol; D002784:Cholesterol; D006903:Hydroxymethylglutaryl CoA Reductases