title: Cholesterol independent effect of LXR agonist TO-901317 on gamma-secretase.
abstract: The balance of intracellular cholesterol has proven to be critical to the production of beta-amyloid (A beta). Reducing cholesterol in vitro leads to decreased production of A beta, whereas an increase in cellular cholesterol induces A beta production. Liver X Receptor (LXR) agonists are known to increase cholesterol efflux from cells, but there are conflicting reports as to the effects of these agonists on A beta production. We therefore examined the effects of efflux-inducing agents on A beta production in vitro. We used methyl-beta-cyclodextrin and an LXR agonist (TO-901317) to induce cholesterol efflux and studied the resulting A beta production in a stable amyloid precursor protein (APP) -transfected cell line. When cholesterol efflux was induced with methyl-beta-cyclodextrin there was a >60% decrease in A beta(40) and A beta(42) production. However, while activation of LXR using TO-901317-induced cholesterol efflux in the presence of a cholesterol acceptor, no changes in A beta levels were recorded. When cells were incubated with TO-901317 above the concentration required for maximal cholesterol efflux, there was a 150% increase in A beta(42) levels. The absence of a cholesterol acceptor from the culture media (preventing cholesterol efflux) did not blunt this increase in A beta(42), suggesting that the effects of TO-901317 on A beta(42) are efflux independent. These results were confirmed in APP stably transfected human H4 cells, which revealed in addition to a 200% increase in A beta(42) levels, a concomitant 80% reduction in A beta(38). A cell-free gamma-secretase assay confirmed that TO-901317 can directly alter gamma-secretase activity. These data demonstrate that TO-901317 can directly modulate the site of cleavage of APP by gamma-secretase in vitro.
authors.affiliation: F. Hoffmann-La Roche, Pharmaceuticals Division, Basel, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Czech
authors.forename: Mark P
authors.initials: MP
authors.lastname: Burns
authors.forename: Lilit
authors.initials: L
authors.lastname: Vardanian
authors.forename: Angelique
authors.initials: A
authors.lastname: Augustin
authors.forename: Helmut
authors.initials: H
authors.lastname: Jacobsen
authors.forename: Karlheinz
authors.initials: K
authors.lastname: Baumann
authors.forename: G William
authors.initials: GW
authors.lastname: Rebeck
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000187:drug effects*; D016229:Amyloid beta-Peptides / Q000378:metabolism; D016564:Amyloid beta-Protein Precursor / Q000235:genetics; D000704:Analysis of Variance; D000818:Animals; D002461:Cell Line, Transformed; D002784:Cholesterol / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D004268:DNA-Binding Proteins / Q000819:agonists*; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D000071518:Liver X Receptors; D013058:Mass Spectrometry; D057093:Orphan Nuclear Receptors; D010446:Peptide Fragments / Q000378:metabolism; D053764:Presenilin-1 / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists*; D014162:Transfection; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D004268:DNA-Binding Proteins; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D010446:Peptide Fragments; D053764:Presenilin-1; D018160:Receptors, Cytoplasmic and Nuclear; C075222:amyloid beta-protein (1-42); D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D002784:Cholesterol; D053829:Amyloid Precursor Protein Secretases