title: 7-Dehydrocholesterol (7-DHC), But Not Cholesterol, Causes Suppression of Canonical TGF-β Signaling and Is Likely Involved in the Development of Atherosclerotic Cardiovascular Disease (ASCVD).
abstract: For several decades, cholesterol has been thought to cause ASCVD. Limiting dietary cholesterol intake has been recommended to reduce the risk of the disease. However, several recent epidemiological studies do not support a relationship between dietary cholesterol and/or blood cholesterol and ASCVD. Consequently, the role of cholesterol in atherogenesis is now uncertain. Much evidence indicates that TGF-β, an anti-inflammatory cytokine, protects against ASCVD and that suppression of canonical TGF-β signaling (Smad2-dependent) is involved in atherogenesis. We had hypothesized that cholesterol causes ASCVD by suppressing canonical TGF-β signaling in vascular endothelium. To test this hypothesis, we determine the effects of cholesterol, 7-dehydrocholesterol (7-DHC; the biosynthetic precursor of cholesterol), and other sterols on canonical TGF-β signaling. We use Mv1Lu cells (a model cell system for studying TGF-β activity) stably expressing the Smad2-dependent luciferase reporter gene. We demonstrate that 7-DHC (but not cholesterol or other sterols) effectively suppresses the TGF-β-stimulated luciferase activity. We also demonstrate that 7-DHC suppresses TGF-β-stimulated luciferase activity by promoting lipid raft/caveolae formation and subsequently recruiting cell-surface TGF-β receptors from non-lipid raft microdomains to lipid rafts/caveolae where TGF-β receptors become inactive in transducing canonical signaling and undergo rapid degradation upon TGF-β binding. We determine this by cell-surface125I-TGF-β-cross-linking and sucrose density gradient ultracentrifugation. We further demonstrate that methyl-β-cyclodextrin (MβCD), a sterol-chelating agent, reverses 7-DHC-induced suppression of TGF-β-stimulated luciferase activity by extrusion of 7-DHC from resident lipid rafts/caveolae. These results suggest that 7-DHC, but not cholesterol, promotes lipid raft/caveolae formation, leading to suppression of canonical TGF-β signaling and atherogenesis. J. Cell. Biochem. 118: 1387-1400, 2017. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Auxagen Inc., St. Louis, Missouri 63132.
authors.forename: Shuan Shian
authors.initials: SS
authors.lastname: Huang
authors.affiliation: Department of Pharmacology, Institute for Drug Evaluation Platform, Development Center for Biotechnology, Taipei, Taiwan.
authors.forename: I-Hua
authors.initials: IH
authors.lastname: Liu
authors.affiliation: Department of Biological Science, National Sun Yat-Sen University and Doctoral Degree Program in Marine Biotechnology, National Sun Yat-Sen University and Academia Sinica, Kaohsiung, Taiwan.
authors.forename: Chun-Lin
authors.initials: CL
authors.lastname: Chen
authors.affiliation: Department of Pharmacology, Institute for Drug Evaluation Platform, Development Center for Biotechnology, Taipei, Taiwan.
authors.forename: Jia-Ming
authors.initials: JM
authors.lastname: Chang
authors.affiliation: Department of Surgery, Saint Louis University Medical Center, 3635 Vista Ave., St. Louis, Missouri 63110.
authors.forename: Frank E
authors.initials: FE
authors.lastname: Johnson
authors.affiliation: Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Doisy Research Center, 1100 S. Grand Blvd., St. Louis, Missouri 63104.
authors.forename: Jung San
authors.initials: JS
authors.lastname: Huang
mesh_terms: D050197:Atherosclerosis / Q000378:metabolism*; D021941:Caveolae / Q000378:metabolism; D002460:Cell Line; D002784:Cholesterol / Q000494:pharmacology*; D003684:Dehydrocholesterols / Q000494:pharmacology*; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051899:Smad2 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D003684:Dehydrocholesterols; D018125:Receptors, Transforming Growth Factor beta; C497782:SMAD2 protein, human; D051899:Smad2 Protein; D016212:Transforming Growth Factor beta; D002784:Cholesterol; C016705:7-dehydrocholesterol
keywords: 7-DHC; CANONICAL TGF-β SIGNALING; CHOLESTEROL; LIPID RAFTS/CAVEOLAE; NON-LIPID RAFT MICRODOMAINS