title: ORMDL3 expression levels have no influence on the activity of serine palmitoyltransferase.
abstract: ORMDL proteins are believed to be negative regulators of serine palmitoyltransferase (SPT), which catalyzes the first and rate limiting step in sphingolipid (SL) de novo synthesis. Several single-nucleotide polymorphisms (SNPs) that are close to the ORMDL3 locus have been reported to increase ORMDL3 expression and to be associated with an elevated risk for early childhood asthma; however, the direct effect of ORMDL3 expression on SPT activity and its link to asthma remains elusive. In this study, we investigated whether ORMDL3 expression is associated with changes in SPT activity and total SL levels. Ormdl3-knockout (Ormdl3-/-) and transgenic (Ormdl3Tg/wt) mice were generated to study the effect of ORMDL3 on total SL levels in plasma and tissues. Cellular SPT activity was measured in mouse embryonic fibroblasts from Ormdl3-/-mice, as well as in HEK293 cells in which ORMDL3 was overexpressed and silenced. Furthermore, we analyzed the association of the reported ORMDL3 asthma SNPs with plasma sphingoid bases in a population-based cohort of 971 individuals. Total C18-long chain bases were not significantly altered in the plasma and tissues of Ormdl3-/-mice, whereas C18-sphinganine showed a small and significant increase in plasma, lung, and liver tissues. Mouse embryonic fibroblast cells from Ormdl3-/-mice did not show an altered SPT activity compared with Ormdl3+/-and Ormdl3+/+mice. Overexpression or knockdown of ORMDL3 in HEK293 cells did not alter SPT activity; however, parallel knockdown of all 3 ORMDL isoforms increased enzyme activity significantly. A significant association of the annotated ORMDL3 asthma SNPs with plasma long-chain sphingoid base levels could not be confirmed. ORMDL3 expression levels seem not to be directly associated with changes in SPT activity. ORMDL3 might influence de novo sphingolipid metabolism downstream of SPT.-Zhakupova, A., Debeuf, N., Krols, M., Toussaint, W., Vanhoutte, L., Alecu, I., Kutalik, Z., Vollenweider, P., Ernst, D., von Eckardstein, A., Lambrecht, B. N., Janssens, S., Hornemann, T. ORMDL3 expression levels have no influence on the activity of serine palmitoyltransferase.
authors.affiliation: Institute of Clinical Chemistry, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
authors.forename: Assem
authors.initials: A
authors.lastname: Zhakupova
authors.affiliation: Laboratory of Immunoregulation and Mucosal Immunology, Vlaams Instituut voor Biotechnologie (VIB) Inflammation Research Center, Ghent, Belgium.|Department of Internal Medicine, Ghent University, Ghent, Belgium.
authors.forename: Nincy
authors.initials: N
authors.lastname: Debeuf
authors.affiliation: Department of Molecular Genetics, VIB Antwerp University, Antwerp, Belgium.
authors.forename: Michiel
authors.initials: M
authors.lastname: Krols
authors.affiliation: Laboratory of Immunoregulation and Mucosal Immunology, Vlaams Instituut voor Biotechnologie (VIB) Inflammation Research Center, Ghent, Belgium.
authors.forename: Wendy
authors.initials: W
authors.lastname: Toussaint
authors.affiliation: Laboratory of Immunoregulation and Mucosal Immunology, Vlaams Instituut voor Biotechnologie (VIB) Inflammation Research Center, Ghent, Belgium.
authors.forename: Leen
authors.initials: L
authors.lastname: Vanhoutte
authors.affiliation: Institute of Clinical Chemistry, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
authors.forename: Irina
authors.initials: I
authors.lastname: Alecu
authors.affiliation: Institute of Social and Preventive Medicine, Centre Hospitalier Universitaire Vaudois, University of Lausanne, Lausanne, Switzerland.|Swiss Institute of Bioinformatics, Lausanne, Switzerland.
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Kutalik
authors.affiliation: Department of Medicine, Internal Medicine, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland; and.
authors.forename: Peter
authors.initials: P
authors.lastname: Vollenweider
authors.affiliation: Institute of Clinical Chemistry, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
authors.forename: Daniela
authors.initials: D
authors.lastname: Ernst
authors.affiliation: Institute of Clinical Chemistry, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
authors.forename: Arnold
authors.initials: A
authors.lastname: von Eckardstein
authors.affiliation: Laboratory of Immunoregulation and Mucosal Immunology, Vlaams Instituut voor Biotechnologie (VIB) Inflammation Research Center, Ghent, Belgium.|Department of Internal Medicine, Ghent University, Ghent, Belgium.|Department of Pulmonary Medicine, Erasmus Medical Center, Rotterdam, The Netherlands.
authors.forename: Bart N
authors.initials: BN
authors.lastname: Lambrecht
authors.affiliation: Laboratory of Immunoregulation and Mucosal Immunology, Vlaams Instituut voor Biotechnologie (VIB) Inflammation Research Center, Ghent, Belgium.|Department of Internal Medicine, Ghent University, Ghent, Belgium.
authors.forename: Sophie
authors.initials: S
authors.lastname: Janssens
authors.affiliation: Institute of Clinical Chemistry, University Hospital Zurich, University of Zurich, Zurich, Switzerland; thorsten.hornemann@usz.ch.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Hornemann
mesh_terms: D000818:Animals; D001249:Asthma / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D050356:Lipid Metabolism / Q000502:physiology*; D008168:Lung / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D018345:Mice, Knockout; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D020033:Protein Isoforms / Q000378:metabolism*; D051102:Serine C-Palmitoyltransferase / Q000378:metabolism*; D013107:Sphingolipids / Q000097:blood
chemical_list: D008565:Membrane Proteins; C464399:ORMDL3 protein, human; C583840:ORMDL3 protein, mouse; D020033:Protein Isoforms; D013107:Sphingolipids; D051102:Serine C-Palmitoyltransferase
keywords: asthma; ceramide; metabolism; sphinganine; sphingolipid