ORMDL proteins regulate ceramide levels during sterile inflammation.
The bioactive sphingolipid metabolite, ceramide, regulates physiological processes important for inflammation and elevated levels of ceramide have been implicated in IL-1-mediated events. Although much has been learned about ceramide generation by activation of sphingomyelinases in response to IL-1, the contribution of the de novo pathway is not completely understood. Because yeast ORM1 and ORM2 proteins negatively regulate ceramide levels through inhibition of serine palmitoyltransferase, the first committed step in ceramide biosynthesis, we examined the functions of individual mammalian ORM orthologs, ORM (yeast)-like (ORMDL)1-3, in regulation of ceramide levels. In HepG2 liver cells, downregulation of ORMDL3 markedly increased the ceramide precursors, dihydrosphingosine and dihydroceramide, primarily from de novo biosynthesis based on [U-(13)C]palmitate incorporation into base-labeled and dual-labeled dihydroceramides, whereas downregulation of each isoform increased dihydroceramides [(13)C]labeled in only the amide-linked fatty acid. IL-1 and the IL-6 family cytokine, oncostatin M, increased dihydroceramide and ceramide levels in HepG2 cells and concomitantly decreased ORMDL proteins. Moreover, during irritant-induced sterile inflammation in mice leading to induction of the acute-phase response, which is dependent on IL-1, expression of ORMDL proteins in the liver was strongly downregulated and accompanied by increased ceramide levels in the liver and accumulation in the blood. Together, our results suggest that ORMDLs may be involved in regulation of ceramides during IL-1-mediated sterile inflammation.
School of Pharmacy, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
Lin
L
Cai
Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
Clement
C
Oyeniran
Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
Debolina D
DD
Biswas
Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
Jeremy
J
Allegood
Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
Sheldon
S
Milstien
Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
Tomasz
T
Kordula
Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
Michael
M
Maceyka
Department of Biochemistry and Molecular Biology and the Massey Cancer Center, Virginia Commonwealth University School of Medicine, Richmond, VA 23298 sarah.spiegel@vcuhealth.org.
Sarah
S
Spiegel
D000818:Animals; D002518:Ceramides / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D056945:Hep G2 Cells; D006801:Humans; D007249:Inflammation / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology*; D008810:Mice, Inbred C57BL
D002518:Ceramides; D016207:Cytokines; D008565:Membrane Proteins; C464259:ORMDL1 protein, human; C464279:ORMDL2 protein, human; C464399:ORMDL3 protein, human
ORM-like protein; ceramide synthase; serine palmitoyltransferase; sphingolipids