Aryl Hydrocarbon Receptor-Mediated Induction of Stearoyl-CoA Desaturase 1 Alters Hepatic Fatty Acid Composition in TCDD-Elicited Steatosis

• Published in: Toxicological sciences 2011-12, Vol.124 (2), p.299-310
• Main Authors: Angrish, Michelle M., Jones, A.D., Harkema, Jack R., Zacharewski, Timothy R.
• Format: Article
• Language: English
• Subjects: Animals; Blotting, Western; Chemical and Drug Induced Liver Injury - genetics; Chemical and Drug Induced Liver Injury - metabolism; Endocrine Toxicology; Fatty Acids - metabolism; Fatty Liver - genetics; Fatty Liver - metabolism; Gas Chromatography-Mass Spectrometry; Liver - drug effects; Liver - metabolism; Mice; Mice, Knockout; Polychlorinated Dibenzodioxins - toxicity; Principal Component Analysis; Real-Time Polymerase Chain Reaction; Receptors, Aryl Hydrocarbon - metabolism; Response Elements - genetics; Stearoyl-CoA Desaturase - biosynthesis; Stearoyl-CoA Desaturase - genetics; Triglycerides - metabolism
• ISSN: 1096-6080; 1096-0929
• DOI: 10.1093/toxsci/kfr226

2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD) induces hepatic dyslipidemia mediated by the aryl hydrocarbon receptor (AhR). Stearoyl-CoA desaturase 1 (Scd1) performs the rate-limiting step in monounsaturated fatty acid (MUFA) synthesis, desaturating 16:0 and 18:0 into 16:1n7 and 18:1n9, respectively. To further examine the role of Scd1 in TCDD-induced hepatotoxicity, comparative studies were performed in Scd1+/+ and Scd1−/ − mice treated with 30 μg/kg TCDD. TCDD induced Scd1 activity, protein, and messenger RNA (mRNA) levels approximately twofold. In Scd1+/+ mice, hepatic effects were marked by increased vacuolization and inflammation and a 3.5-fold increase in serum alanine aminotransferase (ALT) levels. Hepatic triglycerides (TRGs) were induced 3.9-fold and lipid profiling by gas chromatography-mass spectroscopy measured a 1.9-fold increase in fatty acid (FA) levels, consistent with the induction of lipid transport genes. Induction of Scd1 altered FA composition by decreasing saturated fatty acid (SFA) molar ratios 8% and increasing MUFA molar ratios 9%. Furthermore, ChIP-chip analysis revealed AhR enrichment (up to 5.7-fold), and computational analysis identified 16 putative functional dioxin response elements (DREs) within Scd1 genomic loci. Band shift assays confirmed AhR binding with select DREs. In Scd1−/ − mice, TCDD induced minimal hepatic vacuolization and inflammation, while serum ALT levels remained unchanged. Although Scd1 deficiency attenuated TCDD-induced TRG accumulation, overall FA levels remained unchanged compared with Scd1+/+ mice. In Scd1−/ − mice, TCDD induced SFA ratios 8%, reduced MUFA ratios 13%, and induced polyunsaturated fatty acid ratios 5% relative to treated Scd1+/+ mice. Collectively, these results suggest that AhR regulation of Scd1 not only alters lipid composition but also contributes to the hepatotoxicity of TCDD.