title: Moderate activation of IKK2-NF-kB in unstressed adult mouse liver induces cytoprotective genes and lipogenesis without apparent signs of inflammation or fibrosis.
abstract: BACKGROUND
  The NF-kB signaling, regulated by IKK1-p52/RelB and IKK2-p65, is activated by various stresses to protect or damage the liver, in context-specific manners. Two previous studies of liver-specific expression of constitutive active IKK2 (IKK2ca) showed that strong activation of IKK2-NF-kB in mouse livers caused inflammation, insulin resistance, and/or fibrosis. The purpose of this study was to understand how moderate activation of IKK2-NF-kB in adult mouse livers alters hepatic gene expression and pathophysiology.
  
  
  METHODS
  We generated mice with adult hepatocyte-specific activation of Ikk2 (Liv-Ikk2ca) using Alb-cre mice and Ikk2ca Rosa26 knockin mice in which a moderate expression of Ikk2ca transgene was driven by the endogenous Rosa26 promoter.
  
  
  RESULTS
  Surprisingly, compared to wild-type mice, adult male Liv-Ikk2ca mice had higher hepatic mRNA expression of Ikk2 and classical NF-kB targets (e.g. Lcn2 and A20), as well as IKK1, NIK, and RelB, but no changes in markers of inflammation or fibrosis. Blood levels of IL-6 and MCP-1 remained unchanged, and histology analysis showed a lack of injury or infiltration of inflammatory cells in livers of Liv-Ikk2ca mice. Moreover, Liv-Ikk2ca mice had lower mRNA expression of prooxidative enzymes Cyp2e1 and Cyp4a14, higher expression of antioxidative enzymes Sod2, Gpx1, and Nqo1, without changes in key enzymes for fatty acid oxidation, glucose utilization, or gluconeogenesis. In parallel, Liv-Ikk2ca mice and wild-type mice had similar levels of hepatic reduced glutathione, endogenous reactive oxygen species, and lipid peroxidation. Additionally, Liv-Ikk2ca mice had higher Cyp3a11 without down-regulation of most drug processing genes. Regarding nuclear proteins of NF-kB subunits, Liv-Ikk2ca mice had moderately higher p65 and p50 but much higher RelB. Results of ChIP-qPCR showed that the binding of p50 to multiple NF-kB-target genes was markedly increased in Liv-Ikk2ca mice. Additionally, Liv-Ikk2ca mice had moderate increase in triglycerides in liver, which was associated with higher lipogenic factors Pparγ, Lxr, Fasn, Scd1, and CD36.
  
  
  CONCLUSIONS
  In summary, moderate activation of IKK2-NF-kB in unstressed adult mouse hepatocytes produces a cytoprotective gene expression profile and induces lipogenesis without apparent signs of inflammation or fibrosis, likely due to strong activation of the anti-inflammatory IKK1-RelB alternative NF-kB pathway as well as the Lxr.
authors.affiliation: Department of Pharmacology, SUNY Upstate Medical University, 750 E Adams ST, Syracuse, NY, 13210, USA. luh@upstate.edu.
authors.forename: Hong
authors.initials: H
authors.lastname: Lu
authors.affiliation: Department of Pharmacology, SUNY Upstate Medical University, 750 E Adams ST, Syracuse, NY, 13210, USA. Leix@upstate.edu.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Lei
authors.affiliation: Department of Pharmacology, SUNY Upstate Medical University, 750 E Adams ST, Syracuse, NY, 13210, USA. zhangqinghao1982@gmail.com.
authors.forename: Qinghao
authors.initials: Q
authors.lastname: Zhang
mesh_terms: D000818:Animals; D018932:Chemokine CCL2 / Q000097:blood; D019392:Cytochrome P-450 CYP2E1 / Q000235:genetics; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D000072470:Cytochrome P450 Family 4; D019610:Cytoprotection / Q000235:genetics*; D005355:Fibrosis / Q000378:metabolism; D015870:Gene Expression; D022781:Hepatocytes / Q000378:metabolism*; D051550:I-kappa B Kinase / Q000378:metabolism*; D007249:Inflammation; D015850:Interleukin-6 / Q000097:blood; D050155:Lipogenesis; D008099:Liver / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051841:Transcription Factor RelB / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism
chemical_list: C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; C436963:Cyp4a14 protein, mouse; D015850:Interleukin-6; D008565:Membrane Proteins; D016328:NF-kappa B; D012333:RNA, Messenger; C497594:Relb protein, mouse; D014280:Triglycerides; C577686:interleukin-6, mouse; D051841:Transcription Factor RelB; D003577:Cytochrome P-450 Enzyme System; D019392:Cytochrome P-450 CYP2E1; C496508:Cyp3a11 protein, mouse; D051544:Cytochrome P-450 CYP3A; D000072470:Cytochrome P450 Family 4; D051550:I-kappa B Kinase; C496562:Ikbkb protein, mouse