title: Transient Hepatic Overexpression of Insulin-Like Growth Factor 2 Induces Free Cholesterol and Lipid Droplet Formation.
abstract: Although insulin-like growth factor 2 (IGF2) has been reported to be overexpressed in steatosis and steatohepatitis, a causal role of IGF2 in steatosis development remains elusive. Aim of our study was to decipher the role of IGF2 in steatosis development. Hydrodynamic gene delivery of an Igf2 plasmid used for transient Igf2 overexpression employing codon-optimized plasmid DNA resulted in a strong induction of hepatic Igf2 expression. The exogenously delivered Igf2 had no influence on endogenous Igf2 expression. The downstream kinase AKT was activated in Igf2 animals. Decreased ALT levels mirrored the cytoprotective effect of IGF2. Serum cholesterol was increased and sulfo-phospho-vanillin colorimetric assay confirmed lipid accumulation in Igf2-livers while no signs of inflammation were observed. Interestingly, hepatic cholesterol and phospholipids, determined by thin layer chromatography, and free cholesterol by filipin staining, were specifically increased. Lipid droplet (LD) size was not changed, but their number was significantly elevated. Furthermore, free cholesterol, which can be stored in LDs and has been reported to be critical for steatosis progression, was elevated in Igf2 overexpressing mice. Accordingly, Hmgcr/HmgCoAR was upregulated. To have a closer look at de novo lipid synthesis we investigated expression of the lipogenic transcription factor SREBF1 and its target genes. SREBF1 was induced and also SREBF1 target genes were slightly upregulated. Interestingly, the expression of Cpt1a, which is responsible for mitochondrial fatty acid oxidation, was induced. Hepatic IGF2 expression induces a fatty liver, characterized by increased cholesterol and phospholipids leading to accumulation of LDs. We therefore suggest a causal role for IGF2 in hepatic lipid accumulation.
authors.affiliation: Department of Pharmacy, Pharmaceutical Biology, Saarland University Saarbrücken, Germany.
authors.forename: Sonja M
authors.initials: SM
authors.lastname: Kessler
authors.affiliation: Department of Pharmacy, Pharmaceutical Biology, Saarland University Saarbrücken, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Laggai
authors.affiliation: Inflammation Research Center, VIBGhent, Belgium; Department of Biomedical Molecular Biology, Ghent UniversityGhent, Belgium.
authors.forename: Elien
authors.initials: E
authors.lastname: Van Wonterg
authors.affiliation: Department of Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland, Helmholtz Centre for Infection Research and Pharmaceutical Biotechnology, Saarland University Saarbrücken, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Gemperlein
authors.affiliation: Department of Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland, Helmholtz Centre for Infection Research and Pharmaceutical Biotechnology, Saarland University Saarbrücken, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Müller
authors.affiliation: Institute of Pathology, Medical University of Graz Graz, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Haybaeck
authors.affiliation: Inflammation Research Center, VIBGhent, Belgium; Department of Biomedical Molecular Biology, Ghent UniversityGhent, Belgium.
authors.forename: Roosmarijn E
authors.initials: RE
authors.lastname: Vandenbroucke
authors.affiliation: Department of Pharmaceutical Chemistry, University of Vienna Vienna, Austria.
authors.forename: Manfred
authors.initials: M
authors.lastname: Ogris
authors.affiliation: Inflammation Research Center, VIBGhent, Belgium; Department of Biomedical Molecular Biology, Ghent UniversityGhent, Belgium.
authors.forename: Claude
authors.initials: C
authors.lastname: Libert
authors.affiliation: Department of Pharmacy, Pharmaceutical Biology, Saarland University Saarbrücken, Germany.
authors.forename: Alexandra K
authors.initials: AK
authors.lastname: Kiemer
keywords: NASH; fatty liver; hydrodynamic gene delivery; insulin-like growth factor 2 (IGF2); lipid droplets