Kristin Schwerbel1, Anne Kamitz1, Natalie Krahmer2, Nicole Hallahan1, Markus Jähnert1, Pascal Gottmann1, Sandra Lebek3, Tanja Schallschmidt3, Danny Arends4, Fabian Schumacher5, Burkhard Kleuser5, Tom Haltenhof6, Florian Heyd6, Sofiya Gancheva7, Karl W Broman8, Michael Roden7, Hans-Georg Joost1, Alexandra Chadt3, Hadi Al-Hasani3, Heike Vogel1, Wenke Jonas9, Annette Schürmann10. 1. Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, D-14558 Nuthetal, Germany; German Center for Diabetes Research, D-85764 München-Neuherberg, Germany. 2. German Center for Diabetes Research, D-85764 München-Neuherberg, Germany; Department of Proteomics and Signal Transduction, Max-Planck Institute of Biochemistry, D-82152 Martinsried, Germany; Institute for Diabetes and Obesity, Helmholtz Zentrum München, D-85764 München-Neuherberg, Germany. 3. German Center for Diabetes Research, D-85764 München-Neuherberg, Germany; Medical Faculty, Institute for Clinical Biochemistry and Pathobiochemistry, German Diabetes Center, Leibniz Center for Diabetes Research at Heinrich Heine University Düsseldorf, D-40225, Düsseldorf, Germany. 4. Animal Breeding Biology and Molecular Genetics, Albrecht Daniel Thaer-Institute of Agricultural and Horticultural Sciences, Humboldt-Universität zu Berlin, D-10117 Berlin, Germany. 5. Institute of Nutritional Science, Department of Toxicology, University of Potsdam, D-14558 Nuthetal, Germany. 6. Department of Biology, Chemistry, Pharmacy, Freie Universität Berlin, Institute of Chemistry and Biochemistry, Laboratory of RNA Biochemistry, D-14195 Berlin, Germany. 7. German Center for Diabetes Research, D-85764 München-Neuherberg, Germany; Institute for Clinical Diabetology, German Diabetes Center, Leibniz Institute for Diabetes Research, Heinrich-Heine University Düsseldorf, D-40225 Düsseldorf, Germany; Department of Endocrinology and Diabetology, Medical Faculty, Heinrich-Heine University, D-40225 Düsseldorf, Germany. 8. Department of Biostatistics and Medical Informatics, University of Wisconsin, WI 53706 Madison, Wisconsin, United States. 9. Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, D-14558 Nuthetal, Germany; German Center for Diabetes Research, D-85764 München-Neuherberg, Germany. Electronic address: wenke.jonas@dife.de. 10. Department of Experimental Diabetology, German Institute of Human Nutrition Potsdam-Rehbruecke, D-14558 Nuthetal, Germany; German Center for Diabetes Research, D-85764 München-Neuherberg, Germany; University of Potsdam, Institute of Nutritional Sciences, D-14558 Nuthetal, Germany. Electronic address: schuermann@dife.de.
Abstract
BACKGROUND & AIMS: Currently, only a few genetic variants explain the heritability of fatty liver disease. Quantitative trait loci (QTL) analysis of mouse strains has identified the susceptibility locus Ltg/NZO (liver triglycerides from New Zealand obese [NZO] alleles) on chromosome 18 as associating with increased hepatic triglycerides. Herein, we aimed to identify genomic variants responsible for this association. METHODS: Recombinant congenic mice carrying 5.3 Mbp of Ltg/NZO were fed a high-fat diet and characterized for liver fat. Bioinformatic analysis, mRNA profiles and electrophoretic mobility shift assays were performed to identify genes responsible for the Ltg/NZO phenotype. Candidate genes were manipulated in vivo by injecting specific microRNAs into C57BL/6 mice. Pulldown coupled with mass spectrometry-based proteomics and immunoprecipitation were performed to identify interaction partners of IFGGA2. RESULTS: Through positional cloning, we identified 2 immunity-related GTPases (Ifgga2, Ifgga4) that prevent hepatic lipid storage. Expression of both murine genes and the human orthologue IRGM was significantly lower in fatty livers. Accordingly, liver-specific suppression of either Ifgga2 or Ifgga4 led to a 3-4-fold greater increase in hepatic fat content. In the liver of low-fat diet-fed mice, IFGGA2 localized to endosomes/lysosomes, while on a high-fat diet it associated with lipid droplets. Pulldown experiments and proteomics identified the lipase ATGL as a binding partner of IFGGA2 which was confirmed by co-immunoprecipitation. Both proteins partially co-localized with the autophagic marker LC3B. Ifgga2 suppression in hepatocytes reduced the amount of LC3B-II, whereas overexpression of Ifgga2 increased the association of LC3B with lipid droplets and decreased triglyceride storage. CONCLUSION: IFGGA2 interacts with ATGL and protects against hepatic steatosis, most likely by enhancing the binding of LC3B to lipid droplets. LAY SUMMARY: The genetic basis of non-alcoholic fatty liver disease remains incompletely defined. Herein, we identified members of the immunity-related GTPase family in mice and humans that act as regulators of hepatic fat accumulation, with links to autophagy. Overexpression of the gene Ifgga2 was shown to reduce hepatic lipid storage and could be a therapeutic target for the treatment of fatty liver disease.
BACKGROUND & AIMS: Currently, only a few genetic variants explain the heritability of fatty liver disease. Quantitative trait loci (QTL) analysis of mouse strains has identified the susceptibility locus Ltg/NZO (liver triglycerides from New Zealand obese [NZO] alleles) on chromosome 18 as associating with increased hepatic triglycerides. Herein, we aimed to identify genomic variants responsible for this association. METHODS: Recombinant congenic mice carrying 5.3 Mbp of Ltg/NZO were fed a high-fat diet and characterized for liver fat. Bioinformatic analysis, mRNA profiles and electrophoretic mobility shift assays were performed to identify genes responsible for the Ltg/NZO phenotype. Candidate genes were manipulated in vivo by injecting specific microRNAs into C57BL/6 mice. Pulldown coupled with mass spectrometry-based proteomics and immunoprecipitation were performed to identify interaction partners of IFGGA2. RESULTS: Through positional cloning, we identified 2 immunity-related GTPases (Ifgga2, Ifgga4) that prevent hepatic lipid storage. Expression of both murine genes and the human orthologue IRGM was significantly lower in fatty livers. Accordingly, liver-specific suppression of either Ifgga2 or Ifgga4 led to a 3-4-fold greater increase in hepatic fat content. In the liver of low-fat diet-fed mice, IFGGA2 localized to endosomes/lysosomes, while on a high-fat diet it associated with lipid droplets. Pulldown experiments and proteomics identified the lipaseATGL as a binding partner of IFGGA2 which was confirmed by co-immunoprecipitation. Both proteins partially co-localized with the autophagic marker LC3B. Ifgga2 suppression in hepatocytes reduced the amount of LC3B-II, whereas overexpression of Ifgga2 increased the association of LC3B with lipid droplets and decreased triglyceride storage. CONCLUSION:IFGGA2 interacts with ATGL and protects against hepatic steatosis, most likely by enhancing the binding of LC3B to lipid droplets. LAY SUMMARY: The genetic basis of non-alcoholic fatty liver disease remains incompletely defined. Herein, we identified members of the immunity-related GTPase family in mice and humans that act as regulators of hepatic fat accumulation, with links to autophagy. Overexpression of the gene Ifgga2 was shown to reduce hepatic lipid storage and could be a therapeutic target for the treatment of fatty liver disease.
Authors: Chrysi Koliaki; Julia Szendroedi; Kirti Kaul; Tomas Jelenik; Peter Nowotny; Frank Jankowiak; Christian Herder; Maren Carstensen; Markus Krausch; Wolfram Trudo Knoefel; Matthias Schlensak; Michael Roden Journal: Cell Metab Date: 2015-05-05 Impact factor: 27.287
Authors: Anthony Mathelier; Xiaobei Zhao; Allen W Zhang; François Parcy; Rebecca Worsley-Hunt; David J Arenillas; Sorana Buchman; Chih-yu Chen; Alice Chou; Hans Ienasescu; Jonathan Lim; Casper Shyr; Ge Tan; Michelle Zhou; Boris Lenhard; Albin Sandelin; Wyeth W Wasserman Journal: Nucleic Acids Res Date: 2013-11-04 Impact factor: 16.971