title: Bone morphogenetic protein-binding endothelial regulator of liver sinusoidal endothelial cells induces iron overload in a fatty liver mouse model.
abstract: BACKGROUND
  Non-alcoholic fatty liver disease (NAFLD) is frequently accompanied by iron overload. However, because of the complex hepcidin-regulating molecules, the molecular mechanism underlying iron overload remains unknown. To identify the key molecule involved in NAFLD-associated iron dysregulation, we performed whole-RNA sequencing on the livers of obese mice.
  
  
  METHODS
  Male C57BL/6 mice were fed a regular or high-fat diet for 16 or 48 weeks. Internal iron was evaluated by plasma iron, ferritin or hepatic iron content. Whole-RNA sequencing was performed by transcriptome analysis using semiconductor high-throughput sequencer. Mouse liver tissues or isolated hepatocytes and sinusoidal endothelial cells were used to assess the expression of iron-regulating molecules.
  
  
  RESULTS
  Mice fed a high-fat diet for 16 weeks showed excess iron accumulation. Longer exposure to a high-fat diet increased hepatic fibrosis and intrahepatic iron accumulation. A pathway analysis of the sequencing data showed that several inflammatory pathways, including bone morphogenetic protein (BMP)-SMAD signaling, were significantly affected. Sequencing analysis showed 2314 altered genes, including decreased mRNA expression of the hepcidin-coding gene Hamp. Hepcidin protein expression and SMAD phosphorylation, which induces Hamp, were found to be reduced. The expression of BMP-binding endothelial regulator (BMPER), which inhibits BMP-SMAD signaling by binding BMP extracellularly, was up-regulated in fatty livers. In addition, immunohistochemical and cell isolation analyses showed that BMPER was primarily expressed in the liver sinusoidal endothelial cells (LSECs) rather than hepatocytes.
  
  
  CONCLUSIONS
  BMPER secretion by LSECs inhibits BMP-SMAD signaling in hepatocytes and further reduces hepcidin protein expression. These intrahepatic molecular interactions suggest a novel molecular basis of iron overload in NAFLD.
authors.affiliation: Division of Gastroenterology and Hematology/Oncology, Department of Medicine, Asahikawa Medical University, 2-1-1-1 Midorigaoka Higashi, Asahikawa, Hokkaido, 078-8510, Japan. taku-has@asahikawa-med.ac.jp.
authors.forename: Takumu
authors.initials: T
authors.lastname: Hasebe
authors.affiliation: Department of Legal Medicine, Asahikawa Medical University, Asahikawa, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Tanaka
authors.affiliation: Division of Gastroenterology and Hematology/Oncology, Department of Medicine, Asahikawa Medical University, 2-1-1-1 Midorigaoka Higashi, Asahikawa, Hokkaido, 078-8510, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Sawada
authors.affiliation: Division of Gastroenterology and Hematology/Oncology, Department of Medicine, Asahikawa Medical University, 2-1-1-1 Midorigaoka Higashi, Asahikawa, Hokkaido, 078-8510, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Nakajima
authors.affiliation: Department of Gastroenterology, International University of Health and Welfare Hospital, Nasushiobara, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Ohtake
authors.affiliation: Division of Gastroenterology and Hematology/Oncology, Department of Medicine, Asahikawa Medical University, 2-1-1-1 Midorigaoka Higashi, Asahikawa, Hokkaido, 078-8510, Japan.
authors.forename: Mikihiro
authors.initials: M
authors.lastname: Fujiya
authors.affiliation: Department of Gastroenterology, International University of Health and Welfare Hospital, Nasushiobara, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kohgo
mesh_terms: D000818:Animals; D055418:Bone Morphogenetic Protein 6 / Q000097:blood; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D059305:Diet, High-Fat / Q000009:adverse effects; D004195:Disease Models, Animal; D004730:Endothelium, Vascular / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D022781:Hepatocytes / Q000378:metabolism; D064451:Hepcidins / Q000235:genetics / Q000378:metabolism; D019190:Iron Overload / Q000209:etiology* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000378:metabolism / Q000473:pathology; D008297:Male; D008810:Mice, Inbred C57BL; D065626:Non-alcoholic Fatty Liver Disease / Q000150:complications* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009765:Obesity / Q000150:complications / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D051785:Smad Proteins / Q000378:metabolism
chemical_list: C525817:Bmp6 protein, mouse; D055418:Bone Morphogenetic Protein 6; D002352:Carrier Proteins; D064451:Hepcidins; D051785:Smad Proteins; C517553:crossveinless 2 protein, mouse
keywords: Hepcidin; Iron metabolism; Non-alcoholic fatty liver disease; Signal regulation; Whole-RNA sequencing