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Gastroenterology. 2015 Sep;149(3):728-40.e15. doi: 10.1053/j.gastro.2015.05.043. Epub 2015 May 29.

Fibroblast Growth Factor Signaling Controls Liver Size in Mice With Humanized Livers.

Author information

  • 1Department of Medicine, Division of Gastroenterology and Hepatology, Oregon Health & Science Center, Portland, Oregon; Oregon Stem Cell Center, Oregon Health & Science Center, Portland, Oregon. Electronic address: nauglers@ohsu.edu.
  • 2Department of Cell, Developmental, and Cancer Biology, Oregon Health & Science Center, Portland, Oregon.
  • 3OHSU Transgenic Mouse Models Shared Resource, Oregon Health & Science Center, Portland, Oregon.
  • 4Department of Hematology and Oncology, Oregon Health & Science Center, Portland, Oregon.
  • 5Department of Pediatrics, Papé Family Pediatric Research Institute, Oregon Health & Science Center, Portland, Oregon.
  • 6Oregon Stem Cell Center, Oregon Health & Science Center, Portland, Oregon.
  • 7Department of Medicine, Division of Gastroenterology and Hepatology, Oregon Health & Science Center, Portland, Oregon.
  • 8Oregon Stem Cell Center, Oregon Health & Science Center, Portland, Oregon; Department of Hematology and Oncology, Oregon Health & Science Center, Portland, Oregon.

Abstract

BACKGROUND & AIMS:

The ratio of liver size to body weight (hepatostat) is tightly controlled, but little is known about how the physiologic functions of the liver help determine its size. Livers of mice repopulated with human hepatocytes (humanized livers) grow to larger than normal; the human hepatocytes do not recognize the fibroblast growth factor (FGF)-15 produced by mouse intestine. This results in up-regulation of bile acid synthesis in the human hepatocytes and enlargement of the bile acid pool. We investigated whether abnormal bile acid signaling affects the hepatostat in mice.

METHODS:

We crossed Fah(-/-), Rag2(-/-), Il2r(-/-) mice with nonobese diabetic mice to create FRGN mice, whose livers can be fully repopulated with human hepatocytes. We inserted the gene for human FGF19 (ortholog to mouse Fgf15), including regulatory sequences, into the FRGN mice to create FRGN19(+) mice. Livers of FRGN19(+) mice and their FRGN littermates were fully repopulated with human hepatocytes. Liver tissues were collected and bile acid pool sizes and RNA sequences were analyzed and compared with those of mice without humanized livers (controls).

RESULTS:

Livers were larger in FRGN mice with humanized livers (13% of body weight), compared with control FRGN mice; they also had much larger bile acid pools and aberrant bile acid signaling. Livers from FRGN19(+) normalized to 7.8% of body weight, and their bile acid pool and signaling more closely resembled that of control FRGN19(+) mice. RNA sequence analysis showed activation of the Hippo pathway, and immunohistochemical and transcription analyses revealed increased hepatocyte proliferation, but not apoptosis, in the enlarged humanized livers of FRGN mice. Cell sorting experiments showed that although healthy human liver does not produce FGF19, nonparenchymal cells from cholestatic livers produce FGF19.

CONCLUSIONS:

In mice with humanized livers, expression of an FGF19 transgene corrects bile acid signaling defects, resulting in normalization of bile acid synthesis, the bile acid pool, and liver size. These findings indicate that liver size is, in part, regulated by the size of the bile acid pool that the liver must circulate.

Copyright © 2015 AGA Institute. Published by Elsevier Inc. All rights reserved.

KEYWORDS:

CYP7A; Mouse Model; Regeneration; Signal Transduction

PMID:
26028580
[PubMed - indexed for MEDLINE]
PMCID:
PMC4550566
[Available on 2016-09-01]
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