Disrupted Murine Gut-to-Human Liver Signaling Alters Bile Acid Homeostasis in Humanized Mouse Liver Models

Abstract

The humanized liver mouse model is being exploited increasingly for human drug metabolism studies. However, its model stability, intercommunication between human hepatocytes and mouse nonparenchymal cells in liver and murine intestine, and changes in extrahepatic transporter and enzyme expressions have not been investigated. We examined these issues in FRGN [fumarylacetoacetate hydrolase (Fah-/-), recombination activating gene 2 (Rag2-/-), and interleukin 2 receptor subunit gamma (IL-2rg -/-) triple knockout] on nonobese diabetic (NOD) background] and chimeric mice: mFRGN and hFRGN (repopulated with mouse or human hepatocytes, respectively). hFRGN mice showed markedly higher levels of liver cholesterol, biliary bilirubin, and bile acids (liver, bile, and plasma; mainly human forms, but also murine bile acids) but lower transforming growth factor beta receptor 2 (TGFBR2) mRNA expression levels (10%) in human hepatocytes and other proliferative markers in mouse nonparenchymal cells (Tgf-β1) and cholangiocytes [plasma membrane-bound, G protein-coupled receptor for bile acids (Tgr5)], suggestive of irregular regeneration processes in hFRGN livers. Changes in gene expression in murine intestine, kidney, and brain of hFRGN mice, in particular, induction of intestinal farnesoid X receptor (Fxr) genes: fibroblast growth factor 15 (Fgf15), mouse ileal bile acid binding protein (Ibabp), small heterodimer partner (Shp), and the organic solute transporter alpha (Ostα), were observed. Proteomics revealed persistence of remnant murine proteins (cyotchrome P450 7α-hydroxylase (Cyp7a1) and other enzymes and transporters) in hFRGN livers and suggest the likelihood of mouse activity. When compared with normal human liver tissue, hFRGN livers showed lower SHP mRNA and higher CYP7A1 (300%) protein expression, consequences of tβ- and tα-muricholic acid-mediated inhibition of the FXR-SHP cascade and miscommunication between intestinal Fgf15 and human liver fibroblast growth factor receptor 4 (FGFR4), as confirmed by the unchanged hepatic pERK/total ERK ratio. Dysregulation of hepatocyte proliferation and bile acid homeostasis in hFRGN livers led to hepatotoxicity, gallbladder distension, liver deformity, and other extrahepatic changes, making questionable the use of the preparation for drug metabolism studies.