Chenodeoxycholic Acid Modulates Bile Acid Synthesis Independent of Fibroblast Growth Factor 19 in Primary Human Hepatocytes.

Helene Johansson,Ewa C. S. Ellis,Carl Jorns,Jonas Nørskov Søndergaard,Claudia Kutter

doi:10.3389/fendo.2020.554922

Abstract

Bile acids (BAs) are detergents essential for intestinal absorption of lipids. Disruption of BA homeostasis can lead to severe liver damage. BA metabolism is therefore under strict regulation by sophisticated feedback mechanisms. The hormone-like protein Fibroblast growth factor 19 (FGF19) is essential for maintaining BA homeostasis by down regulating BA synthesis. Here, the impact of both FGF19 and chenodeoxycholic acid (CDCA) on primary human hepatocytes was investigated and a possible autocrine/paracrine function of FGF19 in regulation of BA synthesis evaluated. Primary human hepatocytes were treated with CDCA, recombinant FGF19 or conditioned medium containing endogenously produced FGF19. RNA sequencing revealed that treatment with CDCA causes deregulation of transcripts involved in BA metabolism, whereas treatment with FGF19 had minor effects. CDCA increased FGF19 mRNA expression within 1 h. We detected secretion of the resulting FGF19 protein into medium, mimicking in vivo observations. Furthermore, medium enriched with endogenously produced FGF19 reduced BA synthesis by down regulating CYP7A1 gene expression. However, following knockdown of FGF19, CDCA still independently decreased BA synthesis, presumably through the regulatory protein small heterodimer partner (SHP). In summary, we show that in primary human hepatocytes CDCA regulates BA synthesis in an FGF19-independent manner.

Highlights

Bile acids (BAs), synthesized from cholesterol by the liver, enter the enterohepatic circulation to function as detergents in the intestine for absorption of dietary lipids
To explain physiological alterations in BA synthesis, we investigated the underlying molecular responses stimulated upon Fibroblast growth factor 19 (FGF19) and chenodeoxycholic acid (CDCA) treatment in primary human hepatocytes
We measured cholesterol 7-alpha hydroxylase (CYP7A1) gene expression levels and cholic acid (CA) concentrations secreted into the cell medium from primary human hepatocytes that were treated with various concentrations of recombinant FGF19 (400– 1,200 pg/ml) or CDCA (3–20 μM) for 6 h or 24 h (Figure 1)

Summary

Introduction

Bile acids (BAs), synthesized from cholesterol by the liver, enter the enterohepatic circulation to function as detergents in the intestine for absorption of dietary lipids. We have previously established circulating levels of FGF19 under physiological conditions and demonstrated that FGF19, unlike BAs, do not display a gradient over the liver [13]. We evaluated the impact of CDCA and recombinant FGF19, within the physiological range of concentrations, on primary human hepatocytes in respect to BA synthesis. We further investigated the effect of conditioned medium with endogenously produced FGF19 on primary human hepatocytes. Differential expression in primary human hepatocytes by RNA sequencing following treatment with CDCA, recombinant FGF19 or endogenously produced FGF19 was investigated. We demonstrated that CDCA rapidly induced FGF19 in primary human hepatocytes, and conditioned medium suppressed CYP7A1, CDCA still efficiently downregulated CYP7A1 following FGF19 knockdown.

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