Non-alcoholic steatohepatitis (NASH) is a form of non-alcoholic fatty liver disease (NAFLD) characterized by steatosis, inflammation, and fibrosis often associated with metabolic syndrome. Fibroblast growth factor 15 (FGF15), an endocrine factor mainly produced in the distal part of small intestine, has emerged to be a critical factor in regulating bile acid homeostasis, energy metabolism, and liver regeneration. We hypothesized that FGF15 alters the development of each of the listed features of NASH. To test this hypothesis, four-week old male Fgf15−/− and their corresponding wild-type (WT) mice were fed either a high fat diet (HFD) or a control chow diet for six months. The results confirmed that HFD feeding for six months in WT mice recapitulated human NASH phenotype, including macrovesicular steatosis, inflammation, and fibrosis. Whereas FGF15 deficiency had no effect on the severity of liver steatosis or inflammation, it was associated with decreased liver fibrosis. Furthermore, FGF15 deficiency resulted in abnormal bile acid homeostasis, increased insulin resistance, increased HFD-induced serum triglycerides, decreased inductions of hepatic cholesterol content by HFD, and altered gene expression of lipid metabolic enzymes. These data suggest that FGF15 improves lipid homeostasis and reduces bile acid synthesis, but promotes fibrosis during the development of NASH.

Farnesoid X receptor (FXR) induces fibroblast growth factor 15 (FGF15; human ortholog FGF19) in the gut to potently inhibit bile acid (BA) synthesis in the liver. FXR activation in hepatic stellate cells (HSCs) reduces liver fibrosis (LF). Fgf15–/– mice develop attenuated LF, but the underlying mechanisms for this protection are unclear. We hypothesized that FGF15/19 functions as a profibrotic mediator or mitogen to HSCs and increased BAs in Fgf15–/– mice leads to enhanced FXR activation in HSCs, subsequently reducing fibrogenesis. In this study, complimentary in vivo and in vitro approaches were used: (1) CCl4‐induced LF model in wild type (WT), Fgf15–/–, and Fgf15 transgenic (TG) mice with BA levels modulated by feeding cholestyramine‐ or cholic acid–containing diets; (2) analysis of primary HSCs isolated from WT and Fgf15–/– mice; and (3) treatment of a human HSC line, LX‐2, with FXR activators and/or recombinant FGF19 protein. The results showed that Fgf15–/– mice had lower basal collagen expression, which was increased by BA sequestration. CCl4 induced fibrosis with similar severity in all genotypes; however, cholestyramine increased fibrosis severity only in Fgf15–/– mice. HSCs from Fgf15–/– mice showed increased FXR activity and reduced expression of profibrotic mediators. In LX‐2 cells, FXR activation increased peroxisome proliferator‐activated receptor gamma activity and reduced proliferation. FGF19 activated both signal transducer and activator of transcription 3 and c‐Jun N‐terminal kinase pathways and reduced nuclear factor kappa‐light‐chain‐enhancer of activated B cells signaling without increasing fibrogenic gene expression or cell proliferation. Conclusion: FGF15/19 does not act as a direct profibrotic mediator or mitogen to HSCs in our models, and the protection against fibrosis by FGF15 deficiency may be mediated through increased BA activation of FXR in HSCs.

Recent studies have investigated the roles of FXR deficiency in the pathogenesis of alcoholic liver disease (ALD). However, the underlined molecular mechanisms remain unclear. In this study, FXR knockout (FXR −/−) and wild-type (WT) mice were subjected to chronic-plus-binge alcohol feeding to study the effect of FXR deficiency on ALD development. The degree of liver injury was greater in FXR −/− mice compared to WT mice. Ethanol feeding enhanced hepatic steatosis in FXR −/− mice, accompanied by decreased mRNA levels of Pparα and Srebp-1c. The expression of Lcn2 was increased by ethanol treatment, despite unchanged expression of pro-inflammatory cytokines Tnfα, II6 and II-1 β. Furthermore, ethanol treatment altered bile acid (BA) homeostasis to a greater extent in FXR −/− mice, as well as serum and hepatic BA pool composition. The mRNA levels of hepatic Cyp7a1 and Shp, as well as intestinal Fgf15, were decreased in WT mice with ethanol feeding, which were further reduced in FXR −/− mice. Levels of both primary and

Bile acids (BAs) are diverse molecules that are synthesized from cholesterol in the liver. The synthesis of BAs has traditionally been shown to occur through two pathways. Cholesterol 7α‐hydroxylase (CYP7A1) performs the initial and rate‐limiting step in the classical pathway, and sterol 27‐hydroxylase (CYP27A1) initiates the hydroxylation of cholesterol in the alternative pathway. While the role of individual BA species as physiological detergents is relatively ubiquitous, their endocrine functions as signaling molecules and roles in disease pathogenesis have been emerging to be BA species–specific. In order to better understand the pharmacologic and toxicologic roles of individual BA species in an in vivo model, we created cholesterol 7α‐hydroxylase (Cyp7a1) and sterol 27‐hydroxylase (Cyp27a1) double knockout (DKO) mice by cross‐breeding single knockout mice (Cyp7a1–/– and Cyp27a1–/–). BA profiling and quantification by liquid chromatography–mass spectrometry of serum, gallbladder, liver, small intestine, and colon of wild‐type, Cyp7a1–/–, Cyp27a1–/–, and DKO mice showed that DKO mice exhibited a reduction of BAs in the plasma (45.9%), liver (60.2%), gallbladder (76.3%), small intestine (88.7%), and colon (93.6%), while maintaining a similar BA pool composition compared to wild‐type mice. The function of the farnesoid X receptor (FXR) in DKO mice was lower, revealed by decreased mRNA expression of well‐known FXR target genes, hepatic small heterodimer partner, and ileal fibroblast growth factor 15. However, response to FXR synthetic ligands was maintained in DKO mice as treatment with GW4064 resulted in similar changes in gene expression in all strains of mice. Conclusion: We provide a useful tool for studying the role of individual BAs in vivo; DKO mice have a significantly reduced BA pool, have a similar BA profile, and maintained response to FXR activation.