Bile Acid Homeostasis in a Cholesterol 7α‐Hydroxylase and Sterol 27‐Hydroxylase Double Knockout Mouse Model

Abstract

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.

Maternal exercise conveys protection against NAFLD in the offspring via hepatic metabolic programming

“…4 C). Of note, the most regulated protein among the differentially expressed proteins was CYP7A1 (Cholesterol 7 alpha-hydroxylase), a key regulator of hepatic cholesterol and bile acid metabolism 15 , 16 . CYP7A1 protein expression levels were significantly increased in INT-offspring (Fig.…”

Cholesterol-binding translocator protein TSPO regulates steatosis and bile acid synthesis in nonalcoholic fatty liver disease

“…CYP7A1 and CYP27A1, a cholesterol 7α-hydroxylase responsible for the classic pathway and a steroid 27-hydroxylase responsible for the alternative pathway for BA synthesis, were both suppressed in the KO MCD liver compared with the WT MCD liver. The BA level was reduced by 66.7% and 73% in Cyp7a1 −/− and Cyp27a1 −/− mice and even more in double-knockout ( Cyp7a1 −/− ; Cyp27a1 −/− ) mice ( Rizzolo et al., 2019 ), indicative of the critical roles of these two hydroxylases in the BA metabolism. In addition, levels of FXR, a negative regulator of BA production and a BA receptor, were significantly increased in KO MCD rats compared with WT MCD.…”

Role of Farnesoid X Receptor in the Pathogenesis of Respiratory Diseases

“…FXR was first widely recognized for regulating the bile acid pathway in the liver and intestines. Previous studies have demonstrated that FXR regulates the bile acid synthesis through two main pathways [ 32 – 34 ]. In the classical pathway, CYP7A1 is a liver-specific microsomal cytochrome P450 enzyme, which is a rate-limiting enzyme in the classic pathway of bile acid synthesis.…”