A human-like bile acid pool induced by deletion of hepatic Cyp2c70 modulates effects of FXR activation in mice
Supplementary key words liver humanized mouse model cholesterol transintestinal cholesterol excretion cytochrome P450 family 2 subfamily c polypeptide 70 Bile acids (BAs) are amphipathic steroids, produced exclusively by the liver from cholesterol, that act as soaps to facilitate solubilization and absorption of dietary cholesterol, fats, and fat-soluble vitamins in the small intestine (1). Whereas cholesterol is virtually not absorbed in the absence of BAs, fatty acid absorption decreases from 97% to 70% when no BAs are present within the intestinal lumen (2). The capacity to solubilize cholesterol, but also other lipids, in the intestine is largely determined by the size and composition of the circulating BA pool that consists of several species differing in number, position, and orientation of hydroxyl groups (Table BAs also act as signaling molecules by activating the nuclear farnesoid X receptor (FXR; NR1H4) (3, 4) and the membrane-bound Takeda Abstract Bile acids (BAs) facilitate intestinal absorption of lipid-soluble nutrients and modulate various metabolic pathways through the farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5. These receptors are targets for therapy in cholestatic and metabolic diseases. However, dissimilarities in BA metabolism between humans and mice complicate translation of preclinical data. Cytochrome P450 family 2 subfamily c polypeptide 70 (CYP2C70) was recently proposed to catalyze the formation of rodent-specific muricholic acids (MCAs). With CRISPR/Cas9-mediated somatic genome editing, we generated an acute hepatic Cyp2c70 knockout mouse model (Cyp2c70 ako ) to clarify the role of CYP2C70 in BA metabolism in vivo and evaluate whether its activity modulates effects of pharmacologic FXR activation on cholesterol homeostasis. In Cyp2c70 ako mice, chenodeoxycholic acid (CDCA) increased at the expense of MCA, resulting in a more hydrophobic human-like BA pool. Tracer studies demonstrated that, in vivo, CYP2C70 catalyzes the formation of MCA primarily by sequential 6-hydroxylation and C7-epimerization of CDCA, generating MCA as an intermediate metabolite. Physiologically, the humanized BA composition in Cyp2c70 ako mice blunted the stimulation of fecal cholesterol disposal in response to FXR activation compared with WT mice, predominantly due to reduced stimulation of transintestinal cholesterol excretion. Thus, deletion of hepatic Cyp2c70 in adult mice translates into a human-like BA pool composition and impacts the response to pharmacologic FXR activation. This Cyp2c70 ako mouse model may be a useful tool for future studies of BA signaling and metabolism that informs human disease development and treatment.-