Background & Aims
The nuclear receptor subfamily 0 group B member 2 (NR0B2, also called SHP) is expressed at high levels in liver and intestine. Postprandial fibroblast growth factor 19 (human FGF19, mouse FGF15) signaling increases the transcriptional activity of SHP. We studied the functions of SHP and FGF19 in intestines of mice, including their regulation of expression of the cholesterol transporter NPC1-like intracellular cholesterol transporter 1 (NPC1L1) and cholesterol absorption.
We performed histologic and biochemical analyses of intestinal tissues from C57BL/6 and SHP-knockout mice and performed RNA-seq analyses to identify genes regulated by SHP. The effects of fasting and refeeding on intestinal expression of NPC1L1 was examined in C57BL/6, SHP-knockout, and FGF15-knockout mice. Mice were given FGF19 daily for 1 week; fractional cholesterol absorption, cholesterol and bile acid (BA) levels, and composition of BAs were measured. Intestinal organoids were generated from C57BL/6 and SHP-knockout mice and cholesterol uptake was measured. Luciferase reporter assays were performed with HT29 cells.
We genes that regulate lipid and ion transport in intestine, including NPC1L1, to be upregulated and cholesterol absorption was increased in SHP-knockout mice compared with C57BL/6 mice. Expression of NPC1L1 was reduced in C57BL/6 mice following refeeding after fasting, but not in SHP-knockout or FGF15-knockout mice. SHP-knockout mice had altered BA composition compared with C57BL/6 mice. FGF19 injection reduced expression of NPC1L1, decreased cholesterol absorption, and increased levels of hydrophilic BAs, including tauro-alpha- and -beta-muricholic acids; these changes were not observed in SHP-knockout mice. Sterol regulatory element binding transcription factor 2 (SREBF2), which regulates cholesterol, activated transcription of NPC1L1. FGF19 signaling led to phosphorylation of SHP, which inhibited SREBF2 activity.
Postprandial FGF19 and SHP inhibit SREBF2, which leads to repression of intestinal NPC1L1 expression and cholesterol absorption. Strategies to increase FGF19 signaling to activate SHP might be developed for treatment of hypercholesterolemia.
Key Words : FGF15, FXR, bile acids, SREBF2