NPC L NPC Niemann Pick C like like intracellular cholesterol
NPC1L1 (NPC1 [Niemann-Pick C-like-1]-like intracellular cholesterol transporter) is the rate-limiting transmembrane transporter for cholesterol thymidine phosphorylase inhibitor from the intestinal lumen, and it mediates the absorption of both dietary and biliary cholesterol., , NPC1L1 is the target of the cholesterol-lowering drug ezetimibe, which suppresses intestinal cholesterol absorption and promotes TICE., , Despite its importance as a therapeutic target, physiological regulation of intestinal gene expression during feeding and fasting cycles is poorly understood.
In this study, to our knowledge, we have identified a previously unknown intestinal function of SHP and postprandial FGF19 signaling in the inhibition of NPC1L1 expression and fractional cholesterol absorption. In mechanistic studies, we show that SREBF2, a key transcriptional regulator of cholesterol, induces expression of NPC1L1 early after feeding and that SHP inhibits the SREBF2-mediated transactivation of in response to postprandial FGF19 signaling, which contributes to decreased cholesterol absorption in the late-fed state.
Materials and Methods
Discussion SHP is highly expressed in the liver and intestine, but nearly all previous studies have examined its hepatic functions, including transcriptional repression of BA and cholesterol synthesis, circadian lipid metabolism, 1-carbon metabolism, and autophagy.10, 13, 14, 19, 22, 23 In contrast, little is known about the function of SHP in the intestine. In this study, we showed that SHP has intestinal functions in the repression of cholesterol absorption, in part by inhibiting expression of NPC1L1 in response to postprandial FGF19 signaling in mice. Postprandial intestinal expression of NPC1L1 is likely complex and biphasic. Npc1l1 pre-mRNA levels increased to a peak at about 2 hours after feeding and then decreased to levels below those in fasting animals by 6 hours, suggesting active transcriptional repression in the late-fed state. Our data indicate that the FGF19-SHP axis mediates this active repression of Npc1l1. Pre-mRNA levels only transiently increased 2 hours after feeding in WT mice, but increased levels were sustained up to 6 hours in both SHP-knockout and FGF15-knockout mice. Furthermore, our data suggest that early after feeding, SREBF2 activates Npc1l1 and that in the late-fed-state SHP and FGF19 inhibit the SREBF2 activity. Consistent with our findings, expression of Npc1l1 and sterol absorption are increased by glucose,35, 40 and nuclear levels of SREBF2 are increased by feeding and insulin. Inhibition by SHP of other known SHP-interacting factors whose binding motifs were detected in the Npc1l1 promoter, such as LRH-1 or aryl hydrocarbon receptor,14, 36 may contribute to Npc1l1 repression, but SHP inhibition of SREBF2 is likely primary, given the importance of SREBF2 in the regulation of Npc1l1 and sterol levels.35, 36, 37, 38 Recent studies have shown that nuclear localization and the gene-regulatory function of SHP are enhanced by postprandial FGF19 signaling. In the liver, FGF19 mediates phosphorylation of SHP at Thr-55, which is critical for its interaction with RanBP2, a nuclear pore component and SUMO ligase that promotes nuclear localization of SHP, and for interaction with histone demethylase LSD1 (lysine-specific demethylase 1), which promotes the gene-repressive function of SHP. Furthermore, FGF19 increases SHP protein stability by inhibiting ubiquitination and proteasomal degradation in hepatocytes. In the present study, we showed that FGF19 signaling also increases phosphorylation of SHP at Thr-55 in the intestine in mice, in intestinal organoids, and in HT29 cells, and that mutation of Thr-55 in SHP abrogates the inhibition of NPC1L1 and cholesterol uptake in organoids and HT29 cells treated with FGF19. Thus, FGF19 signal-induced phosphorylation of SHP is important for its functions in both the liver and intestine. Collectively, our findings suggest that a postprandial intestinal hormone, FGF15/19, increases the gene-regulatory function of SHP via phosphorylation at Thr-55 and possibly by stabilization of SHP, which results in the inhibition of NPC1L1 expression and cholesterol absorption in enterocytes (Figure 7F).