Nat Commun. 2018 Feb 7;9(1):540 

AhR and SHP regulate phosphatidylcholine and S-adenosylmethionine levels in the one-carbon cycle

Young-Chae Kim


Phosphatidylcholines (PC) and S-adenosylmethionine (SAM) are critical determinants of hepatic lipid levels, but how their levels are regulated is unclear. Here, we show that Pemt and Gnmt, key one-carbon cycle genes regulating PC/SAM levels, are downregulated after feeding, leading to decreased PC and increased SAM levels, but these effects are blunted in small heterodimer partner (SHP)-null or FGF15-null mice. Further, aryl hydrocarbon receptor (AhR) is translocated into the nucleus by insulin/PKB signaling in the early fed state and induces Pemt and Gnmt expression. This induction is blocked by FGF15 signaling-activated SHP in the late fed state. Adenoviral-mediated expression of AhR in obese mice increases PC levels and exacerbates steatosis, effects that are blunted by SHP co-expression or Pemt downregulation. PEMT, AHR, and PC levels are elevated in simple steatosis patients, but PC levels are robustly reduced in steatohepatitis-fibrosis patients. This study identifies AhR and SHP as new physiological regulators of PC/SAM levels.From published liver ChIP-seq data from mice treated with the late fed-state hormone FGF1926, SHP binding peaks were detected at the promoter regions of numerous genes involved in the 1C cycle (Fig. 1b). Confirming these results, in standard mouse liver ChIP assays, treatment with a pharmacological dose of FGF19 increased binding of SHP at all tested 1C cycle genes, including Pemt and Gnmt, two key genes in regulating PC and SAM levels (Fig. 1c), while the binding of SHP at Pemt and Gnmt was not detected in SHP-knockout (SHP-KO) mice (Fig. 1d). Further, mRNA levels of the 1C cycle genes were decreased by FGF19 treatment in control C57BL/6 mice, but not in SHP-KO mice (Fig. 1e).Consistent with these transcriptional changes, FGF19 treatment increased hepatic SAM and PE levels and decreased SAH and PC levels in control C57BL/6 mice, so that the PC/PE and SAH/SAM ratios were decreased, but these changes were blunted in SHP-KO mice (Fig. 1f). These results demonstrate that FGF19 inhibits the expression of 1C cycle genes and decreases hepatic PC/PE and SAH/SAM ratios in the liver in a SHP-dependent manner.Antibodies for SHP (sc-30169), AhR (sc-133088), and actin (sc-1616) were purchased from Santa Cruz Biotechnology and for PEMT and ARNT from Thermo Fisher (PA5-42383) and NOVUS Biologicals (NB100-110), respectively. Texas Red goat anti-rabbit IgG was obtained from Invitrogen (T-2767). A SHP antibody specific to phospho-Thr-55 (p-T55-SHP) was produced commercially (Abmart, Inc.) and used in previous studies19, 26 and its specificity has been described previously19. Endogenous AhR in hepatocytes was downregulated using the pooled small interfering RNAs for AhR (ON-TARGETplus SMART pool, GE Dharmacon, Inc.) to minimize off-target effects. Hepa1c1c7 cells were obtained from ATCC (CRL-2026).We thank Eric H. Xu for providing recombinant FGF19 and David Moore, Li Wang, and Sayee Anakk for providing SHP-KO mice. We thank the Liver Tissue Procurement and Distribution System of the NIH for providing human liver specimens of NAFLD patients. We also thank Lucas Li, Director of Metabolomics Center at UIUC, for assistance with the LC–MS analysis. This study was supported by an American Heart Association Scientist Development Award (16SDG27570006) to Y.-C.K., an American Heart Association post-doctoral fellowship (17POST33410223) to S.B., and by grants from the National Institutes of Health (DK62777 and DK95842) and the American Diabetes Association (1-16-IBS-156) to J.K.K.The authors declare no competing financial interests.Electronic supplementary materialSupplementary Information accompanies this paper at 10.1038/s41467-018-03060-y.Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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