Characterization of chromatin and gene expression changes during fasting and refeeding in mouse liver [RNA-Seq]
The discovery of FoxO1 as an effector of insulin action on gene expression filled a gap in our knowledge of insulin signaling. The metabolic impact of hepatic FoxO1 has been demonstrated in genetic mouse models showing that FoxO1 inhibition can reverse diabetes. However, the gamut of FoxO1 targets is unknown, due to the lack of robust genome-wide chromatin occupancy data. To elucidate the genomic architecture of the FoxO1 effect on liver metabolism, we integrated genome-wide ChIP-seq and RNA-seq. During the physiological transition from fasting to refeeding, hepatic FoxO1 translocated from the nucleus to the cytoplasm. At the same time points, cistrome analysis demonstrated that 60% of FoxO1 target sites were cleared by refeeding. RNA-seq from mice following acute liver-specific FoxO1 ablation allowed us to integrate the data in a comprehensive FoxO1 regulome. We identified four distinct classes of FoxO1 targets. Class I targets are enriched in genes regulating cell homeostasis, have FoxO1 sites clustered in promoters and do not show regulation with fasting/refeeding. Class II is comprised of canonical FoxO1 metabolic targets coordinately regulated with other fasting-inducible TFs, such as PPARA, CREB, and GR through promoters. Class III is enriched in glucose metabolic genes regulated through active enhancers, as detected by H3K4me1 and H3K27ac histone marks. Class IV is comprised of triglyceride (TG) and lipoprotein metabolism genes, regulated through intron sites, and characterized by an uneven response to fasting/refeeding regulation. Overall design: mRNA profiles of liver tissues from constitutive or acute liver specific FoxO1 knockout mice during 4h fasted or 4 hr fasted/1 hr refed. For constitutive liver-specific FoxO1 knockouts, we crossed FoxO1lox/lox and Albumin-cre transgenic mice. Acute liver-specific FoxO1 knockout mice were generated by injection of 1×1011 purified viral particles (AAV8.TBG.eGFP or AAV8.TBG.Cre) per mouse via tail vein. We collected samples on day 21 post-injection.