Transcription factor cascades during fasting amplify gluconeogenesis and instigate a secondary wave of ketogenic gene transcription. [RNA-Seq 2]

During fasting, bodily homeostasis is maintained due to hepatic production of glucose (via gluconeogenesis) and ketone bodies (via ketogenesis). The major hormones governing hepatic fuel production are glucagon and glucocorticoids who initiate a complex transcriptional program aimed at supporting gluconeogenesis and ketogenesis. Here, we found that in addition to the known metabolic genes induced by glucagon and glucocorticoids, these hormones each induce a set of genes encoding transcription factors (TFs) thereby initiating transcriptional cascades. Glucocorticoids activate the glucocorticoid receptor (GR) that induces the genes encoding two TFs - C/EBPβ and PPARα. Transcriptomic analysis combined with gene silencing revealed the role of C/EBPβ as an amplifier of hormone-induced gluconeogenesis. In contrast, the GR-PPARα cascade initiated a secondary transcriptional wave of genes supporting ketogenesis. We show that a dual treatment of glucocorticoids with a PPARα agonist leads to synergistic induction of ketogenic genes and that this induction is dependent on protein synthesis. Genome-wide analysis of enhancer dynamics revealed numerous enhancers activated by the GR-PPARα cascade. These enhancers are proximal to ketogenic genes, are enriched for the PPARα binding motif and show increased PPARα binding as profiled by ChIP-seq. In summary, this study reveals abundant TF cascades occurring during fasting. These cascades serve two separated purposes: the amplification of the primary gluconeogenic transcriptional program and the induction of a secondary gene program aimed at enhancing ketogenesis.