Repeated fasting events sensitize chromatin and gene expression to support augmented ketogenesis

Mammals evolved to withstand frequent fasting periods due to hepatic production of glucose and ketone bodies. Because the fasting response is transcriptionally-regulated, we asked whether enhancer dynamics impose a transcriptional program during recurrent fasting and whether this produces effects distinct from a single fasting bout. We found that mice undergoing alternate-day fasting (ADF) respond to a following fasting bout profoundly differently from mice first experiencing fasting. Hundreds of genes enabling ketogenesis are 'sensitized', i.e. induced more strongly by fasting following ADF. Enhancers regulating these genes are also sensitized and harbor increased binding of the major ketogenic transcription factor. ADF mice show augmented ketogenesis and their sensitized enhancers are covalently marked with ketone body residues. Thus, we found that past fasting events are 'remembered' in hepatocytes, sensitizing their enhancers to the next fasting bout and augmenting ketogenesis. Our findings shed light on transcriptional regulation mediating adaptation to repeated environmental signals. Overall design: Mice were subjected to either a 4-week alternate day fasting (ADF) regimen or unrestricted feeding (URF). At the end of the experiment mice were divided to 3 groups: the first group was euthanized after a 24 h fasting period (ADF_f or URF_f). The second group fasted for 24 h followed by ad libitum refeeding for 24 h at the end of which they were euthanized (ADF_re or URF_re). The third group did not experience any type of fasting (unrestricted feeding). Each group has 3 replicates.