Adaptation to recurring environmental challenges (food availability, seasonal rhythms etc.) is a mainstay of physiology. As such, mammals are exquisitely fitted to tolerate frequent bouts of fasting owing to hepatic production of fuels (glucose, ketones). Indeed, studies show significant health benefits of intermittent fasting. Due to the reliance of the fasting response on chromatin and transcriptional regulation, I hypothesize that mammals adapt to recurring fasting by sensitizing transcriptional programs and maximizing future responses, thereby increasing survival. I plan to uncover transcriptional mechanisms of ‘fasting memory’ that mediate the health benefits of recurrent fasting. I will profile the hepatic transcriptome and genome-wide chromatin landscape of intermittently-fasted mice to discover the mediators of such memory. I will evaluate three plausible mechanisms: (1) Enhancer priming whereby the DNA regulatory elements dictating gene expression are kept in a primed state between fasting episodes. (2) Promoter priming in which RNA polymerase is paused at gene bodies during feeding and rapidly released upon re-fasting. (3) Transcriptional cascades whereby genes induced in the previous fasting bout are active in the next one, directing a second wave of gene expression. The molecular mechanisms mediating memory will be examined in a series of gain/loss of function experiments targeting various components of transcriptional regulation (transcription factors, RNA polymerase, histone and DNA modifications etc.). Both the notion of fasting memory and the cellular mechanisms driving it are supported by preliminary results. The concept raised here has the potential to unravel a fundamental homeostatic response and significantly advance fasting research. More broadly, such a discovery would reshape our view of transcriptional regulation as a cellular adaptation mechanism to recurring challenges and of physiological habituation to the environment.
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