ABSTRACT: Background In the postabsorptive state, the portal-drained viscera are a major energy consumer, but a comprehensive overview of the adaptive fasting response in the liver is lacking. Hence, gene-expression profiling, pathway, network and gene-set enrichment analysis and immunohistochemistry were carried out on mouse liver after 0, 12, 24, and 72 hours of fasting. Results Liver weight has fallen to 50% of control after three days of fasting, hepatocyte size was reduced with no apparent increase in apoptosis, while the basic liver structure and metabolic zonnation were preserved. Expression profiling and pathway analysis depicted four master processes, all with response peaking at 24 hours, and all but one decreasing towards 72h. Changes in gene expression were compatible with cellular energy deficiency, and metabolic adaptations were directed at enhanced glucose production, stimulation of lipid catabolism and ketone body synthesis, and strongly augmented ATP production. Consequently, the expression of genes involved in oxidative and endoplasmic reticulum stress response was increased. In addition, urea cycle genes were strongly upregulated during whole duration of fasting, in spite no obvious increase in amino-acid catabolism. Major physiological change upon continued fasting was restoration of glycogen reserves, but with reverse localization, demonstrating utilization of different glycogenic precursor compared to the fed controls. Conclusion The changes in liver gene expression indicate a rapid onset of generating glucose and ketone bodies during short, and a return to near normal situation in prolonged fasting. The reason apparently lies in glycogen repletion, due to late fasting glucose production by (gut and) kidney. Keywords: fasting response, time course
