Fasting does not promote a metabolic memory effect in mouse liver

Background: Tissues may respond differently to a particular stimulus if they have been previously exposed to that same stimulus. Here we tested the hypothesis that a strong metabolic stimulus may elicit a memory effect in the liver. To that end, we examined whether prior fasting, which profoundly impacts hepatic nutrient metabolism, may influence the metabolic response to a subsequent fast. Methods: 24 mice were exposed to two 16h fasts over a 8 week period, each time being allowed to return to their normal growth trajectory, while another group of 24 mice was fed ad libitum throughout. Of each group, half of the mice were euthanized after a 16h fast, whereas the other half was euthanized in the ab libitum fed state. Results: An acute fast significantly increased plasma NEFA, glycerol, β-hydroxybutyrate and liver triglycerides, and decreased plasma glucose, triglycerides, and liver glycogen levels. An acute fast also markedly changed the liver transcriptome, upregulating genes involved in fatty acid catabolism and downregulating genes involved in cholesterol synthesis, and majorly impacted the liver metabolome, reducing the levels of numerous amino acids, glycolysis and TCA cycle intermediates, and nucleotides. However, none of the these changes were significantly influenced by prior fasting. The limited number of genes that were significantly altered by prior fasting are likely false positives. Finally, no significant effect was observed of prior fasting on glucose tolerance. Conclusion: We conclude that previous exposure to fasting in mice does not influence the metabolic response to a subsequent fast, thus arguing against the concept of metabolic memory in the hepatic response to fasting. Microarray analysis was performed on murine liver tissue after a 16 hour fast or in the fed state