Table_2_The Diurnal Timing of Starvation Differently Impacts Murine Hepatic Gene Expression and Lipid Metabolism – A Systems Biology Analysis Using Self-Organizing Maps.XLSX

Organisms adapt their metabolism and draw on reserves as a consequence of food deprivation. The central role of the liver in starvation response is to coordinate a sufficient energy supply for the entire organism, which has frequently been investigated. However, knowledge of how circadian rhythms impact on and alter this response is scarce. Therefore, we investigated the influence of different timings of starvation on global hepatic gene expression. Mice (n = 3 each) were challenged with 24-h food deprivation started in the morning or evening, coupled with refeeding for different lengths and compared with ad libitum fed control groups. Alterations in hepatocyte gene expression were quantified using microarrays and confirmed or complemented with qPCR, especially for lowly detectable transcription factors. Analysis was performed using self-organizing maps (SOMs), which bases on clustering genes with similar expression profiles. This provides an intuitive overview of expression trends and allows easier global comparisons between complex conditions. Transcriptome analysis revealed a strong circadian-driven response to fasting based on the diurnal expression of transcription factors (e.g., Ppara, Pparg). Starvation initiated in the morning produced known metabolic adaptations in the liver; e.g., switching from glucose storage to consumption and gluconeogenesis. However, starvation initiated in the evening produced a different expression signature that was controlled by yet unknown regulatory mechanisms. For example, the expression of genes involved in gluconeogenesis decreased and fatty acid and cholesterol synthesis genes were induced. The differential regulation after morning and evening starvation were also reflected at the lipidome level. The accumulation of hepatocellular storage lipids (triacylglycerides, cholesteryl esters) was significantly higher after the initiation of starvation in the morning compared to the evening. Concerning refeeding, the gene expression pattern after a 12 h refeeding period largely resembled that of the corresponding starvation state but approached the ad libitum control state after refeeding for 21 h. Some components of these regulatory circuits are discussed. Collectively, these data illustrate a highly time-dependent starvation response in the liver and suggest that a circadian influence cannot be neglected when starvation is the focus of research or medicine, e.g., in the case of treating victims of sudden starvation events.

生物体因食物剥夺而调整其新陈代谢并调用储备资源。肝脏在饥饿反应中的核心作用是协调整个生物体的充足能量供应，这一问题已被广泛研究。然而，关于昼夜节律如何影响并改变这一反应的知识却极为匮乏。因此，我们探讨了不同饥饿时间对整体肝基因表达的影响。将小鼠（每组3只）置于从早晨或晚上开始的24小时食物剥夺中，并配合不同长度的再喂养，与自由摄食对照组进行比较。通过微阵列量化肝细胞基因表达的改变，并使用qPCR进行确认或补充，特别是对于低检测度转录因子。分析采用自组织图（SOMs）进行，该方法基于具有相似表达谱的基因聚类。这为表达趋势提供了直观的概述，并使得在复杂条件下进行全局比较更为便捷。转录组分析揭示了基于转录因子（如Ppara、Pparg）日间表达的饥饿反应的昼夜节律驱动响应。早晨开始的饥饿产生了肝脏已知的代谢适应，例如，从葡萄糖储存转为消耗和糖异生。然而，晚上开始的饥饿产生了受未知调控机制控制的不同表达特征。例如，参与糖异生的基因表达降低，而脂肪酸和胆固醇合成基因被诱导。早晨和晚上饥饿后的差异调节也反映在脂质组水平上。与晚上相比，早晨开始饥饿后肝细胞储存脂质（如三酰甘油、胆固醇酯）的积累显著增加。在再喂养方面，12小时再喂养期间的基因表达模式与相应的饥饿状态相似，但在再喂养21小时后接近自由摄食控制状态。一些调控回路成分被讨论。总的来说，这些数据描绘了肝脏饥饿反应的高度时间依赖性，并表明在研究或医学中将饥饿作为焦点时，例如治疗突发饥饿事件受害者时，不能忽视昼夜节律的影响。