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

Abstract

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.

Tick-tock hedgehog-mutual crosstalk with liver circadian clock promotes liver steatosis

“…The expression of many clock genes was also differently affected by differently timed starvation. 24 According to our paradigm that clock and Hh signaling closely interact we show herein that components of the Hh signaling cascade are also differently affected by the different timing of starvation. As depicted in Fig.…”

“…In a recent study we have shown that different timing of starvation of C57BL/6N mice results in completely different metabolic responses over a 24 h period. 24 Starvation induced in the morning at ZT3 resulted in the well-known response characterized by induced gluconeogenesis, while starvation induced in the evening at ZT15 caused a completely different response involving downregulation of gluconeogenesis and increased fatty acid and cholesterol synthesis. The expression of many clock genes was also differently affected by differently timed starvation.…”

Integrative Epigenomic and Transcriptomic Analysis Reveals Robust Metabolic Switching in the Brain During Intermittent Fasting

“…(responsible for glycogen storage (Akman et al, 2011;Iijima et al, 2018)), were uniquely upregulated in IF16 and EOD, respectively. However, in both IF16 and EOD common genes, such as Elovl2 (involved in de novo lipogenesis, lipid storage, and subsequent fat mass expansion (Pauter et al, 2014;Rennert et al, 2018)) and…”

Differential Proteomic Analysis of Chinese Giant Salamander Liver in Response to Fasting

“…For the South African clawed toad Xenopus laevis, its liver glycogen levels were reduced by 80-90% after 12 months of starvation at 20 • C (Merkle and Hanke, 1988). For other vertebrates, several studies showed that genes involved in ketogenesis, gluconeogenesis, and fatty acid beta-oxidation, were up-regulated in liver of chicken after 16 h of starvation (Desert et al, 2008), in liver of mice after 24 h of starvation (Kinouchi et al, 2018;Rennert et al, 2018), in liver of fishes after 21 days of starvation (Drew et al, 2008;Qian et al, 2016). Compared to other vertebrates, the hypogean salamanders exhibited remarkable resistance to long periods of food deprivation, this may be due to the remarkable accumulation of lipid and glycogen deposits in the liver, and glycogen level maintenance during food deprivation.…”