Transcriptome Analysis Reveals Circadian Rhythmic Regulation of Lipid Metabolism and Immune Function in Chicken Livers

Liver rhythm has a significant effect on lipid metabolism and immune function in chickens. However, reports on its underlying mechanisms and key genes are relatively scarce. We collected liver samples at seven time points during one light/dark cycle and investigated the candidate genes and pathways related to hepatic rhythm through transcriptomic sequencing. Trend analysis revealed that the expression of genes in Profile 5 exhibited rhythmic fluctuations, and these genes (e.g., <i>FAM21C</i>, <i>SRSF4</i>, and <i>TLR2A</i>) were enriched in immune function and biological rhythm. The genes (e.g., <i>MSMO1</i>, <i>ELOVL2</i>, and <i>HMGCR</i>) in Profile 2 that were related to lipid metabolism also exhibited a rhythmic trend. A total of 845 differentially expressed genes (e.g., <i>MSMO1</i> and <i>FAM21C</i>) were detected between light/dark conditions. Lipid metabolism and immune functions showed the most changes between the two conditions. Immune-related processes (e.g., autophagy) were more active in the light phase, while in the dark phase, lipid metabolism (e.g., sterol biosynthesis) was more active. Weighted gene coexpression network analysis revealed that the tan (including <i>C1QA</i>, <i>TLR2A</i>, and others) and cyan (including <i>ELOVL2</i>, <i>IARS1</i>, and others) modules were strongly associated with the hepatic circadian rhythm. Cosinor analysis revealed that 9 lipid-related genes (e.g., <i>MSMO1</i>, <i>HMGCR1</i>, and <i>ELOVL2</i>) and 11 immune-related genes (e.g., <i>FAM21C</i>, <i>TLR4</i>, and <i>TLR2A</i>) exhibited significant rhythmic expression. These findings revealed rhythmic changes in hepatic immune and lipid metabolism, providing important insights into the regulation of disease resistance and lipid deposition in chickens.