Investigating the Molecular Mechanisms of Lysine’s Effect on Feed Intake in Chicks Through the Hypothalamus using RNA-seq and Metabolomics
Authors: Wang Wentao , Bin Chen 
Published: December 2024

Background: There is a current lack of research on the molecular pathways by which lysine regulates feed intake in chicks. Regulation is controlled by the hypothalamus and lysine metabolism links the availability of amino acids and nutritional perception with food intake. The mechanism underlying this phenomenon remains unclear. To investigate the regulatory mechanism of lysine on feed intake in chicks, this study used Yao chickens as a research model. The levels of lysine in the feed of chicks were adjusted to determine the effect on feed intake. The hypothalamus tissue of the chicks was analyzed using RNA-seq and metabolomics to identify the relevant genes. We employed Gene Ontology and identification of signaling pathways to characterize the molecular regulatory biological pathways of lysine in poultry feeding. Methods: This study used RNA-seq technology to investigate the genes and marker metabolites involved in lysine regulation of feed intake in chickens. The study explored the molecular mechanism by which dietary lysine regulates feed intake in chickens via the hypothalamus. Four hundred healthy 1-day-old chicks (Yao chickens) were randomly divided into four groups, with five replicates in each group (n = 20). Result: There was a significant difference in feed intake among chicks fed with diets containing 0.65% (abbreviated as MGO), 0.85% (FIH), 1.0% (MGS) and 1.2% (FIL) lysine levels. The group with the highest feed intake was FIH, while the group with the lowest feed intake was FIL. By conducting RNA-seq of the hypothalamic tissue of chickens in both the highest and lowest feed intake groups, we obtained 2006 differentially expressed genes, comprising 1275 upregulated genes and 731 downregulated genes. Fourteen genes were related to food intake, including growth hormone, recombinant glutamate receptor, metabotropic 1 (GRM1) and recombinant glutamate receptor, metabotropic 3 (GRM3). Using liquid chromatograph mass spectrometer (LC-MS) metabolomics, we identified 25 differential metabolites. Nine metabolites, including C3H5NO4, C10H15NO2 and C13H14N203, were downregulated, while 16 metabolites, including C2H8NO3P, C3H7NO3 and C7H7NO2, were upregulated. Marker metabolites included 5-hydroxytryptophan and L-valine. A KEGG enrichment analysis revealed that the differential metabolites between the FIH and FIL groups were enriched in 26 pathways, with the significantly enriched pathway being the ABC transporter protein pathway (ID: map02010). RNA-seq and LC-MS analyses revealed that in chicks, the expression of the neuropeptides cocaine- and Amphetamine-Regulated Transcript Protein (CARTPT) and neuropeptide Y (NPY)/agouti-related protein (AGRP), along with genes such as sucrose synthase (SS 2), recombinant cholecystokinin A receptor (CCKAR) and recombinant cholecystokinin B receptor (CCKBR), was regulated by the hypothalamic feeding regulation center that senses the level of lysine in the feed. These molecules bind to specific receptors and initiate a signaling cascade in specific hypothalamic neuronal groups, thereby regulating chick feed intake and in turn affecting growth, development and production performance.