Abstract
Amino acids are known to play a key role in gene expression regulation. Amino acid signaling is mediated via two pathways: the mammalian target of rapamycin complex 1 (mTORC1) and the amino acid responsive (AAR) pathways. Cationic amino acid transporters (CATs) are crucial in these pathways due to their sensing, signaling and transport functions. The availability of certain amino acids plays a key role in the intake of other amino acids, hence affecting growth in young birds. However, the specific mechanism for regulating lysine transport for growth is not clear. In this study, we analyze the transcriptome profiles and mRNA expression of selected cationic amino acid transporters in the livers of broilers fed low and high lysine diets. Birds consumed high-lysine (1.42% lysine) or low-lysine (0.85% lysine) diets while the control group consumed 1.14% lysine diet. These concentrations of lysine represent 125% (high lysine), 75% (low lysine) and 100% (control), respectively, of the National Research Council’s (NRC) recommendation for broiler chickens. After comparing the two groups, 210 differentially expressed genes (DEGs) were identified (fold change >1 and false discovery rate (FDR) <0.05). When comparing the high lysine and the low lysine treatments, there were 67 upregulated genes and 143 downregulated genes among these DEGs. Analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG) and the Gene Ontology (GO) enrichment analysis show that cellular growth, lipid metabolism and lysine metabolism pathways were among the significantly enriched pathways. This study contributes to a better understanding of the potential molecular mechanisms underlying the correlation between lysine intake, body weight gain (BWG) and feed intake (FI) in broiler chickens. Moreover, the DEGs obtained in this study may be used as potential candidate genes for further investigation of broiler growth customized responses to individualized nutrients such as amino acids.
Highlights
Lysine is an essential and one of the most limiting amino acids for growth
Results of our Gene Ontology (GO) enrichment analysis indicate that the downregulated and upregulated genes in the comparison of broilers fed the low- vs. high-lysine diets resulted in identification of the differentially expressed genes (DEGs), which were in turn associated with GO biological process terms mainly involved in cell growth, biological adhesion, developmental processes, cell communication, drug metabolic processes, cell proliferation, regulation of insulin-like growth factor receptor signaling pathway, cell death, response to stress, lipid transport, lipid transport, lipid metabolic process, cellular response to starvation, cellular catabolic process, cellular response to fatty acid, cell development, lipid homeostasis, ion homeostasis, lysine anabolic and catabolic processes, lysine transport, metabolic processes, lysine biosynthetic process via aminoadipic acid, biological adhesion and response to stress
Several pathways are related to muscle growth, namely PAK signaling, the peroxisome proliferator-activated receptor (PPAR) signaling pathway and the acetate conversion of Acetyl-CoA signaling pathway, protein kinase A (PKA) signaling
Summary
Lysine is an essential and one of the most limiting amino acids for growth. Amino acids are generally required for muscle development [1]. Lysine is required for protein synthesis and muscle deposition, synthesis of cytokines, gene expression and lymphocyte proliferation and in the optimum functioning of immune system in response to infection. An inadequate supply of lysine would lead to reduced growth and a reduction in antibody response and cell-mediated immunity in chickens [2]. In the case of broilers, it has been shown that there is a negative impact of imbalance and antagonism among amino acids on nutrient intake and utilization. Care should be exercised while developing effective strategies for feed formulation in order to obtain maximum utilization of amino acids
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