Effects of dietary leucine supplementation on the gene expression of mammalian target of rapamycin signaling pathway and intestinal development of broilers

摘要

Abstract This experiment was to investigate the effects of dietary leucine supplementation on the gene expression of mammalian target of rapamycin (mTOR) signaling pathway and intestinal development of broilers. A total of 384 one-day-old broilers were randomly assigned into 4 treatments with 6 replicates (16 broilers per replicate). Broilers in these treatment groups were offered the following diets with 1.37, 1.77, 2.17 and 2.57% of leucine. These diet treatments were named 1.37TM, 1.77TM, 2.17TM, and 2.57TM. The experiment lasted 21 days and all birds had free access to feed and water. Results indicated that there was no significant difference in body weight, average daily gain and average feed intake among all treatments ( P >?0.05). The broiler duodenal villus height in 2.57TM was the lowest, but the highest occurred in 1.37TM on d 7 and 14 ( P Keywords Leucine ; Broiler ; mTOR pathway ; Intestinal development prs.rt("abs_end"); 1. Introduction Leucine is one of branched-chain amino acids, which belong to essential amino acids for both animals and human ( Li et?al., 2011 and Wu et?al., 2014 ). As an essential amino acid, leucine has certain biological properties, such as providing energy, regulating protein, carbohydrate and lipid metabolism, adjusting immune function and mRNA translational origination, thereby leucine can affect nutrient metabolism and animal growth ( Suryawan et?al., 2012a and Suryawan et?al., 2012b ). Presently, the regulatory functions of amino acids in nutrition or physiology as well as the mechanism at cellular or molecular levels have attracted increasing attention of scientists ( Kim and Wu, 2009 and Katane et?al., 2008 ). It has been confirmed that leucine can enhance muscle protein synthesis via promoting protein synthesis and inhibiting its degradation ( Dardevet et?al., 2000 ). Li et?al. (2009) and Palii et?al. (2009) suggested that leucine supplementation in low-protein meal could regulate muscle protein synthesis and animal growth, stimulate growth hormone secretion, and adjust gene expression. Moreover, leucine plays a critical role in enhancing translational efficiency, which refers to inducing the activation of mammalian target of rapamycin (mTOR) and its downstream pathway leading to mRNA translation and relative protein synthesis ( Wu et?al., 2010 and Kimball and Jefferson, 2006 ). Although growing evidence shows beneficial effects of leucine in the regulation of protein synthesis in skeletal muscle ( Anthony et?al., 2002 , Escobar et?al., 2007 , Wilson et?al., 2010 , Boutry et?al., 2013 , Deng et?al., 2014 and Columbus et?al., 2015 ), few studies have determined the effects of dietary supplementation of L-leucine on the development and performance of young broilers, thereby not so much information is available regarding the effects of leucine on the intestinal development and activation of translation initiation. In order to evaluate the potential benefits of leucine supplementation on neonatal growth, it is essential to assess the effects of leucine on protein synthesis not only in skeletal muscle, but also in other tissues of the neonate, considering the tissue specific effect of leucine on stimulating protein synthesis. As the small intestine is the first tissue to encounter the nutritional intervention, determining the effects of a diet supplemented with leucine on translation and protein synthesis in this tissue is essential for future understanding of the role that leucine may play in neonatal growth. Hence, L-leucine may be a biological active nutrient that can regulate the development and maturation of the small intestine. Provision of L-leucine at an earlier age may improve the intestinal development and regulate expression of genes and signaling pathways to affect absorption and metabolism of dietary nutrients in animals ( Yin et?al., 2010 and Zhang et?al., 2013 ). Therefore, different levels of dietary leucine were prepared to explore the potential effects of leucine on the intestinal development and gene expression of mTOR signing pathway of broiler. 2. Materials and methods 2.1. Animals and diets A total of 384 newly hatched healthy Arbor Acres male broilers (BW 45.46?±?0.32?g) from a commercial hatchery (Hua Du Broiler Company, Beijing, China) were randomly assigned into 4 dietary treatments supplemented with leucine with 6 replicates per treatment (16 broilers per replicate). Experimental diets were formulated referring to the nutrient requirements for broilers published by the Ministry of Agriculture of the People's Republic of China (2004). The Leucine percentages in the nutrient composition of these 4 treatments were 1.37% (1.37TM); 1.77% (1.77TM); 2.17% (2.17TM) and 2.57% (2.57TM). Broilers were raised in cages, with 23?h of light per day and ad libitum access to diets and water. Besides, regular managements and poultry vaccination were conducted according to the recommended procedures in the broiler breeding manual. The broilers mental states, a