Abstract
Muscle growth is regulated by the homeostatic balance of the biosynthesis and degradation of muscle proteins. To elucidate the molecular interactions among diet, pig genotype, and physiological stage, we examined the effect of dietary protein concentration, pig genotype, and physiological stages on amino acid (AA) pools, protein deposition, and related signaling pathways in different types of skeletal muscles. The study used 48 Landrace pigs and 48 pure-bred Bama mini-pigs assigned to each of 2 dietary treatments: lower/GB (Chinese conventional diet)- or higher/NRC (National Research Council)-protein diet. Diets were fed from 5 weeks of age to respective market weights of each genotype. Samples of biceps femoris muscle (BFM, type I) and longissimus dorsi muscle (LDM, type II) were collected at nursery, growing, and finishing phases according to the physiological stage of each genotype, to determine the AA concentrations, mRNA levels for growth-related genes in muscles, and protein abundances of mechanistic target of rapamycin (mTOR) signaling pathway. Our data showed that the concentrations of most AAs in LDM and BFM of pigs increased (P<0.05) gradually with increasing age. Bama mini-pigs had generally higher (P<0.05) muscle concentrations of flavor-related AA, including Met, Phe, Tyr, Pro, and Ser, compared with Landrace pigs. The mRNA levels for myogenic determining factor, myogenin, myocyte-specific enhancer binding factor 2 A, and myostatin of Bama mini-pigs were higher (P<0.05) than those of Landrace pigs, while total and phosphorylated protein levels for protein kinase B, mTOR, and p70 ribosomal protein S6 kinases (p70S6K), and ratios of p-mTOR/mTOR, p-AKT/AKT, and p-p70S6K/p70S6K were lower (P<0.05). There was a significant pig genotype-dependent effect of dietary protein on the levels for mTOR and p70S6K. When compared with the higher protein-NRC diet, the lower protein-GB diet increased (P<0.05) the levels for mTOR and p70S6K in Bama mini-pigs, but repressed (P<0.05) the level for p70S6K in Landrace pigs. The higher protein-NRC diet increased ratio of p-mTOR/mTOR in Landrace pigs. These findings indicated that the dynamic consequences of AA profile and protein deposition in muscle tissues are the concerted effort of distinctive genotype, nutrient status, age, and muscle type. Our results provide valuable information for animal feeding strategy.
Highlights
It is economically important to increase the rate and speed of skeletal muscle growth in animals raised for meat including pigs
The concentrations of most amino acids (AA), total AA (TAA), essential AA (EAA), and flavor AA (FAA) in longissimus dorsi muscle (LDM) and biceps femoris muscle (BFM) increased in an age-dependent manner, regardless of pig genotype and dietary protein level
An interaction between genotype and diet was evidenced for concentrations of Phe, TAA, nonessential AA (NEAA), and FAA
Summary
It is economically important to increase the rate and speed of skeletal muscle growth in animals raised for meat including pigs. Muscle cell lineage determination and differentiation require coordinated extracellular and intracellular signaling events that converge upon the nuclear genome to coordinate, depending on the intracellular content composition, specific patterns of gene expression required for normal cellular homeostasis [4] Such programs of gene transcription require cell-specific and more widely expressed DNA binding transcription factors and their attending co-regulators that act on the epigenome for appropriate control of gene expression [5]. The mTOR integrates extracellular signals, phosphorylates the downstream targets, such as p70 ribosomal protein S6 kinases (p70S6K) and eukaryotic initiation factor 4E binding protein 1 (EIF-4EBP1). These coordinately affect gene transcription and protein translation, which are involved in the regulation of cell growth, proliferation and differentiation. Dietary protein concentration, especially level of protein or free AA, is very important as a modulator for the protein deposition and muscle growth
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