Abstract
Nine crossbred finishing barrows (body weight 94.4 ± 6.7 kg) randomly assigned to three dietary treatments were used to investigate the effects of dietary lysine on muscle growth related metabolic and signaling pathways. Muscle samples were collected from the longissimus dorsi of individual pigs after feeding the lysine-deficient (4.30 g/kg), lysine-adequate (7.10 g/kg), or lysine-excess (9.80 g/kg) diet for five weeks, and the total RNA was extracted afterwards. Affymetrix Porcine Gene 1.0 ST Array was used to quantify the expression levels of 19,211 genes. Statistical ANOVA analysis of the microarray data showed that 674 transcripts were differentially expressed (at p ≤ 0.05 level); 60 out of 131 transcripts (at p ≤ 0.01 level) were annotated in the NetAffx database. Ingenuity pathway analysis showed that dietary lysine deficiency may lead to: (1) increased muscle protein degradation via the ubiquitination pathway as indicated by the up-regulated DNAJA1, HSP90AB1 and UBE2B mRNA; (2) reduced muscle protein synthesis via the up-regulated RND3 and ZIC1 mRNA; (3) increased serine and glycine synthesis via the up-regulated PHGDH and PSPH mRNA; and (4) increased lipid accumulation via the up-regulated ME1, SCD, and CIDEC mRNA. Dietary lysine excess may lead to: (1) decreased muscle protein degradation via the down-regulated DNAJA1, HSP90AA1, HSPH1, and UBE2D3 mRNA; and (2) reduced lipid biosynthesis via the down-regulated CFD and ME1 mRNA. Collectively, dietary lysine may function as a signaling molecule to regulate protein turnover and lipid metabolism in the skeletal muscle of finishing pigs.
Highlights
The growth and development of skeletal muscle of pigs essentially requires dietary supply of proteins, or amino acids (AAs), to be exact
Of the 20 AAs that serve as building blocks for protein biosynthesis, lysine makes up the biggest part of the body protein gain in growing-finishing pigs (7.1 g lysine per 100 g body protein) [1], but lysine typically is the first limiting AA in conventional grain based swine diets [1,2]
All the microarray *.cel files generated from the GeneChip Operating Software (GCOS; Affymetrix, Inc., Santa Clara, CA, USA) as well as the GC Robust Multichip Averaging-corrected data processed with the Partek Genomics Suite (PGS) software
Summary
The growth and development of skeletal muscle of pigs essentially requires dietary supply of proteins, or amino acids (AAs), to be exact. Dietary inclusion of sufficient lysine is necessary to optimize pig’s growth performance. It has been reported that dietary lysine supplementation can improve pig’s growth performance, especially the retention of nitrogen [3,4]. Dietary deficiency of lysine can affect pig carcass characteristics by decreasing the lean meat percentage [5], increasing the subcutaneous fat depth [5,6], and increasing the intramuscular fat content of longissimus dorsi muscle [5,6,7]. The underlying molecular mechanisms by which dietary lysine directly or indirectly regulates muscle protein accretion and fat deposition in pigs are still not clear
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