Abstract
Piglets with low birth weight (LBW) usually have reduced muscle mass and increased lipid deposition compared with their normal-birth-weight (NBW) littermates. Supplementation of piglets with amino acids during the first days of life may improve muscle growth and simultaneously alter the intramuscular lipid deposition. The aim of the current study was to investigate the influence of glutamine (Gln) supplementation during the early suckling period on lipid deposition in the longissimus muscle (MLD) and the role of different perilipin (PLIN) family members in this process. Four groups were generated consisting of 72 male LBW piglets and 72 NBW littermates. Piglets were supplemented with either 1 g Gln/kg body weight or an isonitrogenous amount of alanine (Ala) between days post natum (dpn) 1 and 12. Twelve piglets per group were slaughtered at 5, 12, and 26 dpn, and muscle tissue was collected. Perilipins were localized by immunohistochemistry in muscle sections. The mRNA and protein abundances of PLIN family members and related lipases were quantified by quantitative RT-PCR (qPCR) and western blots, respectively. While PLIN1 was localized around lipid droplets in mature and developing adipocytes, PLIN2 was localized at intramyocellular lipid droplets, PLIN3 and 4 at cell membranes of muscle fibers and adipocytes, and PLIN5 in the cytoplasm of undefined cells. The western blot results indicated higher protein abundances of PLIN2, 3, 4, and 5 in LBW piglets (p < 0.05) at 5 dpn compared with their NBW littermates independent of supplementation, while not directly reflecting the mRNA expression levels. The mRNA abundance of PLIN2 was lower while PLIN4 was higher in piglets at 26 dpn in comparison with piglets at 5 dpn (p < 0.01). Relative mRNA expression of LPL and CGI-58 was lowest in piglets at 5 dpn (p < 0.001). However, ATGL mRNA was not influenced by birth weight or supplementation, but the Spearman correlation coefficient analysis revealed close correlations with PLIN2, 4, and 5 mRNA at 5 and 26 dpn (r > 0.5, p < 0.001). The results indicated the importance of birth weight and age for intramuscular lipid deposition and different roles of PLIN family members in this process, but no clear modulating effect of Gln supplementation.
Highlights
Low-birth-weight (LBW) piglets normally have a higher mortality rate and growth retardation of muscles compared with their normal-birth-weight (NBW) littermates, which in turn causes a delay in whole body growth [1]
Our results indicated a higher PLIN1 mRNA level, but not a higher protein level, in low birth weight (LBW) piglets at 5 dpn compared with their NBW littermates
Our results indicated that mRNA expression of CGI-58 was not influenced by birth weight (BiW) or Gln supplementation despite the difference in lipid droplet distribution between LBW and NBW piglets at 5 dpn
Summary
Low-birth-weight (LBW) piglets normally have a higher mortality rate and growth retardation of muscles compared with their normal-birth-weight (NBW) littermates, which in turn causes a delay in whole body growth [1]. LBW piglets normally have greater fat deposition [2] and exhibit increased fatness at slaughter age [1]. We attempted to ameliorate the disadvantages of the LBW piglets with adapted nutrition, in particular with glutamine (Gln) supplementation, which was assumed insufficient in maternal milk especially for LBW piglets [3, 4]. In our previous investigation [5], we observed fewer muscle fibers and more intramyocellular lipid droplets at 5 days post natum (dpn) in LBW piglets. The current study focused on the process of lipid deposition and redistribution between muscle fibers and developing adipocytes as part of the muscle development and how it was influenced by birth weight (BiW) and Gln supplementation
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