Impact of dietary protein on lipid metabolism-related gene expression in porcine adipose tissue

Abstract

Background: High dietary protein can reduce fat deposition in animal subcutaneous adipose tissue, but little is known about the mechanism.

Methods: Sixty Wujin pigs of about 15 kg weight were fed either high protein (HP: 18%) or low protein (LP: 14%) diets, and slaughtered at body weights of 30, 60 or 100 kg. Bloods were collected to measure serum parameters. Subcutaneous adipose tissues were sampled for determination of adipocyte size, protein content, lipid metabolism-related gene expression, and enzyme activities.

Results: HP significantly reduced adipocyte size, fat meat percentage and backfat thickness, but significantly increased daily gain, lean meat percentage and loin eye area at 60 and 100 kg. Serum free fatty acid and triglyceride concentrations in the HP group were significantly higher than in the LP group. Serum glucose and insulin concentrations were not significantly affected by dietary protein at any body weight. HP significantly reduced gene expression of acetyl CoA carboxylase (ACC), fatty acid synthase (FAS) and sterol regulatory element binding protein 1c (SREBP-1c) at 60 kg and 100 kg; however, the mRNA level and enzyme activity of FAS were increased at 30 kg. HP promoted gene and protein expression and enzyme activities of lipoprotein lipase (LPL), carmitine palmtoyltransferase-1B (CPT-1B), peroxisome proliferator-activated receptor gamma (PPARgamma) and adipocyte-fatty acid binding proteins (A-FABP) at 60 kg, but reduced their expression at 100 kg.Gene expression and enzyme activity of hormone sensitive lipase (HSL) was reduced markedly at 60 kg but increased at 100 kg by the high dietary protein. Levels of mRNA, enzyme activities and protein expression of ACC, FAS, SREBP-1c and PPARgamma in both LP and HP groups increased with increasing body weight. However, gene and protein expression levels/enzyme activities of LPL, CPT-1B, A-FABP and HSL in both groups were higher at 60 kg than at 30 and 100 kg.

Conclusion: Fat deposition in Wujin pigs fed high dietary protein for 25 weeks was reduced mainly by depression of lipogenic gene expression. The mechanism of lipid transport, lipolysis and oxidation in adipose tissue regulated by dietary protein appeared to be different at 60 kg and 100 kg body weights.

Figure 1

Effect of dietary protein on adipocyte size. Means ± SE without common letter differ significantly between body weight groups (lower case for LP group and upper case for HP) (P < 0.05). * indicates treatment differences at the same body weight (P < 0.05).

Figure 2

Relative mRNA abundance of lipogenic genes in adipose tissues at 30, 60 and 100 kg body weights of pigs fed high and low dietary protein, based on extraction of total RNA and subsequent real-time PCR analysis. Means ± SE without common letter differ significantly between body weight groups (lower case for LP group and upper case for HP). * indicates treatment differences at the same body weight (P < 0.05).

Figure 3

Relative mRNA abundance of lipolysis genes in adipose tissues at 30, 60 and 100 kg body weights of pigs fed high and low dietary protein, based on extraction of total RNA and subsequent real-time PCR analysis. Means ± SE without common letter differ significantly between body weight groups (lower case for LP group and upper case for HP). * indicates treatment differences at the same body weight (P < 0.05).

Figure 4

Protein expressions in adipose tissues at 30, 60 and 100 kg body weights of pigs fed high and low dietary protein. Means ± SE without common letter differ significantly between age groups (lower case for LP group and upper case for HP). * indicates treatment differences at the same body weight (P < 0.05).

Figure 5

Impact of high dietary protein on lipid metabolism in porcine adipose tissue at body weight 60 kg. ↑: up-regulation of gene expression or increased concentration of metabolite. ↓: down-regulation of gene expression or enzyme activity or decreased concentration of metabolite. +: enhanced metabolic pathway; -: diminished metabolic pathway.

Figure 6

Impact of high dietary protein on lipid metabolism in porcine adipose tissue at body weight 100 kg. ↑: up-regulation of gene expression or increased concentration of metabolites. ↓: down-regulation of gene expression or enzyme activity or decreased concentration of metabolite. +: enhanced metabolic pathway; -: diminished metabolic pathway. At body weight 30 kg, there were no differences except that gene expression of FAS was up-regulated.